(1) Background: Testosterone plays a key role in spermatogenesis and in maintaining semen quality and sperm DNA integrity. Consequently, reduced testosterone levels may disrupt these processes and contribute to male infertility. This study aimed to evaluate the impact of low testosterone levels on semen parameters, sperm DNA fragmentation, and chromatin condensation; (2) Methods: This was a prospective study that included 214 men aged 25–45 years undergoing infertility evaluation. Participants were classified into two groups according to serum testosterone levels: low testosterone and normal testosterone. Total testosterone was determined using electrochemiluminescence immunoassay. Semen analysis was carried out according to the WHO 2021 guidelines. The DNA fragmentation index was assessed using the TUNEL assay. The sperm decondensation index was evaluated by aniline blue staining; (3) Results: Men with low serum total testosterone levels (<2.64 ng/mL) exhibited significantly impaired semen parameters compared with those with normal testosterone levels. Serum total testosterone was positively correlated with sperm concentration (rs = 0.43, p < 0.001), total motility (rs = 0.20, p = 0.005), normal morphology (rs = 0.25, p < 0.001), and sperm vitality (rs = 0.173, p = 0.014). In contrast, testosterone levels were negatively correlated with the DNA fragmentation index (rs = −0.221, p = 0.0017) and the chromatin decondensation index (rs = −0.19, p = 0.0086). A higher proportion of pathological DFI (>15%) was observed in the low testosterone group. (4) Conclusions: These findings support the essential role of testosterone in sustaining spermatogenesis, semen quality, and sperm DNA integrity and highlight the crucial importance of testosterone assessment in the diagnosis and pathophysiological understanding of male infertility.

(1) Background: Oxidative stress (OS) has been extensively associated with male infertility, contributing to its pathophysiology in approximately 30–80% of affected individuals. Excessive reactive oxygen species (ROS) levels trigger a cascade of interconnected processes, including lipid peroxidation, DNA damage, and mitochondrial dysfunction, ultimately impairing sperm quality. (2) Methods: The present study was designed to examine the relationship between seminal oxidative stress biomarkers such as superoxide dismutase (SOD), catalase (CAT), and malondialdehyde (MDA) and sperm DNA integrity in men with unexplained (UMI) and idiopathic (IMI) male infertility. The study population comprised 235 participants, who were divided into three groups: fertile controls (n = 78), UMI (n = 88), and IMI (n = 69). Semen analysis was performed according to WHO criteria. Sperm DNA fragmentation index (DFI) was assessed using the TUNEL assay, while sperm decondensation index (SDI) was evaluated by aniline blue staining. Seminal OS biomarkers were measured in seminal plasma using spectrophotometric methods. (3) Results: DFI and SDI were significantly increased in infertile groups compared with fertile controls (p < 0.001), exceeding the clinical thresholds of 30% and 15%, respectively. Antioxidant enzyme activities (SOD and CAT) were significantly reduced, whereas MDA levels were significantly elevated, particularly in the IMI group (p < 0.001). Correlation analysis revealed strong positive associations between MDA and both DFI (r = 0.76, p < 0.001) and SDI (r = 0.80, p < 0.001). Additionally, MDA, DFI, and SDI were negatively correlated with semen parameters, whereas SOD and CAT were positively correlated with sperm quality (p < 0.001). (4) Conclusions: Our findings emphasize the critical role of oxidative stress and sperm DNA integrity as potential biomarkers for the diagnosis and evaluation of UMI and IMI.

Oxidative stress, defined as an imbalance between reactive oxygen species (ROS) production and antioxidant defenses, plays a central role in the pathophysiology of male infertility and has been reported in approximately 30%–80% of infertile men. Excessive ROS production promotes lipid peroxidation, DNA damage, and mitochondrial dysfunction, ultimately compromising sperm quality. The aim of our study was to evaluate oxidative stress biomarkers in seminal plasma, including malondialdehyde (MDA) as a marker of lipid peroxidation and key enzymatic antioxidants superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), and to assess their impact on sperm DNA fragmentation, semen parameters, and serum total testosterone levels. Semen samples were collected from a total of 150 participants, including 120 infertile men (30 oligozoospermic, 30 teratozoospermic, 30 asthenozoospermic, and 30 necrozoospermic) and 30 fertile controls. Semen analysis was performed according to WHO 2021 criteria. Sperm DNA fragmentation index (DFI) was assessed using the TUNEL assay. Seminal antioxidant enzyme activities (SOD, CAT, and GPx) and lipid peroxidation levels were measured in seminal plasma using spectrophotometric methods. Serum total testosterone levels were measured using an electrochemiluminescence immunoassay. The results showed that DFI and MDA levels were significantly higher in infertile men compared with controls. Conversely, seminal antioxidant enzyme activities and serum testosterone levels were significantly lower in the infertile groups ( p < 0.05). DFI was positively correlated with MDA ( r = 0.63, p < 0.001). In contrast, reduced seminal antioxidant enzyme activities and lower testosterone levels were negatively associated with higher DFI and MDA ( p < 0.001). Additionally, both DFI and MDA showed negative correlations with semen parameters. Our findings highlight the potential value of oxidative stress biomarkers and sperm DNA fragmentation assessment in the evaluation of male infertility, emphasizing the central role of oxidative stress in sperm dysfunction.