Evidence for incorporation of free-floating mesothelial cells as a mechanism of serosal healing

Mesothelial cell differentiation into osteoblast- and adipocyte-like cells

Serosal pathologies including malignant mesothelioma (MM) can show features of osseous and/or cartilaginous differentiation although the mechanism for its formation is unknown. Mesothelial cells have the capacity to differentiate into cells with myofibroblast, smooth muscle and endothelial cell characteristics. Whether they can differentiate into other cell types is unclear. This study tests the hypothesis that mesothelial cells can differentiate into cell lineages of the embryonic mesoderm including osteoblasts and adipocytes. To examine this, a functional assay of bone formation and an adipogenic assay were performed in vitro with primary rat and human mesothelial cells maintained in osteogenic or adipogenic medium (AM) for 0-26 days. Mesothelial cells expressed increasing levels of alkaline phosphatase, an early marker of the osteoblast phenotype, and formed mineralized bone-like nodules. Mesothelial cells also accumulated lipid indicative of a mature adipocyte phenotype when cultured in AM. All cells expressed several key osteoblast and adipocyte markers, including osteoblast-specific runt-related transcription factor 2, and demonstrated changes in mRNA expression consistent with epithelial-to-mesenchymal transition. In conclusion, these studies confirm that mesothelial cells have the capacity to differentiate into osteoblast- and adipocyte-like cells, providing definitive evidence of their multipotential nature. These data strongly support mesothelial cell differentiation as the potential source of different tissue types in MM tumours and other serosal pathologies, and add support for the use of mesothelial cells in regenerative therapies.

Non-neoplastic and neoplastic pleural endpoints following fiber exposure

Exposure to asbestos fibers is associated with non-neoplastic pleural diseases including plaques, fibrosis, and benign effusions, as well as with diffuse malignant pleural mesothelioma. Translocation and retention of fibers are fundamental processes in understanding the interactions between the dose and dimensions of fibers retained at this anatomic site and the subsequent pathological reactions. The initial interaction of fibers with target cells in the pleura has been studied in cellular models in vitro and in experimental studies in vivo. The proposed biological mechanisms responsible for non-neoplastic and neoplastic pleural diseases and the physical and chemical properties of asbestos fibers relevant to these mechanisms are critically reviewed. Understanding mechanisms of asbestos fiber toxicity may help us anticipate the problems from future exposures both to asbestos and to novel fibrous materials such as nanotubes. Gaps in our understanding have been outlined as guides for future research.

Adverse effects of polyvinylidene fluoride-coated polypropylene mesh used for laparoscopic intraperitoneal onlay repair of incisional hernia

BACKGROUND

Polyvinylidene fluoride-coated polypropylene meshes have been developed specifically for intraperitoneal onlay mesh repair. They combine a macroporous design with biomechanical characteristics compatible with the abdominal wall and are reported to have favourable antiadhesive properties. This retrospective study reports complications related to one of these materials, DynaMesh.

METHODS

Twenty-nine patients underwent intraperitoneal onlay mesh repair with DynaMesh at one of two hospitals. Patients characteristics, surgical procedures and postoperative analgesia were comparable at both sites.

RESULTS

Six patients developed DynaMesh-related complications that required surgical reintervention by laparotomy within 1 year of operation. Surgical reintervention was for adhesions in five patients and the mesh had to be explanted in three. One mesh was explanted because of early infection. Adhesions to DynaMesh were found in two patients who had surgery for unrelated reasons.

CONCLUSION

Laparoscopic intraperitoneal onlay DynaMesh repair was associated with a high rate of complications.

Peritoneal repairing cells: a type of bone marrow derived progenitor cells involved in mesothelial regeneration

The peritoneal mesothelium exhibits a high regenerative ability. Peritoneal regeneration is concomitant with the appearance, in the coelomic cavity, of a free-floating population of cells whose origin and functions are still under discussion. We have isolated and characterized this cell population and we have studied the process of mesothelial regeneration through flow cytometry and confocal microscopy in a murine model lethally irradiated and reconstituted with GFP-expressing bone marrow cells. In unoperated control mice, most free cells positive for mesothelin, a mesothelial marker, are green fluorescent protein (GFP). However, 24 hrs after peritoneal damage, free mesothelin⁺/ GFP⁺ cells appear in peritoneal lavages. Cultured lavage peritoneal cells show colocalization of GFP with mesothelial (mesothelin, cytokeratin) and fibroblastic markers. Immunohistochemical staining of the peritoneal wall also revealed colocalization of GFP with mesothelial markers and with procollagen-1 and smooth muscle α-actin. This was observed in the injured area as well as in the surrounding not-injured peritoneal surfaces. These cells, which we herein call peritoneal repairing cells (PRC), are very abundant 1 week after surgery covering both the damaged peritoneal wall and the surrounding uninjured area. However, they become very scarce 1 month later, when the mesothelium has completely healed. We suggest that PRC constitute a type of monocyte-derived cells, closely related with the tissue-repairing cells known as ‘fibrocytes’ and specifically involved in peritoneal reparation. Thus, our results constitute a synthesis of the different scenarios hitherto proposed about peritoneal regeneration, particularly recruitment of circulating progenitor cells and adhesion of free-floating coelomic cells.

