Protein nanoparticles: cellular uptake, intracellular distribution, biodegradation and induction of cytokine gene expression

Self-assembling amyloid-like nanostructures from SARS-CoV-2 S1, S2, RBD and N recombinant proteins

Self-assembling nanoparticles (saNP) and nanofibers were found in the recombinant coronavirus SARS-CoV-2 S1, S2, RBD and N proteins purified by affinity chromatography using Ni Sepharose. Scanning electron (SEM), atomic force (AFM) microscopy on mica or graphite surface and in liquid as well as dynamic light scattering (DLS) revealed nanostructures of various sizes. AFM in liquid cell without drying on the surface showed mean height of S1 saNP 80.03 nm, polydispersity index (PDI) 0.006; for S2 saNP mean height 93.32 nm, PDI = 0.008; for N saNP mean height 16.71 nm, PDI = 0.99; for RBD saNP mean height 16.25 nm, PDI = 0.55. Ratios between the height and radius of each saNP in the range 0.1-0.5 suggested solid protein NP but not vesicles with internal empty spaces. The solid but not empty structures of the protein saNP were also confirmed by STEM after treatment of saNP with the standard contrasting agent uranyl acetate. The saNP remained stable after multiple freeze-thaw cycles in water and hyperosmotic solutions for 2 years at -20 °C. Receptor-mediated penetration of the SARS-CoV-2 S1 and RBD saNP in the African green mokey kidney Vero cells with the specific receptors for β-coronavirus reproduction was more efficient compared to unspecific endocytosis into MDCK cells without the specific receptors. Amyloid-like structures were revealed in the SARS-CoV-2 S1, S2, RBD and N saNP by means of their interaction with Thioflavin T and Congo Red dyes. Taken together, spontaneous formation of the amyloid-like self-assembling nanostructures due to the internal affinity of the SARS-CoV-2 virion proteins might induce proteinopathy in patients, including conformational neurodegenerative diseases, change stability of vaccines and diagnostic systems.

Biodistribution of Fluorescent Albumin Nanoparticles among Organs of Laboratory Animals after Intranasal and Peroral Administration

Natural, environmental and engineered nanoparticles (NP) penetrate into cells by endocytosis and induce innate immunity. The behaviour of the nanomaterials both in vitro and in vivo should be assessed. Our goal was to study protein NP stability in biological fluids and distribution in organs of animals after intranasal and oral administration. Bovine serum albumin (BSA) was labelled with the fluorescent dye RhoB and NP were fabricated by nanoprecipitation. The fluorescent protein NPwere administered intranasally and orally in laboratory-outbred mice ICR and rabbits. RhoB-BSA NP distribution in organs was detected using spectrofluorometry and fluorescent microscopy. Innate immunity was evaluated using reverse transcription with random hexanucleotide primer and subsequent real-time PCR with specific fluorescent hydrolysis probes. The labelled BSA NP were shown to remain stable in blood sera and nasopharyngeal swabs for 5 days at +37 °C. In vivo the maximal accumulation was found in the brain in 2 days posttreatment without prevalent accumulation in olfactory bulbs. For the intestine, heart and liver, the BSA NP accumulation was similar in 1 and 2 days, whereas for kidney samples even decreased after 1 day. Both intranasal and peroral administration of RhoB-BSA NP did not induce innate immunity. Thus, after intranasal or oral instillation RhoB-BSA NP were found mainly in the brain and intestine without interferon gene expression.

Formation of Protein Nanoparticles in Microdroplet Flow Reactors

Nanoparticles are increasingly being used for biological applications, such as drug delivery and gene transfection. Different biological and bioinspired building blocks have been used for generating such particles, including lipids and synthetic polymers. Proteins are an attractive class of material for such applications due to their excellent biocompatibility, low immunogenicity, and self-assembly characteristics. Stable, controllable, and homogeneous formation of protein nanoparticles, which is key to successfully delivering cargo intracellularly, has been challenging to achieve using conventional methods. In order to address this issue, we employed droplet microfluidics and utilized the characteristic of rapid and continuous mixing within microdroplets in order to produce highly monodisperse protein nanoparticles. We exploit the naturally occurring vortex flows within microdroplets to prevent nanoparticle aggregation following nucleation, resulting in systematic control over the particle size and monodispersity. Through combination of simulation and experiment, we find that the internal vortex velocity within microdroplets determines the uniformity of the protein nanoparticles, and by varying parameters such as protein concentration and flow rates, we are able to finely tune nanoparticle dimensional properties. Finally, we show that our nanoparticles are highly biocompatible with HEK-293 cells, and through confocal microscopy, we determine that the nanoparticles fully enter into the cell with almost all cells containing them. Due to the high throughput of the method of production and the level of control afforded, we believe that the approach described in this study for generating monodisperse protein-based nanoparticles has the potential for intracellular drug delivery or for gene transfection in the future.

Stable Enzymatic Nanoparticles from Nucleases, Proteases, Lipase and Antioxidant Proteins with Substrate-Binding and Catalytic Properties

