Journal of Applied Toxicology. 2016 Apr. 36 (4): 543-53.
The responses of immune cells to iron oxide nanoparticles
Yaolin Xu1, Jennifer A. Sherwood1, Kimberly H. Lackey2, Ying Qin3 and Yuping Bao1
1Chemical and Biological Engineering, 2Biological Sciences, and 3Alabama Institute for Manufacturing Excellence, The University of Alabama, Tuscaloosa, Alabama 35487, United States
Human Immune cells, such as monocytes, are important in recognizing and removing nanoparticles for in vivo applications. This study focuses on the surface coating effects of iron oxide nanoparticles on their cellular uptake, toxicity and ability to trigger immune response using human monocyte cell line. Three types of coatings (negatively charged polyacrylic acid, positively charged polyethylenimine and neutral polyethylene glycol) were tested on monocyte cells at various nanoparticle concentrations with 6 h incubation. The cells were also with 50 mg ml−1 nanoparticles at different incubation times (6, 12, 24, 48 or 72 h). For all three types of surface coating, the cells exhibited over 80% viability, despite of nanoparticle concentrations and incubation times. The expression of toll-like receptor 2 and tumor necrosis factor-α were used to assess the immune responses of monocyte cells to iron oxide nanoparticles. Both of these biomarkers were not significant in any case of the surface coatings, nanoparticle concentrations and incubation times. This study is beneficial to identify appropriate surface coatings of nanoparticles for biological and biomedical applications.
The interaction between the human immune system and nanoparticles is critically important to nanomedicine. In particular, the surface coatings of nanoparticles are the first contact with biological system during an application, which critically affect nanoparticle behaviors. Depending on the capping molecules, the surface chemistry for the same iron oxide core can vary greatly, which subsequently affect their biodistrubution, toxicity and ability of triggering immune responses.
In this paper, we prepared iron oxide nanoparticles of the same core, but different surface chemistries, such as negatively charged polyacrylic acid-PAA, positively charged polyethylenimine-PEI and neutral polyethylene glycol-PEG. Subsequently, we performed cellular studies at three different levels. First, the cellular uptake behaviors of these three types of nanoparticles were studied on human monocyte cell lines. The nanoparticle concentration and incubation time were varied, including 50 µg/mL nanoparticle treatments at different incubation times (6, 12, 24, 48 or 72 h) and six hour incubation of various concentrations (5, 10, 20, 30 or 50 µg/mL). Prussian blue staining suggested minimal cellular interaction and uptake of PAA-coated nanoparticles (< 20%). In contrast, cells treated with PEI-coated nanoparticles were almost entirely blue, signs of enhance cell interaction and internalization. PEG-coated nanoparticles showed nearly no cellular interactions and uptake, indicated by the lack of blue staining of cells. Transmission electron microcopy (TEM) visualization of sections of nanoparticle-treated cells showed that PAA-coated nanoparticles were distributed across entire cell cytoplasm when there was cellular uptake while PEI-coated nanoparticles were largely localized on cell surfaces, suggesting enhanced interactions between nanoparticles and cell surfaces through electrostatic interactions. Figure 1a showed an example of TEM images of iron oxide nanoparticles and Figure 1b and c are examples of Prussian blue staining images and TEM images of cell internalization.
Figure 1. Images examples: (a) a TEM images of PEI-coated iron oxide nanoparticles, (b) Prussian blue staining image of monocyte cells treated with PEI-coated nanoparticles, and (c) a TEM image of thin cell slides of cells treated with PAA-coated nanoparticles.
Subsequently, the toxicity of PAA, PEI, PEG-coated nanoparticles were evaluated with a 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyl tetrazolium bromide (MTT) assay. For all three types of surface coating, the nanoparticle-treated cells exhibited over 80% viability, despite of nanoparticle concentrations and incubation times. This study suggested the great biocompatibility of these polymer-coated iron oxide nanoparticles. Finally, the expression of toll-like receptor 2 and tumor necrosis factor-α were used to assess the immune responses of monocyte cells to these polymer-coated iron oxide nanoparticles. Compared to the positive controls, the expression of both of these biomarkers were not significant, despite of surface coating types, nanoparticle concentrations, and incubation times. Therefore, it was concluded that the nanoparticle treatments did not induce evident immune response on human monocyte cell line.
The importance of this study lies in the demonstration of the great biocompatibility of polymer-coated iron oxide nanoparticles.
Yaolin Xu, Jennifer Sherwood, Kimberly H. Lackey, and Yuping Bao, The responses of immune cells to iron oxide nanoparticles, J Appl Toxicol. 36(4):543-553 (2016). doi: 10.1002/jat.3282.
Acknowledgements: This work is in part supported by NSF-DMR 0907204 and DMR1149931.
Contact: Yuping Bao, Ph.D. Associate Professor
Box 870203 Department of Chemical and Biological Engineering
The University of Alabama
Tuscaloosa, Al 35487