5-Lipoxygenase-mediated endogenous DNA damage

The role of human 5-Lipoxygenase (5-LO) in carcinogenesis - a question of canonical and non-canonical functions

5-Lipoxygenase (5-LO), a fatty acid oxygenase, is the central enzyme in leukotriene (LT) biosynthesis, potent arachidonic acid-derived lipid mediators released by innate immune cells, that control inflammatory and allergic responses. In addition, through interaction with 12- and 15-lipoxgenases, the enzyme is involved in the formation of omega-3 fatty acid-based oxylipins, which are thought to be involved in the resolution of inflammation. The expression of 5-LO is frequently deregulated in solid and liquid tumors, and there is strong evidence that the enzyme plays an important role in carcinogenesis. However, global inhibition of LT formation and signaling has not yet shown the desired success in clinical trials. Curiously, the release of 5-LO-derived lipid mediators from tumor cells is often low, and the exact mechanism by which 5-LO influences tumor cell function is poorly understood. Recent data now show that in addition to releasing oxylipins, 5-LO can also influence gene expression in a lipid mediator-independent manner. These non-canonical functions, including modulation of miRNA processing and transcription factor shuttling, most likely influence cancer cell function and the tumor microenvironment and might explain the low clinical efficacy of pharmacological strategies that previously only targeted oxylipin formation and signaling by 5-LO. This review summarizes the canonical and non-canonical functions of 5-LO with a particular focus on tumorigenesis, highlights unresolved issues, and suggests future research directions.

Mitochondrion-Mediated Cell Death through Erk1-Alox5 Independent of Caspase-9 Signaling

Mitochondrial disruption leads to the release of cytochrome c to activate caspase-9 and the downstream caspase cascade for the execution of apoptosis. However, cell death can proceed efficiently in the absence of caspase-9 following mitochondrial disruption, suggesting the existence of caspase-9-independent cell death mechanisms. Through a genome-wide siRNA library screening, we identified a network of genes that mediate caspase-9-independent cell death, through ROS production and Alox5-dependent membrane lipid peroxidation. Erk1-dependent phosphorylation of Alox5 is critical for targeting Alox5 to the nuclear membrane to mediate lipid peroxidation, resulting in nuclear translocation of cytolytic molecules to induce DNA damage and cell death. Consistently, double knockouts of caspase-9 and Alox5 in mice, but not deletion of either gene alone, led to significant T cell expansion with inhibited cell death, indicating that caspase-9- and Alox5-dependent pathways function in parallel to regulate T cell death in vivo. This unbiased whole-genome screening reveals an Erk1-Alox5-mediated pathway that promotes membrane lipid peroxidation and nuclear translocation of cytolytic molecules, leading to the execution of cell death in parallel to the caspase-9 signaling cascade.

Melatonin and cancer: From the promotion of genomic stability to use in cancer treatment

Cancer remains among the most challenging human diseases. Several lines of evidence suggest that carcinogenesis is a complex process that is initiated by DNA damage. Exposure to clastogenic agents such as heavy metals, ionizing radiation (IR), and chemotherapy drugs may cause chronic mutations in the genomic material, leading to a phenomenon named genomic instability. Evidence suggests that genomic instability is responsible for cancer incidence after exposure to carcinogenic agents, and increases the risk of secondary cancers following treatment with radiotherapy or chemotherapy. Melatonin as the main product of the pineal gland is a promising hormone for preventing cancer and improving cancer treatment. Melatonin can directly neutralize toxic free radicals more efficiently compared with other classical antioxidants. In addition, melatonin is able to regulate the reduction/oxidation (redox) system in stress conditions. Through regulation of mitochondrial nction and inhibition of pro-oxidant enzymes, melatonin suppresses chronic oxidative stress. Moreover, melatonin potently stimulates DNA damage responses that increase the tolerance of normal tissues to toxic effect of IR and may reduce the risk of genomic instability in patients who undergo radiotherapy. Through these mechanisms, melatonin attenuates several side effects of radiotherapy and chemotherapy. Interestingly, melatonin has shown some synergistic properties with IR and chemotherapy, which is distinct from classical antioxidants that are mainly used for the alleviation of adverse events of radiotherapy and chemotherapy. In this review, we describe the anticarcinogenic effects of melatonin and also its possible application in clinical oncology.

