bluuebunny/crossref_metadata_2025 huggingface dataset:
Platelet‐activating factor acetylhydrolase activity in human tissues and blood cells
Authors: Stafforini Diana M. , Prescott Stephen M. , Zimmerman Guy A. , McIntyre Thomas M.
Published: February 2007

Human tissues, blood cells, and plasma have enzymes that catalyze the hydrolysis of PAF (1‐O‐alkyl‐2‐acetyl‐sn‐glycero‐3‐phosphocholine). The activities are not due to phospholipases A2 that hydrolyze long chain acyl groups at thesn‐2 position of glycerophospholipids, since they are calcium‐independent and are specific for hydrolysis of short chain acyl groups. We examined the biochemical properties of these PAF acetylhydrolase activities (EC 3.1.1.47) in homogenates of human liver and spleen, in white blood cells (neutrophils and monocytes), and in erythrocytes. The data suggest that the plasma and intracellular PAF acetylhydrolase activities are likely due to different proteins. Second, the intracellular PAF acetylhydrolase activities in liver and spleen share several biochemical features that differentiate them from the activities in blood cells. Third, the activities in monocytes and neutrophils have properties that differentiate them from the activity present in human erythrocytes. Finally, the erythrocyte activity has unique properties that place it in a separate category of short chain acylhydrolases. In conclusion, there is a family of distinct enzymes that can be identified as PAF acetylhydrolases based on their calcium‐independence and specificity for a short residue at thesn02 position of phospholipids.
Platelet‐activating factor (PAF) stimulates the lysoPAF acetyltransferase in leukocyte‐rich plasma: Use in PAF antagonist studies
Authors: Doebber Thomas W. , Wu Margaret S. , Mauriello Anthony , Alberts Alfred
Published: February 2007

Addition of platelet‐activating factor (PAF; 1‐O‐alkyl‐2‐acetyl‐sn‐glycero‐3‐phosphocholine) to leukocyte‐rich plasma from several species resulted in the rapid and pronounced activation of the PAF biosynthetic enzyme acetyl‐CoA:1‐O‐alkyl‐sn‐glycero‐3‐phosphocholine acetyltransferase (EC 2.3.1.67). Activation of acetyltransferase by PAF occurred in leukocyte‐rich plasma from human, chimpanzee, rhesus monkey, and dog. The neutrophil was indicated to be the major cellular source of the activabable acetyltransferase in leukocyte‐rich plasma. The induction of acetyltransferase was substantial with 10 nM PAF, and maximal at 10–30 seconds. Measurable acetyltransferase activation was significantly greater when the PAF‐activated cells were separated from the plasma by centrifugation before the acetyltransferase assay. This may be due in part to the removal of the PAF‐specific acetylhydrolase present in plasma which can cleave the acetyl group from PAF. Measuring PAF activation of acetyltransferase in leukocyte‐rich plasma can be useful to determine the potency of PAF antagonists with neutrophils in plasma compared to isolated neutrophils in aqueous buffer, and as anex vivo assay to determine the efficacy and plasma concentration equivalents of antagonists administered to whole animals. The PAF antagonist L‐659,989 was shown to be 3–5 times more potent in inhibiting PAF induction of acetyltransferase in isolated human neutrophils than in human leukocyte‐rich plasma, with IC50 values of 10 nM and 40 nM, respectively. In theex vivo assay, oral administration of the PAF antagonist L‐667, 131 to dogs resulted in very substantial inhibition of PAF induction of acetyltransferase in the leukocyte‐rich plasma. Utilizing theex vivo assay, oral administration of 1 mg/kg L‐659,989 to rats was found to result in plasma concentration equivalents of approximately 200–300 nM L‐659,989. Our findings offer a new approach for charagerizing thein vitro andin vivo efficacy of PAF receptor antagonists and demonstrate that PAF may be able to activate neutrophils in the bloodin vivo, further enhancing PAF synthesis.
The effect of inhibitors of platelet aggregation on the metabolism of platelet‐activating factor (PAF) in washed rabbit platelets
Authors: O'Neill C. , Ammit A. J. , Korth R. , Fleming S. , Wells X.
Published: February 2007

The rabbit platelet metabolizes platelet‐activating factor (PAF) intracellulary. PAF is deacetylated to produce lysoPAF which, in turn, can be acylated to produce 1‐O‐alkyl‐2‐acyl‐sn‐glycero‐3‐phosphocholine (alkylacyl GPC). Some PAF receptor antagonists have been shown to inhibit this metabolic conversion. In the present study we examined whether the PAF receptor antagonists SRI 63‐441 and WEB 2086 would inhibit the metabolism of PAF by intact rabbit platelets. In addition, we examined whether iloprost, a stable analogue of prostaglandin I2 (PGI2), and a potent inhibitor of platelet activation induced by a range of agonists, would also inhibit PAF metabolism. We found that SRI 63‐441 and WEB 2086 caused an almost complete inhibition of the conversion of PAF to alkylacyl GPC. Iloprost caused up to a 50% inhibition of PAF metabolism compared to antagonist‐free controls. Iloprost (and PGI2) is thought to inhibit platelet response by elevation of cAMP, while receptor antagonists act by blocking PAF binding to its receptor. Since iloprost caused partial inhibition of PAF metabolism, the results of this study suggest that inhibition of PAF metabolism does not occur solely due to competitive inhibition of PAF binding to its receptor.
PAF effects on transmembrane signaling pathways in rat kupffer cells
Authors: Gandhi Chandrashekhar R. , Olson Merle S.
Published: February 2007

