Studying the effect of large neutral amino acid supplements on oxidative stress in phenylketonuric patients

Abstract Background Oxidative stress may be one of the causes responsible for mental retardation in phenylketonuria (PKU) patients. Phenylalanine (Phe) reduces antioxidant defense and promotes oxidative stress by causing increase in reactive oxygen-nitrogen species. Our study aimed to investigate the effect of different treatments (amino acid mixture/large neutral amino acid [LNAA] supplements) on oxidative stress which are applied to late-diagnosed patients. To the best of our knowledge, this is the first study to investigate the effect of LNAA supplements on oxidative stress. Methods Twenty late-diagnosed classic PKU patients were included in this study. Patients were classified into two groups: patients under Phe-restricted diet and using Phe-free amino acid mixtures (Group I) (mean age: 13.8 ± 2.8), and patients taking LNAA supplements (Group II) (mean age: 14.8 ± 3.8). Healthy controls (mean age: 13.6 ± 4.8) with ages consistent with the ages of the patients in the experimental groups were included. Results Glutathione peroxidase is lower in patients of taking LNAA supplements than the control group (p = 0.022). Coenzyme Q10 is lower in patients of using Phe-free amino acid mixtures than the control group and it is significantly higher in Group II than Group I (p = 0.0001, p = 0.028, respectively). No significant differences were detected in total antioxidant status, total oxidant status, oxidative stress index, paraoxonase 1 and L-carnitine levels. Conclusions Different treatments affect oxidative stress parameters in PKU patients. In this study, although patients were followed up with classic PKU, patient-specific adjuvant antioxidant therapies should be implemented in response to oxidative stress.