Advanced glycation end products in vitreous: Structural and functional implications for diabetic vitreopathy

PURPOSE. Advanced glycation end products (AGES) form irreversible cross- links with many macromolecules and have been shown to accumulate in tissues at an accelerated rate in diabetes. In the present study, AGE formation in vitreous was examined in patients of various ages and in patients with diabetes. Ex vivo investigations were performed on bovine vitreous incubated in glucose to determine AGE formation and cross-linking of vitreous collagen. METHODS. By means of an AGE-specific enzyme-linked immunosorbent assay (ELISA), AGE formation was investigated in vitreous samples obtained after pars plana vitrectomy in patients with and without diabetes. In addition, vitreous AGES were investigated in bovine vitreous collagen after incubation in high glucose, high glucose with aminoguanidine, or normal saline for as long as 8 weeks. AGEs and AGE cross-linking was subsequently determined by quantitative and qualitative assays. RESULTS. There was a significant correlation between AGEs and increasing age in patients without diabetes (r = 0.74). Furthermore, a comparison between age-matched diabetic and nondiabetic vitreous showed a significantly higher level of AGEs in the patients with diabetes (P < 0.005). Collagen purified from bovine vitreous incubated in 0.5 M glucose showed an increase in AGE formation when observed in dot blot analysis, immunogold labeling, and AGE ELISA. Furthermore, there was increased cross-linking of collagen in the glucose-incubated vitreous, when observed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein separation. This cross-linking was effectively inhibited by coincubation with 10 mM aminoguanidine. CONCLUSIONS. This study suggests that AGEs may form in vitreous with increasing age. This process seems to be accelerated in the presence of diabetes and as a consequence of exposure to high glucose. Advanced glycation and AGE cross-linking of the vitreous collagen network may help to explain the vitreous abnormalities characteristic of diabetes.

Mutations in sodium-borate cotransporter SLC4A11 cause recessive congenital hereditary endothelial dystrophy (CHED2)

Congenital hereditary endothelial dystrophy ( CHED) is a heritable, bilateral corneal dystrophy characterized by corneal opacification and nystagmus. We describe seven different mutations in the SLC4A11 gene in ten families with autosomal recessive CHED. Mutations in SLC4A11, which encodes a membrane-bound sodium-borate cotransporter, cause loss of function of the protein either by blocking its membrane targeting or nonsense-mediated decay.

Modelling of the sodium complex of a calixarene tetraester in the 1,3-alternate conformation

This paper describes the use of molecular mechanics to model the geometry of the sodium complex of a calix[4] arene tetraester, in the 1,3-alternate conformation 1. Partial charges were assigned to the calixarene on the basis of semi-empirical (AM1, PM3, MNDO, INDO, CNDO and ZINDO) calculations and the binding of the sodium ion to the calixarene was modelled using molecular mechanics. Agreement between the optimised and X-ray structures of the complex was very good. The effect of placing the cation in different starting positions on the energy-minimised geometry of the complex is described.

Highly Ionized sodium X-ray line emission from the solar corona and the abundance of sodium

Context. The X-ray lines between 10.9 and 11.2 Å have attracted little attention but are of interest since they enable an estimate of the coronal abundance of Na to be made. This is of great interest in the continuing debate on the nature of the FIP (first ionization potential) effect. Aims. Observations of the lines with the Solar Maximum Mission Flat Crystal Spectrometer and a rocket-borne X-ray spectrometer are used to measure the Na/Ne abundance ratio, i.e. the ratio of an element with very low FIP to one with high FIP. Methods. New atomic data are used to generate synthetic spectra which are compared with the observations, with temperature and the Na/Ne abundance ratio as free parameters. Results. Temperature estimates from the observations indicate that the line emission is principally from non-flaring active regions, and that the Na/Ne abundance ratio is 0.07 ± 50%. Conclusions. The Na/Ne abundance ratio is close to a coronal value for which the abundances of low-FIP elements (FIP < 10 eV) are enhanced by a factor of 3 to 4 over those found in the photosphere. For low-temperature (Te 1.5 MK) spectra, the presence of lines requires that either a higher-temperature component is present or a revision of ionization or recombination rates is needed.

