Biomedical subjects

Ian Johnson

Publications and source records attributed to Ian Johnson.

15 recordsLinked to original sources

PubMed2006

Genetic variability in Daphnia magna and ecotoxicological evaluation.

The fresh water crustacean Daphnia magna is widely used as a test organism in aquatic toxicology to assess the adverse effects of individual substances or complex mixtures, e.g. industrial wastewaters. Cultures are held in several European testing laboratories and testing is typically carried out according to internationally standardised protocols. However, despite accounting for many potential confounding factors these guidelines do not currently take into account any specification related to the use of a specific clone. Cultures from seven laboratories were used to assess genetic variability by random-amplified polymorphic DNA polymerase chain reaction. Results pointed out the existence of two main clone clusters Responses in the acute Daphnia immobilisation test showed no direct correlation with genetic clusters resulting from random genetic markers (random-amplified polymorphic DNA) analysis. Considering that genetic differences are the most probable cause for the ecotoxicological test data, further analysis concerning gene expression and genetic stability should be performed.

Animals↗

PubMed2006

Household transmission of SARS, 2003.

BACKGROUND: In the 2003 outbreak in Toronto (in Ontario, Canada) of severe acute respiratory syndrome (SARS), about 20% of cases resulted from household transmission. The purpose of our study was to determine characteristics associated with the transmission of SARS within households. METHODS: A retrospective cohort of SARS-affected households was studied to determine risk factors for household transmission. Questionnaires addressed characteristics of the index case, the household and behaviours among household members. Potential risk factors for secondary transmission of infection were assessed in regression models appropriate to the outcome (secondary cases) and nonindependence of household members. RESULTS: The 74 households that participated included 18 secondary cases and 158 uninfected household members in addition to the 74 index cases. The household secondary attack rate was 10.2% (95% confidence interval [CI] 6.7%-23.5%). There was a linear association between the time the index patient spent at home after symptom onset and the secondary attack rate. Infected health care workers who were index cases had lower rates of household transmission. INTERPRETATION: SARS transmission in households is complex and increases with the length of time an ill person spends at home. Risk of transmission was lower when the index case was a health care worker. Rapid case identification is the public health measure most useful in minimizing exposure in the home.

Adolescent↗

PubMed2006

Implications of research on endocrine disruption for the environmental risk assessment, regulation and monitoring of chemicals in the European Union.

We assess the implications which research on endocrine disrupting chemicals (EDCs) has for the regulation of synthetic substances and for the protection of the environment, particularly under the forthcoming European Union (EU) REACH legislation. EDCs present regulatory problems inter alia because they can act additively at concentrations which are individually harmless, and they may have non-classical dose (concentration)-response relationships at low exposure levels. Furthermore, current in vivo testing routines were not specifically designed to assess the endocrine disrupting properties of chemicals, whilst in silico and in vitro methods have only limited applicability and availability for this purpose. We need to ensure that the assessment approaches specified in the draft REACH legislation and Technical Guidance are able to evaluate EDCs efficiently. However, it must also be recognised that environmental monitoring procedures in Europe will need to be improved to detect EDCs that have evaded identification, and where appropriate, control, under REACH.

Dose-Response Relationship, Drug↗

PubMed2006

An assessment of the model of concentration addition for predicting the estrogenic activity of chemical mixtures in wastewater treatment works effluents.

