The effect of the phenol compound ellagic acid on Ca(2+) homeostasis and cytotoxicity in liver cells.

Ellagic acid, a natural phenol compound found in numerous fruits and vegetables, causes various physiological effects in different cell models. However, the effect of this compound on Ca(2+) homeostasis in liver cells is unknown. This study examined the effect of ellagic acid on intracellular Ca(2+) concentration ([Ca(2+)]i) and established the relationship between Ca(2+) signaling and cytotoxicity in liver cells. The data show that ellagic acid induced concentration-dependent [Ca(2+)]i rises in HepG2 human hepatoma cells, but not in HA22T, HA59T human hepatoma cells or AML12 mouse hepatocytes. In HepG2 cells, this Ca(2+) signal response was reduced by removing extracellular Ca(2+) and was inhibited by store-operated Ca(2+) channel blockers (2-APB, econazole or SKF96365) and the protein kinase C (PKC) inhibitor GF109203X. In Ca(2+)-free medium, pretreatment with the endoplasmic reticulum Ca(2+) pump inhibitor thapsigargin abolished ellagic acid-induced [Ca(2+)]i rises. Conversely, incubation with ellagic acid abolished thapsigargin-induced [Ca(2+)]i rises. Inhibition of phospholipase C (PLC) with U73122 also abolished ellagic acid-induced [Ca(2+)]i rises. Ellagic acid (25-100μM) concentration-dependently caused cytotoxicity in HepG2, HA22T or HA59T cells, but not in AML12 cells. Furthermore, this cytotoxic effect was partially prevented by prechelating cytosolic Ca(2+) with BAPTA-AM only in HepG2 cells. Together, in HepG2 cells, ellagic acid induced [Ca(2+)]i rises by inducing PLC-dependent Ca(2+) release from the endoplasmic reticulum and Ca(2+) entry via PKC-sensitive store-operated Ca(2+) channels. Moreover, ellagic acid induced Ca(2+)-associated cytotoxicity.