Tadasu Ikeda

Human organic cation transporter (OCT1 and OCT2) gene polymorphisms and therapeutic effects of metformin

AbstractOrganic cation transporters (OCTs) are responsible for the hepatic and renal transport of metformin. In this study we analyzed variants of OCT1 and OCT2 genes in 33 patients (24 responders and nine non-responders) based on the hypothesis that polymorphisms in both genes contribute to large inter-patient variability in the clinical efficacy of metformin. The sequences of the 5′-flanking and coding regions of the two genes of interest were screened by single-strand conformation polymorphism (SSCP) analysis. To compare the causative factors between responders and non-responders, we performed stepwise discriminant functional analysis. Age, body mass index (BMI) and treatment with lipid-lowering agents were demonstrated as positive predictors, and two mutations in the OCT1 gene, −43T > G in intron 1 and 408Met > Val (1222A > G) in exon 7, were negative and positive predictors, respectively, for the efficacy of metformin; the predictive accuracy was 55.5% (P < 0.05). Subsequent study indicated that OCT1 mRNA levels tended to be lower in human livers with the 408Met (1222A) variant, though the differences did not reach the level of significance. In this study it is suggested that OCT1 and OCT2 gene polymorphisms have little contribution to the clinical efficacy of metformin.

Inhibitory effect of metformin on intestinal glucose absorption in the perfused rat intestine.

To investigate the effect of metformin on intestinal glucose absorption, a perfusion study of the intestine was performed in the rat. Male Wistar albino rats (8 weeks old) were used in the present study. The glucose absorption by the perfused intestine (788.1+/-81.9 micromol/30 min) was not changed significantly by the direct addition of metformin (90 microg/mL) to the perfusing medium (737.0+/-118.2 micromol/30 min) or by intraduodenal metformin (250 mg/kg in saline solution) infusion (772.8+/-106.3 micromol/30 min). In rats orally administered metformin (250 mg/kg) for 5 days, glucose absorption by the perfused intestine (375.0+/-164.3 micromol/30 min) was significantly (P<0.001) lower than that in control rats (811.0+/-83.1 micromol/30 min). These results indicate that metformin had a significant effect on the digestive tract, and that metformin treatment exerted an inhibitory effect on intestinal glucose absorption in the rat.

Long-term effect of epalrestat on cardiac autonomic neuropathy in subjects with non-insulin dependent diabetes mellitus.

To evaluate the effect of long-term administration of an aldose reductase inhibitor on diabetic cardiovascular autonomic neuropathy, 22 subjects with non-insulin dependent diabetes mellitus (NIDDM, 11 men and 11 women, mean age; 64.8 +/- 7.8 years, duration of diabetes; 18.3 +/- 5.6 years) were administered epalrestat, one type of aldose reductase inhibitor, for 36 months. The changes in the coefficient of variation of the R-R interval (CV(R R)) during rest and the QTc interval were compared with 43 age-matched NIDDM (controls). During the study, the CV(R R) value gradually decreased in the controls, while it slightly increased in subjects treated with epalrestat. After 36 months, the CV(R R) value (2.31 +/- 1.09%) in subjects treated with epalrestat was significantly (P < 0.05) higher than that (1.84 +/- 0.75%) in the controls. There were no significant differences in QTc intervals in both groups. These results suggest that long-term administration of an aldose reductase inhibitor may be available for cardiac autonomic neuropathy in even relatively older diabetic subjects with long duration.

Effect of β-hydroxybutyrate and acetoacetate on insulin and glucagon secretion from perfused rat pancreas

Abstract To elucidate the physiological significance of ketone bodies on insulin and glucagon secretion, the direct effects of β-hydroxybutyrate (BOHB) and acetoacetate (AcAc) infusion on insulin and glucagon release from perfused rat pancreas were investigated. The BOHB or AcAc was administered at concentrations of 10, 1, or 0.1 m m for 30 min at 4.0 ml/min. High-concentration infusions of BOHB and AcAc (10 m m ) produced significant increases in insulin release in the presence of 4.4 m m glucose, but low-concentration infusions of BOHB and AcAc (1 and 0.1 mM) caused no significant changes in insulin secretion from perfused rat pancreas. BOHB (10, 1, and 0.1 m m ) and AcAc (10 and 1 m m ) infusion significantly inhibited glucagon secretion from perfused rat pancreas. These results suggest that physiological concentrations of ketone bodies have no direct effect on insulin release but have a direct inhibitory effect on glucagon secretion from perfused rat pancreas.

