Reacylation of platelet activating factor with eicosapentaenoic acid in fish-oil-enriched monkey neutrophils

Regulation of the tumor suppressor PTEN by natural anticancer compounds

The tumor suppressor phosphatase and tensin homologue (PTEN) has phosphatase activity, with phosphatidylinositol (3,4,5)-trisphosphate (PIP3), a product of phosphatidylinositol 3-kinase (PI3K), as one of the principal substrates. PTEN is a negative regulator of the Akt pathway, which plays a fundamental role in controlling cell growth, survival, and proliferation. Loss of PTEN function has been observed in many different types of cancer. Functional inactivation of PTEN as a consequence of germ-line mutations or promoter hypermethylation predisposes individuals to malignancies. PTEN undergoes posttranslational modifications, such as oxidation, acetylation, phosphorylation, SUMOylation, and ubiquitination, which influence its catalytic activity, interactions with other proteins, and subcellular localization. Cellular redox status is crucial for posttranslational modification of PTEN and its functional consequences. Oxidative stress and inflammation are major causes of loss of PTEN function. Pharmacologic or nutritional restoration of PTEN function is considered a reliable strategy in the management of PTEN-defective cancer. In this review, we highlight natural compounds, such as curcumin, indol-3 carbinol, and omega-3 fatty acids, that have the potential to restore or potentiate PTEN expression/activity, thereby suppressing cancer cell proliferation, survival, and resistance to chemotherapeutic agents.

n-3 Polyunsaturated Fatty Acids and their Role in Cancer Chemoprevention

Polyunsaturated fatty acids (PUFAs), including omega-3 (n-3) and omega-6 (n-6) PUFAs, are essential for human health. Recent research shows n-3 PUFAs and their mediators can inhibit inflammation, angiogenesis and cancer via multiple mechanisms, including reduced release of n-6 fatty acid arachidonic acid from cell membranes, inhibition of enzymatic activities, and direct competition with arachidonic acid for enzymatic conversions. In this review, we discuss inflammation-related cancer, anti-inflammatory effects of n-3 PUFA lipid mediators, antineoplastic activities of n-3 PUFA in vitro and in vivo, and present an update on recent human trials.

Mechanisms of omega-3 polyunsaturated fatty acids in prostate cancer prevention

This review focuses on several key areas where progress has been made recently to highlight the role of omega-3 polyunsaturated fatty acid in prostate cancer prevention.

Dietary fat-gene interactions in cancer

Epidemiologic studies have suggested for decades an association between dietary fat and cancer risk. A large body of work performed in tissue culture and xenograft models of cancer supports an important role of various types of fat in modulating the cancer phenotype. Yet, the molecular mechanisms underlining the effects of fat on cancer initiation and progression are largely unknown. The relationships between saturated fat, polyunsaturated fat, cholesterol or phytanic acid with cancer have been reviewed respectively. However, few have considered the relationship between all of these fats and cancer. The purpose of this review is to present a more cohesive view of dietary fat-gene interactions, and outline a working hypothesis of the intricate connection between fat, genes and cancer.

Modulation of prostate cancer genetic risk by omega-3 and omega-6 fatty acids

Although a causal role of genetic alterations in human cancer is well established, it is still unclear whether dietary fat can modulate cancer risk in a predisposed population. Epidemiological studies suggest that diets rich in omega-3 polyunsaturated fatty acids reduce cancer incidence. To determine the influence of fatty acids on prostate cancer risk in animals with a defined genetic lesion, we used prostate-specific Pten-knockout mice, an immune-competent, orthotopic prostate cancer model, and diets with defined polyunsaturated fatty acid levels. We found that omega-3 fatty acids reduced prostate tumor growth, slowed histopathological progression, and increased survival, whereas omega-6 fatty acids had opposite effects. Introducing an omega-3 desaturase, which converts omega-6 to omega-3 fatty acids, into the Pten-knockout mice reduced tumor growth similarly to the omega-3 diet. Tumors from mice on the omega-3 diet had lower proportions of phosphorylated Bad and higher apoptotic indexes compared with those from mice on omega-6 diet. Knockdown of Bad eliminated omega-3-induced cell death, and introduction of exogenous Bad restored the sensitivity to omega-3 fatty acids. Our data suggest that modulation of prostate cancer development by polyunsaturated fatty acids is mediated in part through Bad-dependent apoptosis. This study highlights the importance of gene-diet interactions in prostate cancer.

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.

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.

