TGF-β1 Induced by High Glucose is Controlled by Angiotensin-Converting Enzyme Inhibitor and Angiotensin II Receptor Blocker on Cultured Human Peritoneal Mesothelial Cells

Background

Loss of peritoneal function is a major complication associated with long-term peritoneal dialysis. Observed changes include loss and degeneration of the mesothelium, submesothelial thickening, alterations in the structure and number of blood vessels, and reduplication of the vascular basement membrane. Exposure to high glucose concentrations in peritoneal dialysis solutions is known to cause injury to cultured human peritoneal mesothelial cells (HPMC) as a result of overexpression of transforming growth factor beta 1 (TGF-β1). Previous studies have demonstrated that angiotensin II (AII) increases expression of TGF-β1 in a number of different cell types; although this has not been demonstrated in HPMC.

Objective

To clarify possible mechanisms involved in peritoneal fibrosis, we investigated whether HPMC expressed AII-forming pathway mRNA and whether increases in AII induced by high glucose contribute to the production of TGF-β1. We also examined the effects of the angiotensin-converting enzyme inhibitor (ACEI) perindoprilat and the AII receptor blocker (ARB) candesartan on expression of TGF-β1 and proliferation of HPMC.

Methods

Expression of mRNA for the AII-forming pathway and TGF-β1 in HPMC was examined by reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative RT-PCR. Levels of AII and TGF-β1 following 48 hours of incubation of the cells in a range of glucose concentrations were measured by enzyme immunoassay and enzyme linked immunosorbent assay respectively. The effect of glucose on cell proliferation was examined using the water-soluble tetrazolium salt WST-1 and [3H]-thymidine uptake. We also investigated the effect of ACEI and ARB on the expression of TGF-β1 and the proliferation of HPMC incubated at high glucose for 48 hours.

Results

AII-forming pathway mRNA was detected in HPMC, with expression of angiotensinogen, angiotensin-converting enzyme (ACE), AII type 1 receptor, and TGF-β1 mRNA increasing following exposure to glucose according to glucose concentration. High glucose was also shown to increase the production of AII and TGF-β1 and decrease the proliferation of HPMC. In contrast, we found that both the ACEI and the ARB attenuated the increase in TGF-β1 production and reduced cell proliferation caused by exposure to high glucose. These effects were greater with a combination of the two drugs.

Conclusion

The present study provides evidence that ( 1 ) HPMC express mRNA for the AII-forming pathway; ( 2 ) ACEI and ARB inhibit the TGF-β1 production induced by high glucose; ( 3 ) the AII-forming pathway is one mechanism by which high glucose causes production of TGF-β1. In addition to having antihypertensive and renal-protective effects, combination therapy with an ACEI and an ARB may also be effective in preventing loss of peritoneal function and decreasing peritoneal fibrosis.

Angiogenesis in peritoneal dialysis

Long-term exposure to peritoneal dialysis fluid induces morphological alterations, including angiogenesis, leading to a loss of ultrafiltration (UF) capacity. We discuss the effect of different factors in peritoneal dialysis (PD) on angiogenesis. In addition, we describe the process of angiogenesis and the possible role of different cell types in the peritoneum upon PD contributing to new blood vessel formation. Furthermore, we review several interventions used in our rat PD exposure model to decrease angiogenesis in PD. Moreover, we show new data on the use of sunitinib to inhibit angiogenesis in this rat model. Although various interventions seem to be promising, well-randomised clinical trials showing absolute prevention of angiogenesis and UF failure are, yet, still missing. To make real progress in PD treatment, the aim should be to prevent angiogenesis as well as peritoneal fibrosis and PD-induced inflammation.

