Tissue distribution of cadmium in rats given minimum amounts of cadmium-polluted rice or cadmium chloride for 8 months

Cadmium affects autophagy in the human intestinal cells Caco-2 through ROS-mediated ERK activation

Cadmium is a toxic metal that enters the food chain. Following oral ingestion, the intestinal epithelium has the capacity to accumulate high levels of this metal. We have previously shown that Cd induces ERK1/2 activation in differentiated but not proliferative human enterocytic-like Caco-2 cells. As autophagy is a dynamic process that plays a critical role in intestinal mucosa, we aimed the present study 1) to investigate the role of p-ERK1/2 in constitutive autophagy in proliferative Caco-2 cells and 2) to investigate whether Cd-induced activation of ERK1/2 modifies autophagic activity in postconfluent Caco-2 cell monolayers. Western blot analyses of ERK1/2 and autophagic markers (LC3, SQSTM1), and cellular staining with acridine orange showed that ERK1/2 and autophagic activities both decreased with time in culture. GFP-LC3 fluorescence was also associated with proliferative cells and the presence of a constitutive ERK1/2-dependent autophagic flux was demonstrated in proliferative but not in postconfluent cells. In the latter condition, serum and glucose deprivation triggered autophagy via a transient phosphorylation of ERK1/2, whereas Cd-modified autophagy via a ROS-dependent sustained activation of ERK1/2. Basal autophagy flux in proliferative cells and Cd-induced increases in autophagic markers in postconfluent cells both involved p-ERK1/2. Whether Cd blocks autophagic flux in older cell cultures remains to be clarified but our data suggest dual effects. Our results prompt further studies investigating the consequences that Cd-induced ERK1/2 activation and the related effect on autophagy may have on the intestinal cells, which may accumulate and trap high levels of Cd under some nutritional conditions.

Dermatotoxicity of oral cadmium is strain-dependent and related to differences in skin stress response and inflammatory/immune activity

Adverse effects of non-occupational exposure to cadmium (Cd) are increasingly acknowledged. Since our previous study has showed that orally acquired Cd affects skin, the contribution of genetic background to dermatotoxicity of oral cadmium was examined in two rat strains, Albino Oxford (AO) and Dark Agouti (DA), which differed in response to chemicals. While similar accumulation of Cd in the skin of both strains was noted, the skin response to the metal differed. DA rat individuals mounted antioxidant enzyme defense in the skin already at lower Cd dose, in contrast to AO rats which reacted to higher metal dose solely (and less pronounced), implying higher susceptibility of DA strain to Cd dermatotoxicity. Epidermal cells from both strains developed stress response, but higher intensity of antioxidant response in AO rats implied this strain`s better ability to defend against Cd insult. Cd induced epidermal cells' proinflammatory cytokine response only in DA rats. Increased IL-10 seems responsible for the lack of response in AO rats. Differences in the pattern of skin/epidermal cell responsiveness to cadmium give a new insight into repercussion of genetic variability to dermatotoxicity of orally acquired cadmium, bearing relevance for variations in the link between dietary cadmium and inflammation-based skin pathologies.

Oral cadmium exposure affects skin immune reactivity in rats

Skin can acquire cadmium (Cd) by oral route, but there is paucity of data concerning cutaneous effects of this metal. Cd acquired by oral route can affect skin wound healing, but the effect of Cd on other activities involved in skin homeostasis, including skin immunity, are not explored. Using the rat model of 30-day oral administration of Cd (5 ppm and 50 ppm) in drinking water, basic aspects of immune-relevant activity of epidermal cells were examined. Dose-dependent Cd deposition in the the skin was observed (0.035 ± 0.02 µg/g and 0.127 ± 0.04 µg/g at 5 ppm and 50 ppm, respectively, compared to 0.012 ± 0.009 µg/g at 0 ppm of Cd). This resulted in skin inflammation (oxidative stress at both Cd doses and dose-dependent structural changes in the skin and the presence/activation of innate immunity cells). At low Cd dose inflammatory response (nitric oxide and IL-1β) was observed. Other inflammatory cytokines (IL-6 and TNF) response occurred at 50 ppm, which was increased further following skin sensitization with contact allergen dinitro-chlorobenzene (DNCB). Epidermal cells exposed to both Cd doses enhanced concanavalin A (ConA)-stimulated lymphocyte production of IL-17. This study showed for the first time the effect of the metal which gained access to the skin via gut on immune reactivity of epidermal cells. Presented data might be relevant for the link between dietary Cd and the risk of skin pathologies.

