Yasushi Teshima

Pioglitazone attenuates inflammatory atrial fibrosis and vulnerability to atrial fibrillation induced by pressure overload in rats

BACKGROUND Inflammatory processes are involved in the pathogenesis of atrial fibrillation (AF). OBJECTIVE The purpose of this study was to test the hypothesis that atrial fibrosis and enhanced vulnerability to AF evoked by pressure overload can be attenuated by pioglitazone, a peroxisome proliferator-activated receptor-γ agonist, via suppression of inflammatory profibrotic signals. METHODS Male Sprague-Dawley rats were subjected to abdominal aortic constriction (AAC). Pioglitazone 3 mg/kg/day or vehicle was orally administered for 4 weeks. RESULTS Western blot analysis revealed that AAC enhanced expression of monocyte chemoattractant protein (MCP)-1, transforming growth factor-β1 and α-smooth muscle actin in the left atrium (LA), which was suppressed by pioglitazone. Messenger RNA expression of collagen type 1 and atrial natriuretic peptide in the LA was increased by AAC, which was suppressed by pioglitazone. Gelatin zymography demonstrated that activity of matrix metalloproteinase-9 was increased by AAC, which was suppressed by pioglitazone. Pioglitazone attenuated AAC-induced LA fibrosis. In isolated-perfused heart experiments, AAC did not alter the refractory period of the LA or the right atrium (RA), but it did prolong the interatrial conduction time. Programmed extrastimuli from the RA induced AF in all of the AAC-treated rats (8/8 [100%]). This was suppressed by pioglitazone (2/8 [25%], P <.05) with normalization to interatrial conduction time. CONCLUSION The results of this study suggest that inflammatory profibrotic mechanisms are involved in this pressure-overloaded AF model. The results also suggest that pioglitazone is effective at attenuating atrial fibrosis, possibly via suppression of MCP-1-mediated inflammatory profibrotic processes.

Chronic central leptin infusion restores hyperglycemia independent of food intake and insulin level in streptozotocin-induced diabetic rats

We examined the effects of chronic centrally administered leptin on the glucose metabolism of streptozotocin‐induced diabetic (STZ‐D) rats, a model for insulin‐dependent diabetes mellitus. When 3 μg • rat‐1 • day‐1 of leptin was infused into the third ventricle for 6 consecutive days (STZ‐LEP), STZ‐D rats became completely euglycemic. The effect was not seen when the same dosage was administered s.c. Centrally administered leptin did not affect peripheral insulin levels. The feeding volume of STZ‐LEP rats was suppressed to the level of non‐STZ‐D control rats. No improvement of hyperglycemia was noted when STZ‐D rats were pair‐fed to match the feeding volume of STZ‐LEP rats. Thus, the euglycemia of STZ‐LEP rats cannot be due to the decreased feeding volume. In the STZ‐D rat, glucokinase mRNA, a marker of glycolysis, is down‐regulated whereas glucose‐6‐phosphatase mRNA, a marker of gluconeogenesis, and glucose transporter (GLUT) 2, which is implicated in the release of glucose from liver, are up‐regulated. GLUT4, uncoupling protein (UCP) 1, and UCP3 were down‐regulated in brown adipose tissue. These parameters returned to normal upon central infusion of leptin. GLUT4 was not down‐regulated in the skeletal muscle of STZ‐D rats; however, fatty acid binding protein and carnitine palmitoyltransferase I, markers for utilization and β‐oxidation of fatty acids, were up‐regulated and restored when the rats were treated with leptin. The increase and subsequent decrease of fatty acid utilization suggests a decrease of glucose uptake in the skeletal muscle of STZ‐D rats, which was restored upon central leptin administration. We conclude that centrally infused leptin does not control serum glucose by regulating feeding volume or elevating peripheral insulin, but by regulating hepatic glucose production, peripheral glucose uptake, and energy expenditure. The present study indicates the possibility of future development of a new class of anti‐diabetic agents that act centrally and independent of insulin action.—Hidaka, S., Yoshimatsu, H., Kondou, S., Tsuruta, Y., Oka, K., Noguchi, H., Okamoto, K., Sakino, H., Teshima, Y., Okeda, T., Sakata, T. Chronic central leptin infusion restores hyperglycemia independent of food intake and insulin level in streptozotocin‐induced diabetic rats. FASEB J. 16, 509–518 (2002)

Pioglitazone shift circadian rhythm of blood pressure from non‐dipper to dipper type in type 2 diabetes mellitus

Background  Insulin resistance significantly correlated with a non‐dipper type of essential hypertension. Thiazolidinediones (TZD), oral hypoglycaemic agents that act as insulin sensitizers, have been demonstrated in multiple in vivo and in vitro studies to possess antihypertensive properties. This study examined the efficacy of TZD therapy with pioglitazone at transforming the circadian rhythms of blood pressure from a non‐dipper to a dipper type.

