Interference by toxic metal ions with zinc-dependent proteins involved in maintaining genomic stability

Physiological alterations and genotoxic damage under combined aluminum and cadmium treatments in Bryophyllum daigremontianum clones

BACKGROUND

Cadmium (Cd) is one of the most important stress factors in plants, with its high mobility in soils, ease of uptake by plants and toxicity at low concentrations. Aluminum (Al) is another phytotoxic metal, the accumulation of which is a crucial agricultural complication for plants, especially in acidic soils.

METHODS AND RESULTS

In this study, Bryophyllum daigremontianum clone plantlets were obtained from bulbiferous spurs of a mother plant and separated into four different groups and watered with Hoagland solution and mixtures containing 0, 50, 100, and 200 µM of AlCl3 and CdCl2 each for 75 days. Control groups were maintained under the same conditions without Al and Cd treatment. To simulate acidic soil conditions typical of environments where Al toxicity is prevalent, the soil pH was adjusted to 4.5 by spraying the sulphuric acid (0.2%) with 2-day intervals after each irrigation day. After harvesting, growth parameters such as shoot length and thickness, root, shoot and leaf fresh and dry weights were measured, along with physiological parameters like mineral nutrient status, total protein, and photosynthetic pigment concentrations (chlorophyll a, b, a/b, total chlorophyll, and carotenoid) in both control and experimental groups of B. daigremontianum clones. In response to Al and Cd applications, the plant height, shoot thickness and carotenoid levels were declined, whereas the increments were found in leaf/shoot/root fresh weight, root dry weight, and total protein content. Moreover, differences in genomic alterations were investigated using 21 ISSR and 19 RAPD markers, which both have been used extensively as genetic markers to specify phylogenetic relationships among different cultivars as well as stress-dependent genetic alterations. RAPD primers were used due to their arbitrary sequences and the unknown genome sequence of the plant material used. In contrast, ISSR primers were preferred for a genome-wide genotoxic effect scan via non-arbitrary and more common genetic markers. Distinct types of band polymorphisms detected via RAPD and ISSR markers include band loss, and new band formation under a combination of Al and Cd stress. 17 ISSR and 14 RAPD primers generated clear electrophoretic bands.

CONCLUSION

The study revealed that combined application of Al and Cd affect B. daigremontianum clones in terms of growth, physiology and genotoxicity related to the increasing concentrations.

Perspective: intrinsic interactions of metal ions with biological molecules as studied by threshold collision-induced dissociation and infrared multiple photon dissociation

In this perspective, gas-phase studies of group 1 monocations and group 12 dications with amino acids and small peptides are highlighted. Although the focus is on two experimental techniques, threshold collision-induced dissociation and infrared multiple photon dissociation action spectroscopy, these methods as well as complementary approaches are summarized. The synergistic interplay with theory, made particularly powerful by the small sizes of the systems explored and the absence of solvent and support, is also elucidated. Importantly, these gas-phase methods permit quantitative insight into the structures and thermodynamics of metal cations interacting with biological molecules. Periodic trends in how these interactions vary as the metal cations get heavier are discussed as are quantitative trends with changes in the amino acid side chain and effects of hydration. Such trends allow these results to transcend the limitations associated with the biomimetic model systems.

Prenatal exposure to environmental heavy metals and newborn telomere length: A systematic review and meta-analysis

Exposure to environmental heavy metals is associated with telomere length (TL) alteration. Available information regarding the effect of prenatal exposure to environmental pollutants on newborn TL is controversial. The aim of this study is to systematically review and conduct a meta-analysis of the existing epidemiological studies on the associations between prenatal metal exposure and newborn TL. A comprehensive literature search was performed using the online databases of PubMed, Web of Science, and ScienceDirect from their inception to December 1, 2023. Thirteen eligible studies were included from the overall initial identification of 3559 records. The effect size was expressed as standardized beta coefficients with 95% confidence intervals (CIs) by the restricted maximum-likelihood approach with a weighted random-effects model. Prenatal exposure to environmental heavy metals was associated with a shorter newborn TL (standardized beta = -0.04; 95% CI: -0.08, 0.00; p = 0.05). Subgroup analysis showed that prenatal exposure to cadmium was significantly, negatively associated with TL in newborns (standardized beta = -0.05; 95% CI: -0.10, -0.01; p = 0.021). Heavy metal exposure during the third trimester was significantly associated with a shorter TL in newborns (standardized beta = -0.05; 95% CI: -0.11, -0.01; p = 0.045). No significant association was found between the newborn's sex and exposure sample type. This study provides evidence for the negative effect of prenatal exposure to heavy metals on newborn TL. In particular, cadmium exposure and exposure during the third trimester of pregnancy are critical factors associated with heavy metal-induced TL shortening.

Does the Protective Effect of Zinc on Telomere Length Depend on the Presence of Hypertension or Type 2 Diabetes? Results from the Iwaki Health Promotion Project, Japan

Telomeres, repeated TTAGGG sequences at chromosomal ends, shorten with age and indicate cellular lifespan. Zinc can protect against telomere damage through its anti-oxidative effect. Meanwhile, telomere shortening was correlated with metabolic diseases of hypertension and type 2 diabetes. The objective of this study was to investigate whether the association between zinc and telomere length differs by the presence or absence of hypertension/type 2 diabetes. This is a cross-sectional study with 1064 participants of the Iwaki area, Japan. Multiple linear regression models were performed to test the hypothesis. A higher serum zinc concentration was significantly associated with a longer G-tail length (β = 48.11, 95% confidence intervals [CI]: 25.69, 70.54, p < 0.001). By multivariate linear regression analysis, there was a significant positive association between zinc and G-tail length in both hypertensive (β = 46.84, 95%CI: 9.69, 84.0, p = 0.014) and non-hypertensive groups (β = 49.47, 95%CI: 20.75, 78.18, p = 0.001), while the association was significant only in the non-diabetes group (β = 50.82, 95%CI: 27.54, 74.11, p < 0.001). In conclusion, higher zinc concentration was significantly associated with longer G-tail length. The protective effect of zinc on G-tail did not differ by hypertension status; however, it disappeared in individuals with type 2 diabetes.