Peritoneal adipocytes and their role in inflammation during peritoneal dialysis

Adipose tissue is a major site of chronic inflammation associated with peritoneal dialysis (PD) frequently complicating peritonitis. Adiposity-associated inflammation plays a significant contributory role in the development of chronic inflammation in patients undergoing maintenance PD. However, the molecular and cellular mechanisms of this link remain uncertain. Adipose tissue synthesizes different adipokines and cytokines that orchestrate and regulate inflammation, insulin action, and glucose metabolism locally and systemically. In return, inflammation retards adipocyte differentiation and further exacerbates adipose dysfunction and inflammation. An understanding of the inflammatory roles played by adipose tissue during PD and the healing mechanism of injured mesothelium will help to devise new therapeutic approach to slow the progression of peritoneal damage during peritoneal dialysis. This article reviews the roles of peritoneal adipose tissue in chronic peritoneal inflammation under PD and in serosal repair during PD.

Potential role of bone marrow-derived cells in the turnover of mesothelium

BACKGROUND

Bone marrow cell has been proposed as a source of new mesothelium, but supporting evidence is rare. This study examines the validity of this hypothesis by using green fluorescent protein (GFP) and Y-chromosome trackers to identify the presence of donor marrow cells in peritoneal membrane of bone marrow transplant recipient mice.

METHODS

Cross-gender and GFP-mismatched bone marrow transplantation was undertaken in 20 FVB mice. Five recipients were killed 2, 4, and 6 weeks and 6 months later. Peritoneal tissues were obtained for the detection of GFP and Y chromosome by immunohistochemical staining (IHC) and chromogenic in situ hybridization (CISH).

RESULTS

GFP+ cells could be found in the peritoneal membrane of bone marrow transplant recipients. However, the level of engraftment was low, accounting for 0.9%, 0.8%, 0.7%, and 2.2% of the total counted mesothelial cells in intestinal serosa at 2, 4, and 6 weeks and 6 months post-transplantation, respectively. The presence of donor marrow cells within mesothelium was again confirmed by the detection of Y-chromosome-containing cells. Moreover, Y-chromosome+ cells incorporated within the mesothelium were positively stained by anticytokeratin antibody.

CONCLUSIONS

Donor marrow cells could attach to mesothelium and exhibit mesothelial marker cytokeratin in bone marrow transplant recipients. This finding suggests that bone marrow-derived cells might participate in the turnover of mesothelium.

Omentoplasty for gastrotomy closure after natural orifice transluminal endoscopic surgery procedures (with video)

INTRODUCTION

The utility of the greater omentum has not been assessed in transluminal access closure after natural orifice transluminal endoscopic surgery (NOTES) procedures.

OBJECTIVE

Our purpose was to evaluate the feasibility, efficacy, and safety of omentoplasty for gastrotomy closure.

METHODS AND PROCEDURES

Survival experiments in 9 female 40-kg pigs were randomly assigned to 3 groups: group A, endoscopic full-thickness resection (EFTR) for transgastric access and peritoneoscopy without closure; group B, ETFR and peritoneoscopy with omentoplasty (flap of omentum is pulled into the stomach and attached to the gastric mucosa with clips but no clips are used for gastrotomy closure itself); group C, balloon dilation for opening and peritoneoscopy followed by omentoplasty for closure. The animals were observed for 2 weeks and then underwent endoscopy and necropsy with histologic evaluation.

RESULTS

Transgastric opening and peritoneoscopy were achieved in all pigs. In groups B and C, a flap of omentum was easily placed to seal the gastrotomy and then attached to the gastric mucosa with 2 to 5 clips (median 4) in 7 to 20 minutes (median 15 minutes). In group A, peritonitis developed in all animals. In both groups B and C, all animals survived 15 days with no peritonitis and minimal adhesions outside the gastrotomy site. In addition, all achieved complete healing (transmural, n = 4; mucosal ulceration, n = 2) of the gastrotomy site. One animal in group B had an 18-mm abscess in the omental flap.

LIMITATIONS

Animal model, small sample size, lack of appropriate controls for group C.

CONCLUSIONS

Omentoplasty of the gastrotomy site is a technically feasible method to seal balloon-created transgastric access to the peritoneal cavity after NOTES procedures.

Characterizing omental adhesions by culturing cells isolated from a novel in vivo adhesion model

Although it has been established that postoperative adhesions in the peritoneal cavity are the consequence of injury to the peritoneum, there is much controversy over the nature of the cells giving rise to this neotissue. Here, we establish a novel adhesiogenic model in the rabbit to analyze the phenotype and proliferation in vitro of cells comprising adhesion tissue seven days postsurgery. Adhesion-free omentum tissue was used as control. Cells derived from adhesions and from the control omentum were subcultured and characterized through immunofluorescence and Western blotting procedures to determine markers of cell differentiation and pluripotential, and viability and proliferation assays. Our findings indicate the existence of a mesenchymal population in the omentum revealed by markers of pluripotent cells with high angiogenic capacity. This population seems to be responsible for the adhesions formed in response to mesothelial damage. Depending on the local environment, mesenchymal cells are capable of in vivo differentiation towards at least two different cell phenotypes rendering two types of adhesions with clearly differentiated characteristics. One type of adhesion shows a highly vascularized adipose morphology containing cells differentiating into a vascular lineage. The other adhesions are fibrous with large amounts of collagen and comprised mainly of myofibroblasts conferring less compliance to this tissue.

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.

Highly stomach-selective gene transfer following gastric serosal surface instillation of naked plasmid DNA in rats

BACKGROUND

The purpose of this study was to achieve stomach-selective gene transfer in rats by our simple and novel administration method, which is gastric serosal surface instillation of naked plasmid DNA (pDNA).

METHODS

Naked pDNA encoding firefly luciferase as a reporter gene was instilled onto the gastric serosal surface in male Wistar rats. As controls, we performed intraperitoneal, intragastric and intravenous administration of naked pDNA. At appropriate time intervals, we measured luciferase activities in the stomach and other tissues.

