Arteriosclerosis, Thrombosis, and Vascular Biology, 2014
Background and aims: Diabetic patients have an increased risk of late stent thrombosis formation ... more Background and aims: Diabetic patients have an increased risk of late stent thrombosis formation and restenosis, after angioplasty. It is hypothesized that delayed re-endothelization is a major underlying problem for late-stent thrombosis and also that rapid re-endothelization is essential for preventing restenosis. Exendin-4 is a stable GLP-1 receptor agonist, which is applied in clinical treatment of diabetes. Beside its insulinotropic action, it may also exert direct beneficial effects on endothelial function. We previously reported that exendin-4 is able to activate the GLP-1 receptor on human coronary artery endothelial cells, leading to increased cell proliferation and decreased apoptosis. Therefore, our aim was to study if exendin-4 can influence endothelialization and decrease neointima formation after vascular injury. Materials and Methods: Balloon injury of the left common carotid artery (LCCA) was performed on Sprague-Dawley rats. Rats were randomized into two groups and ...
American Journal of Physiology-Cell Physiology, 2001
To further evaluate the role of polyamines in insulin production and cell replication in diabetic... more To further evaluate the role of polyamines in insulin production and cell replication in diabetic pancreatic islets, we have studied hyperplastic islets of obese-hyperglycemic mice of different ages and normal islets of the same strain. The aims of the study were to investigate the impact of the diabetic state and aging on polyamine contents and requirements in these islets. Cultured islets from lean and obese animals contained significantly less polyamines than freshly isolated islets. Spermine-to-spermidine ratio was elevated in freshly isolated islets from young obese mice compared with those from lean mice. In islets from old obese animals, spermidine content was decreased, whereas the content of spermine was not different from that of young obese mice. The physiological significance of polyamines was investigated by exposing islets in tissue culture to inhibitors of polyamine synthesis. This treatment caused a partial polyamine depletion in whole islets but failed to affect pol...
Molecular and cellular endocrinology, Jan 15, 2007
The pancreatic beta-cell senses nutrients, neurotransmitters and hormones in the circulating bloo... more The pancreatic beta-cell senses nutrients, neurotransmitters and hormones in the circulating blood. The unique function of the cell is to integrate all these ambient signals into an appropriate insulin secretory rate in order to maintain normal glucose homeostasis. A prerequisite for adequate insulin secretion is proper biosynthesis of the hormone. The rate of biosynthesis needs to be regulated in order to compensate for rapid fluctuations in secretory rate. The synthesis of insulin includes transcription of its gene to mRNA, translation of mRNA into preproinsulin, and processing of preproinsulin via proinsulin into mature insulin. It also involves the induction of additional components of the secretory pathway to support processing, transport and exocytosis of insulin granules. The endoplasmic reticulum (ER) is the cell organelle playing a paramount role in these processes. A functional ER is crucial to all eukaryotic cells, but especially important in a professional hormone-secret...
Exendin-4 is a glucagon-like receptor 1 agonist clinically used against type 2 diabetes that has ... more Exendin-4 is a glucagon-like receptor 1 agonist clinically used against type 2 diabetes that has also shown neuroprotective effects in experimental stroke models. However, while the neuroprotective efficacy of Exendin-4 has been thoroughly investigated if the pharmacological treatment starts before stroke, the therapeutic potential of the Exendin-4 if the treatment starts acutely after stroke has not been clearly determined. Further, a comparison of the neuroprotective efficacy in normal and aged diabetic mice has not been performed. Finally, the cellular mechanisms behind the efficacy of Exendin-4 have been only partially studied. The main objective of this study was to determine the neuroprotective efficacy of Exendin-4 in normal and aged type 2 diabetic mice if the treatment started after stroke in a clinically relevant setting. Furthermore we characterized the Exendin-4 effects on stroke-induced neuroinflammation. Two-month-old healthy and 14-month-old type 2 diabetic/obese mice were subjected to middle cerebral artery occlusion. 5 or 50 mg/kg Exendin-4 was administered intraperitoneally at 1.5, 3 or 4.5 hours thereafter. The treatment was continued (0.2 mg/kg/day) for 1 week. The neuroprotective efficacy was assessed by stroke volume measurement and stereological counting of NeuN-positive neurons. Neuroinflammation was determined by gene expression analysis of M1/M2 microglia subtypes and proinflammatory cytokines. We show neuroprotective efficacy of 50 mg/kg Exendin-4 at 1.5 and 3 hours after stroke in both young healthy and aged diabetic/obese mice. The 5 mg/kg dose was neuroprotective at 1.5 hour only. Proinflammatory markers and M1 phenotype were not impacted by Exendin-4 treatment while M2 markers were significantly up regulated. Our results support the use of Exendin-4 to reduce stroke-damage in the prehospital/early hospitalization setting irrespectively of age/diabetes. The results indicate the polarization of microglia/macrophages towards the M2 reparative phenotype as a potential mechanism of neuroprotection.
Dipeptidyl peptidase 4 (DPP-4) inhibitors are current drugs for the treatment of type 2 diabetes ... more Dipeptidyl peptidase 4 (DPP-4) inhibitors are current drugs for the treatment of type 2 diabetes (T2D) based on their main property to enhance endogenous glucagon-like peptide-1 (GLP-1) levels, thus increasing insulin secretion. However, the mechanism of action of DPP-4 inhibition in extra pancreatic tissues has been poorly investigated and it might occur differently from that induced by GLP-1R agonists. Increased adult neurogenesis by GLP-1R agonists has been suggested to play a role in functional recovery in animal models of brain disorders. We recently showed that the DPP-4 inhibitor linagliptin reduces brain damage after stroke in normal and type 2 diabetic (T2D) mice. The aim of this study was to determine whether linagliptin impacts stroke-induced neurogenesis. T2D was induced by 25 weeks of high-fat diet. Linagliptin treatment was carried out for 7 weeks. Standard diet fed-mice were used as controls. Stroke was induced by middle cerebral artery occlusion 4 weeks into the linagliptin treatment. Neural stem cell (NSC) proliferation/neuroblast formation and striatal neurogenesis/ gliogenesis were assessed 3 weeks after stroke. The effect of linagliptin on NSC viability was also determined in vitro. The results show that linagliptin enhances NSC proliferation in T2D mice but not in normal mice. Linagliptin did not increase NSC number in vitro indicating that the effect of linagliptin on NSC proliferation in T2D is indirect. Neurogenesis and gliogenesis were not affected. In conclusion, we found no correlation between acute neuroprotection (occurring in both T2D and normal mice) and increased NSC proliferation (occurring only in T2D mice). However, our results show that linagliptin evokes a differential response on NSC proliferation after stroke in normal and T2D mice suggesting that DPP-4 inhibition effect in the CNS might go beyond the well known increase of GLP-1.
