This paper reviews carnitine’s potential role as a therapy, specifically in HIV/AIDS-infection, and also gives an overview of some popular carnitine uses by the general public.

FUNCTIONS OF CARNITINE AND ACETYL CARNITINE

Carnitine was first discovered in 1905 by Gulewitsch and Krimberg who found it in a popular dietary supplement called Liebig's meat extract. (1)  Since that time, researchers have conducted decades of investigations on the physiological functions of L-carnitine. Carnitine is required for fat metabolism (2, 3) and acts as a fat-transporter within cells. It enters body cells as free carnitine, and in the cytosol, becomes esterified with fatty acid to form acyl-carnitine. In this form it ferries fatty acids across the membranes of the mitochondria into the mitochondrial matrix for beta-oxidation and release of energy. A related supplement, acetyl L-carnitine, is the carnitine-acetate ester.

Until recently, it was thought that carnitine was required only for long chain fatty acid metabolism. Now, however, there is evidence it is involved in medium chain fatty acid metabolism, as well. Carnitine is also now known to ferry potentially toxic fatty acid breakdown products out of the mitochondria. Several enzymes are required during the various steps of carnitine-dependent fat metabolism. Rarely, these enzymes are faulty due to an inborn error of metabolism, and the result is debilitating, often fatal illness. 

Age, diet, and metabolic conditions resulting from stress, fasting and exercise all affect carnitine requirements. (3, 4)  Tissue that burns fat as preferred fuel, mainly heart and skeletal muscle, has higher carnitine needs than tissue dependent on carbohydrate for fuel. The need for carnitine by muscle tissue, underlies the rationale for its use to boost physical performance.

There is evidence to suggest acetyl carnitine can cross the blood-brain barrier and act as a neuroprotective agent. (5)  Based on research in experimental animal models of Parkinson’s disease, Alzheimer’s disease, traumatic brain injury, and in toxicity induced by AZT (azidothymidine, zidovudine, or Retrovir), a possible protective role for acetyl carnitine has been theorized. More generally, acetyl carnitine supplements are promoted for a purported effect on cerebral functions affecting mental performance, learning, concentration and mood. (6)