Physical exercise and pancreatic islets Acute and chronic actions on insulin secretion

Diabetes mellitus (DM) is a great public health problem, which attacks part of the world population, being characterized by an imbalance in body glucose homeostasis. Physical exercise is pointed as a protective agent and is also recommended to people with DM. As pancreatic islets present an important role in glucose homeostasis, we aim to study the role of physical exercise (chronic adaptations and acute responses) in pancreatic islets functionality in Wistar male rats. First, animals were divided into two groups: sedentary (S) and aerobic trained (T). At the end of 8 weeks, half of them (S and T) were submitted to an acute exercise session (exercise until exhaustion), being subdivided as acute sedentary (AS) and acute trained (AT). After the experimental period, periepididymal, retroperitoneal and subcutaneous fat pads, blood, soleus muscle and pancreatic islets were collected and prepared for further analysis. From the pancreatic islets, total insulin content, insulin secretion stimulated by glucose, leucine, arginine and carbachol were analyzed. Our results pointed that body adiposity and glucose homeostasis improved with chronic physical exercise. In addition, total insulin content was reduced in group AT, insulin secretion stimulated by glucose was reduced in trained groups (T and AT) and insulin secretion stimulated by carbachol was increased in group AT. There were no significant differences in insulin secretion stimulated by arginine and leucine. We identified a possible modulating action on insulin secretion, probably related to the association of chronic adaptation with an acute response on cholinergic activity in pancreatic islets.

Allelic variations in the vitamin D receptor gene, insulin secretion and parents' heights are independently associated with height in obese children and adolescents

Polymorphisms in the VDR gene were reported to be associated with variations in intrauterine and postnatal growth and with adult height, but also with other traits that are strongly correlated such as the BMI, insulin sensitivity, insulin secretion and hyperglycemia. Here, we assessed the impact of VDR polymorphisms on body height and its interactions with obesity- and glucose tolerance-related traits in obese children and adolescents. We studied 173 prepubertal (Tanner's stage 1) and 146 pubertal (Tanner's stages 2-5) obese children who were referred for a weight-loss program. Three single nucleotide polymorphisms were genotyped: rs1544410 (BsmI), rs7975232 (ApaI) and rs731236 (TaqI). BsmI and TaqI genotypes were significantly associated with height in pubertal children, but the associations did not reach statistical significance in prepubertal children. In stepwise regression analyses, the lean body mass, insulin secretion, BsmI or TaqI genotypes and the father's and the mother's height were independently and positively associated with height in pubertal children. These covariables accounted for 46% of the trait variance. The height of homozygous carriers of the minor allele of BsmI was 0.65 z-scores (4 cm) higher than the height of homozygous carriers of the major allele (P=.0006). Haplotype analyses confirmed the associations of the minor alleles of BsmI and TaqI with increased height. In conclusion, VDR genotypes were significantly associated with height in pubertal obese children. The associations were independent from the effects of confounding traits, such as the body fat mass, insulin secretion, insulin sensitivity and glucose tolerance. (C) 2012 Elsevier Inc. All rights reserved.

The Regulation of Rasd1 Expression by Glucocorticoids and Prolactin Controls Peripartum Maternal Insulin Secretion

