Investigation for the mechanism of cadmium toxicity at cellular level. II. An electron microscopical study

Distribution of Heavy Metals in the Liver of Foetuses and Female Mice after Oral Administration during Pregnancy - a Histochemical Study

The aim of this work was to study the distribution of heavy metals and of subsequently developed morphological changes in the liver of female mice and their foetuses after oral administration of high doses of lead, mercury, and cadmium (0.03 mg of metal per mouse and day). Heavy metals were administered to pregnant female mice on days 9-20 of pregnancy. The animals were euthanised by cervical dislocation. Samples of mother and foetal liver were subsequently collected and processed by means of the common technique for light and electron microscopy. Histochemical reaction based on metal conversion into appropriate sulphide that conjugates with silver was used for detection of heavy metals. Deposits of heavy metals were found at the periphery of lobules of the central vein in the liver of female mice. On the contrary, in the liver of foetuses no predilection site for localisation of the reaction product could be identified. At the electron microscopy level, accumulation of heavy metals was connected as a rule with the occurrence of certain damage to some organelles. Deposits of the reaction product were located mainly in hepatocytes and Kupffer cells. Heavy metals were bound to the heterochromatin of cell nuclei, as well as to some cytoplasmic organelles, such as rough endoplasmic reticulum, mitochondria, ribosomes, and lysosomes. The presence of heavy metals was associated with obliteration of cisternae of the rough endoplasmic reticulum, separation of ribosomes, and destruction of lysosomes. Vacuolation of cell cytoplasm was also a frequent phenomenon. An interesting finding was the "contrasting" of structures containing nucleic acids. Accumulation of metals in the liver of pregnant mice and their foetuses observed in our study indicated that placental barrier does not protect the foetal organism against penetration of metals. Their higher accumulation in foetal compared to maternal liver can be explained by the intense metabolism of differentiating hepatocytes.

Ultrastructural variations in Lethocerus niloticum (Insecta: Hemiptera) caused by pollution in Lake Mariut, Alexandria, Egypt

Water bugs, Lethocerus niloticum (Hemiptera: Belostomatidae), were collected from polluted and unpolluted areas of Lake Mariut to study ultrastructural alterations of different organs as a response to mainly heavy metal water pollution in the lake. Malpighian tubules are described by light, scanning, and transmission electron microscopy. L. niloticum has four Malpighian tubules floating in the hemolymph. Each tubule opens separately into the hindgut, consisting of one type of epithelium cells, and is divided into four regions. Structural changes in cells of the third distinctive region are examined. The most prominent pathological changes are the occurrence of pleomorphic mitochondria, the presence of enlarged irregular laminated concretions, an increase in lysosomes, and lysis of cytoplasm. Indentations of the nucleus and chromatin clumping are observed. These results allowed determination of the impact of pollutants in Malpighian tubule cells of L. niloticum, and thus this insect can be used as a biomonitor.

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.

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.

An electrophysiological freeze fracture assessment of cadmium nephrotoxicity in vitro

Human proximal tubule cell cultures exposed to doses of cadmium chloride (CdCl2) between 0.05 microgram/ml and 0.5 microgram/ml exhibited alterations in cell membrane structure and transport function. At these Cd concentrations, cell numbers were not significantly altered from control values in either nonreplicating confluent, or actively replicating subconfluent cultures. Transmission electron microscopy revealed few alterations in cultures treated with 0.05 microgram/ml Cd. Tight junctions were intact; organelles and myeloid body formation appeared normal. Freeze fracture analysis confirmed the integrity of the tight junctions as well as increased numbers of vesicles or pits along the lateral cell membrane, indicating increased endocytotic activity. Cells exposed to 0.1 microgram/ml Cd were characterized by decreased numbers of microvilli and inhibited myeloid body formation. Cd doses of 0.5 micrograms/ml elicited nuclear chromatin condensation, fragmented sealing strands in 5 to 10% of the tight junction profiles, sparse microvilli, and inhibited myeloid body formation. Electrophysiologic assessments of transport function by Ussing chamber analysis revealed decreases in transepithelial potentials for all three concentrations, with significant differences at Cd concentrations of 0.5 to 0.1 micrograms/ml. Cells treated with 0.5 micrograms/ml Cd also exhibited slight decreases in electrical resistance, consistent with the minimal fragmentation of sealing strands observed in freeze fracture replicas. Resistance in cultures treated with 0.1 or 0.05 micrograms/ml Cd remained within control values and indicated that drops in potential difference and short circuit current in these cells reflected true alterations in ion transport.

