omega-Hydroxylation of docosahexaenoic acid or arachidonic acid in human colonic well differentiated adenocarcinoma homogenate

Metabolism pathways of arachidonic acids: mechanisms and potential therapeutic targets

The arachidonic acid (AA) pathway plays a key role in cardiovascular biology, carcinogenesis, and many inflammatory diseases, such as asthma, arthritis, etc. Esterified AA on the inner surface of the cell membrane is hydrolyzed to its free form by phospholipase A2 (PLA2), which is in turn further metabolized by cyclooxygenases (COXs) and lipoxygenases (LOXs) and cytochrome P450 (CYP) enzymes to a spectrum of bioactive mediators that includes prostanoids, leukotrienes (LTs), epoxyeicosatrienoic acids (EETs), dihydroxyeicosatetraenoic acid (diHETEs), eicosatetraenoic acids (ETEs), and lipoxins (LXs). Many of the latter mediators are considered to be novel preventive and therapeutic targets for cardiovascular diseases (CVD), cancers, and inflammatory diseases. This review sets out to summarize the physiological and pathophysiological importance of the AA metabolizing pathways and outline the molecular mechanisms underlying the actions of AA related to its three main metabolic pathways in CVD and cancer progression will provide valuable insight for developing new therapeutic drugs for CVD and anti-cancer agents such as inhibitors of EETs or 2J2. Thus, we herein present a synopsis of AA metabolism in human health, cardiovascular and cancer biology, and the signaling pathways involved in these processes. To explore the role of the AA metabolism and potential therapies, we also introduce the current newly clinical studies targeting AA metabolisms in the different disease conditions.

Simultaneous quantitative determination method for ceramide species from crude cellular extracts by high-performance liquid chromatography-thermospray mass spectrometry

I have developed a simple method which enabled simultaneous analysis of ceramides in the subcellular fractions from cultured cells by HPLC-thermospray mass spectrometry. The HPLC-thermospray mass spectra from ceramide standards were characterized by the high intensity of the MNa(+) and MH(+)-H(2)O ions. As the other minor ions, MK(+), MH(+) and m/z 282 ions were detected. Although the preponderance of MNa(+) ions compared with the MH(+)-H(2)O ions was detected in non-hydroxy fatty acid-ceramides, the preponderance of MH(+)-H(2)O ions based on the elimination of the hydroxyl group introduced at the alpha-position of acyl-portion compared with the MNa(+) ions was detected in alpha-hydroxy fatty acid-ceramides. In calibrations for authentic ceramides using N-octanoylsphingosine as an internal standard, an approximately linear relationship existed between the ratios of peak-areas of each ceramide to that of the internal standard and the known amounts of each ceramide. The factor (f) of each ceramide was calculated as follows; N-oleoyl-D-sphingosine (f=0.45), N-palmitoyl-D-sphingosine (f=0.40), N-stearoyl-D-sphingosine (f=0.39), N-nervonoyl-D-sphingosine (f=0.39) and N-lignoceroyl-D-sphingosine (f=0.35). In subcellular fractions from A549 and HepG2 cells, although ceramide species content per mg protein was high in the nuclear envelope fractions, the 7000 g pellet fractions and the 100000 g pellet fractions, a large portion of the ceramide species was concentrated in the nuclear envelope fraction. In addition, this method was applied to a mild alkaline hydrolyzate of total ceramides from pig stratum corneum, and MNa(+)/MH(+)-H(2)O ions corresponding to several omega-hydroxyacyl-ceramides were detected.

Docosahexaenoic/arachidonic acid omega-hydroxylation system and differentiation in the human colonic adenocarcinoma cell line, Caco-2

The homogenate from Caco-2 cells of day 13 or 15 after subculturing had high omega-hydroxylation activity of docosahexaenoic acid (22:6(n-3)) or arachidonic acid (20:4(n-6)). Activity, maximal at pH 8.0, was inhibited in the presence of CO or metyrapone and in the absence of NADPH. Omega-hydroxylation activity of lauric acid in the homogenate was not detected. Apparent Michaelis constant (Km) values for 22:6(n-3) and 20:4(n-6) were found to be 4 and 7 microM. Omega-hydroxylation activity considerably increased with growth up to day 13 and then decreased until day 20 even though alkaline phosphatase (ALP) and leucine-aminopeptidase (LAP) activity increased with growth to day 20. Metyrapone in cultures caused omega-hydroxylation, ALP and LAP activity to decrease, while sodium butyrate dose-dependently increased that of omega-hydroxylation, ALP and an endogenous endonuclease and decreased lactate dehydrogenase (LDH) activity in culture medium. The omega-hydroxylation system thus appears quite likely to be associated with cytochrome P450, differentiation and/or apoptosis rather than cytotoxic cell death of Caco-2 cells. Substrate specificity, however, differed from that of human cytochrome P450 4A11.

