fMRI at 1.5, 3 and 7 T: Characterising BOLD signal changes

Blood oxygenation level dependent (BOLD) signal changes occurring during execution of a simple motor task were measured at field strengths of 1.5, 3 and 7 T using multi-slice, single-shot, gradient echo EPI at a resolution of 1 × 1 × 3 mm³, to quantify the benefits offered by ultra-high magnetic field for functional MRI. Using four different echo times at each field strength allowed quantification of the relaxation rate, R₂ and the change in relaxation rate on activation, ΔR₂. This work adds to previous studies of the field strength dependence of BOLD signal characteristics, through its: (i) focus on motor rather than visual cortex; (ii) use of single-shot, multi-slice, gradient echo EPI for data acquisition; (iii) co-registration of images acquired at different field strengths to allow assessment of the BOLD signal changes in the same region at each field strength. ΔR₂ was found to increase linearly with field strength (0.51 ± 0.06 s^− 1 at 1.5 T; 0.98 ± 0.08 s^− 1 at 3 T; 2.55 ± 0.22 s^− 1 at 7 T), while the ratio of ΔR₂/R₂, which dictates the accessible BOLD contrast was also found to increase (0.042 ± 0.002 at 1.5 T; 0.054 ± 0.002 at 3 T; 0.084 ± 0.003 at 7 T). The number of pixels classified as active, the t-value calculated over a common region of interest and the percentage signal change in the same region were all found to peak at TE   T₂ and increase significantly with field strength. An earlier onset of the haemodynamic response at higher field provides some evidence for a reduced venous contribution to the BOLD signal at 7 T.     

Susceptibility contrast in high field MRI of human brain as a function of tissue iron content

Magnetic susceptibility provides an important contrast mechanism for MRI. Increasingly, susceptibility-based contrast is being exploited to investigate brain tissue microstructure and to detect abnormal levels of brain iron as these have been implicated in a variety of neuro-degenerative diseases. However, it remains unclear to what extent magnetic susceptibility-related contrast at high field relates to actual brain iron concentrations. In this study, we performed susceptibility weighted imaging as a function of field strength on healthy brains in vivo and post-mortem brain tissues at 1.5 T, 3 T and 7 T. Iron histology was performed on the tissue samples for comparison. The calculated susceptibility-related parameters R₂ and signal frequency shift in four iron-rich regions (putamen, globus pallidus, caudate, and thalamus) showed an almost linear dependence (r ≥ 0.90 for R₂; r ≥ 0.83 for phase, p < 0.01) on field strength, suggesting that potential ferritin saturation effects are not relevant to susceptibility-weighted contrast for field strengths up to 7 T. The R₂ dependence on the putative (literature-based) iron concentration was 0.048 Hz/T/ppm. The histological data from brain samples confirmed the linear dependence of R₂ on field strength and showed a slope against iron concentration of 0.0099 Hz/T/ppm dry-weight, which is equivalent to 0.05 Hz/T/ppm wet-weight and closely matched the calculated value in vivo. These results confirm the validity of using susceptibility-weighted contrast as an indicator of iron content in iron-rich brain regions. The absence of saturation effects opens the way to exploit the benefits of MRI at high field strengths for the detection of iron distributions with high sensitivity and resolution.     

Statistical diffusion tensor histology reveals regional dysmyelination effects in the shiverer mouse mutant

Shiverer is an important model of central nervous system dysmyelination characterized by a deletion in the gene encoding myelin basic protein with relevance to human dysmyelinating and demyelinating diseases. Perfusion fixed brains from shiverer mutant (C3Fe.SWV Mbp^shi/Mbp^shi n = 6) and background control (C3HeB.FeJ, n = 6) mice were compared using contrast enhanced volumetric diffusion tensor magnetic resonance microscopy with a nominal isotropic spatial resolution of 80 μm. Images were accurately coregistered using non-linear warping allowing voxel-wise statistical parametric mapping of tensor invariant differences between control and shiverer groups. Highly significant differences in the tensor trace and both the axial and radial diffusivity were observed within the major white matter tracts and in the thalamus, midbrain, brainstem and cerebellar white matter, consistent with a high density of myelinated axons within these regions. The fractional anisotropy was found to be much less sensitive than the trace and eigenvalues to dysmyelination and associated microanatomic changes.     

