Does a High Peritoneal Transport Rate Reflect a State of Chronic Inflammation?

Objective

It has recently been reported that a high peritoneal transport rate was associated with increased mortality in continuous ambulatory peritoneal dialysis (CAPD) patients. One possible explanation is that a high peritoneal transport rate might be caused by a state of chronic inflammation, which also per se might result in increased mortality. Therefore, in this study we investigated whether high peritoneal transport rate patients are in a state of chronic inflammation.

Methods

The study included 39 clinically stable peritoneal dialysis patients (free of peritonitis) who had been on PD for more than 3 months (16.8 ± 11.8 months). Seven patients were treated with continuous cycling peritoneal dialysis (CCPD) and the others were on CAPD. A 4-hour standard peritoneal equilibration test (PET) using 2.27% glucose solution was performed in each patient. Dialysate samples at 4 hours and blood samples at 2 hours were measured for interleukin-1β (IL-β), tumor necrosis factoroc (TNFα), C-reactive protein (CRP), and hyaluronan as markers of inflammation.

Results

There was no significant correlation between dialysate/plasma (D/P) creatinine (0.82 ± 0.15, range 0.51 - 1.15) and blood concentrations of IL-1β (11.2 ng/L, range <5 - 65.9 ng/L), TNFα (12.1 ng/L, range <5 - 85.4 ng/L), CRP (<10 mg/L, range <10 - 76 mg/L), nor with the blood hyaluronan concentration (165 μg/L, range 55 - 955 μg/L). The dialysate concentrations of IL-1β and TNFα were below the detectable level in most of the samples. Although dialysate hyaluronan concentration (334 μg/L, range 89 - 1100 μg/L) was correlated with D/P creatinine ( r = 0.36, p < 0.05), there was no correlation between the total amount of hyaluronan in the effluent and D/P creatinine. However, a significant correlation was found between serum hyaluronan concentration and glomerular filtration rate (GFR) ( r = -0.49, p < 0.005); GFR also tended to be correlated with serum TNFα ( r = -0.31, p = 0.058) but not with serum IL-1β and serum CRP.

Conclusion

Our results suggest that a high peritoneal transport rate is not necessarily related to a state of chronic inflammation in CAPD patients. The high mortality rate observed in high transporters may relate to other issues, such as fluid balance or abnormal nutrition and metabolism, rather than to chronic inflammation.

Physiological Saline is not a Biocompatible Peritoneal Dialysis Solution

We have previously demonstrated that daily exposure to dialysis fluid results in significantly increased peritoneal lymphatic flow. In this study, we investigated if daily intraperitoneal infusion of saline (isotonic, glucose free) could cause similar changes.

Methods

Sixteen male SD rats received daily infusion (i.p) of 20 ml saline for ten days (Saline group). Twenty-four hours after the last infusion, a 4 hour dwell study using 25 ml 3.86% glucose dialysis solution with frequent dialysate and blood sampling was done in each rat as well as in rats which did not receive daily infusion (Control, n=8). Radiolabeled human albumin (RISA) was added to the solution as an intraperitoneal volume marker. Radioactivity, glucose, urea, sodium, and potassium were measured for each sample. In a separate study, the RISA absorption to peritoneal tissue was also determined.

Results

The net ultrafiltration was significantly decreased in the daily infusion group (p<0.05). However, the apparent volume at 3 minutes of the dwell was markedly increased; this was due to a significant increase in the RISA binding (1.5–12.0% in the Saline group vs. 0.45–1.12% in the Control group) to peritoneal tissues as assessed by measurement of RISA recovery at 3 min of the dwell. This resulted in a significant overestimation both of the intraperitoneal volume (IPV) at 3 min and the (apparent) fluid absorption rate (as estimated by the transport of RISA out of peritoneal cavity): 0.087±0.026 ml/min in the Saline group vs. 0.052±0.007 ml/min in the Control group, p<0.001. The direct lymphatic flow as estimated by the clearance of RISA to plasma (which should not be affected by the RISA binding) also increased markedly (0.021±0.005 ml/min in the Saline group vs. 0.008±0.001 ml/min in the control group). There was no significant difference in the D/P values for small solutes (urea, sodium, potassium, urate) and D/D0 for glucose between the two groups.

Conclusions

1) Daily infusion of physiological saline into peritoneal cavity may increase the peritoneal lymphatic flow; 2) The significant (apparent) increase in IPV shortly after infusion may suggest increased RISA binding to peritoneal tissues (which may be related to the damage of the tissues, and results in overestimation of the peritoneal fluid absorption rate); 3) Saline is not a biocompatible peritoneal dialysis solution, and should therefore not be used as a control or flush solution.

