Koichiro Yasuda

Impaired β-cell function and insulin sensitivity in Japanese subjects with normal glucose tolerance

The development of type 2 diabetes mellitus is characterized by both impaired beta-cell function and increasing insulin resistance. To clarify the roles of them in developing type 2 diabetes, we evaluated insulin resistance by HOMA-IR and insulin secretion by HOMA beta-cell in 453 Japanese subjects whose fasting plasma glucose (FPG) and HbA(1c) levels were within normal range. HOMA beta-cell was found to decrease in the over 30 years groups, while HOMA-IR increased with body mass index (BMI). To analyze the reserve capacity of insulin secretion and insulin sensitivity, the 67 of them, who underwent a standard oral glucose tolerance test and were diagnosed with normal glucose tolerance (NGT), were divided into four degrees of BMI age-adjusted to 50 years. They were compared for insulinogenic index and ISI composite proposed by Matsuda and DeFronzo across the range of BMI. ISI composite was significantly less in the highest BMI group, while insulin secretion did not increase in the higher BMI groups. The subjects with higher BMI had remarkably lower insulinogenic indices than those with lower BMI. These data suggest that insulin secretory reserve is insufficient to compensate for increased insulin resistance in Japanese people with NGT at about 50 years of age.

Tissue distribution and species difference of the brain type glucose transporter (GLUT3).

The complementary DNA for the human brain type glucose transporter (GLUT3) was used to determine its tissue specific expression in human, monkey, rabbit, rat, and mouse. Under high stringent conditions, 4.1 and 3.2 kilobase (kb) GLUT3 transcripts in monkey and a single 4.1 kb GLUT3 mRNA in rabbit, rat, and mouse were detected by RNA blot analysis. Although the GLUT3 transcripts were widely distributed, as are the erythrocyte type glucose transporter (GLUT1) transcripts, this mRNA is most abundant in the brain. However, the relative abundance of GLUT3 mRNA in the various regions of the monkey brain shows a different pattern from that of GLUT1 mRNA: GLUT3 is most highly expressed in the frontal lobe of the cerebrum, whereas GLUT1 is most abundant in the basal ganglia and the thalamus. Moderately higher GLUT3 mRNA levels were detected in the parietal lobe of the cerebrum, hippocampus, and cerebellum than the levels of GLUT1 transcripts. We also detected GLUT3 mRNA in adult human psoas major muscle, although it has been reported that the GLUT3 gene is scarcely expressed in adult human skeletal muscle of the thigh. In addition, in the rat and the mouse, no transcripts of the GLUT3 gene were detected in liver, kidney, small intestine, skeletal muscle, or fat besides in brain. Thus, the expression of the GLUT3 gene seems to be restricted to the brain in rodents. These results suggest that the expression of GLUT1 and GLUT3 genes might be regulated by different mechanisms.

Abnormality in fibre type distribution of soleus and plantaris muscles in non-obese diabetic Goto-Kakizaki rats

1. Fibre type distributions of the slow soleus and fast plantaris muscles were investigated in 5‐, 9‐ and 20‐week‐old male Goto‐Kakizaki (GK) rats, as an animal model of non‐obese diabetes, and were compared with those of age‐matched non‐diabetic Wistar rats.

Identification of Two Missense Mutations in the GIP Receptor Gene: A Functional Study and Association Analysis with NIDDM: No Evidence of Association with Japanese NIDDM Subjects

Gastric inhibitory polypeptide (GIP) potently stimulates insulin secretion from pancreatic islets in the presence of glucose as an incretin. Because the insulinotropic effect of GIP is reduced in NIDDM, it should be clarified whether defects in the GIP receptor gene contribute to the impaired insulin secretion in NIDDM. Using genomic DNA samples from Japanese NIDDM and non-NIDDM subjects, we have investigated the entire coding region of the GIP receptor gene by polymerase chain reaction-single strand conformational polymorphism (PCR-SSCP). We have identified two missense mutations, Gly198→Cys (Gly198Cys) in exon 7 and Glu354→Gln (Glu354Gln) in exon 12. Investigation of the function of GIP receptor with either of these mutations reveals a half-maximal stimulation value of GIP-induced cAMP response in Chinese hamster ovary cells expressing the GIP receptor with Gly198Cys of 6.3 ± 1.2 × 10−10 mol/l (n = 3), which was considerably higher than that of the normal GIP receptor, 9.4 ± 3.8 × 10−12 mol/l GIP (n = 3), whereas that of the GIP receptor with Glu354Gln was not significantly different from that of the normal GIP receptor. To assess the possible role of the GIP receptor gene in genetic susceptibility to NIDDM, we have examined the allelic frequencies of Gly198Cys and Glu354Gln in NIDDM and control subjects. Association studies show no relationship between NIDDM and either of the two mutations.

