Biphasic modifying effect of indole-3-carbinol on diethylnitrosamine-induced preneoplastic glutathione S-transferase placental form-positive liver cell foci in Sprague-Dawley rats

The biphasic modifying effects of indole-3-carbinol (I3C), a naturally occurring constituent of edible cruciferous vegetables, on the development of glutathione S-transferase placental form (GST-P)-positive liver cell foci were investigated by using a medium-term liver bioassay system and a newborn rat hepatocarcinogenesis system. In Experiment 1, a total of 65 male Sprague-Dawley (SD) rats were divided into 5 groups. Animals were given a single intraperitoneal (i.p.) injection of 200 mg/kg diethylnitrosamine (DEN) dissolved in saline for groups 1, 2, and 3 or a single i.p. injection of saline for groups 4 and 5. Group 1 was given the diet containing 0.25% I3C for 2 weeks prior to DEN initiation and then basal diet for 8 weeks. Group 2 was given basal diet for 4 weeks prior to and after DEN initiation and then the diet containing 0.25% I3C for 6 weeks. The rats of group 3 were placed on basal diet during the experiment. Animals of groups 4 and 5 were treated in the same manner as those of groups 1 and 2 except for injection with saline instead of DEN solution. All rats were subjected to two-thirds partial hepatectomy at week 3 and were killed at week 8 after DEN or saline injection. In Experiment 2, a total of 45 female SD rats were dosed with DEN (100 mg/kg, i.p.) or saline at 24 h after birth. After weaning at week 3, the rats were fed diet containing 0.25% I3C for 9 weeks and then were killed at week 12. In Experiment 1, preinitiation exposure to 0.25% I3C caused a significant decrease in numbers of GST-P-positive liver cell foci (P < 0.05), while postinitiation exposure to 0.25% I3C caused significant increases in both number (No./cm2) and area (mm2/cm2) of GST-P-positive liver cell foci (P < 0.05 or 0.01). In Experiment 2, the relative liver weight in the DEN + I3C group was significantly increased (P < 0.001). The numbers and areas of GST-P-positive liver cell foci in the DEN + I3C group were significantly increased as compared to the values of the DEN-alone group (P < 0.001). These results clearly demonstrated that I3C exerts a promoting effect on the postinitiation stage as well as an inhibitory effect on the preinitiation stage in the medium-term liver bioassay.

Inhibitory effects of the natural products indole-3-carbinol and sinigrin during initiation and promotion phases of 4-nitroquinoline 1-oxide-induced rat tongue carcinogenesis

The modifying effects of indole-3-carbinol (I3C) and sinigrin (SIN) on the initiation and post-initiation phases of tongue carcinogenesis induced by 4-nitroquinoline 1-oxide (4-NQO) were investigated in male ACI/N rats. Rats were divided into eight groups: group 1 was given 4-NQO (10 ppm) in the drinking water for 12 weeks, starting at 7 weeks of age; groups 2 and 3 were given 4-NQO and fed the diets containing I3C (1,000 ppm) and SIN (1,200 ppm) for 14 weeks, respectively, starting at 6 weeks of age; groups 4 and 5 were given 4-NQO and then they were fed I3C and SIN containing diets for 23 weeks, respectively, starting one week after 4-NQO exposure; groups 6 and 7 were given I3C and SIN alone, respectively, during the experiment; group 8 served as an untreated control. At the termination of the experiment (week 37), the incidence of tongue neoplasms (squamous cell papilloma and carcinoma) in group 2 (1/15, 7%), group 3 (1/15, 7%), group 4 (3/15, 20%) or group 5 (2/15, 13%) was significantly smaller than that in group 1 (12/17, 71%) (P = 0.0003, P = 0.005 or P = 0.002). No tongue carcinomas developed in rats of groups 2, 3, and 5. Similarly, the incidence of preneoplastic lesions (hyperplasia and dysplasia) of the tongue in group 2 (11/15, 73%), group 3 (10/15, 67%), group 4 (11/15, 73%) or group 5 (10/15, 67%) was significantly lower than that in group 1 (17/17, 100%) (P = 0.04 or P = 0.02). There were no tongue neoplasms in rats of groups 6, 7, and 8. Administration of I3C and SIN also caused significant decreases in the number and area of silver-stained nucleolar organizer regions protein (AgNORs), a new cell proliferation index, of tongue squamous epithelium. Thus, I3C and SIN inhibited rat tongue carcinogenesis in both the initiation and post-initiation phases, when administered in these respective phases together with, or following treatment with, 4-NQO.