Chronic ethanol consumption alters transbilayer distribution of phosphatidylcholine in erythrocytes of Sinclair (S-1) miniature swine

Ethanol specifically alters the synthesis, acylation and transbilayer movement of aminophospholipids in rat-liver microsomes

By experimenting with the aminoalcohols [3-3H]serine and [2-14C]ethanolamine we have been able to relate the effects of ethanol upon the biosynthesis of radioactive aminophospholipids (APL) in rat-liver microsomes and their distribution within the bilayer. The translocation of newly synthesized molecules of aminophospholipids labeled with different fatty acids was also investigated. The synthesis of phosphatidylserine (PS) and phosphatidylethanolamine (PE) by base-exchange reaction (BES) was inhibited in membranes exposed to ethanol in direct response to its concentration. In addition, 100 mM ethanol specifically inhibited the transport of newly synthesized PS to the inner leaflet, resulting in similar levels of PS in both leaflets of the bilayer. The inhibition of PE synthesis by ethanol caused a decrease in its distribution in both inner and outer leaflets. An in vitro study of the incorporation of radioactive palmitate and oleate into the PS and PE of microsomes incubated with ethanol showed a decrease in the radioactivity levels of PE, suggesting that ethanol was specifically inhibiting the corresponding acyltransferase. It specifically altered the transbilayer movement of newly acylated phospholipids, modifying the distribution of palmitoyl- and oleoyl-acylated PS and PE in both leaflets. These results demonstrate for the first time that ethanol interferes with both the synthesis and intramembrane transport of aminophospholipids in endoplasmic reticulum (ER) membranes. Bearing in mind that if a membrane is to function properly its structure must be in optimum condition; it is evident that the observed processes may be responsible to some degree for the pathophysiological effects of alcohol upon cells.

Formation of phosphatidylethanol in vitro in red blood cells from healthy volunteers and chronic alcoholics

Phosphatidylethanol (PEth) is an abnormal phospholipid, formed only in the presence of ethanol via a transphosphatidylation reaction of phospholipase D (PLD). PEth in blood is a promising new marker of alcohol abuse. Blood PEth is found almost exclusively in red cells. This study was performed to investigate a possible PEth formation in human red cells from alcoholics and healthy individuals, at physiologically relevant ethanol concentrations. Blood was drawn from six healthy volunteers (controls) and six chronic inpatient alcoholics. Hematological analyses were performed, and red blood cells were separated and incubated in plasma with ethanol to study PEth formation. Lipids were extracted and PEth analyzed with high pressure liquid chromatography and evaporative light-scattering detection. Incubation of red cells in 50 mM ethanol yielded detectable PEth after 12 hours. Formation of PEth was concentration dependent at 10 to 50 mM ethanol. In vitro formation of PEth was significantly higher (P <.001) in red cells from alcoholics (5.2 +/- 1.1 micromol/l) compared to controls (2.4 +/- 0.6 micromol/l) (mean +/- SD). A significant correlation (P <.01) was observed between initial mean corpuscular volume and accumulated PEth. This study demonstrates that PEth is formed in human red cells at physiologically relevant ethanol concentrations. Alcoholics accumulate about twice as much PEth than controls. The accumulation rate of PEth is slower in red cells compared to rates reported for other tissues.

Apoptosis and dysregulated ceramide metabolism in a murine model of alcohol-enhanced lipopolysaccharide hepatotoxicity

BACKGROUND

The role of apoptosis in EtOH-induced liver injury has not been investigated much. Therefore, the question whether apoptosis is a contributory factor to alcoholic liver disease remains to be answered. The purpose of this study was to characterize the liver apoptotic response in a murine model of alcohol-enhanced lipopolysaccharide (LPS) hepatotoxicity.

