Platelet-activating factor in Japanese cedar pollinosis

Japanese cedar pollinosis is a typical allergic disease and has recently become a big social problem. Many population are suffering from this disease every year from the end of February to the beginning of April. In this study, we planned to examine the role of platelet-activating factor (PAF) in this disease, because PAF has been known to be one of the potent chemical mediators in allergic and inflammatory reactions and many evidences indicate that PAF is deeply involved in the pathogenesis of bronchial asthma, a typical allergic disease. We measured the concentrations of the PAF derivative (lyso-PAF) in serum from patients with cedar pollinosis during the pollen season. The level of lyso-PAF in serum from untreated patients with cedar pollinosis (87.8 +/- 8.7 unit.) was significantly higher than that in healthy control (54.9 +/- 7.7 unit.). We also tested the effect of an anti-allergic drug on the level of serum lyso-PAF of cedar pollinosis. Eighteen pairs of serum samples from patients with cedar pollinosis were employed in this study. Lyso-PAF levels after two weeks' therapy with ketotifen (2 mg/day), an anti-allergic drug, decreased the levels significantly (from 82.6 unit to 41.3 unit). These results suggest that PAF could play some important role in cedar pollinosis and that the clinical effect of anti-allergic drug could be partially due to the anti-PAF action.     

Platelet-activating factor in late asthmatic response

The role of platelet-activating factor (PAF) in the late asthmatic responses was studied. The concentrations of lyso-form of PAF in plasma were measured at 0 and 20 min, and 6 and 24 h after the antigen inhalation challenge among patients with bronchial asthma. PAF activities were measured by their aggregating ability of washed rabbit platelets after acetylation of lyso-PAF into the biological active form of PAF, when there were no detectable amounts of PAF in plasma. The concentrations of lyso-PAF were found to be significantly increased in patients with the late asthmatic response compared with patients with the single immediate response at 6 h after the antigen challenge. In contrast, lyso-PAF levels were not significantly different at 20 min after the antigen challenge between these two groups. PAF inactivator activity in plasma increased when there was a decrease in the lyso-PAF level. These results suggest that PAF may participate in the late asthmatic response and may provide a new insight into the pathogenesis and the treatment of bronchial asthma.     

Platelet-activating factor and cellular immune responses

Platelet-activating factor is a phospholipid mediator of the allergic reaction that is a potent stimulator of acute inflammatory processes. It is produced by various inflammatory cells upon activation by immune or nonimmune stimuli. As Pierre Braquet and Marek Rola-Pleszcynski review here, evidence is now accumulating that platelet-activating factor is a component in the regulation of cellular immune responses.     

血小板活化因子的支气管收缩作用及其机理研究

本文研究了血小板活化因子对豚鼠在体和离体支气管平滑肌的收缩作用，同时对ＰＡＦ的这一作用机制进行了讨论。结果：１．ＰＡＦ静脉和雾化吸入均迅速引起支气管收缩，并伴有外周循环血小板数减少。２．单纯ＰＡＦ对离体支气管平滑肌条的收缩作用微弱，当加入洗涤血小板后其收缩作用明显增强。３．血栓素Ａ２受体拮抗剂（ＡＡ－２４１４）明显抑制了ＰＡＦ加血小板而引起的支气管平滑肌收缩。提示ＰＡＦ对支气管平滑肌可有直接作用，     

Platelet-activating factor (PAF-acether): Present status

PAF-acether, first discovered in 1971–72, is now recognized as a 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine released from various cells and organs, including macrophages, neutrophils, platelets, the kidney and heart. In this review, we will concentrate on the newest aspects of PAF-acether biochemistry and pathophysiology: (1) PAF-acether is probably formed by murine macrophages through a two-step process inplicating successively a phospholipase A2-like enzyme and an acetyltransferase; (2) study of phospholipids structurally related to PAF-acether indicates that the ether linkage at position 1, the short acyl chain at position 2 and the natural optical configuration are critical for biological activity; (3) besides platelet aggregation, PAF-acether induces a platelet-dependent, aspirin-independent bronchoconstriction in the guinea-pig and the monkey. It exhibits also a potent antihypertensive action in the rat, and triggers platelet-independent hemodynamic changes in perfused guinea-pig heart. Thus, this class of phospholipids is gaining increasing importance in pathophysiology.     

