Investigation of oxidative stress parameters in treated phenylketonuric patients

Long-Term Renal Function in Adult Patients with Phenylketonuria

INTRODUCTION

In phenylketonuria (PKU), toxic phenylalanine (Phe) can harm other organs beyond the brain. Furthermore, the lifelong therapy of PKU consists of consumption of increased amounts of amino-acid mixture that provoke hyperfiltration in the glomeruli. Therefore, the adherence to therapy in PKU might influence the long-term kidney function in PKU patients.

METHODS

Data from 41 adult, early treated PKU patients were analyzed in this 10-year, retrospective, monocentric study. Two subgroups were created according to their therapy adherence: one with long-term blood Phe levels in the therapeutic range (<600 µmol/L), and one with suboptimal blood Phe levels. Renal function and metabolic parameters were collected over 10 years. Kidney function parameters were compared between the two groups and associations between blood Phe levels and kidney function were tested.

RESULTS

After 10 years, serum creatinine levels (p = 0.369) and estimated glomerular filtration rate (eGFR) (p = 0.723) did not change significantly from baseline in the good therapeutic group. The suboptimal therapeutic group's eGFR decreased in the same period (from 110.4 ± 14 mL/min/1.73 m2 to 94.2 ± 16 mL/min/1.73 m2, p = 0.017). At 10 years, the suboptimal therapeutic group had an increased serum creatinine level (81 ± 14.4 μmol/L vs. 71.5 ± 13 μmol/L, p = 0.038), and a decreased eGFR (94.2 ± 16 mL/min/1.73 m2 vs. 103.3 ± 13 mL/min/1.73 m2p = 0.031) compared to the good adhering group. Significant negative correlation between Phe levels and eGFR (r = -0.41, p = 0.008) was observed.

CONCLUSION

Long-term suboptimal therapy adherence in PKU patients with high blood Phe levels may lead to deterioration in kidney function.

Phenylketonuria oxidative stress and energy dysregulation: Emerging pathophysiological elements provide interventional opportunity

Phenylalanine hydroxylase (PAH) deficient phenylketonuria (PKU) is rightfully considered the paradigm treatable metabolic disease. Dietary substrate restriction (i.e. phenylalanine (Phe) restriction) was applied >60 years ago and remains the primary PKU management means. The traditional model of PKU neuropathophysiology dictates blood Phe over-representation directs asymmetric blood:brain barrier amino acid transport through the LAT1 transporter with subsequent increased cerebral Phe concentration and low concentrations of tyrosine (Tyr), tryptophan (Trp), leucine (Leu), valine (Val), and isoleucine (Ile). Low Tyr and Trp concentrations generate secondary serotonergic and dopaminergic neurotransmitter paucities, widely attributed as drivers of PKU neurologic phenotypes. White matter disease, a central PKU characteristic, is ascribed to Phe-mediated tissue toxicity. Impaired cerebral protein synthesis, by reduced concentrations of non-Phe large neutral amino acids, is another cited pathological mechanism. The PKU amino acid transport model suggests Phe management should be more efficacious than is realized, as even early identified, continuously treated patients that retain therapy compliance into adulthood, demonstrate neurologic disease elements. Reduced cerebral metabolism was an early-recognized element of PKU pathology. Legacy data (late 1960's to mid-1970's) determined the Phe catabolite phenylpyruvate inhibits mitochondrial pyruvate transport. Respirometry of Pah^enu2 cerebral mitochondria have attenuated respiratory chain complex 1 induction in response to pyruvate substrate, indicating reduced energy metabolism. Oxidative stress is intrinsic to PKU and Pah^enu2 brain tissue presents increased reactive oxygen species. Phenylpyruvate inhibits glucose-6-phosphate dehydrogenase that generates reduced niacinamide adenine dinucleotide phosphate the obligatory cofactor of glutathione reductase. Pah^enu2 brain tissue metabolomics identified increased oxidized glutathione and glutathione disulfide. Over-represented glutathione disulfide argues for reduced glutathione reductase activity secondary to reduced NADPH. Herein, we review evidence of energy and oxidative stress involvement in PKU pathology. Data suggests energy deficit and oxidative stress are features of PKU pathophysiology, providing intervention-amenable therapeutic targets to ameliorate disease elements refractory to standard of care.

Comparative metabolomics in the Pahenu2 classical PKU mouse identifies cerebral energy pathway disruption and oxidative stress

Classical phenylketonuria (PKU, OMIM 261600) owes to hepatic deficiency of phenylalanine hydroxylase (PAH) that enzymatically converts phenylalanine (Phe) to tyrosine (Tyr). PKU neurologic phenotypes include impaired brain development, decreased myelination, early onset mental retardation, seizures, and late-onset features (neuropsychiatric, Parkinsonism). Phe over-representation is systemic; however, tissue response to hyperphenylalaninemia is not consistent. To characterize hyperphenylalaninemia tissue response, metabolomics was applied to Pah^enu2 classical PKU mouse blood, liver, and brain. In blood and liver over-represented analytes were principally Phe, Phe catabolites, and Phe-related analytes (Phe-conjugates, Phe-containing dipeptides). In addition to Phe and Phe-related analytes, the metabolomic profile of Pah^enu2 brain tissue evidenced oxidative stress responses and energy dysregulation. Glutathione and homocarnosine anti-oxidative responses are apparent Pah^enu2 brain. Oxidative stress in Pah^enu2 brain was further evidenced by increased reactive oxygen species. Pah^enu2 brain presents an increased NADH/NAD ratio suggesting respiratory chain complex 1 dysfunction. Respirometry in Pah^enu2 brain mitochondria functionally confirmed reduced respiratory chain activity with an attenuated response to pyruvate substrate. Glycolysis pathway analytes are over-represented in Pah^enu2 brain tissue. PKU pathologies owe to liver metabolic deficiency; yet, Pah^enu2 liver tissue shows neither energy disruption nor anti-oxidative response. Unique aspects of metabolomic homeostasis in PKU brain tissue along with increased reactive oxygen species and respiratory chain deficit provide insight to neurologic disease mechanisms. While some elements of assumed, long standing PKU neuropathology are enforced by metabolomic data (e.g. reduced tryptophan and serotonin representation), energy dysregulation and tissue oxidative stress expand mechanisms underlying neuropathology.

