Activation of oncogenes and/or inactivation of anti-oncogenes by reactive oxygen species

Reactive Oxygen Species and NRF2 Signaling, Friends or Foes in Cancer?

The imbalance between reactive oxygen species (ROS) production and clearance causes oxidative stress and ROS, which play a central role in regulating cell and tissue physiology and pathology. Contingent upon concentration, ROS influence cancer development in contradictory ways, either stimulating cancer survival and growth or causing cell death. Cells developed evolutionarily conserved programs to sense and adapt redox the fluctuations to regulate ROS as either signaling molecules or toxic insults. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2)-KEAP1 system is the master regulator of cellular redox and metabolic homeostasis. NRF2 has Janus-like roles in carcinogenesis and cancer development. Short-term NRF2 activation suppresses tissue injury, inflammation, and cancer initiation. However, cancer cells often exhibit constitutive NRF2 activation due to genetic mutations or oncogenic signaling, conferring advantages for cancer cells' survival and growth. Emerging evidence suggests that NRF2 hyperactivation, as an adaptive cancer phenotype under stressful tumor environments, regulates all hallmarks of cancer. In this review, we summarized the source of ROS, regulation of ROS signaling, and cellular sensors for ROS and oxygen (O₂), we reviewed recent progress on the regulation of ROS generation and NRF2 signaling with a focus on the new functions of NRF2 in cancer development that reach beyond what we originally envisioned, including regulation of cancer metabolism, autophagy, macropinocytosis, unfolded protein response, proteostasis, and circadian rhythm, which, together with anti-oxidant and drug detoxification enzymes, contributes to cancer development, metastasis, and anticancer therapy resistance.

A novel methylated analogue of L-Mimosine exerts its therapeutic potency through ROS production and ceramide-induced apoptosis in malignant melanoma

Melanoma is an aggressive and highly metastatic type of skin cancer where the design of new therapies is of utmost importance for the clinical management of the disease. Thus, we have aimed to investigate the mode of action by which a novel methylated analogue of L-Mimosine (e.g., L-SK-4) exerts its therapeutic potency in an in vitro model of malignant melanoma. Cytotoxicity was assessed by the Alamar Blue assay, oxidative stress by commercially available kits, ROS generation, caspase 3/7 activation and mitochondrial membrane depolarisation by flow cytometry, expression of apoptosis-related proteins by western immunoblotting and profiling of lipid biosynthesis by a metabolomic approach. Overall, higher levels of ROS, sphingolipids and apoptosis were induced by L-SK-4 suggesting that the compound's therapeutic potency is mediated through elevated ROS levels which promote the upregulation of sphingolipid (ceramide) biosynthesis thus leading to the activation of both extrinsic and intrinsic apoptosis, in an experimental model of malignant melanoma.

Enzymatically Extracted Apple Pectin Possesses Antioxidant and Antitumor Activity

The biological activity of apple pectin extracted conventionally or enzymatically using endo-xylanase and endo-cellulase, was tested in vitro. The analyses were performerd in tetraplicates and the statistical significance of the differences were assessed using ANOVA, Tukey post hoc and LSD (the least significant difference) tests. Multivariate regression analysis was applied to determine the structural components that have a crucial importance for antioxidant and antitumor properties of pectins. The pectins extracted by enzymes contained up to four times more ferulic acid and showed twice as great ability to neutralize free radicals and Fe(III) reduction. The antiradical potential positively correlated with phenols, fucose and rhamnose content. In the assays performed on HT-29 human adenocarcinoma and B16F10 melanoma cell cultures, the “green” pectins, contrary to acid isolated ones, exhibited remarkable anti-neoplastic potential while being nontoxic to nontransformed L929 cell line. The pectins in the dose of 1 mg/mL were capable of inhibiting adhesion (max 23.1%), proliferation (max 40.4%), invasion (max 76.9%) and anchorage-independent growth (max 90%) of HT-29 cells (significance level p < 0.001). These pectin preparations were slightly less active towards B16F10 cells. The enzyme-isolated apple pectins may be useful as a functional food additive and an ingredient of the ointment formulas for post-surgical melanoma treatment.

