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Biomedical subjects

M Triggiani

Publications and source records attributed to M Triggiani.

At least 73 records · Page 4Linked to original sources
PubMed1993

Mitral valve prosthetic endocarditis: development of left ventricular-coronary sinus fistula following replacement.

We report the history and course of a patient in whom a left ventricular-coronary sinus fistula developed following mitral valve replacement due to prosthetic endocarditis. Six months after the intervention the patient suddenly presented with deterioration of her symptoms, holosystolic murmur and signs of congestive heart failure. Transesophageal echocardiography showed a left-to-right shunt but did not show its exact location. At surgery, exploration of the right atrium revealed a left ventricular-coronary sinus communication due to discontinuation of the left ventricular free wall next to the coronary sinus; repair of the defect was successfully performed by direct suture. The postoperative course was uneventful and the patient recovered quickly. This case is reported to stress that debridement of the mitral annulus and removal of an old prosthesis must be very carefully performed and to facilitate the diagnosis of this rare but severe complication of repeated mitral valve replacement.

Aged↗
PubMed1993

Short-term and long-term role of platelet activating factor as a mediator of in vivo platelet aggregation.

BACKGROUND: Platelet activating factor (PAF) is a phospholipid released upon stimulation by a variety of cells and has been implicated in several pathophysiological events such as asthma and inflammatory diseases. However, although the ability to aggregate platelets in vitro was the first biological activity ascribed to PAF, its role in contributing to the in vivo formation of arterial thrombi has not been thoroughly clarified. METHODS AND RESULTS: Intravascular platelet aggregation was initiated in two different animal models of arterial stenosis and endothelial injury. An external constrictor was positioned around rabbit carotid arteries and canine coronary arteries. After placement of the constrictor, a typical pattern of flow developed in the stenotic vessels. This pattern of flow, characterized by progressive reductions of carotid or coronary blood flow followed by spontaneous or induced restorations of flow (cyclic flow variations, CFVs), is related to recurrent platelet aggregation at the site of the stenosis followed by dislodgment of the thrombus. After observing CFVs for 30 minutes, BN52021 (up to 1.2 mg/kg), a potent and selective PAF antagonist, was given intravenously to rabbits (n = 12) and dogs (n = 10). BN52021 completely inhibited CFVs in 10 of 12 rabbits, whereas it was relatively ineffective in abolishing CFVs in dogs (only 2 of 10 animals inhibited). This different effect of BN52021 was not explained by too small a dose of the drug to achieve a complete blockade of PAF receptors in dogs, since ex vivo platelet aggregation was completely inhibited in both rabbits and dogs in response to exogenous PAF at concentrations up to 10(-5) mol/L. In a second group of 10 dogs, the hypothesis that PAF may become an important mediator of CFVs in dogs only several hours after endothelial injury was tested. After 30 minutes of baseline CFVs, these animals received a bolus of BN52021 up to 1.2 mg/kg. After this treatment, CFVs were completely abolished in 2 of 10 animals. The remaining 8 dogs were followed for an additional 8-hour period, at the end of which a second bolus of BN52021 was given. At this time, BN52021 was effective, as CFVs were abolished in 6 of 8 animals. These effects of BN52021 at 8 hours were not the consequence of a cumulative dose of the compound, since ex vivo platelet aggregation in response to PAF returned to baseline values immediately before administering the second dose. To identify possible sources of PAF other than aggregating platelets at the site of arterial stenosis, dogs in a third group were killed after 30 minutes (n = 7) and after 8 hours (n = 8) of CFVs. Histological sections of the stenotic coronary artery showed a marked leukocyte infiltration in these arterial segments after 8 hours of CFVs, whereas sections from dogs killed after 30 minutes showed only moderate or no infiltration. CONCLUSIONS: These data demonstrate that PAF plays an important role as a mediator of platelet aggregation in vivo in rabbits and dogs. In the canine model, PAF appears to become more important after leukocyte infiltration of the arterial wall, as it may contribute to initiating enough platelet activation to lead to cyclic flow variations at sites of arterial stenosis and endothelial injury. Data from the present study suggest that PAF antagonists may be used as antiplatelet agents.

