Nitric oxide induces metallothionein (MT) gene expression apparently by displacing zinc bound to MT

The Role of Nitric Oxide Signaling in Plant Responses to Cadmium Stress

Nitric oxide (NO) is a widely distributed gaseous signaling molecule in plants that can be synthesized through enzymatic and non-enzymatic pathways and plays an important role in plant growth and development, signal transduction, and response to biotic and abiotic stresses. Cadmium (Cd) is a heavy metal pollutant widely found in the environment, which not only inhibits plant growth but also enters humans through the food chain and endangers human health. To reduce or avoid the adverse effects of Cd stress, plants have evolved a range of coping mechanisms. Many studies have shown that NO is also involved in the plant response to Cd stress and plays an important role in regulating the resistance of plants to Cd stress. However, until now, the mechanisms by which Cd stress regulates the level of endogenous NO accumulation in plant cells remained unclear, and the role of exogenous NO in plant responses to Cd stress is controversial. This review describes the pathways of NO production in plants, the changes in endogenous NO levels in plants under Cd stress, and the effects of exogenous NO on regulating plant resistance to Cd stress.

The Evolving Role for Zinc and Zinc Transporters in Cadmium Tolerance and Urothelial Cancer

Cadmium (Cd) is an environmental toxicant with serious public health consequences due to its persistence within arable soils, and the ease with which it enters food chains and then, accumulates in human tissues to induce a broad range of adverse health effects. The present review focuses on the role of zinc (Zn), a nutritionally essential metal, to protect against the cytotoxicity and carcinogenicity of Cd in urinary bladder epithelial cells. The stress responses and defense mechanisms involving the low-molecular-weight metal binding protein, metallothionein (MT), are highlighted. The efflux and influx transporters of the ZnT and Zrt-/Irt-like protein (ZIP) gene families are discussed with respect to their putative role in retaining cellular Zn homeostasis. Among fourteen ZIP family members, ZIP8 and ZIP14 mediate Cd uptake by cells, while ZnT1 is among ten ZnT family members solely responsible for efflux of Zn (Cd), representing cellular defense against toxicity from excessively high Zn (Cd) intake. In theory, upregulation of the efflux transporter ZnT1 concomitant with the downregulation of influx transporters such as ZIP8 and ZIP14 can prevent Cd accumulation by cells, thereby increasing tolerance to Cd toxicity. To link the perturbation of Zn homeostasis, reflected by the aberrant expression of ZnT1, ZIP1, ZIP6, and ZIP10, with malignancy, tolerance to Cd toxicity acquired during Cd-induced transformation of a cell model of human urothelium, UROtsa, is discussed as a particular example.

Changes in Metallothionein Levels in Freshwater Mussels Exposed to Urban Wastewaters: Effects from Exposure to Heavy Metals?

Municipal effluents are complex mixtures of compounds such as heavy metals, aromatic and aliphatic hydrocarbons, and micro-organisms and are released in aquatic ecosystems. The purpose of this study was to verify whether changes in metallothioneins (MT) were associated with the accumulation of labile metals in tissue of freshwater mussels exposed to the dispersion plume of a major municipal effluent. Mussels were placed in experimental cages deployed at sites 1.5 km upstream, 8 km downstream and 12 km downstream of the outfall of a major, primary-treated municipal effluent in the St. Lawrence River (Québec, Canada). Mussels were analysed for MT and labile zinc levels in their gonads, gills and digestive glands. Lipogenic enzyme (isocitrate and glucose-6-phosphate dehydrogenase) and arachidonic acid cyclooxygenase (COX) activities were also measured in gonad and gill tissues. Although MT was induced in all the tissues examined, the results showed that labile zinc levels were significantly reduced in gill and gonad tissues, with an increase observed only at the 12 km downstream site in the digestive gland. COX activity was readily induced in gills and gonads. Glucose-6-phosphate dehydrogenase activity was reduced at both downstream sites, but isocitrate dehydrogenase activity was significantly induced at the farthest (12 km) site. Analysis of covariance revealed that MT levels in gills were more influenced by COX activity than with distance in the dispersion plume and was negatively correlated with labile zinc levels. In conclusion, MT induction was inversely related to the levels of labile zinc but positively so with the inflammation biomarker COX. Hence, the induction of MT in mussels exposed to the municipal effluent of a large city appears to be associated with either inflammatory processes or as compensation for the loss of labile essential metals. We propose that the simple and complimentary parameters of labile zinc and COX evaluations be used to link MT induction with divalent heavy metal exposure in environmental studies dealing with various type of contaminants in such complex contaminant mixture effluents.

Detection of Zn2+ release in nitric oxide treated cells and proteome: dependence on fluorescent sensor and proteomic sulfhydryl groups

Nitric oxide (NO) is both an important regulatory molecule in biological systems and a toxic xenobiotic. Its oxidation products react with sulfhydryl groups and either nitrosylate or oxidize them. The aerobic reaction of NO supplied by diethylamine NONOate (DEA-NO) with pig kidney LLC-PK₁ cells and Zn-proteins within the isolated proteome was examined with three fluorescent zinc sensors, zinquin (ZQ), TSQ, and FluoZin-3 (FZ-3). Observations of Zn²⁺ labilization from Zn-proteins depended on the specific sensor used. Upon cellular exposure to DEA-NO, ZQ sequestered about 13% of the proteomic Zn²⁺ as Zn(ZQ)₂ and additional Zn²⁺ as proteome·Zn-ZQ ternary complexes. TSQ, a sensor structurally related to ZQ with lower affinity for Zn²⁺, did not form Zn(TSQ)₂. Instead, Zn²⁺ mobilized by DEA-NO was exclusively bound as proteome·Zn-TSQ adducts. Analogous reactions of proteome with ZQ or TSQ in vitro displayed qualitatively similar products. Titration of native proteome with Zn²⁺ in the presence of ZQ resulted in the sole formation of proteome·Zn-ZQ species. This result suggested that sulfhydryl groups are involved in non-specific proteomic binding of mobile Zn²⁺ and that the appearance of Zn(ZQ)₂ after exposure of cells and proteome to DEA-NO resulted from a reduction in proteomic sulfhydryl ligands, favoring the formation of Zn(ZQ)₂ instead of proteome·Zn-ZQ. With the third sensor, FluoZin-3, neither Zn-FZ-3 nor proteome·Zn-FZ-3 was detected during the reaction of proteome with DEA-NO. Instead, it reacted independently with DEA-NO with a modest enhancement of fluorescence.

Metallothionein-1 and nitric oxide expression are inversely correlated in a murine model of Chagas disease

Chagas disease, caused by Trypanosoma cruzi, represents an endemic among Latin America countries. The participation of free radicals, especially nitric oxide (NO), has been demonstrated in the pathophysiology of seropositive individuals with T. cruzi. In Chagas disease, increased NO contributes to the development of cardiomyopathy and megacolon. Metallothioneins (MTs) are efficient free radicals scavengers of NO in vitro and in vivo. Here, we developed a murine model of the chronic phase of Chagas disease using endemic T. cruzi RyCH1 in BALB/c mice, which were divided into four groups: infected non-treated (Inf), infected N-monomethyl-L-arginine treated (Inf L-NAME), non-infected L-NAME treated and non-infected vehicle-treated. We determined blood parasitaemia and NO levels, the extent of parasite nests in tissues and liver MT-I expression levels. It was observed that NO levels were increasing in Inf mice in a time-dependent manner. Inf L-NAME mice had fewer T. cruzi nests in cardiac and skeletal muscle with decreased blood NO levels at day 135 post infection. This affect was negatively correlated with an increase of MT-I expression (r = -0.8462, p < 0.0001). In conclusion, we determined that in Chagas disease, an unknown inhibitory mechanism reduces MT-I expression, allowing augmented NO levels.

