The thrombocyte-activation factor and endotoxin-induced thrombocyte activation

The effect of PAF in aggregation of platelets induced by endotoxin was studied in experiments in vitro. It is indicated that in high concentration (1.10(-7)-1.10(-6) M) PAF did not affect the degree of aggregation of platelets induced by lipopolysaccharides (LPS) S. typhimurium and N. meningitidis. Successive addition to PRP LPS and PAF or joint addition of PAF and LPS did not change the degree of aggregation of each inductor or their sum. A lower concentration of PAF (1.10(-11)-1.10(-9) M) and endotoxin caused a more expressive aggregation of platelets than their successive addition. Stimulating activity of PAF on endotoxin-induced aggregation, perhaps, is caused by involvement of metabolism of arachidonic acid during blood platelets activation.     

A novel enhancing effect of platelet activating factor (PAF) on glucose oxidation in uteri from pregnant rats. Participation of prostaglandins and leukotrienes

The effects of platelet activating factor (PAF) on glucose oxidation in uterine strips isolated from rats in the 4 th and 5 th day of pregnancy, were explored. PAF, at a concentration of 10(-10) and 10(-8) M, augmented significantly the generation of 14CO2 from labelled glucose in uteri from pregnant rats in the 4 th day of pregnancy. When the tissue was obtained from 5 days pregnant rats, the addition of PAF at 10(-8) increased significantly more than PAF at 10(-10) M the metabolism of glucose. On the other hand, PAF at 10(-8) M failed to alter the uterine basal production of 14CO2 from labelled glucose in animals at estrus. BN52021, a specific PAF antagonist employed at 10(-5) M, blocked completely the action of PAF in the pregnant rat uterus. PGE1, PGE2 and PGF2 alpha enhanced significantly the formation of 14CO2 from labelled glucose in uteri from 5 days pregnant rats. Indomethacin, a well known inhibitor of prostaglandin synthesis, did not alter the basal glucose metabolism in uteri from 5 days pregnant rats, but antagonized completely the stimulating action of PAF on 14CO2 production from labelled glucose an effect that was partially reverted by the addition of PGE1, PGE2 or PGF2 alpha (10(-7) M). Furthermore, nordihydroguaiaretic acid (NDHGA), a specific inhibitor of 5-lipoxygenase at 10(-5) M, as well as FPL-55712, an antagonist of leukotrienes (LTs), at the same concentration, blocked the action of PAF on the metabolism of glucose. The action of NDHGA was partially counteracted by the addition of LTC4 at 10(-7) M.(ABSTRACT TRUNCATED AT 250 WORDS)     

Binding of platelet activating factor to albumin

Binding of platelet activating factor (1-O-alkyl-2-O-acetyl-sn-glycero-3-phosphocholine) to albumin is an important facet of the biological activity of this phospholipid. Measurement of that binding has been hampered by the physical nature of the lipid, which made estimation of the free and bound concentrations difficult. With the use of ultracentrifugation to generate an albumin gradient and to produce a region free of protein, the successful measurement of free PAF and PAF bound to albumin was accomplished. This study has demonstrated that PAF binds to albumin at four binding sites and that the average equilibrium dissociation constant for this binding is 1.10(-7) M. Consideration of these data has led to the hypothesis that the receptor active form of PAF is the albumin-PAF complex, rather than free PAF.     

Effect of Platelet-Activating Factor on the Process of Cellular Differentiation of Herpetomonas muscarum muscarum

ABSTRACT. The effects of platelet-activating factor (PAF), at doses ranging from 10⁻⁶ M to 10⁻¹⁰ M, on cell growth and on cell differentiation of Herpetomonas muscarum muscarum were investigated. Cell differentiation was evaluated by both light and electron microscopy. At the concentrations used, PAF did not interfere with the protozoan growth. However, parasites grown in the presence of PAF (10⁻⁶ M) were significantly more differentiated than those grown in the absence of PAF, since the first day of culture. On the first two days of culture, PAF doses ranging from 10⁻¹⁰ M to 10⁻⁷ M, did not significantly interfere with the differentiation of these parasites, although after the third day of culture, all PAF doses used significantly increased the protozoan differentiation. Specific PAF receptor antagonists totally abrogated (WEB 2086 and WEB 2170)or significantly decreased (BN 52021) PAF effect on cell differentiation. These findings indicate PAF triggers the process of cell differentiation in Herpetomonas muscarum muscarum and suggest these parasites have receptors for PAF.     

