Bisphenol A Modulates Calcium Currents and Intracellular Calcium Concentration in Rat Dorsal Root Ganglion Neurons

Alterations induced by Bisphenol A on cellular organelles and potential relevance on human health

Bisphenol A (BPA) is a chemical partially soluble in water and exists in a solid state. Its structural similarity with estrogen makes it an endocrine-disrupting chemical. BPA can disrupt signaling pathways at very low doses and may cause organellar stress. According to in vitro and in vivo studies, BPA interacts with various cell surface receptors to cause organellar stress, producing free radicals, cellular toxicity, structural changes, DNA damage, mitochondrial dysfunction, cytoskeleton remodeling, centriole duplication, and aberrant changes in several cell signaling pathways. The current review summarizes the impact of BPA exposure on the structural and functional aspects of subcellular components of cells such as the nucleus, mitochondria, endoplasmic reticulum, lysosome, ribosome, Golgi apparatus, and microtubules and its consequent impact on human health.

Changes Caused by Bisphenols in the Chemical Coding of Neurons of the Enteric Nervous System of Mouse Stomach

Bisphenol A (BPA), an organic chemical compound which is widely used in the production of plastics, can severely damage live organisms. Due to these findings, the plastic industry has started to replace it with other substances, most often with bisphenol S (BPS). Therefore, during the present investigation, with the use of double immunofluorescence labeling, we compared the effect of BPA and BPS on the enteric nervous system (ENS) in the mouse corpus of the stomach. The obtained results show that both studied toxins impact the amount of nerve cells immunoreactive to substance P (SP), galanin (GAL), vesicular acetylcholine transporter (VAChT is used here as a marker of cholinergic neurons) and vasoactive intestinal polypeptide (VIP). Changes observed under the impact of both bisphenols depended on the neuronal factor, the type of the enteric ganglion and the doses of bisphenols studied. Generally, the increase in the percentage of neurons immunoreactive to SP, GAL and/or VIP, and the decrease in the percentage of VAChT-positive neurons, was noted. Severity of changes was more visible after BPA administration. However, the study has shown that long time exposure to BPS also significantly affects the ENS.

The Comparison of the Influence of Bisphenol A (BPA) and Its Analogue Bisphenol S (BPS) on the Enteric Nervous System of the Distal Colon in Mice

Bisphenol A (BPA), commonly used as a plasticizer in various branches of industry has a strong negative effect on living organisms. Therefore, more and more often it is replaced in production of plastics by other substances. One of them is bisphenol S (BPS). This study for the first time compares the impact of BPA and BPS on the enteric neurons using double immunofluorescence technique. It has been shown that both BPA and BPS affect the number of enteric neurons containing substance P (SP), galanin (GAL), vasoactive intestinal polypeptide (VIP), neuronal isoform of nitric oxide synthase (nNOS-a marker of nitrergic neurons) and/or vesicular acetylcholine transporter (VAChT- a marker of cholinergic neurons). The changes noted under the impact of both bisphenols are similar and consisted of an increase in the number of enteric neurons immunoreactive to all neuronal factors studied. The impact of BPS on some populations of neurons was stronger than that noted under the influence of BPA. The obtained results clearly show that BPS (similarly to BPA) administered for long time is not neutral for the enteric neurons even in relatively low doses and may be more potent than BPA for certain neuronal populations.

Impairment of learning and memory induced by perinatal exposure to BPA is associated with ERα-mediated alterations of synaptic plasticity and PKC/ERK/CREB signaling pathway in offspring rats

The effect of bisphenol A (BPA) on learning and memory has attracted much attention recently, but its underlying mechanism remains unclear. We aimed to investigate whether the impairment of learning and memory induced by perinatal exposure to BPA was associated with the hippocampal estrogen receptor α (ERα)-mediated synaptic plasticity and PKC/ERK/CREB signaling pathway in different sex offspring rats. Pregnant Sprague-Dawley rats were treated with BPA (1 and 10 μg/mL) through drinking water from gestational day (GD) 6 to postnatal day (PND) 21. After weaning, offspring drank BPA-free water until PND 56. Morris water maze, placement and object recognition, and step-down passive avoidance task were performed. The serum estradiol (E2) levels, histopathology of hippocampus, and the expression of learning and memory related proteins were measured. The results showed that spatial and recognition memory were impaired in BPA-exposed female and male offspring, but the impaired passive avoidance memory presented only in males, not in females. The serum E2 levels were increased in BPA-exposed females and males. BPA altered the morphology and quantity of hippocampal neurons. The levels of ERα, NMDA receptor subunit 2B (NR2B), p-NR2B, AMPA receptor 1 (GluA1), p-GluA1, PSD-95, synapsin I, PKC, p-ERK and p-CREB protein expression were decreased in BPA exposed females and males, and there were interactions of sex × BPA exposure in ERα, p-NR2B and p-ERK levels. These findings suggested that perinatal exposure to BPA has sex-specific effects on learning and memory, which is associated with ERα-mediated impairment of synaptic plasticity and down-regulation of PKC/ERK/CREB signaling pathway.

