Amounts Of Arachidonate Research Articles

Changes in phospholipid content and myocardial calcium-independent phospholipase A2 activity during chronic anthracycline administration.

Despite numerous investigations, the causes underlying anthracycline cardiomyopathy are yet to be established. We have recently reported that acute treatment with anthracyclines inhibits membrane-associated calcium-independent phospholipase A(2) (iPLA(2)) activity both in vitro and in vivo. This study presents data that iPLA(2) activity is also suppressed during chronic drug administration. Adult Sprague-Dawley rats were given weekly 1 mg/kg i.v. injections of doxorubicin for a total of 8 weeks. One week after the last injection, the animals were sacrificed, and heart tissue was assessed for phospholipid content and iPLA(2) activity. Membrane-associated iPLA(2) activity in the myocardium of doxorubicin-treated animals was 40% lower than that in control hearts. In addition, doxorubicin treatment resulted in significant alterations in the distribution of fatty acyl moieties esterified to the sn-2 position of choline glycerophospholipids. The ethanolamine species remained unaffected. Elevation in the amount of arachidonate and linoleate esterified to the sn-2 position of choline plasmalogens was consistent with the hypothesis that iPLA(2) displays selectivity for plasmalogen phospholipids; therefore, enzyme inhibition may affect hydrolysis of these phospholipid subclasses. Notably, the changes in phospholipid content occurred at a low cumulative dose of 8 mg/kg at which appearance of structural lesions was minimal. Therefore, these alterations seem to be both specific and early signs of cardiomyocyte pathology. The results support our hypothesis that myocardial iPLA(2) inhibition may be one of the steps that leads to the functional and structural changes associated with chronic anthracycline treatment.

Hyperreactive onchocerciasis exhibits reduced arachidonate and linoleate levels in serum triglycerides.

The mechanism by which the minority of patients with onchocerciasis exhibiting the hyperreactive (sowda) form of the disease may be able to kill the microfilariae of Onchocerca volvulus is still poorly understood. In this study, the relative amounts of arachidonate and linoleate in serum phospholipids and triglycerides were investigated by gas chromatography both in patients infected with O. volvulus who exhibited either a hyperreactive or a generalized form of onchocerciasis and in persons with no filarial infections. Remarkable differences were observed in the serum triglycerides but not in the phospholipids. In comparison to persons without any filarial infection, significantly lower relative amounts of arachidonate--indicated by elevated triene-tetraene ratios--and of linoleate--indicated by lower diene + tetraene - triene values--were detected in patients with hyperreactive onchocerciasis, and less pronounced differences were found in persons with generalized onchocerciasis. The relationship between reduced amounts of arachidonate and linoleate in serum triglycerides and possible implications on the eicosanoid production in the host-parasite relationship leading to parasite elimination are discussed.

Possible mechanisms for the differential effects of high linoleate safflower oil and high α-linolenate perilla oil diets on platelet-activating factor production by rat polymorphonuclear leukocytes

As compared with high dietary linoleate safflower oil, high dietary α-linolenate perilla oil decreased platelet-activating factor (PAF) production by nearly half in calcium ionophore (CaI)-stimulated rat polymorphonuclear leukocytes (PMN). In the CaI-stimulated PMN from the perilla oil group, the accumulated amount of arachidonate (AA) plus eicosapentaenoate (EPA) was 30% less and that of lyso-PAF was 50% less, indicating that the decreased availability of lyso-PAF is a factor contributing to the relatively low PAF production. Consistently, eicosatetraynoic acid (ETYA), a dual inhibitor of cyclooxygenase and lipoxygenase, increased free fatty acids (FFA) and decreased PAF production possibly by decreasing the availability of lyso-PAF. Although, leukotrienes (LTs) have been proposed to stimulate PAF production synergistically, a potent LTB 4 receptor antagonist, ONO-4057, decreased the formation of free fatty acids and LTB 4, but stimulated PAF production somewhat, indicating that LTB 4 may not stimulate PAF production in PMN. Lysophospholipid-induced transacylase (CoA-independent transacylase) activity in PMN homogenates was 25∼30% lower in the perilla oil group but no significant differences were observed in the lyso-PAF acetyltransferase and PAF acetylhydrolase activities between the two dietary groups. Thus, decreased transacylase activity is another factor associated with the relatively low PAF production in the perilla oil group.

Evidence for functional involvement of asparagine 67 in substrate recognition by snake venom phospholipases A2.

Site-directed mutagenesis studies of recombinant Trimeresurus flavoviridis venom gland phospholipase A2 (PLA2) showed that the Asn residue at position 67 takes part in recognition of the substrate 2-arachidonoyl sn-glycero-3-phosphocholine in both monomeric and micellar states. The amount of arachidonate released from phosphatidylcholine mixed micelles was reduced to 30% for N67D and N67K mutants, and to 70% for N67G mutant, but remained unchanged for N67S mutant. In contrast, for monomeric substrate, the activity was decreased to 40% for N67D and N67G and to 60% for N67K but remained unchanged for N67S. These results suggest that the properties of the side chain of residue 67 exert a significant influence on recognition of 2-arachidonoyl sn-glycero-3-phosphocholine.

