Coupling of retinal isomerization to the activation of rhodopsin

Activation of the visual pigment rhodopsin is caused by 11-cis to -trans isomerization of its retinal chromophore. High-resolution solid-state NMR measurements on both rhodopsin and the metarhodopsin II intermediate show how retinal isomerization disrupts helix interactions that lock the receptor off in the dark. We made 2D dipolar-assisted rotational resonance NMR measurements between (13)C-labels on the retinal chromophore and specific (13)C-labels on tyrosine, glycine, serine, and threonine in the retinal binding site of rhodopsin. The essential aspects of the isomerization trajectory are a large rotation of the C20 methyl group toward extracellular loop 2 and a 4- to 5-A translation of the retinal chromophore toward transmembrane helix 5. The retinal-protein contacts observed in the active metarhodopsin II intermediate suggest a general activation mechanism for class A G protein-coupled receptors involving coupled motion of transmembrane helices 5, 6, and 7.     

Which cancer clinical trials should be considered for economic evaluation? Selection criteria from the National Cancer Institute of Canada's Working Group on Economic Analysis

Rising health care costs, expensive new health care technologies and increasing patient expectations are placing huge pressures on the publicly funded health care system in Canada. As a result, policy makers need information on the cost and cost-effectiveness of new therapies in addition to their clinical benefits. In response to this need, the National Cancer Institute of Canada Clinical Trials Group (NCIC CTG) established a Working Group on Economic Analysis (WGEA) to provide advice on the economic evaluation of new cancer therapies. This article describes the WGEA's recommendations on which trials should be considered for concurrent analysis of economic, as well as related issues, such as the number of patients required for an economic analysis within a prospective clinical trial and the selection of participating centres. The recommendations in this document are meant to be pragmatic, as the WGEA recognizes that both the research funds and human resource capacity for this type of research in Canada are limited. These recommendations are currently guiding priority setting with regard to trials for economic evaluation in NCIC trials. Examples of how these recommendations have been applied to actual trials are presented.     

Intestinal absorption of low molecular weight heparin in animals and human subjects

INTRODUCTION: We had previously shown that the use of bile salts, which act as surfactants, facilitates the intestinal absorption of large molecules such as those of heparin and insulin. However, the bioavailability of unfractionated heparin (UFH) administered through the large intestine was low. The aim of the present study was to evaluate the absorption of low molecular weight heparin (LMWH) combined with bile salts through the gut mucosa in animals and human subjects. MATERIALS AND METHODS: LMWH (Fragmin, Kabi-Pharmacia, Stockholm) or UFH with or without sodium cholate (Sch) was administrated rectally in rats and healthy volunteers via a microenema. Absorption was estimated by the activated partial thromboplastin time (aPTT), the plasma anti-factor Xa activity and the plasma lipoprotein lipase (LPL) activation. RESULTS: In groups of 6 rats, LMWH at doses of 100--1,000 U with sodium cholate (10--20 mg/ml) was readily absorbed through the gut mucosa, as indicated by both, anti-factor Xa levels of up to 1 U/ml and a dose-dependent activation of LPL. The absorption was significantly superior to that of UFH with Sch or LMWH given without Sch (p < 0.001). The plasma anti-factor Xa levels in the 6 healthy volunteers who received a microenema containing 25,000 U of LMWH with 20 mg/ml of Sch were 0.38 U/ml at 15 min and 0.1 U/ml at 240 min. LPL activation and aPTT prolongation were also observed in these subjects. The plasma LMWH levels after rectal application were in the same range as those obtained after subcutaneous administration, however the elimination time (t 1/2) was shorter. There were no adverse reactions. CONCLUSIONS: Intestinal absorption of LMWH facilitated by Sch is both feasible and safe. A slow release formulation will be needed to prolong the plasma half-life.     

In vivo platelet activation in beta-thalassemia major reflected by increased platelet-thromboxane urinary metabolites

Increased frequency of thromboembolic events has been recently observed in patients with beta-thalassemia major (TM). Platelet function anomalies including impaired aggregation, increased circulating aggregates, and our finding of shortened platelet survival indicate that platelets may be involved in the hypercoagulability in thalassemia. Consequently, we used a technique based on thin layer chromatography purification and enzyme immunoassay to measure urinary metabolites of thromboxane A2 (TXA2) and prostacyclin (PGI2) in nine splenectomized patients with beta-TM regularly transfused, five non- splenectomized patients with beta-thalassemia intermedia (TI), and 20 healthy individuals. A significant 4- to 10-fold increase was observed in the urinary excretion of 2,3-dinor-TXB2, 11-dehydro-TXB2 and 2,3- dinor-6-keto-PGF1 alpha in patients with TM and TI as compared with healthy controls. No significant differences were found in the concentrations of these metabolites between TM and TI patients. Six TM patients received a very low dose of aspirin (20 mg/day) for 7 days. A significant decrease was observed in the urinary concentrations of 2,3- dinor-TXB2 and 11-dehydro-TXB2 derived from platelets. However, the levels of urinary 2,3-dinor-6-keto-PGF1 alpha reflecting vascular production and TXB2 and 6-keto-PGF1 alpha originating from the kidney were not significantly changed. These results are consistent with those of increased in vivo production of TXA2 because of endogenous platelet activation.     

