Plasminogen activator inhibitor 2 reduces peritoneal fibrinolytic activity in inflammation

Polyvinylpyrrolidone-Alginate Film Barriers for Abdominal Surgery: Anti-Adhesion Effect in Murine Model

Surgical operations on the peritoneum are often associated with the formation of adhesions, which can interfere with the normal functioning of the internal organs. The effectiveness of existing barrier materials is relatively low. In this work, the effectiveness of soluble alginate-polyvinylpyrrolidone (PVP-Alg) and non-soluble Ca ion cross-linked (PVP-Alg-Ca) films in preventing these adhesions was evaluated. Experiments in vivo were performed on mice via mechanical injury to the adjacent peritoneum wall and the caecum, followed by the application of PVP-Alg or PVP-Alg-Ca films to the injured area. After 7 days, samples from the peritoneal wall and caecum were analyzed using histology and quantitative polymerase chain reaction (qPCR). It was shown that the expression of genes responsible for adhesion formation in the caecum in the PVP-Alg group was comparable to that in the control group, while in the PVP-Alg-Ca group, it increased by 5-10 times. These results were consistent with the histology: in the PVP-Alg group, the adhesions did not form, while in the PVP-Alg-Ca group, the adhesions corresponded to five points on the adhesion scale. Therefore, the formation of intraperitoneal adhesions can be effectively prevented by non-crosslinked, biodegradable PVP-Alg films, whereas cross-linked, not biodegradable PVP-Alg-Ca films cause inflammation and adhesion formation.

Pathogenesis of postoperative adhesion formation

Background

Current views on the pathogenesis of adhesion formation are based on the ‘classical concept of adhesion formation’, namely that a reduction in peritoneal fibrinolytic activity following peritoneal trauma is of key importance in adhesion development.

Methods

A non-systematic literature search (1960–2010) was performed in PubMed to identify all original articles on the pathogenesis of adhesion formation. Information was sought on the role of the fibrinolytic, coagulatory and inflammatory systems in the disease process.

Results

One unifying concept emerged when assessing 50 years of studies in animals and humans on the pathogenesis of adhesion formation. Peritoneal damage inflicted by surgical trauma or other insults evokes an inflammatory response, thereby promoting procoagulatory and antifibrinolytic reactions, and a subsequent significant increase in fibrin formation. Importantly, peritoneal inflammatory status seems a crucial factor in determining the duration and extent of the imbalance between fibrin formation and fibrin dissolution, and therefore in the persistence of fibrin deposits, determining whether or not adhesions develop.

Conclusion

Suppression of inflammation, manipulation of coagulation as well as direct augmentation of fibrinolytic activity may be promising antiadhesion treatment strategies.

Addition of nimesulide to small intestinal submucosa biomaterial inhibits postsurgical adhesiogenesis in rats

Adhesion formation is a common complication in abdominal surgery with incidence as high as 93% and small bowel obstruction a common complication. Because the extracellular matrix material, small intestinal submucosa (SIS), is commonly used in various surgical procedures, methods to inhibit adhesiogenesis are of great interest. This study was undertaken to determine if incorporation of nimesulide (NM), a selective cyclooxygenase (COX)-2 inhibitor, could reduce the extent and tenacity of intraabdominal adhesion formation associated with SIS implantation. Female Sprague-Dawley rats underwent a cecal abrasion surgical procedure to induce adhesiogenesis. Rats were either left untreated or treated by direct application over the injured cecum with polypropylene mesh (PPM); SIS; SIS containing a low dose of NM; or SIS containing a high dose of NM. Rats were euthanized 21 days later, and adhesion extent and tenacity were evaluated using standard scales (0 = minimal adhesiogenesis; 4 = severe adhesiogenesis). Addition of NM to SIS resulted in a significant (p < 0.05) reduction in adhesion extent and in a similar reduction in adhesion tenacity for SIS containing a low dose of NM. Adhesions typically extended from the abraded cecal surface to the body wall and were characterized histologically by fibrous tissue adherent to the cecal wall. In conclusion, addition of the nonsteroidal anti-inflammatory, COX-2 selective drug, NM, to SIS attenuates adhesion extent and tenacity when compared with surgical placement of SIS or PPM alone.

