Chronic ethanol feeding impairs endothelin-1-stimulated glucose uptake via decreased G alpha 11 expression in rat adipocytes

Lipid Droplets Specific Fluorophore for Demarcation of Normal and Diseased Tissues

Using high-fidelity, permeable, lipophilic, and bright fluorophores for imaging lipid droplets (LDs) in tissues holds immense potential in diagnosing conditions such as diabetic or alcoholic fatty liver disease. In this work, we utilized linear and Λ-shaped polarity-sensitive fluorescent probes for imaging LDs in both cellular and tissue environments, specifically in rats with diabetic and alcoholic fatty liver disease. The fluorescent probes possess several key characteristics, including high permeability, lipophilicity, and brightness, which make them well-suited for efficient LD imaging. Notably, the probes exhibit a substantial Stokes shift, with 143 nm for DCS and 201 nm for DCN with selective targeting of the lipid droplets. Our experimental investigations successfully differentiated morphological variations between diseased and normal tissues in three distinct tissue types: liver, adipose, and small intestine. They could help provide pointers for improved detection and understanding of LD-related pathologies.

Alcohol, White Adipose Tissue, and Brown Adipose Tissue: Mechanistic Links to Lipogenesis and Lipolysis

According to data from the World Health Organization, there were about 3 million deaths caused by alcohol consumption worldwide in 2016, of which about 50% were related to liver disease. Alcohol consumption interfering with the normal function of adipocytes has an important impact on the pathogenesis of alcoholic liver disease. There has been increasing recognition of the crucial role of adipose tissue in regulating systemic metabolism, far beyond that of an inert energy storage organ in recent years. The endocrine function of adipose tissue is widely recognized, and the significance of the proteins it produces and releases is still being investigated. Alcohol consumption may affect white adipose tissue (WAT) and brown adipose tissue (BAT), which interact with surrounding tissues such as the liver and intestines. This review briefly introduces the basic concept and classification of adipose tissue and summarizes the mechanism of alcohol affecting lipolysis and lipogenesis in WAT and BAT. The adipose tissue-liver axis is crucial in maintaining lipid homeostasis within the body. Therefore, this review also demonstrates the effects of alcohol consumption on the adipose tissue-liver axis to explore the role of alcohol consumption in the crosstalk between adipose tissue and the liver.

Gut Microbiota: Target for Modulation of Gut-Liver-Adipose Tissue Axis in Ethanol-Induced Liver Disease

Consumption of alcohol (ethanol) in various forms has been an integral part of human civilization. Since ages, it also has been an important cause of death and health impairment across the globe. Ethanol-mediated liver injury, known as alcoholic liver disease (ALD), is caused by surplus intake of alcohol. Several studies have proposed the different pathways that may be lead to ALD. One of the factors that may affect the cytochrome P450 (CYP2E1) metabolic pathway is gut dysbiosis. The gut microbiota produces various compounds that play an important role in regulating healthy functions of distal organs such as the adipose tissue and liver. Dysbiosis causes bacteremia, hepatic encephalopathy, and increased intestinal permeability. Recent clinical studies have found better understanding of the gut and liver axis. Another factor that may affect the ALD pathway is dysfunction of adipose tissue metabolism. Moreover, dysfunction of adipose tissue leads to ectopic fat deposition within the liver and disturbs lipid metabolism by increasing lipolysis/decreasing lipogenesis and impaired glucose tolerance of adipose tissue which leads to ectopic fat deposition within the liver. Adipokine secretion of resistin, leptin, and adiponectin is adversely modified upon prolonged alcohol consumption. In the combination of these two factors, a proinflammatory state is developed within the patient leading to the progression of ALD. Thus, the therapeutic approach for treatments and prevention for liver cirrhosis patients must be focused on the gut-liver-adipose tissue network modification with the use of probiotics, synbiotics, and prebiotics. This review is aimed at the effect of ethanol on gut and adipose tissue in both rodent and human alcoholic models.

Protective Effects of Diallyl Sulfide Against Ethanol-Induced Injury in Rat Adipose Tissue and Primary Human Adipocytes

BACKGROUND

Alcohol consumption is the fourth leading cause of death and disability worldwide. Several cellular pathways contribute to alcohol-mediated tissue injury. Adipose tissue apart from functioning as an endocrine organ secretes several hormones and cytokines known as adipokines that are known to play a significant role in alcohol-induced tissue damage. This study was designed to test the efficacy of diallyl sulfide (DAS) in regulating the alcohol-induced outcomes on adipose tissue.

