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Free access

Ruben Rodriguez, Jacqueline N Minas, Jose Pablo Vazquez-Medina, Daisuke Nakano, David G Parkes, Akira Nishiyama and Rudy M Ortiz

Obesity is associated with the inappropriate activation of the renin-angiotensin system (RAS), which increases arterial pressure, impairs insulin secretion and decreases peripheral tissue insulin sensitivity. RAS blockade reverses these detriments; however, it is not clear whether the disease state of the organism and treatment duration determine the beneficial effects of RAS inhibition on insulin secretion and insulin sensitivity. Therefore, the objective of this study was to compare the benefits of acute vs chronic angiotensin receptor type 1 (AT1) blockade started after the onset of obesity, hyperglycemia and hypertension on pancreatic function and peripheral insulin resistance. We assessed adipocyte morphology, glucose intolerance, pancreatic redox balance and insulin secretion after 2 and 11 weeks of AT1 blockade in the following groups of rats: (1) untreated Long-Evans Tokushima Otsuka (lean control; n = 10), (2) untreated Otsuka Long-Evans Tokushima Fatty (OLETF; n = 12) and (3) OLETF + ARB (ARB; 10 mg olmesartan/kg/day by oral gavage; n = 12). Regardless of treatment duration, AT1 blockade decreased systolic blood pressure and fasting plasma triglycerides, whereas chronic AT1 blockade decreased fasting plasma glucose, glucose intolerance and the relative abundance of large adipocytes by 22, 36 and 70%, respectively. AT1 blockade, however, did not improve pancreatic oxidative stress or reverse impaired insulin secretion. Collectively, these data show that AT1 blockade after the onset of obesity, hyperglycemia and hypertension improves peripheral tissue insulin sensitivity, but cannot completely reverse the metabolic derangement characterized by impaired insulin secretion once it has been compromised.

Free access

Saeed Alshahrani and Mauricio Di Fulvio

The intracellular chloride concentration ([Cl]i) in β-cells plays an important role in glucose-stimulated plasma membrane depolarisation and insulin secretion. [Cl]i is maintained above equilibrium in β-cells by the action of Cl co-transporters of the solute carrier family 12 group A (Slc12a). β-Cells express Slc12a1 and Slc12a2, which are known as the bumetanide (BTD)-sensitive Na+-dependent K+2Cl co-transporters 2 and 1 respectively. We show that mice lacking functional alleles of the Slc12a2 gene exhibit better fasting glycaemia, increased insulin secretion in response to glucose, and improved glucose tolerance when compared with wild-type (WT). This phenomenon correlated with increased sensitivity of β-cells to glucose in vitro and with increased β-cell mass. Further, administration of low doses of BTD to mice deficient in Slc12a2 worsened their glucose tolerance, and low concentrations of BTD directly inhibited glucose-stimulated insulin secretion from β-cells deficient in Slc12a2 but expressing intact Slc12a1 genes. Together, our results suggest for the first time that the Slc12a2 gene is not necessary for insulin secretion and that its absence increases β-cell secretory capacity. Further, impairment of insulin secretion with BTD in vivo and in vitro in islets lacking Slc12a2 genes unmasks a potential new role for Slc12a1 in β-cell physiology.

Free access

Ana I Arroba, Alfonso M Lechuga-Sancho, Laura M Frago, Jesús Argente and Julie A Chowen

