In Vivo Metabolic Responses to Different Formulations of Amino Acid Mixtures for the Treatment of Phenylketonuria (PKU)

Phenylketonuria (PKU) is a rare autosomal recessive inborn error of metabolism where the mainstay of treatment is a Phe restricted diet consisting of a combination of limited amounts of natural protein with supplementation of Phe-free or low-Phe protein substitutes and special low protein foods. Suboptimal outcomes may be related to the different absorption kinetics of free AAs, which have lower biological efficacy than natural proteins. Physiomimic Technology^TM is a technology engineered to prolong AA (AA-PT) release allowing physiological absorption and masking the odor and taste of free AAs. The aim of these studies was to assess the impact of AA-PT formulation on selected functional and metabolic parameters both in acute and long-term experimental studies. Adult rats in fasting conditions were randomized in different groups and treated by oral gavage. Acute AA-PT administration resulted in significantly lower BUN at 90 min versus baseline. Both BUN and glycemia were modulated in the same direction as intact casein protein. Long-term treatment with AA-PT significantly reduces the protein expression of the muscle degradation marker Bnip3L (−46%) while significantly increasing the proliferation of market myostatin (+58%). Animals dosed for 15 days with AA-PT had significantly stronger grip strength (+30%) versus baseline. In conclusion, the results suggest that the AA-PT formulation may have beneficial effects on both AA oxidation and catabolism with a direct impact on muscle as well as on other metabolic pathways.     

Experimental attempts to produce phenylketonuria in animals: A critical review.

Studies attempting to produce PKU in animals are extensively reviewed. While some studies claim to have produced and consequently even prevented PKU in animals, such claims were found to be unjustified at this stage of research. Behavioral and biochemical criteria for assessing PKU are discussed along with certain methodological problems inherent in such work. The experimental production of PKU, on the other hand, offers an important model for the study of the relations between development, intellectual functioning, and biochemistry. (2 p. ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

新生儿苯丙酮尿症(PKU)荧光筛查系统的设计

新生儿苯丙酮尿症的早期诊断,对于减少和防止智力发育障碍的出现,有积极的临床意义和社会效益。荧光法因具有灵敏度高、操作简单等优点而成为新生儿苯丙酮尿症筛查的主要方法。新生儿苯丙酮尿症（PKU）荧光筛查系统包括光学检测子系统,精密微孔板扫描结构,嵌入式PC及硬件接口电路等。针对目前进口荧光检测仪器光路复杂、体积大、成本高等缺陷,本文介绍了一种新生儿苯丙酮尿症荧光筛查系统的开发,通过与进口标准仪器的比对实验,证明了该系统的有效性。     

Alchemical Design of Pharmacological Chaperones with Higher Affinity for Phenylalanine Hydroxylase

Phenylketonuria (PKU) is a rare metabolic disease caused by variations in a human gene, PAH, encoding phenylalanine hydroxylase (PAH), and the enzyme converting the essential amino acid phenylalanine into tyrosine. Many PKU-causing variations compromise the conformational stability of the encoded enzyme, decreasing or abolishing its catalytic activity, and leading to an elevated concentration of phenylalanine in the blood, which is neurotoxic. Several therapeutic approaches have been developed to treat the more severe manifestations of the disorder, but they are either not entirely effective or difficult to adhere to throughout life. In a search for novel pharmacological chaperones to treat PKU, a lead compound was discovered (compound IV) that exhibited promising in vitro and in vivo chaperoning activity on PAH. The structure of the PAH-IV complex has been reported. Here, using alchemical free energy calculations (AFEC) on the structure of the PAH-IV complex, we design a new generation of compound IV-analogues with a higher affinity for the enzyme. Seventeen novel analogues were synthesized, and thermal shift and isothermal titration calorimetry (ITC) assays were performed to experimentally evaluate their stabilizing effect and their affinity for the enzyme. Most of the new derivatives bind to PAH tighter than lead compound IV and induce a greater thermostabilization of the enzyme upon binding. Importantly, the correspondence between the calculated alchemical binding free energies and the experimentally determined ΔΔG_b values is excellent, which supports the use of AFEC to design pharmacological chaperones to treat PKU using the X-ray structure of their complexes with the target PAH enzyme.     

Investigation of the potential for a simplified exposure tool in medical nutrition (SETIM) to minimise exposures to sweeteners in young patients aged 1–3 years with PKU and CMPA

Children with phenylketonuria (PKU) and severe cow’s milk protein allergy (CMPA) consume prescribed, specially formulated, foods for special medical purposes (FSMPs) in addition to having restricted intake of normal foods. These vulnerable patients are exposed to artificial sweeteners from the consumption of a combination of both free and prescribed foods. Young patients with PKU and CMPA aged from 1 to 3 years have a higher risk of exceeding the acceptable daily intake (ADI) for sweeteners than age-matched healthy children. A probabilistic modelling approach has been adapted successfully to assess the exposure of young patients with PKU and CMPA to low-calorie sweeteners. To assist professionals in the screening and formulation of foods containing food additives for such patients, a simplified exposure method/tool has been developed. The tool is intended to ensure that total dietary exposure can be considered. The simplified tool is not intended to replace the probabilistic model but may be used as a screening tool to determine if further investigation on exposure is warranted. The aim of this study was to develop and validate this simplified exposure tool to support those currently used by healthcare professionals (HCPs) using data available from the probabilistic modelling of exposure in young children with PKU and CMPA. The probabilistic model does not allow for swift screening of exposure scenarios nor is the present EFSA Food Additive Intake Assessment Model (FAIM) fully suitable for application to medical foods. The simplified exposure tool in medical nutrition (SETIM) reported here is both reliable and consistent and provides additive usage levels which minimise regular exposure above the ADI in patients. In addition to the usefulness of SETIM for the medical nutrition industry, the tool has the potential to enhance the practice of evidence-based medical nutrition by official risk assessment bodies, registration authorities and healthcare professionals.     

