Diphenyl Ether Metabolites Research Articles

Isomer Separation of Polybrominated Diphenyl Ether Metabolites using nanoESI-TIMS-MS.

In this paper, high-resolution nano-electrospray ionization-trapped ion mobility spectrometry coupled to mass spectrometry (nESI-TIMS-MS) is used for the study of hydroxylated polybrominated diphenyl ether (OH-PBDE) metabolites. In particular, experimental ion-neutral collision cross sections (CCS) were measured for five structural OH-PBDE isomers using TIMS-MS. Candidate structures were proposed for each IMS band observed in good agreement with the experimental CCS measurements (5% error). The analytical power of TIMS-MS to baseline and partially separate structural isomers of OH-BDE in binary and ternary mixtures is shown for single charge species with a mobility resolving power of RIMS ~ 400. This work provides the proof of concept for the analysis of low concentration OH-PBDE in environmental samples based on accurate collision cross section and mass measurements without the need for derivatization and pre-fractionation protocols, thus significantly reducing the cost and analysis time.

Identification of polybrominated diphenyl ether metabolites based on calculated boiling points from COSMO-RS, experimental retention times, and mass spectral fragmentation patterns.

The COnductor-like Screening MOdel for Realistic Solvents (COSMO-RS) was used to predict the boiling points of several polybrominated diphenyl ethers (PBDEs) and methylated derivatives (MeO-BDEs) of monohydroxylated BDE (OH-BDE) metabolites. The linear correlation obtained by plotting theoretical boiling points calculated by COSMO-RS against experimentally determined retention times from gas chromatography-mass spectrometry facilitated the identification of PBDEs and OH-BDEs. This paper demonstrates the applicability of COSMO-RS in identifying unknown PBDE metabolites of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and 2,2',4,4',6-pentabromodiphenyl ether (BDE-100). Metabolites of BDE-47 and BDE-100 were formed through individual incubations of each PBDE with recombinant cytochrome P450 2B6. Using calculated boiling points and characteristic mass spectral fragmentation patterns of the MeO-BDE positional isomers, the identities of the unknown monohydroxylated metabolites were proposed to be 2'-hydroxy-2,3',4,4'-tetrabromodiphenyl ether (2'-OH-BDE-66) from BDE-47, and 2'-hydroxy-2,3',4,4',6-pentabromodiphenyl ether (2'-OH-BDE-119) and 4-hydroxy-2,2',3,4',6-pentabromodiphenyl ether (4-OH-BDE-91) from BDE-100. The collective use of boiling points predicted with COSMO-RS, and characteristic mass spectral fragmentation patterns provided a valuable tool toward the identification of isobaric compounds.

Synthesis and tentative identification of novel polybrominated diphenyl ether metabolites in human blood

Hydroxylated polybrominated diphenyl ethers (OH-PDBEs) are exogenous, bioactive compounds that originate, to a large extent, from anthropogenic activities, although they are also naturally produced in the environment. In the present study nine new authentic OH-PBDE reference standards and their corresponding methyl ether derivatives (MeO-PBDEs) were synthesised and characterised by NMR spectroscopy and mass spectrometry. Seven of the authentic reference standards prepared were thereafter tentatively identified in a pooled human blood sample. The tentatively identified OH-PBDEs were 3-hydroxy-2,2′,4,4′,6-pentabromodiphenyl ether, 3′-hydroxy-2,2′,4,4′,6-pentabromodiphenyl ether, 3-hydroxy-2,2′,4,4′,5-pentabromodiphenyl ether, 3-hydroxy-2,2′,4,4′,5,6′-hexabromodiphenyl ether, 3′-hydroxy-2,2′,4,4′,5,6′-hexabromodiphenyl ether, 3-hydroxy-2,2′,4,4′,5,5′-hexabromodiphenyl ether and 4-hydroxy-2,2′,3,4′,5,5′,6-heptabromodiphenyl ether. An additional seven OH-PBDEs were tentatively identified in the pooled human blood sample, of which one OH-PBDE, 4′-hydroxy-2,2′,4,5,5′-pentabromodiphenyl ether, has not been identified in human blood before. The identification was performed using gas chromatography–mass spectrometry (GC–MS) recording the bromine ions m/z 79, 81. The tentative identification was supported by the peaks relative retention times (RRTs) compared to authentic references on two GC columns of different polarities for the hexa-, and heptabrominated OH-PBDEs, and three different GC columns for the pentabrominated OH-PBDEs. The OH-PBDE congeners most likely originate from human metabolism of a flame retardant, i.e. polybrominated diphenyl ethers (PBDEs), due to the relatively high concentrations of PBDEs in the same human blood sample and the fact that these PBDEs could form the tentatively identified OH-PBDEs via metabolic direct hydroxylation or via 1,2-shift.