RESULTS

Gene expression in the stomach 6 h after gastric serosal surface instillation of naked pDNA (5 microg) was significantly higher than that after using other administration methods. The present study is the first report on stomach-selective gene transfer following instillation of naked pDNA onto the gastric serosal surface in rats. Also, the gene expression level in the stomach 6 h after gastric serosal surface instillation of naked pDNA was markedly higher than that in other tissues. In a dose-dependent study, the gene expression level was saturated over 5 microg. Gene expression in the stomach was detected 3 h after gastric serosal surface instillation of naked pDNA. The gene expression level peaked 12-24 h after instillation of naked pDNA, then decreased to a level similar to 3 h at 48 h.

CONCLUSIONS

Gastric serosal surface in stillation of naked pDNA can be a highly stomach-selective gene transfer method in rats.

Vulnerability to oxidative stress and different patterns of senescence in human peritoneal mesothelial cell strains

Both the ascites fluid-derived mesothelial cell line LP-9 and primary cultures of human omentum-derived mesothelial cells (HOMCs) are commonly used in experimental studies. However, they seem to have a different replicative potential in vitro. In the present study, we have attempted to determine the causes of this discrepancy. HOMCs were found to divide fewer times and enter senescence earlier than LP-9 cells. This effect was coupled with earlier increases in the expression of senescence-associated-beta-galactosidase and cell cycle inhibitors p16INK4a and p21WAF1. Moreover, almost 3 times as many early-passage HOMCs as LP-9 cells bore senescence-associated DNA damage foci. In sharp contrast to LP-9 cells, the foci present in HOMCs localized predominantly outside the telomeres, and the HOMC telomere length did not significantly shorten during senescence. Compared with LP-9 cells, HOMCs were found to enter senescence with significantly lower levels of lipofuscin and damaged DNA, and markedly decreased glutathione contents. In addition, early-passage HOMCs generated significantly more reactive oxygen species either spontaneously or in response to exogenous oxidants. These results indicate that compared with LP-9 cells, HOMCs undergo stress-induced telomere-independent premature senescence, which may result from increased vulnerability to oxidative DNA injury.

Serosal mesothelium retains vasculogenic potential

Mesothelia comprise the epithelial covering of coelomic organs and line the cavities in which they are housed. Mesothelia contribute to the vasculature of the heart and the intestinal tract by developmental processes of epithelial-mesenchymal transition (EMT), migration, and differentiation into endothelial cells, vascular smooth muscle cells, and pericytes. Here, we establish a novel in vitro system to analyze the differentiative potential of mesothelia. Using explants from serosal mesothelium (the mesothelial covering of the gut), we demonstrate that much of the developmental program observed in embryonic mesothelia is retained in the adult structure. Namely, processes of epithelial spreading, EMT, and differentiation into smooth muscle cells from these cells are observed. Interestingly, we were unable to stimulate endothelial cell differentiation using serum or various signaling factors. Taken together, these data reveal that differentiated serosal cells retain vasculogenic potential and provide a generalizable model for future studies on the developmental and differentiative capacity of the mesothelial cell type.

Mesothelial cells from tunica vaginalis, a practical source for mesothelial transplantation

Transplantation of mesothelial cells is used to repair peritoneum that is damaged by surgery, peritonitis, and peritoneal dialysis. The largest obstacle for clinical application of mesothelial cell transplantation is the lack of a reliable source of mesothelial cells. So far, they are isolated from omentum, mesentery, parietal wall and ascites. Procedures used to obtain mesothelial cells from the omentum or mesentery are invasive, however, especially in pre-operative situations. Sufficient amounts of ascites for aspiration can not be obtained under physiological conditions. We have developed a novel method of isolating mesothelial cells from the tunica vaginalis. The tunica vaginalis originates from the peritoneum and descends into the scrotum along with the testis during fetal development. This region provides a source of mesothelial cells that is convenient to approach and free from abdominal complications. Transplantation of autologous mesothelial cells that were isolated from tunica vaginalis was effective in preventing post-operative adhesions. In this review, we summarize mesothelial cell transplantation trials and describe the method of isolating mesothelial cells form the tunica vaginalis. Mesothelial cell transplantation might be widely accepted for clinical use in the near future.

Mesothelial cell transplantation in myocardial infarction

Mesothelial cells (MCs) are accessible in human patients by excision and digestion of epiploon or from peritoneal fluid or lavage. MCs are easy to culture to obtain large quantities in vitro and they can be genetically modified with interesting therapeutic genes. The important potential of MCs in tissue engineering has been shown during epiplooplasty to different organs and also in creating artificial blood conduits. MC of epicardium is probably the precursor of coronary arteries during embryogenesis. MCs secrete a broad spectrum of angiogenic cytokines, growth factors and extracellular matrix, which could be useful for repairing damaged tissues. MCs are transitional mesodermal-derived cells and considered as progenitor stem cell, have similar morphological and functional properties with endothelial cells and conserve properties of transdifferentiation. MC therapy in myocardial infarction induced neoangiogenesis in infarcted scar and preserved heart function. In conclusion, a potential therapeutic strategy would be to implant or re-implant genetically modified MCs in post-infarction injury to enhance tissue repair and healing. Imparting therapeutic target genes such as angiogenic genes would also be useful for inducing neovascularization.

