Characterization of sister chromatid exchange induction by hydrogen peroxide

Safety Assessment of Hydrogen Peroxide as Used in Cosmetics

The Expert Panel for Cosmetic Ingredient Safety (Panel) assessed the safety of Hydrogen Peroxide for use in cosmetics. This ingredient is reported to function in cosmetics as an antimicrobial agent, cosmetic biocide, oral health care agent, and oxidizing agent. The Panel reviewed the data relevant to the safety of this ingredient and concluded that Hydrogen Peroxide is safe in cosmetics in the present practices of use and concentration described in this safety assessment.

Assessment of Possible Carcinogenic Risk to Humans Resulting from Exposure to Di(2-ethylhexyl)phthalate (DEHP)

The purpose of this work was to estimate the degree of risk that might be associated with human exposure to low levels of the plasticizer di(2-ethylhexyl)phthalate (DEHP). DEHP is a common component, sometimes at high concentrations, of polyvinyl chloride (PVC) plastics and was recently reported by the National Toxicology Program (NTP) to be carcinogenic in rats and mice, inducing hepatocellular tumors in both species. This work was also designed to illustrate an approach to risk assessment that attempts to incorporate all available biological data. Based on the dose-response data generated by the NTP bioassays, we have performed extrapolations of risk to low dose levels using several procedures, including some that incorporate inferences from the available data that shed light on the likely relationship between dose level and risk at low dose levels. In drawing these inferences, consideration was given to such factors as genotoxicity, metabolism and pharmacokinetics, and physiological and biochemical effects of DEHP that might reveal its mechanism of action. The relative merits of each of the various risk estimates are described, based on current understanding of DEHP's mode of biological action. It is concluded that DEHP's mechanism of carcinogenicity in rodents most likely involves its ability to induce peroxisome proliferation and related enzymatic changes, although other mechanisms cannot be excluded. If humans and rodents are assumed to be at the same risk at the same daily dose level of DEHP, application of the various low dose extrapolation models leads to the prediction that the daily dose resulting in a lifetime risk of no more than 1 in 1 million would be between 1.5 and 791 mg/kg per day, with the most likely figure being 116 mg/kg per day. If the carcinogenicity of DEHP is dependent upon its pattern of metabolism, however, it would be inappropriate to extrapolate from rodents to man without qualification because of the major quantitative differences in metabolism in rats, mice, and primates, including man. One of the major differences in metabolism of DEHP between rats and mice and primates is in production of a metabolite whose level may be an indicator of the level of peroxisomal activity and, hence, if the peroxisome proliferation theory of DEHP carcinogenicity is correct, of carcinogenic risk. However, the substantial doubt that exists regarding the applicability of rodent carcinogenicity data to humans must be expressed in qualitative terms.

Molecular mechanisms of sister-chromatid exchange

Sister-chromatid exchange (SCE) is the process whereby, during DNA replication, two sister chromatids break and rejoin with one another, physically exchanging regions of the parental strands in the duplicated chromosomes. This process is considered to be conservative and error-free, since no information is generally altered during reciprocal interchange by homologous recombination. Upon the advent of non-radiolabel detection methods for SCE, such events were used as genetic indicators for potential genotoxins/mutagens in laboratory toxicology tests, since, as we now know, most forms of DNA damage induce chromatid exchange upon replication fork collapse. Much of our present understanding of the mechanisms of SCE stems from studies involving nonhuman vertebrate cell lines that are defective in processes of DNA repair and/or recombination. In this article, we present a historical perspective of studies spearheaded by Dr. Anthony V. Carrano and colleagues focusing on SCE as a genetic outcome, and the role of the single-strand break DNA repair protein XRCC1 in suppressing SCE. A more general overview of the cellular processes and key protein "effectors" that regulate the manifestation of SCE is also presented.

