Affinity adsorption of glucose degradation products improves the biocompatibility of conventional peritoneal dialysis fluid

BACKGROUND: Reactive carbonyl compounds (RCOs) present in peritoneal dialysis (PD) fluid have been incriminated in the progressive deterioration of the peritoneal membrane in long-term PD patients. They are initially present in fresh conventional heat-sterilized glucose PD fluid and are supplemented during dwell time by the diffusion of blood RCOs within the peritoneal cavity. In the present study, RCO entrapping agents were immobilized on affinity beads to adsorb RCOs both in fresh PD fluid and in PD effluent. METHODS: The RCO trapping potential of various compounds was assessed in vitro first by dissolving them in the tested fluid and subsequently after coupling with either epoxy- or amino-beads. The tested fluids include fresh heat-sterilized glucose and non-glucose PD fluids, and PD effluent. Their RCOs contents, that is, glyoxal (GO), methylglyoxal (MGO), 3-deoxyglucosone (3-DG), formaldehyde, 5-hydroxymethylfuraldehyde, acetaldehyde, and 2-furaldehyde were monitored by reverse-phase high-pressure liquid chromatography. The biocompatibility of PD fluid was assessed by a cytotoxic assay with either human epidermoid cell line A431 cells or with primary cultured human peritoneal mesothelial cells. RESULTS: Among the tested RCO entrapping agents, hydrazine coupled to epoxy-beads proved the most efficient. It lowered the concentrations of three dicarbonyl compounds (GO, MGO, and 3-DG) and those of aldehydes present in fresh heat-sterilized glucose PD fluid toward the low levels observed in filter-sterilized glucose PD fluid. It did not change the glucose and electrolytes concentration of the PD fluid but raised its pH from 5.2 to 5.9. Hydrazine-coupled epoxy-bead also lowered the PD effluent content of total RCOs, measured by the 2,4-dinitrophenylhydrazone (DNPH) method. The cytotoxicity of heat-sterilized PD fluid incubated with hydrazine-coupled epoxy-beads was decreased to the level observed in filter-sterilized PD fluid as the result of the raised pH and the lowered RCOs levels. CONCLUSION: Hydrazine-coupled epoxy-beads reduce the levels of a variety of dicarbonyls and aldehydes present in heat-sterilized glucose PD fluid to those in filter-sterilized PD fluid, without altering glucose, lactate, and electrolytes contents but with a rise in pH. Incubated with PD effluents, it is equally effective in reducing the levels of serum-derived RCOs. RCO entrapping agents immobilized on affinity beads improve in vitro the biocompatibility of conventional heat-sterilized glucose PD fluid. Their clinical applicability requires further studies.     

Advanced glycation and lipidoxidation of the peritoneal membrane: respective roles of serum and peritoneal fluid reactive carbonyl compounds

BACKGROUND: Advanced glycation of proteins has been incriminated in the progressive alteration of the peritoneal membrane during chronic peritoneal dialysis (PD). Advanced glycation end products (AGEs) result from a modification of proteins by reactive carbonyl compounds (RCOs). RCOs resulting from glucose breakdown are present in commercial PD fluid. They also accumulate in uremic plasma. The present study was undertaken to evaluate the respective contribution of these two sources of RCOs in the genesis of peritoneal AGEs. METHODS: Three major RCOs formed during heat sterilization of PD fluid, that is, glyoxal, methylglyoxal, and 3-deoxyglucosone, and total RCOs were measured in commercial PD fluid and in PD effluent. The generation of pentosidine, used as a surrogate marker for AGEs, during one-week incubations of PD fluid and effluent samples fortified with bovine serum albumin (BSA) was measured by high-performance liquid chromatography. Peritoneal samples were stained with antibodies specific for two AGEs derived from carbohydrate-dependent RCOs, Nepsilon-(carboxymethyl)lysine (CML) and pentosidine, or for two advanced lipoxidation end products (ALEs) derived from lipid-dependent RCOs, malondialdehyde (MDA)-lysine and 4-hydroxynonenal (HNE)-protein adduct. RESULTS: Glyoxal, methylglyoxal, and 3-deoxyglucosone were identified in commercial PD fluid. Their levels in PD effluents decreased with dwell time probably by diffusion into blood circulation. In contrast, the levels of total RCOs were initially low in commercial PD fluid, increased in PD effluent with dwell time probably by diffusion from circulation into the peritoneal cavity, and after 12 hours, reached values observed in uremic serum. The relevance of the rise in total RCOs for AGE formation is demonstrated by a parallel increase in the generation of pentosidine during incubations of PD effluents. In contrast with RCOs present in glucose-rich PD fluid, RCOs diffusing from uremic circulation originate from both carbohydrates and lipids. Their role in the modification of peritoneal proteins is demonstrated by the immunohistochemical study of peritoneal tissue. Two AGEs and two ALEs increase in parallel in the mesothelial layers and in vascular wall of small arteries in the peritoneum. CONCLUSIONS: Protein modification of the peritoneum is determined not only by RCOs originating in PD fluid, but also by RCOs originating from the uremic circulation. The present data might be relevant to current attempts to improve PD fluid toxicity by lowering its glucose content.     

