UR-12460

The effector mechanism of intestinal necrosis in rat anaphylaxis was studied following several complementary approaches: (i) the use of monoclonal antibodies (mAb) belonging to different classes (IgG1, IgG2b and IgE anti‐DNP), (ii) the assay of mediators, and (iii) the use of pharmacological tools.Lethality and haemorrhagic necrosis of the small intestine were observed in IgE‐sensitized rats, whereas IgG mAb produced milder physiological disturbances.Inhibition of leukotriene biosynthesis reduced the drop of systemic blood pressure (BP) and the extent of protein‐rich plasma exudation but it did not influence the haemorrhagic component of intestinal necrosis.The antihistamine, pyrilamine, partially diminished the haemorrhagic component of the intestinal necrosis.The involvement of mediators related to platelet‐activating factor (PAF) was studied by examining the pharmacological effects of these autacoids and of PAF‐receptor antagonists (PCA4248, UR12460 and BB823). PAF induced intestinal lesions similar to those observed in IgE‐sensitized rats and PAF‐receptor antagonists markedly decreased haemorrhage in IgE‐sensitized rats.PAF levels were transiently increased after dinitrophenol (DNP)‐ bovine serum albumin (BSA) challenge in the small intestine of IgE‐sensitized rats.These data stress differences in the outcome of anaphylaxis related to the type of receptors for the Fc portion of immunoglobulins that are involved. IgE is the antibody class that elicits the most severe response due to the activation of mast cells via FceRI (surface receptors that bind IgE antibodies with high affinity), and the only one able to produce intestinal haemorrhagic necrosis.The mast‐cell‐derived mediators PAF/acyl‐PAF and histamine, most probably associated with tumour necrosis factor α/cachectin (TNF‐α), seem to play a central role in the production of the vascular changes required for the extravasation of erythrocytes in the small intestine mucosa.

A second generation of (cyanomethyl)piperazines, 1-acyl-4-((2-methyl-3-pyridyl)cyanomethyl)-piperazines, with increased oral activity was prepared and evaluated in vitro in a PAF-induced platelet aggregation assay (PAG) and in vivo in a PAF-induced hypotension test in normotensive rats (HYP). Oral activity was ascertained through a PAF-induced mortality test in mice (MOR). Attachment of a methyl group at position 2 of our earlier pyridine derivatives resulted in an improvement of 1 order of magnitude or greater in the ID50 of the oral test. Three different types of acyl substituents of similar potency emerge from this work: N-(diphenylmethylamino)acetyl, 3-substituted 3-hydroxy-3-phenylpropionyl, and N-substituted 3-amino-3-phenylpropionyl groups. The most interesting compounds, 26 (UR-12460, PAG IC50 = 0.040 microM, HYP, ID50 = 0.021 mg/kg i.v., MOR, ID50 = 0.30 mg/kg po) and 58 (UR-12519, PAG IC50 = 0.041 microM, HYP, ID50 = 0.015 mg/kg i.v., MOR, ID50 = 0.044 mg/kg po), compare favorably with WEB-2086. Compounds 26 and 58 were also tested in active anaphylactic shock (AAS) and endotoxin-induced mortality (EIM) tests. On the basis of these data, compounds 26 and 58 have been selected for further pharmacological development.