Thyroid homeostasis in B6C3F1 mice upon sub-chronic exposure to trifluoroiodomethane (CF3I).

Trifluoroiodomethane (CF3I) is a fire suppressant gas with potential for use in low global-warming refrigerant blends. Data from studies in rats suggest that the most sensitive health effect of CF3I is thyroid hormone perturbation, but the rat is a particularly sensitive species for disruption of thyroid homeostasis. Mice appear to be less sensitive than rats but still a conservative model with respect to humans. The purpose of this study was to test tolerance and thyroid response to CF3I in B6C3F1 male mice. Male mice were exposed to CF3I for 6 h per day, for 28 days, via whole body exposure at concentrations of 2500, 5000 and 10,000 ppm. A 16-day recovery period was included to evaluate reversibility. No adverse clinical signs were observed throughout the study, and body weights were unaffected by exposure. CF3I exposure had no effect on thyroid histology. An increase in relative thyroid weight was observed at 10,000 ppm on day 28 but not in a separate group of animals evaluated on day 29, and thyroid weight was not different from controls at 44 days. Slight and sporadic changes in serum triiodothyronine, thyroxine, and thyroid-stimulating hormone were observed but did not follow a consistent pattern with respect to timing, dose, or direction. Overall, exposure at up to 10,000 ppm (1.0%) of CF3I gas for 28 days produced no overt general toxicity and only transient, recoverable effects on thyroid weight and hormones at certain concentrations. On the basis of the effect of CF3I exposure on the thyroid, including evaluation of thyroid histopathology, the no observed adverse effect level for this study is 10,000 ppm. Considering the apparently greater toxicity reported in prior studies in male rats, our data suggest a species difference between rats and mice in terms of susceptibility to CF3I-induced thyroid hormone perturbation.

Discovery of piperazic acid peptide deformylase inhibitors with in vivo activity for respiratory tract and skin infections.

The discovery of a novel series of peptide deformylase inhibitors incorporating a piperazic acid amino acid found in nature is described. These compounds demonstrated potent in vitro enzymatic potency and antimicrobial activity. Crystal structure analysis revealed the piperazic acid optimized a key contact with the PDF protein that accounted for the increased enzymatic potency of these compounds. We describe lead optimization of the P3' region of the series that resulted in a compound with good potency against three target organisms. One molecule showed in vivo efficacy in a rat respiratory infection model but ultimately did not meet candidate progression criteria.

Pharmacokinetics/Pharmacodynamics of Peptide Deformylase Inhibitor GSK1322322 against Streptococcus pneumoniae, Haemophilus influenzae, and Staphylococcus aureus in Rodent Models of Infection.

GSK1322322 is a novel inhibitor of peptide deformylase (PDF) with good in vitro activity against bacteria associated with community-acquired pneumonia and skin infections. We have characterized the in vivo pharmacodynamics (PD) of GSK1322322 in immunocompetent animal models of infection with Streptococcus pneumoniae and Haemophilus influenzae (mouse lung model) and with Staphylococcus aureus (rat abscess model) and determined the pharmacokinetic (PK)/PD index that best correlates with efficacy and its magnitude. Oral PK studies with both models showed slightly higher-than-dose-proportional exposure, with 3-fold increases in area under the concentration-time curve (AUC) with doubling doses. GSK1322322 exhibited dose-dependent in vivo efficacy against multiple isolates of S. pneumoniae, H. influenzae, and S. aureus. Dose fractionation studies with two S. pneumoniae and S. aureus isolates showed that therapeutic outcome correlated best with the free AUC/MIC (fAUC/MIC) index in S. pneumoniae (R(2), 0.83), whereas fAUC/MIC and free maximum drug concentration (fCmax)/MIC were the best efficacy predictors for S. aureus (R(2), 0.9 and 0.91, respectively). Median daily fAUC/MIC values required for stasis and for a 1-log10 reduction in bacterial burden were 8.1 and 14.4 for 11 S. pneumoniae isolates (R(2), 0.62) and 7.2 and 13.0 for five H. influenzae isolates (R(2), 0.93). The data showed that for eight S. aureus isolates, fAUC correlated better with efficacy than fAUC/MIC (R(2), 0.91 and 0.76, respectively), as efficacious AUCs were similar for all isolates, independent of their GSK1322322 MIC (range, 0.5 to 4 µg/ml). Median fAUCs of 2.1 and 6.3 µg · h/ml were associated with stasis and 1-log10 reductions, respectively, for S. aureus.

