Tokutaro Miki

Effects of 1‐O‐hexyl‐2,3,5‐trimethylhydroquinone on carbon tetrachloride‐induced hepatic cirrhosis in rats

Aim:  The present study was undertaken to evaluate the effects of 1‐O‐hexyl‐2,3,5‐trimethylhydroquinone (HTHQ), a synthesized vitamin E derivative, on carbon tetrachloride (CCl4)‐induced cirrhosis.

Stage and organ dependent effects of 1‐ O‐hexyl‐2,3,5‐trimethylhydroquinone, ascorbic acid derivatives, N‐heptadecane‐8,10‐dione and phenylethyl isothiocyanate in a rat multiorgan carcinogenesis model

The effects of 1‐O‐hexyl‐2,3,5‐trimethylhydroquinone (HTHQ), phenylethyl isothiocyanate (PEITC), 3‐O‐ethylascorbic acid, 3‐O‐dodecylcarbomethylascorbic acid and n‐heptadecane‐8,10‐dione were analyzed in a rat multiorgan carcinogenesis model. Groups of 15 animals were given a single intraperitoneal (i.p.) injection of diethylnitrosamine and 4 i.p. injections of N‐methylnitrosourea as well as N‐butyl‐N‐(4‐hydroxybutyl)nitrosamine in the drinking water during the first 2 weeks. Then 4 subcutaneous (s.c.) injections of dimethylhydrazine and 2,2′‐dihydroxy‐di‐n‐propylnitrosamine were given in the drinking water over the next 2 weeks for initiation. Test compounds were administered during the initiation or post‐initiation periods. The dietary dose was 1% except for n‐heptadecane‐8,10‐dione and PEITC (0.1%). Complete autopsy was performed at the end of experimental week 28. All 5 compounds reduced the number of lung hyperplasia, particularly PEITC when given during the initiation period. In addition, HTHQ lowered the incidence of esophageal hyperplasia in the initiation period, and of small and large intestinal adenomas in the post‐initiation period. However, it also enhanced the development of hyperplasia and papilloma in the forestomach and tongue. PEITC lowered the induction of esophageal hyperplasia, kidney atypical tubules and liver glutathione S‐transferase placental form (GST‐P)‐positive foci when given during the initiation period but enhanced the development of liver GST‐P positive foci and urinary bladder tumors in the post‐initiation period. Moreover, it induced hyperplasia of the urinary bladder. Our results indicate minor adverse effects for HTHQ in the forestomach and tongue, and demonstrate that PEITC, which inhibits carcinogenesis at the initiation stage in several organs, also exhibits promotion potential in liver and urinary bladder in the post‐initiation stage under the present experimental conditions. Int. J. Cancer 76:851–856, 1998.© 1998 Wiley‐Liss, Inc.

Prevention by synthetic phenolic antioxidants of 2-amino-3,8-dimethylimidazo[4,5- f ]quinoxaline (meiqx)- or activated Melqx-induced mutagenesis and Melqx-induced rat hepatocarcinogenesis, and role of antioxidant activity in the prevention of carcinogenesis

Effects of synthetic phenolic antioxidants l-O-hexyl-2,3,5-trimethylhydroquinone (HTHQ), butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), tert-butylhydroquinone (TBHQ) and propyl gallate (PG) on 2-amino-3,8-dimethylimidazo[4,5-F]quinoxaline (MelQx)- or activated MelQx-induced mutagenesis and rat hepatocarcinogenesis were compared, and the association between antioxidative activity and inhibition of carcinogenesis was examined. When the antimutagenic activity of five antioxidants against MelQx- or activated MelQx-induced mutagenesis was compared in the Ames assay using the Salmonella strain TA 98, HTHQ showed the greatest effect, followed by BHA, BHT, PG and TBHQ, in that order. In a rat hepatocarcinogenesis study, 6-week-old male F344 rats were given a single ip injection of 200 mg/kg bw of diethylnitrosamine (DEN) and starting 2 weeks later, groups of 15 animals received a diet containing 0.03% MelQx alone, MelQx together with each antioxidant at a dietary dose of 0.25%, each antioxidant alone, or basal diet alone for 6 weeks. Three weeks after the DEN injection, animals were subjected to 2/3 partial hepatectomy. Liver tissues obtained at partial hepatectomy were processed for the measurement of 8-hydroxydeoxyguanine (8-OHdG) and lipid peroxidation. The average number and areas of glutathione 5-transferase placenta! form (GST-P) positive foci were increased by the treatment with MelQx (27.2 ± 6.5 per cm2 and 3.17 ± 0.96 mm2/cm2, respectively). A significant decrease in these parameters was found with the simultaneous antioxidant treatment, HTHQ demonstrating the greatest effect, followed by BHA, BHT and TBHQ, and PG. Without MelQx, a weak increase in the number of foci was observed in the BHT treatment case. Examination of 8-OHdG levels in liver DNA, as well as malondialdehyde (MDA) and 4-hydroxyalkenals, did not reveal any inter-group variation. These results indicate that antimutagenic activity of antioxidants against MelQx roughly parallels their anticarcinogenic activity, with HTHQ as the most powerful chemopreventor, but that oxidative stress and antioxidative activity may not be responsible for MelQx-induced hepatocarcinogenesis and its inhibition, respectively

