Diurnal variation in glutathione and cysteine redox states in human plasma.
BACKGROUND
Plasma glutathione/glutathione disulfide (GSH/GSSG) and cysteine/cystine (Cys/CySS) couples are oxidized in humans in association with oxidative stress and cardiovascular disease risk. Animal studies show that both pools undergo diurnal variations associated with dietary intake of sulfur amino acids.


OBJECTIVE
The objective of this study was to determine whether the redox state of GSH, Cys, GSH/GSSG, or Cys/CySS undergoes diurnal variation in healthy adults.


METHODS
Plasma samples were collected every hour for 24 h from 63 persons aged 18-86 y who were consuming normal food (protein, 0.8 g kg(-1) d(-1); sulfur amino acids, 20 mg kg(-1) d(-1)) at standardized mealtimes. Measurements of Cys, CySS, GSH, and GSSG were used with the Nernst equation to calculate the redox states.


RESULTS
Plasma Cys and GSH concentrations varied with the time of day. The highest values for plasma Cys occurred approximately 3 h after meals. Glutathione was maximal 6 h after peak plasma Cys. The calculated redox states of the GSH/GSSG and Cys/CySS couples varied in association with the concentrations of the thiol forms. Maximal reduction and oxidation of the Cys/CySS couple occurred at 2130 and 0630, whereas the respective values for the GSH/GSSG couple occurred at 0330 and 1330. The mean diurnal variation for Cys/CySS redox in persons aged >or=60 y was 1.8-fold that in persons aged <40 y.


CONCLUSIONS
Cys/CySS and GSH/GSSG redox states in human plasma undergo diurnal variation with an increased magnitude of variation in Cys/CySS redox state in older persons. This variation could alter sensitivity to oxidative stress over a course of hours.
Blanco
Roberto A
RA
Division of Endocrinology, Metabolism and Lipids, Department of Medicine, Emory University, Atlanta, GA 30322, USA.
Ziegler
Thomas R
TR
Carlson
Bryce A
BA
Cheng
Po-Yung
PY
Park
Youngja
Y
Cotsonis
George A
GA
Accardi
Carolyn Jonas
CJ
Jones
Dean P
DP
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000378:metabolism*; D019540:Area Under Curve; D002318:Cardiovascular Diseases / Q000378:metabolism; D002940:Circadian Rhythm / Q000502:physiology*; D003545:Cysteine / Q000097:blood / Q000378:metabolism*; D003553:Cystine / Q000097:blood / Q000378:metabolism; D005260:Female; D005978:Glutathione / Q000097:blood / Q000378:metabolism*; D019803:Glutathione Disulfide / Q000097:blood / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000502:physiology; D019518:Postprandial Period / Q000502:physiology*; D012737:Sex Factors
D003553:Cystine; D005978:Glutathione; D003545:Cysteine; D019803:Glutathione Disulfide