Comparative transcriptome analysis reveals key genes and coordinated mechanisms in two rice cultivars differing in cadmium accumulation

Although Cd accumulation varies among rice varieties is recognized, the underlying mechanisms are not well clarified. In this study, comparative transcriptome analysis were performed by hydroponic culture system with two rice varieties, Y1540 (high Cd accumulator) and Y15 (low Cd accumulator) under 20 μM Cd stress. Results revealed 17,320 differentially expressed genes (DEGs) in roots of Y15 (7,655 upregulated and 9,665 downregulated) and 17,386 DEGs in roots of Y1540 (8,823 upregulated and 8,563 downregulated) expose to 20 μM Cd stress. Gene ontology (GO) analysis enriched 24 and 26 terms in Y15 and Y1540 respectively, including 23 common terms. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment showed 27 and 28 significant pathways in Y15 and Y1540 respectively, with 19 common pathways. Different responses to Cd stress between cultivars were not only reflected in differently enriched GO terms and KEGG pathways but also in different DEGs of 23 common GO terms and significant sequences represented by p-values of 19 common KEGG pathways. Both cultivars resist Cd through common processes with different weights; hence glutathione metabolism, mineral absorption, biosynthesis of secondary metabolites, and degradation of aromatic compounds could be playing a more important role in Y1540, whereas ribosome biogenesis in eukaryotes, mismatch repair, aminoacyl-tRNA biosynthesis, and the cell cycle maybe playing a more important role in Y15. Weighted gene co-expression network analysis (WGCNA) showed that five and three modules were clustered in Y15 and Y1540, respectively, with yellow and brown modules in Y15 and brown modules in Y1540 being significantly related to Cd stress. Further analysis showed that most of hub genes in Y15 were related to signal transduction or transcription factors, while most of hub genes in Y1540 were related to binding, metabolic, and secondary metabolic processes, which demonstrated their different response patterns at transcriptomic level to Cd stress.

Insights into Cadmium-Induced Carcinogenesis through an In Vitro Study Using C3H10T1/2Cl8 Cells: The Multifaceted Role of Mitochondria

In this paper, we report the metabolic characterization of two foci, F1 and F3, obtained at the end of Cell Transformation Assay (CTA), performed by treating C3H10T1/2Cl8 mouse embryo fibroblasts with 1 μM CdCl₂ for 24 h. The elucidation of the cadmium action mechanism can be useful both to improve the in vitro CTA and to yield insights into carcinogenesis. The metabolism of the two foci was investigated through Seahorse and enzyme activity assays; mitochondria were studied in confocal microscopy and reactive oxygen species were detected by flow cytometry. The results showed that F1 focus has higher glycolytic and TCA fluxes compared to F3 focus, and a more negative mitochondrial membrane potential, so that most ATP synthesis is performed through oxidative phosphorylation. Confocal microscopy showed mitochondria crowded in the perinuclear region. On the other hand, F3 focus showed lower metabolic rates, with ATP mainly produced by glycolysis and damaged mitochondria. Overall, our results showed that cadmium treatment induced lasting metabolic alterations in both foci. Triggered by the loss of the Pasteur effect in F1 focus and by mitochondrial impairment in F3 focus, these alterations lead to a loss of coordination among glycolysis, TCA and oxidative phosphorylation, which leads to malignant transformation.

Selenomethionine protects hematopoietic stem/progenitor cells against cobalt nanoparticles by stimulating antioxidant actions and DNA repair functions

Hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs) can differentiate into all blood lineages to maintain hematopoiesis, wound healing, and immune functions. Recently, cobalt-chromium alloy casting implants have been used extensively in total hip replacements; however, cobalt nanoparticles (CoNPs) released from the alloy were toxic to HSCs and HPCs. We aimed to investigate the mechanism underlying the toxic effect of CoNPs on HSCs/HPCs and to determine the protective effect of selenomethionine (SeMet) against CoNPs in vitro and in vivo. Human and rat CD34+ HSCs/HPCs were isolated from cord blood and bone marrow, respectively. CoNPs decreased the viability of CD34+ HSCs/HPCs and increased apoptosis. SeMet attenuated the toxicity of CoNPs by enhancing the antioxidant ability of cells. The protective effect of SeMet was not completely abolished after adding H2O2 to abrogate the improvement of the antioxidant capacity by SeMet. SeMet and CoNPs stimulated ATM/ATR DNA damage response signals and inhibited cell proliferation. Unlike CoNPs, SeMet did not damage the DNA, and cell proliferation recovered after removing SeMet. SeMet inhibited the CoNP-induced upregulation of hypoxia inducible factor (HIF)-1α, thereby disrupting the inhibitory effect of HIF-1α on breast cancer type 1 susceptibility protein (BRCA1). Moreover, SeMet promoted BRCA1-mediated ubiquitination of cyclin B by upregulating UBE2K. Thus, SeMet enhanced cell cycle arrest and DNA repair post-CoNP exposure. Overall, SeMet protected CD34+ HSCs/HPCs against CoNPs by stimulating antioxidant activity and DNA repair.

Modulation of PARP activity by Monomethylarsonous (MMA+3) acid and uranium in mouse thymus

Arsenic exposure is well established to impair the function of zinc finger proteins, including PARP-1. Previous studies from our lab show that early developing T cells in the thymus are very sensitive to arsenite (As+3)-induced genotoxicity mediated through PARP-1 inhibition. Additionally, it has been shown that uranium (in the form of uranyl acetate, UA) also suppresses PARP-1 activity in HEK cells. However, very little is known about whether the As+3 metabolite, monomethylarsonous acid (MMA+3), also inhibits PARP-1 activity and if this is modified by combined exposures with other metals, such as uranium. In the present study, we found that MMA+3 significantly suppressed PARP-1 function, whereas UA at high concentrations significantly increased PARP-1 activity. To evaluate whether the effects on PARP-1 activity were mediated through oxidative stress, we measured the induction of hemoxygenase-1 (Hmox-1) expression by qPCR. MMA+3, but not UA, significantly induced oxidative stress; however, the inhibition of PARP-1 produced by MMA+3 was not reversed by the addition of the antioxidant, Tempol. Further evaluation revealed minimal interactive effects of MMA+3 and UA on PARP-1 function. Collectively, our results show that contrary to As+3, the suppressive effects of MMA+3 on PARP-1 were not substantially driven by oxidative stress. in mouse thymus cells. Results for this study provide important insights into the effects of MMA+3 and uranium exposures on PARP-1 function, which is essential for future studies focused on understanding the effects of complex environmentally relevant metal mixtures.

