Beneficial effects of combined resveratrol and metformin therapy in treating diet-induced insulin resistance

Morphological and biomechanical characterization of long bones and peri-implant bone repair in type 2 diabetic rats treated with resveratrol

Type 2 diabetes interferes with bone remodeling mechanisms, requiring studies to reverse this damage, and resveratrol is a polyphenol with rich properties. This study aimed to characterize the long bone morphology and peri-implant biomechanics of normoglycemic and type 2 diabetic animals treated with resveratrol. Thirty-two male Wistar rats were used and divided into normoglycemic and diabetic with or without treatment. They had the installation of implants in the tibia and treatment with oral resveratrol within 45 days. Resveratrol was responsible for weight homeostasis and decreased glycemic levels in rats with type 2 diabetes. The three-point bending testing, resveratrol showed positive effects on the biomechanics of long bones, corroborating a more resistant bone in comparison to untreated diabetics. Micro-ct revealed how bone metabolism is affected by systemic disease, decreasing bone quality. The counter-torque of normoglycemic animals showed superior osseointegration to diabetes, with no differences in the administration of the polyphenol, showing the sovereignty of the deleterious effects of the disease when there is a tissue lesion and an inflammatory picture installed. Overall, resveratrol acted positively in the etiopathogenesis of type 2 diabetes and revealed positive effects on the strength of long bones.

Resveratrol as a potential protective compound against skeletal muscle insulin resistance

The increasing prevalence of type 2 diabetes has become a major global problem. Insulin resistance has a central role in pathophysiology of type 2 diabetes. Skeletal muscle is responsible for the disposal of most of the glucose under conditions of insulin stimulation, and insulin resistance in skeletal muscle causes dysregulation of glucose homeostasis in the whole body. Despite the current pharmaceutical and non-pharmacological treatment strategies to combat diabetes, there is still a need for new therapeutic agents due to the limitations of the therapeutic agents. Meanwhile, plant polyphenols have attracted the attention of researchers for their use in the treatment of diabetes and have gained popularity. Resveratrol, a stilbenoid polyphenol, exists in various plant sources, and a growing body of evidence suggests its beneficial properties, including antidiabetic activities. The present review aimed to provide a summary of the role of resveratrol in insulin resistance in skeletal muscle and its related mechanisms. To achieve the objectives, by searching the PubMed, Scopus and Web of Science databases, we have summarized the results of all cell culture, animal, and human studies that have investigated the effects of resveratrol in different models on insulin resistance in skeletal muscle.

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.

A Review on the Antidiabetic Properties of Moringa oleifera Extracts: Focusing on Oxidative Stress and Inflammation as Main Therapeutic Targets

Moringa oleifera is one of the popular plants that have shown significant health benefits. Certainly, preclinical evidence (predominantly from animal models) summarized in the current review supports the beneficial effects of Moringa oleifera leaf extracts in combating the prominent characteristic features of diabetes mellitus. This includes effective control of blood glucose or insulin levels, enhancement of insulin tissue sensitivity, improvement of blood lipid profiles, and protecting against organ damage under sustained conditions of hyperglycemia. Interestingly, as major complications implicated in the progression of diabetes, including organ damage, Moringa oleifera leaf and seed extracts could efficiently block the detrimental effects of oxidative stress and inflammation in these preclinical models. Notably, these extracts (especially leaf extracts) showed enhanced effects in strengthening intracellular antioxidant defences like catalase, superoxide dismutase, and glutathione to lower lipid peroxidation products and reduce prominent pro-inflammatory markers such as tumor necrosis factor-α, interleukin (1L)-β, IL-6, monocyte chemoattractant protein-1 and nitric oxide synthase. From animal models of diabetes, the common and effective dose of leaf extracts of Moringa oleifera was 100-300 mg/kg, within the treatment duration of 2-8 weeks. Whereas supplementation with approximately 20 g leaf powder of Moringa oleifera for at least 2 weeks could improve postprandial blood glucose in subjects with prediabetes or diabetes. Although limited clinical studies have been conducted on the antidiabetic properties of Moringa oleifera, current findings provide an important platform for future research directed at developing this plant as a functional food to manage diabetic complications.