Postoperative intraperitoneal adhesion pathophysiology

Aside from the normal 'ad integrum' peritoneal regeneration, the postoperative intraperitoneal adhesion formation process may be considered as the pathological part of peritoneal healing following any injury, particularly a surgical one. Despite a large body of clinical and experimental studies, its pathophysiology remains controversial. Moreover, a better understanding of the pathophysiological events and of the medical and surgical factors involved in the adhesion formation process is pivotal in any attempt to control this very frequent phenomenon and its serious consequences.

Surgical adhesions: a timely update, a great challenge for the future

Damage to the peritoneum during abdominal surgery triggers a cascade of events aimed at repairing the damage. As part of this process, fibrin is deposited, which is the precursor to the formation of an adhesion between 2 damaged peritoneal surfaces. This can have a significant impact on morbidity and even mortality as well as large cost implications. Strategies to reduce adhesion formation include improving surgical techniques, optimizing laparoscopy conditions, using pharmacologic interventions targeted at the inflammatory response and/or fibrin deposition, and using agents that provide a physical barrier to adhesion formation. While these strategies have provided some success, none have yet proved totally successful in abolishing adhesions. Further research to ensure that adhesion prevention is optimal is therefore essential.

Agents that modulate peritoneal membrane structure and function

Extensive experience with chronic peritoneal dialysis has identified a series of functional and anatomical pathologic changes in the peritoneal membrane thought to be the result of repeated insults from bioincompatible solutions. Laboratory and clinical findings from recent investigations often conflict and are difficult to interpret due to variations in methodologies, animal models, study designs, and data analyses. The principal pathophysiologic mechanisms identified thus far are oxidative stress, inflammation, and their consequences. Many substances used to neutralize the action of these insults, prevent formation of toxic compounds, or directly alter solute and water transport to improve peritoneal membrane performance have been studied. We herein review the most promising of these substances or those that deserve attention because their use has contributed to better understanding of peritoneal pathophysiology. Most peritoneal solution additives have proved useless due to their toxicity and undesirable effects, ineffectiveness, or manufacturing limitations. A few substances deserve more attention, particularly those capable of restoring negatively charged membrane sites, those that somehow improve permselectivity, scavengers of oxidants, and advanced glycation end-product inhibitors and breakers. Recent publications on clinical experience with neutral pH, low glucose degradation product (GDP) peritoneal solutions, although few and preliminary, are most encouraging. The virtual elimination of GDPs in these novel solutions will probably preclude the need for GDP scavengers and inhibitors. Nonetheless, there is room for further significant improvement in solution biocompatibility and for compounds that may restore peritoneal function.

Homogeneity of mesothelial cells with lymphatic endothelium: expression of lymphatic endothelial markers by mesothelial cells

BACKGROUND

Mesothelial cell monolayers cover the serous cavities and internal organs, and provide a protective low-friction interface between apposed organs and tissues. The mesothelium also regulates inflammation, fluid and cell exchange, and tissue repair in these compartments and possibly tumor metastasis. In the present study, a stable pleural mesothelial cell line (MIM) was isolated and characterized, and the expression of several lymphatic specific markers by these cells examined.

METHODS AND RESULTS

MIM were isolated from mice stably expressing a temperature-sensitive SV40 large T antigen ('Immortomouse', strain: H-2K(b)-tsA58). These cells were compared with lymphatic endothelial cells (LEC) derived from the mesenteric adventitia of the Immortomouse. MIM and LEC expression of lymphatic-specific markers (Flt-4, LYVE-1, and Prox-1) was examined, and the tight junction protein (ZO-1) was studied by immunofluorescence and immunoblotting in these cells.

RESULTS

LYVE-1, Prox-1, and Flt-4 were detected in both MIM and LEC, with Prox-1 and LYVE-1 more strongly expressed on LEC than MIM. Conversely, Flt-4 was more densely expressed on MIM than on LEC. Spatially, ZO-1 was prominent at MIM junctions, but was less well organized in LEC.

CONCLUSION

MIM and LEC share several characteristic markers usually associated with lymphatic endothelium. MIM might be useful for studying the biology and pathology of mesothelial cells in vitro and help in the development of therapies for mesothelial-related diseases, such as mesothelioma and pleural effusion.

Response of human peritoneal mesothelial cells to inflammatory injury is regulated by interleukin-1beta and tumor necrosis factor-alpha

Peritoneal injury is often associated with alterations of the mesothelium, resulting in peritoneal healing and adhesion formation. We analyzed the effects of pro-inflammatory cytokines on cell morphology and proliferation of human peritoneal mesothelial cells (HPMC). After 48 hours, HPMC formed a confluent layer with cell volumes of 2,662+/-111 fL. Treatment of HPMC with interleukin-1beta and tumor necrosis factor-alpha (TNF-alpha) induced mesothelial disintegration and alterations in mesothelial cell morphology, which were associated with an interleukin-1beta-triggered increase in cell volume (3,028+/-118 fL; p<0.05) and exfoliation of cells into the supernatants of cell cultures (p<0.05). Whereas TNF-alpha arrested HPMC in the G0/G1 phase (p<0.05), interleukin-1beta caused an increase of cells into the S phase of the cell cycle. In addition, interleukin-1beta and interferon-gamma exerted a proliferative effect on HPMC. These changes were independent from mesothelial Na+/H+ antiporter-1 expression. Our data indicate that the response of HPMC to inflammatory injury is regulated by interleukin-1beta and TNF-alpha reflecting their putative role in peritoneal wound healing and adhesion formation.

