Glycated adducts induce mesothelial cell transdifferentiation: role of glucose and icodextrin dialysis solutions.

BACKGROUND: In peritoneal dialysis (PD), the peritoneum is exposed to intermediate Amadori adducts (AmAs) and advanced (AGE) glycated products of proteins. The aim of this study was to test the capacity of AmAs created in different PD solutions (PDSs) to elicit a fibroblast-like transdifferentiation of human peritoneal mesothelial cells (HPMCs) in culture. METHODS: HPMCs were incubated for 12 hours with AmA obtained by human serum albumin (HSA) incubated for 6 days with commercial 3.86% glucose (Glu), 1.36% Glu and 7.5% icodextrin (Ico) PDS. Mesenchymal (vimentin), epithelial (cadherin) and myofibroblastic (Type I collagen and alpha smooth muscle cell actin [ASMA]) markers were evaluated (RT-PCR, immunostaining and Western blot), as well as TGF-b3 synthesis (ELISA and Western blot). RESULTS: Ico-PDS was less active than 3.86% and 1.36% Glu-PDS in glycating albumin (p<0.001). AmA-HSA-Glu 3.86% and 1.36% induced a significantly higher increase in vimentin and Type I collagen mRNA expression than AmA-HSA-Ico (p<0.0001). By contrast, AmA-HSA-Glu 3.86% and 1.36% induced a reduction in cadherin mRNA expression which was significantly different from AmA- HSA-Ico (p<0.0001). RT-PCR data were confirmed by immunostaining and Western blot analysis. AmA-HSA-Glu 3.86% and 1.36% induced a significantly higher increase in ASMA mRNA expression than AmA-HSA-Ico (p<0.0001). AmA-HSA-Glu 3.86% and 1.36% stimulated ASMA and TGF-b3 synthesis which were significantly higher than AmA-HSA-Ico (p<0.001 and p<0.01, respectively). CONCLUSIONS: Our data suggest that Glu-PDS, but not Ico-PDS, can turn on the fibroblastic-like transdifferentiation in HPMCs, and this mechanism may result in peritoneal sclerosis.

Serological and genetic factors in early recurrence of IgA nephropathy after renal transplantation.

BACKGROUND: The relative role of IgA anomalies and genetic factors in IgA nephropathy (IgAN) recurrence after transplantation has never been investigated in a single cohort. METHODS: Sixty-one transplanted patients who had IgAN as an original disease (30 with biopsy-proved early recurrence, median 2.9 yr post-transplant), and 120 controls, were investigated for aberrantly glycosylated IgA1, IgA binding to mesangial matrix, macromolecular IgA (IgA/fibronectin and uteroglobulin/IgA/fibronectin complexes), and polymorphisms of cytokines [tumor necrosis factor alpha (TNFalpha), interleukin 10 (IL-10), IL-6, interferon gamma and transforming growth factor beta 1] and renin-angiotensin system (angiotensinogen converting enzyme, angiotensin II receptor 1, and angiotensinogen) genes. RESULTS: At multivariate logistic regression analysis, recurrence showed a border-line association with aberrantly glycosylated IgA1 [odds ratio (OR) 8.172, p = 0.077], and was significantly less frequent in carriers of -308 AG/AA TNF-alpha"high producer" genotype (OR 0.125, p = 0.036) and -1082, -819, -592 ACC/ATA IL-10 "low producer" (OR 0.038, p = 0.009) genotypes. CONCLUSION: High levels of aberrantly glycosylated IgA1 do not appear to play a strong crucial role in recurrence of IgAN. Polymorphisms of TNFalpha and IL-10 known to condition Th1 prevalence were associated with protection from early recurrence of IgAN.

Bicarbonate dialysis, unlike acetate-free biofiltration, triggers mediators of inflammation and apoptosis in endothelial and smooth muscle cells.

BACKGROUND: We previously demonstrated that bicarbonate dialysis solutions incubated with endothelial cells (EC) enhance nitric oxide synthase (NOS). We then investigated whether blood circulated in simulated dialysis circuits triggers inflammatory and apoptotic mediators in vessel wall cells, aiming to compare the effects of bicarbonate hemodialysis (BHD) and acetate-free biofiltration (AFB). METHODS: Blood units from 22 healthy donors were dialyzed on AN69 with BHD in 11 sessions and AFB in another 11 sessions. Each dialysate remained endotoxin-free during the 60 min of dialysis. Blood samples having been re-circulated for 15 and 60 min were incubated with EC and smooth muscle cells (SMC), which were then investigated for NOS activity (3H citrulline production from 3H arginine), mRNAs transcription of the inducible isoforms of NOS (iNOS) and cyclooxygenase (COX-2) and the pro-apoptotic p53 protein. To investigate cell-cell interactions, in an-other series of 16 simulated dialyses, lympho-monocytes from blood circulated in either BHD or AFB were incubated with EC co-cultured in transwell devices with SMC. NOS activity was measured in EC and SMC. RESULTS: In comparison to AFB, blood circulated in BHD induced a significantly greater enhancement of NOS activity in EC, SMC and mRNAs transcription of pro-inflammatory iNOS, COX-2 and pro-apoptotic p53 (for each BHD data series p < 0.01 to p < 0.0001 vs. AFB). Lympho-monocytes from blood circulated in BHD but not in AFB, triggered the final SMC activation. CONCLUSIONS: Ex vivo AFB is less effective than BHD in activating vessel wall cells to synthesis/release of pro-inflammatory and pro-apoptotic mediators.

