Role of glutathione and glutathione peroxidase in human platelet arachidonic acid metabolism

Selective removal of intracellular glutathione (GSH) and inhibition of the GSH-dependent peroxidase (GSH-Px) by 1-chloro-2, 4-dinitrobenzene (CDNB) was used to evaluate the role of GSH and GSH-Px in arachidonic acid (AA) metabolism in human platelets. Although total conversion of AA through the lipoxygenase pathway is lowered by GSH depletion, significant 12-HETE formation was observed suggesting that GSH and GSH-Px are not required for the generation of 12-HETE in human platelets. Prolonged treatment of platelets with CDNB (2 h) completely destroyed GSH-Px activity creating a model in which the effects of GSH alone could be determined. Platelet homogenates replenished with GSH, but lacking GSH-Px activity converted significantly higher amounts of AA to 12-HPETE and 12-HETE than control. Platelet cytosolic metabolism of 15-HPETE to 15-HETE decreased after CDNB, while the membrane metabolism remained similar to control due to high GSH-independent peroxidase activity associated with the membranes. These results indicate that GSH and GSH-Px function to enhance lipoxygenase activity, rather than catalyse the reduction of 12-HPETE to 12-HETE.     

Role of glutathione and glutathione peroxidase in human platelet arachidonic acid metabolism

Selective removal of intracellular glutathione (GSH) and inhibition of the GSH-dependent peroxidase (GSH-Px) by 1-chloro-2,4-dinitrobenzene (CDNB) was used to evaluate the role of GSH and GSH-Px in arachidonic acid (AA) metabolism in human platelets. Although total conversion of AA through the lipoxygenase pathway is lowered by GSH depletion, significant 12-HETE formation was observed suggesting that GSH and GSH-Px are not required for the generation of 12-HETE in human platelets. Prolonged treatment of platelets with CDNB (2 h) completely destroyed GSH-Px activity creating a model in which the effects of GSH alone could be determined. Platelet homogenates replenished with GSH, but lacking GSH-Px activity converted significantly higher amounts of AA to 12-HPETE and 12-HETE than control. Platelet cytosolic metabolism of 15-HPETE to 15-HETE decreased after CDNB, while the membrane metabolism remained similar to control due to high GSH-independent peroxidase activity associated with the membranes. These results indicate that GSH and GSH-Px function to enhance lipoxygenase activity, rather than catalyse the reduction of 12-HPETE to 12-HETE.     

Deletion of soluble epoxide hydrolase gene improves renal endothelial function and reduces renal inflammation and injury in streptozotocin-induced type 1 diabetes

Studies suggest that soluble epoxide hydrolase (sEH) inhibition reduces end-organ damage in cardiovascular diseases. We hypothesize that sEH gene (Ephx2) knockout (KO) improves endothelial function and reduces renal injury in streptozotocin-induced diabetes. After 6 wk of diabetes, afferent arteriolar relaxation to acetylcholine was impaired in diabetic wild-type (WT) mice, as the maximum relaxation was 72% of baseline diameter in the WT but only 31% in the diabetic mice. Ephx2 KO improved afferent arteriolar relaxation to acetylcholine in diabetes as maximum relaxation was 58%. Urinary monocyte chemoattractant protein-1 (MCP-1) excretion significantly increased in diabetic WT mice compared with control (868 ± 195 vs. 31.5 ± 7 pg/day), and this increase was attenuated in diabetic Ephx2 KO mice (420 ± 98 pg/day). The renal phospho-IKK-to-IKK ratio and nuclear factor-κB were significantly decreased, and hemeoxygenase-1 (HO-1) expression increased in diabetic Ephx2 KO compared with diabetic WT mice. Renal NADPH oxidase and urinary thiobarbituric acid reactive substances excretion were reduced in diabetic Ephx2 KO compared with diabetic WT mice. Albuminuria was also elevated in diabetic WT mice compared with control (170 ± 43 vs. 37 ± 13 μg/day), and Ephx2 KO reduced this elevation (50 ± 15 μg/day). Inhibition of sEH using trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (tAUCB) also reduced renal inflammation and injury in diabetic WT mice. Furthermore, inhibition of HO with stannous mesoporphyrin negated the reno-protective effects of tAUCB or Ephx2 KO during diabetes. These data demonstrate that Ephx2 KO improves endothelial function and reduces renal injury during diabetes. Additionally, our data also suggest that activation of HO-1 contributes to improved renal injury in diabetic Ephx2 KO mice.     

