Improved Prognosis in Patients with Autosomal Dominant Polycystic Kidney Disease in Denmark

Background and objectives: The introduction of new therapies, including agents that block the renin-angiotensin system, may have affected progression of autosomal dominant polycystic kidney disease (ADPKD). We investigated whether the age when reaching ESRD and survival during renal replacement therapy in Danish patients with ADPKD changed from January 1, 1990, through December 31, 2007.Design, setting, participants, & measurements: According to the Danish National Registry on Regular Dialysis and Transplantation, 693 patients with ADPKD reached ESRD in the study period. The 18 years were divided into three consecutive 6-year intervals.Results: The incidence of reaching ESRD for patients with ADPKD increased from 6.45 per million people in 1990 through 1995 to 7.59 per million people in 2002 through 2007, and the mean age at onset of ESRD increased by 4.7 years. The age-adjusted male-to-female ratio for onset of ESRD changed from 1.6 to 1.1, indicating a trend toward similar progression in both genders. From onset of ESRD, a Cox regression analysis to compare the first and second 6-year intervals, adjusted for age, gender, and treatment modality, showed that patient survival improved by 38%. Although NS, a similar trend was found during the second and third time intervals.Conclusions: This study demonstrates that in Danish patients with ADPKD, the prognosis had significantly improved during the study period. Furthermore, the results indicate that male gender may be losing its importance as a risk factor for progression in ADPKD.Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disorder that affects an estimated 4 to 6 million people worldwide (1). In Denmark, the prevalence of ADPKD has been estimated to be one per 1000 people, and it accounts for approximately 8% of patients who are on renal replacement therapy (RRT) (2,3). ADPKD is a genetically heterogeneous disease with mutations in two genes, PKD1 and PKD2, which accounts for 85 and 15% of cases, respectively (4,5). Mutations in PKD1 lead to more severe disease as a result of earlier development of cysts, compared with PKD2 mutations (6). Hypertension is an important contributor to progression in ADPKD, and cardiovascular morbidity and mortality are the main causes of death (7–9). Activation of the intrarenal renin-angiotensin system may be associated with progression in ADPKD (10), and treatment with angiotensin-converting enzyme inhibitors (ACEIs) has been shown to reduce proteinuria and reduce the left ventricular mass index (LVMI) in patients with ADPKD (11,12). Statins may also have beneficial effects in ADPKD (13), and several ongoing clinical trials are investigating various strategies to slow disease progression in ADPKD (14).This study describes the epidemiology of Danish patients with ADPKD who reached ESRD between 1990 and 2007. Our objective was to investigate how the increasing knowledge of factors that influence progression in ADPKD has affected the prognosis for events such as ESRD and death in the Danish population of patients with ADPKD. This has not previously been described in a national study, but others have demonstrated a significant slowing of renal demise in patients with ADPKD between 1985 and 2001 (15).     

Increased Incidence of Angioedema with ACE Inhibitors in Combination with mTOR Inhibitors in Kidney Transplant Recipients

Background and objective: The clinical manifestation of angioedema ranges from minor facial edema up to life-threatening swelling of mouth and throat. Hereditary defects, drugs, and food allergies may play a role in the development of angioedema. We systematically investigated the incidence of angioedema in renal allograft recipients treated with mTOR inhibitors (mTORis).Design, setting, participants, & measurements: All patients in the authors'' electronic database who had received mTORis (n = 309) between 2000 and 2008 were identified. Of these, 137 were additionally treated with angiotensin-converting enzyme inhibitors (ACEis).Results: Nine patients (6.6%, 3.8 per 100 treatment years) developed angioedema after a mean period of 123 days under combined therapy with mTORi and ACEi. Among the remaining 172 patients on mTORi, including 119 patients treated with angiotensin-receptor blockers, only two developed angioedema (1.2%, 0.5 per 100 treatment years, P = 0.01). In patients receiving mycophenolate and ACEi (n = 462), 10 instances of angioedema were found (2.1%, 0.8 per 100 treatment years, P = 0.004).Conclusions: This systematic investigation demonstrated a noticeable incidence of 6.6% angioedema under combined therapy with mTORi and ACEi in kidney transplant recipients. Treatment with either ACEi or mTORi alone resulted in a significantly lower incidence of angioedema, suggesting that this combination should be avoided.Depending on its magnitude and localization, the clinical picture of angioedema varies widely from moderate self-limiting facial edema up to life-threatening swelling of lips, tongue, or throat. Underlying etiologies include hereditary defects of complement inhibitor C1, drugs, and food allergies (1,2). Increased bradykinin levels may play a role in the development of angioedema; however, the exact pathophysiology of angioedema remains unclear (3). One of the most frequent causes of angioedema is use of angiotensin-converting enzyme inhibitors (ACEis), which are estimated to be responsible for 10% to 25% of all cases of angioedema (4). ACEis are widely used in patients with hypertension, heart failure, kidney diseases, or diabetes because of their convincing efficacy. It has been suggested that ACEi increases the risk of angioedema, most likely due to vasodilatation as a consequence of reduced bradykinin degradation (3). Initial data on the occurrence of angioedema under ACEi therapy came from registration trials and pharmacovigilance registries, but only recent large prospective trials provided reliable insight on the incidence of this rare side effect.In the randomized, double-blind OCTAVE trial with >12,000 patients, angioedema occurred in 0.68% of ACEi-treated patients (5). More recently, an overall incidence of 0.3% (n = 25 of 8576) angioedema was reported for ACEi during the ONTARGET study (6). In contrast, the use of angiotensin-receptor blockers (ARBs) was associated with a much lower risk of angioedema (0.1%; n = 10 of 8542 patients) in this trial. Thus, ARBs may be applied to patients with ACEi-induced angioedema, although 2 of 26 patients with angioedema due to ACEi therapy had also angioedema with ARBs (7). Approximately 60% of ACEi-induced angioedemas start within 1 week, but ACEi-induced angioedema may occur even after years (8).Higher incidence of angioedema under treatment with mTOR inhibitor (mTORi) in organ-transplanted patients has been implicated in case series and several case reports (9–13). Because we were confronted with similar patients in our outpatient clinic, we initiated a systematic search in our database to investigate frequency and clinical course of angioedema in a larger cohort of kidney transplant recipients.     

Effects of Add-on Fluvastatin Therapy in Patients with Chronic Proteinuric Nephropathy on Dual Renin-Angiotensin System Blockade: The ESPLANADE Trial

