Hyaluronic acid-cross-linked filler stimulates collagen type 1 and elastic fiber synthesis in skin through the TGF-β/Smad signaling pathway in a nude mouse model

Summary Compared to pure hyaluronic acid filler, crosslinked hyaluronic acid (HAc) exhibits superior biocompatibility and longevity as a dermal filler. We previously developed composite HAc-hydroxyapatite (HAp) fillers. Herein, we systematically compared the protein-level increase and gene expression between HAc-microHAp and HAc-nanoHAp in mice, and determined the mechanisms underlying the biological responses to HAc and HAp. Five-week-old female BALB/c-nude mice were classified into five groups: normal skin, Radiesse, Restylane, HAc-nanoHAp, and HAc-microHAp. Fillers (200 μl) were injected to evenly fill the backs of mice. Skin biopsies were performed to investigate collagen and elastic fiber synthesis after filler injections. Western blot analysis, real time-polymerase chain reaction analysis, and immunohistochemistry were performed to investigate protein and gene expression changes. Organ (liver, lung, spleen, and kidney) toxicity of HAc-nanoHAp was determined by hematoxylin & eosin (H&E) staining after 12 weeks. Protein, and gene expression analyses indicated that, compared with pure fillers, HAc-nanoHAp and HAc-microHAp hydrogels preferentially promoted collagen and elastic fiber formation via the TGF-β pathway. The composite fillers also exhibited no evidence of organ toxicity. HAc-HAp filler might play an important role in collagen and elastic fiber regeneration. HAc filler stimulates collagen type 1 and elastic fiber synthesis through the TGF-β/Smad pathway. The role of HAc-HAp composite fillers in photoaging in animal models and their effects on skin, including on elasticity and tensile strength, should be investigated.