Hyperglycemia-induced apoptosis in mouse myocardium: mitochondrial cytochrome C-mediated caspase-3 activation pathway

Diabetic cardiomyopathy is related directly to hyperglycemia. Cell death such as apoptosis plays a critical role in cardiac pathogenesis. Whether hyperglycemia induces myocardial apoptosis, leading to diabetic cardiomyopathy, remains unclear. We tested the hypothesis that apoptotic cell death occurs in the diabetic myocardium through mitochondrial cytochrome c-mediated caspase-3 activation pathway. Diabetic mice produced by streptozotocin and H9c2 cardiac myoblast cells exposed to high levels of glucose were used. In the hearts of diabetic mice, apoptotic cell death occurred as detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay. Correspondingly, caspase-3 activation as determined by enzymatic assay and mitochondrial cytochrome c release detected by Western blotting analysis were observed. Supplementation of insulin inhibited diabetes-induced myocardial apoptosis as well as suppressed hyperglycemia. To explore whether apoptosis in diabetic hearts is related directly to hyperglycemia, we exposed cardiac myoblast H9c2 cells to high levels of glucose (22 and 33 mmol/l) in cultures. Apoptotic cell death was detected by TUNEL assay and DAPI nuclear staining. Caspase-3 activation with a concomitant mitochondrial cytochrome c release was also observed. Apoptosis or activation of caspase-3 was not observed in the cultures exposed to the same concentrations of mannitol. Inhibition of caspase-3 with a specific inhibitor, Ac-DEVD-cmk, suppressed apoptosis induced by high levels of glucose. In addition, reactive oxygen species (ROS) generation was detected in the cells exposed to high levels of glucose. These results suggest that hyperglycemia directly induces apoptotic cell death in the myocardium in vivo. Hyperglycemia-induced myocardial apoptosis is mediated, at least in part, by activation of the cytochrome c-activated caspase-3 pathway, which may be triggered by ROS derived from high levels of glucose.

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.

Oxidative stress and diabetic cardiomyopathy: a brief review

Diabetes is a serious public health problem. Improvements in the treatment of noncardiac complications from diabetes have resulted in heart disease becoming a leading cause of death in diabetic patients. Several cardiovascular pathological consequences of diabetes such as hypertension affect the heart to varying degrees. However, hyperglycemia, as an independent risk factor, directly causes cardiac damage and leads to diabetic cardiomyopathy. Diabetic cardiomyopathy can occur independent of vascular disease, although the mechanisms are largely unknown. Previous studies have paid little attention to the direct effects of hyperglycemia on cardiac myocytes, and most studies, especially in vitro, have mainly focused on the molecular mechanisms underlying pathogenic alterations in vascular smooth-muscle cells and endothelial cells. Thus, a comprehensive understanding of the mechanisms of diabetic cardiomyopathy is urgently needed to develop approaches for the prevention and treatment of diabetic cardiac complications. This review provides a survey of current understanding of diabetic cardiomyopathy. Current consensus is that hyperglycemia results in the production of reactive oxygen and nitrogen species, which leads to oxidative myocardial injury. Alterations in myocardial structure and function occur in the late stage of diabetes. These chronic alterations are believed to result from acute cardiac responses to suddenly increased glucose levels at the early stage of diabetes. Oxidative stress, induced by reactive oxygen and nitrogen species derived from hyperglycemia, causes abnormal gene expression, altered signal transduction, and the activation of pathways leading to programmed myocardial cell deaths. The resulting myocardial cell loss thus plays a critical role in the development of diabetic cardiomyopathy. Advances in the application of various strategies for targeting the prevention of hyperglycemia-induced oxidative myocardial injury may be fruitful.

