The objective of the present investigation was to examine the functional reestablishment of polarity in freshly isolated hepatocytes cultured between 2 layers of gelled collagen (sandwich configuration). Immunoblot analysis demonstrated that the canalicular multispecific organic anion transport protein (multidrug resistance-associated protein, Mrp2) was partially maintained in day 5 hepatocytes cultured in a sandwich configuration. Fluorescein-labeled taurocholate and carboxydichlorofluorescein were excreted into and concentrated in the bile canalicular lumen of day 5sandwich-cultured hepatocytes, resulting in formation of fluorescent networks in standard buffer (intact bile canaliculi). Confocal microscopy studies demonstrated that 1) carboxydichlorofluorescein that had concentrated in the canalicular lumen was released into the incubation buffer in the presence of Ca2+-free buffer (disrupted bile canaliculi), and 2) rhodamine-dextran, an extracellular space marker, was only able to diffuse into the canalicular lumen in the presence of Ca2+-free buffer. The cumulative uptake of [3H]taurocholate in day 5 sandwich-cultured hepatocytes was significantly higher in standard buffer compared with Ca2+-free buffer, due to accumulation of taurocholate in canalicular spaces. When [3H]taurocholate was preloaded in the day 5sandwich-cultured hepatocytes, taurocholate efflux was greater in Ca2+-free compared with standard buffer. The biliary excretion index of taurocholate, equivalent to the percentage of retained taurocholate in the canalicular networks, increased from ∼8% at day 0 to ∼60% at day 5 in sandwich-cultured hepatocytes. In summary, hepatocytes cultured in a collagen-sandwich configuration for up to 5 days establish intact canalicular networks, maintain Mrp2, reestablish polarized excretion of organic anions and bile acids, and represent a useful in vitro model system to investigate the hepatobiliary disposition of substrates.

Aflatoxin-serum albumin adducts in the blood of 42 residents of Guangxi Province, People's Republic of China, were determined and compared with intake of aflatoxin B1 (AFB1) and excretion of aflatoxin M1 (AFM1) in urine. Blood specimens were obtained during the same period that urine was collected and that diet was sampled. Serum albumin was isolated from blood by affinity chromatography on Reactive Blue 2-Sepharose and subjected to enzymatic proteolysis using Pronase. Immunoreactive products were purified by immunoaffinity chromatography and quantified by competitive radioimmunoassay. A highly significant correlation (r = 0.60, P less than 0.00003) of adduct level with AFM1 excretion was observed. An equally highly significant correlation of adduct level with intake (r = 0.69, P less than 0.000001) was also observed. From the slope of the regression line for adduct level as a function of intake, it was calculated that 1.4-2.3% of ingested AFB1 becomes covalently bound to serum albumin, a value very similar to that observed when rats are administered AFB1.

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The interactions of human hemoglobin (hHb) with the anti-diol epoxide of benzo[a]pyrene (aBaPDE) and with the corresponding tetrols formed by hydrolysis of the epoxide were investigated with the aim of characterizing the covalent adducts formed by reaction of the epoxide with the protein. The major product (80% of the total) was determined to be an ester resulting from oxirane ring opening by one or several (unidentified) carboxylate group(s). Minor products were characterized as adducts formed by reaction with amino or heterocyclic nitrogen by comparison of their UV spectra with those of model compounds. There was no evidence for reaction with cysteine. Formation of ester adducts by aBaPDE with mouse hemoglobin (mHb) following administration of BaP to mice was also investigated. It was found that esters constituted the majority of the adducts formed by aBaPDE and a substantial fraction of the total adducts formed. The esters formed by mHb were significantly less stable than those formed by hHb, both in vivo and in vitro. The instability of mHb ester adducts is believed by the responsible for differences among previous descriptions of the in vivo binding of BaP to mHb.

A collagen sandwich configuration reestablishes normal morphology and partially restores bile acid uptake properties in primary cultures of rat hepatocytes.