Feasibility of simultaneous intracranial EEG-fMRI in humans: A safety study

In epilepsy patients who have electrodes implanted in their brains as part of their pre-surgical assessment, simultaneous intracranial EEG and fMRI (icEEG-fMRI) may provide important localising information and improve understanding of the underlying neuropathology. However, patient safety during icEEG-fMRI has not been addressed.Here the potential health hazards associated with icEEG-fMRI were evaluated theoretically and the main risks identified as: mechanical forces on electrodes from transient magnetic effects, tissue heating due to interaction with the pulsed RF fields and tissue stimulation due to interactions with the switched magnetic gradient fields. These potential hazards were examined experimentally in vitro on a Siemens 3 T Trio, 1.5 T Avanto and a GE 3 T Signa Excite scanner using a Brain Products MR compatible EEG system.No electrode flexion was observed. Temperature measurements demonstrated that heating well above guideline limits can occur. However heating could be kept within safe limits (< 1.0 °C) by using a head transmit RF coil, ensuring EEG cable placement to exit the RF coil along its central z-axis, using specific EEG cable lengths and limiting MRI sequence specific absorption rates (SARs). We found that the risk of tissue damage due to RF-induced heating is low provided implant and scanner specific SAR limits are observed with a safety margin used to account for uncertainties (e.g. in scanner-reported SAR). The observed scanner gradient switching induced current (0.08 mA) and charge density (0.2 μC/cm²) were well within safety limits (0.5 mA and 30 μC/cm², respectively). Site-specific testing and a conservative approach to safety are required to avoid the risk of adverse events.     

Molecular detection and quantification of the protozoan Bonamia ostreae in the flat oyster, Ostrea edulis

Bonamia ostreae is an intracellular protozoan which is recognized as a cause of mortality in European populations of flat oysters (Ostrea edulis). Based on the recent characterization of actin genes of B. ostreae, specific primers were designed for real-time PCR using SYBR^® Green chemistry. Specificity was demonstrated by the unique melting temperature peak observed in positive samples and by the lack of amplification in samples of oysters infected by closely related parasites, including Bonamia exitiosa. A calibration curve using a cloned template was defined to estimate copy number. The assay had a 6 log- dynamic range, mean inter- and intra-assay variation coefficients of <1% and a minimum detection limit of 50 gene copies per reaction. Using infected oyster samples as templates, the assay was at least 10-fold more sensitive than conventional PCR. The quantitative assay was applied to test 132 oysters, and results were compared with the heart imprint method. There was a strong correlation between both techniques, and the results showed that the real-time PCR assay should be useful for studies of the ecology of B. ostreae and its host–parasite relationship.     

Controlled multiplex PCR of enterotoxigenicClostridium perfringensstrains in food samples

A controlled multiplex polymerase chain reaction (PCR) for the detection ofClostridium(C.)perfringensenterotoxin gene (cpe) was established and compared with anin vitroantigenic detection method. ThecpePCR and the classical method of electric immunodiffusion gave identical results. The predicted specific amplicon of thecpegene was generated from all of the tested enterotoxigenicC. perfringensstrains. In contrast, cultures of any otherClostridiumspecies tested by PCR were negative (100% sensitivity, 100% specificity). Addition of an alphatoxin (plc) gene specific PCR as an in process control reaction was performed in order to prevent false negative PCR results. The PCR detection limit was 0·5 ng of genomicC. perfringensDNA per ml of bouillon culture. By contaminating minced meat withC. perfringensreference strains, the multiplex PCR was established as a tool for routine diagnostic laboratories. The detection limit was approximately 3·0×10⁵C. perfringenscells per gram meat. The results demonstrate the multiplex PCR as an easy, specific, sensitive and time saving diagnostic procedure. Application of this improved method should enhance the knowledge concerning epidemiological aspects of food borne diseases caused by enterotoxigenicC. perfringens.     

