Allosteric inhibition of Staphylococcus aureus MenD by 1,4-dihydroxy naphthoic acid: a feedback inhibition mechanism of the menaquinone biosynthesis pathway

Menaquinones (MKs) are electron carriers in bacterial respiratory chains. In Staphylococcus aureus (Sau), MKs are essential for aerobic and anaerobic respiration. As MKs are redox-active, their biosynthesis likely requires tight regulation to prevent disruption of cellular redox balance. We recently found that the Mycobacterium tuberculosis MenD, the first committed enzyme of the MK biosynthesis pathway, is allosterically inhibited by the downstream metabolite 1,4-dihydroxy-2-naphthoic acid (DHNA). To understand if this is a conserved mechanism in phylogenetically distant genera that also use MK, we investigated whether the Sau-MenD is allosterically inhibited by DHNA. Our results show that DHNA binds to and inhibits the SEPHCHC synthase activity of Sau-MenD enzymes. We identified residues in the DHNA binding pocket that are important for catalysis (Arg98, Lys283, Lys309) and inhibition (Arg98, Lys283). Furthermore, we showed that exogenous DHNA inhibits the growth of Sau, an effect that can be rescued by supplementing the growth medium with MK-4. Our results demonstrate that, despite a lack of strict conservation of the DHNA binding pocket between Mtb-MenD and Sau-MenD, feedback inhibition by DHNA is a conserved mechanism in Sau-MenD and hence the Sau MK biosynthesis pathway. These findings may have implications for the development of anti-staphylococcal agents targeting MK biosynthesis. This article is part of the theme issue 'Reactivity and mechanism in chemical and synthetic biology'.

The structure of His-tagged Geobacillus stearothermophilus purine nucleoside phosphorylase reveals a `spanner in the works'

The 1.72 Å resolution structure of purine nucleoside phosphorylase from Geobacillus stearothermophilus, a thermostable protein of potential interest for the biocatalytic synthesis of antiviral nucleoside compounds, is reported. The structure of the N-terminally His-tagged enzyme is a hexamer, as is typical of bacterial homologues, with a trimer-of-dimers arrangement. Unexpectedly, several residues of the recombinant tobacco etch virus protease (rTEV) cleavage site from the N-terminal tag are located in the active site of the neighbouring subunit in the dimer. Key to this interaction is a tyrosine residue, which sits where the nucleoside ring of the substrate would normally be located. Tag binding appears to be driven by a combination of enthalpic, entropic and proximity effects, which convey a particularly high affinity in the crystallized form. Attempts to cleave the tag in solution yielded only a small fraction of untagged protein, suggesting that the enzyme predominantly exists in the tag-bound form in solution, preventing rTEV from accessing the cleavage site. However, the tagged protein retained some activity in solution, suggesting that the tag does not completely block the active site, but may act as a competitive inhibitor. This serves as a warning that it is prudent to establish how affinity tags may affect protein structure and function, especially for industrial biocatalytic applications that rely on the efficiency and convenience of one-pot purifications and in cases where tag removal is difficult.

Exploring Hong Kong nurses' decision-making processes around presenteeism

BACKGROUND

Presenteeism among nurses is the common behaviour of being physically present at work when one should not be due to personal health and well-being, a stressful work environment, lack of work-life balance, or a sense of professional identity or obligation.

AIMS

To explore nurses' decision-making process related to presenteeism in a large Hong Kong public hospital.

METHODS

As part of a larger study on nurse presenteeism in Hong Kong, we conducted focus groups with nurses to understand their considerations related to working sick.

RESULTS

Eleven major themes emerged from the focus groups, which we grouped into three organizational domains reflecting nurses' decision-making process around presenteeism: consideration for colleagues, organizational factors and professional identity.

CONCLUSIONS

Presenteeism was a familiar behaviour among Hong Kong nurses in our study. We found both overlap and divergence with prior presenteeism research in the domains and themes identified. Loyalty to colleagues, written and unwritten rules and professional identity as nurses all seemed to encourage presenteeism among Hong Kong nurses. Organizations seeking to discourage presenteeism should evaluate policies such as sick leave certificates, ensure appropriate coverage for all nurse ranks and address subcultural norms encouraging presenteeism.

Structure of a double CACHE chemoreceptor ligand-binding domain from Pseudomonas syringae provides insights into the basis of proline recognition

Chemotaxis is the process of sensing chemical gradients and navigating towards favourable conditions. Bacterial chemotaxis is mediated by arrays of trans-membrane chemoreceptor proteins. The most common class of chemoreceptors have periplasmic ligand-binding domains (LBDs) that detect extracellular chemical signs and transduce these signals to the downstream chemotaxis machinery. The repertoire of chemoreceptor proteins in a bacterium determines the range of environmental signals to which it can respond. Pseudomonas syringae pv. actinidiae (Psa) is a plant pathogen which causes bacterial canker of kiwifruit (Actinidia sp.). Compared to many other bacteria, Psa has a large number of chemoreceptors encoded in its genome (43) and most of these remain uncharacterized. A previous study identified PscC as a potential chemoreceptor for l-proline and other amino acid ligands. Here, we have characterized the interaction of PscC-LBD with l-proline using a combination of isothermal titration calorimetry (ITC) and X-ray crystallography. ITC confirmed direct binding of l-proline to PscC-LBD with K_D value of 5.0 μM. We determined the structure of PscC-LBD in complex with l-proline. Our structural analysis showed that PscC-LBD adopts similar double-CACHE fold to several other amino acid chemoreceptors. A comparison of the PscC-LDB to other dCACHE structures highlights residues in the binding cavity which contribute to its ligand specificity.

