In vitro assessment of the toxicity of metal compounds

This review has focused on several parameters related to the delivery of carcinogenic metal compounds to the cell nucleus as a basis for understanding the intermediates formed between metals and cellular components and the effect of these intermediates on DNA structure and function. Emphasis has been placed on metal interactions at the cellular membrane, including lipid peroxidation, metal interactions with glutathione and their relation to membrane injury, and metal effects on the membrane bound enzyme, Na⁺/K⁺ ATPase. Metal binding to metallothionein is also considered, particularly as related to transport and utilization of metal ions and to genetic defects in these processes exemplified in Menkes disease. The ability of cadmium to induce the synthesis of metallothionein more strongly than zinc is also discussed in relation to other toxic and carcinogenic metals. The effects of metal ions on purified DNA and RNA polymerase systems are presented with some of the recent studies using biological ligand-metal complexes. This review points out the importance of considering how metals affect in vitro systems when presented as ionic forms or complexed to relevant biological ligands.     

Comparison of Au(III) and Ga(III) Ions’ Binding to Calf Thymus DNA: Spectroscopic Characterization and Thermal Analysis

Metals have been studied as potential chemotherapeutic agents for cancer therapies due to their high reactivity toward a wide variety of substances. The characterization of metal ion-binding capacities is essential to understand the possible effects of metals on target biomolecules. In the present study, biochemical effects of Au(III) and Ga(III) ions on calf thymus DNA (ctDNA) were studied comparatively via bioanalytical, spectroscopic, and thermal methods. Briefly, UV-Vis absorbance spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, and Fourier transform infrared (FT-IR) spectroscopy were utilized for spectroscopic characterization, and isothermal titration calorimetry (ITC) measurements were performed for thermal analysis. Our results reveal that both Au(III) and Ga(III) ions are capable of interacting with ctDNA, and Au(III) ions display a more favorable interaction and a higher binding affinity. ITC analyses indicate that the Au(III)-DNA interaction displays a binding affinity (K_a) around 1.43?×?10⁶ M^?1, while a K_a around 1.17?×?10⁵ M^?1 was observed for the Ga(III)-DNA binding. It was suggested that both metal ions are unlikely to change the structural B-conformation while interacting with ctDNA.     

Cytoplasmic inorganic polyphosphate participates in the heavy metal tolerance of Cryptococcus humicola

The basidiomycetous yeast Cryptococcus humicola was shown to be tolerant to manganese, cobalt, nickel, zinc, lanthanum, and cadmium cations at a concentration of 2.5 mmol/L, which is toxic for many yeasts. The basidiomycetous yeast Cryptococcus terreus was sensitive to all these ions and did not grow at the above concentration. In the presence of heavy metal cations, С. humicola, as opposed to C. terreus, was characterized by the higher content of acid-soluble inorganic polyphosphates. In vivo 4′,6′-diamino-2-phenylindole dihydrochloride staining revealed polyphosphate accumulation in the cell wall and cytoplasmic inclusions of С. humicola in the presence of heavy metals. In C. terreus, polyphosphates in the presence of heavy metals accumulate mainly in vacuoles, which results in morphological changes in these organelles and, probably, disturbance of their function. The role of polyphosphate accumulation and cellular localization as factors of heavy metal tolerance of Cryptococcus humicola is discussed.     

Inhibitory and stimulating effect of single and multi-metal ions on hexavalent chromium reduction by Acinetobacter sp. Cr-B2

Potential application of chromium reducing bacteria for industrial scale wastewater treatment demands that effect of presence of other metal ions on rate of Cr(VI) reduction be investigated, as industrial wastewaters contain many toxic metal ions. In the current study, the effect of different heavy metal ions (nickel, zinc, cadmium, copper, lead, iron) on chromium reduction by a novel strain of Acinetobacter sp. Cr-B2 that shows high tolerance up to 1,100 mg/L and high Cr(VI) reducing capacity was investigated. The alteration in Cr(VI) reduction capacity of Cr-B2 was studied both in presence of individual metal ions and in the presence of multi-metal ions at different concentrations. The study showed that the Cr(VI) reduction rates decreased in presence of Ni²⁺, Zn²⁺ and Cd²⁺ when present individually. Pb²⁺ at lower concentration did not show significant effect while Cu²⁺ and Fe³⁺ stimulated the rate of Cr(VI) reduction. In the studies on multi-metal ions, it was observed that in presence of Cu²⁺ and Fe³⁺, the inhibiting effect of Ni²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ on Cr(VI) reduction was reduced. Each of these metals affect the overall rate of Cr(VI) reduction by Cr-B2. This work highlights the need to consider the presence of other heavy metal ions in wastewater when assessing the bioreduction of Cr(VI) and while designing the bioreactors for the purpose, as rate of reduction is altered by their presence.     

