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Xin-gang Yao, Xin Xu, Gai-hong Wang, Min Lei, Ling-ling Quan, Yan-hua Cheng, Ping Wan, Jin-pei Zhou, Jing Chen, Li-hong Hu and Xu Shen

Impaired glucose-stimulated insulin secretion (GSIS) and increasing β-cell death are two typical dysfunctions of pancreatic β-cells in individuals that are destined to develop type 2 diabetes, and improvement of β-cell function through GSIS enhancement and/or inhibition of β-cell death is a promising strategy for anti-diabetic therapy. In this study, we discovered that the small molecule, N-(2-benzoylphenyl)-5-bromo-2-thiophenecarboxamide (BBT), was effective in both potentiating GSIS and protecting β-cells from cytokine- or streptozotocin (STZ)-induced cell death. Results of further studies revealed that cAMP/PKA and long-lasting (L-type) voltage-dependent Ca2 + channel/CaMK2 pathways were involved in the action of BBT against GSIS, and that the cAMP/PKA pathway was essential for the protective action of BBT on β-cells. An assay using the model of type 2 diabetic mice induced by high-fat diet combined with STZ (STZ/HFD) demonstrated that BBT administration efficiently restored β-cell functions as indicated by the increased plasma insulin level and decrease in the β-cell loss induced by STZ/HFD. Moreover, the results indicated that BBT treatment decreased fasting blood glucose and HbA1c and improved oral glucose tolerance further highlighting the potential of BBT in anti-hyperglycemia research.

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C. M. Ayling, B. H. Moreland, J. M. Zanelli and D. Schulster

ABSTRACT

The studies describe alterations after hypophysectomy in the proportion of the type-1 and type-2 fibres in rat skeletal muscles, and the effects of replacement treatment with pituitary human (h) GH.

Cytochemical analysis of myosin ATPase, succinate dehydrogenase and lactate dehydrogenase activities in sections of rat hind limb muscles were used as markers of fibre type and revealed that hypophysectomy reduced the proportion of type-1 fibres by 50% in soleus and in extensor digitorum longus muscles. This reduction in the proportion of type-1 fibres was accompanied by the appearance of transitional fibres (type 2C/1B).

Following seven daily injections of hGH (60 mIU/day) to hypophysectomized rats, the proportion of type-1 fibres in both soleus and in extensor digitorum longus was increased with a concomitant reduction in the number of transitional fibres. After 11 days of treatment, all these transitional fibres had reverted back to type-1 fibres. Only hGH was observed to elicit this effect; injections of other pituitary hormones had no effect on the proportions of these transitional fibres.

These alterations in fibre type occurred more rapidly than the changes reported after prolonged electrical stimulation of muscle or following extended exercise.

These findings suggest that hypophysectomy and GH injection can result in a rapid alteration in the fibre composition of skeletal muscle, which may have important implications in terms of the resistance to fatigue and speed of contraction of the muscle.

Journal of Endocrinology (1989) 123, 429–435

Free access

TY Tai, JY Lu, CL Chen, MY Lai, PJ Chen, JH Kao, CZ Lee, HS Lee, LM Chuang and YM Jeng

This study aimed at elucidating the effects of interferon (IFN)-alpha on glucose metabolism in patients with chronic hepatitis B and C infections. Twenty-eight biopsy-proven patients with chronic hepatitis B (ten cases) and hepatitis C (18 cases) were given IFN-alpha for a total of 24 weeks. The patients received a 75 g oral glucose tolerance test (OGTT), glucagon stimulation test, tests for type 1 diabetes-related autoantibodies and an insulin suppression test before and after IFN-alpha therapy. Ten of the 28 patients responded to IFN-alpha therapy. Steady-state plasma glucose of the insulin suppression test decreased significantly in responders (13.32+/-1.48 (S.E.M.) vs 11.33+/-1.19 mmol/l, P=0.0501) but not in non-responders (12.29+/-1.24 vs 11.11+/-0.99 mmol/l, P=0.2110) immediately after completion of IFN-alpha treatment. In the oral glucose tolerance test, no significant difference was observed in plasma glucose in either responders (10.17+/-0.23 vs 10.03+/-0.22 mmol/l) or non-responders (10.11+/-0.22 vs 9.97+/-0.21 mmol/l) 3 Months after completion of IFN-alpha treatment. However, significant differences were noted in C-peptide in both responders (2.90+/-0.13 vs 2.20+/-0.09 nmol/l, P=0.0040) and non-responders (2.45+/-0.11 vs 2.22+/-0.08 nmol/l, P=0.0287) before vs after treatment. The changes of C-peptide in an OGTT between responders and non-responders were also significantly different (P=0.0028), with responders reporting a greater reduction in C-peptide. No case developed autoantibodies during the treatment. In patients who were successfully treated with IFN-alpha, insulin sensitivity improved and their plasma glucose stayed at the same level without secreting as much insulin from islet beta-cells.