Acute intermittent hypoxia enhances regeneration of surgically repaired peripheral nerves in a manner akin to electrical stimulation

The intrinsic repair response of injured peripheral neurons is enhanced by brief electrical stimulation (ES) at time of surgical repair, resulting in improved regeneration in rodents and humans. However, ES is invasive. Acute intermittent hypoxia (AIH) - breathing alternate cycles of regular air and air with ~50% normal oxygen levels (11% O₂), considered mild hypoxia, is an emerging, promising non-invasive therapy that promotes motor function in spinal cord injured rats and humans. AIH can increase neural activity and under moderately severe hypoxic conditions improves repair of peripherally crushed nerves in mice. Thus, we posited an AIH paradigm similar to that used clinically for spinal cord injury, will improve surgically repaired peripheral nerves akin to ES, including an impact on regeneration-associated gene (RAG) expression-a predictor of growth states. Alterations in early RAG expression were examined in adult male Lewis rats that underwent tibial nerve coaptation repair with either 2 days AIH or normoxia control treatment begun on day 2 post-repair, or 1 h ES treatment (20 Hz) at time of repair. Three days post-repair, AIH or ES treatments effected significant and parallel elevated RAG expression relative to normoxia control at the level of injured sensory and motor neuron cell bodies and proximal axon front. These parallel impacts on RAG expression were coupled with significant improvements in later indices of regeneration, namely enhanced myelination and increased numbers of newly myelinated fibers detected 20 mm distal to the tibial nerve repair site or sensory and motor neurons retrogradely labeled 28 mm distal to the repair site, both at 25 days post nerve repair; and improved return of toe spread function 5-10 weeks post-repair. Collectively, AIH mirrors many beneficial effects of ES on peripheral nerve repair outcomes. This highlights its potential for clinical translation as a non-invasive means to effect improved regeneration of injured peripheral nerves.

Advances in menaquinone biosynthesis: sublocalisation and allosteric regulation

Menaquinones (vitamin K2) are a family of redox-active small molecules with critical functions across all domains of life, including energy generation in bacteria and bone health in humans. The enzymes involved in menaquinone biosynthesis also have bioengineering applications and are potential antimicrobial drug targets. New insights into the essential roles of menaquinones, and their potential to cause redox-related toxicity, have highlighted the need for this pathway to be tightly controlled. Here, we provide an overview of our current understanding of the classical menaquinone biosynthesis pathway in bacteria. We also review recent discoveries on protein-level allostery and sublocalisation of membrane-bound enzymes that have provided insight into the regulation of flux through this biosynthetic pathway.

Allosteric regulation of menaquinone (vitamin K2) biosynthesis in the human pathogen Mycobacterium tuberculosis

Menaquinone (vitamin K₂) plays a vital role in energy generation and environmental adaptation in many bacteria, including the human pathogen Mycobacterium tuberculosis (Mtb). Although menaquinone levels are known to be tightly linked to the cellular redox/energy status of the cell, the regulatory mechanisms underpinning this phenomenon are unclear. The first committed step in menaquinone biosynthesis is catalyzed by MenD, a thiamine diphosphate-dependent enzyme comprising three domains. Domains I and III form the MenD active site, but no function has yet been ascribed to domain II. Here, we show that the last cytosolic metabolite in the menaquinone biosynthesis pathway, 1,4-dihydroxy-2-naphthoic acid (DHNA), binds to domain II of Mtb-MenD and inhibits its activity. Using X-ray crystallography of four apo- and cofactor-bound Mtb-MenD structures, along with several spectroscopy assays, we identified three arginine residues (Arg-97, Arg-277, and Arg-303) that are important for both enzyme activity and the feedback inhibition by DHNA. Among these residues, Arg-277 appeared to be particularly important for signal propagation from the allosteric site to the active site. This is the first evidence of feedback regulation of the menaquinone biosynthesis pathway in bacteria, identifying a protein-level regulatory mechanism that controls menaquinone levels within the cell and may therefore represent a good target for disrupting menaquinone biosynthesis in M. tuberculosis.

Treatment-induced remission of medulloblastoma using a chemotherapeutic regimen devoid of vincristine in a child with Charcot-Marie-Tooth disease

Charcot-Marie-Tooth (cmt) disease is the most common form of inherited neuropathy. Core features include peripheral neuropathy and secondary axonal degeneration, with a noted distal predominance of limb-muscle wasting, weakness, and sensory loss. Given the significant prevalence of cmt, superimposed neoplastic disease can be encountered within this patient population. Malignancies that are treated with vincristine (a microtubule-targeting agent), even at low doses as part of standard treatment, pose a significant challenge for patients with cmt. Here, we present the case of a child with cmt who was successfully treated for medulloblastoma without vincristine, a standard drug used for treatment of that disease, to avoid the risk of severe debilitating neuropathy. This report is the first of a patient successfully treated for medulloblastoma without vincristine.

