Colonization-Resistant Antimicrobial-Coated Peritoneal Dialysis Catheters: Evaluation in a Newly Developed Rat Model of Persistent Pseudomonas Aeruginosa Peritonitis

Objective

Development of a rat model of persistent peritonitis and evaluation of the ability of liposomal ciprofloxacin hydrogel-coated silicone to resist colonization.

Design

A newly developed model of persistent Pseudomonas aeruginosa peritonitis to compare the ability of liposomal ciprofloxacin hydrogel (LCH)-coated silicone versus plain silicone for resistance to bacterial colonization.

Animals

Male Sprague–Dawley rats.

Results

Inoculating the peritoneum of rats with 1 mL 0.5% agar containing 106 colony-forming units (cfu)/mL P. aeruginosa in the presence of a plain silicone coupon resulted in persistent peritonitis for at least 7 days. Plain silicone coupons in all 40 rats were colonized (median 2.54 × 103 cfu/cm2; range 5.0 × 101 – 1.0 × 106 cfu/cm2) and peritoneal washings were consistently culture-positive. In contrast, the LCH coupons removed after 7 days from the 40 test rats were sterile, as were the peritoneal washings, and there was no evidence of peritonitis. Blood cultures were negative in both groups.

Conclusions

Liposomal ciprofloxacin hydrogel-coated silicone resists colonization in this rat model of persistent P. aeruginosa peritonitis.

Inhibition of Caspases Improves Bacterial Clearance in Experimental Peritonitis

Background

Inhibition of caspases improves the antibacterial capacity of leukocytes cultured with peritoneal dialysis solutions, and improves the prognosis of septic, polymicrobial experimental peritonitis.

Objective

To test whether inhibition of caspases alters the evolution of peritonitis in the presence of peritoneal dialysis solution.

Design

32 mice were assigned to therapy with either the pan-caspase inhibitor zVAD or vehicle for 48 hours following infection with Staphylococcus aureus, in the presence of lactate-buffered, 4.25% glucose peritoneal dialysis solution. 16 mice received vehicle in phosphate-buffered saline.

Main Outcome Measure

Number of bacteria recovered from the peritoneum at 48 hours.

Results

Peritoneal dialysis solution accelerated leukocyte apoptosis. zVAD decreased the number of apoptotic peritoneal leukocytes and the number of bacteria recovered from the peritoneum at 48 hours (zVAD 2.8 ± 0.3 vs vehicle 3.9 ± 0.2 log colony forming units of S. aureus, p = 0.007).

Conclusions

Inhibition of caspases accelerates peritoneal bacterial clearance in the presence of peritoneal dialysis solutions in vivo in the experimental setting. Inhibition of caspases should be explored as a mean to accelerate recovery following peritonitis in the clinical setting.

Alpha-2-Macroglobulin and Albumin are Useful Serum Proteins to Detect Subclinical Peritonitis in the Rat

Background

In experimental peritoneal dialysis (PD) studies, the occurrence of peritonitis is a confounder in the interpretation of effects of chronic peritoneal exposure to dialysis solutions. Since fluid cannot be drained in most experimental PD models in the rat, it is impossible to diagnose peritonitis based on dialysate white blood cell counts. To study the value of serum markers for the presence of peritonitis, alpha-2-macroglobulin (α2M) and albumin were measured in rats with and without peritonitis after chronic exposure to dialysis solutions. To further investigate the time course of these markers in relation to the severity of peritonitis, nondialyzed rats were challenged with increasing numbers of bacteria and followed for 28 days.

Methods

In the first study, α2M and albumin were measured in rats exposed to glucose/lactate-based dialysis fluid before sacrifice. A comparison was made between animals with peritonitis, as judged from the presence of extensive infiltrates after sacrifice (gold standard) and/or clinical signs of peritonitis, or absence of peritonitis and infiltrates. In the second study, rats were intraperitoneally (IP) injected with 3 different concentrations of Staphylococcus aureus, and serum α2M and albumin were measured at various time points.

Results

In the first study, serum α2M was higher and serum albumin was lower in animals with peritonitis compared to animals without peritonitis (both p < 0.05). In the second study, induction of α2M was clearly dependent on the inoculum concentration. Peak values of α2M were found at days 1 and 3. At all time points after inoculation, α2M was higher in all injected groups compared to the control group. Serum albumin values decreased in the highest inoculum group and remained decreased until 28 days after IP injection. Despite a low sensitivity, serum α2M >40 mg/L and albumin <32 g/L had a specificity of 100% for peritonitis.

Conclusions

Measurement of α2M and albumin once per month is an additional tool in the diagnosis of silent peritonitis in the chronic peritoneal exposure model in the rat. Levels of α2M >40 mg/L and albumin <32 g/L are strong indicators for peritonitis. However, normal values do not exclude infectious peritonitis.

