Relationship between toxicity and cadmium accumulation in rats given low amounts of cadmium chloride or cadmium-polluted rice for 22 months

OUP accepted manuscript

Background

Cadmium (Cd) is a highly toxic heavy metal that adversely affects both human and animal health. Chronic cadmium exposure causes serious kidney damage. The current study investigated the protective role of cerium oxide nanoparticles (CeO₂NPs) against cadmium chloride (CdCl₂)-induced renal injury.

Method

One hundred and twenty male albino rats were divided into 6 equal groups. Group (C): considered as control group which was given distilled water orally. Group (NC_.1 and NC_.5): rats were injected i.p. with nanoceria at a dose of (0.1 and 0.5 mg/kg b.wt), respectively, twice a week for 2 weeks starting at the 15th day of the study. Group (Cd): rats were received CdCl₂ orally (10 mg/kg b.wt) daily for 28 days. Groups (Cd + NC_.1 and Cd + NC_.5): rats were given CdCl₂ orally (10 mg/kg b.wt) for 28 days and CeO₂NPs by i.p. injection at a dose of (0.1 and 0.5 mg/kg b.wt), respectively, twice a week for 2 weeks started at the 15th day of the experiment.

Results

The Cd group exhibited a significant increase in the serum levels of IL-1β, KIM-1, Cys-C, and β2-MG, downregulation of the antioxidant initiator genes such as Nrf-2, and up-regulation of apoptosis markers such as nibrin gene (NBN). Urine examination showed a high level of microalbuminuria, abnormal physical, chemical, and microscopical changes in comparison with control groups.

Conculsion

Remarkably, posttreatment with CeO₂NPs showed significant improvement in kidney histopathological picture and relieved the alterations in kidney biomarkers, inflammatory markers, urine abnormalities, and expressions of different genes as Nrf-2 and NBN.

Oral administration of cadmium depletes intratesticular and epididymal iron levels and inhibits lipid peroxidation in the testis and epididymis of adult rats

Cadmium (Cd)-induced tissue injury depends on the accumulated Cd which differentially affects endogenous iron (Fe). To investigate this, adult rats were treated by oral gavage with Cd (50 mg/kg body wt.) once a week for 15, 30 and 60 days and sacrificed a day after last administration. After the 15th and 30th day of treatment, Cd had no effect on thiobarbituric acid reactive substances (TBARS) and endogenous Fe levels but exhibited anti-androgenic effects (p < 0.05) and caused histological damages. At day 60, Cd was accumulated by 156.30% and 364.77% above control values at concentrations that decreased endogenous Fe levels by 46.41% and 50.31% in the testis and epididymis respectively. The histological damages were characterized by decreased tubular diameter, damage to the epithelium leading to loss of tubular germ cells and absent of spermatozoa in the epididymal lumen. Although myeloperoxidase activities were increased, TBARS levels were found to decrease significantly at day 60 in the serum, testis and epididymis suggesting that the histological damages were not caused by lipid peroxidation. Furthermore, TBARS correlated negatively with Cd in the testis (r = -0.251, p < 0.05) and epididymis (r = -0.286, p < 0.05); Fe correlated positively with TBARS in the testis (r = +0.217, p < 0.05) and Cd correlated negatively with Fe in the testis (r = -0.461, p < 0.05) and epididymis (r = -0.109, p < 0.05). The antioxidant enzymes, superoxide dismutase and glutathione peroxidase were also decreased in the gonads after 60 days Cd treatment. Overall, anti-androgenic effects and histo-pathological changes are early indicators of direct effects of Cd and occur before decrease in TBARS which is secondarily related to the modifying of Fe contents.

