Phase resetting of the mammalian circadian clock by DNA damage

To anticipate the momentum of the day, most organisms have developed an internal clock that drives circadian rhythms in metabolism, physiology, and behavior [1]. Recent studies indicate that cell-cycle progression and DNA-damage-response pathways are under circadian control [2-4]. Because circadian output processes can feed back into the clock, we investigated whether DNA damage affects the mammalian circadian clock. By using Rat-1 fibroblasts expressing an mPer2 promoter-driven luciferase reporter, we show that ionizing radiation exclusively phase advances circadian rhythms in a dose- and time-dependent manner. Notably, this in vitro finding translates to the living animal, because ionizing radiation also phase advanced behavioral rhythms in mice. The underlying mechanism involves ATM-mediated damage signaling as radiation-induced phase shifting was suppressed in fibroblasts from cancer-predisposed ataxia telangiectasia and Nijmegen breakage syndrome patients. Ionizing radiation-induced phase shifting depends on neither upregulation or downregulation of clock gene expression nor on de novo protein synthesis and, thus, differs mechanistically from dexamethasone- and forskolin-provoked clock resetting [5]. Interestingly, ultraviolet light and tert-butyl hydroperoxide also elicited a phase-advancing effect. Taken together, our data provide evidence that the mammalian circadian clock, like that of the lower eukaryote Neurospora[6], responds to DNA damage and suggest that clock resetting is a universal property of DNA damage.

Cardiac overexpression of hormone-sensitive lipase inhibits myocardial steatosis and fibrosis in streptozotocin diabetic mice

Intracellular lipid accumulation (steatosis) and resultant lipotoxicity are key features of diabetic cardiomyopathy. Since cardiac hormone-sensitive lipase (HSL) is activated in diabetic mice, we sought to explore a pathophysiological function of cardiac HSL in the development of diabetic cardiomyopathy. Transgenic (Tg) mice with heart-specific HSL overexpression were generated, and cardiac histology, function, lipid profile, and gene expressions were analyzed after induction of diabetes by streptozotocin. Electron microscopy showed numerous lipid droplets in wild-type (Wt) hearts after 3 wk of diabetes, whereas Tg mice showed no lipid droplet accumulation. Cardiac content of acylglycerides was increased approximately 50% with diabetes in Wt mice, whereas this was blunted in Tg hearts. Cardiac lipid peroxide content was twofold lower in Tg hearts than in Wt hearts. The mRNA expressions for peroxisome proliferator-activated receptor-alpha, genes for triacylglycerol synthesis, and lipoprotein lipase were increased with diabetes in Wt hearts, whereas this induction was absent in Tg hearts. Expression of genes associated with lipoapoptosis was decreased, whereas antioxidant protein metallothioneins were increased in diabetic Tg hearts. Diabetic Wt hearts showed interstitial fibrosis and increased collagen content. However, Tg hearts displayed no overt fibrosis, concomitant with decreased expression of collagens, transforming growth factor-beta, and matrix metalloproteinase 2. Notably, mortality during the experimental period was approximately twofold lower in diabetic Tg mice compared with Wt mice. In conclusion, since HSL overexpression inhibits cardiac steatosis and fibrosis by apparently hydrolyzing toxic lipid metabolites, cardiac HSL could be a therapeutic target for regulating diabetic cardiomyopathy.

Transcription factor Sp1 plays an important role in the regulation of copper homeostasis in mammalian cells

Copper is an essential metal nutrient, yet copper overload is toxic. Here, we report that human copper transporter (hCtr) 1 plays an important role in the maintenance of copper homeostasis by demonstrating that expression of hCtr1 mRNA was up-regulated under copper-depleted conditions and down-regulated under copper-replete conditions. Overexpression of full-length hCtr1 by transfection with a recombinant hCtr1 cDNA clone reduced endogenous hCtr1 mRNA levels, whereas overexpression of N terminus-deleted hCtr1 did not change endogenous hCtr1 mRNA levels, suggesting that increased functional hCtr1 transporter, which leads to increased intracellular copper content, down-regulates the endogenous hCtr1 mRNA. A luciferase assay using reporter constructs containing the hCtr1 promoter sequences revealed that three Sp1 binding sites are involved in the basal and copper concentration-dependent regulation of hCtr1 expression. Modulation of Sp1 levels affected the expression of hCtr1. We further demonstrated that the zinc-finger domain of Sp1 functions as a sensor of copper that regulates hCtr1 up and down in response to copper concentration variations. Our results demonstrate that mammalian copper homeostasis is maintained at the hCtr1 mRNA level, which is regulated by the Sp1 transcription factor.

The role of zinc, copper and iron in the pathogenesis of diabetes and diabetic complications: therapeutic effects by chelators

Zinc (Zn), copper (Cu) and iron (Fe) are essential minerals that are required for a variety of biomolecules to maintain the normal structure, function, and proliferation of cells. These metals can be toxic in excessive amounts, especially in certain genetic disorders. The homeostasis of these trace elements results from a tightly coordinated regulation by different proteins involved in their uptake, excretion and intracellular storage/trafficking. Through the Fenton reaction, Cu and Fe under a non protein-binding condition, can generate various reactive oxygen species, damaging tissues or cells. Abnormal metabolism of Zn, Cu and Fe can lead to several chronic pathogenesis, such as diabetes or diabetic complications. These pathogenic conditions appear to be prevalent in Zn and Cu deficiency, as well as Cu and Fe overload. In the Fe and Cu overloading conditions, Fe and Cu chelating drugs could be used to control diabetes and diabetic complications. The essentiality, toxicity and roles of these metals in the pathogenesis of diabetes and diabetic complications are discussed.

The neurological phenotype of ataxia-telangiectasia: solving a persistent puzzle

Human genomic instability syndromes affect the nervous system to different degrees of severity, attesting to the vulnerability of the CNS to perturbations of genomic integrity and the DNA damage response (DDR). Ataxia-telangiectasia (A-T) is a typical genomic instability syndrome whose major characteristic is progressive neuronal degeneration but is also associated with immunodeficiency, cancer predisposition and acute sensitivity to ionizing radiation and radiomimetic chemicals. A-T is caused by loss or inactivation of the ATM protein kinase, which mobilizes the complex, multi-branched cellular response to double strand breaks in the DNA by phosphorylating numerous DDR players. The link between ATM's function in the DDR and the neuronal demise in A-T has been questioned in the past. However, recent studies of the ATM-mediated DDR in neurons suggest that the neurological phenotype in A-T is indeed caused by deficiency in this function, similar to other features of the disease. Still, major issues concerning this phenotype remain open, including the presumed differences between the DDR in post-mitotic neurons and proliferating cells, the nature of the damage that accumulates in the DNA of ATM-deficient neurons under normal life conditions, the mode of death of ATM-deficient neurons, and the lack of a major neuronal phenotype in the mouse model of A-T. A-T remains a prototype disease for the study of the DDR's role in CNS development and maintenance.