Demonstration of differences in colonic volumes, transit, chyme consistency, and response to psyllium between healthy and constipated subjects using magnetic resonance imaging

BACKGROUND

In functional gastrointestinal disorders a lack of objective biomarkers limits evaluation of underlying mechanisms. We aimed to demonstrate the utility of magnetic resonance imaging for this task using psyllium, an effective constipation treatment, in patients and controls.

METHODS

Two crossover studies: (i) adults without constipation (controls, n = 9) took three treatments in randomized order for 6 days - maltodextrin (placebo), psyllium 3.5 g t.d.s and 7 g t.d.s., (ii) adults with chronic constipation (patients, n = 20) took placebo and psyllium 7 g t.d.s. for 6 days. MRI was performed fasting and postprandially on day 6. Measurements included small bowel and ascending colon water content, colonic volume, transit time, and MR relaxometry (T1, T2) to assess colonic chyme. Stool water percentage was measured.

RESULTS

7 g psyllium t.d.s. increased fasting colonic volumes in controls from median 372 mL (IQR 284-601) to 578 mL (IQR 510-882), and in patients from median 831 mL (IQR 745-934) to 1104 mL (847-1316), P < .05. Mean postprandial small bowel water was higher in controls and patients after 7 g psyllium t.d.s. vs placebo. Whole gut transit was slower in patients than controls (P < .05). T1 of the descending colon chyme (fasting) was lower in patients (213 ms, 176-420) than controls (440 ms, 352-884, P < .05) on placebo, but increased by 7 g psyllium t.d.s. (590 ms, 446-1338), P < .001. Descending colon T1 correlated with baseline stool water content and stool frequency on treatment.

CONCLUSIONS AND INFERENCES

MRI measurements can objectively demonstrate the mode of action of therapy targeting intestinal fluid content in constipation.

Differences in the diagnosis and management of systemic lupus erythematosus by primary care and specialist providers in the American Indian/Alaska Native population

Objectives The objective of this study is to investigate differences in the diagnosis and management of systemic lupus erythematosus (SLE) by primary care and specialist physicians in a population-based registry. Methods This study includes individuals from the 2009 Indian Health Service lupus registry population with a diagnosis of SLE documented by either a primary care provider or specialist. SLE classification criteria, laboratory testing, and medication use at any time during the course of disease were determined by medical record abstraction. Results Of the 320 individuals with a diagnosis of SLE, 249 had the diagnosis documented by a specialist, with 71 documented by primary care. Individuals with a specialist diagnosis of SLE were more likely to have medical record documentation of meeting criteria for SLE by all criteria sets (American College of Rheumatology, 79% vs 22%; Boston Weighted, 82% vs 32%; and Systemic Lupus International Collaborating Clinics, 83% vs 35%; p < 0.001 for all comparisons). In addition, specialist diagnosis was associated with documentation of ever having been tested for anti-double-stranded DNA antibody and complement 3 and complement 4 ( p < 0.001). Documentation of ever receiving hydroxychloroquine was also more common with specialist diagnosis (86% vs 64%, p < 0.001). Conclusions Within the population studied, specialist diagnosis of SLE was associated with a higher likelihood of having SLE classification criteria documented, being tested for biomarkers of disease, and ever receiving treatment with hydroxychloroquine. These data support efforts both to increase specialist access for patients with suspected SLE and to provide lupus education to primary care providers.

Determining an optimal dose of linaclotide for use in Japanese patients with irritable bowel syndrome with constipation: A phase II randomized, double-blind, placebo-controlled study

BACKGROUND

Clinical testing to determine a suitable dose of linaclotide for Japanese patients with irritable bowel syndrome with constipation (IBS-C) was needed.

METHODS

This was a randomized, double-blind, placebo-controlled, dose-finding trial. Japanese patients with IBS-C diagnosed using Rome III criteria (n = 559, men/women: 49/510) were randomly assigned to 1 of 4 linaclotide doses (0.0625, 0.125, 0.25, or 0.5 mg) or placebo for the 12-week treatment period. The primary endpoint was responder rate of global assessment of relief of IBS symptoms during 12 weeks. The secondary endpoints included responder rates of complete spontaneous bowel movement (CSBM), SBM and abdominal pain/discomfort relief and others.

KEY RESULTS

The primary endpoint was 23.2%, 36.2%, 38.7%, 34.8%, and 38.3% in placebo (n = 112), 0.0625 (n = 116), 0.125 (n = 111), 0.25 (n = 112), and 0.5 (n = 107) mg of linaclotide groups with the difference from the placebo group in each linaclotide group (13.0%, 15.5%, 11.6%, 15.1%, P > .05). Monthly responder rate of global assessment of relief of IBS symptoms at month 3 (48.6%), responder rate of CSBM during 12 weeks (45.8%), and responder rate of abdominal pain/discomfort relief during 12 weeks (32.7%) in the 0.5 mg were significantly higher than those in placebo group (29.5%, P < .01; 25.9%, P < .01; and 18.8%, P < .05 respectively). The most frequent adverse event in the linaclotide groups was diarrhea.

CONCLUSIONS & INFERENCES

This study suggests that a linaclotide dose of 0.5 mg may be appropriate in Japanese patients with IBS-C.

Diabetes incidence and prevalence in Hong Kong, China during 2006-2014

AIMS

To estimate recent secular changes in the incidence and prevalence of diabetes and pre-diabetes among Hong Kong Chinese adults, and thus show possible future trends for developing mainland China.

