TMAO: how gut microbiota contributes to heart failure Translational Research L carnitine is primarily synthesized in the liver from the amino acids lysine and methionine through a series of four enzymatic reactions, with the liver and kidneys converting the precursor butyrobetaine into active lCarnitine therapy improves right heart dysfunction through Cpt1dependent fatty acid oxidation Agrawal 2022 Pulmonary Circulation Wiley Online Library Primary carnitine deficiency cardiomyopathy International Journal of Cardiology