Oxygen radical-dependent epoxidation of (7S,8S)-dihydroxy-7,8-dihydrobenzo[a]pyrene in mouse skin in vivo. Stimulation by phorbol esters and inhibition by antiinflammatory steroids

Adventures with Bruce Ames and the Ames test

Bruce Ames has had an enormous impact on human health by developing facile methods for the identification of mutagens. This research also provided important insights into the relationship between mutagenesis and carcinogenesis. Bruce is a highly innovative and creative individual who has followed his interests across disciplines into diverse fields of inquiry. The present author had the pleasure of spending a sabbatical in the Ames lab and utilized the Ames test in multiple aspects of his research. He describes both in this honorific to Bruce on the occasion of his 90^th birthday.

Artificial food colorants inhibit superoxide production in differentiated HL-60 cells

We tested synthetic food colorants for their antioxidative potential by the in vitro superoxide generation assay in differentiated HL-60 cells in response to phorbol ester. Among the 12 colorants tested, such fluorescein-type red colorants as rose bengal showed potent inhibitory activity without any cytotoxicity under dark conditions. The intracellular accumulation and superoxide anion scavenging effect of rose bengal were at least partly involved in the inhibitory activity.

Targeting NOX, INOS and COX-2 in inflammatory cells: chemoprevention using food phytochemicals

Biological, biochemical and physical stimuli activate inflammatory leukocytes, such as macrophages, resulting in induction and synthesis of proinflammatory proteins and enzymes, together with free radicals, as innate immune responses. On the other hand, chronic and dysregulated activation of some inducible enzymes, including NADPH oxidase (NOX), inducible nitric oxide synthase (iNOS) and cyclooxygenase (COX)-2, have been shown to play pivotal roles in the development of certain inflammatory diseases such as oncogenesis. While the use of synthetic agents, especially those targeting molecules, is an attractive and reasonable approach to prevent carcinogenesis, it should be noted that traditional herbs and spices also exist along with their active constituents, which have been demonstrated to disrupt inflammatory signal transduction pathways. In this mini-review, the molecular mechanisms of activation or induction of NOX, iNOS and COX-2, as well as some food phytochemicals with marked potential to regulate those key inflammatory molecules, are highlighted. For example, 1'-acetoxychavicol acetate, which occurs in the rhizomes of the subtropical Zingiberaceae plant, has been shown to attenuate NOX-derived superoxide generation in macrophages, as well as lipopolysaccharide-induced nitric oxide and prostaglandin E(2) production through the suppression of iNOS and COX-2 synthesis, respectively. Notably, this phytochemical has exhibited a wide range of cancer prevention activities in several rodent models of inflammation-associated carcinogenesis. Herein, the cancer preventive potentials of several food phytochemicals targeting the induction of NOX, iNOS and COX-2 are described.

Quantification of benzo[a]pyrene diol epoxide DNA-adducts by stable isotope dilution liquid chromatography/tandem mass spectrometry

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants found in car exhausts, charbroiled food, and tobacco smoke. Three pathways for the metabolic activation of B[a]P to ultimate carcinogens have been proposed. The most widely accepted pathway involves cytochrome-P450 (CYP) 1A1- and/or 1B1-mediated formation of B[a]P-7,8-oxide, which undergoes epoxide hydrolase-mediated metabolism to the proximate carcinogen B[a]P-7,8-dihydro-7,8-diol. Further CYP1A1- and/or CYP1B1-mediated activation of the dihydrodiol results in the formation of 7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (B[a]PDE), the ultimate carcinogen. In previous studies, it was demonstrated that (+)-anti-B[a]PDE was the most potent tumorigen of the CYP-derived B[a]PDE diastereomers. We have developed a stable isotope dilution, liquid chromatography multiple reaction monitoring/mass spectrometry (LC-MRM/MS) assay for all eight (+/-)-anti-B[a]PDE-derived dGuo and dAdo DNA-adducts. The LC-MRM/MS assay was rigorously validated and used to show that (+)-anti-trans-B[a]PDE-dGuo was the major adduct formed when naked DNA and human bronchoalveolar adenocarcinoma H358 cells were treated with (+/-)-anti-B[a]PDE. The preference for DNA-adducts derived from (+)-anti-B[a]PDE was even more apparent in cellular DNA. Thus, the increased potency of (+)-anti-B[a]PDE as a tumorigen is most likely due its ability to preferentially form DNA-adducts when compared with (-)-anti-B[a]PDE. Also, the adduct profile suggests that this occurs by binding of (+)-anti-B[a]PDE to DNA in a manner that facilitates covalent binding to dGuo rather than dAdo residues.

