Role of endothelial hyaluronan in peritoneal membrane transport and disease conditions during peritoneal dialysis

Peritoneal membrane dysfunction in peritoneal dialysis (PD) is primarily attributed to angiogenesis; however, the integrity of vascular endothelial cells can affect peritoneal permeability. Hyaluronan, a component of the endothelial glycocalyx, is reportedly involved in preventing proteinuria in the normal glomerulus. One hypothesis suggests that development of encapsulating peritoneal sclerosis (EPS) is triggered by protein leakage due to vascular endothelial injury. We therefore investigated the effect of hyaluronan in the glycocalyx on peritoneal permeability and disease conditions. After hyaluronidase-mediated degradation of hyaluronan on the endothelial cells of mice, macromolecules, including albumin and β2 microglobulin, leaked into the dialysate. However, peritoneal transport of small solute molecules was not affected. Pathologically, hyaluronan expression was diminished; however, expression of vascular endothelial cadherin and heparan sulfate, a core protein of the glycocalyx, was preserved. Hyaluronan expression on endothelial cells was studied using 254 human peritoneal membrane samples. Hyaluronan expression decreased in patients undergoing long-term PD treatment and EPS patients treated with conventional solutions. Furthermore, the extent of hyaluronan loss correlated with the severity of vasculopathy. Hyaluronan on endothelial cells is involved in the peritoneal transport of macromolecules. Treatment strategies that preserve hyaluronan in the glycocalyx could prevent the leakage of macromolecules and subsequent related complications.

Does Prior Abdominal Surgery Influence Peritoneal Transport Characteristics or Technique Survival of Peritoneal Dialysis Patients?

INTRODUCTION

Prior abdominal surgery may result in peritoneal membrane adhesions and fibrosis, compromising the success of peritoneal dialysis (PD). The impact of this factor on peritoneal membrane function and PD technique survival has not been adequately investigated.

METHODS

Following an observational, retrospective design, we studied 171 incident PD patients, with the main objective of analyzing the influence of prior abdominal surgical procedures (main study variable) on baseline and evolutionary peritoneal transport characteristics (main outcome) and PD patient and technique survival (secondary outcomes). Abdominal surgeries were categorized according to the degree of presumed injury to the peritoneal membrane. We also considered the additive effect of aggressions to the membrane during the first year on PD therapy.

RESULTS

All patients had a baseline peritoneal equilibration test with complete drainage at 60', and 113 patients had a second study at the end of the first year. Sixty-one patients (35.7%) had a record of prior abdominal surgery, including 29 patients with at least one major intraperitoneal surgery, 22 having undergone minor intraperitoneal procedures, and 21 with a background of major abdominopelvic extraperitoneal surgery. We did not observe differences, at baseline or after 1 year, among patients with or without previous abdominal procedures regarding small solute transport, overall capacity of ultrafiltration, free water transport, small pore ultrafiltration, or peritoneal protein excretion. Stratified analysis, considering prior and first-year-on-PD peritoneal aggressions, did not reveal any differences, although in this case our analysis was hampered by a limited statistical power. Abdominal surgical events did not influence patient or PD technique survival.

CONCLUSION

Prior abdominal surgical procedures do not appear to compromise peritoneal membrane function or technique survival in patients successfully started on PD.

Factors associated with systolic hypertension in peritoneal dialysis patients

Background

Hypertension is common in peritoneal dialysis (PD) patients and associated with adverse outcomes. Besides solute clearance, PD convective clearance is used to control extracellular water (ECW) volume and sodium balance. Previous studies have reported on hypertension in PD patients treated with continuous ambulatory peritoneal dialysis (CAPD) using hypertonic glucose dialysates. However, increasing numbers of PD patients are now treated with automated peritoneal dialysis (APD) and icodextrin dialysates. As such, we wished to explore factors associated with systolic blood pressure (SBP) in a modern cohort to identify targets to improve blood pressure control in PD patients.

