Incorporation of 5,8,11,14-eicosatetraynoic acid (ETYA) into cell lipids: competition with arachidonic acid for esterification

The role of annexin A1 in Candida albicans and Candida auris infections in murine neutrophils

Annexin A1 (AnxA1) is an anti-inflammatory protein expressed in various cell types, especially macrophages and neutrophils. Because neutrophils play important roles in infections and inflammatory processes and the relationship between AnxA1 and Candida spp. infections is not well-understood, our study examined whether AnxA1 can serve as a target protein for the regulation of the immune response during fungal infections. C57BL/6 wild-type (WT) and AnxA1 knockout (AnxA1^-/-) peritoneal neutrophils were coinfected with Candida albicans or Candida auris for 4 h. AnxA1^-/- neutrophils exhibited a marked increase in cyclooxygenase 2 (COX-2), phosphorylated extracellular signal-related kinase (ERK), p-38, and c-Jun N-terminal kinase (JNK) levels after coinfection with both Candida spp. A lipidomics approach showed that AnxA1 deficiency produced marked differences in the supernatant lipid profiles of both control neutrophils and neutrophils coinfected with Candida spp. compared with WT cells, especially the levels of glycerophospholipids and glycerolipids. Our results showed that endogenous AnxA1 regulates the neutrophil response under fungal infection conditions, altering lipid membrane organization and metabolism.

Very Long Chain Fatty Acids Are Functionally Involved in Necroptosis

Necroptosis is a form of regulated cell death that is linked to various human diseases. Distinct membrane-related, thus lipid-dependent, alterations take place during necroptosis. However, little is known about the roles of specific lipids in this process. We used an untargeted LC-MS-based approach to reveal that distinct lipid species are regulated at the molecular level during necroptosis. We found that ceramides and very long chain fatty acids accumulate during this process. Intrigued by the specificity of very long chain fatty acid accumulation, we focused on characterizing their involvement during necroptosis. Biochemical characterizations suggested that activated fatty acid biosynthesis and elongation could be responsible for these accumulations. We further showed that inhibition of fatty acid biosynthesis and depletion of very long chain fatty acids prevented loss of plasma membrane integrity and cell death, strongly suggesting that very long chain fatty acids are functionally involved in necroptosis.

Requirements for T lymphocyte migration in explanted lymph nodes

Although the requirements for T lymphocyte homing to lymph nodes (LNs) are well studied, much less is known about the requirements for T lymphocyte locomotion within LNs. Imaging of murine T lymphocyte migration in explanted LNs using two-photon laser-scanning fluorescence microscopy provides an opportunity to systematically study these requirements. We have developed a closed system for imaging an intact LN with controlled temperature, oxygenation, and perfusion rate. Naive T lymphocyte locomotion in the deep paracortex of the LN required a perfusion rate of >13 microm/s and a partial pressure of O(2) (pO(2)) of >7.4%. Naive T lymphocyte locomotion in the subcapsular region was 38% slower and had higher turning angles and arrest coefficients than naive T lymphocytes in the deep paracortex. T lymphocyte activation decreased the requirement for pO(2), but also decreased the speed of locomotion in the deep paracortex. Although CCR7(-/-) naive T cells displayed a small reduction in locomotion, systemic treatment with pertussis toxin reduced naive T lymphocyte speed by 59%, indicating a contribution of Galpha(i)-mediated signaling, but involvement of other G protein-coupled receptors besides CCR7. Receptor knockouts or pharmacological inhibition in the adenosine, PG/lipoxygenase, lysophosphatidylcholine, and sphingosine-1-phosphate pathways did not individually alter naive T cell migration. These data implicate pO(2), tissue architecture, and G-protein coupled receptor signaling in regulation of naive T lymphocyte migration in explanted LNs.

Arachidonic acid in astrocytes blocks Ca(2+) oscillations by inhibiting store-operated Ca(2+) entry, and causes delayed Ca(2+) influx

ATP-elicited oscillations of the concentration of free intracellular Ca(2+) ([Ca(2+)](i)) in rat brain astrocytes were abolished by simultaneous arachidonic acid (AA) addition, whereas the tetraenoic analogue 5,8,11,14-eicosatetraynoic acid (ETYA) was ineffective. Inhibition of oscillations is due to suppression by AA of intracellular Ca(2+) store refilling. Short-term application of AA, but not ETYA, blocked Ca(2+) influx, which was evoked by depletion of stores with cyclopiazonic acid (CPA) or thapsigargin (Tg). Addition of AA after ATP blocked ongoing [Ca(2+)](i) oscillations. Prolonged AA application without or with agonist could evoke a delayed [Ca(2+)](i) increase. This AA-induced [Ca(2+)](i) rise developed slowly, reached a plateau after 5 min, could be reversed by addition of bovine serum albumin (BSA), that scavenges AA, and was blocked by 1 microM Gd(3+), indicative for the influx of extracellular Ca(2+). Specificity for AA as active agent was demonstrated by ineffectiveness of C16:0, C18:0, C20:0, C18:2, and ETYA. Moreover, the action of AA was not affected by inhibitors of oxidative metabolism of AA (ibuprofen, MK886, SKF525A). Thus, AA exerted a dual effect on astrocytic [Ca(2+)](i), firstly, a rapid reduction of capacitative Ca(2+) entry thereby suppressing [Ca(2+)](i) oscillations, and secondly inducing a delayed activation of Ca(2+) entry, also sensitive to low Gd(3+) concentration.

