2001 Harry M. Vars Research Award. Enteral nutrients alter enterocyte function within an in vitro model similar to an acute in vivo rat model during hypoxia

Resistance to hypoxia-induced necroptosis is conferred by glycolytic pyruvate scavenging of mitochondrial superoxide in colorectal cancer cells

Cancer cells may survive under oxygen and nutrient deprivation by metabolic reprogramming for high levels of anaerobic glycolysis, which contributes to tumor growth and drug resistance. Abnormally expressed glucose transporters (GLUTs) are colocalized with hypoxia (Hx) inducible factor (HIF)1α in peri-necrotic regions in human colorectal carcinoma. However, the underlying mechanisms of anti-necrotic resistance conferred by glucose metabolism in hypoxic cancer cells remain poorly understood. Our aim was to investigate signaling pathways of Hx-induced necroptosis and explore the role of glucose pyruvate metabolite in mechanisms of death resistance. Human colorectal carcinoma cells were Hx exposed with or without glucose, and cell necroptosis was examined by receptor-interacting protein (RIP)1/3 kinase immunoprecipitation and (32)P kinase assays. Our results showed increased RIP1/3 complex formation and phosphorylation in hypoxic, but not normoxic cells in glucose-free media. Blocking RIP1 signaling, by necrostatin-1 or gene silencing, decreased lactodehydrogenase (LDH) leakage and plasma membrane disintegration. Generation of mitochondrial superoxide was noted after hypoxic challenge; its reduction by antioxidants inhibited RIP signaling and cell necrosis. Supplementation of glucose diminished the RIP-dependent LDH leakage and morphological damage in hypoxic cells, whereas non-metabolizable sugar analogs did not. Hypoxic cells given glucose showed nuclear translocation of HIF1α associated with upregulation of GLUT-1 and GLUT-4 expression, as well as increase of intracellular ATP, pyruvate and lactate levels. The glucose-mediated death resistance was ablated by iodoacetate (an inhibitor to glyceraldehyde-3-phosphate dehydrogenase), but not by UK5099 (an inhibitor to mitochondrial pyruvate carrier), suggesting that glycolytic pathway was involved in anti-necrotic mechanism. Lastly, replacing glucose with cell-permeable pyruvate derivative also led to decrease of Hx-induced necroptosis by suppression of mitochondrial superoxide in an energy-independent manner. In conclusion, glycolytic metabolism confers resistance to RIP-dependent necroptosis in hypoxic cancer cells partly through pyruvate scavenging of mitochondrial free radicals.

Fructan supplementation and infection affect food intake, fever, and epithelial sloughing from Salmonella challenge in weanling puppies

Our objective was to examine the effects of fructan supplementation on the immune response of weanling puppies subjected to bacterial challenge. Previous studies in bacterial challenged neonatal piglets have reported benefits of fructan supplementation. Thirty hound-cross puppies (12 wk of age) were used in a 2 x 3 factorial randomized complete block design. Following a 7-d baseline period, puppies were assigned to diets containing: 1) no prebiotic, 2) 1% short-chain fructooligosaccharides (scFOS), or 3) 1% inulin. After 14 d on treatment diet, dogs received an oral gavage of: 1) Salmonella typhimurium DT104 (5 x 10(8) colony forming units) or 2) 0.9% saline. Food intake, fecal and activity scores, body temperature, body weight, blood chemistry, intestinal nutrient transport, intestinal morphology and pathology, and gut microbiota were measured. Food intake decreased (P < 0.01) and body temperature increased (P < 0.05) in infected puppies. However, the decrease in food intake was less (P < 0.05) in those consuming fructans. Infected puppies consuming fructans also had decreased (P = 0.05) severity of enterocyte sloughing than those fed the control diet. Ileal Na+-dependent glucose transport was decreased (P = 0.02) in infected vs. noninfected puppies consuming CON, whereas no changes occurred in fructan-supplemented animals. Puppies consuming inulin also had increased fecal acetate (P = 0.03) and total short-chain fatty acid (P = 0.06) concentrations than scFOS-fed puppies and controls. Finally, puppies fed inulin had an increase (P = 0.05) in Lactobacillus concentrations compared with scFOS and CON. In summary, fructan supplementation appeared to attenuate some of the negative responses associated with Salmonella challenge and may provide protection against infection in weanling puppies.

Dietary glutamine supplementation prevents mucosal injury and modulates intestinal epithelial restitution following ischemia-reperfusion injury in the rat

The aim of the present study was to evaluate the preventive effect of a 2-day oral glutamine supplementation against intestinal ischemia-reperfusion (IR) injury in a rat. Male Sprague-Dawley rats were divided into four experimental groups: sham rats underwent laparotomy, sham-GLU rats underwent laparotomy and were treaded with enteral glutamine (GLU) given in drinking water (2%) 48 hr before and following operation, IR rats underwent occlusion of both the superior mesenteric artery and the portal vein for 30 min followed by 24 hr of reperfusion, and IR-GLU rats were treated with enteral glutamine 48 hr before and following IR. Intestinal mucosal damage (Park's injury score), mucosal structural changes, enterocyte proliferation, and enterocyte apoptosis were determined 24 hr following IR. Sham-GLU rats demonstrated a lower rate of cell apoptosis in jejunum and ileum compared to sham animals. IR-GLU animals demonstrated a greater jejunal and ileal bowel and mucosal weight, mucosal DNA, villous height and crypt depth, and enterocyte proliferation index in ileum and a lower injury score grade in jejunum compared to IR-nontreated rats. In conclusion, pretreatment with oral glutamine prevents mucosal injury and improves intestinal recovery following IR injury in the rat.