Masataka Kusunoki

Syndromes of Insulin Resistance in the Rat: Inducement by Diet and Amelioration with Benfluorex

Insulin resistance, mainly in skeletal muscle, is linked to a cluster of prevalent diseases including NIDDM, dyslipidemias, hypertension, and cardiovascular disease. To determine if an oversupply of lipid is associated with the development of skeletal muscle insulin resistance, we examined the effect of the hypolipidemic agent benfluorex in dietary models of insulin resistance. Adult, male Wistar rats were divided into six groups and maintained for 4 wk on diets high in complex carbohydrate, fructose or fat, with or without 50 mg · kg−1 · day−1 of benfluorex, given orally. Insulin action was assessed using a hyperinsulinemic (∼ 100 mU/L) euglycemic clamp, with 2-deoxyglucose tracer for individual tissue evaluation, in chronically cannulated conscious animals. Compared with starch feeding, fructose and fat feeding significantly impaired insulin action at the whole-body level (–46% and –41%, respectively, both P < 0.001), as well as in individual skeletal muscles. Fructose feeding increased circulating TGs (by 80%, P < 0.01) but not skeletal muscle TGs; whereas, fat feeding increased skeletal muscle TGs (by 59%, P < 0.01) but not circulating TGs. With benfluorex, however, diet had no effect on circulating and storage TGs; and development of skeletal muscle insulin resistance in the two diet groups was prevented. Feeding fructose but not fat significantly increased mean arterial BP (by 13%, P < 0.05), an effect prevented by benfluorex. These effects support the hypothesis that the development of muscle insulin resistance in these models is linked to local or systemic oversupply of lipid. These diet models—and the parallel effect of benfluorex on insulin resistance, lipids, and hypertension—may prove useful in the search for the mechanisms that underlie the human disorders associated with insulin resistance.

The lipoprotein lipase activator, NO-1886, suppresses fat accumulation and insulin resistance in rats fed a high-fat diet

Aims/hypothesis. Fat balance is critical in the aetiology of obesity and related diseases. Lipoprotein lipase is of major importance in lipid metabolism. The aim of this study was to investigate the long-term effects of the lipoprotein lipase activator, NO-1886, on substrate utilisation, adiposity and insulin action in rats fed a high-fat diet.¶Methods. Male, Sprague-Dawley rats were fed for 10 weeks on a chow diet or a high-fat diet with, or without, NO-1886 (50 mg · kg–1· day–1). Weight gain, fat accumulation and both hormone-sensitive and lipoprotein, lipase activities were measured. Insulin action was assessed by the euglycaemic hyperinsulinaemic clamp and metabolic rate/substrate utilisation by open-circuit respirometry.¶Results. Compared with chow-fed controls, a high-fat diet increased weight gain, an effect lessened by NO-1886 [weight gain (g): chow, 37 ± 3, high-fat, 222 ± 9; high-fat + NO-1886, 109 ± 6, all groups differed p < 0.001]. A similar pattern existed for fat accumulation [visceral fat (g): chow, 35.9 ± 3.2; high-fat, 81.9 ± 6.6; high-fat + NO-1886, 52.3 ± 4.7, p < 0.01 high-fat vs the other groups]. A high-fat diet induced whole-body insulin resistance (clamp glucose infusion rate: 4.8 ± 1.3 mg · kg–1· min–1 vs 10.6 ± 1.1 for the chow group, p < 0.01) with NO-1886 lessening this effect (8.3 ± 0.5, p < 0.05 vs high-fat). The 24-h respiratory quotient was lower in the high-fat + NO-1886 group (0.825 ± 0.010) compared with high-fat alone (0.849 ± 0.004, p < 0.05). A high-fat diet increased lipoprotein and hormone-sensitive, lipase activities in epididymal fat, an effect not altered by NO-1886. In myocardium and skeletal muscle a high-fat diet lowered lipoprotein lipase activity, an effect lessened by NO-1886.¶Conclusion/interpretation: Lipoprotein lipase activators could have potential benefits for the treatment of obesity by increasing fat utilisation. [Diabetologia (2000) 43: 875–880]

Rat C peptide I and II stimulate glucose utilization in STZ-induced diabetic rats

