Reactive oxygen species modulate Zn(2+)-induced apoptosis in cancer cells

Zinc Oxide Nanoparticles and Cancer Chemotherapy: Helpful Tools for Enhancing Chemo-sensitivity and Reducing Side Effects?

Cancer chemotherapy is still a serious challenge. Chemo-resistance and destructive side effects of chemotherapy drugs are the most critical limitations of chemotherapy. Chemo-resistance is the leading cause of chemotherapy failure. Chemo-resistance, which refers to the resistance of cancer cells to the anticancer effects of chemotherapy drugs, is caused by various reasons. Among the most important of these reasons is the increase in the efflux of chemotherapy drugs due to the rise in the expression and activity of ABC transporters, the weakening of apoptosis, and the strengthening of stemness. In the last decade, a significant number of studies focused on the application of nanotechnology in cancer treatment. Considering the anti-cancer properties of zinc, zinc oxide nanoparticles have received much attention in recent years. Some studies have indicated that zinc oxide nanoparticles can target the critical mechanisms of cancer chemo-resistance and enhance the effectiveness of chemotherapy drugs. These studies have shown that zinc oxide nanoparticles can reduce the activity of ABC transporters, increase DNA damage and apoptosis, and attenuate stemness in cancer cells, leading to enhanced chemo-sensitivity. Some other studies have also shown that zinc oxide nanoparticles in low doses can be helpful in minimizing the harmful side effects of chemotherapy drugs. In this article, after a brief overview of the mechanisms of chemo-resistance and anticancer effects of zinc, we will review all these studies in detail.

Zinc, ω-3 polyunsaturated fatty acids and vitamin D: An essential combination for prevention and treatment of cancers

Zinc, ω-3 polyunsaturated fatty acids (PUFAs) and vitamin D are essential nutrients for health, maturation and general wellbeing. Extensive literature searches have revealed the widespread similarity in molecular biological properties of zinc, ω-3 PUFAs and vitamin D, and their similar anti-cancer properties, even though they have different modes of action. These three nutrients are separately essential for good health, especially in the aged. Zinc, ω-3 PUFAs and vitamin D are inexpensive and safe as they are fundamentally natural and have the properties of correcting and inhibiting undesirable actions without disturbing the normal functions of cells or their extracellular environment. This review of the anticancer properties of zinc, ω-3 PUFAs and vitamin D is made in the context of the hallmarks of cancer. The anticancer properties of zinc, ω-3 PUFAs and vitamin D can therefore be used beneficially through combined treatment or supplementation. It is proposed that sufficiency of zinc, ω-3 PUFAs and vitamin D is a necessary requirement during chemotherapy treatment and that clinical trials can have questionable integrity if this sufficiency is not checked and maintained during efficacy trials.

Improvement of the Anticancer Activities of Telmisartan by Zn(II) Complexation and Mechanisms of Action

To improve the anticancer activity of telmisartan, its structure has been modified by Zn(II) complexation giving [Zn(Telm)₂(H₂O)₂]·2H₂O (ZnTelm). The cytotoxic effect was measured on the human lung cancer cells (A549) and on the lung fibroblast cells (MRC-5). The complex markedly improved anticancer activity (IC₅₀ 75 μM) of telmisartan (IC₅₀ 125 μM) or ZnSO₄ (IC₅₀ 225 μM) and did not show toxicity on non-cancer cells, inducing oxidative stress with cellular ROS generation and GSH/GSSG decrease. Apoptosis was the dominant form of cell death for the complex. The Bax/Bcl-XL ratio was significantly increased as well as caspase-3 activation. Both the complex and the ligand bind to bovine serum albumin (BSA) and can be stored and transported by the protein but the interaction with the complex is greater. Telmisartan binds BSA by hydrophobic interactions while the interaction of ZnTelm occurs through van der Waals forces and hydrogen bonding. Therefore, it can be shown that the coordination complex ZnTelm improved the anticancer activity of the antihypertensive drug telmisartan (IC₅₀ 75 μM and 125 μM, respectively) and the interaction with BSA. Graphical Abstract Improvement of the anticancer activities of telmisartan by Zn(II) complexation and mechanisms of action. Intrinsic apoptotic pathway: induction ofoxidative stress and regulation of proteins related to apoptosis. The complex interacted with bovine serum albumin (BSA) and can be stored and transported by the protein.

Nonviolent Self-Catabolic DNAzyme Nanosponges for Smart Anticancer Drug Delivery

The development of self-assembled DNA nanomedicine requires a facile and accurate DNA degradation strategy for precisely programmable drug release. Conventional DNA catabolic strategies are restrained with the fragile and unclear enzymatic reactions that might lead to inefficient and uncontrollable digestion of DNA scaffolds and thus might bring undesirable side effects to the sophisticated biosystems. Herein we reported a versatile self-sufficient DNAzyme-driven drug delivery system consisting of the rolling circle polymerized DNAzyme-substrate scaffolds and the encapsulated pH-responsive ZnO nanoparticles (NPs). The full DNAzyme nanosponges (NSs) were also encoded with multivalent tandem aptamer sequences to facilitate their efficient delivery into cancer cells, where the acidic endo/lysosomal microenvironment stimulates the dissolution of ZnO into Zn²⁺ ions as DNAzyme cofactors and therapeutic reactive oxygen species generators. The supplement Zn²⁺ cofactors mediated the nonviolent DNAzyme-catalyzed cleavage of DNA scaffolds for precise and efficient drug administrations with synergistically enhanced therapeutic performance. The facile design of DNAzyme, together with their cost-effective and intrinsic robust features, is anticipated to provide extensive insights for the development of DNA-based therapeutic platforms by activating the specific intracellular biocatalytic reactions. As an intelligent and nonviolent self-driven drug delivery platform, the present DNAzyme NS system could be engineered with more therapeutic sequences and agents and was anticipated to show exceptional promise and versatility for applications in biomedicine and bioengineering.

