Intestinal Epithelial Responses to Organic and Inorganic Sources of Zinc

Organic trace minerals, Zn in particular, have proven superior at promoting pig health and performance than inorganic trace mineral in diets for pigs. However, the mechanisms involved in these differences are not understood. To define if organic and inorganic sources of Zn trigger different responses in the intestine, we evaluated the expression of genes coding for nutrient transporters, Zn transporters, and cytokines in mouse enteroids. Enteroids are 3-dimensional structures grown in vitro that have all the cell types and structure of the small intestine, allowing for studies of specific epithelial responses to supplements in the basal side (added to medium) or in the luminal side (by microinjection). To first define the responses to Zn sources when in the basal side, we treated mouse enteroids with 4 ppm and 7.5 ppm of Zn from inorganic (ZnCl₂) and organic (LQ-Zinc, Zinpro Corporation) sources, and same concentrations of FeCl₃ and vehicle as negative controls added to the culture medium. After 48 h of treatment, total mRNA was extracted evaluation of glucose transporters (Sglt1 and Glut2), di-/tri-peptide transporter (Pept1), Met transporter (Slc6a), Zn transporters and binding proteins (ZnT1, Zip4, Zip5, Zip7, Zip8, and Mt1), intestinal cell differentiation markers (Muc2, Ifabp, Villin1, Lgr5, and Olfm4), cell proliferation markers (Ki-67 and Pcna), and inflammatory cytokines (Il-7, Il-18, Il-1Ra and Tnf-α) by quantitative PCR. Results from three independent experiments were analyzed by one-way ANOVA followed by Dunn’s test. As expected, no differences were found in any markers between the vehicle and negative control (FeCl₃). Enteroid treatment with both ZnCl₂ and LQ-Zn increased Glut2 (P < 0.01), Mt1 (P < 0.01) and ZnT1 (P < 0.05) expressions, while decreased Sglt1, Pept1, and Zip4 (P < 0.01 for all three) expressions compared with control at 4 ppm and 7.5 ppm. Expression of Pcna was increased by ZnCl₂ and LQ-Zn compared with control (P < 0.05) only at 4 ppm with no changes observed for Ki-67. ZnCl₂ and LQ-Zn increased Il-18 compared to control at 4 ppm and 7.5 ppm (P < 0.05). Il-1Ra was increased (P < 0.05) with 7.5 ppm ZnCl₂ and LQ-Zn treatments compared with control. Overall, the differences observed in this study were due to Zn independently of the source. However, physiological differences between organic and inorganic sources could be due to responses in the luminal membrane which are currently under study.