Gamma ray-irradiated fibroin protein from Bombyx mori protects against TNF-α-induced oxidative stress and inflammation in human skin keratinocytes through NF-κB and Nrf2 signaling pathways

Silk fibroin from Bombyx mori has traditionally been utilized for garment production; however, recently, it has become feasible to manufacture edible and cosmetic products using this material. Gamma-ray irradiation can improve physiological activity through the modification of the structure of proteins in biological materials. In this study, we examined whether gamma ray-irradiated fibroin protein (gFP) has a protective effect on tumor necrosis factor alpha (TNF-α)-induced cellular stress through a change in protein structure. First, we confirmed that the structure of FP was changed by gamma-ray irradiation using electrophoresis, UV spectra and Fourier-transform infrared spectroscopy (FT-IR). We further investigated the cytoprotective potential of 20 kGy-irradiated fibroin protein (gFP20) in human skin keratinocytes (HaCaT cells) exposed to extracellular stress. gFP20 effectively decreased TNF-α-induced matrix metalloproteinase-1 (MMP-1) overexpression and restored reduced type-1 procollagen in HaCaT cells. This reduction occurred concomitantly with suppressed nuclear factor-κB (NF-κB) nuclear translocation, resulting in a decreased level of inflammatory mediator and pro-inflammatory cytokines. Furthermore, gFP20 protected cells from TNF-α-induced oxidative stress by attenuating reactive oxygen species (ROS) overexpression and increasing the production of the antioxidant enzyme heme oxygenase-1 (HO-1) through the stimulation of the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2) into the nucleus. Taken together, our findings indicate that low-dose irradiated fibroin protein (gFP20) could be considered as a functional material for skincare products.