Cytosolic xanthine oxidoreductase mediated bioactivation of ethanol to acetaldehyde and free radicals in rat breast tissue. Its potential role in alcohol-promoted mammary cancer

Alcohol and breast cancer

Breast cancer is one of the main causes of death in women worldwide. In women, breast cancer includes over half of all tumours caused by alcohol. This paper discusses both ethanol metabolism and the mechanisms of mammary tumourigenesis caused by alcohol. Numerous signalling pathways in neoplastic transformation following alcohol consumption in women have been presented. In addition, primary and secondary prevention, phytochemicals, synthetic chemicals, specific inhibitors of enzymes and selective receptor modulators have been described.

Syk promotes phagocytosis by inducing reactive oxygen species generation and suppressing SOCS1 in macrophage-mediated inflammatory responses

OBJECTIVE

Inflammation, a vital innate immune response against infection and injury, is mediated by macrophages. Spleen tyrosine kinase (Syk) regulates inflammatory responses in macrophages; however, its role and underlying mechanisms are uncertain.

MATERIALS AND METHODS

In this study, overexpression and knockout (KO) cell preparations, phagocytosis analysis, confocal microscopy, reactive oxygen species (ROS) determination, mRNA analysis, and immunoprecipitation/western blotting analyses were used to investigate the role of Syk in phagocytosis and its underlying mechanisms in macrophages during inflammatory responses.

RESULTS

Syk inhibition by Syk KO, Syk-specific small interfering RNA (siSyk), and a selective Syk inhibitor (piceatannol) significantly reduced the phagocytic activity of RAW264.7 cells. Syk inhibition also decreased cytochrome c generation by inhibiting ROS-generating enzymes in lipopolysaccharide (LPS)-stimulated RAW264.7 cells, and ROS scavenging suppressed the phagocytic activity of RAW264.7 cells. LPS induced the tyrosine nitration (N-Tyr) of suppressor of cytokine signaling 1 (SOCS1) through Syk-induced ROS generation in RAW264.7 cells. On the other hand, ROS scavenging suppressed the N-Tyr of SOCS1 and phagocytosis. Moreover, SOCS1 overexpression decreased phagocytic activity, and SOCS1 inhibition increased the phagocytic activity of RAW264.7 cells.

CONCLUSION

These results suggest that Syk plays a critical role in the phagocytic activity of macrophages by inducing ROS generation and suppressing SOCS1 through SOCS1 nitration during inflammatory responses.

Evolution, expression, and substrate specificities of aldehyde oxidase enzymes in eukaryotes

Aldehyde oxidases (AOXs) are a small group of enzymes belonging to the larger family of molybdo-flavoenzymes, along with the well-characterized xanthine oxidoreductase. The two major types of reactions that are catalyzed by AOXs are the hydroxylation of heterocycles and the oxidation of aldehydes to their corresponding carboxylic acids. Different animal species have different complements of AOX genes. The two extremes are represented in humans and rodents; whereas the human genome contains a single active gene (AOX1), those of rodents, such as mice, are endowed with four genes (Aox1-4), clustering on the same chromosome, each encoding a functionally distinct AOX enzyme. It still remains enigmatic why some species have numerous AOX enzymes, whereas others harbor only one functional enzyme. At present, little is known about the physiological relevance of AOX enzymes in humans and their additional forms in other mammals. These enzymes are expressed in the liver and play an important role in the metabolisms of drugs and other xenobiotics. In this review, we discuss the expression, tissue-specific roles, and substrate specificities of the different mammalian AOX enzymes and highlight insights into their physiological roles.

Alcohol Metabolizing Enzymes, Microsomal Ethanol Oxidizing System, Cytochrome P450 2E1, Catalase, and Aldehyde Dehydrogenase in Alcohol-Associated Liver Disease

Once ingested, most of the alcohol is metabolized in the liver by alcohol dehydrogenase to acetaldehyde. Two additional pathways of acetaldehyde generation are by microsomal ethanol oxidizing system (cytochrome P450 2E1) and catalase. Acetaldehyde can form adducts which can interfere with cellular function, leading to alcohol-induced liver injury. The variants of alcohol metabolizing genes encode enzymes with varied kinetic properties and result in the different rate of alcohol elimination and acetaldehyde generation. Allelic variants of these genes with higher enzymatic activity are believed to be able to modify susceptibility to alcohol-induced liver injury; however, the human studies on the association of these variants and alcohol-associated liver disease are inconclusive. In addition to acetaldehyde, the shift in the redox state during alcohol elimination may also link to other pathways resulting in activation of downstream signaling leading to liver injury.

Dietary Carcinogens and DNA Adducts in Prostate Cancer

Prostate cancer (PC) is the most commonly diagnosed non-cutaneous cancer and the second leading cause of cancer-related to death in men. The major risk factors for PC are age, family history, and African American ethnicity. Epidemiological studies have reported large geographical variations in PC incidence and mortality, and thus lifestyle and dietary factors influence PC risk. High fat diet, dairy products, alcohol and red meats, are considered as risk factors for PC. This book chapter provides a comprehensive, literature-based review on dietary factors and their molecular mechanisms of prostate carcinogenesis. A large portion of our knowledge is based on epidemiological studies where dietary factors such as cancer promoting agents, including high-fat, dairy products, alcohol, and cancer-initiating genotoxicants formed in cooked meats have been evaluated for PC risk. However, the precise mechanisms in the etiology of PC development remain uncertain. Additional animal and human cell-based studies are required to further our understandings of risk factors involved in PC etiology. Specific biomarkers of chemical exposures and DNA damage in the prostate can provide evidence of cancer-causing agents in the prostate. Collectively, these studies can improve public health research, nutritional education and chemoprevention strategies.

Alcohol consumption and mortality after breast cancer diagnosis: The health and functioning in women study

OBJECTIVE

To determine the association of prediagnostic alcohol consumption with long-term mortality from breast cancer and other causes in a cohort of women with breast cancer.

