Background:

Senna is a plant product used in laxatives. We tested senna in a genetically modified mouse strain that shows tumor responses more rapidly than in standard mouse strains.

Methods:

We gave groups of male or female heterozygous F1 p53^+/− mice feed that contained senna plant material at concentrations of 100, 300, 1,000, 3,000, or 10,000 parts per million for 40 weeks. Tissues from 22 organs were examined for every animal.

Results:

Epithelial hyperplasia of the large intestine was seen in all the mice receiving the top dose of 10,000 ppm (1%) senna in the feed. The incidences of cancer were not significantly increased in any of the tissues examined.

Conclusions:

We conclude that senna caused epithelial hyperplasia of the large intestine in male and female F1 p53^+/− mice. Senna exposure for 40 weeks did not cause any cancers in this mouse strain.

5-Week Study in C57BL/6NTac Mice:

Groups of five male and five female mice were exposed to 0, 625, 1,250, 2,500, 5,000, or 10,000 ppm senna (equivalent to average daily doses of approximately 115, 245, 490, 975, or 2,075 mg senna/kg body weight to males and 160, 310, 625, 1,190, or 2,570 mg/kg to females) in feed for 5 weeks. All mice survived to the end of the study. Mean body weights of exposed groups were similar to those of the controls. No differences in feed consumption were noted between exposed and control groups. Significantly increased incidences of epithelial hyperplasia of the cecum occurred in males exposed to 10,000 ppm and females exposed to 5,000 or 10,000 ppm; significantly increased incidences of epithelial hyperplasia of the colon occurred in males and females exposed to 5,000 or 10,000 ppm.

40-Week Study in Heterozygous F1 p53^+/− Mice:

Groups of 25 male and 25 female mice were exposed to 0, 100, 300, 1,000, 3,000, or 10,000 ppm senna (equivalent to average daily doses of approximately 12, 36, 120, 365, or 1,260 mg/kg to males and 14, 42, 140, 435, or 1,520 mg/kg to females) in feed for 40 weeks. Mean body weights of exposed male and female mice were within 10% of those of the controls throughout the study. Feed consumption by exposed mice was generally similar to that by the controls.

Significant increases in the incidences of epithelial hyperplasia of the colon and cecum occurred in 10,000 ppm males and females, and the incidence of epithelial hyperplasia of the colon was significantly increased in 3,000 ppm females.

Genetic Toxicology:

Four different samples of senna, including three samples of the same lot that was used in the 40-week study were tested for mutagenicity in bacterial test systems. In two samples, no evidence of mutagenicity was seen in several strains of S. typhimurium and E. coli, with or without exogenous metabolic activation. In the other two samples, mutagenic activity was seen in S. typhimurium strains TA98 and TA100, with variable requirements for exogenous metabolic activation.

In addition to senna, the NTP also tested rhein (a component of senna) for mutagenicity in S. typhimurium strains TA98 and TA100; dose-related increases in mutant colonies were seen with both strains in the presence of rat or hamster liver S9, at lower concentrations than were required for the positive responses seen with senna samples. Another component of senna, chrysophanic acid, was tested for mutagenicity in TA98, TA100, and TA1535; weak and inconsistent responses were seen in TA100 with rat and hamster liver S9. Sennosides A and B were also tested for mutagenicity in bacterial test systems; neither compound was mutagenic, with or without S9 metabolic activation.

In vivo, no increases in the frequencies of micro-nucleated erythrocytes were seen in male mice exposed for 40 weeks to senna via dosed feed. No significant changes in the percentage of reticulocytes among erythrocytes were observed in male mice, suggesting that exposure to senna did not induce bone marrow toxicity.

Conclusions:

Under the conditions of this 40-week feed study, there was no evidence of carcinogenic activity^* of senna in male or female C3B6.129F1/Tac-Trp53^tm1Brd N12 haploinsufficient mice exposed to 100, 300, 1,000, 3,000, or 10,000 ppm.

Senna induced epithelial hyperplasia of the large intestine (colon and cecum) in male and female mice.