Microvessel vascular smooth muscle cells contribute to collagen type I deposition through ERK1/2 MAP kinase, alphavbeta3-integrin, and TGF-beta1 in response to ANG II and high glucose

This study determines that vascular smooth muscle cell (VSMC) signaling through extracellular signal-regulated kinase (ERK) 1/2-mitogen-activated protein (MAP) kinase, alphavbeta(3)-integrin, and transforming growth factor (TGF)-beta1 dictates collagen type I network induction in mesenteric resistance arteries (MRA) from type 1 diabetic (streptozotocin) or hypertensive (HT; ANG II) mice. Isolated MRA were subjected to a pressure-passive-diameter relationship. To delineate cell types and mechanisms, cultured VSMC were prepared from MRA and stimulated with ANG II (100 nM) and high glucose (HG, 22 mM). Pressure-passive-diameter relationship reduction was associated with increased collagen type I deposition in MRA from HT and diabetic mice compared with control. Treatment of HT and diabetic mice with neutralizing TGF-beta1 antibody reduced MRA stiffness and collagen type I deposition. Cultured VSMC stimulated with HG or ANG II for 5 min increased ERK1/2-MAP kinase phosphorylation, whereas a 48-h stimulation induced latent TGF-beta1, alphavbeta(3)-integrin, and collagen type 1 release in the conditioned media. TGF-beta1 bioactivity and Smad2 phosphorylation were alphavbeta(3)-integrin-dependent, since beta(3)-integrin antibody and alphavbeta(3)-integrin inhibitor (SB-223245, 10 microM) significantly prevented TGF-beta1 bioactivity and Smad2 phosphorylation. Pretreatment of VSMC with ERK1/2-MAP kinase inhibitor (U-0126, 1 microM) reduced alphavbeta(3)-integrin, TGF-beta1, and collagen type 1 content. Additionally, alphavbeta(3)-integrin antibody, SB-223245, TGF-beta1-small-intefering RNA (siRNA), and Smad2-siRNA (40 nM) prevented collagen type I network formation in response to ANG II and HG. Together, these data provide evidence that resistance artery fibrosis in type 1 diabetes and hypertension is a consequence of abnormal collagen type I release by VSMC and involves ERK1/2, alphavbeta(3)-integrin, and TGF-beta1 signaling. This pathway could be a potential target for overcoming small artery complications in diabetes and hypertension.

Polymorphisms in metallothionein-1 and -2 genes associated with the risk of type 2 diabetes mellitus and its complications

Metallothionein (MT) as a potent antioxidant can affect energy metabolism. The present study was undertaken to investigate the association between MT gene polymorphism and type 2 diabetes mellitus. Using the PCR-based restriction fragment length polymorphism method, seven single nucleotide polymorphisms (SNPs) in MT genes (rs8052394 and rs11076161 in MT1A gene, rs8052334, rs964372, and rs7191779 in MT1B gene, rs708274 in MT1E gene, and rs10636 in MT2A gene) were detected in 851 Chinese people of Han descent (397 diabetes and 454 controls). Several serum measurements were also examined randomly for 43 diabetic patients and 41 controls. The frequency distributions of the G allele in SNP rs8052394 of MT1A gene were significantly associated with the incidence of type 2 diabetes. There was no difference between patients and controls for the rest of six SNPs. Serum levels of interleukin-6 and tumor necrosis factor-alpha were higher, and serum superoxide dismutase activity was significantly lower in the diabetic group than those in the control group. For diabetic patients, serum superoxide dismutase activity was significantly lower in GG or GA carriers than those of AA carriers of rs8052394 SNP. Increased serum levels in diabetic patients were positively associated with rs964372 SNP, and type 2 diabetes with neuropathy was positively associated with rs10636 and rs11076161. These results suggest that multiple SNPs in MT genes are associated with diabetes and its clinical symptoms. Furthermore, MT1A gene in rs8052394 SNP is most likely the predisposition gene locus for diabetes or changes of serum superoxide dismutase activity.

DNA damage and repair: from molecular mechanisms to health implications

DNA is subjected to several modifications, resulting from endogenous and exogenous sources. The cell has developed a network of complementary DNA-repair mechanisms, and in the human genome, >130 genes have been found to be involved. Knowledge about the basic mechanisms for DNA repair has revealed an unexpected complexity, with overlapping specificity within the same pathway, as well as extensive functional interactions between proteins involved in repair pathways. Unrepaired or improperly repaired DNA lesions have serious potential consequences for the cell, leading to genomic instability and deregulation of cellular functions. A number of disorders or syndromes, including several cancer predispositions and accelerated aging, are linked to an inherited defect in one of the DNA-repair pathways. Genomic instability, a characteristic of most human malignancies, can also arise from acquired defects in DNA repair, and the specific pathway affected is predictive of types of mutations, tumor drug sensitivity, and treatment outcome. Although DNA repair has received little attention as a determinant of drug sensitivity, emerging knowledge of mutations and polymorphisms in key human DNA-repair genes may provide a rational basis for improved strategies for therapeutic interventions on a number of tumors and degenerative disorders.

+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.

Metallothionein induction by hypoxia involves cooperative interactions between metal-responsive transcription factor-1 and hypoxia-inducible transcription factor-1alpha

Mammalian metallothionein (MT) genes are transcriptionally activated by the essential metal zinc as well as by environmental stresses, including toxic metal overload and redox fluctuations. In addition to playing a key role in zinc homeostasis, MT proteins can protect against metal- and oxidant-induced cellular damage, and may participate in other fundamental physiologic and pathologic processes such as cell survival, proliferation, and neoplasia. Previously, our group reported a requirement for metal-responsive transcription factor-1 (MTF-1) in hypoxia-induced transcription of mouse MT-I and human MT-IIA genes. Here, we provide evidence that the protumorigenic hypoxia-inducible transcription factor-1alpha (HIF-1alpha) is essential for induction of MT-1 by hypoxia, but not zinc. Chromatin immunoprecipitation assays revealed that MTF-1 and HIF-1alpha are both recruited to the mouse MT-I promoter in response to hypoxia, but not zinc. In the absence of HIF-1alpha, MTF-1 is recruited to the MT-I promoter but fails to activate MT-I gene expression in response to hypoxia. Thus, HIF-1alpha seems to function as a coactivator of MT-I gene transcription by interacting with MTF-1 during hypoxia. Coimmunoprecipitation studies suggest interaction between MTF-1 and HIF-1alpha, either directly or as mediated by other factors. It is proposed that association of these important transcription factors in a multiprotein complex represents a common strategy to control unique sets of hypoxia-inducible genes in both normal and diseased tissue.

Diabetes-induced alteration of F4/80+ macrophages: a study in mice with streptozotocin-induced diabetes for a long term

Macrophages as an early stage of immune responses form a bridge between innate and acquired immunity and shape the adaptive immune response. The immunoregulatory functions of macrophages in hosts with a prolonged exposure to a diabetic milieu remain to be determined. The levels, phenotype, and immunity including antigen-presenting ability, phagocytosis and immunogenicity of F4/80+ splenic macrophages (SPMs), and peritoneal exudates macrophages (PEMs) were detected in age-matched control mice and mice with streptozotocin (STZ)-induced diabetes for 16 weeks. The numbers of F4/80+ SPMs and PEMs significantly decreased in STZ-induced diabetic mice, compared with age-matched non-diabetic mice (control) at 16 weeks after diabetes induction. Functional analysis showed that F4/80+ SPMs and PEMs in STZ-induced diabetic mice exhibit significantly lower immunogenicity and nonopsonic phagocytosis to allogeneic T cells than those of control mice both in vitro and in vivo. Coincidently, the antigen-presenting capacity of F4/80+ PEMs, but not F4/80+ SPMs, in mice with STZ-induced diabetes for 16 or more weeks is also significantly lower than that of control mice. Our results showed that total cell number and immune function of F4/80+ macrophages were significantly defective in mice with a prolonged exposure to a diabetic milieu, which may be a mechanism responsible for the increased macrophage-related complications in diabetic patients such as the high prevalence of infection and cardiovascular mortality.

