Development of an in vitro test system for assessment of male, reproductive toxicity

A male germ cell assay and supporting somatic cells: its application for the detection of phase specificity of genotoxins in vitro

Male germ stem cells are responsible for transmission of genetic information to the next generation. Some chemicals exert a negative impact on male germ cells, either directly, or indirectly affecting them through their action on somatic cells. Ultimately, these effects might inhibit fertility, and may exhibit negative consequences on future offspring. Genotoxic anticancer agents may interact with DNA in germ cells potentially leading to a heritable germline mutation. Experimental information in support of this theory has not always been reproducible and suitable in vivo studies remain limited. Thus, alternative male germ cell tests, which are now able to detect phase specificity of such agents, might be used by regulatory agencies to help evaluate the potential risk of mutation. However, there is an urgent need for such approaches for identification of male reproductive genotoxins since this area has until recently been dependent on in vivo studies. Many factors drive alternative approaches, including the (1) commitment to the principles of the 3R's (Replacement, Reduction, and Refinement), (2) time-consuming nature and high cost of animal experiments, and (3) new opportunities presented by new molecular analytical assays. There is as yet currently no apparent appropriate model of full mammalian spermatogenesis in vitro, under the REACH initiative, where new tests introduced to assess genotoxicity and mutagenicity need to avoid unnecessary testing on animals. Accordingly, a battery of tests used in conjunction with the high throughput STAPUT gravity sedimentation was recently developed for purification of male germ cells to investigate genotoxicity for phase specificity in germ cells. This system might be valuable for the examination of phases previously only available in mammals with large-scale studies of germ cell genotoxicity in vivo. The aim of this review was to focus on this alternative approach and its applications as well as on chemicals of known in vivo phase specificities used during this test system development.

Ameliorative effects of nano-selenium against NiSO4-induced apoptosis in rat testes

Nickel (Ni) is a common environmental pollutant, which has toxic effects on reproductive system. Nowadays, nano-selenium (Nano-Se) has aroused great attention due to its unique antioxidant effect, excellent biological activities and low toxicity. The aim of this study was to explore the protective effects of Nano-Se on NiSO₄-induced testicular injury and apoptosis in rat testes. Nickel sulfate (NiSO₄) (5 mg/kg b.w.) was administered intraperitoneally and Nano-Se (0.5, 1, and 2 mg Se/kg b.w., respectively) was given by oral gavage in male Sprague-Dawley rats. Histological changes in the testes were determined by H&E staining. The terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and immunohistochemistry were performed to evaluate the apoptosis in testes. Expression levels of mitochondrial apoptosis-related genes and proteins were analyzed by RT-qPCR and Western blot. The results showed that Nano-Se improved lesions of testicular tissue induced by NiSO₄. Nano-Se significantly alleviated NiSO₄-induced apoptosis in rat testes, as well as significantly downregulated the Bak, cytochrome c, caspase-9 and caspase-3 and upregulated Bcl-2 expression levels, all of which were involved in mitochondria-mediated apoptosis. Altogether, we concluded that Nano-Se may potentially exert protective effects on NiSO₄-induced testicular injury and attenuate apoptosis, at least partly, via regulating mitochondrial apoptosis pathways in rat testes.

Roles for Kisspeptin in proliferation and differentiation of spermatogonial cells isolated from mice offspring when the cells are cocultured with somatic cells

Kisspeptin (Kp) expression in testis has caused most of the recent research surveying its functional role in this organ. This peptide influences spermatogenesis and sperm capacitation, so it is considered as a regulator of reproduction. Kp roles exert through hypothalamic/pituitary/gonadal axis. We aimed to evaluate direct roles for Kp on proliferation and differentiation of spermatogonial cells (SCs) when the cells are cocultured with somatic cells. Somatic cells and SCs were isolated from adult azoospermic and newborn mice and then enriched using a differential attachment technique. After the evaluation of identity and colonization for SCs, the cells were cocultured with somatic cells, and three doses of Kp (10^-8 -10^-6  M) was assessed on proliferation (through evaluation of MVH and ID4 markers) and differentiation (via evaluation of c-Kit and SCP₃ , TP_1, TP₂ , and, Prm₁ markers) of the coculture system. Investigations were continued for four succeeding weeks. At the end of each level of testosterone in the culture media was also evaluated. We found positive influence from Kp on proliferative and differentiative markers in SCs cocultured with somatic cells. These effects were dose-dependent. There was no effect for Kp on testosterone level. From our findings, we simply conclude that Kp as a neuropeptide for influencing central part of reproductive axis could also positively affect peripheral processes related to spermatogenesis without having an effect on steroidogenesis.

Diethylstilbestrol induces oxidative DNA damage, resulting in apoptosis of spermatogonial stem cells in vitro

) in SSCs was detected using p-Nitro Blue Tetrazolium (NBT) assay. The viability of cells after DES treatment was examined in the CCK8 (cell counting kit-8) cytotoxicity assay. The results showed that DES-induced DNA damage causes an increase in intracellular superoxide anions which are reduced by the flavonoid, quercetin. Investigating the molecular mechanisms and biology of SSCs provides a better understanding of spermatogonial stem cell regulation in the testis.

