Aluminium binding to serum constituents: a role for transferrin and for citrate

The binding of aluminium in rat serum was studied. Rats were loaded intraperitoneally with different doses of aluminium(III)chloride 4 times during one week, before being killed by cardiac puncture. One ml of serum was applied to a Sephacryl S-200 SF column and 70 fractions were collected. In the collected fractions, the distribution of aluminium was measured and compared with the concentrations of total protein, transferrin, and citrate. The presence of a high molecular weight aluminium-complex in serum is confirmed. Although a possible role for albumin cannot be excluded, it is most likely that transferrin plays a role as a carrier for biological transport of aluminium in plasma. In addition to transferrin, aluminium was shown to be associated with citrate in serum, resulting in a low-molecular weight complex. It is postulated that citrate acts as a chelator for aluminium, and that the Al/citrate complex in serum may play an important role in intracellular accumulation, and hence the toxicity, of aluminium.