Evaluation of the neurotoxicity of pentachlorophenol and its active metabolites on SH-SY5Y neuroblastoma cells

Pentachlorophenol (PCP) is an organochloride pesticide that is ubiquitous within the environment due to its chemical stability. It is classified as a persistent organic pollutant, and has been predominantly used in the wood preservation industry. Workers and populations living close to PCP usage and production are exposed to it via inhalation and dermal absorption, and ingestion of contaminated food and water. It is lipophilic and is able to accumulate within various bodily systems, including the brain. Adverse effects of PCP have been reported to varying degrees in the immune, hepatic, and endocrine systems. Although neurological symptoms have been associated with PCP exposure, knowledge of mechanisms of neurotoxicity is limited. Elucidation of molecular mechanisms at a cellular level within neuronal cells is required to contribute toward the current gap in the knowledge of PCP neurotoxicity. The aim of the study was to evaluate the effects of PCP and its active metabolites, tetrachloro-1,4-benzoquinone (TCBQ) and tetrachlorohydroquinone (TCHQ) in human neuroblastoma SH-SY5Y cells. Effects on cell proliferation were assessed using the sulforhodamine B (SRB) assay. Flow cytometric analysis was employed to investigate effects on cell cycle using propidium iodide (PI), mode of cell death using Annexin V-FITC and PI, reactive oxygen species (ROS) using dichlorofluorescein, and mitochondrial membrane potential (Δᴪm) using JC-1 fluorescence. Caspase-3 activity was assessed with Ac- DEVD-AMC, and glutathione (GSH) with monochlorobimane fluorescence. Effects on acetylcholinesterase (AChE) were assessed in vitro using the Ellman esterase assay, as well as in silico via molecular docking and molecular dynamics simulation. The IC50 concentrations of PCP, TCBQ and TCHQ were 80.0, 35.4, and 63.7 μM, respectively. Cell cycle disruptions were revealed in the form of a G1 block and a G2/M block as a result of PCP and TCHQ exposure, respectively, while TCBQ resulted in a prolonged S phase traverse. The predominant mode of cell death of PCP was necrosis, while TCBQ induced apoptosis. Exposure to TCHQ resulted in one of two fates, being either predominantly apoptotic or necrotic cell death. Decreased Δᴪm was an early event for all compounds, however, differed in their involvement of inducing ROS. Oxidative stress was an evident mechanism of PCP and TCBQ toxicity, as increased ROS was accompanied by lowered GSH, while reductive stress leading to subsequent oxidative stress was indicated by increased ROS and GSH for TCHQ. All compounds yielded increased caspase-3 activity. The fate of TCHQ exposed cells was postulated as a switch from apoptosis to necrosis due to overwhelming ROS insult on apoptotic machinery, surpassing a threshold for apoptosis capability. Inhibition of AChE was observed by only TCHQ in vitro, the Ellman IC50 of which was 79.7 μM. In silico assessment supported a hypothesis of TCHQ inhibition of AChE, with TCHQ-acetate bound ligands binding AChE receptors with binding energies corresponding to the Ellman IC50. Binding stability was confirmed by molecular dynamics. Pentachlorophenol and its active metabolites exhibited different mechanisms of toxicity toward neuronal cells, leading to different modes of cell death. A new hypothesis for the molecular mechanism of TCHQ AChE inhibition was developed, and sets a platform for further investigation.Dissertation (MSc)--University of Pretoria, 2017.PhysiologyMScUnrestricte

Cytotoxic activity of pentachlorophenol and its active metabolites in SH-SY5Y neuroblastoma cells

