Abstract for TR-235

A carcinogenesis bioassay of zearalenone, an estrogenic mycotoxin, was conducted by feeding diets containing 25 or 50 ppm zearalenone to groups of 50 F344/N rats of each sex and 50 or 100 ppm to groups of 50 B6C3F1 mice of each sex for 103 weeks. Groups of 50 rats and 50 mice of each sex served as controls. Estimates based on food consumption data indicate that the low-and high-dose rats received daily doses of about 1 and 2 mg, respectively, of zearalenone per kg of body weight. Low-dose and high-dose mice received estimated daily doses of about 7-10 and 14-20 mg, respectively, of zearalenone per kg of body weight.

Survival of dosed and control rats of each sex was comparable. Mean body weight gains of dosed rats of each sex were lower than those of the corresponding controls; depression in mean body weight gain was dose related. Final body weights of dosed rats were <9% lower than those of control rats. The average daily feed consumption of dosed rats of each sex was 91%-102% that of controls.

Inflammation of the prostate, testicular atrophy, and hepatocellular cytoplasmic vacuolization (male rats), and nephrosis (male and female rats) were compound-related. Retinopathy and cataracts occurred in low-and high-dose male rats and in low-dose female rats, and were associated with the closeness to fluorescent light. No compound-related, increased tumor incidences were observed in rats in the chronic study.

Survival of dosed and control mice of each sex was comparable. Mean body weight gains of high-dose male and low-dose female mice were lower than those of the controls. Terminal body weights of dosed mice were <8% below those of control mice. The average daily feed consumption by dosed mice of each sex was 97-99% that of the controls.

Myelofibrosis in the bone marrow, uterine fibrosis, and cystic ducts in the mammary gland were related to the administration of zearalenone in female mice. The incidence of hepatocellular adenomas in female mice was dose related (P<0.003), and the incidence of these tumors in high-dose female mice was significantly higher (P<0.006) than those in the controls (control, 0/50; low-dose, 2/49; high-dose, 7/49). Pituitary adenomas occurred with statistically significant positive trends (P<0.022 for males and P<0.001 for females). The incidences of these tumors in high-dose mice were significantly increased relative to controls (P<0.032 for males: 0/40, 4/45, 6/44; and P<0.003 for females: 3/46, 2/43, 13/42).

Under the conditions of this bioassay, zearalenone was not carcinogenic for F344/N rats of either sex. Zearalenone should be considered carcinogenic in B6C3F1 mice, as evidenced by the increased proportion of male and female mice with pituitary adenomas and by the increased proportion of female mice with hepatocellular adenomas.