Aberrant Arachidonic Acid Metabolism Research Articles

Thromboxane A2-TP axis promotes adipose tissue macrophages M1 polarization leading to insulin resistance in obesity

Aberrant arachidonic acid metabolism has been implicated in multiple pathophysiological conditions, and the downstream prostanoids levels are associated with adipocyte dysfunction in obesity. However, the role of thromboxane A2 (TXA2) in obesity remains unclear. We observed that TXA2, through its receptor TP, is a candidate mediator in obesity and metabolic disorders. Obese mice with upregulated TXA2 biosynthesis (TBXAS1) and TXA2 receptor (TP) expression in caused insulin resistance and macrophage M1 polarization in white adipose tissue (WAT), which can be prevented by treatment with aspirin. Mechanistically, the activation of TXA2-TP signaling axis leads to accumulation of protein kinase Cɛ (PKCɛ), thereby enhancing free fat acid (FFA) induced Toll-like receptor4 (TLR4) proinflammatory macrophage activation and the tumor necrosis factor–a (TNF-a) production in adipose tissues. Importantly, TP knockout mice reduced the accumulation of proinflammatory macrophages and adipocyte hypertrophy in WAT. Thus, our findings demonstrate that TXA2-TP axis plays a crucial role in obesity-induced adipose macrophage dysfunction, and rational targeting TXA2 pathway may improve obesity and its associated metabolic disorders in future. In this work, we establish previously unknown role of TXA2-TP axis in WAT. These findings might provide new insight into the molecular pathogenesis of insulin resistance, and indicate rational targeting TXA2 pathway to improve obesity and its associated metabolic disorders in future.

Inflammatory macrophage memory in nonsteroidal anti-inflammatory drug–exacerbated respiratory disease

Nonsteroidal anti-inflammatory drug-exacerbated respiratory disease (N-ERD) is a chronic inflammatory condition, which is driven by an aberrant arachidonic acid metabolism. Macrophages are major producers of arachidonic acid metabolites and subject to metabolic reprogramming, but they have been neglected in N-ERD. This study sought to elucidate a potential metabolic and epigenetic macrophage reprogramming in N-ERD. Transcriptional, metabolic, and lipid mediator profiles in macrophages from patients with N-ERD and healthy controls were assessed by RNA sequencing, Seahorse assays, and LC-MS/MS. Metabolites in nasal lining fluid, sputum, and plasma from patients with N-ERD (n= 15) and healthy individuals (n= 10) were quantified by targeted metabolomics analyses. Genome-wide methylomics were deployed to define epigenetic mechanisms of macrophage reprogramming in N-ERD. This study shows that N-ERD monocytes/macrophages exhibit an overall reduction in DNA methylation, aberrant metabolic profiles, and an increased expression of chemokines, indicative of a persistent proinflammatory activation. Differentially methylated regions in N-ERD macrophages included genes involved in chemokine signaling and acylcarnitine metabolism. Acylcarnitines were increased in macrophages, sputum, nasal lining fluid, and plasma of patients with N-ERD. On inflammatory challenge, N-ERD macrophages produced increased levels of acylcarnitines, proinflammatory arachidonic acid metabolites, cytokines, and chemokines as compared to healthy macrophages. Together, these findings decipher a proinflammatory metabolic and epigenetic reprogramming of macrophages in N-ERD.

Chemoprevention of 7,12-dimethylbenz[a]anthracene (DMBA)-induced Hamster Cheek Pouch Carcinogenesis by a 5-Lipoxygenase Inhibitor, Garcinol

