Effect of diindolylmethane on Ca 2+ movement and viability in HA59T human hepatoma cells

The effect of diindolylmethane, a natural compound derived from indole-3-carbinol in cruciferous vegetables, on cytosolic Ca 2+ concentrations ([Ca 2+ ] i ) and viability in HA59T human hepatoma cells is unclear. This study explored whether diindolylmethane changed [Ca 2+ ] i in HA59T cells. The Ca 2+ -sensitive fluorescent dye fura-2 was applied to measure [Ca 2+ ] i . Diindolylmethane at concentrations of 1–50 μM evoked a [Ca 2+ ] i rise in a concentration-dependent manner. The signal was reduced by removing Ca 2+ . Diindolylmethane-induced Ca 2+ influx was not inhibited by nifedipine, econazole, SK&F96365, and protein kinase C modulators but was inhibited by aristolochic acid. In Ca 2+ -free medium, treatment with the endoplasmic reticulum Ca 2+ pump inhibitors thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) inhibited or abolished diindolylmethane-induced [Ca 2+ ] i rise. Incubation with diindolylmethane inhibited thapsigargin or BHQ-induced [Ca 2+ ] i rise. Inhibition of phospholipase C with U73122 reduced diindolylmethane-induced [Ca 2+ ] i rise. At concentrations of 10–75 μM, diindolylmethane killed cells in a concentration-dependent manner. The cytotoxic effect of diindolylmethane was not reversed by chelating cytosolic Ca 2+ with 1,2-bis(2-aminophenoxy)ethane- N , N , N ′, N ′-tetraacetic acid. Propidium iodide staining data suggest that diindolylmethane (25–50 μM) induced apoptosis in a concentration-dependent manner. Collectively, in HA59T cells, diindolylmethane induced a [Ca 2+ ] i rise by causing phospholipase C-dependent Ca 2+ release from the endoplasmic reticulum and Ca 2+ influx via phospholipase A 2 -sensitive channels. Diindolylmethane induced cell death that may involve apoptosis.