Molecular dynamics study of the mechanical properties of drug loaded model systems: A comparison of a polymersome with a bilayer.

In this work we implement a new methodology to study structural and mechanical properties of systems having spherical and planar symmetries throughout Molecular Dynamics simulations. This methodology is applied here to a drug delivery system based in polymersomes, as an example. The chosen model drug was the local anesthetic prilocaine due to previous parameterization within the used coarse grain scheme. In our approach, mass density profiles (MDPs) are used to obtain key structural parameters of the systems, and pressure profiles are used to estimate the curvature elastic parameters. The calculation of pressure profiles and radial MPDs required the development of specific methods, which were implemented in an in-house built version of the GROMACS 2018 code. The methodology presented in this work is applied to characterize poly(ethylene oxide)-poly(butadiene) polymersomes and bilayers loaded with the model drug prilocaine. Our results show that structural properties of the polymersome membrane could be obtained from bilayer simulations, with significantly lower computational cost compared to whole polymersome simulations, but the bilayer simulations are insufficient to get insights on their mechanical aspects, since the elastic parameters are canceled out for the complete bilayer (as consequence of the symmetry). The simulations of entire polymersomes, although more complex, offer a complementary approach to get insights on the mechanical behavior of the systems.

The Effects of Calcium on Lipid-Protein Interactions and Ion Flux in the Cx26 Connexon Embedded into a POPC Bilayer.

Gap junctions provide a communication pathway between adjacent cells. They are formed by paired connexons that reside in the plasma membrane of their respective cell and their activity can be modulated by the bilayer composition. In this work, we study the dynamic behavior of a Cx26 connexon embedded in a POPC lipid bilayer, studying: the membrane protein interactions and the ion flux though the connexon pore. We analyzed extensive atomistic molecular dynamics simulations for different conditions, with and without calcium ions. We found that lipid-protein interactions were mainly mediated by hydrogen bonds. Specific amino acids were identified forming hydrogen bonds with the POPC lipids (ARG98, ARG127, ARG165, ARG216, LYS22, LYS221, LYS223, LYS224, SER19, SER131, SER162, SER219, SER222, THR18 and TYR97, TYR155, TYR212, and TYR217). In the presence of calcium ions, we found subtle differences on the HB lifetimes. Finally, these MD simulations are able to identify and explain differential chlorine flux through the pore depending on the presence or absence of the calcium ions and its distribution within the pore.

A sumatriptan coarse-grained model to explore different environments: interplay with experimental techniques.

In this work, we developed a coarse-grained model of sumatriptan suitable for extensive molecular dynamics simulations. First, we confirmed the interfacial distribution of this drug in bilayers through cryogenic transmission electron microscopy and small-angle X-ray scattering techniques, as was predicted by our previous atomistic simulations. Based on these simulations, we developed a coarse-grained model for sumatriptan able to reproduce its overall molecular behavior, captured by atomistic simulations and experiments. We then tested the sumatriptan model in a micellar environment along with experimental characterization of sumatriptan-loaded micelles. The simulation results showed good agreement with photon correlation spectroscopy and electrophoretic mobility experiments performed in this work. The particle size of the obtained micelles was comparable with the simulated ones; meanwhile, zeta-potential results suggest adsorption of the drug on the micellar surface. This model is a step forward in the search for a suitable drug-delivery system for sumatriptan.

Mechanical properties of drug loaded diblock copolymer bilayers: A molecular dynamics study.

In this work, we present results of coarse-grained simulations to study the encapsulation of prilocaine (PLC), both neutral and protonated, on copolymer bilayers through molecular dynamics simulations. Using a previously validated membrane model, we have simulated loaded bilayers at different drug concentrations and at low (protonated PLC) and high (neutral PLC) pH levels. We have characterized key structural parameters of the loaded bilayers in order to understand the effects of encapsulation of PLC on the bilayer structure and mechanical properties. Neutral PLC was encapsulated in the hydrophobic region leading to a thickness increase, while the protonated species partitioned between the water phase and the poly(ethylene oxide)-poly(butadiene) (PBD) interface, relaxing the PBD region and leading to a decrease in the thickness. The tangential pressures of the studied systems were calculated, and their components were decomposed in order to gain insights on their compensation. In all cases, it is observed that the loading of the membrane does not significantly decrease the stability of the bilayer, indicating that the system could be used for drug delivery.

