Glucocorticoids in vivo induce both insulin hypersecretion and enhanced glucose sensitivity of stimulus-secretion coupling in isolated rat islets

Although glucocorticoids are widely used as antiinflammatory agents in clinical therapies, they may cause serious side effects that include insulin resistance and hyperinsulinemia. To study the potential functional adaptations of the islet of Langerhans to in vivo glucocorticoid treatment, adult Wistar rats received dexamethasone (DEX) for 5 consecutive days, whereas controls (CTL) received only saline. The analysis of insulin release in freshly isolated islets showed an enhanced secretion in response to glucose in DEX-treated rats. The study of Ca2 2+ signals by fluorescence microscopy also demonstrated a higher response to glucose in islets from DEX-treated animals. However, no differences in Ca2 2+signals were found between both groups with tolbutamide or KCl, indicating that the alterations were probably related to metabolism. Thus, mitochondrial function was explored by monitoring oxidation of nicotinamide dinucleotide phosphate autofluorescence and mitochondrial membrane potential. Both parameters revealed a higher response to glucose in islets from DEX-treated rats. The mRNA and protein content of glucose transporter-2, glucokinase, and pyruvate kinase was similar in both groups, indicating that changes in these proteins were probably not involved in the increased mitochondrial function. Additionally,weexplored the status of Ca2 2+-dependent signaling kinases. Unlike calmodulin kinase II, we found an augmented phosphorylation level of protein kinase Cα as well as an increased response of the phospholipase C/inositol 1,4,5-triphosphate pathway in DEX-treated rats. Finally, an increased number of docked secretory granules were observed in the β-cells of DEX animals using transmission electron microscopy. Thus, these results demonstrate that islets from glucocorticoid-treated rats develop several adaptations that lead to an enhanced stimulus-secretion coupling and secretory capacity. Copyright © 2010 by The Endocrine Society.

Acute exercise decreases PTP-1B protein level and improves insulin signaling in the liver of old rats

It is now commonly accepted that chronic inflammation associated with obesity during aging induces insulin resistance in the liver. In the present study, we investigated whether the improvement in insulin sensitivity and insulin signaling, mediated by acute exercise, could be associated with modulation of protein-tyrosine phosphatase 1B (PTP-1B) in the liver of old rats. Aging rats were subjected to swimming for two 1.5-h long bouts, separated by a 45 min rest period. Sixteen hours after the exercise, the rats were sacrificed and proteins from the insulin signaling pathway were analyzed by immunoblotting. Our results show that the fat mass was increased in old rats. The reduction in glucose disappearance rate (Kitt) observed in aged rats was restored 16 h after exercise. Aging increased the content of PTP-1B and attenuated insulin signaling in the liver of rats, a phenomenon that was reversed by exercise. Aging rats also increased the IRβ/PTP-1B and IRS-1/PTP-1B association in the liver when compared with young rats. Conversely, in the liver of exercised old rats, IRβ/PTP-1B and IRS-1/PTP-1B association was markedly decreased. Moreover, in the hepatic tissue of old rats, the insulin signalling was decreased and PEPCK and G6Pase levels were increased when compared with young rats. Interestingly, 16 h after acute exercise, the PEPCK and G6Pase protein level were decreased in the old exercised group. These results provide new insights into the mechanisms by which exercise restores insulin signalling in liver during aging. © 2013 Moura et al; licensee BioMed Central Ltd.

Maternal periodontal disease in rats decreases insulin sensitivity and insulin signaling in adult offspring

Background: Periodontal disease during pregnancy has been recognized as one of the causes of preterm and lowbirth- weight (PLBW) babies. Several studies have demonstrated that PLBW babies are prone to developing insulin resistance as adults. Although there is controversy over the association between periodontal disease and PLBW, the phenomenon known as programming can translate any stimulus or aggression experienced during intrauterine growth into physiologic and metabolic alterations in adulthood. The purpose of the present study is to investigate whether the offspring of rats with periodontal disease develop insulin resistance in adulthood. Methods: Ten female Wistar rats were divided into periodontal disease (PED) and control (CN) groups. All rats were mated at 7 days after induction of periodontal disease. Male offspring were divided into two groups: 1) periodontal disease offspring (PEDO; n = 24); and 2) control offspring (CNO; n = 24). Offspring body weight was measured from birth until 75 days. When the offspring reached 75 days old, the following parameters were measured: 1) plasma concentrations of glucose, insulin, fructosamine, lipase, amylase, and tumor necrosis factor-α (TNF-α); 2) insulin sensitivity (IS); and 3) insulin signal transduction (IST) in insulin-sensitive tissues. Results: Low birth weight was not detected in the PEDO group. However, plasma concentrations of glucose, insulin, fructosamine, lipase, amylase, and TNF-α were increased and IS and IST were reduced (P <0.05) in the PEDO group compared with the CNO group. Conclusion: Maternal periodontal disease may induce insulin resistance and reduce IST in adult offspring, but such alterations are not attributable to low birth weight.

