Naoki Koh

Effect of Niceritrol on Streptozocin-Induced Diabetic Neuropathy in Rats

Niceritrol, a drug with peripheral tissue vasodilatory and serum lipid-lowering activity, was administered for 2 mo to rats with streptozocin-induced diabetes. Physiological and biochemical studies were subsequently conducted on rat nerve tissue. A markedly lower value of ∼ 47% in sciatic nerve blood flow (SNBF) was detected in an untreated diabetic (DC) group than in a nondiabetic control group (CC). A significant delay in caudal motor nerve conduction velocity (MNCV) and significantly higher glucose, sorbitol, and fructose values were observed in the sciatic nerve and serum lipids. In contrast, a niceritrol-treated diabetic (DN) group had significantly higher SNBF, MNCV, and sciatic nerve myo-inositol values and lower serum triglyceride levels than group DC. No differences between these two groups were noted in glucose, sorbitol, and fructose levels in the sciatic nerve, or in cholesterol and glucose in serum. These findings suggest that niceritrol has a clear inhibitory effect on the development of delayed MNCV in the diabetic rat, which may be due to reduced nerve blood flow and/or decreased nerve myo-inositol levels.

Effects of a fructose-rich diet and the aldose reductase inhibitor, ONO-2235, on the development of diabetic neuropathy in streptozotocin-treated rats

SummaryStreptozotocin-diabetic rats were maintained on a 72% fructose diet for 4 weeks and some were treated with an aldose reductase inhibitor (either alrestatin: 0.9 g · kg−1 · day−1 or ONO-2235: 50 mg · kg−1 · day−1). Fructose feeding significantly influenced the development of impaired motor nerve conduction velocity in the diabetic rats and this effect was positively correlated with sorbitol accumulation in the sciatic nerve of diabetic rats maintained on a fructose-rich diet. Treatment with ONO-2235, a new aldose reductase inhibitor, prevented both slowing of motor nerve conduction velocity and elevation of nerve sorbitol concentration. On the other hand, erythrocyte sorbitol levels were significantly correlated to those of the sciatic nerve (r=0.86, p<0.001) and the retina (r=0.91, p<0.001) in these animals. Thus, our findings suggest that increased polyol pathway activity may be related to the pathogenesis of diabetic neuropathy and erythrocyte sorbitol concentrations may prove a useful indicator for the presence of diabetic complications.

Effects of Beraprost Sodium and Insulin on the Electroretinogram, Nerve Conduction, and Nerve Blood Flow in Rats with Streptozotocin-Induced Diabetes

The effect of a prostacyclin analog, beraprost sodium, on the electroretinogram, motor nerve conduction velocity, and nerve blood flow was determined in rats with streptozotocin-induced diabetes and was compared with the effect of insulin. Beraprost sodium (0.01 mg · kg−1 · day−1 for 8 weeks) significantly shortened the peak latency of the electroretinogram b-wave, increased tail nerve conduction velocity, and increased sciatic nerve blood flow in diabetic rats (P < 0.0003, 0.0001, and 0.0001 vs. untreated diabetic rats, respectively). This was accompanied by a significant increase in the 6-keto-prostaglandin F1α content of the thoracic aorta and a marked increase in the cAMP content of the sciatic nerve. Beraprost sodium had no effect on the sorbitol and fructose contents of the sciatic nerve and retina, but insulin (8–10 U/day) significantly reduced both parameters. These findings suggest that beraprost sodium may be useful for prevention of vascular and neural dysfunction in the retina and peripheral nerve.

An Importance of Carbohydrate Ingestion for the Expression of the Effect of α-Glucosidase Inhibitor in NIDDM

OBJECTIVE To examine the usefulness of α-glucosidase inhibitors in glycemic control of patients with NIDDM. The involvement of carbohydrate ingestion in manifestation of the effects of α-glucosidase inhibitors was also investigated. RESEARCH DESIGN AND METHODS A total of 41 patients hospitalized with NIDDM (22 patients receiving sulfonylurea and 19 receiving insulin therapy) were given α-glucosidase inhibitors during the period when their blood glucose levels were well controlled. They were followed for 3 weeks as inpatients and for an additional 6 months as outpatients. They were retrospectively divided into two groups according to the percentage of carbohydrates in all sources of calories during outpatient management: the <50% group and the >50% group. Between these two groups, we compared circadian variation in blood glucose levels, HbA1c, and urine C-peptide. RESULTS Treatment with alpha-glucosidase inhibitors during the hospital stay markedly improved circadian variation in blood glucose levels and HbA1c and decreased urine C-peptide in both groups. While HbA1c returned to its pretreatment level at 6 months after the treatment in the <50% group, HbA1c had further improved in the >50% group at 6 months. CONCLUSIONS α-Glucosidase inhibitors are useful for glycemic control in patients with NIDDM and the percentage of carbohydrate in all calorie sources is an important factor for the expression of their effects.

