A role for nitric oxide in the pathogenesis of necrotizing enterocolitis: Discovery, evaluation and design of a novel prophylactic therapy.

Abstract

Necrotizing enterocolitis (NEC) is an acute, self-limiting, inflammatory bowel disease of unclear pathogenesis affecting premature infants. It is the most common acquired surgical emergency in the neonatal period. NEC is characterized by necrosis of the bowel wall and may lead to peritonitis, stricture formation with bowel obstruction and lower gastrointestinal hemorrhage. Approximately 10% of premature babies develop NEC with up to 94% of cases seen in infants born at less than 36 weeks gestation. As more and more premature infants survive the neonatal period, it is expected that the incidence of this disease will increase. Briefly, the protocol involves laparotomy of anesthetized animals, creation of closed loops from terminal ileum to proximal colon which are injected with acidified casein test solution separated by saline injected control loops. Because NO is involved in neural control of intestinal motility and mucosal protection, we sought to evaluate the effects of manipulation of the nitrergic system on experimentally induced NEC in this model. Developmental changes in piglet intestinal motility were then documented in vivo, as well as those modifications induced by systemic stimulation or inhibition of NO availability. Our results have shown the presence of an ontogenically determined pattern of fasting intestinal motor activity, which is more susceptible to nitrergic manipulation in earlier developmental stages as documented through motility responses of the terminal gut. NO synthase activity was then measured in different regions of the developing piglet gut as well as in various layers of the piglet gut wall and compared to the activity found in NEC-induced gut specimens (test loops) at different stages of development and in different gut regions. Total NOS, iNOS and cNOS activity was assayed using the conversion of 14C L-arginine to 14C citrulline in full thickness gut, and in muscular and mucosal layers separated under the dissecting microscope. The potential therapeutic applications of these findings in preventing or attenuating NEC-induced intestinal damage in premature infants led to the development of a, now ongoing, clinical trial evaluating the effects of intravenous L-arginine administration in premature infants. It is expected that, based on preliminary data, a multi-centre clinical trial may lead to the prophylactic use of L-arginine as a treatment modality for NEC. (Abstract shortened by UMI.)