A broad-spectrum lipidomics screen of antiinflammatory drug combinations in human blood

Current methods of drug screening in human blood focus on the immediate products of the affected pathway and mostly rely on approaches that lack sensitivity and the capacity for multiplex analysis. We have developed a sensitive and selective method based on ultra-performance liquid chromatography-tandem mass spectrometry to scan the effect of drugs on the bioactive eicosanoid lipidome in vitro and ex vivo. Using small sample sizes, we can reproducibly measure a broad spectrum of eicosanoids in human blood and capture drug-induced substrate rediversion and unexpected shifts in product formation. Microsomal prostaglandin E synthase-1 (mPGES-1) is an antiinflammatory drug target alternative to COX-1/-2. Contrasting effects of targeting mPGES-1 versus COX-1/-2, due to differential substrate shifts across the lipidome, were observed and can be used to rationalize and evaluate drug combinations. Finally, the in vitro results were extrapolated to ex vivo studies by administration of the COX-2 inhibitor, celecoxib, to volunteers, illustrating how this approach can be used to integrate preclinical and clinical studies during drug development.

5-lipoxygenase mediates docosahexaenoyl ethanolamide and N-arachidonoyl-L-alanine-induced reactive oxygen species production and inhibition of proliferation of head and neck squamous cell carcinoma cells

Background

Endocannabinoids have recently drawn attention as promising anti-cancer agents. We previously observed that anandamide (AEA), one of the representative endocannabinoids, effectively inhibited the proliferation of head and neck squamous cell carcinoma (HNSCC) cell lines in a receptor-independent manner. In this study, using HNSCC cell lines, we examined the anti-cancer effects and the mechanisms of action of docosahexaenoyl ethanolamide (DHEA) and N-arachidonoyl-L-alanine (NALA), which are polyunsaturated fatty acid (PUFA)-based ethanolamides like AEA.

Methods and Results

DHEA and NALA were found to effectively inhibit HNSCC cell proliferation. These anti-proliferative effects seemed to be mediated in a cannabinoid receptor-independent manner, since the antagonist of cannabinoid receptor-1 (CB1) and vanilloid receptor-1 (VR1), two endocannabinoid receptors, did not reverse the ability of DHEA and NALA to induce cell death. Instead, we observed an increase in reactive oxygen species (ROS) production and a decrease of phosphorylated Akt as a result of DHEA and NALA treatment. Antioxidants efficiently reversed the inhibition of cell proliferation and the decrease of phosphorylated Akt induced by DHEA and NALA; inhibition of 5-lipoxygenase (5-LO), which is expected to be involved in DHEA- and NALA-degradation pathway, also partially blocked the ability of DHEA and NALA to inhibit cell proliferation and phosphorylated Akt. Interestingly, ROS production as a result of DHEA and NALA treatment was decreased by inhibition of 5-LO.

Conclusions

From these findings, we suggest that ROS production induced by the 5-LO pathway mediates the anti-cancer effects of DHEA and NALA on HNSCC cells. Finally, our findings suggest the possibility of a new cancer-specific therapeutic strategy, which utilizes 5-LO activity rather than inhibiting it.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2499-3) contains supplementary material, which is available to authorized users.

Vitamin C supplement intake and postmenopausal breast cancer risk: interaction with dietary vitamin C

BACKGROUND

Experimental and epidemiologic studies have yielded conflicting results on the relation between vitamin C intake and breast cancer risk.

OBJECTIVE

We investigated the relation between vitamin C supplement intake and breast cancer risk while considering dietary vitamin C intake.

DESIGN

Between 1995 and 2008, 2482 invasive breast cancer cases occurred in 57,403 postmenopausal women from the Etude Epidémiologique auprès de femmes de la Mutuelle Générale de l'Education Nationale (E3N) prospective cohort during 581,085 person-years. We estimated vitamin C intake from foods with the use of a validated food-frequency questionnaire that was sent to subjects in 1993-1995 and vitamin C supplement use via questionnaires sent in 1995, 2000, 2002, and 2005. Multivariable HRs (95% CIs) for primary invasive breast cancer were estimated with the use of Cox regression models. All statistical tests were 2-sided.

RESULTS

Vitamin C supplement use (ever compared with never) was not associated with breast cancer risk overall; it was associated with higher breast cancer risk in women in the fourth quartile of vitamin C intake from foods (HR: 1.32; 95% CI: 1.04, 1.67) but not in other quartiles of dietary vitamin C intake (P-interaction = 0.03).

CONCLUSIONS

We observed that vitamin C supplement use was associated with increased postmenopausal breast cancer risk in women with high vitamin C intake from foods. Our data suggest a potential U- or J-shaped relation between total vitamin C intake and postmenopausal breast cancer risk that deserves further investigation.