Effects of Antioxidant 1-O-Hexyl-2,3,5-trimethylhydroquinone or Ascorbic Acid on Carcinogenesis Induced by Administration of Aminopyrine and Sodium Nitrite in a Rat Multi-organ Carcinogenesis Model

The effect of antioxidant, 0.25% 1‐O‐hexyl‐2,3,5‐trimethylhydroquinone (HTHQ) or 0.25% ascorbic acid (AsA), on Carcinogenesis induced by administration of 0.05% aminopyrine (AP) and 0.05% sodium nitrite (NaNO2), was examined using a rat multi‐organ carcinogenesis model. Groups of twenty F344 male rats were treated sequentially with an initiation regimen of N‐diethylnitrosamine, N‐methyl‐N‐nitrosourea, N‐butyl‐N‐(4‐hydroxybutyl) nitrosamine, N, N′‐dimethylhydrazine and 2,2′‐dihydroxy‐di‐n‐propylnitrosamine during the first 4 weeks, followed by AP+NaNO2, AP+NaNO2+HTHQ, AP+NaNO2+AsA, NaNO2+HTHQ, NaNO2+AsA, each of the individual chemicals alone or basal diet and tap water as a control. All surviving animals were killed at week 28, and major organs were examined histopathologically for development of preneoplastic and neoplastic lesions. In the AP+NaNO2 group, the incidences of hepatocelluar adenomas and hemangiosarcomas were 95% and 35%, respectively. When HTHQ or AsA was simultaneously administered, the incidences decreased to 58% and 11%, or to 80% and 15%, respectively. On the other hand, in the AP+NaNO2 group and the NaNO2‐alone group, when HTHQ, but not AsA, was simultaneously administered, the incidence of carcinomas in the forestomach significantly increased. The results suggest that HTHQ can prevent tumor production induced by AP and NaNO2 more effectively than AsA. On the other hand, an enhancing or possible carcinogenic effect of simultaneous administration of HTHQ and NaNO2 only on the forestomach is suggested, while simultaneous treatment with the same dose of AsA and NaNO2 may not be carcinogenic to the fore‐stomach or other organs.

Prevention of Chemically Induced Rat Carcinogenesis by Antioxidants: Focus on HTHQ

The novel lipophilic phenolic antioxidant 1-O-hexyl-2,3,5-trimethylhydroquinone (HTHQ) possesses the strongest potential for inhibiting lipid peroxidation in liver microsomes among known antioxidants including butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl gallate, t-butylhydroquinone (TBHQ), and α-tocopherol. Its antimutagenic activity against 2-amino-6-methyldipyrido[1,2-a:3′,2′-d] imidazole (Glu-P-1), as evaluated in the Ames assay, was also found to be stronger than those of other antioxidants. In addition to these in vitro effects, HTHQ is known to potently inhibit Glu-P-1- or 2-amino-3,8-dimethyl-imidazo[4,5-f]quinoxaline (MeIQx)-induced hepatocarcinogenesis and 2-amino-l-methy-6-phenylimidazo [4,5,-f]pyridine (PhIP)-induced mammary carcinogenesis in rats. Inhibition of metabolic activation, inactivation of proximate carcinogenic species, and possibly inhibition of free radical formation may be involved in the mechanisms underlying inhibition of mutagenesis/carcinogenesis by HTHQ. Similar to other antioxidants that stimulate detoxification pathways, it induces phase II enzymes and increases the glutathione content in rat liver. Although antioxidants may enhance or inhibit carcinogenesis when given in the promotion stage depending on the organ site and dose applied, the only such adverse effect of HTHQ is slight enhancement of forestomach lesion development. Considering that humans do not have a forestomach and that the estimated effective dose for inhibition of heterocyclic amine (HCA)-induced carcinogenesis in humans is low (<10mg/day), we conclude that HTHQ is a promising chemopreventive agent that could find application against environmental carcinogen-associated neoplasia.

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

Post‐initiation dose‐dependent effects of the chemopreventive antioxidant 1‐O‐hexyl‐2,3,5‐trimethylhydroquinone (HTHQ), a potent inhibitor of heterocyclic amine‐induced mutagenesis and carcinogenesis, on the development of forestomach and tongue tumors were investigated in male F344 rats. Groups of 22 rats were treated with 0.01% ethylnitrosourethane (ENUR) as an initiator in the drinking water for 4 weeks, then placed on diet containing 1.0%, 0.5%, 0.25% or 0.125% HTHQ, or basal diet alone for 36 weeks. Further groups of 12 rats each were similarly treated with the different doses of HTHQ or given basal diet alone for 36 weeks without prior ENUR treatment. All animals were killed at week 40. Tongue papillary hyperplasia and papillomas tended to be increased in the groups treated with ENUR followed by 0.5–0.125% HTHQ, though there was no effect at the highest dose, in line with increased bromodeoxyuridine labeling indices. In the forestomach, the incidences of papillomas and carcinomas were also significantly elevated only in the group treated with ENUR followed by 0.125% HTHQ. Without ENUR pretreatment, papillary hyperplasia was found in the 1–0.125% HTHQ groups and the labeling index was also increased, though without clear dose dependence. The results indicate that HTHQ may have very weak or weak promotion potential for tongue and forestomach carcinogenesis, but that both minimum and maximum thresholds for active dose levels may exist.