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Masato Kasuga

Publications and source records attributed to Masato Kasuga.

At least 37 records · Page 2Linked to original sources
PubMed2006

Association studies of variants in the genes involved in pancreatic beta-cell function in type 2 diabetes in Japanese subjects.

Because impaired insulin secretion is characteristic of type 2 diabetes in Asians, including Japanese, the genes involved in pancreatic beta-cell function are candidate susceptibility genes for type 2 diabetes. We examined the association of variants in genes encoding several transcription factors (TCF1, TCF2, HNF4A, ISL1, IPF1, NEUROG3, PAX6, NKX2-2, NKX6-1, and NEUROD1) and genes encoding the ATP-sensitive K(+) channel subunits Kir6.2 (KCNJ11) and SUR1 (ABCC8) with type 2 diabetes in a Japanese cohort of 2,834 subjects. The exon 16 -3c/t variant rs1799854 in ABCC8 showed a significant association (P = 0.0073), and variants in several genes showed nominally significant associations (P < 0.05) with type 2 diabetes. Although the E23K variant rs5219 in KCNJ11 showed no association with diabetes in Japanese (for the K allele, odds ratio [OR] 1.08 [95% CI 0.97-1.21], P = 0.15), 95% CI around the OR overlaps in meta-analysis of European populations, suggesting that our results are not inconsistent with the previous studies. This is the largest association study so far conducted on these genes in Japanese and provides valuable information for comparison with other ethnic groups.

ATP-Binding Cassette Transporters↗
PubMed2006

A polymorphism in the AMPKalpha2 subunit gene is associated with insulin resistance and type 2 diabetes in the Japanese population.

AMP-activated protein kinase (AMPK) acts as a fuel gauge for glucose and lipid metabolism. The gene encoding the alpha2 isoform of the catalytic subunit of AMPK (PRKAA2) is located at one of the Japanese type 2 diabetes loci mapped by our previous genome scan (1p36-32). PRKAA2 is, therefore, a good candidate gene for insulin resistance and type 2 diabetes. We screened all nine exons, their exon-intron boundaries, and the 5' and 3' flanking regions of PRKAA2 to identify single nucleotide polymorphisms (SNPs), and we genotyped 192 type 2 diabetic patients and 272 nondiabetic subjects to assess possible associations between genotypes or haplotypes and type 2 diabetes. None of the 10 SNPs genotyped was associated with type 2 diabetes, but the haplotype analysis, consisting of six representative SNPs, revealed one haplotype, with the A (minor) allele for rs2051040 and a major allele for the other five SNPs, to be associated with type 2 diabetes (P = 0.009). This finding was confirmed in two larger replication samples (657 case and 360 control subjects, P = 0.021; and 356 case and 192 control subjects from the same area in Japan, P = 0.007) and a significant P value was obtained in the joint haplotype analysis of all samples (1,205 case and 824 control subjects, P = 0.0001). Furthermore, insulin resistance was associated with rs2051040 in nondiabetic subjects, and those with the A (minor) allele had a higher homeostasis model assessment of insulin resistance index than those who did not (initial control subjects [n = 272], P = 0.002; and joint replication control subjects [n = 552], P = 0.037). We speculate that the PRKAA2 gene influences insulin resistance and susceptibility to type 2 diabetes in the Japanese population.

3' Untranslated Regions↗
PubMed2006

Expression of thioredoxin and thioredoxin-binding protein-2 in the liver of patients with chronic hepatitis C as a predictor of response to interferon therapy.

Oxidative stress contributes to the pathogenesis of various hepatic injuries. Thioredoxin (TRX) is an indicator of oxidative stress, reported to be increased in the serum of patients with chronic hepatitis C with the progression of fibrosis. The aim of this study was to evaluate the clinical significance of the expression of TRX and thioredoxin-binding protein-2 (TBP-2), which is a negative regulator of TRX function, in the liver of patients with chronic hepatitis C and the relationship of this to the efficacy of interferon (IFN) treatment. A retrospective study was performed using the liver biopsy specimens obtained before IFN treatment from 69 patients with chronic serotype 1 hepatitis C virus (HCV) infection. TRX and TBP-2 mRNA levels in the liver biopsy specimens were amplified by real-time RT-PCR. The serum TRX protein level was estimated with a sandwich enzyme-linked immunosorbent assay kit, and the expression of TRX protein in the liver was examined immunohistochemically in 19 patients. There was no association between the serum TRX level and the TRX level in the liver. There was a significant correlation between the expression level of TRX protein in the liver and the TRX mRNA level in the liver. TRX and TBP-2 levels in the liver tended to decrease slightly with increased fibrosis stage, although not significantly. The TRX level in the liver tended to increase with hepatitis activity index, although not significantly. TBP-2 mRNA levels in the liver were significantly higher in responders than non-responders to the IFN therapy (p<0.05). Among patients who had a high viral load of >850 KIU/ml, the TRX level in the livers of non-responders was significantly lower than that in the livers of responders (p<0.05). TRX and TBP-2 mRNA levels in the liver before IFN therapy may predict the outcome of IFN therapy in patients with chronic serotype 1 HCV infection.