Subacute zinc administration and L-NAME caused an increase of NO, zinc, lipoperoxidation, and caspase-3 during a cerebral hypoxia-ischemia process in the rat

Zinc or L-NAME administration has been shown to be protector agents, decreasing oxidative stress and cell death. However, the treatment with zinc and L-NAME by intraperitoneal injection has not been studied. The aim of our work was to study the effect of zinc and L-NAME administration on nitrosative stress and cell death. Male Wistar rats were treated with ZnCl₂ (2.5 mg/kg each 24 h, for 4 days) and N-ω-nitro-L-arginine-methyl ester (L-NAME, 10 mg/kg) on the day 5 (1 hour before a common carotid-artery occlusion (CCAO)). The temporoparietal cortex and hippocampus were dissected, and zinc, nitrites, and lipoperoxidation were assayed at different times. Cell death was assayed by histopathology using hematoxylin-eosin staining and caspase-3 active by immunostaining. The subacute administration of zinc before CCAO decreases the levels of zinc, nitrites, lipoperoxidation, and cell death in the late phase of the ischemia. L-NAME administration in the rats treated with zinc showed an increase of zinc levels in the early phase and increase of zinc, nitrites, and lipoperoxidation levels, cell death by necrosis, and the apoptosis in the late phase. These results suggest that the use of these two therapeutic strategies increased the injury caused by the CCAO, unlike the alone administration of zinc.

Mitochondriocentric pathway to cardiomyocyte necrosis in aldosteronism: cardioprotective responses to carvedilol and nebivolol

Foci of fibrosis, footprints of cardiomyocyte necrosis, are scattered throughout the failing myocardium and are a major component to its pathologic remodeling. Understanding pathogenic mechanisms contributing to hormone-mediated necrosis is therefore fundamental to developing cardioprotective strategies. In this context, a mitochondriocentric signal-transducer-effector pathway to necrosis is emerging. Our first objective, using cardiomyocytes and subsarcolemmal mitochondria (SSM) harvested from rats receiving a 4-week aldosterone/salt treatment (ALDOST), was to identify the major components of this pathway. Second, to validate this pathway, we used mitochondria-targeted pharmaceutical interventions as cardioprotective strategies using 4-week cotreatment with either carvedilol (Carv) or nebivolol (Nebiv). Compared with controls, we found the 4-week ALDOST to be accompanied by elevated cardiomyocyte free [Ca(2+)]i and SSM free [Ca(2+)]m; increased H(2)O(2) production and 8-isoprostane in SSM, cardiac tissue, and plasma; and enhanced opening of mitochondrial permeability transition pore (mPTP) and myocardial scarring. Increments in the antioxidant capacity augmented by increased cytosolic free [Zn(2+)]i were overwhelmed. Cotreatment with either Carv or Nebiv attenuated [Ca(2+)]i and [Ca(2+)]m overloading, prevented oxidative stress, and reduced mPTP opening while augmenting [Zn(2+)]i and conferring cardioprotection. Thus, major components of the mitochondriocentric signal-transducer-effector pathway to cardiomyocyte necrosis seen with ALDOST include intracellular Ca overloading coupled to oxidative stress and mPTP opening. This subcellular pathway can be favorably regulated by Carv or Nebiv cotreatment to salvage cardiomyocytes and prevent fibrosis.

Enhanced expression of recombinant human cyclooxygenase 1 from stably-transfected Drosophila melanogaster S2 cells by dimethyl sulfoxide is mediated by up-regulation of nitric oxide synthase and transcription factor Kr-h1

Recombinant human cyclooxygenase 1 (COX-1) was expressed from stably-transfected Drosophila melanogaster S2 (S2) cells. DMSO improved the expression of recombinant COX-1 by 180 %. DMSO increased the expression of nitric oxide synthase (NOS) at both the RNA and protein levels; NOS expression was closely correlated with the synthesis of recombinant COX-1 mRNA in stably-transfected S2 cells. DMSO also induced the gene encoding Kr-h1 which binds to the CACCC element of the metallothionein promoter to enhance the expression of recombinant COX-1. Therefore, DMSO improves the expression of recombinant COX-1 via NOS and/or the transcription factor Kr-h1.

The message of nitric oxide in cadmium challenged plants

During the last decade it has been found that cadmium (Cd), one of the most toxic elements occurring in polluted environments, interferes with nitric oxide (NO), a multifunctional signaling molecule in living organisms. The formation of NO has been demonstrated in vivo in various plant tissues exposed to Cd stress, but unfortunately, the time and intensity of NO generation, relatively frequently shows conflicting data. What is more, there is still limited information regarding the functional role of endogenously produced NO in plants challenged with heavy metals. The first pharmacological approaches revealed that exogenously applied NO can alleviate cadmium toxicity in plants, promoting the direct scavenging of reactive oxygen species (ROS) or activating antioxidant enzymes. However, recent reports have indicated that NO even contributes to Cd toxicity by promoting Cd uptake and participates in metal-induced reduction of root growth. In view of this heterogeneous knowledge, much more puzzling if we consider results first obtained using exogenous NO sources, this review is focused mainly on the implication of endogenous NO in plant response to Cd exposure. Furthermore, a basic draft for NO mode of action during cadmium stress is proposed.

Metallothionein-like gene from Cicer microphyllum is regulated by multiple abiotic stresses

Cicer microphyllum, a wild relative of cultivated chickpea, is a high altitude cold desert-adapted species distributed in western and trans-Himalayas. A complementary DNA (cDNA) encoding metallothionein-like protein has been identified from a cold-induced subtraction cDNA library from C. microphyllum. The sequence of the cloned metallothionein gene from C. microphyllum (GQ900702) contains 240-bp-long open reading frame and encodes predicted 79-amino acid protein of 7.9 kDa. Sequence analysis identified the motifs characteristic of type II metallothionein and designated as CmMet-2. Southern hybridization confirms a single copy of the CmMet-2 gene in C. microphyllum genome. In situ hybridization indicated spatial transcript regulation of CmMet-2 in root and aerial parts and also confirmed through real-time PCR-based quantitative transcript analysis. The data revealed a significantly low level of transcript in the aerial parts than the roots. Quantitative analysis using real-time PCR assay revealed induction of transcript in all parts of plants in response to cold stress at 4°C. The transcript abundance was found to increase exponentially with time course from 6 to 24 h after exposure. Further, regulation of transcript accumulation in response to abscisic acid application, polyethylene glycol (100 μM)-induced osmotic stress, or ZnSO(4) (1 μM) foliar spray indicated by Northern hybridization suggests the involvement of CmMet-2 in multiple stress response.

Nitric oxide donor, V-PROLI/NO, provides protection against arsenical induced toxicity in rat liver cells: requirement for Cyp1a1

Arsenic is a cancer chemotherapeutic but hepatotoxicity can be a limiting side effect. O(2)-vinyl 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO) is a nitric oxide (NO) donor prodrug and metabolized by liver cytochromes P450 (CYP450) to release NO. The effects of V-PROLI/NO pretreatment on the toxicity of arsenic (as NaAsO(2)) were studied in a rat liver cell line (TRL 1215). The cells acted upon the prodrug to release NO, as assessed by nitrite levels, in a time-dependent fashion to maximal levels of 8-fold above basal levels. Pretreatment with V-PROLI/NO markedly reduced arsenic cytolethality which was directly related to the level of NO produced by V-PROLI/NO treatment. Cyp1a1 expression was directly related to the level of NO production and to reduced arsenic cytotoxicity. V-PROLI/NO pretreatment markedly reduced arsenic-induced apoptosis and suppressed phosphorylation of JNK1/2. V-PROLI/NO pretreatment facilitated additional increases in arsenic-induced metallothionein, a metal-binding protein important in arsenic tolerance. Thus, V-PROLI/NO protects against arsenic toxicity in rat liver cells, reducing cytolethality, apoptosis and dysregulation of MAPKs, through generation of NO formed after metabolism by liver cell enzymes, possibly including Cyp1a1. CYP450 required for NO production from V-PROLI/NO treatment in the rat and human appears to differ as we have previously studied the ability of V-PROLI/NO to prevent arsenic toxicity in human liver cells where it reduced toxicity apparently through a CYP2E1-mediated metabolic mechanism. None-the-less, it appears that both rat and human liver cells act upon V-PROLI/NO via a CYP450-related mechanism to produce NO and subsequently reduce arsenic toxicity.

