Metabolic products of arachidonic acid in rats

Final Report on the Safety Assessment of Arachidonic Acid

Arachidonic Acid is an essential, polyunsaturated, fatty acid that is used as a surfactant-cleansing agent and a surfactant-emulsifying agent in cosmetic formulations. Arachidonic Acid is well absorbed from the gastrointestinal tract and the circulatory system; it distributes rapidly into the lipid compartment of the body and is rapidly converted to phospholipid by the liver.

Arachidonic Acid may alter the cutaneous immune response; in one study, the effect was more pronounced at lower test concentrations than at higher. Application of Arachidonic Acid to mouse skin produced edema and inflammation, with high dosages possibly causing ulceration of the skin. Arachidonic Acid has mutagenic potential. In a 24 h single insult patch test, a formulation containing 0.04% Arachidonic Acid was not a skin irritant.

The safety of use of this ingredient in cosmetic products has not been documented and substantiated. It cannot be concluded that Arachidonic Acid is safe for use in cosmetic products until the needed additional safety test data have been obtained and evaluated. If the requested skin absorption data indicate that absorption occurs, immunomodulatory data, carcinogenicity and photocarcinogenicity data, human irritation, sensitization, and photosensitization data may also be required.

Non-Invasive Pregnancy Diagnosis in Big Cats using the PGFM (13,14-dihydro-15-keto-PGF2α) Assay

Non-invasive monitoring of hormones using feces has become a vital tool for reproductive management and reliable pregnancy diagnosis in big cats. Previous studies described the PGF_2α metabolite (PGFM) as an indicator of pregnancy in various feline species. The present study aimed to standardize pregnancy detection in big cats like the tiger (Panthera tigris), jaguar (Panthera onca) and lion (Panthera leo) using fecal samples. High-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LCMS) were performed to identify PGFM in feces. An EIA developed against 9α,11α-dihydroxy-15-oxo-prost-5-en-1-oic acid-BSA was used to assay PGFM in fecal samples of the Bengal tiger, Asiatic lion and jaguar. The PGFM levels increased after 9 weeks of pregnancy and remained elevated until parturition. All animals showed elevated levels of PGFM in the last trimester of pregnancy, thus making PGFM a reliable tool for pregnancy diagnosis during this period that can be useful in captive breeding programs in these species.

Metallophilic macrophages of the rodent thymus

For a very long time, we studied the metallophilic macrophages of the rodent thymus and in this review our results on morphological, histochemical, enzymehistochemical, immunohistochemical, ultrastructural and functional features of these cells, as well as the molecular regulation of their development, will be presented. Furthermore, the differences between species will also be discussed and the comparisons with similar/related cell types (metallophilic macrophages in the marginal sinus of the spleen, subcapsular sinus of the lymph nodes and germinal centers of secondary lymphoid follicles) will be made. Metallophilic macrophages are strategically positioned in the thymic cortico-medullary zone and are very likely to be involved in: (i) the metabolism, synthesis and production of bioactive lipids, most likely arachidonic acid metabolites, based on their histochemical and enzymehistochemical features, and (ii) the process of negative selection that occurs in the thymus, based on their ultrastructural features and their reactivity after the application of toxic or immunosuppressive/immunomodulatory agents. Taken together, their phenotypic and functional features strongly suggest that metallophilic macrophages play a significant role in the thymic physiology.

n-3 fatty acids reduce in vitro thromboxane production while having little effect on in vitro prostacyclin production in the rat

Male Sprague-Dawley rats were fed diets with 50% of the energy from fat over a 20-day period. The fats used were hydrogenated beef-fat (HBF), or HBF supplemented with ethyl arachidonate A, safflower oil (SO), or a mixture of SO and linseed oil (LO). For comparative purposes, another group of animals was fed a diet providing 50% of the energy as butter-fat. In vitro aortic prostacyclin (PGI2) and serum thromboxane (TXA2) levels (from clotting blood) were determined by radioimmunoassay of 6-keto PGF1 alpha and TXB2, respectively. The HBF diet had similar AA levels relative to the butter-fed rats but significantly reduced tissue levels of eicosapentaenoic acid (EPA) and this was associated with an increased production of serum TXB2. Supplementing the HBF diet with AA increased tissue levels of AA while maintaining low levels of n-3 fatty acids. These changes were accompanied by significant increases of both TXB2 and 6-keto-PGF1 alpha. LO supplementation to the HBF diet (with constant SO) led to elevated levels of EPA and relatively constant AA levels and this was associated with reduced production of TXB2. These results highlight the responsiveness of TXA2 to n-3 fatty acids in contrast to PGI2 which was more influenced by the level of AA in the tissue phospholipids in the rat.

