Role of peritoneal mesothelial cells in peritonitis

CXCL8 and the peritoneal metastasis of ovarian and gastric cancer

CXCL8 is the most representative chemokine produced autocrine or paracrine by tumor cells, endothelial cells and lymphocytes. It can play a key role in normal tissues and tumors by activating PI3K-Akt, PLC, JAK-STAT, and other signaling pathways after combining with CXCR1/2. The incidence of peritoneal metastasis in ovarian and gastric cancer is extremely high. The structure of the peritoneum and various peritoneal-related cells supports the peritoneal metastasis of cancers, which readily produces a poor prognosis, low 5-year survival rate, and the death of patients. Studies show that CXCL8 is excessively secreted in a variety of cancers. Thus, this paper will further elaborate on the mechanism of CXCL8 and the peritoneal metastasis of ovarian and gastric cancer to provide a theoretical basis for the proposal of new methods for the prevention, diagnosis, and treatment of cancer peritoneal metastasis.

Long-term peritoneal dialysate exposure modulates expression of membrane complement regulators in human peritoneal mesothelial cells

The membrane complement regulators (CRegs) CD46, CD55, and CD59 are highly expressed on human peritoneal mesothelial cells. However, how mesothelial CRegs change according to the peritoneal dialysis (PD) history of patients has remained unclear. We therefore examined longitudinal changes in CRegs in primary cultured mesothelial cells from PD patients (human peritoneal mesothelial cells; HPMCs) and examined which components of PD fluid (PDF) affect CRegs in vitro. We measured levels of soluble C5b-9 in overnight-dwelling PDF in PD patients and also evaluated changes in CRegs expression on HPMCs collected from PDF using flow cytometry and polymerase chain reaction at a 1-year interval of PD therapy. We also evaluated changes in CReg expressions with stimulation by each component of PDF (glucose, lactic acid and pH) using the Met5A human mesothelial cell line. Levels of sC5b-9 in PDF decreased significantly during 1 year, while expressions of CD46 and CD59 proteins and mRNAs increased significantly in HPMCs during 1 year. Analyzing Met-5A cells, we observed that expressions of the three CRegs were increased by glucose and lactic acid in a concentration-dependent manner, but conversely that expressions of CRegs were decreased by lower pH stimulation. History of PD might influence expression of CRegs by HPMCs through properties of PDF such as glucose, lactic acid, and pH. These results suggest that mesothelial cells may alter expression of CRegs for the purpose of protecting the peritoneum and the presence of PDF might affect peritoneal homeostasis associated with the complement system.

Immune Resolution Dilemma: Host Antimicrobial Factor S100A8/A9 Modulates Inflammatory Collateral Tissue Damage During Disseminated Fungal Peritonitis

Intra-abdominal infection (peritonitis) is a leading cause of severe disease in surgical intensive care units, as over 70% of patients diagnosed with peritonitis develop septic shock. A critical role of the immune system is to return to homeostasis after combating infection. S100A8/A9 (calprotectin) is an antimicrobial and pro-inflammatory protein complex used as a biomarker for diagnosis of numerous inflammatory disorders. Here we describe the role of S100A8/A9 in inflammatory collateral tissue damage (ICTD). Using a mouse model of disseminated intra-abdominal candidiasis (IAC) in wild-type and S100A8/A9-deficient mice in the presence or absence of S100A9 inhibitor paquinimod, the role of S100A8/A9 during ICTD and fungal clearance were investigated. S100A8/A9-deficient mice developed less ICTD than wild-type mice. Restoration of S100A8/A9 in knockout mice by injection of recombinant protein resulted in increased ICTD and fungal clearance comparable to wild-type levels. Treatment with paquinimod abolished ICTD and S100A9-deficient mice showed increased survival compared to wild-type littermates. The data indicates that S100A8/A9 controls ICTD levels and antimicrobial activity during IAC and that targeting of S100A8/A9 could serve as promising adjunct therapy against this challenging disease.

