| Nanotechnology, which was born in 1980s, has presented an amazing developmental trend in the first decade of this century, extensively and fundamentally changing the way we make the material world. Nowadays wider and wider applications of nanotechnology in industrial and agricultural production and bio-medicine bring more and more chances human beings actively or passively interact with nanomaterials. Therefore, it is expected that the narrow space of human society will be filled with nanomaterials in the near future. In nanoscale, materials show different physical and chemical properties from their molecular forms and macro forms due to their unique effects such as quantum size effect, surface area effect and surface adsorption. Meanwhile, nanoscale is the minimum space for life activity and almost all bio-macromolecules are at this scale. So nanomaterials can present some special bio-activities in organisms and induce unknown effects on bio-functions. Because of what has mentioned above, the potential effects of nanomaterials on human health and eco-environment deserve high degree of concerns. In order to answer these concerns, a new toxicological subject called nanotoxicology, which is not only the key guarantee of sustainable development of nanotechnology, but also a frontier filed in modern toxicology, came into being and became one of the most active subject of academic research over the past years.Carbon nanotubes (CNTs) are quasi one dimensional carbon nanomterials with layered hollow structure. Because of their superior mechanical, electrical and chemical properties, CNTs have successfully applied to plastics, battery electrode, water purification system, adhesives and so on. Nowadays, the applications of CNTs in drug delivery, tumor thermo-therapy and bio-medical materials are promisingly developed. Therefore, it is significant to evaluate the bio-safety of CNTs. Based on the existing knowledge, CNTs can enter cells via receptor-mediated endocytosis, activate NF-?B signaling pathway and induce oxidative stress. CNTs can also induce apoptosis, inhibit cell proliferation and damage DNA. The in vivo toxicities of CNTs include but are not limited to the inflammation and granuloma in lungs, endothelial dysfunction based on mitochondrial disorder and side effects on cardiovascular system. The previous toxicological studies of CNTs are mainly focused on their injuries to respiratory system and cardiovascular system. However, their potential effects on other physiological-systems also deserve study but are rarely reported.Affected by industrial pollutions and many others, human fertility has shown a declining trend since 1960s. According to incomplete statistics, there are about eight million couples having different degrees of reproductive obstacles in the world and two million in China. Reproductive problems may become the 3rd social illness following cardiovascular/cerebrovascular diseases and cancer in the near future. It is known that some organometallic compounds, heavy metal, nitrogen oxide radicals and drugs are toxic to human reproductive health, and that there is a high degree of correlation between the large scale use of pesticides and the human fertility decline. With the rapid development of chemistry and material sciences, large number of new materials especially nanomaterials are gradually coming into our daily life. Although the reproductive toxicology of nanomaterials has been discussed and there have been reports of reproductive toxicity induced by nanomaterials, there has been no comprehensive study on reproductive toxicity resulting from CNTs.Given the rapid development of nanomaterials in industrial and agricultural production and bio-medicine, and many unknowns about nano reproductive toxicity, we selected amine (NH2)-and carboxylate (COOH)-functionalized multiwalled carbon nanotubes to study their bio-safety to the male reproductive system, female reproductive system and drug safety in lactation period. The findings broadened the knowledge of nanotoxicity and provided important information on safe application of nanomaterials. We firstly studied the toxicological effects of CNTs on the adult male reproductive systems of mice. According to the current knowledge of male reproductive toxicology, the male reproductive disorders are mainly caused by high levels of reactive oxygen species (ROS) in the male reproductive system. The reproductive endocrine disorder induced by the injury to hypothalamus-pituitary-testis axis is another important etiology for male reproductive toxicity. Based on the mechanisms mentioned above and the toxicological process induced by xenobiotics, after two schemes of i.v. administration of MWCNT-COOH and MWCNT-NH2, we systematically evaluated the bio-distribution of CNTs in the testis, the oxidative stress and lipid peroxidation of testis induced by CNTs at different