Mitochondrial apoptotic pathway mediated the Zn-induced lipolysis in yellow catfish Peteobagrus fulvidraco

In the study, effects of waterborne zinc (Zn) exposure on apoptosis were investigated, and the potential mechanism of apoptosis participating in the Zn-induced variations of lipid metabolism was explored in a low vertebrate, yellow catfish Pelteobagrus fulvidraco. We found that Zn induced occurrence of apoptosis of livers and hepatocytes in yellow catfish. Waterborne Zn also increased hepatic transcriptional levels of p53, cytochrome c (Cycs), caspase 3a (Casp3a) and caspase 3b (Casp3b) of yellow catfish. Zn increased caspase 3 activity and reduced the mitochondrial permeability transition (MTP) in yellow catfish hepatocytes. Z-VAD-fmk (caspase inhibitor) and CsA pretreatment (MTP inhibitor) attenuated the Zn-induced apoptosis and reduction in MTP. Z-VAD-fmk pretreatments attenuated the Zn-induced increase in transcriptional levels of p53, Cycs and Casp3b although the differences were not statistically significant between the Zn group and Zn + Z-VAD-fmk group. In contrast, Zn and N-acetylcysteine (NAC) did not significantly influence the reactive oxygen species (ROS) production. Zn significantly reduced triglyceride (TG) content, increased the activities of carnitine palmitoyltransferase 1 (CPT I), hormone-sensitive lipase (HSL) and adipose TAG lipase (ATGL), and the transcriptional levels of p53, Cycs and caspase 3b of the hepatocytes; these Zn-induced effects on TG contents, activities of CPT I, HSL and ATGL, and mRNA levels of p53, Cycs and caspase 3b could partly be reversed by Z-VAD-fmk, suggesting that Zn induced the mitochondrial-mediated apoptosis and reduced lipid accumulation. Taken together, our study demonstrated the importance of mitochondria-mediated apoptosis in Zn-induced lipolysis, which suggested a new mechanism for elucidating metal element influencing lipid metabolism.

Depletion of ATP and Oxidative Stress Underlie Zinc-Induced Cell Injury

The mechanisms of cell injury resulting in a special type of cell death combining the features of apoptosis and necrosis were examined in Hep-2 cells exposed to 300 μM zinc sulfate during 24h. Acute exposure to zinc induced a rapid rise in metallothionein levels and increased oxidative stress occurring in the absence of a significant early ATP depletion. Accentuated ATP loss and elevated levels of superoxide at later treatment intervals (12h and longer) were present along with increased DNA damage. Manipulation with ATP production and inhibition of NADPH oxidase had a positive effect on zinc-related increase in oxidative stress and influenced the observed type of cell death. These results suggest that Hep-2 cells acutely exposed to zinc increase intracellular labile zinc stores and over express metalothioneins. Elevated production of peroxides in zinc-treated cells is at later treatment intervals accompanied by an increase in superoxide levels, possibly by activation of NADPH oxidase, DNA damage and severe ATP loss. Prevention of critical ATP depletion and, in particular, inhibition of oxidative stress attenuates zinc-mediated cell injury and stimulates apoptosis-like phenotype in exposed cells.

Triarylmethyl-based biradical as a superoxide probe

Superoxide radical represents one of the most biologically relevant reactive oxygen species involved in numerous physiological and pathophysiological processes. Superoxide measurement through the decay of an electron paramagnetic resonance (EPR) signal of a triarylmethyl (TAM) radical possesses the advantage of a high selectivity and relatively high rate constant of TAM reaction with the superoxide. Hereby we report a straightforward synthesis and characterization of a TAM-TAM biradical showing a high reactivity with superoxide (second-order rate constant, (6.7 ± 0.2) × 103 M-1 s-1) enabling the measurement of superoxide radical by following the increase of a sharp EPR signal associated with the formation of a TAM-quinone-methide monoradical product.

Increased Uptake of Zinc in Malignant Cells is Associated with Enhanced Activation of MAPK Signalling and P53-Dependent Cell Injury

Excess intracellular zinc has been demonstrated to be responsible for cell injury and cell death in various experimental as well as clinical models. While the cells possess a system of mechanisms regulating intracellular zinc homeostasis, their saturation by acutely increased zinc levels or by a sustained exposure to elevated zinc levels results in liberation of free zinc stores within the cells and ultimate cell damage and cell death. Here we report that in Hep-2 malignant cells enhanced uptake of zinc causes activation of mitogen-activated protein kinase (MAPK) signaling with resulting p53-dependent cell injury which can be significantly prevented by specific p53 inhibition and by prevention of oxidative stress. Our observations are consistent with the view that subacutely increased intracellular free zinc levels stimulate via oxidative stress p53-dependent pathways which are responsible for the final cell damage in tumor cells.

