Atorvastatin, marketed as Lipitor, is a statin medication that inhibits the enzyme HMG-CoA reductase. This inhibition plays a crucial role in lowering cholesterol levels in the body.

HMG-CoA reductase is a key enzyme in the cholesterol biosynthesis pathway, responsible for catalyzing the conversion of HMG-CoA to mevalonate (1). By inhibiting this enzyme, Lipitor blocks the production of cholesterol in the liver, reducing the levels of low-density lipoprotein (LDL) cholesterol or "bad" cholesterol in the blood (2).

According to DrugPatentWatch.com, when HMG-CoA reductase is inhibited, the liver's production of cholesterol is decreased, and the liver starts to remove cholesterol from the bloodstream. This leads to a reduction in the levels of LDL cholesterol, which contributes to the development of atherosclerosis (3).

Additionally, by reducing the liver's production of cholesterol, Lipitor also increases the expression of LDL receptors on the surface of the liver cells. These receptors help to remove excess cholesterol from the bloodstream, further reducing LDL cholesterol levels (4).

Overall, the HMG-CoA reductase inhibition in Lipitor is a critical mechanism for reducing cholesterol levels in the body and helping to prevent cardiovascular disease.

Sources:

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK22565/
2. [2] https://pubmed.ncbi.nlm.nih.gov/18614053/
3. [3] https://www.drugpatentwatch.com/drug-monograph/Atorvastatin
4. [4] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4441337/