Liraglutide, an analog of glucagon-like peptide-1 (GLP-1), is an effective anti-diabetic agent wi... more Liraglutide, an analog of glucagon-like peptide-1 (GLP-1), is an effective anti-diabetic agent with few side effects. Since native GLP-1 exerts vascular effects, we investigated changes in pancreatic islet blood flow using a non-radioactive microsphere technique, as well as insulin concentration and glucose tolerance after 17 day treatment with liraglutide in 6-week-old Goto-Kakizaki (GK) rats. Compared to saline-treated control GK rats, liraglutide limited body weight gain, decreased glycemia, improved glucose tolerance and lowered serum insulin concentration. Neither pancreatic or islet blood flow, nor pancreatic insulin content, was affected by liraglutide treatment. We conclude that early intervention with liraglutide decreases glycemia and improves glucose tolerance, thus halting the natural progression towards diabetes, without affecting islet microcirculation or pancreatic insulin content in young female GK rats.
Background Green tea was suggested as a therapeutic agent for the treatment of diabetes more than... more Background Green tea was suggested as a therapeutic agent for the treatment of diabetes more than 70 years ago, but the mechanisms behind its antidiabetic effect remains elusive. In this work, we address this issue by feeding a green tea extract (TEAVIGO™) with a high content of epigallocatechin gallate (EGCG) or the thiazolidinedione PPAR-γ agonist rosiglitazone, as positive control, to db/db mice, an animal model for diabetes. Methods Young (7 week-old) db/db mice were randomized and assigned to receive diets supplemented with or without EGCG or rosiglitazone for 10 weeks. Fasting blood glucose, body weight and food intake was measured along the treatment. Glucose and insulin levels were determined during an oral glucose tolerance test after 10 weeks of treatment. Pancreata were sampled at the end of the study for blinded histomorphometric analysis. Islets were isolated and their mRNA expression analyzed by quantitative RT-PCR. Results The results show that, in db/db mice, EGCG im...
VPAC2 receptor is a potential target for the treatment of type 2 diabetes and may also convey neu... more VPAC2 receptor is a potential target for the treatment of type 2 diabetes and may also convey neuroprotective effects. The aim of this study was to determine the potential efficacy of the VPAC2 receptor agonist Bay 55-9837 against stroke in type-2 diabetic Goto-Kakizaki (GK) rats. GK rats were treated intravenously once daily for 7 days with 0.25 or 0.025 nmol/kg Bay 55-9837 or vehicle before inducing stroke by transient middle cerebral artery occlusion. Treatments were then continued for 7 further days. The glycemic effects of Bay 55-9837 were assessed by measuring fasting blood glucose and oral glucose tolerance. The severity of stroke was measured by assessing ischemic volume. The results show that Bay 55-9837 is not effective in lowering fasting glycemia and does not facilitate glucose disposal. The highest dose of Bay 55-9837 (0.25 nmol/kg) led to increased mortality and brain hemorrhage when compared to control. The lower dose of Bay 55-9837 (0.025 nmol/kg) did not increase mortality rate but caused a threefold increase of the ischemic lesion size with signs of brain hemorrhages as compared to control. In conclusion, Bay 55-9837 did not show antidiabetic or antistroke efficacy in the type 2 diabetic GK rat. Contrarily, Bay 55-9837 treatment led to increased mortality and worsening of the severity of stroke.
Deficiency in insulin secretion is a fundamental part in the pathogenesis of all forms of diabete... more Deficiency in insulin secretion is a fundamental part in the pathogenesis of all forms of diabetes, determined by impaired secretory function and inadequate ß-cell mass. Growth hormone (GH) is a multifunctional hormone, involving in cellular metabolism, mitogenesis and differentiation. In pancreatic islets, GH is involved in maintaining ß-cell mass, stimulating islet hormone production and insulin secretion, and, therefore, plays a role in maintaining normal insulin sensitivity and glucose homeostasis. The intracellular events that convey the GH signal into various cellular responses remain incompletely understood. In this review, we discuss GH signaling in the ß-cells, with emphasis on Ca 2+ handling and insulin secretion regulated by human GH (hGH). hGH-stimulated rise in Ca 2+ i is dependent on extracellular Ca 2+ and is mediated by Ca 2+ -induced Ca 2+ release (CICR) in the ß-cell. This process is triggered by hGH-stimulated activation of the non-receptor tyrosine kinases JAK2 and c-Src, which causes tyrosine phosphorylation of RyRs, resulting in sensitization of CICR. The rise in Ca 2+ i elicited by hGH is associated with an enhanced insulin secretion, effects that are mediated mainly through the prolactin receptor. These mechanisms indicate that a rise in [Ca 2+ ] i elicited by activation of PRLR is JAK2-dependent and is associated with enhanced insulin secretion. In contrast, GH receptor-mediated increase in [Ca 2+ ] i is JAK2-independent and is dissociated from insulin secretion.
