Platelet serotonin concentrations in PKU patients under dietary control and tetrahydrobiopterin treatment

Coenzyme Q10 Treatment Monitoring in Different Human Biological Samples

Coenzyme Q₁₀ (CoQ) treatment monitoring is a matter of debate since CoQ distribution from plasma to blood cells and tissues is not fully understood. We aimed to analyze the CoQ levels in a wide set of human biological samples (plasma, blood mononuclear cells (BMCs), platelets, urinary cells, and skeletal muscle) from a group of 11 healthy male runners before and after CoQ supplementation. The CoQ content in the different samples was analyzed by HPLC coupled to electrochemical detection. No significant differences were observed in the CoQ levels measured in the BMCs, platelets, and urine after the one-month treatment period. Plasma CoQ (expressed in absolute values and values relative to total cholesterol) significantly increased after CoQ supplementation (p = 0.003 in both cases), and the increase in CoQ in muscle approached significance (p = 0.074). CoQ levels were increased in the plasma of all supplemented subjects, and muscle CoQ levels were increased in 8 out of 10 supplemented subjects. In conclusion, the analysis of CoQ in plasma samples seems to be the best surrogate biomarker for CoQ treatment monitoring. Moreover, oral CoQ administration was effective for increasing muscle CoQ concentrations in most subjects.

Prevalence of sleep disorders in early-treated phenylketonuric children and adolescents. Correlation with dopamine and serotonin status

Phenylketonuric (PKU) patients are a population at risk for sleep disorders due to deficits in neurotransmitter synthesis. We aimed to study the prevalence of sleep disorders in early-treated PKU children and adolescents and assessed correlations with dopamine and serotonin status. We compared 32 PKU patients (16 females, 16 males; mean age 12 years), with a healthy control group of 32 subjects (16 females, 16 males; mean age 11.9 years). 19 PKU patients were under dietary treatment and 13 on tetrahydrobiopterin therapy. Concurrent phenylalanine (Phe), index of dietary control and variability in Phe in the last year, tyrosine, tryptophan, prolactin, and ferritin in plasma, platelet serotonin concentration, and melatonin, homovanillic and 5-hydroxyindoleacetic acid excretion in urine were analyzed. Sleep was assessed using Bruni's Sleep Disturbance Scale for Children. Sleep disorders were similar in both groups, 15.6% in control group and 12.5% in PKU group. In PKU patients, no correlations were found with peripheral biomarkers of neurotransmitter synthesis nor different Phe parameters, 43.3% had low melatonin excretion and 43.8% low platelet serotonin concentrations. Despite melatonin and serotonin deficits in early-treated PKU patients, the prevalence of sleep disorders is similar to that of the general population.

Psychiatric and Cognitive Aspects of Phenylketonuria: The Limitations of Diet and Promise of New Treatments

Phenylketonuria (PKU) is a recessive disorder of phenylalanine metabolism due to mutations in the gene for phenylalanine hydroxylase (PAH). Reduced PAH activity results in significant hyperphenylalaninemia, which leads to alterations in cerebral myelin and protein synthesis, as well as reduced levels of serotonin, dopamine, and noradrenaline in the brain. When untreated, brain development is grossly disrupted and significant intellectual impairment and behavioral disturbance occur. The advent of neonatal heel prick screening has allowed for diagnosis at birth, and the institution of a phenylalanine restricted diet. Dietary treatment, particularly when maintained across neurodevelopment and well into adulthood, has resulted in markedly improved outcomes at a cognitive and psychiatric level for individuals with PKU. However, few individuals can maintain full dietary control lifelong, and even with good control, an elevated risk remains of-in particular-mood, anxiety, and attentional disorders across the lifespan. Increasingly, dietary recommendations focus on maintaining continuous dietary treatment lifelong to optimize psychiatric and cognitive outcomes, although the effect of long-term protein restricted diets on brain function remains unknown. While psychiatric illness is very common in adult PKU populations, very little data exist to guide clinicians on optimal treatment. The advent of new treatments that do not require restrictive dietary management, such as the enzyme therapy Pegvaliase, holds the promise of allowing patients a relatively normal diet alongside optimized mental health and cognitive functioning.

Salivary serotonin does not correlate with central serotonin turnover in adult phenylketonuria (PKU) patients

INTRODUCTION

Phenylketonuria (PKU) is an inborn error of metabolism associated with an increased risk of behavioural and mood disorders. There are currently no reliable markers for monitoring mood in PKU. The purpose of this study was to evaluate salivary serotonin as a possible non-invasive marker of long-term mood symptoms and central serotonin activity in patients with PKU.

