Abstract: BACKGROUND: Recent studies have shown that β-sitosterol has a good inhibitory effect on hypertrophic scar fibroblasts. However, its clinical application is limited by its poor water solubility and unstable physicochemical properties.  
OBJECTIVE: To prepare β-sitosterol-laden nanoparticles with sustained drug release function and to analyze the therapeutic effect of the drug-laden nanoparticles on hypertrophic scars in rats.  
METHODS: Mesoporous silica nanoparticles and mesoporous silica@β-sitosterol nanoparticles were prepared, and the physicochemical properties of the two nanoparticles were characterized. A self-made traction device was used to continuously apply traction force to the wound surface of the tail of 48 SD rats (deep to the periosteum) to establish a tail hypertrophic scar model. On day 21 of continuous traction, the 36 rats with successful modeling were randomly divided into 4 groups for intervention using a random number table method, with 9 rats in each group: the control group was injected with normal saline into the scar tissue, and the mesoporous silica group, β-sitosterol group, and mesoporous silica@β-sitosterol group were injected with mesoporous silica nanoparticle solution, β-sitosterol suspension, and mesoporous silica@β-sitosterol nanoparticle solution into the scar tissue, respectively, once a week for 6 consecutive weeks. Scar area and clinical scar score were recorded before injection and 14 and 42 days after injection. One week after the last injection, hematoxylin-eosin staining and Masson staining were used to evaluate dermal thickness and collagen fiber deposition and arrangement. Immunohistochemical staining was used to evaluate the expression of type I collagen and α-smooth muscle actin in scars. Western blot assay was used to detect the protein expression of autophagy marker LC3-II and apoptosis marker cleaved caspase-3 in scars.
RESULTS AND CONCLUSION: (1) Under transmission electron microscopy, both nanoparticles were hollow spheres, and the mesoporous structure of mesoporous silica@β-sitosterol nanoparticles was fuzzy and the average particle size was slightly larger. Infrared spectroscopy showed that β-sitosterol was successfully encapsulated in mesoporous silica nanoparticles. The drug encapsulation rate and drug loading rate of mesoporous silica@β-sitosterol nanoparticles were 88.34% and 39.77%, respectively. The solubility of mesoporous silica@β-sitosterol nanoparticles was stronger than that of free β-sitosterol, and β-sitosterol could be slowly released in vitro for more than 6 days. (2) The results of animal experiments showed that the scar area of the mesoporous silica @β-sitosterol group was smaller than that of the other three groups 42 days after injection (P < 0.05). The clinical scar scores at 14 and 42 days after injection were lower than those of the control group and the mesoporous silica group (P < 0.05). The results of hematoxylin-eosin staining and Masson staining showed that the scar dermis thickness of the mesoporous silica@β-sitosterol group was reduced compared with the control group, the mesoporous silica group, and the β-sitosterol group (P < 0.05), and the collagen arrangement was relatively neat and regular in direction. The results of immunohistochemical staining showed that the expression of type I collagen and α-smooth muscle actin in the mesoporous silica@β-sitosterol group was lower than that of the other three groups (P < 0.05). The results of western blot assay showed that the expression of LC3-II protein in the mesoporous silica@β-sitosterol group was lower than that of the other three groups (P < 0.05), and the expression of cleaved Caspase-3 protein was higher than that of the other three groups (P < 0.05). (3) The results showed that mesoporous silica@β-sitosterol nanoparticles effectively improved the water solubility and water dispersibility of β-sitosterol, and had excellent drug controlled release properties. They could inhibit the autophagy of fibroblasts in the lesions and induce their apoptosis, thereby inhibiting collagen deposition, promoting the fading and remodeling of hypertrophic scars.

Key words: nanoparticle, hypertrophic scar, mesoporous silica, β-sitosterol, autophagy, apoptosis, engineered material