Ethanol Impairs Insulin's Actions Through Phosphatidylinositol 3-Kinase

Effects of ethanol or ethylene glycol exposure on PPARγ and aromatase expression in adipose tissue

The estrogen-synthesizing enzyme aromatase is expressed in adipose tissue where it controls the local concentration of estrogen. It has been suggested that the organic solvents ethanol and ethylene glycol can induce estrogen synthesis by inhibiting PPARγ activity. Since elevated estrogen synthesis in adipose tissue is a risk factor for breast cancer development, it is of interest to further characterize the mechanisms regulating aromatase expression. Here, we explored the mechanisms by which ethanol and ethylene glycol modulate aromatase mRNA expression and the ultimate conversion of androgens into estrogens. NMR spectroscopy revealed that ethanol and ethylene glycol influence the active state of PPARγ. An inhibitory effect on PPARγ was confirmed by adipogenesis assays and PPARγ target gene expression analysis in adipocytes. However, only ethanol increased aromatase mRNA in differentiated human adipocytes. In contrast, ethylene glycol downregulated aromatase in a PPARγ-independent manner. An animal study using female Wistar rats was conducted to assess the acute effects of ethanol and ethylene glycol on aromatase expression in adipose tissue within a physiological context. No changes in aromatase or PPARγ target gene (Adipoq and Fabp4) levels were observed in adipose tissue or ovary in response to the chemical exposures, suggesting an absence of acute PPARγ-mediated effects in these organs. The results suggest that ethanol and ethylene glycol are weak PPARγ antagonists in mouse and human adipocytes as well as in cell-free NMR spectroscopy. Both compounds seem to affect adipocyte aromatase expression in vitro, where ethanol increased aromatase expression PPARγ-dependently and ethylene glycol decreased aromatase expression independently of PPARγ. No acute effects on aromatase expression or PPARγ activity were observed in adipose tissue or ovary in rats in this study design.

Chronic heavy alcohol consumption influences the association between genetic variants of GCK or INSR and the development of diabetes in men: A 12-year follow-up study

Chronic heavy alcohol consumption is a risk factor for diabetes, which is characterized by impaired β-cell function and insulin resistance. We aimed to determine whether the longitudinal associations between genetic variants of glucokinase (GCK) and insulin receptor (INSR) and the risk of developing diabetes were influenced by chronic heavy alcohol consumption. Data were obtained from the Korean Genome and Epidemiology Study. To identify candidate variants, 1,520 subjects (726 non-drinkers and 794 heavy drinkers) were included in the baseline cross-sectional study. After excluding patients with diabetes at baseline and those with insufficient data on diabetes incidence, prospective analyses were conducted in 773 subjects (353 non-drinkers and 420 heavy drinkers). In the baseline cross-sectional study, one SNP (rs758989) in GCK and four SNPs (rs7245757, rs1035942, rs1035940, and rs2042901) in INSR were selected as candidate SNPs that interact with alcohol to affect prediabetes and diabetes. We identified that these GCK and INSR polymorphisms are affected by chronic heavy alcohol consumption and have an effect on the incidence of diabetes. The incidence of diabetes was increased in chronic heavy alcohol drinkers carrying the C allele of GCK compared with never-drinkers with the C allele (HR, 2.15; 95% CI 1.30-3.57), and was increased in chronic heavy alcohol drinkers who were not carrying the INSR haplotype (-/-) compared with never-drinkers carrying the AACT haplotype (HR, 1.98; 95% CI 1.24-3.18). Moreover, we observed that the aggravating effects on the late insulin secretion (I/G120 and I/G AUC 60-120) in individuals who were chronic heavy drinkers with C allele of GCK. In the INSR haplotype, chronic heavy drinkers not carrying AACT were associated with lower disposition index. These results potentially suggest that chronic heavy alcohol consumption induce β-cell dysfunction partially mediated by decreased GCK expression or decline of insulin sensitivity via inhibition of INSR, thereby contributing to the development of diabetes.

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

BACKGROUND

mild or moderate chronic alcohol intake has been shown to be associated with increased insulin sensitivity, while chronic alcohol abuse demonstrates a contrary effect. The mechanism underlying this biphasic effect has not yet been clarified. We investigated whether chronic ethanol exposure mediates biphasic changes on insulin sensitivity and whether the phosphatidylinositol 3-kinase/Akt pathway is involved in vitro.

METHODS

primary cultured rat skeletal muscle cells were exposed to ethanol (0-400 mM) for 24 h. Insulin sensitivity was assessed by the (3) H-labelled 2-deoxyglucose uptake assay. Phosphatidylinositol 3-kinase, cytosol and cell membrane glucose transporter-4 (GLUT4), as well as the Akt phosphorylated form, were analyzed by Western blots.

RESULTS

biphasic effects of ethanol on insulin sensitivity were observed in primary cultured skeletal muscle cells in a dose-dependent manner. Compared with the untreated group, 50 and 100 mM concentrations of ethanol resulted in a significant increase in 2-deoxyglucose uptake by 29 and 28%, respectively, while higher concentrations of ethanol (200, 400 mM) showed a significant decrease in 2-deoxyglucose uptake by 28 and 47%, respectively. The changes in glucose transport activity were in line with the changes in Akt Ser473 phosphorylation and GLUT4 expression in an ethanol dose-dependent biphasic manner. The phosphorylation of Akt and GLUT4 protein contents were up-regulated after treatment with low concentrations of ethanol (50, 100 mM) and down-regulated with high concentrations of ethanol (200, 400 mM) for 24 h.

CONCLUSION

ethanol mediates biphasic changes on insulin sensitivity at least in part via the Akt pathway and GLUT4 expression.

Screening of senescence-associated genes with specific DNA array reveals the role of IGFBP-3 in premature senescence of human diploid fibroblasts

Repeated exposures to sublethal concentrations of tert-butylhydroperoxide and ethanol trigger premature senescence of WI-38 human diploid fibroblasts. We found 16 replicative senescence-related genes with similar alterations in expression level in replicative senescence and two models of stress-induced premature senescence. Among these genes was IGFBP-3. Using a siRNA approach, we showed that IGFBP-3 regulates the appearance of several biomarkers of senescence after repeated exposures of WI-38 fibroblasts to tert-butylhydroperoxide and ethanol.