Harmonization of VFAs measurement by GC: something more than R2 to evaluate the calibration function

Anaerobic digestion is sensitive to many environmental factors requiring a robust control of this process. One of the analytical measurements considered as key parameter is the volatile fatty acids (VFAs) content. Total amount of volatile acids (TVFA) to control the relative changes over time has been suggested as a useful tool. However, TVFA does not provide sufficient information to reveal the overall reactor performance, and individual components have been considered of particular interest. Although some attempts have been described as on-line measurements for individual VFAs, normally they are determined by off-line chromatographic techniques (GC and HPLC). A previous interlaboratory study showed the lack of harmonization in the analytical methodologies dealing to individual VFAs, and giving an overall analytical performance rather poor. One of the reasons to justify these results was the inappropriate calibration procedures. It is widely used to check the linearity of the calibration curves based on the correlation and determination coefficients. However, these statistical parameters are erroneously interpreted. The objective of this interlaboratory study was to achieve the harmonization of results. By this way, the use of internal standard methodology (ISTD) should be useful to obtain accurate calibration functions. In addition, five different statistical parameters such as lack of fit test, residual standard deviation, relative standard deviation of the slope, relative standard deviation of the sensitivity and relative error were proposed to evaluate the linearity of calibration curves. Of these, lack of fit was unable to detect appropriately the linearity mainly due to its sensitivity to the precision of analytical results. The rest of statistical parameters reported could be considered as starting point for comparative purposes, being useful as acceptance criteria. The principal advantage of the GC/ISTD analytical methodology was the normalization of the slopes obtained by the participating laboratories, being very helpful to the harmonization of results.Peer Reviewe

Reproducibility of quantitative (R)-[11C]verapamil studies

Background P-glycoprotein [Pgp] dysfunction may be involved in neurodegenerative diseases, such as Alzheimer's disease, and in drug resistant epilepsy. Positron emission tomography using the Pgp substrate tracer (R)-[11C]verapamil enables in vivo quantification of Pgp function at the human blood-brain barrier. Knowledge of test-retest variability is important for assessing changes over time or after treatment with disease-modifying drugs. The purpose of this study was to assess reproducibility of several tracer kinetic models used for analysis of (R)-[11C]verapamil data. Methods Dynamic (R)-[11C]verapamil scans with arterial sampling were performed twice on the same day in 13 healthy controls. Data were reconstructed using both filtered back projection [FBP] and partial volume corrected ordered subset expectation maximization [PVC OSEM]. All data were analysed using single-tissue and two-tissue compartment models. Global and regional test-retest variability was determined for various outcome measures. Results Analysis using the Akaike information criterion showed that a constrained two-tissue compartment model provided the best fits to the data. Global test-retest variability of the volume of distribution was comparable for single-tissue (6%) and constrained two-tissue (9%) compartment models. Using a single-tissue compartment model covering the first 10 min of data yielded acceptable global test-retest variability (9%) for the outcome measure K1. Test-retest variability of binding potential derived from the constrained two-tissue compartment model was less robust, but still acceptable (22%). Test-retest variability was comparable for PVC OSEM and FBP reconstructed data. Conclusion The model of choice for analysing (R)-[11C]verapamil data is a constrained two-tissue compartment model

Associations between daily sitting time and the combinations of lifestyle risk factors in men

Background: Understanding the reciprocal role that multiple problematic behaviours play in men's health is important for intervention delivery and for reducing the healthcare burden. Data regarding the concurrence of problematic health behaviours is currently limited but offers insights into risk profiles, and should now include total time spent sitting/day. Methods: Self-reported data on lifestyle health behaviours was collected from 232 men aged ≥18 years who engaged in a men's health promotion programme delivered by 16 English Premier League Clubs. Results: Men at risk due to high sitting display multiple concurrent lifestyle risk factors, 88.6% displayed at least two ancillary risk factors and were three times more likely to report ≥2 lifestyle risk factors (OR. =3.13, 95% confidence interval (CI). =1.52-6.42) than those with low sitting risk. Significant differences in the mean number of risk factors reported between those participants in the higher risk (2.43. ±. 0.90) and lower risk (2.13. ±. 0.96) sitting categories were also found (P=0.015). Conclusions: Hard-to-reach men displayed multiple problematic concurrent behaviours, strongly linked to total sitting time. © 2012 WPMH GmbH

Prediction of fetal and neonatal outcomes after preterm manifestations of placental insufficiency:systematic review of prediction models