Nbs1-dependent binding of Mre11 to adenovirus E4 mutant viral DNA is important for inhibiting DNA replication

Adenovirus (Ad) infections stimulate the activation of cellular DNA damage response and repair pathways. Ad early regulatory proteins prevent activation of DNA damage responses by targeting the MRN complex, composed of the Mre11, Rad50 and Nbs1 proteins, for relocalization and degradation. In the absence of these viral proteins, Mre11 colocalizes with viral DNA replication foci. Mre11 foci formation at DNA damage induced by ionizing radiation depends on the Nbs1 component of the MRN complex and is stabilized by the mediator of DNA damage checkpoint protein 1 (Mdc1). We find that Nbs1 is required for Mre11 localization at DNA replication foci in Ad E4 mutant infections. Mre11 is important for Mdc1 foci formation in infected cells, consistent with its role as a sensor of DNA damage. Chromatin immunoprecipitation assays indicate that both Mre11 and Mdc1 are physically bound to viral DNA, which could account for their localization in viral DNA containing foci. Efficient binding of Mre11 to E4 mutant DNA depends on the presence of Nbs1, and is correlated with a significant E4 mutant DNA replication defect. Our results are consistent with a model in which physical interaction of Mre11 with viral DNA is mediated by Nbs1, and interferes with viral DNA replication.

ATM-NF-kappaB connection as a target for tumor radiosensitization

Ionizing radiation (IR) plays a key role in both areas of carcinogenesis and anticancer radiotherapy. The ATM (ataxia-telangiectasia mutated) protein, a sensor to IR and other DNA-damaging agents, activates a wide variety of effectors involved in multiple signaling pathways, cell cycle checkpoints, DNA repair and apoptosis. Accumulated evidence also indicates that the transcription factor NF-kappaB (nuclear factor-kappaB) plays a critical role in cellular protection against a variety of genotoxic agents including IR, and inhibition of NF-kappaB leads to radiosensitization in radioresistant cancer cells. NF-kappaB was found to be defective in cells from patients with A-T (ataxia-telangiectasia) who are highly sensitive to DNA damage induced by IR and UV lights. Cells derived from A-T individuals are hypersensitive to killing by IR. Both ATM and NF-kappaB deficiencies result in increased sensitivity to DNA double strand breaks. Therefore, identification of the molecular linkage between the kinase ATM and NF-kappaB signaling in tumor response to therapeutic IR will lead to a better understanding of cellular response to IR, and will promise novel molecular targets for therapy-associated tumor resistance. This review article focuses on recent findings related to the relationship between ATM and NF-kappaB in response to IR. Also, the association of ATM with the NF-kappaB subunit p65 in adaptive radiation response, recently observed in our lab, is also discussed.

Metals and neurotoxicology

Metals are ubiquitous and play a critical role in neurobiology. Transition metals are important because they alter the redox state of the physical environment. Biologically, transition metals catalyze redox reactions that are critical to cellular respiration, chemical detoxification, metabolism, and even neurotransmitter synthesis. Many metals are both nutrients and neurotoxicants, such as iron, zinc, copper, and manganese. Other metals, such as lead and cadmium, are metabolized similarly to these metals, particularly iron. Iron metabolism and genes that regulate iron metabolism may be the key to understanding metal toxicity. Finally, recent evidence demonstrates that early life exposures may program later life and adult disease phenotypes via processes of epigenetics. Parallel work in metals demonstrates that epigenetics may be a critical pathway by which metals produce health effects.

Functional induction of P-glycoprotein in the blood-brain barrier of streptozotocin-induced diabetic rats: evidence for the involvement of nuclear factor-kappaB, a nitrosative stress-sensitive transcription factor, in the regulation

The objective of this study was to investigate the transport kinetics of cyclosporin A, a well known substrate for P-glycoprotein (P-gp), across the blood-brain barrier (BBB), and the expression of the transporter in the brain of streptozotocin-induced diabetic rats. The in vivo transport clearance of cyclosporin A was significantly reduced in diabetic rats compared with that in the control. The decreased transport was associated with the increased level of mRNA and the protein for P-glycoprotein in the rat brain. The functional activity of the efflux transporter in mouse brain capillary endothelial (MBEC4) cells, an in vitro model of the BBB, was also stimulated when slow nitric oxide (NO)-releasing donors were present, whereas the stimulation was absent in the case of rapid NO-releasing donors (e.g., S-nitroso-N-acetyl-dl-penicillamine and diethylenetriamine). The stimulatory effect was highest for sodium nitroprusside (SNP) and the functional induction associated with the increased mRNA and protein level of the transporter. The pretreatment of the cell with SNP along with ascorbate, methylene blue, or superoxide dismutase attenuated the induction of function and expression for P-glycoprotein, suggesting that the reaction product between superoxide and NO is involved in the induction of function and expression. The level of nuclear translocation of nuclear factor-kappaB (NF-kappaB) and DNA binding activity of nuclear extracts to the NF-kappaB consensus oligonucleotide was increased in MBEC4 cells pretreated with SNP. Taken together, these observations suggest that nitrosative stress leads to the up-regulation of the message for the efflux transporter and, ultimately, to the enhanced function, probably via a NF-kappaB-dependent mechanism.

Zinc-bound metallothioneins and immune plasticity: lessons from very old mice and humans

The capacity of the remodelling immune responses during stress (named immune plasticity) is fundamental to reach successful ageing. We herein report two pivotal experimental models in order to demonstrate the relevance of the immune plasticity in ageing and successful ageing. These two experimental models will be compared with the capacity in remodelling the immune response in human centenarians. With regard to experimental models, one model is represented by the circadian rhythms of immune responses, the other one is the immune responses during partial hepatectomy/liver regeneration (pHx). The latter is suggestive because it mimics the immunosenescence and chronic inflammation 48 h after partial hepatectomy in the young through the continuous production of IL-6, which is the main cause of immune plasticity lack in ageing. The constant production of IL-6 leads to abnormal increments of zinc-bound Metallothionein (MT), which is in turn unable in zinc release in ageing. As a consequence, low zinc ion bioavailability appears for thymic and extrathymic immune efficiency, in particular of liver NKT cells bearing TCR γδ. The remodelling during the circadian cycle and during pHx of zinc-bound MT confers the immune plasticity of liver NKT γδ cells and NK cells in young and very old mice, not in old mice. With regard to human centenarians and their capacity in remodelling the immune response with respect to elderly, these exceptional individuals display low zinc-bound MT associated with: a) satisfactory intracellular zinc ion availability, b) more capacity in zinc release by MT, c) less inflammation due to low gene expression of IL-6 receptor (gp130), d) increased levels of IFN-gamma and number of NKT cell bearing TCR γδ. Moreover, some polymorphisms for MT tested in PBMCs from human donors are related to successful ageing. In conclusion, zinc-bound MT homeostasis is fundamental to confer the immune plasticity that is a condition "sine qua non" to achieve healthy ageing and longevity.

High level glucose increases mutagenesis in human lymphoblastoid cells

Epidemiological data have suggested an increased cancer rates in diabetic patients, for which the underlying mechanism is poorly understood. We studied whether high level of glucose (HG) treatment that mimic the hyperglycemic condition in diabetes mellitus is mutagenic. Mutagenesis studies were carried out at both hypoxanthine phosphoribosyltransferase (hprt) and thymidine kinase (tk) loci. Role of p53 in HG-induced mutagenesis was also investigated by using human lymphoblastoid cell lines derived from same donor but differs in p53 statuses; TK6 has wild-type p53, NH32 has null p53, and WTK1 has mutant p53 (ile237). In addition, we studied the influence of antioxidant treatment on HG-induced mutagenesis. Mutation fractions at both loci increased significantly in all three lines at 21 and 28 days after HG treatments. At tk locus, the increase of a class of mutants with normal growth rate is mainly responsible for the overall increased mutant fraction. Compared to TK6 cells, both NH32 and WTK1 cells showed an early onset of mutagenesis. Treatment of cells with antioxidant N-acetyl-L-cysteine partially reduced HG induced mutagenesis. This study is the first to indicate that HG is able to induce gene mutation which may be one of the important mechanisms of diabetes-associated carcinogenesis.

