Potency and species specificity of aryl hydrocarbon receptor ligands

The aryl hydrocarbon receptor (AhR) binds a wide range of structurally diverse compounds such as halogenated dibenzo-p-dioxins, dibenzofurans and biphenyls which are abundant in the environment. Activation of AhR leads to the regulation of a battery of xenobiotic enzymes including cytochrome P4501A1 (CYP1A1). The purely chlorinated compounds feature in the World Health Organisation’s (WHO) evaluation of dioxin-like compounds derived from a meta-analysis of previous potency data (toxic equivalency factors; TEFs), which is used to calculate the total toxic equivalence (TEQ). The first aim of this work was to fully characterise the three most environmentally abundant mono-ortho-substituted polychlorinated biphenyls (PCBs; PCB 105, 118 and 156) including a re-evaluation of their putative antagonistic effects on AhR. Secondly, the effects of mixed halogenated compounds, currently not included in the TEQ estimation, were investigated as AhR agonists based on their environmental exposure and potency. Quantitative real-time PCR (qRT-PCR) was used to measure the AhR mediated induction of CYP1A1 mRNA in rat H4IIE and human MCF-7 cells. The three mono-ortho-substituted PCBs were shown to be antagonists of rat and human AhRs, an effect which is not currently included in the TEQ calculation. 2-bromo-3,7,8-trichlorodibenzo-p-dioxin (2-B-3,7,8-TriCDD) was found to be an AhR agonist that was 2-fold more potent than 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; considered one of the most potent in the environment). The majority of the other tested compounds were found to be within 10-fold less potent than TCDD and could therefore have a significant impact on the TEQ. A family of putative AhR agonists from AstraZencea were investigated and one of the compounds was shown to be a highly potent AhR agonist, 5-fold more potent than TCDD at inducing CYP1A1. The results indicate approximately a 15-fold higher sensitivity of the rat cell line to the AhR agonists compared with the human cell line. It is not currently understood what confers these differences whether it is a difference in the mechanism of activation or purely as a result of differences in the AhR sequence. The mechanism of action is thought to be the same in both species and the associated proteins are both comparable. The amino acid sequences of the AhR, in both human and rat are quite similar but may play a significant role in the differences observed between species. Therefore in order to directly compare the rat and human AhRs, two novel cell line models were created using an inducible expression system to infect an AhR-deficient mouse cell line with a replication-defective virus containing either the rat or human AhR. The AhRs were activated with various compounds to induce mouse CYP1A1. The CYP1A1 mRNA was measured using qRT-PCR but showed that the two AhR genes were not expressed enough to produce a response detectable above the background CYP1A1 induction by the low levels of mouse AhR. This research has shown that these dioxin-like compounds can have very different potencies at AhRs in different species so it is not always possible to predict the potency in humans from in vitro or rat in vivo toxicity data. Furthermore, it has identified compounds, such as 5F-203, which are significantly more potent in human compared to rat. This thesis provides information on the AhR species differences between human and rat that can be applied to risk assessment

Potency and species specificity of aryl hydrocarbon receptor ligands

The aryl hydrocarbon receptor (AhR) binds a wide range of structurally diverse compounds such as halogenated dibenzo-p-dioxins, dibenzofurans and biphenyls which are abundant in the environment. Activation of AhR leads to the regulation of a battery of xenobiotic enzymes including cytochrome P4501A1 (CYP1A1). The purely chlorinated compounds feature in the World Health Organisation’s (WHO) evaluation of dioxin-like compounds derived from a meta-analysis of previous potency data (toxic equivalency factors; TEFs), which is used to calculate the total toxic equivalence (TEQ). The first aim of this work was to fully characterise the three most environmentally abundant mono-ortho-substituted polychlorinated biphenyls (PCBs; PCB 105, 118 and 156) including a re-evaluation of their putative antagonistic effects on AhR. Secondly, the effects of mixed halogenated compounds, currently not included in the TEQ estimation, were investigated as AhR agonists based on their environmental exposure and potency. Quantitative real-time PCR (qRT-PCR) was used to measure the AhR mediated induction of CYP1A1 mRNA in rat H4IIE and human MCF-7 cells. The three mono-ortho-substituted PCBs were shown to be antagonists of rat and human AhRs, an effect which is not currently included in the TEQ calculation. 2-bromo-3,7,8-trichlorodibenzo-p-dioxin (2-B-3,7,8-TriCDD) was found to be an AhR agonist that was 2-fold more potent than 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD; considered one of the most potent in the environment). The majority of the other tested compounds were found to be within 10-fold less potent than TCDD and could therefore have a significant impact on the TEQ. A family of putative AhR agonists from AstraZencea were investigated and one of the compounds was shown to be a highly potent AhR agonist, 5-fold more potent than TCDD at inducing CYP1A1. The results indicate approximately a 15-fold higher sensitivity of the rat cell line to the AhR agonists compared with the human cell line. It is not currently understood what confers these differences whether it is a difference in the mechanism of activation or purely as a result of differences in the AhR sequence. The mechanism of action is thought to be the same in both species and the associated proteins are both comparable. The amino acid sequences of the AhR, in both human and rat are quite similar but may play a significant role in the differences observed between species. Therefore in order to directly compare the rat and human AhRs, two novel cell line models were created using an inducible expression system to infect an AhR-deficient mouse cell line with a replication-defective virus containing either the rat or human AhR. The AhRs were activated with various compounds to induce mouse CYP1A1. The CYP1A1 mRNA was measured using qRT-PCR but showed that the two AhR genes were not expressed enough to produce a response detectable above the background CYP1A1 induction by the low levels of mouse AhR. This research has shown that these dioxin-like compounds can have very different potencies at AhRs in different species so it is not always possible to predict the potency in humans from in vitro or rat in vivo toxicity data. Furthermore, it has identified compounds, such as 5F-203, which are significantly more potent in human compared to rat. This thesis provides information on the AhR species differences between human and rat that can be applied to risk assessment

