Metallothionein induction in the liver, kidney, heart and aorta of cadmium and isoproterenol treated rats

Metallothionein (MT), induced in different organs in response to heavy metals and oxidative conditions, exerts antioxidant properties and thus could be implicated in cardiovascular physiopathology. The aim of this study was to investigate the capacity of cadmium (Cd) and isoproterenol to induce in vivo MT not only in rat liver and kidneys but also in heart and aorta. Tissue MT levels, catalase (CAT) and glutathione peroxidase (GPX) activities were assayed at different times after Cd or isoproterenol injection. Cd induced a dose-dependent induction of MT with a higher response in the liver than in the kidney, aorta and heart. The hepatic increase was early (12 h) and maintained (72 h), whereas the elevation was maximal around 48 h for the other organs. Isoproterenol induced a transient (12 h) hepatic and a biphasic (12 and 36 h) renal and cardiac increase. CAT activity was decreased in the liver and increased in the heart with the higher Cd doses. Isoproterenol increased the cardiac GPX activity. In conclusion, the results demonstrate that MT can be induced in rat liver and kidneys but also in heart after a Cd or isoproterenol injection. This enhancement of cardiac and vascular MT levels could be used to study the potential protective effect of MT in cardiovascular diseases.     

Effect of partial hepatectomy on hepatic metallothionein and glutathione levels and cadmium distribution in different tissues

The changes in hepatic metallothionein (MT) and glutathione levels and cadmium distribution were investigated 72 hr after a subcutaneous administration of 1.5 $\text{mg Cd}{}^{\mathrm{2+}}\text{kg}$ as CdCl₂H₂O to normal and partially hepatectomized rats. Partial hepatectomy had no effect on native metallothionein content. Cadmium and MT content in livers of partially hepatectomized rats were comparatively lower than in those of intact rats. However, cadmium content significantly increased in other organs of partially hepatectomized rats. Cadmium exposure decreased glutathione level only in intact rats. The effects of partial hepatectomy and regeneration on hepatic MT level and metal distribution are discussed.     

Metallothionein-null mice are more sensitive than wild-type mice to liver injury induced by repeated exposure to cadmium.

Liver is a major target organ of cadmium (Cd) toxicity following acute and chronic exposure. Metallothionein (MT), a low-molecular-weight, cysteine-rich, metal-binding protein has been shown to play an important role in protection against acute Cd-induced liver injury. This study investigates the role of MT in liver injury induced by repeated exposure to Cd. Wild-type and MT-I/II knockout (MT I/II-null) mice were injected sc with a wide range of CdCl(2) doses, 6 times/week, for up to 10 weeks, and their hepatic Cd content, hepatic MT concentration, and liver injury were examined. Repeated administration of CdCl(2) produced acute and nonspecific chronic inflammation in the parenchyma and portal tracts and around central veins. Higher doses produced granulomatous inflammation and proliferating nodules in liver parenchyma. Apoptosis and mitosis occurred concomitantly in liver following repeated Cd exposure, whereas necrosis was mild. As a result, significant elevation of serum enzyme levels was not observed. In wild-type mice, hepatic Cd concentration increased in a dose- and time-dependent manner, reaching 400 microgram/g liver, along with 150-fold increases in hepatic MT concentrations, the latter reaching 1200 microgram/g liver. In contrast, in MT I/II-null mice, hepatic Cd concentrations were about 10 microgram/g liver. Despite the lower accumulation of Cd in livers of MT I/II-null mice, the maximum tolerated dose of Cd was one-eighth lower than that for wild-type mice at 10 weeks, and liver injury was more pronounced in the MT I/II-null mice, as evidenced by increases in liver/body weight ratios and histopathological analyses. In conclusion, these data indicate that (1) nonspecific chronic inflammation, granulomatous inflammation, apoptosis, liver cell regeneration, and presumably, preneoplastic proliferating nodules are major features of liver injury induced by repeated Cd exposure, and (2) intracellular MT is an important protein protecting against this Cd-induced liver injury.     

