Hydrophilic Coating Microstructure Mediates Acute Drug Transfer in Drug-Coated Balloon Therapy.

Drug-coated balloon (DCB) therapy is a promising endovascular treatment for obstructive arterial disease. The goal of DCB therapy is restoration of lumen patency in a stenotic vessel, whereby balloon deployment both mechanically compresses the offending lesion and locally delivers an antiproliferative drug, most commonly paclitaxel (PTX) or derivative compounds, to the arterial wall. Favorable long-term outcomes of DCB therapy thus require predictable and adequate PTX delivery, a process facilitated by coating excipients that promotes rapid drug transfer during the inflation period. While a variety of excipients have been considered in DCB design, there is a lack of understanding about the coating-specific biophysical determinants of essential device function, namely, acute drug transfer. We consider two hydrophilic excipients for PTX delivery, urea (UR) and poly(ethylene glycol) (PEG), and examine how compositional and preparational variables in the balloon surface spray-coating process impact resultant coating microstructure and in turn acute PTX transfer to the arterial wall. Specifically, we use scanning electron image analyses to quantify how coating microstructure is altered by excipient solid content and balloon-to-nozzle spray distance during the coating procedure and correlate obtained microstructural descriptors of coating aggregation to the efficiency of acute PTX transfer in a one-dimensional ex vivo model of DCB deployment. Experimental results suggest that despite the qualitatively different coating surface microstructures and apparent PTX transfer mechanisms exhibited with these excipients, the drug delivery efficiency is generally enhanced by coating aggregation on the balloon surface. We illustrate this microstructure-function relation with a finite element-based computational model of DCB deployment, which along with our experimental findings suggests a general design principle to increase drug delivery efficiency across a broad range of DCB designs.

Engineering Biological Nanopore Approaches toward Protein Sequencing.

Biotechnological innovations have vastly improved the capacity to perform large-scale protein studies, while the methods we have for identifying and quantifying individual proteins are still inadequate to perform protein sequencing at the single-molecule level. Nanopore-inspired systems devoted to understanding how single molecules behave have been extensively developed for applications in genome sequencing. These nanopore systems are emerging as prominent tools for protein identification, detection, and analysis, suggesting realistic prospects for novel protein sequencing. This review summarizes recent advances in biological nanopore sensors toward protein sequencing, from the identification of individual amino acids to the controlled translocation of peptides and proteins, with attention focused on device and algorithm development and the delineation of molecular mechanisms with the aid of simulations. Specifically, the review aims to offer recommendations for the advancement of nanopore-based protein sequencing from an engineering perspective, highlighting the need for collaborative efforts across multiple disciplines. These efforts should include chemical conjugation, protein engineering, molecular simulation, machine-learning-assisted identification, and electronic device fabrication to enable practical implementation in real-world scenarios.

Cytomegalovirus and Cardiovascular Disease: A Hypothetical Role for Viral G-Protein-Coupled Receptors in Hypertension.

Cytomegalovirus (CMV) is a member of the ß-herpesviruses and is ubiquitous, infecting 50%-99% of the human population depending on ethnic and socioeconomic conditions. CMV establishes lifelong, latent infections in their host. Spontaneous reactivation of CMV is usually asymptomatic, but reactivation events in immunocompromised or immunosuppressed individuals can lead to severe morbidity and mortality. Moreover, herpesvirus infections have been associated with several cardiovascular and post-transplant diseases (stroke, atherosclerosis, post-transplant vasculopathy, and hypertension). Herpesviruses, including CMV, encode viral G-protein-coupled receptors (vGPCRs) that alter the host cell by hijacking signaling pathways that play important roles in the viral life cycle and these cardiovascular diseases. In this brief review, we discuss the pharmacology and signaling properties of these vGPCRs, and their contribution to hypertension. Overall, these vGPCRs can be considered attractive targets moving forward in the development of novel hypertensive therapies.

