Urinary NO_x, a novel potential biomarker for autism spectrum disorder

Nitric oxide (NO) participates in many physiological and pathological processes in human. Urine tests tell a lot about health, which are convenient and harmless. Redox stress, including imbalance of reactive nitrogen species and its metabolites NO_x, has been gaining increased attention in autism spectrum disorder (ASD) research. However, concentrations of urinary nitrite and nitrate among the ASD population stay unclear. In this study, nitrite and nitrate were precisely measured in urine specimens from 44 ASD children, 30 healthy children (the control group) and 28 healthy adults with an optimized and validated analytic method. For the first time, concentrations of urinary NO_x in ASD and healthy children were reported. Nitrite in the ASD population is higher than in the control group, with concentrations of 0.8708 ± 0.1121 μM (0.1556-3.0393 μM) and 0.5938 ± 0.07276 μM (0.1134-2.1004 μM) (p = 0.0420), respectively. Nitrite in the adult groups is 0.5808 ± 0.0985 μM (0.0808-1.9335 μM), which is similar to that in the control group. On the contrary, urinary nitrate concentration in ASD children is lower than that in the control group, which are 2.875 ± 0.2716 mM (0.3264-7.1835 mM) and 4.558 ± 0.5915 mM (1.1860-15.8555 mM) (p = 0.0133), respectively. Nitrate in adults is also significantly lower than that in the control, 2.799 ± 0.3640 mM (0.2507-8.6978 mM) and 4.558 ± 0.5915 mM (p = 0.0146), respectively. Nitrite/nitrate ratios for ASD and the control groups were 0.3496 ± 0.04382 x 10^-3 and 0.1604 ± 0.01862 x 10^-3 (p = 0.0002), which again indicated the probability of NO_x as a novel biomarker. Furthermore, no correlation between NO_x and gender, as well as sample collection timing was found. Taken together, the association between NO_x and ASD was significant. Urinary nitrite, nitrate and NO₂^-/NO₃^-, might serve as a new biomarker for ASD diagnosis during pursuit of harmless, fast, and convenient diagnostic method. Further studies are needed for the metabolic pathways of NO_x in ASD pathogenesis.