Increased serum N-G-hydroxy-L-arginine in patients with rheumatoid arthritis and systemic lupus erythematosus as an index of an increased nitric oxide synthase activity

Objectives-To determine the feasibility of monitoring the serum concentration of N-G-hydroxy-L-arginine (L-NHA) as an index of an increased nitric oxide (NO) synthase activity in patients with rheumatoid arthritis (RA) and systemic lupus erythematosus compared with (SLE) nitrate (NO3-), the major circulating metabolite of NO whose concentration is influenced by dietary intake. Methods-The serum concentrations of L-NHA, L-arginine (L-Arg), and NO3- were determined in 33 patients with RA, 25 patients with SLE and, 29 healthy subjects. Results-Serum L-NHA was significantly increased in RA patients with high disease activity (287% of control, p <0.01), but not with low disease activity (115%), as well as in patients with SLE (173%, p <0.01). In contrast, serum NO3- did not differ significantly between either group of patients and the respective control group. Conclusion-NO synthase activity or expression, or both, is upregulated in RA patients with high disease activity and in patients with SLE. Serum L-NHA seems to be a more specific and reliable index of an increased activity of this enzyme in patients with acute or chronic inflammatory diseases than NO3-.