Potent sub-MIC effect of GSK1322322 and other peptide deformylase inhibitors on in vitro growth of Staphylococcus aureus.

Peptide deformylase (PDF), a clinically unexploited antibacterial target, plays an essential role in protein maturation. PDF inhibitors, therefore, represent a new antibiotic class with a unique mode of action that provides an alternative therapy for the treatment of infections caused by drug-resistant pathogens, including methicillin-resistant Staphylococcus aureus (MRSA). GSK1322322 is a novel PDF inhibitor that is in phase II clinical development for the treatment of lower respiratory tract and skin infections. We have discovered that PDF inhibitors can prevent S. aureus in vitro growth for up to 6 h at concentrations 8- to 32-fold below their MICs. This phenomenon seems specific to PDF inhibitors, as none of the antimicrobial agents with alternative mechanisms of action tested show such a potent and widespread effect. It also appears limited to S. aureus, as PDF inhibitors do not show such an inhibition of growth at sub-MIC levels in Streptococcus pneumoniae or Haemophilus influenzae. Analysis of the effect of GSK1322322 on the early growth of 100 randomly selected S. aureus strains showed that concentrations equal to or below 1/8× MIC inhibited growth of 91% of the strains tested for 6 h, while the corresponding amount of moxifloxacin or linezolid only affected the growth of 1% and 6% of strains, respectively. Furthermore, the sub-MIC effect demonstrated by GSK1322322 appears more substantial on those strains at the higher end of the MIC spectrum. These effects may impact the clinical efficacy of GSK1322322 in serious infections caused by multidrug-resistant S. aureus.

Staphylococcus aureus formyl-methionyl transferase mutants demonstrate reduced virulence factor production and pathogenicity.

Inhibitors of peptide deformylase (PDF) represent a new class of antibacterial agents with a novel mechanism of action. Mutations that inactivate formyl methionyl transferase (FMT), the enzyme that formylates initiator methionyl-tRNA, lead to an alternative initiation of protein synthesis that does not require deformylation and are the predominant cause of resistance to PDF inhibitors in Staphylococcus aureus. Here, we report that loss-of-function mutations in FMT impart pleiotropic effects that include a reduced growth rate, a nonhemolytic phenotype, and a drastic reduction in production of multiple extracellular proteins, including key virulence factors, such as α-hemolysin and Panton-Valentine leukocidin (PVL), that have been associated with S. aureus pathogenicity. Consequently, S. aureus FMT mutants are greatly attenuated in neutropenic and nonneutropenic murine pyelonephritis infection models and show very high survival rates compared with wild-type S. aureus. These newly discovered effects on extracellular virulence factor production demonstrate that FMT-null mutants have a more severe fitness cost than previously anticipated, leading to a substantial loss of pathogenicity and a restricted ability to produce an invasive infection.

Emissions and risks associated with oxyfuel combustion: state of the science and critical data gaps.

UNLABELLED: Oxyfuel combustion is a promising technology that may greatly facilitate carbon capture and sequestration by increasing the relative CO2 content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants (e.g., acid gases, particulates, metals and organics) is not well studied. It is possible that combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry (e.g., by changing the valence state of metals). The data available for addressing these concerns are quite limited and are typically derived from laboratory-scale or pilot-scale tests. A review of the available data does suggest that oxyfuel combustion may decrease the air emissions of some pollutants (e.g., SO2, NO(x), particulates) whereas data for other pollutants are too limited to draw any conclusions. The oxy-combustion systems that have been proposed to date do not have a conventional "stack" and combustion flue gas is treated in such a way that solid or liquid waste streams are the major outputs. Use of this technology will therefore shift emissions from air to solid or liquid waste streams, but the risk management implications of this potential change have yet to be assessed. Truly useful studies of the potential effects of oxyfuel combustion on power plant emissions will require construction of integrated systems containing a combustion system coupled to a CO2 processing unit. Sampling and analysis to assess potential emission effects should be an essential part of integrated system tests. IMPLICATIONS: Oxyfuel combustion may facilitate carbon capture and sequestration by increasing the relative CO2 content of the combustion emission stream. However, the potential effect of enhanced oxygen combustion conditions on emissions of criteria and hazardous air pollutants has not been well studied. Combustion under oxyfuel conditions could produce emissions posing different risks than those currently being managed by the power industry. Therefore, before moving further with oxyfuel combustion as a new technology, it is appropriate to summarize the current understanding of potential emissions risk and to identify data gaps as priorities for future research.