Platelet activating factor (PAF) was found to stimulate the metabolism of inositol phospholipids via deacylation and phospholipase C in Kupffer cells, the resident macrophages in liver. PAF‐induced phosphoinositide metabolism occurred in two phases. Within seconds after stimulation, in the absence of extracellular Ca++, platelet activating factor caused the phosphodiester hydrolysis of phosphatidylinositol 4,5‐bisphosphate and phosphatidylinositol 4‐phosphate with the release of inositol 1,4,5‐trisphosphate and inositol 1,4‐bisphosphate. This was followed by an extracellular Ca++‐dependent release of glycerophosphoinositol, inositol monophosphates and inositol bisphosphates. Various Ca++‐mobilizing agonists failed to evoke hydrolysis of phosphoinositides. Platelet activating factor also stimulated the synthesis and release of prostaglandins from these cells. Platelet activating factor‐stimulated phosphodiester metabolism of phosphoinositides and prostaglandin synthesis was inhibited by treatment with pertussis toxin and cholera toxin. Pertussis toxin also inhibited platelet activating factor‐induced glycerophosphoinositol release. Cholera toxin, in contrast, stimulated platelet activating factor‐induced glycerophosphoinositol release and prostaglandin synthesis and synergistically stimulated the effect of platelet activating factor on these processes. The results suggest that platelet activating factor‐induced metabolism in the Kupffer cells occurs via specific receptors and may be mediated through the activation of different G‐proteins.
Platelet‐activating factor may participate in signal transduction processes in rabbit leukocytes
Authors: Stewart Alastair G. , Harris Trudi
Published: February 2007

The bacterial chemotactic peptide, formyl‐methionyl‐leucyl‐phenylalanine (fMLP), induces the generation of platelet‐activating factor (PAF), the mobilization of arachidonic acid and generation of superoxide anion (O2−) in rabbit polymorphonuclear leukocytes (PMNs). The PAF receptor antagonists, WEB 2086 (10–100 μM) and CV 6209 (1–10 μM), reduced the mobilization of arachidonic acid and the O2− generation in response to fMLP but not that in response to A23187. Pretreatment of PMNs with the phospholipase A2 inhibitor, chloroquine, or the serine protease inhibitor, tosyl‐phenylalanine chloromethyl ketone, reduced the fMLP‐stimulated generation of PAF and also reduced the generation of O2−. The respiratory burst induced by a submaximal concentration of phorbol myristate acetate was not affected by these compounds. These data are consistent with the suggestion that endogenous PAF may contribute to the signal transduction cascade initiated by fMLP.
Phorbol ester stimulates PAF synthesisvia the activation of protein kinase C in rat leukocytes
Authors: Hayashi Masahiko , Imai Yohsuke , Oh‐ishi Sachiko
Published: February 2007

When rat pleural mononuclear leukocytes were stimulated with 1 μM phorbol myristate acetate (PMA), platelet‐activating factor (PAF)‐like activity was detected in the supernatant and the cellular fractions of the incubation mixture, as measured by rabbit platelet aggregation. C16PAF activity peaked at 30 min in both fractions. Acetyltransferase activity in the microsomal fraction of the stimulated cells also increased rapidly and showed a peak at 10 min. A protein kinase C inhibitor, staurosporine, and an inhibitor of phospholipase A2,p‐bromophenacylbromide, inhibited stimulated PAF formation in both fractions. Staurosporine also inhibited PMA induced acetyltransferase activity. The data suggest that PMA stimulates PAF synthesis by the remodeling pathway in rat pleural cells through activation of both phospholipase A2 and acetyltransferase, and that the acetyltransferase, in turn, may be activated through activation of protein kinase C.
Protein kinase C is not involved in the desensitization of platelet activating factor receptor in rabbit platelets
Authors: Chau Lee‐Young
Published: February 2007

Rabbit platelets pretreated with platelet activating factor (PAF) became refractory to further stimulation by PAF. The effect was specific for PAF. In this study, the alteration in the specific agonist binding to PAF receptor in platelets following desensitization was investigated. As revealed by the Scatchard analysis of radioligand binding data, the affinity for specific PAF binding to desensitized platelet membranes was substantially lowered as compared with that to control platelet membranes. Guanine nucleotide triphosphate, which was shown to decrease the affinity of specific PAF binding to platelet membranes, had less effect on the PAF binding affinity to the desensitized preparation. In platelets pretreated with phorbol 12‐myristate‐13‐acetate, the binding affinity of PAF receptor remained unaltered. Pretreatment of platelets with 1‐(5‐isoquinolinesulphonyl)‐2‐methylpiperazine, a protein kinase C inhibitor, or neomycin, an inhibitor of the polyphosphoinositide breakdown, failed to prevent the reduction of specific PAF binding affinity following subsequent exposure to PAF. These results suggest that the agonist‐induced desensitization of PAF receptor in rabbit platelets is independent of activation of protein kinase C.
A unique pool of free arachidonate serves as substrate for both cyclooxygenase and lipoxygenase in platelets
Authors: Chevy Françoise , Wolf Claude , Colard Odile
Published: February 2007

Stimulation of platelets induces a rapid release of arachidonate from specific phospholipids and subsequent remodeling of arachidonate‐containing phospholipids. This process is accompanied by transformation of released arachidonate by cyclooxygenase and lipoxygenase enzymes. We addressed the question of whether the cyclooxygenase and the lipoxygenase products originated from the same arachidonate‐containing phospholipids. [14C]Arachidonate prelabeled platelets were stimulated by thrombin or by ionophore A 23187. We monitored the cyclooxygenase pathway by following 12‐hydroxy‐5,8,10‐heptadecatrienoic acid [12(S)‐HHT] formation and the lipoxygenase pathway by following 12‐hydroxy‐5,8,10,14‐eicosatetraenoic acid [12(S)‐HETE] formation and compared specific activities. The data showed that the same pool of released arachidonate can be utilized by either cyclooxygenase or by lipoxygenase. Indeed, the specific activity of both products was identical when both enzymes were acting. Since cyclooxygenase was rapidly deactivated while lipoxygenase continued to be active, the specific activity of 12(S)‐HETE became lower than the specific activity of 12(S)‐HHT when large amounts of 12(S)‐HETE were synthesized. Based on comparison of specific activity between phospholipids and oxygenated products, the pools of arachidonate‐containing phospholipids involved in the synthesis of oxygenated products are dependent on the amount of arachidonate released.
Paf‐acether in human skin
Authors: Denizot Yves , Michel Laurence , Benveniste Jacques , Meybeck Alain , Thomas Yolène , Duberfret Louis
Published: February 2007

