Comparison of 1-O-alkyl-, 1-O-alk-1'-enyl-, and 1-O-acyl-2-acetyl-sn-glycero-3-phosphoethanolamines and -3-phosphocholines as agonists of the platelet-activating factor family

Structural Elucidation of Irish Organic Farmed Salmon (Salmo salar) Polar Lipids with Antithrombotic Activities

While several marine polar lipids (PL) have exhibited cardioprotective properties through their effects on the platelet-activating factor (PAF) pathways, salmon PL have not been tested so far. In this study, the antithrombotic activities of salmon PL were assessed in human platelets and the structural characterisation of bioactive salmon PL was performed by GC-MS and LC-MS analyses. PL from fillets of Irish organic farmed salmon (Salmo salar) were extracted and separated into several lipid subclasses by thin-layer chromatography (TLC), while their fatty acid profile was fully characterised by GC-MS. Salmon total lipids (TL), total neutral lipids (TNL), total polar lipids (TPL), and each PL subclass obtained by TLC were further assessed for their in vitro effects towards PAF-induced and thrombin-induced platelet aggregation in human platelets. Salmon PL exhibited antithrombotic effects on human platelet aggregation, mostly through their strong inhibitory effects against the PAF pathway with IC50 values comparable to other marine PL, but with lower effects towards the thrombin pathway. PL fractions corresponding to phosphatidylcholine and phosphatidylethanolamine derivatives exhibited the most potent anti-PAF effects, while LC-MS analysis putatively elucidated their structure/function relationship. Several diacyl-PC/PE and alkyl-acyl-PC/PE species containing mostly docosahexaenoic acid at their sn-2 glycerol-backbone may be responsible for the bioactivity. The data presented suggests that salmon contains PL with strong antithrombotic bioactivities.

Enzymatic modification of phospholipids for functional applications and human nutrition

Rapid progress in biochemistry of phospholipids and evolution of modern bioengineering has brought forth a number of novel concepts and technical advancements in the modification of phospholipids for industrial applications and human nutrition. Highlights cover preparation of novel phospholipid analogs based on the latest understanding of pivotal role of phospholipids in manifold biological processes, exploration of remarkable application potentials of phospholipids in meliorating human health, as well as development of new chemical and biotechnological approaches applied to the modification of phospholipids. This work reviews the natural occurrence and structural characteristics of phospholipids, their updated knowledge on manifold biological and nutritional functions, traditional and novel physical and chemical approaches to modify phospholipids as well as their applications to obtain novel phospholipids, and brief introduction of the efforts focusing on de novo syntheses of phospholipids. Special attention is given to the summary of molecular structural characteristics and catalytic properties of multiple phospholipases, which helps to interpret experimental phenomena and to improve reaction design. This will of course provide fundamental bases also for the development of enzymatic technology to produce structured or modified phospholipids.

Structural identification of oxidized acyl-phosphatidylcholines that induce platelet activation

Oxidation of low-density lipoprotein (LDL) generates proinflammatory and prothrombotic mediators that may play a crucial role in cardiovascular and inflammatory diseases. In order to study platelet-activating components of oxidized LDL 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphocholine, a representative of the major phospholipid species in LDL, the 1-acyl-phosphatidylcholines (PC), was oxidized by CuCl(2) and H(2)O(2). After separation by high-performance liquid chromatography, three compounds were detected which induced platelet shape change at low micromolar concentrations. Platelet activation by these compounds was distinct from the pathways stimulated by platelet-activating factor, lyso-phosphatidic acid, lyso-PC and thromboxane A(2), as evidenced by the use of specific receptor antagonists. Further analyses of the oxidized phospholipids by electrospray ionization mass spectrometry structurally identified them as 1-stearoyl-2-azelaoyl-sn-glycero-3-phosphocholine (m/z 694; SAzPC), 1-stearoyl-2-glutaroyl-sn- glycero-3-phosphocholine (m/z 638; SGPC), and 1-stearoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphocholine (m/z 622; SOVPC). These observations demonstrate that novel 1-acyl-PC which had previously been found to stimulate interaction of monocytes with endothelial cells also induce platelet activation, a central step in acute thrombogenic and atherogenic processes.

