Investigation of the mechanism of cadmium toxicity at cellular level. I. A light microscopical study

Cadmium induced apoptotic changes in chromatin structure and subphases of nuclear growth during the cell cycle in CHO cells

CHO cells were grown in the presence of 1 mu M CdCl(2) and subjected to ATP-dependent replicative DNA synthesis after permeabilization. By decreasing the density of the cell culture replicative DNA synthesis was diminishing. At higher than 2 x 10(6) cell/ml concentration Cd had virtually no effect on the rate of DNA replication. Growth at higher cell concentrations could be suppressed by increasing Cd concentration. After Cd treatment cells were synchronized by counterflow centrifugal elutriation. Cadmium toxicity on cell growth in early and mid S phase led to the accumulation of enlarged cells in late S phase. Flow cytometry showed increased cellular and nuclear sizes after Cd treatment. As the cells progressed through the S phase, 11 subpopulations of nuclear sizes were distinguished. Apoptotic chromatin changes were visualized by fluorescent microscopy in a cell cycle dependent manner. In the control untreated cells the main transitory forms of chromatin corresponded to those we have published earlier (veil-like, supercoiled chromatin, fibrous, ribboned structures, chromatin strings, elongated prechromosomes, precondensed chromosomes). Cadmium treatment caused: (a) the absence of decondensed veil-like structures and premature chromatin condensation in the form of apoptotic bodies in early S phase (2.2-2.4 average C-value), (b) the absence of fibrous structures, the lack of supercoiled chromatin, the appearance of uncoiled ribboned chromatin and perichromatin semicircles, in early mid S phase (2.5-2.9 C), (c) the presence of perichromatin fibrils and chromatin bodies in mid S phase (2.9-3.2 C), (d) early intra-nuclear inclusions, elongated forms of premature chromosomes, the extrusion and rupture of nuclear membrane later in mid S phase (3.3-3.4 C), (e) the exclusion of chromatin bodies and the formation of clusters of large-sized perichromatin granules in late S phase (3.5-3.8 C) and (f) large extensive disruptions and holes in the nuclear membrane and the clumping of incompletely folded chromosomes (3.8-4. C).

Distribution of exogenous heavy metals in the hepatocytes of calves: a morphometric study

The objective of this study was to evaluate the presence of heavy metals in the hepatocytes of the animals fed a cadmium-supplemented diet and also receiving zinc and/or selenium in the injection form. The experiment involved four groups of calves (6-8, both sexes) receiving the heavy metals in various combinations for 95 days. Electron micrographs of liver cells were prepared and statistically evaluated using Student's t-test. A modified morphometric apparatus was used for morphometric examination. Exogenous cadmium showed marked accumulation in the hepatocytes. If, however, the cadmium diet was combined with zinc or selenium administration the amount of the reduction product was much lower.

Effect of cadmium (CdCl2) on cell proliferation and production of EDRF (endothelium-derived relaxing factor) by cultured human umbilical arterial endothelial cells

The effect of cadmium chloride (CdCl2) on cell proliferation and EDRF (endothelium-derived relaxing factor) production by cultured human umbilical arterial endothelial cells (HUAECs) was investigated. The viability of HUAECs decreased dose-dependently after the addition of Cd (cadmium chloride). Morphologic examination by phase contrast microscopy revealed severe damaging effects of Cd at higher concentrations. The cytotoxic effect of Cd on DNA synthesis was also concentration-dependent. The effect of Cd on EDRF production by indomethacin-treated HUAECs was assessed by its anti-platelet aggregatory effect. Platelet aggregation studies were carried out in cuvettes lined with HUAECs using an aggregometer. The anti-platelet aggregatory effect was decreased dose-dependently by pretreatment with Cd. These findings suggest that HUAECs are susceptible to concentration-dependent Cd cytotoxicity, and that Cd can inhibit the production of EDRF by HUAECs.