Paf is a phospholipid mediator present in human skin which induces inflammatory events such as neutrophil infiltration and increased vascular permeability. Recent data suggest that cutaneous cells, such as fibroblasts and keratinocytes, produce paf and that paf is released during allergic cutaneous reactions. It is tempting to speculate that paf may contribute to the development of various skin disorders with acute and chronic skin inflammation. Paf antagonists may help in bringing answers to this hypothesis and may offer new prospects for the treatment of cutaneous inflammatory diseases.
Effect of platelet‐activating factor on cortisol and corticosterone secretion by perfused dog adrenal
Authors: Aikawa Tadaomi , Hirose Taeko , Matsumoto Itsuro , Morikawa Toshiko , Shimada Toshio , Mine Yumi , Tsujimoto Yoshiki , Tsuji Yoshiro
Published: February 2007

Administration of platelet‐activating factor (PAF) to perfused adrenal increased cortisol and corticosterone secretion. With hexadecyl PAF (C16PAF; 1‐O‐hexadecyl‐2‐acetyl‐sn‐glycero‐3‐phosphocholine), the increase was significant at 1 nM and maximal at 10 nM. The responses to 10 nM octadecyl PAF (C18PAF; 1‐O‐octadecyl‐2‐acetyl‐sn‐glycero‐3‐phosphocholine) were one fourth of those to 10 nM C16PAF. The addition of C16PAF to dispersed adrenal cells significantly increased cortisol and corticosterone production at 0.1 nM and 10 nM, respectively. C16PAF was about 1000 times more potent than histamine on a molar basis in respect to cortisol response in both perfused adrenal and dispersed adrenal cells. The results suggest that PAF induces cortisol release from dog adrenal.
Radioimmunoassay for platelet‐activating factor
Authors: Karasawa Ken , Satoh Noriko , Hongo Toshio , Nakagawa Yasuhito , Setaka Morio , Nojima Shoshichi
Published: February 2007

A radioimmunoassay (RIA) for measurement of platelet‐activating factor (PAF) was developed. At a final antiserum dilution of 1∶640, the lowest detection limit of PAF was 0.1 pmol (50 pg). The standard curve obtained was suitable for measurement of PAF in amounts ranging from 0.1 pmol to 30 pmol. The antiserum showed high specificity. Cross‐reaction for lysoPAF, lysophosphatidylcholine and long‐chain phosphati‐dylcholines was very low (less than 0.025%). 1‐Palmitoyl‐2‐acetyl‐sn‐glycero‐3‐phosphocholine cross‐reacted slightly (6.25%). PAF exogenously added to macrophage suspensions was quantitatively determined by RIA after solvent extraction and high‐performance liquid chromatographic separation. RIA was also used to estimate PAF formation after stimulation of rabbit alveolar macrophages in suspension with calcium ionophore A23187.
Synthesis of a PAF immunogen and production of PAF‐specific antibodies
Authors: Smal Mary A. , Baldo Brian A. , Redmond John W.
Published: February 2007

Platelet activating factor (PAF), a naturally occurring phospholipid with many potent physiological and pharmacological activities, is implicated as a mediator of many diseases. An immunoassay for PAF would greatly improve quantitation, and hence PAF‐specific antibodies were required. Chemically‐reactive analogs of PAF, containing an aldehyde group at the end of the 1‐O‐alkyl chain (hexyl or dodecyl), were synthesized from readily available materials. During the multi‐step synthetic procedure, the aldehyde group was protected as an acetal, which was converted by mild acidic hydrolysis to the aldehyde immediately prior to protein coupling. These analogs were coupled to methylated bovine serum albumin and the resultant conjugates were injected into rabbits. Antibodies to PAF were detected using a solid phase radioimmunoassay based on Protein A‐Sepharose. The dodecyl PAF conjugate proved to be the more immunogenic conjugate with more than half of the rabbits producing significant levels of antibodies (at least a 10‐fold increase in radioactive uptake over pre‐immune levels). Results from solid phase immunoassays employing nitrocellulose discs impregnated with PAF, lysoPAF, lecithin, lysolecithin and 2‐O‐methyl‐lysoPAF indicated that the antibodies recognized only PAF. PAF‐specific antibodies were isolated by affinity chromatography using a column of PAF‐poly(lysine) conjugated to carboxy‐activated polyacrylamide. The antibodies may be employed in a sensitive and specific immunoassay for PAF and for many other studies involving PAF.
A specific, sensitive and high‐capacity immunoassay for PAF
Authors: Baldo Brian A. , Smal Mary A. , McCaskill Alistair C.
Published: February 2007

A specific radioimmunoassay for platelet‐activating factor (PAF) sensitive in the range 10–1000 pg (0.02–2 pmoles) has been developed. Detailed quantitative hapten inhibition studies showed specificity for the acetyl group at C‐2 of PAF, a requirement for the ether linkage at C‐1 and some tolerance for substituents on the choline nitrogen. No significant cross‐reactivity was found with phosphatidylcholine and lysophosphatidylcholine or with lysoPAF.
Inhibitor(s) of platelet‐activating factor (PAF) in human saliva
Authors: Smal Mary A. , Baldo Brian A.
Published: February 2007

