The subcutaneous ld50 of Ivalin, extracted and purified from Geigeria aspera, in two murine models

Abstract

“Vermeersiekte” or vomiting disease in ruminants is one of the most economically significant toxicities in South Africa and is caused by chronic ingestion of sesquiterpene lactone compounds present in plants of the Geigeria genus. Affected livestock demonstrate stiffness and paralysis, mega-oesophagus with regurgitation of ingesta, production losses and mortality due to actin and myosin damage in the striated muscle of the heart, diaphragm, skeletal muscle and oesophagus. In vitro studies in murine myoblastic cell lines suggest that disruption of desmin intermediate cytoskeletal filaments could be the cause of the muscle lesions. The aim of this study was to determine whether a rodent model is appropriate for in vivo study of ivalin’s toxicodynamics in ruminants and to determine median lethality in rats exposed to the same compound.

We exposed 3 groups of CD-1 mice (6 mice per group) to subcutaneous ivalin, extracted from G. aspera, at doses of 175, 250 and 325 mg/kg BW. The control group (n = 6) received only the PEG 400 vehicle. Subsequently, we exposed Sprague-Dawley rats to ivalin in a sequential dosing procedure, according to the OCED Test Guideline (TG) 425 for Acute Oral Toxicity in rodents. Mortality, clinical signs, histopathology, muscle ultrastructure and desmin immunohistochemistry were evaluated. All mice, except one in the lowest dosing group, died within 24 hours of dosing and the LD50 was estimated at 164 mg/kg BW. Three of the 5 rats exposed to ivalin also died acutely and a maximum likelihood estimate method was used to calculate an LD50 of 135.4 mg/kg BW. There were no significant striated muscle histopathological or ultrastructural changes in exposed animals compared to the controls, and desmin immunoreactivity was highly variable in both exposed and control mice and rats.

Acute single-dose parenteral exposure of rodents to purified sesquiterpene lactones does not provide a viable laboratory animal model for further study of Geigeria spp. ingestion in ruminants. Acute ivalin toxicity in laboratory rodents following parenteral subcutaneous exposure induces sudden mortality with minimal muscle pathology and is in contrast to the more protracted muscular disease which occurs following chronic ingestion of sesquiterpene lactones from Geigeria plants in domestic ruminants. Median lethality is similar across the two rodent species and the lack of significant muscle lesions suggests toxicity at these doses is due to another mechanism, most likely mitochondrial energy pathway disturbances. This pilot study provides a starting dose for further investigation of sesquiterpene lactone plant extracts and chronic lower-dose exposure studies comparing oral and intravenous administration in both ruminants and rodents could potentially drive understanding of toxicokinetic and -dynamic differences between exposure routes and species. Additionally, thedifferences in clinical and pathological findings observed between acute and chronic toxicity could be elucidated.