Adult↗
PubMed2006

[Insulin signaling and pathophysiology of type 2 diabetes mellitus].

The pathophysiology of type 2 diabetes is characterized by defects in insulin action and in insulin secretion. Metabolic actions of insulin are mediated by the insulin receptor/IRS/PI 3-kinase signaling pathway in insulin's target organs including the liver, skeletal muscle and adipose tissue. Recent evidence suggests that insulin action in the brain also plays an important role in the regulation of glucose metabolism in the liver. Insulin signaling in pancreatic beta cells appears to regulate glucose-induced insulin secretion. Although the mechanism how insulin resistance develops is not fully understood, dysregulation of fatty acid metabolism, abnormalities of the function and the secretion of adipokines, as well as the increase in stress signaling might contribute to the development of insulin resistance.

Adipocytes↗
PubMed2005

Association of the -112A>C polymorphism of the uncoupling protein 1 gene with insulin resistance in Japanese individuals with type 2 diabetes.

The -112A>C polymorphism (rs10011540) of the gene for uncoupling protein 1 (UCP1) has been associated with type 2 diabetes mellitus in Japanese individuals. The aim of the present study was to investigate the effects of this polymorphism, as well as the well-known -3826A>G polymorphism (rs1800592), on clinical characteristics of type 2 diabetes. We determined the genotypes of the two polymorphisms in 93 Japanese patients with type 2 diabetes. Intramyocellular lipid content and hepatic lipid content (HLC) were measured by magnetic resonance spectroscopy. No significant differences in age, sex, BMI, or HbA1c level were detected between type 2 diabetic patients with the -112C allele and those without it. However, homeostasis model assessment for insulin resistance (p=0.0089) and HLC (p=0.012) was significantly greater in patients with the -112C allele. We did not detect an association of the -3826A>G polymorphism (rs1800592) of UCP1 gene with any measured parameters. These results suggest that insulin resistance caused by the -112C allele influences the susceptibility to type 2 diabetes.

Age Distribution↗
PubMed2005

Chronic effects of AJ-9677 on energy expenditure and energy source utilization in rats.

The effects of AJ-9677 on metabolic parameters were examined in rats that had or had not been chronically treated with this beta3-adrenoceptor agonist. A challenge administration of AJ-9677 increased both the temperature of brown adipose tissue and energy expenditure in both groups of rats. However, whereas the former effect was subject to desensitization, the latter effect was augmented by prior chronic administration of AJ-9677. Whereas a challenge administration of AJ-9677 induced a decrease in the respiratory quotient that persisted for at least 15 h in rats pretreated with vehicle, the initial decrease in this parameter lasted for only 4 h in rats pretreated with AJ-9677. These results suggest that, in rats subjected to chronic treatment with AJ-9677, a challenge administration of this drug increased energy expenditure by stimulation not only of fat oxidation but also of glucose oxidation.

Acetates↗
PubMed2005

BRAF mutation associated with dysregulation of apoptosis in human colorectal neoplasms.

To understand the role of BRAF dysfunction in the carcinogenesis and progression/development of colorectal tumors, the authors investigated genetic alterations in the BRAF gene in human colorectal neoplasms as well as the effects of an RAS inhibitor in BRAF-mutant cells. Seven colon cancer cell lines and 116 colorectal tumors (34 adenomas and 82 adenocarcinomas) were analyzed. Genetic alterations in the BRAF and K-ras genes were examined using polymerase chain reaction-single strand conformation polymorphism and direct sequencing analyses. The growth-inhibitory and apoptosis-inducing effects of the FTI-277 RAS inhibitor in colon cancer cell lines were analyzed as well. An immunohistochemical study was also performed to investigate the correlations between the clinicopathologic parameters involved in the Ki-67 labeling index and the number of apoptotic bodies in tumor cells. FTI-277 did not suppress the proliferation of BRAF-mutant cells (WiDr and TCO), but remarkably inhibited the growth of K-ras mutant cells (LoVo). Interestingly, LoVo cells underwent apoptosis by FTI-277 in a dose-dependent manner, whereas WiDr cells were resistant to this agent. In tumor samples, BRAF mutations were found in 1 (3.0%) of 33 adenomas and 6 (7.2%) of 83 adenocarcinomas. No tumor exhibited mutations in both the BRAF and K-ras genes. Neither BRAF nor K-ras mutations correlated with the Ki-67 labeling index immunohistochemically. However, the number of apoptotic bodies was significantly decreased in the BRAF-mutant tumors. Mutation in the BRAF gene may contribute to colorectal carcinogenesis by upregulating the antiapoptotic role of the RAS/RAF/MEK/ERK pathway.

