Hydroxycobalamin catalyzes the oxidation of diethyldithiocarbamate and increases its cytotoxicity independently of copper ions

M.E Solovieva,Yu.V Shatalin,V.V Solovyev,A.V Sazonov,V.P Kutyshenko,V.S Akatov

doi:10.1016/j.redox.2018.09.016

M.E Solovieva, Yu.V Shatalin + Show 4 more

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https://doi.org/10.1016/j.redox.2018.09.016

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Abstract

It is known that some metals (Cu, Zn, Cd, Au) markedly increase the toxic effect of thiocarbamates. It was shown in the present study that hydroxycobalamin (a form of vitamin B12, HOCbl), which incorporates cobalt, significantly enhances the cytotoxicity of diethyldithiocarbamate (DDC), decreasing its IC50 value in tumor cells three to five times. The addition of HOCbl to aqueous DDC solutions accelerated the reduction of oxygen. No hydrogen peroxide accumulation was observed in DDC + HOCbl solutions; however, catalase slowed down the oxygen reduction rate. Catalase as well as the antioxidants N-acetylcysteine (NAC) and glutathione (GSH) partially inhibited the cytotoxic effect of DDC + HOCbl, whereas ascorbate, pyruvate, and tiron, a scavenger of superoxide anion, had no cytoprotective effect. The administration of HOCbl into DDC solutions (> 1 mM) resulted in the formation of a crystalline precipitate, which was inhibited in the presence of GSH. The data of UV and NMR spectroscopy and HPLC and Mass Spectrometry (LC/MS) indicated that the main products of the reaction of DDC with HOCbl are disulfiram (DSF) and its oxidized forms, sulfones and sulfoxides. The increase in the cytotoxicity of DDC combined with HOCbl occurred both in the presence of Cu2+ in culture medium and in nominally Cu-free solutions, as well as in growth medium containing the copper chelator bathocuproine disulfonate (BCS). The results indicate that HOCbl accelerates the oxidation of DDC with the formation of DSF and its oxidized forms. Presumably, the main cause of the synergistic increase in the toxic effect of DDC + HOCbl is the formation of sulfones and sulfoxides of DSF.

Highlights

SH-containing compounds are involved in the scavenging of reactive oxygen species (ROS) and are widely used as antioxidants
We have previously shown that hydroxycobalamin, in combination with the antioxidant thiols GSH, NAC, and DTT is capable of catalyzing the formation of hydrogen peroxide at concentrations up to 30–250 μM
DDC in the range of concentrations less than 1 mM did not affect the viability of А549, НЕр–2, and А431 cells over a period of 48 h, which agrees well with the results reported by other authors for pyrrolidine dithiocarbamate, an analog of DDC [19,42]

Summary

Introduction

SH-containing compounds are involved in the scavenging of reactive oxygen species (ROS) and are widely used as antioxidants. In reactions with ions of transition metals, thiols are capable of generating ROS and producing a damaging action on cells and tissues [1,2,3,4]. We have previously shown that hydroxycobalamin (a form of vitamin B12, HOCbl), in combination with the antioxidant thiols GSH, NAC, and DTT is capable of catalyzing the formation of hydrogen peroxide at concentrations up to 30–250 μM. This catalysis considerably enhances the cytotoxic action of these classical thiol compounds and leads to the manifestation of the prooxidant action of DTT, GSH, and NAC [7,8]

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