Role of cytochrome P450 enzymes in oxidized linoleic acid metabolite-mediated inflammatory pain

Abstract

Our group has recently demonstrated that oxidized linoleic acid metabolites (OLAMs) are released from injured tissues and activate TRPV1; a voltage gated ion channel that plays a pivotal role in inflammatory heat hyperalgesia and thermoregulation. However, the mechanism by which linoleic acid is converted to the OLAMs is unknown. Our recent results show the involvement of cytochrome P450 (CYPs) enzymes in the formation of these OLAMs. Importantly, treatment of animals with antibodies against the OLAMs or drugs that inhibit CYPs at peripheral sites results in reversal of thermal allodynia in a rat model of inflammatory pain. To further evaluate possible role of CYPs and/or LOX in the activation of sensory neurons, linoleic acid (LA, 1mM) was applied on to cultured sensory neurons to measure calcium influx as a measure of neuronal activation. LA application produced an I-RTX (100 nM) reversible increase in [Ca]i, indicating the formation of endogenous TRPV1 agonists under these conditions. Pretreatment with the CYP inhibitors: nordihydroguaiaretic acid, ketoconazole, diphenyliodonium and carbon monoxide all blocked LA-evoked increases in [Ca]i, suggesting that OLAM synthesis (from LA) is regulated via the CYP pathway. In addition, injection of linoleic acid caused significant spontaneous nocifensive behavior in inflamed rat hind paws but not in the uninflamed paws. Moreover, analysis of CYP expression in normal vs. inflamed rat tissue shows increased expression of certain CYP isoforms in the inflamed tissue. Taken, together, these results demonstrate that OLAMs may comprise a new family of physiologically relevant endogenous TRPV1 agonists during inflammatory pain and identifying the OLAM system (OLAMs and the enzymes that produce OLAMs) as potential new targets for analgesic drug development.