Prospective Cohort Study of Soluble Urokinase Plasminogen Activation Receptor and Cardiovascular Events in Patients With CKD

Introduction

Soluble urokinase plasminogen activation receptor (suPAR) is an immune-derived pathogenic factor for kidney and atherosclerotic disease. Whether the association between suPAR and cardiovascular (CV) outcomes is dependent on the severity of underlying kidney disease is unclear.

Methods

We measured serum suPAR levels in 4994 participants (mean age 60 years; 60% men; 36% with diabetes mellitus; mean estimated glomerular filtration rate (eGFR) 49 ml/min per 1.73 m2, SD 18) of the German Chronic Kidney Disease (GCKD) cohort and examined its association with all-cause death, CV death, and major CV events (MACE) across the range of eGFR and urine albumin-to-creatinine ratio (UACR).

Results

The median suPAR level was 1771 pg/ml (interquartile range [IQR] 1447-2254 pg/ml). SuPAR levels were positively and independently correlated with age, eGFR, UACR, and parathyroid hormone levels. There were 573 deaths, including 190 CV deaths and 683 MACE events at a follow-up time of 6.5 years. In multivariable analyses, suPAR levels (log2) were associated with all-cause death (hazard ratio [HR] 1.36, 95% confidence interval [CI] 1.21-1.53), CV death (HR 1.27, 95% CI 1.03-1.57), and MACE (HR 1.13, 95% CI 1.00-1.28), and were not found to differ according to diabetes mellitus status, baseline eGFR, UACR, or parathyroid hormone levels. In mediation analysis, suPAR's direct effect on all-cause death, CV death, and MACE accounted for 77%, 67%, and 60% of the total effect, respectively; whereas the effect mediated through eGFR accounted for 23%, 34%, and 40%, respectively.

Conclusion

In a large cohort of individuals with chronic kidney disease (CKD), suPAR levels were associated with mortality and CV outcomes independently of indices of kidney function, consistent with its independent role in the pathogenesis of atherosclerosis.

Effect of benfotiamine in podocyte damage induced by peritoneal dialysis fluid

Background: In peritoneal dialysis (PD), residual renal function (RRF) fundamentally contributes to improved quality of life and patient survival. High glucose and advanced glycation end-products (AGE) contribute locally to peritoneal and systemically to renal damage. Integrity of podocyte structure and function is of special importance to preserve RRF. Benfotiamine could counteract the glucose and AGE-mediated toxicity by blocking hyperglycemia-associated podocyte damage via the pentose-phosphate pathway.

Methods: A human differentiated podocyte cell line was incubated with control solution (control), 2.5% glucose solution (glucose), and 2.5% peritoneal dialysis fluid (PDF) for 48 h either ±50 μM benfotiamine. Podocyte damage and potential benefit of benfotiamine were analyzed using immunofluorescence, western blot analysis, and a functional migration assay. For quantitation, a semiquantitative score was used.

Results: When incubating podocytes with benfotiamine, glucose, and PDF-mediated damage was reduced, resulting in lower expression of AGE and intact podocin and ZO-1 localization. The reorganization of the actin cytoskeleton was restored in the presence of benfotiamine as functional podocyte motility reached control level. Decreased level of inflammation could be shown as well as reduced podocyte apoptosis.

Conclusion: These data suggest that benfotiamine protects podocytes from glucose and PDF-mediated dysfunction and damage, in particular, with regard to cytoskeletal reorganization, motility, inflammation, and podocyte survival.

Increased peritoneal damage in glyoxalase 1 knock-down mice treated with peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is limited by peritoneal fibrosis and ultrafiltration failure. This is in part caused by the high concentration of glucose degradation products (GDPs) present in PD fluids (PDF) as a consequence of heat sterilization. Existing research in long-term PD has mainly dealt with the toxicity induced by GDPs and the development of therapeutic strategies to reduce the cellular burden of GDPs. Currently, there are few data regarding the potential role of detoxification systems of GDP in PD. In this study, the role of glyoxalase 1 (Glo1), the major detoxification pathway for dicarbonyl-derived GD such as methylglyoxal (MG) and glyoxal (Gx), was investigated in vivo using heterozygous knock-down mice for Glo1 (Glo1(-/+)).

METHODS

Wild-type (WT) and Glo1(-/+) mice were repeatedly treated with PDF containing low and high amounts of GDP, particularly with respect to the content of dicarbonyls. After 12 weeks of treatment with PDF, peritoneal damage and function were evaluated.

