Inhibition by azelastine of the effects of platelet-activating factor in lungs from actively sensitised guinea-pigs

Platelet-Activating Factor (PAF) in Allergic Rhinitis: Clinical and Therapeutic Implications

Platelet-activating factor (PAF) is a lipid mediator involved in several allergic reactions. It is released from multiple cells of the immune system, such as eosinophils, neutrophils, and mast cells, and also exerts its effect on most of them upon specific binding to its receptor, becoming a pleiotropic mediator. PAF is considered a potential relevant mediator in allergic rhinitis, with a key role in nasal congestion and rhinorrhoea due to its effect on vascular permeability. Interestingly, despite its potential relevance as a therapeutic target, no specific PAF inhibitors have been studied in humans. However, rupatadine, a second-generation antihistamine with dual antihistamine and anti-PAF effects has shown promising results by both blocking nasal symptoms and inhibiting mast cell activation induced by PAF, in comparison to antihistamine receptor drugs. In conclusion, the inhibition of PAF may be an interesting approach in the treatment of allergic rhinitis as part of a global strategy directed at blocking as many relevant inflammatory mediators as possible.

Azelastine--a novel in vivo inhibitor of leukotriene biosynthesis: a possible mechanism of action: a mini review

Leukotrienes have been proposed as important chemical mediators of allergic inflammation, and there is evidence that azelastine (Astelin) can affect leukotriene-mediated allergic responses. One of the enzymes required for the synthesis of leukotrienes from arachidonic acid is 5-lipoxygenase (5-LO). Azelastine, which is preferentially taken up by the lung and alveolar macrophages, inhibits leukotriene generation in the airways. This property of azelastine may contribute to its therapeutic efficacy in the long-term treatment and management of rhinitis and asthma. Azelastine does not directly inhibit 5-LO in disrupted murine peritoneal cells and rat basophilic leukemia cells (IC50 > 100 microM), but does have moderate 5-LO inhibitory activity in intact murine peritoneal cells (IC50 = 10 microM, 5 min) and in chopped guinea pig liver (IC50 = 14 microM, 2 hr). The generation and release of leukotrienes in human neutrophils and eosinophils is also inhibited by azelastine (IC50 = 0.9-1.1 microM). Furthermore, azelastine is a potent and specific inhibitor of allergen-induced generation of leukotrienes in the nose of the guinea pig (ID50 < 100 micrograms/kg, im, 20 min) as well as in patients with rhinitis (2 mg, po, 4 hr; ID50 < 30 micrograms/kg). Azelastine also inhibits allergen-induced, leukotriene-mediated, pyrilamine-resistant bronchoconstriction (oral ID50 = 60 micrograms/kg, 2 hr and 120 micrograms/kg, 24 hr). This profile suggests that azelastine may be a novel inhibitor of Ca(2+)-dependent translocation of 5-lipoxygenase from cytosol to the nuclear envelope or a FLAP inhibitor rather than a direct 5-LO inhibitor.

Drug modulation of antigen-induced paw oedema in guinea-pigs: effects of lipopolysaccharide, tumour necrosis factor and leucocyte depletion

1. In guinea-pigs previously sensitized with ovalbumin, the intra-plantar administration of the antigen induced dose-dependent and sustained oedema. An intense infiltrate of neutrophils and eosinophils was observed at the peak of the oedema (4 h). 2. Oedema induced by ovalbumin at the doses of 50 or 200 micrograms/paw was not inhibited by antihistamines (meclizine and cetirizine), a PAF antagonist (BN 50730), a cyclo-oxygenase inhibitor (indomethacin), a lipoxygenase inhibitor (MK-886), a dual type lipo- and cyclo-oxygenase inhibitor (NDGA), a bradykinin antagonist (Hoe 140) or the combination of cetirizine, MK-886, indomethacin and BN 50730. These drugs did inhibit paw oedema induced by their specific agonists or by carrageenin. These results suggest that histamine, PAF, prostaglandins, leukotrienes or bradykinin are not important in the development of immune paw oedema in guinea-pigs. 3. Dexamethasone (10 mg kg-1) inhibited oedema induced by ovalbumin (50 or 200 micrograms/paw, P < 0.05). This effect apparently does not result from inhibition of arachidonate metabolism, since indomethacin, MK-886 and NDGA were without effect. 4. Oedema induced by ovalbumin (50 or 200 micrograms/paw) was also inhibited by azelastine. This effect was not due to the anti-histaminic property of azelastine since two other potent-antihistamines, meclizine and cetirizine, were ineffective. 5. Intravenous injection of lipopolysaccharide (LPS) dose-dependently inhibited the oedema induced by ovalbumin (200 micrograms/paw). This effect could not be attributed to hypotension or leucopenia since the maximal dose applied (81 micrograms kg-1) did not induce significant changes in the blood pressure or in the white blood cell levels of the animals. It is suggested that the effect of LPS is mediated by the endogenous release of cytokines, including tumour necrosis factor (TNF alpha). Murine TNF alpha dose dependently(9-81 microg kg-1) inhibited the paw oedema induced by ovalbumin.7. The anti-oedematogenic effects of LPS and/or TNF alpha are possibly associated with their capacity to inhibit leucocyte emigration. Accordingly, guinea-pigs rendered leucopenic with vinblastine exhibited less intense oedema after ovalbumin. Vinblastine did not affect oedema induced by PAF or bradykinin,indicating that vascular responsiveness was not involved.