PubMed Health⌕ Search

Biomedical subjects

M VanRollins

Publications and source records attributed to M VanRollins.

31 records · Page 2Linked to original sources
PubMed1992

Mechanism of action of cerebral epoxyeicosatrienoic acids on cerebral arterial smooth muscle.

Microsomal preparations of cat brain incubated with [14C]arachidonic acid produced epoxyeicosatrienoic acids (EETs) that eluted with the same retention times as synthetically prepared 5,6-, 8,9-, and 11,12-EETs. These compounds dilated serotonin-preconstricted, pressurized cat cerebral arteries in a dose-dependent fashion. Epoxide formation was not found in mitochondrial fractions and was dependent on the presence of NADPH. The maximum effects of 8,9-EET and 11,12-EET were greater than those of 5,6-EET. The cellular basis of this vasodilation was further investigated by examining the effects of 8,9-EET and 11,12-EET on K+ channel activity in vascular muscle cells freshly isolated from cat cerebral arteries. Both 8,9-EET and 11,12-EET increased the frequency of opening, mean open time, and open-state probability of a 98-pS K+ channel recorded in the cell-attached mode with 145 mM KCl in the pipette and 4.7 mM KCl in the bath. Blockade of K+ channel activity with tetraethylammonium attenuated the vasodilatory effects of 11,12-EET on serotonin-preconstricted cat cerebral arteries. These results suggest that endogenously formed EETs may participate in local regulation of cerebral blood flow by dilating cerebral arteries through a mechanism that involves activation of K+ channels.

8,11,14-Eicosatrienoic Acid↗
PubMed1990

Synthesis and characterization of cytochrome P-450 epoxygenase metabolites of eicosapentaenoic acid.

Eicosapentaenoic acid, a major component of fish oil extracts, was recently shown to be metabolized to vicinal diol regioisomers by renal and hepatic cytochrome P-450 epoxygenases. The diol products were also found in the urine of people ingesting fish oil. In the present report, we developed a chemical method of making milligram amounts of the epoxide intermediates and their diol products. Eicosapentaenoic acid was reacted with 0.1 eq. m-chloroperoxybenzoic acid for 15 min. After normal- and reverse-phase high performance liquid chromatography plus capillary gas chromatography and electron impact mass spectrometry, the products were identified as 17,18-cis-epoxy-eicosa-5,8,11,14-tetraenoic, 14,15-cis-epoxy-eicosa-5,8,11,17-tetraenoic, 11,12-cis-epoxy-eicosa-5,8,14,17-tetraenoic, 8,9-cis-epoxy-eicosa-5,11,14,17-tetraenoic and 5,6-cis-epoxy-eicosa-8,11,14,17-tetraenoic acids. The total epoxide yield from eicosapentaenoate was 10% per incubation. By reincubating (cycling) the unused substrate 10-20 times, the total epoxide yield could be increased to 66-88%. Epoxide regioisomers were not produced in equal amounts; epoxygenation was facilitated as the distance between the target double bond and carbomethoxy group increased. Upon hydrolyzing the epoxides, the gas-chromatographic retention times and mass spectra of the diol products were found to match those of biological metabolites. In addition, each of these standards was rapidly and quantitatively synthesized in an amount (milligram) adequate for biological tests.

Chlorobenzoates↗
PubMed1989

Synthesis of epoxide and vicinal diol regioisomers from docosahexaenoate methyl esters.

Docosahexaenoic acid (22:6(n-3)) was recently shown to be metabolized by liver microsomes to vicinal diol regioisomers. To identify the diols, and to compare their biological actions with those of epoxide precursors, we developed a chemical method to synthesize microgram to milligram amounts of epoxides and corresponding diols. In brief, methylated docosahexaenoate was reacted for 15 min with 0.1 eq m-chloroperoxybenzoic acid. After normal- and reverse-phase high performance liquid chromatography, six products were isolated. The underivatized or hydrogenated products were characterized and identified using capillary gas-liquid chromatography and mass spectrometry. The products were identified as 19,20-, 16,17-, 13,14-, 10,11-, 7,8-, and 4,5-epoxy-docosapentaenoate. Per incubation, the total epoxide yield from 22:6(n-3) was 8.6%. By reincubating unused substrate 10-20 times (cycling), the total epoxide could be increased to 55-70%. As found for epoxides of arachidonic and eicosapentaenoic acids, the yield of individual regioisomers increased as the distance between the targeted double bond and carbomethoxy group increased. Each epoxide regioisomer was hydrolyzed to its corresponding vicinal diol. The gas-liquid chromatographic retention times and mass spectra of the diol products were found to match those of metabolites produced by cytochrome P-450 monooxygenases.

Chemical Phenomena↗
PubMed1985

Metabolism of 7,10,13,16-docosatetraenoic acid to dihomo-thromboxane, 14-hydroxy-7,10,12-nonadecatrienoic acid and hydroxy fatty acids by human platelets.

