In vivo activity of 11β-hydroxysteroid dehydrogenase type 1 in man: effects of prednisolone and chenodesoxycholic acid

Chenodeoxycholic Acid: An Update on Its Therapeutic Applications

Chenodeoxycholic acid (CDCA), 3α,7α-dihydroxy-5β-cholan-24-oic acid, is a primary bile acid generated in the liver from cholesterol. In liver cells CDCA is conjugated with glycine or taurine to form two bile salts, Glyco-CDCA and Tauro-CDCA, before being released into the bile ducts. In the intestine, CDCA is further metabolized to generate a 7β epimer, i.e., the ursodeoxycholic acid (UDCA), or dehydroxylate to generate lithocolic acid (LCA). In humans, CDCA is the physiological ligand for the bile acid sensor farnesoid X receptor (FXR), while LCA is a potent agonist for a G protein-coupled receptor, known as GPBAR1 (TGR5). Along with UDCA, CDCA has been clinically used for the dissolution of gallbladder stones at doses ranging from 375 to 750 mg/day, with a success rate of 8 to 18%. Because the efficacy of CDCA was significantly lower than that of UDCA and 18-30% of patients developed significant side effects, the most frequent being diarrhea and a reversible increase in aminotransferases plasma levels, this application has lost its therapeutic relevance. Additionally, the combination of CDCA with UDCA, generally at doses of 5-10 mg/kg each, has failed to provide significant advantages over UDCA alone. In 2017, CDCA has been approved as an orphan indication for the treatment of patients with cerebrotendinous xanthomatosis (CTX), a rare autosomal recessive disorder caused by mutations of sterol 27-hydroxylase (CYP27A1) gene. Since CYP27A1 is essential for cholesterol breakdown, CTX patients develop abnormal lipid storage with increased plasma and tissue levels of cholestanol and very low/absent production of CDCA. CDCA is a potent inhibitor of CYP27A1, and early initiation of CDCA therapy, at doses up to 750 mg/day, is considered the standard medical therapy for CTX resulting in decreased plasma levels of cholestanol and stabilization of neurologic symptoms. Studies in CTX patients have also shown that CDCA might suppress the activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase in the liver. Furthermore, CDCA promotes the release of glucagon-like peptide-1 (GLP-1) in diabetic patients, likely by activating GPBAR1.

Influence of human serum albumin on the bile acid-mediated inhibition of liver microsomal type 1 11β-hydroxysteroid dehydrogenase

The influence of human serum albumin (HSA) on the bile acid-mediated inhibition of liver microsomal type 1 11β-hydroxysteroid dehydrogenase (11β-HSD1) was studied in vitro. A rat liver microsomal fraction was prepared, and the 11β-HSD1 enzyme activity in the presence of various concentrations of bile acids and HSA was determined using hydrocortisone as the substrate. The products of the reaction were extracted and analyzed using high-performance liquid chromatography. The magnitude of the inhibition decreased with the addition of HSA in a dose-dependent manner. Four percent human albumin decreased the inhibitory effects of 100 μM chenodeoxycholic acid and lithocholic acid from 89.9 ± 5.6 to 54.5 ± 6.1% and from 83.8 ± 4.8 to 20.8 ± 4.2%, respectively. In contrast, ursodeoxycholic acid and deoxycholic acid showed no inhibitory effect on the enzyme activity in the presence of 4% human serum albumin, and the addition of 1% γ-globulin to the assay mixture in the presence of bile acids did not affect the enzyme activity. Our in vitro study showed that the addition of HSA ameliorated the inhibition of 11β-HSD1 and that the magnitude of the change is dependent on the species of bile acid, presumably based on the numbers of hydroxyl groups. These results suggest that HSA seems to protect the bile acid-mediated inhibition of 11β-HSD1 in the healthy subject. On the other hand, in the patients with obstructive biliary diseases, not only elevated serum bile acid but also the accompanying hypoalbuminemia is important to evaluate the pathophysiology of the bile acid-mediated inhibition of 11β-HSD1 of the disease.

Pancreatic alpha-cell dysfunction contributes to the disruption of glucose homeostasis and compensatory insulin hypersecretion in glucocorticoid-treated rats

