Chronic Alcohol Exposure Disturbs Lipid Homeostasis at the Adipose Tissue-Liver Axis in Mice: Analysis of Triacylglycerols Using High-Resolution Mass Spectrometry in Combination with In Vivo Metabolite Deuterium Labeling

Abstract

A method of employing high-resolution mass spectrometry in combination with in vivo metabolite deuterium labeling was developed in this study to investigate the effects of alcohol exposure on lipid homeostasis at the white adipose tissue (WAT)-liver axis in a mouse model of alcoholic fatty liver. In order to differentiate the liver lipids synthesized from the fatty acids that were transported back from adipose tissue and the lipids synthesized from other sources of fatty acids, a two-stage mouse feeding experiment was performed to incorporate deuterium into metabolites. Hepatic lipids extracted from mouse liver, epididymal white adipose tissue (eWAT) and subcutaneous white adipose tissue (sWAT) were analyzed. It was found that 13 and 10 triacylglycerols (TGs) incorporated with a certain number of deuterium were significantly increased in alcohol induced fatty liver at two and four weeks of alcohol feeding periods, respectively. The concentration changes of these TGs ranged from 1.7 to 6.3-fold increase. A total of 14 deuterated TGs were significantly decreased in both eWAT and sWAT at the two and four weeks and the fold-change ranged from 0.19 to 0.77. The increase of deuterium incorporated TGs in alcohol-induced fatty liver and their decrease in both eWAT and sWAT indicate that alcohol exposure induces hepatic influx of fatty acids which are released from WATs. The results of time course analysis further indicate a mechanistic link between adipose fat loss and hepatic fat gain in alcoholic fatty liver.

A LC-MS–based workflow for measurement of branched fatty acid esters of hydroxy fatty acids

“…1). This was due to high concentrations of neutral lipids such as triglycerides (TGs) in WAT 28 . TGs are present as an oil at room temperature, and make up a large proportion of the volume of the reconstituted sample.…”

Stratification of Risk of Death in Severe Acute Alcoholic Hepatitis Using a Panel of Adipokines and Cytokines

“…In rodent models, chronic ethanol exposure was associated with decreased adipose fat mass and enhanced ex-vivo adipose triglyceride hydrolysis; furthermore, activation of adipose triglyceride lipase and hormone-sensitive lipase (key enzymes for lipolysis) was increased in alcohol-fed mice (Zhong et al, 2012). Using deuterium-labeling experiments, investigators demonstrated hepatic uptake of adipose-derived FFA in ethanol-fed mice (Wei et al, 2013). Consistent with these findings, patients with severe AAH in our study exhibited evidence of enhanced lipolysis when compared to stable cirrhotic subjects; in particular, serum concentrations of specific saturated and monounsaturated free fatty acids were markedly increased.…”

Therapeutic opportunities for alcoholic steatohepatitis and nonalcoholic steatohepatitis: exploiting similarities and differences in pathogenesis

“…Lipotoxicity occurs through different mechanisms: (a) direct cytotoxicity via perturbed FAO and generation of ROS, which interferes with mitochondrial respiration, leading to a more vulnerable organelle and probably the release of factors that promote apoptosis and induction of other cell death cascades (152)(153)(154)(155)(156); (b) increased insulin resistance and hyperinsulinemia via fatty acid accumulation (157); (c) changes in cell signaling via hepatic nuclear factor-α (HNFα) or TLRs (158,159); (d) ER stress and upregulation of autophagic processes (lipoapoptosis) (160,161); and (e) macrophage recruitment, which is, in part, mediated through proinflammatory cargo on EVs such as CXCL10, TRAIL, and S1P (103). In contrast to NASH, the role of free fatty acids and lipotoxicity in ASH pathogenesis has not yet been defined, although the accumulation of free fatty acids has been documented in ALD (162).…”