Dietary compounds as modulators of metals and metalloids toxicity

A large part of the population is exposed to metals and metalloids through the diet. Most of the in vivo studies on its toxicokinetics and toxicity are conducted by means of exposure through drinking water or by intragastric or intraperitoneal administration of aqueous standards, and therefore they do not consider the effect of the food matrix on the exposure. Numerous studies show that some components of the diet can modulate the toxicity of these food contaminants, reducing their effect on a systemic level. Part of this protective role may be due to a reduction of intestinal absorption and subsequent tissue accumulation of the toxic element, although it may also be a consequence of their ability to counteract the toxicity directly by their antioxidant and/or anti-inflammatory activity, among other factors. The present review provides a compilation of existing information about the effect that certain components of the diet have on the toxicokinetics and toxicity of the metals and metalloids of greatest toxicological importance that are present in food (arsenic, cadmium, lead, and mercury), and of their most toxic chemical species.

Effect of wheat bran and flaxseed on cadmium effects and retention in rats

Dietary fiber can affect cadmium (Cd) absorption and toxicity, but the effect appears to depend on the type of dietary fiber. The aim of the present study was to compare the effect of dietary sources containing distinct amounts of soluble and insoluble fiber on Cd absorption, accumulation and toxicity in growing rats. The absorption of essential macrominerals (Ca, P and Mg) was also evaluated. Animals received a nutritionally balanced diet with cellulose (cel - control), wheat bran or flaxseed as the fiber source with 0 or 50 mg Cd kg(-1) diet, during 30 days. Cd exposure reduced body weight gain, feed efficiency ratio, epididymal fat relative weight and liver relative weight, and increased plasma alanine aminotransferase activity in all fiber groups. The apparent Cd absorption was similar among Cd-groups, but the flax-Cd group had a higher hepatic and renal Cd concentration. Cd decreased the absorption of Ca and P, and increased Mg absorption in the wheat bran and flaxseed groups, but not in the cel group. Although the different fiber sources investigated had no effect on Cd toxicity, the major soluble fiber source, flaxseed, increased Cd retention. Thus, caution should be taken in the intake of flaxseed by Cd-exposed populations.

Influence of cereal bran supplement on cadmium effects in growing rats

Strategies to diminish cadmium (Cd) absorption are highly desirable especially where Cd exposure due to environmental contamination is still inevitable. Cd toxicity may be influenced by dietary components, such as fiber and minerals. Multimixtures are low-cost cereal bran supplements used in Brazil and in other countries to counteract malnutrition in low-income populations. This study was aimed at evaluating whether multimixture would reduce Cd effects in young rats. Animals received a diet with or without the multimixture plus 0, 5, or 25 mg Cd/kg (control, Cd-5, and Cd-25 groups) during 30 days. The Cd-5 groups were similar to control groups in all parameters analyzed, except in the higher renal Cd concentration. However, the Cd-25 groups had lower biological growth parameters and renal delta-aminolevulinate dehydratase activity, besides higher renal Cd concentration and plasma alanine aminotransferase activity compared to the controls. The multimixture did not prevent Cd effects in the Cd-25 group, but caused a small reduction in renal Cd concentration in the Cd-5 group. Although this multimixture was ineffective to prevent Cd effects at the higher concentration, it seemed to reduce Cd accumulation at the lower Cd dietary concentration, which is similar to levels of human exposure in some polluted areas.

Effect of zinc supplementation on bone metabolism in male rats chronically exposed to cadmium