Effect of thyroid hormone on somatomedin-C release from perfused rat liver

The effect of thyroid hormone on plasma somatomedin-C (SmC) level and on SmC release from perfused rat liver was investigated. Plasma SmC levels and liver tissue SmC were significantly increased in thyroxine-treated rats. Physiological doses of triiodothyronine increased SmC release and SmC concentration in the perfused rat liver. These results indicate that thyroid hormone directly enhances the synthesis and release of SmC in the rat.

Effects of anoxia and low free fatty acid on myocardial energy metabolism in streptozotocin-diabetic rats.

To investigate anaerobic glycolysis and glucose oxidation in the diabetic heart, we studied the effects of anoxia and low exogenous free fatty acid (FFA) on myocardial adenosine triphosphate (ATP) content in the isolated perfused heart from streptozotocin-diabetic rats. The perfusate consisted of Krebs-Ringer buffer (pH 7.4) containing 5 mM glucose and 0.30 mM or 0.05 mM FFA, equilibrated with 95% O2 + 5% CO2 or 95% N2 + 5% CO2 gas. Under aerobic conditions, glucose uptake, lactate production and glucose oxidation by the diabetic heart were reduced by 68, 57 and 53% of the control, respectively, and FFA oxidation by the diabetic heart was increased by 67% of the control. Under anoxic conditions, the increments in glucose uptake and lactate production by the diabetic heart were much smaller than those by the control (2.6 and 9.5 mumol/g/30 min vs. 11.4 and 40 mumol/g/30 min, respectively). The ATP content in the diabetic myocardium was decreased more rapidly in the anoxic perfusion than that in the control. In the aerobic perfusion, the ATP content in the control myocardium was maintained for 60 min at low FFA (0.05 mM) in the perfusate. The ATP content in the diabetic myocardium was reduced after 40 min at low FFA but was well maintained for 60 min by the addition of 0.30 mM FFA. Thus the ATP content in aerobic diabetic myocardium was not well maintained when exogenous FFA supply was depleted. These results suggest that diabetic hearts have a primary defect in the stimulation of glycolysis and glucose oxidation, which does not result from increased FFA utilization.

The effect of pioglitazone on glucose metabolism and insulin uptake in the perfused liver and hindquarter of high-fructose-fed rats

To investigate the effect of pioglitazone, a thiazolidinedione oral antidiabetic agent, on the glucose and insulin metabolism in insulin resistance, a perfusion study of the liver and hindquarter was performed in high-fructose-fed rats. Male Wistar albino rats were assigned randomly to one of the following diets for 2 weeks: (1) normal chow (control group), (2) a diet high in fructose (fructose group), or (3) a high-fructose diet plus pioglitazone (pioglitazone intake of approximately 10 mg/kg body weight; pioglitazone group). The elevated levels of plasma insulin, triglyceride, and free fatty acids (FFA) in the fructose group were normalized by pioglitazone administration. In the perfused liver, the glucagon-induced increment in the glucose output of the fructose (57.1+/-9.1 micromol/g liver/20 min) and pioglitazone (44.7+/-10.1 micromol/g liver/20 min) groups was significantly (P < .01) higher than that in the control group (27.6+/-5.7 micromol/g liver/20 min). The level in the pioglitazone group was significantly (P < .05) lower than that in the fructose group. In the presence of 100 or 500 microU/mL insulin, the insulin-mediated decrement in the glucagon-induced glucose output of the fructose group (29.8+/-7.8 or 38.9+/-9.3 micromol/g liver/20 min) was significantly (P < .05) lower than that in the control (45.8+/-14.2 or 54.5+/-8.5 micromol/g liver/20 min) and pioglitazone (44.4+/-9.2 or 56.2+/-10.8 micromol/g liver/20 min) groups, respectively. In the perfused hindquarter, glucose uptake in the fructose group (8.2+/-2.0 micromol/g muscle/30 min) was significantly (P < .05) lower than that in the control (12.1+/-2.3 micromol/g muscle/30 min) and pioglitazone (11.8+/-3.1 micromol/g muscle/30 min) groups. In the presence of 100 or 500 microU/mL insulin, glucose uptake in the fructose group (12.0+/-5.2 or 17.4+/-3.0 micromol/g muscle/30 min) was significantly (P < .05) lower than that in the control (20.2+/-2.4 or 23.0+/-3.1 micromol/g muscle/30 min) and pioglitazone (17.8+/-2.4 or 20.7+/-2.0 micromol/g muscle/30 min) groups, respectively. Insulin uptake by the liver and hindquarter was not significantly different in the control, fructose, and pioglitazone groups. These results indicate that pioglitazone improves the increased glucagon-induced hepatic glucose output and decreases insulin-induced muscular glucose uptake without altering insulin uptake in high-fructose-fed insulin-resistant rats.