Human platelets metabolize 7,10,13,16-docosatetraenoic acid (22:4(n - 6)) into dihomo-thromboxane B2 and 14-hydroxy-7,10,12-nonadecatrienoic acid at about twenty percent of the rate they convert arachidonic acid to thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid. 14-Hydroxy-7,10,12,16-docosatetraenoic was the major metabolite produce via the lipoxygenase pathway. Several other hydroxy acids were also produced in small amounts via an indomethacin-insensitive pathway. Incubation of 20 microM arachidonic acid with various levels of 22:4(n - 6) resulted in a dose-dependent inhibition of both thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid production. Conversely, 12-hydroxy-5,8,10,14-eicosatetraenoic acid synthesis was stimulated because of substrate shunting to the lipoxygenase pathway. These results show that 22:4(n - 6) may modify platelet function both by serving as a precursor for a 22-carbon thromboxane and by suppressing the synthesis of thromboxane A2 from arachidonic acid. In addition, our results suggest that simultaneous release of 22:4(n - 6) and arachidonic acid from platelet phospholipids will result in an elevation of both 12-hydroxy-5,8,10,14-eicosatetraenoic acid levels as well as simultaneous synthesis of 14-hydroxy-7,10,12,16-docosatetraenoic acid.

Blood Platelets↗
PubMed1984

Oxidation of docosahexaenoic acid by rat liver microsomes.

[1-14C]Docosahexaenoic acid (n-3) was incubated at 37 degrees C for 30 min in the presence of rat liver microsomes and 1 mM NADPH. The products were isolated using organic solvent extractions, reverse phase, and normal phase high performance liquid chromatography. Isolates were identified using ultraviolet spectroscopy, capillary gas-liquid chromatography, and gas chromatography-mass spectrometry. The major metabolites were: 19,20-, 16,17-, 13,14-, 10,11-, and 7,8-dihydroxydocosapentaenoic acids, 22-hydroxydocosahexaenoic acid, and 21-hydroxydocosahexaenoic acid. The minor metabolites were 17-hydroxy-4,7,10,13,15,19-, 16-hydroxy-4,7,10,17,19-, 14-hydroxy-4,7,10,12,-16,19-, 13-hydroxy-4,7,10,14,16,19-, 11-hydroxy-4,7,9,13,16,19-, 10-hydroxy-4,7, 11,13,16,19-, 8-hydroxy-4,6,10,13,16,19-, and 7-hydroxy-4,8,10,13,16,19 -docosahexaenoic acids. These metabolites of docosahexaenoic acid resulted from four distinct classes of oxidation, omega-hydroxylations, (omega-1)-hydroxylations, epoxidations, and lipoxygenase-like hydroxylations. The similarity of these product profiles to those reported for comparable microsomal incubations with other essential fatty acids suggest that microsome cytochrome P-450 monooxygenases were involved.

Animals↗
PubMed1984

Autooxidation of docosahexaenoic acid: analysis of ten isomers of hydroxydocosahexaenoate.

Docosahexaenoic acid, an n-3 essential fatty acid, was recently shown to be enzymically converted by platelets, basophils, and liver microsomes into metabolites containing conjugated dienes with allylic hydroxyl groups. To help identify these metabolites, standards were prepared by autooxidation of docosahexaenoic acid. After isolation by reverse phase and normal phase high performance chromatography (HPLC), ten hydroxy isomers of docosahexaenoic acid were identified by capillary gas-liquid chromatography, ultraviolet spectroscopy, and mass spectrometry. From these studies and reported elution orders for similar metabolites derived from linoleic, linolenic, and arachidonic acids, two basic HPLC elution patterns became apparent. Under reverse phase chromatography conditions, the distance of the trans-double bond from the carboxyl group was the critical parameter in determining the elution order. Under silicic acid chromatography conditions, the distance of the hydroxyl from the carbomethoxy group seemed to determine the elution order. The dramatic difference in selectivity between reverse and normal phase HPLC of the hydroxy acids provides critical information useful for identifying endogenous metabolites.

Chromatography, Gas↗
PubMed1983

Lipoxygenase pathway in islet endocrine cells. Oxidative metabolism of arachidonic acid promotes insulin release.