Free access

Jennifer A Crookshank, Daniel Serrano, Gen-Sheng Wang, Christopher Patrick, Baylie S Morgan, Marie-France Paré and Fraser W Scott

It is unknown whether there is a gene signature in pancreas which is associated with type 1 diabetes (T1D). We performed partial pancreatectomies on 30-day preinsulitic, diabetes-prone BioBreeding (BBdp) rats to prospectively identify factors involved in early prediabetes. Microarrays of the biopsies revealed downregulation of endoplasmic reticulum (ER) stress, metabolism and apoptosis. Based on these results, additional investigations compared gene expression in control (BBc) and BBdp rats age ~8, 30 and 60 days using RT-qPCR. Neonates had increased ER stress gene expression in pancreas. This was associated with decreased insulin, cleaved caspase-3 and Ins1 whereas Gcg and Pcsk2 were increased. The increase in ER stress was not sustained at 30 days and decreased by 60 days. In parallel, the liver gene profile showed a similar signature in neonates but with an early decrease of the unfolded protein response (UPR) at 30 days. This suggested that changes in the liver precede those in the pancreas. Tnf and Il1b expression was increased in BBdp pancreas in association with increased caspase-1, cleaved caspase-3 and decreased proinsulin area. Glucagon area was increased in both 30-day and 60-day BBdp rats. Increased colocalization of BIP and proinsulin was observed at 60 days in the pancreas, suggesting insulin-related ER dysfunction. We propose that dysregulated metabolism leads to ER stress in neonatal rats long before insulitis, creating a microenvironment in both pancreas and liver that promotes autoimmunity.

Free access

Xiaofeng Wang and Catherine B Chan

n-3 polyunsaturated fatty acids (PUFAs) are a subgroup of fatty acids with broad health benefits, such as lowering blood triglycerides and decreasing the risk of some types of cancer. A beneficial effect of n-3 PUFAs in diabetes is indicated by results from some studies. Defective insulin secretion is a fundamental pathophysiological change in both types 1 and 2 diabetes. Emerging studies have provided evidence of a connection between n-3 PUFAs and improved insulin secretion from pancreatic β-cells. This review summarizes the recent findings in this regard and discusses the potential mechanisms by which n-3 PUFAs influence insulin secretion from pancreatic β-cells.

Free access

Haijiang Wu, Xinna Deng, Yonghong Shi, Ye Su, Jinying Wei and Huijun Duan

Type 2 diabetes mellitus (T2DM) is a chronic disease characterized by glucose metabolic disturbance. A number of transcription factors and coactivators are involved in this process. Peroxisome proliferator-activated receptor gamma coactivator 1 alpha (PGC-1α) is an important transcription coactivator regulating cellular energy metabolism. Accumulating evidence has indicated that PGC-1α is involved in the regulation of T2DM. Therefore, a better understanding of the roles of PGC-1α may shed light on more efficient therapeutic strategies. Here, we review the most recent progress on PGC-1α and discuss its regulatory network in major glucose metabolic tissues such as the liver, skeletal muscle, pancreas and kidney. The significant associations between PGC-1α polymorphisms and T2DM are also discussed in this review.

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P S Leung, H C Chan, L X M Fu and P Y D Wong

Abstract

Previous studies have demonstrated the existence of several key components of the renin–angiotensin system in the pancreas. In the present study, the localization of angiotensin II receptor subtypes, type I (AT1) and type II (AT2), in the mouse and the rat pancreas was studied by immunocytochemistry using specific antipeptide antibodies against the second extracellular loops of AT1 and AT2 receptors in conjunction with confocal laser scanning microscopy. In the mouse, immunoreactivity for AT1 and AT2 was observed predominantly in the endothelia of the blood vessels and the epithelia of the pancreatic ductal system. Similar distribution of immunoreactivity for AT1 and AT2 was also observed. However, the intensity of immunoreactivity for AT1 and AT2 was stronger in the rat than that found in the mouse pancreas. Much weaker immunostaining for both AT1 and AT2, as compared with that found in ductal regions, was also found in the acini of the rodent pancreas. Together with the previous findings, the present results suggest that AT1 and/or AT2 receptors may play a role in regulating pancreatic functions in the rodent.