Effects of a testicotoxic dose of cadmium on the liver and drug metabolism in the rat

1. The effect of an acute testicotoxic dose of cadmium (CdCl2.H2O, 2.0 mg/kg i.p.) on liver morphology and drug-metabolizing enzyme activities were studied in adult male and female rats. 2. Cd treatment to female rats caused a slight and reversible decrease in hepatic microsomal aryl hydrocarbon hydroxylase (AHH) and aminopyrine N-demethylase (APND) activities. 3. No significant changes were noted in the liver morphology, serum alanine aminotransferase activities, enzyme induction by phenobarbital and 3-methylcholanthrene, and glucuronosyl-transferase (GT) and glutathione S-transferase (GST) activities. 4. The same Cd treatment to male rats, however, resulted in a much more pronounced and prolonged reduction in AHH and APND activities, which was attributable to a Cd-induced testicular necrosis and, hence, impairment of androgen secretion. 5. Accordingly, Cd treatment to castrated male rats did not lower the enzyme activities any further, and full recovery of activities was obtained after the administration of testosterone. 6. Both GT and GST, the two sex-independent enzymes, were not significantly affected by either Cd or gonadectomy in the male rat. 7. The present data show that a low acute dose of Cd induces chemical castration without severely altering hepatic function.

Cadmium induced changes in cell organelles: an ultrastructural study using cadmium sensitive and resistant muntjac fibroblast cell lines

A detailed electron microscopy study of cadmium sensitive and resistant muntjac fibroblast cell lines has identified a wide range of intracellular damage following exposure to cadmium. Damaged organelles included cell membrane, mitochondria, Golgi cisternae and tubular network, chromatin, nucleoli, microfilaments and ribosomes. Although cell membrane damage was generally the earliest indication of adverse cadmium action, particularly with continuous cadmium exposures, cells could tolerate extensive membrane loss. Mitochondrial distortion and some damage to Golgi was also tolerated. The turning point at which cadmium became lethal was generally marked by a cascade of events which included damage to both nuclear and cytoplasmic components. These results for fibroblasts are discussed and compared with damage reported in other types of cells.

The vascular endothelium as a target tissue in acute cadmium toxicity

Sensitivity of tissues to the acute toxicity of cadmium is reviewed. It is concluded that the initial effect of acute cadmium administration is on the integrity and permeability of the vascular endothelium; other necrotic changes occur secondarily to this effect. In a sensitive tissue, not all of the endothelial cells are susceptible to cadmium. Furthermore, after necrosis of the sensitive cells, the resistant cells proliferate and result in regeneration of the vasculature and subsequent acquired resistance to the metal. It is found that sex hormones are probably important in determining susceptibility and response of tissues to cadmium. The role of metallothionein in these phenomena remains to be elucidated.

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.

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.

Time course of cadmium-induced ultrastructural changes in rat liver

Ultrastructural changes in rat liver were studied 1, 2, 4, 6, 8, and 10 hr after administration of a single, high dose of Cd (3.9 mg Cd/kg, iv) or after repeated administration of a lower dose (0.5 mg Cd/kg, sc, 6 days/week for 6 months). These dosing regimens have been previously shown to produce hepatotoxicity and result in large accumulations of Cd in liver. In addition to light and electron microscopy, plasma enzyme activities indicative of liver injury, namely alanine (ALT) and aspartate (AST) aminotransferase, were determined at the aforementioned times. One hour after an acute dose of Cd, electron photomicrographs of liver showed dilation of the rough endoplasmic reticulum with concomitant loss of membrane-associated ribosomes, nucleolar condensation, and an increase in the number of perichromatin granules. At later times (4 and 6 hr), ultrastructural changes included mitochondrial swelling associated with matrical inclusions, further dilation and vesiculation of rough endoplasmic reticulum, and presence of a fibrillar material within cytoplasm. In contrast to changes observed after single administration of Cd, the predominant hepatic lesions in rats injected repeatedly with the metal over 6 months were interstitial fibrosis, nuclear enlargement, and an increase in number and predominance of nucleoli. Ultrastructural evidence of nuclear alterations included condensation of nucleoli and an increase in the number of perichromatin granules. These results indicate that Cd interferes with hepatic protein synthesis early after injection of a large dose, and that further degenerative changes occur later and possibly in response to protein inhibition. Although severe degenerative changes in liver were not evident in rats chronically exposed to the metal, Cd-induced changes in nuclei and nucleoli also indicate the likelihood of altered protein synthesis.

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.