First-Row Transition Metal Complexes Incorporating the 2-(2'-pyridyl)quinoxaline Ligand (pqx), as Potent Inflammatory Mediators: Cytotoxic Properties and Biological Activities against the Platelet-Activating Factor (PAF) and Thrombin.

Inflammatory mediators constitute a recently coined term in the field of metal-based complexes with antiplatelet activities. Our strategy targets Platelet-Activating Factor (PAF) and its receptor, which is the most potent lipid mediator of inflammation. Thus, the antiplatelet (anti-PAF) potency of any substance could be exerted by inhibiting the PAF-induced aggregation in washed rabbit platelets (WRPs), which internationally is a well-accepted methodology. Herein, a series of mononuclear (mer-[Cr(pqx)Cl3(H2O]) (1), [Co(pqx)Cl2(DMF)] (2) (DMF = N,N'-dimethyl formamide), [Cu(pqx)Cl2(DMSO)] (3) (DMSO = dimethyl sulfoxide), [Zn(pqx)Cl2] (4)) and dinuclear complexes ([Mn(pqx)(H2O)2Cl2]2 (5), [Fe(pqx)Cl2]2 (6) and [Ni(pqx)Cl2]2 (7)) incorporating the 2-(2'-pyridyl)quinoxaline ligand (pqx), were biologically evaluated as inhibitors of the PAF- and thrombin-induced aggregation in washed rabbit platelets (WRPs). The molecular structure of the five-co-ordinate analog (3) has been elucidated by single-crystal X-ray diffraction revealing a trigonal bipyramidal geometry. All complexes are potent inhibitors of the PAF-induced aggregation in WRPs in the micromolar range. Complex (6) displayed a remarkable in vitro dual inhibition against PAF and thrombin, with IC50 values of 1.79 µM and 0.46 µM, respectively. Within the series, complex (5) was less effective (IC50 = 39 µM) while complex (1) was almost 12-fold more potent against PAF, as opposed to thrombin-induced aggregation. The biological behavior of complexes 1, 6 and 7 on PAF's basic metabolic enzymatic pathways reveals that they affect key biosynthetic and catabolic enzymes of PAF underlying the anti-inflammatory properties of the relevant complexes. The in vitro cytotoxic activities of all complexes in HEK293T (human embryonic kidney cells) and HeLa cells (cervical cancer cells) are described via the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The results reveal that complex 3 is the most potent within the series.

Protective Effect of Olive Oil Microconstituents in Atherosclerosis: Emphasis on PAF Implicated Atherosclerosis Theory.

Atherosclerosis is a progressive vascular multifactorial process. The mechanisms underlining the initiating event of atheromatous plaque formation are inflammation and oxidation. Among the modifiable risk factors for cardiovascular diseases, diet and especially the Mediterranean diet (MedDiet), has been widely recognized as one of the healthiest dietary patterns. Olive oil (OO), the main source of the fatty components of the MedDiet is superior to the other "Mono-unsaturated fatty acids containing oils" due to the existence of specific microconstituents. In this review, the effects of OO microconstituents in atherosclerosis, based on data from in vitro and in vivo studies with special attention on their inhibitory activity against PAF (Platelet-Activating Factor) actions, are presented and critically discussed. In conclusion, we propose that the anti-atherogenic effect of OO is attributed to the synergistic action of its microconstituents, mainly polar lipids that act as PAF inhibitors, specific polyphenols and α-tocopherol that also exert anti-PAF activity. This beneficial effect, also mediated through anti-PAF action, can occur from microconstituents extracted from olive pomace, a toxic by-product of the OO production process that constitutes a significant ecological problem. Daily intake of moderate amounts of OO consumed in the context of a balanced diet is significant for healthy adults.

Tin(II) and Tin(IV) Complexes Incorporating the Oxygen Tripodal Ligands [(η5-C5R5)Co{P(OEt)2O}3]-, (R = H, Me; Et = -C2H5) as Potent Inflammatory Mediator Inhibitors: Cytotoxic Properties and Biological Activities against the Platelet-Activating Factor (PAF) and Thrombin.