Peroxiredoxin I and II are up-regulated during differentiation of epidermal keratinocytes

Peroxiredoxins (Prxs) are expressed in the epidermis, and the accentuated expression of the Prx I and Prx II isotypes (Prx I/II) in the suprabasal layers suggests the potential role of Prx I/II in epidermal differentiation. To evaluate the novel function of Prx I/II, we checked the modulation of Prx I/II in differentiating keratinocytes. To induce differentiation in vitro, normal human epidermal keratinocytes (NHEK) were cultured for up to 10 days after the confluent state (post-confluency). In Western blot analysis, the marked induction of Prx I was observed from the second day, but the marked induction of Prx II was observed later from the sixth day of post-confluency, when loricrin and transglutaminase 1 were induced (sixth day of post-confluency). When NHEK cells were treated with INF-gamma and TGF-beta1, Prx I/II were up-regulated by INF-gamma, but Prx I/II were down-regulated by TGF-beta1. In summary, Prx I and Prx II are induced at the early and late stage of differentiation of NHEK cells, respectively.

Bioavailability and risk assessment of orally ingested polycyclic aromatic hydrocarbons

Polycyclic aromatic hydrocarbons (PAHs) are a family of toxicants that are ubiquitous in the environment. These contaminants generate considerable interest, because some of them are highly carcinogenic in laboratory animals and have been implicated in breast, lung, and colon cancers in humans. These chemicals commonly enter the human body through inhalation of cigarette smoke or consumption of contaminated food. Of these two pathways, dietary intake of PAHs constitutes a major source of exposure in humans. Although many reviews and books on PAHs have been published, factors affecting the accumulation of PAHs in the diet, their absorption following ingestion, and strategies to assess risk from exposure to these hydrocarbons following ingestion have received much less attention. This review, therefore, focuses on concentrations of PAHs in widely consumed dietary ingredients along with gastrointestinal absorption rates in humans. Metabolism and bioavailability of PAHs in animal models and the processes, which influence the disposition of these chemicals, are discussed. The utilitarian value of structure and metabolism in predicting PAH toxicity and carcinogenesis is also emphasized. Finally, based on intake, disposition, and tumorigenesis data, the exposure risk to PAHs from diet, and contaminated soil is presented. This information is expected to provide a framework for refinements in risk assessment of PAHs from a multimedia exposure perspective.

Benzyl isothiocyanate inhibits oxidative stress in mouse skin: Involvement of attenuation of leukocyte infiltration

The exposure of benzyl isothiocyanate (BITC) to mouse skin resulted in the attenuation of 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced oxidative damage through not only inhibition of the NADPH oxidase system but also leukocyte clearance at inflamed region. In spite of little ability to affect TPA-induced edema formation, pretreatments of mouse skin with BITC before the first or second TPA treatment significantly decrease the H2O2 level. A histological study also demonstrated that BITC enhanced the terminal deoxynucleotidyl transferase-dUTP nick end labeling (TUNEL)-positive index in mouse skin, suggesting that BITC might accelerate the disappearance of infiltrated leukocytes. Thus, these gathered data further supported that BITC has a potential as an anti-inflammatory agent.

