Preventive effect of oleate on palmitate-induced insulin resistance in skeletal muscle and its mechanism of action

Dietary flaxseed oil suppresses hyperglycemia and hyperinsulinemia through increasing in α-linolenic acid content in the muscle

Types of fats and oils affect the onset of lifestyle diseases. In this study, we investigated the relationship between the postprandial hyperglycemia and fatty acids content in the skeletal muscle of C57BL/6 mice given 20% lard, palm oil, corn oil, safflower oil, and flaxseed oil for 16 weeks. Lard increased plasma glucose and insulin levels at the end of feeding period, whereas flaxseed oil did not. It was noteworthy that there is a positive correlation between palmitic acid content in the muscle and postprandial hyperglycemia, and a negative correlation between α-linolenic acid content and hyperglycemia. Alternatively, mice were given 30% lard for 16 weeks. When lard was partially substituted with flaxseed oil (10-50% substitution), flaxseed oil dose-dependently prevented lard-induced hyperglycemia and hyperinsulinemia. In conclusion, flaxseed oil prevents the adverse effects of lard through increasing in α-linolenic acid content in the muscle.

Brain Dopamine-Clock Interactions Regulate Cardiometabolic Physiology: Mechanisms of the Observed Cardioprotective Effects of Circadian-Timed Bromocriptine-QR Therapy in Type 2 Diabetes Subjects

Despite enormous global efforts within clinical research and medical practice to reduce cardiovascular disease(s) (CVD), it still remains the leading cause of death worldwide. While genetic factors clearly contribute to CVD etiology, the preponderance of epidemiological data indicate that a major common denominator among diverse ethnic populations from around the world contributing to CVD is the composite of Western lifestyle cofactors, particularly Western diets (high saturated fat/simple sugar [particularly high fructose and sucrose and to a lesser extent glucose] diets), psychosocial stress, depression, and altered sleep/wake architecture. Such Western lifestyle cofactors are potent drivers for the increased risk of metabolic syndrome and its attendant downstream CVD. The central nervous system (CNS) evolved to respond to and anticipate changes in the external (and internal) environment to adapt survival mechanisms to perceived stresses (challenges to normal biological function), including the aforementioned Western lifestyle cofactors. Within the CNS of vertebrates in the wild, the biological clock circuitry surveils the environment and has evolved mechanisms for the induction of the obese, insulin-resistant state as a survival mechanism against an anticipated ensuing season of low/no food availability. The peripheral tissues utilize fat as an energy source under muscle insulin resistance, while increased hepatic insulin resistance more readily supplies glucose to the brain. This neural clock function also orchestrates the reversal of the obese, insulin-resistant condition when the low food availability season ends. The circadian neural network that produces these seasonal shifts in metabolism is also responsive to Western lifestyle stressors that drive the CNS clock into survival mode. A major component of this natural or Western lifestyle stressor-induced CNS clock neurophysiological shift potentiating the obese, insulin-resistant state is a diminution of the circadian peak of dopaminergic input activity to the pacemaker clock center, suprachiasmatic nucleus. Pharmacologically preventing this loss of circadian peak dopaminergic activity both prevents and reverses existing metabolic syndrome in a wide variety of animal models of the disorder, including high fat-fed animals. Clinically, across a variety of different study designs, circadian-timed bromocriptine-QR (quick release) (a unique formulation of micronized bromocriptine-a dopamine D2 receptor agonist) therapy of type 2 diabetes subjects improved hyperglycemia, hyperlipidemia, hypertension, immune sterile inflammation, and/or adverse cardiovascular event rate. The present review details the seminal circadian science investigations delineating important roles for CNS circadian peak dopaminergic activity in the regulation of peripheral fuel metabolism and cardiovascular biology and also summarizes the clinical study findings of bromocriptine-QR therapy on cardiometabolic outcomes in type 2 diabetes subjects.

