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Effects of busulfan on murine spermatogenesis: cytotoxicity, sterility, sperm abnormalities, and dominant lethal
Abstract:
The alkylating agent busulfan (Myleran) adversely affects spermatogenesis in mammals. We treated male mice with single doses of busulfan in order to quantitate its cytotoxic action on spermatogonial cells for comparison with effects of other chemotherapeutic agents, to determine its long-term effects on fertility, and to assess its possible mutagenic action. Both stem cell and differentiating spermatogonia were killed and, at doses above 13 mg/kg, stem cell killing was more complete than that of differentiating spermatogonia. Azoospermia at 56 days after treatment, which is a result of stem cell killing, was achieved at doses of over 30 mg/kg; this dose is below the LD50 for animal survival, which was over 40 mg/kg. Busulfan is the only antineoplastic agent studied thus far that produces such extensive damage to stem, as opposed to differentiating, spermatogonia. The duration of sterility following busulfan treatment depended on the level of stem cell killing and varied according to quantitative predictions based on stem cell killing by other cytotoxic agents. The return of fertility after a sterile period did not occur unless testicular sperm count reached 15% of control levels. Dominant lethal mutations, measured for assessment of possible genetic damage, were not increased, suggesting that stem cells surviving treatment did not propagate a significant number of chromosomal aberrations. Sperm head abnormalities remained significantly increased at 44 weeks after busulfan treatment, however, the genetic implications of this observation are not clear. Thus, we conclude that single doses of busulfan can permanently sterilize mice at nonlethal doses and cause long-term morphological damage to sperm produced by surviving stem spermatogonia.
Insights
Busulfan (Myleran) causes permanent sterility in male mice at nonlethal doses by damaging spermatogonial stem cells. While not mutagenic, it leads to long-term sperm abnormalities.
Area of Science:
- Reproductive toxicology
- Spermatogenesis research
- Chemotherapeutic agent effects
Background:
- Busulfan (Myleran) is an alkylating agent known to affect mammalian spermatogenesis.
- Understanding its specific cytotoxic and mutagenic actions is crucial for assessing reproductive risks.
Purpose of the Study:
- Quantitate busulfan's cytotoxic effects on spermatogonial cells.
- Determine long-term fertility impacts and potential mutagenicity.
- Compare busulfan's effects to other chemotherapeutic agents.
Main Methods:
- Single-dose administration of busulfan to male mice.
- Quantification of spermatogonial cell killing (stem and differentiating).
- Assessment of fertility, azoospermia, dominant lethal mutations, and sperm head abnormalities.
Main Results:
- Busulfan selectively killed spermatogonial stem cells more effectively than differentiating cells at doses >13 mg/kg.
- Azoospermia was achieved at doses >30 mg/kg, below the LD50 (>40 mg/kg).
- No increase in dominant lethal mutations was observed, but sperm head abnormalities persisted for 44 weeks.
Conclusions:
- Single busulfan doses can cause permanent, nonlethal sterilization in mice.
- Busulfan uniquely damages spermatogonial stem cells compared to other antineoplastics.
- Long-term morphological sperm damage occurs, but genetic implications require further study.