Arachidonic acid cascade inhibitors modulate phorbol ester-induced oxidative stress in female ICR mouse skin: differential roles of 5-lipoxygenase and cyclooxygenase-2 in leukocyte infiltration and activation

We recently developed a short-term assay for skin H2O2 generation induced by double 12-O-tetradecanoylphorbol-13-acetate (TPA) applications for mechanistic study on skin epidermal carcinogenesis. In the present study, we investigated the individual roles of arachidonic acid metabolism in H2O2 generation in mouse skin inflammation. The experiments using inhibitors of arachidonic acid (AA) metabolism showed that corticosteroid and a lipoxygenase (LO) inhibitor expectedly suppressed double TPA application-induced H2O2 generation through the interference of chemotactic action but not by direct decomposition or scavenging. We also demonstrated that the treatment of AA (1 mumol) and 5-LO metabolites including leukotriene B4 (LTB4) partly mimicked, though soybean LO-derived lipid hydroperoxide and prostaglandins did not, the priming effect evaluated by edema formation and leukocyte infiltration. We also confirmed that inflammatory leukocytes accumulated by LTB4 generated a significant amount of H2O2 by TPA stimulation. These results suggested that 5-LO metabolites of AA are the potential key molecules in the TPA-induced priming event. Interestingly, the cyclooxygenase (COX-) 2-selective inhibitor nimesulide (NS) and celecoxib (CXB) showed different responses than those of other inhibitors. These agents showed no specific potential to inhibit the priming event but significantly suppressed H2O2 generation, lipid peroxidation, and hyperplasia in mouse skin. From the results based on an in vitro leukocyte differentiation model, we speculated that the antioxidant effect of the COX-2 inhibitors might be partly associated with both counteraction of proinflammatory cytokine-enhanced ROS generation and inhibition of CD11b, an important molecule for cell adhesion, expression. Indeed, the topical application of NS attenuated the number of infiltrated leukocytes induced by TPA in mouse skin. Thus, these gathered data indicated the differential roles of 5-LO and COX-2 in leukocyte adhesion, infiltration, and H2O2 generation.

Antiperoxidative, anti-inflammatory, and antimutagenic activities of ethanol extract of the mycelium of Ganoderma lucidum occurring in South India

Free radical mediated genetic instability is widely thought to be a major etiological factor for initiation of carcinogenesis. Mushrooms represent a largely untapped source of powerful new pharmaceutical products. In the present study, we examined the antiperoxidative, anti-inflammatory, and antimutagenic activities of the ethanol extract of the mycelium of a medicinal mushroom, Ganoderma lucidum, occurring in south India. Antiperoxidative activity was evaluated using Fe(2+)-ascorbate-induced lipid peroxidation in rat liver homogenate and a phorbol ester (croton oil)-induced lipid peroxidation in mouse skin. Antiinflammatory activity was evaluated against carrageenan-induced acute and formalin-induced chronic inflammatory paw edema in mouse and phorbol ester-induced mouse skin inflammation. Antimutagenic activity was determined by the Ames mutagenicity assay using histidine mutant of Salmonella typhimurium strains TA 98, TA100, and TA102. Sodium azide (NaN(3)), N-methyl-N-nitro-N-nitrosoguanidine (MNNG), 4-nitro-o-phenylenediamine (NPD), and benzo[a]pyrene (B[a]P) were used as the mutagens. The extract showed significant inhibition of Fe(2+)-induced peroxidation of lipid in rat liver (IC(50) 510 +/- 22 microg/ml) and 37% inhibition of croton oil-induced peroxidation on the mouse skin at 20 mg/0.1 ml/skin. Carrageenan-induced acute and formalin-induced chronic inflammatory edema were inhibited by 56 and 60%, respectively, by the extract at 1,000 mg/kg body wt (i.p). The extract at a concentration of 5 mg/plate showed inhibition of mutagenicity elicited by direct acting mutagens, NaN(3) (55.5 and 75.7%) and MNNG (50.0 and 57.5%) for S. typhymurium strains TA100 and TA102, respectively. The extract at the same concentration also inhibited mutagenicity elicited by NPD (52.4 and 64.2%) and B[a]P (60.7 and 59.6%) for TA98 and TA100 strains, respectively. The B[a]P was activated in the presence of rat liver microsomal (S9) fraction. The results of our study revealed that ethanol extract of Ganoderma lucidum mycelium possessed significant antiperoxidative, antiinflammatory, and antimutagenic activities. The findings suggest a medicinal use for the ethanol extract of the mycelium of G. lucidum occurring in South India.

