Day-To-Day Variability of Protein Transport Used as a Method for Analyzing Peritoneal Permeability in CAPD

The transperitoneal transport of macromolecules is dependent on both effective peritoneal surface area and intrinsic permeability of the peritoneum. For passage of small solutes, the effective surface area is the main determinant. We hypothesized that day-to-day variations in peritoneal clearances are caused by changes in the effective surface area and not in the intrinsic permeability. Four CAPD {continuous ambulatory peritoneal dialysis) patients without peritonitis were investigated on 28 consecutive days. Concentrations of beta-2-microglobulin, albumin, IgG, and alpha-2-macroglobulin were determined daily in dialysate {night bags) and weekly in serum. Clearances and their coefficients of variation were calculated. Mean coefficients of the intraindividual variation of protein clearances increased, the higher the molecular weight: they ranged from 12% for beta-2microglobulin clearance to 22% for alpha-2-macroglobulin clearance. Correlations were present between the clearances of albumin, IgG, and alpha-2-macroglobulin, but not between any of these and beta-2-microglobulin clearance. In all patients, protein clearance {C) was a power function of the free diffusion coefficient in water {D) according to the equation: C=a. Db in which b represents the restriction coefficient of the peritoneum, and thus intrinsic permeability. The coefficient of variation of the restriction coefficient was low (range 4–6%). This supports our assumption that the intrinsic permeability is fairly constant on the short term. Day-to-day variations in protein clearances are thus mainly caused by alterations in the effective peritoneal surface area. Longterm follow-up of the restriction coefficient in individual patients might identify those at risk for the development of structural changes in the peritoneal membrane.

High Peritoneal Clearance of Small Molecules Did Not Provide Low Serum β2–Microglobulin Concentrations in Peritoneal Dialysis Patients

Objective

Although early reports demonstrated that serum β2-microglobulin (s-β2m) concentrations in patients on peritoneal dialysis (PD) were lower than those in patients on hemodialysis (HD), more recent studies demonstrated lower s-β2m concentrations in HD patients treated mainly with high-flux synthetic membranes. We therefore compared s-β2m concentrations between patients on PD and on HD, and also analyzed the relationship between s-β2m concentrations and other parameters in patients on PD.

Patients and Methods

We investigated 24 patients who had been undergoing PD [11 on continuous ambulatory peritoneal dialysis, 13 on continuous cycling peritoneal dialysis] for 4.3 ± 2.7 years, and 24 patients who had been undergoing HD with high-flux synthetic membranes for 6.1 ± 3.2 years. Concentrations of s-β2m in the PD patients were compared to concentrations in the HD patients. In patients on PD, we also analyzed the relationship between s-β2m concentration and other parameters, including residual renal function, total weekly Kt/V urea, total weekly creatinine clearance (CCr), and dialysis schedules.

Results

We found no significant difference in s-β2m concentrations between the PD and HD patients (33.6 ± 10.4 mg/L vs 30.3 ± 10.5 mg/L respectively). Concentrations of s-β2m in PD patients rose with PD duration and were significantly inversely correlated with residual renal function ( r = –0.71, p < 0.0001). Unexpectedly, concentrations of s-β2m in anuric PD patients rose as peritoneal CCr increased. And most of the patients with high s-β2m levels fell into the high or high-average transport categories according to a peritoneal equilibration test.

Conclusions

Concentrations of s-β2m in patients on PD did not differ significantly from concentrations in HD patients who were using high-flux synthetic membranes. The contribution of residual renal function to removal of β2m was more important than the contribution of peritoneal clearance. High peritoneal clearance of small molecules did not result in low s-β2m concentrations, especially in anuric patients with accelerated peritoneal permeability.

Beta-2 Microglobulin Amyloidosis in a Patient on LongTerm Continuous Ambulatory Peritoneal Dialysis (CAPD)

A 61-year-old female patient with ESRD due to analge sic nephropathy and treated solely with CAPD for 81 months is described. During this period she developed peritonitis 4 times. She eventually died of acute pulmonary edema due to coronary heart disease. The autopsy showed an analgesic nephropathy with contracted kidneys, diffuse peritoneal fibrosis, and articular and periarticular amyloidosis of AB2m-type. This form of amyloidosis is well known after hemodialysis; it was, however, not observed heretofore after sole long-term CAPD.