Arachidonic acid and docosahexaenoic acid suppress thrombin-evoked Ca2+ response in rat astrocytes by endogenous arachidonic acid liberation

Arachidonic (AA) and docosahexaenoic acid (DHA) are the major polyunsaturated fatty acids (PUFAs) in the brain. However, their influence on intracellular Ca2+ signalling is still widely unknown. In astrocytes, the amplitude of thrombin- induced Ca2+ response was time-dependently diminished by AA and DHA, or by the AA tetraynoic analogue ETYA, but not by eicosapentaenoic acid (EPA). Thrombin-elicited Ca2+ response was reduced (20-30%) by 1-min exposure to AA or DHA. Additionally, 1-min application of AA or DHA together with thrombin in Ca2+-free medium blocked Ca2+ influx, which followed after readdition of extracellular Ca2+. EPA and ETYA, however, were ineffective. Long-term treatment of astrocytes with AA and DHA, but not EPA reduced the amplitude of the thrombin-induced Ca2+ response by up to 80%. AA and DHA caused a comparable decrease in intracellular Ca2+ store content. Only DHA and AA, but not EPA or ETYA, caused liberation of endogenous AA by cytosolic phospholipase A2 (cPLA2). Therefore, we reasoned that the suppression of Ca2+ response to thrombin by AA and DHA could be due to release of endogenous AA. Possible participation of AA metabolites, however, was excluded by the finding that specific inhibitors of the different oxidative metabolic pathways of AA were not able to abrogate the inhibitory AA effect. In addition, thrombin evoked AA release via activation of cPLA2. From our data we propose a novel model of positive/negative-feed-back in which agonist-induced release of AA from membrane phospholipids promotes further AA release and then suppresses agonist-induced Ca2+ responses.

Effects of inhibitors of the lipo-oxygenase family of enzymes on the store-operated calcium current I(CRAC) in rat basophilic leukaemia cells

In non-excitable cells, the major Ca2+ entry pathway is the store-operated pathway in which emptying of intracellular Ca2+ stores activates Ca2+ channels in the plasma membrane. In many cell types, store-operated influx gives rise to a Ca2+-selective current called I(CRAC) (Ca2+ release-activated Ca2+ current). Using both the whole-cell patch clamp technique to measure I(CRAC) directly and fluorescent Ca2+ imaging, we have examined the role of the lipo-oxygenase pathway in the activation of store-operated Ca2+ entry in the RBL-1 rat basophilic leukaemia cell-line. Pretreatment with a variety of structurally distinct lipo-oxygenase inhibitors all reduced the extent of I(CRAC), whereas inhibition of the cyclo-oxygenase enzymes was without effect. The inhibition was still seen in the presence of the broad protein kinase blocker staurosporine, or when Na+ was used as the charge carrier through CRAC channels. The lipo-oxygenase blockers released Ca2+ from intracellular stores but this was not associated with subsequent Ca2+ entry. Lipo-oxygenase blockers also reduced both the amount of Ca2+ that could subsequently be released by the combination of thapsigargin and ionomycin in Ca2+-free solution and the Ca2+ influx component that occurred when external Ca2+ was re-admitted. The inhibitors were much less effective if applied after I(CRAC) had been activated. This inhibition of I(CRAC) could not be rescued by dialysis with 5(S)-hydroxyperoxyeicosa-6E,8Z,11Z,14Z,tetraenoic acid (5-HPETE), the first product of the 5-lipo-oxygenase pathway. Our findings indicate that exposure to pharmacological tools that inhibit the lipo-oxygenase enzymes all decrease the extent of activation of the current. Our results raise the possibility that a lipo-oxygenase might be involved in the activation of I(CRAC). Alternative explanations are also discussed.

Arachidonic acid directly activates members of the mitogen-activated protein kinase superfamily in rabbit proximal tubule cells

BACKGROUND

To explore the roles of eicosanoids in arachidonic acid-induced mitogen-activated protein kinase (MAPK) signal transduction, we have shown that exposure of proximal tubular cells to arachidonic acid induces phosphorylation of c-Jun NH2-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK), two members of the MAPK superfamily. We observed that ketoconazole, an inhibitor of the cytochrome P450 pathway, blocked ERK but not JNK activation.

METHODS

Direct regulation of arachidonic acid on mitogen-activated protein kinase (MAPK) signaling pathways was evaluated more directly by utilizing specific enzyme inhibitors of the cytochrome P450 metabolic pathway and by comparing the relative efficacy of arachidonic acid versus its cytochrome P450 metabolites (exogenous and endogenous), eicosatetraynoic acid (ETYA), and other fatty acids on the phosphorylation of members of the MAPK superfamily (ERKs, JNK, and p38(MAPK)), by utilizing early passage rabbit proximal tubular epithelial cells.