Naturally growing grimmiaceae family mosses as passive biomonitors of heavy metals pollution in urban-industrial atmospheres from the Bilbao Metropolitan area

In analytical chemistry, biomonitoring is known as the methodology, which consider the use of living organisms to monitor and assess the impact of different contaminants in a known area. This type of monitoring is a relatively inexpensive method and easy to implement, being a viable alternative to be developed in sites where there is no infrastructure/instruments for a convenctional air quality monitoring. These organisms, having the capability to monitor the pollution, are also known as passive biomonitors (PBs), since they are able to identify possible contamination sources without the need of any additional tool. In this work, a multianalytical methodology was applied to verify the usefulness of naturally growing Grimmia genus mosses as PBs of atmospheric heavy metals pollution. Once mosses were identified according to their morphology and taxonomy, thei ability to accumulate particulate matter (PM) was determined by SEM. EDS coupled to SEM also allowed to identify the main metallic particles deposited and finally, an acid digestion of the mosses and a subsequent ICP-MS study define more precisely the levels of metals accumulated on each collected moss. The study was focused on six sampling locations from the Bilbao Metropolitan area (Biscay, Basque Country, north of Spain). The experimental evidences obtained allowed to propose naturally growing Grimmia genus as PB of atmospheric heavy metals pollution and to identify the anthropogenic sources that contribute to the emission of the airborne particulate matter rich in metals, evaluating in this sense the atmospheric heavy metals pollution of the selected locations.

Increased Thyroid Cancer Incidence in Volcanic Areas: A Role of Increased Heavy Metals in the Environment?

Thyroid cancer incidence is significantly increased in volcanic areas, where relevant non-anthropogenic pollution with heavy metals is present in the environment. This review will discuss whether chronic lifelong exposure to slightly increased levels of metals can contribute to the increase in thyroid cancer in the residents of a volcanic area. The influence of metals on living cells depends on the physicochemical properties of the metals and their interaction with the target cell metallostasis network, which includes transporters, intracellular binding proteins, and metal-responsive elements. Very little is known about the carcinogenic potential of slightly increased metal levels on the thyroid, which might be more sensitive to mutagenic damage because of its unique biology related to iodine, which is a very reactive and strongly oxidizing agent. Different mechanisms could explain the specific carcinogenic effect of borderline/high environmental levels of metals on the thyroid, including (a) hormesis, the nonlinear response to chemicals causing important biological effects at low concentrations; (b) metal accumulation in the thyroid relative to other tissues; and (c) the specific effects of a mixture of different metals. Recent evidence related to all of these mechanisms is now available, and the data are compatible with a cause–effect relationship between increased metal levels in the environment and an increase in thyroid cancer incidence.

Copper and cadmium administration induce toxicity and oxidative stress in the marine flatworm Macrostomum lignano

The contamination of coastal regions with different toxicants, including heavy metal ions such as copper and cadmium jeopardize health and survival of organisms exposed to this habitat. To study the effects of high copper and cadmium concentrations in these marine environments, we used the flatworm Macrostomum lignano as a model. This platyhelminth lives in shallow coastal water and is exposed to high concentrations of all toxicants that accumulate in these sea floors. We could show that both, cadmium and copper show toxicity at higher concentrations, with copper being more toxic than cadmium. At concentrations below acute toxicity, a reduced long-term survival was observed for both metal ions. The effects of sublethal doses comprise reduced physical activities, an increase in ROS levels within the worms, and alterations of the mitochondrial biology. Moreover, cell death events were substantially increased in response to sublethal concentrations of both metal ions and stem cell activity was reduced following exposure to higher cadmium concentrations. Finally, the expression of several genes involved in xenobiotic metabolism was substantially altered by this intervention. Taken together, M. lignano has been identified as a suitable model for marine toxicological studies as it allows to quantify several relevant life-history traits as well as of physiological and behavioral read-outs.

Cadmium-induced developmental alteration and upregulation of serine-type endopeptidase transcripts in wild freshwater populations of Chironomus plumosus

Cadmium, a toxic heavy metal, is a persistent environmental contaminant with irreversible toxicity to aquatic organisms. Chironomus plumosus, a natural species, is the largest sediment-burrowing aquatic midge in freshwater environments. In this study, we evaluated developmental defects in C. plumosus resulting from Cd exposure. In C. plumosus larvae, Cd exposure induced decreased survival and growth rates, reduction of emergence rate and sex ratio, and delayed emergence, as well as elevating the incidence of split tooth deformities. To identify potential biomarker genes to assess environmental pollutants such as Cd, we identified differentially expressed genes (DEGs) in C. plumosus exposed to various Cd concentrations. Among fourteen characterized DEGs, serine-type endopeptidase (SP) and heat shock protein 70 (HSP70) genes exhibited significant upregulation in C. plumosus larvae after Cd exposure. Therefore, we evaluated SP and HSP70 responses in natural C. plumosus populations collected from three sites of a Korean river and analyzed their correlations with eighteen environmental quality characteristics using principal component analysis. The highest expression of SP and HSP70 transcripts was observed in C. plumosus populations from Yeosu in Korea, which has high concentrations of polluting heavy metals. SP transcript expression was positively correlated with concentrations of Cd, Pb, Al, Fe, NO2, and NO3. These results suggested that environmental pollutants such as Cd can impair proteolytic activity in the digestive system of C. plumosus and may ultimately induce developmental alterations. We therefore suggest SP as a potential biomarker to assess the effects of environmental pollutants in aquatic ecosystems.

Protective role of zinc in Spodoptera exigua larvae under 135-generational cadmium exposure

The aim of this study was to investigate whether zinc supplementation modulates cadmium toxicity in the beet armyworm Spodoptera exigua selected for 135 generations towards cadmium tolerance. To achieve this, larvae originating from three laboratory populations of S. exigua (control strain - C; cadmium-intoxicated for 135 generations strain - Cd, and control strain intoxicated with Cd for 1 generation - CCd) were additionally exposed to zinc in three concentrations (Zn1, 400 μg Zn·g^-1 dry mass of food; Zn2; 200 μg Zn·g^-1 dry mass of food; Zn3, 100 μg Zn·g^-1 dry mass of food). As the markers of toxicity, a life history traits (the duration of L4 and L5 stages), cellular (DNA damage indices) and biochemical parameters (ADP/ATP ratio and ATP and HSP70 concentrations) were chosen. The duration of larval stages of Zn supplemented larvae was prolonged, while cellular and biochemical indicators, in general, appeared to be lower in comparison to the insects from respective reference groups in each laboratory populations. Moreover, the range of the differences depended on zinc concentration in food. We can suspect that zinc supplementation contributed to the protection of S. exigua individuals against negative effects of cadmium intoxication, probably at the cost of growth rate. Significant differences in the response pattern between insects from different laboratory populations indicate that the influence of additional stress factors is dependent on the overall condition of animals and their previous adaptation to other stressors.

