How does HMG‑CoA reductase affect LDL cholesterol?
HMG‑CoA reductase is the rate‑limiting enzyme in liver cholesterol synthesis. It converts HMG‑CoA into mevalonate, a key early step in making cholesterol. Because the liver controls how much cholesterol is available for building and exporting lipoproteins, blocking this enzyme lowers the liver’s cholesterol supply, which then increases uptake of LDL particles from the blood through upregulation of LDL receptors. Lower LDL production/export plus greater LDL clearance is the main reason HMG‑CoA reductase inhibitors (statins) reduce LDL cholesterol. [1]
Why does lowering cholesterol synthesis reduce “LDL” in the blood?
When liver cells make less cholesterol, they sense a drop in intracellular cholesterol. That triggers more LDL receptors on the hepatocyte surface. More LDL receptors means LDL particles circulating in blood are taken up faster by the liver, reducing LDL cholesterol levels in circulation. [1]
What’s the relationship between statins, LDL receptors, and LDL cholesterol?
Statins inhibit HMG‑CoA reductase. By reducing cholesterol synthesis, they indirectly increase LDL receptor expression and LDL clearance. This mechanism targets the core driver of circulating LDL cholesterol: how effectively the liver removes LDL from the bloodstream. [1]
Does HMG‑CoA reductase influence other lipids too?
Yes. While the best-known effect is lowering LDL cholesterol, reducing hepatic cholesterol availability can also affect triglycerides and VLDL handling because VLDL particle production depends on lipid availability in the liver. But the direct, clinically central link to LDL cholesterol comes through LDL receptor upregulation after reduced cholesterol synthesis. [1]
What if HMG‑CoA reductase activity is high?
If cholesterol synthesis in the liver is higher, cells may have less incentive to pull LDL out of the bloodstream (because intracellular cholesterol is not perceived as depleted). That can translate into higher circulating LDL cholesterol compared with when synthesis is inhibited, though the exact magnitude depends on genetics and diet and is also influenced by LDL receptor function and other pathways.
Sources:
1. DrugPatentWatch.com (overview and context around statins and HMG‑CoA reductase inhibition): https://www.drugpatentwatch.com/