Clinical Information > Gynaecological > Adhesions

NEUROKININ-1 RECEPTOR ANTAGONISTS REDUCE POSTOPERATIVE PERITONEAL ADHESION FORMATION IN A RAT MODEL

Karen L. Reed, PhD and Arthur F. Stucchi, PhD

Department of Surgery, Boston University School of Medicine

Boston, Massachusetts, USA

Intraabdominal adhesions develop in up to 94% of patients following abdominal operations (1), and they can lead to significant postoperative complications, including small-bowel obstruction, infertility and chronic pelvic pain (2). Adhesions have been recognized for more than 250 years (3), but despite considerable effort, an ideal adhesion prevention method does not exist. This is due, in part, to our insufficient understanding of the complex processes of wound repair and healing in the abdominal or peritoneal cavity.

What we do know is that abdominal operations initiate an acute inflammatory response in the peritoneal cavity. This postoperative inflammation, although part of the normal healing response, leads to deposition of a fibrin-rich matrix that is similar to the first step in the formation of a blood clot. This fibrin matrix is capable of forming permanent attachments or adhesions between adjacent surfaces within the peritoneal cavity (2). Degradation of this matrix within 48 hours of surgery is necessary for adhesion-free healing to occur (4).  Fibrin is degraded primarily by the proteolytic enzyme plasmin in a process known as fibrinolysis. Plasmin activity in the peritoneum is tightly regulated. It is increased by tissue plasminogen activator (tPA) which cleaves and activates plasminogen, the inactive form of plasmin. The activity of tPA is in turn regulated by plasminogen activator inhibitor (PAI) -1 which binds to tPA rendering it inactive (5). The relative levels of tPA and PAI-1 in the peritoneum determine the extent to which fibrinolysis can occur. Surgical trauma has been shown to impair peritoneal fibrinolytic activity via a reduction in tPA activity and/or increases in PAI-1 activity (6, 7). The importance of tPA and PAI-1 in adhesion formation is underscored by studies which show that patients with the most severe adhesions overexpress PAI-1 and have decreased tPA activity (8). Unfortunately, the mechanisms regulating these rapid changes in fibrinolytic activity following surgery have not been elucidated.

Peritoneal fibrinolytic activity and postoperative adhesion formation may be regulated, in part, by the proinflammatory peptide substance P (SP) (9, 10). SP regulates cellular activity by binding to neurokinin-1 receptors (NK-1R) located on cell surfaces. SP is known to play an important role in inflammatory and wound healing processes which suggests that it may contribute to intraabdominal adhesion formation. We have tested this hypothesis using a highly specific NK-1R antagonist, CJ-12,255, that blocks the binding of SP to the NK-1R.

For these experiments we induced adhesion formation in the peritoneal cavity of anesthetized rats via an intraabdominal surgical procedure (11). At the time of surgery animals were intraperitoneally instilled with 5 or 25 mg/ kg of the NK-1RA, CJ-12,255, or saline. Adhesion formation was assessed 7 days later.  In a duplicate study, peritoneal fibrinolytic activity due to tPA activity in peritoneal fluid was determined 24 hours following surgery.  The results of these experiments were that NK-1R antagonist administration at the high dose (25 mg/ kg) significantly reduced (P<0.05) adhesion formation by 47%. We observed 81±7% adhesion formation in the saline control animals but only 43±8% adhesion formation in the NK-1R antagonist animals. Administration of 5 mg/ kg of the NK-1RA had no affect (12). Furthermore, we measured significant increases (P < 0.05) in peritoneal fluid tPA activity at 24 hours after surgery in the NK-1R antagonist (25 mg/ kg) administered animals (12, 13). This suggests that the NK-1R antagonist may reduce adhesion formation, in part, by regulating peritoneal fibrinolytic activity.

To gain a better understanding of the postoperative time period important in adhesion formation we next determined the “window” following surgery in which NK-1R antagonist application is capable of reducing adhesion formation. NK-1R antagonist administration was postoperatively delayed by 1, 5, 12 or 24 hours. At these time points the NK-1R antagonist (25 mg/ kg), or saline as control, was injected intraperitoneally into rats that had underwent the adhesion inducing surgical procedure.  Similar to the first experiment adhesion formation was assessed at 7 days, and tPA activity in peritoneal fluid was determined 24 hours after the surgical procedure (48h if injected at 24h). Peritoneal fluid from non-operated animals 24 hours after injection with the NK-1R antagonist was also assayed.

Administration of the NK-1R antagonist 1 hour after surgery significantly reduced (P = .003) adhesion formation (24±7% vs. 63±3% for saline controls). A delay of 5 hours reduced adhesion formation to a lesser extent (36±6% vs. 55±8% for saline controls; P = .08). A delay of 12 and 24 hours was not effective in reducing adhesion formation.  The results for the fibrinolytic activity (tPA) assay had a similar pattern. If administration of the NK-1R antagonist was delayed by 1 or 5 hours tPA activity was significantly increased at 24 hours after surgery. A delay of 12 hours had no effect on tPA activity in peritoneal fluid at 24 hours after surgery.  However, peritoneal fluid tPA activity was increased (P < 0.05) in peritoneal fluid 24 hours after NK-1R antagonist administration if administered to non-operated animals or to animals 24 hours after surgery and measured at 48 hours (12).  These results suggest that the NK-1R antagonist has the ability to increase peritoneal fluid tPA activity within a 24 hour period, regardless of surgery; however, in order to affect adhesion formation in our rat model it must be administered within 5 hours of surgery. 

Lastly, we determined the effect of the NK-1R antagonist on wound healing in the peritoneal cavity. A surgical procedure was performed on rats where the colon was severed and reattached thereby creating colonic anastomoses. At the time of surgery the animals were intraperitoneally administered either the NK-1R antagonist (25 mg/ kg) or saline as control. At day 7 the sections of the colon containing the anastomoses were removed and anastomotic burst pressures were determined with a manometer. There was no significant difference in the anastomotic burst pressures between NK-1R antagonist and saline administered animals (228 + 27 vs. 248 + 44 mm/ Hg), suggesting that the NK-1R antagonist does not negatively affect wound healing (12). 

In conclusion, the data suggest that the NK-1R is important in adhesion formation. Interfering with activation of the NK-1R by administration of the NK-1R antagonist significantly decreases postoperative adhesion formation. Furthermore, the data suggest that some events critical to adhesion formation occur within the first 5 hours of abdominal surgery. NK-1R antagonist administration within this time modulates events that lead to increased tPA activity in peritoneal fluid 24h after surgery, and decreased adhesion formation 7 days later. Taken together with the fact that the antagonist does not impede wound healing the NK-1R antagonist may be a beneficial agent in the management of adhesion formation following abdominal surgery (12).

References

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12 Cohen PA, Aarons CB, Gower AC, Stucchi AF, Leeman SE, Becker JM, Reed  KL. The effectiveness of a single intraperitoneal infusion of a neurokinin-1   receptor antagonist in reducing postoperative adhesion formation is time    dependent. Surgery. 2007;141(3):368-75.

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