Plasma Phenylalanine Concentrations Research Articles

Long-term cognitive functioning in individuals with tyrosinemia type 1 treated with nitisinone and protein-restricted diet

IntroductionTyrosinemia Type 1 (HT1) is an autosomal recessive disorder caused by a defect in the enzyme fumarylacetoacetate hydroxylase in the tyrosine pathway. Implementation of nitisinone (NTBC) treatment has dramatically improved survival rate of individuals with HT1, yet recent reports on cognitive impairment in treated patients exist. AimsDescribe long-term neurocognitive outcome individuals with HT1 treated with nitisinone and protein restricted diet. MethodologyTwelve individuals with HT1 were analyzed with respect to psychomotor development and cognitive functioning using standardized psychometric tests. Plasma tyrosine and phenylalanine concentrations were also collected and analyzed, as part of the regular HT1 follow up program in our clinic. ResultsDelayed performance in Bayley scale mental developmental index (MDI) was identified in 29% to 38% of the patients assessed at different ages. At preschool age, mean full scale IQ (FSIQ) was 88±16; six out of nine assessed children preformed within normal range, and one child presented with intellectual disability. At school age mean FSIQ was 79±18, three out of nine children preformed within normal range and two showed intellectual disability. Repeated measures showed IQ decline over time in four out of eight patients, all of whom presented with symptoms in their first months of life. Patients that showed no progressive IQ decline were 8months or older at diagnosis, with a mean age of 17months. Significant correlation between Phe/Tyr ratio and FSIQ at school age was identified (r=−0.689; p<0.044). ConclusionSome patients with HT1 treated with nitisinone and protein restricted diet are at risk of presenting developmental delay and impaired cognitive functioning. Patients with early onset of symptoms could be at risk for progressive cognitive functioning decline over time.

Neuromuscular electrical stimulation prior to presleep protein feeding stimulates the use of protein-derived amino acids for overnight muscle protein synthesis.

Neuromuscular electrical stimulation (NMES) as well as presleep dietary protein ingestion represent effective strategies to stimulate muscle protein synthesis rates. Here we demonstrate that in older men after a day of bed rest, the application of NMES prior to presleep protein feeding stimulates the use of dietary protein-derived amino acids for overnight muscle protein synthesis by 18% compared with presleep protein feeding only.

A single session of neuromuscular electrical stimulation does not augment postprandial muscle protein accretion.

The loss of muscle mass and strength that occurs with aging, termed sarcopenia, has been (at least partly) attributed to an impaired muscle protein synthetic response to food intake. Previously, we showed that neuromuscular electrical stimulation (NMES) can stimulate fasting muscle protein synthesis rates and prevent muscle atrophy during disuse. We hypothesized that NMES prior to protein ingestion would increase postprandial muscle protein accretion. Eighteen healthy elderly (69 ± 1 yr) males participated in this study. After a 70-min unilateral NMES protocol was performed, subjects ingested 20 g of intrinsically l-[1-(13)C]phenylalanine-labeled casein. Plasma samples and muscle biopsies were collected to assess postprandial mixed muscle and myofibrillar protein accretion as well as associated myocellular signaling during a 4-h postprandial period in both the control (CON) and stimulated (NMES) leg. Protein ingestion resulted in rapid increases in both plasma phenylalanine concentrations and l-[1-(13)C]phenylalanine enrichments, which remained elevated during the entire 4-h postprandial period (P < 0.05). Mixed-muscle protein-bound l-[1-(13)C]phenylalanine enrichments increased significantly over time following protein ingestion, with no differences between the CON (0.0164 ± 0.0019 MPE) and NMES (0.0164 ± 0.0019 MPE) leg (P > 0.05). In agreement, no differences were observed in the postprandial rise in myofibrillar protein bound l-[1-(13)C]phenylalanine enrichments between the CON and NMES legs (0.0115 ± 0.0014 vs. 0.0133 ± 0.0013 MPE, respectively, P > 0.05). Significant increases in mTOR and P70S6K phosphorylation status were observed in the NMES-stimulated leg only (P < 0.05). We conclude that a single session of NMES prior to food intake does not augment postprandial muscle protein accretion in healthy older men.