FA15, a hydrophobic derivative of ferulic acid, suppresses inflammatory responses and skin tumor promotion: comparison with ferulic acid

In our previous study, FA15 (2-methyl-1-butyl ferulic acid) was chemically synthesized as a novel ferulic acid (FA) analog, and found to notably suppress phorbol ester-induced Epstein-Barr virus activation and superoxide anion generation in vitro. In this report, we demonstrated that FA15, in contrast to FA, markedly suppressed the combined lipopolysaccharide and interferon-gamma-induced protein expressions of inducible nitric oxide synthase and cyclooxygenase-2, and also inhibited the release of tumor necrosis factor-alpha accompanied by suppression of I-kappa B degradation in RAW264.7, a murine macrophage cell line. In ICR mouse skin, topical application of FA15 significantly attenuated phorbol ester-triggered hydrogen peroxide production and edema formation as well as papilloma development while that of FA did not. Our results suggest that FA15, derived from natural sources, is a novel chemopreventive agent, both structurally and functionally.

Ebselen, a glutathione peroxidase mimetic seleno-organic compound, as a multifunctional antioxidant. Implication for inflammation-associated carcinogenesis

Ebselen, a seleno-organic compound showing glutathione peroxidase-like activity, is one of the promising synthetic antioxidants. In the present study, we investigated the antioxidant activities of ebselen using a 12-O-tetradecanoylphorbol-13-acetate (TPA)-treated mouse skin model. Double pretreatments of mouse skin with ebselen significantly inhibited TPA-induced formation of thiobarbituric acid-reacting substance, known as an overall oxidative damage biomarker, in mouse epidermis, suggesting that ebselen indeed acts as an antioxidant in mouse skin. The antioxidative effect of ebselen is attributed to its selective blockade of leukocyte infiltration and activation leading to attenuation of the H(2)O(2) level. In in vitro studies, ebselen inhibited TPA-induced superoxide generation in differentiated HL-60 cells and lipopolysaccharide-induced cyclooxygenase-2 protein expression in RAW 264.7 cells. In addition, we demonstrated for the first time that ebselen potentiated phase II enzyme activities, including NAD(P)H:(quinone-acceptor) oxidoreductase1 and glutathione S-transferase in cultured hepatocytes and in mouse skin. These results strongly suggest that ebselen, a multifunctional antioxidant, is a potential chemopreventive agent in inflammation-associated carcinogenesis.

A catechol antioxidant protocatechuic acid potentiates inflammatory leukocyte-derived oxidative stress in mouse skin via a tyrosinase bioactivation pathway

The modifying effects of topical application of a catechol antioxidant protocatechuic acid (PA) on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced inflammatory responses in mouse skin were investigated. Treatment with a high dose (20,000 nmol) of PA, based on time of application, modifies inflammatory responses in the skin of the B6C3F(1) mouse, a resistant strain to inflammatory response induction by TPA, but shows much higher tyrosinase expression than that of an albino mouse. The responsibility of a large amount of PA-induced leukocyte infiltration to an inflamed region in a B6C3F(1) mouse is more sensitive than that of an ICR albino mouse. When ICR mice were treated with TPA (1.6 nmol) twice weekly for 5 weeks to induce chronic inflammatory responses, pretreatment with 1600 nmol PA 30 min prior to each TPA treatment significantly enhanced the inflammatory responses including edema formation, leukocyte infiltration, and the level of thiobarbituric acid-reacting substances. The dose-dependency was closely parallel to the results of a tumor promotion study of PA previously reported. Further, the treatment of PA alone resulted in tyrosinase-dependent contact hypersensitivity in ICR mouse skin. In addition, the in vitro study of cytotoxicity demonstrated that bioactivation by tyrosinase but not myeloperoxidase of PA significantly enhanced cytotoxicity and intracellular glutathione consumption. We conclude that the tyrosinase-derived reactive quinone intermediate(s) of PA, which binds nucleophilic residues of proteins including sulfhydryl group and conjugates of which are recognized as haptens, was partially involved in alteration of the cellular immune functions including oxygen radical-generating leukocytes migration to inflamed regions.

