The organoselenium compound 1,4-phenylenebis(methylene)selenocyanate inhibits 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone-induced tumorgenesis and enhances glutathione-related antioxidant levels in A/J mouse lung

Active compounds: A new direction for rice value addition

The development of rice active compounds is conducive to improving the added value of rice. This paper focused on the types and effects of active compounds in rice. Furthermore, it summarized the effect of rice storage and processing technology on rice active compounds. We conclude the following: Rice contains a large number of active compounds that are beneficial to humans. At present, the research on the action mechanism of rice active compounds on the human body is not deep enough, and the ability to deeply process rice is insufficient, greatly limiting the development of the rice active compound industry. To maximize the added value of rice, it is necessary to establish a dedicated preservation and processing technology system based on the physicochemical properties of the required active compounds. Additionally, attention should be paid to the development and application of composite technologies during the development of the rice active compound industry.

Genetic and Enzymatic Characteristics of CYP2A13 in Relation to Lung Damage

Cytochrome P450 2A13 is an omitted brother of CYP2A6 that has an important role in the drug metabolism of liver. Due to extrahepatic expression, it has gained less attention than CYP2A6, despite the fact that it plays a significant role in toxicant-induced pulmonary lesions and, therefore, lung cancer. The purpose of this mini-review is to summarize the basic knowledge about this enzyme in relation to the substrates, inhibitors, genetic polymorphisms, and transcriptional regulation that are known so far (September 2021).

Selenocyanation of Aryl and Styryl Methyl Ketones in the Presence of Selenium Dioxide and Malononitrile: An Approach for the Synthesis of α-Carbonyl Selenocyanates

A convenient method has been developed for the synthesis of α-carbonyl selenocyanates from aryl methyl ketones/styryl methyl ketones using selenium dioxide as the selenating agent under simple reaction conditions. This reaction has notable advantages over the traditional methods in terms of accessibility and affordability of the starting materials. The method features the interaction of aryl methyl ketones/styryl methyl ketones with selenium dioxide and malononitrile to afford a series of α-carbonyl selenocyanates in moderate to good yields.

Synthesis of Novel Selenocyanates and Evaluation of Their Effect in Cultured Mouse Neurons Submitted to Oxidative Stress

Herein, we report the synthesis of novel selenocyanates and assessment of their effect on the oxidative challenge elicited by hydrogen peroxide (H₂O₂) in cultured mouse neurons. First, α-methylene-β-hydroxy esters were prepared as precursors of allylic bromides. A reaction involving the generated bromides and sodium selenocyanate was conducted to produce the desired selenocyanates (3a-f). We next prepared cultures of neurons from 7-day-old mice (n = 36). H₂O₂ (10^-5 M) was added into the culture flasks as an oxidative stress inducer, alone or combined with one of each designed compounds. (PhSe)₂ was used as a positive control. It was carried out assessment of lipid (thiobarbituric acid reactive species, 4-hydroxy-2'-nonenal, 8-isoprostane), DNA (8-hydroxy-2'-deoxyguanosine), and protein (carbonyl) modification parameters. Finally, catalase and superoxide dismutase activities were also evaluated. Among the compounds, 3b, 3d, and 3f exhibited the most pronounced pattern of antioxidant activity, similar to (PhSe)₂. These novel aromatic selenocyanates could be promising to be tried in most sophisticated in vitro studies or even at the preclinical level.

The crosstalk between trace elements with DNA damage response, repair, and oxidative stress in cancer

DNA damage response (DDR) is a regulatory system responsible for maintaining genome integrity and stability, which can sense and transduce DNA damage signals. The severity of damage appears to determine DDRs, which can include damage repair, cell-cycle arrest, and apoptosis. Furthermore, defective components in DNA damage and repair machinery are an underlying cause for the development and progression of various types of cancers. Increasing evidence indicates that there is an association between trace elements and DDR/repair mechanisms. In fact, trace elements seem to affect mediators of DDR. Besides, it has been revealed that oxidative stress (OS) and trace elements are associated with cancer development. In this review, we discuss the role of some critical trace elements in the risk of cancer. In addition, we provide a brief introduction on DDR and OS in cancer. Finally, we will further review the interactions between some important trace elements including selenium, zinc, chromium, cadmium, and arsenic, and DDR, and OS in cancer.

