Stage of cirrhosis predicts the risk of liver-related death in patients with low Model for End-Stage Liver Disease scores and cirrhosis awaiting liver transplantation

The Model for End-Stage Liver Disease (MELD) score has reduced predictive ability in patients with cirrhosis and MELD scores ≤ 20. We aimed to assess whether a 5-stage clinical model could identify liver transplantation (LT) candidates with low MELD scores who are at increased risk for death. We conducted a case-control study of subjects with cirrhosis and MELD scores ≤ 20 who were awaiting LT at a single academic medical center between February 2002 and May 2011. Conditional logistic regression was used to evaluate the risk of liver-related death according to the cirrhosis stage. We identified 41 case subjects who died from liver-related causes with MELD scores ≤ 20 within 90 days of death while they were waiting for LT. The cases were matched with up to 3 controls (66 controls in all) on the basis of the listing year, age, sex, liver disease etiology, presence of hepatocellular carcinoma, and MELD score. The cirrhosis stage was assessed for all subjects: (1) no varices or ascites, (2) varices, (3) variceal bleeding, (4) ascites, and (5) ascites and variceal bleeding. The MELD scores were similar for cases and controls. Clinical states contributing to death in cases were: sepsis 49%, spontaneous bacterial peritonitis 15%, variceal bleeding 24%, and hepatorenal syndrome 22%. In a univariate analysis, variceal bleeding [odds ratio (OR) = 5.6, P = 0.003], albumin (OR = 0.5, P = 0.041), an increasing cirrhosis stage (P = 0.003), reaching cirrhosis stage 2, 3, or 4 versus lower stages (OR = 3.6, P = 0.048; OR = 7.4, P < 0.001; and OR = 4.1, P = 0.008), a sodium level < 135 mmol/L (OR = 3.4, P = 0.006), and hepatic encephalopathy (OR = 2.3, P = 0.082) were associated with liver-related death. In a multivariate model including the cirrhosis stage, albumin, sodium, and hepatic encephalopathy, an increasing cirrhosis stage (P = 0.010) was independently associated with liver-related death. In conclusion, assessing the cirrhosis stage in patients with low MELD scores awaiting LT may help to select candidates for more aggressive monitoring or for living or extended criteria donation.

Polymer chain dynamics: evidence of nonexponential mode relaxation using thermally stimulated depolarization current techniques

The slowest (p=1) mode relaxation of several polyisoprenes has been experimentally isolated by thermally stimulated depolarization current techniques. Close to the glass transition the p=1 mode deviates from the exponential behavior assumed by Rouse and tube-reptation theories. This effect is found to be a consequence of the closeness of τ_{p=1} and α-relaxation time scales. The scenario resembles that of broadened fast component dynamics in polymer blends with high dynamic asymmetry and suggests a possible general interpretation in terms of the effect of local density fluctuations (α relaxation) on chain dynamics.

Multi-orthogonal folding of single polymer chains into soft nanoparticles

Efficient folding of single polymer chains is a topic of great interest due, mainly, to the challenging possibility of mimicking and controlling the structure and functionality of natural biomacromolecules (e.g., enzymes, drug delivery vehicles, and catalysts) by means of artificial single chain nano-objects. By performing extensive molecular dynamics simulations we investigate the formation of soft nanoparticles by irreversible intramolecular cross-linking of polymer precursors of different lengths. In order to optimize the folding process and to obtain more compact structures we vary the number of chemical species among the linker groups (orthogonal chemistry) which selectively form the bonds. The use of orthogonal chemistry protocols, by increasing the number of different chemical species of the linkers, leads to nanoparticles that are systematically smaller and more spherical than their homofunctional counterparts. We characterize the conformational properties of the resulting nanoparticles. These are intrinsically polydisperse in size, with a significant fraction of sparse topologies. We discuss the relevance of our results for synthesis protocols in real systems.

Candida norvegensis fungemia in a liver transplant recipient

BACKGROUND

The incidence of candidemia due to non-Candida albicans Candida species has been progressively increasing in recent years. The use of fluconazole as antifungal prophylaxis has been described as a risk factor for the development of infections by fluconazole resistant Candida strains. We report a case of Candida norvegensis bloodstream infection in a liver transplant recipient.

CASE REPORT

A 61-year-old man, who received a third liver allograft and became worse with the onset of ischemic cholangiopathy and recurrent episodes of cholangitis, was admitted to our hospital due to the development of intra-abdominal abscesses. He received multiple antibiotic schemes, and after 3 months he was discharged, maintaining parenteral antibiotic at home. While he was on fluconazole prophylaxis, a breakthrough candidemia due to C. norvegensis occurred. In vitro susceptibilities of the isolate to several antifungal agents were as follows: amphotericin B MIC 0.5 mg/l, flucytosine 64 mg/l, fluconazole 64 mg/l, itraconazole 4 mg/l, voriconazole 0.75 mg/l, and caspofungin 0.047 mg/l. He was treated with anidulafungin with resolution of candidemia.

