Binding of aflatoxin B1 to melanin

Whole-body autoradiography of pigmented C57BL mice injected with 3H-labelled aflatoxin B1 (AFB1) showed a high degree of labelling of melanin-containing tissues, such as the melanin of eyes and hair follicles. The corresponding tissues in albino NMRI mice contained only low amounts of the label. Liquid chromatography of extracts of pigmented mouse eyes showed the presence of only non-metabolized AFB1. Analysis of the binding of AFB1 to melanin from bovine eyes using the method of Scatchard revealed two classes of binding sites. Incubations in the presence of metallic cations did not affect the binding, indicating that ionic forces play no role in the affinity. Comparisons of the binding of AFB1 to the bovine-eye pigment in media containing n-propanol, ethanol or methanol indicated that hydrophobic interactions play a role in the affinity. Apposition of the aromatic rings in AFB1 and the indole nuclei of the melanin may also result in van der Waals' forces, and the combination of these two types of forces may underly the binding of AFB1 to melanin. The melanin binding implies that AFB1 is retained in pigmented tissues at higher concentrations than in any other tissue of the body. The biological implication of this accumulation is now known, but the possibility that there may be an increased risk for the induction of melanomas is discussed.