Terpinen-4-ol inhibits colorectal cancer growth via reactive oxygen species

Terpinen-4-ol (TP4O) is the main component of the essential oil extracted from Melaleuca alternifolia, known as the tea tree, of the botanical family Myrtaceae. The anticancer effects of TP4O have been reported in several cancer cell lines. Previous reports have demonstrated that TP4O exerts anticancer effects by inducing apoptotic cell death in several cell lines; however, the underlying molecular mechanisms of these effects remain unclear. In the present study, the anticancer effects of TP4O against the colorectal cancer (CRC) cell lines HCT116 and RKO were evaluated using WST-8 and bromodeoxyuridine assays. The mechanism of cell death was investigated by the measurement of caspase-3/7, Annexin V and lactate dehydrogenase release. Reactive oxygen species (ROS) levels induced by TP4O were evaluated by electron spin resonance and quantitative measurement of dihydroethidium. Localization of the ROS derived from mitochondria was observed by confocal inverted microscopy. Protein levels of ROS scavengers were assessed by western blotting analysis. To confirm the role of ROS, cell viability was measured in the presence of antioxidant reagents. In an in vivo xenograft model of ICR-SCID mice implanted with HCT116 cells, 200 mg/kg TP4O was injected locally, and tumor growth was compared with that of the control. TP4O induced apoptotic cell death in HCT116 and RKO cells in a dose-dependent manner, and TP4O also increased the levels of ROS generated by mitochondria. TP4O-induced cell death was rescued by administration of antioxidant regents. In vivo, TP4O inhibited the proliferation of HCT116 xenografts compared with that of the control group. The results of the present study suggest that TP4O induces apoptosis in CRC cells through ROS generation. Furthermore, TP4O is potentially useful for the development of novel therapies against CRC.

Obestatin controls skeletal muscle fiber-type determination

Obestatin/GPR39 signaling stimulates skeletal muscle growth and repair by inducing both G-protein-dependent and -independent mechanisms linking the activated GPR39 receptor with distinct sets of accessory and effector proteins. In this work, we describe a new level of activity where obestatin signaling plays a role in the formation, contractile properties and metabolic profile of skeletal muscle through determination of oxidative fiber type. Our data indicate that obestatin regulates Mef2 activity and PGC-1α expression. Both mechanisms result in a shift in muscle metabolism and function. The increase in Mef2 and PGC-1α signaling activates oxidative capacity, whereas Akt/mTOR signaling positively regulates myofiber growth. Taken together, these data indicate that the obestatin signaling acts on muscle fiber-type program in skeletal muscle.

Zinc suppresses stem cell properties of lung cancer cells through protein kinase C-mediated β-catenin degradation

Highly tumorigenic cancer stem cells (CSCs) residing in most cancers are responsible for cancer progression and treatment failure. Zinc is an element regulator of several cell functions; however, its role in regulation of stem cell program in lung cancer has not been demonstrated. The present study reveals for the first time that zinc can suppress stem cell properties of lung cancer cells. Such findings were proved in different lung cancer cell lines (H460, H23, and H292) and it was found that CSC markers (CD133 and ALDH1A1), stem cell-associated transcription factors (Oct4, Nanog, and Sox-2), and the ability to form tumor spheroid were dramatically suppressed by zinc treatments. Zinc was found to activate protein kinase C-α (PKCα) that further phosphorylated and mediated β-catenin degradation through the ubiquitin-proteasomal pathway. Zinc was found to increase the β-catenin-ubiquitin complex, which can be inhibited by a specific PKC inhibitor, bisindolylmaleimide I. Using specific reactive oxygen species detection and antioxidants, we have demonstrated that superoxide anions generated by zinc are a key upstream mechanism for PKCα activation leading to the subsequent suppression of stem cell features of lung cancer. Zinc increased cellular superoxide anions and the addition of superoxide anion scavenger prevented the activation of PKCα and β-catenin degradation. These findings indicate a novel role for zinc regulation in the PKCα/β-catenin pathway and explain an important mechanism for controlling of stem cell program in lung cancer cells.

Functional role of inorganic trace elements in angiogenesis-Part II: Cr, Si, Zn, Cu, and S

Trace elements play critical roles in angiogenesis events. The effects of nitrogen, iron, selenium, phosphorus, gold, and calcium were discussed in part I. In part II, we evaluated the effect of chromium, silicon, zinc, copper, and sulfur on different aspects of angiogenesis, with critical roles in healing and regeneration processes, and undeniable roles in tumor growth and cancer therapy. This review is the second of series that serves as an overview of the role of inorganic elements in regulation of angiogenesis and vascular function. The methods of exposure, structure, mechanism, and potential activity of these trace elements are briefly discussed. An electronic search was performed on the role of these trace elements in angiogenesis from January 2005 to April 2014. The recent aspects of the relationship between five different trace elements and their role in regulation of angiogenesis, and homeostasis of pro- and anti-angiogenic factors were assessed. Many studies have investigated the effects and importance of these elements in angiogenesis events. Both stimulatory and inhibitory effects on angiogenesis are observed for the evaluated elements. Chromium can promote angiogenesis in pathological manners. Silicon as silica nanoparticles is anti-angiogenic, while in calcium silicate extracts and bioactive silicate glasses promote angiogenesis. Zinc is an anti-angiogenic agent acting on important genes and growth factors. Copper and sulfur compositions have pro-angiogenic functions by activating pro-angiogenic growth factors and promoting endothelial cells migration, growth, and tube formation. Thus, utilization of these elements may provide a unique opportunity to modulate angiogenesis under various setting.

