Topological defect transformation and structural transition of two-dimensional colloidal crystals across the nematic to smectic-A phase transition.

We observe that topological defects in nematic colloids are strongly influenced by the elasticity and onset of smectic layering across the nematic (N) to smectic-A (SmA) phase transition. When approaching the SmA phase from above, the nematic hyperbolic hedgehog defect that accompanies a spherical colloidal inclusion is transformed into a focal conic line in the SmA phase. This phase transformation has a strong influence on the pairwise colloidal interaction and is responsible for a structural transition of two-dimensional colloidal crystals. The pretransitional behavior of the point defect is supported by Landau-de Gennes Q-tensor modeling accounting for the increasing elastic anisotropy.

Antagonistic flexoelectric response in liquid crystal mixtures of bent-core and rodlike molecules.

We report the measurements of the temperature variations of the flexoelastic coefficient (e(*)/K) of a host calamitic liquid crystal (RO) and its mixture with two guest bent-core (BC-120 and BC-60) liquid crystals. The bent-core (BC) molecules have different core structures and bend angles; namely, θ=/~120° and =/~60°, respectively. We find that e(*)/K is independent of temperature and decreases rapidly with increasing concentration of BC-120 molecules and changes sign from positive to negative. In mixtures with BC-60, e(*)/K is always positive and its concentration-dependent variation is not unique. At 7M% it is significantly large (three times) near the nematic-isotropic transition and decreases strongly with reducing temperature. Dielectric measurement suggests antagonistic orientation of the dipole axes (arrow axes) of the two BC molecules in the host liquid crystal, and based on this, the opposite sign of e(*)/K is explained.

Viscoelasticity of ambient-temperature nematic binary mixtures of bent-core and rodlike molecules.

We report measurements of the temperature variations of physical parameters in ambient-temperature nematic liquid crystal mixtures of bent-core (BC) and rodlike molecules (5CB): birefringence Δn; static dielectric constants ε(||) and ε(⊥); splay K(11) and bend K(33) elastic constants; rotational viscosity γ(1); and diffusion coefficients D(||) and D(⊥) of a microsphere. Both Δn and ε(||) decreases rapidly with increasing BC concentration, whereas ε(⊥) remains almost constant. At a shifted temperature (e.g., T-T(NI)=-10 °C), K(11) increases by ~50% and K(33) decreases by ~80% compared to pure 5CB when the BC concentration is increased to ~43 mol % in the mixture. Viscosities parallel and perpendicular to the director, η(||), η(⊥), which are nearly equal to the Miesowicz viscosities η(2) and η(3), respectively, were obtained by D(||) and D(⊥) using the Stokes-Einstein relation. Both the viscosities at room temperature increase by 60 and 50 times, respectively, whereas γ(1) increases by 180 times (at ~43 mol %) compared to the corresponding values of pure 5CB. The stiffening of K(11) and exorbitantly large enhancement in all the viscosities at a higher mol % of BC indicate that the viscoelastic properties are highly impacted by the presence of smectic clusters of BC molecules that results from the restricted free rotation of the molecules along the bow axis in the nematic phase. A possible attachment model of smectic type clusters of BC molecules surrounding the microparticle is presented.

Exenatide decreases hepatic fibroblast growth factor 21 resistance in non-alcoholic fatty liver disease in a mouse model of obesity and in a randomised controlled trial.

