Fern-9(11)-ene-2α,3ß-diol Action on Insulin Secretion under Hyperglycemic Conditions.

The objective of this study was to investigate the effect and the mechanism of action of fernenediol as an insulin secretagogue. Wistar rats were treated with 0.1, 1, and 10 mg/kg fernenediol before inducing hyperglycemia by oral glucose. The glycaemia, insulin, LDH, calcium, and hepatic glycogen were analyzed. Considering the intestine and pancreas as targets for the triterpene action, the duodenum was used to verify the influence of fernenediol on intestinal glycosidases. Additionally, pancreatic islets were used for studies of 14C-deoxyglucose uptake and the influx of 45Ca2+ in hyperglycemic media with/without fernenediol in the presence/absence of an inhibitor/activator of KATP channels, glibenclamide, diazoxide, nifedipine, calcium chelator (BAPTA-AM), and H-89 and ST, the inhibitors of the PKA and PKC enzymes. Fernenediol significantly reduced glycaemia, potentiated glucose-induced insulin secretion, and stimulated liver glycogen deposition in hyperglycemic rats after an in vivo treatment without changing intestinal disaccharidases activities and showing no influence on intestinal glucose absorption. Also, it stimulated the glucose uptake and calcium influx in pancreatic islets. The involvement of voltage-dependent L-type calcium channels and ATP-dependent potassium channels and the release of calcium from intracellular stores are mandatory for the stimulatory effect of fernenediol on calcium influx. Fernenediol did not change PKA and PKC activities or modify calcium levels. This triterpene is a potent antihyperglycemic agent with a strong insulin secretagogue effect on glycogen accumulation as well. As a whole, this compound presents significant perspectives as a future new drug for the treatment of insulin resistance and/or diabetes.

Bis-Pyrano Prenyl Isoflavone Improves Glucose Homeostasis by Inhibiting Dipeptidyl Peptidase-4 in Hyperglycemic Rats.

Isoflavones widely distributed in plants prevent diabetes. This study investigated the in vivo and in vitro effect of 3',4'-dihydroxy-6″,6″,6″',6″'-tetramethylbis(pyrano[2″,3″:5,6::2″',3″':7,8]isoflavone (bis-pyrano prenyl isoflavone) on glucose homeostasis in hyperglycemic rats. The ethyl acetate fraction from aerial parts of Polygala molluginifolia that contain isoflavones was assayed on glucose tolerance, on in vitro maltase activity and on protein glycation. The isoflavone bis-pyrano prenyl isolated from this fraction was investigated on glucose homeostasis. The in vivo action of the isoflavone exhibits an anti-hyperglycemic effect by improving glucose tolerance, augmenting the liver glycogen, inhibiting maltase activity, and stimulating glucagon-like peptide-1 (GLP-1) and insulin secretion. The in vitro isoflavone inhibits dipeptidyl peptidase-4 (DPP-4) activity since the glucose tolerance was improved in the presence of the isoflavone as much as sitagliptin, an inhibitor of DPP-4. However, the co-incubation with isoflavone and sitagliptin exhibited an additive anti-hyperglycemic action. The isoflavone increased the GLP-1 faster than the positive hyperglycemic group, which shows that the intestine is a potential target. Thus, to clarify the main site of action in which isoflavone improves glucose balance, the in vitro mechanism of action of this compound was tested in intestine using calcium influx as a trigger for the signal pathways for GLP-1 secretion. The isoflavone stimulates calcium influx in intestine and its mechanism involves voltage-dependent calcium channels, phospholipase C, protein kinase C, and stored calcium contributing for GLP-1 secretion. In conclusion, the isoflavone regulates glycaemia by acting mainly in a serum target, the DPP-4 inhibitor. Furthermore, the long-term effect of isoflavone prevents protein glycation. J. Cell. Biochem. 118: 92-103, 2017. © 2016 Wiley Periodicals, Inc.

Triterpene derivative: A potential signaling pathway for the fern-9(11)-ene-2α,3ß-diol on insulin secretion in pancreatic islet.