Lansoprazole induces apoptosis of breast cancer cells through inhibition of intracellular proton extrusion

The increased glycolysis and proton secretion in tumors is proposed to contribute to the proliferation and invasion of cancer cells during the process of tumorigenesis and metastasis. Here, treatment of human breast cancer cells with proton pump inhibitor (PPI) lansoprazole (LPZ) induces cell apoptosis in a dose-dependent manner. In the implantation of the MDA-MB-231 xenografts in nude mice, administration of LPZ significantly inhibits tumorigenesis and induces large-scale apopotosis of tumor cells. LPZ markedly inhibits intracellular proton extrusion, induces an increase in intracellular ATP level, lysosomal alkalinization and accumulation of reactive oxygen species (ROS) in breast cancer cells. The ROS scavenger N-acetyl-l-cysteine (NAC) and diphenyleneiodonium (DPI), a specific pharmacological inhibitor of NADPH oxidases (NOX), significantly abolish LPZ-induced ROS accumulation in breast cancer cells. Our results suggested that LPZ may be used as a new therapeutic drug for breast tumor.

The effect of zinc and the role of p53 in copper-induced cellular stress responses

Metals can directly or indirectly cause an increase in reactive oxygen species (ROS) accumulation in cells, and this may result in programmed cell death. A number of previous studies have shown that zinc (Zn) modulates mitogenic activity via several signalling pathways, such as AKT, mitogen-activated protein kinase (MAPK), nuclear factor-kappa B (NF -κB), AP-1 and p53. The exact role that Zn plays in the regulation of apoptosis remains ambiguous. Intracellular free Zn modulates p53 activity and stability, and excess Zn alters the p53 protein structure and down-regulates p53's binding to DNA. Copper (Cu) accumulation causes apoptosis that seems to be mediated by DNA damage and subsequent p53 activation. Cu can also displace Zn from its normal binding site on p53, resulting in abnormal protein folding and disruption of p53 function. In spite of the induction of the tumour suppressor p53, hepatic Cu accumulation significantly increases the risk of cancerous neoplasm both in humans and rats, suggesting that p53 function may be impaired in these cells. It is generally understood that imbalances in Cu and Zn levels may lead to a higher prevalence of p53 mutations. An increased number of p53 mutations have been found in liver samples from Wilson's disease (WD) patients. High levels of the p53 mutation most probably contribute to the pathogenesis of cancer in individuals with WD, but the cause and effect are not clear. The protein p53 also plays a crucial role in the transcriptional regulation of metallothionein, which indicates a novel regulatory role for p53. This review discusses the central role of p53 and the redox-inert metal Zn in the cellular stress responses induced by the redox active biometal Cu.

Zinc and diabetic retinopathy

Zinc (Zn) is an important nutrient that is involved in various physiological metabolisms. Zn dyshomeostasis is often associated with various pathogeneses of chronic diseases, such as metabolic syndrome, diabetes, and related complications. Zn is present in ocular tissue in high concentrations, particularly in the retina and choroid. Zn deficiencies have been shown to affect ocular development, cataracts, age-related macular degeneration, and even diabetic retinopathy. However, the mechanism by which Zn deficiency increases the prevalence of diabetic retinopathy remains unclear. In addition, due to the negative effect of Zn deficiency on the eye, Zn supplementation should prevent diabetic retinopathy; however, limited available data do not always support this notion. Therefore, the goal of this paper was to summarize these pieces of available information regarding Zn prevention of diabetic retinopathy. Current theories and possible mechanisms underlying the role of Zn in the eye-related diseases are discussed. The possible factors that affect the preventive effect of Zn supplementation on diabetic retinopathy were also discussed.

Metallothioneins and zinc in cancer diagnosis and therapy

Metallothioneins (MTs) are involved in protection against oxidative stress (OS) and toxic metals and they participate in zinc metabolism and its homeostasis. Disturbing of zinc homeostasis can lead to formation of reactive oxygen species, which can result in OS causing alterations in immunity, aging, and civilization diseases, but also in cancer development. It is not surprising that altered zinc metabolism and expression of MTs are of great interest in the case of studying of oncogenesis and cancer prognosis. The role of MTs and zinc in cancer development is tightly connected, and the structure and function of MTs are strongly dependent on Zn²⁺ redox state and its binding to proteins. Antiapoptic effects of MTs and their interactions with proteins nuclear factor kappa B, protein kinase C, esophageal cancer-related gene, and p53 as well as the role of MTs in their proliferation, immunomodulation, enzyme activation, and interaction with nitric oxide are reviewed. Utilization of MTs in cancer diagnosis and therapy is summarized and their importance for chemoresistance is also mentioned.