Mesothelial morphology and organisation after peritoneal treatment with solid and liquid adhesion barriers--a scanning electron microscopical study

Separation of traumatized tissue represents the only promising strategy in postoperative adhesion prevention, a relevant clinical problem after surgical intervention. In the present study scanning electron microscopy (SEM) and subsequent morphometry were used to analyse the tissue response to five commercial adhesion barriers. Standardised peritoneal lesions in Wistar rats were covered with solid and viscous barrier materials and semiquantitatively analysed 14 days postoperatively. Striking morphological differences in lesion surface organisation between the barrier groups became apparent with colonisation of the barrier by mesothelial cells to different degrees. Furthermore, the mesothelial cells showed either a normal or activated phenotype depending on the underlying biomaterial. These experiments demonstrate that the examination by SEM gives useful insights into the performance of barrier materials and the cellular processes of adhesion prevention, since mesothelial cells play an active role in the pathogenesis of adhesion formation.

Current strategies and future perspectives for intraperitoneal adhesion prevention

INTRODUCTION

The formation of peritoneal adhesions still is a relevant clinical problem after abdominal surgery. Until today, the most important clinical strategies for adhesion prevention are accurate surgical technique and the physical separation of traumatized serosal areas. Despite a variety of barriers which are available in clinical use, the optimal material has not yet been found.

DISCUSSION

Mesothelial cells play a crucial physiological role in friction less gliding of the serosa and the maintenance of anantiadhesive surface. The formation of postoperative adhesions results from a cascade of events and is regulated by various cellular and humoral factors. Therefore, optimization or functionalization of barrier materials by developments interacting with this cascade on a structural or pharmacological level could give an innovative input for future strategies in peritoneal adhesion prevention. For this purpose, the proper understanding of the formal pathogenesis of adhesion formation is essential. Based on the physiology of the serosa and the pathophysiology of adhesion formation, the available barriers in current clinical practice as well as new innovations are discussed in the present review.

Intraperitoneal adhesions--an ongoing challenge between biomedical engineering and the life sciences

Peritoneal adhesions remain a relevant clinical problem despite the currently available prophylactic barrier materials. So far, the physical separation of traumatized serosa areas using barriers represents the most important clinical strategy for adhesion prevention. However, the optimal material has not yet been found. Further optimization or pharmacological functionalization of these barriers could give an innovative input for peritoneal adhesion prevention. Therefore, a more complete understanding of pathogenesis is required. On the basis of the pathophysiology of adhesion formation the main barriers currently in clinical practice as well as new innovations are discussed in the present review. Physiologically, mesothelial cells play a decisive role in providing a frictionless gliding surface on the serosa. Adhesion formation results from a cascade of events and is regulated by a variety of cellular and humoral factors. The main clinically applied strategy for adhesion prevention is based on the use of liquid or solid adhesion barriers to separate physically any denuded tissue. Both animal and human trials have not yet been able to identify the optimal barrier to prevent adhesion formation in a sustainable way. Therefore, further developments are required for effective prevention of postoperative adhesion formation. To reach this goal the combination of structural modification and pharmacological functionalization of barrier materials should be addressed. Achieving this aim requires the interaction between basic research, materials science and clinical expertise.

Peritoneal damage: the inflammatory response and clinical implications of the neuro-immuno-humoral axis

BACKGROUND

The peritoneum is a bilayer serous membrane that lines the abdominal cavity. We present a review of peritoneal structure and physiology, with a focus on the peritoneal inflammatory response to surgical injury and its clinical implications.

METHODS

We conducted a nonsystematic clinical review. A search of the Ovid MEDLINE database from 1950 through January 2009 was performed using the following search terms: peritoneum, adhesions, cytokine, inflammation, and surgery.

RESULTS

The peritoneum is a metabolically active organ, responding to insult through a complex array of immunologic and inflammatory cascades. This response increases with the duration and extent of injury and is central to the concept of surgical stress, manifesting via a combination of systemic effects, and local neural pathways via the neuro-immuno-humoral axis. There may be a decreased systemic inflammatory response after minimally invasive surgery; however, it is unclear whether this is due to a reduced local peritoneal reaction.

CONCLUSIONS

Interventions that dampen the peritoneal response and/or block the neuro-immuno-humoral pathway should be further investigated as possible avenues of enhancing recovery after surgery, and reducing postoperative complications.

Regulation of adenosine system at the onset of peritonitis

BACKGROUND

Adenosine, a potent regulator of inflammation, is produced under stressful conditions due to degradation of ATP/ADP by the ectoenzymes CD39 and CD73. Adenosine is rapidly degraded by adenosine deaminase (ADA) or phosphorylated in the cell by adenosine kinase (AK). From four known receptors to adenosine, A(1) (A(1)R) promotes inflammation by a G(i)-coupled receptor. We have previously shown that A(1)R is up-regulated in the first hours following bacterial inoculation. The aim of the current study is to characterize the inflammatory mediators that regulate adenosine-metabolizing enzymes and A(1)R at the onset of peritonitis.

