Mutagenicity of dihydroxybenzenes and dihydroxynaphthalenes for Ames Salmonella tester strains

Genetic Toxicology

ELSEVIER

Mutation Research 371 (1996) 293-299

Mutagenicity of dihydroxybenzenes and dihydroxynaphthalenes for Ames Salmonella tester strains Atsushi Hakura *, Yoshie Tsutsui, Hisatoshi Mochida, Yoshiki Sugihara, Takashi Mikami, Fumio Sagami Department of Drug Safe~ Research, Eisai Co., Ltd., 1-3 Tokodai, 5-chome, Tsukuba-shi, lbaraki 300-26, Japan

Received 19 March 1996; revised 30 August 1996; accepted 4 September 1996

Abstract The mutagenicity of 3 dihydroxybenzene (DHB) and 9 dihydroxynaphthalene (DHN) isomers was examined by using 5 different Ames Salmonella mutagenicity tester strains in the presence and absence of phenobarbital and 5,6-benzoflavonetreated rat liver S9-mix. Of the 3 DHB isomers, 1,4-DHB (hydroquinone) was mutagenic, and of the 9 DHN isomers, 1,3-DHN (naphthoresorcinol), 1,4-DHN (hydronaphthoquinone), 1,6-DHN and 1,7-DHN were mutagenic. Mutagenicity of all the compounds tested was observed in the absence of S9-mix, while 1,4-DHN and 1,6-DHN were also mutagenic in the presence of S9-mix. The mutagenicity of 1,4-DHB and 1,4-DHN for TA104, which is a strain sensitive to oxidative mutagens, was almost completely or partially inhibited by superoxide dismutase (SOD) and/or catalase, indicating the involvement of activated oxygen species in mutagenesis. Furthermore, from the finding that the 4 DHNs were mutagenic for TA2637, the strain sensitive to frameshift mutagens, it is possible that the mutagenicity of DHNs for S. ~phimurium was also attributable to DNA adducts that form with quinones and/or semiquinones through oxidation of DHNs. The mutagenicity of 1,3-DHN, which showed the largest number of revertants in strains TA100, TA98, TA2637 and TAI04, was greatly decreased, when their pKM 101 plasmid-deficient strains, TA1535, TA1538, TA1537 and TA2659 were used. This observation suggests that an SOS repair system was involved in the mutagenesis of 1,3-DHN for S. typhimurium. Keywords: Dihydroxybenzene; Dihydroxynaphthalene;Hydroquinone; Mutagenicity; Salmonella t3phimurium

1. Introduction Dihydroxy derivatives of aromatic hydrocarbons include major oxidative metabolites of a number of c a r c i n o g e n i c / m u t a g e n i c aromatic hydrocarbons [1], and reductive metabolites of quinones, which are widely distributed in nature as biological compo-

* Corresponding author.

nents and used in the toxic defense system of certain insects [2,3]. Hydroquinone and catechol, which are the simplest dihydroxyaromatic hydrocarbons, dihydroxybenzene (DHB) isomers, are suggested to be the metabolites involved in the carcinogenesis of benzene in humans and rodent [4-6], and the mutagenicity of hydroquinone has been reported to induce base-pair changes in strain TA1535 of Salmonella typhimurium [7]. It has been suggested that menadiol (2-methyl-l,4-hydronaphthoquinone), one of the di-

0165-1218/96/$15.00 Copyright © 1996 Elsevier Science B.V. All rights reserved. PII S0 165- 12 18(96)00135-8

