Background: Xanthine oxidoreductase (XOR) is an enzyme that catalyzes the formation of uric acid from hypoxanthine and xanthine, leading to an increase in superoxide and reactive oxygen species. Activation of XOR promotes oxidative stress-related tissue injury. We investigated the associations between metabolic parameters and plasma XOR activity measured by a sensitive and accurate assay using a combination of liquid chromatography and triple quadrupole mass spectrometry to detect [13 C 2, 15 N 2]-uric acid using [13 C 2, 15 N 2]-xanthine as a substrate.

Methods and Results: A total of 627 Japanese subjects (M/F, 292/335) from the Tanno-Sobetsu Study, a population-based cohort, were recruited. Plasma XOR activity was significantly higher in males than in females, and habitual smoking was associated with elevation of activity. Plasma XOR activity was positively correlated with body mass index (BMI; r= 0.323, P< 0.001), waist circumference, blood pressure, and levels of liver enzymes including alanine transaminase (r= 0.694, P< 0.001), uric acid (r= 0.249, P< 0.001), triglycerides (r= 0.312, P< 0.001), hemoglobin A1c, fasting glucose, insulin and HOMA-R (r= 0.238, P< 0.001) as a marker of insulin resistance and was negatively correlated with high-density lipoprotein cholesterol level. On stepwise and multivariate regression analyses, BMI, smoking and levels of alanine transaminase, uric acid, triglycerides and HOMA-R were independent predictors of plasma XOR activity after adjustment for age and gender.

Conclusions: Plasma XOR activity is a novel biomarker of metabolic disorders in a general population.