Interaction of DJ-1 with Daxx inhibits apoptosis signal-regulating kinase 1 activity and cell death

Investigations into the cellular and molecular biology of genes that cause inherited forms of Parkinson's disease, as well as the downstream pathways that they trigger, shed considerable light on our understanding the fundamental determinants of life and death in dopaminergic neurons. Homozygous deletion or missense mutation in DJ-1 results in autosomal recessively inherited Parkinson's disease, suggesting that wild-type DJ-1 has a favorable role in maintaining these neurons. Here, we show that DJ-1 protects against oxidative stress-induced cell death, but that its relatively modest ability to quench reactive oxygen species is insufficient to account for its more robust cytoprotective effect. To elucidate the mechanism of this cell-preserving function, we have screened out the death protein Daxx as a DJ-1-interacting partner. We demonstrate that wild-type DJ-1 sequesters Daxx in the nucleus, prevents it from gaining access to the cytoplasm, from binding to and activating its effector kinase apoptosis signal-regulating kinase 1, and therefore, from triggering the ensuing death pathway. All these steps are impaired by the disease-causing L166P mutant isoform of DJ-1. These findings suggest that the regulated sequestration of Daxx in the nucleus and keeping apoptosis signal-regulating kinase 1 activation in check is a critical mechanism by which DJ-1 exerts its cytoprotective function.

Characterization of cellular uptake and distribution of vitamin E

We previously reported that tocotrienols acted as more potent inhibitors against selenium deficiency-induced cell death than the corresponding tocopherol isoforms (J. Biol. Chem. 2003;278:39428-39434). In the present study, we first compared the differences in the cellular uptake between alpha-tocopherol (alpha-Toc) and alpha-tocotrienol (alpha-Toc-3). The initial rate of cellular uptake of alpha-Toc-3 was 70-fold higher than that of alpha-Toc. Subcellular fractionation analysis of alpha-Toc-3 and alpha-Toc-fortified cells showed similar cellular distribution of these antioxidants, which was directly proportional to the lipid distribution. The cells containing similar amounts of alpha-Toc-3 and alpha-Toc showed similar resistance against the oxidative stress caused by peroxides. These results suggest that the apparent higher cytoprotective effect of alpha-Toc-3 than alpha-Toc is primarily ascribed to its higher cellular uptake.

The distal sequence element of the selenocysteine tRNA gene is a tissue-dependent enhancer essential for mouse embryogenesis

Appropriate expression of the selenocysteine tRNA (tRNA(Sec)) gene is necessary for the production of an entire family of selenoprotein enzymes. This study investigates the consequence of disrupting an upstream enhancer region of the mouse tRNA(Sec) gene (Trsp) known as the distal sequence element (DSE) by use of a conditional repair gene targeting strategy, in which a 3.2-kb insertion was introduced into the promoter of the gene. In the absence of DSE activity, homozygous mice failed to develop in utero beyond embryonic day 7.5 and had severely decreased levels of selenoprotein transcript. Cre-mediated removal of the selection cassette recovered DSE regulation of Trsp, restoring wild-type levels of tRNA(Sec) expression and allowing the generation of viable rescued mice. Further analysis of targeted heterozygous adult mice revealed that the enhancer activity of the DSE is tissue dependent since, in contrast to liver, heart does not require the DSE for normal expression of Trsp. Similarly, in mouse cell lines we showed that the DSE functions as a cell-line-specific inducible element of tRNA(Sec). Together, our data demonstrate that the DSE is a tissue-dependent regulatory element of tRNA(Sec) expression and that its activity is vital for sufficient tRNA(Sec) production during mouse embryogenesis.

A Computational Study of Thiolate and Selenolate Oxidation by Hydrogen Peroxide

Ab initio molecular orbital calculations have been used to study the effects of the molecular environment on the oxidation of thiolate and selenolate by hydrogen peroxide. The reaction was first examined in vacuo at the QCISD(T)/6-311+G(2df,2pd)//MP2/6-311+G(d,p) level of theory. It was found for both thiolate and selenolate that a reactant aggregate is formed, which has a dissociation rate constant comparable to the activation rate constant (about 10(-3) s(-1) for thiolate and 10(-1) s(-1) for selenolate). Using the polarizable continuum model (PCM) it was then found that the dissociation barrier energy decreases dramatically in water giving a dissociation rate constant of the order of 10(9) s(-1). In this case, the predicted overall rate constant of the thiolate reaction was about 10.2 mol(-1) dm3 s(-1), which is in good agreement with the experimental rate constant of cysteine oxidation in aqueous solution. The calculated rate constant for the selenolate reaction was somewhat higher (about 35.4 mol(-1) dm3 s(-1)). However, this value is several orders of magnitude smaller than the experimental value reported for the oxidation of selenocysteine in glutathione peroxidase. By considering the effect of the PCM dielectric constant on the reaction rate constant it was concluded that the high reactivity of the selenocysteine in glutathione peroxidase, as compared with cysteine, could be mainly due to the molecular environment of the selenocysteine residue.

Mitochondrial localization of the Parkinson's disease related protein DJ-1: implications for pathogenesis

Both homozygous (L166P, M26I, deletion) and heterozygous mutations (D149A, A104T) in the DJ-1 gene have been identified in Parkinson's disease (PD) patients. The biochemical function and subcellular localization of DJ-1 protein have not been clarified. To date the localization of DJ-1 protein has largely been described in studies over-expressing tagged DJ-1 protein in vitro. It is not known whether the subcellular localization of over-expressed DJ-1 protein is identical to that of endogenously expressed DJ-1 protein both in vitro and in vivo. To clarify the subcellular localization and function of DJ-1, we generated three highly specific antibodies to DJ-1 protein and investigated the subcellular localization of endogenous DJ-1 protein in both mouse brain tissues and human neuroblastoma cells. We have found that DJ-1 is widely distributed and is highly expressed in the brain. By cell fractionation and immunogold electron microscopy, we have identified an endogenous pool of DJ-1 in mitochondrial matrix and inter-membrane space. To further investigate whether pathogenic mutations might prevent the distribution of DJ-1 to mitochondria, we generated human neuroblastoma cells stably transfected with wild-type (WT) or mutant (M26I, L166P, A104T, D149A) DJ-1 and performed mitochondrial fractionation and confocal co-localization imaging studies. When compared with WT and other mutants, L166P mutant exhibits largely reduced protein level. However, the pathogenic mutations do not alter the distribution of DJ-1 to mitochondria. Thus, DJ-1 is an integral mitochondrial protein that may have important functions in regulating mitochondrial physiology. Our findings of DJ-1's mitochondrial localization may have important implications for understanding the pathogenesis of PD.

Relationship of coffee consumption with risk factors of atherosclerosis in rats

AIMS

In experimental animals we investigated the relationship of coffee consumption with risk factors of atherosclerosis such as cholesterol, homocysteine, oxidative stress and inflammatory cytokines.

METHODS

Forty-eight male Wistar rats were assigned to 3 treatment groups (a control diet group, 0.62% coffee diet group, and 1.36% coffee diet group), and animals were maintained on the experimental diets for 140 days.

RESULTS

Coffee diets led to an increase in the caffeine concentration to 0.53 +/- 0.11 and 1.77 +/- 0.22 microg/ml, respectively, although caffeine in serum was not detected in rats fed the control diet. It also led to slightly increased total serum levels of homocysteine and cholesterol, but no significant differences were found between the control and coffee diet groups. Coffee intake did not affect the production of IL-6 and TNF-alpha induced by LPS, which contributes to the atheroma-promoting effect of recurrent bacterial infection. Regarding the biomarkers of oxidative stress, the serum level of 15-isoprostane F(2t), which was significantly increased by LPS injection, was not altered by coffee intake. In contrast, urinary 8-hydroxy-2-deoxyguanosine was significantly increased in the coffee diet groups (p < 0.05). On the other hand, serum glutathione peroxidase (GPx) activity tended to decrease in the coffee groups compared with the control group, but no significant difference was found between the control and coffee diet groups. Interestingly, a significant negative correlation was observed between GPx activity and homocysteine levels in the sera from control and coffee diet groups (r = -0.403, p < 0.05).

