Childhood Kidney Outcomes in Relation to Fetal Blood Flow and Kidney Size

Impaired fetal abdominal blood flow may lead to smaller kidneys and subsequent impaired kidney function in later life. In a prospective cohort study among 923 pregnant women and their children, we measured fetal growth, kidney volumes, and umbilical and cerebral artery blood flow (median gestational age of 30.3 weeks; 95% range, 28.5–32.7 weeks). We used a higher umbilical/cerebral artery pulsatility index ratio as an indicator of preferential fetal blood flow to the upper body parts at the expense of the intra-abdominal organs. At a median age of 5.9 years (95% range, 5.7–6.6 years), we measured childhood kidney volumes, creatinine and cystatin C blood levels, microalbuminuria, BP, and eGFR. A preferential fetal blood flow to the upper body parts at the expense of the intra-abdominal organs associated only with a smaller combined kidney volume in childhood. Fetal combined kidney volume positively associated with childhood combined kidney volume and eGFR, and inversely associated with childhood creatinine and cystatin C levels (all P values <0.05), but did not associate with childhood microalbuminuria and BP. Children within the highest tertile of fetal umbilical/cerebral ratio and the lowest tertile of fetal combined kidney volume had the lowest eGFR (difference, −6.36 ml/min per 1.73 m²; 95% confidence interval, −11.78 to −0.94 compared with children within the middle tertiles). These data suggest that impaired fetal blood to the abdominal organs and smaller fetal kidney size are associated with subclinical changes in kidney outcomes in school-aged children.The third trimester of pregnancy is a critical period for fetal kidney development.¹ Nephrogenesis continues until 36 weeks of gestation, after which the induction of nephron numbers ceases.² A permanent reduction of kidney size and number of nephrons leads to a smaller glomerular filtration surface area, which might predispose the individual to decreased kidney function in childhood and subsequently to kidney disease and hypertension in adulthood.^3,4 This hypothesis is supported by studies showing consistent associations of low birth weight with higher risks of kidney disease and hypertension in later life.^5,6 Although the observed effect estimates from these studies were small, they are important from an etiologic perspective.^5,6 In addition, post mortem studies showed that the nephron number is lower in hypertensive individuals than in normotensive controls⁷ and is positively correlated with birth weight and kidney size.^8,9 Animal studies demonstrated a reduction in nephron number as a result of vascular placental insufficiency.¹⁰ Placental insufficiency is an important risk factor for fetal growth restriction and low birth weight.¹¹ We recently demonstrated that increased third trimester placental insufficiency is associated with a higher BP in childhood.¹² Placental insufficiency is characterized by a preferential fetal blood flow to the brain at the expense of the trunk.¹³ This fetal blood flow redistribution is caused by higher peripheral and lower cerebral arterial resistance,¹¹ and can be measured as a higher umbilical artery pulsatility index (PI) and lower cerebral artery PI, respectively. This combination leads to a higher ratio of these measures (higher umbilical/cerebral (U/C) ratio).¹⁴ It is unknown whether and to what extent impaired abdominal or kidney blood flow and kidney growth restriction during fetal life lead to risk factors for kidney disease in later life.In this population-based prospective cohort study among 923 pregnant women and their children, we evaluated the associations of third trimester fetal blood flow redistribution, at the expense of the abdominal organs, and smaller fetal kidney size with kidney function outcomes in school-aged children. We also explored whether any association was explained by childhood kidney size.     

Type 2 Diabetes Risk Alleles Are Associated With Reduced Size at Birth

OBJECTIVE

Low birth weight is associated with an increased risk of type 2 diabetes. The mechanisms underlying this association are unknown and may represent intrauterine programming or two phenotypes of one genotype. The fetal insulin hypothesis proposes that common genetic variants that reduce insulin secretion or action may predispose to type 2 diabetes and also reduce birth weight, since insulin is a key fetal growth factor. We tested whether common genetic variants that predispose to type 2 diabetes also reduce birth weight.

RESEARCH DESIGN AND METHODS

We genotyped single-nucleotide polymorphisms (SNPs) at five recently identified type 2 diabetes loci (CDKAL1, CDKN2A/B, HHEX-IDE, IGF2BP2, and SLC30A8) in 7,986 mothers and 19,200 offspring from four studies of white Europeans. We tested the association between maternal or fetal genotype at each locus and birth weight of the offspring.

RESULTS

We found that type 2 diabetes risk alleles at the CDKAL1 and HHEX-IDE loci were associated with reduced birth weight when inherited by the fetus (21 g [95% CI 11–31], P = 2 × 10⁻⁵, and 14 g [4–23], P = 0.004, lower birth weight per risk allele, respectively). The 4% of offspring carrying four risk alleles at these two loci were 80 g (95% CI 39–120) lighter at birth than the 8% carrying none (P_trend = 5 × 10⁻⁷). There were no associations between birth weight and fetal genotypes at the three other loci or maternal genotypes at any locus.

CONCLUSIONS

Our results are in keeping with the fetal insulin hypothesis and provide robust evidence that common disease-associated variants can alter size at birth directly through the fetal genotype.Reduced birth weight is associated with late-onset diseases including type 2 diabetes, hypertension, and heart disease (1). The cause of this association is not known. It is often proposed to reflect fetal programming in utero in response to maternal malnutrition in pregnancy (2). An alternative explanation is that genetic variants that increase disease risk could also reduce fetal growth. In accordance with the fetal insulin hypothesis (3), we proposed that genetic variants that reduce insulin secretion or insulin sensitivity might reduce birth weight as well as predisposing to type 2 diabetes in adulthood, since fetal insulin is a key fetal growth factor.The fetal insulin hypothesis was initially based on observations of subjects with glucokinase (GCK) mutations, whose birth weight is reduced by 533 g (4) and who have mild hyperglycemia postnatally. Markedly reduced birth weights in patients with monogenic diabetes due to mutations in the INS, INSR, IPF1, KCNJ11, ABCC8, and HNF1B genes (3,5–8) have further established the principle that gene variants can cause both low birth weight and diabetes. However, mutations causing monogenic diabetes are too rare to explain the association between reduced birth weight and type 2 diabetes observed in population studies.There is epidemiological support for the fetal insulin hypothesis. Offspring of fathers who go on to develop type 2 diabetes later in life have lower birth weights than those born to fathers who do not develop diabetes (9–12). This is consistent with the fetus inheriting, on average, 50% of the father''s genetic predisposition to diabetes and this genetic predisposition reducing fetal growth.Maternal genotypes may have opposing effects on offspring birth weight compared with fetal genotypes (4). Type 2 diabetes risk alleles, which are present in the mother and which raise maternal glycemia in pregnancy, will increase fetal growth by increasing fetal insulin secretion. Maternal inheritance of common risk alleles in the GCK and TCF7L2 genes, which predispose to hyperglycemia and type 2 diabetes, respectively, were reproducibly associated with higher offspring birth weight (13,14). However, neither of these risk alleles at TCF7L2 and GCK or the type 2 diabetes risk alleles in the PPARG and KCNJ11 genes was associated with birth weight directly through the fetal genotype (13–15).In this study, we aimed to further test the relationship between known type 2 diabetes variants and size at birth. We selected variants at five loci (CDKAL1, CDKN2A/B, HHEX-IDE, IGF2BP2, and SLC30A8), recently identified through type 2 diabetes genome-wide association studies (16–21), that have not been investigated in relation to fetal growth. Each of these loci has been shown to predispose to diabetes by reducing insulin secretion (22–24). We used data from 19,200 offspring and 7,986 mothers from four studies of white Europeans to test the hypothesis that these variants are associated with birth weight, either through the fetal or maternal genotype.     