Our previous studies have shown that aberrant arachidonic acid metabolism, especially the 5-lipoxygenase (5-Lox) pathway, is involved in oral carcinogenesis and can be targeted for cancer prevention. To develop potent topical agents for oral cancer chemoprevention, 5 known 5-Lox inhibitors from dietary and synthetic sources (Zileuton, ABT-761, licofelone, curcumin, and garcinol) were evaluated in silico for their potential efficacy. Garcinol, a polyisoprenylated benzophenone from the fruit rind of Garcinia spp., was found to be a promising agent based on the calculation of a theoretical activity index. Computer modeling showed that garcinol well fit the active site of 5-Lox, and potentially inhibited enzyme activity through interactions between the phenolic hydroxyl groups and the non-heme catalytic iron. In a short-term study on 7,12-dimethylbenz[a]anthracene (DMBA)-treated hamster cheek pouch, topical garcinol suppressed leukotriene B4 (LTB4) biosynthesis and inhibited inflammation and cell proliferation in the oral epithelium. In a long-term carcinogenesis study, topical garcinol significantly reduced the size of visible tumors, the number of cancer lesions, cell proliferation, and LTB4 biosynthesis. These results demonstrated that topical application of a 5-Lox inhibitor, garcinol, had chemopreventive effect on DMBA-induced hamster cheek pouch carcinogenesis.

Abstract 1600: Chemoprevention of 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster cheek pouch carcinogenesis by topical garcinol through inhibition of 5-lipoxygenase

Abstract Oral cancer is a common malignancy occurring in developing countries, and remains problematic due to lack of effective strategies of prevention and treatment. Our previous studies have shown that aberrant arachidonic acid metabolism, especially the 5-lipoxygenase (5-Lox) pathway, is involved in oral carcinogenesis, and can be targeted for cancer prevention. In order to develop potent topical agents for oral cancer chemoprevention, five known 5-Lox inhibitors from dietary and synthetic sources were evaluated for their potential efficacy when topically applied on the oral epithelium. Garcinol, a polyisoprenylated benzophenone from the fruit rind of Garcinia spp., was found to be the most promising agent based on our calculation of a theoretical activity index. In a short-term study on 7,12-dimethylbenz[a]anthracene (DMBA)-treated hamster cheek pouch, topical garcinol suppressed leukotriene B4 (LTB4) biosynthesis and inhibited inflammation and cell proliferation in the oral epithelium. In a long-term carcinogenesis study, topical garcinol significantly reduced the size of visible tumors, the number of cancer lesions, cell proliferation, and LTB4 biosynthesis. Furthermore, computer modeling showed that garcinol well fit the active site of 5-Lox, and inhibited enzyme activity through possible interactions between the phenolic hydroxyl groups and the non-heme catalytic iron. These results demonstrated that topical garcinol exerts its chemopreventive effect on DMBA-induced hamster cheek pouch carcinogenesis by inhibiting 5-Lox, inflammation and cell. Chemical modifications of garcinol may produce more potent 5-Lox inhibitors for topical use in oral cancer chemoprevention. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1600. doi:1538-7445.AM2012-1600

Time‐selective chemoprevention of vitamin E and selenium on esophageal carcinogenesis in rats: The possible role of nuclear factor kappaB signaling pathway

Previous human intervention trial demonstrated that vitamin E (Ve) and selenium (Se) supplementation decreased esophageal cancer deaths among younger participants, but may have no effect or produce an opposite effect among older ones. In our study, we intended to mimic this human nutritional trial to determine the chemopreventive effects of Ve/Se supplementation at the early or late stage of esophageal carcinogenesis in rats. Esophageal squamous cell carcinoma (ESCC) was induced in Fischer 344 rats with N-nitrosomethylbenzylamine (NMBzA, 0.35 mg/kg BW, s.c., three times per week for 5 weeks). The rats were maintained on a modified AIN-93M diet with low levels of Ve/Se or supplemented with high levels of Ve/Se at different stages. At Week 25, the number and volume of visible tumors, the numbers of dysplasia and ESCC were significantly lower in rats of supplementation during the early stage (Group C) or during the entire experimental period (Group E), but not during the late stage (Group D). Ve/Se supplementation at the early stage also significantly decreased cell proliferation, nuclear factor kappaB (NFκB) activation, protein and mRNA expression of cyclooxygenase 2 and 5-lipoxygenase and biosynthesis of prostaglandin E2 and leukotriene B4 during the carcinogenesis of rat esophagus. Our results demonstrated that the chemopreventive efficacy of Ve/Se supplementation on NMBzA-induced esophageal cancer is time selective and that supplementation during the early stage is clearly effective but probably ineffective during the late stage of carcinogenesis. NFκB signaling pathway activation and aberrant arachidonic acid metabolism might be the underlying mechanism.

