Glycine prevents the induction of apoptosis attributed to mesenteric ischemia/reperfusion injury in a rat model

Purpose. We have previously demonstrated that glycine has a protective effect in mesenteric ischemia/reperfusion (I/R) injury. The purpose of this study was to elucidate the molecular mechanisms of the cytoprotective action of glycine. Because oxidative stress in I/R injury can lead to apoptosis, rue examined the role of glycine in modulating the apoptotic signals in a rat mesenteric I/R injury model. Methods. Twenty four anesthetized male Sprague Dawley rats were subjected to 1 hour of mesenteric ischemia followed by 2 hours of reperfusion. Control animals (n = 6) received normal saline intravenously at the rate of 0.01 mL/g/h during the ischemia and reperfusion period. Treated animals divided in 3 groups (n = 6 in each) received glycine at a dose of either 0.5, 0.75, or 1.0 mg/g, infused at the rate of 0.01 mL/g/h during the reperfusion period. Animals were killed at the end of the experiment, and proximal, middle, and distal segments of the small bowel were harvested for histopathology, TUNEL assay, and immunohistochemistry. Expression of apoptosis-related molecules, bcl-2, box, caspase-3, death receptor, Fas, and death substrate, poly (ADP-ribose) polymerise (PARP) were studied. Results. In glycine-treated animals, the middle and distal segments of the small intestine were well-preserved and showed better histologic grade and morphometric parameters as compared with saline controls (P < .05) in a dose-independent manner. There was increased apoptosis in saline controls as compared to the treated group (P < .01). Pro-apoptotic box and caspase-3 were downregulated, whereas bcl-2 was upregulated in the glycine-treated animals (P < .02). Increased expression of death receptors and cleavage of PARP was observed in saline controls as compared to treated groups (P < .05). No significant differences were noted between the proximal bowel segments of treated and control animals. Conclusions. These data support the concept that I/R causes formation of death-inducing signal complexes, which may activate the sequential cleavage of caspases and death substrates. We have demonstrated that one of the mechanisms of the protective effect of glycine is the downregulation of the death-inducing signals and abrogation of the apoptotic cascade in this I/R injury model.