Cell death is increased in the anterior pituitary of poorly controlled diabetic rats, but anti-apoptotic mechanisms are also activated. We hypothesized that specific cell types are selectively protected against diabetes-induced cell death. To determine when anti-apoptotic mechanisms are activated, streptozotocin-induced diabetic rats were killed after 1, 4, 6 and 8 weeks of evolution. Anterior pituitaries were processed for western blot analysis to determine changes in the intrinsic cell death pathway and upstream kinases involved in cell protection mechanisms. An increase in cell death was detected by ELISA at 4 weeks of diabetes. TUNEL labelling demonstrated that this corresponded to death of primarily lactotrophs, a few somatotrophs, and no thyrotrophs, corticotrophs or gonadotrophs. Levels of phosphorylated (p) Akt were increased at 1 week of diabetes, while pERK1/2 levels increased at 4 weeks and pJNK at 6 weeks. Activation of caspase 3 decreased and anti-apoptotic members of the Bcl-2 protein family increased as early as 1 week after diabetes onset. These changes were coincident with increased IGF-I receptor levels. Levels of X-linked inhibitor of apoptosis protein (XIAP) increased significantly after 6 weeks of diabetes, as did activation of nuclear factor (NF)κB. Double immunohistochemistry indicated that XIAP was expressed in less than 1% of lactotrophs and gonadotrophs, approximately 50% of somatotrophs and more than 90% of corticotrophs and thyrotrophs. These results suggest that some cell survival mechanisms are rapidly activated in the anterior pituitary, even before increased cell death can be detected, while others are more delayed. Furthermore, both pituitary cell death and expression of protective mechanisms such as XIAP are cell-type specific.

Free access

Ashley Gray, William J Aronson, R James Barnard, Hemal Mehta, Junxiang Wan, Jonathan Said, Pinchas Cohen and Colette Galet

Circulating insulin-like growth factor binding protein 1 (IGFBP1) levels vary in response to nutritional status, and pre-clinical studies suggest that elevated IGFBP1 may be protective against the development and progression of prostate cancer. We hypothesized that global deletion of Igfbp1 would accelerate the development of prostate cancer in a c-Myc transgenic mouse model. To test our hypothesis, c-Myc transgenic mice (Myc/BP-1 wild-type (WT)) were crossed and interbred with the Igfbp1 knockout mice (Myc/BP-1 KO). The animals were placed on a high-protein diet at weaning, weighed every 2 weeks, and euthanized at 16 weeks of age. Prostate histopathology was assessed and proliferation status was determined by Ki-67 and proliferating cell nuclear antigen analyses. IGF-related serum biomarkers and body composition were measured. No significant difference in the incidence of prostate cancer was observed between the Myc/BP-1 KO and the Myc/BP-1 WT mice (65 and 80% respectively, P=0.48). Proliferation was significantly decreased by 71% in prostate tissue of Myc/BP-1 KO mice compared with Myc/BP-1 WT mice. Myc/BP-1 KO mice exhibited a significant 6.7% increase in body weight relative to the Myc/BP-1 WT mice that was attributed to an increase in fat mass. Fasting insulin levels were higher in the Myc/BP-1 KO mice without any difference between the groups in fasting glucose concentrations. Thus, contrary to our hypothesis, global deletion of Igfbp1 in a c-Myc transgenic mouse model did not accelerate the development of prostate cancer. Global Igfbp1 deletion did result in a significant increase in body weight and body fat mass. Further studies are required to understand the underlying mechanisms for these metabolic effects.

Free access

P Scherzer, I Nachliel, H Bar-On, MM Popovtzer and E Ziv

Psammomys obesus, a desert rodent, develops diabetes when displaced from its natural environment and fed a high energy diet in the laboratory. This study was designed to examine variations in renal function in relation to the diabetic state with emphasis on changes in Na-K-ATPase activity. The following groups of Psammomys were studied: (1) Animals fed a saltbush diet; a low energy/high salt diet (natural). (2) Animals fed a low energy/low salt diet (laboratory). Both 1 and 2 were normoglycemic and normoinsulinemic and thus served as control. (3) Animals fed a high energy diet (group C) who were hyperglycemic and hyperinsulinemic; this group was divided into two subgroups: C1 presented with glomerular hyperfiltration rate and C2 with glomerular hypofiltration rate. (4) Animals fed a high energy diet presenting with hyperglycemia-hypoinsulinemia (group D). (5) Group D+I, similar to group D but treated with external insulin (2 U/24 h). Groups D and C1, whose glomerular filtration rose above normal by 30% and 70% respectively, exhibited metabolic similarity to Type I and Type II diabetes. In these groups, Na-K-ATPase activity in the cortex increased by 80-100% and in the medulla by 180% (P<0.001 vs control). In group C2 with reduced glomerular filtration rate (GFR), Na-K-ATPase activity did not differ from control. In group D+I, with normalized glomerular filtration rate, Na-K-ATPase activity was similar to control. There was a linear and significant correlation between GFR and Na-K-ATPase activity both in the cortex and in the medulla. These experiments present a well defined animal model of diabetes mellitus. Variations in glucose and in insulin did not correlate with Na-K-ATPase activity. These results clearly demonstrated that Na-K-ATPase activity in the diabetic Psammomys was determined by glomerular filtration but was independent of plasma glucose or insulin levels.