Efficient in vitro lowering of carbonyl stress by the glyoxalase system in conventional glucose peritoneal dialysis fluid

BACKGROUND: Reactive carbonyl compounds (RCOs) present in heat-sterilized peritoneal dialysis (PD) fluid have been incriminated in the progressive deterioration of the peritoneal membrane observed in long-term PD patients. The present study utilized the glyoxalase I (GLO I) system as a new approach to lower in vitro the peritoneal fluid content of RCOs such as methylglyoxal (MGO), glyoxal (GO) and 3-deoxyglucosone (3-DG). METHODS: GO, MGO, and 3-DG solutions or conventional glucose PD fluids were incubated in vitro with various RCO lowering compounds. The evolution of GO, MGO, and 3-DG levels was monitored by high-performance liquid chromatography. The tested compounds included aminoguanidine and glutathione (GSH), alone or together with GLO I. The human GLO I gene was overexpressed in Chinese hamster ovary (CHO) cells, or ubiquitously in transgenic mice. Cell supernatant of the CHO transfectant and protein extracts of various organs of the transgenic mice were also tested. RESULTS: Aminoguanidine incubated with MGO/GO/3-DG mixtures, promptly reduced RCO levels. GSH alone had a similar but milder and slower effect. Together with GLO I, it promptly decreased GO and MGO levels but was less efficient toward 3-DG. After incubation with glucose PD fluid, GSH together with GLO I had the same effect on MGO, GO, and 3-DG levels. Addition of transfected cell supernatant or tissue extracts overexpressing GLO I, together with GSH to either GO, MGO, or 3-DG solutions, promptly and markedly reduced GO and MGO but not 3-DG levels. CONCLUSIONS: GLO I together with GSH efficiently lowers glucose-derived RCOs, especially GO and MGO, both in conventional glucose PD fluids and in RCO solutions. The fact that genetically manipulated cells overexpressing GLO I activity have a similar effect suggests that maneuvers raising GLO I activity in peritoneal cells or in the peritoneal cavity might help prevent the deleterious effects of the peritoneal carbonyl stress in PD patients. The clinical relevance of this approach is yet to be documented.     

Reduced systemic advanced glycation end products in children receiving peritoneal dialysis with low glucose degradation product content.

BACKGROUND: Glucose degradation products (GDP) in peritoneal dialysis (PD) solutions are toxic to the peritoneal membrane and promote the formation of advanced glycation end products (AGE), which contribute to accelerated atherosclerosis and amyloidosis. Double chamber PD solutions have a markedly reduced GDP content. METHODS: We analysed GDP and AGE kinetics in 21 children (7 months to 18 years) on automated PD in a prospective multicentre trial with randomized administration of single chamber, high-GDP and double-chamber, low-GDP dialysis solution for 12 weeks each. Total AGE fluorescence, carboxymethyllysine (CML, ELISA) and 3-deoxyglucosone (3-DG, HPLC) were measured in plasma and PD effluent during a 4 h peritoneal equilibration test. Plasma AGE profiles were assessed by size selective gel permeation chromatography and compared with 23 healthy controls. RESULTS: Initial effluent 3-DG concentrations were 140+/-55 and 25+/-4 micromol/l with high- and low-GDP PD fluid, respectively and declined to 53+/-32 and 7+/-2 micromol/l within 4 h dwell time (P<0.001). The ex vivo AGE generating capacity was three times higher with the high-GDP solution and decreased significantly with dwell time. Plasma AGE levels were 1.8-7.4-fold above those of healthy controls; the elevation was most marked for the small molecular fraction (<2 kDa). Plasma AGE and CML levels were significantly higher after 12 weeks exposure to high-GDP solution (20991+/-4145 AU and 1505+/-617 ng/ml) than following treatment with low-GDP fluid (17518+/-4676 AU and 1151+/-438 ng/ml; both P<0.05). Four hour AGE clearance was higher with low-GDP solution (0.74+/-0.3 vs 0.44+/-0.15 ml/min*1.73 m2, P<0.01). CONCLUSION: GDP are rapidly absorbed from the peritoneal cavity. Administration of PD solutions with low-GDP content reduces plasma AGE levels and may thus improve the cardiovascular risk profile of dialysed children.     