Oleic acid abomasal infusion limits lipolysis and improves insulin sensitivity in adipose tissue from periparturient dairy cows

Excessive adipose tissue (AT) lipolysis around parturition in dairy cows is associated with impaired AT insulin sensitivity and increased incidence of metabolic diseases. Supplementing cows with oleic acid (OA) reduces circulating biomarkers of lipolysis and improves energy balance. Nevertheless, it is unclear if OA alters lipid trafficking in AT. In the liver and skeletal muscle, OA improves mitochondrial function and promotes lipid droplet formation by activating perilipin 5 (PLIN5) and peroxisome proliferator-activated receptor α (PPARα). However, it is unknown if this mechanism occurs in AT. The objective of this study was to determine the effect of OA on AT lipolysis, systemic and AT insulin sensitivity, and AT mitochondrial function in periparturient dairy cows. Twelve rumen-cannulated Holstein cows were infused abomasally following parturition with ethanol (CON) or OA (60 g/d) for 14 d. Subcutaneous AT samples were collected at 11 ± 3.6 d before calving (-12 d), and 6 ± 1.0 d (7 d) and 13 ± 1.4 d (14 d) after parturition. An intravenous glucose tolerance test was performed on d 14. Adipocyte morphometry was performed on hematoxylin and eosin-stained AT sections. The antilipolytic effect of insulin (1 μg/L) was evaluated using an ex vivo explant culture following lipolysis stimulation. PLIN5 and PPARα transcription and translation were determined by real-time quantitative PCR and capillary electrophoresis, respectively. RNA sequencing was used to evaluate the transcriptomic profile of mitochondrial gene networks. In CON cows, postpartum lipolysis increased the percentage of smaller (<3,000 µm²) adipocytes at 14 d compared with -12 d. However, OA limited adipocyte size reduction at 14 d. Likewise, OA decreased lipolysis plasma markers nonesterified free fatty acids and β-hydroxybutyrate at 5 and 7 d. Over the 14-d period, compared with CON, OA increased the concentration of plasma insulin and decreased plasma glucose. During the glucose tolerance test, OA decreased circulating glucose concentration (at 10, 20, 30, 40 min) and the glucose clearance rate. Moreover, OA increased insulin at 10 and 20 min and tended to increase it at 30 min. Following lipolysis stimulation, OA improved the antilipolytic effect of insulin in the AT at 14 d. PLIN5 and PPARA gene expression decreased postpartum regardless of treatment. However, OA increased PLIN5 protein expression at 14 d and increased PPARA at 7 and 14 d. Immunohistochemical analysis of AT and RNA sequencing data showed that OA increased the number of mitochondria and improved mitochondrial function. However, OA had no effect on production and digestibility. Our results demonstrate that OA limits AT lipolysis, improves systemic and AT insulin sensitivity, and is associated with markers of mitochondrial function supporting a shift to lipogenesis in AT of periparturient dairy cows.

Oleate restores altered autophagic flux to rescue palmitate lipotoxicity in hypothalamic neurons

Accumulation of excess lipids in non-adipose tissues, such as the hypothalamus, is termed lipotoxicity and causative of free fatty acid-mediated pathology in metabolic disease. This study aimed to elucidate the molecular mechanisms behind oleate (OA)- and palmitate (PA)-mediated changes in hypothalamic neurons. Using the well-characterized hypothalamic neuronal cell model, mHypoE-46, we assessed gene changes through qRT-PCR, cell death with quantitative imaging, PA metabolism using stable isotope labeling, and cellular mechanisms using pharmacological modulation of lipid metabolism and autophagic flux. Palmitate (PA) disrupts gene expression, including Npy, Grp78, and Il-6 mRNA in mHypoE-46 hypothalamic neurons. Blocking PA metabolism using triacsin-C prevented the increase of these genes, implying that these changes depend on PA intracellular metabolism. Co-incubation with oleate (OA) is also potently protective and prevents cell death induced by increasing concentrations of PA. However, OA does not decrease U-¹³C-PA incorporation into diacylglycerol and phospholipids. Remarkably, OA can reverse PA toxicity even after significant PA metabolism and cellular impairment. OA can restore PA-mediated impairment of autophagy to prevent or reverse the accumulation of PA metabolites through lysosomal degradation, and not through other reported mechanisms. The autophagic flux inhibitor chloroquine (CQ) mimics PA toxicity by upregulating autophagy-related genes, Npy, Grp78, and Il-6, an effect partially reversed by OA. CQ also prevented the OA defense against PA toxicity, whereas the autophagy inducer rapamycin provided some protection. Thus, PA impairment of autophagic flux significantly contributes to its lipotoxicity, and OA-mediated protection requires functional autophagy. Overall, our results suggest that impairment of autophagy contributes to hypothalamic lipotoxicity.

