Changes in expression of fibrotic markers and histopathological alterations in kidneys of mice chronically exposed to low and high Cd doses

The main target organ for cadmium (Cd) is the kidney, and more specifically the proximal tubular cells. Little is known about the effects of a long-term Cd exposure on the ultrastructure of the kidney and the involvement in tubulointerstitial fibrosis. Therefore, mice were exposed to Cd concentrations varying from 10 to 500 mg CdCl(2)/l in the drinking water during 4, 16 and 23 weeks. Ultrastructural changes were studied by means of light- and electron microscopical analyses. Furthermore, the expression of the extracellular matrix (ECM) proteins collagen I and fibronectin, and the myofibroblast/epithelial-to-mesenchymal transition (EMT) marker alfa-smooth muscle actin (alpha-SMA) were studied by means of immunohistochemistry. The histopathological changes caused by Cd varied considerably from one animal to another, and from one individual cell to another. An exposure to Cd concentrations up to 100mg CdCl(2)/l elicited only minor changes that were restricted to increasing amounts of lysosomes and vacuolisation. When higher Cd concentrations were applied, the changes became more pronounced and featured mitochondrial damage, cellular swelling and loss of basal invaginations. An overproduction of the interstitial matrix component fibronectin and the expression of the myofibroblasts/EMT marker alpha-SMA in kidneys of mice exposed to 100mg CdCl(2)/l clearly indicated that an exposure to relatively low Cd doses might lead ultimately to renal fibrosis. Increasing the Cd dose (up to 500 mg CdCl(2)/l) evoked an increased immunoreactivity for fibrotic markers. In conclusion we may state that concentrations up to 100mg CdCl(2)/l evoked minor changes, although the expression of fibrotic markers was increased. Changes became more pronounced when exposing to higher Cd concentrations.     

Changes in the structure and function of the kidney of rats chronically exposed to cadmium. I. Biochemical and histopathological studies

The aim of this study was to assess the effects of chronic exposure to cadmium (Cd) on the structure and function of kidneys, as well as to establish the body burden of Cd at which the changes occur. For this purpose we have created an experimental model using rats intoxicated with Cd administered in drinking water at the concentration of 5 or 50 mg Cd/l for 6, 12 and 24 weeks. The degree of kidney damage was evaluated biochemically and histopathologically. Sensitive biomarkers of Cd-induced proximal tubular injury such as urinary total N-acetyl-beta- d-glucosaminidase (NAG-T) and its isoenzyme B (NAG-B), and alkaline phosphatase (ALP) were used. Cd content in the kidney increased with the level and duration of exposure leading to dose- and time-dependent structural and functional renal failure. In rats exposed to 5 mg Cd/l, first symptoms of injury of the main tubules of long and short nephrons (structural damage to epithelial cells, increased urinary activities of NAG-T and NAG-B) were noted after 12 weeks of the experiment. The damage occurred at a low kidney Cd concentration amounting to 4.08+/-0.33 micro g/g wet weight (mean +/-SE) and a urinary concentration of 4.31+/-0.28 micro g/g creatinine. On exposure to 50 mg Cd/l, damage to the main tubules (blurred structure of tubular epithelium, atrophy of brush border, partial fragmentation of cells with release of nuclei into tubular lumen as well as increased urinary activities of NAG-T, NAG-B and ALP) was already evident after 6 weeks with the kidney Cd concentration of 24.09+/-1.72 micro g/g wet weight. In rats exposed to 50 mg Cd/l, a lack of regular contour of glomeruli was noted after 12 weeks, whereas after 24 weeks thickening of capillary vessels and widening of filtering space were evident. After 24 weeks of exposure to Cd, increased urea concentration in the serum with simultaneous decrease in its level in the urine, indicating decreased clearance of urea, and increased excretion of total protein were observed, but endogenous creatinine clearance remained unaffected. At the lower exposure, symptoms of structural, but not functional, damage to the glomeruli were also evident after 24 weeks of the experiment. Our results provide evidence that chronic exposure to Cd dose-dependently damages (structurally and functionally) the whole kidney. The injury affects the main resorptive part (proximal convoluted tubules and straight tubules) and the filtering part (glomeruli) of the nephron. But the target site for Cd action is the main tubule. We hypothesize that the threshold for Cd effects on the kidney is less than 4.08+/-0.33 micro g/g wet kidney weight and greater than 2.40+/-0.15 micro g/g (at this Cd concentration no symptoms of kidney damage were noted), and it may be close to the latter value. A very important finding of this study is that Cd acts on the whole kidney, especially on the main tubules, even at relatively low accumulation in this organ. It confirms the hypothesis that humans environmentally exposed to Cd, especially smokers, are at risk of tubular dysfunction.     

