Mechanisms of Fibroblast Growth Factor 21 Adsorption on Macroion Layers: Molecular Dynamics Modeling and Kinetic Measurements

Molecular dynamic modeling and various experimental techniques, including multi-angle dynamic light scattering (MADLS), streaming potential, optical waveguide light spectroscopy (OWLS), quartz crystal microbalance with dissipation (QCM), and atomic force microscopy (AFM), were applied to determine the basic physicochemical parameters of fibroblast growth factor 21 in electrolyte solutions. The protein size and shape, cross-section area, dependence of the nominal charge on pH, and isoelectric point of 5.3 were acquired. These data enabled the interpretation of the adsorption kinetics of FGF 21 on bare and macrocation-covered silica investigated by OWLS and QCM. It was confirmed that the protein molecules irreversibly adsorbed on the latter substrate, forming layers with controlled coverage up to 0.8 mg m-2, while their adsorption on bare silica was much smaller. The viability of two cell lines, CHO-K1 and L-929, on both bare and macrocation/FGF 21-covered substrates was also determined. It is postulated that the acquired results can serve as useful reference systems for designing complexes that can extend the half-life of FGF 21 in its active state.

BDNF-loaded PDADMAC-heparin multilayers: a novel approach for neuroblastoma cell study

Biomaterial science has contributed tremendously to developing nanoscale materials for delivering biologically active compounds, enhancing protein stability, and enabling its therapeutic use. This paper presents a process of formation of polyelectrolyte multilayer (PEM) prepared by sequential adsorption of positively charged polydiallyldimethylammonium chloride (PDADMAC) and negatively charged heparin sodium salt (HP), from low polyelectrolyte concentration, on a solid substrate. PEM was further applied as a platform for the adsorption of a brain-derived growth factor (BDNF), which is a protein capable of regulating neuronal cell development. The multilayers containing BDNF were thoroughly characterized by electrokinetic (streaming potential measurements, SPM) and optical (optical waveguide lightmode spectroscopy, OWLS) techniques. It was found that BDNF was significantly adsorbed onto polyelectrolyte multilayers terminated by HP under physiological conditions. We further explore the effect of established PEMs in vitro on the neuroblastoma SH-SY5Y cell line. An enzyme-linked immunosorbent assay (ELISA) confirmed that BDNF was released from multilayers, and the use of the PEMs intensified its cellular uptake. Compared to the control, PEMs with adsorbed BDNF significantly reduced cell viability and mitochondrial membrane polarization to as low as 72% and 58%, respectively. HPLC analysis showed that both PDADMAC-terminated and HP-terminated multilayers have antioxidative properties as they almost by half decreased lipid peroxidation in SH-SY5Y cells. Finally, enhanced formation of spheroid-like, 3D structures was observed by light microscopy. We offer a well-characterized PEM with antioxidant properties acting as a BDNF carrier, stabilizing BDNF and making it more accessible to cells in an inhomogeneous, dynamic, and transient in vitro environment. Described multilayers can be utilized in future biomedical applications, such as boosting the effect of treatment by selective anticancer as adjuvant therapy, and in biomedical research for future development of more precise neurodegenerative disease models, as they enhance cellular 3D structure formation.

Mechanism of Anti-Salmonella Rabbit Immunoglobulin Adsorption on Polymer Particles

The adsorption of anti-Salmonella rabbit immunoglobulin (IgaR) on negatively charged polymer particles leading to the formation of immunolatex was studied using various techniques comprising atomic force microscopy (AFM) and laser Doppler velocimetry (LDV). Initially, the basic physicochemical properties of IgaR molecules and the particles, inter alia their electrophoretic mobilities, the zeta potentials and hydrodynamic diameters, were determined under different ionic strengths and pHs. Applying AFM, single immunoglobulin molecules adsorbed on mica were also imaged, which allowed to determine their size. The adsorption of the IgaR molecules on the particles leading to changes in their electrophoretic mobility was monitored in situ using the LDV method. The obtained results were interpreted applying a general electrokinetic model which yielded quantitative information about the molecule coverage on the particles. The obtained immunolatex was thoroughly characterized with respect to its acid-base properties and its stability upon storage. Notably, the developed procedure demonstrated better efficiency compared to commercially applied methods, characterized by a higher immunoglobulin consumption.

Polysaccharide-based nano-engineered multilayers for controlled cellular adhesion in label-free biosensors

Controlling cellular adhesion is a critical step in the development of biomaterials, and in cell- based biosensing assays. Usually, the adhesivity of cells is tuned by an appropriate biocompatible layer. Here, synthetic poly(diallyldimethylammonium chloride) (PDADMAC), natural chitosan, and heparin (existing in an extracellular matrix) were selected to assembly PDADMAC/heparin and chitosan/heparin films. The physicochemical properties of macroion multilayers were determined by streaming potential measurements (SPM), quartz crystal microbalance (QCM-D), and optical waveguide lightmode spectroscopy (OWLS). The topography of the wet films was imaged using atomic force microscopy (AFM). The adhesion of preosteoblastic cell line MC3T3-E1 on those well-characterized polysaccharide-based multilayers was evaluated using a resonant waveguide grating (RWG) based optical biosensor and digital holographic microscopy. The latter method was engaged to investigate long-term cellular behavior on the fabricated multilayers. (PDADMAC/heparin) films were proved to be the most effective in inducing cellular adhesion. The cell attachment to chitosan/heparin-based multilayers was negligible. It was found that efficient adhesion of the cells occurs onto homogeneous and rigid multilayers (PDADMAC/heparin), whereas the macroion films forming "sponge-like" structures (chitosan/heparin) are less effective, and could be employed when reduced adhesion is needed. Polysaccharide-based multilayers can be considered versatile systems for medical applications. One can postulate that the presented results are relevant not only for modeling studies but also for applied research.

