Javier Forn

Effects of PAF-antagonists in mouse ear oedema induced by several inflammatory agents

1 Several platelet activating factor (PAF)‐antagonists of different chemical structures were tested in the arachidonic acid‐, tetradecanoylphorbol acetate‐, dithranol‐, and benzoic acid‐induced mouse ear oedema models. 2 Topical application of UR‐10324, UR‐11353, CV‐6209 and WEB‐2086 markedly inhibited ear oedema induced by the four irritants tested, mimicking the profile obtained with dexamethasone. YM‐461 was highly effective only in the dithranol‐induced ear oedema, while BN‐52021 failed to inhibit ear oedema in all models tested. 3 Leukocyte recruitment into the inflamed ears was prevented by PAF‐antagonists, as measured by myeloperoxidase activity in the supernatants of ear homogenates. 4 A relationship between PAF‐antagonist and anti‐inflammatory activities was found in some cases, but other mechanisms cannot be excluded to explain the topical anti‐inflammatory effect of these compounds. 5 Our results suggest that topical formulations containing PAF‐antagonists could be useful in the treatment of some inflammatory skin diseases and provide evidence on the involvement of PAF in these inflammatory processes.

Effects of UR-12633, a new antagonist of platelet-activating factor, in rodent models of endotoxic shock

1 The effects of the selective and potent novel platelet‐activating factor (PAF) antagonist, UR‐12633 (1‐(3,3‐diphenylpropionyl)‐4‐(3‐pyridylcyanomethyl)piperidine) on several markers of endotoxic shock syndrome were evaluated in rats and mice. 2 UR‐12633, administered 60 min after E. coli lipopolysaccharide (LPS), reversed the LPS‐induced sustained hypotension in rats at doses of 0.01 to 1 mg kg−1, i.v. The reference compound WEB‐2086 (1 mg kg−1) also reversed the LPS‐induced hypotension. UR‐12633 (1 mg kg−1), administered 10 min before LPS, almost fully inhibited sustained hypotension. The immediate hypotension (within 1 min) caused by LPS was not prevented by either UR‐12633 or WEB‐2086. 3 Pretreatment with 10 mg kg−1, i.v. of either UR‐12633 or WEB‐2086 inhibited the increase in disseminated intravascular coagulation markers, such as activated partial thromboplastin time (55 and 74% inhibition, respectively), and prothrombin time (22 and 72% inhibition, respectively), and prevented the decrease in plasma fibrinogen content (100 and 29% inhibition). 4 Increases in acid phosphatase (ACP) plasma activity, a marker of lysosomal activation, and in lactate dehydrogenase (LDH), a marker of tissue damage, were inhibited by pretreatment with 10 mg kg−1, i.v. of either UR‐12633 or WEB‐2086 (100% and 69% inhibition, ACP; 62 and 48% inhibition, LDH). Hyperglycaemia (71 and 46%) and hyperlactacidaemia (92 and 56%) were also inhibited. 5 UR‐12633, but not WEB‐2086, inhibited the LPS‐induced increase in vascular permeability in rats, as shown by prevention of haemoconcentration and, to a lesser degree, the increase in Evans blue dye extravasation. 6 In a series of nine reference compounds and UR‐12633, we found a high correlation (P < 0.001) between PAF antagonist activity, measured as the inhibition of PAF‐induced rabbit platelet aggregation or PAF‐induced mortality in mice and the inhibition of LPS‐induced mortality. 7 In spite of the multifactorial nature of endotoxic shock, in which many mediators may be involved, the new potent PAF antagonist, UR‐12633, proved effective in protecting against changes in most shock markers. These data strongly suggest a key role for PAF in the pathogenesis of endotoxic shock in rodents.

Demonstration of inhibition of cyclic AMP accumulation in brain by very low concentrations of lithium in the presence of α-adrenoceptor blockade

In the present paper, we have studied the effect of lithium on cAMP levels induced by isoprenaline and norepinephrine in the presence of alpha- or beta-adrenoceptor antagonists. Our results show that low lithium concentrations, starting at 0.3 x 10(-3) M, have a significant inhibitory effect on cAMP content induced by isoprenaline in brain tissue pretreated with the alpha-adrenoceptor blocker phenoxybenzamine. On the other hand, the inhibitory effect of lithium on cAMP levels induced by norepinephrine when beta-adrenoceptors are blocked with propranolol, is observed at concentrations starting at 2.5 x 10(-3) M. These results show that in the presence of alpha blockade, low lithium concentrations which are within the therapeutic plasma range for treatment of manic patients, are able to act on an adenylate cyclase-cAMP system coupled to beta-adrenoceptors.