METHODS

Male Wistar rats were fed with 36% Lieber-DeCarli liquid diet containing ethanol (EtOH) for 4 weeks. Control rats were pair-fed with isocaloric diet containing maltodextrin instead of EtOH. During the last week of feeding protocol, the EtOH-fed rat group was given 200 mg/kg body weight of DAS through diet. We also studied DAS effect on isolated human primary adipocytes. Viability of human primary adipocytes on DAS treatment was assessed by MTT assay. Malondialdehyde (MDA), a marker of oxidative stress, was measured by HPLC and the thiobarbituric acid method. Expression of inflammatory genes and lipogenic genes was studied by qRT-PCR and Western blotting. Serum inflammatory gene expression was studied by ELISA.

RESULTS

Our study results showed that DAS could alleviate EtOH-induced expression levels of proinflammatory and endoplasmic reticulum (ER) stress genes and improve adipose tissue mass and adipocyte morphology in male Wistar rats fed Lieber-DeCarli diet containing 6% EtOH. Further, we showed that DAS reduced the expression of lipogenic genes and improved lipid accumulation and adipocyte mass in human primary adipocytes treated with EtOH. Subsequently, we also showed that oxidative stress, as measured by the changes in MDA levels, was reduced in both male Wistar rats and human primary adipocytes treated with EtOH plus DAS.

CONCLUSIONS

Our study results prove that DAS is effective in ameliorating EtOH-induced damage to adipose tissue as evidenced by the reduction brought about by DAS in oxidative stress, ER stress, and proinflammatory gene expression levels. DAS treatment also regulated lipogenic gene expression levels, thereby reducing free fatty acid release. In conclusion, this study has clinical implications with respect to alcohol-induced adipose tissue injury among alcohol users.

Alcohol, Adipose Tissue and Lipid Dysregulation

Chronic alcohol consumption perturbs lipid metabolism as it increases adipose tissue lipolysis and leads to ectopic fat deposition within the liver and the development of alcoholic fatty liver disease. In addition to the recognition of the role of adipose tissue derived fatty acids in liver steatosis, alcohol also impacts other functions of adipose tissue and lipid metabolism. Lipid balance in response to long-term alcohol intake favors adipose tissue loss and fatty acid efflux as lipolysis is upregulated and lipogenesis is either slightly decreased or unchanged. Study of the lipolytic and lipogenic pathways has identified several regulatory proteins modulated by alcohol that contribute to these effects. Glucose tolerance of adipose tissue is also impaired by chronic alcohol due to decreased glucose transporter-4 availability at the membrane. As an endocrine organ, white adipose tissue (WAT) releases several adipokines that are negatively modulated following chronic alcohol consumption including adiponectin, leptin, and resistin. When these effects are combined with the enhanced expression of inflammatory mediators that are induced by chronic alcohol, a proinflammatory state develops within WAT, contributing to the observed lipodystrophy. Lastly, while chronic alcohol intake may enhance thermogenesis of brown adipose tissue (BAT), definitive mechanistic evidence is currently lacking. Overall, both WAT and BAT depots are impacted by chronic alcohol intake and the resulting lipodystrophy contributes to fat accumulation in peripheral organs, thereby enhancing the pathological state accompanying chronic alcohol use disorder.

Effect of alcohol on adipose tissue: a review on ethanol mediated adipose tissue injury

BACKGROUND

Alcohol consumption has been in existence in the world for many centuries and it is the major cause of death and injury worldwide. Alcoholic liver disease (ALD) is caused due to excess and chronic alcohol intake. Studies across the globe have identified several pathways leading to ALD. Adipose tissue which has been considered as an energy storage organ is also found to play a major role in ALD progression by secreting hormones and cytokines known as adipokines or adipocytokines. Ethanol affects the metabolic and innate immune activities of adipose tissue contributing to alcohol-induced injury of the tissues.

OBJECTIVE

We aimed at 1) summarizing the metabolism and progression of ALD 2) summarizing about the structure and effect of ethanol induced oxidative stress on adipose tissue 3) reviewing the available data on the effect of ethanol on adipose tissue mass and adipokine secretion in both rodent models and alcoholic patients.

