Lipoprotein Metabolism

Fats absorbed in the intestine are packaged into large, triglyceride-rich particles known as chylomicrons (step 1). These lipoproteins undergo lipolysis (removal of triglyceride) to form chylomicron remnants (step 4), which are taken up by the liver via an apoE receptor (step 5). The liver can also secrete triglyceride-rich lipoproteins known as VLDL (step 2). Following lipolysis, these particles can be converted to LDL (step 6) or taken up by the liver via an apoE receptor (step 7). The LDL formed is catabolized maily by the liver (step 8) or other tissues via an LDL receptor that recognizes both apoB-100 and apoE, but not apoB-48. If LDL is modified or oxidized, it can also be taken up by a scavenger receptor on macrophages, or scavenger cells (step 10). HDL is synthesized by both the liver and the intestine (step 3). HDL picks up lipid and protein constituents from chylomicrons and VLDL as these particles undergo lipolysis (steps 4 and 6). HDL picks up free cholesterol from peripheral tissues (step 9) and macrophages (step 11), and is catabolized mainly in the liver (step 12).

Legend

LPL = lipoprotein lipase

HL = hepatic lipase

LCAT = lecithin: cholesterol acyltransferase

Apo = apolipoprotein

FFA = free fatty acid

HDL = high density lipoprotein

LDL = low density lipoprotein

VLDL = very low density lipoprotein

= synthetic pathways

= transfer pathways

= catabolic pathways

= minor pathways

= receptors