1 research outputs found
Characterization of Mechanisms of Glutathione Conjugation with Halobenzoquinones in Solution and HepG2 Cells
Halobenzoquinones (HBQs) are a class
of emerging disinfection byproducts.
Chronic exposure to chlorinated drinking water is potentially associated
with an increased risk of human bladder cancer. HBQ-induced cytotoxicity
involves depletion of cellular glutathione (GSH), but the underlying
mechanism remains unclear. Here we used ultrahigh performance liquid
chromatography–high resolution mass spectrometry and electron
paramagnetic resonance spectroscopy to study interactions between
HBQs and GSH and found that HBQs can directly react with GSH, forming
various glutathionyl conjugates (HBQ-SG) in both aqueous solution
and HepG2 cells. We found that the formation of HBQ-SG varies with
the initial molar ratio of GSH to HBQ in reaction mixtures. Higher
molar ratios of GSH to HBQ facilitate the conjugation of more GSH
molecules to an HBQ molecule. We deduced the reaction mechanism between
GSH and HBQs, which involves redox cycling-induced formation of halosemiquinone
(HSQ) free radicals and glutathione disulfide, Michael addition, as
well as nucleophilic substitution. The proposed reaction rates are
in the following order: formation of HSQ radicals > substitution
of
bromine by GSH > Michael addition of GSH on the benzoquinone ring
> substitution of chlorine by GSH > substitution of the methyl
group
by GSH. The conjugates identified in HBQ-treated HepG2 cells were
the same as those found in aqueous solution containing a 5:1 ratio
of GSH:HBQs