The effect of dietary supplementation with blueberry, cyanidin-3-O-β-glucoside, yoghurt and its peptides on gene expression associated with glucose metabolism in skeletal muscle obtained from a high-fat-high-carbohydrate diet induced obesity model

Obesity is a leading global health problem contributing to various chronic diseases, including type II diabetes mellitus (T2DM). The aim of this study was to investigate whether blueberries, yoghurt, and their respective bioactive components, Cyanidin-3-O-β-glucoside (C3G) and peptides alone or in combinations, alter the expression of genes related to glucose metabolism in skeletal muscles from diet-induced obese mice. In extensor digitorum longus (EDL), yoghurt up-regulated the expression of activation of 5’adenosine monophosphate-activated protein kinase (AMPK), insulin receptor substrate-1 (IRS-1), phosphatidylinositol-3 kinase (PI3K) and glucose transporter 4 (GLUT4), and down-regulated the expression of angiotensin II receptor type 1 (AGTR-1). The combination of blueberries and yoghurt down-regulated the mRNA expression of AGTR-1 and Forkhead box protein O1 (FoxO1) in the EDL. Whereas the combination of C3G and peptides down-regulated AGTR-1 and up-regulated GLUT4 mRNA expression in the EDL. In the soleus, blueberries and yoghurt alone, and their combination down-regulated AGTR-1 and up-regulated GLUT4 mRNA expression. In summary blueberries and yoghurt, regulated multiple genes associated with glucose metabolism in skeletal muscles, and therefore may play a role in the management and prevention of T2DM.

Evaluation of antidiabetic, antioxidant and antilipidemic potential of natural dietary product prepared from Cyphostemma digitatum in rats’ model of diabetes

Introduction: Cyphostemma digitatum has a high content of antioxidant constituents and has been employed by the traditional healers and local people of Yemen for diabetes treatment. However, scientific evidence regarding its antidiabetic efficacy is largely unknown. Accordingly, the present study aimed to confirm the treatment effects of a dietary natural product prepared from Cyphostemma digitatum (PCD) in diabetic rats.Methods: Diabetes was induced by a high-fat diet and streptozotocin (HF-STZ). PCD (1 g/kg) was given by gavage administration once a day continuously for 30 days. At the end of treatment, blood and skeletal muscle samples were collected for further analysis.Results: The antidiabetic effects of PCD were demonstrated by significant reduction (P ≤ 0.05) in the levels of serum glucose (40%), triglyceride (32%), cholesterol (53%), low-density lipoprotein (LDL) (44%), malondialdehyde (MDA) (61%) in PCD treated groups compared to the diabetic control group. Additionally, PCD treatment significantly (P ≤ 0.05) restored the decreased levels of insulin (70%) and the activities of superoxide dismutase (SOD) (57%) and reduced glutathione (GSH) (544%) when compared to that of diabetic control rats. We found that treatment with PCD for 30 days fully restored the plasmalemmal glucose transporter type 4 (GLUT4) contents, as well as the phosphorylation of phosphatidylinositol 3-kinase (PI3K) (P ≤ 0.05).Conclusion: Thus, PCD treatment can be considered a potential drug candidate for diabetes.

