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Effect of SR 27417, a novel PAF antagonist on antigen-induced hypotension in the rat
ELSEVIER
ANOCEU SIGNULING J. Lipid Mediators Cell Signalling 15 (1996) 1I5- 123
Effect of SR 27417, a novel PAF antagonist antigen-induced hypotension in the rat
on
Jean-Marc HerbertaT*, AndrC Bernat”, Eduardo Tibirigab “Haemobiology Research Department, Sanofi Recherche, 195, Route d’Espagne, 31036, Toulouse Cedex, France bDepartamento de Fisiologia e Farmacodincimica, Institute Osvaldo Crux, FIOCRUZ, Rio de Janeiro, Brasil
Received 3 January 1996; revised 26 February 1996; accepted 28 February 1996
Abstract
SR 27417, a potent PAF receptor antagonist, inhibited in a dose-dependent manner the hypotensive effect of PAF in rats. It protected rats with an ED,, value of 6 f 2 fig/kg (n = 6), when given i.v., 1 min before PAF administration. After iv. administration, SR 27417 exhibited extended duration of action, a significant protective effect was observed up to 48 h after the administration. After i.v. injection, SR 27417 (0.3, 1 and 3 mg/kg) afforded dose-dependent protection of actively sensitized rats against ovalbumin-induced hypotension but also totally reversed established antigen-induced hypotension. These results therefore confirm that PAF plays a major role in anaphylactic shock and suggest that SR 27417 may be an effective prophylactic as well as a potent curative drug in this pathology. Keywords:
SR 27417; Platelet activating factor (PAF); Antigen; Hypotension
* Corresponding
author. Tel.: + 33 62142361; fax: + 33 62142286.
0929-7855/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved PII SO929-7855(96)00452-X
116
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Lipid Mediators Cell Signalling 15 (1996) 115-123
1. Introduction PAF-acether, one of the most potent inducers of platelet aggregation known, has been described as exhibiting, when injected, a wide variety of biological actions including bronchoconstriction, hypotension, increase in vascucardiac effects (Braquet et al., lar permeability and negative inotropic 1987a,b; Handley, 1988). Moreover, PAF is believed to be involved in allergic responses, asthma, inflammation and anaphylactic and septic shock (Braquet et al., 1987a,b; Handley, 1988). The development of specific, potent PAF receptor antagonists is therefore essential for further elucidation of the pathophysiological roles of PAF and for developing new drugs active in the pathophysiological situations where PAF is believed to be involved. Reseveral structurally-unrelated PAF antagonists were shown to cently, exhibit beneficial activities in allergen-induced anaphylactic shock (Damas, 1989; Casals-Stenzel, 1987; Herbert et al., 1991b; Terashita et al., 1987, 1992). These data provided further support for earlier indications that PAF antagonists may protect against respiratory and circulatory dysfunctions such as systemic hypotension associated with a decrease in peripheral vascular resistance and cardiac failure occurring during severe anaphylactic shock syndromes. Recently, SR 27417, the first member of a newly-developed PAF antagonist series, has been described as one of the most potent PAF receptor antagonists described to date (Herbert et al., 1991a). Moreover, this compound has been shown to inhibit and reverse PAF- and endotoxin-induced hypotension in rats and guinea pigs (Bernat et al., 1992) and to protect mice from lethal anaphylactic and endotoxin-induced shock (Herbert et al., 1991b) therefore showing that PAF plays a major role in septic shock and that SR 27417 may be an effective prophylactic as well as a potent curative drug in this pathology. The aim of the present work was therefore to extend such observations to anaphylaxis and to evidence if SR 27417 protects rats from the hypotensive effect of PAF and antigen in actively sensitized animals.
