The effect of magnolol on Ca homeostasis and its related physiology in human oral cancer cells.

Objective: Magnolol, a polyphenol compound from herbal medicines, was shown to alter physiology in various cell models. However, the effect of magnolol on Ca homeostasis and its related physiology in oral cancer cells is unclear. This study examined whether magnolol altered Ca signaling and cell viability in OC2 human oral cancer cells.

Methods: Cytosolic Ca concentrations ([Ca]) in suspended cells were measured by using the fluorescent Ca-sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodophenyl]-2-4(4-nitrophenyl)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay.

Results: Magnolol at concentrations of 20-100 μM induced [Ca] rises. Ca removal reduced the signal by approximately 50%. Magnolol (100 μM) induced Mn influx suggesting of Ca entry. Magnolol-induced Ca entry was partially suppressed by protein kinase C (PKC) regulators, and inhibitors of store-operated Ca channels. In Ca-free medium, treatment with the endoplasmic reticulum Ca pump inhibitor 2,5-di-tert-butylhydroquinone (BHQ) abolished magnolol-evoked [Ca] rises. Conversely, treatment with magnolol abolished BHQ-evoked [Ca] rises. Inhibition of phospholipase C (PLC) with U73122 partially inhibited magnolol-induced [Ca] rises. Magnolol at 20-100 μM decreased cell viability, which was not reversed by pretreatment with the Ca chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM).

Conclusions: Together, in OC2 cells, magnolol induced [Ca] rises by evoking partially PLC-dependent Ca release from the endoplasmic reticulum and Ca entry via PKC-sensitive store-operated Ca entry. Magnolol also caused Ca-independent cell death. Therefore, magnolol-induced cytotoxicity may not be involved in activation mechanisms associated with intracellular Ca mobilization in oral cancer cells.