Abstract
Tannic acid (TA) is an herbal polyphenol containing a galloyl group that has been prescribed to treat gastroenteritis, diarrhea, and irritable bowel syndrome. TA has anti-inflammatory, anti-cancer, and anti-viral properties; however, the molecular mechanisms of these potential therapeutic effects are still largely unknown. Here, we examined the ability of TA to induce anti-inflammatory responses. TA was found to be an agonist of the dopamine D2L receptor. TA reduced interferon (IFN)-γ and interleukin (IL)-1β secretion but upregulated tumor necrosis factor α and IL-10 secretion from lipopolysaccharide (LPS)-stimulated mouse splenocytes. TA also reduced IFN-γ secretion but enhanced IL-10 secretion from anti-cluster of differentiation (CD) 3/CD28 antibody-stimulated splenocytes. An immune subset study confirmed that TA regulated cytokine secretion by various types of immune cells in the context of stimulation with LPS or anti-CD3/CD28 antibodies. Administration of TA to mice with experimentally induced colitis strikingly suppressed weight loss, colon shrinkage, and IL-17 secretion from mesenteric lymph node lymphocytes in response to CD3/CD28 stimulation. These data suggest that TA suppresses inflammatory responses in colitis by regulating cytokine secretion by immune cells in the colon.
Highlights
Tannins are water-soluble herbal polyphenols (Erdelyi et al, 2005) and can be categorized into four major groups: gallotannins, which are known as tannic acid (TA); ellagitannins; complexes of TA and ellagitannins; and condensed tannins
A D1R antagonist, SCH2 3390, ameliorated various types of autoimmune inflammation (Hashimoto et al, 2009; Nakagome et al, 2011; Nakano et al, 2008, 2011; Okada et al, 2009). In agreement with these findings, we found that berberine, an herbal alkaloid that is prescribed for gastroenteritis and diarrhea, is a D1R and D2L receptor (D2LR) antagonist and ameliorated dextran sodium salt (DSS)-induced experimental colitis in mice (Kawano et al, 2015)
We hypothesized that other herbal compounds used to treat gastroenteritis or diarrhea may act on DA receptor (DAR)
Summary
Tannins are water-soluble herbal polyphenols (Erdelyi et al, 2005) and can be categorized into four major groups: gallotannins, which are known as tannic acid (TA); ellagitannins; complexes of TA and ellagitannins; and condensed tannins. TA is hydrolyzable and is the most abundant tannin. TA has been prescribed to treat gastroenteritis (Michalek et al, 2016; Ruszczynski et al, 2014) and acute diarrhea (Lambelin, 2013). TA directly suppresses inflammation (Feldman et al, 2001; Mota et al, 1985), cancer cell proliferation (Fong et al, 1972), and the proliferation of viruses in host cells (Uchiumi et al, 1996)
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