Kidney Metallothionein Research Articles

Supplemental Dietary Cystine Elevates Kidney Metallothionein in Rats by a Mechanism Involving Altered Zinc Metabolism

Dietary sulfur-containing amino acids influence zinc and copper status. This study was conducted to investigate the relationship between the status of these elements and tissue metailothionein in rats fed diets supplemented with sulfur-containing amino acids. In a series of experiments, a diet containing 100 g casein/kg diet was unsupplemented or supplemented with L-cystine (3–50 g/kg diet) or L-methionine (3 or 30 g/kg diet). Kidney concentrations of zinc and copper in rats fed the diet supplemented with high levels of cystine (25 or 50 g/kg) were significantly higher than those in rats fed the unsupplemented diet. Kidney concentrations of metallothionein and metallothionein mRNA were also significantly higher in rats fed cystine-supplemented diets. There was a correlation (r = 0.838, P < 0.01) between the levels of zinc and metallothionein in kidney of rats fed the diets with different levels of cystine and zinc. However, in the rats fed the diets with different levels of cystine and copper, the correlation was not as strong (r = 0.587, P < 0.01). The changes in kidney metallothionein concentration due to the addition of 3 or 30 g/kg cystine were associated with parallel changes in serum zinc concentration and in apparent absorption of zinc, but not in serum copper concentration or apparent absorption of copper. Addition of 3 or 30 g methionine/kg diet to the diet did not affect kidney concentrations of metallothionein or zinc. These results indicate that supplementation of cystine to the diet can induce kidney metallothionein through a mechanism involving altered zinc metabolism.

The Herbal Constituents in An-Gong-Niu-Huang Wan (AGNH) Protect against Cinnabar- and Realgar-Induced Hepatorenal Toxicity and Accumulations of Mercury and Arsenic in Mice.

An-Gong-Niu-Huang Wan (AGNH) has been a well-known cinnabar- and realgar-containing compound recipe for cerebral diseases. Unfortunately, its clinical practice is often restrained by the specific hepatorenal toxicity of cinnabar and realgar (C + R). In previous research studies, we have found that the antioxidative and anti-inflammatory effects of its herbal constituents could mitigate the risks from the toxicity. The underlying detoxification mechanisms are still unsolved. The present study investigated the protective effects of AGNH's herbal constituents on hepatorenal injury induced by C + R. For the mice treated with C + R, the increased expression levels of sensitive biomarkers of metal exposure and hepatorenal toxicity, including metallothionein (MT) in both hepatorenal tissues and kidney induced molecule-1 (KIM-1) in the kidney, were simultaneously reduced when C + R coadministered with other herbal medicines. In addition, the contents of trivalent As (AsIII), pentavalent As (Asv), and mercury (Hg) in hepatorenal tissues of mice were also significantly reduced benefiting from the herbal constituents in AGNH. Further mechanism studies showed that the herbal constituents in AGNH could downregulate the expressions of uptake transporters (AQP9 and OAT1) and upregulate the expressions of efflux transporters (P-gp, MRP2, and MRP4) in mice intoxicated by C + R. Our results suggested that AGNH's herbal constituents protect the body against C + R-induced hepatorenal toxicity and accumulations of Hg and As, which could be associated with the reestablishment of heavy metal homeostasis and the detoxification system.

Effects of corn supplementation on the antioxidant activity, selected minerals, and gene expression of selenoprotein and metallothionein in serum, liver, and kidney of sheep-fed palm kernel cake: urea-treated rice straw diets.

This study aimed to determine influence of corn inclusion on glutathion peroxidase (GPx) activity, selected minerals concentration, and gene expression in sheep-fed palm kernel cake (PKC) and urea-treated rice straw. Twenty-seven of Dorper sheep were divided into three groups and fed a basal diet of (20% rice straw and 80% concentrate) with addition of ground corn at either 0% (T1), 5% (T2), or 10% (T3), respectively. After 120days feeding trial, all animals were slaughtered and tissue samples of kidney, liver, and muscles were taken for enzyme and mineral analyses. The results showed that Cu concentration in the liver was lower treatment T3 compared to the control and T2. The serum activity of GPx was higher in T2 than in T3 at day 120 of experiment. Serum malondialdehyde (MDA) concentrations decreased at day 80 in sheep on T3, whereas MDA of liver increased linearly with increasing corn supplementation. The qRT-PCR analyses revealed significant up-regulation of ATP7A and MIa genes in T3, while hepatic Cu/Zn SOD, GPx1, and GPx4 mRNA showed a higher expression in lamb hepatocytes in T3 compared to those on T1. Present study results suggest that feeding PKC as basal diet can increase antioxidant activity, but cause liver dysfunction in sheep. Inclusion corn was found to regulate transcriptional levels of the GPx family and metallothionein genes. These genes may play a role in the antioxidant protection response and reduce incidence of toxicity associated with Cu.

