New roles of carnitine metabolism in ammonia cytotoxicity

High levels of ammonia in blood and brain due to metabolic disorders are associated with neurological abnormalities. Although the mechanism of ammonia toxicity at the CNS level is still unknown, alterations in brain energy metabolism, in neurotransmitter function and direct effects on nervous impulse have been proposed. In most hyperammonemic conditions morphological changes in the liver and brain have been demonstrated, especially in mitochondria, endoplasmic reticulum and lysosomes, together with an accumulation of intracellular lipids. The treatment of hyperammonemias is uncertain and mostly directed to reduce the level of circulating ammonia; there is no current therapy aimed to counteract the molecular effects of ammonia. Administration of carnitine prevents acute ammonia toxicity and enhances the efficacy of ammonia elimination as urea and glutamine. In addition the cytotoxic effects of ammonia, possibly arising from lipid peroxidation, are ameliorated by carnitine. These data indicate the feasibility of utilization of carnitine in the therapy of human hyperammonemic syndromes, both for reducing the levels of ammonia and preventing its toxic effects.