Silica nanoconstruct cellular toleration threshold in vitro

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Abstract

The influence of geometry of silica nanomaterials on cellular uptake and toxicity on epithelial and phagocytic cells was studied. Three types of amine-terminated silica nanomaterials were prepared and characterized via the modified Stober method, namely spheres (178 ± 27 nm), worms (232 ± 22 nm × 1348 ± 314 nm) and cylinders (214 ± 29 nm × 428 ± 66 nm). The findings of the study suggest that in this size range and for the cell types studied, geometry does not play a dominant role in the modes of toxicity and uptake of these particles. Rather, a concentration threshold and cell type dependent toxicity of all particle types was observed. This correlated with confocal microscopy observations, as all nanomaterials were observed to be taken up in both cell types, with a greater extent in phagocytic cells. It must be noted that there appears to be a concentration threshold at ~ 100 μg/mL, below which there is limited to no impact of the nanoparticles on membrane integrity, mitochondrial function, phagocytosis or cell death. Analysis of cell morphology by transmission electron microscopy, colocalization experiments with intracellular markers and Western Blot results provide evidence of potential involvement of lysosomal escape, autophagic like activity, compartmental fusion and recycling in response to intracellular nanoparticle accumulation. These processes could be involved in cellular coping or defense mechanisms. The manipulation of physicochemical properties to enhance or reduce toxicity paves the way for the safe design of silica-based nanoparticles for use in nanomedicine.

Graphical Abstract

Treatment with three different silica nanogeometries, presented with limited geometric impact. Following uptake, a toleration threshold appeared. Native cell mechanistic processes may be utilized as defense mechanisms to compartmentalize the constructs.

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Introduction

Silica nanoparticles are an appealing biomedical platform for nanomedicine since ease in physicochemical modification, economic affordability and potential for reasonably simplistic scale up provide the feasibility of rapid translation. This has led to an increased academic and industrial interest in the creation of new silica nanomaterials for therapeutic, diagnostic, prognostic and combinatory applications.

The chemistry and science of nanomaterials has drastically improved over the last several decades, facilitating the development of silica nanoparticles with significantly different physicochemical characteristics such as surface functionalization and alterations in geometry [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16]. Silica nanoparticles can be engineered to facilitate controlled release rates, targetability, biocompatibility, and protective stability with which one can encapsulate therapeutics or contrast agents [1], [2], [8], [9], [10], [11], [12], [13]. New mesoporous silica chemistries have allowed for the development of nanoconstructs with variations in nanopore geometry [1], [2]. Such variations provide different mechanisms and path lengths for small molecule encapsulation, which is shown to significantly alter their diffusion patterns [1], [2]. Additionally, mesoporous silica can have stimuli sensitive capabilities, where encapsulated drug content can remain protected in the nanoparticle until it reaches the desired delivery site where release can take place via changes in the local environment such as pH, reactive species or magnetic fields [3], [4], [5], [6], [7]. Investigators have utilized capping agents such as gold nanoparticles, polymeric supports, dendrimers, cadmium sulfide and magnetic nanoparticles to facilitate encapsulation [3], [4], [5], [6], [7]. Additionally, the sol–gel chemistries can facilitate the enclosure of a variety of non-releasing molecular agents, such as organic dyes, iron oxide, quantum dots and gold [8], [9], [10], [11], [12], [13]. These doped materials can be utilized in optical, magnetic resonance or photonic imaging and evidence suggests an increase in biocompatibility and signal yields [14], [15], [16].

With the development of new nanoscale silica-based materials however, comes the necessity to fully understand how they interact with the biological environment to ensure safety. Evidence suggests that both the material's physicochemical properties and the cell type which the experiments are performed on alter the mode and mechanisms of induced cellular toxicity. For example, epithelial cells treated with silica nanoparticles show very little to no cytotoxic effects [17], while cells with longer population doubling times (i.e., fibroblasts), or phagocytic capabilities (i.e., macrophages and endothelial cell types) have a substantial increase in toxicity [18], [19]. Nanoparticle size, geometry and surface modification have also proven to alter uptake and toxicity patterns. For example, smaller nanoparticles are widely thought of as having an increased uptake and thus toxicity, mostly contributed to their increase in surface area and exposure to cell surfaces [20], [21]. Likewise, tubular silica nanostructures showed a decrease in uptake when compared to their spherical counter parts [22]. Mesenchymal stem cells have been shown to endocytose positively charged silica nanoparticles to a greater extent than their unmodified systems [23].

