The effect of the phenol compound ellagic acid on Ca²⁺ 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 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 (25-100 μM) 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.