METHODS

Peritonitis was induced in CD1 mice by intraperitoneal injection of Escherichia coli. TNFalpha and IL-6 levels were determined in peritoneal fluid by enzyme-linked immunosorbent assay. Adenosine-metabolizing enzymes and the A(1)R mRNA or protein levels were analyzed by quantitative PCR or by Western blot analysis, respectively.

RESULTS

We found that CD39 and CD73 were up-regulated in response to bacterial stimuli (6-fold the basal levels), while AK and ADA mRNA levels were down-regulated. Cytokine production and leukocyte recruitment were enhanced (2.5-fold) by treatment with an A(1)R agonist (2-chloro-N(6)-cyclopentyladenosine, 0.1 mg/kg) and reduced (2.5-3-fold) by the A(1)R antagonist (8-cyclopentyl-1, 3-dipropylxanthine, 1 mg/kg). In contrast to lipopolysaccharide, IL-1, TNF and IFNgamma, only low IL-6 levels (0.01 ng/ml), in the presence of its soluble IL-6R (sIL-6R), were found to promote A(1)R expression on mesothelial cells. In mice, administration of neutralizing antibody to IL-6R or soluble gp130-Fc (sgp130-Fc) blocked peritoneal A(1)R up-regulation following inoculation.

CONCLUSION

Bacterial products induce the production of adenosine by up-regulation of CD39 and CD73. Low IL-6-sIL-6R up-regulates the A(1)R to promote efficient inflammatory response against invading microorganisms.

A mesothelial-lined cyst: an unusual presentation

A 12-year-old girl presented with a "threadlike fiber" in her underwear associated with lower abdominal pain. She denied insertion of any foreign body, and at examination under anesthetic, a threadlike substance was seen exiting her external cervical os. Her only medical history was of an open appendicectomy for perforated appendicitis. Subsequent pathologic examination showed a collapsed mesothelial cyst, and laparoscopy showed a cyst and inflammatory changes consistent with previous appendicectomy surrounding her right ovary. We review the possible causes for this most unusual presentation.

Intercellular adhesion molecule-1 and gelatinase expression in human peritoneal mesothelial cells during propagation in culture

Mesothelial cells are involved in a variety of biological processes, which include the formation of peritoneal adhesions. The cultures of human peritoneal mesothelial cells comprise an important tool to investigate the behavior and functions of mesothelial cells. Very little is known about the differences among mesothelial cells isolated from different sources and about the changes in specific functions as caused by cell propagation in vitro or that result from storage of cells at low temperatures. This study aims to characterize 2 particular cellular activities relevant for tissue repair, which include the expression of intercellular adhesion molecule-1 (ICAM-1) and the gelatinase activity; in addition, this study will assess the effect of hyaluronan, which is an antiadhesive agent, on these cellular activities. Viable cell lines were established from both omentum and peritoneal lavage fluid from 7 patients. Both ICAM-1 expression, which was measured by enzyme-linked immunosorbent assay (ELISA), and matrix metalloproteinase (MMP) bioactivity, which was measured by zymography, were measured in the 2nd and 4th passage; the latter also was measured after freezing and storing of cells in liquid nitrogen. The effects of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), phorbol myristate acetate (PMA), and hyaluronan were analyzed. ICAM-1 was constitutively expressed and stimulated by IL-1beta, TNF-alpha, and PMA. All cell lines produced both MMP-2 and MMP-9. Only the latter activity was affected by TNF-alpha and, especially so, PMA. Differences were found between the 2nd and 4th passage, as well as between cells of different lineage, mostly so if the relative stimulation by the various agents was compared. The addition of sodium hyaluronate either to control cultures or to cultures together with any of the 3 stimuli examined did not significantly change either ICAM-1 expression or gelatinase activity. The freezing and storage of cells did not affect their functions. Both the human omentum and peritoneal lavage fluid are good sources to establish mesothelial cell lines, which can be propagated also after freezing without qualitative changes in their ability to express ICAM-1 and produce the gelatinases. For omental cells, a differential effect of stimulation occurs depending on whether the cells have been passaged 2 or 4 times. The presence of hyaluronan did not affect the expression of ICAM-1 or the gelatinases.