Glucose degradation products in PD fluids: do they disappear from the peritoneal cavity and enter the systemic circulation?

BACKGROUND: Glucose degradation products (GDP) are generated in peritoneal dialysis (PD) fluid during heat sterilization and storage. They are thought to adversely affect the peritoneal membrane. The fate of GDP within the peritoneal cavity has not been well characterized. METHODS: A clinical study was designed to determine (1). whether during the dwell in the peritoneal cavity GDP concentration decreases in the PD fluid as assessed by ex vivo formation of AGE; (2). whether exposure to GDP-containing PD fluids increases plasma fluorescence (as an index of plasma AGE concentration) as well as plasma carboxymethyllysine (CML) concentration; and (3). whether exposure to GDP-containing PD fluids adversely affects glycoprotein CA 125 concentration. A two-group crossover design was adopted comprising two consecutive observation periods of eight weeks each. Stable PD patients were exposed in random order either to conventional PD fluid (heat sterilized at pH 5.5) and subsequently to PD test fluid (or the 2 fluids in reverse order). The PD test fluid was sterilized using a multicompartment bag system separating highly concentrated glucose at pH 3 from the buffer solution. Conventional and test fluids differed with respect to concentrations of GDP, that is, 3-deoxyglucosone (118 vs. 12.3 micromol/L), methylglyoxal (5.3 micromol/L vs. below detection threshold), 3, 4-dideoxyglucosone-3-ene (10 micromol/L vs. below detection threshold) and acetaldehyde (226 vs. <1 micromol/L). RESULTS: The following results were obtained. First, methylglyoxal disappeared completely as early as two hours after intraperitoneal instillation of conventional PD fluid. Second, when spent conventional dialysate was recovered after a two hour and particularly an eight hour dwell and subsequently incubated ex vivo with 40 mg of human serum albumin, there was a continuous decrease of AGE-forming capacity, that is, less generation of fluorescence (AGE) and pyrraline (non-fluorescent Amadori product), and an increase of advanced oxidation protein products (AOPP) in the spent dialysate. Third, plasma fluorescence (exc. 350/em. 430 nm) as an index of circulating AGE compounds as well as plasma CML concentrations were significantly higher in the conventional PD fluid period versus low GDP PD fluid period. Fourth, CA 125 concentrations in spent dialysate were higher during the low GDP PD fluid period compared to the conventional PD fluid period. CONCLUSION: Conventional PD fluid undergoes modifications during intraperitoneal dwell with a loss of AGE forming capacity, suggesting breakdown, precipitation or resorption of GDP in vivo. This is accompanied by an increase in plasma AGE compounds.     

The leptin/adiponectin ratio: potential implications for peritoneal dialysis

Leptin and adiponectin are adipokines with respective pro-atherogenic and anti-atherogenic properties, defining the plasma leptin/adiponectin ratio as a novel marker for atherosclerosis. In non-renal patients, both hyperleptinemia and hypoadiponectinemia are associated with cardiovascular complications. In peritoneal dialysis (PD) patients, the leptin/adiponectin ratio is markedly elevated, which is consistent with their increased cardiovascular risk. As glucose metabolism regulates adipokines, we hypothesized that glucose and/or other PD fluid components may affect adipokine production balance. This review summarizes the available data arising from research in this area. In 3T3-L1 adipocytes, glucose-based PD4 1.36% significantly increased leptin secretion vs amino-acid-based (AA) and icodextrin (ICOD)-based PD fluids. In contrast, adiponectin secretion was significantly reduced by PD4 1.36% vs glucose-free dialysates. Glucose concentration in PD fluids was shown to determine leptin secretion. Preliminary data from PD patients showed that a single 6-h dwell with PD4 3.86% glucose acutely increased plasma leptin vs AA (P<0.05). The reduction in glucose load in a standard PD regimen was associated with an improvement in the plasma leptin/adiponectin ratio at 6 months. pH-neutral PD fluids increased leptin secretion in vitro vs acidic PD fluids, without effect on adiponectin. Whether this effect may have an impact on plasma leptin levels in PD patients is unknown. In conclusion, glucose-based PD fluids worsen the adipokine production balance in vitro while glucose-free solutions improve it. In PD patients, hypertonic glucose-based PD fluids may increase plasma leptin levels. Glucose-sparing PD regimens appear to improve the leptin/adiponectin ratio. However, their potential to reduce cardiovascular complications needs to be demonstrated.     