Cholesterol 7-hydroperoxides in rat skin as a marker for lipid peroxidation

Concentrations of cholesterol 7alpha- and 7beta-hydroperoxides (Ch 7-OOHs) in the skin of rats were determined by HPLC with a chemiluminescence detector. We demonstrated that (a) the concentrations of Ch 7-OOHs in rat skin were highly correlated with rat age (r = 0.929; N = 51, 1 to 55 weeks old), (b) the concentrations of Ch 7-OOHs in the skin of rats in an ambient light room were not significantly different from those found in rats kept in a dark room for 12 weeks, and (c) lipid peroxidation in vitro induced by ADP-Fe2+ caused an increase in the concentrations of Ch 7-OOHs in homogenates of rat skin. These results indicated that levels of Ch 7-OOHs in skin might be a good marker for aging of rats and might be independent of housing illumination, thus a good marker for endogenous lipid peroxidation. Furthermore, we observed that ultraviolet light B (UVB) irradiation markedly enhanced the concentrations of Ch 7-OOHs in the skin of rats in vivo depending on the duration of the irradiation, and the increases in Ch 7-OOHs were inhibited by radical scavengers, i.e. tocopherols. Therefore, it was suggested that the levels of Ch 7-OOHs in the skin could also be a good marker for UVB-dependent lipid peroxidation.

A diacetylenic spiroketal enol ether epoxide, AL-1, from Artemisia lactiflora inhibits 12-O-tetradecanoylphorbol-13-acetate-induced tumor promotion possibly by suppression of oxidative stress

The inhibitory effects of the diacetylenic spiroketal enol ether epoxide AL-1 from Artemisia lactiflora on a variety of tumor promoter-induced biological responses such as oxidative stress as well as tumor promotion in ICR mouse skin were investigated. AL-1 inhibited TPA-induced intracellular peroxide formation in differentiated HL-60 cells, suggesting that this suppression might be attributable to the inhibition of O2- generation. In a double TPA application system in mouse skin, double pretreatments of AL-1 (810 nmol) significantly suppressed double TPA application-induced H2O2 generation. Pretreatment of AL-1 only before the second TPA treatment was sufficient to inhibit, while only with first treatment was not. From these results we concluded that AL-1 is a specific inhibitor of the activation phase in H2O2 production induced by double TPA treatments. In addition, AL-1 strongly inhibited tumor promoter-induced Epstein-Barr virus (EBV) activation in Raji cells (IC50 = 0.5 microM), which was comparable to or even stronger than that of curcumin, a well-known antioxidative chemopreventer from turmeric. In a two-stage carcinogenesis experiment with TPA (topical application at 1.6 nmol) and 7,12-dimethylbenz[a]anthracene (DMBA, at 0.19 micromol) in ICR mouse skin, topical application of AL-1 (at 160 nmol) significantly reduced tumor incidence, the numbers of tumors per mouse, and edema formation by 58% (P < 0.01 in t-test), 20% (P < 0.005 in chi2-test) and 42% (P < 0.01), respectively. These results together indicate that an inhibitor of O2 generation is an effective chemopreventer of mouse skin carcinogenesis by their antioxidative property.

