Immunomodulatory effects of arginine supplementation in colitis and colon cancer

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DESCRIPTION (provided by applicant): In the Parent R01, we are studying L-arginine (L-Arg) in vitro and in vivo in mouse models of colitis. Since the start of this grant on 9/15/08, we have made substantial progress. In particular, under Aim 2 we have found that knockout of the L-Arg transporter cationic amino acid transporter (CAT)2 significantly exacerbates murine colitis and under Aim 3 we have found that CAT2 deletion dramatically increases tumor number and size in the AOM-DSS colitis-associated cancer model. In studies beyond those originally proposed, we have studied L-Arg availability in 14 normal human subjects and 22 patients with ulcerative colitis (UC) involving the entire colon (pancolitis). We have found increased serum L-Arg levels in severe colitis vs. moderate colitis or normal controls. There was a strong correlation of serum L-Arg level with the Mayo Disease Activity Index (DAI). In parallel to the increase in serum L-Arg levels, there were also increases in the amino acids L-ornithine (L-Orn) and L-lysine (L-Lys), which compete with L-Arg for uptake into cells by the transporters CAT1 and CAT2, so the net effect was no increase in the arginine availability index (AAI), calculated as the [L-Arg]/[L-Orn + L-Lys]. As a supplement to our Parent R01, we propose to test the hypotheses that there is a functional deficiency of L-Arg availability in UC, and that dietary consumption of L-Arg may be a determinant of L-Arg availability and disease activity. Because L-Arg may represent a biomarker for UC disease severity, we will also determine the DAI and assess for correlation with serum L-Arg. We propose to undertake two specific aims in a prospective manner: 1.) To determine L-Arg availability in UC patients and normal controls, and correlate with disease activity by assessing: A.) Clinical parameters, DAI, and endoscopy score; B.) Tissue histopathology; C.) Serum L-Arg, L-Orn, L-Lys; AAI; and cytokines; D.) Colonic tissue L-Arg, L-Orn, and L-Lys; AAI; and cytokines; E.) Tissue CAT1 and CAT2 levels; and F.) Tissue L-Arg uptake. We will compare normal control subjects, patients with pancolitis, and patients with left-sided colitis. In those with the latter, we will compare involved and uninvolved mucosa. 2.) To assess L-Arg intake in the diet of UC patients and control subjects, using specialized software: A.) To determine if L-Arg intake in the diet correlates inversely with UC clinical status; and B.) To determine if L-Arg intake correlates with serum and/or tissue levels of L-Arg. These studies will provide new insights into the clinical problem of adjunctive treatments for IBD and nutritional issues. Consistent with the goals of the Recovery Act, we will hire two additional personnel, utilize core facilities, and purchase supplies from US companies. This project is responsive to the NCCAM Guidelines for ARRA Competitive Revisions under "studies examining individual or population reliability and variability of outcome measures important to evaluation of specific CAM interventions" because the studies proposed are necessary to understand the biology and methods needed for a future dietary intervention/L-Arg supplementation study. PUBLIC HEALTH RELEVANCE: Over one million Americans have inflammatory bowel disease and about half of those affected have ulcerative colitis (UC), leading many to seek a variety of diets and alternative medicines. In addition to our funded studies under R01 AT004821 studying the importance of the amino acid L-arginine (L-Arg) in animal models, we have exciting new data in humans with ulcerative colitis indicating that there is accumulation of L-Arg in the serum of patients with severe UC, which suggests that there may be a defect in utilization of L-Arg in this disease. In this competitive revision application we propose to use supplemental funds under ARRA to conduct additional studies in human subjects to establish whether there is a functional deficiency of L-Arg in UC that correlates with disease activity and extent, and if dietary levels of L-Arg correlate with L-Arg availability to colonic tissues and reduction of UC disease activity.