Safety of extended treatment with sapropterin dihydrochloride in patients with phenylketonuria: results of a phase 3b study

Efficacy and safety of sapropterin before and during pregnancy: Final analysis of the Kuvan® Adult Maternal Paediatric European Registry (KAMPER) maternal and Phenylketonuria Developmental Outcomes and Safety (PKUDOS) PKU-MOMs sub-registries

Infants born to mothers with phenylketonuria (PKU) may develop congenital abnormalities because of elevated phenylalanine (Phe) levels in the mother during pregnancy. Maintenance of blood Phe levels between 120 and 360 μmol/L reduces risks of birth defects. Sapropterin dihydrochloride helps maintain blood Phe control, but there is limited evidence on its risk-benefit ratio when used during pregnancy. Data from the maternal sub-registries-KAMPER (NCT01016392) and PKUDOS (NCT00778206; PKU-MOMs sub-registry)-were collected to assess the long-term safety and efficacy of sapropterin in pregnant women in a real-life setting. Pregnancy and infant outcomes, and the safety of sapropterin were assessed. Final data from 79 pregnancies in 57 women with PKU are reported. Sapropterin dose was fairly constant before and during pregnancy, with blood Phe levels maintained in the recommended target range during the majority (82%) of pregnancies. Most pregnancies were carried to term, and the majority of liveborn infants were reported as 'normal' at birth. Few adverse and serious adverse events were considered related to sapropterin, with these occurring in participants with high blood Phe levels. This report represents the largest population of pregnant women with PKU exposed to sapropterin. Results demonstrate that exposure to sapropterin during pregnancy was well-tolerated and facilitated maintenance of blood Phe levels within the target range, resulting in normal delivery. This critical real-world data may facilitate physicians and patients to make informed treatment decisions about using sapropterin in pregnant women with PKU and in women of childbearing age with PKU who are responsive to sapropterin.

The treatment of biochemical genetic diseases: From substrate reduction to nucleic acid therapies

Newborn screening (NBS) began a revolution in the management of biochemical genetic diseases, greatly increasing the number of patients for whom dietary therapy would be beneficial in preventing complications in phenylketonuria as well as in a few similar disorders. The advent of next generation sequencing and expansion of NBS have markedly increased the number of biochemical genetic diseases as well as the number of patients identified each year. With the avalanche of new and proposed therapies, a second wave of options for the treatment of biochemical genetic disorders has emerged. These therapies range from simple substrate reduction to enzyme replacement, and now ex vivo gene therapy with autologous cell transplantation. In some instances, it may be optimal to introduce nucleic acid therapy during the prenatal period to avoid fetopathy. However, as with any new therapy, complications may occur. It is important for physicians and other caregivers, along with ethicists, to determine what new therapies might be beneficial to the patient, and which therapies have to be avoided for those individuals who have less severe problems and for which standard treatments are available. The purpose of this review is to discuss the "Standard" treatment plans that have been in place for many years and to identify the newest and upcoming therapies, to assist the physician and other healthcare workers in making the right decisions regarding the initiation of both the "Standard" and new therapies. We have utilized several diseases to illustrate the applications of these different modalities and discussed for which disorders they may be suitable. The future is bright, but optimal care of the patient, including and especially the newborn infant, requires a deep knowledge of the disease process and careful consideration of the necessary treatment plan, not just based on the different genetic defects but also with regards to different variants within a gene itself.

Neuropsychiatric Function Improvement in Pediatric Patients with Phenylketonuria

OBJECTIVE

To evaluate effects of sapropterin dihydrochloride on blood phenylalanine (Phe) and symptoms of neuropsychiatric impairment in children and adolescents with phenylketonuria (PKU).

STUDY DESIGN

PKU subjects 8-17 years of age (n = 86) were randomized to double-blind treatment with sapropterin (n = 43) or placebo (n = 43) for 13 weeks, then all received open-label sapropterin therapy for an additional 13 weeks. Blood Phe and symptoms of inattention, hyperactivity/impulsivity (Attention-Deficit/Hyperactivity Disorder Rating Scale IV [ADHD RS-IV]), executive functioning (Behavior Rating Inventory of Executive Function), depression (Hamilton Rating Scale for Depression), and anxiety (Hamilton Rating Scale for Anxiety) were assessed.