CONCLUSIONS

The use of fluconazole for antifungal prophylaxis may lead to the emergence of fluconazole-resistant Candida infections, with C. norvegensis being a possible emerging pathogen in organ transplant recipients.

Bone disease in patients awaiting liver transplantation. Has the situation improved in the last two decades?

In recent years, there has been speculation about the possibility of a reduction in the incidence of fractures after liver transplantation (LT) because of changes in the characteristics of candidates and the use of different immunosuppressive therapies. We analyzed the characteristics of LT candidates (CTC) and compared them with historical data from a group of LT candidate patients (HTC). Data from 60 CTC patients consecutively included in a screening program of metabolic bone disease were compared with data from 60 HTC patients prospectively evaluated between 1992 and 1993. In all patients, we analyzed the clinical and laboratory characteristics, bone mineral density (BMD) dual-energy X-ray absorptiometry, and skeletal fractures. Patients in the CTC group were older than patients in the HTC group. The CTC group had lower femoral neck T scores. No differences were observed between groups in the proportion of patients with osteoporosis (22 vs. 30 %, p = ns) or fractures (36 vs. 33 %, p = ns). The percentage of patients with normal BMD decreased from 38 to 20 %. 25(OH)D values were low in both groups. Only 7.5 % of the CTC patients received calcium and/or vitamin D supplementation. The prevalence of fractures among CTC patients was similar to that seen two decades ago. At present, candidates for LT are older and have lower femoral bone mass. Vitamin D deficiency remains frequent; however, calcium and/or vitamin D supplementation is uncommon.

Applicability of mode-coupling theory to polyisobutylene: a molecular dynamics simulation study

The applicability of Mode Coupling Theory (MCT) to the glass-forming polymer polyisobutylene (PIB) has been explored by using fully atomistic molecular dynamics simulations. MCT predictions for the so-called asymptotic regime have been successfully tested on the dynamic structure factor and the self-correlation function of PIB main-chain carbons calculated from the simulated cell. The factorization theorem and the time-temperature superposition principle are satisfied. A consistent fitting procedure of the simulation data to the MCT asymptotic power-laws predicted for the α-relaxation regime has delivered the dynamic exponents of the theory-in particular, the exponent parameter λ-the critical non-ergodicity parameters, and the critical temperature T(c). The obtained values of λ and T(c) agree, within the uncertainties involved in both studies, with those deduced from depolarized light scattering experiments [A. Kisliuk et al., J. Polym. Sci. Part B: Polym. Phys. 38, 2785 (2000)]. Both, λ and T(c)/T(g) values found for PIB are unusually large with respect to those commonly obtained in low molecular weight systems. Moreover, the high T(c)/T(g) value is compatible with a certain correlation of this parameter with the fragility in Angell's classification. Conversely, the value of λ is close to that reported for real polymers, simulated "realistic" polymers and simple polymer models with intramolecular barriers. In the framework of the MCT, such finding should be the signature of two different mechanisms for the glass-transition in real polymers: intermolecular packing and intramolecular barriers combined with chain connectivity.

Effect of nanoconfinement on polymer dynamics: surface layers and interphases

We present neutron spin echo experiments that address the much debated topic of dynamic phenomena in polymer melts that are induced by interacting with a confining surface. We find an anchored surface layer that internally is highly mobile and not glassy as heavily promoted in the literature. The polymer dynamics in confinement is, rather, determined by two phases, one fully equal to the bulk polymer and another that is partly anchored at the surface. By strong topological interaction, this phase confines further chains with no direct contact to the surface. These form the often invoked interphase, where the full chain relaxation is impeded through the interaction with the anchored chains.

Positron annihilation and relaxation dynamics from dielectric spectroscopy: poly(vinylmethylether)