Bioactive phospholipid oxidation products

Oxidation of phospholipids results in chain-shortened fragments and oxygenated derivatives of polyunsaturated sn-2 fatty acyl residues, generating a myriad of phospholipid products. Certain oxidation products of phosphatidylcholine bind to and activate the human receptor for PAF, and these PAF-like lipids are potent, selective inflammatory mediators. Formation of PAF-like lipids is nonenzymatic and so their accumulation is unregulated. PAF-like lipids are produced in vivo in response to oxidative stresses and are responsible for attendant acute inflammatory responses. PAF-like lipids almost exclusively contain an ether-linked alkyl residue at the sn-1 position of the phosphatidylcholine backbone and molecular identification of these is facilitated by phospholipase A(1) treatment to remove the bulk of the inactive phospholipids. The identity of biologically active species generated by oxidative fragmentation and oxidation can be elucidated by understanding relevant reactions leading to the formation of PAF-like lipids, and then their structure can be established by tandem mass spectrometry and chemical synthesis.

A metabolic path for the degradation of lysophosphatidic acid, an inhibitor of lysophosphatidylcholine lysophospholipase, in neuronal nuclei of cerebral cortex

Neuronal nuclei isolated from rabbit cerebral cortex were found to be enriched in an NEM-insensitive lysophosphatidic acid (lysoPA) phosphohydrolase activity. LysoPA is an inhibitor of the nuclear lysophosphatidylcholine (lysoPC) lysophospholipase, and by preserving lysoPC levels, lysoPA boosted the nuclear production of the acyl analogue of platelet-activating factor by promoting the acetylation of lysoPC (Baker and Chang, Mol. Cell Biochem., 1999, in press). The nuclear phosphohydrolase converts lysoPA to 1-monoacylglycerol, and thus eliminates this lysoPA inhibition of lysoPC lysophospholipase. The nuclear lysoPA phosphohydrolase specific activity was more than three times that observed for the nuclear lysoPA lysophospholipase (Baker and Chang, Biochim. Biophys. Acta 1438 (1999) 253-263) and represents a more active route for nuclear lysoPA removal. The neuronal nuclear lysoPA phosphohydrolase was inhibited at acidic pH, and also inhibited by calcium ions. The 1-monoacylglycerol product of the phosphohydrolase is rapidly degraded by neuronal monoacylglycerol lipase, an enzyme some sevenfold more active than the phosphohydrolase and sensitive to inhibition by arachidonoyl trifluoromethyl ketone (AACOCF(3)). Both acidic pH and free fatty acid inhibited the lipase. In the absence of AACOCF(3), production of fatty acid from lysoPA substrate could be largely attributed to the sequential actions of the nuclear phosphohydrolase and lipase. This facilitates fatty acid recycling back into phospholipid by lysophospholipid acylation when ATP levels are restored following periods of brain ischemia. At relatively low concentrations, sphingosine-1-phosphate, and alkylglycerophosphate were the most effective phosphohydrolase inhibitors while phosphatidic acid, alkylacetylglycerophosphate and ceramide were without effect. LysoPA is an interesting regulatory molecule that can potentially preserve lysophosphatidylcholine within the nuclear membrane for use in acetylation reactions. Thus conditions relevant to brain ischemia such as falling pH, falling ATP concentrations, rising fatty acid and intracellular calcium levels may, by slowing this metabolic path for lysoPA loss, promote the production of acyl PAF and contribute to the increased levels of the acetylated lipids noted in ischemia.

