Brain P450 Epoxygenase Activity is Required for the Antinociceptive Effects of Improgan, a Non-Opioid Analgesic

The search for the mechanism of action of improgan (a non-opioid analgesic) led to the recent discovery of CC12, a compound which blocks improgan antinociception. Since CC12 is a cytochrome P450 inhibitor, and brain P450 mechanisms were recently shown to be required in opioid analgesic signaling, pharmacological and transgenic studies were performed in rodents to test the hypothesis that improgan antinociception requires brain P450 epoxygenase activity. Intracerebroventricular (icv) administration of the P450 inhibitors miconazole and fluconazole, and the arachidonic acid (AA) epoxygenase inhibitor N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide (MS-PPOH) potently inhibited improgan antinociception in rats at doses which were inactive alone. MW06-25, a new P450 inhibitor which combines chemical features of CC12 and miconazole, also potently blocked improgan antinociception. Although miconazole and CC12 were weakly active at opioid and histamine H 3 receptors, MW06-25 showed no activity at these sites, yet retained potent P450-inhibiting properties. The P450 hypothesis was also tested in Cpr low mice, a viable knock-in model with dramatically reduced brain P450 activity. Improgan (145 nmol, icv) antinociception was reduced by 37-59% in Cpr low mice, as compared with control mice. Moreover, CC12 pretreatment (200 nmol, icv) abolished improgan action (70-91%) in control mice, but had no significant effect in Cpr low mice. Thus, improgan’s activation of bulbospinal non-opioid analgesic circuits requires brain P450 epoxygenase activity. A model is proposed in which 1) improgan activates an unknown receptor to trigger downstream P450 activity, and 2) brainstem epoxygenase activity is a point of convergence for opioid and non-opioid analgesic signaling.