Patricia R. Wahl

Everolimus Retards Cyst Growth and Preserves Kidney Function in a Rodent Model for Polycystic Kidney Disease

Background/Aims: Rapamycin inhibits cyst growth in polycystic kidney disease by targeting the mammalian target of rapamycin (mTOR). To determine if this is a class effect of the mTOR inhibitors, we examined the effect of everolimus, the analogue of rapamycin, on disease progression in the Han:SPRD rat model of polycystic kidney disease. Methods: Four-week-old male heterozygous cystic (Cy/+) and wild-type normal (+/+) Han:SPRD rats were administered everolimus or vehicle (3 mg/kg/day) by gavage for 5 weeks. Kidney function and whole-blood trough levels of everolimus were monitored. After treatment kidney weight and cyst volume density were assessed. Tubule epithelial cell proliferation was assessed by BrdU staining. Results: Everolimus trough levels between 5 and 7 µg/l were sufficient to significantly reduce kidney and cyst volume density by approximately 50 and 40%, respectively. The steady decrease of kidney function in Cy/+ rats was reduced by 30% compared with vehicle-treated Cy/+ rats. Everolimus treatment markedly reduced the number of 5-bromo-2-deoxyuridine-labeled nuclei in cyst epithelia. Body weight gain and kidney function were impaired in everolimus-treated wild-type rats. Conclusion: Moderate dosage of everolimus inhibits cystogenesis in Han:SPRD rats. The inhibitory effect of everolimus appears to represent a class effect of mTOR inhibitors.

Pregnancy-associated plasma protein-A is an independent short-time predictor of mortality in patients on maintenance haemodialysis

AIMS Mortality of maintenance haemodialysis (HD) patients is very high due to polymorbidity, mostly from metabolic and cardiovascular disease. In order to identify patients with high risk for life-threatening complications, reliable prognostic markers would be helpful. Pregnancy-associated plasma protein-A (PAPP-A) has been shown to predict cardiovascular events and death in patients with stable coronary artery disease as well as in acute coronary syndrome in patients with normal renal function. It was the aim of this study to evaluate PAPP-A as a marker for death in patients on maintenance HD. METHODS AND RESULTS PAPP-A serum levels were measured in 170 patients participating in the monitor! trial, a prospective dynamic dialysis cohort multicenter study in Switzerland. Patients were followed up for a median time of 17 months after measuring PAPP-A, and evaluated for death of any cause. Survivors and non-survivors were compared with regard to baseline PAPP-A concentrations. A multivariate logistic regression analysis for death was performed including PAPP-A, age, sex, number of comorbidities, dialysis vintage, Kt/V, IL-6, C-reactive protein, parathyroid hormone (PTH), Ca x PO(4) product, and total serum cholesterol. A cut-off value for PAPP-A was calculated for discrimination between patients with low and high mortality risk, respectively. A total of 23 deaths occurred during follow-up, equalling an incidence rate of 0.1. Baseline median PAPP-A levels were 40% higher in non-survivors vs. survivors (P = 0.023). In a multivariate analysis, only PAPP-A, age, and Ca x PO(4) product were independent predictors of mortality. A cut-off value of 24 mIU/L discriminates significantly (P = 0.015) between patients at low or high risk for death with a negative predictive value of 91%. CONCLUSION PAPP-A is a novel and independent short-time predictor of mortality in a maintenance HD population. The pathogenetic relevance of PAPP-A, particularly in the development of cardiovascular disease, remains to be further elucidated.

Posttransplant acidosis and associated disorders of mineral metabolism in patients with a renal graft.

