Cellular proliferation and lipid metabolism: importance of lipoxygenases in modulating epidermal growth factor-dependent mitogenesis

Lipid Mediators Metabolic Chaos of Asthmatic Mice Reversed by Rosmarinic Acid

BACKGROUND AND OBJECTIVE

Asthma is a common chronic inflammatory disease of the airways with no known cure. Lipid mediators (LMs) are a kind of inflammatory signaling molecules which are believed to be involved in the development of asthma. Hyssopus cuspidatus Boriss. is a traditional Uyghur medicine, which is widely used in the treatment of asthma and other respiratory diseases. Extraction of Hyssopus cuspidatus Boriss. was reported to neutralize asthma symptoms. The purpose of the study was to investigate both the anti-inflammatory and immunoregulation properties of the Hyssopus cuspidatus Boriss. extract (SXCF) and its main active constituent, rosmarinic acid (RosA), in vivo. The effect of RosA, a major constituent of SXCF, was evaluated on an asthmatic model, with both anti-inflammatory and immunoregulation properties.

MATERIALS AND METHODS

Anti-inflammatory effect of SXCF and RosA was assessed using OVA-induced asthma model mice by UPLC-MS/MS method.

RESULTS

Overall, RosA played a critical role in anti-asthma treatment. In total, 90% of LMs species that were significantly regulated by SXCF were covered. On the most important LMs associated with asthma, RosA equivalent induced similar effects as SXCF did. It is believed that some constituents in SXCF could neutralize RosA excessive impacts on LMs.

Platelet-12 lipoxygenase targeting via a newly synthesized curcumin derivative radiolabeled with technetium-99m

Background

One of the most popular techniques for cancer detection is the nuclear medicine technique. The present research focuses on Platelet-12-lipoxygenase (P-12-LOX) as a promising target for treating and radio-imaging tumor tissues. Curcumin was reported to inhibit this enzyme via binding to its active site.

Results

A novel curcumin derivative was successfully synthesized and characterized with yield of 74%. It was radiolabeled with the diagnostic radioisotope technetium-99m with 84% radiochemical yield and in vitro stability up to 6 h. The biodistribution studies in tumor bearing mice confirmed the high affinity predicted by the docking results with a free binding energy value of (ΔG −50.10 kcal/mol) and affinity (13.64 pki) showing high accumulation in solid tumor with target/non-target ratio >6.

Conclusion

The newly synthesized curcumin derivative, as a result of a computational study on platelet-12 lipoxygenase, showed its excellent free binding energy (∆G −50.10 kcal/mol) and high affinity (13.64 pKi). It could be an excellent radio-imaging agent that targeting tumor cells via targeting of P-12-LOX.Graphical abstract

Arachidonoyl-phosphatidylcholine oscillates during the cell cycle and counteracts proliferation by suppressing Akt membrane binding

The activity of protein kinase B (Akt)--a major kinase promoting cell proliferation and survival--oscillates during the cell cycle. To investigate whether membrane phospholipids may regulate Akt phosphorylation and thus activity, we monitored the lipid profile of nocodazole-synchronized mouse NIH 3T3 fibroblasts during the cell cycle by liquid chromatography electrospray ionization tandem mass spectrometry (LC-MS/MS). The proportion of sn-2-arachidonoyl-phosphatidylcholine (20:4-PC) inversely correlated with Akt activity. Increasing the cellular ratio of 20:4-PC by supplementation of 20:4-PC to the cell culture medium diminished Akt [serine (Ser)473] phosphorylation. Saturated and monounsaturated phosphatidylcholines, used as control had no effect; 20:4-PC reduced cell proliferation relative to controls, interfered with S-phase transition, and suppressed Akt downstream signaling and cyclin expression like LY294002, which is a specific inhibitor of the phosphatidylinositol-3-kinase/Akt pathway. Additive effects of 20:4-PC and LY294002 were not observed, underlining the critical role of Akt for 20:4-PC signaling; 20:4-PC suppressed Akt membrane translocation as shown by immunofluorescence microscopy but left the concentration of the anchor lipid phosphatidylinositol-3,4,5-trisphosphate unchanged. An in vitro binding assay suggests that 20:4-PC attenuates the interaction of Akt with its membrane binding site. We conclude that 20:4-PC oscillates during the cell cycle and delays cell cycle progression by inhibiting Akt membrane binding.

Absence of glutathione peroxidase 4 affects tumor angiogenesis through increased 12/15-lipoxygenase activity

The selenoenzyme glutathione peroxidase 4 (GPx4) has been described to control specific cyclooxygenases (COXs) and lipoxygenases (LOXs) that exert substantiated functions in tumor growth and angiogenesis. Therefore, we hypothesized a putative regulatory role of GPx4 during tumor progression and created transformed murine embryonic fibroblasts with inducible disruption of GPx4. GPx4 inactivation caused rapid cell death in vitro, which could be prevented either by lipophilic antioxidants or by 12/15-LOX-specific inhibitors, but not by inhibitors targeting other LOX isoforms or COX. Surprisingly, transformed GPx4(+/-) cells did not die when grown in Matrigel but gave rise to tumor spheroids. Subcutaneous implantation of tumor cells into mice resulted in knockout tumors that were indistinguishable in volume and mass in comparison to wild-type tumors. However, further analysis revealed a strong vascular phenotype. We observed an increase in microvessel density as well as a reduction in the number of large diameter vessels covered by smooth muscle cells. This phenotype could be linked to increased 12/15-LOX activity that was accompanied by an up-regulation of basic fibroblast growth factor and down-regulation of vascular endothelial growth factor A protein expression. Indeed, pharmacological inhibition of 12/15-LOX successfully reversed the tumor phenotype and led to "normalized" vessel morphology. Thus, we conclude that GPx4, through controlling 12/15-LOX activity, is an important regulator of tumor angiogenesis as well as vessel maturation.

