Stereoselective Metabolism of α‑, β‑, and γ‑Hexabromocyclododecanes (HBCDs) by Human Liver Microsomes and CYP3A4

This is the first study investigating the in vitro metabolism of α-, β-, and γ-hexabromocyclododecane (HBCD) stereoisomers in humans and providing semiquantitative metabolism data. Human liver microsomes were incubated with individual racemic mixtures and with individual stereoisomers of α-, β-, and γ-HBCDs, the hydroxylated metabolites formed were analyzed by liquid chromatography–tandem mass spectrometry, and the value of the intrinsic in vitro clearance (Cl_int,vitro) was calculated. Several mono- and dihydroxylated metabolites of α-, β-, and γ-HBCDs were formed, with mono-OH-HBCDs being the major metabolites. No stereoisomerization of any of the six α-, β-, and γ-HBCD isomers catalyzed by cytochrome P450 (CYP) enzymes occurred. The value of Cl_int,vitro of α-HBCDs was significantly lower than that of β-HBCDs, which, in turn, was significantly lower than that of γ-HBCDs (<i>p</i> < 0.05). Such differences were explained by the significantly lower values of Cl_int,vitro of each α-HBCD stereoisomer than those of the β- and γ-HBCD stereoisomers. In addition, significantly lower values of Cl_int,vitro of the (−) over the (+)­α- and β-HBCD stereoisomers, but not γ-HBCDs, were obtained. Our data offer a possible explanation of the enrichment of α-HBCDs over β- and γ-HBCDs on the one hand and, on the other hand, of (−)­α-HBCDs over (+)­α-HBCDs previously reported in human samples. It also offers information about the mechanism resulting in such enrichments, the stereoisomer-selective metabolism of α-, β-, and γ-HBCDs catalyzed by CYPs with the lack of stereoisomerization

Alteration of Diastereoisomeric and Enantiomeric Profiles of Hexabromocyclododecanes (HBCDs) in Adult Chicken Tissues, Eggs, and Hatchling Chickens

The concentrations and enantiomer fractions (EFs) of α-, β-, and γ-hexabromocyclododecanes (HBCDs) were measured in chicken diet sources (soil and chicken feed), home-raised adult chicken (<i>Gallus domesticus</i>) tissues, eggs during incubation, and hatchling chicken tissues. HBCD concentrations were not detected–0.69 ng/g dry weight (dw) and 25.6–48.4 ng/g dw in chicken feed and soil, respectively. HBCDs were detected in all adult chicken tissues, except the brain, at median levels of 13.1–44.0 ng/g lipid weight (lw). The proportions of α-HBCD in total HBCDs increased from 51% in soil to more than 87% in adult chicken tissues. The accumulation ratios (ARs) of α-HBCD from diet to adult chicken tissues were 4.27 for liver, 11.2 for fat, and 7.64–12.9 for other tissues, respectively. The AR and carry-over rate (COR) of α-HBCD from diet to eggs were 22.4 and 0.226, respectively. The concentrations of α-HBCD in hatchling chicken liver (median: 35.4 ng/g lw) were significantly lower than those in hatchling chicken pectoral muscle (median: 130 ng/g lw). The EFs of α-HBCD decreased from soil to adult chicken tissues and from eggs to hatchling chicken liver. Meanwhile, the EFs of γ-HBCD increased from soil to adult chicken tissues. These results indicate the preferential enrichment of (−)-α-HBCD and (+)-γ-HBCD in chickens. The alteration of diastereoisomeric and enantiomeric patterns of HBCDs might be influenced by the different absorption and elimination rates of the six HBCD enantiomers as well as variations in HBCD metabolism in chickens

Pollutant Exposure for Chinese Wetland Birds: Ecotoxicological Endpoints and Biovectors

Levels of heavy metals and organic contaminants in main waters from China were reviewed from literature data to assess the ecological risks of pollutants for wetland birds and the biotransport of pollutants mediated by migratory wetland birds. Cr, Cu, and Pb and polycyclic aromatic hydrocarbons (PAHs) dominated in sediments, with higher concentrations in rivers and estuaries than in lakes and seas. Plants are the main dietary sources of less hydrophobic organic pollutants, while sediment is the primary source of more hydrophobic PAHs in birds. The hazard index (HI) for birds was mainly contributed by mercury (Hg) and polybrominated diphenyl ethers (PBDEs) and ranked as piscivore > omnivore > herbivore. Pollutant exposure risks to birds depend on the biomagnification potential of pollutants, food items of birds, and pollution levels in habitats. Migratory birds are important biovectors of persistent and bioaccumulative pollutants that may serve as a vital geochemical cycling process in addition to atmospheric deposition. This study provided a comprehensive overview of water environment pollution in China and the potential risks for high trophic level wetland birds in aquatic ecosystems. The results also identified the pollution hotspots of wetland birds and habitats, which provide new insights into bird conservation and biodiversity protection

Pollutant Exposure for Chinese Wetland Birds: Ecotoxicological Endpoints and Biovectors