The potential role of advanced glycation end product and iNOS in chronic renal failure-related testicular dysfunction. An experimental study

OBJECTIVES: To investigate the impact of advanced glycation end products (AGEs) and inducible nitric oxide synthase (iNOS) in chronic renal failure (CRF)-associated testicular dysfunction in an experimental model. In additionally, we examined whether different peritoneal dialysis (PD) fluids could contribute to the elevation in AGE level and iNOS expression in the testes. METHODS: Adult male Wistar rats, 10 and 12 weeks of age and weighing 200-330 g, were divided into 5 groups. Group 1 served as the control group. In group 2, CRF was induced and a peritoneal catheter was implanted, but the dialysis procedure was not performed until the end of the study. In group 3, CRF was induced and PD was performed with dialysis fluids containing 1.36% glucose and icodextrin. In group 4, CRF rats received dialysis fluids containing 3.86% glucose and icodextrin. Finally, an indwelling catheter was implanted and the dialysis procedure was performed using dialysis fluids containing 3.86% glucose and icodextrin (group 5). Chronic PD began 4 weeks after insertion of the catheter. Each morning, this fluid was drained and 20 ml dialysis fluid, containing either 1.36 or 3.86% glucose, was given intraperitoneally for 4 h in unanesthetized animals. Each evening, 20 ml icodextrin was given for 10 h. The dialysis procedure was performed for 8 weeks. The AGE level was determined from the 5-hydroxymethyl-2-furaldehyde (5-HMF) content of penis samples and iNOS expression was assessed by immunohistochemistry. RESULTS: The elevation of 5-HMF was significant in the testes from groups 2, 3, 4, and 5 when compared with group 1. Furthermore, the differences between groups 2 and 4, 3 and 4, and 4 and 5 were also significant (p < 0.05). Immunohistochemical analysis revealed the presence of iNOS predominantly in the Leydig cells. While iNOS staining was significantly lower in group 1 than in other groups, there were also significant differences between groups 2 and 3, 2 and 4, 2 and 5, 3 and 5, and 4 and 5 (p < 0.05). Finally, a significant statistical correlation was found between the 5-HMF and iNOS levels (r = 0.698, p = 0.001). CONCLUSIONS: The present study identifies, for the first time, a potential role of AGE and iNOS in experimental CRF-associated testicular dysfunction. In addition, we found that PD fluids containing glucose contribute to this effect. These results may lead to a better understanding of the pathophysiological pathway in CRF-related testicular dysfunction.     

Immunohistochemical evidence for an increased oxidative stress and carbonyl modification of proteins in diabetic glomerular lesions

Advanced glycation end products (AGE) include a variety of protein adducts whose accumulation has been implicated in tissue damage associated with diabetic nephropathy (DN). It was recently demonstrated that among AGE, glycoxidation products, whose formation is closely linked to oxidation, such as carboxymethyllysine (CML) and pentosidine, accumulate in expanded mesangial matrix and nodular lesions in DN, in colocalization with malondialdehyde-lysine (MDA-lysine), a lipoxidation product, whereas pyrraline, another AGE structure whose deposition is rather independent from oxidative stress, was not found within diabetic glomeruli. Because CML, pentosidine, and MDA-lysine are all formed under oxidative stress by carbonyl amine chemistry between protein amino group and carbonyl compounds, their colocalization suggests a local oxidative stress and increased protein carbonyl modification in diabetic glomerular lesions. To address this hypothesis, human renal tissues from patients with DN or IgA nephropathy were examined with specific antibodies to characterize most, if not all, carbonyl modifications of proteins by autoxidation products of carbohydrates, lipids, and amino acids: CML (derived from carbohydrates, lipids, and amino acid), pentosidine (derived from carbohydrates), MDA-lysine (derived from lipids), 4-hydroxynonenal-protein adduct (derived from lipids), and acrolein-protein adduct (derived from lipids and amino acid). All of the protein adducts were identified in expanded mesangial matrix and nodular lesions in DN. In IgA nephropathy, another primary glomerular disease leading to end-stage renal failure, despite positive staining for MDA-lysine and 4-hydroxynonenal-protein adduct in the expanded mesangial area, CML, pentosidine, and acrolein-protein adduct immunoreactivities were only faint in glomeruli. These data suggest a broad derangement in nonenzymatic biochemistry in diabetic glomerular lesions, and implicate an increased local oxidative stress and carbonyl modification of proteins in diabetic glomerular tissue damage ("carbonyl stress").     

Prevention of membrane damage in patient on peritoneal dialysis with new peritoneal dialysis solutions

Peritoneal dialysis (PD) is now an established and successful alternative to hemodialysis. Multiple studies have confirmed its equivalent dialysis adequacy, mortality and fluid balance status, at least for the first 4–5 years. Peritoneal membrane failure is now one of the leading cause of technique failure. This review describes the role of glucose, glucose degradation product, pH, lactate, advanced glycosylation end product (AGE) in causing this membrane damage, and gives insight how the use of newer peritoneal dialysis fluids (PDFs) containing icodextrin, amino acids and bicarbonate buffer can prevent peritoneal membrane damage.     

