Suppression of free fatty acid-induced insulin resistance by phytopolyphenols in C2C12 mouse skeletal muscle cells

Glucose Metabolism-Modifying Natural Materials for Potential Feed Additive Development

Glucose, a primary energy source derived from animals' feed ration, is crucial for their growth, production performance, and health. However, challenges such as metabolic stress, oxidative stress, inflammation, and gut microbiota disruption during animal production practices can potentially impair animal glucose metabolism pathways. Phytochemicals, probiotics, prebiotics, and trace minerals are known to change the molecular pathway of insulin-dependent glucose metabolism and improve glucose uptake in rodent and cell models. These compounds, commonly used as animal feed additives, have been well studied for their ability to promote various aspects of growth and health. However, their specific effects on glucose uptake modulation have not been thoroughly explored. This article focuses on glucose metabolism is on discovering alternative non-pharmacological treatments for diabetes in humans, which could have significant implications for developing feed additives that enhance animal performance by promoting insulin-dependent glucose metabolism. This article also aims to provide information about natural materials that impact glucose uptake and to explore their potential use as non-antibiotic feed additives to promote animal health and production. Further exploration of this topic and the materials involved could provide a basis for new product development and innovation in animal nutrition.

Effects of curcumin/turmeric supplementation on the liver enzymes, lipid profiles, glycemic index, and anthropometric indices in non-alcoholic fatty liver patients: An umbrella meta-analysis

Non-alcoholic fatty liver disease (NAFLD) is one of the leading causes of chronic liver disease worldwide. The evidence for curcumin's effects on patients with NAFLD is accumulating; however, meta-analyses have reported mixed results. The current umbrella meta-analysis aimed to assess the present evidence and provide an accurate estimate of the overall effects of curcumin/turmeric on NAFLD patients. The Web of Science, Scopus, PubMed, ScienceDirect, and Google Scholar databases were searched till March 2023 using MeSH terms and related keywords based on the PICO criteria. Meta-analysis studies evaluating the effects of curcumin/turmeric supplementation on NAFLD patients that reported the effect sizes (ES) and corresponding confidence intervals (CI) were eligible for inclusion in this study. All articles were screened by considering the eligibility criteria by two independent reviewers and required data were extracted from the included meta-analyses. The meta-analysis was performed utilizing a random-effects model by STATA software. Findings of 11 meta-analyses of 99 randomized controlled trials comprising 5546 participants revealed that curcumin/turmeric supplementation reduced AST (ES = -1.072, 95% CI (-1.656, -0.488), p = 0.000), ALT (ES = -0.625, 95% CI (-1.170, -0.134), p = 0.014), and TG (ES = -0.469, 95% CI (-1.057, 0.119), p = 0.128) levels, and HOMA-IR (ES = -0.291, 95% CI (-0.368, -0.214), p = 0.000), BMI (ES = -0.205, 95% CI (-0.304, -0.107), p = 0.000), and WC (ES = -1.290, 95% CI (-2.038, -0.541), p = 0.001) in comparison to the control group. However, the effects of curcumin on GGT, ALP, TC, LDL-C, HDL-C, FBS, and HbA1C levels and body weight were not significant. The findings suggest the beneficial effects of curcumin/turmeric supplementation in patients with NAFLD, such as improving liver function, decreasing serum TG levels, ameliorating insulin resistance, and reducing general and central obesity. Nevertheless, high-quality research is further required to prove these achievements.

Tea-break with epigallocatechin gallate derivatives - Powerful polyphenols of great potential for medicine

Epigallocatechin gallate (EGCG) is a polyphenol present in green tea (Camellia sinensis), which has revealed anti-cancer effects toward a variety of cancer cells in vitro and protective potential against neurodegenerative diseases such as Alzheimer's and Parkinson's. Unfortunately, EGCG presents disappointing bioavailability after oral administration, primarily due to its chemical instability and poor absorption. Due to these limitations, EGCG is currently not used in medication, but only as a dietary supplement in the form of green tea extract. Therefore, it needs further modifications before being considered suitable for extensive medical applications. In this article, we review the scientific literature about EGCG derivatives focusing on their biological properties and potential medical applications. The most common chemical modifications of epigallocatechin gallate rely on introducing fatty acid chains or sugar molecules to its chemical structure to modify solubility. Another frequently employed procedure is based on blocking EGCG's hydroxyl groups with various substituents. Novel derivatives reveal interesting properties, of which, antioxidant, anti-inflammatory, antitumor and antimicrobial, are especially important. It is worth noting that the most promising EGCG derivatives present higher stability and activity than base EGCG.

Overview of Curcumin and Piperine Effects on Glucose Metabolism: The Case of an Insulinoma Patient’s Loss of Consciousness

The hypoglycemic properties of curcumin supplements in therapeutic doses are well-known and may represent a useful tool for the treatment of chronic diseases such as metabolic syndrome, insulin resistance and type 2 diabetes. The poor bioavailability of curcumin can be improved with the concomitant administration of piperine, with no severe adverse effects on glycemia reported so far in the literature. In this article, we further discuss a previously reported case of a helicopter pilot, affected by grade I obesity who, under curcumin and piperine treatment, experienced a transient loss of consciousness (TLOC), during a low-altitude flight. This episode led to a diagnosis of insulinoma, previously asymptomatic. We hypothesized that the combined effects of curcumin and piperine might have caused a severe hypoglycemic episode and subsequent TLOC. Therefore, further studies should be conducted to evaluate the safety of curcumin and piperine supplementation in subjects with impaired glucose metabolism and insulin secretion.

Muscle Cell Insulin Resistance Is Attenuated by Rosmarinic Acid: Elucidating the Mechanisms Involved

Obesity and elevated blood free fatty acid (FFA) levels lead to impaired insulin action causing insulin resistance in skeletal muscle, and contributing to the development of type 2 diabetes mellitus (T2DM). Mechanistically, insulin resistance is associated with increased serine phosphorylation of the insulin receptor substrate (IRS) mediated by serine/threonine kinases including mTOR and p70S6K. Evidence demonstrated that activation of the energy sensor AMP-activated protein kinase (AMPK) may be an attractive target to counteract insulin resistance. We reported previously that rosemary extract (RE) and the RE polyphenol carnosic acid (CA) activated AMPK and counteracted the FFA-induced insulin resistance in muscle cells. The effect of rosmarinic acid (RA), another polyphenolic constituent of RE, on FFA-induced muscle insulin resistance has never been examined and is the focus of the current study. Muscle cell (L6) exposure to FFA palmitate resulted in increased serine phosphorylation of IRS-1 and reduced insulin-mediated (i) Akt activation, (ii) GLUT4 glucose transporter translocation, and (iii) glucose uptake. Notably, RA treatment abolished these effects, and restored the insulin-stimulated glucose uptake. Palmitate treatment increased the phosphorylation/activation of mTOR and p70S6K, kinases known to be involved in insulin resistance and RA significantly reduced these effects. RA increased the phosphorylation of AMPK, even in the presence of palmitate. Our data indicate that RA has the potential to counteract the palmitate-induced insulin resistance in muscle cells, and further studies are required to explore its antidiabetic properties.

