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The histamine H 1 receptor (H 1 R) is a G protein-coupled receptor (GPCR) and represents a main target in the treatment of allergic reactions as well as inflammatory reactions and depressions. Although the overall effect of antagonists on H 1 function has been extensively investigated, rather little is known about the potential modulatory effect of ions or sequence variants on antagonist binding. We investigated the dynamics of a phosphate ion present in the crystal structure and of a sodium ion, for which we determined the position in the allosteric pocket by metadynamics simulations. Both types of ions exhibit significant dynamics within their binding site; however, some key contacts remain stable over the simulation time, which might be exploited to develop more potent drugs targeting these sites. The dynamics of the ions is almost unaffected by the presence or absence of doxepin, as also reflected in their small effect (less than 1 kcal·mol -1 ) on doxepin binding affinity. We also examined the effect of four H 1 R sequence variants observed in the human population on doxepin binding. These variants cause a reduction in doxepin affinity of up to 2.5 kcal·mol -1 , indicating that personalized medical treatments that take into account individual mutation patterns could increase precision in the dosage of GPCR-targeting drugs.

Binding of histamine to the G-protein coupled histamine H 1 receptor plays an important role in the context of allergic reactions; however, no crystal structure of the resulting complex is available yet. To deduce the histamine binding site, we performed unbiased molecular dynamics (MD) simulations on a microsecond time scale, which allowed to monitor one binding event, in which particularly the residues of the extracellular loop 2 were involved in the initial recognition process. The final histamine binding pose in the orthosteric pocket is characterized by interactions with Asp107 3.32 , Tyr108 3.33 , Thr194 5.43 , Asn198 5.46 , Trp428 6.48 , Tyr431 6.51 , Phe432 6.52 , and Phe435 6.55 , which is in agreement with existing mutational data. The conformational stability of the obtained complex structure was subsequently confirmed in 2 μs equilibrium MD simulations, and a metadynamics simulation proved that the detected binding site represents an energy minimum. A complementary investigation of a D107A mutant, which has experimentally been shown to abolish ligand binding, revealed that this exchange results in a significantly weaker interaction and enhanced ligand dynamics. This finding underlines the importance of the electrostatic interaction between the histamine ammonium group and the side chain of Asp107 3.32 for histamine binding.

Histamine H4 receptor (H4R), a member of histamine receptor family, which belongs to class A of G-protein coupled receptors (GPCRs), has been reported to play a critical role in histamine-induced chemotaxis in mast cells and eosinophils. Recently, the crystal structure of human histamine H1 receptor (H1R) was reported, which facilitates structure-based drug discovery of histamine receptor significantly. In the current work, the homology models of H4R and H3R are first constructed based on the crystal structure of H1R. Clobenpropit is then docked into the binding pocket of H4R and two different binding modes can be identified. In order to select a reasonable binding mode, several other ligands including agonists and antagonists are docked into H4R, and the results reveal that all ligands share one preferable binding mode: the protonated NH tightly interacts with Asp(3.32) and the imidazole NH interacts with Glu(5.46). By comparing H3R and H4R, we find that Glu(5.20) and Thr(6.55) in H4R involve in the selectivity of H4R. Then, we perform molecular dynamics (MD) simulations for H4R in complex with its compounds. MD results indicate that the preferable docking mode is more stable. Finally, we dock agonist histamine into H1R and H4R, and then perform 20ns MD simulations for the complexes. H1R or H4R bound with histamine show strong conformational changes from TM5, TM6 and TM7, outward movement of intracellular part of TM6, and conformational change of Tyr(7.53), which is consistent with the recent crystal structures of active GPCRs. Our results reveal the mechanism of selectivity and activation for H4R, which is important for developing selective antagonists and agonists for H4R., (Copyright © 2012 Elsevier Inc. All rights reserved.)

The biogenic amine histamine is an important pharmacological mediator involved in pathophysiological processes such as allergies and inflammations. Histamine H(1) receptor (H(1)R) antagonists are very effective drugs alleviating the symptoms of allergic reactions. Here we show the crystal structure of the H(1)R complex with doxepin, a first-generation H(1)R antagonist. Doxepin sits deep in the ligand-binding pocket and directly interacts with Trp 428(6.48), a highly conserved key residue in G-protein-coupled-receptor activation. This well-conserved pocket with mostly hydrophobic nature contributes to the low selectivity of the first-generation compounds. The pocket is associated with an anion-binding region occupied by a phosphate ion. Docking of various second-generation H(1)R antagonists reveals that the unique carboxyl group present in this class of compounds interacts with Lys 191(5.39) and/or Lys 179(ECL2), both of which form part of the anion-binding region. This region is not conserved in other aminergic receptors, demonstrating how minor differences in receptors lead to pronounced selectivity differences with small molecules. Our study sheds light on the molecular basis of H(1)R antagonist specificity against H(1)R., (©2011 Macmillan Publishers Limited. All rights reserved)

Anhydrous copper(II) acetate was applied to spectrophotometric determination of amitriptilline, doxepin and lignocaine in acetone solutions. The developed method was employed for determining these substances in pharmaceutical preparations. The obtained results has indicated both high precision and accuracy of the method.

A series of N-[3-(5H-dibenzo[a, d]cyclohepten-5-ylidene)propyl]-N-methylamino- (6a) and N-[3-(6H-dibenz-[b, e]oxepin-11-ylidene)propyl]-N-methylamino-alkanoic acid derivatives (6b) and related compounds (6c-f) were synthesized and examined for pharmacological activities in vitro, i.e., inhibitory effect on monoamine [noradrenaline (NA) and 5-hydroxytryptamine (5-HT)] uptake, inhibitory effect on 5-HT-, histamine-, acetylcholine- and NA-induced contraction, and binding affinity for alpha 2-adrenoceptor and dopamine D2-receptor. In vitro tests indicated that zwitter-ionization was capable of maintaining H1-antihistaminic activity while greatly reducing other pharmacological activities. Further, 6a-f showed much stronger inhibitory effects on compound 48/80-induced lethality in rats than did the corresponding N,N-dimethylamines (2a-f). 3-[N-[3-(6H-Dibenz[b, e]oxepin-11-ylidene)propyl]-N-methylamino]- propionic acid (6b-2), selected as a candidate antiallergic agent of a new type, equally potent in rats and guinea-pigs, exhibited strong inhibitory effects on 48 h homologous passive cutaneous anaphylaxis (PCA) in rats (ED50 = 0.019 mg/kg, p.o.) and on histamine-induced bronchoconstriction in anesthetized guinea-pigs (ED50 = 0.0067 mg/kg, p.o.).