Glucocorticoid excess is associated with glucose intolerance and diabetes. In addition to inducin... more Glucocorticoid excess is associated with glucose intolerance and diabetes. In addition to inducing insulin resistance, glucocorticoids impair b-cell function and cause b-cell apoptosis. In this study we show that dexamethasone activates mitogen-activated protein kinases (MAPKs) signaling in MIN6 b-cells, as evident by enhanced phosphorylation of p38 MAPK and c-Jun N-terminal kinase (JNK). In contrast, the integrated stress response pathway was inhibited by dexamethasone. A p38 MAPK inhibitor attenuated dexamethasone-induced apoptosis in b-cells and isolated islets and decreased glucocorticoid receptor phosphorylation at S220. In contrast, a JNK inhibitor augmented DNA fragmentation and dexamethasone-induced formation of cleaved caspase 3. We also show that inhibition of protein phosphatase 5 (PP5) augments apoptosis in dexamethasone-exposed islets and b-cells, with a concomitant activation of p38 MAPK. In conclusion, our data provide evidence that in islets and b-cells, p38 MAPK and JNK phosphorylation work in concert with PP5 to regulate the cytotoxic effects exerted by glucocorticoids.
Background: Type 2 diabetes (T2D) is a strong risk factor for developing neurodegenerative pathol... more Background: Type 2 diabetes (T2D) is a strong risk factor for developing neurodegenerative pathologies. T2D patients have a deficiency in the intestinal incretin hormone GLP-1, which has been shown to exert neuroprotective and anti-inflammatory properties in the brain. Methods: Here we investigate potential sources of GLP-1 in the CNS and the effect of diabetic conditions on the proglucagon mRNA expression in the CNS. The obese mouse model ob/ob, characterized by its high levels of free fatty acids, and the microglia cell line BV-2 were used as models. mRNA expression and protein secretion were analyzed by qPCR, immunofluorescence and ELISA. Results: We show evidence for microglia as a central source of GLP-1 secretion. Furthermore, we observed that expression and secretion are stimulated by cAMP and dependent on microglial activation state. We also show that insulin-resistant conditions reduce the central mRNA expression of proglucagon. The findings that microglial mRNA expression of proglucagon and GLP-1 protein expression are affected by high levels of free fatty acids and that both mRNA expression levels of proglucagon and secretion levels of GLP-1 are affected by inflammatory stimuli could be of pathogenic importance for the premature neurodegeneration and cognitive decline commonly seen in T2D patients, and they may also be harnessed to advantage in therapeutic efforts to prevent or treat such disorders.
Glucocorticoids (GCs) are stress hormones primarily responsible for mobilizing glucose to the cir... more Glucocorticoids (GCs) are stress hormones primarily responsible for mobilizing glucose to the circulation. Due to this effect, insulin resistance and glucose intolerance are concerns in patients with endogenous overproduction of GCs and in patients prescribed GC-based therapy. In addition, hypercortisolemic conditions share many characteristics with the metabolic syndrome. This study reports on a thorough characterization, in terms of glucose control and lipid handling, of a mouse model where corticosterone is given via the drinking water. C57BL/6J mice were treated with corticosterone (100 or 25 μg/ml) or vehicle in their drinking water for 5 weeks after which they were subjected to insulin or glucose tolerance tests. GC-treated mice displayed increased food intake, body weight gain, and central fat deposit accumulations. In addition, the GC treatment led to dyslipidemia as well as accumulation of ectopic fat in the liver and skeletal muscle, having a substantial negative effect on...
Reactive nitrogen and oxygen species have been proposed to be involved in control of insulin rele... more Reactive nitrogen and oxygen species have been proposed to be involved in control of insulin release from the pancreatic b cell. Recent evidence suggests that the supposedly inert anions nitrate and nitrite are metabolized in blood and tissues to form nitric oxide (NO) and other bioactive nitrogen oxides. Here we present evidence for a novel stimulatory role of nitrite in influencing pancreatic islet physiology via a dual mechanism, involving both indirect enhancement (through microcirculation redistribution) and direct insulinotropic effects on the b cell. In rats, intraperitoneal injection of sodium nitrite increased pancreatic islet blood flow by 50% and serum insulin concentrations by 30%, while whole pancreatic blood flow and glycemia remained unaffected. Nitrite also dose dependently enhanced insulin secretion from rat b cells in vitro under nonstimulatory glucose concentrations. This effect was not mimicked by nitrate and was abolished by the guanylyl cyclase (GC) inhibitor ODQ and the NO scavenger cPTIO. It was also mimicked by a cyclic GMP agonist (8-CPT-cGMP) and a classical NO donor (NONOate). Interestingly, a reactive oxygen species scavenger (vitamin E analog, Trolox) abolished the insulin secretion induced by nitrite. We conclude that nitrite exerts dual stimulatory effects on pancreatic islet function, including enhancement of islet blood flow and subsequent insulin secretion in vivo and direct stimulation of insulin release in vitro. The insulinotropic effect of nitrite is cGMP-dependent and involves formation of reactive nitrogen and oxygen species.
Diabetic patients are often treated with an ACEi (angiotensin-converting enzyme inhibitor) or ang... more Diabetic patients are often treated with an ACEi (angiotensin-converting enzyme inhibitor) or angiotensin receptor antagonist against hypertension or albuminuria. These drugs also have a positive impact on glucose tolerance, but the mechanism for this remains elusive. Hypothesizing a positive non-additive effect, we studied whether the angiotensin receptor antagonist telmisartan or the ACEi ramipril acutely influence insulin secretion and glycaemia in vivo in healthy and Type 2 diabetic rats through effects on islet blood perfusion. Telmisartan and ramipril were injected intravenously into anaesthetized non-diabetic Wistar rats or Type 2 diabetic GK (Goto–Kakizaki) rats. In non-diabetic Wistar rats, neither whole PBF (pancreatic blood flow) nor IBF (islet blood flow) were significantly influenced by telmisartan and ramipril, alone or in combination. Renal blood flow was enhanced significantly by telmisartan and ramipril when used in combination, whereas ABF (adrenal blood flow) was ...