METHODS

The article is summarized based on the original literature and reviews in studying the effect of ethanol on adipose tissue.

RESULTS

Studies on alcoholic patients and rodent models has shown that chronic ethanol consumption reduces adipose tissue mass and causes CYP2E1 mediated oxidative stress and inflammation of adipose tissue. Further hyperlipolysis is observed in adipose tissue that leads to excess fatty acid release that gets transported and deposited in the liver resulting in hepatic steatosis.

CONCLUSION

Studies show that adipose tissue plays a major role in the progression of ALD. So understanding of the mechanisms linking ethanol induced adipose tissue injury with ALD progression would help us in identifying potential therapeutic targets.

Ethanol-induced oxidative stress via the CYP2E1 pathway disrupts adiponectin secretion from adipocytes

BACKGROUND

Adipose tissue is an important target for ethanol action. One important effect of ethanol is to reduce the secretion of adiponectin from adipocytes; this decrease is associated with lowered circulating adiponectin in rodent models of chronic ethanol feeding. Adiponectin is an insulin-sensitizing, anti-inflammatory adipokine; decreased adiponectin activity may contribute to tissue injury in response to chronic ethanol. Here, we investigated the role of cytochrome P450 2E1 (CYP2E1) and oxidative stress in the mechanism for impaired adiponectin secretion from adipocytes in response to ethanol.

METHODS

Male Wistar rats were fed a liquid diet containing ethanol as 36% of calories or pair-fed a control diet for 4 weeks. 3T3-L1 adipocyte cultures, expressing CYP2E1 or not, were exposed to ethanol or 4-hydroxynonenal (4-HNE).

RESULTS

Chronic ethanol feeding to rats suppressed the secretion of adiponectin from isolated epididymal adipocytes. Ethanol feeding induced the expression of CYP2E1 in adipocytes and increased markers of oxidative stress, including 4-HNE and protein carbonyls. Because adiponectin is posttranslationally processed in the endoplasmic reticulum and Golgi, we investigated the impact of ethanol on the redox status of high-density microsomes. Chronic ethanol decreased the ratio of reduced glutathione to oxidized glutathione (4.6:1, pair-fed; 2.9:1, ethanol-fed) in high-density microsomes isolated from rat epididymal adipose tissue. We next utilized the 3T3-L1 adipocyte-like cell model to interrogate the mechanisms for impaired adiponectin secretion. Culture of 3T3-L1 adipocytes overexpressing exogenous CYP2E1, but not those overexpressing antisense CYP2E1, with ethanol increased oxidative stress and impaired adiponectin secretion from intracellular pools. Consistent with a role of oxidative stress in impaired adiponectin secretion, challenge of 3T3-L1 adipocytes with 4-HNE also reduced adiponectin mRNA expression and secretion, without affecting intracellular adiponectin concentration.

CONCLUSIONS

These data demonstrate that CYP2E1-dependent reactive oxygen species production in response to ethanol disrupts adiponectin secretion from adipocytes.

Chronic ethanol feeding impairs AMPK and MEF2 expression and is associated with GLUT4 decrease in rat myocardium

Chronic and heavy alcohol consumption is one of the causes of heart diseases. However, the effects of ethanol on insulin sensitivity in myocardium has been unclear. To investigate the effects of ethanol on the expression of AMP-activated protein kinase (AMPK), myocyte enhancer factor 2 (MEF2) and glucose transporter 4 (GLUT4), all of which are involved in the regulation of insulin sensitivity, in the myocardium, we performed three parts of experiments in vivo and in vitro. I: Rats were injected with 5-amino-4-imidazolecarboxamide ribonucleotide (AICAR, 0.8 mg.kg(-l)) for 2 h. II: Rats received different dose (0.5, 2.5 or 5 g.kg(-l).d(-l)) of ethanol for 22-week. III: Primary neonatal rat cardiomyocytes were isolated and treated with or without 100 mM ethanol or 1 mM AICAR for 4 h. The cardiac protein and mRNA expression of AMPKalpha subunits, MEF2 and GLUT4 were observed by western-blotting and RT-PCR, respectively. Serum TNFalpha levels were assessed by ELISA. The results showed chronic ethanol exposure induced insulin resistance. Ethanol decreased the mRNA levels of AMPKalpha1 and alpha2, the protein levels of total- and phospho-AMPKalpha in cardiomyocytes. Similarly, ethanol showed inhibitory effects on both the mRNA and protein levels of MEF2A and 2D, and GLUT4 in a dose-response-like fashion. Correlation analysis implied an association between phospho-AMPKalpha and MEF2A or MEF2D, and between the levels of MEF2 protein and GLUT4 transcription. In addition, ethanol elevated serum TNFalpha level. Taken together, chronic ethanol exposure decreases the expression of AMPKalpha and MEF2, and is associated with GLUT4 decline in rat myocardium.

