Carcinogenic effects of riddelliine on P53 knockout mice

Authors: BROWN, AMMON - Environmental Laboratory, Us Army Engineer Research And Development Center, Waterways Experiment St; Stegelmeier, Bryan; Colegate, Steven; Panter, Kip; Knoppel, Edward; Field, Reuel; HALL, JEFFERY - Utah Veterinary Diagnostics Laboratory

Submitted to: International Symposium on Poisonous Plants
Publication Type: Proceedings
Publication Acceptance Date: 5/30/2015
Publication Date: 6/5/2015
Citation: Brown, A.W., Stegelmeier, B.L., Colegate, S.M., Panter, K.E., Knoppel, E.L., Field, R.A., Hall, J.O. 2015. Carcinogenic effects of riddelliine on P53 knockout mice. International Symposium on Poisonous Plants. 9:276-280.

Interpretive Summary: Riddelliine is a pyrrolizidine alkaloid found in Senecio riddellii and several other Senecio spp. Pyrrolizidine alkaloids are a group of over 600 toxins, found in more than 6,000 plants worldwide. As a result they are likely the most economically significant plant toxin in the world, affecting a wide range of organisms ranging from insects to humans. Bioactivation of pyrrolizidine alkaloids by the P450 enzyme system produces highly reactive toxic metabolites, which can bind to proteins or DNA, forming adducts. DNA adduct formation forms the basis of the carcinogenesis theory for pyrrolizidine alkaloids and why their consumption is associated with multiple types of neoplasia, including hemangiosarcoma, hepatocellular adenoma/carcinoma, and bronchoalveolar adenoma/carcinoma in various rodent models. Current small animal models require large numbers of animals over a long period of time (years), and are insensitive for carcinogenicity. The objective of this work was to develop an animal model for riddelliine carcinogenesis, requiring fewer animals and less time. Heterozygous P53 knockout mice to oral doses of riddelliine ranging from 5mg/kg body weight to 45 mg/kg body weight per day for 10 days. Another group received 1mg/kg body weight daily for the duration of the study. 59% (23 of 39) of mice in all treatment groups combined developed neoplasia after one year compared to 10% (1 of 10) in the control group. 80% of the 45 mg/kg/day group developed neoplasia within one year. Similar to previous studies the most common neoplasm present in all treatment groups was hemangiosarcoma. Hemangiosarcoma was particularly common in the 1mg/kg group, where 4 of 9 animals developed hemangiosarcoma. Interestingly, particularly in the 1mg/kg group, there was also a substantial increase in other vascular malformations. Further study in this area is necessary to determine if there is a relationship between these malformations and hemangiosarcoma. Other neoplasms present in pyrrolizidine alkaloid exposed animals included (in order of prevalence): lymphoma (5), myeloproliferative disease (4), ependymoma (3), mammary carcinoma (3), bronchoalveolar tumors (2), osteosarcoma (2), sarcoma not otherwise specified (2), leydig cell tumor (1), histocytic sarcoma (1), epithelial stromal tumor (1), adrenocortical carcinoma (1), and lacrimal gland adenoma (1). This model can now be used to compare the carcinogenicity of structurally different pyrrolizidine alkaloids. The heterozygous P53 mouse appears to be a valuable model for studying pyrrolizidine alkaloid carcinogenesis.

Technical Abstract: Riddelliine is a pyrrolizidine alkaloid found in Senecio riddellii and several other Senecio spp. Pyrrolizidine alkaloids are a group of over 600 toxins, found in more than 6,000 plants worldwide. As a result they are likely the most economically significant plant toxin in the world, affecting a wide range of organisms ranging from insects to humans. Bioactivation of pyrrolizidine alkaloids by the P450 enzyme system produces highly reactive toxic metabolites, which can bind to proteins or DNA, forming adducts. DNA adduct formation forms the basis of the carcinogenesis theory for pyrrolizidine alkaloids and why their consumption is associated with multiple types of neoplasia, including hemangiosarcoma, hepatocellular adenoma/carcinoma, and bronchoalveolar adenoma/carcinoma in various rodent models. Current small animal models require large numbers of animals over a long period of time (years), and are insensitive for carcinogenicity. The objective of this work was to develop an animal model for riddelliine carcinogenesis, requiring fewer animals and less time. Heterozygous P53 knockout mice to oral doses of riddelliine ranging from 5mg/kg body weight to 45 mg/kg body weight per day for 10 days. Another group received 1mg/kg body weight daily for the duration of the study. 59% (23 of 39) of mice in all treatment groups combined developed neoplasia after one year compared to 10% (1 of 10) in the control group. 80% of the 45 mg/kg/day group developed neoplasia within one year. Similar to previous studies the most common neoplasm present in all treatment groups was hemangiosarcoma. Hemangiosarcoma was particularly common in the 1mg/kg group, where 4 of 9 animals developed hemangiosarcoma. Interestingly, particularly in the 1mg/kg group, there was also a substantial increase in other vascular malformations. Further study in this area is necessary to determine if there is a relationship between these malformations and hemangiosarcoma. Other neoplasms present in pyrrolizidine alkaloid exposed animals included (in order of prevalence): lymphoma (5), myeloproliferative disease (4), ependymoma (3), mammary carcinoma (3), bronchoalveolar tumors (2), osteosarcoma (2), sarcoma not otherwise specified (2), leydig cell tumor (1), histocytic sarcoma (1), epithelial stromal tumor (1), adrenocortical carcinoma (1), and lacrimal gland adenoma (1). This model can now be used to compare the carcinogenicity of structurally different pyrrolizidine alkaloids. The heterozygous P53 mouse appears to be a valuable model for studying pyrrolizidine alkaloid carcinogenesis.