Physicochemical Nature of SARS-CoV-2 Spike Protein Binding to Human Vimentin

Vimentin, a protein that builds part of the cytoskeleton and is involved in many aspects of cellular function, was recently identified as a cell surface attachment site for the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The present study investigated the physicochemical nature of the binding between the SARS-CoV-2 S1 glycoprotein receptor binding domain (S1 RBD) and human vimentin using atomic force microscopy and a quartz crystal microbalance. The molecular interactions of S1 RBD and vimentin proteins were quantified using vimentin monolayers attached to the cleaved mica or a gold microbalance sensor as well as in its native extracellular form present on the live cell surface. The presence of specific interactions between vimentin and S1 RBD was also confirmed using in silico studies. This work provides new evidence that cell-surface vimentin (CSV) functions as a site for SARS-CoV-2 virus attachment and is involved in the pathogenesis of Covid-19, providing a potential target for therapeutic countermeasures.

Kinetics of Immunolatex Deposition at Abiotic Surfaces under Flow Conditions: Towards Quantitative Agglutination Assays

Physicochemical properties of immunolatex, prepared by incubation of negatively charged polystyrene microparticles with polyclonal rabbit IgGs, were determined by a variety of experimental techniques. These comprised dynamic light scattering (DLS), laser Doppler velocimetry (LDV) and atomic force microscopy (AFM). The particle diffusion coefficient, the hydrodynamic diameter, the electrophoretic mobility, the zeta potential and the suspension stability were determined as a function of pH for different ionic strengths. The deposition of the immunolatex on bare and polyallylamine (PAH) functionalized mica was investigated using the microfluidic oblique impinging-jet cell, with an in situ, real-time image analysis module. The particle deposition kinetics was acquired by a direct particle enumeration procedure. The measurements enabled us to determine the range of pH where the specific deposition of the immunolatex on these substrates was absent. We argue that the obtained results have practical significance for conducting efficient flow immunoassays governed by specific antigen/antibody interactions.

SARS-CoV-2 Spike Protein (RBD) Subunit Adsorption at Abiotic Surfaces and Corona Formation at Polymer Particles

The adsorption kinetics of the SARS-CoV-2 spike protein subunit with the receptor binding domain at abiotic surfaces was investigated. A combination of sensitive methods was used such as atomic force microscopy yielding a molecular resolution, a quartz microbalance, and optical waveguide lightmode spectroscopy. The two latter methods yielded in situ information about the protein adsorption kinetics under flow conditions. It was established that at pH 3.5-4 the protein adsorbed on mica and silica surfaces in the form of compact quasi-spherical aggregates with an average size of 14 nm. The maximum coverage of the layers was equal to 3 and 1 mg m^-2 at pH 4 and 7.4, respectively. The experimental data were successfully interpreted in terms of theoretical results derived from modeling. The experiments performed for flat substrates were complemented by investigations of the protein corona formation at polymer particles carried out using in situ laser Doppler velocimetry technique. In this way, the zeta potential of the protein layers was acquired as a function of the coverage. Applying the electrokinetic model, these primary data were converted to the dependence of the subunit zeta potential on pH. It was shown that a complete acid-base characteristic of the layer can be acquired only using nanomolar quantities of the protein.

Chitosan characteristics in electrolyte solutions: Combined molecular dynamics modeling and slender body hydrodynamics

Molecular dynamics modeling was applied to predict chitosan molecule conformations, the contour length, the gyration radius, the effective cross-section and the density in electrolyte solutions. Using various experimental techniques the diffusion coefficient, the hydrodynamic diameter and the electrophoretic mobility of molecules were determined. This allowed to calculate the zeta potential, the electrokinetic charge and the effective ionization degree of the chitosan molecule as a function of pH and the temperature. The chitosan solution density and zero shear dynamic viscosity were also measured, which enabled to determine the intrinsic viscosity increment. The experimental results were quantitatively interpreted in terms of the slender body hydrodynamics exploiting molecule characteristics derived from the modeling. It is also confirmed that this approach can be successfully used for a proper interpretation of previous literature data obtained under various physicochemical conditions.

Human Vimentin Layers on Solid Substrates: Adsorption Kinetics and Corona Formation Investigations

Adsorption kinetics of human vimentin on negatively charged substrates (mica, silica, and polymer particles) was analyzed using atomic force microscopy (AFM), quartz microbalance (QCM), and the laser doppler velocimetry (LDV) method. AFM studies realized under diffusion conditions proved that the adsorbed protein layer mainly consisted of aggregates in the form of compact tetramers and hexamers of a size equal to 11–12 nm. These results were consistent with vimentin adsorption kinetics under flow conditions investigated by QCM. It was established that vimentin aggregates efficiently adsorbed on the negatively charged silica sensor at pH 3.5 and 7.4, forming compact layers with the coverage reaching 3.5 mg m^–2. Additionally, the formation of the vimentin corona at polymer particles was examined using the LDV method and interpreted in terms of the electrokinetic model. This allowed us to determine the zeta potential of the corona as a function of pH and the electrokinetic charge of aggregates, which was equal to −0.7 e nm^–2 at pH 7.4 in a 10 mM NaCl solution. The anomalous adsorption of aggregates exhibiting an average negative charge on the negatively charged substrates was interpreted as a result of a heterogeneous charge distribution. These investigations confirmed that it is feasible to deposit stable vimentin layers both at planar substrates and at carrier particles with well-controlled coverage and zeta potential. They can be used for investigations of vimentin interactions with various ligands including receptors of the innate immune system, immunoglobulins, bacterial virulence factors, and spike proteins of viruses.