The transition from gestation to lactation is characterized by a robust adaptation of maternal pancreatic beta-cells. Consistent with the loss of beta-cell mass, glucose-induced insulin secretion is down-regulated in the islets of early lactating dams. Extensive experimental evidence has demonstrated that the surge of prolactin is responsible for the morphofunctional remodeling of the maternal endocrine pancreas during pregnancy, but the precise molecular mechanisms by which this phenotype is rapidly reversed after delivery are not completely understood. This study investigated whether glucocorticoid-regulated expression of Rasd1/Dexras, a small inhibitoryGprotein, is involved in this physiological plasticity. Immunofluorescent staining demonstrated that Rasd1 is localized within pancreatic beta-cells. Rasd1 expression in insulin-secreting cells was increased by dexamethasone and decreased by prolactin. In vivo data confirmed that Rasd1 expression is decreased in islets from pregnant rats and increased in islets from lactating mothers. Knockdown of Rasd1 abolished the inhibitory effects of dexamethasone on insulin secretion and the protein kinase A, protein kinase C, and ERK1/2 pathways. Chromatin immunoprecipitation experiments revealed that glucocorticoid receptor (GR) and signal transducer and activator of transcription 5b (STAT5b) cooperatively mediate glucocorticoid-induced Rasd1 expression in islets. Prolactin inhibited the stimulatory effect of GR/STAT5b complex on Rasd1 transcription. Overall, our data indicate that the stimulation of Rasd1 expression by glucocorticoid at the end of pregnancy reverses the increased insulin secretion that occurs during pregnancy. Prolactin negatively regulates this pathway by inhibiting GR/STAT5b transcriptional activity on the Rasd1 gene. (Endocrinology 153: 3668-3678, 2012)

Changes in food intake, metabolic parameters and insulin resistance are induced by an isoenergetic, medium-chain fatty acid diet and are associated with modifications in insulin signalling in isolated rat pancreatic islets

LLong-chain fatty acids are capable of inducing alterations in the homoeostasis of glucose-stimulated insulin secretion (GSIS), but the effect of medium-chain fatty acids (MCFA) is poorly elucidated. In the present study, we fed a normoenergetic MCFA diet to male rats from the age of 1 month to the age of 4 months in order to analyse the effect of MCFA on body growth, insulin sensitivity and GSIS. The 45% MCFA substitution of whole fatty acids in the normoenergetic diet impaired whole body growth and resulted in increased body adiposity and hyperinsulinaemia, and reduced insulin-mediated glucose uptake in skeletal muscle. In addition, the isolated pancreatic islets from the MCFA-fed rats showed impaired GSIS and reduced protein kinase Ba (AKT1) protein expression and extracellular signal-related kinase isoforms 1 and 2 (ERK(1/2)) phosphorylation, which were accompanied by increased cellular death. Furthermore, there was a mildly increased cholinergic sensitivity to GSIS. We discuss these findings in further detail, and advocate that they might have a role in the mechanistic pathway leading to the compensatory hyperinsulinaemic status found in this animal model.

LIRAGLUTIDE: NEW RESULTS IN THE TREATMENT OF TYPE 2 DIABETES MELLITUS

New drugs for type 2 diabetes that act on incretin metabolism have been shown to improve glycemic control, reduce body weight and have a low risk for hypoglycemia. Among these, liraglutide is the first glucagon-like peptide 1 (GLP-1) analogue approved for subcutaneous, once-daily administration. According to results from clinical trials, liraglutide is on attractive alternative for the early treatment of type 2 diabetes. The results of the LEAD (Liraglutide Effect and Action in Diabetes) study program demonstrated the efficacy and safety of liraglutide in terms of reduction of glycated hemoglobin (HbA(tc)) levels, significant loss of body weight that was maintained over the long term, better control of the lipid profile and systolic arterial pressure, reduction of the risk for hypoglycemia and reduction of cardiovascular risk. Moreover, the drug was demonstrated to be safe and can be co-administered with oral antidiabetic agents. The product's tolerability has been demonstrated, with nausea as the most common adverse event, which waned from the fourth week of treatment.

Expression of NADPH oxidase in human pancreatic islets

Aims: NADPH oxidase (NOX) is a known source of superoxide anions in phagocytic and non-phagocytic cells. In this study, the presence of this enzyme in human pancreatic islets and the importance of NADPH oxidase in human beta-cell function were investigated. Main methods and key findings: In isolated human pancreatic islets, the expression of NADPH oxidase components was evidenced by real-time PCR (p22(PHOX), p47(PHOX) and p67(PHOX)), Western blotting (p47(PHOX) and p67(PHOX)) and immunohistochemistry (p47(PHOX), p67(PHOX) and gp91(PHOX)). Immunohistochemistry experiments showed co-localization of p47(PHOX), p67(PHOX) and gp91(PHOX) (isoform 2 of NADPH oxidase-NOX2) with insulin secreting cells. Inhibition of NADPH oxidase activity impaired glucose metabolism and glucose-stimulated insulin secretion. Significance: These findings demonstrate the presence of the main intrinsic components of NADPH oxidase comprising the NOX2 isoform in human pancreatic islets, whose activity also contributes to human beta-cell function. (C) 2012 Elsevier Inc. All rights reserved.