Background and objectives: This open, prospective, randomized trial aimed to assess the effects of statins in chronic kidney disease patients on optimized antiproteinuric treatment with combined angiotensin-converting enzyme inhibition and angiotensin receptor blockade.Design, setting, participants, & measurements: After 1-month benazepril therapy followed by 1-month benazepril-valsartan combined therapy (run-in), 186 consenting patients with residual proteinuria >0.5 g/24 h were randomized to 6-month benazepril-valsartan therapy alone or combined with fluvastatin. Between-groups changes in proteinuria (primary outcome), serum lipids, and GFR were compared by ANCOVA. Analyses were blinded and by intention to treat.Results: During the run-in, proteinuria decreased more on benazepril-valsartan than on benazepril alone. Proteinuria reduction correlated with concomitant reduction in total, LDL, and HDL cholesterol, and apolipoprotein B and apolipoprotein A levels. After randomization, median proteinuria similarly decreased from 1.2 (0.6 to 2.2) to 1.1 (0.5 to 1.7) g/24 h on fluvastatin and from 1.5 (0.8 to 2.7) to 1.0 (0.5 to 2.4) g/24 h on benazapril-valsartan therapy alone. Fluvastatin further reduced total and LDL cholesterol and apolipoprotein B versus benazepril-valsartan alone, but did not affect serum triglycerides and GFR. Treatment was well tolerated.Conclusions: In chronic kidney disease patients with residual proteinuria despite combined angiotensin-converting enzyme inhibitor and angiotensin receptor blockade therapy, add-on fluvastatin does not affect urinary proteins, but further reduces serum lipids and is safe. Whether combined angiotensin-converting enzyme inhibitor, angiotensin receptor blockade, and statin therapy may improve cardiovascular outcomes in this high-risk population is worth investigating.Individuals with chronic kidney disease (CKD) have substantially higher mortality rates compared with those in the general population (1). The increased risk is multifactorial in origin, but is largely due to accelerated atherosclerosis, which in turn is driven by high prevalence of traditional cardiovascular risk factors in renal populations. The presence of proteinuria is associated with more rapid kidney function loss (2), and also increases the risks of cardiovascular morbidity and mortality (3). Dyslipidemia is a complication of both decreased kidney function and proteinuria (4) and could accelerate progression of renal disease by several mechanisms. First, tubular epithelial cells reabsorb fatty acid and cholesterol from filtered albumin and lipoproteins, which can stimulate tubulointerstitial inflammation and tissue injury (5). Second, lipoproteins may accumulate in glomerular mesangium, promoting excess matrix production and glomerulosclerosis (6).Inhibitors of the renin-angiotensin system (RAS) such as angiotensin-converting enzyme inhibitors (ACEi) and angiotensin receptor blockers (ARB) reduce proteinuria by mechanisms largely independent of BP control (7), an effect that is enhanced when they are used in combination (8–10) and is associated with significant renoprotection (10–12). They may also ameliorate the dyslipidemia associated with CKD by different mechanisms including amelioration of the nephrotic syndrome and of endothelial dysfunction, an effect that fully manifests at doses higher than those required to reduce the BP (13). Whether this effect is enhanced when they are used in combination is unknown.In animals, 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase inhibitors or statins, in addition to reducing LDL cholesterol, decrease proteinuria and preserve renal function and structure (14), especially when used together with ACEi and/or ARB (15). These renoprotective effects appear to be mediated, at least in part, by the limitation of inflammatory and oxidative stress, endoplasmic reticulum stress, endothelial dysfunction, and RAS activation achieved by cholesterol reduction (reviewed in reference 16). However, inhibited production of nonsteroidal compounds such as farnesyl pyrophosphate and geranyl-geranyl-pyrophosphate involved in subcellular localization and intracellular trafficking of membrane-bound proteins mediating oxidative stress injury such as Rho, Ras, and Rac GTPases may also contribute to decrease in monocyte/macrophage glomerular infiltration, mesangial proliferation, extracellular matrix accumulation, and fibrosis. Endothelin 1 inhibition and upregulation of endothelial nitric synthase expression may also play a role (16).The above mechanisms might also explain some of the effects observed in humans. Subgroup analyses of 15 trials primarily aimed at evaluating the effect of statins on serum lipids in patients at increased cardiovascular risk found that statin therapy significantly decreased proteinuria in those patients who had predialysis CKD at inclusion (17). The antiproteinuric effect was greater among patients with more proteinuria (18). Consistent with experimental data, two randomized clinical trials found that statin therapy decreased proteinuria and ameliorated dyslipidemia more effectively than placebo also in CKD patients on ACEi or ARB therapy (19,20). However, failure of a recent meta-analysis to detect a significant treatment effect on creatinine clearance decline cannot be taken to definitely exclude the possibility of specific renoprotective properties of statins because results were flawed by the unreliability of creatinine clearance to reflect true GFR changes over time, too short follow-up, and significant heterogeneity of considered trials (21). Independent of the above, whether statins limit proteinuria and dyslipidemia also in people who are already receiving combination therapy with ACEi and ARB is unknown.Thus, in the European Study for Preventing by Lipid-lowering Agents aNd ACE-inhibition Dialysis Endpoints (ESPLANADE), we addressed whether and to what extent the proteinuria and dyslipidemia of CKD are ameliorated by add-on statin therapy in hypertensive patients with CKD and residual proteinuria despite combined ACEi and ARB therapy.     

Phase 1 Study of Anti-CTGF Monoclonal Antibody in Patients with Diabetes and Microalbuminuria

Background and objectives: This report summarizes the first phase 1 trial treating patients with microalbuminuric diabetic kidney disease (DKD) using FG-3019, a human monoclonal antibody to connective tissue growth factor (CTGF). CTGF is critically involved in processes of progressive fibrosis, including DKD. This phase 1, open-label, dose-escalation trial evaluated safety, pharmacokinetics, and possible therapeutic effects of FG-3019 on albuminuria, proteinuria, and tubular proteins.Design, setting, participants, and measurements: Microalbuminuric subjects (n = 24) with type 2 (79%) or type 1 (21%) diabetes received 3 or 10 mg/kg FG-3019 dosed intravenously every 14 days for four doses. Albuminuria and safety follow-up were to days 62 and 365, respectively.Results: No infusion was interrupted for symptoms, although 5 of 24 subjects had mild infusion-day adverse events thought to be possibly drug-related. No subject developed anti-FG-3019 antibodies. FG-3019 clearance was lower at 10 mg/kg than at 3 mg/kg, suggesting a saturable elimination pathway. Although this study was not designed for efficacy testing, it was notable that urinary albumin/creatinine ratio (ACR) decreased significantly from mean pretreatment ACR of 48 mg/g to mean post-treatment (day 56) ACR of 20 mg/g (P = 0.027) without evidence for a dose-response relationship.Conclusions: Treatment of microalbuminuric DKD subjects using FG-3019 was well tolerated and associated with a decrease in albuminuria. The data demonstrate a saturable pathway for drug elimination, minimal infusion adverse events, and no significant drug-attributable adverse effects over the year of follow-up. Changes in albuminuria were promising but require validation in a prospective, randomized, blinded study.Patients with diabetic kidney disease (DKD) are at increased risk for cardiovascular complications and early mortality. Those who survive long enough tend to progress to ESRD requiring dialysis or transplantation. Although advances in therapy with angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor type II blockers (ARBs) have attenuated the incident rate of ESRD (1), disease progression remains common (2–4) and diabetes continues to be the leading cause for initiation of dialysis in the United States (1).Connective tissue growth factor (CTGF) is a 349-amino-acid secreted pleiotropic protein belonging to the cysteine-rich CCN (CTGF/Cyr61/Cef10/NOVH) family. Numerous glomerular, tubulointerstitial, and vascular cells types can produce CTGF, and many factors associated with the diabetic condition can stimulate CTGF expression, including hypertension, hyperglycemia, and hyperlipidemia (5–24).CTGF is a critical mediator of extracellular matrix accumulation and coordinates a final common pathway of fibrosis (5,25,26). CTGF has been shown to amplify the fibrogenic activity of TGFβ (27) and IGF-1 (17) and to inhibit the action of antifibrotic and regenerative factors bone morphogenic protein-7 (27,28) and vascular endothelial growth factor (29,30).In type 1 diabetes, plasma and urine CTGF levels correlate with the level of albuminuria and the stage of progressive renal insufficiency (31–34), and the plasma CTGF level is an independent predictor of vascular disease as assessed by intimal medial thickness (35) and of mortality and progression to ESRD (36). In renal biopsy specimens from patients with diabetes, elevated levels of CTGF mRNA are associated with chronic tubulointerstitial damage, albuminuria, and progression of renal insufficiency (37–39).FG-3019 is a recombinant human anti-CTGF monoclonal IgG₁ antibody that has shown activity in rodent models of kidney dysfunction associated with type 1 and 2 diabetes (40–42). Here, we report results of an open-label dose-escalation trial of FG-3019 infusions administered biweekly over 56 days in patients with DKD, the first study designed to evaluate safety and potential therapeutic effect of FG-3019 in this patient population.     

Renal Involvement in Primary Sj?gren's Syndrome: A Clinicopathologic Study

Background & objectives: Renal pathology and clinical outcomes in patients with primary Sjögren''s syndrome (pSS) who underwent kidney biopsy (KB) because of renal impairment are reported.Design, setting, participants, & measurements: Twenty-four of 7276 patients with pSS underwent KB over 40 years. Patient cases were reviewed by a renal pathologist, nephrologist, and rheumatologist. Presentation, laboratory findings, renal pathology, initial treatment, and therapeutic response were noted.Results: Seventeen patients (17 of 24; 71%) had acute or chronic tubulointerstitial nephritis (TIN) as the primary lesion, with chronic TIN (11 of 17; 65%) the most common presentation. Two had cryoglobulinemic GN. Two had focal segmental glomerulosclerosis. Twenty patients (83%) were initially treated with corticosteroids. In addition, three received rituximab during follow-up. Sixteen were followed after biopsy for more than 12 mo (median 76 mo; range 17 to 192), and 14 of 16 maintained or improved renal function through follow-up. Of the seven patients presenting in stage IV chronic kidney disease, none progressed to stage V with treatment.Conclusions: This case series supports chronic TIN as the predominant KB finding in patients with renal involvement from pSS and illustrates diverse glomerular lesions. KB should be considered in the clinical evaluation of kidney dysfunction in pSS. Treatment with glucocorticoids or other immunosuppressive agents appears to slow progression of renal disease. Screening for renal involvement in pSS should include urinalysis, serum creatinine, and KB where indicated. KB with characteristic findings (TIN) should be considered as an additional supportive criterion to the classification criteria for pSS because it may affect management and renal outcome.Primary Sjögren''s syndrome (pSS) is a progressive autoimmune disorder involving the exocrine glands (1), typically presenting with keratoconjunctivitis and xerostomia (2). It is characterized pathologically by a predominant lymphocytic infiltrate around epithelial ducts of exocrine glands on salivary gland biopsy (3). Extraglandular manifestations of pSS, once thought to be uncommon, occur in up to 25% of patients. Patients can be afflicted by severe interstitial lung disease (4), cutaneous vasculitis (5), peripheral neuropathy (6), and hematologic complications such as lymphoma (7). They are also at increased risk for celiac sprue (8) and complications from Helicobacter pylori infection (9) such as mucosa-associated lymphatic tissue (MALT)-type lymphoma.Much of our understanding of the clinical presentation of renal involvement in pSS is based on case reports (10–26) and small retrospective cohorts (27–29). Tubulointerstitial nephritis (TIN) remains the most common presentation of renal involvement in pSS and CD4/CD8 T cell subsets are reported to predominate (27,30). This is often characterized by a distal (type I) renal tubular acidosis (RTA) and less commonly proximal (type II) RTA (Fanconi syndrome) (11,31–33). GN is thought to be a rare occurrence, with only case reports available in the literature (10,12–23), and tends to be a late development (34) in the course of the disease.We examined the renal pathologic findings and clinical trends of all patients with pSS who underwent kidney biopsy (KB) at Mayo Clinic since 1967 and assembled a case series of patients with pSS with renal pathologic disease evaluated by renal biopsy at a single center in the United States. This case series aimed to describe the common clinical presentations of renal disease in pSS, the array of pathologic findings of renal involvement in pSS, and trends during follow-up and treatment.     

