Masao Moroi

Pioglitazone ameliorates insulin resistance and diabetes by both adiponectin-dependent and -independent pathways.

*Thiazolidinediones have been shown to up-regulate adiponectin expression in white adipose tissue and plasma adiponectin levels, and these up-regulations have been proposed to be a major mechanism of the thiazolidinedione-induced amelioration of insulin resistance linked to obesity. To test this hypothesis, we generated adiponectin knock-out (adipo-/-) ob/ob mice with a C57B/6 background. After 14 days of 10 mg/kg pioglitazone, the insulin resistance and diabetes of ob/ob mice were significantly improved in association with significant up-regulation of serum adiponectin levels. Amelioration of insulin resistance in ob/ob mice was attributed to decreased glucose production and increased AMP-activated protein kinase in the liver but not to increased glucose uptake in skeletal muscle. In contrast, insulin resistance and diabetes were not improved in adipo-/-ob/ob mice. After 14 days of 30 mg/kg pioglitazone, insulin resistance and diabetes of ob/ob mice were again significantly ameliorated, which was attributed not only to decreased glucose production in the liver but also to increased glucose uptake in skeletal muscle. Interestingly, adipo-/-ob/ob mice also displayed significant amelioration of insulin resistance and diabetes, which was attributed to increased glucose uptake in skeletal muscle but not to decreased glucose production in the liver. The serum-free fatty acid and triglyceride levels as well as adipocyte sizes in ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were significantly reduced to a similar degree after 30 mg/kg pioglitazone. Moreover, the expressions of TNFα and resistin in adipose tissues of ob/ob and adipo-/-ob/ob mice were unchanged after 10 mg/kg pioglitazone but were decreased after 30 mg/kg pioglitazone. Thus, pioglitazone-induced amelioration of insulin resistance and diabetes may occur adiponectin dependently in the liver and adiponectin independently in skeletal muscle.

Impaired Insulin Signaling in Endothelial Cells Reduces Insulin-Induced Glucose Uptake by Skeletal Muscle

In obese patients with type 2 diabetes, insulin delivery to and insulin-dependent glucose uptake by skeletal muscle are delayed and impaired. The mechanisms underlying the delay and impairment are unclear. We demonstrate that impaired insulin signaling in endothelial cells, due to reduced Irs2 expression and insulin-induced eNOS phosphorylation, causes attenuation of insulin-induced capillary recruitment and insulin delivery, which in turn reduces glucose uptake by skeletal muscle. Moreover, restoration of insulin-induced eNOS phosphorylation in endothelial cells completely reverses the reduction in capillary recruitment and insulin delivery in tissue-specific knockout mice lacking Irs2 in endothelial cells and fed a high-fat diet. As a result, glucose uptake by skeletal muscle is restored in these mice. Taken together, our results show that insulin signaling in endothelial cells plays a pivotal role in the regulation of glucose uptake by skeletal muscle. Furthermore, improving endothelial insulin signaling may serve as a therapeutic strategy for ameliorating skeletal muscle insulin resistance.

Insulin receptor substrate 2 plays a crucial role in β cells and the hypothalamus

We previously demonstrated that insulin receptor substrate 2 (Irs2) KO mice develop diabetes associated with hepatic insulin resistance, lack of compensatory beta cell hyperplasia, and leptin resistance. To more precisely determine the roles of Irs2 in beta cells and the hypothalamus, we generated beta cell-specific Irs2 KO and hypothalamus-specific Irs2 knockdown (betaHT-IRS2) mice. Expression of Irs2 mRNA was reduced by approximately 90% in pancreatic islets and was markedly reduced in the arcuate nucleus of the hypothalamus. By contrast, Irs2 expression in liver, muscle, and adipose tissue of betaHT-IRS2 mice was indistinguishable from that of control mice. The betaHT-IRS2 mice displayed obesity and leptin resistance. At 4 weeks of age, the betaHT-IRS2 mice showed normal insulin sensitivity, but at 8 and 12 weeks, they were insulin resistant with progressive obesity. Despite their normal insulin sensitivity at 8 weeks with caloric restriction, the betaHT-IRS2 mice exhibited glucose intolerance and impaired glucose-induced insulin secretion. beta Cell mass and beta cell proliferation in the betaHT-IRS2 mice were reduced significantly at 8 and 12 weeks but not at 10 days. Insulin secretion, normalized by cell number per islet, was significantly increased at high glucose concentrations in the betaHT-IRS2 mice. We conclude that, in beta cells and the hypothalamus, Irs2 is crucially involved in the regulation of beta cell mass and leptin sensitivity.

