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Proteins with apolipoprotein A-I immunoreactivity were detected in the fraction of non-histone acidic proteins isolated from nuclei of various rat tissue cells. These proteins were detected in the brain, liver, kidney, lung, heart, skeletal muscle, testis, spleen, and bone marrow. In the same fraction from liver nuclei, proteins with apoB and apoE immunoreactivity were also detected. The composition of these proteins was studied by immunoblotting. ApoA-I immunoreactivity in the liver nuclei is due to two proteins. One 28-kD protein corresponds to the mature form of the plasma pool of apoA-I and another 14-kD protein is the product of limited proteolysis of apoA-I. The highest content of apoA-I immunoreactivity was detected in transcriptionally active chromatin and nuclear matrix. ApoB immunoreactivity is due to six proteins with molecular weights from 15 to 100 kD. ApoE immunoreactivity is due to a single protein corresponding to the 35-kD form of plasma apoE. Proteins with apoA-I, apoB, and apoE immunoreactivity may be involved in the regulation of transcriptional activity of chromatin.

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 [3H]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 or 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 (Kd 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.

Changes in electrical charge and clearance rate of LDL after the formation of their complexes with bacterial LPS were studied in experiments on Wistar rats. It was found that binding of S. minnesota R595 LPS with (125)I-LDL sharply accelerated clearance of the greater part of LDL complexes, but on the other hand induced the appearance of an LDL-LPS subfraction with slower elimination rate compared to free LDL. Electrophoresis showed that after binding of LPS, LDL acquired a negative charge. These data suggest that the formation of LDL-LPS complexes is accompanied by modification of LDL due to which they acquire atherogenic properties.