Betaine or folate can equally furnish remethylation to methionine and increase transmethylation in methionine-restricted neonates

摘要

Methionine partitioning between protein turnover and a considerable pool of transmethylation precursors is a critical process in the neonate. Transmethylation yields homocysteine, which is either oxidized to cysteine (i.e., transsulfuration), or is remethylated to methionine by folate- or betaine-(from choline) mediated remethylation pathways. The present investigation quantifies the individual and synergistic importance of folate and betaine for methionine partitioning in neonates. To minimize whole body remethylation, 4-8-d-old piglets were orally fed an otherwise complete diet without remethylation precursors folate, betaine and choline (i.e. methyl-deplete, MD-) (n=18). Dietary methionine was reduced from 0.3 to 0.2 g/(kg.d) on day-5 to limit methionine availability, and methionine kinetics were assessed during a gastric infusion of [C-13(1)]methionine and [H-2(3)-methyl]methionine. Methionine kinetics were reevaluated 2 d after pigs were rescued with either dietary folate (38 mu g/(kg.d)) (MD + F) (n=6), betaine (235 mg/(kg.d)) (MD + B) (n=6) or folate and betaine (MD + FB) (n=6). Plasma choline, betaine, dimethylglycine (DMG), folate and cysteine were all diminished or undetectable after 7 d of methyl restriction (P&.05). Post rescue, plasma betaine and folate concentrations responded to their provision, and homocysteine and glycine concentrations were lower (P&.05). Post-rescue, remethylation and transmethylation rates were-70-80% higher (P&.05), and protein breakdown was spared by 27% (P&.05). However, rescue did not affect transsulfuration (oxidation), plasma methionine, protein synthesis or protein deposition (P&.05). There were no differences among rescue treatments; thus betaine was as effective as folate at furnishing remethylation. Supplemental betaine or folate can furnish the transmethylation requirement during acute protein restriction in the neonate. (C) 2018 Elsevier Inc. All rights reserved.