We previously reported that L-leucine suppresses myofibrillar proteolysis in chick skeletal muscles. In the current study, we compared the effects of L- and D-enantiomers of leucine on myofibrillar proteolysis in skeletal muscle of chicks. We also assessed whether leucine itself or its metabolite, alpha-ketoisocaproate (alpha-KIC), mediates the effects of leucine. Food-deprived (24 h) chicks were orally administered 225 mg/100 g body weight L-leucine, D-leucine or alpha-KIC and were sacrificed after 2 h. L-Leucine administration had an obvious inhibitory effect on myofibrillar proteolysis (plasma N(tau)-methylhistidine concentration) in chicks while D-leucine and alpha-KIC were much more effective. We also examined the expression of the proteolytic-related genes (ubiquitin, proteasome, m-calpain and cathepsin B) by real-time PCR of cDNA in chick skeletal muscles. Ubiquitin mRNA expression was decreased by D-leucine and alpha-KIC but not L-leucine. Proteasome and m-calpain mRNA expressions as well as cathepsin B mRNA expression were likewise decreased by L-leucine, D-leucine and alpha-KIC. These results indicate that D-leucine and alpha-KIC suppress proteolytic-related genes, resulting in an decrease in myofibrillar proteolysis while L-leucine is much less effective in skeletal muscle of chicks, may be explain by conversion of D-leucine to alpha-KIC.
1. The aim of this work was to select lactic acid bacteria (LAB) strains from chicks and hens of egg-laying strains for potential use to control Salmonellae. 2. Nineteen LAB strains obtained from culture collections, and 24 strains isolated from excreta of laying hens and chicks, were evaluated for inhibitory capacities against two Salmonella serotypes using a "Spot-the-lawn" technique and other in vitro properties that could be predictive of antimicrobial activity. 3. The size of the inhibition zone differed slightly between Salmonella serotypes, however, the mean size of the Salmonella inhibition zone differed greatly among the LAB strains. Lactobacillus salivarius, L. plantarum, L. rhamnosus and L. reuteri exhibited powerful inhibitory effects to each Salmonella strain. 4. The result of the acid tolerance test showed that all L. salivarius, L. kitasatonis strains and each of L. ingluviei cannot survive in a low pH environment. In the bile acid tolerance assay, growth was inhibited in all strains, except L. kitasatonis HE4, and a large inhibition was observed in most of the L. salivarius and L. crispatus strains. 5. The results demonstrate that some LAB of poultry origin were able to inhibit the growth of Salmonella and survive simulated passage through the gastrointestinal tract. The selected LAB could act in the lower gastrointestinal tract to prevent salmonellosis in poultry.
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