2. Materials and methods 2.1. PAF-induced hypotension in the rat The method used to evaluate the effect of the tested drugs on PAF-induced hypotension has been described elsewhere (Terashita et al., 1985). Briefly, male Sprague-Dawley rats (280-300 g, Charles River, France) were anaesthetized with sodium pentobarbitone (30 mg/kg, i.p.). A catheter was introduced into the left carotid artery and the mean arterial blood pressure was continuously measured with a P23db pressure transducer connected to a NARCO Physiograph recorder. Another catheter was inserted into the jugular vein for injection of PAF, drugs
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Lipid Mediators Cell SignaIling 15 (1996) 115-123
117
and their respective vehicles. PAF (100 ng/kg) was injected i.v., 1 min. after i.v. administration of the tested compounds. The maximal hypotensive response due to PAF injection was recorded and the effect of the various drugs determined at that time point (usually 2 min after PAF injection). Due to tachyphylaxis phenomena, a single dose of PAF was administered to each animal. The number of animals per group was 6. For each time point in the kinetic studies, a control group (n = 6) was introduced. 2.2. Antigen-induced hypotension in the rat Rats were actively sensitized according to Casals-Stenzel et al. (1987). Briefly, conscious rats were sensitized by injecting i.p. (1 ml/kg) a suspension of ovalbumin (40 pg/kg) and Al(OH), (0.2 g/ml) in saline. Al(OH), was added to the antigen solution 1 h prior to the injection. The rats received an i.p. injection on days 0, 2 and 4. Animals were used 21 to 28 days after the beginning of the sensitization procedure. Pentobarbitone-anaesthetized (30 mg/kg, i.v.) rats were prepared for blood pressure registration as already described above. Animals were challenged i.v. with ovalbumin (0.25 mg/kg, i.v.). The hypotensive response from antigen challenge was recorded every 5 min over a 20 min-period. To establish its efficacy, SR 27417 was given iv. 5 min before the antigen challenge and tested in a dose-response manner. In order to establish the reversal of the hypotensive effect, SR 27417 was also administered 5 min after ovalbumin. In saline-treated animals (non-sensitized) ovalbumin did not show any hypotensive effect. The number of animals per group was 6. 2.3. Drugs and dosage
C,,-PAF (1-0-hexadecyl-2-acetyl-sn-glyceryl-3-phosphoryl-choline) was purchased from Bachem (Switzerland). Stock solutions of PAF were prepared in absolute ethanol and subsequent dilutions were made with Tyrode’s solution containing 0.25% BSA. Ovalbumin was purchased from Sigma Chemical (France). SR 27417 (fumarate salt) (N-(2-dimethylamino ethyl)-N-(3-pyridinyl methyl) [4-(2,4,6_triisopropyl phenyl) thiazol-2-yl] amine) (Herbert et al., 1991a) was from Sanofi Recherche (Toulouse, France). For experiments, fresh solutions of SR 27417 were prepared daily in a mixture of saline and 0.1 N HCl (l/40 v/v). Dilutions were made in saline. Control animals received the same volume of saline. 2.4. Statistical analysis
Results are shown as arithmetic means. Grouped data were analysed for significance by comparison with the vehicle-treated group using the Kruskal-Wallis test. The level of significance was chosen as p < 0.05.
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3. Results 3.1. Effect of SR 27417 on PAF-induced hypotension in the rat Injection of PAF at the dose of 100 ng/kg i.v. produced a 45 + 7.3 mmHg (n = 45) decrease in the mean arterial blood pressure (MAP) (basal blood pressure = 75.2 + 4.3 mmHg, n = 30). The recovery period (time required for blood pressure to return to pre-injection values) was 4 min. Under the same conditions, PAF-induced hypotension in the rat was significantly reduced by i.v. pretreatment with SR 27417 (Fig. 1). SR 27417 when given iv., 1 min before PAF challenge did not show any effect on the basal blood pressure but inhibited the PAF-induced response in a dose related manner with an ED,, value (dose of compound which reduced 50% of the PAF-induced hypotension in the control group) of 6 + 2 pgg/kg (n=6). SR 27417 a d ministered i.v. at 1 mg/kg exhibited an extended duration of activity and was able to protect significantly rats from PAF-induced hypotension for at least 48 h (Fig. 2).
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Fig. 1. Effect of SR 27417 on PAF-induced hypotension in rats. Increasing doses of SR 27417 were injected iv. 1 min before the injection of PAF (100 ng/kg, i.v.). Hypotension was monitored as described under Section 2. Data points represent the mean of 6 animals. Kruskal-Wallis test was used to examine the differences between vehicle and drug-treated groups; * p < 0.05, ** p < 0.01, *** p < 0.001.
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Time (h) Fig. 2. Time-course of the protective effect of i.v. administrations of SR 27417 on PAF-induced hypotension in rats. SR 27417 was injected intravenously (1 mg/kg, iv.) 1 to 80 h before the injection of PAF (100 ng/kg, iv.). Hypotension was measured as described under Section 2. Values are mean of 6 animals/time for each dose.
