Zinc- or cadmium-pre-induced metallothionein protects human central nervous system cells and astrocytes from radiation-induced apoptosis

We have shown the protection of human central nervous system (CNS) cultures by zinc (Zn) or cadmium (Cd)-pre-induced metallothionein (MT) synthesis from radiation-induced cytotoxicity (lactate dehydrogenase (LDH) release and neuronal dendritic injury). The present study is to further define the types of cell death induced by different dose levels of radiation and investigate the effect of MT induction (by Zn or Cd) on radiation-induced apoptosis in primary human CNS and astrocyte cultures. Apoptosis was detected by fragmented DNA electrophoresis, TUNEL technique, and propidium iodide staining. Expression of MT protein was examined by immunofluorescent staining. Results showed that exposure of primary human CNS cultures to 15 and 30 Gy gamma-radiation predominantly induced apoptotic cell death, while exposure to 60 Gy gamma-radiation predominantly induced necrotic cell death. Normal primary human CNS cultures showed weak MT staining, while primary human CNS cultures exposed to Zn or Cd showed intense MT staining. The induced apoptotic cell death by exposure to 30 Gy gamma-radiation increased to a maximum level at 12 and 24 h, and was reduced significantly by Zn or Cd pre-induced MT. Using primary human astrocytes, the induction of MT protein by Zn or Cd was further confirmed. The enhanced MT expression also afforded a significant protection from 30 Gy gamma-ray-induced apoptosis in the primary human astrocytes. These results suggest that MT protected human CNS cells from apoptosis following ionizing radiation, probably through its antioxidant property.

Fluvastatin prevents nephropathy likely through suppression of connective tissue growth factor-mediated extracellular matrix accumulation

Diabetic nephropathy is related to glomerular extracellular matrix (ECM) accumulation that leads to glomerulosclerosis. Fluvastatin as a lipid-lowering medicine significantly prevents diabetic nephropathy, probably not only through its lipid-lowering action, but also mainly through its direct suppression of glomerular ECM accumulation. To test this hypothesis, in the present study, a five-sixths nephrectomized (5/6Nx) rat model to induce a renal ECM accumulation without coexistence of hyperlipidemia was used to investigate the effect of fluvastatin on renal function, glomerular ECM accumulation and expression of connective tissue growth factor (CTGF). 5/6Nx induced a significant nephropathy in rats at 13 weeks, indicated by renal dysfunction including increases in blood urine nitrogen, creatinine and urinary protein excretion, and renal histopathological changes. Administration of fluvastatin significantly prevented the renal dysfunction and histological abnormalities in the 5/6Nx rats. Furthermore, both significant suppression of matrix metalloproteinases (MMPs) activity such as MMP-2 and significant activation of tissue inhibitors of MMP (TIMPs) such as TIMP-2 observed in the 5/6Nx rats were almost completely prevented by fluvastatin, resulting in a significant prevention of glomerular ECM accumulation. For upstream mediator of ECM accumulation, 5/6Nx significantly up-regulated CTGF mRNA expression, but fluvastatin treatment prevented CTGF up-regulation. These results suggest that fluvastatin, as one of well-known lipid-lowering agents, plays an important role in the prevention of nephropathy, likely through suppression of CTGF-mediated ECM accumulation. Therefore, fluvastatin may be a potential candidate for developing a pharmaceutical approach to the prevention of diabetic nephropathy due to its both lipid-lowering and direct anti-renal ECM accumulation actions.

Trace elements in human physiology and pathology: zinc and metallothioneins

Zinc is one of the most abundant nutritionally essential elements in the human body. It is found in all body tissues with 85% of the whole body zinc in muscle and bone, 11% in the skin and the liver and the remaining in all the other tissues. In multicellular organisms, virtually all zinc is intracellular, 30-40% is located in the nucleus, 50% in the cytoplasm, organelles and specialized vesicles (for digestive enzymes or hormone storage) and the remainder in the cell membrane. Zinc intake ranges from 107 to 231 micromol/d depending on the source, and human zinc requirement is estimated at 15 mg/d. Zinc has been shown to be essential to the structure and function of a large number of macromolecules and for over 300 enzymic reactions. It has both catalytic and structural roles in enzymes, while in zinc finger motifs, it provides a scaffold that organizes protein sub-domains for the interaction with either DNA or other proteins. It is critical for the function of a number of metalloproteins, inducing members of oxido-reductase, hydrolase ligase, lyase family and has co-activating functions with copper in superoxide dismutase or phospholipase C. The zinc ion (Zn(++)) does not participate in redox reactions, which makes it a stable ion in a biological medium whose potential is in constant flux. Zinc ions are hydrophilic and do not cross cell membranes by passive diffusion. In general, transport has been described as having both saturable and non-saturable components, depending on the Zn(II) concentrations involved. Zinc ions exist primarily in the form of complexes with proteins and nucleic acids and participate in all aspects of intermediary metabolism, transmission and regulation of the expression of genetic information, storage, synthesis and action of peptide hormones and structural maintenance of chromatin and biomembranes.

Adaptive Response in Embryogenesis: IV. Protective and Detrimental Bystander Effects Induced by X Radiation in Cultured Limb Bud Cells of Fetal Mice

The radioadaptive response and the bystander effect represent important phenomena in radiobiology that have an impact on novel biological response mechanisms and risk estimates. Micromass cultures of limb bud cells provide an in vitro cellular maturation system in which the progression of cell proliferation and differentiation parallels that in vivo. This paper presents for the first time evidence for the correlation and interaction in a micromass culture system between the radioadaptive response and the bystander effect. A radioadaptive response was induced in limb bud cells of embryonic day 11 ICR mice. Conditioning irradiation of the embryonic day 11 cells with 0.3 Gy resulted in a significant protective effect against the occurrence of apoptosis, inhibition of cell proliferation, and differentiation induced by a challenging dose of 5 Gy given the next day. Both protective and detrimental bystander effects were observed; namely, irradiating 50% of the embryonic day 11 cells with 0.3 Gy led to a successful induction of the protective effect, and irradiating 70% of the embryonic day 12 cells with 5 Gy produced a detrimental effect comparable to that seen when all the cells were irradiated. Further, the bystander effect was markedly decreased by pretreatment of the cells with an inhibitor to block the gap junction-mediated intercellular communication. These results indicate that the bystander effect plays an important role in both the induction of a protective effect by the conditioning dose and the detrimental effect of the challenge irradiation. Gap junction-mediated intercellular communication was suggested to be involved in the induction of the bystander effect.

Metallothionein Protects Islets from Hypoxia and Extends Islet Graft Survival by Scavenging Most Kinds of Reactive Oxygen Species

Islet transplantation is a promising therapy for Type 1 diabetes, but many attempts have failed due to early graft hypoxia or immune rejection, which generate reactive oxygen species (ROS). In the current study, we determined that transgenic overexpression of the antioxidant metallothionein (MT) in pancreatic beta cells provided broad resistance to oxidative stress by scavenging most kinds of ROS including H2O2, peroxynitrite radical released from streptozotocin, 3-morpholinosydnonimine (SIN-1), and superoxide radical produced by xanthine/xanthine oxidase. MT also reduced nitric oxide-induced beta cell death. A direct test of hypoxia/reperfusion sensitivity was made by exposing FVB and MT islets to hypoxia (1% O2). MT markedly reduced ROS production and improved islet cell survival. Because MT protected beta cells from a broad spectrum of ROS and from hypoxia, we considered it to be an ideal candidate for improving islet transplantation. We first tested syngeneic transplantation by implanting islets under the kidney capsule of the same strain, FVB mice, thereby eliminating the immune rejection component. Under these conditions, MT islets maintained much greater insulin content than control islets. Allotransplantation was then tested. MT transgenic and normal FVB islets were implanted under the kidney capsule of BALB/c mice that were previously treated with streptozotocin to induce diabetes. We found that MT islets extended the duration of euglycemia 2-fold longer than nontransgenic islets. The benefit of MT was due to protection from ROS since nitrotyrosine staining, an indicator of free radical damage, was much lower in MT grafts than in FVB grafts. The time course of protection suggested that the major mode of MT action may have been protection from hypoxia or hypoxia/reperfusion. These data demonstrate that treatment with a broad spectrum antioxidant protects islets from ROS damage such as that produced during the early phase of islet transplantation.