Adenocarcinoma↗
PubMed2005

Role of Krüppel-like factor 15 in PEPCK gene expression in the liver.

Regulation of hepatic gene expression is important for energy homeostasis. We now show that hepatic expression of the gene for the transcription factor Kruppel-like factor 15 (KLF15) is increased by food deprivation and reduced by feeding in mice. Expression of the KLF15 gene in mouse liver was also down-regulated by a euglycemic-hyperinsulinemic clamp and was increased by inhibition of phosphatidylinositol 3-kinase. In cultured rat hepatocytes, KLF15 gene expression was induced by dexamethasone and a non-hydrolyzing analog of cAMP, and this effect was inhibited by insulin in a manner dependent on phosphatidylinositol 3-kinase signaling. Forced expression of KLF15 in cultured hepatocytes increased both the expression and the promoter activity of the gene for phosphoenolpyruvate carboxykinase (PEPCK). These results suggest that insulin and its counteracting hormones regulate the hepatic expression of KLF15, and that this transcription factor contributes to the regulation of PEPCK gene expression in the liver.

Animals↗
PubMed2005

Deletion of Cdkn1b ameliorates hyperglycemia by maintaining compensatory hyperinsulinemia in diabetic mice.

The protein p27(Kip1) regulates cell cycle progression in mammals by inhibiting the activity of cyclin-dependent kinases (CDKs). Here we show that p27(Kip1) progressively accumulates in the nucleus of pancreatic beta cells in mice that lack either insulin receptor substrate 2 (Irs2(-/-)) or the long form of the leptin receptor (Lepr(-/-) or db/db). Deletion of the gene encoding p27(Kip1) (Cdkn1b) ameliorated hyperglycemia in these animal models of type 2 diabetes mellitus by increasing islet mass and maintaining compensatory hyperinsulinemia, effects that were attributable predominantly to stimulation of pancreatic beta-cell proliferation. Thus, p27(Kip1) contributes to beta-cell failure during the development of type 2 diabetes in Irs2(-/-) and Lepr(-/-) mice and represents a potential new target for the treatment of this condition.

Animals↗
PubMed2005

Role of Krüppel-like factor 15 (KLF15) in transcriptional regulation of adipogenesis.

Krüppel-like zinc finger transcription factors (KLFs) play diverse roles during cell differentiation and development in mammals. We have now shown by microarray analysis that expression of the KLF15 gene is markedly up-regulated during the differentiation of 3T3-L1 preadipocytes into adipocytes. Inhibition of the function of KLF15, either by expression of a dominant negative mutant or by RNA interference, both reduced the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) and blocked adipogenesis in 3T3-L1 preadipocytes exposed to inducers of adipocyte differentiation. However, the dominant negative mutant of KLF15 did not affect the expression of CCAAT/enhancer-binding protein beta (C/EBPbeta) elicited by inducers of differentiation in 3T3-L1 preadipocytes. In addition, ectopic expression of KLF15 in NIH 3T3 or C2C12 cells triggered both lipid accumulation and the expression of PPARgamma in the presence of inducers of adipocyte differentiation. Ectopic expression of C/EBPbeta, C/EBPdelta, or C/EBPalpha in NIH 3T3 cells also elicited the expression of KLF15 in the presence of inducers of adipocyte differentiation. Moreover, KLF15 and C/EBPalpha acted synergistically to increase the activity of the PPARgamma2 gene promoter in 3T3-L1 adipocytes. Our observations thus demonstrate that KLF15 plays an essential role in adipogenesis in 3T3-L1 cells through its regulation of PPAR gamma expression.

3T3-L1 Cells↗
PubMed2005

Circadian variability of pharmacokinetics of 5-fluorouracil and CLOCK T3111C genetic polymorphism in patients with esophageal carcinoma.