Human peritoneal fibroblasts are a potent source of neutrophil-targeting cytokines: a key role of IL-1beta stimulation

Polymorphonuclear leukocyte (PMN) infiltration is a cardinal feature of peritonitis. CXC chemokine ligands 1 and 8 (CXCL1 and CXCL8), and the cytokine granulocyte colony-stimulating factor (G-CSF) are the key mediators of PMN accumulation. Increasing evidence points to an important role of human peritoneal fibroblasts (HPFB) in the response of the peritoneum to infection. We have examined the synthesis of PMN-targeting cytokines by HPFB exposed to intraperitoneal milieu as represented by peritoneal dialysate effluent (PDE) from patients undergoing peritoneal dialysis. PDE obtained during peritonitis, but not during infection-free periods, significantly increased production of CXCL1, CXCL8, and G-CSF by HPFB. The effect was largely blocked by antibodies to interleukin-1beta (IL-1beta), whereas neutralization of tumor necrosis factor-alpha (TNFalpha) had no major effect. Similar pattern of inhibition was observed when HPFB were exposed to conditioned media from endotoxin-stimulated peritoneal macrophages. Significance of IL-1beta stimulation was further shown in experiments with recombinant cytokines. Compared with TNFalpha, exposure of HPFB to recombinant IL-1beta resulted in a much higher release of PMN-targeting cytokines. The assessment of mRNA degradation revealed that the IL-1beta-induced transcripts of CXCL1, CXCL8, and G-CSF were more stable compared with those induced by TNFalpha. These data indicate that HPFB can be a significant source of PMN-targeting cytokines when stimulated with IL-1beta in the inflamed peritoneum.

Tumor-infiltrating lymphocytes and perforation in colon cancer predict positive response to 5-fluorouracil chemotherapy

PURPOSE

The major pathologic markers of prognosis in colorectal cancer include vascular invasion by tumor cells, invasion of adjacent lymph nodes, and perforation of the serosal wall. Recent work suggests that a high density of tumor-infiltrating lymphocytes (TIL) is associated with good outcome independently of these established prognostic markers. The aim of the present study was to investigate the prognostic significance of TILs and other routinely reported pathologic features in colon cancer, particularly in relation to the use of adjuvant chemotherapy.

EXPERIMENTAL DESIGN

Pathologic markers, disease-specific survival, and the use of adjuvant chemotherapy were recorded in a retrospective, population-based series of 1,156 stage III colon cancer patients with a median follow-up time of 52 months.

RESULTS

In patients treated by surgery alone (n = 851), markers with significant prognostic value included poor histologic grade, T4 stage, N2 nodal status, vascular invasion, and perforation, but not the presence of TILs. In patients treated with 5-fluorouracil-based chemotherapy (n = 305), TILs were associated with significantly improved survival [hazard ratio (HR), 0.52; 95% confidence interval, 0.30-0.91; P = 0.02] and perforation with a trend for improved survival (HR, 0.67; 95% confidence interval, 0.27-1.05; P = 0.16). Patients with TILs or perforation seemed to gain more survival benefit from chemotherapy (HR, 0.22 and 0.21, respectively) than patients without these features (HR, 0.84 and 0.82, respectively).

CONCLUSION

The apparent survival advantage from 5-fluorouracil associated with TILs and perforation requires confirmation in prospective studies. Because the presence of TILs reflects an adaptive immune response and perforation is associated with inflammatory response, these results suggest that there may be interactions between the immune system and chemotherapy leading to improved survival of colon cancer patients.

Intracavitary radioimmunotherapy to treat solid tumors

Radioimmunotherapy (RIT) potentially is an attractive treatment for radiosensitive early-stage solid tumors and as an adjuvant to cytoreductive surgery. Topical administration of RIT may improve the efficacy because higher local concentrations are achieved. We reviewed the results of locally applied radiolabeled monoclonal antibodies for the treatment of solid tumors. Intracavitary RIT in patients with ovarian cancer and glioma showed improved targeting after local administration, as compared to the intravenous administration. In addition, various studies showed the feasibility of locally applied RIT in these patients. In studies that included patients with small-volume disease, adjuvant RIT in ovarian cancer and glioma showed to be at least as effective as standard therapy. The information about RIT for peritoneal carcinomatosis of colorectal origin is scarce, while results from preclinical data are promising. RIT may be applied for other, relatively unexplored indications. Studies on the application of radiolabeled antibodies in early urothelial cell cancer have been performed, showing that intracavitary RIT may hold a promise. Moreover, in patients with malignant pleural mesothelioma or malignant pleural effusion, RIT may play a role in the palliative treatment. Intracavitary RIT limits toxicity and improves tumor targeting. RIT is more effective in patients with small-volume disease of solid cancers. RIT may have potential for palliation in patients with malignant pleural mesothelioma or malignant pleural effusion. The future of RIT may, therefore, not only be in the inclusion in contemporary multimodality treatment, but also in the expansion to palliative treatment.