Tooth whitening products and the risk of oral cancer

Tooth whitening products (TWP) containing hydrogen peroxide (HPO) or carbamide peroxide (CPO) were evaluated in relation to potential oral cancer risk from their use. HPO is genotoxic in vitro, but such activity is not expressed in vivo. The genotoxic risk of HPO exposure of the oral mucosa encountered from TWP use is likely therefore to be vanishingly small. Available animal data on the carcinogenicity of HPO are of limited relevance to risk assessment of oral hazard of HPO exposure from TWP, and where relevant, do not indicate that there is an increased oral cancer risk for people using TWP. Clinical data on HPO-containing TWP only show evidence of mild, transient gingival irritation and tooth sensitivity, with no evidence for the development of preneoplastic or neoplastic oral lesions. Exposures to HPO received by the oral cavity, including areas commonly associated with oral cancer, are exceedingly low and do not plausibly pose a risk for the promotion of initiated cells or for induction of co-carcinogenic effects in conjunction with cigarette smoke or alcohol. The use of TWP was concluded not to pose an increased risk for oral cancer in alcohol abusers and/or heavy cigarette smokers. Furthermore, TWP were concluded to be safe for use by all members of the population, including potential accidental use by children.

Hydrogen peroxide tooth-whitening (bleaching): review of safety in relation to possible carcinogenesis

Hydrogen peroxide in the form of carbamide peroxide is widely used in professionally and self-administered products for tooth whitening. Hydrogen peroxide is a highly reactive substance that can damage oral soft and hard tissues when present in high concentrations and with exposures of prolonged duration. This review examines the issue of oral mucosal damage and possible carcinogenicity relating to the use of hydrogen peroxide in the mouth for tooth whitening, with an emphasis on safety with prolonged exposure to low concentrations of peroxide products.

Gamma-tocopherol is less effective than alpha-tocopherol in preventing oxidant-induced sister chromatid exchanges in Chinese hamster V79 cells

Although alpha-tocopherol (alpha-TOC) is the most biologically active form of vitamin E and is found at high levels in plasma, gamma-tocopherol (gamma-TOC) has also been found to be a powerful antioxidant in vitro and constitutes up to 70% of the dietary intake of TOC. Low plasma levels of gamma-TOC and a high alpha-TOC:gamma-TOC ratio may be associated with coronary heart disease, suggesting that there may be a positive protective role for the gamma-form of TOC. In this study the ability of different forms of vitamin E to protect against sister chromatid exchanges (SCE) induced by either hydrogen peroxide or menadione was investigated. Chinese hamster V79 cells were pre-treated with 10 microM TOC for 24 h, and then challenged with a genotoxin. After a 24 h pre-treatment, there was a greater incorporation of gamma-TOC (319.8 +/- 66.2 ng/10(6) cells) into V79 cells compared to alpha-TOC (66.9 +/- 6.4 ng/10(6) cells). Gamma-TOC did not protect the cells against SCE induced by either hydrogen peroxide or menadione, alpha-TOC acetate was partially protective against both genotoxins, whereas alpha-TOC completely abolished the oxidant induced SCE. These results demonstrate that, despite a greater incorporation of gamma-TOC into V79 cells, alpha-TOC but not gamma-TOC was more effective at inhibiting oxidatively-induced SCE in V79 cells.

Assessment of the carcinogenicity associated with oral exposures to hydrogen peroxide

Concern regarding hydrogen peroxide (H(2)O(2)) carcinogenicity arises from its ability to act as a strong oxidizing agent. In short-term genotoxicity tests, H(2)O(2) has given predominantly positive results; however, these assays have been performed using either bacterial strains engineered to be exquisitely sensitive to oxidant damage, or mammalian cells deficient in antioxidant enzymes. Significantly, the addition of antioxidant protective measures (normally present in vivo) to these assay systems protects against H(2)O(2) genotoxicity. In most whole animal studies, H(2)O(2) exposure neither initiates nor promotes tumors. In mice, however, 0.4% H(2)O(2) in drinking water was reported to induce hyperplastic lesions of the duodenum and to erode areas in the glandular stomach epithelium. Owing to the chemistry of dilute H(2)O(2) solutions and the anatomy/physiology of the gastrointestinal tract, it is unlikely that orally ingested H(2)O(2) reaches the duodenum. Instead, greatly decreased water consumption and the resultant abrasion of the luminal lining on ingestion of pelleted dry rodent chow is the most likely cause of the observed gastric and duodenal lesions following H(2)O(2) administration in drinking water. Significantly, when hamsters received high doses of H(2)O(2) by gastric intubation (and water intake was not affected), the gastric and duodenal epithelia appeared normal. In-depth analysis of the available data supports the conclusion that oral ingestion of H(2)O(2) should not be considered a carcinogenic threat.