Diabetic neuropathy in sucrose-fed otsuka long-evans tokushima fatty rats: Effect of an aldose reductase inhibitor, TAT

In an animal model of human non-insulin dependent diabetes mellitus (NIDDM), Otsuka Long-Evans Tokushima Fatty (OLETF) rats were fed with sucrose for 8 weeks to obtain severe hyperglycemia. The effects of sucrose administration on peripheral nerve functions, motor nerve conduction velocity (MNCV) and coefficient of variance of R-R interval (CVR-R), were investigated with concomitant measuring of sciatic nerve blood flow (SNBF), ADP-induced platelet aggregation and polyol content in the sciatic nerves. The effects of an aldose reductase inhibitor, TAT, on these parameters were also studied. Administration of sucrose to OLETF rats caused significant body weight reduction and remarkable hyperglycemia. Sucrose-fed OLETF rats demonstrated significantly delayed MNCV, decreased CVR-R, reduced SNBF and increased platelet aggregation activity to ADP. Sorbitol and fructose accumulation, and myo-inositol depletion in sciatic nerves were observed only in sucrose-fed OLETF rats. These abnormalities were all ameliorated by the treatment with TAT. These observations suggest that the sucrose-fed OLETF rat is a useful animal model for studying the pathogenesis of diabetic neuropathy in human NIDDM, and that an aldose reductase inhibitor is a useful therapeutic agent for the treatment of diabetic neuropathy.

Nerve function and blood flow in Otsuka Long-Evans Tokushima Fatty rats with sucrose feeding: effect of an anticoagulant

To investigate the pathogenesis of diabetic neuropathy in non-insulin-dependent diabetes mellitus, Otsuka Long-Evans Tokushima Fatty rats, an animal model of non-insulin-dependent diabetes mellitus, and non-diabetic Long-Evans Tokushima Otsuka rats were fed with or without sucrose and/or cilostazol, an anticoagulant, for 8 weeks. Sucrose-fed diabetic rats showed a delayed motor nerve conduction velocity, decreased R-R interval variability of electrocardiogram, reduced sciatic nerve blood flow, increased platelet aggregability and a decreased erythrocyte 2,3-diphosphoglycerate concentration compared with non-sucrose-fed diabetic rats and non-diabetic rats. These abnormalities were significantly prevented by treatment with cilostazol without changes in the nerve tissue levels of polyols. These findings indicate that sucrose-fed Otsuka Long-Evans Tokushima Fatty rats may be a useful animal model of neuropathy in non-insulin-dependent diabetes mellitus, and that cilostazol may prevent the development of diabetic neuropathy by modifying vascular factors.

Effects of Glycemic Control on Plasma 3-Deoxyglucosone Levels in NIDDM Patients

OBJECTIVE To clarify the effects of glycemic control on the level of 3-deoxyglucosone (3-DG), a reactive dicarbonyl compound, in plasma from diabetic patients. RESEARCH DESIGN AND METHODS Fasting plasma samples were collected from 15 healthy volunteers and 27 patients with NIDDM. Samples were collected from six poorly controlled patients before and after improved glycemic control for at least 2 months. Plasma 3-DG was determined by high-performance liquid chromatography (HPLC) as a 2,3-diaminonaphthalene derivative. We observed the relationship of 3-DG levels with plasma glucose or HbA1c levels and examined changes in 3-DG levels after glycemic control in the six patients. RESULTS Plasma 3-DG was significantly more increased in diabetic patients than in nondiabetic control subjects (31.8 ± 11.3 vs. 12.8 ± 5.2 ng/ml, means ± SD, P < 0.001), but there was an ∼ threefold difference in 3-DG levels among diabetic patients. 3-DG levels were well correlated with plasma glucose (r = 0.56, P < 0.005) and HbA1c levels (r = 0.74, P < 0.001) in diabeticpatients. The improvement of hyperglycemia in six patients resulted in a significant decrease in 3-DG (35.2 ± 13.2 vs. 21.3 ±3.4 ng/ml, P < 0.05). CONCLUSIONS The results indicate that the plasma glucose level is a predominant determinant of the plasma 3-DG level in diabetic patients and good glycemic control would be important to reduce this reactive metabolite.