Limited membrane permeability and biodegradation hamper the intracellular delivery of the free natural or recombinant enzymes necessary for compensatory therapy. Nanoparticles (NP) provide relative protein stability and unspecific endocytosis-mediated cellular uptake. Our objective was the fabrication of NP from 7 biomedicine-relevant enzymes, including DNase I, RNase A, trypsin, chymotrypsin, catalase, horseradish peroxidase (HRP) and lipase, the analysis of their conformation stability and enzymatic activity as well as possible toxicity for eukaryotic cells. The enzymes were dissolved in fluoroalcohol and mixed with 40% ethanol as an anti-solvent with subsequent alcohol evaporation at high temperature and low pressure. The shapes and sizes of NP were determined by scanning electron microscopy (SEM), atomic force microscopy (AFM) and dynamic light scattering (DLS). Enzyme conformations in solutions and in NP were compared using circular dichroism (CD) spectroscopy. The activity of the enzymes was assayed with specific substrates. The cytotoxicity of the enzymatic NP (ENP) was studied by microscopic observations and by using an MTT test. Water-insoluble ENP of different shapes and sizes in a range 50-300 nm consisting of 7 enzymes remained stable for 1 year at +4 °C without any cross-linking. CD spectroscopy of the ENP permitted us to reveal changes in proportions of α-helixes, β-turns and random coils in comparison with fresh enzyme solutions in water. Despite the minor conformation changes of the proteins in the ENP, the enzymes retained their substrate-binding and catalytic properties. Among the studied bioactive ENP, only DNase NP were highly toxic for 3 cell lines with granulation in 1 day posttreatment, whereas other NP were less toxic (if any). Taken together, the enzymes in the stable ENP retained their catalytic activity and might be used for intracellular delivery.

Activation of Neutrophils by Mucin–Vaterite Microparticles

Nano- and microparticles enter the body through the respiratory airways and the digestive system, or form as biominerals in the gall bladder, salivary glands, urinary bladder, kidney, or diabetic pancreas. Calcium, magnesium, and phosphate ions can precipitate from biological fluids in the presence of mucin as hybrid nanoparticles. Calcium carbonate nanocrystallites also trap mucin and are assembled into hybrid microparticles. Both mucin and calcium carbonate polymorphs (calcite, aragonite, and vaterite) are known to be components of such biominerals as gallstones which provoke inflammatory reactions. Our study was aimed at evaluation of neutrophil activation by hybrid vaterite–mucin microparticles (CCM). Vaterite microparticles (CC) and CCM were prepared under standard conditions. The diameter of CC and CCM was 3.3 ± 0.8 µm and 5.8 ± 0.7 µm, with ƺ-potentials of −1 ± 1 mV and −7 ± 1 mV, respectively. CC microparticles injured less than 2% of erythrocytes in 2 h at 1.5 mg mL−1, and no hemolysis was detected with CCM; this let us exclude direct damage of cellular membranes by microparticles. Activation of neutrophils was analyzed by luminol- and lucigenin-dependent chemiluminescence (Lum-CL and Luc-CL), by cytokine gene expression (IL-6, IL-8, IL-10) and release (IL-1β, IL-6, IL-8, IL-10, TNF-α), and by light microscopy of stained smears. There was a 10-fold and higher increase in the amplitude of Lum-CL and Luc-CL after stimulation of neutrophils with CCM relative to CC. Adsorption of mucin onto prefabricated CC microparticles also contributed to activation of neutrophil CL, unlike mucin adsorption onto yeast cell walls (zymosan); adsorbed mucin partially suppressed zymosan-stimulated production of oxidants by neutrophils. Preliminary treatment of CCM with 0.1–10 mM NaOCl decreased subsequent activation of Lum-CL and Luc-CL of neutrophils depending on the used NaOCl concentration, presumably because of the surface mucin oxidation. Based on the results of ELISA, incubation of neutrophils with CCM downregulated IL-6 production but upregulated that of IL-8. IL-6 and IL-8 gene expression in neutrophils was not affected by CC or CCM according to RT2-PCR data, which means that post-translational regulation was involved. Light microscopy revealed adhesion of CC and CCM microparticles onto the neutrophils; CCM increased neutrophil aggregation with a tendency to form neutrophil extracellular traps (NETs). We came to the conclusion that the main features of neutrophil reaction to mucin–vaterite hybrid microparticles are increased oxidant production, cell aggregation, and NET-like structure formation, but without significant cytokine release (except for IL-8). This effect of mucin is not anion-specific since particles of powdered kidney stone (mainly calcium oxalate) in the present study or calcium phosphate nanowires in our previous report also activated Lum-CL and Luc-CL response of neutrophils after mucin sorption.

Stimulation Of Neutrophil Oxidative Burst By Calcium Phosphate Particles With Adsorbed Mucin

Objective — Mucin can promote formation of gallstones via precipitation with calcium phosphate. The proinflammatory effect of mucin-coated particles is still unclear, and our aim was to study the role of mucin sorption in activation of neutrophil respiratory burst. Material and Methods — Polydisperse calcium phosphate nanowires (CP) were prepared from hot gelatin solution and according to scanning electron microscopy (SEM) had the length 1-10 μm and thickness 50-450 nm. CP were incubated in mucin or human serum albumin (HSA) giving CP-Muc and CP-HSA. Their hemolytic activity towards human erythrocytes was assayed, and neutrophil lucigenin- and luminol- chemiluminescence (Luc-CL and Lum-CL) response to CP, CP-HSA and CP-Muc was measured. Cytokine RNA was detected in neutrophils by means of reverse transcription with subsequent real-time PCR. Cytokines (IL-1β, IL-6, IL-8, IL-10) were assessed in cell medium by ELISA. Results and Conclusion — Hemolytic activity of CP was 3.0±0.5%, mucin sorption (0.019 mg/mg) reduced it to 0.24±0.04% (p<0.05) as well as HSA. CP and CP-HSA stimulated neutrophil Lum-CL and Luc-Cl by 2-3 times vs. spontaneous values while for CP-Muc the effect was 10-fold and higher. No increased cytokine gene expression or cytokine secretion was detected after 1h incubation of neutrophils with samples. Obviously, sorption of mucin but not that of HSA stimulated generation of reactive oxygen and halogen species with no increase in cytokine production. Thus, the mucin-coated CP has the potential to contribute to gallstone-associated cholecystitis via oxidative damage of mucosa and epithelium.