Mecanismos moleculares de acción del Bisfenol A en próstata y corteza prefrontal de rata

Abstract

The widespread exposure of humans to Bisphenol A (BPA) and its potential clinical consequences have recently attracted considerable attention from scientists, government advisors, and the popular press. BPA is an ubiquitous xenoestrogen used in the production of plastic and metal containers for food and beverages that can leach into the contents during processing and storage. The tolerably daily intake (TDI) of BPA has been set to 50 μg/kg bw/day in Europe and the United States. This guidance value was derived from a lowestobservable- adverse-effect-level (LOAEL) for BPA of 50 mg/kg/day identified in the 1980s. Since then, data from numerous studies have reported significant adverse effects of exposure to doses of BPA below the calculated safe levels, leading scientists and other experts to question the adequacy of the TDI-value. BPA has been shown to exert endocrine-disrupting effects on reproduction, development, metabolism, and cancer in humans and other species. However, the mechanisms underlying these effects remain unclear. This dissertation presents a set of experiments conducted to investigate the molecular mechanisms underlying BPA action on prostate and prefrontal cortex (PFC) of rats. This thesis starts with the evaluation of short-term adult exposure to BPA on 5α-Reductase (5α-R) isozymes and aromatase expression in the prostate gland of rats, key enzymes in the biosynthesis of 5α-dihydrotestosterone (DHT) and estradiol (E2) (important hormones for prostate physiopathology). Quantitative RT-PCR, western blot and immunohistochemical analyses showed lower mRNA and protein levels of 5α-R1 and 5α-R2 in BPA-treated groups versus controls but higher mRNA levels of 5α-R3, recently proposed as a biomarker of malignancy. BPA-treated rats also evidenced an increase in aromatase expression as well as in plasma E2/testosterone (T) ratio, both associated with prostate diseases (Study 1) . The decrease of 5α-R1 and 5α-R2 transcription in the prostate gland by BPA was demonstrated to be independent of circulating T levels (Study 2). This hypothesis was tested because: (i) within the prostate T exerts a positive regulatory action on 5α-R expression, and (ii) BPA has shown to decrease circulating T through different mechanisms. The thesis continues with the evaluation of the molecular mechanisms of the BPA action on the PFC of male and female rats exposed during adulthood or the perinatal period. We hypothesize that some of the brain and behavior abnormalities described in experimental animals and humans exposed to BPA might be mediated, at least in part, by alterations in the PFC, since it is an important brain area for cognitive control and complex behaviors, and appears to be altered in many psychopathologies. PFC functions are modulated by different neurotransmitters systems, such as γ-aminobutyric acid (GABA), serotonin (5-HT) and dopamine (DA) systems, therefore, alterations in the expression of genes related with these neurotransmitters might interfere with PFC physiopathology. These effects were investigated using qRT-PCR, western blot and PCR-array technologies. Study 3 details the effects of short-term exposure of adult rats to BPA (50 μg/kg/day, 4 days) on 5α-R and aromatase, enzymes that synthesize GABAA receptor modulators, and tryptophan hydroxylase (Tph), the rate-limiting enzyme in 5-HT biosynthesis. To gain better understanding of BPA action in the adult PFC, 84 genes involved in different mechanisms of neurotoxicity were also analyzed. Study 4 describes the effects of perinatal exposure (from gestational day 12, GD12, to postnatal day 21, PND21) to BPA (10 μg/kg/day) on DA and 5-HT systems-related genes in juvenile and adult male rats. Finally, this thesis also extends and improves scientific knowledge about toxic effects of Bisphenol F (BPF) and Bisphenol S (BPS), current BPA alternatives in many consumer products. Thus, in our last study we aimed to determine whether BPA, BPF or BPS affect precortical 5α-R expression, as well as DA and 5-HT systems-related genes in juvenile female rats perinatally (GD12-PND21) exposed to them (Study 5) .