Signal abnormalities on 1.5 and 3 Tesla brain MRI in multiple sclerosis patients and healthy controls. A morphological and spatial quantitative comparison study

Previous studies in patients with multiple sclerosis (MS) revealed increased lesion count and volume on 3 T compared to 1.5 T. Morphological and spatial lesion characteristics between 1.5 T and 3 T have not been examined. The aim of this study was to investigate the effect of changing from a 1.5 T to a 3 T MRI scanner on the number, volume and spatial distribution of signal abnormalities (SA) on brain MRI in a sample of MS patients and normal controls (NC), using pair- and voxel-wise comparison procedures. Forty-one (41) MS patients (32 relapsing-remitting and 9 secondary-progressive) and 38 NC were examined on both 1.5 T and 3 T within one week in random order. T2-weighted hyperintensities (T2H) and T1-weighted hypointensities (T1H) were outlined semiautomatically by two operators in a blinded fashion on 1.5 T and 3 T images. Spatial lesion distribution was assessed using T2 and T1 voxel-wise SA probability maps (SAPM). Pair-wise analysis examined the proportion of SA not simultaneously outlined on 1.5 T and 3 T. A posteriori unblinded analysis was conducted to examine the non-overlapping identifications of SA between the 1.5 T and 3 T. For pair-wise T2- and T1-analyses, a higher number and individual volume of SA were detected on 3 T compared to 1.5 T (p < 0.0001) in both MS and NC. Logistic regression analysis showed that the likelihood of missing SA on 1.5 T was significantly higher for smaller SA in both MS and NC groups. SA probability map (SAPM) analysis revealed significantly more regionally distinct spatial SA differences on 3 T compared to 1.5 T in both groups (p < 0.05); these were most pronounced in the occipital, periventricular and cortical regions for T2H. This study provides important information regarding morphological and spatial differences between data acquired using 1.5 T and 3 T protocols at the two scanner field strengths.     

Biochemical assay for amyloid β deposits to distinguish Alzheimer's disease from other dementias

Biochemical markers for Alzheimer's disease (AD) are of great value for precise diagnosis and in studies of the pathogenetic processes of this disease. A new biochemical assay allowing to differentiate AD from other forms of dementia is described. The assay is based on the extraction of amyloid β (Aβ) from milligram amounts of brain tissue by using 20% acetonitrile in 0.1% trifluoroacetic acid and its detection by Western blotting. The presence of the 4 kDa Aβ was demonstrated in all cases of AD (n=8) that were diagnosed by the independent histopathological examination of the postmortem tissues. No Aβ was found in tissue extracts from seven out of eight cases of other forms of dementia. In contrast to other biochemical techniques of Aβ detection in brain, the developed assay is simple; it does not require any special equipment and allows detection of Aβ using milligram amounts of brain tissue.     

QT length during methadone maintenance treatment: gene × dose interaction

Methadone is known to be a risk factor for sudden death by enlarging ECG QT corrected (QTc) interval. For other medical conditions, QTc lengthening has been described as the result of interactions between pharmacological treatments and genetic factors. Former heroin‐dependent subjects under methadone maintenance treatment in remission for at last 3 months were recruited. We studied the association between QTc length (Bazett formula) and 126 SNPs located on five genes (KCNE1, KCNQ1, KCNH2, NOS1AP and SCN5A) previously associated with drug‐induced QT prolongation. Both SNP‐based and gene‐based approaches were used, and we tested also the interaction of the top SNP with methadone dosage to predict the QTc length. In our sample of 154 patients, current methadone daily dose was associated with QTc length (r_Pearson = 0.26; P = 10^?3). Only one SNP, rs11911509 on KCNE1, remained significantly associated with QT length after correction for multiple testing (P = 3.84 × 10^?4; p_corrected = 0.049). Using a gene‐based approach, KCNE1 was also significantly associated with QTc length (p_empirical = 0.02). We found a significant interaction between methadone dosage and rs11911509 minor allele count (allele A vs. C; P = 0.01). Stratified analysis revealed that the correlation between QTc length and methadone dosage was restricted only to AA carriers of this top SNP. Patients’ genetic background should be taken into account in the case of clinically relevant QT enlargement during methadone maintenance treatment.     