Animals↗
PubMed1993

Dietary n-3 fatty acid effects on neutrophil lipid composition and mediator production. Influence of duration and dosage.

Healthy volunteers supplemented their usual Western diets with Promega fish oil supplement (eicosapentaenoic acid [EPA], 0.28 g; docosahexaenoic acid [DCHA], 0.12 g; other n-3 fatty acids 0.10 g per capsule) using three protocols. Initial experiments (protocol 1 and 2) investigated the kinetics of incorporation of n-3 fatty acids into serum and neutrophil lipids after 10 capsules/d of Promega. EPA was rapidly detected in both serum and neutrophil lipids; the arachidonic acid (AA) to EPA ratio in neutrophil phospholipids showed a maximal reduction of 49:1 to 8:1 within 1 wk of beginning supplementation. EPA was preferentially incorporated into phosphatidyl-ethanolamine and phosphatidylcholine but not phosphatidylinositol. Long-term supplementation for up to 7 wk did not influence the AA/EPA ratio or the distribution of EPA among neutrophil phospholipids in a manner that was not observed after the first week. Neutrophils produced similar quantities of platelet-activating factor and slightly lower quantities of leukotriene B4 during long-term supplementation when compared with presupplementation values. Experiments examining the influence of Promega dosage indicated that the AA/EPA ratio in neutrophil lipids decreased in a dose-dependent manner. Only when the dose was increased to 15 capsules/d was there a reduction in the AA/DCHA ratio in neutrophil lipids. The quantity of AA in neutrophil lipids remained relatively constant at all supplement doses. Taken together, the current study demonstrates the capacity of n-3 fatty acids provided with a Western diet to be rapidly incorporated into neutrophil lipids. However, dietary n-3 fatty acids appear not to significantly reduce arachidonate content within neutrophil phospholipids. Constant arachidonate levels may account for the lack of large reductions in the biosynthesis of lipid mediators by neutrophils after fish-oil supplementation.

Adult↗
PubMed1993

Successful treatment of coronary artery spasm following coronary artery bypass grafting.

A case of coronary artery spasm developed 6 hours after myocardial revascularization inducing both hemodynamic and electrocardiographic changes, is reported. The spasm was documented by coronary angiography, and it was not reversed by intracoronary infusion of isosorbide dinitrate. Intravenous infusion of nifedipine (initial dose of 0.0104 mg/min to final dose of 0.0208 mg/min), along with infusion of glyceronitrate (1.0 micrograms/kg/min) was able to significantly improve hemodynamic impairment and to reverse electrocardiographic changes in 12 hours. Coronary angiography, repeated in postoperative day 3, after 48 hours of continuous nifedipine infusion, showed a resolution of coronary spasm. There was no evidence of myocardial infarction as resulted from total CPK and MB isoenzyme release. Nifedipine infusion was gradually reduced as oral administration of slow release nifedipine (40 mg twice daily) was started. The combined intravenous infusion of glyceronitrate and nifedipine seems to be able to control and overcome coronary artery spasm following coronary surgery.

Coronary Angiography↗
PubMed1993

Heterogeneity of human Fc epsilon RI-bearing cells.

Basophils and mast cells (Fc epsilon RI-bearing cells) play important but clearly distinct roles in human inflammatory and allergic reactions. While many similarities have been described, it is increasingly evident that many more differences exist between these two cell types. These include maturational and ultrastructural as well as functional differences. Basophils and mast cells can be activated by different stimuli, produce different profiles of inflammatory mediators, and their response can be modulated in a different fashion. The heterogeneity of Fc epsilon RI-bearing cells has recently been extended by studies on mast cells isolated from different human tissues. These studies may suggest the existence of different human mast cell phenotypes the development of which may be regulated by microenvironmental factors. A better understanding of the heterogeneity of basophils and mast cells is a necessary step to define their respective roles in the pathophysiology of human inflammatory responses.