The atherosclerotic process is an ongoing dynamic and progressive state arising from endothelial ... more The atherosclerotic process is an ongoing dynamic and progressive state arising from endothelial dysfunction and inflammation. Although suffering from an acute coronary artery disease, patients with Type II diabetes have a poor outcome compared with non-diabetic patients, which may only partly be explained by traditional risk factors. Our purpose was to compare non-traditional risk factors, such as endothelial function, C-reactive protein (CRP) and adiponectin, in Type II diabetic and non-diabetic patients following AMI (acute myocardial infarction). Twenty Type II diabetic patients were compared with 25 non-diabetic patients at baseline (1–3 days from the onset of chest pain) and at 60 days follow-up after an AMI. Using high-resolution ultrasound, brachial artery responses to FMD (flow-mediated vasodilatation; endothelium-dependent vasodilatation) and NTG (nitroglycerine-induced vasodilatation; endothelium-independent vasodilatation) were measured. Plasma levels of CRP and adiponec...
GLP-1 (glucagon-like peptide 1) and its mimetic exendin-4 are used against Type 2 diabetes. C-pep... more GLP-1 (glucagon-like peptide 1) and its mimetic exendin-4 are used against Type 2 diabetes. C-peptide has also proven promising to enhance insulin action. Since insulin secretion in vivo can be rapidly tuned by changes in islet microcirculation, we evaluated the influence of GLP-1, exendin-4 and C-peptide on pancreatic IBF (islet blood flow), and dynamic changes in insulin secretion and glycaemia in the rat. Adult male Wistar rats were divided into four groups given intravenous saline, GLP-1, exendin-4 or C-peptide respectively and administered either saline or 30% glucose. Furthermore, we investigated the effect of intravenous infusion of different doses of exendin-4 into either the femoral vein or the portal vein on islet microcirculation. A non-radioactive microsphere technique was adopted to measure the regional blood flow. Both GLP-1 and exendin-4 prevented the glucose-induced PBF (pancreatic blood flow) redistribution into the islets. Infusion of exendin-4 into the portal vein...
Saturated fatty acids like palmitate induce endoplasmic reticulum (ER) stress in pancreatic beta‐... more Saturated fatty acids like palmitate induce endoplasmic reticulum (ER) stress in pancreatic beta‐cells, an event linked to apoptotic loss of β‐cells in type 2 diabetes. Sustained activation of the ER stress response leads to expression of growth arrest and DNA damage‐inducible protein 34 (GADD34), a regulatory subunit of protein phosphatase 1. In the present study, we have used small interfering RNA in order to knockdown GADD34 expression in insulin‐producing MIN6 cells prior to induction of ER stress by palmitate and evaluated its consequences on RNA‐activated protein kinase‐like ER‐localized eIF2alpha kinase (PERK) signalling and apoptosis. Salubrinal, a specific inhibitor of eukaryotic initiation factor 2α (eIF2α) dephosphorylation, was used as a comparison. Salubrinal treatment augmented palmitate‐induced ER stress and increased GADD34 levels. Both GADD34 knockdown and salubrinal treatment potentiated the cytotoxic effects of palmitate as evidenced by increased DNA fragmentation...
Biochemical and Biophysical Research Communications, 2001
Reversible protein phosphorylation is an important and versatile mechanism by which cells transdu... more Reversible protein phosphorylation is an important and versatile mechanism by which cells transduce external signals into biological responses. Cellular levels of protein phosphorylation are determined by the balanced actions of both protein kinases and protein phosphatases (PPases). Compared with protein kinases, however, serine/threonine PPases have received less attention. In the present study, the effects of certain insulin secretagogues and intracellular second messengers, known to stimulate or inhibit insulin secretion, on the activities of cation-independent serine/threonine PPases were investigated in insulinsecreting RINm5F insulinoma cells. Raising cellular cAMP through adenylyl cyclase activation and phosphodiesterase inhibition in intact cells, evoked inhibitory effects on PPase activities. The addition of a nitric oxide donor, cyclic nucleotides, or proinflammatory prostaglandins to RINm5F cell homogenates at widely different concentrations did not affect type-1 or -2A PPase activities. Phosphatidyl serine seemingly activated PPase-1, while inactivating PPase-2A. A protein kinase C-activating phorbol ester produced the opposite results when added to RINm5F cell homogenates. These studies suggest that several known intracellular second messengers are without effect on -cell PPase activities. However, phosphatidyl serine and protein kinase C activation, whose activity is transiently increased by glucose, may promote insulin release through PPase inactivation, likely contributing to the increase in phosphorylation state that occurs after stimulation of insulin release. Thus, inhibition of protein dephosphorylation may be a novel regulatory mechanism, assisting in activation of the stimulussecretion coupling in insulin-producing cells.
Biochemical and Biophysical Research Communications, 2007
IGFBP-1 is involved in glucohomeostasis, but the direct action of IGFBP-1 on the b-cell remains u... more IGFBP-1 is involved in glucohomeostasis, but the direct action of IGFBP-1 on the b-cell remains unclear. Incubation of dispersed mouse b-cells with IGFBP-1 for 30 min inhibited insulin secretion stimulated by glucose, glucagon-like peptide 1 (GLP-1) or tolbutamide without changes in basal release of insulin and in cytosolic free Ca 2+ concentration ([Ca 2+ ] i ) and NAD(P)H evoked by glucose. In contrast, IGFBP-1 augmented glucose-stimulated insulin secretion in intact islets, associated with a reduced somatostatin secretion. These results suggest a suppressive action of IGFBP-1 on insulin secretion in isolated b-cells through a mechanism distal to energy generating steps and not involving regulation of [Ca 2+ ] i . In contrast, IGFBP-1 amplifies glucose-stimulated insulin secretion in intact islets, possibly by suppressing somatostatin secretion. These direct modulatory influences of IGFBP-1 on insulin secretion may imply an important regulatory role of IGFBP-1 in vivo and in the pathogenesis of type 2 diabetes, in which loss of insulin release is an early pathogenetic event.
