Assessment of stability, toxicity and immunogenicity of new polymeric nanoreactors for use in enzyme replacement therapy of MNGIE

Opportunities for nanomaterials in enzyme therapy

In recent years, enzyme therapy strategies have rapidly evolved to catalyze essential biochemical reactions with therapeutic potential. These approaches hold particular promise in addressing rare genetic disorders, cancer treatment, neurodegenerative conditions, wound healing, inflammation management, and infectious disease control, among others. There are several primary reasons for the utilization of enzymes as therapeutics: their substrate specificity, their biological compatibility, and their ability to generate a high number of product molecules per enzyme unit. These features have encouraged their application in enzyme replacement therapy where the enzyme serves as the therapeutic agent to rectify abnormal metabolic and physiological processes, enzyme prodrug therapy where the enzyme initiates a clinical effect by activating prodrugs, and enzyme dynamic or starving therapy where the enzyme acts upon host substrate molecules. Currently, there are >20 commercialized products based on therapeutic enzymes, but approval rates are considerably lower than other biologicals. This has stimulated nanobiotechnology in the last years to develop nanoparticle-based solutions that integrate therapeutic enzymes. This approach aims to enhance stability, prevent rapid clearance, reduce immunogenicity, and even enable spatio-temporal activation of the therapeutic catalyst. This comprehensive review delves into emerging trends in the application of therapeutic enzymes, with a particular emphasis on the synergistic opportunities presented by incorporating enzymes into nanomaterials. Such integration holds the promise of enhancing existing therapies or even paving the way for innovative nanotherapeutic approaches.

Clinical trials in mitochondrial diseases

Primary mitochondrial diseases are some of the most common and complex inherited inborn errors of metabolism. Their molecular and phenotypic diversity has led to difficulties in finding disease-modifying therapies and clinical trial efforts have been slow due to multiple significant challenges. Lack of robust natural history data, difficulties in finding specific biomarkers, absence of well-validated outcome measures, and small patient numbers have made clinical trial design and conduct difficult. Encouragingly, new interest in treating mitochondrial dysfunction in common diseases and regulatory incentives to develop therapies for rare conditions have led to significant interest and efforts to develop drugs for primary mitochondrial diseases. Here, we review past and present clinical trials and future strategies of drug development in primary mitochondrial diseases.

Application of polymersomes in membrane protein study and drug discovery: Progress, strategies, and perspectives

Membrane proteins (MPs) play key roles in cellular signaling pathways and are responsible for intercellular and intracellular interactions. Dysfunctional MPs are directly related to the pathogenesis of various diseases, and they have been exploited as one of the most sought-after targets in the pharmaceutical industry. However, working with MPs is difficult given that their amphiphilic nature requires protection from biological membrane or membrane mimetics. Polymersomes are bilayered nano-vesicles made of self-assembled block copolymers that have been widely used as cell membrane mimetics for MP reconstitution and in engineering of artificial cells. This review highlights the prevailing trend in the application of polymersomes in MP study and drug discovery. We begin with a review on the techniques for synthesis and characterization of polymersomes as well as methods of MP insertion to form proteopolymersomes. Next, we review the structural and functional analysis of the different types of MPs reconstituted in polymersomes, including membrane transport proteins, MP complexes, and membrane receptors. We then summarize the factors affecting reconstitution efficiency and the quality of reconstituted MPs for structural and functional studies. Additionally, we discuss the potential in using proteopolymersomes as platforms for high-throughput screening (HTS) in drug discovery to identify modulators of MPs. We conclude by providing future perspectives and recommendations on advancing the study of MPs and drug development using proteopolymersomes.

