For AFB1, its high value of IC50 is different from literature reports measured by MTT
test [10], and this is likely due to different methods used to measure cell viability. SRB refers to the total protein in the cell [22] while MTT test is based on the enzyme activity of NAD(P)H-dependent cellular oxidoreductase [32], so there is possible discrepancy between the two methods, and the value of IC50 is likely dependent Cisplatin ic50 on the cell viability measurement method. Regarding different values of IC50 between AFB1 and ST, there is a literature report that the IC50 of AFB1 (10 μM) is greater than that of ST (3.7 μM) in human lung cancer cell line of A549 [10] and [33], which also showed that ST is more toxic than AFB1. Another literature report [11] also showed noticeable difference between AFB1 and ST in hormonal induction of tyrosine aminotransferase with different values of IC50 in a rat hepatoma cell line of H4-II-E. The cytotoxicity endpoints of ROS, mitochondria membrane permeability (MMP), DNA
and ATP content all showed cytotoxicity of AFB1 and ST (Fig. 3) to HepG2 cells, and all the endpoints show similar trends when HepG2 cells were exposed to individual AFB1 and ST or their combinations. The contents of both ATP and DNA were decreased while the ROS and MMP were increased MS-275 cell line along the treatment concentrations. Comparatively, the decrease of ATP and DNA is more evident than the increase of ROS and MMP, and ST is more potent
to decrease ATP content. However, no significant difference between the measured combinative toxicity and the calculated Megestrol Acetate toxicity (by adding the values of each endpoint at corresponding concentrations used in their combinations) demonstrates an additive nature of their combinative cytotoxicity. Correlation analysis on the relationship among all the endpoints showed that ATP is positively correlated to DNA content, but negatively correlated to ROS and SRB at a significant level. Both ROS and MMP are positively correlated to SRB (Table 1). Thus, decreased cell viability of HepG2 cells islikely caused by the production of ROS, increased MMP and decreased ATP and DNA when exposed to AFB1 and ST. Consistently, the PCA analysis of these endpoints showed that three clusters can be differentiated: SRB is one cluster, DNA and ATP content is the second cluster, and the third cluster includes ROS and MMP. Considering the biochemical processes associated with mycotoxin exposure, the increased intracellular ROS is a common feature for AFB1 or other mycotoxins [34]. The increased intracellular ROS might cause cross-linking of mitochondria membrane protein and to induce membrane permeability transition and increased MMP [35]. The increase of MMP would result in a decrease of mitochondrial membrane electrochemical potential and uncoupling ATP production from mitochondrial respiratory chain, which would lead to a reduction of ATP production.