Strategies for the development of selenium-based anticancer drugs

Many experimental models demonstrated that inorganic and organic selenium (Se) compounds may have an anticancer activity. However, large clinical studies failed to demonstrate that Se supplementations may prevent the outcome of cancers. Moreover, there are few randomized trials in cancer patients and there is not yet any Se compound recognized as anticancer drug. There is still a need to develop new Se compounds with new strategies. For that, it may be necessary to consider that Se compounds may have a dual role, either as anti-oxidant or as pro-oxidant. Experimental studies demonstrated that it is as pro-oxidant that Se compounds have anticancer effects, even though cancer cells have a pro-oxidant status. The oxidative status differs according to the type of cancer, the stage of the disease and to other parameters. We propose to adapt the doses of the Se compounds to markers of the oxidative stress, but also to markers of angiogenesis, which is strongly related with the oxidative status. A dual role of Se on angiogenesis has also been noted, either as pro-angiogenesis or as anti-angiogenesis. The objective for the development of new Se compounds, having a great selectivity on cancer cells, could be to try to normalize these oxidative and angiogenic markers in cancer patients, with an individual adaptation of doses.

Gene Methylation Biomarkers in Sputum and Plasma as Predictors for Lung Cancer Recurrence

Detection of methylated genes in exfoliated cells from the lungs of smokers provides an assessment of the extent of field cancerization, is a validated biomarker for predicting lung cancer, and provides some discrimination when interrogated in blood. The potential utility of this 8-gene methylation panel for predicting tumor recurrence has not been assessed. The Eastern Cooperative Oncology Group initiated a prevention trial (ECOG-ACRIN5597) that enrolled resected stage I non-small cell lung cancer patients who were randomized 2:1 to receive selenized yeast versus placebo for 4 years. We conducted a correlative biomarker study to assess prevalence for methylation of the 8-gene panel in longitudinally collected sputum and blood after tumor resection to determine whether selenium alters their methylation profile and whether this panel predicts local and/or distant recurrence. Patients (N = 1,561) were enrolled into the prevention trial; 565 participated in the biomarker study with 122 recurrences among that group. Assessing the association between recurrence and risk of gene methylation longitudinally for up to 48 months showed a 1.4-fold increase in OR for methylation in sputum in the placebo group independent of location (local or distant). Kaplan-Meier curves evaluating the association between number of methylated genes and time to recurrence showed no increased risk in sputum, while a significant HR of 1.5 was seen in plasma. Methylation detection in sputum and blood is associated with risk for recurrence. Cancer Prev Res; 10(11); 635-40. ©2017 AACR.

Selenium fortification of an Italian rice cultivar via foliar fertilization with sodium selenate and its effects on human serum selenium levels and on erythrocyte glutathione peroxidase activity

Selenium food fortification could be a cost-effective strategy to counteract the inadequacy of selenium intake among the Italian population. In this study, the effect of foliar fertilization with sodium selenate of an Italian rice cultivar and the increase of serum selenium and of erythrocyte glutathione peroxidase (GPx) activity after intake of fortified rice, have been evaluated. The effect of foliar fertilization with sodium selenate (50 g Se/ha) vs. water was studied. Moreover, in a randomized, double-blind study, 10 healthy women supplemented their usual diet with a daily dose of 80 g of Se-enriched-rice and 10 matched-women with 80 g of regular rice. Before, after 5 and 20 days of supplementation, serum Se and GPx-activity were evaluated. The mean selenium content in Se-enriched-rice was 1.64 ± 0.28 μg/g, while in regular rice it was 0.36 ± 0.15 μg/g (p < 0.001). A significant increase of serum Se and GPx-activity was observed only in the intervention group and only after 20 days. The results show that selenium fortification of rice can be achieved with foliar fertilization with sodium selenate and that the 20 days intake of this Se-enriched-rice increases the serum selenium levels and GPx-activity.

