Lung deposition patterns of MWCNT vary with degree of carboxylation

Abstract

Functionalization of multi-walled carbon nanotubes (MWCNT) is known to affect the biological response (e.g. toxicity, inflammation) in vitro and in vivo. However, the reasons for these changes in vivo are not well described. This study examined the degree of MWCNT functionalization with regard to in vivo mouse lung distribution, particle retention, and resulting pathology. A commercially available MWCNT (source MWCNT) was functionalized (f-MWCNT) by systematically varying the degree of carboxylation on the particle’s surface. Following a pilot study using seven variants, two f-MWCNT variants were chosen and for lung pathology and particle distribution using oropharyngeal aspiration administration of MWCNT in Balb/c mice. Particle distribution in the lung was examined at 7 and 28 days post-instillation by bright-field microscopy, CytoViva hyperspectral dark-field imaging, and Stimulated Raman Scattering (SRS) microscopy. Examination of the lung tissue by bright-field microscopy showed some acute inflammation for all MWCNT that was highest with source MWCNT. Hyperspectral imaging and SRS were employed to assess the changes in particle deposition and retention. Highly functionalized MWCNT had a higher lung burden and were more disperse. They also appeared to be associated more with epithelial cells compared to the source and less functionalized MWCNT that were mostly interacting with alveolar macrophages (AM). These results showing a slightly reduced pathology despite the extended deposition have implications for the engineering of safer MWCNT and may establish a practical use as a targeted delivery system.

Keywords:

• MWCNT
• macrophage
• Stimulated Raman Scatter
• functionalization
• carboxylation

Acknowledgments

Mary Buford French and Britt Postma were responsible for conducting the mouse studies. Lou Herritt produced the histology slides for CytoViva and Raman studies. CytoViva and Erin Wood from FDA developed Spectral Feature Fitting method, which appears to be superior to the alternative Spectral Angle Mapping for non-reflective particles like carbon.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

All work was supported by NIH grants R01 ES023209 and P30 GM103338.