Inverting glucuronidation of hymecromone in situ by catalytic nanocompartments

Glucuronidation is a metabolic pathway that inactivates many drugs including hymecromone. Adverse effects of glucuronide metabolites include a reduction of half-life circulation times and rapid elimination from the body. Herein, we developed synthetic catalytic nanocompartments able to cleave the glucuronide moiety from the metabolized form of hymecromone in order to convert it to the active drug. By shielding enzymes from their surroundings, catalytic nanocompartments favor prolonged activity and lower immunogenicity as key aspects to improve the therapeutic solution. The catalytic nanocompartments (CNCs) consist of self-assembled poly(dimethylsiloxane)-block-poly(2-methyl-2-oxazoline) diblock copolymer polymersomes encapsulating β-glucuronidase. Insertion of melittin in the synthetic membrane of these polymersomes provided pores for the diffusion of the hydrophilic hymecromone-glucuronide conjugate to the compartment inside where the encapsulated β-glucuronidase catalyzed its conversion to hymecromone. Our system successfully produced hymecromone from its glucuronide conjugate in both phosphate buffered solution and cell culture medium. CNCs were non-cytotoxic when incubated with HepG2 cells. After being taken up by cells, CNCs produced the drug in situ over 24 hours. Such catalytic platforms, which locally revert a drug metabolite into its active form, open new avenues in the design of therapeutics that aim at prolonging the residence time of a drug.

Therapy Prospects for Mitochondrial DNA Maintenance Disorders

Mitochondrial DNA depletion and multiple deletions syndromes (MDDS) constitute a group of mitochondrial diseases defined by dysfunctional mitochondrial DNA (mtDNA) replication and maintenance. As is the case for many other mitochondrial diseases, the options for the treatment of these disorders are rather limited today. Some aggressive treatments such as liver transplantation or allogeneic stem cell transplantation are among the few available options for patients with some forms of MDDS. However, in recent years, significant advances in our knowledge of the biochemical pathomechanisms accounting for dysfunctional mtDNA replication have been achieved, which has opened new prospects for the treatment of these often fatal diseases. Current strategies under investigation to treat MDDS range from small molecule substrate enhancement approaches to more complex treatments, such as lentiviral or adenoassociated vector-mediated gene therapy. Some of these experimental therapies have already reached the clinical phase with very promising results, however, they are hampered by the fact that these are all rare disorders and so the patient recruitment potential for clinical trials is very limited.

Antimicrobial Honey-Inspired Glucose-Responsive Nanoreactors by Polymerization-Induced Self-Assembly

The rise of antimicrobial resistance is at the forefront of global healthcare challenges, with antimicrobial infections on track to overtake cancer as a leading cause of death by 2050. The high effectiveness of antimicrobial enzymes used in combination with the protective, inert nature of polymer materials represents a highly novel approach toward tackling microbial infections. Herein, we have developed biohybrid glucose oxidase-loaded semipermeable polymersome nanoreactors, formed using polymerization-induced self-assembly, and demonstrate for the first time their ability to "switch on" their antimicrobial activity in response to glucose, a ubiquitous environmental stimulus. Using colony-counting assays, it was demonstrated that the nanoreactors facilitate up to a seven-log reduction in bacterial growth at high glucose concentrations against a range of Gram-negative and Gram-positive bacterial pathogens, including a methicillin-resistant Staphylococcus aureus clinical isolate. After demonstrating the antimicrobial properties of these materials, their toxicity against human fibroblasts was assessed and the dosage of the nanoreactors further optimized for use as nontoxic agents against Gram-positive bacteria under physiological blood glucose concentrations. It is envisaged that such biohybrid nanomaterials will become an important new class of antimicrobial biomaterials for the treatment of bacterial infections.

Organelle-specific targeting of polymersomes into the cell nucleus

Organelle-specific nanocarriers (NCs) are highly sought after for delivering therapeutic agents into the cell nucleus. This necessitates nucleocytoplasmic transport (NCT) to bypass nuclear pore complexes (NPCs). However, little is known as to how comparably large NCs infiltrate this vital intracellular barrier to enter the nuclear interior. Here, we developed nuclear localization signal (NLS)-conjugated polymersome nanocarriers (NLS-NCs) and studied the NCT mechanism underlying their selective nuclear uptake. Detailed chemical, biophysical, and cellular analyses show that karyopherin receptors are required to authenticate, bind, and escort NLS-NCs through NPCs while Ran guanosine triphosphate (RanGTP) promotes their release from NPCs into the nuclear interior. Ultrastructural analysis by regressive staining transmission electron microscopy further resolves the NLS-NCs on transit in NPCs and inside the nucleus. By elucidating their ability to utilize NCT, these findings demonstrate the efficacy of polymersomes to deliver encapsulated payloads directly into cell nuclei.