CONCLUSIONS

This report is the first animal study on the relationship of coffee consumption with risk factors for atherosclerosis. From these results, we conclude that moderate coffee intake is not a risk factor for atherogenesis.

Cytotoxic effect of formaldehyde with free radicals via increment of cellular reactive oxygen species

It is well known that formaldehyde (HCHO) and reactive oxygen species (ROS), such as free radicals, are cytotoxic as well as potentially carcinogenic. Although the individual effects of these reactants on cells have been investigated, the cytotoxicity exerted by the coexistence of HCHO and reactive radicals is poorly understood. The present study using Jurkat cells demonstrated that the coexistence of HCHO with water-soluble radical initiator, 2,2'-azobis-[2-(2-imidazolin-2-yl)propane] dihydrochloride (AIPH) dramatically decreased cell viability, and that under such conditions scant cell death was observable induced by either of the reactants alone. Based on the results of phosphatidylserine exposure and caspase activation, this observed cell death, in fact, was apparently necrotic rather than apoptotic. To understand the mechanisms of the cell toxicity of HCHO and AIPH, we assessed two kinds of oxidative stress markers such as cellular glutathione (GSH) content and cellular ROS, and the DNA-protein cross-links, which formed as the result of HCHO treatment. A marked decrease in total cellular GSH was observed not only in the case of the coexistence conditions but also with AIPH alone. Dichlorodihydrofluorescein (DCF) assay revealed that cellular ROS were synergistically increased before cell death. The formation of DNA-protein cross-links was observed in the presence of HCHO and AIPH, and the extent was similar to HCHO alone. Co-incubation with semicarbazide, which inactivates HCHO, prevented this cell death induced by a combination of HCHO and AIPH. Semicarbazide also exhibited an inhibitory effect on the synergistic increment of cellular ROS and the formation of DNA-protein cross-links. These results suggest that the free radicals from AIPH induced GSH reduction, while HCHO resulted in the formation of DNA-protein cross-links, eventuating in a synergistic, incremental increase of cellular ROS and cell death brought about by this combination.

Genes involved in nonpermissive temperature-induced cell differentiation in Sertoli TTE3 cells bearing temperature-sensitive simian virus 40 large T-antigen

Sertoli TTE3 cells, derived from transgenic mice bearing temperature-sensitive simian virus 40 large T (tsSV40LT)-antigen, proliferated continuously at a permissive temperature (33 degrees C) whereas inactivation of the large T-antigen by a nonpermissive temperature (39 degrees C) led to differentiation as judged by elevation of transferrin. To clarify the detailed mechanisms of differentiation, we investigated the time course of changes in gene expression using cDNA microarrays. Of the 865 genes analyzed, 14 genes showed increased levels of expression. Real-time quantitative PCR revealed that the mRNA levels of p21(waf1), milk fat globule membrane protein E8, heat-responsive protein 12, and selenoprotein P were markedly elevated. Moreover, the differentiated condition induced by the nonpermissive temperature significantly increased mRNA levels of these four genes in several cell lines from the transgenic mice bearing the oncogene. The present results regarding changes in gene expression will provide a basis for a further understanding of molecular mechanisms of differentiation in both Sertoli cells and cell lines transformed by tsSV40LT-antigen.

Lipid peroxidation during ischemia depends on ischemia time in warm ischemia and reperfusion of rat liver

Prolonged hepatic warm ischemia has been incriminated in oxidative stress after reperfusion. However, the magnitude of oxidative stress during ischemia has been controversial. The aims of the present study were to elucidate whether lipid peroxidation progressed during ischemia and to clarify whether oxidative stress during ischemia aggravated the oxidative damage after reperfusion. Rats were subjected to 30 to 120 min of 70% warm ischemia alone or followed by reperfusion for 60 min. Lipid peroxidation (LPO) was evaluated by amounts of phosphatidylcholine hydroperoxide (PC-OOH) and phosphatidylethanolamine hydroperoxide (PE-OOH) as primary LPO products. Total amounts of malondialdehyde and 4-hydroxy-2-nonenal (MDA + 4-HNE), degraded from hydroperoxides, were also determined. PC-OOH and PE-OOH significantly increased at 60 and 120 min ischemia with concomitant increase of oxidized glutathione. These hydroperoxides did not increase at 60 min reperfusion after 60 min ischemia, whereas they did increase at 60 min reperfusion after 120 min ischemia with deactivation of phospholipid hydroperoxide glutathione peroxidase and superoxide dismutase. The amount of MDA + 4-HNE exhibited similar changes, but the velocity of production dropped with ischemic time longer than 60 min. In conclusion, oxidative stress progressed during ischemia and triggered the oxidative injury after reperfusion. Secondary LPO products are less sensitive, especially during ischemia, which may cause possible underestimation and discrepancy.

Hsp70 gene transfer by adeno-associated virus inhibits MPTP-induced nigrostriatal degeneration in the mouse model of Parkinson disease

Mitochondrial dysfunction and oxidative stress have been implicated in Parkinson disease (PD). In addition, genetic evidence points to an important role of protein misfolding, aggregation, and failure in the proteasomal degradation of specific neuronal proteins in the pathogenesis of PD. The chaperone heat-shock protein 70 (Hsp70) reduces protein misfolding and aggregation and protects cells against a variety of adverse conditions, including oxidative stress. Moreover, Hsp70 exerts antiapoptotic activity by blocking the function of several key proapoptotic factors. Recently, Hsp70 was shown to inhibit alpha-synuclein toxicity in a Drosophila model of inherited PD. Here we tested the potential of Hsp70 (approved gene symbol HSPA1A) for gene therapy in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of idiopathic PD. We show that Hsp70 gene transfer to dopamine neurons by a recombinant adeno-associated virus significantly protects the mouse dopaminergic system against MPTP-induced dopamine neuron loss and the associated decline in striatal dopamine levels and tyrosine hydroxylase-positive fibers. Hsp70 reduced MPTP-induced apoptosis in the substantia nigra, and unilateral protection of the dopaminergic system by Hsp70 was associated with increased amphetamine-induced turning toward the uninjected side. Collectively, these results suggest that increasing chaperone activity may be beneficial for the treatment of idiopathic PD.

Selenoprotein expression in Hürthle cell carcinomas and in the human Hürthle cell carcinoma line XTC.UC1

Hürthle cell carcinomas (HTC) are characterized by mitochondrial amplification and enhanced oxygen metabolism. To clarify if defects in enzymes scavenging reactive oxygen species are involved in the pathogenesis of HTC, we analyzed selenium (Se)-dependent expression of various detoxifying selenoproteins in the HTC cell line XTC.UC1. Glutathione peroxidase and thioredoxin reductase activity was found both in cell lysates and conditioned media of XTC.UC1 cells and was increased by Na(2)SeO(3). Western blot analysis demonstrated the presence of thioredoxin reductase both in cell lysates and conditioned media and of glutathione peroxidase 3 in conditioned media. Type I 5'-deiodinase, another selenoprotein that catalyzes thyroid hormone metabolism, was detectable only in cell lysates by enzyme assay and Western blot, and responded to stimulation by both Na(2)SeO(3) and retinoic acid. A selenoprotein P signal was detected in conditioned media by Western blot, but was not enhanced by Na(2)SeO(3) treatment. In situ hybridization revealed glutathione peroxidase mRNAs in HTC specimen; glutathione peroxidase 3 mRNA levels were reduced. These data suggest adequate expression and Se-dependent regulation of a couple of selenoproteins involved in antioxidant defense and thyroid hormone metabolism in XTC.UC1 cells, so far giving no evidence of a role of these proteins in the pathogenesis of HTCs.