Effect of tert-butyl hydroperoxide on cyclooxygenase and lipoxygenase metabolism of arachidonic acid in rabbit platelets

The effect of tert-butyl hydroperoxide (t-BOOH) on the formation of thromboxane (TX) B2, 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) from exogenous arachidonic acid (AA) in washed rabbit platelets was examined. t-BOOH enhanced TXB2 and HHT formation at concentrations of 8 microM and below, and at 50 microM it inhibited the formation, suggesting that platelet cyclooxygenase activity can be enhanced or inhibited by t-BOOH depending on the concentration. t-BOOH inhibited 12-HETE production in a dose-dependent manner. When the platelets were incubated with 12-hydroperoxy-5,8,10,14-eicosatetraenoic acid (12-HPETE) instead of AA, t-BOOH failed to inhibit the conversion of 12-HPETE to 12-HETE, indicating that the inhibition of 12-HETE formation by t-BOOH occurs at the lipoxygenase step. Studies utilizing indomethacin (a selective cyclooxygenase inhibitor) and desferrioxamine (an iron-chelating agent) revealed that the inhibitory effect of t-BOOH on the lipoxygenase is not mediated through the activation of the cyclooxygenase and that this effect of t-BOOH is due to the hydroperoxy moiety. These results suggest that hydroperoxides play an important role in the control of platelet cyclooxygenase and lipoxygenase activities.     

Effects of lipoxygenase metabolites of arachidonic acid on the growth of human mononuclear marrow cells and marrow stromal cell cultures.

The effects of various lipoxygenase metabolites of arachidonic acid (AA) were investigated on the growth of freshly isolated human bone marrow mononuclear cells and marrow stromal cell cultures. LTB4, LXA4, LXB4, 12-HETE and 15-HETE (1 microM) decreased [3H]-thymidine incorporation on marrow stromal cell cultures without affecting cell number. Only 12-HETE showed a dose-response effect on [3H]-thymidine incorporation. While LTB4 (1 microM) decreased thymidine incorporation on marrow mononuclear cells, LTC4, LXA4, LXB4, 12-HETE and 15-HETE had no effect. The lipoxygenase inhibitor NDGA had no effect on both cell types suggesting no role of endogenous lipoxygenase metabolites on cell growth. These results suggest no important role of lipoxygenase metabolites of AA on the proliferation of human marrow mononuclear cells and marrow stromal cell cultures.     

12-Hydroxyeicosatetraenoic acid participates in angiotensin II afferent arteriolar vasoconstriction by activating L-type calcium channels

The lipoxygenase (LO) metabolite, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], constricts renal vessels, contributes to the vascular response to angiotensin, and has been implicated in cardiovascular and renal diseases. The current studies were performed to determine if renal microvascular 12(S)-HETE production is stimulated by angiotensin and the contribution of L-type calcium channels to the vasoconstriction elicited by 12(S)-HETE. Angiotensin increased renal microvascular 12(S)-HETE production by 64%, whereas cyclooxygenase metabolite production was not altered. Renal microvessels also expressed platelet-type 12-LO and leukocyte-type 12-LO. In the juxtamedullary preparation, afferent arteriolar diameter averaged 21 +/- 1 microm and 12(S)-HETE caused a graded decrease in vessel caliber. The afferent arteriolar response to 12(S)-HETE was abolished during L-type calcium channel inhibition. Renal microvascular smooth muscle cells were studied using fluorescence microscopy. Renal myocyte [Ca2+]i averaged 93 +/- 5 nmol/l. The 12(S)-HETE (5 micromol/l) increased myocyte [Ca2+]i to a peak value of 340 +/- 55 nmol/l. The peak [Ca2+]i response following exposure to 12(S)-HETE was greatly attenuated in the absence of extracellular Ca2+ or calcium channel blockade. These results demonstrate that renal microvascular 12(S)-HETE production is increased in response to angiotensin, and activation of L-type calcium channels is an important mechanism responsible for the afferent arteriolar vasoconstriction elicited by 12(S)-HETE.     

