| Prolonged ingestion of the noxious weeds, yellow starthistle ( Centaurea solstitialis) and Russian knapweed (Centaurea repens ) by horses has been shown to result in a fatal neurodegenerative disorder called Equine Nigropallidal Encephalomalacia (ENE) which affects the dopaminergic areas of equine brain and delivers symptoms akin to Parkinson's disease that afflicts humans. While our initial bioassay-guided fractionation suggests that sesquiterpene lactones (SQLs) were responsible for ENE, the compound repin was hypothesized as the chief causative agent, owing to its high abundance in the plant and unique chemical structure vis-à-vis other SQLs in the plant. Initial studies indicate that the conjugate addition of glutathione to repin depletes cellular levels of glutathione, exposing the cells to the deleterious effects of reactive oxidative species (ROS) and ultimately resulting in neuronal cell death. In order to address the molecular basis of repin-induced neurotoxicity, a structure-toxicity profile has been constructed to identify the key functional groups in repin responsible for ENE. In this document is described the isolation of SQLs from C. repens and the first studies reported on the chemical modification of repin. Biological evaluation of the SQLs was accomplished by employing the use of either PC-12 or VERO cell lines. By comparing structural modifications with biological activity, the critical importance of the epoxide functionalities or electrophilic equivalents has been confirmed, in addition to the necessity of exocyclic methylene lactone. It is therefore plausible that while glutathione conjugation is the first step in a series of cellular events, the electrophilic nature of the epoxides of repin contribute significantly in lowering the cells' defenses in the pathogenesis of ENE. Chemical studies were also conducted to produce a biotin-repin probe for future biological analysis of the cellular components involved in ENE. |