No additional effect of different types of physical activity on 10-hour muscle protein synthesis in elderly men on a controlled energy- and protein-sufficient diet

PurposeThe elderly lose skeletal muscle mass with age, which may be detrimental for function and quality of life. Both inactivity and heavy resistance exercise are known to have marked but opposite effects upon muscle mass. However, the potential effects of daily physical activity upon muscle protein synthesis (MPS) are less investigated. The aim of this study was to determine the effects of daily physical activities upon MPS in elderly individuals. MethodsA total of 24 elderly men (70±1year) were recruited and randomly assigned: inactivity in form of bed-rest (IA), daily physical activities (DA), or heavy resistance exercise (RE). All groups undertook a normal eating routine containing carbohydrates (52 E%), fat (32 E%), and protein (16 E%). Ingestion of labeled milk protein ([1-13C]leucine-labeled whey and caseinate) served to maintain tracer enrichment for determination of 10-hour myofibrillar protein fractional synthesis rates (FSR), and typical prerequisites for calculating FSR were fulfilled. Physical activities were monitored, and venous blood and muscle biopsies collected. ResultsPhysical activity was highest in the DA compared to both the IA and RE groups. Nutrient ingestion increased insulin, leucine, and phenylalanine plasma concentrations in all groups. [1-13C]leucine enrichment was stable throughout the 10-hour FSR period. Myofibrillar protein FSR were similar for IA, DA, and RE groups, 0.055±0.003%/h, 0.058±0.006%/h, and 0.065±0.008%/h, respectively (means±SE, P=0.44). ConclusionsIn elderly males, inactivity, daily activities, and resistance exercise interventions result in equal 10-hour, whole day MPS during an energy- and protein-sufficient diet regimen.

Ingestion of Casein in a Milk Matrix Modulates Dietary Protein Digestion and Absorption Kinetics but Does Not Modulate Postprandial Muscle Protein Synthesis in Older Men1–3

Background: The slow digestion and amino acid absorption kinetics of isolated micellar casein have been held responsible for its relatively lower postprandial muscle protein synthetic response compared with rapidly digested proteins such as isolated whey. However, casein is normally consumed within a milk matrix. We hypothesized that protein digestion and absorption kinetics and the subsequent muscle protein synthetic response after micellar casein ingestion are modulated by the milk matrix.Objective: The aim of this study was to determine the impact of a milk matrix on casein protein digestion and absorption kinetics and postprandial muscle protein synthesis in older men.Methods: In a parallel-group design, 32 healthy older men (aged 71 ± 1 y) received a primed continuous infusion of L-[ring-2H5]-phenylalanine, L-[ring-3,5-2H2]-tyrosine, and L-[1-13C]-leucine, and ingested 25 g intrinsically L-[1-13C]-phenylalanine and L-[1-13C]-leucine labeled casein dissolved in bovine milk serum (Cas+Serum) or water (Cas). Plasma samples and muscle biopsies were collected in the postabsorptive state and for 300 min in the postprandial period to examine whole-body and skeletal muscle protein metabolism.Results: Casein ingestion increased plasma leucine and phenylalanine concentrations and L-[1-13C]-phenylalanine enrichments, with a more rapid rise after Cas vs. Cas+Serum. Nonetheless, dietary protein–derived phenylalanine availability did not differ between Cas+Serum (47 ± 2%, mean ± SEM) and Cas (46 ± 3%) when assessed over the 300-min postprandial period (P = 0.80). The milk matrix did not modulate postprandial myofibrillar protein synthesis rates from 0 to 120 min (0.038 ± 0.005 vs. 0.031 ± 0.007%/h) or from 120 to 300 min (0.052 ± 0.004 vs. 0.067 ± 0.005%/h) after Cas+Serum vs. Cas. Similarly, no treatment differences in muscle protein–bound L-[1-13C]-phenylalanine enrichments were observed at 120 min (0.003 ± 0.001 vs. 0.002 ± 0.001) or 300 min (0.015 ± 0.002 vs. 0.016 ± 0.002 mole percent excess) after Cas+Serum vs. Cas.Conclusions: Casein ingestion in a milk matrix delays protein digestion and absorption but does not modulate postprandial muscle protein synthesis when compared to the ingestion of micellar casein only in healthy older men. This trial was registered at Nederlands Trial Register as NTR4429.

Plasma amino acid profiling of "same symptom for different disease" in Uyghur medicine based on high-performance liquid chromatography

To determine the plasma amino acid metabolism of "same symptom for different diseases" in different cancer patients in Uyghur medicine. Plasma amino acid concentration was tested by high-performance liquid chromatography (HPLC) in cancer patients with different symptom, and the spectral profiles were subjected to a t-test for statistical significance. Compared with the healthy group, lung cancer, cervical cancer, breast cancer and gastric cancer patients with abnormal Savda had lower concentration of plasma amino acids except some amino acids. Lung cancer patients with abnormal Savda had higher concentration of plasma phenylalanine, serine, cystine, valine, isoleucine, leucine and aspartic acid than Unsavda patients (P<0.05). Cervical cancer patients with abnormal Savda had low concentration of plasma arginine, but higher concentration of plasma cystine than Unsavda patients (P<0.05). Breast cancer patients with abnormal Savda had higher concentration of plasma leucine, serine, taurine, cystine, tyrosine, valine, isoleucine and asparagine than Unsavda patients (P<0.05). Gastric cancer patients with abnormal Savda had high concentration of plasma cystine but lower concentration of plasma phenylalanine, threonine and arginine than Unsavda patients (P<0.05). Different tumor patients with abnormal Savda have common characteristics and significant differences.

