Apolipoprotein A-I is a protein that in humans is encoded by the APOA1 gene. It has a specific role in lipid metabolism. Recent report suggest that APOA1 mRNA is regulated by endogenously expressed antisense RNA. Apolipoprotein A-I is the major protein component of high density lipoprotein (HDL) in plasma. Chylomicrons secreted from the intestinal enterocyte also contain apo A-I, but it is quickly transferred to HDL in the bloodstream. The protein promotes fat efflux, including cholesterol, from tissues to the liver for excretion. It is a cofactor for lecithin cholesterolacyltransferase (LCAT) which is responsible for the formation of most plasma cholesteryl esters. Apo A-I was also isolated as a prostacyclin (PGI2) stabilizing factor, and thus may have an anticlotting effect. Defects in the gene encoding it are associated with HDL deficiencies, including Tangier disease, and with systemic non-neuropathic amyloidosis. ApoA1 is often used as a biomarker for prediction of cardiovascular diseases and the ratio apoB- 100/apoA1 has been reported as a stronger predictor for the risk of myocardial infarction than any other lipid measurement. ApoA1 is routinely measured using immunoassays such as ELISA or nephelometry. It has an approximate molecular weight of 28.1 kDa.
Table of Contents High low density lipoprotein (LDL)