Pregnancy and Maternal Outcomes Among Kidney Transplant Recipients

Fertility rates, pregnancy, and maternal outcomes are not well described among women with a functioning kidney transplant. Using data from the Australian and New Zealand Dialysis and Transplant Registry, we analyzed 40 yr of pregnancy-related outcomes for transplant recipients. This analysis included 444 live births reported from 577 pregnancies; the absolute but not relative fertility rate fell during these four decades. Of pregnancies achieved, 97% were beyond the first year after transplantation. The mean age at the time of pregnancy was 29 ± 5 yr. Compared with previous decades, the mean age during the last decade increased significantly to 32 yr (P < 0.001). The proportion of live births doubled during the last decade, whereas surgical terminations declined (P < 0.001). The fertility rate (or live-birth rate) for this cohort of women was 0.19 (95% confidence interval 0.17 to 0.21) relative to the Australian background population. We also matched 120 parous with 120 nulliparous women by year of transplantation, duration of transplant, age at transplantation ±5 yr, and predelivery creatinine for parous women or serum creatinine for nulliparous women; a first live birth was not associated with a poorer 20-yr graft or patient survival. Maternal complications included preeclampsia in 27% and gestational diabetes in 1%. Taken together, these data confirm that a live birth in women with a functioning graft does not have an adverse impact on graft and patient survival.One of the many perceived benefits of kidney transplantation has been restoration of pituitary-ovarian function and fertility in women of reproductive age. Prenatal advice for women with a functioning kidney transplant has been primarily based on data derived from observational research,^1–13 and the reported live-birth rates achieved in such women range from 43.2¹⁴ to 82%.¹⁵Although an increased pregnancy event number has been reported for women with a functioning kidney transplant,¹⁶ little is actually known about “pregnancy rate changes” during the past 40 yr. More importantly, long-term graft and maternal survival analyses, referred to when advising women who have undergone transplantation and are considering a pregnancy, have been mostly performed without adequate matching,¹² or, alternatively, matching has been used but outcomes followed up for only brief intervals^14,17,18 and in small cohorts.^19–22 Published graft matching studies to date suggest no adverse impact 10 yr after a live birth.¹⁴In most instances, pregnancies in women with a kidney graft have been encouraged. Historically, renal function,^8,15,17,18 baseline proteinuria,²³ intercurrent hypertension,^1,24 and time from transplantation^{1,3,5,8,14,15,18,24,25} have been used to predict adverse event risks to the mother, kidney, and offspring. To this are added the often unquantifiable inherent risks for genetically transmitted diseases or the problems associated with prematurity.^26,27 More recently, epidemiologic evidence suggests low birth weight may be associated with the development of hypertension,²⁸ cardiovascular disease,²⁹ insulin resistance,³⁰ and end-stage renal failure.³¹ Moreover, low birth weight is associated with an increased risk for hypertension, independent of genetic and shared environmental factors.³²Series published to date have not captured all pregnancy events or their outcomes. Limitations of some of the published studies include short duration of follow-up and studies with no adequate or long-term matching for decade and renal function.We examined fertility rates, pregnancy rates, and pregnancy outcomes over 40 yr in an at-risk population, defined as women who were aged between 15 and 49 and had a functioning kidney transplant, using ANZDATA registry data. In addition, maternal and graft outcomes were analyzed, and, uniquely, a matched cohort analysis of 120 nulliparous and 120 parous women who had undergone transplantation enabled analysis of outcomes at 20 yr.     

Adiponectin Enhances Mouse Fetal Fat Deposition

Maternal obesity increases offspring birth weight and susceptibility to obesity. Adiponectin is an adipocyte-secreted hormone with a prominent function in maintaining energy homeostasis. In contrast to adults, neonatal blood adiponectin levels are positively correlated with anthropometric parameters of adiposity. This study was designed to investigate the role of adiponectin in maternal obesityenhanced fetal fat deposition. By using high-fat diet–induced obese mouse models, our study showed that maternal obesity increased fetal fat tissue mass, with a significant elevation in fetal blood adiponectin. However, adiponectin gene knockout (Adipoq^−/−) attenuated maternal obesity-induced high fetal fat tissue mass. We further studied the effects of fetal adiponectin on fetal fat deposition by using a cross breeding approach to create Adipoq^−/+ and Adipoq^−/− offspring, whereas maternal adiponectin was null. Adipoq^−/+ offspring had more fat tissue mass at both birth and adulthood. Significantly high levels of lipogenic genes, such as sterol regulatory element–binding protein 1c and fatty acid synthase, were detected in the livers of Adipoq^−/+ fetuses. In addition, expression of genes for placental fatty acid transport was significantly increased in Adipoq^−/+ fetuses. Together, our study indicates that adiponectin enhances fetal fat deposition and plays an important role in maternal obesity-induced high birth weight.Obesity impairs glucose and lipid metabolism and is a risk factor for many diseases. In the United States, adult obesity has reached epidemic levels. Most strikingly, the prevalence of obesity in children (aged 6–19 years) has tripled to 17% since 1980 (1). Recent studies have clearly demonstrated that maternal obesity increases not only offspring birth weight, but also offspring susceptibility to obesity during their lifetime (2–4). Therefore, elucidating the underlying mechanism of maternal obesity-induced high birth weight and offspring adiposity will be important to curbing the soaring rate of obesity.Adiponectin is an adipocyte-derived hormone that enhances insulin sensitivity. In contrast to adults, in which adiponectin expression is inversely associated with adiposity, infant blood adiponectin concentrations are positively correlated with body weight and body length (5–9). During late pregnancy, opposite changes in adiponectin gene expression in maternal and fetal compartments create a significant difference in adiponectin concentration between maternal and fetal circulations. At delivery, neonatal blood adiponectin levels are four- to sevenfold higher than those in maternal circulation (10). During the same period, fetal fat is exponentially deposited in humans (11). Adiponectin inhibits energy expenditure (12,13) and enhances lipid accumulation in adipocytes by increasing adipocyte differentiation and suppressing lipolysis (14–16). Overexpression of adiponectin increases adipose tissue mass in adult mice (12,17). These studies prompted us to hypothesize that changes in adiponectin levels in maternal and fetal compartments during gestation coordinately regulates fetal fat deposition and plays an important role in maternal obesity-induced offspring adiposity.By using genetic approaches to manipulate adiponectin gene expression in maternal and fetal tissues and by using high-fat (HF) feeding to induce maternal obesity, our study showed that adiponectin gene knockout attenuated maternal obesity-induced high birth weight in mice. The results indicate that adiponectin increases fetal fat deposition and has a significant impact on fat tissue mass from the neonatal stage to adulthood. Furthermore, our study also suggests that increased placental fatty acid transport and fetal hepatic de novo lipogenesis might contribute to adiponectin-enhanced fetal fat deposition.     