Higher versus lower protein intake in formula-fed low birth weight infants.

The ideal quantity of dietary protein for formula-fed low birth weight infants is still a matter of debate. Protein intake must be sufficient to achieve normal growth without negative effects such as acidosis, uremia, and elevated levels of circulating amino acids. To determine whether higher (≥ 3.0 g/kg/d) versus lower (< 3.0 g/kg/d) protein intake during the initial hospital stay of formula-fed preterm infants or low birth weight infants (< 2.5 kilograms) results in improved growth and neurodevelopmental outcomes without evidence of short- and long-term morbidity.To examine the following distinctions in protein intake. 1. Low protein intake if the amount was less than 3.0 g/kg/d. 2. High protein intake if the amount was equal to or greater than 3.0 g/kg/d but less than 4.0 g/kg/d. 3. Very high protein intake if the amount was equal to or greater than 4.0 g/kg/d.If the reviewed studies combined alterations of protein and energy, subgroup analyses were to be carried out for the planned categories of protein intake according to the following predefined energy intake categories. 1. Low energy intake: less than 105 kcal/kg/d. 2. Medium energy intake: greater than or equal to 105 kcal/kg/d and less than or equal to 135 kcal/kg/d. 3. High energy intake: greater than 135 kcal/kg/d.As the Ziegler-Fomon reference fetus estimates different protein requirements for infants based on birth weight, subgroup analyses were to be undertaken for the following birth weight categories. 1. < 800 grams. 2. 800 to 1199 grams. 3. 1200 to 1799 grams. 4. 1800 to 2499 grams. The standard search methods of the Cochrane Neonatal Review Group were used. MEDLINE, CINAHL, PubMed, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL; The Cochrane Library) were searched. Randomized controlled trials contrasting levels of formula protein intake as low (< 3.0 g/kg/d), high (≥ 3.0 g/kg/d but < 4.0 g/kg/d), or very high (≥ 4.0 g/kg/d) in formula-fed hospitalized neonates weighing less than 2.5 kilograms were included. Studies were excluded if infants received partial parenteral nutrition during the study period or were fed formula as a supplement to human milk. Studies in which nutrients other than protein also varied were added in a post-facto analysis. The standard methods of the Cochrane Neonatal Review Group were used. Five studies compared low versus high protein intake. Improved weight gain and higher nitrogen accretion were demonstrated in infants receiving formula with higher protein content while other nutrients were kept constant. No significant differences were seen in rates of necrotizing enterocolitis, sepsis, or diarrhea.One study compared high versus very high protein intake during and after an initial hospital stay. Very high protein intake promoted improved gain in length at term, but differences did not remain significant at 12 weeks corrected age. Three of the 24 infants receiving very high protein intake developed uremia.A post-facto analysis revealed further improvement in all growth parameters in infants receiving formula with higher protein content. No significant difference in the concentration of plasma phenylalanine was noted between high and low protein intake groups. However, one study (Goldman 1969) documented a significantly increased incidence of low intelligence quotient (IQ) scores among infants of birth weight less than 1300 grams who received a very high protein intake (6 to 7.2 g/kg). Higher protein intake (≥ 3.0 g/kg/d but < 4.0 g/kg/d) from formula accelerates weight gain. However, limited information is available regarding the impact of higher formula protein intake on long-term outcomes such as neurodevelopmental abnormalities. Available evidence is not adequate to permit specific recommendations regarding the provision of very high protein intake (> 4.0 g/kg/d) from formula during the initial hospital stay or after discharge.

Single-dose, subcutaneous recombinant phenylalanine ammonia lyase conjugated with polyethylene glycol in adult patients with phenylketonuria: an open-label, multicentre, phase 1 dose-escalation trial