Metallothionein prevents neurodegeneration and central nervous system cell death after treatment with gliotoxin 6-aminonicotinamide

Transgenic expression of interleukin-6 (IL-6) in the CNS under the control of the glial fibrillary acidic protein (GFAP) gene promoter (GFAP-IL6 mice) induces significant inflammation and neurodegeneration but also affords neuroprotection against acute traumatic brain injury. This neuroprotection is likely mediated by the IL-6-induced protective factors metallothioneins-I and -II (MT-I+II). Here we evaluate the neuroprotective roles of IL-6 vs. MT-I+II during 6-aminonicotinamide (6-AN)-induced neurotoxicity, by using GFAP-IL6 mice and transgenic mice overexpressing MT-I (TgMT) as well as GFAP-IL6 mice crossed with TgMT mice (GFAP-IL6 x TgMT). 6-AN caused acute damage of brainstem gray matter areas identified by necrosis of astrocytes, followed by inflammatory responses. After 6-AN-induced toxicity, secondary damage was observed, consisting of oxidative stress, neurodegeneration, and apoptotic cell death. We hereby show that the primary injury caused by 6-AN was comparable in wild-type and GFAP-IL6 mice, but MT-I overexpression could significantly protect the brain tissue. As expected, GFAP-IL6 mice showed increased CNS inflammation with more gliosis, macrophages, and lymphocytes, including increased cytokine expression, relative to the other mice. However, GFAP-IL6 mice showed reduced oxidative stress (judged from nitrotyrosine, malondialdehyde, and 8-oxoguanine stainings), neurodegeneration (accumulation of neurofibrillary tangles), and apoptosis (determined from TUNEL and caspase-3). MT-I+II expression was significantly higher in GFAP-IL6 mice than in wild types, which may contribute to the IL-6-induced neuroprotection. In support of this, overexpression of MT-I in GFAP-IL6 x TgMT as well as TgMT mice protected the brainstem tissue significantly from 6-AN-induced toxicity and secondary brain tissue damage. Overall, the results demonstrate that brain MT-I+II proteins are fundamental neuroprotective factors, which in the future may become therapeutic agents.

Cytogenetic dose-response and adaptive response in cells of ungulate species exposed to ionizing radiation

In the studies reported here, the micronucleus assay, a common cytogenetic technique, was used to examine the dose-responses in fibroblasts from three ungulate species (white-tailed deer, woodland caribou, and Indian muntjac) exposed to high doses of ionizing radiation (1-4 Gy of (60)Co gamma radiation). This assay was also used to examine the effects of exposure to low doses (1-100 mGy) typical of what these species experience in a year from natural and anthropogenic environmental sources. An adaptive response, defined as the induction of resistance to a stressor by a prior exposure to a small "adapting" stress, was observed after exposure to low doses. This work indicates that very small doses are protective for the endpoint examined. The same level of protection was seen at all adapting doses, including 1 radiation track per cell, the lowest possible cellular dose. These results are consistent with other studies in a wide variety of organisms that demonstrate a protective effect of low doses at both cellular and whole-organism levels. This implies that environmental regulations predicated on the idea that even the smallest dose of radiation carries a quantifiable risk of direct adverse consequences to the exposed organism require further examination. Cytogenetic assays provide affordable and feasible biological effects-based alternatives that are more biologically relevant than traditional contaminant concentration-based radioecological risk assessment.

Thymus cell-cell interactions

The recent advances in molecular biology and genetics, as well as the progress of in vitro techniques, have provided a more coherent image of the thymic function on the molecular level. But they have shifted the attention away from studies on the cellular level, which are necessary to clarify the biological roles of different cell types of the thymic microenvironment. The structure and function of the normal thymus depend on mutual interactions between thymocytes and nonlymphocyte cells. In this review a detailed description of morphological and phenotypic features of both maturing thymocytes and nonlymphocyte cells is given. The recent genetic and biochemical data are presented in conjunction with cytological results to enlighten the thymus cell-cell interactions during thymopoiesis and organization of thymic microstructure. Special emphasis is put on the experimental approaches, which may be used to study the interactions between thymocytes and nonlymphocyte cells in vivo.

Modulation of zinc toxicity by tissue plasminogen activator

The tissue plasminogen activator (tPA)-plasmin proteolytic system mediates excitotoxin-induced neurodegeneration in vivo and in cell culture. tPA also confers neuroprotection from zinc toxicity in cell culture through a proteolysis-independent mechanism. This raises two questions: what is this non-enzymatic mechanism, and why tPA does not synergize with zinc to promote neuronal cell death? We show here that zinc binds to tPA and inhibits its activity in a dose-dependent fashion, thus terminating its protease-dependent neurotoxic capacity. We extend the previously reported culture findings to demonstrate that elevated zinc is neurotoxic in vivo, and even more so when tPA is absent. Thus, physiological levels of tPA confer protection from elevated free zinc. Mechanistically, tPA promotes movement of zinc into hippocampal neuron cells through voltage-sensitive Ca(2+) channels and Ca(2+)-permeable AMPA/KA channels. Therefore, zinc and tPA each appear to be able to limit the potential of the other to facilitate neurodegeneration, a reciprocal set of actions that may be critical in the hippocampus where tPA is secreted during the nonpathological conditions of learning and memory at sites known to be repositories of free and sequestered zinc.

Protective effects of melatonin on the ionizing radiation induced DNA damage in the rat brain

Melatonin is an endogenously produced antioxidant with radioprotective actions while ionizing radiation is a well-known cytotoxic and mutagenic agent of which the biological results are attributable to its free radical producing effects. The effect of melatonin on the DNA strand breakage and lipid peroxidation induced by ionizing radiation in the rat brain were investigated in order to clarify its radioprotective ability. The DNA strand breakage in rat brain exposed to 1000 cGy ionizing radiation was assessed by alkaline single cell gel electrophoresis and the lipid peroxidation was evaluated by measuring thiobarbituric acid reactive substances (TBARS) concentrations. A significant increase in DNA damage (p < 0.05) and TBARS concentrations (p < 0.01) was found in the radiation treated rat brain. Pre-treatment of rats with intraperitoneal doses of 100 mg/kg melatonin provided a significant decrease in the DNA strand breakage and lipid peroxidation. Our results indicate that melatonin can protect brain cells from oxidative damage induced by ionizing radiation.

Molecular and cellular mechanisms of cadmium carcinogenesis

Cadmium is a heavy metal, which is widely used in industry, affecting human health through occupational and environmental exposure. In mammals, it exerts multiple toxic effects and has been classified as a human carcinogen by the International Agency for Research on Cancer. Cadmium affects cell proliferation, differentiation, apoptosis and other cellular activities. Cd2+ does not catalyze Fenton-type reactions because it does not accept or donate electrons under physiological conditions, and it is only weakly genotoxic. Hence, indirect mechanisms are implicated in the carcinogenicity of cadmium. In this review multiple mechanisms are discussed, such as modulation of gene expression and signal transduction, interference with enzymes of the cellular antioxidant system and generation of reactive oxygen species (ROS), inhibition of DNA repair and DNA methylation, role in apoptosis and disruption of E-cadherin-mediated cell-cell adhesion. Cadmium affects both gene transcription and translation. The major mechanisms of gene induction by cadmium known so far are modulation of cellular signal transduction pathways by enhancement of protein phosphorylation and activation of transcription and translation factors. Cadmium interferes with antioxidant defense mechanisms and stimulates the production of reactive oxygen species, which may act as signaling molecules in the induction of gene expression and apoptosis. The inhibition of DNA repair processes by cadmium represents a mechanism by which cadmium enhances the genotoxicity of other agents and may contribute to the tumor initiation by this metal. The disruption of E-cadherin-mediated cell-cell adhesion by cadmium probably further stimulates the development of tumors. It becomes clear that there exist multiple mechanisms which contribute to the carcinogenicity of cadmium, although the relative weights of these contributions are difficult to estimate.

