Neurotoxicity of low bisphenol A (BPA) exposure for young male mice: Implications for children exposed to environmental levels of BPA☆
Graphical abstract
Introduction
Bisphenol A (BPA), a xenoestrogenic environmental endocrine disruptor, is an additive used to produce plastic products of polycabonate plastics and epoxy resin Additionally, it is also widely used in the inner coating of canned foods, thermal papers, dental sealants and many other domestic containers (Chouhan et al., 2014). The production of BPA was reported to be 15 billion pounds in 2013 (Grand View Research, 2014). Given its large volume, BPA is ubiquitous in the environment. In addition to the general detection of BPA in soil, water, dust, sediments and foods (Careghini et al., 2015), many biomonitoring studies showed that BPA could be detectable in more than 70% of urine samples from general populations in different countries and areas at a range of 0.1–2.4 μg/kg·bw (Chouhan et al., 2014, Battal et al., 2014). Increasing concerns have been raised about BPA exposure due to its negative effects on human health. Mounting epidemiologic studies have shown that BPA exposure is correlated with the risk of some diseases, including heart disease, obesity and diabetes (Melzer et al., 2010; Li et al., 2015, Lang et al., 2008).
Previous studies often focused on the reproductive toxicity of BPA exposure. However, recent animal studies have suggested that early exposure to BPA has a significant impact on brain cells because the embryonic and infant period is crucial for the development of the nervous system and brain morphology. For example, perinatal exposure to BPA was confirmed to affect sexual differentiation of brain development in early life (Mccaffrey et al., 2013, Rubin et al., 2006), alter adult sexual behavior (Boudalia et al., 2013, Decatanzaro et al., 2013), increase anxiety-like behavior, reduce exploratory behavior in a corticosterone-regulated way (Poimenova et al., 2010), and impair spatial and passive avoidance memory (Xu et al., 2010). The adverse effects of BPA exposure in the embryonic and infant periods on neural development are well acknowledged. However, BPA studies on the neurotoxic effects for adolescents have been limited.
High-dose effects of BPA were investigated in both in vitro and in vivo experiments and confirmed to exert potential effects on the development of brain and behavior differentiation in infants, children and adolescence (Xu et al., 2011a, Xu et al., 2011b, Iwakura et al., 2010). However, low-dose effects of BPA exposure on human health have often been underestimated. “Low dose” was defined as human exposure in daily lives (i.e., the dose is equal to or lower than the level of human environmental exposure) (Melnick et al., 2002). Although environmental exposure is lower than the reference dose (RfD, 50 μg/kg·bw/day) given by the Environmental Protection Agency (U. S. EPA (United States Environmental Protection Agency), 2012, Rubin, 2011), it is unclear whether a low dose of BPA exposure is safe for children. Several studies reported an inability to detect any effects of BPA within the “low dose” range (Myers et al., 2009, Richter et al., 2006, Vandenberg et al., 2012). However, other researchers reported the opposite views because human exposure to BPA is long-term and results in chronic accumulation; furthermore, their experiments confirmed the relationship between the low dose exposure to BPA and adverse human health effects (vom Saal and Hughes, 2005, vom Saal and Welshons, 2006, Ziv-Gal et al., 2015).
To confirm and investigate the effects of BPA exposure on brain cells and the learning and memory ability of children/adolescents, particularly the effects of the low dose, young male mice aged 4 weeks were used as the model animals. The mice were divided into four groups that were given different levels of oral BPA treatments over 8 weeks to simulate the daily different exposure levels in humans. The comet assay and hippocampal neuron counting were performed to detect brain cell damage. The Y-maze test was conducted to test alterations in the memory performance and ability induced by BPA exposure. Long term potentiation (LTP) induction in the Schaffer-CA1 (cornu ammonis 1) of the hippocampus was used as the potential mechanism for evaluating performance.
Section snippets
Chemicals and instruments
BPA was purchased from Sigma-Aldrich (HPLC grade, St. Louis, MO, USA). Na2EDTA, NaCl, NaOH, Na2HPO4, NaH2PO4, DMSO, ethidium bromide, paraformaldehyde and pentobarbital sodium were purchased from Guangzhou Chemical Reagent Factory (Guangzhou, China). Agarose was purchased from Shanghai Biological Technology Co., LTD (Shanghai, China). Tris-base was purchased from Shanghai Juyuan Biotechnology Co. LTD (Shanghai, China). Triton-X 100 was purchased from Qiangsheng Chemical Co. LTD (Jiangsu,
Results
After a few weeks of oral exposure to BPA, the exposed mice were inclined to be anxious, excited, hyperactive and aggressive, especially the high-exposed group. Some mice had inflammation from biting or fighting each other. After solitary rearing for a period of time, they quickly recovered. The others remained in healthy condition with tight fur and normal coloration. The body weights of the mice steadily increased and no significant differences were observed between the groups.