L-carnitine protects DNA oxidative damage induced by phenylalanine and its keto acid derivatives in neural cells: a possible pathomechanism and adjuvant therapy for brain injury in phenylketonuria

Although phenylalanine (Phe) is known to be neurotoxic in phenylketonuria (PKU), its exact pathogenetic mechanisms of brain damage are still poorly known. Furthermore, much less is known about the role of the Phe derivatives phenylacetic (PAA), phenyllactic (PLA) and phenylpyruvic (PPA) acids that also accumulate in this this disorder on PKU neuropathology. Previous in vitro and in vivo studies have shown that Phe elicits oxidative stress in brain of rodents and that this deleterious process also occurs in peripheral tissues of phenylketonuric patients. In the present study, we investigated whether Phe and its derivatives PAA, PLA and PPA separately or in combination could induce reactive oxygen species (ROS) formation and provoke DNA damage in C6 glial cells. We also tested the role of L-carnitine (L-car), which has been recently considered an antioxidant agent and easily cross the blood brain barrier on the alterations of C6 redox status provoked by Phe and its metabolites. We first observed that cell viability was not changed by Phe and its metabolites. Furthermore, Phe, PAA, PLA and PPA, at concentrations found in plasma of PKU patients, provoked marked DNA damage in the glial cells separately and when combined. Of note, these effects were totally prevented (Phe, PAA and PPA) or attenuated (PLA) by L-car pre-treatment. In addition, a potent ROS formation also induced by Phe and PAA, whereas only moderate increases of ROS were caused by PPA and PLA. Pre-treatment with L-car also prevented Phe- and PAA-induced ROS generation, but not that provoked by PLA and PPA. Thus, our data show that Phe and its major metabolites accumulated in PKU provoke extensive DNA damage in glial cells probably by ROS formation and that L-car may potentially represent an adjuvant therapeutic agent in PKU treatment.

A New View of Bone Loss in Phenylketonuria

Osteopenia is common in phenylalanine hydroxylase deficient phenylketonuria (PKU). PKU is managed by limiting dietary phenylalanine. Osteopenia in PKU might reflect a therapeutic diet, with reduced bone forming materials. However, osteopenia occurs in patients who never received dietary therapy or following short-term therapy. Humans and animal studies find no correlation between bone loss, plasma hyperphenylalaninemia, bone formation, and resorption markers. Work in the Pah^enu2 mouse recently showed a mesenchymal stem cell (MSC) developmental defect in the osteoblast pathway. Specifically, Pah^enu2 MSCs are affected by energy dysregulation and oxidative stress. In PKU, MSCs oximetry and respirometry show mitochondrial respiratory-chain complex 1 deficit and over-representation of superoxide, producing reactive oxygen species affecting mitochondrial function. Similar mechanisms are involved in aging bone and other rare defects including alkaptonuria and homocysteinemia. Novel interventions to support energy and reduce oxidative stress may restore bone formation PKU patients, and in metabolic diseases with related mechanisms.

Phenylalanine hydroxylase deficient phenylketonuria comparative metabolomics identifies energy pathway disruption and oxidative stress

Classical phenylketonuria (PKU, OMIM 261600) owes to hepatic deficiency of phenylalanine hydroxylase (PAH) that enzymatically converts phenylalanine (Phe) to tyrosine (Tyr). PKU neurologic phenotypes include impaired brain development, decreased myelination, early onset mental retardation, seizures, and late-onset features (neuropsychiatric, Parkinsonism). PAH deficiency leads to systemic hyperphenylalaninemia; however, the impact of Phe varies between tissues. To characterize tissue response to hyperphenylalaninemia, metabolomics was applied to tissue from therapy noncompliant classical PKU patients (blood, liver), the Pahenu2 classical PKU mouse (blood, liver, brain) and the PAH deficient pig (blood, liver, brain, cerebrospinal fluid). In blood, liver, and CSF from both patients and animal models over-represented analytes were principally Phe, Phe catabolites, and Phe-related analytes (conjugates, Phe-containing dipeptides). In addition to Phe and Phe-related analytes, the metabolomic profile of PKU brain tissue (mouse, pig) evidenced oxidative stress responses and energy dysregulation. In Pahenu2 and PKU pig brain tissues, anti-oxidative response by glutathione and homocarnosine is apparent. Oxidative stress in Pahenu2 brain was further demonstrated by increased reactive oxygen species. In Pahenu2 and PKU pig brain, an increased NADH/NAD ratio suggests a respiratory chain dysfunction. Respirometry in PKU brain mitochondria (mouse, pig) functionally confirmed reduced respiratory chain activity. Glycolysis pathway analytes are over-represented in PKU brain tissue (mouse, pig). PKU pathologies owe to liver metabolic deficiency; yet, PKU liver tissue (mouse, pig, human) shows neither energy disruption nor anti-oxidative response. Unique aspects of metabolomic homeostasis in PKU brain tissue along with increased reactive oxygen species and respiratory chain deficit provide insight to neurologic disease mechanisms. While some elements of assumed, long standing PKU neuropathology are enforced by metabolomic data (e.g. reduced tryptophan and serotonin representation), energy dysregulation and tissue oxidative stress expand mechanisms underlying neuropathology.

Oxidative stress in phenylketonuria-evidence from human studies and animal models, and possible implications for redox signaling

Phenylketonuria (PKU) is one of the commonest inborn error of amino acid metabolism. Before mass neonatal screening was possible, and the success of introducing diet therapy right after birth, the typical clinical finds in patients ranged from intellectual disability, epilepsy, motor deficits to behavioral disturbances and other neurological and psychiatric symptoms. Since early diagnosis and treatment became widespread, usually only those patients who do not strictly follow the diet present psychiatric, less severe symptoms such as anxiety, depression, sleep pattern disturbance, and concentration and memory problems. Despite the success of low protein intake in preventing otherwise severe outcomes, PKU's underlying neuropathophysiology remains to be better elucidated. Oxidative stress has gained acceptance as a disturbance implicated in the pathogenesis of PKU. The conception of oxidative stress has evolved to comprehend how it could interfere and ultimately modulate metabolic pathways regulating cell function. We summarize the evidence of oxidative damage, as well as compromised antioxidant defenses, from patients, animal models of PKU, and in vitro experiments, discussing the possible clinical significance of these findings. There are many studies on oxidative stress and PKU, but only a few went further than showing macromolecular damage and disturbance of antioxidant defenses. In this review, we argue that these few studies may point that oxidative stress may also disturb redox signaling in PKU, an aspect few authors have explored so far. The reported effect of phenylalanine on the expression or activity of enzymes participating in metabolic pathways known to be responsive to redox signaling might be mediated through oxidative stress.

