The effect of the phenol compound ellagic acid on Ca2+ homeostasis and cytotoxicity in liver cells

Abstract

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 Ca2+ homeostasis in liver cells is unknown. This study examined the effect of ellagic acid on intracellular Ca2+ concentration ([Ca2+]i) and established the relationship between Ca2+ signaling and cytotoxicity in liver cells. The data show that ellagic acid induced concentration-dependent [Ca2+]i rises in HepG2 human hepatoma cells, but not in HA22T, HA59T human hepatoma cells or AML12 mouse hepatocytes. In HepG2 cells, this Ca2+ signal response was reduced by removing extracellular Ca2+ and was inhibited by store-operated Ca2+ channel blockers (2-APB, econazole or SKF96365) and the protein kinase C (PKC) inhibitor GF109203X. In Ca2+-free medium, pretreatment with the endoplasmic reticulum Ca2+ pump inhibitor thapsigargin abolished ellagic acid-induced [Ca2+]i rises. Conversely, incubation with ellagic acid abolished thapsigargin-induced [Ca2+]i rises. Inhibition of phospholipase C (PLC) with U73122 also abolished ellagic acid-induced [Ca2+]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 Ca2+ with BAPTA-AM only in HepG2 cells. Together, in HepG2 cells, ellagic acid induced [Ca2+]i rises by inducing PLC-dependent Ca2+ release from the endoplasmic reticulum and Ca2+ entry via PKC-sensitive store-operated Ca2+ channels. Moreover, ellagic acid induced Ca2+-associated cytotoxicity.