Regulation of Cholesterol Synthesis

Regulation of Cholesterol Biosynthesis

• The rate limiting enzyme of cholesterol biosynthesis is HMG- CoA reductase.
• Cholesterol, mevalonate, bile salts or acids inhibits HMG CoA reductase.
• Insulin and thyroxine increase the activity of HMG CoA reductase
• Glucagon and Glucocorticoids decreases the activity of HMG CoA reductase.
• Hypolipidemic drugs (lovastatin, mevastatin) inhibits cholesterol synthesis by acting as competitive inhibitors of HMG CoA reductase. 

Esterification of Cholesterol

Esterified form of cholesterol are-

1. Linoleic acid
2. Oleic acid
3. Palmitic acid
4. Arachidonic acid

Esterification of cholesterol is catalyzed by two enzymes-

1. In tissues- Increase in intracellular cholesterol activates Acyl cholesterol acyl transferase (ACAT)
2. In Plasma- Lecithin cholesterol acetyl transferase (LCAT) 

Cholesterol Excretion-

• Sterol (coprostenol), which is formed from cholesterol in the lower intestine by the action of intestinal flora.