Acetyl-L-carnitine (ALC) is a synthetic, acetylated version of the naturally occurring nitrogenous substance L-carnitine. This is a substance that enhances oxidative phosphorylation (ATP production in the mitochondria) by supplying the mitochondria with certain fatty acids it needs.
Taking oral L-carnitine does not greatly increase the supply of carnitine to the brain cells (although it does to nonbrain cells) since it does not readily cross the blood-brain barrier; but by sticking an acetyl group on the L-carnitine molecule and forming ALC, we can cross this barrier and thus supply the brain with extra L-carnitine.
Animal studies have shown ALC prevents age-related lipid peroxidation of brain cells and age-associated reduction in nerve growth factor, a critical substance for maintaining normal functioning in the mammalian brain. Other studies show that ALC shields the brain from age-induced damage, including protecting NMDA receptors in the hippocampus against damage by free radicals.