Fatty acid ethyl esters: nonoxidative metabolites of ethanol

Alcohol metabolism

This article describes the pathways and factors that modulate blood alcohol levels and metabolism and describes how the body disposes of alcohol. The various factors that play a role in the distribution of alcohol in the body, influence the absorption of alcohol, and contribute to first-pass metabolism of alcohol are described. Most alcohol is oxidized in the liver, and general principles and overall mechanisms for alcohol oxidation are summarized. The kinetics of alcohol elimination in-vivo and the various genetic and environmental factors that can modify the rate of alcohol metabolism are discussed.

Investigation of chronic alcohol consumption in rodents via ultra-high-performance liquid chromatography-mass spectrometry based metabolite profiling

Alcohol consumption in man, when seen in its extreme form of alcoholism, is a complex and socially disruptive disorder that can result in significant levels of liver injury. Here the rodent "intragastric feeding model" was used together with UHPLC-TOFMS analysis to determine changes in global metabolite profiles for plasma and urine from alcohol treated rats and mice compared to control animals. Multivariate statistical analysis (using principal components analysis, PCA) revealed robust differences between profiles from control and alcohol-treated animals from both species. A large number of metabolites were seen to differ between control and alcohol-treated animals, for both biofluids.

Metabonomic investigation of liver profiles of nonpolar metabolites obtained from alcohol-dosed rats and mice using high mass accuracy MSn analysis

Alcoholism is a complex disorder that, in man, appears to be genetically influenced, although the underlying genes and molecular pathways are not completely known. Here, the intragastric alcohol feeding model in rodents was used together with high mass accuracy LC-MS(n) analysis to assess the metabonomic changes in nonpolar metabolite profiles for livers from control and alcohol-treated rats and mice. Ion signals with a peak area variance of less than 30% (based on repeat analysis of a pooled quality control sample analyzed throughout the batch) were submitted to multivariate statistical analysis (using principal components analysis, PCA). PCA revealed robust differences between profiles from control and alcohol-treated animals from both species. The major metabolites seen to differ between control and alcohol-treated animals were identified using high accuracy MS(n) data and verified using external search engines ( http://www.lipidmaps.org ; http://www.hmdb.ca; http://www.genome.jp/kegg/ ) and authentic standards. The main metabolite classes to show major changes in the alcoholic liver-derived samples were fatty acyls, fatty acid ethyl esters, glycerolipids, and phosphatidylethanol homologues. Significant metabolites that were up-regulated by alcohol treatment in both rat and mouse livers included fatty acyls, metabolites such as octadecatrienoic acid and eicosapentaenoic acid, a number of fatty acid ethyl esters such as ethyl arachidonate, ethyl docosahexaenoic acid, ethyl linoleate, and ethyl oleate and phosphatidylethanol (PEth) homologues (predominantly PEth 18:0/18:2 and PEth 16:0/18:2; PEth homologues are currently considered as potential biomarkers for harmful and prolonged alcohol consumption in man). A number of glycerophospholipids resulted in both up-regulation (m/z 903.7436 [M + H](+) corresponding to a triglyceride) and down-regulation (m/z 667.5296 [M + H](+) corresponding to a diglyceride). Metabolite profiles were broadly similar in both mouse and rat models. However, there were a number of significant differences in the alcohol-treated group particularly in the marked down-regulation of retinol and free cholesterol in the mouse compared to the rat. Unique markers for alcohol treatment included ethyl docosahexaenoic acid. Metabolites were identified with high confidence using predominantly negative ion MS(n) data for the fatty acyl components to match to www.lipidmaps.org MS and MS/MS databases; interpreting positive ion data needed to take into account possible adduct ions which may confound the identification of other lipid classes. The observed changes in lipid profiles were consistent with alcohol-induced liver injury in humans.