Reactivity of Zn-, Cd-, and apo-metallothionein with nitric oxide compounds: in vitro and cellular comparison

The reactivity of Zn(7)- and Cd(7)-metallothionein (MT) with S-nitrosopenicillamine (SNAP), S-nitrosoglutathione (GSNO), and 2-(N,N-diethylamino)-diazenolate-2-oxide (DEA/NO) was investigated to explore the hypothesis that metallothionein is a signficant site of cellular reaction of nitric oxide or NO compounds. Zn(7)-MT reacted with SNAP or GSNO only under aerobic conditions and in the presence of light, which stimulates the decomposition of S-nitrosothiolates to NO. Zn(2+) is released, and protein thiols are modified. DEA/NO, which degrades spontaneously to release NO, also reacted with Zn(7)-MT only when oxygen was present. Anaerobically, DEA/NO reacted with Zn(7)-MT in the presence of 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide, which converts NO to NO(2). Glutathione competed effectively with Zn(7)-MT for reactive nitrogen oxide species in reaction mixtures. Reaction of Cd(7)-MT with SNAP also required oxygen and light to react. In this case, only a fraction of the Cd(2+) bound to Cd(7)-MT was displaced by SNAP. Apo-metallothionein was much more reactive with SNAP and DEA-NO than Zn(7)- or Cd(7)-MT. TE671 and LLC-PK(1) cell lines were incubated with DEA/NO to examine the role that MT might play in the cellular reactions of this NO donor compound. Incubation of cells with 0-80 microM Zn(2+) for 24 h resulted in progressively increasing concentrations of Zn-unsaturated MT. One hour of cellular exposure to a range of DEA/NO concentrations followed by 24 h of incubation caused no evident acute toxicity at less than 0.45 mM. Preinduction of MT did not alter this response. The effects of DEA/NO on proteomic, metallothionein, and low molecular weight (LMW) thiol pools, including glutathione (GSH), were measured. Substantial fractions of the proteomic and LMW thiol pools underwent reaction with little dislocation of Zn(2+). In addition, one-third of the MT thiol pool reacted without labilizing any of the bound Zn(2+). These results demonstrated that it was free thiols associated with MT that reacted with DEA/NO not those bound to Zn(2+). Moreover, under the conditions of the experiments, DEA/NO reacted with the spectrum of cellular thiols in proportion to their fraction in the cytosol and did not preferentially react with MT sulfhydryl groups.

Cadmium induced-oxidative stress in pituitary gland is reversed by removing the contamination source

Cadmium (Cd2+) is one of the most important environmental contaminants and acts as an endocrine disruptor. Previously, we have demonstrated that the simultaneous administration of Cd2+ and melatonin (Mel) in drinking water impaired metal-induced oxidative stress in rat anterior pituitary gland. The aim of this study was to investigate if a treatment started after the toxic manifestations of Cd 2+ became evident could reverse the effects of the metal. Animals exposed to Cd2+ (5 parts per million [ppm], 30 days) were treated with Mel or without the metal during the next 1 or 2 months. Cd2+ exposure increased the expression of heme oxygenase-1 (HO-1), a biomarker of oxidative stress, and an a posteriori Mel treatment reversed oxidative stress induced by Cd2+. This effect was also observed 1 month after metal removal. The Cd2+-induced increase in metallothionein-1 (MT-1) and nitric oxide synthase 1 (NOS1) expression were also reversed by metal removal. In addition, serum prolactin and luteinizing hormone levels affected by Cd 2+ exposure were normalized. Considering that the manifestations of Cd2+ intoxication become evident only after a certain period of metal accumulation, these results show that metal removal is enough to reverse Cd2+ effects in anterior pituitary gland and bring to light the relevance of moving away the individual from the contamination source.

Effects of cadmium exposure and intermittent anoxia on nitric oxide metabolism in eastern oysters, Crassostrea virginica

Nitric oxide (NO) is an intracellular signaling molecule synthesized by a group of enzymes called nitric oxide synthases (NOS) and involved in regulation of many cellular functions including mitochondrial metabolism and bioenergetics. In invertebrates, the involvement of NO in bioenergetics and metabolic responses to environmental stress is poorly understood. We determined sensitivity of mitochondrial and cellular respiration to NO and the effects of cadmium (Cd) and intermittent anoxia on NO metabolism in eastern oysters, Crassostrea virginica. NOS activity was strongly suppressed by exposure to 50 μg l–1 Cd for 30 days (4.76 vs 1.19 pmol NO min–1 mg–1 protein in control and Cd-exposed oysters, respectively) and further decreased during anoxic exposure in Cd-exposed oysters but not in their control counterparts. Nitrate/nitrite content (indicative of NO levels) decreased during anoxic exposure to less than 10% of the normoxic values and recovered within 1 h of re-oxygenation in control oysters. In Cd-exposed oysters, the recovery of the normoxic NO levels lagged behind, reflecting their lower NOS activity. Oyster mitochondrial respiration was inhibited by exogenous NO, with sensitivity on a par with that of mammalian mitochondria, and ADP-stimulated mitochondrial respiration was significantly more sensitive to NO than resting respiration. In isolated gill cells, manipulations of endogenous NOS activity either with a specific NOS inhibitor (aminoguanidine) or a NOS substrate (l-arginine) had no effect on respiration, likely due to the fact that mitochondria in the resting state are relatively NO insensitive. Likewise, Cd-induced stimulation of cellular respiration did not correlate with decreased NOS activity in isolated gill cells. High sensitivity of phosphorylating (ADP-stimulated) oyster mitochondria to NO suggests that regulation of bioenergetics is an evolutionarily conserved function of NO and that NO-dependent regulation of metabolism may be most prominent under the conditions of high metabolic flux when the ADP-to-ATP ratio is high.

Coupled calcium and zinc dyshomeostasis and oxidative stress in cardiac myocytes and mitochondria of rats with chronic aldosteronism

A dyshomeostasis of extra- and intracellular Ca(2+) and Zn(2+) occurs in rats receiving chronic aldosterone/salt treatment (ALDOST). Herein, we hypothesized that the dyshomeostasis of intracellular Ca(2+) and Zn(2+) is intrinsically coupled that alters the redox state of cardiac myocytes and mitochondria, with Ca(2+) serving as a pro-oxidant and Zn(2+) as an antioxidant. Toward this end, we harvested hearts from rats receiving 4 weeks of ALDOST alone or cotreatment with either spironolactone (Spiro), an aldosterone receptor antagonist, or amlodipine (Amlod), an L-type Ca(2+) channel blocker, and from age/sex-matched untreated controls. In each group, we monitored cardiomyocyte [Ca(2+)]i and [Zn(2+)]i and mitochondrial [Ca(2+)]m and [Zn(2+)]m; biomarkers of oxidative stress and antioxidant defenses; expression of Zn transporters, Zip1 and ZnT-1; metallothionein-1, a Zn(2+)-binding protein; and metal response element transcription factor-1, a [Zn(2+)]i sensor and regulator of antioxidant defenses. Compared with controls, at 4-week ALDOST, we found the following: (a) increased [Ca(2+)]i and [Zn(2+)]i, together with increased [Ca(2+)]m and [Zn(2+)]m, each of which could be prevented by Spiro and attenuated with Amlod; (b) increased levels of 3-nitrotyrosine and 4-hydroxy-2-nonenal in cardiomyocytes, together with increased H(2)O(2) production, malondialdehyde, and oxidized glutathione in mitochondria that were coincident with increased activities of Cu/Zn superoxide dismutase and glutathione peroxidase; and (c) increased expression of metallothionein-1, Zip1 and ZnT-1, and metal response element transcription factor-1, attenuated by Spiro. Thus, an intrinsically coupled dyshomeostasis of intracellular Ca(2+) and Zn(2+) occurs in cardiac myocytes and mitochondria in rats receiving ALDOST, where it serves to alter their redox state through a respective induction of oxidative stress and generation of antioxidant defenses. The importance of therapeutic strategies that can uncouple these two divalent cations and modulate their ratio in favor of sustained antioxidant defenses is therefore suggested.