Aims. To study the effects of physiological concentrations of rat proinsulin C peptide I and II, respectively, on whole body glucose utilization in streptozotocin diabetic and healthy rats. Methods. A sequential insulin clamp procedure was used (insulin infusion rates 3.0 and 30.0 mU · kg–1· min–1) in awake animals. C-peptide infusion rates were 0.05 and 0.5 nmol · kg–1· min–1. Blood glucose was clamped at 7.7 ± 0.3 mmol/l in the diabetic rats and at 3.9 ± 0.1 mmol/l in the healthy rats. Results. In diabetic rats infused at lower rates of C peptide and insulin, glucose utilization increased by 79–90 % (p < 0.001) compared with diabetic animals infused with saline and insulin. Increasing the rate of C-peptide infusion tenfold did not elicit a statistically significant further increase in glucose utilization. C peptide I and II exerted similar effects. The metabolic clearance rate for glucose in the diabetic animals infused with C peptide was not different from that of the healthy rats. During high-dose insulin infusion (30.0 mU · kg–1· min–1) glucose utilization increased considerably and no statistically significant C-peptide effects were observed. About 85 % of the increase in glucose utilization induced by C peptide could be blocked by treatment with N-monomethyl-l-arginine. Conclusions/interpretation. Physiological concentrations of homologous C peptide stimulate whole body glucose utilization in diabetic but not in healthy rats. C peptide I and II elicit similar effects. The influence of C peptide on glucose utilization may be mediated by nitric oxide. [Diabetologia (1999) 42: 958–964]

Amelioration of High-Fat Feeding–Induced Insulin Resistance in Skeletal Muscle With the Antiglucocorticoid RU486

Fat feeding produces whole-body insulin resistance and decreased glucose uptake in muscle tissue of rats. To examine the effect of glucocorticoid blockade on the insulin resistance caused by high-fat feeding, four groups of rats were fed diets high in starch (70% of calories) or fat (59% of calories) for 4 weeks with or without the antiglucocorticoid RU486 (69.8 μmol · kg−1 · day−1) in the food. Whole-body insulin action was assessed by the euglycemic clamp technique at an upper physiological insulin level with bolus 2-[3H]deoxyglucose to determine individual tissue insulin-stimulated glucose uptake. Whole-body glucose utilization (clamp glucose infusion rate [GIR]) was decreased by high-fat feeding (GIR 68.3 ± 12.2 vs. 182.6 ± 12.8 μmol · kg−1 · min−1 for the starch-fed group; P < 0.001). Addition of RU486 to the diet significantly improved (GIR 133.9 ± 12.8 μmol · kg−1 · min−1; P < 0.01), but did not fully reverse, the insulin resistance caused by fat feeding. RU486 was without effect in the starch-fed rats. In skeletal muscles, RU486 ameliorated 62 and 68% of the insulin resistance produced by fat feeding in red quadriceps and extensor digitorum longus hindlimb muscles, respectively, but had no effect in heart or white adipose tissue. These results suggest that glucocorticoids play, in a tissue-specific manner, a role in the maintenance and/or production of insulin resistance produced by high-fat feeding.

The actions of a novel lipoprotein lipase activator, NO-1886, in hypertriglyceridemic fructose-fed rats☆

High circulating fasting and prandial triglyceride levels are associated with both insulin resistance and the development of cardiovascular disease. The aim of this investigation was to study the effects of NO-1886, a novel lipoprotein lipase (LPL) activator, on triglyceride levels, fat oxidation, and glucose tolerance in fructose-fed rats, a hypertriglyceridemic model of insulin resistance. Adult male Wistar rats were fed for 4 weeks with a high-starch diet or a high-fructose diet without and with NO-1886 (50 mg x kg[-1] x d[-1] orally). Fructose feeding increased plasma triglyceride levels, an effect that was ameliorated by NO-1886 treatment (week 1/week 4: starch-fed, 2.4 +/- 0.1/2.8 +/- 0.2 mmol/L; fructose-fed, 3.6 +/- 0.5/5.5 +/- 0.5; fructose + NO-1886, 2.7 +/- 0.2/3.6 +/- 0.3). The mean 24-hour respiratory quotient (RQ) was significantly lower in the fructose + NO-1886 group compared with fructose-fed rats, indicating increased oxidation of fat. Fructose feeding elevated liver triglyceride levels by 74% (P < .01), an effect not altered by NO-1886. Red and white quadriceps hindlimb muscle triglyceride levels were not different between groups. Glucose tolerance (intravenous test in long-term cannulated rats) was mildly deteriorated and fasting insulin and glucose levels were elevated in fructose-fed rats, effects which were ameliorated by NO-1886. In conclusion, in the fructose-fed rat model of hypertriglyceridemia and insulin resistance, addition of a LPL activator reduced circulating triglyceride levels without causing increased muscle triglyceride accumulation or deterioration in glucose tolerance. LPL activators may prove to be a fruitful avenue to explore in the search for new therapeutic agents in the treatment of dyslipidemias and insulin resistance.

