On the distribution of genotoxic factors in various organs of mice treated with cycasin

The distribution of genotoxic factors in various organs of mice treated orally with methylazoxymethanol-beta-D-glycoside (cycasin) was investigated using the DNA-repair host mediated assay. Indicator of genotoxic activity was a pair of streptomycin dependent Escherichia coli strains differing vastly in DNA repair capacity; uvrB/recA vs. uvr+/rec+. The animal-mediated assays were performed by injecting mixtures of the two strains i.v. and orally into mice, which were subsequently treated with the test chemical and from which the differential survival of the indicator bacteria present in several organs was determined. The same strains and selection procedures were also used for assessing the DNA-damaging activity in vitro. In the animal-mediated assays in which cycasin was applied orally, significant effects were observed at doses of 100 and 500 mg/kg body weight. The organ distribution of genotoxic factors in the host animal was as follows: the highest genotoxic activity was observed in the liver, followed by intestine and stomach; a clear effect was also observed in the kidneys and, to a lower extent, in the blood stream and in the lungs at the highest dose administered (500 mg/kg body weight). Under in vitro conditions a marginal genotoxic effect was observed even in the absence of liver homogenate, indicating that the test compound is possible activated (hydrolysed) by the E. coli cells. Therefore the genotoxic activity of cycasin observed in the gastrointestinal tract was not unexpected, since the substance was applied orally, thereby exposing the indicator bacteria in these organs to high levels of unmetabolised compound, especially in the stomach. In the intestine members of the microbial flora probably contribute to the metabolic activation of the test compound. The occurrence of genotoxic factors remote from the gastrointestinal tract shows that the present compound or active metabolites thereof penetrate through the intestinal barrier. The extraordinarily high genotoxic activity observed in the liver suggests that the compound is additionally activated in this organ. In compliance with previous in vitro findings this second activation step might lead to the formation of the highly reactive aldehydic form of methylazoxymethanol (MAMAL) mediated by dehydrogenases. Comparison with carcinogenicity studies indicates a good correlation between the distribution of genotoxic effects as determined in the present studies and the localisation of tumors in various organs of rodents treated with cycasin.     

Metabolic changes of lymphocytes and neoplastic cells in mice with Ehrlich ascites carcinoma during tumor growth

Changes in the activities of NAD⁺-and NADP-dependent dehydrogenases of lymphocytes and tumor cells were studied in mice with Ehrlich ascites carcinoma, as well as changes in the concentrations of oxaloacetate, lactate, and NAD⁺ in the course of tumor growth. During the major period of tumor growth, conditions are produced in the lymphocytes for increased intensity of aerobic reactions directed at energy reproduction combined with a somewhat decreased intensity of synthetic processes. In the tumor cells, conditions predominantly arise for intensification of plastic metabolic reactions and reactions related to anaerobic energy reproduction.     

Inorganic phosphate in Ehrlich ascites tumor cells and its distribution across the cell membrane

A regulatory function of the cell membrane in controlling the cytoplasmic level of Pi has been proposed, and in Ehrlich ascites tumor cells an active influx of primary phosphate has been reported in the literature. In the present study, Ehrlich cells were incubated at 1.5--50 mM extracellular Pi at pH 7.4 (Pi mainly secondary phosphate) and at pH 6.0 (mainly primary phosphate), and the measured cell Pi was compared with the value expected from a passive distribution of Pi. At a low extracellular Pi concentration the cell Pi was 3--6 mumol/g or even more. It is suggested that a major part of this cell Pi can be accounted for by enzymic release of Pi during the sampling procedure. If this interpretation is correct, the present results show that both ionic species of Pi are in electrochemical equilibrium across the cell membrane at steady state. Moreover, in vivo the concentration of free Pi in the cytosol will presumably be maintained at a steady-state level of about 0.4 mM, one order of magnitude below the directly measured values. This implies that the ratio [ATP]/[ADP][Pi] which is important in the regulation of energy metabolism, is higher than reported in the literature.     

Analysis of cadmium and lead: their immunosuppressive effects and distribution in various organs of mice

Chronic exposure (3.5 mo) of mice to cadmium (Cd), lead (Pb), or a cadmium-lead mixture at a concentration of 1 ppm in drinking water induced a highly significant inhibition of antibody response to human serum. The highest immunosuppression (84.4%) was induced by the Cd-Pb mixture, whereas Cd caused the lowest immunosuppression (53.6%). The body burden of Cd and Pb in various organs was investigated in the four groups of mice by atomic absorption spectrometry. The highest level of Cd was found in the kidney of the Cd-treated group, and the highest level of Pb was found in the liver of the Pb- and Cd-Pb-treated groups. It is concluded that when mice are exposed concurrently to Cd and Pb, they develop synergistic immunosuppression. Analysis of Cd levels using atomic absorption spectrometry revealed that it was distributed in the following order: kidney > liver > spleen > heart, whereas Pb was distributed in the following order: liver > kidney > spleen > heart.     

Effect of colchamine on Ehrlich ascitic carcinoma cells showing synchronized cell division]

The author studied the 24-hour changes in the number of normal and colchamine mitoses in the cells of Ehrlich's ascites carcinoma in mice after the injection of colchamine argainst the background of partial synchronization of cell division, obtained as a result of preliminary injection of dibutyryl cyclic 3',5'-AMP, and also in mice after the injection of colchamine alone or dibutyryl cyclic 3',5'-AMP. As shown, synchronization of cell division in the tumour led to the 2,6-fold increase in the number of tumour cells blocked by colchamine and also to the accelerated arrest of colchamine mitoses.     

The effect of ascitic fluid on the growth of Ehrlich tumor and Lewis carcinoma]

In the study of the effect of ascitic fluid and dialysate of Ehrlich ascites tumor cells (m.m. less than 15 kDa) on the growth of Ehrlich and Lewis carcinoma it was found that the ascitic fluid significantly decreased the size of Ehrlich tumor (by more than 50% on day 9-25 after the tumor cell inoculation). It also reduced Lewis carcinoma tumor volume by more than 30% during 3 weeks after the tumor cells inoculation. Dialysate of Ehrlich tumor cells significantly inhibited the growth of Ehrlich tumor too. It is suggested that this test-system simulates inhibition of a small tumor by a big tumor in vivo.     

Calcium transport and distribution in Ehrlich mouse ascites tumor cells

Data from isotopic uptake experiments were used to measure calcium fluxes and compartment sizes in ascites tumor cells. The data were analyzed with two kinetic models, A and B. In 80% of the experiments model A, which is based on one exchangeable calcium compartment, was rejected in favor of Model B, which predicts two exchangeable compartments. A statistical evaluation of the model's performance, when fit to the experimental data was used to select between the two models. The results show that calcium was distributed between three cellular compartments in the ratio, non-exchangeable (88%): rapidly exchanging (7%): slowly exchanging (5%). The undirectional fluxes suggested that calcium transport could be described as a series system with the temporal sequence: environment ? rapidly exchanging ? slowly exchanging.