Diblock copolymer bilayers as model for polymersomes: A coarse grain approach.

This paper presents a new model for polymersomes developed using a poly(ethylene oxide)-poly(butadiene) diblock copolymer bilayer. The model is based on a coarse-grained approach using the MARTINI force field. Since no MARTINI parameters exist for poly(butadiene), we have refined these parameters using quantum mechanical calculations and molecular dynamics simulations. The model has been validated using extensive molecular dynamics simulations in systems with several hundred polymer units and reaching up to 6 µs. These simulations show that the copolymer coarse grain model self-assemble into bilayers and that NPT and NPNγT ensemble runs reproduce key structural and mechanical experimental properties for different copolymer length chains with a similar hydrophilic weight fraction.

Magnesium interactions with a CX26 connexon in lipid bilayers.

Following our previous work, where we described the interaction of calcium with the Cx26 hemichannel, we further explore the same system by atomistic molecular dynamics simulations considering a different di-cation, magnesium. Specifically, the interaction of magnesium di-cation with the previously reported calcium binding sites (ASP2, ASP117, ASP159, GLU114, GLU119, GLU120, and VAL226) was investigated to identify similarities and differences between them. In order to do so, four extensive simulations were carried out. Two of them considered a Cx26 hemichannel embedded on a POPC bilayer with one of the di-cations and a sodium-chlorine solution. For the remaining two, no di-cations were included and a sodium-chlorine or potassium-chlorine solution was considered. Potassium has a similar atomic mass to calcium, and sodium to magnesium, but they both differ in charge (1e and 2e respectively). Magnesium and calcium, even having the same charge, showed different affinity for the explored protein. From the calcium binding sites referred above, we found that the magnesium di-cations only binds strongly to the GLU114 site of one connexin. For the sodium and potassium simulations, no specific interactions with the protein were found. Altogether, these results suggest that mass and steric effects play an important role in determining cation binding to Cx26 hemichannels.

Rational design of polymer-lipid nanoparticles for docetaxel delivery.

In this work, a stable nanocarrier for the anti-cancer drug docetaxel was rational designed. The nanocarrier was developed based on the solid lipid nanoparticle preparation process aiming to minimize the total amount of excipients used in the final formulations. A particular interest was put on the effects of the polymers in the final composition. In this direction, two poloxoamers -Pluronic F127 and F68- were selected. Some poloxamers are well known to be inhibitors of the P-glycoprotein efflux pump. Additionally, their poly-ethylene-oxide blocks can help them to escape the immune system, making the poloxamers appealing to be present in a nanoparticle designed for the treatment of cancer. Within this context, a factorial experiment design was used to achieve the most suitable formulations, and also to identify the effects of each component on the final (optimized) systems. Two final formulations were chosen with sizes < 250 nm and PDI < 0.2. Then, using dynamic light scattering and nanotracking techniques, the stability of the formulations was assessed during six months. Structural studies were carried on trough different techniques: DSC, x-ray diffraction, FTIR-AR and Molecular Dynamics. The encapsulation efficiency of the anticancer drug docetaxel (> 90%) and its release dynamics from formulations were measured, showing that the polymer-lipid nanoparticle is suitable as a drug delivery system for the treatment of cancer.

Calcium interactions with Cx26 hemmichannel: Spatial association between MD simulations biding sites and variant pathogenicity.

Connexinophaties are a collective of diseases related to connexin channels and hemichannels. In particular many Cx26 alterations are strongly associated to human deafness. Calcium plays an important role on this structures regulation. Here, using calcium as a probe, extensive atomistic Molecular Dynamics simulations were performed on the Cx26 hemichannel embedded in a lipid bilayer. Exploring different initial conditions and calcium concentration, simulation reached ∼4 µs. Several analysis were carried out in order to reveal the calcium distribution and localization, such as electron density profiles, density maps and distance time evolution, which is directly associated to the interaction energy. Specific amino acid interactions with calcium and their stability were capture within this context. Few of these sites such as, GLU42, GLU47, GLY45 and ASP50, were already suggested in the literature. Besides, we identified novel calcium biding sites: ASP2, ASP117, ASP159, GLU114, GLU119, GLU120 and VAL226. To the best of our knowledge, this is the first time that these sites are reported within this context. Furthermore, since various pathologies involving the Cx26 hemichannel are associated with pathogenic variants in the corresponding CJB2 gene, using ClinVar, we were able to spatially associate the 3D positions of the identified calcium binding sites within the framework of this work with reported pathogenic variants in the CJB2 gene. This study presents a first step on finding associations between molecular features and pathological variants of the Cx26 hemichannel.

