Induction of arginase II by intestinal epithelium promotes the uptake of L-arginine from the lumen of Cryptosporidium parvum-infected porcine ileum.

OBJECTIVES

To determine the specific transport system activities and expression of transporter genes responsible for uptake of L-arginine from the lumen of normal and Cryptosporidium parvum-infected neonatal porcine ileum and the influence of L-arginine catabolic pathways on L-arginine uptake.

METHODS

Intact sheets of ileal mucosa from control and C parvum-infected neonatal piglets were mounted in Ussing chambers and the uptake of 14C-L-arginine was determined under initial rate conditions and in the presence of transport system-selective inhibitors. Epithelial expression of L-arginine transporter genes was quantified by real-time reverse transcription polymerase chain reaction. L-Arginine catabolic enzyme expression was examined by immunoblotting epithelial lysates for arginase I and II. The role of intracellular catabolism in promoting the uptake of L-arginine was determined by pharmacological inhibition of nitric oxide synthase and arginase activities.

RESULTS

C parvum-infected ileum transported L-arginine at rates equivalent to uninfected epithelium despite profound villous atrophy. This was attributed to enhanced uptake of L-arginine by individual epithelial cells in the infection. There were no differences in L-arginine transport system activities (y(+) and B(0, +)) or level of transporter gene expression (CAT-1, CAT-2A, and ATB(0, +)) between uninfected and C parvum-infected epithelial cells. However, infected epithelia had induced expression of the L-arginine hydrolytic enzyme arginase II and lower concentrations of L-arginine. Furthermore, transport of L-arginine by the infected epithelium was significantly inhibited by pharmacological blockade of arginase.

CONCLUSIONS

Intracellular catabolism by arginase II, the induction of which has not been described previously for intestinal epithelium, facilitates uptake of L-arginine by infected epithelium using transport systems that do not differ from those of uninfected cells. Induction of arginase II may limit nitric oxide synthesis by competing with nitric oxide synthase for utilization of L-arginine or promote use of L-arginine for the synthesis of reparative polyamines.