Phenylketonuria is an inherited disease caused by impaired activity of phenylalanine hydroxylase, the enzyme that converts phenylalanine to tyrosine, leading to accumulation of phenylalanine and subsequent neurocognitive dysfunction. Phenylalanine ammonia lyase is a prokaryotic enzyme that converts phenylalanine to ammonia and trans-cinnamic acid. We aimed to assess the safety, tolerability, pharmacokinetic characteristics, and efficacy of recombinant Anabaena variabilis phenylalanine ammonia lyase (produced in Escherichia coli) conjugated with polyethylene glycol (rAvPAL-PEG) in reducing phenylalanine concentrations in adult patients with phenylketonuria. In this open-label, phase 1, multicentre trial, single subcutaneous injections of rAvPAL-PEG were given in escalating doses (0·001, 0·003, 0·010, 0·030, and 0·100 mg/kg) to adults with phenylketonuria. Participants aged 18 years or older with blood phenylalanine concentrations of 600 μmol/L or higher were recruited from among patients attending metabolic disease clinics in the USA. The primary endpoints were safety and tolerability of rAvPAL-PEG. Secondary endpoints were the pharmacokinetic characteristics of the drug and its effect on concentrations of phenylalanine. Participants and investigators were not masked to assigned dose group. This study is registered with ClinicalTrials.gov, number NCT00925054. 25 participants were recruited from seven centres between May 6, 2008, and April 15, 2009, with five participants assigned to each escalating dose group. All participants were included in the safety population. The most frequently reported adverse events were injection-site reactions and dizziness, which were self-limited and without sequelae. Two participants had serious adverse reactions to intramuscular medroxyprogesterone acetate, a drug that contains polyethylene glycol as an excipient. Three of five participants given the highest dose of rAvPAL-PEG (0·100 mg/kg) developed a generalised skin rash. By the end of the study, all participants had developed antibodies against polyethylene glycol, and some against phenylalanine ammonia lyase as well. Drug concentrations peaked about 89-106 h after administration of the highest dose. Treatment seemed to be effective at reducing blood phenylalanine in all five participants who received the highest dose (mean reduction of 54·2% from baseline), with a nadir about 6 days after injection and an inverse correlation between drug and phenylalanine concentrations in plasma. Phenylalanine returned to near-baseline concentrations about 21 days after the injection. Subcutaneous administration of rAvPAL-PEG in a single dose of up to 0·100 mg/kg was fairly safe and well tolerated in adult patients with phenylketonuria. At the highest dose tested, rAvPAL-PEG reduced blood phenylalanine concentrations. In view of the development of antibodies against polyethylene glycol (and in some cases against phenylalanine ammonia lyase), future studies are needed to assess the effect of repeat dosing. BioMarin Pharmaceutical.

Daily living physical activities and muscle protein synthesis: a new and applied method with intrinsically stable isotope‐labeled milk proteins as tracer (702.8)

Aims of this study were to evaluate effects of daily physical activities on muscle protein synthesis (MPS) and to validate a tracer protocol with intrinsically labeled milk proteins. 24 elderly (70 ± 1 y) men were recruited and randomly assigned to: inactivity (IA), daily activities (DA), or strength exercise (SE). The study protocol simulated a normal daily eating routine containing carbohydrates, fat, and [1‐13C]leucine‐labeled whey and caseinate as the primary protein source. Regular ingestion of labeled protein served to prime (whey) and maintain (caseinate) tracer enrichment for determination muscle protein fractional synthesis rates (FSR). Physical activities were monitored and venous blood and muscle biopsies collected. Total physical activity was highest in DA compared to IA and SE. Protein ingestion increased leucine and phenylalanine plasma concentrations in all groups. Plasma [1‐13C]leucine enrichment was stable throughout the 10‐h FSR measurement period. Muscle protein FSR were for IA, DA, and SE 0.065 ± 0.0050 %/h, 0.077 ± 0.0081 %/h, and 0.081 ± 0.0057 %/h, respectively (means ± SE, one‐way ANOVA P = 0.199). The prerequisites for calculating FSR was fulfilled with the tracer coming solely from oral intake of milk proteins. Under these applied settings it was not possible to detect significant differences in MPS between the inactivity, daily activities, and strength exercise interventions.Grant Funding Source: Supported by Arla Foods Ingredients P/S and Lundbeck Foundation

Molecular Characteristics, Phenotypic Diversity and Genotype-Estimated Therapeutic Responsiveness of Serbian Patients with Phenylketonuria / MOLEKULARNE KARAKTERISTIKE, FENOTIPSKA RAZNOLIKOST I PROCENA ODGOVORA NA TERAPIJU ZASNOVANA NA GENOTIPU KOD SRPSKIH PACIJENATA SA FENILKETONURIJOM