Acylprolinamides: a new class of peptide deformylase inhibitors with in vivo antibacterial activity.

A new class of PDF inhibitor with potent, broad spectrum antibacterial activity is described. Optimization of blood stability and potency provided compounds with improved pharmacokinetics that were suitable for in vivo experiments. Compound 5c, which has robust antibacterial activity, demonstrated efficacy in two respiratory tract infection models.

Valve-in-valve transcatheter aortic valve replacement to treat multijet paravalvular regurgitation: A case series and review.

Treatment advances for severe symptomatic aortic stenosis including transcatheter and open surgical valve replacement have improved patient survival, length of stay, and speed to recovery. However, paravalvular regurgitation (PVR) is occasionally seen and when moderate or greater in severity is associated with an at least 2-fold increase in 1 year mortality. While several treatment approaches focused on single-jet PVR have been described in the literature, few reports describe multijet PVR. Multijet PVR can successfully be treated with a variety of catheter-based options including valve-in-valve (ViV) transcatheter aortic valve replacement (TAVR). We present two patients with at least moderate PVR following aortic valve replacement who were successfully treated with ViV TAVR along with a review of literature highlighting our rationale for utilizing each management approach. Multijet PVR can be treated successfully with ViV TAVR, but additional options such as self-expanding occluder devices and bioprosthetic valve fracture have a role as adjunctive treatments to achieve optimal results. The etiology of multijet PVR can differ between patients, this heterogeneity underscores the paucity of data to guide treatment strategies. Therefore, successful treatment of multijet PVR requires familiarity with available therapeutic options to achieve optimal results and, by extension, decrease patient mortality.

Evaluating the Application of Decision Analysis Methods in Simulated Alternatives Assessment Case Studies: Potential Benefits and Challenges of Using MCDA.

We compare how several forms of multicriteria decision analysis (MCDA) can enhance the practice of alternatives assessment (AA). We report on a workshop in which 12 practitioners from US corporations, government agencies, NGOs, and consulting organizations applied different MCDA techniques to 3 AA case studies to understand how they improved the decision process. Participants were asked to select a preferred alternative in each case using a different decision analysis approach: their unaided decision-making method, individual or lightly facilitated group multiattribute value theory (MAVT), and more extensively facilitated group structured decision making (SDM). Surveys conducted after each exercise revealed that participants were positive toward the use of formal decision-making methods for AA, reporting meaningful increases in their understanding of the trade-offs involved and their own values. Participants also reported challenges with each approach. While the MCDA techniques were reported to enhance transparency and communication, they did not consistently lead to higher satisfaction with a decision and/or outcome, and they were not more likely to be adopted within their organizations than unaided approaches. More formal decision-making methods have promise in the context of AA, but practitioners will need more guidance to use such tools successfully. Practitioners will also need to define what "success" constitutes; different approaches may be called for depending on whether the objective is increased understanding, satisfaction with the outcome, satisfaction with the process, or something else. Integr Environ Assess Manag 2021;17:27-41. © 2020 SETAC.

Pulmonary hypertension in patients with interstitial pneumonia with autoimmune features.

Pulmonary hypertension in interstitial lung diseases is associated with increased mortality and hospitalizations and reduced exercise capacity. Interstitial pneumonia with autoimmune features (IPAF) is a recently described interstitial lung disease. The characteristics of pulmonary hypertension in IPAF patients are unknown. We sought to characterize patients with IPAF based on their echocardiographic probability of pulmonary hypertension and compare patients with and without pulmonary hypertension identified by right heart catheterization. We conducted a retrospective study of patients seen in the interstitial lung disease clinic from 2015 to 2018. Forty-seven patients with IPAF were identified. Patients were classified into low, intermediate and high echocardiographic pulmonary hypertension probabilities. A sub-group analysis of patients with pulmonary hypertension and without pulmonary hypertension (IPAF-PH vs. IPAF-no PH) identified by right heart catheterization was also performed. Linear regression analysis was performed to study the association between 6-min-walk-distance (6MWD) and pulmonary vascular resistance (PVR) while adjusting for age and body mass index. Right ventricular hypertrophy (>5 mm), right ventricular enlargement (>41 mm) and right ventricular systolic dysfunction defined as fractional area change% ≤35 was present in 76%, 24%, and 39% of patients, respectively. Pulmonary hypertension was identified in 12.7% of patients. IPAF-PH patients had higher mean pulmonary artery pressure and lower cardiac output compared to the IPAF-no PH group (34 mmHg vs. 19 mmHg, p = 0.002 and 4.0 vs. 5.7 L/min, p = 0.023, respectively). Lower 6MWD was associated with higher PVR on regression analysis (p = 0.002). Pulmonologists should be aware that a significant number of IPAF patients may develop pulmonary hypertension. Reduced 6MWD may suggest the presence of pulmonary hypertension in IPAF patients.