Hypoleptinemia, but not hypoinsulinemia, induces hyperphagia in streptozotocin-induced diabetic rats

To assess the dominance between hypoinsulinemia and hypoleptinemia as factors in the development of hyperphagia in streptozotocin (STZ)‐induced diabetes mellitus (STZ‐DM) rodents with respect to hormone–neuropeptide interactions, changes in gene expression of agouti gene‐related protein (AGRP) in the arcuate nucleus of the hypothalamus were investigated using STZ‐DM rats, fasting Zucker fa/fa rats and STZ‐DM agouti (STZ‐DM Ay/a) mice. AGRP mRNA and neuropeptide Y mRNA were both significantly up‐regulated in STZ‐DM rats, which are associated with body weight loss, hyperglycemia, hypoinsulinemia and hypoleptinemia. We proceeded to analyze whether insulin or leptin played the greater role in the regulation of AGRP using Zucker fa/fa rats. The AGRP mRNA did not differ significantly between fasted fa/fa rats, which have both leptin‐insensitivity and hypoinsulinemia, and fed Zuckers, which have leptin‐insensitivity and hyperinsulinemia. We further found that up‐regulation of AGRP expression was normalized by infusion of leptin into the third cerebroventricle (i3vt), but not by i3vt infusion of insulin, although up‐regulation of AGRP was partially corrected by systemic insulin infusion. The latter finding supports hypoleptinemia as a key‐modulator of STZ‐DM‐induced hyperphagia because systemic insulin infusion, at least partially, restored hypoleptinemia through its acceleration of fat deposition, as demonstrated by the partial recovery of lost body weight. After STZ‐DM induction, Ay/a mice whose melanocortin‐4 receptor (MC4‐R) was blocked by ectopic expression of agouti protein additionally accelerated hyperphagia and up‐regulated AGRP mRNA, implying that the mechanism is triggered by a leptin deficit rather than by the main action of the message through MC4‐R. Hypoleptinemia, but not hypoinsulinemia per se, thus develops hyperphagia in STZ‐DM rodents. These results are very much in line with evidence that hypothalamic neuropeptides are potently regulated by leptin as downstream targets of its actions.

Glucose fluctuations increase the incidence of atrial fibrillation in diabetic rats.

AIMS We investigated whether glucose fluctuations aggravate cardiac fibrosis and increase the occurrence of atrial fibrillation (AF) in rats with diabetes mellitus (DM). METHODS AND RESULTS Streptozotocin-induced diabetic rats were randomly divided into three groups: uncontrolled DM (U-STZ) group, controlled DM (C-STZ) group, and DM with glucose fluctuations (STZ-GF) group. Glucose fluctuations were induced by fasting for 24 h and additional regular insulin injections (0.5 IU/kg) administered three times per week for three consecutive weeks. C-STZ rats were administered long acting insulin (20 IU/kg) twice a day to control blood glucose levels. Cardiac fibrosis evaluated by Masson trichrome staining and the expressions of collagen type 1, collagen type 3, and α-smooth muscle actin were increased in U-STZ rats compared with C-STZ rats, which were more pronounced in STZ-GF rats. The inducibility of AF was significantly larger in U-STZ rats than C-STZ rats and was greatest in STZ-GF rats. To explore the mechanism of cardiac fibrosis, we investigated the levels of reactive oxygen species (ROS) and apoptosis. The expression of malondialdehyde, an indicator of ROS levels, was significantly upregulated in STZ-GF rats compared with U-STZ rats, along with increased thioredoxin-interacting protein (Txnip) expression in STZ-GF rats. Furthermore, caspase-3 expression and the number of TUNEL-positive cells were significantly increased in STZ-GF rats compared with U-STZ and C-STZ rats. CONCLUSION Glucose fluctuations increase the incidence of AF by promoting cardiac fibrosis. Increased ROS levels caused by upregulation of Txnip expression may be a mechanism whereby in glucose fluctuations induce fibrosis.

