ASCORBIC-ACID IN HUMAN SEMINAL PLASMA IS PROTECTED FROM IRON-MEDIATEDOXIDATION, BUT IS POTENTIALLY EXPOSED TO COPPER-INDUCED DAMAGE

The aim of this study was to assess the interaction of endogenous asco rbate with iron and copper ions in aerobic seminal plasma, The rate of ascorbate consumption was measured by high-performance Liquid chromat ography and by the concentration of its primary oxidation product, asc orbyl radical (Asc(.-)) detected by electron spin resonance spectrosco py. 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 ail subj ects and was unaffected by superoxide dismutase, catalase or metal che lators, These findings and the rapid decrease of Asc(.-) under nitroge n suggest that Asc(.-) is probably a result of non-metal-catalysed air auto-oxidation, a reaction generating low levels of reactive oxygen s pecies. Loading of seminal plasma with either Fe2+ or Fe3+ up to a con centration of 50 mu M did not increase, or increased only slightly, th e rate of ascorbate oxidation, Taking into consideration the concentra tions of iron-binding proteins in this fluid, these results suggest th at seminal plasma possesses a 'physiological ligand(s)' able to mainta in iron ions in a catalytically inactive form, Our results indicate th at citrate, which is present in seminal plasma at very high concentrat ions (10-25 mM), is responsible for the inhibition of iron-dependent c atalysis, On the contrary, the loss of ascorbate and the levels of Asc (.-) were significantly increased by the addition of physiologically r elevant concentrations (1 mu M) of copper ions (Cu2+ but especially Cu +). We suggest that seminal plasma is potentially exposed to copper-me diated oxidation, a finding that could be of importance in situations of increased copper-loading such as in some pathological conditions or in smoking subjects.