Maternal Melatonin Programs the Daily Pattern of Energy Metabolism in Adult Offspring

Background: Shift work was recently described as a factor that increases the risk of Type 2 diabetes mellitus. In addition, rats born to mothers subjected to a phase shift throughout pregnancy are glucose intolerant. However, the mechanism by which a phase shift transmits metabolic information to the offspring has not been determined. Among several endocrine secretions, phase shifts in the light/dark cycle were described as altering the circadian profile of melatonin production by the pineal gland. The present study addresses the importance of maternal melatonin for the metabolic programming of the offspring. Methodology/Principal Findings: Female Wistar rats were submitted to SHAM surgery or pinealectomy (PINX). The PINX rats were divided into two groups and received either melatonin (PM) or vehicle. The SHAM, the PINX vehicle and the PM females were housed with male Wistar rats. Rats were allowed to mate and after weaning, the male and female offspring were subjected to a glucose tolerance test (GTT), a pyruvate tolerance test (PTT) and an insulin tolerance test (ITT). Pancreatic islets were isolated for insulin secretion, and insulin signaling was assessed in the liver and in the skeletal muscle by western blots. We found that male and female rats born to PINX mothers display glucose intolerance at the end of the light phase of the light/dark cycle, but not at the beginning. We further demonstrate that impaired glucose-stimulated insulin secretion and hepatic insulin resistance are mechanisms that may contribute to glucose intolerance in the offspring of PINX mothers. The metabolic programming described here occurs due to an absence of maternal melatonin because the offspring born to PINX mothers treated with melatonin were not glucose intolerant. Conclusions/Significance: The present results support the novel concept that maternal melatonin is responsible for the programming of the daily pattern of energy metabolism in their offspring.

Maternal Moderate Physical Training during Pregnancy Attenuates the Effects of a Low-Protein Diet on the Impaired Secretion of Insulin in Rats: Potential Role for Compensation of Insulin Resistance and Preventing Gestational Diabetes Mellitus

The effects of pregestational and gestational low-to-moderate physical training on insulin secretion in undernourished mothers were evaluated. Virgin female Wistar rats were divided into four groups as follows: control (C, n = 5); trained (T, n = 5); low-protein diet (LP, n = 5); trained with a low-protein diet (T + LP, n = 5). Trained rats ran on a treadmill over a period of 4 weeks before mate (5 days week(-1) and 60 min day(-1), at 65% of VO2max). At pregnancy, the intensity and duration of the exercise were reduced. Low-protein groups were provided with an 8% casein diet, and controls were provided with a 17% casein diet. At third day after delivery, mothers and pups were killed and islets were isolated by collagenase digestion of pancreas and incubated for a further 1 h with medium containing 5.6 or 16.7 mM glucose. T mothers showed increased insulin secretion by isolated islets incubated with 16.7 mM glucose, whereas LP group showed reduced secretion of insulin by isolated islets when compared with both C and LP + T groups. Physical training before and during pregnancy attenuated the effects of a low-protein diet on the secretion of insulin, suggesting a potential role for compensation of insulin resistance and preventing gestational diabetes mellitus.

