Gene polymorphisms of VEGF and KDR are associated with initial fast peritoneal solute transfer rate in peritoneal dialysis

Background

Peritoneal dialysis (PD) is an effective and successful renal replacement therapy. The baseline peritoneal solute transfer rate (PSTR) is related to local membrane inflammation and may be partially genetically determined. Herein, we focused on vascular endothelial growth factor (VEGF) and its receptor, kinase insert domain containing receptor (KDR).

Methods

This study recruited 200 PD patients from Renji Hospital in Shanghai, China. We analysed the association between the polymorphisms of VEGF and KDR and the 4-hour dialysate-to-plasma ratio for creatinine (4 h D/P Cr), which was measured between one and three months after initiating PD.

Results

The CC genotype in VEGF rs3025039 and the AA genotype in KDR rs2071559 were both positively associated with a fast baseline PSTR (VEGF rs3025039 CC vs. TT + TC: 0.65 ± 0.12 vs. 0.61 ± 0.11; P = 0.029; KDR rs2071559 AA vs. GA + GG: 0.65 ± 0.12 vs. 0.62 ± 0.12; P = 0.039).

Conclusion

Baseline PSTR was partly determined by VEGF and KDR gene polymorphisms.

Monitoring of Long-Term Peritoneal Membrane Function

Objective

Peritoneal membrane function influences dialysis prescription and clinical outcome and may change with time on treatment. Increasingly sophisticated tools, ranging from the peritoneal equilibration test (PET) to the standard permeability analysis (SPA) and personal dialysis capacity (PDC) test, are available to the clinician and clinical researcher. These tests allow assessment of a number of aspects of membrane function, including solute transport rates, ultrafiltration capacity, effective reabsorption, transcellular water transport, and permeability to macromolecules. In considering which tests are of greatest value in monitoring long-term membrane function, two criteria were set: those that result in clinically relevant interpatient differences in achieved ultrafiltration or solute clearances, and those that change with time in treatment.

Study Selection

Clinical validation studies of the PET, SPA, and PDC tests. Studies reporting membrane function using these methods in either long-term (5 years) peritoneal dialysis patients or longitudinal observations (> 2 years).

Data Extraction

Directly from published data. Additional, previously unpublished analysis of data from the Stoke PD Study.

Results

Solute transport is the most important parameter. In addition to predicting patient and technique survival at baseline, there is strong evidence that it can increase with time on treatment. Whereas patients with initially high solute transport drop out early from treatment, those with low transport remain longer on treatment, although, over 5 years, a proportion develop increasing transport rates. Ultrafiltration capacity, while being a composite measure of membrane function, is a useful guide for the clinician. Using the PET (2.27% glucose), a net ultrafiltration capacity of < 200 mL is associated with a 50% chance of achieving less than 1 L daily ultrafiltration at the expense of 1.8 hypertonic (3.86%) exchanges in anuric patients. Using a SPA (3.86% glucose), a net ultrafiltration capacity of < 400 mL indicates ultrafiltration failure. While there is circumstantial evidence that, with time on peritoneal dialysis, loss of transcellular water transport might contribute to ultrafiltration failure, none of the current tests is able to demonstrate this unequivocally. Of the other membrane parameters, evidence that interpatient differences are clinically relevant (permeability to macro-molecules), or that they change significantly with time on treatment (effective reabsorption), is lacking.

Conclusion

A strong case can be made for the regular assessment by clinicians of solute transport and ultrafiltration capacity, a task made simple to achieve using any of the three tools available.

