Role of metallothionein and other antioxidants in scavenging superoxide radicals and their possible role in neuroprotection

Structural and functional studies of vertebrate metallothioneins: cross-talk between domains in the absence of physical contact

In previous studies, we showed that the chemical and dynamic properties of fish and mouse MTs (metallothioneins) present a number of distinctive differences linked to their primary structures, and that phylogenetic relationships of mammal and fish MTs correlate with their three-dimensional structures. The different behaviours of MTs may also be linked to the interaction between their two domains. In the present study, we have compared the physicochemical properties of the isolated recombinant domains constituting Notothenia coriiceps and mouse MTs, and compared them with those of the corresponding whole MTs. NMR spectra of the separated domains of N. coriiceps are almost superimposable on those of the parent MT, suggesting an apparent lack of interaction between the two domains in the protein. However, certain dynamic and physicochemical features of the isolated domains are unlike those of the whole protein. In particular, the temperature-induced changes in the chiroptical properties, thiol reactivity of the Zn-MT domains and the Zn2+/Cd2+ rate of exchange are different for the two domains and with respect to the whole protein. Taken together, these results provide a strong argument in favour of the interaction of the two domains in the MT molecule, in spite of the elusive evidence provided by the structural analyses.

Plant metallothionein domains: functional insight into physiological metal binding and protein folding

Plant metallothioneins (MTs) differ from animal MTs by a peculiar sequence organization consisting of two short cysteine-rich terminal domains linked by a long cysteine-devoid spacer. The role of the plant MT domains in the protein structure and functionality is largely unknown. Here, we investigate the separate domain contribution to the in vivo binding of Zn and Cu and to confer metal tolerance to CUP1-null yeast cells of a plant type 2 MT (QsMT). For this purpose, we obtained three recombinant peptides that, respectively, correspond to the single N-terminal (N25) and C-terminal (C18) cysteine-rich domains of QsMT, and a chimera in which the spacer is replaced with a four-glycine bridge (N25-C18). The metal-peptide preparations recovered from Zn- or Cu-enriched cultures were characterized by ESI-MS, ICP-OES and CD and UV-vis spectroscopy and data compared to full length QsMT. Results are consistent with QsMT giving rise to homometallic Zn- or Cu-MT complexes according to a hairpin model in which the two Cys-rich domains interact to form a cluster. In this model the spacer region does not contribute to the metal coordination. However, our data from Zn-QsMT (but not from Cu-QsMT) support a fold of the spacer involving some interaction with the metal core. On the other hand, results from functional complementation assays in endogenous MT-defective yeast cells suggest that the spacer region may play a role in Cu-QsMT stability or subcellular localization. As a whole, our results provide the first insight into the structure/function relationship of plant MTs using the analysis of the separate domain abilities to bind physiological metals.

High intrinsic oxidative stress may underlie selective vulnerability of the hippocampal CA1 region

Oxidative stress (OS) causes extensive cell death in the CA1 but not the CA3 region of the hippocampus. We found that the CA1 region of hippocampus explants, cultured under normal conditions, had significantly higher superoxide levels and expressed both anti-oxidant genes and genes related to the generation of reactive oxygen species at significantly higher levels than the CA3. These observations were indicative of high intrinsic OS in CA1.

Metallothionein provides zinc-mediated protective effects against methamphetamine toxicity in SK-N-SH cells

Methamphetamine (METH) is a drug of abuse and neurotoxin that induces Parkinson's-like pathology after chronic usage by targeting dopaminergic neurons. Elucidation of the intracellular mechanisms that underlie METH-induced dopaminergic neuron toxicity may help in understanding the mechanism by which neurons die in Parkinson's disease. In the present study, we examined the role of reactive oxygen species (ROS) in the METH-induced death of human dopaminergic SK-N-SH cells and further assessed the neuroprotective effects of zinc and metallothionein (MT) against METH-induced toxicity in culture. METH significantly increased the production of reactive oxygen species, decreased intracellular ATP levels and reduced the cell viability. Pre-treatment with zinc markedly prevented the loss of cell viability caused by METH treatment. Zinc pre-treatment mainly increased the expression of metallothionein and prevented the generation of reactive oxygen species and ATP depletion caused by METH. Chelation of zinc by CaEDTA caused a significant decrease in MT expression and loss of protective effects of MT against METH toxicity. These results suggest that zinc-induced MT expression protects dopaminergic neurons via preventing the accumulation of toxic reactive oxygen species and halting the decrease in ATP levels. Furthermore, MT may prevent the loss of mitochondrial functions caused by neurotoxins. In conclusion, our study suggests that MT, a potent scavenger of free radicals is neuroprotective against dopaminergic toxicity in conditions such as drug of abuse and in Parkinson's disease.