Microcanonical Thermodynamics of Small Ideal Gas Systems.

We consider the thermal, mechanical, and chemical contact of two subsystems composed of ideal gases, both of which are not in the thermodynamic limit. After contact, the combined system is isolated, and the entropy is determined through the use of its standard connection to the phase space density (PSD), where only those microstates at a given energy value are counted. The various intensive properties of these small systems that follow from a derivative of the PSD, such as the temperature, pressure, and chemical potential (evaluated via a backward difference), while equal when the two subsystems are in equilibrium are nevertheless found not to behave in accordance with what is expected from macroscopic thermodynamics. Instead, it is the entropy, defined from its connection to the PSD, that still controls the behavior of these small (nonextensive) systems. We also analyze the contact of these two subsystems utilizing an alternative entropy definition, through its proposed connection to the phase space volume (PSV), where all microstates at or below a given energy value are counted. We show that certain key properties of these small systems obtained with the PSV either do not become equal or do not consistently describe the two subsystems when in contact, suggesting that the PSV should not be used for analyzing the behavior of small isolated systems.

Soluble and insoluble protein aggregates, endoplasmic reticulum stress, and vascular dysfunction in Alzheimer's disease and cardiovascular diseases.

Dementia refers to a particular group of symptoms characterized by difficulties with memory, language, problem-solving, and other thinking skills that affect a person's ability to perform everyday activities. Alzheimer's disease (AD) is the most common form of dementia, affecting about 6.2 million Americans aged 65 years and older. Likewise, cardiovascular diseases (CVDs) are a major cause of disability and premature death, impacting 126.9 million adults in the USA, a number that increases with age. Consequently, CVDs and cardiovascular risk factors are associated with an increased risk of AD and cognitive impairment. They share important age-related cardiometabolic and lifestyle risk factors, that make them among the leading causes of death. Additionally, there are several premises and hypotheses about the mechanisms underlying the association between AD and CVD. Although AD and CVD may be considered deleterious to health, the study of their combination constitutes a clinical challenge, and investigations to understand the mechanistic pathways for the cause-effect and/or shared pathology between these two disease constellations remains an active area of research. AD pathology is propagated by the amyloid ß (Aß) peptides. These peptides give rise to small, toxic, and soluble Aß oligomers (SPOs) that are nonfibrillar, and it is their levels that show a robust correlation with the extent of cognitive impairment. This review will elucidate the interplay between the effects of accumulating SPOs in AD and CVDs, the resulting ER stress response, and their role in vascular dysfunction. We will also address the potential underlying mechanisms, including the possibility that SPOs are among the causes of vascular injury in CVD associated with cognitive decline. By revealing common mechanistic underpinnings of AD and CVD, we hope that novel experimental therapeutics can be designed to reduce the burden of these devastating diseases. Graphical abstract Alzheimer's disease (AD) pathology leads to the release of Aß peptides, and their accumulation in the peripheral organs has varying effects on various components of the cardiovascular system including endoplasmic reticulum (ER) stress and vascular damage. Image created with BioRender.com.

Liquid-Phase Effects on Adsorption Processes in Heterogeneous Catalysis.

Aqueous solvation free energies of adsorption have recently been measured for phenol adsorption on Pt(111). Endergonic solvent effects of ∼1 eV suggest solvents dramatically influence a metal catalyst's activity with significant implications for the catalyst design. However, measurements are indirect and involve adsorption isotherm models, which potentially reduces the reliability of the extracted energy values. Computational, implicit solvation models predict exergonic solvation effects for phenol adsorption, failing to agree with measurements even qualitatively. In this study, an explicit, hybrid quantum mechanical/molecular mechanical approach for computing solvation free energies of adsorption is developed, solvation free energies of phenol adsorption are computed, and experimental data for solvation free energies of phenol adsorption are reanalyzed using multiple adsorption isotherm models. Explicit solvation calculations predict an endergonic solvation free energy for phenol adsorption that agrees well with measurements to within the experimental and force field uncertainties. Computed adsorption free energies of solvation of carbon monoxide, ethylene glycol, benzene, and phenol over the (111) facet of Pt and Cu suggest that liquid water destabilizes all adsorbed species, with the largest impact on the largest adsorbates.

