Effects of cadmium on the immune system of mice

The Role of Natural Antioxidants Against Reactive Oxygen Species Produced by Cadmium Toxicity: A Review

Cadmium (Cd) is a significant ecotoxic heavy metal that adversely affects all biological processes of humans, animals and plants. Exposure to acute and chronic Cd damages many organs in humans and animals (e.g. lung, liver, brain, kidney, and testes). In humans, the Cd concentration at birth is zero, but because the biological half-life is long (about 30 years in humans), the concentration increases with age. The industrial developments of the last century have significantly increased the use of this metal. Especially in developing countries, this consumption is higher. Oxidative stress is the imbalance between antioxidants and oxidants. Cd increases reactive oxygen species (ROS) production and causes oxidative stress. Excess cellular levels of ROS cause damage to proteins, nucleic acids, lipids, membranes and organelles. This damage has been associated with various diseases. These include cancer, hypertension, ischemia/perfusion, cardiovascular diseases, chronic obstructive pulmonary disease, diabetes, insulin resistance, acute respiratory distress syndrome, idiopathic pulmonary fibrosis, asthma, skin diseases, chronic kidney disease, eye diseases, neurodegenerative diseases (amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, and Huntington disease). Natural antioxidants are popular drugs that are used by the majority of people and have few side effects. Natural antioxidants play an important role in reducing free radicals caused by Cd toxicity. Our goal in this review is to establish the relationship between Cd and oxidative stress and to discuss the role of natural antioxidants in reducing Cd toxicity.

Mercury and arsenic attenuate canonical and non-canonical NLRP3 inflammasome activation

Exposure to heavy metals can cause several diseases associated with the immune system. Although the effects of heavy metals on production of inflammatory cytokines have been previously studied, the role of heavy metals in inflammasome activation remains poorly studied. The inflammasome is an intracellular multi-protein complex that detects intracellular danger signals, resulting in inflammatory responses such as cytokine maturation and pyroptosis. In this study, we elucidated the effects of four heavy metals, including cadmium (Cd), mercury (Hg), arsenic (As), and lead (Pb), on the activation of NLRP3, NLRC4, and AIM2 inflammasomes. In our results, mercury and arsenic inhibited interleukin (IL)-1β and IL-18 secretion resulting from canonical and non-canonical NLRP3 inflammasome activation in macrophages and attenuated elevation of serum IL-1β in response to LPS treatment in mice. In the mechanical studies, mercury interrupted production of mitochondrial reactive oxygen species, release of mitochondrial DNA, and activity of recombinant caspase-1, whereas arsenic down-regulated expression of promyelocytic leukemia protein. Both mercury and arsenic inhibited Asc pyroptosome formation and gasdermin D cleavage. Thus, we suggest that exposure to mercury and/or arsenic could disrupt inflammasome-mediated inflammatory responses, which might cause unexpected side effects.

Mechanism of cadmium induced apoptosis in human peripheral blood lymphocytes: the role of p53, Fas and Caspase-3

Cadmium (Cd) is a major pollutant of environment. It can be fatal to human. In spite of bulk of research and literatures, the mechanism of a fatality against human is still not understood completely. Toxic and carcinogenic effects of Cd in rodents and humans are well known. However, effects of Cd on induction of apoptosis are still elusive. This study indicates immunosuppression and immunotoxicity due to Cd exposure. Present study was undertaken to determine the mechanism of cell death in vitro in human peripheral blood lymphocytes induced by Cd. Our findings suggest the toxicity due to Cd is attributed to programmed cell death-apoptosis. IC₅₀ was calculated at 21.74 μM. A significant increase of expression of the pro-apoptotic genep53, Fas and Caspase-3 in human lymphocytes was found. Cd induced p53-dependent apoptosis through cooperation between Bak upregulation without changing the Bcl-2 and Bax expression. Data of this study compel to speculate that apoptosis may also be attributed to CD95/Fas complex formation, and p53 direct apoptogenic potential at mitochondria. It was confirmed by the increased expression of Caspase-3. Although, this work does not address all the questions regarding the mechanism of Cd induced apoptosis, but these findings establish an important role of p53 and mitochondrial function during apoptosis in human lymphocyte. Moreover, based upon our findings, the role of Fas in Cd induced apoptosis is also undeniable. Hence further investigations are required to understand the different mechanism involved into apoptosis of lymphocytes due to Cd exposure.

