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

Thiopurines exert harmful effects on spermatogenesis in Nudt15R138C knock-in mice

BACKGROUND

The association between thiopurine use and testicular reproductive functions remains unclear. In this study, we investigated whether thiopurines affect testicular functions based on the NUDT15 genotypes using Nudt15R138C knock-in mice.

METHODS

The male Nudt15R138C knock-in mice (9-12 weeks) were treated with mercaptopurine (MP: 0.5 mg/kg/day) for 4 or 12 weeks. To examine reversibility, some mice were maintained for a further 12 weeks under MP-free condition.

RESULTS

After MP treatment for 4 weeks, Nudt15R138C/R138C mice exhibited a significant reduction of testis weight compared to Nudt15+/+ mice and Nudt15+/R138C mice. The epithelial height and diameter of seminiferous tubules were significantly reduced in Nudt15R138C/R138C mice compared to Nudt15+/+ and Nudt15+/R138C mice. Apoptotic cells were significantly increased in Nudt15R138C/R138C mice, and most of apoptotic cells were spermatogonia. There were no significant changes in sperm counts and sperm morphology in MP-treated Nudt15R138C/R138C mice after 4-week MP treatment. On the other hand, after MP treatment for 12 weeks, the Nudt15+/R138C mice, but not Nudt15+/+ mice, exhibited a significant reduction in the testis weight and atrophic changes of seminiferous tubules, but these changes disappeared after 12-week rearing under MP-free condition. Despite a significant increase in abnormal sperm rate, there were no changes in the ability to conceive. No differences in serum levels of follicle-stimulating hormone or testosterone were observed between MP-treated Nudt15+/R138C and Nudt15+/+ mice after 12-week MP treatment.

CONCLUSIONS

Thiopurines exert harmful effects on testicular reproductive function according to host NUDT15 genotypes.

Genotoxicity evaluation using primary hepatocytes isolated from rhesus macaque (Macaca mulatta)

Non-human primates (NHPs) have played a vital role in fundamental, pre-clinical, and translational studies because of their high physiological and genetic similarity to humans. Here, we report a method to isolate primary hepatocytes from the livers of rhesus macaques (Macaca mulatta) after in situ whole liver perfusion. Isolated primary macaque hepatocytes (PMHs) were treated with various compounds known to have different pathways of genotoxicity/carcinogenicity and the resulting DNA damage was evaluated using the high-throughput CometChip assay. The comet data were quantified using benchmark dose (BMD) modeling and the BMD₅₀ values for treatments of PMHs were compared with those generated from primary human hepatocytes (PHHs) in our previous study (Seo et al. Arch Toxicol 2020, 2207-2224). The results showed that despite varying CYP450 enzyme activities, PMHs had the same sensitivity and specificity as PHHs in detecting four indirect-acting (i.e., requiring metabolic activation) and seven direct-acting genotoxicants/carcinogens, as well as five non-carcinogens that are negative or equivocal for genotoxicity in vivo. The BMD₅₀ estimates and their confidence intervals revealed species differences for DNA damage potency, especially for direct-acting compounds. The present study provides a practical method for maximizing the use of animal tissues by isolating primary hepatocytes from NHPs. Our data support the use of PMHs as a reliable surrogate of PHHs for evaluating the genotoxic hazards of chemical substances for humans.

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.

Preclinical and Clinical Evidence of Safety of Antiviral Drug with Immunomodulatory Activity

Antiviral drug Kagocel is widely used in Russia for prevention and treatment of acute respiratory infection, influenza, and herpes. The drug belongs to the group of interferon inductors. The article contains the review and analytical evaluation of safety of antiviral drug Kagocel. Kagocel is registered in the Russian Federation and some CIS countries and refers to the group of interferon inducers. This is a chemical compound of carboxymethyl cellulose and low-molecular natural polyphenol gossypol common in cotton-plant (Gossypium spp.) which protects the plant from depredators and diseases. Authors pay a special attention to the analysis and generalization of data from preclinical and clinical studies including the control of related substances. Absence of free gossypol impurities guaranteed by highly sensitive and specific quality control methods. Preclinical studies data was analyzed and the results were presented with focus on reproductive safety of Kagocel® in immature and mature animals.. No negative effect on animals’ reproductive function was revealed including spermatogenesis and generative function. No long-term product effect on reproductive system or next generations of animals was recorded both at therapeutic doses and at doses 10 times their exceeding. The safety of the drug demonstrated on data obtained from numerous clinical trials, including those involving children aged 2 years and older. Th is confirms the safety of antiviral drug Kagocel usage in clinical practice, including pediatrics.

