Methionine and cysteine metabolism and transsulfuration at different intakes of methionine and 2-hydroxy-4-methylthiobutyrate in weaned piglets
Funding: Evonik Nutrition & Care GmbH
DL-2-Hydroxy-4-methylthiobutyric acid (DL-HMTBA), a methionine (Met) hydroxy analogue, has been suggested as a dietary Met source. How dietary DL-HMTBA compared to Met affects whole-body Met kinetics and the capacity of oxidative stress defense in growing individuals is unknown. We aim to determine to what extent DL-HMTBA supplementation of a Met-deficient diet compared to Met-supplementation affects whole-body Met and cysteine (Cys) kinetics, protein synthesis (PS), the hepatic protein fractional synthesis rate (FSR), GSH fractional synthesis rate (FSR), and basal oxidative stress level in a piglet model. Forty-eight 28-d-old weaned piglets were evenly allocated to 4 dietary groups: Met-deficient diet (Control; 70% of recommended Met plus Cys supply) and Control diet supplemented equimolarly with L-Met (L-Met), DL-Met (DL-Met) or DL-HMTBA (DL-HMTBA). At 47 d of age, the pigs receive a primed continuous intravenous infusion of L-[1-13C; methyl-2H3]-Met and [3,3-2H2]-Cys to determine the kinetics and PS rates in fasted and fed states. At 54 d of age pigs receive a continuous infusion of [1-13C]-Cys to calculate Cys flux. Three days later, GSH FSR will be determined by means of a [2,2-2H2]-glycine infusion and the concentrations of GSH and oxidized GSH (GSSG) will be measured in red blood cells. Plasma concentrations of amino acids, vitamins relevant for transmethylation and transsulfuration, and antioxidative substances will be determined. Fasting hepatic mRNA abundances of Met cycle and transsulfuration enzymes, enzymes involved in GSH metabolism and markers of oxidative stress, as well as hepatic FSR will be measured at age d 62.