Ethanol withdrawal posttranslationally decreases the activity of cytochrome c oxidase in an estrogen reversible manner

Abstract

Cytochrome c oxidase (COX) is a key mitochondrial enzyme that catalyzes electron transfer at the terminal stage of respiratory chain and is composed of multisubunits. We hypothesize that ethanol withdrawal (EW) impairs the activity of COX and estrogen deprivation exacerbates this problem. Five month-old ovariectomized rats with or without 17β-estradiol (E2) replacement received a control dextrin or a liquid ethanol diet (6.5%, five weeks). They were then sacrificed either during ethanol exposure or at 24 hours of EW (EW group). Mitochondria of the cerebellum and cortex were processed to measure the activities of total COX, COX subunit I, and IV. The effects of EW and E2 on the protein levels of these subunits were also assessed using an immunoblotting method. As compared to the control dextrin and ethanol exposure, EW decreased the activities of total COX, COX I, and COX IV. E2 treatment prevented the effects of EW on the activities of total COX and COX IV but not COX I. Neither EW nor E2 altered the protein levels of the subunits. These findings suggest that a counteracting relationship exists between the effects of EW and E2 on the activity of COX in a subunit specific manner. KeywordsCytochrome c oxidase; 17β-estradiol; Ethanol Withdrawal; Mitochondria Mitochondria produce cellular energy (ATP) through a series of mitochondrial enzyme complexes. Electrons are transferred across the enzyme complexes and create the electrochemical gradient between the mitochondrial membranes. Subsequently, the electrochemical gradient provides force to generate ATP. COX is a terminal enzyme complex among the series of enzymes and plays a key role in the mitochondrial function. Therefore, damage to this enzyme can cause serious clinical consequences. Indeed, the decreased activity of COX has been found in a variety of neurodegenerative illnesses such as Parkinson′s disease and Alzheimer′s disease [1][2][3].Accumulated evidence indicates that mitochondria are vulnerable to ethanol/EW toxicity. Reactive oxygen species produced during ethanol metabolism altered mitochondrial function in rodents [4,5]. The mitochondrial membrane permeability and oxidation were dramatically increased during EW [6,7], suggesting that ethanol and/or EW preferentially target mitochondria. However, most of the studies did not differentiate between ethanol exposure and *Corresponding author: Department of Pharmacology and Neuroscience, University of North Texas Health Science Center at Fort Worth, 3500 Camp Bowie Blvd., Fort Worth, TX 76107-2699, USA, Tel.: 817-735-0132, Fax: 817-735-2091, E-mail address: mjung@hsc.unt.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the cont...

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