Rapid Hepatic Metabolism of 7-Ketocholesterol by 11β-Hydroxysteroid Dehydrogenase Type 1

Abstract

The role of 11␤-hydroxysteroid dehydrogenase type 1 (11␤-HSD1) in the local activation of the glucocorticoid receptor by converting inactive 11-ketoglucocorticoids to active 11␤-hydroxyglucocorticoids is well established. Currently, 11␤-HSD1 is considered a promising target for treatment of obese and diabetic patients. Here, we demonstrate a role of 11␤-HSD1 in the metabolism of 7-ketocholesterol (7KC), the major dietary oxysterol. Comparison of recombinant 11␤-HSD1, transiently expressed in human embryonic kidney 293 cells, revealed the stereo-specific interconversion of 7KC and 7␤-hydroxycholesterol by rat and human 11␤-HSD1, whereas the hamster enzyme interconverted 7␣-hydroxycholesterol, 7␤-hydroxycholesterol, and 7KC. In contrast to lysates, which efficiently catalyzed both oxidation and reduction, intact cells exclusively reduced 7KC. These findings were confirmed using rat and hamster liver homogenates, intact rat hepatocytes, and intact hamster liver tissue slices. Reduction of 7KC was abolished upon inhibition of 11␤-HSD1 by carbenoxolone (CBX) or 2-hydroxyflavanone. In vivo, after gavage feeding rats, 7KC rapidly appeared in the liver and was converted to 7␤-hydroxycholesterol. CBX significantly decreased the ratio of 7␤-hydroxycholesterol to 7KC, supporting the evidence from cell culture experiments for 11␤-HSD1-dependent reduction of 7KC to 7␤-hydroxycholesterol. Upon inhibition of 11␤-HSD1 by CBX, 7KC tended to accumulate in the liver, and plasma 7KC concentration increased. Together, our results suggest that 11␤-HSD1 efficiently catalyzes the first step in the rapid hepatic metabolism of dietary 7KC, which may explain why dietary 7KC has little or no effect on the development of atherosclerosis.Several in vitro studies demonstrated disturbances of cholesterol metabolism by 7KC 1 (1), including effects on hydroxymethylglutaryl-CoA-reductase and cholesterol 7␣-hydroxylase activities (2), inhibition of cholesterol release from cells (3), and down-regulation of low density lipoprotein receptor expression (4). In addition, 7KC exerts multiple effects by inhibiting nitric oxide release, decreasing glucose permeability, disrupting Ca 2ϩ -flux and inducing apoptosis in vascular cells (1).Oxidized cholesterol metabolites play a potential role in the development of atherosclerosis (1, 5, 6). Among other oxysterols, 7KC is found at micromolar concentrations in human macrophage-foam cells and atherosclerotic lesions. In contrast, plasma 7KC concentrations are in the nanomolar range. The major oxysterols present in atherosclerotic plaques are 27-hydroxycholesterol and 7KC, although the direct role of 7KC in the development and progression of atherosclerosis is still unclear. 27-Hydroxycholesterol is produced by sterol 27-hydroxylase, the first enzyme of the alternative pathway from cholesterol to bile acids in the liver (7). 7KC is believed to be formed non-enzymatically by free radical oxidation of cholesterol (8) or absorbed from dietary intake of processed cholesterol-rich food (9, 10).It was reported that u...

Interactions between dehydroepiandrosterone and glucocorticoid metabolism in pig kidney: Nuclear and microsomal 11β-hydroxysteroid dehydrogenases

“…This conversion was more than double that observed when CS substrate concentration was 25 times higher, suggesting inhibition by the substrate (CS) or its product (DHC). These results suggest that the conversion of 7α-OH-DHEA to 7-oxo-DHEA is catalyzed by low-affinity/high capacity enzyme(s), while the oxidation of CS to DHC may involve high-affinity/low capacity enzyme (s) as has been described for 11βHSD2 [29].…”

“…The oxidation of 7-hydroxycholesterol and CS by this purified enzyme was inhibited by CBX. Subsequently, human, rat, and mouse 11βHSD1 have been reported to possess a 7β-hydroxycholesterol dehydrogenase activity that allows interconversion between 7-ketocholesterol and 7β-hydroxycholesterol with similar efficiency as observed for GC [28,29]. In the current studies, pig kidney mitochondria oxidized 7α-OH-DHEA in the presence of either NAD + or NADP + at a very low rate (approx.…”

Impaired oxidoreduction by 11β-hydroxysteroid dehydrogenase 1 results in the accumulation of 7-oxolithocholic acid

“…11 ␤ -HSD1 has broad substrate specifi city and metabolizes, besides 11-ketoglucocorticoids, several oxidized endogenous steroids and sterols (19)(20)(21)(22)(23)(24)(25). Performing in vitro experiments, we recently identifi ed a novel role for human 11 ␤ -HSD1 in the metabolism of the secondary bile acid 7-oxoLCA ( 26 ).…”

“…To assess species-dependent differences in the 11 ␤ -HSD1-dependent metabolism of 7-oxoLCA, we transiently transfected HEK-293 (human embryonic kidney-293) cells [cultured in Dulbecco's Modifi ed Eagle's Medium (DMEM) supplemented with 10% fetal bovine serum (FBS), 50 units/ml penicillin, 50 g/ml streptomycin and 2 mM glutamine] with plasmids coding for human, rat, mouse, hamster, canine, and guinea-pig 11 ␤ -HSD1 as described previously ( 23,29,30 ). At 48 h posttransfection (jetPRIME, Polyplus transfection, Illkirch, France) cells were detached and centrifuged, and pellets were stored at Ϫ 80°C.…”

Disruption of Glucocorticoid and Mineralocorticoid Receptor-Mediated Responses by Environmental Chemicals

“…Nevertheless, an accumulation of orally administered 7-ketocholesterol was observed in rats treated with the inhibitor carbenoxolone. [44] More recently, we found that 11β -HSD1 metabolizes 7-ketodehydroepiandrosterone and 7-ketopregnenolone, suggesting a role not only in the detoxification of oxidized cholesterol from food but also of oxidized steroid hormone metabolites. [49] …”