Formation of hydroxylated polybrominated diphenyl ethers from laccase-catalyzed oxidation of bromophenols

Metabolite Profiling of Macroalgae: Biosynthesis and Beneficial Biological Properties of Active Compounds

Macroalgae are known as abundant sources of phytochemicals, which offer a plethora of beneficial biological properties. Besides being the most notable classes of compounds found in macroalgae, phlorotannins, bromophenols, and terpenoids comprise some of the most relevant for their biological properties. Phlorotannins, mainly prevalent in brown algae and structurally characterized as complex polyphenolic compounds derived from phloroglucinol units, possess robust antioxidant, anti-inflammatory, antitumor, and cytotoxic activities, modulated by factors such as the degree of polymerization and environmental conditions. Bromophenols, halogenated compounds found in algae and other marine organisms, exhibit significant antioxidant and antiviral properties. Their diverse structures and bromination patterns contribute to their potential as therapeutic and chemical defense agents. Pigments (chemically described as primary terpenoids) play a critical role in light absorption and energy transfer in macroalgae and are divided into three main groups: (i) carotenoids, which are primarily found in brown algae and provide photoprotective and antioxidant benefits; (ii) chlorophylls, known for facilitating the conversion of light into biological energy; and (iii) phycobilins, which are mostly found in red algae and play important roles in light absorption and energy transfer, besides providing remarkable health benefits. Finally, secondary terpenoids, which are particularly abundant in red algae (e.g., the Rhodomelaceae family) are central to cellular interactions and exhibit significant antioxidant, antimicrobial, antidiabetic, and anti-inflammatory properties. This study represents a detailed analysis of the biosynthesis, structural diversity, and biological activities of these macroalgae metabolites, emphasizing their potential biological properties.

Nitrite facilitated transformation of halophenols in ice

This study investigated the expediated transformation of halophenols in the presence of nitrite (NO2-) under slightly acidic conditions in ice, whereas such transformation was negligible in liquid water at 4 °C. We proposed that this phenomenon was attributed to the freeze-concentration effect, incurring a pH drop and the aggregation of NO2- and halophenols within the liquid-like grain boundary layer amid ice crystals. Within this micro-environment, NO2- underwent protonation to generate reactive nitrous acid (HNO2) and nitrosonium ions (NO+) that facilitate the nitration and oxidation of halophenols. When 10 μМ halophenol was treated by freezing in the presence of 5 μМ NO2-, the total yields of nitrated products reached 2.4 μМ and 1.4 μМ within 12 h for 2-chlorophenol (2CP) and 2-bromophenol (2BP), respectively. NO+ drove oxidative coupling reactions, generating hydroxyl polyhalogenated diphenyl ethers (OH-PBDEs) and hydroxyl polyhalogenated diphenyls via C-O or C-C coupling. These two pathways were intricately intertwined. The presence of natural organic matter (NOM) mitigated the formation of nitrated products and completely suppressed the coupling products. This study offers valuable insights into the fate of halophenols in ice and suggests potential pathways for the formation of nitrophenolic compounds and OH-PBDEs in natural cold environments. These findings also open up a new avenue in environmental chemistry research.

Exploring the biosynthetic possibilities of hydroxylated polybrominated diphenyl ethers from bromophenols in Prorocentrum donghaiense: Implications for bioremediation

Bromophenols has been proven to synthesize hydroxylated polybrominated diphenyl ethers (OH-PBDEs), which may pose additional environmental and health risks in the process of bioremediation. In this study, the removal of 2,4-dibromophenol (2,4-DBP) and 2,4,6-tribromophenol (2,4,6-TBP) and the biosynthetic of OH-PBDEs by Prorocentrum donghaiense were explored. The removal efficiencies of 2,4-DBP and 2,4,6-TBP ranged from 32.71% to 76.89% and 31.15%-78.12%, respectively. Low concentrations of 2,4-DBP stimulated algal growth, while high concentrations were inhibitory. Furthermore, exposure to 10.00 mg L-1 2,4-DBP resulted in the detection of 2'-hydroxy-2,3',4,5'-tetrabromodiphenyl ether (2'-OH-BDE-68) within P. donghaiense. In contrast, increasing concentrations of 2,4,6-TBP considerably inhibited P. donghaiense growth, with 4'-hydroxy-2,3',4,5',6-pentabromodiphenyl ether (4'-OH-BDE-121) detected within P. donghaiense under 5.00 mg L-1 2,4,6-TBP. Metabolomic analysis further revealed that the synthesized OH-PBDEs exhibited higher toxicity than their precursors and identified the oxidative coupling as a key biosynthetic mechanism. These findings confirm the capacity of P. donghaiense to remove bromophenols and biosynthesize OH-PBDEs from bromophenols, offering valuable insights into formulating algal bioremediation to mitigate bromophenol contamination.