Interaction between CETP polymorphism and dietary insulin index and load in relation to cardiovascular risk factors in diabetic adults

Gene-diet interactions may play an important role in the inter individual diversity observed in on cardiovascular disease (CVD) risk factors. Therefore, in the current study, we examined the interaction of CETP TaqB1 polymorphism with dietary insulin index and load (DII and DIL), in altering on CVD risk factors among type 2 diabetes mellitus (T2DM). In this cross-sectional study, blood samples were collected from 220 type 2 diabetic patients (134 females and 86 male) with a mean age of 52.24 years in Tehran, Iran. DIL and DII were obtained via validated food-frequency questionnaire (FFQ). Taq1B polymorphism was genotyped by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Biochemical markers including total cholesterol (TC), low-density lipoprotein (LDL), high-density lipoprotein (HDL), triglyceride (TG), superoxide dismutase (SOD), C-reactive protein (CRP), total antioxidant capacity (TAC), pentraxin-3 (PTX3), isoprostaneF2α (PGF2α). interleukin 18 (IL18), leptin and ghrelin were measured by standard protocol. Patients with B1B1 genotype had lower lipid profiles include LDL/HDL (P < 0.001) and TG (P = 0.04) when they consumed diets higher on the DIL and DII index. Moreover, carriers of B2B2 genotype who were in the last tertile of DIL had higher antioxidant and inflammatory markers include SOD (P = 0.01), PGF2α (P = 0.04) and CRP (P = 0.02). Further, a significant interaction between CETP TaqB1 and DII was shown in terms of WC (P = 0.01), where the highest WC were observed in B2B2 genotype carriers following a DII score. However, the highest inflammatory and antioxidant markers include CRP (P = 0.04), TAC (P = 0.01), SOD (P = 0.02), and PGF2α (P = 0.02) were observed in B2B2 genotype carriers when they consumed diets higher on the DII index. Based on the current study, it could be proposed that CETP polymorphism may be associated with CVD risk factors in T2DM patients with high following insulin indices, including DII and DIL. It seems that CETP Taq1B polymorphism can invert the result produced by insulin. This conclusion illustrates that the CETP Taq1B B1 allele could counteract the CVD risk induced by high DII and DIL.

Diabetes Mellitus and Cardiovascular Diseases: Nutraceutical Interventions Related to Caloric Restriction

Type 2 diabetes (T2DM) and cardiovascular disease (CVD) are closely associated and represent a key public health problem worldwide. An excess of adipose tissue, NAFLD, and gut dysbiosis establish a vicious circle that leads to chronic inflammation and oxidative stress. Caloric restriction (CR) is the most promising nutritional approach capable of improving cardiometabolic health. However, adherence to CR represents a barrier to patients and is the primary cause of therapeutic failure. To overcome this problem, many different nutraceutical strategies have been designed. Based on several data that have shown that CR action is mediated by AMPK/SIRT1 activation, several nutraceutical compounds capable of activating AMPK/SIRT1 signaling have been identified. In this review, we summarize recent data on the possible role of berberine, resveratrol, quercetin, and L-carnitine as CR-related nutrients. Additionally, we discuss the limitations related to the use of these nutrients in the management of T2DM and CVD.

The Anti-Inflammatory Properties of Phytochemicals and Their Effects on Epigenetic Mechanisms Involved in TLR4/NF-κB-Mediated Inflammation

Innate immune response induces positive inflammatory transducers and regulators in order to attack pathogens, while simultaneously negative signaling regulators are transcribed to maintain innate immune homeostasis and to avoid persistent inflammatory immune responses. The gene expression of many of these regulators is controlled by different epigenetic modifications. The remarkable impact of epigenetic changes in inducing or suppressing inflammatory signaling is being increasingly recognized. Several studies have highlighted the interplay of histone modification, DNA methylation, and post-transcriptional miRNA-mediated modifications in inflammatory diseases, and inflammation-mediated tumorigenesis. Targeting these epigenetic alterations affords the opportunity of attenuating different inflammatory dysregulations. In this regard, many studies have identified the significant anti-inflammatory properties of distinct naturally-derived phytochemicals, and revealed their regulatory capacity. In the current review, we demonstrate the signaling cascade during the immune response and the epigenetic modifications that take place during inflammation. Moreover, we also provide an updated overview of phytochemicals that target these mechanisms in macrophages and other experimental models, and go on to illustrate the effects of these phytochemicals in regulating epigenetic mechanisms and attenuating aberrant inflammation.

PGC-1α-Targeted Therapeutic Approaches to Enhance Muscle Recovery in Aging

Impaired muscle recovery (size and strength) following a disuse period commonly occurs in older adults. Many of these individuals are not able to adequately exercise due to pain and logistic barriers. Thus, nutritional and pharmacological therapeutics, that are translatable, are needed to promote muscle recovery following disuse in older individuals. Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) may be a suitable therapeutic target due to pleiotropic regulation of skeletal muscle. This review focuses on nutritional and pharmacological interventions that target PGC-1α and related Sirtuin 1 (SIRT1) and 5' AMP-activated protein kinase (AMPKα) signaling in muscle and thus may be rapidly translated to prevent muscle disuse atrophy and promote recovery. In this review, we present several therapeutics that target PGC-1α in skeletal muscle such as leucine, β-hydroxy-β-methylbuyrate (HMB), arginine, resveratrol, metformin and combination therapies that may have future application to conditions of disuse and recovery in humans.