Synergistic effect of polymorphisms of uncoupling protein 1 and β3-adrenergic receptor genes on autonomic nervous system activity

OBJECTIVE: To investigate the association of the promoter region −3826 A to G polymorphism of the uncoupling protein 1 (UCP1) gene with autonomic nervous system (ANS) activity and the interaction of the polymorphism with the Trp64Arg polymorphism of the β3 adrenergic receptor (β3AR).SUBJECTS: Three-hundred and forty-nine young (mean age 20.4±2.1 y old), healthy Japanese males.MEASUREMENTS: DNA was extracted from whole blood and genotyped by polymerase chain reaction restriction fragment length polymorphism. Plasma glucose, plasma insulin and body mass index (BMI) were measured. Frequency of family history of diabetes or obesity was determined by interview. Subjects randomly chosen from each genotype were examined for ANS activity during supine rest and standing by electrocardiogram power spectral analysis of heart rate variability.RESULTS: UCP1 or β3AR polymorphism was not associated with BMI, plasma glucose, plasma insulin and frequency of family history of diabetes or obesity. The inhibitory effect of UCP1 polymorphism on ANS activity was observed only with occurrence of the variant of β3AR. The very low frequency component associated with thermoregulation in the sympathetic nervous system of homozygotes of UCP1 (GG) at supine rest was significantly lower than normal (AA, 203.2±50.3 vs 462.2±83.6 ms2; mean±s.e., P=0.021). A higher response to postural change to standing was also observed in both sympathetic and parasympathetic nervous activities of AA than of GG.CONCLUSION: While UCP1 polymorphism alone does not affect ANS activity, it has a synergistic effect with β3AR polymorphism in decreasing sympathetic nervous system activity.

Expression of GLUT1 and GLUT2 Glucose Transporter Isoforms in Rat Islets of Langerhans and Their Regulation by Glucose

Previous studies revealed that rat islets express the GLUT2-liver facilitative glucose transporter isoform, a glucose carrier with a low affinity for glucose but a high capacity for glucose transport. These studies indicated the presence of a second glucose transporter in rat islets; however, they did not indicate to which of the five known facilitative glucose transporters it corresponded. In this study, we isolated RNA from rat islets of Langerhans and confirmed the presence of GLUT2 mRNA. In addition, we present dataindicating that the second isoform expressed in islets is the GLUT1-erythrocyte isoform.The effect of culturing islets in 5.5, 8.3, or 11.1 mM glucose on the levels of GLUT1 and GLUT2 mRNA also was examined. The levels of GLUT1 and GLUT2 mRNA were two- and threefold higher, respectively, in islets cultured for 24 h in 11.1 mM glucose compared with those incubated in the presence of 5.5 mM glucose. Therefore, the previously observed increase in GLUT2 mRNA levels in the islets of rats made hyperglycemic by chronic infusion of glucose can be mimicked in vitro, implying that glucose regulates GLUT2 mRNA expression.

Liver and muscle-fat type glucose transporter gene expression in obese and diabetic rats

In order to investigate the regulation of glucose transporter gene expression in the altered metabolic conditions of obesity and diabetes, we have measured mRNA levels encoding GLUT2 in the liver and GLUT4 in the gastrocnemius muscle from various insulin resistant animal models, including Zucker fatty, Wistar fatty, and streptozocin(STZ)-treated diabetic rats. Northern blot analysis revealed that GLUT2 mRNA levels were significantly (P less than 0.001) elevated in 14 wk Zucker fatty and Wistar fatty rats relative to lean littermates but were similar in these two groups at 5 wk of age. Furthermore, there was significant increase (P less than 0.01) in GLUT2 mRNA levels in STZ diabetic rats at 3 wk after treatment. GLUT4 mRNA levels were not significantly different between control and insulin resistant rats in all animal models. These results indicate that neither hyperinsulinemia nor hyperglycemia affects GLUT4 mRNA levels in the muscle. However, GLUT2 mRNA levels in the liver were elevated in obesity and diabetes, although this regulatory event occurred independently from circulating insulin or glucose concentrations.