The innate immune response to secondary peritonitis

Secondary peritonitis continues to cause high morbidity and mortality despite improvements in medical and surgical therapy. This review combines data from published literature, focusing on molecular patterns of inflammation in pathophysiology and prognosis during peritonitis. Orchestration of the innate immune response is essential. To clear the microbial infection, activation and attraction of leukocytes are essential and beneficial, just like the expression of inflammatory cytokines. Exaggeration of these inflammatory systems leads to tissue damage and organ failure. Nonsurvivors have increased proinflammation, complement activation, coagulation, and chemotaxis. In these patients, anti-inflammatory systems are decreased in blood and lungs, whereas the abdominal compartment shows decreased neutrophil activation and decreased or stationary chemokine and cytokine levels. A later down-regulation of proinflammatory mediators with concomitant overexpression of anti-inflammatory mediators leads to immunoparalysis and failure to clear residual bacterial load, resulting in the occurrence of superimposed infections. Thus, in patients with adverse outcome, the inflammatory reaction is no longer contained within the abdomen, and the inflammatory response has shifted to other compartments. For the understanding of the host response to secondary peritonitis, it is essential to realize that the defense systems presumably are expressed differently and, in part, autonomously in different compartments.

Mesh Fixation Devices and Formation of Intraperitoneal Adhesions

PURPOSE

To investigate the effect of mesh fixation devices on the formation of intra-abdominal adhesions.

MATERIALS AND METHODS

Fourteen New Zealand rabbits were used. In seven animals, nickel-titanium (nitinol) anchors (group 1) and titanium tacks (group 2) were applied by laparoscopy on the right and left sides of the abdomen, respectively. In the remaining seven rabbits, the same devices were applied on prosthetic meshes (groups 3 and 4, respectively). On day 30, the rabbits were sacrificed and macroscopic adhesion scoring was performed. All the specimens were assessed by scanning electron microscopy (SEM).

RESULTS

All parameters of adhesion except extension were significantly higher in group 4 than group 3 (P < 0.05). Comparisons of group 1 vs. group 2 were not statistically significant (P > 0.05). All the comparisons between a nonmesh group and a mesh group resulted in significant differences. SEM results revealed that the mesothelial cell layer and connective tissue intensively covered the tacks in group 2 whereas no similar findings were observed in group 1. Comparable appearances were encountered in groups 3 and 4.

CONCLUSION

The nitinol anchor is associated with an acceptable level of adhesion formation and its intraperitoneal use can be considered safe in this regard.

Effect of Sirolimus in the Prevention of Adhesions Around Intraabdominal Prosthetic Graft

BACKGROUND

Adhesions due to the reactions caused by the grafts used in primary vascular operations can lead to various problems when a secondary operation is necessary. These problems include bleeding, injuries to neighboring organs, and complications occurring due to a prolonged operation. We investigated the effects of sirolimus, which has antiproliferative features, on vascular adhesions.

METHODS

The abdominal aorta of rats was explored and abrasions applied. Following the fixation of a polytetrafluoroethylene (PTFE) graft on the abdominal aorta, sirolimus (rapamycin) is applied (in powdered form) onto the grafts of the study group. Eight weeks later a laparotomy was repeated and any adhesions were evaluated.

RESULTS

In the study group the adhesions were determined to be fewer in number and milder in severity. Severe cases of adhesion were determined in the control group.

CONCLUSIONS

Therefore, sirolimus applied around the prosthesis in vascular operations was determined to be effective at preventing possible adhesions.

Effects of Seprafilm on peritoneal fibrinolytic system

BACKGROUND

There is a high incidence of adhesions after ventral hernia repair with polypropylene mesh. The purpose of the present study was to evaluate the efficacy of Seprafilm in the prevention of adhesion formation and effect on peritoneal fibrinolytic activity.

METHODS

An incisional hernia model was created in rats. In the experimental group Seprafilm was placed between polypropylene mesh and abdominal organs. On the 14th day adhesions were evaluated and tissue plasminogen activator (tPA), urokinase plasminogen activator (uPA), plasminogen activator inhibitor (PAI) type 1 and 2 were measured in peritoneal biopsy specimens.

RESULTS

Adhesions were significantly reduced in the Seprafilm group (P = 0.002). Nevertheless, there were no difference between the two groups in levels of tPA, PAI-1 and PAI-2. However, the levels of uPA were significantly decreased in the Seprafilm group.

CONCLUSIONS

The adhesion preventive effect of Seprafilm is not directly related in peritoneal fibrinolytic activity. Instead, the physical properties (barrier, hydroflotation and sliconizing effect) of the membrane are primarily responsible for adhesion prevention.

