I know that cells under tissue culture conditions are different from those in vivo in many ways, but what exactly could trigger antioxidant enzymes such as POX, SOD and CAT in tissue culture media?
Any stresses caused by the cell culture system. It could be pH, osmolarity, microbe contamination, O2 level in the incubator, prolonged exposure to low or hot temperature for observation, cell confluency, wastes produced by cells, etc.
The main sources for oxidative stress in cell culture is dimolecular oxygen O2 which necessary for cells to grow in culture this source is more pronounced in serum and proteins free culture media where serum and proteins are a good contributor to antioxidants and keep oxidants/antioxidants status in balance in normal animal cells while this balance is disrupted in cell culture due to removal of serum and proteins as well as addition of some various compounds and regulators known to disrupt such balance such as ethanol.