title: Cytotoxic activity of extracts from Hypochaeris radicata.
abstract: Pasture-associated stringhalt is an acquired equine disease characterized by peripheral neuropathy and hyperflexion of the pelvic limbs. The disease occurs most commonly during periods of drought in horses grazing pastures heavily contaminated by Hypochaeris radicata. We hypothesized that stringhalt is caused by neurotoxins elaborated by H. radicata in response to the stress of drought conditions. Supernates were collected from H. radicata that were stressed (or not) by immersion in copper chloride solution, then extracted with ethyl acetate and dried. Dilutions of extracts from stressed (SE) and control, unstressed (UE) plants were incubated with myelinating spinal cord cultures (MSCC) established from fetal Swiss mice, and with spinal ganglion cultures (SGC) and dermal fibroblast cultures derived from neonatal mouse tissues. Cytotoxicity in culture monolayers was evaluated both morphologically by microscopy and by release of lactate dehydrogenase activity into culture supernates. Three different SGC preparations were exposed to a single H. radicata extract and single preparations of fibroblasts and MSCC were exposed to three different extracts. Repin, a plant-derived sesquiterpene lactone neurotoxin, was included as a positive control. Significant dose-dependent cytotoxicity was seen within 24 h in all three culture types when incubated with SE or repin. Complete morphologic destruction of culture monolayers was induced by the highest concentrations tested of SE (100 μg/mL) and repin (30 μg/mL). Cytotoxic effect of SE was significantly greater than that of UE for all three cell types and was not due to copper contamination of the extract. This study has identified a cytotoxic activity in leaf exudates of H. radicata that was upregulated by the model stressor, copper chloride.
authors.affiliation: Institute of Veterinary, Animal and Biomedical Sciences, College of Sciences, Massey University, Private Bag 11222, Palmerston North, New Zealand. mackayr@ufl.edu
authors.forename: R J
authors.initials: RJ
authors.lastname: MacKay
authors.forename: S
authors.initials: S
authors.lastname: Wyer
authors.forename: A
authors.initials: A
authors.lastname: Gilmour
authors.forename: K
authors.initials: K
authors.lastname: Kongara
authors.forename: D R
authors.initials: DR
authors.lastname: Harding
authors.forename: S
authors.initials: S
authors.lastname: Clark
authors.forename: I G
authors.initials: IG
authors.lastname: Mayhew
authors.forename: C E
authors.initials: CE
authors.lastname: Thomson
mesh_terms: D000818:Animals; D019659:Asteraceae / Q000737:chemistry*; D002478:Cells, Cultured; D003300:Copper / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006734:Horse Diseases / Q000139:chemically induced / Q000473:pathology*; D006736:Horses; D007783:Lactones / Q000378:metabolism; D051379:Mice; D009468:Neuromuscular Diseases / Q000139:chemically induced / Q000473:pathology / Q000662:veterinary*; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D010936:Plant Extracts / Q000633:toxicity*; D018515:Plant Leaves / Q000737:chemistry; D012717:Sesquiterpenes / Q000633:toxicity*; D013312:Stress, Physiological
chemical_list: D007783:Lactones; D010936:Plant Extracts; D012717:Sesquiterpenes; C064339:repin; D003300:Copper