Evaluation of orally administered PEGylated phenylalanine ammonia lyase in mice for the treatment of Phenylketonuria

Current Advances and Material Innovations in the Search for Novel Treatments of Phenylketonuria

Phenylketonuria (PKU) is a genetically inherited disease caused by a mutation of the gene encoding phenylalanine hydroxylase (PAH) and is the most common inborn error of amino acid metabolism. A deficiency of PAH leads to increased blood and brain levels of phenylalanine (Phe), which may cause permanent neurocognitive symptoms and developmental delays if untreated. Current management strategies for PKU consist of early detection through neonatal screening and implementation of a restrictive diet with minimal amounts of natural protein in combination with Phe-free supplements and low-protein foods to meet nutritional requirements. For milder forms of PKU, oral treatment with synthetic sapropterin (BH4), the cofactor of PAH, may improve metabolic control of Phe and allow for more natural protein to be included in the patient's diet. For more severe forms, daily injections of pegvaliase, a PEGylated variant of phenylalanine ammonia-lyase (PAL), may allow for normalization of blood Phe levels. However, the latter treatment has considerable drawbacks, notably a strong immunogenicity of the exogenous enzyme and the attached polymeric chains. Research for novel therapies of PKU makes use of innovative materials for drug delivery and state-of-the-art protein engineering techniques to develop treatments which are safer, more effective, and potentially permanent.

Roles of the N-terminal motif in improving the activity and soluble expression of phenylalanine ammonia lyases in Escherichia coli

Phenylalanine ammonia-lyase (PAL) has various applications in fine chemical manufacturing and the pharmaceutical industry. In particular, PAL derived from Anabaena variabilis (AvPAL) is used as a therapeutic agent to the treat phenylketonuria in clinical settings. In this study, we aligned the amino acid sequences of AvPAL and PAL derived from Nostoc punctiforme (NpPAL) to obtain several mutants with enhanced activity, expression yield, and thermal stability via amino acid substitution and saturation mutagenesis at the N-terminal position. Enzyme kinetic experiments revealed that the kcat values of NpPAL-N2K, NpPAL-I3T, and NpPAL-T4L mutants were increased to 3.2-, 2.8-, and 3.3-fold that of the wild-type, respectively. Saturation mutagenesis of the fourth amino acid in AvPAL revealed that the kcat values of AvPAL-L4N, AvPAL-L4P, AvPAL-L4Q and AvPAL-L4S increased to 4.0-, 3.7-, 3.6-, and 3.2-fold, respectively. Additionally, the soluble protein yield of AvPAL-L4K increased to approximately 14 mg/L, which is approximately 3.5-fold that of AvPAL. Molecular dynamics studies further revealed that maintaining the attacking state of the reaction and N-terminal structure increased the rate of catalytic reaction and improved the solubility of proteins. These findings provide new insights for the rational design of PAL in the future.

A Customized Bayesian Algorithm to Optimize Enzyme-Catalyzed Reactions

Design of experiments (DoE) plays an important role in optimizing the catalytic performance of chemical reactions. The most commonly used DoE relies on the response surface methodology (RSM) to model the variable space of experimental conditions with the fewest number of experiments. However, the RSM leads to an exponential increase in the number of required experiments as the number of variables increases. Herein we describe a Bayesian optimization algorithm (BOA) to optimize the continuous parameters (e.g., temperature, reaction time, reactant and enzyme concentrations, etc.) of enzyme-catalyzed reactions with the aim of maximizing performance. Compared to existing Bayesian optimization methods, we propose an improved algorithm that leads to better results under limited resources and time for experiments. To validate the versatility of the BOA, we benchmarked its performance with biocatalytic C-C bond formation and amination for the optimization of the turnover number. Gratifyingly, up to 80% improvement compared to RSM and up to 360% improvement vs previous Bayesian optimization algorithms were obtained. Importantly, this strategy enabled simultaneous optimization of both the enzyme's activity and selectivity for cross-benzoin condensation.