Resveratrol and Metformin Recover Prefrontal Cortex AMPK Activation in Diet-Induced Obese Mice but Reduce BDNF and Synaptophysin Protein Content

BACKGROUND

Obesity, insulin resistance, and type 2 diabetes are established risk factors for the development of Alzheimer's disease (AD). Given this connection, two drugs, metformin (MET) and resveratrol (RESV), are considered for the clearance of amyloid-β peptides through AMPK-mediated activation of autophagy. However, overactivation of AMPK observed in late-stage AD brains and relationships between AMPK and neurogenesis (through mTORC1 inhibition), questions treatment with these drugs.

OBJECTIVE

To examine if MET and/or RESV supplementation activates brain AMPK, regulates markers of autophagy, and affects markers of neuronal health/neurogenesis.

METHODS

8-week-old male C57BL/6J mice were fed a low (N = 12; 10% kcal fat; LFD) or high fat diet (N = 40; 60% kcal fat; HFD) for 9 weeks to induce insulin resistance and obesity. HFD mice were then treated with/without MET (250 mg/kg/day), RESV (100 mg/kg/day), or COMBO (MET: 250 mg/kg/day, RESV: 100 mg/kg/day) for 5 weeks. Hippocampus and prefrontal cortex were extracted for western blotting analysis.

RESULTS

Cortex AMPK (T172) and raptor (S792, the regulatory subunit of mTORC1) phosphorylation were upregulated following RESV, COMBO treatments. mTOR (S2448) and ULK1 (S555) activation was seen following MET, COMBO and RESV, COMBO treatments, respectively, in the cortex and hippocampus. p62 content was decreased following RESV, COMBO, with LC3 content being increased following RESV treatment in the cortex. Brain derived neurotropic factor (BDNF) was significantly decreased following RESV, COMBO, and synaptophysin following all treatment in the cortex.

CONCLUSION

These results demonstrate that while treatments upregulated markers of autophagy in the prefrontal cortex, reductions in neuronal health markers question the efficacy of AMPK as a therapy for AD.

Targeting metabolic syndrome with phytochemicals: Focus on the role of molecular chaperones and hormesis in drug discovery

Adaptive cellular stress response confers stress tolerance against inflammatory and metabolic disorders. In response to metabolic stress, the key mediator of cellular adaptation and tolerance is a class of molecules called the molecular chaperones (MCs). MCs are highly conserved molecules that play critical role in maintaining protein stability and functionality. Hormesis in this context is a unique adaptation mechanism where a low dose of a stressor (which is toxic at high dose) confers a stress-resistant adaptive cellular phenotype. Hormesis can be observed at different level of biological organization at various measurable endpoints. The MCs are believed to play a key role in adaptation during hormesis. Several phytochemicals are known for their hormetic response and are called phytochemical hormetins. The role of phytochemical-mediated hormesis on the adaptive cellular processes is proposed as a potential therapeutic approach to target inflammation associated with metabolic syndrome. However, the screening of phytochemical hormetins would require a paradigm shift in the methods currently used in drug discovery.

Dietary natural products as epigenetic modifiers in aging-associated inflammation and disease

Covering: up to 2020Chronic, low-grade inflammation is linked to aging and has been termed "inflammaging". Inflammaging is considered a key contributor to the development of metabolic dysfunction and a broad spectrum of diseases or disorders including declines in brain and heart function. Genome-wide association studies (GWAS) coupled with epigenome-wide association studies (EWAS) have shown the importance of diet in the development of chronic and age-related diseases. Moreover, dietary interventions e.g. caloric restriction can attenuate inflammation to delay and/or prevent these diseases. Common themes in these studies entail the use of phytochemicals (plant-derived compounds) or the production of short chain fatty acids (SCFAs) as epigenetic modifiers of DNA and histone proteins. Epigenetic modifications are dynamically regulated and as such, serve as potential therapeutic targets for the treatment or prevention of age-related disease. In this review, we will focus on the role for natural products that include phytochemicals and short chain fatty acids (SCFAs) as regulators of these epigenetic adaptations. Specifically, we discuss regulators of methylation, acetylation and acylation, in the protection from chronic inflammation driven metabolic dysfunction and deterioration of neurocognitive and cardiac function.

