Abstract
Background: Trauma increases the enzyme arginase, thus depleting arginine necessary for producing nitric oxide. Arginine and ω-3 fatty acids are components in immune-enhancing diets. These diets decrease infections in surgical patients, perhaps by preventing arginine deficiency. This study examines whether ω-3 fatty acids alter the metabolic fate of arginine. Thus, we hypothesized there could be differential effects of varying prostaglandins on regulation of arginase. Methods: Prostaglandins PGE1, PGE2, and PGE3 were tested using RAW 264.7 cells cultured in the presence of these prostaglandins for 24 hours. IL-13 (10 ng/mL) was added 24 hours later to induce arginase I. NO production was induced by adding LPS (2 μg/mL) to the cultures after another 24 hours. Results: Arginase activity (nmol/min/mg) was induced by all prostaglandins but significantly more by PGE1 (466.05 ± 30.25) and PGE2 (248.45 ± 15.05) than PGE3 (139.87 ± 19.88; p< .002) when co-cultured with IL-13. Western blots correlated the increase in arginase I expression. Nitrate levels (μM) were inversely proportional to activity with PGE3 having the highest production (3.89 ± 0.19) and PGE2 and PGE1 with the lowest (2.75 ± 0.49 and 1.54 ± 0.19, respectively). Inhibition of arginase I using nor-hydroxyarginine increased and equalized nitrate levels. Conclusions: Different prostaglandins significantly alter the metabolism of arginine. Prostaglandins from ω-6 fatty acids increases arginase I expression. By decreasing arginase I expression, prostaglandins from ω-3 fatty acids may increase available arginine. The specific combinations of dietary fatty acids and arginine should be considered when tailoring dietary regimens. (Journal of Parenteral and Enteral Nutrition 29:S75–S80, 2005)
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