Inhibition of superoxide generation and associated nitrosative damage is involved in metallothionein prevention of diabetic cardiomyopathy

The mechanisms of metallothionein prevention of diabetic cardiomyopathy are largely unknown. The present study was performed to test whether inhibition of nitrosative damage is involved in metallothionein prevention of diabetic cardiomyopathy. Cardiac-specific metallothionein-overexpressing transgenic (MT-TG) mice and wild-type littermate controls were treated with streptozotocin (STZ) by a single intraperitoneal injection, and both developed diabetes. However, the development of diabetic cardiomyopathy, revealed by histopathological and ultrastructural examination, serum creatine phosphokinase, and cardiac hemodynamic analysis, was significantly observed only in the wild-type, but not in MT-TG, diabetic mice 2 weeks and 6 months after STZ treatment. Formations of superoxide and 3-nitrotyrosine (3-NT), a marker for peroxynitrite-induced protein damage, were detected only in the heart of wild-type diabetic mice. Furthermore, primary cultures of cardiomyocytes from wild-type and MT-TG mice were exposed to lipopolysaccharide/tumor necrosis factor-alpha for generating intracellular peroxynitrite. Increases in 3-NT formation and cytotoxicity were observed in wild-type, but not in MT-TG, cardiomyocytes. Either urate, a peroxynitrite-specific scavenger, or Mn(111) tetrakis 1-methyl 4-pyridyl porphyrin pentachloride (MnTMPyP), a superoxide dismutase mimic, significantly inhibited the formation of 3-NT along with a significant prevention of cytotoxicity. These results thus suggest that metallothionein prevention of diabetic cardiomyopathy is mediated, at least in part, by suppression of superoxide generation and associated nitrosative damage.

Metallothionein in radiation exposure: its induction and protective role

Since its discovery about 40 years ago, there has been a wide interdisciplinary research interest in metallothionein (MT) on its physiological and toxicological aspects. Functionally, MT is involved not only in metal detoxification and homeostasis, but also in scavenging free radicals during oxidative damage. Among over 4500 publications which can be retrieved by Medline search, only about 50 reports have been published on the relationship of MT with ionizing and UV radiation. In this review, we have evaluated critically the published data on the induced synthesis of MT by radiation, and the potential functions of MT in radiation induced cell damage. MT mRNA expression or MT synthesis was found to be induced by exposure of cells in vitro or tissues in vivo to ionizing or UV radiation. In most of the studies in animals and tissue cultures, high doses of ionizing radiation were used to induce MT, and, therefore, it is difficult to extrapolate these results to low level of repeated exposures to radiation in humans. Induced synthesis of MT is considered as one of the mechanisms involved in the adaptive response to low dose radiation exposure. The presence of MT in normal cells may provide protective effects from radiation-induced genotoxicity and cytotoxicity. However, in tumor cells, the presence of MT can result in drug and radiation resistance as well. These effects are modulated by other cellular factors, besides MT, such as antioxidants, and by the cell cycle stages in cell proliferation and differentiation.

Cell death and diabetic cardiomyopathy

Myocardial cell death is a key element in the pathogenesis and progression of various etiological cardiomyopathies such as ischemia-reperfusion, toxic exposure, and various chronic diseases including myocardial infarction, atherosclerosis, and endothelial dysfunction. Myocardial cell death is also observed in the hearts of diabetic patients and animal models; however, its importance in the development of diabetic cardiomyopathy is not completely understood. The goal of this review is to summarize our current understanding of the characteristics of diabetes-induced myocardial cell death. In the search of the mechanisms by which diabetes induces myocardial cell death, multiple cell death pathways have been proposed. Reactive oxygen and nitrogen species accumulation plays a critical role in the cell death process. Several studies have shown that suppression of myocardial cell death by antioxidants or inhibitors for apoptosis-specific signaling pathways results in a significant prevention of diabetic cardiotoxicity, suggesting that cell death in diabetic subjects plays an important role in the development of diabetic cardiomyopathy.