Artificial Cells: Past, Present and Future

Artificial cells are constructed to imitate natural cells and allow researchers to explore biological process and the origin of life. The construction methods for artificial cells, through both top-down or bottom-up approaches, have achieved great progress over the past decades. Here we present a comprehensive overview on the development of artificial cells and their properties and applications. Artificial cells are derived from lipids, polymers, lipid/polymer hybrids, natural cell membranes, colloidosome, metal-organic frameworks and coacervates. They can be endowed with various functions through the incorporation of proteins and genes on the cell surface or encapsulated inside of the cells. These modulations determine the properties of artificial cells, including producing energy, cell growth, morphology change, division, transmembrane transport, environmental response, motility and chemotaxis. Multiple applications of these artificial cells are discussed here with a focus on therapeutic applications. Artificial cells are used as carriers for materials and information exchange and have been shown to function as targeted delivery systems of personalized drugs. Additionally, artificial cells can function to substitute for cells with impaired function. Enzyme therapy and immunotherapy using artificial cells have been an intense focus of research. Finally, prospects of future development of cell-mimic properties and broader applications are highlighted.

Long-Term Metabolic Correction of Phenylketonuria by AAV-Delivered Phenylalanine Amino Lyase

Phenylketonuria (PKU) is an inherited metabolic disorder caused by mutation within phenylalanine hydroxylase (PAH) gene. Loss-of-function of PAH leads to accumulation of phenylalanine in the blood/body of an untreated patient, which damages the developing brain, causing severe mental retardation. Current gene therapy strategies based on adeno-associated vector (AAV) delivery of PAH gene were effective in male animals but had little long-term effects on blood hyperphenylalaninemia in females. Here, we designed a gene therapy strategy using AAV to deliver a human codon-optimized phenylalanine amino lyase in a liver-specific manner. It was shown that PAL was active in lysing phenylalanine when it was expressed in mammalian cells. We produced a recombinant adeno-associated vector serotype 8 (AAV8) viral vector expressing the humanized PAL under the control of human antitrypsin (hAAT) promoter (AAV8-PAL). A single intravenous administration of AAV8-PAL caused long-term correction of hyperphenylalaninemia in both male and female PKU mice (strain Pah^enu2). Besides, no obvious liver injury was observed throughout the treatment process. Thus, our results established that AAV-mediated liver delivery of PAL gene is a promising strategy in the treatment of PKU.

The phenylketonuria patient: A recent dietetic therapeutic approach

Phenylalanine hydroxylase (PAH) deficiency, commonly named phenylketonuria (PKU) is a disorder of phenylalanine (Phe) metabolism inherited with an autosomal recessive trait. It is characterized by high blood and cerebral Phe levels, resulting in intellectual disabilities, seizures, etc. Early diagnosis and treatment of the patients prevent major neuro-cognitive deficits. Treatment consists of a lifelong restriction of Phe intake, combined with the supplementation of special medical foods, such as Amino Acid medical food (AA-mf), enriched in tyrosine (Tyr) and other amino acids and nutrients to avoid nutritional deficits. Developmental and neurocognitive outcomes for patients, however, remain suboptimal, especially when adherence to the demanding diet is poor. Additions to treatment include new, more palatable foods, based on Glycomacropeptide that contains limited amounts of Phe, the administration of large neutral amino acids to prevent phenylalanine entry into the brain and tetrahydrobiopterin cofactor capable of increasing residual PAH activity. Moreover, further efforts are underway to develop an oral therapy containing phenylalanine ammonia-lyase. Nutritional support of PKU future mothers (maternal PKU) is also discussed. This review aims to summarize the current literature on new PKU treatment strategies.

Purification and Characterization of Anabaena flos-aquae Phenylalanine Ammonia-Lyase as a Novel Approach for Myristicin Biotransformation