Caracterización de estudios por imágenes realizados en niños sanos en un centro de atención ambulatoria: percepciones, creencias y expectativas de sus padres / Characterizing imaging studies in healthy pediatric patients in an ambulatory center: parental perceptions, beliefs and expectations

Introducción: los estudios por imágenes (EPI) son de gran ayuda para el diagnóstico clínico, pero su uso irracional puede ocasionar daños. Objetivos: relevar las percepciones y expectativas sobre estudios por imágenes pediátricos en un grupo de padres de niños sanos. Evaluar los datos obtenidos en relación con el registro de EPI solicitados por Guardia durante el mismo período. Materiales y métodos: estudio exploratorio, descriptivo, cuali-cuantitativo mediante una encuesta en una muestra por conveniencia en un centro pediátrico ambulatorio, a lo largo de dos meses. Análisis retrospectivo de solicitud de EPI en el registro informatizado de historias clínicas de Guardia durante el mismo período. Resultados: respondieron 243 padres. El 93,4% refirió conocer métodos de EPI (la radiografía[Rx] fue el más conocido). Se había realizado al menos un EPI al 83,4% de los niños en los últimos doce meses. El estudio fue explicado en forma clara en el 96,4% de los casos. Un 47,7% de los padres refirieron conocer las consecuencias del uso repetitivo de EPI. El 81,6% acordó con que "ante cualquier traumatismo se debe realizar Rx para descartar fractura". Más del 60% consideró que debe realizarse Rx de tórax a todo niño con tos sin fiebre o con fiebre de más de dos días y 55% solicitarían Rx de senos paranasales si el niño elimina mocos verdes. El 49,8% opinó que los médicos piden EPI de menos (por falta de recursos, para trabajar menos o para ahorrar dinero). Durante el período estudiado se solicitó una radiografía al 5% de los pacientes que consultaron por Guardia; no se encontró justificación para solicitar el estudio en el 29% de los casos. Conclusión: un gran porcentaje de padres conoce los EPI; sin embargo, desconocen los riesgos asociados a su uso. Existen errores de concepto que generan expectativas desmedidas con respecto a la indicación de Rx. Se informó un exceso en las solicitudes de EPI por Guardia. Los padres consideran que los médicos solicitan EPI de menos. (AU)

Introduction: ediatric radiologic exams (PRE) are of great value for clinicians. It's over or misuse can lead to irreparable damage that can be prevented. Objective: to describe perceptions and expectations for the use of PRE among healthy children`s parents in an ambulatory center. To analyze these results in relation to the report of PRE performed in the emergency room during the same period. Methods: observational, cross sectional, quali- quantitative study using a survey on a convenience sample conducted in an outpatient pediatric center over a two months period. Retrospective analysis of medical records to evaluate PRE requested on the ER during the 2 months of the study. Results: 243 parents completed the survey. 93,4% were familiar with PRE (X-rays being the most popular among them). 83,4% of children in our sample had at least one PRE in the past 12 months. The need and utility of the study had been explained to the parents clearly in 96,4% of cases. 47,7% of parents knew about the side effects associated with repetitive use of PRE. 81,6% agreed with the statement "in the event that a child should suffer any trauma, an X-Ray should be performed to look for fractures". Over 60% think a chest X ray has to be obtained if the child has fever for over 48 hours and 55% would expect an X ray to be performed whenever a child has green nasal discharge. 49,8% respondents think that doctors order less than necessary (for lack of resources, unwillingness to work in or to save money). The analysis of clinical reports showed that X-Rays were performed to 5% of children at the emergency clinic. Among them, we found no reason for the study in 29% of the cases. Conclusion: we found that parents were very familiar with PRE, however less than half our sample knew of the potential risks related to their use. There are considerable misconceptions among parents regarding X-Ray use. Parents considered that doctors order too little PRE. (AU)