Cadmium-2-acetylaminofluorene interaction in isolated rat hepatocytes

Cadmium (Cd) is a non-essential, highly toxic heavy metal and a ubiquitous environmental contaminant. Evidence exists that Cd can affect parameters which are of great importance in the response towards xenobiotics. However, there is a lack of information about the mechanisms that take place at the cellular and molecular levels upon dual exposure to Cd and other toxins. The purpose of the present work was therefore to examine the biochemical interactions between Cd and a well-known genotoxic hepatocarcinogen, 2-acetylaminofluorene (AAF) in isolated rat hepatocytes. The cells were incubated for 10 hr with a sub-cytotoxic concentration (0.22 M) of ¹⁰⁹Cd. This was followed by a 10 hr exposure to 1 M [³H]AAF. Cellular distribution of Cd and ³H was determined. Sephadex G-75 elution profiles of the cytosol showed that Cd was almost entirely associated with the intermediate molecular weight (IMW) fractions containing metallothionein (MT) (>80%), and with high molecular weight proteins. In parallel, the highest proportion of ³H was found in the low molecular weight components. Further analysis of IMW fractions by DEAE A-25 anion-exchange chromatography revealed that, in addition to Cd, there was some ³H which coeluted along with MT-I and MT-II isoforms, but preferentially with MT-I. Moreover, Cd pretreatment caused a 1.6-fold increase in MT level, as measured by the silver-saturation assay. Under these conditions, there was a 17% lower binding of ³H to the DNA. This reduced binding was neither accompanied by diminished AAF uptake nor by inhibition of cytochrome P-450 activity. Taken together, these results suggest that Cd exposure has a protective effect against the genotoxicity of AAF. MT, whose synthesis is induced, could play a role in the Cd-AAF interaction through scavenging of reactive metabolites.Abbreviations AAF 2-acetylaminofluorene - Cd cadmium - DMSO dimethyl sulfoxide - HBSS Hank's balanced salt solution - LDH lactate dehydrogenase - MT metallothionein - UDS unscheduled DNA synthesis     

Cadmium and zinc influx characteristics by intact corn (Zea mays L.) seedlings

Summary Cadmium and zinc uptake parameters were determined for intact corn (Zea mays L.) seedlings grown for 15 and 22 in nutrient solutions containing levels of Cd and Zn that were similar to those found in soil solutions. Uptake of both elements was assumed to follow Michaelis-Menten kinetics. Calculations were based on the concentrations of free ionic Cd (Cd²⁺) and Zn (Zn²⁺) rather than the total solution concentration. Rates of Zn uptake were measured by determining depletion of Zn for periods of up to 30 h from solutions containing initial concentrations of 1.5 and 10μmol Zn 1⁻¹. Depletion curves suggested that Zn uptake characteristics were similar at both levels of Zn in solution. The Imax for Zn uptake decreased from 550 to 400 pmol m⁻² root surface s⁻¹ between 16 and 22 d of growth while Km decreased from 2.2 to 1.5 μmol Zn²⁺ 1⁻¹. Cadmium uptake parameters were measured by controlling Cd²⁺ activities in nutrient solution betwen 6.3 to 164 nmol l⁻¹ by continuous circulation of nutrient solution through a mixed-resin system. Imax for Cd uptake was 400 pmol m⁻² root surface s⁻¹ at 15 and 22 d of growth. The magnitude of Km increased from 30 to 100 nmol Cd²⁺ 1⁻¹ during this time period. The Km value suggests that corn is efficient for Cd uptake. The results of these uptake studies are consistent with the observed uptake of Zn and Cd by corn seedlings in soils.     

Lead and cadmium content of Indian flue-cured tobacco

Summary Studies on levels of lead and cadmium of Indian flue-cured tobacco indicated that the leaf contained very low amounts of these heavy metals as compared to tobacco from other countries. Indian tobacco can therefore be adjudged as ‘safe and clean’ and least hazardous to the smoker. Of the two heavy metals, lead content of soils is higher than cadmium. But in the leaf, cadmium content is more than lead indicating that soil cadmium may be more available to tobacco and hence more readily absorbed by the plant than lead.     