Mesenchymal stem cell energy deficit and oxidative stress contribute to osteopenia in the Pahenu2 classical PKU mouse

Osteopenia occurs in a subset of phenylalanine hydroxylase (PAH) deficient phenylketonuria (PKU) patients. While osteopenia is not fully penetrant in patients, the Pah^enu2 classical PKU mouse is universally osteopenic, making it an ideal model of the phenotype. Pah^enu2 Phe management, with a Phe-fee amino acid defined diet, does not improve bone density as histomorphometry metrics remain indistinguishable from untreated animals. Previously, we demonstrated Pah^enu2 mesenchymal stem cells (MSCs) display impaired osteoblast differentiation. Oxidative stress is recognized in PKU patients and PKU animal models. Pah^enu2 MSCs experience oxidative stress determined by intracellular superoxide over-representation. The deleterious impact of oxidative stress on mitochondria is recognized. Oximetry applied to Pah^enu2 MSCs identified mitochondrial stress by increased basal respiration with concurrently reduced maximal respiration and respiratory reserve. Proton leak secondary to mitochondrial complex 1 dysfunction is a recognized superoxide source. Respirometry applied to Pah^enu2 MSCs, in the course of osteoblast differentiation, identified a partial complex 1 deficit. Pah^enu2 MSCs treated with the antioxidant resveratrol demonstrated increased mitochondrial mass by MitoTracker green labeling. In hyperphenylalaninemic conditions, resveratrol increased in situ alkaline phosphatase activity suggesting partial recovery of Pah^enu2 MSCs osteoblast differentiation. Up-regulation of oxidative energy production is required for osteoblasts differentiation. Our data suggests impaired Pah^enu2 MSC developmental competence involves an energy deficit. We posit energy support and oxidative stress reduction will enable Pah^enu2 MSC differentiation in the osteoblast lineage to subsequently increase bone density.

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

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.

Newly validated biomarkers of brain damage may shed light into the role of oxidative stress in the pathophysiology of neurocognitive impairment in dietary restricted phenylketonuria patients

Despite a strict dietary control, patient with hyperphenylalaninemia or phenylketonuria may show cognitive and/or behavioral disorders. These comorbid deficits are of great concern to patients, families, and health organizations. However, biomarkers capable of detecting initial stages of neurological damage are not commonly employed. The pathogenesis of phenylketonuria is complex in nature. Increasingly, the role of oxidative stress has gained acceptance and biomarkers reflecting oxidative damage to the brain and easily accessible in peripheral biofluids have been validated using mass spectrometry techniques. In the present review, the role of oxidative stress in the pathogenesis of phenylketonuria and hyperphenylalaninemia has been updated. Moreover, we report on newly validated brain-specific lipid peroxidation biomarkers and inform on their relevance in the detection and monitoring of neurological damage in phenylketonuric patients. In preliminary studies, a correlation between lipid peroxidation biomarkers and neurological dysfunction in patients with PKU was reported. However, there is a need of adequately powered trials to confirm the validity of these biomarkers for early detection of brain damage, initiation of treatment, and reliably monitor evolving disease both in phenylketonuria and hyperphenylalaninemia.

Serum ischemia modified albumin is a possible new marker of oxidative stress in phenylketonuria

The role of oxidative stress in the pathogenesis of phenylketonuria (PKU)-associated disorders has been implicated. Ischemia modified albumin (IMA) is a modified form of serum albumin, which is produced under the conditions of oxidative stress. The aim of this study was to measure the serum level of IMA in the PKU patients and to investigate its ability in predicting the status of oxidative stress in these patients. Fifty treated-PKU patients and fifty age- and sex-matched healthy subjects were included in the study. The blood samples were obtained and the serum level of phenylalanine (Phe) was measured using reverse phase HPLC method. The levels of IMA, malondialdehyde (MDA), gamma-glutamyl transferase (GGT) activity, and uric acid (UA) were determined using colorimetric methods. The levels of serum Phe, IMA, and MDA were significantly higher (p < 0.001) and the level of UA (p < 0.05) was lower in the PKU patients compared to control group. Serum IMA level was positively correlated with MDA (r = 0.585, p < 0.001) and UA (r = 0.6, p < 0.001). An inverse relationship was observed between the serum level of IMA and Phe (r = - 0.410, p < 0. 01). Results of the present study suggest that serum IMA level could be used as a novel marker for the evaluation of oxidative stress in the PKU patients.

Effect of Blood Phenylalanine Levels on Oxidative Stress in Classical Phenylketonuric Patients

Mental retardation, which occurs in phenylketonuric patients, is associated with increased levels of phenylalanine, increased oxidative stress, and an imbalance of amino acids in the brain. Recent studies have shown that oxidative stress plays a role in the pathogenesis of phenylketonuria. In this work, we aimed to compare the influence of blood phenylalanine levels on oxidative stress parameters in phenylketonuric patients who divided patients into groups according to blood Phe levels during follow-up visits and compared these groups with healthy controls. Results showed significant differences in glutathione peroxidase (GSHPx), coenzyme Q10 (Q10), Q10/cholesterol, and L-carnitine levels in phenylketonuria patients and the control group. GSHPx, Q10, and Q10/cholesterol levels were significantly lower in poor adherence patients than in the control groups. L-carnitine levels were significantly increased in good adherence patients than poor adherence patients and decreased in poor adherence patients than healthy controls. No correlations were observed between phenylalanine and L-carnitine concentrations in poor adherence group. No significant differences were observed in paraoxonase 1 (PON1), total antioxidant status (TAS), total oxidant status (TOS) and oxidative stress index (OSI) levels. As a result, in this work, poor adherence patients are prone to oxidative stress. Although the patients may have the same diagnosis, patients have different clinical characteristics and different prognosis. Antioxidants can be used as an adjuvant therapy in order to avoid neurological damage in these patients.

