Effects of intraperitoneal antibiotics on human peritoneal mesothelial cell growth

Antibiotics induce apoptosis of human peritoneal mesothelial cells

The peritoneal mesothelial cell is a critical component of the peritoneal membrane. The intraperitoneal use of several antibiotics to treat bacterial peritonitis is current clinical practice. Our previous study showed that cephalothin (CPL) and cefotaxime (CFT) have cytotoxic effects on human peritoneal mesothelial cells (HPMC), however, the exact mechanism of cytotoxicity has not been elucidated. In the present study, flow cytometry, TdT-mediated dUTP nick-end labelling (TUNEL) staining and electron microscopy were used to detect the apoptosis of HPMCs. Immunofluorescent staining was used to evaluate the cytochrome c distribution pattern. Western blotting was used to assess apoptotic signalling proteins. We found that CPL (0.5 mg/mL) and CFT (1 mg/mL) induced apoptosis of HPMCs, whereas cefazolin (0.5 mg/mL) and ceftriaxone (0.5 mg/mL) failed to induce apoptosis of HPMCs. While the DNA content of CFT- or CPL-treated cells was reduced, as determined by flow cytometry, cefazolin and ceftriaxone had no such effect. The CFT- or CPL-treated cells displayed the features of apoptosis both under the electron microscope and by using TUNEL staining. However, cefazolin and ceftriaxone produced the same result as the medium controls. Furthermore, CFT and CPL increased the expression of Bax and p53, and caused the translocation of cytochrome c from the mitochondria to the cytoplasm. The HPMC treated by CFT but not by CPL induced the cleavage of procaspase-3 to form active caspase-3. In conclusion, cefotaxime and cephalothin induce apoptosis of HPMCs in vitro. Signal transduction may be through the mitochondrial pathway.

Intraperitoneal cefazolin and ceftazidime effects on human peritoneal mesothelial cell release of cancer antigen-125

BACKGROUND

Intraperitoneal (IP) cefazolin and ceftazidime are recommended as empiric treatment for peritoneal dialysis (PD)-associated peritonitis. Human peritoneal mesothelial cells (HPMCs) may be affected by high IP cefazolin and ceftazidime concentrations. Peritoneal dialysate cancer antigen-125 (CA-125) appearance rate can be used to measure HPMC damage.

OBJECTIVE

To determine whether IP cefazolin and ceftazidime increase peritoneal CA-125 appearance rate.

METHODS

The study consisted of 2 phases. In phase I, no antibiotic was administered, and in phase II, patients received IP cefazolin and ceftazidime (15 mg/kg rounded to nearest 100 mg). Phase II occurred immediately after phase I. Each phase used a 4-hour dwell time with 2 L of dextrose 2.5% dialysate. Dialysate samples were collected at 0, 0.5, 1, 2, and 4 hours during each phase. Samples were assayed for CA-125, and CA-125 appearance rate was calculated.

RESULTS

Thirteen patients were recruited (7 men; aged 44.0 +/-16.0 y). The mean +/- SD (range) CA-125 dialysate concentration after phases I and II were 6.6 +/- 3.7 U/mL (2.3-15.0) and 6.4 +/-3.8 U/mL (1.6-13.8), respectively (p = 0.46). The CA-125 appearance rate after phases I and II were 51.9 +/- 31.3 U/min/1.73 m(2) (13.8-113.0) and 50.5 +/- 32.9 U/min/1.73 m(2) (11.0-104.0), respectively (p = 0.57). The slopes of the regression lines of CA-125 appearance rate were not significantly different between phases I and II.

CONCLUSIONS

These findings demonstrate that concurrently administered IP cefazolin and ceftazidime have no effect on HPMC release of CA-125 in non-infected PD patients.

Mesothelial progenitor cells and their potential in tissue engineering

The mesothelium consists of a single layer of flattened mesothelial cells that lines serosal cavities and the majority of internal organs, playing important roles in maintaining normal serosal integrity and function. A mesothelial 'stem' cell has not been identified, but evidence from numerous studies suggests that a progenitor mesothelial cell exists. Although mesothelial cells are of a mesodermal origin, they express characteristics of both epithelial and mesenchymal phenotypes. In addition, following injury, new mesothelium regenerates via centripetal ingrowth of cells from the wound edge and from a free-floating population of cells present in the serosal fluid, the origin of which is currently unknown. Recent findings have shown that mesothelial cells can undergo an epithelial to mesenchymal transition, and transform into myofibroblasts and possibly smooth muscle cells, suggesting plasticity in nature. Further evidence for a mesothelial progenitor comes from tissue engineering applications where mesothelial cells seeded onto tubular constructs have been used to generate vascular replacements and grafts to bridge transected nerve fibres. These findings suggest that mesothelial cell progenitors are able to switch between different cell phenotypes depending on the local environment. However, only by performing detailed investigations involving selective cell isolation, clonal analysis together with cell labelling and tracking studies, will we begin to determine the true existence of a mesothelial stem cell.

Antibiotic Administration in an Animal Model of Chronic Peritoneal Dialysate Exposure

♦ Objectives

The high incidence of intraperitoneal infection remains an important problem in animal models of chronic dialysate exposure. Prophylactic antibiotic administration can be used to resolve this problem, but the isolated effects of antibiotics on peritoneal membrane function and structure are unknown. The present study examined the effects of prophylactic antibiotics on infection rate and peritoneal membrane function and structure in a rat model of chronic dialysate exposure.

♦ Design

A first group of rats (A; n = 12) received 10 mL 3.86% glucose dialysate twice daily through a heparin-coated catheter. In a second group of animals (B; n = 12), oxacillin 2.5 mg/day and gentamicin 0.04 mg/day were added to the dialysate. Group C ( n= 12) was injected twice daily with an identical dose of antibiotics dissolved in 1 mL of buffer solution. Group D ( n = 12) was left untreated. Dialysate cultures were obtained regularly. After 8 weeks of exposure, peritoneal transport studies were performed and samples for histology were obtained.

♦ Results

Technique survival was 92% in group A and 100% in the remaining groups. Five rats in group A but none of the animals in the other groups developed peritonitis. The transport rates of small solutes were elevated and net ultrafiltration was decreased in group A compared to the controls. Fibrosis, as evaluated by quantifying Picro Sirius Red staining with image analysis, was significantly elevated in group A (3.48% ± 1.06% vs 0.72% ± 0.51% in group D, p < 0.05) but not in group B (0.29% ± 0.07%) or in group C (0.52% ± 0.28%). Vascular density, measured by counting the number of blood vessels that stained positive for endothelial NO synthase, was increased in both groups that were exposed to dialysate: 153.0 ± 12.9/μm2 in group A and 131.6 ± 14.3/μm2 in group B, versus 76.76 ± 12.37/μm2 in group C and 73.2 ± 10.4/μm2 in group D ( p < 0.01).

♦ Conclusions

Prophylactic administration of oxacillin and gentamicin adequately prevented intraperitoneal infection in an animal model of chronic dialysate exposure. In addition, fibrosis was absent, suggesting intra-peritoneal infection rather than dialysate exposure is a causative factor.