Genetic and clinical factors influence the baseline permeability of the peritoneal membrane

BACKGROUND

Patients starting peritoneal dialysis (PD) show a significant variability in small solute transport across the peritoneal membrane (PM). The latter parameter determines dialysis prescription and survival. Clinical factors probably influence solute transport across the PM, but the putative role of genetic variants is unknown.

METHODS

We have investigated the influence of functional polymorphisms of VEGF, ENOS, and IL-6, together with clinical and biological factors, on baseline peritoneal equilibration test (PET) parameters in a homogeneous population of 152 unrelated Caucasian PD patients from Belgium and the North of France.

RESULTS

The distribution of the 21 alleles (7 polymorphisms) and linkage disequilibrium parameters were similar in PD patients and healthy subjects. Univariate and multivariate analyses identified comorbidity, serum albumin, and the -174G/C polymorphism of IL-6 as independent predictors of small solute transport. The -174G/C polymorphism of IL-6 was associated with significantly higher IL-6 mRNA levels in the PM and higher plasma and dialysate IL-6 concentrations, suggesting a dominant effect of the C allele. Patients harboring the CC and GC genotypes (N= 92) were characterized by significantly higher permeability parameters and inflammatory markers than patients harboring the GG genotype (N= 60). In contrast with IL-6, VEGF and ENOS polymorphisms had no influence on baseline peritoneal permeability.

CONCLUSION

These data (1) show that, together with clinical parameters, the functionally relevant -174G/C polymorphism of IL-6 contributes to the interpatient variability in small solute transport rate at the start of PD; and (2) substantiate the critical role played by IL-6 in the PM.

Association between C-reactive protein levels and N-terminal pro-B-type natriuretic peptide in pre-dialysis patients

BACKGROUND

The prevalence of inflammation is high among patients with chronic renal failure but the reason of inflammation is unclear. We test the hypothesis that inflammation in chronic renal failure could be the consequence of an increased left-ventricular wall tension related to ventricular dysfunction, hypervolemia or both.

METHODS

For assessing left-ventricular filling pressure, plasma level of N-terminal pro-B-type natriuretic peptide (N-BNP) was used, as B-type natriuretic peptide is secreted from the cardiac ventricles in response to increased wall tension. N-BNP levels and C-reactive protein (CRP) were measured on the same day in 75 pre-dialysis patients. A previous history of cardiomiopathy with systolic dysfunction was present in 27 (36%) of them.

RESULTS

The levels of N-BNP were not normally distributed (mean: 2,589 +/- 4,514 pg/ml; median: 789 pg/ml). The distribution of CRP levels was also not normal (mean: 15 +/- 27 mg/l; median: 5 mg/l). Both parameters correlated significantly (r: 0.41; p < 0.005). N-BNP was higher (p < 0.001) in patients with known ventricular dysfunction. Excluding these patients, the correlation between N-BNP and CRP was stronger (r: 0.88; p < 0.001). Univariate analysis in these patients without known cardiomyopathy showed that N-BNP levels also correlated with systolic and diastolic blood pressure (r: 0.54; p < 0.005) and inversely with creatinine clearance (r: -0.43; p < 0.01), serum albumin (r: 0.6; p < 0.001) and hemoglobin levels (r: 0.37; p < 0.05). CRP levels correlated significantly (p < 0.01) with the same parameters as N-BNP in univariate analysis. However, in multiple stepwise regression analysis in which CRP was the dependent variable, only the association with N-BNP remained significant (r: 0.87; p < 0.001).

CONCLUSIONS

Our results suggest a link between left-ventricular filling pressure and inflammation in patients with advanced renal insufficiency. The importance of strict volume control in these patients, in order to reduce left-ventricular pressure and therefore inflammation, should be considered.

Longitudinal relationship between solute transport and ultrafiltration capacity in peritoneal dialysis patients

BACKGROUND

Time on treatment is associated with a greater risk of impaired ultrafiltration (UF) in peritoneal dialysis (PD) patients. In addition to increasing solute transport, a potentially treatable cause of impaired ultrafiltration, cross-sectional studies suggest that there is also reduced osmotic conductance of the membrane. If this were the case then it would be expected that the UF capacity for a given rate of solute transport would change with time. The purpose of this analysis was to establish how solute transport and UF capacity change relative to one another with time on therapy.

METHODS

Membrane function, using a standard peritoneal equilibration test, was measured at least annually in a well-characterized, single-center observational cohort of PD patients between 1990 and 2003. Demography included age, gender, original cause of renal failure, body surface area (BSA), validated comorbidity score, residual urine volume and urea clearances, peritoneal urea clearances, and plasma albumin.