Diaphragm unloading via controlled mechanical ventilation alters the gene expression profile

RATIONALE

Prolonged controlled mechanical ventilation results in diaphragmatic inactivity and promotes oxidative injury, atrophy, and contractile dysfunction in this important inspiratory muscle. However, the impact of controlled mechanical ventilation on global mRNA alterations in the diaphragm remains unknown.

OBJECTIVES

In these experiments, we used an Affymetrix oligonucleotide array to identify the temporal changes in diaphragmatic gene expression during controlled mechanical ventilation in the rat.

METHODS

Adult Sprague-Dawley rats were assigned to either control or mechanical ventilation groups (n = 5/group). Mechanically ventilated animals were anesthetized, tracheostomized, and ventilated with room air for 6 or 18 h. Animals in the control group were acutely anesthetized but not exposed to mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Compared with control diaphragms, microarray analysis identified 354 differentially expressed, unique gene products after 6 and 18 h of mechanical ventilation. In general, genes in the cell growth/cell maintenance, stress response, and nucleic acid metabolism categories showed predominant upregulation, whereas genes in the structural protein and energy metabolism categories were predominantly downregulated.

CONCLUSIONS

We conclude that mechanical ventilation results in rapid changes in diaphragmatic gene expression, and subsequently, many of these changes may contribute to atrophy and muscle fiber remodeling associated with unloading this primary inspiratory muscle. Importantly, this study also provides new insights into why the diaphragm, after the onset of contractile inactivity, atrophies more rapidly than locomotor skeletal muscles and also highlights unique differences that exist between these muscles in the mRNA response to inactivity.

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.

N-acetyl-L-cysteine ameliorates the inflammatory disease process in experimental autoimmune encephalomyelitis in Lewis rats

We report that N-acetyl-L-cysteine (NAC) treatment blocked induction of TNF-alpha, IL-1beta, IFN-gamma and iNOS in the CNS and attenuated clinical disease in the myelin basic protein induced model of experimental allergic encephalomyelitis (EAE) in Lewis rats. Infiltration of mononuclear cells into the CNS and induction of inflammatory cytokines and iNOS in multiple sclerosis (MS) and EAE have been implicated in subsequent disease progression and pathogenesis. To understand the mechanism of efficacy of NAC against EAE, we examined its effect on the production of cytokines and the infiltration of inflammatory cells into the CNS. NAC treatment attenuated the transmigration of mononuclear cells thereby lessening the neuroinflammatory disease. Splenocytes from NAC-treated EAE animals showed reduced IFN-gamma production, a Th1 cytokine and increased IL-10 production, an anti-inflammatory cytokine. Further, splenocytes from NAC-treated EAE animals also showed decreased nitrite production when stimulated in vitro by LPS. These observations indicate that NAC treatment may be of therapeutic value in MS against the inflammatory disease process associated with the infiltration of activated mononuclear cells into the CNS.