Inflammatory platelet-activating factor-like phospholipids in oxidized low density lipoproteins are fragmented alkyl phosphatidylcholines

Oxidation of human low density lipoprotein (LDL) generates proinflammatory mediators and underlies early events in atherogenesis. We identified mediators in oxidized LDL that induced an inflammatory reaction in vivo, and activated polymorphonuclear leukocytes and cells ectopically expressing human platelet-activating factor (PAF) receptors. Oxidation of a synthetic phosphatidylcholine showed that an sn-1 ether bond confers an 800-fold increase in potency. This suggests that rare ether-linked phospholipids in LDL are the likely source of PAF-like activity in oxidized LDL. Accordingly, treatment of oxidized LDL with phospholipase A(1) greatly reduced phospholipid mass, but did not decrease its PAF-like activity. Tandem mass spectrometry identified traces of PAF, and more abundant levels of 1-O-hexadecyl-2-(butanoyl or butenoyl)-sn-glycero-3-phosphocholines (C(4)-PAF analogs) in oxidized LDL that comigrated with PAF-like activity. Synthesis showed that either C(4)-PAF was just 10-fold less potent than PAF as a PAF receptor ligand and agonist. Quantitation by gas chromatography-mass spectrometry of pentafluorobenzoyl derivatives shows the C(4)-PAF analogs were 100-fold more abundant in oxidized LDL than PAF. Oxidation of synthetic alkyl arachidonoyl phosphatidylcholine generated these C(4)-PAFs in abundance. These results show that quite minor constituents of the LDL phosphatidylcholine pool are the exclusive precursors for PAF-like bioactivity in oxidized LDL.

Inhibition of platelet-activating factor synthesis in human neutrophils and platelets by propionyl-L-carnitine

Propionyl-L-carnitine (PrC) has been shown to exert beneficial effects in the treatment of myocardial and peripheral ischemia in man. These conditions are associated with the activation of circulating neutrophils and platelets. To determine whether PrC could affect the synthesis of lipid mediators known to influence neutrophil and platelet functions, we explored the effects of PrC on the synthesis of platelet-activating factor (PAF) and arachidonic acid (AA) metabolites. Preincubation (90 min) of human neutrophils with PrC (0.1-100 microM) inhibited the synthesis of PAF and of a PAF analog (1-alkyl-1'enyl-2-acetyl-sn-glycero-3-phosphoethanolamine: AEGPE) induced in vitro by the calcium ionophore A23187. In contrast, concentrations of PrC up to 100 microM did not influence the uptake of exogenous AA or the A23187-induced release of AA and eicosanoids from neutrophils in vitro. PrC (1 microM) also inhibited PAF synthesis from human platelets stimulated in vitro with thrombin, but had no effect on thrombin-induced aggregation. Oral administration of PrC (2 g/day for two weeks) to five normal volunteers resulted in a significant inhibition of PAF and AEGPE synthesis by neutrophils stimulated with A23187 ex vivo, with no effect on AA or eicosanoid release. These data indicate that PrC selectively inhibits in vitro and ex vivo PAF synthesis from human neutrophils and platelets without influencing AA metabolism or eicosanoid release. This effect of PrC might represent an additional mechanism by which this molecule can exert protective effects in tissue ischemia and in other inflammatory diseases associated with neutrophil and platelet activation.

Evidence for two distinct lysophospholipase activities that degrade lysophosphatidylcholine and lysophosphatidic acid in neuronal nuclei of cerebral cortex