3.2. Effect of SR 27417 on antigen-induced hypotension in the rat Injection of antigen (ovalbumin, 0.25 mg/kg, i.v.) to actively sensitized animals produced a rapid-onset hypotension, characterized by a decrease in the MAP of 30 to 40% over a l-2 min period (Fig. 3). In the controls, MAP remained at the same level for the whole length of the observation period (20 min). As shown in Fig. 3, SR 27417 administered intravenously (0.3, 1 and 3 mg/kg, i.v.), 5 min prior to the antigen challenge did not affect basal blood pressure of rats (not shown) but prevented significantly ovalbumin-induced hypotension in a dose-dependent manner. SR 27417 (0.3, 1 and 3 mg/kg, i.v.) reversed the established hypotension induced by ovalbumin (Fig. 4).
4. Discussion In the past few years, evidence has been accumulating indicating that PAF contributes to the expression of the haemodynamic and haematological features of anaphylactic shock. The data supporting this concept are, firstly, that all of the major pathophysiological events induced by antigen challenge of pre-sensitized animals, i.e. systemic hypotension, bronchoconstriction, thrombocytopenia,
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leukopenia, increased vascular permeability and death, can be mimicked by PAF injection in animals (Camussi et al., 1983; Chang et al., 1987; McManus et al., 1980), and secondly, that the circulating PAF concentration increases after allergeninduced bronchoconstriction in humans (Chan-Yeung et al., 1991). Therefore, since there is now good evidence that PAF is one of the most prominent mediators of the shock state, it may be worthwhile studying the effect of selective PAF antagonists in such pathophysiological states. Moreover, PAF antagonists of various chemical structures have been shown to inhibit the deleterious effects of anaphylaxis in animals (Damas, 1989; Casals-Stenzel, 1987; Herbert et al., 1991b; Terashita et al., 1987, 1992) (hypotension, bronchopulmonary disturbance and lethality), thus confirming the key role of PAF in this pathology. SR 27417, the first member of a newly-developed PAF antagonist series has been shown to be a highly potent, specific and competitive PAF receptor antagonist by its inhibitory results on the PAF-induced aggregation of rabbit and human platelets and on the oxydative burst of guinea-pig peritoneal macrophages (Herbert et al., 1991a). This potency was not only expressed in vitro, but also by SR 27417’s ability to inhibit PAF-induced in vivo responses in mice and guinea-pigs, this activity being noticeable by its extremely long duration of life. In a recent study (Herbert et al., 1991b), we showed that i.v. or oral doses of SR 27417 afforded complete 85
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Time (min) Fig. 3. Protective effects of SR 27417 on the antigen-induced hypotension in rats. SR 27417 was given i.v. at 0.3 (m), l(A) and 3 mg/kg (7) 5 min before the administration of the antigen challenge (ovalbumin, 0.25 mg/kg, i.v.). Controls (0) were injected with saline. Values are expressed as means + SD (n = 6 animals/group). Kruskal-Wallis test was used to examine the differences between vehicle and drug-treated groups; * p < 0.05, *** p < 0.001.
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Time (mid Fig. 4. Reversal of the antigen-induced hypotension by SR 27417 in rats. SR 27417 was given i.v. at 0.3 (U), l(A) and 3 mg/kg (T), 5 mm after the administration of the antigen (0.25 mg/kg, iv.). Controls (0) were injected with saline. Values are expressed as means + SD (n = 6 animals/group). Kruskal-Wallis test was used to examine the differences between vehicle and drug-treated groups; ** p < 0.01, *** p i 0.001.
protection of mice against antigen and endotoxin-induced lethality, therefore suggesting that it could be an effective preventive drug against shock syndromes. Profound decrease in MAP being one of the most prominent features of anaphylaxis, this study therefore examined the efficacy of SR 27417 in protecting rats from PAF or antigen-induced hypotension in sensitized animals. SR 27417 administered i.v., inhibited in a dose-dependent manner the hypotensive effect of PAF but a further important feature of the activity of SR 27417 is the duration of its protective effect against PAF-induced hypotension. Indeed, SR 27417 was able to protect significantly rats from the effects of PAF for at least 48 h after iv. administration. Such pharmacodynamical features correlate with those already reported in other animal species for SR 27417’s protective effect against PAF-, endotoxin- or anaphylaxis-induced lethality in mice and brochoconstriction, haemoconcentration, thrombocytopaenia and leukopaenia in guinea-pigs (Herbert et al., 1991a,b). Intravenous administration of SR 27417 prevented almost completely antigen induced hypotension. As already reported for this compound in other experimental conditions (Herbert et al., 1991b), the doses of SR 27417 needed to protect animals against ovalbumin-induced responses were 30 to 50 times greater than the doses needed to block PAF-induced hypotension. This may indicate that greater amounts
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of PAF are released during allergen challenge, compared with the amount of PAF used in the PAF-induced hypotension. Alternatively, the release of PAF after anaphylactic shock may result in high local concentrations of PAF which require a greater amount of PAF antagonist to achieve protection. SR 27417 not only inhibited but also reversed the antigen-induced hypotension. The doses required for the preventive and curative action of SR 27417 in antigen-induced hypotension were in the same concentration range. Similar results have been reported for SR 27417 with regard to endotoxin-induced hypotension in rats and guinea pigs (Bernat et al., 1992). These results therefore indicate that SR 27417 is one of the most potent antagonists of PAF- or antigen-induced hypotension in animals and confirms the involvement of PAF in anaphylactic shock. SR 27417, a long-acting, orally-active PAF receptor antagonist, showed a beneficial protective effect in this experimental shock state and therefore may be of great potential interest in the early treatment of anaphylactic shock in man as well as in other pathological situations where PAF is believed to be involved.
