Resveratrol binds to the sulfonylurea receptor (SUR) and induces apoptosis in a SUR subtype-specific manner

Resveratrol Prevents Cell Swelling Through Inhibition of SUR1 Expression in Brain Micro Endothelial Cells Subjected to OGD/Recovery

The SUR1-TRPM4-AQP4 complex is overexpressed in the initial phase of edema induced after cerebral ischemia, allowing the massive internalization of Na+ and water within the brain micro endothelial cells (BMEC) of the blood-brain barrier. The expression of the Abcc8 gene encoding SUR1 depends on transcriptional factors that are responsive to oxidative stress. Because reactive oxygen species (ROS) are generated during cerebral ischemia, we hypothesized that antioxidant compounds might be able to regulate the expression of SUR1. Therefore, the effect of resveratrol (RSV) on SUR1 expression was evaluated in the BMEC cell line HBEC-5i subjected to oxygen and glucose deprivation (OGD) for 2 h followed by different recovery times. Different concentrations of RSV were administered. ROS production was detected with etidine, and protein levels were evaluated by Western blotting and immunofluorescence. Intracellular Na+ levels and cellular swelling were detected by imaging; cellular metabolic activity and rupture of the cell membrane were detected by MTT and LDH release, respectively; and EMSA assays measured the activity of transcriptional factors. OGD/recovery increased ROS production induced the AKT kinase activity and the activation of SP1 and NFκB. SUR1 protein expression and intracellular Na+ concentration in the HBEC-5i cells increased after a few hours of OGD. These effects correlated with cellular swelling and necrotic cell death, responses that the administration of RSV prevented. Our results indicate that the ROS/AKT/SP1-NFκB pathway is involved in SUR1 expression during OGD/recovery in BMEC of the blood-brain barrier. Thus, RSV prevented cellular edema formation through modulation of SUR1 expression.

Modulatory Effect of Medicinal Plants and Their Active Constituents on ATP-Sensitive Potassium Channels (KATP) in Diabetes

Hyperglycemia, which is a chronic metabolic condition caused by either a defect in insulin secretion or insulin resistance, is a hallmark of diabetes mellitus (DM). Sustained hyperglycemia leads to the onset and development of many health complications. Despite the number of available antidiabetic medications on the market, there is still a need for novel treatment agents with increased efficacy and fewer adverse effects. Many medicinal plants offer a rich supply of bioactive compounds that have remarkable pharmacological effects with less toxicity and side effects. According to published evidence, natural antidiabetic substances influence pancreatic β-cell development and proliferation, inhibit pancreatic β-cell death, and directly increase insulin output. Pancreatic ATP-sensitive potassium channels play an essential role in coupling glucose metabolism to the secretion of insulin. Although much of the literature is available on the antidiabetic effects of medicinal plants, very limited studies discuss their direct action on pancreatic KATP. The aim of this review is to focus on the modulatory effects of antidiabetic medicinal plants and their active constituents on pancreatic KATP. The KATP channel should be regarded as a key therapeutic milestone in the treatment of diabetes. Therefore, continuous research into the interaction of medicinal plants with the KATP channel is crucial.

Ameliorative Effect of Citrus Lemon Peel Extract and Resveratrol on Premature Ovarian Failure Rat Model: Role of iNOS/Caspase-3 Pathway

Premature ovarian failure (POF) is described as a loss of oocytes and the absence of folliculogenesis and is considered an adverse effect of chemotherapeutic drugs, which leads to infertility. Subsequently, the existing inquiry was achieved by exploring the potential suspicious influences of lemon peel extract (LPE), and resveratrol (RES) on cyclophosphamide (CPA) induced-POF. The results showed that CPA-induced POF significantly decreased serum estradiol (E2) and progesterone levels, along with a considerable rise in serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels. Moreover, CPA administration to rats significantly increased the serum level of Malondialdehyde (MDA) and significantly lowered the levels of reduced glutathione (GSH) and superoxide dismutase (SOD); in addition, it increased nuclear factor kappa B (NF-κB) levels, tumor necrosis factor-α (TNF-α), as well as cyclooxygenase 2 (COX-2) with the spread expression of inducible nitric oxide synthase (iNOS) mRNA levels and caspase-3 (Casp3) levels in ovarian tissues versus the control rats. However, treatment with LPE and RES suppressed the triggering of NF- κB pathways, evidenced by a considerable reduction in Casp3 & iNOS mRNA expression level and significant ameliorative effects in all evaluated parameters, as confirmed by the histological and immunohistochemical investigation when comparing the model group. In overall findings, both lemon peel extract and resveratrol can mitigate the adverse effects of CPA-induced POF. Most crucially, its combination therapy is a promising pharmacological agent for this disease.

Potassium Channels as Therapeutic Targets in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease with high morbidity and mortality. Deleterious remodeling in the pulmonary arterial system leads to irreversible arterial constriction and elevated pulmonary arterial pressures, right heart failure, and eventually death. The difficulty in treating PAH stems in part from the complex nature of disease pathogenesis, with several signaling compounds known to be involved (e.g., endothelin-1, prostacyclins) which are indeed targets of PAH therapy. Over the last decade, potassium channelopathies were established as novel causes of PAH. More specifically, loss-of-function mutations in the KCNK3 gene that encodes the two-pore-domain potassium channel KCNK3 (or TASK-1) and loss-of-function mutations in the ABCC8 gene that encodes a key subunit, SUR1, of the ATP-sensitive potassium channel (KATP) were established as the first two potassium channelopathies in human cohorts with pulmonary arterial hypertension. Moreover, voltage-gated potassium channels (Kv) represent a third family of potassium channels with genetic changes observed in association with PAH. While other ion channel genes have since been reported in association with PAH, this review focuses on KCNK3, KATP, and Kv potassium channels as promising therapeutic targets in PAH, with recent experimental pharmacologic discoveries significantly advancing the field.

Combined resveratrol and vitamin D treatment ameliorate inflammation-related liver fibrosis, ER stress, and apoptosis in a high-fructose diet/streptozotocin-induced T2DM model

A high fructose diet is a major cause of diabetes and various metabolic disorders, including fatty liver. In this study, we investigated the effects of resveratrol and vitamin D (VitD) treatments on endoplasmic reticulum (ER) stress, oxidative stress, inflammation, apoptosis, and liver regeneration in a rat model of type 2 diabetes mellitus, namely, T2DM Sprague-Dawley rats. This T2DM rat model was created through a combination treatment of a 10% fructose diet and 40 mg/kg streptozotocin (STZ). Resveratrol (1 mg/kg/day) and VitD (170/IU/week) were administered alone and in combination to both the diabetic and control groups. Immunohistochemical staining was performed to evaluate PCNA, NF-κB, TNF-α, IL-6, IL-1β, GRP78, and active caspase-3 in liver tissue. The TUNEL method and Sirius red staining were used to determine apoptosis and fibrosis, respectively. G6PD, 6-PGD, GR, and GST activities were measured to determine oxidative stress status. We found that the expressions of cytokines (TNF-α, IL-6, and IL-1β) correlated with NF-κB activation and were significantly increased in the T2DM rats. Increased GRP78 expression, indicating ER stress, increased in apoptotic cells, enhanced caspase-3 activation, and collagen accumulation surrounding the central vein were observed in the T2DM group compared with the other groups. The combination VitD + resveratrol treatment improved antioxidant defense via increasing G6PD, 6-PGD, GR, and GST activities compared to the diabetic groups. We concluded that the combined administration of resveratrol with VitD ameliorates the adverse effects of T2DM by regulating blood glucose levels, increasing antioxidant defense mechanisms, controlling ER stress, enhancing tissue regeneration, improving inflammation, and reducing apoptosis in liver cells. In conclusion, this study indicates that the combination treatment of resveratrol + VitD can be a beneficial option for preventing liver damage in fructose-induced T2DM.

