Effect of soluble collagen I and antioxidants on endothelial-cell apoptosis caused by HKa and 2-ME. An endothelial-cell proliferation assay was used to quantitate viable cells remaining after 48 hours of stimulation with 10 ng/mL bFGF in the absence or presence of 50 nM HKa. Greater than 100% inhibition of proliferation, as defined in our previous studies,⁹  means that fewer viable cells remain at the end of the experiment than at the beginning. (A) Cells were stimulated with bFGF in the presence of HKa and in the absence (□) or presence (▪) of 150 μg/mL soluble type I collagen. Collagen did not block HKa-induced endothelial-cell apoptosis. (B) Cells were stimulated with bFGF in the presence of HKa and in the absence (□) or presence (▪) of 150 μg/mL GSH, which provided substantial protection against HKa-induced apoptosis. (C) Cells were stimulated with bFGF in the presence of HKa and in the absence (□) or presence (▪) of 150 μg/mL of NAC. (D) Cells were stimulated with bFGF in the presence of 4 μM 2-methoxyestradiol (2-ME) and in the absence or presence of 150 μg/mL GSH. GSH did not protect cells from 2-ME–induced apoptosis. Error bars indicate standard deviation of triplicate points.