Optimization of an assay for studying the effects of agents on cyclooxygenase and lipoxygenase metabolism of arachidonic acid in washed human platelets

Before one can examine the effects of substances on the metabolism of arachidonic acid (AA) by the cyclooxygenase and lipoxygenase pathways, an assay system which allows one to detect increases or decreases in both pathways in needed. In order to develop such a system, we have examined nonaggregating washed human platelets (10(8) platelets/0.5 ml) incubated for various times with 2 microCi 3H-AA and increasing concentrations of AA. T/B2, HHT, 12-HETE, and AA were extracted and separated using reverse phase-HPLC. We first calculated the mass of AA products formed with 10(-7) to 10(-4) M AA and found that the cyclooxygenase was saturated with 10(-5) M AA whereas the lipoxygenase was not saturated with 10(-4) M AA. Cyclooxygenase products were more prevalent than 12-HETE below 10(-5) M AA, while lipoxygenase products predominated at 3 x 10(-5)-10(-4) M AA. Using 3 microM AA, which does not saturate the cyclooxygenase, we examined the effect of 0.25-10 minute incubation durations on the distribution of AA metabolites and found AA product formation to increase throughout this period without completely depleting the substrate. Since substrate depletion does not occur and further metabolism could be detected for both pathways with a 5 minute incubation with 3 microM AA, these incubation parameters were chosen in order to further test the assay system. Using these parameters, we found that 10(-4) M 5-hydroxytryptamine enhanced platelet 12-HETE formation and decreased T/B2 and HHT formation, thus demonstrating the capacity of this system to simultaneously detect changes in cyclooxygenase and lipoxygenase enzyme metabolism.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arachidonic acid metabolism in growth control of A549 human lung adenocarcinoma cells

The role of individual eicosanoids of the arachidonic acid (AA) cascade in the growth control of A549 human lung adenocarcinoma cells has been studied. Cyclooxygenase and lipoxygenase metabolites of [¹⁴C]AA incorporated were actively synthesized in the cultures of tumor cells with full confluence unaccomplished. In such cultures inhibitors of AA metabolism (indomethacin and esculetin) and also a lipoxygenase metabolite of AA, 15-hydroxyeicosatetraenoic acid (15-HETE), significantly suppressed the incorporation of [³H]thymidine and biosynthesis of prostaglandin E₂(PGE₂). Other lipoxygenase metabolites of AA (5-HETE and 12-HETE) had no effect on these parameters. The basic fibroblast growth factor (bFGF) had practically no affect on the growth of A549 cells and the PGE₂ production in cultures with 5% fetal calf serum (FCS); however, in the presence of 0.5% FCS this factor significantly increased the number of tumor cells. The growth-stimulating effect of bFGF was completely abolished by a cyclooxygenase inhibitor indomethacin. The data suggest a key role of PGE₂ in the growth control of A549 cells with an active synthesis of cyclooxygenase and lipoxygenase metabolites of AA, its importance in realization of the mitogenic effect of bFGF, and specific features of 15-HETE as a down-regulator of the PGE₂-dependent proliferation.     

