Plasma histamine and bronchial reactivity in allergic asthma

Discovery of a Highly Selective β2-Adrenoceptor Agonist with a 2-Amino-2-phenylethanol Scaffold as an Oral Antiasthmatic Agent

Asthma patients in resource-poor countries cannot obtain adequate basic asthma medications because most asthma medications are supplied as inhalants. An alternative approach is to create oral antiasthmatic drugs with high β₂/β₁-selectivity, which should reduce treatment costs. In this study, we designed a cohort of compounds 1 using 2-(4-amino-3-chloro-5-(trifluoromethyl)phenyl)-2-(tert-butylamino)ethan-1-ol hydrogen chloride (1a) as the lead compound with an aim to expand the library of compounds possessing the 2-amino-2-phenylethanol scaffold. Structure-activity relationship studies on these compounds revealed that compounds created showed remarkable β₂ selectivity compared to isoproterenol and gave additional insights on the rational design of β₂-adrenoceptor agonists. Moreover, 1a was found as the best candidate compound showing the greatest potential for drug development. Cell-based assays showed that 1a was about 10 times more selective than salbutamol toward the β₂-adrenoceptor. Moreover, 1a exhibited good oral bioavailability and low acute oral toxicity. These data reveal 1a as an oral antiasthmatic agent.

Association between two polymorphisms of histamine-metabolising enzymes and the severity of allergic rhinitis in a group of Mexican children

BACKGROUND

It has been suggested that polymorphisms of histamine metabolising enzymes can be a risk factor for developing histamine-involving diseases. The aim of the present study is to research the possible association between two functional single nucleotide polymorphisms (SNPs): C314T in the Histamine-N-Methyl Transferase gene and C2029G in the Diamine Oxidase gene, with the severity of allergic rhinitis and the number of allergic diseases, in a group of allergic Mexican children.

METHODS

We studied 154 unrelated allergic children. SNPs were analysed by RT-PCR. The total serum IgE was measured by chemiluminescence and the serum histamine by ELISA. We used logistic regression analysis to determine OR.

RESULTS

Patients carrying the mutant allele for any SNP had more risk to develop higher rhinitis severity or a bigger number of allergic diseases. Haplotype analysis revealed that this effect is synergistic. In patients carrying one or two mutant alleles, serum histamine levels were higher than those of patients carrying only wild alleles. Serum IgE levels were not associated with the presence of mutant alleles.

CONCLUSION

The presence of these SNPs in patients with allergic rhinitis can lead to higher serum histamine, therefore to a higher risk of developing more severe symptoms or more associated allergic diseases, even if the serum IgE remains low.

Systems pharmacology models can be used to understand complex pharmacokinetic-pharmacodynamic behavior: an example using 5-lipoxygenase inhibitors

Zileuton, a 5-lipoxygenase (5LO) inhibitor, displays complex pharmaokinetic (PK)-pharmacodynamic (PD) behavior. Available clinical data indicate a lack of dose–bronchodilatory response during initial treatment, with a dose response developing after ~1–2 weeks. We developed a quantitative systems pharmacology (QSP) model to understand the mechanism behind this phenomenon. The model described the release, maturation, and trafficking of eosinophils into the airways, leukotriene synthesis by the 5LO enzyme, leukotriene signaling and bronchodilation, and the PK of zileuton. The model provided a plausible explanation for the two-phase bronchodilatory effect of zileuton–the short-term bronchodilation was due to leukotriene inhibition and the long-term bronchodilation was due to inflammatory cell infiltration blockade. The model also indicated that the theoretical maximum bronchodilation of both 5LO inhibition and leukotriene receptor blockade is likely similar. QSP modeling provided interesting insights into the effects of leukotriene modulation.

Polymorphisms of histamine-metabolizing enzymes and clinical manifestations of asthma and allergic rhinitis

BACKGROUND

Polymorphisms of enzymes involved in histamine biodisposition may affect clinical symptoms in diseases related to histamine, such as asthma or allergic rhinitis (AR).

OBJECTIVE

This study aims to analyse two common polymorphisms in genes coding for histamine-metabolizing enzymes in patients with allergic diseases.