Apoptotic signal transduction pathways in diabetes

Failure of insulin producing pancreatic beta-cells is a common characteristic of type 1 (insulin-dependent) and type 2 (insulin non-dependent) diabetes mellitus. Accumulating evidence suggests that programmed cell death (apoptosis) is the main form of beta-cell death in these disorders. The beta-cell is particularly sensitive to apoptotic stimuli due to the inherent features of the specialized beta-cell phenotype. In type 1 diabetes anti-beta-cell autoimmune reactivity delivers the apoptotic signals in the form of inflammatory mediators or T-cell effectors. In type 2 diabetes, the metabolic derangement is associated with production of inflammatory mediators in insulin-sensitive tissues leading elevated levels of circulating inflammatory mediators such as IL-6 and TNF. Further glucose has been suggested to induce beta-cell apoptosis via the induction of beta-cell synthesis of IL-1 which via autocrine action may elicit signalling cascades analogous to those seen in beta-cell destruction in type 1 diabetes. Considering the apparent importance of IL-1-beta signalling in beta-cell failure in both type 1 and type 2 diabetes, we here review the modulatory effect exerted on IL-1signalling by cellular characteristics related to the specialized beta-cell phenotype. We conclude that beta-cell differentiation signals (Pdx-1), glucose metabolism, calcium handling as well as regulation of naturally occurring inhibitors of cytokine signalling contribute to sensitize the beta-cell to apoptotic stimuli. We hypothesize that immunological stimuli in type 1 diabetes and metabolic/inflammatory signals in type 2 diabetes converge on common signalling pathways leading to beta-cell failure and destruction in these two diseases.

Are β-blockers as efficacious in patients with diabetes mellitus as in patients without diabetes mellitus who have chronic heart failure? A meta-analysis of large-scale clinical trials

BACKGROUND

Diabetes mellitus is a frequent comorbid condition in patients with chronic heart failure (CHF) and confers a worse prognosis. Furthermore, although patients with CHF derive considerable benefit from beta-blockers, these agents are thought by many physicians to be contraindicated in patients with diabetes mellitus. Most published studies on beta-blockers in CHF have been unable to reach definitive conclusions about the mortality benefits of these agents in patients with diabetes mellitus. We therefore performed a meta-analysis of beta-blocker trials that reported mortality outcomes in patients with diabetes mellitus who had CHF to pool all available trial evidence on the benefits (or otherwise) of these agents in this setting.

METHODS

All-cause mortality data on patients with diabetes mellitus were obtained from all completed beta-blocker CHF randomized placebo-controlled trials involving >100 patients exposed to beta-blockers, in which outcomes in patients with diabetes mellitus were described. When events were not directly reported, risk ratios (RRs) were derived from analysis of figures and other manuscript data. Results were pooled with the Mantel-Haenszel method.

RESULTS

A total of 24.6% of patients were reported to have diabetes mellitus in the 6 studies analyzed (Australia and New Zealand [ANZ]-Carvedilol, Beta-blocker Evaluation of Survival Trial [BEST], Carvedilol US Trials, Cardiac Insufficiency Bisoprolol Study [CIBIS-II], Carvedilol Prospective Randomized Cumulative Survival Trial [COPERNICUS], and Metoprolol Controlled-release Randomized Intervention Trial in Heart Failure [MERIT-HF]). Patients with diabetes mellitus had increased mortality rates overall compared with subjects without diabetes mellitus (RR, 1.25; 95% CI, 1.15-1.36; P <.001). Compared with placebo, beta-blocker therapy for CHF was beneficial in patients with diabetes mellitus (RR, 0.84; 95% CI, 0.73-0.96; P =.011) and in subjects without diabetes mellitus (RR, 0.72; 95% CI, 0.65-0.79; P <.001). The absolute risk reduction in mortality with beta-blocker therapy was greater in patients with heart failure but without diabetes mellitus than in patients with diabetes mellitus (P =.023).

CONCLUSIONS

Patients with diabetes mellitus and CHF appear to derive prognostic benefit from beta-blocker therapy, although the magnitude of that benefit is somewhat less than that observed in subjects without diabetes mellitus.

Differential expression of metallothionein 1 and 2 isoforms in breast cancer lines with different invasive potential: identification of a novel nonsilent metallothionein-1H mutant variant

Metallothionein (MT), a low-molecular weight protein with pleiotropic functions, is believed to play an important role in tumorigenesis. The aim of this study was to compare the expression of functional MT-1 and MT-2 mRNA isoforms in five breast cancer cell lines ranging from noninvasive MCF7 breast cancer cells to highly aggressive MDA-MB-231 breast cancer cells together with breast myoepithelial cells in vitro by conventional semiquantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and quantitative real-time RT-PCR. The MT-2A isoform was observed to be differentially upregulated in the invasive phenotype. The MT-1E isoform was found to be present in estrogen receptor-negative breast cancer cell lines (MDA-MB-231 and Hs578T) but not detectable in the estrogen receptor-positive cell lines (T47D, MCF7, and ZR75-1 cells). Only the myoepithelial cells exhibited the presence of the MT-1G transcript. Direct sequencing of the RT-PCR products revealed the occurrence of a variant MT-1H isoform with changes in amino acid residues in the protein sequence and notable differences in the predicted secondary protein structure. The observations in this study are relevant to the development of novel approaches to metastatic breast cancer disease, and may herald the search for novel MT mutants and the elucidation of their biological roles.

Enhanced permeability transition explains the reduced calcium uptake in cardiac mitochondria from streptozotocin-induced diabetic rats

Cardiac dysfunction is associated with diabetes. It was previously shown that heart mitochondria from diabetic rats have a reduced calcium accumulation capacity. The objective of this work was to determine whether the reduction in calcium accumulation by cardiac mitochondria from diabetic rats is related to an enhanced susceptibility to induction of the mitochondrial permeability transition. Streptozotocin-induced diabetic rats were used as a model to study the alterations caused by diabetes in the permeability transition, 21 days after streptozotocin administration. Heart mitochondria were isolated to evaluate respiratory parameters and susceptibility to the calcium-dependent permeability transition. Our results show that streptozotocin diabetes facilitates the mitochondrial permeability transition in cardiac mitochondria, resulting in decreased mitochondrial calcium accumulation. We also observed that heart mitochondria from diabetic rats had depressed oxygen consumption during the phosphorylative state. The reduced mitochondrial calcium uptake observed in heart mitochondria from diabetic rats is related to an enhanced susceptibility to the permeability transition rather than to damage to the calcium uptake machinery.

Antiapoptotic effect and inhibition of ischemia/reperfusion-induced myocardial injury in metallothionein-overexpressing transgenic mice

Previous studies using a cardiac-specific metallothionein (MT)-overexpressing transgenic mouse model have demonstrated that MT inhibits ischemia/reperfusion-induced myocardial injury. The present study was undertaken to test the hypothesis that the MT inhibition is associated with suppression of apoptosis mediated by mitochondrial cytochrome c release and caspase-3 activation. An open-chest coronary artery occlusion and reperfusion procedure to produce ischemia/reperfusion-induced left ventricle infarction was used in MT-overexpressing transgenic mice and non-transgenic controls. After 30 minutes of ischemia, the left ventricle was reperfused to allow blood flow through the previously occluded coronary artery bed. Myocardial infarction produced after reperfusion for 4 hours was significantly reduced in the MT transgenic mice. This inhibition correlated with the antiapoptotic effect of MT, as determined by a terminal deoxynucleotidyl transferase-mediated deoxyuridine 5-triphosphate nick-end labeling assay, mitochondrial cytochrome c release and caspase-3 activation. Ischemia/reperfusion-induced lipid peroxidation was also significantly inhibited in the MT-transgenic heart. Dimethylsulfoxide, a chemical scavenger for reactive oxygen species, was used to confirm the antioxidant effect of MT and found to suppress myocardial infarction and lipid peroxidation just as MT did. This study thus demonstrates that MT suppresses ischemia/reperfusion-induced myocardial apoptosis through, at least in part, the inhibition of cytochrome c-mediated caspase-3 activation pathway. The antiapoptotic effect of MT likely results from the suppression of oxidative stress and correlates with the inhibition of myocardial infarction.

