t0901317 and gamma-sitosterol

Mutations in either adenosine triphosphate- binding cassette (ABC) half-transporter G5 or G8 cause sitosterolemia. It has been proposed that ABCG5/ABCG8 heterodimers mediate secretion of plant sterols and cholesterol by hepatocytes into bile and their efflux from enterocytes into the intestinal lumen.. To test whether deficiency of ABCG5 alone is sufficient to induce sitosterolemia, Abcg5-null mice were generated and characterized with respect to sterol metabolism.. Abcg5 deficiency was associated with strongly elevated plasma levels of beta-sitosterol (37-fold) and campesterol (7.7-fold) as well as reduced plasma cholesterol concentrations (-40%). Retention of orally administered [(3)H]beta-sitosterol in the intestinal wall (+550%) and plasma (+640%) was higher in Abcg5-null mice than in wild-type controls. Surprisingly, high plasma beta-sitosterol and campesterol concentrations were even further elevated in Abcg5-null mice on treatment with the synthetic LXR agonist T0901317 (0.015% dietary supplementation, 10 days), whereas these concentrations were reduced by approximately 75% in wild-type mice. Both cholesterol and phospholipid concentrations in gallbladder bile were decreased, but, unexpectedly, cholesterol/phospholipid ratios were unchanged in the absence of Abcg5 and increased in both genotypes on LXR activation. Hepatic expression of Abcg8 was reduced by about 35% in Abcg5-deficient mice when compared with controls. No compensatory overexpression of other ABC transporters potentially involved in hepatic cholesterol trafficking was observed on messenger RNA level.. Our data show that disruption of the Abcg5 gene alone is sufficient to cause hyperabsorption of dietary plant sterols and sitosterolemia in mice, whereas the ability to secrete cholesterol into bile is maintained.

Topics: Animals; Anticholesteremic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 5; ATP-Binding Cassette Transporters; Bile; Bile Acids and Salts; Cholesterol; DNA-Binding Proteins; Gallbladder; Genotype; Hydrocarbons, Fluorinated; Lipoproteins; Liver X Receptors; Mice; Mice, Knockout; Orphan Nuclear Receptors; Phospholipids; Phytosterols; Receptors, Cytoplasmic and Nuclear; Sitosterols; Sulfonamides

Liver X receptor (LXR) is a nuclear receptor that plays a crucial role in orchestrating the trafficking of sterols between tissues. Treatment of mice with a potent and specific LXR agonist, T0901317, is associated with increased biliary cholesterol secretion, decreased fractional cholesterol absorption, and increased fecal neutral sterol excretion. Here we show that expression of two target genes of LXRalpha, the ATP-binding cassette (ABC) transporters Abcg5 and Abcg8, is required for both the increase in sterol excretion and the decrease in fractional cholesterol absorption associated with LXR agonist treatment. Mice expressing no ABCG5 and ABCG8 (G5G8(-/-) mice) and their littermate controls were treated for 7 days with T0901317. In wild type animals, treatment with the LXR agonist resulted in a 3-fold increase in biliary cholesterol concentrations, a 25% reduction in fractional cholesterol absorption, and a 4-fold elevation in fecal neutral sterol excretion. In contrast, the LXR agonist did not significantly affect biliary cholesterol levels, fractional cholesterol absorption, or neutral fecal sterol excretion in the G5G8(-/-) mice. Thus Abcg5 and Abcg8 are required for LXR agonist-associated changes in dietary and biliary sterol trafficking. These results establish a central role for ABCG5 and ABCG8 in promoting cholesterol excretion in vivo.

Topics: Animals; Anticholesteremic Agents; ATP Binding Cassette Transporter, Subfamily G, Member 5; ATP Binding Cassette Transporter, Subfamily G, Member 8; ATP-Binding Cassette Transporters; Bile; Cholesterol; DNA-Binding Proteins; Feces; Hydrocarbons, Fluorinated; Lipoproteins; Liver; Liver X Receptors; Mice; Mice, Inbred C57BL; Orphan Nuclear Receptors; Receptors, Cytoplasmic and Nuclear; RNA, Messenger; Sitosterols; Sulfonamides