AIMS/HYPOTHESIS: Systemic fibroblast growth factor (FGF)21 levels and hepatic FGF21 production are increased in non-alcoholic fatty liver disease patients, suggesting FGF21 resistance. We examined the effects of exenatide on FGF21 in patients with type 2 diabetes and in a diet-induced mouse model of obesity (DIO). METHODS: Type 2 diabetes mellitus patients (n = 24) on diet and/or metformin were randomised (using a table of random numbers) to receive additional treatment consisting of pioglitazone 45 mg/day or combined therapy with pioglitazone (45 mg/day) and exenatide (10 µg twice daily) for 12 months in an open label parallel study at the Baylor Clinic. RESULTS: Twenty-one patients completed the entire study and were included in the analysis. Pioglitazone treatment (n = 10) reduced hepatic fat as assessed by magnetic resonance spectroscopy, despite a significant increase in body weight (Δ = 3.7 kg); plasma FGF21 levels did not change (1.9 ± 0.6 to 2.2 ± 0.6 ng/ml [mean ± SEM]). However, combined pioglitazone and exenatide therapy (n = 11) was associated with a significant reduction of FGF21 levels (2.3 ± 0.5 to 1.1 ± 0.3 ng/ml) and a greater decrease in hepatic fat. Besides weight gain observed in the pioglitazone-treated patients, lower extremity oedema was observed as a side effect in two of the ten patients. Three patients who received pioglitazone and exenatide combination therapy complained of significant nausea that was self-limiting and did not require them to leave the study. In DIO mice, exendin-4 for 4 weeks significantly reduced hepatic triacylglycerol content, decreased hepatic FGF21 protein and mRNA, and enhanced phosphorylation of hepatic AMP-activated protein kinase (AMPK) and acetyl-CoA carboxylase, although no significant difference in weight and body fat was observed. Hepatic FGF21 correlated inversely with hepatic AMPK phosphorylation CONCLUSIONS/INTERPRETATION: In type 2 diabetes mellitus, combined pioglitazone and exenatide therapy is associated with a reduction in plasma FGF21 levels, as well as a greater decrease in hepatic fat than that achieved with pioglitazone therapy. In DIO mice, exendin-4 treatment reduces hepatic triacylglycerol and FGF21 protein, and enhances hepatic AMPK phosphorylation, suggesting an improvement of hepatic FGF21 resistance. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov NCT 01432405.

Increased abundance of the adaptor protein containing pleckstrin homology domain, phosphotyrosine binding domain and leucine zipper motif (APPL1) in patients with obesity and type 2 diabetes: evidence for altered adiponectin signalling.

AIMS/HYPOTHESIS: The adiponectin signalling pathway is largely unknown, but recently the adaptor protein containing pleckstrin homology domain, phosphotyrosine binding domain and leucine zipper motif (APPL1), has been shown to interact directly with adiponectin receptor (ADIPOR)1. APPL1 is present in C2C12 myoblasts and mouse skeletal muscle, but its presence in human skeletal muscle has not been investigated. METHODS: Samples from type 2 diabetic, and lean and non-diabetic obese participants were analysed by: immunoprecipitation and western blot; HPLC-electrospray ionisation (ESI)-mass spectrometry (MS) analysis; peak area analysis by MS; HPLC-ESI-MS/MS/MS analysis; and RT-PCR analysis of APPL1 mRNA. RESULTS: Immunoprecipitation and western blot indicated a band specific to APPL1. Tryptic digestion and HPLC-ESI-MS analysis of whole-muscle homogenate APPL1 unambiguously identified APPL1 with 56% sequence coverage. Peak area analysis by MS validated western blot results, showing APPL1 levels to be significantly increased in type 2 diabetic and obese as compared with lean participants. Targeted phosphopeptide analysis by HPLC-ESI-MS/MS/MS showed that APPL1 was phosphorylated specifically on Ser(401). APPL1 mRNA expression was significantly increased in obese and type 2 diabetic participants as compared with lean participants. After bariatric surgery in morbidly obese participants with subsequent weight loss, skeletal muscle APPL1 abundance was significantly reduced (p < 0.05) in association with an increase in plasma adiponectin (p < 0.01), increased levels of ADIPOR1 (p < 0.05) and increased muscle AMP-activated protein kinase (AMPK) phosphorylation (p < 0.05). CONCLUSIONS/INTERPRETATION: APPL1 abundance is significantly higher in type 2 diabetic muscle; APPL1 is phosphorylated in vivo on Ser(401). Improvements in hyperglycaemia and hypoadiponectinaemia following weight loss are associated with reduced skeletal muscle APPL1, and increased plasma adiponectin levels and muscle AMPK phosphorylation.

