An evaluation of the toxic norditerpenoid alkaloid content across Delphinium species, and their acute toxicities in a murine model

Authors: Welch, Kevin; GARDNER, DALE - Retired ARS Employee; Cook, Daniel; Lee, Stephen; Stonecipher, Clinton; Green, Benedict

Submitted to: Chemistry and Biodiversity
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/13/2025
Publication Date: 6/6/2025
Citation: Welch, K.D., Gardner, D.R., Cook, D., Lee, S.T., Stonecipher, C.A., Green, B.T. 2025. An evaluation of the toxic norditerpenoid alkaloid content across Delphinium species, and their acute toxicities in a murine model. Chemistry and Biodiversity. Article e00779. https://doi.org/10.1002/cbdv.202500779.
DOI: https://doi.org/10.1002/cbdv.202500779

Interpretive Summary: Larkspur plants are abundant in mountain rangelands in western North America. There are over 60 wild species of larkspur in North America, with taxonomic treatments of greater than 50 species in North America. Larkspurs are acutely toxic to cattle. Consequently, they cause a significant number of cattle death losses every year. The toxicity of larkspurs is due to the more than 18 norditerpenoid alkaloids that are often grouped into two predominant types, the MSAL–type including methyllycaconitine (MLA) and the non MSAL-type including deltaline. However, there is a wide range in the toxicity of larkspurs to cattle, with some species/populations being extremely toxic while others are essentially non-toxic. Research has shown that there is a significant difference in the alkaloid composition between the different species of larkspurs, and for some species, there is a difference between different populations of the same species. Specific information on the alkaloid composition in terms of the MSAL and non-MSAL-type alkaloids is lacking for many Delphinium species. Over the past 30 years, differences in the chemical profiles of the various larkspurs and their associated toxicities in mouse models and in cattle have been documented. However, over that extended period of time, different methods were used to analyze the plant material. Different methods have been utilized, with many variations of mass spectrometry analysis. Additionally, different methods to characterize the toxicity of the plant material, including different methods to isolate the toxins and different strains of mice, or sources of mice, for testing. These variations and differences likely lead to differences in the determination of the norditerpenoid composition of the plant and differences in the associated toxicity determinations. The objective of this study was to use a standard method to analyze, extract and test the toxicity of numerous collections of larkspurs. In this study, we collected various species of larkspur, and populations of the same species, for a total of 20 different collections. These 20 collections were all analyzed using one LC/MS method. Plant material from each collection was extracted using the same method and the acute toxicity of each extract was tested using a mouse LD50 assay with the same mouse strain purchased from one vendor. Consequently, these collections were identically characterized, and thus direct comparisons between the species and populations can be made to more accurately compare the risk of grazing these species/populations of larkspurs. The results from this study provide a standardized comparison of the risk of some of the more common and problematic larkspurs in the western USA. The results from this study demonstrate that there are important differences in the norditerpenoid alkaloid make up and concentrations between larkspur species and even between populations. These differences are critical to the toxicity of the plant material. This study also clearly highlights that the toxicity of larkspur plants is directly correlated to the concentration of the MSAL-type alkaloids. This data can provide a valuable resource for risk analysis of larkspur-infested rangelands of the western USA prior to grazing cattle.

Technical Abstract: Larkspurs (Delphinium spp.) are one of the most problematic plants for cattle producers in western North America. There are more than 60 species of larkspurs in western North America. The toxins in larkspurs are norditerpenoid alkaloids with more than 18 different known alkaloids. Previous research has shown that there is a difference in the alkaloid composition between the different species of larkspurs, and for some species, there is a difference between different populations of the same species. Over the past 30 years, differences in chemical profiles of the various larkspurs and their associated toxicities in rodent models and in cattle have been documented. However, over that period of time, various methods have been used to analyze the plant material and to characterize its toxicity, including different methods to isolate the toxins and different species of mice, or sources of mice for testing. In this study, we collected numerous species of larkspur, and different populations of the same species. Plant material from 20 collections was extracted using the same method, analyzed using the same LC/MS method and the acute toxicity of each extract was tested using a mouse LD50 assay with the same strain of mice purchased from one vendor. The results from this study demonstrate the large variations in alkaloid composition and concentrations between the various species and populations of larkspurs in the western USA. The data also demonstrate a strong correlation between the MSAL content of the plant and its toxicity in a mouse model. The results from this study provide a standardized comparison of the risk of some of the more common and problematic larkspurs in the western USA. This data can provide a valuable resource for risk analyses of larkspur-infested rangelands.