Calcium-dependent lateral organization in phosphatidylinositol 4,5-bisphosphate (PIP2)- and cholesterol-containing monolayers

Biological membrane function, in part, depends upon the local regulation of lipid composition. The spatial heterogeneity of membrane lipids has been extensively explored in the context of cholesterol and phospholipid acyl-chain-dependent domain formation, but the effects of lipid head groups and soluble factors in lateral lipid organization are less clear. In this contribution, the effects of divalent calcium ions on domain formation in monolayers containing phosphatidylinositol 4,5-bisphosphate (PIP2), a polyanionic, multifunctional lipid of the cytosolic leaflet of the plasma bilayer, are reported. In binary monolayers of PIP2 mixed with zwitterionic lipids, calcium induced a rapid, PIP2-dependent surface pressure drop, with the concomitant formation of laterally segregated, PIP2-rich domains. The effect was dependent upon head-group multivalency, because lowered pH suppressed the surface-pressure effect and domain formation. In accordance with previous observations, inclusion of cholesterol in lipid mixtures induced coexistence of two liquid phases. Phase separation strongly segregated PIP2 to the cholesterol-poor phase, suggesting a role for cholesterol-dependent lipid demixing in regulating PIP2 localization and local concentration. Similar to binary mixtures, subphase calcium induced contraction of ternary cholesterol-containing monolayers; however, in these mixtures, calcium induced an unexpected, PIP2- and multivalency-dependent decrease in the miscibility phase transition surface pressure, resulting in rapid dissolution of the domains. This result emphasizes the likely critical role of subphase factors and lipid head-group specificity in the formation and stability of cholesterol-dependent domains in cellular plasma membranes.

Peroxidase: a term of many meanings

Peroxidase research has been instrumental in defining the principles of chemical catalysis. By now, enzymes termed peroxidases represent a heterogeneous group of distinct enzyme families that operate by different catalytic principles and fulfill diverse biological functions, detoxifying H2O2 being just one of many aspects. H2O2 -dependent synthesis of secondary metabolites is the domain of heme peroxidases and related enzymes operating by transition metal catalysis, that often is mediated by free radical formation. Instead, the coenzyme-free glutathione peroxidases and peroxiredoxins only catalyze two-electron transitions and, thus, can reliably remove hydroperoxides without causing radical-mediated collateral damage. However, their ability to use hydroperoxides for the formation of specific disulfide bonds with and within particular proteins broadens their spectrum of biological activities to differentiation phenomena, redox regulation of metabolic processes, redox sensing, and signalling. The present Forum Editorial tries to guide the reader through the 190 years of equally bewildering and fascinating research on peroxidases up to the topical frontiers of the field that are addressed in this issue.

Arachidonic Acid metabolites in the cardiovascular system: the role of lipoxygenase isoforms in atherogenesis with particular emphasis on vascular remodeling

Vascular remodeling refers to lasting structural alterations in the vessel wall that are initiated in response to external and internal stimuli. These changes are distinct from acute functional responses of blood vessels when challenged by increased blood pressure, altered hemodynamics, or vasoactive mediators. In early atherogenesis, when lesion formation is starting to impact local hemodynamics, the vessel wall responds with outward vascular remodeling to maintain normal blood flow. However, inward remodeling may also occur during the time course of plaque formation, contributing to vascular stenosis. Lipoxygenases form a heterogeneous family of lipid-peroxidizing enzymes, which have been implicated in atherogenesis. Several lines of in vitro and in vivo evidence indicated their involvement in disease development, but the precise function of different lipoxygenase isoforms is still a matter of discussion. Vascular remodeling is an early response during plaque development; therefore, lipoxygenases may be involved in this process. Unfortunately, little is known about the potential role of lipoxygenase isoforms in vascular remodeling. This review will briefly summarize our knowledge of the role of lipoxygenases in vascular biology and will critically review the activities of the 3 most athero-relevant lipoxygenase isoforms in atherogenesis, with particular emphasis on vascular remodeling.

Chronic inflammation and oxidative stress in human carcinogenesis

A wide array of chronic inflammatory conditions predispose susceptible cells to neoplastic transformation. In general, the longer the inflammation persists, the higher the risk of cancer. A mutated cell is a sine qua non for carcinogenesis. Inflammatory processes may induce DNA mutations in cells via oxidative/nitrosative stress. This condition occurs when the generation of free radicals and active intermediates in a system exceeds the system's ability to neutralize and eliminate them. Inflammatory cells and cancer cells themselves produce free radicals and soluble mediators such as metabolites of arachidonic acid, cytokines and chemokines, which act by further producing reactive species. These, in turn, strongly recruit inflammatory cells in a vicious circle. Reactive intermediates of oxygen and nitrogen may directly oxidize DNA, or may interfere with mechanisms of DNA repair. These reactive substances may also rapidly react with proteins, carbohydrates and lipids, and the derivative products may induce a high perturbation in the intracellular and intercellular homeostasis, until DNA mutation. The main substances that link inflammation to cancer via oxidative/nitrosative stress are prostaglandins and cytokines. The effectors are represented by an imbalance between pro-oxidant and antioxidant enzyme activities (lipoxygenase, cyclooxygenase and phospholipid hydroperoxide glutathione-peroxidase), hydroperoxides and lipoperoxides, aldehydes and peroxinitrite. This review focalizes some of these intricate events by discussing the relationships occurring among oxidative/nitrosative/metabolic stress, inflammation and cancer.

Dietary factors and growth and metabolism in experimental tumors

Development of a diet that provides adequate nutrition and effective cancer prevention is an important goal in nutrition and cancer research. A confounding aspect of dietary control of tumor growth is the fact that some nutrients may up-regulate tumor growth, whereas other nutrients and nonnutrients down-regulate growth. Both up- and down-regulators may be present in the same foodstuff. Identification of these substances, determination of their mechanisms of action and potencies, as well as the interactions among the different mechanisms are topics of ongoing research. In this review, we describe results obtained in vivo or during perfusion in situ using solid tissue-isolated rodent tumors and human cancer xenografts in nude rats. Linoleic acid (LA), an essential n-6 polyunsaturated fatty acid (PUFA), was identified as an agent in dietary fat that is responsible for an up-regulation of tumor growth in vivo. Tumor LA uptake, mediated by high intratumor cAMP, stimulated formation of the mitogen, 13-hydroxyoctadecadienoic acid (13-HODE) and also increased ERK1/2 phosphorylation, [(3)H]thymidine incorporation and growth. A mechanism for control of this growth-promoting pathway was revealed during studies of the effects of dietary nutrients and nonnutrients known to inhibit tumor growth. These included four groups of lipophilic agents: n-3 fatty acids, melatonin, conjugated LA isomers and trans fatty acids. Each of these agents activated an inhibitory G protein-coupled receptor-mediated pathway that specifically suppressed tumor uptake of saturated, monounsaturated and n-6 PUFAs, thereby inhibiting an early step in the LA-dependent growth-promoting pathway.

