The timing of re-institution of good blood glucose control affects apoptosis and expression of Bax and Bcl-2 in the retina of diabetic rats

Hyperglycemia initiates a sequence of events that leads to the development of diabetic retinopathy. We explored the effect of re-institution of good blood glucose control on apoptosis and apoptosis related genes (Bax and Bcl-2) in the retina of diabetic rats. Fifty male Wistar rats randomly divided into five groups : normal control group (CON), diabetic rats with high blood glucose levels for 8 months group (DM) ,diabetic rats with good blood glucose control for 8 months group (DM₁),diabetic rats with poor blood glucose control for 2 month followed by good blood glucose control for six additional months group (DM₂), rats with poor blood glucose control for 4 months followed by good blood glucose levels for four additional months group (DM₃). Expression of Bax and Bcl-2 in the retina was studied by immunohistochemistry and the apoptotic cells were stained using the TUNEL method. The apoptotic cell, expression of Bax and Bcl-2 and the ratio of Bax to Bcl-2 in the retina was increased in DM group compared with normal rats’ (P < 0.01). There was no significant difference in apoptotic cells and the ratio of Bax to Bcl-2 between DM₁ group and CON group. The number of TUNEL positive cells and Bax to Bcl-2 ratio was partially reversed in DM₂ group. But glucose control had no effect on the apoptotic cells and the expression of Bax and Bcl-2 in DM₃ group. There was a positive correlation between apoptotic cells and Bax/Bcl-2 ratio in the retina (r = 0.808, P < 0.01). Good blood glucose control at early stage can decrease the number of apoptotic cells in the retina; the decreased apoptosis is correlated with the down-regulation of Bax to Bcl-2 ratio.