Self-Assembling Toroidal Cell Constructs for Tissue Engineering Applications.

Developing tissues have intricate, three-dimensional (3D) organizations of cells and extracellular matrix (ECM) that provide the framework necessary to meet morphogenic and necessary demands. Migrating cells, in vivo, are exposed to numerous conflicting signals: chemokines, ECM, growth factors, and physical forces. While most of these have been studied individually in vivo or in vitro, our understanding of how cells integrate these various signals is lacking. We previously developed a novel self-organizing cellularized collagen hydrogel model that is adaptable, tunable, reproducible, and capable of mimicking the multitude of stimuli that cells experience. Our model produced self-assembled toroids of cells that were formed by 24 h. Data we present here show toroids initially form as early as 3 h after seeding. Additionally, toroids formed when cells were seeded on various collagen subtypes and were sensitive to the composition of the hydrogel. Moreover, we found differences in remodeling in toroid gels compared to gels with cells embedded in them using both a collagen binding peptide and rheology. Using scanning electron microscopy, we observed toroids forming a crater-like structure compared to whole gel contractions in mixed in gels. Finally, when multiple cells were mixed prior to seeding, heterogeneous toroids formed with some containing clusters of cells.

On Using the BMCSL Equation of State to Renormalize the Onsager Theory Approach to Modeling Hard Prolate Spheroidal Liquid Crystal Mixtures.

Modifications to the traditional Onsager theory for modeling isotropic-nematic phase transitions in hard prolate spheroidal systems are presented. Pure component systems are used to identify the need to update the Lee-Parsons resummation term. The Lee-Parsons resummation term uses the Carnahan-Starling equation of state to approximate higher-order virial coefficients beyond the second virial coefficient employed in Onsager's original theoretical approach. As more exact ways of calculating the excluded volume of two hard prolate spheroids of a given orientation are used, the division of the excluded volume by eight, which is an empirical correction used in the original Lee-Parsons resummation term, must be replaced by six to yield a better match between the theoretical and simulation results. These modifications are also extended to binary mixtures of hard prolate spheroids using the Boublík-Mansoori-Carnahan-Starling-Leland (BMCSL) equation of state.

How Membrane Geometry Regulates Protein Sorting Independently of Mean Curvature.

Biological membranes have distinct geometries that confer specific functions. However, the molecular mechanisms underlying the phenomenological geometry/function correlations remain elusive. We studied the effect of membrane geometry on the localization of membrane-bound proteins. Quantitative comparative experiments between the two most abundant cellular membrane geometries, spherical and cylindrical, revealed that geometry regulates the spatial segregation of proteins. The measured geometry-driven segregation reached 50-fold for membranes of the same mean curvature, demonstrating a crucial and hitherto unaccounted contribution by Gaussian curvature. Molecular-field theory calculations elucidated the underlying physical and molecular mechanisms. Our results reveal that distinct membrane geometries have specific physicochemical properties and thus establish a ubiquitous mechanistic foundation for unravelling the conserved correlations between biological function and membrane polymorphism.

Determining the Potential of Mean Force for Amyloid-ß Dimerization: Combining Self-Consistent Field Theory with Molecular Dynamics Simulation.