RESULTS

Arachidonic acid activated p38(MAPK), a third member of the MAPK superfamily, in a time- and concentration-dependent manner. Studies designed to evaluate the ability of arachidonic acid and its cytochrome P450 metabolites (endogenously and exogenously) to stimulate ERKs, JNK, and p38(MAPK) found four conclusions. First, the metabolites of arachidonic acid generated endogenously by cytochrome P450 2C1 significantly augmented basal ERK activity, whereas the metabolites generated by the 2C2 isozyme significantly augmented basal p38(MAPK) activity. However, their effects were less profound than arachidonic acid itself. In contrast, there were no significant effects with transfection of either isozyme on basal JNK activity. Second, a variety of exogenous cytochrome P450 products were less potent than arachidonic acid on a molar basis in stimulating the activity of all three MAPKs. Third, ketoconazole and 17-octadecynoic acid, inhibitors of the cytochrome P450 pathway, as well as PPOH and DDMS, inhibitors of the epoxygenase and omega-hydroxylase pathways, respectively, failed to significantly reduce the effects of arachidonic acid to activate ERK and p38(MAPK) (JNK was not evaluated). Finally, arachidonic acid, its inactive analog ETYA, and other fatty acids with differing chain lengths and degrees of saturation stimulated the activity of all three MAPKs.

CONCLUSIONS

These observations substantiate a role for arachidonic acid and other fatty acids in signaling linked to the MAPK superfamily in rabbit proximal tubular epithelium without the necessity of conversion to cytochrome P450 metabolites.

Arachidonic acid reversibly enhances N-type calcium current at an extracellular site

We examined the effects of arachidonic acid (AA) on whole cell Ca(2+) channel activity in rat superior cervical ganglion neurons. Our companion paper (Liu L, Barrett CF, and Rittenhouse AR. Am J Physiol Cell Physiol 280: C1293-C1305, 2001) demonstrates that AA induces several effects, including enhancement of current amplitude at negative voltages, and increased activation kinetics. This study examines the mechanisms underlying these effects. First, enhancement is rapidly reversible by bath application of BSA. Second, enhancement appears to occur extracellularly, since intracellular albumin was without effect on enhancement, and bath-applied arachidonoyl coenzyme A, an amphiphilic AA analog that cannot cross the cell membrane, mimicked enhancement. In addition, enhancement is voltage dependent, in that currents were enhanced to the greatest degree at -10 mV, whereas virtually no enhancement occurred positive of +30 mV. We also demonstrate that AA-induced increases in activation kinetics are correlated with enhancement of current amplitude. An observed increase in the voltage sensitivity may underlie these effects. Finally, the majority of enhancement is mediated through N-type current, thus providing the first demonstration that this current type can be enhanced by AA.

Inhibition of the synthesis of eicosanoid-like substances in a human oral cancer cell line by interferon-gamma and eicosapentaenoic acid

The objectives were to examine the production of eicosanoids in a Chinese human oral cancer cell line (OEC-M1) and to test the effects of interferon-gamma (IFN-gamma), eicosapentaenoic acid (EPA) and enzyme inhibitors on this biosynthesis. The eicosanoids were identified by reverse phase-high performance liquid chromatography. Two predominant peaks appeared in the chromatograms. One compound (P-1) was identified by ultraviolet absorption at a lambda(max) of 278nm with shoulders at 272 and 284nm. The other compound (P-2) was identified by ultraviolet absorption at a lambda(max) of 284 nm with shoulders at 278 and 290 nm. The production of P- was significantly inhibited by the addition of IFN-gamma (200 and 400 U/ml), and EPA (10 to 40 microM). It was only partially inhibited (p < 0.05) by indomethacin (INDO) (0.5 and 1 microM), nordihydroguaiaretic acid (NDGA) (30 and 60 microM/ml), and eicosa-5,8,11,14-tetraynoic acid (ETYA) (20-60 microM). It was almost completely inhibited by indomethacin (2 and 3 microM), and dexamethasone (0.6 and 6 microM). The production of P-2 was almost completely inhibited by IFN-gamma (200 and 400 U/ml), and partially inhibited (p < 0.05) by EPA (10 and 20 microM), NDGA (30 and 60 microM), ETYA (20 and 40 microM), dexamethasone (0.6 and 6 microM). The production of both peaks was significantly reduced by excluding arachidonic acid (AA), and almost completely inhibited by heating at 100 degrees C for 10 min during incubation. These results demonstrate that two eicosanoid-like compounds are synthesized by the OEC-M cell line and that their production can be modulated by IFN-gamma, EPA, indomethacin, NDGA, ETYA, and dexamethasone.

Lipoxygenase inhibitors counteract protein kinase C mediated events in human T lymphocyte proliferation

Four structurally unrelated inhibitors of lipoxygenase (LO), i.e. nordihydroguaiaretic acid (NDGA), Esculetin, AA861 and 5,8,11,14-eicosatetraynoic acid (ETYA) suppressed mitogen induced proliferation of human peripheral blood lymphocytes in a dose-dependent manner. The degree of suppression was influenced by the type of the mitogenic stimulus. Receptor mediated stimulation, i.e. through phytohemagglutinin or the anti-CD3 antibody OKT3, was overall less susceptible, whereas proliferation initiated by direct activation of protein kinase C (PKC), i.e. through phorbol myristate acetate or indolactam V, was profoundly suppressed (up to 90%). The effect of the LO inhibitors was not due to non-specific interference with intracellular radical intermediates, because AA861 and ETYA showed no radical scavenging activity. Two PKC inhibitors, H-7 and H-8, similarly suppressed lymphocyte proliferation and showed essentially the same suppressive pattern as LO inhibitors. The results clearly indicate that LO product(s) participate in signal transduction mechanisms in T lymphocytes, possibly via stimulation of PKC activity and cell proliferation.

