Effects of Detergent Formula Chelating Agents on the Metabolism and Toxicity of Cadmium in Mice

Abstract Chelating agents like NTA (nitrilotriacetic acid) STPP (sodiumtripolyphosphate, Na₅P₃O₁₀) and EDTA (ethylenediaminetetraacetic acid) are used as components of detergents. An increased toxicity of some metal compounds when combined with NTA has led to decreased use of this chelating agent in relation to STPP. In the present studies short-term and long-term effects of these chelating agents on cadmium toxicity in mice were investigated. I: In the short-term study, mice subcutaneously exposed to CdCl₂ (3.2 mg Cd/kg b.wt.) in combination with STPP (32 mg/kg b.wt.) demonstrated a markedly higher mortality compared to animals given CdCl₂ alone. This increase in mortality was similar to the one encountered when CdCl₂ (3.2 mg Cd/kg b.wt.) and NTA (32 mg/kg b.wt.) were combined. Animals exposed subcutaneously to CdCl₂ + STPP or CdCl₂ + NTA showed histological evidence of liver necrosis 24 hrs after exposure not seen in animals given the same dose of CdCl₂ alone and also had markedly lower cadmium concentrations in the livers compared to only Cd-exposed animals. II: In the long-term study, mice were exposed orally to CdSO₄ (50 p.p.m. Cd) alone or in combination with STPP (500 p.p.m.), NTA (500 p.p.m.) or EDTA (50 p.p.m.) by continuous administration via the drinking water for 18 months. A decreased total excretion of urine proteins was seen in all Cd- treated animals irrespectively of the combination with various chelating agents. The conclusion of the present work was that NTA and STPP given by subcutaneous injection to mice markedly increased the toxicity of cadmium but that neither NTA, STPP nor EDTA given orally altered the toxicity of cadmium during a period of long-term exposure of 18 months.     

The Late and Persistent Pathogenic Effects of Cadmium at Very Low Levels on the Kidney of Rats

Cadmium (Cd) is an important nephrotoxic pollutant. To examine late effects on the kidney of individuals previously exposed to chronic Cd at very low levels, male Wistar rats were given 20 nmol/kg i.p. injections of Cd every other day for 4 weeks. At the 20^th, 28^th, 36^th, 44^th and 52^nd week of the study, renal metal accumulation, morphology and function were examined. Immunochemical staining was performed to detect renal 3-nitrotyrosine (3-NT) accumulation, metallothionein (MT) expression, cell proliferation and global DNA methylation. Results showed that renal Cd concentration and MT expression along with 3-NT accumulation were significantly higher in the Cd group than that in the control. Histopathologically renal tubule damage at the early stage and hyperplasia at the late stage were observed in the Cd group. Renal fibrosis in glomeruli was evident in the Cd group, particularly at the late stage of the study. Immunoreactivity of global DNA methylation was markedly diminished in the Cd group at both 20^th and 52^nd weeks. These results suggest that previous exposure to chronic Cd at very low level induced persistent damaging effects on the kidney along with increases in cell proliferation and global DNA hypomethylation.     

Influence of Certain Chelating Agents on Egress of Cadmium from Cultured Epithelial Cells Containing High Amounts of Metallothionein: A Screening of Cd-Releasing and Toxic Effects

Abstract: Cell cultures have been used to study the effect of 6 different metal chelating compounds on the efflux of Cadmium (Cd) from the cells and on cell growth. The cells had previously been made resistant to high levels of Cd (100 μmol/1) in the medium. They contain large amounts of intracellular Cd (40–50 nmol Cd/mg cell protein), the main part of which is bound to cytoplasmic metallothionein. Among the different monothiol and dithiol compounds tested are some old, well-known and to some extent therapeutically tried substances, i.e. 2,3-dimercapto-1-propanol (BAL), D-penicillamine (PA), N-acetyl-DL-penicillamine (NAPA) and some newer metal chelators, i.e. 2,3-dimercaptopropane-1-sulphonate (BAL-Sulph), mercaptosuccinic acid (MSA) and meso-2,3-dimercaptosuccinic acid (DMSA). The three latter ones all showed better effect on the egress of Cd than PA and NAPA and less toxic effect than BAL on an equimolar basis. All the agents tested increased the efflux of Cd from metallothionein-containing cell cultures which seem to be justified as a test system for primary screening of effect and toxicity of new chelators.     

Influence of Age on in Vitro Effect of Cadmium on Rat Liver Cytochrome P-450 Concentration and Monooxygenases Activity

Abstract: Cadmium⁺⁺ added in vitro destroys rat liver cytochrome P-450 (cyt. P-450) with increasing age by 25–50%. Ethylmorphine N-demethylation is inhibited only in rats 30-days old and thereafter. Ethoxycoumarin 0-deethylation is inhibited even in newborn rats, and the maximal inhibition appears to increase with age. It is concluded that in all age groups cadmium resistent cyt. P-450 subspecies are present. Ethoxycoumarin 0-deethylase activity possibly indicates the cadmium sensitive P-450 fraction.     

The Effect of N–acetyJated DL–penicillamine and DL–homocysteine Thiolactone on the Mercury Distribution in Adult Rats,Rat Foetuses and Macaca Monkeys after Exposure to Methyl Mercuric Chloride

Abstract The distribution and excretion of mercury was studied in pregnant rats, given a single intravenous dose of 2 μmol/kg of CH₃²⁰³HgCl on the 13th day of pregnancy. Oral treatment for one week with N–acetyl–DL–penicillamine (4 mmol/kg per day) increased the mercury excretion in faeces (from 45 to 120 nmol) and urine (from 9 to 160 nmol). Such treatment mobilized mercury from all the organs tested, and the foetal and maternal brain levels of mercury were decreased to 1/5 and 1/3 of the controls, respectively. A four–day period of treatment with N–acetyl–DL–penicillamine started three days after the injection of methyl mercury reduced the foetal and maternal brain levels to 1/2 and 2/3 of the controls, respectively. The rapid removal of metal deposits following treatment with N–acetyl–DL–penicillamine is attributed to a free penetration of the complexing thiol into the tissue cells in question. No signs of toxicity were detected in monkeys given an effective daily dose of the agent (4 mmol/kg) for 6 days. In contrast N–acetyl–DL–homocysteine thiolactone was found to be toxic in the monkeys. In addition, the latter agent was ineffective in increasing the mercury elimination from the brains of monkeys, rats and rat foetuses.     

Oral Toxicity of Okadaic Acid in Mice: Study of Lethality,Organ Damage,Distribution and Effects on Detoxifying Gene Expression

In vivo, after administration by gavage to mice and rats, okadaic acid has been reported to produce lesions in liver, small intestine and forestomach. Because several reports differ in the damage detected in different organs, and on okadaic acid distribution after consumption, we determined the toxicity of this compound after oral administration to mice. After 24 hours, histopathological examination showed necrotic foci and lipid vacuoles in the livers of intoxicated animals. By immunohistochemical analysis, we detected this toxin in the liver and kidneys of intoxicated animals. Okadaic acid induces oxidative stress and can be activated in vitro into reactive compounds by the post-mitochondrial S9 fraction, so we studied the okadaic effect on the gene expression of antioxidant and phase II detoxifying enzymes in liver. We observed a downregulation in the expression of these enzymes and a reduction of protein expression of catalase and superoxide dismutase 1 in intoxicated animals.