Hyphaene thebaica (doum)-derived extract alleviates hyperglycemia in diabetic rats: a comprehensive in silico, in vitro and in vivo study

In the present study, we investigated the hypoglycemic effect of different extracts (i.e. organic and aqueous) derived from the fruits of Hyphaene thebaica (doum) on male streptozotocin-induced diabetic rats. Blood glucose levels as well as the relative gene expression of insulin, TNF-α, and TGF-β were determined in the pancreatic tissue of the experimental animals. Treatment of STZ-induced diabetic rats with aqueous extracts of the plant fruit over 7 weeks significantly reduced the elevated blood glucose and increased the relative expression of insulin, while the relative expression of inflammatory mediators (i.e. TNF-α and TGF-β) was significantly reduced. Histopathological investigation also revealed that the aqueous extract treatment effectively reversed the β-cell necrosis induced by STZ and restored its normal morphology. Furthermore, liquid chromatography high resolution mass spectrometry (LC-HRMS) and in silico chemical investigation of the aqueous extract elucidated its major bioactive phytochemicals (i.e. flavonoids) and putatively determined the pancreatic K_ATP channel as a target for these bioactive components. In vitro insulin secretion assay revealed that myricetin, luteolin, and apigenin were able to induce insulin secretion by human pancreatic cells (insulin production = 20.9 ± 1.3, 13.74 ± 1.8, and 11.33 ± 1.1 ng mL^-1, respectively). Using molecular docking and dynamics simulations, we were able to shed the light on the insulin secretagogue's mode of action through these identified bioactive compounds and to determine the main structural elements required for its bioactivity. This comprehensive investigation of this native fruit will encourage future clinical studies to recommend edible and widely available fruits like doum to be a part of DM treatment plans.

Resveratrol reduces cerebral edema through inhibition of de novo SUR1 expression induced after focal ischemia

Cerebral edema is a clinical problem that frequently follows ischemic infarcts. Sulfonylurea receptor 1 (SUR1) is an inducible protein that can form a heteromultimeric complex with aquaporin 4 (AQP4) that mediate the ion/water transport involved in brain tissue swelling. Transcription of the Abcc8 gene coding for SUR1 depends on the activity of transcriptional factor SP1, which is modulated by the cellular redox environment. Since oxidative stress is implicated in the induced neuronal damage in ischemia and edema formation, the present study aimed to evaluate if the antioxidant resveratrol (RSV) prevents the damage by reducing the de novo expression of SUR1 in the ischemic brain. Male Wistar rats were subjected to 2 h of middle cerebral artery occlusion followed by different times of reperfusion. RSV (1.9 mg/kg; i.v.) was administered at the onset of reperfusion. Brain damage and edema formation were recognized by neurological evaluation, time of survival, TTC (2,3,5-Triphenyltetrazolium chloride) staining, Evans blue extravasation, and water content. RSV mechanism of action was studied by SP1 binding activity measured through the Electrophoretic Mobility Shift Assay, and Abcc8 and Aqp4 gene expression evaluated by qPCR, immunofluorescence, and Western blot. We found that RSV reduced the infarct area and cerebral edema, prevented blood-brain barrier damage, improved neurological performance, and increased survival. Additionally, our findings suggest that the antioxidant activity of RSV targeted SP transcription factors and inhibited SUR1 and AQP4 expression. Thus, RSV by decreasing SUR1 expression could contribute to reducing edema formation, constituting a therapeutic alternative for edema reduction in stroke.

Effect of resveratrol on SNARE proteins expression and insulin resistance in skeletal muscle of diabetic rats

Objective(s):

Soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex proteins are involved in membrane trafficking. The expression of isoforms of SNAP-23, syntaxin-4, and VAMP-2 is significantly done in skeletal muscles; they control GLUT4 trafficking. It is believed that type 2 diabetes could be caused by the modifications in the expression of SNARE complex proteins. The purpose of this study was to evaluate the effect of resveratrol on the expression of these proteins in type 2 diabetes.

Materials and Methods:

Forty male Wistar rats were selected. Streptozotocin and nicotinamide were applied for the induction of type 2 diabetes. The animals were divided into five groups. Healthy and diabetic groups were set as control; resveratrol (1, 5, and 10 mg/kg body weight) was applied to treat the three groups of diabetic rats for 30 days. Real-time qRT-PCR was applied to evaluate the expression of SNARE complex proteins.

Results:

There is a link between diabetes and insulin resistance and up-regulation of SNARE proteins expression. Resveratrol improved hyperglycemia and insulin resistance along with a non-significant reduction in the expression of SNARE proteins.

Conclusion:

Increased expression of SNARE proteins was possibly a compensatory mechanism in response to insulin resistance in the skeletal muscles of diabetic rats. Resveratrol non-significantly reduced the expression of SNARE proteins by enhancing insulin sensitivity, where this effect was dose-dependent. Thus, higher doses of resveratrol and longer intervention periods could probably be more effective. Another molecular mechanism of the anti-diabetic properties of resveratrol was identified with an effect on the expression of SNARE proteins.

Resveratrol Directly Controls the Activity of Neuronal Ryanodine Receptors at the Single-Channel Level

Calcium ion dyshomeostasis contributes to the progression of many neurodegenerative diseases and represents a target for the development of neuroprotective therapies, as reported by Duncan et al. (Molecules 15(3):1168-95, 2010), LaFerla (Nat Rev Neurosci 3(11):862-72, 2002), and Niittykoshi et al. (Invest Ophthalmol Vis Sci 51(12):6387-93, 2010). Dysfunctional ryanodine receptors contribute to calcium ion dyshomeostasis and potentially to the pathogenesis of neurodegenerative diseases by generating abnormal calcium ion release from the endoplasmic reticulum, according to Bruno et al. (Neurobiol Aging 33(5):1001 e1-6, 2012) and Stutzmann et al. (J Neurosci 24(2):508-13, 2004). Since ryanodine receptors share functional and structural similarities with potassium channels, as reported by Lanner et al. (Cold Spring Harb Perspect Biol 2(11):a003996, 2010), and small molecules with anti-oxidant properties, such as resveratrol (3,5,4'-trihydroxy-trans-stilbene), directly control the activity of potassium channels, according to Wang et al. (J Biomed Sci 23(1):47, 2016), McCalley et al. (Molecules 19(6):7327-40, 2014), Novakovic et al. (Mol Hum Reprod 21(6):545-51, 2015), Li et al. (Cardiovasc Res 45(4):1035-45, 2000), Gopalakrishnan et al. (Br J Pharmacol 129(7):1323-32, 2000), and Hambrock et al. (J Biol Chem 282(5):3347-56, 2007), we hypothesized that trans-resveratrol can modulate intracellular calcium signaling through direct binding and functional regulation of ryanodine receptors. The goal of our study was to identify and measure the control of ryanodine receptor activity by trans-resveratrol. Mechanisms of calcium signaling mediated by the direct interaction between trans-resveratrol and ryanodine receptors were identified and measured with single-channel electrophysiology. Addition of trans-resveratrol to the cytoplasmic face of the ryanodine receptor increased single-channel activity at physiological and elevated pathophysiological cytoplasmic calcium ion concentrations. The open probability of the channel increases after interacting with the small molecule in a dose-dependent manner, but remains also dependent on the concentration of its physiological ligand, cytoplasmic-free calcium ions. This study provides the first evidence of a direct functional interaction between trans-resveratrol and ryanodine receptors. Such functional control of ryanodine receptors by trans-resveratrol as a novel mechanism of action could provide additional rationales for the development of novel therapeutic strategies to treat and prevent neurodegenerative diseases.