The variations of plasma concentrations of 5-fluorouracil (5-FU) were investigated in 30 esophageal cancer patients treated with repetitive protracted venous infusion (PVI) of 5-FU-based chemoradiotherapy, and in an attempt to find a new possible candidate that explains their variations, CLOCK T3111C genetic polymorphism was examined. The patients have received 2 courses of chemoradiotherapy consisting of 2 cycles of 5-day PVI of 5-FU (400 mg/m/d) with cisplatin and concurrent radiation. The plasma concentrations of 5-FU were determined at 5 PM on day 3 and 5 AM on day 4 after the beginning of each 5-FU infusion. The CLOCK T3111C genotype was determined by polymerase chain reaction-restricted fragment length polymorphism (PCR-RFLP) and by direct sequencing. Plasma concentrations were measured in 239 samples. In the first course, the plasma concentrations of 5-FU at 5 AM were significantly lower than those at 5 PM in the first cycle, whereas a similar tendency was observed in the second cycle, although not significantly (Wilcoxon signed-rank test). The plasma concentrations of 5-FU at 5 PM and 5 AM in the second cycle were both significantly higher than those in the first cycle, and their coefficient of variation in the former was also significantly smaller than that in the latter. These phenomena in the first course were also observed in the second one. These results revealed the elevation of plasma drug concentration and its reduced circadian variation during repetitive PVI of 5-FU. In 5-FU-based chemotherapy, its administration schedule should be made in consideration of these phenomena. The CLOCK T3111C genotype did not have a significant impact on the variation of the plasma concentrations of 5-FU in this study population. Further studies are needed to clarify the mechanism of these phenomena and to identify an easy-to-assess marker of circadian rhythms for use in individualizing delivery of 5-FU.

Aged↗
PubMed2005

Serum hepatitis B virus DNA levels differentiating inactive carriers from patients with chronic hepatitis B.

OBJECTIVE: We compared serum hepatitis B virus (HBV)-DNA levels in different states of hepatitis B infection, and investigated whether there is an HBV-DNA value that can be used for differentiating inactive carriers from patients with hepatitis B e antigen (HBeAg)-negative chronic hepatitis. METHODS: A retrospective study using sera at a followed endpoint from 64 Japanese patients with chronic HBV infection seen in Kobe University Hospital between 1989 and 2002. Sera of patients were assayed using a polymerase chain reaction-based assay. RESULTS: Genotype C was dominant (95.4%). Patients with chronic hepatitis with an elevation of the serum alanine aminotransferase (ALT) level had significantly higher HBV-DNA levels than patients with persistently normal ALT. For one time observation at a followed endpoint, the mean HBV-DNA level of HBeAg-negative inactive carriers was significantly lower than that of HBeAg-negative chronic hepatitis patients (3.6+/-1.0 versus 4.8+/-1.5 log copies/ml, P<0.005). The use of a cutoff value of 4.5 or 5.0 log copies/ml misclassified 23 and 18% of HBeAg-negative inactive carriers and 50 and 55% of patients with HBeAg-negative chronic hepatitis. If testing were performed on two occasions with approximately a 4-month interval, the cutoff values of 4.5 and 5.0 log copies/ml would misclassify 20 and 10% of HBeAg-negative inactive carriers and 28.6 and 28.6% of patients with HBeAg-negative chronic hepatitis. CONCLUSIONS: The measurement of serum HBV DNA more than twice is useful for assessing chronic hepatitis B surface antigen carriers and confirms that 10 copies/ml may be an appropriate level of HBV for characterizing the inactive carrier state.

Adult↗
PubMed2005

Leukocytapheresis therapy for steroid-naïve patients with active ulcerative colitis: its clinical efficacy and adverse effects compared with those of conventional steroid therapy.

BACKGROUND: Steroid administration currently plays a central role in the medical management of ulcerative colitis (UC); however, long-term steroid usage causes adverse effects, which necessitates stoppage of drug intake, leading to worsening of the disease. A steroid-sparing, well-tolerated treatment is therefore required. As several investigators have reported the efficacy of leukocytapheresis (LCAP) combined with steroid therapy, we investigated the clinical usefulness and safety of LCAP for steroid-naïve patients with active UC for comparison with those of conventional steroid therapy. METHODS: Twenty-nine Japanese patients with active UC without a history of steroid usage were selected to be treated with LCAP (n = 9) or prednisolone (PSL) (n = 20). LCAP administration continued for 10 weekly cycles. In the PSL group, patients with moderately severe disease received 0.5 mg/kg per day of PSL and those with severe disease 1.0 mg/kg per day. The PSL dosage was gradually tapered in accordance with improvement. RESULTS: Eight (88.9%) of the LCAP group and 16 (80.0%) of the PSL group showed clinical improvement and three (33.3%) of the LCAP group and seven (35.0%) of the PSL group achieved remission. As for the treatment complications, three major adverse effects were observed in the PSL group, but none were observed in the LCAP group. CONCLUSION: The results of this study suggest that the efficacy and safety of LCAP are equivalent, and in terms of severe adverse effects, superior to those of steroid therapy. LCAP therapy may thus be a promising candidate therapy for steroid-naïve patients with active UC.