Serum amyloid A is a growth factor for 3T3-L1 adipocytes, inhibits differentiation and promotes insulin resistance

BACKGROUND/OBJECTIVES: Serum amyloid A (SAA) is an acute-phase protein that has been recently correlated with obesity and insulin resistance. Therefore, we first examined whether human recombinant SAA (rSAA) could affect the proliferation, differentiation and metabolism of 3T3-L1 preadipocytes. DESIGN: Preadipocytes were treated with rSAA and analyzed for changes in viability and [H-3-methyl]-thymidine incorporation as well as cell cycle perturbations using flow cytometry analysis. The mRNA expression profiles of adipogenic factors during the differentiation protocol were also analyzed using real-time PCR. After differentiation, 2-deoxy-[1,2-H-3]-glucose uptake and glycerol release were evaluated. RESULTS: rSAA treatment caused a 2.6-fold increase in cell proliferation, which was consistent with the results from flow cytometry showing that rSAA treatment augmented the percentage of cells in the S phase (60.9 +/- 0.54%) compared with the control cells (39.8 +/- 2.2%, ***P<0.001). The rSAA-induced cell proliferation was mediated by the ERK1/2 signaling pathway, which was assessed by pretreatment with the inhibitor PD98059. However, the exposure of 3T3-L1 cells to rSAA during the differentiation process resulted in attenuated adipogenesis and decreased expression of adipogenesis-related factors. During the first 72 h of differentiation, rSAA inhibited the differentiation process by altering the mRNA expression kinetics of adipogenic transcription factors and proteins, such as PPAR gamma 2 (peroxisome proliferator-activated receptor gamma 2), C/EBP beta (CCAAT/enhancer-binding protein beta) and GLUT4. rSAA prevented the intracellular accumulation of lipids and, in fully differentiated cells, increased lipolysis and prevented 2-deoxy-[1,2-H-3]-glucose uptake, which favors insulin resistance. Additionally, rSAA stimulated the secretion of proinflammatory cytokines interleukin 6 and tumor necrosis factor alpha, and upregulated SAA3 mRNA expression during adipogenesis. CONCLUSIONS: We showed that rSAA enhanced proliferation and inhibited differentiation in 3T3-L1 preadipocytes and altered insulin sensitivity in differentiated cells. These results highlight the complex role of SAA in the adipogenic process and support a direct link between obesity and its co-morbidities such as type II diabetes.

Birth weight, current body mass index, and insulin sensitivity and secretion in young adults in two Latin American populations

Background and aims: Although studies have shown association of birth weight (BW) and adult body mass index (BMI) with insulin sensitivity in adults, there is limited evidence that BW is associated with insulin secretion. We assessed the associations between BW and current BMI with insulin sensitivity and secretion in young Latin American adults. Methods and results: Two birth cohorts, one from Ribeirao Preto, Brazil, based on 1984 participants aged 23-25 years, and another from Limache, Chile, based on 965 participants aged 22-28 years were studied. Weight and height at birth, and current fasting plasma glucose and insulin levels were measured. Insulin sensitivity (HOMA%S) and secretion (HOMA%beta) were estimated using the Homeostatic Model Assessment (HOMA2). Multiple linear regression analyses were carried out to test the associations between BW and adult BMI z-scores on log HOMA%S and log HOMA%beta. BW z-score was associated with HOMA%S in the two populations and HOMA%beta in Ribeirao Preto when adult BMI z-score was included in the model. BW z-score was associated with decreasing insulin secretion even without adjusting for adult BMI, but only in Ribeirao Preto. BMI z-score was associated with low HOMA%S and high HOMA%beta. No interactions between BW and BMI z-scores on insulin sensitivity were shown. Conclusions: This study supports the finding that BW may affect insulin sensitivity and secretion in young adults. The effect size of BW on insulin status is small in comparison to current BMI. (C) 2010 Elsevier B.V. All rights reserved.