METHODS

Based on a complete census of the public sector health records of 6.4 million people from 2006 to 2014, diabetes cases were ascertained using different methods including the World Health Organization (WHO) 2011 guidelines (HbA_1c , fasting plasma glucose and glucose tolerance test), American Diabetes Association (ADA) 2015 guidelines (plus random plasma glucose), and additionally recorded diagnosis codes and medication dispensation. Pre-diabetes was defined using ADA 2015 guidelines.

RESULTS

We identified 697 201 people with diabetes (54.2% were incident cases); and 1 229 731 people with diabetes or pre-diabetes. In 2014, the overall incidence of diabetes was 9.46 per 1000 person-years [95% confidence interval (CI): 9.38 to 9.54], and overall prevalence was 10.29% (95% CI: 10.27% to 10.32%). Incidence of diabetes decreased significantly from 2007 to 2014 (quadratic trend, P < 0.001). From 2006 to 2014, the prevalence of diabetes increased significantly in both sexes and across all age groups (quadratic trend, P < 0.001). The overall incidence of pre-diabetes in 2014 was 18.88 per 1000 person-years (95% CI: 18.76 to 18.99), and the overall prevalence of pre-diabetes was 8.90% (95% CI: 8.87% to 8.92%).

CONCLUSIONS

Similar to other developed western and Asian populations, diabetes (and pre-diabetes) incidence in Hong Kong Chinese appeared to have stabilized and there have been small declines during the period of observation. Ageing and survivorship will likely drive a continued increase in the prevalence of diabetes and pre-diabetes, albeit with a decelerating growth rate if past trends persist.

Crystal structure of a bicupin protein HutD involved in histidine utilization in Pseudomonas

Cupins form one of the most functionally diverse superfamilies of proteins, with members performing a wide range of catalytic, non-catalytic, and regulatory functions. HutD is a predicted bicupin protein that is involved in histidine utilization (Hut) in Pseudomonas species. Previous genetic analyses have suggested that it limits the upper level of Hut pathway expression, but its mechanism of action is unknown. Here, we have determined the structure of PfluHutD at 1.74 Å resolution in several crystallization conditions, and identified N-formyl-l-glutamate (FG, a Hut pathway intermediate) as a potential ligand in vivo. Proteins 2017; 85:1580-1588. © 2017 Wiley Periodicals, Inc.

Mass spectral determination of phosphopantetheinylation specificity for carrier proteins in Mycobacterium tuberculosis

Phosphopantetheinyl transferases (PPTases) are key elements in the modular syntheses performed by multienzyme systems such as polyketide synthases. PPTases transfer phosphopantetheine derivatives from Coenzyme A to carrier proteins (CPs), thus orchestrating substrate supply. We describe an efficient mass spectrometry-based protocol for determining CP specificity for a particular PPTase in organisms possessing several candidate PPTases. We show that the CPs MbtL and PpsC, both involved in synthesis of essential metabolites in Mycobacterium tuberculosis, are exclusively activated by the type 2 PPTase PptT and not the type 1 AcpS. The assay also enables conclusive identification of the reactive serine on each CP.

Structural Views along the Mycobacterium tuberculosis MenD Reaction Pathway Illuminate Key Aspects of Thiamin Diphosphate-Dependent Enzyme Mechanisms

Menaquinone (MQ) is an essential component of the respiratory chains of many pathogenic organisms, including Mycobacterium tuberculosis (Mtb). The first committed step in MQ biosynthesis is catalyzed by 2-succinyl-5-enolpyruvyl-6-hydroxy-3-cyclohexadiene-1-carboxylate synthase (MenD), a thiamin diphosphate (ThDP)-dependent enzyme. Catalysis proceeds through two covalent intermediates as the substrates 2-oxoglutarate and isochorismate are successively added to the cofactor before final cleavage of the product. We have determined a series of crystal structures of Mtb-MenD that map the binding of both substrates, visualizing each step in the MenD catalytic cycle, including both intermediates. ThDP binding induces a marked asymmetry between the coupled active sites of each dimer, and possible mechanisms of communication can be identified. The crystal structures also reveal conformational features of the two intermediates that facilitate reaction but prevent premature product release. These data fully map chemical space to inform early-stage drug discovery targeting MenD.

Structure and inhibition of subunit I of the anthranilate synthase complex of Mycobacterium tuberculosis and expression of the active complex

The tryptophan-biosynthesis pathway is essential for Mycobacterium tuberculosis (Mtb) to cause disease, but not all of the enzymes that catalyse this pathway in this organism have been identified. The structure and function of the enzyme complex that catalyses the first committed step in the pathway, the anthranilate synthase (AS) complex, have been analysed. It is shown that the open reading frames Rv1609 (trpE) and Rv0013 (trpG) encode the chorismate-utilizing (AS-I) and glutamine amidotransferase (AS-II) subunits of the AS complex, respectively. Biochemical assays show that when these subunits are co-expressed a bifunctional AS complex is obtained. Crystallization trials on Mtb-AS unexpectedly gave crystals containing only AS-I, presumably owing to its selective crystallization from solutions containing a mixture of the AS complex and free AS-I. The three-dimensional structure reveals that Mtb-AS-I dimerizes via an interface that has not previously been seen in AS complexes. As is the case in other bacteria, it is demonstrated that Mtb-AS shows cooperative allosteric inhibition by tryptophan, which can be rationalized based on interactions at this interface. Comparative inhibition studies on Mtb-AS-I and related enzymes highlight the potential for single inhibitory compounds to target multiple chorismate-utilizing enzymes for TB drug discovery.

