Katsuyuki Ando

Angiotensin II–Induced Insulin Resistance Is Associated With Enhanced Insulin Signaling

Abstract—Angiotensin II (AII) is involved in the pathogenesis of both hypertension and insulin resistance, though few studies have examined the relationship between the two. We therefore investigated the effects of chronic AII infusion on blood pressure and insulin sensitivity in rats fed a normal (0.3% NaCl) or high-salt (8% NaCl) diet. AII infusion for 12 days significantly elevated blood pressure and significant insulin resistance, assessed by a hyperinsulinemic-euglycemic clamp study and glucose uptake into isolated muscle and adipocytes. High-salt loading exacerbated the effects of AII infusion significantly. Despite the insulin resistance, insulin-induced tyrosine phosphorylation of the insulin receptor and insulin receptor substrates, activation of phosphatidylinositol (PI) 3-kinase, and phosphorylation of Akt were all enhanced by AII infusion. Subsequently, to investigate whether oxidative stress induced by AII contributes to insulin resistance, the membrane-permeable superoxide dismutase mimetic, tempol, was administered to AII-infused rats. Chronic AII infusion induced an accumulated plasma cholesterylester hydroperoxide levels, indicating the increased oxidative stress, whereas the treatment with tempol normalized plasma cholesterylester hydroperoxide levels in AII-infused rats. In addition, the treatment with tempol normalized insulin resistance in AII-infused rats, shown as a decreased glucose infusion rate in the hyperinsulinemic euglycemic clamp study and a decreased insulin-induced glucose uptake into isolated skeletal muscle, as well as enhanced insulin-induced PI 3-kinase activation to those in the control rats. These results strongly suggest that AII-induced insulin resistance cannot be attributed to impairment of early insulin-signaling steps and that increased oxidative stress, possibly through impaired insulin signaling located downstream from PI 3-kinase activation, is involved in AII-induced insulin resistance.

Enhanced Aldosterone Signaling in the Early Nephropathy of Rats with Metabolic Syndrome: Possible Contribution of Fat-Derived Factors

Metabolic syndrome is an important risk factor for proteinuria and chronic kidney disease independent of diabetes and hypertension; however, the underlying mechanisms have not been elucidated. Aldosterone is implicated in target organ injury of obesity-related disorders. This study investigated the role of aldosterone in the early nephropathy of 17-wk-old SHR/NDmcr-cp, a rat model of metabolic syndrome. Proteinuria was prominent in SHR/NDmcr-cp compared with nonobese SHR, which was accompanied by podocyte injury as evidenced by foot process effacement, induction of desmin and attenuation of nephrin. Serum aldosterone level, renal and glomerular expressions of aldosterone effector kinase Sgk1, and oxidative stress markers all were elevated in SHR/NDmcr-cp. Mineralocorticoid receptors were expressed in glomerular podocytes. Eplerenone, a selective aldosterone blocker, effectively improved podocyte damage, proteinuria, Sgk1, and oxidant stress. An antioxidant tempol also alleviated podocyte impairment and proteinuria, along with inhibition of Sgk1. As for the mechanisms of aldosterone excess, visceral adipocytes that were isolated from SHR/NDmcr-cp secreted substances that stimulate aldosterone production in adrenocortical cells. The aldosterone-releasing activity of adipocytes was not inhibited by candesartan. Adipocytes from nonobese SHR did not show such activity. In conclusion, SHR/NDmcr-cp exhibit enhanced aldosterone signaling, podocyte injury, and proteinuria, which are ameliorated by eplerenone or tempol. The data also suggest that adipocyte-derived factors other than angiotensin II might contribute to the aldosterone excess of this model.

Proadrenomedullin NH(2)-terminal 20 peptide, a new product of the adrenomedullin gene, inhibits norepinephrine overflow from nerve endings.