AIM: Triterpenes and their derivatives influence on carbohydrate metabolism. In vivo and in vitro treatment investigated the effect of the natural triterpene fern-9(11)-ene-2α,3ß-diol (1), isolated from Croton heterodoxus, and a derivative triterpene (2) on glucose homeostasis. MAIN METHODS: The antidiabetic effect of the crude extract from C. heterodoxus leaves, the natural triterpene (1) as well as the derivative triterpene (2) were assayed on glucose tolerance. The effect and the mechanism of action on in vivo treatment with triterpene 2 on glycaemia and insulin secretion were studied. In addition, in vitro studies investigated the mechanism of triterpene 2 on glucose uptake and calcium influx on insulin secretion in pancreatic islets. KEY FINDINGS: The results show the extract slightly reduced the glycaemia when compared with hyperglycemic group. However, the presence of the substituent electron-withdrawing 4-nitrobenzoyl group in the A-ring of triterpene 2 powered the serum glucose lowering compared to triterpene 1. In addition, in vivo treatment with triterpene 2 significantly increased the insulin secretion induced by glucose and stimulated the glucose uptake and calcium influx in pancreatic islet. The effect of triterpene on calcium influx was completely inhibited by diazoxide, nifedipine and stearoylcarnitine treatment. SIGNIFICANCE: The stimulatory effect of triterpene 2 on glucose uptake, calcium influx, regulation of potassium (K(+)-ATP) and calcium (L-VDCCs) channels activity as well as the pathway of PKC highlights the mechanism of action of the compound in pancreatic islets on insulin secretion and glucose homeostasis. In addition, this compound did not induce toxicity in this experimental condition.

Incretinomimetic and Insulinomimetic Effect of (2E)-N'-(1'-Naphthyl)-3,4,5-Trimethoxybenzohydrazide for Glycemic Homeostasis.

To characterize the role and the mechanism of action of (2E)-N'-(1'-naphthyl)-3,4,5-trimethoxybenzohydrazide (BZD) on incretin secretion, glucose uptake in skeletal muscle and α-glucosidase activity on intestine, targets for glucose homeostasis. It was assayed on glucose tolerance test (GTT) to analyze GLP-1 secretion and the activity of DPP-4 enzyme in vitro. In skeletal muscle, mechanism of action on glucose uptake was carried out by in vitro experiments. The activity of intestinal disaccharidases was performed after in vivo and in vitro experiments. The compound improved the glucose tolerance around 30%, 25%, and 20% at 15, 30, and 60 min, respectively and potentiated the sitagliptin effect, an inhibitor of the enzyme that removes GLP-1, about 50, 45, and 54% at 15, 30, and 60 min, respectively. Additionally, BZD did not modify the activity of DPP-4 enzyme. The acute effect of BZD on glucose uptake is mediated by increasing GLUT4 expression (around 140%) and its translocation to the plasma membrane in soleus muscle. The genomic effect as well as GLUT4 translocation involve the activation of PI-3K and MAPK pathways and require the microtubules integrity to the complete stimulatory effect of this compound on glucose uptake. Beyond, BZD acts in an alternative target to ameliorate glycaemia, intestinal disaccharidases. In a whole, these data point an incretino- and insulinomimetic effect of the compound for glycemic control.

Acute effect of 3ß-hidroxihop-22(29)ene on insulin secretion is mediated by GLP-1, potassium and calcium channels for the glucose homeostasis.

The effect of 3ß-hidroxihop-22(29)ene (3-BHO) on insulin and glucagon-like peptide 1 (GLP-1) secretion as well as the mechanism of action of the compound in pancreatic islet on glucose homeostasis was investigated. The data from in vivo treatment show that 3-BHO significantly reduces the hyperglycemia by increasing the insulin and GLP-1 secretion, as well as by accumulating hepatic glycogen in hyperglycemic rats. In rat pancreatic ß-cell, 3-BHO stimulates the glucose uptake, insulin vesicles translocation to the plasma membrane and thus the insulin secretion through the involvement of potassium channels (ATP- and Ca(2+)-dependent K(+) channels) and calcium channels (L-type voltage-dependent calcium channels (L-VDCC)). Furthermore, this study also provides evidence for a crosstalk between intracellular high calcium concentration, PKA and PKC in the signal transduction of 3-BHO to stimulate insulin secretion. In conclusion, 3-BHO diminishes glycaemia, stimulates GLP-1 secretion and potentiates insulin secretion and increase hepatic glycogen content. Moreover, this triterpene modulates calcium influx characterizing ATP-K(+), Ca(2+)-K(+) and L-VDCC channels-dependent pathways as well as PKA and PKC activity in pancreatic islets underlying the signaling of 3-BHO for the secretory activity and contribution on glucose homeostasis.

Effects of taurine supplementation following eccentric exercise in young adults.