HM-Chromanone, a Major Homoisoflavonoid in Portulaca oleracea L., Improves Palmitate-Induced Insulin Resistance by Regulating Phosphorylation of IRS-1 Residues in L6 Skeletal Muscle Cells

This study investigated the effect of (E)-5-hydroxy-7-methoxy-3-(2-hydroxybenzyl)-4-chromanone (HM-chromanone) on palmitate-induced insulin resistance and elucidated the underlying mechanism in L6 skeletal muscle cells. Glucose uptake was markedly decreased due to palmitate-induced insulin resistance in these cells; however, 10, 25, and 50 µM HM-chromanone remarkably improved glucose uptake in a concentration-dependent manner. HM-chromanone treatment downregulated protein tyrosine phosphatase 1B (PTP1B) and phosphorylation of c-Jun N-terminal kinase (JNK) and inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ), which increased because of palmitate mediating the insulin-resistance status in cells. HM-chromanone promoted insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation and suppressed palmitate-induced phosphorylation of IRS-1 serine. This activated phosphoinositide 3-kinase (PI3K) and stimulated protein kinase B (AKT) phosphorylation. Phosphorylated AKT promoted the translocation of Glucose transporter type 4 to the plasma membrane and significantly enhanced glucose uptake into muscle cells. Additionally, HM-chromanone increased glycogen synthesis through phosphorylating glycogen synthase kinase 3 alpha/beta (GSK3 α/β) via AKT. Consequently, HM-chromanone may improve insulin resistance by downregulating the phosphorylation of IRS-1 serine through inhibition of negative regulators of insulin signaling and inflammation-activated protein kinases in L6 skeletal muscle cells.

Molecular Mechanisms of Inflammation in Sarcopenia: Diagnosis and Therapeutic Update

Sarcopenia is generally an age-related condition that directly impacts the quality of life. It is also related to chronic diseases such as metabolic dysfunction associated with diabetes and obesity. This means that everyone will be vulnerable to sarcopenia at some point in their life. Research to find the precise molecular mechanisms implicated in this condition can increase knowledge for the better prevention, diagnosis, and treatment of sarcopenia. Our work gathered the most recent research regarding inflammation in sarcopenia and new therapeutic agents proposed to target its consequences in pyroptosis and cellular senescence. Finally, we compared dual X-ray absorptiometry (DXA), magnetic resonance imaging (MRI), and ultrasound (US) as imaging techniques to diagnose and follow up on sarcopenia, indicating their respective advantages and disadvantages. Our goal is for the scientific evidence presented here to help guide future research to understand the molecular mechanisms involved in sarcopenia, new treatment strategies, and their translation into clinical practice.

The effects of curcumin supplementation on metabolic biomarkers and body mass index in patients with nonalcoholic fatty liver disease, a systematic review and meta-analysis of randomized controlled trials

Background and Aims:

Curcumin is one of the most commonly used indigenous molecules endowed with various shielding functionalities that protect the liver. In the present research, we aimed to investigate the effects of curcumin on metabolic factors and body mass index (BMI) in patients with non-alcoholic fatty liver disease (NAFLD), using a meta-analysis of randomized, controlled trials.

Methods::

Online databases PubMed, Embase, Web of Science, and Science Direct were searched until April 2021 to identify eligible articles. Fourteen trials were included. Results: The results showed that curcumin consumption could significantly reduce AST (-0.35, (-0.57 to -0.14)), total cholesterol (-0.81, (-1.34 to -0.27)), TG (-0.49, (-0.71 to -0.27)), and FBS (-0.28, (-0.46 to -0.09)) in patients with NAFLD. However, the improvements in ALT (-0.29, (-0.58 to 0.00)), LDL (-0.48, (-0.97 to 0.01)), HDL (0.03, (-0.38 to 0.44)), and BMI (-0.13, (-0.29 to 0.02)) were not statistically significant. Furthermore, the findings revealed that the optimal dose and duration of curcumin consumption for patients with NAFLD is <500 mg/d for less than 10 weeks.

Conclusions:

The present study suggests that consuming curcumin can improve liver enzymes, lipid profile, FBS, and BMI in patients with NAFLD. Moreover, curcumin supplementation may provide beneficial effects on metabolic biomarkers and body weight if used at the appropriate dose and duration. Further RCTs are required to confirm our findings.

Investigation of the Effects of Difluorinated Curcumin on Glycemic Indices in Streptozotocin-Induced Diabetic Rats

BACKGROUND

Curcumin is an antioxidant agent that improves glycemia in animal models of diabetes. Clinically curcumin use is limited due to poor solubility, weak absorption, and low bioavailability; therefore, this study to investigate the effects of curcumin's analog, difluorinated curcumin (CDF), on fasting blood glucose (FBG), oral glucose tolerance test (OGTT), and insulin tolerance test (ITT), in streptozotocin (STZ)-induced diabetic rats was undertaken.

METHODS

STZ-induced diabetes rats were randomly assigned to six groups (7 rats per group). They were treated daily by oral gavage with curcumin (200 and 100 mg/kg/day), CDF (200 and 100 mg/kg/day), and metformin (200 mg/kg/day) as a positive control group, for 4 weeks. Two diabetic control (DC) and normal control (NC) groups (non-diabetic rats) received normal saline and citrate buffer, respectively. FBG was measured at the beginning and end of the treatment (Day 0 and week 4) and OGTT and ITT were performed to determine glucose tolerance and insulin sensitivity.

RESULTS

Cur100, CDF 100, and CDF200 significantly decreased FBG levels after 4 weeks oral administration by -34% (-150 mg/dL ± 70, p = 0.02), -36% (123 mg/dL ±67, p < 0.04), and - 40% (-189 mg/dL ± 91, p = 0.03), respectively. Glucose sensitivity by OGTT showed a significant improvement in glucose tolerance ability in all treated groups compared with DC group. ITT demonstrated that insulin response improved significantly in Cur100 and CDF 200 groups.

CONCLUSION

Overall, CDF improved glucose tolerance and insulin sensitivity, while reducing FBG compared to curcumin, suggesting that curcumin analogs may have therapeutic utility in diabetes.

Effect of epicatechin on skeletal muscle

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Loss of skeletal muscle (SkM) quality is associated with different clinical conditions such as aging, diabetes, obesity, cancer and heart failure. Nutritional research has focused on identifying naturally occurring molecules that mitigate the loss of SkM quality induced by a pathology or syndrome. In this context, although few human studies have been conducted, Epicatechin (Epi) is a prime candidate that may positively affect SkM quality by its potential ability to mitigate muscle mass loss. This seems to be a consequence of its antioxidant, anti-inflammatory properties, and its stimulation of mitochondrial biogenesis to increase myogenic differentiation, as well as its modulation of key proteins involved in SkM structure, function, metabolism, and growth. In conclusion, the Epi could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases, however, studies in humans are needed.

The Effect of Simulated In Vitro Digestion on Biological Activity of Viburnum opulus Fruit Juices

In the present study, an in vitro digestion method has been used to assay the influence of the physiological conditions in the mouth, stomach, and intestine on the stability and activity in different cell models of the main phenolic compounds from Viburnum opulus fresh juice (FJ), phenolic-rich juice (PJ), and the bioavailable fractions (DFJ and DPJ). The data obtained indicate that the V. opulus samples achieved after in vitro digestion had an influence on cellular glucose and lipid metabolism. The bioavailable fraction of both digested juices stimulated glucose uptake and decreased lipid accumulation by L6 myoblasts and HepG2 hepatocytes. Both DFJ and DPJ reduced the secretion of inflammatory cytokines by 3T3-L1 adipocytes: interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α). Simultaneously, DFJ and DPJ enhanced oxidative stress in MIN6 cells and decreased glucose-stimulated insulin secretion (GSIS). UPLC-MS analysis revealed qualitative and quantitative changes in hydroxycinnamic acids. In particular, the content of chlorogenic acid decreased drastically; its content in the bioavailable fraction was almost 7 times and 30 times lower than in the FJ and PJ, respectively. Our results suggested that although the phenolic compounds of V. opulus juices undergo transformation during digestion, they are still potent antioxidant agents with biological activity.

