Cadmium toxicity in kidney cells. Resistance induced by short term pretreatment in vitro and in vivo

Acclimation to low level exposure of copper in Bufo arenarum embryos: linkage of effects to tissue residues

The acclimation possibilities to copper in Bufo arenarum embryos was evaluated by means of three different low level copper exposure conditions during 14 days. By the end of the acclimation period the copper content in control embryos was 1.04 +/- 0.09 microg g(-1) (wet weight) while in all the acclimated embryos a reduction of about 25% of copper was found. Thus copper content could be considered as a biomarker of low level exposure conditions. Batches of 10 embryos (by triplicate) from each acclimation condition were challenged with three different toxic concentrations of copper. As a general pattern, the acclimation protocol to copper exerted a transient beneficial effect on the survival of the Bufo arenarum embryos. The acclimation phenomenon could be related to the selection of pollution tolerant organisms within an adaptive process and therefore the persistence of information within an ecological system following a toxicological stressor.

Cadmium distribution and toxicity in tissues of small rodents

The aim of the present paper is to discuss the accumulation and distribution of cadmium (Cd) in the various tissues of animals, the interactions of cadmium with other elements, and the damage to tissues caused by this metal. Cadmium is not physiologically or biochemically essential to an organism. It is absorbed via the gastrointestinal tract and lungs and accumulated in various tissues, mainly the kidneys and liver. The distribution of cadmium between various tissues depends on many endogenous and exogenous factors. Cadmium is bound to a low-molecular-weight protein, metallothionein (MT), and to high-molecular-weight proteins. This metal has a great affinity to thiol groups. Cadmium binds also to O- and N-containing ligands. The distribution of cadmium between organs differs markedly depending on the chemical form of administered Cd and the duration of exposure. Acute exposure results in a different distribution pattern throughout the body than does chronic exposure. Long-term exposure to high doses of cadmium may cause biochemical and functional changes in some critical organs. Cadmium can influence the absorption and distribution of essential elements and can replace them in enzymes. Metallothionein and glutathione play important roles in the transport of metals and in detoxification processes. Reported findings are mainly the results of experiments on laboratory animals. The lack of data concerning the localization of cadmium in various tissues of wild species is noticeable and there is a great need for such data.

Metallothionein induction and cadmium uptake in Bufo arenarum embryos following an acclimation protocol

Bufo arenarum embryos at the end of their embryonic development were acclimated to cadmium (Cd) by means of a 10-day treatment protocol. Embryos were processed for metallothionein (Mt) isolation and Cd and zinc (Zn) contents were measured. The results showed that: (1) the uptake of Cd in the experimental embryos was 7 microg/g embryo (wet weight) representing a bioaccumulation of Cd 255 times higher than in the maintaining medium; (2) a major Mt-like fraction was Cd-induced 7.8 times that in control embryos; two other protein fractions also bound Cd and Zn but were induced by Cd only about 2 and 1.4 times; (3) the Zn concentration was about 44 microg Zn/g embryo (wet weight) and did not change significantly (p>0.01) in the experimental embryos with respect to controls, but in acclimated embryos the essential metal was released from the Mts. The enhanced Mt synthesis and release of Zn from the native Mts are discussed in relation to the acclimation phenomenon.

Exposure of cultured human proximal tubular cells to cadmium, mercury, zinc and bismuth: toxicity and metallothionein induction

The kidney, in particular the proximal convoluted tubule, is a major target site for the toxic effects of various metals. However, little is known about the early effects of these metals after acute exposure in man. In the present study we have evaluated the toxicity of several inorganic metal compounds (CdCl2, HgCl2, ZnCl2, and Bi(NO3)3) and the induction of metallothionein by these compounds in cultured human proximal tubular (HPT) cells for up to 4 days. The results showed that bismuth was not toxic even at the highest dose (100 microM) used, while zinc, cadmium and mercury exhibited varying degrees of toxicity, zinc being the least toxic and mercury the most potent. A significant degree of interindividual variation between the different isolates used in these experiments was also observed. All metals used in the present study induced MT, as revealed by immunocytochemistry. All metals showed maximal induction between 1 and 3 days after treatment. Although a certain amount of constitutive MT was present in the cultures, the intensity of the staining varied with time in culture and between the different isolates studied. No correlation could be made between the intensity of the staining in control cultures (indicating total amount of constitutive MT) and the susceptibility of a given isolate to metal toxicity. Furthermore, no correlation could be made between metal-induced MT and the susceptibility of a given isolate to that particular metal.

