Potential and challenges of tannins as an alternative to in-feed antibiotics for farm animal production

Huang, Qianqian; Liu, Xiuli; Zhao, Guoqi; Hu, Tianming; Wang, Yuxi

Tannins have been shown to have significant activity against some virus, e.g., human immunodeficiency virus (HIV), bovine adeno-associated virus and noroviruses (Uchiumi et al., 2003; Di Pasquale et al., 2012; Zhang et al., 2012) . Yang et al. (2013) found that a HT (chebulagic acid) had considerable anti-enterovirus 71 activities in vitro and efficiently reduced mortality and relieved clinical symptoms through the inhibition of viral replication in mice model. It has been demonstrated that tannin exerted inhibitory effect on HIV-1 through inhibiting HIV-1 replication by targeting the virus reverse transcriptase (Tan et al., 1991) , protease (Xu et al., 2000) , and integrase (Au et al., 2001) , or inhibiting HIV-1 entry into target cells by interfering with the gp41 sex-helix bundle formation (Liu et al., 2004) . Epigallocatechin from green-tea was reported to inhibit hepatitis C virus (HCV) entry (Ciesek et al., 2011; Calland et al., 2012) . Liu et al. (2015a,b) revealed that tannic acid (HT) inhibited HCV entry and cell-to-cell transmission but did not interfere with intracellular HCV replication. Three HT (punicalagin, punicalin and geraniin) inhibited hepatitis B virus cccDNA production via a dual mechanism through preventing the formation of cccDNA and promoting cccDNA decay (Liu et al., 2016) . Ueda et al. (2013) found that tannins from persimmon (Diospyros kaki) significantly reduced viral infectivity of 12 tested viruses whereas tannins derived from green tea, acacia and gallnuts were effective only for some of them, and protein aggregation seems to be a fundamental mechanism underlying the anti-viral effect of persimmon tannin. Phlorotannins isolated from E. cava have been demonstrated to possess strong activity against influenza virus neuraminidase (Ryu et al., 2011) , porcine epidemic diarrhea virus (PEDV) by inhibiting viral entry and/or viral replication (Kwon et al., 2013) and HIV-1 (Karadeniz et al., 2014) . Similar antiviral activity was also demonstrated for PT isolated from Eisenia bicyclis against murine norovirus (Eom et al., 2015) and human papilloma virus (Kim and Kwak, 2015) .