Archives of Toxicology

, Volume 65, Issue 2, pp 129–134 | Cite as

Degradation of methyl and ethyl mercury into inorganic mercury by oxygen free radical-producing systems: Involvement of hydroxyl radical

  • Ikuo Suda
  • Shinji Totoki
  • Hitoshi Takahashi
Original Investigations

Abstract

Degradation of methyl mercury (MeHg) and ethyl Hg (EtHg) with oxygen free radicals was studied in vitro by using three well-known hydroxyl radical (•OH)-producing systems, namely Cu2+-ascorbate, xanthine oxidase (XOD)-hypoxanthine (HPX)-Fe(III)EDTA and hydrogen peroxide (H2O2)-ultraviolet light B. For this purpose, the direct determination method for inorganic Hg was employed. MeHg and EtHg were readily degraded by these three systems, though the amounts of inorganic Hg generated from MeHg were one half to one third those from EtHg. Degradation activity of XOD-HPX-Fe(III)EDTA system was inhibited by Superoxide dismutase, catalase and the •OH scavengers and stimulated by H2O2. Deletion of the •OH formation promoter Fe(III)EDTA from XOD-HPX-Fe(III)EDTA system resulted in the decreased degradation of MeHg and EtHg, which was enhanced by further addition of the iron chelator diethylenetriamine pentaacetic acid. In all these cases, a good correlation was observed between alkyl Hg degradation and deoxyribose oxidation determining •OH. By contrast, their degradation appeared to be unrelated to either Superoxide anion\((O_{2^ - } )\) production or H2O2 production alone. We further confirmed that H2O2 (below 2 mM) itself did not cause significant degradation of MeHg and EtHg. These results suggested that •OH, but not\(O_{2^ - } \) and H2O2, might be the oxygen free radical mainly responsible for the degradation of MeHg and EtHg.

Key words

Methyl mercury Ethyl mercury Biotransformation Free radicals 

Abbreviations

Hg

mercury

MeHg

methyl mercury

EtHg

ethyl mercury

\(O_{2^ - } \)

Superoxide anion

H2O2

hydrogen peroxide

•OH

hydroxyl radical

1O2

singlet oxygen

HOCl

hypochlorous acid

NAC

N-acetyl-l-cysteine

XOD

xanthine oxidase

HPX

hypoxanthine

Fe(III)EDTA

ferric monosodium ethylenediaminetetraacetate

DETAPAC

diethylenetriamine pentaacetic acid

SOD

Superoxide dismutase

UV

ultraviolet light

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Copyright information

© Springer-Verlag 1991

Authors and Affiliations

  • Ikuo Suda
    • 1
  • Shinji Totoki
    • 1
  • Hitoshi Takahashi
    • 1
  1. 1.Department of Pharmacology, Institute for Medical ImmunologyKumamoto University Medical SchoolKumamotoJapan

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