Metallothionein inhibits peroxynitrite-induced DNA and lipoprotein damage

Previous studies have demonstrated that metallothionein functions as an antioxidant that protects against oxidative DNA, protein, and lipid damage induced by superoxide anion, hydrogen peroxide, hydroxyl radical, and nitric oxide. The present study was undertaken to test the hypothesis that metallothionein also protects from DNA and lipoprotein damage induced by peroxynitrite, an important reactive nitrogen species that causes a diversity of pathological processes. A cell-free system was used. DNA damage was detected by the mobility of plasmid DNA in electrophoresis. Oxidation of low density lipoprotein was measured by a thiobarbituric acid-reactive substance, which was confirmed by lipid hydroperoxide assay. Plasmid DNA damage and low density lipoprotein oxidation were induced by 3-morpholinosydnomine, which produces peroxynitrite through the reaction between nitric oxide and superoxide anion or by synthesized peroxynitrite directly. DNA damage by 3-morpholinosydnomine was prevented by both metallothionein and superoxide dismutase, whereas the damage caused by peroxynitrite was prevented by metallothionein only. The oxidation of low density lipoprotein by 3-morpholinosydnomine and peroxynitrite was also significantly inhibited by metallothionein. This study thus demonstrates that metallothionein may react directly with peroxynitrite to prevent DNA and lipoprotein damage induced by this pathological reactive nitrogen species.

Apoptotic germ-cell death and testicular damage in experimental diabetes: prevention by endothelin antagonism

This paper explores the role of endothelins (ETs) in diabetes-induced testicular damage by investigating, in a temporal manner, testes from streptozotocin (STZ)-induced diabetic rats. Testicular and epididymal weights and testicular morphology were assessed. Cell death was evaluated by light microscopy using conventional staining and morphology, and by apoptotic cell staining using the Terminal deoxynucleotidyl transferase-mediated dUTP Nick End-Labeling (TUNEL) technique. Expression of endothelin-1 (ET-1) mRNA was evaluated by a semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) method. Furthermore, effects of a mixed ETA and ETB receptor antagonist, bosentan, were studied. Testicular weights did not show any change at 1 month of follow-up, but were decreased after 6 months of diabetes. However, epididymal weights were significantly decreased at the end of both time periods in the diabetic rats. Morphological evaluations of the testes from diabetic rats showed a reduction in seminiferous tubular diameter, an increase in the number of empty testicular tubules and an increase in vascular density. Furthermore, degenerated germ cells and TUNEL-positive cells were significantly higher in diabetic rats than in control animals. The changes in diabetic animals were associated with increased ET-1 mRNA expression and were prevented by bosentan treatment. Administration of bosentan prevented decreased testicular weights, reduced seminiferous tubule diameters, increased vascular densities and incidences of degenerated and apoptotic germ cells and empty tubules in diabetic rats at the long-term follow-up. These results demonstrated that an ET-1 mediated pathway might be involved in testicular injury and germ-cell apoptosis in diabetes.

Essentiality, toxicology and chelation therapy of zinc and copper

Both zinc and copper are essential minerals that are required for various cellular functions. Although these metals are essential, they can be toxic at excess amounts, especially in certain genetic disorders. Zinc and copper homeostasis results from a coordinated regulation by different proteins involved in uptake, excretion and intracellular storage/trafficking of these metals. Apart from zinc transporters (ZnT) families and Cu-ATPase, metallothionein is an important storage protein for zinc and copper. Metallothioneins are intracellular polypeptides with a remarkable ability to bind metallic ions. These proteins bind both essential metals indispensable for the organism and also toxic metals (e.g. cadmium or lead). Metallothioneins play a critical role to maintain zinc and copper homeostasis. In this review, we summarize the toxicity of zinc and copper and the potential treatment for zinc or copper toxicity by zinc- or copper-specific chelators as well as strategy to up-regulate metallothionein.

