Oxidation of bisphenol A and related compounds

Bisphenols and Oxidative Stress Biomarkers-Associations Found in Human Studies, Evaluation of Methods Used, and Strengths and Weaknesses of the Biomarkers

Bisphenols, particularly bisphenol A (4,4'-(hexafluoroisopropylidene)-diphenol) (BPA), are suspected of inducing oxidative stress in humans, which may be associated with adverse health outcomes. We investigated the associations between exposure to bisphenols and biomarkers of oxidative stress in human studies over the last 12 years (2008‒2019) related to six health endpoints and evaluated their suitability as effect biomarkers. PubMed database searches identified 27 relevant articles that were used for data extraction. In all studies, BPA exposure was reported, whereas some studies also reported other bisphenols. More than a dozen different biomarkers were measured. The most frequently measured biomarkers were 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-OHdG), 8-iso-prostaglandin F2α (8-isoprostane) and malondialdehyde (MDA), which almost always were positively associated with BPA. Methodological issues were reported for MDA, mainly the need to handle samples with caution to avoid artefact formation and its measurements using a chromatographic step to distinguish it from similar aldehydes, making some of the MDA results less reliable. Urinary 8-OHdG and 8-isoprostane can be considered the most reliable biomarkers of oxidative stress associated with BPA exposure. Although none of the biomarkers are considered BPA- or organ-specific, the biomarkers can be assessed repeatedly and non-invasively in urine and could help to understand causal relationships.

Genotoxic activity of bisphenol A and its analogues bisphenol S, bisphenol F and bisphenol AF and their mixtures in human hepatocellular carcinoma (HepG2) cells

The use of bisphenol A (BPA) in manufacturing of plastics is being gradually replaced by presumably safer analogues such as bisphenol S (BPS), bisphenol F (BPF) and bisphenol AF (BPAF). Despite their widespread occurrence in the environment, there is a knowledge gap in their toxicological profiles. We investigated cytotoxic/genotoxic effects as well as changes in the expression of selected genes involved in the xenobiotic metabolism, response to oxidative stress and DNA damage upon exposure to BPs and their mixtures in human hepatocellular carcinoma HepG2 cells. BPS and BPF slightly decreased the viability of HepG2 cells, while BPAF was the most cytotoxic compound tested. BPA, BPF and BPAF induced the formation of DNA double strand breaks determined with γH2AX assay, while BPS was inactive (5-20 μg/mL). All four BPs up-regulated the expression of CYP1A1 and UGT1A1, while BPS up-regulated and BPAF down-regulated also the expression of GST1A. Only BPA up-regulated oxidative stress responsive gene GCLC, while BPAF up-regulated the expression of CDKN1A and GADD45a. At concentrations relevant for human exposure (ng/mL range) BPA and its analogues as individual compounds and in mixtures did not exert genotoxic activity, whereas BPA and BPAF as well as the mixtures up-regulated the expressions of CYP1A1 and UGT1A1.

Polymer-Coated Mesoporous Carbon as Enzyme Platform for Oxidation of Bisphenol A in Organic Solvents

Bisphenol A (BPA) is not only a widely used chemical but also a toxic pollutant, and its biodegradation in an aqueous environment is hard due to its near insolubility in water. While the enzyme tyrosinase can oxidize BPA in organic solvents, it does so only very slowly. In the present study, we have found that in toluene the catalytic activity of tyrosinase deposited onto coated mesoporous carbon is significantly enhanced when the support is precoated with polyethylenimine. The resultant enzymatically formed o-quinone is both easily recoverable and potentially useful monomer. As a particular example, the o-quinone readily reacts with diamine in toluene to form poly(amino-quinone) polymers, which are suitable for anticorrosion, energy storage, or biosensor applications.

Induction of oxidative stress by bisphenol A and its pleiotropic effects

Bisphenol A (BPA) has become a target of intense public scrutiny since concerns about its association with human diseases such as obesity, diabetes, reproductive disorders, and cancer have emerged. BPA is a highly prevalent chemical in consumer products, and human exposure is thought to be ubiquitous. Numerous studies have demonstrated its endocrine disrupting properties and attributed exposure with cytotoxic, genotoxic, and carcinogenic effects; however, the results of these studies are still highly debated and a consensus about BPA's safety and its role in human disease has not been reached. One of the contributing factors is a lack of molecular mechanisms or modes of action that explain the diverse and pleiotropic effects observed after BPA exposure. The increase in BPA research seen over the last ten years has resulted in more studies that examine molecular mechanisms and revealed links between BPA-induced oxidative stress and human disease. Here, a review of the current literature examining BPA exposure and the induction of reactive oxygen species (ROS) or oxidative stress will be provided to examine the landscape of the current BPA literature and provide a framework for understanding how induction of oxidative stress by BPA may contribute to the pleiotropic effects observed after exposure. Environ. Mol. Mutagen. 58:60-71, 2017. © 2017 Wiley Periodicals, Inc.

