Analysis of plasma protein adsorption onto polystyrene particles by two-dimensional electrophoresis: comparison of sample application and isoelectric focusing techniques

Nanoparticle-protein corona complex: understanding multiple interactions between environmental factors, corona formation, and biological activity

The surfaces of pristine nanoparticles become rapidly coated by proteins in biological fluids, forming the so-called protein corona. The corona modifies key physicochemical characteristics of nanoparticle surfaces that modulate its biological and pharmacokinetic activity, biodistribution, and safety. In the two decades since the protein corona was identified, the importance of nanoparticles surface properties in regulating biological responses have been recognized. However, there is still a lack of clarity about the relationships between physiological conditions and corona composition over time, and how this controls biological activities/interactions. Here we review recent progress in characterizing the structure and composition of protein corona as a function of biological fluid and time. We summarize the influence of nanoparticle characteristics on protein corona composition and discuss the relevance of protein corona to the biological activity and fate of nanoparticles. The aim is to provide a critical summary of the key factors that affect protein corona formation (e.g. characteristics of nanoparticles and biological environment) and how the corona modulates biological activity, cellular uptake, biodistribution, and drug delivery. In addition to a discussion on the importance of the characterization of protein corona adsorbed on nanoparticle surfaces under conditions that mimic relevant physiological environment, we discuss the unresolved technical issues related to the characterization of nanoparticle-protein corona complexes during their journey in the body. Lastly, the paper offers a perspective on how the existing nanomaterial toxicity data obtained from in vitro studies should be reconsidered in the light of the presence of a protein corona, and how recent advances in fields, such as proteomics and machine learning can be integrated into the quantitative analysis of protein corona components.

Isolation methods for particle protein corona complexes from protein-rich matrices

Background: Nanoparticles become rapidly encased by a protein layer when they are in contact with biological fluids. This protein shell is called a corona. The composition of the corona has a strong influence on the surface properties of the nanoparticles. It can affect their cellular interactions, uptake and signaling properties. For this reason, protein coronae are investigated frequently as an important part of particle characterization. Main body of the abstract: The protein corona can be analyzed by different methods, which have their individual advantages and challenges. The separation techniques to isolate corona-bound particles from the surrounding matrices include centrifugation, magnetism and chromatographic methods. Different organic matrices, such as blood, blood serum, plasma or different complex protein mixtures, are used and the approaches vary in parameters such as time, concentration and temperature. Depending on the investigated particle type, the choice of separation method can be crucial for the subsequent results. In addition, it is important to include suitable controls to avoid misinterpretation and false-positive or false-negative results, thus allowing the achievement of a valuable protein corona analysis result. Conclusion: Protein corona studies are an important part of particle characterization in biological matrices. This review gives a comparative overview about separation techniques, experimental parameters and challenges which occur during the investigation of the protein coronae of different particle types.

Protein Adsorption Patterns and Analysis on IV Nanoemulsions-The Key Factor Determining the Organ Distribution

Intravenous nanoemulsions have been on the market for parenteral nutrition since the 1950s; meanwhile, they have also been used successfully for IV drug delivery. To be well tolerable, the emulsions should avoid uptake by the MPS cells of the body; for drug delivery, they should be target-specific. The organ distribution is determined by the proteins adsorbing them after injection from the blood (protein adsorption pattern), typically analyzed by two-dimensional polyacrylamide gel electrophoresis, 2-D PAGE. The article reviews the 2-D PAGE method, the analytical problems to be faced and the knowledge available on how the composition of emulsions affects the protein adsorption patterns, e.g., the composition of the oil phase, stabilizer layer and drug incorporation into the interface or oil core. Data were re-evaluated and compared, and the implications for the in vivo distribution are discussed. Major results are that the interfacial composition of the stabilizer layer is the main determining factor and that this composition can be modulated by simple processes. Drug incorporation affects the pattern depending on the localization of the drug (oil core versus interface). The data situation regarding in vivo effects is very limited; mainly, it has to be referred to in the in vivo data of polymeric nanoparticles. As a conclusion, determination of the protein adsorption patterns can accelerate IV nanoemulsion formulation development regarding optimized organ distribution and related pharmacokinetics.

Biomolecular coronas provide the biological identity of nanosized materials

The search for understanding the interactions of nanosized materials with living organisms is leading to the rapid development of key applications, including improved drug delivery by targeting nanoparticles, and resolution of the potential threat of nanotechnological devices to organisms and the environment. Unless they are specifically designed to avoid it, nanoparticles in contact with biological fluids are rapidly covered by a selected group of biomolecules to form a corona that interacts with biological systems. Here we review the basic concept of the nanoparticle corona and its structure and composition, and highlight how the properties of the corona may be linked to its biological impacts. We conclude with a critical assessment of the key problems that need to be resolved in the near future.

