Background: In vitro and rodent studies have shown that arsenic (As) exposure can deplete glutathione (GSH) and induce oxidative stress. GSH is the primary intracellular antioxidant; it donates an electron to reactive oxygen species, thus producing glutathione disulfide (GSSG). Cysteine (Cys) and cystine (CySS) are the predominant thiol/disulfide redox couple found in human plasma. Arsenic, GSH, and Cys are linked in several ways: a) GSH is synthesized via the transsulfuration pathway, and Cys is the rate-limiting substrate; b) intermediates of the methionine cycle regulate both the transsulfuration pathway and As methylation; c) GSH serves as the electron donor for reduction of arsenate to arsenite; and d) As has a high affinity for sulfhydryl groups and therefore binds to GSH and Cys. Objectives: We tested the hypothesis that As exposure is associated with decreases in GSH and Cys and increases in GSSG and CySS (i.e., a more oxidized environment). Methods: For this cross-sectional study, the Folate and Oxidative Stress Study, we recruited a total of 378 participants from each of five water As concentration categories: & 10 (n = 76), 10–100 (n = 104), 101–200 (n = 86), 201–300 (n = 67), and < 300 µg/L (n = 45). Concentrations of GSH, GSSG, Cys, and CySS were measured using HPLC. Results: An interquartile range (IQR) increase in water As was negatively associated with blood GSH (mean change, –25.4 µmol/L; 95% CI: –45.3, –5.31) and plasma CySS (mean change, –3.00 µmol/L; 95% CI: –4.61, –1.40). We observed similar associations with urine and blood As. There were no significant associations between As exposure and blood GSSG or plasma Cys. Conclusions: The observed associations are consistent with the hypothesis that As may influence concentrations of GSH and other nonprotein sulfhydryls through binding and irreversible loss in bile and/or possibly in urine