As knowledge regarding mechanisms of pentachlorophenol (PCP) toxicity in neuronal cell lines is limited, the aim of the study was to evaluate the effects of PCP and its active metabolites, tetrachloro-1,4-benzoquinone (TCBQ) and tetrachlorohydroquinone (TCHQ) in human neuroblastoma SH-SY5Y cells. All compounds induced cytotoxic effects in time- and dose-dependent manners, and resulted in differential modes of cell death. Reduced mitochondrial membrane potential (ΔᴪM) and oxidative damage lead to apoptosis and necrosis following TCBQ and PCP exposure, respectively. Time-dependent investigations revealed transient ΔᴪM recovery in TCHQ exposed cells, and redox stress. Sufficient ΔᴪM recovery allowed apoptosis completion in TCHQ exposed cells, whereas overwhelming metabolic and oxidative stress saw a conversion from apoptotic to necrotic-like cell death. The onset of mitochondrial dysfunction preceded that of redox damage for all compounds, indicating that oxidative damage is secondary to ΔᴪM insult. Cytotoxic events were further linked to cell cycle. S phase and G2/M blocks were observed after 12 h exposure to TCBQ and TCHQ, respectively, while a G1 block occurred after 24 h exposure to PCP. This study provides new insight regarding time-dependant toxic effects of PCP and its metabolites in human neuronal cells.The National Research Foundation, South Africa and Research Committee of the School of Medicine, Faculty of Health Sciences, University of Pretoria.http://www.elsevier.com/locate/tiv2020-08-01hj2020PharmacologyPhysiolog

Oral abstracts 1: SpondyloarthropathiesO1. Detecting axial spondyloarthritis amongst primary care back pain referrals

Background: Inflammatory back pain (IBP) is an early feature of ankylosing spondylitis (AS) and its detection offers the prospect of early diagnosis of AS. However, since back pain is very common but only a very small minority of back pain sufferers have ASpA or AS, screening of back pain sufferers for AS is problematic. In early disease radiographs are often normal so that fulfilment of diagnostic criteria for AS is impossible though a diagnosis of axial SpA can be made if MRI evidence of sacroiliitis is present. This pilot study was designed to indicate whether a cost-effective pick up rate for ASpA/early AS could be achieved by identifying adults with IBP stratified on the basis of age. Methods: Patients aged between 18 and 45 years who were referred to a hospital physiotherapy service with back pain of more than 3 months duration were assessed for IBP. All were asked to complete a questionnaire based on the Berlin IBP criteria. Those who fulfilled IBP criteria were also asked to complete a second short questionnaire enquiring about SpA comorbidities, to have a blood test for HLA-B27 and CRP level and to undergo an MRI scan of the sacroiliac joints. This was a limited scan, using STIR, diffusion-weighted, T1 and T2 sequences of the sacroiliac joints to minimize time in the scanner and cost. The study was funded by a research grant from Abbott Laboratories Ltd. Results: 50 sequential patients agreed to participate in the study and completed the IBP questionnaire. Of these 27 (54%) fulfilled criteria for IBP. Of these, 2 patients reported a history of an SpA comorbidity - 1 psoriasis; 1 ulcerative colitis - and 3 reported a family history of an SpA comorbidity - 2 psoriasis; 1 Crohn's disease. 4 were HLA-B27 positive, though results were not available for 7. Two patients had marginally raised CRP levels (6, 10 -NR ≤ 5). 19 agreed to undergo MRI scanning of the sacroiliac joints and lumbar spine; 4 scans were abnormal, showing evidence of bilateral sacroiliitis on STIR sequences. In all cases the changes met ASAS criteria but were limited. Of these 4 patients 3 were HLA-B27 positive but none gave a personal or family history of an SpA-associated comorbidity and all had normal CRP levels. Conclusions: This was a pilot study yielding only limited conclusions. However, it is clear that: Screening of patients referred for physiotherapy for IBP is straightforward, inexpensive and quick. It appears that IBP is more prevalent in young adults than overall population data suggest so that targeting this population may be efficient. IBP questionnaires could be administered routinely during a physiotherapy assessment. HLA-B27 testing in this group of patients with IBP is a suitable screening tool. The sacroiliac joint changes identified were mild and their prognostic significance is not yet clear so that the value of early screening needs further evaluation. Disclosure statement: C.H. received research funding for this study from Abbott. A.K. received research funding for this study, and speaker and consultancy fees, from Abbott. All other authors have declared no conflicts of interes