Inhibition by BN 52021 (ginkgolide B) of the binding of [3H]-platelet-activating factor to human neutrophil granulocytes

The inhibitory effect of BN 52021, a specific antagonist of platelet-activating factor (PAF) on PAF-induced activation of human polymorphonuclear granulocytes (PMNL) and on the binding of [3H]-PAF to neutrophils were examined. BN 52021 over the range of 10(-9)-10(-4) M inhibited PAF-induced degranulation and superoxide production of PMNLs in a dose-dependent manner with Kd values of 0.6 +/- 0.1 x 10(-6) M and 0.4 +/- 0.1 x 10(-6) M, respectively. BN 52021 (up to 1 mM) did not show any agonistic activity and it did not affect neutrophil responses to N-formyl-methionyl-leucyl-phenylalanine or leukotriene B4. The Ki value of BN 52021 for the specific binding of [3H]-PAF to neutrophils was 1.3 +/- 0.5 x 10(-6) M versus a Ki of 1.1 +/- 0.3 x 10(-7) M for PAF itself. BN 52021 did not affect metabolism of PAF by PMNL. These studies indicate that BN 52021 inhibits neutrophil responses to PAF by inhibiting binding of PAF to its specific PMNL receptor.     

Lipoprotein-dependent synthesis of prostacyclin in smooth muscle cells

Low (LDL) and high density lipoproteins (HDL) stimulated prostacycline (PGI2) synthesis in rabbit and human aorta smooth muscle cells growing in culture. The lipoproteins were added to the cells in concentrations equal to that of cholesterol. It was shown that HDL exerted a stronger stimulating effect as compared to LDL. The maximal effect was observed with HDL3. HDL3 isolated from blood serum of healthy volunteers appeared to be more active in PGI2 synthesis promotion than those of CDH patients with documented coronary atherosclerosis. Purified Apo A-1 stimulated the transformation of [14C]arachidonic acid into the products of its metabolism with increased accumulation of 6-keto-PGF1 alpha among labeled metabolites. Estradiol (1.10(-7) M) showed a stimulating effect; norepinephrine (1.10(-6) M) and progesterone (1.10(-7) M) showed an inhibiting effect, whereas corticosterone (1.10(-6) M) and deoxycorticosterone (1.10(-6) M) did not influence the rate of LDL-dependent PGI2 synthesis.     

Platelet-activating factor induces the production of leukotrienes by human monocytes

The aim of this study was to evaluate the role of platelet-activating factor (PAF) as a stimulator of leukotriene production by human monocytes. The production of leukotrienes was time- and concentration-dependent. Release of leukotrienes was half-maximal after 2 min and reached a maximum after 10 min. At a concentration of 10(-8) M, PAF induced the production of 0.14 +/- 0.01 ng LTB4/10(6) cells (mean +/- S.E., n = 8). At concentrations of 10(-6) M, PAF induced the production of 1.0 +/- 0.04 ng LTB4 and 0.22 +/- 0.03 ng peptidoleukotrienes (mean +/- S.E., n = 16). There was no metabolism of LTB4 as judged from stability of [3H]LTB4 added to the incubations. LTC4 was slowly metabolized by human monocytes to LTD4 and LTE4. The two specific PAF-receptor antagonists BN 52021 and WEB 2086 in concentrations of 10(-4) and 10(-6) M, respectively, inhibited the PAF (10(-6) M) stimulated LTB4 production completely. In this study, we demonstrate that nanomolar concentrations of PAF can stimulate the production of LTB4 and peptidoleukotrienes in human monocytes by a receptor-mediated mechanism.     

CV-3988 - a specific antagonist of platelet activating factor (PAF)

CV-3988, rac-3-(N-n-octadecylcarbamoyloxy)-2-methoxypropyl 2-thiazolioethyl phosphate was shown to be a specific inhibitor of platelet activating factor (PAF). This compound in concentrations of 3 x 10(-6) to 3 x 10(-5)M inhibited aggregation of rabbit platelets induced by PAF (3 x 10(-8)M), while it had no effect on the aggregation induced by arachidonic acid, ADP, collagen or A-23187. CV-3988 alone even at a concentration of 10(-3)M had no effect on platelet aggregation. The inhibitory action of CV-3988 on the PAF-induced aggregation was independent of the formation of micelles. The PAF (0.1 to 1.0 micrograms/kg, i.v.)-induced hypotension in anesthetized rats was also inhibited dose-dependently by the i.v. administration of CV-3988 (1 and 10 mg/kg), while the hypotensive actions induced by the i.v. administration of acetylcholine (1 micrograms/kg), arachidonic acid (1 mg/kg), bradykinin (10 micrograms/kg), isoproterenol (1 microgram/kg) and histamine (100 micrograms/kg) were not altered by CV-3988 (10 mg/kg, i.v.). All these findings indicate that CV-3988 specifically inhibits the action of PAF in vitro and in vivo. This is the first report of a PAF antagonist which can specifically inhibit the PAF-induced hypotension as well as the PAF-induced platelet aggregation.     