Pentadecanoic acid promotes basal and insulin-stimulated glucose uptake in C2C12 myotubes

Background

Saturated fatty acids (SFAs) generally have been thought to worsen insulin-resistance and increase the risk of developing type 2 diabetes mellitus (T2DM). Recently, accumulating evidence has revealed that SFAs are not a single homogeneous group, instead different SFAs are associated with T2DM in opposing directions. Pentadecanoic acid (C15:0, PA) is directly correlated with dairy products, and a negative association between circulating PA and metabolic disease risk was observed in epidemiological studies. Therefore, the role of PA in human health needs to be reinforced. Whether PA has a direct benefit on glucose metabolism and insulin sensitivity needs further investigation.

Objective

The present study aimed to investigate the effect and potential mechanism of action of PA on basal and insulin stimulated glucose uptake in C2C12 myotubes.

Methods

Glucose uptake was determined using a 2-(N-[7-nitrobenz-2-oxa-1,3-diazol-4-yl] amino)-2-deoxyglucose (2-NBDG) uptake assay. Cell membrane proteins were isolated and glucose transporter 4 (GLUT4) protein was detected by western blotting to examine the translocation of GLUT4 to the plasma membrane. The phosphorylation levels of proteins involved in the insulin and 5’-adenosine monophosphate-activated protein kinase (AMPK) pathways were examined by western blotting.

Results

We found that PA significantly promoted glucose uptake and GLUT4 translocation to the plasma membrane. PA had no effect on the insulin-dependent pathway involving insulin receptor substrate 1 (Tyr632) and protein kinase B (PKB/Akt), but increased phosphorylation of AMPK and Akt substrate of 160 kDa (AS160). Compound C (an AMPK inhibitor) blocked PA-induced AMPK activation and reversed PA-induced GLUT4 translocation, indicating that PA promotes glucose uptake via the AMPK pathway in vitro. Moreover, PA significantly promoted insulin-stimulated glucose uptake in myotubes. Under insulin stimulation, PA did not affect the insulin-dependent pathway, but still activated AMPK.

Conclusion

PA, an odd-chain SFA, significantly stimulates glucose uptake via the AMPK-AS160 pathway and exhibits an insulin-sensitizing effect in myotubes.

Improved Stability and Targeted Cytotoxicity of Epigallocatechin-3-Gallate Palmitate for Anticancer Therapy

Although with high antioxidant activity, epigallocatechin-3-gallate (EGCG) was restricted by its poor chemical stability in practical applications. One of EGCG derivatives, EGCG palmitate, was synthesized with EGCG and palmitoyl chloride to overcome instability of EGCG. However, uncertainties still exist in chemical stability and cytotoxicity of EGCG palmitate, which are essential for further exploration in anticancer therapy. Our work aims to analyze the resistance of EGCG palmitate to oxidation and summarize its targeted inhibition efficiency on cancerous cells and normal cells. High-performance liquid chromatography analysis confirmed that EGCG palmitate remained stable in air and Dulbecco's modified eagle medium (DMEM) for a longer time than EGCG. Antioxidative and pro-oxidative effects of EGCG palmitate on treated cells are proposed through reactive oxygen species (ROS) detection, respectively. It reveals that pro-oxidants by H₂O₂ production can exert antiproliferative and proapoptotic effects on cancerous cells and stimulate autophagy, while an antioxidant relieves oxidative stress caused by superoxide as compared to normal cells. Consequently, targeted cytotoxicity is adopted by EGCG palmitate-treated cancerous cells. Results above manifest that EGCG palmitate possesses potential to serve as a promising prodrug in anticancer treatment.

Benzyl Isothiocyanate Ameliorates High-Fat Diet-Induced Hyperglycemia by Enhancing Nrf2-Dependent Antioxidant Defense-Mediated IRS-1/AKT/TBC1D1 Signaling and GLUT4 Expression in Skeletal Muscle

Obesity caused lipotoxicity, which results in insulin resistance. We studied whether benzyl isothiocyanate (BITC) improved insulin resistance in muscle. BITC was studied in vivo in mice fed a high-fat diet (HFD) and in vitro in C2C12 myotubes treated with palmitic acid (PA). In C2C12 cells, BITC mitigated PA inhibition of glucose uptake and phosphorylation of IRS-1, AKT, and TBC1D1 in response to insulin. BITC upregulated the expression of HO-1, GSTP, and GCLM mRNA and protein as well as GSH contents, which suppressed oxidative damage. Knockdown of Nrf2 abrogated BITC enhancement of antioxidant defense and subsequently reversed BITC protection against PA-induced insulin resistance. Moreover, BITC upregulated the expression of GLUT4, PPARγ, and C/EBPα. In HFD-fed mice, plasma total cholesterol, nonesterified fatty acid, and glucose levels and HOMA-IR were dose-dependently decreased with 0.05 or 0.1% BITC administration. In gastrocnemius muscle, compared with the HFD group, BITC increased the phosphorylation of AKT and TBC1D1, GSH contents, and the expression of antioxidant enzymes as well as GLUT4. These results indicate that BITC ameliorates obesity-induced hyperglycemia by enhancing insulin sensitivity in muscle. This is partly attributed to its inhibition of lipotoxicity-induced oxidative insult and upregulation of GLUT4 expression.

Olive Leaf Polyphenols (OLPs) Stimulate GLUT4 Expression and Translocation in the Skeletal Muscle of Diabetic Rats

Skeletal muscles are high-insulin tissues responsible for disposing of glucose via the highly regulated process of facilitated glucose transporter 4 (GLUT4). Impaired insulin action in diabetes, as well as disorders of GLUT4 vesicle trafficking in the muscle, are involved in defects in insulin-stimulated GLUT4 translocation. Since the Rab GTPases are the main regulators of vesicular membrane transport in exo- and endo-cytosis, in the present work, we studied the effect of olive leaf polyphenols (OLPs) on Rab8A, Rab13, and Rab14 proteins of the rat soleus muscle in a model of streptozotocin (SZT)-induced diabetes (DM) in a dose-dependent manner. Glucose, cholesterol, and triglyceride levels were determined in the blood, morphological changes of the muscle tissue were captured by hematoxylin and eosin histological staining, and expression of GLUT4, Rab8A, Rab13, and Rab14 proteins were analyzed in the rat soleus muscle by the immunofluorescence staining and immunoblotting. OLPs significantly reduced blood glucose level in all treated groups. Furthermore, significantly reduced blood triglycerides were found in the groups with the lowest and highest OLPs treatment. The dynamics of activation of Rab8A, Rab13, and Rab14 was OLPs dose-dependent and more effective at higher OLP doses. Thus, these results indicate a beneficial role of phenolic compounds from the olive leaf in the regulation of glucose homeostasis in the skeletal muscle.

Effect of garden cress in reducing blood glucose, improving blood lipids, and reducing oxidative stress in a mouse model of diabetes induced by a high-fat diet and streptozotocin

BACKGROUND

A mouse model in which diabetes mellitus was induced by low-dose streptozotocin (STZ) injection combined with a high-fat diet was used to study the effect of two water cress (Lepidium savitum) preparations. Diabetic mice were treated with dried cress powder or with water-soluble extracts (tested at two doses), together with proper control groups. The mice were evaluated after 4 weeks of continuous intervention for type 2 diabetic and associated markers. We determined blood glucose, body weight, total cholesterol (TC), triglyceride (TG), low-density lipoprotein (LDL), high-density lipoprotein (HDL), serum insulin levels, and DNA integrity of hepatic cells. The concentrations of malondialdehyde (MDA) and lipid peroxide (LPO) and the activities of four enzymes that are part of the antioxidant defense system were determined in liver samples, as well as gene expression (by semi-quantitative reverse transcription polymerase chain reaction) and enzyme activity of IRS-1, IRS-2, PI3K, AKT-2, and GLUT4.