Emerging role of NRF2 in ROS-mediated tumor chemoresistance

Chemoresistance is a central cause for the tumor management failure. Cancer cells disrupt the redox homeostasis through reactive oxygen species (ROS) regulatory mechanisms, leading to tumor progression and chemoresistance. The transcription factor nuclear factor erythroid 2-related factor 2 (NRF2) is a master regulator of neutralizing cellular ROS and restoring redox balance. Understanding the role of NRF2 in ROS-mediated chemoresistance can be helpful in the development of chemotherapy strategies with better efficiency. In this review, we sum up the roles of ROS in the development of chemoresistance to classical chemotherapy agents including cisplatin, 5-fluorouracil, gemcitabine, oxaliplatin, paclitaxel, and doxorubicin, and how to overcome ROS-mediated tumor chemoresistance by targeting NRF2. Finally, we propose that targeting NRF2 might be a promising strategy to resist ROS-driven chemoresistance and acquire better efficacy in cancer treatment.

In Vivo Imaging with Genetically Encoded Redox Biosensors

Redox reactions are of high fundamental and practical interest since they are involved in both normal physiology and the pathogenesis of various diseases. However, this area of research has always been a relatively problematic field in the context of analytical approaches, mostly because of the unstable nature of the compounds that are measured. Genetically encoded sensors allow for the registration of highly reactive molecules in real-time mode and, therefore, they began a new era in redox biology. Their strongest points manifest most brightly in in vivo experiments and pave the way for the non-invasive investigation of biochemical pathways that proceed in organisms from different systematic groups. In the first part of the review, we briefly describe the redox sensors that were used in vivo as well as summarize the model systems to which they were applied. Next, we thoroughly discuss the biological results obtained in these studies in regard to animals, plants, as well as unicellular eukaryotes and prokaryotes. We hope that this work reflects the amazing power of this technology and can serve as a useful guide for biologists and chemists who work in the field of redox processes.

Small molecules regulating reactive oxygen species homeostasis for cancer therapy

Elevated intracellular reactive oxygen species (ROS) and antioxidant defense systems have been recognized as one of the hallmarks of cancer cells. Compared with normal cells, cancer cells exhibit increased ROS to maintain their malignant phenotypes and are more dependent on the "redox adaptation" mechanism. Thus, there are two apparently contradictory but virtually complementary therapeutic strategies for the regulation of ROS to prevent or treat cancer. The first strategy, that is, chemoprevention, is to prevent or reduce intracellular ROS either by suppressing ROS production pathways or by employing antioxidants to enhance ROS clearance, which protects normal cells from malignant transformation and inhibits the early stage of tumorigenesis. The second strategy is the ROS-mediated anticancer therapy, which stimulates intracellular ROS to a toxicity threshold to activate ROS-induced cell death pathways. Therefore, targeting the regulation of intracellular ROS-related pathways by small-molecule candidates is considered to be a promising treatment for tumors. We herein first briefly introduce the source and regulation of ROS, and then focus on small molecules that regulate ROS-related pathways and show efficacy in cancer therapy from the perspective of pharmacophores. Finally, we discuss several challenges in developing cancer therapeutic agents based on ROS regulation and propose the direction of future development.

Organoids Increase the Predictive Value of in vitro Cancer Chemoprevention Studies for in vivo Outcome

Epidemiological and preclinical data suggest that antioxidants are protective against prostate cancer whose pathogenesis has been linked to oxidative stress. However, the selenium and vitamin E Cancer Prevention Trial (SELECT), found no efficacy for selenium in reducing prostate cancer incidence while vitamin E was associated with an increased risk of the disease. These results have called in to question the models used in preclinical chemoprevention efficacy studies and their ability to predict in vivo outcomes. Chemoprevention agents have traditionally been tested on two dimensional monolayer cultures of cell lines derived from advanced prostate cancers. But as SELECT demonstrates, results from advanced disease models were not predictive of the outcome of a primary chemoprevention trial. Additionally, lack of cell-matrix interactions in two dimensional cultures results in loss of biochemical and mechanical cues relevant for native tissue architecture. We use recent findings in three dimensional organoid cultures that recapitulated the SELECT trial results to argue that the organoid model could increase the predictive value of in vitro studies for in vivo outcomes.