Early life inorganic lead exposure induces testicular teratoma and renal and urinary bladder preneoplasia in adult metallothionein-knockout mice but not in wild type mice

Inorganic lead compounds are carcinogenic in animals and have carcinogenic potential in humans. In mice, lead (Pb) is a transplacental carcinogen in the kidney. Metallothionein (MT) is a metal-binding protein that can reduce the toxicity of various metals, including Pb, either by direct sequestration or as an antioxidant for metals that generate reactive oxygen species. Although MT appears to reduce Pb carcinogenicity in adult mice it is unknown how MT deficiency may affect Pb carcinogenicity from early life exposure. Thus, groups (n = 10) of pregnant MT-I/II double knockout (MT-null) or 129/SVJ MT wild type (WT) mice were exposed to Pb acetate in the drinking water (0, 2000, 4000 ppm Pb) from gestation day 8 through birth and during lactation. Maternal drinking water Pb exposure continued to wean at 4 weeks of age and the male offspring were then directly exposed to Pb until 8 weeks of age and observed until 2 years old. High dose (4000 ppm) but not low dose (2000 ppm) Pb reduced survival in the latter part of the study in both MT-null and WT mice. In MT-null mice, but not WT, early life Pb exposure caused a dose-related increase in testicular teratomas, to a maximum incidence of 28% compared to control (4%). Pb-induced renal cystic hyperplasia, considered preneoplastic, was a prominent occurrence in MT-null mice but nearly absent in WT mice. Pb dose-related increases in renal cystic hyperplasia occurred in adult MT-null with early life exposure with maximal incidence of 52%. Pb-treated MT-null mice also showed dose-related increases in urinary bladder hyperplasia with occasional papilloma that were absent in WT mice. Thus, MT deficiency made mice more sensitive to early life Pb exposure with regard to testes tumors, and renal and urinary bladder preneoplastic lesions.     

Involvement of intestinal calcium transporter 1 and metallothionein in cadmium accumulation in the liver and kidney of mice fed a low-calcium diet

Essential metals can affect the metabolism of nonessential metals. Calcium (Ca) is an essential mineral that is commonly lacking in the diet. When we fed 5-week-old male mice for 4 weeks on a purified diet containing 0.005% Ca (CaDF mice), the Ca concentration in the plasma, liver and kidneys did not decreased. Cd accumulation increased in the liver and kidneys of CaDF mice given 1mg/kg Cd orally each day for 5 days, but not in those given intraperitoneal injections of Cd or Cd-metallothionein (Cd-MT). The zinc (Zn) concentration increased significantly in the intestinal cytosol and plasma during the time the mice were fed the low-Ca diet, and expression of both MT-1 and ZnT-1 sharply increased with a similar time course. Intestinal mRNA expression of CaT1, a Ca transporter, was more than 10 times higher in CaDF mice than in controls, although expression of other transporters, including DMT1, decreased in CaDF mice. These results suggest that CaT1 may stimulate the intestinal absorption of Cd and Zn, and some Cd may be distributed to the kidneys along with MT induced by Zn.     

Metallothionein production: similar responsiveness of avian liver and kidney to chronic cadmium administration

The accumulation of hepatic and renal Cd, Zn, Cu, and metallothionein (MT) was investigated in ringed turtle doves (Streptopelia risoria) chronically exposed to 3 different concentrations of dietary Cd. When only tissue-Cd was considered as an inducer of MT, kidney was found to be 35% as responsive as liver in producing MT. However, when all potentially relevant inducing metals (Cd + Zn + Cu) were taken into account, kidney was found to be 85% as responsive as liver. The greater production of MT/mol Cd in liver was accounted for mainly by a greater co-accumulation of Zn/mol Cd in liver than in kidney. We conclude that the apparent tissue specificity in expression of MT may be overestimated by failure to consider fluctuations in multiple inducers. Variability in tissue-MT concentrations after chronic dietary Cd administration is best accounted for by a consideration of tissue-Cd, -Zn, and -Cu, rather than tissue-Cd alone.     