Relevance of C-reactive protein levels in peritoneal dialysis patients

BACKGROUND

C-reactive protein (CRP) levels are increased in 30 to 50% of dialysis patients and predict cardiovascular morbidity and mortality. It is usually considered that raised CRP levels reflect underlying atherosclerosis. However, many patients may have clinically apparent cardiovascular disease without raised CRP levels. This study was designed to assess both the risk factors for high CRP levels and the usefulness of the test as a marker of clinically apparent coronary artery disease (CAD), peripheral vascular disease (PVD) and the presence of ongoing infections/inflammatory disorders (INF-INFL) in peritoneal dialysis patients.

METHODS

A chart review of 190 prevalent peritoneal dialysis patients was performed. CRP, albumin, ferritin, erythropoietin (EPO) dose and resistance, Kt/V, and residual renal function values were obtained and a history or presence of cardiovascular disease (CAD, PVD) and presence of INF-INFL recorded. Data were analyzed by Chi-square, Spearman correlation and logistic regression.

RESULTS

A total of 31% of patients had a raised CRP. INF-INFL was highly predictive of raised CRP levels (OR 16.97; 95% CI 5.41 to 53.14, P=0.000), whereas CAD and PVD either singly or in combination had no such association. The sensitivity/specificity for CRP as a test for INF-INFL was 83/77%. For CAD and PVD, the sensitivities were less than 40% and specificities 70%. Increased CRP values were more common in females but not in diabetics. Weak linear correlations existed between CRP levels and albumin, ferritin and residual renal function (r=-0.212, 0.228 and -0.163 respectively, P < 0.02). By regression analysis, INF-INFL predicted high CRP levels, but CAD and PVD did not. The majority of patients (57%) with high CRP had no identifiable cause; 40% of these patients had subsequent or previous normal CRP values. High transport status predicted high CRP levels (OR 7.28; 95% CI 1.417 to 37.36, P=0.006).

CONCLUSIONS

The majority of elevated CRP levels in peritoneal dialysis patients occur without an obvious cause. Clinically apparent cardiovascular disease does not predict high CRP levels. CRP levels vary over time in the same patient, from normal to high or vice versa, for no obvious reason. Sources of inflammation other than CAD, PVD and clinically obvious INF-INFL in peritoneal dialysis patients remain to be identified.

Peritoneal dialysis fluids with a physiologic pH based on either lactate or bicarbonate buffer-effects on human mesothelial cells

Conventional lactate (Lac)-buffered peritoneal dialysis (PD) solutions have turned out to be detrimental to human peritoneal cells, especially because of a low pH. In the present study, we focus on potential differences between Lac and bicarbonate (Bic) as a buffer when adjusted to a physiological pH. All test fluids were buffered with either 40 mmol/L of Lac or 34 mmol/L of Bic, sterile filtered, and adjusted to a pH of 7.4. Osmotic agents used were 1.36% glucose (Glu), 3.86% Glu, 1% amino acids (AA), and 7.5% Glu polymer (Glupoly). Human peritoneal mesothelial cells (HPMCs) were isolated from the omentum majus, grown to confluence, and incubated after the second passage for 15 minutes (37 degrees C and 5% carbon dioxide) with the test fluids. Cytotoxicity was controlled by measuring apoptotic and necrotic cells with cytofluorometry. Aerobic cell metabolism (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide [MTT] assay) and intracellular adenosine triphosphate (ATP) concentrations were measured to assess cell viability. Release of interleukin-6 (IL-6) from HPMCs was determined as a parameter of cellular host defense. No significant difference in apoptosis or necrosis rates was found between the solutions adjusted to normal pH. However, in the MTT assay, Bic solutions were superior to corresponding Lac pendants at an identical pH of 7.4 (P < 0.01). Intracellular ATP concentrations reflected a very similar pattern (P < 0.05). Glupoly in combination with Lac showed an impaired pattern with both the MTT and ATP assays. Regarding IL-1beta-stimulated IL-6 release, there was a small, but not significantly better, response for Bic. Differences in manifest cell cytotoxicity reflected by apoptosis and necrosis rates could not be detected comparing PD solutions buffered with Lac or Bic at a physiological pH. However, distinct parameters of cell metabolism were superior with Bic compared with Lac. Especially Glupoly was inferior in combination with Lac as a buffer.

Experimental models in peritoneal dialysis: a European experience

BACKGROUND

The development of adequate animal models is important for the in vivo study of selected aspects of peritoneal dialysis (PD) that cannot be evaluated by an in vitro model, such as peritoneal membrane transport, the influence of local defense mechanisms, and for testing new osmotic agents and their biocompatibilities.

METHODS

Our experience with animal models for PD, including the acute Stockholm model in non-uremic rats, the acute and chronic Amsterdam model in non-uremic rats, and the chronic Gent model in uremic rats, is described.