A review on environmental occurrence, toxic effects and transformation of man-made bromophenols

Brominated phenols (BPs) of anthropogenic origin are aromatic substances widely used in the industry as flame retardants (FRs) and pesticides as well as the components of FRs and polymers. In this review, we have focused on describing 2,4-dibromophenol (2,4-DBP), 2,4,6-tribromophenol (2,4,6-TBP) and pentabromophenol (PBP), which are the most commonly used in the industry and are the most often detected in the air, aquatic and terrestrial ecosystems and the human body. This review describes human-related sources of these BPs that influence their occurrence in the environment (atmosphere, surface water, sediment, soil, biota), indoor air and dust, food, drinking water and the human organism. Data from in vitro and in vivo studies showing 2,4-DBP, 2,4,6-TBP and PBP toxicity, including their estrogenic activity, effects on development and reproduction, perturbations of cellular redox balance and cytotoxic action have been described. Moreover, the processes of BPs transformation that occur in human and other mammals, plants and bacteria have been discussed. Finally, the effect of abiotic factors (e.g. UV irradiation and temperature) on BPs conversion to highly toxic brominated dioxins and brominated furans as well as polybrominated biphenyls and polybrominated diphenyl ethers has been presented.

Thyroid Dysfunction of Zebrafish (Danio rerio) after Early-Life Exposure and Discontinued Exposure to Tetrabromobiphenyl (BB-80) and OH-BB-80

3,3',5,5'-Tetrabromobiphenyl (BB-80) was once used as additive flame retardants. Whether its early exposure and discontinued exposure alter thyroid function remains unknown. We investigate adverse effects after early-life exposure and discontinued exposure to BB-80 and hydroxylated BB-80 (OH-BB-80) on thyroid hormone (TH) levels, thyroid tissue, and transcriptome profiles in zebrafish larvae. BB-80 at 10 μg/L induces pathological changes of thyroid with reduced thyroid follicles in larvae (P < 0.05), whereas OH-BB-80 significantly increases T4 and T3 contents (1.8 and 2.5 times of the control, P < 0.05) at 14 days postfertilization (dpf) without morphological thyroid alterations. BB-80 and OH-BB-80 cause transcriptome aberrations with key differentially expressed genes involved in the disruption of TH synthesis and signal transduction (BB-80 at 14 dpf) or TH pathway activation (OH-BB-80 at 21 dpf). After 7 days of discontinued exposure, thyroglobulin (tg) and thyroid peroxidase (tpo) genes are downregulated (P < 0.05) by 52 and 48% for BB-80 and by 49 and 39% for OH-BB-80, respectively; however, the whole-body TH levels fail to fully recover, and the locomotor activity is impaired more by BB-80. Our results indicate significant adverse impacts of BB-80 and OH-BB-80 on TH homeostasis and thyroid function of zebrafish.

Progress of Bromophenols in Marine Algae from 2011 to 2020: Structure, Bioactivities, and Applications

Marine algae contain various bromophenols that have been shown to possess a variety of biological activities, including antiradical, antimicrobial, anticancer, antidiabetic, anti-inflammatory effects, and so on. Here, we briefly review the recent progress of these marine algae biomaterials and their derivatives from 2011 to 2020, with respect to structure, bioactivities, and their potential application as pharmaceuticals.

