Milestones in the biology and pharmacology of H1-receptor antagonists

Seasonal and areal variability in PM2.5 poses differential degranulation and pro-inflammatory effects on RBL-2H3 cells

PM_2.5 pollution is a widespread environmental and health problem, particularly in China. Besides leading to well-known diseases in the respiratory system, PM_2.5 can also alter immune function to induce or aggravate allergic diseases. To determine whether there are temporal and spatial differences in the allergic responses to PM_2.5, monthly samples were collected from four regions (urban, industrial, suburban, and rural areas) through a whole year in Nanjing city, China. Inorganic chemical components (metals and water-soluble ions) of PM_2.5 were analyzed, and the rat basophil cells (RBL-2H3) exposed to PM_2.5 were assessed through quantitative measures of degranulation (β-hex and histamine) and pro-inflammation cytokine (IL-4 and TNF-α) expression. The highest levels of β-hex were measured in winter and spring PM_2.5 from urban and industrial areas, or autumn PM_2.5 from suburban and rural areas. With respect to histamine, autumn PM_2.5 samples were most potent irrespective of the location. Autumn and winter PM_2.5 induced higher levels of IL-4 than spring and summer samples. However, spring and autumn PM_2.5 caused higher levels of TNF-α. The concentrations of water-soluble ions (NH₄⁺, K⁺ and Cl^-), as well as heavy metals (Pb and Cr), were directly and statistically correlated to the inflammation observed in vitro. In general, the differences between regional and seasonal PM_2.5 in stimulating cell degranulation may depend on endotoxin and airborne allergen content of PM_2.5. The heavy metals and water-soluble ions in PM_2.5 were mostly anthropogenic, which increased the particles' mass-based cellular inflammatory potential, therefore, their health risks, e.g. from vehicular exhaust, coal, and biomass combustion, cannot be ignored.

Role of human mast cells and basophils in bronchial asthma

Mast cells and basophils are the only cells expressing the tetrameric (alphabetagamma2) structure of the high affinity receptor for IgE (FcepsilonRI) and synthesizing histamine in humans. Human FcepsilonRI+ cells are conventionally considered primary effector cells of bronchial asthma. There is now compelling evidence that these cells differ immunologically, biochemically, and pharmacologically, which suggests that they might play distinct roles in the appearance and fluctuation of the asthma phenotype. Recent data have revealed the complexity of the involvement of human mast cells and basophils in asthma and have shed light on the control of recruitment and activation of these cells in different lung compartments. Preliminary evidence suggests that these cells might not always be detrimental in asthma but, under some circumstances, they might exert a protective effect by modulating certain aspects of innate and acquired immunity and allergic inflammation.

Cetirizine, a second-generation H1 antagonist, modulates Rantes and MCP-1 levels in allergic rhinitis

Chemokines and their receptors are involved in several allergic diseases. We measured RANTES and MCP-1 levels in sera of allergic rhinitis patients, and also we evaluated the effect of cetrizine, a second-generation H1 antagonist, on these chemoattractant proteins. 15 subjects were studied (10 males and 5 females; mean age: 26.7 years). They were suffering from perennial or seasonal allergic rhinitis induced by Dermatophagoides pteronyssinus (8 patients) or by grasses (7 patients). RANTES and MCP-1 serum levels were detected with an enzyme immunoassay before and after two weeks of treatment with 10 mg of cetirizine daily, and again after two weeks of washout. Baseline serum levels of RANTES and MCP-1 chemokines were significantly higher (p < 0.02 and p = 0.007, respectively) in allergic patients than in the healthy control group. Cetirizine resulted in a significant decrease in RANTES (p < 0.02) and MCP-1 (p = 0.003) versus baseline values. There is an increase in RANTES and MCP-1 in allergic rhinitis, which is counteracted by cetirizine.

Second-generation antihistamines: a comparative review

Second-generation histamine H1 receptor antagonists (antihistamines) have been developed to reduce or eliminate the sedation and anticholinergic adverse effects that occur with older H1 receptor antagonists. This article evaluates second-generation antihistamines, including acrivastine, astemizole, azelastine, cetirizine, ebastine, fexofenadine, ketotifen, loratadine, mizolastine and terfenadine, for significant features that affect choice. In addition to their primary mechanism of antagonising histamine at the H1 receptor, these agents may act on other mediators of the allergic reaction. However, the clinical significance of activity beyond that mediated by histamine H1 receptor antagonism has yet to be demonstrated. Most of the agents reviewed are metabolised by the liver to active metabolites that play a significant role in their effect. Conditions that result in accumulation of astemizole, ebastine and terfenadine may prolong the QT interval and result in torsade de pointes. The remaining agents reviewed do not appear to have this risk. For allergic rhinitis, all agents are effective and the choice should be based on other factors. For urticaria, cetirizine and mizolastine demonstrate superior suppression of wheal and flare at the dosages recommended by the manufacturer. For atopic dermatitis, as adjunctive therapy to reduce pruritus, cetirizine, ketotifen and loratadine demonstrate efficacy. Although current evidence does not suggest a primary role for these agents in the management of asthma, it does support their use for asthmatic patients when there is coexisting allergic rhinitis, dermatitis or urticaria.