Effects of chronic ethanol consumption on levels of adipokines in visceral adipose tissues and sera of rats

AIM

To investigate the effects of ethanol on adipokines (leptin, adiponectin, resistin, visfatin and cartonectin) levels in visceral adipose tissue (VAT) and sera, and explore the correlation between VAT and serum adipokine levels.

METHODS

Forty-eight Wistar rats were randomly divided into control, low, middle and high ethanol treatment groups that received 0, 0.5, 2.5, or 5.0 g of ethanol x kg(-1) x d(-1), respectively, via gastric tubes for 22 weeks. The levels of fasting blood glucose (FBG) and fasting serum insulin (FINS) were measured and homeostasis model assessment of insulin resistance (HOMA-IR) values were calculated. Adipokines in perirenal and epididymal VAT and sera were measured by enzyme-linked immunosorbent assays (ELISAs).

RESULTS

High-dose treatments of ethanol (vs control group) significantly increased FINS (eg 37.86%) and HOMA-IR values (eg 40.63%). In VAT, levels of leptin, resistin and visfatin in the middle- and high-dose groups were significantly elevated, whereas adiponectin and cartonectin levels decreased. In sera, changes in adipokine levels were similar to that observed in VAT, with the exception of cartonectin. These ethanol-induced effects were dose-dependent. A positive correlation existed between VAT and serum adipokine levels, except for cartonectin.

CONCLUSION

Chronic ethanol consumption affects adipokine levels in VAT and sera in a dose-dependent manner, with the exception of serum cartonectin. The altered levels of adipokines in VAT and sera are positively correlated.

Methods to evaluate the effect of ethanol on the folate analogue: fluorescein methotrexate uptake in human proximal tubular cells

Ethanol-induced folate deficiency is due to effects of ethanol on folate metabolism and absorption. We have already shown by using different methods that ethanol interferes with reabsorption of folate from the proximal tubule. In this study, we have used the folate analogue, the fluorescein methotrexate (FL-MTX), in order to evaluate effects of ethanol on FL-MTX uptake by the human proximal tubular (HPT) cells by using a confocal microscope and fluoroskan microplate reader. Since endothelins (ETs) play a major role in a number of diseases and also in the damage induced by a variety of chemicals, we have used endothelin-B (ET-B) and protein kinase-C (PKC) inhibitors to evaluate the role of endothelin in ethanol-mediated FL-MTX uptake by using fluoroskan microplate reader. Confocal microscope and fluoroskan studies reveal that cellular absorption of FL-MTX is concentration-dependent. Moreover, ethanol concentration has an impact on FL-MTX uptake. Fluoroskan studies reveal that the ethanol-induced decrease in FL-MTX uptake is reversed by adding the ET-B receptor antagonist (RES-701-1) or PKC-selective inhibitor (BIM). Thus, we can conclude that ethanol may act via ET and ET in turn may act via ET-B receptor and the PKC signaling pathway to impair FL-MTX transport.

Chronic ethanol feeding to rats decreases adiponectin secretion by subcutaneous adipocytes

Chronic ethanol feeding to mice and rats decreases serum adiponectin concentration and adiponectin treatment attenuates chronic ethanol-induced liver injury. Although it is clear that lowered adiponectin has pathophysiological importance, the mechanisms by which chronic ethanol decreases adiponectin are not known. Here, we have investigated the impact of chronic ethanol feeding on adiponectin expression and secretion by adipose tissue. Rats were fed a 36% Lieber-DeCarli ethanol-containing liquid diet or pair-fed control diet for 4 wk. Chronic ethanol feeding decreased adiponectin mRNA but had no effect on adiponectin protein in subcutaneous adipose tissue. Chronic ethanol feeding also reduced adiponectin secretion by isolated subcutaneous and retroperitoneal adipocytes despite the maintenance of equivalent intracellular concentrations of adiponectin between subcutaneous adipocytes from ethanol- and pair-fed rats. Treatment with brefeldin A suppressed adiponectin secretion by subcutaneous adipocytes from pair-fed rats but had little effect after ethanol feeding. In subcutaneous adipocytes from pair-fed rats, adiponectin was enriched in endoplasmic reticulum (ER)/Golgi relative to plasma membrane; however, after chronic ethanol feeding, adiponectin was equally distributed between plasma membrane and ER/Golgi fractions. In conclusion, chronic ethanol feeding impaired adiponectin secretion by subcutaneous and retroperitoneal adipocytes; impaired secretion likely contributes to decreased adiponectin concentrations after chronic ethanol feeding.