Selective activation of human monocytes by the platelet-activating factor analog 1-O-hexadecyl-2-O-methyl-sn-glycero-3-phosphorylcholine

The capacity of platelet-activating factor (PAF) and its 2-O-methyl analog (methoxy-PAF) to activate human monocytes, neutrophils and platelets were compared. Both PAF and methoxy-PAF increased monocyte cytotoxicity toward WEHI 164 cells with a maximal increase in cell killing at 100 pM to 1 nM. Methoxy-PAF was slightly, but significantly, more potent than PAF for increasing cytotoxicity. PAF and methoxy-PAF increased monocyte release of TNF two- to three-fold above control release with no difference in their potency. Methoxy-PAF increased cell-associated TNF maximally after 2 to 3 h of incubation and increased TNF release maximally after 5 to 18 h of incubation. PAF induced release of the neutrophil granule enzyme beta-glucuronidase with maximal net release of 15 to 20% at 100 nM PAF whereas methoxy-PAF did not induce release of beta-glucuronidase. Similarly, 10 nM PAF induced 30% platelet aggregation whereas methoxy-PAF induced aggregation only at 1000-fold higher concentrations. Analysis of PAF and methoxy-PAF metabolism by monocyte and serum acylhydrolases indicates that methoxy-PAF is substantially more resistant than PAF to degradation by these enzymes. These observations indicate that methoxy-PAF activates monocytes selectively and suggest that this phospholipid or a related compound could be used for in vivo immunotherapy.     

Production of Platelet-Activating Factor from Rat Cerebellar Granule Cells in Culture

Abstract: Platelet-activating factor (PAF) is a potent lipid mediator implicated in various pathological conditions, including CNS neuronal injury. However, the production of PAF by mammalian CNS neurons has not as yet been demonstrated. In the present study, we demonstrate that PAF is produced by cultured rat cerebellar granule cells. PAF was identified on the basis of chemical and enzymatic characteristics, biological activities with washed rabbit platelets, and behavior on TLC and HPLC. PAF was detected both in the cells and in the incubation medium, a result indicating the release of PAF from cultured neurons. The amount of PAF produced during a 30-min incubation was as follows: 1.02 ± 0.10 and 0.93 ± 0.09 pmol/ 4 × 10⁷ cells in incubation buffer and cells, respectively (n = 10). The calcium ionophore A23187 (2.5 μ M ) had only a mild stimulatory effect on PAF production, a finding indicating that the neuron-generated PAF might be synthesized mainly by the de novo pathway of PAF production.     

Role of spermatozoal platelet-activating factor in fertilization

Platelet-activating factor (PAF), a potent lipid mediator of inflammation, has been shown to play a role in both the implantation and viability of mammalian embryos. We examined whether human and mouse spermatozoa release PAF during in vitro incubation and assessed the effect of exogenous PAF and the PAF receptor antagonist WEB 2086, a thieno-triazolodiazepine, on mouse in vitro fertilization (IVF) rate. PAF biological activity was detected in 11 samples of leukocyte-free, purified human spermatozoa (28 pg PAF/10(6) cells/24 hr) and 5 samples of epididymal mouse spermatozoa (7.8 pg PAF/10(6) cells/3 hr). Exogenous PAF (10(-8) and 10(-6) M) increased (p less than 0.01) the fertilization rate 2- and 3-fold, respectively of mouse oocytes by mouse epididymal spermatozoa. 10(-4) M PAF, however, reduced sperm motility and decreased (p less than 0.05) the fertilization rate. 10(-6) M WEB 2086, decreased IVF to approximately 50% of the control fertilization rate (42% vs. 89%). WEB 2086 treatment also promoted the attachment of supernumerary spermatozoa to both fertilized and unfertilized oocytes. The fertilization rate in the presence of WEB 2086 returned to control levels when zona-pellucida-free oocytes were employed, indicating that WEB 2086 did not interfere with the spermatozoal acrosome reaction. These data suggest that PAF, of spermatozoal origin, may be important in mammalian fertilization.     

