6 research outputs found
Absolute Organic Crystal Thermodynamics: Growth of the Asymmetric Unit into a Crystal via Alchemy
The
solubility of organic molecules is of critical importance to
the pharmaceutical industry; however, robust computational methods
to predict this quantity from first-principles are lacking. Solubility
can be computed from a thermodynamic cycle that decomposes standard
state solubility into the sum of solid–vapor sublimation and
vapor–liquid solvation free energies Δ<i>G</i><sub>solubility</sub><sup>°</sup> = Δ<i>G</i><sub>sub</sub><sup>°</sup> + Δ<i>G</i><sub>solv</sub><sup>°</sup>. Over
the past few decades, alchemical simulation methods to compute solvation
free energy using classical force fields have become widely used.
However, analogous methods for determining the free energy of the
sublimation/deposition phase transition are currently limited by the
necessity of a priori knowledge of the atomic coordinates of the crystal.
Here, we describe progress toward an alternative scheme based on <u>g</u>rowth of the <u>a</u>symmetric <u>u</u>nit into a <u>c</u>rystal via alc<u>he</u>my (GAUCHE). GAUCHE computes deposition free energy
Δ<i>G</i><sub>dep</sub><sup>°</sup> = −Δ<i>G</i><sub>sub</sub><sup>°</sup> = −<i>k</i><sub>B</sub><i>T</i> lnÂ(<i>V</i><sub>c</sub>/<i>V</i><sub>g</sub>) + Δ<i>G</i><sub>AU</sub> + Δ<i>G</i><sub>AU→UC</sub> as
the sum of an entropic term to account for compressing a vapor at
1 M standard state (<i>V</i><sub>g</sub>) into the molar
volume of the crystal (<i>V</i><sub>c</sub>), where <i>k</i><sub>B</sub> is Boltzmann’s constant and <i>T</i> is temperature in degrees Kelvin, plus two simulation
steps. In the first simulation step, the deposition free energy Δ<i>G</i><sub>AU</sub> for a system composed of only <i>N</i><sub>AU</sub> asymmetric unit (AU) molecule(s) is computed beginning
from an arbitrary conformation in vacuum. In the second simulation
step, the change in free energy Δ<i>G</i><sub>AU→UC</sub> to expand the asymmetric unit degrees of freedom into a unit cell
(UC) composed of <i>N</i><sub>UC</sub> independent molecules
is computed. This latter step accounts for the favorable free energy
of removing the constraint that every symmetry mate of the asymmetric
unit has an identical conformation and intermolecular interactions.
The current work is based on NVT simulations, which requires knowledge
of the crystal space group and unit cell parameters from experiment,
but not a priori knowledge of crystalline atomic coordinates. GAUCHE
was applied to 5 organic molecules whose sublimation free energy has
been measured experimentally, based on the polarizable AMOEBA force
field and more than a microsecond of sampling per compound in the
program Force Field X. The mean unsigned and RMS errors were only
1.6 and 1.7 kcal/mol, respectively, which indicates that GAUCHE is
capable of accurate prediction of absolute sublimation thermodynamics
Balanced Effects of Surface Reactivity and Self-Association of Bifunctional Polyaspartamide on Stem Cell Adhesion
Extensive efforts
have been made to regulate surface wettability
using bivalent polymers composed of hydrophobic surface-reactive groups
and hydrophilic groups. To further enhance the controllability, this
study demonstrates that the balance between the surface reactivity
and self-aggregation of bivalent polyÂ(hydroxyethyl-<i>co</i>-methacryloxyethyl aspartamide) (PHMAA) is crucial in controlling
the wettability of methacrylated glass and thus the adhesion of stem
cells. In particular, the wettability of the glass and the subsequent
cell spreading became maximal with PHMAA that led to the largest and
most uniform coverage of hydroxyl groups. In summary, this study would
be useful in advancing various molecules used for surface engineering
Decellularized Matrix Produced by Mesenchymal Stem Cells Modulates Growth and Metabolic Activity of Hepatic Cell Cluster
Miniature organlike
three-dimensional cell clusters often called
organoids have emerged as a useful tool for both fundamental and applied
bioscience studies. However, there is still a great need to improve
the quality of organoids to a level where they exhibit similar biological
functionality to an organ. To this end, we hypothesized that a decellularized
matrix derived from mesenchymal stem cell (MSC) could regulate the
phenotypic and metabolic activity of organoids. This hypothesis was
examined by culturing cells of interest in the decellularized matrix
of MSCs cultured on a 2D substrate at confluency or in the form of
spheroids. The decellularized matrix prepared with MSC spheroids showed
a 3D porous structure with a higher content of extracellular matrix
molecules than the decellularized matrix derived from MSCs cultured
on a 2D substrate. HepG2 hepatocarcinoma cells, which retain the metabolic
activity of hepatocytes, were cultured in these decellularized matrices.