A covalent adduct of MbtN, an acyl-ACP dehydrogenase from Mycobacterium tuberculosis, reveals an unusual acyl-binding pocket

Mycobacterium tuberculosis (Mtb) is the causative agent of tuberculosis. Access to iron in host macrophages depends on iron-chelating siderophores called mycobactins and is strongly correlated with Mtb virulence. Here, the crystal structure of an Mtb enzyme involved in mycobactin biosynthesis, MbtN, in complex with its FAD cofactor is presented at 2.30 Å resolution. The polypeptide fold of MbtN conforms to that of the acyl-CoA dehydrogenase (ACAD) family, consistent with its predicted role of introducing a double bond into the acyl chain of mycobactin. Structural comparisons and the presence of an acyl carrier protein, MbtL, in the same gene locus suggest that MbtN acts on an acyl-(acyl carrier protein) rather than an acyl-CoA. A notable feature of the crystal structure is the tubular density projecting from N(5) of FAD. This was interpreted as a covalently bound polyethylene glycol (PEG) fragment and resides in a hydrophobic pocket where the substrate acyl group is likely to bind. The pocket could accommodate an acyl chain of 14-21 C atoms, consistent with the expected length of the mycobactin acyl chain. Supporting this, steady-state kinetics show that MbtN has ACAD activity, preferring acyl chains of at least 16 C atoms. The acyl-binding pocket adopts a different orientation (relative to the FAD) to other structurally characterized ACADs. This difference may be correlated with the apparent ability of MbtN to catalyse the formation of an unusual cis double bond in the mycobactin acyl chain.

The impact of abdominal pain on global measures in patients with chronic idiopathic constipation, before and after treatment with linaclotide: a pooled analysis of two randomised, double-blind, placebo-controlled, phase 3 trials

BACKGROUND

Few clinical trials in chronic idiopathic constipation (CIC) patients have evaluated abdominal symptom severity and whether CIC patients with abdominal symptoms respond similarly to patients with limited abdominal symptoms.

AIMS

To examine abdominal symptom severity and relationships between symptoms and global measures at baseline; compare linaclotide's effect on symptoms in subpopulations with more or less abdominal pain; and assess relationships between symptom improvement and global measures in these two subpopulations.

METHODS

In two phase 3 trials, patients meeting modified Rome II CIC criteria were assigned to linaclotide 145 μg, 290 μg, or placebo once daily. Patients rated abdominal and bowel symptoms daily during 2-week pre-treatment and 12-week treatment periods. Linaclotide's effect on symptoms and global measures [constipation severity, health-related quality of life (HRQOL), treatment satisfaction] and their inter-relationships were assessed in post hoc analyses of abdominal pain subpopulations.

RESULTS

Of 1271 CIC patients, 23%, 32%, and 43% reported moderate-to-severe abdominal pain, discomfort, and bloating, respectively, during baseline. In more-severe abdominal pain patients, abdominal symptoms were more strongly correlated than bowel symptoms with global measures, but in less-severe abdominal pain patients, abdominal and bowel symptoms were similarly correlated with global measures, at baseline and post-treatment. Linaclotide significantly improved all symptoms and global measures in both subpopulations.

CONCLUSIONS

When abdominal pain is present in CIC, abdominal and not bowel symptoms may drive patient assessments of constipation severity, HRQOL, and treatment satisfaction. Linaclotide (145 μg and 290 μg) is an effective treatment for both abdominal and bowel symptoms, even in CIC patients with more severe abdominal pain at baseline. (Clinicaltrials.gov: NCT00765882, NCT00730015).

High-throughput screening identifies compounds that enhance lentiviral transduction

A difficulty in the field of gene therapy is the need to increase the susceptibility of hematopoietic stem cells (HSCs) to ex vivo genetic manipulation. To overcome this obstacle a high-throughput screen was performed to identify compounds that could enhance the transduction of target cells by lentiviral vectors. Of the 1280 compounds initially screened using the myeloid-erythroid-leukemic K562 cell line, 30 were identified as possible enhancers of viral transduction. Among the positive hits were known enhancers of transduction (camptothecin, etoposide and taxol), as well as the previously unidentified phorbol 12-myristate 13-acetate (PMA). The percentage of green fluorescent protein (GFP)-positive-expressing K562 cells was increased more than fourfold in the presence of PMA. In addition, the transduction of K562 cells with a lentiviral vector encoding fVIII was four times greater in the presence of PMA as determined by an increase in the levels of provirus in genetically modified cells. PMA did not enhance viral transduction of all cell types (for example, sca-1(+) mouse hematopoietic cells) but did enhance viral transduction of human bone marrow-derived CD34(+) cells. Notably, the percentage of GFP-positive CD34(+) cells was increased from 7% in the absence of PMA to greater than 22% in the presence of 1 nM PMA. PMA did not affect colony formation of CD34(+) cells or the expression of the hematopoietic markers CD34 and CD45. These data demonstrate that high-throughput screening can be used to identify compounds that increase the transduction efficiency of lentiviral vectors, identifying PMA as a potential enhancer of lentiviral HSC transduction.