Metallothionein I and II mitigate age-dependent secondary brain injury

Both the immediate insult and delayed apoptosis contribute to functional deficits after brain injury. Secondary, delayed apoptotic death is more rapid in immature than in adult CNS neurons, suggesting the presence of age-dependent protective factors. To understand the molecular pathobiology of secondary injury in the context of brain development, we identified changes in expression of oxidative stress response genes during postnatal development and target deprivation-induced neurodegeneration. The antioxidants metallothionein I and II (MT I/II) were increased markedly in the thalamus of adult C57BL/6 mice compared to mice <15 days old. Target deprivation generates reactive oxygen species that mediate neuronal apoptosis in the central nervous system; thus the more rapid apoptosis observed in the immature brain might be due to lower levels of MT I/II. We tested this hypothesis by documenting neuronal loss after target-deprivation injury. MT I/II-deficient adult mice experienced greater thalamic neuron loss at 96 hr after cortical injury compared to that in controls (80 +/- 2% vs. 57 +/- 4%, P < 0.01), but not greater overall neuronal loss (84 +/- 4% vs. 79 +/- 3%, MT I/II-deficient vs. controls). Ten-day-old MT I/II-deficient mice, however, experienced both faster onset of secondary neuronal death (30 vs. 48 hr) and greater overall neuronal loss (88 +/- 2% vs. 69 +/- 4%, P = 0.02). MT I/II are thus inhibitors of age-dependent secondary brain injury, and the low levels of MT I/II in immature brains explains, in part, the enhanced susceptibility of the young brain to neuronal loss after injury. These findings have implications for the development of age-specific therapeutic strategies to enhance recovery after brain injury.

Identification and characterization of metallothionein-1 and -2 gene expression in the context of (+/-)3,4-methylenedioxymethamphetamine-induced toxicity to brain dopaminergic neurons

In mice, the recreational drug (+/-)3,4-methylenedioxymethamphetamine [MDMA ("ecstasy")] produces a selective toxic effect on brain dopamine (DA) neurons. Using cDNA microarray technology in combination with an approach designed to facilitate recognition of relevant changes in gene expression, the present studies sought to identify genes potentially involved in murine MDMA-induced toxicity to DA neurons. Of 15,000 mouse cDNA fragments studied, metallothionein (Mt)-1 and Mt2 emerged as candidate genes possibly involved in MDMA-induced toxicity to DA neurons. Northern blot analysis confirmed the microarray findings and revealed a dynamic upregulation of Mt1 and Mt2 mRNA in the ventral midbrain within 4-12 hr after MDMA treatment. Western blot analysis showed a similar increase in MT protein levels, with peak times occurring subsequent to increases in mRNA levels. Mt1-2 double knock-out mice were more vulnerable to MDMA-induced toxicity to DA neurons than corresponding wild-type mice. Stimulation of endogenous expression of MT protein with zinc acetate conferred complete protection against MDMA-induced toxicity to DA neurons, and administration of exogenous MT protein afforded partial protection. Collectively, these results indicate that MDMA-induced toxicity to DA neurons is associated with increased Mt1 and Mt2 gene transcription and translation, possibly as part of a neuroprotective mechanism. The present findings may have therapeutic implications for neuropathological conditions involving DA neurons.

Down-regulation of metallothionein, a reactive oxygen scavenger, by the small GTPase OsRac1 in rice

Metallothioneins are small, ubiquitous Cys-rich proteins known to be involved in reactive oxygen species (ROS) scavenging and metal homeostasis. We found that the expression of a metallothionein gene (OsMT2b) was synergically down-regulated by OsRac1 and rice (Oryza sativa) blast-derived elicitors. Transgenic plants overexpressing OsMT2b showed increased susceptibility to bacterial blight and blast fungus. OsMT2b-overexpressing cells showed reduced elicitor-induced hydrogen peroxide production. In contrast, homozygous OsMT2b::Tos17-inserted mutant and OsMT2b-RNAi-silenced transgenic cells showed significantly higher elicitor-induced hydrogen peroxide production than the wild-type cells. In vitro assay showed that recombinant OsMT2b protein possessed superoxide- and hydroxyl radical-scavenging activities. Taken together, these results showed that OsMT2b is an ROS scavenger and its expression is down-regulated by OsRac1, thus potentiating ROS, which function as signals in resistance response. The results suggest that OsRac1 plays a dual role as an inducer of ROS production and a suppressor of ROS scavenging.