Reduced neutrophil superoxide generation and plasma lipoperoxide levels in pigs fed with cod liver oil

Circulating neutrophils, isolated from pigs fed for 8 weeks with a diet supplemented with CLO, had an accentuated n-3 fatty acid incorporation into the plasma membrane, as evidenced by an approximately four-fold greater n-3/n-6 ratio as compared with the control diet group. Moreover, the neutrophils of the CLO fed pigs produced less superoxide when stimulated with PMA or f-MLP, as well as showing a more prolonged latency period before O2(-)-generation. In the plasma of pigs fed with CLO there were higher levels of thiobarbituric reactive material and lipofuscin, while the content of GSSG was similar in both dietary groups. The results of this study indicate that dietary supplementation with CLO reduces the activation of circulating neutrophils and favours the presence in the plasma of lipoperoxides.

Acylation of lyso platelet-activating factor by splenocytes of the rainbow trout, Oncorhyncus mykiss

In mammalian systems, platelet-activating factor, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, (PAF) is rapidly inactivated by a deacetylation/reacylation system that produces 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine which is highly enriched in arachidonic acid. There is some evidence that n-3 fatty acids may have an impact on this system in humans but the nature of this impact is unclear. In rainbow trout, n-3 fatty acids are known to be essential dietary components which are derived through the food chain. Substantial quantities of n-3 fatty acids are found in trout membrane phospholipids. We show here that in sharp contrast to mammalian cells, trout cells acylate lyso platelet-activating factor, alkyl-GPC, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine, (lyso-PAF) with a high degree of specificity for n-3 fatty acids. When [3H]lysoPAF was incubated with these cells, only three molecular species of alkylacylglycerophosphocholine were produced, and 92% contained n-3 fatty acids. Since isolated membranes yielded similar results, it appears that the acylation proceeds via a coenzyme A-independent transacylase as found in mammalian systems.

Interaction of platelet-activating factor with cultured guinea pig tracheal epithelial cells

The present study has examined the interaction of platelet-activating factor (PAF) with cultured guinea pig tracheal epithelial cells (GTE). PAF stimulated GTE to release endogenous arachidonic acid and metabolize it to prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha). Prostanoid production by GTE in response to PAF was dose-dependent (0.1-100 nM) and was maximal within 5 min. PGE2 and PGF2 alpha levels increased by 3.3 +/- 0.8 and 3.2 +/- 0.6 ng/10(6) cells respectively over basal levels in response to 100 nM-PAF. The ability of GTE to synthesize and/or catabolize PAF was also examined. GTE readily incorporated [3H]acetate into a product which migrated on t.l.c. with PAF. However, further characterization of this product suggested that label had not been incorporated into PAF, but rather that it was incorporated into another lipid product with chromatographic characteristics similar to those of PAF. In contrast, GTE readily metabolized PAF to inactive products. When [3H]PAF was incubated with GTE, 50% of the total [3H]PAF added was catabolized in approx. 15 min. The major route of catabolism of PAF by GTE was the deacetylation-reacylation pathway, which yielded 1-O-[3H]alkyl-2-acyl-sn-glycerophosphocholine. Determination of the nature of the long-chain acyl group incorporated into the sn-2 position of the newly synthesized products revealed that oleic and linoleic acids were the major fatty acids present. Taken together, these results suggest that respiratory epithelial cells respond to stimulation by PAF with enhanced production of PGE2 and PGF2 alpha, and also have the capacity to modulate inflammatory reactions in the airways by their ability to degrade this potent inflammatory mediator.

Effects of a fish oil diet on the metabolism of endogenous (n-6) and (n-3) fatty acids in rat neutrophils

The present study was carried out to define more precisely how dietary (n-3) fatty acids mediate leukotriene and phospholipid metabolism in neutrophils. Neutrophils from chow-fed rats did not synthesize detectable levels of LTB5 or 5-hydroxyeicosapentanenoic acid. The ratio of esterified 20:4(n-6)/20:5(n-3) in the phospholipids of neutrophils from rats fed a corn oil/fish oil diet was 4.6. The ratio of LTB4/LTB5 made by these cells was 2.6, thus suggesting that 20:5(n-3) release and/or subsequent metabolism was somewhat more efficient than for 20:4(n-6). When tritiated lyso-platelet activating factor was added to neutrophils from chow-fed rats, it was deactivated primarily by acylation with arachidonic acid. With the fish oil-fed animals both arachidonic acid and 20:5(n-3) were transferred to deactivate lyso-platelet activating factor. Molecular species analysis of the resulting radioactive 1-O-alkyl-2-acyl-sn-glycerol-3-phosphocholine showed that 20:5(n-3) pairs with the same 1-O-alkyl groups and in approximately the same ratio as does arachidonate. Collectively, these studies show that once 20:5(n-3) is incorporated into neutrophil lipids it is metabolized in a similar way as is arachidonate.