Effect of Cadmium on Lipid Peroxidation and on Some Antioxidants in the Liver, Kidneys and Testes of Rats Given Diet Containing Cadmium-polluted Radish Bulbs

The aim of this study was to examine the effects of cadmium (Cd), incorporated in radish bulbs, on malondialdehyde and glutathione levels and on superoxide dismutase activity in the liver, kidneys and testes of male rats. The control animals were given diet containing ordinary radish bulbs for 4, 8 and 12 weeks, while contaminated animals were given diet containing Cd-polluted radish bulbs (1.1 mg Cd/g of diet) for the same periods as in the controls. At each time point, rats were euthanized and the liver, kidneys and testes were removed. The results indicated that the body weight gain of contaminated rats was identical to that of the control rats. Cd concentrations in the liver, kidneys and testes increased significantly and gradually from the 4th to 12th week of treatment. Malondialdehyde concentrations decreased significantly in the liver and increased significantly in the kidneys and testes after 12 weeks of treatment, while glutathione levels increased significantly in the liver, and decreased significantly in the kidneys and testes at the same time. No changes were observed in SOD activity in the liver, while in the kidneys and testes, this activity was increased after 12 weeks of treatment as compared with the control rats.

The potential protective role of lysophospholipid mediators in nephrotoxicity induced by chronically exposed cadmium

Cadmium is a hazardous metal whose chronic exposure induces renal failure due to fibrosis, but the mechanisms are not well known. In this study we analyzed the molecular species of lysophosphatidic acid (LPA) and related phospholipids, together with their metabolic enzyme activity, in plasma from Wistar rats exposed up to 300ppm Cd(2+) in drinking water for 114days. Exposure of 300ppm Cd(2+) for 114days enhanced autotoxin (ATX)/lysophospholipase D activity, but significantly lowered the total levels of LPA and lysophosphatidylethanolamine. Interestingly, the total level of sphingosine-1-phosphate (S1P) was elevated dose-dependently by Cd(2+). Cultured rat kidney-derived interstitial fibroblast cells, NRK49F cells and proximal epithelial cells, NRK52E cells, were both responsive to the protective action of LPA or S1P against Cd(2+) toxicity. The former cell expresses ATX RNA. In conclusion, the elevation of LPA-producing enzyme activity and S1P concentrations in plasma after exposure of rats to Cd(2+) would protect from the renal toxicity of Cd(2+).

Effect of lifetime low dose exposure to heavy metals on selected serum proteins of Wistar rats during three subsequent generations

The aim of the study was to assess the effects of exposure to low doses of lead, cadmium and mercury dissolved in drinking water (at a concentration 200-fold of maximum allowable concentration) on selected serum proteins of 120 Wistar rats during three subsequent generations. Animals were divided into four groups in all observed generation-control (C) and three experimental groups exposed to low doses of heavy metals (lead acetate in concentration 100 μM; mercuric chloride in 1 μM; cadmium chloride in 20 μM of drinking water). We studied the biochemical parameters as well as total protein, albumin, transferrin and ferritin in the serum. Exposure to lead and mercury shortened life span, decreased body weight of the animals in each generation whereas cadmium had no such effect. Total protein increased after exposure to lead and mercury (P<0.001), albumin increased after exposure to lead and mercury in 1st filial and 2nd filial generation (P<0.05) and insignificantly decreased after exposure to cadmium in parental and 1st filial generation. Transferrin and ferritin increased in all exposed groups and generations (P<0.05). Transferrin and ferritin are good markers for intoxication of rats with heavy metals. For the results evaluation, not only data at the end of experiment should be taken into account, but entire duration of trials (i.e., more time steps), which makes results more objective.