RESULTS

After 4 weeks of intervention, the levels of TC, TG, and LDL cholesterol were significantly (P < 0.5) decreased and HDL cholesterol was significantly increased. Enzyme activities of liver superoxide dismutase, glutathione, glutathione peroxidase, and catalase were significantly increased, whereas MDA and LPO concentrations were significantly reduced. The transcription level of the five genes assessed was increased, with corresponding increases in protein expression.

CONCLUSION

Oral uptake of garden cress can significantly reduce the blood glucose and improve the blood lipid metabolism of diabetic mice. Considerable improvements in the activity of antioxidant defense enzymes were observed in type 2 diabetic mice that improved the body's antioxidant emergency response. © 2019 Society of Chemical Industry.

Polysaccharide from Rosa roxburghii Tratt Fruit Attenuates Hyperglycemia and Hyperlipidemia and Regulates Colon Microbiota in Diabetic db/db Mice

This study was aimed at investigating the hypoglycemic and hypolipidemic effects of a polysaccharide (RTFP) isolated from Rosa roxburghii Tratt fruit on type-2 diabetic db/db mice. The results indicated that the oral administration of RTFP could significantly decrease the body weight, fat, and liver hypertrophy and the levels of fasting blood glucose, serum insulin, and serum lipids of the db/db mice. Histopathological observation showed that RTFP could effectively protect the pancreas, liver, and epididymal fat against damage and dysfunction. Real-time quantitative polymerase chain reaction analysis confirmed that the gene expression levels of peroxisome proliferator-activated receptors-γ (PPAR-γ), sterol regulatory element-binding protein-1 (SREBP-1c), acetyl-CoA carboxylase-1 (ACC-1), fatty acid synthase (FAS), and glucose-6-phosphatase (G6 Pase) were significantly down-regulated in the liver of db/db mice after treatment with RTFP. Moreover, RTFP treatment reversed gut dysbiosis by lowering the Firmicutes-to-Bacteroidetes ratio and enhancing the relative abundances of beneficial bacteria including Bacteroidaceae, Bacteroidaceae S24-7 group, and Lactobacillaceae. These findings suggest that RTFP can be used as a promising functional supplement for the prevention and treatment of type-2 diabetes mellitus.

Antidiabetic Properties of Curcumin I: Evidence from In Vitro Studies

Type 2 diabetes mellitus (T2DM) is a growing metabolic disease characterized by insulin resistance and hyperglycemia. Current preventative and treatment strategies for T2DM and insulin resistance lack in efficacy resulting in the need for new approaches to prevent and manage/treat the disease better. In recent years, epidemiological studies have suggested that diets rich in fruits and vegetables have beneficial health effects including protection against insulin resistance and T2DM. Curcumin, a polyphenol found in turmeric, and curcuminoids have been reported to have antioxidant, anti-inflammatory, hepatoprotective, nephroprotective, neuroprotective, immunomodulatory and antidiabetic properties. The current review (I of II) summarizes the existing in vitro studies examining the antidiabetic effects of curcumin, while a second (II of II) review summarizes evidence from existing in vivo animal studies and clinical trials focusing on curcumin’s antidiabetic properties.

Comparative Effects of Curcumin versus Nano-Curcumin on Insulin Resistance, Serum Levels of Apelin and Lipid Profile in Type 2 Diabetic Rats

BACKGROUND AND PURPOSE

Type 2 diabetes mellitus (T2DM) is characterized by insulin resistance and abnormalities in insulin production. Apelin is associated with insulin resistance. According to the anti-diabetic properties of curcumin, the purpose of this study was to compare the effects of curcumin and nano-curcumin intake on insulin resistance and serum levels of fasting blood sugar (FBS), Apelin, and lipid profile (cholesterol, triglyceride, LDL, HDL and VLDL) in T2DM rats.

MATERIALS AND METHODS

Forty-eight male Wistar rats were divided into six groups: Control, diabetic, diabetic treated with two doses of curcumin (100 and 200 mg/kg) and diabetic treated with two doses of nano-curcumin (100 and 200 mg/kg). Induction of T2DM was performed by intraperitoneal injection of Nicotinamide (110 mg/kg) and Streptozotocin (45 mg/kg) in the fasting state. Rats received different doses of nano-curcumin and curcumin by gavage (daily) for 28 days. At the end of the intervention period, insulin resistance and serum levels of FBS, apelin and lipid profiles were measured.

RESULTS

Insulin resistance and serum levels of FBS, Apelin, cholesterol, triglycerides, LDL, and VLDL were significantly decreased in diabetic rats treated with curcumin and nano-curcumin (p<0.05) so that nano-curcumin in reducing lipid profile is more effective than curcumin (P<0.05). Serum level of HDL in nano-curcumin groups was significantly higher than diabetic and curcumin groups (p<0.05). Also, with increasing insulin resistance, serum level of apelin increased (P<0.05).

CONCLUSION

The therapeutic effects of curcumin and nano-curcumin were effective in decreasing insulin resistance, serum levels of FBS, apelin and lipid profile. The dose of 100 mg/kg nano-curcumin was more effective in reducing lipid profile.

Shared pathways for neuroprogression and somatoprogression in neuropsychiatric disorders

Activated immune-inflammatory, oxidative and nitrosative stress (IO&NS) pathways and consequent mitochondrial aberrations are involved in the pathophysiology of psychiatric disorders including major depression, bipolar disorder and schizophrenia. They offer independent and shared contributions to pathways underpinning medical comorbidities including insulin resistance, metabolic syndrome, obesity and cardiovascular disease - herein conceptualized as somatoprogression. This narrative review of human studies aims to summarize relationships between IO&NS pathways, neuroprogression and somatoprogression. Activated IO&NS pathways, implicated in the neuroprogression of psychiatric disorders, affect the pathogenesis of comorbidities including insulin resistance, dyslipidaemia, obesity and hypertension, and by inference, metabolic syndrome. These conditions activate IO&NS pathways, exacerbating neuroprogression in psychiatric disorders. The processes whereby proinflammatory cytokines, nitrosative and endoplasmic reticulum stress, NADPH oxidase isoforms, PPARγ inactivation, SIRT1 deficiency and intracellular signalling pathways impact lipid metabolism and storage are considered. Through associations between body mass index, chronic neuroinflammation and FTO expression, activation of IO&NS pathways arising from somatoprogression may contribute to neuroprogression. Early evidence highlights the potential of adjuvants targeting IO&NS pathways for treating somatoprogression and neuroprogression.

Antitumor effects of curcumin: A lipid perspective

Lipid metabolism plays an important role in cancer development due to the necessities of rapidly dividing cells to increase structural, energetic, and biosynthetic demands for cell proliferation. Basically, obesity, type 2 diabetes, and other related diseases, and cancer are associated with a common hyperactivated "lipogenic state." Recent evidence suggests that metabolic reprogramming and overproduction of enzymes involved in the synthesis of fatty acids are the new hallmarks of cancer, which occur in an early phase of tumorigenesis. As the first evidence to confirm dysregulated lipid metabolism in cancer cells, the overexpression of fatty acid synthase (FAS) was observed in breast cancer patients and demonstrated the role of FAS in cancer. Other enzymes of fatty acid synthesis have recently been found to be dysregulated in cancer, including ATP-dependent citrate lyase and acetyl-CoA carboxylase, which further underscores the connection of these metabolic pathways with cancer cell survival and proliferation. The degree of overexpression of lipogenic enzymes and elevated lipid utilization in tumors is closely associated with cancer progression. The question that arises is whether the progression of cancer can be suppressed, or at least decelerated, by modulating gene expression related to fatty acid metabolism. Curcumin, due to its effects on the regulation of lipogenic enzymes, might be able to suppress, or even cause regression of tumor growth. This review discusses recent evidence concerning the important role of lipogenic enzymes in the metabolism of cancer cells and whether the inhibitory effects of curcumin on lipogenic enzymes is therapeutically efficacious.