Metallothionein protects DNA from copper-induced but not iron-induced cleavage in vitro

Iron and copper ions mediate generation of reactive oxygen radicals from O2 and H2O2 by the Fenton reaction: these radicals are capable of damaging DNA. We studied (a) the ability of these metals to induce double-strand breaks in DNA in vitro in the presence of H2O2 and ascorbic acid as donors of reactive oxygen, and (b) the ability of the metal-binding protein metallothionein (MT) to protect DNA from damage. Strand cleavage was measured by loss of fluorescence after binding to ethidium bromide and by increased mobility of DNA in agarose. The results show that Cu(II), Fe(II) and Fe(III) all can induce damage to calf thymus DNA under our experimental conditions. Cu(II)-induced DNA damage was dose-dependent and the degree of damage was proportional to the concentration of H2O2. On the other hand, DNA fragmentation was significant only in the presence of high concentrations of Fe(II) or Fe(III). Addition of Zn-MT to the reaction mixture prior to addition of Cu(II) inhibited fragmentation of DNA in a dose-dependent manner but had little effect on iron induced damage. Other proteins (histone or albumin) were not effective in protecting DNA from Cu-induced damage, as compared to Zn-MT. The formation of Cu(I) from Cu(II) in the presence of hydrogen peroxide and ascorbate was also inhibited by addition of Zn-MT. Thus, MT may protect DNA from damage by free radicals by sequestering copper and preventing its participation in redox reactions.

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.

Diabetic cardiomyopathy and its prevention by metallothionein: experimental evidence, possible mechanisms and clinical implications

Cardiac failure is a leading cause for the mortality of diabetic patients, in part due to a specific cardiomyopathy, referred to as diabetic cardiomyopathy, which occurs with or without co-existence of vascular diseases. Although several mechanisms responsible for diabetic cardiomyopathy have been proposed, oxidative stress is widely considered as one of the major causes for the pathogenesis of the disease. Thus, a few laboratories are trying to develop antioxidants used to prevent diabetic cardiomyopathy. Metallothioneins (MTs) are cysteine-rich metal-binding proteins with several biological roles including antioxidant property. We and others have indicated the significant cardiac protection of MT against diabetes using cardiac-specific MT-overexpressing transgenic mice and OVE26MT mice (cross-bred of cardiac MT transgenic mice with genetically engineered diabetic OVE26 mice). Several possible mechanisms responsible for MT's cardiac protection from diabetes were revealed. These include MT's important roles in calcium regulation, zinc homeostasis, insulin sensitization, and antioxidant action. Since MT is ubiquitously expressed in mammalian tissues and is highly inducible by a variety of reagents such as zinc, the clinical potential for inducing cardiac MT as an antioxidant by zinc supplementation to prevent various diabetic complications, including cardiomyopathy, has been explored in diabetic animal models and patients. Since zinc has been therapeutically used for several other non-diabetic diseases in clinics, it provides further potential use of zinc for diabetic patients. Therefore, this review will briefly introduce the biochemical features of MT along with its critical roles in redox homeostasis and antioxidant function in the heart, and then discuss the current research on the prevention of diabetic cardiomyopathy by MT with an emphasis on experimental evidence, possible mechanisms, and clinical implications.

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.

Protective role of zinc-metallothionein on DNA damage in vitro by ferric nitrilotriacetate (Fe-NTA) and ferric salts

Oxidative DNA damage can be caused by radicals generated by transitional metals like iron in Fenton reaction. Metallothionein (MT) may play an important role in preventing oxidative DNA damage. Therefore, after comparing the effects of ferric salts (Fe), and complexes of ferric salts with nitrilotriacetic acid (Fe-NTA) on DNA damage, the protective effects of zinc-MT (Zn-MT) on DNA damage of Fe salts or Fe-NTA were investigated in vitro. DNA damage was measured by loss of fluorescence of DNA binding to ethidium bromide, and also by increased DNA mobility in agarose gel electrophoresis. Both Fe salts and Fe-NTA could induce calf thymus DNA damage in presence of hydrogen peroxide and ascorbate. However, the degree of DNA damage was lower with Fe salts than that with Fe-NTA complex. Addition of 50 microM Zn-MT could only protect DNA from Fe-NTA, but not from Fe salt induced damage. The protective effect of MT was about five times better than that of glutathione (GSH). These results suggest a potential role for MT in protection from Fe-NTA-induced DNA damage.