Omega-3 fatty acid supplementation decreases DNA damage in brain of rats subjected to a chemically induced chronic model of Tyrosinemia type II

Tyrosinemia type II is an inborn error of metabolism caused by a mutation in a gene encoding the enzyme tyrosine aminotransferase leading to an accumulation of tyrosine in the body, and is associated with neurologic and development difficulties in numerous patients. Because the accumulation of tyrosine promotes oxidative stress and DNA damage, the main aim of this study was to investigate the possible antioxidant and neuroprotective effects of omega-3 treatment in a chemically-induced model of Tyrosinemia type II in hippocampus, striatum and cerebral cortex of rats. Our results showed chronic administration of L-tyrosine increased the frequency and the index of DNA damage, as well as the 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in the hippocampus, striatum and cerebral cortex. Moreover, omega-3 fatty acid treatment totally prevented increased DNA damage in the striatum and hippocampus, and partially prevented in the cerebral cortex, whereas the increase in 8-OHdG levels was totally prevented by omega-3 fatty acid treatment in hippocampus, striatum and cerebral cortex. In conclusion, the present study demonstrated that the main accumulating metabolite in Tyrosinemia type II induce DNA damage in hippocampus, striatum and cerebral cortex, possibly mediated by free radical production, and the supplementation with omega-3 fatty acids was able to prevent this damage, suggesting that could be involved in the prevention of oxidative damage to DNA in this disease. Thus, omega-3 fatty acids supplementation to Tyrosinemia type II patients may represent a new therapeutic approach and a possible adjuvant to the curren t treatment of this disease.

Hyperphenylalaninemia Correlated with Global Decrease of Antioxidant Genes Expression in White Blood Cells of Adult Patients with Phenylketonuria

BACKGROUND

Several studies have highlighted disturbance of redox homeostasis in patients with phenylketonuria (PKU) which may be associated with neurological disorders observed in patients, especially during adulthood when phenylalanine restrictive diets are not maintained. The aim of this study was to assess the antioxidant profile in a cohort of PKU patients in comparison to the controls and to evaluate its relation to biochemical parameters especially phenylalaninemia.

METHODS

We measured RNA expression of 22 antioxidant genes and reactive oxygen species (ROS) levels in white blood cells of 10 PKU patients and 10 age- and gender-matched controls. We also assessed plasma amino acids, vitamins, oligo-elements, and urinary organic acids concentrations. Then we evaluated the relationship between redox status and biochemical parameters.

RESULTS

In addition to expected biochemical disturbances, we highlighted a significant global decrease of antioxidant genes expression in PKU patients in comparison to the controls. This global decrease of antioxidant genes expression, including various isoforms of peroxiredoxins, glutaredoxins, glutathione peroxidases, and superoxide dismutases, was significantly correlated to hyperphenylalaninemia.

CONCLUSION

This study is the first to evaluate the expression of 22 antioxidant genes in white blood cells regarding biochemical parameters in PKU. These findings highlight the association of hyperphenylalaninemia with antioxidant genes expression. New experiments to specify the role of oxidative stress in PKU pathogenesis may be useful in suggesting new recommendations in PKU management and new therapeutic trials based on antioxidant defenses.

Demethylation of the promoter region of GPX3 in a newborn with classical phenylketonuria

OBJECTIVES

Phenylketonuria (PKU) is characterized by a high phenylalanine (phe) in plasma and oxidative stress. However, the monitoring of oxidative stress in newborns with PKU using the activity levels of antioxidant enzymes is not optimal. We investigated the possibility of monitoring an increased reactive oxygen species (ROS) production using DNA methylation changes of an oxidative stress response element in the promoter region of an enzymatic antioxidant gene.

DESIGN AND METHODS

Using DNA extracted from blood leukocytes, the cytosine phosphodiester bond guanine positions of an overlapping CCAAT box/metal response element (CGATTGGCTG) of the glutathione peroxidase 3 promoter activated by oxidative stimuli and expressed in plasma were analysed for methylation changes in 20 newborns with hyperphenylalaninemia and 20 healthy controls.

RESULTS

A demethylated allele was detected in a PKU patient at a phe level of 465μmol/L on day 2 after birth, but not in other patients (phe<465μmol/L, ≥day 2 after birth; phe>465μmol/L, ≥day 3 after birth) and healthy controls (phe<465μmol/L, ≥day 2 after birth).

CONCLUSIONS

The detection of the demethylated allele could be time and phe concentration dependent. The demethylated allele is suggested as an early epigenetic marker for an extracellular monitoring of an increased ROS production in newborns with PKU.

Prooxidant-antioxidant balance in patients with phenylketonuria and its correlation to biochemical and hematological parameters

BACKGROUND

The balance between reactive oxygen species production and antioxidant activity has an important role in oxidative stress associated diseases such as phenylketonuria (PKU). We aimed in this study to evaluate the possible association between oxidative balance and clinical features of PKU patients.

METHODS

Twenty patients and 50 healthy subjects were selected. Prooxidant-antioxidant balance (PAB) was measured and phenylalanine (Phe), tyrosine (Tyr), Phe/Tyr ratio and hematological indices were determined.

RESULTS

A significantly higher PAB value was observed in the patient group (152.0±14.1 HK unit) compared to the controls (88.1±13.88 HK) (p<0.05). There was significant correlation between PAB with serum Phe, Tyr, Phe/Tyr ratio, white blood cells (WBC) and red blood cells (RBC) counts.

CONCLUSIONS

The serum PAB values were higher in patients with PKU and this was associated with the serum Phe and Tyr and Phe/Tyr ratio. Therefore, because of its low cost and simplicity to perform, PAB value might be considered as a useful monitoring marker among the other tools in these patients.

The oxidative molecular regulation mechanism of NOX in children with phenylketonuria

Phenylketonuria (PKU) is the most frequent inherited disorder of amino acid metabolism. In our previous work, we investigated the role of NADPH oxidase (NOX) in a Pahenu2-BTBR PKU mouse model, and an in vitro cell culture model of PKU. In the current study, we evaluated various oxidative stress parameters, namely total antioxidant capacity (T-AOC), glutathione (GSH) and maleic dialdehyde (MDA) in the plasma of 40 PKU children, for further investigating the oxidative molecular regulation mechanism of NOX in PKU. It was observed that T-AOC and GSH markedly decreased in PKU as compared with the control group (P<0.01), and seemed to correlate negatively with Phe level. However, there was no statistical difference in MDA level among the three groups. And 8-isoprostane in the blood samples of PKU2 groups was slightly higher than control group (P<0.05). Additionally, mRNA levels of subunits of NOX included p47(phox) and p67(phox) significantly increased in PKU group (P<0.01). These results reflected that NOX is the important source of reactive oxygen species and is involved in the oxidative molecular regulation mechanism in PKU, which shows a new perspective toward understanding the biological underpinnings of PKU.