References Bernat, A., Herbert, J.M., Salel, V., Lespy, L. and Maffrand, J.P. (1992) Protective effect of SR 27417, a novel PAF antagonist, on PAF- or endotoxin-induced hypotension in the rat and the guinea-pig. J. Lipid Mediators 51, 41-48. Braquet, P., Mencia-Huerta, J.M., Chabriet, P.E., Touqui, L. and Vargaftig, B.B. (1987a) The promise of platelet activating factor. IS1 Atlas of Science, 1, 187- 198. Braquet, P., Shen, T.Y., Touqui, L. and Vargaftig, B.B. (1987b) Perspectives in platelet activating factor research. Pharmacol. Rev., 39, 97-145. Camussi, G., Tefta, C. and Bussolino, F. (1983) Inhibitory effect of prostacyclin (PGIZ) on neutropenia induced by intravenous injection of platelet activating factor (PAF) in rabbit. Prostaglandins 25, 343-351. Casals-Stenzel, J. (1987) Effects of WEB 2086, a novel antagonist of platelet activating factor, in active and passive anaphylaxis. Immunopharmacology, 13, 117- 124. Casals-Stenzel, J., Muacevic, G. and Weber, K.H. (1987) Pharmacological actions of WEB-2086, a new specific antagonist of platelet activating factor. J.Pharmacol. Exp. Ther., 241, 974-981. Chang, SW., Feddersen, C.O., Henson, P.M. and Voelker, N.F. (1987) Platelet activating factor mediates hemodynamic changes and lung injury in endotoxin-treated rats. J. Clin. Invest. 79, 1498-1509. Chan-Yeung, M., Lam, S., Chan, H., Tse, K.S. and Salari, H. (1991) The release of platelet-activating factor into plasma during allergen-induced bronchoconstriction. J. Allergy Clin. Immunol. 87, 667-673. Damas, J. (1989) Involvement of PAF-acether in the anaphylactic shock in the rat. J. Lipid Mediators, 1, 161-170. Handley, D.A. (1988) Development and therapeutic indications for PAF receptor antagonists. Drugs of the Future, 13, 137-152. Herbert, J.M., Bernat, A., Valette, G. et al. (1991a) Biochemical and pharmacological activities of SR 27417, a highly potent, long acting PAF receptor antagonist. J. Pharmacol. Exp. Ther., 259, 4451. Herbert, J.M., Lespy, L. and Maffrand, J.P. (1991b) Protective effect of SR 27417, a novel PAF antagonist, on lethal anaphylactic and endotoxin-induced shocks in mice. Eur. J. Pharmacol., 205, 271-276.
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McManus, L.M., Hanahan, D.J., Demopoulos, CA. and Pinckard, R.N. (1980) Pathobiology of the intravenous infusion of acethyl-glyceryl ester phosphorylcholine (AGEPC), a synthetic platelet-activating factor (PAF), in the rabbit. J. Immunol. 124, 2919-2924. Terashita, Z., Imura, Y., Nishikawa, K. and Sumida, S. (1985) Is platelet activating factor (PAF) a mediator of endotoxin shock? Eur. J. Pharmacol., 109, 257-261. Terashita, Z.I., Imura, Y., Shino, A. and Nishikawa, K. (1987) A lethal role of platelet activating factor in anaphylactic shock in mice. JPET, 243(l), 378-383. Terashita, Z.I., Kawamura, M., Takatani, M., Tsushima, S., Imura, Y. and Nishikawa, K. (1992) Beneficial effects of TCV-309, a novel potent and selective platelet activating factor antagonist in endotoxin and anaphylactic shock in rodents. JPET, 260(2), 748-755.