Effect of the Interaction Between Selenium and Zinc on DNA Repair in Association With Cancer Prevention

Cancer is the most common cause of death worldwide. Annually, more than ten million new cancer cases are diagnosed, and more than six million deaths occur due to cancer. Nonetheless, over 80% of human cancer may be preventable through proper nutrition. Numerous nutritional compounds are effective in preventing cancer. Selenium and zinc are essential micronutrients that have important roles in reducing oxidative stress and protecting DNA from the attack of reactive oxygen species. Selenium is an essential trace element that possesses several functions in many cellular processes for cancer prevention. Meanwhile, zinc may have protective effects on tumor initiation and progression, and it is an essential cofactor of several mammalian proteins. Results show that both selenium and zinc provide an effective progression of DNA repair system; thus, cancer development that originated from DNA damage is decreased. Results mostly focus on the separate effects of these two elements on different cell types, tissues, and organs, and their combined effects are largely unknown. This review aimed to emphasize the joint role of selenium and zinc specifically on DNA repair for cancer prevention.

The crosstalk between trace elements with DNA damage response, repair, and oxidative stress in cancer

DNA damage response (DDR) is a regulatory system responsible for maintaining genome integrity and stability, which can sense and transduce DNA damage signals. The severity of damage appears to determine DDRs, which can include damage repair, cell-cycle arrest, and apoptosis. Furthermore, defective components in DNA damage and repair machinery are an underlying cause for the development and progression of various types of cancers. Increasing evidence indicates that there is an association between trace elements and DDR/repair mechanisms. In fact, trace elements seem to affect mediators of DDR. Besides, it has been revealed that oxidative stress (OS) and trace elements are associated with cancer development. In this review, we discuss the role of some critical trace elements in the risk of cancer. In addition, we provide a brief introduction on DDR and OS in cancer. Finally, we will further review the interactions between some important trace elements including selenium, zinc, chromium, cadmium, and arsenic, and DDR, and OS in cancer.

Ni(II), Hg(II), and Pb(II) Coordination in the Prokaryotic Zinc-Finger Ros87

Zinc ion binding is a principal event in the achievement of the correct fold in classical zinc finger domains since the motif is largely unfolded in the absence of metal. In the case of a prokaryotic zinc finger, the larger βββαα domain contributes to the folding mechanism with a larger hydrophobic core. For these reasons, following the great amount of attention devoted to unveiling the effect of xenobiotic metal ion replacement in zinc fingers and in zinc-containing proteins in general, the prokaryotic zinc finger domain appears to be an interesting model for studying metal ion interaction with metalloproteins. Here, we explore the binding of Ni(II), Hg(II), and Pb(II) to Ros87, the DNA binding domain of the prokaryotic zinc finger protein Ros. We measured Ros87-metal ion dissociation constants and monitored the effects on the structure and function of the domain. Interestingly, we found that the protein folds in the presence of Ni(II) with important structural perturbations, while in the presence of Pb(II) and Hg(II) it does not appear to be significantly folded. Accordingly, an overall strong reduction in the DNA binding capability is observed for all of the examined proteins. Our data integrate and complement the information collected in the past few years concerning the functional and structural effects of metal ion substitution in classical zinc fingers in order to contribute to a better comprehension of the toxicity of these metals in biological systems.

Impact of prenatal heavy metal exposure on newborn leucocyte telomere length: A birth-cohort study

Arsenic, cadmium and lead are toxic environmental contaminants. They were shown to be associated with telomere length (TL) in adults. Although they can cross the placental barrier, the effect of prenatal exposure of these metals on newborn TL is unknown. The aim of this study was to examine whether prenatal exposure to heavy metals has an impact on newborn leucocyte TL. A birth-cohort study was conducted with 409 pregnant women and their newborns in Myanmar. During the first visit, face-to-face interviews were conducted, and maternal spot urine sampling was performed. Cord blood samples were collected during follow-up. Urinary heavy metal concentration was measured by ICP-MS and adjusted for creatinine. Relative TL was measured by quantitative real-time polymerase chain reaction. The extent of prenatal arsenic, cadmium and lead exposure and their associations with newborn leucocyte TL were assessed using multivariate linear regression. The median values of maternal urinary arsenic, cadmium, and lead concentrations were 73.9, 0.9, and 1.8 μg/g creatinine, respectively. Prenatal arsenic and cadmium exposure was significantly associated with newborn TL shortening (lowest vs highest quartile, coefficient = - 0.13, 95% CI: - 0.22, - 0.03, p = 0.002, and coefficient = - 0.17, 95% CI: - 0.27, - 0.07, p = 0.001, respectively), and the associations remained robust after adjusting for confounders. There was no significant association between prenatal lead exposure and newborn TL. The present study identified the effect of arsenic and cadmium exposure on TL shortening, even in utero exposure at a lower concentration.

Methylmercury promotes breast cancer cell proliferation

CONTEXT

Metalloestrogens are small ionic metals that activate the estrogen receptor (ER). Studies have shown that when metalloestrogens bind to the ER, there is an increase in transcription and expression of estrogen-regulated genes, which induces proliferation of estrogen-dependent breast cancer. Methylmercury (MeHg), a metalloestrogen, is present in the environment and is toxic at moderate to high concentrations. However, at lower concentrations MeHg may promote the proliferation of ER-positive breast cancers and protect cells against pro-apoptotic signals.

OBJECTIVE

To investigate the effects of MeHg treatment on breast cancer cells in vitro.

MATERIALS AND METHODS

MCF7 breast cancer cells were treated with concentrations of MeHg ranging from 1 nM to 100 mM. Hg analysis was used to quantify intracellular mercury concentrations. Cell proliferation and apoptosis were determined by cell counting and Annexin-V staining, respectively.

RESULTS

We defined a protocol that maximizes cellular exposure to mercury. Treatment of human ER-positive breast cancer cells with 1 nM MeHg promoted proliferation, while treatment with a concentration of 100 nM induced apoptosis.

DISCUSSION AND CONCLUSIONS

Clarifying the effects of MeHg on breast cancer will improve our understanding of how environmental toxins affect tumor progression and may lead to the development of future therapeutic strategies.