The photo-oxidation of water by sodium persulfate, and other electron acceptors, sensitised by TiO2

A number of different electron acceptors are tested for efficacy in the oxidation of water to oxygen, photocatalysed by titanium dioxide. The highly UV-absorbing metal ion electron acceptors, Ce4+ and Fe3+, appear ineffective at high concentration (10(-2) M), due to UV-screening, but more effective at lower concentrations (10(-3) M). The metal-depositing electron acceptor, Ag+, is initially effective, but loses activity upon prolonged irradiation due to metal deposition which promotes electron-hole recombination as well as UV-screening the titania particles. Most striking of the electron acceptors tested is persulfate, particularly in alkaline solution (0.1 M NaOH). The kinetics of the photo-oxidation of water by persulfate, photocatalysed by titania are studied as a function of pH, [S2O82-] and incident light intensity (I). The initial rate of water oxidation increases with pH, is directly proportional to the concentration of persulfate present and depends upon I-0.6. The TiO2/alkaline persulfate photosystem is robust and shows very little evidence of photochemical wear upon repeated irradiation. The results of this work are discussed with regard to previous work in this area and current mechanistic thinking. The formal quantum efficiency of the TiO2/alkaline persulfate photosystem was estimated as ca. 2%. (C) 2004 Elsevier B.V. All rights reserved.

EFFECT OF ULTRASOUND ON THE KINETICS OF OXIDATION OF OCTAN-2-OL AND OTHER SECONDARY ALCOHOLS WITH SODIUM-BROMATE, MEDIATED BY RUTHENIUM TETRAOXIDE IN A BIPHASIC SYSTEM

The initial rate of oxidation of octan-2-ol and other secondary alcohols to their ketones with NaBrO3, mediated by RuO4 in an aqueous-CCl4 biphasic system, is greater with ultrasonic irradiation than by stirring alone. Under ultrasonic irradiation the initial rate of oxidation of octan-2-ol increases with increasing % duty cycle, [RuO4] and [NaBrO3]. The kinetics of alcohol oxidation appear to be closely linked with the oxidative dissolution of RuO2 to RuO4 by NaBrO3. The observed enhancement in rate with ultrasonic irradiation appear to be association, at least in part, with the increase in interfacial surface area via the formation of an emulsion of aqueous microdroplets containing NaBrO3 in the CCl4 layer containing the non-water-soluble secondary alcohol.

KINETICS OF REDUCTIVE DISSOLUTION OF SODIUM BISMUTHATE BY CE-III AND MN-II IONS

The kinetics of reductive dissolution of NaBiO3, by Mn-II and Ce-III ions are studied as a function of [Mn-II] or [Ce-III], [Bi-III], [H+] and temperature. They fit a simple inverse-cubic rate law and can be readily interpreted using a mechanism in which the rate-determining step is the reaction between an adsorbed reducing species (i.e. a Mn-II or Ce-III ion) and its associated surface site; protonation of the surface site promotes the rate of reaction. The rate of dissolution decreases with increasing initial concentration of Bi-III ions owing to competitive inhibition by the latter species. A kinetic model, based on this mechanism, is applied and provides a quantitative description of the observed kinetics.

Path-selective photoinduced electron transfer (PET) in a membrane-associated system studied by pH-dependent fluorescence

The pH-dependent fluorescence behavior of two regioisomeric 'receptor(1)-spacer(1)-fluorophore-spacer(2)-receptor(2)' systems 1 and 2 in micellar solutions of sodium dodecyl sulfate show that photoinduced electron transfer (PET) only occurs from the amine group connected to the 4-amino position of the aminonaphthalimide fluorophore in both cases. This demonstrates the directing influence of the photogenerated electric field within the aminonaphthalimide excited state on the electron transfer process. Since path-selectivity of PET is also known within the membrane-bound photosynthetic reaction center in bacteria, its origins may be illuminated by the simple experiments described here. (C) 2011 Elsevier B. V. All rights reserved.

Solid-state sodium-selective sensors based on screen-printed Ag/AgCl reference electrodes

The potentiometric and AC impedance characteristics of all solid-state sodium-selective electrodes based on planar screen-printed Ag/AgCl electrodes are described. Two solid-state designs have been investigated. The first was based on the deposition of a sodium-selective PVC membrane directly on top of a screen-printed Ag/AgCl electrode, The second design included a NaCl doped hydrogel layer, between the PVC and Ag\AgCl layers. The hydrogel provides a mechanism to relieve any blockage to charge transfer occurring when PVC membranes are used directly on top of Ag/AgCl and also improves adhesion between the two layers. Results suggest the electrodes display Fast ion exchange kinetics, low noise and drift. The performance compares favorably to that of a conventional ion-selective electrode with internal filling solution.