Enhanced radiation-induced cytotoxic effect by 2-ME in glioma cells is mediated by induction of cell cycle arrest and DNA damage via activation of ATM pathways

Glioblastoma multiform is the most common malignant primary brain tumor in adults, but there remains no effective therapeutic approach. 2-methoxyestradiol (2-ME), which is a naturally occurring metabolite of 17beta-estradiol, was shown to enhance radiotherapeutic effect in certain tumors; however, whether 2-ME can also enhance the sensitivity of glioma cells to radiotherapy remains unknown. The present study, therefore, was to address this issue using two human glioma cell lines (T98G and U251MG). These cells were irradiated with and without 2-ME and then clonogenic assay, apoptosis assay, DNA damage, and cell cycle change were examined. Results showed that 2-ME significantly enhances radiation-induced cell death in both glioma cells, shown by decreasing cell viability and increasing apoptotic cell death. No such radiosensitizing effect was observed if cells pre-treated with Estrodiol, suggesting the specifically radiosensitizing effect of 2-ME rather than a general effect of estrodials. The enhanced radio-cytotoxic effect in glioma cells by 2-ME was found to be associated with its enhancement of G(2)/M arrest and DNA damage, and phosphorylated ATM protein kinases as well as cell cycle checkpoint protein Chk2. Furthermore, inhibition of ATM by ATM inhibitor abolished 2-ME-activated Chk2 and enhanced radio-cytotoxic effects. These results suggest that 2-ME enhancement of the sensitivity of glioma cell lines to radiotherapy is mediated by induction of G2/M cell cycle arrest and increased DNA damage via activation of ATM kinases.

ATR pathway is the primary pathway for activating G2/M checkpoint induction after re-replication

DNA replication is tightly controlled to ensure accurate chromosome duplication and segregation in each cell cycle. Inactivation of Geminin, an inhibitor of origin licensing, leads to re-replication in human tumor cells within the same cell cycle and triggers a G(2)/M checkpoint. We find that the primary pathway to signal that re-replication has been detected is the ATR kinase and the Rad9-Rad1-Hus1 (9-1-1) clamp complex together with Rad17-RFC clamp loader. ATM kinase and the Mre11-Rad50-Nbs1 complex do not appear to play significant roles in the checkpoint. Chk1 activation occurs at early stages, whereas Chk2 activation occurs much later. Overall we conclude that ATR/Chk1 pathway is activated at an early time point after the loss of Geminin and contributes to checkpoint arrest essential for the accumulation of re-replicated cells, whereas activation of the ATM/Chk2 pathway is a by-product of DNA re-replication at a later period.

Diabetic cardiomyopathy revisited

Diabetes mellitus increases the risk of heart failure independently of underlying coronary artery disease, and many believe that diabetes leads to cardiomyopathy. The underlying pathogenesis is partially understood. Several factors may contribute to the development of cardiac dysfunction in the absence of coronary artery disease in diabetes mellitus. This review discusses the latest findings in diabetic humans and in animal models and reviews emerging new mechanisms that may be involved in the development and progression of cardiac dysfunction in diabetes.

Antigen receptor diversification and chromosome translocations

Double-stranded DNA breaks (DSBs) can result in chromosomal abnormalities, including deletions, translocations and aneuploidy, which can promote neoplastic transformation. DSBs arise accidentally during DNA replication and can be induced by environmental factors such as ultraviolet light or ionizing radiation, and they are generated during antigen receptor-diversification reactions in lymphocytes. Cellular pathways that maintain genomic integrity use sophisticated mechanisms that recognize and repair all DSBs regardless of their origin. Such pathways, along with DNA-damage checkpoints, ensure that either the damage is properly repaired or cells with damaged DNA are eliminated. Here we review how impaired DNA-repair or DNA-damage checkpoints can lead to genetic instability and predispose lymphocytes undergoing diversification of antigen receptor genes to malignant transformation.

Preservation of ventricular performance at early stages of diabetic cardiomyopathy involves changes in myocyte size, number and intercellular coupling

In a rat model of diabetic cardiomyopathy, we tested whether specific changes in myocyte turnover and intercellular coupling contribute to preserving ventricular performance after a short period of hyperglycemia. In 41 rats with streptozotocin-induced diabetes and 24 control animals, cardiac electromechanical properties were assessed by telemetry ECG, epicardial potential mapping, and hemodynamic measurements to document normal ventricular function. Myocardial remodeling, expression of gap-junction proteins and myocyte regeneration were evaluated by tissue morphometry, immunohistochemistry and immunoblotting. Ventricular myocyte number and volume were also determined. In diabetic hearts, after 3 weeks of hyperglycemia, left ventricular mass was lowered by 23%, while left ventricular wall thickness and chamber volume were maintained, in the absence of fibrosis and myocyte hypertrophy. In the presence of a marked DNA oxidative damage, an increased rate of DNA replication and mitotic divisions associated with generation of new myocytes were detected. The number of cells expressing the receptor for Stem Cell Factor (c-kit) and their rate of proliferation were preserved in the left ventricle while the atrial storage of these primitive cells was severely reduced by diabetes-induced oxidative stress. Despite a down-regulation of Connexin43 and over-expression of both Connexin40 and Connexin45, the junctional proteins were normally distributed in diabetic ventricular myocardium,justifying the preserved tissue excitability and conduction velocity. In conclusion, before the appearance of the diabetic cardiomyopathic phenotype,myocardial cell proliferation associated with gap junction protein remodeling may contribute to prevent marked alterations of cardiac structure and electrophysiological properties, preserving ventricular performance.

Metallothionein rescues hypoxia-inducible factor-1 transcriptional activity in cardiomyocytes under diabetic conditions

Metallothionein (MT) is effective in the prevention of diabetic cardiomyopathy, and hypoxia-inducible factor-1 (HIF-1) is known to control vascular endothelial growth factor (VEGF) gene expression and regulate angiogenesis in diabetic hearts. We examined whether or not MT affects HIF-1 activity in the heart of diabetic mice and in the cardiac cells cultured in high glucose (HG) media. Diabetes was induced by streptozotocin in a cardiac-specific MT overexpressing transgenic mouse model. The primary cultures of neonatal cardiomyocytes and the embryonic rat cardiac H9c2 cell line were cultured in HG media. HIF-1 and VEGF were determined by immunofluorescent staining and enzyme-linked immunosorbent assay, respectively. The H9c2 cells were transfected with a hypoxia-responsive element-dependent reporter plasmid and the HIF-1 transcriptional activity was measured by luciferase reporter assay. MT overexpression increased HIF-1alpha in diabetic hearts. HG suppressed CoCl(2)-induced VEGF expression in primary cultures of neonatal cardiomyocytes and MT overexpression suppressed the inhibition. The addition of MT into the cultures of H9c2 cells relieved the HG suppression of hypoxia-induced luciferase activity. This study indicates that MT can rescue HIF-1 transcriptional activity in cardiomyocytes under diabetic conditions.