Pathophysiology of intra-abdominal adhesion and abscess formation, and the effect of hyaluronan

BACKGROUND

Intra-abdominal adhesions and abscesses cause significant morbidity and mortality. The formation of fibrin in the abdominal cavity is a common pathophysiological pathway for both. The aim of this review was to investigate the pathophysiology of intra-abdominal adhesions and abscesses, and to explore the possible sites of action of hyaluronan.

METHODS

Data were reviewed from the literature using the Medline database.

RESULTS

Both surgery and peritonitis disturb the equilibrium between coagulation and fibrinolysis in the abdominal cavity in favour of the coagulation system. Hyaluronan-based agents reduce adhesion formation after surgery. Moreover, hyaluronan solution reduces abscess formation in experimental peritonitis. Possible mechanisms of action include mechanical separation of wound surfaces, improvement of peritoneal healing, modulation of the inflammatory response and enhanced fibrinolysis.

CONCLUSION

Diminished fibrin degradation is a common pathway for the formation of adhesions and abscesses. The potential of hyaluronan-based agents to reduce intra-abdominal adhesions and abscesses in abdominal surgery and sepsis is a promising new concept. Elucidating the mechanisms involved and the clinical application of hyaluronan in peritonitis are challenges for future research.

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.

Use of fibrinolytic agents in the prevention of postoperative adhesion formation

OBJECTIVE

To review the events leading to the formation of adhesions, to describe the development of fibrinolytic agents, to review more than a century of research on the use of fibrinolytic agents in adhesion prevention, and to look at future aspects of adhesion prevention.

RESULTS

A better understanding of the pathogenesis of adhesion formation has resulted in the use of fibrinolytic agents in their prevention. Fibrinolytic agents promote fibrinolytic activity during the early period after peritoneal trauma during which an increased formation of fibrin is seen in combination with a deficiency of endogenous fibrinolytic activity. Initially, chemical attacks on fibrin (fibrolysin and hypertonic glucose), foreign digestive ferments (pepsin, trypsin, and papain), and stimulation of intraperitoneal leukocytosis (amniotic fluid) were used. Development of new thrombolytic agents was soon followed by experiments in animal adhesion models and clinical studies to examine their antiadhesion properties. Plasmin preparations (plasmin, actase, and fibrinolysin) and plasmin activators (streptokinase, urokinase, and tissue-type plasminogen activator) were found to be efficacious in preventing adhesion formation in the greater part of reviewed animal and clinical studies.

CONCLUSION(S)

From the current literature, it can be concluded that postoperative intraperitoneal administration of thrombolytic agents can significantly decrease adhesion formation. Given the large number of experimental studies in animals, future studies should focus on the clinical use of fibrinolytic agents in the prevention of postsurgical adhesion formation.

Secretion of plasminogen activator inhibitor 2 by human peripheral blood monocytes occurs via an endoplasmic reticulum-golgi-independent pathway

Plasminogen activator inhibitor 2 (PAI-2) is a serine protease inhibitor (serpin) that is secreted and accumulated intracellularly by monocytes. We investigated PAI-2 synthesis by isolated human peripheral blood monocytes and found that a 47-kDa nonglycosylated form of PAI-2 was abundant in conditioned medium from monocytes. Secretion of PAI-2 by monocytes was not inhibited by agents that inhibit either ER-Golgi pathway-dependent secretion, brefeldin A, or N-linked glycosylation, tunicamycin. IL-1beta served as a control for a protein that is secreted by an ER-Golgi-independent pathway, and secretion of IL-1beta was not inhibited by brefeldin A. This was in contrast to secretion of TNFalpha, which was dependent on the ER-Golgi pathway. None of the treatments was cytotoxic toward monocytes, as measured by release of the intracellular enzyme lactate dehydrogenase (LDH) into the conditioned medium. Subcellular fractionation revealed that PAI-2 and IL-1beta were colocalized. The mechanism for secretion of PAI-2 was not dependent on calcium or intracellular trafficking via the classical vesicular mechanism(s), distinguishing it from IL-1beta secretion. These studies show that PAI-2 is secreted by primary human monocytes via an ER-Golgi-independent pathway.