Impact of zinc, selenium and lycopene on capsaicin induced mutagenicity and oxidative damage in mice

Capsaicin is employed as a condiment and colorant in the cosmetic and pharmaceutical industries. Metabolism of capsaicin produces reactive phenoxy radicals, which inflict damage to DNA. Micronutrients such as zinc and selenium facilitate the expression of tissue repair factors, and lycopene has natural antioxidant action. The current study investigated the possible protective role of zinc, selenium and lycopene singly and in combination in ameliorating capsaicin induced mutagenicity. Fifty four Swiss albino mice received the vehicle, zinc (10 mg/kg), selenium (2 mg/kg), lycopene (2 mg/kg) alone, capsaicin alone (2 mg/kg), and capsaicin along with zinc (10mg/kg), selenium (2 mg/kg) and lycopene (2 mg/kg) in combination by the oral route for 32 days. Animals were killed 24 h after the last treatment, and micronuclei formation in bone marrow and peripheral blood were assessed. Antioxidant status in plasma, the total protein, nucleic acids, and DNA fragmentation was assessed in the liver homogenate. Capsaicin substantially damaged nuclear material and increased oxidative stress. Individual therapy with lycopene was most effective in reducing micronuclei formation, lipid peroxidation, and in augmenting ferric reducing ability of plasma. This was closely followed by zinc and selenium. Zinc protected against DNA fragmentation followed by lycopene and selenium. The combination therapy was effective over individual treatment against DNA fragmentation, micronuclei and malondialdehyde formation. The combination did not exert a substantial benefit over individual therapy in enhancing the total antioxidant ability of plasma. The risk of capsaicin induced mutagenicity was lowered with the combination by reducing the generation of free radicals and by enhancing tissue repair.

Oxidative DNA adducts detected in vitro from redox activity of cigarette smoke constituents

Cigarette smoke contains a variety of carcinogens, cocarcinogens, mutagens, and tumor promoters. In addition to polycyclic aromatic carcinogens and tobacco-specific nitrosamines, cigarette smoke also contains an abundance of catechols, aldehydes, and other constituents, which are DNA damaging directly or indirectly; therefore, they can also contribute to cigarette smoke-mediated carcinogenicity. In this study, we investigated the potential of cigarette smoke constituents to induce oxidative damage to DNA through their capacity to redox cycle. When DNA (300 μg/mL) was incubated with cigarette smoke condensate (0.2 mg of tobacco particulate matter/mL) and CuCl(2) as a catalyst (50-100 μM), a variety of oxidative DNA adducts were detected by (32)P-postlabeling/TLC. Of the total adduct burden (2114 ± 419 adducts/10(6) nucleotides), over 40% of all adducts were attributed to the benchmark oxidative DNA lesion, 8-oxodeoxyguanosine (8-oxodG). Adducts were formed dose dependently. Essentially, similar adduct profiles were obtained when cigarette smoke condensate was substituted with ortho- and para-dihydroxybenzenes. Vehicle treatment with Cu(2+) or CSC alone did not induce any significant amount of oxidative DNA damage. Furthermore, coincubation of cigarette smoke condensate and ortho-dihydroxybenzene with DNA resulted in a higher amount of oxidative DNA adducts than obtained with the individual entity, suggesting that adducts presumably originated from catechols or catechol-like compounds in cigarette smoke condensate. Adducts resulting from both cigarette smoke condensate and pure dihydroxybenzenes were chromatographically identical to adducts formed by reaction of DNA with H(2)O(2), which is known to produce 8-oxodG, and many other oxidative DNA adducts. When the cigarette smoke condensate-DNA reaction was performed in the presence of ellagic acid, a known antioxidant, the adduct formation was inhibited dose dependently, further suggesting that adducts originated from oxidative pathway. Our data thus provide evidence of the capacity of catechols or catechol-like constituents in cigarette smoke to produce oxidative DNA damage, which may contribute to the tumor-promoting activity of cigarette smoke.

A functional trinucleotide repeat polymorphism in the 5'-untranslated region of the glutathione biosynthetic gene GCLC is associated with increased risk for lung and aerodigestive tract cancers

