Annemieke M. Coester

INDUCTION OF CHRONIC KIDNEY FAILURE IN A LONG-TERM PERITONEAL EXPOSURE MODEL IN THE RAT: EFFECTS ON FUNCTIONAL AND STRUCTURAL PERITONEAL ALTERATIONS

♦ Background: A long-term peritoneal exposure model has been developed in Wistar rats. Chronic daily exposure to 3.86% glucose based, lactate buffered, conventional dialysis solutions is possible for up to 20 weeks and induces morphological abnormalities similar to those in long-term peritoneal dialysis (PD) patients. The possible effects of kidney failure in this model are unknown. The aim was to analyze the effects of chronic kidney failure on peritoneal function and morphology, alone and in combination with PD exposure, in a well-established, long term, peritoneal exposure model in the rat. ♦ Methods: 40 male Wistar rats were randomly assigned into four experimental groups: no nephrectomy, no peritoneal exposure (sham; n = 8); nephrectomy, no peritoneal exposure (Nx; n = 12); no nephrectomy, with peritoneal exposure (PD; n = 8); and nephrectomy, with peritoneal exposure (NxPD; n = 12). The nephrectomy consisted of a one-step 70% nephrectomy. The peritoneal exposure groups were infused once daily for 16 weeks with a 3.86% glucose-based dialysis solution. Development of chronic kidney disease was monitored during the experiment. Peritoneal function and morphological assessment of the peritoneal membrane were performed at the end of the experiment. ♦ Results: During follow-up the nephrectomized groups developed uremia with remarkable renal tubular dilatation and glomerular sclerosis in the renal morphology. Functionally, uremia (Nx) and PD exposure (PD) alone showed faster small solute transport and a decreased ultrafiltration capacity, which were most pronounced in the combination group (NxPD). The presence of uremia resulted in histological alterations but the most severe fibrous depositions and highest vessel counts were present in the PD exposure groups (PD and NxPD). Significant relationships were found between the number of vessels and functional parameters of the peritoneal vascular surface area. ♦ Conclusion: It is possible to induce chronic kidney failure in our existing long-term peritoneal infusion model in the rat. The degree of impairment of kidney function after 16 weeks is comparable to chronic kidney disease stage IV. Uremia per se induces both functional and morphological alterations of the peritoneal membrane. An additive effect of these alterations is present with the addition of chronic kidney failure to the model. The latter makes the present long-term model important in better understanding the pathophysiology of the peritoneal membrane in PD.

Peritoneal function in clinical practice: the importance of follow-up and its measurement in patients. Recommendations for patient information and measurement of peritoneal function.

A review is given on peritoneal function, especially ultrafiltration and ultrafiltration failure followed by recommendations on how to translate pathophysiology into clinical practice. The subsequent consequences for management of peritoneal membrane function and for patient information are also included.

Biological markers in the peritoneal dialysate effluent: are they useful.

A review is given on biomarkers in peritoneal effluent. It comprises methods to distinguish between diffusion and local production. This is followed by examples of various biomarkers. Their potential use is discussed in 4 situations: inherent fast transporters, longitudinal follow-up of patients, biocompatibility testing of new dialysis solutions, and their potential use in the detection of patients who are likely to develop encapsulating peritoneal sclerosis.

Can effluent matrix metalloproteinase 2 and plasminogen activator inhibitor 1 be used as biomarkers of peritoneal membrane alterations in peritoneal dialysis patients

♦ Background: Peritoneal effluent contains clinically relevant substances derived from intraperitoneal production or transperitoneal transport, or both. The glycoproteinase matrix metalloproteinase 2 (MMP-2) cleaves denatured collagen and complements other collagenases in the degradation of fibrillar collagens. Elevated intraperitoneal levels of plasminogen activator inhibitor 1 (PAI-1) have been demonstrated to be present in patients with intra-abdominal adhesions. The aim of the present study was therefore to investigate the potential for effluent MMP-2 and PAI-1 to be used as markers of the development of peritoneal alterations. In addition, MMP-2 was analyzed in previously frozen effluent samples from a uremic rat model, in which data concerning the severity of peritoneal fibrosis were available. ♦ Methods: This prospective, single-center cohort study included 86 incident peritoneal dialysis (PD) patients. All patients were treated solely with biocompatible dialysis solutions and underwent a standard peritoneal permeability analysis (SPA). The presence of local MMP-2 and PAI-1 production and the relationships between those markers and peritoneal transport parameters were analyzed. Furthermore, effluent interleukin 6 was analyzed as a marker of local inflammation. ♦ Results: Median effluent levels of 21.4 ng/mL for MMP-2 and 0.9 ng/mL for PAI-1 were found. The median dialysate appearance rates were 218.8 ng/min for MMP-2 and 9.6 ng/min for PAI-1. Local peritoneal production averaged 90% of effluent MMP-2 concentration and 74% of effluent PAI-1 concentration. Furthermore, correlations between peritoneal transport parameters and MMP-2 and PAI-1 were observed. Longitudinal follow-up showed no change for MMP-2 (p = 0.37), but a tendency for PAI-1 to increase with the duration of PD (p < 0.001). In rats, a significant relationship was present between the extent of peritoneal fibrosis and the appearance rate of MMP-2 (r = 0.64, p = 0.03). ♦ Conclusions: The foregoing data illustrate the potential of effluent MMP-2 and PAI-1 as biomarkers of peritoneal modifications, especially fibrosis; however, the components of peritoneal transport and local production should be clearly distinguished in every patient.