Eicosanoid inhibitors enhance synergistically the effect of transforming growth factor beta 1 on CCL 64 cell proliferation

The interactions between drugs suppressing the production of arachidonic acid metabolites-eicosanoids and transforming growth factor beta 1 (TGF-beta 1) were investigated using CCL64 cells. These experiments, designed as complete factorial combination of treatments, demonstrated that both esculetin and eicosatetraynoic acid significantly potentiated the inhibitory effect of TGF-beta 1 on [3H]thymidine incorporation. The expression of overadditive effects depended both on the type and concentration of combined factors. These results corresponded with cell cycle analysis data (increased cell number in G1 and decreased cell number in S and G2/M phases) and with the results monitoring cell number following treatment with eicosatetraynoic acid, esculetin, 3-[1-(4-chlorobenzyl)-3-t-butyl-thio-5-isopropylindol-2-yl]-2,2-di methyl propanoic acid (MK-886) and indomethacin. Summarizing, the degree of significance of combined effects supports the hypothesis of synergistic potentiation of TGF-beta 1 effects caused by eicosanoid inhibitors. The results indicate that either the lack of some eicosanoids or a certain type of misbalance in the metabolism of arachidonic acid leading to its abundance might modulate TGF-beta 1 effects on the cell cycle and proliferation in CCL64 cells.

Activation of NF-kappa B by ER stress requires both Ca2+ and reactive oxygen intermediates as messengers

The eukaryotic transcription factor NF-kappaB is activated by a large variety of stimuli. We have recently shown that ER stress, caused by an aberrant accumulation of membrane proteins within this organelle, also activates NF-kappaB. Here, we show that activation of NF-kappaB by ER stress requires an increase in the intracellular levels of both reactive oxygen intermediates (ROIs) and Ca2+. Two distinct intracellular Ca2+ chelators and a panel of structurally unrelated antioxidants prevented NF-kappaB activation by various ER stress-eliciting agents, whereas only antioxidants but not the Ca2+ chelators prevented NF-kappaB activation by the inflammatory cytokine TNF-alpha. Consistent with an involvement of calcium, the ER-resident Ca2+-ATPase inhibitors thapsigargin and cyclopiazonic acid (CPA), which trigger a rapid efflux of Ca2+ from the ER, also potently activated NF-kappaB. Pretreatment with a Ca2+ chelator abrogated this induction. The Ca2+ chelator BAPTA-AM inhibited ROI formation in response to thapsigargin and CPA treatment, suggesting that the Ca2+ increase preceded ROI formation during NF-kappaB activation. The selective inhibitory effect of the drug tepoxalin suggests that the peroxidase activity of cyclooxygenases or lipoxygenases was responsible for the increased ROI production in response to Ca2+ release by thapsigargin.

Alteration of arachidonate levels in tick salivary glands by dietary modification of host blood lipids

Tick saliva contains prostaglandins of the 2-series, believed to facilitate bloodmeal acquisition. Because ticks cannot synthesize the prostaglandin precursor, arachidonic acid, investigations were undertaken to study the uptake, incorporation, and distribution of arachidonic acid in the salivary glands of the lone star tick in vitro and in vivo. Uptake of [3H]arachidonate by isolated salivary glands was reduced in the presence of low concentrations of arachidonic or eicosapentaenoic acids, but much higher, non-physiological concentrations of oleic and linoleic acids were required to inhibit [3H]arachidonate uptake. The incorporation of [3H]arachidonate into triglycerides increased at high concentrations of arachidonic or eicosapentaenoic acid, but not at any concentration of oleic or linoleic acid. Eicosatetraynoic acid greatly inhibited [3H]arachidonic acid. Guinea pigs fed hydrogenated coconut oil, safflower/primrose oil, or fish oil exhibited altered blood lipids; notably increased levels of eicosapentaenoic acid when fed fish oil. Salivary gland lipids in ticks fed on these hosts were also altered. Ticks parasitizing fish oil-fed guinea pigs contained high levels of eicosapentaenoic acid with a 30% reduction in arachidonate levels. The results demonstrated that eicosapentaenoic acid in the host diet had profound effects on arachidonate assimilation by tick salivary glands, which could lead to altered prostaglandin content in tick saliva.

