Activation of apoptosis and G0/G1 cell cycle arrest along with inhibition of melanogenesis by humic acid and fulvic acid: BAX/BCL-2 and Tyr genes expression and evaluation of nanomechanical properties in A375 human melanoma cell line

Humic acid (HA) and Fulvic acid (FA) are major members of humic substances, which are extracted from organic sources including soil and peat. The pro-apoptotic and anti-melanogenic effects of HA and FA at the cellular and molecular levels in the A375 human melanoma cell line were examined in this study.  The cytotoxicity effect of HA and FA were evaluated by cell viability assay. Apoptosis and cell cycle were investigated by flow cytometry. Real-time PCR was carried out to measure the expression of BAX, BCL-2, and Tyr genes. Moreover, the changes in nanomechanical properties were determined through atomic force microscopy (AFM).  It was found that HA and FA decrease cell viability with an IC50 value of 50 µg/ml (dose-dependent) for 14 hr, arrested cells in the G0/G1 phase, and increased the sub-G1 phase (induce apoptosis). Based on the AFM analysis, Young’s modulus and adhesion force values were increased, also ultrastructural characteristics of cells were changed. Results of Real-time PCR revealed that HA and FA lead to a decrease in the expressions of BCL-2 and Tyr genes, and increase the BAX gene expression. These results exhibited that HA and FA possess pro-apoptotic effects through increasing the BAX/ BCL-2 expression in A375 cells. These molecular reports were confirmed by cellular nanomechanical assessments using AFM and flow cytometry. In addition, HA and FA inhibited melanogenesis by decreasing the expression of the Tyr gene. It is worthwhile to note that, HA and FA can be regarded to design new anti-cancer and anti-melanogenesis products.