EFFECTS OF HYPERBARIC EXPOSURE WITH HIGH OXYGEN CONCENTRATION ON GLUCOSE AND INSULIN LEVELS AND SKELETAL MUSCLE-FIBER PROPERTIES IN DIABETIC RATS

The effects of hyperbaric exposure with high oxygen concentration on glucose and insulin levels and skeletal muscle‐fiber properties were investigated in type 2 diabetic Goto‐Kakizaki rats. Five‐week‐old rats were exposed to a hyperbaric environment (1.25 atmospheric pressure) with a high oxygen concentration (36%) for 6 h daily. Glucose and insulin levels and properties including fiber‐type distribution, cross‐sectional area, and oxidative enzyme activity in the soleus muscle were examined after hyperbaric exposure for 4 weeks. The growth‐related increase in glucose level was inhibited by hyperbaric exposure, and insulin also showed lower levels compared with control rats. The percentage of low‐oxidative type I fibers in the muscle decreased and high‐oxidative type IIA and type IIC fibers, which were not detected in the muscle of control rats, were observed after hyperbaric exposure. The oxidative enzyme activity of type I fibers in the muscle increased after hyperbaric exposure. Hyperbaric exposure with high oxygen concentration might therefore provide a new approach to improve the glucose tolerance, insulin resistance, and altered skeletal muscle metabolism that are caused by diabetes mellitus. Muscle Nerve, 2006

Fibre type distribution and gene expression levels of both succinate dehydrogenase and peroxisome proliferator‐activated receptor‐γ coactivator‐1α of fibres in the soleus muscle of Zucker diabetic fatty rats

We have reported that a change in muscle fibre type distribution is present in two strains of diabetic rats (Otsuka Long–Evans Tokushima Fatty and Goto‐Kakizaki rats). In this study, we determined whether the change in soleus muscle fibre type distribution was caused by diabetes, using obese, diabetic (Zucker diabetic fatty, ZDF), obese, non‐diabetic (Zucker fatty, ZF) and non‐diabetic, non‐obese rats (Zucker lean, ZL). Moreover, we investigated whether the gene expression levels of metabolic key molecules, namely the transcriptional factors of metabolic genes, exemplified by peroxisome proliferator‐activated receptor‐γ coactivator‐1α (PGC‐1α), and the oxidative enzymes in mitochondria, exemplified by succinate dehydrogenase (SDH), were changed in type I and II muscle fibres in each type of rat, using the new technique of laser capture microdissection (LCM). Both plasma glucose and glucosylated haemoglobin levels were significantly higher in ZDF than in ZL and ZF rats. A lower percentage of type IIA fibres was observed in the muscles of ZDF rats than in those of ZL and ZF rats. The mRNA expression levels of SDH in type II fibres and of PGC‐1α in type I fibres were significantly lower in ZDF than in ZL and ZF rats as assessed by LCM and real‐time PCR analysis. We have shown, for the first time, that a lower percentage of type IIA fibres was observed in ZDF rats. We have also discovered that the expression levels of the oxidative metabolism‐related genes, PGC‐1α and SDH, decreased in type I and type II fibres, respectively, of ZDF rats.

Long-term therapeutic effects of voglibose, a potent intestinal alpha-glucosidase inhibitor, in spontaneous diabetic GK rats

The effect of long-term (6 months) administration of voglibose in a dietary mixture (10 ppm) on intestinal disaccharidase activity was examined in non obese type 2 diabetes model Goto-Kakizaki (GK) rats. The postprandial blood glucose level in voglibose-treated GK rats was significantly lower than in untreated GK rats (190+/-19 vs. 250+/-25 mg/dl, P<0.01; 1 h, 212+/-23 vs. 256+/-20, P<0.05; 2 h), and the activities of maltase, sucrase, and isomaltase remained significantly lower throughout the 6 months of voglibose treatment. The expressions of protein and mRNA of sucrase-isomaltase (SI) complex were significantly higher in voglibose-treated GK rats. Voglibose administration then was stopped after 6 months of treatment. The mRNA level and protein level of the SI complex became normalized during the interruption of drug administration, and disaccharidase activities increased almost to the level of the untreated group 1 month after treatment was stopped. After 1 day of re-administration of the drug, however, disaccharidase activities again became significantly inhibited. These results indicate that voglibose may improve glucose tolerance since it inhibits activities of disaccharidases in spite of increasing the expression of them on intestine, furthermore voglibose may be reversible and reproducible through interruption and re-administration.