Understanding the Mechanism Underlie the Antidiabetic Activity of Oleuropein Using Ex-Vivo Approach

Background

Oleuropein, the main constituent of olive fruit and leaves, has been reported to protect against insulin resistance and diabetes. While many experimental investigations have examined the mechanisms by which oleuropein improves insulin resistance and diabetes, much of these investigations have been carried out in either muscle cell lines or in vivo models two scenarios with many drawbacks. Accordingly, to simplify identification of mechanisms by which oleuropein regulates specific cellular processes, we resort, in the present study, to isolated muscle preparation which enables better metabolic milieu control and permit more detailed analyses.

Methods

For this purpose, soleus muscles were incubated for 12 h without or with palmitate (1.5 mM) in the presence or absence of oleuropein (1.5 mM), and compound C. Insulin-stimulated glucose transport, glucose transporter type 4 (GLUT4) translocation, Akt substrate of 160 kDa (AS160) phosphorylation and adenosine monophosphate-activated protein kinase (AMPK) phosphorylation were examined.

Results

Palmitate treatment reduced insulin-stimulated glucose transport, GLUT4 translocation and AS160 phosphorylation, but AMPK phosphorylation was not changed. Oleuropein administration (12 h) fully rescued insulin-stimulated glucose transport, but partially restored GLUT4 translocation. However, it fully restored AS160 phosphorylation, raising the possibility that oleuropein may also have contributed to the restoration of glucose transport by increased GLUT4 intrinsic activity. Inhibition of AMPK phosphorylation with compound C (50 µM) prevented oleuropein -induced improvements in insulin-stimulated glucose transport, GLUT4 translocation, and AS160 phosphorylation.

Conclusion

Our results clearly indicate that oleuropein alleviates palmitate-induced insulin resistance appears to occur via an AMPK-dependent mechanism involving improvements in the functionality of the AS160-GLUT4 signaling system.

Dose- and Time-Dependent Effects of Oleate on Mitochondrial Fusion/Fission Proteins and Cell Viability in HepG2 Cells: Comparison with Palmitate Effects

Mitochondrial impairments in dynamic behavior (fusion/fission balance) associated with mitochondrial dysfunction play a key role in cell lipotoxicity and lipid-induced metabolic diseases. The present work aimed to evaluate dose- and time-dependent effects of the monounsaturated fatty acid oleate on mitochondrial fusion/fission proteins in comparison with the saturated fatty acid palmitate in hepatic cells. To this end, HepG-2 cells were treated with 0, 10 μM, 50 μM, 100 μM, 250 μM or 500 μM of either oleate or palmitate for 8 or 24 h. Cell viability and lipid accumulation were evaluated to assess lipotoxicity. Mitochondrial markers of fusion (mitofusin 2, MFN2) and fission (dynamin-related protein 1, DRP1) processes were evaluated by Western blot analysis. After 8 h, the highest dose of oleate induced a decrease in DRP1 content without changes in MFN2 content in association with cell viability maintenance, whereas palmitate induced a decrease in cell viability associated with a decrease mainly in MFN2 content. After 24 h, oleate induced MFN2 increase, whereas palmitate induced DRP1 increase associated with a higher decrease in cell viability with high doses compared to oleate. This finding could be useful to understand the role of mitochondria in the protective effects of oleate as a bioactive compound.

Network pharmacology combined with metabolomics to study the mechanism of Shenyan Kangfu Tablets in the treatment of diabetic nephropathy

ETHNOPHARMACOLOGICAL RELEVANCE

Shenyan Kangfu Tablets (SYKFT) is a traditional prescription evolved from Shenqi Pills. It has been included in the Synopsis of the Golden Chamber for more than 2000 years. SYKFT was listed as a national Chinese medicine protected class by the China Food and Drug Administration. Diabetic nephropathy (DN) is one of the serious microvascular diseases caused by diabetes and is also one of the important factors leading to the death of patients. The pathogenesis of DN is diverse and complex, and there is no particularly effective drug treatment. There is clinical evidence that SYKFT has a good therapeutic effect on DN with no obvious adverse effects, but the mechanism of treatment is not clear.

