Effects of oral d-aspartate on sperm quality in B6N mice

The goal of this study was to investigate the effects of oral administration of d-aspartate (D-Asp) to sexually immature male C57BL/6NTacCnrm (B6N) mice on the in vitro fertilisation (IVF) rate with cryopreserved-thawed spermatozoa and on cryopreserved sperm quality as well as on LH, epitestosterone, and testosterone levels. Males were treated at 7 weeks of age with a dose of 20 mM sodium d-aspartate in drinking water for 1.3, 2, 4 or 6 weeks so that they were 8.3, 9, 11 or 13 weeks of age, respectively, at the end of the study. The timepoints for controls were week 0 (start of experiment), 1.3, 2, 4 or 6, whereby mice received no D-Asp. At each timepoint, spermatozoa were cryopreserved for IVF and testes as well as sera were frozen for hormone level measurement. After 2 and 4 weeks of treatment, the IVF rate was significantly higher in the D-Asp group than in the controls (64% vs. 44% and 52% vs. 38%, respectively). Spermatozoa from D-Asp-treated males showed lower morphological abnormalities than their control counterparts. After 2 and especially after 4 weeks of treatment, the hormone levels in sera and testes and the total and progressive motility of the spermatozoa were higher in D-Asp-treated males. Although we did not elucidate the full mechanism leading to an improved IVF rate with spermatozoa from D-Asp-treated males lower morphological abnormalities and increased motility contribute to this observation. Importantly, D-Asp significantly improved the IVF rates as early as 2 weeks after treatment when mice were only 9 weeks old. This implies that sperm can be efficiently cryopreserved from younger males, compared to 13-weeks-old males, which are usually used for sperm cryopreservation. This is of relevance when genetic alterations cause premature death in males as well as high severity levels in older mice and aids in better resource management.