METHODS

We studied a Michigan-based cohort of 939 women aged 40-84 years, who provided complete information about the type, amount and intensity of prediagnostic alcohol consumption. Associations of alcohol consumption, based on weekly volume of alcohol consumption during the year prior to breast cancer diagnosis, with mortality were evaluated in Cox proportional hazards models, with adjustment for sociodemographic factors, body mass index, smoking, comorbidity, tumor characteristics, and treatment. Differences among covariates were assessed with Pearson χ2 , Student t -tests and Wilcoxon Rank Sum tests. All statistical tests were two-sided.

RESULTS

During a median follow-up of 11 years, 724 deaths occurred overall, with 303 from breast cancer. Fifty-five percent of the women were categorized as drinkers with volume of alcohol consumption ranging from 0.75 to 36.00 drinks/week. In multivariable models, a decreased risk of other-cause mortality was associated with low alcohol drinking (0.75-3.75 drinks/week; HR = 0.61, 95% CI = 0.47-0.78), moderate volume alcohol drinking (4.00-9.75 drinks/week; HR = 0.57, 95% CI = 0.39-0.85) and low frequency (0.75-3.75 drinks/week) beer and wine intake (HR = 0.69, 95% CI = 0.50-0.96 and HR = 0.68, 95% CI = 0.52-0.88 respectively). Although the risk of breast cancer-specific mortality was not statistically significantly associated with moderate (4.00-9.75 drinks/week) and high volume (10.00-36.00 drinks/week) alcohol drinking in the overall cohort (HR = 1.43, 95% CI = 95% 0.97-2.12 and HR = 1.53, 95% CI = 0.87-2.70 respectively), there was a positive association of alcohol consumption with breast cancer-specific mortality among current smokers (HR = 1.92, 95% CI = 1.03-3.57; Pinteraction = 0.04).

CONCLUSION

In this prospective cohort study, regular consumption of 0.75-36.00 alcoholic drinks per week during the year prior to breast cancer diagnosis was associated with a reduction in other-cause mortality and with an increase in breast cancer-specific mortality among current smokers, after taking into account clinical and sociodemographic factors.

Xanthine oxidoreductase in cancer: more than a differentiation marker

Human xanthine oxidoreductase (XOR) catalyzes the last two steps of purine catabolism and is present in two interconvertible forms, which may utilize O2 or NAD(+) as electron acceptors. In addition to uric acid, XOR products may comprise reactive oxygen and nitrogen species that have many biologic effects, including inflammation, endothelial dysfunction, and cytotoxicity, as well as mutagenesis and induction of proliferation. XOR is strictly modulated at the transcriptional and post-translational levels, and its expression and activity are highly variable in cancer. Xanthine oxidoreductase (XOR) expression has been negatively associated with a high malignity grade and a worse prognosis in neoplasms of the breast, liver, gastrointestinal tract, and kidney, which normally express a high level of XOR protein. However, the level of XOR expression may be associated with a worse outcome in cancer of low XOR-expressing cells, in relation to the inflammatory response elicited through the tissue damage induced by tumor growth. Xanthine oxidoreductase (XOR) has been implicated in the process of oncogenesis either directly because it is able to catalyze the metabolic activation of carcinogenic substances or indirectly through the action of XOR-derived reactive oxygen and nitrogen species. The role of uric acid is characterized by both oxidant and antioxidant action; thus, it is still debatable whether control of uricemia may be helpful to improve the outcomes of tumor illness.

Xanthine Oxidoreductase-Derived Reactive Species: Physiological and Pathological Effects

Xanthine oxidoreductase (XOR) is the enzyme that catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid and is widely distributed among species. In addition to this housekeeping function, mammalian XOR is a physiological source of superoxide ion, hydrogen peroxide, and nitric oxide, which can function as second messengers in the activation of various pathways. This review intends to address the physiological and pathological roles of XOR-derived oxidant molecules. The cytocidal action of XOR products has been claimed in relation to tissue damage, in particular damage induced by hypoxia and ischemia. Attempts to exploit this activity to eliminate unwanted cells via the construction of conjugates have also been reported. Moreover, different aspects of XOR activity related to phlogosis, endothelial activation, leukocyte activation, and vascular tone regulation, have been taken into consideration. Finally, the positive and negative outcomes concerning cancer pathology have been analyzed because XOR products may induce mutagenesis, cell proliferation, and tumor progression, but they are also associated with apoptosis and cell differentiation. In conclusion, XOR activity generates free radicals and other oxidant reactive species that may result in either harmful or beneficial outcomes.

Alcohol drinking and mammary cancer: Pathogenesis and potential dietary preventive alternatives

Alcohol consumption is associated with an increased risk of breast cancer, increasing linearly even with a moderate consumption and irrespectively of the type of alcoholic beverage. It shows no dependency from other risk factors like menopausal status, oral contraceptives, hormone replacement therapy, or genetic history of breast cancer. The precise mechanism for the effect of drinking alcohol in mammary cancer promotion is still far from being established. Studies by our laboratory suggest that acetaldehyde produced in situ and accumulated in mammary tissue because of poor detoxicating mechanisms might play a role in mutational and promotional events. Additional studies indicated the production of reactive oxygen species accompanied of decreases in vitamin E and GSH contents and of glutathione transferase activity. The resulting oxidative stress might also play a relevant role in several stages of the carcinogenic process. There are reported in literature studies showing that plasmatic levels of estrogens significantly increased after alcohol drinking and that the breast cancer risk is higher in receptor ER-positive individuals. Estrogens are known that they may produce breast cancer by actions on ER and also as chemical carcinogens, as a consequence of their oxidation leading to reactive metabolites. In this review we introduce our working hypothesis integrating the acetaldehyde and the oxidative stress effects with those involving increased estrogen levels. We also analyze potential preventive actions that might be accessible. There remains the fact that alcohol drinking is just one of the avoidable causes of breast cancer and that, at present, the suggested acceptable dose for prevention of this risk is of one drink per day.

