Transient conduction block following acute peripheral nerve ischemia

We studied the effects of transient focal ischemia on the electrophysiologic function of rat sciatic nerves. Focal and generalized impairment of impulse conduction, measured by falling evoked muscle and nerve compound action potential amplitudes, occurred within 10 minutes of femoral artery occlusion. Conduction failure reached a nadir at 45-60 minutes and then improved to normal within 24 hours. Fastest motor and mixed nerve conduction velocities were reduced less than 15% of baseline values during the period of acute conduction block. There were no detectable morphological abnormalities at the site of conduction failure. Transient ischemia produces reversible conduction block without evident structural changes. The fall in amplitude without significant conduction slowing implies that slower conducting myelinated fibers are relatively more sensitive to the effect of acute ischemia.

Use of an enzyme-linked immunosorbent asay to diagnose avian tuberculosis in a captive collection of wildfowl

The current study assessed the diagnostic accuracy of an enzyme-linked immunosorbent assay (ELISA) and evaluated it as a diagnostic screening aid for avian tuberculosis (TB) in a wildfowl collection at the Wildfowl and Wetlands Trust Centre at Llanelli, Wales, U.K.. Four hundred and eighteen birds of the collection, including geese, ducks, and swans, were screened for mycobacterial antibody levels. Of those birds tested, 40 died during the period of this study and gross post mortem examinations were performed. The ELISA showed a sensitivity of 76.9% and a specificity of 55.6% using post-mortem findings as the 'gold standard'. Thirteen of the examined birds showed evidence of avian TB at necropsy. In addition, liver and spleen biopsies of 19 birds were examined histopathologically. There was minimal agreement between gross post mortem and histopathological findings. PCR performed on 13 of the specimens prepared for histopathology did not identify the presence of mycobacterial DNA. The findings reveal a need for further research to improve the sensitivity and specificity of this ELISA and the accurate diagnosis of avian TB.

Differential expression of adenylyl cyclase subtypes in human cardiovascular system

In human myocardium, beta1-adrenoceptor stimulation achieves maximal inotropic response but less than 50% of maximal adenylyl cyclase activation, whereas the reverse is true of the beta2-adrenoceptor. Four types of adenylyl cyclase, type IV-VII, have been described in mammalian heart, but their expression and relative distribution in human heart and blood vessels is not known. We found that type IV, V, VI and VII adenylyl cyclases were all expressed in cardiomyocytes. Whereas types IV and VII RNA were more abundant in extra-cardiac than cardiac tissues, both absolute and relative expression of type VI was greatest in heart, and lower in tissues lacking a beta1-adrenoceptor. Type V expression was virtually confined to atrium. In situ mRNA hybridisation showed that the beta1-adrenoceptor co-localised with type VI adenylyl cyclase but not other subtypes in juxtoglomerular cells of human kidney. The tissue specific expression of these adenylyl cyclase subtypes may favour its coupling to corresponding receptors expressed in the given tissue type.

N-acetylcysteine enhances muscle cysteine and glutathione availability and attenuates fatigue during prolonged exercise in endurance-trained individuals