Preventing Peritoneal Dialysis-Associated Fibrosis by Therapeutic Blunting of Peritoneal Toll-Like Receptor Activity

Peritoneal dialysis (PD) is an essential daily life-saving treatment for end-stage renal failure. PD therapy is limited by peritoneal inflammation, which leads to peritoneal membrane failure as a result of progressive fibrosis. Peritoneal infections, with the concomitant acute inflammatory response and membrane fibrosis development, worsen PD patient outcomes. Patients who remain infection-free, however, also show evidence of inflammation-induced membrane damage and fibrosis, leading to PD cessation. In this case, uraemia, prolonged exposure to bio-incompatible PD solutions and surgical catheter insertion have been reported to induce sterile peritoneal inflammation and fibrosis as a result of cellular stress or tissue injury. Attempts to reduce inflammation (either infection-induced or sterile) and, thus, minimize fibrosis development in PD have been hampered because the immunological mechanisms underlying this PD-associated pathology remain to be fully defined. Toll-like receptors (TLRs) are central to mediating inflammatory responses by recognizing a wide variety of microorganisms and endogenous components released following cellular stress or generated as a consequence of extracellular matrix degradation during tissue injury. Given the close link between inflammation and fibrosis, recent investigations have evaluated the role that TLRs play in infection-induced and sterile peritoneal fibrosis development during PD. Here, we review the findings and discuss the potential of reducing peritoneal TLR activity by using a TLR inhibitor, soluble TLR2, as a therapeutic strategy to prevent PD-associated peritoneal fibrosis.

Evaluating Hyponatremia in Non-Diabetic Uremic Patients on Peritoneal Dialysis

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BACKGROUND

An approach to hyponatremia in uremic patients on peritoneal dialysis (PD) necessitates the assessment of intracellular fluid volume (ICV) and extracellular volume (ECV). The aim of the study was to evaluate the association of plasma sodium (Na(+)) concentration and body fluid composition and identify the causes of hyponatremia in non-diabetic PD patients. ♦

METHODS

Sixty non-diabetic uremic patients on PD were enrolled. Baseline body fluid composition, biochemistry, hand-grip test, peritoneal membrane characteristics, dialysis adequacy, Na(+) and water balance, and residual renal function (RRF) were measured. These parameters were reevaluated for those who developed hyponatremia, defined as serum Na(+) concentration < 132 mmol/L and a decline in serum Na(+) > 7 mmol/L, during monthly visits for 1 year. Body fluid composition was determined by multi-frequency bioelectrical impedance (BIA). ♦

RESULTS

There was no significant correlation between serum Na(+) concentrations and any other parameters except a negative correction with overnight ultrafiltration (UF) amount (p = 0.02). The ICV/ECV ratio was positively correlated with serum albumin (p < 0.005) and hand grip strength (p < 0.05). Over 1 year, 9 patients (M:F = 3:6, aged 35 - 77) with 4 different etiologies of hyponatremia were identified. Hyponatremic patients with a body weight (BW) loss had either an increased ICV/ECV ratio associated with primarily a negative Na(+) balance (n = 2) or a reduced ratio of ICV/ECV associated with malnutrition (n = 2). In contrast, hyponatremic patients with a BW gain had either a reduced ICV/ECV ratio associated with a rapid loss of RRF and a higher peritoneal permeability (n = 2) or a normal to increased ICV/ECV ratio associated with high water intake (n = 3). ♦

CONCLUSION

Besides BW change and ultrafiltration rate, the assessment of ICV/ECV ratio is valuable in identifying the etiologies of hyponatremia in PD and provides a guide for optimal therapy.

Histomorphological and functional changes of the peritoneal membrane during long-term peritoneal dialysis

In long-term peritoneal dialysis (PD) morphological and functional changes of the peritoneal membrane are common. Sub-mesothelial fibrosis, angiogenesis and vasculopathy are typical histomorphological alterations of the peritoneal membrane, which, to a certain degree, are induced by uremia and recurrent peritonitis. The most important causative factor, however, represents the chronic exposure to PD solutions. Glucose, glucose degradation products and advanced glycation end-products (AGEs) via different pathways induce inflammation, fibrosis and angiogenesis. As a functional consequence ultrafiltration failure due to peritoneal hyperpermeability and an increased effective peritoneal surface area represents a major clinical problem. An insufficient function of the water-selective aquaporin 1 (AQP-1) channel may also be causative for inadequate ultrafiltration. A rare but life-threatening complication of long-term PD is encapsulating peritoneal sclerosis (EPS). For both impaired AQP-1 function and EPS, the long-term effects of PD fluids are believed to be responsible, even though the mechanisms are not yet understood. The avoidance of glucose and modern PD fluids with fewer glucose degradation products, as well as first pharmacological attempts may help to preserve the peritoneal membrane in the long term.

