S. Fernandez-Gallardo

Inhibition of the vascular actions of IgG aggregates by BN 52021, a highly specific antagonist of paf-acether.

The effect of BN 52021, a selective antagonist of paf-acether (Braquet GB patent 8, 418, 424 July 19, 1984), was studied in normotensive rats challenged with different doses of paf-acether. Sudden death was observed in animals receiving an i.v. dose of 10 micrograms/kg of paf-acether and this was prevented by prior treatment with BN 52021 (5 mg/kg, i.v.). Animals receiving 2.5 micrograms/kg of paf-acether had a fall of mean arterial pressure of 92.5 +/- 4.7 mmHg which recovered to the prechallenge level 20.5 +/- 0.2 min thereafter. Previous treatment with BN 52021 (5 mg/kg, i.v.) reduced the mean arterial pressure fall to 47 +/- 0.9 mmHg and the time of recovery to 5.7 +/- 1.7 min. The extravasation of 125I-bovine serum albumin under the above conditions was reduced by BN 52021 from 36 +/- 3 to 18 +/- 3%. A lower dose of BN 52021 (1 mg/kg, i.v.) was also effective in reducing later extravasation, but was unable to prevent the extravasation which appears up to 10 min after the injection of paf-acether. To extend these findings to a model of endogenous production of paf-acether, other animals were challenged with soluble aggregates of human IgG (40 mg/kg, i.v.; Iñarrea et al., Immunopharmacology 6:7, 1983).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of the platelet-activating factor antagonist BN 52021 on the hemodynamics of rats with experimental cirrhosis of the liver

Previous studies from this laboratory have shown that rats with experimental cirrhosis of the liver induced by the combined administration of oral phenobarbital and inhaled carbon tetrachloride show an hyperdynamic status with enhanced cardiac output (CO), and decreased mean arterial pressure (MAP) and peripheral vascular resistance (PVR). Cirrhotic rats also showed an increased vascular permeability. All these phenomena are similar to some of the known effects of the systemic infusion of low doses of synthetic platelet-activating factor into the systemic circulation of normal rats. The measurement of the levels of platelet-activating factor in samples of blood demonstrated significantly higher levels in cirrhotic (2.65 +/- 0.39; n = 10) than in control rats (1.50 +/- 0.57 ng/ml; n = 10; p less than 0.05). The hemodynamic changes induced by the intravenous injection of the platelet-activating factor receptor antagonist BN 52021 (5 mg/kg body weight) have been measured in 10 control and 10 cirrhotic male Wistar rats, using a radioactive microsphere technique. BN 52021 induced no significant hemodynamic changes in control animals. However, in cirrhotic animals it induced a significant decrease in CO with increase in PVR. MAP increased slightly but not significantly. From these data it can be deduced that platelet-activating factor plays a role in the hemodynamic derangement shown by cirrhotic rats and that these derangement can be reversed by BN 52021, a highly selective antagonist of the platelet-activating factor receptor.

The role of platelet‐activating factor and peptidoleukotrienes in the vascular changes of rat passive anaphylaxis

1 The role of platelet‐activating factor (PAF) and peptidoleukotrienes as putative mediators of some of the vascular changes triggered by antigen was investigated in rats passively sensitized with monoclonal anti‐DNP (2,4‐dinitrophenyl) IgE. 2 Lethal anaphylaxis with respiratory distress, systemic hypotension, detachment of the intestinal mucosa, leukopenia and extravasation of protein‐rich plasma was observed after antigen challenge of rats sensitized with partially purified monoclonal IgE at concentrations of 15 mg protein kg−1. 3 Analysis of the peritoneal fluid obtained after i.v. challenge with DNP‐BSA (bovine serum albumin) showed the presence of significant amounts of PAF (101 ± 8 pg/rat), whereas this mediator was undetectable in control animals. Leukotriene D4 was the predominant peptidoleukotriene that could be recovered after antigen challenge, and showed an extremely high concentration (92 ± 15 ng/rat) as compared to PAF levels. 4 Extravasation of protein‐rich plasma was observed shortly after challenge and reached a maximum at 30 min. Treatment of animals with i.v. PCA 4248 (1–2 mg kg−1) and WEB 2086 (1 mg kg−1), two chemically unrelated compounds which are antagonists of the PAF‐receptor, produced a significant reduction of the extravasation of protein‐rich plasma. 5 The same degree of protection could be afforded by MK‐886, an inhibitor of leukotriene biosynthesis. Combined treatment with WEB 2086 and MK‐886 provided greater inhibition of protein‐rich plasma extravasation than either compound alone. PCA 4248 was also found to inhibit in a dose‐dependent manner the systemic hypotension observed upon DNP‐BSA challenge. 6 These data indicate that the lipid mediators PAF and peptidoleukotrienes are major effectors of the vascular disturbances observed in rat passive IgE‐mediated anaphylaxis.