The aim of the present study is to investigate, based on the rat model of moderate and relatively high human exposure to cadmium (Cd), whether zinc (Zn) supplementation may prevent Cd-induced disorders in bone metabolism. For this purpose, male Wistar rats received Cd (5 and 50mg/l) or/and Zn (30 and 60mg/l) in drinking water for 6 and 12 months. Bone densitometry and biochemical markers of bone turnover were used to assess the effects of Cd or/and Zn. Bone mineral content (BMC) and density (BMD) were measured in the femur. Serum osteocalcin (OC) and alkaline phosphatase in trabecular (bT-ALP) and cortical (bC-ALP) bone were determined as bone formation markers, and carboxy-terminal cross-linking telopeptides of type I collagen (CTX) in serum were measured as bone resorption marker. Serum concentration of calcium (Ca) and its renal handling, as well as Zn and Cd concentrations in the serum/blood, urine and femur were evaluated as well. The exposure to 5 and 50mg Cd/l (0.340+/-0.026 and 2.498+/-0.093mg Cd/kg body wt/24h, respectively), in a dose and duration dependent manner, affected bone turnover (inhibited bone formation and stimulated its resorption) and disturbed bone mineralization (decreased BMC, BMD and Zn concentration). Zn supply at the concentration of 30 and 60mg/l (1.904+/-0.123 and 3.699+/-0.213mg/kg body wt/24h, respectively) during Cd exposure influenced the Cd-induced disorders in bone metabolism. Zn administration to the Cd-exposed rats enhanced the bone ALP activity and prevented Cd-induced bone resorption, but had no statistically significant effect on BMC and BMD; however, mean values of the densitometric parameters in the rats receiving both Cd and Zn were higher than in those treated with Cd alone. Moreover, Zn supplementation at both levels of Cd exposure was found to prevent Cd accumulation in the femur and the Cd-induced decrease in bone Zn concentration. The results of the present study allow the conclusion that Zn supplementation during Cd exposure may partly protect from disorders in bone metabolism. The influence of Zn may be accompanied by its ability to prevent Cd-induced Zn deficiency and to decrease Cd accumulation in bone tissue. The findings seem to indicate that enhanced dietary intake of Zn in subjects chronically exposed to moderate and relatively high Cd levels may have a protective influence on the skeleton.

Safe levels of cadmium intake to prevent renal toxicity in human subjects

The present review attempts to provide an update of the scientific knowledge on the renal toxicity which occurs in human subjects as a result of chronic ingestion of low-level dietary Cd. It highlights important features of Cd toxicology and sources of uncertainty in the assessment of health risk due to dietary Cd. It also discusses potential mechanisms for increased susceptibility to Cd toxicity in individuals with diabetes. Exposure assessment on the basis of Cd levels in foodstuffs reveals that vegetables and cereals are the main sources of dietary Cd, although Cd is also found in meat, albeit to a lesser extent. Cd accumulates particularly in the kidney and liver, and hence offal contains relatively high amounts. Fish contains only small quantities of Cd, while crustaceans and molluscs may accumulate larger amounts from the aquatic environment. Data on Cd accumulation in human kidney and liver obtained from autopsy studies are presented, along with results of epidemiological studies showing the relationship between renal tubular dysfunction and kidney Cd burden. These findings suggest that a kidney Cd level of 50 μg/g wet weight is a maximum tolerable level in order to avoid abnormal kidney function. This renal Cd burden corresponds to a urinary Cd excretion of 2 μg/d. Accordingly, safe daily levels of Cd intake should be kept below 30 μg per person. Individual variations in Cd absorption and sensitivity to toxicity predicts that a dietary Cd intake of 30 μg/d may result in a slight renal dysfunction in about 1 % of the adult population. The previous guideline for a maximum recommended Cd intake of 1 μg/kg body weight per d is thus shown to be too high to ensure that renal dysfunction does not occur as a result of dietary Cd intake.

Immunomodulatory Effects of Estradiol and Cadmium in Adult Female Rats

A wide range of toxic effects has been associated with cadmium (Cd) exposure in mammals. However, the physiological factors that modulate these effects have received limited attention. We have previously demonstrated that neonatal exposure of rats to Cd during lactation results in sex-specific immunotoxic effects in both juvenile and adult rats. The objectives of this study were to determine the effects of 17beta-estradiol (E(2)) on the immunotoxicity of Cd in female rats. We compared the effects of 28 days of exposure to 0, 5, and 25 ppm cadmium chloride (CdCl(2)) through drinking water on ovariectomized Sprague-Dawley rats and on ovariectomized rats with E(2) implant which mimicked the physiological level of E(2) in female rat. Our results clarify the control of important immune functions by E(2) at physiological level and demonstrate significant interactions between Cd and E(2) effects on the cytotoxic activity of natural killer cells and phagocytosis of splenic cells as well as on the total number of thymocytes and of the four subpopulations of the thymocytes as defined by the expression of the cell-surface markers CD4 and CD8. Cd and E(2) share several mechanisms of action that may account for these interactions. The estrogenic potential of Cd could also account for some of the observed effects. These interactions have to be taken into consideration in evaluating the risk of Cd immunotoxicity and the possible interactions with hormonal treatments.

Kidney Dysfunction and Hypertension: Role for Cadmium, P450 and Heme Oxygenases?