Neuronal nuclei were isolated from immature rabbit cerebral cortex and nuclear lysophospholipase activities studied using two different 1-acyl lysophospholipids: lysophosphatidylcholine (lysoPC) and lysophosphatidic acid (lysoPA). Our interest in these two lysolipids arose from the observation that lysoPA could promote the acetylation of lysoPC by substantially inhibiting a very active nuclear lysoPC lysophospholipase activity, in a competitive manner (R.R. Baker, H. -y. Chang, Mol. Cell. Biochem. (1999) in press). As there was also evidence for nuclear lysoPA deacylation, it was of interest to see whether one activity could possibly utilize both lysolipid substrates. We now have evidence for two separate lysophospholipase activities in neuronal nuclei. The lysoPC lysophospholipase activity was the more active, more highly enriched in the neuronal nuclei, and showed optimal activity at pH 8.4-9, while the lysoPA lysophospholipase activity was maintained over a much broader pH range. The lysoPC activity was substantially inhibited by free fatty acid, and showed considerable stimulation by serum albumin, while the activity utilizing lysoPA was much less affected by these agents. When lysoPC was added to incubations containing radioactive lysoPA, there was no significant inhibition found in rates of release of radioactive fatty acid, indicating that the lysoPA lysophospholipase activity did not utilize the lysoPC substrate. In incubations with lysoPC, MgATP and CoA brought about a sizable formation of phosphatidylcholine whose radioactivity was equally distributed between the sn-1 and sn-2 positions suggesting labelling both directly from the lysoPC substrate and from fatty acid produced by the lysophospholipase activity. By comparison, with the radioactive lysoPA substrate, MgATP and CoA promoted relatively lower levels of phosphatidic acid formation whose principal labelling came directly from the radioactive lysoPA. Largely because of the high activity of the nuclear lysoPC lysophospholipase, there is considerable potential in the neuronal nucleus to limit the use of lysoPC in other reactions, such as the formation of acylPAF (1-acyl analogue of platelet activating factor). It is of interest that conditions associated with brain ischaemia such as increased free fatty acid levels, falling pH and declines in MgATP may allow a preservation of neuronal nuclear lysoPC levels for acetylation. The existence of a separate lysophospholipase activity for lysoPA allows an independent control of lysoPA which can serve as an important regulator of the nuclear lysoPC lysophospholipase.

Stimulation of monocytes and platelets by short-chain phosphatidylcholines with and without terminal carboxyl group

Oxidation of unsaturated phosphatidylcholine (PC) produces fragmented phospholipids which have similar bioactivities as the platelet-activating factor (PAF, 1-O-alkyl-2-acetyl-PC). Since a large number of molecular species are produced upon PC oxidation, the active ingredients have not been identified. We synthesized several short-chain PCs which are known to be characteristic PC oxidation products to test their PAF-like activity. The synthetic PCs contained palmitoyl or hexadecyl residues (both C16) in sn-1 position, and propionyl (C3), valeroyl (C5), succinyl (C4 with omega-carboxyl), glutaroyl (C5 with omega-carboxyl), or suberoyl (C8 with omega-carboxyl) residues in sn-2 position. Biological activity was measured by: (1) increase of intracellular calcium in human monocytes; (2) [3H]serotonin release from rabbit platelets; and (3) aggregation of human platelets. Specificity of the cellular response was tested by inhibition with the PAF-receptor antagonists BN 52021 and WEB 2086. Synthetic PC oxidation products activated both monocytes and platelets in a PAF-specific manner. The effective concentration varied with respect to assay system and chemical structure. In general, 1-hexadecyl-PCs were more effective than 1-palmitoyl-PCs, while increasing chain length in sn-2 position lowered biological activity. However, several 1-palmitoyl-PCs activated monocytes in concentrations between 10-8 and 10-6 M. In contrast, platelets were less susceptible to 1-palmitoyl-PCs. No significant difference was found between 2-valeroyl-PC (C5 with omega-methyl) and 2-glutaroyl-PC (C5 with omega-carboxyl). The data suggest that typical products of PC oxidation, containing propionyl, succinyl, or glutaroyl residues in sn-2 position, display PAF-like activity at micromolar concentrations.