γ-Glutamyl transferase 7 is a novel regulator of glioblastoma growth

Background

Glioblastoma (GBM) is the most malignant primary brain tumor in adults, with a median survival time of one and a half years. Traditional treatments, including radiation, chemotherapy, and surgery, are not curative, making it imperative to find more effective treatments for this lethal disease. γ-Glutamyl transferase (GGT) is a family of enzymes that was shown to control crucial redox-sensitive functions and to regulate the balance between proliferation and apoptosis. GGT7 is a novel GGT family member that is highly expressed in brain and was previously shown to have decreased expression in gliomas. Since other members of the GGT family were found to be altered in a variety of cancers, we hypothesized that GGT7 could regulate GBM growth and formation.

Methods

To determine if GGT7 is involved in GBM tumorigenesis, we modulated GGT7 expression in two GBM cell lines (U87-MG and U138) and monitored changes in tumorigenicity in vitro and in vivo.

Results

We demonstrated for the first time that GBM patients with low GGT7 expression had a worse prognosis and that 87% (7/8) of primary GBM tissue samples showed a 2-fold decrease in GGT7 expression compared to normal brain samples. Exogenous expression of GGT7 resulted in a 2- to 3-fold reduction in proliferation and anchorage-independent growth under minimal growth conditions (1% serum). Decreasing GGT7 expression using either short interfering RNA or short hairpin RNA consistently increased proliferation 1.5- to 2-fold. In addition, intracranial injections of U87-MG cells with reduced GGT7 expression increased tumor growth in mice approximately 2-fold, and decreased mouse survival. To elucidate the mechanism by which GGT7 regulates GBM growth, we analyzed reactive oxygen species (ROS) levels in GBM cells with modulated GGT7 expression. We found that enhanced GGT7 expression reduced ROS levels by 11-33%.

Conclusion

Our study demonstrates that GGT7 is a novel player in GBM growth and that GGT7 can play a critical role in tumorigenesis by regulating anti-oxidative damage. Loss of GGT7 may increase the cellular ROS levels, inducing GBM occurrence and growth. Our findings suggest that GGT7 can be a promising biomarker and a potential therapeutic target for GBM.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1232-y) contains supplementary material, which is available to authorized users.

Associations between SNPs within antioxidant genes and the risk of prostate cancer in the Siberian region of Russia

In the present study we investigated the association of a number of polymorphic changes in antioxidant system genes (SNPs rs1050450 in the GPX1 gene, rs1695 and rs1138272 in the GSTP1 gene and rs4880 in the MnSOD gene) with the risk of prostate cancer. The association of disease stage and PSA levels with specific genotypes was also analyzed. A study was conducted with the participation of 736 Russian men. We compared the frequency of occurrence of the studied alleles in patients with prostate cancer (392) to a control group (344) of men without a history of cancer. Genotyping was performed by real-time PCR. Comparison of frequencies of alleles and genotypes were performed using logistic regression analysis. No statistically significant association with the risk of prostate cancer was found for any of the SNPs studied (p > 0.05). For SNP rs1695 in the GSTP1 gene, a correlation with cancer disease stage was observed: a GG genotype is significantly more common in patients with PCa in the 3rd and 4th stage than 1st and 2nd (OR[95%CI] = 2.66[1.15-6.18], p = 0.02). Both studied SNPs of GSTP1 gene are associated with the level of PSA: the GG rs1695 and the TT rs1138272 genotypes are associated with higher PSA levels (p = 1.5*10(-3)).

[Obesity and cancer]

Obesity which is now well recognized as a public health problem increases the risk of developing cancers. Some systematic review and meta-analyses assessed the strength of associations between body mass index and common cancers such as breast, endometrial, colon and adenocarcinoma of oesophagus. The causal mechanisms remain unexplained. However, epidemiological data and animal models have provided some evidence that hormonal alteration linked to obesity, such as hyperinsulinism, high insulin-like growth factor (IGF-1) levels or biodisponibility, low adiponectin serum level and high oestradiol serum level resulting from an enhanced aromatase activity may have mitogenic and antiapoptotic effects. The inflammation associated with visceral adiposity is another factor which promotes cancer. To date, there are no convincing data that weight loss could improve the prognosis of treated neoplasia. However, a regular physical activity and a limited caloric intake are probably safe in healthy subject to prevent cancer and also in cancer survivors.