Objectives: To identify all prediction models for fetal and neonatal outcomes in pregnancies with preterm manifestations of placental insufficiency (gestational hypertension, pre-eclampsia, HELLP syndrome or fetal growth restriction with its onset before 37 weeks' gestation) and to assess the quality of the models and their performance on external validation. Methods: A systematic literature search was performed in PubMed, Web of Science and EMBASE. Studies describing prediction models for fetal/neonatal mortality or significant neonatal morbidity in patients with preterm placental insufficiency disorders were included. Data extraction was performed using the CHARMS checklist. Risk of bias was assessed using PROBAST. Literature selection and data extraction were performed by two researchers independently. Results: Our literature search yielded 22 491 unique publications. Fourteen were included after full-text screening of 218 articles that remained after initial exclusions. The studies derived a total of 41 prediction models, including four models in the setting of pre-eclampsia or HELLP, two models in the setting of fetal growth restriction and/or pre-eclampsia and 35 models in the setting of fetal growth restriction. None of the models was validated externally, and internal validation was performed in only two studies. The final models contained mainly ultrasound (Doppler) markers as predictors of fetal/neonatal mortality and neonatal morbidity. Discriminative properties were reported for 27/41 models (c-statistic between 0.6 and 0.9). Only two studies presented a calibration plot. The risk of bias was assessed as unclear in one model and high for all other models, mainly owing to the use of inappropriate statistical methods. Conclusions: We identified 41 prediction models for fetal and neonatal outcomes in pregnancies with preterm manifestations of placental insufficiency. All models were considered to be of low methodological quality, apart from one that had unclear methodological quality. Higher-quality models and external validation studies are needed to inform clinical decision-making based on prediction models.</p

Impact of New Scatter Correction Strategies on High-Resolution Research Tomograph Brain PET Studies

The aim of this study is to evaluate the impact of different scatter correction strategies on quantification of high-resolution research tomograph (HRRT) data for three tracers covering a wide range in kinetic profiles. Healthy subjects received dynamic HRRT scans using either (R)-[C-11]verapamil (n = 5), [C-11]raclopride (n = 5) or [C-11]flumazenil (n = 5). To reduce the effects of patient motion on scatter scaling factors, a margin in the attenuation correction factor (ACF) sinogram was applied prior to 2D or 3D single scatter simulation (SSS). Some (R)-[C-11]verapamil studies showed prominent artefacts that disappeared with an ACF-margin of 10 mm or more. Use of 3D SSS for (R)-[C-11]verapamil showed a statistically significant increase in volume of distribution compared with 2D SSS (p 0.05). When there is a patient motion-induced mismatch between transmission and emission scans, applying an ACF-margin resulted in more reliable scatter scaling factors but did not change (and/or deteriorate) quantification

Emergent global oscillations in heterogeneous excitable media: The example of pancreatic beta cells

Using the standard van der Pol-FitzHugh-Nagumo excitable medium model I demonstrate a novel generic mechanism, diversity, that provokes the emergence of global oscillations from individually quiescent elements in heterogeneous excitable media. This mechanism may be operating in the mammalian pancreas, where excitable beta cells, quiescent when isolated, are found to oscillate when coupled despite the absence of a pacemaker region.Comment: See home page http://lec.ugr.es/~julya

Quantification of the novel N-methyl-D-aspartate receptor ligand [11C]GMOM in man

[11C]GMOM (carbon-11 labeled N-(2-chloro-5-thiomethylphenyl)-N0-(3-[11C]methoxy-phenyl)-N0-methylguanidine) is a PET ligand that binds to the N-methyl-D-aspartate receptor with high specificity and affinity. The purpose of this first in human study was to evaluate kinetics of [11C]GMOM in the healthy human brain and to identify the optimal pharmacokinetic model for quantifying these kinetics, both before and after a pharmacological dose of S-ketamine. Dynamic 90 min [11C]GMOM PET scans were obtained from 10 subjects. In six of the 10 subjects, a second PET scan was performed following an S-ketamine challenge. Metabolite corrected plasma input functions were obtained for all scans. Regional time activity curves were fitted to various single- and two-tissue compartment models. Best fits were obtained using a two-tissue irreversible model with blood volume parameter. The highest net influx rate (Ki) of [11C]GMOM was observed in regions with high N-methyl-D-aspartate receptor density, such as hippocampus and thalamus. A significant reduction in the Ki was observed for the entire brain after administration of ketamine, suggesting specific binding to the N-methyl-D-aspartate receptors. This initial study suggests that the [11C]GMOM could be used for quantification of N-methyl-D-aspartate receptors

Disruption of beta cell acetyl-CoA carboxylase-1 in mice impairs insulin secretion and beta cell mass