Pathophysiology of Chronic Rhinosinusitis with Nasal Polyp

Chronic rhinosinusitis (CRS) is a common inflammatory condition of the paranasal sinuses and nasal passages. CRS with nasal polyp (CRSwNP) is a subtype of CRS, and the pathogenesis of CRSwNP remains largely unclear. This article reviews the literature regarding the pathophysiology of CRSwNP. Evidence suggests that altered innate immunity, adaptive immunity, tissue remodeling, and/or effects of microorganisms may play a role in the development of CRSwNP. Aberrant arachidonic acid metabolism may also contribute to the pathogenesis of CRSwNP in patients with aspirin-exacerbated respiratory disease. There have been significant advances in the understanding pathophysiology of CRSwNP. Additional research is needed to elucidate these mechanisms and to determine their relative importance in the pathogenesis of CRSwNP.

Pachymic acid inhibits cell growth and modulates arachidonic acid metabolism in nonsmall cell lung cancer A549 cells

Aberrant arachidonic acid (AA) metabolism has been involved in inflammation and carcinogenesis. The key enzymes in AA metabolism such as cytosolic phospholipase A2 (cPLA(2)) and cyclooxygenase-2 (COX-2) have been implicated in the development and progression of many human cancers, including lung cancer. Hence, the blockade of these enzymes may suppress promotion and survival of human cancer cells. We and others have shown that a natural triterpenoid, pachymic acid (PA), can exhibit antiinflammatory and anticancer properties; however, its potential mechanism has not been fully clarified. In this study, we examined the effect of PA on the proliferation of human nonsmall cell lung cancer A549 cells. Furthermore, we investigated the influences of nontoxic levels of PA on AA metabolism. Additionally, the cellular events and signal transduction pathways influenced by PA were also examined. Our results showed that PA (1) inhibited anchorage-dependent and -independent A549 growth in a concentration-dependent manner, (2) induced apoptosis and disrupted mitochondrial membrane potential in A549 cells, and at nonlethal levels, (3) decreased IL-1 beta-induced activation of cPLA(2) and COX-2, (4) suppressed IL-1 beta-induced activation of mitogen-activated protein kinases (MAPKs), and (5) inhibited IL-1 beta-stimulated nuclear factor kappa B (NF-kappaB) signaling pathways. We speculate that inhibition of AA metabolism by PA is mediated in part by its inhibition of MAPKs and NF-kappaB signaling pathways. Our study reveals that, apart from its cytotoxic effect, PA has the chemopreventive potential by reducing production of eicosanoids from AA metabolism.

Zyflamend reduces LTB4 formation and prevents oral carcinogenesis in a 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced hamster cheek pouch model.

Aberrant arachidonic acid metabolism, especially altered cyclooxygenase and 5-lipoxygenase (LOX) activities, has been associated with chronic inflammation as well as carcinogenesis in human oral cavity tissues. Here, we examined the effect of Zyflamend, a product containing 10 concentrated herbal extracts, on development of 7,12-dimethylbenz[alpha]anthracene (DMBA)-induced inflammation and oral squamous cell carcinoma (SCC). A hamster cheek pouch model was used in which 0.5% DMBA was applied topically onto the left cheek pouch of male Syrian golden hamsters either three times per week for 3 weeks (short term) or 6 weeks (long term). Zyflamend was then applied topically at one of three different doses (25, 50 and 100 microl) onto the left cheek pouch three times for 1 week (short-term study) or chronically for 18 weeks. Zyflamend significantly reduced infiltration of inflammatory cells, incidence of hyperplasia and dysplastic lesions, bromodeoxyuridine-labeling index as well as number of SCC in a concentration-dependent manner. Application of Zyflamend (100 microl) reduced formation of leukotriene B(4) (LTB(4)) by 50% compared with DMBA-treated tissues. The reduction of LTB(4) was concentration dependent. The effect of Zyflamend on inhibition of LTB(4) formation was further confirmed with in vitro cell-based assay. Adding LTB(4) to RBL-1 cells, a rat leukemia cell line expressing high levels of 5-LOX and LTA(4) hydrolase, partially blocked antiproliferative effect of Zyflamend. This study demonstrates that Zyflamend inhibited LTB(4) formation and modulated adverse histopathological changes in the DMBA-induced hamster cheek pouch model. The study suggests that Zyflamend might prevent oral carcinogenesis at the post-initiation stage.