The production of reactive oxygen species in skeletal muscle is linked with muscle fatigue. This study investigated the effects of the antioxidant compound N-acetylcysteine (NAC) on muscle cysteine, cystine, and glutathione and on time to fatigue during prolonged, submaximal exercise in endurance athletes. Eight men completed a double-blind, crossover study, receiving NAC or placebo before and during cycling for 45 min at 71% peak oxygen consumption (VO2 peak) and then to fatigue at 92% VO2 peak. NAC was intravenously infused at 125 mg.kg(-1).h(-1) for 15 min and then at 25 mg.kg(-1).h(-1) for 20 min before and throughout exercise. Arterialized venous blood was analyzed for NAC, glutathione status, and cysteine concentration. A vastus lateralis biopsy was taken preinfusion, at 45 min of exercise, and at fatigue and was analyzed for NAC, total glutathione (TGSH), reduced glutathione (GSH), cysteine, and cystine. Time to fatigue at 92% VO2 peak was reproducible in preliminary trials (coefficient of variation 5.6 +/- 0.6%) and with NAC was enhanced by 26.3 +/- 9.1% (NAC 6.4 +/- 0.6 min vs. Con 5.3 +/- 0.7 min; P <0.05). NAC increased muscle total and reduced NAC at both 45 min and fatigue (P <0.005). Muscle cysteine and cystine were unchanged during Con, but were elevated above preinfusion levels with NAC (P <0.001). Muscle TGSH (P <0.05) declined and muscle GSH tended to decline (P=0.06) during exercise. Both were greater with NAC (P <0.05). Neither exercise nor NAC affected whole blood TGSH. Whereas blood GSH was decreased and calculated oxidized glutathione increased with exercise (P <0.05), both were unaffected by NAC. In conclusion, NAC improved performance in well-trained individuals, with enhanced muscle cysteine and GSH availability a likely mechanism.

Assessment of lymphocyte-mediated cytotoxicity using flow cytometry

Cytotoxic lymphocytes, including cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, kill target cells by releasing granules containing perforin and granzymes, and/or via Fas-Fas ligand interactions. Both pathways lead to prompt activation within target cells of caspase cascades responsible for apoptosis induction and cell death. We have utilized cell-permeable fluorogenic caspase substrates and multiparameter flow cytometry to detect caspase activation in target cells, and applied these tools to quantify and visualize cytotoxic lymphocyte activities. This novel assay, referred to as the flow cytometric cytotoxicity (FCC) assay, is a nonradioactive single-cell-based assay that provides a more rapid, biologically informative, and sensitive approach to measure cytotoxic lymphocyte activity when compared to other assays such as the 51chromium (51Cr) release assay. In addition, the FCC assay can be used to study CTL-mediated killing of primary target cells of different cell lineages that are frequently not amenable to study by the 51Cr release assay. Furthermore, the FCC assay enables evaluation of the phenotype and fate of both target and effector cells, and as such, provides a useful new approach to illuminate the biology of cytotoxic lymphocytes.

Chemokine stimulation of human peripheral blood T lymphocytes induces rapid dephosphorylation of ERM proteins, which facilitates loss of microvilli and polarization

Lymphocyte microvilli mediate initial rolling-adhesion along endothelium but are lost during transmigration from circulation to tissue. However, the mechanism for resorption of lymphocyte microvilli remains unexplored. We show that chemokine stimulation of human peripheral blood T (PBT) cells is sufficient to induce rapid resorption of microvilli. Microvilli in other cells are regulated by ezrin/radixin/moesin (ERM) proteins, which link the plasma membrane to the cortical F-actin cytoskeleton; maintenance of these linkages requires ERM activation, reflected by phosphorylation at a specific carboxy-terminal threonine residue. Carboxyphosphorylated-ERM (cpERM) proteins in resting PBT cells show a punctate peripheral distribution consistent with localization to microvilli. cpERM dephosphorylation begins within seconds of stimulation by chemokines (stromal derived factor 1 alpha [SDF-1 alpha] or secondary lymphoid tissue cytokine), and ERM proteins lose their punctate distribution with kinetics paralleling the loss of microvilli. The cpERM proteins are preferentially associated with the cytoskeleton at rest and this association is lost with chemokine-induced dephosphorylation. Transfection studies show that a dominant-negative ERM construct destroys microvilli, whereas a construct mimicking cpERM facilitates formation of microvilli, retards chemokine-induced loss of microvilli, and markedly impairs chemokine-induced polarization. Thus, chemokine induces rapid dephosphorylation and inactivation of cpERM, which may in turn facilitate 2 aspects of cytoskeletal reorganization involved in lymphocyte recruitment: loss of microvilli and polarization.

