The effect of long-term consumption of fish oil on platelet-activating factor synthesis in rat renal microsomes

EPA, but not DHA, decreases mean platelet volume in normal subjects

The first indication of platelet activation is an increase in mean platelet volume (MPV). n-3 FA are known to inhibit platelet function and to reduce the risk for coronary heart disease. The purpose of this study was to determine the effects of EPA and DHA on MPV. Healthy subjects received olive oil placebo for 4 wk and then were randomly assigned to receive 4 g of ethyl esters of either safflower oil (n = 11), EPA (n = 10), or DHA (n = 12) for 4 wk. At the end of placebo run-in and treatment periods, MPV (fL; mean +/- SEM) and platelet count (PLT-CT; 10(3)/microL blood) were measured in the basal state and after ex vivo stimulation with collagen (10 microg/mL), cold (4 degrees C), and heat (37 degrees C). Unlike DHA, EPA lowered MPV as compared with safflower oil (7.2 +/- 0.1 vs. 7.5 +/- 0.1 fL; P < 0.05) and raised PLT-CT (211 +/- 18 vs.192 +/- 18 10(3)/microL; P < 0.05) in the fasting state. Collagen and cold significantly increased MPV whereas heat lowered MPV regardless of treatment. All stimuli decreased PLT-CT. EPA significantly increased platelet EPA (0.2 +/- 0.1 vs. 3.3 +/- 0.4%) and docosapentaenoic acid (DPA; 2.2 +/- 0.3 vs. 2.9 +/- 0.3%) concentrations, but not DHA. DHA treatment significantly increased DHA (1.4 +/- 0.2 vs. 4.1 +/- 0.5%) and DPA (2.0 +/- 0.4 vs. 3.0 +/- 0.4%) concentrations, but not EPA. In conclusion, EPA, but not DHA, reduces platelet activation, an early step in platelet aggregation.

Subcellular localization of enzyme activities involved in the metabolism of platelet-activating factor in rainbow trout leukocytes

The subcellular distribution of an alkyllyso-GPC: acetyl-CoA acetyltransferase (EC 2.3.1.67) and transacylase, two important enzyme activities involved in the remodeling pathway for the biosynthesis of platelet-activating factor (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, PAF) have been examined in leukocytes isolated from the pronephros of the rainbow trout, Oncorhynchus mykiss. Contrary to mammalian systems, in which the acetyltransferase is localized to intracellular membranes, the subcellular distribution of an acetyltransferase activity in rainbow trout leukocytes was localized to the plasma membrane. Analysis of the acetyltransferase products by thin-layer chromatography (TLC) and high performance liquid chromatography (HPLC) confirmed synthesis of two subclasses of PAF, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine and 1-acyl-2-acetyl-sn-glycero-3-phosphocholine. The transacylase activity in this study was detected in membrane fractions in two domains of the intermediate density region which also contained the NADH dehydrogenase activity, a marker enzyme for the endoplasmic reticulum. Acylation of lysoPAF (1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine) exhibited approximately 95% specificity for omega-3 fatty acids. Acylation patterns were not significantly different in either domain of the endoplasmic reticulum. A model is proposed herein for the metabolism of PAF in rainbow trout leukocytes.

Dietary alpha-linolenate suppresses endotoxin-induced platelet-activating factor production in rat kidney

In comparison with dietary high-linoleate safflower oil, high alpha-linolenate perilla oil decreased alkylacyl- and alkenylacyl-glycerophosphocholine (GPC) content in rat kidney by roughly 30 and 25%, respectively. The fatty acid composition was also modified by high alpha-linolenate oil; arachidonic acid (AA) level in alkylacyl-GPC, a platelet-activating factor (PAF) precursor, decreased by 30% along with concomitant increases in the n-3 fatty acid levels. PAF contents under resting conditions were similarly low in the two dietary groups. Fifteen minutes after endotoxin administration, PAF and lyso-PAF contents increased significantly, and the PAF content in the high alpha-linolenate group was 60% lower than in the high linoleate group; the lyso-PAF contents also tended to be lower. Lyso-PAF acetyltransferase and CoA-independent transacylase activities in kidney microsomes increased significantly after endotoxin administration, while PAF acetylhydrolase activity in the cytosol was relatively unchanged. The lyso-PAF acetyltransferase and PAF acetylhydrolase activities did not differ between the two dietary groups, but the CoA-independent transacylase activity was roughly 30% lower in the high alpha-linolenate group. In agreement with in vitro study, our present study demonstrates that dietary high alpha-linolenate suppresses PAF production in rat kidney during systemic endotoxemia, and which is mainly due to the decrease in alkylacyl-GPC content, altered fatty acid compositions of the precursor lipids and lower CoA-independent transacylase activity.

Changes in ether-linked phospholipids in rat kidney by dietary alpha-linolenic acid in vivo

We investigated the effects of perilla oil containing a high level of alpha-linolenic acid on in vivo phospholipid metabolism, particularly three subclasses of choline glycerophospholipids (CGP) and ethanolamine glycerophospholipids (EGP), in rat kidney. After three weeks of feeding, a significantly lower proportion (by 35%) of the alkylacyl subclass of CGP was found in the perilla oil, as compared to corn oil-fed animals. The alkylacyl species of EGP was also higher in the perilla oil than in the corn oil-fed animals. These alterations were accompanied by a remarkably lower proportion of arachidonic acid and a higher level of eicosapentaenoic acid (EPA) in all six subclasses of CGP and EGP in the perilla oil-fed animals. The levels of linoleic acid were even higher in the diacyl subclasses of CGP and EGP in the perilla oil group, suggesting that desaturase and elongase enzymes prefer n-3 to n-6 fatty acids as substrates for diacyl species. These data are useful in defining the effects of alpha-linolenic acid on the biosynthesis of renal phospholipids and on the replacement of n-6 with n-3 fatty acids in the six CGP and EGP subclasses.

Alteration in mouse splenic phospholipid fatty acid composition and lymphoid cell populations by dietary fat

The fatty acid composition of diacyl- and alkylacylglycerophosphocholine (PC), phosphatidylinositol (PI), phosphatidylserine (PS), alkenylacyl-glycerophosphoethanolamine (aPE), and diacyl- and alkylacyl-glycerophosphoethanolamine (dPE) was assessed in isolated splenocytes from C3H/Hen mice fed one of four purified isocaloric diets for six weeks. Diets contained 20% by weight of either a high-linoleate sunflower oil (Hi 18:2), a high-oleate sunflower oil (Hi 18:1), a mixture of 17% menhaden fish oil and 3% high-linoleate sunflower oil (Hi n-3), or a mixture of 17% coconut oil and 3% high-linoleate sunflower oil (Hi SFA). Spleen weight and immune cell yield were significantly higher (P less than 0.05) in mice fed the Hi 18:1 or the Hi n-3 diets compared with those fed the Hi 18:2 and Hi SFA diets. Distinctive patterns of fatty acids were observed for each phospholipid in response to dietary fatty acids. Dietary fat significantly affected (P less than 0.05) total polyunsaturated fatty acids (PUFA) in PC and dPE, total saturated fatty acids (SFA) in PC, total monounsaturated fatty acids (MUFA), and n-3 PUFA in all phospholipid classes examined. In mice fed the Hi n-3 diet, n-3 PUFA were significantly elevated, whereas n-6 PUFA decreased in all of the phospholipids. In these mice, eicosapentaenoic acid (EPA) was the predominant n-3 PUFA in PC and PI, whereas docosahexaenoic acid (DHA) was the major n-3 PUFA in aPE and PS.(ABSTRACT TRUNCATED AT 250 WORDS)