Cadmium (Cd) is a metal toxin of continuing worldwide concern. Daily intake of Cd, albeit in small quantities, is associated with a number of adverse health effects which are attributable to distinct pathological changes in a variety of tissues and organs. In the present review, we focus on its renal tubular effects in people who have been exposed environmentally to Cd at levels below the provisional tolerable intake level set for the toxin. We highlight the data linking such low-level Cd intake with tubular injury, altered abundance of cytochromes P450 (CYPs) in the kidney and an expression of a hypertensive phenotype. We provide updated knowledge on renal and vascular effects of the eicosanoids 20-hydroxyeicosatetraenoic acid (20-HETE) and eicosatrienoic acids (EETs), which are biologically active metabolites from arachidonate metabolism mediated by certain CYPs in the kidney. We note the ability of Cd to elicit "oxidative stress" and to alter metal homeostasis notably of zinc which may lead to augmentation of the defense mechanisms involving induction of the antioxidant enzyme heme oxygenase-1 (HO-1) and the metal binding protein metallothionein (MT) in the kidney. We hypothesize that renal Cd accumulation triggers the host responses mediated by HO-1 and MT in an attempt to protect the kidney against injurious oxidative stress and to resist a rise in blood pressure levels. This hypothesis predicts that individuals with less active HO-1 (caused by the HO-1 genetic polymorphisms) are more likely to have renal injury and express a hypertensive phenotype following chronic ingestion of low-level Cd, compared with those having more active HO-1. Future analytical and molecular epidemiologic research should pave the way to the utility of induction of heme oxygenases together with dietary antioxidants in reducing the risk of kidney injury and hypertension in susceptible people.

Effect of chronic exposure to cadmium on the mineral status and mechanical properties of lumbar spine of male rats

The effect of cadmium (Cd) on the risk of vertebral damage was investigated on a male rat model of human exposure. Young Wistar rats were treated with Cd in drinking water at the concentration of 1, 5 or 50 mgCd/l for 12 months. Bone mineral density (BMD) of the lumbar spine (L1-L5), the rate of deformities and fractures, biomechanical properties (compression test) and the chemical composition of the fourth lumbar vertebral body (L4) were estimated. The exposure to 1 mgCd/l (corresponding to low environmental exposure in non-Cd-polluted areas) had no effect on the L4 composition, density and mechanical strength; in one animal only (10%) it was deformed. In the 5 mgCd/l group, the content of minerals (including calcium, zinc and phosphate) in the L4 and the displacement at ultimate decreased, whereas its ultimate strength and the L1-L5 BMD tended to decline. In most of the rats, the L4 was intact and there were no vertebral fractures. At 50 mgCd/l, the BMD of the L1-L5 and the content of minerals in the L4 (including calcium, magnesium, zinc, copper, iron and phosphate) were lower compared to control, and these changes were accompanied by a weakness in the L4 mechanical strength. The L4 was intact only in 30% of these rats; in other animals it was deformed (40%) or fractured (30%). The results allow for the conclusion that moderate environmental exposure to Cd (5 mgCd/l in the model applied) may enhance the risk of vertebral damage in men. These, together with our previous findings on an analogous female rat model, seem to indicate that males may be less vulnerable to the vertebral fractures due to exposure to Cd compared to females.

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.

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

To clarify toxic effects of long-term oral administration of low dose cadmium (Cd) on the liver and kidney, six groups of female Sprague-Dawley rats were fed a diet containing Cd-polluted rice or CdCl2 at concentrations up to 40 ppm, and killed after 12, 18, and 22 months. With toxicological parameters, including histopathology, there was no evidence of Cd-related hepato-renal toxicity, despite a slight decrease of mean corpuscular volume and mean corpuscular hemoglobin of red blood cells with 40 ppm CdCl2. Dose-dependent accumulation of Cd was observed in the liver and kidneys with peak levels of 130 +/- 42 micrograms/g and 120 +/- 20 micrograms/g, respectively, at 18 months in animals treated with 40 ppm CdCl2. A dose-dependent increase in urinary Cd levels became evident with time. Induction of metallothionein (MT) was also observed in the liver and kidney with a high correlation to the corresponding Cd levels. In the proximal renal tubular epithelia of 40 ppm CdCl2-treated rats at 22 months, prominent accumulation of Cd was observed in secondary lysosomes associated with MT deposits in their exocytotic residual bodies. The results demonstrated that, in contrast to the case with high-dose Cd-administration, renal toxicity is not induced by long-term oral administration of low amounts of Cd, although tissue accumulation does occur. Possible protective mechanisms may be operating.