Glucocorticoid (GC)-based therapies can cause insulin resistance (IR), glucose intolerance, hyperglycemia and, occasionally, overt diabetes. Understanding the mechanisms behind these metabolic disorders could improve the management of glucose homeostasis in patients undergoing GC treatment. For this purpose, adult rats were treated with a daily injection of dexamethasone (1 mg/kg b.w., i.p.) (DEX) or saline as a control for 5 consecutive days. The DEX rats developed IR, augmented glycemia, hyperinsulinemia and hyperglucagonemia. Treatment of the DEX rats with a glucagon receptor antagonist normalized their blood glucose level. The characteristic inhibitory effect of glucose on glucagon secretion was impaired in the islets of the DEX rats, while no direct effects were found on α-cells in islets that were incubated with DEX in vitro. A higher proportion of docked secretory granules was found in the DEX α-cells as well as a trend towards increased α-cell mass. Additionally, insulin secretion in the presence of glucagon was augmented in the islets of the DEX rats, which was most likely due to their higher glucagon receptor content. We also found that the enzyme 11βHSD-1, which participates in GC metabolism, contributed to the insulin hypersecretion in the DEX rats under basal glucose conditions. Altogether, we showed that GC treatment induces hyperglucagonemia, which contributes to an imbalance in glucose homeostasis and compensatory β-cell hypersecretion. This hyperglucagonemia may result from altered α-cell function and, likely, α-cell mass. Additionally, blockage of the glucagon receptor seems to be effective in preventing the elevation in blood glucose levels induced by GC administration.

Genetic polymorphisms in 11β-hydroxysteroid dehydrogenase type 1 correlate with the postdexamethasone cortisol levels and bone mineral density in patients evaluated for osteoporosis

CONTEXT

Higher physiological cortisol levels may increase the risk of age-related osteoporosis. We hypothesized that common polymorphisms in the cortisol synthesis enzyme 11β-hydroxysteroid dehydrogenase (HSD11B) may cause interindividual variations in cortisol levels and age-related bone loss.

STUDY DESIGN AND PATIENTS

We performed a retrospective study in a cohort of 452 ambulatory patients under evaluation for osteoporosis. We investigated the associations of 16 single-nucleotide polymorphisms (in the HSD11B1 and HSD11B2 genes with a postdexamethasone cortisol (PDC) level and bone mineral density (BMD; primary end points) and fracture risk (secondary end point) in a subgroup of 304 patients. The observed associations with BMD were validated in a subgroup of 148 patients.

RESULTS

The PDC level increased with age (R = 0.274, P < 10(-5), n = 287) and was negatively correlated with BMD at the femoral neck (R = -0.278, P < 10(-5), n = 258). Three genetically linked single-nucleotide polymorphisms (in intron 5 of HSD11B1), rs1000283, rs932335, and rs11811440, were significantly associated with BMD, with rs11811440 having the strongest association. The presence of the minor rs11811440 A allele was correlated with a lower PDC level (R = -0.128, P = .03, n = 304). The A allele was also consistently correlated with a higher spinal BMD in both patient subgroups (R = 0.17, Bonferroni corrected P = .006, n = 452). The correlation with BMD remained significant after adjustment for age, gender, body mass index, and type of osteoporosis and was stronger in patients older than 65 years.

CONCLUSION

Genetic variations in HSD11B1 may affect the physiological cortisol levels and the severity of age-related osteoporosis. Underlying functional mechanisms remain to be elucidated.

11β-Hydroxysteroid dehydrogenase type 1: relevance of its modulation in the pathophysiology of obesity, the metabolic syndrome and type 2 diabetes mellitus

Recent evidence strongly argues for a pathogenic role of glucocorticoids and 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) in obesity and the metabolic syndrome, a cluster of risk factors for atherosclerotic cardiovascular disease and type 2 diabetes mellitus (T2DM) that includes insulin resistance (IR), dyslipidaemia, hypertension and visceral obesity. This has been partially prompted not only by the striking clinical resemblances between the metabolic syndrome and Cushing's syndrome (a state characterized by hypercortisolism that associates with metabolic syndrome components) but also from monogenic rodent models for the metabolic syndrome (e.g. the leptin-deficient ob/ob mouse or the leptin-resistant Zucker rat) that display overall increased secretion of glucocorticoids. However, systemic circulating glucocorticoids are not elevated in obese patients and/or patients with metabolic syndrome. The study of the role of 11β-HSD system shed light on this conundrum, showing that local glucocorticoids are finely regulated in a tissue-specific manner at the pre-receptor level. The system comprises two microsomal enzymes that either activate cortisone to cortisol (11β-HSD1) or inactivate cortisol to cortisone (11β-HSD2). Transgenic rodent models, knockout (KO) for HSD11B1 or with HSD11B1 or HSD11B2 overexpression, specifically targeted to the liver or adipose tissue, have been developed and helped unravel the currently undisputable role of the enzymes in metabolic syndrome pathophysiology, in each of its isolated components and in their prevention. In the transgenic HSD11B1 overexpressing models, different features of the metabolic syndrome and obesity are replicated. HSD11B1 gene deficiency or HSD11B2 gene overexpression associates with improvements in the metabolic profile. In face of these demonstrations, research efforts are now being turned both into the inhibition of 11β-HSD1 as a possible pharmacological target and into the role of dietary habits on the establishment or the prevention of the metabolic syndrome, obesity and T2DM through 11β-HSD1 modulation. We intend to review and discuss 11β-HSD1 and obesity, the metabolic syndrome and T2DM and to highlight the potential of its inhibition for therapeutic or prophylactic approaches in those metabolic diseases.