Beneficial effects of metformin on haloperidol-induced motor deficits in rats. A behavioral assessment

Objective: One of the most common side effects of haloperidol is the extrapyramidal syndrome, resulting from inhibition of nigrostriatal dopaminergic circuits and mitochondrial dysfunction due to structural similarities to pyridinium derivative, MPP+ that induce oxidative stress. In exchange, the use of metformin appears to enhance neurogenesis, energy metabolism, and oxidative status, so these properties can be speculated in the context of drug-induced pseudoparkinsonism by haloperidol. Methods: To assess motor coordination and activity, rodents were divided into four groups: CTR (n = 10) - animals that received distilled water, METF (n = 10) - animals that received metformin 500 mg / kgbw, HAL (n = 10) - animals that received haloperidol 2mg / kgbw, HALMETF (n = 10) - haloperidol 2mg / kgbw and metformin 500 mg / kgbw. The treatment was administered for 34 days at the same time by gastric gavage, during which time behavioral tests, rotarod (days 7, 14, 21, 28), catalepsy (day 30), open field (day 32) and novel object recognition (day 34) were performed. Results: The monitored parameters, showed significant differences between the groups of interest (HAL and HALMETF respectively), so that the administration of metformin at the beginning of treatment reduces the cataleptic behavior. The HALMETF group shows an attenuation of the motor deficit during the rotarod test and the freezing period from the Open Field test, is diminished. Conclusions: Metformin treatment has a beneficial effect in haloperidol-treated rats, demonstrated by decreased cataleptic behavior, improved motor performance and reduced haloperidol-induced anxiety behavior.

In vitro Characterization of the Oxidation of a Pyridinium Metabolite of Haloperidol by Human Placenta: The Effect of Smoking

Purpose. The antipsychotic drug haloperidol can be metabolised to pyridinium metabolites haloperidol pyridinium (HP+) and reduced haloperidol pyridinium (RHP+). These pyridinium metabolites were proposed to contribute to the extrapyramidal side effects of haloperidol, because they are structural analogues of N-methyl-4-phenylpyridinium (MPP+), a well-known neurotoxin. RHP+ can be oxidized to HP+ by CYP1A1. In the current study, the oxidation of RHP+ to HP+ was investigated using human placenta microsomal preparations which contain relatively high levels of CYP1A1. Methods. Cytochrome P450 isoenzymes responsible for the metabolism of RHP+ were characterized in vitro using human placenta microsomal preparations from smokers and non-smokers. Results. A comparison of the metabolic activities between smokers and non-smokers suggests that smokers had higher activities for the oxidation of RHP+. A selective antibody against CYP1A1 was a partial inhibitor of RHP+ oxidase in placenta from smokers but had no effect in placenta from non-smokers. Furafylline and ketokonazole were shown to be stronger inhibitors of the oxidation of RHP+ to HP+ in liver than in placenta. This seems to indicate important contributions of CYP1A1 and CYP3A7 as compared to CYP1A2 and CYP3A4, respectively, because furafylline and ketokonazole are stronger inhibitors of CYP1A2 and CYP3A4 than CYP1A1 and CYP3A7, respectively. Interestingly, α-naphathoflavone enhanced the metabolic activity in liver microsomes due to its activator effect on CYP3A4. On the other hand, α-naphathoflavone partially inhibited the activity in placenta microsomes, indicating a role played by CYP1A1 or CYP1A2 in the oxidation of RHP+ in placenta. Conclusions. These data indicate that CYP1A1 plays an important role in the oxidation of RHP+ to HP+ in placenta from smokers. CYP3A7 and CYP3A4 could also play important roles in the metabolism of RHP+ in placenta microsomes. This article is open to POST-PUBLICATION REVIEW. Registered readers (see “For Readers”) may comment by clicking on ABSTRACT on the issue’s contents page.