294

A. Hakura et al. / Mutation Research 371 (1996) 293-299

hydroxynaphthalene (DHN) derivatives, is a metabolite involved in the detoxification of menadione (2methyl-l,4-naphthoquinone)-induced mutagenicity [8,9]. These reports seem to suggest that the mutagenicity of dihydroxyaromatic hydrocarbons contains complex context. Moreover, their mutagenicity is poorly understood except for only a few compounds such as hydroquinone. Ames Salmonella mutagenicity tester strains have been developed and used widely throughout the world to detect carcinogens and mutagens [10]. To better understand the mutagenicity of dihydroxyaromatic compounds, we examined the mutagenicity of the structurally simplest 3 DHB and 9 DHN isomers, which are commercially available. The mutagenicity tester strains used mainly were 5 Ames Salmonella strains (TA100, TA98, TA2637, TAI02 and TAI04), which included the strains used in our previous studies on the mutagenicity of naphthoquinones (NQs) [9] and benzoquinones (BQs) [11]. Their pKM 101 plasmid-deficient strains, TA 1535, TA 1538, TA1537 and TA2659, were also used to determine the involvement of an SOS repair system in the mutagenesis of 1,3-DHN. Moreover, the effect of superoxide dismutase (SOD) and catalase on DHBand DHN-induced mutagenicity was determined.

2.2. Bacterial strains

Table l lists the 9 Salmonella tester strains used with their respective genotypes [ 10,12]. These Ames tester strains were the gifts of Dr. T. Matsushima of the University of Tokyo, and were originally provided by Dr. B.N. Ames of the University of California, Berkeley. 2.3. MutageniciO' assays

The Salmonella mutagenicity assay was carried out with a 20-min preincubation procedure under yellow lamps [9-11]. Each compound was tested to its toxic limit (minimal cytotoxic dose) or 5 rag/plate in a non-toxic case with and without S9-mix. The lowest doses giving a significant decrease in the background lawns of the bacteria are expressed as the minimal cytotoxic doses. Dimethyl sulfoxide was used as the solvent of the DHBs and DHNs. Oxoid nutrient broth No. 2 was used for overnight culture.

OH

OH

OH

1,2-DHB (calechol) [120-80-9]

1,3-DHB (resorcinol) [108-48-3 ]

OH

OH

OH i,4-DHB (hydroquinone) [123-31-9]

2. Materials and methods

OH

2.1. Chemicals

1,2-Dihydroxybenzene (catechol) (I,2-DHB), 1,3-dihydroxybenzene (resorcinol) (1,3-DHB), 1,4dihydroxybenzene (hydroquinone) (I,4-DHB), 1,3dihydroxynaphthalene (naphthoresorcinol) (1,3DHN), 1,4-dihydroxynaphthalene (hydronaphthoquinone) (1,4-DHN), 1,5-dihydroxynaphthalene (1,5-DHN), 1,6-dihydroxynaphthalene (1,6-DHN), 1,7-dihydroxynaphthalene (I,7-DHN), 2,3-dihydroxynaphthalene (2,3-DHN) and 2,7-dihydroxynaphthalene (2,7-DHN) were purchased from Tokyo Chemical Industry Co. (Tokyo, Japan). 1,2-Dihydroxynaphthalene (I,2-DHN) and 2,6-dihydroxynaphthalene (2,6-DHN) were from Aldrich Chemical Co. (Milwaukee, WI). Superoxide dismutase (SOD) and catalase were from Sigma Chemical Co. (St. Louis, MO). Fig. 1 shows the structure and CAS numbers of the compounds tested in this study.

OH

1,2-DHN [574-00-5 ]

1,3-DHN (naphthoresorcinol) [132- 86-5 ]

OH

OH 1,5-DHN [83-56-7]

2,3 DHN [82-44-4]

OH 1,4-DHN (hydronaphth oquino ne) [571-60-8]

OH

OH

1,6-DHN [575-44-0 ]

1,7-DHN [575-38-2 ]

2,5-DHN [581-43-1 ]

2,7-DHN [582-17-2]

Fig. 1. Structureof the 3 DHB and 9 DHN isomers used in the present study. The CAS numbers are shown in brackets.

295

A. H a k u r a et al. / M u t a t i o n R e s e a r c h 371 ( 1 9 9 6 ) 2 9 3 - 2 9 9

Table

3. Results

1

Salmonella

Strain TA 100 TA1535 TA98 TA1538 TA2637 TA1537 TAI02 TA 104 TA2659

tester strains used for mutagenesis testing [10] Genotype

3.1.

