Background & Aims:Intestinal mast cell infiltration may participate to abdominal pain in irritable bowel syndrome (IBS) patients. However, the underlying mechanisms remain unknown. We assessed the effect of mast cell mediators released from the colonic mucosa of IBS patients on the activation of rat sensory neurons in vitro. Methods: Colonic mast cell infiltration and mediator release were assessed with quantitative immunoflorescence and immunoenzymatic assays. The effect of mucosal mediators was tested on mesenteric sensory nerve firing and Ca 2؉ mobilization in dorsal root ganglia in rats. Results: Mediators from IBS patients, but not controls, markedly enhanced the firing of mesenteric nerves (14.7 ؎ 3.2 imp/sec vs 2.8 ؎ 1.5 imp/sec; P < .05) and stimulated mobilization of Ca 2؉ in dorsal root ganglia neurons (29% ؎ 4% vs 11% ؎ 4%; P < .05). On average, 64% of dorsal root ganglia responsive to mediators were capsaicin-sensitive, known to mediate nociception. Histamine and tryptase were mainly localized to mucosal mast cells. IBS-dependent nerve firing and Ca 2؉ mobilization were correlated with the area of the colonic lamina propria occupied by mast cells (r ‫؍‬ 0.74; P < .01, and r ‫؍‬ 0.78; P < .01, respectively). IBS-dependent excitation of dorsal root ganglia was inhibited by histamine H 1 receptor blockade and serine protease inactivation (inhibition of 51.7%; P < .05 and 74.5%; P < .05; respectively). Conclusions: Mucosal mast cell mediators from IBS patients excite rat nociceptive visceral sensory nerves. These results provide new insights into the mechanism underlying visceral hypersensitivity in IBS.

TRPA1 is an excitatory ion channel expressed by a subpopulation of primary afferent somatosensory neurons that contain substance P and calcitonin gene-related peptide. Environmental irritants such as mustard oil, allicin, and acrolein activate TRPA1, causing acute pain, neuropeptide release, and neurogenic inflammation. Genetic studies indicate that TRPA1 is also activated downstream of one or more proalgesic agents that stimulate phospholipase C signaling pathways, thereby implicating this channel in peripheral mechanisms controlling pain hypersensitivity. However, it is not known whether tissue injury also produces endogenous proalgesic factors that activate TRPA1 directly to augment inflammatory pain. Here, we report that recombinant or native TRPA1 channels are activated by 4-hydroxy-2-nonenal (HNE), an endogenous ␣,␤-unsaturated aldehyde that is produced when reactive oxygen species peroxidate membrane phospholipids in response to tissue injury, inflammation, and oxidative stress. HNE provokes release of substance P and calcitonin gene-related peptide from central (spinal cord) and peripheral (esophagus) nerve endings, resulting in neurogenic plasma protein extravasation in peripheral tissues. Moreover, injection of HNE into the rodent hind paw elicits pain-related behaviors that are inhibited by TRPA1 antagonists and absent in animals lacking functional TRPA1 channels. These findings demonstrate that HNE activates TRPA1 on nociceptive neurons to promote acute pain, neuropeptide release, and neurogenic inflammation. Our results also provide a mechanism-based rationale for developing novel analgesic or anti-inflammatory agents that target HNE production or TRPA1 activation.oxidative stress ͉ sensory signaling ͉ TRP channel ͉ nociception

Cigarette smoke (CS) inhalation causes an early inflammatory response in rodent airways by stimulating capsaicin-sensitive sensory neurons that express transient receptor potential cation channel, subfamily V, member 1 (TRPV1) through an unknown mechanism that does not involve TRPV1. We hypothesized that 2 α,β-unsaturated aldehydes present in CS, crotonaldehyde and acrolein, induce neurogenic inflammation by stimulating TRPA1, an excitatory ion channel coexpressed with TRPV1 on capsaicin-sensitive nociceptors. We found that CS aqueous extract (CSE), crotonaldehyde, and acrolein mobilized Ca 2+ in cultured guinea pig jugular ganglia neurons and promoted contraction of isolated guinea pig bronchi. These responses were abolished by a TRPA1-selective antagonist and by the aldehyde scavenger glutathione but not by the TRPV1 antagonist capsazepine or by ROS scavengers. Treatment with CSE or aldehydes increased Ca 2+ influx in TRPA1-transfected cells, but not in control HEK293 cells, and promoted neuropeptide release from isolated guinea pig airway tissue. Furthermore, the effect of CSE and aldehydes on Ca 2+ influx in dorsal root ganglion neurons was abolished in TRPA1-deficient mice. These data identify α,β-unsaturated aldehydes as the main causative agents in CS that via TRPA1 stimulation mediate airway neurogenic inflammation and suggest a role for TRPA1 in the pathogenesis of CS-induced diseases.

The vanilloid receptor-1 (VR1) is a heat-gated ion channel that is responsible for the burning sensation elicited by capsaicin. A similar sensation is reported by patients with esophagitis when they consume alcoholic beverages or are administered alcohol by injection as a medical treatment. We report here that ethanol activates primary sensory neurons, resulting in neuropeptide release or plasma extravasation in the esophagus, spinal cord or skin. Sensory neurons from trigeminal or dorsal root ganglia as well as VR1-expressing HEK293 cells responded to ethanol in a concentration-dependent and capsazepine-sensitive fashion. Ethanol potentiated the response of VR1 to capsaicin, protons and heat and lowered the threshold for heat activation of VR1 from approximately 42 degrees C to approximately 34 degrees C. This provides a likely mechanistic explanation for the ethanol-induced sensory responses that occur at body temperature and for the sensitivity of inflamed tissues to ethanol, such as might be found in esophagitis, neuralgia or wounds.

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