Interestingly, the decellularized matrix from the MSC spheroids served
to develop the hepatic cell clusters with higher levels of E-cadherin-mediated
cell–cell adhesion and detoxification activity than the decellularized
matrix from the MSCs cultured on a 2D substrate. Overall, the results
of this study are useful in improving biological functionality of
a wide array of organoids
Nanothin Coculture Membranes with Tunable Pore Architecture and Thermoresponsive Functionality for Transfer-Printable Stem Cell-Derived Cardiac Sheets
Coculturing stem cells with the desired cell type is an effective method to promote the differentiation of stem cells. The features of the membrane used for coculturing are crucial to achieving the best outcome. Not only should the membrane act as a physical barrier that prevents the mixing of the cocultured cell populations, but it should also allow effective interactions between the cells. Unfortunately, conventional membranes used for coculture do not sufficiently meet these requirements. In addition, cell harvesting using proteolytic enzymes following coculture impairs cell viability and the extracellular matrix (ECM) produced by the cultured cells. To overcome these limitations, we developed nanothin and highly porous (NTHP) membranes, which are ∼20-fold thinner and ∼25-fold more porous than the conventional coculture membranes. The tunable pore size of NTHP membranes at the nanoscale level was found crucial for the formation of direct gap junctions-mediated contacts between the cocultured cells. Differentiation of the cocultured stem cells was dramatically enhanced with the pore size-customized NTHP membrane system compared to conventional coculture methods. This was likely due to effective physical contacts between the cocultured cells and the fast diffusion of bioactive molecules across the membrane. Also, the thermoresponsive functionality of the NTHP membranes enabled the efficient generation of homogeneous, ECM-preserved, highly viable, and transfer-printable sheets of cardiomyogenically differentiated cells. The coculture platform developed in this study would be effective for producing various types of therapeutic multilayered cell sheets that can be differentiated from stem cells
Worm-Like Superparamagnetic Nanoparticle Clusters for Enhanced Adhesion and Magnetic Resonance Relaxivity
Nanosized
bioprobes that can highlight diseased tissue can be powerful
diagnostic tools. However, a major unmet need is a tool with adequate
adhesive properties and contrast-to-dose ratio. To this end, this
study demonstrates that targeted superparamagnetic nanoprobes engineered
to present a worm-like shape and hydrophilic packaging enhance both
adhesion efficiency to target substrates and magnetic resonance (MR)
sensitivity. These nanoprobes were prepared by the controlled self-assembly
of superparamagnetic iron oxide nanoparticles (SPIONs) into worm-like
superstructures using glycogen-like amphiphilic hyperbranched polyglycerols
functionalized with peptides capable of binding to defective vasculature.
The resulting worm-like SPION clusters presented binding affinity
to the target substrate 10-fold higher than that of spherical ones
and T<sub>2</sub> molar MR relaxivity 3.5-fold higher than that of
conventional, single SPIONs. The design principles discovered for
these nanoprobes should be applicable to a range of other diseases
where improved diagnostics are needed
Dual Roles of Graphene Oxide To Attenuate Inflammation and Elicit Timely Polarization of Macrophage Phenotypes for Cardiac Repair
Development of localized
inflammatory environments by M1 macrophages
in the cardiac infarction region exacerbates heart failure after myocardial
infarction (MI). Therefore, the regulation of inflammation by M1 macrophages
and their timely polarization toward regenerative M2 macrophages suggest
an immunotherapy. Particularly, controlling cellular generation of
reactive oxygen species (ROS), which cause M1 differentiation, and
developing M2 macrophage phenotypes in macrophages propose a therapeutic
approach. Previously, stem or dendritic cells were used in MI for
their anti-inflammatory and cardioprotective potentials and showed
inflammation modulation and M2 macrophage progression for cardiac
repair. However, cell-based therapeutics are limited due to invasive
cell isolation, time-consuming cell expansion, labor-intensive and
costly <i>ex vivo</i> cell manipulation, and low grafting
efficiency. Here, we report that graphene oxide (GO) can serve as
an antioxidant and attenuate inflammation and inflammatory polarization
of macrophages <i>via</i> reduction in intracellular ROS.
In addition, GO functions as a carrier for interleukin-4 plasmid DNA
(IL-4 pDNA) that propagates M2 macrophages. We synthesized a macrophage-targeting/polarizing
GO complex (MGC) and demonstrated that MGC decreased ROS in immune-stimulated
macrophages. Furthermore, DNA-functionalized MGC (MGC/IL-4 pDNA) polarized
M1 to M2 macrophages and enhanced the secretion of cardiac repair-favorable
cytokines. Accordingly, injection of MGC/IL-4 pDNA into mouse MI models
attenuated inflammation, elicited early polarization toward M2 macrophages,
mitigated fibrosis, and improved heart function. Taken together, the
present study highlights a biological application of GO in timely
modulation of the immune environment in MI for cardiac repair. Current
therapy using off-the-shelf material GO may overcome the shortcomings
of cell therapies for MI