Background. Persisting disturbances in acid/base homeostasis may have an impact on several metabolic aspects of individuals with a kidney graft, specifically with regard to mineral metabolism and bone. Methods. We undertook a cross-sectional analysis among 823 unselected patients being transplanted with a functioning renal allograft who had at least one measurement of venous serum bicarbonate available within a 4-year period before May 1, 2005. As a determinate of metabolic acidosis bicarbonate was measured along with serum calcium, phosphate, parathyroid hormone, and other routine serological and epidemiological parameters. Data were assessed according to quartiles of serum bicarbonate and by univariate analysis. A multivariate regression model examined the effects of potential predictors of acidosis. Results. Mean serum bicarbonate was 22.5±4 mmol/L, with 58.1% of the examined renal transplant patients having metabolic acidosis as defined by a venous bicarbonate of <24 mmol/L. Bicarbonatemia was highly associated with serum parathyroid hormone, phosphate, and calcium but also with renal graft function (determined as calculated glomerular filtration rate). Multiple stepwise regression analysis revealed age, glomerular filtration rate, parathyroid hormone, and albumin to be the strongest predictors of serum bicarbonate concentration. Therapy with any calcineurin inhibitor was not associated with an increased likelihood of acidosis (odds ratio 1.04), but a significant difference was found between cyclosporine A and tacrolimus, which had an attributed odds ratio for acidosis of 0.6 and 1.8, respectively. Conclusions. Metabolic acidosis is highly prevalent among an unselected cohort of renal transplant patients. A clear association exists between the severity of acidosis and disturbances of mineral metabolism. Thus, persisting acid/base disorders may accentuate bone disease in a setting with other factors predisposing for posttransplant osteopathy.

Limited Costimulatory Molecule Expression on Renal Tubular Epithelial Cells Impairs T Cell Activation

Background/Aims: MHC molecules are upregulated on renal proximal tubular epithelial cells (TEC) under inflammatory conditions. This allows TEC to act as ‘non-professional’ antigen-presenting cells (APC). The aim of this study was to compare the costimulatory molecule expression pattern and the T cell activation capacity between renal TEC and professional APC, e.g. bone marrow-derived dendritic cells (BM-DC). Methods: Flow cytometry analysis was used to study the costimulatory molecule surface expression on TEC or BM-DC. Ovalbumin-specific CD4 and CD8 T cell activation induced by TEC or BM-DC was compared, in terms of T cell proliferation, cytokine production and CTL activity. Results: TEC did not constitutively express significant amounts of costimulatory molecules. Stimulation of TEC with IFN-β or IFN-γ, but not other tested cytokines, enhanced the expression of PD-L1, ICOS-L and CD40. Compared to BM-DC, TEC only induced suboptimal T cell activation. Blockade of PD-L1 on both APC strongly increased T cell activity. Furthermore, high PD-L1-expressing TEC were more resistant to the cytolysis by CTL. Conclusion: The low costimulatory molecule expression may explain the suboptimal T cell activation by TEC. The IFN-upregulated negative costimulatory molecule PD-L1 on TEC may play a protective role to limit tissue injury during renal parenchymal immune responses.

Mitotic activation of Akt signalling pathway in Han:SPRD rats with polycystic kidney disease

Aim:  Autosomal dominant polycystic kidney disease (ADPKD) is characterized by an imbalance between tubular epithelial cell proliferation and apoptosis. We have previously shown that the mammalian target of rapamycin (mTOR) signalling pathway is aberrantly activated in the cystic kidneys of Han:SPRD rats with ADPKD. Because the Akt kinase is an upstream regulator of mTOR, we hypothesized that the activity of Akt could be enhanced in the kidneys of Han:SPRD rats.

Immunolocalization of phospho-S6 kinases: a new way to detect mitosis in tissue sections and in cell culture

During a study on the mTor pathway in the rat kidney we observed a striking increase of the phosphorylation of the S6 kinase in mitosis. In cryostat sections of perfusion-fixed tissue mitotic cells appeared as bright spots in immunofluorescence using an antibody specific for the phosphorylation site Thr421/Ser424. They were easily spotted in overviews with the objective 4× and 10×. Immunofluorescence was weak during the interphase. During the prophase it increased in both the nucleus and the cytoplasm and it remained bright during the subsequent phases of mitosis. All mitotic cells which were found in tubules and in the interstitium of the kidney using a chromatin stain displayed the bright immunofluorescence for phospho-S6 kinase. The same phenomenon was observed in rat liver and in mouse kidney as well as in a human cell line. Provided a rapid fixation, mitotic cells could be identified with the immunoperoxidase technique in paraffin sections of immersion-fixed tissue. This is the first report of phosphorylation of S6 kinase during mitosis in vivo. Thus, immunohistochemistry with anti-phospho-S6 kinase (Thr421/Ser424) appears to provide a convenient way to detect mitotic cells at low magnification.