Agents that inhibit histamine release: A review

It is well known that histamine is found in high concentration in mast cell granules(1). The histamine content of these granules may be released to the extracellular space if an appropriate stimulus is provided(2). Besides histamine, other preformed active substances like enzymes, chemotatic factors and proteoglycans, as well as newly generated mediators like eicosanoids, platelet activating factor and adenosine are released during the secretion process of mast cells(3). The activation of mast cell degranulation has been associated with a number of pathologic disorders, most frequently, diseases derived from the atopic state(4). It is now evident that mast cells are the primary effector cells in the early reaction in both allergic and non-allergic asthma(5,6), although some authors doubt that the late reaction of asthma is a mast cell dependent event(6). Other studies point towards basophils as cellular elements involved in the secondary phase of inflammation in allergic diseases(7). Secretion would depend on a histamine releasing factor, and on the presence of IgE on the basophil's surface(8). There is also evidence suggesting involvement of mast cells in some non-allergic inflammatory processes like arthritis(9). The pharmacological management of these diseases basically consists in the use of methylxantines, beta 2-adrenergic agonists, glucocorticoids, sodium cromoglycate-like drugs, anticholinergic and antihistaminic H 1 antagonists(10). Their therapeutic effects include bronchodilatation, receptor and physiological antagonism, prevention of inflammatory responses induced by secondary cells, and finally, inhibition of mast cell activation(11). This review is concerned with compounds having inhibitory action on mast cell activation, and their possible importance on the pathophysiology of mast cell-related diseases.

Block of the hERG channel by bupivacaine: Electrophysiological and modeling insights towards stereochemical optimization

The hERG voltage-gated potassium channel mediates the cardiac I(Kr) current, which is crucial for the duration of the cardiac action potential. Undesired block of the channel by certain drugs may prolong the QT interval and increase the risk of malignant ventricular arrhythmias. Although the molecular determinants of hERG block have been intensively studied, not much is known about its stereoselectivity. Levo-(S)-bupivacaine was the first drug reported to have a higher affinity to block hERG than its enantiomer. This study strives to understand the principles underlying the stereoselectivity of bupivacaine block with the help of mutagenesis analyses and molecular modeling simulations. Electrophysiological measurements of mutated hERG channels allowed for the identification of residues involved in bupivacaine binding and stereoselectivity. Docking and molecular mechanics simulations for both enantiomers of bupivacaine and terfenadine (a non-stereoselective blocker) were performed inside an open-state model of the hERG channel. The predicted binding modes enabled a clear depiction of ligand-protein interactions. Estimated binding affinities for both enantiomers were consistent with electrophysiological measurements. A similar computational procedure was applied to bupivacaine enantiomers towards two mutated hERG channels (Tyr652Ala and Phe656Ala). This study confirmed, at the molecular level, that bupivacaine stereoselectively binds the hERG channel. These results help to lay the foundation for structural guidelines to optimize the cardiotoxic profile of drug candidates in silico.

Safety and Efficacy of Oral Fexofenadine in Children with Seasonal Allergic Rhinitis - a Pooled Analysis of Three Studies

Allergic rhinitis is one of the most common clinical conditions in children; however, data regarding the safety of antihistamines in children with seasonal allergic rhinitis are limiting. To evaluate the safety and efficacy of fexofenadine in children with seasonal allergic rhinitis, data were pooled from three, double-blind, randomized, placebo-controlled, parallel-group, 2-week trials in children (6-11 year) with seasonal allergic rhinitis. All studies assessed fexofenadine HCl 30 mg b.i.d.; two studies included fexofenadine HCl at 15 and 60 mg b.i.d. Patients (and investigators) reported any adverse events during the trial. Physical examinations, including measurements of vital signs and laboratory tests, were performed. Efficacy assessments (total symptom score and individual symptom scores) were evaluated. Exposure to fexofenadine HCl 30 mg b.i.d. and to any fexofenadine dose exceeded 10,000 and 17,000 patient days, respectively. Incidences of adverse events, and discontinuations because of adverse events, were low and similar across treatment groups. In the placebo group, 24.4% of subjects reported adverse events compared with 24.1% for fexofenadine HCl 30 mg b.i.d., and 28.4% for all fexofenadine-treated groups. The most common adverse event overall was headache (4.3% placebo; 5.8% fexofenadine HCl 30 mg b.i.d.; and 7.2% any fexofenadine doses). Treatment-related adverse events were similar across treatment groups with no sedative effects. Fexofenadine HCl 30 mg b.i.d. was significantly superior to placebo in reducing the total symptom score and all individual seasonal allergic rhinitis symptoms, including nasal congestion (p < 0.05). Fexofenadine, at doses of up to 60 mg b.i.d., is safe and non-sedating, and fexofenadine HCl 30 mg b.i.d. effectively reduces all seasonal allergic rhinitis symptoms in children aged 6-11 years.