Metabolism of benzo[A]pyrene and the related enzyme activities in hamster embryo cells

Enzyme-catalyzed detoxication reactions: mechanisms and stereochemistry

Enzyme catalyzed detoxication reactions are one of the primary defenses organisms have against chemical insult. This article reviews current chemical approaches to understanding the cooperative role of enzymes in the metabolism of foreign compounds. Emphasis is placed on chemical and stereochemical studies which help elucidate the mechanism of action and active-site topologies of the detoxication enzymes. The stereoselectivity of the cytochromes P-450 and flavin containing monooxygenases as well as the role of hemoglobin and lipid peroxidation in the primary metabolism of xenobiotics is discussed. Current knowledge of the mechanism and stereoselectivity of epoxide hydrolase is also presented. Three enzymes involved in secondary metabolism of xenobiotics, UDP-glucuronosyltransferase, sulfotransferase and glutathione S-transferase are discussed with particular emphasis on active site topology and cooperative participation with the enzymes of primary metabolism.

Increase during passage in culture in susceptibility of Syrian hamster embryonic cells to induction of chromosome aberrations by 7,12-dimethylbenz(a)-anthracene

Studies were made on chromosome aberrations in Syrian hamster embryonal fibroblasts (SHEF) at early and late passages in culture. Aberrations were induced with a potent indirect clastogen, 7,12-dimethylbenz(a)anthracene (DMBA). Results showed that cells at late passages were much more susceptible to this chemical than cells at early passages: the frequency of aberrant metaphases was usually less than 20% at the 2nd passage, but it gradually increased with increase in the number of culture passages, reaching 50% or more at the 8th passage in one experiment and 6th-7th passage in another. Induction of chromosome aberrations was also examined in V79 cells co-cultured with hamster cells at early and late passages. V79 cells are known to have no drug-metabolizing enzyme activity. Results demonstrate that the frequency of chromosome aberrations of V79 cells was much greater in the presence of hamster cells at late passages than in the presence of cells at early passages.

Sister-chromatid exchange induction by indirect mutagens/carcinogens, aryl hydrocarbon hydroxylase activity and benzo[alpha]pyrene metabolism in cultured human hepatoma cells

2 human hepatoma cell lines (C-HC-4 and C-HC-20), in which aryl hydrocarbon hydroxylase activity was induced with benz[alpha]anthracene in vitro to about 140- and 64-fold of the respective basal levels, yielded an increased frequency of sister-chromatid exchanges (SCEs) when exposed to benzo[alpha]pyrene (BP), 7,12-dimethylbenz[alpha]anthracene and 3-methylcholanthrene in vitro. Analysis of the metabolism of BP by these cells by high-pressure liquid chromatography revealed that both cell lines produced various BP metabolites including the proximate form BP-7,8-dihydrodiol which has been reported to be the most potent inducer of SCEs among the metabolites of BP. In addition, aflatoxin B1 and cyclophosphamide also induced SCEs in these cell lines. The above findings suggest that these cells may be capable of metabolizing a range of indirect mutagens/carcinogens into DNA-active forms. These cells may therefore serve as a useful test system in vitro for the detection of genotoxic agents, without the use of an exogenous activating system.

Toxicology investigations with cell culture systems

This review concerns some of the cell culture systems that are most frequently used in toxicology investigations. In particular, it sets out to evaluate the effectiveness of these cell culture systems in assessing the toxic potential of chemicals. Metabolic studies and general and specific toxicology investigations are highlighted. Specific toxicology investigations relate to the effects of the tests substances on the highly specialized functions typical of the cell systems chosen. The general toxicology investigations include most of the other studies where differentiated or undifferentiated cells have been used to evaluate the effects of the tested substances on common basic biochemical processes essential for life. Lastly, we have attempted to focus attention on the most promising applications of cell cultures in toxicology studies for the near future and to identify those areas where further research is needed. Because of the several excellent reviews that already exist, we have decided not to consider cell cultures utilized in screening potential mutagens and carcinogens. We have also excluded investigations of drug therapeutic effects and action mechanisms of drugs.

Reversed-phase separation of benzo[a]pyrene metabolites by thin-layer chromatography

The use of reversed-phase thin-layer chromatography for the separation of benzo[a]pyrene metabolites has been investigated. Two systems are described for the separation of the major metabolites of benzo[a]pyrene, including sulfate and glucuronide conjugates.