Clinicopathological significance of metallothioneins in breast cancer

Metallothioneins (MTs) are a family of metal binding proteins that play an important role in maintaining transition metal ion homoeostasis, redox balance in the cell and fundamental cellular processes such as proliferation and apoptosis. In humans, there are 4 groups of MT proteins which are encoded by 10 functional MT isoforms. In breast tissues, MT is primarily expressed in myoepithelial and malignant epithelial cells. Immunohistochemical studies have revealed that 26% to 100% of invasive ductal breast cancers express the MT protein. The MT-1F and MT-2A isoforms have been reported to be associated with higher histological grade in breast cancer, whereas higher MT-1E mRNA expression was found in estrogen receptor-negative tumors compared to their estrogen receptor-positive counterparts. A number of studies have shown that MT expression in breast cancer is associated with poorer prognosis. In addition, metallothionein expression may have a potential role in protecting the breast cancer cell from chemotherapeutic threats to survival.

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.

Gene Expression Profile Changes Are Commonly Modulated across Models and Species after Traumatic Brain Injury

Brain trauma is a major cause of morbidity and mortality, both in adult and pediatric populations. Much of the functional deficit derives from delayed cell death resulting from induction of neurotoxic factors that overwhelm endogenous neuroprotective responses. To identify the potential molecular mechanisms underlying such delayed responses, we compared gene expression patterns using high-density oligonucleotide arrays at 4, 8, 24, and 72 h after moderate levels of lateral fluid percussion-induced brain injury in rats and lateral controlled cortical impact injury in mice (a total of 47 profiles). Expression of 82 genes in 12 functional categories was significantly changed in both species after trauma. The largest number of gene expression changes were found in the functional groups related to inflammation (17%), transcription regulation (16%), and cell adhesion/extracellular matrix (15%). Fifty percent of genes similarly altered across models had not been previously implicated in traumatic brain injury. Of particular interest were expression changes in genes linked to neurodegeneration, such as ATF3 and lysosomal membrane glycoprotein 2, and to neuroprotection including lipocortin 1, calponin 3, gelsolin, Id-1, and p45 NF-E2. Gene expression profiling across species and models may help identify candidate molecular pathways induced by brain injury, some of which may provide novel targets for therapeutic intervention.

Lipid peroxidation and antioxidant defence status during larval development and metamorphosis of giant prawn, Macrobrachium rosenbergii

In the present communication we studied the involvement of reactive oxygen species and alteration in antioxidant defence status during larval development and metamorphosis of giant prawn, Macrobrachium rosenbergii. Overall results indicate that there was a decline in endogenous lipid peroxidation level during larval development. Activity of superoxide dismutase was the lowest in early larval stages (Zoea-I and II) and thereafter increased in V and VI stages, followed by a decrease in the subsequent larval stages. Catalase and glutathione peroxidase did not exhibit specific pattern of changes during development. Reduced glutathione content exhibited an incremental increase during larval progression until metamorphosis. Ascorbic acid content of the larval tissue remained unaltered during development but a sharp fall was marked in its content in the post-larvae. Hence it is concluded that early larvae face high oxidative stress as evident from the high content of thiobarbituric acid reactive substances. This may be due to direct exposure of larvae to ambient oxygen of the water as well as their low antioxidant potential. However, during development with the augmentation in antioxidant reserve of the larval tissues a diminution in the oxidative stress was recorded. Thus it is presumed that antioxidant defences play an important role in providing protection to the developing larvae from oxidative assault during larval progression and metamorphosis.