[Oxidative stress-mediated chemical modifications to biomacromolecules: mechanism and implication of modifications to human skin keratins and angiotensin II]

Dysregulated production of reactive oxygen species (ROS) during oxidative stress has been associated with a number of inflammatory and age-related degenerative diseases. ROS can directly react with DNA to form oxidized DNA bases. Direct protein oxidation and carbonylation occur on certain amino acid residues resulting in various post-translational modifications. ROS can also initiate the formation of lipid hydroperoxides, which undergo homolytic decomposition to the α,β-unsaturated aldehydic bifunctional electrophiles such as 4-oxo-2(E)-nonenal (ONE) and 4-hydroxy-2(E)-nonenal (HNE). Intracellular generation of highly reactive aldehydes can then result in the formation of DNA and protein adducts. ONE-derived heptanone-etheno and HNE-derived propano DNA adducts have been detected and shown to be mutagenic in a variety of biological systems. In addition, ONE and HNE are involved in protein dysfunctions and altered gene regulations through the modification of amino acid residues and crosslinking of proteins. Our recent study on human skin keratins has identified specific K1 methionine residues as the most susceptible sites to oxidation with hydrogen peroxide, which can be potential biomarkers of oxidative skin damage. The reactions of angiotensin (Ang) II with ONE or HNE produced several modified Ang IIs including a novel pyruvamide-Ang II that formed via oxidative decarboxylation of N-terminal aspartic acid. Subsequently, it has been revealed that the oxidative modifications on the N-terminus of Ang II disrupt interactions with Ang II type 1 receptor and aminopeptidase A, which could affect the regulation of cardiovascular function.

N-terminal α-ketoamide peptides: formation and transamination

We have previously reported that N-terminal α-ketoamide peptides can be formed through 4-oxo-2(E)-nonenal (ONE)-derived oxidative decarboxylation of aspartic acid (Asp), which converts angiotensin (Ang) II (DRVYIHPF) to pyruvamide-Ang II (Ang P, CH3COCONH-RVYIHPF). The pyruvamide group significantly inhibits Ang P binding to the Ang II type 1 receptor, which mediates the major biological effects of Ang II. In the present study, we found that ONE can also introduce an α-ketoamide moiety at the N-terminus of peptides containing N-terminal residues other than Asp. Subsequent investigation of alternative biosynthetic pathways for N-terminal α-ketoamide peptides revealed that hydroxyl radical-mediated formation is a much more efficient route. The proposed mechanism involves initial abstraction of the N-terminal α-hydrogen and hydrolysis of the ketimine intermediate. The resulting N-terminal α-ketoamide is then converted to the D- and L-amino acids by nonenzymatic transamination in the presence of pyridoxamine (PM). The formation of the epimeric N-terminus depended on the incubation time and the concentration of PM, and increased further upon the addition of Cu(II) ions. A conversion of approximately 60% after three days of incubation was observed for Ang P. We propose that the reaction intermediate contains a prochiral α-carbon and is stabilized by the chelate effect of Cu(II) ions. The ONE- and hydroxyl radical-derived formation of N-terminal α-ketoamide and its transamination in the presence of PM were also observed in amyloid β 1-11 (DAEFRHDSGYE), where the N-terminal Asp was converted to epimeric alanine. This suggests that these N-terminal modifications could occur in vivo and modulate the biological functions of peptides and proteins.

Targeted chiral analysis of bioactive arachidonic Acid metabolites using liquid-chromatography-mass spectrometry

A complex structurally diverse series of eicosanoids arises from the metabolism of arachidonic acid. The metabolic profile is further complicated by the enantioselectivity of eicosanoid formation and the variety of regioisomers that arise. In order to investigate the metabolism of arachidonic acid in vitro or in vivo, targeted methods are advantageous in order to distinguish between the complex isomeric mixtures that can arise by different metabolic pathways. Over the last several years this targeted approach has become more popular, although there are still relatively few examples where chiral targeted approaches have been employed to directly analyze complex enantiomeric mixtures. To efficiently conduct targeted eicosanoid analyses, LC separations are coupled with collision induced dissociation (CID) and tandem mass spectrometry (MS/MS). Product ion profiles are often diagnostic for particular regioisomers. The highest sensitivity that can be achieved involves the use of selected reaction monitoring/mass spectrometry (SRM/MS); whereas the highest specificity is obtained with an SRM transitions between an intense parent ion, which contains the intact molecule (M) and a structurally significant product ion. This review article provides an overview of arachidonic acid metabolism and targeted chiral methods that have been utilized for the analysis of the structurally diverse eicosanoids that arise.