Amyloid-ß (Aß) protein aggregates through a complex pathway to progress from monomers to soluble oligomers and ultimately insoluble fibrils. Because of the dynamic nature of aggregation, it has proven exceedingly difficult to determine the precise interactions that lead to the formation of transient oligomers. Here, a statistical thermodynamic model has been developed to elucidate these interactions. Aß1-42 was simulated using fully atomistic replica exchange molecular dynamics. We use an ensemble of approximately 5 × 105 configurations taken from simulation as input in a self-consistent field theory that explicitly accounts for the size, shape, and charge distribution of both the amino acids comprising Aß and all molecular species present in solution. The solution of the model equations provides a prediction of the probabilities of the configurations of the Aß dimer and the potential of mean force between two monomers during the dimerization process. This model constitutes a reliable methodology to elucidate the underlying physics of the Aß dimerization process as a function of pH, temperature, and salt concentration. The results obtained with this new model could be valuable in the design of Aß oligomerization inhibitors, a prospective therapeutic for Alzheimer's disease.

Mechanical and geometrical determinants of wall stress in abdominal aortic aneurysms: A computational study.

An aortic aneurysm (AA) is a focal dilatation of the aortic wall. Occurrence of AA rupture is an all too common event that is associated with high levels of patient morbidity and mortality. The decision to surgically intervene prior to AA rupture is made with recognition of significant procedural risks, and is primarily based on the maximal diameter and/or growth rate of the AA. Despite established thresholds for intervention, rupture occurs in a notable subset of patients exhibiting sub-critical maximal diameters and/or growth rates. Therefore, a pressing need remains to identify better predictors of rupture risk and ultimately integrate their measurement into clinical decision making. In this study, we use a series of finite element-based computational models that represent a range of plausible AA scenarios, and evaluate the relative sensitivity of wall stress to geometrical and mechanical properties of the aneurysmal tissue. Taken together, our findings encourage an expansion of geometrical parameters considered for rupture risk assessment, and provide perspective on the degree to which tissue mechanical properties may modulate peak stress values within aneurysmal tissue.

Quantifying Mg2+ Binding to ssDNA Oligomers: A Self-Consistent Field Theory Study at Varying Ionic Strengths and Grafting Densities.

The performance of aptamer-based biosensors is crucially impacted by their interactions with physiological metal ions, which can alter their structures and chemical properties. Therefore, elucidating the nature of these interactions carries the utmost importance in the robust design of highly efficient biosensors. We investigated Mg 2 + binding to varying sequences of polymers to capture the effects of ionic strength and grafting density on ion binding and molecular reorganization of the polymer layer. The polymers are modeled as ssDNA aptamers using a self-consistent field theory, which accounts for non-covalent ion binding by integrating experimentally-derived binding constants. Our model captures the typical polyelectrolyte behavior of chain collapse with increased ionic strength for the ssDNA chains at low grafting density and exhibits the well-known re-entrant phenomena of stretched chains with increased ionic strength at high grafting density. The binding results suggest that electrostatic attraction between the monomers and Mg 2 + plays the dominant role in defining the ion cloud around the ssDNA chains and generates a nearly-uniform ion distribution along the chains containing varying monomer sequences. These findings are in qualitative agreement with recent experimental results for Mg 2 + binding to surface-bound ssDNA.

Membrane Curvature and Lipid Composition Synergize To Regulate N-Ras Anchor Recruitment.

Proteins anchored to membranes through covalently linked fatty acids and/or isoprenoid groups play crucial roles in all forms of life. Sorting and trafficking of lipidated proteins has traditionally been discussed in the context of partitioning to membrane domains of different lipid composition. We recently showed that membrane shape/curvature can in itself mediate the recruitment of lipidated proteins. However, exactly how membrane curvature and composition synergize remains largely unexplored. Here we investigated how three critical structural parameters of lipids, namely acyl chain saturation, headgroup size, and acyl chain length, modulate the capacity of membrane curvature to recruit lipidated proteins. As a model system we used the lipidated minimal membrane anchor of the GTPase, N-Ras (tN-Ras). Our data revealed complex synergistic effects, whereby tN-Ras binding was higher on planar DOPC than POPC membranes, but inversely higher on curved POPC than DOPC membranes. This variation in the binding to both planar and curved membranes leads to a net increase in the recruitment by membrane curvature of tN-Ras when reducing the acyl chain saturation state. Additionally, we found increased recruitment by membrane curvature of tN-Ras when substituting PC for PE, and when decreasing acyl chain length from 14 to 12 carbons (DMPC versus DLPC). However, these variations in recruitment ability had different origins, with the headgroup size primarily influencing tN-Ras binding to planar membranes whereas the change in acyl chain length primarily affected binding to curved membranes. Molecular field theory calculations recapitulated these findings and revealed lateral pressure as an underlying biophysical mechanism dictating how curvature and composition synergize to modulate recruitment of lipidated proteins. Our findings suggest that the different compositions of cellular compartments could modulate the potency of membrane curvature to recruit lipidated proteins and thereby synergistically regulate the trafficking and sorting of lipidated proteins.