Early atorvastatin therapy improves cardiac function in patients with acute myocardial infarction.

BACKGROUND A number of experimental and clinical studies have demonstrated a cardioprotective effect of statins; however, the effect of atorvastatin on cardiac function in patients with an acute myocardial infarction (AMI) has not been established. METHODS AND RESULTS Thirty consecutive patients with an AMI (16 males and 14 females) were enrolled. All the patients underwent successful percutaneous coronary intervention in the early phase after the onset of an AMI. Patients with a total cholesterol level > 200mg/dL on admission (n = 14) were assigned to the atorvastatin group. They began taking 10 mg of atorvastatin daily within 48 h after the onset of the AMI, while the other patients (n = 16) did not receive atorvastatin and served as the control group. Echocardiography and blood sampling to measure brain natriuretic peptide (BNP) and atrial natriuretic peptide (ANP) levels were repeated on the 2nd day (2D), 3 weeks (3W), 12 weeks (12W), and 24 weeks (24W) after the onset of the AMI. The percentage of patients with a high BNP level (BNP > 20 pg/mL) was significantly decreased from 2D to 24W in the atorvastatin group, but not in the control group (100 to 57% in the atorvastatin group, p < 0.05; 100 to 80% in the control group, n.s.). Similar results also occurred with respect to the ANP level (ANP > 40 pg/mL) (62 to 21% in the atorvastatin group, p < 0.05; 57 to 40% in the control group, n.s.). The left ventricular ejection fraction was significantly higher in the atorvastatin group than the control group at 3W (66.0 ± 7.8% vs. 56.5 ± 11.8%, p < 0.05) and 24W (67.5 ± 9.2% vs. 59.7 ± 9.8%, p < 0.05). In the atorvastatin group, the left ventricular systolic diameter was significantly decreased at 24W compared with that at 2D (37.1 ± 8.0 mm to 31.4 ± 6.5 mm, p < 0.05). CONCLUSIONS Initiation of atorvastatin in the early phase of an AMI has beneficial effects on cardiac function, probably by improving left ventricular remodeling.

Alteration of heart uncoupling protein-2 mRNA regulated by sympathetic nerve and triiodothyronine during postnatal period in rats

To provide tissue-specific and developmental characteristics of gene expression of rat heart uncoupling protein-2 (UCP2), we investigated developmental alterations of UCPs mRNA expression in the heart and brown adipose tissue (BAT), and examined possible up-regulators of heart UCP2 expression using in vitro studies. Heart UCP2 mRNA expression was low during the early postnatal days followed by a rapid and significant increase in the 2nd postnatal week. Heart UCP3 mRNA remained undetectable until the 2nd postnatal week when the expression reached a small but significant peak. BAT UCP1 mRNA was abundantly expressed in the neonate, but the expression rapidly decreased to the adult level. The studies using cultured cardiomyocytes demonstrated that both 10(-8) M triiodothyronine and 10(-7) M isoproterenol, but not phenylephrine, increased UCP2 mRNA expression. These results indicate that the sympathetic nervous system and/or thyroid hormones may be involved in the up-regulation of heart UCP2 gene expression during postnatal development. The increase in postnatal heart UCP2 may provide a key link between the postnatal energy shift and adaptation of rat pups to their novel environment.

High-Density Lipoprotein Cholesterol and Insulin Resistance Are Independent and Additive Markers of Left Ventricular Hypertrophy in Essential Hypertension

We examined whether plasma high-density lipoprotein-cholesterol (HDL-C) levels and glucose metabolism parameters are independent or additive predictors of left ventricular hypertrophy (LVH) in patients with untreated essential hypertension. The study group consisted of 41 Japanese patients with untreated essential hypertension and LVH (left ventricular mass index [LVMI] >125 g/m2; age 58±6 years, mean±SD), and the control group consisted of 39 age-matched patients with untreated essential hypertension without LVH (LVMI ≤125 g/m2; age 58±7 years). The following metabolic parameters were higher in the group with LVH: fasting plasma glucose (FPG) (p<0.01), fasting insulin concentration (F-IRI) (p<0.0001), and homeostasis model assessment (HOMA)-index (p<0.0001). Among the laboratory parameters investigated, plasma HDL-C levels were lower (p<0.0001), and triglyceride and uric acid levels were higher in the group with LVH (p<0.05 for both). The nighttime systolic and diastolic ambulatory blood pressure (ABP) (p<0.0001, p<0.01, respectively) and nighttime heart rate (p<0.01) were higher in patients with LVH. Multivariate logistic analysis identified HDL-C (odds ratio [OR]=0.92, 95% confidence interval [CI]=0.87–0.98, p<0.05), HOMA-index (OR=3.83, 95% CI=1.28–11.5, p<0.05) and nighttime systolic ambulatory blood pressure (ABP) (OR=1.06, 95% CI=1.00–1.13, p<0.05) as independent significant risk factors for LVH. Our findings suggest that HDL-C, HOMA-index and nighttime systolic ABP are independent predictors for the presence of LVH in Japanese patients with essential hypertension.