Glutathione metabolism enzymes in brain and liver of hyperphenylalaninemic rats and the effect of lipoic acid treatment

Phenylketonuria (PKU) is a disorder caused by a deficiency in phenylalanine hydroxylase activity, which converts phenylalanine (Phe) to tyrosine, leading to hyperphenylalaninemia (HPA) with accumulation of Phe in tissues of patients. The neuropathophysiology mechanism of disease remains unknown. However, recently the involvement of oxidative stress with decreased glutathione levels in PKU has been reported. Intracellular glutathione (GSH) levels may be maintained by the antioxidant action of lipoic acid (LA). The aim of this study was to evaluate the activity of the enzymes involved in the metabolism and function of GSH, such as glutathione peroxidase (GSH-Px), glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase (GR), glutamate-cysteine ligase (GCL), glutathione-S-transferase (GST) and GSH content in brain and liver of young rats subjected to a chemically induced model of HPA and the effect of LA for a week. In brain, the administration of Phe reduced the activity of the GSH-Px, GR and G6PD and LA prevented these effects totally or partially. GCL activity was increased by HPA and was not affect by LA antioxidant treatment. GST activity did not differ between groups. GSH content was increased by LA and decreased by HPA treatment in brain samples. Considering the liver, all parameters analyzed were increased in studied HPA animals and LA was able to hinder some effects except for the GCL, GST enzymes and GSH content. These results suggested that HPA model alter the metabolism of GSH in rat brain and liver, which may have an important role in the maintenance of GSH function in PKU although liver is not a directly affected organ in this disease. So, an antioxidant therapy with LA may be useful in the treatment of oxidative stress in HPA.

Antioxidant treatment strategies for hyperphenylalaninemia

Hyperphenylalaninemia (HPA) leads to increased oxidative stress in patients with phenylketonuria (PKU) and in animal models of PKU. Early diagnosis and immediate adherence to a phenylalanine-restricted diet prevents HPA and, consequently, severe brain damage. However, treated adolescent and adult PKU patients have difficulties complying with the diet, leading to an oscillation of phenylalanine levels and associated oxidative stress. The brain is especially susceptible to reactive species, and oxidative stress might add to the impaired cognitive function found in these patients. The restricted PKU diet has a very limited nutrient content from natural foods and almost no animal protein, which reduces the intake of important compounds. These specific compounds can act as scavengers of reactive species and can be co-factors of antioxidant enzymes. Supplementation with nutrients, vitamins, and tetrahydropterin has given quite promising results in patients and animal models. Antioxidant supplementation has been studied in HPA, however there is no consensus about its always beneficial effects. In this way, regular exercise could be a beneficial addition on antioxidant status in PKU patients. A deeper understanding of PKU molecular biochemistry, and genetics, as well as the need for improved targeted treatment options, could lead to the development of new therapeutic strategies.

Neurological damage in MSUD: the role of oxidative stress

Maple syrup urine disease (MSUD) is a metabolic disease caused by a deficiency in the branched-chain α-keto acid dehydrogenase complex, leading to the accumulation of branched-chain keto acids and their corresponding branched-chain amino acids (BCAA) in patients. Treatment involves protein-restricted diet and the supplementation with a specific formula containing essential amino acids (except BCAA) and micronutrients, in order to avoid the appearance of neurological symptoms. Although the accumulation of toxic metabolites is associated to appearance of symptoms, the mechanisms underlying the brain damage in MSUD remain unclear, and new evidence has emerged indicating that oxidative stress contributes to this damage. In this context, this review addresses some of the recent findings obtained from cells lines, animal studies, and from patients indicating that oxidative stress is an important determinant of the pathophysiology of MSUD. Recent works have shown that the metabolites accumulated in the disease induce morphological alterations in C6 glioma cells through nitrogen reactive species generation. In addition, several works demonstrated that the levels of important antioxidants decrease in animal models and also in MSUD patients (what have been attributed to protein-restricted diets). Also, markers of lipid, protein, and DNA oxidative damage have been reported in MSUD, probably secondary to the high production of free radicals. Considering these findings, it is well-established that oxidative stress contributes to brain damage in MSUD, and this review offers new perspectives for the prevention of the neurological damage in MSUD, which may include the use of appropriate antioxidants as a novel adjuvant therapy for patients.

Effect of acute administration of L-tyrosine on oxidative stress parameters in brain of young rats

Tyrosinemia type II, also known as Richner-Hanhart syndrome, is an autosomal recessive inborn error of metabolism caused by a deficiency of hepatic cytosolic tyrosine aminotransferase, and is associated with neurologic and development difficulties in numerous patients. Considering that the mechanisms underlying the neurological dysfunction in hypertyrosinemic patients are poorly known and that studies demonstrated that high concentrations of tyrosine provoke oxidative stress in vitro and in vivo in the cerebral cortex of rats, in the present study we investigate the oxidative stress parameters (enzymatic antioxidant defenses, thiobarbituric acid-reactive substances and protein carbonyl content) in cerebellum, hippocampus and striatum of 30-old-day rats after acute administration of L-tyrosine. Our results demonstrated that the acute administration of L-tyrosine increased the thiobarbituric acid reactive species levels in hippocampus and the carbonyl levels in cerebellum, hippocampus and striatum. In addition, acute administration of L-tyrosine significantly decreased superoxide dismutase activity in cerebellum, hippocampus and striatum, while catalase was increased in striatum. In conclusion, the oxidative stress may contribute, along with other mechanisms, to the neurological dysfunction characteristic of hypertyrosinemia and the administration of antioxidants may be considered as a potential adjuvant therapy for tyrosinemia, especially type II.