Humoral and cell mediated immune response to cadmium in mice

The effect of 30, 100 and 300 ppm of cadmium chloride (CdCl2) exposure for 35 days on humoral and cell mediated immune response was examined in Swiss Albino mice. Body burden of cadmium in kidney, spleen and liver was determined and histopathology of these organs was also done. Cadmium chloride in doses of 100 and 300 ppm when fed in drinking water caused significant decrease in IgM and IgG titre against sheep red blood cells (SRBC) and a significant decrease in IgG titre against bovine serum albumin (BSA). The delayed type hypersensitivity response to SRBC and splenic T cell proliferation to BSA was also significantly decreased following 100 amd 300 ppm cadmium exposure. Cadmium accumulation in the spleen, liver and kidney was associated with degeneration and inflammatory changes. It is concluded that cadmium causes significant suppression of humoral and cell mediated immune response in mice which could be due to its cytotoxic action on liver, kidney and immune cells.

Effects of chromium on humoral and cell-mediated immune responses and host resistance to disease in a freshwater catfish, Saccobranchus fossilis (Bloch)

The effects of subtoxic levels of Cr on humoral and cell-mediated immune responses, blood parameters, susceptibility to bacterial (Aeromonas hydrophila) infection, and macrophage activity in the freshwater air-breathing Asian catfish, Saccobranchus fossilis, during a 28-day exposure were examined by a static bioassay test procedure. At 0.1, 1.0, and 3.2 mg / liter Cr, dose-dependent Cr accumulation in kidney, liver, and spleen was observed at the end of the experiment. Chromium exposure caused a significant change in spleen to body weight ratio. Fish exposed to Cr concentrations had lower antibody titer values, reduced numbers of splenic and kidney plaque-forming cells, and higher counts of splenic lymphocytes but reduced counts of kidney cells when compared with the control group. At 0.1, 1.0, and 3.2 mg /liter Cr, dose-dependent decreases in red blood cell counts, hemoglobin content, and packed cell volume were observed. Differential leukocyte counts revealed that Cr exposure caused a significant decrease in large and small lymphocytes, whereas neutrophils and thrombocytes increased. Effects of Cr exposure to mitogen (Con A) on proliferation of splenic and pronephric lymphocytes suggests a decrease in mitogenic response. The eye-allograft rejection time, as a parameter of cell-mediated immunity, was statistically increased at 1.0 and 3.2 mg/liter Cr. Fish exposed to Cr for 28 days exhibited higher susceptibility to A. hydrophila infection than control fish. The results suggest that Cr exposure reduced the resistance of catfish to bacterial infections. The phagocytic activity of splenic and pronephros macrophages was examined in vitro and found to be significantly decreased.

Influence of inhaled cadmium on the immune response to influenza virus

Cadmium may exacerbate pulmonary infections. In a previous study, however, cadmium appeared to enhance mouse resistance to influenza pneumonia. We report herein on the influence of cadmium intoxication in mice on different factors of anti-influenza immunity, e.g., antibody response, local production of interferon, pulmonary cellular response, and the interaction between pulmonary alveolar macrophages and the influenza virus. Cadmium inhalation did not affect production of antibodies or interferon. The protective effect appeared to be related to an enhanced supply to phagocytic cells into the lung.

Effects of mainstream and environmental tobacco smoke on the immune system in animals and humans: a review

This review evaluates the available information on the effects of mainstream and environmental tobacco smoke on the immune system in animals and humans. The primary emphasis is on mainstream smoke since little information is available on the effects of environmental smoke. The effects of mainstream tobacco smoke on the immune system in humans and animals are similar. Animals exposed to mainstream tobacco smoke for periods of a few weeks generally exhibit a slight immunostimulation. However, subchronic and chronic exposure studies indicate that immunosuppressive changes develop. Lymphocyte proliferation in response to the mitogens PHA and LPS is decreased, suggesting compromise of cell function. Antibody production can be suppressed. Smoke-exposed animals that are challenged with metastasizing tumors or viruses have been shown to exhibit a higher incidence of tumorigenic and infectious diseases, respectively. Localized immunological changes in the lung can include reduction of bronchus-associated lymphoid tissue and immunoglobulin levels. Smoking-related changes in the peripheral immune system of humans have included elevated WBC counts, increased cytotoxic/suppressor and decreased inducer/helper T-cell numbers, slightly suppressed T-lymphocyte activity, significantly decreased natural killer cell activity, lowered circulating immunoglobin titers, except for IgE which is elevated, and increased susceptibility to infection. The effects of environmental tobacco smoke on the immune system, in contrast to mainstream tobacco smoke, have just begun to be investigated and information available in the literature, to date, is limited. Immunoreactive substances are known to be present in environmental tobacco smoke, but to date, environmental tobacco smoke has been more closely associated with irritation than sensitization. A few studies have indicated a potential for environmental smoke-induced hypersensitivity and suppression of immunoregulatory substances. In contrast, other investigators have failed to detect immunological or other biological changes associated with environmental smoke. Clearly, more research is needed to resolve these differences.