Postmenopausal hypertension: role of 20-HETE

Blood pressure (BP) increases after menopause. However, the mechanisms responsible have not been elucidated. In this study we tested the hypothesis that 20-hydroxyeicosatetraenoic acids (20-HETE), produced by cytochrome P-450 (CYP450) ω-hydroxylase, contributes to the hypertension in a model of postmenopausal hypertension, aged female spontaneously hypertensive rats (PMR). 1-Aminobenzotriazole, a nonselective inhibitor of arachidonic acid metabolism, for 7 days, reduced BP in PMR but had no effect in young females. Acute intravenous infusion of HET-0016, a specific inhibitor of 20-HETE, over 3 h, also reduced BP in PMR. CYP4A isoform mRNA expression showed no difference in renal CYP4A1 or CYP4A3 but increases in CYP4A2 and decreases in CYP4A8. CYP4A protein expression was decreased in kidney of PMR compared with young females. Endogenous 20-HETE was significantly higher in cerebral vessels of PMR than young females (YF) but was significantly lower in renal vessels of PMR. Omega-hydroxylase activity in cerebral vessels was also higher in PMR but was similar in kidney vessels in both groups. In renal microsomal preparations, endogenous 20-HETE was not different in PMR and young females, but ω-hydroxylase activity was significantly lower in PMR than YF. The data with blockers suggest that 20-HETE contributes to postmenopausal hypertension in SHR. The data also suggest that cerebral production of 20-HETE may be increased and renal tubular production may be decreased in PMR, thus both contributing to their elevated BP.     

Lipoxygenase Pathway of Arachidonic Acid Metabolism in Growth Control of Tumor Cells of Different Type

The influence of inhibitors of different lipoxygenases (LOX) on the growth of human tumor cells with different profiles of synthesized eicosanoids was studied. The studied LOX inhibitors had virtually no influence on the growth of A549 cells actively synthesizing cyclooxygenase and lipoxygenase metabolites of arachidonic acid (AA). The inhibitor of 12-LOX, baicalein, significantly inhibited proliferation in cultures of A431 epidermoid carcinoma cells with a characteristic domination of the major lipoxygenase metabolite of AA, 12-hydroxyeicosatetraenoic acid (12-HETE), in the profile of synthesized eicosanoids and reduced to 70% the incorporation of [3H]thymidine into DNA. Treatment of these cultures with 12-HETE virtually restored the growth potential of the tumor cells. The findings suggest that the lipoxygenase metabolite of AA, 12-HETE, is a growth-limiting factor for tumor cells of definite type.     

12-lipoxygenase in porcine coronary microcirculation: implications for coronary vasoregulation

Noncyclooxygenase metabolites of arachidonic acid (AA) have been proposed to mediate endothelium-dependent vasodilation in the coronary microcirculation. Therefore, we examined the formation and bioactivity of AA metabolites in porcine coronary (PC) microvascular endothelial cells and microvessels, respectively. The major noncyclooxygenase metabolite produced by microvascular endothelial cells was 12(S)-hydroxyeicosatetraenoic acid (HETE), a lipoxygenase product. 12(S)-HETE release was markedly increased by pretreatment with 13(S)-hydroperoxyoctadecadienoic acid but not by the reduced congener 13(S)-hydroxyoctadecadienoic acid, suggesting oxidative upregulation of 12(S)-HETE output. 12(S)-HETE produced potent relaxation and hyperpolarization of PC microvessels (EC(50), expressed as -log[M] = 13.5 +/- 0.5). Moreover, 12(S)-HETE potently activated large-conductance Ca(2+)-activated K(+) currents in PC microvascular smooth muscle cells. In contrast, 12(S)-HETE was not a major product of conduit PC endothelial AA metabolism and did not exhibit potent bioactivity in conduit PC arteries. We suggest that, in the coronary microcirculation, 12(S)-HETE can function as a potent hyperpolarizing vasodilator that may contribute to endothelium-dependent relaxation, particularly in the setting of oxidative stress.     

Gonadotropin releasing hormone activates the lipoxygenase pathway in cultured pituitary cells: role in gonadotropin secretion and evidence for a novel autocrine/paracrine loop.