Induction of a cytogenetic adaptive response in germ cells of irradiated mice with very low-dose rate of chronic gamma-irradiation and its biological influence on radiation-induced DNA or chromosomal damage and cell killing in their male offspring

In earlier studies we have shown that either a single exposure or multiple exposures to a low dose of X-rays (0.05 Gy) induced a significant cytogenetic adaptive response in mouse germ cells. In this paper, a very low-dose rate (20 microGy/min) of chronic 60Co gamma-irradiation was used to pre-irradiate mice for 40 days. Then, another 40 days later, these mice were treated with a subsequent large dose of X-irradiation, followed 24 h later by cytogenetic analysis of their spermatocytes. Analysis for radiation-induced DNA and chromosomal damage was also carried out in splenocytes, bone marrow cells and spermatocytes of the offspring of mice adapted by the low-dose rate of chronic gamma-irradiation. Results demonstrated that (i) cumulative gamma-irradiation (1.10 Gy) at the dose rate 20 microGy/min induced a marked cytogenetic adaptive response in the mouse germ cells (stem spermatogonia); (ii) the sensitivity of offspring's bone marrow cells and spermatocytes to 1.5 Gy X-ray-induced chromosome aberrations was not influenced by the low-dose radiation delivered to paternal germ cells; (iii) either constitutive or post-irradiation DNA repair capacity (UV-induced unscheduled DNA synthesis, UDS) was not modified in the offspring's splenocytes; (iv) the sensitivity of the offspring's splenocytes to radiation-induced cell killing was also not altered. These results suggest that low-dose radiation delivered to the male parents with a significant induction of cytogenetic adaptive response in their germ cell does not likely cause any risk of damaging effects to the offspring of those irradiated male mice.

Roles of vitamin C in radiation-induced DNA damage in presence and absence of copper

Exposure to either ionizing radiation or certain transition metals results in generation of reactive oxygen species that induce DNA damage, mutation, and cancer. Vitamin C (a reactive oxygen scavenger) is considered to be a dietary radioprotective agent. However, it has been reported to be genotoxic in the presence of certain transition metals, including copper. In order to explore the capacity of vitamin C to protect DNA from radiation-induced damage, and the influence of the presence of copper on this protection, we investigated vitamin C-mediated protection against radiation-induced damage to calf thymus DNA in vitro in the presence or absence of copper(II). Vitamin C (0.08-8.00 mM, pH 7.0) significantly reduced DNA damage induced by gamma-irradiation (30-150 Gy) by 30-50%, similar to the protective effect of glutathione. However, vitamin C plus copper (50 microM) significantly enhanced gamma-radiation-induced DNA damage. Low levels of added copper (5 microM), or chelation of copper with 1-N-benzyltriethylenetetraine tetrahydrochloride (BzTrien) and bathocuprinedisulfonic acid (BCSA), abolished the enhanced damage without diminishing the protective effect of vitamin C. These results indicate that vitamin C can act as: (1) an antioxidant to protect DNA damage from ionizing radiation; and (2) a reducing agent in the presence of copper to induce DNA damage. These effects are important in assessing the role of vitamin C, in the presence of mineral supplements or radioprotective therapeutic agents, particularly in patients with abnormally high tissue copper levels.

Induction of an adaptive response to dominant lethality and to chromosome damage of mouse germ cells by low dose radiation

In the present paper, dominant lethal mutations, chromosome aberrations in spermatocytes and reciprocal translocations in stem spermatogonia were analyzed after whole body exposure of mice to X-radiation. Results both from chromosome aberrations in spermatocytes and for reciprocal translocations in spermatogonia showed that pre-exposure to low doses up to 200 mGy could induce a significant dose-dependent reduction in adapted mice compared to the non-adapted mice; the lower the adaptive dose, the greater the reduction. For dominant lethal mutations, it was found that spermatogonia (both stem cells and differentiated cells) and spermatocytes adapted to 50 mGy X-rays could show an adaptive response, but spermatids and spermatozoa could not.