Mechanisms of vitamin D on skeletal muscle function: oxidative stress, energy metabolism and anabolic state

PURPOSE

This review provides a current perspective on the mechanism of vitamin D on skeletal muscle function with the emphasis on oxidative stress, muscle anabolic state and muscle energy metabolism. It focuses on several aspects related to cellular and molecular physiology such as VDR as the trigger point of vitamin D action, oxidative stress as a consequence of vitamin D deficiency.

METHOD

The interaction between vitamin D deficiency and mitochondrial function as well as skeletal muscle atrophy signalling pathways have been studied and clarified in the last years. To the best of our knowledge, we summarize key knowledge and knowledge gaps regarding the mechanism(s) of action of vitamin D in skeletal muscle.

RESULT

Vitamin D deficiency is associated with oxidative stress in skeletal muscle that influences the mitochondrial function and affects the development of skeletal muscle atrophy. Namely, vitamin D deficiency decreases oxygen consumption rate and induces disruption of mitochondrial function. These deleterious consequences on muscle may be associated through the vitamin D receptor (VDR) action. Moreover, vitamin D deficiency may contribute to the development of muscle atrophy. The possible signalling pathway triggering the expression of Atrogin-1 involves Src-ERK1/2-Akt- FOXO causing protein degradation.

CONCLUSION

Based on the current knowledge we propose that vitamin D deficiency results from the loss of VDR function and it could be partly responsible for the development of neurodegenerative diseases in human beings.

The Phosphorylation of IRS1S307 and AktS473 Molecules in Insulin-Resistant C2C12 Cells Induced with Palmitate Is Influenced by Epigallocatechin Gallate from Green Tea

In the current investigation, the effect of epigallocatechin gallate (EGCG) on the phosphorylation of IRS1^S307 and Akt^S473 molecules in insulin-resistant C2C12 muscle cells induced with palmitate was studied and compared with the effect of the antidiabetic drug, rosiglitazone. C2C12 myoblasts were cultured in Dulbecco's modified Eagle's medium and differentiated into myotubes using horse serum and the creatine kinase test was used to confirm their differentiation. The treatment of C2C12 myotubes was carried out with palmitate, where albumin was used as the conjugator. The Western blot technique was used to check the useful phosphorylation of IRS1^S307 and Akt^S473 in C2C12 myotubes, in the presence or absence of palmitate. There was a significant (p < 0.00) and linear increase in the activity of creatine kinase over time (0 to 96 h after differentiation) with everyday myoblast formation. While neither EGCG nor rosiglitazone showed a significant (p > 0.05) effect on palmitate content during 96 h of incubation of IRS1^S307 , EGCG alone or combined with rosiglitazone increased the phosphorylation of Akt^S473 , leading to the increase of glucose uptake into C2C12 cells. Thus, it can be concluded that EGCG alone or in combination with rosiglitazone may show some therapeutic effects for the prevention or treatment of Type 2 diabetes owing to its substantial effect on increasing the phosphorylation of Akt^S473 and the subsequent glucose uptake into the cells.

Clinopodium chinense Attenuates Palmitic Acid-Induced Vascular Endothelial Inflammation and Insulin Resistance through TLR4-Mediated NF- κ B and MAPK Pathways

Elevated palmitic acid (PA) levels are associated with the development of inflammation, insulin resistance (IR) and endothelial dysfunction. Clinopodium chinense (Benth.) O. Kuntze has been shown to lower blood glucose and attenuate high glucose-induced vascular endothelial cells injury. In the present study we investigated the effects of ethyl acetate extract of C. chinense (CCE) on PA-induced inflammation and IR in the vascular endothelium and its molecular mechanism. We found that CCE significantly inhibited PA-induced toll-like receptor 4 (TLR4) expression in human umbilical vein endothelial cells (HUVECs). Consequently, this led to the inhibition of the following downstream adapted proteins myeloid differentiation primary response gene 88, Toll/interleukin-1 receptor domain-containing adaptor-inducing interferon- β and TNF receptor-associated factor 6. Moreover, CCE inhibited the phosphorylation of Ikappa B kinase β , nuclear factor kappa-B (NF- κ B), c-Jun N-terminal kinase, extracellular regulated protein kinases, p38-mitogen-activated protein kinase (MAPK) and subsequently suppressed the release of tumor necrosis factor- α , interleukin-1 β (IL-1 β ) and IL-6. CCE also inhibited IRS-1 serine phosphorylation and ameliorated insulin-mediated tyrosine phosphorylation of IRS-1. Moreover, CCE restored serine/threonine kinase and endothelial nitric oxide synthase (eNOS) activation and thus increased insulin-mediated nitric oxide (NO) production in PA-treated HUVECs. This led to reverse insulin mediated endothelium-dependent relaxation, eNOS phosphorylation and NO production in PA-treated rat thoracic aortas. These results suggest that CCE can significantly inhibit the inflammatory response and alleviate impaired insulin signaling in the vascular endothelium by suppressing TLR4-mediated NF- κ B and MAPK pathways. Therefore, CCE can be considered as a potential therapeutic candidate for endothelial dysfunction associated with IR and diabetes.

Aspalathin-Enriched Green Rooibos Extract Reduces Hepatic Insulin Resistance by Modulating PI3K/AKT and AMPK Pathways

We previously demonstrated that an aspalathin-enriched green rooibos extract (GRE) reversed palmitate-induced insulin resistance in C2C12 skeletal muscle and 3T3-L1 fat cells by modulating key effectors of insulin signalling such as phosphatidylinositol-4,5-bisphosphate 3-kinase/protein kinase B (PI3K/AKT) and AMP-activated protein kinase (AMPK). However, the effect of GRE on hepatic insulin resistance is unknown. The effects of GRE on lipid-induced hepatic insulin resistance using palmitate-exposed C3A liver cells and obese insulin resistant (OBIR) rats were explored. GRE attenuated the palmitate-induced impairment of glucose and lipid metabolism in treated C3A cells and improved insulin sensitivity in OBIR rats. Mechanistically, GRE treatment significantly increased PI3K/AKT and AMPK phosphorylation while concurrently enhancing glucose transporter 2 expression. These findings were further supported by marked stimulation of genes involved in glucose metabolism, such as insulin receptor (Insr) and insulin receptor substrate 1 and 2 (Irs1 and Irs2), as well as those involved in lipid metabolism, including Forkhead box protein O1 (FOXO1) and carnitine palmitoyl transferase 1 (CPT1) following GRE treatment. GRE showed a strong potential to ameliorate hepatic insulin resistance by improving insulin sensitivity through the regulation of PI3K/AKT, FOXO1 and AMPK-mediated pathways.

