Rakkyo (Allium chinense)-Derived Fructan Stimulates Collagen and Hyaluronan Synthesis in Human Dermal Fibroblasts.

Background: Fructans are fructose-based polysaccharides with diverse biological activities; however, their direct activity on skin cells remains unresolved. This study investigated the biological activity of fructan extracted from rakkyo (Allium chinense) (RF) and examined its effects on extracellular matrix (ECM) metabolism, particularly collagen and hyaluronan synthesis, in human dermal fibroblasts. Methods: RF was prepared from fresh rakkyo bulbs by aqueous extraction, alkaline clarification, and membrane filtration. The average molecular weight and structural characteristics of RF were analyzed using size-exclusion chromatography and 13C NMR spectroscopy. Normal human dermal fibroblasts (NHDFs) were treated with RF by culturing cells in RF-supplemented medium (0.1-1.0 mg/mL). Cell viability and viable cell number were evaluated using the thiazolyl blue tetrazolium bromide and trypan blue exclusion assays, respectively. Expression of ECM-related genes was analyzed by qRT-PCR, and collagen and hyaluronan production were quantified by Sirius Red staining and ELISA. Results: RF had an average molecular weight of approximately 11,500 Da and consisted of nearly equal proportions of inulin- and levan-type fructans. RF (≤1 mg/mL) increased the number of viable cells and markedly upregulated collagen, type I, alpha 1 (COL1A1) and hyaluronic acid synthase 2 (HAS2) expression while downregulating Hyal1 expression. After 9 days of treatment, the cumulative production of type I collagen and hyaluronic acid increased by 3.8- and 1.3-fold, respectively, as compared with controls. Upregulation of lysyl oxidase (LOX) mRNA suggested enhanced collagen cross-linking, whereas MMP-1 showed only modest induction. Conclusions: Rakkyo-derived fructan directly stimulates collagen and hyaluronan synthesis in dermal fibroblasts, likely through regulation of ECM-related genes. These results suggest that rakkyo-derived fructan modulates ECM-related readouts in NHDFs under controlled in vitro conditions. Further validation in more complex skin models and in vivo studies is necessary.