Adenoviral-mediated gene expression of hepatocyte growth factor prevents postoperative peritoneal adhesion in a rat model

BACKGROUND

Mesothelial cell proliferation and migration play important roles in reducing formation of postoperative peritoneal adhesions. Hepatocyte growth factor (HGF) is a multifunctional cytokine that stimulates proliferation and migration of various cell types, including mesothelial cells.

METHODS

We investigated the effect of adenovirus-mediated HGF gene expression on the proliferation and migration of mesothelial cells and evaluated its preventive effects on postoperative formation of peritoneal adhesions. Rat mesothelial cells were isolated and characterized by expression of cytokeratin and vimentin.

RESULTS

Immunohistochemical staining showed that these cells expressed c-Met, the receptor for HGF. Adenoviral-mediated HGF gene transfer into mesothelial cells resulted in high expression of HGF and enhanced migration. To evaluate the preventive effects of adenoviral-mediated HGF gene transfer on the formation of postoperative peritoneal adhesion, we employed a rat model of cecum abrasion-induced adhesion formation in which 80% of the rats developed postoperative peritoneal adhesions. Local application of recombinant adenovirus carrying the HGF gene reduced adhesion formation in 16 of 20 control rats compared with 7 of 20 treated rats in this model.

CONCLUSIONS

These results suggest that adenoviral-mediated HGF gene transfer may be a novel strategy for preventing postoperative peritoneal adhesions.

Staphylococcus aureus induces caspase-independent cell death in human peritoneal mesothelial cells

Bacterial peritonitis remains a serious complication of peritoneal dialysis. Although Staphylococcus epidermidis is the most common pathogen involved, infections with Staphylococcus aureus lead to severe peritoneal damage and are often associated with a dramatic loss of mesothelial cells. Induction of cell death appears to be involved in peritoneal damage and mesothelial cell loss during bacterial infections. Using cultured human peritoneal mesothelial cells (HMCs), we investigated the ability of different S. epidermidis and S. aureus strains to damage the HMC monolayer and to trigger cell death. We show that only a subgroup of live S. aureus isolates, characterized by an invasive and alpha-hemolysin-producing phenotype, induces cell death. None of the tested S. epidermidis strains, which were not invasive or hemolytic, had a cytotoxic effect. After host cell invasion, S. aureus resided within phagocytic vacuoles, and HMCs were apparently able to degrade staphylococci. However, even after prolonged infection, a high percentage of S. aureus remained alive within HMCs and might be released after host cell death. Cell death induced by S. aureus was accompanied by apoptotic alterations, such as DNA fragmentation, but was independent of endogenous FasL and tumor necrosis factor-alpha death ligand expression. Moreover, caspases were not involved in S. aureus-induced mesothelial cell death. In conclusion, our data indicate that mesothelial cell death might represent a major mechanism of S. aureus-induced damage of the peritoneum during bacterial peritonitis.

Adenosine is upregulated during peritonitis and is involved in downregulation of inflammation

