Dirty Medicine's Biochemistry Series: Lipid Transport Part 2

Recap of Lipid Transport Part 1

• Dietary lipids initially pass through:
  • Salivary lipase
  • Liver: Bile salts act on lipids
  • Pancreatic lipase: Potent fat destroyer
• Formation of chylomicrons in the small intestine

Lipid Transport Part 2

Chylomicron Journey

• Intestine to Lymphatic System
  • Chylomicron produced in the intestine enters the lymphatic system
  • Apo B48: First apolipoprotein receptor acting on chylomicron
    • Mnemonic: Think of B48 bomber dropping 'chylomicron bombs' into the lymphatic system

Systemic Circulation

• Chylomicrons move from lymph to systemic circulation
• HDL (High-Density Lipoprotein):
  • Known as the "good cholesterol"
  • Donates Apo C2 and Apo E to chylomicrons

Apolipoprotein Roles

• Apo B48: Mediates chylomicron release from GI to lymphatic system
• Apo C2:
  • Activates lipoprotein lipase (LPL)
  • LPL hydrolyzes triglycerides into fatty acids
  • Mnemonic: C2 cuts and cleaves triglycerides
  • Insulin also activates LPL, explaining weight loss in uncontrolled diabetes
• Apo E:
  • Acts as a receptor for uptake of lipid remnants (e.g., chylomicron remnants, LDL, VLDL)
  • Mnemonic: Apo eats the remnants, allowing recycling in the liver

Summary of Apolipoproteins

• Apo B48: Secretes chylomicrons (Mnemonic: B48 bomber)
• Apo C2: Activates LPL (Mnemonic: C2 cuts and cleaves)
• Apo E: Reuptake of remnants (Mnemonic: Apo eats)

Conclusion of Part 2

• Chylomicron converts into a remnant and is taken to the liver
• Apo E: Key gatekeeper in remnant reuptake

Preview of Part 3

• Discussion of other high-yield apolipoproteins involved in lipid transport.