Arteriosclerosis, Thrombosis, and Vascular Biology, 2014
Background and aims: Diabetic patients have an increased risk of late stent thrombosis formation ... more Background and aims: Diabetic patients have an increased risk of late stent thrombosis formation and restenosis, after angioplasty. It is hypothesized that delayed re-endothelization is a major underlying problem for late-stent thrombosis and also that rapid re-endothelization is essential for preventing restenosis. Exendin-4 is a stable GLP-1 receptor agonist, which is applied in clinical treatment of diabetes. Beside its insulinotropic action, it may also exert direct beneficial effects on endothelial function. We previously reported that exendin-4 is able to activate the GLP-1 receptor on human coronary artery endothelial cells, leading to increased cell proliferation and decreased apoptosis. Therefore, our aim was to study if exendin-4 can influence endothelialization and decrease neointima formation after vascular injury. Materials and Methods: Balloon injury of the left common carotid artery (LCCA) was performed on Sprague-Dawley rats. Rats were randomized into two groups and ...
American Journal of Physiology-Cell Physiology, 2001
To further evaluate the role of polyamines in insulin production and cell replication in diabetic... more To further evaluate the role of polyamines in insulin production and cell replication in diabetic pancreatic islets, we have studied hyperplastic islets of obese-hyperglycemic mice of different ages and normal islets of the same strain. The aims of the study were to investigate the impact of the diabetic state and aging on polyamine contents and requirements in these islets. Cultured islets from lean and obese animals contained significantly less polyamines than freshly isolated islets. Spermine-to-spermidine ratio was elevated in freshly isolated islets from young obese mice compared with those from lean mice. In islets from old obese animals, spermidine content was decreased, whereas the content of spermine was not different from that of young obese mice. The physiological significance of polyamines was investigated by exposing islets in tissue culture to inhibitors of polyamine synthesis. This treatment caused a partial polyamine depletion in whole islets but failed to affect pol...
Molecular and cellular endocrinology, Jan 15, 2007
The pancreatic beta-cell senses nutrients, neurotransmitters and hormones in the circulating bloo... more The pancreatic beta-cell senses nutrients, neurotransmitters and hormones in the circulating blood. The unique function of the cell is to integrate all these ambient signals into an appropriate insulin secretory rate in order to maintain normal glucose homeostasis. A prerequisite for adequate insulin secretion is proper biosynthesis of the hormone. The rate of biosynthesis needs to be regulated in order to compensate for rapid fluctuations in secretory rate. The synthesis of insulin includes transcription of its gene to mRNA, translation of mRNA into preproinsulin, and processing of preproinsulin via proinsulin into mature insulin. It also involves the induction of additional components of the secretory pathway to support processing, transport and exocytosis of insulin granules. The endoplasmic reticulum (ER) is the cell organelle playing a paramount role in these processes. A functional ER is crucial to all eukaryotic cells, but especially important in a professional hormone-secret...
Exendin-4 is a glucagon-like receptor 1 agonist clinically used against type 2 diabetes that has ... more Exendin-4 is a glucagon-like receptor 1 agonist clinically used against type 2 diabetes that has also shown neuroprotective effects in experimental stroke models. However, while the neuroprotective efficacy of Exendin-4 has been thoroughly investigated if the pharmacological treatment starts before stroke, the therapeutic potential of the Exendin-4 if the treatment starts acutely after stroke has not been clearly determined. Further, a comparison of the neuroprotective efficacy in normal and aged diabetic mice has not been performed. Finally, the cellular mechanisms behind the efficacy of Exendin-4 have been only partially studied. The main objective of this study was to determine the neuroprotective efficacy of Exendin-4 in normal and aged type 2 diabetic mice if the treatment started after stroke in a clinically relevant setting. Furthermore we characterized the Exendin-4 effects on stroke-induced neuroinflammation. Two-month-old healthy and 14-month-old type 2 diabetic/obese mice were subjected to middle cerebral artery occlusion. 5 or 50 mg/kg Exendin-4 was administered intraperitoneally at 1.5, 3 or 4.5 hours thereafter. The treatment was continued (0.2 mg/kg/day) for 1 week. The neuroprotective efficacy was assessed by stroke volume measurement and stereological counting of NeuN-positive neurons. Neuroinflammation was determined by gene expression analysis of M1/M2 microglia subtypes and proinflammatory cytokines. We show neuroprotective efficacy of 50 mg/kg Exendin-4 at 1.5 and 3 hours after stroke in both young healthy and aged diabetic/obese mice. The 5 mg/kg dose was neuroprotective at 1.5 hour only. Proinflammatory markers and M1 phenotype were not impacted by Exendin-4 treatment while M2 markers were significantly up regulated. Our results support the use of Exendin-4 to reduce stroke-damage in the prehospital/early hospitalization setting irrespectively of age/diabetes. The results indicate the polarization of microglia/macrophages towards the M2 reparative phenotype as a potential mechanism of neuroprotection.
Dipeptidyl peptidase 4 (DPP-4) inhibitors are current drugs for the treatment of type 2 diabetes ... more Dipeptidyl peptidase 4 (DPP-4) inhibitors are current drugs for the treatment of type 2 diabetes (T2D) based on their main property to enhance endogenous glucagon-like peptide-1 (GLP-1) levels, thus increasing insulin secretion. However, the mechanism of action of DPP-4 inhibition in extra pancreatic tissues has been poorly investigated and it might occur differently from that induced by GLP-1R agonists. Increased adult neurogenesis by GLP-1R agonists has been suggested to play a role in functional recovery in animal models of brain disorders. We recently showed that the DPP-4 inhibitor linagliptin reduces brain damage after stroke in normal and type 2 diabetic (T2D) mice. The aim of this study was to determine whether linagliptin impacts stroke-induced neurogenesis. T2D was induced by 25 weeks of high-fat diet. Linagliptin treatment was carried out for 7 weeks. Standard diet fed-mice were used as controls. Stroke was induced by middle cerebral artery occlusion 4 weeks into the linagliptin treatment. Neural stem cell (NSC) proliferation/neuroblast formation and striatal neurogenesis/ gliogenesis were assessed 3 weeks after stroke. The effect of linagliptin on NSC viability was also determined in vitro. The results show that linagliptin enhances NSC proliferation in T2D mice but not in normal mice. Linagliptin did not increase NSC number in vitro indicating that the effect of linagliptin on NSC proliferation in T2D is indirect. Neurogenesis and gliogenesis were not affected. In conclusion, we found no correlation between acute neuroprotection (occurring in both T2D and normal mice) and increased NSC proliferation (occurring only in T2D mice). However, our results show that linagliptin evokes a differential response on NSC proliferation after stroke in normal and T2D mice suggesting that DPP-4 inhibition effect in the CNS might go beyond the well known increase of GLP-1.
