Biphasic effects of chronic ethanol exposure on insulin-stimulated glucose uptake in primary cultured rat skeletal muscle cells: role of the Akt pathway and GLUT4

Quercetin and its metabolite isorhamnetin promote glucose uptake through different signalling pathways in myotubes

Quercetin and its metabolite isorhamnetin elicit various beneficial effects on human health. However, their bioavailability is low. In this study, we investigated whether low concentrations in the physiological range could promote glucose uptake in L6 myotubes, as well as the underlying molecular mechanisms. We found that 0.1 nM and 1 nM quercetin or 1 nM isorhamnetin significantly increased glucose uptake via translocation of glucose transporter type 4 (GLUT4) to the plasma membrane of L6 myotubes. Quercetin principally activated the CaMKKβ/AMPK signalling pathway at these concentrations, but also activated IRS1/PI3K/Akt signalling at 10 nM. In contrast, 1 nM and 10 nM isorhamnetin principally activated the JAK/STAT pathway. Treatment with siAMPKα and siJAK2 abolished quercetin- and isorhamnetin-induced GLUT4 translocation, respectively. However, treatment with siJAK3 did not affect isorhamnetin-induced GLUT4 translocation, indicating that isorhamnetin induced GLUT4 translocation mainly through JAK2, but not JAK3, signalling. Thus, quercetin preferably activated the AMPK pathway and, accordingly, stimulated IRS1/PI3K/Akt signalling, while isorhamnetin activated the JAK2/STAT pathway. Furthermore, after oral administration of quercetin glycoside at 10 and 100 mg/kg body weight significantly induced GLUT4 translocation to the plasma membrane of skeletal muscles in mice. In the same animals, plasma concentrations of quercetin aglycone form were 4.95 and 6.80 nM, respectively. In conclusion, at low-concentration ranges, quercetin and isorhamnetin promote glucose uptake by increasing GLUT4 translocation via different signalling pathways in skeletal muscle cells; thus, these compounds may possess beneficial functions for maintaining glucose homeostasis by preventing hyperglycaemia at physiological concentrations.

The behavioral and physiological effects of high-fat diet and alcohol consumption: Sex differences in C57BL6/J mice

BACKGROUND AND OBJECTIVE

Animal studies can be a great tool to investigate sex differences in a variety of different ways, including behavioral and physiological responses to drug treatments and different "lifestyle variables" such as diets. Consumption of both high-fat diets and alcohol is known to affect anxiety behaviors and overall health. This project investigated how high-fat diet and alcohol access and its combination affected the behavior and physiology of male and female C57BL/6J mice.

METHOD

Mice were separated into three food groups: high-fat diet, 10% fat diet, and regular chow, and each group was paired with either water or 10% alcohol. Behavioral assays included diet and alcohol preference, light-dark box, open field, and feeding and drinking measurements. Physiological measures included glucose tolerance tests and measurement of brain-derived neurotrophic factor, insulin, and leptin levels.

RESULTS

Females and males differed in the open field, as male mice decreased activity, while females increased activity when consuming high-fat diet. While females consumed more ethanol than males, alcohol consumption was able to improve glucose tolerance and increase anxiety in both sexes. Lastly, females were more resistant to the physiological changes caused by high-fat diet than males, as females consuming high-fat diet exhibited decreased insulin secretion, less change to brain-derived neurotrophic factor levels, and better glucose tolerance than males consuming high-fat diet.

CONCLUSION

These results suggest that the response to high-fat diet and alcohol consumption is sex dependent and that males are more affected both behaviorally and physiologically by high-fat diet compared to females.

Acute effects of traditional Japanese alcohol beverages on blood glucose and polysomnography levels in healthy subjects

Background. Alcohol consumption is a lifestyle factor associated with type 2 diabetes. This relationship is reportedly different depending on the type of alcohol beverage. The purpose of this study was to examine the acute effects of traditional Japanese alcohol beverages on biochemical parameters, physical and emotional state, and sleep patterns.