Phenylalanine ammonia-lyase (PAL) catalyzes the reversible deamination of phenylalanine to cinnamic acid and ammonia. Algae have been considered as biofactories for PAL production, however, biochemical characterization of PAL and its potency for myristicin biotransformation into MMDA (3-methoxy-4, 5-methylenedioxyamphetamine) has not been studied yet. Thus, PAL from Anabaena flos-aquae and Spirulina platensis has been purified, comparatively characterized and its affinity to transform myristicin was assessed. The specific activity of purified PAL from S. platensis (73.9 μmol/mg/min) and A. flos-aquae (30.5 μmol/mg/min) was increased by about 2.9 and 2.4 folds by gel-filtration comparing to their corresponding crude enzymes. Under denaturing-PAGE, a single proteineous band with a molecular mass of 64 kDa appeared for A. flos-aquae and S. platensis PAL. The biochemical properties of the purified PAL from both algal isolates were determined comparatively. The optimum temperature of S. platensis and A. flos-aquae PAL for forward or reverse activity was reported at 30°C, while the optimum pH for PAL enzyme isolated from A. flos-aquae was 8.9 for forward and reverse activities, and S. platensis PAL had maximum activities at pH 8.9 and 8 for forward and reverse reactions, respectively. Luckily, the purified PALs have the affinity to hydroaminate the myristicin to MMDA successfully in one step. Furthermore, a successful method for synthesis of MMDA from myristicin in two steps was also established. Gas chromatography-mass spectrometry (GC-MS) analysis was conducted to track the product formation.

A microparticulate based formulation to protect therapeutic enzymes from proteolytic digestion: phenylalanine ammonia lyase as case study

Phenylketonuria is a genetic disorder affecting the metabolism of phenylalanine (phe) due to a deficiency in the enzyme phenylalanine hydroxylase. This disorder is characterized by an elevated phe blood level, which can lead to severe intellectual disabilities in newborns. The current strategy to prevent these devastating consequences is limited to a life-long phe-free diet, which implies major lifestyle changes and restrictions. Recently, an injectable enzyme replacement therapy, Pegvaliase, has been approved for treating phenylketonuria, but is associated with significant side-effects. In this study a phe-metabolizing system suitable for oral delivery is designed to overcome the need for daily injections. Active phenylalanine ammonia-lyase (PAL), an enzyme that catalyses phe metabolism, is loaded into mesoporous silica microparticles (MSP) with pore sizes ranging from 10 to 35 nm. The surface of the MSP is lined with a semipermeable barrier to allow permeation of phe while blocking digestive enzymes that degrade PAL. The enzymatic activity can be partially preserved in vitro by coating the MSP with poly(allylamine) and poly(acrylic acid)-bowman birk (protease inhibitor) conjugate. The carrier system presented herein may provide a general approach to overcome gastro-intestinal proteolytic digestion and to deliver active enzymes to the intestinal lumen for prolonged local action.

The effectiveness of plant hydrocolloids at maintaining the quality characteristics of the encapsulated form of L-phenylalanine-ammonia-lyase

The effect of three types of polysaccharides (agar-agar, carrageenan, hydroxypropyl methylcellulose) on the activity and stability during storage at given temperature conditions of the enzyme preparation L-phenylalanine ammonia-lyase was studied. It was found that the most suitable storage temperature for encapsulated L-phenylalanine-ammonia-lyase is room temperature up to 25 °C for all samples of capsules from plant polysaccharides. Samples of capsules with agar-agar and hydroxypropyl methylcellulose under different temperature conditions inhibited the decrease in enzyme activity, which in other samples of capsules reached 90% in 6 months of storage. In samples of capsules with carrageenan at temperatures of 4 °C and 30 °C, there was a significant decrease in the activity of the enzyme preparation. Selection of capsule samples from plant polysaccharides suitable for L-phenylalanine-ammonia-lyase replacement therapy is done after studying the mechanisms of capsule destruction under conditions close to the conditions of the gastrointestinal tract, to which the next stage of our research will be devoted.