Dynamic Functional Relay between Insulin Receptor Substrate 1 and 2 in Hepatic Insulin Signaling during Fasting and Feeding

Insulin receptor substrate (Irs) mediates metabolic actions of insulin. Here, we show that hepatic Irs1 and Irs2 function in a distinct manner in the regulation of glucose homeostasis. The PI3K activity associated with Irs2 began to increase during fasting, reached its peak immediately after refeeding, and decreased rapidly thereafter. By contrast, the PI3K activity associated with Irs1 began to increase a few hours after refeeding and reached its peak thereafter. The data indicate that Irs2 mainly functions during fasting and immediately after refeeding, and Irs1 functions primarily after refeeding. In fact, liver-specific Irs1-knockout mice failed to exhibit insulin resistance during fasting, but showed insulin resistance after refeeding; conversely, liver-specific Irs2-knockout mice displayed insulin resistance during fasting but not after refeeding. We propose the concept of the existence of a dynamic relay between Irs1 and Irs2 in hepatic insulin signaling during fasting and feeding.

Lack of Insulin Receptor Substrate-2 Causes Progressive Neointima Formation in Response to Vessel Injury

Background Insulin resistance is associated with atherosclerosis, but its mechanism is unknown. It has been reported that insulin receptor substrate (IRS)‐1 deficient (IRS‐1‐/‐) mice showed insulin resistance without type 2 diabetes, whereas the IRS‐2 deficient (IRS‐2‐/‐) mice showed insulin resistance with type 2 diabetes. Methods and Results We investigated neointima formation in the IRS‐1‐/‐ and IRS‐2‐/‐ mice at 8 and 20 weeks. The IRS‐2‐/‐ mice showed much greater neointima formation than the IRS‐1‐/‐ and wild‐type mice at 8 weeks. At 20 weeks, the IRS‐2‐/‐ mice had greater neointima formation than the IRS‐1‐/‐ mice, which showed more enhanced neointima formation than the wild‐type mice. The IRS‐1‐/‐ and IRS‐2‐/‐ mice had dyslipidemia, hypertension, and insulin resistance. The IRS‐2‐/‐ mice had more metabolic abnormalities than the IRS‐1‐/‐ mice at 8 and 20 weeks. IRS‐2 expression was detected, but IRS‐1 expression was not detected in the vessels. Conclusions The neointima formation in the IRS‐1‐/‐ and IRS‐2‐/‐ mice appears to be related to abnormalities induced by the altered metabolic milieu in insulin‐resistant states. Moreover, because neointima formation was much greater in the IRS‐2‐/‐ mice than in the IRS‐1‐/‐ mice at 8 and 20 weeks, it is suggested that a lack of IRS‐2 renders the vasculature more susceptible to injury in the abnormal metabolic milieu, and IRS‐2 may have a protective effect on neointima formation. We conclude that IRS‐2 is protective and retards the development of neointima formation in insulin‐resistant states. (Circulation. 2003;107:3073‐3080.)