Adolescent↗
PubMed2005

PKClambda regulates glucose-induced insulin secretion through modulation of gene expression in pancreatic beta cells.

Altered regulation of insulin secretion by glucose is characteristic of individuals with type 2 diabetes mellitus, although the mechanisms that underlie this change remain unclear. We have now generated mice that lack the lambda isoform of PKC in pancreatic beta cells (betaPKClambda(-/-) mice) and show that these animals manifest impaired glucose tolerance and hypoinsulinemia. Furthermore, insulin secretion in response to high concentrations of glucose was impaired, whereas the basal rate of insulin release was increased, in islets isolated from betaPKClambda(-/-) mice. Neither the beta cell mass nor the islet insulin content of betaPKClambda(-/-) mice differed from that of control mice, however. The abundance of mRNAs for Glut2 and HNF3beta was reduced in islets of betaPKClambda(-/-) mice, and the expression of genes regulated by HNF3beta was also affected (that of Sur1 and Kir6.2 genes was reduced, whereas that of hexokinase 1 and hexokinase 2 genes was increased). Normalization of HNF3beta expression by infection of islets from betaPKClambda(-/-) mice with an adenoviral vector significantly reversed the defect in glucose-stimulated insulin secretion. These results indicate that PKClambda plays a prominent role in regulation of glucose-induced insulin secretion by modulating the expression of genes important for beta cell function.

Animals↗
PubMed2005

Adipocytes from Munc18c-null mice show increased sensitivity to insulin-stimulated GLUT4 externalization.

Insulin-stimulated glucose uptake in adipocytes is mediated by translocation of vesicles containing the glucose transporter GLUT4 from intracellular storage sites to the cell periphery and the subsequent fusion of these vesicles with the plasma membrane, resulting in the externalization of GLUT4. Fusion of the GLUT4-containing vesicles with the plasma membrane is mediated by a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex consisting of vesicle-associated membrane protein 2 (VAMP2), 23-kDa synaptosomal-associated protein (SNAP23), and syntaxin4. We have now generated mouse embryos deficient in the syntaxin4 binding protein Munc18c and show that the insulin-induced appearance of GLUT4 at the cell surface is enhanced in adipocytes derived from these Munc18c-/- mice compared with that in Munc18c+/+ cells. Wortmannin, an inhibitor of PI3K, inhibited insulin-stimulated GLUT4 externalization, without affecting GLUT4 translocation to the cell periphery, in Munc18c+/+ adipocytes, but it did not affect GLUT4 externalization in Munc18c-/- cells. Phosphatidylinositol 3-phosphate, which induced GLUT4 translocation to the cell periphery without externalization in Munc18c+/+ cells, elicited GLUT4 externalization in Munc18c-/- cells. These findings demonstrate that Munc18c inhibits insulin-stimulated externalization of GLUT4 in a wortmannin-sensitive manner, and they suggest that disruption of the interaction between syntaxin4 and Munc18c in adipocytes might result in enhancement of insulin-stimulated GLUT4 externalization.

Adipocytes↗
PubMed2005

Methylglyoxal induces apoptosis through oxidative stress-mediated activation of p38 mitogen-activated protein kinase in rat Schwann cells.

Although recent studies have suggested the potential involvement of apoptotic cell death in the development of diabetic neuropathy, the precise mechanism remains to be elucidated. On the other hand, it is known that the formation of methylglyoxal (MG), a highly reactive dicarbonyl compound, is accelerated under diabetic conditions through several glucose-related metabolisms including the glycation reaction. We found that MG was capable of inducing apoptosis in peripheral nerve-derived Schwann cells (SCs) in a time- and dose-dependent manner, accompanied by a reduction of intracellular glutathione content. Furthermore, MG induced phosphorylation of MKK3/MKK6, an upstream molecule in the p38 MAPK pathway. N-acetyl-L-cysteine, an antioxidant, successfully suppressed the activity of the p38 MAPK signaling pathway along with the inhibition of apoptosis, indicating the involvement of oxidative stress in the MG-induced apoptosis via the p38 MAPK pathway. These results suggest a possible contribution of glucose-derived MG to the development of diabetic neuropathy by injuring the cellular constituent of the peripheral nerve system, such as SCs, in the hyperglycemic milieu.

Acetylcysteine↗