Menditto A, Pietraforte D, Minetti M
Department of Clinical Biochemistry, Istituto Superiore di Sanità, Roma, Italy.
Hum Reprod. 1997 Aug;12(8):1699-705. doi: 10.1093/humrep/12.8.1699.
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.
本研究的目的是评估内源性抗坏血酸与需氧精浆中铁离子和铜离子的相互作用。通过高效液相色谱法测定抗坏血酸的消耗速率，并通过电子自旋共振光谱法检测其主要氧化产物抗坏血酸自由基（Asc.-）的浓度。利用Asc.-水平的变化来实时、非侵入性地研究该液体中存在的或外源添加的金属离子是否具有催化活性。在所有受试者的精浆和全精液中均检测到了Asc.-，且其不受超氧化物歧化酶、过氧化氢酶或金属螯合剂的影响。这些发现以及在氮气环境下Asc.-的快速减少表明，Asc.-可能是非金属催化的空气自动氧化的结果，该反应会产生低水平的活性氧。向精浆中加入浓度高达50 microM的Fe2+或Fe3+，抗坏血酸氧化速率并未增加，或仅略有增加。考虑到该液体中铁结合蛋白的浓度，这些结果表明精浆中存在一种“生理配体”，能够使铁离子保持催化无活性的形式。我们的结果表明，精浆中浓度非常高（10 - 25 mM）的柠檬酸是抑制铁依赖性催化的原因。相反，加入生理相关浓度（1 microM）的铜离子（Cu2+，尤其是Cu+）会显著增加抗坏血酸的损失和Asc.-的水平。我们认为精浆可能会受到铜介导的氧化作用，这一发现在某些病理状况或吸烟人群等铜负荷增加的情况下可能具有重要意义。