The effect of linoleic, arachidonic and eicosapentaenoic acid supplementation on prostacyclin production in rats

We examined the effect of dietary supplementation of linoleic acid (LA), arachidonic acid (AA) or eicosapentaenoic acid (EPA) to rats fed a diet low in linoleic acid on in vitro and in vivo production of prostacyclin. Male Sprague Dawley rats were fed a high-fat diet (50% energy as fat, 1.5% linoleic acid) for two weeks. Three of the groups were then supplemented orally with either 90 mg/d of LA, AA or EPA, all as the ethyl esters, for a further two weeks while remaining on the high-fat diet. Forty-eight hour urine samples were collected at the end of the second and fourth weeks. In vivo prostacyclin production was determined by a stable isotope dilution, gas chromatography/mass spectrometry assay for the major urinary metabolite of prostacyclins (2,3-dinor-6-keto-PGF1 alpha or PGI2-M and delta 17-2,3-dinor-6-keto-PGF1 alpha or PGI3-M). In vitro prostacyclin production was determined by radioimmunoassay of the stable metabolite (6-keto-PGF 1 alpha) following incubation of arterial tissue. Oral supplementation with AA resulted in a rise in plasma and aorta 20:4n-6, and increased in vitro prostacyclin and urinary PGI2-M production. EPA supplementation resulted in a rise in plasma and aorta 20:5n-3 and 22:5n-3, and a decline in plasma 20:4n-6, but not in the aorta. In the EPA-supplemented group, the in vitro prostacyclin and the urinary PGI3-M increased, but urinary PGI2-M decreased. The increase in in vitro prostacyclin production in the EPA-supplemented rats was unexpected and without obvious explanation.(ABSTRACT TRUNCATED AT 250 WORDS)

Arachidonic acid supplementation dose-dependently reverses the effects of a butter-enriched diet in rats

Male Sprague Dawley rats were fed a butter-enriched diet (50% fat) for 2 weeks which was supplemented orally with 9, 18, 36, or 72 mg/day of ethyl arachidonate for a further 2 weeks. The control group of animals were fed a 5% fat diet for 4 weeks. Aortic prostacyclin (PGI2) production, platelet aggregation and thromboxane A2 (TXA2) production and plasma and aortic phospholipid (PL) fatty acids were measured. 50% butter-feeding resulted in a significant reduction in aortic PGI2 production and collagen-induced platelet aggregation and TXA2 production. These changes were accompanied by a reduction in plasma and aortic PL arachidonic acid levels and an increase in eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), 5,8,11-eicosatrienoic acid (ETA) and dihomo-gamma-linolenic acid (DGLA). These changes in prostanoid production, platelet aggregation and PL fatty acid composition were dose-dependently reversed by the daily oral administration of ethyl arachidonate (9, 18, 36, or 72 mg). The threshold dose being as little as 9 mg of ethyl arachidonate/rat/day for reversal of PL fatty acid composition, collagen-induced platelet aggregation and TXA2 production, and 18 mg of ethyl arachidonate/rat/day for reversal of aortic PGI2 production. Full reversal was seen generally with 36 or 72 mg of ethyl arachidonate/rat/day. The data highlight the responsiveness of tissue eicosanoid production to small quantities (ppm) of dietary eicosanoid precursors.