Growth inhibitory factor prevents neurite extension and the death of cortical neurons caused by high oxygen exposure through hydroxyl radical scavenging

Growth inhibitory factor (GIF), a brain-specific member of the metallothionein family (MT-III), has been characterized as a inhibitory substance for neurotrophic factors in Alzheimer's disease brains. However, the function of GIF, other than the inhibition of neurotrophic factors, remains unknown. We demonstrate here that exogenous GIF prevents neurite extension of cortical neurons in the early period of differentiation and the death of differentiated neurons caused by high oxygen exposure. Down-regulation of GIF in cortical neurons with antisense S-oligonucleotides promoted neuronal death under high oxygen conditions. ESR spin-trapping studies demonstrated that GIF at 2-6 microm scavenged hydroxyl radicals generated by a Fenton-type reaction or the photolysis of hydrogen peroxide much more effectively than the same concentration of metallothionein I+II. GIF did not scavenge either superoxide produced by the xanthine/xanthine oxidase reaction or NO generated from 1-hydroxy-2-oxo-3-(N-methyl-3-aminopropyl)-3-methyl-1-triazene. Moreover, GIF at 40-80 microm inhibited tyrosine nitration by peroxynitrite as efficiently as metallothionein I+II at the same concentration. These results indicate that GIF prevents neurite extension of neurons in the early period of differentiation and supports the survival of differentiated neurons by scavenging hydroxyl radicals.

Effects of brief seizures during development

The effects of brief seizures during development depend on multiple factors such as underlying brain pathology, specific age of occurrence and frequency. Studies in rats are frequently used to determine the consequences of seizures in the developing brain. The shorter prepubertal development and life span of the rat compared to humans may suggest that brief seizures in the rat are not necessarily equivalent to brief seizures in humans. Nevertheless, there is substantial evidence that in the rat, the consequences of seizures are age-dependent. The immature brain is relatively resistant to morphological damage, especially in the hippocampus, and functional changes as measured by electrophysiology and behavior. Developmental kindling can be used as a model to study brief seizures early in life. Kindling permanently alters the brain so that rats stimulated again in adulthood require only few kindling stimuli for fully kindled seizures to occur although there are no apparent morphological and functional changes in the hippocampus resulting from kindling early in life. The appreciation that kindling can alter brain function without any discrete (to date) morphological changes may lead to the development of effective neuroprotective strategies to alter the process, but it is not clear that all kindling-induced changes are detrimental to the brain.

Age-related changes in expression of metallothionein-III in rat brain

Metallothionein (MT)-III is a metal binding protein, called growth inhibitory factor, and is mainly expressed in the central nervous system. Since MT-III decreases in the brain of Alzheimer's disease (AD), a growing interest has been focused on its relationship to neurodegenerative diseases. To clarify age-related changes in the MT-III expression and its inducibility against oxidative stress, we analyzed the expression of MT-III and its mRNA in the brain of lipopolysaccharide (LPS)-treated aged rats. In the frontal cortex, basal expression of MT-III mRNA was significantly increased with aging, while it was observed no induction of MT-III mRNA against LPS administration in the aged rat brain. MT-III immunopositive cells were increased in the frontal, parietal and piriform cortices, hypothalamus and amygdaloid nucleus with aging. The LPS treatment induced MT-III expression in the brain of young-adult rats, but not in the aged rat brain. Furthermore, the MT-III induction with LPS treatment was mainly observed in oligodendrocyte and microglia. In the present study, we showed that inducibility of brain MT-III against oxidative stress may be reduced with aging. Since it has been reported that MT-III has neuroprotective roles as an antioxidant, present results suggest that MT-III is closely related to the neurodegeneration in the aged animals.

Aggravation of 6-hydroxydopamine-induced dopaminergic lesions in metallothionein-I and -II knock-out mouse brain

The effects of two major isoforms of metallothioneins (MTs), MT-I and -II, on dopaminergic neurotoxicity of 6-hydroxydopamine (6-OHDA) were examined using intracerebroventricularly 6-OHDA-injected MT-I, II knock-out (KO) mice. The loss of dopamine neurons in the substantia nigra pars compacta induced by the 6-OHDA injection was significantly aggravated in the MT-I, II KO mice, compared with that in the 6-OHDA-injected wild-type mice. The present results, taken together with the antioxidant properties of MT-I and -II suggest that MT-I and -II exert neuroprotective effects against the dopaminergic neurotoxicity of 6-OHDA at the nigral cell body by scavenging free radicals.

