Pharmacological activation of liver X receptors promotes reverse cholesterol transport in vivo.
BACKGROUND
Liver X receptors (LXRs) are ligand-activated transcription factors involved in the control of lipid metabolism and inflammation. Synthetic LXR agonists have been shown to inhibit the progression of atherosclerosis in mice, but the mechanism is uncertain. LXR agonism upregulates the genes encoding ATP binding cassette transporters A1 (ABCA1) and G1 (ABCG1) in macrophages, thus promoting efflux of cholesterol; it also upregulates liver and intestinal ABCG5 and ABCG8, helping to promote biliary and fecal excretion of cholesterol. Thus, LXR agonism may inhibit atherosclerosis through promotion of reverse cholesterol transport (RCT) in vivo, but this has not been proven. We previously described an in vivo method to trace the movement of cholesterol from 3H-cholesterol-labeled J774 macrophages into plasma, into liver, and ultimately into the bile and feces as free cholesterol or bile acids. In the present study we used this approach to test the hypothesis that administration of the synthetic LXR agonist GW3965 would increase the rate of macrophage RCT in vivo.


RESULTS
Three different mouse models-wild-type C57BL/6 mice, LDLR/apobec-1 double knockout mice, and human apolipoprotein (apo)B/cholesteryl ester transfer protein (CETP) double transgenic mice-were treated with either vehicle or GW3965. Mice were injected intraperitoneally with 3H-cholesterol-labeled and cholesterol-loaded macrophages and monitored for the appearance of 3H-tracer in plasma, liver, and feces. Administration of GW3965 significantly increased the levels of 3H-tracer in plasma and feces in all 3 mouse models.


CONCLUSIONS
These results demonstrate that administration of the LXR agonist GW3965 increases the rate of RCT from macrophages to feces in vivo.
Naik
Snehal U
SU
Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
Wang
Xun
X
Da Silva
Jaqueline S
JS
Jaye
Michael
M
Macphee
Colin H
CH
Reilly
Muredach P
MP
Billheimer
Jeffrey T
JT
Rothblat
George H
GH
Rader
Daniel J
DJ
D000071479:APOBEC-1 Deaminase; D000818:Animals; D001565:Benzoates / Q000494:pharmacology; D001596:Benzylamines / Q000494:pharmacology; D001692:Biological Transport; D002784:Cholesterol / Q000097:blood / Q000378:metabolism*; D003564:Cytidine Deaminase / Q000172:deficiency / Q000235:genetics; D004268:DNA-Binding Proteins / Q000819:agonists* / Q000378:metabolism*; D005243:Feces / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D000071518:Liver X Receptors; D008264:Macrophages / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D057093:Orphan Nuclear Receptors; D011849:Radioactive Tracers; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists* / Q000378:metabolism*; D011973:Receptors, LDL / Q000172:deficiency / Q000235:genetics; D014316:Tritium
D001565:Benzoates; D001596:Benzylamines; D004268:DNA-Binding Proteins; C473027:GW 3965; D000071518:Liver X Receptors; D057093:Orphan Nuclear Receptors; D011849:Radioactive Tracers; D018160:Receptors, Cytoplasmic and Nuclear; D011973:Receptors, LDL; D014316:Tritium; D002784:Cholesterol; D000071479:APOBEC-1 Deaminase; C000605089:APOBEC1 protein, human; C000605090:Apobec1 protein, mouse; D003564:Cytidine Deaminase