PREPARATION OF CROSS-LINKED HUMAN-SERUM ALBUMIN LABELED WITH I125 FOR STUDIES OF RETICULOENDOTHELIAL SYSTEM FUNCTION

Glutaraldehyde was used for the cross-linking of human serum albumin. The polymeric product was fractionated by repeated chromatography on Sepharose 6B. Cross-linked material with a particle size of approximately 18 nm, as evidenced by EM, was pooled and labeled with 125I. The surface charge of the albumin polymers, determined by agarose gel electrophoresis, was not significantly changed compared with that of the original albumin monomer. Cross-linking takes place almost entirely between the .epsilon.-amino groups of lysine in the albumin molecules, as confirmed by amino acid analysis. Preliminary biological tests on mice indicate that the cross-linked polymers are phagocytosed mainly by RES cells of the liver and spleen. The disappearance rate was similar to that of other RES test substances. I.v. administration of more than 50 times the usual dose caused no deaths, indicating a very low toxicity. Trace amounts of glutaraldehyde were not detectable by gas chromatography. Juding from these experiments, this new preparation of cross-linked albumin fulfils many of the criteria stated for an ideal RES test substance.