Oxidative Stress Induces ADAM9 Protein Expression in Human Prostate Cancer Cells

The ADAM (a disintegrin and metalloprotease) family is a group of transmembrane proteins containing cell adhesive and proteolytic functional domains. Microarray analysis detected elevated ADAM9 during the transition of human LNCaP prostate cancer cells from an androgen-dependent to an androgen-independent and metastatic state. Using a prostate tissue array (N = 200), the levels of ADAM9 protein expression were also elevated in malignant as compared with benign prostate tissues. ADAM9 protein expression was found in 43% of benign glands with light staining and 87% of malignant glands with increasing intensity of staining. We found that ADAM9 mRNA and protein expressions were elevated on exposure of human prostate cancer cells to stress conditions such as cell crowding, hypoxia, and hydrogen peroxide. We uncovered an ADAM9-like protein, which is predominantly induced together with the ADAM9 protein by a brief exposure of prostate cancer cells to hydrogen peroxide. Induction of ADAM9 protein in LNCaP or C4-2 cells can be completely abrogated by the administration of an antioxidant, ebselen, or genetic transfer of a hydrogen peroxide degradative enzyme, catalase, suggesting that reactive oxygen species (ROS) are a common mediator. The induction of ADAM9 by stress can be inhibited by both actinomycin D and cycloheximide through increased gene transcription and protein synthesis. In conclusion, intracellular ROS and/or hydrogen peroxide, generated by cell stress, regulate ADAM9 expression. ADAM9 could be responsible for supporting prostate cancer cell survival and progression. By decreasing ADAM9 expression, we observed apoptotic cell death in prostate cancer cells.

Reactive oxygen species: role in the development of cancer and various chronic conditions

Oxygen derived species such as superoxide radical, hydrogen peroxide, singlet oxygen and hydroxyl radical are well known to be cytotoxic and have been implicated in the etiology of a wide array of human diseases, including cancer. Various carcinogens may also partly exert their effect by generating reactive oxygen species (ROS) during their metabolism. Oxidative damage to cellular DNA can lead to mutations and may, therefore, play an important role in the initiation and progression of multistage carcinogenesis. The changes in DNA such as base modification, rearrangement of DNA sequence, miscoding of DNA lesion, gene duplication and the activation of oncogenes may be involved in the initiation of various cancers. Elevated levels of ROS and down regulation of ROS scavengers and antioxidant enzymes are associated with various human diseases including various cancers. ROS are also implicated in diabtes and neurodegenerative diseases. ROS influences central cellular processes such as proliferation a, apoptosis, senescence which are implicated in the development of cancer. Understanding the role of ROS as key mediators in signaling cascades may provide various opportunities for pharmacological intervention.

Tumour plasticity and extravascular circulation in ECV304 human bladder carcinoma cells

BACKGROUND

The concepts of vasculogenic mimicry and mosaic vessels have been proposed as novel modes of tumour neovascularisation. However, the presence and significance of these types of neovascularisation remain unclear.

MATERIALS AND METHODS

ECV304 human bladder carcinoma cells were used to determine how tumour cells take part in tumour neovascularisation.

RESULTS

Subcutaneous ECV304 xenografts in mice showed various vessel types, including angiogenic vessels, tumour cell-related vessels and extracellular matrix networks. A tracer experiment demonstrated perfusion of beads in these structures. ECV304 cells, cultured on collagen I gels, formed tube networks with expressions of several endothelial-related markers. In coculture models of ECV304 cells and human umbilical vein endothelial cells, the two cells collaborated to form sprouts or networks.

CONCLUSION

ECV304 cells possess an endothelial character which confers the ability to mimic and collaborate with vascular endothelial cells and facilitates the acquisition of tumour microcirculation.

