Influence of maternal toxicity on the outcome of developmental toxicity studies

Potential occupational exposure of parents to endocrine disrupting chemicals, adverse birth outcomes, and the modification effects of multi-vitamins supplement and infant sex

BACKGROUND

Maternal occupational exposure to endocrine disrupting chemicals (EDCs) may have adverse effect on birth outcomes. However, little is known about paternal EDCs exposure and the combined effect of parental exposure on birth outcomes.

OBJECTIVES

To assess the effects of both maternal and paternal occupational EDCs exposure on adverse birth outcomes, and further explore if multi-vitamins supplement and infant sex modify the association.

METHODS

We conducted a prospective cohort study of 5421 mother-father-newborn groups in Guangzhou, China. A questionnaire informed by a job exposure matrix (JEM) was applied to collect parental occupational EDCs exposure based on the type of work performed. We used logistic regression to estimate association between parental EDCs exposure and birth outcomes (including preterm birth (PTB), low birth weight (LBW), birth defects and congenital heart defects (CHD)). Stratified analyses and Cochran Q tests were performed to assess the modifying effect of maternal multi-vitamins supplement use and infant sex.

RESULTS

Compared with mothers unexposed, we found that mothers those exposed to EDCs were associated with increased odds of birth defects (aOR=1.70, 95% confidence interval (CI): 1.10-2.62), especially for those exposed for > 1.5 years (aOR= 3.00, 95% CIs: 1.78-5.03), or those with directly occupational exposed to EDCs (aOR= 2.94, 95% CIs: 1.72-5.04). Maternal exposure for > 1.5 years and direct exposure increased the risk of CHD, with aORs of 2.47 (1.21-5.02) and 2.79 (1.37-5.69), respectively. Stronger adverse effects were also observed when mothers and fathers were both exposed to EDCs. Paternal occupational EDCs exposure and exposure ≤ 1.5 years was associated with increased odds of LBW, with aORs of 2.14 (1.63-2.79) and 1.54 (1.10-2.15), respectively. When stratified by multi-vitamins supplement and infant sex, we observed slightly stronger effects for maternal exposure on birth defects/CHD as well as paternal EDCs exposure on PTB and LBW, among those without multi-vitamins supplement and among male babies, although the modification effects were not significant.

CONCLUSION

Maternal exposure to EDCs was associated with greater odds of birth defects and CHD, while paternal exposure was mainly associated with greater odds of LBW. These effects tend to be stronger among mothers without multi-vitamins supplement and among male babies.

Hazard characterization of carcinogenicity, mutagenicity, and reproductive toxicity for short chain primary nitroalkanes

Nitroalkanes are organic aliphatic hydrocarbon compounds with a nitro moiety that are commonly used as solvents or intermediates to synthesize a variety of organic compounds due to their inherent reactivity. In June 2020, a harmonized classification and labeling (CLH) proposal was submitted to the European Chemicals Agency (ECHA) for the following harmonized carcinogenicity, mutagenicity, and reproductive toxicity ("CMR") classifications for nitromethane (NM), nitroethane (NE), and 1-nitropropane (1-NP): NM Carc. 1B and Repr. 1B; NE Repr. 1B; and 1-NP Repr. 2. In this assessment, a weight of evidence (WoE) evaluation of studies on animal carcinogenicity and reproductive and developmental toxicity, genotoxicity, and mode of action for these three nitroalkanes was performed to critically assess the relevance of the proposed CMR classifications. Overall, the WoE indicates that NM, NE, and 1-NP are not carcinogenic, genotoxic, nor selective reproductive or developmental toxicants. Based on our analysis, classifying NM, NE, and 1-NP as Category 2 reproductive toxicants is most appropriate. Furthermore, not classifying NE and 1-NP with respect to their carcinogenicity is appropriate based on the available studies for this endpoint coupled with negative results in genotoxicity studies, metabolism data, and in silico predictions. We determined that the classification for NM of Carc. 1B is not appropriate, based on the fact that rat mammary and harderian tumors are likely not relevant to humans and lung and liver tumors reported in mice were equivocal in their dose-response and statistical significance.

Species-specific developmental toxicity in rats and rabbits: Generation of a reference compound list for development of alternative testing approaches

For regulatory information requirements, developmental toxicity testing is often conducted in two mammalian species. In order to provide a set of reference compounds that could be used to explore alternative approaches to supersede testing in a second species, a retrospective data analysis was conducted. The aim was to identify compounds for which species sensitivity differences between rats and rabbits are not caused by maternal toxicity or toxicokinetic differences. A total of 330 compounds were analysed and classified according to their species-specific differences. A lack of concordance between rat and rabbit was observed in 24% of the compounds, of which 10% were found to be selective developmental toxicants in one of the species. In contrast to previously published analyses the presented comparison is based entirely on publically data allowing validating and comparing alternative approaches for developmental toxicity testing. Furthermore, this list could be useful to identify mechanisms leading to species differences.

Guidance on classification for reproductive toxicity under the globally harmonized system of classification and labelling of chemicals (GHS)

The Globally Harmonised System of Classification (GHS) is a framework within which the intrinsic hazards of substances may be determined and communicated. It is not a legislative instrument per se, but is enacted into national legislation with the appropriate legislative instruments. GHS covers many aspects of effects upon health and the environment, including adverse effects upon sexual function and fertility or on development. Classification for these effects is based upon observations in humans or from properly designed experiments in animals, although only the latter is covered herein. The decision to classify a substance based upon experimental data, and the category of classification ascribed, is determined by the level of evidence that is available for an adverse effect on sexual function and fertility or on development that does not arise as a secondary non-specific consequence of other toxic effect. This document offers guidance on the determination of level of concern as a measure of adversity, and the level of evidence to ascribe classification based on data from tests in laboratory animals.

A one-generation reproductive toxicity study of 3,4-methylenedioxy-n-methamphetamine (MDMA, Ecstasy), an amphetamine derivative, in C57BL/6 mice

3,4-Methylenedioxy-N-methamphetamine (MDMA, ecstasy) is an amphetamine derivative and is a popular type of drug that is abused due to its effects on the central nervous system (CNS), including alertness and euphoria. However, life-threatening (brain edema, heart failure, and coma) and fatal hyperthermia sometimes occur in some individuals taking MDMA. In a one-generation reproductive toxicity study, the potential toxicity of chronic exposure of MDMA was investigated on the reproductive capabilities of parental mice (F0), as well as the survival/development of their subsequent offspring (F1). Male and female C57BL/6 mice were administered orally MDMA at 0, 1.25, 5 or 20 mg/kg body weight (b.w.) throughout the study, beginning at the premating period, through mating, gestation, and lactation periods. MDMA did not produce any apparent clinical signs in F0 or F1 mice, and produced no significant changes in body weight, feed/water intake, or organ weights. In contrast, administration of MDMA produced external abnormalities in fetuses, stillbirth and labored delivery, and diminished viability and weaning indices in offspring, but these data were not significant. In addition, physical development of F1 mice was not markedly influenced by MDMA treatment. Nonetheless, serum biochemistry markers showed that levels of alkaline phosphatase (ALP), aspartate aminotransferase (AST), and blood urea nitrogen (BUN) were markedly elevated in a dose-dependent manner from 5 mg and higher MDMA/kg b.w., whereas levels of triglycerides (TG), potassium (K), and uric acid (UA) were reduced. Data suggest that MDMA may exert a weak reproductive and developmental toxicity, and the no-observed-adverse-effect level (NOAEL) of MDMA is estimated to be 1.25 mg/kg b.w./d.