Elevated urinary nitrite and citrulline levels in patients with rheumatoid arthritis

The objective of this research was to determine if NO production, as measured in the serum and urine, is increased in patients with rheumatoid arthritis. Forty-seven patients with RA were recruited in the study and subdivided into inactive and active disease (24 and 23 patients, respectively). Twenty-eight healthy individuals served as controls and nine patients with gastroenteritis were studied to validate the technique of measurement of NO production. Nitrite and citrulline were measured by spectrophotometry, as surrogate markers of NO production. It was found that serum nitrite and citrulline levels of patients with gastroenteritis were not significantly different from controls and the two subgroups of RA. Urine nitrite and citrulline levels were significantly higher in patients with gastroenteritis as compared to the two subgroups of RA and controls (p < 0.001). Serum and urine nitrite levels of patients with active RA were higher than controls and patients with inactive disease (p < 0.05). Serum citrulline levels were not significantly different among the two subgroups of patients with RA. However, they were significantly higher in patients with active disease as compared with controls (p < 0.05). Urinary citrulline levels were significantly higher among patients with active disease as compared to controls and patients with inactive RA (p < 0.05). It is therefore suggested that urinary nitrite and citrulline levels can be useful for the measurement of NO production and are associated with active disease in patients with RA.