Emerging roles for multifunctional ion channel auxiliary subunits in cancer

Several superfamilies of plasma membrane channels which regulate transmembrane ion flux have also been shown to regulate a multitude of cellular processes, including proliferation and migration. Ion channels are typically multimeric complexes consisting of conducting subunits and auxiliary, non-conducting subunits. Auxiliary subunits modulate the function of conducting subunits and have putative non-conducting roles, further expanding the repertoire of cellular processes governed by ion channel complexes to processes such as transcellular adhesion and gene transcription. Given this expansive influence of ion channels on cellular behaviour it is perhaps no surprise that aberrant ion channel expression is a common occurrence in cancer. This review will focus on the conducting and non-conducting roles of the auxiliary subunits of various Ca2+, K+, Na+ and Cl- channels and the burgeoning evidence linking such auxiliary subunits to cancer. Several subunits are upregulated (e.g. Cavβ, Cavγ) and downregulated (e.g. Kvβ) in cancer, while other subunits have been functionally implicated as oncogenes (e.g. Navβ1, Cavα2δ1) and tumour suppressor genes (e.g. CLCA2, KCNE2, BKγ1) based on in vivo studies. The strengthening link between ion channel auxiliary subunits and cancer has exposed these subunits as potential biomarkers and therapeutic targets. However further mechanistic understanding is required into how these subunits contribute to tumour progression before their therapeutic potential can be fully realised.

Resveratrol Influences Pancreatic Islets by Opposing Effects on Electrical Activity and Insulin Release

SCOPE

Resveratrol is suggested to improve glycemic control by activation of sirtuin 1 (SIRT1) and has already been tested clinically. Our investigation characterizes the targets of resveratrol in pancreatic beta cells and their contribution to short- and long-term effects on insulin secretion.

METHODS AND RESULTS

Islets or beta cells are isolated from C57BL/6N mice. Electrophysiology is performed with microelectrode arrays and patch-clamp technique, insulin secretion and content are determined by radioimmunoassay, cAMP is measured by enzyme-linked immunosorbent assay, and cytosolic Ca²⁺ concentration by fluorescence methods. Resveratrol (25 μmol L^-1 ) elevates [Ca²⁺ ]_c and potentiates glucose-stimulated insulin secretion. These effects are associated with increased intracellular cAMP and are sensitive to the SIRT1 blocker Ex-527. Inhibition of EPAC1 by CE3F4 also abolishes the stimulatory effect of resveratrol. The underlying mechanism does not involve membrane depolarization as resveratrol even reduces electrical activity despite blocking K_ATP channels. Importantly, after prolonged exposure to resveratrol (14 days), the beneficial influence of the polyphenol on insulin release is lost.

CONCLUSION

Resveratrol addresses multiple targets in pancreatic islets. Potentiation of insulin secretion is mediated by SIRT1-dependent activation of cAMP/EPAC1. Considering resveratrol as therapeutic supplement for patients with type 2 diabetes mellitus, the inhibitory influence on electrical excitability attenuates positive effects.

Phytoceuticals in Acute Pancreatitis: Targeting the Balance between Apoptosis and Necrosis

Despite recent advances in understanding the complex pathogenesis of pancreatitis, the management of the disease remains suboptimal. The use of phytoceuticals (plant-derived pleiotropic multitarget molecules) represents a new research trend in pancreatology. The purpose of this review is to discuss the phytoceuticals with pancreatoprotective potential in acute pancreatitis and whose efficacy is based, at least in part, on their capacity to modulate the acinar cell death. The phytochemicals selected, belonging to such diverse classes as polyphenols, flavonoids, lignans, anthraquinones, sesquiterpene lactones, nitriles, and alkaloids, target the balance between apoptosis and necrosis. Activation of apoptosis via various mechanisms (e.g., inhibition of X-linked inhibitor of apoptosis proteins by embelin, upregulation of FasL gene expression by resveratrol) and/or inhibition of necrosis seem to represent the essential key for decreasing the severity of the disease. Apart from targeting the apoptosis/necrosis balance, the phytochemicals displayed other specific protective activities: inhibition of inflammasome (e.g., rutin), suppression of neutrophil infiltration (e.g., ligustrazine, resveratrol), and antioxidant activity. Even though many of the selected phytoceuticals represent a promising therapeutic alternative, there is a shortage of human evidence, and further studies are required to provide solid basis to justify their use in the treatment of pancreatitis.

Hepatitis B X-interacting protein promotes the formation of the insulin gene-transcribing protein complex Pdx-1/Neurod1 in animal pancreatic β-cells

The activation of insulin gene transcription depends on multiple nuclear proteins, including the transcription factors PDX-1 and NEUROD1, which form a transcriptional complex. We recently reported that hepatitis B X-interacting protein (HBXIP, also termed LAMTOR5) can modulate glucose metabolism reprogramming in cancer cells. However, the physiological role of HBXIP in the modulation of glucose metabolism in normal tissues is poorly understood. Here, we report that Hbxip is an essential regulator of the effect of the Pdx-1/Neurod1 complex on insulin gene transcription in murine pancreatic β-cells in vitro and in vivo We found that pancreatic β-cell-specific Hbxip-knockout mice displayed higher fasting blood glucose levels and impaired glucose tolerance. Furthermore, Hbxip was involved in the regulation of insulin in the pancreas islets and increased insulin gene expression in rat pancreatic β-cells. Mechanistically, Hbxip stimulated insulin enhancer activity by interacting with Pdx-1 and recruiting Neurod1 to Pdx-1. Functionally, we provide evidence that Hbxip is required for Pdx-1/Neurod1-mediated insulin expression in rat pancreatic β-cells. Collectively, these results indicate that Hbxip is involved in the transcription of insulin by increasing the levels of the Pdx-1/Neurod1 complex in animal pancreatic β-cells. Our finding provides the insight into the mechanism by which Hbxip stimulates the transcription of the insulin gene.

Biological effects of combined resveratrol and vitamin D3 on ovarian tissue

BACKGROUND

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural antioxidant polyphenol able to exert a wide range of biological effect on several tissues. Despite its important beneficial properties, it has a low water solubility, which limits its therapeutic applications in humans. Resveratrol also acts as a phytoestrogen that modulates estrogen receptor (ER)-mediated transcription. In addition, it has been shown that ovarian tissues benefit greatly from vitamin D3, which exerts its beneficial effects through VDR receptors. The aim was to evaluate the cooperative effects of resveratrol combined with vitamin D3 on ovarian cells and tissues and some other organs as well. Moreover, the modulation of specific intracellular pathways involving ER and VDR receptors has been studied.

METHODS

The experiments were performed both in vitro and in vivo, to analyze cell viability, radical oxygen species production, signal transductions through Western Blot, and resveratrol quantification by HPLC.

RESULTS

Cell viability, radical oxygen species production, and intracellular pathways have been studied on CHO-K1 cells. Also, the relative mechanism activated following oral intake in female Wistar rats as animal model was investigated, evaluating bioavailability, biodistribution and signal transduction in heart, kidney, liver and ovarian tissues. Both in in vitro and in vivo experiments, resveratrol exerts more evident effects when administered in combination with vitD in ovarian cells, showing a common biphasic cooperative effect: The role of vitamin D3 in maintaining and supporting the biological activity of resveratrol has been clearly observed. Moreover, resveratrol plus vitamin D3 blood concentrations showed a biphasic absorption rate.

CONCLUSIONS

Such results could be used as a fundamental data for the development of new therapies for gynecological conditions, such as hot-flashes.