Metal complexes displaying antiplatelet properties is a promising research area. In our methodology, Platelet-Activating Factor (PAF), the most potent lipid pro-inflammatory mediator, serves as a biological probe. The antiplatelet activity is exerted by the inhibition of the PAF-induced aggregation in washed rabbit platelets (WRPs) and in rabbit plasma rich in platelets (rPRPs). Herein, the synthesis and biological investigation of a series of organometallic tin(II) and tin(IV) complexes, featuring the oxygen tripodal Kläui ligands [(η5-C5R5)Co{P(OEt)2O}3]-, {R = H, (LOEt-); Me (L*OEt-)}, are reported. Reaction of NaLOEt (1a) and NaL*OEt (1b) with SnCl2, yielded the rare four-coordinate LOEtSnCl (2a) and L*OEtSnCl (2b) complexes. Accordingly, LOEtSnPh3 (3a) and L*OEtSnPh3 (3b) were prepared, starting from Ph3SnCl. Characterization includes spectroscopy and X-ray diffraction studies for 2a, 2b and 3b. The antiplatelet activity of the lead complexes 2b and 3a (IC50 = 0.5 µΜ) is superior compared to that of 1a and 1b, while both complexes display a pronounced inhibitory activity against thrombin (IC50 = 1.8 µM and 0.6 µM). The in vitro cytotoxic activities of 3a and 2b on human Jurkat T lymphoblastic tumor cell line is higher than that of cisplatin.

Is there an interplay between the SARS-CoV-2 spike protein and Platelet-Activating factor?

Previous publications have reported a potent effect of COVID-19 on platelet function and that the Spike protein enhances washed human platelet aggregation induced by various agonists. This study aims to evaluate whether mRNA vaccination for COVID-19 affects human platelet-rich plasma (hPRP) aggregation response, whether a recombinant Spike protein modulates PAF-induced aggregation in hPRP and in washed rabbit platelets (WRP), and to investigate the effect of recombinant Spike protein on the PAF production in the U-937 cell line. Our results showed that PRP from vaccinated individuals exhibited ex vivo lower EC50 values in response to PAF, ADP, and collagen. Platelet incubation with the Spike protein alone did not induce aggregation either in hPRP or in WRP, but resulted in augmentation of in vitro PAF-induced aggregation in hPRP from non-vaccinated individuals and in WRP. When PRP from vaccinated individuals was incubated with the Spike protein and PAF was subsequently added, elimination of the secondary wave of the biphasic aggregation curve was recorded compared with the aggregation induced by PAF alone. Collagen-induced in vitro aggregation was dose-dependently reduced when platelets were pre-incubated with the Spike protein in all tested aggregation experiments. Stimulation of U-937 by the Spike protein induced an increase in intracellular PAF production accompanied by elevation of the activities of all three PAF biosynthetic enzymes. In conclusion, since the Spike protein appears to modulate PAF production and activity, the use of compounds that act as PAF inhibitors, could be considered at least in mild cases of patients infected with SARS-CoV-2.

Anti-inflammatory and anti-thrombotic properties of lipid bioactives from the entomopathogenic fungus Beauveria bassiana.

In the present work the entomopathogenic fungus B. bassiana lipids were studied against the potent pro-inflammatory and thrombotic mediators implicated in several disorders, platelet-activating factor (PAF) and thrombin. Bioactivities of lipid extracts from B. bassiana cells and culture supernatants and of their lipid fractions separated by a one-step HPLC-analysis ere assessed against the PAF/Thrombin-induced aggregation of washed rabbit platelets. Lipid extracts from both cell-biomass and supernatant inhibited strongly PAF/Thrombin-activities and platelet-aggregation, exhibiting higher specificity against PAF. Similarly, HPLC-derived lipid-fractions of phenolics/glycolipids, Sphingomyelins and Phosphatidylcholines (PC) showed strong anti-PAF potency. PC PAF-like molecules exhibited the strongest antagonistic anti-PAF effects, while in higher amounts they agonistically inhibited PAF-activities. Some bioactive lipids with strong anti-PAF effects are exo-cellularly secreted in the culture media during fungal growth, while others are not. The presence of such lipid bioactives in B. bassiana with strong anti-inflammatory and anti-thrombotic properties, provide new perspectives and putative future applications for this entomopathogenic fungus.

One-step separation system of bio-functional lipid compounds from natural sources.

