Review LtjJ01RKihcoC980ebyetu.18Bvon3rS20int1Nee-oa1605w,cl-40iJ1roe/08aj0ftc96pya5bCafnloi.tn1ri1Fuc-ra1el0eBr5Rieoacdhiceamrl iRestersyvea nricdheNJuawptraitnion of the role of hydroxyl radicals in chemicallyinduced mutagenicity and carcinogenicity for the risk assessment of a disinfection system utilizing photolysis of hydrogen peroxide Taro Kanno,1 Keisuke Nakamura,1 Hiroyo Ikai,1 Katsushi Kikuchi,2 Keiichi Sasaki1 and Yoshimi Niwano1,* 1Tohoku University Graduate School of Dentistry, Seiryomachi 41, Aobaku, Sendai 9808575, Japan 2Innovation of New Biomedical Engineering Center, Tohoku University, Seiryomachi 11, Aobaku, Sendai 9808574, Japan (Re7ceived 15 August, 2011; Accepted 26 September, 2011; Published online 3 March, 2012) svCWtirdei2TCecea0hhotdte1ipasdvt2vyheiereusigsdoaCehnreo,itvgmod©eipinlmsoe2atpnorl0ienw1bads2ucoctarJiAekoCsnntsiBte,sraiwNapbrntruioddctipiloserinenrdplfyierLsoctcirtdciiituoebecnnudtst.iesody,nsutwienhmdiaecnrfhoythrpmeoertereamdrlimiuhtmsygo,uifepntnrhoeee-, proving that hydroxyl radicals generated by the photolysis of 1 M hydrogen peroxide could effectively kill oral pathogenic microorganisms. Prior to any clinical testing, the safety of the sys tem especially in terms of the risk of carcinogenicity is examined by reviewing the literature. Previous studies have investigated indirectly the kinds of reactive oxygen species involved in some sort of chemicallyinduced mutagenicity in vitro by using reactive oxygen species scavengers, suggesting the possible involvement of hydroxyl radicals. Similarly, possible involvement of hydroxyl radicals in some sort of chemicallyinduced carcinogenicity has been proposed. Notably, it is suggested that the hydroxyl radical can play a role in heavy metalinduced carcinogenicity that requires chronic exposure to the carcinogen. In these cases, hydroxyl radicals produced by Fentonlike reactions may be involved in the carcinogenicity. Meanwhile, potential advantages have been reported on the use of the hydroxyl radical, being included in host immune defense by polymorphonuclear leuko cytes, and medical applications such as for cancer treatment and antibiotics. From these, we conclude that there would seem to be little to no risk in using the hydroxyl radical as a disinfectant for shortterm treatment of the oral cavity. Key Words: hydroxyl radical, mutagenicity, carcinogenicity, photolysis, hydrogen peroxide A AIpnptlryoindgutchteioonxidative power of hydroxyl radicals to disinfec- tion systems has been attempted by utilizing sonolysis of water and photolysis of hydrogen peroxide in our laboratory.(1–3) In the latter system, designed for oral hygiene, hydroxyl radicals generated by the photolysis of 1 M hydrogen peroxide increased with laser irradiation time and could kill oral pathogenic bacteria in as little as one to three minutes. In other words, the time-dose relationship of this system shows that it is very effective. Therefore, we concluded that a disinfection technique using artificially generated hydroxyl radicals could be applied to the treatment of various oral infectious diseases. Fig. 1 shows a schematic illustra- tion of a device for the treatment of dental infectious diseases. Hydrogen peroxide is released from the tip of the device to the lesion site concomitantly with laser irradiation through an optical fiber. One molar hydrogen peroxide (H2O2) used in the system corresponds to approximately 3% which is a concentration used in oral cavity as a disinfectant. A subcommittee of US Food and Drug Administration (FDA, 2003) also concluded that hydrogen doi: 10.3164/jcbn.11105 ©2012 JCBN peroxide is safe at concentrations of up to 3%. While the experi- mental data suggest a mutagenic effect of hydrogen peroxide, the Subcommittee’s review indicates that, at concentrations of up to 3% in oral care products, the risk appears to be especially minimal and hydrogen peroxide is safe for its intended use (FR Doc 03- 12783). Regarding a safety aspect of the system, we have conducted toxicity studies using rabbits and rats (unpublished data). In the rabbit study, the locally injurious properties of the hydroxyl radical generation system was evaluated by using a bone wound model. As a result, the single treatment with the disinfec- tion system utilizing the photolysis of H2O2 exerted no significant effect on the healing of bone wound produced on the femur and the tibia. In the rat study, oral cavity was exposed to H2O2 with laser irradiation once a day for three days, resulting in that no abnormalities were visually found in oral mucous membrane. In addition, prior to clinical testing, the safety of the system utilizing hydroxyl radical generation must be evaluated in terms of the risk of carcinogenicity. However, it is very hard to assess mutagenicity of the system in vitro by bacterial reverse mutation assay and chromosome aberration test, because bacterial and mammalian cells should be continuously exposed to 1 M H2O2 with laser irradiation for certain period of time. Bibliographically, although there have been many studies on oxidative cellular damage such as membrane lipid peroxidation, protein denaturalization, and nucleic acid modification in relation to reactive oxygen species (ROS) including the hydroxyl radical,(4–6) the relevant effects of the radical on carcinogenicity have not been clearly elucidated possibly because of its extremely short-half life, approximately 10−9 s.(7,8) To assess the risk of carcinogenicity from using hydroxyl radicals to treat oral infections, this paper examines the possible involvement of the hydroxyl radical in chemically-induced mutagenicity and carcinogenicity by reviewing the literature. Hydroxyl Radical and Mutagenicity There have been many reports on the possible role of the hydroxyl radical in chemically induced mutagenicity/genotoxicity. de Kok et al.,(9) used electron spin resonance (ESR) spectroscopy to study oxygen radicals generated by synthetic fecapentaene-12 (FP-12), which belongs to a class of potent fecal mutagens and has been suggested to play an initiating role in colon carcino- *To whom correspondence should be addressed. Email: niwano@m.tohoku.ac.jp J. Clin. Biochem. Nutr. | July 2012 | vol. 51 | no. 1 | 9–14