Influence of Impaired Liver Methionine Metabolism on the Development of Vascular Disease and Inflammation

Methionine (Met) metabolism involves the sequential formation of S-adenosylmethionine (SAM, the main biological methyl donor), S-adenosylhomocysteine (SAH) and homocysteine (Hcy). Hcy can be remethylated to Met or catabolized through the trans-sulfuration pathway. In mammals, as much as 48% of Met metabolism and up to 85% of all transmethylation reactions occur in the liver. These figures underscore the central role played by this organ in Met metabolism. Maintaining the homeostasis of this metabolic cycle has proved to be essential for the preservation of liver function up to the point of preventing its neoplastic transformation. However, an adequate hepatic metabolism of Met is not only important for the liver parenchymal cell. Evidence has accumulated over the past few years supporting the involvement of Met-derived metabolites in the triggering or attenuation of pathological processes with systemic implications. This is best illustrated by the fact that a deteriorated liver function has emerged as a major factor in the development of hyperhomocysteinemia. Elevated plasma levels of Hcy have been related to several disorders including cardiovascular and cerebrovascular diseases. On the other end, liver damage also leads to deficient SAM synthesis. Among the consequences of impaired SAM synthesis in liver tissue are the enhanced production of pro-inflammatory cytokines and mediators. In this review, we will address the mechanisms and consequences of abnormal Met metabolism in liver injury, the systemic implications of such impairment and finally the potential therapeutic interventions.