Psychometric validation of symptom severity measures in irritable bowel syndrome with constipation

BACKGROUND

Historically, measures of symptom severity of irritable bowel syndrome with constipation (IBS-C) in clinical trials have not met the evidence requirements described in the FDA guidance on patient-reported outcomes (PROs), which describes the evidentiary requirements and review criteria for patient-reported outcome measures intended to support product approval or labelling claims.

AIM

Data from two phase 3 trials (N = 1608) of linaclotide for the treatment of IBS-C were analysed to evaluate the psychometric properties of patient-reported outcome measures assessing changes in the severity of abdominal and bowel symptoms.

METHODS

A set of patient-reported outcome assessments addressing abdominal and bowel symptoms, the IBS-C Symptom Severity Measures, were administered daily using interactive voice response system technology. Intraclass correlation coefficients (ICCs), Pearson correlations, factor analyses, F-tests and effect sizes were computed to evaluate the reliability, construct validity, discriminating ability and responsiveness of the IBS-C Symptom Severity Measures in a clinical trial context.

RESULTS

The IBS-C Symptom Severity Measures showed highly satisfactory test-retest reliability (ICCs ranging from 0.79 to 0.95) and construct validity. Factor analyses indicated one factor for abdominal symptoms and another for bowel symptoms. Known-groups F-tests comparing subgroups based on various responder definitions were statistically significant and in the expected direction, substantiating the discriminating ability of the IBS-C Symptom Severity Measures. Responsiveness statistics (ranging from 0.6 to 2.1) demonstrated these measures are also capable of detecting change.

CONCLUSIONS

The psychometric analysis results strongly support the reliability, construct validity, discriminating ability and responsiveness of the IBS-C Symptom Severity Measures and substantiate the conclusion of linaclotide treatment benefit.

Factors affecting implementation of accreditation programmes and the impact of the accreditation process on quality improvement in hospitals: a SWOT analysis

OBJECTIVES

The objectives of this review were to identify factors that influence implementation of hospital accreditation programmes and to assess the impact of the accreditation process on quality improvement in public hospitals.

DATA SOURCES

Two electronic databases, Medline (OvidSP) and PubMed, were systematically searched.

STUDY SELECTION

"Public hospital", "hospital accreditation", and "quality improvement" were used as the search terms. A total of 348 citations were initially identified. After critical appraisal and study selection, 26 articles were included in the review.

DATA EXTRACTION

The data were extracted and analysed using a SWOT (strengths, weaknesses, opportunities, threats) analysis.

DATA SYNTHESIS

Increased staff engagement and communication, multidisciplinary team building, positive changes in organisational culture, and enhanced leadership and staff awareness of continuous quality improvement were identified as strengths. Weaknesses included organisational resistance to change, increased staff workload, lack of awareness about continuous quality improvement, insufficient staff training and support for continuous quality improvement, lack of applicable accreditation standards for local use, and lack of performance outcome measures. Opportunities included identification of improvement areas, enhanced patient safety, additional funding, public recognition, and market advantage. Threats included opportunistic behaviours, funding cuts, lack of incentives for participation, and a regulatory approach to mandatory participation.

CONCLUSIONS

By relating the findings to the operational issues of accreditation, this review discussed the implications for successful implementation and how accreditation may drive quality improvement. These findings have implications for various stakeholders (government, the public, patients and health care providers), when it comes to embarking on accreditation exercises.

Responders vs clinical response: a critical analysis of data from linaclotide phase 3 clinical trials in IBS-C

BACKGROUND

US Food and Drug Administration (FDA) set a rigorous standard for defining patient responders in irritable bowel syndrome-C (IBS-C; i.e., FDA's Responder Endpoint) for regulatory approval. However, this endpoint's utility for health-care practitioners to assess clinical response has not been determined. We analyzed pooled IBS-C linaclotide trial data to evaluate clinically significant responses in linaclotide-treated patients who did not meet the FDA responder definition.

METHODS

Percentages of FDA non-responders reporting improvement in abdominal pain, bowel function and/or global relief measures were determined using pooled data from two linaclotide Phase 3 IBS-C trials.

KEY RESULTS

1602 IBS-C patients enrolled; 34% of linaclotide-treated and 17% of placebo-treated patients met the FDA Responder Endpoint (p < 0.0001). Among FDA non-responders at week 12, 63% of linaclotide-treated patients reported their abdominal pain was at least somewhat relieved, compared with 48% of placebo-treated patients. For stool frequency, 62% of linaclotide-treated patients reported that they were at least somewhat improved at week 12, compared with 46% of placebo-treated patients. For global IBS symptoms, 65% of linaclotide-treated patients reported at least some IBS-symptom relief, 43% reported adequate relief of IBS symptoms, and 57% reported being satisfied with linaclotide treatment, vs placebo rates of 48%, 34%, and 41% respectively.

CONCLUSIONS & INFERENCES

Most linaclotide-treated IBS-C patients who were FDA non-responders reported some improvement in abdominal pain and stool frequency, and global relief/satisfaction. In addition to the FDA Responder Endpoint, differing response thresholds and symptom-specific change from baseline should be considered by clinicians for a complete understanding of clinical response to linaclotide and other IBS-C therapies.

