Amino Acid Regulation of Intestinal Restitution during Infectious Enteritis

North Carolina State University Swine Nutrition Research from 2004-2005. USDA statistics indicate that 57% of non-crushing deaths in swine result from diarrhea and malnutrition. Rotavirus is the leading cause of diarrhea in neonatal pigs and human infants, causing ~700,000 infant deaths annually. Currently, the only treatment for acute viral diarrhea is oral rehyration. The RotashieldTM vaccine has been withdrawn, and no drugs are available to facilitate repair of the damaged intestinal mucosa. We have studied newborn protein-calorie-deprived piglets, a model for ‘protracted diarrhea of infancy,’ in which intestinal recovery is delayed by the malnutrition. Previous studies showed that intestinal cell migration to cover ulcerations correlated with and was dependent upon the activation of ribosomal p70^s6 kinase. This kinase, along with eukaryotic initiation factor 4E-BP1, is activated by the mammalian target of rapamycin (mTOR) and has been called the ‘nutrient sensor’ of mammalian cells. Both p70^s6k and 4E-BP1 are regulated by intracellular amino acids and are major regulators of the rate of mRNA translation. In these investigations, we identified p70^s6k as regulator of protein synthesis in the recovering intestine of rotavirus infected piglets, thereby identifying it as a target for stimulating rate of recovery.

Experiment

In an initial experiment, piglets were separated into two treatment groups, 1) noninfected, full fed and 2) infected, malnourished and euthanized on d 0, 1, 3, 5, and 11 of infection. Infected animals experienced significantly increased diarrhea scores, rotavirus shedding, reduced lactase activity, and blunted intestinal villi. Western blotting of phosphorylated p70^s6k revealed activation of this enzyme 3 and 5 d post infection. Additionally, in vitro protein synthesis of small intestine explants was significantly increased by 50-100% on 1, 3, and 5 d post infection. In a second 2×2 factorial experiment, we separated effects of feeding level (full fed vs. malnourished) and infection, euthanizing pigs on d 3 post infection. In vitro protein synthesis was increased 94% by infection (Figure 1) and p70^s6kwas also increased by infection, but neither was influenced by malnutrition. Rotaviral enteritis increases intestinal protein synthesis and p70^s6k activation acutely following infection and activation is not influenced by plane of nutrition.

Figure 1. In vitro protein synthesis of small intestine explants from piglets fully fed or malnourished and non-infected or infected with rotavirus on day 3 of infection. Superscripts (a,b) indicate a significant effect of rotavirus infection (P<0.05).