DNA damage induced by phenylalanine and its analogue p-chlorophenylalanine in blood and brain of rats subjected to a model of hyperphenylalaninemia

Phenylketonuria (PKU) is a disease caused by a deficiency of phenylalanine hydroxylase (PAH), resulting in an accumulation of phenylalanine (Phe) in the brain tissue, cerebrospinal fluid, and other tissues of PKU patients. Considering that high levels of Phe are associated with neurological dysfunction and that the mechanisms underlying the neurotoxicity in PKU remain poorly understood, the main objective of this study was to investigate the in vivo and in vitro effects of Phe on DNA damage, as determined by the alkaline comet assay. The results showed that, compared to control group, the levels of DNA migration were significantly greater after acute administration of Phe, p-chlorophenylalanine (p-Cl-Phe, an inhibitor of PAH), or a combination thereof in cerebral cortex and blood, indicating DNA damage. These treatments also provoked increase of carbonyl content. Additionally, when Phe or p-Cl-Phe was present in the incubation medium, we observed an increase in the frequency and index of DNA damage in the cerebral cortex and blood, without affecting lactate dehydrogenase (LDH) release. Our in vitro and in vivo findings indicate that DNA damage occurs in the cerebral cortex and blood of rats receiving Phe, suggesting that this mechanism could be, at least in part, responsible for the neurological dysfunction in PKU patients.

Micronutrient status in phenylketonuria

Patients with phenylketonuria (PKU) encompass an 'at risk' group for micronutrient imbalances. Optimal nutrient status is challenging particularly when a substantial proportion of nutrient intake is from non-natural sources. In PKU patients following dietary treatment, supplementation with micronutrients is a necessity and vitamins and minerals should either be added to supplement phenylalanine-free l-amino acids or given separately. In this literature review of papers published since 1990, the prevalence of vitamin and mineral deficiency is described, with reference to age of treatment commencement, type of treatment, dietary compliance, and dietary practices. Biological micronutrient inadequacies have been mainly reported for zinc, selenium, iron, vitamin B12 and folate. The aetiology of these results and possible clinical and biological implications are discussed. In PKU there is not a simple relationship between the dietary intake and nutritional status, and there are many independent and interrelated complex factors that should be considered other than quantitative nutritional intake.

NOX, the main regulator in oxidative stress in experimental models of phenylketonuria?

AIM

To reveal the role of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) in the integration of the redox signal in the oxidative molecular regulation mechanism in phenylketonuria (PKU).

METHODS

The blood samples were obtained from Pahenu2-BTBR PKU and wild-type mice, respectively. Phe concentration, total antioxidant capacity (T-AOC), glutathione (GSH) and maleic dialdehyde (MDA) were analyzed. After collection of the mononuclear cells, reverse transcription polymerase chain reaction (RT-PCR) for NOX was performed. In addition, NOX activity and superoxide in mononuclear cells were determined.

RESULTS

Compared to the control group, Phe concentration, T-AOC and MDA were markedly increased in PKU mice (p<0.01, p<0.05, p<0.01, respectively). However, the GSH level in PKU mice was less than that in control group (p<0.05). The mRNA level of subunits of NOX included p47phox and p67phox, were increased in PKU mice (p<0.05), however, the gp91phox had no obvious change in the two groups (p>0.05). NOX activity and superoxide were also remarkably elevated in PKU mice (p<0.05).

CONCLUSION

NOX may play an important role in the integration of the redox signal in the oxidative molecular regulation mechanism in PKU.

Oxidative stress in phenylketonuria: future directions

Phenylketonuria represents the most prevalent inborn error of amino acid metabolism. In early diagnosed patients adequate and continued dietary treatment results in a good neurologic outcome. Natural protein and phenylalanine-restricted diet, even if rich in fruits and vegetables, represents a serious risk for nutritional deficiencies, albeit universally accepted. In the last few years, a growing number of reports have been describing oxidative stress as a concern in phenylketonuric patients. The diet itself includes good sources of dietary antioxidants (phytochemicals, some vitamins and minerals) but also a risk factor for some deficiencies (selenium, zinc, ubiquinone-10 and L-carnitine). Additionally, the extreme stringency of the diet may impose a reduced synthesis of endogenous antioxidants (like ubiquinone-10 and glutathione). Furthermore, increased phenylalanine levels, and its metabolites, may enhance the endogenous synthesis of reactive species and free radicals and/or interfere with the endogenous synthesis of enzymatic antioxidants (like glutathione peroxidase). Therefore, oxidative stress will probably increase, mainly in late diagnosed patients or in those with bad metabolic control. Considering the known association between oxidative stress, obesity and cardiovascular disease, it seems advisable to look further to the impact of oxidative stress on body macromolecules and structures (like lipoprotein oxidation), especially in phenylketonuric patients with late diagnosis or bad metabolic control, in order to prevent future increased risks. Recommendations for PKU patient's clinical follow-up improvement and educational goals are included.

Antioxidant capacity and environmentally friendly synthesis of dihydropyrimidin-(2H)-ones promoted by naturally occurring organic acids

The Biginelli reaction is a multicomponent reaction involving the condensation between an aldehyde, a β-ketoester, and urea or thiourea, in the presence of an acid catalyst, producing dihydropyrimidinones (DHPMs). Owing to their important pharmacological properties, the DHPMs have been studied by many authors. However, most of the methodologies used for the synthesis of these compounds require drastic reaction conditions. In the current study, we report an efficient and clean procedure for preparing DHPMs by the use of citric acid or tartaric acid as a promoter of the Biginelli synthesis in ethanol as solvent. In addition, we have evaluated the antioxidant capacity of the compounds synthesized by the 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay and the thiobarbituric acid-reactive species test. Two compounds presented antioxidant activity and also reduced lipid peroxidation at concentrations of 200 and 300 µM. In summary, we report an environmentally friendly procedure for the preparation of DHPMs and demonstrate the antioxidant capacity of some of the compounds.