Effect of heparinization of catheters on pulmonary artery oximetry

A clinical study was performed in two phases to determine whether pulmonary artery oximeter catheters that were impregnated or bonded with heparin would affect the accuracy of measurements of in vivo mixed venous oxygen saturation (S O₂). In phase 1, 40 patients were catheterized with either a heparin-impregnated or a plain pulmonary artery catheter. Blood was sampled at random times to correlate in vivo with in vitro S O₂ measurements. In phase 2, 16 patients who were not receiving systemic heparin therapy or aspirin and who had no coagulopathies were catheterized with either a heparin-bonded or a plain pulmonary artery catheter in a blinded order. In phase 1, a total of 364 blood samples were obtained from 40 patients. Linear regression analysis of the pooled data demonstrated y=0.98x–0.01,r=0.93,P<0.001, andn=141 with heparin-impregnated catheters; and y=0.87x+8.0,r=0.81,P<0.001, andn=223 with plain catheters. The mean difference (in vivo minus in vitro) revealed a similar error (–1.3±0.4 versus –1.4±0.4, respectively, mean±SE). The 95% confidence limits of an individual value (±8.1 versus ±12.3) suggested slightly greater accuracy with heparin-impregnated catheters. In phase 2, a total of 134 blood samples were obtained from 16 patients. Linear regression analysis showed nearly equal performance with heparin-bonded and plain catheters (r=0.97 versusr=0.98, respectively) with similar slopes (1.0 versus 1.1, respectively) but different intercepts (–0.6 versus –8.4, respectively). Analysis of the mean difference revealed a measurement error of 0.4±0.3 versus –1.3±0.3 with similar 95% confidence limits of individual values (±5.0 versus ±4.8, respectively). These differences do not appear clinically important. These data suggest that heparinization only minimally enhanced accuracy with a pulmonary artery oximetry system, which accurately measured S O₂ to within 3 to 4% of true values.     

Genetic research and clinical analysis of β‐globin gene cluster deletions in the Chinese population of Fujian province: A 14‐year single‐center experience

BackgroundHeterozygotes of HPFH and δβ thalassemia are clinically asymptomatic or have mild hemoglobin (Hb) values. However, when both HPFH and δβ‐thalassemia are coinherited with heterozygous β‐thalassemia, patients may progress to a clinical phenotype of thalassemia intermedia or thalassemia major. The purpose of this study was to characterize the genotypes and analyze the phenotypes of these disorders in Fujian Province, to offer advice for genetic counseling and accurate prenatal diagnosis in this region. A total of 55 001 subjects were participated in thalassemia screening. 142 subjects with HbF levels ≥10%, before the blood transfusion, were selected for further investigation.MethodsMultiplex ligation‐dependent probe amplification (MLPA) and Gap‐PCR were used to screen for three β‐globin gene cluster deletions: Chinese ^Gγ(^Aγδβ)⁰ thalassemia and Southeast Asia HPFH (SEA‐HPFH) deletion and 1357 bp deletion (NG‐000007.3:g.69997‐71353 del 1357).ResultsA total of 142 patients with HbF (≥10%) were enrolled to characterize the molecular basis of β‐globin gene cluster deletions in our study; 22 cases 0.04% (22/55 001) were definitively diagnosed with β‐globin gene cluster deletions. Ten cases were heterozygous for the Chinese ^Gγ(^Aγδβ)⁰‐thal mutations, 10 cases were heterozygous for SEA‐HPFH, and one case was compound heterozygous for SEA‐HPFH and the α‐thal mutation. The 1357 bp deletion (NG‐000007.3:g.69997‐71353 del 1357) was detected in one case. Moreover, the hemoglobin A₂ levels in patients who were heterozygous for Chinese ^Gγ(^Aγδβ)⁰‐thal were statistically lower than in cases with SEA‐HPFH deletion(p < 0.05).ConclusionIn Fujian Province, the prevalence of common β‐globin gene cluster deletions was 0.04%. What''s more, the most common β‐globin cluster deletions are the Chinese ^Gγ(^Aγδβ)⁰ and SEA‐HPFH.     

Sequence analysis and genetic variability of stearoyl CoA desaturase (SCD) gene in the Italian Mediterranean river buffalo

Stearoyl-CoA desaturase (SCD) plays a key metabolic role by changing the saturated FA content of ruminant milk and meat. In this study we characterized for the first time the stearoyl-CoA desaturase (SCD) gene in river buffalo (Bubalus bubalis) and investigated its genetic variability. On a total of 78 buffaloes, 15 SNPs were detected and 6 of them were preliminarily genotyped. In particular, the g.133A>C SNP was found to create a new consensus site for the SP1 binding site, thus generating a new tandem repeat in the promoter region. A preliminary association study with the milk fatty acid content showed that the C allele significantly affects the total desaturation index (P < 0.01). Linkage disequilibrium analysis allowed identification of 7 haplotypes and 4 tag SNPs. Such polymorphisms could represent useful genetic markers for association studies with fatty acid composition, but further studies are needed to evaluate their potential use to improve the nutritional quality of the dairy products.     

