Assigning atropisomer elution orders using atropisomerically enriched polychlorinated biphenyl fractions generated by microsomal metabolism

Abstract

Changes in the enantiomer fraction of chiral polychlorinated biphenyls (PCBs) are a powerful tool to investigate the movement of PCBs in the environment, for example as part of source apportionment and ecological studies. Environmental studies typically employ a series of cyclodextrin-based gas chromatography columns to separate all environmentally relevant PCB congeners. The elution order of most PCB atropisomers has not been established on different enantioselective columns due to the unavailability of analytical standards. To overcome this limitation, the current study generated atropisomerically enriched fractions of chiral PCBs with rat liver microsomes. Subsequently, the enrichment profile of the enriched PCB fractions was used to determine the elution order of PCB atropisomers on selected enantioselective gas chromatography columns. While the elution order of PCB 95, 131, 132, 136, 149 and 176 atropisomers was identical on all enantioselective columns investigated, an inversion of the elution order was observed for PCB 45, 84, 91 and 174 atropisomers on a few columns. These results demonstrate that atropisomerically enriched fractions obtained from microsomal metabolism can be used to unambiguously establish the relative elution order of the atropisomers of PCBs and potentially other environmental pollutant, especially if pure enantiomers are not available.

Chiral polychlorinated biphenyls: absorption, metabolism and excretion—a review

“…Incubations of individual, racemic PCB congeners or a mixture of several C-PCBs with rat CYP2B1 show preferential transformation of E 2 -PCB 45, (−)-PCB 84, E 1 -PCB 91, E 2 -PCB 95, (−)-PCB 132, (+)-PCB 136 and (−)-PCB 149. The same direction of atropisomeric enrichment is observed in rat liver microsomal incubations (Kania-Korwel et al 2011, Kania-Korwel and Lehmler 2013, Wu et al 2011) and, for PCB 136, in rat liver tissue slices (Wu et al 2013b). At the same time, the formation of HO-PCB metabolites by rat P450 enzymes is atropselective, thus resulting in an atropisomeric enrichment of the HO-PCBs.…”

“…A convenient nomenclature for PCB metabolites has been proposed by Maervoet et al and, as shown for PCB 136 in Fig 3, will be used throughout this manuscript (Maervoet et al 2004). The oxidation of C-PCBs, in particular those with a 2,3,6-trichloro substitution pattern in one phenyl ring, to HO-PCBs has been studied extensively using recombinant enzymes (Lu et al 2013, Lu and Wong 2011, Waller et al 1999, Warner et al 2009), hepatic microsomes (Kania-Korwel et al 2011, Kania-Korwel and Lehmler 2013, Schnellmann et al 1983, Wu et al 2014, Wu et al 2011), isolated hepatocytes (Vickers et al 1986) and, liver, hippocampus and skin slices (Garner et al 2006, Wu et al 2013a, Wu et al 2013b) obtained from mammalian species. To the best of our knowledge, the oxidation of C-PCBs in non-mammalian species, such as amphibians, fish or avian species, has not been investigated to date.…”

“…Several studies using recombinant P450 enzymes (Lu et al 2013, Warner et al 2009), liver microsomes (Kania-Korwel et al 2011, Kania-Korwel and Lehmler 2013, Wu et al 2014, Wu et al 2011) or liver tissue slices (Wu et al 2013a, Wu et al 2013b) demonstrate that PCBs are atropselectively metabolized to HO-CPBs by P450 enzymes, thus resulting in an atropisomeric enrichment of PCBs and HO-PCBs in the microsomal incubation (Table 2). The atropselective biotransformation of C-PCBs to HO-PCB metabolites by recombinant rat and human cytochrome P450 enzymes has been studies in some detail (Lu et al 2013, Warner et al 2009).…”

“…5) (Wu et al 2011). (−)-PCB 136 elutes first on Chirasil-Dex and Cyclosil-B columns (Kania-Korwel and Lehmler 2013). Both HO-PCB metabolites of (−)-PCB 136 also elute first (E 1 ) on both enantioselective columns.…”

Enantioselective accumulation of chiral polychlorinated biphenyls in lotus plant (Nelumbonucifera spp.)

“…Based on our previous report [26], the (−)-enantiomers of PCBs 136, 149 and 176 elute first on Chirasil-Dex column compared to their antipodes, while (−)-enantiomer of PCB 183 also elute first on BGB-172 column [27]. However, we are also able to identify the elution orders of the atropisomers of PCBs 91 and 95, which have not been identified until now.…”