An essay on superoxide dismutase, 2-methoxyestradiol, and the proper uses of scientific methods

detectors. The logical conclusion is that ME is not an inhibitor of SOD. Later, two groups (Golab et al. 2003; Florczak et al. 2009) concluded that their findings support the view that ME inhibits SOD. Let us examine whether this is the case. They used essentially the same method as the one used by Huang et al. except that XTT (2,3-bis[2-methoxy4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide); was replaced by similar tetrazolium salts such as INT (2-(4-iodophenyl)-3-(4-nitrophenol)-5-phenyltetrazolium chloride). However, they did not use other methods. In addition, in some of the cases SOD activity from cancer cells incubated with ME was studied and in such cases the effect of ME might be indirect as actually suggested (Golab et al. 2003). Therefore, the data in these two papers do not refute any of the conflicting views. On the other hand, our results do not contradict the thesis that ME decreases the activity of SODs in vivo or in cultured (cancer) cells by thus far an unknown mechanism. The most recent claim that ME inhibits SOD (Mn SOD from Clostridium difficile) was made by Li et al. (2015). While in both, Huang’s et al. and Li’s et al. assays superoxide anion radical (O2 ·−) was generated by xanthine oxidase (XO) plus xanthine (X), the first group used XTT, and the second, cytochrome c (cyt c), as detectors for O2 ·−. A more detailed inspection of the Li et al. paper follows. In Fig. 4 panel B, Li et al. followed the reduction of cytochrome c at 550 nm (A550) as a function of the concentration of SOD (Mn SOD) after 30 min of reaction. In the absence of ME, A550 nm was ~0.17 in the absence of SOD, while in the presence of ~0.02 μg/ml SOD A550 nm was slightly over 0.11 and in the presence of ~0.16 μg/ml SOD A550 was also slightly over 0.11. Thus, these authors report that an eightfold range SOD concentration inhibited the reduction of cytochrome