High Accuracy Weigh-In-Motion Systems for Direct Enforcement

In many countries, work is being conducted to introduce Weigh-In-Motion (WIM) systems intended for continuous and automatic control of gross vehicle weight. Such systems are also called WIM systems for direct enforcement (e-WIM). The achievement of introducing e-WIM systems is conditional on ensuring constant, known, and high-accuracy dynamic weighing of vehicles. WIM systems weigh moving vehicles, and on this basis, they estimate static parameters, i.e., static axle load and gross vehicle weight. The design and principle of operation of WIM systems result in their high sensitivity to many disturbing factors, including climatic factors. As a result, weighing accuracy fluctuates during system operation, even in the short term. The article presents practical aspects related to the identification of factors disturbing measurement in WIM systems as well as methods of controlling, improving and stabilizing the accuracy of weighing results. Achieving constant high accuracy in weighing vehicles in WIM systems is a prerequisite for their use in the direct enforcement mode. The research results presented in this paper are a step towards this goal.

Deposition of Polymer Particles with Fibrinogen Corona at Abiotic Surfaces under Flow Conditions

The deposition kinetics of polymer particles with fibrinogen molecule coronas at bare and poly-L-lysine (PLL) modified mica was studied using the microfluid impinging-jet cell. Basic physicochemical characteristics of fibrinogen and the particles were acquired using dynamic light scattering and the electrophoretic mobility methods, whereas the zeta potential of the substrates was determined using streaming potential measurements. Subsequently, an efficient method for the preparation of the particles with coronas, characterized by a controlled fibrinogen coverage, was developed. This enabled us to carry out measurements, which confirmed that the deposition kinetics of the particles at mica vanished at pH above 5. In contrast, the particle deposition of PLL modified mica was at maximum for pH above 5. It was shown that the deposition kinetics could be adequately analyzed in terms of the mean-field approach, analogously to the ordinary colloid particle behavior. This contrasts the fibrinogen molecule behavior, which efficiently adsorbs at negatively charged substrates for the entire range pHs up to 9.7. These results have practical significance for conducting label-free immunoassays governed by the specific antigen/antibody interactions.

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.

Effect of the Anchoring Layer and Transport Type on the Adsorption Kinetics of Lambda Carrageenan

The kinetics of lambda carrageenan (λ-car) adsorption/desorption on/from anchoring layers under diffusion- and convection-controlled transport conditions were investigated. The eighth generation of poly(amidoamine) dendrimers and branched polyethyleneimine possessing different shapes and polydispersity indexes were used for anchoring layer formation. Dynamic light scattering, electrophoresis, streaming potential measurements, optical waveguide lightmode spectroscopy, and quartz crystal microbalance were applied to characterize the formation of mono- and bilayers. The unique combination of the employed techniques enabled detailed insights into the mechanism of the λ-car adsorption mainly controlled by electrostatic interactions. The results show that the macroion adsorption efficiency is strictly correlated with the value of the final zeta potentials of the anchoring layers, the transport type, and the initial bulk concentration of the macroions. The type of the macroion forming the anchoring layer had a minor impact on the kinetics of λ-car adsorption. Besides significance to basic science, the results presented in this paper can be used for the development of biocompatible and stable macroion multilayers of well-defined electrokinetic properties and structure.

Novel design of (PEG-ylated)PAMAM-based nanoparticles for sustained delivery of BDNF to neurotoxin-injured differentiated neuroblastoma cells

Brain-derived neurotrophic factor (BDNF) is essential for the development and function of human neurons, therefore it is a promising target for neurodegenerative disorders treatment. Here, we studied BDNF-based electrostatic complex with dendrimer nanoparticles encapsulated in polyethylene glycol (PEG) in neurotoxin-treated, differentiated neuroblastoma SH-SY5Y cells, a model of neurodegenerative mechanisms. PEG layer was adsorbed at dendrimer-protein core nanoparticles to decrease their cellular uptake and to reduce BDNF-other proteins interactions for a prolonged time. Cytotoxicity and confocal microscopy analysis revealed PEG-ylated BDNF-dendrimer nanoparticles can be used for continuous neurotrophic factor delivery to the neurotoxin-treated cells over 24 h without toxic effect. We offer a reliable electrostatic route for efficient encapsulation and controlled transport of fragile therapeutic proteins without any covalent cross-linker; this could be considered as a safe drug delivery system. Understanding the polyvalent BDNF interactions with dendrimer core nanoparticles offers new possibilities for design of well-ordered protein drug delivery systems.