Adaptive response to ionizing radiation-induced chromosome aberrations in rabbit lymphocytes: effect of pre-exposure to zinc, and copper salts

Various stress conditions including exposure to low-dose radiation and low concentrations of chemical mutagens can induce an adaptive response to subsequent radiation-induced chromosome damage. In this study, the effect of pretreatment of rabbit lymphocytes with zinc or copper salts on radiation-induced chromosome damage was investigated. Pretreatment of rabbit peripheral lymphocytes with Zn (50 microM in vitro or 100 mumol/g body weight in vivo) resulted in resistance to gamma radiation (2.0 Gy)-induced chromosome aberrations such as dicentrics plus centric rings and cells with chromosome aberrations. On the other hand, pretreatment with Cu (50 microM in vitro) did not show any protective effect on radiation-induced chromosome damage in rabbit lymphocytes. However, the concentration of metallothionein increased in activated lymphocytes 24 h after in vitro pretreatment with both Zn and Cu. In addition, gamma-radiation-induced calf thymus DNA damage could be prevented directly by the addition of Zn-metallothionein in the cell-free system. These results suggest that the induction of zinc-metallothionein synthesis may act as one of the defensive mechanisms to the induction of cytogenetic adaptive response to ionizing radiation while copper-metallothionein did not show any radioprotective effect.

Endothelin-1-mediated alteration of metallothionein and trace metals in the liver and kidneys of chronically diabetic rats

In the present study, the role of endothelin-1 (ET-1) on alterations of hepatic and renal metallothionein (MT) and trace metals (Zn, Cu, and Fe) were investigated in streptozotocin (STZ)-induced diabetic rats. Diabetic rats, age- and sex-matched controls, as well as control and diabetic animals on a dual ETA/ETB receptor blocker, bosentan, were investigated after 6 months of follow-up. MT was measured by cadmium-heme assay. Metals were measured by atomic absorption spectrometer. ET-1 mRNA was analyzed by reverse transcriptase-polymerase chain reaction (RT-PCR) technique. Hepatic and renal ET-1 mRNA was increased in diabetic rats as compared to control rats, along with an increase in both hepatic and renal MT proteins. The increased hepatic MT protein level was associated with decreases in hepatic Cu and Fe, whereas increased renal MT was associated with increases in renal Cu and Fe accumulation. Zn levels were unaltered in both organs in diabetic rats. Bosentan treatment partially prevented the increase in MT levels in both liver and kidney, along with reduced serum creatinine and increased urinary creatinine levels. Further bosentan treatment corrected the increased Cu and Fe levels in the kidney in diabetic rats, but reduced hepatic Cu and Fe levels. No significant effects of bosentan treatment on nondiabetic rats were observed. The data suggest that the possible effects of ET antagonism in diabetes may be mediated via changes in MT and trace metals.

Metallothionein induction in human CNS in vitro: neuroprotection from ionizing radiation

PURPOSE

There have been extensive studies on the regulation of metallothionein (MT) synthesis, and its biological role in liver and kidney. Although there are few reports on brain MT, there is a growing interest in the role of MT in brain. There have been no publications to date on MT synthesis in the human central nervous system (CNS) following exposure to ionizing radiation. In the present study, primary human CNS cultures were used to examine the effect of ionizing radiation on MT mRNA and protein synthesis. In the same cultures, the neuroprotective effects of zinc (Zn) and cadmium (Cd)-induced MT synthesis from high-dose radiation were also examined.