Effects of cadmium on lymphocyte activation

The effects of cadmium (Cd) on phytohemoagglutinin or phorbol myristate acetate-induced lymphocyte activation were investigated and a dose-dependent inhibition of cell proliferation was found. Kinetic studies revealed that the Cd-sensitive step is an early event of T cell stimulation. Failure of IL2 secretion and reduction of IL2 receptor expression in the Cd-treated cells are also reported. Regardless of which mechanism is responsible for Cd effects, our studies show that the inhibition of lymphocyte activation is associated with reduced [3H]phorbol dibutyrate binding to Ca2+-phospholipid-dependent protein kinase and altered breakdown of phosphatidylinositols. Thus, Cd interferes with two biochemical events which play a critical role in lymphocyte signal transduction and activation.

Modulation of murine T and B cell reactivity after short-term cadmium exposure in vivo

This study assessed early effects of short-term Cd exposure on T and B cell responsiveness. Spleen cells from mice injected s.c. with a daily dosage of 1 mg, 0.33 mg, or 0.11 mg Cd (as CdCl2) per kg body weight for 5 days were examined for their potential to generate alloreactive T cells in a mixed lymphocyte reaction (MLR) and for mitogen reactivity to concanavalin A (Con A) in vitro. Spleen cells from the same mice were also assayed for the total number of IgM- and IgG-secreting B cells. Whereas alloreactivity was reduced, mitogen response to Con A was not different from controls or was even enhanced. The decrease in allogeneic MLR was dependent on the injected Cd dosage. No difference in susceptibility to Cd-induced effects was observed among the mouse strains tested, i.e. BALB/c, DBA/2, C57BL/6, and C3H/He. Co-cultivation of spleen cells, obtained from Cd-treated mice that exhibited deficient T cell reactivity, with splenic responder cells from untreated mice resulted in dose-dependent suppression of the normal MLR. These results indicate that the harmful effects of Cd on the immune system include the inhibition of antigen-specific T cell responses by the activation of an antigen non-specific suppressor system. In contrast to the suppressed allogeneic MLR, the same spleen cell populations showed augmented numbers of IgM- and IgG-antibody producing cells.

The chronic toxicity of aluminium, cadmium, mercury, and lead in birds: a review

The toxicity of chronic dietary metal exposure in birds is reviewed. It is concluded that significant physiological and biochemical responses to such exposure conditions occur at dietary metal concentrations insufficient to cause signs of overt toxicity. Particularly important are reproductive effects which include decreased egg production, decreased hatchability, and increased hatchling mortality. Young, growing birds are typically more sensitive to the toxic effects of chronic metal exposure than adults, and altricial species are often more sensitive than precocial species. Factors which modify the absorption and toxicity of heavy metals, such as Se for the case of Hg, and Ca for the case of Pb and Cd, are discussed. Monitoring strategies for assessing environmental metal exposure in birds are evaluated.

The effect of cadmium on chemical- and viral-induced tumor production in mice

Female Swiss mice were exposed to cadmium in the drinking water at concentrations ranging from 0 to 50 ppm for 105 or 280 day time periods. In the 105 day study, the effect of cadmium on urethan-induced pulmonary adenoma formation was evaluated. Urethan-induced sleeping times observed following i.p. injection of urethan after 3 weeks of cadmium exposure were not affected by cadmium indicating that chronic cadmium exposure did not alter the elimination of urethan. Pulmonary adenoma formation which was evaluated 84 days later was not affected by cadmium. The size and number of tumors remained unchanged. This suggests that the immunosuppressive actions of cadmium do not influence urethan-induced adenoma formation. In the 280-day study, the effects of cadmium on the incidence of spontaneous murine lymphocytic leukemia was evaluated. Mortality from the leukemia virus was greater in the cadmium-exposed mice. Mice exposed to 10 or 50 ppm cadmium experienced 33% more deaths from the virus. The average time till death was unaffected. It appears that the immunosuppressive effects of cadmium impair immunosurveillance mechanisms that control expression of the murine lymphocytic leukemia virus.