A Robust Pneumonia Model in Immunocompetent Rodents to Evaluate Antibacterial Efficacy against S. pneumoniae, H. influenzae, K. pneumoniae, P. aeruginosa or A. baumannii.

Efficacy of candidate antibacterial treatments must be demonstrated in animal models of infection as part of the discovery and development process, preferably in models which mimic the intended clinical indication. A method for inducing robust lung infections in immunocompetent rats and mice is described which allows for the assessment of treatments in a model of serious pneumonia caused by S. pneumoniae, H. influenzae, P. aeruginosa, K. pneumoniae or A. baumannii. Animals are anesthetized, and an agar-based inoculum is deposited deep into the lung via nonsurgical intratracheal intubation. The resulting infection is consistent, reproducible, and stable for at least 48 h and up to 96 h for most isolates. Studies with marketed antibacterials have demonstrated good correlation between in vivo efficacy and in vitro susceptibility, and concordance between pharmacokinetic/pharmacodynamic targets determined in this model and clinically accepted targets has been observed. Although there is an initial time investment when learning the technique, it can be performed quickly and efficiently once proficiency is achieved. Benefits of the model include elimination of the neutropenic requirement, increased robustness and reproducibility, ability to study more pathogens and isolates, improved flexibility in study design and establishment of a challenging infection in an immunocompetent host.

Questions regarding environmental mercury release, special education rates, and autism disorder: an ecological study of Texas by Palmer et al.

Palmer et al. present an analysis in which they look for an association between Toxic Release Inventory (TRI) reporting data for mercury and rates of autism and special education enrollment in Texas. In their analysis, the link between TRI release data and actual mercury exposure is not clear at all, and thus the conclusions drawn from the analysis are questionable.

Derivation of the critical effect size/benchmark response for the dose-response analysis of the uptake of radioactive iodine in the human thyroid.

Potential adverse effects of chemical substances on thyroid function are usually examined by measuring serum levels of thyroid-related hormones. Instead, recent risk assessments for thyroid-active chemicals have focussed on iodine uptake inhibition, an upstream event that by itself is not necessarily adverse. Establishing the extent of uptake inhibition that can be considered de minimis, the chosen benchmark response (BMR), is therefore critical. The BMR values selected by two international advisory bodies were 5% and 50%, a difference that had correspondingly large impacts on the estimated risks and health-based guidance values that were established. Potential treatment-related inhibition of thyroidal iodine uptake is usually determined by comparing thyroidal uptake of radioactive iodine (RAIU) during treatment with a single pre-treatment RAIU value. In the present study it is demonstrated that the physiological intra-individual variation in iodine uptake is much larger than 5%. Consequently, in-treatment RAIU values, expressed as a percentage of the pre-treatment value, have an inherent variation, that needs to be considered when conducting dose-response analyses. Based on statistical and biological considerations, a BMR of 20% is proposed for benchmark dose analysis of human thyroidal iodine uptake data, to take the inherent variation in relative RAIU data into account. Implications for the tolerated daily intakes for perchlorate and chlorate, recently established by the European Food Safety Authority (EFSA), are discussed.

Modeling developmental processes in animals: applications in neurodevelopmental toxicology.

Biologically based dose-response models can provide a framework for incorporating mechanistic information into our assessments of neurotoxicity considering both kinetic and dynamic processes. We have constructed models for normal midbrain and neocortex development and we have extended these models to evaluate the neurodevelopmental toxicity of ethanol and methyl mercury. Using such modeling approaches, we have been able to test hypothesized modes of action for these neurodevelopmental toxicants. Specifically, we have compared ethanol's effects on neocortical neurogenesis and exacerbation of apoptosis during the synaptogenesis period. We have used methylmercury as an example of how one can link toxicokinetic and toxicodynamic models and also as an example of how mechanistic data on gene expression can support model development. In summary, using examples from our research group, this paper illustrates the need for models that evaluate both qualitative and quantitative kinetic and dynamic factors in order to understand the potential impacts of neurodevelopmental toxicants.

Iodine supplementation and drinking-water perchlorate mitigation.

