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Kazuwa Nakao

Publications and source records attributed to Kazuwa Nakao.

At least 19 recordsLinked to original sources
PubMed2007

The effects of long-term smoking on endothelial nitric oxide synthase mRNA expression in human platelets as detected with real-time quantitative RT-PCR.

Endothelium-derived nitric oxide (NO) plays an important role in the prevention of platelet aggregation and adhesion to the vascular wall. Endothelial nitric oxide synthase (eNOS) and L-arginine/NO pathway are both present in human platelets. Platelet-derived NO inhibits excessive activation and aggregation of platelets. However, the expression level of the eNOS gene in human platelets has yet to be elucidated. The current study investigates the individual expression level of platelet eNOS mRNA using the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) detection method. eNOS mRNA expression was examined in platelets isolated from 50 subjects: 11 male smokers, 15 male nonsmokers, and 24 female non-smokers. After extraction of platelet total RNA, eNOS (target) and GAPDH (internal control) mRNA expression levels were quantitated using real-time RT-PCR. The expression levels of eNOS mRNA (relative copy numbers) were significantly lower in male smokers (59+/-17) than in male nonsmokers (195+/-71, P < .03), and higher in female nonsmokers (285+/-60) than in the male nonsmokers (195+/-71, P < .03). By multiple linear regression analysis, cigarette smoking (P = .008) and diabetes mellitus (P = .047) were found to be significantly negative predictors, and antioxidant (vitamin E) treatment (P = .01) was a significantly positive predictor of platelet eNOS mRNA expression. Age, other medications, and other risk factors for coronary artery disease were not significant. Using this method, eNOS mRNA abundance in human platelets was detected and quantitated in real-time. The intraplatelet eNOS mRNA expression levels were significantly decreased in cigarette smokers. Low platelet NO synthesis in smokers may result in the augmentation of platelet aggregation and thrombus formation, developing into acute coronary syndromes.

Adult↗
PubMed2006

Antithyroid drugs inhibit thyroid hormone receptor-mediated transcription.

CONTEXT: Methimazole (MMI) and propylthiouracil (PTU) are widely used as antithyroid drugs (ATDs) for the treatment of Graves' disease. Both MMI and PTU reduce thyroid hormone levels by several mechanisms, including inhibition of thyroid hormone synthesis and secretion. In addition, PTU decreases 5'-deiodination of T(4) in peripheral tissues. ATDs may also interfere with T(3) binding to nuclear thyroid hormone receptors (TRs). However, the effect of ATDs on the transcriptional activities of T(3) mediated by TRs has not been studied. OBJECTIVE: The present study was undertaken to determine whether ATDs have an effect on the gene transcription regulated by T(3) and TRs in vitro. METHODS: Transient gene expression experiments and GH secretion assays were performed. To elucidate possible mechanisms of the antagonistic action of ATDs, the interaction between TR and nuclear cofactors was examined. RESULTS: In the transient gene expression experiments, both MMI and PTU significantly suppressed transcriptional activities mediated by the TR and T(3) in a dose-dependent manner. In mammalian two-hybrid assays, both drugs recruited one of the nuclear corepressors, nuclear receptor corepressor, to the TR in the absence of T(3). In addition, PTU dissociated nuclear coactivators, such as steroid receptor coactivator-1 and glucocorticoid receptor interacting protein-1, from the TR in the presence of T(3). Finally, MMI decreased the GH release that was stimulated by T(3). CONCLUSIONS: ATDs inhibit T(3) action by recruitment of transcriptional corepressors and/or dissociation of coactivators. This is the first report to show that ATDs can modulate T(3) action at the transcriptional level.

Antithyroid Agents↗
PubMed2006

Bezafibrate regulates the expression and enzyme activity of 11beta-hydroxysteroid dehydrogenase type 1 in murine adipose tissue and 3T3-L1 adipocytes.

