Fig. 4

Caspase 3/7 activity in 661W photoreceptor-like cells after various cellular insults. a Increasing concentrations of environmental glucose were associated with a trend of increasing caspase 3/7 activation in response to phototoxic stimuli which became significant in 25mM glucose. Caspase 3/7 cleavage of the fluorescently labelled DEVD peptide was increased 168 %  ± 5 % in 5mM glucose relative to untreated controls, but “diabetic” conditions was associated with a 253 % ± 17 % increase in caspase 3/7 activation (P < 0.01). b Oxidative stress in the form of H₂O₂ increased caspase 3/7 activation in both 5mM and 25mM glucose. 2 h exposure to 1mM H₂O₂ was associated with a 140 % ± 10 % increase in caspase 3/7 activation relative to control in a low glucose environment, and this increased to 168 ± 3 % in the higher glucose environment (P < 0.05). 2.5mM H₂O₂ treatment was not associated with a significant change in activated caspase 3/7 in the different glucose environments at this time point (P < 0.16). c Staurosporine, an inducer of apoptosis, caused a dose dependent increase in caspase 3/7 activation at both low and high glucose levels. However, caspase activation was significantly greater in the 25mM glucose environment at staurosporine concentrations between 10 and 400nM. When treated with 100nM staurosporine, 661W cells showed a 127 % ± 9 % increase in caspase 3/7 activation in “non-diabetic” conditions, and this increased to 199 % ± 8 % in diabetic conditions (P < 0.01). Untreated cells did not show any significant difference in caspase 3/7 activation when exposed to different levels of environmental glucose in any of the experiments. Incubations for other periods confirmed that these results represented a true acceleration of caspase activation in the cultures exposed to excess glucose (not shown). * indicate P < 0.05 between cells treated in the presence of 5mM and 25mM glucose