MATERIALS AND METHODS

Primary, serum-free, human CNS cultures were exposed to 30 or 60 Gy gamma-rays. The total MT protein was then measured by a Cd-heme assay, and mRNA for MT-II and MT-III was detected by reverse transcription polymerase chain reaction (RT-PCR). Cytotoxicity was measured by LDH release and apoptotic cell death by DNA fragmentation analysis. Sublethal neuroglial injury was assessed morphologically using specific astrocytic (glial fibrillary acidic protein--GFAP) and neuronal (microtubule-associated protein 2--MAP2) immunohistochemical markers.

RESULTS

The total MT protein content was increased 12h after exposure to 30Gy. The increase in MT content in response to 60Gy was not statistically significant. MT-II mRNA levels increased at 3 and 6h after exposure to 30Gy gamma-rays, with a maximum expression at 12-24 h. MT-III mRNA was not significantly affected. Exposure to 60 Gy, but not 30 Gy, caused a marked increase in LDH release. Cells exposed to 30 Gy or less showed some apoptotic cell death by DNA fragmentation analysis, while exposure to 60 Gy resulted in a DNA smear confirmed by LDH assays. Preinduction of MT by 5 microM Cd or 100 microM Zn resulted in a significant reduction in radiation-induced LDH release. Morphological evaluations revealed that Cd or Zn preincubation led to relative preservation of MAP2 staining and GFAP.

CONCLUSION

Both MT protein and MT-II mRNA can be induced in human CNS cells by ionizing radiation. Furthermore, induction of MT synthesis with Zn and Cd can protect human CNS cells from radiation-induced cytocidal and sublethal injuries. Both findings have implications in the development of strategies to protect human CNS tissue from damage during radiotherapy.

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.

Cytogenetic adaptive response with multiple small X-ray doses in mouse germ cells and its biological influence on the offspring of adapted males

Cytogenetic adaptive response of mouse germ cells was studied by exposing male mice to a sequence of 4 conditioning doses of 0.05 Gy each (D1) administered at 10-day intervals and subsequently to a single challenging dose of 1.5 Gy (D2). In concurrent experiments, male mice after treatment with D1 doses alone were mated to unirradiated females and the F1 males were given the D2 dose. Chromosomal aberrations in both spermatocytes and bone-marrow cells and UV-induced UDS in splenocytes of these mice were studied. Adapted mice (i.e., D1 + D2 exposures) responded with a significantly lower frequency of chromosomal aberrations than the non-adapted (D2 exposure only) controls. The relative reduction in frequencies was, however, similar to that observed in earlier work with a single conditioning dose of 0.05 Gy. The frequencies of chromosomal aberrations in spermatocytes and bone-marrow cells as well as the levels of UV-induced UDS in splenocytes of the F1 males in the group D1 to fathers + D2 to F1 males were the same as those in F1 males which received only the D2 exposure.

Induction of metallothionein synthesis with preservation of testicular function in rats following long term renal transplantation

Metallothionein (MT), as an acute phase or stress-response protein and free radical scavenger, is related to inflammation and cellular protection from oxidative damage. In order to evaluate long-term testicular damage and the role of MT following renal transplant, nine allogenic (Fisher 344 --> Lewis) and seven isogenic (Lewis --> Lewis) renal transplants were performed and the recipient rats were followed for 140 days when allografts develop chronic transplant rejection. Testicular weight, light microscopic morphology, and lactate dehydrogenase-X enzyme activity were assessed. Testicular MT was determined by Cd-heme assay, and was localized immunocytochemically using a polyclonal rabbit antibody. No differences in testis weight, morphology, or LDH-X enzyme activity were found between allograft and isograft recipients. Testicular MT level was significantly increased in the testis of allograft recipients. Testicular zinc (Zn) and copper (Cu) levels, but not iron (Fe) level, were significantly higher in testis with allograft kidney than that with isograft kidney. In addition, Cu/Zn ratio was also significantly high in the allograft group. However, the MT level did not show any significant correlation either with Cu and Zn alone or with Cu/Zn and Fe/Zn ratios. These data suggest that allogenic stimuli may induce MT synthesis in the recipient testis. The increased MT level in an allograft may offer a protective action from oxidative damage in the testis.