Quantitation of platelet‐activating factor (PAF) in human saliva samples by radioimmunoassay indicated there was, at times, sufficient PAF present to aggregate platelets. However, in certain samples, we observed little or no aggregation, and furthermore, these samples were found to inhibit aggregation induced by PAF (200 pg). Chromatographic fractionation of pooled saliva increased the PAF activity 4‐fold, and the observed inhibitory activity was found to co‐migrate with the fatty acids. The inhibitory fraction was found to be active against platelet aggregation induced by arachidonic acid (3.4 nmole) as well as PAF (25 pg), but not thrombin (20 mU). These results indicate the existence of a PAF inhibitor in saliva, which may explain why potentially toxic levels of PAF can occur in the saliva of normal, healthy individuals. These findings also highlight an important advantage of the radioimmunoassay over platelet aggregation for the quantitation of PAF in, at least, some biological fluids.
L‐659,989: A useful probe in the detection of multiple conformational states of PAF receptors
Authors: Hwang San‐Bao , Lam My‐Hanh
Published: February 2007

L‐659,989 is a potent, specific and competitive plateletactivating factor (PAF) receptor antagonist. The 2,5‐tritium labeled L‐659,989, similar to [3H]PAF, specifically binds to rabbit platelet membranes with an equilibrium dissociation constant (KD) of 1.60 (±0.20) nM in 10 mM MgCl2. However, guanosine 5′‐triphosphate (GTP) and several cations affect the specific binding of [3H]PAF and of [3H]L‐659,989 to rabbit platelet membranes in different ways. K+, Mg2+, Ca2+ and Mn2+ potentiate the specific binding of both ligands. Na+ and Li+ inhibit the specific [3H]PAF binding, but enhance the binding of [3H]L‐659,989; GTP reduces the [3H]PAF binding but has no effect on the binding of [3H]‐L‐659,989. Ni2+ inhibits the [3H]L‐659‐989 binding, but has no effect on the binding of [3H]PAF. In the presence of 150 mM NaCl, [3H]L‐659,989 exhibits identical KD and detectable binding sites (Bmax) values as those in the presence of 10 mM MgCl2, while Kd And Bmax values of [3H]PAF are dramatically reduced in the presence of 150 mM NaCl compared to those in 10 mM MgCl2. These results suggest the existence of multiple conformational states of the PAF specific receptor and that PAF and L‐659,989 bind differently to those states. In the presence of 150 mM NaCl and 1 mM GTP, receptors appear to exist in a single conformational state with an equilibrium dissociation constant (KB) of 0.93 μM for PAF as derived from the Schild plot. In isolated rabbit platelets pretreated with 10 μM ETH 227, a Na+‐specific ionophore, the detectable [3H]PAF binding sites drop from 260 to 100 binding sites per platelet, but the binding sites for [3H]L‐659,989 remain roughly the same. The Na+ binding sites which modulate the conformation of PAF receptors are therefore protected from extracellular Na+ until ionophore is added, and are probably located on the cytoplasmic side of the plasma membrane.
PAF receptor and “cache‐oreilles” effect. Simple PAF antagonists
Authors: Lamotte‐Brasseur J. , Heymans F. , Dive G. , Lamouri A. , Batt J. P. , Redeuilh C. , Hosford D. , Braquet P. , Godfroid J. J.
Published: February 2007

Nine simple and structurally flexible PAF antagonists were synthesized and their inhibitory effects on PAF induced platelet aggregation were measured. Compounds with PAF antagonistic activity exhibited a negative electrostatic potential generated by two trimethoxyphenyl groups (isocontour at −10 Kcal/mole) at various distances between the negative clouds. The optimal distance between the atoms generating the “cache‐oreilles” system for exhibiting potent PAF antagonistic activity is estimated to be 11–13 Å. In the flexible molecules studied, the dispersion of the electronic distribution is not necessarily favorable for anti‐PAF activity. The data support the simple bipolarized model for the PAF receptor that has been proposed by the authors.
PAF inhibitory activity of diketopiperazines: Structure‐activity relationships
Authors: Shimazaki Norihiko , Shima Ichiro , Okamoto Masanori , Yoshida Keizo , Hemmi Keiji , Hashimoto Masashi
Published: February 2007

FR900452, a natural product isolated from the culture broth ofStreptomyces phaeofaciens No. 7739, was found to inhibit PAF‐induced rabbit platelet aggregation with an IC50 of 3.7×10−7M. FR900452, 1‐methyl‐3‐[1‐[5‐methylthiomethyl‐6‐oxo‐3‐(2‐oxo‐3‐cyclopenten‐1‐ylidene)‐2‐piperazinyl]ethyl]‐2‐indoline, has an oxocylopentylidene group incorporated as a vinylogous amide in a diketopiperazine skeleton. This unique structure led us to synthesize diketopiperazine derivatives, 3‐arylalkyl‐6‐substituted‐piperazine‐2,5‐diones. their observed PAF inhibitory activity suggest that the D‐D configuration of diketopiperazine is an important factor for anti‐PAF activity and that the hydrophobic aromatic portion may play a specific role in the binding of the diketopiperazine to the PAF receptor.
Platelet‐activating factor (PAF) receptor antagonists inhibit arachidonic acid induced platelet aggregation in rabbit whole blood
Authors: Ammit Alaina Jean , O'Neill Chris
Published: February 2007

