Lack of increased oxidative stress in catechol-O-methyltransferase (COMT)-deficient mice

Abstract

The effect of catechol-O-methyltransferase (COMT) deficiency on methamphetamine-induced hydroxyl radical production in the brain was assessed by the salicylate trapping method. Methamphetamine-induced hyperthermia was also studied. Furthermore, the effect of COMT deficiency on the activities of glutathione S-transferase, quinone reductase and liver mono-oxygenases was assessed with and without l-dopa challenge. Finally, two alternative pathways of l-dopa metabolism were evaluated. Methamphetamine increased 2,3-dihydroxybenzoic acid levels only slightly (n.s.) at the lowest dose level (2.5 mg/kg x 4 i.p.). This was accompanied by a simultaneous increase in salicylate levels so that the 2,3-dihydroxybenzoic acid/salicylate ratio decreased correspondingly. Most importantly, no COMT genotype-dependent changes were observed. However, hyperthermia was induced even at the lowest methamphetamine dose, the COMT-deficient mice being most sensitive. COMT deficiency did not significantly change the activities of liver glutathione S-transferase, quinone reductase or 7-ethoxyresorufin and 7-pentoxyresorufin O-dealkylation. In COMT-deficient female mice, l-dopa (30-80 mg/kg b.i.d. for 2 days) did not induce any significant changes in liver or brain glutathione S-transferase and quinone reductase activity or liver 7-ethoxyresorufin O-deethylation activity. The levels of l-dopa conjugates in urine were also negligible in COMT-deficient mice. Skin tyrosinase activity was increased in 7- to 8-day-old hairless COMT-deficient pups. The present results suggest that despite the increased hyperthermic response, COMT deficiency does not increase methamphetamine-induced hydroxyl radical production or change significantly the activity of certain enzymes involved in defense against reactive oxygen species. In conclusion, we found no evidence of increased oxidative stress in the liver or brain of adult mice lacking COMT activity.