Cadmium accumulation and metallothionein concentrations after 4-week dietary exposure to cadmium chloride or cadmium-metallothionein in rats.

The distribution of cadmium was examined in rats fed diets containing either cadmium-metallothionein (CdMt) or cadmium chloride (CdCl2) for 4 weeks. The test diets contained 3, 10, or 30 mg Cd/kg diet (3, 10, or 30 ppm) as CdMt or 30 mg Cd/kg diet (30 ppm) as CdCl2. A second study was performed to establish the Cd content in liver and kidneys after exposure to low doses of both CdMt and CdCl2 (1.5 and 8 ppm Cd). The feeding of CdMt resulted in a dose- and time-dependent increase of the Cd concentration in liver, kidneys, and intestinal mucosa. Rats fed 30 ppm CdMt consistently showed less Cd accumulation in liver and intestinal mucosa than did rats fed 30 ppm CdCl2. However, renal accumulation in rats fed 30 ppm was similar until Day 28 regardless of Cd form. At lower dietary Cd levels (1.5 and 8 ppm), relatively more Cd is deposited in the kidneys, although even at these doses the kidney/liver ratio of Cd is still higher with CdMt than with CdCl2. Tissue metallothionein (Mt) levels in the intestinal mucosa were relatively constant but always higher after CdCl2 exposure than after CdMt exposure. Mt levels in both liver and kidney increased after CdCl2 or CdMt exposure during the course of study. Although Mt levels in liver were higher after CdCl2 intake (30 ppm) than after CdMt intake (30 ppm), renal Mt concentrations were the same for both groups. In fact on Day 7, CdMt administration resulted in slightly higher Mt levels than CdCl2 administration, suggesting a direct accumulation of exogenous CdMt in the kidneys. In conclusion, after oral exposure to CdMt in the diet there is a relatively higher Cd accumulation in the kidneys. However, the indirect renal accumulation via redistribution of Cd from the liver might be lower than after CdCl2 exposure. Which of these two phenomena is decisive in the eventual level of renal toxicity of Cd after long-term oral intake could determine the toxicological risk of the chronic intake of biologically incorporated Cd.     

Metabolic profiling of chronic cadmium exposure in the rat

A confounding problem with studying the effects of environmental exposure to contaminants in wild populations is that analytical techniques are invasive, particularly where the physiological effects of the toxin are assessed. In this study, a metabonomic approach to investigate the biochemical effects of chronic oral exposure to environmentally realistic doses of CdCl2 (low, 8 mg/kg; high, 40 mg/kg) is presented. 1H NMR spectra of urine from exposed animals were analyzed using pattern recognition methods to identify biomarkers for a 94 day exposure period. Creatinuria and both increased excretion and complexation of citrate was detected after 19 days of exposure in both exposure groups. This was accompanied by a decrease in plasma Ca2+/Mg2+ ratio in blood plasma after 94 days. Post mortem, magic angle spinning (MAS) 1H NMR spectroscopy was used alongside conventional analytical techniques to investigate intact tissue directly. According to atomic absorption spectroscopy, kidney tissue accumulated 26.8 +/- 2.5 microg of Cd2+/g dry wt (low) and 75.9 +/- 4.3 microg of Cd2+/g dry wt (high). Using high-resolution MAS 1H NMR spectroscopy altered lipid content was detected in kidneys from animals exposed to Cd2+. However, unlike acute exposure, no testicular damage was evident. This systemic approach to metabolism demonstrated the different physiological effects of chronic subacute compared with an acute exposure to Cd2+.     