Studies on cytotoxic and genotoxic effects of cadmium nitrate and lead nitrate in Chinese hamster ovary cells

Cadmium nitrate decreased the viability of Chinese hamster ovary (CHO) cells in a concentration-dependent manner; 50% inhibition (IC50) was achieved at 0.015 mM. In contrast, lead nitrate appeared to be less toxic. Neither cadmium nitrate nor lead nitrate significantly increased frequencies of binucleated CHO cells with micronuclei (MN). However, both cadmium nitrate and lead nitrate could augment sister chromatid exchanges (SCEs). Cadmium nitrate induced SCEs with a potency approximately equal to that of mitomycin C and more than 10 times higher than lead nitrate. Cadmium nitrate also increased chromosome aberrations (CAs), which included breaks, acentrics, interchanges, and dicentrics of chromosomes. In addition, cadmium nitrate induced a decrease in the mitotic index (MI), but lead nitrate increased it. In summary, it appears that both of these two heavy metal salts have cytogenetic toxicities with different degrees of effects on the cytotoxicity, MN, CAs, and SCEs in CHO cells. However, SCE was the most sensitive endpoint for indicating mutagenetic effects of cadmium and lead in the present study.

Combined effect of cadmium (CdCl2) and high temperature on HeLa S3 cells

The combined effect of cadmium (CdCl2) and high temperature on the subsequent growth, the synthesis of nucleic acids and protein, and the cell cycle in HeLa S3 cells was investigated. The subsequent growth rate was depressed by cadmium at 37.1 degrees C. This suppression effect was enhanced at 40.4 degrees C compared with the effect at 37.1 degrees C. The synthesis of DNA, RNA and protein was inhibited at higher temperatures in cultivation without cadmium, and depressed at each temperature in a concentration-dependent manner by the addition of cadmium. The DNA, RNA and protein-IC50 values at 40.4 degrees C decreased compared with the values at 37.1 degrees C. The DNA and RNA-IC50 values were significantly decreased (p less than 0.01, p less than 0.005, respectively) depending on the temperature. After treating the cells with cadmium at 40.4 degrees C, the DNA/BrdUrd distribution showed that the rate of dead cells increased and the rate of the G1/G0 phase decreased. These results indicate that the inhibitory effect of cadmium on the subsequent growth of HeLa S3 cells is enhanced at high temperature and this enhancement is related to the increased inhibitory effect of cadmium on DNA and RNA synthesis at high temperature.

The influence of growth phase and culture conditions of Tetrahymena on effects of cadmium

The batch culture system is used in the majority of toxicity studies employing protozoa and other cell cultures, although it is known that metal toxicity may vary depending on the age and therefore on the physiological state of the culture. The ciliate Tetrahymena was exposed to cadmium during short-term incubations at different stages of the growth cycle. In cultures with cells proliferating at a high rate (log phase cells) the toxicity of cadmium was found to increase with increasing initial cell density. However, in the subsequent stationary growth phase with decreased rate of cell proliferation, the sensitivity against cadmium again decreases. Thus the effect of a given concentration of cadmium depends on the initial cell density of the culture. This effect of cadmium may be explained either by changes in the chemical composition of the culture medium during the growth cycle or by a changed cellular metabolism. Furthermore, it is shown that the cadmium concentration of the medium decreases during prolonged exposure when the cells are grown in batch cultures. Some of the problems associated with the toxicity bioassay performed in a static system may be overcome by using a continuous flow system. In such a system, Tetrahymena can be kept under optimal growth conditions with a generation time of less than 3 h, and any cell density may be maintained for extended periods of time. Furthermore, the cadmium concentration of the medium remained constant during prolonged exposure when maintaining a cell density of about 50 x 10(3) cells/ml. This illustrates the great advantage of using a continuous flow system in such investigations, where for example, long-term adaptations of the organism to a metal may be studied under constant conditions.

Differences in immunological susceptibility to cadmium toxicity between two rat strains as demonstrated with cell biological methods. Effect of cadmium on DNA synthesis of thymus lymphocytes

When 2 inbred rat strains, the Brown-Norway rat and the Lewis rat were exposed to the same amount of CdCl2 for 15 days, a completely different immunological reaction pattern could be demonstrated. Despite the same amount of intrathymic cadmium in both strains, the Brown-Norway rat showed a significant decrease in thymocytes in the S-phase and a significant increase of thymocytes in the G2 phase and mitosis, in contrast with findings in the Lewis rats. A new method for estimating subtle forms of thymus atrophy showed a slight decrease in the number of the smallest thymocytes in the Brown-Norway rat after exposure to cadmium, in contrast with that in the Lewis rat. Evidence is presented that the approximately 1.7 times larger number of thymocytes/mg thymus in the Lewis rat, compared to the Brown-Norway rat, as well as the approximately 2.5 times lower proliferation rate of the thymocytes, and an approximately 1.5 times higher metallothionein content of the thymus medulla epithelial cells in the Lewis rat, might be responsible for the observed difference in toxicity. The zinc content of the thymus was not significantly decreased by exposure to CdCl2, and did not differ significantly between both strains.