METHODS

20 patients were recruited from our Adult Metabolic Diseases Clinic. Age, sex, plasma phenylalanine (Phe) level, DASS (Depression Anxiety Stress Scales) depression score, DASS anxiety score, BMI, salivary serotonin, salivary cortisol, 2-year average Phe, 2-year average tyrosine (Tyr), and 2-year average Phe:Tyr ratio were collected for each patient. Spearman's ρ correlation analysis was used to determine if there was any relationship between any of the parameters.

RESULTS

There were positive correlations between DASS anxiety and DASS depression scores (Spearman's ρ = 0.8708, p-value < 0.0001), BMI and plasma Phe level (Spearman's ρ = 0.6228, p-value = .0034), and 2-year average Phe and BMI (Spearman's ρ = 0.5448, p-value = .0130). There was also a negative correlation between salivary cortisol and plasma Phe level (Spearman's ρ = -0.5018, p-value = .0338). All other correlations were not statistically significant.

CONCLUSION

Salivary serotonin does not correlate with peripheral phenylalanine levels, DASS depression scale scores, or DASS anxiety scale scores, implying that salivary serotonin does not reflect central serotonin turnover. Additionally, this study suggests that salivary serotonin is not a suitable marker for monitoring dietary control, mood, or anxiety in PKU.

SYNOPSIS

Salivary serotonin does not correlate with peripheral phenylalanine levels, DASS depression scale scores, or DASS anxiety scale scores, suggesting that salivary serotonin is not a suitable marker for monitoring dietary control, mood, or anxiety in PKU.

Impaired Neurotransmission in Early-treated Phenylketonuria Patients

Cerebral neurotransmitter (NT) deficiency has been suggested as a contributing factor in the pathophysiology of brain dysfunction in phenylketonuria (PKU), even in early-treated phenylketonuric patients. The study aimed to review dopamine and serotonin status in PKU, and the effect of the impaired neurotransmission. Several mechanisms are involved in the pathophysiology of PKU, primarily characterized by impaired dopamine and serotonin synthesis. These deficits are related to executive dysfunctions and social-emotional problems, respectively, in early treated patients. Blood phenylalanine is the main biomarker for treatment compliance follow-up, but further investigations and validation of peripheral biomarkers may be performed to monitor NT status. The development of new therapies is needed not only for decreasing blood and brain phenylalanine levels but also to improve NT syntheses.

BH4 treatment in BH4-responsive PKU patients: preliminary data on blood prolactin concentrations suggest increased cerebral dopamine concentrations

In phenylketonuria (PKU), cerebral neurotransmitter deficiencies have been suggested to contribute to brain dysfunction. Present treatment aims to reduce blood phenylalanine concentrations by a phenylalanine-restricted diet, while in some patients blood phenylalanine concentrations also respond to cofactor treatment with tetrahydrobiopterin (BH4). Recently, a repurposing approach of BH4 was suggested to increase cerebral neurotransmitter synthesis. To investigate whether BH4 may improve cerebral dopamine concentrations in PKU patients beyond its effect through lowering blood phenylalanine concentrations, we investigated blood prolactin concentrations-as a parameter of brain dopamine availability. We retrospectively compared blood prolactin in relation to blood phenylalanine concentrations of nine (male) BH4-responsive PKU patients, when being treated without and with BH4. Blood prolactin concentrations positively correlated to blood phenylalanine concentrations (p=0.002), being significantly lower with than without BH4 treatment (p=0.047). In addition, even in this small number of male patients, blood prolactin concentrations tended to be lower at increasing BH4 dose (p=0.054), while taking blood phenylalanine concentrations into account (p=0.002). In individual BH4-responsive patients, median blood prolactin concentrations were significantly lower while using BH4 than before using BH4 treatment (p=0.024), whereas median blood phenylalanine concentrations tended to be lower, but this did not reach statistical significance (p=0.107). Therefore, these data show that high blood phenylalanine in BH4-responsive PKU male patients seems to be associated with increased blood prolactin concentrations, suggesting reduced cerebral dopamine availability. Moreover, these data suggest that BH4 treatment in itself could decrease blood prolactin concentrations in a dose-responsive way, independent of blood phenylalanine concentrations. We conclude that these preliminary data indicate that BH4 treatment may improve cerebral dopamine concentrations in PKU patients beyond its effect through lowering blood phenylalanine concentrations, possibly in a dose-dependent manner, but further research would be warranted.

The effects of sapropterin on urinary monoamine metabolites in phenylketonuria

BACKGROUND

Sapropterin 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.

OBJECTIVE

The objective of this study is to determine the impact of sapropterin on monoamine neurotransmitter status in patients with PKU.

