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

Abstract

Aflatoxin B₁ (AFB₁) was shown to react primarily with one or more lysine residues in serum albumin (SA), accounting for more than half of the total binding to this protein. The radioactivity associated with SA following administration of [U-¹⁴C]AFB₁ to rats was cleared with a half-life of 2.5 days, which is not significantly different from the half-life of unmodified albumin in the normal rat. The product isolated from a Pronase digest of in vivo-modified SA was identical by chromatographic retention time and u.v. and mass spectroscopy to the synthetic product obtained by the acylasecatalyzed deacetylation of the reaction product of N_α-acetyl-L-lysine with 8,9-dihydro-8,9-dibromo-AFB₁. The latter was characterized by u.v., fluorescence, 500 MHz ¹H-n.m.r. and fast atom bombardment mass spectrometry. The spectral data strongly support a structure in which the terminal dihydrofuran ring of AFB₁ has been converted to a pyrrolinone ring. It is proposed that the initial adduct is formed by condensation of the dialdehyde tautomer of 8,9-dihydro-8,9-di-hydroxy-AFB₁, with the ε-amino group of lysine, to form a Schiff base, and that the Schiff base undergoes an Amadori rearrangement to an α-amino ketone. The pyrrolinone ring is formed by condensation of the amino group with the remaining aldehyde to yield the final product. The purified product was relatively stable but was shown to decompose significantly under the conditions used to isolate it from modified SA.