Procalcitonin as a marker of micro-inflammation in hemodialysis.

In searching for a rapid and sensitive test to detect micro-inflammation in patients on hemodialysis (HD), we measured serum procalcitonin (PCT) levels and made a comparison with other traditional markers such as C-reactive protein (CRP), serum amyloid (SAA) and homocysteine, considered related to vascular damage. We investigated 51 HD patients, without signs of infection, in basal conditions (during standard bicarbonate dialysis and unselected filters: X) and after 4 months of possibly more biocompatible treatments (on-line hemofiltration (HF) or HD with ultra-pure dialysate and biocompatible membranes: Y). Serum PCT (measured by immunoluminometric assay), CRP and SAA (nephelometric assay) and plasma homocysteine (measured by high performance liquid chromatography) concentrations were assessed at the beginning of dialysis (T0) and after 4 hr (T4). Patients on unselected dialysis displayed mean PCT values significantly increased after 4 hr of dialysis in comparison to those at the start of the sessions (XT4 1.56 +/- 3.93 vs. XT0 0.4 +/- 0.34 ng/mL; p < 0.05). The PCT levels detected after 4 hr of biocompatible treatments were significantly lower than those detected after 4 hr of unselected treatments (YT4 0.78 +/- 0.34 ng/mL; p < 0.05), even though the percentage of patients with positive PCT values (> 0.5 ng/mL) remained almost unchanged. No significant modification in mean levels or in the frequency of positive values was observed for CRP, SAA and homocysteine. After 4 months of highly biocompatible treatments, a reduction in intradialytic enhancements of all inflammation markers was detected. Our data support the conclusion that PCT is a more precise marker than other traditional tests to evaluate micro-inflammation and biocompatibility in HD.

Amadori-configurated albumin induces nitric oxide-dependent apoptosis of endothelial cells: a possible mechanism of diabetic vasculopathy.

BACKGROUND: We have demonstrated previously that Amadori-configurated glycated albumin (GA) enhances nitric oxide synthase (NOS) activity, and this action may modulate glomerular hyperfiltration in early phases of diabetic nephropathy. Since the late stage of diabetic vasculopathy is characterized by reductions in viable cells within an expanded and disorganized matrix, we tested the hypothesis that GA enhances endothelial cell (EC) apoptosis. METHODS: Murine (t End.1) or human umbilical vein ECs (HUVECs) were incubated with graded GA concentrations (furosine 0.48-96 nmol/ml) at levels that approximated those reported in sera of diabetic patients (76 +/- 0.02 nmol/ml). Apoptosis was evaluated using terminal uridine nick end labelling (TUNEL) to detect DNA fragmentation in gel electrophoresis and p53 expression in immunoperoxidase. Transcription of the inducible (i) and constitutive (c) isoforms of NOS was detected by northern analysis, and total NOS activity was measured as [(3)H]citrulline production from [(3)H]arginine. Cells were also incubated with the NOS inhibitors L-nitromethylarginine (L-NAME) at 0.01 M and aminoguanidine (AMG) at 0.01 M, the protein synthesis inhibitor cycloheximide (CHX) at 1 micro g/ml, and the NO donor sodium nitroprusside (SNP) at 0.01 M. RESULTS: ECs cultured in the presence of GA at furosine concentrations corresponding to levels in diabetic patients showed a significant enhancement of apoptosis. GA also caused parallel dose-dependent increases in iNOS mRNA expression and total NOS activity. The pro-apoptotic effect of GA was inhibited by L-NAME, AMG and CHX, but enhanced by SNP. CONCLUSIONS: We found that Amadori-configurated GA at furosine concentrations similar to those in diabetic patients favoured EC apoptosis through enhancement of iNOS activity. We propose that this process may be involved in the progressive cellular loss occurring in vascular and glomerular diabetic sclerosis.

Glucose degradation products increase apoptosis of human mesothelial cells.