Proadrenomedullin NH(2)-terminal 20 peptide (PAMP) and adrenomedullin, which are derived from proadrenomedullin, exhibit remarkable hypotensive action. We investigated the effect of PAMP and adrenomedullin on peripheral sympathetic neutral transmission. Using perfused rat mesenteric arteries, PAMP (0, 1, 5, and 10 pmol/ml) decreased norepinephrine overflow by periarterial electrical nerve stimulation in a dose-dependent fashion (0.244 +/- 0.043, 0.231 +/- 0.048, 0.195 +/- 0.061 and 0.168 +/- 0.051 ng/gram tissue weigh: NS, P < 0.05, and P < 0.02, respectively). In contrast to PAMP, adrenomedullin (1, 5, and 10 pmol/ml) did not change it. In contrast, vasoconstrictive response of mesenteric arteries to exogenous norepinephrine was significantly attenuated by 10 pmol/ml of adrenomedullin but not by the same dose of PAMP. Calcitonin gene-related peptide (8-37) [CGRP(8-37)], a CGRP receptor antagonist, inhibited the vasodilatory effect of adrenomedullin but could not suppress the sympathoinhibitory effect of PAMP. Neither a nicotinic antagonist, hexamethonium, nor a presynaptic alfa2 antagonist, yohimbine, blocked the sympathoinhibitory effect of PAMP. Thus, it suggests that PAMP and adrenomedullin, which are derived from the same gene, exhibit different hypotensive mechanisms: PAMP inhibits neural transmission at peripheral sympathetic nerve ending, although adrenomedullin directly dilates vascular smooth muscle, possibly through CGRP-like receptor.

Rac1 GTPase in rodent kidneys is essential for salt-sensitive hypertension via a mineralocorticoid receptor–dependent pathway

Hypertension is a leading contributor to cardiovascular mortality worldwide. Despite this, its underlying mechanism(s) and the role of excess salt in cardiorenal dysfunction are unclear. Previously, we have identified cross-talk between mineralocorticoid receptor (MR), a nuclear transcription factor regulated by the steroid aldosterone, and the small GTPase Rac1, which is implicated in proteinuric kidney disease. We here show that high-salt loading activates Rac1 in the kidneys in rodent models of salt-sensitive hypertension, leading to blood pressure elevation and renal injury via an MR-dependent pathway. We found that a high-salt diet caused renal Rac1 upregulation in salt-sensitive Dahl (Dahl-S) rats and downregulation in salt-insensitive Dahl (Dahl-R) rats. Despite a reduction of serum aldosterone levels, salt-loaded Dahl-S rats showed increased MR signaling in the kidneys, and Rac1 inhibition prevented hypertension and renal damage with MR repression. We further demonstrated in aldosterone-infused rats as well as adrenalectomized Dahl-S rats with aldosterone supplementation that salt-induced Rac1 and aldosterone acted interdependently to cause MR overactivity and hypertension. Finally, we confirmed the key role of Rac1 in modulating salt susceptibility in mice lacking Rho GDP-dissociation inhibitor α. Therefore, our data identify Rac1 as a determinant of salt sensitivity and provide insights into the mechanism of salt-induced hypertension and kidney injury.

Low-dose aspirin for primary prevention of cardiovascular events in japanese patients 60 years or older with atherosclerotic risk factors: A randomized clinical trial

IMPORTANCE Prevention of atherosclerotic cardiovascular diseases is an important public health priority in Japan due to an aging population. OBJECTIVE To determine whether daily, low-dose aspirin reduces the incidence of cardiovascular events in older Japanese patients with multiple atherosclerotic risk factors. DESIGN, SETTING, AND PARTICIPANTS The Japanese Primary Prevention Project (JPPP) was a multicenter, open-label, randomized, parallel-group trial. Patients (N = 14,464) were aged 60 to 85 years, presenting with hypertension, dyslipidemia, or diabetes mellitus recruited by primary care physicians at 1007 clinics in Japan between March 2005 and June 2007, and were followed up for up to 6.5 years, with last follow-up in May 2012. A multidisciplinary expert panel (blinded to treatment assignments) adjudicated study outcomes. INTERVENTIONS Patients were randomized 1:1 to enteric-coated aspirin 100 mg/d or no aspirin in addition to ongoing medications. MAIN OUTCOMES AND MEASURES Composite primary outcome was death from cardiovascular causes (myocardial infarction, stroke, and other cardiovascular causes), nonfatal stroke (ischemic or hemorrhagic, including undefined cerebrovascular events), and nonfatal myocardial infarction. Secondary outcomes included individual end points. RESULTS The study was terminated early by the data monitoring committee after a median follow-up of 5.02 years (interquartile range, 4.55-5.33) based on likely futility. In both the aspirin and no aspirin groups, 56 fatal events occurred. Patients with an occurrence of nonfatal stroke totaled 114 in the aspirin group and 108 in the no aspirin group; of nonfatal myocardial infarction, 20 in the aspirin group and 38 in the no aspirin group; of undefined cerebrovascular events, 3 in the aspirin group and 5 in the no aspirin group. The 5-year cumulative primary outcome event rate was not significantly different between the groups (2.77% [95% CI, 2.40%-3.20%] for aspirin vs 2.96% [95% CI, 2.58%-3.40%] for no aspirin; hazard ratio [HR], 0.94 [95% CI, 0.77-1.15]; P = .54). Aspirin significantly reduced incidence of nonfatal myocardial infarction (0.30 [95% CI, 0.19-0.47] for aspirin vs 0.58 [95% CI, 0.42-0.81] for no aspirin; HR, 0.53 [95% CI, 0.31-0.91]; P = .02) and transient ischemic attack (0.26 [95% CI, 0.16-0.42] for aspirin vs 0.49 [95% CI, 0.35-0.69] for no aspirin; HR, 0.57 [95% CI, 0.32-0.99]; P = .04), and significantly increased the risk of extracranial hemorrhage requiring transfusion or hospitalization (0.86 [95% CI, 0.67-1.11] for aspirin vs 0.51 [95% CI, 0.37-0.72] for no aspirin; HR, 1.85 [95% CI, 1.22-2.81]; P = .004). CONCLUSIONS AND RELEVANCE Once-daily, low-dose aspirin did not significantly reduce the risk of the composite outcome of cardiovascular death, nonfatal stroke, and nonfatal myocardial infarction among Japanese patients 60 years or older with atherosclerotic risk factors. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00225849.