Uptake of β-hydroxybutyrate in perfused hindquarter of starved and diabetic rats

Abstract To elucidate the peripheral ketone body uptake and the role of insulin in regulating peripheral ketone body utilization in starvation and diabetes mellitus, uptake of β-hydroxybutyrate (BOHB) was investigated in the perfused hindquarter of starved (72 hour) or streptozotocin-induced (65 mg/kg, intraperitoneally) diabetic rats. Blood concentration of BOHB was significantly higher in diabetic (1,380 ± 250 μmol/L) and starved (1,229 ± 245 μmol/L) rats than in controls (104 ± 8 μmol/L). The hindquarter was perfused with synthetic medium at a flow rate of 0.5 mL/g muscle weight/min. BOHB was added to the medium at a concentration of 0.1, 0.5, 2, or 10 mmol/L, and insulin was added at a concentration of 20, 100, or 500 μU/mL. In the hindquarter perfused with 0.1, 0.5, 2, or 10 mmol/L BOHB, fractional uptake of BOHB in the absence or presence of insulin was significantly lower in diabetic and starved rats than in controls. The addition of 100 or 500 μU/mL insulin significantly increased BOHB uptake in the perfused hindquarter of control rats; however, insulin addition did not significantly increase BOHB uptake in the perfused hindquarter of starved and diabetic rats. These results suggest that BOHB uptake is markedly reduced in the perfused hindquarter of starved and diabetic rats, and that physiological dose of insulin stimulates BOHB uptake in control rats, but not in starved and diabetic rats.

Oral and intravenous glucose-induced insulin secretion in hyperthyroid patients

To elucidate glucose intolerance in hyperthyroidism, insulin response to oral (75 g) and intravenous (IV) (20 g) glucose administration was investigated in 18 hyperthyroid patients and six normal control subjects. In oral glucose tolerance tests (OGTT), plasma insulin and C-peptide levels in hyperthyroid patients were not significantly different from that in controls; however, an impaired blood sugar response was observed in hyperthyroid patients. In IVGTT, blood sugar, plasma insulin, and C-peptide levels were significantly higher in hyperthyroid patients than in controls. Insulin secretion in proportion to blood sugar stimulus (the sum of increment in insulin divided by the sum of increment in blood sugar after glucose load, sigma delta IRI/sigma delta BS) in IVGTT was similar in hyperthyroid patients and controls; however, that in OGTT was significantly lower in hyperthyroid patients. After thyroid function tests had returned to normal by treatment with thiamazole, glucose tolerance and sigma delta IRI/sigma delta BS in OGTT were almost normalized. These results indicate that decreased insulin secretion after oral glucose may have an important role in abnormal oral glucose metabolism in hyperthyroidism.

Safety evaluation of excessive ingestion of mozuku fucoidan in human.

Fucoidan is a sulfated polysaccharide in the brown sea algae. This study was conducted in 20 subjects taking excessive fucoidan up to 4.05 g daily for 2 wk. They recorded questionnaire sheets about their health. Blood and urine were collected before and after 2 wk of ingestion. We found that no disorder was apparent in the test period. Although total cholesterol (P value 0.017) and low-density lipoprotein cholesterol (P value 0.017) showed statistically significant reduction and Cl (P value 0.002) showed significant increase, nothing deviated from the range of normal values. In conclusion, this study showed no abnormalities in the abdominal, fecal states, blood and urine at all.