Nitrogen-Doped Multiwalled Carbon Nanotubes Trigger Immune Responses and Inhibit Fat Deposition

Multiwalled carbon nanotubes (MWCNTs) offer immense opportunities to deliver drugs and biomolecules to targeted tissues. However, it's unclear to their effects on fat metabolism. Here, it is demonstrated that nitrogen-doped carboxylate-functionalized MWCNTs (N-MWCNTs) inhibit fat deposition both in vivo and in vitro. N-MWCNTs <0.5 µg mL⁻¹ do not affect the viability of HEK293 cells and adipose-derived stem cells (ASCs). Intramuscular administration of N-MWCNTs does not affect the body weight gain and feed intake of mice, but reduces the fat mass. In in vitro-cultured adipocytes, N-MWCNTs suppress fat accumulation, accompanied by decreased and increased expression of adipogenic and lipolysis genes, respectively. Transcriptome analysis further certifies the N-MWCNT alteration of fat metabolism-related genes. Interestingly, the internalization of N-MWCNTs by macrophage-like cells via Transmission electron microscopy (TEM) imaging is observed. The mRNA sequencing data also shows remarkable variation of the genes involved in the Toll-like receptors (TLRs) pathway, exhibiting down- or up-regulation of inflammatory factors, of which TNF-α, IL-1, IL-7, IL-10, and IL-12 are decreased, whereas IL-6 and IL-11 are increased. In conclusion, N-MWCNTs trigger immune responses and reduction of fat deposition.