The contribution of platelet-activating factor to allergen-induced eosinophil infiltration and bronchial hyperresponsiveness

A pharmacophore for high affinity PAF antagonists. II. Hydrophobicity study using the molecular lipophilicity potential

Platelet-activating factor (PAF) is a powerful phospholipid-derived autacoid involved in many physiopathological mechanisms. Many PAF antagonists have been synthesized and evaluated as therapeutic candidates. In a previous report, we have described an electronic pharmacophore of PAF antagonists using the molecular electrostatic potential. In the present study, a molecular lipophilicity potential is used to compare the hydrophobic properties of 49 "heterocyclic sp2 nitrogen' highly potent PAF antagonists, belonging to six structurally different series (nine hetrazepines, five pyrrolo[1,2-c]thiazoles, 14 carboxamides, nine dihydropyridines, nine pyridinyl-thiazolidines and three imidazo[4,5-c]pyridines). Their common features consist of three hydrophilic (HYD2, HY14(3)B and HYD3) and two lipophilic zones (LIP3 and LIP4), defining the lipophilic pharmacophore of the antagonists. This pharmacophore is also characterized by several zone-to-zone distances: HYD3-HYD2 = 1.3 +/- 1.0 A, HY3B-HYD2 = 7.8 +/- 1.1, HYD3-HY3B = 5.1 +/- 1.1 A, LIP4-LIP3 = 5.4 +/- 1.1 A, LIP3-HYD2 = 11.3 +/- 1.6 A, LIP3-HY3B = 5.9 +/- 1.0 A, LIP3-HYD3 = 4.3 +/- 0.9 A, LIP4-HYD2 = 14.7 +/- 1.6 A, LIP4-HY3B = 8.1 +/- 1.2 A and LIP4-HYD3 = 3.9 +/- 1.1 A. These results represent a new step in the determination of a global pharmacophore for PAF antagonists.

A pharmacophore for high affinity PAF antagonists. I. Electronic model using molecular electrostatic potential

PAF is a powerful phospholipid-derived autacoid involved in many physio-pathological mechanisms. Many PAF antagonists have been synthesized and assayed for therapeutic purposes. In this study, molecular electrostatic potential is used to compare the electronic properties of 48 'heterocyclic sp2 nitrogen' highly potent PAF antagonists, belonging to six series (nine hetrazepines, five pyrrolo[1,2-c]thiazoles, 14 carboxamides, nine dihydropyridines, nine pyridinylthiazolidines and two imidazo[4,5-c]pyridines). Their common features consist of three main electronegative zones (A, B1 and B2) describing the electronic pharmacophore of these ligands. The high affinity of these PAF antagonists seems to be related to this electronegative system A-B(x), which is characterized by three distances A-B1 (9.3 +/- 1.0 A), A-B2 (13.4 +/- 0.7 A) and B1-B2 (4.9 +/- 0.9 A). Moreover, B1 and B2 may surround a common anchorage point in the binding site of the receptor.

Development of a method for monitoring the migration of 111In-labeled eosinophils and neutrophils to the lungs of anaesthetized guinea pigs by gamma scintigraphy and bronchoalveolar lavage

A method to introduce 111In-labelled neutrophils or eosinophils into the circulation of anaesthetized, ovalbumin-sensitized guinea pigs and monitor their pulmonary accumulation using gamma scintigraphy has been developed. The method is based on the ability to use 99mTc macroaggregated albumin (MAA) to create a pulmonary perfusion image as a template for the lungs of individual guinea pigs which can be superimposed on to the image produced by the 111In-labelled leukocytes injected into the same animal. Intravenous injection of the labelled leukocytes was shown to produce a high density radioactivity in the heart and lungs with little circulation to the rest of the body. This suggested an immediate 'trapping' of leukocytes in the pulmonary vascular bed. A more effective distribution of 111In-labelled cells was achieved by injecting them into the right carotid artery. This ensured more efficient circulation of the cells and resulted in their appearance in the lungs, liver and spleen. However, it was found that the contralateral carotid artery had to be tied off to prevent the cells only circulating to the superior left quadrant of the animal. Bronchoalveolar lavage of the lungs following i.v. injection of 111In-labelled neutrophils showed no significant difference in radioactivity of lavage fluid between guinea pigs challenged 24 h beforehand with inhaled saline or ovalbumin. In contrast, when labelled eosinophils were injected, there was a significantly greater mean radioactivity level in lavage fluid after ovalbumin challenge than after saline. In conclusion, gamma scintigraphy provides an accurate measure of the amount of activity from 111In-labelled leukocytes in the lung region which is specific for each animal