Junichi Yokoyama

Influence of highly purified eicosapentaenoic acid ethyl ester on insulin resistance in the Otsuka Long-Evans Tokushima Fatty rat, a model of spontaneous non-insulin-dependent diabetes mellitus

We investigated the effect of long-term administration of highly purified eicosapentaenoic acid ethyl ester (EPA-E), an n-3 polyunsaturated fatty acid derived from fish oil, in comparison to the effects of lard, olive oil, safflower oil, or distilled water as the control on the development of insulin resistance in Otsuka Long-Evans Tokushima Fatty (OLETF) rats, a model of spontaneous non-insulin-dependent diabetes mellitus (NIDDM) with obesity. After 17 or 18 weeks of treatment, the glucose infusion rate (GIR) in the euglycemic insulin-glucose clamp test only showed a significant increase in EPA-E-treated rats compared with control rats given distilled water alone as the vehicle. The GIR in EPA-E-treated animals was approximately three times greater than in the controls. This is the first report to display the influence of various fatty acids on the development of insulin resistance in OLETF rats. We demonstrated that EPA-E prevents the onset of insulin resistance, whereas olive oil and safflower oil have no effect and lard exacerbates insulin resistance. Fatty acid analysis of phospholipids in skeletal muscle showed a significant increase of the C18:2, C20:5, and C22:5 components in EPA-E-treated rats and, conversely, a significant decrease in C20:4. In addition, EPA-E-treated rats showed a significant increase in GLUT4 mRNA in skeletal muscle when compared with control rats. Our results indicate that the beneficial effect of EPA-E on insulin resistance in OLETF rats is likely to be dependent on modification of the phospholipid components of the skeletal muscle membrane. These findings suggest that dietary fatty acids may play a key role in the development of insulin resistance in patients with NIDDM.

Effect of highly purified eicosapentaenoic acid ethyl ester on insulin resistance and hypertension in dahl salt-sensitive rats

We investigated the effect of long-term administration of highly purified eicosapentaenoic acid ethyl ester (EPA-E), an n-3 polyunsaturated fatty acid derived from fish oil, in comparison to lard on the development of hypertension and insulin resistance in Dahl salt-sensitive (Dahl-S) rats fed a high-sucrose diet (HSD), a model of salt-sensitive hypertension. After 16 weeks of treatment, the glucose infusion rate (GIR) during the euglycemic insulin-glucose clamp test significantly increased in the HSD-EPA-E group compared with the HSD-water or -lard control group. The GIR was approximately three times higher in the HSD-EPA-E group versus the HSD-water or -lard control group, and it was about 70% of the rate in the calorically deprived control group fed a low-fat-high-fiber diet (LF-HFD). In addition, EPA-E significantly suppressed the elevation of plasma glucose and insulin levels after oral glucose loading. These results indicate that EPA-E prevents the development of insulin resistance in Dahl-S rats fed a HSD. Fatty acid analysis of phospholipids in skeletal muscle showed a significant increase in C18:2, C20:5, and C22:5 components in the HSD-EPA-E group and, conversely, a significant decrease in C16:0, C20:4, and C22:6. The present results indicate that the beneficial effect of EPA-E on insulin resistance in Dahl-S rats fed a HSD is likely dependent on the modification of phospholipid components in the skeletal muscle membrane. These findings suggest that EPA-E might prevent the development of insulin resistance in dietary obesity. In addition, the HSD-EPA-E group showed a significant increase in the level of uncoupling protein (UCP) in brown adipose tissue as compared with the HSD-water or -lard control group. However, EPA-E had no effect on the development of hypertension and obesity in Dahl-S rats fed the HSD.

Insulin Intervention to Preserve β Cells in Slowly Progressive Insulin‐Dependent (Type 1) Diabetes Mellitusa