Kidney synthesizes less metallothionein than liver in response to cadmium chloride and cadmium-metallothionein

Acute exposure to Cd produces liver injury, whereas chronic exposure results in kidney injury. Tolerance to the hepatotoxicity is observed during chronic exposure to Cd due to the induction of metallothionein (MT). The nephrotoxicity produced by chronic Cd exposure purportedly results from renal uptake of Cd-metallothionein (CdMT) synthesized in liver. The change in target organ from liver to kidney might be due to a lower amount of MT synthesized in the kidney in response to CdMT. Therefore, the purpose of the present study was to quantitate hepatic and renal MT induced by CdCl2 and CdMT. MT levels in mice were quantitated using the Cd-heme assay 24 hr after administration of CdCl2 (0.5-3.0 mg Cd/kg) and CdMT (0.1-0.5 mg Cd/kg). In both liver and kidney, MT reached higher levels following administration of CdCl2 (220 and 60 micrograms/g, respectively) than of CdMT (25 and 35 micrograms/g, respectively), probably because higher dosages of CdCl2 than CdMT are tolerated. CdMT produced 19 and 3 micrograms MT/micrograms Cd in liver and kidney, respectively, while CdCl2 produced 11 and 6 micrograms MT/micrograms Cd, respectively. In conclusion, induction of MT occurs in both the liver and kidney after administration of CdCl2 and CdMT. However, the kidney is less responsive than the liver to the induction of MT by both forms of Cd, which may contribute to making the kidney the target organ of toxicity during chronic Cd exposure.     

The reference dose for subchronic exposure of pigs to cadmium leading to early renal damage by benchmark dose method

Pigs were exposed to cadmium (Cd) (in the form of CdCl(2)) concentrations ranging from 0 to 32mg Cd/kg feed for 100 days. Urinary cadmium (U-Cd) and blood cadmium (B-Cd) levels were determined as indicators of Cd exposure. Urinary levels of β(2)-microglobulin (β(2)-MG), α(1)-microglobulin (α(1)-MG), N-acetyl-β-D-glucosaminidase (NAG), cadmium-metallothionein (Cd-MT), and retinol binding protein (RBP) were determined as biomarkers of tubular dysfunction. U-Cd concentrations were increased linearly with time and dose, whereas B-Cd reached two peaks at 40 days and 100 days in the group exposed to 32mg Cd/kg. Hyper-metallothionein-urinary (HyperMTuria) and hyper-N-acetyl-β-D-glucosaminidase-urinary (hyperNAGuria) emerged from 80 days onwards in the group exposed to 32mg Cd/kg feed, followed by hyper-β2-microglobulin-urinary (hyperβ2-MGuria) and hyper-retinol-binding-protein-urinary (hyperRBPuria) from 100 days onwards. The relationships between the Cd exposure dose and biomarkers of exposure (as well as the biomarkers of effect) were examined, and significant correlations were found between them (except for α(1)-MG). Dose-response relationships between Cd exposure dose and biomarkers of tubular dysfunction were studied. The critical concentration of Cd exposure dose was calculated by the benchmark dose (BMD) method. The BMD(10)/BMDL(10) was estimated to be 1.34/0.67, 1.21/0.88, 2.75/1.00, and 3.73/3.08mg Cd/kg feed based on urinary RBP, NAG, Cd-MT, and β(2)-MG, respectively. The calculated tolerable weekly intake of Cd for humans was 1.4 μg/kg body weight based on a safety factor of 100. This value is lower than the currently available values set by several different countries. This indicates a need for further studies on the effects of Cd and a re-evaluation of the human health risk assessment for the metal.     

Normal levels of cadmium in diet, urine, blood, and tissues of inhabitants of the United States

Cd was measured in the feces, urine, blood, and hair of U.S. inhabitants without known high Cd exposure in Chicago, Illinois, and Dallas, Texas, and in autopsy tissues of accident victims in Dallas. The average intake of Cd in food was estimated to be 13-16 microgram/d and was higher for males than females. The average levels of Cd were 0.59-0.77 microgram/l in urine, 0.09-0.11 microgram per 100 ml in blood, 0.83-1.10 microgram/g in hair, 21 microgram/g in kidney cortex, 1.2 microgram/g in liver, 0.067 microgram/g in muscle, 0.58 microgram/g in pancreas, and 0.040 microgram/g in fat. Hair Cd was higher for males than females. Cd levels increased with age in urine and all tissues and were higher in cigarette smokers than nonsmokers in urine, blood, and all tissues.     