The role of glutathione in cancer

Glutathione is an abundant natural tripeptide found within almost all cells. Glutathione is highly reactive and is often found conjugated to other molecules via its sulfhydryl moiety. It instils several vital roles within a cell including antioxidation, maintenance of the redox state, modulation of the immune response and detoxification of xenobiotics. With respect to cancer, glutathione metabolism is able to play both protective and pathogenic roles. It is crucial in the removal and detoxification of carcinogens, and alterations in this pathway, can have a profound effect on cell survival. However, by conferring resistance to a number of chemotherapeutic drugs, elevated levels of glutathione in tumour cells are able to protect such cells in bone marrow, breast, colon, larynx and lung cancers. Here we present a number of studies investigating the role of glutathione in promoting cancer, impeding chemotherapy, and the use of glutathione modulation to enhance anti-neoplastic therapy.

Effectiveness of selenium supplements in a low-selenium area of China

BACKGROUND

Selenium is an essential micronutrient with a recommended dietary allowance for adults of 55 mug/d. It functions as an essential constituent of selenoproteins. Although there is no evidence of selenium deficiency in the United States, people in many other areas of the world are selenium deficient, with the consequence that they are unable to express their selenoproteins fully.

OBJECTIVE

We carried out a supplementation trial in a selenium-deficient population in China to assess the requirement for selenium as selenite and as selenomethionine.

DESIGN

One hundred twenty subjects with an average selenium intake of 10 mug/d were randomly assigned and administered tablets containing no selenium or amounts as high as 66 mug Se/d for 20 wk. Plasma was sampled before supplementation and at 4-wk intervals during supplementation and was assayed for the 2 plasma selenoproteins, glutathione peroxidase and selenoprotein P.

RESULTS

Full expression of glutathione peroxidase was achieved with 37 mug Se/d as selenomethionine and with 66 mug/d as selenite. Full expression of selenoprotein P was not achieved at the highest doses of either form.

CONCLUSIONS

Full expression of selenoprotein P requires a greater selenium intake than does full expression of plasma glutathione peroxidase. This suggests that selenoprotein P is a better indicator of selenium nutritional status than is glutathione peroxidase and that the recommended dietary allowance of selenium, which was set with the use of glutathione peroxidase as the index of selenium status, should be revised. Selenium as selenomethionine had nearly twice the bioavailability of selenium as selenite.

Age-dependent motor deficits and dopaminergic dysfunction in DJ-1 null mice

Mutations in the DJ-1 gene were recently identified in an autosomal recessive form of early-onset familial Parkinson disease. Structural biology, biochemistry, and cell biology studies have suggested potential functions of DJ-1 in oxidative stress, protein folding, and degradation pathways. However, animal models are needed to determine whether and how loss of DJ-1 function leads to Parkinson disease. We have generated DJ-1 null mice with a mutation that resembles the large deletion mutation reported in patients. Our behavioral analyses indicated that DJ-1 deficiency led to age-dependent and task-dependent motoric behavioral deficits that are detectable by 5 months of age. Unbiased stereological studies did not find obvious dopamine neuron loss in 6-month- and 11-month-old mice. Neurochemical examination revealed significant changes in striatal dopaminergic function consisting of increased dopamine reuptake rates and elevated tissue dopamine content. These data represent the in vivo evidence that loss of DJ-1 function alters nigrostriatal dopaminergic function and produces motor deficits.

The Parkinson's disease-associated DJ-1 protein is a transcriptional co-activator that protects against neuronal apoptosis

Mutations in the DJ-1 gene cause early-onset autosomal recessive Parkinson's disease (PD), although the role of DJ-1 in the degeneration of dopaminergic neurons is unresolved. Here we show that the major interacting-proteins with DJ-1 in dopaminergic neuronal cells are the nuclear proteins p54nrb and pyrimidine tract-binding protein-associated splicing factor (PSF), two multifunctional regulators of transcription and RNA metabolism. PD-associated DJ-1 mutants exhibit decreased nuclear distribution and increased mitochondrial localization, resulting in diminished co-localization with co-activator p54nrb and repressor PSF. Unlike pathogenic DJ-1 mutants, wild-type DJ-1 acts to inhibit the transcriptional silencing activity of the PSF. In addition, the transcriptional silencer PSF induces neuronal apoptosis, which can be reversed by wild-type DJ-1 but to a lesser extent by PD-associated DJ-1 mutants. DJ-1-specific small interfering RNA sensitizes cells to PSF-induced apoptosis. Both DJ-1 and p54nrb block oxidative stress and mutant alpha-synuclein-induced cell death. Thus, DJ-1 is a neuroprotective transcriptional co-activator that may act in concert with p54nrb and PSF to regulate the expression of a neuroprotective genetic program. Mutations that impair the transcriptional co-activator function of DJ-1 render dopaminergic neurons vulnerable to apoptosis and may contribute to the pathogenesis of PD.

Hypersensitivity of DJ-1-deficient mice to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine (MPTP) and oxidative stress

Mutations of the DJ-1 (PARK7) gene are linked to familial Parkinson's disease. We used gene targeting to generate DJ-1-deficient mice that were viable, fertile, and showed no gross anatomical or neuronal abnormalities. Dopaminergic neuron numbers in the substantia nigra and fiber densities and dopamine levels in the striatum were normal. However, DJ-1-/- mice showed hypolocomotion when subjected to amphetamine challenge and increased striatal denervation and dopaminergic neuron loss induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine. DJ-1-/-embryonic cortical neurons showed increased sensitivity to oxidative, but not nonoxidative, insults. Restoration of DJ-1 expression to DJ-1-/- mice or cells via adenoviral vector delivery mitigated all phenotypes. WT mice that received adenoviral delivery of DJ-1 resisted 1-methyl-4-phenyl-1,2,3,6-tetrahydropyrindine-induced striatal damage, and neurons overexpressing DJ-1 were protected from oxidative stress in vitro. Thus, DJ-1 protects against neuronal oxidative stress, and loss of DJ-1 may lead to Parkinson's disease by conferring hypersensitivity to dopaminergic insults.

DJ-1, a novel regulator of the tumor suppressor PTEN

The phosphatidylinositol 3' kinase (PI3'K) pathway, which regulates cell survival, is antagonized by the PTEN tumor suppressor. The regulation of PTEN is unclear. A genetic screen of Drosophila gain-of-function mutants identified DJ-1 as a suppressor of PTEN function. In mammalian cells, DJ-1 underexpression results in decreased phosphorylation of PKB/Akt, while DJ-1 overexpression leads to hyperphosphorylation of PKB/Akt and increased cell survival. In primary breast cancer samples, DJ-1 expression correlates negatively with PTEN immunoreactivity and positively with PKB/Akt hyperphosphorylation. In 19/23 primary non-small cell lung carcinoma samples, DJ-1 expression was increased compared to paired nonneoplastic lung tissue, and correlated positively with relapse incidence. DJ-1 is thus a key negative regulator of PTEN that may be a useful prognostic marker for cancer.

Quantitative proteomic analysis of mitochondrial proteins: relevance to Lewy body formation and Parkinson's disease

The mechanisms underlying Parkinson's disease (PD) and Lewy body (LB) formation, a pathological hallmark of PD, are incompletely understood; however, mitochondrial dysfunction is likely to be at least partially responsible. To study the processes that might be related to nigral neurodegeneration and LB formation, we employed nonbiased quantitative proteomics with isotope-coded affinity tag (ICAT) to compare the mitochondrial protein profiles in the substantia nigra (SN) between controls and mice treated chronically with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), a potent mitochondrial toxicant, and an adjuvant, probenecid (prob), for 5 weeks, which produced selective nigrostriatal neurodegeneration with formation of LB-like cytoplasmic inclusions in the remaining nigral neurons. This method identified a total of more than 300 proteins; of these proteins, more than 100 displayed significant changes in relative abundance in the MPTP/prob-treated mice compared to the controls. We validated one of these proteins, DJ-1, whose mutation has been implicated in familial PD, with Western blot analysis, followed by immunohistochemical studies of its distribution in the SN in relation to cytoplasmic inclusions in mice, as well as in classical LBs in PD patients. The results demonstrated that DJ-1 was not only colocalized with alpha-synuclein in dopaminergic neurons but also to cytoplasmic inclusions in mice treated with MPTP/prob. In addition, DJ-1 was present in the halo but not in the core of classical LBs in patients with PD. Our findings suggested that DJ-1 might play an important role in mitochondrial dysfunction, as well as LB formation in PD.

