Prognostic factors for high sperm <scp>DNA</scp> fragmentation in infertile Japanese men

The number of successful births after assisted reproduction technology (ART) has gradually increased worldwide. With regards to advanced ART, sperm quality rather than quantity is used to evaluate male infertility. In addition to conventional semen analysis, the sperm DNA fragmentation index (sDFI) is widely used to evaluate sperm quality while assessing male infertility. A high sDFI is associated with not only failure to achieve pregnancy but also recurrent pregnancy loss.1 Although studies on factors affecting sDFI have been conducted in several countries,2-4 no large-scale studies have been performed in Japan. Therefore, in this study, we investigated factors that increase sDFI in infertile Japanese men. This study was a retrospective review that analyzed the clinical records of 1360 infertile men at our institution between November 2015 and July 2022. Patients with chronic and acute inflammatory diseases, chronic prostatitis, urinary tract infection, malignant diseases, or a history of anti-cancer chemotherapy and/or radiation therapy were excluded, along with those receiving hormonal or antioxidant treatment. We extracted data on the following patient characteristics: age; body mass index; smoking habit; frequency of alcohol consumption; presence of testicular varicocele; testicular volume by orchidometer; serum levels of luteinizing hormone, follicle-stimulating hormone, and total testosterone (TT); lifestyle-related serum markers (such as lipid protein, glucose, etc.); and blood levels of trace elements. Conventional semen analyses and sDFI measurement were performed as previously described.5 Univariate analysis was performed using the Mann–Whitney U test for continuous variables and the x2-test for categorical variables, followed by multivariate analysis to extract the contributing factors. To evaluate factors influencing sDFI, clinical data were compared between a group with low sDFI (<24.0%) and a group with high sDFI (≥24.0%), based on our previous study.5 The cut off value (24.0%) was set to obviate the outcomes of pregnancies resulting from timed intercourse or intrauterine insemination. The results of univariate analysis revealed that age, average testicular volume, grade 3 testicular varicocele, serum levels of luteinizing hormone, follicle-stimulating hormone, and TT levels differed significantly between the two groups (p < 0.05) (Table 1a). Furthermore, the results of multivariate analysis revealed that age and grade 3 varicocele, TT levels differed significantly between the two groups (p < 0.05), whereas average testicular volume, serum levels of luteinizing hormone, and follicle-stimulating hormone were not significantly different (p > 0.05) (Table 1a). Moreover, sDFI gradually increased with age (particularly above 35 years old) (Table 1b). Age, varicocele and TT levels were found to be more useful prognostic factors compared with lifestyle-related factors (alcohol consumption, smoking, obesity), lifestyle-related disease status (dyslipidemia, liver dysfunction, hyperuricemia, glucose intolerance). We found that sDFI worsened with paternal aging, which is consistent with previous studies.2, 3, 6 A study investigating the association of sDFI with lifestyle-related factors in infertile Chinese men reported that age and semen parameters were independently correlated with sDFI. It is thought that defective sperm chromatin packaging, oxidative stress, and disordered apoptosis play a role in age-related increases in sDFI. With increased age, the accumulation of oxidative stress and decreased antioxidant potential may cause oxidative damage to the nucleus of sperm DNA.6 We also found that sDFI was positively associated with grade 3 varicocele, which is consistent with a previous study.7 Meta-analysis showed that infertile men with varicocele have greater sperm DNA damage than that in patients without varicocele. The correlation of increased sDFI with varicocele was presumably attributed to the accumulation of oxidative stress, which impaired sperm DNA.7 Moreover, sDFI was positively associated with TT levels. Low TT levels, which is involved in the progression and maintenance of spermatogenesis, might be associated with high sDFI. The main limitation of this study is the homogeneity of the samples. We reviewed data from a university-affiliated tertiary hospital database. Therefore, there was minimal variation in patient income, educational level, occupation, and obesity (e.g., a body mass index >35.0 kg/m2 was observed in less than 1% of the patients). In conclusion, there are many potential factors associated with sDFI, including age, varicocele, and seminal reproductive hormones levels. In theory, lifestyle-related factors can affect sDFI. However, the potential effects of seminal reproductive hormones and lifestyle-related factors on sperm DNA damage still require verification via studies with a rigorous design and a larger, more diverse study population. Akiyoshi Osaka: Data curation; writing – original draft; formal analysis. Toshiyuki Iwahata: Data curation. Akinori Nakayama: Formal analysis. Hiroshi Okada: Supervision. Kazutaka Saito: Supervision; writing – review and editing. Kouhei Sugimoto: Supervision. Kazutaka Saito is an Editorial Board member of International Journal of Urology and a co-author of this article. To minimize bias, they were excluded from all editorial decision-making related to the acceptance of this article for publication. This study was approved by the ethics committee of Dokkyo Medical University Saitama Medical Center (approval number: 23021) and conforms to the provisions of the Declaration of Helsinki. N/A. N/A. N/A. This study was not funded by a specific grant from any funding agency in the public, commercial, or not-for-profit sectors.