Metallothionein protects against doxorubicin-induced cardiomyopathy through inhibition of superoxide generation and related nitrosative impairment

Metallothionein (MT) has been shown to be an effective protector against DOX-induced cardiomyopathy, however the involved precise mechanisms are still unknown. The present study was undertaken to clarify whether the inhibition of superoxide generation and related nitrosative damage were involved in the metallothionein attenuation of DOX-induced cardiac injury. MT-I/II null (MT-/-) mice and corresponding wild-type mice (MT+/+) were pretreated with either saline or zinc (300 micromol/kg, s.c., once a day for 2 days) prior to a single dose of DOX (15 mg/kg, i.p.) or equal volume of saline. Animals were sacrificed on the 4th day after DOX administration and samples were collected for further analyses. DOX caused remarkable cardiac damage in both MT+/+ and MT-/- mice as demonstrated by biochemical and histopathological alterations. Zinc pretreatment significantly increased the cardiac MT levels and therefore inhibited the cardiac toxic effects of DOX only in MT+/+ mice, but not in MT-/- mice. Furthermore, elevated formation of superoxide and peroxynitrite were obviously observed after DOX treatment, while these elevation were prevented by MT induction by zinc in MT+/+ mice, but not in MT-/- mice. These findings suggest that metallothionein induction by zinc exhibits protective effects on the cardiac toxicology of DOX, which might be mediated through the prevention of superoxide generation and related nitrosative impairment.     

Production of low molecular weight cadmium-binding proteins in rabbit lung following exposure to cadmium chloride

Low molecular weight cadmium-binding proteins were studied in lung tissue from rabbits exposed to aerosols of CdCl₂. Lungs obtained from animals exposed by inhalation to aerosols of 800 or 1600 μ/m³ CdCl₂ for 2-hr periods/day, every other day for a 5-day period, were found to contain at least three low molecular weight cadmium-binding proteins, two of which were similar electrophoretically and spectrally to rabbit liver metallothionein. The third protein(s), which accounted for the majority of the cadmium in the soluble fraction of the tissue, did not bind to an anionic exchange gel and did not appear to be a polymerized form of metallothionein. Translocation studies of lung cadmium suggest a long half-life for cadmium in lung tissue following inhalation exposure, due perhaps to the high affinity of cadmium for specific lung cadmium-binding proteins. A small but significant redistribution of lung cadmium did occur to both kidney and liver tissue with time.     

Protective effects of selenium (Se) and zinc (Zn) on cadmium (Cd) toxicity in the liver and kidney of the rat: histology and Cd accumulation

To assess the co-effect of Se and Zn on Cd accumulation in the liver and kidney and on their histology, male rats were exposed either to Cd, Cd+Zn, Cd+Se, or Cd+Zn+Se in their drinking water, during 35 days. Exposure to Cd resulted in its accumulation in the liver and kidney. In the Cd-Zn and Cd-Zn-Se groups, Cd contents in the two organs were significantly (p < 0.01) higher than those in the Cd group. Se did not induce any significant difference in hepatic and renal concentrations of Cd in comparison to Cd-treated group. Light microscopic examination indicated severe histological changes in the two organs under Cd influence. Se or Zn partially alleviated the damage observed in the liver. The same effect was remarked in the kidney with Se, but no differences in the renal histological structure have been observed between the Zn-Cd and the control groups. With Se and Zn simultaneous treatment during Cd exposure, the observed morphological changes had practically disappeared from the liver, but were only reduced in the kidney. CONCLUSION: Se and Zn can have a cooperative effect in the protection against Cd-induced structural damage in the liver but not in the kidney.     

