Low Serum Glutathione Peroxidase Activity Is Associated with Increased Cardiovascular Mortality in Individuals with Low HDLc’s

Background Since oxidized LDL is thought to initiate atherosclerosis and the serum glutathione peroxidase (GPx3) reduces oxidized lipids, we investigated whether high GPx3 activity reduces cardiovascular disease (CVD) mortality. Methods We determined GPx3 in stored samples from the Minnesota Heart Survey of 130 participants who after 5 to 12 years of follow-up had died of CVD and 240 controls. Participants were 26 to 85 years old and predominantly white. In a nested case-control, study we performed logistic regressions to calculate odds ratios (OR) adjusted for age, sex, baseline year, body mass index, smoking, alcohol intake, physical activity, total and HDL cholesterols, systolic blood pressure, serum glucose and gamma glutamyltransferase (GTT) activity. The referent was the quartile with the highest GPx3 activity (quartile 4). Results OR’s for CVD mortality for increasing quartiles of GPx3 were 2.37, 2.14, 1.83 and 1.00 (P for trend 0.02). This inverse correlation was confined to those with HDLc’s below the median (P for interaction, 0.006). The OR’s for increasing quartiles of GPx3 in this group were 6.08, 5.00, 3.64 and 1.00 (P for trend, 0.002). Conclusions Individuals with both low HDLc and GPx3 activity are at markedly increased risk for death from CVD

Characterization of an Enantioselective Odorant Receptor in the Yellow Fever Mosquito Aedes aegypti

Enantiomers differ only in the left or right handedness (chirality) of their orientations and exhibit identical chemical and physical properties. In chemical communication systems, enantiomers can be differentially active at the physiological and behavioral levels. Only recently were enantioselective odorant receptors demonstrated in mammals while their existence in insects has remained hypothetical. Using the two-microelectrode voltage clamp of Xenopus oocytes, we show that the yellow fever mosquito, Aedes aegypti, odorant receptor 8 (AaOR8) acts as a chiral selective receptor for the (R)-(—)-enantiomer of 1-octen-3-ol, which in the presence of other kairomones is an attractant used by blood-sucking insects to locate their hosts. In addition to steric constraints, chain length and degree of unsaturation play important roles in this recognition process. This is the first characterization of an enantioselective odorant receptor in insects and the results demonstrate that an OR alone, without helper proteins, can account for chiral specificity exhibited by olfactory sensory neurons (OSNs)

Compensation of magnetic field distortions from paramagnetic instruments by added diamagnetic material: measurements and numerical simulations

In minimally invasive procedures guided by magnetic resonance (MR) imaging instruments usually are made of titanium or titanium alloys (e.g., nitinol), because other more MR-compatible materials often cannot provide sufficient mechanical properties. Artifacts depending on susceptibility arise in MR images due to incorrect spatial encoding and intravoxel dephasing and thereby hamper the surgeon's view onto the region of interest. To overcome the artifact problem, compensation of the paramagnetic properties by diamagnetic coating or filling of the instruments has been proposed in the literature. We used a numerical modeling procedure to estimate the effect of compensation. Modeling of the perturbation of the static magnetic field close to the instruments reflects the underlying problem and is much faster and cost efficient than manufacturing prototypes and measuring artifact behavior of these prototypes in the MR scanner. A numerical model based on the decomposition of the susceptibility distribution in elementary dipoles was developed by us. The program code was written object oriented to allow for both maximum computational speed and minimum random access memory. We used System International units throughout the modeling for the magnetic field, allowing absolute quantification of the magnetic field disturbance. The field outside a simulated needlelike instrument, modeled by a paramagnetic cylinder (out of titan, chi =181.1) of length 8.0 mm and of diameter 1.0 mm, coated with a diamagnetic layer (out of bismuth, chi=-165.0) of thickness 0, 0.1, 0.2, 0.3, and 0.4 mm, was found to be best compensated if the cross-sectional area of the cylinder, multiplied by the absolute susceptibility value of the cylinder material, is equal to the cross-sectional area of the coating, multiplied by the absolute susceptibility value of the coating material. At the extremity of the coated cylinder an uncompensated field distortion was found to remain. We studied various tip shapes and geometries using our computational model: Suitable diamagnetic coating or filling of paramagnetic instruments clearly reduced tip artifacts and diminished the dependency of artifact size on orientation of the instrument with respect to B0 in the numerical studies. We verified the results of the simulations by measuring coated and uncoated titanium wires in a 1.5 T MR scanner

Numerical Simulations of Intra-voxel Dephasing Effects and Signal Voids in Gradient Echo MR Imaging using different Sub-grid Sizes

Signal void artifacts in gradient echo imaging are caused by the intra-voxel dephasing of the spins. Intra-voxel dephasing can be estimated by computing the field distribution on a sub-grid inside each picture element, followed by integration of all magnetization components. The strategy of computing the artifacts based on the integration of the sub-voxel signal components is presented here for different sub-grids. The coarseness of the sub-grid is directly related to computational effort. The possibility to save memory space and computing time for the dipole model by computing the field only on a sub-grid is addressed in the presented article. It is investigated as to how far computational time and memory space can be reduced by using an appropriate sub-grid. Numerical results for a model of a partially diamagnetically coated needle shaft are compared to experimental findings. In the case of a pure titanium needle, it is shown as being sufficient to compute the field distribution on a sub-grid that is at least four times coarser in each direction than the grid used to discretize the object in the related MR image. Due to three nested loops over the 3D grid, the need for memory space and time is saved by a factor 64. Deviations between measurements and simulations for the broad side of the artifact (uncompensated) and for the small side of the artifact (compensated) were 15.5, respectively, 19.1 for orientation parallel to the exterior field, and 22.7, respectively, 23.1 for orientation perpendicular to the exterior field

Numerical modeling of needle tip artifacts in MR gradient echo imaging

Exact determination of needle tip position is obsolete for interventional procedures under control of magnetic resonance imaging (MRI). Exact needle tip navigation is complicated by the paramagnetism of microsurgical instruments: Local magnetic field inhomogeneities are induced resulting in position encoding artifacts and in signal voids in the surrounding of instruments and especially near their tips. The artifacts generated by the susceptibility of the material are not only dependent on the material properties themselves and on the applied MRI sequences and parameters, but also on the geometric shape of the instruments and on the orientation to the static magnetic field in the MR unit. A numerical model based on superposition of induced elementary dipole fields was developed for studying the field distortions near paramagnetic needle tips. The model was validated by comparison with experimental data using field mapping MRI techniques. Comparison between experimental data and numerical simulations revealed good correspondence for the induced field inhomogeneities. Further systematic numerical studies of the field distribution were performed for variable types of concentric and asymmetric tip shapes, for different ratios between tip length and needle diameter, and for different orientations of the needle axis in the external static magnetic field. Based on the computed local inhomogeneities of the magnetic field in the surroundings of the needle tips, signal voids in usual gradient echo images were simulated for a prediction of the artifacts. The practically relevant spatial relation between those artifacts and the hidden tip of the needle was calculated for the different tip shapes and orientations in the external field. As needle tip determination is crucial in interventional procedures, e.g., in taking biopsies, the present model can help to instruct the physician prior to surgical interventions in better estimating the needle tip position for different orientations and needle tip shapes as they appear in interventional procedures. As manufacturing prototypes with subsequent measurements of artifacts in MRI are a costly procedure the presented model may also help to optimize shapes of needle tips and of other parts of MR‐compatible instruments and implants with low expense prior to production if some shape parameters can be chosen freely