Summary Phenylketonuria (PKU) is a rare, inherited metabolic disease which is transmitted in an autosomal recessive pattern. PKU is caused by mutations in the gene encoding the phenylalanine hydroxylase (PAH) enzyme. This review cites the most prominent methods for the detection of mutations in the PAH gene. Since the image of PKU transcends »simple« monogenic disease, the known data on non-coding PAH gene variants and their role and PKU modifier genes have been further reviewed. It has been shown that there is a significant correlation between mutant PAH genotypes and PKU phenotypes. However, genotype-phenotype correlation inconsistencies have also been found. This review discusses the possible causes of phenotypic inconsistencies, such as oversight of more than two mutations present in the patient’s PAH genotype, pitfalls of patient phenotypic classification (plasma phenylalanine concentration and phenylalanine tolerance), the inter-allelic complementation (positive and negative) phenomenon. A new therapeutic approach, tetrahydrobiopterin (BH4) supplementation therapy, is an important innovation in the course of PKU patients’ treatment. How - ever, in countries where the BH4-loading test and BH4-supplementation therapy are not available, a genotype-based estimation of responsiveness to the therapy is a valuable approach. It enables BH4-potential benefit estimation, which provides vital information both for the patient and for the population. An optimal molecular diagnostics algorithm, established according to the published mutation frequencies in Serbian PKU patients, has been suggested. In the future, the molecular-genetic algorithm for PKU could be expanded to include a variety of transcriptional regulatory elements located in noncoding PAH gene regions and yet to be discovered modifier genes.

Behavioral and Neurochemical Characterization of New Mouse Model of Hyperphenylalaninemia

Hyperphenylalaninemia (HPA) refers to all clinical conditions characterized by increased amounts of phenylalanine (PHE) in blood and other tissues. According to their blood PHE concentrations under a free diet, hyperphenylalaninemic patients are commonly classified into phenotypic subtypes: classical phenylketonuria (PKU) (PHE > 1200 µM/L), mild PKU (PHE 600-1200 µM/L) and persistent HPA (PHE 120-600 µM/L) (normal blood PHE < 120 µM/L). The current treatment for hyperphenylalaninemic patients is aimed to keep blood PHE levels within the safe range of 120-360 µM/L through a PHE-restricted diet, difficult to achieve. If untreated, classical PKU presents variable neurological and mental impairment. However, even mildly elevated blood PHE levels, due to a bad compliance to dietary treatment, produce cognitive deficits involving the prefrontal cortical areas, extremely sensible to PHE-induced disturbances. The development of animal models of different degrees of HPA is a useful tool for identifying the metabolic mechanisms underlying cognitive deficits induced by PHE. In this paper we analyzed the behavioral and biochemical phenotypes of different forms of HPA (control, mild-HPA, mild-PKU and classic-PKU), developed on the base of plasma PHE concentrations. Our results demonstrated that mice with different forms of HPA present different phenotypes, characterized by increasing severity of behavioral symptoms and brain aminergic deficits moving from mild HPA to classical PKU forms. In addition, our data identify preFrontal cortex and amygdala as the most affected brain areas and confirm the highest susceptibility of brain serotonin metabolism to mildly elevated blood PHE.

Scientific Opinion on the re‐evaluation of aspartame (E 951) as a food additive

The EFSA ANS Panel provides a scientific opinion on the safety of aspartame (E 951). Aspartame is a sweetener authorised as a food additive in the EU. In previous evaluations by JECFA and the SCF, an ADI of 40 mg/kg bw/day was established based on chronic toxicity in animals. Original reports, previous evaluations, additional literature and data made available following a public call were evaluated. Aspartame is rapidly and completely hydrolysed in the gastrointestinal tract to phenylalanine, aspartic acid and methanol. Chronic and developmental toxicities were relevant endpoints in the animal database. From chronic toxicity studies in animals, a NOAEL of 4000 mg/kg bw/day was identified. The possibility of developmental toxicity occurring at lower doses than 4000 mg/kg in animals could not be excluded. Based on MoA and weight-of-evidence analysis, the Panel concluded that developmental toxicity in animals was attributable to phenylalanine. Phenylalanine at high plasma levels is known to cause developmental toxicity in humans. The Panel concluded that human data on developmental toxicity were more appropriate for the risk assessment. Concentration-response modelling was used to determine the effects of aspartame administration on plasma phenylalanine using human data after phenylalanine administration to normal, PKU heterozygote or PKU homozygote individuals. In normal and PKU heterozygotes, aspartame intakes up to the ADI of 40 mg/kg bw/day, in addition to dietary phenylalanine, would not lead to peak plasma phenylalanine concentrations above the current clinical guideline for the prevention of adverse effects in fetuses. The Panel concluded that aspartame was not of safety concern at the current aspartame exposure estimates or at the ADI of 40 mg/kg bw/day. Therefore, there was no reason to revise the ADI of aspartame. Current exposures to aspartame - and its degradation product DKP - were below their respective ADIs. The ADI is not applicable to PKU patients.