Biological properties of peroxide-containing tooth whiteners

Peroxides have been used in tooth whitening for more than 100 years. Current peroxide-containing whiteners can be classified into three categories: (1) those containing high concentrations of peroxides for professional use only; (2) materials dispensed by dentists and used by patients at home; and (3) over-the-counter products available directly to consumers for home use. Hydrogen peroxide (H2O2) and carbamide peroxide are the most commonly used active ingredients in these whiteners. Both peroxides have long been used safely in oral health products and are accepted by the US Food and Drug Administration. However, questions have been raised regarding the safety of at-home whiteners because the peroxides appear to constitute a new use. Substantial differences exist in the manner of application between at-home whiteners and oral health products. In addition, tooth whiteners are a mixture of various ingredients; possible interactions may occur because of the active nature of peroxides. Therefore, the safety evidence for peroxide-containing whiteners is considered inadequate. This paper will review the history of using peroxides for tooth whitening, the toxicology of H2O2 and carbamide peroxide, and available information on the safety of whiteners. The rationale and approaches for evaluating biological properties of peroxide containing whiteners are also discussed.

Tooth bleaching: its effect on oral tissues

After investigating the literature, we suggest these guidelines for tooth bleaching: If bleaching solutions of high concentration are used, prevent accidental exposure of gingival tissues to the solutions by use of a rubber dam. If using lower concentrations of bleaching solutions, avoid long-term exposures to gingival tissues. To maintain pulp vitality, keep bleaching time and temperatures to a minimum. Check teeth for exposed dentin and enamel fractures. Advise patients that thermal sensitivity may occur after the bleaching procedure and may persist for several days. Prescribe premedication with an anti-inflammatory drug, when necessary. Avoid bleaching the cervical area of the tooth by covering the area with a base to avoid cervical resorption. Avoid dentin exposure by noting that abrasive bleaching techniques can remove significant amounts of enamel. Take special care when bleaching enamel--especially near the cervix of the tooth, where the enamel is thin.

Is home tooth bleaching gel cytotoxic?

Tooth whitening systems are widely used clinically and for home usage. The aim of this study was to determine the effects of two bleaching gels, each containing 10 percent and 15 percent carbamide peroxide, respectively, a 'bleaching gel' without carbamide peroxide, and carbamide peroxide alone on the viability of human endothelial cells in vitro in comparison with culture medium that acted as a negative control. The incubation period used was 30 minutes. A colorimetric viability assay (MTT assay) was employed. The results showed that the gel without carbamide peroxide is not cytotoxic compared to the negative control, while carbamide peroxide on its own and 10 percent and 15 percent carbamide peroxide bleaching gels were cytotoxic, but there were no significant differences (p greater than 0.05) among these latter three test groups. These data indicate that 10 percent and 15 percent carbamide peroxide bleaching gels are cytotoxic and that carbamide peroxide is the component responsible for this cytotoxic effect. This paper also discusses why this in vitro cytotoxic effect appears not to be significant in vivo.

Cytogenetic response to 1,2-dicarbonyls and hydrogen peroxide in Chinese hamster ovary AUXB1 cells and human peripheral lymphocytes

Mutagenic 1,2-dicarbonyls have been reported to occur in coffee and other beverages and in various foods. We have measured the induction of sister-chromatid exchanges (SCEs) and endoreduplicated cells (ERCs) to determine the genotoxicity of various 1,2-dicarbonyl compounds in Chinese hamster ovary (CHO) AUXB1 cells and human peripheral lymphocytes. The 1,2-dicarbonyls glyoxal, methylglyoxal and kethoxal each induced highly significant increases in both SCEs and ERCs in AUXB1 cells. Glyoxal and kethoxal induced SCEs but not ERCs in human peripheral lymphocytes. In addition, hydrogen peroxide induced highly significant levels of SCEs and ERCs in AUXB1 cells. Bisulfite, which reacts with carbonyl groups to form addition products, significantly reduced the frequency of SCEs and the proportion of ERCs when glyoxal, methylglyoxal, kethoxal and diacetyl were administered to AUXB1 cells. In addition, bisulfite blocked the formation of ERCs, but not SCEs, induced by hydrogen peroxide. These in vitro results suggest that 1,2-dicarbonyls may play an important role in the genotoxicity of some foods and beverages.