Histidine mutation

LPS

hisG46

rfa

hisG46

rfa

-

-

hisD3052

rfa

-

+

hisD3052

rfa

-

-

hisC3076

rfa

-

+

hisC3076

rfa

-

-

hisG428(pAQ1)hisA(G)8476

rfa

+

+

hisG428

rfa

-

+

hisG428

rfa

-

-

uvrB -

( a ) 1,4-DHB

( b ) 1,4-DHN

T A t 04, -S9

1000

/

of DHBs

and

DHNs

Ames mutagenicity tests of the 3 DHB and 9 DHN isomers were carried out using the 5 different tester strains (TA100, TA98, TA2637, T A I 0 2 and TA104) with and without phenobarbital and 5,6-benzoflavone-treated rat liver S9-mix. Figs. 2 and 3 are dose-response curves of the DHB and DHNs which showed a positive mutagenic response. As seen in Figs. 2 and 3, among the 3 DHB isomers, 1,4-DHB (hydroquinone) demonstrated mutagenicity for TA104 without S9-mix. Among the 9 DHN isomers, 1,3-DHN, 1,4-DHN, 1,6-DHN and 1,7-DHN were mutagenic. 1,3-DHN induced a relatively large number of revertants for all the strains except TA102 in the absence of S9-mix. 1,4-DHN was mutagenic for strain T A I 0 4 in the absence of S9-mix, and for TA2637 in the presence of S9-mix. 1,6-DHN and 1,7-DHN were also mutagenic for TA102 without S9-mix and for TA2637 with S9-mix, and for TA2637 without S9-mix, respectively.

+

The $9 prepared from male Sprague-Dawley rat liver pretreated with phenobarbital and 5,6-benzoflavone, and the cofactors were purchased from Oriental Yeast Co. (Tokyo, Japan). To assess the effect of SOD and catalase on the mutagenicity of 1,4-DHB, 1,3-DHN, 1,4-DHN and 1,6-DHN, 39 units and 26 units, respectively, were used. Two plates were used per each dose, and each experiment was conducted at least twice.

1500 -

Mutagenici~.

pKM101

(C) 1,4-DHN

TA1 04, -$9 1200

~

T A 2 6 3 7 , +S9

-

200-

8oo-

~

400"

500 -

I0050 J

0

1200 -

N

0

i / i i 250 500 750 1000 dose (nmol/plate) ( d ) 1,6-DHN T A I 02, -S9

320 -

~

800-

u~

~

~

400

i i i 25 5 7.5 dose (nmol/plate)

i 10

0

(e) 1,6-DHN TA2637, +$9

i I i i 100 200 300 400 dose (nmol/plate) ( f ) 1,7-DHN

200 -

T A 2 6 3 7 , -$9

~ lSO-

240-

~

160-

o> 80

10050I

0 0

5000 10000 15000 dose (nmol/plate)

0 0

~

~

~

5000 10000 15000 dose (nmol/plate)

0

800 16oo 2400 3200 dose (nmol/plate)

Fig. 2. Mutagenicity of 1,4-DHB (a), 1,4-DHN (b) and (c), 1,6-DHN (d) and (e), and 1,7-DHN (f), which showed positive responses. The open and closed symbols indicate without S9-mix and with S9-mix, respectively, and the circle, square and triangle symbols indicate strains TA104, TA2637 and TA 102, respectively. Assays were conducted in duplicate. Data points represent the means of the number of revertants per plate in at least two independent experiments, and bars '1' indicate standard deviations.

A. Hakura et al. / Mutation Research 371 (1996) 293-299

296 (a)

(b)

1000

( s t r o n g toxicity) a n d 1 , 3 - D H N ( w e a k toxicity) (Figs. 2 a n d 3).