Fatty acid ethyl ester effects on interleukin-2 production, cyclic AMP synthesis, and calcium influx in human mononuclear cells

BACKGROUND

Fatty acid ethyl esters (FAEE), nonoxidative ethanol metabolites, are produced by the esterification of fatty acids and ethanol. Plasma and serum FAEE correlate linearly with blood ethanol levels and are present in organs most commonly damaged by ethanol abuse. Our previous studies have shown that there is significant synthesis of FAEE by human mononuclear cells within seconds of exposure to physiologic doses of ethanol.

OBJECTIVES

We studied the effects of FAEE on selected early events of mononuclear cell activation that follow stimulation with phytohemagglutinin (PHA). Fatty acid ethyl esters induced changes in cytosolic free calcium ([Ca2+]) levels, the production and secretion of interleukin-2 (IL-2) by the cells, and intracellular cAMP concentrations.

METHODS

A mononuclear fraction of human white blood cells (WBC) was incubated with physiologic doses of FAEE. For experiments involving IL-2 production and calcium influx, PHA-stimulated cells were incubated with 10, 25, 50, or 100 microM ethyl oleate, a representative FAEE species, for 60 minutes. Interleukin-2 was measured by enzyme immunometeric assay and maximum levels of Ca2+ were monitored by spectrofluorimetry. In other experiments, mononuclear cells were incubated with 10, 25, and 50 microM ethyl oleate for 0.08 to 120 minutes, and then the concentration of cAMP was determined by a cAMP competitive enzyme immunoassay system.

RESULTS

Fatty acid ethyl esters inhibited the PHA-induced IL-2 production and secretion in activated human mononuclear cells. Fatty acid ethyl esters also inhibited PHA-induced [Ca2+] influx into cells in a dose-dependent fashion. There was a rapid increase in the intracellular cAMP concentration of mononuclear cells induced by FAEE, with FAEE dose dependence. The cAMP concentration decreased as the incubation time with FAEE was increased.

CONCLUSIONS

Fatty acid ethyl esters inhibited PHA-stimulated IL-2 production and Ca2+ influx into human mononuclear cells and elevated intracellular cAMP concentration. These changes in mononuclear cell signaling may be associated with the immunosuppression associated with alcohol abuse.

Stearic acid stimulates FA ethyl ester synthesis in HepG2 cells exposed to ethanol

FA ethyl esters (FAEE) are nonoxidative metabolites of ethanol produced by the esterification of FA and ethanol. FAEE have been implicated as mediators of ethanol-induced organ damage in vivo and in vitro, and are markers of ethanol intake. Upon ethanol intake, FAEE are synthesized in the liver and pancreas in significant quantities. There is limited information on the stimulation of FAEE synthesis upon addition of exogenous FA in vitro. HepG2 cells were incubated with ethanol alone, ethanol with 25 microM linoleate, and ethanol with 25 microM stearate. The amount of FAEE in human hepatoblastoma (HepG2) cells was determined 1-3 h after ethanol and FA addition. Stearate increased the FAEE concentration in HepG2 cells when incubated with the cells for 1 h, whereas linoleate did not increase the cellular FAEE concentration at any time. Ethyl palmitate, ethyl stearate, and ethyl oleate were the predominant FAEE species identified in all cases, independent of the specific supplemental FA added to the medium.

Fatty acid ethyl esters: recent observations

Fatty acid ethyl esters (FAEE), esterification products of fatty acids and ethanol, have been shown to be mediators of ethanol-induced cell injury and their presence in the blood and tissues is a marker of ethanol intake. Recently, it has been shown that FAEE are produced within seconds of infusion of ethanol into the heart, when using a protocol similar to that used for myocardial ablation. This raises the possibility that the mechanism for the death of myocytes in cardiac ablation involves the generation of toxic FAEE. It has also been recently demonstrated that chronic alcoholics have a high concentration of a specific FAEE species--ethyl oleate. The use of the serum ethyl oleate concentration may be helpful in differentiating binge drinkers from chronic alcoholics.