Temperature- and electric-field-induced inverse Freedericksz transition in a nematogen with weak surface anchoring.

We report electric field dependence of the anchoring transition in a mesogen on cooling in a cell with perfluoropolymer treated surfaces. Below a crossover voltage V(co) the transition is discontinuous between planar and homeotropic alignments, and as the temperature is lowered, the transition temperature decreases quadratically with the field. Above V(co) the transition is continuous between planar and tilted alignments, the transition temperature decreasing essentially linearly with the rms field. We develop a simple model to account for these results and argue that the higher field regime corresponds to a temperature driven inverse Freedericksz transition in which the director orientation starts tilting at the weakly anchored surfaces while the tilt angle remains zero at the midplane of the cell.

Splay bend elasticity of a bent-core nematic liquid crystal.

We measured the splay (K11) and bend (K33) elastic constants in the nematic phase of a bent-core liquid crystal. In the vicinity of the nematic-isotropic transition temperature K33 is proportional to the square of the order parameter. In the nematic range K11 increases monotonically with decreasing temperature, whereas K33 is practically independent of temperature and is smaller than K11 . K33 exhibits a pretransitional slow divergence toward the transition temperature to the smectic phase and becomes slightly larger than K11. The small K33 is explained on the basis of strong coupling of the bent shape of the molecules with the bend distortion.

Splay-bend elasticity of a nematic liquid crystal with T-shaped molecules.

We measured the splay (K11) and bend (K33) elastic constants in the nematic phase of a liquid crystal with T-shaped molecules. We find that the ratio, K33/K11 ≃1 in the entire nematic range except very close to the nematic to Sm-A (SN) transition. Both K33 and K11 show pretransitional divergence as the SN transition is approached from higher temperature. The ratio, K33/K11 suggests that the length (L) to effective width (D) ratio (i.e., L/D ) is significantly smaller due to the presence of long and flexible lateral group, compared to that of rigid rodlike molecules. It is argued that apart from the extra contribution to the elasticity the long and flexible lateral group also has a significant contribution to the suppression of the splay fluctuations in the onset of smectic short-range fluctuation. The structure of the Sm-A phase is investigated by using small angle x-ray diffraction, and a possible arrangement of the molecules in the Sm-A layer is proposed.

A free volume microprobe study of water sorption in a contact lens polymer.

The kinetics of moisture uptake in a rigid gas-permeable contact lens material, Fluoroperm60, has been investigated. The free volume changes accompanied by the sorption of water were monitored using the positron lifetime spectroscopy (PLS) technique. The positron results indicated swelling in the initial stages of sorption and the filling of vacant free volume sites with water in the later stages of sorption. The sorption curve suggests that the diffusion process in this polymer follows the dual-mode sorption model. Using this model, it was possible to separate Fickian-controlled diffusion and relaxation-controlled diffusion. Furthermore, the positron results combined with the sorption results indicated that Fujita's free volume theory does not seem to be valid for the diffusion process in the present sample under study. The variation of the permeability as a function of the free volume suggests that the amount of water in a contact lens is a measure of its permeability.

Role of apoptosis of renal tubular cells in acute renal failure: therapeutic implications.

Acute renal failure (ARF) can be defined as a sudden loss of renal function and is a common and serious clinical problem. There are many causes of ARF but the most common cause results from injury to the renal tubular epithelial cells (RTECs). RTECs can be injured by schemia or by cytotoxic agents and, once injured, can die by necrosis or apotosis. In general, necrosis occurs in response to any severe injury, which leads to the biochemical collapse of the cell. Milder forms of the same types of injury cause apoptosis. At the cellular level there are fundamental differences between necrosis and apoptosis. Necrosis results from the additive effect of a number of independent biochemical events that are activated by severe depletion of cell energy stores. By contrast, apoptosis occurs via a coordinated, predictable and pre-determined pathway. These biochemical differences between apoptosis and necrosis have important therapeutic implications. Once a cell has been severely injured, necrosis is difficult to prevent. By contrast, the apoptotic pathway can potentially be modulated to maintain cell viability. The components of the apoptotic pathway that are potentially amenable to therapeutic modulation are discussed in detail in this review.

