Erik Foehr

NF-κB/Rel Regulates Inhibitory and Excitatory Neuronal Function and Synaptic Plasticity

ABSTRACT Changes in synaptic plasticity required for memory formation are dynamically regulated through opposing excitatory and inhibitory neurotransmissions. To explore the potential contribution of NF-κB/Rel to these processes, we generated transgenic mice conditionally expressing a potent NF-κB/Rel inhibitor termed IκBα superrepressor (IκBα-SR). Using the prion promoter-enhancer, IκBα-SR is robustly expressed in inhibitory GABAergic interneurons and, at lower levels, in excitatory neurons but not in glia. This neuronal pattern of IκBα-SR expression leads to decreased expression of glutamate decarboxylase 65 (GAD65), the enzyme required for synthesis of the major inhibitory neurotransmitter, γ-aminobutyric acid (GABA) in GABAergic interneurons. IκBα-SR expression also results in diminished basal GluR1 levels and impaired synaptic strength (input/output function), both of which are fully restored following activity-based task learning. Consistent with diminished GAD65-derived inhibitory tone and enhanced excitatory firing, IκBα-SR+ mice exhibit increased late-phase long-term potentiation, hyperactivity, seizures, increased exploratory activity, and enhanced spatial learning and memory. IκBα-SR+ neurons also express higher levels of the activity-regulated, cytoskeleton-associated (Arc) protein, consistent with neuronal hyperexcitability. These findings suggest that NF-κB/Rel transcription factors act as pivotal regulators of activity-dependent inhibitory and excitatory neuronal function regulating synaptic plasticity and memory.

Validation of an LC–MS/MS assay for detecting relevant disaccharides from keratan sulfate as a biomarker for Morquio A syndrome

BACKGROUND Mucopolysaccharidosis IVA (MPS IVA, Morquio A syndrome) is an inherited lysosomal storage disease caused by deficiency of N-acetylgalactosamine-6-sulfatase (GALNS), an enzyme required for stepwise degradation of keratan sulfate (KS). We have developed a selective, sensitive, accurate and precise LC-MS/MS assay for the KS-derived disaccharides Galβ1-4GlcNAc(6S) and Gal(6S)β1-4GlcNAc(6S) in human urine and plasma using keratanase II digestion. RESULTS Mean accuracy was 96-106% in urine and 97-108% in plasma. Precision was high, with relative standard deviations of 1-2% (intra-day) and 2-5% (inter-day) in urine and 1-2% (intra-day) and 4-7% (inter-day) in plasma. The lower limit of quantitation was 0.026 µg/ml (plasma) and 0.104 µg/ml (urine), with a quantitation range of 0.026-5 µg/ml (plasma) and 0.104-20 µg/ml (urine). CONCLUSION Clinical sample analysis in 168 MPS IVA patients and 225 healthy controls demonstrates the clinical utility of this method.

Pharmacokinetics of Sapropterin in Patients with Phenylketonuria

AbstractBackground and objective: Untreated phenylketonuria is characterized by neurocognitive and neuromotor impairment, which result from elevated blood phenylalanine concentrations. To date, the recommended management of phenylketonuria has been the use of a protein-restricted diet and the inclusion of phenylalanine-free protein supplements; however, this approach is often associated with poor compliance and a suboptimal clinical outcome. Sapropterin dihydrochloride, herein referred to as sapropterin, a synthetic formulation of 6R-tetrahydrobiopterin (6R-BH4), has been shown to be effective in reducing blood phenylalanine concentrations in patients with phenylketonuria. The objective of the current study was to characterize the pharmacokinetics and pharmacokinetic variability of sapropterin and to identify the characteristics that influence this variability. Patients and methods: This was a 12-week, fixed-dose phase of an open-label extension study. The study was conducted at 26 centres in North America and Europe.Patients with phenylketonuria were eligible to participate if they were ≥8 years of age and had received ≥80% of the scheduled doses in a previous 6-week, randomized, placebo-controlled study or had been withdrawn from that study after exceeding a plasma phenylalanine concentration of ≥1500 μmol/L to ≥1800 μmol/L, depending on the subject’s age and baseline plasma phenylalanine concentration. A total of 78 patients participated. Patients received oral once-daily doses of sapropterin (Kuvan®) 5, 10 or 20 mg/kg/day.Blood samples for the pharmacokinetic analysis were obtained during weeks 6, 10 and 12. A D-optimal sparse sampling strategy was used, and data were analysed by population-based, nonlinear, mixed-effects modelling methods. Main outcome measure: In a prospectively planned analysis, the apparent clearance, apparent volume of distribution, absorption rate constant and associated interindividual variabilities of each parameter were estimated by modelling observed BH4 plasma concentration-time data. Results: The best structural model to describe the pharmacokinetics of sapropterin was a two-compartment model with first-order input, first-order elimination and a baseline endogenous BH4 concentration term. Total bodyweight was the only significant covariate identified, the inclusion of which on both the apparent clearance (mean = 2100 L/h/70 kg) and central volume of distribution (mean = 8350 L/70 kg) substantially improved the model’s ability to describe the data. The mean (SD) terminal half-life of sapropterin was 6.69 (2.29) hours and there was little evidence of accumulation, even at the highest dose. Conclusion: These findings, taken together with the observed therapeutic effect, support bodyweight-based, once-daily dosing of sapropterin 5–20 mg/kg/day.