Influence of gold nanoparticle surface chemistry and diameter upon Alzheimer's disease amyloid-ß protein aggregation.

BACKGROUND: Deposits of aggregated amyloid-ß protein (Aß) are a pathological hallmark of Alzheimer's disease (AD). Thus, one therapeutic strategy is to eliminate these deposits by halting Aß aggregation. While a variety of possible aggregation inhibitors have been explored, only nanoparticles (NPs) exhibit promise at low substoichiometric ratios. With tunable size, shape, and surface properties, NPs present an ideal platform for rationally designed Aß aggregation inhibitors. In this study, we characterized the inhibitory capabilities of gold nanospheres exhibiting different surface coatings and diameters. RESULTS: Both NP diameter and surface chemistry were found to modulate the extent of aggregation, while NP electric charge influenced aggregate morphology. Notably, 8 nm and 18 nm poly(acrylic acid)-coated NPs abrogated Aß aggregation at a substoichiometric ratio of 1:2,000,000. Theoretical calculations suggest that this low stoichiometry could arise from altered solution conditions near the NP surface. Specifically, local solution pH and charge density are congruent with conditions that influence aggregation. CONCLUSIONS: These findings demonstrate the potential of surface-coated gold nanospheres to serve as tunable therapeutic agents for the inhibition of Aß aggregation. Insights gained into the physiochemical properties of effective NP inhibitors will inform future rational design of effective NP-based therapeutics for AD.

A mechanical argument for the differential performance of coronary artery grafts.

Coronary artery bypass grafting (CABG) acutely disturbs the homeostatic state of the transplanted vessel making retention of graft patency dependent on chronic remodeling processes. The time course and extent to which remodeling restores vessel homeostasis will depend, in part, on the nature and magnitude of the mechanical disturbances induced upon transplantation. In this investigation, biaxial mechanical testing and histology were performed on the porcine left anterior descending artery (LAD) and analogs of common autografts, including the internal thoracic artery (ITA), radial artery (RA), great saphenous vein (GSV) and lateral saphenous vein (LSV). Experimental data were used to quantify the parameters of a structure-based constitutive model enabling prediction of the acute vessel mechanical response pre-transplantation and under coronary loading conditions. A novel metric Ξ was developed to quantify mechanical differences between each graft vessel in situ and the LAD in situ, while a second metric Ω compares the graft vessels in situ to their state under coronary loading. The relative values of these metrics among candidate autograft sources are consistent with vessel-specific variations in CABG clinical success rates with the ITA as the superior and GSV the inferior graft choices based on mechanical performance. This approach can be used to evaluate other candidate tissues for grafting or to aid in the development of synthetic and tissue engineered alternatives.

Mode specific elastic constants for the gel, liquid-ordered, and liquid-disordered phases of DPPC/DOPC/cholesterol model lipid bilayers.