RESULTS

The Stockholm model proved to be useful in understanding the normal physiology of peritoneal transport, and for testing new dialysis solutions and their biocompatibilities. It is a rather simple and inexpensive model, and thus is suitable for screening new solutions and additives. The Amsterdam model permits the study of chemokines and mesothelial cell regeneration in vivo, and is applied in a model of chronic peritonitis. The results of the Gent model suggest that chronic peritoneal dialysis in uremic rats is feasible for at least eight weeks. This model is, however, very laborious, time consuming, and expensive.

CONCLUSION

Further improvement of the technique and increase of the dialysis dose should result in a better and more realistic model for peritoneal dialysis. It is hoped that in the future these models will be useful to test the effects of long-term intraperitoneal application of different dialysis solutions and additives in uremic animals.

Effect of two-chambered bicarbonate lactate-buffered peritoneal dialysis fluids on peripheral blood mononuclear cell and polymorphonuclear cell function in vitro

Low pH, high osmolality, increasing glucose concentration, and glucose degradation products (GDP) formed during heat sterilization of conventional peritoneal dialysis (PD) fluids have been shown to have a detrimental effect on cells involved in peritoneal host defense. The two-chambered PD fluid bag in which glucose at pH approximately 3 is separated from a bicarbonate (25 mmol/L)-lactate (15 mmol/L) buffer during heat sterilization permits PD fluids with lower GDP to be delivered to the patient at neutral pH. To establish the possible benefit of two-chambered bag PD fluids on peripheral blood mononuclear cell (PBMC) and polymorphonuclear (PMN) cell function, we compared conventional 1.5% Dianeal (1.5%D) with 1.5% two-chambered bag bicarbonate-lactate (1.5%D-B), and conventional 4.25% Dianeal (4.25%D) with 4.25% two-chambered bag bicarbonate-lactate (4.25%D-B). Furthermore, to study the effect of the sterilization process on PBMC and PMN function, we compared filter-sterilized 4.25%D (4.25%D-F) with 4.25%D and 4.25%D-B. PBMC were harvested by Ficoll-Hypaque separation, and 2.5 x 10(6) cells in RPMI were incubated with an equal volume of the test fluids for 4 hours, pelleted, and resuspended in RPMI containing 10 ng endotoxin for a further 20 hours. Tumor necrosis factor alpha (TNF-alpha) production by endotoxin-stimulated PBMC was not significantly different (P = 0.10) between 1.5%D-B and 1.5%D, but was significantly higher (P = 0.01) with 4.25%D-B compared with 4.25%D. PBMC exposed to filter-sterilized fluid (4.25%D-F) showed significantly higher endotoxin-stimulated TNF-alpha production compared with 4.25%D (P = 0.02), but was not significantly different from 4.25%D-B (P = 0.40). PMN were harvested by Ficoll-Hypaque separation and 10 x 10(6) cells incubated with test fluids for 30 minutes. After incubation, phagocytosis (phagocytosis index) was determined by the uptake of 14C-labeled Staphylococcus aureus, oxidative burst by reduction of ferricytochrome C to ferrocytochrome C on stimulation with PMA, and enzyme release by measurement of endotoxin-stimulated bactericidal/permeability increasing protein (BPI). Bicarbonate-lactate two-chambered fluids of similar osmolality and glucose concentration conferred a significant improvement in phagocytosis (P = 0.02 for 1.5%D-B and P < 0.001 for 4.25%D-B). Oxidative burst and BPI release were significantly higher in 4.25%D-B compared with 4.25%D (P < 0.001). Filter-sterilized 4.25%D-F conferred a significant improvement in phagocytosis and oxidative burst compared with 4.25%D (P < 0.001) or 4.25%D-B (P < 0.001). Furthermore, conventional 4.25%D was associated with significantly lower BPI release compared with 4.25%D-F (P = 0.01). GDP's acetaldehyde and 5-HMF were analyzed in 4.25%D-B, 4.25%D, and 4.25%D-F. Acetaldehyde was below the lower limit (0.79 ppm) of the standard curve in 4.25%D-B and 4.25%D-F fluids but was detected (3.76 to 5.12 ppm) in all of the 4.25%D fluids. Relative levels of 5-HMF in the 4.25%D-B (0.032 to 0.041 Abs @ 284 nm) and 4.25%D (0.031 to 0.036 Abs @ 284 nm) were similar. The lowest levels (0.001 Abs @ 284 nm) were observed in the filter-sterilized 4.25%D-F. The beneficial effects of two-chambered bicarbonate lactate-buffered PD fluids on PBMC and PMN function are probably related to reduction of GDP from heat sterilization of glucose in a separate chamber at a lower pH. This improvement in biocompatibility could have a beneficial affect on peritoneal defenses.