Explain LDL and HDL roles and name a class of drugs that lowers LDL.

• A. HDL contributes to atherosclerosis; LDL is protective; Niacin lowers HDL.
• B. LDL lowers risk; HDL raises risk; Bile acid sequestrants increase LDL.
• C. LDL contributes to atherosclerosis; HDL is cardioprotective; Statins lower LDL by inhibiting cholesterol synthesis.
• D. LDL is protective; HDL causes atherosclerosis; Fibrates lower LDL.

Answer: (C)

LDL and HDL have opposite roles in cholesterol traffic and atherosclerosis. LDL carries cholesterol from the liver to peripheral tissues; when LDL is high or becomes oxidized in artery walls, it promotes plaque formation and atherosclerosis. HDL works in reverse cholesterol transport, scooping cholesterol from tissues and plaques and delivering it back to the liver for excretion, which helps protect against cardiovascular disease.

A class of drugs that lowers LDL is statins. They inhibit HMG-CoA reductase, the key enzyme in hepatic cholesterol synthesis. This lowers liver cholesterol, leading to upregulation of LDL receptors and increased clearance of LDL from the blood, thereby reducing plasma LDL levels. The other options either misstate the roles of LDL and HDL or the effects of the drugs (for example, niacin mainly raises HDL rather than lowers it, and bile acid sequestrants lower LDL rather than raise it).