Inhibition of blood platelet aggregation by dioxo-ene compounds.

Compounds with a conjugated oxo-ene-oxo system were tested for inhibition of blood platelet aggregation. All compounds with this structure in trans configuration were effective inhibitors of aggregation induced by thrombin and by arachidonic acid. While the oxo-trans-ene-oxo system is prerequisite for such activity, other structural features of the compounds may be varied without loss of activity. Inhibition is exemplified by 9,12-dioxo-trans-10- and 10,13-dioxo-trans-11-octadecenoic acids and their methyl esters, by 11,14-dioxo-trans-12- eicosenoic acid, by 4,7-dioxo-trans-5- decene and by trans- dibenzoylethylene . The half-inhibition concentrations are in the order of 2-6 microM, with complete inhibition at 8-20 microM. According to experiments with the inhibiting 9,12-dioxo-trans-10-octadecenoic acid, the normal oxygenation of exogenous arachidonic acid by platelets is not affected but the thrombin-induced internal release of this acid seems to be abolished by the inhibitor. The inhibition of aggregation in the presence of exogenous arachidonic acid and its products suggests that the inhibitor also interferes with other events leading to aggregation. By implication from other properties of the oxo-trans-ene-oxo system, reaction with SH groups may be a mechanism for inhibition.

Metabolism of furan fatty acids in fish.

In vivo experiments on interconversions of furan fatty acids in fish are described. Administration of 2- or 3-14C-labelled furan fatty acids showed that the heterocycle does not interfere with conversions at the carboxyl group, such as shortening and elongating the chain, or its reduction to alcohol. There was no indication for desaturation of proximal chains, methylation or demethylation of the ring, or changes in the terminal chains. According to these restricted metabolic correlations, the furan fatty acids can be classified in specific structural families of bis-homologs. Distinct parent furan compounds are likely for each of these families. [1-14C]Acetate was incorporated by fish into furan fatty acids. Their chemical oxidation showed that only the resulting dicarboxylic fragments were labelled. They represent the proximal chain including alpha-C of the ring. Label was not found in the monocarboxylic acids which represent terminal chains with alpha'-C, and ring-methyl substituents with beta- and beta'-C. Accordingly, fish do not synthesize from acetate the terminal alkyl chain including the carbons in the cyclic portion of the furan fatty acids.

Catabolism of fish furan fatty acids to urofuran acids in the rat.

A mixture of long-chain furan fatty acids was prepared as methyl esters from testes lipids of Northern pike (Esox lucius). Upon feeding these esters to rats, dicarboxylic acids, which still contained the furan structure, were found in the urine. The first phase of a rapid but incomplete catabolism is beta-oxidation of the proximal chain of the furan fatty acids. It proceeds to a distance of three carbon atoms from the ring. omega-Oxidation of the terminal alkyl chain, followed by alpha-oxidation gives rise to a second alkylcarboxyl chain with five carbon atoms or less. The ring methyl substituents of the precursor acids seem to be more resistant to oxidation than the alkyl substituent with three or five carbon atoms. The urinary catabolites from furan fatty acids in the rat are similar to furan acids found in human urine, but only one of the structures occurs in both sources.

Reduction of fatty acids to alcohols in roe of gourami (Trichogaster cosby).

Reduction of fatty acids to alcohols in gourami roe homogenates and fractions thereof was studied. The reducing activity is associated with the microsomal fraction. Activation of the acid and NADPH as reducing cofactor are required. The optimal pH for reduction is between 6.5 and 7.5. Reduction rates were highest for palmitic acid and were about half of that for oleic and linoleic acids. In contrast to the equal reduction rates of the latter acids in vitro, the percentages of oleyl and linoleyl alcohols in wax esters are greatly different in vivo. Very small amounts of aldehyde are found during the reduction and some substrate label is incorporated into the phospholipids. The traces of triacylglycerols in roe lipids are not markedly labelled. In homogenates, newly formed as well as added substrate alcohol is efficiently incorporated into wax esters. Roe homogenate is capable also of oxidizing fatty alcohol to acid. In contrast to reduction, oxidation proceeds with either NADP+ or NAD+ as cofactor. Only a small portion of the newly formed acid is esterified.

