Form of cadmium in rat liver subcellular particle

Cadmium chloride-induced DNA and lysosomal damage in a hepatoma cell line

Cadmium is a toxic metal and no uniform mechanism of toxicity has so far been proposed. The aim of this study was to investigate the biochemical effects of cadmium chloride in a rat hepatoma cell line (HTC cells) and the cellular events mediating DNA damage. HTC cells were exposed to various concentrations of cadmium chloride for 5 and 8 h and lysosomal damage was assessed with the neutral red assay (NR) and fluorescence microscopy. Mitochondrial integrity was assessed from ATP levels and DNA damage determined with the single cell gel electrophoresis/comet assay. The formation of reactive oxygen species (ROS) was also determined under the same experimental conditions with the dichlorofluorescein assay. Cytotoxicity was assessed with the LDH leakage assay and the levels of glutathione were measured and correlated with the other effects. The results indicate that lysosomal damage occurs at a lower concentration of cadmium chloride (20 microM) than DNA damage (500 microM) in HTC cells. The latter effect was accompanied by an increase of reactive oxygen species without any significant LDH leakage whereas lysosomal damage was significant as determined by the neutral red assay and confirmed with fluorescence microscopy. The effect of CdCl2 on mitochondria and glutathione levels were observed at concentrations or incubation times higher than the ones required to induce lysosomal damage. The data suggest that DNA damage may be due to the formation of reactive oxygen species. It is possible that cadmium induced lysosomal damage is an earlier event than DNA damage and can mediate other cellular events that lead to cell death.

Biliary excretion of exogenous cadmium, and endogenous copper and zinc in the Eisai hyperbilirubinuric (EHB) rat with a near absence of biliary glutathione

Mutant Eisai hyperbilirubinuric (EHB) rats derived from an inbred strain of Sprague-Dawley (SD) rats are characterized by a near absence of biliary excretion of glutathione (GSH) due to inherently impaired ATP-driven organic anion transport. Cd (0.1 mg/kg bw from CdCl2) was injected intravenously into EHB rats and control SD rats. Output of biliary excretion of Cd was followed over 15-min intervals up to 60 min. Cd was excreted rapidly and reached the maximum level (73.2 ng/15 min) in the period from 15 to 30 min in SD rats. Its excretion in EHB rats, however was one-fortieth (only 1.8 ng/15 min) of that in SD rats. Biliary concentrations of two endogenous metals, Cu and Zn were also measured. The output of Cu in EHB rat bile (50 ng/15 min before Cd injection) was about one-fifth of that in SD rat bile (270 ng/15 min). The output was not influenced by the Cd injection in the two groups. There was a slight difference of Zn output between the two groups. The biliary excretion of GSH was 500 to 700 micrograms/15 min and only 1 to 2 micrograms/15 min in SD and EHB rats, respectively. Sixty min after Cd injection, the Cd concentrations in the serum, liver and kidney were slightly higher in EHB rats than in SD rats. There was no difference in the hepatic metallothionein (MT-I and-II) concentration between SD (34 micrograms/g liver) and EHB (33 micrograms/g liver) rats. The renal Cu concentration was about four times in the higher in the EHB rat than in the SD rat. These results suggest that reduced biliary excretion of Cd is mainly, but that of Cu is only partly, based in reduced canalicular transport of GSH due to lack of an ATP-driven organic anion transport system, not MT induction in EHB rats. It seems likely that biliary excretion of Cd is regulated mainly by the canalicular anion transport in rats.

A possible mechanism of cadmium-copper interaction in embryonic chick bone in tissue culture

Femurs from 9-day-old embryo were cultured for 4 days by the roller-tube method in the presence of Cd and/or Cu. The combination of both Cd and Cu caused a significantly interactive decrease in hydroxyproline (Hyp) synthesis as well as bone growth compared with that in the presence of Cd (1.1 or 3.3 microM) or Cu (1.1 or 2.2 microM) alone. The presence of both 2.2 microM Cd and 3.3 microM Cu also showed a significantly interactive decrease in the incorporation of [3H]proline (Pro) into collagenase-digestible protein (CDP), but it showed no interactive inhibition of the hydroxylation of [3H]Pro in CDP. The two metals were also interactive with respect to the inhibition of the synthesis of protein, RNA and DNA. Culture of epiphysis in the presence of both Cd and Cu resulted in higher content of Cd and Cu compared to those cultured in Cd or Cu alone. Subcellular fractions from epiphysis cultured in Cd plus Cu contained more Cd than those cultured in Cd alone. Cu was increased in two fractions, nuclei and cytosol, following co-incubation. The cytosol from epiphysis cultured in the presence of both Cd and Cu contained more Cd in both a metallothionein (MT)-like protein and a high-molecular-weight (HM) protein than cytosol from Cd-treated bones. The amount (nmol) of Cu in the MT fraction was nearly equal to the sum of the increased amounts (nmol) of Cd in HM fraction of cytosol and particulate fractions. This indicates that some Cd in MT-like protein induced by Cd is replaced with Cu and the released Cd redistribution to HM fraction and particulate fractions. Most of the Cd in the solubilized particulate fractions was detected in the HM fraction. A marker enzyme or component in each fraction was interactively inhibited by both Cd and Cu. Therefore, the interactive inhibition of bone metabolism by both Cd and Cu in the cultured bone is at least partly due to the increase in Cd content of HM fraction of cytosol and particulate fractions.

Heavy metal detoxication in the mussel Mytilus edulis-composition of Cd-containing kidney granules (tertiary lysosomes)

A new method for isolation and purification of lipofuschin granules (tertiary lysosomes) from mussel kidney is described. The results confirm previous ultrastructural evidence for the accumulation of Cd in these organelles. Granules from Cd-exposed animals contain higher concentrations of protein, Ca, Cd and S than those from control animals. Gel filtration experiments indicate that secondary lysosomes contain metallothionein whilst only low molecular weight Cd-complexes can be solubilised from tertiary lysosomes. Amino acid analysis of Cd-containing tertiary lysosomes show that they are not enriched in cysteine, indicating the absence of insoluble polymerised metallothionein.