Targeting 5-Lipoxygenase for Prevention and Treatment of Cancer

Aberrant arachidonic acid metabolism has been recognized as a dominant mechanism underlying the development and progression of a range of human cancers. Metabolism of arachidonic acid through the 5-lipoxygenase (5-Lox) pathway generates an array of highly reactive eicosanoids categorized into two distinct groups; the leukotrienes (LTs) and the 5-hydroxyeicosatetraenoids (5-HETEs). Evidence documenting prominent roles of these two groups of eicosanoids in the development and progression of cancer are accumulating rapidly both by in vitro cell culture experiments using cancer cells originating from many tissues, and by in vivo tumor model studies. Moreover, significantly higher levels of expression of 5-Lox has been observed in patient tumor specimens in grade-specific manner, and production of elevated levels of 5-Lox metabolites were observed in cancer cells compared to normal counterparts. Thus, 5-Lox has emerged as a new potential target for the prevention and treatment of cancer. Metabolites of 5-Lox are potent signaling molecules and elicit diverse biological activities that are involved in neoplastic transformation and progression, such as cell proliferation, invasion and motility, and apoptosis-resistance. Blocking 5-Lox activity by pharmacological agents will deprive cancer cells of the critical metabolites for their survival and growth, and thus may be effective in the prevention as well as treatment of cancer. Indeed some studies have already shown promise for using 5-Lox inhibitors for the prevention and treatment of cancers of the prostate, lung, pancreas, brain, esophagus, oral cavity, etc.

Chemoprevention of 7,12-dimethylbenz[ a]anthracene (DMBA)-induced oral carcinogenesis in hamster cheek pouch by topical application of a dual inhibitor of epidermal growth factor receptor (EGFR) and ErbB2 tyrosine kinases

Oral cancer is a common neoplasm worldwide with tobacco and alcohol being the major etiological factors contributing to its pathogenesis. Epidermal growth factor receptor (EGFR) and ErbB2 are known to be involved in the development of oral cancer with the former up-regulated in up to 90% human cases. The goal of this study was to evaluate the chemopreventive effects of a dual inhibitor of EGFR and ErbB2 tyrosine kinases, GW2974, in the 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster cheek pouch model. A short-term experiment (3-week topical DMBA followed by 1-week topical GW2974) was conducted to examine the effects of GW2974 on aberrant arachidonic acid (AA) metabolism and cell proliferation in the hamster oral epithelium. Topical application of 0.1 ml GW2974 (160 microM, three times a week) significantly reduced the levels of prostaglandin E2 (PGE2), leukotriene B4 (LTB4), 5-, 12-, 15-hydroxyeicosatetraenoic acid (HETE), and cell proliferation (BrdU-labeling index). In a long-term post-initiation experiment (6-week topical DMBA followed by 18-week topical GW2974), GW2974 (4 mM and 8 mM) significantly inhibited the incidence, number and size of visible tumors. Under microscope, the numbers of oral lesions (hyperplasia, dysplasia, carcinoma) and the incidence of squamous cell carcinoma (SCC) were also significantly suppressed by GW2974. In summary, our study indicated that dual inhibition of EGFR and ErbB2 tyrosine kinases by GW2974 was effective in preventing oral carcinogenesis in DMBA-induced hamster cheek pouch model. GW2974 exerted its chemopreventive effects in part by suppressing aberrant AA metabolism.

Inhibition Of Tumorigenesis in ApcMin/+ Mice by a Combination of (–)-Epigallocatechin-3-gallate and Fish Oil

The effect of a combination of (-)-epigallocatechin-3-gallate (EGCG) with fish oil on intestinal tumorigenesis in Apc (Min/+) mice fed a high-fat diet was investigated in the present study. The combined treatment of EGCG and fish oil for 9 weeks reduced the tumor number by 53% as compared to controls while neither agent alone had a significant effect. Apoptosis was significantly increased in all treatment groups. beta-Catenin nuclear positivity in adenomas from the combination group was lower than control mice, implicating the modulation of Wnt signaling by the combination. Fish oil and the combination significantly reduced prostaglandin E 2 (PGE 2) levels in small intestinal tumors as compared to controls, suggesting modulation of aberrant arachidonic acid metabolism by fish oil. Akt phosphorylation in adenomas was significantly reduced in all treatment groups, which may have contributed to the observed increase in apoptosis. The results indicate that a combination of low doses of EGCG and fish oil can inhibit tumor multiplicity in Apc (Min/+) mice.