Identification and pharmacological characterization of platelet-activating factor and related 1-palmitoyl species in human inflammatory blistering diseases

Through its pro-inflammatory effects on leukocytes, endothelial cells, and keratinocytes, the lipid mediator platelet-activating factor (PAF) has been implicated in cutaneous inflammation. Although the 1-alkyl PAF species has been considered historically the most abundant and important ligand for the PAF receptor (PAF-R), other putative ligands for this receptor have been described including 1-acyl analogs of sn-2 acetyl glycerophosphocholines. Previous bioassays have demonstrated a PAF-like activity in lesions of the autoimmune blistering disease bullous pemphigoid. To assess the actual sn-2 acetyl glycerophosphocholine species that result in this PAF agonistic activity, we measured PAF and related sn-2 acetyl GPCs in fresh blister fluid samples from bullous pemphigoid and noninflammatory (suction-induced) bullae by mass spectrometry. We report the presence of 1-hexadecyl as well as the 1-acyl PAF analog 1-palmitoyl-2-acetyl glycerophosphocholine (PAPC) in inflammatory blister fluid samples. Because PAPC is the most abundant sn-2 acetyl glycerophosphocholine species found in all samples examined, the pharmacological effects of this species with respect to the PAF-R were determined using a model system created by transduction of a PAF-R-negative epidermoid cell line with the PAF-R. Radioligand binding and intracellular calcium mobilization studies indicated that PAPC is approximately 100x less potent than PAF. Though a weak agonist, PAPC could induce PAF biosynthesis and PAF-R desensitization. Finally, intradermal injections of PAF and PAPC into the ventral ears of rats demonstrated that PAPC was 100x less potent in vivo. These studies suggest possible involvement of PAF and related species in inflammatory bullous diseases.

Dose-dependent agonist and antagonist effects of the platelet-activating factor analogue 1-palmitoyl-2-acetoyl-sn-glycero-3-phosphocholine on B lymphocytes

BACKGROUND

Platelet activating-factor (PAF), an ether-linked phospholipid, is a potent activator of B lymphocyte cell lines. The related ester-linked phospholipid, 1-palmitoyl-2-acetoyl-sn-glycero-3-phosphocholine (PAGPC), is synthesized by tissues important in B-cell development.

OBJECTIVES

We examined whether PAGPC was capable of influencing immunoglobulin synthesis in B lymphocytes and compared its action with that of PAF. We also examined the interaction of the two mediators as agonists or competitive antagonists.

METHODS

Ramos, an IgM-secreting immature B-cell line that expresses PAF receptor, was used in these experiments. The effect of PAF, PAGPC, or both mediators together on IgM secretion and anti-IgM-mediated apoptosis was measured.

RESULTS

Both PAF and PAGPC stimulated IgM production in Ramos cells in a dose-dependent fashion, with PAGPC being approximately three logs less potent than PAF. The effect of both mediators was inhibited by specific PAF receptor antagonists. Preincubation with suboptimal concentrations of PAGPC inhibited the ability of PAF to increase IgM secretion by Ramos cells. Additionally, preincubation with low concentrations of PAGPC prevented PAF from rescuing Ramos cells from apoptosis induced by cross-linking the B-cell receptor with anti-IgM antibodies. PAGPC caused PAF receptor desensitization because displacement of bound PAGPC with high concentrations of bovine serum albumin did not reverse its PAF antagonist effect.

CONCLUSIONS

PAF and PAGPC are biologically active phospholipids, but PAF is approximately 1000 times more potent. At high concentrations, PAGPC acts similarly to PAF, whereas at lower concentrations, PAGPC acts as a functional PAF antagonist. Because it is secreted at sites of inflammation and allergic reactions, PAGPC may be an endogenous regulator of the effects of PAF.