Priming interactions between platelet activating factor and histamine in the in vivo microcirculation.

To elucidate whether priming exists between platelet-activating factor (PAF) and histamine in the microcirculation, we measured the clearance of FITC-dextran 150 in response to the topical applications of substimulatory concentrations of PAF and histamine. Maximal priming by PAF was observed when a 5-min interval separated the applications of 10(-9) M PAF and 10(-6) M histamine. The mean (+/- SEM) clearance resulting from this sequence of agonist administration was 7529 +/- 659 nl.2 h-1.g-1, representing a 4.5-fold enhancement in FITC-dextran 150 clearance compared with that evoked by 10(-6) M histamine alone (1664 +/- 397 nl.2 h-1.g-1). Lowering the PAF priming dose to 10(-11) M, or reversing the order of agonist addition to the microcirculation, resulted in diminished but significant responses of 3545 +/- 1143 and 4467 +/- 1170 nl.2 hr-1.g-1, respectively. Coapplication of PAF and histamine or increasing the time interval between the agonists to 15 min greatly reduced the responses to 1906 +/- 678 and 2770 +/- 837, respectively. The PAF receptor antagonist WEB 2086 (2 mg/kg i.v.), the H1 blocker pyrilamine (10 mg/kg i.v.), and leukocyte depletion with cyclophosphamide (150 mg/kg i.p.) completely abolished the PAF priming effect. In addition, the 5-lipoxygenase inhibitor RG 5901 (1 or 10 mg/kg i.v.) produced a two-thirds attenuation in PAF priming. We conclude that 1) PAF has the ability to prime the in vivo microvascular actions of histamine in both a concentration and time-dependent fashion; 2) this primed response is receptor mediated; and 3) histamine can prime the microcirculation for enhanced responses to PAF. Our data also demonstrate that leukocytes and the release of leukotrienes participate in PAF priming.     

Oxidative metabolism of energy substrates by preimplantation mouse embryos in the presence of platelet-activating factor

The effects of exogenous platelet-activating factor (PAF, 0.0186-18.6 microM) on the production of CO2 from [U-14C]glucose and [1-14C]lactate by mouse embryos in vitro were investigated. Two-cell embryos displayed significant dose-dependent responses for both energy substrates. The maximal response was observed at 9.3 microM-PAF for glucose metabolism and 1.86 microM-PAF for lactate with increases of 62% and 18%, respectively, over control treatments. After culture from the 2-cell stage for 72 h in the presence of PAF, the resulting blastocysts exhibited a significant dose-dependent increase in metabolism of lactate. It was also apparent that such embryos were not desensitized to PAF as demonstrated by a further enhancement of the metabolic response after re-exposure to PAF. The specificity of action of PAF was confirmed by the absence of any effect on the oxidative metabolism of glucose by lyso-PAF (a catabolite of PAF) over a concentration range of 0.0202-20.2 microM and by the demonstration that SRI 63-441 (a PAF-receptor antagonist) significantly reduced the amount of CO2 produced from glucose in response to 9.3 microM-PAF and abolished the effect on lactate metabolism in response to 1.86 microM-PAF. These results demonstrate a specific, direct influence of exogenous PAF on the oxidative metabolism of glucose and lactate by the preimplantation mouse embryo and suggest an autocrine role for embryo-derived PAF in early pregnancy.     

Evidence for a platelet-activating factor receptor on human lymphoblastoid B cells: activation of the phosphatidylinositol cycle and induction of calcium mobilization

In this report we demonstrate evidence which strongly suggests that a receptor for platelet-activating factor (PAF) exists on a lymphoblastoid B cell line, LA350. PAF ranging in concentration from 10(-6)-10(-9)M initiated the incorporation of 32P into phosphatidic acid (PA) and phosphatidylinositol (PI) with no change in phosphatidylethanolamine (PE) and phosphatidylcholine (PC) over baseline. Lyso-PAF, the inactive precursor, at 10(-7)M had no effect on membrane phospholipid metabolism. In addition, PAF from 10(-6)-10(-8)M when added to Fura-2 containing B cells induced a rapid and significant rise of calcium within the cell, with lyso-PAF having no effect. These data suggest that PAF binds to a receptor on B cells and induces the hydrolysis of PI and a subsequent increase of intracellular calcium.     

