ABSTRACT
PURPOSE: Proliferation control in adult retinal pigment epithelial (ARPE) cells is an essential factor in the clinical management of proliferative vitreoretinopathy (PVR). Factors which inhibit PVR and which are without toxic potential are therefore of interest in controlling proliferation. The aim of the present study was to gain insight into a possible function of high intraocular ascorbic acid levels as a physiological modulator of proliferation. METHODS: Adult retinal pigment epithelial cells were incubated in vitro with increasing concentrations of ascorbic acid (0.5-4 mmol, pH 7.4). Cell proliferation was assayed by the bromide-deoxy-uridine (BrdU) assay. The culture medium (CM) containing ascorbic acid was replaced with normal CM and the recovery of proliferation was measured after 24 hours. In order to be able to distinguish between proliferation inhibition, apoptosis, necrosis and recovery of proliferation, we performed TUNEL assays and fluorescence analysis cell-counter (FAC) analysis. RESULTS: Ascorbic acid significantly inhibits ARPE cell proliferation if it is present in concentrations above 2 mmol. Proliferation resumed in all ARPE cell cultures after pre-incubation with ascorbic acid, indicating that direct toxicity of ascorbic acid is a negligible factor. The time-point and extent of recovery in proliferation was dependent on the initial ascorbic acid concentration. Fluorescence-labelled cell counts on apoptosis markers (FAC) data showed some induction of apoptosis and necrosis after incubation with 4 mmol ascorbic acid. CONCLUSIONS: Ascorbic acid has a dose-dependent influence on the proliferation of vital ARPE cells. This possibly reflects the role of ascorbic acid at a physiological level within the vitreous cavity in preventing proliferative vitreoretinopathy (PVR). These findings may stimulate the development of new strategies in the clinical treatment of PVR.
