Endoplasmic Reticulum Stress in Leukocytes From Phenylketonuric Patients

Abstract

Objectives: Phenylketonuria (PKU) is a proteinopathy due to the deficiency of phenylalanine hydroxylase (PAH) enzyme. The pathological elevation of phenylalanine (Phe) and its metabolites in PKU is linked to neurological hall- marks and mental disabilities. The aim of this study was to examine the hypothesis that high levels of Phe caused endoplasmic reticulum (ER) stress in PKU patients. Methods: We primarily evaluated ER stress markers glucose-regulated protein78 (GRP78) and C/-EBP homolo- gous protein (CHOP), and thiobarbituric acid-reactive substances (TBARS) as a biomarker of oxidative stress in leukocytes and correlated it with blood Phe values from patients with PKU. Patients in this study were selected from individuals who were diagnosed with PKU as a result of the national neonatal screening program and undergone treatment at our university hospital. The subjects were divided into four groups: healthy controls, patients with hyperphenylalaninemia (HPA), BH4 -responsive patients with PKU and patients with classic PKU. GRP78, CHOP and TBARS levels were estimated in leukocytes isolated from whole blood of subjects, Phe and tyrosine levels were determined in plasma. Results: The levels of Phe in BH 4-responsive PKU and classic PKU groups were statistically higher as compared to healthy controls, and Phe levels were higher in classic PKU compared to HPA group. CHOP levels were elevated by 35.3% in BH4 -responsive group compared to control. GRP78, CHOP and TBARS showed no statistical differences between control and patient groups. GRP78 was also negatively correlated with Phe levels. Conclusions: These results suggested that blood Phe concentrations might not be associated to ER stress in white blood cells obtained from the PKU patient groups under treatment