Dirty Medicines: Dirty Biochemistry Series - Lipid Transport Part 2

Introduction

• Continuation from Part 1 where dietary lipids pass through several stages, ending with the formation of chylomicrons.
• Part 2 resumes with chylomicrons at the intestine.

Chylomicron Journey

From Intestine to Lymphatic System

• Chylomicron:
  • Formed in the small intestine.
  • Enters the lymphatic system.
• Apo B48:
  • First apolipoprotein receptor to act on chylomicrons in the lymph.
  • Mnemonic: B48 bomber drops chylomicron bombs into the lymphatic system.

From Lymphatic System to Systemic Circulation

• HDL Role:
  • Known as 'good cholesterol'.
  • Donates additional apolipoproteins to chylomicrons.
  • Donated apolipoproteins: Apo C2 and Apo E.
• Apo B48:
  • Continues to help in transferring chylomicrons into the blood.

Functions of Apolipoproteins

Apo C2

• Function: Activates lipoprotein lipase (LPL).
• LPL: Hydrolyzes triglycerides into fatty acids for absorption.
• Mnemonic: C2 for "cuts and cleaves" triglycerides.
• Clinical Note: Insulin also activates LPL, explaining weight loss in uncontrolled diabetics.

Apo E

• Function: Mediates the reuptake of lipid remnants (chylomicron remnants, VLDL, IDL, LDL) by hepatocytes.
• Mnemonic: Apo "eats" the remnants (recycling process).

Summary of Apolipoprotein Functions

• Apo B48: Mediates secretion of chylomicrons from GI to lymphatic system.
• Apo C2: Hydrolyzes triglycerides via LPL activation.
• Apo E: Responsible for recycling lipid remnants into the liver.

Conclusion

• The chylomicron is converted into a remnant which is taken into the liver for further processing and recycling.
• Upcoming Part 3 will cover additional high-yield apolipoproteins involved in lipid transport.

Final Notes

• The video ends with a reminder of key mnemonics for each apolipoprotein discussed and a preview of topics for the next section.