Chlorpheniramine attenuates histamine-mediated aquaporin 5 downregulation in human nasal epithelial cells via suppression of NF-κB activation.

Background: Aquaporin 5 (AQP5) is most likely the primary water channel in the human nasal mucosa and acts as a key tight junction protein. The signaling cascades responsible for AQP5 regulation are still works in progress. Objective: This study sought to determine the effects of histamine and chlorpheniramine on AQP5 expression in human nasal epithelial cells (HNEpC) and to detect the signaling cascades responsible for these effects. Methods: HNEpC were cultured with four concentrations of histamine or chlorpheniramine in vitro. The sub-cellular distribution of AQP5 was explored using immunocytochemistry. The pharmacologic effects of histamine and chlorpheniramine on the expression of the phosphorylation of cyclic adenosine monophosphate-responsive element binding protein (p-CREB), the AQP5 and the NF-κB protein were examined using Western blotting. Results: AQP5 was found to be located in cell membrane and cytoplasm and present in every group without significant difference. Histamine inhibits the expression of AQP5 and p-CREB in HNEpC, while chlorpheniramine dose-dependently increases these protein levels with statistical significance. HNEpC treated with histamine and chlorpheniramine in turn showed the same trends as those intervened separately with these two drugs. Moreover, chlorpheniramine had the ability to reverse the inhibitory effect of histamine. Western blotting analysis revealed that after incubation with 10-4 M histamine, NF-κB protein was significantly heightened by 165% compared with the untreated control group. Again, such increase can be significantly reversed after chlorpheniramine treatment. Conclusions: The current study demonstrated that histamine inhibits CREB phosphorylation in HNEpC, which results in decreased AQP5 expression via activation of NF-κB pathway. Chlorpheniramine attenuates the inhibitory effect of histamine in p-CREB/AQP5 expression via suppression of NF-κB signal cascades. This observation could provide additional insight into the anti-inflammatory effects of H1-antihistamines that contribute to maintain airway surface liquid and mucosal defense.

Dexamethasone attenuates methacholine-mediated aquaporin 5 downregulation in human nasal epithelial cells via suppression of NF-κB activation.

BACKGROUND: Cholinergic stimulation plays a major role in inflammatory airway diseases. However, its role in airway surface liquid homeostasis and aquaporin 5 (AQP5) regulation remains unclear. In this study we sought to determine the effects of methacholine and dexamethasone on AQP5 expression in human nasal epithelial cells (HNEpC). METHODS: HNEpC were cultured with methacholine or dexamethasone at 4 concentrations in vitro. The subcellular distribution of AQP5 was explored using immunocytochemistry. The pharmacologic effects of methacholine and dexamethasone on the expression of the phosphorylation of cyclic adenosine monophosphate-responsive element binding protein (p-CREB), AQP5, and nuclear factor-kappaB (NF-κB) were examined using Western blotting. RESULTS: AQP5 was found to be located in cell membrane and cytoplasm and present in every group without a statistically significant difference. Methacholine inhibited expression of AQP5 and p-CREB in HNEpC, whereas dexamethasone increased these protein levels dose-dependently in a statistically significant manner. In turn, HNEpC treated with methacholine and dexamethasone showed the same trends as those intervened separately with these 2 drugs. Moreover, dexamethasone had the ability to reverse the inhibitory effect of methacholine. Western blotting revealed that, after incubation with 10-4 mol/L methacholine, NF-κB increased significantly, by 186.67%, compared with the untreated control group. Again, such an increase could be significantly reversed after dexamethasone treatment. CONCLUSION: NF-κB activation is important for inhibition of p-CREB/AQP5 expression after methacholine intervention, and dexamethasone adjusts it to the opposite side. This observation could provide additional insight into the anti-inflammatory effects of glucocorticoids that contribute to maintaining airway surface liquid and mucosal defense.