Efficacy of Withania somnifera on seminal plasma metabolites of infertile males: A proton NMR study at 800 MHz

Ethnopharmacological relevanceTraditional Indian systems of medicine use roots of Withania somnifera for impotence, infertility treatment, stress, and the aging process. Although Withania somnifera improves semen quality by regulating reproductive hormone levels and oxidative stress, the molecular mechanism is not clear. Aim of the studyOur study uses high-resolution Nuclear Magnetic Resonance (NMR) spectroscopy to explore the scientific basis to reveal the pre- and post-treatment efficacy of Withania somnifera on seminal plasma of infertile men—which remains unexplored to date. Materials and methodsA total of 180 infertile male patients were administered Withania somnifera root powder at the rate of 5g/d for a 3-month period. The study included age-matched, healthy men as a control (n=50) group. Proton NMR spectroscopy was used to measure lactate, alanine, glutamate, glutamine, citrate, lysine, choline, glycerophosphocholine (GPC), glycine, tyrosine, histidine, phenylalanine, and uridine in all seminal plasma samples. To appraise infertility levels, we also measured sperm concentration, motility, lipid peroxide, and hormonal perturbation. ResultsWithania somnifera therapy repairs the disturbed concentrations of lactate, alanine, citrate, GPC, histidine, and phenylalanine in seminal plasma and recovers the quality of semen of post-treated compared to pre-treated infertile men. Serum biochemistry was also improved over post-therapy in infertile men. Our findings reveal that Withania somnifera not only reboots enzymatic activity of metabolic pathways and energy metabolism but also invigorates the harmonic balance of seminal plasma metabolites and reproductive hormones in infertile men. ConclusionThe results suggest that Withania somnifera may be used as an empirical therapy for clinical management and treatment of infertility.

The effects of sapropterin on urinary monoamine metabolites in phenylketonuria

BackgroundSapropterin dihydrochloride (BH4, tetrahydrobiopterin) can lower plasma phenylalanine (Phe) concentrations for a subset of patients with phenylketonuria (PKU), an inborn error of metabolism. Studies suggest that monoamine neurotransmitter concentrations are low in PKU patients. Sapropterin functions as a cofactor for hydroxylases specific to Phe, tyrosine, and tryptophan metabolism, pathways essential for catecholamine and serotonin synthesis. ObjectiveThe objective of this study is to determine the impact of sapropterin on monoamine neurotransmitter status in patients with PKU. Design58 PKU subjects were provided 20mg/kg of sapropterin for 1month. Those who responded with at least a 15% decrease in plasma Phe received sapropterin for 1year, while Non-responders discontinued it. After an additional 3months, Responders who demonstrated increased Phe tolerance and decreased medical food dependence were classified as Definitive, whereas Responders unable to liberalize their diet without compromising plasma Phe control were identified as Provisional. At study visits, patients provided blood for plasma amino acids, 3-day diet records, and 12-hour urine samples analyzed for epinephrine (E), dopamine (DA), dihydroxyphenylacetate (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3MT), serotonin (5HT), and 5-hydroxyindole acetic acid (5HIAA) using HPLC with electrochemical detection. ResultsCompared with healthy non-PKU controls, subjects with PKU had significantly lower baseline concentrations of DA, HVA, 3MT, 5HT, and 5HIAA (p<0.001 for all). Medical food protein intake had a direct association with DA, HVA, 5HT, and 5HIAA during the study (p<0.05 for all), while plasma Phe had an inverse association with these markers (p<0.01 for all). DOPAC was also associated with plasma Phe throughout the year (p=0.035), although not at baseline. Patients with PKU had a significant increase in HVA (p=0.015) after 1month of sapropterin. When stratifying by Responder and Non-Responder status, significance of HVA increase in Non-responders (p=0.041) was confirmed, but not in Responders (p=0.081). A declining trend in urinary 5HIAA, significant only after controlling for plasma Phe (p=0.019), occurred for Definitive Responders during the 1-year study. ConclusionUrinary monoamine concentrations are low in patients with PKU and are influenced by oral sapropterin and medical food intake, highlighting the importance of these therapies to neurotransmitter metabolism in phenylketonuria.

Maternal Hyperphenylalaninemia: Rapid achievement of metabolic control predicts overall control throughout pregnancy

Women with hyperphenylalaninemia are at risk of having offspring affected with the maternal phenylketonuria syndrome. Here we analyze the effect of the intervention of a nutritionist on plasma phenylalanine control in Maternal Hyperphenylalaninemia. We analyzed a retrospective cohort of 35 completed pregnancies in 20 women with Maternal Hyperphenylalaninemia who visited the metabolic nutritionist during the pregnancy to achieve metabolic control. Women who promptly achieved metabolic control had lower plasma phenylalanine concentrations for the remainder of the pregnancy when compared to women who did not achieve prompt control, and this difference reached statistical significance. The achievement of plasma phenylalanine concentrations within the desired target range by the time of the second visit to the nutritionist is a strong predictor of the ability to maintain the desired target range of plasma phenylalanine for the remainder of the pregnancy. Furthermore, we demonstrate that phenylalanine tolerance increases significantly by trimester in women with classical and variant hyperphenylalaninemia.