Biomarker analysis of Morquio syndrome: identification of disease state and drug responsive markers

BackgroundThis study was conducted to identify potential biomarkers that could be used to evaluate disease progression and monitor responses to enzyme replacement therapy (ERT) in patients with mucopolysaccharidosis (MPS) IVA.MethodsLevels of 88 candidate biomarkers were compared in plasma samples from 50 healthy controls and 78 MPSIVA patients not receiving ERT to test for significant correlations to the presence of MPSIVA. MPSIVA samples were also tested for correlations between candidate biomarkers and age, endurance, or urinary keratin sulfate (KS) levels. Then, levels of the same 88 analytes were followed over 36 weeks in 20 MPSIVA patients receiving ERT to test for significant correlations related to ERT, age, or endurance.ResultsNineteen candidate biomarkers were significantly different between MPSIVA and unaffected individuals. Of these, five also changed significantly in response to ERT: alpha-1-antitrypsin, eotaxin, lipoprotein(a), matrix metalloprotein (MMP)-2, and serum amyloid P. Three of these were significantly lower in MPSIVA individuals versus unaffected controls and were increased during ERT: alpha-1-antitrypsin, lipoprotein(a), and serum amyloid P.ConclusionsCandidate biomarkers alpha-1-antitrypsin, lipoprotein(a), and serum amyloid P may be suitable markers, in addition to urinary KS, to follow the response to ERT in MPSIVA patients.

Relative Bioavailability of Sapropterin From Intact and Dissolved Sapropterin Dihydrochloride Tablets and the Effects of Food: A Randomized, Open-Label, Crossover Study in Healthy Adults

BACKGROUND Phenylketonuria (PKU) is an autosomal recessive metabolic disorder characterized by hyperphenylalaninemia in association with neurocognitive and neuromotor impairment. Sapropterin dihydrochloride (hereafter referred to as sapropterin) administered orally as dissolved tablets is approved by the US Food and Drug Administration for hyperphenylalaninemia in patients with tetrahydrobiopterin responsive PKU. OBJECTIVES This study compared the relative oral bioavailability of sapropterin when administered as intact and dissolved tablets. It also assessed the effect of food on the oral bioavailability of sapropterin administered as intact tablets. METHODS This was a randomized, open-label, 3-treatment, 6-sequence, 3-period crossover study in healthy male and female subjects. Subjects were randomized to receive single oral 10-mg/kg doses of sapropterin administered as dissolved tablets after a fast; as intact tablets after a fast; and as intact tablets with a high-calorie, high-fat meal. The 3 dosing periods were separated by a washout period of at least 7 days. In each dosing period, blood samples were obtained within 40 minutes before and at 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 5, 6, 8, 10, 12, 18, and 24 hours after dosing. A follow-up assessment was performed 5 to 7 days after the last dosing period. The relative bioavailability of sapropterin from the 3 dosing regimens was assessed based on C(max), AUC(0-t), and AUC(0-infinity), estimated from calculated plasma tetrahydrobiopterin concentrations using a noncompartmental model. Safety assessments included physical examinations, clinical laboratory tests, and ECGs at the beginning and end of the study. Vital signs were monitored periodically during each treatment period. RESULTS The study enrolled 32 healthy subjects (16 men, 16 women) with a mean (SD) age of 29.2 (9.0) years, height of 172.7 (10.0) cm, weight of 73.0 (13.9) kg, and body mass index ranging from 18 to 30 kg/m(2). Twenty-three were white, 5 African American, 2 Asian/Pacific Islander, 1 Hispanic, and 1 Native American. The estimated geometric mean ratio of AUC(0-t) for intact compared with dissolved tablets under fasting conditions was 141.24% (90% CI, 122.05-163.43), and the geometric mean ratio of AUC(0-t) for intact tablets under fed compared with fasting conditions was 143.46% (90% CI, 124.22-165.69). Nine subjects (28.1%) reported a total of 20 treatment-emergent adverse events (AEs). The most frequently reported AEs were gastrointestinal disorders (6 subjects [18.8%]) and central nervous system disorders (4 [12.5%]). Eight AEs considered possibly or probably related to sapropterin were reported by 4 subjects (12.5%); these were of mild severity and gastrointestinal in nature. No severe or serious AEs or discontinuations due to AEs occurred during the study. CONCLUSIONS Administration of sapropterin as intact tablets and with a high-calorie, high-fat meal was associated with increased drug exposure. Oral administration of sapropterin 10 mg/kg as intact tablets with or without food was generally well tolerated.

Quantitative bioanalysis of strontium in human serum by inductively coupled plasma-mass spectrometry

Aim: A bioanalytical method using inductively-coupled plasma-mass spectrometry to measure endogenous levels of strontium in human serum was developed and validated. Results & methodology: This article details the experimental procedures used for the method development and validation thus demonstrating the application of the inductively-coupled plasma-mass spectrometry method for quantification of strontium in human serum samples. The assay was validated for specificity, linearity, accuracy, precision, recovery and stability. Significant endogenous levels of strontium are present in human serum samples ranging from 19 to 96 ng/ml with a mean of 34.6 ± 15.2 ng/ml (SD). Discussion & conclusion: Calibration procedures and sample pretreatment were simplified for high throughput analysis. The validation demonstrates that the method was sensitive, selective for quantification of strontium (88Sr) and is suitable for routine clinical testing of strontium in human serum samples.