ANOCEU SIGNULING J. Lipid Mediators Cell Signalling 15 (1996) 1I5- 123
Effect of SR 27417, a novel PAF antagonist antigen-induced hypotension in the rat
on
Jean-Marc HerbertaT*, AndrC Bernat”, Eduardo Tibirigab “Haemobiology Research Department, Sanofi Recherche, 195, Route d’Espagne, 31036, Toulouse Cedex, France bDepartamento de Fisiologia e Farmacodincimica, Institute Osvaldo Crux, FIOCRUZ, Rio de Janeiro, Brasil
Received 3 January 1996; revised 26 February 1996; accepted 28 February 1996
Abstract
SR 27417, a potent PAF receptor antagonist, inhibited in a dose-dependent manner the hypotensive effect of PAF in rats. It protected rats with an ED,, value of 6 f 2 fig/kg (n = 6), when given i.v., 1 min before PAF administration. After iv. administration, SR 27417 exhibited extended duration of action, a significant protective effect was observed up to 48 h after the administration. After i.v. injection, SR 27417 (0.3, 1 and 3 mg/kg) afforded dose-dependent protection of actively sensitized rats against ovalbumin-induced hypotension but also totally reversed established antigen-induced hypotension. These results therefore confirm that PAF plays a major role in anaphylactic shock and suggest that SR 27417 may be an effective prophylactic as well as a potent curative drug in this pathology. Keywords:
SR 27417; Platelet activating factor (PAF); Antigen; Hypotension
* Corresponding
author. Tel.: + 33 62142361; fax: + 33 62142286.
0929-7855/96/$15.00 0 1996 Elsevier Science B.V. All rights reserved PII SO929-7855(96)00452-X
116
J.-M. Herbert et al. /J.
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1. Introduction PAF-acether, one of the most potent inducers of platelet aggregation known, has been described as exhibiting, when injected, a wide variety of biological actions including bronchoconstriction, hypotension, increase in vascucardiac effects (Braquet et al., lar permeability and negative inotropic 1987a,b; Handley, 1988). Moreover, PAF is believed to be involved in allergic responses, asthma, inflammation and anaphylactic and septic shock (Braquet et al., 1987a,b; Handley, 1988). The development of specific, potent PAF receptor antagonists is therefore essential for further elucidation of the pathophysiological roles of PAF and for developing new drugs active in the pathophysiological situations where PAF is believed to be involved. Reseveral structurally-unrelated PAF antagonists were shown to cently, exhibit beneficial activities in allergen-induced anaphylactic shock (Damas, 1989; Casals-Stenzel, 1987; Herbert et al., 1991b; Terashita et al., 1987, 1992). These data provided further support for earlier indications that PAF antagonists may protect against respiratory and circulatory dysfunctions such as systemic hypotension associated with a decrease in peripheral vascular resistance and cardiac failure occurring during severe anaphylactic shock syndromes. Recently, SR 27417, the first member of a newly-developed PAF antagonist series, has been described as one of the most potent PAF receptor antagonists described to date (Herbert et al., 1991a). Moreover, this compound has been shown to inhibit and reverse PAF- and endotoxin-induced hypotension in rats and guinea pigs (Bernat et al., 1992) and to protect mice from lethal anaphylactic and endotoxin-induced shock (Herbert et al., 1991b) therefore showing that PAF plays a major role in septic shock and that SR 27417 may be an effective prophylactic as well as a potent curative drug in this pathology. The aim of the present work was therefore to extend such observations to anaphylaxis and to evidence if SR 27417 protects rats from the hypotensive effect of PAF and antigen in actively sensitized animals.
2. Materials and methods 2.1. PAF-induced hypotension in the rat The method used to evaluate the effect of the tested drugs on PAF-induced hypotension has been described elsewhere (Terashita et al., 1985). Briefly, male Sprague-Dawley rats (280-300 g, Charles River, France) were anaesthetized with sodium pentobarbitone (30 mg/kg, i.p.). A catheter was introduced into the left carotid artery and the mean arterial blood pressure was continuously measured with a P23db pressure transducer connected to a NARCO Physiograph recorder. Another catheter was inserted into the jugular vein for injection of PAF, drugs
J.-M.
Herbert et al. /J.