Nitric oxide is involved in cadmium-induced programmed cell death in Arabidopsis suspension cultures

Exposure to cadmium (Cd(2+)) can result in cell death, but the molecular mechanisms of Cd(2+) cytotoxicity in plants are not fully understood. Here, we show that Arabidopsis (Arabidopsis thaliana) cell suspension cultures underwent a process of programmed cell death when exposed to 100 and 150 microm CdCl(2) and that this process resembled an accelerated senescence, as suggested by the expression of the marker senescence-associated gene12 (SAG12). CdCl(2) treatment was accompanied by a rapid increase in nitric oxide (NO) and phytochelatin synthesis, which continued to be high as long as cells remained viable. Hydrogen peroxide production was a later event and preceded the rise of cell death by about 24 h. Inhibition of NO synthesis by N(G)-monomethyl-arginine monoacetate resulted in partial prevention of hydrogen peroxide increase, SAG12 expression, and mortality, indicating that NO is actually required for Cd(2+)-induced cell death. NO also modulated the extent of phytochelatin content, and possibly their function, by S-nitrosylation. These results shed light on the signaling events controlling Cd(2+) cytotoxicity in plants.

V-PROLI/NO, a nitric oxide donor prodrug, protects liver cells from arsenic-induced toxicity

Inorganic arsenic shows great promise in human cancer chemotherapy, although hepatotoxicity is a major limiting side-effect. O(2)-Vinyl 1-[2-(Carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO) [Correction added after publication 19 December 2008: 1-[2-(Carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO) was corrected to O(2)-Vinyl 1-[2-(Carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate (V-PROLI/NO)] is a nitric oxide (NO) donor prodrug that is metabolized by liver cytochromes P450 to release NO. Other NO-releasing agents have been shown to mitigate arsenic toxicity. Thus, the effects of V-PROLI/NO pretreatment on the toxicity of inorganic arsenic (as NaAsO(2)) were studied in vitro in a human liver (HepG2) cell line. HepG2 cells acted upon the prodrug to release NO, as assessed by nitrite levels, in a dose- and time-dependent fashion to maximal levels of 57-fold above control levels. In cells pretreated with V-PROLI/NO (200 microM, 24 h) then exposed to arsenic for an additional 24 h, arsenic was much less toxic (LC(50) = 151.9 +/- 5.9 microM) than in control cells (LC(50) = 90.5 +/- 6.5 microM) and the reduced cytolethality was directly related to the level of NO produced. V-PROLI/NO also increased CYP2E1 transcriptional expression in a dose-dependent manner and CYP2E1 expression was directly related to the level of NO produced and the reduction in arsenic cytotoxicity. V-PROLI/NO pretreatment markedly reduced arsenic-induced apoptosis as measured by DNA fragmentation. Pretreatment with V-PROLI/NO suppressed phosphorylation of JNK1/2 after arsenic exposure. Arsenic increased metallothionein, a metal-binding protein important in arsenic tolerance, and V-PROLI/NO pretreatment caused additional increases in metallothionein levels. Thus, the prodrug, V-PROLI/NO, protects against arsenic toxicity in cultured human liver cells, reducing cytolethality, apoptosis and dysregulation of mitogen-activated protein kinases, through generation of NO formed after metabolism by liver cell enzymes, possibly including CYP2E1.

Nitric oxide: an active nitrogen molecule that modulates cellulose synthesis in tomato roots

Nitric oxide (NO) is a bioactive molecule involved in several growth and developmental processes in plants. These processes are mostly characterized by changes in primary and secondary metabolism. Here, the effect of NO on cellulose synthesis in tomato (Solanum lycopersicum) roots was studied. The phenotype of roots, cellulose content, the incorporation of 14C-glucose into cellulosic fraction and the expression of tomato cellulose synthase (CESA) transcripts in roots treated with the NO donor sodium nitroprusside (SNP) were analysed. Nitric oxide affected cellulose content in roots in a dose dependent manner. Low concentrations of SNP (pmoles of NO) increased cellulose content in roots while higher concentrations of SNP (nmoles of NO) had the opposite effect. This result correlated with assays of 14C-glucose incorporation into cellulose in roots. The effect of NO on 14C-glucose incorporation into cellulose was transient and reversible. Microscopic analysis of roots suggested that NO affected primary cell wall cellulose synthesis. Three tomato cellulose synthase (SICESA) transcripts were identified. Reverse transcriptase polymerase chain reaction experiments were carried out and indicated that SICESA1 and SICESA3 levels were affected by high NO concentrations. Together, these results support the hypothesis that variations in NO levels influence cellulose synthesis and content in roots.

+647 A/C and +1245 MT1A polymorphisms in the susceptibility of diabetes mellitus and cardiovascular complications

Diabetes mellitus is a chronic disease characterized by an overproduction of reactive oxygen species, which perturbs zinc metabolism and promotes the onset of cardiovascular disease (CVD) in diabetic patients. Metallothioneins (MT) are cysteine-rich metal-binding proteins which, by means of their antioxidant and zinc-buffering properties, might prevent the development of diabetic cardiovascular complications. A recent investigation shows that a polymorphism (+647 A/C) in the human MT-1A gene, affects the intracellular zinc ion release (iZnR) from the proteins and is associated with longevity in Italian population. The aim of the present study is to assess the involvement of +647 A/C and +1245 A/G MT1A polymorphisms with the susceptibility to type 2 diabetes (DM2) and cardiovascular complications. The study included 694 old individuals: 242 old healthy controls, 217 DM2 patients without clinical evidence of CVD (DNC) and 235 diabetic patients with diagnosis of CVD (DCVD). +647 A/C MT1A polymorphism, but not the second SNP, was associated with DM2. C allele carriers were more prevalent in DNC and DCVD patients than in control group (OR=1.37, p=0.034; OR=1.54, p=0.002, respectively). C+ carriers was associated with higher glycemia and glycosylated hemoglobin in DCVD patients, but not in DNC or control subjects. No differences in plasma zinc, but a modulation of MT levels and iZnR in PBMCs were observed in DCVD cohort when related to +647 A/C MT1A polymorphism. In summary, this work provides novel evidence on the association of the +647 A/C MT1A polymorphism with DM2. Moreover, C+ carriers in DCVD patients presented a worse glycemic control, a reduced iZnR and a higher MT levels, suggesting a possible role of MT in diabetic cardiovascular complications.

