LIPID PATHWAY BASICS: Absorption, Transport and Storage of Triglyceride and Cholesterol
Exogenous (Dietary) Lipid Supply
Small Intestine: Absorption of dietary triglycerides and cholesterol
Lymph, then Plasma: Chylomicrons (ApoC2 , ApoB48 ) Transport of dietary Triglycerides and Cholesterol
Peripheral Tissues: Triglyceride uptake and Chylomicron metabolism via Lipoprotein Lipase receptors (in presence of ApoC2)
Plasma: Chylomicron Remnants (ApoE)
Liver: Chylomicron Remnant uptake via surface LDL receptors and LRP1 (in presence of ApoE)
Note: Key component carrier lipoproteins are indicated in bold parentheses. i.e. (ApoC2). _DL are Density Lipoproteins which can be High (HDL), Intermediate (IDL), Low (LDL), and Very Low (VLDL) Deficiencies in these lipoproteins often result in inability to shuttle lipids and ensuing hyperlipidemias.
Endogenous Triglyceride Supply
Liver: Synthesis of VLDL from FFAs, ApoB100, and Cholesterol
Plasma: VLDL (ApoB100, ApoC2, ApoE) Transport of endogenous triglycerides and Cholesterol
Peripheral Tissues: Triglyceride uptake and VLDL cleavage via Lipoprotein Lipase receptors (in presence of ApoC2)
Endogenous Cholesterol Supply
Plasma: IDL (ApoE ) Transport of Cholesterol and Triglycerides to Liver
Liver: IDL uptake via surface LDL receptors (in presence of ApoE)
IDL metabolism to LDL via Hepatic Lipase
Plasma: LDL (ApoB100, Apo E) Transport of Cholesterol
Peripheral Tissues: Cholesterol uptake via surface LDL receptors (in presence of ApoB100)
Author: David Lincoln Reviewers: Harjot Atwal Usama Malik Dr. Alexander A-C Leung* * MD at time of publication
Reverse Cholesterol Transport
Plasma: Immature HDL (ApoAl) Nascent in plasma
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Peripheral Tissues: Cholesterol export via surface ABCA1/ABCG1 transporters
Abbreviations: • ABCA1 – ATP-Binding Cassette Transporter Al • ABCG1 – ATP-Binding Cassette Transporter G1 • FFAs – Free Fatty Acids • LCAT – Lecithin Cholesterol Acetyl Transferase • LRP1 – LDL Receptor-related protein • SRB1 – Scavenger Receptor B1
Plasma: Mature HDL (ApoAl) Free cholesterol is esterified via LCAT.
Some cholesterol remains in plasma via CTEP-mediated transfer of Cholesterol to lower density lipoproteins (i.e. VLDL, IDL)
Liver: Cholesterol ester uptake into liver via SRB1
Legend: Pathophysiology Mechanism Sign/Symptom/Lab Finding Complications Published September, 24,2017 on www.thecalgaryguide.com