Dietary Zinc Supplemented in Organic Form Affects the Expression of Inflammatory Molecules in Swine Intestine

SIMPLE SUMMARY: Zinc is an essential mineral supplemented to human and pig diets as inorganic (inorganic salts) or organic (bound to an organic compound) sources. Some studies reported that pigs fed diets with organic zinc sources respond better to stress conditions than those fed diets with inorganic sources. In this study, we identified genes in the small intestine that may explain those differences. We fed finisher pigs with diets containing organic or inorganic zinc sources for 32 days and conducted gene expression analysis of intestinal ileum samples. The organic Zn source induced lesser level of pro-inflammatory cytokine interleukin 18 (IL18), but greater Toll-like receptor 2 (TLR2) gene expression than inorganic Zn, suggesting that an organic Zn source may improve the condition and immune response of animals under stress by modulating gene expression in the intestine. We also explored if intestinal epithelial cells, which are in direct contact with diet components, are the main cells showing these changes. We exposed intestinal organoids or epithelial “mini-guts” to zinc sources in vitro. Organoids showed changes related to Zn supplementations but did not reproduce the changes of immune-related genes observed in the animal samples, indicating cells other than epithelial are affected by Zn sources. ABSTRACT: Animals receiving Zinc (Zn) dietary supplementation with organic sources respond better to stress than inorganic Zn sources supplementation. The study aimed to identify the effect of different Zn sources on intestinal epithelial gene expression. In total, 45 pigs (9 per treatment) (77.5 ± 2.5 kg weight) were fed for 32 days, a corn-soybean meal diet without supplemented Zn (ZnR) or supplemented with 50 and 100 ppm of inorganic ZnCl(2) (Zn50 and Zn100), and amino acid-bound organic Zn sources (LQ50 and LQ100). Gene expression changes form RNA-seq in ileum tissues of ZnR revealed changes associated with Zn insufficiency. Comparing organic with inorganic Zn sources by one-way ANOVA, pro-inflammatory cytokine interleukin 18 (IL18) was downregulated (p = 0.03) and Toll-like receptor 2 (TLR2) upregulated (p = 0.02). To determine the role of epithelial cells in response to dietary Zn, swine intestinal organoids (enteroids) were exposed to Zn restriction, ZnCl(2) or LQ-Zn. In enteroids, ZIP4 expression decreased with added Zn compared with Zn-restriction (p = 0.006) but Zn sources did not affect (p > 0.05) IL18 or TLR2 expression. These results suggest that organic Zn may stimulate TLR2 signaling possibly affecting immune response, while decreasing the proinflammatory cytokine IL18 expression in non-epithelial cells of intestinal mucosa.