Influence of thiol balance on micellar cholesterol handling by polarized Caco-2 intestinal cells

The in vitro thiol redox modulation of cholesterol homeostasis was investigated in polarized Caco-2 intestinal cells. Cells were pre-incubated with the pro-oxidant compound CuSO4 or with the antioxidant N-acetylcysteine (NAC), to induce a mild shift of the intracellular redox potential toward, respectively, a more oxidizing or a more reducing equilibrium, via a manipulation of intracellular soluble thiols (glutathione). Then, monolayers were exposed to micellar cholesterol and both the cholesterol uptake and export, as well as the cholesteryl ester cycle, were analyzed. We found that pro-oxidizing conditions induced a significant cholesterol retention within the cells, particularly in the unesterified form (FC), as a result of an augmented sterol incorporation coupled with a reduced rate of FC esterification. A reduction in FC export was also evident. Furthermore, the combination of FC retention and the oxidative imbalance leads to significant alterations of the monolayer integrity, evidenced by both the enhanced tight junction permeability and the lactate dehydrogenase release into the basolateral medium. In contrast, a more reducing environment generated by NAC pre-treatment favors the limitation of the resident time of FC into the cells, via a reduced cholesterol uptake and a concomitant increased cholesterol esterification. In addition, a significant higher FC extrusion into the basolateral medium was also appreciable. Our results indicate that the thiol balance of intestinal cells may be critical for the regulation of cholesterol homeostasis at the intestinal level, influencing the lipid transport throughout the intestinal barrier.

Involvement of LEU13 in interferon-induced refractoriness of human RSa cells to cell killing by X rays

Culture of human cells with human interferon alpha and beta (IFNA and IFNB) results in increased resistance of the cells to cell killing by X rays. To identify candidate genes responsible for the IFN-induced X-ray resistance, we searched for genes whose expression levels are increased in human RSa cells treated with IFNA, using an mRNA differential display method and Northern blotting analysis. RSa cells, which showed increased survival (assayed by colony formation) after X irradiation when they were treated with IFNA prior to irradiation, showed increased expression levels of LEU13 (IFITM1) mRNA after IFNA treatment alone. In contrast, IF(r) and F-IF(r) cells, both of which are derived from RSa cells, showed increased X-ray resistance and high constitutive LEU13 mRNA expression levels compared to the parental RSa cells. Furthermore, the IFNA-induced resistance of RSa cells to killing by X rays was suppressed by antisense oligonucleotides for LEU13 mRNA. LEU13, a leukocyte surface protein, was previously reported to mediate the actions of IFN such as inhibition of cell proliferation. The present results suggest a novel role of LEU13 different from that in the inhibition of cell proliferation, involved in IFNA-induced refractoriness of RSa cells to X rays.

Modulation of hOGG1 DNA repair enzyme in human cultured cells in response to pro-oxidant and antioxidant challenge

The putative modulation of the base excision repair enzyme, human 8-oxoguanine glycosylase (hOGG1), important in the removal of the potentially mutagenic lesion 8-oxo-2'-deoxyguanosine (8-oxodG), was investigated in human cell culture models. The expression of specific mRNA and protein was measured following pro-oxidant and antioxidant treatments in one human lymphoblastoid and one keratinocyte line. The measurement of intracellular reactive oxygen species generation was monitored by a fluorogenic assay and potential genotoxic effects confirmed by the dose-dependent increase in formamidopyrimidine-DNA glycosylase (Fpg) sensitive sites by alkaline unwinding following sub-lethal doses of hydrogen peroxide. The generation of a potentially antioxidant environment was assessed by the intracellular increase and extracellular depletion in ascorbic acid, confirmed by capillary electrophoresis. Despite these pro-oxidant and antioxidant treatments no significant change in mRNA of hOGG1 was observed in either cell line. Western analysis revealed that relatively high, yet noncytotoxic, doses of hydrogen peroxide caused a consistent approximate 50% decrease in hOGG1 protein in lymphoblastoid cells. The lack of upregulation of hOGG1 suggests the gene is constitutively expressed, which is further supported by studies examining the sequence of its promoter region. However, hOGG1 protein turnover may be sensitive to intracellular redox changes.

Astrocyte-targeted expression of interleukin-6 protects the central nervous system during neuroglial degeneration induced by 6-aminonicotinamide

6-aminonicotinamide (6-AN) is a niacin antagonist, which leads to degeneration of gray matter astrocytes mainly in the brainstem. We have examined the role of interleukin-6 (IL-6) in this degenerative process by using transgenic mice with astrocyte-targeted IL-6 expression (GFAP-IL6 mice). This study demonstrates that transgenic IL-6 expression significantly increases the 6-AN-induced inflammatory response of reactive astrocytes, microglia/macrophages, and lymphocytes in the brainstem. Also, IL-6 induced significant increases in proinflammatory cytokines IL-1, IL-12, and tumor necrosis factor-alpha as well as growth factors basic fibroblast growth factor (bFGF), transforming growth factor-beta, neurotrophin-3, angiopoietin, vascular endothelial growth factor, and the receptor for bFGF. In accordance, angiogenesis was increased in GFAP-IL6 mice relative to controls after 6-AN. Moreover, oxidative stress and apoptotic cell death were significantly reduced by transgenic IL-6 expression. IL-6 is also a major inducer in the CNS of metallothionein I and II (MT-I+II), which were significantly increased in the GFAP-IL6 mice. MT-I+II are antioxidants and neuroregenerative factors in the CNS, so increased MT-I+II levels in GFAP-IL6 mice could contribute to the reduction of oxidative stress and cell death in these mice.

Tissue-dependent induction of heme oxygenase-1 and metallothionein-1/2 by methyl methanesulfonate

Methyl methanesulfonate (MMS), a methylating agent, is known to be a genotoxicant in testis. The purpose of this study was to investigate roles of oxidative stress-responsive proteins, heme oxygenase-1 (HO-1) and metallothionein-1/2 (MT-1/2), in genotoxicity of MMS. Cadmium, a potent genotoxicity inducer, induced HO-1 and MT-1/2 in rat livers and kidneys. Then we comparatively investigated MMS-induced HO-1 and MT-1/2 in rat livers, kidneys and testes. We found that a single administration of MMS (40 mg/kg) resulted in the induction of MT-1/2 mRNA in the liver, but not HO-1 mRNA, reaching maximum level at 6 hr and returning to the control levels by 24 hr. Interestingly, MMS induced both HO-1 and MT-1/2 mRNAs in the kidney. In contrast, MMS induced HO-1 mRNA, but not MT-1/2 mRNA in the testis. Since HO-1 and MT-1/2 have been recognized to respond to various oxidative stimuli, we further examined the inducing effect of MMS on these two proteins. MMS at dosages of 20 to 40 mg/kg for 2 consecutive weeks induced HO-1 mRNA (123 to 187% of the control) and protein (274 to 404% of the control) in rat testes. However, MT-1/2 mRNA was not induced by MMS administration, although a high level of expression was observed in comparison with the liver and kidney. These findings suggest that MMS induces HO-1 and/or MT-1/2 mRNA and its protein tissue-dependently, and the heme catabolites by HO-1 in the testis may contribute in some manner to its genotoxicity.

AT1 blockade prevents glucose-induced cardiac dysfunction in ventricular myocytes: role of the AT1 receptor and NADPH oxidase

Enhanced tissue angiotensin (Ang) II levels have been reported in diabetes and might lead to cardiac dysfunction through oxidative stress. This study examined the effect of blocking the Ang II type 1 (AT1) receptor on high glucose-induced cardiac contractile dysfunction. Rat ventricular myocytes were maintained in normal- (NG, 5.5 mmol/L) or high- (HG, 25.5 mmol/L) glucose medium for 24 hours. Mechanical and intracellular Ca2+ properties were assessed as peak shortening (PS), time to PS (TPS), time to 90% relengthening (TR90), maximal velocity of shortening/relengthening (+/-dL/dt), and intracellular Ca2+ decay (tau). HG myocytes exhibited normal PS; decreased +/-dL/dt; and prolonged TPS, TR90, and tau. Interestingly, the HG-induced abnormalities were prevented with the AT1 blocker L-158,809 (10 to 1000 nmol/L) but not the Janus kinase-2 (JAK2) inhibitor AG-490 (10 to 100 micromol/L). The only effect of AT1 blockade on NG myocytes was enhanced PS at 1000 nmol/L. AT1 antagonist-elicited cardiac protection against HG was nullified by the NADPH oxidase activator sodium dodecyl sulfate (80 micromol/L) and mimicked by the NADPH oxidase inhibitors diphenyleneiodonium (10 micromol/L) or apocynin (100 micromol/L). Western blot analysis confirmed that the protein abundance of NADPH oxidase subunit p47phox and the AT1 but not the AT2 receptor was enhanced in HG myocytes. In addition, the HG-induced increase of p47phox was prevented by L-158,809. Enhanced reactive oxygen species production observed in HG myocytes was prevented by AT1 blockade or NADPH oxidase inhibition. Collectively, our data suggest that local Ang II, acting via AT1 receptor-mediated NADPH oxidase activation, is involved in hyperglycemia-induced cardiomyocyte dysfunction, which might play a role in diabetic cardiomyopathy.