Methods

We retrospectively reviewed the results from PD patients attending for peritoneal membrane assessment who had corresponding bioimpedance ECW and brain natriuretic peptide (NT-proBNP) measurements.

Results

We studied 510 PD patients: 317 (72.2%) male, 216 (42.4%) diabetics, median age 59 (47–72) years, and 51% treated by APD with a day-time icodextrin exchange. Mean systolic blood pressure (SBP) was 140 ± 24.8 mmHg. SBP was independently associated with 4-hour dialysate to plasma creatinine ratio (β = 29.5 (95% confidence limits 11.4–47.5, p = 0.001), N-terminal brain natriuretic peptide [β = 11.9 (7.2–16.7), p < 0.001], and daily urine sodium excretion [β = 1.7 (1.0–2.3), p < 0.001].

Conclusion

In the era of APD cyclers and icodextrin, SBP is associated with increased NT-proBNP, a marker of ECW expansion, and faster peritoneal transport, a risk factor for a positive sodium balance, and increased urinary sodium suggestive of higher dietary sodium intake. Patients should be encouraged to restrict sodium intake and PD prescriptions targeted to control ECW to improve SBP control.

Baseline higher peritoneal transport had been associated with worse nutritional status of incident continuous ambulatory peritoneal dialysis patients in Southern China: a 1-year prospective study

The aim of the present study was to investigate the relationship between baseline peritoneal transport types and nutritional status in Chinese continuous ambulatory peritoneal dialysis (CAPD) patients. In the present single-centre, prospective study, incident CAPD patients were included from 15 April 2010 to 31 December 2011 and were followed up for 12 months. According to the results of baseline peritoneal equilibration test, patients were divided into lower peritoneal transport group (lower transporters) and higher peritoneal transport group (higher transporters). Nutritional status was evaluated by both subjective global assessment (SGA) and protein-energy wasting (PEW) score. The body composition parameters were assessed by body impedance analysis. A total of 283 CAPD patients were included in the study, of which 171 (60.4 %) were males with a mean age of 47.0 (sd 14.9) years. Compared with lower transporters (n 92), higher transporters (n 181) had lower levels of serum albumin (37.1 (sd 4.3) v. 39.6 (sd 4.3) g/l, P< 0.001), serum pre-albumin (356 (sd 99) v. 384 (sd 90) mg/l, P= 0.035), phase angle (6.15 (sd 0.39) v. 6.27 (sd 0.47)°, P< 0.05) and higher rate of malnutrition defined by SGA (52.5 v. 25.0%, P< 0.001) and PEW score (37.0 v. 14.1 %, P< 0.001) at 1-year of follow-up. Baseline higher peritoneal transport, analysed by multivariate binary logistic regressions, was independently associated with malnutrition (SGA mild to moderate and severe malnutrition: OR 3.43, 95% CI 1.69, 6.96, P< 0.01; PEW: OR 2.40, 95% CI 1.08, 5.31, P= 0.03). It was concluded that baseline higher peritoneal transport was independently associated with worse nutritional status of CAPD patients in Southern China.

Peritoneal Dialysis in Western Countries

BACKGROUND

Peritoneal dialysis (PD) for the treatment of end-stage renal failure was introduced in the 1960s. Nowadays it has evolved to an established therapy that is complementary to hemodialysis (HD), representing 11% of all patients treated worldwide with dialysis. Despite good clinical outcomes and similar results in patient survival between PD and HD, the penetration of PD is decreasing in the Western world.

SUMMARY

First the major events in the history of the development of PD are described. Then important insights into the physiology of peritoneal transport are discussed and linked to the changes in time observed in biopsies of the peritoneal membrane. Furthermore, the developments in peritoneal access, more biocompatible dialysate solutions, automated PD at home, the establishment of parameters for dialysis adequacy and strategies to prevent infectious complications are mentioned. Finally non-medical issues responsible for the declining penetration in the Western world are analyzed.