Renal Dendritic Cells Ameliorate Nephrotoxic Acute Kidney Injury

Inflammation contributes to the pathogenesis of acute kidney injury. Dendritic cells (DCs) are immune sentinels with the ability to induce immunity or tolerance, but whether they mediate acute kidney injury is unknown. Here, we studied the distribution of DCs within the kidney and the role of DCs in cisplatin-induced acute kidney injury using a mouse model in which DCs express both green fluorescence protein and the diphtheria toxin receptor. DCs were present throughout the tubulointerstitium but not in glomeruli. We used diphtheria toxin to deplete DCs to study their functional significance in cisplatin nephrotoxicity. Mice depleted of DCs before or coincident with cisplatin treatment but not at later stages experienced more severe renal dysfunction, tubular injury, neutrophil infiltration and greater mortality than nondepleted mice. We used bone marrow chimeric mice to confirm that the depletion of CD11c-expressing hematopoietic cells was responsible for the enhanced renal injury. Finally, mixed bone marrow chimeras demonstrated that the worsening of cisplatin nephrotoxicity in DC-depleted mice was not a result of the dying or dead DCs themselves. After cisplatin treatment, expression of MHC class II decreased and expression of inducible co-stimulator ligand increased on renal DCs. These data demonstrate that resident DCs reduce cisplatin nephrotoxicity and its associated inflammation.Innate immune responses are pathogenic in both ischemic and toxic acute renal failure. In response to renal injury, inflammatory chemokines and cytokines are produced both by renal parenchymal cells, such as proximal tubule epithelial cells, and resident or infiltrating leukocytes.^1–4 The elaborated chemokines and cytokines, including TNF-α, IL-18, keratinocyte-derived chemokine, and monocyte chemoattractant protein 1, subsequently recruit additional immune cells to the kidney, such as neutrophils, T cells, monocytes, and inflammatory dendritic cells (DCs), which may cause further injury through pathways that are not fully defined.^2,5–12 DCs are sentinels of the immune system and under steady-state conditions induce tolerance by various mechanisms, including production of TGF-β, IL-10, or indoleamine 2,3-dioxygenase^13–16; expression of PDL-1, PDL-2, or FcγR2B^17,18; clonal deletion of autoreactive T cells¹⁹; and induction of T regulatory cells via the inducible co-stimulator (ICOS) pathway.^20–23 In response to pathogens or products of tissue injury, DCs mature and initiate immunity or inflammatory diseases.^24,25 Monocytes recruited to inflamed tissue can also differentiate into inflammatory DCs and mediate defense against pathogens or contribute to inflammatory tissue responses.^12,26–28Although DCs represent a major population of immune cells in the kidney,²⁹ their role in renal disease is poorly defined. Liposomal clodronate has been used to study the pathophysiologic role of phagocytic cells, which include DCs and macrophages.^3,30–32 An alternative DC-specific approach uses expression of the simian diphtheria toxin receptor (DTR) driven by the CD11c promoter to target DCs for DT-mediated cell death.²⁴ This model has been used extensively to study the role of DCs in various physiologic and pathophysiologic contexts^32,33; however, its application in kidney disease has been limited to recent studies of immune complex–mediated glomerulonephritis.^12,23We have reported that inflammation plays an important role in the pathogenesis of cisplatin-induced acute kidney injury (AKI).^1,4,5,34 Given the dearth of information regarding the role of renal DCs in AKI, this study examined the renal DC population and the impact of its depletion on cisplatin nephrotoxicity. We show that DCs are the most abundant population of renal resident leukocytes and form a dense network throughout the tubulointerstitium. Renal DCs displayed surface markers that distinguished them from splenic DCs. Using a conditional DC depletion model, we determined that DC ablation markedly exacerbates cisplatin-induced renal dysfunction, structural injury, and infiltration of neutrophils.     

Examination of Type 2 Diabetes Loci Implicates CDKAL1 as a Birth Weight Gene

OBJECTIVE

A number of studies have found that reduced birth weight is associated with type 2 diabetes later in life; however, the underlying mechanism for this correlation remains unresolved. Recently, association has been demonstrated between low birth weight and single nucleotide polymorphisms (SNPs) at the CDKAL1 and HHEX-IDE loci, regions that were previously implicated in the pathogenesis of type 2 diabetes. In order to investigate whether type 2 diabetes risk–conferring alleles associate with low birth weight in our Caucasian childhood cohort, we examined the effects of 20 such loci on this trait.

RESEARCH DESIGN AND METHODS

Using data from an ongoing genome-wide association study in our cohort of 5,465 Caucasian children with recorded birth weights, we investigated the association of the previously reported type 2 diabetes–associated variation at 20 loci including TCF7L2, HHEX-IDE, PPARG, KCNJ11, SLC30A8, IGF2BP2, CDKAL1, CDKN2A/2B, and JAZF1 with birth weight.

RESULTS

Our data show that the minor allele of rs7756992 (P = 8 × 10⁻⁵) at the CDKAL1 locus is strongly associated with lower birth weight, whereas a perfect surrogate for variation previously implicated for the trait at the same locus only yielded nominally significant association (P = 0.01; r² rs7756992 = 0.677). However, association was not detected with any of the other type 2 diabetes loci studied.

CONCLUSIONS

We observe association between lower birth weight and type 2 diabetes risk–conferring alleles at the CDKAL1 locus. Our data show that the same genetic locus that has been identified as a marker for type 2 diabetes in previous studies also influences birth weight.It has been reported that reduced birth weight is associated with an increased risk of type 2 diabetes later in life (1–3). The largest such study was a meta-analysis of 14 studies involving a total of 132,180 individuals that demonstrated an association between lower birth weight and type 2 diabetes risk with an odds ratio of 1.32 (2). On a global level, reduced birth weight has been shown to be correlated with increased type 2 diabetes risk in 28 of 31 populations studied (3). Furthermore, low birth weight has been associated with both type 2 diabetes (P = 0.008) and impaired insulin secretion (P = 0.04) in 2,003 participants from the Helsinki Birth Cohort Study (HBCS) (4).It has been proposed that the relationship between low birth weight and type 2 diabetes is genetically mediated, namely, the fetal insulin hypothesis (5,6). Because insulin is a key fetal growth factor, the genetic variants that reduce insulin secretion or insulin sensitivity might also reduce birth weight as well as increase the risk of developing type 2 diabetes later in life (5,6).Studies of monogenic diabetes support the fetal insulin hypothesis where gene mutations such as GCK, INS, INSR, and KCNJ11 have been shown to track with both low birth weight and diabetes (5,7,8). It has also been shown from epidemiological studies that paternal genetic contributions can directly predispose the offspring to general type 2 diabetes through reduced birth weight (9), whereas the maternal genetic contribution to the trait is less clear because it is more difficult to separate the influence of genes transferred from mother to offspring from that of the maternal environment (which in turn may be influenced by the mother''s own genes) (10,11).Recent genome-wide association (GWA) studies of type 2 diabetes have revealed a number of loci (12–22), some of which have been subsequently explored in the context of birth weight. In the HBCS study, the type 2 diabetes risk–conferring allele in HHEX-IDE yielded a trend toward low birth weight, whereas the equivalent allele at the CDKN2A/2B locus was associated with high birth weight; in addition, risk variants at HHEX-IDE, CDKN2A/2B, and JAZF1 genes were shown to interact with birth weight but not TCF7L2, PPARG, KCNJ11, SLC30A8, IGF2BP2, and CDKAL1. Indeed, the highest risk of going on to develop type 2 diabetes was among the lower birth weight participants carrying the implicated risk variants (4). More recently, examination in four studies of Caucasian Europeans consisting of 7,986 mothers and 19,200 offspring of the five type 2 diabetes genes CDKAL1, CDKN2A/2B, HHEX-IDE, IGF2BP2, and SLC30A8 with lower birth weight revealed strong association with CDKAL1 and HHEX-IDE when inherited by the fetus but not for CDKN2A/2B, IGF2BP2, and SLC30A8 (6).In this study, we sought to clarify these reported associations between low birth weight and type 2 diabetes loci using data from an ongoing GWA study in a cohort of 5,465 European American children with recorded birth weights. The criteria for locus selection were that they either came directly from published type 2 diabetes GWA studies or were type 2 diabetes genes found through the candidate gene approach that have also been reported to be associated with birth weight previously. We queried for known variants at the type 2 diabetes–associated loci of TCF7L2, HHEX-IDE, PPARG, KCNJ11, SLC30A8, IGF2BP2, CDKAL1, CDKN2A/2B, and JAZF1 with respect to their correlation with birth weight to directly compare and contrast with what was recently reported by two European groups (4,6). We also queried for an additional 11 established type 2 diabetes loci that have not been previously reported with respect to birth weight including MNTR1B, which was first implicated in multiple GWA studies of the related trait of fasting glucose and was subsequently associated with type 2 diabetes within the same studies (15,17,22).     

