PubMed · 13455723
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M ROCHA E SILVA. 1957. Histamine.. https://pubmed.ncbi.nlm.nih.gov/13455723/
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Infrared and Raman spectroscopy in H(2)O and D(2)O and quantum Density Functional calculations were used to determine the structure of histamine free-base in aqueous solution. A quantum mechanical study of the tautomeric equilibrium of histamine free-base in solution was performed at the 6-311G level. Electronic correlation energies were included by using the hybrid functional B3LYP. The solvent was simulated as a continuum characterized by a dielectric constant, and the quantum system (solute) was placed in an ellipsoidal cavity. Solute-solvent electrostatic interaction was calculated by means a multipolar moment expansion introduced in the Hamiltonian. Four relevant histamine conformations were optimized by allowing all the geometrical parameters to vary independently, which involved both the gauche-trans and the N3H-N1H tautomerisms. The calculated free energies predicted N3H-gauche as the most stable one of histamine free-base in solution. The order of stability is here completely altered with respect to previous results in gas phase, which presented the N1H-gauche conformer as the most stable structure. Our results also differ from previous Monte Carlo simulations, which obtained the N3H-trans conformer as the most stable in solution, although in this case, the histamine structures were kept frozen to the gas-phase geometry. Vibrational spectroscopy results support theoretical ones. Quadratic force fields for the four histamine conformers were achieved under the same calculation methodology. Previously, a general assignment of the infrared and Raman spectra of histamine free-base was proposed for solutions in both natural and heavy water. This allowed us to compare the experimental set of both wavenumbers and infrared intensities with the calculated ones. The lowest quadratic mean wavenumber deviation was obtained for the N3H-gauche conformer, in agreement with the free-energy calculations. Calculated infrared intensities were also compared to the experimental intensities, supporting this conformer as the relevant structure of histamine free-base in solution. It was then selected for a complete vibrational dynamics calculation, starting with a low-level scaling procedure to fit the set of calculated wavenumbers to the experimental values. The results were presented in terms of quadratic force constants, potential energy distribution, and normal modes.
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OBJECTIVE: To review the emerging concept of minimal persistent inflammation in allergic rhinitis and its implications for therapy. DATA SOURCES: Relevant clinical studies in the English language were reviewed. STUDY SELECTION: Material was taken from academic/scholarly journals. RESULTS: Accumulating evidence suggests that allergic rhinitis is a chronic inflammatory disease instead of a disease of acute symptoms. An approach to the therapy for allergic rhinitis should consider that even when symptoms are absent, a minimal level of persistent inflammation may persist. To prevent unexpected exacerbations, the treatment strategy may need to include managing subclinical persistent inflammation. Therapeutic options addressing the major inflammatory elements in allergic rhinitis, including eosinophils, the cysteinyl leukotrienes, and histamine, must be evaluated as management strategies that can achieve effective control. Traditional medications include intranasal corticosteroids, antihistamines, and immunotherapy. Recently, a leukotriene receptor antagonist has been approved for major rhinitis symptoms (congestion, rhinorrhea, sneezing, and pruritus), suggesting a new option for the treatment of allergic rhinitis. CONCLUSIONS: Because of the possible presence of a minimal persistent inflammation during rhinitis patients' asymptomatic periods, it is important to consider a prophylactic approach to treating allergic rhinitis to prevent or reduce exacerbations during an acute increase in allergen. In light of the advances in the understanding of the pathogenesis of allergic rhinitis, agents must be considered based on their safety, efficacy, and ability to deal with underlying inflammation as well as symptom relief.