METHODS

Mice were fed an alcohol-containing liquid diet for 49 days followed by an acute LPS challenge. The liver state was judged on the basis of histological appearance, plasma liver enzyme activity (alanine:2-oxoglutarate and aspartate:2-oxoglutarate aminotransferases, as markers of hepatocytolysis), and plasma hyaluronan levels (as a marker of the sinusoidal endothelial cell scavenging function). The liver apoptotic response was assessed by DNA fragmentation (TUNEL procedure), and caspases-3 and -8 activity. To determine if ceramide played a role in the liver apoptotic response, the activity of acidic sphingomyelinase and tissue content of ceramide were also quantified.

RESULTS

Alcohol exposure induced fat accumulation and sensitized the liver to LPS injurious effects. Plasma liver enzyme activity was elevated by alcohol and this effect was potentiated by LPS. Liver apoptosis was augmented by both alcohol and LPS treatment as reflected by high frequency of positive TUNEL staining nuclei and by an increased activity of caspase-3 and -8. Acidic sphingomyelinase activity was also increased and it was associated with an elevated tissue content of ceramide. In addition, LPS also increased plasma TNF-alpha levels. These changes were accompanied by elevated plasma hyaluronan, reflecting an impaired sinusoidal endothelial cell scavenging function.

CONCLUSIONS

These results provide a more complete description of the liver apoptotic response to both alcohol and LPS and may constitute the basis for further mechanistic studies on a possible role apoptosis may play in alcoholic liver injury.

Rat erythrocyte susceptibility to lipid peroxidation after chronic ethanol intake

Erythrocytes, from 2- and 7-month-old rats chronically fed with a liquid diet containing ethanol, were analyzed for their susceptibility to lipid peroxidation estimated as thiobarbituric acid reactive substance (TBARS) products. In spite of a lower alcohol consumption, adult rats were the more affected by the ethanol treatment. Erythrocyte membranes prepared from alcoholic animals were more sensitive to lipid peroxidation than those prepared from control rats. In both age groups lipid analysis revealed similar changes: 1) an increased cholesterol/phospholipid molar ratio mainly derived from a higher content of cholesterol that accounts for the lower membrane fluidity and the higher tolerance to the disordering effect exerted by ethanol in vitro; 2) an increase of phospholipid unsaturated fatty acids, especially C20:4; 3) a modification of the phospholipid pattern, characterized in the ethanol group by an increase of PE and decrease of PE and decrease of PC levels; moreover, significant increases of the anionic phospholipids were detected in the adult group.

Chronic ethanol intoxication induces adaptive changes at the membrane protein/lipid interface

Modifications were found to occur at the membrane protein/lipid interface of liver microsomes in animals that had been subjected to chronic ethanol ingestion. The effects were revealed by probing this region with 1,6-diphenyl-1,3,5-hexatriene (DPH), trimethylammonium-DPH (TMA-DPH) and DPH attached to the sn-2 chain of phosphatidylcholine (1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5-hexatrienyl) phenyl]ethyl]carbonyl]-3-sn-phosphatidylcholine, DPH-PC). In intact membranes, it was found that the decay of the excited state was heterogeneous, this being modeled by fitting the data to a fluorescence lifetime distribution. The full-width of the distribution at half-maximum, which relates to the degree of excited state environmental heterogeneity, increased for each fluorophore, as a result of chronic ethanol treatment. For TMA-DPH and DPH the excited state heterogeneity could have arisen from, (i) the protein/lipid interface and (ii) varied degrees of water penetration into the lipid, due to the ability of these fluorophores to sample along the bilayer normal. By contrast, the DPH in DPH-PC, due to its tethering, was only able to sample the heterogeneity at the protein/lipid interface, as confirmed by a homogeneous decay in vesicles of microsomal lipid extracts. The increased degree of DPH-PC fluorescence decay heterogeneity in microsomes from chronic ethanol-treated animals as compared to controls, was found to persist in vesicles of extracted lipids, when apocytochrome C was included in the vesicle preparations as a model protein. This effectively eliminated a protein modification from being responsible and indicated that a chronic-ethanol induced alteration in the lipids was being expressed in the form of a physico-chemical modification at the protein/lipid interface. The degree of DPH-PC environmental heterogeneity was also directly increased by ethanol, however, membranes from chronic ethanol-treated animals were resistant to this effect, showing that the phenomenon of 'membrane tolerance' extends to the membrane protein/lipid interface.