To provide validity to these existing and future investigations it will be imperative to correlate physicochemical properties with specified induced biological mechanisms in a systematic fashion. This can lead to the development of safer nanoconstructs, and further lead to the potential for effective manipulation of these properties to facilitate better bioengineered materials for use in nanomedicine. In this work, we set out to investigate the safety and biocompatibility of three silica nanoconstructs, namely spherical, worm-like and cylindrical nanoparticles. The induced biological mechanisms following in vitro treatment of these constructs on model epithelial and phagocytic cell lines is further elucidated.

Section snippets

Silica nanoparticle synthesis and characterization

Spherical silica nanoparticles, nanoworms, and nanocylinders were prepared utilizing previously reported modified Stober methods [24], [25]. Changes in geometry were facilitated by altering the ratios during synthesis of cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), sodium hydroxide (NaOH), aminopropyltrimethoxysilane (APTMS) and water respectively. The following ratios were used respectively to synthesize the worm-like (1.0:8.16:3.85:2.55:4857), cylinder-like

Particle synthesis and characterization

Three silica nanoparticle types with various geometries were synthesized; worms, cylinders, and spheres. Each construct had a common dimension of approximately 200 nm, with an average equivalent positive charge density and an approximate 20% variation in the size of the nanoparticle (Table 1, Fig. 1).

Variations in nanoparticle geometries were due to alterations in incorporated APTMS and CTAB ratios. CTAB is a surfactant and self associates at a critical concentration, facilitating the formation

Conclusion

This work demonstrates cell type dependent toxicity of cationic silica nanoparticles and illustrates limited geometric dependence in biological results across the two cell lines, and in the size range studied. Evidence collected suggests the existence of a cellular toleration concentration threshold and the involvement of autophagic processes in cellular coping mechanisms for silica nanoparticles.

Acknowledgments

This research was supported by the National Institutes of Health (R01-DE19050), National Science Foundation (NSF-NIRT: 0835342) and the Utah Science Technology and Research (USTAR) Initiative. The authors would also like to thank Nancy Chandler from the Health Sciences Center Research Microscopy Facility at the University of Utah for her help with transmission electron microscopy.

References (42)

  • J.J. Li et al.

    Autophagy and oxidative stress associated with gold nanoparticles

    Biomaterials

    (2010)
  • M. Stromme et al.

    Mesoporous silica-based nanomaterials for drug delivery: evaluation of structural properties associated with release rate

    Wiley interdisciplinary reviews

    (2009)
  • U. Brohede et al.

    Sustained release from mesoporous nanoparticles: evaluation of structural properties associated with release rate

    Current Drug Delivery

    (2008)
  • D.R. Radu et al.

    Gate keeping layer effect: a poly(lactic acid)-coated mesoporous silica nanosphere-based fluorescence probe for detection of amino-containing neurotransmitters

    Journal of the American Chemical Society

    (2004)
  • E. Aznar et al.

    pH- and photo-switched release of guest molecules from mesoporous silica supports

    Journal of the American Chemical Society

    (2009)
  • J.A. Gruenhagen et al.

    Real-time imaging of tunable adenosine 5-triphosphate release from an MCM-41-type mesoporous silica nanosphere-based delivery system

    Applied Spectroscopy

    (2005)
  • C.Y. Lai et al.

    A mesoporous silica nanosphere-based carrier system with chemically removable CdS nanoparticle caps for stimuli-responsive controlled release of neurotransmitters and drug molecules

    Journal of the American Chemical Society

    (2003)
  • J.E. Lee et al.

    Uniform mesoporous dye-doped silica nanoparticles decorated with multiple magnetite nanocrystals for simultaneous enhanced magnetic resonance imaging, fluorescence imaging, and drug delivery

    Journal of the American Chemical Society

    (2009)
  • A.A. Burns et al.

    Fluorescent silica nanoparticles with efficient urinary excretion for nanomedicine

    Nano letters

    (2009)
  • M. Liong et al.

    Multifunctional inorganic nanoparticles for imaging, targeting, and drug delivery

    ACS Nano

    (2008)
  • N. Insin et al.

    Incorporation of iron oxide nanoparticles and quantum dots into silica microspheres

    ACS Nano

    (2008)
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