Effects Of Tributyltin On Spermatogenesis And Sperm Maturation In Mice

This study was conducted to investigate the toxic effects of tributyltin chloride(TBTCl) at low doses(0.5,5,and 50μg/kg,respectively) on reproductive system in KM male mice as orally garaged from puberty for 45 days and gain insight into the mechanisms.The evaluation indexes of spermatogenetic disorder included testicular histology,testicular mature degree,the levels of serum gonadotropin-releasing hormones and testicular sex hormones,testicular cell apoptosis and proliferation, serum triiodothyronine(T3) and thyroxine(T4) levels,and thyroid hormone receptors(TRs) expression levels in the testes.The methods used for evaluating sperm maturation included histopathology of epididymis,sperm parameters,the activities of epididymal biochemical markers(neutralα-G]ucosidase and acid phosphatase),sperm functional parameters (acrosin and LDH-X activities),and the gene expression profiles of matrix metallopeptidase 7(or matrilysin,MMP7) and tryptophan 2,3- dioxygenase (TD02) in the epididymides.1 The effect of TBT on the spermatogenesis of testis.After exposure for 45 days,histological damage occurred in the testes of mice treated with TBT,although the gonadosomatic index(GSI) was not altered.The severity of histopathologic damage observed correlated positively with the increase of TBT concentration.Spermatogenic cells in 50μg/kg TBT group were arranged chaoticly.Large space between germ cells,increments of detached debris and some sloughed cells in seminiferous tubules were also observed in this group.Compared to the control group,TBT treatment resulted in a significant dose-dependent increase of testosterone level and a moderate dose-dependent decrease of 17β-estradiol level in the testicle.Exposure to TBT also resulted in a slight decrease of serum LH and FSH levels.TBT treatment reduced PCNA expression in a dose-dependent manner by Western blotting assay,but no significant differnce was observed compared to the control.The results of the Western blotting were compatible with the immunocytochemical data.There was a moderate increase in apoptotic-cells in the testes of mice after TBT exposure as assessed by TUNEL method,but no significant difference between the treated groups and the control was observed.TBT exposure significantly decreased serum T3 levels and the ratio of T3 to T4 in a dose-dependent manner,while the serum T4 levels were not significantly altered compared to the control.Testicular TRαtranscript levels in the treatment groups declined compared to the control.2 The effect and potential mechanism of TBT on the epididymal function and sperm maturation.TBT treatment resulted in a significant decrease in sperm count,viability and a significant increase in abnormality compared to the control in a dose-dependent manner.No obvious histological damage was found in caput epididymis,but in corpus and cauda epididymis,the severity of histological damage increased dose-dependently after treatment.The primary pathological changes observed in the treatment groups were listed as follows:The epithelial cells of corpus epididymal tubules were arranged loosely,and the inter-tubule space became large.Sperm amount in the lumens of epididymal duct decreased.A large amount of sperm was agglutinated in the epididymal lumen area in the middle and high dose groups.Loosely arranged epithelial cells,large inter-tubule space and decreased sperm amount were also found in cauda epididymis,furthermore,connective tissue between tubules in cauda epididymis lessened.No significant alteration was observed in neutralα- glucosidase activity in the epididymides of the treatment groups compared to the control,even though there is a slight decline after TBT exposure.There was a dose-dependent decline trend in the acid phosphatase activity,compared with the control.Acrosin activity from the cauda epididymal spermatozoa showed a dose-dependent decrease,which reach significance in 50μg/kg TBT group.Lactate dehydrogenase-x isoenzyme(LDH-X) activity was also significantly inhibited in the high dose group.The transcript expression of MMP7 in the epididymides of mice exposed to TBT was significantly decreased in 5 and 50μg/kg groups, and the expression of TD02 transcript was significantly reduced in a dose-dependent manner.In conclusion,the results in this study strongly suggest that TBT exposure perturb spermatogenesis of pubertal mice.By histological observation and mature degree assessment,we confirmed that normal tissue structure of testis was impaired by TBT,and the development of testis was suppressed.Elevated testosterone level and decreased 17β-estradiol, LH and FSH levels suggested that TBT adminstration induced reproductive endocrine dysfunction,and thereby affected the spermatogenesis in the testes.TBT exposure significantly decreased serum T3 level and T3/T4 ratio.The TRαtranscript in the testes was decreased after TBT treatment. These results indicated that TBT could affect the normal function of thyroid gland,which can further interrupt spermatogenesis.Moreover,TBT can induce cell apoptosis and inhibit cell proliferation,which would be one of the mechanisms of TBT-induced spermatogenetic disorder.The spermatogenetic abnormality present in this study should result from the interaction of many factors and pathways mentioned above.The results in the present study show that TBT has a potential role in affecting the epididymal function and sperm maturation.The normal tissue structure of epididymis was impaired by this compound.The decline of sperm count and quality caused by TBT suggests that this chemical compound could affect sperm qualtity.The decline of acid phosphatase activity might somewhat relate with the TBT- induced increase in sperm abnormality. Acrosin and lactate dehydrogenase-x isoenzyme(LDH-X) activities from the cauda epididymal spermatozoa significantly decreased after TBT treatment, which favor the conclusion drawn from the results of sperm parameters detection that TBT could cause a spermatotoxic effects.TBT also significantly inhibited the expression of some genes(MMP7 and TD02) which might be correlated with epididymal function and sperm maturation.The results mentioned above indicate that TBT could cause epididymal and sperm toxicity.The decline of sperm count and quality caused by TBT could further impair fertility in animals.