Effect of α2-adrenoceptor blockade on lithium action in the rat brain

The inhibitory effect of different concentrations of lithium (0.15-10 x 10(-3) M) on cAMP production induced by isoprenaline (1 x 10(-4) M) after the blockade of alpha(2)-adrenoceptors in the rat cerebral cortex was investigated. Low lithium concentrations (0.3-0.6 x 10(-3) M) exerted a significant inhibitory effect after yohimbine (1 x 10(-5) M) addition, but had no effect when isoprenaline alone or prazosin (1 x 10(-7) M) was added. The recovery of [3H]yohimbine binding after irreversible inactivation by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) was evaluated in cortical membranes to study how alpha(2)-adrenoceptor repopulation affects the action of lithium on the adenylyl cyclase-cAMP system. When the density of alpha(2)-adrenoceptors was lower than 21%, lithium showed a significant inhibitory effect at all concentrations tested. However, at higher densities, increased concentrations of lithium were required to inhibit cAMP production. Our results suggest that the inhibitory effect of lithium on cAMP levels in the rat brain is conditioned by alpha(2D)-adrenoceptors.

A Short, Efficient Synthesis of 6-Cyano-1-tetralones

Abstract A new, short and high-yield synthesis of 6-cyano-1-tetralones is described. Triflate intermediates 8 and 9 are versatile intermediates for the synthesis of other 6-substituted tetralones.

Chronic treatment of guinea pigs with lithium chloride: effects on myenteric plexus preparations and on cyclic AMP levels

We studied the effects of lithium chloride, given i.p. in doses of 0.05, 1, 2, 4 and 8 mEq/kg twice daily for 14 days, on preparations of guinea pig myenteric plexus. The effects of lithium added to isolated myenteric plexus preparations derived from chronically treated animals showed that relatively low lithium concentrations produced a statistically significant decrease in the force of contraction, this effect being concentration-dependent. 3-Isobutyl-1-methylxanthine (IBMX) induced a statistically significant inhibition, between 30 and 50%, of the lithium effects. cAMP levels in animals treated chronically with lithium were studied, using an isotopic displacement technique. Our results show that only the highest dose of lithium (8 mEq/kg per day) significantly decreased basal levels of cAMP. In the presence of IBMX, low doses of lithium (1 mEq/kg per day) induced a very significant decrease in cAMP levels, but the inhibition remained constant, approximately 30-35%, at doses from 2 mEq/kg per day. In guinea pig myenteric plexus preparations from acutely treated animals, our results show a direct relationship between lithium concentration and inhibition of the cAMP accumulation induced by IBMX.

Effect of endotoxin and platelet-activating factor on rat vascular permeability: role of vasoactive mediators

The contribution of several vasoactive mediators such as histamine, serotonin, bradykinin, arachidonic acid metabolites and PAF to vascular permeability changes was determined in a rat model of acute endotoxemia. Lipopolysaccharide (10-40 mg/kg, i.v.) from E. coli 0127:B8 (LPS) elicited an increase in Evans blue extravasation in trachea, thymus, seminal vesicle and stomach, whereas other organs remained unaffected. LPS (25 mg/kg)-induced extravasation was not inhibited by intravenous pretreatment with histamine (H1) antagonist mepyramine (5 mg/kg) or bradykinin (B2) antagonist HOE-140 (0.1 mg/kg), whereas other standard drugs selectively inhibited leakage in particular tissues, e.g. the cyclooxygenase inhibitor indomethacin (5 mg/kg) in trachea (78%) and seminal vesicle (64%), the serotonin and H1 antagonists cyproheptadine (2 mg/kg) in trachea (88%) and stomach (56%) and the dual cyclooxygenase/lipoxygenase inhibitor phenidone (10 mg/kg) in seminal vesicle (87%). PAF antagonists lexipafant and UR-12460 (10 mg/kg), but not apafant, potently inhibited extravasation in trachea (59, 84%) and seminal vesicle (81, 78%) and in stomach only UR-12460 (52%), whereas all of them were ineffective in thymus. When extravasation was induced by PAF (4 micrograms/kg) a low dose (0.1 mg/kg) of the three PAF antagonists strongly reduced extravasation in thymus and seminal vesicle, whereas lexipafant and UR-12460 did so in trachea (82, 100%) and only lexipafant in stomach (100%). Mepyramine, cyproheptadine, HOE-140 and indomethacin did not inhibit the effect of PAF, whereas phenidone inhibited it by 58% in trachea. These results suggest that most of the LPS-induced increase in vascular permeability is mediated by secondary vasoactive mediators among which PAF plays a pivotal role, although their relative contribution may vary from tissue to tissue.