Metallothionein: A Multifunctional Protein from Toxicity to Cancer

The metallothionein (MT) family is a class of low molecular weight, intracellular and cysteine-rich proteins presenting high affinity for metal ions. Although the members of this family were discovered nearly 40 years ago, their functional significance remains obscure. Four major MT isoforms, MT-1, MT-2, MT-3 and MT-4, have been identified in mammals. MTs are involved in many pathophysiological processes such as metal ion homeostasis and detoxification, protection against oxidative damage, cell proliferation and apoptosis, chemoresistance and radiotherapy resistance. MT isoforms have been shown to be involved in several aspects of the carcinogenic process, cancer development and progression. MT expression has been implicated as a transient response to any form of stress or injury providing cytoprotective action. Although MT participates in the carcinogenic process, its use as a potential marker of tumor differentiation or cell proliferation, or as a predictor of poor prognosis remains unclear. In the present review the involvement of MT in defense mechanisms to toxicity and in carcinogenicity is discussed.

Cadmium-induced neurotoxicity: still much ado

Cadmium (Cd) is a highly toxic heavy metal that accumulates in living system and as such is currently one of the most important occupational and environmental pollutants. Cd reaches into the environment by anthropogenic mobilization and it is absorbed from tobacco consumption or ingestion of contaminated substances. Its extremely long biological half-life (approximately 20–30 years in humans) and low rate of excretion from the body cause cadmium storage predominantly in soft tissues (primarily, liver and kidneys) with a diversity of toxic effects such as nephrotoxicity, hepatotoxicity, endocrine and reproductive toxicities. Moreover, a Cd-dependent neurotoxicity has been also related to neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, and multiple sclerosis. At the cellular level, Cd affects cell proliferation, differentiation, apoptosis and other cellular activities. Among all these mechanisms, the Cd-dependent interference in DNA repair mechanisms as well as the generation of reactive oxygen species, seem to be the most important causes of its cellular toxicity. Nevertheless, there is still much to find out about its mechanisms of action and ways to reduce health risks. This article gives a brief review of the relevant mechanisms that it would be worth investigating in order to deep inside cadmium toxicity.

An improved method for purification and refolding of recombinant HIV Vif expressed in Escherichia coli

Virion infectivity factor (Vif) is a 23 kDa protein that protects HIV-1 from deamination of its proviral DNA by APOBEC3G. The active form of Vif is a multimer that interacts simultaneously with CBF-beta, the elongin B and C subunits, Cullin 5, and APOBEC3G to form a ubiquitin ligase complex targeting the latter for degradation. Vif clearly represents an attractive target for developing novel antiviral drugs for the therapy of HIV/AIDS, and this goal requires a source of well folded, readily available protein. For that purpose, we have cloned Vif in the pET28a expression vector, expressing the resulting His-tagged recombinant protein in the BL21(DE3) Escherichia coli strain. After lysis, Vif was solubilized from the insoluble fraction with 6 M guanidinium chloride and purified by denaturing immobilized-metal affinity chromatography, refolding the protein afterwards by dialysis. The use of 2-(N-morpholino)ethanesulfonic acid buffer at pH 6.2 and the presence of EDTA improved Vif refolding yields by reducing the formation of insoluble aggregates. The purified protein was bound by two monoclonal antibodies against sequential and conformational epitopes located at the C and N terminus, respectively.

Cadmium alters the expression of small heat shock protein genes in the aquatic midge Chironomus riparius

Cadmium (Cd) is a widespread and highly toxic heavy metal of particular ecotoxicological relevance for aquatic ecosystems. It occurs naturally in the environment but is also an industrial pollutant with extensively researched carcinogenic potentials. Heat shock proteins (HSPs) are chaperones that play an important role in maintaining protein homeostasis under stress conditions. Small heat shock proteins (sHSPs) comprise the most diverse group of the HSPs family. They are expressed both constitutively and by stress-induction. The midge Chironomus riparius is widely used as a test species in aquatic toxicology. In the present study, Reverse Transcription Polymerase Chain Reaction (RT-PCR) was used to evaluate the effects of acute Cd exposure to the expression profile of seven shsp genes (hsp17, hsp21, hsp22, hsp23, hsp24, hsp27, and hsp34) in C. riparius larvae. Results show a specific pattern of response with a rapid response by hsp27, which was downregulated at 2-6 h, while the rest of the shsp genes remained unaltered except for hsp17 at 2 h, which was upregulated. However, at 24 h of exposure are observed high levels of hsp23, hsp24, hsp27, and hsp34 transcription while hsp22 mRNA levels were downregulated and hsp17 and hsp21 remained unaltered. These changes in gene expression suggest a functional diversity between the sHSPs in the cellular response to heavy metal stress. The differential pattern in comparison with heat shock supports a specific profile depending on the stress supporting the use of shsp genes as suitable biomarkers for ecotoxicological studies on aquatic systems.

A comprehensive look of poly(ADP-ribose) polymerase inhibition strategies and future directions for cancer therapy

The finding of promising drugs represents a huge challenge in cancer therapeutics, therefore it is important to seek out novel approaches and elucidate essential cellular processes in order to identify potential drug targets. Studies on DNA repair pathway suggested that an enzyme, PARP, which plays a significant role in DNA repair responses, could be targeted in cancer therapy. Hence, the efficacy of PARP inhibitors in cancer therapy has been investigated and has progressed from the laboratory to clinics, with olaparib having already been approved by the US FDA for ovarian cancer treatment. Here, we have discussed the development of PARP inhibitors, strategies to improve their selectivity and efficacy, including innovative combinational and synthetic lethality approaches to identify effective PARP inhibitors in cancer treatment.

Copper Alters the Conformation and Transcriptional Activity of the Tumor Suppressor Protein p53 in Human Hep G2 Cells

The tumor suppressor protein p53 plays a role in the molecular response to DNA damage by acting as a DNA-binding transcription factor that regulates specific target genes to arrest the cell cycle, induce repair mechanisms, and initiate apoptotic cell death. To test the effect of copper on the transcriptional activity of p53, Hep G2 cells were transiently transfected with a luciferase reporter gene downstream from multiple p53 response elements. Co-transfection with the p53 gene resulted in a 6-fold increase in luciferase activity, showing that p53 acts as a transcription factor in this system. However, in the presence of copper, luciferase activity was significantly reduced. Oligonucleotide arrays representing 145 known p53-associated genes were hybridized with biotinylated cDNAs from mRNA extracted from control and copper-treated Hep G2 cells. Among the genes that were differentially regulated were fos, RB1, glutathione peroxidase, TGF-β, and 15-lipoxygenase, a gene known to be activated by mutant p53. Although control Hep G2 cells synthesize wild-type p53, immunocytochemistry identified not only wild type, but also mutant p53 in the presence of copper and other agents that induce oxidative damage. Thus, this report not only identifies genes that may play a role in copper-mediated apoptosis, but also suggests that copper-induced oxidative processes result in the synthesis of mutant p53 with altered transcriptional properties.