Pharmacokinetics of ethanol: a review of the methodology

This paper reviews current concepts on tools for studying the pharmacokinetics of alcohol. It has been known that ethanol metabolism occurs mainly in the liver via alcohol dehydrogenase and an accessory microsomal pathway. The contribution of each pathway has been examined by administration of metabolic inhibitors. The role of gastric alcohol dehydrogenase in the first-pass effects of ethanol has been speculative and may be relatively low. Some pharmacokinetic approaches with mathematical models have elucidated the role of gastric alcohol dehydorgenase, hepatic alcohol dehydrogenase and cytochrome P450 2E1 in ethanol elimination. The scale-up of ethanol elimination kinetics has enabled extrapolation from animal models to human kinetics. The clarification of the pharmacokinetics of ethanol is very important for estimating the effects of ethanol on biological events.

Heart 7-hydroperoxycholesterol and oxysterols are elevated in chronically ethanol-fed rats

Recently, cholesterol hydroperoxides have been shown to be sensitive pathogenic markers of reactive oxygen species (ROS)-mediated damage though they have never been measured in heart tissue. We hypothesized that cholesterol hydroperoxides and oxysterols, putative cardiotoxic products of cholesterol oxidation, are elevated in the hearts of alcoholics as a consequence of ROS-mediated reactions. To test this, we measured 7alpha- and 7beta-hydroperoxycholest-5-en-3beta-ol (7alpha-OOH and 7beta-OOH) by HPLC with postcolumn chemiluminescence as well as 7alpha- and 7beta-hydroxycholesterol (7alpha-OH and 7beta-OH) and 3beta-hydroxycholest-5-en-7-one (also termed 7-ketocholesterol; 7-keto) by HPLC-UV in cardiac muscle of alcohol-fed rats. Alcohol feeding was carried out using a pair-feeding protocol with 35% of total dietary energy as ethanol; controls were pair-fed isocaloric glucose. After 6-7 wk treatment with alcohol, heart 7alpha-OOH, 7beta-OOH and 7beta-OH were significantly greater than in controls. Levels of heart phospholipid 16:0 and 18:1 were lower than in controls, while 18:0 and 18:2 were greater. This is the first report of the presence of 7alpha-OOH, 7beta-OOH and 7alpha-OH in cardiac tissue. The elevations in 7alpha-OOH and 7beta-OOH as well as 7beta-OH are evidence of increased oxidative stress and possible membrane changes. Alterations in the proportions of 16:0, 18:1, 18:2 and 18:0 in heart phospholipids provide further evidence of an altered membrane domain.

Metabolic consequences of alcohol ingestion

Many of the pathophysiological effects of alcohol ingestion relate to the pathways of ethanol metabolism. However, some of the acute and chronic effects of ethanol use are also attributable to the direct effects of ethanol, e.g. on membrane fluidity. Oxidation of ethanol to acetaldehyde is catalysed by alcohol dehydrogenase (ADH). There are at least six classes of ADH, some of which show inter-individual variation, i.e. genetic polymorphism, that influences the rate of ethanol oxidation. A consequence of ethanol oxidation is an increase in the NADH/NAD redox potential within the cytosol and mitochondria with subsequent alteration in several tissue metabolites. The popular hypothesis that most, if not all, of the consequences of chronic alcohol ingestion can be explained by these redox changes is still unproven. This should be considered in the context that most metabolic pathways of the liver are affected by alcohol, as are several endocrine axes in the whole body. In fact most, if not all, tissues and organs are deleteriously affected by chronic ingestion. Acetaldehyde, the product of ethanol oxidation, is chemically highly reactive, toxic and immunogenic. However, the concentrations achieved in vivo usually fall short of those used to produce these toxic effects in experimental situations. Oxidation of acetaldehyde is also coupled to redox changes, although primarily affecting the intra-mitochondrial redox. In addition, further oxidative pathways of ethanol metabolism can lead to the formation of fatty acid ethyl esters, hydroxyethyl free radicals and reactive oxygen species via the ethanol-specific cytochrome P450-2E1 system. There is no conclusive evidence that nutrient supplementation has beneficial effects on overall ethanol-mediated tissue damage.