Lead accumulation and metallothionein content in female rats of different ages and generations after daily intake of Pb-contaminated food.

Female Wistar rats of different ages (45, 90 and 140 days) and generations (mothers and offspring) were fed a feed containing 2.0mg of Pb kg-1 daily from weaning and the Pb accumulation was determined in different organs and in maternal milk, in addition metallothioneins (MTs) content was determined in the liver and kidneys. The results showed that Pb accumulation exhibited the following pattern: bone>liver>kidney>gut>blood cells>muscle>brain>ovary. Bones accumulated the most Pb in all animals, with its concentration increasing with age and prenatal exposure. Pb accumulation in the liver, kidney and blood cells, did not follow a consistent pattern with increasing age and our data did not indicate a relationship between the presence of MTs in liver and kidney and metal accumulation in these organs. However, in the offspring and with increasing age, Pb accumulated in more organs. Mothers fed with Pb produced contaminated milk, exposing their offspring to the metal via nursing Thus, increasing age and prenatal exposure increases susceptibility to Pb toxicity-induced damage.

Carbon Tetrachloride-Induced Nephrotoxicity in Mice Is Prevented by Pretreatment with Zinc Sulfate.

Carbon tetrachloride (CCl4) is commonly used as a chemical inducer of experimental liver injury. In addition, many studies showed that CCl4 can induce kidney damage. In the current study, we evaluated the protective effect of zinc (Zn) against CCl4-induced nephrotoxicity. We hypothesized that this protective effect would result from the ability of Zn to serve as an inducer of metallothionein (MT), a known endogenous scavenger of free radicals. We administered Zn (as ZnSO4) 50 mg/kg subcutaneously once daily for 3 successive days prior to a single intraperitoneal administration of CCl4 4 g/kg in male ddY mice. Our results showed that Zn pretreatment significantly decreased creatinine and blood urea nitrogen levels and reduced renal histopathological damage at 6 h post-CCl4 injection, observations consistent with enhanced antioxidative activity in the kidney. Moreover, kidney MT levels in the Zn+CCl4-treated group decreased by greater than 70% compared with levels in the Zn-alone group, implying that MT was consumed by CCl4-induced radicals. These findings suggest that prophylaxis with Zn protects mice from CCl4-induced acute nephrotoxicity, presumably by induction of MT, which in turn scavenges radicals induced by CCl4 exposure.

Modulation of metallothionein and metal partitioning in liver and kidney of Solea senegalensis after long-term acclimation to two environmental temperatures

Juveniles of Solea senegalensis were fed with commercial pellets under controlled conditions at two environmental Mediterranean temperatures (15 and 20°C) for two months. After this period, the accumulation of essential and non-essential metals and metallothionein (MT) levels was measured in liver and kidney by inductively coupled plasma mass spectrometry (ICP-MS) and pulse polarography, respectively. The bioaccumulation factor (BAF) for selected metals in both tissues was calculated in relation to levels present in the feed. Tissue partitioning (liver/kidney) and molar ratios, considering the metal protective mechanisms: MT and Selenium (Se), were included for evaluating the detoxification capacity of each tissue. Ag, Cd, Cu and Mn were preferentially accumulated in the liver whereas Co, Fe, Hg, Se and Zn were found in larger concentrations in the kidney, and higher temperature enhanced the accumulation of some of them, but not all. MT content in liver, but not in kidney, was also influenced by temperature changes and by length of exposure. The BAF revealed that Cu was taken up mainly by the liver whereas Se was efficiently taken up by both tissues. The high molar ratios of MT and most metals denoted the kidney׳s remarkable spare capacity for metal detoxification through MT binding. Moreover, the potential protective role of Se was also more evident in kidney as a higher Se:Cd and Se:Ag molar ratios were reached in this organ. In contrast to other fish, the storage of Cd in kidney was particularly low.

