Promutagen activation in partially hepatectomized mice

Infection of rats with Taenia taeniformis metacestodes increases hepatic CYP450, induces the activity of CYP1A1, CYP2B1 and COH isoforms and increases the genotoxicity of the procarcinogens benzo[a]pyrene, cyclophosphamide and aflatoxin B(1)

Infection of rat liver by Taenia taeniformis metacestodes produced an increase in total CYP450 content and induced activity of the CYP1A1, CYP2B1 and COH isoforms. Variations in activity and p450 total content were found with increasing time of infection. During increased activity of p450 isoforms, rats were challenged with carcinogens metabolized by the mentioned isozymes and an increased amount of genotoxic damage was found when benzo[a] pyrene, cyclophosphamide and aflatoxin B(1) were used. No change was seen in CYP2E1 activity. These results support previous findings regarding an increased susceptibility to genotoxic damage of infected organisms.

Analysis of lacI mutations in Big Blue transgenic mice subjected to parasite-induced inflammation

Parasite infections have long been associated with specific types of human cancers. Schistosoma hematobium is an inducer of urinary bladder cancer, Helicobacter pylori is a gastric carcinogen, and hepatitis B virus and Opisthorchis viverrini are causative agents of hepatocellular carcinoma. Another liver fluke, Fasciola hepatica, has also been identified as a neoplastic risk agent, primarily in animals. We used F. hepatica-induced inflammation in mice to determine if the presence of an aggressive liver fluke could induce mutagenic events in mammalian tissue. This provides a perspective on the relationship between chronic inflammation and cancer and may be a model for future studies on this complex association. In previous studies using the Big Blue transgenic mouse assay, we demonstrated an increase in lacI mutations in liver cells harvested from mice harboring F. hepatica flukes when compared to uninfected control animals. In these studies, we report on the types of mutations associated with this parasite infection. The observed mutational spectrum roughly corresponded to the spectrum of spontaneous mutations in liver cells when compared to control (uninfected) animals. However, the spectrum of mutations from parasitized animals showed a significant increase in complex changes and multiple mutations (18.2%) when compared to what would be expected from control animals (2.8%).

Enhanced liver cell mutations in trematode-infected Big Blue transgenic mice

Parasite infections in humans have long been associated with specific types of cancers. Schistosoma hematobium is a known inducer of urinary bladder cancer, Helicobacter pylori is a gastric carcinogen, and hepatitis B virus and Opisthorchis viverrini are causative agents of liver cell cancers. Another liver fluke, Fasciola hepatica, has also been identified as a neoplastic risk agent, primarily in animals. We used F. hepatica as a model agent to determine if the presence of an aggressive liver fluke could induce mutagenic events in mammalian tissue. Using the Big Blue(R) transgenic mouse assay, we found a two-fold increase in lacI mutations in cells harvested from mice harboring F. hepatica worms when compared to uninfected control animals. These data indicate that biological infections can cause increased genetic damage in surrounding host tissue.

Implications for the involvement of the immune system in parasite-associated cancers

Biological factors can be carcinogenic risk factors in humans and in animals. Numerous theories have been developed to explain the causal link between biologically-associated disease and the ensuing neoplasia. In this paper we discuss the merits of one of these theories, the possible association between the mammalian inflammatory response and cancer.

Schistosome related cancers: a possible role for genotoxins

Schistosomiasis has long been associated with cancer. This association is most prevalent between Schistosoma hematobium and bladder cancer. Numerous theories have been proposed to explain the causal link between the parasite infestation and the ensuing neoplasia. One theory that has not received as much attention as others, however, is the role of genotoxins in the neoplastic process. Considering the substantial amount of supportive evidence for the cocarcinogenic effects of schistosomes, concern for the health effects resulting from exposure of infested individuals to either exogenous or endogenous genotoxins is certainly warranted.

Modified mutagen metabolism in Schistosoma hematobium-infested organisms

The relationship between parasite infestation and chemical mutagen metabolism was investigated in this study. Schistosoma hematobium, long associated with increased incidence of bladder cancer in humans, was chosen as a model parasite. Urine samples, serum samples, and liver tissue extracts (S-9) from infested and control hamsters were used with the Ames Salmonella/microsome test to follow 3,3'-dichlorobenzidine (DCB), aflatoxin B1 (AFB1), and 2-acetylaminofluorene (AAF) mutagenicity. Liver S-9 preparations from infested and control hamsters showed little difference in activation potential for DCB and AFB1. Aroclor 1254-induced rat liver S-9, however, was remarkably efficient at reducing the mutagenicity of DCB. This process was reversible by beta-glucuronidase (BG). Studies on infested and control hamsters indicated increased BG activity in serum and urine. Urine concentrates (UC) from infested and control animals were not mutagenic by themselves, but did enhance the mutagenicity of AAF and DCB in the presence of S-9 and BG. Urine concentrates from infested animals showed greater enhancement of DCB mutagenicity than did UC from control animals. These data suggest that increased BG and unknown urinary factors in infested hamsters play a role in altering chemical mutagen activity.