Acute Kidney Injury Associates with Increased Long-Term Mortality

Acute kidney injury (AKI) associates with higher in-hospital mortality, but whether it also associates with increased long-term mortality is unknown, particularly after accounting for residual kidney function after hospital discharge. We retrospectively analyzed data from US veteran patients who survived at least 90 d after discharge from a hospitalization. We identified AKI events not requiring dialysis from laboratory data and classified them according to the ratio of the highest creatinine during the hospitalization to the lowest creatinine measured between 90 d before hospitalization and the date of discharge. We estimated mortality risks using multivariable Cox regression models adjusting for demographics, comorbidities, medication use, primary diagnosis of admission, length of stay, mechanical ventilation, and postdischarge estimated GFR (residual kidney function). Among the 864,933 hospitalized patients in the study cohort, we identified 82,711 hospitalizations of patients with AKI. In the study population of patients who survived at least 90 d after discharge, 17.4% died during follow-up (AKI 29.8%, without AKI 16.1%). The adjusted mortality risk associated with AKI was 1.41 (95% confidence interval [CI] 1.39 to 1.43) and increased with increasing AKI stage: 1.36 (95% CI 1.34 to 1.38), 1.46 (95% CI 1.42 to 1.50), and 1.59 (95% CI 1.54 to 1.65; P < 0.001 for trend). In conclusion, AKI that does not require dialysis associates with increased long-term mortality risk, independent of residual kidney function, for patients who survive 90 d after discharge. Long-term mortality risk is highest among the most severe cases of AKI.Acute kidney injury (AKI) affects up to 15.3% of all hospitalized patients.^1,2 Regardless of the underlying cause, AKI is associated with significantly increased in-hospital morbidity, mortality, and costs.^2–16 The majority of previous studies linking AKI to mortality examined in-hospital mortality only and did not address postdischarge morbidity and mortality.^{2,4,7,8,10,11,13–16} Studies examining postdischarge mortality have focused primarily on critically ill patients with AKI that requires dialysis.⁹ Consequently, it remains unclear whether AKI that does not require dialysis is associated with a higher long-term risk for all-cause mortality.One of the challenges of long-term mortality studies is to estimate the mortality risk independently associated with AKI from risk associated with chronic kidney disease (CKD). Some patients have incomplete recovery of their kidney function after AKI, and CKD is associated with a higher risk for mortality.^17,18 To evaluate the independent long-term mortality risk of AKI, it is essential to adjust for postdischarge kidney function. The objective of this study was to estimate the postdischarge, long-term mortality risk associated with AKI while adjusting for residual kidney function in a large cohort of US veterans.     

Recurrence of Lupus Nephritis after Kidney Transplantation

The frequency and outcome of recurrent lupus nephritis (RLN) among recipients of a kidney allograft vary among single-center reports. From the United Network for Organ Sharing files, we estimated the period prevalence and predictors of RLN in recipients who received a transplant between 1987 and 2006 and assessed the effects of RLN on allograft failure and recipients'' survival. Among 6850 recipients of a kidney allograft with systemic lupus erythematosus, 167 recipients had RLN, 1770 experienced rejection, and 4913 control subjects did not experience rejection. The period prevalence of RLN was 2.44%. Non-Hispanic black race, female gender, and age <33 years each independently increased the odds of RLN. Graft failure occurred in 156 (93%) of those with RLN, 1517 (86%) of those with rejection, and 923 (19%) of control subjects without rejection. Although recipients with RLN had a fourfold greater risk for graft failure compared with control subjects without rejection, only 7% of graft failure episodes were attributable to RLN compared and 43% to rejection. During follow-up, 867 (13%) recipients died: 27 (16%) in the RLN group, 313 (18%) in the rejection group, and 527 (11%) in the control group. In summary, severe RLN is uncommon in recipients of a kidney allograft, but black recipients, female recipient, and younger recipients are at increased risk. Although RLN significantly increases the risk for graft failure, it contributes far less than rejection to its overall incidence; therefore, these findings should not keep patients with lupus from seeking a kidney transplant.The frequency and clinical impact of recurrent lupus nephritis (RLN) in the kidney allograft of recipients with systemic lupus erythematosus (SLE) varies considerably in both prospective and retrospective studies.^1–25 In 1996, Mojcik and Klippel²⁶ pooled data from a total of 366 allografts transplanted in 338 recipients. In that review, histologic RLN was present in 3.8% of the grafts. Contrasting, in the studies by Goral et al.²⁷ and Nyberg et al.,¹⁰ RLN was reported in a much higher proportion: 30 and 44% of recipients, respectively.The clinical consequences of RLN on patient and allograft survival have ranged from no effect to a significant increase in the risk for graft loss and patient mortality.^24,27–31 In this case-control study, we estimated the period prevalence of RLN in kidney transplant recipients who had ESRD secondary to lupus nephritis and received a transplant between October 1987 and October 2006. We assessed the effects of RLN on graft failure and recipient survival and the risk factors leading to the development of RLN.     

Placental Structure in Type 1 Diabetes: Relation to Fetal Insulin, Leptin, and IGF-I

OBJECTIVE

Alteration of placental structure may influence fetal overgrowth and complications of maternal diabetes. We examined the placenta in a cohort of offspring of mothers with type 1 diabetes (OT1DM) to assess structural changes and determine whether these were related to maternal A1C, fetal hematocrit, fetal hormonal, or metabolic axes.

RESEARCH DESIGN AND METHODS

Placental samples were analyzed using stereological techniques to quantify volumes and surface areas of key placental components in 88 OT1DM and 39 control subjects, and results related to maternal A1C and umbilical cord analytes (insulin, leptin, adiponectin, IGF-I, hematocrit, lipids, C-reactive protein, and interleukin-6).

RESULTS

Intervillous space volume was increased in OT1DM (OT1DM 250 ± 81 cm³ vs. control 217 ± 65 cm³; P = 0.02) with anisomorphic growth of villi (P = 0.025). The placentas showed a trend to increased weight (OT1DM 690 ± 19 g; control 641 ± 22 g; P = 0.08), but villous, nonparenchymal, trophoblast, and capillary volumes did not differ. Villous surface area, capillary surface area, membrane thickness, and calculated morphometric diffusing capacity were also similar in type 1 diabetic and control subjects. A1C at 26–34 weeks associated with birth weight (r = 0.27, P = 0.03), placental weight (r = 0.41, P = 0.0009), and intervillous space volume (r = 0.38, P = 0.0024). In multivariate analysis of cord parameters in OT1DM, fetal IGF-I emerged as a significant correlate of most components (intervillous space, villous, trophoblast, and capillary volumes, all P < 0.01). By contrast, fetal insulin was only independently associated with capillary surface area (positive, r² = 6.7%; P = 0.02).