Lipid metabolite involvement in the activation of the human heme oxygenase-1 gene

Cellular effects of ultraviolet A (UVA) radiation include peroxidation of membrane lipids as well as a decrease in intracellular glutathione. We have investigated whether damage to membrane lipids is involved in the activation of the human heme oxygenase-1 gene by UVA. Irradiation of human skin fibroblasts in the presence of the lipophilic antioxidants, butylated hydroxytoluene and alpha-tocopherol, enhances the UVA-induced HO-1 mRNA accumulation, suggesting that peroxidation of plasma membrane lipids is not involved. Furthermore, sodium ascorbate, which induces lipid peroxidation mainly in the plasma membrane, induces HO-1 mRNA to low levels only. The decrease in GSH by UVA radiation is not affected by the presence of the lipophilic antioxidants while ascorbate treatment increases the intracellular GSH by twofold above controls. These results indicate that peroxidation of internal membrane lipids, a decrease in the intracellular GSH levels and the integrity of the plasma membrane are all important for the UVA-induction of heme oxygenase-1. Both nonenzymatic as well as enzymatic lipid peroxidation metabolites are inducers of heme oxygenase-1. The nonenzymatic lipid peroxidation product 4-hydroxynonenal induces heme oxygenase-1 mRNA up to 40-fold and the phospholipase metabolites diacylglycerol and arachidonic acid induce this mRNA by three-to sixfold above basal levels. We also demonstrate that the cyclooxygenase metabolites of arachidonic acid are important for the UVA-activation of the heme oxygenase-1 gene.

Phytanic acid must be activated to phytanoyl-CoA prior to its alpha-oxidation in rat liver peroxisomes

alpha-Oxidation of the branched-chain fatty acid, phytanic acid, is defective in patients with Refsum's disease, the disorders of peroxisome biogenesis (e.g., Zellweger syndrome), and in rhizomelic chondrodysplasia punctata. 3H-Release from [2,3-3H]phytanic acid, which is impaired in cultured skin fibroblasts from these patients, was investigated in rat liver peroxisomes. Cofactors necessary for optimal 3H-release, ATP, Mg2+, and coenzyme A, were also necessary for optimal acyl-CoA synthetase activity, suggesting that the substrate for 3H-release might be phytanoyl-CoA. 5,8,11,14-Eicosatetraynoic acid (ETYA), an inhibitor of long-chain acyl-CoA synthetase activity, blocked phytanoyl-CoA synthesis as well as 3H-release from [2,3-3H]phytanic acid in a dose-dependent manner. However, this inhibitor had little effect on 3H-release from [2,3-3H]phytanoyl-CoA. Tetradecylglycidic acid (TDGA) inhibited 3H-release from [2,3-3H]phytanic acid in peroxisomal but not in mitochondrial fractions from rat liver. This agent inhibited 3H-release from [2,3-3H]phytanic acid and [2,3-3H]phytanoyl-CoA equally. In contrast to ETYA, which appeared to decrease 3H-release as a consequence of synthetase inhibition, TDGA appeared to act directly on the enzyme catalyzing 3H-release. This enzyme was partially purified from rat liver. The purified enzyme, which did not possess phytanoyl-CoA synthetase activity, catalyzed tritium release from [2,3-3H]phytanoyl-CoA. This enzyme catalyzed 3H-release from [2,3-3H]phytanic acid only if a source of phytanoyl-CoA synthetase was present. We conclude that in rat liver peroxisomes, phytanic acid must be activated to its coenzyme A derivative prior to subsequent alpha-oxidation.

Spontaneous chemiluminescence of ETYA (5,8,11,14-eicosatetraynoic acid) is inhibited by catalase or peroxidase

5,8,11,14-eicosatetraynoic acid (ETYA), an isomorphic competitive analogue of arachidonic acid, spontaneously generates a chemiluminescence signal detected with a liquid scintillation spectrometer operated at ambient temperature in the out-of-coincidence mode. The intensity of the signal was 10- or more-fold above background, required oxygen for its generation, was inhibited by antioxidants, and approximately doubled in D2O. Arachidonic acid, which contains 4-alkene rather than alkyne bonds did no more than double the chemiluminescent signal above background. When examined at 37 degrees C in a Berthold AutoLumat 958 luminometer, DBA (lucigenin) was required to detect a signal above background. Catalase or peroxidase, and to a lesser extent mannitol or histidine but not superoxide dismutase, strongly diminished the signal intensity. These observations provide a baseline for interpreting the functional and electron microscopic changes produced by ETYA in PC3 prostate and A172 glioblastoma cell lines, consistent with a contribution from oxidative stress associated with free radicals, and the absence of these morphological changes in U937 monoblastoid cells.

Reactive oxygen species and not lipoxygenase products are required for mouse B-lymphocyte activation and differentiation