The effects of simple mixtures of chemicals, with similar mechanisms of action, can be predicted using the concentration addition model (CA). The ability of this model to predict the estrogenic effects of more complex mixtures such as effluent discharges, however, has yet to be established. Effluents from 43 U.K. wastewater treatment works were analyzed for the presence of the principal estrogenic chemical contaminants, estradiol, estrone, ethinylestradiol, and nonylphenol. The measured concentrations were used to predict the estrogenic activity of each effluent, employing the model of CA, based on the relative potencies of the individual chemicals in an in vitro recombinant yeast estrogen screen (rYES) and a short-term (14-day) in vivo rainbow trout vitellogenin induction assay. Based on the measured concentrations of the four chemicals in the effluents and their relative potencies in each assay, the calculated in vitro and in vivo responses compared well and ranged between 3.5 and 87 ng/L of estradiol equivalents (E2 EQ) for the different effluents. In the rYES, however, the measured E2 EQ concentrations in the effluents ranged between 0.65 and 43 ng E2 EQ/L, and they varied against those predicted by the CA model. Deviations in the estimation of the estrogenic potency of the effluents by the CA model, compared with the measured responses in the rYES, are likely to have resulted from inaccuracies associated with the measurement of the chemicals in the extracts derived from the complex effluents. Such deviations could also result as a consequence of interactions between chemicals present in the extracts that disrupted the activation of the estrogen response elements in the rYES. E2 EQ concentrations derived from the vitellogenic response in fathead minnows exposed to a series of effluent dilutions were highly comparable with the E2 EQ concentrations derived from assessments of the estrogenic potency of these dilutions in the rYES. Together these data support the use of bioassays for determining the estrogenic potency of WwTW effluents, and they highlight the associated problems for modeling approaches that are reliant on measured concentrations of estrogenic chemicals.

Dose-Response Relationship, Drug↗

PubMed2006

A perspective on the environmental risk of halogenated by-products from uses of hypochlorite using a whole effluent toxicity based approach.

An assessment has been made of the potential for toxic effects to aquatic life that may arise from halogenated organic by-products formed by reaction of hypochlorite with organic matter in various use scenarios as a contribution to the risk assessment of sodium hypochlorite under the European Union Existing Chemicals legislation. In the study, samples that would represent worst-case models for effluents containing halogenated by-products from a range of uses of hypochlorite were prepared by chlorinating and then dechlorinating (removing residual chlorine) raw settled sewage (C/D-RSS). This sample was then compared to raw settled sewage that had not been treated (RSS) to assess whether halogenated by-products formed in the chlorination process were toxic or bioaccumulable and persistent. The relative toxicity of the samples was assessed using a series of tests with representatives of different taxonomic groups (bacteria, algae, and invertebrates). The persistence and potential for bioaccumulation of chlorinated by-products was assessed by exposing solid-phase microextraction fibers to samples of RSS and C/D-RSS before and after degradation in a Zahn-Wellens test. For all the taxa tested in the study, the mixture of by-products formed in the C/D-RSS sample did not increase toxicity relative to that measured in the RSS sample. Chlorination of the raw settled sewage did produce additional potentially bioaccumulable halogenated substances compared to the raw settled sewage. However, after degradation, the amount of potentially bioaccumulable halogenated substances in the RSS and C/D-RSS samples was comparable, indicating that these substances were degradable. The results are discussed in the context of the overall risk assessment for sodium hypochlorite.

Adsorption↗

PubMed2005

Origin and evolution of the chloroplast trnK (matK) intron: a model for evolution of group II intron RNA structures.

The trnK intron of plants encodes the matK open reading frame (ORF), which has been used extensively as a phylogenetic marker for classification of plants. Here we examined the evolution of the trnK intron itself as a model for group II intron evolution in plants. Representative trnK intron sequences were compiled from species spanning algae to angiosperms, and four introns were newly sequenced. Phylogenetic analyses showed that the matK ORFs belong to the ML (mitochondrial-like) subclass of group II intron ORFs, indicating that they were derived from a mobile group II intron of the class. RNA structures of the introns were folded and analyzed, which revealed progressive RNA structural deviations and degenerations throughout plant evolution. The data support a model in which plant organellar group II introns were derived from bacterial-like introns that had "standard" RNA structures and were competent for self-splicing and mobility and that subsequently the ribozyme structures degenerated to ultimately become dependent upon host-splicing factors. We propose that the patterns of RNA structure evolution seen for the trnK intron will apply to the other group II introns in plants.

Base Sequence↗

PubMed2005

A strong neuroprotective effect of the autonomous C-terminal peptide of IGF-1 Ec (MGF) in brain ischemia.