Diethyldithiocarbamate and Nitric Oxide Synergize with Oxidants and with Membrane-Damaging Agents to Injure Mammalian Cells

The effect of diethyldithiocarbamate (DDC) and sodium nitroprusside (SNP) on the killing of endothe-lial cells and on the release of arachidonate by mixtures of oxidants and membrane-damaging agents was studied in a tissue culture model employing bovine aortic endothelial cells labeled either with 51Chromium or 3arachidonic acid. While exposure to low, subtoxic concentrations of oxidants (reagent H2O2, glucose-oxidase generated peroxide, xanthine xanthine oxidase, AAPH-generated peroxyl radical, menadione-generated oxidants) did not result either in cell death or in the loss of membrane-associated arachidonic acid, the addition of subtoxic amounts of a variety of membrane-damaging agents (streptolysin S, PLA2, histone, taurocholate, wheatgerm agglutinin) resulted in a synergistic cell death. However, no significant amounts of arachidonate were released unless proteinases were also present. The addition to these reaction mixtures of subtoxic amounts of DDC (an SOD inhibitor and a copper chelator) not only very markedly enhanced cell death but also resulted in the release of large amounts of arachidonate (in the complete absence of added proteinases). Furthermore, the inclusion in DDC-containing reaction mixtures of subtoxic amounts of SNP, a generator of NO, further enhanced, in a synergistic manner, both cell killing and the release of arachidonate. Cell killing and the release of arachidonate induced by the DDC and SNP- containing mixtures of agonists were strongly inhibited by catalase, glutathione, N-acetyl cysteine, vitamin A, and by a nonpenetrating PLAz inhibitor as well as by tetracyclines. A partial inhibition of cell killing was also obtained by 1,10-phenanthroline and by antimycin. It is suggested that DDC might amplify cell damage by forming intracellular, loosely-bound complexes with copper and probably also by depleting antioxidant thiols. It is also suggested that “cocktails” containing oxidants, membrane-damaging agents, DDC, and SNP might be beneficial for killing of tumor cells in vivo and for the assessment of the toxicity of xenobiotics in vitro.

Attenuation of Mammary Duct Development by Menhaden Oil in BALB/c Mice

The predominant polyunsaturated fatty acids of the n-6 family found in corn oil (CO) are crucial for normal mammary duct formation when fed to animals. However, as shown here, not all polyunsaturated fatty acids are equally effective in stimulating mammary gland development. The n-3 fatty acids in a 10% menhaden oil (MO) diet fed to mice effectively reduced both the diameter and the length of the growing mammary ducts. Previously, we demonstrated a similar reduction in duct growth by feeding a 10% fat diet high in those saturated fats found in hydrogenated cotton seed oil. The inhibited rate of duct maturation caused by hydrogenated cotton seed oil was reversed when the mice were allowed to mature on a diet containing n-6 fatty acids prior to feeding the saturated fat diet. The addition of 1% CO to a 9% hydrogenated cotton seed oil diet fed to immature mice was also sufficient to restore duct growth. Mice fed menhaden oil diets, on the other hand, continued to show impaired ductal growth well into adulthood. Examination of the ovaries from MO-fed mice as compared with CO-fed mice revealed significantly fewer corpora lutea. When exogenous progesterone was given to MO-fed mice, ductal growth was partially restored, but not to the extent seen in mice fed corn oil diets. Investigation of the fatty acid contents of livers of these mice revealed reduced amounts of arachidonate (20:4) in MO-fed mice when compared with CO-fed animals. The addition of 1% CO to the 9% MO diets did not alter the arachidonate content, indicating a block in the conversion of linoleate (18:2) to 20:4 by the n-3 fatty acids. Hence, dietary n-6 fatty acids are essential for normal mammary ductal development when fed prior to maturation. Although saturated rats are ineffective, n-3 fatty acids can partially substitute for the required n-6 fatty acids in both ductal and ovarian development.

Measurement of arachidonate and its metabolites extracted from human normal and malignant gastrointestinal tissues.

This is the first report of human gastrointestinal arachidonate and prostanoids measured quantitatively by gas chromatography-mass spectrometry (GC-MS) in extracts of human cancers and macroscopically normal tissues from the stomach and colon. There were microgram/g amounts of arachidonate, and the particularly high yield from the tumours may explain why they usually produce more prostaglandins than the normal tissues in which they arise. There was only a small conversion of the arachidonate into prostanoids. 6-Keto-PGF1 alpha was the most abundant metabolite measured, particularly in the tumour extracts, with smaller amounts of prostaglandins E2, F2 alpha and D2.

Fatty acid composition of cultured aortic cells from white carneau and show racer pigeons

Summary Cell cultures have been established from aortic intimal tissue of White Carneau and Show Racer pigeons. Analyses of the higher fatty acid (> laurate) compositioni of the cultures revealed the absence of arachidonate in aortic cells from atherosclerosis-susceptible White Carneaux. A metabolic defect in the formation of arachidonate by these cells is suggested since aortic cells cultured from atherosclerosis-resistant Show Racers have the normal amount of arachidonate.