Structural and dynamical basis of broad substrate specificity, catalytic mechanism, and inhibition of cytochrome P450 3A4

Cytochrome P450 (CYP) 3A4 is responsible for the oxidative degradation of more than 50% of clinically used drugs. By means of molecular dynamics simulations with the newly developed force field parameters for the heme-thiolate group and its dioxygen adduct, we examine the differences in structural and dynamic properties between CYP3A4 in the resting form and its complexes with the substrate progesterone and the inhibitor metyrapone. The results indicate that the broad substrate specificity of CYP3A4 stems from the malleability of a loop (residues 211-218) that resides in the vicinity of the channel connecting the active site and bulk solvent. However, the high-amplitude motion of the flexible loop is found to be damped out upon binding of the inhibitor or the substrate in the active site. In the resting form of CYP3A4, a structural water molecule is bound to the sixth coordination position of the heme iron, stabilizing the octahedral coordination geometry. In addition to the direct coordination of metyrapone to the heme iron, the hydrogen bond interaction between the inhibitor carbonyl group and the side chain of Ser119 also contributes significantly to stabilizing the CYP3A4-metyrapone complex. On the other hand, progesterone is stabilized in the active site by the formation of two hydrogen bonds with Ser119 and Arg106, as well as by the van der Waals interactions with the heme and hydrophobic residues. The structural and dynamic features of the CYP3A4-progesterone complex indicate that the oxidative degradation of progesterone occurs through hydroxylation at the C16 position by the reactive oxygen coordinated to the heme iron.     

Evogliptin,a dipeptidyl peptidase-4 inhibitor,attenuates pathological retinal angiogenesis by suppressing vascular endothelial growth factor-induced Arf6 activation

Dipeptidyl peptidase-4 (DPP-4) inhibitors are used for the treatment of type 2 diabetes mellitus (DM). Recent studies have shown that beyond their effect in lowing glucose, DPP-4 inhibitors mitigate DM-related microvascular complications, such as diabetic retinopathy. However, the mechanism by which pathological retinal neovascularization, a major clinical manifestation of diabetic retinopathy, is inhibited is unclear. This study sought to examine the effects of evogliptin, a potent DPP-4 inhibitor, on pathological retinal neovascularization in mice and elucidate the mechanism by which evogliptin inhibits angiogenesis mediated by vascular endothelial growth factor (VEGF), a key factor in the vascular pathogenesis of proliferative diabetic retinopathy (PDR). In a murine model of PDR, an intravitreal injection of evogliptin significantly suppressed aberrant retinal neovascularization. In human endothelial cells, evogliptin reduced VEGF-induced angiogenesis. Western blot analysis showed that evogliptin inhibited the phosphorylation of signaling molecules associated with VEGF-induced cell adhesion and migration. Moreover, evogliptin substantially inhibited the VEGF-induced activation of adenosine 5′-diphosphate ribosylation factor 6 (Arf6), a small guanosine 5′-triphosphatase (GTPase) that regulates VEGF receptor 2 signal transduction. Direct activation of Arf6 using a chemical inhibitor of Arf-directed GTPase-activating protein completely abrogated the inhibitory effect of evogliptin on VEGF-induced activation of the angiogenic signaling pathway, which suggests that evogliptin suppresses VEGF-induced angiogenesis by blocking Arf6 activation. Our results provide insights into the molecular mechanism of the direct inhibitory effect of the DPP-4 inhibitor evogliptin on pathological retinal neovascularization. In addition to its glucose-lowering effect, the antiangiogenic effect of evogliptin could also render it beneficial for individuals with PDR.Subject terms: Vascular diseases, Growth factor signalling     

Optimal salt concentration of vehicle for plasmid DNA enhances gene transfer mediated by electroporation

In vivo electroporation has emerged as a leading technology for developing nonviral gene therapies, and the various technical parameters governing electroporation efficiency have been optimized by both theoretical and experimental analysis. However, most electroporation parameters focused on the electric conditions and the preferred vehicle for plasmid DNA injections has been normal saline. We hypothesized that salts in vehicle for plasmid DNA must affect the efficiency of DNA transfer because cations would alter ionic atmosphere, ionic strength, and conductivity of their medium. Here, we show that half saline (71 mM) is an optimal vehicle for in vivo electroporation of naked DNA in skeletal muscle. With various salt concentrations, two reporter genes, luciferase and beta-galactosidase were injected intramuscularly under our optimal electric condition (125 V/cm, 4 pulses x 2 times, 50 ms, 1 Hz). Exact salt concentrations of DNA vehicle were measured by the inductively coupled plasma-atomic emission spectrometer (ICP-AES) and the conductivity change in the tissue induced by the salt in the medium was measured by Low-Frequency (LF) Impedance Analyzer. Luciferase expression increased as cation concentration of vehicle decreased and this result can be visualized by X-Gal staining. However, at lower salt concentration, transfection efficiency was diminished because the hypoosmotic stress and electrical injury by low conductivity induced myofiber damage. At optimal salt concentration (71 mM), we observed a 3-fold average increase in luciferase expression in comparison with the normal saline condition (p < 0.01). These results provide a valuable experimental parameter for in vivo gene therapy mediated by electroporation.     

