L-Acetylcarnitine (Acetylcarnitine or ALC or LAC) is an acetic acid ester of carnitine that facilitates the movement of acetyl-CoA into the matrices of mammalian mitochondria during the oxidation of fatty acids. Acetylcarnitine is an endogenous compound widely distributed in many tissues, including brain. Chemically, acetylcarnitine is the acetylated derivative of the amino acid L-carnitine whose function is generally correlated with regulation of energy metabolism within mitochondria. The synthesis of acetylcarnitine is catalyzed by the enzyme carnitine acetyltransferase (CAT), which is located on the inner mitochondrial membrane as well as in endoplasmic reticulum and peroxisome. CAT promotes the transfer of an acetyl group from acetyl-Coenzyme A (acetyl-CoA) to carnitine, thereby producing acetylcarnitine and free CoA (PMID: 29267192). After being synthetized, acetylcarnitine is transported outside mitochondria into the cytosol by the enzyme carnitine/acetylcarnitine translocase (CACT). This is a crucial metabolic reaction for beta-oxidation of fatty acids whereby acetylcarnitine facilitates the transport of acetyl-CoA across mitochondrial membranes (PMID: 29267192).  In addition to his metabolic role, L-acetylcarnitine possesses unique neuroprotective, neuromodulatory, and neurotrophic properties. acetylcarnitine is mobile throughout the plasma membranes and can rapidly cross blood-brain barrier. Indeed, acetylcarnitine can be transported by the high-affinity sodium-dependent organic cation/transporter (OCTN2), which is functionally expressed in cells forming the blood-brain barrier (PMID: 29267192). A wide range of mechanisms have been proposed to explain the multiplicity of acetylcarnitine activities within nervous tissues. In particular, it has been demonstrated that acetylcarnitine modulates the activity of nerve growth factor (NGF) and enhances the expression of NGF receptors in striatum/hippocampus during development (PMID: 29267192).  Moreover, acetylcarnitine modulates different neurotransmitter systems, including the GABAergic, dopaminergic, and cholinergic system by increasing acetyl-CoA content and choline acetyltransferase (ChAT) activity. This may play an important role in counteracting various neurodegenerative disease processes (PMID: 15363640).