P-glycoprotein promotes epithelial T helper 2-associated cytokine secretion in chronic sinusitis with nasal polyps

Background Sinonasal epithelial cells are recognized as drivers of inflammation in chronic sinusitis with nasal polyps (CRSwNP) through secretion of T helper 2 (Th2)-promoting cytokines. P-glycoprotein (P-gp) is overexpressed in nasal polyps and modulates epithelial cytokine secretion in healthy mucosa. The objective of this study is to determine whether P-gp overactivity promotes Th2-associated cytokine secretion in CRSwNP. Methods Polyp explants (n = 4) and primary epithelial cell cultures (n = 5) were cultivated from patients with CRSwNP. Explant P-gp activity was determined using a calcein assay. In culture, P-gp was quantified by enzyme-linked immunosorbent assay (ELISA) and sensitivity to PSC-833 inhibition was determined using a calcein assay. Lipopolysaccharide (LPS)-stimulated cytokine secretion of interleukin 6 (IL-6), IL-8, IL-25, and granulocyte macrophage colony stimulating factor (GM-CSF) were quantified by ELISA and compared to secretion following P-gp inhibition. Differences in P-gp expression and cytokine secretion were compared using a Mann-Whitney U test. Secretion was correlated with P-gp expression using a Pearson correlation coefficient. Results Calcein retention is increased in P-gp inhibited vs uninhibited polyp explants (mean +/- standard deviation [SD]; 5.17 +/- 1.76 vs 2.55 +/- 0.62; p < 0.05) but not in controls, indicating increased nasal polyp P-gp activity. P-gp is sensitive to dose-dependent P-gp inhibition with PSC-833 in vitro. LPS-stimulated secretion of normalized GM-CSF (45.21 +/- 41.39) and IL-6 (63.16 +/- 36.37) were significantly reduced following P-gp inhibition (8.47 +/- 3.28; p < 0.01, and 39.94 +/- 31.07; p < 0.05; respectively) and secretion was highly correlated with P-gp expression(r = 0.824, p < 0.05, and r = 0.833, p < 0.05; respectively). Conclusion P-gp overactivity promotes Th2-associated epithelial cytokine secretion in nasal polyps, suggesting a novel mechanism for maintaining chronic inflammation in CRSwNP.