Metabolism of oxidized linoleic acid by glutathione transferases: Peroxidase activity toward 13-hydroperoxyoctadecadienoic acid

The oxidation of linoleic acid produces several products with biological activity including the hydroperoxy fatty acid 13-hydroperoxyoctadecadienoic acid (13-HPODE), the hydroxy fatty acid 13-hydroxyoctadecadienoic acid (13-HODE), and the 2,4-dienone 13-oxooctadecadienoic acid (13-OXO). In the present work, the peroxidase activity of glutathione transferases (GST) A1-1, M1-1, M2-2, and P1-1(Val 105) toward 13-HPODE has been examined. The alpha class enzyme is the most efficient peroxidase while the two enzymes from the mu class exhibit weak peroxidase activity toward 13-HPODE. It was also determined that the conjugated diene 13-HODE is not a substrate for GST from the alpha and mu classes but that 13-HODE does inhibit the GST-catalyzed conjugation of CDNB by enzymes from the alpha, mu, and pi classes. Finally, both 13-HODE and 13-OXO were shown to be inducers of GST activity in HT-29 and HCT-116 colon tumor cells. These data help to clarify the role of GST in the metabolic disposition of linoleic acid oxidation products.

Synthetic curcuminoids modulate the arachidonic acid metabolism of human platelet 12-lipoxygenase and reduce sprout formation of human endothelial cells

Platelet 12-lipoxygenase (P-12-LOX) is overexpressed in different types of cancers, including prostate cancer, and the level of expression is correlated with the grade of this cancer. Arachidonic acid is metabolized by 12-LOX to 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], and this biologically active metabolite is involved in prostate cancer progression by modulating cell proliferation in multiple cancer-related pathways inducing angiogenesis and metastasis. Thus, inhibition of P-12-LOX can reduce these two processes. Several lipoxygenase inhibitors are known, including plant and mammalian lipoxygenases, but only a few of them are known inhibitors of P-12-LOX. Curcumin is one of these lipoxygenase inhibitors. Using a homology model of the three-dimensional structure of human P-12-LOX, we did computational docking of synthetic curcuminoids (curcumin derivatives) to identify inhibitors superior to curcumin. Docking of the known inhibitors curcumin and NDGA to P-12-LOX was used to optimize the docking protocol for the system in study. Over 75% of the compounds of interest were successfully docked into the active site of P-12-LOX, many of them sharing similar binding modes. Curcuminoids that did not dock into the active site did not inhibit P-12-LOX. From a set of the curcuminoids that were successfully docked and selected for testing, two were found to inhibit human lipoxygenase better than curcumin. False-positive curcuminoids showed high LogP (theoretical) values, indicating poor water solubility, a possible reason for lack of inhibitory activity or/and nonrealistic binding. Additionally, the curcuminoids inhibiting P-12-LOX were tested for their ability to reduce sprout formation of endothelial cells (in vitro model of angiogenesis). We found that only curcuminoids inhibiting human P-12-LOX and the known inhibitor NDGA reduced sprout formation. Only limited inhibition of sprout formation at approximately IC(50) concentrations has been seen. At IC(50), a substantial amount of 12-HETE can be produced by lipoxygenase, providing a stimulus for angiogenic sprouting of endothelial cells. Increasing the concentration of lipoxygenase inhibitors above IC(50), thus decreasing the concentration of 12(S)-HETE produced, greatly reduced sprout formation for all inhibitors tested. This universal event for all tested lipoxygenase inhibitors suggests that the inhibition of sprout formation was most likely due to the inhibition of human P-12-LOX but not other cancer-related pathways.

Conjugated linoleic acid, cis-9,trans-11, is a substrate for pulmonary 15-lipoxygenase-1 in rat

The objective of this study was to determine whether two of the major conjugated linoleic acid (CLA) isomers, cis-9,trans-11 (c9,t11) and trans-10,cis-12 (t10,c12), are possible substrates for pulmonary 15-lipoxygenase-1 (15-LOX-1) and, therefore, they are also involved in the production of 13(S)-hydroxyoctadecadienoic acid [13(S)-HODE] in biological systems. 13(S)-HODE, a major bioactive metabolite of linoleic acid, is an important intracellular signal agent and is involved in cell proliferation and differentiation in various biological systems. Nordihydroguaiaretic acid (NDGA), a known LOX inhibitor, was used as a control for measuring 15-LOX-1 enzyme activity. It was found that c9,t11-CLA was 25% as active as linoleic acid as a substrate for 15-LOX-1; however, t10,c12-CLA was not a substrate for 15-LOX-1 as measured by 13(S)-HODE production. The authenticity of the production of 13(S)-HODE from c9,t11 as a substrate was established by isolation and cochromatography with pure standard on HPLC using non-radioactive and [14C]-c9,t11-CLA.

Prostanoids and prostanoid receptors in signal transduction

Prostanoids are arachidonic acid metabolites and are generally accepted to play pivotal functions in amongst others inflammation, platelet aggregation, and vasoconstriction/relaxation. Inhibition of their production with, for instance, aspirin has been used for over a century to combat a large variety of pathophysiological processes, with great clinical success. Hence, the cellular changes induced by prostanoids have been subject to an intensive research effort and especially prostanoid-dependent signal transduction has been extensively studied. In this review, we discuss the impact of the five basic prostanoids, TxA(2), PGF(2alpha), PGE(2), PGI(2), and PGD(2), via their receptors on cellular physiology. These inflammatory lipids may stimulate serpentine plasma membrane-localized receptors, which in turn affect major signaling pathways, such as the MAP kinase pathway and the protein kinase A pathway, finally resulting in altered cellular physiology. In addition, prostanoids may activate the PPARgamma members of the steroid/thyroid family of nuclear hormone receptors, which act as transcription factors and may thus directly influence gene transcription. Finally, evidence exists that prostanoids act as second messengers downstream of mitogen receptor activation, mediating events, such as cytoskeletal changes, maybe via direct interaction with GTPase activating proteins. The final cellular reaction to prostaglandin stimulation will most likely depend on combined effects of the above-mentioned levels of interaction between prostaglandins and their cellular receptors.