Cadmium inhalation exposure estimates: their significance with respect to kidney and liver cadmium burden

Cadmium exposure histories based on employment records, area monitoring techniques, and personal sampling data were obtained for 82 industrially exposed workers. From these data, a time-weighted cumulative exposure index (TWE) was calculated for each worker by multiplying the length of time (ti) in a given work area by the estimated exposure conditions for that area and year (Ei) and then summing these values for the total exposure history TWE = sigma iEiti The cadmium body burden for each worker was measured directly by the in vivo prompt-gamma neutron activation technique. The cadmium content of the left kidney and the liver were measured. For the actively employed workers, a significant correlation (r = 0.70, p less than 0.001) was observed between the exposure index (TWE) and the liver cadmium burden. Furthermore, whenever the worker's liver burden exceeded 40 ppm and the exposure index exceeded 400-500 micrograms/m3 X yr, there was evidence of renal abnormalities (usually elevated urinary beta 2-microglobulin). The highest correlation (r = 0.83, p less than 0.001) was obtained between the kidney cadmium burden data and the exposure index for the active workers without evidence of kidney dysfunction. The percentage of workers with renal abnormalities was found to increase as the exposure index increased. When this relationship was examined using linear logistic regression analysis, the following model was indicated: logit p = 1.24 In TWE--8.34 where p is the individual worker's probability of being classified as having renal dysfunction.     

Detoxification/toxification of cadmium in scorpionfish (Scorpaena guttata): Acute exposure

Scorpionfish were exposed to sea water (control), sea water dosed with 25 mg Cd/l (0.4 96-h LC₅₀), and 50 mg Cd/l (0.8 96-h LC₅₀) as CdCl₂ for 96 h. These fish were then analyzed to determine the effects of near-lethal Cd exposure on mechanisms of detoxification by metallothionein and the potential for toxification of enzymes in several tissues. In scorpionfish exposed to 50 mg Cd/l, the highest concentrations of metallothionein pool Cd occurred in liver ($\text{532 ± 68 μ}\text{mol/wet}\text{kg; mean}\text{±}\text{sd}\text{; n=3}$) followed by intestine (151 ± 55 μmol/wet kg), gills (27.1 ± 9.6 μmol/wet kg) and then kidney (26.8 ± 6.1 μmol/wet kg). In these same fish, the highest concentrations of enzyme pool Cd occurred in kidney (65 ± 41 μmol/wet kg), followed by gills (33.4 ± 2.2 μmol/wet kg), intestine (21 ± 12 μmol/wet kg) and then liver (3.9 ± 1.6 μmol/wet kg). Based upon this partitioning of Cd, the order of sensitivity of tissues, at near-lethal Cd concentrations, would appear to be kidney > gills > intestine > liver.     

Transport pathways for cadmium in the intestine and kidney proximal tubule: Focus on the interaction with essential metals

Cadmium (Cd) is a toxic metal with a propensity to accumulate in the proximal tubules cells (PTC) of the kidney where it can lead to tubular dysfunction and eventually renal failure. Although Cd²⁺-induced nephrotoxicity has been well described there is still uncertainty about how this metal gains entry into these cells to induce toxicity. As a non-essential metal, specific transport proteins for Cd are unlikely to exist. Rather transport proteins/channels used by essential metals (iron, zinc, calcium) are thought to be responsible. When these dietary essential metals are in short supply and deficiencies develop, Cd absorption and toxicity are enhanced. This is primarily due to increased expression of essential metal transport proteins such as divalent metal transporter 1 (DMT1) which can transport Cd in the intestine and enhance toxicity in the kidney. The zinc/bicarbonate sympoters ZIP8 and 14 are expressed at the apical membrane of enterocytes and PTC, and can transport Cd into cells. TRPV5 and 6 are major transporters for calcium in intestine and kidney and may be involved in Cd transport in these locations. Cd in the circulation is bound to proteins such as metallothioneins (MT) which are readily filtered. Two multiligand receptors, megalin and cubulin, reabsorb filtered proteins including albumin and MT by the process of receptor-mediated endocytosis. This review summarises the transport pathways for Cd in the intestine and kidney proximal tubule focusing in particular at how Cd uses essential metal transport processes to gain entry to the circulation and the kidney.     

