Influence Of Platelet Activating Factor Research Articles

Influence of platelet-activating factor, lyso-platelet-activating factor and edelfosine on Langmuir monolayers imitating plasma membranes of cell lines differing in susceptibility to anti-cancer treatment: the effect of plasmalogen level

Three structurally related but differing in biological activities single-chained ether phospholipids (PAF (platelet-activating factor) and lyso-PAF) and an anti-cancer drug (edelfosine (ED)) were investigated in Langmuir monolayers imitating natural membranes. The aim of the undertaken experiments was to study the influence of these lipids on monolayers mimicking plasma membranes of cell lines differing in susceptibility to the anti-cancer activity of ED, i.e. promyelocytic leukaemia cells (HL-60) and promyeloblastic leukaemia cells (K-562). As these cells differ essentially in the cholesterol/phospholipid ratio and plasmalogen concentration in the membrane, we have carried out systematic investigations in artificial systems of various compositions. The results for model leukaemia cell membrane were compared with data acquired for systems imitating normal leucocytes. Our results show that the level of plasmalogens significantly modulates the influence of the single-chained phospholipids on the investigated systems. The experiments confirmed also that the interactions of ether lipids with a model membrane of HL-60 cells (in biological tests sensitive to ED) have opposite character when compared with K-562, being resistant to ED. Moreover, the values of the parameters characterizing monolayers serving as membrane models (strength of interactions, monolayers fluidity and morphology) proved both sensitivity of these cells to ED and lack of their susceptibility towards PAF. Interestingly, it has been found that lyso-PAF, which is usually described as an inactive precursor of PAF, displays a stronger effect on HL-60 model membranes than ED.

The influence of platelet activating factor on the effects of platelet agonists and antiplatelet agents in vitro

We assessed the effect of the intercellular mediator of inflammation, platelet activating factor (PAF), on platelet function. The interaction between PAF and the platelet agonists ADP, thrombin and convulxin was analyzed in vitro in whole blood with the use of flow cytometry and was further characterized with the use of receptor antagonists to PAF (ABT-491), P2Y1 (MRS-2179), and P2Y12 (cangrelor) as well as a monoclonal anti-PSGL-1 antibody (anti-CD162). Low concentrations of PAF (0.1 nM) synergistically augmented platelet activation induced by other agonists (P < 0.01). Augmentation by PAF was receptor mediated and did not require platelet-leukocyte interaction. With >99% inhibition of P2Y receptor-mediated platelet activation, greater than additive activation was still observed with the combination of ADP plus PAF. Accordingly, PAF synergistically augments platelet activation in response to ADP and thrombin, and the extent of inhibition exerted by P2Y receptor antagonists is decreased in the presence of PAF.

Influence of platelet activating factor and its antagonist on portal hypertension associated with liver cirrhosis: an experiment with rats

To investigate the influence of platelet activating factor (PAF) and its antagonist BN52021 on portal hypertension associated with liver cirrhosis. Ten SD rats were injected intraperitoneally with carbon tetrachloride to establish a liver cirrhosis model and 10 rats were injected with olive oil as controls. The concentrations of PAF in the blood and liver was examined by rapid (3)H-PAF scintillation proximity assay and the hepatic PAF binding capacity was examined by receptor saturation binding technique. The pressure of portal vein and pressure of femoral artery were measured by intubation method. BN52021 was infused into the portal vein to observe its influence on the blood pressure. The hepatic PAF levels of the cirrhotic rats was 4.0 ng/g +/- 0.4 ng/g, significantly higher than that of the control rats (2.7 ng/g +/- 0.5 ng/g, P < 0.01). The hepatic efflux PAF level of the cirrhotic rats was 6.3 ng/g +/- 0.6 ng/g, significantly higher than that of the control rats (3.4 ng/g +/- 0.6 ng/g, P < 0.01). The hepatic output PAF levels of the cirrhotic rats was 1.0 ng/g +/- 0.6 ng/g, significantly lower than that of the control rats (0.3 ng/g +/- 0.5 ng/g, P < 0.01). The maximum PAF binding capacity of the cirrhotic rats was 2.8 +/- 0.21 fmol/microg protein, significantly higher than that of the control rats (0.9 +/- 0.06 fmol/microg protein, P < 0.01). However, the receptor affinity was not significantly different between these 2 groups. The portal pressure of the cirrhotic rats was 12.2 mm Hg +/- 0.7 mm Hg, significantly higher than that of the control rats (5.3 mm Hg +/- 0.6 mm Hg, P < 0.01). The femoral arterial pressure of the cirrhotic rats was 82 mm Hg +/- 10 mm Hg, significantly lower than that of the control rats (114 mm Hg +/- 9 mm Hg, P < 0.01). Infusion of PAF via the portal vein increased the portal pressure from 12.1 mm Hg +/- 0.6 mm Hg with an increase of 32% (P < 0.01) in the cirrhotic rats, and from 7.7 mm Hg +/- 0.8 mm Hg with an increase of 23%. The PAF response of the cirrhotic rats was 4.1 mm Hg +/- 1.0 mm Hg (227%), significantly higher than that of the control rats (1.8 mm Hg +/- 0.3 mm Hg, P < 0.01). The femoral artery pressure decreased from 82 mm Hg +/- 10 mm Hg to 48 mm Hg +/- 4 mm Hg (P < 0.01) in the cirrhotic rats, and from 114 mm Hg +/- 9 mm Hg to 52 mm Hg +/- 4 mm Hg (P < 0.01). After portal infusion of BN52021 the portal pressure decreased from 14.6 mm Hg +/- 1.6 mm Hg to 12.3 mm Hg +/- 0.8 mm Hg (P < 0.05) with a decrease of 16%, however, did not significantly influenced the femoral arterial pressure in the cirrhotic rats, and did not significantly influenced the portal pressure and femoral arterial pressure in the control rats. The increased hepatic PAF synthesis in cirrhotic is the major source of elevated circulating PAF It upregulates the hepatic hemodynamics that contributes to portal hypertension. The increased portal pressure by endogenous PAF can be decreased to a certain extent by BN52021 which may be used in treatment of portal hypertension.