Conversion of alkylacetylglycerol to platelet-activating factor in HL-60 cells and subcellular localization of the mediator

A human promyelocytic leukemia (HL-60) cell line was used to investigate the conversion of 1-alkyl-2-acetyl-sn-glycerol (alkylacetyl-G) to platelet-activating factor (PAF; 1-alkyl-2-acetyl-sn-glycero-3-phosphocholine) by intact cells and in subcellular fractions in order to examine the fate of PAF synthesized de novo. Lipid extracts obtained from undifferentiated HL-60 cells incubated with [3H]alkylacetyl-G contained 2-4% of the label as [3H]PAF; several related metabolites were also detected. The yield of [3H]PAF could be dramatically increased by pretreating the cells with either oleic acid, an activator of CTP:phosphocholine cytidylyltransferase, or phenylmethylsulfonyl fluoride, an inhibitor of PAF acetylhydrolase. These results, together with a kinetic study of [3H]alkylacetyl-G metabolism, indicate the sequential participation of a cholinephosphotransferase for the conversion of [3H]-alkylacetyl-G to PAF and acetylhydrolase and transacylase activities in the remodeling pathway that metabolize the newly formed [3H]PAF to 1-[3H]alkyl-2-acyl(long chain)-sn-glycero-3-phosphocholine. The dithiothreitol-insensitive cholinephosphotransferase activity capable of converting alkylacetyl-G to PAF was localized in subcellular fractions that contain CDP-choline:1,2-dioleoyl-sn-glycerol cholinephosphotransferase (dithiothreitol-sensitive), as well as marker enzyme activities for the endoplasmic reticulum and Golgi membranes. Subcellular localization analyses also indicated that the majority of newly formed [3H]PAF and a large portion of its deacetylated metabolite were associated with the plasma membrane-containing fractions, whereas most of the 1-[3H]alkyl-2-acyl(long chain)-sn-glycero-3- phosphocholine was present in the intracellular organelles. Incubations of HL-60 cells with exogenous [3H]PAF produced a similar subcellular distribution of metabolites. Very little (less than 10%) of the [3H]PAF produced from [3H]alkylacetyl-G was released from intact cells under a variety of incubation conditions but 50% of the de novo-derived mediator was recovered in the medium of cells that were permeabilized with saponin. Our results indicate that PAF is rapidly translocated from its intracellular site of enzymatic synthesis to the plasma membrane where it is apparently sequestered in a pool that is not accessible to extracellular acceptors in contact with intact cells.     

Mechanism of increased angiotensin-converting enzyme activity stimulated by platelet-activating factor

We studied the effects of platelet activating factor (PAF) on angiotensin-converting enzyme (ACE). PAF (1 x 10(-10) to 1 x 10(-6) M) had a novel effect on angiotensin I conversion. Pulmonary artery endothelial cells converted 1 nmol/dish of 125I-angiotensin I to angiotensin II in the absence of PAF. ACE activity was increased to 2.5 nmol/dish by the addition of 1 x 10(-6) M of PAF. To clarify the mechanism of this stimulatory effect of PAF on ACE, Ca2+ influx and inositol 1,4,5-trisphosphate (IP3) release in pulmonary artery endothelial cells were determined. PAF stimulated Ca2+ influx in a dose-dependent manner. PAF also stimulated phospholipase C (PLC) activity and released IP3. To study the relationship between PLC activity and ACE activity, neomycin was added. The Ca2+ influx and IP3 release stimulated by 10(-6) M of PAF were suppressed by about 60-70%. ACE activity was also inhibited up to 70% in the presence of PAF (10(-10) - 10(-6) M) by 50 M of neomycin. These results suggest that ACE was stimulated by PAF, and that its activity in endothelial cells may be mediated by the PI-turnover pathway via changes in PLC activity and IP3-mediated Ca2+ release from intracellular stores.     

1-O-alkylglycerols improve boar sperm motility and fertility.