Glutathione (GSH), the major intracellular antioxidant, protects against cancer development by detoxifying carcinogens and free radicals and strengthening the immune system. Recently, a GAG-trinucleotide repeat polymorphism in the 5'-untranslated region of the gene for the rate-limiting enzyme for GSH biosynthesis, γ-glutamine cysteine ligase (GCL), was shown to be associated with lowered GCL activity and GSH levels in vitro and in vivo. We tested the hypothesis that this functional polymorphism in GCL is associated with the risk for lung and aerodigestive tract cancers. To this end, we conducted a case-control study that included 375 lung cancer cases, 200 aerodigestive tract cancer cases, and 537 controls. GAG repeat genotype (4, 7, 8, 9, and 10 repeat alleles) was determined by capillary electrophoresis of PCR products from the repeat region of the GCL catalytic subunit (GCLC). Odds ratios (OR) were calculated by logistic regression and adjusted for risk factors, including age, sex, body mass index, and smoking history. The GAG-7/7 genotype was associated with a 1.9-fold increased risk of lung cancer and 2.6-fold increased risk of aerodigestive tract cancer compared to the wild-type GAG-9/9 (P < 0.05). Similarly, the GAG-7 allele was associated with an increased risk of lung cancer (OR = 1.5, P = 0.01) and aerodigestive tract cancer (OR = 2.3, P < 0.001) compared to subjects without GAG-7 allele. These findings suggest that GSH synthesis affects the risk of lung and aerodigestive tract cancers, and further implicates a role for oxidative stress in the development of these cancers.

Induction of lung glutathione and glutamylcysteine ligase by 1,4-phenylenebis(methylene)selenocyanate and its glutathione conjugate: role of nuclear factor-erythroid 2-related factor 2

The synthetic organoselenium agent 1,4-phenylenebis(methylene)selenocyanate (p-XSC) and its glutathione (GSH) conjugate (p-XSeSG) are potent chemopreventive agents in several preclinical models. p-XSC is also an effective inducer of GSH in mouse lung. Our objectives were to test the hypothesis that GSH induction by p-XSC occurs through upregulation of the rate-limiting GSH biosynthetic enzyme glutamylcysteine ligase (GCL), through activation of antioxidant response elements (AREs) in GCL genes via activation of nuclear factor-erythroid 2-related factor 2 (Nrf2). p-XSC feeding (10 ppm Se) increased GSH (230%) and upregulated the catalytic subunit of GCL (GCLc) (55%), extracellular-related kinase (220%), and nuclear Nrf2 (610%) in lung but not liver after 14 days in the rat (P<0.05). Similarly, p-XSeSG feeding (10 ppm) induced lung GCLc (88%) and GSH (200%) (P<0.05), whereas the naturally occurring selenomethionine had no effect. Both p-XSC and p-XSeSG activated a luciferase reporter in HepG2 ARE-reporter cells up to threefold for p-XSC and greater than or equal to fivefold for p-XSeSG. Luciferase activation by p-XSeSG was associated with enhanced levels of GSH, GCLc, and nuclear Nrf2, which were significantly reduced by co-incubation with short interfering RNA targeting Nrf2. The dependence of GCL induction on Nrf2 was confirmed in Nrf2-deficient mouse embryonic fibroblasts, in which p-XSeSG induced GCL subunits in wild-type but not in Nrf2-deficient cells (P<0.05). These results indicate that p-XSC may act through the Nrf2 pathway in vivo and that p-XSeSG is the putative metabolite responsible for such activation, thus offering p-XSeSG as a less toxic, yet highly efficacious, inducer of GSH.

Age related changes in selenium and glutathione levels in different lobes of the rat prostate

Aging represents a major risk factor for prostate cancer; however, mechanisms responsible for this relationship remain unclear. Preclinical and some clinical investigations support the protective role of selenium against prostate cancer possibly through the reduction of oxidative stress. While increased levels of oxidative stress together with decreases in selenium and the major cellular antioxidant glutathione (GSH) are common in tissues of old animals, there is little data available on these parameters in the prostate. In the present study we have compared the levels of selenium, GSH and protein-bound GSH (GSSP) in blood and prostate tissues in young (4-month), mature (12-month), old (18 month), and very old (24 month) male F344 rats. Each prostate lobe (dorsolateral, DL; anterior, AL; ventral, VL) was analyzed separately based upon their differing potential for prostate cancer development. At all ages, selenium levels were lowest in DL<VL<AL. After 12 mo, an 85% reduction in selenium in the DL was observed (P<0.05), while levels in other lobes were unchanged. In animals of all ages, levels of GSH were lowest in the VL<DL=AL and no significant changes were observed in GSH levels by 18 mo. However, GSSP, a marker of oxidative stress, was increased 90% after 18 mo in the DL only (P<0.01). These findings of age-related changes in GSSP and selenium in the DL prostate are consistent with the sensitivity of this lobe to carcinogenesis and, thus, may be playing a mechanistic role.

