Satoru Inaba

11β-Hydroxysteroid Dehydrogenase in Cultured Human Vascular Cells: Possible Role in the Development of Hypertension

11beta-Hydroxysteroid dehydrogenases (11beta-HSD) interconvert cortisol, the physiological glucocorticoid, and its inactive metabolite cortisone in humans. The diminished dehydrogenase activity (cortisol to cortisone) has been demonstrated in patients with essential hypertension and in resistance vessels of genetically hypertensive rats. 11beta-Hydroxysteroid dehydrogenase type 2 (11beta-HSD2) catalyzes only 11beta-dehydrogenation. However, a functional relationship between diminished vascular 11beta-HSD2 activity and elevated blood pressure has been unclear. In this study we showed the expression and enzyme activity of 11beta-HSD2 and 11beta-HSD type 1 (which is mainly oxoreductase, converting cortisone to cortisol) in human vascular smooth muscle cells. Glucocorticoids and mineralocorticoids increase vascular tone by upregulating the receptors of pressor hormones such as angiotensin II. We found that physiological concentrations of cortisol-induced increase in angiotensin II binding were significantly enhanced by the inhibition of 11beta-HSD2 activity with an antisense DNA complementary to 11beta-HSD2 mRNA, and the enhancement was partially but significantly abolished by a selective aldosterone receptor antagonist. This may indicate that impaired 11beta-HSD2 activity in vascular wall results in increased vascular tone by the contribution of cortisol, which acts as a mineralocorticoid. In congenital 11beta-HSD deficiency and after administration of 11beta-HSD inhibitors, suppression of 11beta-HSD2 activity in the kidney has been believed to cause renal mineralocorticoid excess, resulting in sodium retention and hypertension. In the present study we provide evidence for a mechanism that could link impaired vascular 11beta-HSD2 activity, increased vascular tone, and elevated blood pressure without invoking renal sodium retention.

Mechanisms of FK 506–Induced Hypertension in the Rat

-Tacrolimus (FK 506) is a powerful, widely used immunosuppressant. The clinical utility of FK 506 is complicated by substantial hypertension and nephrotoxicity. To clarify the mechanisms of FK 506-induced hypertension, we studied the chronic effects of FK 506 on the synthesis of endothelin-1 (ET-1), the expression of mRNA of ET-1 and endothelin-converting enzyme-1 (ECE-1), the endothelial nitric oxide synthase (eNOS) activity, and the expression of mRNA of eNOS and C-type natriuretic peptide (CNP) in rat blood vessels. In addition, the effect of the specific endothelin type A receptor antagonist FR 139317 on FK 506-induced hypertension in rats was studied. FK 506, 5 mg. kg-1. d-1 given for 4 weeks, elevated blood pressure from 102+/-13 to 152+/-15 mm Hg and increased the synthesis of ET-1 and the levels of ET-1 mRNA in the mesenteric artery (240% and 230%, respectively). Little change was observed in the expression of ECE-1 mRNA and CNP mRNA. FK 506 decreased eNOS activity and the levels of eNOS mRNA in the aorta (48% and 55%, respectively). The administration of FR 139317 (10 mg. kg-1. d-1) prevented FK 506-induced hypertension in rats. These results indicate that FK 506 may increase blood pressure not only by increasing ET-1 production but also by decreasing NO synthesis in the vasculature.

Endogenous Renal 11β-Hydroxysteroid Dehydrogenase Inhibitory Factors in Patients With Low-Renin Essential Hypertension

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) modulates the access of corticosteroids to their receptors and is important in blood pressure control. The excretion of renal 11 beta-HSD (ie, NAD(+)-dependent isoform) is thought to protect renal mineralocorticoid receptors from cortisol. To examine whether endogenous renal 11 beta-HSD inhibitory factor(s) may be involved in the pathophysiology of hypertension, we studied the urinary excretion of such inhibitors in 30 patients with low-renin essential hypertension and 20 normotensive control subjects. The effect of sodium restriction on the urinary excretion of the inhibitors wa also evaluated in six normotensive control subjects. Urine was extracted with Sep-Pak cartridges and high-performance liquid chromatography. Endogenous renal 11 beta-HSD inhibitors were measured by the inhibition of 11 beta-HSD bioactivity in microsomes from the human kidney. The urinary excretion of the inhibitors was significantly increased in patients with low-renin essential hypertension (1280 +/- 88 nmol/d, mean +/- SEM) compared with normotensive control subjects (704 +/- 56 nmol/d) (P < .05). Ratios of urinary tetrahydrocortisol+allo-tetrahydrocortisol to tetrahydrocortisone did not differ significantly. Sodium restriction reduced the urinary excretion of the endogenous renal 11 beta-HSD inhibitors but did not affect the ratio of urinary tetrahydrocortisol+allo-tetrahydrocortisol to tetrahydrocortisone. Endogenous renal 11 beta-HSD inhibitory factors may contribute to the pathogenesis of low-renin essential hypertension by modulating the activity of 11 beta-HSD. Sodium intake may directly or indirectly regulate the inhibitory factors.