Long fasting is effective in inhibiting physiological myocardial 18F-FDG uptake and for evaluating active lesions of cardiac sarcoidosis

BackgroundF-fluorodeoxyglucose (FDG) positron emission tomography (PET) is a promising modality for detecting active lesions of cardiac sarcoidosis (CS). However, determining whether 18F-FDG uptake in the myocardium is physiological is challenging due to metabolic shift in myocardial cells. Although methods for inhibiting physiological myocardial 18F-FDG uptake have been proposed, no standard methods exist. This study therefore aimed to compare the effect of an 18-h fast (long fasting (LF)) with heparin loading plus a 12-h fast (HEP) before 18F-FDG PET scan.MethodsWe analyzed the effects of LF and HEP on the inhibition of physiological myocardial 18F-FDG uptake in healthy subjects (18 in HEP and 19 in LF) and in patients with known or suspected CS (96 in HEP and 69 in LF). In CS, the lower uptake of 18F-FDG in the myocardium was evaluated. A visual four-point scale was used to assess myocardial 18F-FDG uptake in comparison with hepatic uptake (1 lower, 2 similar, 3 somewhat higher, 4 noticeably higher).ResultsMyocardial 18F-FDG uptake was 1.68 ± 1.06 in LF and 3.17 ± 1.16 in HEP in healthy subjects (p < 0.0001), whereas it was 1.48 ± 0.99 in LF and 2.48 ± 1.33 in HEP in CS patients (p < 0.0001). Logistic regression and regression trees revealed the LF was the most effective in inhibiting myocardial 18F-FDG uptake. In addition, serum free fatty acid levels on intravenous 18F-FDG injection were a possible biomarker.ConclusionsLF is effective in inhibiting myocardial 18F-FDG uptake, and consequently, it could be useful for evaluating active lesions of CS in 18F-FDG PET images.

Recommendations for (18)F-fluorodeoxyglucose positron emission tomography imaging for cardiac sarcoidosis: Japanese Society of Nuclear Cardiology recommendations.

Sarcoidosis is a systemic granulomatous disease that forms epithelioid cell granuloma (accompanied by infiltration of inflammatory cells) without caseous necrosis in organs throughout the body, including the lungs, lymph nodes, skin, eyes, heart, and muscles. Generally there is a good prognosis for spontaneous resolution of sarcoidosis; however, for cardiac-involvement sarcoidosis, the prognosis is extremely poor, and careful management is required. The most common cause of death from sarcoidosis is cardiac complications of the disease, and therefore early detection and treatment of these are very important in the management of cardiac-involvement sarcoidosis. Guidelines for the diagnosis of cardiac sarcoidosis were first published by Hiraga et al. [1] in 1992 (Table 1). These guidelines were modified by the joint committee of the Japan Society of Sarcoidosis and Other Granulomatous Disorders and the Japanese College of Cardiology in 2006 (Table 2) [2]. These modified guidelines stipulate the following: a histopathological or clinical diagnosis of sarcoidosis in organs other than the heart is essential, and the following cases should be diagnosed as cardiac sarcoidosis: (1) cases histopathologically diagnosed as positive for cardiac sarcoidosis on the basis of myocardial biopsy (histopathologically diagnosed group) and (2) cases with clinical findings indicating characteristic cardiac abnormalities including principal and secondary signs and symptoms (clinically diagnosed group) (Tables 1, 2). In the histopathologically diagnosed group, the positivity rate for detection of cardiac sarcoidosis may be low owing to sampling errors in myocardial biopsy. Hence, in actual clinical settings, the number of cases in the clinically diagnosed group is higher than in the histopathologically diagnosed group. Upon diagnosis of cardiac sarcoidosis, it is important to determine the disease activity to develop a treatment strategy, assess severity, predict prognosis, and Committee for diagnosis of cardiac sarcoidosis using 18F-FDG PET, Japanese Society of Nuclear Cardiology.