Loss of function of the peritoneal membrane is associated with peritonitis. Adenosine levels in sites of inflammation were shown to increase and exhibit immunoregulatory effects. Our aim was to elucidate the regulatory role of adenosine during peritonitis and to test the involvement of peritoneal mesothelial cells (PMC) in adenosine regulation. In a mice model of Escherichia coli peritonitis, the adenosine A(2A) receptor (A(2A)R) agonist (CGS21680) prevented leukocyte recruitment and reduced tumor necrosis factor alpha (TNF-alpha) and interleukin-6 (IL-6) levels. Peritonitis induced the elevation of adenosine with a peak at 24 h. Analysis of adenosine receptor levels on peritoneum showed that A(1) receptor (A(1)R) protein levels peak at 12 h after inoculation and then return to baseline at 24 h, whereas high affinity A(2A)R protein levels peak at 24 h concomitantly with the peak of adenosine concentration. Low affinity A(2B) receptor (A(2B)R) levels elevated slowly, remaining elevated up to 48 h. In human PMC (HPMC), the early cytokines, IL-1-alpha, and TNF-alpha upregulated the A(2B) and A(2A) receptors. However, interferon-gamma (IFN-gamma) upregulated the A(2B)R and decreased A(2A)R levels. Treatment with the A(2A)R agonist reduced IL-1-dependent IL-6 secretion from HPMC. In conclusion, the kinetics of adenosine receptors suggest that at early stage of peritonitis, the A(1)R dominates, and later its dominance is replaced by the G stimulatory (Gs) protein-coupled A(2A)R that suppresses inflammation. Early proinflammatory cytokines are an inducer of the A(2A)R and this receptor reduces their production and leukocyte recruitment. Future treatment with adenosine agonists should be considered for attenuating the damage to mesothelium during the course of acute peritonitis.

The peritoneal cavity is a distinct compartment of angiogenic molecular mediators

OBJECTIVE

This study was designed to analyze porcine plasma and peritoneal fluid for concentration differences of angiogenic molecular mediators and to determine local peritoneal sites of production of these molecules.

BACKGROUND

The peritoneum is now recognized as a dynamic cellular membrane with important functions, including antigen presentation; transport and movement of fluid, solutes, and particulate matter across serosal cavities; and secretion of glycosaminoglycans, extracellular matrix proteins, proinflammatory cytokines, and growth factors. The mechanisms of the peritoneal response to injury and the factors that determine the outcome of the reactive or reparative processes of the peritoneum remain poorly defined.

METHODS

Domestic swine (n = 12) underwent percutaneous diagnostic peritoneal lavage to obtain preincision peritoneal fluid for biochemical analysis. Open biopsy samples of parietal peritoneum and omentum were obtained for immunochemical and molecular analysis. Vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) levels were quantitated by enzyme-linked immunosorbent assay, and nitrite/nitrate (NOx) measured by nonenzymatic assay. Sections of formalin-fixed tissue were stained for immunoreactivity to VEGF, bFGF, and nitric oxide synthase (NOS). Frozen homogenized peritoneum and omentum were prepared for isolation of protein and RNA. An endothelial growth assay was created using human umbilical vein endothelial cells cultured with peritoneal fluid with or without anti-VEGF or anti-bFGF antibodies.

RESULTS

The mean plasma concentrations of VEGF, bFGF, and NOx were 20 +/- 5 pg/mL, 35 +/- 9 pg/mL, and 4.5 +/- 1.3 microm, compared with mean peritoneal fluid concentrations of 395 +/- 75 pg/mL, 486 +/- 72 pg/mL, and 35.0 +/- 8.8 mum respectively (P < 0.05 for each molecule). Immunochemistry demonstrated VEGF, bFGF, and NOS protein in mesothelium, submesothelium, and omentum. The use of Western blotting and reverse transcription polymerase chain reaction confirmed peritoneal and omental presence of VEGF and NOS-2. The use of endothelial bioassay documented peritoneal fluid angiogenic activity, which was inhibited by addition of neutralizing antibody to VEGF or bFGF.

CONCLUSION

Peritoneal compartmentalization of angiogenic mediators important in wound healing, inflammation, and tumor growth suggests that the plasma concentrations of these mediators do not reflect their tissue concentrations or local biological activity.

Amadori adducts activate nuclear factor-kappaB-related proinflammatory genes in cultured human peritoneal mesothelial cells

