Niacinamide Down-Regulates the Expression of DKK-1 and Protects Cells from Oxidative Stress in Cultured Human Dermal Papilla Cells

PURPOSE: An increasing number of people are suffering from hair loss disorders. Niacinamide has long been used as an active ingredient for anti-hair loss preparations but the exact mechanism has not been clearly elucidated yet. The effects of niacinamide were investigated in cultured human dermal papilla cells (hDPCs). METHODS: To investigate the anti-hair loss effect of niacinamide and its molecular mechanisms, Western blot analysis, ELISA, quantitative RT-PCR and immunocytochemistry were performed. To study the protective effects of niacinamide against H(2)O(2)-induced oxidative stress, ROS generation and cytotoxicity were evaluated by DCF-DA assay and LDH release assay, respectively. Minoxidil was used as a positive control. RESULTS: Niacinamide decreased the protein expression level of DKK-1 which promotes regression of hair follicles by inducing catagen. The protein expression levels of cell senescence markers, p21 (CDKN1A) and p16 (CDKN2A) which are related to cell cycle arrest, were decreased. The expression of versican was increased by niacinamide treatment in cultured hDPCs. We have found that niacinamide decreased the H(2)O(2)-induced intracellular ROS production in cultured hDPCs. Moreover, niacinamide decreased the protein expression levels of H(2)O(2)-induced p21 and p16 and diminished the secretion of H(2)O(2)-induced DKK-1. CONCLUSION: Our data demonstrate that niacinamide could enhance hair growth by preventing oxidative stress-induced cell senescence and premature catagen entry of hair follicles.