DESIGN

58 PKU subjects were provided 20 mg/kg of sapropterin for 1 month. Those who responded with at least a 15% decrease in plasma Phe received sapropterin for 1 year, while Non-responders discontinued it. After an additional 3 months, 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.

RESULTS

Compared 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 1 month 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.

CONCLUSION

Urinary 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.

Correlation of serotonin levels in CSF, platelets, plasma, and urine

BACKGROUND

Neurotransmitter levels are best measured in the cerebrospinal fluid (CSF), but that requires an invasive procedure.

METHODS

Samples were collected from humans and rats. Eighteen women age 38-51 years with fibromyalgia provided samples of CSF, plasma, platelets, and urine. Samples of CSF, plasma, platelets, and urine were also collected from Sprague-Dawley rats, adult male, 6 months old. One group of rats was treated with p-chlorophenylalanine to decrease their levels of serotonin, and another group of rats was treated with amphetamine to increase their levels of serotonin. Methodological improvements include: 1) the use of siliconized glassware, plasticware, and tubing to prevent adsorption of serotonin, 2) the extraction of serotonin from the CSF, plasma, and platelets, 3) repeated washing of the platelets with an improved buffer, and 4) early morning sample collection. HPLC/MS was used to measure serotonin after extraction.

RESULTS

For serotonin, the new method of measuring platelet levels resulted in a very high correlation with levels of serotonin in CSF in rats (r=0.97) and humans (r=0.97). There were lower correlations of levels of serotonin in CSF with levels in plasma (r=0.77 for rats and r=0.57 in humans) and urine (r=0.67 in rats and r=0.62 in humans).

GENERAL SIGNIFICANCE

This method of measuring serotonin levels in platelets results in a very strong correlation with levels in CSF, so in most cases platelet measurements will be preferable since it is much less invasive to collect. Levels of serotonin in plasma and urine are significantly but less strongly correlated with levels in CSF.

Suboptimal outcomes in patients with PKU treated early with diet alone: revisiting the evidence

BACKGROUND

The National Institute of Health (NIH) published a Consensus Statement on the screening and management of Phenylketonuria (PKU) in 2000. The panel involved in the development of this consensus statement acknowledged the lack of data regarding the potential for more subtle suboptimal outcomes and the need for further research into treatment options. In subsequent years, the approval of new treatment options for PKU and outcome data for patients treated from the newborn period by dietary therapy alone have become available. We hypothesized that a review of the PKU literature since 2000 would provide further evidence related to neurocognitive, psychosocial, and physical outcomes that could serve as a basis for reassessment of the 2000 NIH Consensus Statement.

METHODS

A systematic review of literature residing in PubMed, Scopus and PsychInfo was performed in order to assess the outcome data over the last decade in diet-alone early-treated PKU patients to assess the need for new recommendations and validity of older recommendations in light of new evidence.

RESULTS

The majority of publications (140/150) that contained primary outcome data presented at least one suboptimal outcome compared to control groups or standardized norms/reference values in at least one of the following areas: neurocognitive/psychosocial (N=60; 58 reporting suboptimal outcomes); quality of life (N=6; 4 reporting suboptimal outcomes); brain pathology (N=32; 30 reporting suboptimal outcomes); growth/nutrition (N=34; 29 reporting suboptimal outcomes); bone pathology (N=9; 9 reporting suboptimal outcomes); and/or maternal PKU (N=19; 19 reporting suboptimal outcomes).

CONCLUSIONS

Despite the remarkable success of public health programs that have instituted newborn screening and early introduction of dietary therapy for PKU, there is a growing body of evidence that suggests that neurocognitive, psychosocial, quality of life, growth, nutrition, bone pathology and maternal PKU outcomes are suboptimal. The time may be right for revisiting the 2000 NIH Consensus Statement in order to address a number of important issues related to PKU management, including treatment advancements for metabolic control in PKU, blood Phe variability, neurocognitive and psychological assessments, routine screening measures for nutritional biomarkers, and bone pathology.