Epigallocatechin Gallate Modulates Muscle Homeostasis in Type 2 Diabetes and Obesity by Targeting Energetic and Redox Pathways: A Narrative Review

Obesity is associated with the hypertrophy and hyperplasia of adipose tissue, affecting the healthy secretion profile of pro- and anti-inflammatory adipokines. Increased influx of fatty acids and inflammatory adipokines from adipose tissue can induce muscle oxidative stress and inflammation and negatively regulate myocyte metabolism. Muscle has emerged as an important mediator of homeostatic control through the consumption of energy substrates, as well as governing systemic signaling networks. In muscle, obesity is related to decreased glucose uptake, deregulation of lipid metabolism, and mitochondrial dysfunction. This review focuses on the effect of epigallocatechin-gallate (EGCG) on oxidative stress and inflammation, linked to the metabolic dysfunction of skeletal muscle in obesity and their underlying mechanisms. EGCG works by increasing the expression of antioxidant enzymes, by reversing the increase of reactive oxygen species (ROS) production in skeletal muscle and regulating mitochondria-involved autophagy. Moreover, EGCG increases muscle lipid oxidation and stimulates glucose uptake in insulin-resistant skeletal muscle. EGCG acts by modulating cell signaling including the NF-κB, AMP-activated protein kinase (AMPK), and mitogen-activated protein kinase (MAPK) signaling pathways, and through epigenetic mechanisms such as DNA methylation and histone acetylation.

Catechins enhance skeletal muscle performance

Muscle-related disorders, such as sarcopenia and cachexia, caused by aging and chronic diseases can lead to the loss of muscle mass and strength to different degrees, severely affecting human health. Globally, tea is one of the three most popular beverages, and its major active ingredient catechins have been reported to delay muscular atrophy and enhance movement. However, currently, there is no systematic review to elaborate its roles and the associated mechanisms. This article reviews the (1) functions and mechanisms of catechins in the differentiation of myogenic stem cells, biogenesis of mitochondria, synthesis and degradation of proteins, regulation of glucose level, and metabolism of lipids in muscle cells; and (2) effect of catechins on the blood vessels, bones, and nerves that are closely related to the skeletal muscles. Catechins could prevent, mitigate, delay, and even treat muscle-related disorders caused by aging and diseases.

Pathophysiological mechanisms of diabetic cardiomyopathy and the therapeutic potential of epigallocatechin-3-gallate

Cardiovascular complications are considered one of the leading causes of morbidity and mortality among diabetic patients. Diabetic cardiomyopathy (DCM) is a type of cardiovascular damage presents in diabetic patients independent of the coexistence of ischemic heart disease or hypertension. It is characterized by impaired diastolic relaxation time, myocardial dilatation and hypertrophy and reduced systolic and diastolic functions of the left ventricle. Molecular mechanisms underlying these pathological changes in the diabetic heart are most likely multifactorial and include, but not limited to, oxidative/nitrosative stress, increased advanced glycation end products, mitochondrial dysfunction, inflammation and cell death. The aim of this review is to address the major molecular mechanisms implicated in the pathogenesis of DCM. In addition, this review provides studies conducted to determine the pharmacological effects of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol in green tea, focusing on its therapeutic potential against the processes involved in the pathogenesis and progression of DCM. EGCG has been shown to exert several potential therapeutic properties both in vitro and in vivo. Given its therapeutic potential, EGCG might be a promising drug candidate to decrease the morbidity and mortality associated with DCM and other diabetes complications.

Attenuation of Free Fatty Acid-Induced Muscle Insulin Resistance by Rosemary Extract

Elevated blood free fatty acids (FFAs), as seen in obesity, impair muscle insulin action leading to insulin resistance and Type 2 diabetes mellitus. Serine phosphorylation of the insulin receptor substrate (IRS) is linked to insulin resistance and a number of serine/threonine kinases including JNK, mTOR and p70 S6K have been implicated in this process. Activation of the energy sensor AMP-activated protein kinase (AMPK) increases muscle glucose uptake, and in recent years AMPK has been viewed as an important target to counteract insulin resistance. We reported recently that rosemary extract (RE) increased muscle cell glucose uptake and activated AMPK. However, the effect of RE on FFA-induced muscle insulin resistance has never been examined. In the current study, we investigated the effect of RE in palmitate-induced insulin resistant L6 myotubes. Exposure of myotubes to palmitate reduced the insulin-stimulated glucose uptake, increased serine phosphorylation of IRS-1, and decreased the insulin-stimulated phosphorylation of Akt. Importantly, exposure to RE abolished these effects and the insulin-stimulated glucose uptake was restored. Treatment with palmitate increased the phosphorylation/activation of JNK, mTOR and p70 S6K whereas RE completely abolished these effects. RE increased the phosphorylation of AMPK even in the presence of palmitate. Our data indicate that rosemary extract has the potential to counteract the palmitate-induced muscle cell insulin resistance and further studies are required to explore its antidiabetic properties.

Curcumin, Cardiometabolic Health and Dementia

Current research indicates curcumin [diferuloylmethane; a polyphenolic compound isolated from the rhizomes of the dietary spice turmeric (Curcuma longa)] exerts a beneficial effect on health which may be partly attributable to its anti-oxidative and anti-inflammatory properties. The aim of this review is to examine potential mechanisms of the actions of curcumin in both animal and human studies. Curcumin modulates relevant molecular target pathways to improve glucose and lipid metabolism, suppress inflammation, stimulate antioxidant enzymes, facilitate insulin signalling and reduce gut permeability. Curcumin also inhibits Aβ and tau accumulation in animal models and enhances mitochondria and synaptic function. In conclusion, in high-dose animal studies and in vitro, curcumin exerts a potential beneficial effect on cardiometabolic disease. However, human studies are relatively unconvincing. More intervention studies should be conducted with the new curcumin formulation with improved oral bioavailability.

Vaccinium ashei leaves extract alleviates insulin resistance via AMPK independent pathway in C2C12 myotube model

Blueberry (Vaccinium ashei) leaf has recently attracted attention as an anti-obesity food component. In this study, we examined the effects of blueberry leaf extract (BLEx) on insulin signaling in C2C12 differentiated myoblasts. The results showed that BLEx promotes the intracellular uptake of 2-[N-(7-Nitrobenz-2-oxa-1,3-diazol-4-yl)amino]−2-deoxy-D-glucose (2-NBDG) and phosphorylation of Akt under insulin stimulation. In addition, pretreatment with BLEx ameliorated TNF-α-nduced insulin resistance with regard to 2-NBDG uptake and Akt phosphorylation. Moreover, BLEx prevented the TNF-α−induced activation of JNK and NF-kB pathways and phosphorylation of IRS-1 at serine residue. BLEx failed to induce phosphorylation of AMPK as well as did not prevent the restoration of 2-NBDG uptake under TNF-α–induced insulin resistance. Overall, skeletal muscle is a putative target for the anti-diabetic effect of BLEx by amelioration of insulin resistance.

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Blueberry leaf extract (BLEx) promotes the intracellular uptake of 2-NBDG.

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BLEx prevented the TNF-α−induced insulin resistance.

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BLEx failed to activate AMPK pathway.

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Skeletal muscle is putative target of the BLEx for its anti-diabetic effect.

Curcumin ameliorates palmitate-induced inflammation in skeletal muscle cells by regulating JNK/NF-kB pathway and ROS production

Curcumin, a natural polyphenol compound, has the beneficial effects on several diseases such as metabolic syndrome, cancer, and diabetes. The anti-inflammatory property of curcumin has been demonstrated in different cells; however, its role in prevention of palmitate-induced inflammation in skeletal muscle C2C12 cells is not known. In this study, we examined the effect of curcumin on the inflammatory responses stimulated by palmitate in C2C2 cells. The results showed that palmitate upregulated the mRNA expression and protein release of IL-6 and TNF-α cytokines in C2C12 cells, while pretreatment with curcumin was able to attenuate the effect of palmitate on inflammatory cytokines. The anti-inflammatory effect of curcumin was associated with the repression of phosphorylation of IKKα-IKKβ, and JNK. Palmitate also caused an increase in reactive oxygen species (ROS) level that curcumin abrogated it. Collectively, these findings suggest that curcumin may represent a promising therapy for prevention of inflammation in skeletal muscle cells.