Continuous intravascular monitoring of PO2 and PCO2. A comparativein vitro-in vivo study

Two electrodes placed at the tip of catheters forin vivo determinations of and respectively, were tested in dogs. Results were satisfactory when compared to a highly accurate reference method, correlation coefficients were close to 1 (P < 10^–9). Means of the differences were respectively –1.74 ± 1.14 torr for the probe (P < 0.01) and –1.62 ± 0.72 torr for the sensor (P < 0.0001). While no drift was detected in the electrode that of the was significant but negligible compared to the variability of measurements. Thus, for values between 20 and 85 torr, and values between 20 and 140 torr,in vivo monitoring is sufficiently reliable for clinical use.This study was supported by a grant-in-aid from I.N.S.E.R.M., C.N.R.S. and Paris VII University.     

Stimulus-induced Rotary Saturation (SIRS): a potential method for the detection of neuronal currents with MRI

Neuronal currents produce local transient and oscillatory magnetic fields that can be readily detected by MEG. Previous work attempting to detect these magnetic fields with MR focused on detecting local phase shifts and dephasing in T₂ or T₂-weighted images. For temporally biphasic and multi-phasic local currents the sensitivity of these methods can be reduced through the cancellation of the accrued phase induced by positive and negative episodes of the neuronal current. The magnitude of the phase shift is also dependent on the distribution of the current within the voxel. Since spins on one side of a current source develop an opposite phase shift relative to those on the other side, there is likely to be significant cancellation within the voxel.We introduce a potential method for detecting neuronal currents though their resonant T_1ρ saturation during a spin-lock preparation period. The method is insensitive to the temporal and spatial cancellation effects since it utilizes the multi-phasic nature of the neuronal currents and thus is not sensitive to the sign of the local field. To produce a T_1ρ reduction, the Larmor frequency in the rotating frame, which is set by γB_1lock (typically 20 Hz–5 kHz), must match the major frequency components of the stimulus-induced neuronal currents. We validate the method in MRI phantom studies. The rotary saturation spectra showed a sharp resonance when a current dipole within the phantom was driven at the Larmor frequency in the rotating frame. A 7 min block-design experiment was found to be sensitive to a current dipole strength of 56 nAm, an approximate magnetic field of 1 nT at 1.5 mm from the dipole. This dipole moment is similar to that seen using the phase shift method in a similar experimental setup by Konn et al. [Konn, D., Gowland, P., Bowtell, R., 2003. MRI detection of weak magnetic fields due to an extended current dipole in a conducting sphere: a model for direct detection of neuronal currents in the brain. Magn. Reson. Med. 50, 40–49], but is potentially less encumbered by temporal and spatial cancellation effects.     

Weak A phenotypes associated with novel ABO alleles carrying the A2‐related 1061C deletion and various missense substitutions

BACKGROUND: The 1061delC single‐nucleotide polymorphism (SNP) has been reported mostly in the context of the common A²[A201] allele and typically produces an A₂ phenotype. This study evaluated new A^weak alleles, each containing 1061delC. STUDY DESIGN AND METHODS: Twenty samples were referred to our laboratory for analysis due to suspected A_weak phenotypes originally detected at the referring centers. ABO Exons 1 through 7 and flanking intronic regions were sequenced. A antigen expression on red blood cells was analyzed by flow cytometry. Plasma enzyme activity was studied in one case. Molecular three‐dimensional modeling techniques studied the potential effects of amino acid changes on the resulting glycosyltransferases (GTs). RESULTS: Thirteen alleles were discovered, each featuring 1061delC with at least 1 of 12 additional SNPs in the coding region. One of these SNPs disrupts the translation initiation codon. Another constitutes the first reported change in the DVD motif. One SNP found in three alleles causes a substitution of one of the four amino acids that differentiates the wild‐type A and B enzymes but plasma enzyme analysis by two methods showed only slightly decreased or normal A₂ activity. Flow cytometric analysis semiquantified the A antigen levels in 16 cases featuring 10 of the alleles and ranged from very weak to nearly A₂ levels. However, the majority of the samples displayed A_x‐like patterns. Molecular modeling of some of the GT variants indicated conformational changes that may explain the diminished A expression observed. CONCLUSION: Missense SNPs were identified in 13 novel A²‐like alleles, which produced a variety of A subgroup phenotypes.     