Long-chain carboxychromanols are the major metabolites of tocopherols and tocotrienols in A549 lung epithelial cells but not HepG2 cells

Human lung type II cell derived A549 epithelial cancer cells and HepG2 hepatocytes constitutively express cytochrome P4504F2, a P450 we previously identified as a tocopherol-omega-hydroxylase. To determine if A549 cells would metabolize tocochromanols via the omega-hydroxylase pathway, we compared the metabolism of tocopherols (alpha-, gamma-, delta-TOH) and tocotrienols (alpha-, gamma-, delta-T3) in these 2 cell lines. Cultures were incubated with alpha-, gamma-, or delta-TOH, or the analogous T3s, and synthesis of their metabolites quantitated by GC-MS. A549 cells metabolized all tocochromanols 2-3 times more extensively than HepG2 cells (P < 0.001) except alpha-TOH, a difference not related to cell uptake of substrate but rather was reflective of greater microsomal TOH-omega-hydroxylase enzyme activity. Notably, 9'-carboxychromanols were the major metabolites of all gamma- and delta-TOHs and T3s in A549 cultures, whereas 3'- and 5'-carboxychromanols predominated in HepG2 cultures. Accumulation of 9'-carboxychromanols in A549 cultures was due to their inefficient conversion to 7'-carboxychromanols relative to HepG2 cells. Sesamin inhibited tocochromanol metabolism in both cells types, and neither cell type exhibited evidence of alternative (sesamin-insensitive) pathways of metabolism. TOH-omega-hydroxylase activity was undetectable in rat primary lung type II cells, suggesting that expression of activity was associated with transformation of normal type II cells to cancer cells. Long-chain carboxychromanol metabolites of gamma-TOH and other forms of vitamin E can be biosynthesized in A549 cultures for assessment of their biological activity, including their potential inhibition of synthesis of inflammatory mediators.

Engineering glutathione transferase to a novel glutathione peroxidase mimic with high catalytic efficiency. Incorporation of selenocysteine into a glutathione-binding scaffold using an auxotrophic expression system

Glutathione peroxidase (GPx, EC 1.11.1.9) protects cells against oxidative damage by catalyzing the reduction of hydroperoxides with glutathione (GSH). Several attempts have been made to imitate its function for mechanical study and for its pharmacological development as an antioxidant. By replacing the active site serine 9 with a cysteine and then substituting it with selenocysteine in a cysteine auxotrophic system, catalytically essential residue selenocysteine was bioincorporated into GSH-specific binding scaffold, and thus, glutathione S-transferase (GST, EC 2.5.1.18) from Lucilia cuprina was converted into a selenium-containing enzyme, seleno-LuGST1-1, by genetic engineering. Taking advantage of the important structure similarities between seleno-LuGST1-1 and naturally occurring GPx in the specific GSH binding sites and the geometric conformation for the active selenocysteine in their common GSH binding domain-adopted thioredoxin fold, the as-generated selenoenzyme displayed a significantly high efficiency for catalyzing the reduction of hydrogen peroxide by glutathione, being comparable with those of natural GPxs. The catalytic behaviors of this engineered selenoenzyme were found to be similar to those of naturally occurring GPx. It exhibited pH and temperature-dependent catalytic activity and a typical ping-pong kinetic mechanism. Engineering GST into an efficient GPx-like biocatalyst provided new proof for the previous assumption that both GPx and GST were evolved from a common thioredoxin-like ancestor to accommodate different functions throughout evolution.

Mitochondria take center stage in aging and neurodegeneration

A critical role of mitochondrial dysfunction and oxidative damage has been hypothesized in both aging and neurodegenerative diseases. Much of the evidence has been correlative, but recent evidence has shown that the accumulation of mitochondrial DNA mutations accelerates normal aging, leads to oxidative damage to nuclear DNA, and impairs gene transcription. Furthermore, overexpression of the antioxidant enzyme catalase in mitochondria increases murine life span. There is strong evidence from genetics and transgenic mouse models that mitochondrial dysfunction results in neurodegeneration and may contribute to the pathogenesis of Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, hereditary spastic paraplegia, and cerebellar degenerations. Therapeutic approaches targeting mitochondrial dysfunction and oxidative damage in these diseases therefore have great promise.

Total hydroxyoctadecadienoic acid as a marker for lipid peroxidation in vivo

An improved method for the measurement of lipid peroxidation in vivo has been recently developed, where total hydroxyoctadecadienoic acid (HODE) and 7-hydroxycholesterol (FCOH) were determined by GC/MS analysis from physiological samples after reduction with sodium borohydride and saponification by potassium hydroxide. In this method, both free and ester forms of hydroperoxides and ketones as well as hydroxides of linoleic acid and cholesterol are measured as HODE and FCOH, respectively. The ratio of stereo-isomer, (Z, E)-HODE/(E, E)-HODE, could be also measured. In the present study, in order to examine the effect of continuous, slow flux of free radicals in vivo, a water-soluble radical generator was administered to rats and mice and the amounts of HODE and 8-isoprostane in plasma and liver were measured. It was found that the administration of free radical-generating azo compound increased the level of HODE and decreased the (Z, E)-HODE/(E, E)-HODE ratio in both plasma and liver. The level of HODE was much higher than 8-isoprostane.

Domain structure of bi-functional selenoprotein P

Human selenoprotein P (SeP), a selenium-rich plasma glycoprotein, is presumed to contain ten selenocysteine residues; one of which is located at the 40th residue in the N-terminal region and the remaining nine localized in the C-terminal third part. We have shown that SeP not only catalyses the reduction of phosphatidylcholine hydroperoxide by glutathione [Saito, Hayashi, Tanaka, Watanabe, Suzuki, Saito and Takahashi (1999) J. Biol. Chem. 274, 2866-2871], but also supplies its selenium to proliferating cells [Saito and Takahashi (2002) Eur. J. Biochem. 269, 5746-5751]. Treatment of SeP with plasma kallikrein resulted in a sequential limited proteolysis (Arg-235-Gln-236 and Arg-242-Asp-243). The N-terminal (residues 1-235) and C-terminal (residues 243-361) fragments exhibited enzyme activity and selenium-supply activity respectively. These results confirm that SeP is a bi-functional protein and suggest that the first selenocysteine residue is the active site of the enzyme and the remaining nine residues function as a selenium supplier.

The cytotoxicity of vitamin E is both vitamer- and cell-specific and involves a selectable trait

During a study of the effect of vitamin E in activated mouse macrophages, we observed a reduction in the viability of cells treated with various forms of vitamin E. We show in this report that some tocopherols (both gamma- and delta-tocopherol) are cytotoxic to some but not all cell types. Mouse macrophages were especially sensitive (40 micromol/L), whereas human hepatocytes and bovine endothelial cells were almost completely refractory (90 micromol/L). The fully methylated tocopherol, alpha-tocopherol (alpha-Toc), was not cytotoxic in any cell type tested. The cytotoxicity observed with delta-tocopherol (delta-Toc) was associated with 2 markers of apoptosis. Vitamer-specific cytotoxicity was not due to differences in cellular uptake/accumulation because both alpha-Toc and delta-Toc accumulated equally in any cell type tested. In contrast, the cell-specific cytotoxicity was related in part to uptake/accumulation of the tocopherols. Macrophages accumulated nearly 5 times more tocopherol compared with hepatocytes cultured under similar conditions. To address the hypothesis that uptake accounted for the cell-specific sensitivity, we developed a macrophage "subtype" that was markedly resistant (>150 micromol/L) to delta-Toc. Under many different cell culture conditions (including human serum) uptake/accumulation of tocopherols was reduced in this subtype by approximately 50%. Further selection and evaluation of this phenotype, however, demonstrated no cytotoxicity even when cellular levels were elevated. Our results show that undermethylated tocopherols are cytotoxic to macrophages and that there are independent and selectable processes that determine cellular tocopherol uptake/accumulation and delta-Toc cytotoxicity.