Debrominated and methoxylated polybrominated diphenyl ether metabolites in rainbow trout ( Oncorhynchus mykiss) after exposure to decabromodiphenyl ether

Abstract Decabromodiphenyl ether (BDE209) is the primary component in a commonly used flame retardant. Previous studies had proved that BDE209 itself was not toxic, while its metabolites including debrominated diphenyl ethers (De-BDEs) and methoxylated brominated diphenyl ethers (MeO-BDEs) posed a potential threat to organisms. Many studies had indicated that BDE209 could metabolize quickly in mammals, but lacking in the basic data about the metabolism of BDE209 in fish. In the present study, two replicate treatment groups of rainbow trout ( Oncorhynchus mykiss) were exposed to BDE209 via a single intraperitoneal injection approximately 100 and 500 ng/g, respectively. Muscle, liver and blood samples were collected to analyze the specific metabolites on day 1 and day 28 post injection. The highest concentration of BDE209 was detected in muscle tissues, from 796.1 ng/g wet weight (day 1) to 687.1 ng/g wet weight (day 28) in high dose group, suggesting that BDE209 could accumulate slightly in muscle tissues. However, BDE209 was not detected in the blood for all treatments. Most congeners of De-BDEs were found in muscle and liver tissues, with the highest concentration in the liver. The main De-BDEs were nona-, octa-, hepta- and penta-De-BDEs. A total of seven MeO-BDE metabolites were observed among different fish tissues. Blood had the highest contribution of the MeO-BDE metabolites. Each MeO-BDE congener increased over the 28 days. These results in contrast to other studies suggested possible species-specific differences in metabolic abilities.

Analysis of hydroxylated polybrominated diphenyl ether metabolites by liquid chromatography/atmospheric pressure chemical ionization tandem mass spectrometry

Hydroxylated polybrominated diphenyl ether (OH-PBDEs) metabolites have the potential to cause endocrine disruption as well as other health effects. Currently, gas chromatography/mass spectrometry (GC/MS) after derivatization is used for the analysis of OH-PBDEs. However, there is a need for the direct analysis of OH-PBDEs at relatively low concentrations in environmental and biological samples. Liquid chromatography with atmospheric pressure chemical ionization tandem mass spectrometry (LC/APCI-MS/MS) was evaluated for the analysis of nine OH-PBDEs, ranging from tri- to hexabrominated. Separation of the nine isomeric metabolites was achieved with reversed-phase liquid chromatography, followed by detection by APCI-MS in negative mode. Notably, a significant decrease in ionization was observed in 6-hydroxyl-substituted PBDE metabolites in the presence of an ortho-substituted bromine, relative to the other hydroxylated metabolites. This is probably due to the formation of dioxins in the source as a result of the high-temperature conditions, which prevented ionization by hydrogen abstraction. The MS/MS experiments also provided evidence of the neutral losses of HBr and Br(2), indicating the possible use of neutral loss scanning and selected reaction monitoring (SRM) for the screening of brominated metabolites in samples. The applicability of LC/APCI-MS/MS was demonstrated for the analysis of metabolites of BDEs 47 and 99 formed in human liver microsomes. The LC/APCI-MS/MS method was able to detect metabolites that had previously been identified by GC/MS following derivatization.