Lipid Mediators Cell SignaIling 15 (1996) 115-123
117
and their respective vehicles. PAF (100 ng/kg) was injected i.v., 1 min. after i.v. administration of the tested compounds. The maximal hypotensive response due to PAF injection was recorded and the effect of the various drugs determined at that time point (usually 2 min after PAF injection). Due to tachyphylaxis phenomena, a single dose of PAF was administered to each animal. The number of animals per group was 6. For each time point in the kinetic studies, a control group (n = 6) was introduced. 2.2. Antigen-induced hypotension in the rat Rats were actively sensitized according to Casals-Stenzel et al. (1987). Briefly, conscious rats were sensitized by injecting i.p. (1 ml/kg) a suspension of ovalbumin (40 pg/kg) and Al(OH), (0.2 g/ml) in saline. Al(OH), was added to the antigen solution 1 h prior to the injection. The rats received an i.p. injection on days 0, 2 and 4. Animals were used 21 to 28 days after the beginning of the sensitization procedure. Pentobarbitone-anaesthetized (30 mg/kg, i.v.) rats were prepared for blood pressure registration as already described above. Animals were challenged i.v. with ovalbumin (0.25 mg/kg, i.v.). The hypotensive response from antigen challenge was recorded every 5 min over a 20 min-period. To establish its efficacy, SR 27417 was given iv. 5 min before the antigen challenge and tested in a dose-response manner. In order to establish the reversal of the hypotensive effect, SR 27417 was also administered 5 min after ovalbumin. In saline-treated animals (non-sensitized) ovalbumin did not show any hypotensive effect. The number of animals per group was 6. 2.3. Drugs and dosage
C,,-PAF (1-0-hexadecyl-2-acetyl-sn-glyceryl-3-phosphoryl-choline) was purchased from Bachem (Switzerland). Stock solutions of PAF were prepared in absolute ethanol and subsequent dilutions were made with Tyrode’s solution containing 0.25% BSA. Ovalbumin was purchased from Sigma Chemical (France). SR 27417 (fumarate salt) (N-(2-dimethylamino ethyl)-N-(3-pyridinyl methyl) [4-(2,4,6_triisopropyl phenyl) thiazol-2-yl] amine) (Herbert et al., 1991a) was from Sanofi Recherche (Toulouse, France). For experiments, fresh solutions of SR 27417 were prepared daily in a mixture of saline and 0.1 N HCl (l/40 v/v). Dilutions were made in saline. Control animals received the same volume of saline. 2.4. Statistical analysis
Results are shown as arithmetic means. Grouped data were analysed for significance by comparison with the vehicle-treated group using the Kruskal-Wallis test. The level of significance was chosen as p < 0.05.
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3. Results 3.1. Effect of SR 27417 on PAF-induced hypotension in the rat Injection of PAF at the dose of 100 ng/kg i.v. produced a 45 + 7.3 mmHg (n = 45) decrease in the mean arterial blood pressure (MAP) (basal blood pressure = 75.2 + 4.3 mmHg, n = 30). The recovery period (time required for blood pressure to return to pre-injection values) was 4 min. Under the same conditions, PAF-induced hypotension in the rat was significantly reduced by i.v. pretreatment with SR 27417 (Fig. 1). SR 27417 when given iv., 1 min before PAF challenge did not show any effect on the basal blood pressure but inhibited the PAF-induced response in a dose related manner with an ED,, value (dose of compound which reduced 50% of the PAF-induced hypotension in the control group) of 6 + 2 pgg/kg (n=6). SR 27417 a d ministered i.v. at 1 mg/kg exhibited an extended duration of activity and was able to protect significantly rats from PAF-induced hypotension for at least 48 h (Fig. 2).
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Fig. 1. Effect of SR 27417 on PAF-induced hypotension in rats. Increasing doses of SR 27417 were injected iv. 1 min before the injection of PAF (100 ng/kg, i.v.). Hypotension was monitored as described under Section 2. Data points represent the mean of 6 animals. Kruskal-Wallis test was used to examine the differences between vehicle and drug-treated groups; * p < 0.05, ** p < 0.01, *** p < 0.001.
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Time (h) Fig. 2. Time-course of the protective effect of i.v. administrations of SR 27417 on PAF-induced hypotension in rats. SR 27417 was injected intravenously (1 mg/kg, iv.) 1 to 80 h before the injection of PAF (100 ng/kg, iv.). Hypotension was measured as described under Section 2. Values are mean of 6 animals/time for each dose.
