3,3'-Dichlorobiphenyl (PCB 11) is a byproduct of industrial processes and detected in environmental samples. PCB 11 and its metabolites are present in human serum, and emerging evidence demonstrates that PCB 11 is a developmental neurotoxicant. However, little is known about the metabolism of PCB 11 in humans. Here we investigated the metabolism of PCB 11 and the associated metabolomics changes in HepG2 cells using untargeted high-resolution mass spectrometry. HepG2 cells were exposed for 24 h to PCB 11 in DMSO or DMSO alone. Cell culture media were analyzed with ultra-high-performance liquid chromatography coupled with high-resolution mass spectrometry. Thirty different metabolites were formed by HepG2 cells exposed to 10 μM PCB 11, including monohydroxylated, dihydroxylated, hydroxylatedmethoxylated, and methoxylated-di-hydroxylated metabolites, and the corresponding sulfo and glucuronide conjugates. The methoxylated PCB metabolites were observed for the first time in a human-relevant model. 4-OH-PCB 11 (3,3'-dichlorobiphenyl-4-ol) and the corresponding catechol metabolite, 4,5-di-OH-PCB 11 (3',5-dichloro-3,4-dihydroxybiphenyl), were unambiguously

The characterization of the metabolism of lower chlorinated PCB, such as 4-chlorobiphenyl (PCB3), is challenging because of the complex metabolite mixtures formed in vitro and in vivo. We performed parallel metabolism studies with PCB3 and its hydroxylated metabolites to characterize the metabolism of PCB3 in HepG2 cells using nontarget high-resolution mass spectrometry (Nt-HRMS). Briefly, HepG2 cells were exposed for 24 h to 10 μM PCB3 or its seven hydroxylated metabolites in DMSO or DMSO alone. Six classes of metabolites were identified with Nt-HRMS in the culture medium exposed to PCB3, including monosubstituted metabolites at the 3′-, 4′-, 3-, and 4-(1,2-shift product) positions and disubstituted metabolites at the 3′,4′-position. 3′,4′-Di-OH-3 (4′-chloro-3,4-dihydroxybiphenyl), which can be oxidized to a reactive and toxic PCB3 quinone, was a central metabolite that was rapidly methylated. The resulting hydroxylated-methoxylated metabolites underwent further sulfation and, to a lesser extent, glucuronidation. Metabolomic analyses revealed an altered tryptophan metabolism in HepG2 cells following PCB3 exposure. Some PCB3 metabolites were associated with alterations of endogenous metabolic pathways, including amino acid metabolism, vitamin A (retinol) metabolism, and bile acid biosynthesis. Indepth studies are needed to investigate the toxicities of PCB3 metabolites, especially the 3′,4′-di-OH-3 derivatives identified in this study.

The toxicity of polychlorinated biphenyls (PCBs) has been attributed widely to receptor-mediated effects, buttressed by the popularity of the Toxic Equivalency Factor. We propose that a crucial toxic mechanism of lower-chlorinated PCBs is their enzymatic biotransformation to electrophiles, including quinoid metabolites, that bind intracellular sulfhydryl groups, such as those found in microtubulin and enzymes like telomerase. To test this hypothesis, we have examined micronuclei induction, cell cycle, and telomere shortening in cells in culture. Our findings show a large increase in micronuclei frequency and cell cycle perturbation in V79 cells, and a marked decrease in telomere length in HaCaT cells exposed to 2-(4'-chlorophenyl)-1,4-benzoquinone (PCB3pQ).

4-Monochlorobiphenyl (PCB3) is a component of commercial polychlorinated biphenyl (PCB) products and is an airborne environmental pollutant. Our recent study with transgenic Fischer 344 rats revealed the mutagenic potential of PCB3 in the livers of male rats. PCB3 is converted in vitro to hydroxylated metabolites, to hydroquinones (HQs, e.g., 2',5'-HQ and 3',4'-HQ), and can be further oxidized to quinones (Qs, e.g., 2',5'-Q and 3',4'-Q). This raises the question whether the mutagenic potential of PCB3 is due to the mutagenicity of PCB3 itself or of one of the metabolites. In this study, we investigated the mutagenicity of PCB3, of the monohydroxylated metabolites 2'-hydroxy (HO)-, 3'-HO-, and 4'-HO, of the HQs 3',4'-HQ and 2',5'-HQ and of the Qs 3',4'-Q and 2',5'-Q in cultured Chinese hamster V79 cells. The induction of gene mutations was determined at the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene locus by selection with 6-thioguanine. The induction of chromosome and genome mutations was assessed using the micronucleus assay and immunochemical differentiation of micronuclei containing whole chromosomes (kinetochore positive) and DNA fragments (kinetochore negative). The induction of chromosome and genome mutations, detected as micronuclei, was only observed at higher, cytotoxic concentrations of monohydroxylated, catecholic, and quinoid metabolites of PCB3. However, both PCB3-Qs induced a significant increase in the mutant frequency of the hprt gene and did so at submicromolar concentrations. Thus, the present study demonstrates for the first time the mutagenicity of PCB3 metabolites in mammalian cells and identifies quinoid metabolites of PCB3 as potential ultimate mutagens.

Few in vivo inhalation studies have explored the toxicity of environmentally relevant mixtures of polychlorinated biphenyls (PCBs). The manufacture of industrial PCBs was banned in 1978, but PCBs continue to be formed in industrial and consumer products. Schools represent a significant source of airborne exposures to legacy and nonlegacy PCBs, placing children at risk. To evaluate the impact of these exposures, we generated an airborne mixture of PCBs, called the School Air Mixture (SAM), to match the profile of an older school from our adolescent cohort study. Female Sprague− Dawley rats were exposed either to SAM or filtered air in nose-only exposure systems, 4 h/day for 4 weeks. Congener-specific air and tissue PCB profiles were assessed using gas chromatography with tandem mass spectrometry (GC−MS/MS). PCB exposures recapitulated the target school air profile with a similarity coefficient, cos θ of 0.83. PCB inhalation yielded μg/g ∑ 209 PCB levels in tissues. Neurobehavioral testing demonstrated a modest effect on spatial learning and memory in SAM-exposed rats. PCB exposure induced oxidative stress in the liver and lungs, affected the maturational stages of hematopoietic stem cells, reduced telomerase activity in bone marrow cells, and altered the gut microbiota. This is the first study to emulate PCB exposures in a school and comprehensively evaluate toxicity.