AIM OF THE STUDY

In this study, network pharmacology was combined with metabolomics technology to explore the mechanism of SYKFT in the treatment of DN.

MATERIALS AND METHODS

First, the research team conducted a qualitative study of the chemical components contained in SYKFT, and carried out network pharmacology to search for potential targets based on the characterized chemical components. Second, we analysed the metabolic profile of db/db mouse urine based on UHPLC-QTOF-MS technology, and biomarkers were identified by multivariate statistical analysis. Then, we performed further pathway enrichment analysis. Finally, the results of metabolomics and network pharmacology were conjointly analysed.

RESULTS

Seventy-five chemical components of SYKFT were identified. According to the TCMSP database, the corresponding targets of the qualitatively identified components were searched, and a total of 36 potentially active components and 160 targets related to DN were obtained. A total of 38 biomarkers were found in metabolomics based on UHPLC-QTOF-MS technology. Biosynthesis of unsaturated fatty acids and starch and sucrose metabolism are the most related pathways, the former of which has been rarely reported concerning DN. Finally, the results of the joint analysis show that two targets, hexokinase 2 (HK2) and maltase glucoamylase (MGAM), are the overlapping targets. It means they are not only the related targets of pathways involved in potential biomarkers in metabolomics but also the intersection targets of diseases and drugs identified by network pharmacology.

CONCLUSIONS

The study reveals that the potential mechanism of SYKFT is most related to insulin resistance (IR) in the treatment of DN. It also proves that network pharmacology combined with metabolomics to find the mechanisms by which herbs treat complex diseases is a feasible tool.

Oleate Ameliorates Palmitate-Induced Impairment of Differentiative Capacity in C2C12 Myoblast Cells

A common observation in metabolic disorders and aging is the elevation of free fatty acids (FFAs), which can form ectopic fat deposition and result in lipotoxicity. Ectopic fat deposition of skeletal muscle has been recognized as an important component of aging, frailty, and sarcopenia. Previous studies have suggested that lipotoxicity caused by FFAs mainly stemmed from saturated fatty acids and decreased unsaturated/saturated fatty acid ratio in serum are also observed among metabolic disorder patients. However, the different effects of saturated fatty acids and unsaturated fatty acids on skeletal muscle are not fully elucidated. In this study, we verified that palmitate (PA), a saturated fatty acid, could lead to impaired differentiative capacity of C2C12 myoblasts by affecting Pax7, MyoD, and myogenin (MyoG), which are master regulators of lineage specification and the myogenic program. Then, oleate (OA), a monounsaturated fatty acid, were added to culture medium together with PA. Results showed that OA could ameliorate the impairment of differentiative capacity in C2C12 myoblast cells. In addition, we found PI3K/Akt signaling pathway played an important role during the process by RNA sequencing and bioinformatics analysis. The positive effect of OA on myoblast differentiative capacity disappeared if PI3K inhibitor LY294002 was added. In conclusion, our study showed that PA could destroy differentiative capacity of C2C12 myoblasts by affecting the expression of Pax7, MyoD, and MyoG, and OA could improve this impairment through PI3K/Akt signaling pathway.

Oleic Acid Protects Against Insulin Resistance by Regulating the Genes Related to the PI3K Signaling Pathway

BACKGROUND

The effects of different types of fatty acids on the gene expression of key players in the IRS1/PI3K signaling pathway have been poorly studied.

MATERIAL AND METHODS

We analyzed IRS1, p85α, and p110β mRNA expression and the fatty acid composition of phospholipids in visceral adipose tissue from patients with morbid obesity and from non-obese patients. Moreover, we analyzed the expression of those genes in visceral adipocytes incubated with oleic, linoleic, palmitic and dosahexaenoic acids.