Immunomodulatory effects of cadmium and Gynostemma pentaphyllum herbal tea on rat splenocyte proliferation

Gynostemma pentaphyllum Makino (GP) is a herbal tea widely grown in Southeast Asia. However, this herbal tea can be contaminated with some heavy metals, especially cadmium (Cd), from agricultural areas, which may affect human health. The objective of this study is to evaluate the immunomodulatory effects of Cd contaminated in GP herbal tea and inorganic Cd on rat splenocytes. Rats were divided into groups and treated with drinking water (control), high CdCl 2 in drinking water (HCd; 0.05 mg/L), GP herbal tea containing 0.05 mg/L Cd (GP-HCd) for 4 months, low CdCl 2 in drinking water (LCd; 0.006 mg/L), and GP herbal tea containing 0.006 mg/L Cd (GP-LCd) for 6 months. After the treatments, Cd accumulation in organs and blood was detected by using a graphite furnace atomic absorption spectrophotometer. In spleen, HCd-treated rats had 4-fold higher Cd accumulations than GP-HCd-treated rats. Cd accumulation in liver and kidney in the HCd group also increased significantly. There were no significant changes in total leucocyte and lymphocyte counts; however, these parameters tended to decrease slightly in LCd, GP-LCd, and GP-HCd groups. The HCd group (ex vivo) significantly produced suppressive effects on T cell mitogen-induced splenocyte proliferation, with 1 mug/mL Con A and PHA-P. In addition, 0.5 mug/mL PWM-induced B cell proliferation, through T cell functions, was also significantly inhibited by HCd as compared to the control group, while GP-HCd had no effects. However, both GP-LCd- and LCd-treated rats had a slight increase in Con A-stimulated splenocyte proliferation. This study indicated that high Cd contamination in drinking water alone had suppressive effects on T cell functions, but these effects could not be found with the same Cd level contamination in GP herbal tea.

[Anemia induced by cadmium intoxication]

Anemia is commonly induced by chronic cadmium (Cd) intoxication. Three main factors are involved in the development of Cd-induced anemia: hemolytic, iron-deficiency, and renal. Intravascular hemolysis can occur at the early stage of Cd exposure owing to the direct damaging effect on erythrocytes. In addition, Cd that accumulates in erythrocytes affects membrane cytoskeletons and decreases cell deformability, and these cells are then trapped and destroyed in the spleen. Iron deficiency can be detected in animals after an oral exposure to Cd, which competes with iron for absorption in the intestines, leading to anemia. However, an increase in body iron content along with anemia is often observed in cases of parenteral exposure or itai-itai disease. Therefore, it is estimated that Cd disrupts the efficient usage of iron in hemoglobin synthesis in the body. Renal anemia is observed during the very last phase of chronic, severe Cd intoxication, such as itai-itai disease, showing a decrease in the production of erythropoietin from renal tubular cells. Because the renal anemia is based on the same pathophysiology as Cd-induced osteomalacia, which is derived from the disturbance of mineral metabolism due to renal tubular dysfunction, it is reasonable to include renal anemia in the criteria for the diagnosis of itai-itai disease. Hemodilution could also contribute to the development of Cd-induced anemia. Bone marrow hypoplasia or the inhibition of heme synthesis might only be involved in Cd-induced anemia in severe cases of Cd intoxication.

Subcellular changes of essential metal shown by in-air micro-PIXE in oral cadmium-exposed mice

To clarify the relation of essential metals to cadmium (Cd) toxicity, we evaluated metallothionein expression and analyzed the subcellular distribution of essential metals using in-air micro-Particle-Induced X-ray Emission (PIXE). Four mice were dosed orally with 100 mg/L of Cd in drinking water for 1.5 or 2 years. Frozen samples of organs were used for micro-PIXE analysis and formalin-fixed samples were used for metallothionein staining. Immunohistochemically, metallothionein induction by 1.5y-Cd exposure was higher in the renal cortex than in the liver. Metallothionein expression was reduced after 2y-Cd administration compared to the 1.5y-Cd-exposed mice. Cd-induced tissue damage became marked in the 2y-Cd-exposed mice compared to the 1.5y-Cd-exposed mice, in which nephrotoxicity was more prominent than hepatotoxicity. Cd yield was higher in the renal cortex of the 2y-Cd-exposed mouse than in that of the 1.5y-Cd-exposed mouse, whereas no such increasing tendency was found in the liver. Compared to the control, the Cd-exposed mice markedly accumulated zinc in the liver and renal cortex. In the Cd-exposed mice, iron was mildly accumulated in the renal cortex and was slightly deprived in the liver. Elemental maps showed that a large amount of Cd was spatially combined with zinc in the 1.5y-Cd mouse. Free Cd became abundant in the 2y-Cd-exposed mouse. In addition, a small amount of Cd was colocalized with iron. The data suggest that zinc may contribute to protect against oral-administrated Cd toxicity, and impaired induction of MT may participate in hepato-nephrotoxicity of the 2y-Cd-exposed mouse.

