0
Tight junctions are one of the most important components of the intestinal mucosal barrier against macromolecular transmission. They are made up of a complex of integral membrane proteins, which are tethered to cytoplasmic plaque proteins. An increase in intestinal permeability induced by weaning might be attributed to the alterations of tight junction protein expression. Therefore, it would be of interest to examine whether supplementation of pharmacological levels of Zn modulates the expression of tight junction proteins. The purpose of the present experiment was to evaluate the beneficial role of pharmacological levels of Zn for post-weaning diarrhoea, intestinal permeability and expression of tight junction proteins, mainly occludin, zonula occludens protein-1 (ZO-1) and claudin-1.
Therefore a total of seventy-two piglets weaned at 24 d, were allocated to three dietary treatments: (1) control diet without supplemental Zn; (2) control diet supplemented with 2000 mg Zn/kg from ZnO; (3) control diet supplemented with 2000 mg Zn/kg from tetrabasic zinc chloride (TBZC). At the end of a 14 d experiment period, piglets were weighed, feed consumption was measured, and mucosal barrier function was determined using the lactulose/mannitol test. Expression of mucosal tight junction protein was measured at RNA and protein level.
Inclusion of TBZC or ZnO in the diet significantly increased average daily gain (P<0.01) and average daily feed intake (P<0.05), while leading to reduced feed conversion ratio (P<0.05) and faecal scores (P<0.01). TBZC reduced urinary lactulose:mannitol ratios of weaning piglets (P<0.05), while dietary supplementation with ZnO tended to reduce urinary lactulose:mannitol ratios (P=0.061). ZnO or TBZC significantly enhanced the mRNA and protein expression of occludin (P<0.05) and zonula occludens protein-1 (ZO-1) (P<0.05) in the ileal mucosa. Piglets fed the TBZC-supplemented diet had a higher level of occludin than pigs fed the ZnO-supplemented diet (P<0.05).
The results indicate that Zn supplementation decreased faecal scores and the reduction was accompanied by reduced intestinal permeability, which was evident from the reduced urinary lactulose:mannitol ratios and increased expression of occludin and ZO-1. Therefore, the protective effect of pharmacological levels of dietary Zn in reducing diarrhoea might, at least partly, be associated with reduced intestinal permeability.
B Zhang and Y Guo, 2009. British Journal of Nutrition, 102: 687-693.