The triggering of human peritoneal mesothelial cell apoptosis and oncosis by glucose and glycoxydation products.

BACKGROUND: Peritoneal dialysis fluids (PDFs) have been shown to alter mesothelial cell functions. To further determine the mechanisms involved, we investigated the effects of glucose, glucose degradation products (GDPs) and advanced glycation end products (AGEs) on the inhibition of human peritoneal mesothelial cell (HPMC) proliferation and the induction of apoptosis and oncosis. METHODS: Four PDF solutions, heat-sterilized dextrose-lactate, filtered dextrose-lactate and heat-sterilized dextrose-bicarbonate-lactate, each containing 15 or 45 g/l glucose, and heat-sterilized icodextrin-lactate, containing 75 g/l icodextrin, were tested. In addition, we analysed the independent and synergistic effects of two glucose compounds, i.e. 3-deoxyglucosone (3-DG), a major GDP, and Nepsilon-(carboxymethyl)-lysine (CML), a high-affinity AGE receptor (RAGE) ligand on HPMC viability. Cell proliferation was measured by methyl-[(3)H]thymidine incorporation. Oncosis was quantified by nuclear propidium iodide (PI) DNA-intercalating capability, and apoptosis by the decrease in mitochondrial transmembrane potential ( triangle up psim). RESULTS: It was found that heat-sterilized dextrose-lactate inhibited HPMC proliferation to a greater extent than filtered dextrose-lactate, heat-sterilized dextrose-bicarbonate-lactate, or heat-sterilized icodextrin-lactate (P<0.001). Compared to filtered dextrose-lactate, heat-sterilized dextrose-lactate induced a significantly greater degree of apoptosis (P<0.05) and oncosis (P<0.01). Glucose-induced cell death and antiproliferative activity were significantly potentiated by the action of 3-DG or CML-albumin. By blocking the AGE-RAGE interaction recombinant soluble-RAGE reduced the PDF-induced inhibitory effect on cell proliferation (P<0.001) and apoptosis (P<0.05). CONCLUSION: Heat-sterilized PDFs that contain high glucose concentrations and GDPs, which are AGE precursors, reduce cell proliferation, induce mesothelial cell apoptosis and oncosis, and may be involved in peritoneal damage. PDFs containing lower glucose derivative products are more biocompatible.     

Biocompatibility pattern of a bicarbonate/lactate-buffered peritoneal dialysis fluid in APD: a prospective, randomized study.

BACKGROUND: In chronic ambulatory peritoneal dialysis, bicarbonate-buffered fluids, with their neutral pH and less advanced glycosylation end-products (AGE) and glucose degradation products (GDP), have better biocompatibility than conventional peritoneal dialysis (PD) solutions. That difference may be more beneficial in automated peritoneal dialysis (APD), due to its more frequent exchanges and longer contact times with fresh dialysate. We performed a prospective, randomized study in APD patients to compare the biocompatibility of conventional and bicarbonate/lactate-buffered PD fluids. METHODS: We randomized 14 APD patients to have APD with either conventional or bicarbonate/lactate-based fluids. After 6 months, both groups changed to the other solution. The overall observation period was 12 months. After 1 and 5 months and again after 7 and 11 months, phagocytotic and respiratory burst capacities of effluent peritoneal macrophages were determined. Plasma interleukin (IL)-6 and C-reactive protein (CRP) as well as effluent IL-6, CRP, transforming growth factor (TGF)-beta 1, AGE and CA125 concentrations were measured. Inflow pain was quantified using a patient questionnaire. RESULTS: Respiratory burst capacity remained unchanged and phagocytotic activity increased significantly during APD (P<0.001) with the bicarbonate/lactate fluid. Effluent IL-6 release was significantly lower than with the lactate fluid (P<0.05). While in the effluent TGF-beta 1 was unaffected, AGE concentration was lower after bicarbonate/lactate treatment (P<0.05). Effluent CA125 concentration, an indicator of mesothelial cell integrity, was higher (P<0.05) in neutral effluents. Finally, patients' inflow pain diminished (P = 0.05) when using the neutral fluid. CONCLUSIONS: The use of a neutral PD fluid in APD improved patients' inflow pain as well as biocompatibility parameters reflecting enhanced phagocytotic activity of peritoneal macrophages, reduced constitutive inflammatory stimulation (IL-6), reduced AGE accumulation in the peritoneal cavity and better preservation of the mesothelial cell integrity. From the biocompatibility point of view, a neutral fluid with low GDP content can be recommended as the primary choice for APD.     