Increase of cadmium-thiolate clusters as a measure of morphological non-toxic cadmium accumulation in the rat liver

When cadmium is chronically administered to rats, an increase by more than 10% of protein bound disulphides and cadmium-thiolate clusters appears to be an indicator for non-toxic accumulation of cadmium in liver and kidney and probably in other organs as well. Using enzyme histochemistry, no damage could be observed in these livers, on the contrary, even signs of increased cellular activity could be demonstrated with specific staining for single stranded RNA. It is clearly demonstrated that in the case of 2 livers with the same quantity of accumulated cadmium morphological damage is completely dependent on dose and schedule of administration. However, despite the fact that cadmium is retained very well in rat livers showing an increase in protein-bound disulphides and cadmium-thiolate clusters, there are still small morphological changes, especially in cells and tissues that appear to have a relatively small potency for producing cadmium-binding proteins.

Transformation of prostatic epithelial cells and fibroblasts with cadmium chloride in vitro

Primary cultures of fibroblasts and epithelial cells were established from rat ventral prostate (RVP), canine (CP), baboon (BP), and human (HP) prostates, and were used in an assay system to evaluate cadmium chloride (CdCl2) cytotoxicity in vitro. Fibroblasts were always more susceptible to CdCl2 cytotoxicity than the epithelial cells of the same species. There was a distinct species variability to CdCl2 cytotoxicity, with RVP cells being greater than 200 times more susceptible than HP. Primary cultures treated with CdCl2 were subcultivated to establish cell lines. Only RVP fibroblast and epithelial cells resulted in permanent cell lines. Two fibroblast and two epithelial cell lines were derived from CdCl2-treated RVP cell cultures. The epithelial cell lines possessed tonofilaments, desmosomes and keratin. All four cell lines were resistant to CdCl2, had different karyotypes and an excess of chromosome 13. These results demonstrate the transforming potential of cadmium on prostate cells. The role of metallothionein and the significance of extra chromosomes 13 are discussed as possible factors of cadmium resistance.

Large increase in disulphide bonds containing cytosol proteins after chronic cadmium administration, estimated in isolated rat liver cells

Using histochemical staining, followed by cytophotometric quantitation of disulphide bonds and total protein in isolated liver cells of rats treated for a long time with low doses of CdCl2, a large increase in disulphide bonds containing proteins could be demonstrated in cells of one ploidy class. This increase seems to be due to an increase in high molecular weight (HMW) cytosol proteins as estimated biochemically. They probably represent polymers of metallothionein.

Cadmium-induced hepatotoxicity in cultured rat hepatocytes as evaluated by morphometric analysis

Freshly isolated hepatocytes from neonatal rats were cultured for approximately 24 h; incubated for 5, 30, or 60 min in solutions containing 0, 50, 100, or 200 microM cadmium; embedded in plastic; and sectioned for optical microscopy. The extent of cadmium-induced hepatotoxicity was evaluated by double-blind morphometric analysis (a geometricostatistical processing of two-dimensional data for the collection of three-dimensional information) whereby hepatocytes were classified on the basis of the severity of morphologic damage at the optical level. Both time and concentration effects were studied. Cultures exposed to 200 microM cadmium, for various intervals of time from 5 to 60 min, showed statistically significant reductions in the relative volume percent of normal hepatocytes, elevations (then reductions) in the relative volume percent of slightly damaged hepatocytes, increases in the relative volume percent of moderately damaged cells, and increases in the relative volume percent of severely damaged liver cells. As the concentration of cadmium was increased from 50 to 200 microM cadmium (during both 30 and 60-min exposures), significant trends were observed in cellular distribution patterns based on relative volume percent. Morphologically normal cells decreased, both slightly damaged and moderately damaged cells increased, and severely damaged cells remained unchanged. These results indicated that morphometric analysis at the optical level provided quantitative estimates for the evaluation of time- and concentration-effects of cadmium on cultured hepatocytes.