Health and cellular impacts of air pollutants: from cytoprotection to cytotoxicity

Air pollution as one of the ravages of our modern societies is primarily linked to urban centers, industrial activities, or road traffic. These atmospheric pollutants have been incriminated in deleterious health effects by numerous epidemiological and in vitro studies. Environmental air pollutants are a heterogeneous mixture of particles suspended into a liquid and gaseous phase which trigger the disruption of redox homeostasis—known under the term of cellular oxidative stress—in relation with the establishment of inflammation and cell death via necrosis, apoptosis, or autophagy. Activation or repression of the apoptotic process as an adaptative response to xenobiotics might lead to either acute or chronic toxicity. The purpose of this paper is to highlight the central role of oxidative stress induced by air pollutants and to focus on the subsequent cellular impacts ranging from cytoprotection to cytotoxicity by decreasing or stimulating apoptosis, respectively.

Perchlorotrityl radical-fluorophore conjugates as dual fluorescence and EPR probes for superoxide radical anion

Perchlorotrityl radicals, mono-substituted with a fluorophore using an amide linker of varying chain length, were synthesized and characterized. Electron paramagnetic resonance (EPR) spectroscopic study indicated free-electron coupling with the aromatic hydrogen nuclei and long-range coupling with the methylene hydrogens of the linker group. Reactivity of the fluorophore-conjugated trityls with superoxide radical anion showed quenching of EPR signal and enhancement of fluorescence emission spectrum. This work presents the first example of a perchlorotrityl-fluorophore conjugate that can potentially be employed as a dual probe for the detection of superoxide under oxidative stress-mediated conditions in biological systems.

Tl(I) and Tl(III) activate both mitochondrial and extrinsic pathways of apoptosis in rat pheochromocytoma (PC12) cells

Thallium (Tl) is a highly toxic metal though yet its mechanisms are poorly understood. Previously, we demonstrated that rat pheochromocytoma (PC12) cells exposure to thallous (Tl(I)) or thallic (Tl(III)) cations leads to mitochondrial damage and reduced cell viability. In the present work we comparatively characterized the possible pathways involved in Tl(I)- and Tl(III)- (10-100 muM) mediated decrease in PC12 cells viability. We observed that these cations do not cause cell necrosis but significantly increased the number of cells with apoptotic features. Both cations lead to Bax oligomerization and caused apoptosis inducing factor (AIF), endonuclease G (Endo G), and cytochrome c release from mitochondria, but they did not activate caspase dependent DNAse (CAD). Tl(I)- and Tl(III)-dependent caspases 9 and 3 activation followed similar kinetics, with maximal effects at 18 h of incubation. In addition, Tl(I) promoted phosphatidylserine (PS) exposure. Tl(III) induced 2- and 18-fold increase in Fas content and caspase 8 activity, respectively. Together, experimental results show that Tl(I) and Tl(III) induce PC12 cells apoptosis, although differential pathways are involved. While Tl(I)-mediated cell apoptosis was mainly associated with mitochondrial damage, Tl(III) showed a mixed effect triggering both the intrinsic and extrinsic pathways of apoptosis. These findings contribute to a better understanding of the mechanisms underlying Tl-induced loss of cell viability in PC12 cells.

Zinc improves the development of human CD34+ cell progenitors towards Natural Killer cells and induces the expression of GATA-3 transcription factor

The Natural Killer cell maturation from CD34(+) hematopoietic cell precursors is a complex process that requires the synergistic effect of different cytokines and growth factors. Although there have been a number of important advances in our understanding of the Natural Killer differentiation, the developmental step leading to mature Natural Killer cells is still poorly defined. We evaluated the effect of two zinc concentrations (10 and 20microM) on the kinetic of development of CD34(+) cell progenitors towards Natural Killer cells. CD34(+) cells were purified from peripheral blood and cultured in medium supplemented with interleukin-15, interleukin-7, Flt 3 ligand, and stem cell factor. CD34(+) cells underwent proliferation and progressively lost CD34 antigen and acquired a CD56(+) phenotype. These CD56(+) cells exerted cytotoxic activity and expressed the CD94 inhibitory receptor. The supplementation with zinc greatly increased both the number of cells in culture and the absolute number of CD56(+) cells. Zinc induced higher levels of cytotoxic activity and a higher number of perforin-producing and of CD94-bearing CD56(+) cells in comparison with zinc unsupplemented cultures in early stages of Natural Killer cell development. The zinc-induced changes in CD34-derived CD56(+) cells were associated with an increased expression of GATA-3, a zinc-finger transcription factor providing for maturation and activity of T and Natural Killer cells. The increase was related to a higher CD56(+) cell number (10microM zinc), or to an increased GATA-3 mRNA transcription in CD56(+) cells (20microM zinc). Our data demonstrate that zinc influences the proliferation and differentiation of CD34(+) progenitors.

