38411-22-2Relevant articles and documents
Enantiomeric enrichment of 2,2′,3,3′,6,6′- hexachlorobiphenyl (PCB 136) in mice after induction of CYP enzymes
Kania-Korwel, Izabela,Xie, Wei,Hornbuckle, Keri C.,Robertson, Larry W.,Lehmler, Hans-Joachim
, p. 510 - 517 (2008)
Several PCB congeners, present in commercial PCB formulations, are chiral. These PCBs can undergo enantiomeric enrichment in many animal species and in humans due to currently uncharacterized enantioselective biotransformation processes. To investigate if certain cytochrome P-450 enzymes (CYPs), such as CYP2B's, are responsible for this enantiomeric enrichment, we investigated the enantioselective disposition of (±)-PCB 136 in female mice after induction of different CYP enzymes by pretreatment with corn oil alone, β-naphthoflavone (CYP1A's), phenobarbital (CYP2B's), or dexamethasone (2B's and 3A's), followed by oral PCB administration. PCB 136 levels were significantly lower in phenobarbital- and, to a lesser extent, in dexamethasone-pretreated animals, presumably due to the induction of PCB 136 metabolizing enzymes. Although (+)-PCB 136 was enriched in all tissues, none of the pretreatments altered the enantioselective disposition of PCB 136 in a manner that suggests a particular CYP subfamily as the cause of the enrichment of (+)-PCB 136. Fecal PCB levels and enantiomeric fraction values changed over time in a manner consistent with slower digestive motility in the mice pretreated with phenobarbital and dexamethasone. Overall, this study does not support the hypothesis that metabolism by CYP2B enzymes is responsible for the enrichment of (+)-PCB 136 in mice.
2,2',3,3',6,6'-Hexachlorobiphenyl hydroxylation by active site mutants of cytochrome P450 2B1 and 2B11
Waller, Stephen C.,He, You Ai,Harlow, Greg R.,He, You Qun,Mash, Eugene A.,Halpert, James R.
, p. 690 - 699 (2007/10/03)
The structural basis of species differences in cytochrome P450 2B- mediated hydroxylation of 2,2',3,3',6,6'-hexachlorobiphenyl (236HCB) was evaluated by using 14 site-directed mutants of cytochrome P450 2B1 and three point mutants of 2B11 expressed in Escherichia coli. To facilitate metabolite identification, seven possible products, including three hydroxylated and four dihydroxylated hexachlorobiphenyls, were synthesized by direct functionalization of precursors and Ullmann and crossed Ullmann reactions. HPLC and GCfMS analysis and comparison with authentic standards revealed that 2B1, 2B11, and all their mutants produced 4,5-dihydroxy-236HCB and 5-hydroxy- 236HCB, while 2B11 L363V and 2B1 I114V mutants also catalyzed hydroxylation at the 4-position. The amount of products formed by 2B1 mutants I114V, F206L, L209A, T302S, V363A, V363L, V367A, I477A, I477L, G478S, I480A, and I480L was smaller than that of the wild type. I477V exhibited unaltered 236HCB metabolism, and I480V produced twice as much dihydroxy product as the wild type. For 2B11, substitution of Val-114 or Asp-290 with Ile decreased the product yields. Replacement of Leu-363 with Val dramatically altered the profile of 236HCB metabolites. In addition to an increase in the overall level of hydroxylation, the mutant mainly catalyzed hydroxylation at the 4- position. Incubation of P450 2B1 with 5-hydroxy-236HCB produced 4,5- dihydroxy-236HCB, which indicates that 4,5-dihydroxy-236HCB may be formed by a direct hydroxylation of 5-hydroxy-236HCB. The findings from this study demonstrate the importance of residues 114, 206, 209, 302, 363, 367, 477, 478, and 480 in 2B1 and 114, 290, and 363 in 2B11 for 236HCB metabolism.
Physical, spectral and chromatographic properties of all 209 individual PCB congeners
Bolgar,et al.
, p. 2687 - 2705 (2007/10/03)
Through the use of two capillary GC columns: 40% octadecyl/ 15% phenyl methyl siloxane and 50% phenyl methyl siloxane, it was possible to separate 201 PCB congeners with only four unresolved pairs. The data compiled in this study for all 209 congeners will aid in the identification of selected individual components of these environmental pollutants. The use of this data also presents the opportunity for the improved quantification of the commercial PCB formulations. -from Authors