RESULTS

We found a reduced IRS1 expression in patients with morbid obesity, independent of insulin resistance, and a reduced p110β expression in those with lower insulin resistance. A positive correlation was found between p85α and stearic acid, and between IRS1 and p110β with palmitic and dosahexaenoic acid. In contrast, a negative correlation was found between p85α and oleic acid, and between IRS1 and p110β with linoleic, arachidonic and adrenic acid. Incubation with palmitic acid decreased IRS1 expression. p85α was down-regulated after incubation with oleic and dosahexaenoic acid and up-regulated with palmitic acid. p110β expression was increased and decreased after incubation with oleic and palmitic acid, respectively. The ratio p85α/p110β was decreased by oleic and dosahexaenoic acid and increased by palmitic acid.

CONCLUSIONS

Our in vitro results suggest a detrimental role of palmitic acid on the expression of gene related to insulin signaling pathway, with oleic acid being the one with the higher and more beneficial effects. DHA had a slight beneficial effect. Fatty acid-induced regulation of genes related to the IRS1/PI3K pathway may be a novel mechanism by which fatty acids regulate insulin sensitivity in visceral adipocytes.

Oleic Acid Counters Impaired Blastocyst Development Induced by Palmitic Acid During Mouse Preimplantation Development: Understanding Obesity-Related Declines in Fertility

Obesity is associated with altered fatty acid profiles, reduced fertility, and assisted reproductive technology (ART) success. The effects of palmitic acid (PA), oleic acid (OA), and their combination on mouse preimplantation development, endoplasmic reticulum (ER) stress pathway gene expression, lipid droplet formation, and mitochondrial reactive oxygen species (ROS) were characterized. Two-cell stage mouse embryos collected from superovulated and mated CD1 females were placed into culture with KSOMaa medium, or PA alone or in combination with OA for 46 h. PA significantly reduced blastocyst development in a concentration-dependent manner, which was prevented by co-treatment with OA. PA and OA levels in mouse reproductive tracts were assessed by liquid chromatography coupled to mass spectrometry (LC-MS). LC-MS indicated higher concentrations of PA in the mouse oviduct than the uterus. Transcript analysis revealed that PA alone groups had increased ER stress pathway (ATF3, CHOP, and XBP1 splicing) mRNAs, which was alleviated by OA co-treatment. OA co-treatment significantly increased lipid droplet accumulation and significantly decreased mitochondrial ROS from PA treatment alone. PA treatment for only 24 h significantly reduced its impact on blastocyst development from the 2-cell stage. Thus, PA affects ER stress pathway gene expression, lipid droplet accumulation, and mitochondrial ROS in treated preimplantation embryos. These mechanisms may serve to offset free fatty acid exposure effects on preimplantation development, but their protective ability may be overwhelmed by elevated PA.

Non-esterified fatty acids in the ovary: friends or foes?

A majority of common metabolic diseases can result in excessive lipolysis, leading to elevated levels of non-esterified fatty acids (NEFAs) in the body fluids. In females, increased NEFA levels in the follicular fluid markedly alter the functions of intrafollicular cells such as granulosa cells (GCs) and oocytes. Therefore, elevated levels of NEFAs have been suggested to be a significant player of subfertility in females of both human and economically important animal species such as cattle, buffalo, sheep, pig, chicken, and dog. However, the effects imposed by saturated and unsaturated fatty acids (SFAs and UFAs) on ovarian follicles are controversial. The present review emphasizes that SFAs induce apoptosis in granulosa and cumulus cells of ovarian follicles in different species. They further could adversely affect oocyte maturation and developmental competence. Many types of UFAs affect steroidogenesis and proliferation processes and could be detrimental for follicular cells, especially when at elevated concentrations. Interestingly, monounsaturated fatty acids (MUFAs) appear to contribute to the etiology of the polycystic ovarian syndrome (PCOS) as they were found to induce the transcription and translation of the androgenic transcription factor SOX9 while downregulating its estrogenic counterpart FOXL2 in GCs. Overall, this review presents our revised understanding of the effects of different fatty acids on the female reproductive success, which may allow other researchers and clinicians to investigate the mechanisms for treating metabolic stress-induced female infertility.