Overexpression of metallothionein in pancreatic beta-cells reduces streptozotocin-induced DNA damage and diabetes

The release of reactive oxygen species (ROS) has been proposed as a cause of streptozotocin (STZ)-induced beta-cell damage. This initiates a destructive cascade, consisting of DNA damage, excess activation of the DNA repair enzyme poly(ADP-ribose) polymerase, and depletion of cellular NAD+. Metallothionein (MT) is an inducible antioxidant protein that has been shown to protect DNA from chemical damage in several cell types. Therefore, we examined whether overexpression of MT could protect beta-cell DNA and thereby prevent STZ-induced diabetes. Two lines of transgenic mice were produced with up to a 30-fold elevation in beta-cell MT. Cultured islets from control mice and MT transgenic mice were exposed to STZ. MT was found to decrease STZ-induced islet disruption, DNA breakage, and depletion of NAD+. To assess in vivo protection, transgenic and control mice were injected with STZ. Transgenic mice had significantly reduced hyperglycemia. Ultrastructural examination of islets from STZ-treated mice showed that MT prevented degranulation and cell death. These results demonstrate that MT can reduce diabetes and confirm the DNA damage mechanism of STZ-induced beta-cell death.

Expression of metallothionein-III mRNA and its regulation by levodopa in the basal ganglia of hemi-parkinsonian rats

In the brain, metallothionein (MT)-III exhibits a free radical scavenging activity. Here we examined the expression of MT-III mRNA in the basal ganglia of 6-hydroxydopamine (6-OHDA)-lesioned hemi-parkinsonian rats and its regulation by levodopa. The level of MT-III mRNA was significantly decreased in the striatum of 6-OHDA-lesioned side. Levodopa treatment significantly increased the expression of striatal MT-III mRNA in the non-lesioned side, but showed no significant effect in the 6-OHDA-lesioned side. These results suggest that the regulation of MT-III mRNA may be related to the progressive degeneration in parkinsonism.

Dietary vitamin-E modulates antioxidant defence system in giant freshwater prawn, Macrobrachium rosenbergii

The objectives of the present study were to determine the effect of supplementary vitamin-E (200, 400 and 600 mg/kg feed) on lipid peroxidation (LPX) and antioxidant defence system in gills and hepatopancreas of the freshwater prawn, Macrobrachium rosenbergii. Results indicated that vitamin-E inhibited LPX in the hepatopancreas in a comparatively lower dose than gills. Superoxide dismutase (SOD) activity was decreased significantly in gills in response to all the three supplemented diet, but in hepatopancreas decrease was observed only in response to higher doses of vitamin-E (400 and 600 mg/kg feed). Catalase (CAT) activity was reduced significantly only in gills but not in hepatopancreas. While glutathione peroxidase (GPX) activity was significantly elevated in the hepatopancreas by vitamin-E, its activity remains unaltered in gills. On the contrary, glutathione reductase (GR) activity was decreased in gills but that of hepatopancreas was constant. Glutathione (GSH) content of both gills and hepatopancreas was substantially elevated in the vitamin-E supplemented prawns. Although the ascorbic acid (ASA) content of gills was unchanged by vitamin-E, its level elevated significantly in hepatopancreas. Thus the findings of the present investigation suggest that dietary vitamin-E is capable of reducing LPX level and can modulate antioxidant defence system in gills and hepatopancreas, nevertheless, the response is highly tissue specific. It is further observed that highest dose of vitamin-E (600 mg/kg feed) could not render much additional protection in both the tissues.

Induction, regulation, degradation, and biological significance of mammalian metallothioneins

MTs are small cysteine-rich metal-binding proteins found in many species and, although there are differences between them, it is of note that they have a great deal of sequence and structural homology. Mammalian MTs are 61 or 62 amino acid polypeptides containing 20 conserved cysteine residues that underpin the binding of metals. The existence of MT across species is indicative of its biological demand, while the conservation of cysteines indicates that these are undoubtedly central to the function of this protein. Four MT isoforms have been found so far, MT-1, MT-2, MT-3, and MT-4, but these also have subtypes with 17 MT genes identified in man, of which 10 are known to be functional. Different cells express different MT isoforms with varying levels of expression perhaps as a result of the different function of each isoform. Even different metals induce and bind to MTs to different extents. Over 40 years of research into MT have yielded much information on this protein, but have failed to assign to it a definitive biological role. The fact that multiple MT isoforms exist, and the great variety of substances and agents that act as inducers, further complicates the search for the biological role of MTs. This article reviews the current knowledge on the biochemistry, induction, regulation, and degradation of this protein in mammals, with a particular emphasis on human MTs. It also considers the possible biological roles of this protein, which include participation in cell proliferation and apoptosis, homeostasis of essential metals, cellular free radical scavenging, and metal detoxification.