Bisphenol A exposure disrupts aspartate transport in HepG2 cells

The liver is the organ responsible for bisphenol A (BPA) metabolism, an environmental chemical agent. Exposure to this toxin is associated with liver abnormalities and dysfunction. An important role played by excitatory amino acid transporters (EAATs) of the slc1 gene family has been reported in liver injuries. To gain insight into a plausible effect of BPA exposure in the liver glutamate/aspartate transport, using the human hepatoblastoma cell line HepG2, we report a BPA-dependent dynamic regulation of SLC1A3 and SLC1A2. Through the use of radioactive [³ H]- d-aspartate uptake experiments and immunochemical approaches, we characterized time and dose-dependent regulation of the protein levels and function of these transporters after acute exposure to BPA. An increase in nuclear Yin Yang 1 was found. These results suggest an important involvement of the EAATs in liver physiology and its disruption after acute BPA exposure.

Potentiation of the Glycine Response by Bisphenol A, an Endocrine Disrupter, on the Substantia Gelatinosa Neurons of the Trigeminal Subnucleus Caudalis in Mice

Lamina II, also called the substantia gelatinosa (SG) of the medullary dorsal horn (the trigeminal subnucleus caudalis, Vc), is thought to play an essential role in the control of orofacial nociception because it receives the nociceptive signals from primary afferents, including thin myelinated Aδ- and unmyelinated C-fibers. Glycine, the main inhibitory neurotransmitter in the central nervous system, plays an essential role in the transference of nociceptive messages from the periphery to higher brain regions. Bisphenol A (BPA) is reported to alter the morphological and functional characteristics of neuronal cells and to be an effector of a great number of ion channels in the central nervous system. However, the electrophysiological effects of BPA on the glycine receptors of SG neurons in the Vc have not been well studied. Therefore, in this study, we used the whole-cell patch-clamp technique to determine the effect of BPA on the glycine response in SG neurons of the Vc in male mice. We demonstrated that in early neonatal mice (0-3 postnatal day mice), BPA did not affect the glycine-induced inward current. However, in the juvenile and adult groups, BPA enhanced the glycine-mediated responses. Heteromeric glycine receptors were involved in the modulation by BPA. The interaction between BPA and glycine appears to have a significant role in regulating transmission in the nociceptive pathway.

Neurochemical characterization of the enteric neurons within the porcine jejunum in physiological conditions and under the influence of bisphenol A (BPA)

BACKGROUND

Bisphenol A (BPA) is commonly used in the production of plastics and has multidirectional, negative effects on the living organisms. It may also affect the enteric nervous system (ENS) located in the wall of the gastrointestinal tract. Enteric neurons express many active substances, which regulate majority of intestinal activities not only in physiological conditions but also under the impact of pathological factors.

METHODS

The influence of various doses of BPA on the ENS of jejunum has been investigated using the double immunofluorescence technique. The commercial antibodies against substance P (SP), vasoactive intestinal polypeptide (VIP), galanin (GAL), vesicular acetylcholine transporter (VAChT), and cocaine- and amphetamine-regulated transcript peptide (CART) were used.

KEY RESULTS

Both doses of BPA studied changed the number of the enteric neurons immunoreactive to SP, VIP, GAL, VAChT, and CART, and the intensity of fluctuations depended on the BPA dose and on the type of the enteric plexus. Bisphenol A causes the increase in the number of neurons immunoreactive to the majority of substances studied. The only exception was VAChT-positive neurons, the number of which was lower under the impact of BPA in the comparison with physiological conditions.

CONCLUSIONS & INFERENCES

Even low doses of BPA cause the changes in neurochemical characterization of the enteric neurons in the jejunum. These changes may be the first sign of subclinical BPA intoxication. The mechanisms of observed changes are probably connected with neurotoxic and/or pro-inflammatory activity of BPA, but their exact mechanisms are not fully explained.