Effect of low dose gamma rays on certain essential metals and oxidative stress in different rat organs

The present work aimed to determine the effect of low dose (0.03 Gy) γ-rays on certain essential metals namely Fe, Cu, Zn and Ca levels in various tissues (liver, kidney, testis, spleen, intestine, heart and brain) in rats. Also, lipid peroxidation as malondialdehyde (MDA) and metallothionein (MT) levels were measured in liver, kidney and testis. Rats were exposed to total dose of 0.03 Gy γ-rays along 12 h at a low dose rate (2.5 mGy/h). The results obtained manifested elevation in all essential metals studied in liver. All organs showed elevated Ca levels except that of brain with non-significant change in intestine. Decrease in Fe levels were observed in kidney, testis, intestine, heart and brain tissues with insignificant change in spleen tissue. Elevation in MDA in liver and kidney tissues was recorded and an inhibition in MT in liver, kidney and testis tissues was demonstrated. In conclusion, the previous essential metals tested are very sensitive to low dose (0.03 Gy) γ-rays. Such dose can induce alterations in the oxidative stress parameters under investigation.

Differential Susceptibility to Cadmium-Induced Liver and Kidney Injury in Wild and Laboratory-Bred Bank Voles Myodes glareolus

The objective of the study was to compare the sensitivity of wild and laboratory-bred bank voles to cadmium (Cd)-induced histopathological changes in the liver and kidneys. For 4 weeks, the male bank voles—both wild and laboratory-bred—were provided with diet containing Cd in quantities <0.1 (control), 30, and 60 μg/g dry weight. At the end of exposure period, histopathology and analyses of Cd, metallothionein (MT), glutathione (GSH), zinc (Zn), copper (Cu), iron (Fe), and lipid peroxidation—all considered to be critical factors during the development of Cd toxicity in the liver and kidneys—were carried out. Histopathological changes (focal hepatocyte swelling, vacuolation and inflammation [leukocyte infiltration] in the liver, and focal proximal tubule degeneration [including epithelial cell swelling] in the kidneys) occurred only in the wild bank voles fed a diet containing 60 μg Cd/g. There were no differences in concentrations of Cd, MT, GSH, Zn, and Cu in liver and kidney between the respective groups of wild and laboratory-bred animals. However, a decrease of hepatic Fe and lipid peroxidation was observed in the wild voles exhibiting histopathological changes. These data indicate the following: (1) wild bank voles are more susceptible to Cd-induced liver and kidney injury than those bred and raised in the laboratory; (2) the difference in sensitivity may be associated with a distinct decrease of hepatic Fe in response to Cd exposure between the two groups of bank voles; and (3) dietary Cd may produce histopathological changes indirectly through decreasing the hepatic Fe and Fe-dependent oxidative processes. These results also suggest that histopathology in the liver and kidney of wild bank voles living in a contaminated environment may occur at relatively low levels of tissue Cd.

Expression of metallothionein in liver and kidney of freshwater fish Cyprinus carpio var. communis (Linn) exposed to arsenic trioxide

In the present study, the toxic effects of arsenic trioxide (Ar2O3) to freshwater fish C. carpio were estimated at different median lethal concentration levels and its influences on the expression of metallothionein (MT) activity in liver and kidney were also observed. During this study, LC50 values were found to be 25.7, 27.4, 29.5, and 32 ppm for the period of 24, 48, 72, and 96 hrs respectively and LC16 and LC84 values of ArO3 also measured. The MT activity was estimated in liver and kidney of fish treated with different concentrations of ArO3 (5, 15, and 20 ppm) at different time intervals (48, 96, and 144 hrs) by using SDS-PAGE technique. From the results, 5 KD and 6 KD polypeptides were known to be metallothionein in liver and kidney respectively when the fishes were treated with different concentrations of arsenic arsenic trioxide. In the present investigation, ArO3 induced significant expression on metallothionein activity and it can be useful biomarker in environmental biomonitoring of arsenic contamination

Multiple biomarkers of pollution effects in Solea solea fish on the Tunisia coastline

This field study investigates the morphological indices (condition index, hepatosomatic index) and biochemical (catalase (CAT), glutathione S-transferase (GST), acetylcholinesterase (AChE), metallothionein (MT), lipid peroxidation) parameters in liver, gills and kidney of common sole (Solea solea) originating from different sites of the Tunisian coast area impacted by different anthropogenic activities. Differences among sites and tissues for AChE, GST, CAT, MT and TBARS were found and possibly related to known sources of domestic and industrial discharges in the studied sites. Liver, gills and kidney CAT, liver and kidney MT and brain AChE were key biomarkers to discriminate fish of different sites. So, we suggest using these biomarkers in future biomonitoring.