Metabolism of Polybrominated Diphenyl Ethers (PBDEs) by Human Hepatocytes in Vitro

BackgroundPolybrominated diphenyl ethers (PBDEs) are flame-retardant chemicals that accumulate in human tissues and are potential toxicants. Concentrations of PBDEs in human tissues have increased recently, and body burdens in the U.S. and Canadian populations are higher than in any other region.ObjectivesAlthough metabolism in animal laboratory studies has been examined, no studies have explored the metabolism of these contaminants in human tissues. We undertook this study to determine whether PBDEs could be metabolized by human liver cells in vitro and to identify what types of metabolites are formed.MethodsWe exposed hepatocytes from three different donors (two cryopreserved batches and one fresh batch) to solutions containing 10 μM of either of two environmentally relevant and prominent PBDE congeners—BDE-99 or BDE-209—for periods of 24–72 hr. We also conducted gene expression analysis to provide information on potential induction of xenobiotic metabolizing enzymes.ResultsExposing hepatocytes to BDE-99 resulted in the formation of 2,4,5-tribromo phenol, two monohydroxylated pentabrominated diphenyl ether metabolites, and a yet unidentified tetrabrominated metabolite. No hydroxylated or debrominated metabolites were observed in the cells exposed to BDE-209. This suggests that BDE-209 was not metabolized, that nonextractable, covalently protein-bound metabolites were formed, or that the exposure time was not long enough for BDE-209 to diffuse into the cell to be metabolized. However, we observed up-regulation of genes encoding for cytochrome P450 monooxygenase (CYP) 1A2, CYP3A4, deiodinase type 1, and glutathione S-transferase M1 in hepatocyes exposed to both BDE-99 and BDE-209.ConclusionsOur in vitro results suggest that the human liver will likely metabolize some BDE congeners (e.g., BDE-99) in vivo. These metabolites have been shown to elicit greater toxicity than the parent BDE congeners in laboratory bioassays; thus, more research on body burdens and human health effects from these metabolites are warranted.

RP-HPLC measurement and quantitative structure - property relationship analysis of the n-octanol - water partitioning coefficients of selected metabolites of polybrominated diphenyl ethers

Environmental context. Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants and numerous studies have demonstrated a marked increase in the levels of PBDEs in human biological tissues and fluids, especially breast milk. How PBDEs are transported through the environment, taken up by biota, transported across membranes, and metabolised depends strongly on such fundamental properties as lipophilicity (log KOW). However, very little data on log KOW exist for PBDEs. In the present paper, the authors determine PBDE metabolites’ log KOW using reversed-phase high performance liquid chromatography, as recommended by the Organisation for Economic Co-operation and Development and US Environmental Protection Agency, along with quantitative structure–property relationships. Abstract. n-Octanol–water partitioning coefficient (log KOW) values of selected hydroxylated and methoxylated polybrominated diphenyl ether metabolites were measured for the first time by reversed-phase high performance liquid chromatography (RP-HPLC) using a C18 stationary phase with a water/methanol mixture as a mobile phase. The retention parameters, log kw (extrapolated retention indices) and k′ (gradient retention indices) were calibrated to log KOW by a set of calibration standards. For the PBDE metabolites investigated, extrapolated retention indices from isocratic elution seem to be more reliable and their RP-HPLC-derived log KOW values were found to range from 4.63 to 7.67. Some commonly available software, including ClogP, KowWin, AclogP, MlogP, AlogP, MilogP, and XlogP, was used to estimate the log KOW values of the analytes. Significant correlations were obtained between the RP-HPLC-derived log KOW and the software-computed log KOW, with squared correlation coefficients (R2) ranging from 0.793 to 0.922, but the difference between them was also significant. Then a quantitative structure–property relationship model based on topological descriptors was established and showed good reliability and predictive power for the estimation of RP-HPLC-derived log KOW values of PBDE metabolites. It was applied to estimate the log KOW values of some PBDE metabolites that are commercially available or have appeared in the literature. Lastly, factor analysis was carried out using the theoretical linear salvation/free-energy relationships, which indicated the average polarisability (α) and the most negative atomic partial Mulliken charge in the molecule (q–) were the most important parameters affecting their partition between n-octanol and water, supporting the factorisation of log KOW in bulk and electronic terms.