RESULTS

Following the 13-week randomization phase, the sapropterin and placebo groups had mean changes in blood Phe of -20.9% and +2.9%, respectively. Corresponding least square mean differences in ADHD RS-IV scores were significantly greater for the sapropterin vs the placebo group: Total (-3.2 points, P = .02), Inattention subscale (-1.8 points, P = .04), and Hyperactivity/Impulsivity subscale (-1.6 points, P = .02). Forest plots favored sapropterin treatment over placebo for all ADHD RS-IV and Behavior Rating Inventory of Executive Function indices. There were no significant differences in reported problems with attention or executive function between the 2 groups at baseline or at week 26 following the 13-week open-label treatment period. Anxiety and depression scores did not differ significantly between cohorts at any time. Sapropterin was well tolerated, with a favorable safety profile.

CONCLUSIONS

Sapropterin reduced blood Phe and was associated with significant improvement in parent-reported symptoms of inattention, hyperactivity/impulsivity, and executive functioning in children and adolescents with PKU.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT01114737. Registered 27 April 2010, https://clinicaltrials.gov/ct2/show/NCT01114737.

Development of a practical dietitian road map for the nutritional management of phenylketonuria (PKU) patients on pegvaliase

Background

The metabolic dietitian/nutritionist (hereafter ‘dietitian’) plays an essential role in the nutritional management of patients with phenylketonuria (PKU), including those on pegvaliase. Currently, more educational support and clinical experience is needed to ensure that dietitians are prepared to provide optimal nutritional management and counselling of pegvaliase-treated patients.

Methods

Via a face-to-face data-review meeting, followed by a virtual consolidation meeting, a group of expert dietitians and one paediatrician discussed and developed a series of recommendations on the nutritional evaluation and management of patients receiving pegvaliase. The consensus group consisted of 10 PKU experts: six dietitians and one paediatrician from Europe and three dietitians from the US. One European and three US dietitians had experience with pegvaliase-treated patients.

Results

The consensus group recommended that a physician, dietitian and nurse are part of the pegvaliase treatment team. Additionally, a psychologist/counsellor should be included if available. Practical proposals for the nutritional evaluation of pegvaliase-treated patients at baseline, during the induction and titration phases and for long-term maintenance were developed. The consensus group suggested assessment of blood Phe at least monthly or every 2 weeks in the event of low blood Phe (i.e., blood Phe <30 μmol/L). It may be appropriate to increase blood Phe monitoring when adjusting protein intake and/or pegvaliase dose. It was recommended that natural protein intake is increased by 10–20 g increments if blood Phe concentrations decrease to <240 μmol/L in patients who are not meeting the dietary reference intake for natural protein of 0.8 g/kg. It was proposed that with pegvaliase treatment blood Phe levels could be maintained <240 μmol/L but more evidence on the safety of achieving physiological blood Phe levels is necessary before any recommendation on the lower blood Phe target can be given. Finally, both patients and dietitians should have access to educational resources to optimally support patients receiving pegvaliase.

Conclusion

This practical road map aims to provide initial recommendations for dietitians monitoring patients with PKU prescribed pegvaliase. Given that practical experience with pegvaliase is still limited, nutritional recommendations will require regular updating once more evidence is available and clinical experience evolves.

Treatment With Tetrahydrobiopterin Improves White Matter Maturation in a Mouse Model for Prenatal Hypoxia in Congenital Heart Disease

Background Reduced oxygen delivery in congenital heart disease causes delayed brain maturation and white matter abnormalities in utero. No treatment currently exists. Tetrahydrobiopterin (BH4) is a cofactor for neuronal nitric oxide synthase. BH4 availability is reduced upon NOS activation, such as during hypoxic conditions, and leads to toxin production. We hypothesize that BH4 levels are depleted in the hypoxic brain and that BH4 replacement therapy mitigates the toxic effects of hypoxia on white matter. Methods and Results Transgenic mice were used to visualize oligodendrocytes. Hypoxia was introduced during a period of white matter development equivalent to the human third trimester. BH4 was administered during hypoxia. BH4 levels were depleted in the hypoxic brain by direct quantification (n=7-12). The proliferation (n=3-6), apoptosis (n=3-6), and developmental stage (n=5-8) of oligodendrocytes were determined immunohistologically. Total oligodendrocytes increased after hypoxia, consistent with hypoxia-induced proliferation seen previously; however, mature oligodendrocytes were less prevalent in hypoxia, and there was accumulation of immature oligodendrocytes. BH4 treatment improved the mature oligodendrocyte number such that it did not differ from normoxia, and accumulation of immature oligodendrocytes was not observed. These results persisted beyond the initial period of hypoxia (n=3-4). Apoptosis increased with hypoxia but decreased with BH4 treatment to normoxic levels. White matter myelin levels decreased following hypoxia by western blot. BH4 treatment normalized myelination (n=6-10). Hypoxia worsened sensory-motor coordination on balance beam tasks, and BH4 therapy normalized performance (n=5-9). Conclusions Suboptimal BH4 levels influence hypoxic white matter abnormalities. Repurposing BH4 for use during fetal brain development may limit white matter dysmaturation in congenital heart disease.