Import of TAT-Conjugated Propionyl Coenzyme A Carboxylase Using Models of Propionic Acidemia

Propionic acidemia is caused by a deficiency of the enzyme propionyl coenzyme A carboxylase (PCC) located in the mitochondrial matrix. Cell-penetrating peptides, including transactivator of transcription (TAT), offer a potential to deliver a cargo into the mitochondrion. Here, we investigated the delivery of an α₆β₆ PCC enzyme into mitochondria using the HIV TAT peptide at several levels: into isolated mitochondria, in patient fibroblast cells, and in a mouse model. Results from Western blots and enzyme activity assays confirmed the import of TAT-PCC into mitochondria, as well as into patient fibroblasts, where the colocalization of imported TAT-PCC and mitochondria was also confirmed by confocal fluorescence microscopy. Furthermore, a single-dose intraperitoneal injection into PCC-deficient mice decreased the propionylcarnitine/acetylcarnitine (C3/C2) ratio toward the normal level. These results show that a cell-penetrating peptide can deliver active multimeric enzyme into mitochondria in vitro, in situ, and in vivo and push the size limit of intracellular delivery achieved so far. Our results are promising for other mitochondrion-specific deficiencies.

Engineering erythrocytes for the modulation of drugs' and contrasting agents' pharmacokinetics and biodistribution

Pharmacokinetics, biodistribution, and biological activity are key parameters that determine the success or failure of therapeutics. Many developments intended to improve their in vivo performance, aim at modulating concentration, biodistribution, and targeting to tissues, cells or subcellular compartments. Erythrocyte-based drug delivery systems are especially efficient in maintaining active drugs in circulation, in releasing them for several weeks or in targeting drugs to selected cells. Erythrocytes can also be easily processed to entrap the desired pharmaceutical ingredients before re-infusion into the same or matched donors. These carriers are totally biocompatible, have a large capacity and could accommodate traditional chemical entities (glucocorticoids, immunossuppresants, etc.), biologics (proteins) and/or contrasting agents (dyes, nanoparticles). Carrier erythrocytes have been evaluated in thousands of infusions in humans proving treatment safety and efficacy, hence gaining interest in the management of complex pathologies (particularly in chronic treatments and when side-effects become serious issues) and in new diagnostic approaches.

Metabolism and Pathogenicity of Pseudomonas aeruginosa Infections in the Lungs of Individuals with Cystic Fibrosis

Individuals with the genetic disease cystic fibrosis (CF) accumulate mucus or sputum in their lungs. This sputum is a potent growth substrate for a range of potential pathogens, and the opportunistic bacterium Pseudomonas aeruginosa is generally most difficult of these to eradicate. As a result, P. aeruginosa infections are frequently maintained in the CF lung throughout life, and are the leading cause of death for these individuals. While great effort has been expended to better understand and treat these devastating infections, only recently have researchers begun to rigorously examine the roles played by specific nutrients in CF sputum to cue P. aeruginosa pathogenicity. This chapter summarizes the current state of knowledge regarding how P. aeruginosa metabolism in CF sputum affects initiation and maintenance of these infections. It contains an overview of CF lung disease and the mechanisms of P. aeruginosa pathogenicity. Several model systems used to study these infections are described with emphasis on the challenge of replicating the chronic infections observed in humans with CF. Nutrients present in CF sputum are surveyed, and the impacts of these nutrients on the infection are discussed. The chapter concludes by addressing the future of this line of research including the use of next-generation technologies and the potential for metabolism-based therapeutics.

Descriptive and hedonic analyses of low-Phe food formulations containing corn (Zea mays) seedling roots: toward development of a dietary supplement for individuals with phenylketonuria

BACKGROUND

Seedling roots of anthocyanin-rich corn (Zea mays) cultivars contain high levels of phenylalanine ammonia lyase (PAL) activity. The development of a natural dietary supplement containing corn roots could provide the means to improve the restrictive diet of phenylketonuria (PKU) patients by increasing their tolerance to dietary phenylalanine (Phe). Therefore this research was undertaken to explore the sensory characteristics of roots of four corn cultivars as well as to develop and evaluate food products (cereal bar, beverage, jam-like spread) to which roots had been added.

RESULTS

Sensory profiles of corn roots were investigated using ten trained judges. Roots of Japanese Striped corn seedlings were more bitter, pungent and astringent than those of white and yellow cultivars, while roots from the Blue Jade cultivar had a more pronounced earthy/mushroom aroma. Consumer research using 24 untrained panelists provided hedonic (degree-of-liking) assessments for products with and without roots (controls). The former had lower mean scores than the controls; however, the cereal bar had scores above 5 on the nine-point scale for all hedonic assessments compared with the other treated products.