Cholesterol exchange and lateral cholesterol pools in synaptosomal membranes of pair-fed control and chronic ethanol-treated mice

Most studies on effects of ethanol on membrane cholesterol have reported on changes in the total or bulk amount of cholesterol. Membrane cholesterol, however, can be described in terms of its kinetics and domains. The kinetics and size of lateral cholesterol exchangeable and nonexchangeable pools were examined in synaptosomes of pair-fed controls and chronic ethanol-treated mice. Effects of sphingomyelin, an exofacial leaflet phospholipid, that has been shown to affect cholesterol pools, were also examined. Radiolabeled small unilamellar vesicles were used to exchange cholesterol with synaptosomes. The total amounts of membrane cholesterol, phospholipid phosphorus, and the ratio of cholesterol to phospholipid did not differ between the pair-fed control and ethanol groups. In control mice, the rate constant (hr-1) and the t1/2 (hr) of cholesterol exchange were 0.065 +/- 0.001 and 10.7 +/- 0.25 (hr), respectively. The rate constant was significantly slower (0.053 +/- 0.001, p < 0.05) and the t1/2 significantly longer (13.33 +/- 0.58, p < 0.05) in synaptosomes of the ethanol group compared with the control group. The size of the exchangeable pool of cholesterol did not differ significantly between the two groups. Sphingomyelinase-induced hydrolysis of sphingomyelin significantly slowed cholesterol exchange with the largest effect in synaptosomes of the control group as compared with the ethanol group (p < 0.05). Hydrolysis of sphingomyelin had significantly (p < 0.05) less of an effect on cholesterol exchange in synaptosomes of the ethanol group. Membrane cholesterol can be described in terms of total content, transbilayer distribution, kinetics, and size of lateral pools.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of chronic ethanol administration on poly-phosphoinositide metabolism in the mouse brain: variance with age

Using a procedure in which poly-phosphoinositides (poly-PI) in C57Bl mouse brain were labeled with [32P]Pi or [32P]ATP, the effects of chronic ethanol administration and age on metabolism of these anionic phospholipids were examined. Within 4 h after intracerebral injection, both labeled precursors were effectively incorporated into membrane phospholipids with high proportions of labeling among phosphatidylcholine, phosphatidylinositol and phosphatidylinositol 4,5-bisphosphate. With few exceptions, the phospholipid labeling patterns in different brain regions, e.g. cortex, hippocampus and hypothalamus, were similar. However, when the brain homogenate was subjected to differential and sucrose-Ficoll gradient centrifugation, different phospholipid labeling patterns were observed in the subcellular membrane fractions. Young adult mice given an ethanol (5% w/v) liquid diet for 2 months showed an increase in the levels of labeled phosphatidylinositol 4-phosphate, phosphatidylinositol 4,5-bisphosphate and phosphatidylserine in the cortex and hippocampus as compared to the pair-fed controls, but these changes were not observed in the hypothalamus. In another study, 12- and 26-month-old mice were administered either an ethanol (8 g/kg in two doses daily) or a control diet by gavage for 3 weeks. The 12-month-old group given the ethanol diet showed an increase in labeled poly-PI which was found largely in the synaptosomal fraction. Surprisingly, the 26-month-old mice given the same ethanol paradigm showed a decrease in labeled poly-PI. Consistent with our previous observations, the 26-month-old mice showed a higher proportion of labeled poly-PI in the synaptosomal fraction as compared to the younger age group.(ABSTRACT TRUNCATED AT 250 WORDS)