CONCLUSIONS

There are minimal placental structural differences between OT1DM and control subjects. Fetal IGF-I but not fetal insulin emerges as a key correlate of placental substructural volumes, thereby facilitating feedback to the placenta regarding fetal metabolic demand.Maternal diabetes is associated with adverse consequences to mother and baby, with increased risks of perinatal morbidity and mortality, in particular in association with fetal macrosomia. The Pedersen hypothesis (1) proposed that maternal hyperglycemia drives increased transplacental glucose transfer and thereby compensatory fetal hyperinsulinemia and induction of fetal growth. Although the fetal consequences of maternal glycemia are clearly recognized, there is still uncertainty about the role of the placenta in determining these outcomes. Specifically, the nature and scale of attendant structural change within the type 1 diabetic placenta remains contentious. Notably, the respective contribution of placental structural differences and how these relate to fetal hormonal axes in the attainment of enhanced placental and fetal growth is also unknown, even in control populations.Classically, older histological studies of type 1 diabetic placentas have described grossly abnormal placentas that are enlarged, thick, and plethoric, with abnormalities of villous maturation (2). These changes would all support the increased incidence of placental-related complications observed in diabetic pregnancy (3). However, other historical series have not detected significant differences (2), and more recent stereological studies continue to differ with either no disparity in placental composition (4,5) or isolated changes including increases in capillary volume and surface area (6,7), increased villous surface area (8), increased total diffusive conductance (9), and increased intervillous and trophoblast volume (7,10). This lack of consistency may reflect a combination of small series, grouping of different classes of maternal diabetes, differences in glycemic control between individual patients, recent improvements in antenatal care, and differing methodology.To date, studies in diabetes have also largely used fetal macrosomia as a surrogate of maternal glycemia and excessive transplacental glucose transfer (7,10) rather than assessment of the fetal hormonal response including hyperinsulinemia. Certainly, fetal hyperinsulinemia has an independent positive association with birth weight and placental weight in offspring of mothers with type 1 diabetes (OT1DM) (11). IGF-I and IGF-II also influence feto-placental growth. IGF-I has strong correlations to both birth weight and placental weight in control subjects and OT1DM (11–13). The role of IGF-II is less clear in human studies and is likely modified by circulating IGF-II receptor (12). Adiponectin, although not directly associated with birth weight, does correlate with placental weight and contributes to the matching of fetal and placental growth in control subjects and OT1DM (11,14). Finally, leptin also correlates with placental weight in control subjects and OT1DM and has recently been proposed as an in utero signal of nutrient availability (11,15). Collectively, these fetal hormone axes may therefore facilitate enhanced growth of the fetus and compensatory changes within the placenta, including structural modification, particularly in response to an excessive glucose supply as seen in diabetic pregnancy. To address this potential interaction of maternal environment, fetal hormones, and placental structure, we have examined placentas in relation to birth weight, neonatal adiposity, and fetal hormonal indexes, in particular those of insulin and IGF-I in OT1DM.     

Hyperglycemia and Adverse Pregnancy Outcome (HAPO) Study: Common Genetic Variants in GCK and TCF7L2 Are Associated With Fasting and Postchallenge Glucose Levels in Pregnancy and With the New Consensus Definition of Gestational Diabetes Mellitus From the International Association of Diabetes and Pregnancy Study Groups

OBJECTIVE

Common genetic variants in GCK and TCF7L2 are associated with higher fasting glucose and type 2 diabetes in nonpregnant populations. However, their associations with glucose levels from oral glucose tolerance tests (OGTTs) in pregnancy have not been assessed in a large sample. We hypothesized that these variants are associated with quantitative measures of glycemia in pregnancy.

RESEARCH DESIGN AND METHODS

We analyzed the associations between variants rs1799884 (GCK) and rs7903146 (TCF7L2) and OGTT outcomes at 24–32 weeks'' gestation in 3,811 mothers of European (U.K. and Australia) and 1,706 mothers of Asian (Thailand) ancestry from the HAPO cohort. We also tested associations with offspring birth anthropometrics.

RESULTS

The maternal GCK variant was associated with higher fasting glucose in Europeans (P = 0.001) and Thais (P < 0.0001), 1-h glucose in Europeans (P = 0.001), and 2-h glucose in Thais (P = 0.005). It was also associated with higher European offspring birth weight, fat mass, and skinfold thicknesses (P < 0.05). The TCF7L2 variant was associated with all three maternal glucose outcomes (P = 0.03, P < 0.0001, and P < 0.0001 for fasting and 1-h and 2-h glucose, respectively) in the Europeans but not in the Thais (P > 0.05). In both populations, both variants were associated with higher odds of gestational diabetes mellitus according to the new International Association of Diabetes and Pregnancy Study Groups recommendations (P = 0.001–0.08).

CONCLUSIONS

Maternal GCK and TCF7L2 variants are associated with glucose levels known to carry an increased risk of adverse pregnancy outcome in women without overt diabetes. Further studies will be important to determine the variance in maternal glucose explained by all known genetic variants.Maternal glycemia in pregnancy is associated with adverse pregnancy outcomes including birth weight >90th percentile, delivery by cesarean section, neonatal hypoglycemia, and fetal hyperinsulinemia (1). These associations occur across the full range of maternal glucose levels below those classified as overt diabetes.In healthy, nondiabetic, nonpregnant populations, approximately one-third of the variation in fasting glucose is genetic (2), and common genetic variants at multiple loci are now robustly associated with fasting glucose (3–10) and with type 2 diabetes and related glycemic traits (11–18). Thus, genetic factors are likely to contribute to variation in glucose levels in pregnancy. However, these variants have not been examined extensively in large studies of pregnant women.Studies of birth weight in Europeans have provided indirect evidence that two common genetic variants influence maternal glycemia in pregnancy. The T-allele of the rs1799884 variant in the GCK gene is associated with higher fasting glucose in the general population (4) and with type 2 diabetes (10). Pregnant women who carry this allele give birth to babies that are, on average, 32 g (95% CI 11–53) heavier at birth (4). Similarly, each additional T-allele of rs7903146 in the TCF7L2 gene—which is associated with reduced β-cell function, raised fasting glucose, and type 2 diabetes (10,13,19)—is also associated with a 30-g (95% CI 15–45) higher offspring birth weight when carried by the mother (20). We hypothesize that these associations with birth weight reflect higher levels of maternal glucose, which result in greater fetal insulin secretion and a consequent increase in fetal size at birth (21).There is some evidence from small studies that the GCK and TCF7L2 variants are associated with fasting glucose in pregnancy or gestational diabetes mellitus. The GCK variant was associated with higher fasting glucose in 755 European pregnant women from the U.K. (22) and with gestational diabetes mellitus in a Scandinavian sample (23). Variation at the TCF7L2 locus was not associated with fasting glucose in 921 European pregnant women (20) but was associated with gestational diabetes mellitus in Scandinavian (24,25), Korean (26), and Mexican-American (27) samples.The large sample size and detailed pregnancy and birth phenotype data available in the Hyperglycemia and Adverse Pregnancy Outcome (HAPO) study provide a unique opportunity to investigate more thoroughly the associations of the GCK and TCF7L2 variants with maternal glycemia, as measured in an oral glucose tolerance test (OGTT), during pregnancy as well as fetal size at birth and body composition. We used OGTT results from 5,517 pregnant women of European and South East Asian ancestry to assess associations both with quantitative measures of maternal glucose and with the new International Association of Diabetes and Pregnancy Study Groups (IADPSG) recommendations for the diagnosis of gestational diabetes mellitus (28).     

Fetal Exposure to Maternal Type 1 Diabetes Is Associated With Renal Dysfunction at Adult Age

OBJECTIVE

In animal studies, hyperglycemia during fetal development reduces nephron numbers. We tested whether this observation translates into renal dysfunction in humans by studying renal functional reserve in adult offspring exposed in utero to maternal type 1 diabetes.

RESEARCH DESIGN AND METHODS

We compared 19 nondiabetic offspring of type 1 diabetic mothers with 18 offspring of type 1 diabetic fathers (control subjects). Glomerular filtration rate (⁵¹Cr-EDTA clearance), effective renal plasma flow (¹²³I-hippurate clearance), mean arterial pressure, and renal vascular resistances were measured at baseline and during amino acid infusion, which mobilizes renal functional reserve.

RESULTS

Offspring of type 1 diabetic mothers were similar to control subjects for age (median 27, range 18–41, years), sex, BMI (23.1 ± 3.7 kg/m²), and birth weight (3,288 ± 550 vs. 3,440 ± 489 g). During amino acid infusion, glomerular filtration rate and effective renal plasma flow increased less in offspring of type 1 diabetic mothers than in control subjects: from 103 ± 14 to 111 ± 17 ml/min (8 ± 13%) vs. from 108 ± 17 to 128 ± 23 ml/min (19 ± 7%, P = 0.009) and from 509 ± 58 to 536 ± 80 ml/min (5 ± 9%) vs. from 536 ± 114 to 620 ± 140 ml/min (16 ± 11%, P = 0.0035). Mean arterial pressure and renal vascular resistances declined less than in control subjects: 2 ± 5 vs. −2 ± 3% (P = 0.019) and 3 ± 9 vs. −14 ± 8% (P = 0.001).

