LINK

dear Bruna,

 have you normalized for the number of cells survived to the treatment? if you kill cells no activity will be measured while survived cells are trying to repear DNA damages with enhanced activity

Hi Daniel, 

Thanks for your answer.

And yes I have normalized the cell number before the treatment. But after that, I have an increase in cell death in ther higher concentration

I have a couple of thoughts, first, could the metal(s) you're adding be interfering with the kit you're using? I know that it is a big problem when using nanopaticles, but I'm not sure if this kit might be affected by whatever metal(s) you're using. I don't know if you've included a positive control that you've spiked with the metal(s) or not, if you haven't I'd give that a try and see if it affects the kit.

Second, I'm unclear about how you're running the experiment. Is your exposure at the LC50 the length of the LC50? What I mean is that if you are using a 48 hour LC50 as your exposure concentration and exposing for 48 hours, then normalizing cell death before the exposure may not be sufficient, you may need to compensate for the number of surviving cells (as Diego says above). If you kill 50% of the cells in the dish, then you're measuring caspase activity in half the population you started with (I'm assuming caspase 3/7 denature quickly after cell death). 

Hope that's helpful!