Role of oxygen free radicals in the induction of sister chromatid exchanges by cigarette smoke

Cigarette smoke has been reported to contain free radicals and free radical generators in both the gas and particulate phases. Studies in our laboratory have shown that both cigarette smoke condensate (CSC) and smoke bubbled through phosphate buffered saline solution (smoke-PBS) increased sister chromatid exchanges (SCE) in Chinese hamster ovary cells in a dose-dependent manner. Since oxygen free radicals have been shown to cause SCEs and other chromosomal damage, we investigated the role of these radicals in the induction of SCEs by CSC and smoke-PBS. Addition of the antioxidant enzymes catalase and superoxide dismutase or the oxygen-radical scavenger ascorbic acid failed to reduce the SCE frequency in the presence of either CSC or smoke-PBS. Additional studies indicated that the quantity of hydrogen peroxide produced in CSC or smoke-PBS is too small to account for the observed SCE induction. It appears, therefore, that SCE induction by CSC or smoke-PBS does not involve the participation of oxygen free radicals.

Effects of hydrogen peroxide on oral carcinogenesis in hamsters

The effects of twice weekly topical applications of hydrogen peroxide on the buccal epithelium of Syrian hamsters were studied. Animals were treated either with hydrogen peroxide alone, with hydrogen peroxide and the carcinogen 9, 10-dimethyl-1,2-benzanthracene (DMBA), or with DMBA alone. In animals treated with 30% H2O2 alone, histopathologic examination after 22 weeks revealed hyperkeratosis and hyperplasia in all animals with hyperchromatic cells and mild dysplasia in four of nine: no tumors were seen. In animals treated with DMBA alone, three of seven (43%) developed epidermoid carcinoma, while six of 11 (55%) of animals treated with DMBA plus 3% hydrogen peroxide and five of five (100%) of animals treated with DMBA plus 30% hydrogen peroxide (P = 0.054) developed carcinoma. Thus, hydrogen peroxide can, by itself, induce pathologic changes frequently associated with preneoplastic lesions; it may also augment carcinogenesis associated with DMBA.

The relationship between the induction of SCEs and mutations in Chinese hamster cells. I. Experiments with hydrogen peroxide and caffeine

Hydrogen peroxide (H2O2) and caffeine were examined for their capacity for inducing SCEs and mutations at the HPRT locus in V79 Chinese hamster cells. Although, under standard conditions, both substances induced SCEs neither caused gene mutations. The SCE induction by both H2O2 and caffeine is influenced by BrdUrd substitution. Whereas H2O2 also induces lesions leading to SCEs in normal DNA, the SCe induction by caffeine depends on the replication of BrdUrd-substituted DNA. In cells with BrdUrd-substituted DNA, H2O2 induces mutations at the HPRT locus parallel to its SCE induction, whereas caffeine in the presence of BrdUrd only has an influence on the SCE rate. It is shown that the experimental conditions of the two test systems can play a decisive role when contradictory results are obtained.

Variation in sister chromatid exchange frequencies between human and pig whole blood, plasma leukocyte, and mononuclear leukocyte cultures