A novel stable isotope tracer method to measure muscle protein fractional breakdown rate during a physiological non-steady-state condition

The measurement of the fractional breakdown rate (FBR) of muscle proteins during physiological non-steady state of amino acids (AAs) presents some challenges. Therefore, the goal of the present experiment was to modify the bolus stable isotope tracer injection approach to determine both fractional synthesis rate (FSR) and FBR of leg muscle protein during a physiological non-steady state of AAs. The approach uses the traditional precursor-product principle but is modified with the assumption that inward transport of AAs is proportional to their plasma concentrations. The FBR value calculated from the threonine tracer served as a reference to evaluate the validity of the FBR measurement from the phenylalanine tracer, which was under a non-steady-state condition due to the concomitant injection of unlabeled phenylalanine. Plasma phenylalanine concentration increased more than fourfold after the bolus injection, and thereafter it decreased exponentially, whereas the threonine concentration remained stable. FBR values were similar with the two tracers [0.133 ± 0.003 and 0.148 ± 0.003%/h (means ± SE) for the phenylalanine and threonine tracers, respectively, P > 0.05]. In addition, FSR values for the two tracers were similar (0.069 ± 0.002 and 0.067 ± 0.001%/h for the phenylalanine and threonine tracers, respectively, P > 0.05), indicating that the traditional FSR approach can also be used in the non-steady state. Accordingly, net balance (NB) values were similar (-0.065 ± 0.002 and -0.081 ± 0.002%/h for the phenylalanine and threonine tracers, respectively, P > 0.05). This new method of measuring muscle protein FBR during physiological non-steady state gives reliable results and allows simultaneous measurement of muscle protein FSR and thus a calculation of NB.

Utility of phenylalanine hydroxylase genotype for tetrahydrobiopterin responsiveness classification in patients with phenylketonuria

BackgroundA need exists to expand the characterization of tetrahydrobiopterin (BH4) responsiveness in patients with phenylketonuria (PKU), beyond simply evaluating change in blood phenylalanine concentrations. The clinical interpretation of BH4 responsiveness should be evaluated within the context of phenylalanine hydroxylase (PAH) genotype. AimThis investigation seeks to use a modified version of a previously developed PAH genotype severity tool, the assigned value (AV) sum, to assess the molecular basis of responsiveness in a clinical cohort and to explore the tool's ability to differentiate BH4 responsive groups. MethodsBH4 response was previously clinically classified in 58 patients with PKU, with three response groups emerging: definitive responders, provisional responders, and non-responders. Provisional responders represented a clinically ambiguous group, with an initial decrease in plasma phenylalanine concentrations, but limited ability to improve dietary phenylalanine tolerance. In this retrospective analysis, mutations in the PAH gene were identified in each patient. PAH genotype was characterized through the AV sum approach, in which each mutation is given an AV of 1, 2, 4, or 8; the sum of both mutations' AV corresponds to genotype severity, with a lower number representing a more severe phenotype. An AV sum cutoff of 2 (indicative of the most severe genotypes) was used to dichotomize patients and predict BH4 responsiveness. Provisional responders were classified with the definitive responders then the non-responders to see with which group they best aligned. ResultsIn 17/19 definitive responders, at least one mutation was mild or moderate in severity (AV sum>2). In contrast, 7/9 provisional responders carried two severe or null mutations (AV sum=2), suggesting little molecular basis for responsiveness. Non-responders represent a heterogeneous group with 15/25 patients carrying two severe mutations (AV sum=2), 5/25 patients carrying one moderate or mild mutation in combination with a severe or null mutation (AV sum>2), and the remaining five patients carrying an uncharacterized mutation in combination with a severe mutation. Predictive sensitivity of the AV sum was maximized (89.5% vs. 67.9%) with limited detriment to specificity (79.4% vs. 80.0%), by classifying provisional responders with the non-responders rather than with the definitive responders. ConclusionsIn our clinical cohort, the AV sum tool was able to identify definitive responders with a high degree of sensitivity. As demonstrated by both the provisional responder group and the substantial number of non-responders with AV sums>2, a potential exists for misclassification when BH4 response is determined by relying solely on change in plasma phenylalanine concentrations. PAH genotype should be incorporated in the clinical evaluation of BH4 responsiveness.

