Effects of carbenoxolone administered acutely to adrenalectomized rats (in vivo) on renal and hepatic handling of corticosterone by 11 beta-hydroxysteroid dehydrogenase

Carbenoxolone treatment attenuates symptoms of metabolic syndrome and atherogenesis in obese, hyperlipidemic mice

Glucocorticoids, which are well established to regulate body fat mass distribution, adipocyte lipolysis, hepatic gluconeogenesis, and hepatocyte VLDL secretion, are speculated to play a role in the pathology of metabolic syndrome. Recent focus has been on the activity of 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1), which is capable of regenerating, and thus amplifying, glucocorticoids in key metabolic tissues such as liver and adipose tissue. To determine the effects of global 11beta-HSD1 inhibition on metabolic syndrome risk factors, we subcutaneously injected "Western"-type diet-fed hyperlipidemic mice displaying moderate or severe obesity [LDL receptor (LDLR)-deficient (LDLR(-/-)) mice and mice derived from heterozygous agouti (A(y)/a) and homozygous LDLR(-/-) breeding pairs (A(y)/a;LDLR(-/-) mice)] with the nonselective 11beta-HSD inhibitor carbenoxolone for 4 wk. Body composition throughout the study, end-point fasting plasma, and extent of hepatic steatosis and atherosclerosis were assessed. This route of treatment led to detection of high levels of carbenoxolone in liver and fat and resulted in decreased weight gain due to reduced body fat mass in both mouse models. However, only A(y)/a;LDLR(-/-) mice showed an effect of 11beta-HSD1 inhibition on fasting insulin and plasma lipids, coincident with a reduction in VLDL due to mildly increased VLDL clearance and dramatically decreased hepatic triglyceride production. A(y)/a;LDLR(-/-) mice also showed a greater effect of the drug on reducing atherosclerotic lesion formation. These findings indicate that subcutaneous injection of an 11beta-HSD1 inhibitor allows for the targeting of the enzyme in not only liver, but also adipose tissue, and attenuates many metabolic syndrome risk factors, with more pronounced effects in cases of severe obesity and hyperlipidemia.

Expression of 11beta-hydroxylase in rat Leydig cells

11Beta-hydroxy (11beta-OH) derivatives of certain steroids function as inhibitors of 11beta-hydroxysteroid dehydrogenase isoform 1 (11betaHSD1), an enzyme expressed in Leydig cells that catalyzes the reversible oxidation of biologically active glucocorticoids to inactive 11-dehydro metabolites. 11beta-Hydroxylase is an adrenal enzyme responsible for glucocorticoid biosynthesis, catalyzing 11beta-hydroxylation of steroids and thus producing 11beta-OH-steroid derivatives. The aims of the present study were 1) to examine whether 11beta-hydroxylase is expressed in testis, 2) to define the biochemical characteristics of the testicular form of this enzyme, and 3) to establish whether 11beta-hydroxylated steroids inhibit Leydig cell 11betaHSD1 activities. 11beta-Hydroxylase mRNA was detected in purified rat Leydig cells by RT-PCR. Sequencing confirmed that the PCR products had 100% identity with the published rat adrenal enzyme cDNA sequence. Immunohistochemistry and Western blot analysis using a mouse monoclonal antibody confirmed the expression of 11beta-hydroxylase protein in Leydig cells. Moreover, 11beta-hydroxylase activity, synthesis of corticosterone from 11-deoxycorticosterone, was measurable in Leydig cells, and the K(m) and maximum velocity values were 7.28 +/- 0. 92 microM and 1.13 +/- 0.04 micromol/10(6) cell x h, respectively. When assayed in Leydig cells, several 11beta-hydroxylated steroids were efficient inhibitors of 11betaHSD1 dehydrogenase activity, whereas other 11-keto compounds were effective as inhibitors of oxidoreductase activity. These results provide the first direct evidence that rat Leydig cells express 11beta-hydroxylase, which may be involved in the regulation of glucocorticoid metabolism within the testis through local biosynthesis of endogenous inhibitors of 11betaHSD1.

Distal tubular electrolyte transport during inhibition of renal 11beta-hydroxysteroid dehydrogenase

To test the proposal that the enzyme 11beta-hydroxysteroid dehydrogenase (11beta-HSD) confers aldosterone specificity on mineralocorticoid receptors in the distal nephron by inactivating glucocorticoids, we performed a free-flow micropuncture study of distal tubular function in adrenalectomized rats infused with high-dose corticosterone. One-half of the rats were additionally given intravenous carbenoxolone (CBX; 6 mg/h) to inhibit renal 11beta-HSD activity. Although this maneuver lowered fractional Na(+) excretion (1.1 +/- 0.2 vs. 1.9 +/- 0.2%, P < 0.01), Na(+) reabsorption within the accessible distal tubule was found to be similar in the two groups of animals. In contrast, distal tubular K(+) secretion was enhanced in CBX-treated rats: fractional K(+) deliveries to the early and late distal collection sites in the corticosterone-alone group were 13 +/- 1 and 20 +/- 3%, respectively (not significant), whereas corresponding data in the CBX-treated group were 9 +/- 1 and 24 +/- 2% (P < 0.01). This stimulation of distal K(+) secretion provides the first direct in vivo evidence that 11beta-HSD normally prevents corticosterone from exerting a mineralocorticoid-like effect in the distal tubule. The reduction in fractional Na(+) excretion during inhibition of 11beta-HSD, in the absence of a change in end-distal Na(+) delivery, suggests enhanced Na(+) reabsorption in the collecting ducts.

Selective inhibition of sheep kidney 11 beta-hydroxysteroid dehydrogenase isoform 2 activity by 5 alpha-reduced (but not 5 beta) derivatives of adrenocorticosteroids

We have previously reported that 5 alpha and 5 beta pathways of steroid metabolism are controlled in vivo by dietary Na+ and glycyrrhetinic acid, see Gorsline et al. 1988; Latif et al. 1990. The present investigations provide evidence supporting the suggestion that endogenous substances may regulate the glucocorticoid inactivating isoenzymes, 11 beta-HSD (hydroxysteroid dehydrogenase) 1 (liver) and 11 beta-HSD2 (kidney). The activity of 11 beta-HSD is impaired in essential hypertension, following licorice ingestion, and in patients with apparent mineralocorticoid excess where 11 beta-HSD2 is particularly affected. In all three conditions, excretion of the less common 5 alpha metabolites is elevated in urine. We now report on the differential abilities of a series of Ring A reduced (5 alpha and 5 beta) adrenocorticosteroid and progesterone metabolites to inhibit these isoenzymes. Using liver microsomes with NADP+ as co-factor (11 beta-HSD1), and sheep kidney microsomes with NAD+ as co-factor (11 beta-HSD2), we have systematically investigated the abilities of a number of adrenocorticosteroids and their derivatives to inhibit the individual isoforms of 11 beta-HSD. A striking feature is the differential sensitivity of the two isoenzymes to inhibition by 5 alpha and 5 beta derivatives. 11 beta-HSD1 is inhibited by both 5 alpha and certain 5 beta derivatives. 11 beta-HSD-2 was selectively inhibited only by 5 alpha derivatives: 5 beta derivatives were without inhibitory activity toward this isoform of 11 beta-HSD. These results indicate the importance of the structural conformation of the A and B Rings in conferring specific inhibitory properties on these compounds. In addition, we discuss the effects of additions or substitutions of other functional groups on the inhibitory potency of these steroid molecules against 11 beta-HSD1 and 11 beta-HSD2.