Carbon Nanomaterials Interfacing with Neurons: An In vivo Perspective

Abstract

Developing new tools that outperform current state of the art technologies for imaging, drug delivery or electrical sensing in neuronal tissues is one of the great challenges in neurosciences. Investigations into the potential use of carbon nanomaterials for such applications started about two decades ago. Since then, numerous in vitro studies have examined interactions between these nanomaterials and neurons, either by evaluating their compatibility, as vectors for drug delivery, or for their potential use in electric activity sensing and manipulation. The results obtained indicate that carbon nanomaterials may be suitable for medical therapies. However, a relatively small number of in vivo studies have been carried out to date. In order to facilitate the transformation of carbon nanomaterial into practical neurobiomedical applications, it is essential to identify and highlight in the existing literature the strengths and weakness that different carbon nanomaterials have displayed when probed in vivo. Unfortunately the current literature is sometimes sparse and confusing. To offer a clearer picture of the in vivo studies on carbon nanomaterials in the central nervous system, we provide a systematic and critical review. Hereby we identify properties and behavior of carbon nanomaterials in vivo inside the neural tissues, and we examine key achievements and potentially problematic toxicological issues.

Keywords: carbon nanomaterials; central nervous system; drug delivery; imaging; in vivo studies; neuroprotection.

Figure 1

Schematic representation of (A) SWCNTS and (C) MWCNTs. (B) HRTEM micrograph of a single SWCNT; reprinted with permission from Zhang Y. et al. (2010), Copyright (2010) American Chemical Society. (D) HRTEM micrograph of MWCNTs, functionalized with N-methylpyrrolidine groups to improve their solubility in organic solvents; adapted from Cellot et al. (2011), copyright Society for Neurosciences (2011).

Figure 2

Coronal brain slices showing short and long term effects of PF-127 coated MWCNTs intracortical injection. (A) Localization of the injection site (star); cc, cerebral cortex; wm, white matter. (B,C) Magnifications of the injection site 3 days after the injection: outside the lesion area (dashed line) cerebral tissues show normal neuronal density and tissue layering. (D,E) Control mice and (F,G) PF-127 coated MWCNTs injected mice brain slices 18 days after the injection: both the lesion sites present normal gliosis surrounding the injection site. Reprinted from Bardi et al. (2009), Copyright (2009), with permission from Elsevier.

Figure 3

Morphological and functional neuroprotective effects of the SWCNTs-NH₂pretreatment after ischemia-reperfusion. (A) Coronal brain sections (stained with tetrazolium chloride) of sham, PBS and SWCNTs-NH₂ (here called a-SWNT) treated mice, where white areas correspond to the infarcted regions after MCAO. (B) Quantification of the lesion in the brain sections showed in (A). (C) Schedule of motor functionality experiments. (D) Motor coordination results from Rotarod tests indicating complete recovery of motor coordination in SWCNTs-NH₂ treated mice. Data reported as mean + s.e.m. ^*P < 0.001 vs. pre-MCAO. Reprinted by permission from Mcmillan Publishers Ltd.: Nature Nanotechnology, Lee H. J. et al. (2011), Copyright (2011).

Figure 4

Schematic representation of C₆₀ fullerene.

Figure 5

(A,B) Positron emission tomography (PET) brain images using from two control primates (M1, M2) and two carboxyfullerene-treated primates (M3, M4) before MPTP injection (pre) and at the end of the treatment (post). [¹¹C] dihydrotetrabenazine (DTBZ) and 6-[¹⁸F] fluorodopa (FD) are used as probe for evaluating the nigrostriatal dopaminergic activity. As clearly visible placebo-treated animals are showing unsymmetrical distribution of tracers in the two hemispheres indicating partial loss of dopaminergic activity, while carboxyfullerene-treated animals are showing dopaminergic activity in both the hemispheres. (C) Parkinsonian rating score at the end of the treatment, indicating reduction of bradykinesia in carboxyfullerene (C3) treated animals with respect to animals receiving placebo. Data reported as mean + s.e.m. ^*p = 0.007. Adapted from Dugan et al. (2014) with permission from John Wiley and Sons, Copyright (2014).

Figure 6

(A) Schematic representation of GO. The nanomaterial surface and edges are characterized by the presence of carboxyls, carbonyls, alcohols, and epoxydes. (B) TEM micrograph of GO sheets; adapted from Zhang L. et al. (2010) with permission from John Wiley and Sons, Copyright (2010).

Figure 7

Imaging of GO nanoparticles in a mouse brain using two-photon luminescence. (A) Schematic representation of the experimental conditions used. (B) Reconstructed 3D luminescence image of GO-PEG nanoparticles inside the brain parenchyma. Reprinted from Qian et al. (2012) with permission from John Wiley and Sons, Copyright (2012).

Figure 8

In vivo luminescence imaging of luminescence-labeled U87 tumor xenografted into nude mice brains. Animals receiving the treatment consisting in administration of magnetic GO-PEG-EPI nanoparticles followed by magnetic targeting and LFUS (NMGO–mPEG–EPI/MT) show an improved tumor reduction at 7 and 13 days after the treatment with respect to control mice. Adapted from Yang H.-W. et al. (2013) with permission from John Wiley and Sons, Copyright (2013).

Figure 9

(A) Schematic representation of NDs. (B) HRTEM micrograph of ~7 nm oxidized diamond nanoparticles; adapted with permission from Rojas et al. (2011). Copiright (2011) American Chemical Society.

Figure 10

Schematic representation of SWCNHs (A) and stacked-cup CNFs (C). (B) TEM micrograph of ~80 nm SWCNHs peapods. (D) TEM micrograph of stacked-cup CNFs. (A,B) adapted from Voiry et al. (2015) with permission from The Royal Society of Chemistry. (C,D) adapted from Sato et al. (2005) with permission from The Royal Society of Chemistry.

Figure 11

(A) Schematic representation of CDs. (B) HRTEM micrograph of 4–7 nm carbon dots produced by carbonization of chitosan; adapted from Yang et al. (2012) with permission from The Royal Society of Chemistry.

Figure 12

In vivo and ex vivo imaging of glioma bearing mice after administration of 3–4 nm glycine-derived CDs. (A) Epifluorescence imaging of CDs distribution after i.v. injection, showing the rapid accumulation inside the glioma and the fast excretion of the nanoparticles after few hours. (B) 3-D reconstruction of CDs distribution 2 h after the injection, confirming the localization in the brain. (C) Ex vivo fluorescence imaging of main organs 2 h after CDs injection, indicating high accumulation in liver and kidney but also a good retention inside the glioma. Reproduced from Ruan et al. (2014) with permission from The Royal Society of Chemistry.