Through
Discussion
In addition to reports that BPA has reproductive and genetic toxicity (Melnick et al., 2002, Ulutaş et al., 2011, Iso et al., 2006), in vivo experiments indicated that a low dose of BPA exposure in utero reduces the spine densities in the hippocampal CA1 of 14-month-old mice (Kimura et al., 2016) and perinatal exposure to BPA impairs spatial memory through upregulating the expression of synaptic proteins, Nrxn1 and Nlgn3, and increasing the dendritic spine density in the cerebral cortex and
Conclusion
In conclusion, our results showed that chronic BPA exposure in adolescent male mice increased DNA damage in brain cells, impaired learning and memory ability, changed the cell density in the hippocampus and inhibited induction of hippocampal long-term potentiation in Schaffer-CA1. The comet assay indicated that even a low dose exposure to BPA could result in DNA damage in brain cells. The effects of a non-monotonic, dose-independent trend were observed in neuron quantity counting experiments.
Declaration of conflict of interest
The authors declare no conflict of interest.
Acknowledgments
This research was supported by grants from National Natural Science Foundation of China (No. 81671946 and No. 21477041) and Science and Technology Plan Projects in Guangzhou City (201510010107).
References (52)
- et al.
Metabolic disruption in male mice due to fetal exposure to low but not high doses of bisphenol A (BPA): evidence for effects on body weight, food intake, adipocytes, leptin, adiponectin, insulin and glucose regulation
Repro. Toxicol.
(2013) - et al.
Effects of cordycepin on Y-maze learning task in mice
Eur. J. Pharmacol.
(2013) - et al.
Baicalin improved the spatial learning ability of global ischemia/reperfusion rats by reducing hippocampal apoptosis
Brain Res.
(2012) - et al.
The kinetics of repair of oxidative DNA damage (strand breaks and oxidized pyrimdines) in human cells
Mut. Res.
(1995) - et al.
Perturbation of male sexual behavior in mice (mus musculus) within a discrete range of perinatal bisphenol-A doses in the context of a high- or low-phytoestrogen diet
Food Chem. Toxicol.
(2013) - et al.
In vitro effects of bisphenol A on developing hypothalamic neurons
Toxicol.
(2010) - et al.
4-nonylphenol, bisphenol-A and triclosan levels in human urine of children and students in China, and the effects of drinking these bottled materials on the levels
Environ. Int.
(2013) - et al.
Effects of intrahippocampal GABAB receptor antagonist treatment on the behavioral long-term potentiation and Y-maze learning performance
Neurobiol. Learn. Mem.
(2014) - et al.
Sex specific impact of perinatal bisphenol A (BPA) exposure over a range of orally administered doses on rat hypothalamic sexual differentiation
Neurotoxicol.
(2013) - et al.
Urinary levels of bisphenol A, triclosan and 4-nonylphenol in a general Belgian population
Environ. Int.
(2012)
Corticosterone-regulated actions in the rat brain are affected by perinatal exposure to low dose of bisphenol A
Neurosci.
Bisphenol A: an endocrine disruptor with widespread exposure and multiple effects
J. Steroid. Biochem. Mol. Biol.
Large effects from small exposures. ii. the importance of positive controls in low-dose research on bisphenol A
Environ. Res.
Perinatal exposure to bisphenol-A impairs learning-memory by concomitant down-regulation of n-methyl-d-aspartate receptors of hippocampus in male offspring mice
Horm. Behav.
Bisphenol-A rapidly enhanced passive avoidance memory and phosphorylation of nmda receptor subunits in hippocampus of young rats
Toxicol. Appl. Pharm.
Sex-specific influence of exposure to bisphenol-A between adolescence and young adulthood on mouse behaviors
Neuropharmacol.
The effects of in utero bisphenol A exposure on reproductive capacity in several generations of mice
Toxicol. Appl. Pharm.
Bisphenol A impairs the double-strand break repair machinery in the germline and causes chromosome abnormalities
Proc. Natl. Acad. Sci. U. S. A.
Use of the γh2ax assay for assessing the genotoxicity of bisphenol A and bisphenol F in human cell lines
Arch. Toxicol.
Determination of urinary levels of bisphenol A in a Turkish population
Environ. Monit. Assess.
A multi-generational study on low-dose BPA exposure in wistar rats: effects on maternal behavior, flavor intake and development
Neurotoxicol. Teratol.
Exposure of the U.S. population to bisphenol A and 4-tertiary-octylphenol: 2003-2004
Environ. Health Perspect.
Bisphenol A, nonylphenols, benzophenones, and benzotriazoles in soils, groundwater, surface water, sediments, and food: a review
Environ. Sci. Pollut. Res. Int.
Effect of neonatal rat bisphenol A exposure on performance in the morris water maze
J. Toxicol. Environ. Health Part A
Effect of Bisphenol A on human health and its degradation by microorganisms: a review
Ann. Microbiol.
Low circulating levels of bisphenol-A induce cognitive deficits and loss of asymmetric spine synapses in dorsolateral prefrontal cortex and hippocampus of adult male monkeys
J. Comp. Neurol.
Cited by (70)
NeuTox: A weighted ensemble model for screening potential neuronal cytotoxicity of chemicals based on various types of molecular representations
2024, Journal of Hazardous MaterialsLow-dose bisphenols exposure sex-specifically induces neurodevelopmental toxicity in juvenile rats and the antagonism of EGCG
2023, Journal of Hazardous MaterialsDysfunction of the medial prefrontal cortex contributes to BPA-induced depression- and anxiety-like behavior in mice
2023, Ecotoxicology and Environmental Safety
- ☆
This paper has been recommended for acceptance by Dr. Harmon Sarah Michele.