Rib number and shell color in hybridized subspecies of the Atlantic bay scallop, Argopecten irradians

Bay scallops, Argopecten irradians (Lamarck), from populations with low rib number (Texas) and high rib number (Virginia) were bred separately and also hybridized. The results suggest that rib number is under genetic control and that the two populations are genetically differentiated. Scallops taken from a population polymorphic for shell color (Massachusetts) were bred in groups, each group containing a single color. The results suggest that color is also under genetic control and is not strongly influenced by the environmen

Modelling of a power-to-gas system to predict the levelised cost of energy of an advanced renewable gaseous transport fuel

Power to gas (P2G) has been mooted as a means of producing advanced renewable gaseous transport fuel, whilst providing ancillary services to the electricity grid through decentralised small scale (10 MW) energy storage. This study uses a discounted cash flow model to determine the levelised cost of energy (LCOE) of the gaseous fuel from non-biological origin in the form of renewable methane for various cost scenarios in 2020, 2030, and 2040. The composition and sensitivity of these costs are investigated as well as the effects of incentives and supplementary incomes. The LCOE was found to be €107-143/MWh (base value €124) in 2020, €89-121/MWh (base value €105) in 2030, and €81-103/MWh (base value €93) in 2040. The costs were found to be dominated by electricity charges in all scenarios (56%), with the total capital expenditure the next largest contributor (33%). Electricity costs and capacity factor were the most sensitive parameters followed by total capital expenditure, project discount rate, and fixed operation and maintenance. For the 2020 base scenario should electricity be available at zero cost the LCOE would fall from €124/MWh to €55/MWh. Valorisation of the produced oxygen (€0.1/Nm3 profit) would generate an LCOE of €105/MWh. A payment for ancillary services to the electricity grid of €15/MWe for 8500 h p.a would lower the LCOE to €87/MWh. Price parity with diesel, exclusive of sales tax, is achieved with an incentive of €19/MWh

Does wage rank affect employees' well-being?

How do workers make wage comparisons? Both an experimental study and an analysis of 16,000 British employees are reported. Satisfaction and well-being levels are shown to depend on more than simple relative pay. They depend upon the ordinal rank of an individual's wage within a comparison group. “Rank” itself thus seems to matter to human beings. Moreover, consistent with psychological theory, quits in a workplace are correlated with pay distribution skewness

Toolkit of Approaches To Support Target-Focused Drug Discovery for Plasmodium falciparum Lysyl tRNA Synthetase

There is a pressing need for new medicines to prevent and treat malaria. Most antimalarial drug discovery is reliant upon phenotypic screening. However, with the development of improved target validation strategies, target-focused approaches are now being utilized. Here, we describe the development of a toolkit to support the therapeutic exploitation of a promising target, lysyl tRNA synthetase (PfKRS). The toolkit includes resistant mutants to probe resistance mechanisms and on-target engagement for specific chemotypes; a hybrid KRS protein capable of producing crystals suitable for ligand soaking, thus providing high-resolution structural information to guide compound optimization; chemical probes to facilitate pulldown studies aimed at revealing the full range of specifically interacting proteins and thermal proteome profiling (TPP); as well as streamlined isothermal TPP methods to provide unbiased confirmation of on-target engagement within a biologically relevant milieu. This combination of tools and methodologies acts as a template for the development of future target-enabling packages

Microbiome-derived carnitine mimics as previously unknown mediators of gut-brain axis communication

Alterations to the gut microbiome are associated with various neurological diseases, yet evidence of causality and identity of microbiome-derived compounds that mediate gut-brain axis interaction remain elusive. Here, we identify two previously unknown bacterial metabolites 3-methyl-4-(trimethylammonio)butanoate and 4-(trimethylammonio)pentanoate, structural analogs of carnitine that are present in both gut and brain of specific pathogen–free mice but absent in germ-free mice. We demonstrate that these compounds are produced by anaerobic commensal bacteria from the family Lachnospiraceae (Clostridiales) family, colocalize with carnitine in brain white matter, and inhibit carnitine-mediated fatty acid oxidation in a murine cell culture model of central nervous system white matter. This is the first description of direct molecular inter-kingdom exchange between gut prokaryotes and mammalian brain cells, leading to inhibition of brain cell function