A comparison of covalent immobilization and physical adsorption of a cellulase enzyme mixture

This paper reports the first use of a linker-free covalent approach for immobilizing an enzyme mixture. Adsorption from a mixture is difficult to control due to varying kinetics of adsorption, variations in the degree of unfolding and competitive binding effects. We show that surface activation by plasma immersion ion implantation (PIII) produces a mildly hydrophilic surface that covalently couples to protein molecules and avoids these issues, allowing the attachment of a uniform monolayer from a cellulase enzyme mixture. Atomic force microscopy (AFM) showed that the surface layer of the physically adsorbed cellulase layer on the mildly hydrophobic surface (without PIII) consisted of aggregated enzymes that changed conformation with incubation time. The evolution observed is consistent with the existence of transient complexes previously postulated to explain the long time constants for competitive displacement effects in adsorption from enzyme mixtures. AFM indicated that the covalently coupled bound layer to the PIII-treated surface consisted of a stable monolayer without enzyme aggregates, and became a double layer at longer incubation times. Light scattering analysis showed no indication of aggregates in the solution at room temperature, which indicates that the surface without PIII-treatment induced enzyme aggregation. A model for the attachment process of a protein mixture that includes the adsorption kinetics for both surfaces is presented.

Lipid–drug conjugate nanoparticles of the hydrophilic drug diminazene—cytotoxicity testing and mouse serum adsorption

Sleeping sickness is a widely distributed disease in great parts of Africa. It is caused by Trypanosoma brucei gambiense and rhodiense, transmitted by the Tse-Tse fly. After a hemolymphatic stage, the parasites enter the central nervous system where they cannot be reached by hydrophilic drugs. To potentially deliver the hydrophilic antitrypanosomal drug diminazene diaceturate to the brain of infected mice, the drug was formulated as lipid-drug conjugate (LDC) nanoparticles (NP) by combination with stearic- (SA) and oleic acid (OA). To estimate the in vivo compatibility, the particles were incubated with human granulocytes. Because as potential delivery mechanism the absorption of specific serum proteins (ApoE, Apo AI and Apo AIV) was found to be responsible for the delivery of nanoparticles to the brain, demonstrated using PBCA nanoparticles coated with polysorbate 80 (LDL uptake mechanism) the nanoparticles were incubated with mouse serum and the adsorption pattern was determined using the 2-D PAGE technique. As a result of this study, the cytotoxic potential was shown to decrease when diminazene is part of the particle matrix compared to pure fatty acid nanoparticles and the mouse serum protein adsorption pattern differs from the samples studied earlier in human serum. Especially, the fact concerning Apo-E that could be detected when the particles were incubated in human serum is absent after the mouse serum incubation, potentially, is a critical point for the delivery via the LDL-uptake mechanism but the data demonstrate that LDC nanoparticles, with 33% (wt/wt) drug loading capacity possess the potential to act as a delivery system for hydrophilic drugs like diminazene diaceturate and that further studies have to demonstrate the usability as a brain delivery system.

Functional groups on polystyrene model nanoparticles: influence on protein adsorption

The surface characteristics of intravenously administered particulate drug carriers decisively influence the protein adsorption that is regarded as a key factor for the in vivo fate of the carriers. Latex nanoparticles were synthesized to study the influence of different basic and acidic functional groups on particulate surfaces on the protein adsorption from human serum. The protein mass adsorbed to the particles was assessed by BCA protein assay, the protein adsorption patterns were analyzed by two-dimensional electrophoresis. Considerable differences in the protein adsorption with regard to preferential adsorbed proteins were detectable for the different functional groups. Possible correlations between the surface characteristics and the protein adsorption are shown and discussed. The knowledge concerning the interactions of proteins and nanoparticles can be used for a rational development of particulate drug carriers and can also be useful for an optimized design of medical devices, e.g., hemodialysis membranes or implants.

Interaction of bronchoalveolar lavage fluid with polyplexes and lipoplexes: analysing the role of proteins and glycoproteins

BACKGROUND

Plasmid DNA complexed with cationic lipids (lipoplexes) or cationic polymers (polyplexes) has been used for gene transfer into the lung. Topical gene administration of lipoplexes or polyplexes into the lung after intratracheal instillation or aerosolisation could cause interaction of the complexes with extracellular substances of the airway surface liquid (ASL). These extracellular interactions might be causal for the observed inefficient transfection rate in vivo after topical administration. Therefore, we studied the impact of bronchoalveolar lavage fluid (BALF) on reporter gene expression mediated by non-viral gene vectors. BALF was considered as a model system to mimic possible interactions of the gene vectors with the ASL.