CONCLUSIONS

Reduced functional reserve may reflect a reduced number of nephrons undergoing individual hyperfiltration. If so, offspring of type 1 diabetic mothers may be predisposed to glomerular and vascular diseases.A reduced number of nephrons may cause hypertension and favor renal and cardiovascular risks in humans (1). Autopsy findings support this assumption (2). In addition, birth weight is a determinant of nephron numbers in humans (3). In animal models, moderate hyperglycemia during pregnancy affects birth weight and nephron numbers in offspring (4), and favors the development of hypertension in adulthood (5). In addition, angiogenesis affects kidney development (6,7). In this respect, moderate hyperglycemia induces a defect in angiogenesis as reported in experimental conditions (8).We hypothesized that the effects of moderate hyperglycemia on kidney development reported in animal studies might have clinical relevance in humans. Thus, we studied kidney function in subjects who had been exposed to hyperglycemia during their fetal development. For this purpose, we investigated, as previously (9), adults whose mothers had type 1 diabetes at the time of their conception and used the offspring of type 1 diabetic fathers as control subjects to minimize potential genetic heterogenicity between groups. Type 1 diabetes as a source of hyperglycemia during fetal development also minimizes confounding factors associated with type 2 diabetes such as hypertension. Counting nephron numbers and/or visualizing glomerular size by noninvasive methods is not currently feasible in humans. Thus, we measured global kidney function at baseline and during vasodilatation produced by amino acid infusion, i.e., renal functional reserve. Reduction in renal functional reserve can be interpreted as reflecting a reduced surface available for filtration, suggesting that the number of functional nephrons is reduced. As a result, the global hemodynamic load provokes hyperfiltration at the single nephron level (1). This disturbance in renal hemodynamics was associated with renal and vascular diseases, both in experimental models (1,4,5) and clinical settings (10–13). We report here that renal functional reserve is reduced in offspring of type 1 diabetic mothers.     

Albuminuria and Estimated Glomerular Filtration Rate Independently Associate with Acute Kidney Injury

Acute kidney injury (AKI) is increasingly common and a significant contributor to excess death in hospitalized patients. CKD is an established risk factor for AKI; however, the independent graded association of urine albumin excretion with AKI is unknown. We analyzed a prospective cohort of 11,200 participants in the Atherosclerosis Risk in Communities (ARIC) study for the association between baseline urine albumin-to-creatinine ratio and estimated GFR (eGFR) with hospitalizations or death with AKI. The incidence of AKI events was 4.0 per 1000 person-years of follow-up. Using participants with urine albumin-to-creatinine ratios <10 mg/g as a reference, the relative hazards of AKI, adjusted for age, gender, race, cardiovascular risk factors, and categories of eGFR were 1.9 (95% CI, 1.4 to 2.6), 2.2 (95% CI, 1.6 to 3.0), and 4.8 (95% CI, 3.2 to 7.2) for urine albumin-to-creatinine ratio groups of 11 to 29 mg/g, 30 to 299 mg/g, and ≥300 mg/g, respectively. Similarly, the overall adjusted relative hazard of AKI increased with decreasing eGFR. Patterns persisted within subgroups of age, race, and gender. In summary, albuminuria and eGFR have strong, independent associations with incident AKI.It has long been recognized that an episode of acute kidney injury (AKI) can have serious health consequences.^1–4 Even a relatively small degree of renal injury increases a patient''s risk of a prolonged hospital stay, chronic kidney disease (CKD), ESRD, and death.^2,5–10 Over the last 2 decades, the incidence of hospitalized AKI has increased dramatically.^11–14 Precise estimations vary depending on population and method of case identification, but a recent community-based study of AKI estimated the incidence of nondialysis requiring AKI at 522 per 100,000 population per year and dialysis-requiring AKI at 30 per 100,000,¹³ which is well over that of ESRD.¹⁴ This increase in the burden of disease, taken with the associated poor long-term outcomes, has established AKI as a major public health issue.¹⁴Beyond routine supportive care, there exists little established medical therapy for AKI.¹⁵ Many current lines of research are focused on the prevention of AKI. However, few prospective, population-based studies have evaluated the development of AKI.^3,13,16 Hsu et al.,^13,17 along with multiple observational series in various clinical settings, have clearly established older age and CKD as risk factors for AKI.^18–24 Other observed associations with AKI include black race and male gender.^11,18,25 Proteinuria, an established risk factor in the development of cardiovascular disease,^26,27 ESRD,²⁸ and death,²⁹ is less studied in its role in the development of AKI. Hsu and colleagues demonstrated the prospective association of proteinuria with dialysis-requiring AKI; however, the proteinuria classification was binary and based on dipstick measurement.¹⁷ To our knowledge, no study has quantified the independent dose response of albuminuria with AKI hospitalization, including less severe AKI. Our study''s objective was thus to characterize prospectively the association between baseline urine albumin-to-creatinine ratio (UACR) and hospitalizations for AKI, controlling for established and potential risk factors such as CKD, age, and cardiovascular comorbidities.     

Kidney and Recipient Weight Incompatibility Reduces Long-Term Graft Survival

Long-term function of kidney allografts depends on multiple variables, one of which may be the compatibility in size between the graft and the recipient. Here, we assessed the long-term consequences of the ratio of the weight of the kidney to the weight of the recipient (KwRw ratio) in a multicenter cohort of 1189 patients who received a transplant between 1995 and 2006. The graft filtration rate increased by a mean of 5.74 ml/min between the third and sixth posttransplantation months among patients with a low KwRw ratio (<2.3 g/kg; P < 0.0001). In this low KwRw ratio group, the graft filtration rate remained stable between 6 months and 7 years but then decreased at a mean rate of 3.17 ml/min per yr (P < 0.0001). In addition, low KwRw ratios conferred greater risk for proteinuria, more antihypertensive drugs, and segmental or global glomerulosclerosis. Moreover, a KwRw ratio <2.3 g/kg associated with a 55% increased risk for transplant failure by 2 years of follow-up. In conclusion, incompatibility between graft and recipient weight is an independent predictor of long-term graft survival, suggesting that avoiding kidney and recipient weight incompatibility may improve late clinical outcome after kidney transplantation.The effect of nephron reduction has long been described in animal models as well as in humans^1,2 and is thought to be a potential “nonimmunologic” risk factor for chronic graft dysfunction after kidney transplantation.^3,4 The paradigm generally considered to account for the deleterious effect of nephron reduction on graft function is that of “adaptive” hyperfiltration of the remaining glomeruli, ultimately leading to glomerulosclerosis.^5–7 In accordance with this hypothesis, individuals who have undergone nephrectomy have been shown to develop high BP and proteinuria decades after the nephrectomy,^8–11 as in the case of older recipients with a higher body mass index¹²; however, renal insufficiency only appears in the case of a 75% reduction in kidney mass and after at least 10 years of follow-up.⁹ Kidney transplantation has been proposed as an accelerated model of nephron reduction resulting from the accumulation of several unfavorable factors. For example, repeated injuries, from initial brain death of the donor¹³ to ischemia-reperfusion injury,¹⁴ negatively affect the transplant. Moreover, superimposed immunologic and nonimmunologic events further decrease the initial nephron mass of a transplant and serve only to exacerbate the consequences of hyperfiltration related to its single kidney status.Given that kidney weight (Kw) and glomerular volume (but not nephron number) correlate with body surface area (BSA),¹⁵ several studies have already analyzed the effect of donor and recipient BSA mismatches.^7,16–19 The effect of kidney graft size and recipient weight (Rw)^20,21 has also been studied; however, the direct impact of matching the Kw itself (which correlates with both glomerular volume and nephron number)¹⁵ to the Rw has been studied only in relatively small cohorts of <300 patients and only in living donors,^22,23 where the graft does not incur the same accumulating injuries as those from deceased donors.We previously reported on the results of a first study²⁴ focusing on the impact of graft weight on clinical outcome; however, within the relatively short survey period of the latter study (mean 32 months; range 8 days to 94 months), no impact on short-term graft survival was observed. Because renal failure has been described a decade after nephron reduction,^3,10,25 we reappraised our historical cohort to which an additional 47 patients were included (whole population n = 1189) at a mean of 6.2 years from transplantation (range 8 days to 13 years). We now report that the magnitude of the Kw and Rw incompatibility is significantly associated not only with sustained “adaptive” hyperfiltration and early proteinuria but also with an increased risk for hypertension requiring more medication, a higher incidence of segmental or global glomerulosclerosis, and a significantly poorer long-term transplant survival.     

