Methionine Metabolism in Parenterally Fed Critically Ill Children

Critically ill children have abnormal utilization of nutrients such as glucose, lipids and protein. Protein synthesis is increased mainly in the form of immune and signaling proteins, while synthesis of muscle and structural proteins is decreased. The metabolism of sulfur amino acids and specifically methionine and cysteine have not been investigated in critically ill septic children, despite that sulfur amino acids have important roles on thiol, antioxidant and epigenetic reactions, as well as precursor of glutathione (GSH). Methionine metabolism in critically ill children will be influenced by its rate of utilization through the transmethylation, remethylation and transsulfuration pathways, which are the major pathways of methionine metabolism.

The investigators study aims to investigate the metabolism of methionine and cysteine in parenterally fed critically ill septic children. The investigators aim to determine the rates of transmethylation, remethylation, transsulfuration and GSH synthesis rates in critically ill septic children, to determine in vivo, whole body sulfur amino acid metabolism when sulfur amino acids are supplied by the parenteral route. The objective is to determine whether current parenteral intakes support GSH synthesis and if methionine metabolism differs when supplied by the parenteral versus the enteral route. Methionine parenteral requirements will be also studied by using the indicator amino acid oxidation and balance technique.