Human Reproduction, Vol 12, 1699-1705, Copyright © 1997 by Oxford University Press
A Menditto, D Pietraforte and M Minetti
The aim of this study was to assess the interaction of endogenous ascorbate
with iron and copper ions in aerobic seminal plasma. The rate of ascorbate
consumption was measured by high-performance liquid chromatography and by
the concentration of its primary oxidation product, ascorbyl radical
(Asc.-) detected by electron spin resonance spectroscopy. The modification
in the levels of Asc.- was used to investigate non-invasively and in real
time whether metal ions, either present in this fluid or exogenously added,
were catalytically active. The Asc.- was detected in seminal plasma as well
as in whole semen of all subjects and was unaffected by superoxide
dismutase, catalase or metal chelators. These findings and the rapid
decrease of Asc.- under nitrogen suggest that Asc.- is probably a result of
non-metal-catalysed air auto-oxidation, a reaction generating low levels of
reactive oxygen species. Loading of seminal plasma with either Fe2+ or Fe3+
up to a concentration of 50 microM did not increase, or increased only
slightly, the rate of ascorbate oxidation. Taking into consideration the
concentrations of iron-binding proteins in this fluid, these results
suggest that seminal plasma possesses a 'physiological ligand(s)' able to
maintain iron ions in a catalytically inactive form. Our results indicate
that citrate, which is present in seminal plasma at very high
concentrations (10-25 mM), is responsible for the inhibition of
iron-dependent catalysis. On the contrary, the loss of ascorbate and the
levels of Asc.- were significantly increased by the addition of
physiologically relevant concentrations (1 microM) of copper ions (Cu2+ but
especially Cu+). We suggest that seminal plasma is potentially exposed to
copper-mediated oxidation, a finding that could be of importance in
situations of increased copper-loading such as in some pathological
conditions or in smoking subjects.
ARTICLES
Ascorbic acid in human seminal plasma is protected from iron-mediated oxidation, but is potentially exposed to copper-induced damage
Department of Clinical Biochemistry, Istituto Superiore di Sanita, Roma, Italy.
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