Levels of heavy metals and organic contaminants in main waters from China were reviewed from literature data to assess the ecological risks of pollutants for wetland birds and the biotransport of pollutants mediated by migratory wetland birds. Cr, Cu, and Pb and polycyclic aromatic hydrocarbons (PAHs) dominated in sediments, with higher concentrations in rivers and estuaries than in lakes and seas. Plants are the main dietary sources of less hydrophobic organic pollutants, while sediment is the primary source of more hydrophobic PAHs in birds. The hazard index (HI) for birds was mainly contributed by mercury (Hg) and polybrominated diphenyl ethers (PBDEs) and ranked as piscivore > omnivore > herbivore. Pollutant exposure risks to birds depend on the biomagnification potential of pollutants, food items of birds, and pollution levels in habitats. Migratory birds are important biovectors of persistent and bioaccumulative pollutants that may serve as a vital geochemical cycling process in addition to atmospheric deposition. This study provided a comprehensive overview of water environment pollution in China and the potential risks for high trophic level wetland birds in aquatic ecosystems. The results also identified the pollution hotspots of wetland birds and habitats, which provide new insights into bird conservation and biodiversity protection

MoDnm1 Dynamin Mediating Peroxisomal and Mitochondrial Fission in Complex with MoFis1 and MoMdv1 Is Important for Development of Functional Appressorium in <i>Magnaporthe oryzae</i>

<div><p>Dynamins are large superfamily GTPase proteins that are involved in various cellular processes including budding of transport vesicles, division of organelles, cytokinesis, and pathogen resistance. Here, we characterized several dynamin-related proteins from the rice blast fungus <i>Magnaporthe oryzae</i> and found that MoDnm1 is required for normal functions, including vegetative growth, conidiogenesis, and full pathogenicity. In addition, we found that MoDnm1 co-localizes with peroxisomes and mitochondria, which is consistent with the conserved role of dynamin proteins. Importantly, MoDnm1-dependent peroxisomal and mitochondrial fission involves functions of mitochondrial fission protein MoFis1 and WD-40 repeat protein MoMdv1. These two proteins display similar cellular functions and subcellular localizations as MoDnm1, and are also required for full pathogenicity. Further studies showed that MoDnm1, MoFis1 and MoMdv1 are in complex to regulate not only peroxisomal and mitochondrial fission, pexophagy and mitophagy progression, but also appressorium function and host penetration. In summary, our studies provide new insights into how MoDnm1 interacts with its partner proteins to mediate peroxisomal and mitochondrial functions and how such regulatory events may link to differentiation and pathogenicity in the rice blast fungus.</p></div

MoDnm1, MoMdv1, and MoFis1 are important for peroxisomal and mitochondrial morphology.

<p>(A) Transmission electron microscopy (Hitachi H-7650) observation of peroxisomes in conidia of the indicated strains. Bar = 0.5 μm. P, peroxisome; M, mitochondria; N, nucleus. (B) Transmission electron microscopy (Hitachi H-7650) observation of mitochondria in hyphae of the indicated strains. Bar = 1 μm. M, mitochondria.</p

MoMdv1 functions as an adaptor linking MoDnm1 to MoFis1.

<p>(A) Yeast two hybrid assays for the interaction between MoDnm1, MoFis1 and MoMdv1. The AD and BD plasmids were co-transformed into yeast AH109, and transformants were plated on SD-Leu-Trp for 3 d and on selective SD-Leu-Trp-His-Ade with 1 mM X-gal and 5 mM 3-AT (3-amino-1,2,4-triazole) for 5 d. (B) GST pull down assays for MoDnm1, MoFis1 and MoMdv1. His₆-Mdv1, His₆-Fis1, GST-Dnm1 and GST-Fis1 were expressed and purified by affinity chromatography. Bound proteins were separated by SDS-PAGE in duplicate and analyzed by Western blotting with monoclonal anti-His (Mouse; M20001; Abmart) and anti-GST antibodies (Mouse; M20007; Abmart). Asterisks indicate GST-Dnm1.</p

MoDnm1, MoMdv1 and MoFis1 are required for normal endocytosis.

<p>Hyphae of the indicated strains were cultured in liquid CM for 40 h, then stained with FM4-64 and examined under confocal fluorescence microscope (Zeiss LSM710, 63x oil). Bar = 5 μm.</p

MoPex11A, MoDnm1, MoMdv1, and MoFis1 all have functions on peroxisomal fission.

<p>(A) a, Disease symptoms on the rice seedlings which were sprayed with conidial suspensions at 7 dpi. b, Disease symptoms on the detached barley which were drop-inoculated with conidial suspensions and examined at 24 hpi. Bar = 10 μm. (B) Observation of peroxisomal morphology in the indicated strains using confocal fluorescence microscope (Leica TCS SP8, 100x oil). Bar = 5 μm.</p

MoMdv1 contributes to the peroxisomal localization of MoDnm1 and MoFis1.

<p>(A) GFP-Dnm1 and RFP-PTS1 were co-expressed in Δ<i>Modnm1</i> (top), Δ<i>Mofis1</i> (middle), and Δ<i>Momdv1</i> mutants (bottom). Punctate GFP-Dnm1 localization was observed in hyphae by Axio Observer A1 Zeiss inverted microscope. PTS1, a peroxisome marker protein. Bar = 5 μm. (B) GFP-Fis1 and RFP-PTS1 were co-expressed in Δ<i>Mofis1</i> (top), Δ<i>Modnm1</i> (middle), and Δ<i>Momdv1</i> mutants (bottom). GFP-Fis1 localization was observed in hyphae by Axio Observer A1 Zeiss inverted microscope. PTS1, a peroxisome marker protein. Bar = 5 μm. (C) GFP-Mdv1 and RFP-PTS1 were co-expressed in Δ<i>Momdv1</i> (top), Δ<i>Mofis1</i> (middle), and Δ<i>Modnm1</i> mutants (bottom). GFP-Mdv1 localization was observed in hyphae by Axio Observer A1 Zeiss inverted microscope. PTS1, a peroxisome marker protein. Bar = 5 μm.</p