Modifications of carcinogen metabolism in hepatic microsomes of suckling young by 3-methylcholanthrene or β-naphthoflavone administered to lactating rats |
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Authors: | Danuta Malejka-Giganti Richard W Decker Clare L Ritter |
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Institution: | Laboratory for Cancer Research, Veterans Administration Medical Center, and Department of Laboratory Medicine and Pathology, University of Minnesota, Minneapolis, MN 55417, U.S.A. |
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Abstract: | The effects of treating lactating rats with 3-methylcholanthrene (3-MC) or β-naphthoflavone (β-NF) (three i.p. injections of 20 or 40 mg compound/kg of body weight) on hepatic microsomal enzymes of their suckling young were examined. This treatment had no apparent effect on the contents of cytochromes P-450 and b5 or on the activities of NADH- and NADPH-cytochrome c reductases in hepatic microsomes of the pups. However, these microsomes had 8- and 6-fold increased capacities for hydroxylations of benzoa]pyrene (Ba]P) and N-2-fluorenylacetamide (2-FAA) respectively. These increases were about 5-fold greater in the hepatic microsomes of the dams, in which they were inhibited by 0.1 mM α-naphthoflavone (α-NF) invitro 72–81 and 89–95% and by 0.1 mM β-NF in vitro 12–41 and 60–76% respectively. In the pups, the induced activities were also inhibited, whereas the basal hydroxylations of Ba]P and 2-FAA were stimulated by α-NF 2.7- and 5.0-fold and by β-NF 1.4- and 2.4-fold respectively. The inhibition of the induced hydroxylations by α-NF and β-NF may be explained by their higher affinities (Ks, 0.14 and 0.28 μM, respectively) than those of Ba]P and 2-FAA (Ks 4.4 to 8.8 and 2.4 to 3.1 μM, respectively) for cytochrome P-450. Whereas β-NF gave a type I binding spectrum, α-NF gave a spectrum composed of type I and reverse-type I elements. Analysis of metabolites of 2-FAA showed differences in their type and amounts formed by hepatic microsomes of β-NF-treated lactating rats and their pups. Thus, in the dams the formation of 1-, 3-, 5-, 7-, 9- and N-hydroxy-2-FAA was increased by 9-, 30-, 40-, 5-, 20- and 5-fold respectively. In the pups, the formation of 1-, 3-, 5-, 7- and N-hydroxy-2-FAA was increased by 2-, 30-, 18-, 4- and 27-fold respectively. All these increased hydroxylations were inhibited by 0.1 mM α-NF in vitro. In the hepatic microsomes of pups from the corn oil-treated dams, α-NF stimulated all ring-hydroxylations, but not N-hydroxylation of 2-FAA. The results support earlier findings that microsomal enzymes differ in immature and mature rat liver and suggest that N-hydroxylation of 2-FAA, the activation required for carcinogenesis, and specific ring-hydroxylations are catalyzed by different cytochrome P-450 isozymes. Our studies showed that 3-MC and β-NF and/or their metabolites were transferred with milk of dams to their suckling pups in which they modified metabolism of carcinogens. |
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Keywords: | 3-MC 3-methylcholanthrene β-NF β-naphthoflavone or 5 6-benzoflavone MFO mixed function oxidase α-NF α-naphthoflavone or 7 8-benzoflavone DTT dithiothreitol PB phenobarbital DMSO dimethyl sulfoxide HPLC high performance liquid chromatography and CO carbon monoxide |
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