The effects of NBS1 knockdown by small interfering RNA on the ionizing radiation-induced apoptosis in human lymphoblastoid cells with different p53 status

Mutations of NBS1 are responsible for the human hereditary disease Nijmegen breakage syndrome (NBS), which is characterized by an extremely high cancer rate. In this study, we investigated the influence of NBS1 on ionizing radiation (IR) induced apoptosis. Using small interfering RNA (siRNA) transfection, we knocked down NBS1 protein in three closely related human lymphoblastoid cell lines differing in p53 status: TK6 with a wild-type p53, NH32 with a null mutation of p53, and WTK1 with a mutant p53. We found that up to 48h after 5Gy IR, all three lines showed an obvious induction of apoptosis regardless of the p53 status. The magnitude of apoptosis induction was TK6>NH32>WTK1. This suggested that although p53 is an important modulator of IR-induced apoptosis, other p53-independent apoptosis pathway also exists. Moreover, NBS1 knockdown led to reduction of IR-induced apoptosis in all three lines and both NBS1/ATM/p53/BAX and NBS1/ATM/CHK2/E2F1 apoptosis pathways were partially inactivated. Our results suggest that NBS1 plays an important role in IR-induced apoptosis via both p53-dependent and p53-independent mechanisms. The impaired apoptosis response to DNA damage in NBS1 deficient cells might be one of the important mechanisms of cancer predisposition in NBS patients.

Saccharomyces cerevisiae vacuole in zinc storage and intracellular zinc distribution

Previous studies of the yeast Saccharomyces cerevisiae indicated that the vacuole is a major site of zinc storage in the cell. However, these studies did not address the absolute level of zinc that was stored in the vacuole nor did they examine the abundances of stored zinc in other compartments of the cell. In this report, we describe an analysis of the cellular distribution of zinc by use of both an organellar fractionation method and an electron probe X-ray microanalysis. With these methods, we determined that zinc levels in the vacuole vary with zinc status and can rise to almost 100 mM zinc (i.e., 7 x 10(8) atoms of vacuolar zinc per cell). Moreover, this zinc can be mobilized effectively to supply the needs of as many as eight generations of progeny cells under zinc starvation conditions. While the Zrc1 and Cot1 zinc transporters are essential for zinc uptake into the vacuole under steady-state growth conditions, additional transporters help mediate zinc uptake into the vacuole during "zinc shock," when zinc-limited cells are resupplied with zinc. In addition, we found that other compartments of the cell do not provide significant stores of zinc. In particular, zinc accumulation in mitochondria is low and is homeostatically regulated independently of vacuolar zinc storage. Finally, we observed a strong correlation between zinc status and the levels of magnesium and phosphorus accumulated in cells. Our results implicate zinc as a major determinant of the ability of the cell to store these other important nutrients.

Heavy Metal Ions in Normal Physiology, Toxic Stress, and Cytoprotection

As a group, heavy metals include both those essential for normal biological functioning (e.g., Cu and Zn), and nonessential metals (e.g., Cd, Hg, and Pb). Both essential and nonessential metals can be present at concentrations that disturb normal biological functions, and which evoke cellular stress responses. The cellular targets for metal toxicity include tissues of the kidney, liver, heart, and the immune response and nervous systems. Intriguingly, manipulations of specific metals, their reservoirs, and the cellular stress response can have therapeutic effects on certain diseases. In this minireview, we will consider both the biological responses to stressful levels of heavy metal cations, and experimental and clinical manipulations of these cations as a means to improve human health parameters.

Untangling the relationships between DNA repair pathways by silencing more than 20 DNA repair genes in human stable clones

Much effort has long been devoted to unraveling the coordinated cellular response to genotoxic insults. In view of the difficulty of obtaining human biological samples of homogeneous origin, I have established a set of stable human clones where one DNA repair gene has been stably silenced by means of RNA interference. I used pEBVsiRNA plasmids that greatly enhance long-term gene silencing in human cells. My older clones reached >500 days in culture. Knock-down HeLa clones maintained a gene silencing phenotype for an extended period in culture, demonstrating that I was able to mimic cells from cancer-prone syndromes. I have silenced >20 genes acting as sensors/transducers (ATM, ATR, Rad50, NBS1, MRE11, PARG and KIN17), or of different DNA repair pathways. In HeLa cells, I have switched off the expression of genes involved in nucleotide excision repair (XPA, XPC, hHR23A, hHR23B, CSA and CSB), nonhomologous end-joining (DNA-PKcs, XRCC4 and Ligase IV), homologous recombination repair (Rad51 and Rad54), or base excision repair (Ogg1 and Ligase III). These cells displayed the expected DNA repair phenotype. We could envisage untangling the complex network between the different DNA repair pathways. In this study, no viral vehicles, with their attendant ethical and safety concerns, were used.

Mechanisms underlying the chronic pioglitazone treatment-induced improvement in the impaired endothelium-dependent relaxation seen in aortas from diabetic rats

The objectives of this study were to determine the effects of chronic treatment with pioglitazone, a peroxisome proliferator-activated receptor gamma agonist, on the impaired endothelium-dependent relaxation seen in aortas from established streptozotocin (STZ)-induced diabetic rats, and to identify some of the molecular mechanisms involved. Starting at 8 weeks of diabetes, pioglitazone (10 mg/kg) was administered to STZ-induced diabetic rats for 4 weeks. In untreated STZ rats (vs age-matched control rats): (1) ACh-induced relaxation, cGMP accumulation, phosphorylation of the cGMP-dependent protein kinase substrate vasodilator-stimulated phosphoprotein at Ser-239 [an established biochemical end-point of nitric oxide (NO)/cGMP signaling], and Cu/Zn-superoxide dismutase (SOD) expression and SOD activity were all reduced; (2) aortic superoxide generation, nitrotyrosine expression, and NAD(P)H oxidase activity were increased; (3) plasma endothelin-1 (ET-1) and aortic c-Jun (AP-1 component) protein expressions were increased. Pioglitazone treatment markedly corrected the above abnormalities. Collectively, these results suggest that pioglitazone treatment improves endothelium-dependent relaxation by reducing oxidative stress via increased SOD activity, decreased NAD(P)H oxidase activity, and a decreased ET-1 level, and that this decreased ET-1 level may be attributable to an inhibition of the AP-1 signaling pathway.

Ku70/80 Modulates ATM and ATR Signaling Pathways in Response to DNA Double Strand Breaks

Double strand break (DSB) recognition is the first step in the DSB damage response and involves activation of ataxia telangiectasia-mutated (ATM) and phosphorylation of targets such as p53 to trigger cell cycle arrest, DNA repair, or apoptosis. It was reported that activation of ATM- and Rad3-related (ATR) kinase by DSBs also occurs in an ATM-dependent manner. On the other hand, Ku70/80 is known to participate at a later time point in the DSB response, recruiting DNA-PKcs to facilitate non-homologous end joining. Because Ku70/80 has a high affinity for broken DNA ends and is abundant in nuclei, we examined their possible involvement in other aspects of the DSB damage response, particularly in modulating the activity of ATM and other phosphatidylinositol (PI) 3-related kinases during DSB recognition. We thus analyzed p53(Ser18) phosphorylation in irradiated Ku-deficient cells and observed persistent phosphorylation in these cells relative to wild type cells. ATM or ATR inhibition revealed that this phosphorylation is mainly mediated by ATM-dependent ATR activity at 2 h post-ionizing radiation in wild type cells, whereas in Ku-deficient cells, this occurs mainly through direct ATM activity, with a secondary contribution from ATR via a novel ATM-independent mechanism. Using ATM/Ku70 double-null cell lines, which we generated, we confirmed that ATM-independent ATR activity contributed to persistent phosphorylation of p53(Ser18) in Ku-deficient cells at 12 h post-ionizing radiation. In summary, we discovered a novel role for Ku70/80 in modulating ATM-dependent ATR activation during DSB damage response and demonstrated that these proteins confer a protective effect against ATM-independent ATR activation at later stages of the DSB damage response.

