Anti-mutagenic lichen extract has double-edged effect on azoxymethane-induced colorectal oncogenesis in C57BL/6J mice

Abstract

This study compared the effects of three anti-mutagenic lichen extracts on colorectal oncogenesis in azoxymethane (AOM)-treated mice and determined whether the extracts also regulated the homeostatic response to genotoxic damage. C57BL/6J mice (n = 12 per group) were treated with the lichen extracts Antimutagen-He (AMH): AMH-C, AMH-D, or AMH-E dimethyl sulfoxide (DMSO, control) for 2 weeks. At the end of the treatment, mice were given a single AOM injection to induce DNA damage and killed 6 h later for measuring apoptosis and proliferation. Apoptotic and proliferation indexes in mice treated with AMH-C, AMH-D, and AMH-E were 0.61%, 1.41%, and 0.77%; and 30.62%, 21.93%, and 27.27%, respectively, which were significantly lower than those of control mice (5.88% and 38.69%) (p < 0.05). To examine the effects of lichen extracts on colorectal cancer, separate groups of mice (n = 25 per group) treated with AMH-C, AMH-D, AMH-E, or DMSO were given 4-weekly AOM injections to induce oncogenesis. Mice were killed 24 weeks after the last AOM injection for assessing colon tumor formation. Colonic tumor incidences were 47.3%, 13%, and 20%; the tumor volumes were 18.47, 2.75, and 10.78 mm³, respectively, in mice treated with AMH-C (p < 0.05), AMH-D (p < 0.05), and AMH-E (p > 0.05), compared to 24% and 13.28 mm³ in mice of control correspondingly. No lichen extract showed evident toxic effects on mice. No usnic acid was found in these lichen extracts. The regulation of acute apoptosis and cell proliferation in colonic epithelial cells and the anti-mutagenesis do not seem directly related to the cancer protective effect.

Keywords::

• Lichen extract
• apoptosis
• cell proliferation
• colon tumor
• anti-mutagenesis

Acknowledgements

This study was supported by the Gastroenterology Department, Flinders Medical Centre, South Australia. The authors thank Dr David Smolilo and Mrs Olga Pennino for technical assistance. A special acknowledgement goes to the government of Yunnan Province, China for the scholarship of the first author in Australia.