Acetaldehyde content and oxidative stress in the deleterious effects of alcohol drinking on rat uterine horn

After alcohol exposure through a standard Lieber and De Carli diet for 28 days, a severe atrophy in the rat uteirne horn was observed, accompanied by significant alterations in its epithelial cells. Microsomal pathway of acetaldehyde production was slightly increased. Hydroxyl radicals were detected in the cytosolic fraction, and this was attributed to participation of xanthine oxidoreductase. They were also observed in the microsomal fraction in the presence of NADPH generating system. No generation of 1-hydroxyethyl was evidenced. The t-butylhydroperoxide-induced chemiluminescence analysis of uterine horn homogenates revealed a significant increase in the chemiluminiscence emission due to ethanol exposure. In the animals repeatedly exposed to alcohol, sulfhydryl content from uterine horn proteins was decreased, but no significant changes were observed in the protein carbonyl content from the same samples. Minor but significant decreasing changes were observed in the GSH content accompanied by a tendency to decrease in the GSH/GSSG ratio. A highly significant finding was the diminished activity content of glutathione peroxidase. Results suggest that acetaldehyde accumulation plus the oxidative stress may play an additional effect to the alcohol-promoted hormonal changes in the uterus reported by others after chronic exposure to alcohol.

Germline variation in NCF4, an innate immunity gene, is associated with an increased risk of colorectal cancer

Chronic inflammation has been implicated in the etiology of colorectal adenoma and cancer; however, few key inflammatory genes mediating this relationship have been identified. In this study, we investigated the association of germline variation in innate immunity genes in relation to the risk of colorectal neoplasia. Our study was based on the analysis of samples collected from the prostate, lung, colorectal and ovarian (PLCO) Cancer Screening Trial. We investigated the association between 196 tag single nucleotide polymorphisms (SNPs) in 20 key innate immunity genes with risk of advanced colorectal adenoma and cancer in 719 adenoma cases, 481 cancer cases and 719 controls. Logistic regression was used to estimate odds ratios (OR) and 95% confidence intervals (CIs). After Bonferroni correction, the AG/GG genotype of rs5995355, which is upstream of NCF4, was associated with an increased risk of colorectal cancer (OR = 2.43, 95% CI = 1.73-3.39; p < 0.0001). NCF4 is part of the NAPDH complex, a key factor in biochemical pathways and the innate immune response. While not definitive, our analyses suggest that the variant allele does not affect expression of NCF4, but rather modulates activity of the NADPH complex. Additional studies on the functional consequences of rs5995355 in NCF4 may help to clarify the mechanistic link between inflammation and colorectal cancer.

Identification of candidate polymorphisms on stress oxidative and DNA damage repair genes related with clinical outcome in breast cancer patients

Diverse polymorphisms have been associated with the predisposition to develop cancer. On fewer occasions, they have been related to the evolution of the disease and to different responses to treatment. Previous studies of our group have associated polymorphisms on genes related to oxidative stress (rs3736729 on GCLC and rs207454 on XDH) and DNA damage repair (rs1052133 on OGG1) with a predisposition to develop breast cancer. In the present work, we have evaluated the hypothesis that these polymorphisms also play a role in a patient's survival. A population-based cohort study of 470 women diagnosed with primary breast cancer and a median follow up of 52.44 months was conducted to examine the disease-free and overall survival in rs3736729, rs207454 and rs1052133 genetic variants. Adjusted Cox regression analysis was used to that end. The Kaplan-Meier analysis shows that rs3736729 on GCLC presents a significant association with disease-free survival and overall survival. The polymorphisms rs1052133 on OGG1 and rs207454 on XDH show a trend of association with overall survival. The analysis based on hormonal receptor status revealed a stronger association. The CC genotype on rs207454 (XDH) was significantly associated with lower time of disease free survival (p = 0.024) in progesterone receptor negative (PGR-) patients and rs3736729 (GCLC) was significantly associated with disease free survival (p = 0.001) and overall survival (p = 0.012) in the subgroup of estrogen receptor negative (ER-) patients. This work suggests that unfavorable genetic variants in the rs207454 (XDH) and rs3736729 (GCLC) polymorphisms may act as predictors of the outcome in negative progesterone receptor and negative estrogen receptor breast cancer patients, respectively.

Acquired xanthine dehydrogenase expression shortens survival in patients with resected adenocarcinoma of lung

Xanthine dehydrogenase (XDH), also known as xanthine oxidoreductase (XOR), has long been recognized as the key enzyme in the catabolism of purines, oxidizing hypoxanthine into xanthine and then xanthine into uric acid. In addition, levels of XDH expression are reportedly related to the prognosis of patients with malignant tumors, though the relationship between the clinicopathological features of lung cancer and XDH is not fully understood. We therefore used semiquantitative real-time reverse transcription polymerase chain reaction to assess expression of XDH mRNA in tumor samples from 88 patients with adenocarcinoma of the lung. We then correlated XDH mRNA levels with known clinicopathological factors. We found that the 5-year overall survival rate among patients strongly expressing XDH was significantly poorer than among those expressing lower levels of XDH (P < 0.001; log-rank test). Normal lung tissue does not express XDH. Multivariate Cox proportional hazard analyses revealed that being male (hazard ratio, 3.14; 95 % confidence interval (CI), 1.45-7.07; P = 0.004), nodal metastasis positivity (hazard ratio, 5.74; 95 % CI, 1.94-19.3; P = 0.001), and high XDH expression (hazard ratio, 2.33; 95 % CI, 1.11-5.02; P = 0.026) were all independent factors affecting 5-year disease-free survival. In conclusion, high tumoral XDH expression is an independent predictor of a poor prognosis in patients with adenocarcinoma of the lung.