Degradation of 2,2',4,4'-tetrabromodiphenyl ether by Pycnoporus sanguineus in the presence of copper ions

The degradation of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) by Pycnoporus sanguineus was investigated in order to explore the impact of the heavy metal Cu²⁺ on BDE-47 decomposition and the subsequent formation of metabolites, as well as to further elucidate the degradation mechanism of BDE-47. An increase in degradation rate from 18.63% to 49.76% in the first four days and its stabilization at (51.26 ± 0.08)% in the following days of BDE-47 incubation were observed. The presence of Cu²⁺ at 1 and 2 mg/L was found to promote the degradation rate to 56.41% and 60.79%, respectively, whereas higher level of Cu²⁺ (≥5 mg/L) inhibited the removal of BDE-47. The similar concentration effects of Cu²⁺ was also found on contents of fungal protein and amounts of metabolites. Both intracellular and extracellular enzymes played certain roles in BDE-47 transportation with the best degradation rate at 27.90% and 27.67% on the fourth and third day, individually. During the degradation of BDE-47, four types of hydroxylated polybrominated diphenyl ethers (OH-PBDEs), i.e., 6'-OH-BDE-47, 5'-OH-BDE-47, 4'-OH-BDE-17, 2'-OH-BDE-28, and two bromophenols, i.e., 2,4-DBP and 4-BP were detected and considered as degradation products. These metabolites were further removed by P. sanguineus at rates of 22.42%, 23.01%, 27.04%, 27.96%, 64.21%, and 40.62%, respectively.

Activation of ferrate by carbon nanotube for enhanced degradation of bromophenols: Kinetics, products, and involvement of Fe(V)/Fe(IV)

Very recently, several studies have found that homogeneous reducing agents (e.g., sodium thiosulfate (Na₂S₂O₃), and sodium sulfite (Na₂SO₃)) can activate ferrate to enhance the degradation of selected contaminants. In this work, it was found that heterogeneous carbon nanotube (CNT) could accelerate ferrate (Fe(VI)) for the degradation of bromophenols (BrPs) of environmental concerns and alleviate the appearance of undesired by-products in effluent. Fe(VI) could react with BrPs over a wide pH range of 6-10 with apparent second-order rate constants of 1.8-1850 M^-1 s^-1. Electrospray ionization-triple quadrupole mass spectrometry (ESI-QqQMS) analysis showed that dibrominated dihydroxylated biphenyls and dibrominated phenoxyphenols were possibly formed via coupling reaction of BrPs radicals generated from Fe(VI) oxidation through one-electron transfer. The presence of CNT could remarkably accelerate the degradation rates of BrPs by Fe(VI) in a wide pH range from 7 to 10. Moreover, the formed undesired polybrominated products during Fe(VI)/CNT oxidation were absorbed on CNT surface and thus removed from treated water. The Fe(VI)/CNT system was capable of selectively oxidizing electron-rich pollutants (e.g., BrPs, and sulfamethoxazole (SMX)), but reluctant to iopamidol (IPM) and nitrobenzene (NB). High-valent metal-oxo intermediates Fe(V)/Fe(IV) formed in situ from the reaction of CNT with Fe(VI) were likely responsible for this activation effect of CNT, which was further confirmed via using methyl phenyl sulfoxide (PMSO) as a probe compound. Comparatively, homogeneous reducing agent Na₂S₂O₃ could enhance Fe(VI) degradation of BrPs at pH 7 and 8, while undesired polybrominated products were detected in effluent from Fe(VI)/Na₂S₂O₃ system. These findings have crucial implications for the development of a promising oxidation process by combination of Fe(VI) and CNT for water and wastewater treatment.

Formation of 1,3,8-tribromodibenzo-p-dioxin and 2,4,6,8-tetrabromodibenzofuran in the oxidation of synthetic hydroxylated polybrominated diphenyl ethers by iron and manganese oxides under dry conditions