Metal resistance in acidophilic microorganisms and its significance for biotechnologies

Extremely acidophilic microorganisms have an optimal pH of <3 and are found in all three domains of life. As metals are more soluble at acid pH, acidophiles are often challenged by very high metal concentrations. Acidophiles are metal-tolerant by both intrinsic, passive mechanisms as well as active systems. Passive mechanisms include an internal positive membrane potential that creates a chemiosmotic gradient against which metal cations must move, as well as the formation of metal sulfate complexes reducing the concentration of the free metal ion. Active systems include efflux proteins that pump metals out of the cytoplasm and conversion of the metal to a less toxic form. Acidophiles are exploited in a number of biotechnologies including biomining for sulfide mineral dissolution, biosulfidogenesis to produce sulfide that can selectively precipitate metals from process streams, treatment of acid mine drainage, and bioremediation of acidic metal-contaminated milieux. This review describes how acidophilic microorganisms tolerate extremely high metal concentrations in biotechnological processes and identifies areas of future work that hold promise for improving the efficiency of these applications.     

Exogenous EDDS modifies copper-induced various toxic responses in rice

Copper is a micronutrient required for living organisms, but is potentially toxic in excess. EDDS enhances the phytoextraction of many metals, but the underlying mechanism is fully unclear. Exposure of 200 μM Cu²⁺ for 3 days resulted in rice seedling growth inhibition, accompanied by a decrease in plasma membrane H⁺-ATPase activity, and an increase in relative electrolyte leakage ratios, indicating that maintaining of membrane structure integrity is crucial in acclimation of plants to heavy metal stress. In addition, the chlorophyll and carotenoid content was markedly decreased and the level of the mRNA of Cytochrome P450 gene, OsHMA9, the sulfate transporter gene, and the metallothionein-like protein gene was observed to increase in response to Cu stress. Cu treatment also induced a global epigenetic response which is associated with cell nucleus condensation. These physiological, genetic, and epigenetic responses of rice seedlings to excess copper were modified by the addition of EDDS, suggesting that the supply of EDDS in medium containing a high concentration of Cu ions could enhance plant tolerance potential to excess Cu toxicity through alleviating Cu-induced poisonous effects at various levels.     

Activation of GABAB Receptors Ameliorates Cognitive Impairment via Restoring the Balance of HCN1/HCN2 Surface Expression in the Hippocampal CA1 Area in Rats With Chronic Cerebral Hypoperfusion

Hyperpolarization-activated cyclic-nucleotide-gated cation nonselective (HCN) channels are involved in the pathology of nervous system diseases. HCN channels and γ-aminobutyric acid (GABA) receptors can mutually co-regulate the function of neurons in many brain areas. However, little is known about the co-regulation of HCN channels and GABA receptors in the chronic ischemic rats with possible features of vascular dementia. Protein kinase A (PKA) and TPR containing Rab8b interacting protein (TRIP8b) can modulate GABA_B receptors cell surface stability and HCN channel trafficking, respectively, and adaptor-associated kinase 1 (AAK1) inhibits the function of the major TRIP8b-interacting protein adaptor protein 2 (AP2) via phosphorylating the AP2 μ2 subunit. Until now, the role of these regulatory factors in chronic cerebral hypoperfusion is unclear. In the present study, we evaluated whether and how HCN channels and GABA_B receptors were pathologically altered and investigated neuroprotective effects of GABA_B receptors activation and cross-talk networks between GABA_B receptors and HCN channels in the hippocampal CA1 area in chronic cerebral hypoperfusion rat model. We found that cerebral hypoperfusion for 5 weeks by permanent occlusion of bilateral common carotid arteries (two-vessel occlusion, 2VO) induced marked spatial and nonspatial learning and memory deficits, significant neuronal loss and decrease in dendritic spine density, impairment of long-term potentiation (LTP) at the Schaffer collateral-CA1 synapses, and reduction of surface expression of GABA_B R1, GABA_B R2, and HCN1, but increase in HCN2 surface expression. Meanwhile, the protein expression of TRIP8b (1a-4), TRIP8b (1b-2), and AAK1 was significantly decreased. Baclofen, a GABA_B receptor agonist, markedly improved the memory impairment and alleviated neuronal damage. Besides, baclofen attenuated the decrease of surface expression of GABA_B R1, GABA_B R2, and HCN1, but downregulated HCN2 surface expression. Furthermore, baclofen could restore expression of AAK1 protein and significantly increase p-PKA, TRIP8b (1a-4), TRIP8b (1b-2), and p-AP2 μ2 expression. Those findings suggested that, under chronic cerebral hypoperfusion, activation of PKA could attenuate baclofen-induced decrease in surface expression of GABA_B R1 and GABA_B R2, and activation of GABA_B receptors not only increased the expression of TRIP8b (1a-4) and TRIP8b (1b-2) but also regulated the function of TRIP8b via AAK1 and p-AP2 μ2, which restored the balance of HCN1/HCN2 surface expression in rat hippocampal CA1 area, and thus ameliorated cognitive impairment.     