Further studies on the potential contribution of acetaldehyde accumulation and oxidative stress in rat mammary tissue in the alcohol drinking promotion of breast cancer

There is available evidence supporting a positive association between alcohol intake and risk of breast cancer. However, there is limited information regarding possible mechanisms for this effect. Past studies from our laboratory suggest that acetaldehyde accumulation in mammary tissue after alcohol intake may be of particular relevance and that cytosolic and microsomal in situ bioactivation of ethanol to acetaldehyde and free radicals and the resulting stimulation of oxidative stress could be a significant early event related to tumor promotion. In the present studies repetitive alcohol drinking for 28 days was found to produce significant decreases in the mammary tissue content of GSH and alpha tocopherol and in glutathione S-transferase or glutathione reductase activities. In contrast, glutathione peroxidase activity was slightly increased. Malondialdehyde determinations did not show the occurrence of lipid peroxidation while the xylenol orange procedure gave positive results. The mammary microsomal metabolism of ethanol to acetaldehyde was not induced after an acute dose of ethanol or acetone able to induce the activity of its liver counterpart. The cytosolic pathway of alcohol metabolism instead was significantly enhanced by these two treatments. No increased generation of comet images was found either in mammary tissue or in liver under the experimental conditions tested. Results suggest that, while acetaldehyde accumulation in mammary tissue could be a critical event resulting from increasing production of acetaldehyde in situ plus an additional amount of it arriving via blood, other factors such as poor handling of the accumulated acetaldehyde could be also relevant.

Metabolism of ethanol to acetaldehyde by rat uterine horn subcellular fractions

Controversial studies from others suggested that alcohol intake could be associated with some deleterious effects in the uterus. Not all the effects of alcohol drinking on female reproductive organs can be explained in terms of endocrine disturbances. Deleterious effect of alcohol or its metabolites in situ could also play a role. Accordingly, we found a metabolism of alcohol to acetaldehyde in the rat uterine horn tissue cytosolic fraction mediated by xanthine oxidoreductase, requiring a purine cosubstrate and inhibited by allopurinol. This activity was detected by histochemistry in the epithelium and aldehyde dehydrogenase activity was detected in the muscular layer and in the serosa. There was a microsomal process, not requiring NADPH and of enzymatic nature, oxygen-dependent and inhibited by diethyldithiocarbamate, diphenyleneiodonium and partially sensitive to esculetin and nordihydroguaiaretic acid. The presence of metabolic pathways in the uterine horn able to generate acetaldehyde, accompanied by a low capacity to destroy it through aldehyde dehydrogenase, led to acetaldehyde accumulation in the uterus during ethanol exposure. Results suggest that any acetaldehyde produced in situ or arriving to the uterine horn via blood would remain in this organ sufficiently to have the opportunity to react with critical molecules to cause deleterious effects.

Inhibition of rat mammary microsomal oxidation of ethanol to acetaldehyde by plant polyphenols

We previously reported that the microsomal fraction from rat mammary tissue is able to oxidize ethanol to acetaldehyde, a mutagenic-carcinogenic metabolite, depending on the presence of NADPH and oxygen but not inhibited by carbon monoxide or other cytochrome P450 inhibitors. The process was strongly inhibited by diphenyleneiodonium, a known inhibitor of NADPH oxidase, and by nordihydroguaiaretic acid, an inhibitor of lipoxygenases. This led us to suggest that both enzymes could be involved. With the purpose of identifying natural compounds present in food with the ability to decrease the production of acetaldehyde in mammary tissue, in the present studies, several plant polyphenols having inhibitory effects on lipoxygenases and of antioxidant nature were tested as potential inhibitors of the rat mammary tissue microsomal pathway of ethanol oxidation. We included in the present screening study 32 polyphenols having ready availability and that were also tested against the rat mammary tissue cytosolic metabolism of ethanol to acetaldehyde. Several polyphenols were also able to inhibit the microsomal ethanol oxidation at concentrations as low was 10-50 μM. The results of these screening experiments suggest the potential of several plant polyphenols to prevent in vivo production and accumulation of acetaldehyde in mammary tissue.

Ethanol enhances the interaction of breast cancer cells over-expressing ErbB2 with fibronectin

BACKGROUND

Ethanol is a tumor promoter and may enhance the metastasis of breast cancer. However, the underlying cellular/molecular mechanisms remain unknown. Amplification of ErbB2 or HER2, a receptor tyrosine kinase of the ErbB family, is found in 20 to 30% of patients with breast cancer. We have previously demonstrated that the effect of ethanol on the migration/invasion of breast cancer cells positively correlated with the expression levels of ErbB2. Adhesion to the extracellular matrix (ECM) is an important initial step for cancer cell invasion and metastasis. In this study, we investigated the effects of ethanol on the adhesion of MCF7 breast cancer cells over-expressing ErbB2 (MCF7(ErbB2)) to human plasma fibronectin.

METHODS

To test the hypothesis that ethanol may enhance the attachment of human breast cancer cells to fibronectin, an important component of the ECM, we evaluated the effect of ethanol on the expression of focal adhesions, cell attachment, and ErbB2 signaling in cultured MCF7(ErbB2) cells.

RESULTS

Exposure to ethanol drastically enhanced the adhesion of MCF(ErbB2) cells to fibronectin and increased the expression of focal adhesions. Ethanol induced phosphorylation of ErbB2 at Tyr1248, FAK at Tyr861, and cSrc at Try216. Ethanol promoted the interaction among ErbB2, FAK, and cSrc, and the formation of a focal complex. AG825, a selective ErbB2 inhibitor, attenuated the ethanol-induced phosphorylation of ErbB2 and its association with FAK. Furthermore, AG825 blocked ethanol-promoted cell/fibronectin adhesion as well as the expression of focal adhesions.

CONCLUSIONS

Our results suggest that ethanol enhances the adhesion of breast cancer cells to fibronectin in an ErbB2-dependent manner, and the FAK pathway plays an important role in ethanol-induced formation of a focal complex.

