Lipid Transport

Lipoprotein Structure and Function

Plasma LipoproteinsStructurefigure 19-1

LP core Triglycerides Cholesterol

esters LP surface

Phospholipids Proteins cholesterol

Plasma LipoproteinsClasses & Functions

Chylomicrons Synthesized in small

intestine Transport dietary lipids 98% lipid, large sized,

lowest density

Plasma LipoproteinsClasses & Functions

Very Low Density Lipoprotein (VLDL) Synthesized in liver Transport

endogenous triglycerides

90% lipid, 10% protein

Plasma LipoproteinsClasses & Functions Intermediate Density

Lipoprotein (IDL) Synthesized from VLDL during VLDL

degradation

Triglyceride transport and precurser to LDL

Plasma LipoproteinsClasses & Functions

Low Density Lipoprotein (LDL) Synthesized from IDL Cholesterol transport 78% lipid, 58%

cholesterol & CE

Plasma LipoproteinsClasses & Functions

High Density Lipoprotein (HDL)

Synthesized in liver and intestine

Reservoir of apoproteins Reverse cholesterol transport 52% protein, 48% lipid, 35%

C & CE

Heterogeneity of LDL-particles Not all LDL-particles the same

Small dense LDL (diameter <256A) Large buoyant LDL (diameter >256 A) Lamarche B, St-Pierre AC, Ruel IL, et al. A prospective,

population-based study of low density lipoprotein particle size as a risk factor for  Can J Cardiol 2001;17:859-65.

2057 men with hi LDL, 5 year follow-up Those with elevated small dense LDL had RR of 2.2 for IHD

compared to men with elevated large buoyant LDL Detection expensive Treatment for lowering small dense LDL similar to

lowering all LDL (diet, exercise, drugs) Some drugs (niacin, fibrates) may be more effective at

lowering small dense LDL.

HDL : Functions Apoprotein exchange

provides apo C and apo E to/from VLDL and chylomicrons

Reverse cholesterol transport

Reverse cholesterol transportfigure 19-6

Uptake of cholesterol from peripheral tissues (binding by apo-A-I)

Esterification of HDL-C by LCAT

LCAT activated by apoA1 Transfer of CE to

lipoprotein remnants (IDL and CR) by CETP

removal of CE-rich remnants by liver, converted to bile acids and excreted