The effect of low intensity bicycle exercise on the insulin-induced glucose uptake in obese patients with Type 2 diabetes

OBJECTIVE The present study was undertaken to reveal the effect of low intensity bicycle exercise on the insulin-induced glucose uptake in obese patients. SUBJECTS AND METHODS Seven obese men with Type 2 diabetes (OBDM) and seven healthy young men (HY) participated in this study. The glucose infusion rate (GIR) was determined by glucose clamp procedure at an insulin infusion rate of 40 mU m-2 min-1 (plasma insulin concentrations: 700-800 pmol l-1). Confirming stabilized GIR, a 30-min bicycle exercise was performed during the glucose clamp which was continued for 120 min after exercise. RESULTS Average GIR in OBDM for last 30 min prior to exercise were significantly lower than HY (28.3 +/- 1.7, 47.4 +/- 1.8 mumol kg-1 min-1 respectively, P < 0.05). GIR abruptly increased during exercise and gradually decreased after exercise to the nadir almost at the time from 30 to 60 min in recovery period in both groups. GIR in OBDM, however, gradually increased significantly over pre-exercise levels (P < 0.05), following exercise and reached the same levels compared to HY after 80 min of recovery period. CONCLUSION These results indicated that in obese Type 2 diabetes, 30 min of low intensity bicycle exercise significantly enhances the lower level of insulin-induced glucose uptake shortly after exercise and might be useful for the treatment of post-prandial hyperglycemia.

A lipoprotein lipase activator, NO-1886, improves endothelium-dependent relaxation of rat aorta associated with aging

Endothelial function is closely related to development of atherosclerosis and is impaired with aging. The novel compound NO-1886, 4-diethoxyphosphorylmethyl-N-(4-bromo-2-cyanophenyl)benzamid e, is a lipoprotein lipase activator and its long term administration protects against the development of experimental atherosclerosis in animals. The aim of this study was to ascertain whether NO-1886 ameliorates the impaired endothelium-dependent relaxation of rat aorta associated with aging. NO-1886 (50 mg/kg p.o.) was administered to 7-month old rats for 3 months. Plasma lipid, glucose and insulin levels in old control rats (10 months of age) were significantly higher than those of young rats (2 months of age). NO- 1886 decreased plasma triglyceride levels (old rats, 233+/-10 mg/dl; old rats + NO-1886, 172+/-16 mg/dl, P < 0.01) and increased plasma high density lipoprotein (HDL) cholesterol level (old rats, 72+/-6 mg/dl; old rats + NO-1886, 142+/-6 mg/dl, P < 0.001) in old rats, but had no effects on plasma glucose or insulin. The endothelium-dependent relaxation of the thoracic aorta caused by histamine was significantly impaired in old rats (% relaxation at 10(-5.5) M histamine: young rats 25.4+/-3.1%; old rats 14.1+/-1.9%, P < 0.01), an effect completely prevented by NO-1886 (old rats + NO-1886; 22.8+/-2.8%, P < 0.05 vs. old rats). In contrast, NO-1886 showed no effect on the endothelium-independent relaxation by sodium nitroprusside. These results indicate that NO-1886 improves impaired endothelium-dependent relaxation of rat aorta associated with aging, possibly by correcting lipid metabolism.

DPP-4 Inhibitor Teneligliptin Improves Insulin Resistance and Serum Lipid Profile in Japanese Patients with Type 2 Diabetes.