Aryl Thiol Substrate 3-Carboxy-4-Nitrobenzenethiol Strongly Stimulating Thiol Peroxidase Activity of Glutathione Peroxidase Mimic 2, 2'-Ditellurobis(2-Deoxy-β-Cyclodextrin)

Artificial glutathione peroxidase (GPx) model 2, 2'-ditellurobis(2-deoxy-beta-cyclodextrin) (2-TeCD) which has the desirable properties exhibited high substrate specificity and remarkably catalytic efficiency when 3-carboxy-4-nitrobenzenethiol (ArSH) was used as a preferential thiol substrate. The complexation of ArSH with beta-cyclodextrin was investigated through UV spectral titrations, fluorescence spectroscopy, 1H NMR and molecular simulation, and these results indicated that ArSH fits well to the size of the cavity of beta-cyclodextrin. Furthermore, 2-TeCD was found to catalyze the reduction of cumene peroxide (CuOOH) by ArSH 200,000-fold more efficiently than diphenyl diselenide (PhSeSePh). Its steady-state kinetics was studied and the second rate constant kmax/KArSH was found to be 1.05 x 10(7) M(-1) min(-1) and similar to that of natural GPx. Moreover, the kinetic data revealed that the catalytic efficiency of 2-TeCD depended strongly upon the competitive recognition of both substrates for 2-TeCD. The catalytic mechanism of 2-TeCD catalysis agreed well with a ping-pong mechanism, in analogy with natural GPx, and might exert its thiol peroxidase activity via tellurol, tellurenic acid, and tellurosulfide.

Association of DJ-1 and parkin mediated by pathogenic DJ-1 mutations and oxidative stress

The identification of rare monogenic forms of Parkinson's disease (PD) has provided tremendous insight into the molecular pathogenesis of this disorder. Heritable mutations in alpha-synuclein, parkin, DJ-1 and PINK1 cause familial forms of PD. In the more common sporadic form of PD, oxidative stress and derangements in mitochondrial complex-I function are considered to play a prominent role in disease pathogenesis. However, the relationship of DJ-1 with other PD-linked genes and oxidative stress has not been explored. Here, we show that pathogenic mutant forms of DJ-1 specifically but differentially associate with parkin, an E3 ubiquitin ligase. Chemical cross-linking shows that pathogenic DJ-1 mutants exhibit impairments in homo-dimer formation, suggesting that parkin may bind to monomeric DJ-1. Parkin fails to specifically ubiquitinate and enhance the degradation of L166P and M26I mutant DJ-1, but instead promotes their stability in cultured cells. The interaction of parkin with L166P DJ-1 may involve a larger protein complex that contains CHIP and Hsp70, perhaps accounting for the lack of parkin-mediated ubiquitination. Oxidative stress also promotes an interaction between DJ-1 and parkin, but this does not result in the ubiquitination or degradation of DJ-1. Parkin-mediated alterations in DJ-1 protein stability may be pathogenically relevant as DJ-1 levels are dramatically increased in the detergent-insoluble fraction from sporadic PD/DLB brains, but are reduced in the insoluble fraction from parkin-linked autosomal recessive juvenile-onset PD brains. These data potentially link DJ-1 and parkin in a common molecular pathway at multiple levels that may have important implications for understanding the pathogenesis of inherited and sporadic PD.

Selenium deficiency as a model of experimental pre-eclampsia in rats

Epidemiological studies andin vitroanalysis demonstrate correlations between selenium status and human pre-eclampsia (PET). Selenium is an essential component in the anti-oxidant proteins glutathione peroxidase and thioredoxin reductase, which are produced in lower amounts in pre-eclamptic placenta. This study examined the effect of modulating dietary selenium content in pregnant rats. Rats were fed diets containing no selenium, 239 μg/kg selenium or 1000 μg/kg selenium, four weeks prior to and following conception. Significant pregnancy-specific increases in systolic blood pressure (116.4 ± 5.2 mmHg vs 108 ± 6.8 mmHg vs 111.4 ± 4.7 mmHg) and proteinuria (9.68 ± 2.12 μg/ml vs 5.93 ± 1.59 μg/ml vs 4.43 ± 0.96 μg/ml) were demonstrated in animals fed a selenium free-diet when compared with normal or high selenium diets. Placental weight and pup number were not affected by selenium deprivation, however a significant decrease in the pup weight was evident. Selenium deprivation caused dose-dependent decreases in liver glutathione peroxidase (28.55 ± 3.82 mmoles/min/mg vs 34.68 ± 8.64 mmoles/min/mg) and thioredoxin reductase (2.37 ± 1.25 U/mg vs 6.68 ± 1.82 U/mg) activity, whereas superoxide dismutase activity remained constant. Placental activity of these enzymes also decreased leading to oxidative stress as measured by increased lipid peroxides (17.92 ± 1.78 μmoles/mg vs 8.30 ± 5.52 μmoles/mg) and protein carbonyls in tissue extracts from selenium-free animals. These results suggest that selenium deficiency in pregnant rats leads to symptoms similar to those seen in human PET and may provide an experimental model for studying this complex disease.

The Yeast Prion Protein Ure2 Shows Glutathione Peroxidase Activity in Both Native and Fibrillar Forms

Ure2p is the precursor protein of the Saccharomyces cerevisiae prion [URE3]. Ure2p shows homology to glutathione transferases but lacks typical glutathione transferase activity. A recent study found that deletion of the Ure2 gene causes increased sensitivity to heavy metal ions and oxidants, whereas prion strains show normal sensitivity. To demonstrate that protection against oxidant toxicity is an inherent property of native and prion Ure2p requires biochemical characterization of the purified protein. Here we use steady-state kinetic methods to characterize the multisubstrate peroxidase activity of Ure2p using GSH with cumene hydroperoxide, hydrogen peroxide, or tert-butyl hydroperoxide as substrates. Glutathione-dependent peroxidase activity was proportional to the Ure2p concentration and showed optima at pH 8 and 40 degrees C. Michaelis-Menten behavior with convergent straight lines in double reciprocal plots was observed. This excludes a ping-pong mechanism and implies either a rapid-equilibrium random or a steady-state ordered sequential mechanism for Ure2p, consistent with its classification as a glutathione transferase. The mutant 90Ure2, which lacks the unstructured N-terminal prion domain, showed kinetic parameters identical to wild type. Fibrillar aggregates showed the same level of activity as native protein. Demonstration of peroxidase activity for Ure2 represents important progress in elucidation of its role in vivo. Further, establishment of an in vitro activity assay provides a valuable tool for the study of structure-function relationships of the Ure2 protein as both a prion and an enzyme.

Role of oxidative modifications in atherosclerosis

This review focuses on the role of oxidative processes in atherosclerosis and its resultant cardiovascular events. There is now a consensus that atherosclerosis represents a state of heightened oxidative stress characterized by lipid and protein oxidation in the vascular wall. The oxidative modification hypothesis of atherosclerosis predicts that low-density lipoprotein (LDL) oxidation is an early event in atherosclerosis and that oxidized LDL contributes to atherogenesis. In support of this hypothesis, oxidized LDL can support foam cell formation in vitro, the lipid in human lesions is substantially oxidized, there is evidence for the presence of oxidized LDL in vivo, oxidized LDL has a number of potentially proatherogenic activities, and several structurally unrelated antioxidants inhibit atherosclerosis in animals. An emerging consensus also underscores the importance in vascular disease of oxidative events in addition to LDL oxidation. These include the production of reactive oxygen and nitrogen species by vascular cells, as well as oxidative modifications contributing to important clinical manifestations of coronary artery disease such as endothelial dysfunction and plaque disruption. Despite these abundant data however, fundamental problems remain with implicating oxidative modification as a (requisite) pathophysiologically important cause for atherosclerosis. These include the poor performance of antioxidant strategies in limiting either atherosclerosis or cardiovascular events from atherosclerosis, and observations in animals that suggest dissociation between atherosclerosis and lipoprotein oxidation. Indeed, it remains to be established that oxidative events are a cause rather than an injurious response to atherogenesis. In this context, inflammation needs to be considered as a primary process of atherosclerosis, and oxidative stress as a secondary event. To address this issue, we have proposed an "oxidative response to inflammation" model as a means of reconciling the response-to-injury and oxidative modification hypotheses of atherosclerosis.