Mitochondrial neurogastrointestinal encephalomyopathy: approaches to diagnosis and treatment

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is an ultra-rare disease caused by mutations in TYMP, the gene encoding for the enzyme thymidine phosphorylase. The resulting enzyme deficiency leads to a systemic accumulation of thymidine and 2’-deoxyuridine and ultimately mitochondrial failure due to a progressive acquisition of secondary mitochondrial DNA (mtDNA) mutations and mtDNA depletion. MNGIE is characterised by gastrointestinal dysmotility, cachexia, peripheral neuropathy, ophthalmoplegia, ptosis and leukoencephalopathy. The disease is progressively degenerative and leads to death at an average age of 37.6 years. Patients invariably encounter misdiagnoses, diagnostic delays, and non-specific clinical management. Despite its rarity, MNGIE has invoked much interest in the development of therapeutic strategies, mainly because it is one of the few mitochondrial disorders where the molecular abnormality is metabolically and physically accessible to manipulation. This review provides a resume of the current diagnosis and treatment approaches and aims to increase the clinical awareness of MNGIE and thereby facilitate early diagnosis and timely access to treatments, before the development of untreatable and irreversible organ damage.

Recent Progress in Micro/Nanoreactors toward the Creation of Artificial Organelles

Artificial organelles created from a bottom up approach are a new type of engineered materials, which are not designed to be living but, instead, to mimic some specific functions inside cells. By doing so, artificial organelles are expected to become a powerful tool in biomedicine. They can act as nanoreactors to convert a prodrug into a drug inside the cells or as carriers encapsulating therapeutic enzymes to replace malfunctioning organelles in pathological conditions. For the design of artificial organelles, several requirements need to be fulfilled: a compartmentalized structure that can encapsulate the synthetic machinery to perform an enzymatic function, as well as a means to allow for communication between the interior of the artificial organelle and the external environment, so that substrates and products can diffuse in and out the carrier allowing for continuous enzymatic reactions. The most recent and exciting advances in architectures that fulfill the aforementioned requirements are featured in this review. Artificial organelles are classified depending on their constituting materials, being lipid and polymer-based systems the most prominent ones. Finally, special emphasis will be put on the intracellular response of these newly emerging systems.

Nanoreactors based on DNAzyme-functionalized magnetic nanoparticles activated by magnetic field

A new biomimetic nanoreactor design, MaBiDz, is presented based on a copolymer brush in combination with superparamagnetic nanoparticles. This cellular nanoreactor features two species of magnetic particles, each functionalized with two components of a binary deoxyribozyme system. In the presence of a target mRNA analyte and a magnetic field, the nanoreactor is assembled to form a biocompartment enclosed by the polymeric brush that enables catalytic function of the binary deoxyribozyme with enhanced kinetics. MaBiDz was demonstrated here as a cellular sensor for rapid detection and imaging of a target mRNA biomarker for metastatic breast cancer, and its function shows potential to be expanded as a biomimetic organelle that can downregulate the activity of a target mRNA biomarker.

Toward Artificial Mitochondrion: Mimicking Oxidative Phosphorylation in Polymer and Hybrid Membranes

For energy supply to biomimetic constructs, a complex chemical energy-driven ATP-generating artificial system was built. The system was assembled with bottom-up detergent-mediated reconstitution of an ATP synthase and a terminal oxidase into two types of novel nanocontainers, built from either graft copolymer membranes or from hybrid graft copolymer/lipid membranes. The versatility and biocompatibility of the proposed nanocontainers was demonstrated through convenient system assembly and through high retained activity of both membrane-embedded enzymes. In the future, the nanocontainers might be used as a platform for the functional reconstitution of other complex membrane proteins and could considerably expedite the design of nanoreactors, biosensors, and artificial organelles.