Ensuring adequate iodine intake is important, particularly among women of reproductive age, because iodine is necessary for early life development. Biologically based dose-response modeling of the relationships among iodide status, perchlorate dose, and thyroid hormone production in pregnant women has indicated that iodide intake has a profound effect on the likelihood that exposure to goitrogens will produce hypothyroxinemia. We evaluated the possibility of increasing iodine intake to offset potential risks from perchlorate exposure. We also explored the effect of dietary exposures to nitrate and thiocyanate on iodine uptake and thyroid hormone production. Our modeling indicates that the level of thyroid hormone perturbation associated with perchlorate exposures in the range of current regulatory limits is extremely small and would be overwhelmed by other goitrogen exposures. Our analysis also shows that microgram levels of iodine supplementation would be sufficient to prevent the goitrogenic effects of perchlorate exposure at current regulatory limits among at risk individuals. The human health risks from supplementing drinking water with iodine are negligible; therefore, this approach is worthy of regulatory consideration.

Investigations of methylmercury-induced alterations in neurogenesis.

Methylmercury (MeHg) has been an environmental concern to public health and regulatory agencies for over 50 years because of its toxicity to the human nervous system. Its association with nervous system toxicity in adults and infants near Minamata Bay, Japan, in the 1950s initiated environmental health research inquiries that continue to this day. Observations of greater neurotoxicity with gestational compared with adult exposure suggest a unique susceptibility of the developing nervous system to MeHg. Despite extensive research conducted over the last half century, determination of definitive molecular mechanisms underlying the observed neurotoxic effects of MeHg have not been identified. This paper summarizes results of a series of experiments conducted to examine the effects of MeHg on neuroepithelial cell proliferation, a hypothesized mode of action for its selective effects on neurogenesis. Observed effects of MeHg on cell cycle entry and progression were associated with alterations in a variety of cell cycle regulatory molecules, including p21 signaling pathways. We place these studies in the context of other cellular responses involved in signal transduction, including oxidative stress, altered protein phosphorylation, and altered intracellular calcium homeostasis. Although existing information suggests that no single mechanism underlies the diverse array of effects associated with MeHg-induced developmental neurotoxicity, we demonstrate characteristic effects of MeHg on cell signaling that contribute to observed effects on cell proliferation. Experimentally derived cell cycle kinetic and cytotoxicity data allowed development of a biologically based dose-response model of MeHg-induced alterations in neurodevelopment, which can form the basis for information synthesis and hypothesis testing and for use in assessing risks from environmental exposures.

Changes in cell cycle parameters and cell number in the rat midbrain during organogenesis.

We employed 5-bromo-2'-deoxyuridine (BrdU) labeling to identify in vivo changes in the cell cycle patterns of the rat midbrain during the major period of midbrain organogenesis, gestational days (gd) 11 to 16. We also used quantitative stereology to determine changes in absolute cell numbers during these gestational time points. Between gd 12 and 16, the length of S-phase did not change significantly while the fraction of cycling cells decreased from 73 to 11%. The average cell cycle length was determined to be 15 h on gd 12 and 17 h on gd 16, the difference not being statistically significant. The cell number in the midbrain increased from 1.3E5 cells on gd 11 to 1.7E7 cells on gd 16. On gd 12 and gd 13, there was a significant negative correlation between litter position and midbrain cell number, the effect diminishing on later days of gestation. The combined use of quantitative stereology and flow cytometry to study brain development represents a novel application that allows for simultaneous evaluation of changes in cell proliferation kinetics and the resulting effect of those kinetic changes on embryonic midbrain development.

Administrative censoring in ecological analyses of autism and a Bayesian solution.

Widely cited ecological analyses of autism have reported associations with mercury emissions, with precipitation, and race at the level of counties or school districts. However, state educational agencies often suppress any low numerical autism counts before releasing data--a phenomenon known as "administrative censoring." Previous analyses did not describe appropriate methods for censored data analysis; common substitution or exclusion methods are known to introduce bias and produce artificially narrow confidence intervals. We apply a Bayesian censored random effects Poisson model to reanalyze associations between 2001 Toxic Release Inventory reported mercury emissions and 2000-2001 autism counts in Texas. Relative risk estimates for autism decreased from 4.44 (95% CI: 4.16, 4.74) per thousand lbs. of air mercury emissions using a naive zero-substitution approach to 1.42 (95% CI: 1.09, 1.78) using the Bayesian approach. Inadequate attention to censoring poses a serious threat to the validity of ecological analyses of autism and other health outcomes.