Subtoxic levels hydrogen peroxide-induced production of interleukin-6 by retinal pigment epithelial cells.

PURPOSE

To study the effect of subtoxic levels of hydrogen peroxide (H(2)O(2)) on the expression and release of interleukin-6 (IL-6) by cultured retinal pigment epithelial (RPE) cells and to explore the relevant signal pathways.

METHODS

Cultured human RPE cells were stimulated with various subtoxic concentrations of H(2)O(2) for different periods. Conditioned medium and cells were collected. IL-6 in the medium and IL-6 mRNA in the collected cells were measured using an IL-6 enzyme-linked immunosorbent assay kit and reverse transcriptase polymerase chain reaction, respectively. Nuclear factor-kappaB (NF-κB) in nuclear extracts and phosphorylated p38 mitogen-activated protein kinase (MAPK), extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinases (JNK) in cells cultured with and without H(2)O(2) were measured by NF-κB and MAPK enzyme-linked immunosorbent assay kits. Inhibitors of p38 (SB203580), ERK (UO1026), JNK (SP600125), and NF-κB (BAY11-7082) were added to the cultures before the addition of H(2)O(2) to test their effects(.)

RESULTS

Subtoxic levels of H(2)O(2) (100 µM and less) increased the IL-6 mRNA level and the release of IL-6 protein by the cultured human RPE cells in a dose- and time-dependent manner. This was accompanied by an increase of NF-κB in nuclear extracts and phosphorylated p38 MAPK, ERK, and JNK in cell lysates, particularly in the p38 and NF-κB. The NF-κB inhibitor decreased the H(2)O(2)-induced expression of IL-6. The p38 inhibitor, but not the ERK or JNK inhibitor, completely abolished H(2)O(2)-induced expression of IL-6 by RPE cells. The p38 inhibitor also abolished the increase of NF-κB in nuclear extracts in cells treated with H(2)O(2).

CONCLUSIONS

H(2)O(2) stimulated the production of IL-6, a key factor in the modulation of immune responses, inflammatory processes, and the occurrence of autoimmune diseases, which recently has been documented to be increased in age-related macular degeneration (AMD). This may be a molecular linkage for the oxidative stress and inflammatory/autoimmune reactions in AMD and may provide a novel target for the treatment of AMD.