Genotoxic and mutagenic studies of teratogens in developing rat and mouse

In this review, genotoxic and mutagenic effects of teratogenic chemical agents in both rat and mouse have been reviewed. Of these chemicals, 97 are drugs and 33 are pesticides or belong to other groups. Large literature searches were conducted to determine the effects of chemicals on chromosome abnormalities, sister chromatid exchanges, and micronucleus formation in experimental animals such as rats and mice. In addition, studies that include unscheduled DNA synthesis, DNA adduct formations, and gene mutations, which help to determine the genotoxicity or mutagenicity of chemicals, have been reviewed. It has been estimated that 46.87% of teratogenic drugs and 48.48% of teratogenic pesticides are positive in all tests. So, all of the teratogens involved in this group have genotoxic and mutagenic effects. On the other hand, 36.45% of the drugs and 21.21% of the pesticides have been found to give negative results in at least one test, with the majority of the tests giving positive results. However, only 4.16% of the drugs and 18.18% of the pesticides were determined to give negative results in the majority of the tests. Among tests with major negative results, 12.50% of the teratogenic drugs and 12.12% of the teratogenic pesticides were negative in all conducted tests.

The associations of thiopurines with male fertility and paternally exposed offspring: a systematic review and meta-analysis

BACKGROUND

Thiopurines are widely used immunosuppressive agents. In high dosages, they inhibit the purine synthesis and are considered to be possibly harmful to spermatogenesis, and subsequently to men's fertility and their offspring. However, the clear association between thiopurine exposure and male fertility and reproduction safety, if any, is still poorly understood.

OBJECTIVE AND RATIONALE

The aim of this review was to systematically summarize and meta-analyse the available data, derived from animal and human studies, regarding the influence of thiopurine exposure on fertility and conception safety in men and their offspring.

SEARCH METHODS

A systematic literature search of the MEDLINE and EMBASE databases was performed using a combination of relevant terms related to 'thiopurines', 'fertility', 'conception', 'reproduction', 'semen quality' and 'birth outcome', combined with 'male', 'men', 'father' and 'paternal'. The search was not restricted exclusively to human subjects, neither to a type of disease or condition, to gather all available studies with regards to this topic. All published articles on thiopurines and male fertility, written in English and published until May 2017, were screened for eligibility. The GRADE guidelines were used to assess the quality of evidence of the included articles.

OUTCOMES

A total of 28 studies (including 14 observational studies in humans) were included in this review and six of these were included in the meta-analysis. In various rodents, thiopurines adversely affected the germ cells (in administered doses of 2 to 20 times the human equivalent dose). In human studies, thiopurine therapy was not evidently associated with impaired testicular function or semen quality in 83 men with a variety of underlying diseases. In total, 53 out of 975 offspring with congenital anomalies (5.4%, the background prevalence is 3%), possibly as a result of paternal thiopurine exposure, were described in all studies together. The risk of congenital anomalies was not significantly increased when compared with offspring without paternal thiopurine exposure (4.7%) (pooled odds ratio 1.32, 95% confidence interval 0.75, 2.34).

WIDER IMPLICATIONS

Thiopurines have spermatotoxic effects in rodents. In humans, overall data are limited and derived from underpowered studies, and therefore not conclusive with regards to the possible effects of thiopurines on spermatogenesis or paternally exposed offspring. Larger, epidemiological trials evaluating the safety of thiopurines to men's fertility and their offspring are mandatory to adequately counsel thiopurine treated men who wish to conceive.