Subchronic dietary exposure of rats to cadmium alters the metabolism of metals essential to bone health

Cadmium (Cd) was recently identified as a risk factor for osteoporosis. Skeletal damage may be the critical effect of low-level long-term exposure to Cd in the general population exposed via food, but the mechanisms behind this are not clearly understood. We investigated the effect of dietary Cd exposure on metals involved in bone turnover. Female rats received a Cd-supplemented diet (0, 10, 50, or 200 CdCl2 mg/kg diet) for 13 weeks. Cd and essential metals stored in the liver were measured by ICP-MS multianalysis. Mineral content of the livers was modified according to Cd level: iron, magnesium and selenium decreased while copper, zinc and manganese increased with increasing Cd levels. Iron was the most strikingly affected metal, falling to one-fifth of control values at high dietary Cd exposure. In this dosage group, selenium decreased to 36% of mean control concentrations while zinc increased to 168%. This mineral imbalance, especially depleted iron stores, can contribute, at least in part, to the Cd-associated risk of osteoporosis. The association between iron metabolism and Cd exposure should be investigated in humans, as Cd and low iron stores could act synergistically as risk factors for osteoporosis.

A study on electrophysiological effects of subchronic cadmium treatment in rats

Male Wistar rats were treated for 4, 8 and 12 weeks with 3.5, 7.0 or 14.0 mg/kg cadmium (in the form of cadmium chloride) by gavage. Changes induced in certain electrophysiological parameters-electrocorticogram frequency; latency and duration of cortical sensory evoked potentials; conduction velocity and relative and absolute refractory periods of a peripheral nerve-were analyzed. On the electrocorticogram, increased frequency was seen. Lengthened latency and duration of the cortical evoked potentials, as well as lowered conduction velocity and increased refractory periods in the peripheral nerve, were observed. These changes seemed to increase with the dose and the treatment time and were statistically significant mainly in the highest dose groups following 12 weeks of treatment. The results show that subchronic, low-level exposure by cadmium affects the rat's spontaneous and evoked bioelectric activity and point at the possible consequences in exposed humans.

Perspectives on cadmium toxicity research

Since there are a plethora of studies on cadmium toxicity and poisoning in laboratory animals and humans, we have limited this review to studies that are relevant to human health issues by focusing on carcinogenicity, genotoxicity, circulatory disease, nephrotoxicity and life expectancy. Cadmium exposure has been established to induce cancer in various tissues of laboratory animals. Contrary to early findings of the lack of genotoxicity by cadmium, recent findings of mammalian cell culture studies have revealed genotoxic effects. Furthermore, cadmium exposure at relatively low doses induces circulatory diseases in laboratory animals. Despite such results of various cadmium toxicities in animal studies, data from human studies are lacking and insufficient to support the cause-effect relationship. Although cadmium is currently considered to be a human carcinogen by the International Agency for Research and Cancer, it is inappropriate to conclude that sufficient evidence on the carcinogenicity of cadmium in humans exists. It is also thought that epidemiological studies so far reported do not support the occurrence of cadmium-induced circulatory disease in humans. Since there are inconsistent reports on the relationship of cadmium exposure with the life expectancy of people living in cadmium-polluted areas, further studies are needed for clarification. It is also necessary to examine apparent discrepancies in result between humans and experimental animals. It has been established that long-term exposure to cadmium causes renal dysfunction in both humans and experimental animals, and whether there are any differences in the inducibility of metallothionein in the kidney warrants further study.