Interaction of hematopoietic progenitor kinase 1 and c-Abl tyrosine kinase in response to genotoxic stress.

The c-Abl protein tyrosine kinase is activated by certain DNA-damaging agents and regulates induction of the stress-activated protein kinase/c-Jun N-terminal kinase (SAPK/JNK). The hematopoietic progenitor kinase 1 (HPK1) has also been shown to act upstream to the SAPK/JNK signaling pathway. We report here that exposure of hematopoietic Jurkat T cells to genotoxic agents is associated with activation of HPK1. The results demonstrate that exposure of Jurkat cells to DNA-damaging agents is associated with translocation of active c-Abl from nuclei to cytoplasm and binding of c-Abl to HPK1. Our findings also demonstrate that c-Abl phosphorylates HPK1 in cytoplasm and stimulates HPK1 activity. The functional significance of the c-Abl-HPK1 interaction is supported by the demonstration that this complex regulates SAPK/JNK activation. Overexpression of c-Abl(K-R) inhibits HPK1-induced activation of SAPK/JNK. Conversely, the dominant negative mutant of HPK1 blocks c-Abl-mediated induction of SAPK/JNK. These findings indicate that activation of HPK1 and formation of HPK1/c-Abl complexes are functionally important in the stress response of hematopoietic cells to genotoxic agents.

Transseptal insertion of left atrial line: a simple and safe technique.

The widespread use of left atrial lines underscores the importance of left atrial pressure monitoring in open heart operations. We present a simple and safe method of intraoperative insertion of a left atrial line during an open heart operation. Foremost among the several advantages of this method is that there would no longer be any concern of postoperative bleeding after removal of the left atrial line.

Percutaneous balloon versus surgical closed commissurotomy for mitral stenosis. A prospective, randomized trial.

BACKGROUND: We performed a prospective, randomized trial comparing percutaneous balloon commissurotomy with surgical closed commissurotomy in 40 patients with severe rheumatic mitral stenosis. METHODS AND RESULTS: Data were analyzed by investigators who were masked to treatment assignment or phase of study. Patients randomized to balloon (n = 20) or surgical (n = 20) commissurotomy had severe mitral stenosis without significant baseline differences (left atrial pressure, 26.1 +/- 4.2 versus 27.6 +/- 6.2 mm Hg; mitral valve gradient, 18.0 +/- 4.2 versus 19.7 +/- 6.3 mm Hg; mitral valve area, 1.0 +/- 0.2 versus 1.0 +/- 0.4 cm2, respectively). At 1-week follow-up after balloon commissurotomy, pulmonary wedge pressure was 14.3 +/- 7.2 mm Hg; mitral valve gradient was 9.6 +/- 5.1 mm Hg; and mitral valve area was 1.6 +/- 0.6 cm2 (all p less than 0.0001). At 1-week follow-up after surgical closed commissurotomy, wedge pressure was 13.7 +/- 5.4 mm Hg; mitral valve gradient was 9.4 +/- 4.2 mm Hg (both p less than 0.0001); and mitral valve area was 1.6 +/- 0.7 cm2 (p less than 0.003). At 8-month follow-up, improvement occurred in both groups: Mitral valve area was 1.6 +/- 0.6 cm2 in the balloon commissurotomy group (p less than 0.002) and was 1.8 +/- 0.6 cm2 in the surgical closed commissurotomy group (p less than 0.0001). There was no difference between the groups at 1-week or 8-month follow-up (all p greater than 0.4). One case of severe mitral regurgitation occurred in each group; complications were otherwise related to transseptal catheterization. There was no death, stroke, or myocardial infarction. Cost analysis revealed that balloon commissurotomy may substantially exceed the cost of surgical commissurotomy in developing countries, whereas it may represent a significant savings in industrialized nations. CONCLUSIONS: We conclude that percutaneous balloon commissurotomy and surgical closed commissurotomy result in comparable hemodynamic improvement that is sustained through 8 months of follow-up.