Metabolic Disorders and Adipose Tissue Insulin Responsiveness in Neonatally STZ-Induced Diabetic Rats Are Improved by Long-Term Melatonin Treatment

Diabetes mellitus is a product of low insulin sensibility and pancreatic beta-cell insufficiency. Rats with streptozotocin-induced diabetes during the neonatal period by the fifth day of age develop the classic diabetic picture of hyperglycemia, hypoinsulinemia, polyuria, and polydipsia aggravated by insulin resistance in adulthood. In this study, we investigated whether the effect of long-term treatment with melatonin can improve insulin resistance and other metabolic disorders in these animals. At the fourth week of age, diabetic animals started an 8-wk treatment with melatonin (1 mg/kg body weight) in the drinking water at night. Animals were then killing, and the sc, epididymal (EP), and retroperitoneal (RP) fat pads were excised, weighed, and processed for adipocyte isolation for morphometric analysis as well as for measuring glucose uptake, oxidation, and incorporation of glucose into lipids. Blood samples were collected for biochemical assays. Melatonin treatment reduced hyperglycemia, polydipsia, and polyphagia as well as improved insulin resistance as demonstrated by constant glucose disappearance rate and homeostasis model of assessment-insulin resistance. However, melatonin treatment was unable to recover body weight deficiency, fat mass, and adipocyte size of diabetic animals. Adiponectin and fructosamine levels were completely recovered by melatonin, whereas neither plasma insulin level nor insulin secretion capacity was improved in diabetic animals. Furthermore, melatonin caused a marked delay in the sexual development, leaving genital structures smaller than those of nontreated diabetic animals. Melatonin treatment improved the responsiveness of adipocytes to insulin in diabetic animals measured by tests of glucose uptake (sc, EP, and RP), glucose oxidation, and incorporation of glucose into lipids (EP and RP), an effect that seems partially related to an increased expression of insulin receptor substrate 1, acetyl-coenzyme A carboxylase and fatty acid synthase. In conclusion, melatonin treatment was capable of ameliorating the metabolic abnormalities in this particular diabetes model, including insulin resistance and promoting a better long-term glycemic control. (Endocrinology 153: 2178-2188, 2012)

BDKRB2+9/-9 Polymorphism Is Associated with Higher Risk for Diabetes Mellitus in the Brazilian General Population

Some mechanisms have been proposed to explain the role of bradykinin on glucose homeostasis and some studies reported that the BDKRB2 +9/-9 polymorphism was associated to the transcriptional activity of the receptor. In this scenario, the main aim of this study was to evaluate the association of the BDKRB2 +9/-9 polymorphism with diabetes mellitus risk in the Brazilian general population. This study included 1,032 subjects of the general urban population. Anthropometrical, blood pressure, biochemical, and genotype analyses for the BDKRB2 +9/-9 bp insertion/deletion polymorphism were performed. Individuals carrying +9/+9 or +9/-9 genotypes had higher glucose values (84.5 mg/dL versus 80.6 mg/dL, resp.) and higher frequency of diabetes mellitus (7.6% versus 3.6%, resp.) compared to individuals carrying -9/-9, adjusting for age and gender. In addition, higher diabetes mellitus risk was associated to presence of the +9/+9 or +9/-9 genotypes (OR = 1.91; 95% CI = 1.09-4.19; P = 0.03). Our data suggest that the BDKRB2 +9/-9 polymorphism may act as a genetic modulator of glucose homeostasis. It was previously associated to insulin sensitivity, glucose uptake, and insulin secretion, and, in this study, data suggest that the polymorphism may increase susceptibility to chronic metabolic conditions such as diabetes in the Brazilian population.

Monosodium glutamate neonatal treatment induces cardiovascular autonomic function changes in rodents