Monomethyl branched-chain fatty acids play an essential role in Caenorhabditis elegans development

Monomethyl branched-chain fatty acids (mmBCFAs) are commonly found in many organisms from bacteria to mammals. In humans, they have been detected in skin, brain, blood, and cancer cells. Despite a broad distribution, mmBCFAs remain exotic in eukaryotes, where their origin and physiological roles are not understood. Here we report our study of the function and regulation of mmBCFAs in Caenorhabditis elegans, combining genetics, gas chromatography, and DNA microarray analysis. We show that C. elegans synthesizes mmBCFAs de novo and utilizes the long-chain fatty acid elongation enzymes ELO-5 and ELO-6 to produce two mmBCFAs, C15ISO and C17ISO. These mmBCFAs are essential for C. elegans growth and development, as suppression of their biosynthesis results in a growth arrest at the first larval stage. The arrest is reversible and can be overcome by feeding the arrested animals with mmBCFA supplements. We show not only that the levels of C15ISO and C17ISO affect the expression of several genes, but also that the activities of some of these genes affect biosynthesis of mmBCFAs, suggesting a potential feedback regulation. One of the genes, lpd-1, encodes a homolog of a mammalian sterol regulatory element-binding protein (SREBP 1c). We present results suggesting that elo-5 and elo-6 may be transcriptional targets of LPD-1. This study exposes unexpected and crucial physiological functions of C15ISO and C17ISO in C. elegans and suggests a potentially important role for mmBCFAs in other eukaryotes.

Lipoxygenase and cyclooxygenase metabolism: new insights in treatment and chemoprevention of pancreatic cancer

The essential fatty acids, linoleic acid and arachidonic acid play an important role in pancreatic cancer development and progression. These fatty acids are metabolized to eicosanoids by cyclooxygenases and lipoxygenases. Abnormal expression and activities of both cyclooxygenases and lipoxygenases have been reported in pancreatic cancer. In this article, we aim to provide a brief summary of (1) our understanding of the roles of these enzymes in pancreatic cancer tumorigenesis and progression; and (2) the potential of using cyclooxygenase and lipoxygenase inhibitors for pancreatic cancer treatment and prevention.

Conjugation of the linoleic acid oxidation product, 13-oxooctadeca-9,11-dienoic acid, a bioactive endogenous substrate for mammalian glutathione transferase

The oxidation of linoleic acid leads to the generation of several products with biological activity, including 13-oxooctadeca-9,11-dienoic acid (13-OXO), a bioactive 2,4-dienone that has been linked to cell differentiation. In the current work, the conjugation of 13-OXO by human glutathione transferases (GSTs) of the alpha (A1-1, A4-4), mu (M1-1, M2-2) and pi (the allelic variants P1-1/ile, and P1-1/val) classes, and a rat theta (rT2-2) class enzyme has been evaluated. The kinetics and stereoselectivity of the production of the 13-OXO-glutathione conjugate (13-OXO-SG) have been examined. In contrast to many xenobiotic substrates, the endogenous substrate 13-OXO does not exhibit an appreciable non-enzymatic rate of conjugation under physiological conditions. Therefore, the GST-catalyzed conjugation takes on greater significance as it provides the only realistic means for formation of 13-OXO-SG in most biological systems. Alpha class enzymes are most efficient at catalyzing the formation of 13-OXO-SG with kcat/Km values of 8.9 mM(-1) s(-1) for GST A1-1 and 2.14 mM(-1) s(-1) for GST A4-4. In comparison, enzymes from the mu and pi classes exhibit specificity constants from 0.4 to 0.8 mM(-1) s(-1). Conjugation of 13-OXO with glutathione at C-9 of the substrate can yield a pair of diastereomers that can be resolved by chiral HPLC. GSTs from the mu and pi classes are the most stereoselective enzymes and there is no apparent relationship between catalytic efficiency and stereoselectivity. The role of GST in the metabolic disposition of the bioactive oxidation products of linoleic acid has implications for the regulation of normal cellular functions by these versatile enzymes.

Polyunsaturated fatty acids, melatonin, and cancer prevention 1 1Abbreviations: 13-HODE, 13-hydroxyoctadecadienoic acid; NDGA, nordihydroguaiaretic acid; EGF, epidermal growth factor; EPA, eicosapentaenoic acid; DHA, docosahexaenoic acid; 8-Br-cAMP, 8-bromo-cyclic adenosine monophosphate; FATP, fatty acid transport protein; cAMP, cyclic adenosine monophosphate; TGFα, tumor growth factor alpha; MAPK, mitogen-activated protein kinase; and FAT, fatty acid translocase

Many nutritional, hormonal, and environmental factors affect carcinogenesis and growth of established tumors in rodents. In some cases, these factors may either enhance or attenuate the neoplastic process. Recent experiments performed in our laboratory using tissue-isolated rat hepatoma 7288CTC in vivo or during perfusion in situ have demonstrated new interactions among four of these factors. Two agents, dietary linoleic acid (C18:2n6) and "light at night," enhanced tumor growth, and two others, melatonin and n3 fatty acids, attenuated growth. Linoleic acid stimulated tumor growth because it is converted by hepatoma 7288CTC to the mitogen, 13-hydroxyoctadecadienoic acid (13-HODE). Melatonin, the neurohormone synthesized and secreted at night by the pineal gland, and dietary n3 fatty acids are potent antitumor agents. Both inhibited tumor linoleic acid uptake and 13-HODE formation. Artificial light, specifically "light at night," increased tumor growth because it suppressed melatonin synthesis and enhanced 13-HODE formation. Melatonin and n3 fatty acids acted via similar or identical G(i) protein-coupled signal transduction pathways, except that melatonin receptors and putative n3 fatty acid receptors were used. The results link the four factors in a common mechanism and provide new insights into the roles of dietary n6 and n3 polyunsaturated fatty acid intake, "light at night," and melatonin in cancer prevention in humans.