The nitric oxide prodrug, V-PYRRO/NO, mitigates arsenic-induced liver cell toxicity and apoptosis

Arsenite is an important cancer chemotherapeutic. The liver is a major target tissue of arsenic toxicity and hepatotoxicity may limit its chemotherapeutic efficacy. O(2)-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2-diolate (V-PYRRO/NO) is a liver-selective nitric oxide (NO)-producing prodrug metabolized by hepatic P450 enzymes to release NO locally. V-PYRRO/NO protects against various organic or inorganic hepatotoxicants but any role in arsenic hepatotoxicity is undefined. Thus, we studied the effects of V-PYRRO/NO (0-1000muM) pretreatment on inorganic arsenic-induced toxicity in cultured rat liver (TRL 1215) cells. These cells metabolized the prodrug to release NO, producing extracellular nitrite levels to 41.7-fold above control levels (7.50+/-0.38 microM) after 24h V-PYRRO/NO (1000 microM) exposure. The effect of pretreatment with V-PYRRO/NO (24h) on the cytolethality of arsenic (as NaAsO(2)) exposure (24h) was assessed. Arsenic was markedly less toxic in V-PYRRO/NO pretreated cells (LC(50)=30.3 microM) compared to control (LC(50)=20.1 microM) and the increases in LC(50) showed a direct relationship to the level of NO produced (measured as nitrite). Consistent with the cytolethality data, V-PYRRO/NO pretreatment markedly reduced arsenic-induced apoptosis as assessed by DNA fragmentation. Activation of the c-Jun N-terminal kinase (JNK) pathway can be critical to apoptosis and pretreatment with V-PYRRO/NO suppressed arsenic-induced JNK activation. V-PYRRO/NO pretreatment modestly increased metallothionein (MT), a metal-binding protein, but greatly enhanced arsenic induction of MT. Thus, V-PYRRO/NO pretreatment directly mitigates arsenic toxicity in cultured liver cells, reducing cytolethality, apoptosis and related JNK pathway activation, apparently through generation of NO. The role of NO in reducing the hepatotoxicity of arsenical chemotherapeutics in vivo deserves additional study.

Cell proliferation and hepatocarcinogenesis in rat initiated by diethylnitrosamine and promoted by phenobarbital: Potential roles of early DNA damage and liver metallothionein expression

Cell proliferation plays an important role in multistage chemical carcinogenesis. Again, several reports demonstrated that upregulation of metallothionein (MT) expression is associated with increased cell proliferation that may contribute to the pathogenesis of preneoplastic phenotype to frank malignancy. In this study, we evaluated the roles of early DNA damage, altered expressions of liver MT and Ki-67 nuclear antigen, and altered hepatic levels of zinc (Zn) and copper (Cu) on cell proliferation and the progression of hepatocarcinogenesis through premalignant, late premalignant and malignant transformation phases in male Sprague-Dawley rats. We have further studied the association between MT expression and cell proliferation in hepatocarcinogenesis. There was substantial induction of DNA single-strand breaks (SSBs) (P<0.001) and development of hepatocellular premalignant lesions along with significant decrease in hepatic levels of Zn and increase in Cu content following a single, necrogenic, intraperitoneal (i.p.) injection (200 mg/Kg body weight) of diethylnitrosamine (DEN) at week 4 of the experimental protocol. Moreover, DEN+phenobarbital (PB)-treatment significantly elevated MT-, Ki-67-, and BrdU-immunoexpressions along with their immunolabeling indices. Furthermore, positive correlations between MT- and Ki-67- labeling (P=0.0006) at various time intervals, as well as, between MT immunoreactivity and 5'-bromo-2'-deoxyuridine-labeling index (BrdU-LI) (P=0.0007) indicate that, MT expression might be associated with Ki-67 expression and cell proliferation thereby. The study suggests that DEN treatment may lead to alteration of Zn and Cu levels resulting in early DNA damage along with elevation of MT expression that may ultimately lead to hepatic cell proliferation. The results thus provide evidence in support of the role of MT as a potential positive regulator of cell growth during the early stages of hepatocellular transformation in rats.

Cellular stress and intracellular zinc dyshomeostasis

Various stressful conditions like oxidative or nitrosative stress, heavy metal load or thiol-modifying compounds have been shown to disturb the intracellular zinc homeostasis leading to increasing concentrations of free zinc within the cytoplasm or nuclei of cells. However, much less is known about the consequences of a disturbed intracellular Zn2+ homeostasis under these conditions. Current knowledge is reviewed here.

Cytokine-induced Metallothionein Expression and Modulation of Cytokine Expression by Metallothionein

A multifunctional protein metallothionein (MT) is induced by various chemicals and cytokines. We have found novel functions of MT as follows: 1) Cytokine expression such as IL-1alpha, IL-6, and TNFalpha responding to lipopolysaccharide is reduced in MT-deficient macrophages compared with in wild-type cells. 2) Nitric oxide production responding to TNFalpha and LPS is reduced in MT-deficient macrophages compared with in wild-type cells. 3) M-CSF expression responding to zinc is reduced in MT-deficient fibroblasts compared with in wild-type cells, and increased in MT-overexpressed fibroblasts compared with in control cells. 4) LIF, a STAT3 activating cytokine, protects the heart from ischemia/reperfusion injury. Transgenic mice overexpressing STAT3 have tolerance to ischemia/reperfusion-induced damage, whereas MT-null mutation cancels the myocardial protection. In this review, we discuss the relation of MT and stress responses from the point of view of cytokine-induced expression of MT and modulation of cytokine expression by MT.

Cytotoxicity of nitric oxide is alleviated by zinc-mediated expression of antioxidant genes

Metallothioneins (MTs) are small, cysteine-rich zinc binding proteins that are powerful antioxidants. In this study, we investigated the interaction between zinc, MTs, and other components of the antioxidant defense system in HepG2 cells. Cells were preincubated with zinc and then exposed to sodium nitroprusside (SNP), a nitric oxide (NO) donor. Both zinc pretreatment and SNP exposure separately induced transcription of MT genes (MT1A, MT2A, MT1E, MT1X), as measured using real time-polymerase chain reaction (PCR) after reverse transcription (RT). Pretreatment of HepG2 cells with zinc sulfate (ZnSO4) followed by SNP exposure caused MT and glucose-6-phosphate dehydrogenase (G6PD) mRNA levels to increase more than in cells only exposed to SNP. However, when cells were incubated with N,N,N',N'-tetrakis(2-pyridylmethyl)ethyl-enediamine (TPEN), a membrane-permeant Zn2+ chelator, the stimulation of MT transcription by SNP was blocked, suggesting that SNP-induced upregulation of these genes is zinc-dependent. Human glutathione-S-transferase (hGSTA1) and G6PD mRNA levels in the cells treated with 5 microM TPEN decreased. Additionally, the induction of MT by SNP after zinc pretreatment appears to be mediated by metal-activated transcription factor-1 (MTF-1), which is induced by labile zinc in the cytosol. SNP cytotoxicity was inhibited by preincubation with zinc. Taken together, these results suggest that NO plays an important role in regulation of cellular zinc homeostasis and that NO-mediated release of protein-bound Zn2+ may be an important signal in antioxidant defense.

Cell-surface protein disulfide isomerase is required for transnitrosation of metallothionein by S-nitroso-albumin in intact rat pulmonary vascular endothelial cells

S-nitrosation of the metal binding protein, metallothionein (MT) appears to be a critical link in affecting endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS)-derived nitric oxide (NO)-induced changes in cytoplasmic and nuclear labile zinc, respectively. Although low molecular weight S-nitrosothiols also appear to affect this signaling system, less is known about the ability of extracellular protein nitrosothiols to transnitrosate MT. Accordingly, we synthesized fluorescently labeled S-nitroso-albumin (SNO-albumin, a major protein S-nitrosothiol in plasma) and determined, via confocal microscopy in fixed tissue, that it is transported into cultured rat pulmonary vascular endothelial cells in a temperature sensitive fashion. The cells were transfected with an expression vector that encodes human MT-IIa cDNA sandwiched between enhanced cyan (donor) and yellow (acceptor) fluorescent proteins (FRET-MT) that can detect conformational changes in MT through fluorescence resonance energy transfer (FRET). SNO-albumin and the membrane-permeant low molecular weight S-nitroso-l-cysteine ethyl ester (l-SNCEE) caused a conformational change in FRET-MT as ascertained by full spectral laser scanning confocal microscopy in live rat pulmonary vascular endothelial cells, a result which is consistent with transnitrosation of the reporter molecule. Transnitrosation of FRET-MT by SNO-albumin, but not l-SNCEE, was sensitive to antisense oligonucleotide-mediated inhibition of the expression of cell surface protein disulfide isomerase (csPDI). These results extend the original observations of Ramachandran et al. (Ramachandran N, Root P, Jiang XM, Hogg PJ, Mutus B. Proc Natl Acad Sci U S A 98: 9539-9544, 2001) and suggest that csPDI-mediated denitrosation helps to regulate the ability of the major plasma NO carrier (SNO-albumin) to transnitrosate endothelial cell molecular targets (e.g. MT).