Inherited Metabolic Disorders: Aspects of Chronic Nutrition Management

The introduction of newborn screening and the development of new therapies have led to an expanding population of patients with inherited metabolic disorders, and these patients are now entering adulthood. Dietary therapy is the mainstay of treatment for many of these disorders, and thus, trained metabolic dietitians are critical members of the multidisciplinary team required for management of such patients. The main goals of dietary therapy in inborn errors of metabolism are the maintenance of normal growth and development while limiting offending metabolites and providing deficient products. Typically, the offending metabolite is either significantly reduced or removed completely from the diet and then reintroduced in small quantities until blood levels are within the normal range. Such treatment is required in infancy, childhood, and adulthood and requires careful monitoring of micronutrient and macronutrient intake throughout the life span. The goal of this review is to highlight the basic principles of chronic nutrition management of the inborn errors of protein, carbohydrate, and fat metabolism.

Long-term developmental progression in infants and young children taking sapropterin for phenylketonuria: a two-year analysis of safety and efficacy

PURPOSE

Sapropterin is an oral synthetic formulation of tetrahydrobiopterin prescribed as adjunctive therapy for phenylketonuria. The efficacy of sapropterin in reducing blood phenylalanine levels has been demonstrated in clinical studies of individuals with phenylketonuria older than 4 years of age. Its effect on neurocognitive functioning in younger children has not been examined.

METHODS

A 2-year interim analysis of blood phenylalanine levels, prescribed dietary phenylalanine intake, and neurocognitive functioning was performed in children who started receiving sapropterin at 0-6 years of age and responded with a ≥30% mean blood phenylalanine reduction. Children were evaluated at baseline and 2-year follow-up.

RESULTS

Sapropterin had a favorable safety profile and lowered blood phenylalanine levels with increased prescribed dietary phenylalanine intakes. Mean full-scale intelligence quotient was 103 ± 12 at baseline and 104 ± 10 at 2-year follow-up (P = 0.50, paired t-test, n = 25). For children younger than 30 months of age, the cognitive composite score from the Bayley Scales of Infant and Toddler Development, Third Edition, remained within the average range.

CONCLUSION

Sapropterin had a favorable safety profile, was effective in lowering blood phenylalanine levels while clinically requiring dietary adjustment, resulting in increased phenylalanine intake, and preserved neurocognitive performance in children who started therapy between 0 and 6 years of age.

Alternative therapies to address the unmet medical needs of patients with phenylketonuria

Standard therapy for phenylketonuria (PKU), the most common inherited disorder in amino acid metabolism, is an onerous phenylalanine-restricted diet. Adherence to this stringent diet regimen decreases as patients get older, and this lack of adherence is directly associated with cognitive and executive dysfunction and psychiatric issues. These factors emphasize the need for alternative pharmacological therapies to help treat patients with PKU. Sapropterin dihydrochloride is a synthetic form of tetrahydrobiopterin, the cofactor of phenylalanine hydroxylase that in pharmacological doses can stabilize and increase residual enzyme activity in some patients with PKU. About one-third of all patients with PKU respond to oral sapropterin. Phenylalanine ammonia lyase (PAL) is a prokaryotic enzyme that converts phenylalanine to ammonia and trans-cinnamic acid. Phase I and II trials have shown that injectable recombinant Anabaena variabilis PAL produced in Escherichia coli conjugated with PEG can reduce phenylalanine levels in subjects with PKU. The most frequently reported adverse events were injection-site reactions, dizziness and immune reactions. Additionally, oral administration of PAL and delivery of enzyme substitution therapies by encapsulation in erythrocytes are being investigated. Novel therapies for patients with PKU appear to be options to reduce phenylalanine levels, and may reduce the deleterious effects of this disorder.

