Biochemistry

Carnitine, via carnitine palmitoyltransferase (CPT), transfers long-chain fatty acyl groups across the inner mitochondrial membrane, enabling their oxidation in the matrix.

Acetoacetate is the first ketone body formed from two molecules of Acetyl-CoA via HMG-CoA synthase. It can be reduced to beta-hydroxybutyrate or decarboxylated to acetone.

Myelin contains approximately 80% lipid by weight, with cholesterol being the most abundant lipid (27% of total myelin mass), followed by galactocerebroside.

LDL carries cholesterol into arterial walls and can be oxidized, promoting atherosclerosis. HDL mediates reverse cholesterol transport, removing cholesterol from tissues and delivering it to the liver.

Approximately 70-80% of body cholesterol is synthesized de novo, primarily in the liver. The remaining 20-30% comes from dietary sources.

Niemann-Pick disease results from deficiency of sphingomyelinase, leading to accumulation of sphingomyelin in lysosomes, particularly affecting the nervous system and liver.

ApoE acts as a ligand recognized by hepatic receptors (LDL receptor and LDL receptor-related protein), mediating the uptake of chylomicron remnants and VLDL remnants.

LCAT esterifies free cholesterol on lipoprotein surfaces, forming cholesterol esters that move to the hydrophobic core. This process is essential for lipoprotein maturation.

During fasting, the liver increases synthesis and secretion of VLDL to transport endogenous triglycerides produced from gluconeogenesis and fatty acid oxidation.

Familial hypercholesterolemia results from mutations in the LDL receptor gene, leading to impaired LDL uptake and elevated plasma LDL cholesterol levels.