The Effect of Magnolol on Ca2+ 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 Ca2+ homeostasis and its related physiology in oral cancer cells is unclear. This study examined whether magnolol altered Ca2+ signaling and cell viability in OC2 human oral cancer cells. Methods: Cytosolic Ca2+ concentrations ([Ca2+](i)) in suspended cells were measured by using the fluorescent Ca2+ -sensitive dye fura-2. Cell viability was examined by 4-[3-[4-lodopheny1]-2-4(4-nitropheny1)-2H-5-tetrazolio-1,3-benzene disulfonate] water soluble tetrazolium-1 (WST-1) assay. Results: Magnolol at concentrations of 20-100 mu M induced [Ca2+](i) rises. Ca2+ removal reduced the signal by approximately 50%. Magnolol (100 mu M) induced Mn2+ influx suggesting of Ca2+ entry. Magnolol-induced Ca2+ entry was partially suppressed by protein kinase C (PKC) regulators, and inhibitors of store-operated C-a2+ channels. In Ca2+-free medium, treatment with the endoplasmic reticulum Ca2+ pump inhibitor 2,5-di-tertbutylhydroquinone (BHQ) abolished magnolol-evoked [Ca2+](i) rises. Conversely, treatment with magnolol abolished BHQ-evoked [Ca2+](i) rises. Inhibition of phospholipase C (PLC) with U73122 partially inhibited magnolol-induced [Ca2+](i) rises. Magnolol at 20-100 mu M decreased cell viability, which was not reversed by pretreatment with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA/AM). Conclusions: Together, in OC2 cells, magnolol induced [Ca2+](i) rises by evoking partially PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-sensitive store-operated Ca-2+ entry. Magnolol also caused Ca2+-independent cell death. Therefore, magnolol-induced cytotoxicity may not be involved in activation mechanisms associated with intracellular Ca2+ mobilization in oral cancer cells.