METHODS

BALF was taken from 15 patients who underwent diagnostic bronchoscopy. Lipoplexes and polyplexes were incubated with increasing concentrations of BALF and major components of the BALF such as albumin, mucin and alpha(1)-glycoprotein, as a representative of glycosylated proteins. As cationic polymers, we tested dendrimers (fractured PAMAM) and polyethylenimine 25 kDa (PEI) and, as cationic liposomes, we used Lipofect-AMINE. The effect of BALF on polyplexes and lipoplexes was analysed by transfection experiments, fluorescence-quenching assay, 2-D-gel electrophoresis, SDS-PAGE, DNAse protection assay, size and zeta-potential measurements.

RESULTS

BALF inhibited polyplex- and lipoplex-mediated gene transfer. Analysing components of BALF, we found that dendrimer-mediated gene transfer was not inhibited by any specific component. PEI-mediated gene transfer was dose-dependently inhibited by alpha(1)-glycoprotein, slightly inhibited by mucin, but not inhibited in the presence of albumin. Lipoplex-mediated gene transfer was inhibited by mucin at higher concentrations and by albumin, but not by alpha(1)-glycoprotein. 2-D-gel electrophoresis revealed that proteins of the BALF were adsorbed more intensively to lipoplexes than to polyplexes. In addition, mucin and alpha(1)-glycoprotein also adsorbed more intensively to lipoplexes than to polyplexes. Adsorption of BALF components led to a decrease in the positive zeta-potential of lipoplexes and led to a negative zeta-potential of polyplexes. Complement cleavage fragment C3 beta, and in the case of lipoplexes also the C3 alpha fragment, were found among the proteins opsonised on gene vectors.

CONCLUSIONS

Our study shows that BALF contains inhibitory components for non-viral gene transfer. We could not detect a specific inhibitory component, but inhibition was most likely due to the change in the surface charge of the gene vectors. Interestingly, there is evidence for complement activation when the route of pulmonary gene vector administration is chosen. Consequently, shielding of gene vectors to circumvent interaction with the ASL environment should be a focus for pulmonary administration in the future.

Influence of surface charge density on protein adsorption on polymeric nanoparticles: analysis by two-dimensional electrophoresis

Plasma protein adsorption is regarded as a key factor for the in vivo organ distribution of intravenously administered colloidal drug carriers, and strongly depends on their surface characteristics, e.g. surface hydrophobicity or charge. A range of polymeric nanoparticles with a steep variation of the surface charge density was synthesized as model drug carriers. Physicochemical parameters, i.e. particle size, surface charge density, hydrophobicity and surface topography were determined. Two-dimensional electrophoresis (2-DE) was employed for determination of particle interactions with human plasma proteins. Increasing surface charge density showed an increase in plasma protein adsorption, but did not show differences in the detected protein species. For the first time it was possible to show plasma protein adsorption patterns on a range of nanoparticles with variation of only one parameter, i.e. the charge, while size and surface hydrophobicity remain practically unchanged. The knowledge about the interactions of proteins with particulate surfaces can be exploited for the future controlled design of colloidal drug carriers and possibly in the controlled creation of biocompatible surfaces of other devices that come into contact with proteins (e.g. microparticles and implants).

Comparison of protein adsorption patterns onto differently charged hydrophilic superparamagnetic iron oxide particles obtained in vitro and ex vivo

Protein adsorption patterns of superparamagnetic iron oxides (SPIO) were evaluated by two-dimensional electrophoresis (2-DE) after in vitro incubation of the particles in plasma or serum. SPIO particles having positive (MKK 1211), negative (MKA 1211), or neutral (MKG 1411) charge were used. Protein adsorption patterns of different charged SPIO particles acquired in vitro and recollected 5 min after intravenous injection into rats (ex vivo) were compared. For the uncharged MKG 1411 particles, the differences of protein adsorption patterns were negligible and only minor differences were found for the negatively charged MKA 1211 and positively charged MKK 1211 particles. A good correlation between in vitro and ex vivo data could be shown. For the evaluation of protein adsorption patterns of SPIO particles determining organ distribution and allowing estimation of site-specific delivery (drug targeting), the currently used protocol for 2-DE analysis could be confirmed.