Cell-based detection of electrochemical oxidative stress by a fluorescent tryptophan intermediate

The present study suggests a sensitive and rapid cell analysis method to evaluate the oxidative stress produced in a physiological culture medium, by anodic electrochemical products. The detection of these oxidizing agents, probably involving hypochlorite, is carried out by measuring the presence of an oxidized tryptophan intermediate, entrapped and stabilized in the cell cytoplasm. The formation of this tryptophan intermediate depends solely on the presence of a free tryptophan in the extracellular medium near the anode. This intermediate possesses a characteristic emission maximum at λ ~ 560 nm, which can be abolished by the presence of anti-oxidants in the media during the cells’ exposure to electric current. However, this intermediate's emission is unaffected by increased concentrations of intracellular anti-oxidants. This suggests that the anodic produced unstable tryptophan intermediate permeates the cell plasma membrane and becomes stabilized by cytoplasmic proteins. Tryptophan oxidative intermediates with similar spectra could also be formed by the chemical reaction of hypochlorite with tryptophan in solution. The analysis of the intracellularly stabilized tryptophan intermediate by flow cytometry can be used for measuring external oxidation stress without the disturbance of intracellular anti-oxidative capacity.

► Electrochemical oxidation of Trp produce short-lived orange-red fluorescent byproduct
► Oxidized Trp penetrates the cell membrane and is entrapped by cytoplasmic proteins
► Cells acquire orange-red fluorescence under anodic electrochemical oxidation of Trp
► The cellular fluorescence can be used to probe the anodic induced oxidative stress