Search results

In the evaluation of chemical compounds for carcinogenic risk, regulatory agencies such as the U.S. Environmental Protection Agency and National Toxicology Program (NTP) have traditionally fit a dose‐response model to data from rodent bioassays, and then used the fitted model to estimate a Virtually Safe Dose or the dose corresponding to a very small increase (usually 10−6) in risk over background. Much recent interest has been directed at incorporating additional scientific information regarding the properties of the specific chemical under investigation into the risk assessment process, including biological mechanisms of cancer induction, metabolic pathways, and chemical structure and activity. Despite the fact that regulatory agencies are currently poised to allow use of nonlinear dose‐response models based on the concept of an underlying threshold for nongenotoxic chemicals, there have been few attempts to investigate the overall relationship between the shape of dose‐response curves and mutagenicity. Using data from an historical database of NTP cancer bioassays, the authors conducted a repeated‐measures analysis of the estimated shape from fitting extended Weibull dose‐response curves. It was concluded that genotoxic chemicals have dose‐response curves that are closer to linear than those for nongenotoxic chemicals, though on average, both types of compounds have dose‐response curves that are convex and the effect of genotoxicity is small.

In the assessment of developmental and reproductive effects, the timing and duration of exposures to chemical compounds or other environmental contaminants are of particular interest, as the gestational cycle is known to have periods of increased sensitivity. The goal of this research is to identify optimal experimental designs for conducting developmental toxicity studies when the effects of both exposure level and duration of exposure are of interest. The elements of the study design considered in this evaluation are the allocation of animals to dose‐duration exposure groups and the determination of the most efficient intermediate exposure levels. The optimality of various designs is assessed via the accuracy of the estimated excess risk as well as testing criteria. Simulation studies are conducted to compare these criteria and determine optimal design strategies under various underlying dose‐response patterns. Asymptotic results are also derived to lend support to the simulation studies.

Standard experimental designs for conducting developmental toxicity studies typically include three‐ or four‐dose levels in addition to a control group. Some researchers have suggested that designs with more exposure groups would improve dose‐response characterization and risk estimation. Such proposals have not, however, been supported by the results of simulation studies, which instead back the use of fewer dose levels. This discrepancy is partly due to using a known dose–response pattern to generate data, making model choice obvious. While the carcinogenicity literature has explored implications of different study designs, little attention has been given to the role of design in developmental toxicity risk assessment (or noncancer toxicology in general). In this research, we explore the implications of various experimental designs for developmental toxicity by resampling data from a large study of 2,4,5‐trichlorophenoxyacetic acid in mice. We compare the properties of benchmark dose (BMD) estimation for different design strategies by randomly selecting animals within particular dose groups from the entire 2,4,5‐T database of over 77,000 birth outcomes to create smaller "pseudo‐studies" that are representative of standard bioassay sample sizes. Our results show that experimental designs which include more dose levels have advantages in terms of risk characterization and estimation.

Abstract
Organochlorine chemicals and lead are environmental exposures that have endocrine disrupting properties (EDCs) which interfere with many aspects of hormone action. Childhood and adolescence are windows of susceptibility for adverse health effects of EDCs. Our ongoing study, the Russian Children's Study (RCS), is one of the few longitudinal studies investigating the impact of EDCs on growth and puberty in boys. It is conducted in the historically contaminated city of Chapaevsk, in the Samara region. The study focuses on evaluating the associations of persistent organochlorine chemicals and lead with growth and pubertal timing. At enrollment in 2003–2005, we collected blood from 516 boys at ages 8–9 years to measure dioxins, furans, polychlorinated biphenyls (PCBs), chlorinated pesticides and lead. At enrollment and at annual visits through the ages of 18–19 years, a physician performed physical examinations that included pubertal staging and testicular volume measurements. We review the history of Chapaevsk as a research site and summarize published RCS data on the association of peripubertal serum concentrations of organochlorines and blood lead levels with growth, pubertal onset and sexual maturity. Overall, we found that persistent organochlorines and lead negatively affected growth during puberty. Our results also suggest that total toxic equivalents (TEQs), dioxin-like compounds, organochlorine pesticides and lead may delay, while nondioxin-like-PCBs may advance, the timing of male puberty. These findings promoted remediation programs in Chapaevsk, with improvement in health indicators, resulting in Chapaevsk being designated a member of the World Health Organization (WHO) network "Healthy Cities" in 2015.

