Abstract
Bracken fern (genus Pteridium) is the only plant known to cause cancer naturally in animals. In addition to the well recognised syndromes of thiamine deficiency, acute haemorrhage associated with myeloid aplasia and blindness due to retinal degeneration, it causes neoplasia of urinary bladder and in some circumstances oesophagus origin. In addition, it has been shown to cause neoplasia in a wide range of tissues in many experimental species. The major carcinogen has been shown to be ptaquiloside (PT), a norsesquiterpene glucoside that can be present in bracken in extraordinary concentrations, up to 13000 ppm. The highest concentrations were found in the crosiers and young fronds. The mutagenicity, clastogenicity, tetratogenicity and carcinogenicity of PT have been convincingly demonstrated. Under alkaline conditions the loss of the glucose give rise to the formation of a dienone intermediate which possess a highly reactive cyclopropyl ring capable of reacting with cellular macromolecules. Pt has been shown to alkylate DNA at N3 of adenines in the minor groove, preferentially in 5′‐TAG and 3′‐A in 5′‐AA‐3′ sequences. It also alkylates N7 guanines in the major groove occurring in 5′‐TG sequences. It is believed that these alkylation lead to mismatch repair and subsequent mutations in particular proto‐oncogene. Recently a rat model of carcinogenesis has been established using intravenously administrated PT. Some epidemiological evidence has indicated higher risk of cancer in people who consume bracken fern crosiers, people who consume milk of cows feeding on bracken and those live in bracken‐infested areas. PT has been found in the milk of cows fed on bracken fern experimentally and the milk of bracken fed cows has been shown to cancer in rats. PT carcinogenesis presents an excellent model of environmental carcinogenesis. More recently it has been found that immunosuppressive effects of bracken fern (P. aquilinum) and that many of the functions that were modulated could contribute to the increased risk of cancer formation in exposed hosts.
Citation Information: Cancer Prev Res 2010;3(1 Suppl):A36.
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