Yoshimitsu Yamasaki

Possible novel therapy for diabetes with cell-permeable JNK-inhibitory peptide

The JNK pathway is known to be activated in several tissues in the diabetic state, and is possibly involved in the development of insulin resistance and suppression of insulin biosynthesis. Here we show a potential new therapy for diabetes using cell-permeable JNK-inhibitory peptide. Intraperitoneal administration of the peptide led to its transduction into various tissues in vivo, and this treatment markedly improved insulin resistance and ameliorated glucose tolerance in diabetic mice. These data indicate that the JNK pathway is critically involved in diabetes and that the cell-permeable JNK-inhibitory peptide may have promise as a new therapeutic agent for diabetes.

Oxidative stress, ER stress, and the JNK pathway in type 2 diabetes

Pancreatic β-cell dysfunction and insulin resistance are observed in type 2 diabetes. Under diabetic conditions, oxidative stress and ER stress are induced in various tissues, leading to activation of the JNK pathway. This JNK activation suppresses insulin biosynthesis and interferes with insulin action. Indeed, suppression of the JNK pathway in diabetic mice improves insulin resistance and ameliorates glucose tolerance. Thus, the JNK pathway plays a central role in pathogenesis of type 2 diabetes and may be a potential target for diabetes therapy.

A Crucial Role of MafA as a Novel Therapeutic Target for Diabetes

MafA, a recently isolated pancreatic β-cell-specific transcription factor, is a potent activator of insulin gene transcription. In this study, we show that MafA overexpression, together with PDX-1 (pancreatic and duodenal homeobox factor-1) and NeuroD, markedly increases insulin gene expression in the liver. Consequently, substantial amounts of insulin protein were induced by such combination. Furthermore, in streptozotocin-induced diabetic mice, MafA overexpression in the liver, together with PDX-1 and NeuroD, dramatically ameliorated glucose tolerance, while combination of PDX-1 and NeuroD was much less effective. These results suggest a crucial role of MafA as a novel therapeutic target for diabetes.

Metformin or gliclazide, rather than glibenclamide, attenuate progression of carotid intima-media thickness in subjects with type 2 diabetes

Aim/hypothesisMetformin is a well-known oral hypoglycaemic agent and has been commonly used, in combination with sulphonylurea, to treat type 2 diabetes. However, the advantageous effect of metformin plus sulphonylurea on diabetic macroangiopathy has yet to be clarified. To evaluate whether sulphonylurea or sulphonylurea plus metformin prevent diabetic macroangiopathy, we examined the progression of carotid artery intima-media thickness (IMT) as a surrogate end point.MethodsSubjects with type 2 diabetes were divided into three groups, receiving the following treatments: (i) glibenclamide (n=59); (ii) gliclazide (n=30); and (iii) glibenclamide + metformin (n=29). Maximum IMT and average IMT (the greatest value among 6 average values of each 3 points including greatest thickness) were measured at the beginning and end of the observation period.ResultsFor the follow-up period of 3 years, the annual change in average IMT of the glibenclamide plus metformin group (0.003±0.048xa0mm) was smaller than that of the glibenclamide group (0.064±0.045xa0mm) and gliclazide group (0.032±0.036xa0mm) (p<0.0001 and p=0.043 respectively). In the gliclazide group, average IMT increased during the follow-up period, but annual change in average IMT was significantly smaller than that of the glibenclamide group (p=0.005). Glibenclamide + metformin or gliclazide also attenuated the progression of maximum IMT, compared with that of glibenclamide (0.041±0.105, 0.044±0.106, 0.114±0.131xa0mm/year respectively, p=0.029 and p=0.035 respectively). Multivariable regression analysis implied that administration of metformin or gliclazide significantly and independently (p<0.05) reduces the progression of average IMT, compared with glibenclamide monotherapy.Conclusions/interpretationThese data indicate that metformin or gliclazide, rather than glibenclamide, have a potent anti-atherogenic effect in type 2 diabetes.