Efficient immobilization of mushroom tyrosinase utilizing whole cells from Agaricus bisporus and its application for degradation of bisphenol A

A simple and efficient procedure for preparation and immobilization of tyrosinase enzyme was developed utilizing whole cells from the edible mushroom Agaricus bisporus, without the need for enzyme purification. Tyrosinase activity in the cell preparation remained constant during storage at 21 °C for at least six months. The cells were entrapped in chitosan and alginate matrix capsules and characterized with respect to their resulting tyrosinase activity. A modification of the alginate with colloidal silica enhanced the activity due to retention of both cells and tyrosinase from fractured cells, which otherwise leached from matrix capsules. The observed activity was similar to the activity that was obtained with immobilized isolated tyrosinase in the same material. Mushroom cells in water were susceptible to rapid inactivation, whereas the immobilized cells maintained 73% of their initial activity after 30 days of storage in water. Application in repeated batch experiments resulted in almost 100% conversion of endocrine disrupting bisphenol A (BPA) for 11 days, under stirring conditions, and 50-60% conversion after 20 days, without stirring under continuous usage. The results represent the longest yet reported application of immobilized tyrosinase for degradation of BPA in environmental water samples.

Possible role of laccase from Fusarium incarnatum UC-14 in bioremediation of Bisphenol A using reverse micelles system

Bisphenol A [2,2 bis (4 hydroxyphenyl) propane] is widely used in the variety of industrial and residential applications such as the synthesis of polymers including polycarbonates, epoxy resins, phenol resins, polyesters and polyacrylates. BPA has been recognized as an Endocrine Disrupting Chemicals (EDC), thus it is necessary to assess its biodegradability or fate in the natural environment. In general, environmental pollutant such as BPA does not dissolve in aqueous media, owing to their high hydrophobicity, and hence non-aqueous catalysis can be employed to enhance biodegradability of phenolic environmental pollutant. Purified laccase hosted in reverse micelles using ternary system of isooctane: AOT [Bis (2-ethylhexyl) sulphosuccinate sodium salt)]:water having hydration ratio (Wo) of 30 with protein concentration of 43.5 μg/ml was found to eliminate 91.43% of 200 ppm of Bisphenol A at 50 °C, pH-6.0 when incubated with laccase/Reverse Micelles system for 75 min. GC-MS analysis of isooctane soluble fractions detected the presence of 4,4'-(2 hydroxy propane 1,2 diyl) diphenol, bis (4-hydroxylphenyl) butenal and 2-(1-(4-hydroxyphenyl) vinyl) pent-2-enal indicated degradation of BPA by two oxidation steps and one ring opening step (C-C bond cleavage). Laccase/RM system exhibited several advantages for the oxidative degradation of hydrophobic phenols mainly because of the solubility of either enzyme or substrate was improved in organic media and the stable activity of laccase in organic media was achieved.

How safe is bisphenol A? Fundamentals of toxicity: metabolism, electron transfer and oxidative stress

The FDA recently announced concern about the safety of bisphenol A (BPA) and the need for more research. In the current controversy, scant attention is being paid to toxicity at the fundamental, molecular level, which is the topic of this report. Important information is provided by extensive studies on metabolism. The principal pathway is detoxification, mainly by conjugation leading to a glucuronide. A minor route entails oxidation by hydroxylation to a catechol followed by further transformation to an o-quinone. The catechol-o-quinone couple is capable of redox cycling with generation of reactive oxygen species (ROS) and oxidative stress (OS). o-Quinones are highly electron affinic with very favorable reduction potentials that permit electron transfer (ET) under physiological conditions. Only small amounts are sufficient to generate large quantities of ROS catalytically. There is extensive evidence for production of ROS, which buttresses ET by o-quinone as a plausible source. In addition, there are numerous reports on toxicity to body constituents by BPA. Those adversely affected include the liver, DNA, genes, CNS, reproductive system and kidney. Since a plethora of prior studies links ROS-OS with toxicity, it is reasonable to propose a similar connection for BPA. Cell signaling also plays a role. There are various other factors involved with toxic responses, including age, with the fetus and infants being the most vulnerable. A report concludes that human exposure to BPA is not negligible. The present overview represents a novel, integrated approach to BPA toxicity. A similar article was recently published in this journal which deals with toxicity of prevalent phthalate plasticizers.

