A unique pool of free arachidonate serves as substrate for both cyclooxygenase and lipoxygenase in platelets

L-4F alters hyperlipidemic (but not healthy) mouse plasma to reduce platelet aggregation

Background and Purpose- Hyperlipidemia is associated with platelet hyperreactivity. We hypothesized that L-4F, an apolipoprotein A-I mimetic peptide, would inhibit platelet aggregation in hyperlipidemic mice.

METHODS AND RESULTS

Injecting L-4F into apolipoprotein E (apoE)-null and low-density lipoprotein receptor-null mice resulted in a significant reduction in platelet aggregation in response to agonists; however, there was no reduction in platelet aggregation after injection of L-4F into wild-type (WT) mice. Consistent with these results, injection of L-4F into apoE-null mice prolonged bleeding time; the same result was not found in WT mice. Incubating L-4F in vitro with apoE-null platelet-rich plasma also resulted in decreased platelet aggregation. However, incubating washed platelets from either apoE-null or WT mice with L-4F did not alter aggregation. Compared with WT mice, unstimulated platelets from apoE-null mice contained significantly more 12-hydroxy 5,8,10,14-eicosatetraenoic acid, thromboxane A(2), and prostaglandins D(2) and E(2). In response to agonists, platelets from L-4F-treated apoE-null mice formed significantly less thromboxane A(2), prostaglandins D(2) and E(2), and 12-hydroxy 5,8,10,14-eicosatetraenoic acid.

CONCLUSIONS

By binding plasma-oxidized lipids that cause platelet hyperreactivity in hyperlipidemic mice, L-4F decreases platelet aggregation.

Fatty acid composition, eicosanoid production and permeability in skin tissues of rainbow trout (Oncorhynchus mykiss) fed a control or an essential fatty acid deficient diet

Rainbow trout (Oncorhynchus mykiss) were fed either a control diet containing fish oil or an essential fatty acid (EFA) deficient diet containing only hydrogenated coconut oil and palmitic acid as lipid source (93.4% saturated fatty acids) for 14 weeks and the fatty acid compositions of individual phospholipid classes from skin and opercular membrane (OM) determined. The permeability of skin and OM to water and the production of eicosanoids in skin and gills challenged with the Ca2+ ionophore A23187 were also measured. Phospholipid (PL) fatty acid compositions were substantially modified in EFA-deficient fish, with increased saturated fatty acids and decreased polyunsaturated fatty acids (PUFA), especially arachidonic acid (AA) and eicosapentaenoic acid (EPA), while docosahexaenoic acid (DHA) was largely retained. The onset of EFA deficiency was shown by the appearance of n-9 PUFA, particularly 20:3n-9. The main effects of EFA deficiency on phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were to increase saturated fatty acids and monoenes, especially 16:1 and 18:1, and to decrease EPA and DHA. The content of DHA in phosphatidylserine (PS) was high in control animals (40% in skin and 35% in opercular membrane) and was mostly retained in EFA deficient animals. Arachidonic acid (AA) was the most abundant PUFA esterified to phosphatidylinositol (PI) and was significantly reduced in EFA deficient animals (from 31% to 13% in skin), where a large amount of 20:3n-9 (9% in skin) was also present. Influxes and effluxes of water through skin and opercular membrane were measured in vitro. No differences were detected between rainbow trout fed the control or the EFA deficient diet. 12-Hydroxyeicosatetraenoic acid (12-HETE), 12-hydroxyeicosapentaenoic acid (12-HEPE) and 14-hydroxydocosahexaenoic acid (14-HDHE) could not be detected in skin from control or EFA deficient fish. There was no difference between control and EFA deficient trout in the levels of leukotriene C4 (LTC4) and leukotriene C5 (LTC5) in skin cells challenged with the calcium ionophore A23187, and of prostaglandin F2alpha (PGF2alpha), 12-HETE and 12-HEPE in gill cells challenged similarly. Prostaglandin F3alpha (PGF3alpha) production by ionophore stimulated gill cells was significantly reduced in fish fed the EFA-deficient diet. 14-HDHE produced by gill cells was 3.3 fold higher in EFA deficient fish compared to controls.

The platelet-activating factor precursor of the injured cornea is selectively implicated in arachidonate and eicosanoid release

The purpose of this study was to isolate the platelet-activating factor (PAF) precursor and other choline phosphoglycerides (GPC) i.e. the alkenylacyl and diacyl lipids from the rabbit cornea, to analyze their fatty acid content and to determine which pool was the most susceptible to arachidonate depletion when activated corneal tissue released arachidonic acid (AA) and metabolites. Rabbit iridal GPC was also analyzed for comparative purposes. The fatty acid methyl esters of the GPC components extracted from the rabbit cornea and iris-ciliary body, isolated by high performance liquid chromatography (HPLC), were determined by capillary gas liquid chromatography. Rabbit corneas were labelled in vivo by intracameral injection of 3H-AA (1 microCi, specific activity = 218 Ci/mmol) and cryogenically injured 18 h later. Corneas were incubated in vitro and the AA and eicosanoids released into the medium were extracted and separated by HPLC. The GPC was extracted from the tissues and the labeling of the three GPC constituents was quantified by liquid scintillation counting. The corneal and iridal PAF precursor represented 4.1 +/- 0.2% and 2.9 +/- 0.2% respectively of total GPC in those tissues. On a mole basis, the alkyl arachidonoyl species constituted 12.7 +/- 0.7% of the corneal and 38 +/- 0.6% of the iridal PAF precursors respectively. The release of AA and prostaglandins by the cornea was linear until 15 min; whereas 12-HETE levels continuously increased until 60 min. All GPC components lost label but 1-O-alkyl-2-arachidonoyl was the most affected, with its labeled content 50% less than the non-injured control.(ABSTRACT TRUNCATED AT 250 WORDS)