Reverse cholesterol transport

Reverse cholesterol transport is a multi-step process resulting in the net movement of cholesterol from peripheral tissues back to the liver via the plasma.^[1]

Cholesterol from non-hepatic peripheral tissues is transferred to HDL by the ABCA1 (ATP-binding cassette transporter).^[2] Apolipoprotein A1 (ApoA-1), the major protein component of HDL, acts as an acceptor, and the phospholipid component of HDL acts as a sink for the mobilised cholesterol. The cholesterol is converted to cholesteryl esters by the enzyme LCAT (lecithin-cholesterol acyltransferase). The cholesteryl esters can be transferred, with the help of CETP (cholesterylester transfer protein) in exchange for triglycerides, to other lipoproteins (such as LDL and VLDL), and these lipoproteins can be taken up by secreting unesterified cholesterol into the bile or by converting cholesterol to bile acids.

Uptake of HDL₂ is mediated by hepatic lipase, a special form of lipoprotein lipase found only in the liver. Hepatic lipase activity is increased by androgens and decreased by estrogens, which may account for higher concentrations of HDL₂ in women.

References

↑ Tall, AR (February 1998). "An overview of reverse cholesterol transport.". Eur. Heart J. 19 Suppl A: A31–5. doi:10.1093/eurheartj/19.Abstract_Supplement.1. PMID 9519340.
↑ http://biochemistry.med.uoc.gr/photos/kardasis_research-07.gif in

Metabolism, catabolism, anabolism

General

Energy
metabolism

Aerobic respiration	Glycolysis → Pyruvate decarboxylation → Citric acid cycle → Oxidative phosphorylation (electron transport chain + ATP synthase)

Anaerobic respiration	Electron acceptors are other than oxygen

Fermentation	Glycolysis → Substrate-level phosphorylation ABE Ethanol Lactic acid

Specific
paths

Protein metabolism

Carbohydrate metabolism
(carbohydrate catabolism
and anabolism)

Human

Glycolysis ⇄ Gluconeogenesis

Glycogenolysis ⇄ Glycogenesis

Pentose phosphate pathway Fructolysis Galactolysis

Glycosylation N-linked O-linked

Nonhuman

Photosynthesis Anoxygenic photosynthesis Chemosynthesis Carbon fixation

Xylose metabolism Radiotrophism

Lipid metabolism
(lipolysis, lipogenesis)

Fatty acid metabolism	Fatty acid degradation (Beta oxidation) Fatty acid synthesis

Other	Steroid metabolism Sphingolipid metabolism Eicosanoid metabolism Ketosis Reverse cholesterol transport

Amino acid

Nucleotide
metabolism

Other

Metabolism: lipid metabolism – ketones/cholesterol synthesis enzymes/steroid metabolism

Mevalonate pathway

To HMG-CoA	Acetyl-Coenzyme A acetyltransferase HMG-CoA synthase (regulated step)

Ketogenesis	HMG-CoA lyase 3-hydroxybutyrate dehydrogenase Thiophorase

To Mevalonic acid	HMG-CoA reductase

To DMAPP	Mevalonate kinase Phosphomevalonate kinase Pyrophosphomevalonate decarboxylase Isopentenyl-diphosphate delta isomerase

Geranyl-	Dimethylallyltranstransferase Geranyl pyrophosphate

To cholesterol

To lanosterol	Farnesyl-diphosphate farnesyltransferase Squalene monooxygenase Lanosterol synthase

7-Dehydrocholesterol path	Lanosterol 14α-demethylase Sterol-C5-desaturase-like 7-Dehydrocholesterol reductase

Desmosterol path	24-dehydrocholesterol reductase

To Bile acids

Steroidogenesis

To pregnenolone

Side-chain cleavage

To corticosteroids

aldosterone: 18-hydroxylase

To sex hormones

To androgens	17α-hydroxylase/17,20 lyase 3β dehydrogenase 17β dehydrogenase 5α reductase 1 2

To estrogens	Aromatase

Other/ungrouped

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