Ferritin—A general metal detoxicant

Binding of nonferrous metal ions to ferritin was compared to that of the phosphate-free or phosphate containing synthetic iron cores. The Scatchard plots for the synthetic cores reveal a high affinity site for Cd, Zn, Be, and Al, with K_D in the range 10^?5–10^?7 M. Preloading the cores with phosphate increased the number of metal ions bound without altering the K_D. The metal ions with smaller ionic radii (Be, Al) were bound in larger numbers than those with larger ionic radii (Cd, Zn). Ferritin isolated from soybean (Glycina max), horse spleen, and rat liver bound the metal ions in amounts larger than predicted from their iron core. Whereas the iron cores and their nonferrous metal ion complexes were insoluble, those in the protein shell remained in solution. Thus apoferritin precipitated with lower concentrations of aluminum than did holoferritin. Also, Al bound to apoferritin reduced the rate of iron loading into the protein.     

Muscimol as an Ionotropic GABA Receptor Agonist

Muscimol, a psychoactive isoxazole from Amanita muscaria and related mushrooms, has proved to be a remarkably selective agonist at ionotropic receptors for the inhibitory neurotransmitter GABA. This historic overview highlights the discovery and development of muscimol and related compounds as a GABA agonist by Danish and Australian neurochemists. Muscimol is widely used as a ligand to probe GABA receptors and was the lead compound in the development of a range of GABAergic agents including nipecotic acid, tiagabine, 4,5,6,7-tetrahydroisoxazolo(5,4-c)pyridin-3-ol, (Gaboxadol^®) and 4-PIOL.     

The GABAA Antagonist DPP-4-PIOL Selectively Antagonises Tonic over Phasic GABAergic Currents in Dentate Gyrus Granule Cells

GABA_A receptors mediate two different types of inhibitory currents: phasic inhibitory currents when rapid and brief presynaptic GABA release activates postsynaptic GABA_A receptors and tonic inhibitory currents generated by low extrasynaptic GABA levels, persistently activating extrasynaptic GABA_A receptors. The two inhibitory current types are mediated by different subpopulations of GABA_A receptors with diverse pharmacological profiles. Selective antagonism of tonic currents is of special interest as excessive tonic inhibition post-stroke has severe pathological consequences. Here we demonstrate that phasic and tonic GABA_A receptor currents can be selectively inhibited by the antagonists SR 95531 and the 4-PIOL derivative, 4-(3,3-diphenylpropyl)-5-(4-piperidyl)-3-isoxazolol hydrobromide (DPP-4-PIOL), respectively. In dentate gyrus granule cells, SR 95531 was found approximately 4 times as potent inhibiting phasic currents compared to tonic currents (IC₅₀ values: 101 vs. 427 nM). Conversely, DPP-4-PIOL was estimated to be more than 20 times as potent inhibiting tonic current compared to phasic current (IC₅₀ values: 0.87 vs. 21.3 nM). Consequently, we were able to impose a pronounced reduction in tonic GABA mediated current (>70 %) by concentrations of DPP-4-PIOL, at which no significant effect on the phasic current was seen. Our findings demonstrate that selective inhibition of GABA mediated tonic current is possible, when targeting a subpopulation of GABA_A receptors located extrasynaptically using the antagonist, DPP-4-PIOL.     