Liraglutide, an analog of glucagon-like peptide-1 (GLP-1), is an effective anti-diabetic agent wi... more Liraglutide, an analog of glucagon-like peptide-1 (GLP-1), is an effective anti-diabetic agent with few side effects. Since native GLP-1 exerts vascular effects, we investigated changes in pancreatic islet blood flow using a non-radioactive microsphere technique, as well as insulin concentration and glucose tolerance after 17 day treatment with liraglutide in 6-week-old Goto-Kakizaki (GK) rats. Compared to saline-treated control GK rats, liraglutide limited body weight gain, decreased glycemia, improved glucose tolerance and lowered serum insulin concentration. Neither pancreatic or islet blood flow, nor pancreatic insulin content, was affected by liraglutide treatment. We conclude that early intervention with liraglutide decreases glycemia and improves glucose tolerance, thus halting the natural progression towards diabetes, without affecting islet microcirculation or pancreatic insulin content in young female GK rats.
Background Green tea was suggested as a therapeutic agent for the treatment of diabetes more than... more Background Green tea was suggested as a therapeutic agent for the treatment of diabetes more than 70 years ago, but the mechanisms behind its antidiabetic effect remains elusive. In this work, we address this issue by feeding a green tea extract (TEAVIGO™) with a high content of epigallocatechin gallate (EGCG) or the thiazolidinedione PPAR-γ agonist rosiglitazone, as positive control, to db/db mice, an animal model for diabetes. Methods Young (7 week-old) db/db mice were randomized and assigned to receive diets supplemented with or without EGCG or rosiglitazone for 10 weeks. Fasting blood glucose, body weight and food intake was measured along the treatment. Glucose and insulin levels were determined during an oral glucose tolerance test after 10 weeks of treatment. Pancreata were sampled at the end of the study for blinded histomorphometric analysis. Islets were isolated and their mRNA expression analyzed by quantitative RT-PCR. Results The results show that, in db/db mice, EGCG im...
VPAC2 receptor is a potential target for the treatment of type 2 diabetes and may also convey neu... more VPAC2 receptor is a potential target for the treatment of type 2 diabetes and may also convey neuroprotective effects. The aim of this study was to determine the potential efficacy of the VPAC2 receptor agonist Bay 55-9837 against stroke in type-2 diabetic Goto-Kakizaki (GK) rats. GK rats were treated intravenously once daily for 7 days with 0.25 or 0.025 nmol/kg Bay 55-9837 or vehicle before inducing stroke by transient middle cerebral artery occlusion. Treatments were then continued for 7 further days. The glycemic effects of Bay 55-9837 were assessed by measuring fasting blood glucose and oral glucose tolerance. The severity of stroke was measured by assessing ischemic volume. The results show that Bay 55-9837 is not effective in lowering fasting glycemia and does not facilitate glucose disposal. The highest dose of Bay 55-9837 (0.25 nmol/kg) led to increased mortality and brain hemorrhage when compared to control. The lower dose of Bay 55-9837 (0.025 nmol/kg) did not increase mortality rate but caused a threefold increase of the ischemic lesion size with signs of brain hemorrhages as compared to control. In conclusion, Bay 55-9837 did not show antidiabetic or antistroke efficacy in the type 2 diabetic GK rat. Contrarily, Bay 55-9837 treatment led to increased mortality and worsening of the severity of stroke.
Deficiency in insulin secretion is a fundamental part in the pathogenesis of all forms of diabete... more Deficiency in insulin secretion is a fundamental part in the pathogenesis of all forms of diabetes, determined by impaired secretory function and inadequate ß-cell mass. Growth hormone (GH) is a multifunctional hormone, involving in cellular metabolism, mitogenesis and differentiation. In pancreatic islets, GH is involved in maintaining ß-cell mass, stimulating islet hormone production and insulin secretion, and, therefore, plays a role in maintaining normal insulin sensitivity and glucose homeostasis. The intracellular events that convey the GH signal into various cellular responses remain incompletely understood. In this review, we discuss GH signaling in the ß-cells, with emphasis on Ca 2+ handling and insulin secretion regulated by human GH (hGH). hGH-stimulated rise in Ca 2+ i is dependent on extracellular Ca 2+ and is mediated by Ca 2+ -induced Ca 2+ release (CICR) in the ß-cell. This process is triggered by hGH-stimulated activation of the non-receptor tyrosine kinases JAK2 and c-Src, which causes tyrosine phosphorylation of RyRs, resulting in sensitization of CICR. The rise in Ca 2+ i elicited by hGH is associated with an enhanced insulin secretion, effects that are mediated mainly through the prolactin receptor. These mechanisms indicate that a rise in [Ca 2+ ] i elicited by activation of PRLR is JAK2-dependent and is associated with enhanced insulin secretion. In contrast, GH receptor-mediated increase in [Ca 2+ ] i is JAK2-independent and is dissociated from insulin secretion.
