Aluminium speciation studies in biological fluids. Part 8. A quantitative investigation of Al(III)–amino acid complex equilibria and assessment of their potential implications for aluminium metabolism and toxicity

Aluminium bioavailability has raised much interest in the last two decades because of both the acute toxicity of high doses of the metal in some therapies and the chronic toxicity of dietary intakes in respect of senile dementias. In particular, a number of common dietary acids has recently been shown to play a part in this context. Essential amino acids, which are naturally released by digestion of vegetal and animal proteins, are also present as such in a large majority of industrial foods and drinks. They may, therefore, also interact with aluminium metabolism, especially in the gastrointestinal tract where they can reach quite appreciable levels. The objective of this work was to assess the extent of such potential interactions quantitatively. Aluminium complex formation equilibria of a series of essential amino acids involving glycine (used as a reference for all glycine-like amino acids), serine, threonine and histidine, were investigated under physiological conditions of ionic strength and temperature through glass electrode potentiometry and NMR. The only significant complex identified with the four ligands is M2LH−2. Simulations based on corresponding formation constants indicate that no particular risk is to be expected from these amino acids in normal conditions of alimentation and aluminium-based therapy.