Clastogenic but Not Apoptotic Effects on Human Artery Endothelial Cells by Concentrations of Inorganic Lead Inhibiting Their Nitric Oxide Production

Human coronary artery endothelial cells (HCAEC 5156) were cultured as monolayers and exposed to concentrations of lead (as acetate, Pb) in the culture medium similar or lower than those commonly found in the blood of human beings occupationally or environmentally exposed to this element. Only at the concentration of 200 ng/mL, Pb reduced growth rate of HCAEC 5156 cells starting from the 3rd day and up to the 5th day of incubation. On the other hand, Pb (0.2, 2 and 200 ng/mL) increased concentration-dependently micronuclei formation in binucleated HCAEC5156 cells, as it was shown by the cytokinesis-blocked micronucleus assay (CBMN assay) carried out after 48 hours of exposure to the metal. However, Pb was unable, at all the above concentrations, to induce apoptosis in HCAEC 5156 cells following a 48 hour-exposure, as shown by an electrophoretic apoptotic DNA fragmentation test. Moreover, Pb (2 and 200 ng/mL) reduced significantly the concentration of nitric oxide (NO, determined analytically as L-citrulline) in both culture medium and cytosol of HCAEC 5156 cells following a 7 day-exposure to the element. Results were discussed also in relation to evidences of other studies reporting genotoxic and/or apoptotic effects of Pb on various cell types at very elevated dosages or concentrations. The observed clastogenic effects of Pb were explained through a series of mechanisms involving interactions between oxygen reactive species and NO and/or reduced NO synthesis in the endothelium, thus leading to a depressed NO bioavailability. This research first shows that Pb is provided with clastogenic but not apoptotic effects on cultured human endothelial cells. It was emphasized that such effects are induced by Pb concentrations similar to those commonly found in blood and tissues of laboratory animals showing Pb induced cardiovascular and/or neuropsychological alterations.

Heavy Metal Exposure Influences Double Strand Break DNA Repair Outcomes

Heavy metals such as cadmium, arsenic and nickel are classified as carcinogens. Although the precise mechanism of carcinogenesis is undefined, heavy metal exposure can contribute to genetic damage by inducing double strand breaks (DSBs) as well as inhibiting critical proteins from different DNA repair pathways. Here we take advantage of two previously published culture assay systems developed to address mechanistic aspects of DNA repair to evaluate the effects of heavy metal exposures on competing DNA repair outcomes. Our results demonstrate that exposure to heavy metals significantly alters how cells repair double strand breaks. The effects observed are both specific to the particular metal and dose dependent. Low doses of NiCl2 favored resolution of DSBs through homologous recombination (HR) and single strand annealing (SSA), which were inhibited by higher NiCl2 doses. In contrast, cells exposed to arsenic trioxide preferentially repaired using the "error prone" non-homologous end joining (alt-NHEJ) while inhibiting repair by HR. In addition, we determined that low doses of nickel and cadmium contributed to an increase in mutagenic recombination-mediated by Alu elements, the most numerous family of repetitive elements in humans. Sequence verification confirmed that the majority of the genetic deletions were the result of Alu-mediated non-allelic recombination events that predominantly arose from repair by SSA. All heavy metals showed a shift in the outcomes of alt-NHEJ repair with a significant increase of non-templated sequence insertions at the DSB repair site. Our data suggest that exposure to heavy metals will alter the choice of DNA repair pathway changing the genetic outcome of DSBs repair.

Heavy Metal Exposure Influences Double Strand Break DNA Repair Outcomes

Heavy metals such as cadmium, arsenic and nickel are classified as carcinogens. Although the precise mechanism of carcinogenesis is undefined, heavy metal exposure can contribute to genetic damage by inducing double strand breaks (DSBs) as well as inhibiting critical proteins from different DNA repair pathways. Here we take advantage of two previously published culture assay systems developed to address mechanistic aspects of DNA repair to evaluate the effects of heavy metal exposures on competing DNA repair outcomes. Our results demonstrate that exposure to heavy metals significantly alters how cells repair double strand breaks. The effects observed are both specific to the particular metal and dose dependent. Low doses of NiCl₂ favored resolution of DSBs through homologous recombination (HR) and single strand annealing (SSA), which were inhibited by higher NiCl₂ doses. In contrast, cells exposed to arsenic trioxide preferentially repaired using the “error prone” non-homologous end joining (alt-NHEJ) while inhibiting repair by HR. In addition, we determined that low doses of nickel and cadmium contributed to an increase in mutagenic recombination-mediated by Alu elements, the most numerous family of repetitive elements in humans. Sequence verification confirmed that the majority of the genetic deletions were the result of Alu-mediated non-allelic recombination events that predominantly arose from repair by SSA. All heavy metals showed a shift in the outcomes of alt-NHEJ repair with a significant increase of non-templated sequence insertions at the DSB repair site. Our data suggest that exposure to heavy metals will alter the choice of DNA repair pathway changing the genetic outcome of DSBs repair.

Gallium as a Therapeutic Agent: A Thermodynamic Evaluation of the Competition between Ga(3+) and Fe(3+) Ions in Metalloproteins

Gallium has been employed (in the form of soluble salts) to fight various forms of cancer, infectious, and inflammatory diseases. The rationale behind this lies in the ability of Ga(3+) cation to mimic closely in appearance the native ferric ion, Fe(3+), thus interfering with the biological processes requiring ferric cofactors. However, Ga(3+) ion cannot participate in redox reactions and, when substituting for the "native" Fe(3+) ion in the enzyme active site, renders it inactive. Although a significant body of information on the Ga(3+)-Fe(3+) competition in biological systems has been accumulated, the intimate mechanism of the process is still not well understood and several questions remain: What are the basic physical principles governing the competition between the two trivalent cations in proteins? What type of metal centers are the most likely targets for gallium therapy? To what extent are the Fe(3+)-binding sites in the key enzyme ribonucleotide reductase vulnerable to Ga(3+) substitution? Here, we address these questions by studying the competition between Ga(3+) and Fe(3+) ions in model metal binding sites of various compositions and charge states. The results obtained are in line with available experimental data and shed light on the intimate mechanism of the Ga(3+)/Fe(3+) selectivity in various model metal binding sites and biological systems such as serum transferrin and ribonucleotide reductase.