Subcellular changes of essential metal shown by in-air micro-PIXE in oral cadmium-exposed mice

To clarify the relation of essential metals to cadmium (Cd) toxicity, we evaluated metallothionein expression and analyzed the subcellular distribution of essential metals using in-air micro-Particle-Induced X-ray Emission (PIXE). Four mice were dosed orally with 100 mg/L of Cd in drinking water for 1.5 or 2 years. Frozen samples of organs were used for micro-PIXE analysis and formalin-fixed samples were used for metallothionein staining. Immunohistochemically, metallothionein induction by 1.5y-Cd exposure was higher in the renal cortex than in the liver. Metallothionein expression was reduced after 2y-Cd administration compared to the 1.5y-Cd-exposed mice. Cd-induced tissue damage became marked in the 2y-Cd-exposed mice compared to the 1.5y-Cd-exposed mice, in which nephrotoxicity was more prominent than hepatotoxicity. Cd yield was higher in the renal cortex of the 2y-Cd-exposed mouse than in that of the 1.5y-Cd-exposed mouse, whereas no such increasing tendency was found in the liver. Compared to the control, the Cd-exposed mice markedly accumulated zinc in the liver and renal cortex. In the Cd-exposed mice, iron was mildly accumulated in the renal cortex and was slightly deprived in the liver. Elemental maps showed that a large amount of Cd was spatially combined with zinc in the 1.5y-Cd mouse. Free Cd became abundant in the 2y-Cd-exposed mouse. In addition, a small amount of Cd was colocalized with iron. The data suggest that zinc may contribute to protect against oral-administrated Cd toxicity, and impaired induction of MT may participate in hepato-nephrotoxicity of the 2y-Cd-exposed mouse.

Redox silencing of copper in metal-linked neurodegenerative disorders: reaction of Zn7metallothionein-3 with Cu2+ ions

Dysregulation of copper and zinc homeostasis in the brain plays a critical role in Alzheimer disease (AD). Copper binding to amyloid-beta peptide (Abeta) is linked with the neurotoxicity of Abeta and free radical damage. Metallothionein-3 (MT-3) is a small cysteine- and metal-rich protein expressed in the brain and found down-regulated in AD. This protein occurs intra- and extracellularly, and it plays an important role in the metabolism of zinc and copper. In cell cultures Zn7MT-3, by an unknown mechanism, protects neurons from the toxicity of Abeta. We have, therefore, used a range of complementary spectroscopic and biochemical methods to characterize the interaction of Zn7MT-3 with free Cu2+ ions. We show that Zn7MT-3 scavenges free Cu2+ ions through their reduction to Cu+ and binding to the protein. In this reaction thiolate ligands are oxidized to disulfides concomitant with Zn2+ release. The binding of the first four Cu2+ is cooperative forming a Cu(I)4-thiolate cluster in the N-terminal domain of Cu4,Zn4MT-3 together with two disulfides bonds. The Cu4-thiolate cluster exhibits an unusual stability toward air oxygen. The results of UV-visible, CD, and Cu(I) phosphorescence at 77 K suggest the existence of metal-metal interactions in this cluster. We have demonstrated that Zn7MT-3 in the presence of ascorbate completely quenches the copper-catalyzed hydroxyl radical (OH.) production. Thus, zinc-thiolate clusters in Zn7MT-3 can efficiently silence the redox-active free Cu2+ ions. The biological implication of our studies as to the protective role of Zn7MT-3 from the Cu2+ toxicity in AD and other neurodegenerative disorders is discussed.

Mouse models for studies of cardiovascular complications of type 1 diabetes

Mouse models represent a powerful tool for investigating the underlying mechanisms of disease. Type 1 diabetes results in a markedly increased risk of cardiovascular disease. The cardiovascular complications are manifested primarily as ischemic heart disease caused by accelerated atherosclerosis, but also as cardiomyopathy, defined as ventricular dysfunction in the absence of clear ischemic heart disease. Several mouse models are now available to study atherosclerosis and cardiomyopathy associated with type 1 diabetes. For studies of diabetes-accelerated atherosclerosis, these models include low-density lipoprotein (LDL) receptor-deficient and apolipoprotein E-deficient mice in which diabetes is induced by streptozotocin or viral infection. In these mouse models, type 1 diabetes can be induced without marked changes in plasma lipid levels, thereby mimicking the accelerated atherosclerosis seen in patients with type 1 diabetes. However, mouse models that exhibit thrombotic events and myocardial infarctions as a result of diabetes still need to be developed. Conversely, cardiomyopathy associated with diabetes has now been extensively evaluated in streptozotocin-treated C57BL/6 mice, and in transgenic mice expressing calmodulin under a beta-cell-specific promoter. These mouse models have given significant insight into the molecular mechanisms causing cardiomyopathy, and indicate that increased oxidative stress contributes to diabetes-associated cardiomyopathy. In this review, we will discuss the available mouse models for studies of cardiovascular complications of type 1 diabetes, the potential mechanisms underlying these complications, and the need for new and improved mouse models.

Metallothionein protects against doxorubicin-induced cardiomyopathy through inhibition of superoxide generation and related nitrosative impairment

Metallothionein (MT) has been shown to be an effective protector against DOX-induced cardiomyopathy, however the involved precise mechanisms are still unknown. The present study was undertaken to clarify whether the inhibition of superoxide generation and related nitrosative damage were involved in the metallothionein attenuation of DOX-induced cardiac injury. MT-I/II null (MT-/-) mice and corresponding wild-type mice (MT+/+) were pretreated with either saline or zinc (300 micromol/kg, s.c., once a day for 2 days) prior to a single dose of DOX (15 mg/kg, i.p.) or equal volume of saline. Animals were sacrificed on the 4th day after DOX administration and samples were collected for further analyses. DOX caused remarkable cardiac damage in both MT+/+ and MT-/- mice as demonstrated by biochemical and histopathological alterations. Zinc pretreatment significantly increased the cardiac MT levels and therefore inhibited the cardiac toxic effects of DOX only in MT+/+ mice, but not in MT-/- mice. Furthermore, elevated formation of superoxide and peroxynitrite were obviously observed after DOX treatment, while these elevation were prevented by MT induction by zinc in MT+/+ mice, but not in MT-/- mice. These findings suggest that metallothionein induction by zinc exhibits protective effects on the cardiac toxicology of DOX, which might be mediated through the prevention of superoxide generation and related nitrosative impairment.

Distribution of trace metal concentrations in paired cancerous and non-cancerous human stomach tissues

AIM

To assess whether trace metal concentrations (which influence metabolism as both essential and non-essential elements) are increased or decreased in cancerous tissues and to understand the precise role of these metals in carcinogenesis.

METHODS

Concentrations of trace metals including Cd, Ni, Cu, Zn, Fe, Mg and Ca in both cancerous and non-cancerous stomach tissue samples were determined by atomic absorption spectrometry (AAS). Tissue samples were digested using microwave energy. Slotted tube atom trap was used to improve the sensitivity of copper and cadmium in flame AAS determinations.