Increased resistance against cadmium toxicity by means of pretreatment with low cadmium/zinc concentrations in Bufo arenarum embryos

A significantly increased resistance against cadmium toxicity in Bufo arenarum embryos was obtained by means of pretreatments with low cadmium/zinc concentrations, allowing embryos to tolerate lethal cadmium concentrations. Slight variations in the pretreatment schedule could result in significant differences within this acclimation phenomenon. The probable mechanisms of action of this protective effect are discussed.

Primary rat Sertoli and interstitial cells exhibit a differential response to cadmium

Two cell types central to the support of spermatogenesis, the Sertoli cell and the interstitial (Leydig) cell, were isolated from the same cohort of young male rats and challenged with cadmium chloride to compare their susceptibility to the metal. Both cell types were cultured under similar conditions, and similar biochemical endpoints were chosen to minimize experimental variability. These endpoints include the uptake of 109Cd, reduction of the vital tetrazolium dye MTT, incorporation of 3H-leucine, change in heat-stable cadmium binding capacity, and production of lactate. Using these parameters, it was observed that the Sertoli cell cultures were adversely affected in a dose-and time-dependent manner, while the interstitial cell cultures, treated with identical concentrations of CdCl2, were less affected. The 72-hr LC50's for Sertoli cells and interstitial cells were 4.1 and 19.6 microM CdCl2, respectively. Thus, different cell populations within the same tissue may differ markedly in susceptibility to a toxicant. These in vitro data suggest that the Sertoli cell, in relation to the interstitium, is particularly sensitive to cadmium. Because the Sertoli cell provides functional support for the seminiferous epithelium, the differential sensitivity of this cell type may, in part, explain cadmium-induced testicular dysfunction, particularly at doses that leave the vascular epithelium intact.

Renal proximal tubular cells in suspension or in primary culture as in vitro models to study nephrotoxicity

The kidney forms a frequent target for xenobiotic toxicity. The complex biochemical mechanisms underlying nephrotoxicity are best studied in vitro provided that reliable and relevant in vitro models are available. Since most nephrotoxicants affect primarily the cells of the proximal tubules (PTC), much effort has been directed towards the development of in vitro models of PTC. This review focuses on the preparation of PTC and the use of these cells. Discussed are important criteria such as the viability (survival time) of the cells and the parameters to assess toxicity. Recent studies have shown that isolated PTC in suspension are especially suitable for studies on the biochemical mechanisms of 'acute' nephrotoxicity, whereas PTC in primary culture may be used to investigate mechanisms of nephrotoxic damage at very low concentrations, upon prolonged exposure. PTC cultured on porous filter membranes provide new possibilities to study toxicity in relation to cell and transport polarity. Primary cell cultures of human PTC have been set up. Although a further characterization of these systems is needed, recent data indicate their usefulness.

Cadmium nephrotoxicity in human proximal tubule cell cultures

Human proximal tubule kidney cells grown in a serum-free tissue culture medium were exposed to concentrations of CdCl2 in a range of 0.5 to 10 micrograms/ml. Cells were observed from 1 to 20 d upon initiation of cadmium in the culture fluid. Both confluent and subconfluent populations of cells were treated and evaluated for cytotoxicity. Both populations exhibited a concentration-dependent toxicity to ionic cadmium. For cells treated with 2.0 to 10 micrograms/ml Cd, the decreases in cell numbers were largely irreversible. However, cells treated with Cd in a range of 0.5 to 1.0 micrograms/ml exhibited a partial recovery of cell number and control morphology. In this range, recovery was more efficient in the subconfluent cultures. Fine structural alterations in Cd-treated tubule cells included condensation of nuclear chromatin, loss of microvilli structure, disorganization of lateral membrane interdigitation, as well as decreased uptake of aminoglycoside antibiotics as evidenced by decreased numbers of myeloid bodies in these cells. The results of this study imply that use of a human proximal tubule culture system has potential in discerning structural and functional effects of cadmium as well as other nephrotoxic metals and compounds on the human kidney.

Modulation of metal toxicity by metallothionein

Toxic properties of several metals may be modified, since they are bound to metallothionein in vivo. Such modulation is particularly well known for cadmium (Cd), whose acute effects are prevented by metallothionein induction, whereas chronic effects on the kidney are partly explained on the basis of transport of cadmium-metallothionein (CdMt) into the kidney. Although intracellular Mt synthesis is induced by Cd, offering partial protection, nephrotoxicity may occur at times when such protection is insufficient. Perturbations in renal calcium metabolism may be an important basis for membrane dysfunction leading to proteinuria.