The −174G/C variant of IL6 as risk factor for mortality and technique failure in a large cohort of peritoneal dialysis patients

BACKGROUND Functional variants in the IL6 gene, in particular the -174G/C polymorphism (rs1800795), affect the mortality risk in dialysis patients. Peritoneal dialysis (PD) patients harbouring the C allele of the -174G/C polymorphism of IL6 showed faster peritoneal transport. The aim of this study was to investigate this IL6 variant as risk factor for mortality and technique failure in a large cohort of Caucasian PD patients. METHODS A Dutch multicentre cohort of 398 incident PD patients (NECOSAD) was analysed. Survival analysis was performed for death and technique failure with a maximum follow-up of 5 years. A combined PD cohort from Amsterdam (Academic Medical Center, N = 71) and Brussels (Université catholique de Louvain Medical School, N = 102) was used for independent replication. RESULTS In NECOSAD, 105 patients died on dialysis [incidence rate 10.3/100 person-years (py)], and 138 patients experienced technique failure (16.2/100 py), with peritonitis as important cause. Patients with the C/C genotype had a 71% increased mortality risk compared to patients with the G/G genotype (95% confidence interval 0.98-2.98); this effect was mainly a long-term effect: a 2.7-fold increased mortality risk was found in patients having survived 2 years since the start on dialysis, and a 1.7-fold increased risk for the combined end point (mortality or technique failure). In the combined replication cohort, no increased risks were found in patients with the C/C genotype. CONCLUSIONS The C/C genotype of the -174G/C polymorphism was associated with an increased mortality risk in 398 Dutch incident PD patients. The existence of substantial differences between the two academic replication cohorts and the discovery cohort from NECOSAD and the limited power of these cohorts prevented an independent replication of the NECOSAD findings.

Variability of effluent cancer antigen 125 and interleukin-6 determination in peritoneal dialysis patients

BACKGROUND Cancer antigen (CA) 125 is a glycoprotein that provides data on the state of the peritoneal membrane in peritoneal dialysis (PD). Interleukin-6 (IL-6) acts as a mediator in acute-phase responses. The study evaluated the usefulness of CA125 and IL-6 in random effluent samples, by assessing their variability in individual patients during clinical practice at the outpatient department. METHODS This longitudinal prospective study was conducted from 2007 till 2009. Participants included 52 stable PD patients aged ≥ 18 years. Effluent samples were obtained during regular outpatient visits and appearance rates (ARs) were calculated. Inter- and intra-individual variability was determined by the coefficient of variation (CV). A linear mixed model was used to analyse time courses. Furthermore, release patterns of these effluent markers were studied. RESULTS CA125-AR of short-term patients (≤ 24 months) ranged from 39.2 to 766.7 U/min and IL-6-AR from 15.5 to 220.0 pg/min. Long-term patients (≥ 25 months) had a CA125-AR of 7.3-1534.0 U/min and IL-6-AR of 6.9-956.4 pg/min. Overall, CV(intra) was 15% in effluent CA125-AR and 28% in IL-6-AR. Intermediate sampling during a 4-h dwell showed a linear increase of CA125 and IL-6 effluent concentrations. The trend of CA125-AR was different (P = 0.001) between short- and long-term patients. A negative relationship was found between CA125 (r = -0.44, P = 0.02) and PD duration. CONCLUSIONS The clinical relevance of effluent CA125 determinations from an unstandardized dwell during every outpatient visit is reasonable, as judged from the CV(intra). The inferior CV(intra) values of ARs as compared to effluent values indicate that ARs should only be calculated under standardized conditions. A single IL-6 measurement, as a predictor of outcome, should be interpreted cautiously.

