Isolation and characterization of the major serum albumin adduct formed by aflatoxin B1 in vivo in rats

Aflatoxin B₁ (AFB₁) was shown to react primarily with one ormore lysine residues in serum albumin (SA), accounting for morethan half of the total binding to this protein. The radioactivityassociated with SA following administration of [U-¹⁴C]AFB₁ torats was cleared with a half-life of 2.5 days, which is notsignificantly different from the half-life of unmodified albuminin the normal rat. The product isolated from a Pronase digestof in vivo-modified SA was identical by chromatographic retentiontime and u.v. and mass spectroscopy to the synthetic productobtained by the acylasecatalyzed deacetylation of the reactionproduct of N-acetyl-L-lysine with 8,9-dihydro-8,9-dibromo-AFB₁.The latter was characterized by u.v., fluorescence, 500 MHz¹H-n.m.r. and fast atom bombardment mass spectrometry. The spectraldata strongly support a structure in which the terminal dihydrofuranring of AFB₁ has been converted to a pyrrolinone ring. It isproposed that the initial adduct is formed by condensation ofthe dialdehyde tautomer of 8,9-dihydro-8,9-di-hydroxy-AFB₁,with the -amino group of lysine, to form a Schiff base, andthat the Schiff base undergoes an Amadori rearrangement to an-amino ketone. The pyrrolinone ring is formed by condensationof the amino group with the remaining aldehyde to yield thefinal product. The purified product was relatively stable butwas shown to decompose significantly under the conditions usedto isolate it from modified SA.