GDF15 and cancer: Although studies have reported that proanthocyanidins can trigger the apoptosis of cancer cells [14,21,34,35], their effects on the expression and modulation of mitogen-activated protein kinases (MAPK) pathway-related proteins and non-steroidal anti-inflammatory drug-activated gene-1 (NAG-1), as well as their relationship in HepG2 cells, still remain unclear.