Regular exercise prevents oxidative stress in the brain of hyperphenylalaninemic rats

Phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase, leading to accumulation of phenylalanine and its metabolites. Clinical features of PKU patients include mental retardation, microcephaly, and seizures. Oxidative stress has been found in these patients, and is possibly related to neurophysiopatology of PKU. Regular exercise can leads to adaptation of antioxidant system, improving its capacity to detoxification reactive species. The aim of this study was to verify the effects of regular exercise on oxidative stress parameters in the brain of hyperphenylalaninemic rats. Animals were divided into sedentary (Sed) and exercise (Exe) groups, and subdivided into saline (SAL) and hyperphenylalaninemia (HPA). HPA groups were induced HPA through administration of alpha-methylphenylalanine and phenylalanine for 17 days, while SAL groups (n = 16-20) received saline. Exe groups conducted 2-week aerobic exercise for 20 min/day. At 18th day, animals were killed and the brain was homogenized to determine thiobarbituric acid reactives substances (TBA-RS) content, superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) activities. Soleus muscles were collected to determine glycogen content as a marker of oxidative adaptation. Exe groups showed enhanced glycogen content. HPA condition caused an increase in TBA-RS and SOD, and reduces CAT and GPx. Exercise was able to prevent all changes seen in the HPA group, reaching control values, except for SOD activity. No changes were found in the ExeSAL group compared to SedSAL. Hyperphenylalaninemic rats were more responsive to the benefits provided by regular exercise. Physical training may be an interesting strategy to restore the antioxidant system in HPA.

Mechanisms regulating superoxide generation in experimental models of phenylketonuria: an essential role of NADPH oxidase

This study was designed to investigate whether nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, a superoxide-producing enzyme, could be involved in phenylketonuria (PKU)-associated oxidative stress. A Pah(enu2)-BTBR PKU mouse model, and an in vitro cell culture model of PKU mimicking high phenylalanine insults in PKU, were employed for this study. The concentration of phenylalanine in mouse cerebral cortex was determined by liquid chromatography-tandem mass spectrometry. Superoxide production was displayed with dihydroethidium staining. NADPH oxidase expression level was measured by real-time RT-PCR, Western blotting and immunofluorescence. NADPH oxidase activity was measured by the colorimetric method. The phenylalanine concentrations in cerebral cortices of PKU mice were significantly higher than those in wild-type control mice. Similar results concerning superoxide production and NADPH oxidase protein expression and activity, were also found in this brain region. In addition, it was found that cerebral cortical neurons subjected to an in vitro high phenylalanine insult, displayed increased superoxide production accompanied by increases of NADPH oxidase protein expression and activity. Pretreatment with the inhibitor of this oxidase (diphenylene iodonium or apocynin) prevented this superoxide-increasing effect. Collectively, these findings provide evidence that NADPH oxidase might be a key enzyme involved in enhanced superoxide production in PKU and suggest that it may be a potential therapeutic target in neuroprotective strategies against phenylalanine-evoked oxidative brain injury in PKU.

Oxidative stress in patients with mucopolysaccharidosis type II before and during enzyme replacement therapy

Mucopolysaccharidosis type II (MPS II) is a lysosomal storage disorder caused by deficiency of the enzyme iduronate-2-sulfatase, responsible for the degradation of glycosaminoglycans dermatan and heparan sulfate. Once the generation of free radicals is involved in the pathogenesis of many diseases, including some inborn errors of metabolism, the aim of this study was to evaluate blood oxidative stress parameters in MPS II patients, before and during 6 months of enzyme replacement therapy. We found significantly increased levels of malondialdehyde and carbonyl groups in plasma as well as erythrocyte catalase activity in patients before treatment compared to the control group. Plasma sulfhydryl group content and total antioxidant status were significantly reduced before treatment, while superoxide dismutase enzyme was not altered at this time when compared to controls. During enzyme replacement therapy, there was a significant reduction in levels of malondialdehyde when compared to pretreatment. Sulfhydryl groups were significantly increased until three months of treatment in MPS II patients in comparison to pretreatment. There were no significant alterations in plasma total antioxidant status and carbonyl groups as well as in catalase and superoxide dismutase activities during treatment in relation to pretreatment. The results indicate that MPS II patients are subject to lipid and protein oxidative damage and present reduction in non-enzymatic antioxidants, suggesting a possible involvement of free radicals in the pathophysiology of this disease. Also, the results may suggest that enzyme replacement therapy seems to protect against lipid peroxidation and protein damage in these patients.

Asymmetric dimethylarginine in children with homocystinuria or phenylketonuria

Plasma concentration of asymmetric dimethylarginine (ADMA), an endogenous inhibitor of nitric oxide (NO) synthesis from L-arginine and a cardiovascular risk factor, was found to be elevated in plasma of homocysteinemic adults. Enhanced cardiovascular risk due to homocystinuria and impaired renal function has been found in patients with phenylketonuria (PKU) on protein-restricted diet. However, it is still unknown whether ADMA synthesis is also elevated in children with homocystinuria due to cystathionine beta-synthase deficiency (classical homocystinuria), and whether ADMA may play a role in phenylketonuria in childhood. In the present study, we investigated the status of the L-arginine/NO pathway in six young patients with homocystinuria, in 52 young phenylketonuria patients on natural protein-restricted diet, and in age- and gender-matched healthy children serving as controls. ADMA in plasma and urine was determined by GC-MS/MS. The NO metabolites nitrate and nitrite in plasma and urine, and urinary dimethylamine (DMA), the dimethylarginine dimethylaminohydrolase (DDAH) metabolite of ADMA, were measured by GC-MS. Unlike urine ADMA excretion, plasma ADMA concentration in patients with homocystinuria was significantly higher than in controls (660±158 vs. 475±77 nM, P=0.035). DMA excretion rate was considerably higher in children with homocystinuria as compared to controls (62.2±24.5 vs. 6.5±2.9 μmol/mmol creatinine, P=0.068), indicating enhanced DDAH activity in this disease. In contrast and unexpectedly, phenylketonuria patients had significantly lower ADMA plasma concentrations compared to controls (512±136 vs. 585±125 nM, P=0.009). Phenylketonuria patients and controls had similar L-arginine/ADMA molar ratios in plasma. Urinary nitrite excretion was significantly higher in phenylketonuria as compared to healthy controls (1.7±1.7 vs. 0.7±1.2 μmol/mmol creatinine, P=0.003). Our study shows that the L-arginine/NO pathway is differently altered in children with phenylketonuria and homocystinuria. Analogous to hyperhomocysteinemic adults, elevated ADMA plasma concentrations could be a cardiovascular risk factor in children with homocystinuria. In phenylketonuria, the L-arginine/NO pathway seems not be altered. Delineation of the role of ADMA in childhood phenylketonuria and homocystinuria demands further investigation.