Mechanisms of Fibrinogen Adsorption on Silica Sensors at Various pHs: Experiments and Theoretical Modeling

The adsorption kinetics of human serum fibrinogen at silica substrates was studied using optical waveguide lightmode spectroscopy (OWLS) and quartz crystal microbalance (QCM) techniques. Measurements were performed at pH 3.5, 4, and 7.4 for various ionic strengths. The experimental data were interpreted in terms of a hybrid random sequential adsorption model. This allowed the mass transfer rate coefficient for the OWLS cell and maximum coverages to be determined at various pHs. The appearance of different, pH-dependent mechanisms of fibrinogen adsorption on silica substrates was confirmed. At pH 3.5 the molecules mostly adsorb in the side-on orientation that produces a low maximum coverage of ca. 1 mg m^-2. At this pH, the kinetics derived from the OWLS measurements agree with those theoretically predicted using the convective-diffusion theory. In consequence, a comparison of the OWLS and QCM results allows the water factor and the dynamic hydration of fibrinogen molecules to be determined. At pH 7.4, the OWLS method gives inaccurate kinetic data for the low coverage range. However, the maximum coverage that was equal to ca. 4 mg m^-2 agrees with the QCM results and with previous literature results. It is postulated that the limited accuracy of the OWLS method for lower coverage stems from a heterogeneous structure of fibrinogen monolayers, which consist of side-on and end-on adsorbed molecules. One can expect that the results acquired in this work allow development of a robust procedure for preparing fibrinogen monolayers of well-controlled coverage and molecule orientation, which can be exploited for efficient immunosensing purposes.

Human Serum Albumin Adsorption Kinetics on Silica: Influence of Protein Solution Stability

Adsorption kinetics of human serum albumin (HSA) on silica substrates was studied using optical waveguide lightmode spectroscopy (OWLS) and quartz microbalance (QCM) techniques. Measurements were performed at pH 3.5, 5.6, and 7.4 for various bulk suspension concentrations and ionic strengths. The diffusion coefficient measurements showed that for pH 3.5 the HSA molecules are stable for NaCl concentrations from 10^-3 to 0.15 M. This allowed us to precisely determine the mass transfer rate coefficients for the OWLS and QCM cells. The experimental data were adequately interpreted in terms of a hybrid random sequential adsorption model. The OWLS maximum coverage of HSA at pH 3.5, which is equal to 1.3 mg m^-2, agrees with the QCM result and with previous results derived from streaming potential measurements. Thus, the results obtained at pH 3.5 served as reference data for the analysis of adsorption kinetics at higher pHs. In this way, it was confirmed that the adsorption kinetics of HSA molecules at pH 5.6 and 7.4 was considerably slower than at pH 3.5. This effect was attributed to aggregation of HSA solutions and interpreted in terms of a theoretical model combining the Smoluchowski aggregation theory with the convective diffusion mass transfer theory. New analytical equations were derived that can be used for the interpretation of other protein adsorption from unstable solutions.

Silver nanoparticle/fibrinogen bilayers - Mechanism of formation and stability determined by in situ electrokinetic measurements

The kinetics of negatively charged silver nanoparticle (AgNP) deposition on the supporting fibrinogen monolayers of well-characterized coverage was determined by the atomic force microscopy (AFM). The kinetics was quantitatively interpreted in terms of the hybrid random sequential adsorption model. The electrokinetic properties of the fibrinogen monolayers and fibrinogen/AgNP bilayers were thoroughly characterized in situ by the streaming potential measurements. These results were interpreted in terms of the general electrokinetic model expressing the particle coverage in terms of the zeta potential of the bilayers. This allowed one to determine the adsorption constants and the binding energy of AgNPs, which was equal to -20.8 and -21.3 kT for pH 3.5 and 7.4, respectively. These results confirmed the end-on mechanism of fibrinogen adsorption and the presence of positively charged spots at its molecule at pH 7.4 where it exhibits an average negative charge. Besides significance to basic science, the obtained results can be exploited for developing a procedure for producing AgNP monolayers of well-defined coverage and controlled particle release profile.

Interfacial and structural characteristics of polyelectrolyte multilayers used as cushions for supported lipid bilayers

The surface properties of polyelectrolyte multilayers (PEMs) obtained via sequential adsorption of oppositely charged polyions from their solutions and used as cushions for supported lipid bilayers were investigated. Five types of polyelectrolytes were used: cationic polyethyleneimine (PEI), poly(diallyldimethylammonium)chloride (PDADMAC), and poly-l-lysine hydrobromide (PLL); and anionic polysodium 4-styrenesulfonate (PSS) and poly-l-glutamic acid sodium (PGA). The wettability and surface free energy of the PEMs were determined by contact angle measurements using sessile drop analysis. Electrokinetic characterisation of the studied films was performed by streaming potential measurements of selected multilayers and the structure of the polyelectrolyte multilayer was characterized by synchrotron X-ray reflectometry. The examined physicochemical properties of the PEMs were correlated with the kinetics of the formation of supported lipid bilayers atop the PEM cushion.

Spheroidal Microparticle Monolayers Characterized by Streaming Potential Measurements

An efficient method was developed enabling the synthesis of spheroidal polymer microparticles. Thorough physicochemical characteristics of the particles were acquired comprising the size, shape, electrophoretic mobility, and the diffusion coefficient. The particles were monodisperse, and their shape was well-fitted by prolate spheroids having the axis ratio equal to 4.17. Knowing the diffusion coefficient, their hydrodynamic diameter of 449 nm was calculated, which matched the value derived from Brenner's analytical expression. Particle deposition kinetics on mica and silicon/silica substrates, modified by poly(allylamine hydrochloride) (PAH) adsorption, was studied by optical microscopy and AFM imaging. The validity of the random sequential adsorption model was confirmed. Additionally, monolayers of the particles on these substrates were thoroughly characterized in situ by the streaming potential measurements for different ionic strengths. These measurements confirmed that the ζ potential change with the spheroidal particle coverage is less abrupt than for spheres and agrees with theoretical predictions. Exploiting these results, a useful analytical expression was derived that allows one to calculate the spheroidal particle coverage in situ via the streaming potential measurements. This expression, especially accurate for low coverage range, can be used for a quantitative interpretation of adsorption and desorption kinetics of anisotropic macromolecules, e.g., proteins on solid substrates.

