S are shown in red. These metabolites are probably reactive and highly toxic. Metadrug predicted

S are shown in red. These metabolites are probably reactive and highly toxic. Metadrug predicted metabolites with orange backgrounds. P450: cytochrome P450 enzyme; Glc: glucuronide; SULT: sulfotransferase; UGT: uridine 5-diphosphoglucuronosyltransferase; COMT: catechol-O-methyltransferase.chlorinated PCBs are preferentially oxidized in meta and para positions in studies with recombinant human cytochrome P450 5-HT3 Receptor MedChemExpress enzymes or human liver microsomes.41,42,71,72,74,75 Kinesin-14 MedChemExpress Similarly, the oxidation of PCB metabolites in the para or meta position is generally observed in mammalian model systems, each in vitro and in vivo.21-24,41,46,56,76 Research with rats exposed to PCB3 through inhalation identified 3-, 4-, and 3-PCB3 sulfate isomers and three,4-di-OH-3 conjugates.21,22 Interestingly, rats receiving an intraperitoneal injection of PCB3 excreted 2-, 3-, and 4-PCB3 sulfate within the urine, suggesting that ortho-hydroxylated PCB3 metabolites are formed in rats in vivo.23 2-OH-3, 3-OH-3, and 4-OH-3, with each other with two unidentified monohydroxylated metabolites, were observed in a metabolism study with rat liver microsomes.25 At the least some monohydroxylated PCB3 metabolites are formed via an arene oxide intermediate, followed by a 1,2shift, as indicated by the formation of 4-PCB 2 sulfate. Similarly, 1,2-shift metabolites are formed from other PCB congeners by human cytochrome P450 enzymes.41,42,71,72,77 General, our results confirm that HepG2 cells metabolize decrease chlorinated PCBs, which include PCB3, within a manner that shows some similarities to rats. Metabolic Pathway of PCB3 and Its Toxicological Implications. We propose the metabolism pathway shown inFigure three for the PCB3 metabolism in HepG2 cells based on our experimental findings. Briefly, PCB3 is oxidized to meta- or para-OH-PCB3. Additional oxidation final results inside the formation of PCB3 catechol metabolites, including three,4-di-OH-3. Subsequently, OH-PCB3 metabolites are biotransformed by SULTs and UGTs to sulfate and glucuronide conjugates. PCB3 sulfates but not PCB3 glucuronides might be additional oxidized to hydroxylated compounds plus the corresponding downstream metabolites. 3,4-Di-OH-3 seems to be a pivotal PCB3 metabolite that is certainly only transiently formed in HepG2 cells. This metabolite is methylated to methoxylated-hydroxylated PCB3 metabolites, followed by conjugation to type MeO-PCB3 sulfate and MeOPCB3 glucuronide conjugates. 3,4-Di-OH-3 also can be converted to OH-PCB3 glucuronides. It is actually unclear to which extent these metabolic pathways stop the oxidation of three,4di-OH-3 for the corresponding PCB3 quinone. Studies in the resistant hepatocyte model demonstrated that this quinone acts because the ultimate carcinogenic metabolite resulting from the bioactivation of PCB3 in rat liver.40 It’s also unknown to which extent PCB3 quinone adducts had been formed with cellular nitrogen and sulfur nucleophiles, including proteins and DNAs,31,32,34 in HepG2 cells. Future studies are required to confirm the proposed metabolic pathway of PCB3 andhttps://doi.org/10.1021/acs.est.1c01076 Environ. Sci. Technol. 2021, 55, 9052-Environmental Science Technologypubs.acs.org/estArticleFigure 4. Metabolomic analysis of medium samples revealed distinct variations among experiments with HepG2 cells exposed for two, 8, or 24 h to PCB3 and also a vehicle (DMSO). (a) Volcano plots with information from 2, eight, or 24 h incubations selected 555, 534, and 1929 features utilizing a threshold of p = 0.05 (yellow line) and 10, 20, and 966 attributes employing FDR threshold = 0.05 (red l.