Anticoccidial activity of the secondary metabolites in alpine plants frequently ingested by wild Japanese rock ptarmigans

The Japanese rock ptarmigan (Lagopus muta japonica) is an herbivorous species of partridges that inhabits only alpine zones. Alpine plants are their main source of food. These alpine plants contain toxic compounds to deter herbivores from consuming them. A previous analysis of the alpine plants frequently consumed by Japanese rock ptarmigans revealed the presence of a unique mixture of secondary metabolites and a novel compound. Additionally, wild Japanese rock ptarmigans are often infected by two species of Eimeria parasites. When these parasites were experimentally administered to Svalbard rock ptarmigans (Lagopus muta hyperborean), which do not feed on alpine plants, the birds exhibited symptoms, such as diarrhea and depression, and in some cases, they died. Although little is known about the pathogenesis of these parasites in wild Japanese rock ptarmigans, it was hypothesized that compounds found in alpine plants, their main food source, may reduce the pathogenicity of Eimeria parasites. In the present study, we evaluated the anticoccidial activity of the compounds derived from alpine plants in vitro using Eimeria tenella, which infects chickens belonging to the same pheasant family, as an experimental model. Twenty-seven natural components were extracted from eight alpine plants. The natural components were added to E. tenella sporozoites and incubated for 24 h to evaluate their direct effect. Additionally, Madin-Darby bovine kidney cells were incubated with sporozoites and natural components for 24 h to evaluate the inhibitory effect of the components on sporozoite cell invasion. Six compounds from four alpine plants decreased sporozoite viability by up to 88.3%, and two compounds inhibited sporozoite invasion into the cells. Although further studies are needed to evaluate the effects of these components against Eimeria infections in vivo, our findings suggest that these alpine plants may reduce the degree of infection by decreasing the number of sporozoites in the intestinal tract.