Enzymes as key features in therapeutic cell mimicry

Cell mimicry is a nature inspired concept that aims to substitute for missing or lost (sub)cellular function. This review focuses on the latest advancements in the use of enzymes in cell mimicry for encapsulated catalysis and artificial motility in synthetic bottom-up assemblies with emphasis on the biological response in cell culture or more rarely in animal models. Entities across the length scale from nano-sized enzyme mimics, sub-micron sized artificial organelles and self-propelled particles (swimmers) to micron-sized artificial cells are discussed. Although the field remains in its infancy, the primary aim of this review is to illustrate the advent of nature-mimicking artificial molecules and assemblies on their way to become a complementary alternative to their role models for diverse biomedical purposes.

PDMS-b-PMOXA polymersomes for hepatocyte targeting and assessment of toxicity

Nanoparticles, such as polymersomes, can be directed to the hepatic asialoglycoprotein receptor to achieve targeted drug delivery. In this study, we prepared asialofetuin conjugated polymersomes based on the amphiphilic di-block copolymer poly(dimethylsiloxane)-b-poly(2-methyloxazoline) (PDMS-b-PMOXA). They had an average diameter of 150nm and formed monodisperse vesicles. Drug encapsulation and sustained release was monitored using the hydrophilic model compound carboxyfluorescein. Asialoglycoprotein receptor specific uptake by HepG2 cells in vitro was energy dependent and could be competitively inhibited by the free targeting ligand. Mechanistic uptake studies revealed intracellular trafficking of asialofetuin conjugated polymersomes from early endosomes and to the lysosomal compartment. Polymersomes showed no toxicity in the MTT assay up to concentrations of 500μg/mL. In addition, acute toxicity and tolerability of our PDMS-b-PMOXA polymersome formulations was assessed in vivo using zebrafish embryos as a vertebrate screening model. In conclusion, a hepatocyte specific drug delivery system was designed, which is safe and biocompatible and which can be used to implement liver-specific targeting strategies.

Determination of Permeability Coefficients of Polymersomal Membranes for Hydrophilic Molecules

Polymer vesicles, so-called polymersomes, can be applied as carrier-systems and universal reaction compartments, due to the possibility to encapsulate guest molecules. Compared to common lipid vesicles, polymersomes show an increased stability and decreased membrane permeability. Control of the mass transport across the membrane is necessary for any application, requiring the precise knowledge of the permeability. So far, data on permeability coefficients of polymersomal membranes are scarce because commonly applied release assays are confronted with the challenge of high detection limits and alternative methods developed so far are either restricted to the use of a certain permeating molecule or rely on the use of nuclear magnetic resonance measurements. In contrast, an influx assay that is broadly applicable to hydrophilic molecules and does not involve specialized equipment was developed in this work, which is based on the passive diffusion of compounds into initially empty vesicles. The method is valid for hydrophilic molecules that show no membrane retention and, thus, do not accumulate within the membrane. Using this method, the permeability of polymersomes made of poly(2-methyloxazoline)₁₅-poly(dimethylsiloxane)₆₈-poly(2-methyloxazoline)₁₅ for seven model compounds was investigated under varying conditions. Permeability coefficients as low as 1.9 × 10^-14 cm s^-1 could be measured.

Mitochondrial Neurogastrointestinal Encephalomyopathy Caused by Thymidine Phosphorylase Enzyme Deficiency: From Pathogenesis to Emerging Therapeutic Options

