Lipid & Cholesterol Metabolism and Transport

Lipid Metabolism and Transport

• 90% of Lipid we eat is triacylglycerol (TAG)
• TAG gets broken down to glycerol and fatty acids (FA).
• FA gets broken down by β-oxidation → acetyl-CoA → Ketone bodies.
• Lipids are transported lipoproteins. Fatty acids are transported in blood in association with albumin.

Cholesterol Metabolism and Transport

• Cholesterol is made from acetyl-CoA.
• Cholesterol is made into hormones and bile salts.
• Cholesterol is transported to cells by LDL.
• Cholesterol is returned to the liver by HDL.

Lipoproteins

• Chylomicrons
  • Carry TAG and Cholesterol from small intestine.
  • Apolipoproteins: A-I, A-II, B-48, C-I, C-II, C-III, E.
  • Large diameter.
  • Lipoprotein Lipase (LPL) releases free fatty acids from these particles.
  • Type I dyslipidemia (hyperchylomicronemia): too much chylomicrons due to LPL deficiency or altered C-II.
• Chylomicron remnants
  • Chylomicrons depleted of TAG, leaving cholesterol.
  • Carries cholesterol to liver (remnant receptors bind apoE).
• VLDL
  • Carries TAG and Cholesterol from liver.
  • Apolipoproteins: B-100, C-I, C-II, C-III, E
  • LPL releases FA.
  • Type IV dyslipidemia (hypertriglyceridemia): too much TAG due to overproduction of VLDL.
• IDL = intermediate between VLDL and LDL = VLDL after LPL action.
• LDL
  • VLDL depleted of TAG, leaving cholesterol.
  • Carries cholesterol to cells with LDL receptors (bind apoE and B-100).
  • Apolipoproteins: B-100.
  • Type IIa dyslipidemia (hypercholesterolemia): too much LDL due to absent or decreased LDL receptors.
• HDL
  • Scavenge cholesterols on cell membranes and bring back to liver (SR-BI / Scavenger Receptor BI).
  • Apolipoproteins: A-I, A-II, C-I, C-II, C-III, D, E.
  • Small diameter.
• Abeta-lipoproteinemia: deficient B-100 and B-48. Symptoms appear in the first few months of life. Failure to thrive, steatorrhea, acanthocytosis, ataxia, night blindness.