RESULTS

Data from 574 new PD patients were available for analysis. Independent demographic factors associated with higher solute transport at baseline were male gender and higher residual urine volume. Throughout time on therapy there was a negative relationship between solute transport and UF capacity and a significant increase and decrease in these parameters, respectively. During the first 12 months of treatment, the increase in solute transport was not associated with the expected fall in UF capacity, a phenomenon that was not explained by informative censoring, but was associated with an increased, albeit weak, correlation with BSA. In contrast, later in treatment there was a disproportionate fall in UF capacity, more accelerated in patients developing UF failure. Early exposure to higher intraperitoneal glucose concentrations, in the context of more comorbidity and relative lack of residual renal function, was associated with more rapid deterioration in membrane function.

CONCLUSION

Despite a causal link between solute transport and UF capacity of the membrane, due to the effect of the former on the osmotic gradient, there is evidence of their longitudinal dissociation. This implies a change in the structure-function relationship with time on treatment that can, to some extent, be predicted from clinical factors present within the first year of treatment. Dialysis-induced membrane injury must involve at least two processes, for example, increased vascular surface area contact with dialysate combined with changes in hydraulic conductance due to scarring of the vessels and interstitium.

Longitudinal membrane function in functionally anuric patients treated with APD: Data from EAPOS on the effects of glucose and icodextrin prescription

BACKGROUND

Peritoneal dialysis is associated with changes in membrane function that can lead eventually to ultrafiltration (UF) failure. Factors driving these changes are thought to include hypertonic glucose exposure, but previously reported associations are confounded by the presence of residual renal function.

METHODS

Longitudinal membrane function (solute transport and UF capacity) were measured annually in a prospective cohort of 177 functionally anuric patients as part of the European Automated Peritoneal Dialysis Outcomes Study (EAPOS). Subgroup analysis was performed according to glucose exposure and icodextrin use at baseline.

RESULTS

The whole cohort experienced an increase in solute transport and reduction in UF capacity at 12 and 24 months that could not be explained by informative censoring. These changes were accelerated and more severe in patients using either 2.27% or 3.86% glucose, or those not using icodextrin at baseline. These differences could not be explained by age, comorbidity score, previous time spent on renal replacement, differential dropout from the study, peritonitis rates, or, by definition, residual renal function. Patients using icodextrin at baseline had worse membrane function and were more likely to be diabetic. There was an association between membrane function changes and achieved 24-hour ultrafiltration over the 2-year study period.

CONCLUSION

Anuric automated peritoneal dialysis (APD) patients experience significant detrimental changes in membrane function over a relatively short time period. Glucose appears to enhance these changes independent of residual renal function. Icodextrin use in these circumstances is associated with less deterioration in membrane function.

Superiority of icodextrin compared with 4.25% dextrose for peritoneal ultrafiltration

Several clinical observations suggest the superiority of icodextrin compared with 4.25% dextrose in optimizing peritoneal ultrafiltration (UF), but no rigorous controlled evaluation has hitherto been performed. For comparing icodextrin and 4.25% dextrose during the long dwell of automated peritoneal dialysis, a multicenter, randomized, double-blind trial was conducted in 92 patients (control, 45; icodextrin, 47) with 4-h dialysate to plasma ratio creatinine >0.70 and D/D(0) glucose <0.34. Long-dwell net UF and the UF efficiency ratio (net UF volume per gram of dialysate carbohydrate absorbed) were determined at baseline, week 1, and week 2. The control and treatment groups were comparable at baseline (all patients using 4.25% dextrose for the long dwell) with regard to mean (+/-SEM) net UF (201.7 +/- 103.1 versus 141.6 +/- 75.4 ml, respectively; P = 0.637) and the percentage of patients with negative net UF (control, 37.8%; treatment, 42.6%; P = 0.641). During the study period, net UF was unchanged from baseline in the control group but increased significantly (P < 0.001) in the icodextrin group from 141.6 +/- 75.4 to 505.8 +/- 46.8 ml at week 1 and 540.2 +/- 46.8 ml at week 2. In the icodextrin group, the incidence of negative net UF was significantly lower (P < 0.0001) than in the control group. Findings were similar for UF efficiency ratio. Rash was reported significantly more often in the icodextrin group. This study showed that in high-average and high transporters, icodextrin is superior to 4.25% dextrose for long-dwell fluid and solute removal.

Increases in peritoneal small solute transport in the first month of peritoneal dialysis predict technique survival

BACKGROUND

Peritoneal transport of small solutes generally increases during the first month of peritoneal dialysis (PD). The aim of this study was to prospectively evaluate the ability of the peritoneal equilibration test (PET), carried out 1 and 4 weeks after the commencement of PD, to predict subsequent technique survival.