Expression of metallothionein gene at different time in testicular interstitial cells and liver of rats treated with cadmium

AIM: Rodent testes are generally more susceptible to cadmium (Cd)-induced toxicity than liver. To clarify the molecular mechanism of Cd-induced toxicity in testes, we compared metallothionein (MT) gene expression, MT protein accumulation, and Cd retention at different time in freshly isolated testicular interstitial cells and liver of rats treated with Cd.

METHODS: Adult male Sprague-Dawley rats weighing 250-280 g received a s.c injection of 4.0 μmol Cd/kg and were euthanized by CO₂ asphyxiation 1 h, 3 h, 6 h, or 24 h later. Tissue was sampled and testicular interstitial cells were isolated. There were three replicates per treatment and 3 animals per replicate for RNA analyses, others, three replicates per treatment and one animal per replicate. MT1 and MT2 mRNA levels were determined by semi-quantitative RT-PCR analysis followed by densitometry scanning, and MT was estimated by the enzyme-linked immunosorbent assay (ELISA) method. Cadmium content was determined by atomic absorption spectrophotometry. The same parametersd were also analyzed in the liver, since this tissue unquestionably accumulate MT.

RESULTS: The rat testis expressed MT1 and MT2, the major isoforms. We also found that untreated animals contained relatively high basal levels of both isoform mRNA, which were increased after Cd treatment in liver and peaked at 3 h, followed by a decline. In contrast, the mRNA levels in interstitial cells peaked at 6 h. Interestingly, the induction of MT1 mRNA was lower than MT2 mRNA in liver of rat treated with Cd, but it was opposite to interstitial cells. Cd exposure substantially increased hepatic MT (3.9-fold increase), but did not increase MT translation in interstitial cells.

CONCLUSION: Cd-induced expression of MT isoforms is not only tissue dependent but also time-dependent. The inability to induce the metal-detoxicating MT-protein in response to Cd, may account for a higher susceptibility of testes to Cd toxicity and carcinogenesis compared to liver.

Flow cytometry as a strategy to study radiation-induced bystander effects in co-culture systems

BACKGROUND

There is growing interest in the role of bystander effects in the biological response of mammalian cells to ionizing radiation. Qualitative and quantitative assessment of bystander effects requires quick and reliable methodologies. The present work uses a flow cytometric approach to study proliferation of bystander cells co-cultured with irradiated cells.

METHODS

Confluent monolayers of rat liver epithelial cells (WB-F344) were irradiated with 137Cs gamma-rays at dose ranges 0.5, 1, 5, 10, and 20 Gy. Irradiated cells were mixed with unirradiated cells (i.e., bystander cells) at a ratio of 1:1 and cultured together for 24 h followed by a flow cytometry (FCM) study of their proliferation. In order to discriminate the two populations of co-cultured cells, one of the cell populations (unirradiated cells) was stained with the lipophilic fluorescent dye DiI.

RESULTS

Unirradiated cells, in the presence of cells irradiated at doses above 0.5 Gy, showed an enhanced cell growth by approximately 14-17%.

CONCLUSIONS

Cells irradiated with gamma rays can induce increased proliferation in neighboring unirradiated bystander cells. FCM provides an excellent basis for characterization of these and other bystander effects in co-culture systems.

Ozone-induced disruptions of lung transcriptomes

We have analyzed changes in approximately 4000 lung mRNAs, with GeneChips, in mice exposed to 1 ppm O(3) for three consecutive nights (8 h per night). Differential gene expression analysis identified approximately 260 O(3) sensitive genes; approximately 80% of these were repressed and approximately 20% were induced in O(3)-exposed mice compared to the air-exposed controls. A 20-fold induction of serum amyloid A3 mRNA by O(3) suggested activation of NF-kappaB and CCAAT/enhancer binding protein-mediated pathways by inflammatory cytokines. Induction (up to 14-fold) of 12 genes that increase DNA synthesis and cell cycle progression, and increase (approximately 7-fold) in CD44 mRNA and macrophage metalloelastase suggested a state of O(3)-induced hyperplasia and lung remodeling. Several mRNAs encoding enzymes of xenobiotic metabolism and cytoskeletal functions were repressed and may suggest cytokine mediated suppression of cytochrome P450 expression and cachexia-like inflammatory state in ozone-exposed lungs. The expressions of approximately 30 genes of immune response were also repressed. Collectively this genome-wide analysis of lungs identified ozone-induced disruption of gene transcriptional profile indicative of increased cellular proliferation under suppressed immune surveillance and xenobiotic metabolism.

Discrete and complementary mechanisms of protection of beta-cells against cytokine-induced and oxidative damage achieved by bcl-2 overexpression and a cytokine selection strategy

We have been investigating the potential utility of engineered cell lines as surrogates for primary islet cells in treatment of type 1 diabetes. To this end, two strategies that have emerged for procuring cell lines with resistance to immune-mediated damage are 1) selection of cytokine-resistant cell lines by growth of INS-1 insulinoma cells in iteratively increasing concentrations of interleukin (IL)-1beta + gamma-interferon (IFN-gamma), and 2) stable overexpression of the anti-apoptotic gene bcl-2 in INS-1 cells. Herein, we show that bcl-2-overexpressing cells are resistant to the cytotoxic effects of reactive oxygen and nitrogen species (ROS/RNS), but are only modestly protected against high concentrations of IL-1beta + INF-gamma, whereas the converse is true in cytokine selected cells. We also found that the combination of bcl-2 expression and cytokine selection confers a broader spectrum of resistance than either procedure alone, such that the resultant cells are highly resistant to cytokines and ROS/RNS, with no impairment in glucose-stimulated insulin secretion. INS-1-derived cells with combined bcl-2 expression and cytokine selection are also more resistant to damage induced by coculture with mitogen-activated peripheral blood mononuclear cells. Surprisingly, application of the cytokine selection procedure to bcl-2-overexpressing cells does not result in impairment of nuclear factor-kappaB translocation, iNOS expression, and NO production, as clearly occurs upon application of the selection procedure to cells without bcl-2 overexpression. Further investigation of the diverse pathways involved in the development of cytokine and ROS/RNS resistance may define simplified and specific strategies for preservation of beta-cell mass.

Astrocyte-targeted expression of IL-6 protects the CNS against a focal brain injury

The effect of CNS-targeted IL-6 gene expression has been thoroughly investigated in the otherwise nonperturbed brain but not following brain injury. Here we examined the impact of astrocyte-targeted IL-6 production in a traumatic brain injury (cryolesion) model using GFAP-IL6 transgenic mice. This study demonstrated that transgenic IL-6 production significantly increased wound healing following the cryolesion. Thus, at 20 days postlesion (dpl) the GFAP-IL6 mice showed almost complete wound healing compared to litter mate nontransgenic controls. It seems likely that a reduced inflammatory response in the long term could be responsible for this IL-6-related effect. Thus, while in the acute phase following cryolesion (1-6 dpl) the recruitment of macrophages and T lymphocytes was higher in GFAP-IL6 mice, at 10-20 dpl it was significantly reduced compared to controls. Reactive astrogliosis was also significantly increased up to but not including 20 dpl in the GFAP-IL6 mice. Oxidative stress as well as apoptotic cell death was significantly decreased throughout the time period studied in the GFAP-IL6 mice compared to controls. This could be linked to the altered inflammatory response as well as to the transgenic IL-6-induced increase of the antioxidant, neuroprotective proteins metallothionein-I + II. These results indicate that although in the brain the chronic astrocyte-targeted expression of IL-6 spontaneously induces an inflammatory response causing significant damage, during an acute neuropathological insult such as following traumatic injury, a clear neuroprotective role is evident.

