Metabolism of 3-Chlorobiphenyl (PCB 2) in a Human-Relevant Cell Line: Evidence of Dechlorinated Metabolites

Abstract

Lower chlorinated polychlorinated biphenyls (LC-PCBs) and their metabolites make up a class of environmental pollutants implicated in a range of adverse outcomes in humans; however, the metabolism of LC-PCBs in human models has received little attention. Here we characterize the metabolism of PCB 2 (3-chlorobiphenyl), an environmentally relevant LC-PCB congener, in HepG2 cells with in silico prediction and nontarget high-resolution mass spectrometry. Twenty PCB 2 metabolites belonging to 13 metabolite classes, including five dechlorinated metabolite classes, were identified in the cell culture media from HepG2 cells exposed for 24 h to 10 μM or 3.6 nM PCB 2. The PCB 2 metabolite profiles differed from the monochlorinated metabolite profiles identified in samples from an earlier study with PCB 11 (3,3′-dichlorobiphenyl) under identical experimental conditions. A dechlorinated dihydroxylated metabolite was also detected in human liver microsomal incubations with monohydroxylated PCB 2 metabolites but not PCB 2. These findings demonstrate that the metabolism of LC-PCBs in human-relevant models involves the formation of dechlorination products. In addition, untargeted metabolomic analyses revealed an altered bile acid biosynthesis in HepG2 cells. Our results indicate the need to study the disposition and toxicity of complex PCB 2 metabolites, including novel dechlorinated metabolites, in human-relevant models.

Distribution of 2,2′,5,5′-Tetrachlorobiphenyl (PCB52) Metabolites in Adolescent Rats after Acute Nose-Only Inhalation Exposure

“…In addition, two dechlorinated OH-PCB sulfates (OH-Tri-CB sulfate) were detected in the lungs of the high-dose exposure group (DF from 17 to 42%). This sulfated metabolite is likely produced from an OH-PCB by replacing a chlorine substituent with a hydroxyl group, followed by sulfation of the dechlorinated dihydroxy metabolite …”

“…These metabolites are likely formed via the methylation of PCB52 catechols by catechol- O -methyltransferases (COMT). These metabolites have also been observed in cell culture − and animal studies. ,, However, the disposition and toxicity of methoxylated PCB metabolites have received little attention.…”

“…Accurate masses and peak areas of PCB52 metabolites were extracted based on a subject screening list of known or likely PCB52 metabolites from raw data files with Thermo Xcalibur (version 4.1, Thermo Fisher Scientific) with a m / z tolerance of 5 ppm, mass precision decimals of 5, and the smoothing factor of 7 (Table ). ,,, The isotopic pattern of chlorine was used to confirm the identification of putative metabolites. ,, …”

“…This sulfated metabolite is likely produced from an OH-PCB by replacing a chlorine substituent with a hydroxyl group, followed by sulfation of the dechlorinated dihydroxy metabolite. 31 Multiple metabolites were discovered in both the liver and the serum (Figure S9; Table 1). The relative levels of these metabolites were higher in the serum (Figure 4A).…”

“…For example, 3,3′-dichlorobiphenyl (PCB11) and its metabolites are quickly metabolized and eliminated in rats. , Intratracheal administration of 14 C-PCB11 and inhalation of 3-chlorobiphenyl (PCB3) in rats reveal the dominant elimination of more water-soluble metabolites, such as PCB sulfates, with the urine and feces. ,, More comprehensive studies of the disposition of individual PCB congeners and their metabolites following inhalation are unavailable for PCB congeners with ≥3 chlorine substituents. Because PCB found in the indoor air of US schools, such as 2,2′,5,5′-tetrachlorobiphenyl (PCB52), can be metabolized to metabolites that contribute to neurotoxic outcomes, − there is a need to characterize the metabolite profiles in target tissue in rodent models following acute, nose-only PCB inhalation, the mode of inhalation exposure preferred by regulatory agencies …”