Effect of vitamin C on caspase-3 activity. (A) U937 cells loaded with approximately 13 mM vitamin C prior to treatment with FASL (200 ng/mL) were lysed, and the activity of caspase-3 in the cell lysates was determined as described in “Materials and methods.” (B) Monocytes loaded with approximately 14 mM vitamin C prior to treatment with FASL (100 ng/mL) were lysed, and the activity of caspase-3 in the cell lysates analyzed. The results are presented as the percentage increase in caspase activity compared with cells without treatment and are the mean of triplicate samples. These results are representative of 3 independent experiments for each cell type. Asterisks indicate statistically significant differences (in A, P = .03 and in B, P = .02) in caspase activity between cells loaded with vitamin C and control.