What Is Cholesterol Biosynthesis?

The key enzyme that regulates cholesterol synthesis is HMG-CoA reductase. The enzyme is inhibited by cholesterol, and the enzyme's phosphorylation can also regulate the enzyme's activity. For severe hypercholesterolemia, HMG-CoA reductase inhibitors such as lovastatin are often used.

Biosynthesis of cholesterol

Except for brain tissue and mature red blood cells, almost all tissues in the whole body can synthesize cholesterol, and the liver has the strongest synthesis ability, accounting for more than 3/4 of the total.

Acetyl CoA is the starting material and requires ATP and NADPH for hydrogen.

The synthesis process is complicated, with nearly 30 steps of enzymatic reactions, which are roughly divided into three stages:

1. Bile acid: 3/4 of cholesterol can be converted into bile acid in the liver, enter the intestine with bile, and participate in the digestion and absorption of lipids. This is the main way to cholesterol metabolism.

2. Steroid hormones: Cholesterol can be converted into adrenal cortex hormones in the adrenal cortex, regulating sugar, lipid, and protein metabolism; and can be changed by the androgen and a small amount of estrogen in the adrenal cortex. After being converted into dihydrotestosterone or estradiol, it plays a physiological role.

3.VD3: Cholesterol can be converted into 7-dehydrocholesterol (prototype VD3) in intestinal mucosal cells, transported to the skin through the blood, converted to VD3 under ultraviolet irradiation, and then hydroxylated twice in the liver and kidney to produce 1, 25- (OH) 2-D3, regulate calcium and phosphorus metabolism.

4. Cholesteryl esters: In the tissues of the liver, adrenal cortex, and small intestine, cholesterol and fatty acyl CoA are produced by fatty acyl CoA cholesterol acyltransferase (ACAT) to produce cholesterol esters. (Cholesterol esterase hydrolyzes it to cholesterol.)

In plasma, cholesterol is reacted with lecithin cholesterol acyltransferase (LCAT) to accept fatty acyl groups in lecithin molecules to produce cholesterol esters.

A small part of cholesterol can be excreted through the intestine after the action of intestinal bacteria.