Oxidation of fatty alcohols to acids in the caecum of a gourami (Trichogaster cosby).

Oxidation of fatty alcohols to acids in gourami caeca was investigated by measuring the reduction of NAD+ and the formation of labeled hexadecanoic acid from [1(-14)C]hexadecanol. Virtually all dehydrogenase activity is in the microsomal fraction. Maximal activity is obtained with NAD+ as cofactor whereas with NADP+ 60% of that activity is obtained. The enzyme is rather specific for long chain alcohols and 2 NADH are formed for each molecule of hexadecanol oxidized to acid. It is stabilized by mercaptoethanol, and completely inhibited by p-chloromercuribenzoate. The activity is optimal at pH 9.5. At higher pH, small amounts of aldehyde are found. The first reaction in the sequence, fatty alcohol leads to aldehyde leads to acid seems to occur under the more physiological condition at a much slower rate than the second reaction so that free aldehyde is not detected. Addition of palmitic acid indicated an uncompetitive product inhibition. The oxidation of alcohol to acid is reversible only to a very minor extent even in the presence of NADPH, CoA, ATP and Mg2+. Location, activity and properties of the enzyme are in agreement with the earlier observation from dietary experiments that in the gourami fatty alcohols of wax esters are oxidized to acids in the course of absorption.

Metabolism of oleic, linoleic and linolenic acids in gourami (Trichogaster cosby) fry and mature females.

1. Female gouramis incorporated pulse-fed [U-14C]oleic, linoleic and linolenic acids more readily into roe than body lipids. Labeling was highest in eggs spawned 20-30 days after feeding. 2. In the fry, linoleic and linolenic were catabolized more slowly than oleic acid, indicating conservation of the polyunsaturated acids in the early stage of life. 3. In the mature female, metabolism of linolenic was distinct from that of the other acids by more extensive conversions and greater use of 14C for de novo synthesis of fatty acids.

Furanoid fatty acids from fish lipids.

Fatty acids, recently reported as constituents of certain fish lipids, were identified to be derivatives of furan (furanoid fish fatty acids). 12,15-Epoxy-13,14-dimethyleicosa-12,14-dienoic acid is predominant among the furan acids and is associated with bis-homologs in regard to chain length. Monomethyl acids, such as 12,15-epoxy-13-methyleicosa-12,14-dienoic, are present in appreciable amounts. The structures were concluded from oxidative degradations, from mass spectrometry of methyl esters of the novel acids and fatty acids derived from them by opening the ring, and from nuclear magnetic resonance, infrared, and Raman spectra. The results from chemical procedures and from spectrometric methods were in agreement with those obtained with authentic methyl 9,12-epoxyoctadeca-9,11-dienoate. The number of substituents at the furan ring greatly influences hydrogenation, hydrogenolysis, and hydrolysis reactions of the ring.

Wax esters in fish: Turnover of oleic acid in wax esters and triglycerides of gouramis.

Methyl U-(14)C oleate was fed to mature male and female gouramis (Trichogaster cosby) and the radioactivity in lipids measured over a period of four months. Initial incorporations were 70-80% and more than half of that was still in the lipids at the end of the experiment. Very little conversion of the 18∶1 chain had occurred. Main storage of the labeled 18∶1 chain was in the wax esters of the roe and in the triglycerides of the body. In the wax esters, 18∶1 occurred in both the alcohol and acid moieties. Initially the females had less radioactivity in the triglycerides than in the wax esters but at the end of the experiment this was reversed. An appreciable amount of 18∶1 had been transferred from roe to body lipids. The biological half life of 18∶1 in gouramis is estimated to be about four months. This time is equal for males and females although translocation from roe to body and transformation of wax ester to triglyceride take place in the female, whereas wax esters do not play any role in the lipid metabolism of the male.