CRP Polymorphisms and Progression of Chronic Kidney Disease in African Americans

Background and objectives: Chronic inflammation may play a role in chronic kidney disease (CKD) progression. CRP gene polymorphisms are associated with serum C-reactive protein (CRP) concentrations. It is unknown if CRP polymorphisms are associated with CKD progression or modify the effectiveness of anti-hypertensive therapy in delaying CKD progression.Design, setting, participants, & measurements: We genotyped 642 participants with CKD from the African American Study of Kidney Disease and Hypertension (AASK), selecting five tag polymorphisms: rs2808630, rs1205, rs3093066, rs1417938, and rs3093058. We compared the minor allele frequencies (MAF) of single nucleotide polymorphisms (SNPs) in AASK to MAFs of African Americans from NHANES III. Among AASK participants, we evaluated the association of SNPs with CRP levels and prospectively with a composite: halving the GFR, ESRD, or death.Results: The MAF was higher for the rs2808630_G allele (P = 0.03) and lower for the rs1205_A allele (P = 0.03) in the AASK compared with NHANES III. Among AASK participants, the rs3093058_T allele predicted higher CRP concentrations (P < 0.0001) but not CKD progression. The rs2808630_GG genotype was associated with higher risk of the composite endpoint compared with the AA genotype (P = 0.002). Participants with the rs2808630_GG genotype on angiotensin converting enzyme inhibitors (ACEIs) versus β blockers had increased risk of progression (P = 0.03).Conclusion: CRP SNPs that were associated with higher levels of CRP did not predict CKD progression. The rs2808630_GG genotype was associated with higher risk of CKD progression, and in patients with this genotype, ACEIs did not slow progression.Familial clustering of chronic kidney disease (CKD) and ESRD has been reported in populations throughout the world for most types of nephropathy (1–6). This genetic predisposition to ESRD seems to be strongly associated with race (7,8). Compared with people with no family history of kidney disease, African Americans with a first-degree relative with ESRD have a nine-fold increase in the risk of ESRD compared with a three- to five-fold increase in whites (8). Recently, the candidate gene MYH9 has been identified as associated with nondiabetic ERSD in African Americans, and this association explains some of the disparity in incidence of ESRD observed between whites and African Americans (7,9). However, it is possible that additional genetic variants, such as those related to inflammatory pathways, may also be associated with ESRD.Biomarkers of inflammation, including C-reactive protein (CRP), are increased even in early stages of CKD and have been linked to the risk of CKD progression (10–15). These observations have led to studies examining the genetic basis of inflammation and identification of several candidate genes for ESRD susceptibility (16–19). Recently, several large population-based studies showed that plasma CRP levels are under genetic influence (20–25). Some of these polymorphisms have been consistently associated with CRP levels (higher levels associated with rs3093058_T and lower levels associated with rs1205_A and rs2808630_G) and the risk of cardiovascular events (rs3093058_T) in African Americans (23).CRP gene polymorphisms that affect CRP concentrations may reflect lifetime exposure to CRP more accurately than single time point measurements of serum CRP concentrations. The primary goal of this study was to characterize CRP gene polymorphisms and evaluate their association with CKD progression. We hypothesized that polymorphisms associated with higher levels of CRP would be associated with higher risk of CKD progression. Additionally, we examined whether these polymorphisms modify the renoprotective effects of angiotensin converting enzyme inhibitors (ACEIs), a drug class known to have anti-inflammatory effects (26–28). We hypothesized that patients with polymorphisms associated with higher levels of CRP would benefit most from ACEIs.     

Early Renal Abnormalities in Autosomal Dominant Polycystic Kidney Disease

Background and objectives: Potential therapeutic interventions are being developed for autosomal dominant polycystic kidney disease (ADPKD). A pivotal question will be when to initiate such treatment, and monitoring disease progression will thus become more important. Therefore, the prevalence of renal abnormalities in ADPKD at different ages was evaluated.Design, setting, participants, & measurements: Included were 103 prevalent ADPKD patients (Ravine criteria). Measured were mean arterial pressure (MAP), total renal volume (TRV), GFR, effective renal plasma flow (ERPF), renal vascular resistance (RVR), and filtration fraction (FF). Twenty-four-hour urine was collected. ADPKD patients were compared with age- and gender-matched healthy controls.Results: Patients and controls were subdivided into quartiles of age (median ages 28, 37, 42, and 52 years). Patients in the first quartile of age had almost the same GFR when compared with controls, but already a markedly decreased ERPF and an increased FF (GFR 117 ± 32 versus 129 ± 17 ml/min, ERPF 374 ± 119 versus 527 ± 83 ml/min, FF 32% ± 4% versus 25% ± 2%, and RVR 12 (10 to 16) versus 8 (7 to 8) dynes/cm², respectively). Young adult ADPKD patients also had higher 24-hour urinary volumes, lower 24-hour urinary osmolarity, and higher urinary albumin excretion (UAE) than healthy controls, although TRV in these young adult patients was modestly enlarged (median 1.0 L).Conclusions: Already at young adult age, ADPKD patients have marked renal abnormalities, including a decreased ERPF and increased FF and UAE, despite modestly enlarged TRV and near-normal GFR. ERPF, FF, and UAE may thus be better markers for disease severity than GFR.Autosomal dominant polycystic kidney disease (ADPKD) is the most prevalent inherited renal disease with an estimated prevalence between 1:400 and 1:1000 (1). The disease is characterized by pain, hematuria, and most importantly by progressive cyst formation in both kidneys, often leading to ESRD. Annually, 7.8 male and 6.0 female individuals per million of the population start renal replacement therapy in Europe because of polycystic kidneys, which is 6% of the new ESRD patients (2).Current treatment cannot prevent renal failure.(3,4) However, a better understanding of the pathophysiology of the disease and the availability of animal models identified promising candidate drugs for renal preservation (5). Clinical trials have been initiated for vasopressin-2 receptor antagonists, long-acting somatostatin analogues, and mammalian target of rapamycin inhibitors (6).When efficacy of these agents has been established, a pivotal question will be when to initiate such treatment. Given that ADPKD is a progressive condition, it seems most appropriate to initiate intervention as early in life as possible to delay or prevent long-term consequences, including renal failure and cardiac complications. On the other hand, ESRD occurs in approximately 50% of affected subjects (7,8), and it is not appropriate to expose those subjects that will not reach ESRD to excessive medical treatment to such an extent as to cause adverse events, especially because all candidate drugs have considerable side effects. Because of these reasons, it will be important to discover markers that identify ADPKD patients who will develop rapid disease progression. In such patients, therapy could be instituted in an early phase.It will therefore become important to define disease severity in ADPKD. Criteria to make this distinction are not crystal clear. GFR is believed to be stable for a long period, despite progression of renal anatomical abnormalities, because of compensatory hyperfiltration. GFR is therefore assumed not to be representative of disease severity (9,10). Total renal volume (TRV) has been proposed as a surrogate marker for disease progression (10). However, despite a significant overall association, there are subjects with a high TRV but normal renal function (11). Another parameter that is decreased early in the disease is urine concentrating capacity (12). Other candidate markers to define disease severity are albuminuria (13,14) and renal blood flow (RBF) (15,16). Despite evidence for the importance of finding early renal abnormalities in ADPKD, systematic evaluation of hemodynamic parameters, especially with respect to RBF, renal vascular resistance (RVR), and filtration fraction (FF), has received little attention. Therefore, we investigated renal parameters in ADPKD at different ages in comparison to healthy subjects.     