3.2. Effect of SR 27417 on antigen-induced hypotension in the rat Injection of antigen (ovalbumin, 0.25 mg/kg, i.v.) to actively sensitized animals produced a rapid-onset hypotension, characterized by a decrease in the MAP of 30 to 40% over a l-2 min period (Fig. 3). In the controls, MAP remained at the same level for the whole length of the observation period (20 min). As shown in Fig. 3, SR 27417 administered intravenously (0.3, 1 and 3 mg/kg, i.v.), 5 min prior to the antigen challenge did not affect basal blood pressure of rats (not shown) but prevented significantly ovalbumin-induced hypotension in a dose-dependent manner. SR 27417 (0.3, 1 and 3 mg/kg, i.v.) reversed the established hypotension induced by ovalbumin (Fig. 4).
4. Discussion In the past few years, evidence has been accumulating indicating that PAF contributes to the expression of the haemodynamic and haematological features of anaphylactic shock. The data supporting this concept are, firstly, that all of the major pathophysiological events induced by antigen challenge of pre-sensitized animals, i.e. systemic hypotension, bronchoconstriction, thrombocytopenia,
120
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leukopenia, increased vascular permeability and death, can be mimicked by PAF injection in animals (Camussi et al., 1983; Chang et al., 1987; McManus et al., 1980), and secondly, that the circulating PAF concentration increases after allergeninduced bronchoconstriction in humans (Chan-Yeung et al., 1991). Therefore, since there is now good evidence that PAF is one of the most prominent mediators of the shock state, it may be worthwhile studying the effect of selective PAF antagonists in such pathophysiological states. Moreover, PAF antagonists of various chemical structures have been shown to inhibit the deleterious effects of anaphylaxis in animals (Damas, 1989; Casals-Stenzel, 1987; Herbert et al., 1991b; Terashita et al., 1987, 1992) (hypotension, bronchopulmonary disturbance and lethality), thus confirming the key role of PAF in this pathology. SR 27417, the first member of a newly-developed PAF antagonist series has been shown to be a highly potent, specific and competitive PAF receptor antagonist by its inhibitory results on the PAF-induced aggregation of rabbit and human platelets and on the oxydative burst of guinea-pig peritoneal macrophages (Herbert et al., 1991a). This potency was not only expressed in vitro, but also by SR 27417’s ability to inhibit PAF-induced in vivo responses in mice and guinea-pigs, this activity being noticeable by its extremely long duration of life. In a recent study (Herbert et al., 1991b), we showed that i.v. or oral doses of SR 27417 afforded complete 85
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Lipid Mediators Cell Signalling 15 (1996) 115-123
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Time (mid Fig. 4. Reversal of the antigen-induced hypotension by SR 27417 in rats. SR 27417 was given i.v. at 0.3 (U), l(A) and 3 mg/kg (T), 5 mm after the administration of the antigen (0.25 mg/kg, iv.). Controls (0) were injected with saline. Values are expressed as means + SD (n = 6 animals/group). Kruskal-Wallis test was used to examine the differences between vehicle and drug-treated groups; ** p < 0.01, *** p i 0.001.
protection of mice against antigen and endotoxin-induced lethality, therefore suggesting that it could be an effective preventive drug against shock syndromes. Profound decrease in MAP being one of the most prominent features of anaphylaxis, this study therefore examined the efficacy of SR 27417 in protecting rats from PAF or antigen-induced hypotension in sensitized animals. SR 27417 administered i.v., inhibited in a dose-dependent manner the hypotensive effect of PAF but a further important feature of the activity of SR 27417 is the duration of its protective effect against PAF-induced hypotension. Indeed, SR 27417 was able to protect significantly rats from the effects of PAF for at least 48 h after iv. administration. Such pharmacodynamical features correlate with those already reported in other animal species for SR 27417’s protective effect against PAF-, endotoxin- or anaphylaxis-induced lethality in mice and brochoconstriction, haemoconcentration, thrombocytopaenia and leukopaenia in guinea-pigs (Herbert et al., 1991a,b). Intravenous administration of SR 27417 prevented almost completely antigen induced hypotension. As already reported for this compound in other experimental conditions (Herbert et al., 1991b), the doses of SR 27417 needed to protect animals against ovalbumin-induced responses were 30 to 50 times greater than the doses needed to block PAF-induced hypotension. This may indicate that greater amounts
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of PAF are released during allergen challenge, compared with the amount of PAF used in the PAF-induced hypotension. Alternatively, the release of PAF after anaphylactic shock may result in high local concentrations of PAF which require a greater amount of PAF antagonist to achieve protection. SR 27417 not only inhibited but also reversed the antigen-induced hypotension. The doses required for the preventive and curative action of SR 27417 in antigen-induced hypotension were in the same concentration range. Similar results have been reported for SR 27417 with regard to endotoxin-induced hypotension in rats and guinea pigs (Bernat et al., 1992). These results therefore indicate that SR 27417 is one of the most potent antagonists of PAF- or antigen-induced hypotension in animals and confirms the involvement of PAF in anaphylactic shock. SR 27417, a long-acting, orally-active PAF receptor antagonist, showed a beneficial protective effect in this experimental shock state and therefore may be of great potential interest in the early treatment of anaphylactic shock in man as well as in other pathological situations where PAF is believed to be involved.