Spectral modification and catalytic inhibition of human cytochromes P450 1A1, 1A2, 1B1, 2A6, and 2A13 by four chemopreventive organoselenium compounds

Several organoselenium compounds including benzyl selenocyanate (BSC), 1,2-phenylenebis(methylene)selenocyanate (o-XSC), 1,3-phenylenebis(methylene)selenocyanate (m-XSC), and 1,4-phenylenebis(methylene)selenocyanate (p-XSC) have been shown to prevent cancers caused by polycyclic aromatic hydrocarbons (PAHs) and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) in experimental animals; these chemical carcinogens are activated by human P450 1 and 2A family enzymes, respectively, to carcinogenic metabolites. In this study, we examined whether these selenium compounds interact with and inhibit human P450 1 and 2A enzymes in vitro. Four organoselenium compounds induced reverse Type I binding spectra with P450 1A1, 1A2, and 1B1 and Type I binding spectra with P450 2A6 and 2A13. The spectral dissociation constants (K(s)) for the interaction of P450 1B1 with these chemicals were 3.6-5.7 μM; the values were lower than those with seen with P450 1A1 (19-30 μM) or 1A2 (6.3-13 μM). The K(s) values for Type I binding of P450 2A13 with m-XSC and BSC were both 0.20 μM; the values were very low compared to those for the interaction of P450 2A6 with m-XSC (5.7 μM) and BSC (2.0 μM). Four selenium compounds directly inhibited 7-ethoxyresorufin O-deethylation activities catalyzed by P450 1A1, 1A2, and 1B1 with IC(50) values <1.0 μM, except for the inhibition of P450 1A2 by BSC (1.3 μM). Coumarin 7-hydroxylation activities of P450 2A13 were more inhibited by four selenium compounds than those of P450 2A6, with IC(50) values of 0.22-1.4 μM for P450 2A13 and 2.4-6.2 μM for P450 2A6. Molecular docking studies of the interaction of four organoselenium compounds with human P450 enzymes suggest that these chemicals can be docked into the active sites of these human P450 enzymes and that the sites of the selenocyanate functional groups of these chemicals differ between the P450 1 and 2A family enzymes.

NNK-Induced Lung Tumors: A Review of Animal Model

The incidence of lung adenocarcinoma has been remarkably increasing in recent years due to the introduction of filter cigarettes and secondary-hand smoking because the people are more exposed to higher amounts of nitrogen oxides, especially 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone(NNK), which is widely applied in animal model of lung tumors. In NNK-induced lung tumors, genetic mutation, chromosome instability, gene methylation, and activation of oncogenes have been found so as to disrupt the expression profiles of some proteins or enzymes in various cellular signal pathways. Transgenic animal with specific alteration of lung cancer-related molecules have also been introduced to clarify the molecular mechanisms of NNK in the pathogenesis and development of lung tumors. Based on these animal models, many antioxidant ingredients and antitumor chemotherapeutic agents have been proved to suppress the NNK-induced lung carcinogenesis. In the future, it is necessary to delineate the most potent biomarkers of NNK-induced lung tumorigenesis, and to develop efficient methods to fight against NNK-associated lung cancer using animal models.

Association of selenium status and blood glutathione concentrations in blacks and whites

Selenium deficiency has been linked with increased cancer risk and, in some studies, selenium supplementation was protective against certain cancers. Previous studies have suggested that selenium chemoprevention may involve reduced oxidative stress through enhanced glutathione (GSH). Our objectives were to examine the relationships between selenium and GSH in the blood and the modifying effects of race and sex in free-living adults and individuals supplemented with selenium. Plasma selenium concentrations and free and bound GSH concentrations and γ-glutamyl cysteine ligase (GCL) activity in the blood were measured in 336 healthy adults (161 Blacks, 175 Whites). Plasma selenium and blood GSH were also measured in 36 healthy men from our previously conducted placebo-controlled trial of selenium-enriched yeast (247 μg/day for 9 mo). In free-living adults, selenium concentrations were associated with increased blood GSH concentration and GCL activity (P < 0.05). Further, selenium was significantly higher in Whites than in Blacks (P < 0.01). After 9 mo of supplementation, plasma selenium increased 114% in Whites and 50% in Blacks (P < 0.05), and blood GSH increased 35% in Whites (P < 0.05) but was unchanged in Blacks. These results indicate a direct association between selenium and GSH in the blood of both free-living and selenium-supplemented individuals, with race being an important modifying factor.