Mitochondrial neurogastrointestinal encephalomyopathy (MNGIE) is a progressive metabolic disorder caused by thymidine phosphorylase (TP) enzyme deficiency. The lack of TP results in systemic accumulation of deoxyribonucleosides thymidine (dThd) and deoxyuridine (dUrd). In these patients, clinical features include mental regression, ophthalmoplegia, and fatal gastrointestinal complications. The accumulation of nucleosides also causes imbalances in mitochondrial DNA (mtDNA) deoxyribonucleoside triphosphates (dNTPs), which may play a direct or indirect role in the mtDNA depletion/deletion abnormalities, although the exact underlying mechanism remains unknown. The available therapeutic approaches include dialysis and enzyme replacement therapy, both can only transiently reverse the biochemical imbalance. Allogeneic hematopoietic stem cell transplantation is shown to be able to restore normal enzyme activity and improve clinical manifestations in MNGIE patients. However, transplant related complications and disease progression result in a high mortality rate. New therapeutic approaches, such as adeno-associated viral vector and hematopoietic stem cell gene therapy have been tested in Tymp^-/-Upp1^-/- mice, a murine model for MNGIE. This review provides background information on disease manifestations of MNGIE with a focus on current management and treatment options. It also outlines the pre-clinical approaches toward future treatment of the disease.

Durable vesicles for reconstitution of membrane proteins in biotechnology

The application of membrane proteins in biotechnology requires robust, durable reconstitution systems that enhance their stability and support their functionality in a range of working environments. Vesicular architectures are highly desirable to provide the compartmentalisation to utilise the functional transmembrane transport and signalling properties of membrane proteins. Proteoliposomes provide a native-like membrane environment to support membrane protein function, but can lack the required chemical and physical stability. Amphiphilic block copolymers can also self-assemble into polymersomes: tough vesicles with improved stability compared with liposomes. This review discusses the reconstitution of membrane proteins into polymersomes and the more recent development of hybrid vesicles, which blend the robust nature of block copolymers with the biofunctionality of lipids. These novel synthetic vesicles hold great promise for enabling membrane proteins within biotechnologies by supporting their enhanced in vitro performance and could also contribute to fundamental biochemical and biophysical research by improving the stability of membrane proteins that are challenging to work with.

Engineering Intrinsically Zirconium-89 Radiolabeled Self-Destructing Mesoporous Silica Nanostructures for In Vivo Biodistribution and Tumor Targeting Studies

A systematic study of in vitro and in vivo behavior of biodegradable mesoporous silica nanoparticles (bMSNs), designed to carry multiple cargos (both small and macromolecular drugs) and subsequently self-destruct following release of their payloads, is presented. Complete degradation of bMSNs is seen within 21 d of incubation in simulated body fluid. The as-synthesized bMSNs are intrinsically radiolabeled with oxophilic zirconium-89 (89Zr, t1/2 = 78.4 h) radionuclide to track their in vivo pharmacokinetics via positron emission tomography imaging. Rapid and persistent CD105 specific tumor vasculature targeting is successfully demonstrated in murine model of metastatic breast cancer by using TRC105 (an anti-CD105 antibody)-conjugated bMSNs. This study serves to illustrate a simple, versatile, and readily tunable approach to potentially overcome the current challenges facing nanomedicine and further the goals of personalized nanotheranostics.

Stimuli-Triggered Activity of Nanoreactors by Biomimetic Engineering Polymer Membranes

The development of advanced stimuli-responsive systems for medicine, catalysis, or technology requires compartmentalized reaction spaces with triggered activity. Only very few stimuli-responsive systems preserve the compartment architecture, and none allows a triggered activity in situ. We present here a biomimetic strategy to molecular transmembrane transport by engineering synthetic membranes equipped with channel proteins so that they are stimuli-responsive. Nanoreactors with triggered activity were designed by simultaneously encapsulating an enzyme inside polymer compartments, and inserting protein "gates" in the membrane. The outer membrane protein F (OmpF) porin was chemically modified with a pH-responsive molecular cap to serve as "gate" producing pH-driven molecular flow through the membrane and control the in situ enzymatic activity. This strategy provides complex reaction spaces necessary in "smart" medicine and for biomimetic engineering of artificial cells.