肝脏损害对染镉大鼠镉分布的影响

大鼠腹腔内注射ＣｄＣｌ２０．５ｍｇＣｄ＾２＋／Ｋｇ体重，每周三次，共１０周。注射ＣｄＣｌ２第４周末，其中一组动物灌胃ＣＣｌ４９００ｍｇ／ｋｇ体重。结果表明ＣｄＣｌ２＋ＣＣｌ４组动物肝脏损害后肝镉浓度明显低于单纯ＣｄＣｌ２组，同时伴随血镉，肾镉水平显著升高。肝、肾中金属硫蛋白浓度也与相应组织中隔浓度呈类似的变化形式。ＣｄＣｌ２＋ＣＣｌ４组动物尿镉和尿金属硫蛋白浓度均明显高于ＣｄＣｌ２组。这些实验     

Effect of oral and inhalation exposure to cadmium on the oestrous cycle in rats

Female rats were administered by gavage an aqueous solution of CdCl2 for 14 weeks, 5 days per week, at doses of 0.04, 0.4, 4 and 40 mg Cd/kg/day or exposed by inhalation to CdO for 20 weeks (5 h per days, 5 days per week) at concentrations of 0.02, 0.16 and 1 mg Cd/m3. A pronounced increase in the mean duration of the oestrous cycle mainly due to lengthening of dioestrus was noted already 6 weeks after treatment of females given per os 40 mg Cd/kg or exposed to a concentration of 1 mg Cd/m3. No changes in the mean duration of the oestrous cycle were found in other experimental groups, although in the 0.16 mg Cd/m3 group an increased percentage of females with oestrous cycles lasting over 6 days was shown 18 weeks after exposure. Since Cd-induced lethality and decrease in body weight gain were observed in females given by gavage 40 mg Cd/kg or exposed by inhalation to a concentration of 1 mg Cd/m3, it is concluded that exposure to cadmium does not affect the sexual cycle unless other overt signs of Cd-toxicity are induced.     

Effects of chronic exposure to cadmium on renal cytochrome P450-dependent monooxygenase system in rats

The aim of this study was to evaluate the effects of chronic exposure to cadmium (Cd) on the renal cytochrome P450-dependent monooxygenase system. For this purpose, male Wistar rats were intoxicated with Cd administered in drinking water at a concentration of 5 or 50 mg Cd/l for 6, 12 and 24 weeks. Concentrations of cytochrome P450 and cytochrome b₅ as well as activities of NADPH-cytochrome P450 reductase and NADH-cytochrome b₅ reductase were determined in the kidney microsomal fraction. Protein content of CYP1A1, CYP2E1 and CYP3A1 cytochrome P450 isoforms was evaluated as well. In the rats exposed to 5 mg Cd/l, the concentration of cytochrome P450 decreased (by 41%) after 24 weeks of the experiment. The activity of NADPH-cytochrome P450 reductase decreased (by 24%) after 6 and 12 weeks, whereas after 24 weeks it remained unchanged, compared with the control group. Moreover, a decrease in the concentration of cytochrome b₅ (by 25, 15 and 26% at 6, 12 and 24 weeks, respectively) and the activity of its NADH reductase (by 26 and 31% at 6 and 24 weeks, respectively) was noted in these animals. At the exposure to 50 mg Cd/l, the concentrations of cytochrome P450 and cytochrome b₅ and the activities of their corresponding reductases were decreased at each time-point. Western blot analysis revealed that all isoforms of cytochrome P450 studied were affected by Cd and the effect was dependent on the level and the duration of exposure. The results of this study indicate that chronic exposure to Cd in a dose- and time-dependent manner affects the kidney cytochrome P450-dependent monooxygenase system by decreasing the concentrations of cytochrome P450 and cytochrome b₅ and inhibiting the activities of their corresponding reductases. The effect of Cd on the cytochrome P450 content is associated with its ability to stimulate or inhibit of various P450 isoforms. A very important finding of this study is that Cd affects the kidney cytochrome P450-dependent monooxygenase system at relatively low exposure and low kidney Cd accumulation (2.40±0.15 g/g). As the experimental model used reflects human exposure to Cd, we conclude that Cd can affect the kidney cytochrome P450-dependent monooxygenase system in environmentally exposed humans. Previously we have reported disorders in the system in the liver of rats at the same levels of exposure as in this study. Thus, we hypothesize that the metabolism and detoxification of many substances, including xenobiotics, may be seriously affected in Cd-exposed subjects.Part of this work was presented at the EUROTOX 2001, Istanbul, Turkey, 2001     

