4-(4-chlorophenyl)-3-methylbut-3-en-2-oxime and Inflammation

Craniofacial muscle pain, such as spontaneous pain and bite-evoked pain, are major symptoms in patients with temporomandibular disorders and infection. However, the underlying mechanisms of muscle pain, especially mechanisms of highly prevalent spontaneous pain, are poorly understood. Recently, we reported that transient receptor potential vanilloid 1 (TRPV1) contributes to spontaneous pain but only marginally contributes to bite-evoked pain during masseter inflammation. Here, we investigated the role of transient receptor potential ankyrin 1 (TRPA1) in spontaneous and bite-evoked pain during masseter inflammation, and dissected the relative contributions of TRPA1 and TRPV1. Masseter inflammation increased mouse grimace scale (MGS) scores and face wiping behaviors. Pharmacological or genetic inhibition of TRPA1 significantly attenuated MGS but not face wiping behaviors. MGS scores were also attenuated by scavenging putative endogenous ligands for TRPV1 or TRPA1. Simultaneous inhibition of TRPA1 by AP18 and TRPV1 by AMG9810 in masseter muscle resulted in robust inhibition of both MGS and face wiping behaviors. Administration of AP18 or AMG9810 to masseter muscle induced conditioned place preference (CPP). The extent of CPP following simultaneous administration of AP18 and AMG9810 was greater than that induced by the individual antagonists. In contrast, inflammation-induced reduction of bite force was not affected by the inhibition of TRPA1 alone or in combination with TRPV1. These results suggest that simultaneous inhibition of TRPV1 and TRPA1 produces additive relief of spontaneous pain, but does not ameliorate bite-evoked pain during masseter inflammation. Our results provide further evidence that distinct mechanisms underlie spontaneous and bite-evoked pain from inflamed masseter muscle.

Topics: Acrylamides; Animals; Behavior, Animal; Bridged Bicyclo Compounds, Heterocyclic; Conditioning, Operant; Inflammation; Masseter Muscle; Mice; Myalgia; Oximes; Pain Measurement; TRPA1 Cation Channel; TRPV Cation Channels

The transient receptor potential ankyrin 1 (TRPA1) channel is activated by a series of by-products of oxidative/nitrative stress, produced under inflammatory conditions or in the case of tissue damage, thus generating inflammatory and neuropathic pain and neurogenic inflammatory responses. These findings have identified TRPA1 as an emerging opportunity for the design and synthesis of selective inhibitors as potential analgesic and antiinflammatory agents. Herein we present the synthesis and functional evaluation of a new series of 7-substituted-1,3-dimethyl-1,5-dihydro-pyrrolo[3,2-d]pyrimidine-2,4-dione derivatives designed as TRPA1 antagonists. A small library of compounds has been built by the introduction of differently substituted N(7)-phenylacetamide or N(7)-[4-(substituted-phenyl)-thiazol-2-yl]-acetamide chains. All the synthesized compounds were assayed to evaluate their ability to block acrolein-mediated activation of native human and rat TRPA1 channels employing a fluorometric calcium imaging assay. Our study led us to the identification of compound 3h which showed considerably improved potency (IC(50)=400nM) against human TRPA1 with regard to some of the most representative antagonists previously reported and integrated in our screening program as reference compounds. In addition, 3h proved to maintain its efficacy toward rTRPA1, which designates it as a possible candidate for future evaluation of in vivo efficacy in rodent animal model of inflammatory and neuropathic pain.

Topics: Analgesics; Animals; Anti-Inflammatory Agents, Non-Steroidal; Calcium Channels; Humans; Inflammation; Male; Nerve Tissue Proteins; Pain; Pyrimidines; Rats; Rats, Sprague-Dawley; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPC Cation Channels