Functional Adrenocorticotropic Hormone Receptor in Cultured Human Vascular Endothelial Cells Possible Role in Control of Blood Pressure

Hypertension is a prominent feature of patients with Cushing’s disease and ectopic adrenocorticotropic hormone (ACTH) syndrome, who have elevated ACTH levels. Chronic administration of ACTH (1-24) also raises blood pressure in humans. This effect has been postulated to be due to ACTH-induced increases in cortisol secretion in the adrenal gland. It is well known that cortisol increases vascular tone by potentiating the vasoconstrictor action of a number of pressor hormones. In the present study, we show direct evidence that human aortic endothelial cells possess the ACTH receptor. 11&bgr;-Dehydrogenation, converting cortisol to its inactive metabolite, cortisone, mediated by vascular 11&bgr;-hydroxysteroid dehydrogenase type 2 is essential for the control of vascular tone, and the reduced activity may be relevant to the pathogenesis of hypertension. We found that ACTH (1-24) dose-dependently decreased the gene expression and enzyme activity of 11&bgr;-hydroxysteroid dehydrogenase type 2 in these cells, and the decrease was partially abolished by a selective ACTH receptor antagonist. This may indicate that ACTH potentiates the action of cortisol through its direct effect on the vasculature. Therefore, the present study provides important information for understanding the mechanism of ACTH-induced hypertension.

Synergy of aldosterone and high salt induces vascular smooth muscle hypertrophy through up-regulation of NOX1.

Aldosterone and excessive salt intake are obviously implicated in human arteriosclerosis. Aldosterone activates NADPH oxidase that induces superoxide production and cardiovascular cell hypertrophy. The activity of NADPH oxidase is influenced by the expression of its subunit, through which, vasoactive agents activate in the enzyme. Here, we show that aldosterone elicited overexpression of the NOX1 catalytic subunit of NADPH oxidase in the presence of high salt in A7r5 vascular smooth muscle cells. We also showed that NOX1 is a key subunit involved in physiological aldosterone-induced NADPH oxidase activation. Aldosterone dose-dependently increased NOX1 expression and NADPH activity, which subsequently caused superoxide over-production and A7r5 cell hypertrophy. However, aldosterone had little effect on any of NOX1, superoxide over-production and cell hypertrophy in NOX1 knock-down A7r5 cells. These results suggest that the aldosterone-induced effects are mainly generated through NOX1. Aldosterone-induced NOX1 over-expression was augmented by 145 mM sodium chloride, as compared with control medium containing 135 mM NaCl. However, NOX1 over-expression was not induced in the absence of aldosterone, even in the presence of 185 mM NaCl. The mineralocorticoid receptor antagonist, eplerenone, completely abolished NOX1 over-expression, indicating that aldosterone is essential for this process.

Aldosterone inhibits endothelial morphogenesis and angiogenesis through the downregulation of vascular endothelial growth factor receptor-2 expression subsequent to peroxisome proliferator-activated receptor gamma

Angiogenesis plays a pivotal role in cardiovascular diseases such as ischemic heart disease, limb ischemia and heart failure, and has recently been shown to mediate various biological activities related to the pathogenesis of these diseases. In the present study, we evaluated the role of aldosterone in angiogenesis. Tube formation assay on Matrigel using human umbilical vein endothelial cells (HUVEC) revealed that aldosterone inhibited endothelial morphogenesis in a manner sensitive to eplerenone, a selective mineralocorticoid receptor antagonist. The anti-angiogenic effect of aldosterone was further confirmed by an in vivo angiogenesis assay using a Matrigel plug model in mice. Reverse transcription-mediated polymerase chain reaction and immunoblotting demonstrated that aldosterone downregulated the expression levels of vascular endothelial growth factor receptor-2 (VEGFR-2) and peroxisome proliferators-activated receptor gamma (PPAR gamma). VEGFR-2 expression was found to be enhanced in response to PPAR gamma activation by troglitazone, and attenuated by GW9662, a specific antagonist of PPAR gamma. In the tube formation assay, endothelial morphogenesis was stimulated by troglitazone, and inhibited by GW9662, indicating that PPAR gamma activation mediates positive regulation of angiogenesis through enhancement of VEGFR-2 expression. These data suggest that aldosterone inhibits angiogenesis through VEGFR-2 downregulation, subsequent to, at least in part, attenuation of PPAR gamma expression. The present findings provide a new insight into the possible therapeutic application of mineralocorticoid receptor blockade to various cardiovascular diseases.

