Effects Of Methionine Hydroxy Analogue On Muscle Redox Status And Protein Metabolism In Broilers

Objectives: Skeletal muscle, a major component of body mass, its protein metabolism isclosely related to the redox state. Methionine, the first limiting factor in classic diets basedwith maize-soybean meal, is playing a key role in protein synthsis. Dietary methioninesupplementation is usually provided with DL-methionine (DLM) or its liquid hydroxylanalogue,2-hydroxy-(4-methylthio)butanoic acid(HMTBA) and its third product, methioninehydroxy analogue calcium salt (HMTB-Ca). They may exert different influences onantioxidation and muscle protein metabolism, as they are structurally different molecules. Atpresent, no studies have been found on the mechanism how the three methionine sourcesregulate muscle redox state and protein metabolism. Furthermore, broiler Chickens have highbody temperature, strong metabolic acivities, could be a good animal model for the study ofoxidative stress. Therefore, the experiment was carried out to investigate the impact ofdifferent doses of DLM, HMTBA and HMTB-Ca on growth performance, flesh textue andantioxidation in broilers. Also the roles of three met sources in controlling gene expression forprotein metabolism and antioxidation will be preliminarily discussed in the study.Methods: The differences of DLM, HMTBA and HMTB-Ca on free radical scavenging(·OH) capacity in vitro were studied. One hundred and sixty-eight male Ross broiler chickens(1day,49g) were randomly divided into seven equal groups. The control group was fedwithout methionine sources and the trial groups were fed with the supplementation of DLM,HMTBA or HMTB-Ca at2equimolar level. The levels of of Met supplementation in thestarter (day1-21) diets was0.2%and0.3%, and was0.16%and0.24%in the finisherdiets(day22-46). Body weights were measured weekly and food intake was monitoredthroughout the experiment to determine feed-to-gain ratio. Birds were sacrificed bydecapitation and samples were collected on21d and46d, respectively. The growthperformances of birds were monitored and the related metabolic hormones were tested. Theflesh texture, the index about energy metabolism and the ribosomal capacity were measured.The redox status in body were also tested and correlation analysis was carried on withmetabolic hormones. RT-PCR was used to determine the relative mRNA expression ofantioxidation-related genes and the key genes related about muscle protein synthesis anddegradation.Results:1) Met sources could improve the body weight, but they had no significantdifferences on the food intake and feed-to-gain ratio(p>0.05). Compared with control,0.24%HMTBA,0.16%or0.24%HMTB-Ca significantly improved body weight, leg weight,breast weight,,and leg muscle rate(p<0.05).2) Compared with DLM, HMTBA andHMTB-Ca supplementation in appropriate dose led to a significantly high levels of T3, T4and FT3in serum, significantly increased ATPase activity, RNA content, and ribosomalcapacity (CS) ratio in muscle(p<0.05), enhanced the ability of muscle protein synthesis.3)Basal diet with HMTBA and HMTB-Ca in appropriate dose could significantly decrease thelevel of free radicals in peripheral blood and MDA in liver and muscle tissue(p<0.05),whereas significantly increased T-AOC, GSH/GSSG, CAT levels in blood, muscle and liver tissue(p<0.05).4) By correlation analysis, the thyroid hormone levels were correlated with theredox state, whereas the ROS level and lipid peroxidation level were negatively correlatedwith GH, T3, T4, FT3levels.5) Compared with DLM, HMTBA and HMTB-Ca effectivelyupregulated the mRNA expression levels of antioxidation-related genes Nrf-1,Metallothionein-1and SOD1and protein synthesis-related genes m-TOR, S6K1and Eif4e,while significantly downregulated protein degradation-related genes Ubiquitin andCathepsinB(p<0.05).Conclusions: Met sources could accelerate the growth of broilers. Compared with DLM,HMTBA and HMTB-Ca can better impove the growth performances, the muscle deposition，the levels of energy metabolism-related hormones and the antioxidation in muscle. Bettereffects of HMTBA and HMTB-Ca on accelerating muscle protein deposition may be realtedabout their role in regulating the mRNA expression levels of key genes related aboutantioxidation, protein synthesis and degradation in muscle.