Resveratrol reduces chronic inflammation and improves insulin action in the myocardium of high-fat diet-induced obeserats

OBJETIVO: Avaliar o efeito do resveratrol sobre a via de sinalização da insulina e melhora do quadro inflamatório no miocárdio de ratos Wistar obesos induzidos por dieta.MÉTODOS: Ratos Wistar foram divididos em grupos: controle (dieta padrão para roedores), obeso (dieta hiperlipídica) e obeso suplementado com resveratrol (20 mg/kg/dia), por 8 semanas (n=10). Ao final do período experimental, realizou-se o teste de tolerância à insulina, nos tempos 0 (sem insulina), 5, 10, 15, 20, 25 e 30 minutos após injeção intraperitoneal de insulina (2 U/kg). O peso corporal e o tecido adiposo epididimal foram mensurados. Fragmentos do miocárdio foram extraídos para análises da via da insulina e moléculas pró-inflamatórias através de Western blot.RESULTADOS: Os resultados indicam que a intervenção com resveratrol aumenta a constante de decaimento da glicose, fosforilação do receptor de insulina, substrato do receptor de insulina e da proteína quinase B. A suplementação de resveratrol também reduziu os níveis proteicos do fator de necrose tumoral alfa e de moléculas envolvidas com a transdução do sinal pró-inflamatório (quinase indutora do kappa B e fator nuclear kappa B). Os resultados ainda sugerem que a melhora na sensibilidade à insulina e a redução das moléculas pró-inflamatórias ocorreram independentemente da perda de peso corporal e da redução do tecido adiposo epididimal.CONCLUSÃO: A suplementação de resveratrol aumenta a sensibilidade à insulina, o que está relacionado à redução de fatores inflamatórios no miocárdio.

Effects of different intensities of physical exercise on insulin sensitivity and protein kinase B/Akt activity in skeletal muscle of obese mice

Objetivo: Investigar os efeitos do exercício físico agudo com diferentes intensidades sobre a sensibilidade à insulina e a atividade da proteína quinase B/Akt no músculo esquelético de camundongos obesos. Método: Foram utilizados camundongos Swiss, divididos aleatoriamente em quatro grupos, que receberam dieta padrão (grupo controle) ou dieta hiperlipídica (grupos obeso sedentário e grupos obesos exercitados 1 e 2), por período de 12 semanas. Dois diferentes protocolos de exercício foram utilizados: natação durante 1 hora com ou sem sobrecarga de 5% da massa corporal. O teste de tolerância à insulina foi realizado para estimar a sensibilidade à insulina. E os níveis protéicos da proteína quinase B/Akt e de sua fosforilação foram determinados no músculo esquelético dos camundongos, através da técnica de Western blot. Resultado: Uma sessão de exercício físico foi capaz de inibir a resistência à insulina em decorrência de uma dieta hiperlipídica. Foi possível demonstrar um aumento na fosforilação da proteína quinase B/Akt, melhora da sinalização da insulina e redução da glicemia de jejum nos camundongos que realizaram 1 hora de natação sem sobrecarga adicional e nos camundongos que realizaram 1 hora de natação com sobrecarga adicional de 5% de sua massa corporal. Entretanto, não houve diferença significativa entre os grupos que realizaram o exercício em diferentes intensidades. Conclusão: Independente da intensidade, o exercício físico aeróbio conseguiu aumentar a sensibilidade à insulina e a fosforilação da proteína quinase B/Akt, revelando ser uma boa forma de tratamento e prevenção do diabetes tipo 2.

