Adaptation of lipogenesis and lipolysis to dietary ethanol

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.

Heterogeneity of p53 dependent genomic responses following ethanol exposure in a developmental mouse model of fetal alcohol spectrum disorder

Prenatal ethanol exposure can produce structural and functional deficits in the brain and result in Fetal Alcohol Spectrum Disorder (FASD). In rodent models acute exposure to a high concentration of alcohol causes increased apoptosis in the developing brain. A single causal molecular switch that signals for this increase in apoptosis has yet to be identified. The protein p53 has been suggested to play a pivotal role in enabling cells to engage in pro-apoptotic processes, and thus figures prominently as a hub molecule in the intracellular cascade of responses elicited by alcohol exposure. In the present study we examined the effect of ethanol-induced cellular and molecular responses in primary somatosensory cortex (SI) and hippocampus of 7-day-old wild-type (WT) and p53-knockout (KO) mice. We quantified apoptosis by active caspase-3 immunohistochemistry and ApopTag™ labeling, then determined total RNA expression levels in laminae of SI and hippocampal subregions. Immunohistochemical results confirmed increased incidence of apoptotic cells in both regions in WT and KO mice following ethanol exposure. The lack of p53 was not protective in these brain regions. Molecular analyses revealed a heterogeneous response to ethanol exposure that varied depending on the subregion, and which may go undetected using a global approach. Gene network analyses suggest that the presence or absence of p53 alters neuronal function and synaptic modifications following ethanol exposure, in addition to playing a classic role in cell cycle signaling. Thus, p53 may function in a way that underlies the intellectual and behavioral deficits observed in FASD.

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.

Metabolic effects of alcohol on skeletal muscle

The purpose of this review is to summarize our current understanding of the acute and chronic interactions between alcohol and nutrient metabolism in skeletal muscle. Insulin is well known to play an important regulatory role in nutrient, especially glucose, uptake and utilization in skeletal muscle. Several studies have shown that alcohol can acutely reduce the normal metabolic responses of skeletal muscle to the action of insulin. The most obvious of these is an acute impairment in glucose metabolism associated with alcohol consumption. While the exact mechanism(s) underlying this acute insulin resistance is presently unclear, several possible factors are discussed in this review. In contrast to these short-term effects, the effects of alcohol on skeletal muscle insulin sensitivity in chronic alcohol abusers are not as well established. Chronic alcohol abuse is known to be associated with skeletal myopathies, believed to result from alcohol induced abnormalities in muscle protein synthesis. Finally, the alcohol-mediated impairments of many aspects of skeletal muscle metabolism are discussed in relation to the insulin resistance associated broad spectrum of common lifestyle-related disorders, including non-insulin dependent diabetes mellitus and obesity, the consequences of which may be important to the pathogenesis of alcohol-related diseases.

Disposition of dietary ethanol carbons in rats: effects of gender and nutritional status