Increases in cholesterol 7-hydroperoxides in lipids of human skin by sunlight exposure

Free and ester forms of cholesterol 7alpha- and 7beta-hydroperoxides (Ch 7-OOHs) in skin lipids of humans were separated and determined by high performance liquid chromatography with a chemiluminescence detector. We first demonstrated the presence of Ch 7-OOHs in lipids of human skin. The levels of Ch 7-OOHs found in skin lipids of healthy Japanese volunteers (n = 5) ranged from 2.78 to 25.2 pmol/cm2 skin, indicating large inter-individual differences. However, the intra-individual differences of Ch 7-OOHs levels in skin lipids between right and left arms were less than 25% (-16.4% to 24.0%). Inter-day differences of Ch 7-OOHs in 5 subjects at 1 week interval were also small (-36.7% to 47.7%). Additionally, we investigated effects of sunlight exposure on the levels of Ch 7-OOHs in skin lipids of healthy Japanese volunteers (n = 24). The levels of Ch 7-OOHs in skin lipids significantly increased from 10.0+/-6.7 to 38.9+/-38.0 pmol/cm2 skin by sunlight exposure (10-40 mJ/cm2/min) for 3 h. Therefore, natural sunlight exposure causes lipid peroxidation in skin lipids of humans. These results suggest that the level of Ch 7-OOHs is a good marker for lipid peroxidation in human skin.

Plasma ubiquinone to ubiquinol ratio in patients with hepatitis, cirrhosis, and hepatoma, and in patients treated with percutaneous transluminal coronary reperfusion

To assess the degree of oxidative stress, we measured plasma ubiquinone-10 percentage (%CoQ-10) in total amounts of ubiquinone-10 in patients with chronic active hepatitis, liver cirrhosis, and hepatocellular carcinoma, and in age-matched control subjects, %CoQ-10 values were 12.9 +/- 10.3 (n = 28), 10.6 +/- 6.8 (n = 28), 18.9 +/- 11.1 (n = 20), and 6.4 +/- 3.3 (n = 16), respectively, showing a significant increase in oxidative stress in patient groups as compared to control subjects. There were no differences in total amounts of ubiquinone-10 and ubiquinol-10 among the four groups. We next measured %CoQ-10 in plasmas obtained from nine patients treated with percutaneous transluminal coronary angioplasty (PTCA). Plasmas were collected when hospitalized, and at the time (0, 4, 8, 12, 16, and 20 hr, and 1, 2, 3, 4, and 7 days) after the PTCA. %CoQ-10 values before and right after PTCA were 9.9 +/- 2.8 and 11.4 +/- 2.0, respectively, reached a maximum (20-45) at 1 or 2 days later, and decreased to 7.9 +/- 2.7 at 7 days after PTCA, indicating an increase in oxidative stress in patients during coronary reperfusion.

Effects of resveratrol on 12-O-tetradecanoylphorbol-13-acetate-induced oxidative events and gene expression in mouse skin

Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural product shown to inhibit carcinogen-induced pre-neoplastic lesions in mouse mammary organ culture and 12-O-tetradecanoylphorbol-13-acetate (TPA)-promoted mouse skin tumors. Application of TPA to mouse skin induces oxidative stress, as evidenced by numerous biochemical responses, including significant generation of H2O2 and enhanced levels of myeloperoxidase and oxidized glutathione reductase activities and decreases in glutathione levels and superoxide dismutase activity. TPA treatment also elevates the expression of cyclooxygenase-1 (COX-1), cyclooxygenase-2 (COX-2), c-myc, c-fos, c-jun, transforming growth factor-beta1 (TGF-beta1) and tumor necrosis factor-alpha (TNF-alpha). As currently reported, pre-treatment of mouse skin with resveratrol negated several of these TPA-induced effects in a dose-dependent manner. H2O2 and glutathione levels were restored to control levels, as were myeloperoxidase, oxidized glutathione reductase and superoxide dismutase activities. As judged by reverse transcriptase-polymerase chain reaction (RT-PCR), TPA-induced increases in the expression of c-fos and TGF-beta1 were selectively inhibited. These data suggest that resveratrol inhibits tumorigenesis in mouse skin through interference with pathways of reactive oxidants and possibly by modulating the expression of c-fos and TGF-beta1.