Platelet 12-lipoxygenase Arg261Gln polymorphism: functional characterization and association with risk of esophageal squamous cell carcinoma in combination with COX-2 polymorphisms

Aberrant arachidonic acid metabolism by 12-lipoxygenase (12-LOX) and cyclooxygenase-2 (COX-2) has been implicated in human carcinogenesis. Inherited polymorphisms in 12-LOX and COX-2 contributed to differential expression or activity of these enzymes might confer interindividual susceptibility to cancer. To examine the functional significance of 12-LOX 261 Arg> Gln polymorphism and its association, alone and in combination with COX-2 -1195G > A and -765G > C polymorphisms, with risk of developing esophageal squamous cell carcinoma (ESCC). The platelet 12-LOX activity was measured by quantifying 12-HETE in the lipoxygenation reaction. Genotypes of 12-LOX261Arg>Gln and COX-2 -1195G>A and -765G>C polymorphisms were determined in a case-control study consisting of 1026 patients and 1270 controls. Associations with the risk of ESCC were estimated by logistic regression. Subjects with the 12-LOX Gln/Gln genotype had higher platelet 12-LOX activity (mean+/-SEM nmol/mg/min) than those with the Arg/Arg genotype (0.405+/-0.047 [n=10] versus 0.136+/-0.022 [n=6]; P=0.001). Genotyping data showed that the 12-LOX Gln/Gln genotype was associated with increased risk of developing ESCC (odds ratio [OR]=1.42, 95% confidence interval [CI]=1.12-1.81), compared with the Arg/Arg genotype adjusted for sex, age, and smoking. An increased risk of ESCC was also associated with the COX-2 -1195GA (OR=1.34, 95% CI=1.08-1.68; P=0.008), -1195AA (OR=1.72, 95% CI=1.35-2.20; P=<0.001), and -765GC (OR=2.24, 95% CI=1.59-3.16; P<0.001) genotypes. Furthermore, a multiplicative interaction between the 12-LOX Gln/Gln and COX-2 -1195AA or -765GC genotype in intensifying risk of ESCC was observed, with the ORs for the presence of both 12-LOX Gln/Gln and COX-2 -1195AA or -765GC genotypes being 3.21 (95% CI=1.93-5.34) and 3.33 (95% CI=1.59-6.98). A multiplicative interaction between the -765GC genotype and smoking was also evident (OR=4.45, 95% CI=2.71-7.29). These observations suggest that inherited polymorphisms in arachidonic acid-metabolizing enzymes, which result in heightened gene expression or enzymatic activity, may confer host susceptibility to ESCC.

Associations of functional polymorphisms in cyclooxygenase-2 and platelet 12-lipoxygenase with risk of occurrence and advanced disease status of colorectal cancer

Aberrant arachidonic acid metabolism by cyclooxygenase (COX)-2 and 12-lipoxygenase (LOX) has implicated in carcinogenesis. Genetic polymorphisms in COX-2 and 12-LOX might therefore affect susceptibility to colorectal cancer (CRC). To examine this hypothesis, genotypes of COX-2 -1290A>G, -1195G>A, -765G>C and 12-LOX 261Arg>Gln polymorphisms were determined in 1000 CRC patients and 1300 controls. Increased risk of developing CRC was associated with the COX-2 -1195GA [adjusted odds ratio (OR) = 1.24, 95% confidence interval (CI) = 1.00-1.54] and -1195AA (adjusted OR = 1.77, 95% CI = 1.38-2.25) genotypes compared with the -1195GG genotype. Similarly, the increased risk for CRC was also associated with the COX-2 -765GC genotype (adjusted OR = 1.73, 95% CI = 1.23-2.43) compared with the -765GG genotype. Consistent with the results of genotype analyses, the ORs for the A_(1195)-C_(765)-containing haplotypes were significantly higher than those for the G_(1195)-G_(765)-containing haplotypes (P < 0.01). Furthermore, the -1195A allele was further associated with advanced CRC, with adjusted ORs of Dukes D CRC against Dukes A CRC being 2.43 (95% CI = 1.15-4.97) and 2.66 (95% CI = 1.23-5.74) for the -1195GA and -1195AA genotypes, respectively. The increased risk of CRC was also associated with the 12-LOX 261Gln/Gln genotype compared with the Arg/Arg genotype (adjusted OR = 1.38, 95% CI = 1.09-1.74). Together, these observations indicate that inherited polymorphisms in arachidonic acid-metabolizing enzymes may confer susceptibility to CRC.

