Effect of dietary ethanol and cholesterol on phospholipid composition of hepatic mitochondria and microsomes from the monkey, Macaca nemestrina

Ethanol and membrane lipids

Although ethanol is known to exert its primary mode of action on the central nervous system, the exact molecular interaction underlying the behavioral and physiological manifestations of alcohol intoxication has not been elucidated. Chronic ethanol administration results in changes in organ functions. These changes are reflective of the adaptive mechanisms in response to the acute effects of ethanol. Biophysical studies have shown that ethanol in vitro disorders the membrane and perturbs the fine structural arrangement of the membrane lipids. In the chronic state, these membranes develop resistance to the disordering effects. Tolerance development is also accompanied by biochemical changes. Although ethanol-induced changes in membrane lipids have been implicated in both biophysical and biochemical studies, measurements of membrane lipids, such as cholesterol content, fatty acid unsaturation, phospholipid distribution, and ganglioside profiles, have not produced conclusive evidence that any of these parameters are directly involved in the action of ethanol. On the other hand, there is increasing evidence indicating that although ethanol in vitro produces a membrane-fluidizing effect, the chronic response to this effect is not to change the membrane bulk lipid composition. Instead, changes in membrane lipids may pertain to small metabolically active pools located in certain subcellular fractions. Most likely, these lipids are involved in important membrane functions. For example, the increase in PS in brain plasma membranes may provide an explanation for the adaptive increase in synaptic membrane ion transport activity, especially (Na,K)-ATPase. There is also evidence that the lipid pool involved in the deacylation-reacylation mechanism (i.e., PI and PC with 20:4 groups) is altered after ethanol administration. An increase in metabolic turnover of these phospholipid pools may have important implications for the membrane functional changes. Obviously, there are other lipid-metabolizing enzyme systems that may exert similar effects but have not yet been investigated in detail. From the results of these studies, it is concluded that the multiple actions of ethanol are associated with changes in enzymic systems important in the functional expression of the membranes.

Phospholipid association with the bovine cardiac mitochondrial adenosine triphosphatase

The association of different phospholipids with a lipid-depleted oligomycin-sensitive ATPase from bovine cardiac mitochondria [Serrano, Kanner & Racker (1976) J. Biol. Chem. 251, 2453-2461] has been examined using three approaches. First, reconstitution of the ATPase with different synthetic diacyl phospholipids resulted in a 2-10-fold stimulation of ATPase specific activity depending upon the particular phospholipid employed. The phospholipid headgroup region displayed the following order of ATPase reactivation potential: dioleoylphosphatidylglycerol greater than dioleoylphosphatidic acid greater than dioleoylphosphatidylcholine. Furthermore, the ATPase showed higher levels of specific activity when reconstituted with dioleoyl phospholipid derivatives compared with dimyristoyl derivatives. Second, examination of the phospholipid remaining associated with the lipid-depleted ATPase upon purification showed that phosphatidylcholine, phosphatidylethanolamine, and diphosphatidylglycerol were present. No relative enrichment of any of these phospholipids (compared with their distribution in submitochondrial particles) was noted. Therefore, no preferential association between the ATPase and any one phospholipid could be found in the mitochondrial ATPase. Third, the sodium cholate-mediated phospholipid exchange procedure was employed for studying the phospholipid requirements of the ATPase. Replacement of about 50% of the mitochondrial phospholipid remaining with the lipid-depleted ATPase could be achieved utilizing either synthetic phosphatidic acid or phosphatidylcholine. Examination of the displaced mitochondrial phospholipid showed that phosphatidylcholine, phosphatidylethanolamine, and diphosphatidylglycerol were replaced with equal facility.

Alcohol-induced mitochondrial changes in the liver

The chronic ingestion of ethanol results in liver-cell damage, and characteristic features of this injury are the marked alterations in both the functions and morphology of the mitochondria. Morphologically, the changes observed in human alcoholics and experimental animals appear similar. Bizarrely shaped mitochondria and megamitochondria are detected at the fatty liver stage and persist as the disease progresses. As yet, however, no correlation has been found between the severity of these morphological changes and the development of cirrhosis. Analysis of the mitochondrial membranes indicates that ethanol consumption produces changes in both the protein and lipid composition of the membrane. Profound decreases in the components of the respiratory chain have been detected, and these changes are associated with marked depressions in the activity of NAD+-linked dehydrogenases, cytochrome oxidase, and the ATP synthetase complex. On the other hand, no consistent pattern has emerged as to the effect of chronic ethanol consumption on the composition of the membrane phospholipids. Many of the changes appear to be dependent on the sex of the animal, the dietary status, and the duration of ethanol intake, and are suggestive of changes in fatty acid desaturase activity. Mitochondria isolated from ethanol-fed rats displayed impaired respiration and a lowered steady-state rate of ATP synthesis. Whether or not these functional changes are directly related to alterations in the physical properties of the membranes remains to be resolved. This marked depression of respiratory functions in isolated mitochondria was not reflected by a significant decrease in O2 consumption by the livers of ethanol-fed animals.

Ethanol-related changes in liver microsomes and mitochondria from the monkey, Macaca fascicularis

Four Macaca fascicularis monkeys were maintained 1 year on a liquid diet containing 26% of calories as ethanol. Four control animals were fed a liquid diet of equivalent calories with protein, carbohydrate, and fat being substituted for ethanol calories. In liver mitochondria prepared from ethanol-fed monkeys (ethanol mitochondria), respiratory control was lowered 20% due to a decrease in state 3 respiration (28%). This was also accompanied by a 20% decrease in ADP translocation into ethanol mitochondria. The major change was a 61% decrease in cytochrome oxidase activity. The respiratory rate in the presence of uncoupler was also lowered 14%, but the decrease was not statistically significant. In contrast with our earlier observations with Macaca nemestrina, no significant ethanol-induced changes were observed in enzyme activities associated with the microsomal electron transport system, and no ethanol-elicited fatty liver was evident. The major changes in fatty acid composition of microsomal and mitochondrial phospholipids were increased amounts of palmitoleic and oleic acids, and decreased amounts of linoleic and arachidonic acids.