Monolayers of Poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) Microparticles Formed by Controlled Self-Assembly with Potential Application as Protein-Repelling Substrates

The kinetics of the self-assembly of poly(styrene/α-tert-butoxy-ω-vinylbenzyl-polyglycidol) microparticles on poly(allylamine hydrochloride)-derivatized silicon/silica substrate was determined by direct AFM imaging and streaming potential (SP) measurements. The kinetic runs acquired under diffusion-controlled transport were quantitatively interpreted in terms of the extended random sequential adsorption (RSA) model. This allowed confirmation of a core/shell morphology of the microparticles. The polyglycidol-rich shell of thickness equal to 25 nm exhibited a fuzzy structure that enabled penetration of particles into each other resulting in high coverage inaccessible for ordinary microparticles. The SP measurements interpreted by using the 3D electrokinetic model confirmed this microparticle structure. Additionally, the acid-base characteristics of the microparticle monolayers were determined for a broad pH range. By using the streaming potential measurements, human serum albumin (HSA) adsorption on the microparticle monolayers was investigated under in situ conditions. It was confirmed that the protein adsorption was considerably lower than for the reference case of bare silicon/silica substrate under the same physicochemical conditions. This effect was attributed to the presence of the shell diminishing the protein/microparticle physical interactions.

Revealing fibrinogen monolayer conformations at different pHs: electrokinetic and colloid deposition studies

Adsorption mechanism of human fibrinogen on mica at different pHs is studied using the streaming potential and colloid deposition measurements. The fibrinogen monolayers are produced by a controlled adsorption under diffusion transport at pH of 3.5 and 7.4. Initially, the electrokinetic properties of these monolayers and their stability for various ionic strength are determined. It is shown that at pH 3.5 fibrinogen adsorbs irreversibly on mica for ionic strength range of 4×10(-4) to 0.15 M. At pH 7.4, a partial desorption is observed for ionic strength below 10(-2) M. This is attributed to the desorption of the end-on oriented molecules whereas the side-on adsorbed molecules remain irreversibly bound at all ionic strengths. The orientation of molecules and monolayer structure is evaluated by the colloid deposition measurements involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential is observed. At pH 3.5 measurable deposition of latex is observed even at low ionic strength where the approach distance of latex particles exceeded 70 nm. At pH 7.4 this critical distance is 23 nm. This confirms that fibrinogen monolayers formed at both pHs are characterized by the presence of the side-on and end-on oriented molecules that prevail at higher coverage range. It is also shown that positive charge is located at the end parts of the αA chains of the adsorbed fibrinogen molecules. Therefore, it is concluded that the colloid deposition method is an efficient tool for revealing protein adsorption mechanisms at solid/electrolyte interfaces.

Mechanisms of fibrinogen adsorption at solid substrates

The aim of this work was to critically review recent results pertinent to fibrinogen adsorption at solid/electrolyte interfaces with the emphasis focused on a quantitative analysis of these processes in terms of the electrostatic interactions. Accordingly, in the first part, the primary chemical structure of fibrinogen is analyzed. Physicochemical data pertinent to the bulk properties derived from hydrodynamic, dynamic light scattering and micro-electrophoretic measurements aided by theoretical modeling are discussed. Possible conformations and the effective charge distribution over the fibrinogen molecule for various pH an ionic strength are defined, especially the semi-collapsed conformation prevailing at physiological conditions. Adsorption kinetics of fibrinogen at hydrophilic and hydrophobic (polymer modified) substrates determined by various techniques is described. Adsorption at polymeric carrier particles, pertinent to immunological assays, studied in terms of electrokinetic and concentration depletion methods, are also considered. The reversibility of adsorption, fibrinogen molecule orientations and maximum coverages are thoroughly discussed. The stability of fibrinogen monolayers formed at these carrier particles in respect to pH and ionic strength cyclic changes is also discussed. In the final section interactions and deposition of model colloid particles on fibrinogen monolayers are analyzed which allows one to derive valuable information about molecule orientations. Based on the physicochemical data, adsorption kinetics and colloid particle deposition measurements, probable adsorption mechanisms of fibrinogen on solid/electrolyte interfaces are defined.

