Variability of Peritoneal Protein Loss in Diabetic and Nondiabetic Patients on Continuous Ambulatory Peritoneal Dialysis

In order to evaluate the Influence of diabetes mellitus on peritoneal membrane permeability, we studied the peritoneal protein loss In two groups of patients. Group A consisted of 16 patients (9 nondlabetics and 7 diabetics) who were In the first month of treatment on continuous ambulatory peritoneal dialysis (CAPO). Group B consisted of 13 patients (7 nondlabetics and 6 diabetics) who had been on CAPO for approximately 15 months.

In both groups we measured the body weight, serum total protein, albumin, and total protein, urea, and glucose In the peritoneal fluid.

We did not find any difference In groups A and B between diabetics and nondlabetics as far as the estimated parameters were concerned. Age, body weight, serum biochemistry, and protein and urea content In peritoneal fluid were similar, when group A was compared to group B. Patients of group B hed on average higher protein losses than those who had been on the method for a short period (mean 7.9 g/dL, vs 6.09 g/dL).

Six patients were followed for over 15 months and were found to have significantly Increased protein losses (p=0.02).

Glucose levels In peritoneal fluid were significantly lower In patients In group B, p<0.05 (mean 51.8 g/dL vs 37.1 g/dL).

Peritoneal protein loss does not seem to differ between diabetic and nondiabetic patients with end-stage renal disease treated with CAPO, at any given time of the treatment.

We observed an Increase In protein loss In some patients and a tendency to Increase the protein loss In others. This, along with the fall In glucose levels, might reflect progressive alterations In structure and permeability of the elements Involved In peritoneal transport, and It should receive further evaluation.

The Initial Decrease in Effective Peritoneal Surface Area is Not Caused by an Increase in Hematocrit

The possible relationship between Initial changes In functional characteristics of the peritoneal membrane In time and hemoglobin (Hb) or hematocrit (Ht) was analyzed as part of a prospective longitudinal study. The patients were Investigated twice: the first time within 3 months after the start of continuous ambulatory peritoneal dialysis (CAPD), and again 4 months later. Mass transfer area coefficients (MTC) for low molecular weight solutes and net fluid removal were calculated during a 4-hour dwell, glucose 1.36%. Thirty-four patients were analyzed. MTC (mean±SD, mL/min/1.73 m2) were higher during the first examination: urea 22.6 versus 19.9, p<0.05; lactate 15.6 versus 13.8, p<0.001; creatinine 10.5 versus 9.3, p<0.05; glucose 9.4 versus 7.9, p<0.001. Net fluid removal was lower during the first examination: 28 versus 99 mL/mln/1.73 m2, p<0.05. Hb and Ht increased between the two examinations (Hb: 5.4 vs 6.1 mmol/L, p<0.001; Ht: 0.26 vs 0.29, p<0.001). No relation was found between the absolute or relative change In Hb or Ht and the absolute or relative change In solute and fluid transport between the same examinations. In conclusion, Hb and Ht Increased between the first and second examinations. The simultaneously observed changes in peritoneal transport kinetics could not be attributed to changes In Hb or Ht. Therefore, the changes In transport kinetics during the first months on CAPD are probably due to the recent start of the treatment, possibly by an Increase In peritoneal surface area. LocalIrritation by the dialysate may be the causative mechanism.

Animal Models in Peritoneal Dialysis Research: A Need for Consensus

The development of an adequate animal model for peritoneal research remains an object of concern. In vivo peritoneal dialysis (PD) research is hampered by the large variety of available models that make interpretation of results and comparison of studies very difficult. Species and strain of experimental animals, method of peritoneal access, study duration, measures of solute transport and ultrafiltration, and sampling for histology differ substantially among the various research groups. A collective effort to discuss the shortcomings and merits of the different experimental models may lead to a consensus on a standardized animal model of PD.

Alterations in Water and Solute Transport with Time on Peritoneal Dialysis

Peritoneal ultrafiltration capacity and small -solute transport characteristics seem to be relatively stable in most patients treated with PD for up to 3 years. However, in patients treated with PD for 4 years or more, there is a tendency towards increasing diffusive transport for small solutes as well as a tendency towards decreasing net UF, whereas the peritoneal protein clearances seem to be reduced or stable.

Loss of UFC is a well-known complication during long-term PD treatment, and the risk for loss of UFC may be as high as 50% after 6 years on PD. Several different mechanisms of UFC loss have been reported. In particular, the most common mechanism for loss of UFC is increased diffusive transport resulting in rapid glucose absorption and thus rapid loss of the osmotic driving force. Also reported as causes of UFC loss have been: reduced efficiency of the osmotic agent (perhaps owing to decreased transcellular water transport); loss of peritoneal surface area with slow solute transport owing to fibrosis and the formation of adhesions (during the late stage of sclerosing peritonitis); and increased peritoneal fluid absorption. In individual patients, a combination of several mechanisms may be involved in the apparent UFC failure.