Diabetes mellitus leads to a high incidence of several so-called complications, sharing similar pathophysiological features in several territories. Previous reports points at early nonenzymatic glycosylation products (Amadori adducts) as mediators of diabetic vascular complications. In the present study, we analysed a possible role for Amadori adducts as stimulators of proinflammatory pathways in human peritoneal mesothelial cells (HPMCs). Cultured HPMCs isolated from 13 different patients (mean age 38.7+/-16 years) were exposed to different Amadori adducts, that is, highly glycated haemoglobin (10 nM) and glycated bovine serum albumin (0.25 mg ml(-1)), as well as to their respective low glycosylation controls. Amadori adducts, but not their respective controls, elicited a marked increase of NF-kappaB activation, as determined by electromobility shift assays and transient transfection experiments. Additionally, Amadori adducts significantly increased the production of NF-kappaB-related proinflammatory molecules, including cytokines, such as TNF-alpha, IL-1beta or IL-6, and enzymes, such as cyclooxygenase-2 and inducible nitric oxide (NO) synthase, this latter leading to the release of NO by HPMCs. The effects of Amadori adducts were mediated by different reactive oxygen and nitrosative species (e.g. superoxide anions, hydroxyl radicals, and peroxynitrite), as they were blunted by coincubation with the appropriate scavengers. Furthermore, NO generated upon exposure to Amadori adducts further stimulated NF-kappaB activation, either directly or after combination with superoxide anions to form peroxynitrite. We conclude that Amadori adducts can favour peritoneal inflammation by exacerbating changes in NO synthesis pathway and triggering NF-kappaB-related proinflammatory signals in human mesothelial cells.

Peritoneal mesothelial cells produce inflammatory related cytokines

BACKGROUND

Peritonitis involves cascading interactions between cytokines that initiate robust signalling processes via the interferon-g and nuclear factor kappa B pathways. The present study evaluates the interplay between various putative inducers of peritonitis and a battery of inflammation-related cytokines.

METHODS

Cultures of peritoneal mesothelial cells were isolated from omenta harvested from male Wistar rats. These cultures were exposed to tumour necrosis factor (TNF)-alpha, lipopolysaccharide, zymosan, myeloperoxidase, peritoneal fluid from rats with zymosan-induced peritonitis, and peritoneal fluid from control animals. The production of TNF-alpha, interleukin (IL)-1beta, IL-6, and IL-10 was assessed after 4, 12 and 24 h.

RESULTS

Lipopolysaccharide and zymosan stimulated TNF-alpha, IL-1beta, and IL-10 production; and peritoneal fluids from both control animals and animals with zymosan-induced peritonitis stimulated the production of TNF-alpha, IL-1RII, and IL-6. Expression and secretion of TNF-alpha occurred in a constitutive manner and was regulation at the protein level. The decoy molecule IL-1 receptor type II (IL-1RII) was produced at the same time as IL-1beta and production of the anti-inflammatory cytokine IL-10 was evident within 4 h. IL-6 was constitutively expressed and regulated at the transcriptional level as indicated by a marked discontinuity between the amount of IL-6 produced and the extent IL-6 messenger ribonucleic acid (mRNA) expression.

CONCLUSIONS

Tumour necrosis factor-alpha might not be the sole primary mediator of peritonitis. The anti-inflammatory molecules IL-1RII and IL-10 are induced at the same time as the pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6. This suggests that complex control systems are set in place by the factors that stimulate peritoneal mesothelial cells and might have the potential to cause peritonitis.

Lavage enhances the production of proinflammatory mediators by peritoneal mesothelial cells in an experimental model

PURPOSE

There is a lack of clinical evidence supporting the use of lavage in patients with peritonitis. It is known that fluids such as normal saline cause temporary damage to the peritoneum and that increased production of proinflammatory mediators is associated with a poor outcome. This study used an experimental model to evaluate the effect of lavage on the peritoneal mesothelium and the ability of peritoneal mesothelial cells to produce a battery of proinflammatory mediators (TNFalpha, IL-1beta, GROalpha, and ICAM-I.).

METHODS

Wistar rats were allocated into four groups (control, peritonitis, lavage, peritonitis plus lavage). Peritonitis was induced by exposure to zymosan and saline was used for lavage. After 18, 24, and 43 hours, mesothelial imprints were taken from the peritoneum for histology, semiquantitative reverse transcription-polymerase chain reaction, Western blot analyses, and immunocytochemistry.

RESULTS

Both peritonitis and lavage caused peritoneal damage at 18 and 24 hours, and this effect was additive. At varying times, peritoneal mesothelial cells from animals undergoing lavage had greater up-regulation (P < 0.05) of mRNA expression for TNFalpha, IL-1beta, GROalpha, and ICAM-I and greater production (P < 0.05) of TNFalpha, IL-1RII, GROalpha, and ICAM-I. The latter was heavily concentrated at the cell membrane.

CONCLUSIONS

Lavage causes self-limiting peritoneal damage and this is associated with an up-regulation of proinflammatory mediators in animals with peritonitis.