Differential effects of α-glucosidase inhibitors on postprandial plasma glucose and lipid profile in patients with type 2 diabetes under control with insulin lispro mix 50/50.

BACKGROUND The additive effect of α-glucosidase inhibitors (α-GIs) was investigated in patients with type 2 diabetes (T2D) under control with rapid-acting insulin analog. SUBJECTS AND METHODS Thirty-six poorly controlled T2D patients were recruited, and plasma glucose (PG) was controlled by three times daily injection of insulin lispro mix 50/50 (Mix50) to maintain fasting PG <130 mg/dL and 2-h postprandial PG (PPG) <180 mg/dL. Another group of 20 patients was randomly assigned to either 0.3 mg of voglibose or 50 mg of miglitol, which was administered at breakfast every other day. Another group of 16 patients was assigned to a crossover study, in which each α-GI was switched every day during the 6-day study. PPG, C-peptide, and lipid profile were analyzed. RESULTS The addition of voglibose had no effect on PPG, but miglitol blunted the PPG rise and significantly decreased 1-h and 2-h postprandial C-peptide levels compared with Mix50 alone. In addition, miglitol significantly decreased the 1-h postprandial triglyceride rise and the remnant-like particle-cholesterol rise, while it increased the 1-h postprandial high-density lipoprotein-cholesterol and apolipoprotein A-I levels in the crossover study. CONCLUSIONS Miglitol appears to have rapid action, which appears earlier than that of lispro. The combination of miglitol and Mix50 seems effective for the control of PPG and lipid profile in T2D.

Effect of FK 506 on the expression of endothelin receptor mRNA in the vasculature

Summary: Tacrolimus (FK 506) is a new, more powerful immunosuppressant and is more effective in the prevention and treatment of allograft rejection in humans than cyclosporine (CysA). The present study was conducted to determine whether FK 506 increases ETA receptor mRNA in blood vessels in rats. FK 506 5 mg/kg/day for 4 weeks increased blood pressure and expression of ETA receptor mRNA in mesenteric arteries of Wistar-Kyoto rats. However, 0.5 mg/kg/day of FK 506 did not increase blood pressure or ETA mRNA levels in the vasculature. The dose of 0.1 μM CysA used in clinical practice induced expression of ETA receptor mRNA in cultured rat vascular smooth-muscle cells (VSMCs). A clinical dose (0.01 μM) of FK 506 did not increase expression of ETA receptor mRNA in VSMCs. However, 0.1 μM FK 506 increased the levels of ETA receptor mRNA in VSMCs. These results indicate that the upregulating effect of FK 506 on the ETA receptor in the vasculature may contribute to the genesis of FK 506-induced hypertension. The lower incidence of complications seen with FK 506 may be due in part to its use at a lower clinical dose compared to that of CysA.

Effects of chronic neutral endopeptidase inhibition in rats with cyclosporine-induced hypertension.

Objective Cyclosporine (CysA), a potent immunosuppressant, is associated with hypertension and nephrotoxicity. Neutral endopeptidase (NEP) degrades vasoactive peptides, including the natriuretic peptides and endothelin-1 (ET-1). We conducted the present study to determine whether or not the NEP inhibitor, ecadotril, prevents cyclosporine-induced hypertension and to clarify the mechanisms responsible for the hypotensive effects of ecadotril. Design and methods We studied the chronic effects of ecadotril (30 mg/kg per day) on blood pressure; the production of ET-1 and C-type natriuretic peptide (CNP); endothelial nitric oxide synthase (eNOS) activity; and the expression of messenger RNA (mRNA), for each substance in blood vessels of CysA-induced hypertensive rats. Results CysA (25 mg/kg per day) given for 4 weeks increased the blood pressure from 116 6 14 mmHg to 159 ± 15 mmHg, in rats. This increase was blunted by the co-administration of ecadotril (blood pressure: 134 ± 14 mmHg). CysA increased plasma NEP activity. CysA increased the production of ET-1 and the expression of ET-1 mRNA without affecting CNP synthesis and endothelin converting enzyme (ECE)-1 mRNA expression. CysA decreased the eNOS activity and eNOS mRNA levels. Addition of the NEP inhibitor decreased the synthesis of ET-1 and ET-1 mRNA levels and increased the eNOS activity and the eNOS mRNA levels. Vascular CNP synthesis and ECE-1 mRNA expression in rats treated with ecadotril did not differ from those in rats treated with CysA and ecadotril. Conclusion These results indicate that chronic NEP inhibition may prevent the CysA-induced hypertension by decreasing local ET-1 synthesis and partly increasing vascular nitric oxide production.