Superoxide release and cellular gluthatione peroxidase activity in leukocytes from children with persistent asthma

Asthma is an inflammatory condition characterized by the involvement of several mediators, including reactive oxygen species. The aim of the present study was to investigate the superoxide release and cellular glutathione peroxidase (cGPx) activity in peripheral blood granulocytes and monocytes from children and adolescents with atopic asthma. Forty-four patients were selected and classified as having intermittent or persistent asthma (mild, moderate or severe). The spontaneous or phorbol myristate acetate (PMA, 30 nM)-induced superoxide release by granulocytes and monocytes was determined at 0, 5, 15, and 25 min. cGPx activity was assayed spectrophotometrically. The spontaneous superoxide release by granulocytes from patients with mild (N = 15), moderate (N = 12) or severe (N = 6) asthma was higher at 25 min compared to healthy individuals (N = 28, P < 0.05, Duncan test). The PMA-induced superoxide release by granulocytes from patients with moderate (N = 12) or severe (N = 6) asthma was higher at 15 and 25 min compared to healthy individuals (N = 28, P < 0.05 in both times of incubation, Duncan test). The spontaneous or PMA-induced superoxide release by monocytes from asthmatic patients was similar to healthy individuals (P > 0.05 in all times of incubation, Duncan test). cGPx activity of granulocytes and monocytes from patients with persistent asthma (N = 20) was also similar to healthy individuals (N = 10, P > 0.05, Kruskal-Wallis test). We conclude that, under specific circumstances, granulocytes from children with persistent asthma present a higher respiratory burst activity compared to healthy individuals. These findings indicate a risk of oxidative stress, phagocyte auto-oxidation, and the subsequent release of intracellular toxic oxidants and enzymes, leading to additional inflammation and lung damage in asthmatic children.

Sensitivity to oxidative stress in DJ-1-deficient dopamine neurons: an ES- derived cell model of primary Parkinsonism

The hallmark of Parkinson's disease (PD) is the selective loss of dopamine neurons in the ventral midbrain. Although the cause of neurodegeneration in PD is unknown, a Mendelian inheritance pattern is observed in rare cases, indicating a genetic factor. Furthermore, pathological analyses of PD substantia nigra have correlated cellular oxidative stress and altered proteasomal function with PD. Homozygous mutations in DJ-1 were recently described in two families with autosomal recessive Parkinsonism, one of which is a large deletion that is likely to lead to loss of function. Here we show that embryonic stem cells deficient in DJ-1 display increased sensitivity to oxidative stress and proteasomal inhibition. The accumulation of reactive oxygen species in toxin-treated DJ-1-deficient cells initially appears normal, but these cells are unable to cope with the consequent damage that ultimately leads to apoptotic death. Furthermore, we find that dopamine neurons derived from in vitro-differentiated DJ-1-deficient embryonic stem cells display decreased survival and increased sensitivity to oxidative stress. These data are consistent with a protective role for DJ-1, and demonstrate the utility of genetically modified embryonic stem cell-derived neurons as cellular models of neuronal disorders.

DJ-1 is a redox-dependent molecular chaperone that inhibits alpha-synuclein aggregate formation

Parkinson's disease (PD) pathology is characterized by the degeneration of midbrain dopamine neurons (DNs) ultimately leading to a progressive movement disorder in patients. The etiology of DN loss in sporadic PD is unknown, although it is hypothesized that aberrant protein aggregation and cellular oxidative stress may promote DN degeneration. Homozygous mutations in DJ-1 were recently described in two families with autosomal recessive inherited PD (Bonifati et al. 2003). In a companion article (Martinat et al. 2004), we show that mutations in DJ-1 alter the cellular response to oxidative stress and proteasomal inhibition. Here we show that DJ-1 functions as a redox-sensitive molecular chaperone that is activated in an oxidative cytoplasmic environment. We further demonstrate that DJ-1 chaperone activity in vivo extends to α-synuclein, a protein implicated in PD pathogenesis.

The interaction of the proteins DJ-1 and α- synuclein described here may be important for understanding the molecular basis of Parkinson's disease

Selenoprotein P, as a predictor for evaluating gemcitabine resistance in human pancreatic cancer cells

Gemcitabine is a new standard chemotherapeutic agent used in the treatment of pancreatic cancer, but the mechanisms of gemcitabine sensitivity are still controversial. In our study to determine a mechanism that regulates gemcitabine sensitivity, we carried out molecular analysis on the susceptibility of the pancreatic cancer cells. Using a gemcitabine-sensitive pancreatic cancer cell line KLM1, we established a resistant cell line KLM1-R exhibiting a 20-fold IC50-value (the concentration of gemcitabine causing 50% growth inhibition). Microarray analysis of genes showed specific expression of selenoprotein P, one of the anti-oxidants, in the KLM1-R cell line but not in the KLM1 cell line. Administration of selenoprotein P inhibited the gemcitabine-induced cytotoxicity in the pancreatic cell lines. The levels of intracellular reactive oxygen species (ROS) were increased in the KLM1 cells by gemcitabine, but selenoprotein P suppressed the gemcitabine-induced ROS levels. Furthermore interferon-gamma suppressed the expression of selenoprotein P mRNA and increased intracellular ROS level, leading to the recovery of the gemcitabine sensitivity in KLM1-R. These results suggest a novel mechanism that selenoprotein P reduces the intracellular ROS levels, resulting in the insusceptibility to gemcitabine.

Genetics of Parkinson's disease

The etiology of most cases of Parkinson's disease (PD) remains unknown. In recent years, however, research has successfully focused on genetic factors contributing to the degeneration of dopaminergic neurons. Causative mutations have been identified in several monogenically inherited forms of the disease. Although these genetic forms of PD are usually rare, the gene discoveries are likely to identify molecular pathways that are also relevant in the sporadic disorder. These studies have led to the identification of (i) the central role of α-synuclein aggregation, secondary to either point mutations or an amplification of the α-synuclein gene; and (ii) the relevance of defects in the proteasomal protein degradation pathway in the molecular pathogenesis of recessive parkin-linked forms of PD. The recent discoveries of two additional recessive forms associated with mutations in the genes DJ-1 and PINK1 have brought the mitochondrial energy metabolism and the cell's defence against toxic free radicals into the focus of research.

Antioxidant function of a novel selenoprotein in Drosophila melanogaster

BACKGROUND

Insects appear to have diverged from both higher and lower organisms in their defense mechanisms against oxidative damage. They do not encode glutathione peroxidases or glutathione reductases, and their thioredoxin reductases exhibit distinct properties from those of higher and lower species. Nonetheless, appropriate balance of anti-oxidants and pro-oxidants, and protection from damaging reactive oxygen species are clearly crucial in insects for viability, normal functioning of signalling pathways and morphogenesis, and have been implicated in studies on longevity in flies and other organisms.

RESULTS

Two novel selenoproteins, dselH and dselK, were recently identified in Drosophila melanogaster. We have used RNAi in D. melanogaster embryos and in Schneider S2 cells to inhibit expression of these proteins. We report that inhibition of either dselH or dselK expression significantly reduces viability in embryos. We further show that dselH silencing decreases total anti-oxidant capacity in embryos and Schneider cells, and increases lipid peroxidation in cells. Conversely, transient expression of dselH in the cell line decreases lipid peroxidation, and reverses the toxic effects of a glutathione-depleting drug. The latter correlates with sparing of glutathione levels.

CONCLUSIONS

These studies suggest that the well-known role of selenoproteins in vertebrate anti-oxidant defenses also extends to include invertebrates.