A phosphodiesterase inhibitor, cilostazol, prevents the onset of silent brain infarction in Japanese subjects with Type II diabetes

Aims/hypothesisThis study aimed to evaluate the effect of a phosphodiesterase inhibitor, cilostazol, on the prevention of silent brain infarction in diabetic patients without symptoms of vascular events. MethodsA total of 89 subjects were allocated at random to the cilostazol group (n = 43) or the control group (n = 46). ResultsAfter the study period (3.2 ± 0.5 years), carotid intima-media thickness (IMT) (means ± SD) had increased (p < 0.01) by 0.18 ± 0.19 mm in the control group. In the cilostazol group, intima-media thickness showed almost no change (–0.00 ± 0.16 mm). In the control group, 2 out of 46 subjects showed symptomatic brain infarctions and 10 out of 34 subjects without infarct-like region assessed by standard brain MRI examination showed silent brain infarctions after the observation period. On the other hand, no subjects in the cilostazol group showed silent brain infarction or strokes during the study period. Both at the beginning and end of the study period, the number of infarct-like regions positively correlated with IMT (r = 0.335, p < 0.001 or r = 0.347, p < 0.001 respectively). The progression of infarct-like regions was directly related to the increase in IMT during the study period (r = 0.299, p = 0.004). Conclusion/interpretationThese data demonstrated that cilostazol could prevent the onset of silent brain infarction in Japanese subjects with Type II (non-insulin-dependent) diabetes mellitus. Also, an increase in intima-media thickness of the carotid artery wall could be able to predict the onset of silent brain infarction. [Diabetologia (2002) 45: 188–194]

Association of -786T-C mutation of endothelial nitric oxide synthase gene with insulin resistance

Abstractn Aims/hypothesis. Endothelial derived nitric oxide synthase (eNOS) gene polymorphisms affect eNOS activity and are associated with abnormal vasomotility and impaired local blood flow. A decrease in local blood flow has been reported to cause insulin resistance. The aim of this study was to examine a possible association of two eNOS polymorphisms, Glu298Asp (G894T) in exon 7 and -786T-C mutation with insulin resistance.n Methods. Genotypes of both Glu298Asp and -786T-C mutation were examined by the PCR-RFLP method. Plasma nitrate and nitrite concentrations were also measured.n Results. The allele frequencies of both polymorphisms showed no considerable differences in 233 non-diabetic subjects and 301 patients with Type II (non-insulin-dependent) diabetes mellitus. Non-diabetic subjects with the -786C allele had (p<0.05) higher fasting plasma insulin and homeostasis model assessment of insulin resistance than those with the -786T/ -786T genotype. Diabetic subjects with -786C allele showed higher HbA1c than those with the -786T/-786T genotype. A euglycaemic hyperinsulinemic clamp study done on 71 of the 301 patients showed a lower glucose infusion rate in diabetic patients with the -786C allele than those without it. In diabetic patients with the -786C allele, plasma nitrate and nitrite concentrations were lower than in subjects without it (p=0.026). No differences were observed between mutant carriers of Glu298Asp and non-carriers among both non-diabetic subjects and Type II diabetic patients.n Conclusions/interpretation. The -786T-C mutation of the eNOS gene is associated with insulin resistance in both Japanese non-diabetic subjects and Type II diabetic patients.

Heart rate elevation and diabetic retinopathy in patients with type 2 diabetes mellitus and normoalbuminuria

To investigate the role of heart rate (HR) and blood pressure (BP) for diabetic retinopathy, 24-h ambulatory HR and BP were monitored for 162 in patients with type 2 diabetes and normoalbuminuria. The fundus was assessed as no retinopathy, simple diabetic retinopathy (SDR) and proliferative retinopathy (PDR). Comparing the highest with the lowest quartile of diabetic duration, the relative risk for retinopathy was 9.3 and for nocturnal HR, it was 3.6. Comparison among three retinopathy groups (no retinopathy, group 1, n=122; SDR, group 2, n=24; Pre-PDR or PDR, group 3, n=16) showed that 24-h and nocturnal HR were significantly higher in group 3 (80+/-9 and 71+/-9 beats per min) than in group 2 (73+/-8 and 64+/-8) and group 1 (72+/-7 and 60+/-7). In multiple logistic analysis, the odds ratio of diabetic duration and nocturnal HR to the existence of retinopathy was 1.17 (95% CI, 1.10-1.25, P=0.00001) and 1.11 (95% CI, 1.05-1.17, P=0.0002). We concluded that diabetic retinopathy is related to diabetic duration and high heart rate in type 2 diabetes mellitus with normoalbuminuria. Heart rate elevation may be a predictor of advanced retinopathy.