Antioxidant enzymes activity and lipid peroxidation in liver and kidney of rats exposed to cadmium and ethanol.

The oxidative status of liver and kidney of rats co-exposed to cadmium (50 mg Cd/l in drinking water) and ethanol (5 g EtOH/kg body weight/24 h, intragastrically) for 12 weeks was studied. The activities of antioxidant enzymes such as superoxide dismutase (SOD) and catalase (CAT) as well as the concentration of malondialdehyde (MDA), as an indicator of lipid peroxidation, were measured in homogenates of the liver and kidney. Concentrations of zinc (Zn), copper (Cu), iron (Fe) and Cd in the serum or blood, and their content in the liver and kidney as well as EtOH concentration in the whole blood were assayed. Daily Cd intake in the Cd and Cd+EtOH groups was similar and ranged from 2.39 to 4.88 mg/kg body weight/24 h and from 2.64 to 4.14 mg/kg body weight/24 h, respectively. After the administration of EtOH alone, the activity of SOD increased in the kidney and decreased in the liver, whereas the activity of CAT decreased in both these organs, and MDA concentration increased in the liver and was unchanged in the kidney. The exposure to 50 mg Cd/l led to a decrease in the activities of SOD in the liver and CAT in the liver and kidney, and an increase in the kidney activity of SOD and MDA concentration in both these organs. In the rats co-exposed to Cd and EtOH, the kidney activity of SOD and the liver concentration of MDA were lower, whereas the kidney activity of CAT was higher compared to the Cd group. The concentration of Fe in the serum and its content in the liver of rats treated with EtOH increased, whereas the concentrations of Zn and Cu in the serum and the content of Zn, Cu and Fe in the kidney and that of Zn and Cu in the liver were unchanged. In the liver and kidney of rats treated with Cd alone, the content of Fe was decreased and that of Zn and Cu was enhanced. After EtOH administration to Cd-exposed rats, a decrease in Cu serum concentration and its liver content and an increase in Fe concentration in the serum and its content in the liver and kidney, compared to the group exposed to Cd alone, were noted. Moreover, EtOH decreased the blood Cd concentration and its accumulation in the liver and kidney of these animals. EtOH alone decreased Cd content in the liver and increased in the kidney, however the whole content of Cd in these organs was unchanged compared with control. The results of this study indicate that despite the ability of Cd and EtOH to induce the oxidative stress the effect in the liver and kidney is not intensified at simultaneous exposure to both substances. The changes in the studied indicators of oxidative stress (SOD, CAT and MDA) observed in the kidney and especially in the liver of the rats co-exposed to Cd and EtOH may result from an independent effect of Cd and/or EtOH and also from their interaction. The interactive effect may involve, among others, changes in Cd accumulation and content of Zn, Cu and Fe in these organs and their concentration in serum. Since the rats treated with Cd and Cd+EtOH had reduced drinking fluids intake that might result in dehydratation, the effect of the both xenobiotics on the oxidative status of the body may be not solely due to Cd and/or EtOH, but also the modyfing influence of accompanying alterations such as reduced water intake and dehydratation. The results of the study allow us to hypothesize that Cd-exposed alcohol misusers are not at enhanced risk of liver and kidney damage due to lipid peroxidation.     

Detection of cadmium exposure in rats by induction of lymphocyte metallothionein gene expression.