Abstract: Slowly progressive insulin‐dependent (type 1) diabetes mellitus (SPIDDM) is characterized by (1) late age of onset, with initial features of NIDDM and subsequent progression to insulin‐dependent stage; (2) high predictive value of autoantibodies against glutamic acid decarboxylase (GADAb) and islet cell antibodies (ICA) for progression of β cell failure; (3) less predominant T cell response, which may attack and eventually destroy β‐cells in affected pancreas. These findings may suggest a rationale for intervention to prevent slowly progressive β cell dysfunction in this type of diabetes. We identified three independent risk factors for progression of β cell failure in SPIDDM: (1) sulfonylurea treatment; (2) ICA‐positive periods; and (3) initial body weight. We hypothesized that removal of the risk factors for further progression of β cell dysfunction will have beneficial effects on intervention strategy in treating SPIDDM. In our pilot study, we used a small dose of insulin instead of sulfonylurea in the early stage of treatment of patients with SPIDDM. Insulin‐treated SPIDDM patients had a sustained C peptide response (CPR), while most of sulfonylurea‐treated patients progressed to an insulin‐dependent state. We organized a randomized multicenter clinical trial to study early treatment to prevent the progression of β cell dysfunction in SPIDDM (the Tokyo Study). It was demonstrated that early intervention with insulin therapy is an effective treatment modality in the early stage of SPIDDM patients who had preserved β cell function at entry (integrated value of serum C peptide values at 0, 30, 60, 90, and 120 minutes; Sigma CPR ≥ 10 ng/mL) and high GADAb (>10 U/mL). Preventive insulin treatment was ineffective in the patients who had diminished insulin reserve at entry (Sigma CPR < 10 ng/mL). Insulin intervention to preserve β cell dysfunction in SPIDDM is effective and safe in patients with preserved β cell function and high GADAb titers at the initiation of insulin.

Diabetic strain (WBN/Kob) of rat characterized by endocrine-exocrine pancreatic impairment due to distinct fibrosis.

A spontaneously developed endocrine-exocrine pancreatic dysfunction was observed in the aged males of an inbred strain of Wistar rats, WBN/Kob. Nonobese male WBN/Kob rats developed glycosuria and hyperglycemia at around 9 months of age. Cumulative incidence of diabetes in male rats was 43% (33 of 76) at 12 months of age and reached 90% at the age of 21 months. In contrast, female rats did not become diabetic. Urinary excretion of amylase in WBN/Kob rats was significantly increased in comparison with control Wistar rats. Moreover, the exocrine pancreatic function test was impaired in WBN/Kob rats. Pathological examination of pancreata revealed infiltration of inflammatory cells, hemorrhage, deposition of hemosiderin, and fibrinous exudation around pancreatic ducts and blood vessels at 3 months of age. A gradual increase of fibrous tissue into the exocrine tissue and islets was observed with advancing age. The extremely enlarged interlobular lymph nodes were also observed. At the age of 12 months, the fibrous tissue replaced extensive areas of the pancreas and involved islets. The amylase content of pancreata in WBN/Kob rats was markedly decreased in comparison with that in Wistar rats at 12 months of age. Islets composed of few endocrine cells were detected. Immunohistochemical staining for insulin and glucagon showed a decreased number of not only B cells but also A cells. Moreover, both the pancreatic insulin and glucagon contents were markedly decreased in WBN/Kob rats in comparison with Wistar rats. This new diabetic strain (WBN/Kob) of rat is characterized by the destruction of not only B cells but also A cells, accompanied by exocrine pancreatic insufficiency due to fibrous changes in exocrine tissue. The pathophysiology of this diabetes is quite different from that of previously reported diabetic animal models.

Multicenter Prevention Trial of Slowly Progressive Type 1 Diabetes with Small Dose of Insulin (the Tokyo Study)

Abstract: In 1996, we designed a randomized multicenter study to assess the effects of small doses of insulin on beta cell failure in slowly progressive type 1 diabetes (the Tokyo Study). We report here the preliminary results of this study. Glutamic acid decarboxylase 65 antibody (GADA)‐positive patients were randomly divided into 2 groups: one group received insulin (Ins group), the other a sulfonylurea (SU group). Fifty‐four patients (24 Ins group, 30 SU group) were analyzed at the end of a 4‐year period. All patients underwent a 75 g oral‐glucose test (O‐GTT) every 6‐12 months. The insulin‐dependent stage was defined based on an integrated value of serum C‐peptide levels on O‐GTT (∑CPR; sum of CPR at 0, 30, 60, 90, and 120 min) below 4.0 ng/mL. The ∑CPR in the SU group decreased progressively from 22.0 ± 10.6 to 11.3 ± 7.5 ng/mL over the 48‐month period (p < 0.001 vs. baseline). The ∑CPR in the Ins group was unchanged. Among the SU group, 30% of subjects (9/30) progressed to IDDM, while 8.3% of Ins group subjects (2/24) progressed to IDDM (p= 0.087). With regard to the subjects who had a preserved C‐peptide response (∑CPR ≥ 10 ng/mL), the proportion of SU group subjects who progressed to IDDM was significantly higher than that of the Ins group (7/28, 25% vs. 0/21, 0%, p= 0.015). Among subjects with a high GADA titer (≥0 U/mL), 9/14 (64.3%) of the SU group, but only 2/16 (12.5%) of the Ins group, developed IDDM (p= 0.0068). As to those with a high GADA titer and a preserved C‐peptide response, SU group subjects progressed to IDDM (7/12, 58.3%) more frequently than Ins group subjects (0/14, 0%) (p= 0.0012). In summary, our results suggest that small doses of insulin effectively prevent beta cell failure in slowly progressive type 1 diabetes. We recommend avoiding SU treatment and instead administering insulin to NIDDM patients with high GADA titer.