CONCLUSION

By evaluating low-Phe food products containing corn roots, this research ascertained that the root-containing low-Phe cereal bar was an acceptable 'natural' dietary supplement for PKU-affected individuals.

Phenylketonuria: a review of current and future treatments

Phenylketonuria (PKU) is an autosomal recessive inborn error of metabolism caused by a deficiency in the hepatic enzyme phenylalanine hydroxylase (PAH). If left untreated, the main clinical feature is intellectual disability. Treatment, which includes a low Phe diet supplemented with amino acid formulas, commences soon after diagnosis within the first weeks of life. Although dietary treatment has been successful in preventing intellectual disability in early treated PKU patients, there are major issues with dietary compliance due to palatability of the diet. Other potential issues associated with dietary therapy include nutritional deficiencies especially vitamin D and B12. Suboptimal outcomes in cognitive and executive functioning have been reported in patients who adhere poorly to dietary therapy. There have been continuous attempts at improving the quality of medical foods including their palatability. Advances in dietary therapy such as the use of large neutral amino acids (LNAA) and glycomacropeptides (GMP; found within the whey fraction of bovine milk) have been explored. Gene therapy and enzyme replacement or substitution therapy have yielded more promising data in the recent years. In this review the current and possible future treatments for PKU are discussed.

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.

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.

Nanodevices for the immobilization of therapeutic enzymes

Therapeutic enzymes are one of the most promising applications of this century in the field of pharmaceutics. Biocatalyst properties can be improved by enzyme immobilization on nano-objects, thereby increasing stability and reusability and also enhancing the targeting to specific tissues and cells. Therapeutic biocatalyst-nanodevice complexes will provide new tools for the diagnosis and treatment of old and newly emerging pathologies. Among the advantages of this approach are the wide span and diverse range of possible materials and biocatalysts that promise to make the matrix-enzyme combination a unique modality for therapeutic delivery. This review focuses on the most significant techniques and nanomaterials used for enzyme immobilization such as metallic superparamagnetic, silica, and polymeric and single-enzyme nanoparticles. Finally, a review of the application of these nanodevices to different pathologies and modes of administration is presented. In short, since therapeutic enzymes constitute a highly promising alternative for treating a variety of pathologies more effectively, this review is aimed at providing the comprehensive summary needed to understand and improve this burgeoning area.

Phenylalanine ammonia-lyase, a key component used for phenylpropanoids production by metabolic engineering

Phenylalanine ammonia-lyase, a versatile enzyme with industrial and medical applications.

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: translating research into novel therapies

Phenylketonuria (PKU) is an inborn error of metabolism of the amino acid phenylalanine. It is an autosomal recessive disorder with a rate of incidence of 1 in 10,000 in Caucasian populations. Mutations in the phenylalanine hydroxylase (PAH) gene are the major cause of PKU, due to the loss of the catalytic activity of the enzyme product PAH. Newborn screening for PKU allows early intervention, avoiding irreparable neurological damage and intellectual disability that would arise from untreated PKU. The current primary treatment of PKU is the limitation of dietary protein intake, which in the long term may be associated with poor compliance in some cases and other health problems due to malnutrition. The only alternative therapy currently approved is the supplementation of BH4, the requisite co-factor of PAH, in the orally-available form of sapropterin dihydrochloride. This treatment is not universally available, and is only effective for a proportion (estimated 30%) of PKU patients. Research into novel therapies for PKU has taken many different approaches to address the lack of PAH activity at the core of this disorder: enzyme replacement via virus-mediated gene transfer, transplantation of donor liver and recombinant PAH protein, enzyme substitution using phenylalanine ammonia lyase (PAL) to provide an alternative pathway for the metabolism of phenylalanine, and restoration of native PAH activity using chemical chaperones and nonsense read-through agents. It is hoped that continuing efforts into these studies will translate into a significant improvement in the physical outcome, as well as quality of life, for patients with PKU.

