Carvacrol-induced [Ca2+]i rise and apoptosis in human glioblastoma cells

This study examined whether the essential oil component carvacrol altered cytosolic free Ca(2+) level ([Ca(2+)](i)) and viability in human glioblastoma cells.

The Ca(2+)-sensitive fluorescent dye fura-2 was applied to measure [Ca(2+)](i). Cell viability was measured by detecting reagent WST-1. Apoptosis and reactive oxygen species (ROS) were detected by flow cytometry.

Carvacrol at concentrations of 400-1000 μM induced a [Ca(2+)](i) rise in a concentration-dependent fashion. The response was decreased partially by removal of extracellular Ca(2+). Carvacrol-induced Ca(2+) 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 Ca(2+) was removed, incubation with the endoplasmic reticulum Ca(2+) pump inhibitor thapsigargin or 2,5-di-tert-butylhydroquinone (BHQ) abolished carvacrol-induced [Ca(2+)](i) rise. Incubation with carvacrol also abolished thapsigargin or BHQ-induced [Ca(2+)](i) rise. Inhibition of phospholipase C with U73122 abolished carvacrol-induced [Ca(2+)](i) rise. At concentrations of 200-800 μM, carvacrol killed cells in a concentration-dependent manner. This cytotoxic effect was not changed by chelating cytosolic Ca(2+) 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 carvacrol (200, 400 and 600 μM) induced apoptosis in a concentration-dependent manner. At concentrations of 200, 400 and 600 μM, carvacrol induced production of ROS.

In human glioblastoma cells, carvacrol induced a [Ca(2+)](i) rise by inducing phospholipase C-dependent Ca(2+) release from the endoplasmic reticulum and Ca(2+) entry via protein kinase C-sensitive, non store-operated Ca(2+) channels. Carvacrol induced cell death that might involve ROS-mediated apoptosis.