Single and Combination Toxic Metal Exposures Induce Apoptosis in Cultured Murine Podocytes Exclusively via the Extrinsic Caspase 8 Pathway

Arsenite, cadmium, and mercury are among the most abundant toxic metals (TM) in the environment. Although the most common renal manifestation of TM toxicity is proximal tubular dysfunction, significant glomerular injury can also occur. We hypothesized that glomerular injury following TM exposure results from TM-induced apoptosis of podocytes. To test this hypothesis we examined the extent of apoptosis and the apoptotic pathways induced in cultured murine podocytes incubated for three days with arsenite, cadmium, or mercury, and with equimolar combinations of all three metals. Apoptosis was detected by DNA laddering, and the number of apoptotic nuclei determined by Tunel assay. Treatment for three days with each TM resulted in DNA laddering and induced a dose-dependent increase in apoptotic nuclei. In contrast, treatment with equimolar combinations of TM induced significantly fewer apoptotic nuclei than individual TM treatments. Apoptosis induced by each TM was associated with a significant (approximately 400%) increase in caspase 8 activity, but no change in caspase 9 activity, and Western analyses revealed a marked up-regulation of Fas (approximately 500%) and FADD (approximately 300%) with no change in expression of Bax, Bcl-2, or Bcl-xL. Similar to the apoptotic response, combinations of TM induced less caspase 8 activity and Fas/FADD expression than individual TM treatments. Collectively, these results demonstrate that (1) TM induced apoptosis in cultured murine podocytes via the extrinsic Fas-FADD caspase 8 pathway, rather than the mitochondrial apoptotic pathway, and (2) combination TM exposure induced less apoptosis than individual TM, indicating an antagonistic rather than an additive or synergistic toxicity.

Inhibition of extracellular signal regulated kinase (ERK) leads to apoptosis inducing factor (AIF) mediated apoptosis in epithelial breast cancer cells: the lack of effect of ERK in p53 mediated copper induced apoptosis

Recent studies have shown that MEK/ERK-mediated signals play a major role in regulation of activity of p53 tumor suppressor protein. In this study, we investigated whether or not there is functional interaction between p53 and MEK/ERK pathways in epithelial breast cancer cells exposed to copper or zinc. We demonstrated that expression of wild-type p53 induced by copper or zinc significantly reduced phosphorylation of extracellular signal regulated kinase (ERK) in epithelial breast cancer MCF7 cells. Mutation or suppression of p53 in MDA-MB231 and MCF7-E6 cells, respectively, resulted in a strong ERK phosphorylation in the presence of metals. Weak ERK phosphorylation in MCF7 cells induced by copper or zinc was linked to mitochondrial disruption and apoptosis. Furthermore, inhibition of ERK through addition of PD98059 stimulated p53 activation in MCF7 cells and also led to upregulation of p53 downstream targets, p21 and Bax, which is a proapototic member of Bcl-2 family triggering mitochondrial pore opening. Moreover, blockage of the MEK/ERK pathway caused a breakdown of the mitochondrial membrane potential accompanied by an elevation in the ROS production. Disruption of p53 expression attenuated the depolarization of the mitochondrial membrane and ROS generation. Furthermore, PD98059 initiated apoptosis inducing factor (AIF) translocation from mitochondria to the nucleus in MCF7 cells; which are depleted in caspase 3. Interestingly, repression of MEK/ERK pathway did not intensify the cell stress caused by metal toxicity. Therefore, these findings demonstrate that MEK/ERK pathway plays an important role in downregulation of p53 and cell survival. Inhibition of ERK can lead to apoptosis via nuclear relocation of AIF. However, metal-induced activation of p53 and mitochondrial depolarization appears to be independent of ERK. Our data suggest that copper induces apoptosis through depolarization of mitochondrial membrane with release of AIF, and this process is MEK/ERK independent.

Effects of increased cellular zinc levels on gene and protein expression in HT-29 cells

High cellular zinc concentrations lead to impairments in ATP synthesis and cell cycle control particularly in neurons and epithelial cells. The molecular basis for these dysfunctions is still not fully elucidated. Here we analyzed the effects of a high zinc exposure (10 ppm) on gene and protein expression in the human epithelial cell line HT-29. Of the 1176 genes analyzed with cDNA arrays, nine differentially expressed genes were identified. Proteome analysis based on 1310 detected proteins identified 11 molecular targets. Most of the identified genes/proteins have not been linked to cellular zinc status before (e.g. PEC-60, R-ras3). More than half of the targets participate in ATP production or stress response. Therefore, it appears that higher zinc concentrations mediate their effects mainly via impairments in cellular energy metabolism and stress response.

Zinc deficiency, DNA damage and cancer risk

A large body of evidence suggests that a significant percentage of deaths resulting from cancer in the United States could be avoided through greater attention to proper and adequate nutrition. Although many dietary compounds have been suggested to contribute to the prevention of cancer, there is strong evidence to support the fact that zinc, a key constituent or cofactor of over 300 mammalian proteins, may be of particular importance in host defense against the initiation and progression of cancer. Remarkably, 10% of the U.S. population consumes less than half the recommended dietary allowance for zinc and are at increased risk for zinc deficiency. Zinc is known to be an essential component of DNA-binding proteins with zinc fingers, as well as copper/zinc superoxide dismutase and several proteins involved in DNA repair. Thus, zinc plays an important role in transcription factor function, antioxidant defense and DNA repair. Dietary deficiencies in zinc can contribute to single- and double-strand DNA breaks and oxidative modifications to DNA that increase risk for cancer development. This review will focus on potential mechanisms by which zinc deficiency impairs host protective mechanisms designed to protect against DNA damage, enhances susceptibility to DNA-damaging agents and ultimately increases risk for cancer.