BACKGROUND: The heat sterilization of glucose solutions for peritoneal dialysis (PDS) induces the formation of glucose degradation products (GDPs), a phenomenon amplified by lactate and neutral pH. In the new three-compartment bag (3CB) PDS, a glucose solution at pH 3 is kept apart from the buffer until use, and the final solution delivers glucose concentrations that are similar to traditional PDS (TPD), with pH 6 and a lower content of GDPs. As GDPs have oxidant activity that may favour apoptosis, we investigated mesothelial cell apoptosis modulation by 12 h cultures in media supplemented with: (i) two relevant GDPs, methylglyoxal (MGly) and formaldehyde (For) in time and dose-dependence assays, (ii) GDPs at concentrations detected in TPD and 3CB, and (iii) commercial TPD and 3CB PDS, both with 1.36% glucose. METHODS: Apoptosis was evaluated by terminal 3' uridine labelling. Key proteins involved in the apoptotic pathway were investigated by reverse transcription polymerase chain reaction (RT-PCR) mRNA expression and immunoperoxidase staining (caspase 9, tumour suppressor protein p53, inducible cyclooxygenase COX-2). RESULTS: The apoptotic effects of MGly and For were dose and time dependent. GPDs at concentrations detected in TPD induced greater transcription and translation of apoptotic pathway proteins (caspase 9, p53 and COX-2) than GPDs in 3CB. This resulted in a higher apoptotic rate, which was not influenced by addition of sterile glucose. A similar enhancement of apoptosis was detected when mesothelial cells were incubated with TPD, whereas incubation in 3CB PDS resulted in less enhanced apoptosis. The 12 h incubation effect of PDS on cultured mesothelial cells was not related to advanced glycosylated end-product formation. CONCLUSIONS: As the rate of mesothelial cell apoptosis is lower in 3CB than in TPD solutions, the 3CB appears to provide improved biocompatibility.

In human IgA nephropathy uteroglobin does not play the role inferred from transgenic mice.

BACKGROUND: Uteroglobin (UG)-knockout and UG-antisense transgenic mice develop clinical and pathological features of immunoglobulin A (IgA) nephropathy with heavy proteinuria. These models suggested that UG, an anti-inflammatory protein with high affinity for fibronectin (Fn), prevents the formation of IgA-Fn complexes and mesangial deposits in mice. We aim to elucidate whether similar mechanisms underlie the development and severity of human IgA nephropathy. METHODS: Specific enzyme-linked immunosorbent assays were devised to detect serum levels of UG binding to Fn or incorporated into IgA-Fn complexes and IgA binding to Fn or collagen IV. Sera from 75 patients with IgA nephropathy with normal renal function and various degrees of proteinuria (0.2 to 5 g/d of protein) stable over the previous 3 months without therapy were investigated and compared with healthy controls. RESULTS: Levels of UG binding to Fn were similar in patients with IgA nephropathy and healthy controls. UG incorporated into circulating IgA-Fn complexes, as well as levels of IgA-Fn complexes and IgA binding Fn and collagen IV, were significantly greater in patients than healthy controls. Greater amounts of UG incorporated into IgA-Fn complexes reduced the risk for proteinuria with protein greater than 1 g/d (odds ratio = 0.67; P < 0.001). Logistic regression analysis assigned a predictive value for proteinuria persistently greater than 1 g/d of protein to lower amounts of UG incorporated into IgA-Fn complexes (R = -0.267; P = 0.008) and increased binding of IgA to collagen IV (R = 0.214; P = 0.0003). CONCLUSION: This first report of human IgA nephropathy after the publication of the mouse model shows that UG is not reduced in circulation and is even increased in IgA-Fn complexes. Because aberrant IgA1 glycosylation is the event initiating IgA nephropathy in humans, we speculate that the enhanced incorporation of UG into IgA-Fn complexes might represent feedback to reduce the formation of macromolecular aggregates.

Glycosylation of circulating IgA in patients with IgA nephropathy modulates proliferation and apoptosis of mesangial cells.

Abnormalities in circulating IgA1 have been demonstrated in patients with IgA nephropathy (IgAN). This study addresses the question of the functional significance of this alteration in creating mesangial injury. Biologic effects of selected IgA glycoforms isolated from serum of IgAN patients and controls and in vitro deglycosylated normal IgA were tested on cultured human mesangial cells (MC). IgA glycoforms, ranging from 250 to 500 kD molecular weight, were isolated by lectin affinity chromatography followed by HPLC. IgA and IgG content was measured by enzyme-linked immunosorbent assay. HPLC fractions were incubated with MC to evaluate proliferation and apoptosis rates and nitric oxide synthesis. Moreover, MC were conditioned with in vitro desialylated and degalactosylated normal IgA. Patients with IgAN displayed increased levels of IgA glycoforms exposing sialic acid in alpha2,6 linkage with N-acetylgalactosamine (Neu5Acalpha2,6GalNAc) (P < 0.02) and GalNAc (P < 0.05), indicating truncation of O-linked glycans of IgA1. Moreover, IgA glycoforms with increased exposure of mannose were observed (P < 0.03), suggesting a defective N-linked glycosylation. No modification in IgG glycosylation was detected. When incubated with MC, the IgA glycoforms isolated from patients with increased exposure of GalNAc, Neu5Acalpha2,6GalNAc, or mannose, significantly depressed the proliferation and increased the apoptotic rate and nitric oxide synthesis activity of cultured MC, in comparison with fractions isolated from controls. Similarly, in vitro desialylated and degalactosylated IgAs significantly depressed the proliferation and enhanced the apoptosis rates of MC. In conclusion, a significant modulation of several human MC functions exerted by serum IgA with increased exposure of GalNAc, Neu5Acalpha2,6GalNAc, and mannose residues isolated from IgAN patients is reported for the first time.