Sister chromatid exchange (SCE) induction by ultraviolet (UV) light was studied in both human and pig whole blood cultures (WBC) and plasma leukocyte cultures (PLC). No variation in SCE frequency was observed between pig WBC and PLC in control as well as in treated cells. Conversely, SCE frequencies of human PLC were consistently higher than those of WBC in control and UV-exposed cells. Thus, red blood cells (RBCs) do not influence the sensitivity of lymphocytes to UV light exposure, and there must be some different culture condition(s) in the induction of SCEs between human WBC and PLC but not in swine lymphocyte cultures. Since the BrdUrd/lymphocyte ratio of WBC was halved in PLC, the effect of BrdUrd concentration in inducing the SCE baseline frequency of PLC may be ruled out. Also, Ficoll-Hypaque-separated human mononuclear leukocytes in culture (MLC), but not pig MLC, showed a two-fold increase in SCE frequency over WBC values. Thus, neither the cell separation technique nor polymorphonuclear leukocytes had a significant role in the elevated SCE frequency of human PLC or MLC. Experiments where human RBCs were titrated into human PLC showed that the induction of an elevated SCE frequency of PLC was suppressed in a dose-dependent manner by the presence of RBCs in the culture medium. Since the incorporation of pig or human RBCs into human PLC as well as into MLC reduced the SCE frequency to that of WBC, a common component and/or function existing in these cells is suggested. Analysis of different RBC components showed that RBCs, specifically RBC ghosts, release a diffusible but not dialyzable "corrective" factor into culture medium that is able to reduce the SCE frequencies of PLC. Antioxidant enzymes such as catalase and horseradish peroxidase were unable to reduce the SCE frequency of human PLC to WBC values.

Differences in the induction of SCEs between human whole blood cultures and purified lymphocyte cultures and the effect of an S9 mix

Studies for SCE induction are frequently performed on human blood cultures. Either whole blood cultures (WBC) or purified lymphocyte cultures (PLC) are employed. However, it has been shown that fundamental differences with respect to metabolic activity exist between these two systems. In order to further characterize the whole blood culture and the purified lymphocyte culture, differently acting substances were studied comparatively with and without an Aroclor-1254-induced S9 mix. Treatment with ethyl methanesulfonate (EMS), a direct mutagen, produced distinct SCE induction in both systems. Cyclophosphamide (CP) and benzo[a]pyrene (BP), two indirect mutagens, also led to a significant increase of SCEs both in WBC and PLC without S9 mix. Only with CP was this effect more pronounced after addition of S9 mix. Sodium selenite (Na2SeO3), which induced SCEs in WBC, did not show this effect in the PLC. After S9 mix was added to purified lymphocytes, an increase of SCEs by sodium selenite was observed as in WBC. H2O2, a radical former, led to SCE induction in purified lymphocytes but not in the whole blood culture. By adding S9 mix, a distinct reduction of the SCEs induced by H2O2 was established. These results show that human lymphocytes can metabolize indirect mutagens and that it should be kept in mind when using S9 mix that, besides mixed-function oxygenases, it also contains enzymes which influence the SCE-inducing effects of substances.

Chronic treatment with hydrogen peroxide. Is it safe?

The regular application of hydrogen peroxide to gingival tissues is becoming widely used as part of dental hygiene. Since hydrogen peroxide can be toxic under certain experimental conditions, proof of both safety and efficacy of its chronic administration should be available before prescription to the general public.

The contribution of DNA single-strand breaks to the formation of chromosome aberrations and SCEs

The induction of sister chromatid exchanges (SCEs) and chromosomal aberrations (CAs) with bleomycin (BLM), hydrogen peroxide (H2O2), short-wave ultraviolet (UV)-irradiation, and long-wave UV-irradiation was investigated in V79 cells with BrdUrd-substituted DNA. The application of a Neurospora endonuclease (NE) which specifically cleaves single-stranded DNA after these treatments showed that DNA single-strand breaks (SSBs) are induced by these agents. The SSBs are converted to double-strand breaks (DSBs) by NE and become visible as CAs on metaphase chromosomes. H2O2 and both types of UV-irradiation also led to an induction of CAs and SCEs, whereas BLM only induced aberrations. Cysteine (Cys) reduced the frequency of the induced SSB-dependent CAs in all treatments, but had no influence on the SCE frequencies after BLM and H2O2 treatment and had only a slight effect on the UV-induced SCEs. The results confirm the opinion that directly induced SSBs can contribute to the induction of CAs in cells with BrdUrd-substituted DNA, but that these SSBs are not efficiently converted to SCEs. The more recent conceptions regarding the mechanism of SCE are in accordance with these findings and the conclusions derived therefrom.

