Valproic Acid Inhibits Human Retinal Pigment Epithelial (hRPE) Cell Proliferation Via a P38 MAPK Signaling Mechanism

Valproic acid (VPA) has been reported to inhibit cancer cell growth and has therapeutic use in retinal diseases. However, the mechanism of this action remains unclear. In order to explore this mechanism, primary human retinal pigment epithelial (hRPE) cell cultures were established. Cell viability was assessed by the trypan blue exclusion method (T), and the cell proliferation was measured by H-3-thymidine incorporation (3H-thy). P38 synthesis was quantitated by using 14C-methionine-labeled P38 (14C-P38) by using P38-specific antibody. SB203580 (SB), a selective inhibitor of p38 MAPK, was also used to test the specificity of P38 stimulation. Antinuclear staining (NS) studies were performed by DAPI. Statistical significance was established by student's t-test. We observed that VPA (1 mM) inhibited 10% fetal bovine serum (FBS)-stimulated cell proliferation (1.75 +/- 0.37 vs. 3.25 +/- 0.68 cells per 1 mu l +/- SEM, p < 0.05, n = 4). VPA also stimulated 14C-P38 synthesis in a dose-dependent manner. SB (30 mu M) inhibited VPA (4 mM)-stimulated 14C-P38 synthesis (197.74 +/- 41.17 vs. 425.89 +/- 59.17, CPM +/- SEM, p < 0.05, n = 4) and increased hRPE cell proliferation (1.79 +/- 0.45 vs. 4.93 +/- 1.12 cells per 1 mu l +/- SEM, p < 0.05, n = 4); NS demonstrated VPA-induced cell damage. We conclude that VPA inhibits hRPE cell growth via P38 MAP mechanism and may be of therapeutic value in treating or preventing proliferative eye diseases.