The cell cycle related apoptotic susceptibility to arsenic trioxide is associated with the level of reactive oxygen species

Double staining flow cytometry was performed using 7-amino actinomycin D and 6-carboxy-2', 7'-dichlorodihydrofluorescein diacetate, to detect the level fluctuation of reactive oxygen species (ROS) during the cell cycle of normal NB4 cells. Our results showed that NB4 cells possessed higher level of ROS in G2/M phase than in G1 and S phases. Double staining flow cytometry, with TdT mediated dUTP nick end labeling (Tunel) and propidium iodide (PI), indicated that As2O3 (2 microM) could induce apoptosis in NB4 cells prevailingly from G2/M phase, and this efficacy was enhanced upon co-administration of 2, 3-dimethoxy-1, 4-naphthoquinone (DMNQ) (2.5 microM) which could produce the endogenous ROS. These results suggested that different ROS level in different cell cycle phases of NB4 cells might determine the selective induction of G2/M apoptosis and the cells' susceptibility to apoptosis by As2O3.

Zinc has ambiguous effects on chromium (VI)-induced oxidative stress and apoptosis

Zinc is an important cellular antioxidant. We investigated its role in chromium-induced oxidative stress and apoptosis in human tumor cell line Hep-2. The measured parameters included intracellular labile zinc content (Zinquin-E fluorescence), cell viability (WST-1 assay), oxidative stress (spectrophotometry), mitochondrial potential (flow cytometry), caspase-3 activity, and PARP cleavage (immunofluorescence). We found that Hep-2 cells contain abundant labile zinc stores that may be depleted by the ionophore TPEN or increased by external zinc supplementation. Chromium (VI)-induced cytotoxicity and apoptosis were enhanced in zinc-depleted cells after 24 h, in particular at chromium (VI) concentrations of 50 and 150 micromol/l. On the other hand, elevated levels of labile zinc were able to protect against apoptosis induced by 10 micromol/l chromium (VI) but at higher chromium (VI) concentrations (50 and 150 micromol/l) acted synergistically, significantly enhancing oxidative stress and the course of apoptosis, possibly through oxidative stress and mitochondrial damage.

Zinc induced apoptosis in HEP-2 cancer cells: the role of oxidative stress and mitochondria

Induction of apoptosis by zinc sulfate was investigated during 96 h exposure on the cancer Hep-2 cell line. During 48 h of exposure, zinc translocated into mitochondria and stimulated production of reactive oxygen species (ROS), affected cellular GSH management and induced moderate activation of p53 and dissipation of mitochondrial membrane potential. In Zn-exposed cells, mitochondria released cytochrome c and AIF, whose translocation to the cytoplasm or the nucleus coincided with the activation of apoptosis. The use of various pharmacological inhibitors inhibiting particular apoptotic targets (antioxidants such as N-acetyl-cysteine and coenzyme Q, the caspase inhibitors z-DEVD-fmk and z-VAD-fmk, cyclosporin A and bonkgrekic acid) proved that Zn acts both directly and indirectly on mitochondria and observed apoptosis is executed by caspase-dependent and caspase-independent pathways.

The effect of zinc sulphate in the prevention of radiation-induced dermatitis

There is currently substantial clinical interest in zinc (Zn) as a protective agent against radiation-related normal tissue injury. To further assess this drug's potential, the effect of Zn was studied in rats using a radiation-induced skin injury model. Sprague-Dawley rats were divided into four groups. Group 1 received neither Zn nor irradiation (control group). Group 2 received 30 Gy of gamma irradiation as a single dose to the right hind legs of the rats (RT Group). Groups 3 and 4 received the same irradiation plus 5 mg/kg/day Zn (RT+5 Zn group) or 10 mg/kg/day Zn orally (RT+10 Zn group), respectively. The rats were irradiated using a cobalt-60 teletherapy unit. Acute skin reactions were assessed every three days by two independent radiation oncology experts. At the endpoint of the study, light-microscopic findings were assessed by two independent expert pathology physicians. Clinically and histopathologically, irradiation increased dermatitis when compared with the control group (p < 0.05). The severity of radiodermatitis of the rats in the RT+5 Zn and RT+10 Zn groups was significantly lower than in the RT group (p < 0.05); radiodermatitis was seen earlier in the RT group than in the other groups (p < 0.05). Zn was found to be efficacious in preventing epidermal atrophy, dermal degeneration such as edema and collagen fiber loss, and hair follicle atrophy. The most protection for radiation dermatitis was observed in the RT+10 Zn group. It would be worthwhile studying the effects of zinc sulphate supplements in radiation-treated cancer patients, in the hope of reducing radiation-induced toxicity.

Zinc might protect oxidative changes in the retina and pancreas at the early stage of diabetic rats

It is well documented that oxidative stress is a basic mechanism behind the development of diabetic retinopathy (DR). The current study was undertaken to elucidate the possible role of zinc as an antioxidant and a biological membrane stabilizer in the protection against (DR). Male Wistar rats weighing 250 +/- 50 g were made diabetic by injection with a single ip dose of alloxan (100 mg/kg). Another group of rats was simultaneously treated with alloxan (100 mg/kg) and a single ip dose of zinc chloride (ZnCl2) (5 mg/kg). Blood and tissue samples were collected at 24, 48, and 72 h post-treatment in both groups. Diabetic state was confirmed by the determination of plasma glucose levels (significantly elevated at any time of the experiment when compared with controls receiving vehicle). Plasma insulin was significantly increased 24 h after treatment in both alloxan and alloxan plus ZnCl2-treated groups, and then decreased markedly 48 and 72 h post treatment in both groups. Alloxan treatment depleted both retinal and liver glutathione contents. The decrease in retinal and liver GSH in alloxan-treated rats was accompanied with a sustained increase in their thiobarbituric acid (TBA) content. Simultaneous treatment of rats with alloxan and ZnCl2 blunted the sustained increment in plasma glucose induced by alloxan. The combined administration of alloxan and zinc reversed the depleting effect on retinal and hepatic GSH in alloxan-treated rats and reduced the elevations in TBA content of both retinas and livers. At variance with many other antioxidants the current results clearly indicate the beneficial effects of Zn in both controlling hyperglycemia and the protection of the retina against oxidative stress in diabetes which may help set a new direction toward the development of effective treatments of DR.