Influence of immunologic activation and cellular fatty acid levels on the catabolism of platelet-activating factor within the murine mast cell (PT-18)

The present study has examined the catabolism of 1-O-[3H]hexadecyl-2-acetyl-GPC (C16-PAF) and of 1-O-octadecyl-2-acetyl-GPC (C18-PAF) in spleen-derived PT-18 murine mast cells (mast cells). Mast cells catabolized exogenous PAF into two inactive metabolites, 1-O-alkyl-2-lyso-sn-glycero-3-phosphocholine (lysoPAF) and 1-O-alkyl-2-acyl-sn-glycero-3-phosphocholine (1-O-alkyl-2-acyl-GPC). The rate of conversion of C16-PAF to metabolites was more rapid than that of C18-PAF. Analysis of the acyl composition of 1-O-alkyl-2-acyl-GPC formed during the metabolism of PAF revealed that arachidonic acid (20:4) was the major fatty acyl chain incorporated at the sn-2 position. However, 25% of newly formed 1-O-alkyl-2-acyl-GPC was reacylated with docosahexaenoic acid (22:6). The influence of cellular fatty acid content on PAF catabolism was further explored in mast cells in which the ratio of fatty acids within cellular phosphoglycerides had been altered by supplementing the cells with various fatty acids in culture. Mast cells supplemented with 20:4 or 22:6 converted PAF to 1-O-alkyl-2-acyl-GPC at a significantly higher rate than non-supplemented cells. In contrast, cells supplemented with linoleic acid (18:2) metabolized PAF at rates similar to non-supplemented cells. Analysis of the acyl composition of 1-O-alkyl-2-acyl-GPC derived from the metabolism of PAF in 20:4-supplemented cells indicated that 20:4 was incorporated exclusively into the sn-2 position. Conversely, 22:6-supplemented cells incorporated predominantly 22:6 at the sn-2 position of 1-alkyl-2-lyso-GPC. Supplementation with 18:2 had no effect on the acylation pattern seen in newly formed 1-O-alkyl-2-acyl-GPC. Activation of passively sensitized mast cells with antigen or with ionophore A23187 significantly enhanced the rate of catabolism of exogenously-provided PAF but had no effect on the acylation pattern of 1-O-alkyl-2-acyl-GPC. Experiments performed with the soluble fraction of the cells showed that acetyl hydrolase activity was increased in mast cells stimulated with antigen. In addition, supernatant fluids from antigen or ionophore-treated mast cells converted PAF to lysoPAF, suggesting that acetyl hydrolase activity was released during cell activation. These data indicate that the ability of mast cells to catabolize PAF to inactive metabolites is influenced by cell activation and by the cellular levels of certain fatty acids.

Effects of dietary fish oil supplementation on membrane fluidity and enzyme activity in rat small intestine

Rats were fed either a fat-free diet supplemented with 10% menhaden oil or a control diet for four months. Intestinal brush border membranes were isolated; phospholipid fatty acid analysis revealed that the membranes from the fish-oil fed animals had higher levels of palmitoleic (C16:1) and eicosapentaenoic (C20:5) acids and lesser levels of stearic (C18:0) linoleic (C18:2) acids compared with controls. The membranes from the fish-oil fed animals had increased levels of alkaline phosphatase activity compared with controls but disaccharidase levels were equivalent in the two groups. Rocket immunoelectrophoresis studies revealed that the increase in alkaline phosphatase activity was due to an increase in the specific activity of the enzyme rather than an increase in the amount of enzyme. Membrane fluidity was assessed by fluorescence anisotropy using diphenylhexatriene and 12-anthroyl stearate as fluorescent probes. The anisotropy of both probes was similar in the two membranes. These studies indicate that fish-oil supplementation alters the fatty acid composition of the intestinal brush border membrane and increases alkaline phosphatase activity without affecting membrane fluidity. Thus the effects of changes in membrane lipid composition on alkaline phosphatase activity appear to result from changes in the local lipid environment of the enzyme rather than from changes in the biophysical characteristics of the membrane.

