DIFFERENTIAL TOXICITY OF PROTEASE INHIBITORS IN CULTURES OF CEREBELLAR GRANULE NEURONS

Involvement of proteases has been postulated in several neurodegenerat ive processes. Accordingly, protease inhibition has been proposed as a potential therapeutic tool to limit damage in some neuropathological states. The timed turn-over of proteins is, however, an essential bioc hemical process and its prolonged block may be dangerous to the cell. We report here data on toxicity consequent to 24-h exposure of cerebel lar granule neurons in culture to inhibitors of different classes of p roteases. Inhibition of calpains (calcium-activated cysteine proteases ) resulted in dose-dependent neuronal death which largely occurred thr ough apoptotic process. Leupeptin, an inhibitor acting on a broad spec trum of cellular serine proteases, was less toxic but resulted in defi nite morphological alteration of the cells. On the contrary, inhibitor s of caspases, proteases belonging to the ICE (interleukin 1-beta conv erting enzyme) family did not apparently damage granule neurons upon e xposure for 24 h to high concentrations (up to 200 mu M) of two inhibi tors specific for ICE (Ac-YAVD-CHO) and CPP-32 (Ac-DEVD-CHO), respecti vely. These results suggest that inhibition of proteases that are acti vated by stressful stimuli but are not essential for the normal functi oning of healthy cells, as it is likely the case for caspases, may not be harmful to neurons. Instead, the potential risks and side effects of prolonged inhibition of proteases such as calpains, that regulate t he disposal and the turn-over of key cellular proteins, should be care fully tested in the assessment of possible neuroprotective roles, (C) 1998 Academic Press.