Alteration of protein profile in cerebral cortex of rats exposed to bisphenol a: a proteomics study

Highlights

• Oral administration of BPA NOAEL dose induced oxidative stress in the rat brain cortex.

• 2-D gel electrophoresis indicated that BPA altered the levels of some proteins that are involved in neuronal functions.

• Western blot analysis has confirmed that BPA reduced Alpha-enolase levels and in this way exert some neurotoxic effects.

Abstract

Bisphenol A (BPA) is one of the most widely used chemicals in plastic industry, which enters the human body through occupational and food contact. We studied the protein changes in rat cerebral cortex to evaluate the neurotoxicity of BPA. Twenty-four adult male rats were randomly selected and divided into four groups and each group respectively received 0, 0.5, 5 and 50 mg/kg of BPA for 4 weeks orally. To determine the oxidative status, reduced glutathione content and the level of malondialdehyde were measured in brain cortical tissue. The proteins of each sample extracted and separated on a two-dimensional acrylamide gel electrophoresis. From the obtained protein map, the 10 most altered protein spots were used for mass spectroscopy analysis. The lipid peroxidation in both doses of 0.5 and 5 mg/kg was significantly higher than the control group, but the glutathione content had no significant difference between the groups. Based on the results of the MS data analysis by the MASCOT database search engine, 10 proteins with altered intensity were identified as pyruvate kinase, alpha-enolase, aconitate hydratase, creatine kinase B-type, phosphatidylethanolamine-binding protein 1, 14-3-3 protein eta, guanine nucleotide-binding protein subunit beta-1, dihydropyrimidinase-related protein 2, glutamine synthetase and the neurofilament light polypeptide. There are several reports suggesting that the increase or decrease in the level and activity of these 10 proteins, similar to those observed in this study, is related to some neurological and psychosocial disorders including neurodegenerative diseases, schizophrenia, depression, epilepsy and some brain tumors.

Introduction

Bisphenol A [BPA; CAS no. 80-05-7] is a chemical substance with the formula 2,2-bis (4-hydroxyphenyl) propane or (CH₃)₂C(C₆H₄OH)₂ (Fig. 1) which has broad applications in the industry. This substance is used in the production of polycarbonate plastics and epoxy resins; the resins used in the manufacture of interior protective coatings of cans, children's glasses, sealants and dental composites (Calafat et al., 2008). Notably, only 3 % of produced polycarbonate and 10 % of produced epoxy resins are used in materials that potentially expose to human foods, while others are used in sunglasses, construction materials, CDs, medical equipment, dental materials etc. (Geens et al., 2012). It is noteworthy that the steric bonds that link BPA monomers together are unstable, and their breakage leads to the gradual release of monomers in the food products. Remarkably, some studies which had addressed BPA toxicological concerns are sponsored by companies that use this substance, and their results are different from those of government-funded studies. Hence, wider and deeper studies on the toxicity of this substance are of great importance (vom Saal and Hughes, 2005).

Animal models have indicated that BPA intake can result reproductive and immune system impairments, fetal development disorders and increased risk of metabolic diseases and inflammation (Rochester, 2013). This substance also could affect endocrine and immune systems in animals and several in vitro and in vivo studies have documented its mutagenic, estrogenic, teratogenic and hepatotoxic activities (Michalowicz, 2014). According to various animal studies, the toxic effects of BPA on the reproductive system of male animals, metabolic processes and the development of the nervous system have been proven. Negative effects of this substance on the reproductive system of female animals, the immune system and the development of the reproductive system in female animals are also likely, but require further studies (Molina et al., 2018; Richter et al., 2007).

However, BPA can also affect the nervous system through different ways. It may alter the intra-synaptic levels of neurotransmitters in adult animals and induce apoptosis in some neuronal cells; it can increase dopamine brain levels in pregnant mice with the dose of 20 μg/kg (SC) and induce apoptosis of hippocampal neuronal cells in high concentrations (above 100 μM) (Michalowicz, 2014). Considering that most of the neurotoxicity evaluations of BPA have been conducted during the embryonic period and have surveyed its negative effects on neuronal development (Beronius et al., 2013; Nakamura et al., 2012, 2010, Nakamura et al., 2007, 2006; Palanza et al., 2002; Stump et al., 2010; Yin et al., 2015), either in young animals (Zhou et al., 2017), we aimed to study the molecular and toxicological properties of BPA in adulthood period by evaluation of the proteome change after its sub-acute toxicity in the brain cortex of adult male rats. Although BPA is able to pass blood brain barrier easily and affect central nervous system intensively, however the toxicological studies has evaluated its neurotoxic effects in varying doses from 25 ng/kg/day to 50 mg/kg/day (Inadera, 2015). Accordingly, we decided to design our study with relatively wide range dose of BPA administration including 0.1, 1 and 10 fold of its NOAEL.