Exploring the Comparative Efficacy of Metformin and Resveratrol in the Management of Diabetes-associated Complications: A Systematic Review of Preclinical Studies

Food-derived bioactive compounds such as resveratrol are increasingly explored for their protective effects against metabolic complications. Evidence supports the strong antioxidant properties and therapeutic effects of resveratrol in managing diabetes and its associated complications. However, evidence informing on the comparative or combination effects of this natural compound with an accomplished and well-characterized antidiabetic agent like metformin has not been revised. Thus, we conducted a comprehensive systematic search of the major electronic databases which included MEDLINE, Cochrane Library, and EMBASE. The cumulative evidence strongly supports the comparative effects of metformin and resveratrol in ameliorating diabetes-associated complications in preclinical settings. In particular, both compounds showed strong ameliorative effects against hyperglycemia, dyslipidemia, insulin resistance, a pro-inflammatory response, and lipid peroxidation in various experimental models of diabetes. Enhancing intracellular antioxidant capacity in addition to activating NAD-dependent deacetylase sirtuin-1 (SIRT1) and AMP-activated protein kinase (AMPK) are the prime mechanisms involved in the therapeutic effects of these compounds. Of interest, preclinical evidence also demonstrates that the combination treatment with these compounds may have a greater efficacy in protecting against diabetes. Thus, confirmation of such evidence in well-organized clinical trials remains crucial to uncover novel therapeutic strategies to manage diabetes and its linked complications.

Epinephrine responsiveness is reduced in livers from trained mice

The liver is the primary metabolic organ involved in the endogenous production of glucose through glycogenolysis and gluconeogenesis. Hepatic glucose production (HGP) is increased via neural-hormonal mechanisms such as increases in catecholamines. To date, the effects of prior exercise training on the hepatic response to epinephrine have not been fully elucidated. To examine the role of epinephrine signaling on indices of HGP in trained mice, male C57BL/6 mice were either subjected to 12 days of voluntary wheel running or remained sedentary. Epinephrine, or vehicle control, was injected intraperitoneally on day 12 prior to sacrifice with blood glucose being measured 15 min postinjection. Epinephrine caused a larger glucose response in sedentary mice and this was paralleled by a greater reduction in liver glycogen in sedentary compared to trained mice. There was a main effect of epinephrine to increase the phosphorylation of protein kinase-A (p-PKA) substrates in the liver, which was driven by increases in the sedentary, but not trained, mice. Similarly, epinephrine-induced increases in the mRNA expression of hepatic adrenergic receptors (Adra1/2a, Adrb1), and glucose-6-phosphatase (G6pc) were greater in sedentary compared to trained mice. The mRNA expression of cAMP-degrading enzymes phosphodiesterase 3B and 4B (Pde3b, Pde4b) was greater in trained compared to sedentary mice. Taken together, our data suggest that prior exercise training reduces the liver's response to epinephrine. This could be beneficial in the context of training-induced glycogen sparing during exercise.

A review on the potential of Resveratrol in prevention and therapy of diabetes and diabetic complications

Diabetes mellitus (DM) is a major world health problem and one of the most studied diseases, which are highly prevalent in the whole world, it is frequently associated with severe clinical complications, such as diabetic cardiomyopathy, nephropathy, retinopathy, neuropathy etc. Scientific research is continuously casting about for new monomer molecules from Chinese herbal medicine that could be invoked as candidate drugs for fighting against diabetes and its complications. Resveratrol (RES), a polyphenol phytoalexin, possesses diverse biochemical and physiological actions, including antiplatelet, estrogenic, and anti-inflammatory properties. It is recently gaining scientific interest for RES in controlling blood sugar and fighting against diabetes and its complications properties in various types of diabetic models. These beneficial effects seem to be due to the multiple actions of RES on cellular functions, which make RES become a promising molecule for the treatment of diabetes and diabetic complications. Here, we review the mechanism of action and potential therapeutic use of RES in prevention and mitigation of these diseases in recent ten years to provide a reference for further research and development of RES.

Effects of Resveratrol, Berberine and Their Combinations on Reactive Oxygen Species, Survival and Apoptosis in Human Squamous Carcinoma (SCC-25) Cells

Background:

Levels of cellular Reactive Oxygen Species (ROS) influence the oxidized/reduced states of cellular proteins, and create redox-signaling pathways that can activate transcription factors, kinases, and phosphatases. ROS levels can be increased radically by external factors, including ionizing and UV radiation or exposure to chemical compounds. These increased ROS levels can, in turn, lead to oxidative damage of DNA. Natural plant treatments against cancer can modulate these processes by inducing or decreasing ROS production.

