Antioxidants J811 and 17?-estradiol protect cerebellar granule cells from methylmercury-induced apoptotic cell death

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Abstract
Cerebellar granule cells (CGC) have provided a reliable model for studying the toxicity of methylmercury (MeHg), a well‐known neurotoxicant contaminating the environment. In the present study we report that doses of MeHg ranging from 0.1 μM to 1.5 μM activated apoptosis, as shown by cell shrinkage, nuclear condensation, and formation of high‐molecular‐weight DNA fragments. Nevertheless, caspase‐3‐like activity was not significantly induced, and the broad caspase inhibitor Z‐VAD‐FMK was not capable of protecting the cells. This argues for a minor role of caspases in the intracellular pathways leading to MeHg‐induced cell death in CGC. Instead, proteolytic fragments obtained by specific calpain cleavage of procaspase‐3 and α‐fodrin were increased consistently in samples exposed to MeHg, pointing to a substantial activation of calpain. Notably, two antioxidants, 17β‐estradiol (10 μM) and the Δ8,9‐dehydro derivative of 17α‐estradiol J811 (10 μM), protected from MeHg damage, preventing morphological alterations, chromatin fragmentation, and activation of calpain. These findings underscore the key role of oxidative stress in MeHg toxicity, placing it upstream of calpain activation. The shielding effect of the 17β‐estradiol and the radical scavenger J811 is potentially relevant for the development of therapeutic strategies for MeHg intoxication. J. Neurosci. Res. 62:557–565, 2000.