Optimum utilization of sewage sludge of low and high metal content for grain production on arid lands

Summary Two municipal sludges, one from a highly industrialized city, Chicago, Il, and another from a little industrialized, highly agricultural area, Tucson, AZ are compared for winter barley production on Pima c 1 (Typic torrifluvent). Both sludges were responsible for highly significant additions of Zn, Cu, Ni, Cd and P to the soil each year when applied at the rates of 100 mt/ha singly and 20 mt/ha each year for 4 years. Nitrogen responses for barley straw and grain were observed from both sludges. Tucson sludge appears to be attractive as a potential fertilizer, not only as an NPK source, but also for its organic matter and minimal amounts of heavy metals. The Chicago sludge with relatively high levels of heavy metals, particularly Cd, appears poorly suited as a fertilizer, if used for an extended period of time, because of the plant's tendency to take up elevated levels of certain heavy metals. Some parts of barley plants proved to be a better indicator of heavy metal uptake and concentration than others. The diagnostic-tissue test promises to be a useful tool to warn against undesirable accumulation of heavy metals. Fortunately, when compared with other plant parts, the heavy metal in grain was the least altered as a result of continued sewage sludge use on arid land. The soil's neutral to slightly alkaline pH and the presence of lime throughout the soil profile appeared to be critical factors in keeping plant uptake of heavy metals relatively low as compared with soils of other climates.     

Structural analysis of a maize gene coding for glutathione-S-transferase involved in herbicide detoxification

Summary We have used the cDNA clone encoding maize glutathione-S-transferase (GST I) to isolate a genomic DNA clone containing the complete GST I gene. Nucleotide sequence analysis of the cDNA and genomic clones has yielded a complete amino acid sequence for maize GST I and provided the exon-intron map of its gene. The mRNA homologous sequences in the maize GST I gene consist of a 107 bp 5 untranslated region, a 642 bp coding region and 340 bp of the 3 untranslated region. They are divided into three exons by two introns which interrupt the coding region. The 5 untranslated spacer contains an unusual sequence of pentamer AGAGG repeated seven times. The inbred maize line (Missouri 17) contains a single gene for GST I, whereas the hybrid line (3780A) contains two genes. Nucleotide sequence analysis of the primer extended cDNA products reveals that the 5 untranslated regions of the two genes in the hybrid 3780A are identical except for a 6 bp internal deletion (or insertion). The amino acid sequence of maize GST I shares no apparent sequence homology with the published sequences of animal GST's and represents the first published sequence of a plant GST. re]19850813 ac]19851126     

Variation in the relationship between nitrogen fixation, leghemoglobin, nodule numbers and plant biomass in alfalfa (Medicago sativa) caused by treatment with arsenate, heavy metals and fluoride

Potential relationships between alfalfa ( Medicago sativa L. cv. Vernal) acetylene reduction activity (ARA) and leghemoglobin content, nodule numbers, shoot biomass, root biomass, or total plant biomass were estimated using linear regression analysis after treatment with a range of concentrations of arsenate, Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, and F^–. There were highly significant positive linear regressions between ARA and all the other plant values in the control plants, but this linear relationship was significantly altered between ARA and one or more of the other parameters in all treatments. There was also evidence for an alteration of the slope in some of the treatments when compared to control treatments even though a linear model was still applicable.     

Accumulation of cadmium by immobilizedZoogloea ramigera 115

Summary Zoogloea ramigera 115 was immobilized into beads of calcium-alginate and placed into batch air-bubbled column reactors. In the absence of any added nutrients the immobilized bacterium adsorbed Cd from solutions containing levels of 2 and 20 g ml^–1 per day, over a period of 21 and 20 days, respectively. Adsorption of Cd from solutions containing 20 g ml^–1 Cd was better than 90% for 16 days. Beads treated with Cd at 2 g ml^–1 never adsorbed less than 95% of the metal. Alginate adsorbed Cd as well, but inclusion of cells changed the effectiveness of adsorption. Of a 250 g ml^–1 Cd solution, alginate adsorbed 70.4% Cd in 60 min whereas alginate plus cells adsorbed 90.5% in the same time span. Temperature had no effect on adsorption by immobilized cells at levels of 2 and 10 g ml^–1 Cd. However at higher concentrations, binding was enhanced as temperature increased.Z. ramigera beads were stable during all treatments and for prolonged periods of time (21 days).     