Dietary ethanol is an important contributor to total caloric intake and has been associated with gender-specific alterations in body weight and the risk for coronary heart disease. To understand the metabolic basis of these effects, it is important to first clarify the effects of gender and nutritional state on the metabolic fate of dietary ethanol. Tracer studies were therefore performed using 14C-labeled ethanol in fasted or fed male and female Sprague-Dawley rats (N = 64) previously unexposed to ethanol. 1-(14C)-ethanol (4.5 microCi) was mixed with unlabeled ethanol (for a total ethanol dose equal to 10% of total daily caloric intake) and a 3-kcal liquid meal and administered through gastric feeding tubes. 14CO2 production was measured over the subsequent 8 hours. The 14C content of skeletal muscle, liver, adipose tissue, gastrointestinal (GI) tract, brain, heart, kidney, and serum was determined at 4 time points following tracer administration (20 minutes and 3, 8, and 24 hours; n = 4 at each time point). Tracer content on a whole-body level was significantly greater in skeletal muscle compared with liver in all groups (1.32 +/- 0.02 x 10(6) v 0.27 +/- 0.02 x 10(6) dpm, P < .001). Skeletal muscle tracer content decreased rapidly after 3 hours, whereas liver tracer content remained fairly constant throughout the study period. Fed female rats were the exception, with a significant increase in the tracer content of total liver and liver lipid at 8 hours. The tracer content was higher in the lipid extracts in liver from fed rats compared with fasted rats (1.08 +/- 0.19 x 10(5) v 0.48 +/- 0.08 x 10(5) dpm, P = .002). While male rats exhibited a fairly constant tracer content in adipose tissue throughout the 24-hour period, female rats showed an increase in adipose tissue tracer content at 8 and 24 hours, with levels 3 to 4 times those of the male animals (5.91 +/- 1.42 x 10(4) v 1.55 +/- 0.42 x 10(4) dpm, P = .02). These results demonstrate that (1) skeletal muscle plays an important role in the metabolism of dietary ethanol, (2) the fed state appears to favor the conversion of ethanol-derived carbons to lipid, and (3) female rats have a greater propensity to convert ethanol-derived carbons to lipid and to store these carbons in adipose tissue.

Dose-dependent effects of chronic ethanol on mouse adipose tissue lipase activity and cyclic AMP accumulation

1. The effects of two chronic ethanol treatment schedules, which produce different plasma ethanol concentrations, on the specific activities of adipose tissue lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) have been investigated in brown and white fat. 2. Mice provided with 20% ethanol solution as sole drinking fluid for 28 days consumed between 13 and 15 g ethanol kg-1 body weight day-1 over days 22-28. The mean plasma ethanol concentration was 4.94 +/- 1.4 mM (n = 8) at 09 h 00 min on day 28 when the lipase assays were performed. Mice given ethanol in a liquid diet for 7 days consumed between 15 and 18 g ethanol day-1 over days 3-7. The mean plasma ethanol concentration was 15.9 +/- 4.7 mM (n = 8) at 09 h 00 min on day 7. These concentrations of ethanol had no effect on the activity of either LPL or HSL in vitro. 3. LPL activity in white and brown fat (expressed as nmol fatty acids released h-1 mg-1 acetone powder) was unaltered 60 min following an acute injection of ethanol (2.5 g kg-1, i.p.) which produced a mean blood ethanol level of 37.5 +/- 6.7 mM. HSL activity in white fat (expressed as nmol fatty acid released h-1 mg-1 protein) was also unaffected by this acute dose of ethanol, but the activity in brown fat was significantly reduced: 3.07 +/- 0.30 (n = 8) after ethanol compared to 4.36 +/- 0.25 (n = 12) in controls (P < 0.01). 4. LPL activity in white fat was little altered by either of the chronic ethanol treatment schedules whilst LPL activity in the brown fat from the same animals was significantly increased compared to the respective control values: 0.27 +/- 0.03 (ethanol drinking), control: 0.16 +/- 0.01; 0.79 +/- 0.14 (ethanol liquid diet), control: 0.39 +/- 0.05. 5. HSL activity in white fat was significantly increased by the chronic drinking treatment (7.7 +/- 0.5; control: 3.78 +/- 0.17, n = 8) at the same time that the activity in brown fat was reduced (3.76 +/- 0.2; control: 4.74 +/- 0.16). The ethanol liquid diet also reduced HSL activity in brown fat but had negligible effect in white fat. 6. The effects of the two chronic ethanol treatments on adenosine 3':5'-cyclic monophosphate (cyclic AMP) accumulation in brown and white fat were very similar, both qualitatively and quantitatively, to the effects on HSL. 7. It has been shown that brown and white adipose tissues respond differently to the presence of chronic ethanol and that the response is dependent both upon the concentration of ethanol and the nature of the diet with which the ethanol is administered. The effects of ethanol on adipose tissue HSL activity appear to be mediated via changes in the tissue cyclic AMP level and, in this respect, brown fat is more sensitive to ethanol than white fat.