HSF1 down-regulates XAF1 through transcriptional regulation

Studies have indicated the role of HSF1 (heat-shock transcription factor 1) in repressing the transcription of some nonheat shock genes. XAF1 (XIAP-associated factor 1) was an inhibitor of apoptosis-interacting protein with the effect of antagonizing the cytoprotective role of XIAP. XAF1 expression was lower in gastrointestinal cancers than in normal tissues with the mechanism unclear. Here we showed that gastrointestinal cancer tissues expressed higher levels of HSF1 than matched normal tissues. The expression of XAF1 and HSF1 was negatively correlated in gastrointestinal cancer cell lines. Stress stimuli, including heat, hypo-osmolarity, and H2O2, significantly suppressed the expression of XAF1, whereas the alteration of HSF1 expression negatively correlated with XAF1 expression. We cloned varying lengths of the 5'-flanking region of the XAF1 gene into luciferase reporter vectors, and we evaluated their promoter activities. A transcription silencer was found between the -592- and -1414-nucleotide region that was rich in nGAAn/nT-TCn elements (where n indicates G, A, T, or C). A high affinity and functional HSF1-binding element within the -862/-821-nucleotide region was determined by electrophoretic mobility shift assay and chromatin immunoprecipitation assay. Inactivation of this "heat-shock element" by either site-directed mutation or an HSF1 inhibitor, pifithrin-alpha, restored the promoter activity of the silencer structure. Moreover, pretreatment with antioxidants suppressed HSF1 binding activity and increased the transcriptional activity and expression of XAF1. These findings suggested that endogenous stress pressure in cancer cells sustained the high level expression of HSF1 and subsequently suppressed XAF1 expression, implicating the synergized effect of two anti-apoptotic protein families, HSP and inhibitors of apoptosis, in cytoprotection under stress circumstances.

Lycopene

Oxidative stress is now recognized as an important etiological factor in the causation of several chronic diseases including cancer, cardiovascular diseases, osteoporosis, and diabetes. Antioxidants play an important role in mitigating the damaging effects of oxidative stress on cells. Lycopene, a carotenoid antioxidant, has received considerable scientific interest in recent years. Epidemiological, tissue culture, and animal studies provide convincing evidence supporting the role of lycopene in the prevention of chronic diseases. Human intervention studies are now being conducted to validate epidemiological observations and to understand the mechanisms of action of lycopene in disease prevention. To obtain a better understanding of the role of lycopene in human health, this chapter reviews the most recent information pertaining to its chemistry, bioavailability, metabolism, role in the prevention of prostate cancer and cancer of other target organs, its role in cardiovascular diseases, osteoporosis, hypertension, and male infertility. A discussion of the most relevant molecular markers of cancer is also included as a guide to future researchers in this area. The chapter concludes by reviewing global intake levels of lycopene, suggested levels of intake, and future research directions.

Can we prevent prostate cancer? Rationale and current status of prostate cancer chemoprevention

Prostate cancer has been one of the most frequent cancers among men in Western countries for the past decade. Investigation of prostate cancer prevention is very attractive, because prostate cancer has a high incidence, long-term natural history, regional difference in incidence, and is effected by sex steroids. Chemoprevention is defined as the use of specific agents to suppress or reverse carcinogenesis and to prevent the development of cancer. The development of chemoprevention strategies against prostate cancer would be of medical and economic importance. Basic and clinical research of chemoprevention of prostate cancer are under active investigation. This article aims to summarize and review the basic evidence and clinical trials on prostate cancer chemoprevention. Recent research has demonstrated that many agents, such as agents altering sex steroid signaling, drugs inducing antiproliferation/differentiation, retinoids, anti-inflammatory drugs, and antioxidants, could be potential preventatives for prostate cancer. Large-scale clinical trials have suggested that 5alpha-reductase inhibitor finasteride, selenium, and vitamin E can function as a chemopreventive agent. Although no definitely effective strategies of prostate cancer prevention have been identified yet, increasing evidence will provide effective and safe strategies that bring clinical benefits.

A meta-analysis of the association of physical activity with reduced risk of colorectal cancer

BACKGROUND

Physical activity may be associated with reduced risk of colorectal cancer. The main aim of this paper is to review the available evidence for a link between exercise and large bowel cancer.

METHODS

A Cochrane-type methodology was performed. Data extracted included, type of study, type of physical activity measured and the numerical results. The risk ratios (RR) of the studies have been pooled according to the type of study, type of exercise, type of cancer and sex. Pooling was undertaken using fixed effect meta-analysis. A random effect meta-analysis was used where substantial heterogeneity existed.