Basophils↗
PubMed1992

Factors that influence the proportions of platelet-activating factor and 1-acyl-2-acetyl-sn-glycero-3-phosphocholine synthesized by the mast cell.

Recent studies have demonstrated that inflammatory cells can be divided into two groups depending on the type of 2-acetylated phospholipids [1-radyl-2-acetyl-sn-glycero-3-phosphocholine (GPC)] they produce: those that produce predominantly platelet-activating factor (PAF), and those that produce predominantly its 1-acyl analogue (1-acyl-2-acetyl-GPC; AAGPC) [Triggiani, Schleimer, Warner & Chilton (1991) J. Immunol. 147, 660-666]. The present study has examined the factors that regulate the production of these two molecules in mouse bone marrow-derived mast cells (BMMC). Initial experiments indicated that PAF and AAGPC were catabolized by BMMC in a differential manner via two pathways: the first, exclusive for AAGPC, involved a 1-acyl hydrolase that removed the long chain at the sn-1 position of the molecule, and the second, common to AAGPC and PAF, involved acetylhydrolase that removed the acetate at the sn-2 position of the two molecules. Experiments were next designed to identify conditions where the differential catabolism of AAGPC and PAF could be eliminated in order to uncover other factors that regulate the proportions of AAGPC and PAF produced. Phenylmethanesulphonyl fluoride (PMSF) completely blocked the 1-acylhydrolase activity while having little or no effect on the acetyl hydrolase activity, thereby eliminating the influence of the catabolic pathway unique to AAGPC. Moreover, PMSF did not alter the release of arachidonic acid from phospholipid subclasses. PMSF-treated BMMC produced larger quantities of AAGPC than of PAF. The AAGPC/PAF ratio detected in PMSF-treated BMMC was very similar to the ratio of arachidonate contained in and released from 1-acyl-/1-alkyl-linked phosphatidylcholine (PC). BMMC supplemented with arachidonic acid in culture for 3 days increased their total arachidonic acid content in PC as well as the ratio of 1-acyl-2-arachidonoyl-GPC to 1-alkyl-2-arachidonoyl-GPC. These changes resulted in parallel and significant increases in both the total amount of 1-radyl-2-acetyl-GPC and the AAGPC/PAF ration in BMMC. These data indicate that the AAGPC/PAF ratio produced by inflammatory cells is regulated by at least two factors: (1) differential catabolism of these two molecules, and (2) the distribution of arachidonate in 1-acyl- and 1-alkyl-2-arachidonyl-GPC. These observations support the concept of a common pathway for AAGPC and PAF biosynthesis in which the two precursor molecules are 1-acyl-2-arachidonoyl-GPC and 1-alkyl-2-arachidonoyl-GPC, respectively.

Animals↗
PubMed1992

Metabolism of platelet-activating factor in the guinea-pig heart.