Clinical therapeutics for phenylketonuria.

Phenylketonuria was amongst the first of the metabolic disorders to be characterised, exhibiting an inborn error in phenylalanine metabolism due to a functional deficit of the enzyme phenylalanine hydroxylase. It affects around 700,000 people around the globe. Mutations in the gene coding for hepatic phenylalanine hydroxylase cause this deficiency resulting in elevated plasma phenylalanine concentrations, leading to cognitive impairment, neuromotor disorders and related behavioural symptoms. Inception of low phenylalanine diet in the 1950s marked a revolution in the management of phenylketonuria and has since been a vital element of all therapeutic regimens. However, compliance to dietary therapy has been found difficult and newer supplement approaches are being examined. The current development of gene therapy and enzyme replacement therapeutics may offer promising alternatives for the management of phenylketonuria. This review outlines the pathological basis of phenylketonuria, various treatment regimes, their associated challenges and the future prospects of each approach. Briefly, novel drug delivery systems which can potentially deliver therapeutic strategies in phenylketonuria have been discussed.

Diurnal variation of phenylalanine concentrations in tyrosinaemia type 1: should we be concerned?

Tyrosinaemia type 1 (HT1) is treated with a tyrosine and phenylalanine-restricted diet, amino acids free of phenylalanine and tyrosine, and nitisinone (NTBC). Treatment guidelines recommend plasma tyrosine between 200-400 μm and phenylalanine at least >30 μm. There is little information on the diurnal variation of plasma tyrosine or phenylalanine in HT1. Low plasma phenylalanine <30 μm may be associated with poor growth and cognitive delay. The present study aimed to document diurnal variation of tyrosine and phenylalanine plasma concentrations and growth in children with HT1. Median tyrosine and phenylalanine plasma concentrations were reviewed retrospectively over 3 years in 11 subjects (median age 4 years) with HT1. Subjects routinely collected morning fasting blood samples but afternoon nonfasted samples were taken in the clinic (<10% of samples). Growth Z-scores were calculated. The percentage of all plasma phenylalanine concentrations <30 μm was 8.6% and <40 μm was 13.6%. Only 2% of fasting morning phenylalanine concentrations were <30 μm, compared to 83% of nonfasting afternoon samples. All but one child had a height Z-score <0. Blood phenylalanine concentrations were consistently lower in the afternoon. Taking blood samples at variable time points in the day may lead to variation in interpreting dietary control. A detailed study is necessary to examine the 24-h diurnal variation of plasma phenylalanine and tyrosine in HT1. It is possible that phenylalanine concentrations may be very low for a substantive time over 24 h and the potential impact that this may have on cognitive development and growth in children is unknown.

Using change in plasma phenylalanine concentrations and ability to liberalize diet to classify responsiveness to tetrahydrobiopterin therapy in patients with phenylketonuria

Tetrahydrobiopterin (BH4) responsiveness is currently defined as a decrease in plasma phenylalanine concentrations in patients with phenylketonuria (PKU). This definition does not offer insight beyond the initial assessment of patients, which may lead to treatment ambiguity in patients who only experience an initial decrease in plasma phenylalanine concentrations. We present our experience with a novel classification approach using sequentially-applied criteria. Plasma phenylalanine concentrations were measured at baseline and after one month of BH4 therapy (20mg/kg/day) in 58 PKU patients (34 M, 24 F; age 17.3±11.0years). Thirty-two patients (55.2%) were classified as “preliminary responders” at one month, experiencing at least a 15% decrease in plasma phenylalanine concentrations. Preliminary responders' ability to liberalize their dietary restrictions was then systematically assessed. “Definitive responders” were defined as preliminary responders who could increase their dietary phenylalanine tolerance by at least 300mg/day and lower prescribed medical food needs by at least 25% while maintaining metabolic control (plasma phenylalanine ≤360μmol/L) and consuming adequate dietary protein. Preliminary responders who could not liberalize their diets according to these criteria were classified as “provisional responders.” Nineteen patients (32.8% of patients initiating BH4 therapy) met the definitive responder criteria, increasing dietary phenylalanine tolerance from 704±518mg/day to 1922±612mg/day and reducing medical food to 16.7±19.5% of their baseline prescription. Nine patients (15.5% of patients initiating BH4 therapy) were classified as provisional responders, all remaining on 100% of their baseline medical food prescription. From this classification approach, a subgroup of provisionally responsive patients emerged who experienced an initial decrease in plasma phenylalanine concentrations but who could not substantially increase their dietary phenylalanine tolerance or decrease medical food needs. Diet liberalization is an essential component of BH4-responsiveness classification.