Cadmium and lead interactive effects on oxidative stress and antioxidative responses in rice seedlings

Interactive effects of two heavy metal pollutants Cd and Pb in the growth medium were examined on their uptake, production of reactive oxygen species (ROS), induction of oxidative stress and antioxidative defence responses in Indica rice (Oryza sativa L.) seedlings. When rice seedlings in sand culture were exposed to 150 μM Cd (NO₃)₂ or 600 μM Pb (CH₃COO)₂ individually or in combination for 8–16 days, a significant reduction in root/shoot length, fresh weight, relative water content, photosynthetic pigments and increased production of ROS (O₂˙^? and H₂O₂) was observed. Both Cd and Pb were readily taken up by rice roots and localisation of absorbed metals was greater in roots than in shoots. When present together in the growth medium, uptake of both the metals Cd and Pb declined by 25–40 %. Scanning electron microscope (SEM) imaging of leaf stomata revealed that Pb caused more distortion in the shape of guard cells than Cd. Dithizone staining of roots showed localisation of absorbed Cd on root hairs and epidermal cells. Both Cd and Pb caused increased lipid peroxidation, protein carbonylation, decline in protein thiol and increase in non-protein thiol. The level of reduced forms of non-enzymic antioxidants glutathione (GSH) and ascorbate (AsA) and their redox ratios (GSH/AsA) declined, whereas the activities of antioxidative enzymes superoxide dismutase (SOD) and guaiacol peroxidase (GPX) increased in metal treated seedlings compared to controls. In-gel activity staining also revealed increased intensities of SOD and GPX isoforms with metal treatments. Catalase (CAT) activity increased during early days (8 days) of metal exposure and declined by 16 days. Results suggest that oxidative stress is an important component in expression of Cd and Pb toxicities in rice, though uptake of both metals gets reduced considerably when present together in the medium.     

Green synthesis of silver and gold nanoparticles using Zingiber officinale root extract and antibacterial activity of silver nanoparticles against food pathogens

In the present study, we synthesized silver and gold nanoparticles with a particle size of 10–20 nm, using Zingiber officinale root extract as a reducing and capping agent. Chloroauric acid (HAuCl₄) and silver nitrate (AgNO₃) were mixed with Z. officinale root extract for the production of silver (AgNPs) and gold nanoparticles (AuNPs). The surface plasmon absorbance spectra of AgNPs and AuNPs were observed at 436–531 nm, respectively. Optimum nanoparticle production was achieved at pH 8 and 9, 1 mM metal ion, a reaction temperature 50 °C and reaction time of 150–180 min for AgNPs and AuNPs, respectively. An energy-dispersive X-ray spectroscopy (SEM–EDS) study provides proof for the purity of AgNPs and AuNPs. Transmission electron microscopy images show the diameter of well-dispersed AgNPs (10–20 nm) and AuNPs (5–20 nm). The nanocrystalline phase of Ag and Au with FCC crystal structures have been confirmed by X-ray diffraction analysis. Fourier transform infrared spectroscopy analysis shows the respective peaks for the potential biomolecules in the ginger rhizome extract, which are responsible for the reduction in metal ions and synthesized AgNPs and AuNPs. In addition, the synthesized AgNPs showed a moderate antibacterial activity against bacterial food pathogens.     

Presence and Colocalization of Type-1 Cannabinoid Receptors with Acetylcholine Receptors in the Motor End-Plate of Twitch Skeletal Muscle Fibers in the Frog

Using polyclonal and monoclonal antibodies to visualize under a confocal microscope type-1 cannabinoid receptors (CB₁) and acetylcholine (ACh) receptors, respectively, or α-bungarotoxin conjugated to Alexa-Fluor 555 for Ach receptors, we found that they colocalize on twitch muscle fibers in the frog (Rana pipiens). We show that both the CB₁ and ACh receptors are present on the fast skeletal muscle motor end-plate. The CB₁ receptor is present along the entire membrane of the muscle fiber, whereas the ACh receptor is expressed primarily at the motor end-plate. Analysis of the colocalization produced a cross-correlation coefficient of 0.519 ± 0.021 (n = 9) for both receptors at the muscle motor end-plate. This study suggests a close proximity between these two types of receptor proteins and that they could interact. CB₁ could function at some stage of excitation–contraction coupling in these muscle fibers. However, further investigation is needed in order to clarify these issues.     