Rapid effect of bisphenol A on glutamate-induced Ca2+ influx in hippocampal neurons of rats

Intracellular Ca²⁺ signaling plays an essential role in synaptic plasticity. This study examined the effect of BPA on concentration of intracellular Ca²⁺ ([Ca²⁺]_i) by measuring fluorescence intensity of Ca²⁺ in hippocampal neurons in vitro. The results showed that BPA for 30 min exerted dose-dependently dual effects on glutamate-elevated [Ca²⁺]_i: BPA at 1-10 μM suppressed but at 1-100 nM enhanced glutamate-raised [Ca²⁺]_i. BPA-potentiated [Ca²⁺]_i was blocked by the antagonist of NMDA receptor and was eliminated by an estrogen-related receptor gamma (ERRγ) antagonist rather than an AR antagonist. Both inhibitors of MAPK/ERKs and MAPK/p38 blocked BPA-enhanced [Ca²⁺]_i. Co-treatment of BPA with 17β-E₂ or DHT eliminated the enhancement of 17β-E₂, DHT, and BPA in glutamate-elevated [Ca²⁺]_i. These results suggest that BPA at nanomole level rapidly enhances Ca²⁺ influx through NMDA receptor by ERRγ-mediated MAPK/ERKs and MAPK/p38 signaling pathways. However, BPA antagonizes both estrogen and androgen enhancing NMDA receptor-mediated Ca²⁺ influx in hippocampal neurons.

The effects of Bisphenol A (BPA) on sympathetic nerve fibers in the uterine wall of the domestic pig

Bisphenol A (BPA), used in the production of plastic, shows multidirectional negative effects on the living organism. BPA may affect the reproductive and nervous systems; however, its influence on the nerves supplying the uterus has not been studied. During the present study, the impact of BPA on the sympathetic nerves in the uterus was investigated using a double immunofluorescence technique. The results have shown that even low doses of BPA may change the neurochemical characterization of uterine sympathetic nerves, and the severity of these changes depends on the part of the uterus and the dose of the toxic substance. Probably the changes observed during the present study resulted from the neurotoxic and/or pro-inflammatory activity of BPA, but the exact mechanism for the observed fluctuation still remains unknown. The fluctuations of the neurochemical characterization of the uterine intramural nerves may be the first subclinical signs of harmful exposure to BPA.

The Influence of Bisphenol A (BPA) on Neuregulin 1-Like Immunoreactive Nerve Fibers in the Wall of Porcine Uterus

Bisphenol A (BPA), a substance commonly used in the manufacture of plastics, shows multidirectional negative effects on humans and animals. Due to similarities to estrogens, BPA initially leads to disorders in the reproductive system. On the other hand, it is known that neuregulin 1 (NRG-1) is an active substance which enhances the survivability of cells, inhibits apoptosis, and protects tissues against damaging factors. Because the influence of BPA on the nervous system has also been described, the aim of the present study was to investigate for the first time the influence of various doses of BPA on neuregulin 1-like immunoreactive (NRG-1-LI) nerves located in the porcine uterus using the routine single- and double-immunofluorescence technique. The obtained results have shown that BPA increases the number and affects the neurochemical characterization of NRG-1-LI in the uterus, and changes are visible even under the impact of small doses of this toxin. The character of observed changes depended on the dose of BPA and the part of the uterus studied. These observations suggest that NRG-1 in nerves supplying the uterus may play roles in adaptive and protective mechanisms under the impact of BPA.

Nitric oxide as an active substance in the enteric neurons of the porcine digestive tract in physiological conditions and under intoxication with bisphenol A (BPA)

Bisphenol A (BPA) is an organic substance, which is commonly used in the production of plastic. It is known that BPA has the negative impact on the living organism, affecting among others the reproductive organs, nervous, endocrine and immune systems. Nevertheless the knowledge about the influence of BPA on the enteric nervous system (ENS) is extremely scanty. On the other hand, nitric oxide is considered to be one of the most important neuronal factors in the ENS. The aim of the study was to investigate the influence of low and high doses of BPA on neuronal isoform nitric oxide synthase - like immunoreactive (nNOS-LI) nervous structures in the various parts of the porcine gastrointestinal (GI) tract using double immunofluorescence technique. The obtained results show that BPA affects nNOS-LI enteric neurons and nerve fibers, and the character and severity of observed changes depend on the fragment of the gastrointestinal tract, part of the ENS and dose of the toxin. It should be pointed out that even relatively low doses of BPA (0.05 mg/kg body weight/day) are not neutral for the organism and may change the number of nitrergic nervous structures in the stomach and intestine. Observed changes are probably connected with neurotoxic activity of BPA, but the exact mechanisms of them still remain unclear.