Methods:

Here we report new observations that squamous carcinoma (SCC-25) cells, exposed to 24 hours of combined resveratrol and berberine treatment, contain increased ROS levels. Using flow cytometry, for drug activity characteristics, an accumulation of ROS was observed. A combination of different dyes, CellROX Green (Life Technologies) and DCFH-DA (Sigma), allowed for flow cytometric estimation of levels of cellular ROS as well as cellular localization.

Results:

Live staining and microscopic observations confirmed the accumulation of ROS in SCC-25 cells following a combination treatment at concentrations of 10μg/ml. Additionally, the cytotoxicity of the compounds was significantly improved after their combined application. Additive effects were observed for doses lower than the calculated IC50 of berberine [IC50=23µg/ml] and resveratrol [IC50=9µg/ml]. Viability (MTS) assays and analysis of isobolograms revealed a significant impact on cell viability upon combination treatment.

Conclusion:

These results suggest that administration of berberine, in the presence of resveratrol, could be decreased even to 50% (half the IC50 for berberine) for cancer treatment.

Deficiency of the autophagy gene ATG16L1 induces insulin resistance through KLHL9/KLHL13/CUL3-mediated IRS1 degradation

Connections between deficient autophagy and insulin resistance have emerged, however, the mechanism through which reduced autophagy impairs insulin-signaling remains unknown. We examined mouse embryonic fibroblasts lacking Atg16l1 (ATG16L1 KO mouse embryonic fibroblasts (MEFs)), an essential autophagy gene, and observed deficient insulin and insulin-like growth factor-1 signaling. ATG16L1 KO MEFs displayed reduced protein content of insulin receptor substrate-1 (IRS1), pivotal to insulin signaling, whereas IRS1myc overexpression recovered downstream insulin signaling. Endogenous IRS1 protein content and insulin signaling were restored in ATG16L1 KO mouse embryonic fibroblasts (MEF) upon proteasome inhibition. Through proximity-dependent biotin identification (BioID) and co-immunoprecipitation, we found that Kelch-like proteins KLHL9 and KLHL13, which together form an E3 ubiquitin (Ub) ligase complex with cullin 3 (CUL3), are novel IRS1 interactors. Expression of Klhl9 and Klhl13 was elevated in ATG16L1 KO MEFs and siRNA-mediated knockdown of Klhl9, Klhl13, or Cul3 recovered IRS1 expression. Moreover, Klhl13 and Cul3 knockdown increased insulin signaling. Notably, adipose tissue of high-fat fed mice displayed lower Atg16l1 mRNA expression and IRS1 protein content, and adipose tissue KLHL13 and CUL3 expression positively correlated to body mass index in humans. We propose that ATG16L1 deficiency evokes insulin resistance through induction of Klhl9 and Klhl13, which, in complex with Cul3, promote proteasomal IRS1 degradation.

Acute administration of IL-6 improves indices of hepatic glucose and insulin homeostasis in lean and obese mice

Obesity can lead to impairments in hepatic glucose and insulin homeostasis, and although exercise is an effective treatment, the molecular targets remain incompletely understood. As IL-6 is an exercise-inducible cytokine, we aimed to identify whether IL-6 itself influences hepatic glucose and insulin homeostasis and whether this response differs during obesity. In vivo, male mice were fed a low-fat diet (LFD; 10% kcal) or a high-fat diet (HFD; 60% kcal) for 7 wk, which induced obesity and hepatic lipid accumulation. LFD- and HFD-fed mice were injected with IL-6 (400 ng, 75 min) or PBS and then with insulin (1 U/kg; ~15 min) or saline, at which point livers were collected. In both LFD- and HFD-fed mice, IL-6 decreased blood glucose and mRNA expression of gluconeogenic genes alongside increased phosphorylation of AKT in comparison to PBS controls, and this occurred without changes in circulating insulin. To determine whether this effect of IL-6 was directly on the liver, we completed in vitro isolated primary hepatocyte experiments from chow-fed mice and cultured with or without exposure to free fatty acid (250 μm palmitate and 250 μm oleate, 24 h) to induce lipid accumulation. In both control and free fatty acid-treated hepatocytes, IL-6 (20 ng/ml, 75 min) slightly attenuated insulin-stimulated (10 nM; ~15 min) AKT phosphorylation. Together, these data suggest that IL-6 may lead to improvements in indices of hepatic glucose and insulin homeostasis in vivo; however, this is likely due to an indirect effect on the hepatocyte. NEW & NOTEWORTHY In this study, we used lean and obese mice and found that a single injection of IL-6 improved glucose tolerance, decreased hepatic gluconeogenic gene expression, and increased hepatic phosphorylation of AKT. In primary hepatocytes cultured under control and lipid-laden conditions, IL-6 had a mild, but deleterious, effect on phosphorylation of AKT. Our results show that the beneficial effects of IL-6 on glucose and insulin homeostasis, in vivo, are maintained in obesity.