Advanced glycation end product precursors impair epidermal growth factor receptor signaling

Formation of advanced glycation end products (AGEs) is considered a potential link between hyperglycemia and chronic diabetic complications, including disturbances in cell signaling. It was hypothesized that AGEs alter cell signaling by interfering with growth factor receptors. Therefore, we studied the effects of two AGE precursors, glyoxal (GO) and methylglyoxal (MGO), on the epidermal growth factor receptor (EGFR) signaling pathway in cultured cells. Both compounds prevented tyrosine autophosphorylation induced by epidermal growth factor (EGF) in a time- and dose-dependent manner as well as phospholipase Cgamma1 recruitment and subsequent activation of extracellular signal-regulated kinases. AGE precursors inhibit EGF-induced EGFR autophosphorylation and tyrosine kinase activity in cell membranes and in EGFR immunoprecipitates. In addition, AGE precursors strongly inhibited cellular phosphotyrosine phosphatase activities and residual EGFR dephosphorylation. AGE precursors induced the formation of EGFR cross-links, as shown by the cross-reactivity of modified EGFR with an anti-N(epsilon)(carboxymethyl)lysine antibody, suggesting that altered EGFR signaling was related to carbonyl-amine reactions on EGFR. Aminoguanidine, an inhibitor of AGE formation, partially prevented the EGFR dysfunction induced by GO and MGO. These data introduce a novel mechanism for impaired cellular homeostasis in situations that lead to increased production of these reactive aldehydes, such as diabetes.     

Impact of chronic renal failure and peritoneal dialysis fluids on advanced glycation end product and iNOS levels in penile tissue: an experimental study

Objectives. To investigate the impact of chronic renal failure (CRF) on advanced glycation end product and inducible nitric oxide synthase (iNOS) in penile tissue, we examined the advanced glycation end product 5-hydroxy methyl furfural (5-HMF) content and iNOS expression in rats in which uremia had been produced by greater than 85% nephrectomy. In addition, the contribution of peritoneal dialysis (PD) fluids to the elevation of penile tissue 5-HMF levels and iNOS staining scores has been investigated.Methods. Adult male Wistar rats, aged between 10 and 12 weeks and weighing 200 to 330 g, were divided into five groups that each included 6 animals. The first group served as a control group. In the second group, CRF was induced and a peritoneal catheter was implanted, but PD was not performed. In group 3, CRF was induced and PD was performed using dialysis fluids containing 1.36% glucose and icodextrin. In group 4, CRF was also induced and PD was performed using 3.86% glucose and icodextrin. Finally, in group 5, without CRF, an indwelling catheter was implanted, and the PD procedure was performed using dialysis fluids containing 3.86% glucose and icodextrin.Results. The elevation in 5-HMF levels and iNOS staining scores in penile tissue from groups 2, 3, 4, and 5 was significant compared with group 1 (P <0.05). The elevation in 5-HMF levels and iNOS staining scores was also significant between groups 2 and 3, 2 and 4, 3 and 4, 3 and 5, and 4 and 5 (P <0.05). Moreover, the correlation between the 5-HMF levels and iNOS staining scores was statistically significant (r = 0.525, P = 0.003).Conclusions. In the present experimental study, we found that 5-HMF levels and iNOS staining scores were significantly elevated in rat penile tissue in which uremia had been produced compared with the groups without CRF. Additionally, PD fluids containing glucose had an effect on the elevation of penile tissue 5-HMF levels and iNOS staining scores.     

Mechanisms for the formation of glycoxidation products in end-stage renal disease

BACKGROUND: Advanced glycation end products (AGEs) accumulate on tissue and plasma proteins in patients with renal failure far in excess of normal aging or diabetes. The aim of these studies was to elucidate the nature of the precursors and the pathways that lead to an accelerated formation of two structurally identified AGEs [pentosidine and Nepsilon(carboxymethyl)lysine (CML)] in the uremic milieu. METHODS: Serum levels of the glycoxidation products, pentosidine and CML, were quantitated by high-performance liquid chromatography in uremic patients treated by dialysis. The formation of early glycation products (as furosine) and late glycoxidation products was modeled in uremic serum and in spent peritoneal dialysate. RESULTS: Clinical factors that affect circulating levels of AGEs included dialysis clearance and dialyzer membrane pore size, but not the presence or absence of diabetes. Both pentosidine and CML form at an accelerated rate in serum from uremic patients. Chelating agents most effectively slow the formation in vitro. In uremic fluids, the primary mechanism of formation of pentosidine is through the Amadori pathway. The primary mechanism of formation of CML is through metal-chelated autoxidation of reducing sugars generating reactive carbonyl precursors. In uremic serum, the presence of an unidentified reactive low molecular weight precursor accelerates the formation of pentosidine. CONCLUSIONS: The formation of the two glycoxidation products, pentosidine and CML, proceeds by different pathways and is enhanced by different precursors in the uremic milieu. The formation of both AGEs is markedly enhanced by metal-catalyzed reactions, evidence for the presence of increased metal-ion mediated oxidant stress in uremia.     

