Aloe-emodin induces apoptotic cell death via oxidative stress and JNK activation in human hepatoma cells.

B100

Aloe-emodin (AE) is one of the main bioactive anthraquinones of Rheum palmatum, a widely used herbal medicine. Several recent studies suggested that AE possesses potent anti-tumor properties, although the mechanisms have yet to be fully elucidated. The present study aimed to identify the molecular targets involved in AE-induced apoptosis. We first used a proteomic approach with 2D-DIGE and revealed marked up-regulation and oxidation of some redox-sensitive proteins (e.g. peroxiredoxin 2, 4 and DJ-1), suggesting that redox imbalance occurred in HepG2 cells treated with AE. Further biochemical studies demonstrated that AE enhanced the intracellular level of reactive oxygen species (ROS) and decreased the ratio of reduced glutathione/oxidized glutathione. Manipulation of the intracellular reduced glutathione (GSH) levels by pretreatment of a GSH scavenger (buthionine-L-sulfoinine), or a glutathione peroxidase inhibitor (mercaptosuccinic acid) sensitized cells to AE-induced apoptosis. In contrast, pretreatment with a GSH donor (GSH-MEE) protected cells from AE-induced apoptotic cell death. Furthermore, we found that AE caused sustained activation of JNK via the ASK1-JNK pathway by dissociation/activation of the inactive ASK1-thioredoxin complex and JNK-GST-pi complex. Over-expression of antioxidant gene sod1 significantly reduced AE-induced JNK activation and cell death. Consistently, knockdown of JNK by siRNA protected cells from AE-induced apoptosis, while over-expression of constitutively active JNK or ASK1 augmented AE-induced cell death. Taken together, these results suggest that AE may induce apoptotic cell death via oxidative stress and sustained JNK activation in human hepatoma cells.