2-Halopropionic acid-induced cerebellar granule cell necrosis in the rat: in vivo and in vitro studies

Daily oral administration of 2.3 mmol/kg L-2-chloropropionic acid (L-2-CPA), DL-2-bromopropionic acid (2-BPA) or DL-2-iodopropionic acid (2-/PA) but not DL-2-fluoropropionic acid (2-FPA) produced cerebellar granule cell necrosis in the rat. Twenty four hours after three doses of L-2-CPA or two doses of 2-BPA, animals showed clinical signs of motor incoordination and reduced hindlimb function which was associated with marked cerebellar oedema and cerebellar granule cell necrosis. Biochemical analyses showed a marked increase in cerebellar water and Na+ content, and a reduction in cerebellar glutamate and aspartate. 2-IPA at this dose was toxic, the animals not surviving a second dose, histopathology showed hepatic and renal necrosis with mild cerebellar granule cell necrosis. 2-FPA was not neurotoxic after four daily doses. A marked decrease in hepatic and cerebellar non-protein sulphydryl (NP-SH) content was observed 4 h after a single dose of 2.3 mmol/kg L-2-CPA, 2-BPA and 2-IPA but not 2-FPA. Daily doses of 2-BPA for 3 days produced a sustained 50% depletion in cerebellar NP-SH. In vitro, L-2-CPA, 2-BPA and 2-IPA produced glutathione (GSH) depletion in the presence of rat liver cytosol, while 2-FPA did not. Depletion of GSH in the presence of cerebellar cytosol was only observed with 2-IPA. Studies using primary cultures of rat cerebellar granule cells, showed that all analogues produced a concentration dependent loss of cell viability. Mean EC50 values for 2-FPA, L-2-CPA, 2-BPA and 2-IPA toxicity were 1.7, >10, 0.5 and 0.3 mM, respectively, for 24 h continuous exposure. MK-801 and Vitamin E afforded protection against L-2-CPA-induced cytotoxicity but not against the other analogues. In summary, in addition to L-2-CPA, both 2-BPA and 2-IPA produce cerebellar granule cell necrosis in the rat. Depletion of GSH in the cerebellum may be contributory factor in the cascade of events leading to neurotoxicity.