AI is a viable alternative to high throughput screening: a 318-target study

: High throughput screening (HTS) is routinely used to identify bioactive small molecules. This requires physical compounds, which limits coverage of accessible chemical space. Computational approaches combined with vast on-demand chemical libraries can access far greater chemical space, provided that the predictive accuracy is sufficient to identify useful molecules. Through the largest and most diverse virtual HTS campaign reported to date, comprising 318 individual projects, we demonstrate that our AtomNet® convolutional neural network successfully finds novel hits across every major therapeutic area and protein class. We address historical limitations of computational screening by demonstrating success for target proteins without known binders, high-quality X-ray crystal structures, or manual cherry-picking of compounds. We show that the molecules selected by the AtomNet® model are novel drug-like scaffolds rather than minor modifications to known bioactive compounds. Our empirical results suggest that computational methods can substantially replace HTS as the first step of small-molecule drug discovery

Health-status outcomes with invasive or conservative care in coronary disease

BACKGROUND In the ISCHEMIA trial, an invasive strategy with angiographic assessment and revascularization did not reduce clinical events among patients with stable ischemic heart disease and moderate or severe ischemia. A secondary objective of the trial was to assess angina-related health status among these patients. METHODS We assessed angina-related symptoms, function, and quality of life with the Seattle Angina Questionnaire (SAQ) at randomization, at months 1.5, 3, and 6, and every 6 months thereafter in participants who had been randomly assigned to an invasive treatment strategy (2295 participants) or a conservative strategy (2322). Mixed-effects cumulative probability models within a Bayesian framework were used to estimate differences between the treatment groups. The primary outcome of this health-status analysis was the SAQ summary score (scores range from 0 to 100, with higher scores indicating better health status). All analyses were performed in the overall population and according to baseline angina frequency. RESULTS At baseline, 35% of patients reported having no angina in the previous month. SAQ summary scores increased in both treatment groups, with increases at 3, 12, and 36 months that were 4.1 points (95% credible interval, 3.2 to 5.0), 4.2 points (95% credible interval, 3.3 to 5.1), and 2.9 points (95% credible interval, 2.2 to 3.7) higher with the invasive strategy than with the conservative strategy. Differences were larger among participants who had more frequent angina at baseline (8.5 vs. 0.1 points at 3 months and 5.3 vs. 1.2 points at 36 months among participants with daily or weekly angina as compared with no angina). CONCLUSIONS In the overall trial population with moderate or severe ischemia, which included 35% of participants without angina at baseline, patients randomly assigned to the invasive strategy had greater improvement in angina-related health status than those assigned to the conservative strategy. The modest mean differences favoring the invasive strategy in the overall group reflected minimal differences among asymptomatic patients and larger differences among patients who had had angina at baseline

Initial invasive or conservative strategy for stable coronary disease

BACKGROUND Among patients with stable coronary disease and moderate or severe ischemia, whether clinical outcomes are better in those who receive an invasive intervention plus medical therapy than in those who receive medical therapy alone is uncertain. METHODS We randomly assigned 5179 patients with moderate or severe ischemia to an initial invasive strategy (angiography and revascularization when feasible) and medical therapy or to an initial conservative strategy of medical therapy alone and angiography if medical therapy failed. The primary outcome was a composite of death from cardiovascular causes, myocardial infarction, or hospitalization for unstable angina, heart failure, or resuscitated cardiac arrest. A key secondary outcome was death from cardiovascular causes or myocardial infarction. RESULTS Over a median of 3.2 years, 318 primary outcome events occurred in the invasive-strategy group and 352 occurred in the conservative-strategy group. At 6 months, the cumulative event rate was 5.3% in the invasive-strategy group and 3.4% in the conservative-strategy group (difference, 1.9 percentage points; 95% confidence interval [CI], 0.8 to 3.0); at 5 years, the cumulative event rate was 16.4% and 18.2%, respectively (difference, 121.8 percentage points; 95% CI, 124.7 to 1.0). Results were similar with respect to the key secondary outcome. The incidence of the primary outcome was sensitive to the definition of myocardial infarction; a secondary analysis yielded more procedural myocardial infarctions of uncertain clinical importance. There were 145 deaths in the invasive-strategy group and 144 deaths in the conservative-strategy group (hazard ratio, 1.05; 95% CI, 0.83 to 1.32). CONCLUSIONS Among patients with stable coronary disease and moderate or severe ischemia, we did not find evidence that an initial invasive strategy, as compared with an initial conservative strategy, reduced the risk of ischemic cardiovascular events or death from any cause over a median of 3.2 years. The trial findings were sensitive to the definition of myocardial infarction that was used