Statins inhibit HMG-CoA reductase, reducing cholesterol synthesis. Which compensatory cellular response limits the efficacy of low-dose statin monotherapy?

• A Upregulation of LDL receptor expression, which paradoxically increases circulating LDL
• B Upregulation of HMG-CoA reductase protein and upregulation of LDL receptor expression — the latter actually enhances statin efficacy while reductase upregulation limits it ✓
• C Downregulation of PCSK9 secretion, which preserves LDL receptor recycling
• D Activation of ACAT, which esterifies intracellular cholesterol for storage rather than increasing its synthesis

Explanation

Statin-induced reduction of intracellular cholesterol activates SREBP-2 (sterol regulatory element binding protein-2). SREBP-2 simultaneously upregulates HMG-CoA reductase (partially counteracting the statin) AND LDL receptor gene expression. The LDL receptor upregulation is therapeutically beneficial (clears LDL from blood). The reductase upregulation is the pharmacological resistance mechanism — this is why combination therapy (statin + ezetimibe or PCSK9 inhibitor) is more effective. PCSK9 degrades LDL receptors; statins actually increase PCSK9 secretion, which is why PCSK9 inhibitors work synergistically.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

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