The potency of several platelet‐activating factor (PAF) receptor antagonists was measured by observing their inhibitory effects against PAF induced platelet aggregation. Their selectivity was assessed by monitoring their effect on platelet aggregation induced by arachidonic acid (AA) and adenosine diphosphate (ADP). The antagonists inhibited platelet aggregation induced at the PAF EC50 (0.023 μM) with the following rank order of potency: WEB 2086> WEB 2170> SRI 64–412> SRI 63–675> BN 52021>kadsurenone> SRI 63–441> alprazolam. While the antagonists had no inhibitory effect at the EC50 for ADP (10 μM), they did inhibit platelet aggregation induced at the EC50 for AA (55 μM). However, there was considerable variability in the slope of the inhibitory response and the relative potency of each antagonist against PAF induced platelet aggregation as compared to AA induced platelet aggregation. The antagonist IC50 (μM) against PAF and AA were as follows, with those that showed significantly different (p<0.01) slopes indicated by an asterisk: SRI 63‐441* (3.8, 15.1); SRI 63‐675 (1.4, 36.2); SRI 64‐412 (0.5, 10.5); BN 52021* (2.4, 58.9); kadsurenone* (2.8, 28.3); alprazolam* (10, 25); WEB 2086 (0.055, 0.220), and WEB 2170 (0.107, 0.534). Therefore, in rabbit whole blood the antagonists were potent, although not completely selective, inhibitors of PAF induced platelet aggregation. These results suggest that the mode of action of PAF and AA induced platelet aggregation may share some common features. However, since the slope of the inhibitory response against PAF and AA for some antagonists differed, mechanistic differences in their action appear to exist.
Biological response of guinea pig peritoneal macrophages to platelet‐activating factor
Authors: Hayashi Hidetoshi , Kudo Ichiro , Nojima Shoshichi , Inoue Keizo
Published: February 2007

We investigated the effects of platelet‐activating factor (PAF) on guinea pig peritoneal macrophages. Specific and high‐affinity binding sites for PAF were detected on guinea pig peritoneal macrophages. Scatchard analysis of PAF binding revealed high affinity binding sites (7.9×104/cell) with a dissociation constant of 2.3×10−10 M. When treated with 10−9−10−5 M PAF, guinea pig peritoneal macrophages released hydrogen peroxide into the medium in a time‐dependent manner. The release reaction upon stimulation with 10−5 M PAF reached a plateau within 30 min and the extent of release was twice as high as that when stimulated byN‐formyl‐L‐methionyl‐leucyl‐L‐phenylalanine (fMLP; 2 μM)‐treated cells. Neither lysoPAF nor the PAF enantiomer was effective. PAF‐induced H2O2 release was inhibited specifically by PAF antagonists, suggesting that PAF activated macrophages through binding to specific sites. Lysosomal enzyme (N‐acetyl‐β‐D‐glucosaminidase) was released from guinea pig peritoneal macrophages upon treatment with 10−5 M PAF for 60 min. Guinea pig peritoneal macrophages were treated with PAF for 8 hr and the conditioned medium was examined for cytokines. The medium exhibited cytocidal activity against mouse fibroblast L929 cells [tumor necrosis factor (TNF) activity], and this activity was comparable to that detected after treatment of cells with the bacterial lipopolysaccharide (LPS). Furthermore, the same conditioned medium also showed colony‐stimulating factor (CSF) activity. Generation of these cytokines was stereospecific. Our findings suggest that PAF is a unique macrophage activator that potentiates both respiratory burst/lysosomal enzyme release (early‐phase response) and monokine production/glucose consumption (late‐phase response).
Production of platelet‐activating factor by human normodense and hypodense eosinophils
Authors: Ojima‐Uchiyama Ayako , Masuzawa Yasuo , Sugiura Takayuki , Waku Keizo , Fukuda Takeshi , Makino Sohei
Published: February 2007

Normodense eosinophils and neutrophils from normal donors produced considerable amounts of plateletactivating factor (PAF) when stimulated with ionophore A23187. PAF produced by eosinophils appeared to be degraded more rapidly than PAF formed by neutrophils, suggesting a higher activity of PAF‐degrading enzyme in eosinophils. Substantial proportions of PAF newly formed by both eosinophils and neutrophils were shown to be cell‐associated. By comparison, hypodense eosinophils obtained from a patient with idiopathic hypereosinophilic syndrome produced an extremely large amount of PAF and released much of it into the incubation medium. The accelerated formation of PAF in hypodense eosinophils may be related to various cardiovascular complications associated with hypereosinophilic syndrome.
Immunoregulatory functions of paf‐acether. VI. Dual effect on human B cell proliferation
Authors: Leprince Corinne , Vivier Eric , Treton Dominique , Galanaud Pierre , Benveniste Jacques , Richard Yolande , Thomas Yolene
Published: February 2007

The role of paf‐acether (paf), a phospholipid cytokine, in the modulation of human B cell function was investigated. Paf, from 1×10−5 M to 10−6 M, decreased B cell proliferation induced by both phorbol myristate acetate (PMA) and anti‐IgM antibodies (anti‐IgM Ab). By contrast, 1×10−7 M to 1×10−9 M paf enhanced PMA triggered, but not anti‐IgM triggered B cell proliferation. B cell proliferation was modulated between 24 and 72 hr of culture indicating that the effect of paf did not merely reflect a shift in proliferation kinetics. Interestingly, paf also enhanced the spontaneous proliferation of a Burkitt lymphoma‐derived B cell line, Raji, which suggests that paf can directly act on B cells. The modulatory effect of paf on peripheral blood B cells was independent of PMA concentration, yet the effect on Raji cells was dependent upon cell density. The data suggest that paf is a potent modulator of B cell function, and may be involved in the control of humoral immune response.
Calcium channel blockade inhibits platelet activating factor production by human umbilical vein endothelial cells
Authors: Tolins J. P. , Melemed A. , Sulciner D. , Gustafson K. S. , Vercellotti G. M.
Published: February 2007