The induction of metallothionein (MT) gene expression in lymphocytes of rats was determined in order to detect exposure in vivo to cadmium. Both acute and chronic CdCl2 exposures resulted in the induction of the MT-1 gene in lymphocytes as measured by standard RNA Northern blot analysis. Twenty-four hours following an ip injection of 3.4 mg/kg CdCl2, a ninefold increase in MT gene expression was observed in lymphocytes, as well as five- and sevenfold increases in liver and kidney, respectively. Oral exposure of rats to 1-100 ppm CdCl2 via drinking water resulted in an approximate twofold enhanced MT signal in lymphocytes after 6 wk, and a threefold increase after 13 wk of exposure to 100 ppm Cd. No increases in lymphocyte MT gene expression were observed after 3 wk of Cd exposure. Liver MT gene expression was substantially induced following chronic Cd exposure, while kidney was not, although this organ had a higher basal expression of the MT-1 gene. Analysis of tissue Cd burdens demonstrated a dose-response Cd accumulation in liver and kidney, but only kidney burdens increased substantially with prolonged Cd exposure. These results demonstrate the utility of lymphocyte gene expression assays to detect in vivo toxicant exposure, and thus their applicability as molecular biomarker assays for human exposure assessment.     

Preclinical evaluation of novel urinary biomarkers of cadmium nephrotoxicity

As a result of the widespread use of Cd in industry and its extensive dissemination in the environment, there has been considerable interest in the identification of early biomarkers of Cd-induced kidney injury. Kim-1 is a transmembrane glycoprotein that is not detectable in normal kidney, but is up-regulated and shed into the urine following ischemic or nephrotoxic injury. Recent studies utilizing a sub-chronic model of Cd exposure in the rat have shown that Kim-1 is an early urinary marker of Cd-induced kidney injury. Kim-1 was detected in the urine 4-5 weeks before the onset of proteinuria and 1-3 weeks before the appearance of urinary metallothionein and Clara cell protein 16, which are standard markers of Cd nephrotoxicity. In the present study, we have compared the time course for the appearance of Kim-1 in the urine with the time course for the appearance of alpha glutathione-S-transferase (α-GST), N-acetyl-β-d-glucose amidase (NAG) and Cd, each of which have been used or proposed as urinary markers of Cd nephrotoxicity. Adult male Sprague-Dawley rats were given daily subcutaneous injections of 0.6 mg (5.36 μmoles)/kg Cd, 5 days per week for up to 12 weeks. One day each week, 24 h urine samples were collected and analyzed for protein, creatinine and the various markers. The results showed that significant levels of Kim-1 appeared in the urine as early as 6 weeks into the treatment protocol and then continued to rise for the remainder of the 12 week treatment period. By contrast, significant levels of α-GST and NAG did not appear in the urine until 8 and 12 weeks, respectively, while proteinuria was not evident until 10 weeks. The urinary excretion of Cd was below the level of detection until week 4 and then showed a slow, linear increase over the next 6 weeks before increasing markedly between weeks 10 and 12. These results provide additional evidence that Kim-1 is a sensitive biomarker of the early stages of Cd-induced proximal tubule injury.     

Ethanol consumption modifies the body turnover of cadmium: a study in a rat model of human exposure

Ethanol (Et) abusers may also be exposed to excessive amounts of cadmium (Cd). Thus, the study was aimed at estimating the influence of Et on the body turnover of Cd in a rat model reflecting excessive alcohol consumption in humans chronically exposed to moderate and relatively high levels of this metal. For this purpose, Cd apparent absorption, retention in the body and concentration in the blood, stomach, duodenum, liver, kidney, spleen, brain, heart, testis and femur as well as its fecal and urinary excretion in the rats exposed to 5 and 50mg Cd l^?1 (in drinking water; for 16 weeks from the fifth week of the animal's life) and/or Et (5 g kg^?1 b.w. per 24 h, by oral gavage; for 12 weeks from the ninth week of life) were estimated. Moreover, the duodenal, liver and kidney pool of the nonmetallothionein (Mt)‐bound Cd was evaluated. The administration of Et during the exposure to 5 or 50mg Cd l^?1 increased Cd accumulation in the gastrointestinal tract and its urinary excretion, and decreased Cd concentration in the blood, femur and numerous soft tissues (including liver and kidney) as well as the total pool of this metal in internal organs. Et modified or not the pool of the non‐Mt‐bound Cd, depending on the level of treatment with this metal. The results show that excessive Et consumption during Cd exposure may decrease the body burden of this metal, at least partly, by its lower absorption and increased urinary excretion. Based on this study, it can be concluded that Cd concentration in the blood and tissues of alcohol abusers chronically exposed to moderate and relatively high levels of this metal may be lower, whereas its urinary excretion is higher than in their nondrinking counterparts. However, since Et is toxic itself, the decreased body burden of Cd owing to alcohol consumption does not allow for the conclusion that the risk of health damage may be lower at co‐exposure to these xenobiotics. In a further study, it will be investigated how the Et‐induced changes in the body status of Cd influence the effects of its toxic action. Copyright © 2012 John Wiley & Sons, Ltd.     