Long-term analysis of peritoneal plasminogen activator activity and adhesion formation after surgical trauma in the rat model

OBJECTIVE

Recent literature has shown that a common pathway in postsurgical adhesion formation is a transient reduction in local plasminogen activator activity, shortly after peritoneal trauma. This deficit in fibrinolysis permits deposited fibrin to become organized into fibrous, permanent adhesions. Although adhesion formation is a process that continues beyond the first postoperative days, long-term analysis of this theory has not been performed.

DESIGN

A standardized peritoneal adhesion model in the rat.

MAIN OUTCOME MEASURE(S)

Long-term analysis of the peritoneal fibrinolytic activity (extraction technique) was related to the extent of postsurgical adhesion formation, up to 1 year postoperatively.

RESULT(S)

Total and tissue plasminogen activator activity were significantly increased at days 3 and 8, and 1 month postoperatively. A mean adhesion percentage of 75% per peritoneal defect was found to persist throughout all evaluation times, which was directly related to the increase of fibrinolysis.

CONCLUSION(S)

In contrast to the classical concept that adhesion formation is related to a reduction in fibrinolysis, an impressive increase of the fibrinolysis was found to be associated with the persistence of adhesions.

Plasminogen activator inhibitor-2 expression in inflamed appendix

Plasminogen activator inhibitors are thought to be responsible for the abolition of fibrinolytic activity in inflamed peritoneum. This reduction in the fibrin clearing capacity of the peritoneum promotes the formation of intra-abdominal adhesions. High concentrations of plasminogen activator inhibitor-2 (PAI-2) have been previously found in inflamed peritoneal tissue using immunoassays, but it is undetectable in normal peritoneum. The aim of this study was to localize plasminogen activator inhibitor-2 production in tissue by in situ mRNA hybridisation. Sections of normal and inflamed human appendix were hybridised with a digoxigenin labelled cDNA probe. In normal appendix staining was confined to macrophages in the mucosa. Macrophage staining was also seen in inflamed tissue but with a wider distribution throughout the appendix wall. PAI-2 was also localized to mesothelial cells of inflamed but not normal appendix. Cell identities were confirmed using immunohistochemistry directed against cell specific markers. Staining was absent from control slides incubated with plasmid DNA or PAI-2 probe following ribonuclease digestion. The identification of the cells expressing the PAI-2 gene in peritoneum increases our understanding of the pathophysiological process leading to fibrin deposition within the abdomen during peritonitis.

Human intraperitoneal fibrinolytic response to elective surgery

Intra-abdominal adhesions develop in over 90 per cent of patients undergoing laparotomy. Peritoneal fibrinolysis is believed to be important in the pathophysiology of adhesion formation. This study investigated the fibrinolytic response of postoperative peritoneal fluid in 12 patients undergoing elective laparotomy. There was a significant reduction in the plasminogen activating activity to undetectable levels at 24 h, which was sustained at 48 h (P < 0.05). While there was an early reduction in the concentration of tissue plasminogen activator (median 40.0, 28.2, 16.3 and 31.9 ng/ml at 2, 6, 24 and 48 h respectively; P < 0.05), the abolition of functional fibrinolytic activity appeared to be secondary to a marked increase in the concentration of plasminogen activator inhibitor (PAI) 1 (median 86, 196, 800 and 730 ng/ml at 2, 6, 24 and 48 h respectively; P < 0.05) and PAI-2 (median less than 6, 12, 155 and 245 ng/ml at 2, 6, 24 and 48 h respectively; P < 0.05). This reduction in the plasminogen activating activity of peritoneal fluid may favour the formation of permanent fibrous adhesions following surgery.

Fibrinolytic activity in the abdominal cavity of rats with faecal peritonitis

Generalized peritonitis causes a reduction in abdominal fibrinolytic activity, resulting in persistence of intraabdominal fibrin with subsequent adhesion and abscess formation. The activities of tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI) were measured in the peritoneal fluid of rats with faecal peritonitis and correlated with the extent of peritoneal damage to determine the cause of decreased fibrinolysis. Activity of tPA was low during the study period of 8 days, but higher in rats with peritonitis than in controls. The activity of PAI in rats with peritonitis was significantly increased compared with that of controls during the whole study period (P < 0.001). Histological signs of damage to the peritoneum were similar in rats with peritonitis and controls. There was no correlation between the extent of peritoneal damage and tPA or PAI activity. The increased activity of PAI in the peritoneal fluid of rats with faecal peritonitis may be the main cause of reduced fibrinolysis in the abdominal cavity. Activities of tPA and PAI may originate not only from the mesothelium but from other sources.