Temperature sensitive supramolecular self assembly of per-6-PEO-β-cyclodextrin and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) in water

The host/guest interactions in water of a star polymer consisting of a β-cyclodextrin (β-CD) core bearing six poly(ethylene oxide) arms linked to the C6 positions of β-CD (β-CD-PEO7, Mn 5000 g mol(-1)) and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) (Ad-PNIPAM-12K, Mn 12,000 g mol(-1)) were studied by 1D and 2D (1)H and (13)C NMR spectroscopy, isothermal calorimetry (ITC), and light scattering (LS). In cold water (T < 26 °C) supramolecular "dumbbell" assemblies, consisting of PNIPAM chains with β-CD/Ad inclusion complexes at each end, formed viaβ-CD-insertion of the terminal Ads through the β-CD secondary face. Light scattering, microcalorimetry (DSC), and DOSY NMR studies indicated that mixed aqueous solutions of β-CD-PEO7 and Ad-PNIPAM-12K undergo a reversible heat-induced phase transition at ∼32 °C, accompanied by a release of a fraction of the Ad-bound β-CD-PEO7 into bulk solution and the formation of aggregated Ad-PNIPAM-12K stabilized by a β-CD-PEO7 shell.

Aquaporin-Based Biomimetic Polymeric Membranes: Approaches and Challenges

In recent years, aquaporin biomimetic membranes (ABMs) for water separation have gained considerable interest. Although the first ABMs are commercially available, there are still many challenges associated with further ABM development. Here, we discuss the interplay of the main components of ABMs: aquaporin proteins (AQPs), block copolymers for AQP reconstitution, and polymer-based supporting structures. First, we briefly cover challenges and review recent developments in understanding the interplay between AQP and block copolymers. Second, we review some experimental characterization methods for investigating AQP incorporation including freeze-fracture transmission electron microscopy, fluorescence correlation spectroscopy, stopped-flow light scattering, and small-angle X-ray scattering. Third, we focus on recent efforts in embedding reconstituted AQPs in membrane designs that are based on conventional thin film interfacial polymerization techniques. Finally, we describe some new developments in interfacial polymerization using polyhedral oligomeric silsesquioxane cages for increasing the physical and chemical durability of thin film composite membranes.

A general strategy for creating self-defending surfaces for controlled drug production for long periods of time

Infections associated with bacterial adhesion and subsequent biofilm formation constitute a grave medical issue for which conventional antibiotic therapies remain ineffective. Here, we introduce a new strategy employing nanotechnology to create smart surfaces with self-defending properties that result in controlled drug production and controlled release for long periods of time. Self-defending surfaces on solid supports are prepared by immobilizing polymer nanoreactors containing an encapsulated biocatalyst that can convert non-antibiotic substrates to an abiotic drug. For medical applications and biosensing, the immobilization method must fulfill specific criteria, and these were achieved by an immobilization strategy based on Schiff base formation between aldehyde groups on the outer surface of nanoreactors and amino groups on the solid support surface, followed by reductive amination. The resulting self-defending surfaces allow control of drug production at a specific rate for a specific period of time by adding predetermined amounts of substrate to the outer medium, minimization of dosages and therefore systemic toxicity, and limitation of the immune response. Such self-defending surfaces producing drugs offer a versatile strategy for the development of smart surfaces with improved stability and efficacy (by changing the biocatalyst) to serve as biosensors, antifouling surfaces, or smart packages.

Enzyme encapsulated hollow silica nanospheres for intracellular biocatalysis

Hollow silica nanospheres (HSN) with low densities, large interior spaces and permeable silica shells are suitable for loading enzymes in the cavity to carry out intracellular biocatalysis. The porous shell can protect the encapsulated enzymes against proteolysis and attenuate immunological response. We developed a microemulsion-templating method for confining horseradish peroxidase (HRP) in the cavity of HSN. This simple one-pot enzyme encapsulation method allows entrapping of the enzyme, which retains high catalytic activity. Compared with HRP supported on solid silica spheres, HRP@HSN with thin porous silica shells displayed better enzyme activity. The small HRP@HSN (∼50 nm in diameter), giving satisfactory catalytic activity, can act as an intracellular catalyst for the oxidation of the prodrug indole-3-acetic acid to produce toxic free radicals for killing cancer cells. We envision this kind of hollow nanosystem could encapsulate multiple enzymes or other synergistic drugs and function as therapeutic nanoreactors.