Crown ether mediated cadmium halide dimers and polymers

The reactions of cadmium halides with the 15-membered macrocyclic crown ethers, 15-crown-5 and benzo-15-crown-5, have been carried out and six new complexes have been isolated and structurally characterized. Metal to ligand stoichiometries of 1:1, 2:1, 3:1 and 3:2 have been observed with a variety of different formulations. Examples of charge separated ion pairs ([(NH₄)(benzo-15-crown-5)₂]₂[Cd₂I₆]), halogen bridged monomers, dimers or polymers ([Cd(15-crown-5)(OHMe)(μ-Br)CdBr₃], [Cd(15-crown-5)(μ-Br)₂CdBr(μ-Br)]₂(isolated from the same reaction mixture) and [(CdCl₂)₂CdCl₂(15-crown-5)]_n), and hydrogen bonded finite chains or polymers ([(Cd(OH₂)₂(15-crown-5)][CdI₃(OH₂)]₂·2(15-crown-5)·2CH₃CN and [CdI₂(OH₂)₂(THF)]·benzo-15-crown-5) have been isolated. Three different types of 15-crown-5 coordination modes have been observed in these complexes. In-cavity coordination resulting in pentagonal bipyramidal geometries about Cd²⁺ was observed in [(CdCl₂)₂CdCl₂(15-crown-5)]_n, [Cd(15-crown-5)(OHMe)(μ-Br)CdBr₃], and [Cd(OH₂)₂(15-crown-5)][CdI₃(OH₂)]₂·2(15-crown-5)·2CH₃CN, [Cd(15-crown-5)(μ-Br)₂CdBr(μ-Br)]₂ displays out-of-cavity coordination with one etheric donor distorted into an axial position of a distorted pentagonal bipyramid. The third coordination mode is secondary sphere coordination via hydrogen bonding which is observed for [Cd(OH₂)₂(15-crown-5)][CdI₃(OH₂)]₂·2(15-crown-5)·2CH₃CN. The good fit of Cd²⁺ within the cavity of 15-crown-5 results in shorter bonding contacts and a more narrow distribution in Cd---O values (2.273(7)-2.344(6) Å) than observed for cadmium halide complexes of 18-crown-6 (Cd---O = 2.69(1)–2.81(1) Å).     

Calcium-cadmium interaction on sugar absorption across the rabbit jejunum

The element Cd is considered to have no biological function and is highly toxic to humans and animals. Toxic effects of this metal upon cell membrane structure and function have been shown. On the other hand, Ca is an essential element in a wide variety of cellular activities. The present study was initiated to research whether the interaction between Ca and Cd could affect D-galactose absorption across the rabbit jejunum in vitro. In media with Ca²⁺, when CdCl₂ was present at 0.5 or 1 mM, Cd was found to significantly reduce the sugar absorption. In Ca²⁺-free media, where CaCl₂, was omitted and replaced isotonically with choline chloride, the sugar transport was not modified by Cd, but when CaCl₂ was replaced isotonically with MgCl₂, the inhibition is observed. Verapamil at 10⁻⁶ M (blocking mainly Ca²⁺ transport) did not modify the inhibitory effect of cadmium on D-galactose transport. When 10⁻⁶ M of A 23187 (Ca²⁺ specific ionophore) was added in media with/without Ca²⁺; CdCl₂ produced no change in D-galactose transport. These results suggest that Ca and Cd could have affinity for the same chemical groups of enterocyte membrane, which would be related with the intestinal absorption of D-galactose.     

The role of glutathione biosynthesis in heavy metal resistance in the fission yeast Schizosaccharomyces pombe

Abstract: Plants and the fission yeast Schizosaccharomyces pombe synthesize small cadmium-binding peptides, called phytochelatins, in response to cadmium. Derived from glutathione (GSH: λ-Glu-Cys-Gly), they have the general structure (λ-Glu-Cys) n Gly, where n is 2–11. In order to study the biosynthesis of phytochelatins, we used the mutagen N -methyl- N '-nitro- N nitrosoguanidine (MNNG) to select mutants with a lowered GSH content. GSH-deficient mutants show a Cd-sensitive phenotype, whereas resistance to Cu is only slightly influenced. These Cd-sensitive mutants contain 2–15% of the wild-type GSH level. For three mutants a lowered activity of λ-glutamylcysteine synthetase was measured. One of the mutants was transformed to Cd-resistance and the complementing fragment was analyzed further. The complementing fragment hybridized with chromosome III. In the transformants, GSH content was restored up to wild-type levels, whereas the activity of λ-glutamylcysteine synthetase was significantly increased compared with the wild-type. Possible mechanisms for Cd-resistance in the transformants are discussed.