Differential release and distribution of Nod1 and Nod2 immunostimulatory molecules among bacterial species and environments

Nod1 and Nod2 are intracellular proteins that are involved in recognition of bacterial molecules and their genetic variations have been linked to several inflammatory diseases that are strongly affected by environmental factors. However, the distribution of Nod1- and Nod2-stimulatory molecules in different bacterial species and environments is unknown. Here we established a quantitative bioassay to screen and characterize Nod1- and Nod2-stimulatory activities in different environmental sites and bacterial species. Using this system, we found that common environments including foods and soils contain high levels of Nod1- and Nod2-stimulatory activities. Several Bacillus species were identified to possess the highest Nod1-stimulatory activity among soil bacteria. Unlike other immunostimulatory molecules, the higher level of Nod1-stimulatory activity was found in the culture supernatant and not in extracts from whole cell bacteria. Nod1-stimulatory molecules were highly stable at extreme pH and boiling conditions and were synthesized in an amidase- and sltY-independent manner. These results suggest a novel mechanism by which bacteria present in the environment stimulate the host immune system through Nod1.

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.

Apparent successful mesothelial cell transplantation hampered by peritoneal activation

BACKGROUND

Mesothelial cell transplantation has been suggested to improve mesothelial repair after surgery, recurrent peritonitis and peritoneal dialysis.

METHODS

In this study we evaluated mesothelial cell transplantation during the resolution phase of experimentally thioglycollate-induced peritonitis in rats. To this end 4 x 10(6) DiO-labeled autologous mesothelial cells were transplanted 1 week after peritonitis induction. Peritoneal inflammation and permeability characteristics were evaluated after another week.

RESULTS

Mesothelial cell transplantation after peritonitis resulted in incorporation of these cells in the parietal mesothelial lining, leading to an acute transient submesothelial thickening which was not seen in transplanted animals without prior peritonitis induction. Long-term functioning of these repopulated mesothelial cells leaded to peritoneal activation as evidenced by a approximately twofold increase in peritoneal lymphocytes (P < 0.01) and omental mast cell counts (P < 0.05), accompanied by the induction of inflammation markers monocyte chemoattractant protein-1 (MCP-1) (P < 0.01) and hyaluronan (P < 0.01) in the transplanted peritonitis group, but not in rats with peritonitis without mesothelial cell transplantation or in control rats without mesothelial cell transplantation (all four parameters P < 0.01). In addition, trapping of transplanted mesothelial cells in the milky spots of omental tissue and lymphatic stomata of the diaphragm both in control and thioglycollate rats seems to increase microvascular permeability, reflected by apparent increased diffusion rates of small solutes and proteins.

CONCLUSION

Altogether, our data underscore the importance of controlling peritoneal (patho)physiology and function in mesothelial transplantation protocols.

Novel and simple method for isolating autologous mesothelial cells from the tunica vaginalis

OBJECTIVE

To report the development of a new method of isolating autologous mesothelial cells from the tunica vaginalis that are easily obtained and generally free from the effects of abdominal cancer, and to investigate whether transplanting these mesothelial cells is effective in preventing postoperative adhesions.

MATERIALS AND METHODS

The tunica vaginalis was resected from male Lewis rats, and mesothelial cells were collected by enzymatic disaggregation. To investigate the efficacy of mesothelial cells in preventing adhesion, harvested cells were transplanted into a rat intestinal hernia adhesion model.

RESULTS

Cells isolated from the tunica vaginalis were homogenous, polygonal when confluent, expressed cytokeratin and vimentin, and the cell surface was covered with microvilli, which is the characteristic appearance of endogenous mesothelial cells. The transplantation of autologous mesothelial cell sheets reduced peritoneal adhesion.

CONCLUSION

We developed a new method of obtaining autologous mesothelial cells from the tunica vaginalis. These cells may provide a valuable option for treating patients at risk of postoperative adhesions.

The serosal mesothelium is a major source of smooth muscle cells of the gut vasculature

Most internal organs are situated in a coelomic cavity and are covered by a mesothelium. During heart development, epicardial cells (a mesothelium) move to and over the heart, undergo epithelial-mesenchymal transition (EMT), and subsequently differentiate into endothelial and vascular smooth muscle cells. This is thought to be a unique process in blood vessel formation. Still,structural and developmental similarities between the heart and gut led us to test the hypothesis that a conserved or related mechanism may regulate blood vessel development to the gut, which, similar to the heart, is housed in a coelomic cavity. By using a combination of molecular genetics, vital dye fate mapping, organ culture and immunohistochemistry, we demonstrate that the serosal mesothelium is the major source of vasculogenic cells in developing mouse gut. Our studies show that the gut is initially devoid of a mesothelium but that serosal mesothelial cells expressing the Wilm's tumor protein (Wt1)move to and over the gut. Subsequently, a subset of these cells undergoes EMT and migrates throughout the gut. Using Wt1-Cre genetic lineage marking of serosal cells and their progeny, we demonstrate that these cells differentiate to smooth muscle of all major blood vessels in the mesenteries and gut. Our data reveal a conserved mechanism in blood vessel formation to coelomic organs, and have major implications for our understanding of vertebrate organogenesis and vascular deficiencies of the gut.

Effect of a matrix metalloproteinase activity and TNF-alpha converting enzyme inhibitor on intra-abdominal adhesions

BACKGROUND

Formation of intra-abdominal adhesions depends, in part, on the activity of serine proteinases. Matrix metalloproteinases (MMP) are required for epithelialization of skin wounds but their involvement in mesothelialization of peritoneal wounds and in adhesion pathogenesis is not known. Early tumor necrosis factor-alpha (TNF-alpha) levels have been proposed to reflect propensity to adhesion formation.