Platelet-activating factor modulates interleukin-6 production by mouse fibroblasts

We compared the effects of platelet-activating factor (PAF), interleukin-1 beta (IL-1 beta) and polyriboinositic-polyribocytidylic acid (poly-I:C) on IL-6 production by confluent L929 mouse fibroblasts. At concentrations above 1 microM, PAF dose-dependently enhanced IL-6 production; at 5 microM PAF this increase (72.7 +/- 19.9 U/ml) was higher than that evoked by 100 U/ml IL-1 beta (5.7 +/- 0.4 U/ml) or 50 micrograms/ml poly-I:C (39.3 +/- 6.7 U/ml). The IL-6 production induced by 5 microM PAF was not inhibited by addition of the specific PAF antagonist BN 52021 (10 microM) to the incubation medium. These results demonstrate that, as this is the case for IL-1, PAF also modulates IL-6 production.     

Platelet-activating factor primes human eosinophil generation of superoxide.

Platelet-activating factor (PAF) is a potent inflammatory mediator that can cause airway obstruction and hyperresponsiveness; these processes are also associated with pulmonary eosinophilia, suggesting a link between these two events. Thus, PAF's interaction with eosinophils may provide a mechanism for airway damage. However, direct in vitro activation of eosinophils by PAF requires concentrations that are likely higher than those achieved in vivo. As a result, we investigated whether lower, more physiologic concentrations of PAF could prime eosinophils for subsequent activation to another receptor-stimulated factor, in this case formylmethionylleucylphenylalanine (FMLP). To test this hypothesis, eosinophils were preincubated (1 and 15 min) with low concentrations of PAF (1 x 10(-8) and 1 x 10(-10) M); this exposure to PAF resulted in enhanced generation of superoxide anion to FMLP stimulation. Moreover, similar concentrations of PAF decreased eosinophil density and increased expression of cell surface CR3 receptors. Finally, low, nonactivating concentrations of PAF (1 x 10(-10) to 1 x 10(-8) M) caused transient increases in eosinophil cytosolic free Ca2+ concentrations. Collectively, these responses are consistent with the hypothesis that short-term exposure to low concentrations of PAF primes eosinophils to cause an enhanced inflammatory response upon subsequent activation to another receptor agonist. The consequences of this PAF-associated phenomenon can produce an enhanced inflammatory response and airway injury.     

Platelet-activating factor and lyso-PAF possess direct antimicrobial properties in vitro

The effects of platelet-activating factor (PAF) and lyso-platelet-activating factor (L-PAF) at concentrations of 0.25-20 microg/ml on potassium transport and growth of gram-positive and gram-negative bacteria have been investigated in vitro and compared with those of lysophosphatidylcholine (LPC). Potassium transport was determined using 86Rb+ as tracer, while growth was measured according to the extent of uptake of radiolabeled amino acids. All of the test phospholipids caused dose-related inhibition of 86Rb+-uptake and growth of gram-positive bacteria, the order of potency being PAF>LPC>L-PAF. Gram-negative bacteria, on the other hand, were less sensitive to the inhibitory effects of the phospholipids on K+ transport and growth. Some, but not all, of the gram-positive and gram-negative bacteria were able to degrade LPC, but not PAF or L-PAF, demonstrating that enzymatic degradation of phospholipids does not explain the differential sensitivity to these agents. The bioactive phospholipids LPC, PAF and L-PAF may represent an oxygen-independent antimicrobial host defense system operative primarily against gram-positive bacteria.     

Platelet-activating factor (PAF-acether), an activator of neutrophil functions

The effect of totally synthetic PAF-acether (1-O-octadecyl-2-O-acetyl-sn-glyceryl-3-phosphorylcholine), 2-lyso PAF-acether (1-O-octadecyl-sn-glyceryl-3-phosphorylcholine) and lyso-phosphatidylcholine on enzyme release and superoxide production from human polymorphonuclear neutrophils (PMN were studied. PMN (2×10⁶ ml^–1) were incubated at 37°C with various concentrations of phospholipids in the absence of cytochalasin B. At 10^–7 M, PAF-acether induced superoxide production and -glucuronidase, acid phosphatase and lysosyme release, but not that of cytoplasmic lactic dehydrogenase. In the same condition 2-lyso PAF-acether and lyso-phosphatidylcholine were ineffective. In the presence of phagocytic stimuli PAF-acether enhanced in the range from 10^–7 M to 10^–10 M the enzyme release and only at 10^–7 M the superoxide production. Thus, the capacity of PAF-acether to stimulate PMN, as well as platelet function, indicates a prominent role for this lipid mediator in inflammatory processes.     

