Synergistic Effect of Heat and Hydrogen Peroxide on Airway Reflex: Role of Pulmonary Sensory C Neurons

Airway hypersensitivity, characterized by exaggerated sensory and reflex responses to various stimuli, is a common pathophysiological feature in patients with airway inflammatory diseases (e.g., asthma, bronchitis). TRPV1 and TRPA1 receptors, located on the sensory nerve endings of pulmonary C fibers, play a vital role in the pathogenesis of airway hypersensitivity. By using synthetic agonists, our recent study reported that a synergistic effect of simultaneous TRPV1 and TRPA1 activations on pulmonary C neurons. However, whether the synergistic effect is still existed while the receptors are activated by pathophysiological activators is still unknown. During pulmonary inflammation, local tissue hyperthermia and oxidant stress are two common signs, which have suggested to contribute independently to pathogenesis of airway hypersensitivity via activation of TRPV1 and TRPA1 receptors, respectively. This proposal aims to investigate whether lung hyperthermia and oxidant stress works synergistically in exaggeration of airway reflexes. The proposed study of the 1st-year aims to determine the synergistic effect of heat and oxidant on stimulation of pulmonary C neurons and airway reflex. The 2nd-year aims to study the cellular signal transduction pathways involved in this synergistic effect on pulmonary C neurons. Because of the high permeability to Ca2+ for TRPV1 and TRPA1 receptors, the possible signaling pathways investigated will include Ca2+ and Ca2+-sensitive signaling pathways (cAMP/PKA). Airway exposure to heat and oxidant are conducted by inhalation of humidified hot air and hydrogen peroxide (H2O2), respectively. Synergistic effect is determined by exaggerated responses evoked by heat and oxidant applied in combination than individually. Airway reflex will be determined by breathing pattern changes after airway exposure to heat or H2O2 in anesthetized, spontaneously breathing rats. Neuronal responses will be determined using perforated whole-cell patch-clamp in rat cultured primary pulmonary sensory C neurons. Our preliminary results reveal that reflexly breathing changes triggered by heat and H2O2 applied in combination was greatly larger than that applied individually in anesthetized rats, (2) this synergistic effect was also existed in isolated pulmonary C-neurons, and (3) the synergistic effect in isolated pulmonary C-neurons was nearly abolished by pretreatment of HC-030031 (a TRPA1 antagonist) or Ca2+-free extracellular solution. Thus, these results suggest the feasibility of this proposed study. The findings of this proposal may provide a new insight into potential therapies of airway hypersensitive diseases.