Effects of resistance training frequency on body composition and metabolics and inflammatory markers in overweight postmenopausal women

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Pancreatic Alpha-Cell Dysfunction Contributes to the Disruption of Glucose Homeostasis and Compensatory Insulin Hypersecretion in Glucocorticoid-Treated Rats

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Low-Level Fluoride Exposure Increases Insulin Sensitivity in Experimental Diabetes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Periapical lesions decrease insulin signaling in rat skeletal muscle

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Double-Stranded RNA-Activated Protein Kinase Is a Key Modulator of Insulin Sensitivity in Physiological Conditions and in Obesity in Mice

The molecular integration of nutrient-and pathogen-sensing pathways has become of great interest in understanding the mechanisms of insulin resistance in obesity. The double-stranded RNA-dependent protein kinase (PKR) is one candidate molecule that may provide cross talk between inflammatory and metabolic signaling. The present study was performed to determine, first, the role of PKR in modulating insulin action and glucose metabolism in physiological situations, and second, the role of PKR in insulin resistance in obese mice. We used Pkr(-/-) and Pkr(+/+) mice to investigate the role of PKR in modulating insulin sensitivity, glucose metabolism, and insulin signaling in liver, muscle, and adipose tissue in response to a high-fat diet. Our data show that in lean Pkr(-/-) mice, there is an improvement in insulin sensitivity, and in glucose tolerance, and a reduction in fasting blood glucose, probably related to a decrease in protein phosphatase 2A activity and a parallel increase in insulin-induced thymoma viral oncogene-1 (Akt) phosphorylation. PKR is activated in tissues of obese mice and can induce insulin resistance by directly binding to and inducing insulin receptor substrate (IRS)-1 serine307 phosphorylation or indirectly through modulation of c-Jun N-terminal kinase and inhibitor of kappa B kinase beta. Pkr(-/-) mice were protected from high-fat diet-induced insulin resistance and glucose intolerance and showed improved insulin signaling associated with a reduction in c-Jun N-terminal kinase and inhibitor of kappa B kinase beta phosphorylation in insulin-sensitive tissues. PKR may have a role in insulin sensitivity under normal physiological conditions, probably by modulating protein phosphatase 2A activity and serine-threonine kinase phosphorylation, and certainly, this kinase may represent a central mechanism for the integration of pathogen response and innate immunity with insulin action and metabolic pathways that are critical in obesity. (Endocrinology 153:5261-5274, 2012)

Endurance exercise training increases APPL1 expression and improves insulin signaling in the hepatic tissue of diet-induced obese mice, independently of weight loss

Hepatic insulin resistance is the major contributor to fasting hyperglycemia in type 2 diabetes. The protein kinase Akt plays a central role in the suppression of gluconeogenesis involving forkhead box O1 (Foxo1) and peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1a), and in the control of glycogen synthesis involving the glycogen synthase kinase beta (GSK3 beta) in the liver. It has been demonstrated that endosomal adaptor protein APPL1 interacts with Akt and blocks the association of Akt with its endogenous inhibitor, tribbles-related protein 3 (TRB3), improving the action of insulin in the liver. Here, we demonstrated that chronic exercise increased the basal levels and insulin-induced Akt serine phosphorylation in the liver of diet-induced obese mice. Endurance training was able to increase APPL1 expression and the interaction between APPL1 and Akt. Conversely, training reduced both TRB3 expression and TRB3 and Akt association. The positive effects of exercise on insulin action are reinforced by our findings that showed that trained mice presented an increase in Foxo1 phosphorylation and Foxo1/PGC-1a association, which was accompanied by a reduction in gluconeogenic gene expressions (PEPCK and G6Pase). Finally, exercised animals demonstrated increased at basal and insulin-induced GSK3 beta phosphorylation levels and glycogen content at 24?h after the last session of exercise. Our findings demonstrate that exercise increases insulin action, at least in part, through the enhancement of APPL1 and the reduction of TRB3 expression in the liver of obese mice, independently of weight loss. J. Cell. Physiol. 227: 29172926, 2012. (C) 2011 Wiley Periodicals, Inc.