Deoxynucleoside stress exacerbates the phenotype of a mouse model of mitochondrial neurogastrointestinal encephalopathy

Balanced pools of deoxyribonucleoside triphosphate precursors are required for DNA replication, and alterations of this balance are relevant to human mitochondrial diseases including mitochondrial neurogastrointestinal encephalopathy. In this disease, autosomal recessive TYMP mutations cause severe reductions of thymidine phosphorylase activity; marked elevations of the pyrimidine nucleosides thymidine and deoxyuridine in plasma and tissues, and somatic multiple deletions, depletion and site-specific point mutations of mitochondrial DNA. Thymidine phosphorylase and uridine phosphorylase double knockout mice recapitulated several features of these patients including thymidine phosphorylase activity deficiency, elevated thymidine and deoxyuridine in tissues, mitochondrial DNA depletion, respiratory chain defects and white matter changes. However, in contrast to patients with this disease, mutant mice showed mitochondrial alterations only in the brain. To test the hypothesis that elevated levels of nucleotides cause unbalanced deoxyribonucleoside triphosphate pools and, in turn, pathogenic mitochondrial DNA instability, we have stressed double knockout mice with exogenous thymidine and deoxyuridine, and assessed clinical, neuroradiological, histological, molecular, and biochemical consequences. Mutant mice treated with exogenous thymidine and deoxyuridine showed reduced survival, body weight, and muscle strength, relative to untreated animals. Moreover, in treated mutants, leukoencephalopathy, a hallmark of the disease, was enhanced and the small intestine showed a reduction of smooth muscle cells and increased fibrosis. Levels of mitochondrial DNA were depleted not only in the brain but also in the small intestine, and deoxyribonucleoside triphosphate imbalance was observed in the brain. The relative proportion, rather than the absolute amount of deoxyribonucleoside triphosphate, was critical for mitochondrial DNA maintenance. Thus, our results demonstrate that stress of exogenous pyrimidine nucleosides enhances the mitochondrial phenotype of our knockout mice. Our mouse studies provide insights into the pathogenic role of thymidine and deoxyuridine imbalance in mitochondrial neurogastrointestinal encephalopathy and an excellent model to study new therapeutic approaches.

Biphase stratification approach to three-dimensional dendritic biodegradable mesoporous silica nanospheres

A kind of novel uniform monodispersed three-dimensional dendritic mesoporous silica nanospheres (3D-dendritic MSNSs) has been successfully synthesized for the first time. The 3D-dendritic MSNSs can have hierarchical mesostructure with multigenerational, tunable center-radial, and dendritic mesopore channels. The synthesis was carried out in the heterogeneous oil-water biphase stratification reaction system, which allowed the self-assembly of reactants taking place in the oil-water interface for one-pot continuous interfacial growth. The average pore size of each generation for the 3D-dendritic MSNSs can be adjusted from 2.8 to 13 nm independently, which can be controlled by the varied hydrophobic solvents and concentration of silica source in the upper oil phase. The thickness of each generation can be tuned from ∼ 5 to 180 nm as desired, which can be controlled by the reaction time and amount of silica source. The biphase stratification approach can also be used to prepare other core-shell and functional mesoporous materials such as Au nanoparticle@3D-dendritic MSNS and Ag nanocube@3D-dendritic MSNS composites. The 3D-dendritic MSNSs show their unique advantage for protein loading and releasing due to their tunable large pore sizes and smart hierarchical mesostructures. The maximum loading capacity of bovine β-lactoglobulin with 3D-dendritic MSNSs can reach as high as 62.1 wt % due to their large pore volume, and the simulated protein releasing process can be tuned from 24 to 96 h by flexible mesostructures. More importantly, the releasing rates are partly dependent on the hierarchical biodegradation, because the 3D-dendritic MSNSs with larger pore sizes have faster simulated biodegradation rates in simulated body fluid. The most rapid simulated biodegradation can be finished entirely in 24 h, which has been greatly shortened than two weeks for the mesoporous silica reported previously. As the inorganic mesoporous materials, 3D-dendritic MSNSs show excellent biocompatibility, and it would have a hopeful prospect in the clinical applications.

