Nitrooleic Acid, an Endogenous Product of Nitrative Stress, Activates Nociceptive Sensory Nerves via the Direct Activation of TRPA1

Abstract

Transient Receptor Potential A1 (TRPA1) is a nonselective cation channel, preferentially expressed on a subset of nociceptive sensory neurons, that is activated by a variety of reactive irritants via the covalent modification of cysteine residues. Excessive nitric oxide during inflammation (nitrative stress), leads to the nitration of phospholipids, resulting in the formation of highly reactive cysteine modifying agents, such as nitrooleic acid (9-OA-NO 2 ). Using calcium imaging and electrophysiology, we have shown that 9-OA-NO 2 activates human TRPA1 channels (EC 50 , 1 M), whereas oleic acid had no effect on TRPA1. 9-OA-NO 2 failed to activate TRPA1 in which the cysteines at positions 619, 639, and 663 and the lysine at 708 had been mutated. TRPA1 activation by 9-OA-NO 2 was not inhibited by the NO scavenger carboxy-PTIO. 9-OA-NO 2 had no effect on another nociceptive-specific ion channel, TRPV1. 9-OA-NO 2 activated a subset of mouse vagal and trigeminal sensory neurons, which also responded to the TRPA1 agonist allyl isothiocyanate and the TRPV1 agonist capsaicin. 9-OA-NO 2 failed to activate neurons derived from TRPA1(Ϫ/Ϫ) mice. The action of 9-OA-NO 2 at nociceptive nerve terminals was investigated using an ex vivo extracellular recording preparation of individual bronchopulmonary C fibers in the mouse. 9-OA-NO 2 evoked robust action potential discharge from capsaicin-sensitive fibers with slow conduction velocities (0.4 -0.7 m/s), which was inhibited by the TRPA1 antagonist AP-18. These data demonstrate that nitrooleic acid, a product of nitrative stress, can induce substantial nociceptive nerve activation through the selective and direct activation of TRPA1 channels.Oxidative stress and nitrative stress have been implicated as contributing to acute and chronic inflammation (Radi, 2004;Szabó et al., 2007;Valko et al., 2007). Nitric oxide (NO) is an endogenous mediator with multiple cellular functions that is produced by many cell types including vascular endothelium, neutrophils, fibroblasts, and nerves (Bian and Murad, 2003). NO, generated from L-arginine by NO synthases (NOS), reacts with the reactive oxygen species (ROS) superoxide-which is formed through multiple pathways in inflammation, including NADPH oxidase, xanthine oxidase, and perverted mitochondrial function-to produce the reactive nitrogen species (RNS), peroxynitrite (ONOOϪ), and nitrogen dioxide (*NO 2 ). RNS are potent inflammatory molecules that can react with lipids, proteins, and DNA (Szabó et al., 2007). Within membranes, where the hydrophobic environment maximizes RNS production (Möller et al., 2007), RNS react with unsaturated fatty acids (e.g., oleic acid), causing the addition of an NO 2 group (nitration) Jain et al., 2008;Trostchansky and Rubbo, 2008). Nitrated fatty acids (e.g., nitrooleic acid) are highly reactive electrophilic compounds that can modulate a variety of cellular targets, including thiol residues and peroxisome proliferator-activated receptor ␥ Trostchansky and Rubbo, 2008 ABBREVIATIONS: NOS, nitric-oxide ...

Nitro-Oleic Acid Inhibits Firing and Activates TRPV1- and TRPA1-Mediated Inward Currents in Dorsal Root Ganglion Neurons from Adult Male Rats

“…As reported previously (Taylor-Clark et al, 2009), the effect of NO donors in DRG neurons is small compared with that seen in response to OA-NO 2 . In addition, in their experiments pretreatment with the NO scavenger cPTIO did not prevent the OA-NO 2 -evoked Ca 2ϩ transients.…”

Novel Therapeutic Strategy to Prevent Chemotherapy-Induced Persistent Sensory Neuropathy By TRPA1 Blockade

“…TRPA1 has been identified as a sensor of oxidative stress, in as much as it is activated by an unprecedented series of ROS, RNS, or RCS (16,45,46). Thus, we hypothesized that oxidative stress by-products, generated by bortezomib, may target the TRPA1 channel in sensory nerve terminals.…”

Sensory and Signaling Mechanisms of Bradykinin, Eicosanoids, Platelet-Activating Factor, and Nitric Oxide in Peripheral Nociceptors

“…Moreover, applied superoxide alone induced hyperalgesia that was blocked by NOS inhibition, suggesting that endogenous NO was required to form hyperalgesic peroxynitrite. Nitrooleic acid, a highly reactive cysteine-modifying agent formed through nitration of oleic acid by peroxynitrite and nitrogen dioxide, was also shown to activate TRPA1, but not TRPV1, in transfected host cells via covalent modification of cysteine residues (713). Nitrooleic acid caused an elevation of intracellular Ca 2ϩ in cultured trigeminal and vagal sensory neurons, and induced action potential discharges from vagal pulmonary C-fibers in an ex vivo mouse lung preparation, with both responses being mediated by TRPA1.…”