Five-Lipoxygenase Pathway of Arachidonic Acid Metabolism in Carcinogenesis and Cancer Chemoprevention

Aberrant arachidonic acid metabolism has recently received intensive attention in the field of cancer research. Recent discoveries regarding the long-term cardiovascular side effects of cyclooxygenase 2 inhibitors have cast doubts on their use for cancer chemoprevention. Although such a problem does not undermine the importance of cyclooxygenase 2 as a cancer chemopreventive target, investigation into other AA-metabolizing pathways that are also important in inflammation and inflammation-associated carcinogenesis is necessary. Here, the important role of the 5-lipoxygenase pathway in carcinogenesis is reviewed. Inhibition of the 5-lipoxygenase pathways clearly has chemopreventive effects on various cancers, and hence further studies on its enzymes, metabolites and receptors for cancer chemoprevention and therapy are warranted.

Bioavailability and stability issues in understanding the cancer preventive effects of tea polyphenols

AbstractThe cancer preventive activities of tea (Camellia sinensis) have received a great deal of attention from researchers and the general public. The inhibition of carcinogenesis by tea and tea polyphenols has been demonstrated in different animal models of skin, lung, intestinal and other cancer types by many investigators. Numerous mechanisms for the cancer preventive activity have been proposed based on studies of human cancer cell lines without considering the bioavailability of tea polyphenols. The proposed inhibition of mitogen activated protein (MAP) kinases, aberrant arachidonic acid metabolism, nuclear factor κB (NFκB) and activator protein 1 (AP‐1) mediated transcription, growth factor‐mediated signaling, and other activities could lead to the inhibition of tumor cell growth or induction of apoptosis as well as the inhibition of angiogenesis. In many cases, however, the concentrations of tea polyphenols required to observe these biological effects in vitro exceed the concentrations achievable in blood and tissues by 10‐ to 100‐fold. In addition, in vitro studies are complicated by the fact that tea polyphenols are not stable and reactive oxygen species are generated under most cell culture conditions. It is not clear whether these reactions occur in vivo. From the bioavailability and stability viewpoints, we herein discuss the relevance of in vitro observations to the mechanisms of the cancer preventive activities of tea polyphenols in vivo. Copyright © 2006 Society of Chemical Industry

Involvement of the 5-lipoxygenase/leukotriene A4 hydrolase pathway in 7,12-dimethylbenz[a]anthracene (DMBA)-induced oral carcinogenesis in hamster cheek pouch, and inhibition of carcinogenesis by its inhibitors

Previous studies have shown that aberrant arachidonic acid (AA) metabolism, especially cyclooxygenase-2 (Cox-2) and 5-lipoxygenase (5-Lox) pathways, are activated during oral carcinogenesis, and can be targeted for cancer prevention. This study was designed to investigate the importance of 5-Lox/leukotriene A4 hydrolase (LTA4H) pathway of AA metabolism in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster cheek pouch carcinogenesis. In a short-term study, topical application of DMBA for 3 weeks induced severe inflammation and aberrant AA metabolism. Subsequent topical treatment with zileuton, celecoxib, or their combination for 1 week significantly suppressed aberrant AA metabolism and cell proliferation in the oral epithelium. Interestingly, zileuton was effective in inhibiting biosynthesis of multiple AA metabolites, including leukotriene B4 (LTB4), 5-, 12-, 15-hydroxyeicosatetraenoic acid and prostaglandin E2 (PGE2), while celecoxib only suppressed PGE2 biosynthesis significantly at a high dose. In a long-term carcinogenesis study topical application of LTB4 or PGE2 enhanced oral carcinogenesis by increasing the incidence and volume of visible tumors, and the incidence of squamous cell carcinoma (SCC). To further examine the role of LTB4 in oral carcinogenesis, two LTA4H inhibitors, bestatin and SA6541, were evaluated in a long-term chemoprevention experiment. Both agents significantly inhibited SCC, and such an inhibition correlated with reduced levels of LTB4 in hamster cheek pouch. In summary, our studies have demonstrated that 5-Lox/LTA4H pathway is one of the major AA-metabolizing pathways involved in DMBA-induced oral carcinogenesis in hamsters, and may be targeted for chemoprevention.