Polymer nanoreactors shown to produce and release antibiotics locally

We designed and prepared nanoreactors based on a poly(2-methyloxazoline)-block-poly(dimethylsiloxane)-block-poly(2-methyloxazoline (PMOXA-b-PDMS-b-PMOXA) amphiphilic triblock copolymer encapsulating the enzyme penicillin acylase for local and controlled production of antibiotics.

Virus-mimicking nano-constructs as a contrast agent for near infrared photoacoustic imaging

We report the first proof-of-principle demonstration of photoacoustic imaging using a contrast agent composed of a plant virus protein shell, which encapsulates indocyanine green (ICG), the only FDA-approved near infrared chromophore. These nano-constructs can provide higher photoacoustic signals than blood in tissue phantoms, and display superior photostability compared to non-encapsulated ICG. Our preliminary results suggest that the constructs do not elicit an acute immunogenic response in healthy mice.

Template synthesis of test tube nanoparticles using non-destructive replication

Nano test tubes are a promising delivery vehicle for a range of therapeutics, including small molecule drugs and biologics. However, current template synthesis methods of producing nano test tubes are prohibitively expensive and time consuming. Here, non-destructive template replication was used to increase nano test tube yield from porous alumina by more than a hundredfold. We demonstrate how to produce nano test tubes of several sizes and compositions, including hybrid tubes with different inner and outer surfaces for targeted surface chemistry. Nano test tubes were readily suspended and stored in aqueous solutions without the need for chemical treatment. These nano test tubes should find application as delivery vehicles for therapeutics, particularly for processive 'bionanoreactors' loaded with enzymes.

Light-responsive polymer nanoreactors: a source of reactive oxygen species on demand

Various domains present the challenges of responding to stimuli in a specific manner, with the desired sensitivity or functionality, and only when required. Stimuli-responsive systems that are appropriately designed can effectively meet these challenges. Here, we introduce nanoreactors that encapsulate photosensitizer-protein conjugates in polymer vesicles as a source of "on demand" reactive oxygen species. Vesicles made of poly(2-methyloxazoline)-poly(dimethylsiloxane)-poly(2-methyloxazoline) successfully encapsulated the photosensitizer Rose Bengal-bovine serum albumin conjugate (RB-BSA) during a self-assembly process, as demonstrated by UV-Vis spectroscopy. A combination of light scattering and transmission electron microscopy indicated that the nanoreactors are stable over time. They serve a dual role: protecting the photosensitizer in the inner cavity and producing in situ reactive oxygen species (ROS) upon irradiation with appropriate electromagnetic radiation. Illumination with appropriate wavelength light allows us to switch on/off and to control the production of ROS. Because of the oxygen-permeable nature of the polymer membrane of vesicles, ROS escape into the environment around vesicles, as established by electron paramagnetic resonance. The light-sensitive nanoreactor is taken up by HeLa cells in a Trojan horse fashion: it is nontoxic and, when irradiated with the appropriate laser light, produces ROS that induce cell death in a precise area corresponding to the irradiation zone. These nanoreactors can be used in theranostic approaches because they can be detected via the fluorescent photosensitizer signal and simultaneously produce ROS efficiently "on demand".

Biomedical applications of immobilized enzymes: an update

Immobilized enzymes have been widely studied during the last few decades. Biocatalyst systems may work as biosensors or may be used for the treatment of different diseases. This chapter presents different attempts to immobilize enzymes in the biomedical field, particularly the use of prolidase and superoxide dismutase as two examples of this approach. Although this chapter focuses on liposomes and nanoparticles for the entrapment of these enzymes, the methods detailed here could be adapted for the immobilization of other enzymes with therapeutic purposes.