The use of PQQ in nutrition is increasingly being discussed in the literature[13, 21]. Zhang et al reported that dietary PQQ·Na2 supplementation during gestation and lactation of female rats can significantly increase the duodenum villous height, jejunum villous height, the activities of maltase and sucrase, the number of Lactobacillus spp. and the expression of ZO-1 and Claudin mRNA in weaned rats. Yin et al suggested that the expression of the jejunal tight junction protein ZO-1 was significantly higher in pigs with PQQ·Na2 supplementation. The major objective of the present study was to investigate the influence of maternal dietary PQQ·Na2 supplementation during gestation and lactation on intestinal health in piglets.
Unlike in humans, the weaning process for pigs involves an abrupt dietary shift from sow milk to a completely feed-based diet, which consequentially inhibits the intestinal architecture and function, resulting in gut associated disorders, such as inflammation and diarrhea. Weaning stress disrupted free-radical metabolism and antioxidative system and then caused serious oxidative stress. Weaning pigs are easily attacked by oxidative stress owning to its imbalance and immature antioxidant system in the intestine. In this context, it seems like a feasible way to overcome impaired antioxidant status and poor immune response in piglets by using dietary antioxidant compounds after weaning[26–27]. Thus, dietary antioxidant concentrations need to be added in diets, especially to prevent excessive oxidative stress during weaning. In this study, the activities of SOD and GSH-Px were significantly increased and MDA was decreased by PQQ·Na2 supplementation in the plasma and small intestine of piglets. SOD is known to serve a protective function for eliminating reactive free radicals and, therefore, it is an important antioxidant defense for almost all cells exposed to oxygen. GSH forms an essential part of the nonenzymatic antioxidants. As other sulfhydryl-containing products, GSH also shows regulatory and protective roles in the body, owning to its establishment of the defenses of the body against tissue injury due to chemicals through its ROS scavenging, cell viability and membrane-stabilizing effects. MDA is an end product of free-radical chain reactions and lipid peroxidation, so it is frequently used to measure lipid peroxide levels, and it correlates well with the degree of lipid peroxidation. Yin et al shown that dietary PQQ·Na2 increased the activities of SOD, GSH-Px and CAT, but reduced the concentration of MDA in the small intestine of piglets, and this is consistent with our study results. HO1 is conducive to the catalysis of heme to carbon monoxide, free ferrous iron and biliverdin. GCLM is the modifier subunit of glutamate cysteine ligase, an important antioxidant that contributes to the maintenance of cellular redox status, which catalyzes the rate-limiting reaction in the de novo synthesis of glutathione. Furthermore, the increased mRNA expression of the family of glutathione peroxidases (GPX), including GPX1 and GPX4, is in accord with enzyme activity in placenta. Organisms with exogenous toxins have a certain ability to detoxify. In biological detoxification systems, the glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UGT) families play an extremely important role in biological detoxification systems, which are regulated by Nrf2 and ARE. In this study dietary PQQ·Na2 supplementation in the diet of sows improved the antioxidant status of intestine. The mRNA expression levels of SOD1, CAT and MGST1 in the jejunum were increased of newborn piglets and the mRNA expression levels of HO1, SOD1, CAT, SOD2, GPX4, GPX1 and GCLC in the jejunum were increased of weaned piglets. Accumulated evidences have shown that it has been practiced to enhance the antioxidant system, relieve stress, and regulate the dynamic balance of intestinal microbiota in livestock husbandry through supplementing natural antioxidants such as vitamins E and C, tea polyphenols, and probiotics.
The gastrointestinal tract acts as the primary immune organ because it must respond to pathogenic stimuli and maintain resistance to co-immunization and dietary antigens. Intestinal immunity is also closely related to other intestinal functions. Previous studies have shown that reduced the level of expression of inflammatory cytokine genes may help to establish a more stable ecosystem and interfere with the growth of certain bacterial populations. The balance between pro-inflammatory and anti-inflammatory cytokines is all-important in the health of weaned piglets. Jiro Omata et al reported that PQQ is not included in parenteral nutrient solutions for clinically treated because it has not been proven to be an essential nutrient for the body. However, in patients receiving parenteral nutrition, it is possible to prevent gastrointestinal mucosal immune disorders exists by supplementation of PQQ. Cytokines play a critical role in the immune response and inflammation and can be important mediators to prevent susceptibility to infection and some gastrointestinal dysfunctions happening. Both in vitro and in vivo studies showed that a negative contribution to gut integrity and epithelial function, including permeability to macromolecules and transport of nutrients and ions partly derives from the uncontrolled synthesis of pro-inflammatory cytokines.