An increase in intracellular calcium level is an important signal in the regulation of cellular responses under normal and pathological conditions. Because two key enzymes in the synthetic pathway of platelet activating factor (PAF), phospholipase A2 and acetyltransferase, are calcium dependent, we hypothesized that calcium channel blockade may inhibit agonist‐induced PAF synthesis. Primary cultures of human umbilical vein endothelial cells (EC), pre‐incubated with [3H]acetate, were exposed to thrombin (5 U/mL) and PAF production was quantitated by incorporation of radiolabel into the EC lipid fraction co‐migrating with exogenous PAF in thin‐layer chromatography. The effect of pre‐incubation with calcium channel blockers (verapamil, diltiazem, 10−4 M) or buffer was determined. Results (triplicate experiments,*P<0.05 vs buffer, † P<0.05 vs thrombin) demonstates that pre‐incubation with calcium channel blocker markedly inhibits thrombin‐induced PAF production (verapamil: buffer 273±122, thrombicin 10,735±1524*, thrombin+verapamil 178±91 † cpm/plate; diltiazem: buffer 1097±581, thrombin 15,283±2661*, thrombin+diltiazem 280±56 † cpm/plate). The effect of dialtiazem was dosedependent (% inhibition: 10−7 M, 46%; 10−5 M, 60%; 10−4 M, 98%). Diltiazem also inhibited bradykinin (10−8 M) induced PAF synthesis. In calcium‐free medium or in the presence of LaCl3 (10−3 M), the PAF response of EC to thrombin was blunted (buffer 582±360, thrombin 5394±1069, thrombin+calcium free medium 1055 ±571, thrombin+LaCl3 1271±58 cpm/plate). We conclude that calcium channel blockers present agonist‐induced PAF synthesis, possibly by preventing cellular calcium influx and activation of PAF synthetic enzymes. We speculate that this mechanism may underlie, at least in part, the beneficial effect of calcium channel blockade under various pathological conditions.
The effect of eicosapentaenoic acid consumption on human neutrophil chemiluminescence
Authors: Thompson Philip J. , Misso Neil L. A. , Passarelli Marion , Phillips Martin J.
Published: February 2007

The effect of eicosapentaenoic acid (EPA) on the inflammatory potential of neutrophils was investigated by supplementing the diets of 12 subjects with 2.16 g of EPA or 12 g of olive oil per day for 4 weeks in a double blind crossover study. Neutrophil function as assessed by luminol enhanced chemiluminescence responses to plateletactivating factor (PAF) and formyl‐methionyl‐leucyl‐EPA but not after olive oil consumption in the subjects who consumed EPA first. In contrast, EPA had no significant effect on neutrophil chemiluminescence in the subjects who consumed olive oil first. Dietary supplementation with EPA inhibits neutrophil responses to inflammatory mediators such as PAF while other fatty acids appear to modify the effects of EPA.
IgA immune aggregates stimulate platelet‐activating factor and superoxide anion production by human neutrophils. A comparison with IgG aggregates
Authors: Hernando Paloma , Egido Jesus , de Nicolas Rosario , Gonzalez Eva
Published: February 2007

We have examined the possibility that human polymorphonuclear cells exposed to IgA immune complexes can mediate the production of platelet‐activating factor (PAF) and oxygen radicals. We found that human IgA and IgG immune aggregates stimulated, to a similar extent, PAF and O2− production by human polymorphonuclear cells (PMN) in a concentration and time dependent manner. The PAF, that was largely associated with cells, was shown to be identical to synthetic PAF, as determined by physicochemical, chromatographic and enzymatic assay. Furthermore,de novo synthesis of PAF by PMN was shown to occur by incorporation of radioactive precursors, such as [3H]acetate. The addition of normal human serum to PMN incubated with IgG aggregates resulted in a significant amount of PAF formation which was not observed with IgA aggregates. By contrast, no change was seen in PMN O2− with either aggregates. The preincubation of PMN with cytochalasin B, an inhibitor of phagocytosis, did not affect PAF and O2− production by both aggregates. The results suggest that the interaction of PMN with the IgA complexes in blood vessel of lipid mediators, such as PAF and oxygen radicals that could contribute to the inflammatory response.
Calcium ion mobilization in neuronal cells induced by PAF
Authors: Kornecki Elizabeth , Ehrlich Yigal H.
Published: February 2007

We have reported previously that platelet‐activating factor (PAF) interacts with the neuronal cell line NG108‐15 (neuroblastoma X glioma hybrid) and the pheochromocytoma cell line, PC12. PAF acts on these cells by raising levels of intracellular free calcium ions. In the present report, we extend these studies. PAF induced the vesicular release of adenosine 5′‐triphosphate (ATP) from PC12 cells in a dose‐dependent manner. The PAF‐induced ATP release was inhibited by the PAF antagonists, CV‐3988 and CV‐6209, and the calcium antagonist prenylamine. The relevance of the interaction of PAF with neuronal cells was investigated further by using brain synaptosomal preparations and primary cortical and neostriatal cells. Nanomolar concentrations of PAF induced calcium transients in aequorin‐loaded synaptosomal preparations, and cortical and neostriatal cells were sensitive to the action of PAF. The possible physiological and pathophysiological roles of PAF in brain function are discussed.
Role of platelet‐activating factor in aggregation of leukocytes and platelets in cerebral ischemia
Authors: Uchiyama S. , Yamazaki M. , Maruyama S.
Published: February 2007

Leukocyte and platelet aggregation stimulated with formyl‐methionyl‐leucyl‐phenylalanine (FMLP) was measured in 32 patients with cerebral ischemia and in 15 controls, using a whole blood aggregometer. The increases in impedance and the reductions in leukocyte and platelet counts were significantly greater in stroke patients than in controls. Aggregation was inhibited by oral ticlopidine, but not by oral aspirin. The effects were clearly counteracted by platelet‐activating factor (PAF) antagonists, and counteracted in part by a 5‐lipoxygenase inhibitor. The results suggest that platelets tend to be activated by PAF and leukotrienes liberated from hyperaggregable leukocytes in patients with ischemic stroke.
Platelet‐activating factor in cardiovascular stress situations
Authors: Rabinovici Reuven , Yue Tian‐Li , Feuerstein Giora
Published: February 2007