RESULTS

Glo1(-/+) mice treated with PDF showed increased formation of advanced glycation endproduct (AGE) when compared with WT mice, particularly the Gx-derived AGE, carboxymethyl-lysine. This was associated with increased inflammation, neovascularization, increased peritoneal fibrosis and impaired peritoneal function.

CONCLUSIONS

This study suggests a pivotal and underestimated role for Glo1 as a detoxifying enzyme in GDP-associated peritoneal toxicity in PD. The indirect and direct modulation of Glo1 may therefore offer a new therapeutic option in prevention of GDP-induced peritoneal damage in PD.

Cellular effects of everolimus and sirolimus on podocytes

Everolimus (EVL) and Sirolimus (SRL) are potent immunosuppressant agents belonging to the group of mammalian target of rapamycin (mTOR) inhibitors used to prevent transplant rejection. However, some patients develop proteinuria following a switch from a calcineurin inhibitor regimen to mTOR inhibitors. Whether different mTOR inhibitors show similar effects on podocytes is still unknown. To analyze this, human podocytes were incubated with different doses of EVL and SRL. After incubation with EVL or SRL, podocytes revealed a reduced expression of total mTOR. Phosphorylation of p70S6K and Akt was diminished, whereas pAkt expression was more reduced in the SRL group. In both groups actin cytoskeletal reorganization was increased. Synaptopodin and podocin expression was reduced as well as nephrin protein, particularly in the SRL group. NFκB activation and IL-6 levels were lower in EVL and SRL, and even lower in SRL. Apoptosis was more increased in SRL than in the EVL group. Our data suggests that mTOR inhibitors affect podocyte integrity with respect to podocyte proteins, cytoskeleton, inflammation, and apoptosis. Our study is the first to analyze both mTOR inhibitors, EVL and SRL, in parallel in podocytes. Partially, the impact of EVL and SRL on podocytes differs. Nevertheless, it still remains unclear whether these differences are of relevance regarding to proteinuria in transplant patients.

Glucose effects on the peritoneum: what can we learn from rodent models?

During long-term peritoneal dialysis (PD) the peritoneal membrane underlies processes of structural and functional reorganization mediated by high glucose and reactive glucose metabolites that are contained in PD solutions; this process is accompanied by increasing fibrosis. Mechanistically, the peritoneal damage is triggered by the interaction of advanced glycation end-products with their receptor; this is true for rodents as well as for humans. With this knowledge interventional strategies can be tested in rodent models, among them are the lipid soluble vitamin B1 analogue benfotiamine (BF) or detoxifying enzymes such as glyoxalase. Of additional interest is the finding that PD fluids do not only cause local but also systemic damage, in particular renal and cardiovascular. In the case of kidney damage, the intervention with BF was also successful. Taken together, PD can be regarded as a local model for long-term diabetes together with systemic aspects of damage.

Benfotiamine protects against peritoneal and kidney damage in peritoneal dialysis

Residual renal function and the integrity of the peritoneal membrane contribute to morbidity and mortality among patients treated with peritoneal dialysis. Glucose and its degradation products likely contribute to the deterioration of the remnant kidney and damage to the peritoneum. Benfotiamine decreases glucose-induced tissue damage, suggesting the potential for benefit in peritoneal dialysis. Here, in a model of peritoneal dialysis in uremic rats, treatment with benfotiamine decreased peritoneal fibrosis, markers of inflammation, and neovascularization, resulting in improved characteristics of peritoneal transport. Furthermore, rats treated with benfotiamine exhibited lower expression of advanced glycation endproducts and their receptor in the peritoneum and the kidney, reduced glomerular and tubulointerstitial damage, and less albuminuria. Increased activity of transketolase in tissue and blood contributed to the protective effects of benfotiamine. In primary human peritoneal mesothelial cells, the addition of benfotiamine led to enhanced transketolase activity and decreased expression of advanced glycation endproducts and their receptor. Taken together, these data suggest that benfotiamine protects the peritoneal membrane and remnant kidney in a rat model of peritoneal dialysis and uremia.

Glucose degradation products result in cardiovascular toxicity in a rat model of renal failure

BACKGROUND

It has been shown that glucose degradation products (GDP) generated during heat sterilization of peritoneal dialysis (PD) fluids impair the peritoneal membrane locally, then enter the systemic circulation and cause damage to the remnant kidney. Here we examined in subtotally nephrectomized (SNX) rats whether GDP also affect the cardiovascular system.

MATERIALS AND METHODS

Standard 5/6 nephrectomy was carried out in Sprague-Dawley rats; other rats were sham operated and left untreated for 3 weeks. Through an osmotic mini-pump, SNX+GDP group received GDP intravenously for 4 weeks; the SNX and the sham-operated groups remained without GDP. The experiment was terminated for all groups 7 weeks postoperatively. We analyzed cardiovascular damage by serum analyses and immunohistochemical investigation.