Cyclooxygenase- and lipoxygenase-mediated DNA damage

Cancer is a disease of aging, and so with the increasing age of the US population, the incidence of cancer is also increasing. Furthermore the global burden of cancer continues to increase largely because of aging and growth of the world population together with increasing smoking rates in economically developing countries. Tumor formation is critically dependent upon two processes--initiation and progression. The initiation step is mediated by DNA damage, which causes activating mutations in proto-oncogenes and inactivation of tumor suppressor genes in many cancers. This is then thought to facilitate tumor progression and metastasis. Cyclooxygenase-2 (COX-2) is upregulated at an early stage in tumorigenesis and has been implicated as an important mediator of proliferation through the increased formation of bioactive arachidonic acid (AA) metabolites such as prostaglandin E(2). Significantly, we have found that COX-2-mediated AA metabolism also results in the formation of heptanone-etheno (Hε)-DNA adducts. Furthermore, we showed that the Hε-DNA adducts arose from the reaction of DNA with the lipid hydroperoxide-derived bifunctional electrophile, 4-oxo-2(E)-nonenal (ONE). Similarly, 5-lipoxoygenase-mediated AA metabolism also results in the formation of ONE-derived DNA adducts. The resulting Hε-DNA adducts are highly mutagenic in mammalian cell lines suggesting that these pathways could be (in part) responsible for the somatic mutations observed in tumorigenesis. As approximately 80% of cancers arise from somatic mutations, this provides an additional link between the upregulation of COX-2 and tumorigenesis.

Enhanced vascular permeability is hypothesized to promote inflammation-induced carcinogenesis and tumor development via extravasation of large molecular proteins into the tissue

We propose that the growth of solid tumors is dependent, in part, on the entry of large molecular blood-borne growth regulators into the tissue and is facilitated by the highly permeable nature of tumor blood vessels. There is abundant evidence that the tumor vasculature is hyperpermeable and tumor growth is dependent on mediators that increase vascular permeability (e.g., VEGF and mast cells). Therefore, the extravasation of plasma proteins into the interstitial space could be an important determinant of tumor growth. Angiogenesis promotes cancer by creating a network of blood vessels that supplies oxygen and nutriment. A highly permeable vasculature could complement this by facilitating the entry of plasma proteins into the tumor space, permitting them to exert effects on growth and survival pathways. Plasma proteins could act directly (on the cancer cells) or indirectly (via the stroma), and could conceivably stimulate cell proliferation, enhance cell survival, promote angiogenesis, and/or provide the cells with essential nutrients. Since increased vascular permeability is a hallmark of inflammation and since chronic inflammation is a forerunner to cancer, we also suggest that the prolonged influx of plasma proteins during chronic inflammation could contribute to the carcinogenic process. Perhaps over time and in sufficient quantity, the extruded plasma proteins and the attendant edema set up a feed-forward cycle that exacerbates the inflammation and potentiates the formation of mutagens and growth regulators. It is tempting to speculate that differences in tumor growth/metastasis and patient outcome are at least partly due to the degree of permeability of the tumor vasculature.

Detection of lipid peroxidation-induced DNA adducts caused by 4-oxo-2(E)-nonenal and 4-oxo-2(E)-hexenal in human autopsy tissues

DNA adducts are produced both exogenously and endogenously via exposure to various DNA-damaging agents. Two lipid peroxidation (LPO) products, 4-oxo-2(E)-nonenal (4-ONE) and 4-oxo-2(E)-hexenal (4-OHE), induce substituted etheno-DNA adducts in cells and chemically treated animals, but the adduct levels in humans have never been reported. It is important to investigate the occurrence of 4-ONE- and 4-OHE-derived DNA adducts in humans to further understand their potential impact on human health. In this study, we conducted DNA adductome analysis of several human specimens of pulmonary DNA as well as various LPO-induced DNA adducts in 68 human autopsy tissues, including colon, heart, kidney, liver, lung, pancreas, small intestine, and spleen, by liquid chromatography tandem mass spectrometry. In the adductome analysis, DNA adducts derived from 4-ONE and 4-OHE, namely, heptanone-etheno-2'-deoxycytidine (HεdC), heptanone-etheno-2'-deoxyadenosine (HεdA), and butanone-etheno-2'-deoxycytidine (BεdC), were identified as major adducts in one human pulmonary DNA. Quantitative analysis revealed 4-ONE-derived HεdC, HεdA, and heptanone-etheno-2'-deoxyguanosine (HεdG) to be ubiquitous in various human tissues at median values of 10, 15, and 8.6 adducts per 10(8) bases, respectively. More importantly, an extremely high level (more than 100 per 10(8) bases) of these DNA adducts was observed in several cases. The level of 4-OHE-derived BεdC was highly correlated with that of HεdC (R(2) = 0.94), although BεdC was present at about a 7-fold lower concentration than HεdC. These results suggest that 4-ONE- and 4-OHE-derived DNA adducts are likely to be significant DNA adducts in human tissues, with potential for deleterious effects on human health.