Longitudinal Study of Proteins in Plasma and Dialysate during Continuous Ambulatory Peritoneal Dialysis (CAPD)

The aim was to evaluate plasma proteins during continuous ambulatory peritoneal dialysis (CAPD) in relation to dialysis losses, membrane permeability, renal insufficiency, and time on CAPD. Ten male patients, established on CAPD for at least 14 months, were studied every 8 weeks for 56 weeks. Blood and dialysate from the morning exchange were analysed for urea, creatinine, and 7 proteins, and used to calculate dialysate to plasma concentration ratios (DIP). These ratios were not significantly changed suggesting that permeability remained constant. However, there was a trend for β2-microglobulin, creatinine, and urea to increase progressively. After 56 weeks, β2-microglobulin had increased from 27.9 to 31.3 mglL (p < 0.05) and creatinine 1006 to 1099 μmoLIL (p < 0.05) and both correlated with time on CAPD (p < 0.001). Plasma α1-acid glycoprotein, albumin, transferrin, IgG, IgA, and complement C3 were not significantly changed, although IgA and complement C3 were each negatively correlated with time on CAPD (r = −0.70 and −0.67, respectively), creatinine (r = 0.51 and −0.54), and urea (r = −0.61 and −0.61) (p < 0.001 for all). It is concluded that increases in β2-microglobulin, creatinine, and urea are not due to loss of membrane permeability but reflect a slight increase in uraemia. Long-term decreases in immunological proteins may be caused by uraemia or progressive depletion.

Cystatin C, Beta2 Microglobulin, N-Acetyl-beta-D-glucosaminidase, Retinol-Binding Protein, and Endothelin 1 Levels in the Evaluation of Sickle Cell Disease Nephropathy

OBJECTIVES

Renal involvement is common in sickle cell disease (SCD). Early demonstration of renal injury and commencement of appropriate treatment will increase survival and quality of life in these patients. We investigated renal manifestations in our pediatric and adult SCD patients and evaluated the role of cystatin C, Beta2 microglobulin (B2M), retinol-binding protein (RBP), N-acetyl-beta-D-glucosaminidase (NAG), and endothelin-1 (ET-1) to indicate renal damage.

METHODS

The study involved 45 pediatric and 10 adult patients with SCD and 20 healthy children and 10 healthy adults as a control. All the patients were questioned for possible renal manifestations. 24-hour urine samples were collected and glomerular filtration rates (GFRs) were calculated by using creatinine (GFR(creatinine)), Schwartz formula (GFR(Schwartz)), and cystatin C (GFR(cystatin C)). Blood and urine samples were collected and serum cystatin C, urine B2M, RBP, NAG, and ET-1 levels were measured.

RESULTS

Nocturnal enuresis and proteinuria were the most common renal manifestations in SCD patients. When the groups were compared in terms of GFR, GFR(creatinine) and GFR(Schwartz) levels were higher in group 1 and 2 patients than in control 1 and 2 patients (P < .05). Cystatin C, B2M, RBP, NAG, and ET-1 values were normal in both the patient and the control groups. However, B2M/creatinine levels were higher than 160 μg/mg creatinine levels in 10 patients.

CONCLUSIONS

Serum cystatin C, urine NAG, RBP, and ET-1 levels were found to be insufficient for the evaluation of SCD nephropathy. Increased B2M/creatinie levels can be valuable in estimating possible glomerular and tubular damage in SCD.

Uremic toxins and peritoneal dialysis

Uremic toxicity is related in part to the accumulation of toxic substances, the nature of which has only partly been characterized. Because of the use of a highly permeable membrane and better preservation of the residual renal function, it could be anticipated that some of these uremic toxins are more efficiently cleared across the peritoneal membrane, and that the plasma and tissue levels of these compounds are lower than in hemodialysis patients. This article analyzes the generation and removal of several uremic toxins in peritoneal dialysis patients. The following uremic toxins are discussed: beta2-microglobulin, advanced glycation end products, advanced oxidation protein products, granulocyte inhibitory proteins, p-Cresol, and hyperhomocysteinemia. Some recent studies are reviewed suggesting that uremic toxins are involved in the progression of renal failure and are at least partially removed by peritoneal dialysis. We conclude that, although the plasma levels of some of these compounds are lower in peritoneal dialysis versus hemodialysis patients, it does not mean that the peritoneal dialysis patient is "better" protected against the numerous disturbances caused by these toxins.

Role of bioincompatibility in dialysis morbidity and mortality

This review examines the mechanisms by which bioincompatibility in dialysis systems may have an effect on morbidity and mortality in the dialysis population. Direct toxic effects of membrane materials and various chemical substances have been well demonstrated in the chronic dialysis population. Activation of the complement cascade and stimulation of cytokine production may have autocrine effects on leukocyte function with sequelae such as enhanced rates of infection and the development of B2-microglobulin amyloidosis. The variable effect of different membrane materials on each of these effector systems is examined. Bioincompatibility may effect the incidence of infection, malignancy, cardiopulmonary disease, and malnutrition as well as induce novel disease processes. All these confounding variables must be considered when evaluating the effect of dialysis on mortality and morbidity.