A potential role for lipoxygenase (LO) products and reactive oxygen species (ROS) in mouse B-lymphocyte activation and differentiation was investigated. Previously published investigations with the nonspecific 5-LO (EC 1.13.11.34) and 12-LO (EC 1.13.11.31) inhibitors such as nordihydroguaiaretic acid (NDGA) and 6,7-dihydroxycoumarin (Esculetin), are misleading in that they suggest lymphocyte LO activity is required for activation and differentiation of these cells. In initial support of this concept, we report that NDGA and Esculetin completely inhibited B-lymphocyte activation mediated by either membrane immunoglobulin (mIg), or the lipopolysaccharide (LPS) receptor. NDGA and Esculetin completely inhibited cell enlargement and proliferation, exhibiting half maximal inhibitory concentrations (IC50S) of approximately 1 x 10(-6) M. In contrast, the highly specific 5-LO inhibitors BAY X 1005, MK-886 and Wy 50,295 did not inhibit cell enlargement or proliferation. Moreover, 5,8,11-eicosatriynoic acid (ETI) which inhibits 5- and 12-LO, and 5, 8, 11, 14-eicosatetraynoic acid (ETYA) which inhibits all known LOs did not affect B-lymphocyte proliferation. Interestingly, NDGA and Esculetin are antioxidants, unlike BAY X 1005, MK-886, Wy 50,295, ETI and ETYA. Our hypothesis was that the antioxidant activities of NDGA and Esculetin were reponsible for inhibiting B-lymphocyte activation and proliferation and we speculated that ROS and not LO activity was required for both processes. Additional antioxidants such as butylated hydroxy toluene, o-phenanthroline, thiourea, and alpha-tocopherol (vitamin E), also inhibited B-lymphocyte proliferation induced by either the LPS or mIg receptors. These agents exhibited IC50S of 1 x 10(-8) M, 5 x 10(-10) M, 6 x 10(-3) M and 5 x 10(-5) M, respectively. When resting B-lymphocytes were treated with a source of ROS (1 x 10(-5) M H2O2), cells enlarged in a temperature-sensitive manner, which is similar to LPS-induced enlargement. Both NDGA and Esculetin completely inhibited H2O2-induced enlargement. These results further indicate that ROS are required for B-lymphocyte activation and proliferation. Similar results were obtained for B-lymphocyte differentiation. NDGA and Esculetin completely inhibited the development of plasma cells and displayed IC50S of 5 x 10(-6) M. Conversely, BAY X 1005, MK-886, Wy 50,295, ETI, and ETYA did not block the formation of plasma cells. Therefore, ROS are also crucial for differentiation into plasma cells. These experiments are the first to directly illustrate that intracellular ROS mediate B-lymphocyte activation, proliferation and differentiation and that LO products are not required for these processes.(ABSTRACT TRUNCATED AT 400 WORDS)

5,8,11,14-eicosatetraynoic acid-induced destruction of mitochondria in human prostate cells (PC-3)

Culturing human prostate PC-3 cells for 4, 24, or 72 h in the presence of 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of arachidonic acid metabolism and cholesterol biosynthesis, markedly altered the morphology and reduced the number of mitochondria in the treated cells. Using quantitative electron microscopic morphometry, we documented changes in the number, form, area, matrix density, and integrity of the cristae and limiting membranes of mitochondria in cells cultured with ETYA. The inhibition of cholesterol synthesis or the substitution of ETYA for polyunsaturated fatty acids in the inner membrane may participate in the disruption of the mitochondria, which resembles the morphologic sequelae of oxidative stress. If sufficiently extensive, these changes could contribute to the inhibition of cellular proliferation by ETYA.

Eicosatetraynoic and arachidonic acid-induced changes in cell membrane fluidity consonant with differences in computer-aided design-structures

ETYA (5,8,11,14-eicosatetraynoic acid), a competitive analogue of arachidonic acid (AA), inhibits the proliferation of U937 (human monoblastoid) and PC3 (human prostate) cancer cells, without the overt cytotoxicity associated with AA at similar concentrations. The mechanism of inhibition is not established. ETYA at 100 microM acutely increased whole cell and isolated microsomal membrane fluidity of both cell lines to a greater extent than arachidonic acid. PC3 cells incubated with ETYA for 72 h evidenced increased membrane fluidity. This was measured by the fluorescence polarization parameter, R, using the probes TMA-DPH and DPH for whole cell and isolated membrane fractions, respectively. Compared with whole cells, isolated membranes yielded a 10-20-fold increase in fluorescence intensity. The intramolecular conformational profiles of both ETYA and AA were explored using a combination of molecular mechanics energy minimization and molecular dynamics simulation. While it is possible that not all of the low energy conformational states of either molecule were sampled, the large number of low-energy conformers determined for ETYA correspond to kink deformed conformers relative to the family of AA conformers. These kinks make the molecular cross sections of ETYA larger than AA and arise from the four alkyne bond geometries. This structural finding is consistent with ETYA's greater effect on membrane fluidity. Dissociation between the extent of change in membrane fluidity due to ETYA or AA and inhibition of DNA synthesis can suggest that either (A) increased fluidity and inhibition of DNA synthesis are independent, or as we believe more likely, (B) greater membrane fluidity evoked by ETYA is important for inhibiting DNA synthesis, while changes induced by AA are insufficient or differ qualitatively from those required to initiate and sustain these nonlethal events.