Free access

Mathieu Lafontaine-Lacasse, Geneviève Doré and Frédéric Picard

The activity and levels of SIRT1, which promotes cell survival in several models, are linked to glucose concentrations and cellular energy metabolism. The present study aimed to determine whether impaired Sirt1 activity is involved in the induction of apoptosis by the nutrient-sensing hexosamine biosynthesis pathway (HBP). Pancreatic Nit-1, Rin-m5F, and Min6 β-cells were acutely treated at different doses and times with glucosamine, which enters and stimulates the HBP. Sirt1 levels were genetically modulated by retroviral infection. Expression levels, cellular localization, and activity of apoptosis-related markers were determined by qPCR, immunoblotting, and co-immunoprecipitation. Glucosamine treatment dose- and time dependently induced cell apoptosis in all cell lines studied. HBP stimulation time dependently modified SIRT1 protein levels, notably in the cytoplasm. This was concomitant with increased E2F1 binding to the c-myc promoter. In both NIT-1 and min6 β-cells, genetic knockdown of Sirt1 expression resulted in higher susceptibility to HBP-stimulated apoptosis, whereas overexpression of Sirt1 had the opposite impact. These findings indicate that reduction of SIRT1 levels by hexosamines contributes to β-cell apoptosis. Methods to increase SIRT1 levels or activity could thus prevent the decrease in β-cell mass, notably that observed in type 2 diabetes.

Full access

Hui-Fang Wang, Qing-Qing Yu, Rui-Fang Zheng and Ming Xu

Cardiovascular complications of type 2 diabetes mellitus (T2DM) are associated with vascular remodeling in the arteries. Perivascular sympathetic neurons release an abundance of trophic factors to regulate vascular function via a paracrine signaling. Netrin-1, a diffusible protein that can be secreted outside the cell, is one of common signals of ‘conversation’ between nerve and vessel. The present study investigated whether netrin-1 is a novel modulator of sympathetic neurons paracrine signaling and played a critical role in vascular adventitial remodeling under T2DM. Vascular adventitial remodeling was observed in adventitial fibroblasts (AFs) responding to netrin-1 deficiency in the supernatant from primary rat superior cervical ganglia (SCG) neurons, shown as AFs proliferation, migration, and collagen deposition. Conditioned medium from the high glucose (HG)-treated SCG neurons contributed to AFs remodeling, which was effectively alleviated by exogenous netrin-1 supplementation. Further, it was found that uncoordinated-5-B (Unc5b) was mainly expressed in AFs among netrin-1 specific receptors. Treatment of netrin-1 inhibited H2O2 production derived from NADPH oxidase 4 (NOX4) through the UNC5b/CAMP/PKA signal pathway in AFs remodeling. In vivo, aorta adventitial remodeling was accompanied with the downregulation of netrin-1 in the perivascular sympathetic nerve in T2DM rats. Such abnormalities were restored by netrin-1 intervention, which was associated with the inhibition of NOX4 expression in the aorta adventitia. In conclusion, netrin-1 is a novel modulator of sympathetic neurons paracrine signaling to maintain AFs function. Vascular adventitial remodeling was aggravated by sympathetic neurons paracrine signaling under hyperglycemia, which was ameliorated by netrin-1 treatment through the UNC5b/CAMP/PKA/NOX4 pathway.