In vitro responses to known in vivo genotoxic agents in mouse germ cells

Genotoxic compounds have induced DNA damage in male germ cells and have been associated with adverse clinical outcomes including enhanced risks for maternal, paternal and offspring health. DNA strand breaks represent a great threat to the genomic integrity of germ cells. Such integrity is essential to maintain spermatogenesis and prevent reproduction failure. The Comet assay results revealed that the incubation of isolated germ cells with n-ethyl-n-nitrosourea (ENU), 6-mercaptopurine (6-MP) and methyl methanesulphonate (MMS) led to increase in length of Olive tail moment and % tail DNA when compared with the untreated control cells and these effects were concentration-dependent. All compounds were significantly genotoxic in cultured germ cells. Exposure of isolated germ cells to ENU produced the highest concentration-related increase in both DNA damage and gene expression changes in spermatogonia. Spermatocytes were most sensitive to 6-MP, with DNA damage and gene expression changes while spermatids were particularly susceptible to MMS. Real-time PCR results showed that the mRNA level expression of p53 increased and bcl-2 decreased significantly with the increasing ENU, 6-MP and MMS concentrations in spermatogonia, spermatocytes and spermatids respectively for 24 hr. Both are gene targets for DNA damage response and apoptosis. These observations may help explain the cell alterations caused by ENU, 6-MP and MMS in spermatogonia, spermatocytes and spermatids. Taken together, ENU, 6-MP and MMS induced DNA damage and decreased apoptosis associated gene expression in the germ cells in vitro. Environ. Mol. Mutagen. 58:99-107, 2017. © 2017 Wiley Periodicals, Inc.

Detection of phase specificity of in vivo germ cell mutagens in an in vitro germ cell system

In vivo tests for male reproductive genotoxicity are time consuming, resource-intensive and their use should be minimised according to the principles of the 3Rs. Accordingly, we investigated the effects in vitro, of a variety of known, phase-specific germ cell mutagens, i.e., pre-meiotic, meiotic, and post-meiotic genotoxins, on rat spermatogenic cell types separated using Staput unit-gravity velocity sedimentation, evaluating DNA damage using the Comet assay. N-ethyl-N-nitrosourea (ENU), N-methyl-N-nitrosourea (MNU) (spermatogenic phase), 6-mercaptopurine (6-MP) and 5-bromo-2'-deoxy-uridine (5-BrdU) (meiotic phase), methyl methanesulphonate (MMS) and ethyl methanesulphonate (EMS) (post-meiotic phase) were selected for use as they are potent male rodent, germ cell mutagens in vivo. DNA damage was detected directly using the Comet assay and indirectly using the TUNEL assay. Treatment of the isolated cells with ENU and MNU produced the greatest concentration-related increase in DNA damage in spermatogonia. Spermatocytes were most sensitive to 6-MP and 5-BrdU while spermatids were particularly susceptible to MMS and EMS. Increases were found when measuring both Olive tail moment (OTM) and% tail DNA, but the greatest changes were in OTM. Parallel results were found with the TUNEL assay, which showed highly significant, concentration dependent effects of all these genotoxins on spermatogonia, spermatocytes and spermatids in the same way as for DNA damage. The specific effects of these chemicals on different germ cell types matches those produced in vivo. This approach therefore shows potential for use in the detection of male germ cell genotoxicity and could contribute to the reduction of the use of animals in such toxicity assays.

Effects of nickel exposure on testicular function, oxidative stress, and male reproductive dysfunction in Spodoptera litura Fabricius

Nickel is an environmental pollutant that adversely affects the male reproductive system. In the present study, the effects of nickel exposure on Spodoptera litura Fabricius were investigated by feeding larvae artificial diets containing different doses of nickel for three generations. Damage to testes and effects on male reproduction were examined. The amount of nickel that accumulated in the testes of newly emerged males increased as the nickel dose in the diet increased during a single generation. Nickel exposure increased the amount of thiobarbituric acid reactive substances and decreased the amount of glutathione in treatment groups compared with the control. The activity levels of the antioxidant response indices superoxide dismutases, catalase, and glutathione peroxidase in the testes showed variable dose-dependent relationships with nickel doses and duration of exposure. Nickel doses also disrupted the development of the testes by decreasing the weight and volume of testes and the number of eupyrene and apyrene sperm bundles in treatment groups compared with the control. When the nickel-treated males mated with normal females, fecundity was inhibited by the higher nickel doses in all three generations, but fecundity significantly increased during the second generation, which received 5 mg kg(-1) nickel. Hatching rates in all treatments significantly decreased in a dose-dependent manner in the three successive generations. The effects of nickel on these parameters correlated with the duration of nickel exposure. Results indicate assays of testes may be a novel and efficient means of evaluating the effects of heavy metals on phytophagous insects in an agricultural environment.