Hepatocytes aflatoxins

Decad, G.M., D.P. Hsieh, and J.L. Byard. Maintenance of cytochrome P-450 and metabolism of aflatoxin Bj in primary hepatocyte cultures. Biochem. Biophys. 

Jhee EC, Ho LL, Tsuji K, Gopalan P, Lotlikar PD Effect of butylated hydroxyanisole pretreatment on aflatoxin Bj-DNA binding and aflatoxin Bi-glutathione conjugation in isolated hepatocytes from rats. Cancer Res 1989 49 1357-1360. 

A number of chemicals with demonstrable suppression of immune function produce this action via indirect effects. By and large, the approach that has been most frequently used to support an indirect mechanism of action is to show immune suppression after in vivo exposure but no immune suppression after in vitro exposure to relevant concentrations. One of the most often cited mechanisms for an indirect action is centered around the limited metabolic capabilities of immunocompetent cells and tissues. A number of chemicals have caused immune suppression when administered to animals but were essentially devoid of any potency when added directly to suspensions of lymphocytes and macrophages. Many of these chemicals are capable of being metabolized to reactive metabolites, including dime-thylnitrosamine, aflatoxin Bi, and carbon tetrachloride. Interestingly, a similar profile of activity (i.e., suppression after in vivo exposure but no activity after in vitro exposure) has been demonstrated with the potent immunosuppressive drug cyclophosphamide. With the exception of the PAHs, few chemicals have been demonstrated to be metabolized when added directly to immunocompetent cells in culture. A primary role for a reactive intermediate in the immune suppression by dimethylnitrosamine, aflatoxin Bi, carbon tetrachloride, and cyclophosphamide has been confirmed in studies in which these xenobiotics were incubated with suspensions of immunocompetent cells in the presence of metabolic activation systems (MASs). Examples of MASs include primary hepatocytes, liver microsomes, and liver homogenates. In most cases, confirmation of a primary role for a reactive metabolite has been provided by in vivo studies in which the metabolic capability was either enhanced or suppressed by the administration of an enzyme inducer or a metabolic inhibitor, respectively. 

The development of procedures for the isolation of hepatocytes from livers of different species, including man, have allowed the use of this model for comparative studies on the species-related biotransformation and toxicity of xenobiotics. In vitro studies with aflatoxin Bj showed that rat hepatocytes were more sensitive than those from mice, as became apparent by the death of the cells at much lower concentrations, the much higher levels of binding of metabolites of aflatoxin B1 to TCA-precipitable cell-material 33, 34), and the much higher levels of unscheduled DNA-synthesis (55). In addition, the mycotoxin caused segregation of nucleolar components in rat hepatocytes, but not in cells from mice 36). 

Langouet S, Coles B, Morel E, Becquemont L, Beaune P, Guengerich FP, Ketterer B, Guillouzo A. Inhibition of CYPl A2 and CYP3A4 by oltipraz results in reduction of aflatoxin B1 metabolism in human hepatocytes in primary culture. Cancer Res 1995 55 5574-5579. 

Chen, Z.Y., Yan, R.Q., Qin, G.Z., and Chia, K.B., Effect of six edible plants on the development of aflatoxin Bi-induced y-glutamyltranspeptidase positive hepatocyte foci in rats, Chung Hua liu TsaChih, 9,109-111,1987. 

Figure 5. Indirect inmmofluorescence staining of hepatocytes treated with 40uM aflatoxin Bi (A) and control untreated cells (B). Slides were treated with 50nM sodium carbonate pH 9.5 after fixation, then with RNase, proteinase K and 50mM NaOH. Antibody 6A10 was used at a 1 2 dilution and goat anti-mouse IgG conjugated with fluorescein at 1 40.

Harris, A.J., Shaddock, J.G., Manjanatha, M.G., et al. 1998. Identification of differentially expressed genes in aflatoxin Bl-treated cultured primary rat hepatocytes and Fischer 344 rats. Carcinogenesis 19(8) 1451-1458. 

Decad, G.M., K.K, Dougherty, D.P.H, Hsieh and J.L. Byard, 1979, Metabolism of aflatoxin in cultured mouse hepatocytes Comparison with rat and effects of cyclohexene oxide and diethyl maleate, Toxicol Appl, Pharmacol, 50 429. 

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