240-

7S0-

180-

soo

3.2. Effect o f S O D and catalase on D H B - and DHN-mutagenicity

~ 12o-

TA98

>~ 250-

~

O' 0

Strains T A I 0 4 a n d T A I 0 2 , s e n s i t i v e to o x i d a t i v e m u t a g e n s , w e r e e x p o s e d to 1,4-DHB, 1 , 3 - D H N a n d

6o-

i

i

0'

i 12150 18~75 2500 i 625 dose (nmol/plate)

625 125o 1875 2500 dose (nmol/plate)

(a) lOOO-

(c) 3000 -

o

o 375 -

A

~ . 750-

f

~ g

250

i I0000

_7

~ 200-

250-

,I

125-

625 12501875 2500 dose(nrnol/plate)

TA2659

1

1,4-DHN, TA1 04

400-

500-

TA2637

800-

2~ ~-;6~°°

(d)

500 -

(b)

1,4-DHB, TAI 04

0~

250 500 750 1000 dose (nmol/plate)

dose (nmol/plate)

°4"ds 40 18,5 2!00 dose (nmol/plate)

Fig. 3. Involvement of an SOS repair system, which is organized by mucAB operon coded in the pKMI01 plasmid, in the mutagenesis of 1,3-DHN for strains TAI00 (O) and TA1535 (A) (a), TA98 (O) and TA1538 (z~) (b), TA2637 (O) and TA1537 (z~) (c), and TA104 (O) and TA2659 (I,). Strains indicated with the symbol zx are the pKMI01 plasmid-deficient strains, and strains indicated with the symbol O are the pKM101 plasmid-carrying strains. Assays were performed by the Ames test modified by 20-min preincubation at 37°C in the absence of S9-mix. Data points represent the means of the number of revertants in at least two independent experiments, and bars T indicate standard deviations.

T h e strain m o s t s e n s i t i v e to the m u t a g e n i c i t y o f the D H B s a n d D H N s w a s T A 1 0 4 , a n d the s e c o n d m o s t s e n s i t i v e strain was T A 2 6 3 7 (Figs. 2 a n d 3). L a r g e d i f f e r e n c e s in the d e g r e e o f m u t a g e n i c i t y were o b s e r v e d a m o n g the i s o m e r s a n d the strains. A m o n g the 5 m u t a g e n i c d i h y d r o x y d e r i v a t i v e s , 1 , 4 - D H N was the m o s t potent, f o l l o w e d in o r d e r b y 1 , 3 - D H N > 1 , 4 - D H B , 1 , 7 - D H N > 1,6-DHN, w h e n c o m p a r e d o n the b a s i s o f m i n i m a l m u t a g e n i c dose, w h e r e a s 1,3-DHN was most mutagenic, when compared on the b a s i s o f the f o l d - i n c r e a s e o f the n u m b e r o f r e v e r t a n t s i n d u c e d b y the c h e m i c a l relative to that o f s p o n t a n e o u s r e v e r t a n t s . T h i s is due to the d i f f e r e n c e in the d e g r e e o f the c y t o t o x i c i t y o f b e t w e e n 1 , 4 - D H N

(d)

(c) 2oooo --~.lSO0

~ 1000500-

0

1,6-DHN, TAq 02

1,3-DHN, TA104

f

0~5 dso 18;s 2?o0

dose (nmol/plate)

6OO

4 450 300-

~

lSO-

8= OI 0

2 5 0 0 5000 7500 10000 dose (nmol/plate)

Fig. 4. Effect of superoxide dismutase (SOD) and catalase on DHB- and DHN-mutagenicity without $9 mix. The 3 compounds mutagenic for S. tvphimurium strain TA 104 1,4-DHB (a), 1,4-DHN (b), and 1,3-DHN (c), and 1,6-DHN (d) mutagenic for TAI02 were chosen to determine the effect of SOD and catalase on DHBor DHN-induced mutagenicity. Assays were performed by the Ames test modified by 20-min preincubation at 37°C. SOD and catalase were used in the reaction mixture at levels of 39 and 26 units, respectively. The mutagenicity of the DHB and DHN isomers is shown with phosphate buffer alone (O) and in the presence of SOD (Q), catalase ( • ) , and SOD plus catalase ( • ) . Addition of bovine albumin, 10 ~g, to the phosphate buffer, which corresponded to the amount of SOD and catalase protein used, did not affect the mutagenicity or cytotoxicity of the DHB and the DHNs. Assays were conducted simultaneously in duplicate, and data points represent the means of the number of induced revertants subtracted from that of spontaneous revertants per plate in at least two independent experiments.