Evidence for stimulatory and inhibitory effects of cadmium on the [3H]thymidine incorporation into various organs of the mouse

The effects of cadmium chloride on the DNA turnover in various organs of the mouse were evaluated by measuring the incorporation of intraperitoneally injected [6-3H]thymidine. This approach is considered to be a useful complement to other short-term in vivo tests in the screening for genotoxic properties of chemicals. A moderate amount of CdCl2 (1 mg/kg body wt) lacked inhibitory effects on the incorporation of [3H] thymidine, but produced a significantly increased uptake of the DNA precursor into the liver. Whereas the genotoxic polycyclic aromatic hydrocarbon 3-methylcholanthrene suppressed the [3H]thymidine incorporation into several organs when given in a dose of 30 mg/kg body wt, cadmium chloride was inhibitory only when injected in a sublethal dose (4 mg/kg body wt). When the injected amount of CdCl2 was 4 mg/kg, an initial and transient inhibition of the [3H]thymidine incorporation was observed in several organs. After extending the time between the injection of cadmium and sacrifice to 72 h, such a high dose of cadmium produced potent stimulatory effects on the [3H]thymidine incorporation not only into the liver but also into the pancreas, kidney, small intestine, and testis. The mechanism behind the cadmium-induced stimulation of the DNA synthesis remains obscure but may be due to an increased biosynthesis of the cytoplasmatic protein metallothionein. The stimulatory effects of cadmium on the incorporation of [3H]thymidine correlate well both with reported sites of extensive accumulation of the heavy metal and the presence of high concentrations of cadmium-induced metallothionein.

Strain differences in cadmium-mediated suppression of lymphocyte proliferation in mice

Strain differences were investigated on the proliferative responses of splenic lymphocytes obtained from C3H/He, BALB/c, and DBA/2 mice that were treated with cadmium (Cd) for 5 days (0.5 or 1.0 mg Cd/kg/day, sc), and the results were compared with those of in vitro treatment of spleen cells with Cd. Following in vivo treatment, splenocytes from the C3H strain were significantly more susceptible to suppressive effects of Cd exposure on all indices for proliferative responses to mitogens (concanavalin A, phytohemagglutinin, and lipopolysaccharide) and allogeneic lymphocytes, while those from DBA and BALB strains were fairly resistant. Among the three strains, the highest Cd concentrations in plasma and spleen were obtained in the C3H strain with the lowest hepatic concentration of Cd. On the other hand, the Cd exposure hardly affected the splenic concentration of zinc in the C3H strain in contrast to its decrease in the others. When spleen cells obtained from normal mice were treated in vitro with Cd, the C3H strain was more resistant to the suppressive effect of Cd than the other strains. These results indicate that the mouse strain variations in Cd-mediated suppression of lymphocyte proliferation are not based on intrinsic lymphocyte sensitivities, but likely are due to differences in the metabolism of Cd, which is under genetic control.

The effect of cadmium on antibody responses to antigens with different cellular requirements

Six week old BDF1 or CD-1 female mice were exposed to cadmium chloride in the drinking water at concentrations ranging from 0 to 50 ppm cadmium for 3 weeks. The in vivo antibody response against dinitrophenyl-aminoethylcarbamylmethyl-Ficoll (DNP-Ficoll), a T-lymphocyte independent, macrophage dependent response, was enhanced by cadmium. Similarly, the in vivo antibody response against Escherichia coli 0127 (LPS), a T-lymphocyte and macrophage independent response, was also enhanced by cadmium. In contrast, the in vitro antibody response against sheep red blood cells (SRBC), a T-lymphocyte and macrophage dependent response, was suppressed in spleen cell cultures that contained cadmium-exposed non-adherent cells (lymphocytes). Cultures containing cadmium-exposed adherent cells (macrophages) were not suppressed by cadmium. These results suggest that the immunosuppressive effects of cadmium as it relates to humoral immunity involve T-lymphocyte function rather than macrophage or B-lymphocyte activity. The enhanced T-lymphocyte independent antibody responses which accompany suppressed T-lymphocyte-dependent responses following cadmium exposure are an indication of compensatory mechanisms that are associated with the immune system.