Weaning in pigs is associated with an early and transient response in gene expression of inflammatory cytokines in the gut. It has been shown that pro-inflammatory cytokines such as IL-1β and IL-2 mediate the host inflammatory response to prevent infection; IL-1β also can increase the tight junction permeability. The intestinal expression of pro-inflammatory cytokine genes, such as IL-1β, IL-6, and TNF-α, has been reported to be up-regulated in weaned piglets. In this study, the data suggest that dietary supplementation with 20 mg/kg PQQ·Na2 in sows modulated immune responsivity by inhibiting the expression of pro-inflammatory cytokines in weaned piglets. Hu et al reported that dietary supplementation with 50 mg/kg low-molecularweight chitosan which has antioxidant activity significantly reduced the jejunal mucosal expression of pro-inflammatory cytokines. Yin et al suggested that the concentrations of IFN-γ, IL-1β and IL-2 were decreased in pigs as the PQQ·Na2 supplementation was increased and this is consistent with our study results.
Parenteral nutrition can be useful to prevent and reverse malnutrition and to maintain the nutritional status of patients who are unable to receive adequate enteral nutrition. During weaning, the morphology of intestinal tract often changes greatly, characterized by a decrease in the height of the villi and an increase in the depth of the crypt. This finding suggests that owning to nutrient absorption, the surface area present on the villi is so small that the increase in immature fluff formed in the crypt may reduce the overall growth performance of the animal. In this study, the villous height of duodenum and jejunum of weaned piglets was increased by dietary PQQ·Na2. Variations in villous height and the villous height: crypt ratio are both good indicators of ameliorative nutrient digestion and absorption capacity of the small intestine. Previous studies have shown that lower villus height: crypt depth is associated with microbial challenges and the composition of animal feed. Hedemann et al reported that the growth of many pathogens can be inhibited by the increases in villus length. The intestinal epithelial layer plays a role of a barrier to the infiltration of harmful intestinal contents into the bloodstream. In the jejunum, when the microvilli become more sparse and shorter, the permeability of the intestinal epithelial layer, the inflammatory response and the inflammatory response all increases. Therefore, we have further investigations of the gene expression of tight junction proteins and cytokine concentrations in the jejunum of piglets. The balance between pro-inflammatory and anti-inflammatory cytokines is of great importance for the health of weaned piglets. Tight junction proteins (Claudin 1, ZO-1 and Occludin) have an enormous importance in intestinal barrier integrity and permeability. They can prevent the paracellular diffusion of intestinal bacteria and other antigens across the epithelium by sealing the paracellular space between epithelial cells. Friedman JA, et al reported that continuous exposure to PQQ improved barrier dysfunction. Yin et al suggested that with the increase of PQQ·Na2, the expression of the jejunal tight junction protein ZO-1 was significantly higher in pigs. In this study, the mRNA expression of Occludin and ZO-1 were increased in the jejunal of weaned piglets with the PQQ·Na2 supplementation. Zhang et al reported that dietary PQQ·Na2 supplementation during gestation and lactation of female rats can significantly increase the expression of ZO-1 and Claudin mRNA in the jejunal mucosa of weaned rats which is consistent with our study results.
The mammalian intestinal microbiota is consist of trillions of microbes that facilitate host health, including colonization resistance against gastrointestinal disorders. There is a far-reaching implication for the gastrointestinal microbiota of newborn animals on host health through regulating intestinal nutritional metabolism, maturating immune system, and establishing the gut barrier. Microbial dysbiosis, characterized aberrations in the structure and function of gut microbiota, is a key factor that impact several bowel diseases and inflammatory intestinal disorders. In the present study, we analyzed the fecal microbiota in weaning by 16S rDNA sequencing. At the at the phylum level, Firmicutes and Bacteroidetes were predominant in weaned piglets, which is in agreement with that of Bian et al. Firmicutes was the most predominant phylum in weaned piglets, because Firmicutes are predominant bacteria in intestinal tract, including the Clostridia and Bacilli class and the Lactobacteriales, and capable of oxidising organic sugars via fermentation to produce large amounts of lactic acid[51–52]. In this study, the Firmicutes level was increased and the Proteobacteria level was decreased. Earlier studies have shown that Firmicutes, Bacteroidetes and Proteobacteria were the most dominant phyla in pigs[53–54] which was similar with our study. At the genus level, we observed that the Escherichia was significantly decreased. Post-weaning diarrhoea, induced by enterotoxigenic Escherichia coli, is one of reasons causing poor growth performance and swine disease. Recent studies have also shown that enterotoxigenic Escherichia coli infection could impair intestine and induce the inflammatory response in weaned piglets[56–57]. In this study, the results shown that dietary PQQ·Na2 in sows could decreased the Escherichia in weaned piglets in order to improve the intestinal health.