The Methylerythritol Phosphate Pathway and its Significance as a Novel Drug Target

Isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) are the precursors for all isoprenoid compounds. Two pathways are found in Nature for their biosynthesis. The mevalonate (MVA) pathway is found in eukaryotes, algae, archae and some gram-positive bacteria. Gram-negative bacteria, plants and some gram-positive bacteria utilize the methyl erythritol phosphate (MEP) pathway. The distribution and the orthogonal nature of the pathways make the MEP pathway an attractive new target for antibiotics and herbicides. The MEP pathway is essential for bacterial viability. Inhibitors to the MEP pathway represent a "dual-use technology" because potential targets include potential biological warfare agents in addition to common human pathogens. The CDC has three categories designated for Biological Diseases/Agents. Three of the six entities designated as the highest priority (Category A) are organisms that utilize, or appear to utilize, the MEP pathway. Among the 12 second highest priority agents (Category B) listed, 8 are organisms that appear to utilize the MEP pathway. Common human pathogens that can be targeted include the organisms responsible for peptic ulcers, tuberculosis, malaria, food safety threats, and sexually transmitted diseases. There is so far only one inhibitor reported that specifically blocks the MEP pathway and is being investigated clinically. This compound, fosmidomycin, has been shown to be somewhat effective in treating Plasmodium falciparum, the parasite responsible for malaria. We foresee that new MEP pathway inhibitors will open up an entirely new class of antibiotics. An MEP pathway intermediate has also been shown to be the most potent gammadelta T cell activator.

N-acetylcysteine infusion alters blood redox status but not time to fatigue during intense exercise in humans

Infusion of the antioxidant N-acetylcysteine (NAC) reduces fatigability in electrically evoked human muscle contraction, but due to reported adverse reactions, no studies have investigated NAC infusion effects during voluntary exercise in humans. We investigated whether a modified NAC-infusion protocol (125 mg. kg(-1). h(-1) for 15 min, then 25 mg. kg(-1). h(-1)) altered blood redox status and enhanced performance during intense, intermittent exercise. Eight untrained men participated in a counterbalanced, double-blind, crossover study in which they received NAC or saline (control) before and during cycling exercise, which comprised three 45-s bouts and a fourth bout that continued to fatigue, at 130% peak oxygen consumption. Arterialized venous blood was analyzed for glutathione status, hematology, and plasma electrolytes. NAC infusion induced no severe adverse reactions. Exercise decreased the reduced glutathione (P < 0.005) and increased oxidized glutathione concentrations (P < 0.005); NAC attenuated both effects (P < 0.05). NAC increased the rise in plasma K(+) concentration-to-work ratio (P < 0.05), indicating impaired K(+) regulation, although time to fatigue was unchanged (NAC 102 +/- 45 s; saline 107 +/- 53 s). Thus NAC infusion altered blood redox status during intense, intermittent exercise but did not attenuate fatigue.

Better blood pressure control: how to combine drugs

Prospective comparisons of different drug classes have shown that differences in blood pressure control, rather than differences between drug classes, have the over-riding influence on overall outcome. The same studies have also reinforced the need, in the majority of patients, to use combinations of drugs in order to achieve the target of <140/85 mmHg. By contrast, most patients in routine practice receive single agents and consequently fail to achieve target blood pressure. This failure reflects in part the emphasis in individual studies and subsequent guidelines on comparison of individual drugs. In this article we show how the consistency of both theory and a broad range of evidence permits a didactic approach to combination therapy. Our advice is based on the growing recognition that essential hypertension and its treatment fall into two main categories. Younger Caucasians usually have renin-dependent hypertension that responds well to angiotensin-converting-enzyme inhibition or angiotensin receptor blockade (A) or ss blockade (B). Most other patients have low-renin hypertension that responds better to calcium channel blockade (C) or diuretics (D). These latter drugs activate the renin system rendering patients responsive to the addition of renin suppressive therapy. Coincidence of the initials of these main drug classes with the first four letters of the alphabet permits an AB/CD rule, according to which recommended combinations are one drug from each of the "AB" and "CD" categories of drugs. However, the diabetogenic potential of the older "B" and "D" classes leads us to advise against combining "B" and "D" in older patients, and to recommend "A" + "C" + "D" as standard triple therapy for resistant hypertension.