Chemopreventive effect of vanadium in a rodent model of chemical hepatocarcinogenesis: reflections in oxidative DNA damage, energy-dispersive X-ray fluorescence profile and metallothionein expression

In the present study, we investigated the antitumour efficacy of vanadium in a defined rodent model of experimental hepatocarcinogenesis. Hepatic preneoplasia was induced in male Sprague-Dawley rats with a single, necrogenic, intraperitoneal injection of diethylnitrosamine (DEN) (200 mg/kg body weight) followed by promotion with phenobarbital (PB). The levels of modified DNA bases 8-hydroxy-2'-deoxyguanosine (8-OHdG), a potential marker involved in the initiation of carcinogenesis, were measured by high-performance liquid chromatography, whereas tissue trace element status and expression of metallothionein (MT), a Cu-Zn metalloprotein associated with neoplastic cell growth and subsequent development of premalignant phenotype of the cell, were studied by energy-dispersive X-ray fluorescence spectrometry and enzyme-coupled immunohistochemistry, respectively. There was a significant and steady elevation of modified bases (8-OHdG) along with substantial increase in MT immunoexpression and disturbance in trace element homeostasis following DEN exposure. Supplementation of vanadium at a dose of 0.5 ppm for four consecutive weeks strictly abated the formation of 8-OHdG (P < 0.0001; 81.28%) in preneoplastic rat liver. In a long-term DEN plus PB regimen, vanadium was able to limit in situ MT expression with a concomitant decrease in MT immunoreactivity (P < 0.05). Furthermore, vanadium treatment throughout the study restored hepatic levels of essential trace elements and decreased nodular incidence (58.34%) and nodule multiplicity (P < 0.001; 66.89%) in rats treated with DEN plus PB. Taken together, the study provides evidence in support of the chemopreventive potential of vanadium in limiting neoplastic transformation during the preneoplastic stages of hepatocarcinogenesis in rats.

Nitrosative/oxidative modifications and ageing

We present here a brief description of the relationships among metals, nitric oxide metabolism, and ageing. In particular, we will discuss the interactions occurring between redox (copper, iron) and non-redox (zinc) metals and nitric oxide, the metal- and nitric oxide-catalyzed formation of thiol adducts (nitrosothiols, mixed disulphides) and the possible involvement of these species in the ageing process.

Nitric oxide protects the mitochondria of anterior pituitary cells and prevents cadmium-induced cell death by reducing oxidative stress

Cadmium (Cd2+) is a highly toxic metal that affects the endocrine system. We have previously shown that Cd2+ induces caspase-3 activation and apoptosis of anterior pituitary cells and that endogenous nitric oxide (NO) protects these cells from Cd2+. Here we investigate the mechanisms by which NO exerts this protective role. Cd2+ (25 microM) reduced the mitochondrial membrane potential (MMP) as measured by flow cytometry. Cd2+-induced apoptosis was mitochondrial dependent since cyclosporin A protected the cells from this metal. Inhibition of NO synthesis with 0.5 mM L-NAME increased the effect of Cd2+ on MMP, whereas the NO donor DETANONOate (0.1 mM) reduced it. Cd2+ increased the production of reactive oxygen species (ROS) as measured by flow cytometry. This effect was electron-transfer-chain-dependent since it was inhibited by rotenone. In fact, rotenone reduced the cytotoxic effect of the metal. The action of Cd2+ on mitochondrial integrity was ROS dependent. Trolox, an antioxidant, inhibited the effect of the metal on the MMP. Cd2+-induced increase in ROS generation was reduced by DETANONOate. There are discrepancies concerning the role of NO in Cd2+ toxicity. Here we show that NO reduces Cd2+ toxicity by protecting the mitochondria from oxidative stress in a system where NO plays a regulatory role.

Reduced bactericidal activity and nitric oxide production in metallothionein-deficient macrophages in response to lipopolysaccharide stimulation

This study was designed to investigate bactericidal activity of and nitric oxide (NO) production in lipopolysaccharide (LPS)-stimulated peritoneal exudate macrophages (Mvarphi) from metallothionein (MT)-null mice. Control Mvarphi had a bactericidal effect on Staphylococcus aureus, but MT-null Mvarphi had significantly lower activity. NO is an important factor in the bactericidal function of Mvarphi. LPS-stimulated MT-null Mvarphi produced less NO than those of control mice. LPS-stimulated Mvarphi produce cytokines such as tumor necrosis factor (TNF)-alpha. TNF-alpha activate Mvarphi and stimulates NO production. We evaluated NO production by TNF-alpha-stimulated Mvarphi. MT-null Mvarphi produced less NO in response to TNF-alpha stimulation. Levels of expression of inducible NO synthase (iNOS) mRNA and production of iNOS protein in response to LPS stimulation were similar in MT-null and control cells, as were levels of expression of arginase, which competes in arginine metabolism with iNOS. No notable changes were found in arginine uptake or in expression of cationic amino acid transporter 2 (a major arginine transporter in Mvarphi) between control and MT-null Mvarphi. The rate of conversion of [(14)C]-l-arginine to citrulline, which is formed with NO by the action of iNOS, was much lower in MT-null Mvarphi than in control cells. These results indicate that the reduced production of NO in MT-deficient Mvarphi is due mainly to reduced activity of iNOS. Thus, MT plays important roles in bactericidal activity, NO production, and arginine metabolism in activated Mvarphi.

The nitric oxide prodrug, V-PYRRO/NO, protects against cadmium toxicity and apoptosis at the cellular level

The liver is an important target tissue of cadmium. The compound O2-vinyl 1-(pyrrolidin-1-yl)diazen-1-ium-1,2 diolate (V-PYRRO/NO) is a liver-selective nitric oxide (NO) prodrug that is metabolized by hepatic P450 enzymes to release NO in hepatocytes. In vivo, V-PYRRO/NO can protect against the toxicity of various hepatotoxicants, including cadmium. Since NO is an effective vasodilator, whether this protective effect against cadmium toxicity is at the level of the hepatic vascular system or actually within the liver cells has not been defined. Thus, we studied the effects of V-PYRRO/NO pretreatment on cadmium-induced toxicity and apoptosis in cultured rat liver epithelial (TRL 1215) cells. Cells were pretreated with V-PYRRO/NO at 500 or 1000 microM for up to 24 h, then exposed to cadmium (as CdCl2) for additional 24 h and cytotoxicity was measured. Cadmium was significantly less cytotoxic in V-PYRRO/NO (1000 microM) pretreated cells (LC50=6.1+/-0.6 microM) compared to control cells (LC50=3.5+/-0.4 microM). TRL 1215 cells acted upon the prodrug to release NO, producing nitrite levels in the extracellular media after 24 h of exposure to 500 or 1000 microM V-PYRRO/NO measured at 87.0+/-4.2 and 324+/-14.8 microM, respectively, compared to basal levels of 7.70+/-0.46 microM. V-PYRRO/NO alone produced small increases in metallothionein (MT), a metal-binding protein associated with cadmium tolerance. However, V-PYRRO/NO pretreatment greatly enhanced cadmium induction of MT. V-PYRRO/NO pretreatment also markedly reduced apoptotic cell death induced by cadmium (5 microM), apparently by blocking cadmium-induced activation of the c-Jun N-terminal kinase (JNK) pathway. Thus, the prodrug, V-PYRRO/NO, protects against the adverse effects of cadmium directly within rat liver cells apparently through generation of NO and, at least in part, by facilitation of cadmium-induced MT synthesis.