Using microscopic molecular theory, we determine the bending and saddle-splay constants of three-component lipid bilayers. The membrane contains cholesterol, dipalmitoyl-phosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) and the predictions of the theory have been shown to qualitatively reproduce phase diagrams of giant unilamellar vesicles (GUVs) of the same three components. The bending and saddle-splay constants were calculated for the gel, liquid-ordered (lo) and liquid-disordered (ld) phases. By proper expansion of the free energy, the molecular theory enables us to determine the effects of the mode of membrane bending deformation on the value of the elastic constants for different phases. In particular, we refer to the ability of the molecules to arrange the composition between the two monolayers upon deformation. The bending and saddle-splay constants obtained from the free energy expansion can be expressed in terms of moments of the local lateral pressures and their derivatives, all evaluated for a symmetric planar bilayer. The effect of blocked vs. free exchange of lipids across the two monolayers on the values of the bending constant is as high as 50 k(B)Tin the ld phase to as high as 200 k(B)T in the lo phase. These results show that one must strongly consider the mode of deformation in determining the mechanical properties of lipid bilayers. We discuss how the different contributions to the lateral pressures affect the values of the elastic constants, including the effects of the cholesterol concentration and temperature on the membrane elastic constants. We also calculate the equilibrium binding concentrations of lipid tail anchors as a function of membrane curvature by explicitly determining the chemical potential difference of species across a curved bilayer. Our results are in excellent agreement with recent experimental results.

Phase behavior of lipid bilayers under tension.

Given the proposed importance of membrane tension in regulating cellular functions, we explore the effects of a finite surface tension on phase equilibrium using a molecular theory that captures the quantitative structure of the phase diagram of the tensionless DPPC/DOPC/Cholesterol lipid bilayer. We find that an increase in the surface tension decreases the temperature of the transition from liquid to gel in a pure DPPC system by ∼1.0 K/(mN/m), and decreases the liquid-disordered to liquid-ordered transition at constant chemical potentials by approximately the same amount. Our results quantitatively isolate the role of tension in comparison to other thermodynamic factors, such as pressure, in determining the phase behavior of lipid bilayers.

Effects of the salt concentration on charge regulation in tethered polyacid monolayers.

Charge regulation in polyacid monolayers attached at one end to a planar surface is studied theoretically. The polyacid layers are designed to mimic single-stranded DNA monolayers. The effects of the local pH and salt concentration on the protonation states of the polyacid layer are studied using a molecular mean-field theory that includes a microscopic description of the conformations of the polyacid molecule along with electrostatic interactions, acid-base equilibrium, and excluded volume interactions. We predict that, in the case of a monovalent salt, NaCl, the amount of proton binding increases dramatically for high surface coverage of polyacid and low bulk salt concentration. When the polyelectrolyte is almost completely charge neutralized by bound protons, there is an expulsion of sodium from the layer. We show that the degree of protonation can go all the way from 0% to 100% when the bulk pH is kept fixed at 7 by changing the surface coverage of polyacid and the bulk salt concentration. The effects of increasing protonation and the expulsion of the cations from the monolayer are reduced when sodium ions are replaced by divalent magnesium ions. Our theoretical results concur with X-ray photoelectron spectroscopy studies of ssDNA monolayers on gold.

Interleaflet coupling and domain registry in phase-separated lipid bilayers.

There is clear evidence of an interleaflet coupling in model lipid/cholesterol membranes exhibiting liquid-liquid phase separation. The strength of this coupling is quantified by the mismatch free energy, γ. We calculate it using a molecular mean-field model of a phase-separated lipid/cholesterol bilayer and obtain values that increase as the concentration of saturated lipids in the coexisting phases is increased. These values lie in the range 0.01-0.03 k(B)T/nm(2). We clarify the relationship between the interleaflet coupling and the extent of interleaflet alignment of liquid domains by analyzing a statistical mechanical model of coupled fluctuating domain interfaces. The model is solved exactly using the correspondence between statistical mechanics and quantum mechanics, yielding an expression for the characteristic size of fluctuations out of domain registry. This length scale depends only weakly on the strength of the interleaflet coupling and inevitably is only of the order of nanometers, which explains the experimental result that fluctuations out of domain registry have not been observed by optical microscopy.