Low Socioeconomic Status Associates with Higher Serum Phosphate Irrespective of Race

Hyperphosphatemia, which associates with adverse outcomes in CKD, is more common among blacks than whites for unclear reasons. Low socioeconomic status may explain this association because poverty both disproportionately affects racial and ethnic minorities and promotes excess intake of relatively inexpensive processed and fast foods enriched with highly absorbable phosphorus additives. We performed a cross-sectional analysis of race, socioeconomic status, and serum phosphate among 2879 participants in the Chronic Renal Insufficiency Cohort Study. Participants with the lowest incomes or who were unemployed had higher serum phosphate concentrations than participants with the highest incomes or who were employed (P < 0.001). Although we also observed differences in serum phosphate levels by race, income modified this relationship: Blacks had 0.11 to 0.13 mg/dl higher serum phosphate than whites in the highest income groups but there was no difference by race in the lowest income group. In addition, compared with whites with the highest income, both blacks and whites with the lowest incomes had more than twice the likelihood of hyperphosphatemia in multivariable-adjusted analysis. In conclusion, low socioeconomic status associates with higher serum phosphate concentrations irrespective of race. Given the association between higher levels of serum phosphate and cardiovascular disease, further studies will need to determine whether excess serum phosphate may explain disparities in kidney disease outcomes among minority populations and the poor.Racial disparities in kidney disease outcomes are among the most glaring inequities in the United States health care system.^1–5 Despite a similar prevalence of early-stage chronic kidney disease (CKD), blacks are up to 4 times more likely to progress to ESRD than whites.^1–4 In addition, compared with whites, blacks have higher rates of cardiovascular disease and mortality in early CKD.^6,7 Although these differences have largely been attributed to socioeconomic inequalities leading to inadequate access to medical care among minority populations,^5,8 increasing evidence suggests that biologic factors, such as disorders of mineral metabolism, also contribute to racial disparities in CKD outcomes.^9,10Increased serum phosphate is associated with cardiovascular disease, kidney disease progression, and death.^11–15 Although the mechanisms for these relationships are unclear, experimental data showing that excess phosphate promotes vascular calcification, endothelial dysfunction, and renal injury suggest a causal link between an elevated serum phosphate and adverse health outcomes.^16–19 Large cohort studies have shown that hyperphosphatemia is more common and more severe in blacks than in whites, both among patients with CKD and among individuals with normal kidney function.^20–22 Given the emerging connections between increased serum phosphate and accelerated cardiovascular and kidney disease progression, understanding the mechanisms underlying the excess prevalence of hyperphosphatemia among blacks may elucidate novel approaches for reducing racial disparities in CKD outcomes.Racial and ethnic minorities disproportionately reside in low-income neighborhoods that have limited access to healthy food choices, resulting in the overconsumption of inexpensive processed and fast foods that are rich in highly absorbable phosphorus additives.^23–27 High intake of these foods has been associated with increased serum phosphate in CKD,²⁵ and dietary counseling aimed at reducing the consumption of these foods lowered serum phosphate in hemodialysis patients.²⁸ Furthermore, increasing poverty was independently associated with higher serum phosphate levels and greater likelihood of hyperphosphatemia in a cohort of over 14,000 adults with largely preserved kidney function in the Third National Health and Nutrition Examination Survey.²⁹ Collectively, these observations suggest that lower socioeconomic status may contribute to elevated serum phosphate concentrations by promoting excess dietary phosphorus intake. Whether this accounts for higher serum phosphate concentrations among blacks compared with whites with CKD is unclear. We examined the associations between race, socioeconomic status, and serum phosphate concentrations among participants in the Chronic Renal Insufficiency Cohort (CRIC) Study.     

The NLRP3 Inflammasome Promotes Renal Inflammation and Contributes to CKD

Inflammation significantly contributes to the progression of chronic kidney disease (CKD). Inflammasome-dependent cytokines, such as IL-1β and IL-18, play a role in CKD, but their regulation during renal injury is unknown. Here, we analyzed the processing of caspase-1, IL-1β, and IL-18 after unilateral ureteral obstruction (UUO) in mice, which suggested activation of the Nlrp3 inflammasome during renal injury. Compared with wild-type mice, Nlrp3^−/− mice had less tubular injury, inflammation, and fibrosis after UUO, associated with a reduction in caspase-1 activation and maturation of IL-1β and IL-18; these data confirm that the Nlrp3 inflammasome upregulates these cytokines in the kidney during injury. Bone marrow chimeras revealed that Nlrp3 mediates the injurious/inflammatory processes in both hematopoietic and nonhematopoietic cellular compartments. In tissue from human renal biopsies, a wide variety of nondiabetic kidney diseases exhibited increased expression of NLRP3 mRNA, which correlated with renal function. Taken together, these results strongly support a role for NLRP3 in renal injury and identify the inflammasome as a possible therapeutic target in the treatment of patients with progressive CKD.Chronic kidney disease (CKD) is a significant cause of morbidity and mortality in the general population.^1,2 In nondiabetic CKD, the progression from mild/moderate kidney disease to ESRD is a complex process that involves many factors, including tubulointerstitial inflammation and fibrosis. The involvement of mononuclear inflammatory cells in the damaged renal interstitium is a universal finding in failing kidneys and correlates inversely with renal function.^3–9 The molecular mechanisms that regulate inflammation in CKD, however, remain unclear.An inflammatory response is induced during cellular injury such as necrosis.¹⁰ Cellular contents that are inappropriately released after loss of plasma membrane, integrity are endogenous adjuvants or danger-associated molecular patterns (DAMPs).^11–13 These DAMPs alert the innate immune system to cellular injury and produce a proinflammatory response to aid the repair of damaged tissues. Although beneficial in the case of pathogens, the reaction to endogenous (nonmicrobial) injury can contribute to tissue damage and disease progression.The NOD-like receptors (NLRs) compose a group of pattern recognition receptors involved in a wide variety of host innate immune responses to microbial and nonmicrobial stimuli.¹⁴ The best understood members include NOD2 (NLRC2, implicated in Crohn''s disease)¹⁵ and NLRP3 (also known as NALP3 or cryopyrin). Upon activation, the NLRP3 proteins oligomerize and recruit via homotypic molecular interactions, the adaptor protein ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain), and the protease caspase-1 to form a protein complex termed “the inflammasome.”¹⁶ The formation of the inflammasome induces caspase-1 autoprocessing and activation that results in the processing of cellular substrates including the cytokines pro-IL-1β and pro-IL-18.^17,18 In the case of IL-1β, caspase-1 cleaves the 35-kD pro-IL-1β to generate the mature and secreted 17-kD cytokine.Recent reports have implicated the NLRP3 inflammasome in the recognition of endogenous danger signals released from damaged and dying cells. DAMPs capable of activating the NLRP3 inflammasome include reactive oxygen species, extracellular ATP, monosodium urate crystals, nucleic acids, and extracellular matrix components including hyaluronan and biglycan.^19–24 Consistent with these observations, the NLRP3 inflammasome has been implicated in the pathogenesis of various nonmicrobial diseases, including diabetes, gout, silicosis, and acetaminophen liver toxicity.^19,20,25,26 The coexistence of cellular injury and inflammation suggests that the NLRP3 inflammasome may also play a role in regulating inflammation in CKD. Furthermore, the NLRP3 agonist biglycan and cytokines such as IL-1β, IL-18, and the IL-1 receptor all contribute to renal inflammation and fibrosis.^24,27–30 In this study, we demonstrated that the Nlrp3 inflammasome regulates renal inflammation and fibrosis during unilateral ureteral obstruction (UUO) in mice. In addition, studies of humans demonstrated increased NLRP3 in a variety of nondiabetic kidney diseases and CKD. These data provide valuable insight into the processes driving renal inflammation and CKD progression and identify NLRP3 as a novel target for therapeutic intervention.     

