Whilst the rational for doing this experiment is clear in terms of understanding the metabolomic effects of PQ on human mesencephalic neurons, I am concerned that not enough prior characterization was done on this LUMES model before performing this experiment. First, it would need to be shown that they are generating dopaminergic neurons e.g. TH+ as a minimum as these neurons, as opposed to the cholinergic neurons (as indicated by the changed levels in acetylcholine), are the neurons that are primarily lost within PD patients. Second, the cell loss induced by PQ are very modest and then only at extremely high concentrations (up 500 uM). Other have reported have reported >50% TH+ neuron loss at 50 uM PQ (e.g. Choi et al., 2008 PNAS). Third, the Leist group has done extensive work with MPTP in this cellular model. Considering the mentioned similarities between MPTP and PQ, an MPTP positive control should have been conducted in parallel. Fourth, there was no attempt to rescue/protect these modest effects (e.g. through the use of antioxidants), something that has been shown to be effective in numerous cellular models including the LUMES model. Consequently, I am not sure what the value of the performed metabolomic profiling is and the conclusions drawn from them based on the very limited prior characterization/optimization.