Incorporation and distribution of saturated and unsaturated fatty acids into nuclear lipids of hepatic cells

Liver nuclear incorporation of stearic (18:0), linoleic (18:2n-6), and arachidonic (20:4n-6) acids was studied by incubation in vitro of the [1-14C] fatty acids with nuclei, with or without the cytosol fraction at different times. The [1-14C] fatty acids were incorporated into the nuclei as free fatty acids in the following order: 18:0 > 20:4n-6 >> 18:2n-6, and esterified into nuclear lipids by an acyl-CoA pathway. All [1-14C] fatty acids were esterified mainly to phospholipids and triacylglycerols and in a minor proportion to diacylglycerols. Only [1-14C]18:2n-6-CoA was incorporated into cholesterol esters. The incorporation was not modified by cytosol addition. The incorporation of 20:4n-6 into nuclear phosphatidylcholine (PC) pools was also studied by incubation of liver nuclei in vitro with [1-14C]20:4n-6-CoA, and nuclear labeled PC molecular species were determined. From the 15 PC nuclear molecular species determined, five were labeled with [1-14C]20:4n-6-CoA: 18:0-20:4, 16:0-20:4, 18:1-20:4, 18:2-20:4, and 20:4-20:4. The highest specific radioactivity was found in 20:4-20:4 PC, which is a minor species. In conclusion, liver cell nuclei possess the necessary enzymes to incorporate exogenous saturated and unsaturated fatty acids into lipids by an acyl-CoA pathway, showing specificity for each fatty acid. Liver cell nuclei also utilize exogenous 20:4n-6-CoA to synthesize the major molecular species of PC with 20:4n-6 at the sn-2 position. However, the most actively synthesized is 20:4-20:4 PC, which is a quantitatively minor component. The labeling pattern of 20:4-20:4 PC would indicate that this molecular species is synthesized mainly by the de novo pathway.

A redox signaling mechanism for density-dependent inhibition of cell growth

Reactive oxygen species (ROS) have recently drawn significant attention as putative mitogenic mediators downstream of activated growth factor receptors and oncogenic Ras; however, the possibility that a redox-related mechanism also operates in the negative control of cell proliferation by inhibitory signals has not been investigated thus far. Here we show that the arrest of growth induced by cell confluence ("contact inhibition") is due, at least in part, to a decrease in the steady-state levels of intracellular ROS and the consequent impairment of mitogenic redox signaling. In confluent fibroblast cultures, the decrease in the concentration of oxygen species was associated with diminished activity of the small GTPase Rac-1, a signal transducer directly involved in the ligand-dependent generation of oxygen-derived molecules, and was effectively mimicked by exposure of sparse cultures to dithiothreitol (DTT) and inhibitors of enzymes (phospholipase A2 and lipoxygenase) acting in the arachidonic acid cascade downstream of growth factor receptors and Rac-1. Sparse fibroblasts treated with nontoxic amounts of DTT underwent growth arrest, whereas a low concentration of hydrogen peroxide significantly increased thymidine incorporation in confluent cultures, demonstrating a causal link between redox changes and growth control by cell density. Removal of oxygen species from sparse cultures was accompanied by a drastic decrease of protein tyrosine phosphorylation after epidermal growth factor stimulation, which, at a biochemical level, reproduced the signaling hallmarks of contact inhibition. Moreover, the cytosolic tyrosine phosphatase SHP-2 was identified as a putative target for redox signaling by cell density because the enzyme itself and the associated substrates appear markedly dephosphorylated in both confluent and reductant-treated cells after exposure to epidermal growth factor, and SHP-2 enzymatic activity is strongly activated by DTT in vitro. Taken together, these data support a model in which impaired generation of ROS and increased protein tyrosine phosphatase activity impede mitogenic signaling in contact-inhibited cells.

Lipocalins and cancer

Lipocalins are mainly extracellular carriers of lipophilic molecules, though exceptions with properties like prostaglandin synthesis and protease inhibition are observed for specific lipocalins. The interest concerning lipocalins in cancer has so far been focussed to the variations in concentration and the modification of lipocalin expression in distinct cancer forms. In addition, lipocalins have been assigned a role in cell regulation. The influence of the extracellular lipocalins on intracellular cell regulation events is not fully understood, but several of the lipocalin ligands are also well-known agents in cell differentiation and proliferation. Lipophilic ligands can, after lipocalin-mediated transport to the cell surface, penetrate the cell membrane and interact with proteins in the cytosol and/or the nucleus. The signaling routes of the lipocalin ligands, retinoids and fatty acids are presented and discussed. Tumor growth in tissue is restricted by extracellular protease/protease inhibitor interactions. Several lipocalins also have protease inhibitory properties and possess the ability to interact with tumor specific proteases, revealing another pathway for lipocalins to interact with cancer cells.

Expression, subcellular localization and putative function of platelet-type 12-lipoxygenase in human prostate cancer cell lines of different metastatic potential

The involvement of 12-lipoxygenase (12-LOX) expression and function in tumor metastasis has been demonstrated in several murine tumor cell lines. In addition, 12-LOX expression was detected in human prostatic tumors and correlated to the clinical stage of disease. Here we provide data that human prostate cancer cell lines express the platelet-type isoform of 12-LOX at both the mRNA and protein levels, and immunohistochemistry revealed 12-LOX expression in human prostate tumors. The enzyme was localized to the plasma membrane, cytoplasmic organelles and nucleus in non-metastatic cells (PC-3 nm) and to the cytoskeleton and nucleus in metastatic cells (DU-145). After orthotopic/intraprostatic injection of tumor cells into SCID mice, the metastatic prostate carcinoma cells (DU-145) expressed 12-LOX at a significantly higher level compared with the non-metastatic counterparts, PC-3nm. The functional involvement of 12-LOX in the metastatic process was demonstrated when DU-145 cells were pretreated in vitro with the 12-LOX inhibitors N-benzyl-N-hydroxy-5-phenylpentamide (BHPP) or baicalein, the use of which significantly inhibited lung colonization. These data suggest a potential involvement of 12-LOX in the progression of human prostate cancer.

Dim light during darkness stimulates tumor progression by enhancing tumor fatty acid uptake and metabolism

Tumor linoleic acid uptake and metabolism, and growth are suppressed by melatonin, the synthesis of which is inhibited by light. Linoleic acid, via its mitogenic metabolite 13-hydroxyoctadecadienoic acid (13-HODE) is an important growth stimulant of rat hepatoma 7288CTC. Here we compared the effects of an alternating light:dark cycle (12L:12D), dim light (0.25 lux) present during the dark phase of a diurnal light cycle, and constant light on growth and fatty acid metabolism in hepatoma 7288CTC. Our results show that dim light suppressed melatonin release by the pineal gland, increased tumor linoleic acid uptake and 13-HODE production, and promoted tumor growth as effectively as did constant light.

