Roles of spermine in modulating the antioxidant status and Nrf2 signalling molecules expression in the thymus and spleen of suckling piglets—new insight
It is well known that weaning induces an increase in the content of spermine in the intestinal mucosal of piglet (Wang, Tan, et al., 2016), implying that spermine has the important biological effects in animals. Spermine, known as polyamine, is a low‐molecular‐weight molecule ubiquitous in all living tissues and cells of mammals and non‐mammals (Polticelli, Salvi, Mariottini, Amendola, & Cervelli, 2012). In the literature, spermine has been implicated in diverse biological and physiological events, such as in regulating replication, transcription, translation and post‐translational modification (Mandala, Mandal, Johansson, Orjalo, & Hee Park, 2013); controlling protein synthesis and cell membrane transporter (Igarashi & Kashiwagi, 2010); modulating ion channel activities (Pegg, 2014); interacting with intracellular messengers (Igarashi & Kashiwagi, 2010); changing intestinal morphology (Fang, Jia, et al., 2016); and promoting immune response (Pegg, 2014). Spermine can also change systemic metabolic processes of the body through affecting lipid metabolism, energy metabolism, amino acid metabolism, cell membrane metabolism and gut microbiota metabolism (Liu, Fang, Yan, Jia, Zhao, Chen, et al., 2014, Liu, Fang, Yan, Jia, Zhao, Huang et al., 2014, Liu et al., 2015). Supplementation with spermine in breast milk can accelerate the early presence of splenic B cells in suckling rats (Pérez‐Cano, González‐Castro, Castellote, Franch, & Castell, 2010), but the effect of spermine intake on the spleen and thymus of pigs remains unknown. Spermine supplementation and extended spermine administration can improve the antioxidant capacity of the jejunum in suckling rats by enhancing free radical scavenging ability (Cao et al., 2015). Pigs can function as appropriate models for human studies because they are similar to humans than rats in terms of anatomy, neurobiology, cardiovascular systems, gastrointestinal tract, metabolic features and genome (Fan & Lai, 2013). However, no study has indicated the effects of spermine intake and its extended duration on the antioxidant status of the thymus and spleen in pigs. Currently, spermine and prolonged spermine ingestion focus on the changes in antioxidant enzymes in suckling animals (Cao et al., 2015; Fang, Liu, et al., 2016). Nevertheless, the relationship between spermine intake and its extended duration and antioxidant enzyme gene expression remains largely unclear. Previous studies showed that the expression levels of endogenous antioxidant enzyme genes are usually regulated by transcription factor nuclear factor erythroid 2‐related factor 2 (Nrf2) (Kensler, Wakabayashi, & Biswal, 2007; Zhang et al., 2013).