The ischemic stroke is the third leading cause of death in developed countries. The C-terminal peptide of mechano-growth factor (MGF), an alternatively spliced variant of insulin-like growth factor 1 (IGF-1), was found to function independently from the rest of the molecule and showed a neuroprotective effect in vivo and in vitro. In vivo, in a gerbil model of transient brain ischemia, treatment with the synthetic MGF C-terminal peptide provided very significant protection to the vulnerable neurons. In the same model, ischemia evoked increased expression of endogenous MGF in the ischemia-resistant hippocampal neurons, suggesting that the endogenous MGF might have an important neuroprotective function. In an in vitro organotypic hippocampal culture model of neurodegeneration, the synthetic peptide was as potent as the full-length IGF-1 while its effect lasted significantly longer than that of recombinant IGF-1. While two peptides showed an additive effect, the neuroprotective action of the C-terminal MGF was independent from the IGF-1 receptor, indicating a new mode of action for this molecule. Although MGF is known for its regenerative capability in skeletal muscle, our findings demonstrate for the first time a neuroprotective role against ischemia for this specific IGF-1 isoform. Therefore, the C-terminal MGF peptide has a potential to be developed into a therapeutic modality for the prevention of neuronal damage.

Alternative Splicing↗

PubMed2004

A regulatory framework for controlling effluent discharges using toxicity testing in the UK.

Legislation designed to regulate effluent discharges is expressed in terms of minimising the risk of harm of that discharge to the environment. Practical implementation is usually based on the control and measurement of a limited number of individual chemicals. However, this is not always effective because of the complex nature of some discharges or the lack of data for some chemicals, preventing the definition of acceptable levels in the environment. Direct Toxicity Assessment (DTA) clearly has a role in such circumstances because it avoids the need for a comprehensive chemical characterisation of effluent discharges. Several scenarios in which DTA can play a useful role in water quality management under current legislation have been identified. A 'generic' framework for the implementation of bioassays for effluent control is proposed. This provides a number of options in terms of the level of environmental protection afforded and the 'starting point' for a DTA programme (i.e. whether it is based on local measurable impacts on water quality or directed from the outset towards the risk assessment of particular discharges). A DTA programme can be developed that meets both the technical and regulatory requirements of these different scenarios. Guidance on the design of such programmes for different scenarios is provided.

Animals↗

PubMed2004

Bioassay selection, experimental design and quality control/assurance for use in effluent assessment and control.

In the UK Direct Toxicity Assessment Programme, carried out in 1998-2000, a series of internationally recognised short-term toxicity test methods for algae, invertebrates and fishes, and rapid methods (ECLOX and Microtox) were used extensively. Abbreviated versions of conventional tests (algal growth inhibition tests, Daphnia magna immobilisation test and the oyster embryo-larval development test) were valuable for toxicity screening of effluent discharges and the identification of causes and sources of toxicity. Rapid methods based on chemiluminescence and bioluminescence were not generally useful in this programme, but may have a role where the rapid test has been shown to be an acceptable surrogate for a standardised test method. A range of quality assurance and control measures were identified. Requirements for quality control/assurance are most stringent when deriving data for characterising the toxic hazards of effluents and monitoring compliance against a toxicity reduction target. Lower quality control/assurance requirements can be applied to discharge screening and the identification of causes and sources of toxicity.

Animals↗

PubMed2004

Estimating spatial patterns of effluent exposure concentrations in direct toxicity assessment studies.

Hydrodynamic models of differing scale and complexity were used to estimate spatial patterns of effluent concentration in discharge plumes in the River Esk and the Lower Tees Estuary. The output from the Tees model was used, in conjunction with measurements of toxicity determined in short-term oyster embryo tests, to predict contours/zones of toxicity in the estuary associated with effluent discharges from four chemical processing sites. One of the discharges also combined the input from a municipal sewage treatment works. The models appeared to be effective in predicting patterns of dilution and dispersion of the effluent discharges in the respective receiving environments. Confirmation of the predictive capabilities of the Tees model was achieved by comparing predicted and measured toxicity in different regions of the plumes associated with the four discharges. Differences between predicted and measured toxicity for two of the four discharges were explicable in terms of failure to take account of the effects of real-time wind conditions when test samples were collected or overlap of adjacent discharge plumes. Suggested refinements to the models and measurement of effluent toxicity would further enhance the utility of this approach for determining the extent and significance of the effects of effluent discharges in receiving environments.