Influence of platelet activating factor on expression of adhesion molecules in experimental pancreatitis.

To determine whether Platelet activating factor (PAF) has a regulation role in the expression of adhesion molecules and accumulation of neutrophils in a murine model of acute pancreatitis. One hundred twenty-eight Kunming mice were divided into four groups. Group 1 received 0.1 ml saline s.c. every hour for three hours (sham). Group 2 received cerulein (50 microg/kg dose s.c.) every hour for three hours. Group 3 received AP and additional challenge of PAF (50 mg/kg in absolute ethanol) (AP/PAF). Group 4 received AP, plus therapeutic treatment with GAB (25 mg dose i.p.) immediately after the first challenge of cerulein (AP/GAB). Animals were sacrificed at 12 h after the first challenge of saline or cerulein. Adhesion molecules of pancreas were semi-quantified by SP methods. Standard assays were performed for serum amylase and myeloperoxidase activity (MPO) of pancreas. Histology of pancreas was scored in a blind manner. Water content of pancreas was also measured at the same time. Control pancreata showed negligible adhesion molecule expression and neutrophil accumulation. There were evident adhesion molecules expression and neutrophil accumulation in AP and AP/PAF compared with sham (P<0.05). AP/GAB had a lower level of adhesion molecules, neutrophils, and water content versus AP and AP/PAF (P<0.05). Histology showed a trend toward improvement in AP/GAB, but did not reach statistical significance. PAF can induce the expression of adhesion molecules that mediate neutrophil accumulation. The PAF antagonist reduces the expression of adhesion molecules and the severity of inflammation when given immediately after the induction of mild AP in mice. These results suggest that PAF antagonism may be useful in the treatment of mild pancreatitis after its clinical onset.

Influence of platelet-activating factor, its cell analogs, and antagonist on the production of superoxide radicals by blood leukocytes of healthy and hypercholesterolemic individuals.

The influence of the phospholipid platelet-activating factor (PAF), its cell analogs, and lipid PAF antagonist on the production of superoxide radicals by leukocytes isolated from the blood of healthy and hypercholesterolemia IIA individuals was studied. It was found that endogenous superoxide production level in the leukocytes of hypercholesterolemic individuals more than 4-5 times higher than in the leukocytes of healthy individuals. Exogenous PAF stimulates the superoxide production in the leukocytes of healthy individuals but significantly inhibits the superoxide production in the leukocytes of hypercholesterolemic individuals. The compounds 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-PAF) and 1-alk-1;-enyl-2-acetyl-sn-glycero-3-phosphocholine (1-alkenyl-PAF) only slightly inhibited the endogenous superoxide production in the leukocytes of hypercholesterolemia individuals. However, pretreatment of leukocytes by 1-alkenyl-PAF or PAF-antagonist (1-O-alk-1;-enyl-2-(2;-acetoxybenzoyl)-sn-glycero-3-phosphocholine) results in a 50% inhibition of the PAF-induced superoxide production by leukocytes of healthy individuals. This PAF-antagonist alone or in combination with PAF induces a substantial (65-70%) inhibition of superoxide production in the leukocytes of hypercholesterolemic individuals. It is concluded that superoxide production by leukocytes of healthy individuals and especially by leukocytes of hypercholesterolemic individuals is process that depends on PAF or PAF-like lipids.