AbstractIntroductionAntiretrovirals such as dolutegravir (DTG) and tenofovir alafenamide (TAF) have been associated with excessive weight gain. The objective of this study was to understand the potential impact of ART‐associated weight gain on pregnancy outcomes among women living with HIV.MethodsUsing data from the Tsepamo birth outcomes surveillance study in Botswana, we evaluated the relationship between maternal weight (and weight gain) and severe birth outcomes (very preterm delivery <32 weeks, very small for gestational age (SGA) <3rd percentile, perinatal death), macrosomia (birthweight > 4000 g) and maternal hypertension. We estimated the relative risk of each outcome by baseline weight (first weight in pregnancy <24 weeks) and second trimester average weekly weight gain (kg/week from 12 ± 2 to 24 ± 2 weeks) using log binomial regression and evaluated effect modification by ART regimen (DTG vs. Efavirenz (EFV)).ResultsOf 22,828 women on ART at conception with singleton deliveries between August 2014 and April 2020, 16,300 (71.4%) had a weight measured <24 weeks' gestation (baseline weight) and 4437 (19.2%) had weight measured both at 12 (±2) weeks and 24 (±2) weeks, allowing second trimester weight gain calculation. Compared to women with baseline weight 60 to 70 kg, low baseline weight (<50 kg) was associated with increased risk of very preterm delivery (aRR 1.30, 95% CI 1.03, 1.65) and very SGA (aRR1.96, 95% CI 1.69, 2.28). High baseline weight (>90 kg) was associated with increased risk of macrosomia (aRR 3.24, 95% CI 2.36, 4.44) and maternal hypertension (aRR 1.79, 95% CI 1.62, 1.97). Baseline weight was not associated with stillbirth or early neonatal death. For all outcomes, second trimester weight gain showed weaker associations than did baseline weight. Duration of pre‐pregnancy ART (years) was associated with higher baseline weight for DTG but not for EFV, and the risk of maternal hypertension by baseline weight category was higher for DTG than EFV for all strata.ConclusionsART regimens associated with weight gain may reduce the number of women at risk for certain severe adverse pregnancy outcomes associated with low weight but increase the number at risk of macrosomia and maternal hypertension. Further research could determine whether weight‐based ART treatment strategies improve maternal and child health.

AbstractIntroductionStudies have reported a higher risk of suboptimal neurodevelopment among children who are HIV‐exposed uninfected (HEU) compared to children HIV‐unexposed uninfected (HUU). Actual academic performance among school‐aged children by HIV exposure status has not been studied.MethodsAcademic performance in Mathematics, Science, English, Setswana and overall among children enrolled in the Botswana‐based FLOURISH study who were attending public primary school and ranging in age from 7.1 to 14.6 years were compared by HIV exposure status using a Cochran‐Mantel‐Haenszel test. Lower academic performance was defined as a grade of "C" or lower (≤60%). Unadjusted and adjusted logistic regression models were fit to assess for an association between HIV exposure and lower academic performance.ResultsBetween April 2021 and December 2022, 398 children attending public primary school enrolled in the FLOURSH study, 307 (77%) were HEU. Median age was 9.4 years (IQR 8.9–10.2). Only 17.9% of children HEU were breastfeed versus 100% of children HUU. Among children HEU, 80.3% had foetal exposure to three‐drug antiretroviral treatment, 18.7% to zidovudine only and 1.0% had no antiretroviral exposure. Caregivers of children HEU were older compared to caregivers of children HUU (median 42 vs. 36 years) and more likely to have no or primary education only (15.0% vs. 1.1%). In unadjusted analyses, children HEU were more likely to have lower overall academic performance compared to their children HUU (odds ratio [OR]: 1.96 [95% confidence interval (CI): 1.16, 3.30]), and lower performance in Mathematics, Science and English. The association was attenuated after adjustment for maternal education, caregiver income, breastfeeding, low birth weight and child sex (aOR: 1.86 [95% CI: 0.78, 4.43]).ConclusionsIn this Botswana‐based cohort, primary school academic performance was lower among children HEU compared to children HUU. Biological and socio‐demographic factors, including child sex, appear to contribute to this difference. Further research is needed to identify modifiable contributors, develop screening tools to identify the risk of poor academic performance and design interventions to mitigate risk.