A clinically employed antihyperlipidemic drug, bezafibrate, has been characterized as a PPAR(alpha, -gamma, and -delta) pan-agonist in vitro. Recent extended trials have highlighted its antidiabetic properties in humans. However, the underlying molecular mechanism is not fully elucidated. The present study was designed to explore potential regulatory mechanisms of intracellular glucocorticoid reactivating enzyme, 11beta-HSD1 and anti-diabetic hormone, adiponectin by bezafibrate in murine adipose tissue, and cultured adipocytes. Treatment of db/db mice with bezafibrate significantly ameliorated hyperglycemia and insulin resistance, accompanied by a marked reduction of triglyceride and nonesterified fatty acids. Despite equipotent in lipid-lowering effects, another fibrate, fenofibrate, did not show such beneficial effects on glycemic control. Treatment of bezafibrate caused a marked decrease in the mRNA level of 11beta-HSD1 preferentially in adipose tissue of db/db mice (-47%, P<0.05), concomitant with a significant increase in plasma adiponectin level (+37%, P<0.01). Notably, treatment of bezafibrate caused a marked decrease in the mRNA level (-34%, P<0.01) and enzyme activity (-32%, P<0.01) of 11beta-HSD1, whereas the treatment substantially augmented the expression (+71%, P<0.01) and secretion (+27%, P<0.01) of adiponectin in 3T3-L1 adipocytes. Knockdown of 11beta-HSD1 by siRNA confirmed that 11beta-HSD1 acts as a distinct oxoreductase in adipocytes and validated the enzyme activity assays in the present study. Effects of bezafibrate on regulation of 11beta-HSD1 and adiponectin in murine adipocytes were comparable with those in thiazolidinediones. This is the first demonstration that bezafibrate directly regulates 11beta-HSD1 and adiponectin in murine adipocytes, both of which may contribute to metabolically-beneficial effects by bezafibrate.

11-beta-Hydroxysteroid Dehydrogenase Type 1↗
PubMed2006

Short-term effects of atorvastatin on bone turnover in male patients with hypercholesterolemia.

No consensus has been reached on whether the 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, known as statins, have beneficial effects on bone health. The purpose of our study was to evaluate the effects of atorvastatin on bone metabolism by means of measuring bone turnover markers in male patients with hypercholesterolemia both at diagnosis and prospectively after 3 months of treatment. Twenty-two Japanese male patients (mean age 62.36 +/- 10.1 years) with untreated hypercholesterolaemeia were selected for this study. After 3-months treatment of atorvastatin, total cholesterol and low density lipoprotein cholesterol significantly decreased as expected (p<0.001 for both parameters). Bone-specific alkaline phosphatase (BAP) did not change significantly (p = 0.444). However, serum N-terminal telopeptide of type I collagen (NTx) significantly decreased by -19.86 +/- 26.4% (p = 0.020). In addition, delta NTx during the course of this study was negatively correlated with NTx at baseline (r = -0.645, p = 0.0008). Although there was a tendency of positive correlations of delta NTx with delta total cholesterol, delta triglycerides, and delta low density lipoprotein cholesterol, and of negative correlations of delta NTx and delta BAP with delta high density lipoprotein cholesterol, none of them reached statistical significance. Our findings suggest that atorvastatin may have potentially beneficial effects on bone metabolism in patients with hypercholesterolemia mostly by reducing bone resorption rather than by stimulating bone formation. Further studies with more patients and longer duration are warranted to evaluate its effects, if any, on prevention of osteoporosis and subsequent fractures.

Aged↗
PubMed2006

A case of secretin-responsive insulinoma with low serum C-peptide levels.

Insulinoma is the most common cause of fasting hypoglycemia resulting from autonomous insulin hypersecretion. A 59-year-old woman who had previously had an insulinoma and had undergone a partial pancreatectomy was admitted to our hospital because of recurrence of hypoglycemia after 27 years. She had two unusual endocrinological features: 1) the serum insulin response to intravenous secretin injection was not impaired, and 2) the serum C-peptide levels and ratios of serum C-peptide to insulin were relatively low. Two pancreatic tumors were readily detectable by computed tomography (CT) and magnetic resonance imaging (MRI). The selective arterial calcium injection (SACI) test showed a hyperinsulinemic response by calcium administration to the gastroduodenal artery. A partial pancreatectomy was done and her hypoglycemia disappeared. Histology revealed that the tumors were composed of monotonous, small round cells that were positive for both insulin and cathepsin B. As previous in vitro studies have shown that C-peptide can be metabolized within human insulinoma cells by proteolytic cleavage by cathepsin B, our patient's low serum C-peptide levels might have been caused by degradation of C-peptide by cathepsin B. According to the data from the literature, the molar ratio of serum C-peptide to insulin is generally decreased in patients with insulinoma than normal subjects. This case highlights the need for careful interpretation of C-peptide levels and the intravenous secretin injection test in the diagnosis of insulinoma.

Blood Glucose↗
PubMed2006

NRSF regulates the developmental and hypertrophic changes of HCN4 transcription in rat cardiac myocytes.