References Bernat, A., Herbert, J.M., Salel, V., Lespy, L. and Maffrand, J.P. (1992) Protective effect of SR 27417, a novel PAF antagonist, on PAF- or endotoxin-induced hypotension in the rat and the guinea-pig. J. Lipid Mediators 51, 41-48. Braquet, P., Mencia-Huerta, J.M., Chabriet, P.E., Touqui, L. and Vargaftig, B.B. (1987a) The promise of platelet activating factor. IS1 Atlas of Science, 1, 187- 198. Braquet, P., Shen, T.Y., Touqui, L. and Vargaftig, B.B. (1987b) Perspectives in platelet activating factor research. Pharmacol. Rev., 39, 97-145. Camussi, G., Tefta, C. and Bussolino, F. (1983) Inhibitory effect of prostacyclin (PGIZ) on neutropenia induced by intravenous injection of platelet activating factor (PAF) in rabbit. Prostaglandins 25, 343-351. Casals-Stenzel, J. (1987) Effects of WEB 2086, a novel antagonist of platelet activating factor, in active and passive anaphylaxis. Immunopharmacology, 13, 117- 124. Casals-Stenzel, J., Muacevic, G. and Weber, K.H. (1987) Pharmacological actions of WEB-2086, a new specific antagonist of platelet activating factor. J.Pharmacol. Exp. Ther., 241, 974-981. Chang, SW., Feddersen, C.O., Henson, P.M. and Voelker, N.F. (1987) Platelet activating factor mediates hemodynamic changes and lung injury in endotoxin-treated rats. J. Clin. Invest. 79, 1498-1509. Chan-Yeung, M., Lam, S., Chan, H., Tse, K.S. and Salari, H. (1991) The release of platelet-activating factor into plasma during allergen-induced bronchoconstriction. J. Allergy Clin. Immunol. 87, 667-673. Damas, J. (1989) Involvement of PAF-acether in the anaphylactic shock in the rat. J. Lipid Mediators, 1, 161-170. Handley, D.A. (1988) Development and therapeutic indications for PAF receptor antagonists. Drugs of the Future, 13, 137-152. Herbert, J.M., Bernat, A., Valette, G. et al. (1991a) Biochemical and pharmacological activities of SR 27417, a highly potent, long acting PAF receptor antagonist. J. Pharmacol. Exp. Ther., 259, 4451. Herbert, J.M., Lespy, L. and Maffrand, J.P. (1991b) Protective effect of SR 27417, a novel PAF antagonist, on lethal anaphylactic and endotoxin-induced shocks in mice. Eur. J. Pharmacol., 205, 271-276.
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McManus, L.M., Hanahan, D.J., Demopoulos, CA. and Pinckard, R.N. (1980) Pathobiology of the intravenous infusion of acethyl-glyceryl ester phosphorylcholine (AGEPC), a synthetic platelet-activating factor (PAF), in the rabbit. J. Immunol. 124, 2919-2924. Terashita, Z., Imura, Y., Nishikawa, K. and Sumida, S. (1985) Is platelet activating factor (PAF) a mediator of endotoxin shock? Eur. J. Pharmacol., 109, 257-261. Terashita, Z.I., Imura, Y., Shino, A. and Nishikawa, K. (1987) A lethal role of platelet activating factor in anaphylactic shock in mice. JPET, 243(l), 378-383. Terashita, Z.I., Kawamura, M., Takatani, M., Tsushima, S., Imura, Y. and Nishikawa, K. (1992) Beneficial effects of TCV-309, a novel potent and selective platelet activating factor antagonist in endotoxin and anaphylactic shock in rodents. JPET, 260(2), 748-755.