Bisphenol-A and Nonylphenol Induce Apoptosis in Reproductive Tract Cancer Cell Lines by the Activation of ADAM17

Endocrine-disruptor chemicals (EDCs), such as bisphenol A (BPA) and nonylphenol (NP), have been widely studied due to their negative effects on human and wildlife reproduction. Exposure to BPA or NP is related to cell death, hormonal deregulation, and cancer onset. Our previous studies showed that both compounds induce A Disintegrin And Metalloprotease 17 (ADAM17) activation. Here, we show that BPA and NP induce apoptosis in prostate and ovary cancer cell lines, in a process dependent on ADAM17 activation. ADAM17 knockdown completely prevented apoptosis as well as the shedding of ADAM17 substrates. Both compounds were found to induce an increase in intracellular calcium (Ca²⁺) only in Ca²⁺-containing medium, with the NP-treated cells response being more robust than those treated with BPA. Additionally, using a phosphorylated protein microarray, we found that both compounds stimulate common intracellular pathways related to cell growth, differentiation, survival, and apoptosis. These results suggest that BPA and NP could induce apoptosis through ADAM17 by activating different intracellular signaling pathways that may converge in different cellular responses, one of which is apoptosis. These results confirm the capacity of these compounds to induce cell apoptosis in cancer cell lines and uncover ADAM17 as a key regulator of this process in response to EDCs.

The Influence of High and Low Doses of Bisphenol A (BPA) on the Enteric Nervous System of the Porcine Ileum

Bisphenol A, used in the production of plastic, is able to leach from containers into food and cause multidirectional adverse effects in living organisms, including neurodegeneration and metabolic disorders. Knowledge of the impact of BPA on enteric neurons is practically non-existent. The destination of this study was to investigate the influence of BPA at a specific dose (0.05 mg/kg body weight/day) and at a dose ten times higher (0.5 mg/kg body weight/day), given for 28 days, on the porcine ileum. The influence of BPA on enteric neuron immunoreactive to selected neuronal active substances, including substance P (SP), vasoactive intestinal polypeptide (VIP), galanin (GAL), vesicular acetylcholine transporter (VAChT—used here as a marker of cholinergic neurons), and cocaine- and amphetamine-regulated transcript peptide (CART), was studied by the double immunofluorescence method. Both doses of BPA affected the neurochemical characterization of the enteric neurons. The observed changes depended on the type of enteric plexus but were generally characterized by an increase in the number of cells immunoreactive to the particular substances. More visible fluctuations were observed after treatment with higher doses of BPA. The results confirm that even low doses of BPA may influence the neurochemical characterization of the enteric neurons and are not neutral for living organisms.

Acute effect of bisphenol A: Signaling pathways on calcium influx in immature rat testes

We investigated the acute effect of low concentrations of BPA on calcium influx and the mechanism of action of BPA in this rapid response in the rat testis. BPA increased calcium influx at 1 pM and 1 nM at 300 s of incubation, in a similar manner to that of estradiol. At 1 pM, BPA stimulated calcium influx independently of classical estrogen receptors, consistent with a G-protein coupled receptor. This effect also involves the modulation of ionic channels, such as K⁺, TRPV1 and Cl^- channels. Furthermore, BPA is able to modulate calcium from intracellular storages by inhibiting SERCA and activating IP₃ receptor/Ca²⁺ channels at the endoplasmic reticulum and activate kinase proteins, such as PKA and PKC. The rapid responses of BPA on calcium influx could, in turn, trigger a cross talk by MEK and p38^MAPK activation and also mediate genomic responses.

Divergent Mechanisms Leading to Signaling Dysfunction in Embryonic Muscle by Bisphenol A and Tetrabromobisphenol A