Hyperbranched polyglycerol is an efficacious and biocompatible novel osmotic agent in a rodent model of peritoneal dialysis

OBJECTIVES

To enhance the effectiveness of peritoneal dialysis (PD), new biocompatible PD solutions may be needed. The present study was designed to test the efficacy and biocompatibility of hyperbranched polyglycerol (HPG)-a nontoxic, nonimmunogenic water-soluble polyether polymer-in PD.

METHODS

Adult Sprague-Dawley rats were instilled with 30 mL HPG solution (molecular weight 3 kDa; 2.5% - 15%) or control glucose PD solution (2.5% Dianeal: Baxter Healthcare Corporation, Deerfield, IL, USA), and intraperitoneal fluid was recovered after 4 hours. Peritoneal injury and cellular infiltration were determined by histologic and flow cytometric analysis. Human peritoneal mesothelial cells were assessed for viability in vitro after 3 hours of PD fluid exposure.

RESULTS

The 15% HPG solution achieved a 4-hour dose-related ultrafiltration up to 43.33 ± 5.24 mL and a dose-related urea clearance up to 39.17 ± 5.21 mL, results that were superior to those with control PD solution (p < 0.05). The dialysate-to-plasma (D/P) ratios of urea with 7.5% and 15% HPG solution were not statistically different from those with control PD solution. Compared with fluid recovered from the control group, fluid recovered from the HPG group contained proportionally fewer neutrophils (3.63% ± 0.87% vs 9.31% ± 2.89%, p < 0.0001). Detachment of mesothelial cells positive for human bone marrow endothelial protein 1 did not increase in the HPG group compared with the stain control (p = 0.1832), but it was elevated in the control PD solution group (1.62% ± 0.68% vs 0.41% ± 0.31%, p = 0.0031). Peritoneal biopsies from animals in the HPG PD group, compared with those from control PD animals, demonstrated less neutrophilic infiltration and reduced thickness. Human peritoneal mesothelial cell survival after HPG exposure was superior in vitro (p < 0.0001, 7.5% HPG vs control; p < 0.01, 15% HPG vs control). Exposure to glucose PD solution induced cytoplasmic vacuolation and caspase 3-independent necrotic cell death that was not seen with HPG solution.

CONCLUSIONS

Our novel HPG PD solution demonstrated effective ultrafiltration and waste removal with reduced peritoneal injury in a rodent model of PD.

Peritoneal fluid markers of mesothelial cells and function

Peritoneal structural changes are likely to result in functional deterioration of the peritoneal membrane. For the purpose of early detection of these changes, markers of mesothelial cells that can be measured in peritoneal effluent could provide easily accessible information in individual peritoneal dialysis (PD) patients. In this review, current knowledge on a number of these markers is summarized, such as cancer antigen (CA) 125, phospholipids, hyaluronan, and factors involved in the coagulation system. Although only analyzed in limited studies so far, this approach to understanding changes in the peritoneal membrane seems to be valid and warrants further evaluation in the future, especially in combination with functional studies and peritoneal biopsies.

A prospective study of peritoneal transport in CAPD patients

A prospective two year follow-up study of the functional characteristics of the peritoneal membrane was conducted in 61 CAPD patients. Peritoneal transport of solutes, calculated by mass transfer area coefficients for urea and creatinine, peritoneal clearances for proteins, percentage of absorption of glucose, as well as net ultrafiltration were measured every four months. After five months on CAPD a decrease was found for the transport of most solutes (P < 0.05, mean values, ml/min/1.73 m2): urea 18.1 to 16.2, creatinine 9.5 to 8.4, IgG 0.049 to 0.040 and alpha 2-macroglobulin 0.020 to 0.015, as well as for the absorption of glucose (57.9 to 53.2%, P < 0.05). Net ultrafiltration increased simultaneously from 44.6 to 100.5 ml/4 hr/1.73 m2, P < 0.05. From five months to two years on CAPD a significant increase in the transport of all solutes except alpha 2-macroglobulin was found, as well as a decrease in net ultrafiltration. Peritoneal transport at the end of the study was not significantly different from the starting values. Our findings indicate an initial effect of CAPD itself on peritoneal transport, probably due to the recent start of the treatment. Baseline values were reached after five months on CAPD. Thereafter a gradual increase in peritoneal solute transport occurred during two years of treatment. This can be explained by an increase in the effective peritoneal surface area.