Different effects of mutagens on sister chromatid exchange induction in three Chinese hamster cell lines

The sister chromatid exchange (SCE) induction of mutagens with different mechanisms of action was comparatively investigated on permanent cell lines of the Chinese hamster (CHO, V-79, and DON) with and without exogenous metabolic activation and with the use of various experimental protocols. CHO and V-79 cells were treated with ethylmethanesulfonate (EMS), a direct mutagen; with the two indirect mutagens cyclophosphamide (CP) and benzo[a]pyrene (BP); as well as with the radical former hydrogen peroxide (H2O2) and hydroxyurea (HU), an inhibitor of DNA synthesis. Aside from an increased basal SCE level and a higher bromodeoxyuridine (BrdUrd) sensitivity, there was no decisive difference between CHO and V-79 cells. However, there was a distinct relationship between SCE induction and the experimental protocol used, which was most pronounced after HU treatment. Neither cell line was able to metabolize the indirect mutagen BP. Only in CHO cells did CP lead to increased SCE frequencies. However, in all cases, the simultaneous application of S9 mix produced a distinct SCE induction. In contrast, BP caused SCE induction in DON cells, whereas CP was not metabolized. The reason for these findings must obviously be sought in the metabolization of CP and BP via different monooxygenase systems, whose activity can differ in these permanent cell lines. One notable finding was that the number of SCE induced by H2O2 could be distinctly reduced by the simultaneous application of S9 mix. This effect can be explained by the fact that S9 mix contains H2O2-degrading enzymes. The results indicate that closely related cell lines differ in their capability for inducing SCE and that investigations of SCE inductions performed on only one cell line do not necessarily produce a representative response.

Dietary carcinogens and anticarcinogens. Oxygen radicals and degenerative diseases

The human diet contains a great variety of natural mutagens and carcinogens, as well as many natural antimutagens and anticarcinogens. Many of these mutagens and carcinogens may act through the generation of oxygen radicals. Oxygen radicals may also play a major role as endogenous initiators of degenerative processes, such as DNA damage and mutation (and promotion), that may be related to cancer, heart disease, and aging. Dietary intake of natural antioxidants could be an important aspect of the body's defense mechanism against these agents. Many antioxidants are being identified as anticarcinogens. Characterizing and optimizing such defense systems may be an important part of a strategy of minimizing cancer and other age-related diseases.

Implications of an elevated sister-chromatid exchange frequency in rat lymphocytes cultured in the absence of erythrocytes

One important variable in complex culture systems such as whole blood is the interaction of the cell types present. To investigate the effects of erythrocytes (RBCs) and monocytes on the sister-chromatid exchange (SCE) frequency, Ficoll-Hypaque-separated Fischer-344 rat leukocytes were added to 1.9 ml of culture medium containing either 4 micrograms phytohemagglutinin or 4-8 micrograms concanavalin A/ml. Bromodeoxyuridine (BrdU;2 microM) was added at 24 h, and the cultures were harvested at 54 or 72 h. SCE frequencies in the mononuclear leukocyte cultures were consistently about 1.5- to 2-fold higher than in the whole-blood cultures. The titration of rat or human RBCs (0.05-2.5 X 10(9)) into purified rat leukocyte cultures reduced the SCE frequency to that of whole-blood cultures. Monocyte depletion decreased the elevated SCE frequency by approximately 50%. Scintillation counting of [14C]BrdU uptake in isolated RBCs revealed that less than 8% of the total amount of BrdU was sequestered. Also, BrdU induced a concentration-dependent increase in SCE in purified leukocytes, but the absolute increase was no greater than in whole-blood lymphocytes. Thus, BrdU had a minor role in the elevated SCE frequency in purified lymphocytes. Neither anti-oxidant enzymes such as catalase and superoxide dismutase nor the hydroxyl radical scavenger, dimethyl sulfoxide, decreased the SCE frequency. Although purified human lymphocytes had a small, but significant increase in SCE compared to whole blood, the magnitude of the dichotomous response between man and rat may represent a fundamental species difference.