Cadmium absorption in mice: effects of broiling on bioavailability of cadmium in foods of animal origin

The absorption and organ distribution of organic Cd from raw and broiled horse kidney was compared to that of CdCl2 at two dose levels (0.05 and 3 mg Cd/kg feed) in a feeding study in mice. The high Cd concentration in the horse kidney (raw 112 mg/kg; broiled 53 mg/kg) made it possible to mix kidney into mouse feed without marked effects on the composition of the feed. The weight of the mice, feed and water consumption, and Cd levels in the feed were determined once a week. After 9 wk of exposure, the liver and kidneys of the mice were sampled and Cd was analyzed. The Cd concentration in horse kidney was halved by broiling, and the content of soluble Cd decreased from 12% in raw kidney to 5% in broiled kidney. The majority of the soluble Cd was associated with proteins with the same molecular weight as metallothionein (MT) in both raw and broiled kidney. Broiling of the kidney had no marked effect on the fractional accumulation of organic Cd in mice. The fractional accumulation of inorganic CdCl2, on the other hand, was significantly higher than that of organic Cd in the low dose groups but not in the high dose groups. The ratio between Cd accumulation in kidney and that in liver was higher in the group receiving raw kidney compared to the ratio in the group receiving CdCl2 at both the high and low exposure levels. This indicates that the raw kidney contained a Cd form that was more preferentially distributed to the kidneys.     

Indirect and lactation-associated changes in renal alkaline phosphatase of newborn rats prenatally exposed to cadmium chloride.

Pregnant Sprague-Dawley rats were intraperitoneally injected with physiological saline solution (vehicle) or cadmium chloride (CdCl2) at 2.5 mg kg-1 body wt. on days 8, 10, 12 and 14 of gestation. Offspring were examined for renal alkaline phosphatase activity (ALP) on postnatal days (PND) 3 and 12, and for kidney metallothionein (MTh) and for liver, kidney and entire gastrointestinal tract 109Cd content at birth and on PND 3 and 12. No effects were observed on neonatal survival or on body, liver and kidney weights of pups up to PND 12. Newborns born and fed by mothers exposed to CdCl2 during pregnancy exhibited a significant decrease in ALP activity on PND 3. Conversely, no significant changes were observed in newborns lactated by surrogate non-treated mothers. Renal MTh increased with age but was not influenced by maternal treatment. Traces of 109Cd were present in the liver at birth (5-7 ng). Thereafter, 109Cd was mainly found in the gastrointestinal tract of newborns lactated by their biological mothers (610-690 ng on PND 12), with a marginal uptake in the liver (10-12 ng on PND 12). 109Cd was not detectable in the kidneys at any age (less than 4 ng). These results show that prenatal exposure to Cd cannot be the sole aetiological agent in the induction of the subtle and transitory changes in renal biochemistry observed in offspring born and fed by female rats intraperitoneally injected with 2.5 mg CdCl2 kg-1 body wt. on days 8, 10, 12 and 14 of gestation. The results also contradict the role of a direct effect on the kidney.     