Since the elucidation of its chemical structure two decades ago, platelet‐activating factor (PAF) has emerged as an important mediator of various cardiovascular stress situations. Most notably, PAF was implicated as a key factor in the septic shock syndrome, based on the similarities between endotoxin and PAF biological effects, the elevation of circulating and tissue levels of PAF during endotoxemia, and the protective effect of PAF antagonists in the septic state. In addition, accumulating data suggest the involvement of PAF in the pathophysiological processes associated with ischemia, hemorrhage and trauma, where PAF exerts its effects directly on cells and blood elements or indirectly through interactions with other mediators such as cytokines and prostaglandins. Nevertheless, the relative contribution of PAF to the pathophysiological processes in endotoxemia is still unknown and should await further investigations. The primary aims of this chapter are: to delineate the effects of PAF on the cardiovascular system, to summarize the data which suggest the involvement of PAF in stress situations of the cardiovascular system, and to identify areas where future experimental efforts should be focused.
Intravascular release of a platelet‐activating factor‐like lipid (PAF‐LL) induced by cigarette smoking
Authors: Imaizumi Tada‐atsu
Published: February 2007

To assess the role of platelet‐activating factor (PAF) in smoking‐induced vascular injury, the effect of cigarette smoking on PAF‐like lipid (PAF‐LL) in plasma was studied. The subjects were 12 young smokers (22±1.3 years old), 13 young non‐smokers (22±2.1 years old), 14 older smokers (59±9.6 years old), and 11 older non‐smokers (60±8.7 years old). Lipids were extracted from 5 mL of plasma and then were separated by thin‐layer chromatography. The fraction with the same migration as authentic PAF was recovered and tested for the ability to aggregate human polymorphonuclear neutrophils (PMN). The activity was identified as PAF‐LL because it was inactivated by phospholipase A2, and because the effects on PMN were blocked by CV‐3988, a competitive antagonist of the PAF receptor. PAF‐LL was detected in plasma from 3 young non‐smokers (23%), 5 young smokers (42%), 3 older non‐smokers (27%) and 11 older smokers (79%). The incidence of the detection of plasma PAF‐LL in older smokers was significantly higher than those in young non‐smokers (p<0.01) or in older non‐smokers (p<0.05). In young smokers, the acute effect of smoking was also studied. Plasma PAF‐LL was detected in all of the 12 subjects immediately after smoking a cigarette, in sharp contrast to the incidence of 42% before smoking. Plasma β‐thromboglobulin was highest in older smokers, and it increased significantly after smoking a cigarette in young smokers. Smoking is associated with increased production of PAF or a similar lipid, which may play an important role in the pathogenesis of smoking‐induced vascular diseases.
Platelet‐activating factor (PAF) induces contraction of saponin‐skinned smooth muscle of coronary artery
Authors: Soloviev A. I. , Braquet P.
Published: February 2007

The effect of platelet‐activating factor (PAF) on the development of isometric tension by saponin‐skinned coronary artery was studied. PAF caused two types of contractions of coronary smooth muscle cells (SMC):(i) rapid, transient (phasic) contractions of SMC were induced by inositol 1,4,5‐trisphosphate dependent Ca2+ release from sarcoplasmic reticulum (SR); (ii) slow sustained (tonic) contractions were induced by increase in Ca2+‐ensitivity of the contractile apparatus of SMC by protein kinase C activation. The present results support the hypothesis that, in SMC of coronary artery, PAF receptors are located not only on the plasma membrane, but also on the SR membranes.
The contribution of platelet‐activating factor to allergen‐induced eosinophil infiltration and bronchial hyperresponsiveness
Authors: Page C. P.
Published: February 2007

Platelet‐activating factor (PAF) is an ether‐linked phospholipid having a range of biological properties of relevance to our understanding of the pathogenesis of bronchial asthma and related allergic diseases. In particular the ability of PAF to induce eosinophil activation and recruitment has received considerable attention. Since in experimental animals PAF and allergen‐induced eosinophil infiltration are dependent upon platelet activation, it is suggested that platelet activation may be an important component of the allergic process. The ability of PAF antagonists to inhibit various aspects of the allergic response has been demonstrated in a number of animal models but not all of them have been extended into man.
Effect of the selective PAF antagonist SM‐10661 on an asthmatic model. 2. Effect on antigen‐induced dual asthmatic response and infiltration of leukocytes into airways in actively sensitized conscious guinea pigs
Authors: Sugasawa Toshinari , Imanishi Noriaki , Morooka Shigeaki
Published: February 2007

