Copper(II) interactions with nonsteroidal antiinflammatory agents. I. Salicylic acid and acetylsalicylic acid.

Recently a growing body of evidence has accumulated on the beneficial effects of copper compounds toward various models of inflammation, and copper complexes of nonsteroidal antiinflammatory drugs (NSAIDs) have been shown to be more effective in this respect than the parent agents. However, the origin of this activity remains unclear: The ability of NSAIDs to influence copper metabolism is still questionable, and apart from the claimed SOD-like activity of copper salts in vivo, relatively little is known about how copper-NSAID interactions may help regulate the inflammatory process. Before the potential role of copper-NSAID complexes versus inflammation can be elucidated, speciation studies are necessary (i) to analyze the overall influence of these drugs on copper metabolism and (ii) to discriminate the individual complexes likely to represent the active form of the drug in vivo. In this paper, copper(II) complex equilibria with salicylic and acetylsalicylic acids--and benzoic acid used as a reference--as well as the mixed-ligand complex equilibria generated by these binary systems and L-histidine [main low-molar-mass ligand of copper(II) in blood plasma] have been investigated under physiological conditions (37 degrees C; 0.15-M NaCl). Confirming previous observations by others, resulting simulated plasma copper distributions virtually rule out any quantitative influence of salicylate on copper tissue diffusion at therapeutic levels. Even though, as is presently shown, both salicylate and acetylsalicylate may favor the gastrointestinal absorption of copper, it seems unlikely that salicylate can exert its antinflammatory activity predominantly through copper complexation. The assertion that copper-NSAID complexes represent the active forms of NSAIDs therefore seems to be of limited significance for salicylate.