Antioxidant-prooxidant properties of a new organoselenium compound library

The present study describes the biological evaluation of a library of 59 organo-selenium compounds as superoxide (O₂⁻) generators and cytotoxic agents in human prostate cancer cells (PC-3) and in breast adenocarcinoma (MCF-7). In order to corroborate that the biological activity for selenium compounds depends on the chemical form, a broad structural variety is presented. These structures include selenocyanates, diselenides, selenoalkyl functional moieties and eight newly synthesized symmetrically substituted dithioselenites and selenylureas. Eleven of the derivatives tested showed high levels of superoxide generation in vitro via oxidation of reduced glutathione (GSH) and nine of them were more catalytic than the reference compound, diselenodipropionic acid. Eighteen of the library compounds inhibited cell growth more than or similar to reference chemotherapeutic drugs in PC-3 and eleven were more potent cytotoxic agents than etoposide in the MCF-7 cell line. Considering both parameters (superoxide generation and cell cytotoxicity) compounds B1, C6 and C9 displayed the best therapeutic profiles. Considering that many diselenide compounds can generate superoxide (O₂⁻) in vitro via oxidation of GSH and other thiols, the analogue B1, that contains a diselenide moiety, was selected for a preliminary mechanistic investigation, which revealed that B1 has apoptogenic effects similar to camptothecin mediated by reactive oxygen species (ROS) in lymphocytic leukemia cells (CCRF-CEM) and affected the MCF-7 cell-cycle in G₂/M and S-phases.

Selenium: a double-edged sword for defense and offence in cancer

Selenium (Se) is an essential dietary component for animals including humans and is regarded as a protective agent against cancer. Although the mode of anticancer action of Se is not fully understood yet, several mechanisms, such as antioxidant protection by selenoenzymes, specific inhibition of tumor cell growth by Se metabolites, modulation of cell cycle and apoptosis, and effect on DNA repair have all been proposed. Despite the unsupported results of the last SELECT trial, the cancer-preventing activity of Se was demonstrated in majority of the epidemiological studies. Moreover, recent studies suggest that Se has a potential to be used not only in cancer prevention but also in cancer treatment where in combination with other anticancer drugs or radiation, it can increase efficacy of cancer therapy. In combating cancer cells, Se acts as pro-oxidant rather than antioxidant, inducing apoptosis through the generation of oxidative stress. Thus, the inorganic Se compound, sodium selenite (SeL), due to its prooxidant character, represents a promising alternative for cancer therapy. However, this Se compound is highly toxic compared to organic Se forms. Thus, the unregulated intake of dietary or pharmacological Se supplements mainly in the form of SeL has a potential to expose the body tissues to the toxic levels of Se with subsequent negative consequences on DNA integrity. Hence, due to a broad interest to exploit the positive effects of Se on human health and cancer therapy, studies investigating the negative effects such as toxicity and DNA damage induction resulting from high Se intake are also highly required. Here, we review a role of Se in cancer prevention and cancer therapy, as well as mechanisms underlying Se-induced toxicity and DNA injury. Since Saccharomyces cerevisiae has proven a powerful tool for addressing some important questions regarding Se biology, a part of this review is devoted to this model system.

Current issues of selenium in cancer chemoprevention

The element selenium (Se) was identified, nearly 40 years ago, as being essential in the nutrition of animals and humans. In addition, antitumorigenic effects of Se compounds have been described in a variety of in vitro and animal models, suggesting that supplemental Se in human diets may reduce cancer risk. Apparent mechanisms underlying the potential of Se compounds as cancer chemopreventive agents have been suggested. Some recent clinical trials, however, have shed doubt on the anticancer effects of Se. The contradictory findings and consequent controversy might be due to the lack of understanding of the mechanisms underlying Se biology. This article reviews current knowledge on this topic and addresses the disparate viewpoints on the chemopreventive effects of Se, the human populations.