Journal of Endocrinology (1997) 153, 269–274

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Jennifer H Stern, Gordon I Smith, Shiuwei Chen, Roger H Unger, Samuel Klein and Philipp E Scherer

Hyperglucagonemia, a hallmark in obesity and insulin resistance promotes hepatic glucose output, exacerbating hyperglycemia and thus predisposing to the development type 2 diabetes. As such, glucagon signaling is a key target for new therapeutics to manage insulin resistance. We evaluated glucagon homeostasis in lean and obese mice and people. In lean mice, fasting for 24 h caused a rise in glucagon. In contrast, a decrease in serum glucagon compared to baseline was observed in diet-induced obese mice between 8 and 24 h of fasting. Fasting decreased serum insulin in both lean and obese mice. Accordingly, the glucagon:insulin ratio was unaffected by fasting in obese mice but increased in lean mice. Re-feeding (2 h) restored hyperglucagonemia in obese mice. Pancreatic perfusion studies confirm that fasting (16 h) decreases pancreatic glucagon secretion in obese mice. Consistent with our findings in the mouse, a mixed meal increased serum glucagon and insulin concentrations in obese humans, both of which decreased with time after a meal. Consequently, fasting and re-feeding less robustly affected glucagon:insulin ratios in obese compared to lean participants. The glucoregulatory disturbance in obesity may be driven by inappropriate regulation of glucagon by fasting and a static glucagon:insulin ratio.

Free access

Tetsuhiro Kakimoto, Hirotaka Kimata, Satoshi Iwasaki, Atsushi Fukunari and Hiroyuki Utsumi

Type 2 diabetes is characterized by impaired insulin secretion from pancreatic β-cells. Quantification of the islet area in addition to the insulin-positive area is important for detailed understanding of pancreatic islet histopathology. Here we show computerized automatic recognition of the islets of Langerhans as a novel high-throughput method to quantify islet histopathology. We utilized state-of-the-art tissue pattern recognition software to enable automatic recognition of islets, eliminating the need to laboriously trace islet borders by hand. After training by a histologist, the software successfully recognized even irregularly shaped islets with depleted insulin immunostaining, which were quite difficult to automatically recognize. The results from automated image analysis were highly correlated with those from manual image analysis. To establish whether this automated, rapid, and objective determination of islet area will facilitate studies of islet histopathology, we showed the beneficial effect of chronic exendin-4, a glucagon-like peptide-1 analog, treatment on islet histopathology in Zucker diabetic fatty (ZDF) rats. Automated image analysis provided qualitative and quantitative evidence that exendin-4 treatment ameliorated the loss of pancreatic insulin content and gave rise to islet hypertrophy. We also showed that glucagon-positive α-cell area was decreased significantly in ZDF rat islets with disorganized structure. This study is the first to demonstrate the utility of automatic quantification of digital images to study pancreatic islet histopathology. The proposed method will facilitate evaluations in preclinical drug efficacy studies as well as elucidation of the pathophysiology of diabetes.

Free access

Zhenping Liu, Per Bendix Jeppesen, Søren Gregersen, Lotte Bach Larsen and Kjeld Hermansen

Chronic hyperglycemia and hyperlipidemia cause deleterious effects on β-cell function. Interestingly, increased circulating amino acid (AA) levels are also a characteristic of the prediabetic and diabetic state. The chronic effects of AAs on β-cell function remain to be determined. Isolated mouse islets and INS-1E cells were incubated with or without excess leucine. After 72 h, leucine increased basal insulin secretion and impaired glucose-stimulated insulin secretion in both mouse islets and INS-1E cells, corroborating the existence of aminoacidotoxicity-induced β-cell dysfunction. This took place concomitantly with alterations in proteins and genes involved in insulin granule transport, trafficking (e.g. collapsin response mediator protein 2 and GTP-binding nuclear protein Ran), insulin signal transduction (proteasome subunit α type 6), and the oxidative phosphorylation pathway (cytochrome c oxidase). Leucine downregulated insulin 1 gene expression but upregulated pancreas duodenum homeobox 1 and insulin 2 mRNA expressions. Importantly, cholesterol (CH) accumulated in INS-1E cells concomitantly with upregulation of enzymes involved in CH biosynthesis (e.g. 3-hydroxy-3-methylglutaryl-CoA reductase, mevalonate (diphospho) decarboxylase, and squalene epoxidase) and LDL receptor, whereas triglyceride content was decreased. Our findings indicate that chronic exposure to elevated levels of leucine may have detrimental effects on both β-cell function and insulin sensitivity. Aminoacidotoxicity may play a pathogenic role in the development of type 2 diabetes.