Reduction in Central H2O2 Levels Prevents Voluntary Ethanol Intake in Mice: A Role for the Brain Catalase-H2O2 System in Alcohol Binge Drinking
Hydrogen peroxide (H2O2) is the cosubstrate used by the enzyme catalase to form Compound I (the catalase-H2O2 system), which is the major pathway for the conversion of ethanol (EtOH) into acetaldehyde in the brain. This centrally formed acetaldehyde has been shown to be involved in some of the psychopharmacological effects induced by EtOH in rodents, including voluntary alcohol intake. It has been observed that different levels of this enzyme in the central nervous system (CNS) result in variations in the amount of EtOH consumed. This has been interpreted to mean that the brain catalase-H2O2 system, by determining EtOH metabolism, mediates alcohol self-administration. To date, however, the role of H2O2 in voluntary EtOH drinking has not been investigated.
In the present study, we explored the consequence of a reduction in cerebral H2O2 levels in volitional EtOH ingestion. With this end in mind, we injected mice of the C57BL/6J strain intraperitoneally with the H2O2 scavengers alpha-lipoic acid (LA; 0 to 50 mg/kg) or ebselen (Ebs; 0 to 25 mg/kg) 15 or 60 minutes, respectively, prior to offering them an EtOH (10%) solution following a drinking-in-the-dark procedure. The same procedure was followed to assess the selectivity of these compounds in altering EtOH intake by presenting mice with a (0.1%) solution of saccharin. In addition, we indirectly tested the ability of LA and Ebs to reduce brain H2O2 availability.
The results showed that both LA and Ebs dose-dependently reduced voluntary EtOH intake, without altering saccharin consumption. Moreover, we demonstrated that these treatments decreased the central H2O2 levels available to catalase.
Therefore, we propose that the amount of H2O2 present in the CNS, by determining brain acetaldehyde formation by the catalase-H2O2 system, could be a factor that determines an animal's propensity to consume EtOH.