Suppression of nitric oxide oxidation to nitrite by curcumin is due to the sequestration of the reaction intermediate nitrogen dioxide, not nitric oxide.

Curcumin, a phytochemical with antioxidant and other cytoprotective properties, has been reported to reduce nitrite formation during nitric oxide (NO) oxidation in solution. This decrease in nitrite production was attributed to the direct sequestration of NO by curcumin. In this report, we confirm that curcumin inhibits nitrite formation from DEA/NO-derived NO in a concentration-dependent manner. However, curcumin over a concentration range of 3-50 microM had no effect on the concentration of free NO (0.5 microM) in solution at 37 degrees C as assessed using an NO electrode. We conclude that the inhibitory effect of curcumin on the oxidation of NO to nitrite is due to its known sequestration of the reaction intermediate nitrogen dioxide (NO(2)). The ability of curcumin to sequester NO(2), but not NO, suggests that curcumin may be useful for separating the actions of NO(2) from those of NO in various biological systems.