Influence of telmisartan on insulin response after glucose loading in obese patients with hypertension: ARB Trial of hypertension in obese patients with hyperinsulinemia assessed by oral glucose tolerance test (ATHLETE)

IntroductionThe number of patients with both hypertension and obesity has been increasing in Japan. Many of these patients may also have insulin resistance. Telmisartan, an angiotensin II receptor blocker (ARB), selectively activates peroxisome proliferatoractivated receptor (PPAR)-gamma, and this effect is considered to markedly improve insulin resistance in obese patients with hypertension. We compared the antihypertensive and insulin resistance-improving effects of telmisartan with those of candesartan and valsartan in this patient population.MethodsTwenty-eight elderly patients with an average body mass index (BMI) of 27.1 kg/m2 were enrolled in this 6-month study. Patients were randomly selected to either switch from candesartan or valsartan to telmisartan or to continue with their current ARB. A 75 g oral glucose tolerance test (OGTT) was performed before and after switching, and the effect of telmisartan on the insulin response to glucose loading was investigated.ResultsThere was no significant difference in blood pressure between the two groups after drug administration, but glucose tolerance significantly improved in the telmisartan group. The hyperinsulin response to glucose loading also significantly improved in those taking telmisartan, as well as homeostasis model assessment of insulin resistance (HOMA-IR). These changes were not observed in the control group.ConclusionIn patients with hypertension and obesity showing insulin resistance, treatment with telmisartan significantly improved the hyperinsulin response to glucose loading. Telmisartan may therefore be beneficial in these patients.

Effects of sitagliptin on 24-h glycemic changes in Japanese patients with type 2 diabetes assessed using continuous glucose monitoring.

BACKGROUND This study was performed to examine the efficacy of sitagliptin, a dipeptidyl peptidase-4 inhibitor, in Japanese patients with type 2 diabetes using continuous glucose monitoring (CGM) of 24-h glycemic changes. SUBJECTS AND METHODS The study was a prospective open-label pilot study in patients with type 2 diabetes who were admitted to our hospital and treated with sitagliptin alone or concomitantly with another oral hypoglycemic drug. CGM was performed for 2 days before sitagliptin administration and for another 2 days after administration. The average 24-h blood glucose level, SD of the 24-h blood glucose level, 24-h glycemic fluctuation range, mean amplitude of glycemic excursions (MAGE), and hyperglycemic and hypoglycemic time periods were compared before and after administration. RESULTS Sitagliptin administration alone and with a concomitant drug decreased the average 24-h blood glucose level, SD of the 24-h blood glucose level, 24-h glycemic fluctuation range, MAGE, and hyperglycemic time, compared with these parameters before administration. There were significant correlations between the average 24-h blood glucose level before administration and the decrease in the average 24-h blood glucose level after administration and between MAGE before administration and the decrease in MAGE after administration. CONCLUSIONS Sitagliptin decreased the average glycemic level and also improved 24-h glycemic fluctuation, including postprandial hyperglycemia.

Liraglutide Narrows the Range of Circadian Glycemic Variations in Japanese Type 2 Diabetes Patients and Nearly Flattens These Variations in Drug-Naive Type 2 Diabetes Patients: A Continuous Glucose Monitoring–Based Study