Fibrinogen monolayer characterization by colloid deposition

Colloid particle deposition was applied to characterize bovine and human fibrinogen (Fb) monolayers on mica produced by controlled adsorption under diffusion transport at pH 3.5. The surface concentration of Fb was determined by AFM enumeration of single molecules adsorbed over the substrate surface. The electrokinetic properties of Fb monolayers for various ionic strength were studied using the in situ streaming potential measurements. It was shown that Fb adsorbs irreversibly on mica for a broad range of ionic strength of 4 × 10(-4) to 0.15 M, NaCl. The overcharging of initially negative mica surface occurred for fibrinogen surface concentrations higher than 1400 μm(-2). The orientation of fibrinogen molecules in the monolayers was evaluated by the colloid deposition method involving negatively charged polystyrene latex microspheres, 820 nm in diameter. An anomalous deposition of negative latex particles on substrates exhibiting a negative zeta potential was observed, which contradicts the mean-field DLVO predictions. Measurable deposition was observed even at low ionic strength where the minimum approach distance of latex particles to the interface exceeds 70 nm (for 6 × 10(-4) M NaCl). This confirms that, at this pH, fibrinogen molecules adsorb end-on on mica assuming extended conformations with the positive charge located mostly in the end part of the αA chains. This agrees with previous experimental and theoretical results discussed in the literature (Santore, M. M.; Wertz Ch. F. Protein spreading kinetics at liquid-solid interfaces via an adsorption probe method. Langmuir 2005, 21, 10172-10178 (experimental); Adamczyk, Z.; Barbasz, J.; Cieśla, M.; Mechanisms of fibrinogen adsorption at solid substrates. Langmuir, 2011, 25, 6868-6878 (theoretical)). This unusual latex deposition on Fb monolayers was quantitatively interpreted in terms of the model developed in ref 55 (Jin, X.; Wang, N. H. L.; Tarjus, G.; Talbot, J. Irreversible adsorption on nonuniform surfaces: the random site model. J. Phys. Chem. 1993, 97, 4256-4258). It was concluded that the colloid deposition method is an efficient tool for revealing protein adsorption mechanisms at solid/electrolyte interfaces.

Mechanisms of fibrinogen adsorption at solid substrates at lower pH

Adsorption of fibrinogen was theoretically studied using the three-dimensional random sequential adsorption (RSA) model. Fibrinogen molecule shape was approximated by the bead model considering the presence of flexible side arms. Various cases were considered inter alia, the side-on adsorption mechanisms and the simultaneous side-on/end-on adsorption mechanism. The latter mechanisms is pertinent to fibrinogen adsorption at lower pH (below isoelectric point of 5.8) where the entire molecule is positively charged. Extensive calculations enabled one to determine the jamming surface concentration (coverage) of molecules adsorbed under the side-on and end-on orientations as well as the total coverage. For the simultaneous side-on/end-on model the maximum surface concentration was 7.29 × 10(3) μm(-2) corresponding to the protein coverage of 4.12 mg m(-2) (without considering hydration). Additionally, the surface blocking functions for different adsorption regimes were determined and analytically approximated for the entire range of coverage by the interpolating polynomials. Using these blocking functions, fibrinogen adsorption kinetics for diffusion controlled transport conditions was evaluated. Comparison of these theoretical results with experimental data was made. It was demonstrated that the simultaneous side-on/end-on model properly reflects the maximum coverage of fibrinogen adsorbed on latex particles determined via the electrokinetic (electrophoretic mobility) and AFM measurements. Also, streaming potential measurements of fibrinogen adsorption kinetics on mica were successfully interpreted in terms of this model. The theoretical results derived in this work have implications for basic science providing information on mechanisms of anisotropic protein adsorption.

Colloid particle and protein deposition - electrokinetic studies

Recent developments in the electrokinetic determination of particle, polyelectrolyte and protein deposition at solid/electrolyte interfaces, are reviewed. In the first section basic theoretical results are discussed enabling a quantitative interpretation of the streaming current/potential and microelectrophoretic measurements. Experimental results are presented, pertinent to electrokinetic characteristics of simple (homogeneous) surfaces such as mica, silica and various polymeric surfaces used in protein studies. The influence of the ionic strength, background electrolyte composition and pH is discussed, and the effective (electrokientic) charge of these interfaces is evaluated. In the next section, experimental data obtained by streaming potential measurements for colloid particle mono- and bilayers are presented and interpreted successfully in terms of available theoretical approaches. These results, obtained for model systems of monodisperse colloid particles are used as reference data for discussion of more complicated experiments performed for polyelectrolyte and protein covered surfaces. Results are discussed, obtained for cationic polyelectrolytes (PEI, PAH) and fibrinogen adsorbing on mica, interpreted quantitatively in terms of the theoretical approach postulating a heterogeneous 3D charge distribution. The Gouy-Chapman model, based on the continuous charge distribution proved inadequate. Interesting experimental data are also discussed, obtained by electrophoretic methods in the case of protein adsorption on colloid latex particles. In the last section, supplementary results on particle deposition on heterogeneous surfaces produced by controlled protein adsorption are discussed. Quantitative relationships between the amount of adsorbed protein, zeta potential of the interface and the particle coverage are specified. Possibility of evaluating the heterogeneity of protein charge distribution is pointed out. The anomalous deposition of colloid particles on protein molecules bearing the same sign of zeta potential, which contradicts classical DLVO theory, is interpreted in terms of the fluctuation theory. It is concluded that theoretical and experimental results obtained for model colloid systems and flat interfaces can be effectively used for interpretation of protein adsorption phenomena, studied by electrophoresis. In this way the universality of electrokinetic phenomena is underlined.

Fibrinogen adsorption on mica studied by AFM and in situ streaming potential measurements