Tissue Specific Metallothionein Gene Expression in Air-Breathing Teleost, Channa punctata (Bloch)

Cellular levels of specific transcripts or proteins are often measured in relation to a variety of biological events, using a selection of qualitative and quantitative methodologies. Changes in expression levels, measured in a native sentinel species may serve as biomarkers for the effects of environmental perturbations. A quantitative real-time reverse-transcriptase polymerase chain reaction study was conducted using freshwater air-breathing fish, Channa punctata (Bloch) as a test model for observing metallothionein mRNA expression pattern under the influence of varied concentrations of heavy metal, cadmium for an exposure span of 14 days. The findings revealed that metallothionein gene expression is a tissue specific phenomenon in C. punctata and liver is a prominent site for first-line defence during early exposure phase to cadmium, whereas kidney metallothionein mRNA indicates prolong presence of metal in the body.

Zinc Supplementation Attenuates Metallothionein and Oxidative Stress Changes in Kidney of Streptozotocin-Induced Diabetic Rats

Zinc is an element that under physiological conditions preferentially binds to and is a potent inducer of metallothionein under physiological conditions. The present study was conducted to explore whether zinc supplementation morphologically and biochemically protects against diabetic nephropathy through modulation of kidney metallothionein induction and oxidative stress in streptozotocin-induced diabetic rats. Thirty-two Wistar albino male rats were equally divided into four groups. The first group was used as untreated controls and the second group was supplemented with 30mg/kg/day zinc as zinc sulfate. The third group was treated with streptozotocin to induce diabetes and the fourth group was treated with streptozotocin and supplemented with zinc as described for group 2. The blood glucose and micro-albuminuria levels, body and kidney weights were measured during the 42-day experimental period. At the end of the experiment, the kidneys were removed from all animals from the four groups. Diabetes resulted in degenerative kidney morphological changes. The metallothionein immunoreactivity level was lower and the kidney lipid peroxidation levels were higher in the diabetes group than in the controls. The metallothionein immunoreactivity levels were higher in the tubules of the zinc-supplemented diabetic rats as compared to the non-supplemented diabetic group. The zinc and metallothionein concentrations in kidney tissue were higher in the supplemented diabetic group compared to the non-supplemented diabetes group. The activity of glutathione peroxidase did not change in any of the four groups. In conclusion, the present study shows that zinc has a protective effect against diabetic damage of kidney tissue through stimulation of metallothionein synthesis and regulation of the oxidative stress.

The involvement of metallothionein in hepatic and renal Cd, Cu and Zn accumulation in pigs

This study investigated the involvement of metallothionein (MT) in hepatic and renal cadmium (Cd) accumulation and the interactions of this element with the essential elements copper (Cu) and zinc (Zn) in pigs receiving diets with or without Cu and Zn supplementation, in intensive and extensive production systems respectively. Animals from intensive systems showed significantly higher Cd concentrations in the liver (83.3μg/kg wet weight) and kidney (343μg/kg) than animals from extensive systems (33.2 and 130μg/kg respectively). Cu (liver 16.9, kidney 5.52mg/kg) and Zn (82.8 and 29.7mg/kg) concentrations were also significantly higher in pigs from intensive than in animals from extensive systems (Cu 10.1 and 4.64mg/kg, Zn 66.2 and 23.1mg/kg). Pigs from intensive systems showed 50% higher kidney MT concentrations than animals from extensive systems (278 and 183mg/kg respectively), whereas liver MT concentrations were very similar in the two groups (1696 and 1517mg/kg respectively). MT concentrations in both the liver and the kidney were strongly dependent on the Zn status of the animal. In the liver neither Cu nor Cd displaced Zn from MT, and the proportion of MT binding sites apparently occupied by Cu and Cd decreased with increasing hepatic MT concentration, despite the fact that both Cu and Cd have higher affinity for MT than Zn. The proportion of MT binding sites occupied by Cu and Cd was also directly related to Zn:Cu ratio in hepatic cells. In the kidney, in contrast, Cu seems able to compete with Zn for MT binding sites, and the proportion of MT binding sites occupied by Cu increased with increasing renal MT concentration.