Overexpression of 5-Lipoxygenase and Cyclooxygenase 2 in Hamster and Human Oral Cancer and Chemopreventive Effects of Zileuton and Celecoxib

Previous studies have suggested an important role of aberrant arachidonic acid metabolism, especially the cyclooxygenase (Cox) pathway, in oral carcinogenesis. However, it is unknown whether the 5-lipoxygenase (5-Lox) pathway contributes to oral carcinogenesis, and whether combination of inhibitors of both pathways may have synergistic or additive effects of chemoprevention. 5-Lox expression was examined in 7,12-dimethylbenz[a]anthracene (DMBA)-induced hamster and human oral cancer tissues by immunohistochemistry, and Cox2 expression was investigated in hamster oral tissues using in situ hybridization. Zileuton (a specific 5-Lox inhibitor) and celecoxib (a specific Cox2 inhibitor), either alone or in combination, were investigated for their chemopreventive effects on the DMBA-induced hamster model at the post-initiation stage through topical application. 5-Lox was overexpressed during oral carcinogenesis in hamsters and humans, as well as Cox2 in the hamster tissues. In a chemoprevention study using the post-initiation DMBA model, incidence of hamster oral squamous cell carcinoma was reduced from 76.9% (20 of 26) to 45.8% (11 of 24, P < 0.05) and 32.1% (9 of 28, P < 0.01) by 3% and 6% topical zileuton, respectively; and to 57.6% (15 of 26, P > 0.05) and 50% (12 of 24, P < 0.05) by 3% and 6% topical celecoxib, respectively. When used in combination, celecoxib and zileuton (3% of each) had an additive inhibitory effect on the incidence of squamous cell carcinoma (36%, 9 of 25, P < 0.01). Other pathologic variables and the levels of leukotriene B4 and prostaglandin E2 of the hamster tissues were reduced as well. The results clearly showed that both 5-Lox and Cox2 played important roles in oral carcinogenesis. Zileuton and celecoxib prevented oral carcinogenesis at the post-initiation stage through their inhibitory effects on arachidonic acid metabolism.

Overexpression of 5-lipoxygenase in rat and human esophageal adenocarcinoma and inhibitory effects of zileuton and celecoxib on carcinogenesis.

Aberrant arachidonic acid (AA) metabolism, especially through the cyclooxygenase (Cox) and 5-lipoxygenase (5-Lox) pathways, has been suggested to play an important role in the development of esophageal adenocarcinoma (EAC). The purpose of this study was to investigate the expression of 5-Lox in EAC of a rat model and in human samples as well as the chemopreventive effects of zileuton (a specific 5-Lox inhibitor) and celecoxib (a specific Cox2 inhibitor) in the rat EAC model. 5-Lox expression in EAC of a rat esophagogastroduodenal anastomosis model and of humans was examined with immunohistochemistry. A chemoprevention study was designed to test whether zileuton and celecoxib could suppress aberrant AA metabolism and esophageal adenocarcinogenesis. With immunohistochemistry, we found that 5-Lox was overexpressed during esophageal adenocarcinogenesis in our rat model and in humans. In the chemoprevention study, EAC incidence was reduced in a dose-dependent manner from 68.8% (11 of 16) to 44.4% (8 of 18; P > 0.05) and 31.3% (5 of 16; P < 0.05) by 500 and 1,000 ppm zileuton, respectively, and to 33.3% (7 of 21; P < 0.05) and 20% (3 of 15; P < 0.05) by 500 and 1,000 ppm celecoxib, respectively. With isobolographic analysis, zileuton and celecoxib, both at a dose of 500 ppm, had an additive effect by reducing the tumor incidence to 16.7% (3 of 18, P < 0.01). Leukotriene B4 and prostaglandin E2 levels in the esophageal tissues were also significantly reduced by zileuton and celecoxib. This study clearly demonstrated that 5-Lox and Cox2 play important roles in the development of EAC. Both zileuton and celecoxib had inhibitory effects on esophageal adenocarcinogenesis through inhibition on their respective enzymes of AA metabolism.