times, three important reproductive hormones (LH, FSH, Testosterone) in plasma, testicular pathological changes and testis indice at different times, sperm quantity/quality evaluation and male-factor based fertility. Using 64Cu-labelled carboxylated carbon nanotubes, we examined the translocation of MWCNT-COOH in the testis after a single dose with an increasing trend within 24 hours. Single dose of i.v. administration of CNTs did not induce any changes of MDA (an important biomarker for lipid peroxidation) levels in testis while five doses of MWCNT-COOH induced slight increase of MDA in testis, indicating that repeated exposure of MWCNT-COOH caused oxidative stress and lipid peroxidation in the testis of mice. This change returned to normal in day 60 and 90. The testicular pathology presented the similar changes to the MDA alteration. The testis showed little alteration after a single dose of CNTs, but the testis from mice treated with five doses of MWCNT-COOH at day 15 were characterized by partially damaged seminiferous tubules, a reduction in the thickness of the germinative layer, and a reduction in the number of spermatogonia. Histologic studies also showed a partial disappearance or vacuolization of Sertoli cells in the basal zones of some seminiferous tubules and some necrotic and degenerative cells vasodilatation and hyperemia in the testis. MWCNT-NH2 produced similar but slightly less severe alterations in the testis. The above-mentioned alterations were observed only occasionally in the testis of mice examined on days 60 and 90, indicating that these alterations can be repaired over time. Plasma levels of testosterone, LH and FSH were determined after five doses of CNTs. The results indicate that the CNTs did not alter plasma sex hormone levels compared with those of controls under our exposure conditions. Although increased level of MDA in testis was detected and some testicular pathological changes occurred within 15 days, the alterations were of slight degree. To determine whether these initial alterations could generate any adverse outcomes, we finally evaluated the possible reproductive toxicological consequences and found that the sperm health and male fertility were not affected.The possible adverse effects of nanomaterials on the female reproductive system also need to be highly concerned. There is evidence that nanomaterials can induce apoptosis of ovarian granulosa cells and alter in vitro estrogen accumulation. However, there is little knowledge on in vivo nano female reproductive safety. In part two, we studied the effects of MWCNT-COOH by i.v. and i.p. injection on the estrus cycle and ovarian pathology. Using 64Cu-labelled carboxylated carbon nanotubes, we examined the translocation of nanotubes in the ovary after a single dose with a decreasing trend within 24 hours, indicating that there is a quick excretion mechanism in ovary. Estrus cycle assay showed that under our experimental condition, MWCNT-COOH did not perturb the estrus cyclicity. The primordial follicles, growing follicles, mature follicles and corpora luteum in the ovaries of iv. and i.p. administrated female mice showed no obvious missing or damage. Based on the negative results we concluded that MWCNT-COOH has good biocompatibility with regard to female reproductive health in mice.Lactation period is an important stage following reproduction and embryonic development. It is quiet necessary to evaluate the bio-safety of nanomaterials in lactation period in view of the importance of milk to the infant's growth and development, the specificity for the lactating females and susceptibility to drug use. There is evidence that injected C6o nanoparticles can enter mice pups via milk. But that study aimed at finding the excretion of nanomaterials and the bio-safety of nanomaterials in lactation period still remains unknown. In part three, we evaluated the potential effects of i.v. injected MWCNT-COOH on mice dams in lactation period. Due to technical constraints, we were not able to detect whether MWCNT-COOH was transferred to pups via milk. Therefore, we cannot discuss here if MWCNT-COOH directly affected the early development of new-born pups or not. But by comparing the affordability and toxicity after exposing MWCNT-COOH between lactating mice and non-lactating mice, we found that although there were no meaningful pathological alterations in mammary glands of lactating mice, they showed more severe post-exposing responses than non-breast feeding mice and a higher chance of death. A further study revealed that i.v. administrated MWCNT-COOH increased the possibilities of thrombosis formation in heart cavities of breast-feeding mice, although the exact mechanism is still unclear. Based on this finding we proved that CNTs have certain risks in specific physiological period, which needs high degree of concern in the future. |
PDF Full Text Request