Protein adducts and crosslinking by reactive metabolites of polychlorinated biphenyls (PCBs)

Polychlorinated biphenyls (PCBs) are the persistent environmental pollutants with the continuous concerns over adverse human health effects. As semi-volatile compounds, PCBs were found in indoor and outdoor air. The observation of high levels of airborne PCBs in old school buildings raised the concerns of inhalation exposure and toxicity of PCBs. Lower chlorinated PCBs (LC-PCBs), major components of airborne PCBs, are subject to biotranformation. In vitro and in vivo studies revealed that reactive metabolites of LC-PCBs formed covalent adducts on DNA and proteins. The hypothesis of the project is that the reactive metabolites of LC-PCBs are able to form adducts on proteins or even protein crosslinks, and the formation of protein adducts and crosslinks causes the dysfunction of the target proteins. In addition, the objectives of the project are also to identify protein targets by PCB metabolites, which may be related to the mechanism of toxicity of LC-PCBs. The alkaline permethylation (AP) was established and optimized to identify and measure the protein adducts from LC-PCB metabolites. The AP method evidenced PCB metabolites formed protein adducts through the sulfhydryl groups and also one molecule of PCB quinoid metabolites was able to bind to more than one protein. Application of cytochrome c as the model protein revealed PCB quinoid metabolites also formed adducts on lysine and glutamic acid. The adduct formation and crosslinks caused the dysfunction of cytochrome c. In addition, the quinone protein adducts still kept the ability for redox reactions, which may lead to unexpected toxicity. The SILAC method was applied to identify the target proteins in the samples of in vitro proteome incubation. The instability of PCB quinone protein adducts was found by further reaction of quinone protein adducts. This may be the reason why cysteine-PCB quinone adducts were not frequently identified by proteomics method. The further understanding of protein adducts by reactive PCB metabolites helps to identify the target proteins, and ultimately reveal the role of protein adducts impacting on human health.