Identification of Hydroxylated Polybrominated Diphenyl Ether Metabolites in Blood Plasma from Polybrominated Diphenyl Ether Exposed Rats

Polybrominated diphenyl ethers (PBDEs) are ubiquitous environmental contaminants due to their use as flame retardants. Similarly to PCBs, the PBDEs are metabolized to hydroxylated metabolites (OH-PBDEs) in mammals. In the present study equimolar doses of seven environmentally relevant PBDE congeners were given intraperitoneally as a mixture to rats, and their blood plasma was analyzed for parent compounds and hydroxylated metabolites 1 and 5 days after dosing. Sixteen OH-PBDEs and two diOH-PBDEs were detected as PBDE metabolites in the rat plasma, a novel finding. Four OH-tetraBDEs were structurally identified by comparison (gas chromatography/mass spectrometry) with authentic reference standards. The position of the hydroxyl groups was suggested according to the mass spectrometric fragmentation patterns of the corresponding PBDE methyl ether derivatives. The OH-PBDE metabolites were dominated by hydroxyl groups in the meta- and parapositions. The results show that OH-PBDE congeners have an ability to be retained in rat blood, most likely by a mechanism similar to that of OH-PCBs. The results will be useful for determination of the origin of OH-PBDEs present in wildlife and in humans, since OH-PBDEs are also common natural products in marine environments.

Synthesis of Hydroxylated and Methoxylated Polybrominated Diphenyl Ethers — Natural Products and Potential Polybrominated Diphenyl Ether Metabolites.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of Hydroxylated and Methoxylated Polybrominated Diphenyl Ethers − Natural Products and Potential Polybrominated Diphenyl Ether Metabolites

AbstractHydroxylated and methoxylated polybrominated diphenyl ethers (OH‐PBDEs and MeO‐PBDEs) may be natural products or they may be formed as metabolites of polybrominated diphenyl ethers (PBDEs), frequently used as flame retardants. The aim of this work was to synthesize authentic OH‐ and MeO‐PBDE reference standards for analytical and toxicological studies. Brominated phenoxybenzaldehydes were prepared either by coupling of 2,4‐dibromophenol with various fluorobenzaldehydes or by coupling of brominated hydroxybenzaldehydes with 2,2′,4,4′‐tetrabromodiphenyliodonium chloride. OH‐PBDEs were synthesized via the brominated phenoxybenzaldehydes by Baeyer−Villiger oxidation and acid‐catalyzed hydrolysis. These OH‐PBDEs were ortho‐ and para‐brominated (relative to the hydroxy group) with benzyltrimethylammonium tribromide and/or ortho‐brominated with bromine/tert‐butylamine, and were also brominated with bromine in one case. MeO‐PBDEs were obtained by methylation of the prepared OH‐PBDEs. MeO‐PBDEs were also prepared through the coupling of brominated methoxyphenols with 2,2′,4,4′‐tetrabromodiphenyliodonium salts, the corresponding OH‐PBDEs being obtained after demethylation. A majority of the OH‐/MeO‐PBDEs prepared have the hydroxy/methoxy group in the ortho position relative to the diphenyl ether bond. All OH‐/MeO‐PBDEs prepared have 2,4‐dibromo substitution patterns (relative to the diphenyl ether bond) in the non‐hydroxy‐/non‐methoxy‐containing ring. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Biotransformation of diphenyl ether by trout and guinea-pigs after intraperitoneal administration.

Diphenyl ether (DPE) was administered intraperitoneally to rainbow trout (Salmo gairdneri) and guinea-pigs (Duncan Hartley). DPE metabolites in the urine and bile of trout and the urine of guinea-pigs were isolated and analysed by g.l.c.-mass spectrometry. No unchanged DPE was found in the biological fluids of guinea-pigs and trout. Only conjugated metabolites of DPE were present in the bile and urine of the trout: 4-hydroxy- and possible 3-hydroxy-DPE conjugates were found in the bile whereas 4-hydroxy- and 4,4-dihydroxy-DPE conjugates were detected in the urine. Both free and conjugated metabolites of DPE were isolated from the urine of guinea-pigs. These metabolites were 2-hydroxy-, 4-hydroxy, 4,4'-dihydroxy-, 4-methoxy-monohydroxy- and methoxy-dihydroxy-derivatives of DPE.