Possible involvement of cathepsin B/D and caspase-3 in deferoxamine-related neuroprotection of early brain injury after subarachnoid haemorrhage in rats.

AIMS: Deferoxamine (DFX) has recently been shown to have a neuroprotective effect in animal models of subarachnoid haemorrhage (SAH). However, the precise mechanisms underlying these effects remain unclear. Our previous studies found that iron overload in lysosomes leads to lysosomal membrane damage and rupture, and then induces cell apoptosis in the oxidative stress conditions in vitro. We therefore analysed the time-course of the two of major lysosomal cathepsins (cathepsin B/D) and caspase-3 expression in brain and evaluated how DFX might affect these proteins and the parameters concerning early brain injury (EBI) after SAH.
METHODS: We investigated the time-course of cathepsin B/D and caspase-3 expression in the cortex after SAH in rats. Furthermore, we assessed the effect of DFX on regulation of cathepsin B/D and caspase-3 and EBI following SAH. All SAH animals were subjected to a single injection of autologous blood into the prechiasmatic cistern. Protein concentrations were measured using Western blot analysis and immunohistochemistry. The extent of brain oedema was measured using the wet/dry method. Blood-brain barrier (BBB) permeability was assessed using IgG extravasation. Cortical apoptosis was examined using terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL).
RESULTS: Cathepsin B/D and caspase-3 were up-regulated in the cortices of affected rats after SAH. Levels of both peaked at 48-h post-SAH. After intraperitoneal DFX administration, the elevated expression of cathepsin B/D and caspase-3 was down-regulated in the cortex 48 h after blood injection. In the DFX-treated group, early brain damage events, such as brain oedema, BBB impairment, cortical apoptosis, and alterations in clinical behaviour were significantly ameliorated relative to vehicle-treated SAH rats.
CONCLUSIONS: These results suggest that the lysosomal membrane may be damaged after SAH, which leads to the release of proteases (cathepsin B/D) and activates the apoptotic pathway. Iron overload may be one key mechanism underlying SAH-induced oxidative stress and DFX may protect the lysosomal membrane, inhibit the release of cathepsin B/D, and ameliorate EBI by suppressing iron overload in the acute phase of SAH.