Evidence of a role for paf-acether in the pathophysiology of the shock state

The pathophysiology of the shock state includes a variety of hemodynamic changes such as systemic hypotension, pulmonary hypertension and increased vascular permeability leading to the extravasation of protein rich plasma. These changes can be initiated by different etiological factors, but many of them have been related to the stimulation of activation systems (complement, kinins, etc.) or to the generation of inflammatory mediators. The purpose of the present study has been to obtain evidence of the involvement of paf-acether in the pathogenesis of the shock state initiated in rat and mouse by Gram-negative bacteria and soluble aggregates of immunoglobulin G. The injection of 1-2 MDa aggregates of immunoglobulin G to normal Sprague-Dawley rats, induced a dose-dependent systemic hypotension which appeared about five minutes after completion of the intravenous challenge. Simultaneously, extravasation of protein-rich plasma occurred as judged from the finding of an increased clearance of 125I-BSA. In similar experiments in mice, a reduction of the vascular volume was observed using 51Cr-labelled homologous red blood cells. Under these conditions, a lipid compound analogous to paf-acether was obtained from the liver and the spleen of these animals. The generation of this compound preceded the development of blood volume depletion and could be suppressed by either quinacrine or depletion of mononuclear phagocytes by total irradiation with 700 rads. The previous treatment of the rats with the compound BN 52021 (a specific antagonist of the paf-acether receptor) at a dose of 5mg/kg, i.v., prevented the appearance of hypotension and extravasation in response to an i.v. challenge with soluble aggregates of immunoglobulin G. Interestingly, the reversal of hypotension was also observed when BN 52021 was infused after the immunoaggregates (5mg/kg). The possible involvement of paf-acether in the hemodynamic changes of Gram-negative sepsis was studied in rats which had received an intraperitoneal inoculation of E. coli. The animals inoculated with the doses of bacteria which produced mortality showed a time- and dose-dependent increase of vascular permeability as judged from the presence of abundant peritoneal exudate and the reduction of the circulating volume. Simultaneously, significant amounts of paf-acether could be obtained from the peritoneal exudate and from the spleen preceding to the development of the circulating volume depletion.(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet-activating factor antagonists do not protect against the development of experimental autoimmune encephalomyelitis

There is evidence suggesting the involvement of the platelet-activating factor (PAF) in central nervous system (CNS) functions. The possibility exists that PAF may be relevant in eliciting cell-mediated autoimmune phenomena in CNS. To assess the role of PAF in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), male Lewis rats were primed with whole spinal cord from guinea pig, emulsified in Freunds adjuvant supplemented with 10 mg/ml of Mycobacterium tuberculosis, H37Ra strain. Treatment with two different PAF antagonists (PCA 4248, WEB 2170) was applied starting from day 1 or day 5 postinoculation on a twice-daily basis. Neither PCA 4248 nor WEB 2170 suppressed the clinical signs of EAE. PAF concentration was measured in CNS tissue from the 9th day after inoculation to the 15th day, and no differences were found between control and EAE animals. These results suggest that PAF is not involved in the mediation of EAE.

Effect of immunological stimulation on the production of platelet-activating factor by rat peritoneal cells : its relevance to anaphylactic reactions