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) are ubiquitous and highly toxic emerging endocrine disruptors found in surface and subsurface soils and clay deposits. Seriously, they could be easily transformed to the more toxic dioxins (PBDD/Fs) in photochemical processes and incineration, but the spontaneous formation of PBDD/Fs has rarely been reported. This study focused on the formation of 1,3,8-tribromodibenzo-p-dioxin (1,3,8-TrBDD) and 2,4,6,8-tetrabromodibenzofuran (2,4,6,8-TeBDF) from 2'-OH-BDE-68 and 2,2'-diOH-BB-80 under the oxidization of iron and manganese oxides (goethite and MnO_x). Approximately 0.09 μmol/kg (2.33%) and 0.17 μmol/kg (4.15%) were transformed to 1,3,8-TrBDD and 2,4,6,8-TeBDF by goethite in 8 days and a higher conversion 0.15 μmol/kg (3.77%) and 0.23 μmol/kg (5.74%) were observed for MnO_x in 4 days. However, the formation of PBDD/Fs, probably proceeding via Smiles rearrangements and bromine elimination processes, was greatly inhibited by the presence of water. Transformation of OH-PBDEs by goethite and MnO_x was accompanied by release of Fe and Mn ions and the possible pathways for the formation of reaction products were proposed. In view of the ubiquity of OH-PBDEs and metal oxides in the environment, oxidation of OH-PBDEs mediated by goethite and MnO_x is likely an abiotic route for the formation of PBDD/Fs.

Metabolic profiling on the effect of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) in MCF-7 cells

Polybrominated diphenyl ethers (PBDEs) are commonly used to prevent the development of fire in various factory products. Due to the adverse effects on human health and the bio-accumulation capacity, PBDEs are considered as one kind of persistent organic pollutants (POPs). BDE-47 is one of the most frequently detected PBDEs congeners in human samples. Although numerous studies have shown the close connection between BDE-47 and human health, few reports were related to breast carcinoma. In the present study, the toxicity mechanism of BDE-47 was investigated by using MCF-7 breast cancer cells. Metabolomics analysis was conducted by using ultra-high performance liquid chromatography coupled with mass spectrometry (UHPLC-MS). Results showed that the toxicity to MCF-7 cells gradually increased when the concentration of BDE-47 exceeded 1 μM in the medium with 1% fetal bovine serum (FBS). It was found that pyrimidine metabolism, purine metabolism and pentose phosphate pathway (PPP) were the most influenced metabolic pathways, and the metabolites in the three metabolic pathways were significantly downregulated. Moreover, the increase of reactive oxygen species (ROS) was detected by using the 2',7'-dichlorodihydrofluorescein diacetate (DCFH-DA) staining method. The obtained results suggested that the BDE-47 induced oxidative stress by downregulating the NADPH generation in PPP. The pyrimidine metabolism and purine metabolism might be downregulated by the downregulation of mRNA transcripts. Therefore, BDE-47 could induce oxidative stress by inhibiting PPP and disorder the metabolism of the entire cell subsequently. This research provided evidence for investigating mechanism of the adverse effect of BDE-47 on human health.

Biosynthesis of hydroxylated polybrominated diphenyl ethers and the correlation with photosynthetic pigments in the red alga Ceramium tenuicorne

Hydroxylated polybrominated diphenyl ethers (OH-PBDEs) have been identified in a variety of marine organisms from different trophic levels indicating a large spread in the environment. There is much evidence pointing towards natural production as the major source of these compounds in nature. However, much is still not known about the natural production of these compounds. Seasonal trend studies have shown large fluctuations in the levels of OH-PBDEs in Ceramium tenuicorne from the Baltic Sea. Yet, even though indications of stimuli that can induce the production of these compounds have been observed, none, neither internal nor external, has been assigned to be responsible for the recorded fluctuations. In the present study the possible relationship between the concentration of pigments and that of OH-PBDEs in C. tenuicorne has been addressed. Significant correlations were revealed between the concentrations of all OH-PBDEs quantified and the concentrations of both chlorophyll a and Σxanthophylls + carotenoids. All of which displayed a concentration peak in mid-July. The levels of OH-PBDEs may be linked to photosynthetic activity, and hence indirectly to photosynthetic pigments, via bromoperoxidase working as a scavenger for hydrogen peroxide formed during photosynthesis. Yet the large apparent investment in producing specific OH-PBDE congeners point towards an targeted production, with a more specific function than being a waste product of photosynthesis. The OH-PBDE congener pattern observed in this study is not agreeable with some currently accepted models for the biosynthesis of these compounds, and indicates a more selective route than previously considered in C. tenuicorne.