Cláudio T. De Souza

Unsaturated fatty acids revert diet-induced hypothalamic inflammation in obesity.

Background In experimental models, hypothalamic inflammation is an early and determining factor in the installation and progression of obesity. Pharmacological and gene-based approaches have proven efficient in restraining inflammation and correcting the obese phenotypes. However, the role of nutrients in the modulation of hypothalamic inflammation is unknown. Methodology/Principal Findings Here we show that, in a mouse model of diet-induced obesity, partial substitution of the fatty acid component of the diet by flax seed oil (rich in C18:3) or olive oil (rich in C18:1) corrects hypothalamic inflammation, hypothalamic and whole body insulin resistance, and body adiposity. In addition, upon icv injection in obese rats, both ω3 and ω9 pure fatty acids reduce spontaneous food intake and body mass gain. These effects are accompanied by the reversal of functional and molecular hypothalamic resistance to leptin/insulin and increased POMC and CART expressions. In addition, both, ω3 and ω9 fatty acids inhibit the AMPK/ACC pathway and increase CPT1 and SCD1 expression in the hypothalamus. Finally, acute hypothalamic injection of ω3 and ω9 fatty acids activate signal transduction through the recently identified GPR120 unsaturated fatty acid receptor. Conclusions/Significance Unsaturated fatty acids can act either as nutrients or directly in the hypothalamus, reverting diet-induced inflammation and reducing body adiposity. These data show that, in addition to pharmacological and genetic approaches, nutrients can also be attractive candidates for controlling hypothalamic inflammation in obesity.

IL-6 and IL-10 Anti-Inflammatory Activity Links Exercise to Hypothalamic Insulin and Leptin Sensitivity through IKKβ and ER Stress Inhibition

Physical activity confers beneficial metabolic effects by inducing anti-inflammatory activity in the hypothalamus region of the brain in rodents, resulting in a reorganization of the set point of nutritional balance and reduced insulin and leptin resistance.

Reversal of diet-induced insulin resistance with a single bout of exercise in the rat: the role of PTP1B and IRS-1 serine phosphorylation

Lifestyle interventions including exercise programmes are cornerstones in the prevention of obesity‐related diabetes. In this study, we demonstrate that a single bout of exercise inhibits high‐fat diet‐induced insulin resistance. Diet‐induced obesity (DIO) increased the expression and activity of the protein tyrosine phosphatase 1B (PTP1B) and attenuated insulin signalling in gastrocnemius muscle of rats, a phenomenon which was reversed by a single session of exercise. In addition, DIO was observed to lead to serine phosphorylation of insulin receptor substrate 1 (IRS‐1), which was also reversed by exercise in muscle in parallel with a reduction in c‐Jun N‐terminal kinase (JNK) activity. Thus, acute exercise increased the insulin sensitivity during high‐fat feeding in obese rats. Overall, these results provide new insights into the mechanism by which exercise restores insulin sensitivity.

Interleukin-10 is a protective factor against diet-induced insulin resistance in liver☆

BACKGROUND/AIMS The anti-inflammatory cytokine, interleukin-10 (IL-10), is known to exert a protective role in hepatic damage caused by viruses, alcohol, autoimmunity and a number of experimental aggressors. Recently, a protective role for IL-10 has also been proposed in diet-induced hepatic dysfunction. However, studies about the mechanisms involved in this process are controversial. The objective of this study was to evaluate the role of endogenous IL-10 in the development of hepatic insulin resistance, associated with diet-induced fatty liver disease. METHODS Male Swiss mice treated for eight weeks with a high-fat diet became diabetic and developed non-alcoholic fatty liver disease, which is characterized by increased hepatic fat deposition and liver infiltration by F4/80 positive cells. This was accompanied by an increased hepatic expression of TNF-alpha, IL-6, IL-1beta and IL-10, and by an impaired insulin signal transduction through the insulin receptor/IRS1-IRS2/PI3-kinase/Akt/FOXO1 signaling pathway. RESULTS Upon endogenous IL-10 inhibition for 5 days, using two distinct methods, a neutralizing anti-IL-10 antibody and an antisense oligonucleotide against IL-10, increased hepatic expression of the inflammatory markers TNF-alpha, IL-6, IL-1beta and F4/80 was observed. This was accompanied by a significant negative modulation of insulin signal transduction through insulin receptor/IRS1-IRS2/PI3-kinase/Akt/FOXO1, and by the stimulation of hepatic signaling proteins involved in gluconeogenesis and lipid synthesis. CONCLUSIONS Thus, in an animal model of diet-induced fatty liver disease, the inhibition of IL-10 promotes the increased expression of inflammatory cytokines, the worsening of insulin signaling and the activation of gluconeogenic and lipidogenic pathways.

