In vivo disposition of 3-nitro-L-tyrosine in rats: Implications on tracking systemic peroxynitrite exposure

In many pathological conditions such as inflammatory and neurodegenerative diseases, the in vivo toxicity of nitric oxide has been attributed to the t oxic oxidant peroxynitrite. Interaction of peroxynitrite with biological mo lecules can modify tyrosine residues on the proteins at the ortho position resulting in the formation of the stable end-product, 3-nitro-L-tyrosine (3 -NT). Recent investigations indicate that changes in the circulating concen trations of 3-NT in pathological conditions may reflect the extent of nitri c oxide-dependent oxidative damage and peroxynitrite toxicity. In the prese nt study,we examined the in vivo disposition characteristics of 3-NT in rat s after either a single i.v. bolus dose (10 mg/kg) or a loading and mainten ance infusion at 10 or 30 mg/kg, Plasma concentrations of 3-NT were analyze d by a reversed-phase HPLC method. After a single bolus dose of 3-NT at 10 mg/kg, the average half-life of the elimination phase for the drug was 68.5 +/- 18.4 min (n = 5). Infusions of 3-NT at two different doses (10 and 30 mg/kg) indicated that the pharmacokinetic properties of 3-NT below plasma c oncentrations of 100 mu M were both linear and stationary. Urinary excretio n of unchanged 3-NT was minimal, but two distinct metabolites of 3-NT were identified in the urine collected throughout the study. These findings may be useful in the interpretation of the plasma and urine 3-NT concentrations as possible indices of systemic peroxynitrite exposure.