The effects of trans-resveratrol on insulin resistance, inflammation, and microbiota in men with the metabolic syndrome: A pilot randomized, placebo-controlled clinical trial

BACKGROUND AND AIM

The metabolic syndrome (MetS) is a pathological condition comprised of abdominal obesity, insulin resistance, hypertension, and hyperlipidemia. It has become a major threat globally, resulting in rapidly increasing rates of diabetes, coronary heart disease, and stroke. The polyphenol resveratrol (RES) is believed to improve glucose homeostasis and insulin resistance by activating sirtuin, which acetylates and coactivates downstream targets and affects glucose and lipid homeostasis in the liver, insulin secretion in the pancreas, and glucose uptake in skeletal muscle. We studied the effects of RES on insulin resistance, glucose homeostasis, and concomitant effects on adipose tissue metabolism and fecal microbiota in insulin-resistant subjects with the MetS.

METHODS

A total of 28 obese men with the MetS were studied during a 35-day stay in the Rockefeller University Hospital metabolic unit. Subjects were randomized to receive RES 1 g orally twice daily or placebo while kept weight stable and consuming a western-style diet. At baseline, and after 30 days of RES or placebo administration, subjects underwent testing that included a euglycemic, hyperinsulinemic clamp, 2-h oral glucose tolerance test (GTT), resting energy expenditure, daily blood pressure monitoring, abdominal adipose tissue biopsy, and fecal and blood collections.

RESULTS

RES induced no changes in insulin resistance but reduced the 120-min time point and the area under the curve for glucose concentration in the 2-h GTT. In post-hoc analysis, Caucasian subjects showed a significant improvement in insulin sensitivity and glucose homeostasis after GTT, whereas non-Caucasians showed no similar effects. Levels of fasting plasma RES and its primary metabolite dihydroresveratrol were variable and did not explain the racial differences in glucose homeostasis. RES administration to Caucasian subjects leads to an increase in several taxa including Akkermansia muciniphila.

CONCLUSIONS

RES 2 g administered orally to obese men with MetS and insulin resistance marginally altered glucose homeostasis. However, in a small group of Caucasians, insulin resistance and glucose homeostasis improved. No concomitant changes in adipose tissue metabolism occurred, but fecal microbiota showed RES-induced changes.

RELEVANCE FOR PATIENTS

The MetS increases the risk of diabetes, heart disease, and stroke. A major component of the syndrome is insulin resistance, resulting in systemic inflammation and hyperinsulinemia. The primary treatment consists of lifestyle changes, improved diet, and increased physical activity. This is often unsuccessful. In this study, RES was well tolerated. In Caucasian men, it significantly improved insulin sensitivity and glucose homeostasis. Similar results were found in studies that consisted exclusively of Caucasian men. However, RES presents a novel addition to the current treatment of the MetS and its sequelae.

Aspalathin, a C-glucosyl Dihydrochalcone From Rooibos Improves the Hypoglycemic Potential of Metformin in Type 2 Diabetic (db/db) Mice

Metformin is the first line therapy of type 2 diabetics, but continued reduction of their life expectancy warrants further investigation into alternative treatment strategies. This study reports on the combinational use of metformin with aspalathin, a C-glucosyl dihydrochalcone with known glucose lowering and antioxidant properties, as an effective hypoglycemic therapy in a type 2 diabetic (db/db) mouse model. When tested as a monotherapy, a low dose of aspalathin (13 mg/kg) showed no effect, while a high dose (130 mg/kg) has already displayed a better potential than metformin in protecting against diabetes associated symptoms in db/db mice. Thus, it remains of interest to determine whether this dihydrochalcone can improve the efficacy of metformin. The results showed that this combination therapy was more effective than the use of metformin as a monotherapy in ameliorating diabetes associated symptoms, including abnormal raised fasting plasma glucose levels, impaired glucose tolerance, as well as excessively increased body weights and fat content. The treated mice also had reduced food and water consumption when compared to untreated controls, with a pronounced effect evident in the last week of treatment. Therefore, this study supports further investigations into the ameliorative effect of combination therapy of metformin and aspalathin against diabetes associated symptoms.