Heart disease in diabetic patients

Both type 1 and type 2 diabetic patients have an increased incidence of ischemic heart disease and congestive heart failure. Cardiovascular disease accounts for up to 80% of the excess mortality in patients with type 2 diabetes. The burden of cardiovascular disease is especially pronounced in diabetic women. Factors that underlie diabetic heart disease include multiple vessel coronary artery disease, long-standing hypertension, metabolic derangements such as hyperglycemia and dyslipidemia, microvascular disease, and autonomic neuropathy. There is also increased sudden death associated with diabetes, which is due, in part, to the underlying autonomic neuropathy. This article reviews diabetic cardiac disease, with an emphasis on type 2 diabetes.

Hormesis, an update of the present position

The ongoing debate over the possible beneficial effects of ionising radiation on health, hormesis, is reviewed from different perspectives. Radiation hormesis has not been strictly defined in the scientific literature. It can be understood as a decrease in the risk of cancer due to low-dose irradiation, but other positive health effects may also be encompassed by the concept. The overwhelming majority of the currently available epidemiological data on populations exposed to ionising radiation support the assumption that there is a linear non-threshold dose-response relationship. However, epidemiological data fail to demonstrate detrimental effects of ionising radiation at absorbed doses smaller than 100-200 mSv. Risk estimates for these levels are therefore based on extrapolations from higher doses. Arguments for hormesis are derived only from a number of epidemiological studies, but also from studies in radiation biology. Radiobiological evidence for hormesis is based on radio-adaptive response; this has been convincingly demonstrated in vitro, but some questions remain as to how it affects humans. Furthermore, there is an ecologically based argument for hormesis in that, given the evolutionary prerequisite of best fitness, it follows that humans are best adapted to background levels of ionising radiation and other carcinogenic agents in our environment. A few animal studies have also addressed the hormesis theory, some of which have supported it while others have not. To complete the picture, the results of new radiobiological research indicate the need for a paradigm shift concerning the mechanisms of cancer induction. Such research is a step towards a better understanding of how ionising radiation affects the living cell and the organism, and thus towards a more reliable judgement on how to interpret the present radiobiological evidence for hormesis.

Metallothionein attenuates 3-morpholinosydnonimine (SIN-1)-induced oxidative stress in dopaminergic neurons

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the substantia nigra zona compacta, and in other subcortical nuclei associated with a widespread occurrence of Lewy bodies. The causes of cell death in Parkinson's disease are still poorly understood, but a defect in mitochondrial oxidative phosphorylation and enhanced oxidative stress have been proposed. We have examined 3-morpholinosydnonimine (SIN-1)-induced apoptosis in control and metallothionein-overexpressing dopaminergic neurons, with a primary objective to determine the neuroprotective potential of metallothionein against peroxynitrite-induced neurodegeneration in Parkinson's disease. SIN-1 induced lipid peroxidation and triggered plasma membrane blebbing. In addition, it caused DNA fragmentation, alpha-synuclein induction, and intramitochondrial accumulation of metal ions (copper, iron, zinc, and calcium), and enhanced the synthesis of 8-hydroxy-2-deoxyguanosine. Furthermore, it down-regulated the expression of Bcl-2 and poly(ADP-ribose) polymerase, but up-regulated the expression of caspase-3 and Bax in dopaminergic (SK-N-SH) neurons. SIN-1 induced apoptosis in aging mitochondrial genome knockout cells, alpha-synuclein-transfected cells, metallothionein double-knockout cells, and caspase-3-overexpressed dopaminergic neurons. SIN-1-induced changes were attenuated with selegiline or in metallothionein-transgenic striatal fetal stem cells. SIN-1-induced oxidation of dopamine to dihydroxyphenylacetaldehyde was attenuated in metallothionein-transgenic fetal stem cells and in cells transfected with a mitochondrial genome, and enhanced in aging mitochondrial genome knockout cells, in metallothionein double-knockout cells and caspase-3 gene-overexpressing dopaminergic neurons. Selegiline, melatonin, ubiquinone, and metallothionein suppressed SIN-1-induced down-regulation of a mitochondrial genome and up-regulation of caspase-3 as determined by reverse transcription-polymerase chain reaction. The synthesis of mitochondrial 8-hydroxy-2-deoxyguanosine and apoptosis-inducing factors were increased following exposure to 1-methyl-4-phenylpyridinium ion or rotenone. Pretreatment with selegiline or metallothionein suppressed 1-methyl-4-phenylpyridinium ion-, 6-hydroxydopamine-, and rotenone-induced increases in mitochondrial 8-hydroxy-2-deoxyguanosine accumulation. Transfection of aging mitochondrial genome knockout neurons with mitochondrial genome encoding complex-1 or melanin attenuated the SIN-1-induced increase in lipid peroxidation. SIN-1 induced the expression of alpha-synuclein, caspase-3, and 8-hydroxy-2-deoxyguanosine, and augmented protein nitration. These effects were attenuated by metallothionein gene overexpression. These studies provide evidence that nitric oxide synthase activation and peroxynitrite ion overproduction may be involved in the etiopathogenesis of Parkinson's disease, and that metallothionein gene induction may provide neuroprotection.

High levels of apoptosis induced by total body irradiation in mice fed a low protein-low vitamin E diet

Apoptosis in response to total body irradiation (TBI) in mice fed four kinds of diets was assessed. Male mice were fed a low protein-low vitamin E diet, a low protein-basal vitamin E diet, a basal protein-low vitamin E diet or a basal protein-basal vitamin E diet for 2 weeks, then received TBI at a dose of 0, 1 or 4 Gy, and were sacrificed 4 h after TBI. Apoptosis was assessed according to the appearance of DNA fragmentation patterns [DNA laddering and positive in situ end-labeling by terminal transferase (TUNEL) assay] and apoptotic index (AI). Electrophoresis of DNA from the spleen in the groups that did not receive TBI showed no cleavage, whereas that of DNA in the groups with 4 Gy of TBI displayed a ladder pattern, indicative of internucleosomal cleavage characteristic of apoptosis. In the groups with 4 Gy of TBI, apoptosis was enhanced in the low protein-low vitamin E group.

Age-related impairment of the transcriptional responses to oxidative stress in the mouse heart

To investigate the transcriptional response to oxidative stress in the heart and how it changes with age, we examined the cardiac gene expression profiles of young (5-mo-old), middle-aged (15-mo-old), and old (25-mo-old) C57BL/6 mice treated with a single intraperitoneal injection of paraquat (50 mg/kg). Mice were killed at 0, 1, 3, 5, and 7 h after paraquat treatment, and the gene expression profile was obtained with high-density oligonucleotide microarrays. Of 9,977 genes represented on the microarray, 249 transcripts in the young mice, 298 transcripts in the middle-aged mice, and 256 transcripts in the old mice displayed a significant change in mRNA levels (ANOVA, P < 0.01). Among these, a total of 55 transcripts were determined to be paraquat responsive for all age groups. Genes commonly induced in all age groups include those associated with stress, inflammatory, immune, and growth factor responses. Interestingly, only young mice displayed a significant increase in expression of all three isoforms of GADD45, a DNA damage-responsive gene. Additionally, the number of immediate early response genes (IEGs) found to be induced by paraquat was considerably higher in the younger animals. These results demonstrate that, at the transcriptional level, there is an age-related impairment of specific inducible pathways in the response to oxidative stress in the mouse heart.

Association of metallothionein expression and lack of apoptosis with progression of carcinogenesis in Barrett's esophagus

Barrett's esophagus is the transformation of normal esophageal squamous epithelium to specialized intestinal metaplasia (SIM). Among the Barrett's specialized cells, those that can develop protective mechanisms against apoptosis may have potential to become malignant. Studies have shown that overexpression of metallothionein (MT), low molecular protein that protects cells from apoptotic stimuli, appears to be associated with more advanced, highly malignant tumors. We thus investigated the relationship between MT expression and apoptosis in different stages of Barrett's carcinogenesis. Terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end labeling and immunohistochemical dual-staining assay were performed in human biopsy samples of normal, SIM, dysplasia, and adenocarcinoma. Apoptotic index and MT expression were quantified by using an image system to analyze the converted digital data. A negative correlation between MT expression and apoptotic index was found. MT expression was significantly increased along with the histologic progression towards adenocarcinoma. This study thus suggests that MT may contribute to cytoprotection, thereby inhibiting apoptosis and leading to carcinogenesis of Barrett's esophageal cells.