Differential effects of ETYA, a PUFA-analogue, on prostate (PC3) and monoblastoid U937 ultrastructure; lack of correlation with reduced proliferation

ETYA (5,8,11,14-eicosatetraynoic acid), a polyunsaturated fatty acid analogue, inhibits proliferation of PC3 and U937 cells and induces a limited differentiation in U937 cells. Human prostate PC3 cells cultured for 72 h with 40 microM ETYA in fetal calf serum contained putative lipofuscin bodies, myelin figures and mitochondria with damaged cristae and matrices. These changes were absent from human U937 monoblastoid cells incubated with ETYA in CPSR3, a semipurified serum replacement. U937 cells cultured with ETYA in fetal calf serum contained occasional lipofuscin bodies, while PC3 cells cultured in CPSR3 exhibited all of the changes described. ETYA reduced the oxygen consumption of both cell lines. Therefore we conclude: (a) The response to ETYA by cells of dissimilar developmental origin is not identical; (b) unidentified serum components can augment potential ETYA-induced oxidative stress-responses of cells; (c) inhibition of U937 proliferation by ETYA does not depend upon the morphologic changes seen in PC3 cells, which resemble sequelae of oxidative stress with excess free radicals; and (d) rapid ETYA-induced inhibition of oxygen consumption in both cell lines implies a reduced synthesis of ATP that could contribute to the reversible impairment of cellular proliferation.

ETYA, a pleotropic membrane-active arachidonic acid analogue affects multiple signal transduction pathways in cultured transformed mammalian cells

ETYA (5,8,11,14-eicosatetraynoic acid), an arachidonic acid analogue, inhibited DNA synthesis in human transformed U937 (monoblastoid), PC3 (prostate) and A172 (glioblastoma) cells, and partially differentiated the U937 and A172 lines. The agent is not primarily cytotoxic at the concentrations employed, based upon exclusion of trypan blue, continued attachment of PC3 and A172 cells, unchanged release of Cr51, and reversibility of inhibited thymidine incorporation after removal of ETYA. Leukotriene C4 partially reversed the suppression of U937 DNA synthesis, suggesting its modulation by leukotrienes. U937 and A172 cells partially differentiated, as judged by a number of criteria. ETYA increased whole cell and microsomal membrane fluidity, increased intracellular Ca2+ in PC3 and U937 cells, altered the distribution and activity of protein kinase C in U937 cells, and rapidly downregulated the transcription of U937 c-myc. Evidence from transmission electron microscopy consistent with oxidative stress including putative lipofuscin bodies, myelin figures and disordered mitochondrial cristae and matrices was especially evident in PC3 cells, less so in A172 and essentially absent in U937 cells. A specific 5'-lipoxygenase inhibitor, A63162 inhibited PC3 and U937 proliferation. Some of these events are believed to represent components of "signal" transduction pathways responsible for reversible inhibition of DNA synthesis and the induction of partial phenotypic differentiation in competent cells. Arachidonic acid analogues which exert selective effects on physical and functional properties of cell membranes may represent an additional class of membrane-active agents with potential anticancer activity. A subset of their activities can be duplicated by inhibitors of 5' lipoxygenase.

Activation of osmolyte efflux from cultured renal papillary epithelial cells

The rabbit renal papillary epithelial cell line PAP-HT25 accumulates sorbitol and other organic osmolytes when cultured in hypertonic media. When returned to isotonic media, PAP-HT25 cells swell because of water influx and then shrink to their normal volume because of rapid osmolyte and water efflux (volume regulatory decrease, VRD). Sorbitol efflux from PAP-HT25 cells during VRD was reduced to 18% of control by incubation of the cells with 100 microM eicosatetraynoic acid (ETYA), indicating that an enzyme that metabolizes arachidonic acid (AA) is a key component of the efflux process. Sorbitol efflux was unaffected by incubation with cyclooxygenase and lipoxygenase inhibitors but was reduced to 9% by incubation with 100 microM ketoconazole and to 37% by incubation with 100 microM SKF-525A, indicating that the cytochrome P-450 limb of the AA cascade is involved in the efflux process. The efflux of other organic osmolytes betaine and myoinositol, but not glycerolphosphorylcholine, was also inhibited by incubation with ETYA and ketoconazole.

Targetted destruction of PC3 mitochondria by ETYA: a 'Trojan horse' membrane-suicide molecule

The reported incorporation of ETYA in place of arachidonic acid, itself enriched in mitochondria, and the autooxidation of alkyne groups, as indicated by spontaneous chemiluminescence, encompasses several features appropriate for an organelle-specific 'suicide' molecule. In point of fact, ETYA selectively destroys PC3 mitochondria.

Tumor cell mitochondrial matrix/cristae complexes as potential sites for anticancer therapy with polyunsaturated fatty acid analogues

The consequences of incubating human cancer cells with ETYA, a competitive analogue of arachidonic acid, and the reported responses of cells cultured with polyunsaturated fatty acids indicate that polyunsaturated fatty acid analogues or their modified congeners could represent potential cytotoxic anticancer agents. The inner mitochondrial membrane and matrix may represent important targets for such agents, since they seem unusually susceptible to ETYA-induced oxidative stress.

Effects of eicosatetraynoic acid on membrane lipids of trout liver and intestine

After two months feeding either an (n-3) or an (n-6) fatty acid-rich diet, two groups of trout were switched to the (n-6) or the (n-3) fatty acid-rich diet, respectively. Half of each group was treated with 0.03% 5,8,11,14-eicosatetraynoic acid (ETYA) in the diet. Liver and intestinal brush border membrane lipids were analyzed. No effect was observed on their cholesterol content. ETYA induced an accumulation of 18:2(n-6), and it did not affect the 20:4(n-6) content but decreased the 22:5(n-6) content. ETYA induced an increase of 18:3(n-3) content in the brush border membrane and a decrease of the 22:6(n-3) content in the liver. Those results suggest that ETYA blocks mainly the delta 6-desaturase, which should have two different sites in the liver and one in the intestine.