Induction of Cd-metallothionein in cadmium exposed monkeys under different nutritional stresses

Induction of cadmium metallothionein (MT) in chronic cadmium exposure in Rhesus monkeys undergoing protein calorie malnutrition (PCM) and calcium deficiency has been studied. A positive correlation between cadmium content and levels of MT in kidney, liver, intestine, testis, heart and lung, has been observed. The accumulation of cadmium and synthesis of MT in these tissues was highest in monkeys subjected to cadmium exposure during calcium deficiency. Although more of cadmium is directed towards kidneys of calcium-deficient monkeys the MT-inducing ability of kidney is lower than that of liver. Monkeys on PCM diet also showed enhanced accumulation of cadmium and MT as compared to those on normal diet during cadmium exposure.     

镉、铅、汞、砷和铬致肾损伤机制的研究进展

重金属镉、铅、汞、砷和铬是最常见的环境和职业危害因素。不同的重金属对人体损伤的表现不尽相同,但都具有肾损伤特性。多年来,国内外学者对这些重金属的肾损伤机制进行了较多的研究。本文综述了其氧化应激、细胞凋亡、金属硫蛋白、生物膜损伤和细胞内Ca²⁺平衡失调的几种肾损伤机制。     

Cadmium accumulation and subcellular distribution in relation to cadmium chloride induced cytotoxicity in vitro

A bovine kidney cell culture system was used to assess what relationship cadmium (Cd) uptake and subcellular distribution had to cadmium chloride induced cytotoxicity. Twenty-four hour incubation with 0.1–10 μM Cd elicited 0–90% cytotoxicity. Fifty percent cytotoxicity was estimated to result from 0.8 μM Cd. A concentration-related Cd accumulation paralleled the cytotoxicity profile. The time-course for Cd accumulation was linear for the first 6 h of exposure and plateaued by 18 h post-exposure. When the degree of cytotoxicity was compared with the cellular Cd burden at 24 h post-treatment a least-squares linear regression analysis (r = 0.93) indicated a direct relationship. Subcellular distribution studies indicated greater than 90% Cd recovery from the soluble supernatant (105 000 g) at all levels of cytotoxicity studied. Metallothionein sequestered less than 25% of the cellular Cd. As a result of the correlation of the degree of cytotoxicity with the cellular Cd burden and the independence of subcellular distribution from cytotoxicity, a cumulative mechanism of toxicity for Cd in MDBK cells was suggested.     

Glutathione depletion and oxidative damage in mitochondria following exposure to cadmium in rat liver and kidney.

The dose-dependent effects of cadmium (Cd) on mitochondria and post-mitochondrial supernatant (PMS) of liver and kidney were investigated in adult male albino rats. Two groups of rats were injected intraperitoneally with 0.1 mg Cd/kg body weight and 1 mg/kg body weight, respectively, for a period of 3 months (5 days/week). This resulted in a significant decrease in total glutathione (GSH) levels, irrespective of the doses, in mitochondrial as well as in PMS fractions of liver and kidney. In contrast, end products of lipid and protein were significantly increased in a dose-dependent manner in subcellular fractions of liver and kidney. These results suggest that the depletion of tissue glutathione levels is not a primary reason of the observed oxidative damage in liver and kidney caused by Cd.     

