Critical evaluation of plasma and LDL oxidant-trapping potential in hemodialysis patients.
BACKGROUND
We investigated whether the total peroxyl radical-trapping antioxidant potential (TRAP) assay, which has recently been proposed as a gauge of oxidative stress, could serve to evaluate plasma and low density lipoprotein (LDL) antioxidant state in hemodialysis (HD) patients.


METHODS
TRAP was determined by the lag time of the chemiluminescence reaction induced by azo-initiator-catalyzed linoleic acid peroxidation in the plasma and corresponding LDL preparations of 23 HD patients and 22 healthy subjects. Antioxidant systems, including glutathione peroxidase (GSH-Px), ascorbate, vitamin E, and uric acid, oxidative stress markers including malondialdehyde (MDA), carbonyls, and advanced oxidation protein products (AOPP), and lipids, including cholesterol and triglycerides, were also determined in the plasma.


RESULTS
Both plasma and LDL-TRAP were significantly increased in HD patients despite decreased GSH-Px and ascorbate and increased MDA, carbonyl, and AOPP plasma levels. Plasma TRAP values were closely related to both uric acid and AOPP levels, and LDL-TRAP values were related to triglycerides and AOPP levels. In vitro studies showed that: (a) plasma TRAP of control plasma increased regularly with supplementation of uric acid, although not reaching that of HD plasma with similar uric acid levels; (b) the addition of human serum albumin-AOPP also regularly increased control plasma TRAP, but was close to that of HD plasma with similar AOPP levels; and (c) LDL-TRAP was increased following LDL enrichment with triglycerides.


CONCLUSIONS
Our study demonstrates that TRAP is not a relevant parameter for evaluating plasma or LDL antioxidant capacity in HD patients, due to the high plasma levels of uric acid, triglycerides and AOPP, which by themselves do not exert efficient antioxidant activity in vivo, but in vitro are able to scavenge the peroxyl radicals involved in the TRAP assay.
Nguyen-Khoa
T
T
INSERM U507, Division of Nephrology, Necker Hospital, Paris, France.
Massy
Z A
ZA
Witko-Sarsat
V
V
Thévenin
M
M
Touam
M
M
Lambrey
G
G
Lacour
B
B
Drüeke
T B
TB
Descamps-Latscha
B
B
D000368:Aged; D000975:Antioxidants / Q000378:metabolism*; D001205:Ascorbic Acid / Q000097:blood; D015415:Biomarkers; D005260:Female; D016166:Free Radical Scavengers / Q000097:blood; D005979:Glutathione Peroxidase / Q000097:blood; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood* / Q000628:therapy; D008077:Lipoproteins, LDL / Q000097:blood*; D008297:Male; D008315:Malondialdehyde / Q000097:blood; D008875:Middle Aged; D010084:Oxidation-Reduction; D018384:Oxidative Stress / Q000187:drug effects / Q000502:physiology; D006435:Renal Dialysis; D014280:Triglycerides / Q000097:blood; D014527:Uric Acid / Q000097:blood / Q000494:pharmacology; D014810:Vitamin E / Q000097:blood
D000975:Antioxidants; D015415:Biomarkers; D016166:Free Radical Scavengers; D008077:Lipoproteins, LDL; D014280:Triglycerides; C099252:oxidized low density lipoprotein; D014810:Vitamin E; D014527:Uric Acid; D008315:Malondialdehyde; D005979:Glutathione Peroxidase; D001205:Ascorbic Acid