Endothelin-1- and endothelin-3-induced vasorelaxation via common generation of endothelium-derived nitric oxide

The vasorelaxant effects by endothelin-1 (ET-1) and endothelin-3 (ET-3), and their mechanisms of action were studied in isolated porcine pulmonary arterial strips. ET-1 and ET-3 dose-dependently (10(-9) - 10(-8) M) relaxed vascular strips precontracted with norepinephrine only in the presence of endothelium. The maximal vasorelaxant effect by ET-1 was about 70% of that by ET-3. The ET-1- and ET-3- induced vasorelaxation was blocked by NG-nitro-L-arginine, an inhibitor of nitric oxide synthesis, and methylene blue, an inhibitor of soluble guanylate cyclase. The present data suggest that vascular smooth muscle relaxation induced by ET-1 and ET-3 is mainly ascribed to synthesis and release of nitric oxide from L-arginine in endothelium.

Rimonabant Ameliorates Insulin Resistance via both Adiponectin-dependent and Adiponectin-independent Pathways

Rimonabant has been shown to not only decrease the food intake and body weight but also to increase serum adiponectin levels. This increase of the serum adiponectin levels has been hypothesized to be related to the rimonabant-induced amelioration of insulin resistance linked to obesity, although experimental evidence to support this hypothesis is lacking. To test this hypothesis experimentally, we generated adiponectin knock-out (adipo(-/-))ob/ob mice. After 21 days of 30 mg/kg rimonabant, the body weight and food intake decreased to similar degrees in the ob/ob and adipo(-/-)ob/ob mice. Significant improvement of insulin resistance was observed in the ob/ob mice following rimonabant treatment, associated with significant up-regulation of the plasma adiponectin levels, in particular, of high molecular weight adiponectin. Amelioration of insulin resistance in the ob/ob mice was attributed to the decrease of glucose production and activation of AMP-activated protein kinase (AMPK) in the liver induced by rimonabant but not to increased glucose uptake by the skeletal muscle. Interestingly, the rimonabant-treated adipo(-/-)ob/ob mice also exhibited significant amelioration of insulin resistance, although the degree of improvement was significantly lower as compared with that in the ob/ob mice. The effects of rimonabant on the liver metabolism, namely decrease of glucose production and activation of AMPK, were also less pronounced in the adipo(-/-)ob/ob mice. Thus, it was concluded that rimonabant ameliorates insulin resistance via both adiponectin-dependent and adiponectin-independent pathways.

Coronary revascularization does not decrease cardiac events in patients with stable ischemic heart disease but might do in those who showed moderate to severe ischemia

BACKGROUND As an initial management strategy for stable ischemic heart disease (IHD), coronary revascularization therapy is thought to be equal to optimal medical therapy alone regarding prognosis. METHODS Whether or not the effects of revascularization on the prognosis of patients with stable IHD are associated with the amount of ischemic myocardium detected by nuclear stress imaging was evaluated. This retrospective study analyzed data from 4629 patients with suspected or known IHD who underwent gated stress myocardial-perfusion SPECT at 117 hospitals in Japan. The follow-up periods were three years and the combined endpoints consisted of cardiac death, nonfatal myocardial infarction, and congestive heart failure requiring hospitalization. After matching propensity scores between patients who underwent early revascularization and those who did not (n=316 per group), we compared cardiac event rates in relation to the amount of ischemic myocardium. RESULTS Cardiac event rates did not significantly differ between patients who underwent early revascularization and those who did not (5.4% vs. 6.4%). Among patients with ≤ 5%, 6-10%, and >10% ischemic myocardium, cardiac event rates were 8%, 3% and 0% respectively, who underwent early revascularization compared with 4.5%, 6.1%, and 12.3%, respectively, among those who did not. Cardiac event rates were significantly lower among patients with >10% ischemic myocardium who underwent early revascularization compared with those who did not (0% vs. 12.3%, p=0.0062). CONCLUSIONS Coronary revascularization for stable IHD does not decrease major cardiac events in all patients but might do in patients with moderate to severe ischemia.