Factors Contributing to Peritoneal Tissue Remodeling in Peritoneal Dialysis

Peritoneal dialysis (PD) is associated with functional and structural changes of the peritoneal membrane. In this review we describe factors contributing to peritoneal tissue remodeling, including uremia, peritonitis, volume loading, the presence of a catheter, and the PD fluid itself. These factors initiate recruitment and activation of peritoneal cells such as macrophages and mast cells, as well as activation of peritoneal cells, including mesothelial cells, fibroblasts, and endothelial cells. We provide an overview of cytokines, growth factors, and other mediators involved in PD-associated changes. Activation of downstream pathways of cellular modulators can induce peritoneal tissue remodeling, leading to ultrafiltration loss. Identification of molecular pathways, cells, and cytokines involved in the development of angiogenesis, fibrosis, and membrane failure may lead to innovative therapeutic strategies that can protect the peritoneal membrane from the consequences of long-term PD.

Angiotensin II upregulates Toll-like receptor 4 and enhances lipopolysaccharide-induced CD40 expression in rat peritoneal mesothelial cells

OBJECTIVE

Activation of Toll-like receptor 4 (TLR4) in peritoneal mesothelial cells by endotoxin contributes to peritoneal inflammation and fibrosis. Here we investigated TLR4 expression induced by angiotensin II (Ang II) and functional consequences of nuclear factor-kappaB (NF-kappaB) activation and CD40 expression in rat peritoneal mesothelial cells (RPMCs).

METHODS

TLR4, CD40, tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6) were determined by reverse transcription polymerase chain reaction (RT-PCR) and TLR4, IkappaBalpha, phospho-IkappaBalpha, NF-kappaB p65, and phospho-NF-kappaB p65 were analyzed by Western blot. The intracellular distribution of NF-kappaB p65 was detected by immunofluorescence.

RESULTS

Treatment of RPMCs with Ang II resulted in an increase in the expression of TLR4 mRNA and protein levels. Preincubation of RPMCs with Ang II significantly increased lipopolysaccharide (LPS)-induced phospho-IkappaBalpha and phospho-NF-kappaB p65 protein (P < 0.05 vs. LPS alone) and CD40, TNF-alpha, and IL-6 mRNA levels (P < 0.05 vs. LPS alone). A significantly increased nuclear staining of NF-kappaB p65 in cells treated with Ang II plus LPS was also observed.

CONCLUSIONS

Ang II upregulates the expression of TLR4 by RPMCs, resulting in enhanced NF-kappaB signaling and induction of CD40, TNF-alpha, and IL-6 expression. Locally produced Ang II in the peritoneum may have an amplified role in LPS-induced peritoneal inflammation.

Use of ACE inhibitors or angiotensin receptor blockers and survival in patients on peritoneal dialysis

BACKGROUND

Angiotensin-converting enzyme (ACE) inhibitors have been shown to improve outcome in patients with renal failure not on dialysis therapy and patients on haemodialysis (HD). However, their effect on survival has not been studied in peritoneal dialysis (PD) patients. The present study examined the association between therapy with ACE inhibitor/ARB and mortality in patients undergoing chronic PD.

METHODS

All patients who commenced PD between 1 January 2000 and 31 December 2005 at the University Health Network were included. Patients were grouped according to whether they had been treated with ACE inhibitor/ARB. They were followed up from the date of PD initiation until death, cessation of PD, transfer to other centres or to the end of the study (31 December 2006).

RESULTS

A total of 306 patients were included in the study. One hundred and sixty-five were treated with ACE inhibitors/ARB (treated group) and 141 were not (untreated group). The treated group patients were younger (56.9 +/- 16.6 versus 62.3 +/- 17.8 years, P < 0.01) and more likely to have a history of hypertension than the untreated group. At the initiation of PD, systolic and diastolic blood pressures were higher in the treated than the untreated group (138.8 +/- 21.8 versus 128.6 +/- 22.4 mmHg, P < 0.001; 79.8 +/- 14.1 versus 74.5 +/- 12.5 mmHg, P = 0.001) and remained significantly higher during the follow-up (133.5 +/- 16.4 versus 125.1 +/- 16.7 mmHg; 77.3 +/- 9.8 versus 73.2 +/- 9.7 mmHg, both P < 0.001). The treated group had a significantly longer survival compared to the untreated group (log rank 19.191, P < 0.001). After adjusting for age, blood pressure and other demographic and clinical parameters, multivariable Cox proportional hazards modelling showed that the use of ACE inhibitor/ARB was associated with 62% reduced risk for death (HR 0.382, 95% CI 0.232-0.631, P < 0.001).