Role of Resveratrol (RES) in Regenerative Medicine

Within the last quarter century, technology has been a major catalyst of the advancement in various fields of scientific knowledge, particularly medical research. This new enlightenment has spurred the exploration of alternative treatment methods to some of society's most problematic diseases. One such innovative treatment is the use of Resveratrol (RES) to treat a number of pathophysiological conditions. RES is a natural polyphenolic compound found in the skin(s) of blueberries, red grapes (a major constituent of red wine), some vegetables, and even peanuts. The compound has a number of potent regenerative properties, which include: anti-aging, anti-inflammatory, and antioxidative. Research has confirmed both in vivo and in vitro RES's beneficial applications to numerous diseases. This chapter centers on its unique healing powers and beneficial applications against myriad debilitating conditions.

The Impact of Resveratrol Supplementation on Blood Glucose, Insulin, Insulin Resistance, Triglyceride, and Periodontal Markers in Type 2 Diabetic Patients with Chronic Periodontitis

The aim of this study was to investigate the impact of resveratrol supplementation along with non-surgical periodontal treatment on blood glucose, insulin, insulin resistance, triglyceride (TG), and periodontal markers in patients with type 2 diabetes with periodontal disease. In this double-blind clinical trial study, 43 patients with diabetes with chronic periodontitis were participated. Subjects were randomly allocated to intervention and control groups. The intervention and control groups received either 480 mg/day of resveratrol or placebo capsules (two pills) for 4 weeks. Fasting blood glucose, insulin, insulin resistance (homeostasis model assessment of insulin resistance), TGs, and pocket depth were measured in all subjects' pre-intervention and post-intervention. The mean serum levels of fasting insulin and insulin resistance (homeostasis model assessment of insulin resistance) were significantly lower in the intervention group compared with control group (10.42 ± 0.28 and 10.92 ± 0.9; 3.66 ± 0.97 and 4.49 ± 1.56, respectively). There was a significant difference in the mean pocket depth between intervention and control groups (2.35 ± 0.6 and 3.38 ± 0.5, respectively) following intervention. No significant differences were observed in the mean levels of fasting blood glucose and TGs between two groups' post-intervention. It is recommended that resveratrol supplementation may be beneficial as adjuvant therapy along with non-surgical periodontal treatment in insulin resistance and improving periodontal status among patients with diabetes with periodontal disease. Copyright © 2016 John Wiley & Sons, Ltd.

Effects of Bisphenol A on ion channels: Experimental evidence and molecular mechanisms

Bisphenol A (BPA) is an endocrine-disrupting chemical (EDC) produced in huge quantities in the manufacture of polycarbonate plastics and epoxy resins. It is present in most humans in developed countries, acting as a xenoestrogen and it is considered an environmental risk factor associated to several diseases. Among the whole array of identified mechanisms by which BPA can interfere with physiological processes in living organisms, changes on ion channel activity is one of the most poorly understood. There is still little evidence about BPA regulation of ion channel expression and function. However, this information is key to understand how BPA disrupts excitable and non-excitable cells, including neurons, endocrine cells and muscle cells. This report is the result of a comprehensive literature review on the effects of BPA on ion channels. We conclude that there is evidence to say that these important molecules may be key end-points for EDCs acting as xenoestrogens. However, more research on channel-mediated BPA effects is needed. Particularly, mechanistic studies to unravel the pathophysiological actions of BPA on ion channels at environmentally relevant doses.

Administration of resveratrol for 5 wk has no effect on glucagon-like peptide 1 secretion, gastric emptying, or glycemic control in type 2 diabetes: a randomized controlled trial

BACKGROUND

Resveratrol has been reported to lower glycemia in rodent models of type 2 diabetes associated with the stimulation of glucagon-like peptide 1 (GLP-1), which is known to slow gastric emptying, stimulate insulin secretion, and suppress glucagon secretion and energy intake.

OBJECTIVE

We evaluated the effects of 5 wk of resveratrol treatment on GLP-1 secretion, gastric emptying, and glycemic control in type 2 diabetes.

DESIGN

Fourteen patients with diet-controlled type-2 diabetes [mean ± SEM glycated hemoglobin (HbA1c): 6.4 ± 0.2% (46.4 ± 2.2 mmol/mol)] received resveratrol (500 mg twice daily) or a placebo over two 5-wk intervention periods with a 5-wk washout period in between in a double-blind, randomized, crossover design. Before and after each intervention period (4 visits), body weight and HbA1c were measured, and patients were evaluated after an overnight fast with a standardized mashed-potato meal labeled with 100 μg (13)C-octanoic acid to measure blood glucose and plasma GLP-1 concentrations and gastric emptying (breath test) over 240 min. Daily energy intake was estimated from 3-d food diaries during the week before each visit.

RESULTS

Fasting and postprandial blood glucose and plasma total GLP-1 as well as gastric emptying were similar at each assessment, and the change in each variable from weeks 0 to 5 did not differ between resveratrol and placebo groups. Similarly, changes in HbA1c, daily energy intake, and body weight after 5 wk did not differ between the 2 treatments.

CONCLUSIONS

In patients with diet-controlled type 2 diabetes, 5 wk of twice-daily 500 mg-resveratrol supplementation had no effect on GLP-1 secretion, glycemic control, gastric emptying, body weight, or energy intake. Our observations do not support the use of resveratrol for improving glycemic control. This trial was registered at www.anzctr.org.au as ACTRN12613000717752.

Use of metformin and risk of kidney cancer in patients with type 2 diabetes

BACKGROUND

The anticancer effect of metformin has been reported in the literature but requires additional confirmation in epidemiologic studies. With respect to kidney cancer scarce data are available. This study investigates whether metformin use in patients with type 2 diabetes mellitus (T2DM) might affect kidney cancer risk.

METHODS

The reimbursement database of the National Health Insurance in Taiwan was used. T2DM patients aged ≥ 40 years and newly treated with either metformin (n=171,753, "ever users of metformin") or other antidiabetic drugs (n=75,499, "never users of metformin") within 1998-2002 were followed for at least 6 months for kidney cancer until 31 December 2009. The treatment effect was estimated by Cox regression using propensity score weighting by inverse probability of treatment weighting approach. Hazard ratios were estimated for ever versus never users, and for tertiles of cumulative duration of metformin therapy.

RESULTS

During follow-up, 917 ever users and 824 never users developed kidney cancer, with respective incidence of 80.09 and 190.30 per 100,000 person-years. The hazard ratio (95% confidence intervals) for ever versus never users is 0.279 (0.254-0.307); and is 0.598 (0.535-0.668), 0.279 (0.243-0.321) and 0.104 (0.088-0.124), respectively, for the first, second, and third tertile of cumulative duration of <14.5, 14.5-45.8 and >45.8 months. In subgroup analyses, the lower risk of kidney cancer associated with metformin use is consistently observed in both sexes, and in patients with or without concomitant use of other antidiabetic drugs.

CONCLUSION

Metformin use is associated with a decreased risk of kidney cancer in patients with T2DM.

Resveratrol in the treatment of pancreatic cancer

Pancreatic cancer (PCa), which is now the fourth most frequent cause of cancer-related death, has a median survival of less than 6 months and a 5-year survival rate of <6%. The hallmarks of this cancer include poor outcome, short survival duration, and resistance to therapy. The poor prognosis of PCa is related to its local recurrence, lymph node and liver metastases, and peritoneal dissemination. Recent studies have indicated that resveratrol has cancer-chemopreventive and anticancer activities. In this short review we summarize the chemopreventive and treatment effects of resveratrol in PCa, as follows: resveratrol inhibits the proliferation of pancreatic cancer cells; induces apoptosis and cell cycle arrest; inhibits metastasis and invasion of PCa cells; inhibits the proliferation and viability of PCa stem cells; enhances the chemoradiosensitization of PCa cells; and can affect diabetes mellitus in addition to PCa. On the basis of these data, resveratrol may be considered a potential anticancer agent for the treatment of PCa.

