Limitation of cell culture technique
Absence of immune effect, blood proteins, the endocrine system and the general lack of complex interaction of the whole animal in most in vitro system is limiting the potential transfer of some cell culture-based results of nanoparticle studies to animals/humans [48]. Tissue-specific differentiation functions of many cells and their physiological context of the primary cell cultures in in vitro systems are lost, like the loss of bio-transformational enzymes in primary liver cell cultures [49]. This lost in bio-transformational enzymes of liver cells will hinder the usage of primary liver cells in assessing nanoparticle for metabolism and toxicity potentials.
The assumption of neurotoxic potential of a compound if tested on neuronal cell line without considering the effect of blood brain barrier in animal model may lead to erroneous conclusion [48]. Recently, a group of researchers tried to evaluate the toxicity potential of zinc oxide nanoparticle on both cell and animal based models [50]. The two models showed a dose-dependent toxicity potential by the nanoparticle. However, in animal-based study, additional information emerged that relate route of administration and toxicity by the same delivery system. Another disturbing conclusion made from in vitro studies are that of glass fibre’s ability in generating reactive oxygen species and causing oxidant stress leading to DNA damage, but a low pathogenic potential was reported when tested in animal models [51]. In vitro study also reported kaolin to be as cytotoxic as quartz, and purified single-walled carbon nanotubes not inducing oxidative stress in cell studies but resulted in progressive interstitial fibrosis in mice [51]. In general, animal systems are extremely complicated, and the closer a proposed nanoparticle is for human use, the more it requires animal model research. However, properly planned in vitro technique will likely serve as a good screening mechanism for NDS. This will likely reduce cost, time and more importantly preserve more lives of animal in the future.
Conclusion