Metabolism of ethanol to acetaldehyde and increased susceptibility to oxidative stress could play a role in the ovarian tissue cell injury promoted by alcohol drinking

It is known that drinking alcohol can lead to reproductive problems in women. In this study, we analyzed the possibility that part of those effects were mediated through alterations of ovarian function related to ethanol oxidation to acetaldehyde occurring in situ. Biotransformation in the rat ovary cytosolic fraction was partially inhibited by allopurinol, suggesting the participation of xanthine oxidoreductase in the process. Microsomal pathway was of enzymatic nature, requiring nicotinamide adenine dinucleotide phosphate-oxidase (NADPH), sensitive to oxygen and significantly inhibited by sodium diethyldithiocarbamate, 4-methylpyrazole and diphenyleneiodonium. Aldehyde dehydrogenase activity was detected by histochemistry in the ovarian tissue, in the strome surrounding the follicle while no alcohol dehydrogenase was detected. However, biochemical determination of alcohol dehydrogenase and aldehyde dehydrogenase activities in rat ovarian tissue revealed the presence of some activity of both enzymes but significantly lower than those found in the liver. By repetitive exposure of animals to ethanol, the microsomal metabolism to acetaldehyde was increased but not in the case of the cytosolic fraction. In these animals, t-butylhydroperoxyde-promoted chemiluminiscence was increased in comparison to control, revealing an increased susceptibility to oxidative stress due to alcohol drinking. Ultrastructure of ovarian tissue from rats exposed chronically to alcohol revealed alterations at the level of the granulosa; theca interna and pellucida zones. In the secondary follicle, alterations consisted of marked condensation of chromatin attached to the nuclear inner membrane. Intense dilatation of the outer perinuclear space could be observed. There was a marked dilatation of the rough endoplasmic reticulum accompanied of significant detachment of ribosomes from their membranes. Mitochondria appeared swollen. In the zona pellucida, most of the cell processes from oocyte and corona radiata cells were absent or broken totally or in part. Results suggest that in the rat ovary, metabolism of ethanol to acetaldehyde may play a role in alcohol effects on female reproductive function.

Alcohol and breast cancer: the mechanisms explained

Breast cancer is a leading cause of death amongst women, several studies have shown significant association between alcohol consumption and breast cancer. The aim of this overview is to highlight some of the mechanisms by which alcohol consumption could increase the risk of developing breast cancer. Using online Medline search engine, article containing details about mechanisms which explain the link between alcohol and breast cancer were examined. A number of mechanisms were found by which alcohol could increase the risk of breast cancer, alcohol's interaction and effect on oestrogen secretion; number of oestrogen receptors; the generation of acetaldehyde and hydroxyl free radicals; cells migration and metastasis; secretion of IGF1 and interaction with HRT and folate metabolism. In conclusion, it is essential for clinicians to understand these mechanisms and inform patients of the link between alcohol and breast cancer.

Nitroreductive metabolic activation of some carcinogenic nitro heterocyclic food contaminants in rat mammary tissue cellular fractions

Several nitrofurans and nitroimidazoles have been widely used in veterinary medicine. Some of these compounds are breast carcinogens in rodents and their mechanism of action is hypothesized to be related to reactive metabolites generated by nitroreduction and/or via oxygen-dependent redox cycling. The present work describes the nitroreductive metabolism of nitrofurazone, nitrofurantoin, furazolidone, and metronidazole by the cytosolic and microsomal fractions of mammary tissue from female Sprague-Dawley rats. The data obtained were compared with those obtained with nifurtimox and benznidazole, two well-known rodent carcinogen/mutagens nitroheterocycles. The nitroreductase activity of pure milk xanthine-oxidoreductase (XOR) was evaluated for screening purposes. All the nitrofurans were nitroreduced either by the pure XOR or the cytosolic fraction in the presence of hypoxanthine, and these activities were inhibited by allopurinol. Furthermore, they were nitroreduced by the microsomal fraction in the presence of NADPH, except for the nitrofurazone, suggesting the participation of cytochrome P450 reductase. Nitrofurans metabolism was significantly more intense than that of NFX. No equivalent nitroreductase activity was observed in either subcellular fraction using nitroimidazolic compounds as substrates. These results suggest that the nitroreductive metabolism of nitrofurans and the subsequent redox cycling might be involved in the associated mammary tissue carcinogenic effects.

Identification of proteins binding to E-Box/Ku86 sites and function of the tumor suppressor SAFB1 in transcriptional regulation of the human xanthine oxidoreductase gene

The xanthine oxidoreductase gene (XOR) encodes an important source of reactive oxygen species and uric acid, and its expression is associated with various human diseases including several forms of cancer. We previously reported that basal human XOR (hXOR) expression is restricted or repressed by E-box and TATA-like elements and a cluster of transcriptional proteins, including AREB6-like proteins and DNA-dependent protein kinase (DNA-PK). We now demonstrate that the cluster contains the tumor suppressors SAFB1, BRG1, and SAF-A. We further demonstrate that SAFB1 silencing increases hXOR expression and that SAFB1 directly binds to the E-box. Multiple studies in vitro and in vivo including pulldown, immunoprecipitation and chromatin immunoprecipitation analyses indicate that SAFB1, Ku86, and BRG1 associate with each other. The results suggest that the SAFB1 complex binds to the hXOR promoter in a chromatin environment and plays a critical role in restricting hXOR expression via its direct interaction with the E-box, DNA-PK, and tumor suppressors. Moreover, we demonstrate that the cytokine, oncostatin M (OSM), induces the phosphorylation of SAFB1 and that the OSM-induced hXOR mRNA expression is significantly inhibited by silencing the DNA-PK catalytic subunit or SAFB1 expression. The present studies for the first time demonstrate that hXOR is a tumor suppressor-targeted gene and that the phosphorylation of SAFB1 is regulated by OSM, providing a molecular basis for understanding the role of SAFB1-regulated hXOR transcription in cytokine stimulation and tumorigenesis.

