Binding and transport of benzo[a]pyrene by blood plasma lipoproteins: The possible role of apolipoprotein B in this process

The role of plasma lipoproteins as carriers in the transport of benzo[a]pyrene was assessed in in vitro and in vivo studies. Addition of [H-3]benzo[a]pyrene to rat plasma resulted in binding of the xenobiotic to lipoproteins. Studies of labeled benzo[a]pyrene distribution in rat blood plasma by the method of ultracentrifugation have given the following results: high-density lipoproteins, 40%; low-density lipoproteins, 14%; very-low-density lipoproteins, 23%; other plasma proteins, 23%. Complexes of benzo[a]pyrene-lipoproteins were isolated by gel filtration with Sephadex G-25 and used for intravenous injection in rats. Biodistribution studies have shown different localization of benzo[a]pyrene in rat organs and tissues depending on lipoprotein classes. A high amount of radioactivity was bound by the liver and adrenals when all classes of lipoproteins were used, but especially with high-density lipoproteins. High levels of benzo[a]pyrene were measured in the kidneys. Equilibrium dissociation constants for complexes of benzo[a]pyrene with high-density lipoproteins and low-density lipoproteins were obtained (Ka 4.1 x 10(-5) and 1.5 x 10(-5) M, respectively). Binding and distribution of the protein component of lipoproteins were studied by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. More than 80% of the radioactivity recovered from the gel was localized in the area of apolipoprotein B. After isolation and purification of apolipoprotein B, the equilibrium dissociation constant for complexes of benzo[a]pyrene with apolipoprotein B was obtained, and its value indicated that apolipoprotein B might be the main protein carrier for benzo[a]pyrene.