Age-related changes in arachidonic acid peroxidation and glutathione-peroxidase activity in human platelets

Lipid peroxidation, vitamin E level and glutathione-peroxidase activity were determined in platelets from elderly (greater than 68 years) and young (21-43 years) people. To further assess the platelet lipid peroxidation, the metabolism of endogenous arachidonic acid in unstimulated platelets as well as that of the exogenous one were measured in the two groups. The oxygenated metabolites of arachidonic acid were enhanced in the elder population under both conditions tested. In addition, the platelet malondialdehyde content, a marker of the overall lipid peroxidation, was also found significantly increased in platelets from aged subjects. On the other hand, the platelet vitamin E level and the glutathione-peroxidase activity were significantly depressed in the elder group compared to the young one. These results suggest that the increased platelet activation observed with age could be linked to the accumulation of lipoxygenase-dependent peroxides associated with the decreased antioxidative defence of the cells, especially glutathione-peroxidase activity.

Influence of dietary fish on eicosanoid metabolism in man

Two groups of 40 volunteers were given a dietary supplement consisting of 135 g of mackerel or meat (control) paste per day for 6 weeks. Compliance was about 80% in both groups and the daily intake of 20:5(n-3) and 22:6(n-3) from the mackerel supplement was about 1.3 and 2.3 g, respectively. In collagen-activated platelet rich plasma, the potency of blood platelet to produce HHT from arachidonic acid (AA) clearly reduced in the mackerel group, whereas the formation of HHTE from timnodonic acid (TA) increased slightly. Changes in the formation of HHT and HHTE, measured by HPLC, correlated significantly with those of TxB2 and TxB3, respectively, measured by GC/MS. Changes in the formation of the lipoxygenase products HETE (ex AA) and HEPE (ex TA) were qualitatively similar to that seen for the cyclo-oxygenase products, but quantitatively the responses were smaller. Formation of ir TxB2 in clotting blood significantly reduced in the mackerel group. In collagen-activated, citrated whole blood, TxB2 formation tended to be reduced in the mackerel-supplemented volunteers. Mackerel consumption was associated with the formation of considerable amounts of PGI3, as judged from the appearance of 2,3-dinor-delta 17-6-keto-PGF1 alpha in urine. The amount of the major metabolite of PGI2, 2,3-dinor-6-keto-PGF1 alpha was not reduced, or even increased. The daily amount of tetranor prostaglandin metabolites in the urine did not change significantly, which indicates that mackerel supplementation did not alter the formation of prostaglandins E and F.

n-3 fatty acids as precursors for active metabolic substances: dissonance between expected and observed events

It may be hypothesized that many diseases are associated with an overproduction of eicosanoids from the n-6 acid, arachidonic acid (20:4n-6), and the formation and function of these n-6 eicosanoids can be antagonized by dietary n-3 fats. This hypothesis provides a basis for evaluating the benefits and risks of including various amounts of n-3 and n-6 fats in the diet. Understanding the impact of dietary polyunsaturated fats leads inevitably to a reappraisal of what is 'normal' in terms of what is typical and what is desirable for the fatty acid composition of tissue lipids, the magnitude of eicosanoid-mediated responses, and the frequency and severity of certain diseases.

The effect of dietary fish oils on eicosanoid biosynthesis in peritoneal macrophages is influenced by both dietary N-6 polyunsaturated fats and total dietary fat

Recent research has implicated dietary fish oils in the reduction of eicosanoids formed from arachidonic acid and amelioration of chronic diseases such as coronary heart disease, atherosclerosis and inflammation. Feeding studies were conducted to determine if the efficacy of dietary n-3 polyunsaturated fatty acids (PUFA) from fish oils was influenced by the quantity of n-6 polyunsaturated fatty acids and the total level of fat in the diet. Groups of mice were fed diets composed of 5 and 20% total fat with varying proportions of linoleic acid as a source of n-6 PUFA. Menhaden oil as a source of n-3 PUFA was fed at two levels of n-6 at each level of total fat. Eicosanoid biosynthesis was stimulated and assayed in the mouse peritoneum using zymosan as an inflammatory stimulus. Production of LTE4 and PGE2 was enhanced by increasing n-6 PUFA in the diet at both levels of total fat. High dietary fat significantly suppressed leukotriene (LT) synthesis. Dietary menhaden oil reduced LTE4 and PGE2 synthesis at both levels of dietary n-6 in the low fat study. In animals on 20% dietary fat menhaden oil significantly reduced LT synthesis only at a relatively low dietary n-6 PUFA. On a high n-6 PUFA high fat diets, menhaden oil did not significant affect LTE4 synthesis in response to zymosan stimulation. The results suggest that the effectiveness of fish oils in reducing eicosanoids in response to specific stimulation is influenced by the level of n-6 and the total quantity of fat in the diet.