Serum levels of total homocysteine,homocysteine metabolites and of advanced glycation end-products (AGEs) in patients after renal transplantation

AIMS: Hyperhomocysteinemia has been described as an independent risk factor for cardiovascular diseases (CVD) influencing patient outcome. Advanced glycation end-products (AGEs) are involved in the pathogenesis of vascular damage in uremia. This study was undertaken to assess whether high serum levels of total homocysteine (tHcy) with its metabolites methylmalonic acid (MMA), methylcitric acid (MCA) and cystathionine (CYSTA) as well as elevated serum concentrations of the AGEs pentosidine and Nepsilon-carboxymethyllysine (CML) are independent risk factors for CVD, left ventricular hypertrophy (LVH) or hypertension as well as kidney dysfunction in renal transplant recipients (RTR). METHODS: Serum levels of tHCy, MMA, MCA and CYSTA were measured by a gas chromatographic-mass spectrometric assay, pentosidine by HPLC and CML using an ELISA assay. RESULTS: All measured parameters were significantly higher in RTRs than in healthy subjects (p < 0.0001). The levels of pentosidine and CML as well as of tHcy and its metabolites correlated significantly with each other, but not with those ofMMA and CYSTA. Significant correlations were also found between pentosidine and tHcy, MMA or MCA as well as between CML, MMA and MCA, respectively. Acute or chronic rejection did not influence these values. No significant differences were observed between patients with or without CVD or with hypertension. In RTRs with LVH, only the tHcy levels were significantly higher than in those RTRs without LVH (p = 0.006). Logistic regression analysis revealed an independent influence of tHcy on the presence of LVH. CONCLUSION: These results may indicate an association between high tHcy values and LVH. Further investigation is needed to determine whether a reduction of tHcy and Hcy metabolites and/or AGE serum concentrations would significantly improve patient outcome after undergoing renal transplantation.     

Pharmacokinetics of icodextrin in peritoneal dialysis patients

Pharmacokinetics of icodextrin in peritoneal dialysis patients. BACKGROUND: Icodextrin is a glucose polymer osmotic agent used to provide sustained ultrafiltration during long peritoneal dialysis (PD) dwells. A number of studies have evaluated the steady-state blood concentrations of icodextrin during repeated use; however, to date the pharmacokinetics of icodextrin have not been well studied. The current study was conducted to determine the absorption, plasma kinetics and elimination of icodextrin and metabolites following a single icodextrin exchange. METHODS: Thirteen PD patients were administered 2.0 L of solution containing 7.5% icodextrin for a 12-hour dwell. Icodextrin (total of all glucose polymers) and specific polymers with degrees of polymerization ranging from two to seven (DP2 to DP7) were measured in blood, urine and dialysate during the dwell and after draining the solution from the peritoneal cavity. RESULTS: A median of 40.1% (60.24 g) of the total administered dose (150 g) was absorbed during the 12-hour dwell. Plasma levels of icodextrin and metabolites rose during the dwell and declined after drain, closely corresponding to the one-compartment pharmacokinetic model assuming zero-order absorption and first-order elimination. Peak plasma concentrations (median C peak = 2.23 g/L) were observed at the end of the dwell (median Tmax = 12.7 h) and were significantly correlated with patients' body weight (R2 = 0.805, P < 0.001). Plasma levels of icodextrin and metabolites returned to baseline within 3 to 7 days. Icodextrin had a plasma half-life of 14.73 hours and a median clearance of 1.09 L/h. Urinary excretion of icodextrin and metabolites was directly related to residual renal function (R2 = 0.679 vs. creatinine clearance, P < 0.01). In the nine patients with residual renal function, the average daily urinary excretion of icodextrin was 473 +/- 77 mg per mL of endogenous renal creatinine clearance. Icodextrin metabolites DP2 to DP4 were found in the dialysate of subsequent dextrose exchanges, contributing to their elimination from blood. Changes in intraperitoneal concentrations of icodextrin metabolites during the dwell revealed a dual pattern, with a progressive rise in the dialysate concentration of smaller polymers (DP2 to DP4) and a progressive decline in the dialysate concentrations of the larger polymers (DP5 to DP7), suggesting some intraperitoneal metabolism of the glucose polymers. This increase in dialysate metabolite levels, however, did not contribute significantly to dialysate osmolality. In addition, some diffusion of maltose (DP2) from blood to dialysate may have occurred. There were no changes in serum insulin or glucose levels during icodextrin administration, indicating that icodextrin does not result in hyperglycemia or hyperinsulinemia as occurs during dextrose-based dialysis. Serum sodium and chloride declined in parallel with the rise in plasma levels of icodextrin, supporting the hypothesis that these electrolyte changes are the result of the increased plasma osmolality due to the presence of icodextrin metabolites. CONCLUSIONS: The pharmacokinetics of icodextrin in blood following intraperitoneal administration conforms to a simple, single-compartment model that can be approximated by zero-order absorption and first-order elimination. A small amount of intraperitoneal metabolism of icodextrin occurs but does not contribute significantly to dialysate osmolality. The metabolism of absorbed icodextrin and the resultant rise in plasma levels of small glucose polymers (DP2 to DP4) do not result in hyperglycemia or hyperinsulinemia, but may result in a small decrease in serum sodium and chloride.     