Aims/hypothesis Pancreatic beta cells secrete insulin to maintain glucose homeostasis, and beta cell failure is a hallmark of type 2 diabetes. Glucose triggers insulin secretion in beta cells via oxidative mitochondrial pathways. However, it also feeds mitochondrial anaplerotic pathways, driving citrate export and cytosolic malonyl-CoA production by the acetyl-CoA carboxylase 1 (ACC1) enzyme. This pathway has been proposed as an alternative glucose-sensing mechanism, supported mainly by in vitro data. Here, we sought to address the role of the beta cell ACC1-coupled pathway in insulin secretion and glucose homeostasis in vivo. Methods Acaca, encoding ACC1 (the principal ACC isoform in islets), was deleted in beta cells of mice using the Cre/loxP system. Acaca floxed mice were crossed with Ins2cre mice (βACC1KO; life-long beta cell gene deletion) or Pdx1creER mice (tmx-βACC1KO; inducible gene deletion in adult beta cells). Beta cell function was assessed using in vivo metabolic physiology and ex vivo islet experiments. Beta cell mass was analysed using histological techniques. Results βACC1KO and tmx-βACC1KO mice were glucose intolerant and had defective insulin secretion in vivo. Isolated islet studies identified impaired insulin secretion from beta cells, independent of changes in the abundance of neutral lipids previously implicated as amplification signals. Pancreatic morphometry unexpectedly revealed reduced beta cell size in βACC1KO mice but not in tmx-βACC1KO mice, with decreased levels of proteins involved in the mechanistic target of rapamycin kinase (mTOR)-dependent protein translation pathway underpinning this effect. Conclusions/interpretation Our study demonstrates that the beta cell ACC1-coupled pathway is critical for insulin secretion in vivo and ex vivo and that it is indispensable for glucose homeostasis. We further reveal a role for ACC1 in controlling beta cell growth prior to adulthood

Synthesis and Evaluation of New Fluorine-18 Labeled Verapamil Analogs To Investigate the Function of P-Glycoprotein in the Blood-Brain Barrier

P-glycoprotein is an efflux transporter located in the blood brain barrier. (R)-[C-11]Verapamil is widely used as a PET tracer to investigate its function in patients with epilepsy, Alzheimer's disease, and other neurodegenerative diseases. Currently it is not possible to use this successful tracer in clinics without a cyclotron, because of the short half-life of carbon-11. We developed two new fluorine-18 labeled (R)-verapamil analogs, with the benefit of a longer half-life. The synthesis of (R)-N[F-18]fluoroethylverapamil ([F-18]1) and (R)-O-[F-18]fluoroethylnorverapamil ([F-18]2) has been described. [F-18]1 was obtained in reaction of (R)-norverapamil with the volatile [F-18]fluoroethyltriflate acquired from bromoethyltosylate and a silver trilate column with a radiochemical yield of 2.7% +/- 1.2%. [F-18]2 was radiolabeled by direct fluorination of precursor 13 and required final Boc-deprotection with TFA resulting in a radiochemical yield of 17.2% 9.9%. Both tracers, [F-18]1 and [F-18]2, were administered to Wistar rats, and blood plasma and brain samples were analyzed for metabolic stability. Using [F-18] 1 and [F-18]2, PET scans were performed in Wistar rats at baseline and after blocking with tariquidar, showing a 3.6-and 2.4-fold increase in brain uptake in the blocked rats, respectively. In addition, for both [F-18]1 and [F-18]2, PET scans in Mdri1a/b((-1-)), Bcrpl((-1-)), and WT mice were acquired, in which [F-18]2 showed a more specific brain uptake in MdrIa/b((-1-)) mice and no increased signal in Bcrpl((-/-)) mice. [F-18]2 was selected as the best performing tracer and should be evaluated further in clinical studies

Improving metabolic stability of fluorine-18 labeled verapamil analogs

INTRODUCTION: Fluorine-18 labeled positron emission tomography (PET) tracers were developed to obtain more insight into the function of P-glycoprotein (P-gp) in relation to various conditions. They allow research in facilities without a cyclotron as they can be transported with a half-life of 110 min. As the metabolic stability of previously reported tracers [18F]1 and [18F]2 was poor, the purpose of this study was to improve this stability using deuterium substitution, creating verapamil analogs [18F]1-d4, [18F]2-d4, [18F]3-d3 and [18F]3-d7. METHODS: The following deuterium containing tracers were synthesized and evaluated in mice and rats: [18F]1-d4, [18F]2-d4, [18F]3-d3 and [18F]3-d7. RESULTS: The deuterated analogs [18F]2-d4, [18F]3-d3 and [18F]3-d7 showed increased metabolic stability compared with their non-deuterated counterparts. The increased metabolic stability of the methyl containing analogs [18F]3-d3 and [18F]3-d7 might be caused by steric hindrance for enzymes. CONCLUSION: The striking similar in vivo behavior of [18F]3-d7 to that of (R)-[11C]verapamil, and its improved metabolic stability compared with the other fluorine-18 labeled tracers synthesized, supports the potential clinical translation of [18F]3-d7 as a PET radiopharmaceutical for P-gp evaluation