Revisiting the Role of Carnitine in Heart Disease Through the Lens of the Gut Microbiota 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 Blood carnitine as a biomarker for acute myocardial infarction. Linear association of 10 year changes in L carnitine levels with the Download Scientific Diagram TMAO pathway and its association with cardiovascular disease. TMA, Download Scientific Diagram