BACKGROUND Liraglutide was examined for its effects on 24-h glucose fluctuations in Japanese type 2 diabetes patients as well as for its differential effects depending on glucose tolerance status after favorable glycemic control was obtained in these patients. PATIENTS AND METHODS In this prospective open-label pilot study, a total of 20 type 2 diabetes patients hospitalized for glycemic control were given liraglutide 0.3 mg, followed by liraglutide 0.6 mg and 0.9 mg, with each given at 1-week intervals. The patients were continuously monitored for their 24-h glucose levels before treatment and during the course of treatment with liraglutide 0.3 mg, 0.6 mg, and 0.9 mg, respectively, using continuous glucose monitoring (CGM). At the start of treatment with liraglutide, 12 patients were on diet therapy alone, of which six were drug-naive, and eight were being treated with glimepiride. RESULTS Liraglutide not only significantly reduced 24-h mean glucose levels but also significantly improved all the indices for glycemic variation evaluated, which included SDs of 24-h glucose levels, mean amplitude of glycemic excursions (MAGE), and total area under the glucose fluctuation curve (AUC) for 24 h. The study showed a significant negative correlation for mean glucose levels, SD, and AUC immediately before treatment versus their changes with liraglutide. A 75-g oral glucose tolerance test (OGTT) was given in 11 patients treated with liraglutide monotherapy once favorable glycemic control was achieved. The OGTT revealed that of these, six were found to have normal glucose tolerance, four had impaired glucose tolerance, and one had diabetes, and that of the six drug-naive patients, five patients were found to have normal glucose tolerance, and one had impaired glucose tolerance. CONCLUSIONS Study results showed that liraglutide is expected not only to reduce mean glucose levels but also to improve 24-h glucose fluctuations, including postprandial glucose excursions, with its effects being particularly conspicuous in patients with early-stage type 2 diabetes.

Effects of Add-On Treatment with Sitagliptin on Narrowing the Range of Glucose Fluctuations in Japanese Type 2 Diabetes Patients Receiving Insulin Therapy

BACKGROUND In an earlier continuous glucose monitoring (CGM)-based study, we reported that sitagliptin not only reduced 24-h mean glucose levels but also suppressed postprandial glucose increases, thus reducing the range of glycemic fluctuations in type 2 diabetes patients. In this study, we investigated whether sitagliptin might provide similar benefits in type 2 diabetes patients receiving insulin therapy by using CGM. PATIENTS AND METHODS The study included a total of 13 type 2 diabetes patients in whom stable glycemic control had been achieved after admission for glycemic control. Insulin regimens used included long-acting insulin preparations once daily in four patients and biphasic insulin preparations twice daily in nine, with the daily insulin dose being 19.0±12.7 U. During the CGM-based study, the patients were given insulin therapy alone on Days 1 and 2 and were given sitagliptin 50 mg/day as add-on treatment on Days 3-6, with their daily insulin doses maintained. RESULTS The add-on treatment with sitagliptin led to significant decreases in 24-h mean glucose levels and SDs of 288 glucose levels measured by CGM for 24 h, as well as in the indices for magnitude of glucose variability and proportion of time in hyperglycemia, compared with insulin therapy alone (P<0.01), whereas there was no significant change seen in regard to the proportion of time in hypoglycemia with or without add-on treatment with sitagliptin. CONCLUSIONS This CGM-based study clearly demonstrated that insulin therapy alone, whether with long-acting or biphasic insulin preparations, does not provide adequate glycemic control in type 2 diabetes patients. In contrast, add-on sitagliptin was shown to narrow the range of 24-h glucose fluctuations in these patients, suggesting that add-on treatment with sitagliptin is effective for postprandial glucose control in type 2 diabetes patients receiving insulin therapy.

Development of diabetic complications in a new diabetic strain of rat (WBN/Kob)

The development of ocular, renal, and neural lesions was examined in male diabetic WBN/Kob rats with endoexocrine pancreatic insufficiency. As for the ocular lesions, around 15 months of age, opacity of the lens began to appear. Opacity was first observed in the periphery of the lens, and then increased rapidly in severity, extending concentrically and centripetally, until total cataracts developed. The incidence of cataracts in male rats was gradually increased and reached almost 100% at 24 months of age. As for renal lesions, the 24–h urinary total protein began to increase at about 13 months of age and reached 50–300 mg/24 h at 13–28 month of age, which was significantly higher than in age-matched male Wistar rats (15–25 mg/24 h). Electrophoretic analysis revealed that the urinary protein was almost all albumin. Morphologically, an increased GBM thickness and glomeruli with segmental or global enlargement of mesangial areas were observed. As for neural lesions, a reduction in motor nerve conduction velocity was demonstrated electrophysiologically, and a marked decrease in density and diameter of myelinated fibers in the sciatic nerves were observed morphometrically. In conclusion, the WBN/Kob rat strain with slowly developing but severe lesions associated with pancreatopathy presents a suitable model for human diabetic complications.