Bifunctional mechanisms of autophagy and apoptosis regulations in melanoma from Bacillus subtilis natto fermentation extract

Melanoma is one of the most dangerous malignant epidermal cancers. Natto freeze-drying extract (NFDE) and natto water extract (NWE) were isolated from natto, soybeans fermented by Bacillus subtilis natto, which were assessed as potential anti-melanoma agents. Cell cytotoxicity assays revealed significant anti-melanoma effects of NFDE and NWE in a dose-dependent manner, and exhibited low influences on normal skin cells, including Hs68, HaCaT and adipose tissue-derived stem cells (ADSCs), respectively. Through a flow cytometer assay and autophagy acridine orange staining, the cellular death phenomenon shifted from autophagy to apoptosis with the increased dosages. Reactive oxygen species (ROS) were enhanced using DCFDA (2,7-dichlorodihydrofluorescein diacetate) staining when melanoma cells were treated with the extract. NFDE and NWE treatments increase the oxidative stress of cancer cells and cause apoptosis by inhibiting AMP-activated protein kinase (AMPK). NFDE and NWE were considered to play a critical role in cell death through ROS adjustment, autophagy regulation and apoptosis promotion.