Adsorption of fibrinogen from aqueous solutions on mica was studied using AFM and in situ streaming potential measurements. In the first stage, bulk physicochemical properties of fibrinogen and the mica substrate were characterized for various ionic strength and pH. The zeta potential and number of uncompensated (electrokinetic) charges on the protein surfaces were determined from microelectrophoretic measurements. Analogously, using streaming potential measurements, the electrokinetic charge density of mica was determined for pH range 3-10 and the NaCl background electrolyte concentration of 10(-3) and 10(-2) M. Next, the kinetics of fibrinogen adsorption at pH 3.5 and 7.4 in the diffusion cell was studied using a direct AFM determination of the number of molecules per unit area of the mica substrate. Then, streaming potential measurements were performed to determine the apparent zeta potential of fibrinogen-covered mica for different pH and ionic strength in terms of its surface concentration. A quantitative interpretation of these streaming potential measurements was achieved in terms of the theoretical model postulating a side-on adsorption of fibrinogen molecules as discrete particles. On the basis of these results, the maximum coverage of fibrinogen Θ close to 0.29 was predicted, in accordance with previous theoretical predictions. It was also suggested that anomalous adsorption for pH 7.4, where fibrinogen and the mica substrate were both negatively charged, can be explained in terms of a heterogeneous charge distribution on fibrinogen molecules. It was estimated that the positive charge was 12 e (for NaCl concentration of 10(-2) M and pH 7.4) compared with the net charge of fibrinogen at this pH, equal to -21 e. Results obtained in this work proved that the coverage of fibrinogen can be quantitatively determined using the streaming potential method, especially for Θ < 0.2, where other experimental methods become less accurate.

Structure of fibrinogen in electrolyte solutions derived from dynamic light scattering (DLS) and viscosity measurements

Bulk physicochemical properties of bovine plasma fibrinogen (Fb) in electrolyte solutions were characterized. These comprised determination of the diffusion coefficient (hydrodynamic radius), electrophoretic mobility, and isoelectric point (iep). The hydrodynamic radius of Fb for the ionic strength of 0.15 M was 12.7 nm for pH 7.4 (physiological conditions) and 12 nm for pH 9.5. Using these values, the number of uncompensated (electrokinetic) charges on the protein N(c) was calculated from the electrophoretic mobility data. It was found that for physiological condition (pH 7.4, I = 0.15), N(c) = -7.6. For pH 9.5 and I = 10(-2), N(c) = -26. On the other hand, N(c) became zero independent of the ionic strength at pH 5.8, which was identified as the iep. Consequently, for pH < 5.8, N(c) attained positive values, approaching 26 for lower ionic strength and pH 3.5. It was also found from the hydrodynamic diameter measurements that for a pH range close to the iep, that is, 4-7, the stability of Fb suspension was very low. These physicochemical characteristics were supplemented by dynamic viscosity measurements, carried out as a function of Fb bulk volume concentration, for various pH values. Using these experimental data the contour length of 80 nm was predicted for Fb molecules in electrolyte solutions. On the other hand, the effective length of the molecule was 53-55 nm for physiological conditions, which suggested a collapsed state of the terminal chains. However, for the range of pH outside the iep, its effective length increased to 65-68 nm. This was interpreted in terms of a significant unfolding of the terminal chains of Fb caused by electrostatic repulsion. The effective charge, contour length, and effective length data derived in this work seem to be the first of this type reported in the literature.

Characterization of globular protein solutions by dynamic light scattering, electrophoretic mobility, and viscosity measurements

In this work, physicochemical properties of two globular proteinsbovine serum albumin (BSA) having a molecular weight of 67 kDa and human serum albumin (HSA) having a molecular weight of 69 kDawere characterized. The bulk characteristics of these proteins involved the diffusion coefficient (hydrodynamic radius), electrophoretic mobility, and dynamic viscosity as a function of protein solution concentration for various pH values. The hydrodynamic radius data suggested an association of protein molecules, most probably forming compact dimers. Using the hydrodynamic diameter and the electropheretic mobility data allowed the determination of the number of uncompensated (electrokinetic) charges on protein surfaces. The electrophoretic mobility data were converted to zeta potential values, which allowed one to determine the isoelectric point (iep) of these proteins. It was found to be at pH 5.1 for both proteins, in accordance with previous experimental data and theoretical estimations derived from amino acid composition and p K values. To determine further the stability of protein solutions, dynamic viscosity measurements were carried out as a function of their bulk volume concentration for various pH values. The intrinsic viscosity derived from these measurements was interpreted in terms of the Brenner model, which is applicable to hard spheroidal particles. It was found that the experimental values of the intrinsic viscosity of these proteins were in good agreement with this model when assuming protein dimensions of 9.5 x 5 x 5 nm3 (prolate spheroid). The possibility of forming linear aggregates of association degree higher than 2 was excluded by these measurements. It was concluded that the combination of dynamic viscosity and dynamic light scattering can be exploited as a convenient tool for detecting not only the onset of protein aggregation in suspensions but also the form and composition of these aggregates.

[Own experience in supracricoid laryngectomy with GHP and GHEP type of reconstruction due to larynx cancer]

The results of the surgical treatment of the larynx cancer (glottic-supraglottic) by supracricoid laryngectomy with CHP and CHEP type of reconstruction were presented. Material consists of 160 cases (88 after CHP and 72 after CHEP). 5 years survival rate was obtained in over 71% of cases in all material. Decannulation was possible in 126 (79%) patients. Feeding tube removal before 4 weeks after operation was done in 139 (87%) cases. In subjective assessment all patients had social efficient speech. Favourable results of the treatment encourage wider application of supracricoid laryngectomy.

[Laryngotracheal separation procedure after oncological pharyngeal and laryngeal operations]

Principles of the operative technique and indication for permanent laryngotracheal separation in chronic aspiration after oncological operations are being presented. The operation is done while the tracheostomy is present. It consists of horizontal section of the trachea on the level of the tracheostomy and formation the new one by using the lower of the trachea with the skin. Upper sublaryngeal section of the trachea is being closed by stitches. This operation was performed in our clinic in one patient after partial laryngectomy due to the cancer and in two patients after extended resection of the palatal tonsil, base of the tongue and lateral wall of the hypopharynx. In all the cases the follow up was without major complications.