Kir6.2-containing ATP-sensitive K(+) channel is required for cardioprotection of resveratrol in mice

Background

Resveratrol is a natural compound that affects energy metabolism and is also known to possess an array of cardioprotective effects. However, its overall effects on energy metabolism and the underlying mechanism involved in cardioprotection require further investigation. Herein we hypothesize that ATP-sensitive potassium (K-ATP) channels as molecular sensors of cellular metabolism may mediate the cardioprotective effects of resveratrol.

Methods

Kir6.2 knockout, Kir6.1 heterozygous and wild-type (WT) mice were subjected to ischemia/reperfusion injury and were injected with resveratrol (10 mg/kg, i.p). Myocardial infarct size, serum lactate dehydrogenase (LDH) and creatine kinase (CK) activities were determined. Neonatal cardiomyocytes were used in in vitro assays to investigate the underlying mechanism of resveratrol in cardioprotection.

Results

Resveratrol treatment significantly reduced myocardial infarct size and serum LDH and CK activity and inhibited oxygen-glucose deprivation/reoxygenation – induced cardiomyocyte apoptosis in WT and Kir6.1 heterozygous mice, but Kir6.2 deficiency can abolish the cardioprotective effects of resveratrol in vivo and in vitro. We further found that resveratrol enhanced 5′-AMP-activated protein kinase (AMPK) phosphorylation and promoted the association of AMPK with Kir6.2. Suppression of AMPK attenuated and activation of AMPK mimicked the cardioprotective effects of resveratrol in cardiomyocytes. Notably, Kir6.2 knockout also reversed the cardioprotection of AMPK activator.

Conclusions

Our study demonstrates that resveratrol exerts cardioprotective effects through AMPK -Kir6.2/K-ATP signal pathway and Kir6.2-containing K-ATP channel is required for cardioprotection of resveratrol.

Regulation of neurons in the dorsal motor nucleus of the vagus by SIRT1

Neurons in the dorsal motor nucleus of the vagus (DMV) play a critical role in the regulation of autonomic functions. Previous studies indicated that central activation of sirtuin 1 (SIRT1) has beneficial effects on homeostasis, most likely via modulation of the autonomic output. Sirtuins are NAD⁺-dependent deacetylases and have been associated with longevity. SIRT1 is one of the best-characterized sirtuins expressed in mammals, and may be involved in the regulation of metabolism. Resveratrol, a SIRT1 activator reduced hyperglycemia likely through activation of vagal output; however, the cellular mechanisms of action have not been determined. In this study, whole-cell patch-clamp electrophysiology on acute brainstem slices was used to test the hypothesis that activation of SIRT1 with resveratrol enhances neurotransmission in DMV neurons. Application of resveratrol increased the frequency of spontaneous excitatory postsynaptic currents (sEPSC). This effect was K_ATP channel-dependent and was prevented with pre-application of SIRT1 inhibitor, EX527. Resveratrol also increased miniature EPSC (mEPSC) frequency without change in amplitude. Furthermore, our data demonstrated that resveratrol regulates excitatory neurotransmission in a PI3 kinase-dependent manner, since wortmannin, a PI3K inhibitor prevented the increase of mEPSC frequency caused by resveratrol. In conclusion, our data demonstrate that resveratrol via SIRT1 increases excitatory neurotransmission to DMV neurons. These observations suggest that activation of SIRT1 may regulate the function of subdiaphragmatic organs through controlling the activity of parasympathetic DMV neurons.

Extracts from Leonurus sibiricus L. increase insulin secretion and proliferation of rat INS-1E insulinoma cells

ETHNOPHARMACOLOGICAL RELEVANCE

Traditional Mongolian medicine (TMM) uses preparations from herbs as one form of medication for the treatment of a diversity of diseases including diabetes mellitus (DM). We evaluated the effect of extracts from the plant Leonurus sibiricus L. (LS), used in TMM to treat typical symptoms of type 2 DM, on insulin secretion, electrophysiological properties, intracellular calcium concentration and cell proliferation of INS-1E insulinoma cells under standard cell culture conditions (SCC; 11.1mM glucose).

MATERIALS AND METHODS

Insulin secretion was measured by ELISA, electrical properties were assessed by whole cell patch clamping, intracellular calcium concentration (Cai) by Fluo-4 time lapse imaging, insulin receptor expression was verified by RT-PCR and cell proliferation assessed by CellTiter-Glo® cell viability assay.

RESULTS

Insulin released from INS-1E cells into the culture medium over 24h was significantly increased in presence of 500 mg/L aqueous LS extract (LS OWE) as well as methanolic LS extract (LS MeOH/H2O) but not in the presence of the butanol-soluble extract (LS MeOH/BuOH). Acute application of LS OWE resulted in a depolarization of the cell membrane potential paralleled by an initial increase and subsequent decline and silencing of action potential frequency, by KATP channel inhibition, persisting depolarization and an increase in Cai. The electrophysiological effects were comparable to those of 100 μM tolbutamide, which, however failed to elevate insulin secretion under SCC. Furthermore all LS extracts stimulated INS-1E cell proliferation.

CONCLUSIONS

The finding that extracts from Leonurus sibiricus L. enhance insulin secretion and/or foster cell proliferation may provide possible explanations for the underlying therapeutic principles in the empirical use of LS-containing formulations in DM and DM-related disorders as applied in TMM.

Pancreatic cancer chemoprevention by phytochemicals

Pancreatic cancer is fourth leading cause of cancer-related deaths in the United States of America. In spite of recent advances in the current therapeutic modalities such as surgery, radiation and chemotherapy patients, the average five year survival rate remains still less than 5%. Recently, compounds from natural sources receive ample of attention as anti-cancer agents. Many epidemiological studies published over the past few decades provide a strong correlation between consumption of vegetables, fruits or plant derived products and reduced incidence of cancer. The present review focuses on the potential antitumor effects of various natural products.

The protective effect of resveratrol on islet insulin secretion and morphology in mice on a high-fat diet

The aim of this study was to investigate the effect of resveratrol on beta cells in male C57BL/6J mice fed a high-fat diet and the possible mechanisms. Male C57BL/6J mice were randomly divided into three groups: normal control (NC) group, high-fat diet (HF) group and high-fat diet and resveratrol treatment (HFR) group (15 in each group). HFR group was fed with high fat diet for 8 weeks and then orally administered resveratrol at 400mg/kg daily. Twenty-four weeks later, the function of insulin secretion in vivo and in vitro was improved robustly in HFR group compared with HF group. The levels of glucose and lipid metabolism, beta cell mass, lipid content, and oxidative stress were lower in HFR group than in HF group. Simultaneously, resveratrol administration promoted the expression of SIRT1 in islets, while the expression of uncoupling protein 2 (UCP2) was restrained. Resveratrol, as well, also had a beneficial effect on the ratios of expressions of Bcl-2/Bax and levels of malondialdehyde/glutathione peroxidase. Resveratrol can protect islets from abnormal insulin secretion and morphological changes induced by a high-fat diet. The effect might be partly related to activated SIRT1 signal pathway, improved oxidative stress induced damage and incidence of apoptosis.

Nuciferine stimulates insulin secretion from beta cells-an in vitro comparison with glibenclamide

ETHNOPHARMACOLOGICAL RELEVANCE

Several Asian plants are known for their anti-diabetic properties and produce alkaloids and flavonoids that may stimulate insulin secretion.