Outcomes Associated with Serum Calcium Level in Men with Non-Dialysis-Dependent Chronic Kidney Disease

Background and objectives: Elevated serum calcium has been associated with increased mortality in dialysis patients, but it is unclear whether the same is true in non-dialysis-dependent (NDD) chronic kidney disease (CKD). Outcomes associated with low serum calcium are also not well-characterized.Design, setting, participants, & measurements: We examined associations of baseline, time-varying, and time-averaged serum calcium with all-cause mortality in a historic prospective cohort of 1243 men with moderate and advanced NDD CKD by using Cox models.Results: The association of serum calcium with mortality varied according to the applied statistical models. Higher baseline calcium and time-averaged calcium were associated with higher mortality (multivariable adjusted hazard ratio (95% confidence interval): 1.31 (1.13, 1.53); P < 0.001 for a baseline calcium 1 mg/dl higher). However, in time-varying analyses, lower calcium levels were associated with increased mortality.Conclusions: Higher serum calcium is associated with increased long-term mortality (as reflected by the baseline and time-averaged models), and lower serum calcium is associated with increased short-term mortality (as reflected by the time-varying models) in patients with NDD CKD. Clinical trials are warranted to determine whether maintaining normal serum calcium can improve outcomes in these patients.Mineral and bone disorders in chronic kidney disease (CKD) (1) have emerged as novel mortality risk factors in dialysis patients (2–8). Some of these abnormalities (such as serum phosphorus and parathyroid hormone (PTH) levels) have also been implicated in similar ways in patients with non-dialysis-dependent (NDD) CKD (9–12). Serum calcium''s effect on outcomes has been the focus of attention mainly in dialysis patients, where calcium metabolism is significantly distorted (13–19). The use of calcium-containing phosphate binders further complicates the picture because these medications could be involved in the etiology of vascular calcification (20,21), and their roles as therapeutic agents have been intensely debated (22). Supporting the potential role for calcium in cardiovascular disease were epidemiologic studies showing an association between higher calcium and increased mortality (2–8). Some of the same studies have also suggested that extremely low calcium levels may themselves be deleterious (2,3), which has ultimately resulted in recommendations to attain a low-normal serum calcium level in dialysis patients (23). Studies examining the role of calcium in NDD CKD patients are fewer and failed to unequivocally show an association between abnormal calcium levels and vascular calcification (24–27). No study has yet examined the association of calcium levels with mortality in NDD CKD.We examined the association of serum calcium levels with all-cause mortality in a large number of male US veterans with moderate and advanced NDD CKD at a single medical institution.     

Hypophosphatemic Effect of Niacin in Patients without Renal Failure: A Randomized Trial

Background and objectives: Niacin administration lowers the marked hyperphosphatemia that is characteristic of renal failure. We examined whether niacin administration also reduces serum phosphorus concentrations in patients who have dyslipidemia and are free of advanced renal disease.Design, setting, participants, & measurements: We performed a post hoc data analysis of serum phosphorus concentrations that had been determined serially (at baseline and weeks 4, 8, 12, 18, and 24) among 1547 patients who had dyslipidemia and were randomly assigned in a 3:2:1 ratio to treatment with extended release niacin (ERN; 1 g/d for 4 weeks and dose advanced to 2 g/d for 20 weeks) combined with the selective prostaglandin D2 receptor subtype 1 inhibitor laropiprant (L; n = 761), ERN alone (n = 518), or placebo (n = 268).Results: Repeated measures analysis revealed that ERN-L treatment resulted in a net mean (95% confidence interval) serum phosphorus change comparing ERN-L with placebo treatment of −0.13 mmol/L (−0.15 to −0.13 mmol/L; −0.41 mg/dl [−0.46 to −0.37 mg/dl]). These results were consistent across the subgroups defined by estimated GFR of <60 or ≥60 ml/min per 1.73 m², a serum phosphorus of >1.13 mmol/L (3.5 mg/dl) versus ≤1.13 mmol/L (3.5 mg/dl), the presence of clinical diabetes, or concomitant statin use.Conclusions: We have provided definitive evidence that once-daily ERN-L treatment causes a sustained 0.13-mmol/L (0.4-mg/dl) reduction in serum phosphorus concentrations, approximately 10% from baseline, which is unaffected by estimated GFR ranging from 30 to ≥90 ml/min per 1.73 m² (i.e., stages 1 through 3 chronic kidney disease).Abnormalities in calcium-phosphorus homeostasis, including significant elevations in serum phosphorus concentrations, are thought to contribute to arterial stiffening, hypertension, and cardiovascular disease (CVD) risk in patients with advanced chronic kidney disease and ESRD that requires maintenance dialysis (1–6). Observational data from population-based studies suggested that even serum phosphorus concentrations within the normative range are linearly associated with measures of subclinical arteriosclerosis and the development of incident CVD outcomes (7–12). Two cross-sectional studies from patients who underwent cardiac catheterization have further indicated that serum phosphorus concentrations, primarily within the normative range, were directly associated with both the presence and the severity of angiographic coronary artery disease (13,14). Moreover, a graded, independent association between serum phosphorus concentrations (again, within the normative range) and recurrent CVD events was reported among a large clinical trial cohort of patients with a previous myocardial infarction (15).Supplementation of calcium salts, despite their efficacy and tolerability as a phosphorus-lowering treatment in ESRD, may enhance coronary artery and aortic valve calcification (16,17). This observation highlights the need for hyperphosphatemia treatment protocols to balance potential benefits and adverse effects (18–22). Phosphorus-lowering drugs that target other cardiovascular risk factors in chronic kidney disease (CKD), simultaneously, including, for example, dyslipidemia (23), might have additive or synergistic benefits. These findings may also be relevant to populations with less advanced CKD or normal renal function.Preliminary studies suggested that niacin administration (as niacinamide, niceritrol, or nicotinic acid) could be a useful primary or adjunctive treatment for the marked hyperphosphatemia that is characteristic of ESRD (24–30). Several reports from clinical trials of extended-release niacin (ERN) that was given to patients who had dyslipidemia and were free of clinical renal disease and hyperphosphatemia have contained limited additional data noting up to 10% reductions in the serum phosphorus concentrations of actively treated patients (31–34). These repeated clinical observations (24–34) are most plausibly explained by the direct inhibitory effect of niacin compounds on active transport-mediated phosphorus absorption in the mammalian small intestine (35–39).Published studies of patient populations who had dyslipidemia and were receiving ERN that included phosphorus data may have failed to provide information on baseline phosphorus values (33,34), and none (31–34) performed repeated measures analyses to examine the potential effects of niacin treatment on serum phosphorus and calcium concentrations, as well as the calcium-phosphorus products.Focused reexamination of the large, placebo-controlled clinical trial data set assembled by Maccubbin et al. (34) afforded us a unique opportunity to elucidate these and other unresolved issues regarding the impact of niacin given as the fixed-dose combination of ERN and laropiprant (ERN-L), a selective prostaglandin D2 receptor subtype 1 inhibitor that reduces niacin-induced flushing (34) or ERN alone on serum phosphorus and calcium concentrations and calcium-phosphorus products. We further evaluated whether there was evidence for significant effect modification by estimated GFR (eGFR), baseline serum phosphorus concentration, the presence of diabetes, or concurrent hepatic hydroxymethyl glutaryl–CoA reductase inhibitor (statin) use when assessing the potential impact of niacin on these routine clinical measures of calcium-phosphorus homeostasis.     

Associations between Serum Leptin Level and Bone Turnover in Kidney Transplant Recipients