The prokaryotic zinc-finger: structure, function and comparison with the eukaryotic counterpart

Classical zinc finger (ZF) domains were thought to be confined to the eukaryotic kingdom until the transcriptional regulator Ros protein was identified in Agrobacterium tumefaciens. The Ros Cys2 His2 ZF binds DNA in a peculiar mode and folds in a domain significantly larger than its eukaryotic counterpart consisting of 58 amino acids (the 9-66 region) arranged in a βββαα topology, and stabilized by a conserved, extensive, 15-residue hydrophobic core. The prokaryotic ZF domain, then, shows some intriguing new features that make it interestingly different from its eukaryotic counterpart. This review will focus on the prokaryotic ZFs, summarizing and discussing differences and analogies with the eukaryotic domains and providing important insights into their structure/function relationships.

Exchange of Alkyl and Tris(2-mercapto-1-t-butylimidazolyl)hydroborato Ligands Between Zinc, Cadmium and Mercury

The tris(2-mercaptoimidazolyl)hydroborato ligand, [Tm^But ], has been used to investigate the exchange of alkyl and sulfur donor ligands between the Group 12 metals, Zn, Cd and Hg. For example, [Tm^But ]₂Zn reacts with Me₂Zn to yield [Tm^But ]ZnMe, while [Tm^But ]CdMe is obtained readily upon reaction of [Tm^But ]₂Cd with Me₂Cd. Ligand exchange is also observed between different metal centers. For example, [Tm^But ]CdMe reacts with Me₂Zn to afford [Tm^But ]ZnMe and Me₂Cd. Likewise, [Tm^But ]HgMe reacts with Me₂Zn to afford [Tm^But ]ZnMe and Me₂Hg. However, whereas the [Tm^But ] ligand transfers from mercury to zinc in the methyl system, [Tm^But ]HgMe/Me₂Zn, transfer of the [Tm^But ] ligand from zinc to mercury is observed upon treatment of [Tm^But ]₂Zn with HgI₂ to afford [Tm^But ]HgI and [Tm^But ]ZnI. These observations demonstrate that the phenomenological preference for the [Tm^But ] ligand to bind one metal rather than another is strongly influenced by the nature of the co-ligands.

Altering Genomic Integrity: Heavy Metal Exposure Promotes Transposable Element-Mediated Damage

Maintenance of genomic integrity is critical for cellular homeostasis and survival. The active transposable elements (TEs) composed primarily of three mobile element lineages LINE-1, Alu, and SVA comprise approximately 30% of the mass of the human genome. For the past 2 decades, studies have shown that TEs significantly contribute to genetic instability and that TE-caused damages are associated with genetic diseases and cancer. Different environmental exposures, including several heavy metals, influence how TEs interact with its host genome increasing their negative impact. This mini-review provides some basic knowledge on TEs, their contribution to disease, and an overview of the current knowledge on how heavy metals influence TE-mediated damage.

Hepatic metallothioneins in molecular responses to cobalt, zinc, and their nanoscale polymeric composites in frog Rana ridibunda

Despite numerous studies suggesting a dramatic decline of amphibians, the biochemical mechanisms of adaptation in these animals to polluted environment are poorly studied. The aim of this study was to elucidate the ability to release cobalt (Co) and zinc (Zn) from their nanoscale complexes (NCs) derived from the polymeric substance of N-vinylpyrrolidone (PS) in the liver of amphibian (Rana ridibunda). Frog males were subjected to 14days exposure to waterborne Co(2+) (50μg/L), Zn(2+) (100μg/L), as well as corresponding concentrations of Co-NC, Zn-NC or PS. Main attention was paid to MT's interrelations with indices of stress and toxicity. Only Co(2+) and Zn(2+) caused elevation of the correspondent metal in MTs. Co(2+) caused down-regulation of cathepsin D activity, while Zn(2+), Zn-NC and the PS up-regulated this activity. Zn(2+) provoked 1.6 times increase of metal-bounded form of the MT (MT-Me), while all other exposures caused the elevation of the ratio of MT total protein concentration (MT-SH) and concentrations of the MT-Me and/or immunoreactive (MTi) form (up to ~10 times) accompanied by a decrease in the levels of oxyradicals. The increased DNA fragmentation and down-regulation of caspase-3 activity in relation to the redox state of glutathione and/or lactate/pyruvate were shown at all exposures. These data indicate the vulnerability of the redox state of cellular thiols and inability to release Co and Zn from NCs in frog's liver.

Epigenetic effects of cadmium in cancer: focus on melanoma

Cadmium is a highly toxic heavy metal, which has a destroying impact on organs. Exposure to cadmium causes severe health problems to human beings due to its ubiquitous environmental presence and features of the pathologies associated with pro-longed exposure. Cadmium is a well-established carcinogen, although the underlying mechanisms have not been fully under-stood yet. Recently, there has been considerable interest in the impact of this environmental pollutant on the epigenome. Be-cause of the role of epigenetic alterations in regulating gene expression, there is a potential for the integration of cadmium-induced epigenetic alterations as critical elements in the cancer risk assessment process. Here, after a brief review of the ma-jor diseases related to cadmium exposure, we focus our interest on the carcinogenic potential of this heavy metal. Among the several proposed pathogenetic mechanisms, particular attention is given to epigenetic alterations, including changes in DNA methylation, histone modifications and non-coding RNA expression. We review evidence for a link between cadmium-induced epigenetic changes and cell transformation, with special emphasis on melanoma. DNA methylation, with reduced expression of key genes that regulate cell proliferation and apoptosis, has emerged as a possible cadmium-induced epigenetic mechanism in melanoma. A wider comprehension of mechanisms related to this common environmental contaminant would allow a better cancer risk evaluation.

Iron inhibits Escherichia coli topoisomerase I activity by targeting the first two zinc-binding sites in the C-terminal domain

Escherichia coli DNA topoisomerase I (TopA) contains a 67 kDa N-terminal catalytic domain and a 30 kDa C-terminal zinc-binding region (ZD domain) which has three adjacent tetra-cysteine zinc-binding motifs. Previous studies have shown that E. coli TopA can bind both iron and zinc, and that iron binding in TopA results in failure to unwind the negatively supercoiled DNA. Here, we report that each E. coli TopA monomer binds one atom of iron via the first two zinc-binding motifs in ZD domain and both the first and second zinc-binding motifs are required for iron binding in TopA. The site-directed mutagenesis studies further reveal that while the mutation of the third zinc-binding motif has very little effect on TopA's activity, mutation of the first two zinc-binding motifs in TopA greatly diminishes the topoisomerase activity in vitro and in vivo, indicating that the first two zinc-binding motifs in TopA are crucial for its function. The DNA-binding activity assay and intrinsic tryptophan fluorescence measurements show that iron binding in TopA may decrease the single-stranded (ss) DNA-binding activity of ZD domain and also change the protein structure of TopA, which subsequently modulate topoisomerase activity.