Glucocorticoid excess is associated with glucose intolerance and diabetes. In addition to inducin... more Glucocorticoid excess is associated with glucose intolerance and diabetes. In addition to inducing insulin resistance, glucocorticoids impair b-cell function and cause b-cell apoptosis. In this study we show that dexamethasone activates mitogen-activated protein kinases (MAPKs) signaling in MIN6 b-cells, as evident by enhanced phosphorylation of p38 MAPK and c-Jun N-terminal kinase (JNK). In contrast, the integrated stress response pathway was inhibited by dexamethasone. A p38 MAPK inhibitor attenuated dexamethasone-induced apoptosis in b-cells and isolated islets and decreased glucocorticoid receptor phosphorylation at S220. In contrast, a JNK inhibitor augmented DNA fragmentation and dexamethasone-induced formation of cleaved caspase 3. We also show that inhibition of protein phosphatase 5 (PP5) augments apoptosis in dexamethasone-exposed islets and b-cells, with a concomitant activation of p38 MAPK. In conclusion, our data provide evidence that in islets and b-cells, p38 MAPK and JNK phosphorylation work in concert with PP5 to regulate the cytotoxic effects exerted by glucocorticoids.
Background: Type 2 diabetes (T2D) is a strong risk factor for developing neurodegenerative pathol... more Background: Type 2 diabetes (T2D) is a strong risk factor for developing neurodegenerative pathologies. T2D patients have a deficiency in the intestinal incretin hormone GLP-1, which has been shown to exert neuroprotective and anti-inflammatory properties in the brain. Methods: Here we investigate potential sources of GLP-1 in the CNS and the effect of diabetic conditions on the proglucagon mRNA expression in the CNS. The obese mouse model ob/ob, characterized by its high levels of free fatty acids, and the microglia cell line BV-2 were used as models. mRNA expression and protein secretion were analyzed by qPCR, immunofluorescence and ELISA. Results: We show evidence for microglia as a central source of GLP-1 secretion. Furthermore, we observed that expression and secretion are stimulated by cAMP and dependent on microglial activation state. We also show that insulin-resistant conditions reduce the central mRNA expression of proglucagon. The findings that microglial mRNA expression of proglucagon and GLP-1 protein expression are affected by high levels of free fatty acids and that both mRNA expression levels of proglucagon and secretion levels of GLP-1 are affected by inflammatory stimuli could be of pathogenic importance for the premature neurodegeneration and cognitive decline commonly seen in T2D patients, and they may also be harnessed to advantage in therapeutic efforts to prevent or treat such disorders.
Glucocorticoids (GCs) are stress hormones primarily responsible for mobilizing glucose to the cir... more Glucocorticoids (GCs) are stress hormones primarily responsible for mobilizing glucose to the circulation. Due to this effect, insulin resistance and glucose intolerance are concerns in patients with endogenous overproduction of GCs and in patients prescribed GC-based therapy. In addition, hypercortisolemic conditions share many characteristics with the metabolic syndrome. This study reports on a thorough characterization, in terms of glucose control and lipid handling, of a mouse model where corticosterone is given via the drinking water. C57BL/6J mice were treated with corticosterone (100 or 25 μg/ml) or vehicle in their drinking water for 5 weeks after which they were subjected to insulin or glucose tolerance tests. GC-treated mice displayed increased food intake, body weight gain, and central fat deposit accumulations. In addition, the GC treatment led to dyslipidemia as well as accumulation of ectopic fat in the liver and skeletal muscle, having a substantial negative effect on...
Reactive nitrogen and oxygen species have been proposed to be involved in control of insulin rele... more Reactive nitrogen and oxygen species have been proposed to be involved in control of insulin release from the pancreatic b cell. Recent evidence suggests that the supposedly inert anions nitrate and nitrite are metabolized in blood and tissues to form nitric oxide (NO) and other bioactive nitrogen oxides. Here we present evidence for a novel stimulatory role of nitrite in influencing pancreatic islet physiology via a dual mechanism, involving both indirect enhancement (through microcirculation redistribution) and direct insulinotropic effects on the b cell. In rats, intraperitoneal injection of sodium nitrite increased pancreatic islet blood flow by 50% and serum insulin concentrations by 30%, while whole pancreatic blood flow and glycemia remained unaffected. Nitrite also dose dependently enhanced insulin secretion from rat b cells in vitro under nonstimulatory glucose concentrations. This effect was not mimicked by nitrate and was abolished by the guanylyl cyclase (GC) inhibitor ODQ and the NO scavenger cPTIO. It was also mimicked by a cyclic GMP agonist (8-CPT-cGMP) and a classical NO donor (NONOate). Interestingly, a reactive oxygen species scavenger (vitamin E analog, Trolox) abolished the insulin secretion induced by nitrite. We conclude that nitrite exerts dual stimulatory effects on pancreatic islet function, including enhancement of islet blood flow and subsequent insulin secretion in vivo and direct stimulation of insulin release in vitro. The insulinotropic effect of nitrite is cGMP-dependent and involves formation of reactive nitrogen and oxygen species.
Diabetic patients are often treated with an ACEi (angiotensin-converting enzyme inhibitor) or ang... more Diabetic patients are often treated with an ACEi (angiotensin-converting enzyme inhibitor) or angiotensin receptor antagonist against hypertension or albuminuria. These drugs also have a positive impact on glucose tolerance, but the mechanism for this remains elusive. Hypothesizing a positive non-additive effect, we studied whether the angiotensin receptor antagonist telmisartan or the ACEi ramipril acutely influence insulin secretion and glycaemia in vivo in healthy and Type 2 diabetic rats through effects on islet blood perfusion. Telmisartan and ramipril were injected intravenously into anaesthetized non-diabetic Wistar rats or Type 2 diabetic GK (Goto–Kakizaki) rats. In non-diabetic Wistar rats, neither whole PBF (pancreatic blood flow) nor IBF (islet blood flow) were significantly influenced by telmisartan and ramipril, alone or in combination. Renal blood flow was enhanced significantly by telmisartan and ramipril when used in combination, whereas ABF (adrenal blood flow) was ...
