The effects of dietary methyl donors on methionine partitioning in the neonatal piglet

Methionine is an amino acid that is not only required for growth, but its methyl group also contributes to the regulation of genes and the synthesis of more than 50 nutrients. As an essential amino acid, the neonate’s supply of methionine is dependent on the dietary intake and thus, the partitioning of methionine between these various roles is of clinical interest. When methionine is not partitioned into protein for growth, its metabolism forms the methionine cycle, which can be summarized by three major processes: transmethylation which transfers methyl groups to nutrient precursors and DNA, transsulfuration which represents the irreversible removal of demethylated methionine to cysteine, and remethylation which reforms methionine and completes the cycle. Remethylation is facilitated by the dietary methyl donors folate and choline (via betaine). Dietary intakes of folate vary drastically and choline intakes are often below the adequate intake in most populations. We hypothesized that dietary methyl donors significantly impact neonatal methionine partitioning, and possibly the methionine requirement. To test our hypothesis, we fed 4-8 day old neonatal piglets a low-methionine diet that was either deficient, or replete, in dietary methyl donors. Using a variety of tracer techniques we demonstrate significant effects of dietary methyl donors on methionine partitioning into protein, as well as whole-body rates of transmethylation and remethylation. Furthermore, we show that dietary methyl donors affect methyl group partitioning towards specific transmethylation reactions. Dietary methyl donors should be considered when evaluating the neonatal methionine requirement.