Bisphenol A (BPA) and its brominated derivative tetrabromobisphenol A (TBBPA) are high production volume chemicals used in the manufacture of various consumer products. Although regarded as endocrine disruptors, these chemicals are suspected to exert nongenomic actions on muscle function that are not well understood. Using skeletal muscle microsomes, we examined the effects of BPA and TBBPA on ryanodine receptor type 1 (RyR1), dihydropyridine receptor (DHPR), and sarcoplasmic/endoplasmic reticulum Ca2+ ATPase (SERCA). We assessed the impact of these chemicals on Ca2+ dynamics and signaling in embryonic skeletal myotubes through fluorescent Ca2+ imaging and measurement of resting membrane potential (Vm). TBBPA activated RyR1 and inhibited DHPR and SERCA, inducing a net efflux of Ca2+ from loaded microsomes, whereas BPA exhibited little or no activity at these targets. Regardless, both compounds disrupted the function of intact myotubes. TBBPA diminished and eventually abrogated Ca2+ transients, altered intracellular Ca2+ equilibrium, and caused Vm depolarization. For some cells, BPA caused rapid Ca2+ transient loss without marked changes in cytosolic and sarcoplasmic reticulum Ca2+ levels, likely owing to altered cellular excitability as a result of BPA-induced Vm hyperpolarization. BPA and TBBPA both interfere with skeletal muscle function through divergent mechanisms that impair excitation-contraction coupling and may be exemplary of their adverse outcomes in other muscle types.

Bisphenol A, Dichlorodiphenyltrichloroethane (DDT) and Vinclozolin Affect ex-vivo Uterine Contraction in Rats via Uterotonin (Prostaglandin F2α, Acetylcholine and Oxytocin) Related Pathways

Bisphenol-A (BPA), dichrolodiphenyltrichloroethane (DDT) and vinclozolin were found able to induce abnormal uterine contraction. The mechanisms involved remains unclear. We hypothesized that the effect of these compounds were mediated via the uterotonin pathways. Therefore, in this study, effects of BPA, vinclozolin and DDT-only and in combination with uterotonins (PGF-2α, acetylcholine and oxytocin) on the force and pattern of uterine contraction were observed.

METHODS

Uteri were harvested from intact adult female rats 24 hours after a single injection (1 mg/kg/b.w) of estrogen to synchronize their oestrous cycle. The uterine horns were subjected for ex-vivo contraction studies in an organ bath connected to Powerlab data acquisition system. Different doses of BPA, vinclozolin and DDT were added into the bathing solution and changes in the pattern and strength of uterine contraction were recorded. Further, increasing doses of uterotonins were concomitantly administered with these compounds and changes in the force and pattern of contraction were observed.

RESULTS

In the absence of uterotonins, uterine contractile force decreased with increasing doses of BPA and DDT. However, vinclozolin induced sharp increase in the contractile forces which then gradually decrease. Administration of BPA, DDT and vinclozolin alone reduced the force of uterine contraction following stimulation of contraction by uterotonins. However, BPA, vinclozolin or DDT effects were relieved upon co-administration with uterotonins at increasing doses.

CONCLUSIONS

The antagonizing effect of uterotonins on BPA, vinclozolin and DDT actions could explain the mechanism underlying the adverse effect of these compounds on uterine contraction.

Modulation of oxidative stress and Ca(2+) mobilization through TRPM2 channels in rat dorsal root ganglion neuron by Hypericum perforatum

A main component of St. John's Wort (Hypericum perforatum, HP) is hyperforin which has antioxidant properties in dorsal root ganglion (DRG) neurons, due to its ability to modulate NADPH oxidase and protein kinase C. Recent reports indicate that oxidative stress through NADPH oxidase activates TRPM2 channels. HP may be a useful treatment for Ca(2+) entry and oxidative stress through modulation of TRPM2 channels in the DRG. We aimed to investigate the protective role of HP on Ca(2+) entry and oxidative stress through TRPM2 channels in DRG neurons of rats. The native rat DRG neurons were used in whole-cell patch-clamp, Fura-2 and antioxidant experiments. Appropriate, nontoxic concentrations and incubation times for HP were determined in the DRG neurons by assessing cell viability. The H2O2-induced TRPM2 currents were inhibited by 2-aminoethyl diphenylborinate (2-APB) and N-(p-amylcinnamoyl)anthranilic acid (ACA). TRPM2 current densities and cytosolic free Ca(2+) concentration in the neurons were also reduced by HP (2 and 24h). In Fura-2 experiments, cytosolic Ca(2+) mobilization was reduced by voltage-gated calcium channel blockers (verapamil+diltiazem, V+D) and HP. Glutathione peroxidase activity and GSH values in the DRG were high in HP, 2-APB and V+D groups although lipid peroxidation level was low in the groups. In conclusion, we observed a protective role for HP on Ca(2+) entry through a TRPM2 channel in the DRG neurons. Since over-production of oxidative stress and Ca(2+) entry are implicated in the pathophysiology of neuropathic pain and neuronal inflammation, our findings may be relevant to the etiology and treatment of neuropathology in DRG neurons.