Platelet-activating factor (PAF; 1-alkyl-2-acetyl-glycero-phosphocholine) is a biologically active phospholipid which is synthesized by a variety of blood cells and organ systems. PAF exerts many effects on the cardiovascular system including hypotension, depression of myocardial contractility and coronary constriction. The present study has examined the capacity of the guinea-pig heart to regulate the levels of exogenous PAF in two different models: isolated perfused heart and isolated ventricular myocytes. In the first model, isolated hearts were perfused with labeled PAF (10(-10) M) in a recirculating manner at flow rates of 15 ml/min (normal flow perfusion; NFP) and 2 ml/min (low flow perfusion, LFP). Exogenously provided PAF appeared in the tissue in a time-dependent manner. The rate of extraction of PAF was higher during LFP than during NFP. PAF was metabolized by the heart to two major products, lyso-PAF and 1-alkyl-2-acyl-sn-glycero-3-phosphocholine (1-alkyl-2-acyl-GPC). Lyso-PAF was found primarily in the perfusion buffer while both lyso-PAF and 1-alkyl-2-acyl-GPC were detected in the tissue. No qualitative difference in the metabolic products derived from PAF catabolism was observed between hearts undergoing NFP and LFP. Acetyl hydrolase activity was detected in the perfusion fluid at both flow rates, probably accounting for the formation of lyso-PAF in the perfusate. However, perfusion fluid from LFP contained a higher acetyl hydrolase activity, per micrograms of protein as compared to fluid from NFP. Isolated ventricular myocytes incubated with labeled PAF (3 x 10(-9) M) also converted it to 1-alkyl-2-acyl-GPC. Kinetic experiments suggested that PAF was initially deacetylated to form lyso-PAF and that this intermediate was then rapidly reacylated with a fatty acyl moiety at the sn-2 position. HPLC analysis of the fatty acids inserted at the sn-2 position of 1-alkyl-2-acyl-GPC revealed that the myocytes reacylated lyso-PAF predominantly with arachidonic acid. These data indicate that the guinea-pig heart may regulate PAF levels by at least two mechanisms: (1) it may release acetyl hydrolase into the vascular compartment, particularly under low flow conditions; and (2) the ventricular myocyte has the capacity to take up PAF and catabolize it to inactive products.

1-Alkyl-2-acetylglycerophosphocholine Esterase↗
PubMed1992

Relative amounts of 1-O-alkyl- and 1-acyl-2-acetyl-sn-glycero-3-phosphocholine in stimulated endothelial cells.

The specific precursor for platelet-activating factor, 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine, constitutes 10 per cent of the 1-radyl-2-acyl-sn-glycero-3-phosphocholines in endothelial cells. Stimulation of endothelial cells results in accumulation of PAF and its sn-1-acyl- analog (acylPAF), with acylPAF the predominant product. Mass spectrometry confirmed these relative amounts and confirmed that stimulated endothelial cells accumulate 1-3 ng PAF per million cells. These data suggest that stimulated endothelial cells accumulate both PAF and acylPAF and that the PAF synthetic pathway in endothelial cells is not highly selective for the specific PAF precursor (1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine).

Animals↗
PubMed1992

Characterization of platelet-activating factor synthesized by normal and granulocyte-macrophage colony-stimulating factor-primed human eosinophils.

Platelet-activating factor (PAF; 1-alkyl-2-acetyl-sn-glycero-3- phosphocholine) is a mediator involved in the pathogenesis of inflammatory diseases associated with tissue eosinophil infiltration. Previous studies utilizing bioassay or assaying enzymes associated with PAF biosynthesis have suggested that human eosinophils produce PAF. The present study has extended these initial studies by identifying and quantifying the different PAF molecular species and analogues synthesized by human eosinophils in response to A23187 and f-Met-Leu-Phe (FMLP). Gas chromatography-mass spectrometric analysis indicated that A23187-stimulated eosinophils produce at least three molecular species of PAF. The predominant species is 1-hexadecyl-2-acetyl-GPC (16:0) followed by 1-octadecyl-2-acetyl-GPC (18:0) and 1-octadecyl-2-acetyl-GPC (18:1). Eosinophils stimulated with FMLP produce approximately 100-fold smaller quantities of PAF relative to those produced in response to A23187 and only the 16:0 molecular species could be measured. A small percentage (comprising between 2 and 5%) of the 2-acetylated phospholipids produced by eosinophils was the 1-acyl analogue of PAF. Long-term (72 hr) incubation with granulocyte-macrophage colony-stimulating factor (GM-CSF) resulted in a three- to fourfold increase in PAF synthesis from eosinophils stimulated with FMLP, without changes in the profile of PAF molecular species or in the percentage of the 1-acyl analogue of PAF. These data indicate that human eosinophils can produce various molecular species of PAF and that this process can be quantitatively enhanced by GM-CSF.

Calcimycin↗
PubMed1991

Arachidonic acid metabolism during antigen and ionophore activation of the mouse bone marrow derived mast cell.