Effects of High Glucose Concentrations and Epalrestat on Sorbitol and myo-Inositol Metabolism in Cultured Rabbit Aortic Smooth Muscle Cells

To clarify the relationship between abnormality of sorbitol and/or myo-inositol metabolism caused by hyperglycemia and diabetic macroangiopathy, we investigated the effects of high glucose concentrations and epalrestat, an aldose reductase inhibitor, on the metabolism of sorbitol and myo-inositol in cultured rabbit aortic smooth muscle cells. In cells incubated in the presence of 30 mM glucose for 72 h, the sorbitol content increased ∼4.5-fold, and the myo-inositol level decreased by 55% compared with control values. Kinetic analysis of high-affinity myo-inositol uptake suggested that smooth muscle cells exposed to high glucose concentrations exhibited a noncompetitive type of inhibition characterized by ouabain-sensitive, energy-dependent active transport. Epalrestat blocked glucose-induced changes in sorbitol and myo-inositol metabolism, suggesting that these changes were caused by the accumulation of sorbitol in the cells. These metabolic changes may impair function of smooth muscle cells, contributing to the pathology of diabetic atherosclerosis, especially Mönckebergs calcific medial sclerosis. The use of an aldose reductase inhibitor may prevent these glucose-induced changes.

Physiological and morphometric analyses of neuropathy in sucrose-fed OLETF rats

To investigate the characteristic features of diabetic neuropathy in type 2 diabetes mellitus, Otsuka Long-Evans Tokushima fatty (OLETF) rats, an animal model of human type 2 diabetes mellitus, and non-diabetic Long-Evans Tokushima Otsuka (LETO) rats were fed with or without sucrose and/or an aldose reductase inhibitor, [5-(3-thienyl) tetrazol-1-yl] acetic acid (TAT), for 24 weeks, and physiological, biochemical and morphological assessments were performed. Sucrose administration caused remarkable hyperglycemia in OLETF rats but not in LETO rats. Sucrose-fed OLETF rats demonstrated delayed nerve conduction velocity, decreased coefficient of variation of R-R interval, reduced sciatic nerve blood flow, increased platelet aggregation activity, a lower concentration of erythrocyte 2,3-diphosphoglycerate, and decreased Na+/K+-ATPase activity in sciatic nerves, compared with the non-sucrose-fed OLETF and LETO rats. TAT prevented all these deficits except hyperglycemia. Sorbitol and fructose accumulation and myo-inositol depletion in tail nerves of sucrose-fed OLETF rats were ameliorated by TAT. Myelinated fiber size and density in sural nerves of sucrose-fed OLETF rats were decreased and increased, respectively, compared with non-sucrose-fed OLETF and LETO rats. These morphological abnormalities were normalized by TAT. These observations suggest that the sucrose-fed OLETF rat developed diabetic neuropathy not only electrophysiologically but also histologically, and that an aldose reductase inhibitor, TAT, possesses therapeutic value for the treatment of diabetic neuropathy.

Effects of an aldose reductase inhibitor on erythrocyte fructose 3-phosphate and sorbitol 3-phosphate levels in diabetic patients

Fructose 3-phosphate and sorbitol 3-phosphate are novel metabolites that have been shown to associate with the polyol pathway in animal experiments. Fructose 3-phosphate is of particular interest because of its potent glycation capability as compared with other glycolytic intermediates, e.g., fructose. We observed the effects of treatment with epalrestat, an aldose reductase inhibitor, on their concentrations in erythrocytes from diabetic patients. The levels of both metabolites were significantly higher in diabetic patients than in non-diabetic subjects. A group of patients who had been treated with epalrestat showed significantly lower levels of both metabolites as compared with those untreated. A treatment of three patients with epalrestat for one month resulted in obvious decreases in their concentrations. The results suggest a possible explanation for the preventive effect of an aldose reductase inhibitor on nonenzymatic glycation.