Cell, animal liver cells

Toxicity. Many /V-nitrosamines are toxic to animals and cells in culture (4,6—8,88). /V-Nitrosodimethy1amine [62-75-9] (NDMA) is known to be acutely toxic to the Hver in humans, and exposure can result in death (89). Liver damage, diffuse bleeding, edema, and inflammation are toxic effects observed in humans as a result of acute and subacute exposure to NDMA. These effects closely resemble those observed in animals dosed with NDMA (89,90). 

Cholesterol is found in many biological membrane and is the main sterol of animal organisms. It is eqnimolar with phospholipids in membranes of liver cell, erythrocytes, and myelin, whereas in human stratum comeum it lies in the outermost layer of the epidermis... 

On the other hand, microsomes may also directly oxidize or reduce various substrates. As already mentioned, microsomal oxidation of carbon tetrachloride results in the formation of trichloromethyl free radical and the initiation of lipid peroxidation. The effect of carbon tetrachloride on microsomes has been widely studied in connection with its cytotoxic activity in humans and animals. It has been shown that CCI4 is reduced by cytochrome P-450. For example, by the use of spin-trapping technique, Albani et al. [38] demonstrated the formation of the CCI3 radical in rat liver microsomal fractions and in vivo in rats. McCay et al. [39] found that carbon tetrachloride metabolism to CC13 by rat liver accompanied by the formation of lipid dienyl and lipid peroxydienyl radicals. The incubation of carbon tetrachloride with liver cells resulted in the formation of the C02 free radical (identified as the PBN-CO2 radical spin adduct) in addition to trichoromethyl radical [40]. It was found that glutathione rather than dioxygen is needed for the formation of this additional free radical. The formation of trichloromethyl radical caused the inactivation of hepatic microsomal calcium pump [41]. 

Fig. 5. G-6-PDH activity in liver cell homogenates of rats under physiological and pathological conditions. Activity in livers of normal fed animals = 100%. Cf. (W10). 

In summary, genetic toxicity tests with both bacterial and mammalian cells are normally carried out with rat liver cell-free systems (S9 fraction) from animals pretreated with enzyme inducers. However, investigations should not slavishly follow this regimen there may be sound scientifically based reasons for using preparations from different species or different organs, or for using whole cells such as hepatocytes. 

Genotoxic effects have been reported in animals treated with 3,3 -dichlorobenzidine. A single dose of 3,3 -dichlorobenzidine (1,000 mg/kg) administered to male and pregnant female mice induced micronuclei in polychromatic erythrocytes in the bone marrow of the males and in the liver of the fetuses, but not in bone marrow of the dams (Cihak and Vontorkova 1987). A micronucleus test is performed to detect a chemical s ability to induce chromosomal aberrations. However, the relevance of micronuclei formation to human health is not known. The reason for the lack of effect of 3,3 -dichlorobenzidine on bone marrow micronuclei formation in the mothers is unclear, but it may be related to deficiencies in the metabolic activation of 3,3 -dichlorobenzidine in female mice. The relative importance of pregnancy is unknown since the study did not evaluate nonpregnant females. In another study, an increase in unscheduled deoxyribonucleic acid synthesis (UDS) was observed in cultured liver cells from male mice previously pretreated orally with single doses of 500 mg/kg 3,3 -dichlorobenzidine no response was observed at a dose of 200 mg/kg (Ashby and Mohammed 1988). 

The test is used to identify substances that induce DNA repair in liver cells of treated animals. UDS is DNA repair synthesis after excision and removal of a stretch of DNA containing a region of damage induced by a chemical substance. The test is usually based on the incorporation of tritium-labeled thymidine ( H-TdR) into the DNA of liver cells, which have a low frequency of cells in the S-phase of the cell cycle. 

Animal studies demonstrate that carbon tetrachloride produces hepatocellular carcinomas in the mouse, rat, and hamster." Mice administered 1250 or 2500mg/kg approached nearly a 100% incidence of hepatocellular carcinomas vs. 6% or less in various controls. Hamsters receiving 190 and 380mg/kg by gavage had a 100% liver cell carcinoma incidence for those animals surviving past week 43. ... 

Administered in the drinking water for 113 weeks, 42mg/l crotonaldehyde induced neoplastic lesions in rats 2 of 27 animals had hepatocellular carcinomas and 9 of 27 had neoplastic lesions. Altered liver cell foci occurred in 23 of the 27 animals. The increased incidence of neoplastic and preneoplastic lesions was not observed at the higher dose (421 mg/1). Crotonaldehyde produced variable results in a variety of genetic assays. ... 

Toxic symptoms in various animal species were similar and consisted of excitement and hyperactivity tremor spasms slow, labored respiration clonic convulsions and terminal coma. On histologic examination, there was degeneration and necrosis of liver cells and renal tubules, perivascular edema and swelling of the lungs, and degeneration of the cells of the cerebral cortex. 

Repeated subcutaneous injection of MOCA in 34 rats (total dose 25g/kg for 620 days) resulted in nine liver cell carcinomas and seven lung carcinomas 13 of 50 control animals developed tumors, but no malignant tumors of the liver or the lungs were observed. ... 

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