Alcohol & Alcoholism Vol. 43, No. 4, pp. 401–407, 2008 doi: 10.1093/alcalc/agn012 Advance Access publication 8 March 2008 GENETICS AND CELL BIOLOGY Distribution and Differential Induction of CYP2E1 by Ethanol and Acetone in the Mesocorticolimbic System of Rat M. Jos´ e S´ anchez-Catal´ an 1 , Luc´ ıa Hip´ olito 1 , Consuelo Guerri 2 , Luis Granero 1 and Ana Polache 1,∗ 1 Departamento de Farmacia y Tecnolog´ ıa Farmac´ eutica, Universidad de Valencia, Avda Vicente Andr´ es Estell´ es s/n, 46100, Burjassot, Spain and 2 Department of Cellular Pathology, Centro de Investigaci´ on Pr´ ıncipe Felipe, Avda Autopista del Saler, 16 46013-Valencia, Spain ∗ Author to whom correspondence should be addressed at: Departamento de Farmacia y Tecnolog´ ıa Farmac´ eutica, Universidad de Valencia, Avda Vicente Andr´ es Estell´ es s/n, 46100, Burjassot, Spain. Tel.: + 34 96 3544910; Fax: + 34 96 3544911; E-mail: ana.polache@uv.es (Received 10 October 2007; first review notified 6 December 2007; in revised form 13 December 2007; accepted 29 January 2008; advance access publication 8 March 2008) Abstract — Aims: The expression of cytochrome P4502E1 (CYP2E1) in the brain has been demonstrated in several regions, nevertheless there is a lack of specific studies on the constitutive expression and induction at the mesocorticolimbic system, the most relevant brain pathway in the context of drug addiction and alcoholism. Hence, we have performed a detailed study of the CYP2E1 expression and induction in three key areas of the mesocorticolimbic system of the rat brain: prefrontal cortex (PFC), nucleus accumbens (NAc), and ventral tegmental area (VTA). Methods: Expression levels of CYP2E1 were analyzed by Western blot. The induction of the enzyme in the selected brain areas by chronic acetone (1% v/v acetone in drinking water for 11 days) and ethanol (3 g/kg by gavage for 7 days) was also assessed. Results: (i) CYP2E1 was expressed in PFC, Nac, and VTA, with the order of magnitude of the levels being VTA ∼ PFC > Nac, and approximately 3–13% of it was encountered in liver; (ii) acetone treatment significantly increased CYP2E1 expression in Nac, up to 212% of the control levels, whereas not significant changes were observed in VTA and PFC; (iii) chronic ethanol treatment only resulted in a significant induction of enzyme levels in VTA (124%). A similar enhancement, though not significant, was found to occur in NAc. Conclusions: CYP2E1 was present in the mesocorticolimbic system at different levels of expression. Chronic acetone and ethanol treatments are able to increase enzyme levels in specific areas of this system with the pattern of induction of the two agents being different. INTRODUCTION A vast amount of evidence has emerged suggesting that both natural rewards and drugs of abuse, including ethanol, derive their reinforcing properties by acting through a common path- way involving the brain neurotransmitter dopamine (DA) (Wise and Rompre, 1989; Hyman and Malenka, 2001; Koob and Le Moal, 2006). Concretely, the reinforcing effects of ethanol have been found to be associated with several brain structures be- longing to the mesocorticolimbic dopamine system. In this system, dopamine neurons originate in the ventral tegmental area (VTA) of the brain stem and innervate the prefrontal cor- tex (PFC) and the nucleus accumbens (NAc) (Koob and Le Moal, 2006). Furthermore, numerous behavioral studies also indicate that brain metabolism of ethanol may explain part of its neurobiological effects (Quertemont et al., 2005). Accord- ing to these studies, acetaldehyde itself or its condensation products with biogenic amines (tetrahydroisoquinolines and β -carbolines, derived from the condensation with dopamine and serotonin, respectively), locally originated inside the brain after ethanol ingestion, could be responsible for some of the effects of this drug. For example, recently it has been reported that acetaldehyde induces robust reinforcing effects, especially when administered into the VTA (Rodd-Henricks et al., 2002). These effects have been postulated to be due not only to direct actions of acetaldehyde but also to the formation of conden- sation products (tetrahydroisoquinolines, TIQs) with various neurotransmitters including dopamine (Collins, 1985; Myers, 1996). The enzymatic machinery necessary to metabolize ethanol has been reported to be present in the brain, consisting of several enzymes of which catalase and cytochrome P4502E1 (CYP2E1) are particularly relevant (Zimatkin et al., 2006). In relation to CYP2E1, the major –ethanol-inducible CYP, the identification of its constitutive expression in the brain as well as its regional distribution has been extensively investigated in the last and present decade employing very different method- ologies (Tindberg and Ingelman-Sundberg, 1996; Upadhya et al., 2000; Kapoor et al., 2006). Although, the expression of this enzyme in the brain is clearly region- and cell-specific (Hip´ olito et al., 2007), discrepancies exist regarding its precise distribution within the brain. Similarly, though all the studies demonstrate that brain enzyme levels are significantly lower than those observed in liver, a debate exists in relation to the precise levels of enzyme expression. Thus, some reports indi- cate extremely low levels of expression in the brain (Hansson et al., 1990; Roberts et al., 1994; Warner and Gustafsson, 1994; Montoliu et al., 1995; Tindberg and Ingelman-Sundberg, 1996; Yadav et al., 2006) whereas other studies show CYP2E1 levels to be 25% of liver levels (Anandatheerthavarada et al., 1993; Upadhya et al., 2000). Moreover, it is surprising that there is a lack of detailed and specific studies on the constitutive expression at the mesocor- ticolimbic system, which is probably, as we have commented above, the most relevant brain pathway in the context of drug addiction and alcoholism. The small amount of data reported, using immunochemistry methods, show CYP2E1 immunore- activity in the rat nucleus accumbens (Hansson et al., 1990; Joshi and Tyndale, 2006) and in the cytoplasm of cells in the VTA and pars compacta of substantia nigra (SN) (no in pars reticulata) (Riedl et al., 1996). These data do not always agree; for example, Hansson et al. (1990) showed a high intensity of staining in NAc of rat brain whereas, more recently, Joshi and Tyndale (2006) reported weak immunocytochemical staining in NAc of monkey brain. Surprisingly, other authors (Yadav et al., 2006) were unable to detect CYP2E1 immunoreactivity, by Western blot, in the striatum and in the cortex. Additionally, to our knowledge, the expression levels of CYP2E1 in relevant C  The Author 2008. Published by Oxford University Press on behalf of the Medical Council on Alcohol. All rights reserved Downloaded from https://academic.oup.com/alcalc/article/43/4/401/128139 by guest on 15 March 2021