Long-term safety and efficacy of sapropterin: the PKUDOS registry experience

The Phenylketonuria (PKU) Demographics, Outcomes and Safety (PKUDOS) registry is designed to provide longitudinal safety and efficacy data on subjects with PKU who are (or have been) treated with sapropterin dihydrochloride. The PKUDOS population consists of 1189 subjects with PKU: N = 504 who were continuously exposed to sapropterin from date of registry enrollment, N = 211 who had intermittent exposure to the drug, and N = 474 with some other duration of exposure. Subjects continuously exposed to sapropterin showed an average 34% decrease in blood phenylalanine (Phe)--from 591 ± 382 μmol/L at baseline to 392 ± 239 μmol/L (p = 0.0009) after 5 years. This drop in blood Phe was associated with an increase in dietary Phe tolerance [from 1000 ± 959 mg/day (pre-sapropterin baseline) to 1539 ± 840 mg/day after 6 years]. Drug-related adverse events (AEs) were reported in 6% of subjects, were mostly considered non-serious, and were identified in the gastrointestinal, respiratory, and nervous systems. Serious drug-related AEs were reported in ≤ 1% of subjects. Similar safety and efficacy data were observed for children<4 years. Long-term data from the PKUDOS registry suggest that sapropterin has a tolerable safety profile and that continuous use is associated with a significant and persistent decrease in blood Phe and improvements in dietary Phe tolerance.

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.

Individualized long-term outcomes in blood phenylalanine concentrations and dietary phenylalanine tolerance in 11 patients with primary phenylalanine hydroxylase (PAH) deficiency treated with Sapropterin-dihydrochloride

We analyzed long-term sustainability of improved blood Phenylalanine (Phe) control and changes to dietary Phe tolerance in 11 patients (1 month to 16 years), with various forms of primary PAH deficiency (classic, moderate, severe phenylketonuria [PKU], mild hyperphenylalaninemia [HPA]), who were treated with 15-20mg/kg/d Sapropterin-dihydrochloride during a period of 13-44 months. 7/11 patients had a sustainable, significant reduction of baseline blood Phe concentrations and 6 of them also had an increase in mg/kg/day Phe tolerance. In 2 patients with mild HPA, blood Phe concentrations remained in the physiologic range even after a 22 and 36% increase in mg/kg/day Phe tolerance and an achieved Phe intake at 105% and 268% of the dietary reference intake (DRI) for protein. 2 of these responders had classic PKU. 1 patient with mild HPA who started treatment at 2 months of life, had a significant and sustainable reduction in pretreatment blood Phe concentrations, but no increase in the mg/kg/day Phe tolerance. An increase in Phe tolerance could only be demonstrated when expressing the patient's daily Phe tolerance with the DRI for protein showing an increase from 58% at baseline to 78% of normal DRI at the end of the observation. Long-term follow-up of patients with an initial response to treatment with Sapropterin is essential to determine clinically meaningful outcomes. Phenylalanine tolerance should be expressed in mg/kg/day and/or % of normal DRI to differentiate medical therapy related from physiologic growth related increase in daily Phe intake.

A randomized, placebo-controlled, double-blind study of sapropterin to treat ADHD symptoms and executive function impairment in children and adults with sapropterin-responsive phenylketonuria

Symptoms of attention deficit-hyperactivity disorder (ADHD), particularly inattention, and impairments in executive functioning have been reported in early and continuously treated children, adolescents, and adults with phenylketonuria (PKU). In addition, higher blood phenylalanine (Phe) levels have been correlated with the presence of ADHD symptoms and executive functioning impairment. The placebo-controlled PKU ASCEND study evaluated the effects of sapropterin therapy on PKU-associated symptoms of ADHD and executive and global functioning in individuals who had a therapeutic blood Phe response to sapropterin therapy. The presence of ADHD inattentive symptoms and executive functioning deficits was confirmed in this large cohort of 206 children and adults with PKU, of whom 118 responded to sapropterin therapy. In the 38 individuals with sapropterin-responsive PKU and ADHD symptoms at baseline, sapropterin therapy resulted in a significant improvement in ADHD inattentive symptoms in the first 4 weeks of treatment, and improvements were maintained throughout the 26 weeks of treatment. Sapropterin was well-tolerated with a favorable safety profile. The improvements in ADHD inattentive symptoms and aspects of executive functioning in response to sapropterin therapy noted in a large cohort of individuals with PKU indicate that these symptoms are potentially reversible when blood Phe levels are reduced.

