Collaborative work to evaluate toxicity on male reproductive organs by repeated dose studies in rats 15). Two-week and 4-week administration study of methyl methanesulfonate (MMS)

Development of a Test Method for the Evaluation of DNA Damage in Mouse Spermatogonial Stem Cells

Although alternative test methods based on the 3Rs (Replacement, Reduction, Refinement) are being developed to replace animal testing in reproductive and developmental toxicology, they are still in an early stage. Consequently, we aimed to develop alternative test methods in male animals using mouse spermatogonial stem cells (mSSCs). Here, we modified the OECD TG 489 and optimized the in vitro comet assay in our previous study. This study aimed to verify the validity of in vitro tests involving mSSCs by comparing their results with those of in vivo tests using C57BL/6 mice by gavage. We selected hydroxyurea (HU), which is known to chemically induce male reproductive toxicity. The 50% inhibitory concentration (IC₅₀) value of HU was 0.9 mM, as determined by the MTT assay. In the in vitro comet assay, % tail DNA and Olive tail moment (OTM) after HU administration increased significantly, compared to the control. Annexin V, PI staining and TUNEL assays showed that HU caused apoptosis in mSSCs. In order to compare in vitro tests with in vivo tests, the same substances were administered to male C57BL/6 mice. Reproductive toxicity was observed at 25, 50, 100, and 200 mg/kg/day as measured by clinical measures of reduction in sperm motility and testicular weight. The comet assay, DCFH-DA assay, H&E staining, and TUNEL assay were also performed. The results of the test with C57BL/6 mice were similar to those with mSSCs for HU treatment. Finally, linear regression analysis showed a strong positive correlation between results of in vitro tests and those of in vivo. In conclusion, the present study is the first to demonstrate the effect of HU-induced DNA damage, ROS formation, and apoptosis in mSSCs. Further, the results of the current study suggest that mSSCs could be a useful model to predict male reproductive toxicity.

Testicular spermiation failure in rats exposed prenatally to 3,3',4,4',5-pentachlorobiphenyl

Testicular spermatogenesis was studied in 7-, 10-, 13- and 17-week-old Sprague-Dawley rats whose dams had been administered intragastrically with 2.5, 25, or 250 ng of 3,3',4,4',5-pentachlorobiphenyl (PCB126) or vehicle on days 13-19 of gestation. The 250 ng groups among the 7-, 10- and 13-week-old offspring showed significant inhibition of mature spermatid release (spermiation), but 17-week-old offspring did not show this. These alterations were not observed in other PCB126 and vehicle groups, and no germ cell or Sertoli cell degeneration were observed in any group. Spermiation failure at puberty appeared in those rats born to dams exposed 250 ng/kg PCB126 on days 13-19 of gestation was reversible change that recovered at adulthood. Because the serum testosterone, luteinizing hormone and follicle-stimulating hormone concentrations were similar in the PCB126 and vehicle groups, a direct endocrine cause for the observed effects was unlikely.

Evaluation of Testicular Toxicity and Sperm Morphology in Rats Treated with Methyl Methanesulphonate (MMS)

Methyl methanesulphonate (MMS), a potent alkylating agent and testicular toxicant, was orally administered to rats for 5 days at 40 mg/kg. During the recovery period of up to 5 weeks, males were evaluated for testicular toxicity and sperm morphology. The 5-week recovery period were designated as follows: Day 1 (the day after final treatment); Week 1, Week 2, Week 3, Week 4 and Week 5 (1, 2, 3, 4 and 5 weeks after final treatment). Morphologically abnormal sperm increased beginning in Week 3, peaked in Week 4 and declined slightly in Week 5. Histopathological examinations indicated retention of step 19 spermatids at stage IX from Day 1 through Week 3. Quantitative evaluation of spermatogenic cells indicated a decrease in the number of late pachytene spermatocytes and early spermatids on Day 1. TUNEL examination showed a significantly high frequency of apoptosis in the meiosis cells in Week 1. In the present study, genetic damage induced by treatment with MMS affected spermatogenesis and a wide variety of spermatogenic cells in the testis. Apoptosis in the course of meiosis seemed to be involved in the elimination process of genetically insulted germ cells, and this process seems to play an important role in eliminating and/or decreasing the germ cells with retention of spermatids and the potential to express morphologically abnormal spermatozoa.

A TIME-COURSE CHARACTERIZATION OF MALE REPRODUCTIVE TOXICITY IN RATS TREATED WITH METHYL METHANESULPHONATE (MMS)

Methyl methanesulphonate (MMS), a potent alkylating agent and testicular toxicant, was orally administered to rats for 5 days at doses of 20, 30, and 40 mg/kg. During the recovery period of 5 weeks, males were evaluated for multiple endpoints such as organ weights, fertility, and sperm parameters. The 5-week recovery periods are designated as follows: Day 1 (1 day after final treatment); Week 1, Week 2, Week 3, Week 4, and Week 5 (first, second, third, fourth, and fifth week after final treatment). A clear time-course of dominant lethals was observed. The peak severities of the dominant lethals were observed in Week 2. It was judged that the most sensitive cellular targets for the dominant lethals are late spermatids. Sperm examination revealed a clear time-course and dose-dependent changes in the frequency of sperm morphological abnormalities. The peak severities of the sperm morphological alterations in cauda epididymis were observed in Week 4. Sensitive cellular stages for the induction of sperm morphological abnormalities were judged to be late spermatocytes and early spermatids. The most frequently observed type of morphologically abnormal spermatozoa was tailless sperm, followed by no-hook head sperm. Although the initial cause for both sperm morphological alterations and dominant lethals was suggested to be genetic insult to the germ cells, there were no obvious relationships observed between these two findings.

Tissue-dependent induction of heme oxygenase-1 and metallothionein-1/2 by methyl methanesulfonate

Methyl methanesulfonate (MMS), a methylating agent, is known to be a genotoxicant in testis. The purpose of this study was to investigate roles of oxidative stress-responsive proteins, heme oxygenase-1 (HO-1) and metallothionein-1/2 (MT-1/2), in genotoxicity of MMS. Cadmium, a potent genotoxicity inducer, induced HO-1 and MT-1/2 in rat livers and kidneys. Then we comparatively investigated MMS-induced HO-1 and MT-1/2 in rat livers, kidneys and testes. We found that a single administration of MMS (40 mg/kg) resulted in the induction of MT-1/2 mRNA in the liver, but not HO-1 mRNA, reaching maximum level at 6 hr and returning to the control levels by 24 hr. Interestingly, MMS induced both HO-1 and MT-1/2 mRNAs in the kidney. In contrast, MMS induced HO-1 mRNA, but not MT-1/2 mRNA in the testis. Since HO-1 and MT-1/2 have been recognized to respond to various oxidative stimuli, we further examined the inducing effect of MMS on these two proteins. MMS at dosages of 20 to 40 mg/kg for 2 consecutive weeks induced HO-1 mRNA (123 to 187% of the control) and protein (274 to 404% of the control) in rat testes. However, MT-1/2 mRNA was not induced by MMS administration, although a high level of expression was observed in comparison with the liver and kidney. These findings suggest that MMS induces HO-1 and/or MT-1/2 mRNA and its protein tissue-dependently, and the heme catabolites by HO-1 in the testis may contribute in some manner to its genotoxicity.