Strong anti-mutagenic activity of the novel lipophilic antioxidant 1-O-hexyl-2,3,5-trimethylhydroquinone against heterocyclic amine-induced mutagenesis in the Ames assay and its effect on metabolic activation of 2-Amino-6-methyldipyrido[1,2-a:3′, 2′-d]imidazole (Glu-P-1)

Abstract

Antimutagenic effects of a novel lipophilic antioxidant, 1-O-hexyl-2,3,5-trimethylhydroquinone (HTHQ), and other known antioxidants against heterocyclic amine- or other mutagen-induced mutagenesis were examined in the Ames assay using Salmonella strain TA 98 to access the chemo-preventive effects of antioxidants on heterocyclic amine-induced carcinogenesis. Further the mechanisms of inhibition by HTHQ were accessed. HTHQ was shown to potently inhibit mutagenesis induced by all of 8 different heterocyclic amines at rates between 100% and 63% in the presence of S9 mix. When the protection of HTHQ against 2-amino-6- methyldipyrido[1,2-alpha:3',2'-d]imidazole (Glu-P-1)-induced mutagenesis was compared with known antioxidants t-butylhydroquinone, propyl gallate, BHA, BHT and alpha-tocopherol, HTHQ showed the greatest effect. Among hexyl, butyl, ethyl and methyl derivatives of 1-O-alkyl-2,3,5-trimethylhydroquinone, HTHQ was the most effective in inhibiting Glu-P-1-, 3-amino-1-methyl-5-H-pyrido[4,3-b]indole (Trp-P-2)- or 2-amino-3-methylimidazo[4,5-f]quinoline (IQ)-induced mutagenesis. On the other hand, HTHQ did not inhibit mutagenic activity induced by other mutagens such as N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), 2-(2-furyl)-3-(5-nitro-2-furyl)acrylamide (AF-2) and benzo[a]pyrene. HTHQ weakly inhibited that due to direct mutagen 2-nitro derivative of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) only in the presence of S9 mix. No such influence on a 2-nitro derivative of 2-amino-3,4-dimethylimidazo[4,5-f]quinoline (MeIQ) or 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-induced mutagenesis, was observed with or without the S9 mix. HTHQ slightly inhibited mutagenesis induced by activated Glu-P-1, a direct acting proximate metabolite of Glu-P-1, in the absence of the S9 mix. HPLC analysis revealed activated Glu-P-1 to be formed by incubating Glu-P-1 with the S9 mix, but this was considerably decreased by the addition of HTHQ. These results indicate that HTHQ is a powerful antimutagenic compound and specifically acts against heterocyclic amines. Its antimutagenic activity appeared to exert by both inhibiting metabolic activation of heterocyclic amines and action on activated N-hydroxy species.

Dose Dependence of 1‐O‐Hexyl‐2,3,5‐trimethylhydroquinone Promotion of Forestomach Carcinogenesis in Rats Pretreated with N‐Ethylnitrosourethane

“…HTHQ has the highest anti-mutagenic activity against Glu-P-1-induced mutagenesis 2) and chemopreventive effect against MeIQx-induced hepatocarcinogenesis among HTHQ, BHA, BHT, TBHQ, propyl gallate and α-tocopherol (unpublished results). In addition HTHQ inhibits colon 6) and mammary carcinogenesis 5) when given in the post-initiation stage in multi-organ and DMBA models, respectively.…”

“…2) In in vivo animal experiments, it potently reduced both the multiplicity and the area of 2-amino-6-methyldipyrido[1,2-a:3′,2′-d]imidazole (Glu-P-1)-or 2-amino-3,8-dimethylimidazo [4,5-f]quinoxaline (MeIQx)-induced liver glutathione S-transferase placental form-positive foci in our in vivo medium term liver bioassay system, 3) indicating that HTHQ inhibits MeIQx-and Glu-P-1-induced hepatocarcinogenesis. HTHQ also inhibits 2-amino-1-methyl-6-phenylimidazo [4,5-b]pyridine (PhIP)-induced mammary carcinogenesis when given together with PhIP, 4) and 7,12-dimethylbenz(a)anthracene (DMBA)-initiated mammary carcinogenesis in the postinitiation stage in female Sprague-Dawley rats.…”

Structure Antimutagenicity Relationship of Anthraquinones

“…The quinoidic metabolites of butylated hydroxyanisole were active against Trp-P-2 [66]. Moreover, 1-O-hexyl-2,3,5-trimethylhydroquinone and derivatives with other alkyl substituents were active against eight HAAs [67,68].…”

Mechanism of Oxidative DNA Damage Induced by a Heterocyclic Amine, 2‐Amino‐3,8‐dimethylimidazo[4,5‐f]quinoxaline

“…12) On the other hand, it has been reported that several antioxidants [13][14][15] significantly inhibited MeIQx-induced hepatocarcinogenesis in rats. Kato et al.…”

“…That is, MeIQx is oxidized to the N-hydroxy derivative [MeIQx(NHOH)] in the liver by cytochrome P450 IA2 isozyme, and the latter is esterified by O-acetyltransferase to the N-acetoxy derivative, which reacts with DNA to form adducts. 10,11) DNA adducts generated by MeIQx were found in vitro and in vivo by means of the 32 P-postlabeling method.12) On the other hand, it has been reported that several antioxidants [13][14][15] significantly inhibited MeIQx-induced hepatocarcinogenesis in rats. Kato et al.…”