Diet-Induced Inflammation of the Hypothalamus in Obesity

Dysfunction of specific hypothalamic neurons is regarded as an important mechanism predisposing to the development of obesity. Recent studies have revealed that the consumption of fat-rich foods can activate an inflammatory response in the hypothalamus, which disturbs the anorexigenic and thermogenic signals generated by the hormones leptin and insulin, leading in turn to anomalous body mass control. Depending on diet composition, cytokines are expressed in the hypothalamus, contributing to the activation of intracellular inflammatory signal transduction. At least 4 distinct signaling pathways have been identified and the molecular mechanisms leading to the impairment of the leptin and insulin actions have been determined. Here, we present the mechanisms involved in diet-induced resistance to leptin and insulin action in the hypothalamus and discuss some of the potential applications of this knowledge in the therapeutics of obesity.

Ketamine plus imipramine treatment induces antidepressant-like behavior and increases CREB and BDNF protein levels and PKA and PKC phosphorylation in rat brain

A growing body of evidence has pointed to the N-methyl-d-aspartate (NMDA) receptor antagonists as a potential therapeutic target for the treatment of major depression. The present study investigated the possibility of synergistic interactions between antidepressant imipramine with the uncompetitive NMDA receptor antagonist ketamine. Wistar rats were acutely treated with ketamine (5 and 10mg/kg) and imipramine (10 and 20mg/kg) and then subjected to forced swimming tests. The cAMP response element bindig (CREB) and brain-derived neurotrophic factor (BDNF) protein levels and protein kinase C (PKC) and protein kinase A (PKA) phosphorylation were assessed in the prefrontal cortex, hippocampus and amygdala by imunoblot. Imipramine at the dose of 10mg/kg and ketamine at the dose of 5mg/kg did not have effect on the immobility time; however, the effect of imipramine (10 and 20mg/kg) was enhanced by both doses of ketamine. Ketamine and imipramine alone or in combination at all doses tested did not modify locomotor activity. Combined treatment with ketamine and imipramine produced stronger increases of CREB and BDNF protein levels in the prefrontal cortex, hippocampus and amygdala, and PKA phosphorylation in the hippocampus and amygdala and PKC phosphorylation in prefrontal cortex. The results described indicate that co-administration of antidepressant imipramine with ketamine may induce a more pronounced antidepressant activity than treatment with each antidepressant alone. This finding may be of particular importance in the case of drug-resistant patients and could suggest a method of obtaining significant antidepressant actions whilst limiting side effects.

Acute physical exercise reverses S-nitrosation of the insulin receptor, insulin receptor substrate 1 and protein kinase B/Akt in diet-induced obese Wistar rats

Early evidence demonstrates that exogenous nitric oxide (NO) and the NO produced by inducible nitric oxide synthase (iNOS) can induce insulin resistance. Here, we investigated whether this insulin resistance, mediated by S‐nitrosation of proteins involved in early steps of the insulin signal transduction pathway, could be reversed by acute physical exercise. Rats on a high‐fat diet were subjected to swimming for two 3 h‐long bouts, separated by a 45 min rest period. Two or 16 h after the exercise protocol the rats were killed and proteins from the insulin signalling pathway were analysed by immunoprecipitation and immunoblotting. We demonstrated that a high‐fat diet led to an increase in the iNOS protein level and S‐nitrosation of insulin receptor β (IRβ), insulin receptor substrate 1 (IRS1) and Akt. Interestingly, an acute bout of exercise reduced iNOS expression and S‐nitrosation of proteins involved in the early steps of insulin action, and improved insulin sensitivity in diet‐induced obesity rats. Furthermore, administration of GSNO (NO donor) prevents this improvement in insulin action and the use of an inhibitor of iNOS (l‐N6‐(1‐iminoethyl)lysine; l‐NIL) simulates the effects of exercise on insulin action, insulin signalling and S‐nitrosation of IRβ, IRS1 and Akt. In summary, a single bout of exercise reverses insulin sensitivity in diet‐induced obese rats by improving the insulin signalling pathway, in parallel with a decrease in iNOS expression and in the S‐nitrosation of IR/IRS1/Akt. The decrease in iNOS protein expression in the muscle of diet‐induced obese rats after an acute bout of exercise was accompanied by an increase in AMP‐activated protein kinase (AMPK) activity. These results provide new insights into the mechanism by which exercise restores insulin sensitivity.

