Human bronchial epithelial cells express an active and inducible biosynthetic pathway for leukotrienes B4 and C4

Background Human bronchial epithelial cells synthesize cyclooxygenase and 15lipoxygenase products, but the 5-lipoxygenase (5-LO) pathway that generates the "ukotriene (LT) family of bronchoconstrictor and pro-inflammatory mediators is thought to be restricted to leucocytes. Objective We hypothesized that human bronchial epithelial cells (HBECs) express a complete and active 5-LO pathway for the synthesis of LTB4 and LTC4, either constitutively or after stimulation. Methods Flow cytometry, RT-PCR, Western blotting, enzyme immunoassays and reverse-phase high-performance liquid chromatography were used to investigate constitutive and stimulated expression of 5-LO pathway enzymes and the synthesis of LTs B-4 and C-4 in primary HBECs and in the 16-HBE 14o(-) cell line. Results Constitutive mRNA and protein expression for 5-LO, 5-LO-activating protein (FLAP), LTA(4) hydrolase and LTC4 synthase were demonstrated in primary HBECs and in the 16-HBE 14o(-) cell line. In 16-HBE 14o(-) cells, treatment with calcium ionophore A23187, bradykinin or LPS up-regulated the expression of these enzymes. The up-regulation of 5-LO was blocked by the anti-inflammatory glucocorticoid. dexamethasone. Human bronchial epithelial cells were shown to generate bioactive Us, with primary HBECs generating 11-fold more LTC4 and five-fold more LTB4 than 16-HBE 14o(-) cells. LT production was enhanced by ionophore treatment and blocked by the FLAP inhibitor MK-886. Conclusions Expression of an active and inducible 5-LO pathway in HBEC suggests that damaged or inflamed bronchial epithelium may synthesize Us that contribute directly to bronchoconstriction and leucocytosis in airway inflammation.