Oxidative stress in patients with hepatitis, cirrhosis, and hepatoma evaluated by plasma antioxidants

We have applied our method for the simultaneous detection of plasma ubiquinol-10 (reduced form) and ubiquinone-10 (oxidized form) (S. Yamashita and Y. Yamamoto, Anal. Biochem. 250, 66-73, 1997) to plasmas of normal subjects (n = 16) and patients with chronic active hepatitis (n = 28), liver cirrhosis (n = 16), and hepatocellular carcinoma (n = 20) to evaluate the pressure of oxidative stress in these patients. The average ubiquinone-10 percentages (+/- S.D.) in total ubiquinone-10 and ubiquinol-10 in the four groups were 6.4 +/- 3.3, 12.9 +/- 10.3, 10.6 +/- 6.8, and 18.9 +/- 11.1, respectively, indicating a significant increase in ubiquinone-10 percentage in patient groups in comparison to normal subjects. These results and a significant decrease in the plasma ascorbate level in patient groups indicate that oxidative stress is evident after the onset of hepatitis and the subsequent cirrhosis and liver cancer.

Inhibitory effects of curcumin and tetrahydrocurcuminoids on the tumor promoter-induced reactive oxygen species generation in leukocytes in vitro and in vivo

The inhibitory effects of curcumin and two tetrahydrocurcuminoids on tumor promoter-induced oxidative stress in vitro and in vivo were investigated. Curcumin, tetrahydrocurcumin (THC) and dihydroxytetrahydrocurcumin (DHTHC) exhibited significant inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced O2-generation in differentiated HL-60 cells. The inhibitory activity of THC was weaker than that of curcumin. This tendency was the inverse of the results of previous studies on in vitro antioxidative activity against lipid peroxidation. The curcuminoids inhibited TPA-induced intracellular peroxide formation in differentiated HL-60 cells. THC exhibited much weaker inhibition of intracellular peroxide formation than curcumin, suggesting that this inhibition might be attributable to the inhibition of O2-generation. The inhibitory effects of curcuminoids on TPA-induced H2O2 formation in female ICR mouse skin were further examined using the double-TPA-application model. Each TPA application induces two distinct biochemical events, 1) recruitment of inflammatory cells to the inflammatory regions and 2) activation of oxidant-producing cells. Double pretreatment of mice with curcuminoids before each TPA treatment significantly suppressed double TPA application-induced H2O2 formation in the mouse skin. Coadministrations of curcumin with either first or second TPA treatment significantly inhibited H2O2 formation. In addition, THC tends to show weaker inhibitory activities than curcumin in bioassays related to tumor promotion, i.e., inhibition of tumor promoter-induced inflammation in mouse skin and Epstein-Barr virus activation. These tendencies were parallel to those in the tumor-suppressive potential of curcumin and THC in mouse skin, as previously reported. Thus, we concluded that curcuminoids significantly suppress TPA-induced oxidative stress via both interference with infiltration of leukocytes into the inflammatory regions and inhibition of their activation.

Cigarette smoke radicals and the role of free radicals in chemical carcinogenicity

This article consists of two parts: a brief overview of the ways in which free radicals can be involved in chemical carcinogenesis, and a review of cigarette smoke chemistry. Carcinogenesis is generally agreed to involve at least three stages: initiation, promotion, and progression. It is suggested that radicals sometimes are involved in the initiation step, either in the oxidative activation of a procarcinogen (such as benzo[a]pyrene) to its carcinogenic form or in the binding of the carcinogenic species to DNA, or both. The fraction of initiation events that involve radicals, as opposed to two-electron steps, is not known, but radicals probably are involved in a substantial number, although probably not a majority, of cancer initiation reactions. Promotion always involves radicals, at least to some extent. Progression probably does not normally involve radicals. The second part of this article reviews the molecular mechanisms involved in cigarette-induced tumors, particularly by aqueous cigarette tar (ACT) extracts and by a model of these solutions, aged solutions of catechol. ACT solutions as well as aged solutions of catechol contain a quinone-hydroquinone-semiquinone system that can reduce oxygen to produce superoxide and hence hydrogen peroxide and the hydroxyl radical. Both the cigarette tar radical and the catechol-derived radical can penetrate viable cells, bind to DNA, and cause nicks.