Oxidative stress and neuroinflammation in Alzheimer's disease and amyotrophic lateral sclerosis: common links and potential therapeutic targets.

Many neurological diseases, including Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS), are now recognized to share atypical inflammatory reactions as a major pathological feature. Neuroinflammation can both be a cause, and a consequence, of chronic oxidative stress. Cytokine-stimulated microglia generate copious amounts of reactive oxygen and reactive nitrogen species, creating a stress upon ambient neurons. Conversely, oxidants can stimulate pro-inflammatory gene transcription in glia, leading to various inflammatory reactions. This review compares literature regarding neuroinflammation in AD and ALS, with special emphasis on roles played by tumor necrosis factor alpha (TNFalpha) and aberrant arachidonic acid metabolism in the genesis of chronic oxidative conditions. Based on our observations made in the G93A-SOD1 mouse model of ALS, and a body of Alzheimer's disease findings, we hypothesize a prominent pathological role for the TNFalpha-signaling axis and neuroinflammation in the pathogenesis of both diseases. A discussion is made regarding the relevance of neuroinflammation to potential therapeutic implications for both ALS and AD.

Aberrant arachidonic acid metabolism in esophageal adenocarcinogenesis, and the effects of sulindac, nordihydroguaiaretic acid, and alpha-difluoromethylornithine on tumorigenesis in a rat surgical model.

Human esophageal adenocarcinoma (EAC) develops in a sequence from gastroesophageal reflux disease (GERD), columnar-lined esophagus (CLE), dysplasia, and eventually to EAC. We established a rat surgical EAC model with esophagogastroduodenal anastomosis (EGDA) to mimic the staged process of esophageal adenocarcinogenesis. Profiling of the AA metabolites with mass spectrometry showed that prostaglandin E2 (PGE2), leukotriene B4 (LTB4), 15-hydroeicosatetraenoic acid (HETE), 12-HETE, 8-HETE and 5-HETE all increased at the esophagoduodenal junction after EGDA as compared with the proximal esophagus, with PGE2 as the major metabolite. Consistent with this profile, cyclooxygenase 2 (Cox2) was overexpressed in the basal cell layer of esophageal squamous epithelium, CLE cells and EAC tumor cells of the EGDA rats, as compared with the normal esophageal epithelium. Sulindac (a Cox inhibitor), nordihydroguaiaretic acid (NDGA, a lipoxygenase inhibitor) and alpha-difluoromethylornithine (DFMO, an ornithine decarboxylase inhibitor) were tested for their possible inhibitory actions against the formation of EAC in the rat EGDA model. In a short-term study (for 4 weeks after surgery), dietary administration of both sulindac (300 and 600 p.p.m.) and NDGA (100 p.p.m.) effectively reduced the EGDA-induced inflammation. In a long-term chemoprevention study (for 40 weeks after surgery), 300 p.p.m. sulindac, alone or in combination with 100 p.p.m. NDGA or 0.5% DFMO, decreased the tumor incidence from 57.7 to 26.9%, or 16.7 or 20%, respectively (P < 0.05). NDGA alone (100 and 200 p.p.m.) slightly decreased the tumor incidence to 52.4 and 37%, respectively, although the difference was not statistically significant. DFMO alone did not show significant effects on tumor incidence. Inhibition of tumor formation by sulindac was correlated with lowered levels of PGE2. In conclusion, sulindac exerted its chemopreventive effect against the formation of EAC in the rat EGDA model possibly through its inhibition of Cox.