Copper(II) interactions with non-steroidal anti-inflammatory agents. III--3-Methoxyanthranilic acid as a potential *OH-inactivating ligand: a quantitative investigation of its copper handling role in vivo.

Pharmacological activities of copper(II) complexes are a direct function of the nature of their ligands associated with the metal ion in vivo. Some of these, defined as *OH-inactivating ligands (G. Berthon, Agents Actions 39 (1993) 210-217), may act as specific "lures" for hydroxyl radicals at inflammatory sites and behave as pseudo-catalase-like agents. This property has been advanced for anthranilic acid (H. Miche, V. Brumas, G. Berthon, J. Inorg. Biochem. 68 (1997) 27-38). With a view to improve the chemical features required to render such inactive substances effective anti-inflammatory drugs through their association with copper(II), an in vitro investigation into copper(II) interactions with the anionic form of an anthranilic acid derivative, namely 3-methoxyanthranilate (Man), has been performed under experimental conditions pertaining in vivo. Copper(II)-Man complex equilibria have been determined using glass electrode potentiometry, then checked by UV-vis and mass spectrometries. Given the prime role of histidine as a copper(II) ligand in blood plasma, copper(II)-histidine-Man ternary equilibria have also been studied. Subsequent computer simulations of the distribution of copper(II) in the extracellular fluid revealed that Man can specifically mobilize Cu(II) ions under inflammatory conditions without affecting their distribution under normal physiological conditions. Thiobarbituric acid reactive substances (TBARS) tests conducted with respect to standardized copper-mediated Fenton-type reactions (P. Maestre, L. Lambs, J.P. Thouvenot, G. Berthon, Free Rad. Res. 20 (1994) 205-218) have shown that, like anthranilic acid, Man can effectively both increase the Fenton-like reactivity of copper and decrease the amount of TBARS detected in solution, i.e., act as a potential *OH-inactivating ligand.

Aluminium, iron, zinc and copper influence the in vitro formation of amyloid fibrils of Abeta42 in a manner which may have consequences for metal chelation therapy in Alzheimer's disease.

Metals are found associated with beta-pleated sheets of Abeta42 in vivo and may be involved in their formation. Metal chelation has been proposed as a therapy for Alzheimer's disease on the basis that it may safely dissolve precipitated Abeta peptides. We have followed fibrillisation of Abeta42 in the presence of an additional metal ion (Al(III), Fe(III), Zn(II), Cu(II)) over a period of 32 weeks and we have investigated the dissolution of these aged peptide aggregates in the presence of both desferrioxamine (DFO) and ethylenediaminetetraacetic acid (EDTA). Abeta42 either alone or in the presence of Al(III) or Fe(III) formed beta-pleated sheets of plaque-like amyloids which were dissolved upon incubation with either chelator. Zn(II) inhibited whilst Cu(II) prevented the formation of beta-pleated sheets of Abeta42and neither of these influences were affected by incubation of the aged peptide aggregates with either DFO or EDTA. Freshly prepared solutions of Abeta42 either alone or in the presence of added Al(III) or Fe(III) did not form beta-pleated amyloid in the presence of DFO when incubated for up to 8 weeks. EDTA did not prevent beta-pleated amyloid formation in the same treatments and promoted beta-pleated amyloid formation in the presence of either Zn(II) or Cu(II). The presence of significant concentrations of Al(III) and Fe(III) as contaminants of 'Abeta42 only' preparations suggested that both of these metals were involved in either triggering the formation or stabilising the structure of beta-pleated amyloid. If the formation of such amyloid is critical to the aetiology of AD then the chelation of Al(III) and Fe(III) may prove to be a protective mechanism whilst the chelation of Cu(II) and Zn(II) without also chelating Al(III) and Fe(III) might actually exacerbate the condition.

Aluminum speciation studies in biological fluids. Part 9. A quantitative investigation of aluminum(III)-glutamate complex equilibria and their potential implications for aluminum metabolism and toxicity.

As a nonessential element, aluminum is likely to be toxic both at low usual dietary levels in the long run (chronic toxicity) and at high therapeutic levels in shorter periods of time (acute toxicity). In both situations, aluminum toxicity is a direct function of aluminum bioavailability, which is itself dependent on Al(3+) solubility and charge neutralization. Dietary acids, by their intrinsic acidity and coordinating capacity, can extend the pH range, thus the section of the gastrointestinal tract, within which the Al(3+) ion remains soluble, and also help Al(3+) diffusion across the intestinal epithelium through the formation of neutral complex species. The present work examines the impact of glutamic acid, an essential amino acid also widely used in industrial food and drinks, on aluminum speciation in the gastrointestinal tract and blood plasma. Complex formation between the Al(3+) ion and glutamate has first been investigated through potentiometric titrations, complex stoichiometries being then checked by ESI mass spectrometry and NMR measurements. A series of mono- and polynuclear species has been characterized, whose influence on aluminum distribution in vivo has been assessed by computer simulation. The capacity of glutamate to maintain Al(3+) ions in solution under normal dietary conditions is predicted to be intermediate between glycine-like amino acids and succinate on the one hand, and tartrate and malate on the other hand, its Al(3+) neutralization effect being similar to that of succinate, tartrate and malate. These results, which point to a potential aggravating role of glutamate on aluminum gastrointestinal absorption, substantiate recent observations made on rats. In spite of the moderate effect expected from glutamate on aluminum bioavailability under most aluminum-based therapies investigated, attention is therefore called to the risk of glutamic acid ingestion simultaneously to any aluminum therapeutic form. Incidentally, the former implication of 'the' aluminum glutamate complex in the transfer of aluminum through the blood-brain barrier of aluminum loaded rats may effectively be attributed to one of the species characterized here, but is of no significance at all to aluminum contamination in humans, even at most extreme levels.