Evaluation of urinary biomarkers of oxidative/nitrosative stress in children with Down syndrome

It has been suggested that oxidative stress plays a key role in the pathogenesis of Down syndrome (DS). However, urinary biomarkers of oxidative stress have been little studied in this condition. Thus, we aimed to assess a set of urinary oxidative/nitrosative stress biomarkers in children with DS, with and without hypothyroidism, which comprise: 8-hydroxy-2′-deoxyguanosine (8-OHdG), isoprostane 15-F2t-IsoP, thiobarbituric acid-reacting substances (TBARS), advanced glycation end products (AGEs), dityrosine (diTyr), hydrogen peroxide (H2O2) and nitrite/nitrate (NOx). Fluorimetric and spectrophotometric assays were performed in children with DS (n=26), some of them taking levothyroxine for hypothyroidism (n=7), and their non-Down siblings (n=19). We found that only levels of diTyr were increased in DS, although no differences were obtained when hypothyroid DS children were excluded. Levels of 8-OHdG, 15-F2t-IsoP, TBARS, AGEs, H2O2 and NOx did not differ neither between DS and controls nor between hypothyroid DS children and DS without hypothyroidism diagnosed. However, diTyr is increased in hypothyroid DS children compared with controls. Negative correlations with age were obtained for 8-OHdG, diTyr and NOx in DS and controls and for 8-OHdG, 15-F2t-IsoP, TBARS and AGEs in DS. Increased oxidative stress in children with DS cannot be explained by the urinary levels of 8-OHdG, 15-F2t-IsoP, TBARS, AGEs, diTyr, H2O2 and NOx, at least with the assays used. Nonetheless, urinary diTyr could be used as oxidative/nitrosative stress biomarker in hypothyroid DS children. The present work presents evidence of a probable renal impairment in children with DS receiving levothyroxine for hypothyroidism.