Rosiglitazone prevents the progression of preinvasive lung cancer in a murine model

There is a critical need to identify efficacious chemopreventive agents for lung cancer that can be taken chronically with no side effects and whose mechanisms of action do not involve genotoxicity that could drive, rather than impede, cancer progression. We evaluated the ability of a chemopreventive cocktail that included selenium (antioxidant), rosiglitazone (peroxisome proliferator-activated receptor gamma agonist), sodium phenylbutyrate or valproic acid (histone deacetylase inhibitors) and hydralazine (cytosine-demethylating agent) to prevent the progression of lung cancer in A/J mice treated with NNK. Agents were administered alone or in various combinations. Effects of the chemopreventive agents were quantified based on the proportion of hyperplasias and adenomas within the mouse lung. Significant effects on tumor progression were seen in all treatment groups that included rosiglitazone as reflected by a 47-57% increase in number of hyperplasias and a 10-30% decrease in adenomas. Cell proliferation was also reduced in these treatment groups by approximately 40%. Interestingly, while treatment with rosiglitazone alone did not significantly affect lesion size, striking effects were seen in the combination therapy group that included sodium phenylbutyrate, with the volume of hyperplasias and adenomas decreasing by 40 and 77%, respectively. These studies demonstrate for the first time that chronic in vivo administration of rosiglitazone, used in the management of diabetes mellitus, can significantly block the progression of premalignant lung cancer in the A/J mouse model.

Carcinogenic effect of arsenate in C57BL/6J/Han mice and its modulation by different dietary selenium status

In this study, carcinogenic effects of arsenate in female C57BL/6J/Han mice exposed in drinking water to 50, 200 or 500microgAs/L for 24 months were investigated. All animals were fed low-selenium diet, however half of them were supplemented with sodium selenite in drinking water (200microgSe/L) to ensure the normal dietary level of selenium. Glutathione peroxidase activity in erythrocytes and plasma as well as selenium concentration in plasma after 3, 6, 12 and 18 months in satellite groups showed considerable decrease in animals from non-selenium supplemented groups in comparison to supplemented groups. A clear arsenic concentration-dependent increase in the number of malignant lymphoma associated with increase in the risk of death was observed (hazard ratio=0.91, 1.46, and 2.24, for 50, 200 and 500microgAs/L, respectively). No significant influence of selenium dietary status on arsenic carcinogenicity was shown. A significant association between selenium supplementation status and increased risk of death of the animals from causes other than malignant tumors was found (HR=1.79, p=0.04).

Chemoprevention of lung carcinogenesis in addicted smokers and ex-smokers

Chemoprevention of lung carcinogenesis is one approach to controlling the epidemic of lung cancer caused by cigarette smoking. The target for chemoprevention should be the activities of the multiple carcinogens, toxicants, co-carcinogens, tumour promoters and inflammatory compounds in cigarette smoke. At present there are many agents, both synthetic and naturally occurring, that prevent lung tumour development in well-established animal models. It seems likely that logically constructed mixtures of these agents, developed from the ground up, will be necessary for the prevention of lung carcinogenesis.

Selenium compounds and selenoproteins in cancer

An adequate selenium (Se) status has for long been considered to prevent the development of various forms of cancer. However, underlying molecular mechanisms remained unknown. In mammals, selenium exerts its functions as selenocysteine incorporated into selenoproteins. Therefore, Se compounds can either act as Se source for selenoproteins or, depending on their chemical forms, in distinct ways. Most potent chemopreventive effects have been attributed to compounds in which the Se moiety is methylated. These compounds are able to induce phase 2 enzymes which are involved in the cellular defense system that is regulated by the Nrf2 transcription factor. Selenoproteins best studied in cancer development are members of the glutathione peroxidase (GPx) and thioredoxin reductase (TrxR) family. In various cancer cells and tissues, GPx2 and/or TrxR1 are up-regulated. Interestingly, both enzymes are targets of Nrf2. An enhanced expression of these enzymes may represent a mechanism to counteract carcinogenic pathways. They may, however, also provide a selective advantage for pre-existing tumor cells in guaranteeing survival and continuous proliferation.

Thiols and the chemoprevention of cancer

Thiols such as glutathione interfere with the complex carcinogenic process. Under stress conditions, they scavenge harmful molecules: Glutathione conjugation of electrophilic carcinogens may prevent tumor initiation, and reduced thiols may defend against oxidative stress. Thus, associated chemopreventive strategies involve enhancement of antioxidant or conjugating capacity by increasing the levels of, particularly, glutathione through precursor application or synthesis stimulation and by inducing the corresponding enzymes. The antioxidant potential of thiols is, however, a part of a more general capacity to regulate redox status even in the absence of unequivocal stress conditions. Redox status controls the activities of various cellular signalling proteins through oxidation or reduction of particular sensor structures that are also mostly thiols. The development of feasible chemotherapeutic strategies on the basis of this complex system of redox-sensitive messenger proteins is a goal in ongoing and future research.