Selenium and brain function: a poorly recognized liaison

Molecular biology has recently contributed significantly to the recognition of selenium (Se)2 and Se-dependent enzymes as modulators of brain function. Increased oxidative stress has been proposed as a pathomechanism in neurodegenerative diseases including, among others, Parkinson's disease, stroke, and epilepsy. Glutathione peroxidases (GPx), thioredoxin reductases, and one methionine-sulfoxide-reductase are selenium-dependent enzymes involved in antioxidant defense and intracellular redox regulation and modulation. Selenium depletion in animals is associated with decreased activities of Se-dependent enzymes and leads to enhanced cell loss in models of neurodegenerative disease. Genetic inactivation of cellular GPx increases the sensitivity towards neurotoxins and brain ischemia. Conversely, increased GPx activity as a result of increased Se supply or overexpression ameliorates the outcome in the same models of disease. Genetic inactivation of selenoprotein P leads to a marked reduction of brain Se content, which has not been achieved by dietary Se depletion, and to a movement disorder and spontaneous seizures. Here we review the role of Se for the brain under physiological as well as pathophysiological conditions and highlight recent findings which open new vistas on an old essential trace element.

Genetics of Parkinson's disease

The etiology of most cases of Parkinson's disease (PD) remains unknown. In recent years, however, research has successfully focused on genetic factors contributing to the degeneration of dopaminergic neurons. Causative mutations have been identified in several monogenically inherited forms of the disease. Although these genetic forms of PD are usually rare, the gene discoveries are likely to identify molecular pathways that are also relevant in the sporadic disorder. These studies have led to the identification of (i) the central role of α-synuclein aggregation, secondary to either point mutations or an amplification of the α-synuclein gene; and (ii) the relevance of defects in the proteasomal protein degradation pathway in the molecular pathogenesis of recessive parkin-linked forms of PD. The recent discoveries of two additional recessive forms associated with mutations in the genes DJ-1 and PINK1 have brought the mitochondrial energy metabolism and the cell's defence against toxic free radicals into the focus of research.

Molecular pathways to neurodegeneration

The molecular bases underlying the pathogenesis of neurodegenerative diseases are gradually being disclosed. One problem that investigators face is distinguishing primary from secondary events. Rare, inherited mutations causing familial forms of these disorders have provided important insights into the molecular networks implicated in disease pathogenesis. Increasing evidence indicates that accumulation of aberrant or misfolded proteins, protofibril formation, ubiquitin-proteasome system dysfunction, excitotoxic insult, oxidative and nitrosative stress, mitochondrial injury, synaptic failure, altered metal homeostasis and failure of axonal and dendritic transport represent unifying events in many slowly progressive neurodegenerative disorders.

Genetic contributions to Parkinson's disease

Sporadic Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by the loss of midbrain dopamine neurons and Lewy body inclusions. It is thought to result from a complex interaction between multiple predisposing genes and environmental influences, although these interactions are still poorly understood. Several causative genes have been identified in different families. Mutations in two genes [alpha-synuclein and nuclear receptor-related 1 (Nurr1)] cause the same pathology, and a third locus on chromosome 2 also causes this pathology. Other familial PD mutations have identified genes involved in the ubiquitin-proteasome system [parkin and ubiquitin C-terminal hydroxylase L1 (UCHL1)], although such cases do not produce Lewy bodies. These studies highlight critical cellular proteins and mechanisms for dopamine neuron survival as disrupted in Parkinson's disease. Understanding the genetic variations impacting on dopamine neurons may illuminate other molecular mechanisms involved. Additional candidate genes involved in dopamine cell survival, dopamine synthesis, metabolism and function, energy supply, oxidative stress, and cellular detoxification have been indicated by transgenic animal models and/or screened in human populations with differing results. Genetic variation in genes known to produce different patterns and types of neurodegeneration that may impact on the function of dopamine neurons are also reviewed. These studies suggest that environment and genetic background are likely to have a significant influence on susceptibility to Parkinson's disease. The identification of multiple genes predisposing to Parkinson's disease will assist in determining the cellular pathway/s leading to the neurodegeneration observed in this disease.

Reduced anti-oxidative stress activities of DJ-1 mutants found in Parkinson’s disease patients

DJ-1 is a multi-functional protein that plays roles in transcriptional regulation and anti-oxidative stress, and loss of its function is thought to result in onset of Parkinson's disease. We have previously reported that L166P, a mutant DJ-1 found in Parkinson's disease patients, had no activity to prevent hydrogen peroxide (H2O2)-induced cell death. In this study, we analyzed other mutants of DJ-1 found in Parkinson's disease patients, including M26I, R98Q, and D149A, as well as L166P. We first found that all of the mutants made heterodimers with wild-type DJ-1, while all of the mutants except for L166P made homodimers. We then found that M26I and L166P, both of which are derived from homozygous mutations of the DJ-1 gene, were unstable and that their stabilities were recovered, in part, in the presence of proteasome inhibitor, MG132. NIH3T3 cell lines stably expressing these mutants of DJ-1 showed that cell lines of L166P and C106S, a mutant for protease activity (-) of DJ-1, had no activity to scavenge even endogenously producing reactive oxygen species. These cell lines also showed that all of the mutants had reduced activities to eliminate exogenously added H2O2 and that these activities, except for that of D149A, were parallel to those preventing H2O2-induced cell death.

Genetic clues to the pathogenesis of Parkinson's disease

Recent years have seen an explosion in the rate of discovery of genetic defects linked to Parkinson's disease. These breakthroughs have not provided a direct explanation for the disease process. Nevertheless, they have helped transform Parkinson's disease research by providing tangible clues to the neurobiology of the disorder.

Causes of Parkinson?s disease: genetics of DJ-1

The identification of Mendelian mutations in rare forms of familial Parkinson's disease (PD) have provided significant insights into the molecular pathogenesis of this common complex disorder. DJ-1 is the third of four genes known to be definitively causal in familial PD, the three others being alpha-synuclein, parkin and the recently identified PINK1. Mutations in the DJ-1 gene were identified in two European families, a Dutch kindred harbouring a large homozygous genomic deletion encompassing exons 1-5 of the gene and an Italian kindred with a homozygous L166P missense mutation. The clinical phenotype of the two families was similar to that of parkin cases. Age of onset was in the mid-thirties with good responsiveness to l-dopa and slow disease progression. Focal dystonias and blepharospasm were also evident as were behavioural disturbances early in the course of the disease. To date, there are no studies of pathological material from known DJ-1 patients. It therefore remains to be determined whether these patients form Lewy bodies and/or Lewy neurites, the eosinophilic fibrillary inclusions that contain predominantly alpha-synuclein and that are the pathological hallmark of PD.

The Parkinson's disease protein DJ-1 is neuroprotective due to cysteine-sulfinic acid-driven mitochondrial localization

Loss-of-function DJ-1 mutations can cause early-onset Parkinson's disease. The function of DJ-1 is unknown, but an acidic isoform accumulates after oxidative stress, leading to the suggestion that DJ-1 is protective under these conditions. We addressed whether this represents a posttranslational modification at cysteine residues by systematically mutating cysteine residues in human DJ-1. WT or C53A DJ-1 was readily oxidized in cultured cells, generating a pI 5.8 isoform, but an artificial C106A mutant was not. We observed a cysteine-sulfinic acid at C106 in crystalline DJ-1 but no modification of C53 or C46. Oxidation of DJ-1 was promoted by the crystallization procedure. In addition, oxidation-induced mitochondrial relocalization of DJ-1 and protection against cell death were abrogated in C106A but not C53A or C46A. We suggest that DJ-1 protects against neuronal death, and that this is signaled by acidification of the key cysteine residue, C106.

