Imbalance between Urinary Hexanoyl-lysine and Total Antioxidant Capacity Levels and Plasma Superoxide Dismutase Levels in Individuals with Autism Spectrum Disorder

Abstract

Bachgraund and aim: The imbalance between oxidants and antioxidants contributes to the pathophysiology of ASD. Methods: We measured the urinary levels of an oxidative stress biomarker, hexanoyl-lysine (HEL), the total antioxidant capacity (TAC) and the DNA methylation biomarker 8-hydroxy-2′-deoxyguanosine (8-OHdG), and the plasma levels of a major antioxidant enzyme, superoxide dismutase (SOD). We examined the relationship between these four biomarkers and social responsiveness in 20 individuals with ASD and in 11 healthy controls. Results: The sex and age distributions (11.4 ± 5.1 years vs. 13.9 ± 6.6 years) were not significantly different between the groups. Social responsiveness was assessed using the Social Responsiveness Scale (SRS). Dietary TAC from chocolate, biscuits and cookies, jam and marmalade was significantly higher in the ASD group than in the control group, although the nutrient intake was not significantly different between the two groups. Urinary TAC levels were significantly lower, but the urinary HEL levels were significantly higher in the ASD group compared to the control group. Urinary 8-OHdG levels and plasma SOD levels were not significantly difference between the groups. SRS scores were significantly higher in the ASD group than in the control group. Plasma SOD levels significantly correlated with the urinary TAC levels. Stepwise regression analysis revealed that urinary TAC and HEL levels may predict differences in the biomarkers and SRS scores between the groups. Discussion and Conclusion: A critical imbalance between the urinary HEL and TAC levels may contribute to impaired social responsiveness in individuals with ASD without the DNA methylation. Plasma SOD levels may affect the impaired antioxidant capacity.