Background and objectives: Obesity is associated with increased parathyroid hormone (PTH) in the general population and in patients with chronic kidney disease (CKD). A direct effect of adipose tissue on bone turnover through leptin production has been suggested, but such an association has not been explored in kidney transplant recipients.Design, setting, participants, & measurements: This study examined associations of serum leptin with PTH and with biomarkers of bone turnover (serum beta crosslaps [CTX, a marker of bone resorption] and osteocalcin [OC, a marker of bone formation]) in 978 kidney transplant recipients. Associations were examined in multivariable regression models. Path analyses were used to determine if the association of leptin with bone turnover is independent of PTH.Results: Higher leptin levels were associated with higher PTH and lower vitamin D levels, and adjustment for vitamin D attenuated the association between leptin and PTH. However, higher leptin was also significantly associated with lower levels of the bone turnover markers: 1 SD higher leptin was associated with 0.13 lower log-OC (−0.17, −0.08, P < 0.001) and 0.030 lower log-CTX (−0.045, −0.016, P < 0.001) after multivariable adjustments. Path analysis indicated that the association of leptin with PTH was mostly mediated through vitamin D, and that the association between leptin and bone turnover was independent of PTH and vitamin D.Conclusions: Elevated leptin level is associated with lower bone turnover independent of its effects on serum PTH in kidney transplant recipients.Secondary hyperparathyroidism (SHPT) develops early in the course of chronic kidney disease (CKD) (1), and it has been associated with higher cardiovascular morbidity (2) and mortality (3) in hemodialysis patients and with higher mortality in patients with nondialysis-dependent CKD (4). In addition to factors directly related to worsening kidney function (e.g., abnormalities in calcium, phosphorus, vitamin D, and FGF23 metabolism) (1,5–8), PTH levels are also affected by demographic (9,10) and co-morbidity characteristics (11) in CKD. There is mounting evidence that obesity is also associated with higher PTH levels in the general population (12–16) and in patients with CKD (17,18). Furthermore, measurements of body composition suggest that the higher PTH associated with elevated body mass index (BMI) is directly related to the higher adiposity of these individuals (16). There have been speculations that obesity and adiposity indirectly cause elevated PTH levels by affecting vitamin D metabolism (15,19). This would logically imply a consequent increase in bone turnover mediated by PTH. More recently it has been suggested that adipose tissue may also exert a direct effect on bone tissue, possibly mediated through leptin secretion (20), providing an explanation for the decrease in bone turnover reported by some studies in obese individuals, despite relatively higher PTH levels (12). Earlier studies in dialysis patients reported an inverse association between leptin level and bone turnover (21,22). It is unclear if similar associations are present in kidney transplant recipients, a population that is also characterized by distinct changes in bone metabolism (23–26).The gold standard of determining bone turnover is bone histology, but this method is not feasible for application in large groups of patients. Possible alternatives to bone histology are biochemical markers of bone turnover such as serum beta crosslaps (CTX)—the C-terminal telopeptide fragments of type I collagen, a marker of bone resorption (27), or serum osteocalcin (OC) and serum alkaline phosphatase (ALP), markers of bone formation (28,29). To test the hypothesis that leptin may be directly associated with bone metabolism rather than through its effects on PTH, we examined the association of serum leptin with serum PTH level and with biochemical markers of bone resorption and formation in a large prevalent cohort of kidney transplant recipients.     

Phosphoinositides and SNARE chaperones synergistically assemble and remodel SNARE complexes for membrane fusion

Yeast vacuole fusion requires 4 SNAREs, 2 SNARE chaperone systems (Sec17p/Sec18p/ATP and the HOPS complex), and 2 phosphoinositides, phosphatidylinositol 3-phosphate [PI(3)P] and phosphatidylinositol 4,5-bisphosphate [PI(4,5)P₂]. By reconstituting proteoliposomal fusion with purified components, we now show that phosphoinositides have 4 distinct roles: PI(3)P is recognized by the PX domain of the SNARE Vam7p; PI(3)P enhances the capacity of membrane-bound SNAREs to drive fusion in the absence of SNARE chaperones; either PI(3)P or PI(4,5)P₂ can activate SNARE chaperones for the recruitment of Vam7p into fusion-competent SNARE complexes; and either PI(3)P or PI(4,5)P₂ strikingly promotes synergistic SNARE complex remodeling by Sec17p/Sec18p/ATP and HOPS. This ternary synergy of phosphoinositides and 2 SNARE chaperone systems is required for rapid fusion.Intracellular membrane fusion is a conserved reaction, vital for vesicle trafficking, hormone secretion, and neurotransmission. Fusion is regulated by NSF (N-ethylmaleimide-sensitive factor)/Sec18p, αSNAP (soluble NSF attachment protein)/Sec17p, SNAREs (SNAP receptors), Sec1p/Munc18–1p family (SM) proteins, Rab GTPases, and Rab:GTP-binding proteins, termed “Rab effectors” (1–3). Lipids, including phosphoinositides, sterols, diacylglycerol (DAG), and phosphatidic acid (PA), have specific roles in fusion (4–14). Proteins and lipids cooperate for their enrichment in membrane fusion microdomains (6, 8, 15, 16).SNARE proteins are integral or peripheral membrane proteins required for membrane fusion. SNAREs have either a Q or R residue at the center of their SNARE domain and associate in 4-helical QabcR complexes in cis (anchored to one membrane) or in trans (anchored to apposed membranes), where a, b, and c are families of related Q-SNAREs (2, 17, 18). Reconstituted proteoliposomes (RPLs) bearing Q-SNAREs fuse with RPLs bearing an R-SNARE through trans-SNARE-complex assembly (19, 20). This fusion has slow kinetics, requires nonphysiologically high SNARE densities, and causes substantial leakage of luminal contents of the RPLs (21–24).We study membrane fusion with yeast vacuoles (lysosomes). Vacuole fusion (25) requires 3 Q-SNAREs (Vam3p, Vti1p, and Vam7p) and 1R-SNARE (Nyv1p) (26, 27), two SNARE chaperone systems, Sec17p/Sec18p/ATP (28), and the HOPS (homotypic fusion and vacuole protein sorting)/Vps Class C complex (29, 30), the Rab-GTPase Ypt7p (31), and chemically minor but functionally vital “regulatory lipids”: ergosterol (ERG), DAG, PI(3)P, and PI(4,5)P₂ (8). Inactive 4SNARE cis-complexes on isolated organelles are disassembled by Sec17p/Sec18p/ATP (27). The heterohexameric HOPS complex, containing the SM protein Vps33p as a subunit, promotes and proofreads SNARE-complex assembly (32–34). HOPS can physically interact with the Q-SNAREs [Vam7p (35) and Vam3p (36, 37)], 4SNARE cis-complexes (32), GTP-bound Ypt7p (29), and phosphoinositides (35). PI(3)P supports the membrane association of the Qc-SNARE Vam7p, which has no transmembrane domain, through binding its PX domain (38). SNAREs, HOPS, Ypt7p, and regulatory lipids assemble in an interdependent fashion to form a fusion-competent membrane microdomain, the “vertex ring” (8, 16, 39). Trans-SNARE complexes are essential for fusion (26), yet fusion can be accelerated by SNARE-associating factors such as HOPS (14, 35) and by cycles of SNARE complex disassembly and reassembly, termed “remodeling” (40).Membrane fusion has been reconstituted with all purified yeast vacuolar components, including 4SNAREs, vacuolar lipids, 2 SNARE chaperone systems, and phosphoinositides (14). We now show distinct functions of phosphoinositides in RPL fusion: the PX-domain of the SNARE Vam7p recognizes PI(3)P, as reported (38); PI(3)P activates the 3Q-SNAREs to be more fusogenic in the absence of SNARE chaperones; either PI(3)P or PI(4,5)P₂ accelerates fusion by promoting the synergy between Sec17p/Sec18p and HOPS, although this synergy is not a function of the membrane recruitments of these SNARE chaperones. This ternary synergy between phosphoinositides and SNARE chaperones is essential for the assembly and remodeling of SNARE complexes.     

Long-Term Outcome of Adults Who Undergo Transplantation with Single Pediatric Kidneys: How Young Is too Young?

Background and objectives: The optimal donor age for transplanting a single pediatric kidney in an adult recipient remains unknown. En block kidney transplantation is usually performed when the donor age is <5 yr.Design, setting, participants, & measurements: We compared the outcomes of adult patients who underwent transplantation with single pediatric kidneys from donors who were younger than 5 yr (group 1, n = 40) and from donors who were aged 5 to 10 yr of age (group 2, n = 39) in our center.Results: The donor kidney sizes were significantly smaller in group 1 than in group 2 (P < 0.001), and group 1 required more ureteral stents than group 2 (73 versus 38%). The surgical complications, delayed graft function, and development of proteinuria were similar in both groups. Group 1 had slightly higher rejection episodes than group 2 (25 versus 18%; P = 0.67), and graft function was comparable in both groups. There were no statistical differences between the two groups in patient (P = 0.73) or death-censored graft (P = 0.68) survivals over 5 yr.Conclusions: Single pediatric kidney transplants from donors who are younger than 5 yr can be used with acceptable complications and long-term outcomes as those from older donors.Transplantation of en block pediatric kidneys into an adult was first performed in 1972 (1). Giving both pediatric kidneys instead of one theoretically provides sufficient nephron mass to an adult body. Good long-term graft survival has been demonstrated (2,3). Splitting en block kidneys and transplanting a single pediatric kidney into each recipient could potentially increase kidney transplants. Mixed results have been reported (4–9). The technical concerns of vascular and ureteral complications (4,5,10,11) and the medical concerns of delayed graft function (DGF), rejection, and hyperfiltration injury have been raised (4,8,12).The minimum donor age or body weight that allows successfully splitting en block kidneys for adult recipients remains controversial. Registry data reported worse outcomes in single pediatric kidney transplants than en block transplants from donors who were younger than 5 yr or weighed <21 kg (2,3). As a result, en block transplantation has generally been considered the “preferred” method when donor age is <5 yr (2). In this study, we summarize our experience using single pediatric kidneys from donors who were younger than 5 yr. We compare the posttransplantation complications and the long-term outcomes of adult patients who underwent transplantation with single pediatric kidneys from donors who were younger than 5 yr with those who underwent transplantation with single kidneys from donors who were older than 5 but younger than 10 yr.     

