Dietary sulfur amino acid effects on fasting plasma cysteine/cystine redox potential in humans.
OBJECTIVE
Oxidation of plasma cysteine/cystine (Cys/CySS) redox potential (E(h)CySS) has been associated with risk factors for cardiovascular disease in humans. Cys and CySS are derived from dietary sulfur amino acids (SAA), but the specific effects of SAA depletion and repletion on Cys/CySS redox indices are unknown. The present study examined the effect of dietary SAA intake level on free Cys, free CySS, and E(h)CySS in human plasma under fasting conditions.


METHODS
Healthy individuals aged 18-36 y (n = 13) were equilibrated to foods providing the RDA for SAA and then fed chemically defined diets without SAA (0 mg · kg(-1) · d(-1); n = 13) followed by SAA at levels approximating the mean (56 mg · kg(-1) · d(-1); n = 8) or 99th percentile (117 mg · kg(-1) · d(-1); n = 5) intake levels of Americans. Fasting plasma samples were collected daily during 4-d study periods and analyzed for free Cys, free CySS, and the E(h)CySS.


RESULTS
The SAA-free diet significantly (P < 0.05) decreased plasma-free Cys concentrations and oxidized E(h)CySS values after 4 d of SAA depletion. With SAA repletion at 56 mg · kg(-1) · d(-1), plasma-free Cys increased significantly and values for E(h)CySS became more reduced. Administration of a diet providing a higher dose of SAA (117 mg · kg(-1) · d(-1)) resulted in a significantly higher level of free Cys and a more reduced E(h)CySS.


CONCLUSIONS
These results show that free Cys and Cys/CySS redox potential (E(h)CySS) in fasting plasma are affected by dietary SAA intake level in humans. Significant changes occur slowly over 4 d with insufficient SAA intake, but rapidly (after 1 d) with repletion.
Jones
Dean P
DP
Division of Pulmonary, Allergy and Critical Care Medicine, Emory University, Atlanta, Georgia, USA. dpjones@emory.edu
Park
Youngja
Y
Gletsu-Miller
Nana
N
Liang
Yongliang
Y
Yu
Tianwei
T
Accardi
Carolyn Jonas
CJ
Ziegler
Thomas R
TR
D000293:Adolescent; D000328:Adult; D000603:Amino Acids, Sulfur / Q000008:administration & dosage* / Q000009:adverse effects; D002318:Cardiovascular Diseases / Q000453:epidemiology; D003545:Cysteine / Q000097:blood*; D003553:Cystine / Q000097:blood*; D004032:Diet; D004044:Dietary Proteins / Q000008:administration & dosage* / Q000009:adverse effects; D005215:Fasting; D005260:Female; D006801:Humans; D008297:Male; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010949:Plasma / Q000378:metabolism*; D055815:Young Adult
D000603:Amino Acids, Sulfur; D004044:Dietary Proteins; D003553:Cystine; D003545:Cysteine
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