The effect of mono-sized liquid crystal domains on electro-optical properties in a polymer dispersed liquid crystal prepared by using monodisperse poly(methylmethacrylate)/liquid crystal microcapsules

Highly mono-sized poly(methyl methacrylate) (PMMA)/liquid crystal (LC) microcapsules having a mono-sized single LC domain were prepared by the solute codiffusion method and solvent evaporation. The size of the LC domain in the microcapsules could be controlled by the amount of LC introduced during the swelling stage. The electro-optical properties of the polymer dispersed liquid crystal (PDLC) prepared by using the microcapsules was highly improved. In particular, the threshold voltage was lowered and the switching behaviour with an applied electric field was sharpened drastically compared with PDLC prepared simply by solvent evaporation-induced phase separation.     

PCPP derivatives containing carbazole pendant as hole transporting moiety for efficient blue electroluminescence

The syntheses and characterization of poly((2,6‐(4,4‐bis(4‐((2‐ethylhexyl)oxy)phenyl)‐4H‐cyclopenta[def]phenanthrene))‐co‐(2,6‐(4,4‐bis(4‐(((9‐carbazolyl)hexyl)oxy)phenyl))‐4H‐cyclopenta[def]phenanthrene)) (BCzPh‐PCPPs) and poly((2,6‐(4,4‐bis(4‐((2‐ethylhexyl)oxy)phenyl)‐4H‐cyclopenta[def]phenanthrene))‐co‐(2,6‐(4‐(4‐(((9‐carbazolyl)hexyl)oxy)phenyl)‐4‐(4‐((2‐ethylhexyl)oxy)phenyl)‐4H‐cyclopenta[def]phenanthrene))) (CzPh‐PCPPs), with carbazole unit as pendants, are presented. The carbazole moiety, which can improve the hole injection ability, was introduced as a pendant on the PCPP backbone. The devices of the polymers with the configurations of ITO/PEDOT:PSS/polymers/Ca/Al generate EL emission with maximum peaks at 400–450 nm, CIE coordinates of (x = 0.11–0.29, y = 0.11–0.33), low turn‐on voltages of 4–6 V, maximum brightness of 60–810 cd/m², and luminescence efficiencies of 0.04–0.22 cd/A. The PL spectra of CzPh‐PCPPs films did not show any peak at around 550 nm, which corresponds to keto defect or aggregate/excimer formation, even after annealing for 30 h at 150 °C in air. Out of the series, CzPh‐PCPP1 (PCPP derivative with 10% of carbazole moiety as pendant) shows blue emission with the maximum brightness of 810 cd/m² at 9 V, and the highest luminescence efficiency of 0.22 cd/A at 395 mA/cm². © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1327–1342, 2009     

Analysis of Linear Viscous Flow with a Free Surface in a Circular Cylinder Subjected to Small-Amplitude Circular Oscillations

A fluid flow with a free surface inside a circular cylinder subjected to horizontal, circular oscillation was analyzed theoretically and numerically under the assumption of small-amplitude oscillation and high Reynolds number. It was shown that the nature of the oscillatory flow is of a standing-wave type when projected onto the axial plane and of a progressive-wave type when projected onto the azimuthal plane. The Stokes drift motion in the azimuthal direction and the steady streaming velocity at the edge of the bottom- and side-wall boundary layers are then used in the numerical computation for the steady axisymmetric recirculatory flow outside the boundary layers. We have found that the solutions can be well predicted by asymptotic analysis for the full Navier–Stokes equations in the low streaming-Reynolds-number limit. A simple experiment on flow visualization revealed a good agreement in the surface flow pattern on the bottom wall. It also provided steady recirculatory flows that were not much different from the numerical results on the whole. Received 16 August 1999 and accepted 14 January 2000