Molecular Mechanisms Underlying Curcumin-Mediated Therapeutic Effects in Type 2 Diabetes and Cancer

The growing prevalence of age-related diseases, especially type 2 diabetes mellitus (T2DM) and cancer, has become global health and economic problems. Due to multifactorial nature of both diseases, their pathophysiology is not completely understood so far. Compelling evidence indicates that increased oxidative stress, resulting from an imbalance between production of reactive oxygen species (ROS) and their clearance by antioxidant defense mechanisms, as well as the proinflammatory state contributes to the development and progression of the diseases. Curcumin (CUR; diferuloylmethane), a well-known polyphenol derived from the rhizomes of turmeric Curcuma longa, has attracted a great deal of attention as a natural compound with beneficial antidiabetic and anticancer properties, partly due to its antioxidative and anti-inflammatory actions. Although this polyphenolic compound is increasingly being recognized for its growing number of protective health effects, the precise molecular mechanisms through which it reduces diabetes- and cancer-related pathological events have not been fully unraveled. Hence, CUR is the subject of intensive research in the fields Diabetology and Oncology as a potential candidate in the treatment of both T2DM and cancer, particularly since current therapeutic options for their treatment are not satisfactory in clinics. In this review, we summarize the recent progress made on the molecular targets and pathways involved in antidiabetic and anticancer activities of CUR that are responsible for its beneficial health effects.

Beneficial effects of oleuropein on glucose uptake and on parameters relevant to the normal homeostatic mechanisms of glucose regulation in rat skeletal muscle

Oleuropein, the main constituents of leaves and fruits of the olive tree, has been demonstrated to exert various therapeutic and pharmacological properties including antidiabetic effect. However, the effectiveness of oleuropein on glucose homeostasis in intact rat skeletal muscle ex vivo has never been explored. Therefore, our current study was carried out to investigate and confirm the beneficial effect of oleuropein (1.5 mM) on glucose uptake and on parameters relevant to the normal homeostatic mechanisms of glucose regulation in rat skeletal muscle. For this purpose, soleus muscles were incubated for 12 hr without (control) or with oleuropein, in the presence or absence of AMP-activated protein kinase (AMPK) inhibitor, compound C, or wortmannin, an inhibitor of phosphatidylinositol kinase. Oleuropein-stimulated glucose transport, plasmalemmal glucose transporter 4 (GLUT4), and phosphorylation of phosphatidylinositol kinase and AMPK were examined. We observed that oleuropein treatment enhanced glucose transport, GLUT4 translocation, and AMPK phosphorylation. The oleuropein-stimulated glucose uptake and GLUT4 translocation were inhibited by compound C and were not affected by wortmannin. These results suggest that increased glucose uptake induced by oleuropein might be mediated through activation of AMPK and the subsequent increase in GLUT4 translocation in skeletal muscles.

Eburicoic Acid, a Triterpenoid Compound from Antrodia camphorata, Displays Antidiabetic and Antihyperlipidemic Effects in Palmitate-Treated C2C12 Myotubes and in High-Fat Diet-Fed Mice

This study was designed to investigate the antidiabetic and antihyperlipidemic effects and mechanisms of eburicoic acid (TRR); one component of Antrodia camphorata in vitro and in an animal model for 14 weeks. Expression levels of membrane glucose transporter type 4 (GLUT4); phospho-5′-adenosine monophosphate-activated protein kinase (AMPK)/total AMPK; and phospho-Akt/total Akt in insulin-resistant C2C12 myotube cells were significantly decreased by palmitate; and such decrease was prevented and restored by TRR at different concentrations. A group of control (CON) was on low-fat diet over a period of 14 weeks. Diabetic mice; after high-fat-diet (HFD) induction for 10 weeks; were randomly divided into six groups and were given once a day oral gavage doses of either TRR (at three dosage levels); fenofibrate (Feno) (at 0.25 g/kg body weight); metformin (Metf) (at 0.3 g/kg body weight); or vehicle (distilled water) (HF group) over a period of 4 weeks and still on HFD. Levels of glucose; triglyceride; free fatty acid (FFA); insulin; and leptin in blood were increased in 14-week HFD-fed mice as compared to the CON group; and the increases were prevented by TRR, Feno, or Metf as compared to the HF group. Moreover, HFD-induction displayed a decrease in circulating adiponectin levels, and the decrease was prevented by TRR, Feno, or Metf treatment. The overall effect of TRR is to decrease glucose and triglyceride levels and improved peripheral insulin sensitivity. Eburicoic acid, Feno, and Metf displayed both enhanced expression levels of phospho-AMPK and membrane expression levels of GLUT4 in the skeletal muscle of HFD-fed mice to facilitate glucose uptake with consequent enhanced hepatic expression levels of phospho-AMPK in the liver and phosphorylation of the transcription factor forkhead box protein O1 (FOXO1) but decreased messenger RNA (mRNA) of phosphenolpyruvate carboxykinase (PEPCK) to inhibit hepatic glucose production; resulting in lowered blood glucose levels. Moreover; TRR treatment increased hepatic expression levels of the peroxisome proliferator-activated receptor α (PPARα) to enhance fatty acid oxidation; but displayed a reduction in expressions of hepatic fatty acid synthase (FAS) but an increase in fatty acid oxidation PPARα coincident with a decrease in hepatic mRNA levels of sterol response element binding protein-1c (SREBP-1c); resulting in a decrease in blood triglycerides and amelioration of hepatic ballooning degeneration. Eburicoic acid-treated mice reduced adipose expression levels of lipogenic FAS and peroxisome proliferator-activated receptor γ (PPARγ) and led to decreased adipose lipid accumulation. The present findings demonstrated that TRR exhibits a beneficial therapeutic potential in the treatment of type 2 diabetes and hyperlipidemia.

Hispidin rescues palmitate‑induced insulin resistance in C2C12 myotubes

Skeletal muscle serves an important role in the utilization of glucose during insulin‑stimulated conditions. Excessive saturated fatty acids are considered to be a major contributing factor to insulin resistance in skeletal muscle cells. The present study investigated the effects of hispidin on palmitate‑induced insulin resistance in C2C12 skeletal muscle myotubes via an MTT assay, glucose uptake assay, Oil‑Red‑O staining and western blot analysis. Hispidin reversed the palmitate‑induced inhibition of glucose uptake, and inhibited palmitate‑induced intracellular lipid accumulation. Hispidin suppressed insulin receptor substrate‑1 Ser307 phosphorylation, and significantly promoted the activation of phosphatidylinositol‑3‑kinase and Akt, via inhibition of protein kinase C theta. Furthermore, hispidin treatment of C2C12 muscle cells increased glucose uptake via activation of adenosine monophosphate‑activated protein kinase. These findings indicated that hispidin may improve palmitate‑induced insulin resistance in skeletal muscle myotubes, and therefore hispidin treatment may be beneficial for patients with diabetes.

