Toxicity and Phototoxicity of Hypericin to Human Lens Epithelial Cells

Abstract

Abstract: : Purpose: To determine phototoxicity of hypericin, the active ingredient in St. John's Wort, in vitro with human lens epithelial cells. Hypericin photooxidizes lens proteins (Roberts et al. 1999, Photochem. Photobiol. 69:42) and therefore may present a hazard to the human lens. Methods: Human epithelial lens cells (cell line HLE B-3) were incubated in the dark for 1 hour with 10^-9 to 10^-6 M hypericin in MEM. Fluorescence emission spectra were measured to detect uptake of hypericin into the cells. Cells were washed and resuspended in PBS buffer and then irradiated with 4J cm^-2 UVA (Houvalite F20T12BL-HO PUVA) with cut-off filter to remove all radiation below 300 nm. In other experiments, cells were incubated with both hypericin and the protective antioxidants lutein (60 uM) and N-acetyl cysteine (1 mM). Damage to all irradiated and dark control cells was assessed by flow cytometry in combination with Annexin V/propidium iodide double staining, to identify apoptosis from necrosis induced by hypericin Results: Fluorescence emission spectra detected from the lens epithelial cells (λ_exc = 550 nm; λ_em = 601 and 651 nm) confirmed hypericin uptake by human lens epithelial cells. Hypericin induced both necrosis and apoptosis at all concentrations in these cells, both in the dark and when irradiated. Lutein offered significant protection against apoptosis (50%) but both N-acetyl cysteine and lutein offered little protection (>8%) against necrosis induced by hypericin. Conclusions: Hypericin is toxic at low concentrations to human lens epithelial cells. Precaution should be taken to protect the eye from intense sunlight while taking this over the counter antidepressant medication.

Keywords: radiation damage: light/UV • cataract • antioxidants