Skin Extracellular Matrix Stimulation following Injection of a Hyaluronic Acid–Based Dermal Filler in a Rat Model

Background: Hyaluronic acid–based dermal fillers have gained rapid acceptance for treating facial wrinkles and deep tissue folds. Although their space-filling properties are well understood, this study evaluates the cellular and molecular changes in skin, as a secondary effect, following injection of a commercially available, 24-mg/ml, cross-linked hyaluronic acid–based filler (HYC-24L+) in a rodent model. Methods: Sprague-Dawley rats, aged 2 to 4 months, were injected intradermally with 20 μl of HYC-24L+ using a linear threading technique and followed to 12 weeks after injection. Untreated skin and saline injection were used as study controls. Enzyme-linked immunosorbent assay and reverse-transcriptase polymerase chain reaction methods were used to investigate changes in the expression of several extracellular matrix proteins and genes over time. Results: HYC-24L+ significantly increased the protein expression levels of collagen types I and III in rat dermal tissue for up to 12 weeks. The ratio of collagen type III to type I protein, however, remained unchanged, suggesting maintenance of collagen homeostasis. A significant increase in dermal elastin after HYC-24L+ injection was also observed. Gene expression analysis confirmed that several genes associated with extracellular matrix production and assembly were also transiently up-regulated, and that these changes temporally preceded those observed at the protein level. Conclusion: In addition to its well-understood space-filling function, as a secondary effect, the authors demonstrate that HYC-24L+ stimulates the production of several extracellular matrix components, including dermal collagen and elastin.