Evaluation of (-)-epigallocatechin-3-gallate (EGCG)-induced cytotoxicity on astrocytes: A potential mechanism of calcium overloading-induced mitochondrial dysfunction.

(-)-epigallocatechin-3-gallate (EGCG), the main component of green tea, has long been explored in the treatment and/or prevention of central nervous system (CNS) disorders. However, EGCG has been recently shown to exhibit acute and subacute toxicity. Although a lot of work has been done, the mechanisms of EGCG-induced mitochondrial dysfunction has not been delineated in primary astrocyte. Here, the mitotoxic effect of EGCG on primary astrocytes was investigated by measuring Ca overloading-induced mitochondrial dysfunction. As expected, EGCG dose-dependently inhibited astrocytes growth depending on Ca overloading, especially at 50 μM EGCG group. It is interesting to note that Ca influx from the extracellular space was responsible for an increase in the cytosolic Ca level ([Ca]) by opening voltage-gated calcium channels (VGCCs) and, consequently, mitochondrial Ca ([Ca]) overloaded via the mitochondrial Ca uniporter (MCU). As a result, mitochondrial dysfunction was induced, including the opening of the mitochondrial permeability transition pore (mPTP), mitochondrial membrane depolarization, an increasing in reactive oxygen species (ROS), and cytochrosome c (cyt c) releasing. Therefore, more apoptotic cells were observed in 50 μM EGCG group than that of in 1 μM EGCG group. These findings suggested that a high dose of EGCG was toxic to astrocytes partly by targeting mitochondria via calcium pathway, which would extend our understanding of the toxicity of EGCG and the underlying mechanisms.