Lipids are a very heterogeneous class of biomolecules with distinct structures and functions. Total lipids (TLs) obtained from natural sources are regularly further separated into lipid subclasses, with the two major ones being the polar lipids (PLs) and neutral lipids (NLs). Traditional analytical methods for fractionating TLs into NLs, PLs, and their subclasses, usually comprise difficult, costly and time-consuming steps. Instead, several benefits and applications are derived by implementing a novel one-step semi-preparative and reversed-phase HPLC-analysis for separating TLs into all kinds of lipid subclasses. This method allows a one-step separation/fractionation of several subclasses of bio-functional PLs (i.e. phospholipids, glycolipids, phenolic compounds, N-acyl-homoserine-lactones, etc.) and NLs (i.e. triacylglycerols, fatty acids, esters, etc.) from TL-extracts of a natural source, prior to further testing them for their bio-functionality (i.e. in bioassays/cell models) and structure-activity relationships (i.e. LC-MS/GC-MS).•This method can be applied in several natural sources, such as animal and marine sources, plants, microorganisms of biotechnological and agricultural interest, foods, beverages and related products, and by-products.•This method can also be applied for separating specific bio-functional lipids from complex medical and pharmaceutical samples (i.e. cells, tissues, blood, plasma, liposomes, etc.), either for evaluating their role in diseases (i.e. PAF/PAF-like molecules) or by elucidating their protective roles (i.e. PLs rich in ω3 PUFA) for supplements and nutraceuticals' applications.

Micronutrients, Phytochemicals and Mediterranean Diet: A Potential Protective Role against COVID-19 through Modulation of PAF Actions and Metabolism.

The new coronavirus disease 2019 (COVID-19) pandemic is an emerging situation with high rates of morbidity and mortality, in the pathophysiology of which inflammation and thrombosis are implicated. The disease is directly connected to the nutritional status of patients and a well-balanced diet is recommended by official sources. Recently, the role of platelet activating factor (PAF) was suggested in the pathogenesis of COVID-19. In the present review several micronutrients (vitamin A, vitamin C, vitamin E, vitamin D, selenium, omega-3 fatty acids, and minerals), phytochemicals and Mediterranean diet compounds with potential anti-COVID activity are presented. We further underline that the well-known anti-inflammatory and anti-thrombotic actions of the investigated nutrients and/or holistic dietary schemes, such as the Mediterranean diet, are also mediated through PAF. In conclusion, there is no single food to prevent coronavirus Although the relationship between PAF and COVID-19 is not robust, a healthy diet containing PAF inhibitors may target both inflammation and thrombosis and prevent the deleterious effects of COVID-19. The next step is the experimental confirmation or not of the PAF-COVID-19 hypothesis.

Coronavirus 2019, Microthromboses, and Platelet Activating Factor.

Recent articles have reported elevated markers of coagulation, endothelial injury, and microthromboses in lungs from deceased patients with coronavirus 2019 (COVID-19). Platelets are critical in the formation of thrombi, and their most potent trigger is platelet activating factor (PAF). PAF is produced by cells involved in host defense, and its biological actions bear similarities with COVID-19 disease manifestations, including pulmonary microthromboses and inflammation, possibly via activation of mast cells. The histamine1 receptor antagonist rupatadine was developed to have anti-PAF activity and inhibits activation of human mast cells in response to PAF. Rupatadine could be repurposed for COVID-19 prophylaxis.

Forty Years Since the Structural Elucidation of Platelet-Activating Factor (PAF): Historical, Current, and Future Research Perspectives.

In the late 1960s, Barbaro and Zvaifler described a substance that caused antigen induced histamine release from rabbit platelets producing antibodies in passive cutaneous anaphylaxis. Henson described a 'soluble factor' released from leukocytes that induced vasoactive amine release in platelets. Later observations by Siraganuan and Osler observed the existence of a diluted substance that had the capacity to cause platelet activation. In 1972, the term platelet-activating factor (PAF) was coined by Benveniste, Henson, and Cochrane. The structure of PAF was later elucidated by Demopoulos, Pinckard, and Hanahan in 1979. These studies introduced the research world to PAF, which is now recognised as a potent phospholipid mediator. Since its introduction to the literature, research on PAF has grown due to interest in its vital cell signalling functions and more sinisterly its role as a pro-inflammatory molecule in several chronic diseases including cardiovascular disease and cancer. As it is forty years since the structural elucidation of PAF, the aim of this review is to provide a historical account of the discovery of PAF and to provide a general overview of current and future perspectives on PAF research in physiology and pathophysiology.

Wine and its metabolic effects. A comprehensive review of clinical trials.