Methods. Six healthy subjects (three men and three women; age, 28.8 ± 9.5 years; body mass index, 21.4 ± 1.6 kg/m²) consumed three different types of alcohol beverages (beer, shochu, and sake, each with 40 g ethanol) or mineral water with dinner on different days in the hospital. Blood samples were collected before and 1, 2, and 12 h after drinking each beverage, and assessments of physical and emotional state were administered at the same time. In addition, sleep patterns and brain waves were examined using polysomnography.

Results. Blood glucose levels at 1 h and the 12-h area under the curve (AUC) value after drinking shochu were significantly lower than that with water and beer. The 12-h blood insulin AUC value after drinking shochu was significantly lower than that with beer. Blood glucose × insulin level at 1 h and the 2-h blood glucose × insulin AUC value with shochu were significantly lower than that with beer. The insulinogenic indexes at 2 h with beer and sake, but not shochu, were significantly higher than that with water. The visual analogue scale scores of physical and emotional state showed that the tipsiness levels with beer, shochu, and sake at 1 h were significantly higher than that with water. These tipsiness levels were maintained at 2 h. The polysomnography showed that the rapid eye movement (REM) sleep latency with shochu and sake were shorter than that with water and beer.

Conclusions. Acute consumption of alcohol beverages with a meal resulted in different responses in postprandial glucose and insulin levels as well as REM sleep latency. Alcohol beverage type should be taken into consideration for people with impaired glucose tolerance.

Impact of Alcohol on Glycemic Control and Insulin Action

Alcohol has profound effects on tissue and whole-body fuel metabolism which contribute to the increased morbidity and mortality in individuals with alcohol use disorder. This review focuses on the glucose metabolic effects of alcohol, primarily in the muscle, liver and adipose tissue, under basal postabsorptive conditions and in response to insulin stimulation. While there is a relatively extensive literature in this area, results are often discordant and extrapolating between models and tissues is fraught with uncertainty. Comparisons between data generated in experimental cell and animals systems will be contrasted with that obtained from human subjects as often times results differ. Further, the nutritional status is also an important component of the sometimes divergent findings pertaining to the effects of alcohol on the regulation of insulin and glucose metabolism. This work is relevant as the contribution of alcohol intake to the development or exacerbation of type 2 diabetes remains ill-defined and a multi-systems approach is likely needed as both alcohol and diabetes affect multiple targets within the body.

Suppression of phosphatase and tensin homolog protects insulin-resistant cells from apoptosis

In the present study, a glucosamine-induced model of insulin-resistant skeletal muscle cells was established in order to investigate the effect of inhibition of phosphatase and tensin homolog (PTEN)/5'-adenosine monophosphate-activated protein kinase (AMPK) on these cells. The glucosamine-induced insulin-resistant skeletal muscle cells were produced and the rate of glucose uptake was measured using the glucose oxidase-peroxidase method. The expression levels of PTEN and phosphorylated PTEN (p-PTEN) were assessed using western blotting. Glucose transporter 4 (GLUT4) translocation was detected by immunofluorescence. Cell apoptosis was evaluated using flow cytometry. Following insulin stimulation, the rate of glucose uptake was significantly reduced in the cells with glucosamine-induced insulin-resistance in comparison with those in the control group. The expression and translocation of GLUT4 were reduced in the insulin-resistant muscle cells. By contrast, the expression of PTEN and p-PTEN as well as apoptosis were significantly increased. Following treatment with bisperoxopicolinatooxovanadate (BPV) or metformin in the insulin-resistant skeletal muscle cells, there was an increase in the rate of glucose uptake, an increase in GLUT4 expression and its translocation, a reduction in the expression of PTEN and p-PTEN, and a decrease in cell apoptosis compared with untreated insulin-resistant cells. Glucosamine may be used to produce an effective model of insulin-resistant skeletal muscle cells. Cells with glucosamine-induced insulin-resistance exhibited a reduced expression of GLUT4 and dysfunction in GLUT4 translocation, as well as increased activation of PTEN and increased cell apoptosis. Inhibition of PTEN or its upstream regulator, AMPK, protects glucosamine-induced insulin-resistant skeletal muscle cells from apoptosis.