The urinary excretion of prostaglandins E and their corresponding tetranor metabolites by rats fed a diet rich in eicosapentaenoate

An HPLC method was developed to determine simultaneously in a single analysis prostaglandin E2, prostaglandin E3, tetranor-prostaglandin E1 and delta 17-tetranor-prostaglandin E1 in rat urine. As internal standard omega-nor-prostaglandin E2 was added to the samples at the beginning of the analysis. The assay was applied in feeding experiments in which rats were fed diets with mixtures of (n-6) and (n-3) fatty acids (linoleate, arachidonate, alpha-linolenate and eicosapentaenoate). The level of urinary prostaglandin E2 was not very much affected by the diet and prostaglandin E3 could never be detected in significant amounts. These primary prostaglandins are assumed to reflect prostaglandin biosynthesis in the kidney medulla. Tetranor-prostaglandin E1 is a characteristic urinary metabolite of prostaglandin E2 in the rat; its level increased after feeding arachidonic acid. delta 17-Tetranor-prostaglandin E1 became a major metabolite when the rats received eicosapentaenoic acid. However, we found that the ratio of urinary tetranor-prostaglandin E1/delta 17-tetranor-prostaglandin E1 is not a very reliable measure of the ratio of prostaglandin E2/prostaglandin E3 formed in the body, because prostaglandin E3 is converted to a much greater extent into delta 17-tetranor-prostaglandin E1 than is prostaglandin E2 into tetranor-prostaglandin E1. As a matter of fact, incubations of tissue homogenates of rats resulted always in predominant formation of prostaglandins of the 2-series, even after high eicosapentaenoate diets. We conclude, in agreement with work carried out earlier, that biosynthetic pathways leading to prostaglandins of the 3-series are of minor importance.

Biochemical and cellular actions of membrane lipids

A network of intercellular signals is modulated by eicosanoids derived from arachidonate that can be supplied from either the diet or the membrane lipids. Fatty acid oxygenases controlling the first committed step in the biosynthesis of prostaglandins and leukotrienes are suppressed in normal tissues but are activated by lipid hydroperoxides. Because hydroperoxides are also produced by the action of the oxygenases, they provide positive feedback amplification during eicosanoid biosynthesis. This relationship among membrane lipids, lipid peroxides, and eicosanoids can lead to amplification of the intercellular signals mediated by cytokines and immune globulins in ways that create hyperresponsive states and lead to pathophysiology.

Measurement of the incorporation of orally administered arachidonic acid into tissue lipids

The applicability of a stable isotope method to monitor the mixing of dietary arachidonic acid with endogenous arachidonic acid in tissue lipids was evaluated. Rats were fed octadeuterated arachidonic acid during a 20-day period, and the entry of the dietary acid into lipid esters of various tissues was examined by gas chromatography-mass spectrometric (GC-MS) analysis of their fatty acids. The rats were maintained on a fat-free diet from weaning until 63 days old to enhance the ratio of the dietary acid to endogenous arachidonate. Three separate forms of eicosatetraenoic acid in the tissue lipids could be distinguished by GC-MS: octadeuterated arachidonic acid (recent dietary origin), unlabeled arachidonic acid (maternal origin) and unlabeled 4,7,10,13-eicosatetraenoic acid (originating from palmitoleic acid). The total eicosatetraenoic acid in the tissue lipids contained about 90% arachidonate from recent dietary origin in lung, kidney, heart and fat, 70% in muscle and liver and 27% in brain. The n-7 isomer of eicosatetraenoic acid was estimated to make up 6% or less of the total eicosatetraenoic acid in lung, kidney, brain, muscle and heart tissue lipids, but it comprised around 15% of the total eicosatetraenoic acid in liver. The unlabeled arachidonic acid of maternal origin thus comprised only about 10% of the eicosatetraenoic acid in all tissues examined except muscle and brain, where it was 24% and 70% of the eicosatetraenoic acid, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)