OBJECTIVE

The impact of MMP activity and secreted TNF-alpha on peritoneal adhesion formation and healing was investigated through systemic administration of the synthetic broad-spectrum MMP and TNF-alpha-converting enzyme (TACE) inhibitor GM 6001.

METHODS

Female Sprague-Dawley rats of 4-6 weeks of age were injected subcutaneously daily with GM 6001 100 mg/kg (n = 12) or vehicle (n = 10) starting two days before surgery. In each rat, two standardized peritoneal wounds, 20 mm x 5 mm, were made. One peritoneal wound was sutured whereas the contralateral wound healed by secondary intention. Adhesion formation and peritoneal healing, cell proliferation, and hydroxyproline concentrations were evaluated on postoperative day 7.

RESULTS

Total serum TNF-alpha levels increased in vehicle-treated rats (p = 0.019) while GM 6001 treatment effectively prevented the rise in the postoperative phase (p < 0.001). No significant differences were observed in the extent of adhesion formation (p = 0.67) between control (65.0%) and GM 6001-treated (61.5%) animals, or peritoneal wound healing or cell proliferation. Hydroxyproline levels increased in the wounds (p = 0.014) but were not different between the two groups (p = 0.14).

CONCLUSIONS

Lack of a striking effect of the MMP and TACE antagonist GM 6001 on postoperative adhesions suggests that MMP activity and TNF-alpha might not be major adhesiogenic factors.

Surgical trauma and peritoneal recurrence of colorectal carcinoma

BACKGROUND

Local peritoneal recurrence is a relatively common complication after intentionally curative surgery for colorectal cancer and has unfavourable prognosis.

METHODS

This manuscript reviews the relevant experimental and clinical literature on surgical trauma and development of local recurrences, which was obtained by extensive search in the PubMed database.

RESULTS AND CONCLUSION

Although surgery is required as the only option for treatment, operative trauma and subsequent wound healing promote development of local recurrences. Minimizing peritoneal trauma reduces local tumour outgrowth in animal models, but clinical trials have not been conclusive so far. Recognition of the increased susceptibility to tumour establishment in the early post-operative phase challenges the aim for further research, targeting at strategies that obstruct local tumour implantation or outgrowth and/or improve (local) anti-tumour response.

Activation of proteinase-activated receptor-2 in mesothelial cells induces pleural inflammation

Pleural inflammation underlies many pleural diseases, but its pathogenesis remains unclear. Proteinase-activated receptor-2 (PAR(2)) is a novel seven-transmembrane receptor with immunoregulatory roles. We hypothesized that PAR(2) is present on mesothelial cells and can induce pleural inflammation. PAR(2) was detected by immunohistochemistry in all (19 parietal and 11 visceral) human pleural biopsies examined. In cultured murine mesothelial cells, a specific PAR(2)-activating peptide (SLIGRL-NH(2)) at 10, 100, and 1,000 muM stimulated a 3-, 42-, and 1,330-fold increase of macrophage inflammatory protein (MIP)-2 release relative to medium control, respectively (P < 0.05 all) and a 2-, 32-, and 75-fold rise over the control peptide (LSIGRL-NH(2), P < 0.05 all). A similar pattern was seen for TNF-alpha release. Known physiological activators of PAR(2), tryptase, trypsin, and coagulation factor Xa, also stimulated dose-dependent MIP-2 release from mesothelial cells in vitro. Dexamethasone inhibited the PAR(2)-mediated MIP-2 release in a dose-dependent manner. In vivo, pleural fluid MIP-2 levels in C57BL/6 mice injected intrapleurally with SLIGRL-NH(2) (10 mg/kg) were significantly higher than in mice injected with LSIGRL-NH(2) or PBS (2,710 +/- 165 vs. 880 +/- 357 vs. 88 +/- 46 pg/ml, respectively; P < 0.001). Pleural fluid neutrophil counts were higher in SLIGRL-NH(2) group than in the LSIGRL-NH(2) and PBS groups (by 40- and 26-fold, respectively; P < 0.05). This study establishes that activation of mesothelial cell PAR(2) potently induces the release of inflammatory cytokines in vitro and neutrophil recruitment into the pleural cavity in vivo.

Peritoneal dialysis fluid-induced changes of the peritoneal membrane are reversible after peritoneal rest in rats

BACKGROUND

Peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane. However, the (ir)reversibility of these pathological changes of the peritoneum is not understood fully.

METHODS

In an experimental PD model, rats (n = 15) received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. After 5 weeks of treatment, the first group of animals (PDF; n = 10) was sacrificed, while peritoneal catheters of the remaining group of rats (PD-rest; n = 5) were removed 1 week later. The latter group (PD-rest) was sacrificed 12 weeks after removing catheters. At both time points, untreated rats were included as controls. Cellular and morphological parameters were analysed by light and electron microscopy.

RESULTS

Rats exposed to PD fluid for 5 weeks showed a severe angiogenesis in various peritoneal tissues. Peritoneal rest resulted in a significant reduction in blood vessel density in visceral (mesentery, P<0.05), but not in parietal peritoneum. Five weeks' exposure to PD fluid resulted in a profound fibrosis in the parietal peritoneum, whereas the degree of fibrosis was significantly reduced in the PD-rest group (P<0.02). Daily exposure to PD fluid induced a higher number of mast cells in the omentum compared with untreated rats, whereas peritoneal rest normalized the increased mast cell density completely (P<0.03). Likewise, continued PD fluid instillation evoked a strong omental milky spot response, which was returned to the control level after peritoneal rest (P<0.009). Furthermore, the number of mesothelial cells on the liver was significantly increased in rats treated with PD fluid, whereas animals from the PD-rest group had a lower number of mesothelial cells, although this was not statistically significant (P = 0.08). Finally, as evidenced by electron microscopy, daily exposure to PD fluid resulted in severe damage to the mesothelial cell layer covering the peritoneum, whereas this cell layer was completely recovered after peritoneal rest.

