Oxidative stress is produced under diabetic conditions and possibly causes various forms of tissue damage in patients with diabetes. The aim of this study was to examine the involvement of oxidative stress in the progression of pancreatic beta-cell dysfunction in type 2 diabetes and to evaluate the potential usefulness of antioxidants in the treatment of type 2 diabetes. We used diabetic C57BL/KsJ-db/db mice, in whom antioxidant treatment (N-acetyl-L-cysteine [NAC], vitamins C plus E, or both) was started at 6 weeks of age; its effects were evaluated at 10 and 16 weeks of age. According to an intraperitoneal glucose tolerance test, the treatment with NAC retained glucose-stimulated insulin secretion and moderately decreased blood glucose levels. Vitamins C and E were not effective when used alone but slightly effective when used in combination with NAC. No effect on insulin secretion was observed when the same set of antioxidants was given to nondiabetic control mice. Histologic analyses of the pancreases revealed that the beta-cell mass was significantly larger in the diabetic mice treated with the antioxidants than in the untreated mice. As a possible cause, the antioxidant treatment suppressed apoptosis in beta-cells without changing the rate of beta-cell proliferation, supporting the hypothesis that in chronic hyperglycemia, apoptosis induced by oxidative stress causes reduction of beta-cell mass. The antioxidant treatment also preserved the amounts of insulin content and insulin mRNA, making the extent of insulin degranulation less evident. Furthermore, expression of pancreatic and duodenal homeobox factor-1 (PDX-1), a beta-cell-specific transcription factor, was more clearly visible in the nuclei of islet cells after the antioxidant treatment. In conclusion, our observations indicate that antioxidant treatment can exert beneficial effects in diabetes, with preservation of in vivo beta-cell function. This finding suggests a potential usefulness of antioxidants for treating diabetes and provides further support for the implication of oxidative stress in beta-cell dysfunction in diabetes.

Type 2 diabetes is one of the most prevalent and serious metabolic diseases in the world, and insulin resistance and pancreatic ␤-cell dysfunction are the hallmarks of the disease. In this study, we have shown that endoplasmic reticulum (ER) stress, which is provoked under diabetic conditions, plays a crucial role in the insulin resistance found in diabetes by modifying the expression of oxygen-regulated protein 150 (ORP150), a molecular chaperone that protects cells from ER stress. Sense ORP overexpression in the liver of obese diabetic mice significantly improved insulin resistance and markedly ameliorated glucose tolerance. Conversely, expression of antisense ORP150 in the liver of normal mice decreased insulin sensitivity. The phosphorylation state of IRS-1 and Akt, which are key molecules for insulin signaling, and the expression levels of phosphoenolpyruvate carboxykinase and glucose-6-phosphatase, key enzymes of gluconeogenesis, were also altered by ORP150 overexpression. This is the first report showing that ER stress plays a crucial role in the insulin resistance found in diabetes and thus could be a potential therapeutic target for diabetes.

Type 2 diabetes is the most prevalent and serious metabolic disease all over the world, and its hallmarks are pancreatic β-cell dysfunction and insulin resistance. Under diabetic conditions, chronic hyperglycemia and subsequent augmentation of reactive oxygen species (ROS) deteriorate β-cell function and increase insulin resistance which leads to the aggravation of type 2 diabetes. In addition, chronic hyperglycemia and ROS are also involved in the development of atherosclerosis which is often observed under diabetic conditions. Taken together, it is likely that ROS play an important role in the development of type 2 diabetes and atherosclerosis.

The C1/RIPE3b1 (؊118/؊107 bp) binding factor regulates pancreatic-␤-cell-specific and glucose-regulated transcription of the insulin gene. In the present study, the C1/RIPE3b1 activator from mouse ␤TC-3 cell nuclear extracts was purified by DNA affinity chromatography and two-dimensional gel electrophoresis. C1/RIPE3b1 binding activity was found in the roughly 46-kDa fraction at pH 7.0 and pH 4.5, and each contained N-and C-terminal peptides to mouse MafA as determined by peptide mass mapping and tandem spectrometry. MafA was detected in the C1/RIPE3b1 binding complex by using MafA peptide-specific antisera. In addition, MafA was shown to bind within the enhancer region (؊340/؊91 bp) of the endogenous insulin gene in ␤TC-3 cells in the chromatin immunoprecipitation assay. These results strongly suggested that MafA was the ␤-cell-enriched component of the RIPE3b1 activator. However, reverse transcription-PCR analysis demonstrated that mouse islets express not only MafA but also other members of the large Maf family, specifically c-Maf and MafB. Furthermore, immunohistochemical studies revealed that at least MafA and MafB were present within the nuclei of islet ␤ cells and not within pancreas acinar cells. Because MafA, MafB, and c-Maf were each capable of specifically binding to and activating insulin C1 element-mediated expression, our results suggest that all of these factors play a role in islet ␤-cell function.Insulin is an essential regulator of metabolism. This hormone, which is synthesized by the ␤ cells of the islets of Langerhans, increases the storage of glucose, fatty acids, and amino acids through its actions in liver, adipose tissue, and muscle. Experiments performed in vivo with transgenic animals have established that the cis-acting elements controlling ␤-cell-selective expression are located within the insulin enhancer region, which is found between nucleotides Ϫ340 and Ϫ91 relative to the transcription start site. Several key control elements within the enhancer have been identified, including C2 (Ϫ317/ Ϫ311 bp), A3 (Ϫ201/Ϫ196 bp), C1 (Ϫ118/Ϫ107 bp), and E1 (Ϫ100/Ϫ91 bp) (37,60,67). Mutations that decrease the binding affinity of the A3, C1, and E1 activators also reduce glucose-regulated transcription (37,60,67).The activator of insulin C2-element stimulated transcription is Pax6 (61). Proteins in the Pax family all contain a paired box bipartite DNA-binding domain, although Pax6 also has a homeodomain. The Pdx-1 homeodomain protein (formerly known as IPF-1, STF-1, and IDX-1) is the regulator of A3 elementactivated expression (46,48,49,50), whereas the E1 activator is a heterodimer composed of proteins in the basic helix-loophelix family that are enriched in islets (i.e., BETA2 [42]) and generally distributed (i.e., HEB [51] and E2A [2,10,17,65]). In the adult pancreas, Pax6 (61) and BETA2 (42) are found in all islet cell types, whereas Pdx-1 appears to be found only in ␤ cells, a subset of islet ␦ cells (48,49), and exocrine acinar cells (71,80). These transcription factors are necessary for ma...

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.