Protective Effects of Black Rice Bran against Chemically-Induced Inflammation of Mouse Skin

We investigated the inhibitory effects of black rice (cv. LK1-3-6-12-1-1) bran against 12-O-tetradecanolylphorbol-13-acetate (TPA)-induced skin edema and 2,4-dinitrofluorobenzene (DNFB)-induced allergic contact dermatitis (ACD) in inflammatory mouse models. We also determined the effects of the bran extract on the following biomarkers: pro-inflammatory cytokines tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), eicosanoids leukotriene B4 (LTB4), and prostaglandin E2 (PGE2). Topical application of TPA to ears of CD-1 mice induced inflammation accompanied with substantial increase in TNF-α, IL-1β, IL-6, LTB4, and PGE2 levels and an elevation in intercellular adhesion molecule-1 (ICAM-1) gene expressions in ear skin tissues. Intraperitoneal injection of black rice bran extract prior to TPA application in mice significantly suppressed TPA-induced inflammation (edema) and induced a marked decrease in the production of TNF-α, IL-1β, IL-6, and LTB4. Feeding mice a standard diet with added 10% black rice bran also significantly suppressed DNFB-induced allergic contact dermatitis on the skin of the mice. By contrast, a nonpigmented brown rice bran extract did not inhibit the TPA-induced edema and failed to significantly suppress production of pro-inflammatory biomarkers (mediators). These in vivo findings further demonstrate the potential value of black rice bran as an anti-inflammatory and antiallergic food ingredient and possibly also as a therapeutic agent for the treatment and prevention of diseases associated with chronic inflammation.