This study has examined the metabolism of arachidonic acid in the mouse bone marrow-derived mast cell (BMMC) during immunologic and nonimmunologic activation. The predominant pools of endogenous arachidonate in the mast cells were found in ethanolamine (46%), choline (39%) and inositol (14%) containing glycerolipids. Initial studies established conditions where equilibrium labelling of these major phospholipids in the BMMC could be reached. Upon challenge, arachidonate was lost from all major phospholipid classes (phosphatidylethanolamine greater than phosphatidylcholine greater than phosphatidylinositol). There was a small but significant increase in the amount of label associated with phosphatidic acid during cell activation. Arachidonate was distributed among 1-acyl, 1-alkyl and 1-alk-1-enyl-linked subclasses of PC and PE. The rank order of loss of labelled arachidonate from the major PE and PC subclasses during antigen and ionophore activation was 1-alk-enyl-2-arachidonoyl-GPE greater than 1-acyl-2-arachidonoyl-GPC greater than 1-acyl-2-arachidonoyl-GPE greater than 1-alkyl-2-arachidonoyl-GPC. Labelled products released into the supernatant fluids and free arachidonic acid within the cell accounted for the bulk of arachidonate lost from phospholipids. Labelled products in the supernatant fluids were composed of LTB4, LTC4, PGD2 and free arachidonic acid. BMMC phospholipids were also labelled for 24 hr with [3H]choline, [3H]myoinositol or [14H]ethanolamine and labelled 2-lyso phospholipids were measured after cell activation. Radioactivity in lysophospholipids from PC, PE and PI increased significantly between 30 s and 2 min after antigen activation and then declined. Taken together, these studies suggest that arachidonate is mobilized predominantly from PE and in particular 1-alk-1-enyl-2-arachidonoyl-GPE by the direct removal of arachidonate from the sn-2 position of the molecule. Most of this arachidonate is then released from cells as eicosanoids or free fatty acid.

Animals↗
PubMed1991

Differential synthesis of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine and platelet-activating factor by human inflammatory cells.

The synthesis of platelet-activating factor (PAF) and of the 1-acyl analogue of PAF, 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-2-acetyl-GPC) was examined in seven human cell preparations (lung mast cell, basophil, endothelial cell, neutrophil, eosinophil, lung macrophage, platelet) and in human lung fragments. Cells were activated by either an appropriate receptor-mediated stimulus or by ionophore A23187 in the presence of [3H]acetate. All cell types, with the exception of the platelet, responded to stimulation with at least a twofold increase in the formation of labeled 1-radyl-2-acetyl-GPC as compared with control values. A23187 was the more potent stimulus in all cell types examined except the lung mast cell, in which anti-IgE consistently induced the synthesis of more 1-radyl-2-acetyl-GPC. Human lung fragments stimulated by anti-IgE, Ag Amb a I (after passive sensitization), or A23187 also incorporated [3H]acetate into 1-radyl-2-acetyl-GPC. Subclass analysis of 1-radyl-2-acetyl-GPC produced by each cell indicated that the cell types examined can be divided into two groups according to the predominant type of 1-radyl-2-acetyl-GPC produced. Some cell types (mast cell, basophil, endothelial cell) produced predominantly 1-acyl-2-acetyl-GPC, whereas others (neutrophil, eosinophil, lung macrophage) produced almost exclusively PAF. In some cell types, such as the lung mast cell and the basophil, A23187 stimulation increased the synthesis of PAF relative to 1-acyl-2-acetyl-GPC as compared with anti-IgE stimulation. In the lung fragments, [3H]acetate was predominantly incorporated into 1-acyl-2-acetyl-GPC upon IgE-mediated stimulation (anti-IgE, Amb a I) and into PAF upon A23187 stimulation. The differential production of these two phospholipids was confirmed by determining their sensitivity to lipase A1 and phospholipase A2 hydrolysis and by HPLC. These data demonstrate that 1-acyl-2-acetyl-GPC can be synthesized by a variety of human cells involved in the inflammatory reaction. This finding raises fundamental questions about the biologic role of this molecule and the factors regulating its synthesis within inflammatory cells.

