Prevention of N-methylnitrosourea-induced colon carcinogenesis in F344 rats by lycopene and tomato juice rich in lycopene.

Epidemiological studies have suggested a protective effect of lycopene and lycopene-rich tomatoes against various cancers. Here, the inhibition of colon carcinogenesis by lycopene and tomato juice was investigated. Seven-week-old female F344/NSlc rats received an intrarectal dose of 2 mg (experiment I) or 4 mg (experiment II) of N-methylnitrosourea 3 times a week for 3 weeks, and had free access to one of 4 drinking fluids: plain water (control group), 17 ppm lycopene water solution (Ly group), and diluted tomato juice containing 17 ppm (Tj group) or 3.4 ppm (tj group) lycopene, throughout the experiments. The colon cancer incidence at week 35 was significantly lower in the Tj group, but not in the Ly group, than in the control group: 21% and 33% vs. 54%, in experiment I (24 rats in each group). It was significantly lower in the Tj group than in the tj and control groups, 40% vs. 72% and 84%, in experiment II (25 rats in each group). An appreciable amount of lycopene (0.02 microgram/g) was detected in the colon mucosa of rats in the Tj group, but not in the tj group. The results suggest that tomato juice rich in lycopene may have a protective effect against colon carcinogenesis.