Adherence to tetrahydrobiopterin therapy in patients with phenylketonuria

Phenylketonuria (PKU) is an inborn error in phenylalanine metabolism due to deficiency of the enzyme, phenylalanine hydroxylase (PAH). Treatment includes restriction of dietary phenylalanine, and in some individuals, supplementation with the PAH cofactor, tetrahydrobiopterin (sapropterin dihydrochloride). A survey was conducted among patients with PKU who had been prescribed sapropterin to assess reasons for continuing or discontinuing the drug. The primary reason that sapropterin responders discontinued the drug was because of side effects, followed by insufficient reduction of blood phenylalanine and insurance issues. Conversely, those who remained on therapy cited increased tolerance for dietary protein as the main reason for continuation, along with lower blood phenylalanine concentrations and feeling better. This study suggests that adherence to sapropterin therapy is mainly dependent upon the increase in dietary protein allowed when on the drug.

Phenylketonuria Scientific Review Conference: state of the science and future research needs

New developments in the treatment and management of phenylketonuria (PKU) as well as advances in molecular testing have emerged since the National Institutes of Health 2000 PKU Consensus Statement was released. An NIH State-of-the-Science Conference was convened in 2012 to address new findings, particularly the use of the medication sapropterin to treat some individuals with PKU, and to develop a research agenda. Prior to the 2012 conference, five working groups of experts and public members met over a 1-year period. The working groups addressed the following: long-term outcomes and management across the lifespan; PKU and pregnancy; diet control and management; pharmacologic interventions; and molecular testing, new technologies, and epidemiologic considerations. In a parallel and independent activity, an Evidence-based Practice Center supported by the Agency for Healthcare Research and Quality conducted a systematic review of adjuvant treatments for PKU; its conclusions were presented at the conference. The conference included the findings of the working groups, panel discussions from industry and international perspectives, and presentations on topics such as emerging treatments for PKU, transitioning to adult care, and the U.S. Food and Drug Administration regulatory perspective. Over 85 experts participated in the conference through information gathering and/or as presenters during the conference, and they reached several important conclusions. The most serious neurological impairments in PKU are preventable with current dietary treatment approaches. However, a variety of more subtle physical, cognitive, and behavioral consequences of even well-controlled PKU are now recognized. The best outcomes in maternal PKU occur when blood phenylalanine (Phe) concentrations are maintained between 120 and 360 μmol/L before and during pregnancy. The dietary management treatment goal for individuals with PKU is a blood Phe concentration between 120 and 360 μmol/L. The use of genotype information in the newborn period may yield valuable insights about the severity of the condition for infants diagnosed before maximal Phe levels are achieved. While emerging and established genotype-phenotype correlations may transform our understanding of PKU, establishing correlations with intellectual outcomes is more challenging. Regarding the use of sapropterin in PKU, there are significant gaps in predicting response to treatment; at least half of those with PKU will have either minimal or no response. A coordinated approach to PKU treatment improves long-term outcomes for those with PKU and facilitates the conduct of research to improve diagnosis and treatment. New drugs that are safe, efficacious, and impact a larger proportion of individuals with PKU are needed. However, it is imperative that treatment guidelines and the decision processes for determining access to treatments be tied to a solid evidence base with rigorous standards for robust and consistent data collection. The process that preceded the PKU State-of-the-Science Conference, the conference itself, and the identification of a research agenda have facilitated the development of clinical practice guidelines by professional organizations and serve as a model for other inborn errors of metabolism.

[Phenylketonuria: new treatments]

Low phenylalanine diet has been the key treatment of phenylketonuria for more than 50years, allowing efficient management of thousands of PKU patients to date. However, non-compliance exists, mainly after adolescence. A medication for PKU received approval in Europe in 2009 (sapropterine dihydrochloride or Kuvan(®)) and can benefit to patients responsive to this drug. Other treatment options are available in some countries (glycomacropeptides, large neutral amino acids) or are currently under investigation (phenylalanine ammonia lyase, chaperones molecules, gene therapy).

Sapropterin dihydrochloride for the treatment of hyperphenylalaninemias

INTRODUCTION

Phenylketonuria (PKU) is caused by mutation of the enzyme, phenylalanine (Phe) hydroxylase (PAH). The hyperphenylalaninemia characteristic of PKU causes devastating neurological damage if not identified and treated at birth with a Phe-restricted diet. Sapropterin dihydrochloride, a pharmaceutical formulation of the natural cofactor for PAH (6R-tetrahydrobiopterin; BH4), is now available for the management of hyperphenylalaninemia in some PKU patients, including BH4 deficiencies. Sapropterin dihydrochloride improves dietary Phe tolerance in about 20% of patients with PKU.