The purpose of the present study was to investigate the effects of taurine supplementation on muscle performance, oxidative stress, and inflammation response after eccentric exercise (EE) in males. Twenty-one participants (mean age, 21 ± 6 years; weight, 78.2 ± 5 kg; height, 176 ± 7 cm) were selected and randomly divided into two groups: placebo (n = 10) and taurine (n = 11). Fourteen days after starting supplementation, subjects performed EE (3 sets until exhaustion, with EE of the elbow flexors on the Scott bench, 80% 1 repetition maximum (RM)). Blood samples were collected and muscle performance was measured on days 1, 14, 16, 18, and 21 after starting the supplements. Then, performance, muscle damage, oxidative stress, and inflammatory markers were analyzed. The taurine supplementation resulted in increased strength levels and thiol total content and decreased muscle soreness, lactate dehydrogenase level, creatine kinase activity, and oxidative damage (xylenol and protein carbonyl). Antioxidant enzymes (superoxide dismutase, catalase, and gluthatione peroxidase) and inflammatory markers (tumor necrosis factor, interleukin-1ß (IL-1ß), and interleukin-10 (IL-10)) were not altered during the recovery period compared with the placebo group. The results suggest that taurine supplementation represents an important factor in improving performance and decreasing muscle damage and oxidative stress but does not decrease the inflammatory response after EE.

Endurance exercise training ameliorates insulin resistance and reticulum stress in adipose and hepatic tissue in obese rats.

Obesity-induced endoplasmatic reticulum (ER) stress has been demonstrated to underlie the induction of obesity-induced JNK and NF-κB activation inflammatory responses, and generation of peripheral insulin resistance. On the other hand, exercise has been used as a crucial tool in obese and diabetic patients, and may reduce inflammatory pathway stimulation. However, the ability of exercise training to reverse endoplasmatic reticulum stress in adipose and hepatic tissue in obesity has not been investigated in the literature. Here, we demonstrate that exercise training ameliorates ER stress and insulin resistance in DIO-induced rats. Rats were fed with standard rodent chow (3,948 kcal kg(-1)) or high-fat diet (5,358 kcal kg(-1)) for 2 months. After that rats were submitted to swimming training (1 h per day, 5 days for week with 5% overload of the body weight for 8 weeks). Samples from epididymal fat and liver were obtained and western blot analysis was performed. Our results showed that swimming protocol reduces pro-inflammatory molecules (JNK, IκB and NF-κB) in adipose and hepatic tissues. In addition, exercise leads to reduction in ER stress, by reducing PERK and eIF2α phosphorylation in these tissues. In parallel, an increase in insulin pathway signaling was observed, as confirmed by increases in IR, IRSs and Akt phosphorylation following exercise training in DIO rats. Thus, results suggest that exercise can reduce ER stress, improving insulin resistance in adipose and hepatic tissue.

Exercise training reduces insulin resistance and upregulates the mTOR/p70S6k pathway in cardiac muscle of diet-induced obesity rats.

Obesity and insulin resistance are rapidly expanding public health problems. These disturbances are related to many diseases, including heart pathology. Acting through the Akt/mTOR pathway, insulin has numerous and important physiological functions, such as the induction of growth and survival of many cell types and cardiac hypertrophy. However, obesity and insulin resistance can alter mTOR/p70S6k. Exercise training is known to induce this pathway, but never in the heart of diet-induced obesity subjects. To evaluate the effect of exercise training on mTOR/p70S6k in the heart of obese Wistar rats, we analyzed the effects of 12 weeks of swimming on obese rats, induced by a high-fat diet. Exercise training reduced epididymal fat, fasting serum insulin and plasma glucose disappearance. Western blot analyses showed that exercise training increased the ability of insulin to phosphorylate intracellular molecules such as Akt (2.3-fold) and Foxo1 (1.7-fold). Moreover, reduced activities and expressions of proteins, induced by the high-fat diet in rats, such as phospho-JNK (1.9-fold), NF-kB (1.6-fold) and PTP-1B (1.5-fold), were observed. Finally, exercise training increased the activities of the transduction pathways of insulin-dependent protein synthesis, as shown by increases in Raptor phosphorylation (1.7-fold), p70S6k phosphorylation (1.9-fold), and 4E-BP1 phosphorylation (1.4-fold) and a reduction in atrogin-1 expression (2.1-fold). Results demonstrate a pivotal regulatory role of exercise training on the Akt/mTOR pathway, in turn, promoting protein synthesis and antagonizing protein degradation.

Acute exercise reduces hepatic glucose production through inhibition of the Foxo1/HNF-4alpha pathway in insulin resistant mice.