The HCN4 channel shows differential expression patterns during the embryonic development and hypertrophy of hearts. Briefly, HCN4 expression is maximally activated in embryonic hearts and quickly diminishes after birth. However, it is reactivated during cardiac hypertrophy. The sequence analysis of HCN4 gene revealed the presence of a conserved NRSE motif, which is known to bind the transcriptional factor neuron-restrictive silencing factor (NRSF). A promoter analysis of HCN4 with rat cardiac myocytes identified the region inducing a basal transcriptional activity. This region drove a high activity in embryonic myocytes, but not in neonatal myocytes treated with hypertrophic agents. After confirming that NRSF protein binds to the NRSE, HCN4 promoter activities modified by NRSE were evaluated. With wild-type NRSE, the promoter activity correlated well with the developmental and hypertrophic changes of HCN4 expression, whereas mutant NRSE constructs failed. We conclude that the NRSE-NRSF system was implicated in HCN4 expression in cardiac myocytes.

Animals↗
PubMed2006

Effect of acute activation of 5'-AMP-activated protein kinase on glycogen regulation in isolated rat skeletal muscle.

5'-AMP-activated protein kinase (AMPK) has been implicated in glycogen metabolism in skeletal muscle. However, the physiological relevance of increased AMPK activity during exercise has not been fully clarified. This study was performed to determine the direct effects of acute AMPK activation on muscle glycogen regulation. For this purpose, we used an isolated rat muscle preparation and pharmacologically activated AMPK with 5-aminoimidazole-4-carboxamide-1-beta-D-ribonucleoside (AICAR). Tetanic contraction in vitro markedly activated the alpha(1)- and alpha(2)-isoforms of AMPK, with a corresponding increase in the rate of 3-O-methylglucose uptake. Incubation with AICAR elicited similar enhancement of AMPK activity and 3-O-methylglucose uptake in rat epitrochlearis muscle. In contrast, whereas contraction stimulated glycogen synthase (GS), AICAR treatment decreased GS activity. Insulin-stimulated GS activity also decreased after AICAR treatment. Whereas contraction activated glycogen phosphorylase (GP), AICAR did not alter GP activity. The muscle glycogen content decreased in response to contraction but was unchanged by AICAR. Lactate release was markedly increased when muscles were stimulated with AICAR in buffer containing glucose, indicating that the glucose taken up into the muscle was catabolized via glycolysis. Our results suggest that AMPK does not mediate contraction-stimulated glycogen synthesis or glycogenolysis in skeletal muscle and also that acute AMPK activation leads to an increased glycolytic flux by antagonizing contraction-stimulated glycogen synthesis.

AMP-Activated Protein Kinases↗
PubMed2006

Efficacy and safety of leptin-replacement therapy and possible mechanisms of leptin actions in patients with generalized lipodystrophy.

BACKGROUND: Lack of leptin is implicated in insulin resistance and other metabolic abnormalities in generalized lipodystrophy; however, the efficacy, safety, and underlying mechanisms of leptin-replacement therapy in patients with generalized lipodystrophy remain unclear. METHODS: Seven Japanese patients with generalized lipodystrophy, two acquired and five congenital type, were treated with the physiological replacement dose of recombinant leptin during an initial 4-month hospitalization followed by outpatient follow-up for up to 36 months. RESULTS: The leptin-replacement therapy with the twice-daily injection dramatically improved fasting glucose (mean +/- SE, 172 +/- 20 to 120 +/- 12 mg/dl, P < 0.05) and triglyceride levels (mean +/- SE, 700 +/- 272 to 260 +/- 98 mg/dl, P < 0.05) within 1 wk. The leptin-replacement therapy reduced insulin resistance evaluated by euglycemic clamp method and augmented insulin secretion at glucose tolerance test with different responses between acquired and congenital types. Improvement of the fatty liver was also observed. The efficacy and safety of the once-daily injection were comparable to those of the twice-daily injection. The leptin-replacement therapy ameliorated macro- and microalbuminuria and showed no deterioration of neuropathy and retinopathy of these patients. The leptin-replacement therapy is beneficial to diabetic complications and lipodystrophic ones. Two patients developed antileptin antibodies but not neutralizing antibodies. The therapy was well tolerated, and its effects were maintained for up to 36 months without any notable adverse effects such as hypoglycemia, high blood pressure, or reduction of bone mineral density. CONCLUSIONS: The present study demonstrates the efficacy and safety of the long-term leptin-replacement therapy and possible mechanisms of leptin actions in patients with generalized lipodystrophy.

Adolescent↗
PubMed2006

Class II HDACs mediate CaMK-dependent signaling to NRSF in ventricular myocytes.