High-Salt Diet Enhances Insulin Signaling and Induces Insulin Resistance in Dahl Salt-Sensitive Rats

A high-salt diet, which is known to contribute to the pathogenesis of hypertension, is also reportedly associated with insulin resistance. We investigated the effects of a high-salt diet on insulin sensitivity and insulin signaling in salt-sensitive (Dahl-S) and salt resistant (Dahl-R) strains of the Dahl rat. Evaluation of hyperinsulinemic-euglycemic clamp studies and glucose uptake into the isolated soleus muscle revealed that salt loading (8% NaCl) for 4 weeks induced hypertension and significant insulin resistance in Dahl-S rats, whereas no significant effects were observed in Dahl-R rats. Despite the presence of insulin resistance, insulin-induced tyrosine phosphorylation of the insulin receptor and insulin receptor substrates, activation of phosphatidylinositol 3-kinase, and phosphorylation of Akt were all enhanced in Dahl-S rats fed a high-salt diet. The mechanism underlying this form of insulin resistance thus differs from that previously associated with obesity and dexamethasone and is likely due to the impairment of one or more metabolic steps situated downstream of phosphatidylinositol 3-kinase and Akt activation. Interestingly, supplementation of potassium (8% KCl) ameliorated the changes in insulin sensitivity in Dahl-S rats fed a high-salt diet; this was associated with a slight but significant decrease in blood pressure. Evidence presented suggest that there is an interdependent relationship between insulin sensitivity and salt sensitivity of blood pressure in Dahl-S rats, and it is suggested that supplementing the diet with potassium may exert a protective effect against both hypertension and insulin resistance in salt-sensitive individuals.

Metabolic syndrome and oxidative stress.

Metabolic syndrome is an obesity-associated collection of disorders, each of which contributes to cardiovascular risk. Metabolic syndrome is also associated with overproduction of reactive oxygen species (ROS). ROS contribute to the interrelationship between metabolic syndrome and salt-sensitive hypertension, which are both caused by obesity and excess salt consumption and are major threats to health in developed countries. ROS can induce insulin resistance, which is indispensable for the progression of metabolic syndrome, and salt-sensitive hypertension stimulates ROS production, thereby promoting the development of metabolic syndrome. Moreover, ROS activate mineralocorticoid receptors (MRs) and the sympathetic nervous system, which can contribute to the development of metabolic syndrome and salt-sensitive hypertension. Salt-induced progression of cardiovascular disease (CVD) is also accelerated in animal models with metabolic syndrome, probably owing to further stimulation of ROS overproduction and subsequent ROS-induced MR activation and sympathetic excitation. Therefore, ROS contribute to the progression of the metabolic syndrome itself and to the CVD accompanying it, particularly in conjunction with excessive salt consumption.

Sympathoexcitation by Oxidative Stress in the Brain Mediates Arterial Pressure Elevation in Obesity-Induced Hypertension