CONCLUSIONS

We show that PD fluid-induced cellular and morphological alterations of the peritoneal membrane are generally reversible.

Mesothelial primary cilia of peritoneal and other serosal surfaces

The conspicuous presence of primary cilia, a small immotile cilium present on most cell types, left researchers with little doubt of their functional relevance. Recently mechanosensitive functional significance was established and a link with the pathogenesis of polycystic kidney disease. Together these discoveries have raised the profile of this, previously considered "vestigial", organelle. Primary cilia are expressed on the apical surface of serosal mesothelium and display regional variation but are more abundant on biosynthetically active cells. Adult mesothelial cells are highly biosynthetic producing a phospholipid rich surfactant that lubricates and protects the visceral organs. The mesothelium is utilized as a semipermeable membrane during peritoneal dialysis for patients with end stage renal failure. However, little is known about the functional role of primary cilia on this highly specialized cell type. The present review, examines the significance of the primary cilium in serosal mesothelial cell biology with an emphasis on ciliary location, structure, form and function. Future research is identified and discussed in view of the emerging role cilia have in other cells and the established function of the serosal mesothelium in development, normal function, peritoneal dialysis and pathology of the serosal membranes.

Mesothelial cell proliferation and apoptosis

Mesothelial cells line the pleural and peritoneal surfaces, where under normal conditions they proliferate and undergo cell death at a slow rate, thereby maintaining a constant number of cells. These tightly regulated processes are disrupted in malignancy. By developing a better understanding of the mechanisms that regulate cell proliferation and apoptosis in mesothelial and mesothelioma cells, we may be able to develop more effective therapeutic agents that target specific steps in these pathways to induce apoptosis more efficiently. This paper reviews our current knowledge of the signaling pathways involved in the regulation of mesothelial cell proliferation and apoptosis. The latest advancements in identifying proteins that play key roles in the resistance to apoptosis are highlighted.

In vivo bioluminescent imaging of virus-mediated gene transfer and transduced cell transplantation in the intervertebral disc

STUDY DESIGN

Work presented here used a small animal model to demonstrate the feasibility and usefulness of in vivo bioluminescent imaging to studying degenerative disc disease.

OBJECTIVES

To determine the utility of in vivo bioluminescent imaging to monitor the temporal and spatial expression of genetically modified cells within the intervertebral disc of a rodent model.

SUMMARY OF THE BACKGROUND DATA

Noninvasive imaging of genetically engineered cells in the spine has the advantage of allowing events to be tracked without killing the animal and can be used to follow the time course of a particular therapy. Results are presented on the use of Sprague-Dawley rats in experimental studies in which the luciferase reporter gene was delivered to the lumbar intervertebral disc through adenovirus-mediated or cell-based transfer techniques to demonstrate the feasibility to monitor gene expression noninvasively over time.

METHODS

Tissue culture, disc surgery, and in vivo bioluminescent imaging were used. The intervertebral disc of the rat was either injected in situ with an adenovirus containing the luciferase reporter gene or implanted with fat, bone marrow or intervertebral disc cells transduced ex vivo and contained in a bioresorbable carrier. Results were assessed with in vivo bioluminescent imaging at several time points.

CONCLUSION

Data from 11 animals were obtained with imaging up to 14 days. To our knowledge, this is the first description of in vivo bioluminescence imaging to study spinal conditions. We have characterized the relative expression of three cell types transduced with the Ad-luc virus by ex vivo transfection followed by cell implantation in the rat spine and compared them to one another and to direct infection of Ad-luc adenovirus in situ. Our results demonstrate the feasibility of tracing genetically altered cells in the spine. This technique has the potential to be used to noninvasively track the fate and expression of therapeutic genes within the spine of small animals used in disc research.

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.

Mesothelial Differentiation as Reflected by Differential Gene Expression

Human mesothelial cells obtained from benign effusions retain their proliferative capacity and grow uniformly either with a fibroblastic or epithelioid morphology in vitro. These cultures therefore provide a model for the process of mesothelial differentiation in vivo. To study this differentiation, we isolated differentially expressed genes obtained by suppression subtractive hybridization. Of the nine genes found to be overexpressed in fibroblastic mesothelial cells, three are matrix-associated (integrin alpha5, collagen binding protein 2, human cartilage glycoprotein 39), whereas the others are associated with a proliferative cell type (14-3-3 epsilon, plexin B2, N33, and three genes encoding ribosomal elements). Seven of the eight genes upregulated in the epithelioid phenotype are related rather to specialized functions, such as metabolism (aldose reductase, lecithin:cholesterol acyltransferase, ATPase 6), cytoskeletal composition (cytokeratins 7 and 8), and regulation of differentiation (granulin, annexin II). Immunohistochemistry with available antibodies to six of the differentially expressed gene products confirmed the differences also in pleural tissues, where submesothelial cells displayed the fibroblastic markers, whereas surface cells displayed the epithelioid markers. In summary, this approach revealed a pattern of genes coordinately regulated during mesothelial differentiation and suggests that mesothelium may regenerate also by recruiting cells from the submesothelial layer. Some of the gene products may also be useful markers for differentiation and activation in serosal tissues.

