Molecular and Cellular PharmacologyEffect of thymol on Ca2+ homeostasis and viability in human glioblastoma cells

The effect of the natural essential oil thymol on cytosolic Ca2+ concentrations ([Ca2+]i) and viability in human glioblastoma cells was examined. The Ca2+-sensitive fluorescent dye fura-2 was applied to measure [Ca2+]i. Thymol at concentrations of 400-1000 μM induced a [Ca2+]i rise in a concentration-dependent fashion. The response was decreased partially by removal of extracellular Ca2+. Thymol-induced Ca2+ signal was not altered by nifedipine, econazole, SK&F96365, and protein kinase C activator phorbol myristate acetate (PMA), but was inhibited by the protein kinase C inhibitor GF109203X. When extracellular Ca2+ was removed, incubation with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) abolished thymol-induced [Ca2+]i rise. Incubation with thymol also abolished thapsigargin or BHQ-induced [Ca2+]i rise. Inhibition of phospholipase C with U73122 abolished thymol-induced [Ca2+]i rise. At concentrations of 200-800 μM, thymol killed cells in a concentration-dependent manner. This cytotoxic effect was not changed by chelating cytosolic Ca2+ with 1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid/acetoxy methyl (BAPTA/AM). Annexin V/propidium iodide staining data suggest that thymol (200, 400 and 600 μM) induced apoptosis in a concentration-dependent manner. Collectively, in human glioblastoma cells, thymol induced a [Ca2+]i rise by inducing phospholipase C- and protein kinase C-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via non store-operated Ca2+ channels. Thymol induced cell death that may involve apoptosis.