Blood Platelets↗
PubMed1991

Biological effects of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine in the human neutrophil.

The synthesis of large quantities of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-2-acetyl-GPC) relative to 1-alkyl-2-acetyl-GPC (PAF; platelet-activating factor) has been demonstrated in several inflammatory cells. The present study has examined agonist and antagonist activities of 1-acyl-2-acetyl-GPC in the human neutrophil. 1-Acyl-2-acetyl-GPC induced a rapid increase in cytosolic calcium in the neutrophil; this effect was detected at 2 x 10(-9) M and was maximal at 10(-6) M. The peak response induced by 1-acyl-2-acetyl-GPC was similar to that induced by PAF although the potency of 1-acyl-2-acetyl-GPC was 300-fold lower than that of PAF. The dose response curves for both 1-acyl-2-acetyl-GPC and PAF were shifted in a parallel fashion by L-652,731 (10(-6) M), a PAF receptor antagonist, suggesting that both 1-acyl-2-acetyl-GPC and PAF act on the same receptor. High concentrations of 1-acyl-2-acetyl-GPC (10(-5) M) induced the release of beta-glucuronidase and lysozyme from the human neutrophil. The percent release of lysozyme induced by 1-acyl-2-acetyl-GPC was consistently higher than that of beta-glucuronidase. Prior stimulation of neutrophils with 1-acyl-2-acetyl-GPC dose-dependently inhibited the increase in cytosolic calcium induced by a subsequent challenge with an optimal concentration of PAF. Similarly, preincubation of neutrophils with 1-acyl-2-acetyl-GPC dose-dependently inhibited beta-glucuronidase and lysozyme release induced by a subsequent stimulation with PAF. The inhibitory effect on degranulation could not be surmounted even by concentrations of PAF 10-fold higher than that of 1-acyl-2-acetyl-GPC. The inhibition appeared to be selective for PAF since 1-acyl-2-acetyl-GPC did not affect f-met peptide-induced degranulation. This study suggests that 1-acyl-2-acetyl-GPC may act as a naturally-occurring specific inhibitor of PAF-induced activation of the human neutrophil.

Calcium↗
PubMed1991

Metabolism of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine in the human neutrophil.

The biosynthesis of 1-acyl-2-acetyl-sn-glycero-3-phosphocholine (1-acyl-2-acetyl-GPC) together with that of 1-alkyl-2-acetyl-GPC (platelet-activating factor) has been demonstrated in a variety of inflammatory cells and tissues. It has been hypothesized that the relative proportion of these phospholipids produced upon cell activation may be influenced by their rates of catabolism. We studied the catabolism of 1-acyl-2-acetyl-GPC in resting and activated human neutrophils and compared it to that of 1-alkyl-2-acetyl-GPC. Neutrophils rapidly catabolize both 1-alkyl-2-acetyl-GPC and 1-acyl-2-acetyl-GPC; however, the rate of catabolism of 1-acyl-2-acetyl-GPC is approximately 2-fold higher than that of 1-alkyl-2-acetyl-GPC. In addition, most of 1-acyl-2-acetyl-GPC is catabolized through a pathway different from that of 1-alkyl-2-acetyl-GPC. The main step in the catabolism of 1-acyl-2-acetyl-GPC is the removal of the long chain at the sn-1 position; the long chain residue is subsequently incorporated either into triglycerides or into phosphatidylcholine. The 1-lyso-2-acetyl-GPC formed in this reaction is then further degraded to glycerophosphocholine, choline, or phosphocholine. 1-Acyl-2-acetyl-GPC is also catabolized, to a lesser extent, through deacetylation at the sn-2 position and reacylation with a long chain fatty acid. Stimulation of neutrophils by A23187 results in a higher rate of catabolism of 1-acyl-2-acetyl-GPC by increasing both the removal of the long chain at the sn-1 position and the deacetylation-reacylation at the sn-2 position. In a broken cell preparation, the cytosolic fraction of the neutrophil was shown to contain an enzyme activity which cleaved the sn-1 position of 1-acyl-2-acetyl-GPC and 1-acyl-2-lyso-GPC but not of 1,2-diacyl-GPC. Taken together, these data demonstrate that the human neutrophil is able to catabolize 1-acyl-2-acetyl-GPC in a manner both quantitatively and qualitatively different from that of platelet-activating factor. The differential catabolism may regulate the relative proportion of these two bioactive phospholipids in the neutrophil.