Prevalence of Renal Artery and Kidney Abnormalities by Computed Tomography among Healthy Adults

Background and objectives: Management of incidental renal artery and kidney abnormalities in patients undergoing computed tomography scans is a clinical challenge because their frequency in healthy subjects has not been precisely estimated. Therefore, the prevalence and management of these abnormalities were determined among a large cohort of potential kidney donors undergoing protocol evaluations.Design, setting, participants, & measurements: All patients at the Mayo Clinic who underwent computed tomographic angiography and urography as part of their kidney donor evaluation between 2000 and 2008 were identified. Radiographic reports were abstracted for abnormalities of the renal arteries and kidneys. The prevalence of radiographic abnormalities was stratified by age and gender, and the effect on approval for kidney donation was determined.Results: Among 1957 potential kidney donors, the mean ± SD age was 43 ± 12 years, and 58% were women. The most common abnormalities were kidney stones (11%), focal scarring (3.6%), fibromuscular dysplasia (2.8%), and other renal artery narrowing or atherosclerosis (5.3%). Fibromuscular dysplasia, focal scarring, parenchymal atrophy, and upper tract dilation were more common in women. Renal artery narrowing, focal scarring, and indeterminate masses increased with age. Overall, 25% of potential donors had at least one abnormality. However, these incidental radiographic abnormalities contributed to exclusion from donation in only 6.7% of potential donors.Conclusions: Incidental radiographic abnormalities of the renal arteries and kidneys are common. The majority of imaging findings are not perceived to be harmful enough to prevent kidney donation, but future studies are needed to determine their clinical relevance.Potential living kidney donors are a useful population in which to examine the prevalence and perceived significance of renal artery and kidney abnormalities in asymptomatic healthy adults because the donors undergo a rigorous evaluation for underlying disease that might preclude donation. Although the evaluation protocols vary between transplant centers, general guidelines have been developed (1). In addition to the standard history and examination, a laboratory evaluation is performed. Patients who have an abnormally low GFR, proteinuria, or significant risk factors for chronic kidney disease (e.g., diabetes mellitus) are not approved for kidney donation (2). Protocol renal imaging has also become a component of the potential kidney donor evaluation. Imaging of the kidneys and renal vessels not only defines surgical anatomy but also detects occult pathology that might preclude donation (3). Prior studies examining the prevalence of radiographic kidney abnormalities in normal adults have been limited by small sample size (4–20). The purpose of this study is to determine the variety and prevalence of incidental renal artery and kidney abnormalities present by computed tomographic (CT) angiography and urography among asymptomatic healthy adults. In addition, we assessed whether these abnormalities differed by age or gender, reviewed their clinical management, and assessed their effect on approval for donation.     

Coronary Calcification in Patients with Chronic Kidney Disease and Coronary Artery Disease

Background and objectives: A close linkage between chronic kidney disease (CKD) and cardiovascular disease (CVD) has been demonstrated. Coronary artery calcification (CAC) is considered to be the causal link connecting them. The aim of the study is to determine the relationship between level of kidney function and the prevalence of CAC.Design, setting, participants, & measurements: Autopsy subjects known to have coronary artery disease and a wide range of kidney function were studied. Patients without CKD were classified into five groups depending on estimated GFR (eGFR) and proteinuria: eGFR ≥60 ml/min/1.73 m² without proteinuria; CKD1/2: eGFR ≥60 ml/min/1.73 m² with proteinuria; CKD3: 60 ml/min/1.73 m² >eGFR ≥30 ml/min/1.73 m²; CKD4/5: eGFR <30 ml/min/1.73 m²; and CKD5D: on hemodialysis. Intimal and medial calcification of the coronary arteries was evaluated. Risk factors for CVD and uremia were identified as relevant to CAC using logistic regression analysis.Results: Intimal calcification of plaques was present in all groups, but was most frequent and severe in the CKD5D group and less so in the CKD4/5 and CKD3 groups. Risk factors included luminal stenosis, age, smoking, diabetes, calcium-phosphorus product, inflammation, and kidney function. Medial calcification was seen in a small number of CKD4/5 and CKD5D groups. Risk factors were use of calcium-containing phosphate binders, hemodialysis treatment, and duration.Conclusions: It was concluded that CAC was present in the intimal plaque of both nonrenal and renal patients. Renal function and traditional risks were linked to initimal calcification. Medial calcification occurred only in CKD patients.Cardiovascular disease (CVD) is the main cause of morbidity and mortality in patients with end-stage renal disease (ESRD) (1,2) or chronic kidney disease (CKD) (3–7). The mechanisms underlying this increased cardiovascular risk are not clearly understood. In the general population, traditional risk factors for CVD have been well characterized (8), and these are also present in CKD (3–6,9). The mechanisms involved in the connection between CKD and CVD are probably numerous (3–6). Vascular calcification, such as coronary artery calcification (CAC) (10,11), is considered to be the causal link between them.Vascular calcification is common in physiologic and pathologic conditions such as aging, diabetes, dyslipidemia, genetic diseases, and diseases with disturbances of calcium metabolism (12–14). In CKD patients, vascular calcification is even more common, developing early and contributing to the markedly increased cardiovascular risk. Pathomorphologically, atherosclerosis (plaque-forming degenerative changes of the aorta and of large elastic arteries) and arteriosclerosis (concentric medial thickening and hyalinosis of muscular arteries) can be distinguished. Increased knowledge about the mechanisms of calcification together with improved imaging techniques have provided evidence that vascular calcification should be divided into two distinct entities according to the specific site of calcification within the vascular wall: plaque calcification, involving patchy calcification of the intima in the vicinity of lipid or cholesterol deposits, and calcification of the media in the absence of such lipid or cholesterol deposits, known as Mönckeberg-type atherosclerosis (12–14). These two types of calcification may vary in terms of the type of vessel affected, the location along the arterial tree (proximal versus distal), clinical presentation, and treatment and prognosis (12–14). In the general population and in patients with CKD, electron-beam computed tomography (EBCT) has proven CAC as a potent predictor of cardiac events (15–18). Both the prevalence and intensity of CAC are increased in patients with CKD (19–27). Several studies have been undertaken to investigate whether calcification occurs in the intima or media of the coronaries and whether the morphologic details of calcified plaques differ between renal and nonrenal patients (12–14,24). Causal elements for either type of CAC have not been definitively determined (12–14).Autopsy studies are limited in terms of patient selection, but have a major advantage in terms of being able to distinguish intimal from medial calcification. Therefore, our primary goal is to determine whether, among autopsy subjects known to have CAD, there exists a direct relationship between level of kidney function and the prevalence of intimal or medial calcification.     

Variations in methanobactin structure influences copper utilization by methane-oxidizing bacteria