Determination of optimum process parameters for peroxidase-catalysed treatment of bisphenol A and application to the removal of bisphenol derivatives

Systematic investigations were carried out to determine the optimum process parameters such as the hydrogen peroxide (H2O2) concentration, concentration and molar mass of poly(ethylene glycol) (PEG) as an additive, pH value, temperature and enzyme dose for treatment of bisphenol A (BPA) with horseradish peroxidase (HRP). The HRP-catalysed treatment of BPA was effectively enhanced by adding PEG, and BPA was completely converted into phenoxy radicals by HRP dose of 0.10 U/cm3. The optimum conditions for HRP-catalysed treatment of BPA at 0.3 mM was determined to be 0.3 mM for H2O2 and 0.10 mg/cm3 for PEG with a molar mass of 1.0 x 10(4) in a pH 6.0 buffer at 30 degrees C. Different kinds of bisphenol derivatives were completely or effectively treated by HRP under the optimum conditions determined for treatment of BPA, although the HRP dose was further increased as necessary for some of them. The aggregation of water-insoluble oligomers generated by the enzymatic radicalization and radical coupling reaction was enhanced by decreasing the pH values to 4.0 with HCl after the enzymatic treatment, and BPA and bisphenol derivatives were removed from aqueous solutions by filtering out the oligomer precipitates.

Removal of phenolic endocrine disruptors by Portulaca oleracea

Portulaca oleracea, a garden plant prevalent from spring to autumn in Japan, showed the ability to efficiently remove from water bisphenol A (BPA), which is well known as an endocrine disrupting compound (EDC) having estrogenic properties. In water culture, 50 muM BPA was almost completely removed within 24 h when the ratio of whole plant weight to the water volume was set up at 1 g to 25 ml. The estrogenic activity of the water decreased in parallel with the elimination of BPA. This plant also rapidly removed other EDCs having a phenol group including octylphenol (OP), nonylphenol (NP), 2,4-dichlorophenol (2,4-DCP) and 17beta-estradiol and, thereby, removed the endocrine disrupting activities. In addition, the ability of P. oleracea to remove BPA was not affected by BPA concentration (up to 250 microM), by cultivation in the dark, by temperatures ranging from 15 degrees C to 30 degrees C, or by pH ranging from 4 to 7. Moreover, the ability of P. oleracea to individually remove BPA, NP, and OP was the same as when they were all present. These results suggest that P. oleracea is a promising material for practical phytoremediation of landfill leachates and industrial wastewater contaminated with the tested EDCs.

Adsorption of bisphenol A by lactic acid bacteria, Lactococcus, strains

Ten strains of the genus Lactococcus were examined for their ability to remove bisphenol A [2, 2-bis(4-hydroxyphenyl)propane; BPA], which is known as an endocrine disrupter. Nine strains of the lactococci tested could remove BPA from media during growth, although the removal ratio was below 9%. When BPA was incubated with lyophilized cells of lactococci for 1 h, the concentration of BPA in the media was decreased by 9-62%. Especially, the highest removal ratio of BPA was observed for Lactococcus lactis subsp. lactis 712. The lactococci could adsorb BPA but not degrade it, because the lactococci maintained the ability to remove BPA from the medium after autoclaving. When the lyophilized cells of L. lactis subsp. lactis 712 were also incubated with six analogues of BPA, they effectively adsorbed hydrophobic compounds such as 2, 2'-diphenylpropane and bisphenol A dimethylether. The BPA-adsorbing ability of lactococci could be due to the hydrophobic binding effect. The removal ratio of BPA by L. lactis subsp. lactis 712 was increased after treatment with sodium dodecyl sulfate and decreased after digestion with trypsin. These results suggest that the hydrophobic proteins on cell surface may be involved in the BPA-adsorbing ability of lactococci.

Gender differences in the levels of bisphenol A metabolites in urine

The metabolism of bisphenol A (BPA), a suspected endocrine disruptor, should be considered for monitoring human exposure to BPA, because the conjugation with beta-D-glucuronide and sulfate reduces the estrogenic activity. In this study, BPA levels in 30 healthy Koreans (men, N=15, 42.6+/-2.4 years; women, N=15, 43.0+/-2.7 years) were analyzed from urine treated with/without beta-glucuronidase and/or sulfatase by an RP-HPLC with fluorescence detection. The total BPA concentrations including free BPA and the urinary conjugates were similar in men and women (2.82+/-0.73 and 2.76+/-0.54 ng ml(-1), respectively), but gender differences were found in the levels of urinary BPA conjugates. Men had significantly higher levels of BPA-glucuronide (2.34+/-0.85 ng ml(-1)) than women (1.00+/-0.34 ng ml(-1)), whereas women had higher levels of BPA-sulfate (1.20+/-0.32 ng ml(-1)) than men (0.49+/-0.27 ng ml(-1)).