Morphine-induced depression of spinal excitation is not altered following acute disruption of GABAA or GABAB receptor activity

Loss of spinal inhibitory mechanisms is thought to contribute to the pathophysiology of abnormal pain states, including neuropathic pain. By using an evoked spinal field potential technique, the hypothesis was tested here that decreased spinal GABAergic control underlies poor response to morphine (MOR) that often accompanies neuropathic pain. Therefore, field potentials evoked by electrical peripheral nerve stimulation during spinal superfusion with MOR were recorded in rats rendered neuropathic by a spinal nerve ligation (SNL) procedure, and compared to responses recorded in naı¨ve rats. MOR effects on evoked field potentials were then assessed in rats in which spinal GABAergic inhibition had been acutely reduced by treatment with GABA_A and GABA_B receptor-antagonists.In naı¨ve animals, field potentials evoked by peripheral C fibre-input were significantly decreased by spinal superfusion with 1 μM MOR, whereas those elicited by Aδ fibre input were reduced to a lesser extent also (10 μM, p < 0.05). Nine to eleven days after surgery, animals subjected to SNL exhibited significantly reduced thresholds to plantar stimulation with von Frey filaments. In electrophysiological experiments, a small but significant decrease of the IC₅₀ value (2.17 ± 0.38 μM) for MOR was found in rats subjected to SNL, relative to naı¨ve rats (8.65 ± 0.76 μM). In contrast, MOR failed to reduce field potentials evoked by peripheral Aδ fibre-activation at any dose tested (up to 1 mM).C fibre- and Aδ fibre-evoked spinal field potentials disinhibited by prior application of the GABA_B or GABA_A receptor-antagonists CGP35348 (1 mM) or bicuculline (50 μM), respectively, were both significantly reduced by MOR, with IC₅₀ values not significantly differing from those in naı¨ve animals. Two-way analysis of variance revealed no interaction of MOR with either CGP354348 (p = 0.42) or BIC (p = 0.14).Evidence is presented here that injury to the primary afferent system results in significant changes in the ability of spinal MOR to depress field potentials evoked by peripheral input. However, the present findings do not support a pathogenic role for decreased GABAergic inhibition in such changes.     

Genetic variability of the Stearoyl-CoA desaturase gene in sheep

Stearoyl-CoA desaturase (SCD) plays a key role in lipid metabolism in humans and livestock. In ruminants, changes in the coding and/or regulatory sequences of the SCD gene could generate alterations in the enzymatic activity, producing variations in the fatty acid content in milk and meat. In this study, we investigated the genetic variability in 3989 bp of the ovine SCD gene. A total of 85 animals belonging to eight sheep breeds with different selection goals (dairy vs. meat) and fat metabolisms (fat-tailed vs. thin-tailed) were analysed. No polymorphisms were found within the coding region of the SCD gene (1080 bp). Analysis of the non-coding region (2909 bp) allowed the identification of four SNPs located in the promoter region (SCD01), intron 2 (SCD02 and SCD03) and intron 3 (SCD04). The most polymorphic SNP in the studied breeds was SCD01, which displayed intermediate frequencies in the highly specialised breeds, whereas it was less variable in the meat populations. Further efforts are needed to evaluate the potential use of the identified SNPs as markers for fat content and fatty acid composition of sheep products, and to assess the possible use of sheep as an animal model for human diseases related to lipid metabolism.     

In vitro activity of tigecycline and comparator agents against a global collection of Gram-negative and Gram-positive organisms: Tigecycline Evaluation and Surveillance Trial 2004 to 2007

