Study On Toxicity Mechanism Of Nanomaterial PAMAM

Nanosize-materials have unusual physical and chemical properties specialized in small size effect, quantum effects and large surface area differing from those of the bulk materials. As dendrimers are new type materials of synthetic polymer used in drug delivery, medical imaging and clinical diagnosis. The studies on dendrimers have important significance.Polyamide dendrimer nano-materials (PAMAM dendrimer) are a type of macromolecules with branches of highly symmetric and radiating. They are made of the central core, inner branches of repeated subunits and the surface functional groups. Whole generation of PAMAM nano-materials are synthetized with amino as surface functional groups, as with carboxyl surface for half-generation. Whole generation PAMAM dendrimers with high-density surface of the amino combined with DNA and other biological macromolecules are highly compressed in space. As non-viral vectors, they can efficiently deliver some genetic material and drugs such as DNA or oligonucleotide to cell. Dendrimers themself are also used as drugs for eliminating infection and inhibiting viruses, bacterias. They have great prospects in the medical field.However, we also observed that easy accesses to a variety of cells are different from other synthetic materials carrier. It is the advantage of dendrimers, but more potential risks exist. Therefore, compatibility between cells and dendrimers is particularly concerned by the researchers. It is reported that the PAMAM G3, G5, G7 have been studied in toxicity, immunogenicity and biological distribution in vivo and it could be effected by particle size. But the research is in its infancy, needs a lot of follow-up studies.In previous study, we explained the mechanism of cell toxicity of PAMAM G3 and G5. We also showed that PAMAM G3 induced acute lung injury in vivo. PAMAM G3 triggered autophagic cell death by deregulating the Akt-TSC2-mTOR signaling pathway. The autophagy inhibitor 3-methyladenine(3-MA) rescued cell death treated with PAMAM dendrimer and ameliorated acute lung injury caused by PAMAM G3 in mice. We proved at the same time that the PAMAM G5 could downregulate ACE2 expression in lung tissues, thereby upregulate angiotensin Ⅱ production and precipitate acute lung failure in mice. But the mechanism of acute liver injury induced by PAMAM G5 was found in different signaling pathway. And also It seemed that the mechanism of different generations of PAMAM nanomaterials is completely different. Therefore, we decided to do some more research on PAMAM nanomaterials.PAMAM G7 was supposed to be different in mechanism of tissue damages. In this report, we found G7 could induce acute lung injury when we used some methods of pathology, lung edema, elastance and vascular permeability. Then we proved that G7 could elevate the level of cytokines in mouse BALF (bronchoalveolar lavage fluid). And in order to know upstream of cytokines, we detected changes of NF-κB pathway in wild type and PI3K knockout mice. Exciting results were found that cytokines were deduced and lung injury was ameliorated in PI3K knockout mice. So we could conclude that the PI3K-NF-KB-cytokine storm signaling pathway is identified as a key role in severity of acute lung injury induced by PAMAM G7. Our datas provide a new target for acute lung failure induced by nanomaterials.So as to clarify toxicity of PAMAM materials, We determined to do more research on mice administrated with PAMAMs. Complete blood count, blood chemistry and blood gas analysis were detected with blood from the mice administered PAMAM G4 or G5. The results showed the mice treated with PAMAM G4 or G5 might trigger thrombocytopenia and multiple organ injury/failure. According to the results of pathology, mice injected with PAMAM G5 appeared DIC and severe bleeding Symptoms. After detection of further tissue pathology and molecular experiment, the results showed the mice treated with PAMAM G5 triggered multiple organ dysfunction syndrome.The hypothesis was that PAMAM G5 triggered multiple organ dysfunctionby deregulating the TLR4-NF-κB signaling pathway. So we used PBMC (peripheral blood mononuclear cell) as model. And we found PAMAM G5 could activate TLR4 receptor in PBMC, thereby led to elevate level of proinflammatory cytokines. These changes increased vascular permeability and induced tissue injury. In this study we also found that PAMAM G5 could activate ROS in PBMC, which could be the reason of TLR4 activation.