The introduction of the term "French Paradox" motivated an extensive and in-depth research into health benefits of moderate wine consumption. The superiority of wine is thought to be attributed to its micro-constituents and consequent effort was made to isolate and identify these bioactive compounds as well as to elucidate the mechanisms of their action. Controlled trials offer more concrete answers to several raised questions than observational studies. Under this perspective, clinical trials have been implemented, mainly in healthy volunteers and rarely in patients, in order to investigate the acute or chronic effect of wine consumption on metabolism and physio-pathological systems, which are mainly associated with cardiovascular diseases. The aim of this review is to update the knowledge about the acute and long term effect of wine consumption on lipid and glucose/insulin metabolism as well as on the inflammatory and haemostatic systems, based on the reported data of controlled clinical trials. In conclusion, the most repeated result of wine consumption is on lipid metabolism, attributed mainly to ethanol, while wine micro-constituents seem to have an important role mainly in haemostatic and inflammatory/endothelial systems.

A Review on Platelet Activating Factor Inhibitors: Could a New Class of Potent Metal-Based Anti-Inflammatory Drugs Induce Anticancer Properties?

In this minireview, we refer to recent results as far as the Platelet Activating Factor (PAF) inhibitors are concerned. At first, results of organic compounds (natural and synthetic ones and specific and nonspecific) as inhibitors of PAF are reported. Emphasis is given on recent results about a new class of the so-called metal-based inhibitors of PAF. A small library of 30 metal complexes has been thus created; their anti-inflammatory activity has been further evaluated owing to their inhibitory effect against PAF in washed rabbit platelets (WRPs). In addition, emphasis has also been placed on the identification of preliminary structure-activity relationships for the different classes of metal-based inhibitors.

Postprandial effects of wine consumption on Platelet Activating Factor metabolic enzymes.

Platelet Activating factor (PAF) is a potent inflammatory mediator that is involved in the initiation and the prolongation of atherosclerosis. The purpose of the study was to investigate the effect of wine consumption on the activity of PAF metabolic enzymes and on IL-6 levels as a cytokine inflammatory marker. Healthy men participated in 4 daily trials and consumed a standardized meal along with Robola wine (trial R), or Cabernet Sauvignon (trial CS), or ethanol solution (trial E), or water (trial W). A significant trial effect was found in the activity of lyso-PAF acetyltransferase (Lyso-PAF AT) (ptrial=0.01). In specific, R trial decreased enzyme activity compared to E trial (p=0.03) while a trend for differentiation was observed between CS trial and E one (p=0.06) as well as between R trial and W one (p=0.07). Concerning PAF-cholinephosphotransferase (PAF-CPT) activity, a significant trial effect was found (ptrial<0.00). Specifically, both R (p=0.002) and CS (p=0.001) trials decreased enzyme activity compared to E trial. Concerning lipoprotein-associated phospholipase A2 (LpPLA2) no time either trial effect was observed. Concerning IL-6 levels a significant time effect was found (ptime<0.00) while no trial effect was revealed. In conclusion, the protective effect of wine consumption could partly be explained through the modulation of PAF metabolism by wine micro-constituents that lead to lower PAF levels.

In Vitro Effects of Anti-Glaucomatous Eye Drops on Platelet-Activating Factor and its Metabolism.

PURPOSE: The purpose of this study is to determine the effect of various commonly used antiglaucoma eye drops on inflammatory mediators such as the platelet activating factor (PAF). METHODS: Various intraocular pressure (IOP) lowering drops were tested to examine their inhibitory effect on PAF. Multiple eye drops were tested in washed rabbit platelets (WRPs) in order to determine the interaction between these eye drops and the inhibition of PAF in the PAF-induced platelet aggregation model. In addition, we examined the eyedrops' effect on PAF-metabolism, through in vitro analysis on PAF basic metabolic enzymes (PAF-CPT, lyso PAF-AT, and PAF-AH). RESULTS: Latanoprost (Xalatan) was found to be the most potent in inhibiting PAF, suggesting that it is the most effective in decreasing IOP amongst the eye drops tested. Conversely, dorzolamide hydrochloride-timolol (Cosopt) exhibited the least anti-PAF action. CONCLUSIONS: This is the first study examine the relationship between PAF activity and glaucoma medication. Potency in PAF inhibition may be related to drop efficacy.

Impact of prostaglandin glaucoma drops on platelet-activating factor action: an in vitro study.

