Cellular Internalization and Epithelial Penetration of Fluorescent-labeled Mesoporous Silica Nanoparticles

Objectives: Understanding of cellular internalization and epithelial penetration capacity is crucial to develop the nano-vehicles for drug application in dentistry. This study investigated the cellular uptake, internalization and tissue penetration of our newly synthesized fluorescent spherical mesoporous silica nanoparticles (S-MSNs).
Methods: The fabricated MSNs were surface-modified with amine groups, and subsequently labeled with rhodamine B isothiocyanate (RITC-NP). The RITC-NP fluorescence was detected by fluorescence spectrometer, and the RITC-NP cytotoxicity was evaluated in primary human gingival epithelial cells (HGECs) and differentiated THP-1 cells using CCK-8 kit. Meanwhile, the cellular uptake of RITC-NP was accessed by the confocal scanning laser microscopy after 24h of treatment. Furthermore, the isolated porcine ear skins and reconstituted human gingival epithelia (RHGE) were treated with 200 μg/mL of RITC-NP for 2, 6 and 24 h, and then fixed in 4% paraformaldehyde. The tissue cryosections were stained with DAPI, and subsequently the fluorescence-labeled MSNs were assessed by the fluorescent microscope. The H&E stain was conducted on the cryosections for histological analysis.
Results: The RITC-NP (average size of 250 nm) with shifted emission wavelength at 580 nm exhibited a relatively low cytotoxicity on the cells. These labeled-MSNs were mainly distributed around the cellular nuclei after 24 h of treatment. Moreover, the RITC-NP began to penetrate the corneum of porcine ear skin after 2 h of treatment, and notably these particles could be detected in the deep layers of epithelia at 24 h. Interestingly, the RITC-NP accumulated merely in the corneum layer of RHGE during the 24h experiment without causing tissue damage.
Conclusions: This pioneering study demonstrates the penetration and biodistribution of the MSNs in both cells and tissues. It may facilitate further development of nano-based drug delivery for clinical application.