Zinc to cadmium replacement in the prokaryotic zinc-finger domain

Given the similar chemical properties of zinc and cadmium, zinc finger domains have been often proposed as mediators of the toxic and carcinogenic effects exerted by this xenobiotic metal. The effects of zinc replacement by cadmium in different eukaryotic zinc fingers have been reported. In the present work, to evaluate the effects of such substitution in the prokaryotic zinc finger, we report a detailed study of its functional and structural consequences on the Ros DNA binding domain (Ros87). We show that this protein, which bears important structural differences with respect to the eukaryotic domains, appears to structurally tolerate the zinc to cadmium substitution and the presence of cadmium does not affect the DNA binding activity of the protein. Moreover, we show for the first time how zinc to cadmium replacement can also take place in a cellular context. Our findings both complement and extend previous results obtained for different eukaryotic zinc fingers, suggesting that metal substitution in zinc fingers may be of relevance to the toxicity and/or carcinogenicity mechanisms of this metal.

Cellular mechanisms of cadmium-induced toxicity: a review

Cadmium is a widespread toxic pollutant of occupational and environmental concern because of its diverse toxic effects: extremely protracted biological half-life (approximately 20-30 years in humans), low rate of excretion from the body and storage predominantly in soft tissues (primarily, liver and kidneys). It is an extremely toxic element of continuing concern because environmental levels have risen steadily due to continued worldwide anthropogenic mobilization. Cadmium is absorbed in significant quantities from cigarette smoke, food, water and air contamination and is known to have numerous undesirable effects in both humans and animals. Cadmium has a diversity of toxic effects including nephrotoxicity, carcinogenicity, teratogenicity and endocrine and reproductive toxicities. At the cellular level, cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Current evidence suggests that exposure to cadmium induces genomic instability through complex and multifactorial mechanisms. Most important seems to be cadmium interaction with DNA repair mechanism, generation of reactive oxygen species and induction of apoptosis. In this article, we have reviewed recent developments and findings on cadmium toxicology.

Responses of hepatic metallothioneins and apoptotic activity in Carassius auratus gibelio witness a release of cobalt and zinc from waterborne nanoscale composites

The main goal of this study was to evaluate the ability of fish Carassius auratus tissues to release cobalt (Co) and zinc (Zn) cations present in the applied Co- and Zn-containing nanoscale composites (NCs). Male fish was subjected to 14day long action of Co- and Zn-NCs, as well as of Co(2+) and Zn(2+) or polymeric substance (PS) used for the NC preparation and derived from the vinylpyrrolidone. 50μg∙L(-1) of Co and 100μg∙L(-1) of Zn were applied either as a salt or a nanocomposite. Both Co and Co-NC increased (3.1 and 2.3 times, respectively) concentration of total Co, metallothionein-related Co (3.7 and 6.6 times, respectively) and thiols (by 71 and 95%, respectively), and caspase-3 activity (2.2 and 3.7 times, respectively) in the fish liver. At the same time, Co and Co-NC decreased glutathione level (1.8 and 1.9 times, respectively) and activated vitellogenesis (5.1 and 9.9 times, respectively) in the fish liver. Both Zn and Zn-NC increased markedly concentrations of metallothionein-related Zn (2.4 and 2.9 times, respectively) and Cu (2.8 and 3.2 times, respectively), and decreased metallothionein-related thiol (2.5 and 4.2 times, respectively), oxyradical (by 30.4 and 44.2%, respectively), and caspase-3 (3.0 and 5.3 times, respectively) levels in the fish liver. These peculiarities are common for metal and metal-NC and witness a release of metal from NS in fish organism. The differences in the levels of DNA strand breaks, biotransformation enzymes and total Zn levels in the liver were dependent on the kind of exposure.

Arsenite binding-induced zinc loss from PARP-1 is equivalent to zinc deficiency in reducing PARP-1 activity, leading to inhibition of DNA repair

Inhibition of DNA repair is a recognized mechanism for arsenic enhancement of ultraviolet radiation-induced DNA damage and carcinogenesis. Poly(ADP-ribose) polymerase-1 (PARP-1), a zinc finger DNA repair protein, has been identified as a sensitive molecular target for arsenic. The zinc finger domains of PARP-1 protein function as a critical structure in DNA recognition and binding. Since cellular poly(ADP-ribosyl)ation capacity has been positively correlated with zinc status in cells, we hypothesize that arsenite binding-induced zinc loss from PARP-1 is equivalent to zinc deficiency in reducing PARP-1 activity, leading to inhibition of DNA repair. To test this hypothesis, we compared the effects of arsenite exposure with zinc deficiency, created by using the membrane-permeable zinc chelator TPEN, on 8-OHdG formation, PARP-1 activity and zinc binding to PARP-1 in HaCat cells. Our results show that arsenite exposure and zinc deficiency had similar effects on PARP-1 protein, whereas supplemental zinc reversed these effects. To investigate the molecular mechanism of zinc loss induced by arsenite, ICP-AES, near UV spectroscopy, fluorescence, and circular dichroism spectroscopy were utilized to examine arsenite binding and occupation of a peptide representing the first zinc finger of PARP-1. We found that arsenite binding as well as zinc loss altered the conformation of zinc finger structure which functionally leads to PARP-1 inhibition. These findings suggest that arsenite binding to PARP-1 protein created similar adverse biological effects as zinc deficiency, which establishes the molecular mechanism for zinc supplementation as a potentially effective treatment to reverse the detrimental outcomes of arsenic exposure.

Metal interaction with redox regulation: an integrating concept in metal carcinogenesis?

The carcinogenicity of cadmium, arsenic, and chromium(VI) compounds has been recognized for some decades. However, the underlying molecular mechanisms seem to be complex and are not completely understood at present. Although, with the exception of chromium(VI), direct DNA damage seems to be of minor importance, interactions with DNA repair processes, tumor suppressor functions, and signal transduction pathways have been described in diverse biological systems. In addition to the induction of damage to cellular macromolecules by reactive oxygen species, the interference with cellular redox regulation by reaction with redox-sensitive protein domains or amino acids may provide one plausible mechanism involved in metal carcinogenicity. Consequences are the distortion of zinc-binding structures and the activation or inactivation of redox-regulated signal transduction pathways, provoking metal-induced genomic instability. Nevertheless, the relevance of the respective mechanisms depends on the actual metal or metal species under consideration and more research is needed to further strengthen this hypothesis.