Strain-dependent differences for suppression of insulin-stimulated glucose uptake in skeletal and cardiac muscle by ethanol

BACKGROUND

Chronic ethanol (EtOH) consumption impairs the ability of insulin to suppress hepatic glucose production in a strain-dependent manner, with hepatic insulin resistance being greater in Long-Evans (LE) than Sprague-Dawley (SD) rats. We assessed whether strain differences exist for whole-body and tissue glucose uptake under basal and insulin-stimulated conditions and whether they were associated with coordinate strain-dependent elevations in muscle cytokines.

METHODS

Male rats (160 g) were provided the Lieber-DeCarli EtOH-containing (36% total energy) diet or pair-fed a control diet for 8 weeks. Rats were studied in the basal state or during a euglycemic hyperinsulinemic clamp, and whole-body glucose flux assessed using (3) H-glucose and in vivo tissue glucose uptake by (14) C-2-deoxyglucose.

RESULTS

EtOH impaired whole-body insulin-mediated glucose uptake (IMGU) more in SD than LE rats. This difference was due to impaired IMGU by gastrocnemius and heart in EtOH-fed SD versus LE rats. However, decreased IMGU in adipose tissue (epididymal and perirenal) produced by EtOH was comparable between strains. EtOH-induced insulin resistance in muscle from SD rats was associated with reduced AKT and AS160 phosphorylation and plasma membrane-localized GLUT4 protein as well as enhanced phosphorylation of c-Jun N-terminal kinase (JNK) and IRS-1 (S307), changes which were absent in muscle from LE rats. EtOH increased tumor necrosis factor alpha (TNFα) mRNA in gastrocnemius and fat under basal conditions in both SD and LE rats; however, hyperinsulinemia decreased TNFα in skeletal muscle from LE, but not SD rats. Interleukin (IL)-6 mRNA in gastrocnemius was increased under basal conditions and increased further in response to insulin in SD rats, but no EtOH- or insulin-induced change was detected in muscle IL-6 of LE rats.

CONCLUSIONS

These data indicate strain-dependent differences in EtOH-induced IMGU in skeletal and cardiac muscle, but not fat, associated with sustained increases in TNFα and IL-6 mRNA and JNK activation and decreased plasma membrane GLUT4 in response to insulin.

Alcohol consumption improves insulin signaling in the myocardium

BACKGROUND

In a previous study, we demonstrated that swine with metabolic syndrome treated with alcohol had improved insulin signaling. We developed a follow-up study to evaluate the effects of alcohol on ischemic myocardium in animals without metabolic syndrome.

METHODS

Fourteen Yorkshire swine underwent placement of an ameroid constrictor to induce chronic myocardial ischemia. Postoperatively, one group was supplemented with ethanol (ETOH), and one group was supplemented with sucrose (SUC) daily to normalize caloric intake. After 7 weeks, all animals underwent dextrose challenge and harvest of nonischemic and ischemic myocardium. Tissues were analyzed for protein expression and histologic analysis.

RESULTS

There was no difference in body mass index, serum glucose or insulin levels. However, ethanol supplementation up-regulated phosphoinostitide 3-kinase, phosphorylated protein kinase B, protein kinase B, and phosphorylated Forkhead Box 01 expression, which may promote insulin signaling, and down-regulated inhibitors of insulin signaling pIRS1 and pIRS2. There was no difference in intramyocardial glycogen but there was increased GLUT4 expression in the ETOH group, which may promote glucose use.

