Abstract
Intact hepatocytes have been prepared from a number of adult mammalian species by a procedure involving digestion of the finely sliced liver in a mixture of collagenase and hyaluronidase enzymes. The cell yield, viability index and ability of the hepatocytes to form non-proliferating monolayer cultures was assessed. This procedure was also applied to the isolation of viable renal tubule fragments from several species. The metabolism of a number of aromatic compounds, namely biphenyl, 7-ethoxycoumarin, benzo(a)pyrene and 4-methylumbelliferone was studied in hepatocytes isolated from the rat, ferret and hamster. Overall, hamster hepatocytes exhibited the greatest degree of mixed function oxidase and UDP-glucuronyltransferase activity. Rat hepatocytes were superior to ferret hepatocytes in metabolising capability. The ferret hepatocytes were generally less efficient at conjugation, particularly with glucuronic acid. Renal metabolic activities were considerably less than those of liver. The metabolism of benzoic acid was studied in liver and renal cell preparations from the rat,hamster, ferret and dog. Benzoic acid was conjugated extensively with glycine by hepatocytes and renal cells of the rat and hamster, whereas, the renal cells alone, performed this reaction in the dog and ferret. Hepatocytes from these animals showed a limited ability to form benzoylglucuronide. The metabolism of [[3]H]-benzo(a)pyrene (BP) was investigated more fully in the hepatocyte suspensions and cultures. In the rat hepatocyte suspensions, significant differences in the distribution of the metabolites between the cells and extracellular medium were observed. Phenols accumulated intracellularly and only small amounts were released into the medium. Sulphate esters of the phenols also accumulated but to a lesser extent. 4,5-Dihydrodiol and 7,8-dihydrodiol were distributed more evenly between the cells and medium whereas 9,10-dihydrodiol was found mainly in the medium. Conjugates of the phenols, 4,5-dihydrodiol, 7,8-dihydrodiol and 9,10-dihydroxyBP (catechol) were detected in the extracellular medium. 7,8,9,10-Tetrahydrotetrol was identified as a further metabolite of 7,8-dihydrodiol. Low amounts of radioactivity were bound to cellular macromolecules. Hamster hepatocytes formed significantly greater amounts of 4,5-dihydrodiol and a quinone, probably 3,6-quinone, than the rat. Ferret hepatocytes metabolised BP in a manner comparable to the rat but the proportion of conjugates formed was lower and the primary products were not retained to such a degree within the cells. The extent of BP metabolism by the cultured hepatocytes was only 10-20% of that measured in the freshly isolated cells although the metabolic profile was the same. After 3-4 days, the hepatocyte cultures become overrun with fibroblasts which could metabolise BP in a manner comparable to the hepatocytes. Pure fibroblast cultures were more susceptible to the toxicity of BP but when grown in the presence of hepatocytes, this toxicity was significantly reduced. Hepatocytes exposed to BP in culture, showed increased levels of NADPH-diaphorase, succinic dehydrogenase and leucylnaphthylamidase activity; the activity of glucose-6-phosphate dehydrogenase was inhibited and DNA repair synthesis was increased.