Background— Obesity is one of the major risk factors for cardiovascular disease and is often associated with increased oxidative stress and sympathoexcitation. We have already suggested that increased oxidative stress in the brain modulates the sympathetic regulation of arterial pressure in salt-sensitive hypertension, which is often associated with obesity. The present study was performed to determine whether oxidative stress could mediate central sympathoexcitation in the initial stage of obesity-induced hypertension. Methods and Results— Four-week-old male Sprague-Dawley rats were fed a high-fat (45% kcal as fat) or low-fat (10% kcal as fat) diet for 6 weeks. Fat loading elicited hypertension and sympathoexcitation, along with visceral obesity. In urethane-anesthetized and artificially ventilated rats, arterial pressure and renal sympathetic nerve activity decreased in a dose-dependent fashion when 53 or 105 &mgr;mol/kg tempol, a membrane-permeable superoxide dismutase mimetic, was infused into the lateral cerebral ventricle. Central tempol reduced arterial pressure and renal sympathetic nerve activity to a significantly greater extent in high-fat diet–fed hypertensive rats than in low-fat diet–fed normotensive rats. Intracerebroventricular apocynin or diphenyleneiodonium, a reduced NADPH oxidase inhibitor, also elicited markedly greater reductions in arterial pressure and renal sympathetic nerve activity in the high-fat diet–fed rats. In addition, fat loading increased NADPH oxidase activity and NADPH oxidase subunit p22phox, p47phox, and gp91phox mRNA expression in the hypothalamus. Conclusions— In obesity-induced hypertension, increased oxidative stress in the brain, possibly via activation of NADPH oxidase, may contribute to the progression of hypertension through central sympathoexcitation.

Sympathoexcitation by Oxidative Stress in the Brain Mediates Arterial Pressure Elevation in Salt-Sensitive Hypertension

Central sympathoexcitation is involved in the pathogenesis of salt-sensitive hypertension. We have suggested that oxidative stress in the brain modulates the sympathetic regulation of arterial pressure. Thus, we investigated whether oxidative stress could mediate central sympathoexcitation in salt-sensitive hypertension. Five- to 6-week-old male Dahl salt-sensitive rats and salt-resistant rats were fed with a normal (0.3%) or high- (8%) salt diet for 4 weeks. In urethane-anesthetized and artificially ventilated rats, arterial pressure, renal sympathetic nerve activity, and heart rate decreased in a dose-dependent fashion, when 20 or 40 &mgr;mol of tempol, a membrane-permeable superoxide dismutase mimetic, was infused into the lateral cerebral ventricle. The same degree of reduction was noted in salt-sensitive and salt-resistant rats without salt loading. Salt loading significantly increased central tempol-induced reductions in arterial pressure (−29.1±4.8% versus −10.6±3.3% at 40 &mgr;mol; P<0.01), sympathetic nerve activity (−18.7±2.0% versus −7.1±1.8%; P<0.01), and heart rate (−10.7±2.8% versus −2.0±0.7%; P<0.05) in salt-sensitive rats but not in salt-resistant rats. Intracerebroventricular diphenyleneiodonium, a reduced nicotinamide-adenine dinucleotide phosphate oxidase inhibitor, also elicited significantly greater reduction in each parameter in salt-loaded salt-sensitive rats. Moreover, salt loading increased reduced nicotinamide-adenine dinucleotide phosphate–dependent superoxide production in the hypothalamus in salt-sensitive rats but not in salt-resistant rats. In addition, reduced nicotinamide-adenine dinucleotide phosphate oxidase subunits p22phox, p47phox, and gp91phox mRNA expression significantly increased in the hypothalamus of salt-loaded salt-sensitive rats. In conclusion, in salt-sensitive hypertension, increased oxidative stress in the brain, possibly via activation of reduced nicotinamide-adenine dinucleotide phosphate oxidase, may elevate arterial pressure through central sympathoexcitation.

Report of the Working Group for Dietary Salt Reduction of the Japanese Society of Hypertension: (2) Assessment of Salt Intake in the Management of Hypertension

Restriction of dietary salt is widely recommended in the management of hypertension, but assessment of individual salt intake has drawn little attention. The understanding of salt intake is important as a guide for optimizing salt-restriction strategies. However, precise evaluation of salt intake is difficult. More reliable methods are more difficult to perform, whereas easier methods are less reliable. Thus, the method to assess salt intake should be determined as the situation demands. The Working Group for Dietary Salt Reduction of the Japanese Society of Hypertension recommends the assessment of individual salt intake using one of the following methods in the management of hypertension. 1) The measurement of the sodium (Na) excretion from 24-h urine sampling or nutritionists analysis of the dietary contents, which are reliable but difficult to perform, are suitable for facilities specializing in the treatment of hypertension. 2) Estimation of the Na excretion from the Na/creatinine (Cr) ratio in spot urine is less reliable but practical and is suitable for general medical facilities. 3) Estimation using an electronic salt sensor equipped with a calculation formula is also less reliable but is simple enough that patients can use it themselves. The patients are considered to be compliant with the salt-restriction regimen if salt intake measured by whichever method is less than 6 g (100 mmol)/day.