Evaluation of host resistance and immune function in cadmium-exposed mice

Adult female B6C3F1 mice received distilled water only or water containing 10, 50, or 250 ppm of cadmium chloride (CdCl2) for 90 days. Body weights were measured weekly. On selected days during exposure and on Day 91, Cd tissue concentrations were measured along with changes in primary antibody responses. On Day 91 mice also received a primary challenge with various infectious agents. T- and B-cell mitogenesis, natural killer (NK) cell function, delayed type hypersensitivity (DTH) as well as macrophage bactericidal activity, and phagocytosis were measured. There was no change in body weight gain, organ weights, or in humoral immunity during treatment even though cadmium had accumulated in significant quantities in the tissues. Compared with controls, exposure to cadmium had no statistically significant effect on mortality and mean survival time following primary or secondary challenge with any of the infectious agents. However, there was a dose-related, increased susceptibility to Herpes simplex type 2 virus. T- and B-lymphocyte proliferation was significantly reduced, and macrophage phagocytosis was significantly increased following cadmium exposure. NK cell activity was augmented, but not significantly. Macrophage bactericidal activity and DTH were not significantly altered.

Natural and acquired resistance of mice to infection by airborne Klebsiella pneumoniae after subchronic intoxication by cadmium administered orally

Mice daily ingested about 22 mg of cadmium per kg of body weight in drinking water for 30 days. On the 30th day, the liver and kidneys of the mice contained about 18 micrograms of Cd2+ per g of fresh organ. A group of these mice was immunized against Klebsiella pneumoniae using two injections of vaccine, the first on the 7th day and the second on the 14th day of intoxication. On the 28th day, the non-immunized and the immunized mice were infected via a respiratory route by one lethal dose 50% of K. pneumoniae (the LD50 for the immunized mice was 2.4 times higher than the LD50 for the non-immunized mice). Comparison with the non-intoxicated control mice showed that the ingestion of Cd2+ did not significantly modify the natural resistance or the acquired resistance of the mice to the infection by airborne K. pneumoniae.

Altered immune response during cadmium administration in mice

C57BL/6 mice were administered 50 or 200 ppm of Cd as CdCl2 in the drinking water for either 3 to 4 (short term) or 9 to 11 (long term) weeks. In other experimental designs, mice were exposed orally to 300 ppm of Cd or injected with 2.5 mg/kg of Cd ip. The proliferative response to the T cell mitogens Con A and PHA was increased in cultures of spleen cells from orally treated mice in most of the experiments performed. After primary immunization with sheep red blood cells, the number of IgM antibody forming cells per 10(7) spleen cells was also moderately higher in mice exposed to 50 or 200 ppm of Cd for short or long term. In contrast, long-term exposure to 300 ppm of Cd depressed the antibody response to SRBC. Administration of ZnCl2 prevented the enhancement of the PFC response in mice orally administered 50 ppm of Cd. The capacity to suppress the antibody response of spleen cells preincubated with sodium periodate was decreased after short-term oral or ip. Cd administration but was completely or partially recovered after long-term exposure to either 50 or 200 ppm of Cd.

Biochemical and hematological studies on perch, Perca fluviatilis, from the cadmium-contaminated river Emån

In a field investigation, biochemical and hematological parameters were measured in perch, Perca fluviatilis, living in the cadmium-contaminated river Emån in the southeast of Sweden. The number of lymphocytes was 45-100% higher in perch from the contaminated area than in the reference perch, indicating a stimulated immune defense. In addition, the cadmium-loaded fish suffered from a slight anemia and a disturbed carbohydrate metabolism and blood plasma ion composition. The observed effects suggest that cadmium affects fish in the environment similar to what has been observed in laboratory studied. However, the weaker response may imply that the perch in the field stimulation have been adapted and thus acquired an increased resistance to cadmium.