7,12-dimethylbenz[a]anthracene induces oxidative DNA modification in vivo

Initiation and promotion are major stages in the multistage carcinogenesis process. Formation of initiating carcinogen-DNA base adducts leads to heritable genetic changes, but the tumor-promoting events induced by complete carcinogens have not, as yet, been elucidated. Oxidant production and oxidative DNA damage induced by phorbol esters (i.e., 12-O-tetradecanoyl-phorbol-13-acetate) are associated with tumor promotion, while antioxidants and inhibitors of oxidative DNA damage suppress promotion and carcinogenesis. Our goal was to establish whether a carcinogen that requires oxidative metabolism for its activity can also induce oxidant production and DNA base oxidation. We found that topical treatment of SENCAR mice with 7,12-dimethylbenz[a]anthracene, which induces tumors in 40-50% of the mice, also causes hydrogen peroxide production and formation of oxidized bases (i.e., 8-hydroxyl-2'-deoxyguanosine and 5-hydroxymethyl-2'-deoxyuridine) in epidermal DNA. The levels of oxidized bases were of comparable magnitude to those mediated by the potent tumor promoter 12-O-tetradecanoyl-phorbol-13-acetate. The oxidized bases persisted over several weeks in epidermal DNA. These oxidative events appear to be temporally associated with inflammatory responses that include edema and polymorphonuclear leukocyte infiltration, which remained elevated over longer periods of time and at higher levels than those induced by phorbol ester. Because these processes are usually associated with tumor promotion, our results support the conjecture that oxidative events may be involved in what is operationally referred to as the tumor promotion process by 7,12-dimethylbenz[a]anthracene.

Methods used for analyses of "environmentally" damaged nucleic acids

In this review, we present various techniques, currently applied in many laboratories, which are useful in the detection of "environmentally"-induced damage to DNA. These techniques include: (a) chromatographic methods, which allow determination of chemical changes within DNA, be they formation of adducts with or oxidation of bases in DNA; (b) electrophoretic methods, which facilitate finding the site(s) in DNA where that chemical modification occurred; and (c) immunological assays, which help to detect DNA damage using externally produced antibodies that recognize the specific chemical changes in DNA or its fragments, as well as by detection of autoantibodies that develop in response to environmental exposures of animals and humans.

Recognition of oxidized DNA bases by sera of patients with inflammatory diseases

Chronic inflammatory conditions result from or contribute to many diseases. Prominent among them is systemic lupus erythematosus (SLE). Sera of SLE patients contain an array of various auto-antibodies (Ab), including antinuclear Ab of unknown etiologies. The most puzzling is formation of Ab directed against autologous DNA. Our hypothesis was that increased oxidant production causes oxidation of DNA bases, which provide antigenic determinants that elicit antioxidized DNA Ab. To test this hypothesis, we used oxidized DNA nucleoside (5-hydroxymethyl-2'-deoxyuridine [HMdU]) conjugated to bovine serum albumin (HMdU-BSA) as the antigen. The results of the enzyme-linked immunosorbent assay showed that these Abs are sensitively detectable in SLE sera and sera of various other inflammatory autoimmune diseases. The titers of anti-HMdU Ab were significantly higher (p < .01) than those present in the control sera. Anti-HMdU Ab were predominantly of the IgM isotype, with low levels of IgG and no IgA. Anti-HMdU Ab bound to the HMdU-BSA-coated wells in a concentration- and time-dependent manner. That binding was inhibited by HMdU-BSA and to a lesser extent by thymidine-BSA, a normal nucleoside conjugate. The specific binding appears to be inversely related to the age of the patients, but no significant differences were observed between the sexes of the same age.