Peritoneal Transport Status Influence on Atherosclerosis/Inflammation in CAPD Patients

OBJECTIVE

Peritoneal transport status is one of the main determinants of dialysis adequacy and dialysis-related complications in end-stage renal disease patients receiving continuous ambulatory peritoneal dialysis (CAPD). In this study we aimed to investigate the relationship between peritoneal transport characteristics and known promoters of atherosclerosis in a group of patients receiving CAPD for a minimum of 36 months.

DESIGN AND PARTICIPANTS

We performed a cross-sectional study of a cohort of 84 patients with end-stage renal disease (37 men, 47 women; age, 44.0 +/- 15.7 years; dialysis duration, 40.3 +/- 8.1 months) who were receiving CAPD for minimum 36 months. Peritoneal transport characteristics were identified after a peritoneal equilibration test (PET) determined at the third month of CAPD using Dialysate/Plasma (D/P) reference values. Patients were classified according to one of four peritoneal transport types: high (H), high-average (HA), low-average (LA), and low (L). After PET, patients were grouped as high (H/HA group, n = 51) or low (L/LA group, n = 33) transporters. The patient groups' clinical and laboratory data before dialysis and after initiation of the CAPD were collected retrospectively. The patients' follow-up data were retrieved for the diagnosis of any atherosclerosis-related event after the initiation of CAPD. The following events were collected, including myocardial infarction, having been diagnosed as having coronary artery disease by angiography or myocardium scintigraphy, cerebrovascular accident, and development of clinically evident peripheral arterial disease.

RESULTS

A comparison of follow-up data revealed that the H/HA transport characteristic was associated with lower albumin (P < .01), higher C-reactive protein (CRP) (P < .0001) levels, and higher recombinant human erythropoietin (rHuEPO) needs (P < .001) when compared with the L/LA type. During follow-up, 28 patients showed an atherosclerosis-related event. Twenty-two of these were in the H/HA group (43.1%), whereas only six were in the L/LA group (18.1%, P < .01). Reanalysis of 18 patients with atherosclerosis-related events and high CRP levels (> 10 mg/L) showed that 15 were in the H/HA and 3 were in the L/LA group. Sixty-eight percent of the H/HA patients with atherosclerosis and 50% of the L/LA patients with an atherosclerotic event also had chronic inflammation (P < .001). A Pearson correlation analysis showed that there was a positive correlation between D/P creatinine levels and 36-month mean CRP levels (r = 0.608, P < .0001), and a negative correlation between D/P creatinine levels and 36-month mean albumin levels (r = -0.299, P < .005).

CONCLUSIONS

This study shows that the high transporter peritoneal membrane characteristic is a risk factor for inflammatory state in patients with end-stage renal disease. High-transporter patients are at an increased risk of atherosclerosis when compared with their low-transporter counterparts through chronic inflammation.

Pathogenic effects of a high peritoneal transport rate

Recent studies have shown that patients with high peritoneal transport characteristics have substantially increased morbidity and mortality. This finding is counter-intuitive, since HTs will a priori achieve higher clearances. There are many possible causes: increased protein losses with consequent hypoalbuminemia; poor ultrafiltration capacity causing fluid retention, ventricular hypertrophy and hypertension; increased glucose absorption leading to anorexia, hyperinsulinism, and local AGE formation; and the development of an atherogenic lipid profile. While common pathogenic causes of high peritoneal transport and atherosclerosis have been hypothesized, it is more likely that CAPD as currently practiced is unsuitable for HTs, who should be switched to HD or NIPD. Renal and peritoneal clearances have different clinical effects and should be assessed separately. Current measures of dialysis adequacy, such as total Kt/V, do not therefore describe the patient's clinical situation accurately and are insufficient.