Role of ATP in the ROS-mediated laryngeal airway hyperreactivity induced by laryngeal acid-pepsin insult in anesthetized rats

Abstract

The pathogenetic mechanisms of laryngeal airway hyperreactivity (LAH) in patients with extraesophageal reflux are unclear. We recently reported that a laryngeal acid-pepsin insult produces LAH that is mediated through sensitization of the capsaicin-sensitive laryngeal afferent fibers by reactive oxygen species (ROS) in rats. Since ROS may promote the release of ATP from cells, we hypothesized that activation of P2X purinoceptors by ATP subsequent to an increase in ROS induces LAH in an inflamed larynx that has been insulted by acid-pepsin or H(2)O(2) (a major type of ROS). The larynxes of 208 anesthetized rats were functionally isolated while the animals breathed spontaneously. Ammonia vapor was delivered into the larynx to measure laryngeal reflex reactivity. Laryngeal insult with acid-pepsin or H(2)O(2) produced LAH with similar characteristics. The H(2)O(2)-induced LAH was prevented by laryngeal pretreatment with dimethylthiourea (a hydroxyl radical scavenger), suggesting a critical role for ROS. The LAH induced by both insults were completely prevented by ATP scavengers (a combination of apyrase and adenosine deaminase) or a P2X receptor antagonist (iso-pyridoxalphosphate-6-azophenyl-2',5'-disulfonate). Laryngeal application of a P2X receptor agonist (alpha,beta-methylene-ATP) also produced LAH. An insult with either acid-pepsin or H(2)O(2) similarly promoted an increase in the levels of ATP, lipid peroxidation, and inflammation in the larynx. Our findings suggest that laryngeal insult with acid-pepsin or H(2)O(2) induces inflammation and produces excess ROS in the rat's larynx. The latter may in turn promote the release of ATP to activate P2X receptors, resulting in sensitization of capsaicin-sensitive laryngeal afferent fibers and LAH.

Sensitization by Pulmonary Reactive Oxygen Species of Rat Vagal Lung C-Fibers: The Roles of the TRPV1, TRPA1, and P2X Receptors

“…Shen et al [14] reported that acute intermittent hypoxia augmented the afferent and reflex responses to stimulants of VLCFs in rats. Tsai et al [15], [16] demonstrated that laryngeal acid-pepsin insult augmented the reflex responses to stimulants of the superior laryngeal C-fibers in rats. The exaggerated reflex responses observed in these studies can be prevented by pretreatment with antioxidants, indicating the possible involvement of ROS in the sensitization of airway C-fibers and the development of airway hypersensitivity.…”

“…Additionally, studies investigating the responses of VLCFs to oxidants have suggested that ROS derived from the oxidants may activate these three types of receptors [18], [24]–[27]. Importantly, it has been proposed that these three types of pharmacological receptors have roles in the development of the airway hypersensitivity that is mediated by airway C-fibers [1], [2], [14], [15], [28], [29]. Taken together, these lines of evidence lend support to the possibility that the TRPV1, TRPA1, and P2X receptors are likely to play contributory roles in ROS-induced VLCF-mediated airway hypersensitivity.…”

Extracellular ATP Exerts Opposite Effects on Activated and Regulatory CD4+ T Cells via Purinergic P2 Receptor Activation

“…Under pathologic conditions, a large amount of ATP is released by dying cells upon tissue injury, inflammatory reactions, hyperreactivity, and tumor cell growth (5,6). Purinergic signaling has been shown to play a pivotal role in allergen-driven lung inflammation (7,8), in inducing laryngeal AHR (9), in T cell-mediated inflammation in experimental models of type 1 diabetes and inflammatory bowel disease (4), in rheumatoid arthritis and multiple sclerosis (10), and in graft-versus-host disease (11). It has been proposed that extracellular ATP, via activation of purinergic P2 receptors (P2Rs), is an important regulator of inflammatory and immune response (12,13) by modulating B cells (14), monocytes (MO)/macrophages (15), eosinophils (16), and dendritic cells (DCs) (17,18).…”

Hypersensitivity of lung vagal C fibers induced by acute intermittent hypoxia in rats: role of reactive oxygen species and TRPA1

“…ROS not only sensitize the carotid sinus nerves but also the capsaicin-sensitive afferent fibers. Recent studies demonstrated that laryngeal acidpepsin insult can evoke laryngeal airway hyperreactivity through sensitization of the capsaicin-sensitive laryngeal afferent fibers by ROS (54,55). This concept is supported by the present finding that both AIH-enhanced reflex apnea and LVCF sensitivity to capsaicin and ␣,␤-methylene-ATP were significantly prevented by dimethylthiourea (a hydroxyl radical scavenger) or N-acetyl-L-cysteine (an antioxidant), so ROS may be a causative factor in the development of afferent hypersensitivity.…”