The formation and role of arachidonic acid (AA) and its metabolites during gonadotropin releasing hormone- (GnRH-) induced gonadotropin secretion were investigated in primary cultures of rat pituitary cells. Prelabeled cells ([3H]AA) responded to GnRH challenge with increased formation (about 2-fold) of the leukotrienes LTC4, LTD4, and LTE4 as well as 5- and 15-eicosatetraenoic acids (5- and 15-HETE) as identified by HPLC. Formation of leukotrienes and 15-HETE was further verified by specific radioimmunoassays. No significant increase in the formation of 12-HETE or of the cyclooxygenase products prostaglandin E (PGE) and thromboxane A2 by GnRH was noticed. Addition of physiological concentrations of LTC4 enhanced basal LH release, while subphysiological concentrations of LTC4 (10(-15)-10(-12) M) inhibited GnRH-induced LH release by about 35% (p less than 0.02). Using specific lipoxygenase inhibitors L-656,224 and MK 886, we found inhibition of GnRH-induced LH release by about 40% at concentrations known to specifically inhibit the 5-lipoxygenase pathway. The peptidoleukotriene receptor antagonist ICI 198,615 inhibited LTC4- and LTE4-induced LH release and surprisingly also the effect of GnRH on LH release by 40%. The data strongly suggest a role for AA and its lipoxygenase metabolites in the on/off reactions of GnRH upon LH release. The data also present a novel amplification cycle in which newly formed leukotrienes become first messengers and establish an autocrine/paracrine loop.     

Ingestion of the epoxide hydrolase inhibitor AUDA modulates immune responses of the mosquito,Culex quinquefasciatus during blood feeding

Epoxide hydrolases (EHs) are enzymes that play roles in metabolizing xenobiotic epoxides from the environment, and in regulating lipid signaling molecules, such as juvenile hormones in insects and epoxy fatty acids in mammals. In this study we fed mosquitoes with an epoxide hydrolase inhibitor AUDA during artificial blood feeding, and we found the inhibitor increased the concentration of epoxy fatty acids in the midgut of female mosquitoes. We also observed ingestion of AUDA triggered early expression of defensin A, cecropin A and cecropin B2 at 6 h after blood feeding. The expression of cecropin B1 and gambicin were not changed more than two fold compared to controls. The changes in gene expression were transient possibly because more than 99% of the inhibitor was metabolized or excreted at 42 h after being ingested. The ingestion of AUDA also affected the growth of bacteria colonizing in the midgut, but did not affect mosquito longevity, fecundity and fertility in our laboratory conditions. When spiked into the blood, EpOMEs and DiHOMEs were as effective as the inhibitor AUDA in reducing the bacterial load in the midgut, while EETs rescued the effects of AUDA. Our data suggest that epoxy fatty acids from host blood are immune response regulators metabolized by epoxide hydrolases in the midgut of female mosquitoes, inhibition of which causes transient changes in immune responses, and affects growth of microbes in the midgut.     

Arachidonate metabolism in the mouse thyroid implication of the lipoxygenase pathway in thyrotropin action

The present study of compares the effects of various inhibitors of arachidonate metabolism on mouse thyroid cyclo-oxygenase and lipoxygenase activities and thyrotropin-augmented cyclic-AMP accumulation. Mouse thyroid homogenate converts [1-14C]- arachidonate to several products of the cyclo-oxygenase pathway as well as one major product of the lipoxygenase pathway, 12-L-hydroxyeicosatetraenoic acid (12-Hete). Prostaglandin (PG) formation in thyroid homogenates is inhibited by 1-10 microM indomethacin and etya. 12-HETE accumulation is reduced by 91%, 83% and 20% by 5 microM ETYA, 15-HETE, and indomethacin, respectively. Thyrotropin-stimulated cyclic-AMP accumulation, measured in whole thyroid lobes by radioimmunoassay, is reduced by 45% and 73% by 50 microM and 100 microM ETYA, respectively; indomethacin is without effect at these concentrations. 15-HETE reduces thyrotropin-augmented cyclic-AMP accumulation by 57% and 100 microM. In product inhibition studies, 10 microM 12-HETE reduced the formation of radiolabeled 12-HETE by 20%. 10 microM PGE2, PGF2 alpha or PGD2 had no effect on [1-14C]-PG formation. 12-HETE, however, reduced PG synthesis by 76% at 10 microM. This is the first report implicating the arachidonate lipoxygenase pathway in thyrotropin action at the level of cyclic-AMP regulation. Additionally, our finding that 12-HETE inhibits prostaglandin synthesis suggests that the cyclo-oxygenase and lipoxygenase pathways in the mouse thyroid may be highly integrated.     

