Horseradish peroxidase embedded in polyacrylamide nanoparticles enables optical detection of reactive oxygen species

Horseradish Peroxidase-Functionalized Gold Nanoconjugates for Breast Cancer Treatment Based on Enzyme Prodrug Therapy

Introduction

Breast cancer has the highest mortality rate among cancers in women. Patients suffering from certain breast cancers, such as triple-negative breast cancer (TNBC), lack effective treatments. This represents a clinical concern due to the associated poor prognosis and high mortality. As an approach to succeed over conventional therapy limitations, we present herein the design and evaluation of a novel nanodevice based on enzyme-functionalized gold nanoparticles to efficiently perform enzyme prodrug therapy (EPT) in breast cancer cells.

Results

In particular, the enzyme horseradish peroxidase (HRP) – which oxidizes the prodrug indole-3-acetic acid (IAA) to release toxic oxidative species – is incorporated on gold nanoconjugates (HRP-AuNCs), obtaining an efficient nanoplatform for EPT. The nanodevice is biocompatible and effectively internalized by breast cancer cell lines. Remarkably, co-treatment with HRP-AuNCs and IAA (HRP-AuNCs/IAA) reduces the viability of breast cancer cells below 5%. Interestingly, 3D tumor models (multicellular tumor spheroid-like cultures) co-treated with HRP-AuNCs/IAA exhibit a 74% reduction of cell viability, whereas the free formulated components (HRP, IAA) have no effect.

Conclusion

Altogether, our results demonstrate that the designed HRP-AuNCs nanoformulation shows a remarkable therapeutic performance. These findings might help to bypass the clinical limitations of current tumor enzyme therapies and advance towards the use of nanoformulations for EPT in breast cancer.

Combining Active Carbonic Anhydrase with Nanogels: Enzyme Protection and Zinc Sensing

Background

Due to its excellent biocompatibility, the polyacrylamide (PAAm) hydrogel has shown great potential for the immobilization of enzymes used in biomedical applications. The major challenge involved is to preserve, during the immobilization process, both the biological activity and the structural integrity of the enzymes. Here we report, for the first time, a proof-of-concept study for embedding active carbonic anhydrase (CA) into polyacrylamide (PAAm) nanogels. By immobilizing CA in these nanogels, we hope to provide important advantages, such as matrix protection of the CA as well as its targeted delivery, and also for potentially using these nanogels as zinc nano-biosensors, both in-vitro and in-vivo.

Methods and Results

Two methods are reported here for CA immobilization: encapsulation and surface conjugation. In the encapsulation method, the common process was improved, so as to best preserve the CA, by 1) using a novel biofriendly nonionic surfactant system (Span 80/Tween 80/Brij 30) and 2) using an Al₂O₃ adsorptive filtration purification procedure. In the surface conjugation method, blank PAAm nanogels were activated by N-hydroxysuccinimide and the CA was cross-linked to the nanogels. The amount of active CA immobilized in the nanoparticles was quantified for both methods. Per 1 g nanogels, the CA encapsulated nanogels contain 11.3 mg active CA, while the CA conjugated nanogels contain 22.5 mg active CA. Also, the CA conjugated nanoparticles successfully measured free Zn²⁺ levels in solution, with the Zn²⁺ dissociation constant determined to be 9 pM.

Conclusion

This work demonstrates universal methods for immobilizing highly fragile bio-macromolecules inside nanoparticle carriers, while preserving their structural integrity and biological activity. The advantages and limitations are discussed, as well as the potential biomedical applications.

Encapsulation Capacity of β-Cyclodextrin Stabilized Silver Nanoparticles towards Creatinine Enhances the Colorimetric Sensing of Hydrogen Peroxide in Urine

