A Chemically Defined Diet With Insufficient Sulfur Amino Acids Induces Oxidation of Plasma Cysteine/Cystine and Glutathione/Glutathione Disulfide Redox State in Humans

Sulfur amino acid (SAA) availability is critical for glutathione (GSH) synthesis. GSH has an important role in detoxification and maintenance of intracellular glutathione/glutathione disulfide (GSH/GSSG) redox as well as extracellular cysteine/cystine (Cys/CySS) redox in vitro. Intermittent periods of SAA insufficiency are common due to food selection, dieting, and fasting. To examine the effects of dietary SAA insufficiency on redox status in vivo, young, healthy volunteers were studied on 2 separate occasions for 60 hours in the General Clinical Research Center (GCRC) at Emory University Hospital. During each study period, volunteers consumed 1 of 2 chemically defined diets modified for SAA content (100% or 0% of the Recommended Dietary Allowance for SAA intake) for 3 days. Blood was drawn hourly for 12 hours on day 3. Results from 4 individuals show that consumption of the 0% SAA diet resulted in a significant oxidation (~ 9 mV) of plasma Cys/CySS redox status as compared to consumption of the 100% SAA diet (−73± 0.8 mV vs. −82± 0.8 mV respectively). In contrast, consumption of the 0% SAA diet did not affect plasma GSH/GSSG redox status as compared to control diet (−123± 2 mV vs. −124.3± 1 mV respectively). We conclude that 3-day consumption of a diet insufficient in SAA induces significant oxidation of the plasma Cys/CySS redox state while having no affect on plasma GSH/GSSG redox status in humans. Support: NIEHS RO1 09047.