Ethanol feeding impairs insulin-stimulated glucose uptake in isolated rat skeletal muscle: role of Gs alpha and cAMP

BACKGROUND

The mechanism by which chronic alcohol consumption impairs insulin sensitivity is unclear. We investigated the role of the Gs alpha-mediated pathway in decreasing insulin sensitivity in skeletal muscle after ethanol consumption.

METHODS

Sixty male Wistar rats, divided into four groups, received either distilled water (controls; group I) or ethanol, which was administered by a gastric tube as a single daily dose of 5 g/kg (group II), 2.5 g/kg (group III), or 0.5 g/kg (group IV). After 20 weeks, fasting plasma glucose and serum insulin levels were measured. The hyperinsulinemic-euglycemic clamp study was performed under anesthesia to estimate whole-body insulin sensitivity. Insulin-stimulated glucose uptake was measured in vitro in dissected gastrocnemius muscle. Expression of glut4, Gs alpha, and Gi alpha was quantified using real-time PCR analysis and western blotting. cAMP levels were measured by ELISA.

RESULTS

Compared with controls, the following observations were made: (1) the hyperinsulinemic-euglycemic clamp study revealed impaired insulin action at the whole-body level after ethanol treatment; (2) chronic ethanol feeding at 5 g/kg and 2.5 g/kg significantly decreased both basal and insulin-stimulated glucose uptakes in isolated skeletal muscle (p<0.05), which was accompanied by decreased expression of glut4 (p<0.05); (3) Gs alpha (mRNA and protein) expression in skeletal muscle was significantly increased in all three ethanol groups (p<0.05), and cAMP levels were also increased by ethanol treatment (p<0.05); and (4) there was no significant change in Gi alpha expression in all three ethanol groups.

CONCLUSIONS

Chronic ethanol exposure decreased insulin-induced glucose uptake in rat skeletal muscle, which was associated with increased expression of Gs alpha. Because Gs alpha is a negative regulator of insulin sensitivity, the alteration in Gs alpha expression may contribute to the ethanol-induced impairment of insulin signal transduction.

Decreased insulin-dependent glucose transport by chronic ethanol feeding is associated with dysregulation of the Cbl/TC10 pathway in rat adipocytes

Heavy alcohol consumption is an independent risk factor for type 2 diabetes. Although the exact mechanism by which alcohol contributes to the increased risk is unknown, impaired glucose disposal is a likely target. Insulin-stimulated glucose disposal in adipocytes is regulated by two separate and independent pathways, the PI3K pathway and the Cbl/TC10 pathway. Previous studies suggest that chronic ethanol feeding impairs insulin-stimulated glucose transport in adipocytes in a PI3K-independent manner. In search of potential targets of ethanol that would affect insulin-stimulated glucose transport, we investigated the effects of 4-wk ethanol feeding to male Wistar rats on the Cbl/TC10 pathway in isolated adipocytes. Chronic ethanol feeding inhibited insulin-stimulated cCbl phosphorylation compared with pair feeding. Insulin receptor and Akt/PKB phosphorylation were not affected by ethanol feeding. Chronic ethanol exposure also impaired cCbl and TC10 recruitment to a lipid raft fraction isolated from adipocytes by detergent extraction. Furthermore, chronic ethanol feeding increased the amount of activated TC10 and filamentous actin in adipocytes at baseline and abrogated the ability of insulin to further activate TC10 or polymerize actin. These results demonstrate that the impairment in insulin-stimulated glucose transport observed in adipocytes after chronic ethanol feeding to rats is associated with a disruption of insulin-mediated Cbl/TC10 signaling and actin polymerization.