A. Hakura et al. / Mutation Research371 (1996)293-299

1,4-DHN, and 1,6-DHN, respectively, in the presence and absence of SOD a n d / o r catalase in phosphate buffer to determine the effect of SOD and catalase on the mutagenicity of these compounds. The mutagenicity of 1,4-DHB was markedly inhibited by SOD and catalase (Fig. 4a), and the mutagenicity of 1,4-DHN was reduced by half by catalase (Fig. 4b). On the other hand, SOD and catalase did not affect the magnitude of the mutagenicity of 1,3-DHN (Fig. 4c) and 1,6-DHN (Fig. 4d). Confirmation that these effects of the scavengers of activated oxygen species on the mutagenicity of the DHB and DHNs were not attributable to their protein or other factors was obtained by experiments using bovine albumin, 10 ~zg, in phosphate buffer in a test tube, which corresponded to the amount of SOD or catalase protein used (data not shown). 3.3. Involvement of SOS repair system in the mutagenesis of 1,3-DHN

Involvement of the SOS repair system in the mutagenesis of DHNs for S. typhimurium was determined by using 1,3-DHN, which induced a relatively large number of revertants for strains TAI00, TA98, TA2637 and TA104. Since the mucAB operon coded in plasmid pKM101 is implicated in an SOS repair system [13,14], their pKM101 plasmid-deficient strains TA1535, TA1538, TA1537 and TA2659, respectively were used for the comparison of the mutagenicity. As shown in Fig. 3, the pKM101 plasmiddeficient strains showed virtually no mutagenic activity, when compared with their plasmid-proficient strains. This finding suggests that an SOS repair system was largely involved in the mutagenesis of 1,3-DHN. 3.4. Cytotoxicity of DHBs and DHNs

Each compound was tested to its minimal cytotoxic dose or 5 mg/plate in a non-toxic case with and without S9-mix. The minimal cytotoxic doses of the 3 DHB and 9 DHN isomers obtained from the results of the Ames tests were approximately as follows (the first and second figures in parentheses are the doses (nmol) per plate without and with S9-mix, respectively): 1,2-DHB (4400, 46000), 1,3DHB ( > 4 6 0 0 0 , >46000), 1,4-DHB (900, >

297

46000), 1,2-DHN (130, 2500), 1,3-DHN (2500, 13000), 1,4-DHN (10, 470), 1,5-DHN (4700, 4700), 1,6-DHN (13000, 13000), 1,7-DHN (1600, 6300), 2,3-DHN (2500, 2500), 2,6-DHN (7500, 7500) and 2,7-DHN (13 000, 13 000).

4. Discussion To better understand the basis of the mutagenicity of dihydroxyaromatic hydrocarbons, we selected 3 DHB and 9 DHN isomers which are structurally simple and commercially available (Fig. 1). Five Ames bacterial tester strains (TA100, TA98, TA2637, TA102 and TA104) were chosen to assess the mutagenicity of the DHBs and DHNs, since these strains were sensitive to the mutagenicity of compounds BQs [11] and NQs [9], closely related to them. The DHBs and DHNs used in this study can be divided into two groups: (1) dihydroxy derivatives able, and (2) those unable to form electrophilic quinone structures. With respect to the former DHBs and DHNs, we can rather easily postulate the mechanisms of the mutagenesis from genotoxicological studies on 1,4-DHB (hydroquinone). Several studies have suggested that the genotoxicity of 1,4-DHB is induced by activated oxygen species [5,15-17], a n d / o r by an electrophilic benzoquinone a n d / o r semiquinone produced in the process of oxidation of 1,4-DHB [4,6]. These explanations may be the reasons why the mutagenicity of 1,4-DHB, 1,4-DHN and 1,7-DHN, which are able to form quinone structures, was detected in TAI04 and TA2637, which are sensitive to oxidative mutagens, and to frameshift mutagens, respectively (Fig. 2). The finding that these two strains are sensitive to the mutagenicity of the dihydroxy derivatives is consistent with those observed for BQ [11]- and NQ [9]-induced mutagenicity, supporting the correlations of the mutagenicity of between DHBs and DHNs, and of BQs and NQs. On the other hand, almost nothing is understood about the mutagenicity of the latter DHBs and DHNs, dihydroxy derivatives which are unable to form quinone structures. The mutagenicity of 1,4-DHB and 1,4-DHN was detected without S9-mix in the TA104 and TA102 strains, which are known to be sensitive to oxidative mutagens [8,12,18,19]. To confirm the involvement