RESULTS

From the obtained data in this study, the concentrations of nickel, copper and iron in the cancerous human stomach were found to be significantly higher than those in the non-cancerous tissues, by using t-test for the paired samples. Furthermore, the average calcium concentrations in the cancerous stomach tissue samples were found to be significantly lower than those in the non-cancerous stomach tissue samples by using t-test. Exceedingly high Zn concentrations (207-826 mg/kg) were found in two paired stomach tissue samples from both cancerous and non-cancerous parts.

CONCLUSION

In contrast to the literature data for Cu and Fe, the concentrations of copper, iron and nickel in cancerous tissue samples are higher than those in the non-cancerous samples. Furthermore, the Ca levels are lower in cancerous tissue samples than in non-cancerous tissue samples.

Neuroprotective effect of MnTMPyP, a superoxide dismutase/catalase mimetic in global cerebral ischemia is mediated through reduction of oxidative stress and DNA fragmentation

Excessive generation of free radicals and decreased levels of the antioxidant enzymes such as superoxide dismutase (SOD) and catalase have been observed after brain ischemic reperfusion injury. In the present study, we have investigated the neuroprotective potential of MnTMPyP (Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin pentachloride), a SOD/Catalase mimetic in bilateral carotid artery occlusion model of global cerebral ischemia in Mongolian gerbils. Five minutes of bilateral carotid artery occlusion produced global cerebral ischemia, which was evident from the neurological deficits, spontaneous motor activity and the decrease in the number of viable hippocampal CA1 neurons. Global ischemia was also associated with increased levels of malondialdehyde, decreased levels of SOD and catalase, and increased TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) positive cells, indicating oxidative stress and DNA fragmentation. Administration of a single dose of MnTMPyP, 1 mg/kg i.p. (30 min before occlusion), produced no significant neuroprotection; however, 3 mg/kg i.p. (30 min before to occlusion) produced significant reduction in neurological score, spontaneous motor activity and CA1 pyramidal neuronal damage. MnTMPyP also attenuated the increased levels of malondialdehyde and improved the levels of SOD and catalase, and inhibited DNA fragmentation in the ischemic animals. Multiple administration of MnTMPyP, 3 mg/kg i.p. (three times: 30 min before, 1 h and 3 h after occlusion), produced better neuroprotection as compared to single dose administration. This study demonstrates that the neuroprotective effect of MnTMPyP in global ischemia is mediated through reduction in oxidative stress and DNA fragmentation.

Different membrane modifications revealed by atomic force/lateral force microscopy after doping of human pancreatic cells with Cd, Zn, or Pb

The interaction of the cytotoxic metals cadmium, zinc, and lead with pancreatic cells was studied by atomic force/lateral Force microscopy (AFM/LFM), an approach that provides both topographic (with nanometer scale lateral resolution) and chemical information on the membrane. Different morphological modifications of the overall cell shape and roughness took place as consequence of 100 muM metal-dependent treatment. Furthermore, after exposure to Cd(Cl(2)) and Zn(Cl(2)), but not Pb(Cl(2)), the LFM images revealed several areas of the cell's surface showing lateral friction contrasts that have been interpreted as marker of different alterations of the cell physiology induced by the metal loading. Thus, the coupling of LFM detection to topographic AFM characterization allows to distinguish, through a nondestructive and surface characterising approach, between different metal-induced cytotoxic effects on cells. In this framework, the role of the LFM as an important tool to discriminate between different alteration of a biological system has to be highlighted.

Diabetes, metallothionein, and zinc interactions: a review

Epidemiological evidence, associating diabetes with zinc (Zn) deficiencies, has resulted in numerous research studies describing the effects of Zn and associated metallothionein (MT), on reducing diabetic complications associated with oxidative stress. MT has been found to have a profound effect on the reduction of oxidative stress induced by the diabetic condition. Over expression of MT in various metabolic organs has also been shown to reduce hyperglycaemia-induced oxidative stress, organ specific diabetic complications, and DNA damage in diabetic experimental animals, which have been further substantiated by the results from MT-knockout mice. Additionally, supplementation with Zn has been shown to induce in vivo MT synthesis in experimental animals and to reduce diabetes related complications in both humans and animal models. Although the results are promising, some caution regarding this topic is however necessary, due to the fact that the majority of the studies done have been animal based. Hence more human intervention trials are needed regarding the positive effects of MT and Zn before firm conclusions can be made regarding their use in the treatment of diabetes.

Lovastatin protects mesenchymal stem cells against hypoxia- and serum deprivation-induced apoptosis by activation of PI3K/Akt and ERK1/2

Cell therapy with bone marrow-derived mesenchymal stem cells (MSCs) has been shown to have great promises in cardiac repair after myocardial infarction. However, poor viability of transplanted MSCs in the infracted heart has limited the therapeutic efficacy. Our previous studies have shown in vitro that rat MSCs undergo caspase-dependent apoptosis in response to hypoxia and serum deprivation (Hypoxia/SD). Recent findings have implicated statins, an established class of cholesterol-lowering drugs, enhance the survival of cells under various conditions. In this study, we investigated the effect of lovastatin on rat MSCs apoptosis induced by Hypoxia/SD, focusing in particular on regulation of mitochondrial apoptotic pathway and the survival signaling pathways. We demonstrated that lovastatin (0.01-1 microM) remarkably prevented MSCs from Hypoxia/SD-induced apoptosis through inhibition of the mitochondrial apoptotic pathway, leading to attenuation of caspase-3 activation. The loss of mitochondrial membrane potential and cytochrome-c release from mitochondria to cytosol were significantly inhibited by lovastatin. Furthermore, the antiapoptotic effect of lovastatin on mitochondrial apoptotic pathway was effectively abrogated by both PI3K inhibitor, LY294002 and ERK1/2 inhibitor, U0126. The phosphorylations of Akt/GSK3 beta and ERK1/2 stimulated by lovastatin were detected. The activation of ERK1/2 was inhibited by a PI3K inhibitor, LY294002, but U0126, a ERK1/2 inhibitor did not inhibit phosphorylation of Akt and GSK3 beta. These data demonstrate that lovastatin protects MSCs from Hypoxia/SD-induced apoptosis via PI3K/Akt and MEK/ERK1/2 pathways, suggesting that it may prove a useful therapeutic adjunct for transplanting MSCs into damaged heart after myocardial infarction.

Cardioprotective effects of cerium oxide nanoparticles in a transgenic murine model of cardiomyopathy

OBJECTIVE

Cerium oxide (CeO2) nanoparticles have been shown to protect cells in culture from lethal stress, but no protection in vivo has been reported. Cardiac-specific expression of monocyte chemoattractant protein (MCP)-1 in mice causes ischemic cardiomyopathy associated with activation of endoplasmic reticulum (ER) stress. The aim of this study was to assess the effects of CeO2 nanoparticles on cardiac function and remodeling as well as ER stress response in this murine model of cardiomyopathy.

METHODS

MCP-1 transgenic mice (MCP mice) and wild-type controls were administered intravenously 15 nmol of CeO2 nanoparticles or vehicle only twice a week for 2 weeks. Cardiac function, myocardial histology, nitrotyrosine formation, expression of cytokines, and ER stress-associated genes were evaluated.

RESULTS

Treatment with CeO2 nanoparticles markedly inhibited progressive left ventricular dysfunction and dilatation in MCP mice and caused a significant decrease in serum levels of MCP-1, C-reactive protein, and total nitrated proteins. The infiltration of monocytes/macrophages, accumulation of 3-nitrotyrosine, apoptotic cell death, and expression of proinflammatory cytokines, tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and IL-6 in the myocardium were markedly inhibited by CeO2 nanoparticles. Expression of the key ER stress-associated genes, including glucose-regulated protein 78 (Grp78), protein disulfide isomerase (PDI), and heat shock proteins (HSP25, HSP40, HSP70), were also suppressed by CeO2 nanoparticles.