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)

Trans fatty acid intake is associated with insulin sensitivity but independently of inflammation

High saturated and trans fatty acid intake, the typical dietary pattern of Western populations, favors a proinflammatory status that contributes to generating insulin resistance (IR). We examined whether the consumption of these fatty acids was associated with IR and inflammatory markers. In this cross-sectional study, 127 non-diabetic individuals were allocated to a group without IR and 56 to another with IR, defined as homeostasis model assessment-IR (HOMA-IR) >2.71. Diet was assessed using 24-h food recalls. Multiple linear regression was employed to test independent associations with HOMA-IR. The IR group presented worse anthropometric, biochemical and inflammatory profiles. Energy intake was correlated with abdominal circumference and inversely with adiponectin concentrations (r = -0.227, P = 0.002), while saturated fat intake correlated with inflammatory markers and trans fat with HOMA-IR (r = 0.160, P = 0.030). Abdominal circumference was associated with HOMA-IR (r = 0.430, P < 0.001). In multiple analysis, HOMA-IR remained associated with trans fat intake (beta = 1.416, P = 0.039) and body mass index (beta = 0.390, P < 0.001), and was also inversely associated with adiponectin (beta = -1.637, P = 0.004). Inclusion of other nutrients (saturated fat and added sugar) or other inflammatory markers (IL-6 and CRP) into the models did not modify these associations. Our study supports that trans fat intake impairs insulin sensitivity. The hypothesis that its effect could depend on transcription factors, resulting in expression of proinflammatory genes, was not corroborated. We speculate that trans fat interferes predominantly with insulin signaling via intracellular kinases, which alter insulin receptor substrates.

Quercetin decreases inflammatory response and increases insulin action in skeletal muscle of ob/ob mice and in L6 myotubes

Quercetin is a potent anti-inflammatory flavonoid, but its capacity to modulate insulin sensitivity in obese insulin resistant conditions is unknown. This study investigated the effect of quercetin treatment upon insulin sensitivity of ob/ob mice and its potential molecular mechanisms. Obese ob/ob mice were treated with quercetin for 10 weeks, and L6 myotubes were treated with either palmitate or tumor necrosis factor-alpha (TNF alpha) plus quercetin. Cells and muscles were processed for analysis of glucose transporter 4 (GLUT4), TNF alpha and inducible nitric oxide synthase (iNOS) expression, and c-Jun N-terminal kinase (JNK) and inhibitor of nuclear factor-kappa B (NF-kappa B) kinase (I kappa K) phosphorylation. Myotubes were assayed for glucose uptake and NF-kappa B translocation. Chromatin immunoprecipitation assessed NF-kappa B binding to GLUT4 promoter. Quercetin treatment improved whole body insulin sensitivity by increasing GLUT4 expression and decreasing JNK phosphorylation, and TNF alpha and iNOS expression in skeletal muscle. Quercetin suppressed palmitate-induced upregulation of TNF alpha and iNOS and restored normal levels of GLUT4 in myotubes. In parallel, quercetin suppressed TNF alpha-induced reduction of glucose uptake in myotubes. Nuclear accumulation of NF-kappa B in myotubes and binding of NF-kappa B to GLUT4 promoter in muscles of ob/ob mice were also reduced by quercetin. We demonstrated that quercetin decreased the inflammatory status in skeletal muscle of obese mice and in L6 myotubes. This effect was followed by increased muscle GLUT4, with parallel improvement of insulin sensitivity. These results point out quercetin as a putative strategy to manage inflammatory-related insulin resistance. (C) 2012 Elsevier B.V. All rights reserved.

Loss of insulin-induced activation of TRPM6 magnesium channels results in impaired glucose tolerance during pregnancy

Hypomagnesemia affects insulin resistance and is a risk factor for diabetes mellitus type 2 (DM2) and gestational diabetes mellitus (GDM). Two single nucleotide polymorphisms (SNPs) in the epithelial magnesium channel TRPM6 (V(1393)I, K(1584)E) were predicted to confer susceptibility for DM2. Here, we show using patch clamp analysis and total internal reflection fluorescence microscopy, that insulin stimulates TRPM6 activity via a phosphoinositide 3-kinase and Rac1-mediated elevation of cell surface expression of TRPM6. Interestingly, insulin failed to activate the genetic variants TRPM6(V(1393)I) and TRPM6(K(1584)E), which is likely due to the inability of the insulin signaling pathway to phosphorylate TRPM6(T(1391)) and TRPM6(S(1583)). Moreover, by measuring total glycosylated hemoglobin (TGH) in 997 pregnant women as a measure of glucose control, we demonstrate that TRPM6(V(1393)I) and TRPM6(K(1584)E) are associated with higher TGH and confer a higher likelihood of developing GDM. The impaired response of TRPM6(V(1393)I) and TRPM6(K(1584)E) to insulin represents a unique molecular pathway leading to GDM where the defect is located in TRPM6.