Ptaquiloside-induced, B-cell lymphoproliferative and early-stage urothelial lesions in mice

Bracken (Pteridium aquilinum) has long been known to cause cancer in farm and laboratory animals. Ptaquiloside, a norsesquiterpene glycoside found in bracken, is considered its main carcinogenic toxin and is capable of inducing tumours in a variety of organ systems, but especially in the urinary bladder, depending on the animal species, the administration route employed and the duration of exposure. In the present study, 12 male CD-1 mice were intraperitoneally administered with 0.5 mg ptaquiloside weekly for 15 weeks, followed by 15 weeks without any treatment. Twelve animals used as controls were administered the vehicle solution (phosphate buffered saline). Two exposed animals died during the experimental work. On necropsy, blood and tissue samples (brain, eyes, thymus, heart, lungs, liver, digestive system, spleen, bladder, kidney, adrenal gland, urinary bladder, sexual accessory glands, testes, muscle, skin and femur) were collected for histological analysis. Leukograms were prepared from blood smears and total WBC counts obtained with a Neubauer chamber. Flow cytometry was used to assess blood T-(CD3(+)) and B-(CD19(+))-lymphocytes, medullary granulocytic (CD11b(+)/Ly-6G(-), CD11b(+)/Ly-6G(+)) and lymphocytic (CD19(+)/IgM(-), CD19+/IgM(+)) populations and thymic lymphoid (CD4(+), CD8(+), CD4(+)/CD8(+)) populations. Lymphoproliferative lesions were analysed immunohistochemically using antibodies against CD45R and CD3. All of the 10 surviving mice developed a lymphoproliferative malignancy. Lymphoproliferative disease was characterized by multifocal B-(CD45(+)/CD3(-))-lymphocytic renal (10/10 animals) and hepatic (2/10 animals) invasion, splenic white pulp hyperplasia (10/10) together with a significant increase in circulating B-(CD19(+))-lymphocytes and the appearance of circulating dysplastic lymphoid cells. Eight out of 10 ptaquiloside-exposed animals developed urothelial dysplasia (six low-grade dysplasia and two high-grade dysplasia). No lesions were detected in control mice. These results show that ptaquiloside is capable of inducing malignant transformation in mice and provide an in-depth characterisation of lymphoproliferative lesions. Furthermore, the urinary bladder is shown to be a target organ for this toxin in mice as well as in other animal species.