Adsorption/Desorption Transition of Recombinant Human Neurotrophin 4: Physicochemical Characterization

A mica filter enables bacterial enrichment from large volumes of natural water for sensitive monitoring of pathogens by nanopore sequencing

Nanopore sequencing is extremely promising for the high-throughput detection of pathogenic bacteria in natural water; these bacteria may be transmitted to humans and cause waterborne infectious diseases. However, the concentration of pathogenic bacteria in natural water is too low to be detected directly by nanopore sequencing. Herein, we developed a mica filter to enrich over 85% of bacteria from > 10 L of natural water in 100 min, which led to a 102-fold improvement in the assay limits of the MinION sequencer for assessing pathogenic bacteria. Correspondingly, the sequencing time of S. Typhi detection at a concentration as low as 105 CFU/L was reduced from traditional 48 h to 3 h. The bacterial adsorption followed pseudo-first-order kinetics and the successful adsorption of bacteria to the mica filter was confirmed by scanning electron microscopy and Fourier infrared spectroscopy et al. The mica filter remained applicable to a range of water samples whose quality parameters were within the EPA standard limits for freshwater water. The mica filter is thus an effective tool for the sensitive and rapid monitoring of pathogenic bacteria by nanopore sequencing, which can provide timely alerts for waterborne transmission events.

In vitro and in vivo characterization of human serum albumin-based PEGylated nanoparticles for BDNF and NT3 codelivery

The utilization of neurotrophins in medicine shows significant potential for addressing neurodegenerative conditions, such as age-related macular degeneration (AMD). However, the therapeutic use of neurotrophins has been restricted due to their short half-life. Here, we aimed to synthesize PEGylated nanoparticles based on electrostatic-driven interactions between human serum albumin (HSA), a carrier for adsorption; neurotrophin-3 (NT3); and brain-derived neurotrophic factor (BDNF). Electrophoretic (ELS) and multi-angle dynamic light scattering (MADLS) revealed that the PEGylated HSA-NT3-BDNF nanoparticles ranged from 10 to 430 nm in diameter and exhibited a low polydispersity index (<0.4) and a zeta potential of -8 mV. Based on microscale thermophoresis (MST), the estimated dissociation constant (Kd) from the HSA molecule of BDNF was 1.6 μM, and the Kd of NT3 was 732 μM. The nanoparticles were nontoxic toward ARPE-19 and L-929 cells in vitro and efficiently delivered BDNF and NT3. Based on the biodistribution of neurotrophins after intravitreal injection into BALB/c mice, both nanoparticles were gradually released in the mouse vitreous body within 28 days. PEGylated HSA-NT3-BDNF nanoparticles stabilize neurotrophins and maintain this characteristic in vivo. Thus, given the simplicity of the system, the nanoparticles may enhance the treatment of a variety of neurological disorders in the future.

The Impact of Serum Protein Adsorption on PEGylated NT3-BDNF Nanoparticles-Distribution, Protein Release, and Cytotoxicity in a Human Retinal Pigmented Epithelial Cell Model

The adsorption of biomolecules on nanoparticles' surface ultimately depends on the intermolecular forces, which dictate the mutual interaction transforming their physical, chemical, and biological characteristics. Therefore, a better understanding of the adsorption of serum proteins and their impact on nanoparticle physicochemical properties is of utmost importance for developing nanoparticle-based therapies. We investigated the interactions between potentially therapeutic proteins, neurotrophin 3 (NT3), brain-derived neurotrophic factor (BDNF), and polyethylene glycol (PEG), in a cell-free system and a retinal pigmented epithelium cell line (ARPE-19). The variance in the physicochemical properties of PEGylated NT3-BDNF nanoparticles (NPs) in serum-abundant and serum-free systems was studied using transmission electron microscopy, atomic force microscopy, multi-angle dynamic, and electrophoretic light scattering. Next, we compared the cellular response of ARPE-19 cells after exposure to PEGylated NT3-BDNF NPs in either a serum-free or complex serum environment by investigating protein release and cell cytotoxicity using ultracentrifuge, fluorescence spectroscopy, and confocal microscopy. After serum exposure, the decrease in the aggregation of PEGylated NT3-BDNF NPs was accompanied by increased cell viability and BDNF/NT3 in vitro release. In contrast, in a serum-free environment, the appearance of positively charged NPs with hydrodynamic diameters up to 900 nm correlated with higher cytotoxicity and limited BDNF/NT3 release into the cell culture media. This work provides new insights into the role of protein corona when considering the PEGylated nano-bio interface with implications for cytotoxicity, NPs' distribution, and BDNF and NT3 release profiles in the in vitro setting.