298

A. Hakura et al. / Mutation Research 371 (1996) 293 299

of activated oxygen species in the mutagenesis of 1,4-DHB and 1,4-DHN, an experiment was conducted using the scavengers of activated oxygen species, SOD and catalase. As shown in Fig. 4a and b, the mutagenicity of 1,4-DHB was inhibited almost completely by both SOD and catalase, and that of 1,4-DHN reduced by half by catalase. These results indicate that activated oxygen species, including hydrogen peroxide, contributed to the mutagenicity of, at least, 1,4-DHB and 1,4-DHN for the TA104 strain. Therefore, we can speculate that the mutagenesis of these two compounds for T A I 0 4 may be due to the production of superoxide a n d / o r hydrogen peroxide, which are accompanied by 1,4-BQ and 1,4-NQ and their semiquinone radicals produced in the process of oxidation of 1,4-DHB and 1,4-DHN, respectively. Strain TA2637, sensitive to frameshift mutagens, detected the mutagenicity of 1,4-DHN and 1,7-DHN, which are able to form quinone structures (Fig. 2). From the finding, it is possible that the mutagenicity of the two DHNs was attributable to quinone-DNA damage that forms with their oxidized forms, quinones or semiquinone radicals having an electrophilic property. The mutagenicity of all of the 5 mutagenic dihydroxy derivatives was observed in the absence of S9-mix (Figs. 2 and 3). The finding may account for the autooxidation of the dihydroxy derivatives, by which activated oxygen species and the corresponding quinones a n d / o r semiquinones were produced. On the other hand, in the presence of S9-mix, the mutagenicity of 1,4-DHB, 1,3-DHN and 1,7-DHN was not observed. Possible explanations for the effect of S9-mix are the stabilization of these compounds by reductase(s) a n d / o r reductant(s) such as NADPH and NADH, or the reduction of activated oxygen species by scavengers such as SOD or catalase, which are present in S9-mix. With respect to 1,4-DHN and 1,6-DHN, their mutagenicity was also observed in the presence of S9-mix. This finding suggests the possibility that the mutation is induced by metabolic activation of the DHNs. However, there remains another possibility that the observed mutagenicity in the presence of S9-mix was due to the low toxicity of these DHNs. Interestingly, 1,3-DHN showed relatively strong mutagenic activity (when compared on the basis of fold-increase) without S9-mix for all strains except

TA102, including strain TA100, which is sensitive to base-pair substitution mutagens, and strains TA98 and TA2637, which are sensitive to frameshift mutagens (Fig. 3). The reason why 1,3-DHN is a potent mutagenic in spite of its inability to form an electrophilic quinone structure is unclear. A possible reason is that DNA adduct(s) formed by the reaction of DNA with 1,3-naphthosemiquinone, or the tautomeric forms of 1,3-DHN contribute to the mutagenesis. To further elucidate the mutagenesis of 1,3DHN, the mutagenicity of this compound was also examined by using TA1535, TA1538, TA1537 and TA2659, which are deficient in the pKM101 plasmid of TA100, TA98, TA2637 and TA104, respectively. As shown in Fig. 3, 1,3-DHN showed virtually no mutagenicity for the pKM101-deficient strains, indicating the large involvement of SOS repair in the mutagenesis.