Calcimycin↗
PubMed1991

Recent advances in our understanding of the biochemical interactions between platelet-activating factor and arachidonic acid.

In the last few years, it has become increasingly apparent that the biochemistry of PAF (platelet-activating factor) and that of arachidonic acid are interrelated in a number of inflammatory cells. Experiments presented here further point out that arachidonic acid plays a crucial role in the catabolism and biosynthesis of PAF. In addition, they suggest that the same phospholipid molecular species may serve as a source for both arachidonic acid and 1-alkyl-2-lyso-sn-glycero-3-phosphocholine during cell activation. Finally, they reveal that there may be common regulatory mechanisms for the biosynthesis of PAF and arachidonic acid metabolites. Taken together, studies examining the relationship between PAF and arachidonic acid suggest it may be difficult to consider the biochemistry of PAF without considering arachidonic acid metabolism and vice versa.

Animals↗
PubMed1990

Evidence that increasing the cellular content of eicosapentaenoic acid does not reduce the biosynthesis of platelet-activating factor.

Our study has examined platelet-activating factor (PAF) biosynthesis in neutrophils from individuals on a fish oil-enriched diet and in mast cells enriched with eicosapentaenoic acid (EPA) in vitro. Neutrophils isolated from males who were fed fish oil supplement (EPA; 2.8 g/day) for 5 wk contained large quantities of eicosapentaenoate in phosphatidylcholine (PC) and phosphatidylethanolamine and less in phosphatidylinositol. The ratio arachidonate/eicosapentaenoate in PC and phosphatidylethanolamine decreased from greater than 10 before the enriched diet to approximately 3 after the diet. The putative precursor of PAF, 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (1-O-alkyl-2-acyl-GPC) contained the bulk of eicosapentaenoate in PC subclasses with smaller quantities found in 1-acyl and 1-alk-1'-enyl linked species. Ionophore A23187-stimulated neutrophils produced similar quantities of PAF before and after enriched diet. Neutrophils during normal diet acylated 1-O-alkyl-2-lyso-GPC only with arachidonate whereas neutrophils from individuals on enriched diet transferred both arachidonate and eicosapentaenoate into exogenously-provided 1-O-alkyl-2-lyso-GPC. This allowed for the labeling of neutrophils with 1-O-[3H]-alkyl-2-arachidonoyl-GPC (before diet) as well as neutrophils with 1-O-[3H]-alkyl-2-eicosapentaenoyl-GPC and 1-O-[3H]-alkyl-2-arachidonoyl-GPC (after diet). Neutrophils after diet converted similar quantities of these labeled precursors to labeled PAF upon stimulation as those before the diet. Analysis of the nature of the long chain acyl residue remaining in the sn-2 position of 1-alkyl-2-acyl-GPC after cell stimulation indicated that arachidonate and eicosapentaenoate were both released from 1-O-alkyl-2-acyl-GPC at comparable rates. Finally, in vitro supplementation of murine mast cells (PT-18) with arachidonic acid or EPA caused a marked increase in the amount of PAF produced by the cell without having any effect on histamine release. Data from these experiments suggest that EPA is incorporated into a PAF precursor pool. However, this appears not to inhibit PAF production because phospholipase A2 can use eicosapentaenoate- as well as arachidonate-containing phospholipids in the initial step of PAF biosynthesis.

Acylation↗