TGR5 agonist ameliorates insulin resistance in the skeletal muscles and improves glucose homeostasis in diabetic mice

BACKGROUND AND PURPOSE

TGR5 plays an important role in many physiological processes. However, the functions of TGR5 in the regulation of the glucose metabolism and insulin sensitivity in the skeletal muscles have not been fully elucidated. We synthesized MN6 as a potent and selective TGR5 agonist. Here, the effect of MN6 on insulin resistance in skeletal muscles was evaluated in diet-induced obese (DIO) mice and C2C12 myotubes, and the underlying mechanisms were explored.

METHODS

The activation of MN6 on human and mouse TGR5 was evaluated by a cAMP assay in HEK293 cell lines stable expressing hTGR5/CRE or mTGR5/CRE cells. GLP-1 secretion was measured in NCI-H716 cells and CD1 mice. The acute and chronic effects of MN6 on regulating metabolic abnormalities were observed in ob/ob and DIO mice. 2-deoxyglucose uptake was examined in isolated skeletal muscles. Akt phosphorylation, glucose uptake and glycogen synthesis were examined to assess the effects of MN6 on palmitate-induced insulin resistance in C2C12 myotubes.

RESULTS

MN6 potently activated human and mouse TGR5 with EC₅₀ values of 15.9 and 17.9 nmol/L, respectively, and stimulated GLP-1 secretion in NCI-H716 cells and CD1 mice. A single oral dose of MN6 significantly decreased the blood glucose levels in ob/ob mice. Treatment with MN6 for 15 days reduced the fasting blood glucose and HbA1c levels in ob/ob mice. MN6 improved glucose and insulin tolerance and enhanced the insulin-stimulated glucose uptake of skeletal muscles in DIO mice. The palmitate-induced impairment of insulin-stimulated Akt phosphorylation, glucose uptake and glycogen synthesis in C2C12 myotubes could be prevented by MN6. The effect of MN6 on palmitate-impaired insulin-stimulated Akt phosphorylation was abolished by siRNA-mediated knockdown of TGR5 or by the inhibition of adenylate cyclase or protein kinase A, suggesting that this effect is dependent on the activation of TGR5 and the cAMP/PKA pathway.

CONCLUSIONS

Our study identified that a TGR5 agonist could ameliorate insulin resistance by the cAMP/PKA pathway in skeletal muscles; this uncovered a new effect of the TGR5 agonist on regulating the glucose metabolism and insulin sensitivity in skeletal muscles and further strengthened its potential value for the treatment of type 2 diabetes.

Resveratrol attenuates endothelial oxidative injury by inducing autophagy via the activation of transcription factor EB

Background

Endothelial oxidative injury is a key event in the pathogenesis of atherosclerosis (AS). Resveratrol (RSV) attenuates the oxidative injury in human umbilical vein endothelial cells (HUVECs). Autophagy is critical for the RSV-induced protective effects. However, the exact underlying mechanisms haven’t been completely elucidated. Thus, we aimed to explore the role of autophagy of the anti-oxidation of RSV and the underlying mechanism in palmitic acid (PA)-stimulated HUVECs.

Methods

HUVECs were pretreated with 10 μM of RSV for 2 h and treated with 200 μM of PA for an additional 24 h. Cell viability, intracellular reactive oxygen species (ROS) and malondialdehyde (MDA) levels were estimated with a microplate reader and confocal microscope. Autophagosomes were analyzed by transmission electron microscopy, while lysosomes by confocal microscopy. The expression of transcription factor EB (TFEB) and related genes were quantified by qRT-PCR assay. Furthermore, TFEB levels, autophagy, and lysosomes were examined by western blot assay.

Results

RSV pretreatment suppressed the PA-induced decline in cell viability and elevation in ROS and MDA levels in HUVECs. RSV pretreatment also increased LC3 production and P62 degradation while promoted the autophagosomes formation. However, 3-methyladenine (3-MA) treatment attenuated RSV-induced autophagy. RSV pretreatment upregulated the TFEB and TFEB-modulated downstream genes expression in a concentration-dependent manner. Additionally, in cells transfected with TFEB small interfering RNA, RSV-induced TFEB expression and subsequent autophagy were abolished. Meanwhile, the TFEB-modulated genes expression, the lysosomes formation and the RSV-induced anti-oxidation were suppressed.

