Dibenzoyl peroxide

Endpoint summary

Additional information

In vitro data

Several key and supporting studies showed that benzoyl peroxide (BPO) is non-mutagenic to Salmonella typhimurium TA97, TA97a, TA98, TA100, TA102, TA104, TA1535 and/or TA1537 strains (Willem, 1979; NIER Korea, 2001; Dillon et al., 1998; Zeiger et al., 1988; Ishidate et al., 1984; Brusick, 1975; Fujita and Sasaki, 1987), Escherichia coli WP2 uvrA (NIER Korea, 2001) and Saccharomyces cerevisia D4 (Brusick, 1975) in the presence and absence of a metabolic activation system.

DNA repair was induced by BPO without metabolic activation in E. coli PQ37, but not in PM21 and GC4798 strains in a SOS Chromotest (Eder et al., 1989).

In a key mouse lymphoma assay (OECD guideline and GLP), BPO did not show any mutagenic activity (Sire, 2010).

BPO produced an increase in levels of 8-hydroxy-2’-deoxyguanosine (8-OUdG) in the DNA of cultured mouse keratinocytes (King et al., 1996) and Human leukemia HL-60 cells (Kawanishi et al., 1999). Subsequently, BPO induced DNA single-strand breaks in cultured epidermal cells from newborn BALB/c mice and cells derived from chemically induced mouse skin papillomas (Hartley et al., 1987).

In human peripheral lymphocyte cultures without metabolic activation, BPO induced a weak increase of sister chromatid exchange (SCE), chromosome aberration (CA), and micronucleus (MN) at cytotoxic concentrations (Yavuz et al, 2010). However, Ishidate, et al. (1984) reported negative results for induction of chromosome aberrations in a Chinese hamster fibroblast lung cell line (CHL) even with long exposure of 48 hours to 200 µg/ml.

Results have been reported that are consistent with both the addition of benzoyloxyl and phenyl radicals to the C5-C6 double bond of pyrimidines and, to a lesser extent, hydrogen abstraction from sugar rings of RNA and DNA. The benzoyloxyl radical appears to be responsible for the majority of DNA strand breaks and high yields of altered bases through the formation of base adducts (Hazlewood & Davies, 1996).

In vivo data

An in vivo mammalian erythrocytes micronucleus test was conducted in accordance with OECD TG 474 and GLP (Nier Korea, 2001). Benzoyl peroxide was administered once by intraperitoneal injection to male and female ICR mice at doses up to 200 mg/kg b. w. Benzoyl peroxide did not influence the incidence of micronuclei up to a maximum concentration of 200 mg/kg.

The ability of benzoyl peroxide (BPO) to produce DNA damage as 8-OH-dG formation, CAA->CTA transversions in codon 61 of the mouse Ha-ras gene and sustained epidermal hyperplasia was evaluated when administered to female Sencar mice topically twice weekly for four weeks (Slaga, 1997; Hanausek et al., 2004). Epidermal and dermal hyperplasia and total dermal cellularity were measured at day 2 and day 4 after last dosing. 8-0H-dG/dG ratio was determined by HPLC/ECD using DNA isolated from frozen skins. Ha-ras gene mutation was determined in DNA isolated from 25 paraffin sections (8µm) using MSP-32P assay. When applied repetitively, to the dorsal skin of Sencar mice in doses of 6.25, 62.5 and 125 µmol/mouse, BPO caused an increase in epidermal thickness over the threshold, but these results were not statistically significant. Slight increase (x2.4) of 8-0H-dG but no Ha-ras gene mutation were detected in DNA isolated from the epidermis after repetitive applications of 125 µmol/mouse BPO. The results indicate that 8-0H-dG is formed in vivo in cellular DNA upon treatment with BPO but didn’t lead to gene mutations. The positive control, DMBA (100 nmoles), effectively induced DNA damage (8-0H-dG), Ha-ras gene mutation, epidermal hyperplasia and dermal hyperplasia.

Cooke et al. (2003) discussing that the mere presence of 8-OH-dG in DNA is unlikely to be necessary or sufficient to cause tumor formation. There are many pathological conditions in which levels of oxidative DNA damage are elevated with no increased incidence of carcinogenesis. This has led us to raise the following issues.

1) Oxidative DNA damage may be an epiphenomenon to an on-going pathophysiological process, and elevated levels do not have a role in carcinogenesis.

2) Cause or consequence? The mere presence of elevated levels of damage in tumors does not indicate it was oxidative damage that led to the tumorigenic changes. Elevation in levels may have occurred as a result of well-established characteristics of tumors, e.g., increased metabolism or cell turnover.

3) For DNA mutations to arise from oxidative damage, the nuclei of undifferentiated, proliferating stem cells must be affected. Given that tissue samples from tumors and normal cells will represent a heterogeneous mixture of differentiated and undifferentiated cells (with the former likely to predominate), current analytical procedures will not reflect lesion levels in the most important target cells.

4) Not only must the DNA of target cells be affected; to result in a mutation the damage must be within a coding region of the DNA.

Issues like these will have to be addressed before the link between oxidative DNA damage and cancer is proven.

Short description of key information:
Even though some of the in vitro studies suggest that benzoyl peroxide (BPO) may be a weak mutagen, the negative studies along with the overall genotoxicity profile do not warrant concluding that benzoyl peroxide is a genotoxic agent. The positive genotoxicity results are likely due to the oxidative DNA damage caused by benzoyl peroxide, which has been shown in numerous studies. In vivo there are oxidative repair mechanisms that would likely prevent BPO causing DNA damage. In an extensive review of the genotoxicity data, Binder et al. 1995 concluded that BPO has at most weak genotoxic potential in some in vitro systems, but this does not appear to be manifested in vivo, based on a lack of initiating or complete carcinogenic activity.

Justification for classification or non-classification

Benzoyl peroxide is not genotoxic, and is no classified according to EU Regulation (EC) N0. 1272/2008 (CLP).