RESULT

Data from 19 cohort studies showed a statistically significant reduction in the risk of colon cancer in physically active males, RR being 0.79 (95% CI 0.72-0.87) and 0.78 (95% CI 0.68-0.91) for occupational and recreational activities, respectively. In women only recreational activities are protective against colon cancer (RR = 0.71, 95%CI 0.57-0.88). Case-control studies showed significantly reduced risks of colon cancer in both sexes irrespective of the type of activity. No protection against rectal cancer is seen in either sex.

CONCLUSION

There is considerable evidence that physical activity is associated with reduced risk of colon cancer in both males and females.

Oxidative stress and cyclooxygenase activity in prostate carcinogenesis: targets for chemopreventive strategies

Over the last decade, epidemiological, experimental and clinical studies have implicated oxidative stress in the development and progression of prostate cancer. Oxidative stress may be linked to the effects of androgens, anti-oxidant systems and the pre-malignant condition, high-grade prostatic intraepithelial neoplasia. Cyclooxygenase-2 activity has been linked with prostate carcinogenesis. Evidence suggests that oxidative stress and cyclo-oxygenase-2 activity may be mechanistically linked. Agents such as anti-oxidants and cyclo-oxgenase-2 inhibitors may be of value in the chemoprevention of prostate cancer. The feasibility of intervention with such agents will depend on the development and validation of biomarkers for clinical trials, particularly markers of oxidative damage caused by reactive oxygen species (ROS). A greater understanding of the molecular events associated with oxidative stress will enhance the development of such biomarkers and should result in better strategies for the chemoprevention of prostate cancer.

The role of cyclooxygenase-2 inhibition for the prevention and treatment of prostate carcinoma

Experimental and epidemiologic studies have demonstrated that nonsteroidal antiinflammatory drugs (NSAIDs) are effective in the prevention of human cancers. Nonsteroidal antiinflammatory drugs inhibit the cyclooxygenase (COX) enzyme that functions to convert arachidonic acid to prostaglandins (PGs). Cyclooxygenase-2, a key COX isoenzyme, is rapidly induced in response to inflammatory stimuli, growth factors, cytokines, and promoters of neoplastic growth. Cyclooxygenase-2-catalyzed reactions may be involved in carcinogenesis via 2 distinct mechanisms: (1). DNA damage and (2). PG-mediated effects. Reactions mediated by COX-2 form reactive oxygen species that can directly induce the oxidation of DNA or instigate the bioactivation of carcinogens. Prostaglandin E2, a byproduct of COX-2-mediated arachidonic acid metabolism, exhibits several biologic actions that have been shown to promote tumorigenesis and tumor progression. These actions include increased cell proliferation, promotion of angiogenesis, and the elevated expression of the antiapoptotic protein Bcl-2. In addition, PGE2 decreases natural killer cell activity and alters immune surveillance. In vitro experimental studies find that COX-2 inhibitors decrease cellular proliferation, increase apoptosis, and modulate genes involved in cell cycle regulation. Evidence from animal studies supports a role for NSAIDs in prostate cancer (CaP) prevention. Population-based studies have observed a reduced incidence of CaP among men using NSAIDs. Because CaP evolves slowly and rarely strikes men before the sixth or seventh decade of life, any strategy to delay or lengthen the time to development of clinically evident CaP, such as chemoprevention strategies, would greatly impact the natural history of this disease. Recent progress and critical analyses in the roles of COX-2 inhibition on prostate carcinogenesis and CaP prevention will be presented.

Gut glutathione metabolism and changes with 7,12-DMBA and glutamine

INTRODUCTION

The mechanism by which oral glutamine (GLN) prevents 7,12-dimethylbenz(a)anthracene (DMBA)-induced breast cancer is unknown. While GLN triples the negative extraction of gut glutathione (GSH) in rats, DMBA significantly disrupts it. Actual gut GSH flux has not been reported. We hypothesized that the gut is a producer of GSH; DMBA blocks gut GSH production and supplemental oral GLN antagonizes this effect.