1-O-alkylglycerols are naturally occurring ether lipids with potent biological activities. They may interfere with lipidic signaling, and they amplify platelet-activating factor (PAF) biosynthesis in a monocyte cell line. The PAF is produced by mammalian sperm and is an important activator of sperm motility. The aim of this study was to evaluate the effect of in vitro treatment of boar spermatozoa with natural 1-O-alkylglycerols (10 microM) on 1) boar sperm motility; 2) production of PAF and its metabolite, lyso-PAF, by spermatozoa; and 3) fertility in artificial inseminations of breeding sows. Using a computer-assisted spermatozoa analyzer, we found that 1-O-alkylglycerols increased percentage motility as well as velocity parameters after 24 h. These effects were partially or totally reversed by the PAF receptor-antagonist SR 27417. After [3H]-1-O-alkylglycerol incubation with boar spermatozoa, we identified [3H]lyso-PAF by high-performance liquid chromatography. Production of PAF and lyso-PAF was measured with a biological assay using [3H]serotonin release from rabbit platelets. 1-O-alkylglycerols significantly increased lyso-PAF production but had no effect on PAF production. The effect of 1-O-alkylglycerols on fertilization was also evaluated in industrial breedings: 1-O-alkylglycerol-treated or untreated semen dilutions were alternately used for artificial inseminations of sows on 12 farms. 1-O-alkylglycerol treatment increased the number of farrows but had no effect on the mean size of the litters. This study demonstrates that 1-O-alkylglycerol treatment of boar spermatozoa in vitro improves their motility and fertility, and it suggests that this effect is related to PAF metabolism and function in boar spermatozoa.     

The Effect of Lyso-PAF on Ciliary Activity of Human Paranasal Sinus Mucosa in vitro

The effect of lyso-PAF on ciliated cells was investigated in vitro. Normal mucosa was surgically obtained from human paranasal sinuses and incubated in the form of tissue culture. Ciliated epithelium was magnified under an inverted microscope, and ciliary movement was photo-electrically measured. Ciliary activity was significantly inhibited by 10(-8) M lyso-PAF and could be restored. The effect of lyso-PAF was completely blocked by CV-6209, a specific PAF antagonist. The PAF concentration in the incubation medium of lyso-PAF was determined by radioimmunoassay, because PAF is a well known inhibitor of ciliary activity. PAF gradually increased and after 20 min reached its maximal level. These findings indicated the existence of an enzyme in the paranasal sinus mucosa, by which lyso-PAF is converted to PAF, and that lyso-PAF can inhibit ciliary activity by means of PAF.     

Role of platelets in contraction of canine tracheal muscle elicited by PAF in vitro

To elucidate mechanisms of platelet-activating factor (PAF)-induced contraction, we studied the effect of PAF on 203 canine tracheal smooth muscle (TSM) strips from 45 dogs in vitro in the presence and absence of platelets. PAF (10(-11) to 10(-7) M) alone caused no contraction of TSM even in the presence of airway epithelium. In the presence of 2 x 10(5) platelets/microliter, PAF was an extremely potent contractile agonist (threshold 10(-11) M). This response was inhibited by the PAF antagonist, CV-3988 (10(-6) M), and reversed by the serotonin antagonist, methysergide (EC50 = 3.7 +/- 0.79 x 10(-9) M). Neither atropine nor chlorpheniramine (10(-9) to 10(-6) M) attenuated the response to PAF + platelets. In the presence of platelets, 10(-7) M PAF caused an increase in perfusate concentration of serotonin from 0.93 +/- 0.037 x 10(-8) to 1.7 +/- 0.046 x 10(-8) M (P less than 0.001). Tachyphylaxis, previously demonstrated to be irreversible, was shown to be a platelet-dependent phenomenon; contraction could be repeated in the same TSM after addition of fresh platelets. We demonstrate that PAF-induced contraction of canine TSM is caused by the release of cellular intermediates such as serotonin from platelets. We also demonstrate the site of PAF-induced tachyphylaxis in airway smooth muscle contraction.     

The metabolism of platelet-activating factor in human T-lymphocytes

The metabolism of 1-[3H]alkyl-2-acetyl-sn-glycero-3-phosphocholine (1-[3H]alkyl-2-acetyl-GPC; platelet-activating factor; PAF) was investigated in purified human peripheral blood T-lymphocytes and a human leukemia cell line of T-cell origin (MOLT-4). The major metabolic products of T-lymphocyte PAF metabolism are 1-alkyl-2-acyl-GPC, 1-alkyl-2-lyso-GPC and neutral lipid. The pattern of PAF metabolism in peripheral blood T-lymphocytes and MOLT-4 lymphoblasts was similar, although MOLT-4 lymphoblasts transformed PAF to 1-alkyl-2-acyl-GPC faster than peripheral blood T-lymphocytes (67% vs. 21% of added label after 64 min at 37 degrees C, respectively). Pre-exposure of MOLT-4 lymphoblasts to 1 mM of the serine hydrolase inhibitor phenylmethylsulfonyl fluoride resulted in an inhibition of PAF metabolism. Our results indicate that intact T-lymphocytes actively metabolize this biologically active phospholipid by the deacetylation-transacylation pathway.