CONCLUSION

In this retrospective analysis, ACE inhibitor/ ARB therapy was associated with a dramatically reduced mortality in patients on peritoneal dialysis independent of blood pressure and other clinical and demographic variables.

Reviews: Altered Laboratory Findings Associated with End-Stage Renal Disease

Several laboratory parameters can be altered in advanced renal failure. Results may be difficult to interpret and may become misleading and unreliable in such a context. On the other hand, some of the alterations may reflect real abnormalities. Thus sufficient knowledge and careful judgment are required by the clinician. We reviewed different publications related to biochemical anomalies in renal failure and report some of the main findings. The sections are divided as follows: cardiovascular risk factors and markers, inflammation markers, pancreatic and liver function tests, hormones, bone turnover indices and parathyroid hormone assays, tumor markers, carbohydrate metabolism indicators, and others. The information provided should be useful to clinicians involved in the care of renal failure patients.

Evaluation of peritoneal transport properties at onset of peritoneal dialysis and longitudinal follow-up

BACKGROUND

The clinical determinants of baseline peritoneal membrane (PM) transport characteristics, as evaluated by a hypertonic peritoneal equilibration test (PET), remain ill-defined. Likewise, the longitudinal evolution of PM transport properties in peritoneal dialysis (PD) patients given automated PD (APD) and icodextrin still needs to be determined precisely. The aims of the present study were (1) to determine the clinical and biological factors affecting PM transport characteristics at PD onset and (2) to assess the longitudinal evolution of these markers.

METHODS

Seventy-two consecutive patients performed a baseline 3.86% glucose dialysate PET and were enrolled. Subgroups of 35 and 18 patients underwent another PET 1 and 2 year(s) later, respectively, and were included in the longitudinal part. For each patient, clinical and biological data were reviewed and PM transport markers calculated.

RESULTS

At onset of PD, angiotensin-converting enzyme (ACE) inhibitor intake (r = 0.31, P = 0.01), presence of a diabetes (r = 0.26, P = 0.03) and body surface area (BSA) (r = 0.26, P = 0.03) independently affected the mass transfer area coefficient (MTAC) of creatinine. Serum albumin (r = -0.46, P<0.001) and net ultrafiltration (r = -0.33, P = 0.009) inversely correlated with MTAC creatinine. Sodium sieving was inversely correlated with BSA (r = -0.33, P = 0.01). Serum albumin also inversely correlated with albumin clearance (r = -0.39, P = 0.02). Finally, the independent covariates that affected alpha2-macroglobulin clearance were age (P = 0.03), diabetes (P = 0.01) and the level of residual renal function (P<0.01). Serum albumin decreased with time on PD (P = 0.02). A rise in small solute transport and a decrease in net ultrafiltration, but no change in protein clearances, were also observed after 2 years of PD.

CONCLUSIONS

Transport properties across the PM, as evaluated by MTAC creatinine and sodium sieving determinations, are correlated with anthropometric characteristics (BSA) and by comorbid conditions (witnessed by the presence of diabetes, a low serum albumin concentration and the prescription of an ACE inhibitor). The short-term evolution (2 years) of the PM transport properties of patients on APD and icodextrin is still characterized by a progressive increase in small solute transport and a loss of ultrafiltration capacity, as documented in ancient studies, but not with a modification in protein clearances. This conclusion merits, however, to be further evaluated in a larger cohort of PD patients after a longer follow-up.