MATERIALS AND METHODS

Using Vietnamese plants (Nelumbo nucifera, Gynostemma pentaphyllum, Smilax glabra, and Stemona tuberosa), we extracted two alkaloids (neotuberostemonine, nuciferine) and four flavonoids (astilbin, engeletin, smitilbin, and 3,5,3'-trihydroxy-7,4'-dimethoxyflavone), and studied their insulin stimulatory effects.

RESULTS

Nuciferine, extracted from Nelumbo nucifera, stimulated both phases of insulin secretion in isolated islets, whereas the other compounds had no effect. The effect of nuciferine was totally abolished by diazoxide and nimodipine, and diminished by protein kinase A and protein kinase C inhibition. Nuciferine and potassium had additive effects on insulin secretion. Nuciferine also stimulated insulin secretion in INS-1E cells at both 3.3 and 16.7 mM glucose concentrations. Compared with glibenclamide, nuciferine had a stronger effect on insulin secretion and less beta-cell toxicity. However, nuciferine did not compete with glibenclamide for binding to the sulfonylurea receptor.

CONCLUSIONS

Among several compounds extracted from anti-diabetic plants, nuciferine was found to stimulate insulin secretion by closing potassium-adenosine triphosphate channels, explaining anti-diabetic effects of Nelumbo nucifera.

Resveratrol-activated SIRT1 in liver and pancreatic β-cells: a Janus head looking to the same direction of metabolic homeostasis

Sirtuins are energy sensors which mediate effects of calorie restriction-induced lifespan extension. The mammalian sirtuin homolog SIRT1 is a protein deacetylase playing a central role in metabolic homeostasis. SIRT1 is one of the targets of resveratrol, a polyphenol that has been shown to increase lifespan and to protect animal models against high-calorie diet induced obesity and insulin resistance. The beneficial effects of resveratrol mediated by SIRT1 activation can be contributed by different organs. Among them, the liver and pancreatic β-cells have been shown to be responsive to resveratrol in a SIRT1-dependent manner. Downstream of SIRT1, transcription factors being activated are tissue-specific, in turn inducing expression of metabolic genes in an apparent paradoxical way. In this review, we discuss specificities of SIRT1 effects in the liver versus pancreatic β-cells, ultimately converging towards metabolic homeostasis at the organism level.

Lithospermic acid B protects β-cells from cytokine-induced apoptosis by alleviating apoptotic pathways and activating anti-apoptotic pathways of Nrf2-HO-1 and Sirt1

Lithospermic acid B (LAB) has been reported to protect OLETF rats, an established type 2 diabetic animal model, from the development of diabetes-related vascular complications. We investigated whether magnesium lithospermate B (LAB) has a protective role under cytokine-induced apoptosis in INS-1 cells in vitro and whether it slows the development of diabetes in OLETF rats in vivo. Pretreatment with 50 μM LAB significantly reduced the 1000 U/mL INF-γ and 100 U/mL IL-1β-induced INS-1 cell death. LAB significantly alleviated cytokine-induced phosphorylations of p38 and JNK in accordance with a decrease in cleaved caspase-3 activity in beta-cells. LAB also protected against the cytokine-induced caspase-3 apoptotic pathway via significant activation of Nrf2-HO (heme-oxygenase)-1 and Sirt1 expression. OLETF rats treated with 40 mg/kg/day LAB showed a significant improvement in glucose tolerance compared to untreated OLETF control rats in vivo. Our results suggest that the cytoprotective effects of LAB on pancreatic β-cells are related with both alleviating apoptotic pathways and activating anti-apoptotic pathways of Nrf2-HO-1 and Sirt1.

Multifaceted approach to resveratrol bioactivity: Focus on antioxidant action, cell signaling and safety

Resveratrol (RVT) is a naturally occurring trihydroxy stilbene that displays a wide spectrum of physiological activity. Its ability to behave therapeutically as a component of red wine has attracted wide attention. The phenol acts as a protective agent involving various body constituents. Most attention has been given to beneficial effects in insults involving cancer, aging, cardiovascular system, inflammation and the central nervous system. One of the principal modes of action appears to be as antioxidant. Other mechanistic pathways entail cell signaling, apoptosis and gene expression. There is an intriguing dichotomy in relation to pro-oxidant property. Also discussed are metabolism, receptor binding, rationale for safety and suggestions for future work. This is the first comprehensive review of RVT based on a broad, unifying mechanism.

Resveratrol: a relevant pharmacological approach for the treatment of metabolic syndrome?

PURPOSE OF REVIEW

The metabolic syndrome is associated with increased risk for development of both cardiovascular disease and type 2 diabetes in humans. Because experimental data and clinical experience have shown that metabolic syndrome and caloric restriction have, at least partly, opposite pathophysiological pathways, the activation of sirtuins may constitute a pharmacological approach to treat metabolic syndrome. Resveratrol is a polyphenol produced by plants that has multiple beneficial activities similar to those associated with caloric restriction.

RECENT FINDINGS

Through its regulatory action of both AMP kinase and the sirtuin sirtuin-1, resveratrol is a natural sirtuin activator that certainly will be the head of a new pharmacological family of drugs targeted on sirtuin-1 activity exacerbation in order to treat/protect from obesity and diabetes, and thus metabolic syndrome.

SUMMARY

This review discusses the therapeutic use of resveratrol and sirtuin activators in the context of insulin resistance and obesity, the two main features of metabolic syndrome.

Effects of resveratrol on NO secretion stimulated by insulin and its dependence on SIRT1 in high glucose cultured endothelial cells

To investigate the effects of resveratrol on the secretion of NO induced by insulin in high glucose cultured primary human umbilical vein endothelial cells (HUVEC). HUVEC were treated with 1 μmol/l resveratrol for 24 h before cultured in high glucose medium for 48 h, then all cells were stimulated by 100 nmol/l insulin for 30 min. Method based on nitric acid reductase was used to analyze the NO contents in the supernatant. Cells were collected to analyze the expression of eNOS, endothelin-1, E-selectin, and SIRT1. In order to investigate the dependence of resveratrol on SIRT1, the effects of resveratrol on cells treated by SIRT1 siRNA were also examined. Compared with control cells, high glucose decreased the secretion of NO induced by insulin. Resveratrol treatment increased the expression of SIRT1 and the secretion of NO. After interfering the expression of SIRT1 using SIRT1 siRNA, the effects of resveratrol on the NO secretion induced by insulin was impaired. Resveratrol also counteracted other pro-atherosclerotic effects of high glucose, including the up-regulating roles of high glucose on the expression of endothelin-1 mRNA and E-selectin mRNA, and the down-regulating roles of high glucose on the expression of eNOS mRNA and the basal NO secretion without the stimulating of insulin. Resveratrol can improve the NO stimulating function of insulin in high glucose cultured HUVEC in SIRT1-dependent manner. Thus, our results imply that resveratrol may have the preventive roles of atherosclerosis in diabetic patients.

Diabetes mellitus, inflammation, obesity: proposed treatment pathways for current and future therapies

OBJECTIVE

To review the pathophysiology, pharmacology, and current or future therapies under study for use in treating diabetes mellitus, inflammation associated with diabetes mellitus, and/or obesity related to diabetes mellitus, through 1 of 4 investigational pathways: adiponectin, ghrelin, resveratrol, or leptin.

DATA SOURCES

A literature search using MEDLINE (1966-December 12, 2009), PubMed (1950-December 12, 2009), Science Direct (1994-December 12, 2009), and International Pharmaceutical Abstracts (1970-December 12, 2009) was performed using the terms adiponectin, ghrelin, resveratrol, leptin, inflammation, obesity, and diabetes mellitus. English-language, original research, and review articles were examined, and citations from these articles were assessed as well.

