Figure 3. The effects of subtoxic levels of hydrogen peroxide on nuclear factor factor-kappaB in nuclear extracts and phosphorylated extracellular signal-regulated kinases, c-Jun N-terminal kinase and p38 mitogen-activated protein kinase. Retinal pigment epithelium (RPE) cells (ARPE-19) were plated into 24-well plates. After 24 h incubation, 100 µm hydrogen peroxide (H₂O₂) was added to the medium. Cells were collected 30 min later. The nuclear factor factor-kappaB (NF-κB) levels in nuclear extracts (A) and phosphorylated p38 mitogen-activated protein kinase (p38; B), c-Jun N-terminal kinase (JNK; C) and extracellular signal-regulated kinases (ERK; D) in cell lysates were measured using the relevant NF-κB enzyme-linked immunosorbent assay (ELISA) kit and phosphorylated MAPK ELISA kits (Biosource). The levels of NF-κB in nuclear extracts were expressed as pg/ml and phosphorylated p38, ERK and JNK in cell lysates were expressed as U/ml (mean±standard deviation in triplicate tests). *0.01< p<0.05, **p<0.01, compared with the controls (cells cultured without H₂O₂).