Uric acid and allantoin levels in Down syndrome: antioxidant and oxidative stress mechanisms?

Abstract

Background: Down syndrome (DS) is a chromosomal abnormality (trisomy 21) leading to mental retardation, to the characteristic change of individual's phenotype and to the pathological features of Alzheimer disease. Patients with DS have elevated ratio of superoxide dismutase to (catalase plus glutathione peroxidase) with respect to controls in all age categories suggesting that oxidative imbalance contributes to the clinical manifestation of accelerated aging. Results: We report that persons with DS have elevated uric acid levels compared with controls, 348.56±22.78 versus 284.00±20.86 μmol/l ( p=0.018). The levels of hypoxanthine and xanthine in DS children (6.35±0.31 and 1.02±0.23 μmol/l) were significantly lower than in controls (7.83±0.59 and 2.43±0.66 μmol/l). This result suggests increased conversion of hypoxanthine and xanthine to uric acid with subsequent free radical-dependent oxidation of uric acid to allantoin, mechanisms potentiated by the oxidative stress in DS. Allantoin is a nonenzymatic oxidative product of uric acid in human. In DS individuals, the levels of allantoin were significantly higher than those in healthy controls (18.58±2.27 and 14.07±1.07 μmol/l, respectively, p=0.03). Conclusions: Our data supported the presumption of increased oxidative stress in DS.