Studies on the incorporation and transacylation of various fatty acids in choline and ethanolamine-containing phosphoacylglycerol subclasses in human neutrophils

The incorporation of eight 14C-labeled fatty acids into human neutrophil phospholipids was investigated and the results were expressed as percent of the total phospholipid associated 14C-labeled substrate incorporated after an initial 15 min labeling and a subsequent 2 h reincubation in fatty acid-free buffer. In all cases, the PC fraction accounted for more than 40% of the total phospholipid radioactivity. The inositol-containing phosphoacylglycerols were also labeled well by all the fatty acids except 22:6(n - 3) and 16:0; however, a greater percentage of [14C]22:6(n - 3) was found in PE than that of any other labeled fatty acid substrate. In all cases, most of the radioactivity in PC after 15 min was in the diacyl subclass. After 2 h, there was a shift of [14C]20:4(n - 6), [14C]20:5(n - 3), [14C]22:6(n - 3) and [14C]18:4(n - 4) into the ether-linked subclass. No such shift was observed for [14C]16:0 or [14C]18:2(n - 6) and, although there was an increase in the percent radioactive 20:3(n - 6) and 20:3(n - 9) in ether-linked PC after 2 h, the total radioactivity in this fraction remained low by comparison. A similar shift in label occurred in the plasmalogenic-linked PE subspecies in cells labeled with [14C]20:4(n - 6), [14C]20:5(n - 3) and [14C]22:6(n - 3).

Dietary triacylglycerol modulates sodium-dependent D-glucose transport, fluidity and fatty acid composition of rat small intestinal brush-border membrane

Rats were maintained on nutritionally complete diets enriched in unsaturated (menhaden fish oil) or saturated (butter fat) triacylglycerols. After 4 weeks, the animals were killed, proximal small intestinal brush-border membranes were prepared, and examined and compared with respect to their lipid composition, molecular species of phosphatidylcholine, lipid fluidity and sodium-dependent D-glucose transport. Membranes prepared from the two dietary groups were found to possess similar ratios of cholesterol/phospholipid (mol/mol), sphingomyelin/phosphatidylcholine (mol/mol), and protein/lipid (w/w). In contrast to these findings, however, striking differences were noted in the total fatty acid compositions of these membranes. Plasma membranes prepared from animals fed the fish oil diet possessed higher percentages of saturated fatty acids as well as (n - 3) unsaturated fatty acids and lower percentages of monounsaturated and (n - 6) unsaturated fatty acids than those prepared from animals fed the butter fat diet. Analysis of the molecular species of phosphatidylcholine by HPLC, moreover, revealed that membranes from rats fed fish oil had higher levels of 16:0-20:5, 16:0-22:6 and 18:0-20:5 and lower levels of 18:0-18:2 and 16:0-18:1 than their butter fat counterparts. As assessed by steady-state fluorescence polarization, differential polarized phase fluorometric and excimer/monomer fluorescence intensity techniques using various fluorophores, the lipid fluidity of membranes from rats fed fish oil was also found to be significantly lower compared to membranes from rats fed butter fat. Finally, comparison of the kinetic parameters of Na+-dependent D-glucose transport revealed that fish oil-membrane vesicles had a higher maximum velocity (Vmax) than butter fat membrane vesicles but a similar Km for glucose.

Distribution of omega-3 and omega-6 fatty acids in the ether- and ester-linked phosphoglycerides from tissues of the rainbow trout, Salmo gairdneri

1. Data presented here demonstrate that polyunsaturated fatty acids in the phospholipids of rainbow trout tissues are compartmentalized differently than in mammalian tissues. 2. We have determined the distribution of omega-3 (n-3) and omega-6 (n-6) fatty acids in the alkyl-, alk-1-enyl-, and diacyl- subclasses of phosphatidylcholines (PC), phosphatidyl-ethanolamines (PE), phosphatidylinositols (PI), and phosphatidylserines (PS) from gill, kidney and spleen of rainbow trout. 3. Alkyl-linked PC and alk-1-enyl-linked PE were the most abundant ether-containing phospholipids, amounting to 10-15% of each class; no ether-linked PI or PS was detected. 4. C20:4 n-6 was found in high concentrations only in PI; the n-3 fatty acids were found in highest concentration in the ether-linked phospholipids as compared with the diacyl subclasses and C20:5 n-3 was especially prevalent in 1-O-alk-1'-enyl-2-acyl-sn-glycero-3-phosphoethanolamine and C22:6 n-3 was prevalent in PS.