AREAS COVERED

This evaluation describes the identification of patients suitable for treatment of sapropterin dihydrochloride, together with its indications, therapeutic properties and efficacy. Furthermore, the article reviews its safety and tolerability in patients with PKU or BH4 deficiency.

EXPERT OPINION

A reduction in blood Phe of at least 30% occurred in ∼ 20 - 30% of sapropterin-treated PKU patients (mostly with milder forms of PKU). Treatment with sapropterin resulted in clinically significant and sustained reductions in blood Phe concentrations and increased dietary Phe tolerance in well-designed clinical studies in PKU patients who responded to BH4. Successful treatment with sapropterin may lead to a relaxation of the Phe-restricted diet, although continued monitoring of blood Phe is required. Sapropterin was well tolerated.

Sepiapterin ameliorates chemically induced murine colitis and azoxymethane-induced colon cancer

The effects of modulating tetrahydrobiopterin (BH4) levels with a metabolic precursor, sepiapterin (SP), on dextran sodium sulfate (DSS)-induced colitis and azoxymethane (AOM)-induced colorectal cancer were studied. SP in the drinking water blocks DSS-induced colitis measured as decreased disease activity index (DAI), morphologic criteria, and recovery of Ca(2+)-induced contractility responses lost as a consequence of DSS treatment. SP reduces inflammatory responses measured as the decreased number of infiltrating inflammatory macrophages and neutrophils and decreased expression of proinflammatory cytokines interleukin 1β (IL-1β), IL-6, and IL-17A. High-performance liquid chromatography analyses of colonic BH4 and its oxidized derivative 7,8-dihydrobiopterin (BH2) are inconclusive although there was a trend for lower BH4:BH2 with DSS treatment that was reversed with SP. Reduction of colonic cGMP levels by DSS was reversed with SP by a mechanism sensitive to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific inhibitor of the NO-sensitive soluble guanylate cyclase (sGC). ODQ abrogates the protective effects of SP on colitis. This plus the finding that SP reduces DSS-enhanced protein Tyr nitration are consistent with DSS-induced uncoupling of NOS. The results agree with previous studies that demonstrated inactivation of sGC in DSS-treated animals as being important in recruitment of inflammatory cells and in altered cholinergic signaling and colon motility. SP also reduces the number of colon tumors in AOM/DSS-treated mice from 7 to 1 per unit colon length. Thus, pharmacologic modulation of BH4 with currently available drugs may provide a mechanism for alleviating some forms of colitis and potentially minimizing the potential for colorectal cancer in patients with colitis.

Tetrahydrobiopterin, its mode of action on phenylalanine hydroxylase, and importance of genotypes for pharmacological therapy of phenylketonuria

In about 20%-30% of phenylketonuria (PKU) patients (all phenotypes of PAH deficiency), Phe levels may be controlled through phenylalanine hydroxylase cofactor tetrahydrobiopterin therapy. These patients can be diagnosed by an oral tetrahydrobiopterin challenge and are characterized by mutations coding for proteins with substantial residual PAH activity. They can be treated with a commercially available synthetic form of tetrahydrobiopterin, either as a monotherapy or as adjunct to the diet. This review article summarizes molecular and metabolic bases of PKU and the importance of the tetrahydrobiopterin loading test used for PKU patients. On the basis of in vitro residual PAH activity, more than 1,200 genotypes from patients challenged with tetrahydrobiopterin were categorized as predictive for tetrahydrobiopterin responsiveness or non-responsiveness and correlated with the loading test, phenotype, and residual in vitro PAH activity. The coexpression of two distinct PAH mutant alleles revealed possible dominance effects (positive or negative) by one of the mutations on residual activity as result of interallelic complementation. The treatment of the transfected cells with tetrahydrobiopterin showed an increase in residual PAH activity with several mutations coexpressed.

Long-term follow-up and outcome of phenylketonuria patients on sapropterin: a retrospective study

OBJECTIVE

Sapropterin dihydrochloride, the synthetic form of 6R-tetrahydrobiopterin (BH4), is an approved drug for the treatment of patients with BH4-responsive phenylketonuria (PKU). The purpose of this study was to assess genotypes and data on the long-term effects of BH4/sapropterin on metabolic control and patient-related outcomes in 6 large European countries.

METHODS

A questionnaire was developed to assess phenotype, genotype, blood phenylalanine (Phe) levels, Phe tolerance, quality of life, mood changes, and adherence to diet in PKU patients from 16 medical centers.