Conserved metallomics in two insect families evolving separately for a hundred million years

Μetal cofactors are required for enzymatic catalysis and structural stability of many proteins. Physiological metal requirements underpin the evolution of cellular and systemic regulatory mechanisms for metal uptake, storage and excretion. Considering the role of metal biology in animal evolution, this paper asks whether metal content is conserved between different fruit flies. A similar metal homeostasis was previously observed in Drosophilidae flies cultivated on the same larval medium. Each species accumulated in the order of 200 µg iron and zinc and approximately ten-fold less manganese and copper per gram dry weight of the adult insect. In this paper, data on the metal content in fourteen species of Tephritidae, which are major agricultural pests worldwide, are presented. These fruit flies can be polyphagous (e.g., Ceratitis capitata) or strictly monophagous (e.g., Bactrocera oleae) or oligophagous (e.g., Anastrepha grandis) and were maintained in the laboratory on five distinct diets based on olive oil, carrot, wheat bran, zucchini and molasses, respectively. The data indicate that overall metal content and distribution between the Tephritidae and Drosophilidae species was similar. Reduced metal concentration was observed in B. oleae. Feeding the polyphagous C. capitata with the diet of B. oleae resulted in a significant quantitative reduction of all metals. Thus, dietary components affect metal content in some Tephritidae. Nevertheless, although the evidence suggests some fruit fly species evolved preferences in the use or storage of particular metals, no metal concentration varied in order of magnitude between these two families of Diptera that evolved independently for over 100 million years.     

Nickel and zinc effects,accumulation and distribution in ruderal plants Lepidium ruderale and Capsella bursa-pastoris

Ruderal plants can grow in polluted areas, but little is known about heavy metal accumulation and distribution in them. Here Ni and Zn accumulation, distribution and effects were investigated in Lepidium ruderale and Capsella bursa-pastoris grown at 5–30 µM Ni(NO₃)₂ or 10–80 µM Zn(NO₃)₂. Metal contents were measured by flame atomic absorption spectrophotometry and tissue distribution of metals was studied histochemically. Ni was more toxic than Zn for both plants. When metal-induced growth-inhibiting effects were compared at various metal concentrations in solution, L. ruderale was more tolerant to Ni, whereas C. bursa-pastoris to Zn. However, when compared at similar Zn or Ni contents in roots, root growth of C. bursa-pastoris was more tolerant than that of L. ruderale. On the contrary, at similar Zn or Ni contents in shoots, shoot growth of L. ruderale was more tolerant. Both plants are excluders maintaining low metal levels in shoots. In roots, Ni located in protoplasts while Zn was also detected in cell walls. Metal accumulation in root apices resulted in growth inhibition. Ni accumulation in root cortex constrained metal translocation into central cylinder and then to shoots, where it located only in conductive tissues and epidermis, particularly in leaf trichomes of C. bursa-pastoris. Zn was translocated to shoots more actively and distributed in all shoot tissues, being accumulated in leaf vascular bundles and epidermis. To conclude, these patterns of Ni and Zn distribution are aimed at metal sequestration in roots and leaf epidermis, thus keeping mesophyll from metal penetration and pigment degradation.     