METHODS

Five-hundred and sixty-five individuals participated in the study, including 270 unrelated patients with asthma and/or AR recruited from a single centre and 295 healthy volunteers. Participants were analysed for the presence of Thr105Ile and His645Asp amino acid substitutions at histamine N-methyltransferase (HNMT) and diamine oxidase (amiloride binding protein 1) enzymes, respectively, by amplification-restriction procedures.

RESULTS

The variant HNMT allele frequencies were slightly higher among patients with asthma [16.0%, 95% confidence interval (CI) 12.0-20.0] and among patients with rhinitis (13.2, 95% CI 10.3-16.1) as compared with healthy subjects (11.5 95% CI 8.9-14.1). The variant ABP1 allele frequencies were similar among patients with asthma (30.8%, 95% CI 25.7-35.9), rhinitis (28.7, 95% CI 24.8-32.6) and healthy subjects (26.8 95% CI 23.2-30.3). Individuals carrying mutated ABP1 alleles presented allergy symptoms with significantly lower IgE levels as compared with individuals without mutated genes, with a significant gene-dose effect (P<0.001). In addition, the percentage of individuals presenting symptoms without eosinophilia was significantly higher among homozygous carriers of ABP1 variant alleles (P<0.020) as compared with the rest of the atopic patients.

CONCLUSION

There is a lack of association between the allelic variants studied and the risk of developing allergic asthma and rhinitis. However, patients carrying the His645Asp polymorphism of ABP1 are more prone to developing symptoms with lower IgE levels.

A sensitive and selective determination method of histamine by HPLC with intramolecular excimer-forming derivatization and ?uorescence detection

A highly sensitive, selective and simple method is described for the determination of histamine by high-performance liquid chromatography (HPLC) with fluorescence detection. The method is based on an intramolecular excimer-forming fluorescence derivatization of histamine with 4-(1-pyrene)butyric acid N-hydroxysuccinimide ester (PSE), followed by reversed-phase HPLC. Histamine, having two amino moieties in a molecule, was converted to the dipyrene-labeled derivative by reaction with PSE. The derivative afforded intramolecular excimer fluorescence (450-540 nm), which can clearly be discriminated from the monomer fluorescence (370-420 nm) emitted from PSE. Typically, a 10 micro L sample solution was mixed with 100 micro L of derivatization reagent solution, which was a mixture of 0.5 mm PSE in acetonitrile and 0.5 mm potassium carbonate in water (8:2, v/v). The derivatization was carried out at 100 degrees C for 90 min. The PSE derivative of histamine could be separated by reversed-phase ODS column with isocratic elution using acetonitrile:water (82:18, v/v) containing 0.03% triethylamine. The detection limit (singnal-to-noise ratio = 3) of histamine was 0.5 fmol for a 30 micro L injection. The method was successfully applied to the determination of histamine in human urine, and had enough selectivity and sensitivity for urinary histamine quantification.

Histamine stimulates alveolar macrophages to release neutrophil and monocyte chemotactic activity

Histamine and serotonin are important inflammatory mediators in the pathophysiology of asthma, and asthmatic patients have higher plasma histamine and serotonin levels than non-asthmatic control subjects. Alveolar macrophages (AMs) synthesize and secrete a large number of substances that play a key role in acute and chronic inflammation including asthma. We postulated that AMs might release chemotactic activity for neutrophils and monocytes in response to histamine or serotonin. To test this hypothesis, bovine AMs were cultured, and the supernatant fluids were evaluated for neutrophil chemotactic activity (NCA) and monocyte chemotactic activity (MCA) by a blind well chamber technique. AMs released chemotactic activity in response to histamine and serotonin in a dose- and time-dependent manner (P <.05). Partial characterization and molecular sieve column chromatography revealed that low-molecular-weight lipid-soluble activity was predominant. Lipoxygenase inhibitors significantly blocked the release of chemotactic activity. Leukotriene B(4) receptor antagonists blocked the chemotactic activity. Immunoreactive leukotriene B(4) significantly increased in supernatant fluids in response to histamine and serotonin. The receptor responsible for the release of chemotactic activity in response to histamine was the H2 receptor. These data demonstrate that AMs release NCA and MCA in response to histamine or serotonin (or both) and may modulate the inflammatory cell recruitment into the lung.