RESULTS

One hundred forty-seven patients, of whom 41.9% had mild hyperphenylalaninemia, 50.7% mild PKU, and 7.4% classic PKU, were followed up over ≤12 years. A total of 85 different genotypes were reported. With the exception of two splice variants, all of the most common mutations were reported to be associated with substantial residual Phe hydroxylase activity. Median Phe tolerance increased 3.9 times with BH4/sapropterin therapy, compared with dietary treatment, and median Phe blood concentrations were within the therapeutic range in all patients. Compared with diet alone, improvement in quality of life was reported in 49.6% of patients, improvement in adherence to diet was reported in 47% of patients, and improvement in adherence to treatment was reported in 63.3% of patients. No severe adverse events were reported.

CONCLUSIONS

Our data document a long-term beneficial effect of orally administered BH4/sapropterin in responsive PKU patients by improving the metabolic control, increasing daily tolerance for dietary Phe intake, and for some, by improving dietary adherence and quality of life. Patient genotypes help in predicting BH4 responsiveness.

Achieving the "triple aim" for inborn errors of metabolism: a review of challenges to outcomes research and presentation of a new practice-based evidence framework

Across all areas of health care, decision makers are in pursuit of what Berwick and colleagues have called the “triple aim”: improving patient experiences with care, improving health outcomes, and managing health system impacts. This is challenging in a rare disease context, as exemplified by inborn errors of metabolism. There is a need for evaluative outcomes research to support effective and appropriate care for inborn errors of metabolism. We suggest that such research should consider interventions at both the level of the health system (e.g., early detection through newborn screening, programs to provide access to treatments) and the level of individual patient care (e.g., orphan drugs, medical foods). We have developed a practice-based evidence framework to guide outcomes research for inborn errors of metabolism. Focusing on outcomes across the triple aim, this framework integrates three priority themes: tailoring care in the context of clinical heterogeneity; a shift from “urgent care” to “opportunity for improvement”; and the need to evaluate the comparative effectiveness of emerging and established therapies. Guided by the framework, a new Canadian research network has been established to generate knowledge that will inform the design and delivery of health services for patients with inborn errors of metabolism and other rare diseases.

Genet Med 2013:15(6):415–422

Long-term treatment with tetrahydrobiopterin in phenylketonuria: treatment strategies and prediction of long-term responders

Tetrahydrobiopterin (BH4) responsive phenylketonuria has been described more than 10 years ago. However, criteria for the identification of long-term BH4 responsive patients are not yet established. 116 patients with phenylketonuria, aged 4-18 years, were screened for potential long-term BH4 responsiveness by at least two of the following criteria: positive neonatal BH4 loading test, putative BH4 responsive genotype, and/or milder phenotype. Patients had to be on permanent dietary treatment. 23 patients fulfilled these criteria and were tested for long-term BH4 responsiveness: 18/23 were long-term BH4 responsive, 5/23 were not. On long-term BH4 treatment over a period of 48 ± 27 months in a dose of 14.9 ± 3.3mg/kg/day phenylalanine tolerance was increased from 452 ± 201 mg/day to 1593 ± 647 mg/day, corresponding to a mean increase of 1141 ± 528 mg/day. Dietary phenylalanine intake was increased stepwise according to a clear defined protocol. In 8/18 patients, diet was completely liberalized; 10/18 patients still received phenylalanine-free amino acid formula with 0.63 ± 0.23 g/kg/day. The most predictive value for long-term BH4 responsiveness was the combination of pretreatment phenylalanine of < 1200 μmol/L, pretreatment phenylalanine/tyrosine ratio of <15, phenylalanine/tyrosine ratio of <15 on treatment, phenylalanine tolerance of >20mg/kg/day at age 3 years, positive neonatal BH4 loading, and at least one putative BH4 responsive mutation (p = 0.00024). Our data show that long-term BH4 responsiveness may be predicted already during neonatal period by determining maximum pretreatment phenylalanine and phenylalanine/tyrosine concentrations, neonatal BH4 loading and PAH genotype. A clear defined protocol is necessary to install long-term BH4 treatment.

A Systematic Review of BH4 (Sapropterin) for the Adjuvant Treatment of Phenylketonuria

CONTEXT

Dietary management is the mainstay of effective treatment in PKU, but dietary restriction is difficult and additional treatment options are needed.

OBJECTIVE

To systematically review evidence regarding sapropterin (BH4) use as an adjunct to dietary restriction in individuals with PKU.

DATA SOURCES

Five databases including MEDLINE up to August 2011.