Vanadium induces apoptosis and modulates the expressions of metallothionein, Ki-67 nuclear antigen, and p53 during 2-acetylaminofluorene-induced rat liver preneoplasia

Our previous studies have shown that vanadium, a dietary micronutrient, has an inhibitory effect against experimentally induced rat hepatocarcinogenesis. In this study, we evaluated the role of vanadium on some potential protein expression markers of carcinogenesis, such as metallothionein (MT), an intracellular metal-binding protein linked with cell proliferation and apoptosis, Ki-67 nuclear antigen, and p53 tumor suppressor during 2-acetylaminofluorene (2-AAF)-induced (0.05% in basal diet) rat liver preneoplasia. In a short-term regimen, supplementation of vanadium at a dose of 0.5 ppm effectively suppressed the formation of DNA 'comets' (29.55%; P < 0.02), thereby indicating its nongenotoxicity at this particular dose. Vanadium administration throughout the study reduced relative liver weight (RLW), nodular incidence (57.15%), total number, and multiplicity (48.45%) with restoration of hepatic zinc (Zn), magnesium (Mg), selenium (Se), copper (Cu), iron (Fe), and calcium (Ca) contents when compared to the carcinogen control. Moreover, treatment with vanadium significantly abated the expressions of MT and Ki-67, studied at four sequential time points. An increased immunopositivity of p53 protein (1.03 +/- 0.23%; P < 0.02) was found in vanadium-treated rat liver with an elevated apoptotic-labeling index (AI; P < 0.001) as documented by TUNEL assay. Furthermore, a positive correlation between MT expression and Ki-67 labeling along with a strong negative correlation between MT immunoreactivity and AI (r = -0.9000, P = 0.0004 at week 24) at various time intervals suggest that, vanadium-mediated suppression of MT and Ki-67 expressions may be associated with induction of apoptosis. The results thus provide evidence for the first time in support of the potential role of vanadium on induction of p53 and apoptosis with concurrent suppression of MT and Ki-67 in order to have an understanding, in part, of the chemopreventive mechanism of this trace element in limiting neoplastic transformation in a defined model of experimental rat hepatocarcinogenesis.

Characterization of a rice class II metallothionein gene: tissue expression patterns and induction in response to abiotic factors

Data mining the complete rice genome sequences revealed a genomic fragment encoding a characteristic metallothionein (MT) protein, and its full-length cDNA was isolated from rice developing seeds by RT-PCR. This cDNA, designated OsMT-II-1a, contains an open reading frame of 264 bp encoding a protein of 87 amino acid residues. The predicted amino acid sequence was shown to have structural features characteristic of plant class II MT proteins. By sequence analysis of its 5'-flanking region, one putative TATA box, four putative CAAT boxes, and several short sequences homologous to previously reported regulatory cis-elements were identified. Northern blot analysis showed that accumulation of OsMT-II-1a mRNA is specifically abundant in developing seeds and 2-day glumes after pollination, and OsMT-II-1a transcription can markedly be induced by H2O2, paraquat, SNP, ethephon, ABA and SA, but barely by metal ions or other exogenous abiotic factors such as low temperature and PEG. These results coincide with the prediction of existing regulatory cis-elements in its 5'-flanking region. Taken together, the above results suggest that the processes of pollination and seed development might be mediated, at least in part, by expression of the OsMT-II-1a gene that is regulated by several abiotic factors.

Nitric oxide protects anterior pituitary cells from cadmium-induced apoptosis

Cadmium (Cd2+) is a potent toxic metal for both plants and animals. Chronic exposure to low doses of Cd2+ results in damage to several organs. We have previously reported that Cd2+ induces apoptosis in anterior pituitary cells by a caspase- and oxidative stress-dependent mechanism. Nitric oxide (NO) synthesis is affected by Cd2+ in several systems. NO has been shown to be either cytoprotective or cytotoxic in many systems. The aim of this study was to evaluate the possible participation of NO in the cytotoxic effect of Cd2+ on rat anterior pituitary cells. Cell viability was evaluated by mitochondrial dehydrogenase activity assay and confirmed by microscopy, studying nuclear morphology. Here we show that DETA NONOate ((Z)-1-[2 (2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate), a long-term NO donor, at concentrations below 0.5 mM, reduces nuclear condensation and fragmentation and reverses the decrease in cellular activity induced by Cd2+. Cd2+, by itself, induced NO synthesis, and inhibition of this synthesis enhanced Cd2+ cytotoxicity. NO also prevented caspase-3 activation and lipidic peroxidation induced by Cd2+. The NO/cGMP pathway does not seem to be involved in the cytoprotective effect of NO. These results indicate that NO has a cytoprotective role in Cd2+ -induced apoptosis, suggesting that endogenous NO could have a physiological role in protecting anterior pituitary cells.

Modulation of nitric oxide-mediated metal release from metallothionein by the redox state of glutathione in vitro

Metallothioneins (MTs) release bound metals when exposed to nitric oxide. At inflammatory sites, both metallothionein and inducible nitric oxide synthase (iNOS) are induced by the same factors and the zinc released from metallothionein by NO suppresses both the induction and activity of iNOS. In a search for a possible modulatory mechanism of this coexpression of counteracting proteins, we investigated the role of the glutathione redox state in vitro because the oxidation state of thiols is involved in the metal binding in Cd-S or Zn-S clusters found in metallothioneins, and NO also binds to reduced glutathione via S-nitrosation. Using a variety of techniques, we found that NO and also ONOO(-)-mediated metal release from purified MTs is suppressed by reduced glutathione (GSH), but not by oxidized glutathione. Considering the millimolar concentrations of GSH present in mammalian cells, the metal release from MTs by NO should play no role in living systems. Therefore, the fact that it has been observed in vivo points to a hitherto unknown mechanism or additional compound(s) being involved in this physiologically relevant reaction and as long as this additional factor is not found experimental results on the MT-NO interaction should be treated with caution. Contrary to the peroxynitrite-induced activation of guanylyl cyclase, where GSH is needed, we found that the metal release from metallothionein by peroxynitrite is not enhanced, but also suppressed by reduced glutathione. In addition, we show that zinc, the major natural metal ligand in mammalian MTs and suppressor of iNOS, is released more readily under the influence of NO than cadmium, but in contrast to the MT isoform 1, the amount of metal released from the beta-domain of MT-2 is comparable to that from the alpha-domain.

Globus pallidus: a target brain region for divalent metal accumulation associated with dietary iron deficiency

Recently, iron deficiency has been connected with a heterogeneous accumulation of manganese in the rat brain. The striatum is particularly vulnerable, for there is a significant negative correlation between accumulated manganese and gamma-aminobutyric acid levels. The effect of dietary iron deficiency on the distribution of zinc and copper, two other divalent metals with essential neurobiological roles, is relatively unexplored. Thus, the primary goal of this study was to examine the effect of manipulating dietary iron and manganese levels on the concentrations of copper, iron, manganese and zinc in five rat brain regions as determined with inductively coupled plasma mass spectrometry analysis. Because divalent metal transporter has been implicated as a transporter of brain iron, manganese, and to a lesser extent zinc and copper, another goal of the study was to measure brain regional changes in transporter levels using Western blot analysis. As expected, there was a significant effect of iron deficiency (P < 0.05) on decreasing iron concentrations in the cerebellum and caudate putamen; and increasing manganese concentrations in caudate putamen, globus pallidus and substantia nigra. Furthermore, there was a significant effect of iron deficiency (P < 0.05) on increasing zinc concentration and a statistical trend (P = 0.08) toward iron deficiency-induced copper accumulation in the globus pallidus. Transporter protein in all five regions increased due to iron deficiency compared to control levels (P < 0.05); however, the globus pallidus and substantia nigra revealed the greatest increase. Therefore, the globus pallidus appears to be a target for divalent metal accumulation that is associated with dietary iron deficiency, potentially caused by increased transporter protein levels.