MATERIALS AND METHODS

Eighty Sprague-Dawley rats were randomized to four groups (n = 20/group): DMBA + GLN, DMBA + FA, OIL + GLN, OIL + FA. Rats (age 50 days) were gavaged with a one-time dose of 100 mg/kg DMBA or oil. Rats were gavaged with AES-14 as GLN (1 gm/kg/day) or an isonitrogenous amount of Freamine (FA) from 1 week before till sacrifice at 1 week after DMBA (greatest effect on gut GSH extraction). Arterial and portal blood was taken for GLN and GSH levels, and blood flow was measured using (14)C-PAH. Gut GLN and GSH fluxes (uptake or production) were calculated.

RESULTS

DMBA abrogated the normal GSH production (negative flux) in OIL + FA while not affecting GLN metabolism. GLN maintained GSH production in DMBA + GLN.

CONCLUSIONS

Oral GLN restores to normal GSH production in DMBA-treated animals suggesting one of the mechanism(s) by which GLN prevents breast cancer in this model. Unchanged uptake of GLN in the DMBA-treated animals may indicate a block in GSH transport rather than actual intracellular production.

Overexpression of hMTH in peripheral lymphocytes and risk of prostate cancer: a case-control analysis

Oxidative damage is an important factor in prostate carcinogenesis, and overexpression of human MutT homolog (hMTH), a repair gene that removes oxidative damage, is a molecular marker of cellular oxidative stress. Therefore, we tested the hypothesis that overexpression of hMTH in unaffected (normal) surrogate tissue is associated with risk of prostate cancer in a pilot study of 51 patients with diagnosed prostate cancer and 50 age- and ethnicity-matched controls. Total RNA was extracted from phytohemagglutinin-stimulated peripheral blood lymphocytes of these subjects. We performed the real-time reverse transcription-polymerase chain reaction assay to evaluate the relative mRNA expression of three oxidative-damage-repair genes, human MutM homolog (hMMH), hMTH, and human MutY homolog (hMYH), with beta-actin and human O(6)-methylguanine DNA methyltransferase (hMGMT) as the internal controls. The relative gene expression levels of hMMH and hMTH were borderline higher in the cases than in controls (15.3% and 28.8% higher, respectively; P = 0.046 and P = 0.035, respectively), whereas no increase was observed for hMYH and hMGMT. With the median of the controls' values as the cutoff point, we observed that a high expression level of hMTH, but not of other genes, was associated with a significantly increased risk of prostate cancer (odds ratio = 2.62; 95% confidence interval = 1.13-6.75) after adjustment for age and ethnicity. These results suggested that increased expression of hMTH in peripheral lymphocytes may be a risk factor for prostate cancer and support our priori hypothesis. Although our findings were biologically plausible and consistent with the literature, they were preliminary and need to be confirmed in larger studies. In addition, a correlation between the expression level of hMTH and the level of oxidative DNA damage in the target tissues needs to be established as well.

Effect of 7,12-dimethylbenz[a]anthracene (DMBA) on gut glutathione metabolism

BACKGROUND

One mechanism of the mammary carcinogenesis of 7,12-dimethylbenz[a]anthracene (DMBA) is thought to be the generation of reactive oxygen species known to play an important role in initiation and progression. We hypothesized that DMBA would disrupt gut glutathione (GSH) metabolism and this disruption would correlate with mammary cell carcinogenesis.

METHODS

Sixty-four Sprague-Dawley rats were randomized to the DMBA versus control groups. At age 50 days, rats were gavaged with a one-time dose of 20 mg DMBA or sesame oil. Rats from each group were sacrificed at 1 week (n = 16), 2 weeks (n = 16), 4 weeks (n = 16), and 11 weeks (n = 16). Tumor appearance, arterial and gut GSH concentration, and gut GSH extraction were measured over time.

RESULTS

Gut GSH extraction (normally negative; production) was significantly depressed over the time points, even showing uptake (positive extraction) at Weeks 1 and 2. Tumors developed in all animals in the DMBA group by Week 11.

CONCLUSIONS

A one-time oral administration of DMBA has a significant and prolonged depressive effect on gut GSH production that has not previously been described. These data support the hypothesis that the carcinogenic effect of DMBA is mediated, at least in part, by oxidative damage and that the disruption of gut GSH metabolism may play a greater role in carcinogenesis than previously realized.

