Vitamin C decreases FAS-induced apoptosis in U937 cells and monocytes. (A) Intracellular accumulation of vitamin C in U937 cells after exposure to 1.0 mM DHA or AA. Results are presented as the intracellular concentration of accumulated AA, determined by cell-associated radioactivity. The standard deviation is smaller than the symbols in the graphs, and was always less than 10% of the values for each point. (B-C) U937 cells loaded with vitamin C were treated for 3 hours with 200 ng/mL FASL or 1 μg/mL anti-FAS Ab, and apoptosis was measured by annexin V+/PI- staining or by analysis of the sub-G1 region. The intracellular accumulation of AA was estimated by HPLC. (D) Accumulation of AA in monocytes after exposure to 0.1 mM DHA or AA, calculated by cell-associated radioactivity. (E-F) Monocytes were loaded with different amounts of vitamin C estimated by HPLC analysis before treatment with 100 ng/mL FASL or 0.1 μg/mL anti-FAS Ab for 3 hours to measure apoptosis by analysis of the sub-G1 region. Asterisks indicate statistically significant differences (P ≤ .05) using the Student t test between control and cells loaded with vitamin C before challenge with FASL. These experiments were repeated 6 times for each cell type with similar results. A representative experiment is shown. Error bars represent the SD of triplicate values.