Comparison of intraperitoneal antithrombin III and heparin in experimental peritonitis

The antifibrotic effect of heparin, an anticoagulant used routinely in the treatment of peritonitis, is unknown, whereas antithrombin III (AT-III) has both anticoagulant and anti-inflammatory actions. The aim of this study was to compare the antifibrotic and anti-inflammatory effects of AT-III and heparin in rats with experimentally developed peritonitis while on peritoneal dialysis (PD). Sixty-four Wistar albino rats (in four groups of 16) were used in the study. Group 1 received PD solution only, group 2 had experimentally developed peritonitis in addition to PD solution; group 3 received heparin intraperitoneally for 3 days, in addition to group 2; and group 4 received AT-III intraperitoneally for 3 days, in addition to group 2. Plasma and dialysate levels of tissue-plasminogen activator were similar in heparin and AT-III groups on both day 3 and day 14. The inflammation scores of heparin and AT-III groups were also similar in both early and late phases. The fibrosis score of the AT-III group was low compared with both peritonitis and heparin groups in the early phase (p = 0.03), though it was similar in the late phase. The effects of AT-III are comparable with that of heparin in PD peritonitis in rats with experimentally developed peritonitis while on PD.

Dipyridamole inhibits human peritoneal mesothelial cell proliferation in vitro and attenuates rat peritoneal fibrosis in vivo

BACKGROUND

Peritoneal fibrosis (PF) is one of the most serious complications after long-term continuous ambulatory peritoneal dialysis (CAPD). Proliferation of human peritoneal mesothelial cells (HPMC) and matrix over-production are regarded as the main processes predisposing to PF. Dipyridamole (DP) has been reported to have potential as an antiproliferative and antifibrotic agent. We thus investigated the effect of DP in inhibiting proliferation and collagen synthesis of HPMC. A rat model of peritonitis-induced PF was also established to demonstrate the in vivo preventive effect of DP.

METHODS

HPMC was cultured from human omentum by an enzyme digestion

METHOD

Cell proliferation was measured by the methyltetrazolium assay. Intracellular cAMP was measured using an enzyme immunoassay (EIA) kit. Total collagen synthesis was measured by (3)H-proline incorporation assay. Expression of collagen alpha1 (I) and collagen alpha 1 (III) mRNAs was determined by Northern blotting. The rat model of peritonitis-induced PF was developed by adding dextran microbeads (Cytodex, 8 mg/1 mL volume) to a standardized suspension (3 x 10(9)) of Staphylococcus aureus. DP was administrated via intravenous infusion (4 mg in 1 h) daily for seven days. Macroscopic grading of intraperitoneal adhesions and histological analyses of peritoneal thickness and collagen expression were performed.

RESULTS

Addition of DP to HPMC cultures suppressed serum-stimulated cell proliferation and collagen synthesis. The antimitogenic and antifibrotic effects of DP appear to be predominantly mediated through the cAMP pathway, as DP increased intracellular cAMP in a dose-dependent manner. The macroscopic grade of intraperitoneal adhesion and peritoneal thickness were both significantly increased in animals treated with Cytodex plus S. aureus; on the other hand, DP attenuated these fibrotic changes with statistical significance (P < 0.01). Analysis of gene expression of collagen alpha 1 (I) and alpha1 (III) in the peritoneal tissue of experimental animals yielded similar results.

CONCLUSIONS

This study suggests that dipyridamole may have therapeutic potential in treating peritoneal fibrosis.

Peritoneal lymphatic absorption and solute exchange during zymosan-induced peritonitis in the rat

Lymph flow is elevated in most inflammatory conditions. However, a few previous studies have indicated that peritoneal lymph flow may actually fall during acute peritonitis. This study was performed to explore this issue further and to study the pathophysiology of peritoneal exchange during peritonitis. Therefore, we wanted to assess the total peritoneal clearance (Cl) and the clearance from peritoneum to plasma (Cl --> P) of 125I-labeled albumin (125I-albumin) as well as plasma-to-dialysate clearance (Cl --> D) of Evans blue-labeled albumin together with peritoneal ultrafiltration (UF) profiles and mass transfer area coefficients of 51Cr-EDTA and glucose in rats after acute peritonitis induced by zymosan. Zymosan incubation of the peritoneal cavity (120 mg) for 4 h generally led to a 4- to 10-fold increase in peritoneal fluid white blood cell count, indicating that acute peritonitis had been induced. Then 16 ml of 3.86% Dianeal and 125I-albumin were instilled intraperitoneally, whereas Evans blue-labeled albumin and 51Cr-EDTA were given as infusions intravenously. Compared with control, mass transfer area coefficients for glucose and 51Cr-EDTA increased markedly from 0.43 +/- 0.06 and 0.25 +/- 0.04 to 0.91 +/- 0.06 and 0.59 +/- 0.05 (SE) ml/min, respectively, during peritonitis, whereas Cl and Cl --> D increased from 32.8 +/- 5.6 and 8.6 +/- 1.6 to 74.5 +/- 7.3 and 12.9 +/- 1.0 microl/min, respectively. The UF profile in peritonitis indicated type I loss of UF (resulting from the increases in permeability-surface area product for glucose). However, the Cl --> P declined to 5.9 +/- 1.0 microl/min from 7.9 +/- 0.8 microl/min (P < 0.05) in control. In conclusion, despite marked effects on peritoneal solute transport and on UF, conceivably resulting from vasodilatation and increases in capillary permeability, zymosan-induced peritonitis did not cause any acute increases in direct peritoneal lymphatic absorption.

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.