The C3a Anaphylatoxin Receptor Is a Key Mediator of Insulin Resistance and Functions by Modulating Adipose Tissue Macrophage Infiltration and Activation

OBJECTIVE

Significant new data suggest that metabolic disorders such as diabetes, obesity, and atherosclerosis all posses an important inflammatory component. Infiltrating macrophages contribute to both tissue-specific and systemic inflammation, which promotes insulin resistance. The complement cascade is involved in the inflammatory cascade initiated by the innate and adaptive immune response. A mouse genomic F2 cross biology was performed and identified several causal genes linked to type 2 diabetes, including the complement pathway.

RESEARCH DESIGN AND METHODS

We therefore sought to investigate the effect of a C3a receptor (C3aR) deletion on insulin resistance, obesity, and macrophage function utilizing both the normal-diet (ND) and a diet-induced obesity mouse model.

RESULTS

We demonstrate that high C3aR expression is found in white adipose tissue and increases upon high-fat diet (HFD) feeding. Both adipocytes and macrophages within the white adipose tissue express significant amounts of C3aR. C3aR^−/− mice on HFD are transiently resistant to diet-induced obesity during an 8-week period. Metabolic profiling suggests that they are also protected from HFD-induced insulin resistance and liver steatosis. C3aR^−/− mice had improved insulin sensitivity on both ND and HFD as seen by an insulin tolerance test and an oral glucose tolerance test. Adipose tissue analysis revealed a striking decrease in macrophage infiltration with a concomitant reduction in both tissue and plasma proinflammatory cytokine production. Furthermore, C3aR^−/− macrophages polarized to the M1 phenotype showed a considerable decrease in proinflammatory mediators.

CONCLUSIONS

Overall, our results suggest that the C3aR in macrophages, and potentially adipocytes, plays an important role in adipose tissue homeostasis and insulin resistance.The complement system is an integral part of both the innate and adaptive immune response involved in the defense against invading pathogens (1). Complement activation culminates in a massive amplification of the immune response leading to increased cell lysis, phagocytosis, and inflammation (1). C3 is the most abundant component of the complement cascade and the convergent point of all three major complement activation pathways. C3 is cleaved into C3a and C3b by the classical and lectin pathways, and iC3b is generated by the alternative pathway (2,3). C3a has potent anaphylatoxin activity, directly triggering degranulation of mast cells, inflammation, chemotaxis, activation of leukocytes, as well as increasing vascular permeability and smooth muscle contraction (3). C3a mediates its downstream signaling effects by binding to the C3a receptor (C3aR), a Gi-coupled G protein–coupled receptor. Several studies have demonstrated a role for C3a and C3aR in asthma, sepsis, liver regeneration, and autoimmune encephalomyelitis (1,3). Therefore, targeting C3aR may be an attractive therapeutic option for the treatment of several inflammatory diseases.Increasing literature suggests that metabolic disorders such as diabetes, obesity, and atherosclerosis also possess an important inflammatory component (4–7). Several seminal reports have demonstrated that resident macrophages can constitute as much as 40% of the cell population of adipose tissue (7–9) and can significantly affect insulin resistance (10–18). Several proinflammatory cytokines, growth factors, acute-phase proteins, and hormones are produced by the adipose tissue and implicated in insulin resistance and vascular homeostasis (4–7,19). An integrated genomics approach was performed with several mouse strains to infer causal relationships between gene expression and complex genetic diseases such as obesity/diabetes. This approach identified the C3aR gene as being causal for omental fat pad mass (20). The C3aR^−/− mice were shown to have decreased adiposity as compared with wild-type mice on a regular diet (20). Monocytes and macrophages express the C3aR (21–28). Increased C3a levels also correlate with obesity, diabetes, cholesterol, and lipid levels (29–34). We therefore sought to investigate the specific role of the C3aR in insulin resistance, obesity, and macrophage function utilizing both normal diet and the diet-induced obesity model.     

Human Recombinant ACE2 Reduces the Progression of Diabetic Nephropathy

OBJECTIVE

Diabetic nephropathy is one of the most common causes of end-stage renal failure. Inhibition of ACE2 function accelerates diabetic kidney injury, whereas renal ACE2 is downregulated in diabetic nephropathy. We examined the ability of human recombinant ACE2 (hrACE2) to slow the progression of diabetic kidney injury.

RESEARCH DESIGN AND METHODS

Male 12-week-old diabetic Akita mice (Ins2^WT/C96Y) and control C57BL/6J mice (Ins2^WT/WT) were injected daily with placebo or with rhACE2 (2 mg/kg, i.p.) for 4 weeks. Albumin excretion, gene expression, histomorphometry, NADPH oxidase activity, and peptide levels were examined. The effect of hrACE2 on high glucose and angiotensin II (ANG II)–induced changes was also examined in cultured mesangial cells.

RESULTS

Treatment with hrACE2 increased plasma ACE2 activity, normalized blood pressure, and reduced the urinary albumin excretion in Akita Ins2^WT/C96Y mice in association with a decreased glomerular mesangial matrix expansion and normalization of increased α-smooth muscle actin and collagen III expression. Human recombinant ACE2 increased ANG 1–7 levels, lowered ANG II levels, and reduced NADPH oxidase activity. mRNA levels for p47^phox and NOX2 and protein levels for protein kinase Cα (PKCα) and PKCβ1 were also normalized by treatment with hrACE2. In vitro, hrACE2 attenuated both high glucose and ANG II–induced oxidative stress and NADPH oxidase activity.

CONCLUSIONS

Treatment with hrACE2 attenuates diabetic kidney injury in the Akita mouse in association with a reduction in blood pressure and a decrease in NADPH oxidase activity. In vitro studies show that the protective effect of hrACE2 is due to reduction in ANG II and an increase in ANG 1–7 signaling.Chronic kidney disease is recognized as an increasing global public health problem due in part to the increasing prevalence of diabetes (1–3). Activation of the renin-angiotensin system (RAS) and the generation of angiotensin II (ANG II) play an important pathogenic role in diabetic nephropathy, and blockade of the RAS attenuates the development of diabetic kidney injury (4–8). The discovery of a homologue of the classical ACE, ACE2, has introduced a new enzyme in ANG peptide metabolism (9–12). Like ACE, ACE2 is membrane bound, but it is a monocarboxypeptidase that generates ANG (1–7) from the octapeptide ANG II (9,10,12,13). As such, ACE2 serves as an endogenous negative regulator of the renin-angiotensin system.In animal models of diabetes, early increases in ACE2 mRNA levels, protein expression, and ACE2 activity occurs (14,15), whereas ACE2 mRNA and protein levels have been found to decrease in older streptozotocin-induced diabetic rats (16). Loss of ACE2 is associated with age-dependent glomerulosclerosis and albuminuria (17) and exacerbation of diabetic kidney injury in Akita mice (18) and is preventable by angiotensin type 1 (AT1) receptor blockade. In patients with type 2 diabetes, glomerular and tubular ACE2 expressions are reduced in the setting of increased ACE expression (19,20). Taken together, these studies suggest that ACE2 may play an early protective role against the development of diabetic nephropathy (18,21,22). We hypothesized that treatment with human recombinant ACE2 (hrACE2) will target the diabetic glomerulus and slow progression of diabetic nephropathy in the Akita mouse (Ins2^WT/C96Y), a model of type 1 diabetes.