title: Receptor-independent, vacuolar ATPase-mediated cellular uptake of histamine receptor-1 ligands: possible origin of pharmacological distortions and side effects.
abstract: The aims of this study were to investigate whether several histamine receptor agonists and antagonists are subjected to receptor-independent ion trapping into acidic organelles, and whether this sequestration influences their pharmacological or toxicological properties. Vacuolar (V)-ATPase-dependent intracellular sequestration of agonists was recognized as morphological alterations (large fluid-filled vacuoles for betahistine and 1-methylhistamine, granular uptake for fluorescent BODIPY FL histamine) prevented by the specific V-ATPase inhibitor bafilomycin A1 in rabbit vascular smooth muscle cells. Lipophilicity was the major determinant of these cellular effects (order of potency: BODIPY FL histamine>betahistine>1-methylhistamine>histamine) that occurred at high concentrations. This ranking was dissociable from the potency order for H(1) receptor-mediated contraction of the rabbit aorta, a response uninfluenced by bafilomycin. Antihistamines are inherently more lipophilic and caused vacuolization of a proportion of cells at 5-500 microM. Agonist or antagonist-induced vacuoles were of macroautophagic nature (labeled with GFP-conjugated LC3, Rab7 and CD63; detection of LC3 II). Further, the 2 most lipophilic antihistamines tested, astemizole and terfenadine, were potentiated by V-ATPase blockade in the aortic contractility assay (13- and 3.6-fold more potent, respectively, pA(2) scale), suggesting that V-ATPase-mediated cation trapping sequesters these antagonists from the vicinity of H(1) receptors in the therapeutic concentration range. This potentiation did not apply to less lipophilic antagonists (pyrilamine, diphenhydramine). While some agonists and all tested antagonists of the histamine H(1) receptors induce the V-ATPase-dependent vacuolar and autophagic cytopathology, sequestration affects the pharmacology of only the most lipophilic antagonists, the ones prone to off-target arrhythmogenic side effects.
authors.affiliation: Centre de Recherche en Rhumatologie et Immunologie, Centre Hospitalier Universitaire de Québec, Québec QC, Canada G1V 4G2.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Morissette
authors.forename: Robert
authors.initials: R
authors.lastname: Lodge
authors.forename: Johanne
authors.initials: J
authors.lastname: Bouthillier
authors.forename: François
authors.initials: F
authors.lastname: Marceau
mesh_terms: D000818:Animals; D001011:Aorta / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D001692:Biological Transport; D004305:Dose-Response Relationship, Drug; D017442:Histamine Agonists / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000633:toxicity; D006634:Histamine H1 Antagonists / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000633:toxicity; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D018942:Macrolides / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D011817:Rabbits; D011969:Receptors, Histamine H1 / Q000187:drug effects* / Q000378:metabolism; D025262:Vacuolar Proton-Translocating ATPases / Q000187:drug effects / Q000378:metabolism*; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism
chemical_list: D017442:Histamine Agonists; D006634:Histamine H1 Antagonists; D008024:Ligands; D018942:Macrolides; D011969:Receptors, Histamine H1; C040929:bafilomycin A1; D025262:Vacuolar Proton-Translocating ATPases