Vanadium suppresses sister-chromatid exchange and DNA-protein crosslink formation and restores antioxidant status and hepatocellular architecture during 2-acetylaminofluorene-induced experimental rat hepatocarcinogenesis

Vanadium is an important regulator of cellular growth, differentiation, and cell death, and thus has received increasing attention to be an effective cancer chemopreventive agent. In the present study, attempts have been made to investigate the in vivo antineoplastic effect of this micronutrient at the 0.5 ppm dosage in drinking water, by monitoring hepatic nodulogenesis and hepatocellular phenotype followed by antioxidant status and atomic absorption spectrometric estimation of some essential biometals during the multistage of carcinogenesis induced by 2-acetylaminofluorene (2-AAF; 0.05% in basal diet). Finally, sister-chromatid exchange (SCE) and DNA-protein crosslink (DPC) formation, as potential biomarkers were estimated to find out the suppressive effect of vanadium at the molecular level. The results showed that vanadium administration throughout the experiment reduced the relative liver weight, nodular incidence (48.40%), total number, and multiplicity (63.91%), and altered the size of visible persistent nodules (PNs) with concurrent restoration of hepatic glutathione (P < 0.01), glutathione-S-transferase (P < 0.001) and manganese-dependent superoxide dismutase (P < 0.001) activities as well as, hepatic zinc and copper contents (P < 0.001) when compared to the carcinogen control. Moreover, vanadium treatment significantly reduced SCE frequency (50.24%) and DPC coefficient (P < 0.001; 21.30%). Our results, thus, strongly suggest that supplementary vanadium at a dose of 0.5 ppm, when administered continuously throughout the study, than administered either in the initiation or promotion phase alone, is very much effective in suppressing neoplastic transformation during 2-AAF-induced in vivo rat hepatocarcinogenesis.

Nitrosative stress and potassium channel-mediated neuronal apoptosis: is zinc the link?

Nitrosative stress has been implicated in a large number of neurological disorders. The molecular mechanisms underlying the neuronal injury associated with this stimulus, however, are not clearly understood. Emerging evidence suggests that the liberation of intracellular zinc as well as over-activation of potassium channels may be two important components of nitrosative stress-induced neuronal death.

Liver Protection by Bis(Maltolato)Zinc(II) Complex

The aim of this study was to perform screening of a novel drug for treating liver injury. Bis(maltolato)zinc(II) complex [Zn(Mal)(2)], which was previously reported to possess insulinomimetic activity, was found to have potency against experimentally induced liver injury both in vitro and in vivo. Cultured rat hepatocytes were treated with bromobenzene for 24 h to induce cellular injury. Zn(Mal)(2) of various concentrations was added along with bromobenzene in order to evaluate the hepatoprotective activity of Zn(Mal)(2) in vitro. The number of viable hepatocytes decreased by 42% in the culture with bromobenzene. However, hepatocyte viability was maintained when Zn(Mal)(2) was added to the bromobenzene culture. The hepatoprotective activity of Zn(Mal)(2) in vivo was investigated using a concanavalin A-induced liver injury model in BALB/c mice. Changes in serum aminotransferase activities and the secretion of several cytokines were measured. The hepatoprotective effect of Zn(Mal)(2) was also demonstrated in vivo by the suppression of serum aspartate aminotransferase and alanine aminotransferase elevation. No significant changes in serum cytokines associated with the induction of hepatic damage were observed in the concanavalin A-induced injury model. However, examination of concanavalin A-treated mouse splenocytes revealed a dose-dependent suppression of cytokine secretions by Zn(Mal)(2). Zn(Mal)(2) possessed hepatoprotective activity and might exert its effect by a number of mechanisms.

Manganese causes differential regulation of glutamate transporter (GLAST) taurine transporter and metallothionein in cultured rat astrocytes

Neurotoxicity due to excessive brain manganese (Mn) can occur due to environmental (air pollution, soil, water) and/ or metabolic aberrations (decreased biliary excretion). Manganese is associated with oxidative stress, as well as alterations in neurotransmitter metabolism with concurrent neurobehavioral deficits. Based on the few existing studies that have examined brain regional [Mn], it is likely that in pathological conditions it can reach 100-500 microM. Amino acid (e.g. aspartate, glutamate, taurine), as well as divalent metal (e.g. zinc, manganese) concentrations are regulated by astrocytes in the brain. Recently, it has been reported that cultured rat primary astrocytes exposed to Mn displayed decreased glutamate uptake, thereby, increasing the excitotoxic potential of glutamate. Since the neurotoxic mechanism(s) Mn employs in terms of glutamate metabolism is unknown, a primary goal of this study was to link altered glutamate uptake in Mn exposed astrocytes to alterations in glutamate transporter message. Further, we wanted to examine the gene expression of metallothionein (MT) and taurine transporter (tau-T) as markers of Mn exposure. Glutamate uptake was decreased by nearly 40% in accordance with a 48% decrease in glutamate/aspartate transporter (GLAST) mRNA. Taurine uptake was unaffected by Mn exposure even though tau-T mRNA increased by 123%. MT mRNA decreased in these Mn exposed astrocytes possibly due to altered metal metabolism, although this was not examined. These data show that glutamate and taurine transport in Mn exposed astrocytes are temporally different.

Glutamate/aspartate transporter (GLAST), taurine transporter and metallothionein mRNA levels are differentially altered in astrocytes exposed to manganese chloride, manganese phosphate or manganese sulfate

Manganese (Mn)-induced neurotoxicity can occur due to environmental exposure (air pollution, soil, water) and/or metabolic aberrations (decreased biliary excretion). High brain manganese levels lead to oxidative stress, as well as alterations in neurotransmitter metabolism with concurrent neurobehavioral deficits. Based on the few existing studies that have examined brain regional Mn concentration, it is likely that in pathological conditions, Mn concentration can reach between 100 and 500 microM. Environmental Mn exposure as a result of methylcyclopentadienyl manganese tricarbonyl (MMT) combustion is in the form of phosphate or sulfate (MnPO4, MnSO4, respectively). Pharmacokinetic studies have shown that the Mn salt will determine the rate of transport into the brain: MnCl2 > MnSO4 > MnPO4. The salt-specific neurotoxicity of these species is unknown. The primary goal of this study was to examine gene expression of glutamate/aspartate transporter (GLAST), taurine transporter (tau-T), and metallothionein-I (MT-I) in astrocytes exposed to manganese chloride (MnCl2), manganese sulfate (MnSO4), and manganese phosphate (MnPO4). We hypothesized that the effects of MnPO4 and MnSO4 exposure on GLASTexpression in astrocytes would be similar to those induced by MnCl2, since irrespective of salt species exposure, once internalized by astrocytes, the Mn ion would be identically complexed. At the same time, we hypothesized that the magnitude of the effect would be salt-dependent, since the chemical speciation would determine the rate of intracellular uptake of Mn. MnCl2 caused a significant overall decrease (P < 0.0001) in astrocytic GLAST mRNA levels with MnSO4 causing a moderate decrease. MnPO4 exposure did not alter GLAST mRNA in astrocytes. We also sought to examine astrocytic metallothionein and taurine transporter gene expression as markers of manganese exposure. Our findings suggest that manganese chloride significantly decreased (P < 0.0001) astrocytic metallothionein mRNA compared to both the sulfate and phosphate species. However, astrocytic taurine transporter mRNA was not affected by Mn exposure, irrespective of the salt species. These data are consistent with the hypothesis that astrocytic neurotoxicity due to Mn exposure is dependent upon its species, with solubility, and by inference, intracellular concentration, representing a major determinant of its neurotoxicity.