Inhibition of UCP2 expression reverses diet-induced diabetes mellitus by effects on both insulin secretion and action

Recent characterization of the ability of uncoupling protein 2 (UCP2) to reduce ATP production and inhibit insulin secretion by pancreatic β‐cells has placed this mitochondrial protein as a candidate target for therapeutics in diabetes mellitus. In the present study we evaluate the effects of short‐term treatment of two animal models of type 2 diabetes mellitus with an antisense oligonucleotide to UCP2. In both models, Swiss mice (made obese and diabetic by a hyperlipidic diet) and ob/ob mice, the treatment resulted in a significant improvement in the hyperglyce‐mic syndrome. This effect was due not only to an improvement of insulin secretion, but also to improved peripheral insulin action. In isolated pancreatic islets, the partial inhibition of UCP2 increased ATP content, followed by increased glucose‐stimulated insulin secretion. This was not accompanied by increased expression of enzymes involved in protection against oxida‐tive stress. The evaluation of insulin action in peripheral tissues revealed that the inhibition of UCP2 expression significantly improved insulin signal trans‐duction in adipose tissue. In conclusion, short‐term inhibition of UCP2 expression ameliorates the hyper‐glycemic syndrome in two distinct animal models of obesity and diabetes. Metabolic improvement is due to a combined effect on insulin‐producing pancreatic islets and in at least one peripheral tissue that acts as a target for insulin.—De Souza, C. T., Araújo, E. P., Stoppiglia, L. F., Pauli, J. R., Ropelle, E., Rocco, S. A., Marin, R. M., Franchini, K. G., Carvalheira, J. B., Saad, M. J., Boschero, A. C., Carneiro, E. M., Velloso, L. A. Inhibition of UCP2 expression reverses diet‐induced diabetes mellitus by effects on both insulin secretion and action. FASEB J. 21, 1153–1163 (2007)

Taurine supplementation decreases oxidative stress in skeletal muscle after eccentric exercise

Infrequent exercise, typically involving eccentric actions, has been shown to cause oxidative stress and to damage muscle tissue. High taurine levels are present in skeletal muscle and may play a role in cellular defences against free radical‐mediated damage. This study investigates the effects of taurine supplementation on oxidative stress biomarkers after eccentric exercise (EE). Twenty‐four male rats were divided into the following groups (n = 6): control; EE; EE plus taurine (EE + Taurine); EE plus saline (EE + Saline). Taurine was administered as a 1‐ml 300 mg kg−1 per body weight (BW) day−1 solution in water by gavage, for 15 consecutive days. Starting on the 14th day of supplementation, the animals were submitted to one 90‐min downhill run session and constant velocity of 1·0 km h−1. Forty‐eight hours after the exercise session, the animals were killed and the quadriceps muscles were surgically removed. Production of superoxide anion, creatine kinase (CK) levels, lipoperoxidation, carbonylation, total thiol content and antioxidant enzyme were analysed. Taurine supplementation was found to decrease superoxide radical production, CK, lipoperoxidation and carbonylation levels and increased total thiol content in skeletal muscle, but it did not affect antioxidant enzyme activity after EE. The present study suggests that taurine affects skeletal muscle contraction by decreasing oxidative stress, in association with decreased superoxide radical production. Copyright

Cold Exposure Induces Tissue‐Specific Modulation of the Insulin‐Signalling Pathway in Rattus Norvegicus

Cold exposure provides a reproducible model of improved glucose turnover accompanied by reduced steady state and glucose‐induced insulin levels. In the present report we performed immunoprecipitation and immunoblot studies to evaluate the initial and intermediate steps of the insulin‐signalling pathway in white and brown adipose tissues, liver and skeletal muscle of rats exposed to cold. Basal and glucose‐induced insulin secretion were significantly impaired, while glucose clearance rates during a glucose tolerance test and the constant for glucose decay during a 15 min insulin tolerance test were increased, indicating a significantly improved glucose turnover and insulin sensitivity in rats exposed to cold. Evaluation of protein levels and insulin‐induced tyrosine (insulin receptor, insulin receptor substrates (IRS)‐1 and −2, ERK (extracellular signal‐related kinase)) or serine (Akt; protein kinase B) phosphorylation of proteins of the insulin signalling cascade revealed a tissue‐specific pattern of regulation of the molecular events triggered by insulin such that in white adipose tissue and skeletal muscle an impaired molecular response to insulin was detected, while in brown adipose tissue an enhanced response to insulin was evident. In muscle and white and brown adipose tissues, increased 2‐deoxy‐D‐glucose (2‐DG) uptake was detected. Thus, during cold exposure there is a tissue‐specific regulation of the insulin‐signalling pathway, which seems to favour heat‐producing brown adipose tissue. Nevertheless, muscle and white adipose tissue are able to take up large amounts of glucose, even in the face of an apparent molecular resistance to insulin.