The production of platelet-activating factor (PAF) by rat peritoneal cells was studied using as stimuli either monoclonal IgE, IgG1 or IgG2b anti-DNP (2,4-dinitrophenyl), and DNP-BSA. Peritoneal cells sensitized in vitro with any of these antibodies at concentrations higher than 10 nM and challenged with 1 microM DNP-BSA produced PAF. PAF production was also elicited by preformed IgE/ and IgG2b/DNP-BSA immune complexes, preferentially at a large antigen/antibody ratio. The production of PAF was unrelated to the activation of mast cells, since it occurred in populations depleted of mast cells by adherence to plastic dishes. Moreover, the release of [3H]serotonin from IgE-sensitized mast cells showed a time-course more rapid than PAF production and occurred in cells sensitized with IgE at concentrations lower than those required for PAF formation. In contrast, peritoneal cells sensitized with IgG1 and IgG2b failed to release [3H]serotonin. Rat peritoneal cells showed a significant ability to catabolize PAF by intracellular PAF-acetylhydrolase in view of both the amounts of enzyme activity assayed in cellular homogenates, and the 15-fold increase on controls of PAF quantities detected in peritoneal cells treated with phenylmethylsulfonyl fluoride (PMSF), a known inhibitor of PAF-acetylhydrolase. The PAF activity produced upon PMSF addition showed a retention time on reverse-phase HPLC which suggests structural identity to PAF produced by either immunological challenge or ionophore A23187. These data suggest that PAF formed during rat passive anaphylaxis reactions depends on the activation of mononuclear phagocytes. This production may be triggered by two types of low affinity receptors: Fc epsilon RII/CD23 and Fc gamma R. The ability of peritoneal cells to catabolize PAF by intracellular acetylhydrolase seems unaffected by immunological stimulation.

Role of PAF-acether in the mediation of pathophysiological responses to aggregated immunoglobulins. Studies with the platelet-activating factor receptor antagonist BN 52021

Sprague-Dawley rats were challenged with an intravenous (i.v.) infusion of soluble aggregates of immunoglobulin G. Animals receiving a dose of aggregates of 40 mg/kg showed a significantly reduced time of lysis of diluted blood clot, which paralleled the appearance in plasma of tissue-type plasminogen activator. These changes occurred about 5-10 min after the challenge, which is a more protracted time-course than that observed in response to paf-acether. A significant increase in serum levels of N-acetylglucosaminidase was also observed in the animals several minutes after challenge. Blood neutrophil count showed a 50% reduction that reached its maximum at 10 min and was followed by an overshoot after 30 min. In experiments in rats previously depleted of circulating PMN by treatment with vinblastine, no significant differences were observed in N-acetylglucosaminidase release as compared to non-treated animals. Since prior evidence indicated that endogenously generated paf-acether could be a mediator responsible for these changes, at least to some extent, the compound BN 52021, a specific antagonist of the paf-acether receptor was given to these animals prior to the challenge with the complexes. All the above mentioned responses were significantly reduced by BN 52021, which is in keeping with the hypothesis involving endogenous paf-acether release in the mediation of these changes. By contrast, BN 52021 did not interfere with the clearance of the aggregates from the circulation, which seems to be a beneficial mechanism to reduce immune-mediated tissue injury. These data extend the number of paf-acether mediated pathophysiological changes that can be observed in response to immune aggregates.

Lack of platelet-activating factor release on acute myocardial ischemia in the isolated interventricular septum of rabbit heart

The effects of platelet-activating factor (PAF) on myocardial injury after 1 h global ischemia-30 min reperfusion were investigated in isolated arterially perfused interventricular septum of rabbit heart. PAF did not significantly affect developed tension, +/- dT/dtmax, resting tension and the times of active state in non-ischemic septa. The recovery of developed tension was significantly reduced by PAF (100 nM), after an ischemia-reperfusion challenge, from the control value of 20.9 +/- 3.5% to 10.5 +/- 1.8%, without a change in the resting tension (15.7 +/- 2.8 vs. 15.6 +/- 1.3 g). BN 52021 (20 microM), alone did not modify either parameter of ischemic damage, but antagonized the aggravating effect of PAF. Evidence of PAF activity was not found in any of the samples of the effluent perfusate obtained from ischemic control experiments. On the basis of the present results, we suggest a direct role for PAF in aggravating the myocardial damage induced by ischemia, and discard heart cells as the source of PAF in this state.

Platelet-Activating Factor: An Inflammatory Mediator Involved in the Pathophysiology of Shock

The shock state is an important clinical condition characterized by the occurrence of profound hemodynamic disturbances and the subsequent development of functional failure of many organs. The pathophysiology of shock is very complex, and many important aspects remain to be elucidated. Hemodynamic changes such as reduction of arterial pressure and cardiac output, a decrease in the count of platelets and leukocytes, an elevation of pulmonary arterial pressure and the stimulation of blood coagulation, kinin and complement system have been repeatedly observed in the process of shock evolution. At the present time, many chemical mediators and activation systems have been implicated in the pathogenesis of these disturbances, and this has surely opened the door to a vista of new therapeutic trends for this severe condition. Histamine, kinin, serotonin and endorphins have been found to be released during shock evolution, and most recently metabolites of arachidonic acid have been recognized to play a central role in the pathophysiology of shock in view of their potent actions on the cardiovascular system.