Acknowledgements We wish to thank Dr. T. Matsushima for the S. strains. We also thank Professor Y. Kawazoe of Nagoya City University, and Dr. N. Miyata of the National Institute of Hygienic Sciences for their encouragement and helpful advice. typhimurium

References [1] Guengerich, F.P. and T. Shimada (1991) Oxidation of toxic and carcinogenic chemicals by human cytochrome P-450 enzymes. Chem. Res. Toxicol., 4, 391-407. [2] Smith, M.T. (1985) Quinones as mutagens, carcinogens, and anticancer agents: introduction and overview. J. Toxicol. Environ. Health, 16, 665-672. [3] O'Brien, P.J. (1991) Molecular mechanisms of quinone cytotoxicity. Chem.-Biol. Interact., 80, 1-41. [4] Smart, R.C. and V.G. Zannoni (1984) DT-Diaphorase and peroxidase influence the covalent binding of the metabolites of phenol, the major metabolite of benzene. Mol. Pharmacol., 26, 105-111. [5] Lewis, J.G., W. Stewart and D.O. Adams (1988) Role of oxygen radicals in induction of DNA damage by metabolites of benzene. Cancer Res., 48, 4762-4765. [6] Levay, G., K. Pongracz and W.J. Bodell (1991) Detection of DNA adducts in HL-60 cells treated with hydroquinone and p-benzoquinone by 32p-postlabeling. Carcinogenesis, 12,

1181-1186. [7] Gocke, E., M.-T. King, K. Eckhardt, and D. Wild (1981)

A. Hakura et a l . / Mutation Research 371 (1996) 293-299

[8]

[9]

[10] [11]

[12]

[13] [14]

Mutagenicity of cosmetics ingredients licensed by the European Communities. Mutation Res., 90, 91-109. Chesis, P.L., D.E. Levin, M.T. Smith, L. Ernster, and B.N. Ames (1984) Mutagenicity of quinones: pathways of metabolic activation and detoxification. Proc. Natl. Acad. Sci. USA, 81, 1696-1700. Hakura, A., H. Mochida, Y. Tsutsui, and K. Yamatsu (1994) Mutagenicity and cytotoxicity of naphthoquinones for Ames Salmonella tester strains. Chem. Res. Toxicol., 7, 559-567. Maron, D.M. and B.N. Ames (1983) Revised methods for the Salmonella mutagenicity test. Mutation Res., 113, 173-215. Hakura, A., H. Mochida, Y. Tsutsui, and K. Yamatsu (1995) Mutagenicity of benzoquinones for Ames Salmonella tester strains. Mutation Res., 347. 37-43. Levin, D.E., M. Hollstein, M.F. Christman, E,A. Schwiers, and B.N. Ames (1982) A new Salmonella tester strain (TA102) with A • T base pairs at the site of mutation detects oxidative mutagens. Proc. Natl. Acad. Sci. USA, 79, 74457449. Walker, G.C. (1985) Inducible DNA repair systems. Annu. Rev. Biochem., 54, 425-457. Perry, K.L., S.J. Elledge, B.B. Mitchell, L. Marsh, and G.C. Walker (1985) UmuDC and mucAB operons whose products are required for UV light- and chemical-induced mutagene-

[15]

[16]

[17]

[18]

[19]

299

sis: UmuD, MucA, and LexA proteins share homology. Proc. Natl. Acad. Sci. USA, 82, 4331-4335. Leanderson, P. and C. Tagesson (1990) Cigarette smoke-induced DNA-damage: role of hydroquinone and catechol on the formation of the oxidative DNA-adduct, 8-hydroxydeoxyguanosine. Chem.-Biol. Interact., 75, 71-81. Li, Y. and M.A. Trush (1993) DNA damage resulting from the oxidation of hydroquinone by copper: role for a Cu(lI)/Cu(I) redox cycle and reactive oxygen generation. Carcinogenesis, 14, 1303-1311. Li, Y., P. Kuppusamy, J.L. Zweier, and M.A. Trush (1995) ESR evidence for the generation of reactive oxygen species from the copper-mediated oxidation of the benzene metabolite, hydroquinone: role in DNA damage. Chem.-Biol. Interact., 94, 101-120. Levin, D.E., L.J. Marnett and B.N. Ames (1984) Spontaneous and mutagen-induced deletions: mechanistic studies in Salmonella tester strain TAI02. Proc. Natl. Acad. Sci. USA, 81, 4457-4461. Han, J. (1992) Effects of various chemical compounds on spontaneous and hydrogen peroxide-induced reversion in strain TAI04 of Salmonella ~.,phimurium. Mutation Res., 266, 77-84.