Cytotoxic effects of repin, a principal sesquiterpene lactone of Russian knapweed.
Repin is the principal sesquiterpene lactone isolated from Russian knapweed (Centaurea repens), a perennial weed found in many parts of the United States. Ingestion of Centaurea repens by horses has been reported to cause a movement disorder simulating Parkinson's disease (PD) and nigrostriatal degeneration, called equine nigrostriatal encephalomalacia (ENE). To understand the mechanisms whereby ingestion of Centaurea repens induces ENE and a PD-like disorder, repin cytotoxicity was examined to explore its pathogenetic relationship to ENE and to PD. Repin was highly cytotoxic to both PC12 cells and mouse astrocytes in a dose- and time-dependent manner. The cytotoxic effects were accompanied by depletion of glutathione (GSH), a rise in the level of reactive oxygen species (ROS) and damage to cellular membranes. Although repin is a highly reactive electrophile that can readily conjugate GSH, GSH depletion may not be the sole mechanism underlying repin cytotoxicity as shown by our study using buthionine sulfoximine, in which severe GSH depletion did not result in a parallel increase in cell death. However, pre-treatment with GSH-glycoside or with lipoic acid provided significant protection from repin-induced cell death. These data suggest that oxidative stress plays a major role in repin cytotoxicity. Since oxidative stress is considered to play a major role in neuronal degeneration accompanied by depletion of mitochondrial GSH and an increase in lipid peroxides in the substantia nigra of PD, further elucidation of mechanisms of repin neurotoxicity may generate clues regarding not only the mechanisms of neuronal degeneration but also the possible role of environmental factors in the pathogenesis of PD.