High-performance liquid chromatography-thermospray mass spectrometry of 5,6-dihydroxyeicosatrienoate-1,5-lactone from tissue homogenates

We have developed a method for the analysis of 5,6-dihydroxyeicosatrienoate-1,5-lactone (5,6-DiHETriE-delta-lactone) in tissue homogenates, supplemented with NADPH and arachidonic acid [20:4(n-6)] as a substrate. During the incubation and the extraction, most of the 5,6-epoxyeicosatrienoic acid (5,6-EpETriE) was converted to 5,6-dihydroxyeicosatrienoic acid (5,6-DiHETriE), and most of the 5,6-DiHETriE was converted to 5,6-DiHETriE-delta-lactone. Consequently, the chief degradation product of 5,6-EpETriE and 5,6-DiHETriE in the incubation mixture was 5,6-DiHETriE-delta-lactone. 5,6-DiHETriE-delta-lactone, corresponding to [20:4(n-6)], was shown to be characterized by a high intensity of quasimolecular ions (MH+ and MNH4+), using ion analysis obtained by reversed-phase HPLC-thermospray MS. On selected-ion monitoring (SIM) chromatograms of 5,6-DiHETriE-delta-lactone and with deuterium-labeled 15(S)-hydroxyeicosatetraenoic acid as the internal standard, the regression equation of the peak-area ratio and the amount of 5,6-DiHETriE-delta-lactone was y = 12.2x + 0.7 (r = 0.9996). 5,6-Epoxygenase activity was represented as the sum of the amount of 5,6-DiHETriE-delta-lactone, 5,6-EpETriE and 5,6-DiHETriE per mg protein, after 30 min in an incubation mixture. The activity from rat brain homogenate decreased considerably with growth of the rat.

Subcellular localization of docosahexaenoic acid and arachidonic acid omega-hydroxylation activity in the brain, liver and colonic adenocarcinoma

A homogenate of rat brain, rat liver or human colonic well differentiated adenocarcinoma was prepared in 250 mM sucrose isoosmolaric buffer (pH 7.6) and fractionated by differential centrifugation at 10(3), 10(4) and 10(5) g. Each precipitate or supernatant was incubated with NADPH and docosahexaenoic acid or arachidonic acid as a substrate for 30 min at 37 degrees c under aerobic conditions. omega-Hydroxydocosahexaenoic acid or omega-hydroxyeicosatetraenoic acid from an incubation mixture was detected by reversed-phase high-performance liquid chromatography-thermospray mass spectrometry with selected-ion monitoring. omega-Hydroxy polyunsaturated fatty acids were characterized by high intensity of the molecular ion (MH+) although common hydroxy polyunsaturated fatty acids were characterized by high intensity of the MH+ -H2O ion. For the rat brain, omega-hydroxylation activity (the amount of omega-hydroxy product produced in 30 min) was concentrated to a 10(3) g precipitate although the specific activity (the activity per 1 mg of protein) in the 10(3) g precipitate did not indicate superiority over other fractions. However, the specific activity of the rat brain increased on addition of a 10(4) or 10(5) g precipitate. For the rat liver, although omega-hydroxylation activity was concentrated to a 10(3) g precipitate, the specific activity was concentrated to a 10(5) g precipitate and the subcellular localization differed from that of rat brain. In the human colonic well differentiated adenocarcinoma, although omega-hydroxylation activity was relatively high in the 10(3) g supernatant, the specific activity was relatively high in the 10(3) g precipitates. These results suggest that there is a difference regarding subcellular localization of the omega-hydroxylation activity depending on the species of the organs.

Properties of the omega-hydroxylation system of docosahexaenoic or arachidonic acid in brain or liver homogenate of rat

The homogenate of a brain or liver obtained from a 1-55-day-old rat was incubated with NADPH and docosahexaenoic or arachidonic acid as the substrate. omega-Hydroxydocosahexaenoic or omega-hydroxyeicosatetraenoic acid from an incubation mixture of the homogenate was detected on a selected-ion monitoring chromatogram of reversed phase-HPLC-thermospray-mass spectrometry. omega-Hydroxylation activity in the brain homogenate considerably increased with growth up to 55 days. Activity in the liver homogenate decreased much with growth up to 55 days. omega-Hydroxylation activity in homogenates of rat brain gray matter, white matter, medula oblongata and cerebellum was much the same. omega-Hydroxylation activity of docosahexaenoic acid in rat brain homogenate was maximal at pH 7.5-8.0 in 50 mM Tris-HCl buffer and was inhibited by CO gas, metyrapone, ADP-Fe3+, heat treatment at 100 degrees C for 5 min and without NADPH. Based on these results, it is suggested that omega-hydroxylation activity is associated with cytochrome P-450 without NADPH-ADP-Fe(3+)-dependent lipid peroxidation, and the omega-hydroxylation system may be a metabolic pathway of the fatty acids in adult rat brain or neonatal rat liver. Since omega-hydroxyeicosatetraenoic acid produces relaxation of artery, it is suggested that blood flow changes in rat brain or liver with growth are caused by omega-hydroxylation activity changes in these organs with growth.