Effect of Synthetic Corticosteroids on Vascular Reactivity in the Human Forearm

No difference in glycosphingolipid metabolism and mitochondrial function in glucocorticoid-induced insulin resistance in healthy men

OBJECTIVE

Glucocorticoids (GCs) are well known to induce insulin resistance; however, mechanisms that cause the impairement of the insulin signaling pathway have not yet been identified. In this study we measured whether GC-induced insulin resistance in humans is related to changes in muscle ceramide, GM3, and muscle mitochondrial function.

METHODS

In a randomized, placebo-controlled, double-blind, dose-response intervention study, 32 healthy males (aged 22 ± 3 years; body mass index 22.4 ± 1.7 kg/m(-2)) were allocated to prednisolone (PRED) 7.5 mg once daily (n = 12), PRED 30 mg once daily (n = 12), or placebo (n = 8) for 2 weeks using block randomization. Insulin sensitivity was measured by hyperinsulinemic-euglycemic clamp before and after treatment. Muscle biopsies were performed to measure ceramide, monosialodihexosylganglioside (GM3), and mitochondrial function.

RESULTS

Peripheral insulin sensitivity was dose dependently decreased after the PRED treatment. Muscle ceramide and GM3 concentration and mitochondrial function were not altered by 2 weeks of PRED treatment.

CONCLUSION

Short-term GC treatment dose dependently impaired whole-body insulin sensitivity in healthy males, without concomitant changes in muscle ceramide, GM3, or mitochondrial function. These findings suggest that other mechanisms play a role in GC-related impairment of insulin sensitivity.

Glycyrrhetinic acid attenuates vascular smooth muscle vasodilatory function in healthy humans

Abnormal glucocorticoid metabolism contributes to vascular dysfunction and cardiovascular disease. Cortisol activation of vascular mineralocorticoid and glucocorticoid receptors is regulated by two types of 11β-HSD (11-β hydroxysteroid dehydrogenase), namely 11β-HSD2 and 11β-HSD1 (type 2 and type 1 11β-HSD respectively). We hypothesized that inhibition of 11β-HSD would attenuate vascular function in healthy humans. A total of 15 healthy subjects were treated with the selective 11β-HSD inhibitor GA (glycyrrhetinic acid) or matching placebo in a randomized double-blinded cross-over trial. 11β-HSD activity was assessed by the urinary cortisol/cortisone ratio, and vascular function was measured using strain-gauge plethysmography. Endothelial function was measured through incremental brachial artery administration of methacholine (0.3–10 μg/min) and vascular smooth muscle function with incremental verapamil (10–300 μg/min). GA increased the 24-h urinary cortisol/cortisone ratio compared with placebo (P=0.008). GA tended to reduce the FBF (forearm blood flow) response to methacholine (P=0.09) and significantly reduced the FBF response to verapamil compared with placebo (P=0.04). MAP (mean arterial pressure) did not differ between the study conditions. 11β-HSD inhibition attenuated vascular smooth muscle vasodilatory function in healthy humans. Disturbances in cortisol activity resulting from 11β-HSD inactivation is therefore a second plausible mechanism for mineralocorticoid-mediated hypertension in humans.

Hemodynamics of dexamethasone-induced hypertension in the rat

Although dexamethasone (DEX) is known to cause hypertension in humans and in animals, the hemodynamic characteristics of DEX-induced hypertension (DEX-HT) in the rat remain unclear. This study evaluated central and regional hemodynamics, and the role of total peripheral resistance (TPR) using a vasodilator minoxidil. Rats were divided into four groups, namely saline (n=20), DEX (n=21), minoxidil+saline (n=10) and minoxidil+DEX (n=10). Tail-cuff systolic blood pressure was recorded every second day. After 10-14 days of treatment, central (saline: n=9, DEX: n=10) and regional (saline: n=11, DEX: n=11) hemodynamic parameters were measured. Central hemodynamic data were also obtained from minoxidil-treated rats. DEX increased blood pressure (P<0.0005) in association with an increase in TPR (P<0.05). However, individual assessments of renal, mesenteric and hindquarter circulations did not detect any significant increase in resistance in these beds. Minoxidil increased cardiac output (P'<0.01) and cardiac index (P'<0.005) as well as decreased TPR (P'<0.05) without affecting DEX-HT. DEX prevented weight gain and decreased thymus weight. The increase in TPR in DEX-HT in rats was not simply explained by isolated alterations to resistance in the renal, mesenteric or hindquarter circulations. Minoxidil effectively prevented the increase in TPR but not the increase in blood pressure, suggesting that an increase in TPR is not essential for DEX-induced blood pressure increase.

Effect of an inhaled glucocorticoid on endothelial function in healthy smokers

Cigarette smoking is associated with attenuated endothelium-dependent vasodilation (endothelial dysfunction) in the systemic circulation, including the airway circulation. We wished to determine whether an inhaled corticosteroid could restore endothelial function in the airway of lung-healthy current smokers, ex-smokers, and nonsmokers. We measured baseline airway blood flow (Qaw) and Qaw reactivity to inhaled albuterol as an index of endothelium-dependent vasodilation and to sublingual nitroglycerin as an index of endothelium-independent vasodilation in lung-healthy current smokers, ex-smokers, and nonsmokers. Current smokers were then treated with inhaled fluticasone for 3 wk, and all measurements were repeated after fluticasone treatment and after a subsequent 3-wk fluticasone washout period. Baseline mean Qaw and endothelium-independent Qaw reactivity were similar in the three groups. Mean endothelium-dependent Qaw reactivity was 49.5% in nonsmokers, 42.7% in ex-smokers, and 10.8% in current smokers (P < 0.05 vs. nonsmokers). In current smokers, mean baseline Qaw was unchanged after fluticasone treatment, but endothelium-dependent Qaw reactivity significantly increased to 34.9%. Qaw reactivity was again blunted after fluticasone washout. Endothelial dysfunction, as assessed by vascular reactivity, can be corrected with an inhaled corticosteroid in the airway of lung-healthy current smokers. This proof of concept can serve as the basis for future clinical investigations on the effect of glucocorticoids on endothelial function in smokers.