Biocompatible Macroion/Growth Factor Assemblies for Medical Applications

Growth factors are a class of proteins that play a role in the proliferation (the increase in the number of cells resulting from cell division) and differentiation (when a cell undergoes changes in gene expression becoming a more specific type of cell) of cells. They can have both positive (accelerating the normal healing process) and negative effects (causing cancer) on disease progression and have potential applications in gene therapy and wound healing. However, their short half-life, low stability, and susceptibility to degradation by enzymes at body temperature make them easily degradable in vivo. To improve their effectiveness and stability, growth factors require carriers for delivery that protect them from heat, pH changes, and proteolysis. These carriers should also be able to deliver the growth factors to their intended destination. This review focuses on the current scientific literature concerning the physicochemical properties (such as biocompatibility, high affinity for binding growth factors, improved bioactivity and stability of the growth factors, protection from heat, pH changes or appropriate electric charge for growth factor attachment via electrostatic interactions) of macroions, growth factors, and macroion-growth factor assemblies, as well as their potential uses in medicine (e.g., diabetic wound healing, tissue regeneration, and cancer therapy). Specific attention is given to three types of growth factors: vascular endothelial growth factors, human fibroblast growth factors, and neurotrophins, as well as selected biocompatible synthetic macroions (obtained through standard polymerization techniques) and polysaccharides (natural macroions composed of repeating monomeric units of monosaccharides). Understanding the mechanisms by which growth factors bind to potential carriers could lead to more effective delivery methods for these proteins, which are of significant interest in the diagnosis and treatment of neurodegenerative and civilization diseases, as well as in the healing of chronic wounds.

Molecular Mechanistic Insights into the Ionic-Strength-Controlled Interfacial Behavior of Proteins on a TiO2 Surface

By adjusting the ionic strengths through changing the concentration of the buffer ions, the molecular force and the interfacial behavior of cytochrome c (Cyt c) and TiO₂ are systematically studied. The molecular forces determined by combining the adhesion force and adsorption capacity are found to first increase and then decrease with the increasing ionic strength, with a peak obtained at an ionic strength between 0.8 and 1.0 M. The mechanism is explained based on the dissociation and hydration of ions at the interfaces, where the buffer ions could be completely dissociated at ionic strengths of <0.8 M but were partially associated when the ionic strength increased to a high value (>1.2 M), and the strongest hydration was observed around 1.0 M. The hydrodynamic size and the zeta potential value representing the effective contact area and protein stability of the Cyt c molecule, respectively, are also affected by the hydration and are proportional to the molecular forces. The interfacial behavior of Cyt c molecules on the TiO₂ surface, determined through surface-enhanced Raman scattering (SERS), is extremely affected by the ionic strength of the solution as the ion dissociation and hydration also increase the electron transfer ability, where the best SERS enhancement is observed at the ionic strength of around 1.0 M, corresponding to the largest molecular force. Our results provide a detailed understanding at the nanoscale on controlling the protein interfacial behavior with solid surfaces, adjusted by the buffer ions.

The role of the electrokinetic charge of neurotrophis-based nanocarriers: protein distribution, toxicity, and oxidative stress in in vitro setting

Background

The rational chemical design of nanoparticles can be readily controlled and optimized by quantitatively studying protein adsorption at variously charged polymer carriers, determining their fate in biological fluids. We manufactured brain-derived neurotrophic factor (BDNF) -based electrostatic nanocomplexes with a different type of dendrimer core (anionic or cationic), encapsulated or not in polyethylene glycol (PEG), and studied their physicochemical properties and behavior in a biological setting. We investigated whether the electrokinetic charge of dendrimer core influences BDNF loading and desorption from the nanoparticle and serves as a determinant of nanoparticles’ behavior in in vitro setting, influencing mitochondrial dysfunction, lipid peroxidation, and general nanoparticles’ cellular toxicity.

Results

We found that the electrokinetic charge of the dendrimer core influences nanoparticles in terms of BDNF release profile from their surfaces and their effect on cell viability, mitochondrial membrane potential, cell phenotype, and induction of oxidative stress. The electrostatic interaction of positively charged core of nanoparticles with cell membranes increases their cytotoxicity, as well as serious phenotype alterations compared to negatively charged nanoparticles core in neuron-like differentiated human neuroblastoma cells. Moreover, PEG adsorption at nanoparticles with negatively charged core presents a distinct decrease in metabolic cell activity. On the contrary, charge neutralization due to PEG adsorption on the surface of nanoparticles with positively charged core does not reduce their cytotoxicity, makes them less biocompatible with differentiated cells, and presumably shows non-specific toxicity.