The mesothelial cell

Mesothelial cells form a monolayer of specialised pavement-like cells that line the body's serous cavities and internal organs. The primary function of this layer, termed the mesothelium, is to provide a slippery, non-adhesive and protective surface. However, mesothelial cells play other pivotal roles involving transport of fluid and cells across the serosal cavities, antigen presentation, inflammation and tissue repair, coagulation and fibrinolysis and tumour cell adhesion. Injury to the mesothelium triggers events leading to the migration of mesothelial cells from the edge of the lesion towards the wound centre and desquamation of cells into the serosal fluid which attach and incorporate into the regenerating mesothelium. If healing is impaired, fibrous serosal adhesions form between organs and the body wall which impede vital intrathoracic and abdominal movement. Neoplastic transformation of mesothelial cells gives rise to malignant mesothelioma, an aggressive tumour predominantly of the pleura. Although closely associated with exposure to asbestos, recent studies have implicated other factors including simian virus 40 (SV40) in its pathogenesis.

Glucose degradation products (GDP) retard remesothelialization independently of d-glucose concentration

BACKGROUND

Glucose degradation products (GDP) present in heat-sterilized dialysis fluids are thought to contribute to cellular dysfunction and membrane damage during peritoneal dialysis. To examine the effects of specific GDP on the remesothelialization process, the impact of conventional and low GDP peritoneal dialysis solutions, D-glucose, and individual GDP in a scratch-wounding model was assessed.

METHODS

Scratch (0.5 to 0.6 mm)-wounded human peritoneal mesothelial cells (HPMC) were treated, at pH 7.4, with either (1) control medium (M199), (2) laboratory-prepared heat or filter-sterilized solutions, (3) 10% to 80% vol/vol solution of Gambrosol or Gambrosol-trio (1.5% and 4.0% glucose), (4) D-glucose (5 to 80 mmol/L), or (5) individual or combined GDP [acetaldehyde, formaldehyde, glyoxal, methylglyoxal, 3-deoxyglucosone (3-DG), 5-hydroxy methylfufural (5-HMF), or 3,4-di-deoxyglucosone-3-ene (3,4-DGE)]. Wound closure was recorded by time-lapse photomicroscopy.

RESULTS

In untreated HPMC, the rate of wound closure was linear and the process was complete by 18.4 +/- 3.6 hours (N = 16). In wounded HPMC exposed to dilutions of heat-sterilized but not filtered laboratory solutions (1.5% or 4.0% glucose, pH 7.4), remesothelialization was significantly retarded (P = 0.04 and P = 0.009 vs. M199, respectively). In Gambrosol, remesothelialization was significantly retarded in both 1.5% and 4.0% solutions. In contrast in Gambrosol-trio-treated HPMC, this rate was not significantly reduced in either 1.5% or 4.0% glucose peritoneal dialysis fluids. Remesothelialization was dose-dependently retarded in HPMC exposed to 3,4-DGE (>10 microl/L), formaldehyde (>5 micromol/L) but not by exposure to the other GDP tested even at 5 times the concentration present in low glucose solutions. The rate of remesothelialization was not significantly altered by exposure to D-glucose concentrations up to 80 mmol/L.

CONCLUSION

These data identify that the formaldehyde and 3,4-DGE present in heat-sterilized peritoneal dialysis solutions are important in reducing mesothelial cell regeneration. Specifically targeting their removal may have major benefits in preserving the mesothelium during long-term peritoneal dialysis.

Role of peritoneal mesothelial cells in peritonitis

Background

Peritoneal mesothelial cells have a remarkable capacity to respond to peritoneal insults. They generate an intense biological response and play an important role in the formation of adhesions. This review describes these activities and comments on their relationship to surgical drainage, peritoneal lavage and laparostomy in the management of patients with peritonitis.

Methods and results

Material was identified from previous review articles, references cited in original papers and a Medline search of the literature. The peritoneal mesothelium adapts to peritonitis by facilitating the clearance of contaminated fluid from the peritoneal cavity and inducing the formation of fibrinous adhesions that support the localization of contaminants. In addition, the fluid within the peritoneal cavity is a battleground in which effector mechanisms generated with the involvement of peritoneal mesothelial cells meet the contaminants. The result is a complex mix of cascading processes that have evolved to protect life in the absence of surgery.

Conclusion

Future advances in the management of patients with severe peritonitis may depend upon molecular strategies that modify the activity of peritoneal mesothelial cells.

Mesothelial cells: their structure, function and role in serosal repair

The mesothelium is composed of an extensive monolayer of specialized cells (mesothelial cells) that line the body's serous cavities and internal organs. Traditionally, this layer was thought to be a simple tissue with the sole function of providing a slippery, non-adhesive and protective surface to facilitate intracoelomic movement. However, with the gradual accumulation of information about serosal tissues over the years, the mesothelium is now recognized as a dynamic cellular membrane with many important functions. These include transport and movement of fluid and particulate matter across the serosal cavities, leucocyte migration in response to inflammatory mediators, synthesis of pro-inflammatory cytokines, growth factors and extracellular matrix proteins to aid in serosal repair, release of factors to promote both the deposition and clearance of fibrin, and antigen presentation. Furthermore, the secretion of molecules, such as glycosaminoglycans and lubricants, not only protects tissues from abrasion, but also from infection and possibly tumour dissemination. Mesothelium is also unlike other epithelial-like surfaces because healing appears diffusely across the denuded surface, whereas in true epithelia, healing occurs solely at the wound edges as sheets of cells. Although controversial, recent studies have begun to shed light on the mechanisms involved in mesothelial regeneration. In the present review, the current understanding of the structure and function of the mesothelium and the biology of mesothelial cells is discussed, together with recent insights into the mechanisms regulating its repair.