STUDY SELECTION AND DATA EXTRACTION

Clinical studies and in vitro studies were included in addition to any Phase 1, 2, or 3 clinical trials.

DATA SYNTHESIS

Mechanistic pathways regarding adiponectin, ghrelin, resveratrol, and leptin are of interest as future treatment options for diabetes mellitus. Each of these pathways has produced significant in vitro and in vivo clinical data warranting further research as a possible treatment pathway for diabetes-related inflammation and/or obesity reduction. While research is still underway to determine the exact effects these pathways have on metabolic function, current data suggest that each of these compounds may be of interest for future therapies.

CONCLUSIONS

While several pathways under investigation may offer additional benefits in the treatment of diabetes mellitus and associated impairments, further investigation is necessary for both investigational and approved therapies to ensure that the impact in new pathways does not increase risks to patient safety and outcomes.

Identification of a novel proapoptotic function of resveratrol in fat cells: SIRT1-independent sensitization to TRAIL-induced apoptosis

The phytochemical resveratrol has recently gained attention for its protection against metabolic disease and for extension of life span, which have been linked to its metabolic effects and SIRT1 activation in fat cells. However, little is known about the effect of resveratrol on fat cell apoptosis. Here, we identify a novel, SIRT1-independent mechanism by which resveratrol regulates fat cell numbers. We demonstrate for the first time that resveratrol enhances TNF-related apoptosis-inducing ligand (TRAIL)- or CD95-induced apoptosis of human preadipocytes in a highly synergistic manner (EC(50) at 72 h: resveratrol, >300 microM; TRAIL, >100 ng/ml; combination: 30 microM resveratrol and 10 ng/ml TRAIL, combination index 0.4). Similar results in primary human preadipocytes prepared from subcutaneous white adipose tissue and mature human adipocytes underline the relevance to human physiology. Mechanistic studies reveal that resveratrol inhibits PI3K-driven phosphorylation of Akt, leading to increased Bax activation, loss of mitochondrial membrane potential, cytochrome c release, and caspase-dependent apoptosis. The synergistic interaction of resveratrol and TRAIL depends on the intrinsic apoptosis pathway and caspases, since Bcl-2 overexpression and the caspase inhibitor zVAD.fmk inhibit apoptosis, whereas knockdown of SIRT1 by RNA interference has no effect. The discovery of this novel activity of resveratrol significantly advances the knowledge of fat tissue regulation by resveratrol and has important implications for its use in metabolic and age-related diseases.

Resveratrol: its biologic targets and functional activity

The polyphenolic phytoalexin resveratrol (RSV) and its analogues have received tremendous attention over the past couple of decades because of a number of reports highlighting their benefits in vitro and in vivo in a variety of human disease models, including cardio- and neuroprotection, immune regulation, and cancer chemoprevention. These studies have underscored the high degree of diversity in terms of the signaling networks and cellular effector mechanisms that are affected by RSV. The activity of RSV has been linked to cell-surface receptors, membrane signaling pathways, intracellular signal-transduction machinery, nuclear receptors, gene transcription, and metabolic pathways. The promise shown by RSV has prompted heightened interest in studies aimed at translating these observations to clinical settings. In this review, we present a comprehensive account of the basic chemistry of RSV, its bioavailability, and its multiple intracellular target proteins and signaling pathways.

Sulfonylurea receptor 1 subunits of ATP-sensitive potassium channels and myocardial ischemia/reperfusion injury

K(ATP) channels are generally cardioprotective under conditions of metabolic impairment, consisting of pore-forming (Kir6.1 and/or Kir6.2) and sulphonylurea-binding, modulatory subunits [sulfonylurea receptor (SUR) 1, 2A, or 2B]. Cardiovascular K(ATP) channels are generally thought to consist of Kir6.2/SUR2A subunits (in the case of heart muscle) or Kir6.1/SUR2B subunits (smooth muscle), whereas SUR1-containing channels have well-documented roles in pancreatic insulin release. Recent data, however, demonstrated the presence of SUR1 subunits in mouse cardiac tissue (particularly in atria) and a surprising protection from myocardial ischemia/reperfusion in SUR1-null mice. Here, we review some of the extra-pancreatic roles assigned to SUR1 subunits and consider whether these might be involved in the sequelae of ischemia/reperfusion.

Resveratrol and chemoprevention

Resveratrol is a phytoalexin, highly abundant in skins of red grapes and moderately abundant in peanuts and blueberries. Originally a constituent of oriental medicines, it has lately been rediscovered for a plethora of beneficial properties such as anti-cancer, anti-aging, antiviral, cardiovascular and neuroprotective effects, thereby making it one of the most sought after phytochemicals for supplementing human diet. Studies done in various laboratories have shown its modulatory effects on multitudes of cell signaling and gene expression pathways. Although most of its effects have been observed in cultured cells, quite a few have also been validated in whole animals as well. It is thus necessary to have a comprehensive look at all those effects of resveratrol in an organismal context. The following review summarizes the effects of resveratrol in the context of chemoprevention.

17beta-Estradiol modulates apoptosis in pancreatic beta-cells by specific involvement of the sulfonylurea receptor (SUR) isoform SUR1

Apoptosis of pancreatic beta-cells is an important factor in the pathophysiology of diabetes. Previously, we have shown that the "phytoestrogen" resveratrol can induce beta-cell apoptosis dependent on the expression of sulfonylurea receptor (SUR) 1, the regulatory subunit of pancreatic ATP-sensitive K(+) channels. Here, we investigate whether 17beta-estradiol also influences beta-cell apoptosis in a SUR1-dependent manner. Therefore, islets from wild type or SUR1 knock-out mice, clonal beta-cells, or HEK293 cells expressing different SUR forms were treated with 17beta-estradiol or estrone. Different apoptotic parameters were determined and estrogen binding to SUR was analyzed. In murine islets, 17beta-estradiol treatment resulted in significant apoptotic changes, which in their nature (either apoptotic or anti-apoptotic) were dependent on the age of the animal. These effects were not observed in SUR1 knock-out mice. Furthermore, 17beta-estradiol, which specifically binds to SUR, induced enhanced apoptosis in SUR1-expressing HEK293 cells and clonal beta-cells, whereas apoptosis in recombinant cells expressing SUR2A or SUR2B (cardiac or vascular SUR-isoforms) or sham-transfected control cells was significantly lower. The apoptotic potency of 17beta-estradiol was much higher than that of resveratrol or estrone. SUR1-specific 17beta-estradiol-induced apoptosis was either abolished by the mutation M1289T in transmembrane helix 17 of SUR1 or clearly enhanced by two mutations in nucleotide binding fold 2 (R1379C, R1379L). In conclusion, 17beta-estradiol treatment modulates beta-cell apoptosis under specific involvement of SUR1 in an age-dependent manner. 17beta-Estradiol-induced apoptosis can be influenced by certain SUR1 mutations. These findings may contribute to the understanding of pathophysiological changes in beta-cell mass and could, for instance, provide interesting aspects concerning the etiology of gestational diabetes.

Chicoric acid, a new compound able to enhance insulin release and glucose uptake

Caffeic acid and chlorogenic acid (CGA), a mono-caffeoyl ester, have been described as potential antidiabetic agents. Using in vitro studies, we report the effects of a dicaffeoyl ester, chicoric acid (CRA) purified from Cichorium intybus, on glucose uptake and insulin secretion. Our results show that CRA and CGA increased glucose uptake in L6 muscular cells, an effect only observed in the presence of stimulating concentrations of insulin. Moreover, we found that both CRA and CGA were able to stimulate insulin secretion from the INS-1E insulin-secreting cell line and rat islets of Langerhans. In the later case, the effect of CRA is only observed in the presence of subnormal glucose levels. Patch clamps studies show that the mechanism of CRA and CGA was different from that of sulfonylureas, as they did not close K(ATP) channels. Chicoric acid is a new potential antidiabetic agent carrying both insulin sensitizing and insulin-secreting properties.

