Seminal Oxidation–Reduction Potential Correlates with Not Only Seminal Oxidative But Also Nitrosative Stresses

Reactive oxygen species and reactive nitrogen species in semen are both essential for fertilization process; however, they become harmful at excessive levels, causing oxidative stress and nitrosative stress, respectively. Recently, oxidation–reduction potential (ORP) has been used as a marker for measuring oxidative stress, and this study investigated the possibility of comprehensively evaluating nitrosative stress. The correlation between standardized ORP (sORP) and 8-hydroxy-2′-deoxyguanosine (8-OHdG) and NOx per unit sperm was tested. Based on the previously reported cutoff value, samples were classified into oxidative stress-positive and negative groups. Thereafter, a receiver operating characteristic curve was drawn on 8-OHdG and NOx, and each optimal cutoff value was determined. Both standardized 8-OHdG and NOx significantly correlated with sORP. Although both correlated significantly with sORP in the oxidative stress group, no correlation was found in the nonoxidative stress group. The optimal standardized 8-OHdG level to determine oxidative stress status was 0.52 ng/106 spermatozoa, and the standardized NOx was 0.17 µM/106 spermatozoa/mL. The ORP is a simpler and quicker assay that can comprehensively assess oxidative and nitrosative stresses. Optimal cutoff values for both stresses were established in this study.