Mechanisms linking diet and colorectal cancer: the possible role of insulin resistance

Diet is clearly implicated in the origin of colorectal cancer, with risk factors for the disease including reduced consumption of vegetables, fiber, and starch and increased consumption of red meat and animal fat. Several hypotheses have been developed to explain these associations. Most recently, McKeown-Eyssen and Giovannucci noted the similarity of the risk factors for colorectal cancer and those for insulin resistance and suggested that insulin resistance leads to colorectal cancer through the growth-promoting effect of elevated levels of insulin, glucose, or triglycerides. We briefly review the evidence from observational, epidemiological, and experimental animal studies linking diet with insulin resistance and colorectal cancer. The evidence suggests that diets high in energy and saturated fat and with high glycemic index carbohydrate and low levels of fiber and n-3 fatty acids lead to insulin resistance with hyperinsulinemia, hyperglycemia, and hypertriglyceridemia. We then consider how insulin, the related insulin-like growth factors, triglycerides, and nonesterified fatty acids could lead to increased growth of colon cancer precursor lesions and the development of colorectal cancer. Finally, we consider the implications of this scheme on possible future research directions, including studies of satiety and clinical tests of the importance of insulin resistance in the colon carcinogenesis process.

Antioxidant dietary supplements: Rationale and current status as chemopreventive agents for prostate cancer

Epidemiologic data suggest that the environment is responsible for most prostate cancers (PCA). One major mechanism by which the environment can influence carcinogenesis is oxidative damage. This refers to the generation of reactive oxygen species (ROS) that then damage important biomolecules, including DNA, protein, and lipids. Experimental observations suggest that oxidative damage is associated with PCA. These include: a) the association of PCA and dietary fat consumption (a major substrate for oxidative stress), b) oxidative biomarker data (suggesting increased oxidative stress among patients with PCA), c) ubiquitous defects in the glutathione-s-transferase pi pathway (a major endogenous antioxidant mechanism), and d) evidence that androgens (an important promoter of PCA growth) work in part via generation of ROS. Perhaps the best indirect evidence for oxidative stress comes from randomized double-blind prevention trials of antioxidants. Vitamin E and selenium have both been shown to reduce prostate cancer incidence. Although PCA prevention was not the primary endpoint of these studies, the statistical likelihood that both would prove beneficial by chance alone is 1 in 400. These data suggest that antioxidants may be beneficial in preventing PCA. Further research including randomized trials is warranted.

Carotenoids and chronic diseases

Chronic diseases such as cancer and cardiovascular diseases are the major causes of deaths in North America. Dietary intake of fruits and vegetables has been suggested to have protective effects against such chronic diseases. Carotenoids are important plant pigments which are thought to contribute towards the beneficial effects of fruit and vegetable consumption. This review focuses on the role of carotenoids and particularly lycopene in chronic diseases.

Oxidative stress in keratinocytes as an etiopathogenetic factor of psoriasis

A new etiopathogenetic concept of psoriasis is proposed, which considers psoriasis as a typical inflammatory process characterized by increased antioxidant activity and overexpression of apoptotic receptors. Under these conditions, hyperstimulation of germinative layer cells proliferation dramatically accelerates keratinocyte passage towards apoptotic effect of atmospheric oxygen and its reactive species dooming to death cells with enhanced expression of apoptotic receptors. Oxidative stress of nondifferentiated keratinocytes triggers the formation of defective horny layer, the key mechanism of psoriasis.

Deleterious network hypothesis of Alzheimer's disease

Numerous studies indicate that aberrant amyloid precursor protein metabolism, elevated peroxidative damage, depressed energy metabolism and altered calcium homeostasis are four pivotal deleterious factors in the pathogenesis of Alzheimer's disease. Cumulative evidence further suggests that these four factors are intimately interrelated, forming a deleterious network. Based on this new concept of 'deleterious network', a unifying hypothesis-the deleterious network hypothesis of Alzheimer's disease-is proposed. The main ideas of the hypothesis are delineated as follows: increases in free radical damage, alterations in amyloid precursor protein metabolism, impairment of energy metabolism and abnormalities of calcium homeostasis are four cornerstones of a deleterious network. Various risk factors of Alzheimer's disease can triger the network by promoting the occurrence of one of these key components, resulting in the biological abnormalities of Alzheimer's disease. Based on this new theory, a majority of the important observations about Alzheimer's disease can be explained consistently and succinctly.