KEY MESSAGES

Only after introduction of the concept of continuous ambulatory PD by Moncrief and Popovich has this treatment evolved in time to a renal replacement therapy. Of all structures present in the peritoneal membrane, the capillary endothelium offers the rate-limiting hindrance for solute and water transport for the diffusive and convective transport of solutes and osmosis. The functional and anatomical changes in the peritoneal membrane in time can be monitored by the peritoneal equilibrium test. Peritonitis incidence decreased by introduction of the Y-set and prophylaxis using mupirocin on the exit site. The decrease in the proportion of patients treated with PD in the Western world can be explained by non-medical issues such as inadequate predialysis patient education, physician experience and training, ease of HD initiation, overcapacity of in-center HD, lack of adequate infrastructure for PD treatment, costs and reimbursement issues of the treatment.

FACTS FROM EAST AND WEST

(1) PD is cheaper than HD and provides a better quality of life worldwide, but its prevalence is significantly lower than that of HD in all countries, with the exception of Hong Kong. Allowing reimbursement of PD but not HD has permitted to increase the use of PD over HD in many Asian countries like Hong Kong, Vietnam, Taiwan, Thailand, as well as in New Zealand and Australia over the last years. In the Western world, however, HD is still promoted, and the proportion of patients treated with PD decreases. Japan remains an exception in Asia where PD penetration is very low. Lack of adequate education of practitioners and information of patients might as well be reasons for the low penetration of PD in both the East and West. (2) Patient survival of PD varies between and within countries but is globally similar to HD. (3) Peritonitis remains the main cause of morbidity in PD patients. South Asian countries face specific issues such as high tuberculosis and mycobacterial infections, which are rare in developed Asian and Western countries. The infection rate is affected by climatic and socio-economic factors and is higher in hot, humid and rural areas. (4) Nevertheless, the promotion of a PD-first policy might be beneficial particularly for remote populations in emerging countries where the end-stage renal disease rate is increasing dramatically.

Peritoneal resting with heparinized lavage reverses peritoneal type I membrane failure. A comparative study of the resting effects on normal membranes

BACKGROUND

Ultrafiltration failure (UFF) is a serious complication of long-term peritoneal dialysis (PD). Peritoneal rest (PR) has been demonstrated as a valid treatment to reverse the functional changes that occur in UFF. The effects of PR on a normally functioning human peritoneum are unknown but are expected to be neutral. Our hypothesis was that PR positively modifies peritoneal function in patients with UFF, in contrast to the absence of effects when PR is applied under normal conditions.

PATIENTS AND METHODS

We studied 84 PR periods, comparing 35 patients with UFF and 49 controls (resting for abdominal surgery with temporary discontinuation of PD). We analyzed peritoneal transport pre-PR and post-PR by calculating the mass transfer coefficients of creatinine (Cr-MTAC), the dialysate/plasma creatinine ratio (D/P Cr) and the ultrafiltration (UF).

RESULTS

Baseline data was similar for the 2 groups, although the UFF group had a longer median time in PD (39 [18 - 60] vs 10 [5 - 23] months; p = 0.00001). Peritoneal rest induced a decrease in D/P Cr, Cr-MTAC and an increase in UF capacity in the UFF group (p = 0.0001, p = 0.004 and p = 0.001, respectively), without causing changes in the control group. Peritoneal rest in patients with more than 6 months of UFF was not able to reduce peritoneal solute transport or improve UF capacity. Response to PR did not differ among UFF patients with or without a previous history of peritonitis. Peritoneal rest enabled patients with UFF to continue on PD for a median time of 23 months (range, 13 - 46 months).

CONCLUSIONS

Peritoneal rest induces functional changes in patients with UFF but not in those with no functional abnormalities. This demonstrates that PR works only when abnormal but reversible functional conditions are present. However, the effect is highly dependent on how early PR is applied.