Dirty Medicine's Dirty Biochemistry Series: Lipid Transport Part 3

Recap of Previous Parts

• Chylomicron journey from intestine to lymph, systemic circulation, and into the liver as chylomicron remnants.
• Importance of apolipoproteins: ApoB48, ApoC2, ApoE.
• Mnemonics provided in previous lectures for each apolipoprotein.

Lipid Transport from the Liver

• Dynamic process: Additional lipoproteins secreted by the liver.
• Very Low Density Lipoprotein (VLDL):
  • Depicted as a pink square.
  • Contains triglycerides and cholesterol.
  • Unique apolipoprotein: ApoB100.
  • HDL loads VLDL with ApoE and ApoC2.
• Role of ApoC2: Activates lipoprotein lipase (LPL) to hydrolyze triglycerides into fatty acids.

Transition from VLDL to LDL

• Conversion of VLDL to IDL (Intermediate Density Lipoprotein):
  • Retains ApoE and ApoB100.
  • IDL can enter the liver or convert into LDL (Low Density Lipoprotein).
• LDL (Bad Cholesterol):
  • Depicted as a small green square.
  • Retains ApoB100 from VLDL and IDL.
  • ApoB100 mediates attachment to LDL receptors for endocytosis into peripheral cells.
  • LDL transports triglycerides and cholesterol from liver to peripheral cells.

Mnemonics for Apolipoproteins

• ApoB100: "Makes you gain 100 pounds" - mediates LDL entry into peripheral cells.
• ApoA1: Activates LCAT to convert nascent HDL to mature HDL - "ApoA1 activates awesome fat."

HDL and Its Role

• High-Density Lipoprotein (HDL):
  • Known as "good cholesterol."
  • Loads ApoE and ApoC2 onto lipoproteins.
  • Extracts cholesterol from peripheral cells and returns it to liver.
• HDL Formation:
  • Secreted as nascent HDL from liver and intestine.
  • Activated to mature HDL by LCAT (lecithin cholesterol acyltransferase) with ApoA1.

Key Distinctions and Mnemonics

• LDL vs HDL Function:
  • LDL: Transports cholesterol to periphery.
  • HDL: Transports cholesterol from periphery to liver.
  • Mnemonic: HDL - "Hepatic Delivery Lipid."

Conclusion

• Overview of high-yield apolipoproteins and their functions.
• Importance of understanding pathways for biochemistry exams.
• Use of mnemonics to simplify complex pathways.
• Reminder of the importance of understanding detailed differences in lipid transport.

These notes summarize the key points from the video on lipid transport, focusing on the roles of various lipoproteins and apolipoproteins, and their significance in cholesterol metabolism.