Conclusions

In HUVECs, RSV attenuates endothelial oxidative injury by inducing autophagy in a TFEB-dependent manner.

Resveratrol attenuates oxidative injury in human umbilical vein endothelial cells through regulating mitochondrial fusion via TyrRS-PARP1 pathway

Background/aims

Oxidative stress-induced damage in endothelial cells is a crucial initiator of atherosclerosis (AS), which is highly related to excessive reactive oxygen species (ROS) and mitochondrial dynamics. Resveratrol (RSV) exerts beneficial effects against endothelial oxidative injury, while the underlying mechanisms have not been fully elucidated. Thus, we aimed to explore the role of mitochondria dynamics during the anti-oxidative activities of RSV in palmitic acid (PA)-stimulated human umbilical vein endothelial cells (HUVECs) and to verify whether tyrosyl transfer- RNA synthetase (TyrRS) and poly (ADP-ribose) polymerase 1 (PARP1) are targeted during this process.

Methods

HUVECs were exposed to 200 μM of PA for 16 h before treated with 10 μM of RSV for 8 h. Cell viability was detected using Cell counting kit-8 (CCK-8) assay. The intracellular ROS level and mitochondria membrane potential (MMP) were measured using microplate reader and flow cytometry. The malondialdehyde and superoxide dismutase were measured using the microplate reader. The mitochondrial morphology and fusion process was observed under transmission electron microscopy and confocal microscopy. TyrRS and PARP1 were knocked down with the specific small interference RNAs (siRNA), and the protein expressions of TyrRS, PARP1, and mitochondrial fusion proteins (MFN1, MFN2, and OPA1) were measured by western blot.

Results

RSV treatment suppressed the PA-induced injuries in HUVECs, including the damage to cell viability, oxidative stress, and loss of MMP. Additionally, RSV improved the protein levels of MFN1, MFN2, and OPA1 as well as inhibited the PA-induced fragmentation of mitochondria. However, the effects of RSV on oxidative stress and mitochondrial fusion were abolished by the pretreatment of siRNAs of TyrRS and PARP1, indicating that these effects of RSV were dependent on the TyrRS-PARP1 pathway.

Conclusions

RSV attenuated endothelial oxidative injury by regulating mitochondrial fusion via TyrRS-PARP1 signaling pathway.

Electronic supplementary material

The online version of this article (10.1186/s12986-019-0338-7) contains supplementary material, which is available to authorized users.

Effect of Aluminum Exposure on Glucose Metabolism and Its Mechanism in Rats

The effects of aluminum (Al) exposure on glucose metabolism and its mechanism were investigated. A total of 30 healthy Wistar male rats were randomly divided into two groups: control (GC) and experimental (GE). The GC group received intraperitoneal normal saline. The GE was established by intraperitoneal injected AlCl₃ solution at 10 mg/kg for 30 days. Fasting blood glucose (FBG) and serum levels of insulin (FINS) were measured. The insulin resistance index (HOMA-IR) and pancreatic β cell function index (HOMA-β) were calculated and analyzed with homeostasis model assessment (HOMA). Pancreatic tissue was taken for pathological examination. Glucose transporter 4 (GLUT4) expression in skeletal muscle was detected by quantitative PCR and Western blot. Levels of FBG and HOMA-IR in GE were higher than those in GC at day 10 and 20 (P < 0.05). FINS in GE were higher than those in GC at day 10 and 20, and lower than those in GC at day 30 (P < 0.05). HOMA-β in GE was lower than that of GC at every time point (P < 0.05). Pathology showed that pancreatic damage changed more profoundly with prolongation of time in GE. Expression levels of GLUT4 mRNA and protein in rat skeletal muscle in GE were significantly lower than those in GC (P < 0.05). The results suggested that Al exposure affected glucose metabolism through pancreatic damage and reduction of GLUT4 expression.

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.