The β-cyclodextrin shell of synthesized silver nanoparticles (βCD-AgNPs) are found to enhance the detection of hydrogen peroxide in urine when compared to the Horse Radish Peroxidase assay kit. Nanoparticles are confirmed by the UV-Vis absorbance of their localized surface plasmonic resonance (LSPR) at 384 nm. The mean size of the βCD-AgNPs is 53 nm/diameter; XRD analysis shows a face-centered cubic structure. The crystalline structure of type 4H hexagonal nature of the AgNPs with 2.4 nm β-CD coating onto is confirmed using aberration corrected high-resolution transmission electron microscopy (HRTEM). A silver atomic lattice at 2.50 Å and 2.41 Å corresponding to (100) and (101) Miller indices is confirmed using the HRTEM. The scope of βCD-AgNPs to detect hydrogen peroxide (H2O2) in aqueous media and human urine is investigated. The test is optimized by examining the effect of volumes of nanoparticles, the pH of the medium, and the kinetic and temperature effect on H2O2 detection. The βCD-AgNPs test is used as a refined protocol, which demonstrated improved sensitivity towards H2O2 in urine compared to the values obtained by the Horse Radish Assay kit. Direct assessment of H2O2 by the βCD-AgNPs test presented always with a linear response in the nM, μM, and mM ranges with a limit of detection of 1.47 nM and a quantitation limit of 3.76 nM. While a linear response obtained from 1.3 to 37.3 nmoles of H2O2/mole creatinine with a slope of 0.0075 and regression coefficient of 0.9955 when the βCD-AgNPs is used as refined test of creatinine. Values ranging from 34.62 ± 0.23 nmoles of H2O2/mole of creatinine and 54.61 ± 1.04 nmoles of H2O2/mole of creatinine when the matrix is not diluted and between 32.16 ± 0.42 nmoles of H2O2/mole of creatinine and 49.66 ± 0.80 nmoles of H2O2/mole of creatinine when the matrix is twice diluted are found in freshly voided urine of seven apparent healthy men aged between 20 and 40 years old.

A quantitative method for the detection and validation of catalase activity at physiological concentration in human serum, plasma and erythrocytes

A novel method has been proposed to develop a simple, rapid, sensitive and affordable chromogenic attempt for the quantification of catalase (CAT) activity in blood samples. The method is based on the oxidation of pyrocatechol (PC) to give quinone form which by oxidative coupling with aminyl radical of 4-aminoantipyrine (4-AAP) resulting from H₂O₂/CAT to produce a pink colored quinone-imine product with λ_max = 530 nm in a 100 mmol/L of tris buffer of pH 9.8 at room temperature (30 °C). The linearity of CAT assay was between 0.316 and 10 U/mL. The accuracy ranges for CAT having concentrations of 1.25, 5 and 7.5 μmol/L were 89-105.52, 90-107%, and 91-104.58% respectively. Within-run and between-run precision studies showed CV's of 1.98-3.02% (n = 7) and 2.97-4.40% (n = 7), respectively. The detection and quantification limits of CAT were 0.12 and 0.225 μmol/L, respectively. The Michaelis-Menten constant and maximum velocity of the reaction was K_m = 1.052 mM and V_max = 0.168 μmol/min, respectively. The present method provides a convenient means for investigating the usefulness of CAT measurements in biological sample assessing the potential for free radical-induced pathology.

Flexible enzyme cascade sensing platform based on a G-quadruplex nanofiber biohydrogel for target colorimetric sensing

Enzyme cascade reactions can greatly improve catalytic efficiency and achieve selective and sensitive detection of targets. This paper presents a novel strategy for colorimetric sensing of targets by loading natural enzymes into a hemin-doped G-quadruplex (G4-hemin) biohydrogel to form a flexible enzyme cascade sensing (FECS) platform. The biohydrogel has advantages of biocompatibility, printability and flexibility. The biohydrogel not only participates in the cascade reaction as the mimic enzyme but also provides a mild microenvironment for the natural enzyme. The FECS platform has a linear range from 0.4 μM to 120 μM and a detection limit of 3.6 × 10^-6 M for hydrogen peroxide detection. Additionally, the FECS platform has a low detection limit and wide linear range for glucose and xanthine by loading xanthine oxidase (XOD) and glucose oxidase (GOD) into the biohydrogel, respectively. These results indicate that the novel FECS platform is an effective detection platform that can detect multiple targets and is expected to be widely used in flexible sensing.

Hydrogel-Based Technologies for the Diagnosis of Skin Pathology

Hydrogels, swellable hydrophilic polymer networks fabricated through chemical cross-linking or physical entanglement are increasingly utilized in various biomedical applications over the past few decades. Hydrogel-based microparticles, dressings and microneedle patches have been explored to achieve safe, sustained and on-demand therapeutic purposes toward numerous skin pathologies, through incorporation of stimuli-responsive moieties and therapeutic agents. More recently, these platforms are expanded to fulfill the diagnostic and monitoring role. Herein, the development of hydrogel technology to achieve diagnosis and monitoring of pathological skin conditions are highlighted, with proteins, nucleic acids, metabolites, and reactive species employed as target biomarkers, among others. The scope of this review includes the characteristics of hydrogel materials, its fabrication procedures, examples of diagnostic studies, as well as discussion pertaining clinical translation of hydrogel systems.