AIM: The aim of this study was to investigate the effect of different prostaglandin analogs on platelet-activating factor (PAF) levels. METHODS: Three prostaglandin analogs were selected: bimatoprost 0.3 mg/mL, latanoprost 50 µg/mL, and tafluprost 15 µg/mL. Each drug sample was tested for its ability to cause platelet aggregation, which was measured as PAF-induced aggregation, before and after the addition of various concentrations of the examined sample, creating a linear curve of percentage inhibition (ranging from 0% to 100%) versus different concentrations of the sample. The concentration of the sample that inhibited 50% PAF-induced aggregation was calculated based on this curve, and this value was defined as IC50. In addition, the effect of eye drops on PAF metabolism was examined, through an in vitro analysis on PAF basic metabolic enzymes (PAF-cholinephosphotransferase, PAF-acetyl-CoA:1-O-alkyl-sn-glycero-3-phosphocholine acetyltransferase, and PAF-acetylhydrolase). RESULTS: The IC50 values for Lumigan UD® (bimatoprost 0.3 mg/mL), Monoprost® (latanoprost 50 µg/mL), and Saflutan (tafluprost 15 µg/mL) were 8.7, 0.28, and 1.4 µg/mL, respectively. DISCUSSION: All three prostaglandin analogs suspended PAF, but bimatoprost induced the most potent inhibition, compared to tafluprost and to the weak effect of latanoprost.

In vivo effect of two first-line ART regimens on inflammatory mediators in male HIV patients.

BACKGROUND: Persistent immune activation and inflammation are lying behind HIV-infection even in the setting of ART mediated viral suppression. The purpose of this study is to define the in vivo effect of two first-line ART regimens on certain inflammatory mediators in male HIV patients. METHODS: Male, naive, HIV-infected volunteers were assigned either to tenofovir-DF/emtricitabine/efavirenz (Group_T) or abacavir/lamivudine/efavirenz (Group_A). Platelet Activating Factor (PAF) levels and metabolic enzymes together with HIV-implicated cytokines (IL-1beta, IL-6, IL-8, IL-10, IL-12p70, TNFa) and VEGF were determined for a 12-month period. Differences within each group were determined by non-parametric Friedman and Wilcoxon test, while the differences between the groups were checked by ANOVA repeated measures. RESULTS: Both ART regimens present pronounced effect on inflammatory mediators, resulting in decreased PAF levels and Lipoprotein-associated phospholipase A2 (Lp-PLA2) activity for tenofovir-containing regimen and same as baseline PAF levels with a peak though at the 3rd month as well as elevated Lp-PLA2 activity for abacavir-containing regimen. CONCLUSIONS: Studies regarding the effect of first-line ART regimens on inflammation may be beneficial in preventing chronic morbidities during HIV-treatment. From this point of view, the present study suggests an anti-inflammatory effect of tenofovir-containing ART, while the temporary increase of PAF levels in abacavir-containing ART may be the link between the reported cardiovascular risk and abacavir administration.

Re(I) tricarbonyl complex of 1,10-phenanthroline-5,6-dione: DNA binding, cytotoxicity, anti-inflammatory and anti-coagulant effects towards platelet activating factor.

The complex fac-[Re(CO)3(phendione)Cl] (1) (where phendione=1,10-phenanthroline-5,6-dione) has been synthesized and fully characterized by UV-visible, FTIR, and NMR techniques. The DNA binding properties of 1 are investigated by UV-spectrophotometric (melting curves), covalent binding assay, CV (cyclic voltammetry), circular dichroism (CD) and viscosity measurements. Experimental data indicate that 1 fits into the major groove without disrupting the helical structure of the B-DNA in contrast to the free phendione which intercalates within the base pairs of DNA. Upon irradiation, complex 1 promotes the cleavage of plasmid pBR322 DNA from supercoiled form I to nicked form II via a proton coupled electron transfer mechanism. This comes as a result of experimental data in anaerobic/aerobic conditions and in the presence of DMSO. The biological activities of 1 and its precursors [Re(CO)5Cl] and phendione are tested towards a series of cancerous cell lines as glioblastoma (T98G), prostate cancer (PC3) and breast cancer (MCF-7) as well as platelet activating factor (PAF)-aggregation. Moreover, all the aforementioned compounds are tested for their ability to modulate PAF-basic metabolic enzyme activities in preparations of rabbit leukolytes. The in vitro experiments indicate that phendione has a better antitumor effect than cisplatin whereas [Re(CO)5Cl] is a better PAF inhibitor than both the phendione ligand and 1. Moreover, for the first time it is indicated that [Re(CO)5Cl], with a IC50 of 17nM is comparable to the widely used PAF receptor antagonists, BN52021 and WEB2170 with IC50 of 30 and 20nM, respectively, whereas 1 affects PAF-catabolism.

