Genetic Vulnerability to Alcohol, Oxidative Homeostasis, and NAC Efficacy

Portland Va Medical Center, Portland OR

Investigators

Linked publications & trials

Abstract

? DESCRIPTION (provided by applicant): Alcohol dependence (alcoholism) is a common condition in veterans and alcohol abuse is a complicating factor in most chronic medical and psychiatric illnesses. Although alcoholism is substantially (40-60%) genetically determined, the genetic determinants of risk are largely unknown, hindering effective prevention and treatment of dependent individuals. For these reasons and more, there is a clear need to expand pharmacotherapy options for alcohol abuse and dependence to improve outcomes and sustained abstinence. Although no animal model duplicates clinically-defined alcoholism, models for specific factors (including withdrawal/negative effect, which constitutes a motivational force that perpetuates alcohol use and contributes to relapse) are useful to identify potential determinants of liability and pharmacotherapy in humans. A unique strength of this proposal is that we show for the first time that N-acetylcysteine (NAC), an FDA approved antioxidant, mitigates alcohol withdrawal. An important goal of this research proposal is to characterize NAC efficacy to reduce withdrawal (convulsions, anxiety-like behavior) in dependent mice. Using preclinical models, we were also the first to identify quantitative trait loci (QTL) with proven, large effects on alcohol physical dependence and associated withdrawal. One hypothesis that has emerged from our work is that the QTL of largest effect (Adw1) may also affect alcohol seeking behavior. Adw1 is also unique in that it affects alcohol but not pentobarbital withdrawal, providing an important clue to its mechanism of action. Notably, ethanol exposure and withdrawal introduce oxidative stress, while pentobarbital has neutral or anti-oxidative effects in the brain. Some of the most useful tools that we have created thus far are congenic mice with the Adw1 region from a donor strain introgressed onto a different genetic background. These genetic models have been invaluable to map Adw1 to a small interval and identify high-quality candidate genes, the most promising of which (so far) have roles in oxidative homeostasis/stress; and gene co-expression network analyses using Adw1 congenics indicate disruption of the oxidative phosphorylation pathway. Thus, a hypothesis that has emerged from our data is the idea that oxidative homeostasis/stress may play an important role in genetic vulnerability to alcohol physical dependence and withdrawal, and that this pathway may also be a pharmacotherapeutic target to manage withdrawal and beyond. We have now published the first studies of mitochondria respiratory complex activities and organization in the mouse brain and find remarkable genetic differences, providing a framework to gain mechanistic information. Although NAC is thought to affect this pathway, it may have additional actions that could also contribute to its therapeutic efficacy. Using a systems biology network approach, we will assess both possibilities to provide additional mechanistic information. Interestingly, a growing body of evidence implicates natural variation in oxidative homeostasis in genetically influenced differences in mice, disproportionately affecting the brain, so we expect that our results may direct research beyond the addictions.