Anhydroretinol induces oxidative stress and cell death

The retro-retinoid anhydroretinol (AR), a physiological metabolite of retinol (vitamin A), induces cell death in multiple in vitro systems. AR-induced cell death is blocked by retinol and its metabolite 14-hydroxy-4,14-retro-retinol. AR has been shown also to prevent mammary cancer induced by N-methyl-N-nitrosourea in rats. We report that AR kills cells by generating reactive oxygen species. Direct measurements show that the addition of AR to lymphoblastoid cells increases the intracellular oxidative stress in a time- and dose-dependent manner. Furthermore, the amount of induced oxidative stress directly correlates with the number of dying cells. The addition of retinol, 14-hydroxy-4,14-retro-retinol, or the antioxidant, alpha-tocopherol (vitamin E), decreases AR-induced oxidative stress and proportionally reduces AR-induced cell death. In contrast, pretreatment with caspase inhibitors, known to inhibit apoptosis, has no effect on AR-induced cell death. This is the first demonstration of cellular reactive oxygen species production by a natural retinoid.