Oxidative stress in phenylketonuric patients

Phenylketonuria is the most frequent disturbance of amino acid metabolism. Untreated patients present mental retardation whose pathophysiology is not completely established. In this work we discuss the oxidative stress in phenylketonuric patients. Several studies have shown reduction in antioxidant defenses, possibly due to dietary restriction of nutrients with antioxidant properties and increase in oxidative damage to biomolecules, probably secondary to increased formation of reactive species. Therefore, antioxidants could be considered an adjuvant therapy in phenylketonuria.

Nutritional issues in treating phenylketonuria

A phenylalanine (Phe)-restricted diet is the mainstay of phenylketonuria (PKU) treatment, and, in recent years, the nutritional management of PKU has become more complex in order to optimize patients' growth, development and diet compliance. Dietary restriction of Phe creates a diet similar to a vegan diet, and many of the nutritional concerns and questions applicable to vegans who wish to avoid animal products are also relevant to patients with PKU. Owing to their nutritional characteristics, breast milk and breastfeeding should be given greater consideration as a useful food in patients with PKU and in those with other inborn errors of metabolism. Further key issues for consideration include the quality of the available amino acid substitutes, the neurotrophic and neuroprotective effects of added long-chain polyunsaturated fatty acids (e.g. docosahexaenoic acid), micronutrient deficiencies, bone disease and antioxidant status. Long-term dietary guidance and monitoring of the nutritional status of patients with PKU should be part of a follow-up programme that continues for life.

Challenges and pitfalls in the management of phenylketonuria

Despite recent advances in the management of phenylketonuria and hyperphenylalaninemia, important questions on the management of this disorder remain unanswered. Consensus exists on the need for neonatal screening and early treatment, yet disagreement persists over threshold levels of blood phenylalanine for starting treatment, target blood phenylalanine levels, and the management of older patient groups. The mainstay of treatment is a phenylalanine-restricted diet, but its application varies between and within countries. Beyond diet treatment, there is a lack of consensus on the use of newer treatments such as tetrahydrobiopterin. Although neonatal screening and early treatment has meant that most well-treated children grow up with near-normal IQ scores, the effect of relaxing metabolic control on cognitive and executive function later in life is still not fully understood. Although it is clear from the available literature that the active control of blood phenylalanine levels is of vital importance, there are other treatment-related factors that affect outcome. A uniform and firmly evidence-based approach to the management of phenylketonuria is required.

Evidence that DNA damage is associated to phenylalanine blood levels in leukocytes from phenylketonuric patients

Phenylketonuria (PKU) is an inborn error of phenylalanine (Phe) metabolism, biochemically characterized by the accumulation of Phe and its metabolites in blood and tissues of affected patients. Treatment for PKU consists of a protein restricted diet supplemented with a mixture containing essential amino acids (other than Phe) and micronutrients. In recent years several authors have studied the pathomechanisms of the disease and demonstrated the existence of lipid and protein oxidative damage in PKU patients. In this work we investigated the in vivo and in vitro effects of Phe on DNA damage determined by the alkaline comet assay using silver staining and visual scoring. We found a dose-dependent effect of Phe on DNA damage in leukocytes from normal individuals incubated with different concentrations of Phe. Additionally, by analyzing blood leukocytes from two groups of treated PKU patients based on their blood Phe levels, we verified that the DNA damage index was significantly higher in PKU patients with high Phe blood levels (DI = 68.2 +/- 12.3), compared to well-treated patients and the control group (healthy individuals). Furthermore, well-treated PKU patients had greater DNA damage (DI = 44.9 +/- 7.6) relatively to controls (DI = 12.7 +/- 4.1). Our present in vitro and in vivo findings indicate that DNA damage occurs in peripheral blood from PKU patients and is associated to Phe blood levels.

Inhibition of creatine kinase activity by lysine in rat cerebral cortex

Accumulation of lysine (Lys) in tissues and biochemical fluids is the biochemical hallmark of patients affected by familial hyperlysinemia (FH) and also by other inherited neurometabolic disorders. In the present study, we investigated the in vitro effect of Lys on various parameters of energy metabolism in cerebral cortex of 30-day-old Wistar rats. We verified that total (tCK) and cytosolic creatine kinase activities were significantly inhibited by Lys, in contrast to the mitochondrial isoform which was not affected by this amino acid. Furthermore, the inhibitory effect of Lys on tCK activity was totally prevented by reduced glutathione, suggesting a possible role of reactive species oxidizing critical thiol groups of the enzyme. In contrast, Lys did not affect (14)CO(2) production from [U-(14)C] glucose (aerobic glycolytic pathway) and [1-(14)C] acetic acid (citric acid cycle activity) neither the various activities of the electron transfer chain and synaptic Na(+)K(+)-ATPase at concentrations as high as 5.0 mM. Considering the importance of creatine kinase (CK) activity for brain energy metabolism homeostasis and especially ATP transfer and buffering, our results suggest that inhibition of this enzyme by Lys may contribute to the neurological signs presented by symptomatic patients affected by FH and other neurodegenerative disorders in which Lys accumulates.

Effect of short- and long-term exposition to high phenylalanine blood levels on oxidative damage in phenylketonuric patients

Phenylketonuria is the most frequent disturbance of amino acid metabolism. Treatment for phenylketonuric patients consists of phenylalanine intake restriction. However, there are patients who do not adhere to treatment and/or are not submitted to neonatal screening. These individuals are more prone to develop brain damage due to long-lasting toxic effects of high levels of phenylalanine and/or its metabolites. Oxidative stress occurs in late-diagnosed phenylketonuric patients, probably contributing to the neurological damage in this disorder. In this work, we aimed to compare the influence of time exposition to high phenylalanine levels on oxidative stress parameters in phenylketonuric patients who did not adhere to protein restricted diet. We evaluated a large spectrum of oxidative stress parameters in plasma and erythrocytes from phenylketonuric patients with early and late diagnosis and of age-matched healthy controls. Erythrocyte glutathione peroxidase activity and glutathione levels, as well as plasma total antioxidant reactivity were significantly reduced in both groups of patients when compared to the control group. Furthermore, protein oxidative damage, measured by carbonyl formation and sulfhydryl oxidation, and lipid peroxidation, determined by malondialdehyde levels, were significantly increased only in patients exposed for a long time to high phenylalanine concentrations, compared to early diagnosed patients and controls. In conclusion, exposition to high phenylalanine concentrations for a short or long time results in a reduction of non-enzymatic and enzymatic antioxidant defenses, whereas protein and lipid oxidative damage only occurs in patients with late diagnosis.