Overestimation of advanced oxidation protein products in uremic plasma due to presence of triglycerides and other endogenous factors.
BACKGROUND
Advanced oxidation protein products (AOPP), a suggested protein biomarker of oxidative stress, are elevated in patients with chronic kidney disease (CKD), who also often suffer from hypertriglyceridemia.


METHODS
The analysis included plasma AOPP, TG, cholesterol, albumin and total protein, inflammation and oxidative stress markers from healthy subjects, non-dialyzed CKD, HD and CAPD patients. We studied, at two different European centres, effects of a meal, comparison between serum and plasma, L-index (indicating turbidity), spiking with fat and protein, and centrifugation on the AOPP concentrations. AOPP was measured at 340 nm and expressed as chloramine-T equivalents.


RESULTS
AOPP correlated with TG levels not only in CKD patients, but also in healthy subjects. Weak to absent correlations were observed between AOPP and markers of inflammation and oxidative stress in CKD patients. A meal increased the TG levels several-fold paralleled by a rise in measured AOPP to patient levels. Spiking of the plasma with Intralipid or protein resulted in increased absorbances at 340 nm, due to turbidity or real absorbance, while centrifugation similarly decreased the apparent AOPP and TG levels.


CONCLUSIONS
AOPP concentration, especially due to the influence of turbidity at all levels of TG concentration, but also due to other factors on top of TG, is overestimated in all plasma samples, including controls at fasting and non-fasting conditions. Thus, AOPP is a questionable biomarker of oxidative stress and inflammation in CKD patients.
Valli
Alessandro
A
Divisions of Renal Medicine and Baxter Novum, Department of Clinical Science, Intervention and Technology, Karolinska Institutet, Huddinge, Stockholm, Sweden.
Suliman
Mohamed E
ME
Meert
Natalie
N
Vanholder
Raymond
R
Lindholm
Bengt
B
Stenvinkel
Peter
P
Watanabe
Makoto
M
Barany
Peter
P
Alvestrand
Anders
A
Anderstam
Björn
B
D000368:Aged; D015415:Biomarkers / Q000097:blood; D001798:Blood Proteins / Q000032:analysis*; D005260:Female; D006801:Humans; D015228:Hypertriglyceridemia / Q000150:complications / Q000175:diagnosis*; D007676:Kidney Failure, Chronic / Q000150:complications / Q000175:diagnosis*; D007677:Kidney Function Tests / Q000592:standards*; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D014280:Triglycerides / Q000097:blood*; D014511:Uremia / Q000097:blood / Q000150:complications / Q000175:diagnosis*
D015415:Biomarkers; D001798:Blood Proteins; D014280:Triglycerides