Which apolipoprotein acts as an inhibitor of lipoprotein lipase (LPL)?

• A. Apolipoprotein C1
• B. Apolipoprotein C2
• C. Apolipoprotein C3
• D. Apolipoprotein E

Answer: (C)

Understanding how apolipoproteins regulate lipoprotein lipase activity. Lipoprotein lipase (LPL) hydrolyzes triglycerides in chylomicrons and VLDL to release fatty acids for tissue use. This process is modulated by apolipoproteins on lipoprotein surfaces. Apolipoprotein C-II acts as a cofactor that activates LPL, promoting triglyceride hydrolysis. In contrast, apolipoprotein C-III inhibits LPL, reducing its activity and slowing the clearance of triglyceride-rich particles, which can contribute to hypertriglyceridemia when C-III levels are elevated. Apolipoprotein E mainly facilitates receptor-mediated remnant uptake and does not directly inhibit LPL. Apolipoprotein C-I has regulatory roles but is not the primary inhibitor of LPL. Therefore, the apolipoprotein that inhibits LPL is apolipoprotein C-III.