4-(2-pyridyl)-2,2-dimethylnaphthalen-1-ones as new potassium channel activators with increased airways selectivity

Abstract A new series of 4-(2-pyridyl)-2,2-dimethylnaphthalen-1-one potassium channel activators has been prepared and their in vitro 1 relaxant activities in isolated rat portal vein and guinea-pig tracheal spirals as well as their hypotensive and bronchodilatory effects have been evaluated. Oxidation of the pyridyl nitrogen atom and a double bond between positions 3 and 4 provide compounds with some degree of airways selectivity.

The effect of fosfosal and acetylsalicylic acid on leukocyte migration and PGE2 concentration in experimentally induced acute inflammation

The effect of fosfosal, a non-acetylated salicylic acid derivative, on the content of prostaglandin E2 (PGE2) and the migration of polymorphonuclear leukocytes in inflammatory exudates induced by s.c. implantation of 0.5% carrageenan soaked sponges in rats has been determined. Fosfosal, which does not inhibit PG synthesis in vitro, is capable of reducing, in a dose-dependent manner, the PGE2 content of the exudates, with a maximum reduction of 50-60% at a total dose of 100 mg/kg i.p. Acetylsalicylic acid was slightly more potent (68% reduction, 2 x 50 mg/kg i.p.). Six hours after fosfosal administration, salicylic acid, the principal metabolite of fosfosal, accumulated in the exudates at concentrations of about 100 micrograms/ml. These concentrations were sufficient to inhibit PG synthetase activity in vitro. Neither fosfosal nor acetylsalicyclic acid affected polymorphonuclear leukocyte migration at doses which significantly reduced the concentrations of PGE2. Indomethacin, used as reference, reduced leukocyte migration by 28 and 45% at a dose of 1 and 10 mg/kg i.p. respectively. The results indicate that fosfosal, in spite of its lack of effect on PG biosynthesis in vitro, exerts an effect on the inflammatory locus in vivo which may account, at least in part, for its anti-inflammatory activity. Moreover, our results confirm that the inhibition of PG synthesis and leukocyte migration are mediated by different mechanisms.

Characterization of [3H]apafant binding to PAF receptor on rabbit platelet membranes: A comparison of a Microplate Filtration System and a standard method

This article describes the application of a Microplate Filtration System (MFS) to a binding assay, with the results being compared to those obtained with a conventional 24-Well Filtration Manifold (24WFM). The data reported here characterize the PAF receptor on rabbit platelet membranes using [3H]apafant. The results showed that [3H]apafant labelled a homogenous population of high-affinity binding sites in a concentration-dependent manner. Binding was very specific, saturable, reversible, and proportional to receptor concentration. [3H]Apafant interacted with membranes in an apparently competitive manner, with pseudo-Hill coefficients not significantly different from unity, thus indicating that apafant did not interact cooperatively at these binding sites. A number of PAF antagonists (apafant, lexipafant, BN-52021, SCH-37370, SR-27417, UR-12670) inhibited [3H]apafant binding with slopes near unity and with a rank order of potency in good agreement with their ability to inhibit PAF-induced rabbit platelet aggregation, suggesting that the sites labelled are functional PAF receptors. C18-PAF also competed with [3H]apafant for the receptor, but yielded biphasic inhibition curves which could be resolved into high- and low-affinity components. No significant differences were found either in the equilibrium binding parameters or in the PAF antagonists affinities obtained with the 24WFM and the MFS. The use of the latter system improved sample handling efficiency and shortened overall labor time, thus representing a more suitable way to perform receptor binding assays.