Expression of the platelet-activating factor receptor results in enhanced ultraviolet B radiation-induced apoptosis in a human epidermal cell line

Recent studies have demonstrated that ultraviolet B radiation (UVB) damages human keratinocytes in part by inducing oxidative stress and cytokine production. Severe UVB damage to the keratinocyte can also result in apoptosis or programmed cell death. Although the lipid mediator platelet-activating factor (PAF) is synthesized in response to epidermal cell damage and epidermal cells express PAF receptors, it is not known whether PAF is involved in UVB-induced epidermal cell apoptosis. These studies examined the role of the PAF system in UVB-induced epidermal cell apoptosis using a novel model system created by retroviral-mediated transduction of the PAF receptor-negative human epidermal cell line KB with the human PAF receptor (PAF-R). Expression of the PAF-R in KB cells did not affect base-line growth or apoptosis, yet resulted in a decrease in the lag time between treatment of the cells and the induction of apoptosis following irradiation with 400 J/m2 UVB. This effect was inhibited by pretreatment with the PAF-R antagonists WEB 2086 and A-85783, confirming involvement of the PAF-R in this process. At lower doses (100-200 J/m2) of UVB, only KB cells that expressed the PAF-R became apoptotic. Treatment of PAF-R-expressing KB clones with the metabolically stable PAF-R agonist 1-hexadexyl-2-N-methylcarbamoyl-3-glycerophosphocholine (CPAF) alone did not induce apoptosis but augmented the degree of apoptosis observed if CPAF was used in combination with lower doses (200 J/m2) of UVB irradiation. Interestingly, UVB irradiation was found to stimulate PAF synthesis only in PAF-R-expressing KB cell clones. The antioxidants N-acetyl cysteine, 1,1,3,3-tetramethyl-2-thiourea, and vitamin E inhibited both UVB-induced PAF biosynthesis as well as the augmentation of UVB-induced apoptosis in PAF-R-expressing KB clones, suggesting the possibility that UVB stimulates the production of oxidized lipid species with PAF-R agonistic activity in this model system. Thus, these studies indicate that a component of UVB-induced epidermal cell cytotoxicity can be modulated by PAF-R activation through the production of PAF and PAF-like species.

Species differences in PAF receptor binding in the lungs between hamster and guinea pig

Platelet-activating factor (PAF) receptor in normal Golden Syrian hamster lung was characterized using radioligand binding studies and compared with guinea pig lung PAF receptor. [3H]WEB2086, a potent and specific PAF antagonist, was used as a radioligand for equilibrium binding, kinetic studies, competitive binding in receptor preparation (0-110000 g fraction of lung homogenate) from hamster and guinea pig lungs. Binding of [3H]WEB 2086 to the receptor preparation was saturable, reversible and specific in both hamster and guinea pig lungs. Scatchard plot analysis of equilibrium binding data indicates a single binding site in hamster lung with the equilibrium dissociation constant (KD) of 66.1 +/- 36.7 nM (n = 4) and maximal binding (Bmax) of 135.4 +/- 63.1 fmol/mg, but two binding sites in guinea pig lung with a high affinity site (KD = 1.7 +/- 0.6 nM; Bmax = 48.6 +/- 2.6 fmol/mg) and a low affinity site (KD = 83.8 +/- 32 nM; Bmax = 480.8 +/- 158 fmol/mg). The heterogeneity of [3H]WEB2086 binding to guinea pig lung but not to hamster lung was also confirmed by dissociation kinetic studies, in which biphasic dissociation kinetic was shown in guinea pig and monophasic kinetic in hamster lung. Although the specific [3H]WEB 2086 binding to lungs of both species was displaced by PAF-C18 and antagonists L659989 and CL184005 in a dose-dependent manner and not by lyso-PAF (a biologically inactive form of PAF), the potencies of the competitive inhibition were significantly different between the two species. The relative potencies ranked WEB2086 approximately L659989 > PAF > CL184005 in hamster lung, whereas in guinea pig lung the potencies ranked PAF > WEB2086 approximately L659989 approximately CL184005. The present study demonstrates for the first time the existence of PAF receptor in the hamster lung and its binding characteristics different from guinea pig lung suggest the possible existence of different PAF receptor subtypes in hamster lung.

