528 Original article Polymorphisms in mitochondrial genes encoding complex I subunits are maternal factors of voluntary alcohol consumption in the rat Amalia Sapag a , Ginez Gonza ´ lez-Martı ´nez a , Lorena Lobos-Gonza ´ lez a , Gonzalo Encina a , Lutske Tampier b , Yedy Israel a,b and Marı ´a Elena Quintanilla b Objective Alcohol is detoxified in the liver by oxidizing enzymes that require nicotinamide adenine dinucleotide (NAD + ) such that, in the rat, the availability of NAD + contributes to control voluntary ethanol intake. The UChA and UChB lines of Wistar rats drink low and high amounts of ethanol respectively and differ in the capacity of their mitochondria to oxidize NADH into NAD + . This function resides in complex I of the respiratory chain and its variation is linked to genes transmitted through the maternal line. The aim of this study was to identify the genetic basis for the difference in the reoxidation of NADH in these nondrinker (UChA) and drinker (UChB) rats. Methods Seven mitochondrial genes and two chromosome X genes encoding complex I subunits from rats of both lineages were amplified from liver DNA and sequenced. Results The UChA and UChB rat lines differ in their Nd2, Nd4, Nd5 and Nd6 mitochondrial genes and in the encoded proteins. Most noteworthy are ND2 and ND4 whose amino acid variations lead to changes in three-dimensional structure models. The ND2 proteins also differ in the number of predicted transmembrane domains. The Nd1 and Nd3 genes have silent substitutions, whereas Nd4L and the exonic sequences of the nuclear genes Ndufa1 and Ndufb11 show no differences between the UChA and UChB lines. Conclusion Amino acid variations in four complex I subunits encoded in the mitochondrial genome may contribute to explain the differences between UChA and UChB rats in their capacity to reoxidize NADH and in their alcohol intake, suggesting that mitochondrial genes may constitute maternal factors of alcoholism. Pharmacogenetics and Genomics 19:528–537  c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins. Pharmacogenetics and Genomics 2009, 19:528–537 Keywords: alcohol preference, complex I, mitochondrial genes, NAD + , ND2, ND4, ND5, ND6, polymorphisms, UChA and UChB rats a Laboratory of Gene Pharmacotherapy, Department of Pharmacological and Toxicological Chemistry, Faculty of Chemical and Pharmaceutical Sciences and b Molecular and Clinical Pharmacology Programme, Faculty of Medicine, Universidad de Chile, Santiago, Chile Correspondence to Amalia Sapag, PhD, Laboratorio de Farmacoterapia Ge ´ nica, Facultad de Ciencias Quı ´micas y Farmace ´ uticas, Universidad de Chile, Olivos 1007, Independencia, Santiago, RM 838-0492, Chile Tel: + 562 9782936; fax: + 562 7377291; e-mail: asapag@uchile.cl Received 18 March 2009 Accepted 5 May 2009 Introduction Alcoholism is a multifactorial disease in which genetic factors play a major role (50–60%) [1,2]. The identifica- tion of permissive and protective factors in alcoholism has drawn important contributions from studies performed on several lines of alcohol drinker and nondrinker rats bred in different parts of the world [3–9]. The UChA and UChB rat lines have been established at Universidad de Chile (UCh) by selective breeding of the Wistar strain on the basis of differences in voluntary alcohol consumption [3,10]. UChA rats (‘Abstemious’) drink between 0.1 and 1 g of ethanol/kg/day whereas UChB rats (‘Bibulous’) drink between 4 and 7 g of ethanol/kg/day when given a choice between distilled water and a solution of 10% ethanol. Underlying these two extreme alcohol-drinking phenotypes are genetic variations in both nuclear and mitochondrial genes [11]. In both man and rat [12–14], alcohol is metabolized mainly in the liver where alcohol dehydrogenase (ADH) transforms ethanol into acetaldehyde, which is in turn oxidized to acetate by mitochondrial aldehyde dehydro- genase (ALDH2). Both ADH and ALDH2 use nicotin- amide adenine dinucleotide (NAD + ) as a cofactor for these oxidation reactions. In humans, there is an ALDH2 variant associated with protection against alcoholism in the East Asian population [15,16]. The ALDH2*2 allele encodes an inactive enzyme (Glu487Lys) [17] which, upon ethanol intake, results in high levels of acetalde- hyde [18], an aversive metabolite of ethanol. Likewise, allelic variants of the Aldh2 gene have been found in the UChA and UChB rat lineages [19]. The Aldh2 2 allele is present only in the nondrinker UChA line, whereas both Aldh2 1 and Aldh2 3 alleles are common in the UChB line, with Aldh2 3 being exclusively present in drinker rats. The 1744-6872  c 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins DOI: 10.1097/FPC.0b013e32832dc12a Copyright © Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.