[Investigative findings on the reconstruction with tissue materials after partial laryngectomy]

Between 1987 and 1999--1289 patients were treated by surgery in the Department of Otolaryngology and Laryngologic Oncology PAM in Szczecin due to the cancer of the larynx. In this group total, eventual subtotal excision of the larynx was carried out in 801 cases. In 154 cases the phonation way was restored. In this study the remaining group of 502 patients was analysed, which underwent partial aiming at restoration of all basic functions of the larynx. In the mentioned group partial vertical laryngectomy was done in 176 cases, and partial horizontal laryngectomy in 326 cases. Larynx reconstruction with the use of tissue materials was carried out in 59 cases after vertical and in 88 cases after horizontal laryngectomy. Shortcomings and advantages of the method of various tissue application were discussed (cartilage of epiglottis, vasculary based pedicle flap of thyroid gland, submaxillary salivary gland, strap muscles among others were used).

[The results of treatment of hypopharyngeal carcinoma: some prognostic factors]

Eighty nine patients with hypopharynx carcinoma treated from 1970 to 1997 at the ENT Clinic of Pomeranian Medical Academy were studied retrospectively. There were only IV stage patients. The treatment consisted of surgery alone (n = 21), radiotherapy and post-radiotherapy surgery (n = 7), a planned combination of surgery and post-operative radiotherapy (n = 61). The 3-year survival was 34.88%, whereas the 5-year disease-free survival was 25.04%. The 5-year survival was related to the preoperative nodal staging (N0--52.8%; N1--17.8%; N2--28.3% and N3--0%), the number of lymph nodes metastases (no metastases 45.1%, 1--28.2%, 2-4--23.9%, > 4--0%), and the size of nodes (0 cm--31.6%, 1-3 cm--21.9%, > 3 cm--30.7%). Radiotherapy applied to operative treatment failed to exert any meaningful positive influence on the overall percentage of survivals. 17 patients had local recurrences and 6 node recurrences. Mainly following factors exerted the influence on appearance of nodal recurrence: component N and the number of metastatic nodes. It was pointed out that the result of treatment of hypopharynx carcinoma are still poor and unchanged despite of developing our skills and using new technology of treatment.

[Results of nasopharynx cancer treatment: some prognostic factors]

42 cases of nasopharynx cancer treated between 1985 and 1995 in ENT and Radiotherapeutic Clinic of the Pomeranian Medical Academy were analyzed. In 15 patients (34.5%) planoepithelial carcinoma was found, in 9 (20.9%)--anaplastic carcinoma, in 6 (13.9%)--lymphoepithelial, and in individual cases--spindle-shaped and mucoepidermal carcinoma solidum. 34 patients were treated by radical irradiation (60-70 Gy doses) and 8--by palliative (20-35 Gy). In 7 patients neck dissection was carried out. Better results were achieved in older patients (over 60 years old) than in younger ones. Prognosis in women was better than in men. 5 years' survival rate for T1-2 group was achieved in 77% of cases. For T3-4 group it amounted to 48%; in N0-1--69% and in N2-3 group--52%. 71% patients with planoepithelial carcinoma, whereas only 48% with undifferentiated carcinoma survived 5 years. The rate of 56% of 5 years' survival time is comparable with good results of other authors.

[The results of radiation and surgical treatment of early vocal cord carcinoma (T1a, T1b)]

Results of surgery treatment from the external access and radiotherapy in early, stage of vocal cords carcinoma were presented. Clinical material consisted of 94 cases with squamous cell carcinoma of vocal cords with stage T1a and T1b treated in Szczecin University Department of Otorhinolaryngology from 1987 to 1996. 51 cases were operated on (26 by chordectomy and 25 by frontolateral laryngectomy). Radiotherapy was applied in 43 patients. The 3 and 5 years' survival rate in the surgery group was 97% and after radiotherapy 88 to 80%. The functional results were also presented. It was concluded that the mode of treatment in early stages of vocal cord carcinoma should be individualized.

[Surgical treatment of hypopharyngeal cancer: reconstructive methods]

The paper presents a 26-year experience of the ENT Clinic of the Pomeranian Medical Academy in Szczecin with 20 patients who underwent reconstruction of the hypopharynx after resection for locally advanced carcinoma. The procedures were carried out in years 1970-1995. The reconstructions included 7 musculomucosal pedicle flaps obtained from the base of the tongue, 5 epiglottis pedicle flaps, 4 tubed pectoralis major musculocutaneous flaps, 1 vascular pedicle submandibular gland flap, 1 deltopectoral flap, 1 skin flap and 1 island pectoralis major musculocutaneous flap. An analysis of the procedures with emphasis on the oncological and functional results indicates that each techniques has advantages in specific circumstances. Guidelines for the application of the techniques are described.

Blastic transformation of blood lymphocytes in patients with laryngeal carcinoma

In 40 patients with carcinoma of the larynx transformation of lymphocytes under the influence of PHA was studied. In 20 patients, in addition, venous blood flowing from the tumor, collected during the operation was also examined. In 33 patients the index of blastic transformation was lowered as compared with that in the control group. In 15 of 20 patients, the lymphocytes of venous blood from the vicinity of the tumor showed significantly higher indices of blastic transformation in comparision with those from peripheral blood. It was assumed that difference was due to an increased participation of T-lymphocytes in venous blood flowing from the tumor area. T-lymphocytes might move into the blood from the lymphoid infiltrates which accompany the neoplastic tissue.