Methane-oxidizing bacteria are nature’s primary biological mechanism for suppressing atmospheric levels of the second-most important greenhouse gas via methane monooxygenases (MMOs). The copper-containing particulate enzyme is the most widespread and efficient MMO. Under low-copper conditions methane-oxidizing bacteria secrete the small copper-binding peptide methanobactin (mbtin) to acquire copper, but how variations in the structures of mbtins influence copper metabolism and species selection are unknown. Methanobactins have been isolated from Methylocystis strains M and hirsuta CSC1, organisms that can switch to using an iron-containing soluble MMO when copper is limiting, and the nonswitchover Methylocystis rosea. These mbtins are shorter, and have different amino acid compositions, than the characterized mbtin from Methylosinus trichosporium OB3b. A coordinating pyrazinedione ring in the Methylocystis mbtins has little influence on the Cu(I) site structure. The Methylocystis mbtins have a sulfate group that helps stabilize the Cu(I) forms, resulting in affinities of approximately 10²¹ M^-1. The Cu(II) affinities vary over three orders of magnitude with reduction potentials covering approximately 250 mV, which may dictate the mechanism of intracellular copper release. Copper uptake and the switchover from using the iron-containing soluble MMO to the copper-containing particulate enzyme is faster when mediated by the native mbtin, suggesting that the amino acid sequence is important for the interaction of mbtins with receptors. The differences in structures and properties of mbtins, and their influence on copper utilization by methane-oxidizing bacteria, have important implications for the ecology and global function of these environmentally vital organisms.Copper is an essential protein cofactor involved in many important cellular processes (1, 2), and copper-trafficking systems have been extensively studied (1, 3–8). Although copper uptake by eukaryotes is well defined (1, 4, 9), acquisition of this metal by prokaryotes remains poorly understood. Methane-oxidizing bacteria secrete the small copper-binding molecule methanobactin (mbtin) when copper is limiting (10–18), presumably for sequestration of this metal. These organisms have conditionally high requirements for copper (19), primarily for the active site (20) of the particulate methane monooxygenase (pMMO). Almost all known methane-oxidizing bacteria use pMMO for the consumption of methane (19), an important greenhouse gas. A subclass of “switchover” organisms exists that can also produce a less efficient iron-containing soluble MMO (sMMO) under copper-deficient conditions, with pMMO expression up-regulated in response to an increase in the copper-to-cell ratio (15, 21).Methanobactin production has been examined in a number of methane-oxidizing bacteria (22–24), but mbtins from only two organisms have been characterized (13, 18). The mbtin (two forms) from Methylosinus trichosporium OB3b (a switchover organism) is the most extensively studied (13, 15–17, 25–29), and binds a single copper ion coordinated in a distorted tetrahedral arrangement by the nitrogens from two oxazolone rings (29) and the sulfurs from two enethiolate groups. The molecule has a compact arrangement stabilized by a disulfide bridge. The very high affinities for copper that have been determined for the M. trichosporium OB3b molecules are consistent with mbtins playing a role in the acquisition of copper (17). Direct evidence of uptake and cytoplasmic localization has recently been obtained for Cu(I)-mbtin from M. trichosporium OB3b (30). These studies confirm that mbtin is the primary component of an active copper-acquisition system in methane-oxidizing bacteria. Comparisons have been made (13, 15, 16) between mbtins and iron-sequestering siderophores (31, 32), particularly the structurally related pyoverdines. Whereas detailed information is available for siderophore-mediated iron uptake and utilization, almost nothing is known about how mbtins acquire and deliver copper.In this work mbtins have been isolated and characterized from three Methylocystis strains, including switchover and nonswitchover organisms. All of these mbtins have high Cu(I) affinities that are similar to those of the M. trichosporium OB3b mbtins. The N-terminal group present in the Methylocystis mbtins alters the Cu(II) affinity, which will influence acquisition of the metal, and results in different reduction potentials (E_m values) that could dictate the copper release mechanism. Variations in the structures of mbtins affect their ability to provide copper to methane-oxidizing bacteria and to initiate the transition from using sMMO to pMMO in switchover organisms. We have identified features of mbtins that influence how methane-oxidizing bacteria uptake and utilize copper that may influence their capacity to suppress methane in the natural environment.     

Correlation of Kidney Function,Volume and Imaging Findings,and PKHD1 Mutations in 73 Patients with Autosomal Recessive Polycystic Kidney Disease

Background and objectives: Renal function and imaging findings have not been comprehensively and prospectively characterized in a broad age range of patients with molecularly confirmed autosomal recessive polycystic kidney disease (ARPKD).Design, setting, participants, & measurements: Ninety potential ARPKD patients were examined at the National Institutes of Health Clinical Center. Seventy-three fulfilled clinical diagnostic criteria, had at least one PKHD1 mutation, and were prospectively evaluated using magnetic resonance imaging (MRI), high-resolution ultrasonography (HR-USG), and measures of glomerular and tubular function.Results: Among 31 perinatally symptomatic patients, 25% required renal replacement therapy by age 11 years; among 42 patients who became symptomatic beyond 1 month (nonperinatal), 25% required kidney transplantation by age 32 years. Creatinine clearance (CrCl) for nonperinatal patients (103 ± 54 ml/min/1.73 m²) was greater than for perinatal patients (62 ± 33) (P = 0.002). Corticomedullary involvement on HR-USG was associated with a significantly worse mean CrCl (61 ± 32) in comparison with medullary involvement only (131 ± 46) (P < 0.0001). Among children with enlarged kidneys, volume correlated inversely with function, although with wide variability. Severity of PKHD1 mutations did not determine kidney size or function. In 35% of patients with medullary-only abnormalities, standard ultrasound was normal and the pathology was detectable with HR-USG.Conclusions: In ARPKD, perinatal presentation and corticomedullary involvement are associated with faster progression of kidney disease. Mild ARPKD is best detected by HR-USG. Considerable variability occurs that is not explained by the type of PKHD1 mutation.Autosomal recessive polycystic kidney disease (ARPKD) occurs in 1 in 20,000 births and is the most common hepatorenal fibrocystic disease of childhood (1–7). It is caused by mutations in PKHD1, which encodes fibrocystin/polyductin (8,9), a protein localized to the primary cilium, an organelle functioning as the cell''s “sensory antenna” (10). Proteins defective in other diseases having fibrocystic pathology, such as autosomal dominant polycystic kidney disease, nephronophthisis, Bardet–Biedl, Meckel, and Joubert syndromes, also localize to the primary cilium; these disorders, along with ARPKD, comprise the “ciliopathies” (10–12).Individuals with ARPKD have nonobstructive fusiform dilations of the renal collecting ducts, leading to progressive renal insufficiency. All ARPKD patients manifest some degree of congenital hepatic fibrosis (CHF) caused by ductal plate malformation of the developing portobiliary system; some patients also have macroscopic dilations of the intrahepatic bile ducts, a combination termed Caroli''s syndrome (7,13,14). Portal hypertension complicates CHF and often results in esophageal varices and hypersplenism (15–18). Early-onset severe hypertension, often requiring multiagent therapy, occurs in most ARPKD patients (5).Most ARPKD patients present perinatally with oligohydramnios and massively enlarged, diffusely microcystic kidneys. Many such newborns subsequently succumb to pulmonary hypoplasia. Characterization of the clinical phenotype of ARPKD has been based primarily upon this subtype (i.e., perinatally symptomatic patients) (1,4,5). Documentation of the kidney disease in patients presenting late in childhood or adulthood has been more limited (3,19,20). In this paper, we detail the clinical, biochemical, imaging, and molecular characteristics of 73 children and adults with PKHD1 mutations and a spectrum of clinical presentations. Our data document the extent of renal glomerular and tubular dysfunction; correlate molecular, functional, and imaging findings; and provide prognostic information.     

Incidence of Contrast-Induced Nephropathy after Contrast-Enhanced Computed Tomography in the Outpatient Setting

Background and objectives: No prospective study has reported the incidence of contrast-induced nephropathy (CIN) or the associated morbidity and mortality after contrast-enhanced computed tomography (CECT) in the outpatient setting.Design, setting, participants, & measurements: We enrolled and followed a prospective, consecutive cohort (June 2007 through January 2009) of patients who received intravenous contrast for CECT in the emergency department of a large, academic, tertiary care center. Outcomes measured were as follows (1) CIN: An increase in serum creatinine ≥0.5 mg/dl or ≥25% 2 to 7 d after contrast administration; (2) severe renal failure: An increase in serum creatinine to ≥3.0 mg/dl or the need for dialysis at 45 d; and (3) renal failure as a contributing cause of death (consensus of three independent physicians) at 45 d.Results: The incidence of CIN was 11% (70 of 633) among the 633 patients enrolled. Fifteen (2%) patients died within 45 d, including six deaths after study-defined CIN. Seven (1%) patients developed severe renal failure, six of whom had study-defined CIN. Of the six patients with CIN and severe renal failure, four died, and adjudicators determined that renal failure significantly contributed to all four deaths. Thus, CIN was associated with an increased risk for severe renal failure and death from renal failure.Conclusions: CIN occurs in >10% of patients who undergo CECT in the outpatient setting and is associated with a significant risk for severe renal failure and death.Contrast-induced nephropathy (CIN) is a known complication of intravenous, iodinated contrast; is a common cause of renal failure in the inpatient setting (1–5); and is associated with both short- and long-term adverse outcomes (6,7). Previous reports indicated that CIN occurs in 4 to 20% of patients after intra-arterial administration after coronary angiography (5–9). In the outpatient setting, the use of intravenous contrast to enhance (contrast-enhanced computed tomography [CECT]) imaging has increased sharply in recent years. Despite that >6% of all emergency department (ED) patients undergo CECT in the United States (10), no prospective data allow clinicians to estimate the rate of CIN or the associated morbidity and mortality after CECT in the outpatient setting in a heterogeneous population. Previous, retrospective work in outpatients who underwent CECT found the prevalence of CIN to be 5 to 13% (11–14) and indicates that patients without baseline renal insufficiency or chronic kidney disease may still be at risk for CIN in this population (11); however, these studies were limited by retrospective design and selection bias related to inclusion of inpatients with existing kidney disease (11–14). Thus, the absence of predicate literature required to estimate both the incidence and the clinical significance of CIN after CECT provided rationale for this work.In this study, we sought to define prospectively the incidence of CIN in an unselected, consecutive, heterogeneous population of ED patients who received low-osmolar, nonionic contrast for a CECT study of any body region. We tested the hypothesis that the incidence of CIN in the ED population exceeds 4% and that CIN is associated with a high rate of severe renal failure and death (5–9,11).     