METHODS

Fifty consecutive patients commencing PD at the Princess Alexandra Hospital between 1 February 2001 and 31 May 2003 participated in the study. Paired 1 week and 1 month PET data were collated and correlated with subsequent technique survival.

RESULTS

A significant increase was observed in the dialysate : plasma creatinine ratio at 4 h (D/P Cr) between 1 and 4 weeks after the onset of PD (0.55 +/- 0.12 vs 0.66 +/- 0.11, P <0.001). Mean death-censored technique survival was superior in patients who experienced > or =20% rise in D/P Cr during the first month of PD compared with those who did not (2.3 +/- 0.2 vs 1.6 +/- 0.2 years, P <0.05). Using a multivariate Cox proportional hazards model analysis, the significant independent predictors of death-censored technique survival were an increase in D/P Cr of greater than 20% during the first month (adjusted hazard ratio [HR] 0.20, 95% CI 0.05-0.75), the absence of diabetes mellitus, the absence of ischaemic heart disease, body mass index and baseline peritoneal creatinine clearance.

CONCLUSIONS

A 20% or greater rise in D/P Cr during the first month of commencing PD is independently predictive of PD technique survival. Further investigations of the mechanisms underlying this phenomenon are warranted.

Inflammation in patients on peritoneal dialysis is associated with increased extracellular fluid volume

BACKGROUND

Cardiovascular disorders (CD) are the most frequent cause of death in patients on dialysis. CD have been related to increased extracellular fluid volume, peritoneal transport type (PTT), hypertension, and inflammation. Inflammation is in itself a risk factor for mortality. The aim of this study was to assess the relationship of increased extracellular fluid volume, inflammation, and PTT in patients on continuous ambulatory peritoneal dialysis (CAPD) and automated peritoneal dialysis (APD).

METHODS

A cross-sectional study was carried out with 20 healthy controls (C), 21 patients on CAPD, and nine patients on APD. Clinical and demographic variables were measured and registered. Peritoneal equilibrium test (PET) was done. Blood volume (BV), total body water (TBW), inferior vena cava diameter during inspiration (IVCDi) and expiration (IVCDe), serum albumin, and serum C-reactive protein (CRP) were measured.

RESULTS

All patients on peritoneal dialysis (PD) had at least one sign or symptom of increased extracellular fluid volume, hypertension being the most common. Patients also had higher TBW (C, 60.7 +/- 7.2; APD, 62.6 +/- 8.7; CAPD, 66.1 +/- 8.3, as percentage of body weight, p <0.02), higher BV (C, 7.9 +/- 1.6; APD, 9.8 +/- 2.3; CAPD, 9.6 +/- 2.3, as percentage of body weight, p <0.02), higher DIVCi (C, 2.9 +/- 1.2; APD, 4.6 +/- 2.5; CAPD, 4.5 +/- 2.4 mm/m2 BSA, p <0.02), and higher DIVCe (C, 6.2 +/- 1.7; APD, 8.3 +/- 3.4; CAPD, 8.0 +/- 2.8 mm/m2 BSA, p <0.05). PD patients also had hypoalbuminemia and higher CRP levels. There was significant positive correlation between CRP and DIVCi (r=0.43, p <0.05) and IVCe (r=0.45, p <0.05) and between serum albumin and creatinine dialysate-to-plasma ratio (D/P Cr, r=0.57, p <0.01). Serum albumin and CRP were negatively correlated (r= -0.54, p <0.02).

CONCLUSIONS

Patients on PD have increased extracellular fluid volume as compared with healthy controls. Hyperhydration is related to inflammation and to higher peritoneal transport types.

The Euro-Balance Trial: The effect of a new biocompatible peritoneal dialysis fluid (balance) on the peritoneal membrane

BACKGROUND

Although peritoneal dialysis (PD) is a widely accepted form of renal replacement therapy (RRT), concerns remain regarding the bioincompatible nature of standard PD fluid. In order to evaluate whether a newly formulated fluid of neutral pH, and containing low levels of glucose degradation products (GDP), resulted in improved in vivo biocompatibility, it was compared in a clinical study to a standard PD fluid.

METHODS

In a multicenter, open, randomized, prospective study with a crossover design and parallel arms, a conventional, acidic, lactate-buffered fluid (SPDF) was compared with a pH neutral, lactate-buffered, low GDP fluid (balance). Overnight effluent was collected and assayed for cancer antigen 125 (CA125), hyaluronic acid (HA), procollagen peptide (PICP), vascular endothelial growth factor (VEGF), and tumor necrosis factor alpha (TNFalpha). Serum samples were assayed for circulating advanced glycosylation end products (AGE), N(epsilon)-(carboxymethyl)lysine (CML), and imidazolone. Clinical end points were residual renal function (RRF), adequacy of dialysis, ultrafiltration, and peritoneal membrane function. Eighty-six patients were randomized to either group I starting with SPDF for 12 weeks (Phase I), then switching to "balance" for 12 weeks (Phase II), or group II, which was treated vice versa. Seventy-one patients completed the study with data suitable for entry into the per protocol analysis. Effluent and serum samples, together with peritoneal function tests and adequacy measurements, were undertaken at study centers on three occasions during the study: after the four-week run-in period, after Phase I, and again after Phase II.