Hydrogel-Encapsulated Enzyme Facilitates Colorimetric Acute Toxicity Assessment of Heavy Metal Ions

Conventional analysis of heavy metal ions in water requires highly skilled staff and sophisticated equipment. These limitations make conventional approaches difficult to perform analysis on-site without delay. Herein, we report a facile colorimetric sensing system developed for acute toxicity assessment of heavy metal ions. A bioactive enzyme, β-galactosidase, was used as sensing agent rather than bacteria or other higher organisms to improve selectivity and response time. The developed bioassay is capable of assessing the toxicity of heavy metal ions such as Hg(II), Cd(II), Pb(II), and Cu(II). The effects of enzyme concentration on the assessing performances (i.e., sensitivity and response time) of bioassay were explored and illustrated. Generally, low enzyme concentration facilitates sensitivity enhancement, achieving a 50% inhibiting concentration (IC₅₀) of 0.76 μM (=152 ppb) Hg(II), and high enzyme concentration ensures quick response, enabling a response time down to 9 min. Moreover, the enzyme and substrate were respectively encapsulated by hydrogel to further simplify the assay procedure and enhance the stability of the enzyme. The hydrogel-encapsulated enzyme worked well even when heated up to 60 °C and retained ca. 90% activity after storage for 5 months. Moreover, the developed toxicity-assessing system is feasible for assessing toxicity of actual water samples. This assay approach is low cost and time effective and has no potential ethic issues. In addition, this work paves the way for the development of toxicity assessment kits for on-site analysis based on functional bioactive molecules.

Nanoparticles and DNA - a powerful and growing functional combination in bionanotechnology

Functionally integrating DNA and other nucleic acids with nanoparticles in all their different physicochemical forms has produced a rich variety of composite nanomaterials which, in many cases, display unique or augmented properties due to the synergistic activity of both components. These capabilities, in turn, are attracting greater attention from various research communities in search of new nanoscale tools for diverse applications that include (bio)sensing, labeling, targeted imaging, cellular delivery, diagnostics, therapeutics, theranostics, bioelectronics, and biocomputing to name just a few amongst many others. Here, we review this vibrant and growing research area from the perspective of the materials themselves and their unique capabilities. Inorganic nanocrystals such as quantum dots or those made from gold or other (noble) metals along with metal oxides and carbon allotropes are desired as participants in these hybrid materials since they can provide distinctive optical, physical, magnetic, and electrochemical properties. Beyond this, synthetic polymer-based and proteinaceous or viral nanoparticulate materials are also useful in the same role since they can provide a predefined and biocompatible cargo-carrying and targeting capability. The DNA component typically provides sequence-based addressability for probes along with, more recently, unique architectural properties that directly originate from the burgeoning structural DNA field. Additionally, DNA aptamers can also provide specific recognition capabilities against many diverse non-nucleic acid targets across a range of size scales from ions to full protein and cells. In addition to appending DNA to inorganic or polymeric nanoparticles, purely DNA-based nanoparticles have recently surfaced as an excellent assembly platform and have started finding application in areas like sensing, imaging and immunotherapy. We focus on selected and representative nanoparticle-DNA materials and highlight their myriad applications using examples from the literature. Overall, it is clear that this unique functional combination of nanomaterials has far more to offer than what we have seen to date and as new capabilities for each of these materials are developed, so, too, will new applications emerge.

Hydrogel nanosensors for biophotonic imaging of chemical analytes

Polymer-based hydrogel nanosensors have been developed and extensively utilized for the imaging and dynamic monitoring of chemical properties, response to external stimulants, and metabolism of cells and tissues, in real time, using optical imaging techniques. A large fraction of these polymeric nanoparticles are based on polyacrylamide (PAA) owing to its excellent properties such as nontoxicity, biocompatibility and flexibility of engineering. The properties of the PAA matrix can be specifically tailored, depending on the application, and the molecules can be loaded into the matrix. Various surface modifications enable one to control its behavior in cells and in vivo, and can be utilized for specific targeting to cells and subcellular organelles. This special report describes the recent advances in the design and application of the latest generation of PAA nanosensors for some physiologically important ions and small molecules.