Determinants of Human Plasma Glutathione Peroxidase (GPx-3) Expression

Plasma glutathione peroxidase (GPx-3) is a selenocysteine-containing protein with antioxidant properties. GPx-3 deficiency has been associated with cardiovascular disease and stroke. The regulation of GPx-3 expression remains largely uncharacterized, however, and we studied its transcriptional and translational determinants in a cultured cell system. In transient transfections of a renal cell line (Caki-2), the published sequence cloned upstream of a luciferase reporter gene produced minimal activity (relative luminescence (RL) = 0.6 +/- 0.4). Rapid amplification of cDNA ends was used to identify a novel transcription start site that is located 233 bp downstream (3') of the published site and that produced a >25-fold increase in transcriptional activity (RL = 16.8 +/- 1.9; p < 0.0001). Analysis of the novel GPx-3 promoter identified Sp-1- and hypoxia-inducible factor-1-binding sites, as well as the redox-sensitive metal response element and antioxidant response element. Hypoxia was identified as a strong transcriptional regulator of GPx-3 expression, in part through the presence of the hypoxia-inducible factor-1-binding site, leading to an almost 3-fold increase in expression levels after 24 h compared with normoxic conditions (normalized RL = 3.5 +/- 0.3 versus 1.2 +/- 0.1; p < 0.001). We also investigated the role of the translational cofactors tRNA(Sec), SECIS-binding protein-2, and SelD (selenophosphate synthetase D) in GPx-3 protein expression. tRNA(Sec) and SelD significantly enhanced GPx-3 expression, whereas SECIS-binding protein-2 showed a trend toward increased expression. These results demonstrate the presence of a novel functional transcription start site for the human GPx-3 gene with a promoter regulated by hypoxia, and identify unique translational determinants of GPx-3 expression.

Distribution of tocopherols and tocotrienols to rat ocular tissues after topical ophthalmic administration

With increasing evidence suggesting the involvement of oxidative stress in various disorders and diseases, the role of antioxidants in vivo has received much attention. Chemically, tocopherols and tocotrienols are closely related; however, it has been observed that they have widely varying degrees of biological effectiveness. The present study has been carried out in an attempt to deepen our understanding of whether there is a significant difference in distribution between tocopherol and tocotrienol homologs to rat eye tissues. Rats were administered 5 microL of pure tocopherol or tocotrienol to each eye once a day for 4 d. Various tissues of the eyes were separated and analyzed for tocopherol and tocotrienol concentrations. The concentration of alpha-to-cotrienol increased markedly in every tissue to which it was administered; however, no significant increase was observed in the case of alpha-tocopherol. The intraocular penetration of gamma-tocopherol and gamma-tocotrienol did not differ significantly. Additionally, a significant increase in total vitamin E concentration was observed in ocular tissues, including crystalline lens, neural retina, and eye cup, with topical administration using a relatively small amount (5 microL) of vitamin E, whereas no significant increase was observed when the same amount of vitamin E was administered orally. Topical administration of tocotrienols is thus an effective way to increase ocular tissue vitamin E concentration.

Efficient selenium transfer from mother to offspring in selenoprotein-P-deficient mice enables dose-dependent rescue of phenotypes associated with selenium deficiency

Mice deficient in selenoprotein P exhibit a disturbed selenium distribution and reduced activities of other selenoenzymes and display defects in growth and motor co-ordination. We have normalized selenoenzyme activities and rescued the phenotype of mutant mice by supplementing their nursing mothers with sodium selenite. Our results indicate that selenium from inorganic sources can be transferred efficiently via mother's milk to the developing offspring in a form that is both highly bioavailable by target tissues and yet sufficiently safe to prevent overdosages.

Hepatocellular bioactivation and cytotoxicity of the synthetic endoperoxide antimalarial arteflene

Arteflene is a synthetic endoperoxide antimalarial. Its peroxide bridge undergoes iron(II)-mediated reduction in vitro which yields a carbon-centered cyclohexyl radical and a mixture of cis- and trans-alpha,beta-unsaturated ketones (enones). The enones are biliary metabolites in rats and therefore surrogate markers of bioactivation. Arteflene is reported to be more cytotoxic to primary rat hepatocytes than some non-endoperoxide antimalarials. Hepatic metabolism of arteflene was investigated in recirculating isolated perfused rat livers, and the drug's metabolism and cytotoxicity were compared using hepatocytes from male rats. Both preparations metabolized [(14)C]arteflene to cis- and trans-[(14)C]enone, 8-hydroxyarteflene glucuronide and an unassigned isomeric glucuronide. During a 2 h liver perfusion, the cis- and trans-enones recovered in bile represented 8.1 +/- 3.4 and 11.3 +/- 4.6% (mean +/- S.D., N=6), respectively, of the [(14)C]arteflene (52 microM) added to the perfusate. After a 3 h incubation of [(14)C]arteflene (10 microM) with hepatocytes in suspension, the cis- and trans-enones comprised, respectively, 14.8 +/- 7.1 and 2.1 +/- 1.0% (N = 4) of the recovered radioactivity; the corresponding data for cultured hepatocytes being 18.6 +/- 6.9 and 3.3 +/- 2.2%. Arteflene was significantly (P < 0.05) toxic to isolated hepatocytes with reference to extramitochondrial reductase activity (tetrazolium reduction) but not enzyme leakage when the cells were exposed to drug concentrations > or =50 microM for 24 h. Cellular glutathione was depleted under these conditions. Therefore arteflene was acutely cytotoxic, though only at relatively high concentrations, when it was metabolized via a pathway which generates carbon-centered radicals.

Rapid formation of 4-hydroxy-2-nonenal, malondialdehyde, and phosphatidylcholine aldehyde from phospholipid hydroperoxide by hemoproteins

4-Hydroxy-2-nonenal (HNE) and malondialdehyde (MDA) are well-known toxic products of lipid peroxidation. Phosphatidylcholine aldehydes are also known as oxidation products of phosphatidylcholine. The mechanism of the formation of these compounds in vivo has been a long-standing question. We observed that the rapid reaction of hemoproteins (methemoglobin, metmyoglobin, and cytochrome c) with 1-palmitoyl-2-(13-hydroperoxy-cis-9, trans-11-octadecadienoyl) phosphatidylcholine (PLPC-OOH), having a hydroperoxylinoleoyl residue, generated HNE, MDA, and the phosphatidylcholine aldehyde 1-palmitoyl-2-(9-oxononanoyl) phosphatidylcholine. The efficiencies (mol% yield) of the formation of HNE and MDA from decomposed PLPC-OOH by methemoglobin, metmyoglobin, and cytochrome c after incubation for 10 min were 1.6, 1.0, and 1.0% for HNE and 1.2, 0.6, and 0.9% for MDA, respectively. When 1-palmitoyl-2-linoleoyl phosphatidylcholine was incubated with lipoxidase and methemoglobin, the formation of HNE and the phosphatidylcholine aldehyde 1-palmitoyl-2-(9-oxononanoyl) phosphatidylcholine was observed. When 1-palmitoyl-2-arachidonyl phosphatidylcholine was used instead of 1-palmitoyl-2-linoleoyl phosphatidylcholine, the phosphatidylcholine aldehyde 1-palmitoyl-2-oxovaleroyl phosphatidylcholine was obtained. These data suggest that HNE and phosphatidylcholine aldehydes might be rapidly formed from phosphatidylcholine by lipoxygenase and hemoproteins. Furthermore, hemichrome, converted from methemoglobin by deoxycholic acid and ursodeoxycholic acid, showed marked decomposition of HNE. These results suggest that hemoproteins are related to both the formation and the decomposition of HNE.

The neurobiology of selenium: lessons from transgenic mice

The brain represents a privileged organ with respect to selenium (Se) supply and retention. It contains high amounts of this essential trace element, which is efficiently retained even in conditions of Se deficiency. Accordingly, no severe neurological phenotype has been reported for animals exposed to Se-depleted diets. They are, however, more susceptible to neuropathological challenges. Recently, gene disruption experiments supported a pivotal role for different selenoproteins in brain function. Using these and other transgenic models, longstanding questions concerning the preferential supply of Se to the brain and the hierarchy among the different selenoproteins are readdressed. Given that genes for at least 25 selenoproteins have been identified in the human genome, and most of these are expressed in the brain, their specific roles for normal brain function and neurological diseases remain to be elucidated.