Specific protein targets of 13-oxooctadecadienoic acid (13-OXO) and export of the 13-OXO-glutathione conjugate in HT-29 cells

The linoleic acid metabolite, 13-oxooctadecadienoic acid (13-OXO), is reactive with cellular thiols. In the present report, incubations of HT-29 or CaCo-2 homogenates with 13-OXO and GSH indicate that HT-29 cell homogenates produce a 13-OXO-GSH conjugate. The conjugate formed was likely of enzymatic origin as chiral-phase HPLC showed the major product consisted of only one of two possible diastereomers. The glutathione transferase activity (GST), using chlorodinitrobenzene, was found to be 126 nmol/mg/min in HT-29 cells and 21 nmol/mg/min in CaCo-2 cells. These levels of activity are consistent with the relative ability of the two cell lines to conjugate GSH to 13-OXO. Incubation of intact HT-29 cells with either 13-OXO, or the metabolic precursor 13-hydroxyoctadecadienoic acid (13-HODE), showed detectable 13-OXO-GSH conjugate in the media, but none in the cells. The stereochemistry of the extracellular conjugate suggested an enzymatic origin. In additional experiments, the labeling of cellular protein by 13-HODE was much more specific than the labeling of protein by 13-OXO suggesting that in situ generation of 13-OXO from 13-HODE confers selectivity on the reactions between cellular thiols and 13-OXO. These results demonstrate that in HT-29 cells, 13-HODE is converted to 13-OXO which then either reacts with cellular protein or is conjugated to GSH by GST. The 13-OXO-GSH conjugate is then exported from the cell.

Regional distribution, ontogeny, purification, and characterization of the Ca2+-independent phospholipase A2 from rat brain

We purified an 80-kDa Ca2+-independent phospholipase A2 (iPLA2) from rat brain using octyl-Sepharose, ATP-agarose, and calmodulin-agarose column chromatography steps. This procedure gave a 30,000-fold purification and yielded 4 microg of a near-homogeneous iPLA2 with a specific activity of 4.3 micromol/min/mg. Peptide sequences of the rat brain iPLA2 display considerable homology to sequences of the iPLA2 from P388D1 macrophages, Chinese hamster ovary cells, and human B lymphocytes. Under optimal conditions, the iPLA2 revealed the following substrate preference toward the fatty acid chain in the sn-2 position of phosphatidylcholine: linoleoyl > palmitoyl > oleoyl > arachidonoyl. The rat brain iPLA2 also showed a head group preference for choline > or = ethanolamine >> inositol. The iPLA2 is inactivated when exposed to pure phospholipid vesicles. The only exception is vesicles composed of phosphatidylcholine and phosphatidylinositol 4,5-bisphosphate. Studies on the regional distribution and ontogeny of various phospholipase A2 (PLA2) types in rat brain indicate that the iPLA2 is the dominant PLA2 activity in the cytosolic fraction, whereas the group IIA secreted PLA2 is the dominant activity in the particulate fraction. The activities of these two enzymes change during postnatal development.

Do lipoxygenases modulate normal or aberrant lympho-hematopoiesis?

Whether 5- (and the 12- or 15-) lipoxygenases participate in normal or malignantly transformed hematopoietic cell proliferation and differentiation, or contribute to programmed or necrotic cell death has been difficult to decide. Recent evidence concerning these questions is reviewed and some reasons for these difficulties are considered.

Diminution of the development of experimental metastases produced by murine metastatic lines in essential fatty acid-deficient host mice

In a previous study we found that the capacity for spontaneous metastases of tumors developed after subcutaneous transplantation of RSV-transformed Balb/c 3T3 cells was reduced in essential fatty acids (EFA)-deficient host animals. In the present study, we have extended our investigation by considering the requirement of EFA for the formation of lung colonies obtained by i.v. injection of two metastatic murine cell lines of different origin: (1) T3 cells, a highly metastatic cell line isolated from a fibrosarcoma, and (2) the F10 variant of B16 melanoma (B16-F10 cells). We found that EFA deficiency reduces the lung colonization of both T3 cells and B16-F10 cells without affecting the retention of tumor cells in the lung. NK cells did not seem to be involved in the diminution of lung colonization in EFA-deficient animals. Furthermore, by examining histologically the lung parenchyma at successive intervals after tumor cell injection, we found that, in comparison with control mice, EFA-deficient animals had fewer lung colonies and a prevalence of smaller microcolonies during the entire period of observation. This led us to conclude that the diminution in development of tumor colonies in the lungs of EFA-deficient host animals was related to a reduced growth rate of tumor cells at this site.

The proliferation of mouse mammary epithelial cells in response to specific mitogens is modulated by the mammary fat pad in vitro

The ability of the murine mammary fat pad to directly stimulate the growth of mammary epithelial cells and to modulate the effects of various mammogenic agents has been investigated in a newly described, hormone- and serum-free coculture system. COMMA-1D mouse mammary epithelial cells were cultured for 5 or 7 d with various supplements in the absence or presence of epithelium-free mammary fat pad explants from virgin female BALB/c mice. Cocultured fat pad stimulated increases in the DNA content of COMMA-1D cultures by two- to threefold or six- to eightfold after 5 or 7 d, respectively. The mitogenic effect was additive to that of 10% fetal calf serum and could not be attributed to the release of prostaglandin E2 or synthesis of prostaglandins by epithelial cells. In addition, bovine serum albumin attenuated (P < 0.05) the mitogenic effect of cocultured mammary fat pad. Added alone, insulinlike growth factor-I, epidermal growth factor, and insulin increased (P < 0.05) total DNA of COMMA-1D cultures by 2.5-, 3.7-, and 2.3-fold, respectively. Cocultured mammary fat pad markedly interacted (P < 0.01) with these mitogens to yield final DNA values that were 21.2-, 13.3-, and 22.1-fold greater than in basal medium only. Associated with this proliferation was the formation of numerous domes above the COMMA-1D monolayer. There was no proliferative response to growth hormone or prolactin in the absence or presence of cocultured fat pad (P > 0.05). Whereas hydrocortisone did not alter cell number, it attenuated (P < 0.05) the mitogenic effect of cocultured mammary fat pad. These results indicate that the murine mammary fat pad is not only a direct source of mitogenic activity, but also modulates the response of mammary epithelial cells to certain mammogens.