Platelet-activating factor and cardiac diseases: therapeutic potential for PAF inhibitors

Platelet-activating factor (PAF) is a potent phospholipid mediator released from inflammatory cells in response to diverse immunologic and non-immunologic stimuli. Animal studies have implicated PAF as a major mediator involved in coronary artery constriction, modulation of myocardial contractility and the generation of arrhythmias which may bear on cardiac disorders such as ischemia, infarction and sudden cardiac death. PAF effects are induced by direct actions of PAF on cardiac tissue to modify chronotropic and inotropic activity, or indirectly via the release of eicosanoids such as thromboxane A2 (TXA2), leukotrienes (LT) or cytokines (TNF alpha). The development of selective, high affinity PAF receptor antagonists has permitted investigations on the role of PAF in experimental animal models of cardiac injury. In vivo and in vitro studies strongly suggest that PAF receptor antagonists might convey therapeutic benefits in ischemic conditions and certain arrhythmias. In addition, PAF antagonists might have a cardiac allograft-preservation effect. Although clinical studies with PAF receptor antagonists in patients with cardiac diseases have not yet been reported, the experimental results to date suggest that PAF receptor antagonists might be useful in some specific cardiac disorders in humans.

Protein kinase C inhibitors and PAF stimulate phosphatidylserine synthesis in human leucocytes

To study the regulation and turnover of phosphatidylserine (PtdSer) in human leucocytes, we investigated the effect of 12-O-tetradecanoylphorbol 13-acetate (TPA), I-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3 or edelfosine), staurosporine and platelet activating factor (PAF) on [14C]serine incorporation into phospholipids. More than 80% of lipid radioactivity was in PtdSer. ET-18-OCH3 stimulated incorporation into PtdSer 5-fold, without increasing incorporation into other lipids. PAF stimulated PtdSer synthesis 3-fold after 1 h, while staurosporine stimulated the synthesis 2-fold after 3 h. TPA inhibited PtdSer synthesis. It abolished the ET-18-OCH3 stimulation, and reduced the staurosporine stimulation. ET-18-OCH3 and TPA did not significantly alter the incorporation of [14C]arachidonic acid into PtdSer, and did not increase PtdSer turnover judged from chase and stability experiments. The results demonstrate that PKC inhibitors and PAF induce increased incorporation of [14C]serine into PtdSer, while TPA inhibits stimulated PtdSer synthesis. This suggests that modulation of PtdSer synthesis may regulate PKC activity in PMN cells.

Molecular heterogeneity of PAF in normal human mixed saliva: quantitative mass spectral analysis after direct derivatization of PAF with pentafluorobenzoic anhydride

Platelet-activating factor (PAF), a family of phospholipid autacoids with potent pro-inflammatory activities, is present in saliva. The current study has quantitated various species of PAF isolated from normal human mixed saliva. Choline-containing, sn-2 acetylated phospholipids with sn-1 ether- or ester-linked fatty alcohol/acid moieties (alkyl-PAF or acyl-PAF, respectively) were evaluated after direct derivatization with pentafluorobenzoic (PFB) anhydride. Individual species of PFB-derivatized PAF were separated by gas chromatography prior to mass spectral analysis; quantitative estimates of six different species of PAF in saliva were made by comparison to corresponding authentic, synthetic PAF standards. In each saliva sample, all six species of PAF were readily detected by this facile procedure. The predominant PAF was 1-O-hexadecyl-2-acetyl-sn-glycero-3-phosphocholine or 16:0-alkyl-PAF (0.75 +/- 0.09 pmol/ml saliva; mean +/- S.E.; n = 5) which represented only 30.4 +/- 1.5% of the total PAF. Substantial amounts of 18:1- and 18:0-alkyl-PAF and 16:0-acyl-PAF were also identified (0.52 +/- 0.07, 0.35 +/- 0.06, and 0.35 +/- 0.02 pmol/ml saliva, respectively). In summary, mass spectrometric analysis of PAF after direct derivatization with PFB anhydride has revealed that at least six different species of PAF are present in normal human mixed saliva. This structural diversity may represent an important aspect of homeostasis in the healthy oral cavity.