Effects of Chronic Cadmium Poisoning on Zn, Cu, Fe, Ca, and Metallothionein in Liver and Kidney of Rats

An experiment was conducted to invest effects of chronic cadmium poisoning on Zn, Cu, Fe, Ca, and metallothionein gene expression and protein synthesis in liver and kidney in rats. Forty rats, 6 weeks old, were randomly allocated into two groups. A group was given CdCl(2) (1 mg/KgCd(2+)) by intraperitoneal injection once a day. The other group was treated with normal saline in the same way. Liver and kidney were collected for analysis at the end of the third week. Results showed that Cd exposure increased Cd (P<0.01) and Zn (P<0.01) content both in liver and kidney. Fe and Ca concentration had a considerable increase in kidney (P<0.01), while both had different degree reduction in liver. Discrepancies between MT mRNA and protein were observed in liver and kidney. In liver, both MT mRNA and protein had a significant increase (P<0.01), while in kidney, only MT gene increase was checked. Meanwhile, the expression levels of MT-1 mRNA and MT-2 mRNA were distinct between liver and kidney. The present study indicated that changes in tissue Cd and Zn levels tended to reflect MT mRNA expression, but bear no clear relationship with MT protein. There did not have a strict dose-dependent relationship among Cd content, MT gene expression, and MT protein synthesis. What is more, changes of Zn, Fe, Cu, and Ca had a certain interaction with both MT mRNA and protein.

A novel report of metallothioneins in fish bile: SDS-PAGE analysis, spectrophotometry quantification and metal speciation characterization by liquid chromatography coupled to ICP-MS

Metallothioneins (MT) are a validated biomarker for metal exposure. In fish they are usually determined in the liver, while some studies have observed MT in kidney, muscle and gills. There are, however, no reports on MT in fish bile. This study aimed to verify if these proteins are present in fish bile, if they can be used as biomarkers for metal exposure and to characterize the metal speciation present in the different species. Three independent methods to verify MT presence in fish bile were conducted: 1D/2D gel electrophoresis, spectrophotometric analyses and SEC-HPLC–ICP-MS. Results show that all methods verified the presence of these proteins in fish bile, while SEC-HPLC–ICP-MS also characterized also characterized metals responsible for the contamination of the studied sites. Quantification was successfully conducted by two methods, densitometry (1D electrophoresis) and spectrophotometry, and the data indicates that bile MTs follow the same trend as in liver. Therefore, Biliary MT show the potential to be used the same way as MT from other matrices in metal exposure studies, with the advantage of being a simpler matrix and showing the possibility of not sacrificing the animals, as chronic duct cannulation is available.

Role of non-enzymatic antioxidants in stimulation of Metallothionein against metal toxicity

Metallothionein (MT) is a low molecular-weight protein considered to be protective in function. It has been estimated in the liver and kidney of cadmium, mercury, copper and zinc treated rats offered antioxidative protection by selenium (Se), vitamin E and glutathione (GSH). These antioxidants stimulated induction of MT in liver and kidney of metal treated rats. Induction was greater in liver than kidney. α -tocopherol induced maximum synthesis of MT in the liver of mercury treated rats during lipid peroxidation, whereas maximum induction of MT in Cd fed rats was observed after GSH treatment. Minimum accumulation of mercury in comparison to other metals was observed in liver as well as kidney in glutathione treated rats. It is suggested that different metal species induced specific metallothionein(s) that express specific effects. The mechanism for maintaining high levels of MT might result from increased translation and transcription of MT. Present results suggest that these proteins not only scavenge free radicals (FR) but also decrease accumulation of metals in soft tissue.

Hexavalent chromium‐induced multiple biomarker responses in liver and kidney of goldfish, Carassius auratus

Hexavalent chromium [Cr (VI)] is a constituent of chromite ore. Although it is known to have several industrial and technological applications, its release into the aquatic environment as a result of chemical spill or inadequate waste discharge may hamper the health of aquatic organisms. In this study, we have investigated the effects of Cr (VI) on multiple biomarkers responses in goldfish under subchronic exposure conditions. Laboratory-acclimatized fish were exposed to 4.25 ppm and 8.57 ppm Cr (VI) for four weeks using a continuous flow-through system. During exposure, fish samples were collected on a weekly basis and analyzed for multiple biomarkers including catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), metallothionein (MT), and total protein in liver and kidney. Study results indicated that the CAT activity and total protein levels in Cr (VI) - treated goldfish did not significantly differ (P > 0.05) from their respective controls during experimentation. However, highly significant up-regulations (P < 0.05) of SOD, GPx, and MT expression in Cr (VI) - treated goldfish were recorded at different exposure times depending on Cr (VI) concentration, test organ, and/or biomarker of interest. For example, significantly higher liver GPx levels were found at weeks 2 and 3 in the 4.25 ppm concentration, and at weeks 3 and 4 in the 8.57 ppm, while kidney GPx levels were significantly higher at weeks 1, 2 and 3 in the 4.25 ppm concentration, and at weeks 2, 3 and 4 in the 8.57 ppm concentration. In summary, Cr (VI)-induced oxidative stress was characterized by statistically significant increases in SOD, GPx, and MT expression in goldfish tissues; with the kidney showing a relatively higher sensitivity to Cr (VI) toxicity compared with the liver.