Sapropterin: a review of its use in the treatment of primary hyperphenylalaninaemia

Sapropterin dihydrochloride (Kuvan), hereafter referred to as sapropterin, is a synthetic formulation of the active 6R-isomer of tetrahydrobiopterin, a naturally occurring cofactor for phenylalanine hydroxylase. In the EU, sapropterin is approved for the treatment of hyperphenylalaninaemia in patients >or=4 years of age with tetrahydrobiopterin-responsive phenylketonuria (PKU) and in adults and children with tetrahydrobiopterin deficiency who have been shown to be responsive to such treatment. In the US, it is approved to reduce blood phenylalanine levels in patients with hyperphenylalaninaemia due to tetrahydrobiopterin-responsive PKU. Oral sapropterin effectively lowers blood phenylalanine levels in a proportion of patients with PKU; to date, there are no published efficacy trials of the specific sapropterin formulation under review in patients with tetrahydrobiopterin deficiency. Sapropterin was well tolerated in patients with PKU, although longer-term tolerability data are required. Sapropterin is the first non-dietary treatment for patients with PKU that has been shown in randomized, double-blind trials to be effective in lowering blood phenylalanine levels. Thus, sapropterin provides a promising treatment option for patients with PKU who are tetrahydrobiopterin-responsive. PHARMACOLOGICAL PROPERTIES: The mechanism of action of sapropterin in lowering blood phenylalanine levels in patients with PKU has not been fully elucidated, but appears to be related, in part, to its effect in augmenting and stabilizing mutant phenylalanine hydroxylases, resulting in increased clearance of phenylalanine from the body. In tetrahydrobiopterin deficiency, its mechanism of action is presumed to be secondary to replacement of endogenous tetrahydrobiopterin. In healthy adults, orally-administered sapropterin is absorbed into the bloodstream, reaching maximum concentrations in 3-4 hours. It has a mean elimination half-life of approximately 4 hours in healthy adults and, based on a population pharmacokinetic study, 6.7 hours in patients with tetrahydrobiopterin-responsive PKU. Age, from 9 to 49 years, had no effect on key pharmacokinetic parameters. THERAPEUTIC EFFICACY: In an 8-day screening study in patients aged >or=8 years with PKU, approximately 20% of patients responded to sapropterin 10 mg/kg/day (i.e. were tetrahydrobiopterin responsive). Tetrahydrobiopterin-responsive patients from this study were entered into a randomized, double-blind, placebo-controlled trial in which they received sapropterin 10 mg/kg/day or placebo. At the end of 6 weeks of treatment, sapropterin recipients experienced a significant 28% decrease from baseline in mean blood phenylalanine level, while there was no significant change in placebo recipients. The difference in mean blood phenylalanine level between sapropterin and placebo groups was statistically significant at -245 micromol/L. In an extension of this trial, significantly greater reductions in blood phenylalanine levels were observed with sapropterin dosages of 10 and 20 mg/kg/day than with sapropterin 5 mg/kg/day (each dose administered for 2 weeks), indicating a dose dependent effect. During 12 weeks of treatment with the sapropterin dosage individualized to the patient according to the earlier response to sapropterin 5, 10 or 20 mg/kg/day, reductions in plasma phenylalanine were observed in all dosage groups. In a randomized, double-blind trial in children aged 4-12 years with tetrahydrobiopterin-responsive PKU, patients treated with sapropterin 20 mg/kg/day had reduced blood phenylalanine levels after 3 weeks of treatment. Over the full 10-week trial, sapropterin and placebo recipients experienced a significantly increased tolerance to dietary phenylalanine (20.9 mg/kg/day in sapropterin and 2.9 mg/kg/day in placebo recipients).

TOLERABILITY

Sapropterin was well tolerated in patients with PKU. In clinical trials in patients with PKU, the following adverse events were identified: headache, rhinorrhoea (both at a frequency of >or=10%), pharyngolaryngeal pain, nasal congestion, cough, diarrhoea, vomiting, abdominal pain and hypophenylalaninaemia (all at a frequency of >or=1% to <10%). There were no serious adverse events that were thought to be related to sapropterin treatment.

Maternal serotonin is crucial for murine embryonic development

The early appearance of serotonin and its receptors during prenatal development, together with the many effects serotonin exerts during CNS morphogenesis, strongly suggest that serotonin influences the development and maturation of the mammalian brain before it becomes a neuromodulator/neurotransmitter. Sites of early serotonin biosynthesis, however, have not been detected in mouse embryos or extraembryonic structures, suggesting that the main source of serotonin could be of maternal origin. This hypothesis was tested by using knockout mice lacking the tph1 gene, which is responsible for the synthesis of peripheral serotonin. Genetic crosses were performed to compare the phenotype of pups born from homozygous and heterozygous mothers. Observations provide the first clear evidence that (i) maternal serotonin is involved in the control of morphogenesis during developmental stages that precede the appearance of serotonergic neurons and (ii) serotonin is critical for normal murine development. Most strikingly, the phenotype of tph1-/- embryos depends more on the maternal genotype than on that of the concepti. Consideration of the maternal genotype may thus help to clarify the influence of other genes in complex diseases, such as mental illness.