Modified distribution of lymphocyte subpopulation in blood and spleen from mice exposed to cadmium

The effect of cadmium (Cd) on the lymphocyte subpopulation in peripheral blood and spleen was studied in ICR mice given a daily subcutaneous injection of 0.5 and 1.0 mg Cd/kg body weight for 5 days or mice fed with the drinking water containing 3, 30 and 300 ppm Cd for 10 weeks. The reduction of blood B lymphocytes observed in Cd-injected mice was accompanied by the increase of the number of splenic B lymphocytes. On the other hand in Cd-fed mice the reduction of blood T lymphocytes was found and associated with the increase of the number of splenic T lymphocytes. These findings suggest that circulating lymphocytes may redistribute differentially in lymphoid organs responded to the Cd exposure.

Effect of cadmium chloride on rat brain synaptosomal ATPases

Cadmium has been shown to alter membrane-bound ATPases both in vitro and in rats treated with the metal. However, cadmium effects on the substrate and ionic activation kinetics of Na+-K+ ATPase activity were determined by a coupled enzymatic method. A concentration-response curve was determined using 5-30 microM cadmium chloride in the reaction medium. The data showed a 50% inhibition at 15 microM cadmium chloride. Cadmium effects on ATP, Na+ and K+ activation of Na+-K+ ATPase were determined by varying the concentration of these substrates at 15 microM cadmium chloride. The double-reciprocal plots showed that cadmium inhibition of Na+-K+ was competitive with ATP and Na+ in that the Km values were increased but not the Vmax values. In contrast, cadmium inhibition was noncompetitive with K+ activation where both Km and Vmax values were decreased. The present data suggest that cadmium may be competing with ATP and Na+ sites on Na+-K+ ATPase in rat brain synaptosomes.

Effect of cadmium on the immune response in rats

Adult male inbred Wistar rats were given a subtoxic dose of cadmium (25 ppm) orally for 4 weeks prior to and during immunization with sheep erythrocytes (E). The control group received tap water during the experimental period. No difference in the antibody response to E was found between the two groups. Mononuclear peripheral blood cells from experimental and control rats were stimulated with concanavalin A (Con A). The experimental rats had received 25 ppm Cd in the drinking water from weaning until sacrifice at 15 weeks of age. There was no difference in [3H]thymidine incorporation between the cells of the experimental group and those of the control group. Addition of Cd at very low concentrations to the cultures significantly depressed the [3H]thymidine incorporation of the cells from both groups of rats. Thus, a subtoxic dose of Cd apparently had no effect on the in vivo immune response in rats.

Strain variations in cadmium-induced suppression of lymphocyte transformation in mice

Cadmium is an environmental pollutant which has been shown in numerous studies to significantly affect immune responses. However, a review of the literature reveals many inconsistencies, both qualitative and quantitative, in the effects of cadmium on the immune system. In the present study, we examine the influence of genetic background on the effects of cadmium using lymphocyte transformation as an index of immunocompetence. Cadmium was added in vitro to mitogen and non-mitogen stimulated splenocyte cultures obtained from Balb/c, C57BL and C3HeB mice. Cadmium, 1-30 microM, was associated with a dose-dependent, linear inhibition of lymphocyte transformation in all strains. In unstimulated and Con A-stimulated cultures, the cadmium-inhibition plots were parallel but non-coincident in the three strains of mice with C57 being the most susceptible and C3H the most resistant to the inhibitory effects of cadmium. For LPS-stimulated lymphocyte transformation, the cadmium inhibition plots had different slopes in the three strains of mice suggesting a possible difference in the mechanism of action of cadmium. The relationship between these findings and cadmium-induced cytotoxicity as well as metallothionein synthesis are discussed.

Effect of chronic cadmium treatment on the ascorbic acid status of the rat

In rats chronically treated with varying doses of cadmium (Cd) (0.25, 0.50, 0.75 and 1.0 mg/kg body wt.), i.p., every alternate day for 7 weeks, a decrease in the ascorbic acid (AA) content of adrenals and liver was observed. In the adrenals AA depletion was significant and dose-dependent at all concentrations. In liver the decrease was significant only at a concentration of 0.75 and 1.00 mg/kg but the spleen did not show any change in AA content. Urinary excretion of beta2-microglobulin with increasing doses of Cd indicated progressive renal tubular damage. The decrease in tissue AA status was correlated with the severity of the renal tubular damage resulting in an inhibition of its reabsorption from the kidneys.