Preservation of high phenylalanine ammonia lyase activities in roots of Japanese Striped corn: a potential oral therapeutic to treat phenylketonuria

Phenylketonuria (PKU) is an inherited metabolic disorder caused by deficient phenylalanine hydroxylase (PAH) activity, the enzyme responsible for the disposal of excess amounts of the essential amino acid phenylalanine (Phe). Phenylalanine ammonia-lyase (PAL, EC 4.3.1.5) has potential to serve as an enzyme substitution therapy for this human genetic disease. Using 7-day-old Japanese Striped corn seedlings (Japonica Striped maize, Zea mays L. cv. japonica) that contain high activities of PAL, we investigated a number of methods to preserve the roots as an intact food and for long-term storage. The cryoprotectant effects of maple syrup and other edible sugars (mono- and oligosaccharides) were evaluated. Following thawing, the preserved roots were then examined to determine whether the rigid plant cell walls could protect the PAL enzyme from proteolysis during simulated (in vitro) digestion comprised of gastric and intestinal phases. While several treatments led to retention of PAL activity during freezing, upon thawing and in vitro digestion, root tissues that had been previously frozen in the presence of maple syrup exhibited the highest residual PAL activities (∼50% of the initial enzyme activity), in marked contrast to all of the treatments using other edible sugars. The structural integrity of the root cells, and the stability of the functional PAL tetramer were also preserved with the maple syrup protocol. These results have significance for the formulation of oral enzyme/protein therapeutics. When plant tissues are adequately preserved, the rigid cell walls constitute a protective barrier even under harsh (e.g. gastrointestinal-like) conditions.

Improving the stability and activity of oral therapeutic enzymes-recent advances and perspectives

Exogenous, orally-administered enzymes are currently in clinical use or under development for the treatment of pathologies, such as celiac disease and phenylketonuria. However, the administration of therapeutic enzymes via the oral route remains challenging due to potential inactivation of these fragile macromolecular entities in the harsh environment of the gastrointestinal tract. Enzymes are particularly sensitive because both proteolysis and unfolding can lead to their inactivation. Current efforts to overcome these shortcomings involve the application of gastro-resistant delivery systems and the modification of enzyme structures by polymer conjugation or protein engineering. This perspective manuscript reviews and critically discusses recent progress in the oral delivery of therapeutic enzymes, whose substrate is localized in the gastrointestinal tract.

[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).

Biotechnological production and applications of microbial phenylalanine ammonia lyase: a recent review

Phenylalanine ammonia lyase (PAL) catalyzes the nonoxidative deamination of l-phenylalanine to form trans-cinnamic acid and a free ammonium ion. It plays a major role in the catabolism of l-phenylalanine. The presence of PAL has been reported in diverse plants, some fungi, Streptomyces and few Cyanobacteria. In the past two decades, PAL has gained considerable significance in several clinical, industrial and biotechnological applications. Since its discovery, much knowledge has been gathered with reference to the enzyme's importance in phenyl propanoid pathway of plants. In contrast, there is little knowledge about microbial PAL. Furthermore, the commercial source of the enzyme has been mainly obtained from the fungi. This study focuses on the recent advances on the physiological role of microbial PAL and the improvements of PAL biotechnological production both from our laboratory and many others as well as the latest advances on the new applications of microbial PAL.

Priming ammonia lyases and aminomutases for industrial and therapeutic applications

Ammonia lyases (AL) and aminomutases (AM) are emerging in green synthetic routes to chiral amines and an AL is being explored as an enzyme therapeutic for treating phenylketonuria and cancer. Although the restricted substrate range of the wild-type enzymes limits their widespread application, the non-reliance on external cofactors and direct functionalization of an olefinic bond make ammonia lyases attractive biocatalysts for use in the synthesis of natural and non-natural amino acids, including β-amino acids. The approach of combining structure-guided enzyme engineering with efficient mutant library screening has extended the synthetic scope of these enzymes in recent years and has resolved important mechanistic issues for AMs and ALs, including those containing the MIO (4-methylideneimidazole-5-one) internal cofactor.