We recently reported that a transcriptional repressor, neuron-restrictive silencer factor (NRSF), represses expression of fetal cardiac genes, including atrial and brain natriuretic peptide (ANP and BNP), by recruiting class I histone deacetylase (HDAC) and that attenuation of NRSF-mediated repression contributes to the reactivation of fetal gene expression during cardiac hypertrophy. The molecular mechanism by which the activity of the NRSF-HDAC complex is inhibited in cardiac hypertrophy remains unresolved, however. In the present study, we show that class II HDACs (HDAC4 and 5), which are Ca/calmodulin-dependent kinase (CaMK)-responsive repressors of hypertrophic signaling, associate with NRSF and participate in NRSF-mediated repression. Blockade of the CaMK-class II HDAC signaling pathway using a CaMK-resistant HDAC5 mutant, a CaMK inhibitor (KN62) or a dominant-negative CaMK mutant inhibited ET-1-inducible ANP and BNP promoter activity, but that inhibitory effect was abolished by mutation of the neuron-restrictive silencer element (NRSE) within the ANP and BNP promoter. In addition, adenovirus-mediated expression of a dominant-negative NRSF mutant abolished the inhibitory effect of KN62 on ET-1-inducible endogenous ANP gene expression in ventricular myocytes. Finally, the interaction between NRSF and class II HDACs was decreased in both in vitro and in vivo models of cardiac hypertrophy. These findings show that ET-1-induced CaMK signaling disrupts class II HDAC-NRSF repressor complexes, thereby enabling activation of ANP and BNP gene transcription in ventricular myocytes, and shed light on a novel mechanism by which the fetal cardiac gene program is reactivated.

Animals↗
PubMed2006

Redistribution of connexin43 expression in glomerular podocytes predicts poor renal prognosis in patients with type 2 diabetes and overt nephropathy.

BACKGROUND: Significance of podocyte injury in the progression of diabetic nephropathy is not well-understood. In this study, we examined whether alteration of gap junction protein connexin43 (Cx43) expression in podocytes is associated with the progression of overt diabetic nephropathy. METHODS: We recruited 29 type 2 diabetic patients with overt nephropathy who underwent renal biopsy. Nephrectomized kidney samples obtained from seven subjects with localized neoplasm and biopsy specimens from five patients diagnosed as minor glomerular abnormalities were used as controls. Cx43 staining on paraffin-embedded kidney sections were studied by immunohistochemistry. RESULTS: In controls, Cx43 was expressed at podocytes in a linear pattern along the glomerular basement membrane. In contrast, downregulation and loss of uniformly linear staining of Cx43 (Cx43 heterogeneity) in podocytes were observed in diabetic nephropathy. Cx43 intensity correlated with current renal function (R = 0.647, P < 0.005), whereas the magnitude of Cx43 heterogeneity correlated well with the degree of future decline in renal function (R = -0.705, P < 0.001). CONCLUSIONS: Alteration of Cx43 expression in podocytes was closely associated with the progression of overt diabetic nephropathy. These results indicate that change in Cx43 expression at podocytes represents a progressive stage in overt diabetic nephropathy and that it may be a convenient way to predict future decline in renal function.

Adult↗
PubMed2006

Adrenomedullin/cyclic AMP pathway induces Notch activation and differentiation of arterial endothelial cells from vascular progenitors.

OBJECTIVE: The acquisition of arterial or venous identity is highlighted in vascular development. Previously, we have reported an embryonic stem (ES) cell differentiation system that exhibits early vascular development using vascular endothelial growth factor (VEGF) receptor-2 (VEGFR2)-positive cells as common vascular progenitors. In this study, we constructively induced differentiation of arterial and venous endothelial cells (ECs) in vitro to elucidate molecular mechanisms of arterial-venous specification. METHODS AND RESULTS: ECs were induced from VEGFR2+ progenitor cells with various conditions. VEGF was essential to induce ECs. Addition of 8bromo-cAMP or adrenomedullin (AM), an endogenous ligand-elevating cAMP, enhanced VEGF-induced EC differentiation. Whereas VEGF alone mainly induced venous ECs, 8bromo-cAMP (or AM) with VEGF supported substantial induction of arterial ECs. Stimulation of cAMP pathway induced Notch signal activation in ECs. The arterializing effect of VEGF and cAMP was abolished in recombination recognition sequence binding protein at the Jkappa site deficient ES cells lacking Notch signal activation or in ES cells treated with gamma-secretase inhibitor. Nevertheless, forced Notch activation by the constitutively active Notch1 alone did not induce arterial ECs. CONCLUSIONS: Adrenomedullin/cAMP is a novel signaling pathway to activate Notch signaling in differentiating ECs. Coordinated signaling of VEGF, Notch, and cAMP is required to induce arterial ECs from vascular progenitors.

8-Bromo Cyclic Adenosine Monophosphate↗