Longitudinal modelling of the exposure of young UK patients with PKU to acesulfame K and sucralose

ABSTRACT

Artificial sweeteners are used in protein substitutes intended for the dietary management of inborn errors of metabolism (phenylketonuria, PKU) to improve the variety of medical foods available to patients and ensure dietary adherence to the prescribed course of dietary management. These patients can be exposed to artificial sweeteners from the combination of free and prescribed foods. Young children have a higher risk of exceeding acceptable daily intakes (ADI) for additives than adults, due to higher food intakes per kg body weight. Young patients with PKU aged 1–3 years can be exposed to higher levels of artificial sweeteners from these dual sources than normal healthy children and are at a higher risk of exceeding the ADI. Standard intake assessment methods are not adequate to assess the additive exposure of young patients with PKU. The aim of this study was to estimate the combination effect on the intake of artificial sweeteners and the impact of the introduction of new provisions for an artificial sweetener (sucralose, E955) on exposure of PKU patients using a validated probabilistic model. Food consumption data were derived from the food consumption survey data of healthy young children in the United Kingdom from the National Diet and Nutrition Survey (NDNS, 1992–2012). Specially formulated protein substitutes as foods for special medical purposes (FSMPs) were included in the exposure model to replace restricted foods. Inclusion of these protein substitutes is based on recommendations to ensure adequate protein intake in these patients. Exposure assessment results indicated the availability of sucralose for use in FSMPs for PKU leads to changes in intakes in young patients. These data further support the viability of probabilistic modelling as a means to estimate food additive exposure in patients consuming medical nutrition products.     

Predictive modelling of the exposure to steviol glycosides in Irish patients aged 1-3 years with phenylketonuria and cow’s milk protein allergy

Children with Phenylketonuria (PKU) and severe cow’s milk protein allergy (CMPA) consume prescribed, specially formulated, foods for special medical purposes (FSMPs) as well as restricted amounts of normal foods. These patients are exposed to artificial sweeteners from the consumption of a combination of free and prescribed foods. Young patients with PKU and CMPA have a higher risk of exceeding acceptable daily intakes (ADI) for additives than age-matched healthy children. A predictive modelling approach has been adapted successfully to assess the additive exposure of young patients with PKU and CMPA to artificial sweeteners. Steviol glycosides (E960) are at various stages of regulatory approval for the various food categories in the EU but are not as yet permitted for use in products intended for young children. The aim of this study was to predict potential steviol glycoside exposure in young children with PKU and CMPA considering the potential for future provisions for the use of this sweetener. The recent introduction of steviol glycosides means that no exposure data are available for children with CMPA and PKU. Food consumption data were derived from the food consumption survey data of healthy young children in Ireland from the National Preschool and Nutrition Survey (NPNS, 2010–11). Specially formulated amino acid-based FSMPs are used to replace whole or milk protein foods and were included in the exposure model to replace restricted foods. The recommendations to ensure adequate protein intake in these patients were used to determine FSMP intake. Exposure assessment results indicated that the maximum permitted level (MPL) for FSMPs would warrant careful consideration to avoid exposures above the ADI. These data can be used to inform recommendations for the medical nutrition industry.     

Timing is everything: Executive functions in children exposed to elevated levels of phenylalanine.

This study addresses how the timing of a known biological insult affects the developmental progression of executive functions. The sample consisted of children exposed to elevated levels of phenylalanine, either postnatally, as in phenylketonuria (PKU; n = 46), or prenatally, as in maternal PKU (n = 15). Nonhyperphenylalaninemic siblings of children with PKU (n = 18) served as controls. Results indicated that elevated levels of phenylalanine are toxic to the neurological systems that manage executive functions and cognitive tempo. This toxicity is dose dependent, with higher levels of phenylalanine being more detrimental. Executive function difficulties noted in PKU are consistent with attention deficit hyperactivity disorder (ADHD)-inattentive type, whereas maternal PKU offspring had executive function difficulties consistent with ADHD-combined type. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Systematic Modification and Evaluation of Enzyme-Loaded Chitosan Nanoparticles

Polymeric-based nano drug delivery systems have been widely exploited to overcome protein instability during formulation. Presently, a diverse range of polymeric agents can be used, among which polysaccharides, such as chitosan (CS), hyaluronic acid (HA) and cyclodextrins (CDs), are included. Due to its unique biological and physicochemical properties, CS is one of the most used polysaccharides for development of protein delivery systems. However, CS has been described as potentially immunogenic. By envisaging a biosafe cytocompatible and haemocompatible profile, this paper reports the systematic development of a delivery system based on CS and derived with HA and CDs to nanoencapsulate the model human phenylalanine hydroxylase (hPAH) through ionotropic gelation with tripolyphosphate (TPP), while maintaining protein stability and enzyme activity. By merging the combined set of biopolymers, we were able to effectively entrap hPAH within CS nanoparticles with improvements in hPAH stability and the maintenance of functional activity, while simultaneously achieving strict control of the formulation process. Detailed characterization of the developed nanoparticulate systems showed that the lead formulations were internalized by hepatocytes (HepG2 cell line), did not reveal cell toxicity and presented a safe haemocompatible profile.