Inhibition of EGF-dependent mitogenesis by prostaglandin E2 in Syrian hamster embryo fibroblasts

Lipid metabolism can play an important role in the development and progression of human cancers. We have used Syrian hamster embryo (SHE) fibroblasts as a model system to study how lipid metabolites can alter cell proliferation and apoptosis. For example, the linoleic acid metabolite 13(S)-HpODE enhances EGF-dependent growth by inhibiting de-phosphorylation of the EGFR which leads to activation of the MAP kinase pathway. In contrast, the arachidonic acid metabolite, PGE2, inhibits EGF-dependent mitogenesis and the expression of the proto-oncogenes c-myc, c-jun, and jun-B. In this study, we have investigated the mechanism by which PGE2 attenuates these responses by studying the EGF signaling cascade in SHE cells. PGE2 pretreatment caused a concentration-dependent decrease in EGF-dependent phosphorylation of MAP kinase and a corresponding inhibition of EGF-stimulated MAP kinase activity. Pretreatment of the SHE cells with PGE2 had little effect on the magnitude of EGF-dependent receptor auto-phosphorylation and the phosphorylation of GAP suggesting a down-stream target. Treatment of cells with forskolin and EGF causes similar inhibition of MAP kinase phosphorylation as observed with PGE2 and EGF. Since PGE2 elevates cAMP in these cells, it may act by altering cAMP accumulation. Raf-1 activity can be inhibited by a cAMP-dependent process. Raf-1 activity, measured by phosphorylation of Mek-1, was attenuated by the addition of PGE2. To determine if inhibition of Raf-1 activity causes inhibition of the MAP kinase pathway, cells were concomitantly incubated with PGE2 and EGF. Inhibition of MAP kinase phosphorylation was observed. From these data, we propose that in SHE cells PGE2 increases cAMP levels, which in turn causes inhibition of Raf-1 activity. The MAP kinase pathway is thus downregulated which decreases mitogenesis and proto-oncogene expression. This study demonstrates that an arachidonic acid metabolite can modulate phosphorylation and activity of key signal transduction proteins in a growth factor mitogenic pathway.

Substrate specificity and characterization of partially purified rat liver 13-hydroxyoctadecadienoic acid (13-HODE) dehydrogenase

Oxidation products of linoleic acid, such as 13-hydroxyoctadecadienoic acid (13-HODE), exhibit biological activity in a number of systems. One major metabolic fate of 13-HODE is oxidation to the 2,4-dienone, 13-oxooctadecadienoic acid by an NAD(+)-dependent dehydrogenase (13-HODE dehydrogenase). The present work describes the partial purification and characterization of 13-HODE dehydrogenase from rat liver cytosol. The enzyme was purified using a combination of ammonium sulfate precipitation, as well as hydroxylapatite, gel permeation, and hydrophobic interaction chromatography. Analysis of the most purified preparation by SDS-polyacrylamide gel electrophoresis indicates two subunits of approximately 55 kDa, suggesting the possibility of a heterodimeric enzyme. However, due to aggregation in the purified preparation, an accurate molecular mass for the native enzyme has not yet been obtained. Using 13-HODE as a substrate, the purified enzyme has a Km of 6.3 microM and a Vmax of 5.7 nmol/min/mg. More importantly, the enzyme has a narrow substrate specificity with 13-HODE being the preferred substrate. From a series of 17 potential substrates, only 9-HODE (53% the activity of 13-HODE) and 15-hydroxyeicosatetraenoic acid (64% the activity of 13-HODE) showed significant activity as substrates. A number of other unsaturated hydroxy fatty acids, including several eicosanoids, are not substrates. The narrow substrate specificity displayed by the enzyme suggests that it could play a key role in modulating the effects of oxidized derivatives of linoleic acid.

Occurrence of 13(S)-hydroxyoctadecadienoic acid in biological samples

The oxygenated metabolite of linoleic acid, 13(S)-hydroxyoctadecadienoic acid has recently been shown to play a role in cellular regulation. To detect this molecule in biological systems, we recently developed a specific polyclonal antibody. Using this antibody, we report the presence of 13(S)-hydroxyoctadecadienoic acid in human urine, cell culture media, and untreated goat serum for the first time by a specific, sensitive, and rapid enzyme immunoassay. Furthermore, the enzyme linked immunosorbent assay data are verified by gas chromatography/mass spectrometry analysis of the same samples.

Is there a role for 15-lipoxygenase in atherogenesis?

15-Lipoxygenase has been suggested to play a role in atherogenesis. The proposed action of this enzyme is to oxidize low density lipoprotein (LDL) to the extent that LDL becomes a ligand for the macrophage scavenger receptor. 15-Lipoxygenase and oxidized LDL are co-localized in atherosclerotic lesions; antioxidant drugs that block the lipoxygenase also block oxidation of LDL and the progression of experimental atherosclerosis. Biochemical experiments have demonstrated that the lipoxygenase can be induced by cytokines and/or another factor(s) associated with hypercholesterolemia. However, molecular biological work has shown that induction of the enzyme alone is not sufficient to induce lesion formation. Furthermore, the mechanism of action of 15-lipoxygenase in atherogenesis remains unclear. Predictions of the stereochemistry of enzyme-oxidized linoleate products appear to conflict with the available data. In fact, most studies have discovered substantial levels of racemic 13-hydroxyoctadecadienoic acid (13-HODE) in arterial lesions rather than the stereochemically pure 13(S)-HODE expected from purified enzyme. The possibility that the generation of products of 15-lipoxygenase metabolism must occur in a specific cellular location and during a brief time window in the development of the disease has been discussed. It is also possible that the true function of the linoleate metabolites is to modulate gene expression and regulate mitogenesis, and that oxidation of LDL may play a secondary role. The advent of transgenic species that both develop atherosclerosis and either fail to express or overexpress the lipoxygenase presents an opportunity to clarify some of these issues in the near future.

