Does Prenatal Exposure to Low-Dose Di-2-Ethylhexyl Phthalate Impair Neurodevelopment in a Val66met BDNF Mouse Model?

Background Diethylhexyl phthalate (DEHP) is a widely used plastic additive chemical ubiquitous in the modern environment. Given increasing epidemiological evidence of a link between prenatal DEHP exposure and adverse neurodevelopmental outcomes in humans (including autism and ADHD symptoms), we used a humanized Val66Met BDNF mouse model to investigate the effect of prenatal DEHP exposure at an environmentally relevant dose within the daily allowable range. The Val66Met polymorphism is the most common mutation in human BDNF, a gene integral to neuronal development, and has been associated with neuropsychiatric disorders including schizophrenia. Aims & Objectives This study aims to obtain causal evidence that exposure to DEHP at a dose within the daily allowable range at the critical prenatal period has adverse effects on neurodevelopment which present postnatally in offspring. ​This includes behavioural tests which assess symptoms relevant to autism, ADHD, and schizophrenia. This study also uses a Val66Met BDNF mouse model to investigate how each genotype interacts with DEHP exposure in relation to neurodevelopment. Method Using a factorial design, we investigated the effects of prenatal DEHP exposure on wildtype, heterozygous, and homozygous mice for the Val66Met mutation. During mid-gestation (embryonic day 10.5-14.5), pregnant dams received either 0μg/kg/day or 20μg/kg/day DEHP through voluntary oral administration. After weaning, male and female offspring underwent a battery of behavioral tests relevant to neurodevelopmental conditions including autism, ADHD, and schizophrenia. Linear mixed models were used with litter as a random effect to account for within-litter similarities. qPCR was performed using frontal cortex tissue from offspring mice to quantify changes in key genes involved in neurodevelopment which may explain changes observed in the behavioural battery including BDNF, Homer1a, Homer1b/c, and Homer2. Results DEHP-exposed male offspring displayed social deficit (p=0.034) (wildtype only), increased repetitive grooming (p=0.0016), increased weight (p=0.0036), and increased measures of central obesity (p=0.037) compared to vehicle males. In wildtype females, prenatal DEHP exposure caused a prepulse-inhibition deficit (p=0.020) compared to vehicle. Though we observed effects of Val66Met genotype on behavior, there was no evidence of an interaction between Val66Met genotype and prenatal DEHP exposure despite both mechanisms being known to work at least partially through BDNF. Moreover, there was no effect of prenatal treatment or genotype on BDNF expression in the brain. In wildtype males, there was a trend for a decrease in Homer2 expression in the brain (p=0.070). For analysis of Homer1, there was a significant interaction between prenatal DEHP exposure and Homer1 gene expression (inducible Homer1a vs. constitutive ​Homer1b/c) in wildtype females (p=0.0133). Discussion & Conclusions Our comprehensive battery of behaviour relating to autism, ADHD and schizophrenia symptoms, provides insights into the sex-specific effects of DEHP on these behavioural domains in males and females. Our findings suggest that males may be more susceptible to the adverse neurodevelopmental effects prenatal DEHP exposure, a finding which may provide insight towards the high male bias in autism and ADHD diagnoses. Decrease in brain expression of Homer2 in male and Homer1a in female mice may be an important mechanism through which DEHP acts and should be investigated further in human birth cohort studies.