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

Paul W Caton, Nanda K Nayuni, Julius Kieswich, Noorafza Q Khan, Muhammed M Yaqoob and Roger Corder

Abnormal elevation of hepatic gluconeogenesis is central to the onset of hyperglycaemia in patients with type 2 diabetes mellitus (T2DM). Metformin corrects hyperglycaemia through inhibition of gluconeogenesis, but its mechanism of action is yet to be fully described. SIRT1 and GCN5 (listed as KAT2A in the MGI Database) have recently been identified as regulators of gluconeogenic gene expression through modulation of levels and activity of the coactivators cAMP-response element binding protein-regulated transcription coactivator 2 (TORC2 or CRTC2 as listed in the MGI Database) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC1α or PPARGC1A as listed in the MGI Database). We report that in db/db mice, metformin (250 mg/kg per day; 7 days) increases hepatic levels of GCN5 protein and mRNA compared with the untreated db/db mice, as well as increases levels of SIRT1 protein and activity relative to controls and untreated db/db mice. These changes were associated with reduced TORC2 protein level and decreased gene expression and activation of the PGC1α gene target phosphoenolpyruvate carboxykinase, and lower plasma glucose and insulin. Inhibition of SIRT1 partially blocked the effects of metformin on gluconeogenesis. SIRT1 was increased through an AMP-activated protein kinase-mediated increase in gene expression of nicotinamide phosphoribosyltransferase, the rate-limiting enzyme of the salvage pathway for NAD+. Moreover, levels of GCN5 were dramatically reduced in db/db mice compared with the controls. This indicates that loss of GCN5-mediated inhibition of gluconeogenesis appears to constitute a major mechanism for the onset of abnormally elevated hepatic glucose production in db/db mice. In conclusion, induction of GCN5 and SIRT1 potentially represents a critical mechanism of action of metformin. In addition, these data identify induction of hepatic GCN5 as a potential therapeutic strategy for treatment of T2DM.

Restricted access

E. M. W. Maunder, A. V. Pillay and A. D. Care

ABSTRACT

An i.v. injection of calcitriol (1,25-(OH)2D3) had no effect within 2·5 h on plasma concentrations of calbindin-D9k (vitamin D-induced calcium-binding protein; CaBP) in hypocalcaemic pigs with inherited vitamin D-dependent rickets type I or in their normocalcaemic siblings or half-siblings. Three days later the plasma concentration of CaBP had doubled in the hypocalcaemic pigs, but was unaltered in the normocalcaemic siblings and half-siblings. Following daily i.v. injections of 1,25-(OH)2D3 for a further 5 days (days 4–8) plasma concentrations of CaBP increased in both the hypocalcaemic (days 4–8) and normocalcaemic (day 8) pigs, the effect being more rapid and greater in the hypocalcaemic 1,25-(OH)2D3-deficient animals. An i.v. injection of 1,25-(OH)2D3 to pure Yucatan pigs also had no effect on plasma concentrations of CaBP within 1·5 h, but in the following 1 h there was some indication of an increase in plasma CaBP levels.

In contrast to the normal pigs, insulin-induced hypoglycaemia did not lead to a peak in plasma CaBP concentrations in the hypocalcaemic pigs. There was also no change in the plasma concentrations of 1,25-(OH)2D3 associated with the peak in plasma CaBP following insulin-induced hypoglycaemia in normocalcaemic pigs. These results suggest that changes in plasma concentrations of 1,25-(OH)2D3 are not directly involved in mediating the increase in plasma CaBP which follows hypoglycaemia induced by insulin in normal pigs, although 1,25-(OH)2D3 probably plays a permissive role.

J. Endocr. (1987) 115, 129–134