Echocardiographic, electrocardiographic and blood pressure changes induced by icodextrin solution in diabetic patients on peritoneal dialysis

The use of icodextrin as an osmotic agent in solutions for peritoneal dialysis (PD) has important cardiovascular effects related with better control of extracellular volume. Among them, reduction of arterial pressure and an improvement in echocardiographic parameters stand out. In diabetic patients, icodextrin has additional potential advantages related with better metabolic control. In a multicenter, open-label randomized controlled trial, the effects of icodextrin solutions were compared to glucose solutions on echocardiographic, electrocardiographic, and blood pressure changes in diabetic patients on PD. Two phases were noted in the follow-up. In the early phase (6 months), reduction in ambulatory blood pressure (ABP) and left ventricular end diastolic diameter were found in the icodextrin group. These changes correlated with changes in body fluids. In the late phase (12 months), a trend towards baseline values in ABP was seen. Changes in inferior vena cava diameter and in low frequency R-R variability spectral analysis in the icodextrin group suggest that icodextrin increases circulating blood volume and sympathetic tone, probably by accumulation of icodextrin metabolites in the bloodstream and improvement in diabetic neuropathy as a result of lower peritoneal glucose absorption. The effects of icodextrin in diabetic patients were related to better fluid management and metabolic control.     

Mechanism of the inhibitory effect of OPB-9195 [(+/-)-2-isopropylidenehydrazono-4-oxo-thiazolidin-5-yla cetanilide] on advanced glycation end product and advanced lipoxidation end product formation

The accumulation in uremic plasma of reactive carbonyl compounds (RCO) derived from both carbohydrates and lipids ("carbonyl stress") contributes to uremic toxicity by accelerating the advanced glycation and lipoxidation of proteins. It was previously demonstrated that OPB-9195 [(+/-)-2-isopropylidenehydrazono-4-oxo- thiazolidin-5-ylacetanilide] inhibited the in vitro formation of advanced glycation end products (AGE) in uremic plasma. This study was designed to elucidate the mechanism of action of OPB-9195 by further delineating the AGE and advanced lipoxidation end product (ALE) precursors targeted by this drug. The inhibitory effects of OPB-9195 on the formation of two AGE (N:epsilon-carboxymethyllysine and pentosidine) on bovine serum albumin incubated with various AGE precursors were examined. Inhibition of N:epsilon-carboxymethyllysine and pentosidine formation with OPB-9195 was more efficient than with aminoguanidine. OPB-9195 also proved effective in blocking the carbonyl amine chemical processes involved in the formation of two ALE (malondialdehyde-lysine and 4-hydroxynonenal-protein adduct). The efficiency of OPB-9195 was similar to that of aminoguanidine. When glucose-based peritoneal dialysis fluid was incubated in the presence of OPB-9195, a similar inhibition of AGE formation was observed. The direct effect of OPB-9195 on major glucose-derived RCO in peritoneal dialysis fluids was then evaluated. The effects of OPB-9195 could be accounted for by its ability to trap RCO. The concentrations of three major glucose-derived RCO (glyoxal, methylglyoxal, and 3-deoxy-glucosone) were significantly lower in the presence of OPB-9195 than in its absence. Aminoguanidine had a similar effect. In conclusion, OPB-9195 inhibits both AGE and ALE formation, probably through its ability to trap RCO. OPB-9195 might prove to be a useful tool to inhibit some of the effects of RCO-related uremic toxicity.