Correlative studies of urine fluorescence and free radical indicators

Inflammation results in the production of free radicals which damage proteins, lipids, and nucleic acids. The products of these reactions are cleared, in part, by the kidney and appear in the urine. In this study, urine fluorescence was measured in individuals with various nephropathies to determine the value of these assays for detecting the excretion of end products of radical-mediated chemical reactions.

Urine fluorescence was quantified at wavelengths which correspond to the presence of advanced glycosylation endproducts (AGE) and dityrosine (di-TYR). The samples were also tested for isoprostanes, nitrite/nitrate, hydrogen peroxide, and thiobarbituric acid reactive substances (TBARS).

Fluorescence values, expressed per ml urine or per mg creatinine (crt), were not normally distributed and covered a wide range. There were significant differences in fluorescence among groups of patients classified by diagnosis, but the differences did not allow sharp distinction of diagnostic categories. Fluorescence assays correlated significantly with TBARS but not with isoprostanes, nitrite/nitrate, or hydrogen peroxide. Fluorescence tended to increase with age. Gender and race did not affect the results.

Because of the many factors which can affect free radical production and tissue injury, the value of urine fluorescence assays to screen for radical-mediated toxicity appears to be limited. Serial studies of patients will be needed to determine whether urine fluorescence will be useful to monitor responses to treatment or be predictive of progression vs. remission of renal disease.