Novel pharmacological chaperones that correct phenylketonuria in mice

Phenylketonuria (PKU) is caused by inherited phenylalanine-hydroxylase (PAH) deficiency and, in many genotypes, it is associated with protein misfolding. The natural cofactor of PAH, tetrahydrobiopterin (BH(4)), can act as a pharmacological chaperone (PC) that rescues enzyme function. However, BH(4) shows limited efficacy in some PKU genotypes and its chemical synthesis is very costly. Taking an integrated drug discovery approach which has not been applied to this target before, we identified alternative PCs for the treatment of PKU. Shape-focused virtual screening of the National Cancer Institute's chemical library identified 84 candidate molecules with potential to bind to the active site of PAH. An in vitro evaluation of these yielded six compounds that restored the enzymatic activity of the unstable PAHV106A variant and increased its stability in cell-based assays against proteolytic degradation. During a 3-day treatment study, two compounds (benzylhydantoin and 6-amino-5-(benzylamino)-uracil) substantially improved the in vivo Phe oxidation and blood Phe concentrations of PKU mice (Pah(enu1)). Notably, benzylhydantoin was twice as effective as tetrahydrobiopterin. In conclusion, we identified two PCs with high in vivo efficacy that may be further developed into a more effective drug treatment of PKU.

Phenylketonuria: nutritional advances and challenges

Despite the appearance of new treatment, dietary approach remains the mainstay of PKU therapy. The nutritional management has become complex to optimize PKU patients' growth, development and diet compliance. This paper review critically new advances and challenges that have recently focused attention on potential relevant of LCPUFA supplementation, progress in protein substitutes and new protein sources, large neutral amino acids and sapropterin. Given the functional effects, DHA is conditionally essential substrates that should be supplied with PKU diet in infancy but even beyond. An European Commission Programme is going on to establish quantitative DHA requirements in this population. Improvements in the palatability, presentation, convenience and nutritional composition of protein substitutes have helped to improve long-term compliance with PKU diet, although it can be expected for further improvement in this area. Glycomacropeptide, a new protein source, may help to support dietary compliance of PKU subject but further studies are needed to evaluate this metabolic and nutritional issues. The PKU diet is difficult to maintain in adolescence and adult life. Treatment with large neutral amino acids or sapropterin in selected cases can be helpful. However, more studies are necessary to investigate the potential role, dose, and composition of large neutral amino acids in PKU treatment and to show long-term efficacy and tolerance. Ideally treatment with sapropterin would lead to acceptable blood Phe control without dietary treatment but this is uncommon and sapropterin will usually be given in combination with dietary treatment, but clinical protocol evaluating adjustment of PKU diet and sapropterin dosage are needed.

In conclusion PKU diet and the new existing treatments, that need to be optimized, may be a complete and combined strategy possibly positive impacting on the psychological, social, and neurocognitive life of PKU patients.

Phenylalanine hydroxylase misfolding and pharmacological chaperones

Phenylketonuria (PKU) is a loss-of-function inborn error of metabolism. As many other inherited diseases the main pathologic mechanism in PKU is an enhanced tendency of the mutant phenylalanine hydroxylase (PAH) to misfold and undergo ubiquitin-dependent degradation. Recent alternative approaches with therapeutic potential for PKU aim at correcting the PAH misfolding, and in this respect pharmacological chaperones are the focus of increasing interest. These compounds, which often resemble the natural ligands and show mild competitive inhibition, can rescue the misfolded proteins by stimulating their renaturation in vivo. For PKU, a few studies have proven the stabilization of PKU-mutants in vitro, in cells, and in mice by pharmacological chaperones, which have been found either by using the tetrahydrobiopterin (BH(4)) cofactor as query structure for shape-focused virtual screening or by high-throughput screening of small compound libraries. Both approaches have revealed a number of compounds, most of which bind at the iron-binding site, competitively with respect to BH(4). Furthermore, PAH shares a number of ligands, such as BH(4), amino acid substrates and inhibitors, with the other aromatic amino acid hydroxylases: the neuronal/neuroendocrine enzymes tyrosine hydroxylase (TH) and the tryptophan hydroxylases (TPHs). Recent results indicate that the PAH-targeted pharmacological chaperones should also be tested on TH and the TPHs, and eventually be derivatized to avoid unwanted interactions with these other enzymes. After derivatization and validation in animal models, the PAH-chaperoning compounds represent novel possibilities in the treatment of PKU.