Purification, crystallization and preliminary X-ray studies of MbtN (Rv1346) from Mycobacterium tuberculosis

In Mycobacterium tuberculosis, the protein MbtN (Rv1346) catalyzes the formation of a double bond in the fatty-acyl moiety of the siderophore mycobactin, which is used by this organism to acquire essential iron. MbtN is homologous to acyl-CoA dehydrogenases, whose general role is to catalyze the α,β-dehydrogenation of fatty-acyl-CoA conjugates. Mycobactins, however, contain a long unsaturated fatty-acid chain with an unusual cis double bond conjugated to the carbonyl group of the mycobactin core. To characterize the role of MbtN in the dehydrogenation of this fatty-acyl moiety, the enzyme has been expressed, purified and crystallized. The crystals diffracted to 2.3 Å resolution at a synchrotron source and were found to belong to the hexagonal space group H32, with unit-cell parameters a = b = 139.10, c = 253.09 Å, α = β = 90, γ = 120°.

An evaluation of the FDA responder endpoint for IBS-C clinical trials: analysis of data from linaclotide Phase 3 clinical trials

BACKGROUND

Our objective was to evaluate the performance of the Food and Drug Administration (FDA) Responder Endpoint for clinical trials in IBS-C, using data from two large Phase 3 clinical trials of linaclotide. The FDA interim endpoint requires that, for 50% of trial weeks, patients report ≥30% decrease in Abdominal Pain at its worst and (in the same week) an increase in Complete Spontaneous Bowel Movements (CSBMs) of ≥1 from baseline.

METHODS

Anchor-based methodology was used to estimate thresholds of clinically meaningful change using symptom-specific patient rating of change questions (PRCQs) and symptom severity questions. The diagnostic accuracy of the FDA Responder Endpoint was assessed using sensitivity/specificity-based methods.

KEY RESULTS

Using anchor-based methods, the estimates of the clinically meaningful improvement thresholds for Abdominal Pain ranged from 25.9% to 32.4% and thresholds for increase in weekly CSBM rate ranged from 1.4 to 1.6 CSBMs per week. Compared with the symptom-specific PRCQs for patient rating of relief, the FDA Responder Endpoint has a sensitivity of 60.7%, a specificity of 93.5%, and an accuracy of 82.0%. Changing the number of weeks required to be a responder or the percentage improvement in the Abdominal Pain criteria did not result in notable improvement in the accuracy of the FDA Responder Endpoint.

CONCLUSIONS & INFERENCES

The FDA Responder Endpoint for IBS-C clinical trials represents clinically meaningful improvements in IBS-C symptoms for patients with excellent specificity and reasonable sensitivity.

Effects of built environment on walking among Hong Kong older adults

1. Reliable and valid interviewer-administered questionnaires were developed to investigate associations of perceived neighbourhood attributes of Hong Kong older adults with their walking for transportation and recreation. 2. Access to and availability of different types of services and destinations, provision of facilities for resting/sitting in the neighbourhood, and easy access to/from residential buildings may help maintain an active lifestyle by facilitating walking for transport in the neighbourhood. 3. Access to services, indoor places for walking, environmental aesthetics, low traffic, and absence of physical barriers may promote recreational walking..

Crystal structures of E. coli native MenH and two active site mutants

Recent revision of the biosynthetic pathway for menaquinone has led to the discovery of a previously unrecognized enzyme 2-succinyl-6-hydroxy-2,4-cyclohexadiene-1-carboxylate synthase, also known as MenH. This enzyme has an α/β hydrolase fold with a catalytic triad comprising Ser86, His232, and Asp210. Mutational studies identified a number of conserved residues of importance to activity, and modeling further implicated the side chains of Tyr85 and Trp147 in formation of a non-standard oxyanion hole. We have solved the structure of E. coli MenH (EcMenH) at 2.75 Å resolution, together with the structures of the active site mutant proteins Tyr85Phe and Arg124Ala, both at 2.5 Å resolution. EcMenH has the predicted α/β hydrolase fold with its core α/β domain capped by a helical lid. The active site, a long groove beneath the cap, contains a number of conserved basic residues and is found to bind exogeneous anions, modeled as sulfate and chloride, in all three crystal structures. Docking studies with the MenH substrate and a transition state model indicate that the bound anions mark the binding sites for anionic groups on the substrate. The docking studies, and careful consideration of the active site geometry, further suggest that the oxyanion hole is of a conventional nature, involving peptide NH groups, rather than the proposed site involving Tyr85 and Trp147. This is in accord with conclusions from the structure of S. aureus MenH. Comparisons with the latter do, however, indicate differences in the periphery of the active site that could be of relevance to selective inhibition of MenH enzymes.

Randomised clinical trials: linaclotide phase 3 studies in IBS-C - a prespecified further analysis based on European Medicines Agency-specified endpoints

BACKGROUND

Treatment options that improve overall symptoms of irritable bowel syndrome with constipation (IBS-C) are lacking.

AIM

A prespecified further analysis to evaluate the efficacy and safety of linaclotide, a guanylate cyclase C agonist, in patients with IBS-C, based on efficacy parameters prespecified for European Medicines Agency (EMA) submission.

METHODS

Two randomised, double-blind, multicentre Phase 3 trials investigated once-daily linaclotide (290 μg) for 12 weeks (Trial 31) or 26 weeks (Trial 302) in patients with IBS-C. Prespecified primary endpoints were the EMA-recommended co-primary endpoints: (i) 12-week abdominal pain/discomfort responders [≥30% reduction in mean abdominal pain and/or discomfort score (11-point scales), with neither worsening from baseline, for ≥6 weeks] and (ii) 12-week IBS degree-of-relief responders (symptoms 'considerably' or 'completely' relieved for ≥6 weeks).

