Abstract: Objective The systemic redox imbalance can lead to the occurrence of oxidative stress, which is closely associated with tumor, aging and various diseases. The redox potentials (E_h) measuring the poise of thiol/disulfide redox couples such as cysteine/cystine (Cys/CySS) and reduced glutathione/oxidized glutathione (GSH/ GSSG) in plasma are useful indicators of systemic oxidative stress and other physiological states. This study describes a rather sensitive new method to determine the levels of Cys/CySS and GSH/GSSG in plasma. Methods After removal of the red blood cells and proteins in rats’ blood, iodoacetate was used to alkylate free thiols, followed by derivatization with dansyl. The levels of Cys/CySS and GSH/GSSG were separated by HPLC and the corresponding redox potentials(E_h) were caculated by Nernst equation. Results With high sensitivity and accuracy, this method can be used simultaneously to detect the levels of both Cys/CySS and GSH/GSSG in plasma and to calculate the corresponding redox potentials(E_h). Conclusion The study provides a more convenient and effective method to detect the redox environment of plasma that might be helpful for the diagnosis of clinical diseases related to oxidative stress.

Key words: high performance liquid chromatography (HPLC), redox potentials (E_h), cysteine/cystine(Cys/CySS), reduced glutathione/oxidized glutathione(GSH/GSSG), oxidative stress