Metabolism of arachidonic acid (AA) via the cyclooxygenase pathway reduces glucose-stimulated insulin release. However, metabolism of AA by the lipoxygenase pathway and the consequent effects on insulin secretion have not been simultaneously assessed in the endocrine islet. Both dispersed endocrine cell-enriched pancreatic cells of the neonatal rat, as well as intact islets of the adult rat, metabolized [(3)H]AA not only to cyclooxygenase products (prostaglandins E(2), F(2alpha), and prostacyclin) but also to the lipoxygenase product 12-hydroxyeicosatetraenoic acid (12-HETE). 12-HETE was identified by coelution with authentic tritiated or unlabeled 12-HETE using four high performance liquid chromatographic systems under eight mobile-phase conditions and its identity was confirmed by gas chromatography/mass spectrometry using selected ion monitoring. The predominant effect of exogenous AA (5 mug/ml) was to stimulate insulin release from pancreatic cells grown in monolayer. This effect was concentration- and time-dependent, and reversible. The effect of AA upon insulin release was potentiated by a cyclooxygenase inhibitor (indomethacin) and was prevented by either of two lipoxygenase inhibitors (5,8,11,14-eicosatetraynoic acid [ETYA] and BW755c). In addition, glucose, as well as two structurally dissimilar agents (the calcium ionophore A23187 and bradykinin), which activate phospholipase(s) and thereby release endogenous AA in several cell systems, also stimulated insulin secretion. The effects of glucose, glucagon, bradykinin and high concentrations of A23187 (5 mug/ml) to augment insulin release were blocked or considerably reduced by lipoxygenase inhibitors. However, a lower concentration of the ionophore (0.25 mug/ml), which did not appear to activate phospholipase, was resistant to blockade. Exogenous 12-HETE (up to 2,000 ng/ml) did not alter glucose-induced insulin release. However, the labile intermediate 12-hydroperoxy-ETE increased insulin release. Furthermore, diethylmaleate (which binds intracellular glutathione and thereby impedes conversion of the lipoxygenase intermediates hydroperoxy-ETE and leukotriene A(4) to HETE and leukotriene C(4), respectively) potentiated the effect of glucose and of exogenous AA. Finally, 5,6-epoxy, 8,11,14-eicosatrienoic acid (a relatively stable epoxide analogue of leukotriene A(4)) as well as two other epoxy-analogues, potentiated glucose-induced insulin release. We conclude that dual pathways of AA metabolism exist in islet endocrine cells and have opposing regulatory effects on the beta cell-an inhibitory cyclooxygenase cascade and a stimulatory lipoxygenase cascade. Labile products of the latter pathway may play a pivotal role in stimulus-secretion coupling in the islet.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1983

Separation and quantitation of free fatty acids and fatty acid methyl esters by reverse phase high pressure liquid chromatography.

Reverse phase high pressure liquid chromatography (HPLC) on octadecylsilyl columns separates mixtures of either free fatty acids or fatty acid methyl esters prepared from mammalian tissue phospholipids. Acetonitrile-water mixtures are used for the elution of esters. Aqueous phosphoric acid is substituted for water for the separation of the free acids. Unsaturated compounds are detected and quantitated by their absorption at 192 nm. Saturates are detected better at 205 nm. The order of elution of fatty acids in complex mixtures varies as a function of acetonitrile concentration. At any given concentration, some compounds overlap. However, by varying the solvent strength, any fatty acid of interest can be resolved including many geometrical and positional isomers. Methyl esters prefractionated according to unsaturation by argentation thin-layer chromatography (TLC) are rapidly and completely separated by elution with CH3CN alone. Argentation TLC-reverse phase HPLC can be used as an analytical as well as a preparative procedure. Octylsilyl columns are used for rapid resolution and improved detection of minor or low ultraviolet-absorbing components in the fractions. For example, monoenoic fatty acids with up to 32 carbons have been detected in bovine brain glycerophospholipids. Specific radioactivities of 3H- and 14C-labeled fatty acids and the distribution of radioactivity among acyl groups from complex lipids are measured. The method is not recommended for complete compositional analysis, but is useful for determinations of specific radioactivities during studies on turnover and metabolic conversions of labeled fatty acids.

Animals↗
PubMed1981

Selective inhibitors of platelet lipoxygenase: 4,7,10,13-eicosatetraynoic acid and 5,8,11,14-henicosatetraynoic acid.

Nine acetylenic acids were evaluated to determine what structural features are required for selective inhibition of platelet lipoxygenase. Both 4,7,10,13-icosatetraynoic acid and 5,8,11,14-henicosatetraynoic acid inhibited the synthesis of 12-L-hydroxy-5,8,10,14-icosatetraenoic acid (HETE) more than 95 percent without significantly altering the production of either thromboxane B2 or 12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT). The ID50 concentrations (microM) for inhibiting the synthesis of thromboxane B2 and HETE were respectively 51 and 0.46 with 4,7,10,13-icosatetraynoic acid while similar concentrations of 64 and 0.31 were found for 5,8,11,14-henicosatetraynoic acid.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1980

Complete separation by high performance liquid chromatography of metabolites of arachidonic acid from incubation with human and rabbit platelets.

Separation of all major cyclooxygenase and lipoxygenase metabolites of arachidonic acid were obtained by high performance liquid chromatography (HPLC). A C18 reverse-phase column was used in ion suppression mode to separate underivatized metabolites of arachidonic acid isolated from human and rabbit platelets. The metabolites were monitored by measuring radioactivity or ultraviolet light absorption at 192 nm (absorption by double bonds). Comparisons of TLC and HPLC separations demonstrated that the HPLC separation of metabolites of [1-14C]arachidonic acid was quantitative. HPLC also resolved several metabolites that were not detected by scanning of TLC separations.

Animals↗