The absence of reactive astrocytosis is indicative of a unique inflammatory process in Parkinson's disease

Virtually any neurological disorder leads to activation of resident microglia and invasion of blood-borne macrophages, which are accompanied by an increase in number and change in phenotype of astrocytes, a phenomenon generally termed reactive astrocytosis. One of the functions attributed to activation of astrocytes is thought to involve restoration of tissue damage. Hitherto, the role of astrocytes in the inflammatory reaction occurring in Parkinson's disease has not received much attention. In the present study, we examined the inflammatory events in autopsies of the substantia nigra and putamen from Parkinson's disease patients using age-matched autopsies from normal patients as controls. In the substantia nigra, activation of microglia was consistently observed in all Parkinson's disease autopsies as verified from immunohistochemical detection of CR3/43 and ferritin. Activation of resident microglia was not observed in the putamen. No differences were observed between controls and Parkinson's disease autopsies from the substantia nigra and putamen, in terms of distribution, cellular density or cellular morphology of astrocytes stained for glial fibrillary acidic protein or metallothioneins I and II, the latter sharing high affinity for metal ions and known to be induced in reactive astrocytes, possibly to exert anti-oxidative effects. Together, these findings indicate that the inflammatory process in Parkinson's disease is characterized by activation of resident microglia without reactive astrocytosis, suggesting that the progressive loss of dopaminergic neurons in Parkinson's disease is an ongoing neurodegenerative process with a minimum of involvement of the surrounding nervous tissue. The absence of reactive astrocytosis in Parkinson's disease contrasts what follows in virtually any other neurological disorder and may indicate that the inflammatory process in Parkinson's disease is a unique phenomenon.

Silica-induced chemokine expression in alveolar type II cells is mediated by TNF-alpha-induced oxidant stress

We have shown previously that epithelial cells may contribute to the inflammatory response in the lung after exposure to crystalline silica through the production of and response to specific chemokines and cytokines. However, the exact cellular and molecular responses of epithelial cells to silica exposure remain unclear. We hypothesize that non-oxidant-mediated silica-cell interactions lead to the upregulation of tumor necrosis factor-alpha (TNF-alpha), whereby TNF-alpha-induced generation of reactive oxygen species (ROS) leads to the activation of the monocyte chemotactic protein (MCP)-1 and macrophage inflammatory protein (MIP)-2 genes. Using a murine alveolar type II cell line, murine lung epithelial (MLE)-15, we measured the early changes in TNF-alpha, MCP-1, and MIP-2 mRNA species after exposure of the cells to 18 micrograms/cm2 silica (cristobalite) in combination with various antioxidants. Total mRNA was isolated and assayed using an RNase protection assay after 6 h of particle exposure. We found that extracellular GSH could completely attenuate the cristobalite-induced expression of MCP-1 and MIP-2 mRNAs, whereas TNF-alpha mRNA levels were unaltered. We also found using the oxidant-sensitive dye 6-carboxy-2', 7'-dichlorodihydrofluorescein diacetate di(acetoxymethyl ester) that treatment of MLE-15 cells with cristobalite and TNF-alpha (1 ng/ml) resulted in ROS production. This ROS production could be inhibited with extracellular GSH treatment, and in the case of cristobalite-induced ROS, inhibition was also achieved with an anti-TNF-alpha antibody. The results support the hypothesis that TNF-alpha mediates cristobalite-induced MCP-1 and MIP-2 expression through the generation of ROS.