Conclusions

The surface charge transformation after adsorption of protein or polyelectrolyte during nanocarriers formulation has an important role not only in designing nanomaterials with potent neuroprotective and neuroregenerative properties but also in applying them in a cellular environment.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00984-4.

The Impact of Physical Exercise on the Circulating Levels of BDNF and NT 4/5: A Review

(1) Background: One mechanism through which physical activity (PA) provides benefits is by triggering activity at a molecular level, where neurotrophins (NTs) are known to play an important role. However, the expression of the circulating levels of neurotrophic factors, brain-derived neurotrophic factor (BDNF) and neurotrophin-4 (NT-4/5), in response to exercise, is not fully understood. Therefore, the aim was to provide an updated overview on the neurotrophin (NT) variation levels of BDNF and NT-4/5 as a consequence of a long-term aerobic exercise intervention, and to understand and describe whether the upregulation of circulating NT levels is a result of neurotrophic factors produced and released from the brain, and/or from neurotrophic secreting peripheral organs. (2) Methods: The articles were collected from PubMed, SPORTDiscus, Web of Science, MEDLINE, and Embase. Data were analyzed through a narrative synthesis. (3) Results: 30 articles studied humans who performed training protocols that ranged from 4 to 48 weeks; 22 articles studied rodents with an intervention period that ranged from 4 to 64 weeks. (4) Conclusions: There is no unanimity between the upregulation of BDNF in humans; conversely, concerning both BDNF and NT-4/5 in animal models, the results are heterogeneous. Whilst BDNF upregulation appears to be in relative agreement, NT-4/5 seems to display contradictory and inconsistent conclusions.

Influence of ion size effects on the electrokinetics of aqueous salt-free colloids in alternating electric fields

Electrokinetics is the science of the physical phenomena appearing at the solid-liquid interface of dispersed particles subjected to external fields. Techniques based on electrokinetic phenomena constitute an important set of tools for the electrical characterization of colloids because of their sensitivity to the properties of particle-solution interfaces. Their rigorous description may require inclusion of the effects of finite size of chemical species in the theoretical models, and, particularly in the case of salt-free (no external salt added) aqueous colloids, also consideration of water dissociation and possible carbon dioxide contamination in the aqueous solution. A new ac electrokinetic model is presented for concentrated salt-free spherical colloids for arbitrary characteristics of the particles and aqueous solution, including finite-size effects of chemical species by appropriate modifications of the chemical reaction equations to include such non-ideal aspects. The numerical solution of the electrokinetic equations in an alternating electric field has also been carried out by using a realistic non-equilibrium scenario accounting for association-dissociation processes in the chemical reactions. The results demonstrate the importance of including finite-size effects in the electrokinetic response of the colloid, mainly at high frequencies of the electric field, and for highly charged colloids. Findings of previous models for pointlike ions or for ideal salt-free colloids including finite ion size effects are recovered with the present model, for the appropriate limiting conditions.

Electrostatic complex of neurotrophin 4 with dendrimer nanoparticles: controlled release of protein in vitro and in vivo

Background: NT4 has been regarded as a promising therapeutic protein for treatment of damaged retinal pigment epithelium cells.

Purpose: Here, we studied physicochemical parameters of an NT4–polyamidoamine (PAMAM) electrostatic complex, which can provide a sustained concentration of protein in intraocular space over an extended period after delivery. Adsorption/desorption of NT4 molecules to/from positively charged PAMAM dendrimers were precisely determined to control the concentration of bounded/unbounded protein molecules, diffusion coefficient, and size of a protein-laden dendrimer structure. We determined kinetics of NT4 desorption in PBS, vitreous, and damaged retina.

Methods: Initially, adsorption of NT4 molecules on PAMAM dendrimers was studied in PBS using dynamic light scattering, electrophoresis, solution depletion, ELISA, and atomic force microscopy. This allowed us precisely to determine desorption of NT4 from nanoparticles under in situ conditions. The maximum coverage of irreversibly adsorbed NT4 determined by ELISA allowed us to devise a robust procedure for preparing stable and well-controlled coverage of NT4 on PAMAM nanoparticles. Thereafter, we studied diffusion of nanospheres containing NT4 molecules by injecting them into vitreous cavities of mice exposed to intravenous injections of sodium iodate and evaluated their intraocular desorption kinetics from drug carriers in vivo.

Results: Our measurements revealed NT4–dendrimer nanoparticles can be used for continuous neurotrophic factor delivery, enhancing its distribution into mouse vitreous, as well as damaged retina over 28 days of postinjury observation.

Conclusion: Understanding of polyvalent neurotrophin interactions with dendrimer nanoparticles might be useful to obtain well-ordered protein layers, targeting future development of drug-delivery systems, especially for neuroprotection of damaged retinal neurons.