Correlation between environmental low-dose cadmium exposure and early kidney damage: A comparative study in an industrial zone vs. a living quarter in Shanghai,China

To investigate heavy metal exposure in an industrial zone vs. a living quarter in Shanghai and explore the relationship between the heavy metal source and urine cadmium (Cd) and early kidney damage. Blood lead and urine Cd, manganese (Mn), mercury (Hg), arsenic (As) and EKD indexes were compared between residents in Exposure group (n = 168) and Control group (n = 168). It was found that PM_2.5 level in Exposure group was significantly higher than that in Control group, and serum Cys-C and urine Cd, NAG, mAlb, KIM-1 and Cd-MT levels in Exposure group were also significantly higher than those in Control group, suggesting that differences in urine Cd and heavy metal levels between the residents of the two groups may be due to different PM_2.5 concentrations in the environments of the two areas. Cd accumulation within the human body can induce kidney damage, probably through its potential hazard to the proximal tubular epithelial cells.     

Gadolinium chloride pretreatment prevents cadmium chloride-induced liver damage in both wild-type and MT-null mice

The heavy metal cadmium (Cd) causes hepatotoxicity upon acute administration. Kupffer cells, the resident macrophages of the liver, have been suggested to play a role in Cd-induced hepatotoxicity. Gadolinium chloride (GdCl3) may prevent Cd-induced hepatotoxicity by suppressing Kupffer cells. However, GdCl3 also induces the Cd-binding protein, metallothionein (MT). Therefore, this study was conducted to determine whether GdCl3 prevents Cd-induced hepatotoxicity via the induction of MT. Hepatic MT and Kupffer cell counts were analyzed 24 h after wild-type (WT) mice were administered saline or 10, 30, or 60 mg GdCl3/kg. GdCl3 induced MT in a dose-dependent manner without affecting nonprotein sulfhydryl content. All examined doses of GdCl3 were effective at eliminating Kupffer cells from the liver. To examine the hepatoprotective effects of GdCl3, WT and MT-null mice were pretreated with saline or 10, 30, or 60 mg GdCl3 24 h prior to a hepatotoxic dose of Cd (2.5 mg Cd/kg). Blood and livers were removed 16 h later and analyzed for hepatotoxicity as well as MT, Cd, and Kupffer cell content. Hepatotoxicity was alleviated in both WT and MT-null mice that were pretreated with 30 or 60 mg GdCl3/kg, indicating that MT induction is not required for the hepatoprotective effects of GdCl3. Hepatic Cd content was not decreased by GdCl3, demonstrating that GdCl3 does not negatively affect Cd distribution to the liver. Kupffer cells were depleted at all three doses of GdCl3, whereas hepatoprotection was only observed at doses of 30 and 60 mg GdCl3/kg. This does not rule out Kupffer cells in the mechanism of Cd-induced hepatotoxicity, but it does suggest that GdCl3 exerts hepatoprotective effects on the liver aside from depleting Kupffer cells. In summary, these data substantially rule out MT induction and decrease the importance of Kupffer cells as mechanisms of GdCl3-induced protection from Cd-induced hepatotoxicity.     

Effect of dipyridamole with or without aspirin on urine protein excretion in patients with membranous glomerulonephritis

Summary The antiproteinuric effect of the antiplatelet agent dipyridamole has been assessed after inhibiton of thromboxane B₂ (TxB₂) synthesis in 8 patients with confirmed membranous glomerulonephritis. There were three study periods, each of 30 days, and 45 days apart, namely a washout period, treatment with dipyridamole 300 mg/d, and dipyridamole 225 mg/d plus aspirin 150 mg/d. On Days 1 and 30 of each study period serum and urine creatinine, 24-h excretion of protein, creatinine clearance, platelet aggregometry on whole blood and serum TxB₂ were measured. Treatment with dipyridamole alone or with aspirin produced significant inhibition of platelet aggregation and a fall in 24-h protein excretion; the latter amounted to 54% with dipyridamole alone and 56 % with dipyridamole plus aspirin (NS). Dipyridamole plus aspirin caused an 82 % reduction in serum TxB₂.