Peripheral Tissue Trauma Triggers an Inflammatory Response Causing Intestinal Microvascular Serum Leak Which Disrupts Gastrointestinal Motility

Abstract

Introduction: Combat and civilian trauma is the leading cause of death for individuals in the prime of their life. Gastrointestinal dysfunction plays a key role in the detrimental sequelae of trauma (systemic inflammatory response, feeding intolerance, reflux/aspiration pneumonia and bacterial overgrowth/dissemination through mucosal barrier failure), but the mechanisms through which peripheral tissue injury can induce these responses is unclear. Aims: To investigate the mechanism of trauma-induced gastrointestinal dysfunction in a precisely controllable non-narcotic, tissue-bone matrix (TBX) trauma model, which is known to reproducibly display significant gastrointestinal dysmotility. Methods: A non-narcotic murine tissue trauma model was constructed by the dorsal subcutaneous implantation of minced donor syngeneic tissue-bone matrix (TBX) precisely adjusted to 17.5% body weight and studied after 21 hrs. Inflammatory mediators in serum, fresh TBX and TBX wound fluid at 21hrs were measured by electrochemiluminescence detection and intestinal muscularis microvascular leak was microscopically quantified in whole-mounts after i.v. injection of FITC-dextran (70k MW). Gastrointestinal transit and jejunal circular muscle contractility was assessed after injection of normal mouse serum (i.p. 100μl q1h x 8). Results: Compared to normal serum, TNF α was only acutely elevated in fresh TBX fluid (1.1±0.01, 4.1±0.22 and 1.1±0.01 ng/ml) and IL 1β exhibited increased levels in both fresh TBX fluid and in TBX wound fluid (1.9±0.22, 107.6±1.45 and 92.2±6.12 ng/ml). Whereas, IL-6 (80.4±10.0, 158.5±4.08 and 26851.1±4883.39 ng/ml) and kerotinocyte chemokine (KC; 237.5±47.14, 110.4±1.59 and 9763.2±817.29 ng/ml) were significantly increased in the re-harvested TBX wound fluid after 21 hours of implantation. The systemic response to the implanted TBX resulted in significant serum elevations in IL-6, KC and IL-10 compared to control and sham surgical groups at 21 hrs (N=6 each), as well as causing significant intestinal muscularis microvascular leak. Interestingly, i.p. injections of normal serum into naive mice recapitulated the TBX-induced dysmotility causing delayed gastrointestinal transit (9.8±0.15 vs. 3.4±0.22) and a 49.5% suppression in bethanechol stimulated jejunal muscle strip contractility compared to saline injections (N=6). Conclusion: Peripheral tissue injury and consequent systemic inflammatory response cause intestinal muscularis microvascular leak and dysmotility, which can be recapitulated by intraperitoneal injection of exogenous normal serum. These novel findings demonstrate the key regulatory effect of intestinalmicrovascular leak on gastrointestinal motility in trauma.