Obesity exacerbates the acute metabolic side effects of olanzapine

Olanzapine is a second-generation antipsychotic used in the management of schizophrenia and various off-label conditions. The acute metabolic responses of olanzapine recapitulate many of the side effects associated with obesity. Obesity rates are high in the schizophrenic population, but it is unknown whether pre-existing obesity-associated metabolic dysfunction augments the acute side effects of olanzapine. To address this question, we compared the responses to olanzapine in lean and high-fat diet-induced (HFD) obese mice. Four weeks of HFD (60%kcal from fat) led to obese, hyperglycemic, and insulin resistant mice. Olanzapine-induced hyperglycemia and systemic insulin resistance were exacerbated in HFD-induced obese mice. Olanzapine also profoundly inhibited insulin signalling in skeletal muscle and liver, which appears to be exacerbated by obesity. The greater olanzapine-induced hyperglycemia may also result from increased hepatic glucose output in obese mice as pyruvate challenge led to significantly higher blood glucose concentrations, with associated increases in hepatic content of gluconeogenic enzymes. Olanzapine also suppressed RER while acutely increasing oxygen consumption in obese mice. A single olanzapine treatment reduced physical activity for up to 24h, regardless of obesity. Considering obesity is very common in the schizophrenic population, these data suggest that previous research may be under-estimating the severity of olanzapine's acute side effects.

Metabolic pathways at the crossroads of diabetes and inborn errors

Research over the past two decades has led to advances in our understanding of the genetic and metabolic factors that underlie the pathogenesis of type 2 diabetes mellitus (T2DM). While T2DM is defined by its hallmark metabolic symptoms, the genetic risk factors for T2DM are more immune-related than metabolism-related, and the observed metabolic disease may be secondary to chronic inflammation. Regardless, these metabolic changes are not benign, as the accumulation of some metabolic intermediates serves to further drive the inflammation and cell stress, eventually leading to insulin resistance and ultimately to T2DM. Because many of the biochemical changes observed in the pre-diabetic state (i.e., ectopic lipid storage, increased acylcarnitines, increased branched-chain amino acids) are also observed in patients with rare inborn errors of fatty acid and amino acid metabolism, an interesting question is raised regarding whether isolated metabolic gene defects can confer an increased risk for T2DM. In this review, we attempt to address this question by summarizing the literature regarding the metabolic pathways at the crossroads of diabetes and inborn errors of metabolism. Studies using cell culture and animal models have revealed that, within a given pathway, disrupting some genes can lead to insulin resistance while for others there may be no effect or even improved insulin sensitivity. This differential response to ablating a single metabolic gene appears to be dependent upon the specific metabolic intermediates that accumulate and whether these intermediates subsequently activate inflammatory pathways. This highlights the need for future studies to determine whether certain inborn errors may confer increased risk for diabetes as the patients age.

Subcutaneous inguinal white adipose tissue is responsive to, but dispensable for, the metabolic health benefits of exercise

Exercise training has robust effects on subcutaneous inguinal white adipose tissue (iWAT), characterized by a shift to a brown adipose tissue (BAT)-like phenotype. Consistent with this, transplantation of exercise-trained iWAT into sedentary rodents activates thermogenesis and improves glucose homeostasis, suggesting that iWAT metabolism may contribute to the beneficial effects of exercise. However, it is yet to be determined if adaptations in iWAT are necessary for the beneficial systemic effects of exercise. To test this, male C57BL/6 mice were provided access to voluntary wheel running (VWR) or remained as a cage control (SED) for 11 nights after iWAT removal via lipectomy (LIPX) or SHAM surgery. We found that SHAM and LIPX mice with access to VWR ran similar distances and had comparable reductions in body mass, increased food intake, and increased respiratory exchange ratio (RER). Further, VWR improved indexes of glucose homeostasis and insulin tolerance in both SHAM and LIPX mice. The lack of effect of LIPX in the response to VWR was not explained by compensatory increases in markers of mitochondrial biogenesis and thermogenesis in skeletal muscle, epididymal white adipose tissue, or interscapular brown adipose tissue. Together, these data demonstrate that mice with and without iWAT have comparable adaptations to VWR, suggesting that iWAT may be dispensable for the metabolic health benefits of exercise.

Antitumour activity of resveratrol on human melanoma cells: A possible mechanism related to its interaction with malignant cell telomerase

BACKGROUND

trans-Resveratrol (tRES) is a polyphenolic stilbene found in plant products which has attracted great attention because of its antioxidant, anti-inflammatory and anticancer properties.