Platelet activating factor degradation in tear fluid from guinea pigs with allergic conjunctivitis.

The purpose of this study was to investigate the role of platelet-activating factor (PAF) and PAF acetylhydrolase (AH) in conjunctiva. The influence of PAF on conjunctival vascular permeability and the presence of PAF or its metabolites in tears from guinea pigs with allergic conjunctivitis were investigated. We instilled PAF to the eyes of guinea pigs and evaluated vascular permeability. Tear samples were collected from passively sensitized guinea pigs, and the concentration of PAF and its metabolites determined by liquid chromatography-tandem mass spectrometry. Exogenous PAF degradation in tear samples was evaluated with or without diisopropyl fluorophosphate (DFP). Topically applied PAF increased vascular permeability in conjunctiva. In the tear samples from guinea pigs with allergic conjunctivitis, PAF could not be detected. However, 40 +/- 6 ng/ml of lyso-platelet activating factor (lyso-PAF) and 230 +/- 50 ng/ml of 1-alkyl-2-acyl-sn-glycero-3-phosphocholine were detected at 10 min after challenge. Exogenous PAF was rapidly degraded in the tear samples from guinea pigs with allergic conjunctivitis, but not from normal guinea pigs. This PAF degradation was inhibited by DFP. These results suggest that PAF in the tear fluid is quickly hydrolyzed to lyso-PAF by PAF AH, which may be released or activated in allergic conjunctivitis.

Platelet activating factor alters receptor-coupled function in the isolated perfused rat heart.

Sepsis induces primary myocardial dysfunction. Yet, both hyper- and hypodynamic cardiac states characterize the sepsis syndrome, suggesting a modulatory role of septic mediators. Platelet activating factor (PAF), implicated in the pathogenesis of sepsis, is an endogenous phospholipid with diverse intracellular and extracellular effects. The purpose of this study was to investigate the influence of PAF (1) upon basal mechanical function of the heart, (2) upon receptor-coupled function of the heart, and (3) on basal and stimulated myocardial function at differing concentrations. In order to focus on the relationship between PAF and cardiac mechanical function, rat hearts were isolated and crystalloid perfused using a modified Langendorf preparation. Separate hearts received intracoronary vehicle (5% ethanol, 2.5% BSA) or PAF (20 or 40 microM) as a bolus, followed 10 min later by 0.25 microM isoproterenol (beta-receptor agonist) infusion over 3 min. Both 20 and 40 microM PAF produced a rapid decrease in rate pressure product (RPP = HR X LVDPmax) relative to control (P < 0.05). The depressive effect of PAF upon basal myocardial function did not persist and by 10 min RPP was not different (P > 0.05) among the groups. Isoproterenol infusion increased (P < 0.05) RPP in all groups. However, hearts pretreated with 20 microM PAF demonstrated a greater (P < 0.05) response to beta-adrenergic stimulation relative to vehicle-pretreated controls. This amplified response to isoproterenol was not observed with pretreatment at a higher concentration of PAF (40 microM, P > 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of platelet activating factor and a nonmetabolizable analogue on superoxide production by bone marrow derived macrophages.

Serum-free cultured macrophages could be stimulated for lucigenin-dependent chemiluminescence by platelet activating factor (PAF) and phorbol myristate acetate (PMA). Stimulation with PMA resulted in a desensitization against PAF, whereas prestimulation with PAF had no influence on a following response caused by PMA. The PAF analogue, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (Et-18-OCH3), did not induce chemiluminescence by itself and desensitized the cells against PAF, like substimulating concentrations of PAF. PAF and PMA responsiveness was rapidly modulated in a similar manner during adherence of the cells to polystyrene tubes. At higher concentrations, Et-18-OCH3 as well as lysophosphatidylcholines potentiated PMA-induced chemiluminescence. The PAF analogue was most effective. Although PMA-induced chemiluminescence was stimulated at least 5-fold by Et-18-OCH3, this compound increased the PMA-induced activation of protein kinase C only 1.39-fold. The priming effect of Et-18-OCH3 was not reduced in the absence of extracellular Ca2+ and after cell membrane depolarisation.