Blockade of receptor-mediated cyclic GMP formation by hydroxyeicosatetraenoic acid

Receptor-mediated cyclic GMP formation in N1E-115 murine neuroblastoma cells appears to involve oxidative metabolism of arachidonic acid. Evidence in support of this includes the blockade of this response by lipoxygenase inhibitors, e.g., eicosatetraynoic acid (ETYA) or other metabolic perturbants, e.g., methylene blue. It was recently discovered that the lipoxygenase products 15-hydroxyeicosatetraenoic (15-HETE) acid and 12-HETE, like ETYA, were inhibitors of M1 muscarinic receptor-mediated cyclic GMP formation. In the present report, the effects of monoHETEs are explored in more detail, particularly with regard to the function of the muscarinic receptor. Like 12-HETE and 15-HETE (IC50 = 13 and 11 microM, respectively), 5-HETE inhibited the cyclic GMP response to the muscarinic receptor (IC50 = 10 microM). All three of these monoHETEs were shown also to be inhibitors of the cyclic GMP responses to receptors stimulated by carbachol, histamine, thrombin, neurotensin, and bradykinin. 15-HETE was shown to inhibit the muscarinic receptor-mediated response in a complex manner (apparent noncompetitive and uncompetitive components; IC50 = 18 and 2 microM, respectively). 15-HETE did not inhibit either the M1 muscarinic receptor-stimulated release of [3H]inositol phosphates from cellular phospholipids or the M2 muscarinic receptor-mediated inhibition of hormone (prostaglandin E1)-induced AMP formation. It seemed possible that the monoHETEs could enter into biochemical pathways for arachidonate in N1E-115 cells. [3H]Arachidonate and the three [3H]-monoHETEs all rapidly labeled the membrane lipids of intact N1E-115 cells, with each [3H]eicosanoid producing a unique labeling profile. [3H]15-HETE labeling was noteworthy in that 85% of the label found in the phospholipids was in phosphatidylinositol (PI;t1/2 to steady state = 3 min). Exogenous 15-HETE inhibited the labeling of PI by [3H]arachidonate (IC50 = 28 microM) and elevated unesterified [3H]arachidonate levels. Thus, the mechanism of blockade of receptor-mediated cyclic GMP responses by monoHETEs is likely to be more complex than the simple inhibition of cytosolic mechanisms, e.g., generation of a putative second messenger by lipoxygenase, and may involve also alterations of membrane function accompanying the redistributions of esterified arachidonate.

Eicosadiynoic acid: a non-toxic inhibitor of multiple enzymatic steps in the production of icosanoids from arachidonic acid

We have studied the acetylenic fatty acid 20:2 delta 8a, 11a (eicosadiynoic acid, EDYA). It was found that this compound acts as an inhibitor of several steps in the production of icosanoids from arachidonic acid. First, the compound was shown to inhibit arachidonate uptake by platelets. Second, using a detergent solubilized preparation from calf brain, EDYA was found to inhibit both the arachidonoyl and the non-specific long chain acyl-CoA synthetase, which convert arachidonate to its CoA ester. Third, the compound decreased the conversion of dihomo gamma linolenic acid to arachidonate in the mouse fibrosarcoma HSDM1C1 cell line, acting as an apparent delta 5 desaturase inhibitor. Finally, EDYA (50 microM) inhibited cyclooxygenase activity. The compound was not toxic to cultured cells. Cells were grown for months in tissue culture medium at concentrations as high as 50 microM, with no morphologic changes by light microscopy and no prolongation of the doubling time over untreated cells. Our findings with this compound indicate that it limits icosanoid production by inhibiting cyclooxygenase and also by limiting arachidonate uptake, activation, and production from precursor fatty acids.

Studies of the regulation of basal adenylate cyclase activity by membrane polyunsaturated fatty acids in cultured neuroblastoma

The role of membrane polyunsaturated fatty acids (PUFAs) in the regulation of basal adenylate cyclase activity was examined in intact N1E-115 neuroblastoma cells. Addition of linoleic acid (50 microM) to the culture medium for 48 h resulted in a significant increase in phospholipid PUFA content and in a two- to fivefold increase in basal accumulation of cyclic AMP (cAMP). Both phenomena were reversed on removal of linoleate from the medium. PUFA enrichment stimulated cell proliferation by approximately 20% without altering the relative proportion of cellular protein. The supplemented cells synthesized significantly larger amounts of prostaglandin (PG) E and D than did the controls; however, blockade of PG synthesis by indomethacin or ibuprofen did not alter cAMP formation. Supplemented cells contained higher levels of malondialdehyde (MDA) than did controls, and MDA formation was reduced by coculture with alpha-tocopherol; however, its inclusion in the medium did not affect cAMP accumulation. Linoleate-supplemented cells responded to cyclase-activating agonists to the same extent as did control cells. Responses to inhibitory agonists (e.g., isoproterenol and carbamylcholine) were altered, but not to a sufficient extent to account for the PUFA-dependent increases in basal adenylate cyclase activity.