Greater inotropic and cyclic AMP responses evoked by noradrenaline through Arg389 beta 1-adrenoceptors versus Gly389 beta 1-adrenoceptors in isolated human atrial myocardium

1. We studied the biochemical and contractile responses of isolated human myocardial tissue expressing native receptor variants of the 389G>R beta(1)-adrenoceptor polymorphism. 2. Right atrial appendage was obtained from homozygous RR patients (n=37) and homozygous GG patients (n=17) undergoing elective cardiac surgery. The positive inotropic effect of noradrenaline in these tissues, mediated through beta(1)-adrenoceptors, was studied using electrically stimulated (1 Hz) atrial strips, as well as the effects of noradrenaline on cyclic AMP levels and cyclic AMP-dependent protein kinase. 3. Tissue from RR homozygotes (n=14) showed significantly increased inotropic potency to noradrenaline (-log EC(50), M=6.92+/-0.12) compared to GG homozygotes (n=8, -log EC(50), M=6.36+/-0.11, P<0.005). This difference was not dependent on tissue basal force. 4. Tissue cyclic AMP levels (pmol mg(-1)) were also greater in RR homozygotes (basal 34.8+/-3.7 n=12, 300 nM noradrenaline 41.4+/-7.6 n=9, 30 micro M noradrenaline 45.2+/-3.2 n=22, 0.2 mM isoprenaline 48.3+/-4.2 n=16) compared to GG homozygotes (basal 30.7+/-4.4 n=5, 300 nM noradrenaline 32.6+/-6.92 n=5, 30 micro M noradrenaline 38.1+/-3.1 n=8, 0.2 mM isoprenaline 42.6+/-5.2 n=6, P=0.007). There were no differences between the variants in terms of cyclic AMP-dependent protein kinase activity. 5. These data provide the first evidence that enhanced G-protein coupling of the R389 beta(1)-adrenoceptor variant reported in rodent fibroblast expression systems is also present in native human receptors. The functional consequence of this is to significantly alter the inotropic potency of beta(1)-adrenoceptor activation depending on its genotype at the 389 position.

Noise exposure and hearing loss among student employees working in university entertainment venues

OBJECTIVES

Most studies to date on sound levels in entertainment establishments have concentrated on exposure levels for the attending public, rather than employees who may be at greater risk of hearing loss. Of particular concern are young employees. The aim of this pilot study was to (i) estimate typical sound levels in different areas where amplified music was played, (ii) measure temporary threshold shift (TTS) and (iii) estimate the dependence of hearing threshold shifts on measured noise levels.

METHODS

This study focused on students working part-time (up to 16 h/week) in music bars and discotheques in a university entertainment venue. All 28 staff were invited to participate in the study. Pre- and post-exposure audiometry was used to determine hearing threshold at both high and low frequencies. Personal dosemeters and static measurements were made to assess noise levels and frequency characteristics. A questionnaire was used to determine patterns of noise exposure and attitudes to noise levels and hearing loss.

RESULTS

Of the 28 student employees working in the three areas, 14 (50%) agreed to take part in the study, giving 21 pre- and post-shift audiograms. The mean personal exposure levels for security staff were higher than those of bar staff, with both groups exceeding 90 dB(A). The maximum peak pressure reading for security staff was 124 dB. Although TTS values were moderate, they were found to be highly significant at both low and high frequencies and for both ears. Twenty-nine per cent of subjects showed permanent hearing loss of more than 30 dB at either low or high frequencies. The correlation between TTS and personal exposure was higher at 4 kHz than the low and high frequencies.

CONCLUSIONS

Contemporary music may be an important yet little considered contributor to total personal noise exposure, especially amongst young employees. Employees need to be better informed of risks of hearing loss and the need to report changes in hearing acuity. Suggestions are made on strategies for improving the assessment of noise exposure in entertainment venues.