Stable-isotope dilution LC–MS for quantitative biomarker analysis

The ability to conduct validated analyses of biomarkers is critically important in order to establish the sensitivity and selectivity of the biomarker in identifying a particular disease. The use of stable-isotope dilution (SID) methodology in combination with LC–MS/MS provides the highest possible analytical specificity for quantitative determinations. This methodology is now widely used in the discovery and validation of putative exposure and disease biomarkers. This review will describe the application of SID LC–MS methodology for the analysis of small-molecule and protein biomarkers. It will also discuss potential future directions for the use of this methodology for rigorous biomarker analysis.

Targeted chiral lipidomics analysis of bioactive eicosanoid lipids in cellular systems

We have developed a targeted lipidomics approach that makes it possible to directly analyze chiral eicosanoid lipids generated in cellular systems. The eicosanoids, including prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs) and alcohols (HETEs), have been implicated as potent lipid mediators of various biological processes. Enzymatic formations of eicosanoids are regioselective and enantioselective, whereas reactive oxygen species (ROS)-mediated formation proceeds with no stereoselectivity. To distinguish between enzymatic and non-enzymatic pathways of eicosanoid formation, it is necessary to resolve enantiomeric forms as well as regioisomers. High sensitivity is also required to analyze the eicosanoid lipids that are usually present as trace amounts (pM level) in biological fluids. A discovery of liquid chromatography-electron capture atmospheric pressure chemical ionization/mass spectrometry (LCECAPCI/MS) allows us to couple normal phase chiral chromatography without loss of sensitivity. Analytical specificity was obtained by the use of collision-induced dissociation (CID) and tandem MS (MS/MS). With combination of stable isotope dilution methodology, complex mixtures of regioisomeric and enantiomeric eicosanoids have been resolved and quantified in biological samples with high sensitivity and specificity. Targeted chiral lipidomics profiles of bioactive eicosanoid lipids obtained from various cell systems and their biological implications have been discussed.

15-oxo-Eicosatetraenoic acid, a metabolite of macrophage 15-hydroxyprostaglandin dehydrogenase that inhibits endothelial cell proliferation

The formation of 15-oxo-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid (15-oxo-ETE) as a product from rabbit lung 15-hydroxyprostaglandin dehydrogenase (PGDH)-mediated oxidation of 15(S)-hydroperoxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid was first reported more than 30 years ago. However, the pharmacological significance of 15-oxo-ETE formation has never been established. We have now evaluated 15-lipoxygenase (LO)-1-mediated arachidonic acid (AA) metabolism to 15-oxo-ETE in human monocytes and mouse RAW macrophages that stably express human 15-LO-1 (R15L cells). A targeted lipidomics approach was used to identify and quantify the oxidized lipids that were formed. 15-oxo-ETE was found to be a major AA-derived LO metabolite when AA was given exogenously or released from endogenous esterified lipid stores by calcium ionophore (CI) calcimycin (A-23187). This established the R15L cells as a useful in vitro model system. Pretreatment of the R15L cells with cinnamyl-3,4-dihydroxycyanocinnamate significantly inhibited AA- or CI-mediated production of 15(S)-hydroperoxy-5,8,11,13-(Z,Z,Z,E)-eicosatetraenoic acid [15(S)-HETE] and 15-oxo-ETE, confirming the role of 15-LO-1 in mediating AA metabolite formation. Furthermore, 15(S)-HETE was metabolized primarily to 15-oxo-ETE. Pretreatment of the R15L cells with the 15-hydroxyprostaglandin dehydrogenase (PGDH) inhibitor 5-[[4-(ethoxycarbonyl)phenyl]azo]-2-hydroxy-benzeneacetic acid (CAY10397) reduced AA- and 15(S)-HETE-mediated formation of 15-oxo-ETE in a dose-dependent manner. This confirmed that macrophage-derived 15-PGDH was responsible for catalyzing the conversion of 15(S)-HETE to 15-oxo-ETE. Finally, 15-oxo-ETE was shown to inhibit the proliferation of human vascular vein endothelial cells by suppressing DNA synthesis, implicating a potential antiangiogenic role. This is the first report describing the biosynthesis of 15-oxo-ETE by macrophage/monocytes and its ability to inhibit endothelial cell proliferation.