Animals↗

PubMed2004

Toxicity reduction evaluation, toxicity identification evaluation and toxicity tracking in direct toxicity assessment.

Toxicity reduction evaluations (TREs) in the River Esk and Lower Tees Estuary were based on the approach described by USEPA, but adapted to tackle the specific problems of the two sites. A combination of toxicity tracking and toxicity identification evaluation (TIE) was used at both locations to enhance the understanding of source and type of toxicants present. The assessment of toxicity at Langholm focussed on pesticides present in the sewerage network. The TIE programme indicated that the most likely toxic agents within the effluent were the organophosphate pesticides diazinon and to lesser extent propetamphos, although these did not account for all of the observed toxicity. The exact source of these toxicants was not clear although toxicity tracking identified two potential candidates. The TRE undertaken on the discharge to the lower Tees utilised high-throughput methods with standard test organisms to generate toxicity information throughout a complex sewerage network. The toxicity tracking information was used in conjunction with TIEs to identify a number of key sources of toxicity. Substantial toxicity was associated with a currently untreated industrial effluent. Chemical analysis and TIE highlighted cyanide as the likely toxicant in this effluent and its possible significance in the final discharge.

Animals↗

PubMed2002

The colon-selective spasmolytic otilonium bromide inhibits muscarinic M(3) receptor-coupled calcium signals in isolated human colonic crypts.

1. Otilonium bromide (OB) is a smooth muscle relaxant used in the treatment of irritable bowel syndrome. Otilonium bromide has been shown to interfere with the mobilization of calcium in intestinal smooth muscle, but the effects on other intestinal tissues have not been investigated. We identified the muscarinic receptor subtype coupled to calcium signals in colonic crypt derived from the human colonic epithelium and evaluated the inhibitory effects of OB. 2. Calcium signals were monitored by fluorescence imaging of isolated human colonic crypts and Chinese hamster ovary cells stably expressing the cloned human muscarinic M(3) receptor subtype (CHO-M(3)). Colonic crypt receptor expression was investigated by pharmacological and immunohistochemical techniques. 3. The secretagogue acetylcholine (ACh) stimulated calcium mobilization from intracellular calcium stores at the base of human colonic crypts with an EC(50) of 14 micro M. The muscarinic receptor antagonists 4-DAMP, AF-DX 384, pirenzepine and methroctamine inhibited the ACh-induced calcium signal with the following respective IC(50) (pK(b)) values: 0.78 nM (9.1), 69 nM (7.2), 128 nM (7.1), and 2510 nM (5.8). 4. Immunohistochemical analyses of muscarinic receptor expression demonstrated the presence of M(3) receptor subtype expression at the crypt-base. 5. Otilonium bromide inhibited the generation of ACh-induced calcium signals in a dose dependent manner (IC(50)=880 nM). 6. In CHO-M(3) cells, OB inhibited calcium signals induced by ACh, but not ATP. In addition, OB did not inhibit histamine-induced colonic crypt calcium signals. 7. The present studies have demonstrated that OB inhibited M(3) receptor-coupled calcium signals in human colonic crypts and CHO-M(3) cells, but not those induced by stimulation of other endogenous receptor types. We propose that the M(3) receptor-coupled calcium signalling pathway is directly targeted by OB at the level of the colonic epithelium, suggestive of an anti-secretory action in IBS patients suffering with diarrhoea.

Acetylcholine↗

PubMed2002

Antibacterial activities and characterization of novel inhibitors of LpxC.