Protein hepatocyte nuclear factor 4alpha (HNF-4alpha) is atypically activated in the liver of diabetic rodents and contributes to hepatic glucose production. HNF-4alpha and Foxo1 can physically interact with each other and represent an important signal transduction pathway that regulates the synthesis of glucose in the liver. Foxo1 and HNF-4alpha interact with their own binding sites in the phosphoenolpyruvate carboxykinase (PEPCK) and glucose-6-phosphatase (G6Pase) promoters, and this binding is required for their effects on those promoters. However, the effect of physical activity on the HNF-4alpha/Foxo1 pathway is currently unknown. Here, we investigate the protein levels of HNF-4alpha and the HNF-4alpha/Foxo1 pathway in the liver of leptin-deficient (ob/ob) and diet-induced obese Swiss (DIO) mice after acute exercise. The ob/ob and DIO mice swam for four 30 min periods, with 5 min rest intervals for a total swimming time of 2h. Eight hours after the acute exercise protocol, the mice were submitted to an insulin tolerance test (ITT) and determination of biochemical and molecular parameters. Acute exercise improved insulin signalling, increasing insulin-stimulated Akt and Foxo1 phosphorylation and decreasing HNF-4alpha protein levels in the liver of DIO and ob/ob mice under fasting conditions. These phenomena were accompanied by a reduction in the expression of gluconeogenesis genes, such as PEPCK and G6Pase. Importantly, the PI3K inhibitor LY292004 reversed the acute effect of exercise on fasting hyperglycaemia, confirming the involvement of the PI3K pathway. The present study shows that exercise acutely improves the action of insulin in the liver of animal models of obesity and diabetes, resulting in increased phosphorylation and nuclear exclusion of Foxo1, and a reduction in the Foxo1/HNF-4alpha pathway. Since nuclear localization and the association of these proteins is involved in the activation of PEPCK and G6Pase, we believe that the regulation of Foxo1 and HNF-4alpha activities are important mechanisms involved in exercise-induced improvement of glucose homeostasis in insulin resistant states.

Exercise training provides cardioprotection via a reduction in reactive oxygen species in rats submitted to myocardial infarction induced by isoproterenol.

Exercise training has demonstrated cardioprotection effects. However, the exact mechanism behind this effect is not is clear. The present study evaluated the effects of 12 weeks of previous treadmill training on the levels of oxidative damage, antioxidant enzyme activity and injury in the myocardium of rats submitted to infarction induced by isoproterenol (ISO). Isoproterenol treatment (80 mg/kg given over 2 days in two equal doses) caused arrhythmias and 60% mortality within 24 h of the last injection in the control group (C + ISO) group when compared with the saline control group (saline). Creatine Kinase--MB levels were markedly increased in hearts from ISO-treated animals in the C + ISO group. Twelve weeks of treadmill training reduced superoxide production, lipid peroxidation levels and protein carbonylation in these animals, as well as increasing the activities and expressions of SOD and CAT. Previous training also reduced CK-MB levels and numbers of deaths by 40%, preventing the deleterious effects of ISO. Based on the data obtained in this study, it is suggested that 12-week treadmill training increases antioxidant enzymes, decreases oxidative damage and reduces the degree of infarction induced by ISO in the hearts of male rats.

Inhibition of hypothalamic Foxo1 expression reduced food intake in diet-induced obesity rats.

Insulin signalling in the hypothalamus plays a role in maintaining body weight. The forkhead transcription factor Foxo1 is an important mediator of insulin signalling in the hypothalamus. Foxo1 stimulates the transcription of the orexigenic neuropeptide Y and Agouti-related protein through the phosphatidylinositol-3-kinase/Akt signalling pathway, but the role of hypothalamic Foxo1 in insulin resistance and obesity remains unclear. Here, we identify that a high-fat diet impaired insulin-induced hypothalamic Foxo1 phosphorylation and degradation, increasing the nuclear Foxo1 activity and hyperphagic response in rats. Thus, we investigated the effects of the intracerebroventricular (i.c.v.) microinfusion of Foxo1-antisense oligonucleotide (Foxo1-ASO) and evaluated the food consumption and weight gain in normal and diet-induced obese (DIO) rats. Three days of Foxo1-ASO microinfusion reduced the hypothalamic Foxo1 expression by about 85%. i.c.v. infusion of Foxo1-ASO reduced the cumulative food intake (21%), body weight change (28%), epididymal fat pad weight (22%) and fasting serum insulin levels (19%) and increased the insulin sensitivity (34%) in DIO but not in control animals. Collectively, these data showed that the Foxo1-ASO treatment blocked the orexigenic effects of Foxo1 and prevented the hyperphagic response in obese rats. Thus, pharmacological manipulation of Foxo1 may be used to prevent or treat obesity.