Histamine H1‐receptor antagonists inhibit nuclear factor‐kappaB and activator protein‐1 activities via H1‐receptor‐dependent and ‐independent mechanisms

Summary Background Histamine H1‐receptor antagonists are used to relieve the symptoms of an immediate allergic reaction. They have additional anti‐inflammatory effects that could result from an inhibition of the transcription factors activator protein‐1 (AP‐1) and nuclear factor‐kappa B (NF‐κB). The implication of the H1‐receptor in these effects is controversial. Diphenhydramine is a first‐generation H1‐receptor antagonist while mizolastine and desloratadine are second‐generation compounds. Mizolastine is also an inhibitor of 5‐lipoxygenase (5‐LO), an enzyme that has been involved in NF‐κB activation. Objective We measured the ability of antihistamines to reverse histamine‐induced smooth muscle contraction, an effect that involves the H1‐receptor. We then investigated whether these drugs affect NF‐κB and AP‐1 activities in A549 lung epithelial cells, and whether this potential regulation involves H1‐receptor and 5‐LO. Methods Muscle tone was measured on tracheal segments of guinea‐pigs. The H1‐receptor was overexpressed by transfection and detected by Western blotting and immunofluorescence microscopy. NF‐κB and AP‐1 activities were assessed by reporter gene assays in cells overexpressing or not overexpressing the H1‐receptor. Production of regulated upon activation, normal T cell expressed andsecreted (RANTES), a chemokine whose expression is induced through NF‐κB, was measured using an immunoassay. Results H1‐receptor antagonists reversed histamine‐induced contraction in a dose‐dependent manner. Induction of AP‐1 and NF‐κB activities by histamine and the down‐regulatory effect of antihistamines required overexpression of the H1‐receptor. In contrast, when tumour necrosis factor‐α and a phorbol ester were used to stimulate NF‐κB and AP‐1 activities, respectively, repression of these activities did not involve the H1‐receptor. Indeed, repression was triggered only by a subset of H1‐receptor antagonists and was not stronger after overexpression of the H1‐receptor. Mizolastine and desloratadine dose‐dependently decreased tumour necrosis factor‐α‐induced production of RANTES. Diphenhydramine, H2‐ and H3‐receptor antagonists as well as selective inhibitors of 5‐LO were ineffective in this assay. Conclusion Repression of NF‐κB and AP‐1 activities by H1‐receptor antagonists involves H1‐receptor‐dependent and ‐independent mechanisms but not 5‐LO.