CONCLUSIONS

CeO2 nanoparticles protect against the progression of cardiac dysfunction and remodeling by attenuation of myocardial oxidative stress, ER stress, and inflammatory processes probably through their autoregenerative antioxidant properties.

Enalapril improves impairment of SERCA-derived relaxation and enhancement of tyrosine nitration in diabetic rat aorta

We investigated the involvement of angiotensin II and vascular smooth muscle sarco/endoplasmic reticulum Ca(2+)-ATPase (SERCA) function in the impaired NO-induced relaxation seen in established streptozotocin-induced diabetes. Plasma angiotensin II levels, which were elevated in untreated diabetic rats (vs age-matched controls), were improved by treatment with the angiotensin-converting enzyme inhibitor enalapril. Systolic blood pressure was significantly decreased in chronic enalapril-treated diabetics (vs the other two groups). Intact aortae from diabetic rats and chronic angiotensin II-infused control rats, but not those from diabetic rats treated with enalapril, showed impaired endothelium-dependent relaxations to acetylcholine (vs controls). The relaxation induced by Angeli's Salt (a NO donor) was significantly impaired in endothelium-denuded aortae from diabetic rats (vs controls) but it was normalised by enalapril treatment. After preincubation with the irreversible SERCA inhibitor, thapsigargin, the relaxation induced by Angeli's Salt was significantly impaired in endothelium-denuded aortae from the controls, but not from the diabetics, and there was no significant difference between the thapsigargin-treated groups. Nitrotyrosine, an indirect marker of peroxynitrite, was markedly increased in aortic smooth muscle from diabetic rats, while chronic enalapril administration reduced this increase. These results suggest that in streptozotocin-induced diabetic rats, excessive angiotensin II production may lead to the generation of peroxynitrite and that this may in turn trigger a dysfunction of vascular smooth muscle SERCA. Enalapril improved the diabetes-related impairments.

Cadmium distribution and metallothionein expression in lizard tissues following acute and chronic cadmium intoxication

The present report is an attempt to investigate the influence of intraperitoneal and dietary cadmium exposure on the distribution of cadmium accumulation and induction of metallothionein gene expression in different tissues of the lizard Podarcis sicula. Cadmium accumulation in liver, kidney, ovary, brain and intestine was measured by atomic absorption spectrometry. Metallothionein gene induction was determined by dot blot analyses on the total RNA extracted from the same organs. Our data indicate that cadmium exposure results in significant cadmium uptake, but the patterns of this uptake varies with organ and exposure route. After a single intraperitoneal treatment, concentrations of cadmium and metallothionein transcript are positively correlated in kidney, liver and ovary. Following a dietary cadmium treatment, a positive correlation between the increase of metallothionein mRNA and cadmium accumulation is found in intestine, ovary and kidney, while no correlation is present in liver and brain.

Metallothionein redox cycle and function

The biologic function of metallothionein (MT) has been a perplexing topic ever since the discovery of this protein. Many studies have suggested that MT plays a role in the homeostasis of essential metals such as zinc and copper, detoxification of toxic metals such as cadmium, and protection against oxidative stress. However, mechanistic insights into the actions of MT have not been adequately achieved. MT contains high levels of sulfur. The mutual affinity of sulfur and transition metals makes the binding of these metals to MT thermodynamically stable. Under physiologic conditions, zinc-MT is the predominant form of the metal-binding protein. The recognition of the redox regulation of zinc release from or binding to MT provides an alternate perspective on biologic function of MT. Oxidation of the thiolate cluster by a number of mild cellular oxidants causes zinc release and formation of MT-disulfide (or thionin if all metals are released from MT, but this is unlikely to occur in vivo), which have been demonstrated in vivo. Therefore, the thermodynamic stability of zinc binding makes MT an ideal zinc reservoir in vivo, and the redox regulation of zinc mobilization enables MT function in zinc homeostasis. MT-disulfide can be reduced by glutathione in the presence of selenium catalyst, restoring the capacity of the protein to bind zinc. This MT redox cycle may play a crucial role in MT biologic function. It may link to the homeostasis of essential metals, detoxification of toxic metals and protection against oxidative stress.

Attenuation by metallothionein of early cardiac cell death via suppression of mitochondrial oxidative stress results in a prevention of diabetic cardiomyopathy

OBJECTIVES

We aimed to test whether attenuation of early-phase cardiac cell death can prevent diabetic cardiomyopathy.

BACKGROUND

Our previous study showed that cardiac apoptosis as a major early cellular response to diabetes is induced by hyperglycemia-derived oxidative stress that activates a mitochondrial cytochrome c-mediated caspase-3 activation pathway. Metallothionein (MT) as a potent antioxidant prevents the development of diabetic cardiomyopathy.

METHODS

Diabetes was induced by a single dose of streptozotocin (STZ) (150 mg/kg) in cardiac-specific, metallothionein-overexpressing transgenic (MT-TG) mice and wild-type (WT) controls. On days 7, 14, and 21 after STZ treatment, cardiac apoptosis was examined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay and caspase-3 activation. Cardiomyopathy was evaluated by cardiac ultrastructure and fibrosis in the diabetic mice 6 months after STZ treatment.

RESULTS

A significant reduction in diabetes-induced increases in TUNEL-positive cells, caspase-3 activation, and cytochrome c release from mitochondria was observed in the MT-TG mice as compared to WT mice. Cardiac protein nitration (3-nitrotyrosine [3-NT]) and lipid peroxidation were significantly increased, and there was an increase in mitochondrial oxidized glutathione and a decrease in mitochondrial reduced glutathione in the WT, but not in the MT-TG, diabetic mice. Double staining for cardiomyocytes with alpha sarcomeric actin and caspase-3 or 3-NT confirmed the cardiomyocyte-specific effects. A significant prevention of diabetic cardiomyopathy and enhanced animal survival were observed in the MT-TG diabetic mice as compared to WT diabetic mice.

CONCLUSIONS

These results suggest that attenuation of early-phase cardiac cell death by MT results in a significant prevention of the development of diabetic cardiomyopathy. This process is mediated by MT suppression of mitochondrial oxidative stress.

Suppression of nitrative damage by metallothionein in diabetic heart contributes to the prevention of cardiomyopathy

Diabetic cardiomyopathy has become a major contributor to the increased mortality of diabetic patients. Although the development and progression of diabetic cardiomyopathy are considered to be associated with diabetes-derived oxidative stress, the precise mechanisms for and effectively preventive approaches to diabetic cardiomyopathy remain to be explored. Recent studies showed that reactive oxygen or nitrogen species (ROS/RNS) not only play a critical role in the initiation of diabetic cardiomyopathy, but also play an important role in physiological signaling. Therefore, this review will first discuss the dual roles of ROS/RNS in the physiological signaling and pathogenic remodeling leading to cardiomyopathy under diabetic conditions. The significant prevention of diabetic cardiomyopathy by metallothionein (MT) as a potent and nonspecific antioxidant will be also summarized. It is clearly revealed that although dual roles of peroxynitrite-nitrated proteins have been indicated under both physiological and pathogenic conditions, suppression of nitrative damage by MT in the diabetic heart is the major mechanism responsible for its prevention of diabetic cardiomyopathy. Finally the potential for clinical enhancement of the cardiac MT expression to prevent or delay the occurrence of cardiomyopathy in diabetic patients will also be addressed.