血小板活化因子促进大鼠气道平滑肌细胞增殖及其作用机制

目的研究血小板活化因子（PAF）对大鼠气道平滑肌细胞（ASMC）增殖活性的影响，并探讨其作用机制。方法以10^-7mol／LPAF作为刺激因素，以20mmol／LN-乙酰半胱氨酸（NAC）进行干预。用四唑盐（MTT）比色法检测细胞增殖活力；流式细胞仪测定细胞周期；免疫细胞化学染色（SABC法）检测细胞核增殖抗原（PCNA）的表达；EMSA法检测ASMC中NF-κB的活性。结果发现PAF能显著促进ASMC的增殖，明显增加细胞增殖指数及其PCNA阳性表达率，并使ASMC细胞核内NF-κB活性明显增加。预先用NAC干预可显著缓解上述变化（P〈0．05）。结论PAF能促进ASMC的增殖，这一调控部分是通过激活NF-κB通路而发挥作用。提示PAF是气道重建的重要刺激因子。     

Platelet-activating factor (PAF-acether): Historical background and definition

The platelet-activating factor (PAF-acether) was first described as released from sensitized basophils. It is now recognized as a mediator of inflammation, since it is released from most stimulated pro-inflammatory cells. It has a unique phospholipid structure and, as yet, is the most potent platelet-activating agent acting at the 1×10^–12 to 1×10^–10 M level. It also degranulates and attracts neutrophils. Its release from alveolar macrophages might play a role in the onset of bronchoconstriction in experimental animals and in man. Thus, PAF-acether is gaining increasing importance as a major intermediate of inflammatory reactions.     

Platelet-activating factor enhances interleukin-6 production by alveolar macrophages.

The production of the cytokine interleukin-6 (IL-6) by rat alveolar macrophages (AMs) was analyzed after their stimulation with muramyl dipeptide (1 microgram/ml), in the presence of graded concentrations of platelet-activating factor (PAF). Significantly enhanced production of IL-6 was observed at 10(-10) to 10(-8) mol/L PAF, with peak effect at 10(-10) mol/L. This enhancement was blocked by three structurally unrelated specific PAF receptor antagonists BN 52021, WEB 2170, and CV 3988. The biologically inactive PAF precursor/metabolite, lyso-PAF, and the enantiomer enantio-PAF failed to induce significant enhancement in IL-6 production. In parallel, addition of PAF to AM triggered leukotriene B4 (LTB4) release. Inhibition of 5-lipoxygenase pathway by AA-861 or MK 886 inhibited the PAF-induced augmentation of both IL-6 and LTB4 production, suggesting an implication of endogenous leukotrienes in this mechanism. Furthermore, addition of exogenous LTB4 to AMs could augment their IL-6 production, with peak activity at 10(-12) mol/L LTB4, and reverse the inhibitory effects of 5-lipoxygenase inhibitors. Taken together, these observations suggest that PAF can modulate lung immune and inflammatory responses by enhancing IL-6 production and that this activity may be dependent on secondary 5-lipoxygenase metabolites. This may have clinical relevance in PAF-mediated events in the lung, such as the cellular components of late-phase asthma.     

Platelet-activating factor induces eosinophil peroxidase release from purified human eosinophils.

The degranulation response of purified human eosinophils to platelet-activating factor (PAF) has been studied. PAF induced release of eosinophil peroxidase (EPO) and beta-glucuronidase from highly purified human eosinophils with an EC50 of 0.9 nM. The order of release was comparable with that induced by phorbol myristate acetate (PMA). The new specific PAF antagonist 3-[4-(2-chlorophenyl)-9-methyl-H-thieno[3,2-f] [1,2,4]triazolo-[4,3a][1,4]-diazepin-2-yl](4-morpholinyl)- 1-propane-one (WEB 2086) inhibited the PAF-induced enzyme release by human eosinophils in a dose-dependent manner. The viability of eosinophils were unaffected both by PAF and WEB 2086. The results suggest that PAF may amplify allergic and inflammatory reactions by release of preformed proteins from eosinophil granules.     

沙土鼠及大鼠局部脑缺血时血小板活化因子的变化

目的：血小板活化因子（ＰＡＦ）拮抗剂能改善局部脑缺血所致功能和组织损伤,本文在沙土鼠单侧脑缺血及大鼠大脑中动脉凝闭的局部脑缺血观察了缺血后大脑组织ＰＡＦ的变化。方法：ＰＡＦ的测定采用薄层层析进行ＰＡＦ分离提取,用生物法测定ＰＡＦ含量的变化。结果：１沙土鼠右侧颈总动脉结扎３ｈ再灌２ｈ,右侧大脑组织ＰＡＦ含量明显高于左侧。２大鼠左侧脑中动脉凝闭后４８ｈ,左侧大脑组织ＰＡＦ含量明显高于右侧。结论：ＰＡＦ在局部脑缺血继发神经元损伤中可能有一定作用。