RESULTS

In SNX+GDP animals, expression of the advanced glycation end product (AGE) marker carboxymethyllysine and receptor of AGE (RAGE) were significantly higher in the myocardium and the aorta compared to the SNX rats. We also found significantly higher levels of apoptosis measured by caspase 3 staining in the cardiovascular system in the SNX+GDP group. Moreover, we observed a more pronounced expression of oxidative stress in the SNX+GDP rats compared to the SNX rats. In serum analyses, advanced oxidation protein products and reactive oxygen species were increased, as was immunohistochemical endothelial nitric oxide synthase.

CONCLUSIONS

In addition to local toxic effects, GDP cause systemic toxicity. Here we showed that, in SNX rats, administration of GDP increased cardiovascular damage. In particular, we found increased levels of AGE, RAGE, oxidative stress, and apoptosis. Whether these findings are of clinical relevance has to be further investigated.

RAGE expression in the human peritoneal membrane

BACKGROUND

Experimental animal models have demonstrated that the interaction of advanced glycation end-products (AGE) with their receptor RAGE is, at least in part, responsible for peritoneal damage. This study investigates the in vivo expression of RAGE in the peritoneal membrane of uraemic human patients.

METHODS

Peritoneal biopsies of 89 subjects (48 uraemic and 41 healthy age-matched patients) were examined. The expression of CD3, IL-6, activated NFkappaBp65, VEGF, transforming growth factor (TGF)-beta1, smooth-muscle actin (SMA), methylglyoxal (MGO) and RAGE was analysed immunohistochemically. Additionally, in 4 of the 48 uraemic patients, peritoneal biopsies were repeated after 15 months at the time of catheter removal to analyse the above parameters and the extent of NFkappaB-binding activity determined by electrophoretic mobility shift assay (EMSA) in the long-term follow-up.

RESULTS

In comparison to the healthy controls, uraemic patients showed a significant increase in fibrosis, angiogenesis, submesothelial thickness, MGO-derived protein adducts, RAGE, IL-6, VEGF, TGF-beta1, SMA and NFkappaBp65 in their peritonea. Four patients, followed up longitudinally from peritoneal dialysis (PD) catheter insertion to removal, demonstrated further significant increase in the above parameters, particularly in RAGE expression and NFkappaB activation.

CONCLUSIONS

Along with a higher expression of several indicators for inflammation, angiogenesis, fibrosis and AGE accumulation, the peritoneal membrane of the uraemic patients showed an increased submesothelial thickness and a marked induction of RAGE expression and NFkappaB-binding activity, which both further increased after PD treatment. These findings in human peritoneum support the concept of the AGE-RAGE interaction being crucial in peritoneal damage due to uraemia and PD.

Renal toxicity mediated by glucose degradation products in a rat model of advanced renal failure

BACKGROUND

In peritoneal dialysis (PD) residual renal function contributes to improved patient survival and quality of life. Glucose degradation products (GDP) generated by heat sterilization of PD fluids do not only impair the peritoneal membrane, but also appear in the systemic circulation with the potential for organ toxicity. Here we show that in a rat model of advanced renal failure, GDP affect the structure and function of the remnant kidney.

MATERIALS AND METHODS

Sprague-Dawley rats were randomly assigned to a two stage subtotal nephrectomy (SNX) or sham operation and were left untreated for 3 weeks. The SNX + GDP group continuously received chemically defined GDP intravenously for 4 weeks; the SNX and the sham-operated rats remained without GDP. The complete follow-up for all groups was 7 weeks postoperatively. We analysed renal damage using urinary albumin excretion as well as a semiquantitative score for glomerulosclerosis and tubulointerstitial damage, as well as for immunohistochemical analyses.

RESULTS

The SNX + GDP rats developed significantly more albuminuria and showed a significantly higher score of glomerulosclerosis index (GSI) and tubulointerstitial damage index (TII) as compared to SNX or control rats. In the SNX + GDP group the expression of carboxymethyllysine and methylglyoxal was significantly higher in the tubulointerstitium and the glomeruli compared to the SNX rats. Caspase 3 staining and TUNEL assay were more pronounced in the tubulointerstitium and the glomeruli of the SNX + GDP group. In SNX + GDP animals, the expression of the slit diaphragm protein nephrin, was significantly lower compared to SNX or control animals.

CONCLUSION

In summary, our data suggests that GDP can significantly advance chronic kidney disease and argues that PD solutions containing high GDP might deteriorate residual renal function in PD.