Metallothionein 2A induction by zinc protects HEPG2 cells against CYP2E1-dependent toxicity

Zinc has been shown to have antioxidant actions, which may be due, in part, to induction of metallothionein (MT). Such induction can protect tissues against various forms of oxidative injury because MT can function as an antioxidant. The objective of this study was to investigate if zinc or MT induction by zinc could afford protection against CYP2E1-dependent toxicity. HepG2 cells overexpressing CYP2E1 (E47cells) were treated with 60 microM arachidonic acid (AA), which is known to be toxic to these cells by a mechanism dependent on CYP2E1, oxidative stress, and lipid peroxidation. E47 cells were preincubated overnight in the absence or presence of metals such as zinc or cadmium that can induce MT. The culture medium containing the metals was removed, AA was added, and cell viability determined after 24 h incubation. Preincubation overnight with 150 microM zinc sulfate or 5 microM cadmium chloride induced a 20- to 30-fold increase of MT2A mRNA; high levels of MT2A mRNA were maintained during the subsequent challenge period with AA, even after the zinc was removed. MT protein levels were increased about 4- to 5-fold during the overnight preincubation with zinc and a 20- to 30-fold increase was observed 24 h after zinc removal during the AA challenge. The treatment with zinc was associated with significant protection against the loss of cell viability caused by AA in E47 cells. The zinc pretreatment protected about 50% against the DNA fragmentation, cell necrosis, the enhanced lipid peroxidation and increased generation of reactive oxygen species, and the loss of mitochondrial membrane potential induced by AA treatment in E47 cells. CYP2E1 catalytic activity and components of the cell antioxidant defense system such as glutathione (GSH), glutathione-S-transferase (GST), glutathione peroxidase (GPX), catalase, Cu,Zn superoxide dismutase (SOD), and MnSOD were not altered under these conditions. Zinc preincubation also protected the E47 cells against BSO-dependent toxicity. When E47 cells were coincubated with zinc plus AA for 24 h (i.e., zinc was not removed, nor was there a preincubation period prior to challenge with AA), AA toxicity was increased. Thus, zinc had a direct pro-oxidant effect in this model and an indirect antioxidant effect, perhaps via induction of MT. MT may have potential clinical utility for the prevention or improvement of liver injury produced by agents known to be metabolized by CYP2E1 to reactive intermediates and to cause oxidative stress.

Human sensitive to apoptosis gene protein inhibits peroxynitrite-induced DNA damage

Sensitive to apoptosis gene (SAG) protein, a novel zinc RING finger protein, which is redox responsive and protects mammalian cells from apoptosis, is a metal chelator and a potential reactive oxygen species scavenger, but its antioxidant properties have not been completely defined. The present study was undertaken to test the hypothesis that human SAG protects from DNA damage induced by peroxynitrite, a potent physiological inorganic toxin. The present study has shown that SAG significantly inhibits single strand breaks in supercoiled plasmid DNA induced by synthesized peroxynitrite (ONOO(-)) and 3-morpholinosydnomine N-ethylcarbamide (SIN-1), a generator of peroxynitrite through the reaction between nitric oxide and superoxide anion. The formation of 8-hydroxy-2(')-deoxyguanosine in calf thymus DNA by peroxynitrite and SIN-1 was also significantly inhibited by SAG. The protective effect on peroxynitrite-mediated DNA damage was completely abolished by the reaction of SAG with N-ethylmaleimide, a chemical modification agent for the sulfhydryl group of proteins. These observations suggested that the sulfhydryl group of cysteines in SAG could react directly with peroxynitrite to prevent DNA damage.

Zinc-metallothionein protects from DNA damage induced by radiation better than glutathione and copper- or cadmium-metallothioneins

Protection of radiation-induced DNA damage by metallothionein (MT) has been documented, but there is no detailed information about its efficiency compared to other antioxidants or the effect of metals which bind to MT on the protective effect of MT in radiation-induced DNA damage. In this study, we used a cell-free system to investigate the effect of MT with other antioxidants, such as albumin and glutathione and we compared the efficiency of MT bound to different metals on radiation-induced DNA damage. DNA damage was measured by loss in ethidium bromide/DNA fluorescence and increased mobility of DNA on gel electrophoresis. Gamma rays at 30 Gy induced significant DNA damage and zinc-MT showed a significant higher protection from radiation-induced DNA damage than both glutathione and albumin. Metallothionein bound to other metals, such as copper and cadmium, also showed protection of radiation-induced DNA damage, but the protective effect by zinc-MT was the highest. These results suggest that MT, in particular bound to zinc, is a high-capacity antioxidant to protect radiation-induced DNA damage.

Radiation-induced apoptosis in scid mice spleen after low dose irradiation

To assess the radioadaptive response of the whole body system in mice, we examined the temporal effect of low dose priming as an indicator of challenging irradiation-induced apoptosis through a p53 tumor suppressor protein- mediated signal transduction pathway. The p53 protein also plays an important role both in cell cycle control and DNA repair through cellular signal transduction. Using severe combined immunodeficiency mice defective in DNA-dependent protein kinase catalytic subunit, we examined the role of DNA-dependent protein kinase activity in radioadaptation induced by low dose irradiation. Specific pathogen free 5-week-old female severe combined immunodeficiency mice and the parental mice (CB- 17 Icr +/+) were irradiated with X-ray at 3.0 Gy at 1, 2, 3 or 4 weeks after the conditioning irradiation at 0.15, 0.30, 0.45 or 0.60 Gy. The mice spleens were fixed for immunohistochemistry 12 h after the challenging irradiation. The p53-dependent apoptosis related Bax proteins on formalin-fixed paraffin-embedded sections were stained by the avidin-biotin peroxidase complex method. The apoptosis incidence in the sections was measured by hematoxylin-eosin staining. The frequency of Bax- and apoptosis-positive cells increased up to 12 h after the challenging irradiation in the spleen of both mice. However, these cells were not observed after a low dose irradiation at 0.15-0.60 Gy. When pre-irradiation at 0.45 Gy 2 weeks before the challenging irradiation at 3.0 Gy was performed, Bax accumulation and apoptosis induced by challenging irradiation were depressed in the spleens of CB-17 Icr +/+ mice, but not in severe combined immunodeficiency mice. These data suggest that DNA-dependent protein kinase might play a major role in radioadaptation induced by pre-irradiation with a low dose in mice spleen. We expect that the present findings will provide useful information in the health care of space crews.

Oxidative stress: the special case of diabetes

The implication of oxidative stress (OS) in diabetes is a major concern for the development of therapeutics aimed at improving the metabolic and/or vascular dysfunctions of this burdening disease. Ample evidence is available suggesting that OS is present in essentially all tissues and can even be observed in prediabetic states. This raises the question of the origin of OS and suggests that, although hyperglycemia is largely linked with free radical production, its role may mainly be the aggravation of a preexisting state. Indeed other factors are also causally linked to OS, such as hormones and lipids. The main debate is about the pertinence of antioxidant therapy since the large scale clinical trials performed recently have essentially failed to show any significant improvement in metabolic or vascular disturbances of diabetic patients. However this conclusion must be tempered by the fact that they have mainly been using vitamin E +/-C; indeed many arguments suggest that either the choice or the application modalities of these substances may have been inadequate. Potential reasons for the actual failure of antioxidant therapy in diabetes are discussed; the indisputable involvement of OS in this disease still leaves hope for alternative therapeutic approaches.

Review article: oxidative stress as a pathogenic factor in inflammatory bowel disease--radicals or ridiculous?

Virtually all inflammatory mediators investigated to date seem to be dysregulated in the inflamed intestinal mucosa of patients with inflammatory bowel disease. However, which of these are actually involved in the initiation and perpetuation of intestinal tissue damage is still not fully understood. Amongst these mediators are the reactive oxygen metabolites, produced in large amounts by the massively infiltrating leucocytes. These reactive oxygen metabolites are believed to constitute a major tissue-destructive force and may contribute significantly to the pathogenesis of inflammatory bowel disease. This paper provides a concise overview of reactive oxygen metabolite biochemistry, the types of cell and tissue damage potentially inflicted by them, and the endogenous antioxidants which should prevent these harmful effects. An up-to-date summary of the available human experimental data suggests that reactive oxygen metabolite-mediated injury is important in both the primary and downstream secondary pathophysiological mechanisms underlying intestinal inflammation. Nonetheless, how the individual components of the mucosal antioxidant enzymatic cascade respond to inflammatory conditions is a neglected area of research. This particular aspect of intestinal mucosal oxidative stress therefore merits further study, in order to provide a sound, scientific basis for the design of antioxidant-directed treatment strategies for inflammatory bowel disease patients.