The effect of a selective platelet‐activating factor (PAF) receptor antagonist, SM‐10661, on antigen‐induced dual asthmatic response and leukocyte infiltration into the airways of actively sensitized conscious guinea pigs was investigated. The animals were pretreated with mepyramine maleate (10 mg/kg i.p.) and then challenged with ovalbumin. The inhalation of ovalbumin caused an immediate decline in specific airway conductance (sGaw) which peaked at 5 min after the challenge. sGaw gradually returned to the baseline 6 hr after the challenge. After the early asthmatic response (EAR), a second phase change, a late asthmatic response (LAR) in sGaw peaking at 17–20 hr was observed. When 1% w/v disodium cromoglycate was inhaled for 2 min on two occasions, EAR was not affected, but LAR was significantly inhibited. Oral administration of 50 mg/kg fenoterol (30 min before challenge) significantly inhibited EAR, but had no significant effect on LAR. SM‐10661 administered orally 1 hr before the challenge inhibited EAR dose‐dependently (50% inhibitory dose (ID50); 59 mg/kg, but was even more effective against the LAR (ID50); 13–16 mg/kg). When 30 mg/kg of SM‐10661 was administered orally 6 hr after ovalbumin challenge, LAR was completely inhibited. The number of total cells, macrophages and eosinophils in bronchoalveolar lavage fluids rose significantly 17 hr after antigen challenge compared to that observed after saline challenge. The number of neutrophils and lymphocytes also increased in response to the ovalbumin challenge, but not significantly. SM‐10661 (30 mg/kg) administered orally 1 hr before the challenge significantly inhibited the increase in total cells, macrophages and eosinophils. By comparison, when 30 mg/kg SM‐10661 was administered orally 6 hr after the challenge, these increases were not significantly inhibited. These results suggest that PAF is involved in EAR and LAR, and that SM‐10661 may be a useful therapeutic agent for the treatment of allergic asthma.
The role of platelet‐activating factor (PAF) in experimental glomerular injury
Authors: Artiz A. , Gomez‐Chiarri M. , Lerma J. L. , Gonzalez E. , Egido J.
Published: February 2007

Platelet‐activating factor (PAF) is a potent autacoid that participates in inflammation and other pathophysiological processes. In this review we deal with recent evidence suggesting that PAF is a mediator that is released early during glomerular injury. PAF can be synthesized in the glomerulus by infiltrating intrinsic glomerular cells. Normal glomeruli produce PAF upon stimulation, and glomerular PAF synthesis is increased in a variety of experimental glomerulopathies. The local infusion of PAF into the renal artery of isolated blood‐free kidneys induces proteinuria. PAF attracts and activates inflammatory cells. Glomerular mesangial, endothelial and epithelial cells are also targets for PAF. Therapy with specific PAF receptor antagonists has prevented or reduced proteinuria and improved glomerular inflammation in several experimental models of proliferative glomerulonephritis and minimal change nephrosis. However, the beneficial effect of administration of PAF antagonists once proteinuria is fully developed has been minimal. PAF may also play a role in the recruitment of inflammatory interstitial cells.
Nephrotoxicity of cyclosporine: The role of platelet‐activating factor and thromboxane
Authors: Pavão dos Santos Oscar F. , Boim Mirian A. , Barros Elvino J. G. , Pirotzky Eduardo , Braquet Pierre , Schor Nestor
Published: February 2007

Cyclosporine (CsA), an immunosuppressive agent, is potentially nephrotoxic. We had previously observed that acute administration of CsA to Munich‐Wistar rats induced a decrease in single nephron glomerular filtration rate, due to a decline in glomerular plasma flow, and in the glomerular ultrafiltration coefficient. Moreover, these alterations were prevented when an antagonist of platelet‐activating factor (PAF) was administered. In the present study we examined whether the protective effect of the PAF blocker in CsA nephrotoxicity could have been mediated by thromboxane (TxA2). Our data show that the PAF effects were not mediated by TxA2, since administration of dazmegrel, a thromboxane synthetase inhibitor, did not ameliorate the acute renal failure caused by CsA. Thus, PAF appears to be a direct mediator of acute CsA nephrotoxicity, while TxA2 is not significantly involved in this process.
Presence of platelet‐activating factor in pyuria in humans
Authors: Ikeda Ichiro , Oda Makoto , Sakakura Muneki , Yasunaga Kojiro
Published: February 2007

The relationship between the occurrence of platelet‐activating factor (PAF) and neutrophils in urine from patients with urinary tract infection was examined. PAF was detected in human pyuria, when leukocyte levels reached at least 300 cells/μL (n=45), but not in normal urine (n=12). The amount of PAF found in pyuria, measured by platelet aggregation assay, was 0.01 to 13.3 pmol/mL. A close correlation was seen between the amount of PAF present and the number of urinary leukocytes (p<0.01, r=0.70). The leukocytes in pyuria consisted almost entirely of neutrophils (96±4%, mean ±S.D.). Our findings suggest that the occurrence of PAF is associated with the accumulation of neutrophils in urine.
The effect of CV‐3988 and CV‐6209 on the acute gastric erosions of rats due to water‐immersion and restraint stress
Authors: Nogami Makoto , Hoshihara Yoshio , Tsubura Kunihiko , Yamamoto Takashi , Tabuchi Masafumi , Miyamoto Terumasa , Shiga Junji
Published: February 2007

CV‐3988 and CV‐6209 inhibited gastric erosions in rats due to water‐immersion and restraint stress in a dose‐dependent manner. The above inhibitory effects of CV‐3988 were observed in the presence of indomethacin, which may indicate that the inhibition is not prostaglandin dependent. The studies indicate that platelet‐activating factor may be involved in the formation of erosions in rats under water‐immersion and restraint stress.
Myoelectric intestinal disturbances inEscherichia coli endotoxic shock in rats. Involvement of platelet‐activating factor
Authors: Pons Laurent , Droy‐Lefaix Marié‐Thèrese , Braquet Pierre , Buéno Lionel
Published: February 2007

Administration of BN 52021 (50 mg/kgi.v.), a specific antagonist of platelet‐activating factor (PAF), significantly reduced the intestinal myoelectric disturbances induced byE. coli endotoxin injection (50 μg/kgi.v.) by 62%. Thus, PAF may be involved in the intestinal motor alterations observed in endotoxic shock. When given in combination with indomethacin (10 mg/kgi.p.), BN 52021 inhibited endotoxic shock intestinal disturbances. Indomethacin alone also reduced PAF induced (25 μg/kgi.p.) disruption of migrating myoelectric complexes. Endotoxins may act on intestinal motilityvia release of endogenous PAF and prostaglandins, the effects of PAF being mediated through the release of prostaglandins.