Free water transport in children on peritoneal dialysis is higher with more biocompatible dialysis solutions, higher with older age and declines with time

BACKGROUND Water transport in peritoneal dialysis occurs through small pores and aquaporins. Free water transport (FWT) occurs through aquaporins only and gives a reflection of peritoneal aquaporin function. In this study, FWT in children was calculated for the first time in different settings. METHODS A prospective cohort study was performed; 87 peritoneal equilibrium tests (PETs) were analysed in 65 patients. Three subgroups were analysed: patients with their first PET; patients in their second year on dialysis; patients in their third year on dialysis or thereafter. Patients using 3.86% glucose solution with low pH/high glucose degradation products (GDP) were compared to patients using 3.86% glucose solution with neutral pH/low GDP. Sixteen patients using neutral pH/low GDP solution were followed longitudinally. FWT was calculated using the dialysate/plasma ratio of sodium. RESULTS The proportional contribution of FWT was significantly higher in patients using dialysis solution with neutral pH/low GDP solution compared to patients using solutions with low pH/high GDP (50 versus 40%). Transcapillary ultrafiltration (TCUF) showed the same trend but was not statistically significant. Total FWT was higher as well. Higher FWT was observed with older age. In the longitudinal group, TCUF and water transport through small pores declined, while FWT remained stable in the first 1.5 years. The contribution of FWT increased in this period (48-61%), then slowly declined again to baseline level during the third year. CONCLUSIONS Total FWT and relative contribution of FWT were significantly higher with neutral pH/low GDP solution. This can reflect a better preservation of aquaporins. The decline in the contribution of FWT in long-term dialysis could hypothetically implicate aquaporin dysfunction or different trafficking of aquaporins.

Fluid transport with time on peritoneal dialysis: the contribution of free water transport and solute coupled water transport.

Ultrafiltration in peritoneal dialysis occurs through endothelial water channels (free water transport) and together with solutes across small pores: solute coupled water transport. A review is given of cross-sectional studies and on the results of longitudinal follow-up.

Soluble VCAM-1 and E-selectin in PD patients: the additive value of the free diffusion coefficient in the assessment of local peritoneal production

Vascular peritoneal membrane changes may develop with duration of peritoneal dialysis (PD). Patients with end-stage renal disease are already at high risk for the development of atherosclerotic disease, due to the effects of uremia (1). Peritoneal dialysis in combination with the uraemic state may therefore accelerate vascular damage. It is likely that endothelial dysfunction precedes the development of the peritoneal vascular abnormalities. Markers of endothelial dysfunction include soluble forms of the adhesion molecules vascular cell adhesion molecule 1 (VCAM-1) and E-selectin. These molecules are almost exclusively produced by endothelium (2) and are elevated during various chronic inflammatory conditions (2–5). At present, no knowledge is available about their levels in effluent of PD patients and their relationships with other parameters, like solute and fluid transport. The aim of this study was to analyze the presence of soluble (s) VCAM-1 and E-selectin in effluent of PD patients in relationship to serum concentrations. The contribution of local peritoneal production of these markers to the levels observed in effluent was determined to assess their value as markers for endothelial dysfunction in PD patients.

The relationship between effluent potassium due to cellular release, free water transport and CA125 in peritoneal dialysis patients.

Background. Recently, we found evidence of effluent potassium (K+) additional to diffusion and convection, suggesting cellular release (CR). Its relationship with free water transport (FWT) in stable peritoneal dialysis (PD) patients suggested an effect of hypertonicity of the dialysis solution leading to cell shrinkage. The aim of the present study was to reproduce these findings in groups according to PD duration and to further investigate the role of mesothelial cells in the observed phenomenon. Methods. Standard peritoneal permeability analyses done with 3.86% glucose were analysed cross-sectionally in three different groups: short-term (n = 53) 0–2 years PD treatment; medium-term (n = 24) 2–4 years PD and long-term (n = 26) > 4 years PD. Results. The time courses for FWT and cellular release of K+ (CR-K+) during the dwell were not significantly different among the groups. Cancer antigen (CA) 125 was highest in the short-term group (P ≤ 0.02) and had a strong positive correlation with mass transfer area coefficient of creatinine (MTAC-creatinine) only in the short-term group (r = 0.62, P ≤ 0.01). CA125 had no relationship with either CR-K+ or FWT, except for negative relationships in the short-term group (CR-K+, r = −0.41, P ≤ 0.05; FWT, r = −0.54, P ≤ 0.05). Conclusion. We conclude that the correlation of CA125 and MTAC-creatinine is dependent on PD duration and underlines the in vitro observation that mesothelial cells produce vasoactive substances that may increase the peritoneal surface area. However, CA125 is not directly related to CR-K+ or FWT. Therefore, the relationship between FWT and CR-K+ is likely to reflect hypertonic cell shrinkage, regardless of the duration of PD, and confirms our earlier findings.