Xanthine dehydrogenase processes retinol to retinoic acid in human mammary epithelial cells

Retinoic acid is considered to be the active metabolite of retinol, able to control differentiation and proliferation of epithelia. Retinoic acid biosynthesis has been widely described with the implication of multiple enzymatic activities. However, our understanding of the cell biological function and regulation of this process is limited. In a recent study we evidenced that milk xanthine oxidase (E.C. 1.17.3.2.) is capable to oxidize all-trans-retinol bound to CRBP (holo-CRBP) to all-trans-retinaldehyde and then to all-trans-retinoic acid. To get further knowledge regarding this process we have evaluated the biosynthetic pathway of retinoic acid in a human mammary epithelial cell line (HMEC) in which xanthine dehydrogenase (E.C. 1.17.1.4.), the native form of xanthine oxidase, is expressed. Here we report the demonstration of a novel retinol oxidation pathway that in the HMEC cytoplasm directly conduces to retinoic acid. After isolation and immunoassay of the cytosolic protein showing retinol oxidizing activity we identified it with the well-known enzyme xanthine dehydrogenase. The NAD+ dependent retinol oxidation catalyzed by xanthine dehydrogenase is strictly dependent on cellular retinol binding proteins and is inhibited by oxypurinol. In this work, a new insight into the biological role of xanthine dehydrogenase is given.

Acetaldehyde accumulation in rat mammary tissue after an acute treatment with alcohol

Previous studies reported the presence in rat mammary tissue of a cytosolic xanthine oxidoreductase pathway for the metabolism of alcohol to acetaldehyde and hydroxyl radicals and to the microsomal biotransformation of ethanol to acetaldehyde. It was also reported that after chronic ethanol drinking stressful oxidative conditions can be observed. The present work reports that even after single doses of ethanol, given at three different levels (6.3 g kg(-1); 3.8 g kg(-1) or 0.6 g kg(-1) p.o.), acetaldehyde accumulates for prolonged periods of time in the mammary tissue to reach concentrations higher than in blood (e.g. 5.1+/-1.2 nmol g(-1) versus 0.2+/-0.1 nmol ml(-1), for 6.3 g kg(-1) dose, 6 h after intoxication). The presence in rat mammary tissue of low activities of additional enzymes able to generate acetaldehyde was established (alcohol dehydrogenase: 0.97+/-0.84 mU mg(-1) protein; CYP2E1: 1.30+/-0.12 x 10(-2) pmol 4-nitrocatechol min(-1) mg(-1) protein) and a low activity of aldehyde dehydrogenase was observed in the cytosolic, mitochondrial and microsomal fractions (0.02+/-0.04; 0.35+/-0.09 and 0.72+/-0.19 mU mg(-1) protein, respectively). After a single high dose of ethanol, an increased susceptibility to oxidative stress was observed, as evidenced by changes in the shape of t-butylhydroperoxide induced emission of chemiluminescence in mammary tissue (6.3 g kg(-1) dose; at 3 and 6 h). In summary, the results show that even after single doses of ethanol, acetaldehyde, either formed in situ or arriving via blood, tends to accumulate in mammary tissue and that this condition might decrease cell defenses against injury.

PPARalpha and PPARbeta are differentially affected by ethanol and the ethanol metabolite acetaldehyde in the MCF-7 breast cancer cell line

The activity and/or the level of the peroxisome proliferator-activated receptors (PPARs) in liver and oligodendrocytes are regulated by ethanol. Despite the association between ethanol consumption and breast cancer risk, and the increasing evidence for an involvement of PPARs in some cancers, there have been no studies on the effect of ethanol or its metabolite acetaldehyde on PPARs in breast cancer. Using the MCF-7 breast cancer cell line, we examined the relationship between ethanol and its metabolite acetaldehyde on PPARalpha and PPARbeta transactivation. Ethanol (20 mM) reduced the potency of the PPARbeta ligand GW0742, evident by a rightward shift in the GW0742 dose-response curve, whereas for PPARalpha activation by GW7647, ethanol mediated its effects primarily through reducing efficacy as evidenced by a reduction in maximal response. Using the enzyme inhibitors 4-methylpyrazole and cyanamide and the metabolite acetaldehyde, we showed that PPARalpha and PPARbeta are differentially modulated by ethanol and acetaldehyde. While acetaldehyde is responsible for the inhibition of PPARalpha ligand inhibition with a concentration that inhibits 50% of activity (IC50) of 111 nM, acetaldehyde has no effect on PPARbeta or its ligand activation. Instead, inhibition of PPARbeta transactivation is mediated directly by ethanol. The differential effect of ethanol and acetaldehyde on PPARalpha and PPARbeta further underscores the differences between these receptors and may indicate the relevance of PPARs in the effects of ethanol in the human breast.

Xanthine oxidase catalyzes the oxidation of retinol

In mammals, xanthine oxidase (E.C. 1.17.3.2) catalyzes the hydroxylation of a wide variety of heterocyclic substrates such as purines, pyrimidines, and pterins, in addition to aldehydes [1] as all-trans-retinaldehyde [2-5]. Here, we show that buttermilk xanthine oxidase was capable to oxidizing all-trans-retinol (t-ROL) to all-trans-retinaldehyde (t-RAL) that was successively oxidized to all-trans-retinoic acid (t-RA). A rise in the enzyme activity, when t-ROL-CRBP complex was assayed, with respect to the free t-ROL, was observed. Furthermore, treatment of the enzyme with Na2S and glutathione resulted in a significant increment in catalytic activity toward t-ROL and t-RAL, due to the reconstitution of the native structural organization of the molybdenum centre of molybdopterin cofactor of the desulfo form of xanthine oxidase.