Trace Elements and Metallothionein in Liver and Kidney of Felis catus

Trace metals such as Zn, Cu, and Fe are essential for life; differently, no biochemical function is known for Cd. Changes in dietary metal concentrations can cause deficiency or toxicity. Studies on trace elements in cat are lacking. This paper aimed to analyze Zn, Cu, Fe and Cd concentrations in liver and kidney of pathological domestic cat and to isolate metallothionein (MT) in these tissues. It was not possible to explore a possible correlation between metal concentrations and pathologies because the incidence for each of them was too low. Fe was the most abundant metal; in particular, the liver accumulates average Fe concentrations one order of magnitude higher than Zn and Cu, ranging from 66.75 and 1,444.23 microg/g. Significantly, higher levels of Fe were found in the liver of elder animals. Zn concentrations varied between 26.31 and 84.78 microg/g in the liver whereas in the kidney, ranged between 7.69 and 71.15 microg/g. Cu concentrations were between 2.37 and 112.91 microg/g in liver and between 2.12 and 9.85 microg/g in kidney. Cd was the least abundant metal with the exception of the kidney of the oldest cats where it reached a maximum of 13.71 microg/g. Gel-filtration metal distribution profiles from cytosolic extracts revealed the presence of Cd, Cu, Zn thioneins either in the liver or in the kidney. Because tissue samples were taken from pathological cats from different breed and age, care must be taken to use these data as a baseline profile of trace elements in healthy animals. Our results are indicative that for some specimens the feed levels of Fe and Cu could be higher than the optimal dietary intake and in few cats, there was also an exposure to Cd that was counteracted by MT biosynthesis.

Behavioural effects of cadmium (Cd) in free-living willow ptarmigan (Lagopus lagopus)

The objective of this study was to examine effects of sublethal cadmium (Cd) contamination on parental behaviour and chick survival in willow ptarmigan (Lagopus lagopus) in an area that does not have high environmental levels of Cd due to geology but have high environmental levels of Cd due to anthropogenic deposition and acidification. One group of willow ptarmigan hens were exposed to Cd (83.2 mg Cd/L) after egg-laying using osmotic minipumps; whereas, another group given saline served as a control. No statistically significant difference in Cd concentration between the two groups was found. There was a significant correlation between the Cd concentrations in the liver and kidney of the birds and between Cd and metallothionein (MT) concentration in the kidney. No significant differences were found between the control hens and the Cd-contaminated hens with respect to any of the behaviour parameters. Age seemed to be more important than Cd treatment as adult hens showed more distraction display, had lower flushing distance, and higher brood attendance than juveniles. There were no difference in chick survival between Cd-contaminated and control hens, and there was no correlation between Cd concentrations and chick survival. The non-significant effects of Cd concentrations on parental behaviour may be due high environmental levels of Cd caused by anthropogenic deposition and acidification. We suggest that willow ptarmigan in the area have gradually evolved abilities to cope with high environmental levels of Cd, for instance, by binding Cd to MT in kidney and liver. This may suggest that Cd exerts a strong selection pressure on birds causing a relatively rapid evolution of protection mechanisms.

Effects of Lead and/or Cadmium on the Expression of Metallothionein in the Kidney of Rats

Lead acetate (300 mg/L) and/or cadmium chloride (50 mg/L) were administered as drinking water of Sprague-Dawley rats for 8 weeks to investigate the possible combined effect of these metals on the expression of metallothionein (MT) in kidneys. Immunohistochemical staining and real-time quantitative polymerase chain reaction analyses were performed on kidney samples to identify the distribution of MT and to quantify the relative expression levels of MT-1 and MT-2 gene, respectively. There is no significant difference in distribution of the intensity, amount of MT immunostaining, and expression level of MT-1 and MT-2 gene in the kidneys between the lead group and control group (P > 0.05), whereas those in the cadmium group and (Pb + Cd) group were significantly higher than that in the control group (P < 0.01). Compared to the (Pb + Cd) group with the lead or cadmium group, the expression level of MT-1 and MT-2 gene increased significantly (P < 0.01). In summary, there was an obvious synergistic effect of lead combined with cadmium on the expression of metallothionein in the kidney of rats.