Melittin-loaded solid lipid nanoparticles inhibit pulmonary fibrosis via the NOVA2-TGF-β/Smads signaling pathway

Melittin (MLT) is a cationic hemolytic peptide that suppresses inflammation and fibrosis in various animal models. However, the application of MLT in clinical practice is limited owing to its side effects. Solid lipid nanoparticles have the advantages of cell-specific delivery and sustained release of hydrophobic drugs, which can be exploited against many diseases. This study aimed to evaluate the effects of MLT-loaded solid lipid nanoparticles (MLT@NPs) on pulmonary fibrosis.

In this study, the MLT-loaded solid lipid nanoparticles (MLT@NPs) were designed and their antifibrotic effects in bleomycin-induced mice and lipopolysaccharide-treated L929 cells were investigated. Characterization of MLT@NPs in the terms of zeta potential and particle size were measured by the dynamic light scattering and those of encapsulation efficiency and drug loading were determined using spectrophotometer. The Masson's trichrome and hematoxylin and eosin staining for the histopathological study. The contents and expressions of pro-inflammatory and pro-fibrotic factors in the bronchoalveolar lavage fluid and lung tissues were mesaured by ELISA, biochemical analysis, and Western blotting. High-throughput mRNA sequencing was performed for selecting differentially expressed genes among different groups of mice and further confirmed by RT-qPCR and Western blotting. Cell viability and migration were examined by CCK8 and Transwell, respectively.

The MLT@NPs were physically characterized for their particle size (263.3 ± 6.18 nm), zeta potential (29.4 ± 2.59 mV), encapsulation efficiency (39.65 ± 1.15 %), and drug loading (16.80 ± 0.63 %). When bleomycin-induced mice were exposed to free MLT and MLT@NPs, the content and expression of pro-inflammatory (IL-6 and TNF-α) and pro-fibrotic factors (TGF-β1, PDGF, CTGF, hydroxyproline, α-SMA, and p-Smad2/3) in the bronchoalveolar lavage fluid and lung tissues were decreased. In particular, these effects were more obvious when mice were treated with MLT@NPs. Moreover, MLT@NPs also inhibited cell viability, migration, and fibrogenesis in lipopolysaccharide-treated L929 cells and the mechanism involved in Nova2, resulting in activation of the TGF-β1-Smad2/3 signaling pathway.

MLT@NPs offer a good alternative for increasing the efficiency of MLT. Therefore, MLT@NPs may be a promising therapeutic alternative for idiopathic pulmonary fibrosis.