Species-Specific Differences and Structure−Activity Relationships in the Debromination of PBDE Congeners in Three Fish Species

Abstract

Previous studies have suggested that there may be species-specific differences in the metabolism of polybrominated diphenyl ethers (PBDEs) among different fish species. In this study, we investigated the in vitro hepatic metabolism of eleven individual PBDE congeners (tri-through decaBDEs) in three different fish species: rainbow trout (Oncorhynchus mykiss), common carp (Cyprinus carpio), and Chinook salmon (O. tschwatcha). In addition, we evaluated the influence of PBDE structural characteristics (i.e., bromine substitution patterns) on metabolism. Six of the eleven congeners we evaluated, BDEs 99, 153, 183, 203, 208, and 209, were metabolically debrominated to lower brominated congeners. All of the congeners that were metabolized contained at least one meta-substituted bromine. Metabolites were not detected for congeners without one meta-substituted bromine (e.g., BDEs 28, 47, and 100). Metabolite formation rates were generally 10-100 times faster in carp than in trout and salmon. BDEs 47, 49, 101, 154, and 183 were the major metabolites observed in all three species with the exception of BDE 47, which was only detected in carp. Carp demonstrated a preference towards meta-debromination, while trout and salmon debrominated meta-and para-bromine atoms to an equal extent. We compared glutathione-S-transferase (GST) and deiodinase (DI) activity among all three species as these enzyme systems have been hypothesized to play a role in PBDE debromination among teleosts. Carp exhibited a preference for meta-deiodination of the thyroid hormone thyroxine, which was consistent with the preference for meta-debromination of PBDEs observed in carp.

Separation of polybrominated diphenyl ethers in fish for compound-specific stable carbon isotope analysis

“…The significant depletion in 13 C for BDE-47 in common carp indicates that a large amount of BDE-47 was formed from metabolic debromination of more highly brominated congeners. The constant δ 13 C value for BDE-100 in common carp and in Penta-BDE indicated that BDE-100 was accumulated by common carp with or without undetectable biotransformation, which is in line with the results of laboratory exposure experiments (Roberts et al, 2011).…”

Experimental exposure of eggs to polybrominated diphenyl ethers BDE‐47 and BDE‐99 in red‐eared sliders (Trachemys scripta elegans) and snapping turtles (Chelydra serpentina) and possible species‐specific differences in debromination

“…Although early embryonic development of red-eared sliders and snapping turtles is similar [42,43], species-specific differences are likely in enzymatic systems potentially responsible for differential capacities for debromination, as has been shown in fish exposed to BDE-99 [7,10]. Several studies of fish have shown debromination of BDE-99 to BDE-47 in carp, but other species such as Chinook salmon and rainbow trout demonstrate different reductive metabolite products and slower formation rates [6,7,9,10]. Deiodinase enzymes (DIs)-which are responsible for the removal of iodine atoms from thyroid hormones, resulting in activation or deactivation of the hormones-have been suggested as the primary enzymatic system for debromination of BDE-99 to BDE-47 in fish, particularly in carp [7,9,10].…”

“…McKernan et al [8] reported the presence of several PBDE congeners in the egg contents of several species of birds that had been injected with DE-71 but were not detected in the dosing solution or control eggs. Although early embryonic development of red-eared sliders and snapping turtles is similar [42,43], species-specific differences are likely in enzymatic systems potentially responsible for differential capacities for debromination, as has been shown in fish exposed to BDE-99 [7,10]. Several studies of fish have shown debromination of BDE-99 to BDE-47 in carp, but other species such as Chinook salmon and rainbow trout demonstrate different reductive metabolite products and slower formation rates [6,7,9,10].…”

“…Several studies of fish have shown debromination of BDE-99 to BDE-47 in carp, but other species such as Chinook salmon and rainbow trout demonstrate different reductive metabolite products and slower formation rates [6,7,9,10]. Deiodinase enzymes (DIs)-which are responsible for the removal of iodine atoms from thyroid hormones, resulting in activation or deactivation of the hormones-have been suggested as the primary enzymatic system for debromination of BDE-99 to BDE-47 in fish, particularly in carp [7,9,10]. Preliminary data suggest higher DI activity in red-eared sliders than in snapping turtles, suggesting that the DIs may be a hypothetical metabolic pathway for reductive debromination in red-eared sliders [44].…”

“…The lower brominated congeners, including BDE-47, -99, -100, and -153, are most widely detected and usually in the greatest quantity, which has been attributed to metabolism of the higher brominated congeners through debromination [4,5] as well as exposures to the penta-BDE commercial mixture present in older products that remain in use. There is evidence that in fish, rats, and birds, reductive debromination is a potential pathway for metabolism of PBDEs [6][7][8][9][10][11]. The environmental persistence of PBDEs as well as metabolism to the more bioaccumulative and toxic lower brominated congeners suggests that they are likely to remain contaminants of concern despite recently imposed restrictions on use.…”