CONCLUSION

Despite similar serum glucose and insulin levels, alcohol consumption up-regulates the insulin signaling pathway in the absence of metabolic syndrome in both nonischemic and chronically ischemic myocardium. These results suggest that alcohol selectively up-regulates the insulin signaling pathway despite normoglycemia.

Vodka and wine consumption in a swine model of metabolic syndrome alters insulin signaling pathways in the liver and skeletal muscle

BACKGROUND

The purpose of this study was to examine the effects of alcohol in the context of metabolic syndrome on insulin signaling pathways in the liver and skeletal muscle.

METHODS

Twenty-six Yorkshire swine were fed a hypercaloric, high-fat diet for 4 weeks then split into 3 groups: hypercholesterolemic diet alone (HCC, n = 9), hypercholesterolemic diet with vodka (HCVOD, n = 9), and hypercholesterolemic diet with wine (HCW, n = 8) for 7 weeks. Animals underwent intravenous dextrose challenge before euthanasia and tissue collection.

RESULTS

HCC, HCVOD, and HCW groups had similar blood fasting glucose levels, liver function test, and body mass index. Thirty and 60 minutes after dextrose infusion, HCVOD and HCW groups had significantly increased blood glucose levels compared with the HCC group. The HCW group had significantly increased levels of insulin compared with the HCC group. Immunoblotting in skeletal muscle demonstrated that alcohol up-regulates p-IRS1, IRS2, AKT, AMPKα, PPARα, Fox01, and GLUT4. In the liver, HCW had up-regulation of AKT, AMPKα, and GLUT4 compared with HCC. Skeletal muscle immunohistochemistry demonstrated increased sarcolemmal expression of GLUT4 in both alcohol groups compared with HCC.

CONCLUSION

Moderate alcohol consumption in a swine model of metabolic syndrome worsens glucose metabolism by altering activation of the insulin signaling pathway in the liver and skeletal muscle.

Ameliorative effects of polyunsaturated fatty acids against palmitic acid-induced insulin resistance in L6 skeletal muscle cells

Background

Fatty acid-induced insulin resistance and impaired glucose uptake activity in muscle cells are fundamental events in the development of type 2 diabetes and hyperglycemia. There is an increasing demand for compounds including drugs and functional foods that can prevent myocellular insulin resistance.

Methods

In this study, we established a high-throughput assay to screen for compounds that can improve myocellular insulin resistance, which was based on a previously reported non-radioisotope 2-deoxyglucose (2DG) uptake assay. Insulin-resistant muscle cells were prepared by treating rat L6 skeletal muscle cells with 750 μM palmitic acid for 14 h. Using the established assay, the impacts of several fatty acids on myocellular insulin resistance were determined.

Results

In normal L6 cells, treatment with saturated palmitic or stearic acid alone decreased 2DG uptake, whereas unsaturated fatty acids did not. Moreover, co-treatment with oleic acid canceled the palmitic acid-induced decrease in 2DG uptake activity. Using the developed assay with palmitic acid-induced insulin-resistant L6 cells, we determined the effects of other unsaturated fatty acids. We found that arachidonic, eicosapentaenoic and docosahexaenoic acids improved palmitic acid-decreased 2DG uptake at lower concentrations than the other unsaturated fatty acids, including oleic acid, as 10 μM arachidonic acid showed similar effects to 750 μM oleic acid.

Conclusions

We have found that polyunsaturated fatty acids, in particular arachidonic and eicosapentaenoic acids prevent palmitic acid-induced myocellular insulin resistance.

Hormesis: why it is important to biogerontologists

This paper offers a broad assessment of the hormetic dose response and its relevance to biogerontology. The paper provides detailed background information on the historical foundations of hormesis, its quantitative features, mechanistic foundations, as well as how the hormesis concept could be further applied in the development of new therapeutic advances in the treatment of age-related diseases. The concept of hormesis has direct application to biogerontology not only affecting the quality of the aging process but also experimental attempts to extend longevity.