Treatment with IFN-α, -β, or -γ Is Associated with Collapsing Focal Segmental Glomerulosclerosis

Background and objectives: Treatment with IFN is rarely associated with nephrotic syndrome and renal biopsy findings of minimal-change disease or FSGS.Design, setting, participants, & measurements: We report 11 cases of collapsing FSGS that developed during treatment with IFN and improved after discontinuation of therapy.Results: The cohort consists of seven women and four men with a mean age of 48.2 yr. Ten of the 11 patients were black. Six patients were receiving IFN-α for hepatitis C virus infection (n = 5) or malignant melanoma (n = 1), three were receiving IFN-β for multiple sclerosis, and two were treated with IFN-γ for idiopathic pulmonary fibrosis. After a mean and median duration of therapy of 4.0 and 12.6 months, respectively, patients presented with acute renal failure (mean creatinine 3.5 mg/dl) and nephrotic-range proteinuria (mean 24-hour urine protein 9.7 g). Renal biopsy revealed collapsing FSGS with extensive foot process effacement and many endothelial tubuloreticular inclusions. Follow-up was available for 10 patients, all of whom discontinued IFN. At a mean of 23.6 months, nine of 10 patients had improvement in renal function, including one with complete remission and two with partial remission. Among the seven patients with available data, mean proteinuria declined from 9.9 to 3.0 g/d. Four of the seven patients were treated with immunosuppression, and there was no detectable benefit.Conclusions: Collapsing FSGS may occur after treatment with IFN-α, -β, or -γ and is typically accompanied by the ultrastructural finding of endothelial tubuloreticular inclusions. Optimal therapy includes discontinuation of IFN.FSGS is the most common cause of idiopathic nephrotic syndrome in black patients and may be the most frequent cause of nephrotic syndrome in the general population (1–6). The spectrum of FSGS includes primary forms mediated by a putative circulating or permeability factor and a number of secondary forms caused by such diverse insults as hereditable mutations in podocyte genes, drugs, viral infections, and adaptive responses to reduced renal mass or other hemodynamic stress (1). A variety of histologic variants of FSGS have been identified and can be applied to both primary and secondary forms (7–9). Many secondary forms tend to manifest as particular morphologic subtypes (1).The collapsing variant of FSGS is defined by implosive wrinkling and “collapse” of the glomerular basement membrane associated with hypertrophy and hyperplasia of overlying podocytes (10–12). Collapsing FSGS was mainly described in patients with HIV-associated nephropathy (HIVAN) (13) but also was recognized as a variant of idiopathic FSGS (11,12). Both idiopathic collapsing FSGS and HIVAN are most commonly seen in young black patients (8–12,14). Compared with the usual, most common form of FSGS with discrete segmental scars (FSGS not otherwise specified [FSGS NOS]), collapsing FSGS is distinguished by more severe nephrotic syndrome and renal insufficiency at presentation and a more rapid course to renal failure (8–12,14). Central to the morphogenesis of the collapsing variant is podocyte injury that leads to podocyte dedifferentiation, apoptosis, and proliferation, in part through dysregulation of cell cycle–related proteins (15–19). Podocyte precursor cells from the parietal cell layer may contribute to the glomerular epithelial cell proliferation (20).HIVAN is not the only established secondary cause of collapsing FSGS. Collapsing FSGS has been reported in the setting of Parvovirus B19 infection (21) and in patients with hemophagocytic syndrome (with or without underlying lymphoma) (22). Collapsing FSGS also may follow treatment with pamidronate (23), with 15 cases reported in the medical literature (23,24). In contrast, FSGS NOS has been reported to result from treatment with lithium (25), sirolimus (26), and more recently anabolic steroids (27). Although rare cases of collapsing FSGS also have been reported after treatment with IFN-α (28–30), this therapeutic agent is more commonly associated with minimal-change disease (MCD) (31–38) and FSGS NOS (39–47). We report 11 additional cases of collapsing FSGS that developed during treatment with IFN, including six IFN-α (for hepatitis C virus [HCV] infection or melanoma), three IFN-β (for multiple sclerosis [MS]), and two IFN-γ (for idiopathic pulmonary fibrosis).     

Urinary Netrin-1 Is an Early Predictive Biomarker of Acute Kidney Injury after Cardiac Surgery

Background and objectives: Netrin-1, a laminin-related axon guidance molecule, is highly induced and excreted in the urine after acute kidney injury (AKI) in animals. Here, we determined the utility of urinary netrin-1 levels to predict AKI in humans undergoing cardiopulmonary bypass (CPB).Design, setting, participants, & measurements: Serial urine samples were analyzed by enzyme-linked immunosorbent assay for netrin-1 in 26 patients who developed AKI (defined as a 50% or greater increase in serum creatinine after CPB) and 34 controls (patients who did not develop AKI after CPB).Results: Using serum creatinine, AKI was detected on average only 48 hours after CPB. In contrast, urine netrin-1 increased at 2 hours after CPB, peaked at 6 hours (2462 ± 370 pg/mg creatinine), and remained elevated up to 48 hours after CPB. The predictive power of netrin-1 as demonstrated by area under the receiver-operating characteristics curve for diagnosis of AKI at 2, 6, and 12 hours after CPB was 0.74, 0.86, and 0.89, respectively. The 6-hour urine netrin-1 measurement strongly correlated with duration and severity of AKI, as well as length of hospital stay (all P < 0.05). Adjusting for CPB time, the 6-hour netrin-1 remained a powerful independent predictor of AKI, with an odds ratio of 1.20 (95% confidence interval: 1.08 to 1.41; P = 0.006).Conclusion: Our results suggest that netrin-1 is an early, predictive biomarker of AKI after CPB and may allow for the reliable early diagnosis and prognosis of AKI after CPB, before the rise in serum creatinine.The incidence of acute kidney injury (AKI) is increasing worldwide, affecting about 6% of all hospitalized patients in whom it is an independent predictor of mortality and morbidity (1–3). In the critical care setting, the prevalence of AKI requiring dialysis is about 6%, with a mortality rate exceeding 60% (4). Once established, the treatment is largely supportive, at an annual cost surpassing $10 billion in the United States alone (5). The diagnosis currently depends on detection of reduced kidney function by the rise in serum creatinine concentration, which is a delayed and unreliable measure in the acute setting (5). Ironically, experimental studies have identified interventions that may prevent or treat AKI if instituted early in the disease process, well before the serum creatinine rises (6). The lack of early predictive biomarkers has impaired our ability to translate these promising findings to human AKI.Cardiopulmonary bypass (CPB) surgery is the most frequent major surgical procedure performed in hospitals worldwide, with well over a million operations undertaken each year. AKI is a frequent and serious complication encountered in 30% to 40% of adults and children after CPB (7–14). AKI requiring dialysis occurs in up to 5% of these patients, in whom the mortality rate approaches 80%, and is indeed the strongest independent risk factor for death (15). However, even a minor degree of postoperative AKI as manifested by only a 0.2 to 0.3 mg/dl rise in serum creatinine from baseline is also associated with a significant increase in mortality (16,17). Additionally, AKI after cardiac surgery is associated with adverse outcomes, such as prolonged intensive care and hospital stay, dialysis dependency, and increased long-term mortality (18). Infants and children with congenital heart diseases may be especially vulnerable to developing AKI, because many require multiple surgeries for step-by-step repair of complex congenital anomalies (8–14). These patients comprise an important population for the initial validation of AKI biomarkers because they do not exhibit common comorbid variables that complicate similar studies in adults, such as diabetes, hypertension, atherosclerosis, and nephrotoxin use (19).Experimental studies aimed at a better understanding of the early adaptive response of the stressed kidney have recently yielded several candidate genes and proteins that are serendipitously emerging as noninvasive candidate biomarkers of AKI (20,21). One example of such a protein is netrin. The netrins were discovered more than a decade ago as neuronal guidance cues (22). Netrins are molecules with a distinctive domain organization that belong to the laminin-related family of axon-guidance molecules (23). Recent studies indicate various other roles for netrins beyond axonal guidance, including development of mammary gland, lung, pancreas, and blood vessels; inhibition of leukocyte migration during sepsis; mitogenesis; and chemoattraction of endothelial cells (23,24). The kidney has one of the highest levels of netrin-1 expression, and administration of recombinant netrin-1 before ischemia reperfusion reduces kidney injury and inflammation (25). Preclinical studies also indicate that netrin-1 protein is markedly induced in kidney tubule cells and appears in the urine early (within 1 to 3 hours) after murine renal ischemic injury as well as other forms of AKI (26). Therefore, the objective of this study was to determine whether urinary netrin-1 levels predict the development of AKI in pediatric patients undergoing CPB.