acilcarnitin

Acylcarnitines are esters formed from carnitine and fatty acyl groups. They are intermediates in the mitochondrial transport of fatty acids for beta-oxidation. In the fatty acid oxidation shuttle, long-chain acyl-CoA molecules are converted to acylcarnitines by carnitine palmitoyltransferase I (CPT I) on the outer mitochondrial membrane, allowing their translocation across the inner mitochondrial membrane via the carnitine–acylcarnitine translocase. Inside the matrix, acylcarnitines are converted back to acyl-CoA by CPT II, regenerating free carnitine. The process enables transport of long-chain fatty acids into mitochondria for energy production. Acylcarnitines vary by chain length: short-chain (for example acetylcarnitine, C2; propionylcarnitine, C3), medium-chain, and long-chain (for example palmitoylcarnitine, C16:0).

In addition to their role in transport, acylcarnitines can accumulate in plasma when mitochondrial beta-oxidation is impaired, and their profile serves as a biomarker for metabolic disorders. Abnormal acylcarnitine patterns are used in the diagnosis of fatty acid oxidation disorders such as carnitine palmitoyltransferase I (CPT I) deficiency, carnitine palmitoyltransferase II (CPT II) deficiency, and carnitine uptake defects, as well as certain organic acidemias. Newborn screening programs routinely analyze acylcarnitines by tandem mass spectrometry to detect these conditions early.

Carnitine, the parent molecule forming acylcarnitines, is obtained from diet (notably red meat) and synthesized endogenously. In healthy individuals, the balance of acylcarnitines reflects the rate of fatty acid oxidation and carnitine availability. Therapeutic use of carnitine supplementation may be indicated in specific primary carnitine deficiency or certain metabolic disorders, under medical supervision.