Regulation of renal 12(S)-hydroxyeicosatetraenoic acid in diabetes by angiotensin AT1 and AT2 receptors

Diabetes is associated with increased production of 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE]. The mechanisms involved in this process remain unclear. We hypothesized that hyperglycemia and angiotensin II (ANG II) regulate renal 12(S)-HETE production via a balance between angiotensin AT(1) and AT(2) receptors activities. Using a microdialysis technique, renal interstitial fluid (RIF) levels of ANG II and 12(S)-HETE were monitored in normal control and streptozotocin-induced diabetic rats at baseline and then weekly thereafter for 12 wk. In a second group of normal and diabetic rats, 3 wk after development of diabetes, we monitored RIF 12(S)-HETE levels in response to acute AT(1) receptor blockade with valsartan or AT(2) receptor blockade with PD123319 individually or combined. Two weeks after induction of diabetes there was a 404% increase in ANG II (P < 0.05), a 149% increase in 12S-HETE (P < 0.05), and a 649% increase in urinary albumin excretion (P < 0.05). These levels remained elevated throughout the study. PD123319 given alone had no effect on 12(S)-HETE. Valsartan decreased 12(S)-HETE by 61.6% (P < 0.0001), a response that was abrogated when PD123319 was given with valsartan. These data demonstrate that hyperglycemia increases renal ANG II and 12(S)-HETE levels. The increase in 12(S)-HETE is mediated via AT(1) receptor. The attenuation of the effects of AT(1) receptor blockade by PD123319 suggests that AT(2) receptor contributes to the downregulation of renal 12(S)-HETE production.     

Lipoxygenase- and cyclooxygenase-reaction products and incorporation into glycerolipids or radiolabeled arachidonic acid in the bovine retina

The metabolism of radiolabeled arachidonic acid (AA) by the intact bovine retina in vitro has been studied. Synthesis of prostaglandins (PGs) and hydroxyeicosatetraenoic acids (HETEs), and incorporation of AA into glycerolipids has been measured by reverse-phase and straight-phase high performance liquid chromatography with flow scintillation detection, and by thin-layer chromatography. AA was actively acylated into glycerolipids, particularly triglycerides, phosphatidylcholine and phosphatidylinositol. AA was also converted to the major PGs, PGF2 alpha, PGE2, PGD2, 6-keto-PGF1 alpha and TXB2, and to the lipoxygenase reaction products, 12-HETE, 5-HETE, and other monohydroxy isomers. Approximately 6% of the radiolabeled AA was converted to eicosanoids. The synthesis of HETEs was inhibited in a concentration-dependent manner (IC50 = 8.3 nM) by nordihydroguaiaretic acid (NDGA). PG synthesis was inhibited by aspirin (10 microM), indomethacin (1 microM) and NDGA (IC50 = 380 nM). Metabolism of AA via lipoxygenase, cyclooxygenase and activation-acylation was inhibited by boiling retinal tissue prior to incubation. These studies demonstrate an active system for the uptake and utilization of AA in the bovine retina, and provide the first evidence of lipoxygenase-mediated metabolism of AA, resulting in the synthesis of mono-hydroxyeicosatetraenoic acids, in the retina.     