Empirical Testing of the External Validity of a Discrete Choice Experiment to Determine Preferred Treatment Option: The Case of Sleep Apnea

There is an increasing use of the discrete choice experiment (DCE) method in health care to estimate preferences of individuals and the public for different services. Despite this increasing use, there are few studies that investigate the validity of the DCE in health. This study investigates the external validity of DCE by comparing the predicted treatment choices from the DCE to the actual treatment choices made by the same respondents using a decision board (DB) approach. The sample includes 140 patients who came for a sleep apnea routine visit in a hospital setting. Each respondent answered 10 DCE tasks and 1 DB task. The preferences were estimated with a generalized multinomial logit model and the predicted and actual treatment choices were compared both at the sample and individual levels. The results raise questions about the external validity of DCE in health. At the sample level, the comparison showed large but not significant differences between the two methods. This can be explained in part by the aggregation process that obscures variability in the individuals’ preferences. At the individual level, the comparison showed that the two methods led to significantly different patterns of choices. Copyright © 2014 John Wiley & Sons, Ltd.     

Assessment of fetal myocardial performance using myocardial deformation analysis

Conventional techniques for the assessment of cardiac function on the basis of M-mode or 2-dimensional modalities are technically difficult, load dependent, and provide information on global ventricular function only. Newer techniques, which analyze myocardial performance, such as tissue velocity, strain, and especially the less load dependent strain rate, may provide more appropriate information. Myocardial systolic and diastolic motion and performance were calculated using tissue velocity, strain, and strain rate imaging on a large cohort of normal fetuses. The assessment of myocardial performance was feasible in all 98 normal fetuses. Normal systolic and diastolic values for tissue velocity, strain, and strain rate were established. All data were highly reproducible. Tissue velocity was age dependent, whereas strain and strain rate were stable throughout gestation. All parameters were heart rate independent. In conclusion, fetal myocardial velocity, strain, and strain rate measurements are easy to obtain and reproducible, and therefore, may serve as reference data. Increases in tissue velocity throughout gestation probably reflect the growth of the fetal heart, whereas intrinsic myocardial properties as measured by strain rate do not change. In comparison with recently published myocardial performance values in children, these strain rate data suggest that fetal myocontractile properties that are already established during the second half of pregnancy remain constant throughout gestation and after birth.     

Improved left ventricular mass index in children after renal transplantation

Left ventricular hypertrophy (LVH) is a risk factor for cardiovascular disease, and it is prevalent in children with end-stage renal disease (ESRD) and after renal transplantation (RTx) on cross-sectional studies. Our aim was to compare prospectively left ventricular mass index (LVMI) in children with ESRD, before and after RTx. Thirteen patients aged 1.5-15 years underwent echocardiogram prior to and at least 3 months after RTx, and again in the second year after transplantation. A control group consisted of children with ESRD who remained on dialysis. Systolic and diastolic blood pressure index decreased significantly over the study period only in the children who had undergone RTx. Mean LVMI in children with ESRD decreased from 45.4 +/- 12.6 g/m(2.7) to 34.9 +/- 10.4 g/m(2.7) after RTx (P = 0.001), but it remained unchanged in patients who remained on dialysis. The prevalence of LVH decreased from 54% to 8% (P = 0.03) after RTx. Systolic and diastolic blood pressure index were correlated with LVMI. Mean body mass index increased during the study period from 17.3 +/- 2.5 to 20 +/- 4.6 (P = 0.05); however, no correlation was found with LVMI. LVH in children with ESRD is potentially reversible after RTx, especially with good control of hypertension.     

Estimation, power and sample size calculations for stochastic cost and effectiveness analysis

Various methods have been proposed to address uncertainty in economic evaluations of healthcare programmes. One approach suggested in the literature is to estimate separate confidence intervals for the incremental costs and effects of a new health programme in comparison with an existing programme. These intervals are then combined to generate a rectangular confidence region in the cost-effectiveness plane that implicitly defines a corresponding confidence interval for the incremental cost-effectiveness ratio (ICER). The same approach has been used to calculate sample sizes and study power. This application of the rectangle method is consistent with the adoption of ICERs and a threshold as a decision rule, this being the most commonly used approach in empirical applications of cost-effectiveness analysis, as well as the one recommended by agencies that assess medical technology around the world. In this paper, we first outline the rectangle method, and then propose a modification that recognises that separate inferences are being drawn on the cost and effectiveness domains, and that corrects for multiple statistical comparisons. The confidence rectangle is otherwise too small, the corresponding confidence interval for the ICER is too narrow and sample sizes are under-estimated. Our modification corrects these problems. A further difficulty is that the placement of the confidence rectangle around the null value is somewhat arbitrary, and does not correspond to a unique value of ICERs. As a result, different values of sample size and power for the estimation of ICERs can be obtained, depending on the null values of the cost and effectiveness. We conclude that it is important to clearly identify the analytic goal in terms of estimating differential costs, differential effects or a combination of the two using the ICER index. These ideas are illustrated using numerical examples.