Glyoxalase 1 (GLO1) Inhibition or Genetic Overexpression Does Not Alter Ethanol's Locomotor Effects: Implications for GLO1 as a Therapeutic Target in Alcohol Use Disorders

Abstract

Background: Glyoxalase 1 (GLO1) is an enzyme that metabolizes methylglyoxal (MG), which is a competitive partial agonist at GABA_A receptors. Inhibition of GLO1 increases concentrations of MG in the brain and decreases binge-like ethanol (EtOH) drinking. This study assessed whether inhibition of GLO1, or genetic overexpression of Glo1, would also alter the locomotor effects of EtOH, which might explain reduced EtOH consumption following GLO1 inhibition. We used the prototypical GABA_A receptor agonist muscimol as a positive control.

Methods: Male C57BL/6J mice were pretreated with either the GLO1 inhibitor S-bromobenzylglutathione cyclopentyl diester (pBBG; 7.5 mg/kg; Experiment 1) or muscimol (0.75 mg/kg; Experiment 2), or their corresponding vehicle. We then determined whether locomotor response to a range of EtOH doses (0, 0.5, 1.0, 1.5, 2.0, and 2.5) was altered by either pBBG or muscimol pretreatment. We also examined the locomotor response to a range of EtOH doses in FVB/NJ wild-type and transgenic Glo1 overexpressing mice (Experiment 3). Anxiety-like behavior (time spent in the center of the open field) was assessed in all 3 experiments.

Results: The EtOH dose-response curve was not altered by pretreatment with pBBG or by transgenic overexpression of Glo1. In contrast, muscimol blunted locomotor stimulation at low EtOH doses and potentiated locomotor sedation at higher EtOH doses. No drug or genotype differences were seen in anxiety-like behavior after EtOH treatment.

Conclusions: The dose of pBBG used in this study is within the effective range shown previously to reduce EtOH drinking. Glo1 overexpression has been previously shown to increase EtOH drinking. However, neither manipulation altered the dose-response curve for EtOH's locomotor effects, whereas muscimol appeared to enhance the locomotor sedative effects of EtOH. The present data demonstrate that reduced EtOH drinking caused by GLO1 inhibition is not due to potentiation of EtOH's stimulant or depressant effects.

Keywords: GABAA; Anxiety-Like Behavior; Ethanol; Glyoxalase 1; Locomotor Activity.

Figure 1

Total distance traveled in 30 min for each dose of ethanol (EtOH) in mice treated with 7.5 mg/kg of the GLO1 inhibitor pBBG or vehicle. Significant results of the post-hoc tests for the main effect of ethanol dose (F_5,143=31.11, p<0.001) are noted, where # indicates the entire dose group (collapsed on inhibitor treatment) is significantly different from 0 g/kg (saline) ethanol group.

Figure 2

Time courses of locomotor activity by ethanol dose for pBBG- and vehicle-treated groups. No significant main effects or interactions were seen for the drug groups.

Figure 3

Percent of total time spent in the center of the open field apparatus during 30 min test for each dose of ethanol in mice treated with 7.5 mg/kg of the GLO1 inhibitor pBBG or vehicle. * indicates significant difference between pBBG and vehicle groups.

Figure 4

Total distance traveled in 30 min for each dose of ethanol in mice treated with 0.75 mg/kg muscimol or vehicle. # indicates statistically significant difference from the 0 g/kg (saline) group of the same drug treatment.

Figure 5

Time courses of locomotor activity by ethanol dose for muscimol- and vehicle-treated groups. * indicates statistically significant difference from the vehicle treated group for a given time bin.

Figure 6

Percent of total time spent in the center of the open field apparatus during 30 min test for each dose of ethanol in mice treated with 0.75 mg/kg muscimol or vehicle. * indicates statistically significant difference between the muscimol and vehicle groups.

Figure 7

Total distance traveled in 30 min for each dose of ethanol in wild type (WT) and transgenic mice heterozygous for the Glo1 over expression (TG), collapsed on sex. Significant results of the post-hoc tests for the main effect of ethanol dose (F_6,152=11.77, p<0.001) are noted, where # indicates the entire dose group (collapsed on genotype) is significantly different from 0 g/kg (saline) ethanol group

Figure 8

Percent of total time spent in the center of the open field apparatus during 30 min test for each dose of ethanol in wild type (WT) and transgenic mice heterozygous for the Glo1 over expression (TG), collapsed on sex. Significant results of the post-hoc tests for the main effect of ethanol dose (F_6,151= 3.22, p=0.006) are noted, where # indicates the entire dose group (collapsed on genotype) is significantly different from 0 g/kg (saline) ethanol group.