Lipid A is the hydrophobic anchor of lipopolysaccharide (LPS) and forms the major lipid component of the outer monolayer of the outer membrane of gram-negative bacteria. Lipid A is required for bacterial growth and virulence, and inhibition of its biosynthesis is lethal to bacteria. UDP-3-O-(R-3-hydroxymyristoyl)-N-acetylglucosamine deacetylase (LpxC) is a metalloenzyme that catalyzes the second step in the biosynthesis of lipid A. Inhibitors of LpxC have previously been shown to have antibiotic activities. We have screened a metalloenzyme inhibitor library for antibacterial activities against an Escherichia coli strain with reduced LpxC activity. From this screen, a series of sulfonamide derivatives of the alpha-(R)-amino hydroxamic acids, exemplified by BB-78484 and BB-78485, have been identified as having potent inhibitory activities against LpxC in an in vitro assay. Leads from this series showed gram-negative selective activities against members of the Enterobacteriaceae, Serratia marcescens, Morganella morganii, Haemophilus influenzae, Moraxella catarrhalis, and Burkholderia cepacia. BB-78484 was bactericidal against E. coli, achieving 3-log killing in 4 h at a concentration 4 times above the MIC, as would be predicted for an inhibitor of lipid A biosynthesis. E. coli mutants with decreased susceptibility to BB-78484 were selected. Analysis of these mutants revealed that resistance arose as a consequence of mutations in the fabZ or lpxC genes. These data confirm the antibacterial target of BB-78484 and BB-78485 and validate LpxC as a target for gram-negative selective antibacterials.

Amidohydrolases↗

PubMedDate not supplied

Approaches to the assessment of toxicity data with endpoints related to endocrine disruption.

There has been a substantial proliferation in the number of studies reporting endocrine effects as an endpoint. The vast majority have focused on oestrogenicity in vitro but, with recent recommendations by the USEPA Endocrine Disrupter Screening and Testing Advisory Committee, tests are now being developed for (anti)-androgenicity and effects on the thyroid, largely because of the potential for altering reproduction or development via these mechanisms. Despite being a vital organ and involved in reproduction and development, there is currently no provision for assessing adrenocortical function. Similarly, the entire process of steroidogenesis poses multiple molecular targets for toxic disruption that are not included in current test strategies and at present there is no clear position on the significance of the data being generated. This review provides a framework for approaching endocrine data: that all the glands, tissues, receptors, transporter proteins and enzymes that comprise the endocrine system are targets for toxicity. They should be considered in much the same way as other target organs, with appropriate provision for the special cases of carcinogenesis and teratogenesis, and a pragmatic weight of evidence approach should be adopted considering all available data and recognizing its limitations. In this approach, structure-activity relationships and in vitro and targeted in vivo screens provide useful data but repeat-dose regulatory studies with defined endpoints provide the most powerful tools for hazard assessment. Pragmatic consideration should be given to exposure issues (which may highlight the practical irrelevance, for example, of very low potency oestrogens) and subsequently whether endocrine disruption is the critical or most sensitive endpoint for a compound. Finally, endocrine disruption may be considered a mechanism and, as with other toxic endpoints, knowledge of effect and no-observable-effect levels and reversibility is as important as identifying the target tissue or any inherent hormone-like property.

Animals↗

PubMedDate not supplied

Defining needs-based urban health planning areas is feasible and desirable: a population-based approach in Toronto, Ontario.

Reporting health data for large urban areas presents numerous challenges. In the case of Toronto, Ontario, amalgamation in 1998 merged six census subdivisions into one mega-city, resulting in the disappearance of standard reporting units. A population-based approach was used to define new health planning areas. Census tracts were used as building blocks and combined according to residential income homogeneity, respecting natural and man-made boundaries, forward sortation areas and the City of Toronto's community neighbourhoods whenever possible. Correlations and maps were used to establish area boundaries. The city was divided into 5 major planning areas which were further subdivided creating 15 minor areas. Both major and minor areas showed significant differences in population characteristics, health status and health service utilization. This commentary demonstrates the feasibility and describes the outcomes of one method for establishing planning and reporting areas in large urban centres. Next steps include the further generation of health data for these areas, comparisons with other Canadian urban areas, and application of these methods to recently announced Ontario Local Health Integration Networks. These areas can be used for planning and evaluating health service delivery, comparison with other Canadian urban areas and ongoing monitoring of and advocacy for equity in health.

Catchment Area, Health↗