Molecular biology of inhibitory amino acid receptors

Biochemical approaches to neurotransmitter receptors have been extensively exploited in recent years. With the introduction of radiolabeled analogs of transmitters or drugs thought to act at these transmitter receptors, it has become possible to directly study the binding sites of neurotransmitter receptors and draw conclusions as to the relative order of potency of drugs at these sites and their putative pharmacological properties. In addition, many conclusions about the properties of the neurotransmitter receptors have been reached by comparing the equilibrium binding constants and apparent numbers of receptors following various pharmacological and physiological manipulations. Although some of these conclusions may be justified, many investigators do not possess the expertise to study the more sophisticated aspects of protein structure and molecular dynamics. One unfortunate result of this is that each time an unexplainable break in a binding or displacement curve occurs, a new receptor is “discovered,” leading to a generalized confusion in some areas of neurotransmitter research. One has an overall sense that these areas will continue to circle around the core issues until a more sophisticated generation of researchers has broken with the past. In contrast, in the last 10 yr, research into the mode of action of the minor tranquilizers and related drugs has solidified behind a number of unifying hypotheses that possess value for the development of new compounds with predictable pharmacological properties. In addition, this research has led to a rather sophisticated view of the actions of these compounds and to identification of their sites of action at a receptor site for γ-aminobutyric acid (GABA), one of the brain's major inhibitory neurotransmitters. In spite of very limited amounts of receptor molecules available, advances in molecular approaches to their study have led to the isolation of this receptor complex, preparation of monoclonal antibodies against it, and cloning of genes coding for two of the major subunits of the complex. In this review we will discuss two major areas: first, protein structure as it relates to the function of membrane ionic channels and the kinetic and equilibrium binding constants of transmitter and drug-binding sites; second, how these general principles apply to the functional properties of transmitter-controlled anion channels and related proteins.     

Life and death of <Emphasis Type="Italic">Trypanosoma cruzi</Emphasis> in presence of metals

Trypanosoma cruzi has many molecules that need metallic elements to work, allowing cell invasion and the establishment of infection, causing Chagas disease. Nonetheless, knowledge regarding how the parasites address metals and maintain homeostasis is lacking. To study this relationship, zinc, cadmium and mercury were chosen. Epimastigote, trypomastigote and intracellular forms of T. cruzi were incubated with these metals for different times and at different concentrations. In general, epimastigotes were the most sensitive and trypomastigotes the most resistant to metals. ZnCl₂ induced low toxic effects to all parasite forms. Although the parasites were very sensitive to the toxic effects of CdCl₂ and HgCl₂, pretreatment with ZnCl₂ decreased the death rate. The trypomastigotes pretreated with CdCl₂ were unable to infect the host cells, and the treated intracellular forms were damaged after 2 h of incubation, when the toxic effects were poorly reverted. New insights on metal toxicity mechanisms are provided, helping to understand how metallic ions influence the parasite’s biochemical and physiological processes.     

MicroRNA–target gene responses to lead-induced stress in cotton (Gossypium hirsutum L.)

MicroRNAs (miRNAs) play key roles in plant responses to various metal stresses. To investigate the miRNA-mediated plant response to heavy metals, cotton (Gossypium hirsutum L.), the most important fiber crop in the world, was exposed to different concentrations (0, 25, 50, 100, and 200 µM) of lead (Pb) and then the toxicological effects were investigated. The expression patterns of 16 stress-responsive miRNAs and 10 target genes were monitored in cotton leaves and roots by quantitative real-time PCR (qRT-PCR); of these selected genes, several miRNAs and their target genes are involved in root development. The results show a reciprocal regulation of cotton response to lead stress by miRNAs. The characterization of the miRNAs and the associated target genes in response to lead exposure would help in defining the potential roles of miRNAs in plant adaptation to heavy metal stress and further understanding miRNA regulation in response to abiotic stress.     

Metal tolerance assisted antibiotic susceptibility profiling in <Emphasis Type="Italic">Comamonas acidovorans</Emphasis>

Metal ions are known selective agents for antibiotic resistance and frequently accumulate in natural environments due to the anthropogenic activities. However, the action of metals that cause the antibiotic resistance is not known for all bacteria. The present work is aimed to investigate the co-selection of metals and antibiotic resistance in Comamonas acidovorans. Tolerance profile of 16 metals revealed that the strain could tolerate high concentrations of toxic metals i.e., Cr (710 ppm), As (380 ppm), Cd (320 ppm), Pb (305 ppm) and Hg (205 ppm). Additionally, metal tolerant phenotypes were subjected to antibiotic resistance profiling; wherein several metal tolerant phenotypes (Cr 1.35-fold; Co-1.33 fold; Mn-1.29 fold) were resistant, while other metal tolerant phenotypes (Mg 1.32-fold; Hg 1.29-fold; Cu 1.28-fold) were susceptible than control phenotype. Metal accumulation may alter the metabolism of C. acidovorans that activates or inactivates the genes responsible for antibiotic resistance, resulting in the resistance and/or susceptibility pattern observed in metal resistant phenotypes.