Evaluation of land use/land cover datasets for urban watershed modeling

Land use/land cover (LULC) data are a vital component for nonpoint source pollution modeling. Most watershed hydrology and pollutant loading models use, in some capacity, LULC information to generate runoff and pollutant loading estimates. Simple equation methods predict runoff and pollutant loads using runoff coefficients or pollutant export coefficients that are often correlated to LULC type. Complex models use input variables and parameters to represent watershed characteristics and pollutant buildup and washoff rates as a function of LULC type. Whether using simple or complex models an accurate LULC dataset with an appropriate spatial resolution and level of detail is paramount for reliable predictions. The study presented in this paper compared and evaluated several LULC dataset sources for application in urban environmental modeling. The commonly used USGS LULC datasets have coarser spatial resolution and lower levels of classification than other LULC datasets. In addition, the USGS datasets do not accurately represent the land use in areas that have undergone significant land use change during the past two decades. We performed a watershed modeling analysis of three urban catchments in Los Angeles, California, USA to investigate the relative difference in average annual runoff volumes and total suspended solids (TSS) loads when using the USGS LULC dataset versus using a more detailed and current LULC dataset. When the two LULC datasets were aggregated to the same land use categories, the relative differences in predicted average annual runoff volumes and TSS loads from the three catchments were 8 to 14% and 13 to 40%, respectively. The relative differences did not have a predictable relationship with catchment size.

The structure of phosphorylated GSK-3beta complexed with a peptide, FRATtide, that inhibits beta-catenin phosphorylation

BACKGROUND

Glycogen synthase kinase-3 (GSK-3) sequentially phosphorylates four serine residues on glycogen synthase (GS), in the sequence SxxxSxxxSxxx-SxxxS(p), by recognizing and phosphorylating the first serine in the sequence motif SxxxS(P) (where S(p) represents a phosphoserine). FRATtide (a peptide derived from a GSK-3 binding protein) binds to GSK-3 and blocks GSK-3 from interacting with Axin. This inhibits the Axin-dependent phosphorylation of beta-catenin by GSK-3.

RESULTS

Structures of uncomplexed Tyr216 phosphorylated GSK-3beta and of its complex with a peptide and a sulfate ion both show the activation loop adopting a conformation similar to that in the phosphorylated and active forms of the related kinases CDK2 and ERK2. The sulfate ion, adjacent to Val214 on the activation loop, represents the binding site for the phosphoserine residue on 'primed' substrates. The peptide FRATtide forms a helix-turn-helix motif in binding to the C-terminal lobe of the kinase domain; the FRATtide binding site is close to, but does not obstruct, the substrate binding channel of GSK-3. FRATtide (and FRAT1) does not inhibit the activity of GSK-3 toward GS.

CONCLUSIONS

The Axin binding site on GSK-3 presumably overlaps with that for FRATtide; its proximity to the active site explains how Axin may act as a scaffold protein promoting beta-catenin phosphorylation. Tyrosine 216 phosphorylation can induce an active conformation in the activation loop. Pre-phosphorylated substrate peptides can be modeled into the active site of the enzyme, with the P1 residue occupying a pocket partially formed by phosphotyrosine 216 and the P4 phosphoserine occupying the 'primed' binding site.

GSK-3 inhibition by adenoviral FRAT1 overexpression is neuroprotective and induces Tau dephosphorylation and beta-catenin stabilisation without elevation of glycogen synthase activity

Glycogen synthase kinase 3 (GSK-3) has previously been shown to play an important role in the regulation of apoptosis. However, the nature of GSK-3 effector pathways that are relevant to neuroprotection remains poorly defined. Here, we have compared neuroprotection resulting from modulation of GSK-3 activity in PC12 cells using either selective small molecule ATP-competitive GSK-3 inhibitors (SB-216763 and SB-415286), or adenovirus overexpressing frequently rearranged in advanced T-cell lymphomas 1 (FRAT1), a protein proposed as a negative regulator of GSK-3 activity towards Axin and beta-catenin. Our data demonstrate that cellular overexpression of FRAT1 is sufficient to confer neuroprotection and correlates with inhibition of GSK-3 activity towards Tau and beta-catenin, but not modulation of glycogen synthase (GS) activity. By comparison, treatment with SB-216763 and SB-415286 proved more potent in terms of neuroprotection, and correlated with inhibition of GSK-3 activity towards GS in addition to Tau and beta-catenin.