Hydrogen peroxide (H₂O₂) detection with nanoprobes for biological applications: a mini-review

Hydrogen peroxide (H2O2) is an important member of the reactive oxygen species, playing various roles in biology and medicine. The conventional detection methods for H2O2 are often restricted by their limited sensitivity, poor selectivity towards H2O2, inappropriate physicochemical properties for detection in biological environments, long response time, etc. We briefly review here some recent nanotechnology--based approaches for H2O2 detection, which present an effective improvement, overcoming some of the limitations of the conventional H2O2 sensing techniques.

Quantification and evaluation of kinetic bio-catalytic pathway of horseradish peroxidase in an electron mediated reaction system and its applications in plant extracts

The intermolecular coupling of 2,5-dimethoxyaniline (DMA) as mediated electron transfer reaction in presence of H(2)O(2) and peroxidase in acetate buffer of pH 4.2 resulting green colored product having maximum absorption at λ(max)=740 nm was investigated by spectrophotometer. Under optimum conditions, linearity range for the quantification of H(2)O(2) was 2.0-288.0 μM and for peroxidase were 0.59-9.46 and 0.443-9.46 nM by kinetic and fixed-time method, respectively. The catalytic efficiency and catalytic power were K(eff)(D)=2.354 × 10(5)M(-1)min(-1) and K(pow)(D)=4.59 × 10(-4)min(-1), respectively. From the plot of d(1/D(o)) vs d(1/V(o)) and d(1/H(o)) vs d(1/V(o)), Michaelis-Menten constants for DMA and H(2)O(2)were found that K(m)(D)=1,458 μM and [Formula: see text] =301 μM. Applicability of the method was tested for peroxidase activity in some plant extracts and compared with guaiacol/peroxidase system. Regarding superiority of the method, it is suggested that DMA/peroxidase system can be a better hydrogen donor for HRP assay than guaiacol system as evident from kinetic data.

Tissue distribution and pharmacokinetics of stable polyacrylamide nanoparticles following intravenous injection in the rat

A variety of polymer nanoparticles (NP) are under development for imaging and therapeutic use. However, little is known about their behavior. This study examined pharmacokinetics, distribution and elimination of stable polyacrylamide (PAA) nanoparticles (~31 nm average diameter). PAA NPs and polyethylene glycol-coated PAA NPs were injected into the tail veins of healthy male rats. Blood, tissues and excreta were collected at times ranging from 5 min to 120 h and their radioactive content was quantified. A mathematical model was then applied to analyze the distribution dynamics of both NPs. Elimination from the blood could be accounted for by a quick but finite relocation to the major organs (about 20%, 0.6 to 1.3h half-lives), and a slower distribution to the carcass (about 70%, 35 to 43 h half-lives). Excreted urinary levels correlated with blood concentrations. Combined cumulative urinary and fecal output accounted for less than 6% of the dose at 120 h. Compared to five other polymeric nanoparticles, the studied particles are at the highest half-lives and Area Under the Curve (4000 to 5000%-h). These two parameters decrease by three orders of magnitude when nanoparticle size increases from the 30 nm range up to 250 nm. For similar sizes, pegylated nanoparticles are more persistent in the blood than non-pegylated ones, but this difference is much smaller in the 30 nm and relatively high dose range than above 100 nm. Persistence of PAA NPs is not associated with acute toxicity signs as measured by typical serum markers of inflammation and cellular damage.

Aptamers embedded in polyacrylamide nanoparticles: a tool for in vivo metabolite sensing

We describe a new type of aptamer-based optical nanosensor which uses the embedding of target responsive oligonucleotides in porous polyacrylamide nanoparticles to eliminate nuclease instability. The latter is a common problem in the use of aptamer sensors in biological environments. These aptamers embedded in nanoparticles (AptaNPs) are proposed as a tool in real-time metabolite measurements in living cells. The AptaNPs comprise 30 nm polyacrylamide nanoparticles, prepared by inverse microemulsion polymerization, which contain water-soluble aptamer switch probes (ASPs) trapped in the porous matrix of the nanoparticles. The matrix acts as a molecular fence allowing rapid diffusion of small metabolites into the particles to interact with the aptamer molecules, but at the same time it retains the larger aptamer molecules inside the nanoparticles providing protection against intracellular degradation. We tested the ability of the AptaNPs to measure the adenine-nucleotide content in yeast cells. Our results successfully demonstrate the potential for monitoring any metabolite of interest in living cells by selecting specific aptamers and embedding them in nanoparticles.