We report on the temperature dependence of the lifetime of the ortho-positronium (o-Ps), τ(3), annihilation in amorphous polymer poly(vinylmethylether) (PVME) from positron annihilation lifetime spectroscopy (PALS). We show that the behavior of τ(3)(T) can be divided into five regions, each of them having a linear temperature dependence, and that the crossover PALS temperatures situated at T(b1)(G), 0.76T(g)(PALS), T(b1)(L) = 1.14T(g)(PALS) and T(b2)(L) = 1.37T(G)(PALS), and marking the discontinuity in the free volume microstructure are related to various dynamic features from neutron scattering (NS) and broadband dielectric spectroscopy (BDS). First, a slight change in the PALS response in the glassy PVME at T(b1)(G) is related to the onset of the excess wing in an apparent correspondence with the fast secondary β motion from NS. A further slight bend in the liquid state at T(b1)(L) is related to a high-frequency tail of the primary α process as well as to the slow secondary β relaxation from BDS. In addition, it lies also in the vicinity of the crossover temperature, T(B)(βKWW), in the spectral dispersion of the primary α process, indicating a connection of the change in the o-Ps lifetime with the variation in the width of the primary α relaxation times distribution. Finally, the τ(3) value at T(b2)(L) is close to the mean relaxation time of the primary α process, τ(α), in coincidence with the crossover in the secondary effective β process between two regimes in the liquid PVME. All these relationships point to very close connections between the PALS response and the dynamic behavior of PVME, which can be explained in terms of the temperature dependence of the probability function of the liquid-like and the solid-like domains, as obtained from the two-order parameter (TOP) model description of the liquid to glass transition in glass-formers.

Quasielastic neutron scattering study of hydrogen motions in an aqueous poly(vinyl methyl ether) solution

We present a quasielastic neutron scattering (QENS) investigation of the component dynamics in an aqueous Poly(vinyl methyl ether) (PVME) solution (30% water content in weight). In the glassy state, an important shift in the Boson peak of PVME is found upon hydration. At higher temperatures, the diffusive-like motions of the components take place with very different characteristic times, revealing a strong dynamic asymmetry that increases with decreasing T. For both components, we observe stretching of the scattering functions with respect to those in the bulk and non-Gaussian behavior in the whole momentum transfer range investigated. To explain these observations we invoke a distribution of mobilities for both components, probably originated from structural heterogeneities. The diffusive-like motion of PVME in solution takes place faster and apparently in a more continuous way than in bulk. We find that the T-dependence of the characteristic relaxation time of water changes at T ≲ 225 K, near the temperature where a crossover from a low temperature Arrhenius to a high temperature cooperative behavior has been observed by broadband dielectric spectroscopy (BDS) [S. Cerveny, J. Colmenero and A. Alegría, Macromolecules, 38, 7056 (2005)]. This observation might be a signature of the onset of confined dynamics of water due to the freezing of the PVME dynamics, that has been selectively followed by these QENS experiments. On the other hand, revisiting the BDS results on this system we could identify an additional "fast" process that can be attributed to water motions coupled with PVME local relaxations that could strongly affect the QENS results. Both kinds of interpretations, confinement effects due to the increasing dynamic asymmetry and influence of localized motions, could provide alternative scenarios to the invoked "strong-to-fragile" transition.

Contrast inversion in electrostatic force microscopy imaging of trapped charges: tip-sample distance and dielectric constant dependence

We present a numerical and analytical study of the behavior of both electrostatic force and force gradient created by a charge trapped below the surface of a dielectric on an atomic force microscope tip as a function of the dielectric constant and tip-sample distance. As expected, the force decreases monotonously when the dielectric constant increases. However, a maximum in the dielectric constant dependence of the force gradient is found. This maximum occurs in the typical experimental parameters' range and depends on the tip-sample distance and the sample thickness. The analytical study permits us to understand the physical origin of this phenomenon and is in good agreement with the numerical simulation for small tip-sample distances. We also report a study exemplifying a possible contrast inversion in electrostatic force microscopy (EFM) signals while scanning, at different heights, two charges trapped in a sample having heterogeneous dielectric domains. In addition to this particular contrast inversion effect, this study can be considered as a way to gain insight into the mechanisms of EFM image formation as a function of the dielectric constant and tip-sample.

Numerical study of the lateral resolution in electrostatic force microscopy for dielectric samples

We present a study of the lateral resolution in electrostatic force microscopy for dielectric samples in both force and gradient modes. Whereas previous studies have reported expressions for metallic surfaces having potential heterogeneities (Kelvin probe force microscopy), in this work we take into account the presence of a dielectric medium. We introduce a definition of the lateral resolution based on the force due to a test particle being either a point charge or a polarizable particle on the dielectric surface. The behaviour has been studied over a wide range of typical experimental parameters: tip-sample distance (1-20) nm, sample thickness (0-5) µm and dielectric constant (1-20), using the numerical simulation of the equivalent charge method. For potential heterogeneities on metallic surfaces expressions are in agreement with the bibliography. The lateral resolution of samples having a dielectric constant of more than 10 tends to metallic behaviour. We found a characteristic thickness of 100 nm, above which the lateral resolution measured on the dielectric surface is close to that of an infinite medium. As previously reported, the lateral resolution is better in the gradient mode than in the force mode. Finally, we showed that for the same experimental conditions, the lateral resolution is better for a polarizable particle than for a charge, i.e. dielectric heterogeneities should always look 'sharper' (better resolved) than inhomogeneous charge distributions. This fact should be taken into account when interpreting images of heterogeneous samples.