Development
and Validation of the First Assay Method
Coupling Liquid Chromatography with Chemiluminescence for the Simultaneous
Determination of Menadione and Its Thioether Conjugates in Rat Plasma
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Abstract
Menadione
(2-methyl-1,4-naphthoquinone, MQ), a component of multivitamin
drugs with antihemorrhagic, antineoplastic, and antimalarial activity,
is frequently used to investigate quinone-induced cytotoxicity. The
formation of MQ conjugates with glutathione (GSH) by Michael addition
and subsequent biotransformation to yield <i>N</i>-acetyl-l-cysteine conjugates is believed to be an important detoxification
process. However, the resulting conjugates, 2-methyl-3-(glutathione-<i>S</i>-yl)-1,4-naphthoquinone (MQ-GS) and 2-methyl-3-(<i>N</i>-acetyl-l-cysteine-<i>S</i>-yl)-1,4-naphthoquinone
(MQ-NAC), retain the ability to redox cycle and to arylate cellular
nucleophiles. Although the nephrotoxicity and hepatotoxicity of MQ-thiol
conjugates have been reported <i>in vitro</i>, methods for
their determination <i>in vivo</i> have yet to be published.
Herein, a highly sensitive, simple, and selective HPLC-chemiluminescence
(HPLC-CL) coupled method is reported, allowing for the first time
the simultaneous determination of MQ, MQ-GS, and MQ-NAC in rat plasma
after MQ administration. Our method exploits the unique redox characteristics
of MQ, MQ-GS, and MQ-NAC to react with dithiothreitol (DTT) to liberate
reactive oxygen species (ROS) which are detected by a CL assay using
luminol as a CL probe. To verify the proposed mechanism, MQ-GS and
MQ-NAC were synthetically prepared. Specimen preparation involved
solid-phase extraction on an Oasis HLB cartridge followed by isocratic
elution on an ODS column. No interference from endogenous substances
was detected. Linearity was observed in the range of 5β120
nM for MQ-GS and MQ-NAC and 10β240 nM for MQ, with detection
limits (S/N of 3) of 1.4, 0.8, and 128 fmol for MQ-GS, MQ-NAC, and
MQ, respectively. The application of our method reported here is the
first to extensively study the stability and reversibility of thiol-quinones