STUDY SELECTION

Two reviewers independently assessed studies against predetermined inclusion/exclusion criteria.

DATA EXTRACTION

Two reviewers independently extracted data regarding participant and intervention characteristics and outcomes and assigned overall quality and strength of evidence ratings based on predetermined criteria.

RESULTS

BH4 research includes two randomized controlled trials (RCTs) and three uncontrolled open-label trials. Phenylalanine (Phe) levels were reduced by at least 30 % in up to half of treated participants (32-50 %). In one RCT comparing placebo on likelihood of a 30 % reduction in Phe, 9 % of those on placebo achieved this effect, compared with 44 % of the treated group after 6 weeks. Phe tolerance and variability were improved in treated participants in studies assessing those outcomes. No comparative studies assessed long-term outcomes including cognitive effects, nutritional status, or quality of life.

CONCLUSIONS

Adjuvant pharmacologic therapy has the potential to support individuals in achieving optimal Phe levels. BH4 has been shown to reduce Phe levels in some individuals, with significantly greater reductions seen in treated versus placebo groups. The strength of the evidence is moderate for short-term effects on reducing Phe in a subset of initially BH4-responsive individuals, moderate for a lack of significant harms, low for longer-term effects on cognition, and insufficient for all other outcomes.

Improvement of endothelial nitric oxide synthase activity retards the progression of diabetic nephropathy in db/db mice

Impaired endothelial nitric oxide synthase (eNOS) activity may be involved in the pathogenesis of diabetic nephropathy. To test this, we used the type 2 diabetic db/db mouse (BKS background) model and found impaired eNOS dimerization and phosphorylation along with moderate glomerular mesangial expansion and increased glomerular basement membrane (GBM) thickness at 34 weeks of age. Cultured murine glomerular endothelial cells exposed to high glucose had similar alterations in eNOS dimerization and phosphorylation. Treatment with sepiapterin, a stable precursor of the eNOS cofactor tetrahydrobiopterin, or the nitric oxide precursor L-arginine corrected changes in eNOS dimerization and phosphorylation, corrected permeability defects, and reduced apoptosis. Sepiapterin or L-arginine, administered to db/db mice from weeks 26 to 34, did not significantly alter hyperfiltration or affect mesangial expansion, but reduced albuminuria and GBM thickness, and decreased urinary isoprostane and nitrotyrosine excretion (markers of oxidative stress). Although there was no change in glomerular eNOS monomer expression, both sepiapterin and L-arginine partially reversed the defect in eNOS dimerization and phosphorylation. Hence, our results support an important role for eNOS dysfunction in diabetes and suggest that sepiapterin supplementation might have therapeutic potential in diabetic nephropathy.

Recommendations for the use of sapropterin in phenylketonuria

Phenylketonuria (PKU) is an inherited disorder of phenylalanine (Phe) metabolism. Until recently, the only treatment for PKU was a Phe-restricted diet. Increasing evidence of suboptimal outcomes in diet-treated individuals, inconsistent PKU management practices, and the recent availability of tetrahydrobiopterin (BH(4)) therapy have fueled the need for new management and treatment recommendations for this metabolic disorder. BH(4), now available as sapropterin dihydrochloride (sapropterin), may offer the potential for improved metabolic control as well as enhanced dietary Phe tolerance in some PKU patients. A group of metabolic dietitians from North America convened in June 2011 to draft recommendations for the use of sapropterin therapy in PKU. Physicians with extensive experience in PKU management were invited at a later date to contribute to the development of these recommendations. Based on extensive clinical experience and current evidence, the present recommendations provide guidance from patient selection and determination of sapropterin response to the long-term management of patients on sapropterin therapy. Target Phe levels, nutritional adequacy, neurocognitive screening and adherence to treatment are addressed to optimize patient outcomes.

Evolving patient selection and clinical benefit criteria for sapropterin dihydrochloride (Kuvan®) treatment of PKU patients

PURPOSE

To understand current patient selection, dosing, and response criteria used for sapropterin dihydrochloride (sapropterin, Kuvan®) to treat phenylketonuria (PKU).

METHODS

Results of a 2010 survey of twenty-nine academic medical centers are reported to describe practice patterns in comparison to results of a survey done in 2008 and to what is reported in the literature.

RESULTS/CONCLUSIONS

In addition to reduction in blood phenylalanine (Phe) levels, clinicians report using broader disease-management approaches when evaluating clinical benefit of sapropterin, including consideration of increased Phe tolerance and behavioral changes. Similar approaches are reported in the literature.