Porphyrin-nanosensor conjugates. New tools for the measurement of intracellular response to reactive oxygen species

Reactive oxygen species (ROS) have for some time been implicated in the onset and progression of medical conditions including cancer, ageing, heart disease and Alzheimer's disease. Recently, it has been postulated that ROS play a much more subtle role in intracellular signalling mechanisms as second messengers. Given the importance of these species in influencing cellular processes, it is surprising that tools for studying intracellular levels of ROS are extremely limited and devices for studying the cells' response to internally generated ROS are virtually non-existent. In order to study the response of cells to intracellular ROS we have designed a nano-scale device that can both generate ROS and simultaneously monitor the cells' reaction as a function of changes in the important signalling ion, calcium. Here we report the synthesis, characterisation, and calibration of a new ROS nano-probe and demonstrate its ability to detect cellular response to elevated levels of intracellular ROS.

Nanoencapsulation method for high selectivity sensing of hydrogen peroxide inside live cells

Reactive oxygen species (ROS) are ubiquitous in life and death processes of cells (Finkel, T.; Holbrook, N. J. Nature 2000, 408 (6809), 239-247), with a major role played by the most stable ROS, hydrogen peroxide (H(2)O(2)). However, the study of H(2)O(2) in live cells has been hampered by the absence of selective probes. Described here is a novel nanoprobe ("nanoPEBBLE") with dramatically improved H(2)O(2) selectivity. The traditional molecular probe, 2',7'-dichlorofluorescin (DCFH), which is also sensitive to most other ROS, was empowered with high selectivity by a nanomatrix that blocks the interference from all other ROS (hydroxyl radical, superoxide, nitric oxide, peroxynitrite, hypochlorous acid, and alkylperoxyl radical), as well as from enzymes such as peroxidases. The blocking is based on the combination of multiple exclusion principles: time barrier, hydrophobic energy barrier, and size barrier. However, H(2)O(2) sensitivity is maintained down to low nanomolar concentrations. The surface of the nanoprobe was engineered to address biological applications, and the power of this new nanoPEBBLE is demonstrated by its use on RAW264.7 murine macrophages. These nanoprobes may provide a powerful chemical detection/imaging tool for investigating biological mechanisms related to H(2)O(2) or other species, with high spatial and temporal resolution.

Investigation on binding of nitric oxide to horseradish peroxidase by absorption spectrometry

Binding of nitric oxide to horseradish peroxidase (HRP) has been investigated by absorption spectrometry in 0.2M anaerobic phosphate buffer solution (pH 7.4). Based on this binding equilibrium, a model equation for evaluating the binding constant of nitric oxide to HRP is developed and the binding constant is calculated to be (1.55+/-0.06)x10(4)M(-1), indicating that HRP can form a stable complex with nitric oxide. The type of inhibition by nitric oxide is validated on the basis of studying initial reaction rates of HRP-catalyzed oxidation of guaiacol in the presence of hydrogen peroxide and nitric oxide. The inhibition mechanism is found to follow an apparent non-competitive inhibition by Lineweaver-Burk method. Based on this kinetic mechanism, the binding constant is also calculated to be (5.22+/-0.06)x10(4)M(-1). The values of the binding constant determined by the two methods are almost identical. The non-competitive inhibition model is also applicable to studying the effect of nitric oxide on other metalloenzymes, which catalyze the two-substrate reaction with the "ping-pong" mechanism.

Nanoparticle PEBBLE sensors in live cells and in vivo

Nanoparticle sensors have been developed for real-time imaging and dynamic monitoring, both in live cells and in vivo, of molecular and ionic components, constructs, forces, and dynamics observed during biological, chemical, and physical processes. With their biocompatible small size and inert matrix, nanoparticle sensors have been successfully applied to noninvasive real-time measurements of analytes and fields in cells and in rodents, with spatial, temporal, physical, and chemical resolution. This review describes the diverse designs of nanoparticle sensors for ions and small molecules, physical fields, and biological features, as well as the characterization, properties, and applications of these nanosensors to in vitro and in vivo measurements. Their floating as well as localization abilities in biological media are captured by the acronym PEBBLE: photonic explorer for bioanalysis with biologically localized embedding.

Silver nanocoral structures on electrodes: a suitable platform for protein-based bioelectronic devices

We report a simple strategy for constructing silver coral-like nanostructures on graphite electrodes suitable for bioelectronic applications. The nanocorals are conductive, have dimensions adequate for high protein loading, and are remarkably stable. They also provide a strong Raman surface enhancement that allows for in situ structural characterization of the immobilized proteins. The potential of the Ag nanocoral electrodes is exemplified by the construction and characterization of a hydrogen peroxide amperometric sensor based on cytochrome c.