Aldehyde sources, metabolism, molecular toxicity mechanisms, and possible effects on human health

Aldehydes are organic compounds that are widespread in nature. They can be formed endogenously by lipid peroxidation (LPO), carbohydrate or metabolism ascorbate autoxidation, amine oxidases, cytochrome P-450s, or myeloperoxidase-catalyzed metabolic activation. This review compares the reactivity of many aldehydes towards biomolecules particularly macromolecules. Furthermore, it includes not only aldehydes of environmental or occupational concerns but also dietary aldehydes and aldehydes formed endogenously by intermediary metabolism. Drugs that are aldehydes or form reactive aldehyde metabolites that cause side-effect toxicity are also included. The effects of these aldehydes on biological function, their contribution to human diseases, and the role of nucleic acid and protein carbonylation/oxidation in mutagenicity and cytotoxicity mechanisms, respectively, as well as carbonyl signal transduction and gene expression, are reviewed. Aldehyde metabolic activation and detoxication by metabolizing enzymes are also reviewed, as well as the toxicological and anticancer therapeutic effects of metabolizing enzyme inhibitors. The human health risks from clinical and animal research studies are reviewed, including aldehydes as haptens in allergenic hypersensitivity diseases, respiratory allergies, and idiosyncratic drug toxicity; the potential carcinogenic risks of the carbonyl body burden; and the toxic effects of aldehydes in liver disease, embryo toxicity/teratogenicity, diabetes/hypertension, sclerosing peritonitis, cerebral ischemia/neurodegenerative diseases, and other aging-associated diseases.

Ethanol-induced oxidative stress and acetaldehyde formation in rat mammary tissue: potential factors involved in alcohol drinking promotion of breast cancer

Recent studies from our laboratory provided evidence that part of the carcinogenic effects of ethanol consumption might be related to its in situ metabolism at cytosolic and microsomal levels, to the mutagen acetaldehyde and to hydroxyl and 1-hydroxyethyl radicals. In this work, we report on our experiments where Sprague-Dawley female rats were exposed to the standard Lieber & De Carli diet for 28 days. We observed: the induction of the (xanthineoxidoreductase mediated) cytosolic and microsomal (lipoxygenase mediated) pathways of ethanol metabolism; promotion of oxidative stress as shown by increased formation of lipid hydroperoxides; delay in the t-butylhydroperoxide induced chemiluminiscence, and a significant decrease in protein sulfhydryls. In addition, the epithelial cells showed ultrastructural alterations consisting of markedly irregular nuclei, with frequent invaginations at the level of the nuclear envelope, condensation of chromatin around the inner nuclear membrane, and marked dilatation of the nuclear pores showing filamentous material exiting to the cytoplasm. In conclusion, the presence in mammary epithelial cells of cytosolic and microsomal pathways of ethanol bioactivation to carcinogenic and to tumorigenic metabolites might play a role in alcohol promotion of breast cancer.

Inhibition of the rat breast cytosolic bioactivation of ethanol to acetaldehyde by some plant polyphenols and folic acid

There is a well-established association between alcohol consumption and breast cancer risk. About 4% of the breast cancers in developed countries are estimated to be attributable to drinking alcohol. The mechanism of tumor promotion by alcohol remains unknown. Recent studies from our laboratory and others showed the ability of mammary tissue to bioactivate ethanol to mutagenic/carcinogenic acetaldehyde and free radicals. Xanthine oxidoreductase (XOR) is an enzyme involved in those biotransformation processes. In the present study, we provide evidence of the ability of different natural polyphenols and of folic acid derivatives to inhibit the biotransformation of alcohol to acetaldehyde by rat breast cytosolic XOR. Folic acid and dihydrofolic acid, at concentrations of 10 microM, inhibited 100% and 84%, respectively, of the cytosolic acetaldehyde formation. Thirty-five polyphenols were tested in these initial experiments: ellagic acid, myricetin, quercetin, luteolin, and apigenin inhibited 79-95% at 10 microM concentrations. The remaining polyphenols were either less potent or noninhibitory of acetaldehyde formation at similar concentrations in these screening tests. Results are relevant to the known preventive effects of folic acid against alcohol-induced breast cancer and to their potential preventive actions if added to foods or alcoholic beverages.

The etiology of alcohol-induced breast cancer

Breast cancer is the most common cancer in women in the United States, and it is second among cancer deaths in women. Results of most epidemiologic studies, as well as of most experimental studies in animals, have shown that alcohol intake is associated with increased breast cancer risk. Alcohol consumption may cause breast cancer through different mechanisms, including through mutagenesis by acetaldehyde, through perturbation of estrogen metabolism and response, and by inducing oxidative damage and/or by affecting folate and one-carbon metabolism pathways. Alcohol-metabolizing enzymes are present in human breast tissue. Acetaldehyde is a known, although weak, mutagen. However, results of some studies with human subjects implicate this agent in the context of genetic susceptibilities to increased ethanol metabolism. Reactive oxygen species, resulting from ethanol metabolism, may be involved in breast carcinogenesis by causing damage, as well as by generating DNA and protein adducts. Alcohol interferes with estrogen pathways in multiple ways, influencing hormone levels and effects on the estrogen receptors. With regard to one-carbon metabolism, alcohol can negatively affect folate levels, and the folate perturbation affects DNA methylation and DNA synthesis, which is important in carcinogenesis. Some study results indicate that genetic variants of one-carbon metabolism genes might increase alcohol-related breast cancer risk. For all these pathways, genetic polymorphisms might play a role in increasing further a woman's risk for breast cancer. Additional studies are needed to determine the relative importance of these pathways, as well as the modifying influence by genetic variation.

