S. T. Zakhidov

Gold nanoparticles disturb nuclear chromatin decondensation in mouse sperm in vitro

The effect of gold nanoparticles on mouse epididymal sperm has been studied using the model system of nuclear chromatin decondensation in vitro. It is shown that the treatment of gametes, preliminary membrane-freed by sodium dodecyl sulfate, in the mediums containing gold nanoparticles (with diameter ∼2.5 nm) in concentrations 1.0 × 1015 or 0.5 × 1015 particles/ml and following incubation in dithiothreitol solution (DTT) resulted in failure of chromatin decondensation process and nucleus structure. We conclude that gold nanoparticles possess spermatotoxicity. The mechanism of cytotoxic effect of gold nanoparticles may be related with their interaction with molecules of double-helix DNA. The model system studied in this research is applicable for further investigations of cytotoxic effects of nanoparticles of different origin and made of different metals.

Carnosine-induced changes in the development of spermatogenic epithelial cells in senescence accelerated SAM mice.

Carnosine significantly increased the number of spermatogonia and Sertoli cells in mice prone (SAMP1) and resistant (SAMR1) to accelerated aging and appreciably reduced cell yield in meiosis and spermiogenesis in SAMP1 mice. In experimental SAMP1 mice catastrophic changes in the number of gametes were paralleled by intensive degradation of the spermatogenic epithelium. In SAMR1 mice treated with carnosine highly ordered spermatogenic structure was preserved.

Cytogenetic Aberrations in the Cells of Liver and Spermatogenic Epithelium in Senescence Accelerated SAMP1 and SAMR1 Mice

It was shown that during ontogenesis, the mice prone to (SAMP1) and resistant (SAMR1) against accelerates senescence did not differ substantially in the frequency of cytogenetic aberrations in the hepatocytes and spermatogenic cells (spermatogonia and round spermatids). These data suggest that in the mice of both lines, the processes of appearance, development, and functioning of complex biological systems, such as liver and spermatogonic epithelium take place against the background of high genetic instability. The role of genetic instability in senescence is discussed.

Retention of gold nanoparticles in the structure of quasinematic layers formed by DNA molecules

Gold nanoparticles are shown to get incorporated into double-stranded DNA molecules forming quasinematic layers in the cholesteric liquid-crystalline dispersion particles. The process of nanoparticle incorporation results in distortion in an ordered arrangement of the neighboring dsDNA molecules in a layer and in global spatial structure of particles of the dispersion, which may be one of the possible causes of the genotoxicity of gold nanoparticles.

Response of the spermatogenic system to chemical mutagen dipin in SAMP1 senescence-accelerated mice

Specific features of spermatogenesis were studied in senescence-accelerated mice of the strain SAMP1 after one-time injection of the chemical mutagen dipin. Quantitative and histomorphological changes in the spermatogenic epithelium proved to develop gradually. Cell loss and disorganization of spermatogenesis reached the peak as late as on days 28 and 35 after the injection. Differentiating spermatogonia manifested increased sensitivity to dipin. In prophase I of meiosis, developing spermatocytes proved to be less sensitive to the cytotoxic action of dipin at the pachytene than at the preleptotene-leptotene stages. Spermatogenesis in most seminiferous tubules was restored by day 56 after dipin treatment. At the end of the experiment (day 100), both quantitative parameters and morphological pattern of spermatogenesis did not differ significantly from those in the control. Thus, the cytotoxic action of dipin does not lead to irreversible structural disorganization of the spermatogenic epithelium in SAMP1 mice. Radioautography revealed a large proportion of highly differentiated Sertoli cells with 3H-thymidine-labeled nuclei in experimental animals. In some cases, structures resembling embryonic seminiferous tubules were revealed in the vicinity of rete testis in histological sections of testes of experimental mice. These structures contained the cells morphologically similar to gonocytes and immature Sertoli cells.

[Analysis of spermatogenesis in senescence-accelerated mice].

A comparative analysis of age-related dynamics of spermatogenesis has been performed in mutant mouse lines predisposed or resistant to accelerated senescence (SAMP1 and SAMR1 respectively). The results show that quantitative and morphohistological trends in the development of sperm cells and Sertoli cells in both lines are similar in both lines. Their comparison with data obtained in our previous studies (Zakhidov et al., 2001; Gordeeva et al., 2001) shows that sharp quantitative and qualitative changes in the structure of the spermatogenic system have occurred in senescence-accelerated mice of new generations, which confirms the fact of dynamic instability of the germinal lineage. The role of stem spermatogonial cells in restoration of spermatogenesis in animals reaching the critical age is discussed.

Carnosine modifies the incidence of genetically abnormal sex cells in the testes of senescence-accelerated mice.

The quantitative micronucleus test showed that the natural dipeptide carnosine increases the count of aberrant spermatogonia and round spermatids in the testes in SAMR1 mice resistant to accelerated aging by 64 and 85%, respectively, compared to the control. However, this agent did not modify the incidence of chromosome mutations in spermatogenic cells in SAMP1 mice predisposed to accelerated aging.

Changes of chromosomes and cell cycle (endoreduplication, somatic crossing-over, and robertsonian fusions) in hepatocytes of senescence accelerated SAMR1 mice.

Liver cells were isolated four days after partial hepatectomy using in situ perfusion with collagenase. One hour before the perfusion, the animals were injected with 0.5 ml of 0.01% colchicine. Hepatocyte metaphases were characterized by the presence of unusual configurations and chromosome associations, which were apparently related to the mechanisms of development of genome instability in senescence accelerated mice (Fig. 1).

Genetic Instability of Male Gametes in Long-lived Mice of the SAMP1 Strain Prone to Accelerated Aging

The model of mice with accelerated aging (or senescence-accelerated mice), which Japanese researchers obtained via selective inbreeding of AKR/J mice with hereditary leukemia of viral origin [1, 2], introduced geneticists and biologists to a fundamentally new phenomenon, namely, an extremely rapid extinction of vital functions. This gave rise to intense research in many fields of biology. The knowledge of specific nonlinear relationships in the system of senescent-accelerated mice is important not only in terms of the general theory of aging, but also for understanding the nature of superfast processes and their role in development and evolution.

Experimental evidence of proliferation and reproduction of highly differentiated Sertoli cells

The main results of studies regarding the biology of Sertoli cells under various experimental conditions are considered. Possible potential mechanisms underlying the transition of highly differentiated Sertoli cells to dedifferentiation, limited by proliferation and reproduction and not accompanied by significant phenotypic changes, are discussed.