Effect of taurine, L-glutamine and L-histidine addition in an amino acid glucose solution on the cellular bioavailability of zinc.

Radioactive zinc was used to study the effect of a binary parenteral nutrient solution, composed of amino acids and glucose, on zinc uptake by fibroblasts. The influence of addition of taurine, L-glutamine and of the increase in L-histidine content of the admixture was assessed. The pure mixture was highly toxic for cells and so it was diluted 1/5 in tyrode buffer with 2% albumin. As compared with cells incubated in the buffer containing albumin, zinc absorption was significantly higher (P < 0.05) in the presence of the amino acids of the mixture. Amino acids thus increased bioavailability by displacing zinc bound to albumin. When the histidine concentration in the nutrient medium (4.2 mM) was doubled, inhibition was noted after 30 min of incubation and zinc uptake thereafter remained comparable to that in histidine-free medium. The addition of glutamine (4.2 mM), usually not present in binary mixtures, resulted in significant differences as compared with glutamine-free control medium. Taurine (0.8 mM), led to a constant increase in zinc uptake by fibroblasts as compared with that obtained with taurine-free mixture. However, ultrafiltration showed that taurine was not able to displace zinc from albumin.