Ethanol inhibits benzo[a]pyrene-DNA adduct removal and increases 8-oxo-deoxyguanosine formation in human mammary epithelial cells

The effect of ethanol and acetaldehyde treatment on the removal of benzo[a]pyrene diol-epoxide (BPDE)-DNA adducts in the immortalized, human mammary epithelial cell line MCF-10F was examined. Treatment of cells with 15 mM and 25 mM ethanol resulted in significantly more BPDE-DNA adducts/unit DNA remaining at multiple time points, compared to controls. The half-life of BPDE-DNA adducts in cells exposed to both 15 and 25 mM ethanol were 11.9 and 12.3 h, respectively, compared to a half-life of 9.8 h for the control cells. In contrast, for cells exposed to acetaldehyde at doses of 2.5 and 5.0 microM no significant trend in BPDE-DNA adduct persistence occurred, compared to controls. The inhibition of adduct removal for cells treated with ethanol was not associated with any changes in cell viability due to ethanol exposure. However, BP-treated cells exposed to 25 mM ethanol exhibited a significant 2-fold increase in 8-oxo-deoxyguanosine (8-oxo-deG) adducts compared to BP-treated cells alone. No significant increase in 8-oxo-deG was observed for cells treated with BP and exposed to 5.0 microM acetaldehyde. Thus, ethanol exposure of human mammary epithelial cells is associated with a decreased capacity to remove BPDE-DNA adducts. This inhibitory effect of ethanol on adduct removal in part may be related to ethanol-associated oxidative stress.

Rat breast microsomal biotransformation of ethanol to acetaldehyde but not to free radicals: its potential role in the association between alcohol drinking and breast tumor promotion

We recently showed that mammary cytosolic xanthineoxidoreductase had the ability to bioactivate ethanol (EtOH) to acetaldehyde (AC) and free radicals. In the present study, we report that the microsomal fraction also biotransforms EtOH to AC. One pathway requires NADPH and the others do not. Both need oxygen. The NADPH-dependent pathway is not inhibited by CO:O(2) (80:20) or SKF 525A and that excludes the participation of cytochrome P450. It is inhibited by diethyldithiocarbamate (DDTC), sodium azide, and diphenyleneiodonium (DPI) but not by desferrioxamine, which suggests a possible role of a non-iron copper-requiring flavoenzyme. The process was partially inhibited by thiobenzamide (TBA), methylmercaptoimidazole (MMI), and nordihydroguaiaretic acid (NDG) but not by dapsone, aminotriazole, or indomethacin. These results suggest the potential participation of flavine monooxygenase and of lipooxygenase or of peroxidases/oxidases having similar characteristics but not of lactoperoxidase or cyclooxygenase. The pathway not requiring NADPH could also be partially inhibited by DDTC, NDG, azide, DPI, and TBA or MMI but not by the other chemicals. Little activity proceeds under nitrogen. Oxidases or peroxidases might be involved. No formation of 1-hydroxyethyl radicals was detected either in the presence or absence of NADPH. The nature of the EtOH bioactivating enzymes involved remains to be established. However, the fact remains that an activation of EtOH to AC was found in mammary tissue and could have a significant effect in some stages of the process of breast tumor promotion by EtOH.

Overexpression of ErbB2 enhances ethanol-stimulated intracellular signaling and invasion of human mammary epithelial and breast cancer cells in vitro

Both epidemiological and experimental studies indicate that ethanol is a tumor promoter and may promote metastasis of breast cancer. However, the molecular mechanisms underlying ethanol-mediated tumor promotion remain unknown. Overexpression of ErbB proteins in breast cancer patients is generally associated with poor prognosis. The ErbB proteins are a family of receptor kinases that include four closely related members: epidermal growth factor receptor (EGFR/ErbB1), ErbB2/neu, ErbB3, and ErbB4. Particularly, ErbB2 plays a pivotal role in ErbB-mediated activities. Here we demonstrated that amplification of ErbB2 expression sensitized a specific cellular response to ethanol. Human breast cancer cells or mammary epithelial cells with a high expression of ErbB2 exhibited an enhanced response to ethanol-stimulated cell invasion in vitro. Ethanol also stimulated cell proliferation; however, this stimulation was independent of ErbB2 levels. Ethanol triggered divergent intracellular signaling among cells expressing different ErbB2 levels. In the cells overexpressing ErbB2, ethanol was more effective in the activation of c-Jun NH2 terminal protein kinases (JNKs) and p38 mitogen-activated protein kinase (p38 MAPK) as well as the induction of reactive oxygen species (ROS) than the cells with normal ErbB2 expression. Blockage of either JNKs or p38 MAPK activation eliminated ethanol-mediated cell invasion. In contrast, the reduction of hydrogen peroxide concentration by catalase exposure had little effect on ethanol-induced cell invasion. These results indicated that ethanol-induced cell invasion was primarily mediated by JNKs and p38 MAPK, whereas the involvement of ROS formation might be minimal. Our study suggests that overexpression of ErbB2 may augment ethanol-elicited signaling and promote ethanol-stimulated tumor metastasis.

Exploring environmental causes of altered ras effects: fragmentation plus integration?

Mutations in ras genes are the most common abnormality of oncogenes in human cancer and a major example of activation by point mutation. Experimental and epidemiological studies support the notion that Ki-ras activation and expression may be chemically related. We discuss the potential role of several environmental compounds in the induction or promotion of ras mutations in humans, with a focus on exocrine pancreatic cancer, the human tumor with the highest prevalence at diagnosis of Ki-ras mutations. Organochlorine compounds, organic solvents, and coffee compounds may play an indirect role in causing Ki-ras mutations, rather than as direct inducers of the mutations. Although for some organochlorine compounds the induction of point mutations in ras oncogenes cannot be excluded, it seems more likely that the effects of these compounds are mediated through nongenomic or indirectly genotoxic mechanisms of action. Organic solvents also may act via enzymatic induction of ras mutagens or by providing a proliferation advantage to ras-mutated cell clones. In exocrine pancreatic cancer, caffeine, other coffee compounds, or other factors with which coffee drinking is associated could modulate Ki-ras activation by interfering with DNA repair, cell-cycle checkpoints, and apoptosis. Asbestos, cigarette smoking, and some dietary factors also may be involved in the initiation or the promotion of Ki-ras mutations in lung and colon cancers. Further development of the mechanistic scenarios proposed here could contribute to a meaningful integration of biological, clinical, and environmental knowledge on the causes of altered ras effects.