Quercetin and Green Tea Extract Supplementation Downregulates Genes Related to Tissue Inflammatory Responses to a 12-Week High Fat-Diet in Mice

Quercetin (Q) and green tea extract (E) are reported to counter insulin resistance and inflammation and favorably alter fat metabolism. We investigated whether a mixture of E + Q (EQ) could synergistically influence metabolic and inflammation endpoints in a high-fat diet (HFD) fed to mice. Male C57BL/6 mice (n = 40) were put on HFD (fat = 60%kcal) for 12 weeks and randomly assigned to Q (25 mg/kg of body weight (BW)/day), E (3 mg of epigallocatechin gallate/kg BW/day), EQ, or control groups for four weeks. At 16 weeks, insulin sensitivity was measured via the glucose tolerance test (GTT), followed by area-under-the-curve (AUC) estimations. Plasma cytokines and quercetin were also measured, along with whole genome transcriptome analysis and real-time polymerase chain reaction (qPCR) on adipose, liver, and skeletal muscle tissues. Univariate analyses were conducted via analysis of variance (ANOVA), and whole-genome expression profiles were examined via gene set enrichment. At 16 weeks, plasma quercetin levels were higher in Q and EQ groups vs. the control and E groups (p < 0.05). Plasma cytokines were similar among groups (p > 0.05). AUC estimations for GTT was 14% lower for Q vs. E (p = 0.0311), but non-significant from control (p = 0.0809). Genes for cholesterol metabolism and immune and inflammatory response were downregulated in Q and EQ groups vs. control in adipose tissue and soleus muscle tissue. These data support an anti-inflammatory role for Q and EQ, a result best captured when measured with tissue gene downregulation in comparison to changes in plasma cytokine levels.

Therapeutic Potential of Epigallocatechin Gallate Nanodelivery Systems

Nowadays, the society is facing a large health problem with the rising of new diseases, including cancer, heart diseases, diabetes, neurodegenerative diseases, and obesity. Thus, it is important to invest in substances that enhance the health of the population. In this context, epigallocatechin gallate (EGCG) is a flavonoid found in many plants, especially in tea. Several studies support the notion that EGCG has several benefits in fighting cancer, heart diseases, diabetes, and obesity, among others. Nevertheless, the poor intestinal absorbance and instability of EGCG constitute the main drawback to use this molecule in prevention and therapy. The encapsulation of EGCG in nanocarriers leads to its enhanced stability and higher therapeutic effects. A comprehensive review of studies currently available on the encapsulation of EGCG by means of nanocarriers will be addressed.

Discovery of Bisindole as a Novel Scaffold for Protein Tyrosine Phosphatase 1B Inhibitors

Protein tyrosine phosphatase 1B (PTP1B) has been proposed to be an effective target for the treatment of both type II diabetes and obesity. However, no PTP1B inhibitor has come into clinic application. Herein, we report mixed 3,3'-bisindoles as novel PTP1B inhibitors with low micromole-ranged inhibitory activity. The best active compound 9f inhibited PTP1B activity with an IC₅₀ of 2.79 µM. Meanwhile, it had low cytotoxicity and enhanced glucose uptake in vitro. Further studies demonstrated that some of these active compounds had a specific selectivity over other PTPs. Computational analysis further showed the binding mode of compound 9f with the active pocket of PTP1B. Our studies provide a novel scaffold for further development of more promising PTP1B inhibitors and potential drugs for type II diabetes and obesity.

Curcumin and insulin resistance-Molecular targets and clinical evidences

Curcumin ((1E,6E)-1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione), the main component of the Indian spice turmeric, has been used in traditional medicine to improve diabetes and its comorbidities. Since the last two decades, scientific research has shown that in addition to its antioxidant properties, curcumin could also work as protein homeostasis regulator and it is able to modulate other intracellular pathways. Curcumin supplementation has been proposed to improve insulin resistance (IR) through the activation of the insulin receptor and its downstream pathways in several experimental models, pointing out that its clinical use may be a good and innocuous strategy to improve IR-related diseases. IR is associated with many diseases and syndromes like carbohydrate intolerance, diabetes, metabolic syndrome, and cardiovascular disease. Therefore, it is imperative to identify safe therapeutic interventions aimed to reduce side effects that could lead the patient to leave the treatment. To date, many clinical trials have been carried out using turmeric and curcumin to improve metabolic syndrome, carbohydrate intolerance, diabetes, and obesity in individuals with IR. Results so far are inconclusive because dose, time of treatment, and type of curcumin can change the study outcome significantly. However, there is some clinical evidence suggesting a beneficial effect of curcumin on IR. In this review, we discuss the factors that could influence curcumin effects in clinical trials aimed to improve IR and related diseases, and the conclusions that can be drawn from results obtained so far. © 2016 BioFactors, 42(6):561-580, 2016.

Myristic Acid Enhances Diacylglycerol Kinase δ-Dependent Glucose Uptake in Myotubes

Decreased expression of diacylglycerol kinase (DGK) δ in skeletal muscles attenuates glucose uptake and is closely related to the pathogenesis of type 2 diabetes. Therefore, up-regulation of DGKδ expression is thought to protect and improve glucose homoeostasis in type 2 diabetes. We recently determined that myristic acid (14:0), but not palmitic (16:0) or stearic (18:0) acid, significantly increased DGKδ2 protein expression in mouse C2C12 myotubes. In the current study, we analyzed whether myristic acid indeed enhances glucose uptake in C2C12 myotubes. We observed that myristic acid caused ~1.4-fold increase in insulin-independent glucose uptake. However, palmitic and stearic acids failed to enhance glucose uptake. DGKδ-specific siRNA decreased myristic acid-dependent increase of glucose uptake. Moreover, overexpression of DGKδ2 enhanced glucose uptake in C2C12 cells in the absence of myristic acid treatment. Taken together, these results strongly suggest that myristic acid enhances basal glucose uptake in myotubes in a DGKδ2 expression-dependent manner.

Aspalathin improves glucose and lipid metabolism in 3T3-L1 adipocytes exposed to palmitate

SCOPE

Saturated-free fatty acids, such as palmitate, are associated with insulin resistance. This study aimed to establish if an aspalathin-enriched green rooibos extract (GRE) and, its major flavanoid, aspalathin (ASP) could contribute significantly to the amelioration of experimentally induced insulin resistance in 3T3-L1 adipocytes.

METHODS AND RESULTS

3T3-L1 adipocytes were cultured in DMEM containing 0.75 mM palmitate for 16 h to induce insulin resistance before treatment for 3 h with GRE (10 μg/mL) or ASP (10 μM). GRE and ASP reversed the palmitate-induced insulin resistance. At a protein level GRE and ASP suppressed nuclear factor kappa beta (NF-κB), insulin receptor substrate one (serine 307) (IRS1 (Ser (307) )) and AMP-activated protein kinase phosphorylation and increased serine/threonine kinase AKT (AKT) activation, while only GRE increased glucose transporter four (Glut4) protein expression. Peroxisome proliferator-activated receptor alpha and gamma (PPARα and γ), and carnitine palmitoyltransferase one (CPT1) expression were increased by ASP alone.

CONCLUSION

Together these effects offer a plausible explanation for the ameliorative effect of GRE and ASP on insulin-resistance, an underlying cause for obesity and type 2 diabetes.

Antihyperglycemic Activity of Eucalyptus tereticornis in Insulin-Resistant Cells and a Nutritional Model of Diabetic Mice

Eucalyptus tereticornis is a plant used in traditional medicine to control diabetes, but this effect has not been proved scientifically. Here, we demonstrated through in vitro assays that E. tereticornis extracts increase glucose uptake and inhibit their production in insulin-resistant C2C12 and HepG2 cells, respectively. Furthermore, in a nutritional model using diabetic mice, the administration of ethyl acetate extract of E. tereticornis reduced fasting glycaemia, improved tolerance to glucose, and reduced resistance to insulin. Likewise, this extract had anti-inflammatory effects in adipose tissue when compared to control diabetic mice. Via bioguided assays and sequential purification of the crude extract, a triterpenoid-rich fraction from ethyl acetate extracts was shown to be responsible for the biological activity. Similarly, we identified the main compound responsible for the antihyperglycemic activity in this extract. This study shows that triterpenes found in E. tereticornis extracts act as hypoglycemic/antidiabetic compounds and contribute to the understanding of their use in traditional medicine.