Dietary obesity in the rat induces endothelial dysfunction without causing insulin resistance: a possible role for triacylglycerols

Impaired arterial vasorelaxation, due primarily to endothelial dysfunction, is associated with obesity. To clarify the relationship with insulin resistance and other metabolic disturbances, we studied endothelial-dependent and -independent vascular responses in rats with dietary-induced obesity. Dietary-obese rats had significantly higher body weights (10-32%; P<0.001) and fat-pad masses (220-280%; P<0.001) than lean controls, together with raised plasma levels of triacylglycerols (15-80%; P<0.001), non-esterified fatty acids (13-38%; P<0.05) and leptin (85-180%; P<0.001). However, measures of insulin sensitivity (including the hyperinsulinaemic-euglycaemic clamp in a parallel experiment) were comparable with those in controls. Contractions induced in mesenteric arteries by noradrenaline (0.5-8 micromol/l) were comparable in lean and obese groups, but vasorelaxation in noradrenaline-preconstricted arteries was markedly reduced in dietary-obese rats of both sexes. Concentration-response curves to endothelium-dependent vasorelaxants (acetylcholine, A23187 and insulin) showed significant reductions in maximal relaxation (20-95% less than in leans; P<0.001) and significant rightward shifts in EC(40) (concentration giving 40% of maximal response) (P<0.01). Relaxation in response to the direct NO donor, sodium nitroprusside, showed a lesser impairment (12%; P<0.01) in dietary-obese rats. Maximal relaxation to acetylcholine was correlated inversely in both sexes with fat-pad mass (r(2)=0.37, P<0.05) and plasma triacylglycerols (r(2)=0.51, P<0.01), and with leptin in males only (r(2)=0.35, P<0.05). Independent determinants of acetylcholine-induced relaxation were fat mass and plasma triacylglycerols; plasma insulin and insulin sensitivity had no effect. Dietary-induced obesity severely impaired arterial relaxation in both sexes, particularly at the endothelial level. This is not attributable to insulin resistance, but may be related to moderate hypertriglyceridaemia.

Childhood methanol ingestion treated with fomepizole and hemodialysis

Fomepizole (4-methylpyrazole; Antizol) is used increasingly in the treatment of methanol toxicity in adults. Little experience exists with this drug in the pediatric population, however. We present a case of methanol poisoning in a child in whom the use of fomepizole averted intravenous ethanol infusion and the attendant side effects of this therapy.

Real experiences of uHTS: a prototypic 1536-well fluorescence anisotropy-based uHTS screen and application of well-level quality control procedures

This paper describes, for the first time, a true ultra-high throughput screen (uHTS) based upon fluorescence anisotropy and performed entirely in 1536-well assay plates. The assay is based upon binding and displacement of a BODIPY-FL-labeled antibiotic to a specific binding site on 70S ribosomes from Escherichia coli (Kd approximately 15 nM). The screen was performed at uHTS rates (i.e., >100,000 assay wells/24 h) using entirely commercially available equipment. In order to examine the reproducibility of detection of test compound effects, assays were performed in duplicate. Both overall assay statistics and reproducibility for individual compound results were excellent, at least equivalent to conventional HTS assays. Interference artifacts occurred mainly as a result of autofluorescence from test compounds. Well-level quality control procedures were developed to detect, eliminate, or even correct for such effects. Moreover, development of a brighter, longer wavelength probe (based upon Cy3B) markedly reduced such interferences. Overall, the data demonstrate that fluorescence anisotropy-based uHTS is now a practical reality.