Dipeptidyl peptidase-4 (DPP-4) inhibitors have been reported to improve the glycemic control and blood hemoglobin A1c (HbA1c) concentrations. However, there are few reports as yet suggesting that DPP-4 inhibitors may also improve insulin resistance and the serum lipid profile in the clinical setting. This study was aimed at investigating the effect of 14-week treatment with teneligliptin (20 mg/day) on the homeostasis model assessment ratio (HOMA-R), an indicator of insulin resistance, and serum lipid profile in 9 patients with type 2 diabetes. The treatment produced a significant decrease of the blood glucose and HbA1c concentration (blood glucose: p=0.008; HbA1c: p=0.038), and also improved HOMA-R (p=0.039). Furthermore, the patients showed elevation of the serum HDL-cholesterol level (p=0.032), and a tendency towards reduction of the serum triglyceride level. The results indicate that teneligliptin acts not only to improve the blood glucose control, but also to improve the insulin resistance and serum lipid profile in Japanese type 2 diabetes patients.

Pioglitazone-induced body weight gain is prevented by combined administration with the lipoprotein lipase activator NO-1886.

Pioglitazone improves insulin resistance in diabetics but often causes body weight gain. The lipoprotein lipase activator NO-1886 has been shown to exert both anti-obesity and anti-insulin-resistance effects. In this study, we investigated the effect of the combined administration of pioglitazone with NO-1886 (pioglitazone+NO-1886) in preventing body weight gain in insulin-resistant, high-fat fed rats. The rats were fed a standard or high-fat diet for 16 weeks. The high-fat fed rats were randomized at week 9 into 4 groups (i.e., control, pioglitazone (30 mg/kg/day), NO-1886 (100mg/kg/day), and pioglitazone+NO-1886 (30 and 100mg/kg/day, respectively)). The high-fat fed control rats developed obesity and insulin resistance. After 7 weeks of drug treatment, pioglitazone+NO-1886 was found to prevent the body weight gain caused by pioglitazone alone (pioglitazone+NO-1886: Δ76.0 ± 16.8 g vs. pioglitazone: Δ127.8 ± 39.5 g, P<0.05) and to increase glucose infusion rate during insulin clamp, compared with the results in the high-fat fed control group. No differences in plasma nonesterified fatty acid, leptin, adiponectin, glucose, or insulin levels were observed between the pioglitazone+NO-1886 and the pioglitazone-alone groups. However, plasma total cholesterol and HDL-cholesterol levels were significantly increased and plasma triglyceride levels were slightly decreased in the pioglitazone+NO-1886 group, compared with the values in the pioglitazone-alone group. In summary, the combined administration of pioglitazone and NO-1886 prevented the pioglitazone-induced body weight gains and ameliorated insulin resistance observed in high-fat fed rats. These results indicate that combined therapy with pioglitazone and NO-1886 may be beneficial for the treatment of type 2 diabetes.

A lipoprotein lipase activator, NO-1886 prevents impaired endothelium-dependent relaxation of aorta caused by exercise in aged rats.

Exercise decreases plasma total cholesterol and triglycerides, and simultaneously, increases high density lipoprotein (HDL) cholesterol. As a result, exercise is believed to aid in preventing atherosclerosis. However, we do not know whether exercise protects against the development of atherosclerosis in the elderly. The aim of this study was to ascertain whether the lipoprotein lipase activator NO-1886 had an effect on the prevention of atherosclerosis in aged rats which undergo exercise. Exercise for 3 months did not affect plasma lipids but decreased the accumulation of visceral fat in 2-year-old rats (aged rat). Exercise also resulted in an elevation of plasma lipid peroxide (LPO) levels and impaired the endothelium-dependent relaxation of the thoracic aorta caused by acetylcholine in aged rats. On the other hand, NO-1886 decreased plasma triglycerides and increased HDL cholesterol and suppressed the elevation of plasma LPO levels caused by exercise. Furthermore, NO-1886 prevented impaired endothelium-dependent relaxation caused by exercise. In summary, the results of our study indicate that exercise may cause impaired endothelium-dependent relaxation by elevation of LPO in aged rats, and that NO-1886 prevents this impaired endothelium-dependent relaxation of aorta by reducing plasma triglycerides, elevating HDL cholesterol, and suppressing the elevation of plasma LPO caused by exercise.