RESULTS

Overall, 803 (Trial 31) and 805 patients (Trial 302) were randomised. A significantly greater proportion of linaclotide-treated vs. placebo-treated patients were 12-week abdominal pain/discomfort responders (Trial 31: 54.8% vs. 41.8%; Trial 302: 54.1% vs. 38.5%; P < 0.001) and IBS degree-of-relief responders (Trial 31: 37.0% vs. 18.5%; Trial 302: 39.4% vs. 16.6%; P < 0.0001). Similarly, significantly more linaclotide- vs. placebo-treated patients were responders for ≥13 weeks in Trial 302 (abdominal pain/discomfort: 53.6% vs. 36.0%; IBS degree-of-relief: 37.2% vs. 16.9%; P < 0.0001). The proportion of sustained responders (co-primary endpoint responders plus responders for ≥2 of the last 4 weeks of treatment) was also significantly greater with linaclotide vs. placebo in both trials (P < 0.001).

CONCLUSION

Linaclotide treatment significantly improved abdominal pain/discomfort and degree-of-relief of IBS-C symptoms compared with placebo over 12 and 26 weeks.

TRIAL REGISTRATION

ClinicalTrials.gov (identifiers: NCT00948818 and NCT00938717).

The nature of the stimulatory role of the supernatant fraction on triglyceride synthesis by the alpha-Glycerophosphate pathway

Evidence is presented as to the nature and mechanism of the stimulatory effect of the supernatant fraction on the biosynthesis of triglycerides via the alpha-glycerophosphate pathway in the intestinal mucosa. When microsomes are employed as the enzyme source, the major lipid formed from either labeled palmitic acid orL: -alpha-glycerophosphate is phosphatidic acid and only a limited amount of triglyceride is synthesized. The addition of the supernatant fraction to microsomes results in a stimulation of triglyceride biosynthesis at the expense of phosphatidic acid. Employing the same microsomal fraction, the reaction sequence was followed step by step and the intermediates were isolated. The results suggest that the stimulatory role of the supernatant fraction can be attributed to the presence ofL: -alpha-phosphatidate phosphohydrolase (EC 3.1.3.4). The hydrolysis of the biosynthesized microsomal phosphatidic acid by the supernatant enzyme occurs at a faster rate than the hydrolysis of added phosphatidic acid prepared from egg lecithin. The initial acylation steps in the biosynthesis of triglycerides or phosphatidic acid via the glycerophosphate pathway occur only in the presence of fatty acid and the cofactors necessary for its activation. Under these conditions, fatty acyl-CoA will not substitute for the fatty acid activation system.

Strategic and tactical limits of comparison studies

A comparison study is an experiment whose primary purpose is to compare directly (regardless of experimental design) at least two different procedures for changing behavior or two or more components of such a procedure. This paper argues that, in spite of their popularity, such studies typically lead to inappropriate inferences with poor generality based on improper evidence gathered in support of the wrong question, thus wasting the limited experimental resources. The discussion considers problems concerning the functions of comparison studies, the nature of the comparisons that are attempted, the generality of their findings, and the limited role that they can play in technological research.

Positive behavior support and applied behavior analysis

This article reviews the origins and characteristics of the positive behavior support (PBS) movement and examines those features in the context of the field of applied behavior analysis (ABA). We raise a number of concerns about PBS as an approach to delivery of behavioral services and its impact on how ABA is viewed by those in human services. We also consider the features of PBS that have facilitated its broad dissemination and how ABA might benefit from emulating certain practices of the PBS movement.

Distinguishing between applied research and practice

Behavior-analytic research is often viewed along a basic-applied continuum of research goals and methods. The applied portion of this continuum has evolved in ways that combine applied research and service delivery. Although these two facets of applied behavior analysis should be closely related, more clearly distinguishing between them, particularly in how we conceptualize and conduct applied research, may enhance the continuing development of each. This differentiation may improve the recruitment and training of graduate students.

Applying the least restrictive alternative principle to treatment decisions: A legal and behavioral analysis

The least restrictive alternative concept is widely used in mental health law. This paper addresses how the concept has been applied to treatment decisions. The paper offers both a legal and a behavioral analysis to some problems that have emerged in recent years concerning the selection of behavioral procedures used to change client behavior. The paper also offers ways of improving the application of the concept, which involve developing a more behaviorally functional perspective toward restrictiveness.

Logic, reasoning, and verbal behavior

This paper analyzes the traditional concepts of logic and reasoning from the perspective of radical behaviorism and in the terms of Skinner's treatment of verbal behavior. The topics covered in this analysis include the proposition, premises and conclusions, logicality and rules, and deductive and inductive reasoning.

Behavior analysis and the R&D paradigm

This paper considers research and development (R&D) as a style of investigation that holds promise for the field of behavior analysis. Contrasted with academic-style research, R&D tends to be highly targeted toward achievement of specific outcomes, which are determined by a user community. R&D is typically multidisciplinary in character and is coordinated by a funding source. R&D usually includes extensive field testing and systematically addresses technology transfer. A program of R&D focused on detector dogs serves as an exemplar of this approach for behavior analysis.