Expression of hsp 90 in the human kidney and in proximal tubule cells exposed to heat,sodium arsenite and cadmium chloride

The expression of heat shock protein (hsp) 90alpha and beta mRNA and protein were determined in the human kidney and in human proximal tubule (HPT) cells exposed to lethal and sub-lethal concentrations of Cd(+2) under both acute and extended conditions of exposure. Using immunohistochemical analysis, it was demonstrated that hsp 90 was widely distributed in the human adult and fetal kidney. Moderate to strong staining was observed in the straight portions of the distal and proximal tubules, the distal convoluted tubule, the collecting ducts and the parietal epithelium of Bowmans capsule in the glomerulus. Moderate staining was observed in the proximal convoluted tubule of the cortex and the thick loops of Henle within the medulla. In addition, the fetal kidney demonstrated strong staining of the blastema, the 'S-shaped' bodies, and the developing glomeruli. Analysis of hsp 90alpha and beta mRNA expression in total RNA isolated from in situ microdissected proximal tubules or HPT cells demonstrated similar expression levels of both the alpha and beta isoforms in this tubule segment. It was demonstrated that HPT cells exhibited the classic heat shock response when subjected to a physical (heat) or chemical stress (NaAsO(2)). Heat stress, elevated temperature at 42.5 degrees C for 1 h, caused a modest increase in both hsp 90alpha and beta mRNA and protein. Similar results were obtained when the cells were subjected to a classic chemical stress of exposure to 100 microM NaAsO(2) for 4 h. In contrast, acute exposure of HPT cells to 53.4 microM CdCl(2) for 4 h resulted in no consistent increase in hsp 90alpha and beta mRNA or protein. Chronic exposure to Cd(+2) likewise failed to increase either hsp 90 mRNA or protein expression, even at concentrations of Cd(+2) that were lethal to the cells during the time course. This study shows that the HPT has a high basal expression of hsp 90, which is not induced by Cd(+2) exposure.     

Exogenous metallothionein and renal toxicity of cadmium and mercury in rats.

The relative tissue distribution and toxicity of cadmium (Cd) and mercury (Hg) in the liver and kidneys of rats when the metals are administered as either inorganic salts or complexed with MT were studied. Male Sprague-Dawley rats were injected (i.v.) with Cd or Hg inorganic salt of chloride or in a complex of MT at a dose of 0.3 mg/kg body weight. The concentration of MT and metals in plasma and urine was monitored for 7 days, at the end of which the rats were killed. Injection of both HgCl2 and Hg-MT induced the synthesis of MT only in the kidney but not in the liver, whereas CdCl2 and Cd-MT injections induced MT synthesis in both liver and kidney, respectively. Plasma MT levels increased 3 days after CdCl2 but not after HgCl2 injection, suggesting that hepatic MT may be an important source of plasma MT under our experimental conditions. Renal toxicity was observed morphologically and by an increase in blood urea nitrogen, plasma creatinine, proteinuria in rats injected with Cd-MT and both forms of Hg. Urinary MT excretion was significantly elevated in Cd-MT injected rats compared with those injected with CdCl2. However, HgCl2 and Hg-MT injected rats showed no significant difference in urinary MT excretion. The magnitude in the renal accumulation of Hg is similar after the administration of Hg-MT or HgCl2, but our findings suggest that the site of epithelial injury may be different. Injury effects of Hg-MT localized mainly in the terminal portions of the proximal convoluted tubule and the initial portions of the proximal straight tubule whereas inorganic Hg caused necrosis in pars recta segments of the proximal tubule.     

Beta 2-microglobulin levels in serum and urine of cadmium exposed rabbits

Male rabbits were exposed to cadmium during 16 weeks by subcutaneous injections of either 0.25 mg or 0.5 md Cd as cadmium chloride per kg body weight 3 times per week. beta 2-microglobulin (beta 2-m) and creatinine in serum, cadmium in blood, as well as total protein, creatinine, beta 2-m and cadmium in urine were determined before exposure and after 3 and 7 weeks of exposure. Measurements were also made at 19 weeks, 3 weeks after the last exposure. During exposure, there was a slight increase in the serum beta 2-m/creatinine ratio among rabbits with the highest exposure, while no effect of the cadmium burden could be observed once exposure had ceased. Urinary excretion of beta 2-m was related to urinary pH, which appeared to be the case also for excretion of total protein. In the high exposure group, a significant increase in urinary beta 2-m excretion, indicative of renal tubular dysfunction was seen after 7 weeks of exposure. This was, however, not related to serum beta 2-m levels. It was concluded that before renal damage has occurred even heavy cadmium exposure has very little influence on serum beta 2-m levels.