Effects of 1,4-phenylenebis(methylene)selenocyanate on mutagenesis and p53 protein expression in the tongue of lacI rats treated with 4-nitroquinoline-N-oxide

Previously we showed that the organoselenium compound, 1,4-phenylenebis(methylene)selenocyanate (p-XSC)(1) inhibits 4-nitroquinoline-N-oxide (4-NQO)-induced tongue tumorigenesis in Fisher rats. Here we investigate possible mechanisms of this inhibition by monitoring mutagenesis and p53 protein levels in lacI and conventional Fisher rats treated with: (1) a carcinogenic dose of 4-NQO for 10 weeks in drinking water, (2) 4-NQO+p-XSC (15 ppm as selenium), and (3) 4-NQO followed by p-XSC. For mutagenesis studies, rats were euthanized at 7, 12 or 23 weeks after the start of 4-NQO. For studies on p53 levels, rats were euthanized at 11, 15 and 23 weeks. Appropriate controls were also monitored. In the 4-NQO-alone groups, the mutant fraction (MF) in the cII gene in tongue increased at least 50x background level. The MF (in units of mutants/10(5) plaque forming units) for the 7, 12, and 23 weeks 4-NQO groups were respectively, 184 +/- 88, 237 +/- 105, and 329 +/- 110. Thus, mutagenesis increased with length of exposure and post-treatment time. p-XSC modestly (ca. 15-30%) inhibited mutagenesis under all conditions. The inhibition reached significance at the last time point. When p-XSC was administered after 4-NQO, the MF was also modestly reduced. In 4-NQO-alone animals, levels of p53 in tongue (determined by Western blotting) were 1, 1.5 and 2.4 control levels at 10, 15 and 23 weeks, respectively. In the p-XSC+4-NQO group, the enhancement in p53 levels by 4-NQO treatment was decreased about 90% at 15 weeks and 45% (P<0.05) at 23 weeks, and by slightly smaller percentages in corresponding post-treatment groups. p-XSC alone did not alter p53 levels. As p53 levels generally increase in response to DNA damage, these results suggest that p-XSC reduces 4-NQO-induced DNA damage, resulting in reduced 4-NQO-induced mutagenesis and carcinogenesis. However, the fact that p-XSC is also effective when administered after 4-NQO, suggests additional mechanisms of inhibition exist.

Antioxidant activity of diphenyl diselenide prevents the genotoxicity of several mutagens in Chinese hamster V79 cells

Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. Studies have shown its antioxidant, hepatoprotective, neuroprotective, anti-inflammatory, and antinociceptive effects. We recently showed the antioxidant effect of DPDS in V79 cells, and established the beneficial and toxic doses of this compound in this cell line. Here, we report the antigenotoxic and antimutagenic properties of DPDS, investigated by using a permanent lung fibroblast cell line derived from Chinese hamsters. We determined the cytotoxicity by clonal survival assay, and evaluated DNA damage in response to several mutagens by comet assay and micronucleus test in binucleated cells. In the clonal survival assay, at concentrations ranging from 1.62 to 12.5microM, DPDS was not cytotoxic, while at concentrations up to 25microM, it significantly decreased survival. The treatment with this organoselenium compound at non-cytotoxic dose range increased cell survival after challenge with hydrogen peroxide, methyl-methanesulphonate, and UVC radiation, but did not protect against 8-methoxypsoralen plus UVA-induced cytotoxicity. In addition, the treatment prevented induced DNA damage, as verified in the comet assay. The mutagenic effect of these genotoxins, as measured by the micronucleus test, similarly attenuated or prevented cytotoxicity and DNA damage. Treatment with DPDS also decreased lipid peroxidation levels after exposure to hydrogen peroxide MMS, and UVC radiation, and increased glutathione peroxidase activity in the extracts. Our results clearly demonstrate that DPDS at low concentrations presents antimutagenic properties, which are most probably due to its antioxidant properties.