METHODS

The possible correlation between tRES-induced suppression of melanoma cell growth and its influence on telomerase expression has been investigated by biological assays. Moreover, in order to gain new knowledge about possible mechanisms of action of tRES as antineoplastic agent, its interaction with biologically relevant secondary structure-forming DNA sequences, its aggregation properties and copper-binding activity have been studied by CD, UV and fluorescence spectroscopies.

RESULTS

Biological assays have confirmed that growth inhibitory properties of tRES well correlate with the reduction of telomerase activity and hTERT gene transcript levels in human melanoma cells. Biophysical studies in solution have proved that tRES binds all the studied DNA model systems with low affinity, however showing high ability to discriminate G-quadruplex vs. duplex DNA. In addition, tRES has shown no propensity to form aggregates in the explored concentration range and has been found able to bind Cu²⁺ ions with a 2:1 stoichiometry.

CONCLUSIONS

From these biological and biophysical analyses it has emerged that tRES produces cytotoxic effects on human melanoma cells and, at a molecular level, is able to bind Cu²⁺ and cancer-involved G-quadruplexes, suggesting that multiple mechanisms of action could be involved in its antineoplastic activity.

GENERAL SIGNIFICANCE

Expanding the knowledge on the putative mechanisms of action of tRES as antitumour agent can help to develop novel, effective tRES-based anticancer drugs.

Beneficial effects of combined resveratrol and metformin therapy in treating diet-induced insulin resistance

The polyphenol compound resveratrol (RSV) has attracted attention due to its reputed beneficial effects on insulin sensitivity. Our lab has previously identified protective effects of RSV against the development of type 2 diabetes in rats. These effects occurred in a manner similar to thiazolidinedione's (TZDs), a class of insulin sensitizing drugs. TZDs are commonly prescribed in combination with metformin (MET) and thus we sought to examine the combined effects of RSV and MET in treating insulin resistance. Male C57BL6 mice were fed a low‐ (LFD; 10% Kcal from fat) or high‐fat diet (HFD; 60% Kcal from fat) for 9 weeks to induce glucose and insulin intolerance. HFD mice were then assigned to control (HFD), MET (231.28 ± 12.24 mg/kg/day), RSV (93.68 ± 3.51 mg/kg/day), or combined (COM; MET 232.01 ± 17.12 mg/kg/day and RSV 92.77 ± 6.92 mg/kg/day) treatment groups. Changes in glucose and insulin tolerance and tissue‐specific insulin signaling were measured 4 weeks post‐treatment. RSV or MET alone did not have beneficial effects on glucose tolerance, although MET significantly improved insulin tolerance compared to HFD. Glucose and insulin tolerance were significantly improved in COM compared to HFD and this was mirrored by enhanced insulin‐stimulated AKT phosphorylation in triceps muscle and inguinal subcutaneous adipose tissue in COM compared to HFD mice. Improvements with COM treatment were not explained by differences in body weight, adiposity, or markers of adipose tissue inflammation. In summary, this study provides evidence of beneficial effects of combined RSV and MET therapy in treating impairments in glucose homeostasis.

Implications of Resveratrol on Glucose Uptake and Metabolism

Resveratrol—a polyphenol of natural origin—has been the object of massive research in the past decade because of its potential use in cancer therapy. However, resveratrol has shown an extensive range of cellular targets and effects, which hinders the use of the molecule for medical applications including cancer and type 2 diabetes. Here, we review the latest advances in understanding how resveratrol modulates glucose uptake, regulates cellular metabolism, and how this may be useful to improve current therapies. We discuss challenges and findings regarding the inhibition of glucose uptake by resveratrol and other polyphenols of similar chemical structure. We review alternatives that can be exploited to improve cancer therapies, including the use of other polyphenols, or the combination of resveratrol with other molecules and their impact on glucose homeostasis in cancer and diabetes.

Inflammation, dysregulated metabolism and aromatase in obesity and breast cancer

Obesity is associated with an increased risk of estrogen-dependent breast cancer after menopause. Adipose tissue undergoes important changes in obesity due to excess storage of lipids, leading to adipocyte cell death and the recruitment of macrophages. The resultant state of chronic low-grade inflammation is associated with the activation of NFkB signaling and elevated levels of aromatase, the rate-limiting enzyme in estrogen biosynthesis. This occurs not only in the visceral and subcutaneous fat, but also in the breast fat. The regulation of aromatase in the breast adipose stromal cell in response to inflammatory mediators is under the control of complex signaling pathways, including metabolic pathways involving LKB1/AMPK, p53, HIF1α and PKM2. Interventions aimed at modifying weight, including diet and exercise, are associated with changes in adipose tissue inflammation and estrogen production that are likely to impact breast cancer risk. This review will present an overview of these topics.