The modulation by metallothionein of cadmium-induced cytotoxicity in primary hepatocyte cultures

The cytotoxicity of CdCl2 and 2 isoforms of hepatic cadmium-metallothionein (CdMT I and II), was investigated using primary cultures of rat hepatocytes. The cell cultures were exposed to cadmium as CdCl2 or as either isoform of CdMT for a 20-h period at concentrations ranging from 50 to 500 ng Cd X ml-1. Cytotoxicity was assessed by determining the amount of lactic dehydrogenase released from the cells into the incubation medium and the incorporation of [3H] arginine into cell protein. The uptake of Cd by the cells was also measured. Cadmium chloride and both isoforms of CdMT were found to be toxic to hepatocytes although partial protection was afforded by the binding of cadmium to metallothionein (MT). At the higher exposure concentrations and in accordance with the toxicity data, the cells exposed to CdCl2 were found to accumulate more cadmium than those exposed to CdMT. The distribution of cadmium in the culture medium was examined using Sephadex G-75 chromatography. The speciation of cadmium is discussed in relation to its cytotoxicity.

Influence of cadmium-metallothionein pretreatment on tolerance of rat kidney cortical cells to cadmium toxicity in vitro and in vivo

Kidney cells were isolated from rats pretreated by daily subcutaneous doses of cadmium metallothionein (CdMT: 0.05-0.2 mg Cd/kg X 5) and from non-pretreated rats. Upon exposure to CdCl2 in vitro (0-200 micrograms Cd/ml), a concentration dependent decrease in viability was observed in the non-pretreated cells, while no such decrease occurred in the pretreated cells indicating that these cells were more resistant to the toxic action of cadmium. There was a higher in vitro uptake of Cd+2 and an increased metallothionein (MT) concentration in the pretreated cells (compared to non-pretreated cells). Subcellular distribution studies revealed that Cd was mainly recovered in the "cytosol" fraction. The higher total cadmium uptake in pretreated cells corresponded to an increase of Cd in "cytosol" and "nuclear" fractions. This observation may be explained by MT-binding of Cd in the cells and is in accordance with a possible protective effect of induced MT in the pretreated cells. In order to assess whether pretreatment-induced tolerance to cadmium toxicity--indicated by the cellular studies--could also be observed in vivo, some whole animal experiments were also performed. A dose-related proteinuria was observed in non-pretreated rats after a single subcutaneous administration of 109Cd-MT at doses of 0.05 and 0.4 mg Cd/kg. Urinary total Cd, 109Cd and MT was also increased in a dose-related fashion. Cadmium concentrations in kidney were dose related and reached 19 micrograms/g wet weight. In contrast, in animals repeatedly pretreated with CdMT according to 1), no proteinuria was observed after administration of the same single doses of 109CdMT. Total Cd. 109Cd and particularly MT-concentrations in urine were lower in such pretreated animals than in in non-pretreated ones in spite of the accumulation of higher tissue concentrations of total Cd (up to 80 micrograms/g). The pretreatment was thus shown to prevent some of the acute nephrotoxicity of CdMT, possibly by means of induction of MT synthesis.

Uptake of cadmium in isolated kidney cells--influence of binding form and in vivo pretreatment

Uptake of cadmium as 109CdCl2, 109Cd-cysteine, 109Cd-albumin and 109Cd-metallothionein was studied in isolated kidney cells from rat. Cd as 109CdCl2 and 109Cd-albumin was taken up at similar rates. The uptake of cadmium as 109Cd-cysteine was greater and that of 109Cd-metallothionein lower compared with that of the other substances. These observations were made on non-pretreated cells. In cells taken from rats pretreated with CdCl2 in vivo, the uptake of cadmium as 109CdCl2, 109Cd-cysteine and 109Cd-albumin was lower than in cells from non-pretreated rats. However, the uptake of 109Cd-metallothionein was considerably enhanced in pretreated cells. In pretreated kidney cells the decreased uptake of Cd (as Cd-albumin) might be related to protection of the kidney against acute Cd toxicity and increased uptake of metallothionein-Cd might contribute to the explanation of renal damage in long-term Cd exposure.