The Tigecycline Evaluation and Surveillance Trial began in 2004 to monitor the in vitro activity of tigecycline and comparator agents against a global collection of Gram-negative and Gram-positive pathogens. Against Gram negatives (n = 63 699), tigecycline MIC₉₀'s ranged from 0.25 to 2 mg/L for Escherichia coli, Haemophilus influenzae, Acinetobacter baumannii, Klebsiella oxytoca, Enterobacter cloacae, Klebsiella pneumoniae, and Serratia marcescens (but was ≥32 for Pseudomonas aeruginosa). Against Gram-positive organisms (n = 32 218), tigecycline MIC₉₀'s were between 0.06 and 0.25 mg/L for Streptococcus pneumoniae, Enterococcus faecium, Streptococcus agalactiae, Staphylococcus aureus, and Enterococcus faecalis. The in vitro activity of tigecycline was maintained against resistant phenotypes, including multidrug-resistant A. baumannii (9.2% of isolates), extended-spectrum β-lactamase–producing E. coli (7.0%) and K. pneumoniae (14.0%), β-lactamase–producing H. influenzae (22.2%), methicillin-resistant S. aureus (44.5%), vancomycin-resistant E. faecium (45.9%) and E. faecalis (2.8%), and penicillin-resistant S. pneumoniae (13.8%). Tigecycline represents a welcome addition to the armamentarium against difficult to treat organisms.     

Identification of PLCL1 Gene for Hip Bone Size Variation in Females in a Genome-Wide Association Study

Osteoporosis, the most prevalent metabolic bone disease among older people, increases risk for low trauma hip fractures (HF) that are associated with high morbidity and mortality. Hip bone size (BS) has been identified as one of the key measurable risk factors for HF. Although hip BS is highly genetically determined, genetic factors underlying the trait are still poorly defined. Here, we performed the first genome-wide association study (GWAS) of hip BS interrogating ~380,000 SNPs on the Affymetrix platform in 1,000 homogeneous unrelated Caucasian subjects, including 501 females and 499 males. We identified a gene, PLCL1 (phospholipase c-like 1), that had four SNPs associated with hip BS at, or approaching, a genome-wide significance level in our female subjects; the most significant SNP, rs7595412, achieved a p value of 3.72×10⁻⁷. The gene's importance to hip BS was replicated using the Illumina genotyping platform in an independent UK cohort containing 1,216 Caucasian females. Two SNPs of the PLCL1 gene, rs892515 and rs9789480, surrounded by the four SNPs identified in our GWAS, achieved p values of 8.62×10⁻³ and 2.44×10⁻³, respectively, for association with hip BS. Imputation analyses on our GWAS and the UK samples further confirmed the replication signals; eight SNPs of the gene achieved combined imputed p values<10⁻⁵ in the two samples. The PLCL1 gene's relevance to HF was also observed in a Chinese sample containing 403 females, including 266 with HF and 177 control subjects. A SNP of the PLCL1 gene, rs3771362 that is only ~0.6 kb apart from the most significant SNP detected in our GWAS (rs7595412), achieved a p value of 7.66×10⁻³ (odds ratio=0.26) for association with HF. Additional biological support for the role of PLCL1 in BS comes from previous demonstrations that the PLCL1 protein inhibits IP3 (inositol 1,4,5-trisphosphate)-mediated calcium signaling, an important pathway regulating mechanical sensing of bone cells. Our findings suggest that PLCL1 is a novel gene associated with variation in hip BS, and provide new insights into the pathogenesis of HF.     

The extended release properties of HPMC matrices in the presence of dietary sugars

The mechanisms and structure-activity by which dissolved dietary sugars influence drug release from hydroxypropyl methylcellulose (Methocel^® K4M) matrices were investigated. Drug release was retarded at lower sugar concentrations, but above a critical solute concentration (S_CRIT), there was marked acceleration of release. Studies of early gel layer formation suggested this resulted from sugar-induced suppression of HPMC particle swelling and coalescence, leading to gel structures with poorer diffusion-barrier properties and reduced resistance to physical erosion. Sucrose, lactose, D-glucose, D-galactose and D-fructose all exhibited this pattern but S_CRIT values varied widely between sugars (0.5 M lactose, 1.15 M D-fructose). A polynomial relationship (r² = 0.994) existed between S_CRIT and the ability of the sugar to depress the polymer sol–gel transition temperature (ΔCPT). Structure activity relationships across a wide range of sugars suggested ΔCPT was related to molar hydroxyl number, the orientation of the C₄ hydroxyl and the β 1→4 linkage, all factors which influence sugar compatibility with water structure. The study demonstrates how sugars in high concentration can directly influence the performance of the gel diffusion barrier and matrix drug release characteristics. There is therefore potential for influencing drug release kinetics when high concentrations of sugars are co-administered in the fed state or when they are present in HPMC ER formulations.