Potential role of p53 on metallothionein induction in human epithelial breast cancer cells

The expression and induction of metallothionein has been associated with protection against oxidative stress and apoptosis. This study examines the effect of tumour suppressor protein p53 on metallothionein expression following CdCl2 treatment in eight human epithelial breast cancer cell lines differing in p53 and oestrogen-receptor status. Cells were treated with 10 microM CdCl2 for 24 h and metallothionein protein levels were measured by cadmium binding assay. MCF7 cells which are p53-positive (p53+) and oestrogen-receptor-positive showed a large induction in metallothionein synthesis by 10.79+/-1.36-fold. Other breast cancer cell lines which are p53-negative (p53-) and oestrogen-receptor-negative or weakly oestrogen-receptor-positive showed a small induction ranging from 1.40+/-0.10 to 3.65+/-0.30-fold. RT-PCR analysis showed an induction of metallothionein mRNA in MCF7 cells by about 1.61+/-0.08-fold, while in HCC1806 cells (p53-, oestrogen-receptor-negative) by 1.11+/-0.13-fold, and in MDA-MB-231 (p53-, oestrogen-receptor-negative) by 1.25+/-0.06-fold. Metallothionein localisation was determined by immunohistochemical staining. Prior to metal treatment, metallothionein was localised mainly in the cytoplasm of MCF7 and MDA-MB-231 cells. After treatment with 10 microM CdCl2 for 24 h, MCF7 cells showed intense nuclear and cytoplasmic staining for metallothionein, while MDA-MB-231 cells showed staining in the cytoplasm with weak nuclear staining. Apoptosis induced by 10-40 microM CdCl2 at time points between 4 and 48 h was examined with TUNEL assay. In MCF7 cells, apoptosis increased with higher concentrations of CdCl2, it peaked at 6-8 h and appeared again at 48 h for all concentrations of CdCl2 tested. In MDA-MB-231 cells, apoptosis remained at low levels for 10-40 microM CdCl2 at all time points. Studies on cadmium uptake showed similar uptake and accumulation of cadmium at 8 and 24 h in all the cell lines. The data demonstrate that treatment of epithelial breast cancer cells with 10 microM CdCl2 for 24 h caused a greater induction of metallothionein protein and mRNA expression in p53+ and oestrogen-receptor-positive cells as compared to p53- and oestrogen-receptor-negative or weakly oestrogen-receptor-positive cells. This effect may be associated with the occurrence of apoptosis and suggests a role for p53 and oestrogen-receptor on the expression and induction of metallothionein in epithelial cells.

Role of metallothioneins in irradiated human rectal carcinoma

BACKGROUND

Metallothioneins (MT) are low-molecular weight, metal-binding proteins that play a role in cellular proliferation and differentiation, as well as in cellular defense mechanisms. They act as scavengers of free radicals produced by irradiation. A number of in vitro and in vivo studies have linked overexpression of cellular MT with tumor cell resistance to radiation. This is the first study that investigates whether MT expression is involved in the radioresistance of rectal carcinoma.

METHODS

Using a mouse monoclonal antibody, MT expression was analyzed by immunohistochemistry on surgical samples (n = 85) from 85 patients with locally advanced rectal carcinoma who were treated preoperatively with a hyperfractionated and accelerated radiotherapy schedule and on tumor biopsies (n = 13) obtained before treatment. The potential correlations between MT expression and pathologic variables and survival were examined.

RESULTS

MT were expressed strongly in both the cytoplasm and nucleus of tumor cells in 7 biopsy and 42 surgical samples. A comparison of MT expression in biopsy and surgical specimens showed that MT expression did not change after irradiation in most cases. Against all expectations, MT were expressed more frequently in tumors from responders than in those from the nonresponders (P = 0.02). There was no correlation between MT expression and tumor stage, histology after radiotherapy, or survival.

CONCLUSION

These findings do not Cansupport the hypothesis that MT overexpression at the end of radiotherapy is a marker for radiation resistance.

Low-dose radiation action: possible implications of bystander effects and adaptive response

Several experimental studies performed in the last decade have suggested the occurrence of low-dose-specific phenomena such as the bystander effect (BE, damage induction in cells not directly hit by radiation) and adaptive response (AR, induction of resistance to subsequent irradiation with higher doses). Although the underlying mechanisms are still not known in detail, cellular communication is widely regarded as a key factor. BE and AR may have a non-negligible role in modulating low-dose radiation effects not only in cells, but also in tissues and organs. Whether these phenomena would imply an increase or a decrease of low-dose cancer risk is still an open question. In this context a few representative findings are discussed, focusing on their possible implications for low-dose risk.

A reliable primary human CNS culture protocol for morphological studies of dendritic and synaptic elements

Primary dissociated human fetal forebrain cultures were grown in defined serum-free conditions. At 4 weeks in vitro the cultures contained abundant morphologically well differentiated neurons with complex dendritic arbors. Astrocytic proliferation was negligible without the use of antimitotic agents. Confocal scanning laser microscopy (CSLM) and electron microscopy confirmed the presence of a dense neuropil, numerous cell-cell contacts and synapses. Neurons expressed a variety of proteins including growth associated protein-43 (GAP43), microtubule associated protein-2ab (MAP), class-III beta tubulin (C3BT), neurofilaments (NF), synaptophysin (SYN), parvalbumin (PA) and calbindin (CB). The cultures have proven to be reliable and simple to initiate and maintain for many weeks without passaging. They are useful in investigations of dendritic growth and injury of primary human CNS neurons.

Adaptive response induction and variation in human lymphoblastoid cell lines

Adaptive response is a term used to describe the ability of a low, priming dose of ionizing radiation to modify the effects of a subsequent higher, challenge dose, but it has been observed to be highly variable in both presence and magnitude. To examine this variability, 10 human lymphoblastoid cell lines were screened for adaptability to 137Cs radiation by determining the frequency of micronuclei in binucleated cells. Of these, six adapted, three did not adapt and one was synergistic. The assay was then repeated on each of the cell lines to test for reproducibility. Five cell lines showed the same result both times; four of these adapted and one did not. To determine whether fluctuations in the cell cycle distribution in the irradiated population of cells could alter the adaptive response, and therefore explain some of the observed variability, two of the cell lines were tested for adaptation after enriching the population, by synchronization, for a given cell cycle stage. In both cell lines, the direction of the response was altered when the distribution of cells within the cell cycle was changed, suggesting that the adaptive response can be affected by cell cycle stage at the time of irradiation.

Metallothionein suppresses collagen-induced arthritis via induction of TGF-beta and down-regulation of proinflammatory mediators

Metallothionein is a low molecular weight, cysteine-rich, stress response protein that can act as an antioxidant and as an immunosuppressive agent in instances of antigen-dependent adaptive immunity. In this context, we assessed the therapeutic potential and mechanisms of action of metallothionein in a collagen-induced arthritis model. Repeated administration of metallothionein-I + II during the course of disease dramatically reduced the incidence and severity of the disease. Joint tissues isolated from boostered paws of metallothionein-I + II-treated mice expressed significantly reduced levels of proinflammatory mediators, such as tumour necrosis factor (TNF)-alpha and cyclooxygenase-2, when compared with those of control-treated mice. Lymph node cells obtained from metallothionein-I + II -injected mice exhibited a significant decrease in the proliferative response and a remarkable increase in tumour growth factor (TGF)-beta production in response to type II collagen. Taken together, these results suggest that metallothionein-I + II promote the development of type II collagen-specific, TGF-beta-producing cells to antagonize the expansion of arthritogenic cells. This could lead to local suppression of inflammatory responses by inhibiting the expression of proinflammatory molecules. Thus, this study demonstrates the suppressive effects of metallothionein on collagen-induced arthritis, and indicates that there may be a potential therapeutic application for manipulation of metallothionein during the treatment of autoimmune disorders.