OBJECTIVES: The aim of this study was to evaluate cardiovascular autonomic function in a rodent obesity model induced by monosodium glutamate injections during the first seven days of life. METHOD: The animals were assigned to control (control, n = 10) and monosodium glutamate (monosodium glutamate, n = 13) groups. Thirty-three weeks after birth, arterial and venous catheters were implanted for arterial pressure measurements, drug administration, and blood sampling. Baroreflex sensitivity was evaluated according to the tachycardic and bradycardic responses induced by sodium nitroprusside and phenylephrine infusion, respectively. Sympathetic and vagal effects were determined by administering methylatropine and propranolol. RESULTS: Body weight, Lee index, and epididymal white adipose tissue values were higher in the monosodium glutamate group in comparison to the control group. The monosodium glutamate-treated rats displayed insulin resistance, as shown by a reduced glucose/insulin index (-62.5%), an increased area under the curve of total insulin secretion during glucose overload (39.3%), and basal hyperinsulinemia. The mean arterial pressure values were higher in the monosodium glutamate rats, whereas heart rate variability (>7 times), bradycardic responses (>4 times), and vagal (similar to 38%) and sympathetic effects (similar to 36%) were reduced as compared to the control group. CONCLUSION: Our results suggest that obesity induced by neonatal monosodium glutamate treatment impairs cardiac autonomic function and most likely contributes to increased arterial pressure and insulin resistance.

Pancreatic islets from dexamethasone-treated rats show alterations in global gene expression and mitochondrial pathways

Chronic administration of glucocorticoids (GC) leads to characteristic features of type 2 diabetes in mammals. The main action of dexamethasone in target cells occurs through modulation of gene expression, although the exact mechanisms are still unknown. We therefore investigated the gene expression profile of pancreatic islets from rats treated with dexamethasone using a cDNA array screening analysis. The expression of selected genes and proteins involved in mitochondria] apoptosis was further analyzed by PCR and immunoblotting. Insulin, triglyceride and free fatty acid plasma levels, as well as glucose-induced insulin secretion, were significantly higher in dexamethasone-treated rats compared with controls. Out of 1176 genes, 60 were up-regulated and 28 were down-regulated by dexamethasone treatment. Some of the modulated genes are involved in apoptosis, stress response, and proliferation pathways. RT-PCR confirmed the cDNA array results for 6 selected genes. Bax alpha protein expression was increased, while Bcl-2 was decreased. In vivo dexamethasone treatment decreased the mitochondrial production of NAD(P)H, and increased ROS production. Concluding, our data indicate that dexamethasone modulates the expression of genes and proteins involved in several pathways of pancreatic-islet cells, and mitochondria dysfunction might be involved in the deleterious effects after long-term GC treatment.

Incidental mild hyperglycemia in children: two MODY 2 families identified in Brazilian subjects

Maturity-onset diabetes of the young (MODY) is characterized by an autosomal dominant mode of inheritance, early onset of hyperglycemia, and defects of insulin secretion. MODY subtypes described present genetic, metabolic, and clinical differences. MODY 2 is characterized by mild asymptomatic fasting hyperglycemia, and rarely requires pharmacological treatment. Hence, precise diagnosis of MODY is important for determining management and prognosis. We report two heterozygous GCK mutations identified during the investigation of short stature. Case 1: a prepubertal 14-year-old boy was evaluated for constitutional delay of growth and puberty. During follow-up, he showed abnormal fasting glucose (113 mg/dL), increased level of HbA1c (6.6%), and negative beta-cell antibodies. His father and two siblings also had slightly elevated blood glucose levels. The mother had normal glycemia. A GCK heterozygous missense mutation, p.Arg191Trp, was identified in the proband. Eighteen family members were screened for this mutation, and 11 had the mutation in heterozygous state. Case 2: a 4-year-old boy investigated for short stature revealed no other laboratorial alterations than elevated glycemia (118 mg/dL); beta-cell antibodies were negative. His father, a paternal aunt, and the paternal grandmother also had slightly elevated glycemia, whereas his mother had normal glycemia. A GCK heterozygous missense mutation, p.Glu221Lys, was identified in the index patient and in four family members. All affected patients had mild elevated glycemia. Individuals with normal glycemia did not harbor mutations. GCK mutation screening should be considered in patients with chronic mild early-onset hyperglycemia, family history of impaired glycemia, and negative beta-cell antibodies. Arq Bras Endocrinol Metab. 2012;56(8):519-24