Production of 13-hydroxyoctadecadienoic acid (13-HODE) by prostate tumors and cell lines

The major lipoxygenation product derived from linoleic acid, 13-(S)-hydroxyoctadecadienoic acid (13-HODE), has been shown to be involved in cell proliferation and differentiation in a number of systems. Rapid detection of picogram amounts of this bioactive lipid in biological samples, however, has been hindered due to lack of immunological reagents. In the current report, we have used a polyclonal antibody specific for 13-(S)-HODE to detect this bioactive lipid for the first time in human prostate adenocarcinoma specimens (PCa) and the prostate cancer cell lines LNCaP and PC-3 by enzyme immunoassay. In addition, we have verified-the quantitation of 13-HODE by chiral-phase HPLC and examined the levels of lipoxygenase expression by Western, Northern, and RT-PCR analysis. Immunohistochemically detectable 13-HODE was observed in human PCa, whereas adjacent normal tissue showed no immunoreactivity. The presence of 15-lipoxygenase was evident by Western and RT-PCR analysis in both LNCaP and PC-3 cells, while Northern blot analysis showed the presence of 15-lipoxygenase message in LNCaP cells but failed to detect any 15-lipoxygenase message in PC-3 cells. In contrast, quantitation of 13-HODE by enzyme immunoassay and chiral-phase HPLC showed significant levels of the compound in PC-3 cells but minimal enzymatically produced 13-HODE in LNCaP cells. These data provide a link between linoleic acid metabolism and the development or progression of prostate cancer.

Characterization of a 15-lipoxygenase in human breast carcinoma BT-20 cells: stimulation of 13-HODE formation by TGF alpha/EGF

Epidemiological and experimental data suggest a role for polyunsaturated fatty acids in the etiology of breast cancer. In this report we have studied arachidonic acid and linoleic acid metabolism in the human breast carcinoma cell line BT-20 which overexpresses both EGF receptor and the homologous erbB-2 oncogene product. EGF and TGF alpha stimulated DNA synthesis in these cells which was attenuated by the addition of a lipoxygenase inhibitor, NDGA. The addition of a prostaglandin H synthase inhibitor did not alter DNA synthesis. Analytical studies reveal little arachidonic acid metabolism while linoleic acid was metabolized to 13-hydroxyoctadecadienoic acid (13-HODE). The formation of 13-HODE was inhibited by the addition of NDGA and was dependent on EGF or TGF alpha. These results suggest the metabolism of linoleic acid by a n-6 or 15-lipoxygenase regulated by EGF/TGF alpha, RT-PCR was used to isolate a clone, and sequenced the cDNA for this enzyme and it was found to be identical to the human 15-lipoxygenase previously characterized from human pulmonary tissue. EGF/TGF alpha did not alter the expression of this enzyme suggesting a potential post-translational regulation of activity. This study provides a link between metabolism of linoleic acid and growth factor regulation of cell proliferation in a human breast carcinoma cell line.

Relationship between arachidonate--phospholipid remodeling and apoptosis

Our previous studies reveal that three structurally distinct inhibitors of the enzyme CoA-independent transacylase, including the antiproliferative alkyllysophospholipid ET-18-O-CH3, induce programmed cell death (apoptosis) in the promyelocytic cell line HL-60. The objective of the current study was to better elucidate the mechanism responsible for apoptosis. CoA-IT is an enzyme believed to be responsible for the remodeling of long chain polyunsaturated fatty acids like arachidonate between the phospholipids of mammalian cells. The chronic (24-48 h) treatment of HL-60 cells with all three CoA-IT inhibitors resulted in the inhibition of the remodeling of labeled arachidonate from choline- into ethanolamine-containing phospholipid molecular species. GC-MS analysis of the fatty acids in phospholipids revealed that CoA-IT inhibitor treatment induced a marked loss of arachidonate-containing phosphatidylethanolamine and an increase in arachidonate-containing phosphatidylcholine. This redistribution was specific to arachidonate since the mass distribution of linoleic acid in glycerolipids was not affected. In spite of the dramatic redistribution of arachidonate, the total cellular arachidonate content was not altered nor was the relative distribution of total phospholipid classes. The increase of arachidonate in phosphatidylcholine was specifically due to an increase in 1-acyl-2-arachidonoyl-sn-glycero-3-phosphocholine species, whereas the loss of arachidonate in PE was from both 1-acyl- and 1-alk-1-enyl-2-arachidonoyl-sn-glycero-3-phosphoethanolamine species. The incubation of cells with exogenous arachidonic acid or ethanolamine did not reverse the inhibition of proliferation induced by CoA-IT inhibitor treatment. Incubation with CoA-IT inhibitors also induced the characteristic cytoplasmic and nuclear changes associated with apoptosis as assessed by transmission electron microscopy and DNA fragmentation as determined by flow cytometry. Taken together, these data show that apoptosis in HL-60 cells, induced by blocking arachidonate-phospholipid remodeling, is correlated with a redistribution of arachidonate in membrane phospholipids and suggest that such alterations represent a signal which controls the capacity of cells to proliferate.

Identification and quantification of regioisomeric cholesteryl linoleate hydroperoxides in oxidized human low density lipoprotein and high density lipoprotein

Oxidation of human LDL is implicated as an initiator of atherosclerosis. Isolated low density lipoprotein (LDL) and high density lipoprotein (HDL2) were exposed to aqueous radicals generated from the thermolabile azo compound 2,2'-azobis(2-amidinopropane) dihydrochloride. The primary nonpolar lipid products formed from the autoxidation of LDL and HDL were the regioisomeric cholesteryl linoleate hydroperoxides. In LDL oxidations, 9- and 13-hydroperoxides with trans,cis conjugated diene were formed as the major oxidation products if endogenous alpha-tocopheral was present in the LDL. After extended oxidation of LDL, at the time when endogenous alpha-tocopherol was consumed, the two trans,cis conjugated diene hydroperoxides began to disappear and the 9- and 13-hydroperoxides with trans,trans conjugated diene appeared. At very long oxidation times, none of the primary products, the conjugated diene hydroperoxides, were present. In HDL2, which has only very low levels of antioxidants, both the 9- and 13-hydroperoxides with trans,cis conjugated diene and the 9- and 13-hydroperoxides with trans,trans conjugated diene were formed at early stages of oxidation. The corresponding alcohols were also formed in the HDL2 oxidations. A mechanistic hypothesis consistent with these observations is presented.