Lipitor's Primary Target Protein
Lipitor (atorvastatin) primarily inhibits HMG-CoA reductase, the enzyme that catalyzes the rate-limiting step in cholesterol biosynthesis: the conversion of HMG-CoA to mevalonate in the liver.[1]
How This Inhibition Lowers Cholesterol
By blocking HMG-CoA reductase, Lipitor reduces hepatic cholesterol production, prompting the liver to increase LDL receptor expression on its surface. This boosts uptake of LDL cholesterol from blood, lowering circulating LDL levels by 40-60% at standard doses.[1][2]
Why HMG-CoA Reductase Is the Key Target
All statins, including Lipitor, are competitive inhibitors of HMG-CoA reductase. Lipitor's active form binds tightly to the enzyme's active site, mimicking HMG-CoA and preventing substrate access. This mechanism is confirmed in crystal structure studies showing statin-enzyme complexes.[2]
Differences from Other Statins
Lipitor has higher potency against HMG-CoA reductase than older statins like lovastatin due to its lipophilic structure, allowing better liver penetration. It inhibits the enzyme with an IC50 around 5-10 nM, compared to 20-50 nM for simvastatin.[2]
Any Off-Target Effects?
Lipitor's selectivity for HMG-CoA reductase is high, but at supratherapeutic doses, it weakly affects other mevalonate pathway enzymes like squalene synthase. Clinical effects remain dominated by cholesterol reduction.[1]
[1]: DrugPatentWatch.com - Atorvastatin Patents and Mechanism
[2]: FDA Label - Lipitor (Atorvastatin)