Metabolic activation of WHO-congeners PCB28, 52, and 101 by human CYP2A6: evidence from in vitro and in vivo experiments.

Despite extensive research on the metabolism of polychlorinated biphenyls (PCBs), knowledge gaps persist regarding their isoform-specific biotransformation pathways. This study aimed to elucidate the role of different cytochrome P450 enzymes in PCB metabolism, focusing on WHO-congeners 2,4,4'-trichlorobiphenyl (PCB28), 2,2',5,5'-tetrachlorobiphenyl (PCB52), and 2,2',4,5,5'-pentachlorobiphenyl (PCB101). Utilizing engineered HEK293 cell lines, we investigated the in vitro metabolism of these PCBs by CYP1A2, CYP2C8, CYP2C9, CYP3A4, CYP2A6, and CYP2E1, revealing robust production of hydroxylated metabolites. Our results show that CYP2A6 plays a major role in the metabolism of these congeners responsible for predominant formation of para-position hydroxylated metabolites, with concentrations reaching up to 1.61 µg/L (5,89 nM) for PCB28, 316.98 µg/L (1,03 µM) for PCB52, and 151.1 µg/L (441 nM) for PCB101 from a 20 µM parent PCB concentration. Moreover, concentration-dependent cytotoxic and cytostatic effects induced by reactive intermediates of the PCB hydroxylation pathway were observed in HEK293CYP2A6 cells, for all three congeners tested. CYP2A6 was specifically capable of activating PCBs 28 and 101 to genotoxic metabolites which produced genetic defects which were propagated to subsequent generations, potentially contributing to carcinogenesis. In a clinical study examining CYP2A6 enzyme activity in formerly exposed individuals with elevated internal PCB levels, a participant with increased enzyme activity showed a direct association between the phenotypic activity of CYP2A6 and the metabolism of PCB28, confirming the role of CYP2A6 in the in vivo metabolism of PCB28 also in humans. These results altogether reinforce the concept that CYP2A6 plays a pivotal role in PCB congener metabolism and suggest its significance in human health, particularly in the metabolism of lower chlorinated, volatile PCB congeners.

Ten years after: findings from the medical surveillance program on Health Effects in High-Level Exposure to PCB (HELPcB).

After the detection of high environmental and occupational exposure to polychlorinated biphenyls (PCBs) in a German recycling company for transformers and capacitors in 2010, the multidisciplinary medical surveillance program "HELPcB" (Health Effects in High-Level Exposure to PCB) was established for former PCB-exposed workers of the company, their family members, employees of surrounding companies, and area residents to investigate potential adverse health effects by PCB exposure in a longitudinal study approach with up to seven examination time points between 2010 and 2019. More than 300 individuals were enrolled into the program. Assessments particularly included plasma and urine concentrations of PCB congeners and their metabolites, clinical laboratory parameters, Comet assay, analysis of telomere length, neuropsychological examinations, psychological screening, abdominal and thyroid ultrasound examination. This review summarizes the main results of the studies conducted in the HELPcB program yielding relevant new data on potential adverse effects of PCB exposure in humans and potential mechanisms that underlie these effects. Even larger studies in PCB-exposed individuals are warranted to confirm the results of this program and to further establish causality between PCB exposure and clinical effects in humans.

Decomposition Products of the Initiator Bis(2,4-dichlorobenzoyl)peroxide in the Silicone Industry: Human Biomonitoring in Plasma and Urine of Workers.

Bis(2,4-dichlorobenzoyl)peroxide (2,4-DCBP) is used as an initiator for silicone rubber production. During hot curing, 2,4-DCBP decomposes into 2,4-dichlorobenzoic acid, 1,3-dichlorobenzene, and the polychlorinated biphenyl (PCB) congeners PCB-47, PCB-51, and PCB-68. The extent of occupational exposure to these decomposition products has not been investigated yet. We determined for the first time the corresponding internal exposure of employees (n = 104) of a German silicone rubber facility by human biomonitoring in plasma and urine. Collected samples were investigated by gas chromatography/mass spectrometry for levels of PCBs in plasma and by liquid chromatography/tandem mass spectrometry for urinary post-shift levels of 2,4-dichlorobenzoic acid (2,4-DCBA) and the metabolites 3,5-dichlorocatechol (3,5-DCK), 2,4-dichlorophenol (2,4-DCP), and 3,5-dichlorophenol (3,5-DCP). PCB-47 and PCB-68 levels correlated significantly and were found in >97% of all samples with maximum values of 4.43 and 0.77 µg/L, respectively. 2,4-DCBA, 3,5-DCK, 2,4-DCP, and 3,5-DCP were quantified in >80% of all urine samples with maximum levels of 1.46; 26.92; 7.68; and 0.39 mg/L, respectively. There is a considerable uptake of decomposition products of 2,4-DCBP in workers of a silicone rubber facility, affecting employees in all work areas. Individual levels depended on the work task. Considering the carcinogenic potential of PCBs, the workers' additional exposure to PCB-47 and PCB-68 might be of concern.

Iron-sulfur cluster loss in mitochondrial CISD1 mediates PINK1 loss-of-function phenotypes.

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra of the midbrain. Familial cases of PD are often caused by mutations of PTEN-induced kinase 1 (PINK1) and the ubiquitin ligase Parkin, both pivotal in maintaining mitochondrial quality control. CISD1, a homodimeric mitochondrial iron-sulfur-binding protein, is a major target of Parkin-mediated ubiquitination. We here discovered a heightened propensity of CISD1 to form dimers in Pink1 mutant flies and in dopaminergic neurons from PINK1 mutation patients. The dimer consists of two monomers that are covalently linked by a disulfide bridge. In this conformation CISD1 cannot coordinate the iron-sulfur cofactor. Overexpressing Cisd, the Drosophila orthologue of CISD1, and a mutant Cisd incapable of binding the iron-sulfur cluster in Drosophila reduced climbing ability and lifespan. This was more pronounced with mutant Cisd and aggravated in Pink1 mutant flies. Complete loss of Cisd, in contrast, rescued all detrimental effects of Pink1 mutation on climbing ability, wing posture, dopamine levels, lifespan, and mitochondrial ultrastructure. Our results suggest that Cisd, probably iron-depleted Cisd, operates downstream of Pink1 shedding light on PD pathophysiology and implicating CISD1 as a potential therapeutic target.