The atherosclerotic process is an ongoing dynamic and progressive state arising from endothelial ... more The atherosclerotic process is an ongoing dynamic and progressive state arising from endothelial dysfunction and inflammation. Although suffering from an acute coronary artery disease, patients with Type II diabetes have a poor outcome compared with non-diabetic patients, which may only partly be explained by traditional risk factors. Our purpose was to compare non-traditional risk factors, such as endothelial function, C-reactive protein (CRP) and adiponectin, in Type II diabetic and non-diabetic patients following AMI (acute myocardial infarction). Twenty Type II diabetic patients were compared with 25 non-diabetic patients at baseline (1–3 days from the onset of chest pain) and at 60 days follow-up after an AMI. Using high-resolution ultrasound, brachial artery responses to FMD (flow-mediated vasodilatation; endothelium-dependent vasodilatation) and NTG (nitroglycerine-induced vasodilatation; endothelium-independent vasodilatation) were measured. Plasma levels of CRP and adiponec...
GLP-1 (glucagon-like peptide 1) and its mimetic exendin-4 are used against Type 2 diabetes. C-pep... more GLP-1 (glucagon-like peptide 1) and its mimetic exendin-4 are used against Type 2 diabetes. C-peptide has also proven promising to enhance insulin action. Since insulin secretion in vivo can be rapidly tuned by changes in islet microcirculation, we evaluated the influence of GLP-1, exendin-4 and C-peptide on pancreatic IBF (islet blood flow), and dynamic changes in insulin secretion and glycaemia in the rat. Adult male Wistar rats were divided into four groups given intravenous saline, GLP-1, exendin-4 or C-peptide respectively and administered either saline or 30% glucose. Furthermore, we investigated the effect of intravenous infusion of different doses of exendin-4 into either the femoral vein or the portal vein on islet microcirculation. A non-radioactive microsphere technique was adopted to measure the regional blood flow. Both GLP-1 and exendin-4 prevented the glucose-induced PBF (pancreatic blood flow) redistribution into the islets. Infusion of exendin-4 into the portal vein...
Saturated fatty acids like palmitate induce endoplasmic reticulum (ER) stress in pancreatic beta‐... more Saturated fatty acids like palmitate induce endoplasmic reticulum (ER) stress in pancreatic beta‐cells, an event linked to apoptotic loss of β‐cells in type 2 diabetes. Sustained activation of the ER stress response leads to expression of growth arrest and DNA damage‐inducible protein 34 (GADD34), a regulatory subunit of protein phosphatase 1. In the present study, we have used small interfering RNA in order to knockdown GADD34 expression in insulin‐producing MIN6 cells prior to induction of ER stress by palmitate and evaluated its consequences on RNA‐activated protein kinase‐like ER‐localized eIF2alpha kinase (PERK) signalling and apoptosis. Salubrinal, a specific inhibitor of eukaryotic initiation factor 2α (eIF2α) dephosphorylation, was used as a comparison. Salubrinal treatment augmented palmitate‐induced ER stress and increased GADD34 levels. Both GADD34 knockdown and salubrinal treatment potentiated the cytotoxic effects of palmitate as evidenced by increased DNA fragmentation...
Biochemical and Biophysical Research Communications, 2001
Reversible protein phosphorylation is an important and versatile mechanism by which cells transdu... more Reversible protein phosphorylation is an important and versatile mechanism by which cells transduce external signals into biological responses. Cellular levels of protein phosphorylation are determined by the balanced actions of both protein kinases and protein phosphatases (PPases). Compared with protein kinases, however, serine/threonine PPases have received less attention. In the present study, the effects of certain insulin secretagogues and intracellular second messengers, known to stimulate or inhibit insulin secretion, on the activities of cation-independent serine/threonine PPases were investigated in insulinsecreting RINm5F insulinoma cells. Raising cellular cAMP through adenylyl cyclase activation and phosphodiesterase inhibition in intact cells, evoked inhibitory effects on PPase activities. The addition of a nitric oxide donor, cyclic nucleotides, or proinflammatory prostaglandins to RINm5F cell homogenates at widely different concentrations did not affect type-1 or -2A PPase activities. Phosphatidyl serine seemingly activated PPase-1, while inactivating PPase-2A. A protein kinase C-activating phorbol ester produced the opposite results when added to RINm5F cell homogenates. These studies suggest that several known intracellular second messengers are without effect on -cell PPase activities. However, phosphatidyl serine and protein kinase C activation, whose activity is transiently increased by glucose, may promote insulin release through PPase inactivation, likely contributing to the increase in phosphorylation state that occurs after stimulation of insulin release. Thus, inhibition of protein dephosphorylation may be a novel regulatory mechanism, assisting in activation of the stimulussecretion coupling in insulin-producing cells.
Biochemical and Biophysical Research Communications, 2007
IGFBP-1 is involved in glucohomeostasis, but the direct action of IGFBP-1 on the b-cell remains u... more IGFBP-1 is involved in glucohomeostasis, but the direct action of IGFBP-1 on the b-cell remains unclear. Incubation of dispersed mouse b-cells with IGFBP-1 for 30 min inhibited insulin secretion stimulated by glucose, glucagon-like peptide 1 (GLP-1) or tolbutamide without changes in basal release of insulin and in cytosolic free Ca 2+ concentration ([Ca 2+ ] i ) and NAD(P)H evoked by glucose. In contrast, IGFBP-1 augmented glucose-stimulated insulin secretion in intact islets, associated with a reduced somatostatin secretion. These results suggest a suppressive action of IGFBP-1 on insulin secretion in isolated b-cells through a mechanism distal to energy generating steps and not involving regulation of [Ca 2+ ] i . In contrast, IGFBP-1 amplifies glucose-stimulated insulin secretion in intact islets, possibly by suppressing somatostatin secretion. These direct modulatory influences of IGFBP-1 on insulin secretion may imply an important regulatory role of IGFBP-1 in vivo and in the pathogenesis of type 2 diabetes, in which loss of insulin release is an early pathogenetic event.
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Papers by Åke Sjöholm