RESULTS

In patients treated with balance there were significantly higher effluent levels of CA125 and PICP in both arms of the study. Conversely, levels of HA were lower in patients exposed to balance, while there was no change in the levels of either VEGF or TNFalpha. Serum CML and imidazolone levels fell significantly in balance-treated patients. Renal urea and creatinine clearances were higher in both treatment arms after patients were exposed to balance. Urine volume was higher in patients exposed to balance. In contrast, peritoneal ultrafiltration was higher in patients on SPDF. When anuric patients were analyzed as a subgroup, there was no significant difference in peritoneal transport characteristics or in ultrafiltration on either fluid. There were no changes in peritonitis incidence on either solution.

CONCLUSION

This study indicates that the use of balance, a neutral pH, low GDP fluid, is accompanied by a significant improvement in effluent markers of peritoneal membrane integrity and significantly decreased circulating AGE levels. Clinical parameters suggest an improvement in residual renal function on balance, with an accompanying decrease in peritoneal ultrafiltration. It would appear that balance solution results in an improvement in local peritoneal homeostasis, as well as having a positive impact on systemic parameters, including circulating AGE and residual renal function.

Compared time profiles of ultrafiltration, sodium removal, and renal function in incident CAPD and automated peritoneal dialysis patients

BACKGROUND

Fluid and sodium removal rates may not be equivalent in patients undergoing automated peritoneal dialysis (APD) and continuous ambulatory peritoneal dialysis (CAPD). This may influence compared cardiovascular outcomes in both groups.

METHODS

The authors compared prospectively the time courses of ultrafiltration, sodium removal, and residual renal function (RRF) in a group of incident patients treated with CAPD (n = 53) or APD (n = 51) for at least 1 year (mean follow-up, 28.9 months; range, 13 to 62). The authors analyzed potential effects of these factors on blood pressure (BP) control and cardiovascular morbidity and mortality.

RESULTS

Ultrafiltration and sodium removal rates were consistently lower in APD patients (mean differences, 236 mL/d; P = 0.012, and 36 mmol/d; P = 0.018, respectively, end of first year). Moreover, univariate and multivariate analysis indicated that APD therapy results in a moderate, but significantly faster decline of RRF than CAPD therapy. Analysis of clinical outcomes showed that CAPD (versus APD) therapy or higher ultrafiltration or sodium removal rates were associated with a better time course of systolic, but not diastolic, BP. We were unable to identify PD modality, ultrafiltration, or sodium removal rates as independent predictors of cardiovascular morbidity and mortality.

CONCLUSION

Ultrafiltration and sodium removal rates are consistently lower in incident APD patients than in their counterparts undergoing CAPD. Moreover, RRF declines faster during APD than during CAPD therapy, although this difference may be partially counteracted by a detrimental effect of ultrafiltration on RRF. Aside from a better control of systolic BP in CAPD patients, these differences do not portend significant cardiovascular consequences during the first years of PD therapy.

The implications of the ADEMEX study for the peritoneal dialysis prescription: the role of small solute clearance versus salt and water removal

PURPOSE OF REVIEW

This review examines the results of the ADEMEX (Adequacy of Peritoneal Dialysis in Mexico) study in the context of other recent advances in peritoneal dialysis, and assesses the implication of this new knowledge for the optimal peritoneal dialysis prescription.

RECENT FINDINGS

The prospective randomized controlled ADEMEX study demonstrated no survival advantage of an increased dose of peritoneal small molecule clearance delivered by chronic ambulatory peritoneal dialysis. Coincident with this finding, there has been increasing awareness that many peritoneal dialysis patients are volume expanded, and that there are adverse cardiovascular consequences to this chronic overhydration. As a result there has been a shift away from interest in peritoneal small solute clearance with renewed interest in peritoneal removal of salt and water. There is also increasing evidence of the importance of residual renal function in maintaining euvolemia and as a prognostic indicator for survival.

SUMMARY

The ADEMEX study and subsequent investigations have changed the way we perceive the optimal peritoneal dialysis prescription. This has resulted in de-emphasis of peritoneal small molecule clearance and increased emphasis on clinical assessment of dialysis adequacy, preservation of residual renal function, and optimization of salt and water removal.