Evaluation of the apoptosis-related proteins of the BCL-2 family in the traumatic penumbra area of the rat model of cerebral contusion, treated by hyperbaric oxygen therapy: a quantitative immunohistochemical study

The growth and progression of traumatic brain injury (TBI) lesions depend significantly on developments in the traumatic penumbra area, perilesional region, where delayed neuronal death occurs. Recent data supports the important role of apoptosis in delayed cell death in TBI. Previously we demonstrated a significant reduction of apoptosis in traumatic penumbra in animals treated by hyperbaric oxygen (HBO). In this study we evaluate the expression of apoptosis-related proteins of the Bcl-2 family (Bcl-2, Bax and Bcl-xL) in the traumatic penumbra area in correlation with the extent of apoptosis in the rat model of focal cerebral contusion, treated by HBO. Sprague-Dawley rats underwent cortical dynamic deformation, some with subsequent hypoxemia. A group of both hypoxemic and non-hypoxemic animals was treated by HBO. The pathological study was based on immunohistochemical staining of the brain sections for Bcl-2, Bax and Bcl-xL with quantitative evaluation of staining by image analysis. The expression of Bcl-2 in hypoxemic animals was lower than in non-hypoxemic animals, but a significant increase in Bcl-2 expression was seen in both groups after HBO treatment. Bcl-xL also demonstrated an increase after HBO treatment but less significant. Staining for Bax protein did not demonstrate significant change after treatment. These data correlate well with the reduction of TUNEL-positive cells in traumatic penumbra after HBO treatment. We concluded that the apoptotic mechanisms are important in delayed cell death in TBI and that post-traumatic hypoxemia increases the intensity of apoptosis, probably through a decrease in Bcl-2 and BclxL expression which normally repress apoptosis. The beneficial effect of HBO treatment in our model of brain contusion correlates well with the increased expression of anti-apoptotic proteins (Bcl-2 and Bcl-xL) following treatment and the appropriate decrease in the extent of apoptosis. In light of these results, the usage of HBO is justified as neuroprotective treament in TBI.