The effect of clonidine on VEGF expression in human retinal pigment epithelial cells (ARPE-19)

The purpose of this study was to investigate the effect of clonidine, an alpha(2)-adrenergic receptor (alpha(2)-ADR) agonist, on vascular endothelial growth factor (VEGF) expression and secretion in the human retinal pigment epithelial cell line (ARPE-19) stimulated with interleukin-1 beta (IL-1 beta). Alpha(2)-ADRs (alpha(2)A, alpha B-2, and alpha C-2) mRNA expression in ARPE-19 cells was examined by semiquantitative reverse transcription polymerase chain reaction (RT-PCR). Clonidine and inhibitors against protein kinases that are involved in the regulation of the intracellular signal transduction were added to serum-free medium before stimulation of IL-1 beta. The alpha(2)-ADR antagonist, Yohimbine, was loaded 30 min before the addition of clonidine. The expression of VEGF mRNA and protein was measured by real-time PCR and enzyme-linked immunosorbent assay. Alpha(2)A-ADR, alpha B-2-ADR, and alpha C-2-ADR mRNA was expressed in RPE cells. Clonidine, an inhibitor of p38MAPK and MEK1/2, inhibited the expression of VEGF protein and mRNA in the RPE cells stimulated with IL-1 beta. The inhibitory effect of clonidine on the secretion of VEGF protein stimulated with IL-1 beta was blocked by alpha(2)-ADR antagonists. The effect of clonidine on the expression of VEGF may be via suppression of the p38MAPK and MEK1/2 signal transduction pathways activated with IL-1 beta.