C8Acylcarnitine

C8 acylcarnitine, also known as octanoylcarnitine, is an acylcarnitine composed of carnitine linked to an eight-carbon acyl group. It is one member of a large family of acylcarnitines that arise during fatty acid transport and beta-oxidation in mitochondria, and its presence in blood or other fluids reflects intermediate steps of fatty acid metabolism.

Formation and role in metabolism: Acylcarnitines form when fatty acyl groups are transferred to carnitine by carnitine palmitoyltransferase I (CPT1) on the outer mitochondrial membrane. The acylcarnitine is transported across the inner mitochondrial membrane by the carnitine–acylcarnitine translocase and re-esterified to CoA by CPT2 in the matrix for beta-oxidation. Octanoyl groups can arise from dietary or endogenous sources and may be released back into circulation, providing a useful indicator of mitochondrial fatty acid flux.

Clinical significance and testing: C8 acylcarnitine is routinely measured as part of acylcarnitine profiling by tandem mass spectrometry in newborn screening and metabolic investigations. Elevated C8 is a marker that can indicate fatty acid oxidation disorders, most notably medium-chain acyl-CoA dehydrogenase deficiency (MCAD). It can also be affected by other disorders or nonpathologic factors. Interpretation typically relies on the overall acylcarnitine pattern and ratios (for example, C8 relative to C2 or C0) alongside clinical context and confirmatory testing.

See also: acylcarnitine profiling, fatty acid oxidation disorders, tandem mass spectrometry.