Incorporation of [3H]Arachidonic and [14C]Eicosapentaenoic Acids into Glycerophospholipids and Their Metabolism via Lipoxygenases in Isolated Brain Cells from Rainbow Trout Oncorhaynchus mykaiss

The incorporation of [3H]arachidonate [( 3H]AA) and [14C]eicosapentaenoate [( 14C]EPA) into glycerophospholipids was studied in isolated brain cells from rainbow trout, a teleost fish whose lipids are rich in (n-3) polyunsaturated fatty acids (PUFAs). EPA was incorporated into total lipid to a greater extent than AA, but the incorporation of both PUFAs into total glycerophospholipids was almost identical. The incorporation of both AA and EPA was greatest into phosphatidylethanolamine (PE). However, when expressed per milligram of individual phosphoglycerides, both AA and EPA were preferentially incorporated into phosphatidylinositol (PI), the preference being significantly greater with AA. On the same basis, significantly more EPA than AA was incorporated into phosphatidylcholine (PC). When double-labelled cells were challenged with calcium ionophore A23187, the 3H and 14C released from the cells closely paralleled each other, peaking at 10 min after addition of ionophore. The 12-monohydroxylated derivative was the pre-dominant lipoxygenase product from both AA and EPA with a rank order of 12-hydroxyeicosatetraenoic acid (12-HETE) greater than leukotriene B4 (LTB4) greater than 5-HETE greater than 15-HETE for the AA products and 12-hydroxyeicosapentaenoic acid (12-HEPE) greater than 5-HEPE greater than LTB5 greater than 15 HEPE for EPA products. The 3H/14C (dpm/dpm) ratios in the glycerophospholipids, total released radioactivity, and the lipoxygenase products suggested that PC rather than PI was the likely source of eicosanoid precursors in trout brain cells.     

Influence of N-phenyllinoleamide from toxic oil samples on the lipoxygenase metabolism of exogenous arachidonic acid in mouse peritoneal macrophages.

N-phenyllinoleamide (NPLA) is a useful marker for adulterated oil samples associated with cases of toxic oil syndrome (TOS). To date, NPLA has not reproduced the human poisoning episode in experimental animal models and, thus, its pathological role in the syndrome remains controversial. The present report describes the effect of NPLA on the lipoxygenase metabolism of exogenous arachidonic acid (AA) in mouse peritoneal macrophages (MPM). Results show that MPM cells exposed to 1mM NPLA for 2 h, when subsequently incubated with exogenous 3H-AA, undergo a significant increase in the biosynthesis of 3H-12-hydroxyeicosatetraenoic acid (3H-12-HETE) whereas levels of 3H-15-HETE are relatively stable. These data indicate that NPLA selectively potentiates the lipoxygenase metabolism of exogenous AA, supporting the possible implication of lipid peroxidative processes in the ethiopathology of TOS, although the relatively high NPLA concentration required 'in vitro' makes it unlikely that this xenobiotic could be directly related to human toxicity.     

Metabolism of arachidonic acid in sheep uterus: in vitro studies

Arachidonic acid (AA) metabolism in the non-pregnant sheep uterus was studied in vitro using conventional chromatographic and HPLC techniques. High expression of both lipoxygenase (LOX) as well as cyclooxygenase (COX) enzymes and their activities was found in the uterine tissues. On incubation of uterine enymes with AA, the LOX products formed were identified as 5-hydroperoxyeicosatetraenoic acid (5-HPETE), 12- and 15-hydroxyeicosatetraenoic acids (12- and 15-HETEs), based on their separation on TLC and HPLC. By employing differential salt precipitation techniques, the LOXs generating products 5-HPETE (5-LOX), 12-HETE and 15-HETE (12- and 15-dual LOX) were isolated. Based on their analysis on TLC, the COX products formed were identified as prostaglandins - PGF2alpha and prostacyclin derivative 6-keto PGF1alpha. The study forms the first report on the comprehensive analysis on the metabolism of AA in sheep uterus in vitro via the LOX and COX pathways.