Dietary influences on endocrine-inflammatory interactions in prostate cancer development

Prostate cancer is the most frequently diagnosed non-cutaneous cancer and is the second leading cause of cancer death in American men. The focus of this review is to define the relationship between hormonal (testosterone/estrogens) stimulation of chronic inflammation, generation of reactive oxygen species (ROS), and uncontrolled prostate cell proliferation, and review putative dietary chemoprevention strategies that focus on these processes. It has been proposed that elevated estrogen in men who already have high blood testosterone are at high risk for prostate cancer. We hypothesized that elevated estrogen, in the presence of testosterone, causes prolonged activation of a redox-sensitive transcription factor, nuclear factor kappa B (NF kappa B), that initiates and amplifies an inflammatory cascade within the prostate and results in sustained oxidative and nitrative damage. The inflammatory cascade is proposed to link with uncontrolled proliferation through up-regulated Wnt signal and abnormal catenin accumulation in the prostate. Finally, a strategy that emphasizes a "whole food" based approach to cancer prevention by selecting food products that bear anti-inflammatory and anti-proliferative properties may be most promising as an effective dietary chemopreventive strategy.

Effects of supplementation with vitamins A, C, and E, selenium, and zinc on immune function in a murine sensitization model

OBJECTIVE

We compared the effects of supplementing with vitamins A, C, and E, selenium, and zinc on a range of innate and specific T-helper 1 (Th1) and Th2-driven adaptive immune responses.

METHODS

BALB/c mice were fed semi-purified AIN93 diets and randomly assigned to receive a diet supplemented with 120 mg/kg of vitamin A, 2500 mg/kg of vitamin C, 1000 mg/kg of vitamin E, 2 mg/kg of selenium, and 500 mg/kg of zinc (n = 15/group). After 4 wk of supplementation, mice were sensitized by topical application of di-nitro-chlorobenzene (DNCB); 2 wk later mice were challenged; and 5 d later they were killed to assess the effect on a range of innate responses (phagocytic activity, oxidative burst and tumor necrosis factor-alpha), adaptive Th1-driven responses (delayed-type hypersensitivity, DNCB-specific immunoglobulin [Ig] G2a and IgG2b, and interferon-gamma [IFN-gamma]), and adaptive Th2-driven responses (DNCB-specific IgE and IgG1 and interleukin-4 [IL-4]).

RESULTS

Immune function was affected only in the vitamin A group. These mice gained less weight and were less capable of resolving the inflammatory response elicited during sensitization. The oxidative burst of blood cells was increased, but production of IFN-gamma and IL-4 and the ratio of IFN-gamma to IL-4 were markedly depressed. In concordance with the latter result, production of Th1-driven IgG2a antibodies was decreased, whereas Th2-driven isotypes were not affected (IgG1, IgE) and mucosal IgA was increased.

CONCLUSIONS

These findings confirmed that supplementary amounts of vitamin A above dietary requirements enhance inflammatory responses accompanied by decreased Th1 and increased mucosal responses. However, supplementation of these sufficiently fed, non-stressed, young adult mice with vitamins C and E, selenium, or zinc had no effect on immune function. We speculate that using this model in aged, physiologically, or nutritionally stressed mice may provide outcomes more similar to those in sensitive human populations. If so, this would improve the usefulness of the model to assess, characterize, and rank effects of foods or nutrients on a range of immune functions, including Th1/Th2 polarization.

Differential regulation of signal transduction pathways in wild type and mutated p53 breast cancer epithelial cells by copper and zinc

Previous studies have suggested that cells may differ in their response to metal stress. This study was undertaken to investigate the role of PI3K/Akt signaling pathway in metal resistance in human breast cancer epithelial cells with different p53 and estrogen receptor status. Exposure to copper and zinc increased Akt phosphorylation with its nuclear localization only in MDA-MB-231 cells with no estrogen receptor and mutated p53. Cyclin D1 expression and cell-cycle progression followed the metal-induced Akt phosphorylation. Treatment with LY294002 abrogated these effects, suggesting the essential role of PI3-kinase. In contrast, in MCF-7 cells with wild type p53 and estrogen receptor, there was no change in Akt activation, while suppression of p53 activity by pifithrin-alpha increased phosphorylation of Akt after the treatment with copper. In MCF-7 cells, the metal treatment increased the phosphorylation of p53 at serine 15, up-regulated p21 expression, and resulted in cell-cycle arrest in G1 phase with apoptosis. These results demonstrate that copper-induced apoptosis in MCF-7 cells is p53 dependent, whereas the metal resistance in MDA-MB-231 cells may be due to activation of Akt in the absence of a functional p53.