In vitro effects of vitamin supplements on platelet-activating factor and its metabolism in age-related macular degeneration.

OBJECTIVE: The purpose of our study was to investigate for the first time a series of vitamin supplements used for age-related macular degeneration (AMD) as potential inhibitors of platelet-activating factor (PAF). MATERIALS AND METHODS: Various vitamin supplements were tested in washed rabbit platelets (WRPs), in order to investigate the interaction between vitamin supplements (InShape, Nutrof, Ocuvite, Vitalux) and inhibition of PAF-induced platelet aggregation. Additionally, we examined their ability to affect PAF-metabolism, through their in vitro effect on PAF basic metabolic enzymes (PAF-CPT, lyso PAF-AT, and PAF-AH). RESULTS: Nutrof exhibited the strongest anti-PAF activity, while Vitalux was the most potent anti-inflammatory factor. CONCLUSION: This is the first study to bring in surface potent anti-inflammatory and anti-angiogenic activities of some vitamin supplements used against AMD, through their in vitro anti-PAF effects in WRPs and the rabbit plasma and leukocyte PAF metabolism, suggesting a promising role of vitamin supplements and especially resveratrol, concerning its potent anti-angiogenic activity in AMD.

Evaluation of the in vitro anti-atherogenic properties of lipid fractions of olive pomace, olive pomace enriched fish feed and gilthead sea bream (Sparus aurata) fed with olive pomace enriched fish feed.

Given the pivotal role of Platelet-Activating-Factor (PAF) in atherosclerosis and the cardio-protective role of PAF-inhibitors derived from olive pomace, the inclusion of olive pomace in fish feed has been studied for gilthead sea bream (Sparus aurata). The aim of the current research was to elucidate the anti-atherogenic properties of specific HPLC lipid fractions obtained from olive pomace, olive pomace enriched fish feed and fish fed with the olive pomace enriched fish feed, by evaluating their in vitro biological activity against washed rabbit platelets. This in vitro study underlines that olive pomace inclusion in fish feed improves the nutritional value of both fish feed and fish possibly by enriching the marine lipid profile of gilthead sea bream (Sparus aurata) with specific bioactive lipid compounds of plant origin.

Interleukin-1beta stimulates platelet-activating factor production in U-937 cells modulating both its biosynthetic and catabolic enzymes.

Interleukin-1beta (IL-1ß) is a potent agonist of platelet-activating factor (PAF) synthesis. The monocyte-derived PAF may amplify the inflammatory and thrombotic processes. The IL-1ß-induced enzymatic alterations leading to increased PAF synthesis are ill-defined. In the present study the last enzymatic activities of the remodeling (acetyl-CoA:lyso-PAF acetyltransferase) and de novo (DTT-insensitive CDP-choline:1-alkyl-2-acetyl-sn-glycerol cholinephosphotransferase) biosynthetic routes of PAF and its main catabolic enzyme, PAF acetylhydrolase, along with the intracellular and extracellular PAF levels were determined in homogenates and medium of U-937 after their stimulation with recombinant IL-1ß. IL-1ß at 2.5ng/mL induced an early (0.5-3h) and a late (12h) elevation of intracellular PAF levels (2-fold). Only a small portion of intracellular PAF (∼10%) was released to the extracellular medium. IL-1ß increased lyso-PAF acetyltrasnferase activity which was peaked at 3h and kept elevated till 12h. A rapid 1.5-fold increase of cholinephosphotransferase activity was observed in IL-1ß stimulated cells. Finally, a transient stimulation of intracellular PAF-AH was induced by IL-1ß at 3h while incubation of U-937 with the PAF acetylhydrolase inhibitor pefabloc in the presence or absence of IL-1ß led to a strong sustained increase of intracellular PAF levels. In conclusion, both biosynthetic routes of PAF, along with its degradation can be modulated by IL-1ß in a time-specific manner. The inhibition of PAF acetylhydrolase strongly augments PAF's intracellular levels implying its crucial role for the regulation of cellular PAF. The regulation of PAF's enzymatic machinery under inflammatory conditions is more complicated than we thought to be.