Despite advances in the field of male reproductive health, idiopathic male infertility, in which a man has altered semen characteristics without an identifiable cause and there is no female factor infertility, remains a challenging condition to diagnose and manage. Increasing evidence suggests that oxidative stress (OS) plays an independent role in the etiology of male infertility, with 30% to 80% of infertile men having elevated seminal reactive oxygen species levels. OS can negatively affect fertility via a number of pathways, including interference with capacitation and possible damage to sperm membrane and DNA, which may impair the sperm's potential to fertilize an egg and develop into a healthy embryo. Adequate evaluation of male reproductive potential should therefore include an assessment of sperm OS. We propose the term Male Oxidative Stress Infertility, or MOSI, as a novel descriptor for infertile men with abnormal semen characteristics and OS, including many patients who were previously classified as having idiopathic male infertility. Oxidation-reduction potential (ORP) can be a useful clinical biomarker for the classification of MOSI, as it takes into account the levels of both oxidants and reductants (antioxidants). Current treatment protocols for OS, including the use of antioxidants, are not evidence-based and have the potential for complications and increased healthcare-related expenditures. Utilizing an easy, reproducible, and cost-effective test to measure ORP may provide a more targeted, reliable approach for administering antioxidant therapy while minimizing the risk of antioxidant overdose. With the increasing awareness and understanding of MOSI as a distinct male infertility diagnosis, future research endeavors can facilitate the development of evidence-based treatments that target its underlying cause.

These guidelines can be applied in clinical work and indicate future research needs.

The longest part of the sperm flagellum, the principal piece, contains the fibrous sheath, a cytoskeletal element unique to spermiogenesis. We performed mass spectrometry proteomics on isolated human fibrous sheaths identifying a unique ADP/ATP carrier protein, SFEC [AAC4], seven glycolytic enzymes previously unreported in the human sperm fibrous sheath, and sorbitol dehydrogenase. SFEC, pyruvate kinase and aldolase were co-localized by immunofluorescence to the principal piece. A homology model constructed for SFEC predicted unique residues at the entrance to the nucleotide binding pocket of SFEC that are absent in other human ADP/ATP carriers, suggesting opportunities for selective drug targeting. This study provides the first evidence of a role for an ADP/ATP carrier family member in glycolysis. The co-localization of SFEC and glycolytic enzymes in the fibrous sheath supports a growing literature that the principal piece of the flagellum is capable of generating and regulating ATP independently from mitochondrial oxidation in the mid-piece. A model is proposed that the fibrous sheath represents a highly ordered complex, analogous to the electron transport chain, in which adjacent enzymes in the glycolytic pathway are assembled to permit efficient flux of energy substrates and products with SFEC serving to mediate energy generating and energy consuming processes in the distal flagellum, possibly as a nucleotide shuttle between flagellar glycolysis, protein phosphorylation and mechanisms of motility.

Chronic genital tract inflammations are a frequent cause or at least a concomitant factor of male fertility disturbances. The diagnosis is difficult because of the mostly asymptomatic course of the disease. Therefore, determination of biochemical markers of inflammation in addition to the number of leucocytes in the seminal plasma has been recommended. The aim of the study was to find out whether determination of granulocyte elastase and interleukin-6 provide comparable and reliable results with regard to diagnosis of genital tract inflammation; in addition, the association between genital tract inflammation and semen quality should be evaluated with special focus on potentially disturbed sperm functions like sperm motility and DNA integrity. In a prospective study, the concentrations of interleukin-6 (IL-6) and granulocyte elastase were determined in seminal plasma samples from 340 patients to investigate the relationship with other parameters of genital tract inflammation such as the number of peroxidase-positive cells and conventional semen parameters. Microbiological investigations were included. As post-testicular inflammatory influences may cause sperm DNA damage, the correlation between IL-6 and elastase and DNA integrity was evaluated by the sperm chromatin structure assay. IL-6 and elastase were significantly correlated both with each other (P < 0.01) and the number of peroxidase-positive cells (P < 0.01). IL-6 showed a highly significant negative correlation with sperm vitality (P < 0.01) and a significant negative correlation with sperm motility (P < 0.05). Elastase concentrations were highly significantly associated with the number of peroxidase-positive cells (P < 0.01) and negatively correlated with sperm vitality (P < 0.01). Moreover, there were significantly negative correlations with sperm motility (P < 0.05), progressive motility according to WHO a quality (P < 0.05) as well as sperm morphology (P < 0.05). In addition, a significant negative correlation was observed between elastase concentrations and percentage of spermatozoa with intact DNA, which may suggest the use of anti-inflammatory treatment. It can be concluded that both IL-6 and granulocyte elastase are useful and suitable as markers for silent genital tract inflammation; in contrast to previous contributions there were clear correlations of IL-6 and granulocyte elastase with sperm parameters, the relationship of elastase with semen quality being more marked. Moreover, the results of the study confirm the need for a change of the threshold value of peroxidase-positive cells according to WHO definition to lower levels for definition of silent genital tract inflammation.

Low levels of ROS exert critical function in normal sperm physiology, such as fertilizing ability (acrosome reaction, hyperactivation, capacitation, and chemotaxis) and sperm motility; while increased ROS generation and/or decreased antioxidant capacity leads to the imbalance between oxidation and reduction in living systems, which is called sperm oxidative stress. This condition was widely considered to be a significant contributory factor to sperm DNA damage/apoptosis, lipid peroxidation, and reduced motility, which in turn, increased risk of male factor infertility/subfertility and birth defects. Under the current status quo, numerous subsequent studies have concentrated on antioxidant therapy. Although utility of such a therapeutic strategy significantly improved sperm function and motility in a myriad of experimental and clinical reports, the overall effectiveness still remains controversial mainly due to non-standardized assay to measure the level of ROS and sperm DNA damage, various antioxidant supplementation strategies, and inadequate fertilization and pregnancy data after clinical treatment. Therefore, standardized assessment and evaluation of ROS and total antioxidant capacity in semen should be established to keep ROS in a physiological level and prevent over-treatment of antioxidants toward reductive stress, which should be kept in mind, especially in assisted reproductive procedure. Moreover, the significance of large sample size populations, double-blind randomized, placebo-controlled clinical trials of antioxidant therapies is emphasized in this review to achieve optimal ingredients and dosage of antioxidants for patients with reactive oxygen-induced male fertility/subfertility.