Role of Indoxyl Sulfate as a Predisposing Factor for Atrial Fibrillation in Renal Dysfunction.

Background Renal dysfunction is a major risk factor for atrial fibrillation (AF). The uremic toxin indoxyl sulfate may contribute to the progression of cardiac fibrosis and AF substrate in renal dysfunction. Methods and Results Male Sprague–Dawley rats were assigned randomly to the following groups: 5/6 nephrectomy (5/6Nx) with vehicle, 5/6Nx with AST‐120, sham procedure with vehicle, and sham procedure with AST‐120. Vehicle and AST‐120 were administered for 4 weeks. Serum levels of IS were significantly increased in 5/6Nx groups. Expression of malondialdehyde, an indicator of oxidative stress, was upregulated in the left atrium of 5/6Nx groups and was accompanied by an increase in expression of NADPH oxidase 2 and 4. Monocyte‐mediated inflammatory signals such as CD68, monocyte chemoattractant protein 1, and vascular cell adhesion molecule 1 were also upregulated in 5/6Nx groups. Interstitial fibrosis was promoted heterogeneously, and expression of profibrotic indicators such as transforming growth factor β1, α‐smooth muscle actin, and collagen type 1 was upregulated in left atrium tissue of 5/6Nx groups. In cultured atrial fibroblasts, incubation with IS upregulated expression of the markers of oxidative stress, inflammation, and profibrotic factors. These results suggest the direct effects of IS on the progression of AF substrate. AF was consistently and invariably induced by atrial extrastimuli in 5/6Nx groups in electrophysiological experiments. AST‐120 treatment significantly alleviated renal dysfunction–induced oxidative stress, inflammation, and atrial fibrosis and, consequently, attenuated AF inducibility. Conclusions Indoxyl sulfate facilitates atrial fibrosis and AF and thus is a novel therapeutic target for prevention of renal dysfunction–induced AF.

Glucose Fluctuations Aggravate Cardiac Susceptibility to Ischemia/Reperfusion Injury by Modulating MicroRNAs Expression.

BACKGROUND The influence of glucose fluctuations (GF) on cardiovascular complications of diabetes mellitus (DM) has been attracting much attention. In the present study, whether GF increase susceptibility to ischemia/reperfusion in the heart was investigated. METHODS AND RESULTS Male rats were randomly assigned to either a control, DM, and DM with GF group. DM was induced by an injection of streptozotocin, and glucose fluctuation was induced by starvation and insulin injection. One sequential program comprised 2 hypoglycemic episodes during 4 days. The isolated hearts were subjected to 20-min ischemia/30-min reperfusion. The infarct size was larger in hearts with GF than those with sustained hyperglycemia. Activities of catalase and superoxide dismutase were decreased, and expressions of NADPH oxidase and thioredoxin-interacting protein were upregulated by GF accompanied by an increase of reactive oxygen species (ROS). Swollen mitochondria with destroyed cristae were observed in diabetic hearts; they were further devastated by GF. Microarray analysis revealed that the expressions of microRNA (miRNA)-200c and miRNA-141 were abundant in those hearts with GF. Overexpression of miRNA-200c and miRNA-141 decreased mitochondrial superoxide dismutase and catalase activities, and increased ROS levels. Meanwhile, knockdown of miRNA-200c and miRNA-141 significantly decreased ROS levels in cardiomyocytes exposed to GF. CONCLUSIONS GF increased ROS generation and enhanced ischemia/reperfusion injury in the diabetic heart. Upregulated miRNA-200c and miRNA-141 may account for the increased ROS.