Interaction of asymmetric ABCC9-encoded nucleotide binding domains determines KATP channel SUR2A catalytic activity

Nucleotide binding domains (NBDs) secure ATP-binding cassette (ABC) transporter function. Distinct from traditional ABC transporters, ABCC9-encoded sulfonylurea receptors (SUR2A) form, with Kir6.2 potassium channels, ATP-sensitive K+ (K ATP) channel complexes. SUR2A contains ATPase activity harbored within NBD2 and, to a lesser degree, NBD1, with catalytically driven conformations exerting determinate linkage on the Kir6.2 channel pore. While homodomain interactions typify NBDs of conventional ABC transporters, heterodomain NBD interactions and their functional consequence have not been resolved for the atypical SUR2A protein. Here, nanoscale protein topography mapped assembly of monodisperse purified recombinant SUR2A NBD1/NBD2 domains, precharacterized by dynamic light scattering. Heterodomain interaction produced conformational rearrangements inferred by secondary structural change in circular dichroism, and validated by atomic force and transmission electron microscopy. Physical engagement of NBD1 with NBD2 translated into enhanced intrinsic ATPase activity. Molecular modeling delineated a complemental asymmetry of NBD1/NBD2 ATP-binding sites. Mutation in the predicted catalytic base residue, D834E of NBD1, altered NBD1 ATPase activity disrupting potentiation of catalytic behavior in the NBD1/NBD2 interactome. Thus, NBD1/NBD2 assembly, resolved by a panel of proteomic approaches, provides a molecular substrate that determines the optimal catalytic activity in SUR2A, establishing a paradigm for the structure-function relationship within the K ATP channel complex.

Resveratrol-induced inhibition of insulin secretion from rat pancreatic islets: evidence for pivotal role of metabolic disturbances

Resveratrol is a stilbene present in different plant species and exerting numerous beneficial effects, including prevention of diabetes and attenuation of some diabetic complications. Its inhibitory effect on insulin secretion was recently documented, but the exact mechanism underlying this action remains unknown. Experiments employing diazoxide and a high concentration of K(+) revealed that, in depolarized pancreatic islets incubated for 90 min with resveratrol (1, 10, and 100 microM), insulin secretion stimulated by glucose and leucine was impaired. The attenuation of the insulin secretory response to 6.7 mM glucose was not abrogated by blockade of intracellular estrogen receptors and was found to be accompanied by diminished islet glucose oxidation, enhanced lactate production, and reduced ATP levels. Glucose-induced hyperpolarization of the mitochondrial membrane was also reduced in the presence of resveratrol. Moreover, in depolarized islets incubated with 2.8 mM glucose, activation of protein kinase C or protein kinase A potentiated insulin release; however, under these conditions, resveratrol was ineffective. Further studies also revealed that, under conditions of blocked voltage-dependent calcium channels, the stilbene reduced insulin secretion induced by a combination of glucose with forskolin. These data demonstrate that resveratrol 1) inhibits the amplifying pathway of insulin secretion, 2) exerts an insulin-suppressive effect independently of its estrogenic/anti-estrogenic activity, 3) shifts islet glucose metabolism from mitochondrial oxidation to anaerobic,4) fails to abrogate insulin release promoted without metabolic events, and 5) does not suppress hormone secretion as a result of the direct inhibition of Ca(2+) influx through voltage-dependent calcium channels.

SIRT1 improves insulin sensitivity under insulin-resistant conditions by repressing PTP1B

Insulin resistance is often characterized as the most critical factor contributing to the development of type 2 diabetes. SIRT1 has been reported to be involved in the processes of glucose metabolism and insulin secretion. However, whether SIRT1 is directly involved in insulin sensitivity is still largely unknown. Here we show that SIRT1 is downregulated in insulin-resistant cells and tissues and that knockdown or inhibition of SIRT1 induces insulin resistance. Furthermore, increased expression of SIRT1 improved insulin sensitivity, especially under insulin-resistant conditions. Similarly, resveratrol, a SIRT1 activator, enhanced insulin sensitivity in vitro in a SIRT1-dependent manner and attenuated high-fat-diet-induced insulin resistance in vivo at a dose of 2.5 mg/kg/day. Further studies demonstrated that the effect of SIRT1 on insulin resistance is mediated by repressing PTP1B transcription at the chromatin level. Taken together, the finding that SIRT1 improves insulin sensitivity has implications toward resolving insulin resistance and type 2 diabetes.

Mitochondria, Calcium, and Calpain are Key Mediators of Resveratrol-Induced Apoptosis in Breast Cancer

Resveratrol (RES), a natural plant polyphenol, has gained interest as a nontoxic chemopreventive agent capable of inducing tumor cell death in a variety of cancer types. However, the early molecular mechanisms of RES-induced apoptosis are not well defined. Using the human breast cancer cell lines MDA-MB-231 and MCF-7, we demonstrate that RES is antiproliferative and induces apoptosis in a concentration- and time-dependent manner. Preceding apoptosis, RES instigates a rapid dissipation of mitochondrial membrane potential by directly targeting mitochondria. This is followed by release of cytochrome c and second mitochondria-derived activator of caspase/direct inhibitor of apoptosis-binding protein with low pI (Smac/DIABLO) into the cytoplasm and substantial increase in the activities of caspases-9 and -3 in MDA-MB-231 cells. In addition, live cell microscopy demonstrates that RES causes an early biphasic increase in the concentration of free intracellular calcium ([Ca2+]i), probably resulting from depletion of the endoplasmic reticulum stores in breast cancer cells. In caspase-3-deficient MCF-7 cells, apoptosis is mediated by the Ca2+-activated protease, calpain, leading to the degradation of plasma membrane Ca2+-ATPase isoform 1 and fodrin; the degradation is attenuated by buffering [Ca2+]i and blocked by calpain inhibitors. Mitochondrial permeability transition pore antagonists also blocked calpain activation. In vivo mouse xenograft studies demonstrate that RES treatment inhibits breast cancer growth with no systemic toxicities. Together, these results suggest a critical role for mitochondria not only in the intrinsic apoptotic pathway but also in the Ca2+ and calpain-dependent cell death initiated by RES. Thus, RES may prove useful as a nontoxic alternative for breast cancer treatment.

Resveratrol enhances insulin secretion by blocking K(ATP) and K(V) channels of beta cells

The present study investigated the effect of resveratrol on the electrophysiology and insulin secretion of pancreatic beta cells, and examined resveratrol-induced alterations in insulin levels and plasma glucose of normal and streptozotocin-induced diabetic rats. Whole-cell voltage clamp study in the MIN6 cell, a mouse beta cell line, revealed that resveratrol significantly inhibited ATP-sensitive K(+) current at 3 micromol/l, and voltage-gated K(+) currents at 30 micromol/l. Ca(2+)-activated K(+) current was activated by resveratrol at 100 micromol/l. In MIN6 cells stained with membrane potential dye DiBAC(4)(5), resveratrol markedly depolarized membrane potential at the concentrations of 3-100 micromol/l. Insulin secretion was increased in the presence of resveratrol in MIN6, Hit-T15, and RIN-m5F cells. Resveratrol (3 mg/kg, i.p.) increased insulin secretion associated with a lowering in plasma glucose in normal rats, but not in streptozotocin-diabetic rats within the initial 60 min. In conclusion, resveratrol can act as an insulin-secretagogue through I(KATP) and I(KV) inhibition which can contribute to plasma glucose lowering effect in normal rats.