Mechanisms of 4-hydroxynonenal-induced neuronal microtubule dysfunction

Reactive Carbonyl Species and Protein Lipoxidation in Atherogenesis

Atherosclerosis is a multifactorial disease of medium and large arteries, characterized by the presence of lipid-rich plaques lining the intima over time. It is the main cause of cardiovascular diseases and death worldwide. Redox imbalance and lipid peroxidation could play key roles in atherosclerosis by promoting a bundle of responses, including endothelial activation, inflammation, and foam cell formation. The oxidation of polyunsaturated fatty acids generates various lipid oxidation products such as reactive carbonyl species (RCS), including 4-hydroxy alkenals, malondialdehyde, and acrolein. RCS covalently bind to nucleophilic groups of nucleic acids, phospholipids, and proteins, modifying their structure and activity and leading to their progressive dysfunction. Protein lipoxidation is the non-enzymatic post-translational modification of proteins by RCS. Low-density lipoprotein (LDL) oxidation and apolipoprotein B (apoB) modification by RCS play a major role in foam cell formation. Moreover, oxidized LDLs are a source of RCS, which form adducts on a huge number of proteins, depending on oxidative stress intensity, the nature of targets, and the availability of detoxifying systems. Many systems are affected by lipoxidation, including extracellular matrix components, membranes, cytoplasmic and cytoskeletal proteins, transcription factors, and other components. The mechanisms involved in lipoxidation-induced vascular dysfunction are not fully elucidated. In this review, we focus on protein lipoxidation during atherogenesis.

An integrated omics approach to investigate summer mortality of New Zealand Greenshell™ mussels

BACKGROUND

Green-lipped mussels, commercially known as Greenshell™ mussels (Perna canaliculus Gmelin 1791), contribute > $300 million to New Zealand's aquaculture exports. However, mortalities during summer months and potential pathogenic outbreaks threaten the industry. Thermal stress mechanisms and immunological responses to pathogen infections need to be understood to develop health assessment strategies and early warning systems.

METHODS

P. canaliculus were collected during a mortality event at a commercial aquaculture farm in Firth of Thames, New Zealand. Gill tissues from six healthy and six unhealthy mussels were excised and processed for metabolomic (GC-MS) and label-free proteomic (LC-MS) profiling. Univariate analyses were conducted separately on each data layer, with data being integrated via sparse multiple discriminative canonical correlation analysis. Pathway enrichment analysis was used to probe coordinated changes in functionally related metabolite sets.

RESULTS

Findings revealed disruptions of the tricarboxylic acid (TCA) cycle and fatty acid metabolism in unhealthy mussels. Metabolomics analyses also indicated oxidative stress in unhealthy mussels. Proteomics analyses identified under-expression of proteins associated with cytoskeleton structure and regulation of cilia/flagellum in gill tissues of unhealthy mussels. Integrated omics revealed a positive correlation between Annexin A4 and CCDC 150 and saturated fatty acids, as well as a negative correlation between 2-aminoadipic acid and multiple cytoskeletal proteins.

CONCLUSIONS

Our study demonstrates the ability of using integrative omics to reveal metabolic perturbations and protein structural changes in the gill tissues of stressed P. canaliculus and provides new insight into metabolite and protein interactions associated with incidences of summer mortality in this species.

Can Medicinal Plants and Bioactive Compounds Combat Lipid Peroxidation Product 4-HNE-Induced Deleterious Effects?

The toxic reactive aldehyde 4-hydroxynonenal (4-HNE) belongs to the advanced lipid peroxidation end products. Accumulation of 4-HNE and formation of 4-HNE adducts induced by redox imbalance participate in several cytotoxic processes, which contribute to the pathogenesis and progression of oxidative stress-related human disorders. Medicinal plants and bioactive natural compounds are suggested to be attractive sources of potential agents to mitigate oxidative stress, but little is known about the therapeutic potentials especially on combating 4-HNE-induced deleterious effects. Of note, some investigations clarify the attenuation of medicinal plants and bioactive compounds on 4-HNE-induced disturbances, but strong evidence is needed that these plants and compounds serve as potent agents in the prevention and treatment of disorders driven by 4-HNE. Therefore, this review highlights the pharmacological basis of these medicinal plants and bioactive compounds to combat 4-HNE-induced deleterious effects in oxidative stress-related disorders, such as neurotoxicity and neurological disorder, eye damage, cardiovascular injury, liver injury, and energy metabolism disorder. In addition, this review briefly discusses with special attention to the strategies for developing potential therapies by future applications of these medicinal plants and bioactive compounds, which will help biological and pharmacological scientists to explore the new vistas of medicinal plants in combating 4-HNE-induced deleterious effects.

The Role of Calpain and Proteasomes in the Degradation of Carbonylated Neuronal Cytoskeletal Proteins in Acute Experimental Autoimmune Encephalomyelitis

The present study was designed to investigate the role of calpain and the proteasome in the removal of oxidized neuronal cytoskeletal proteins in myelin basic protein-induced experimental autoimmune encephalomyelitis (EAE). To this end, EAE rats received a single intrathecal injection of calpeptin or epoxomicin at the first sign of clinical disease. Forty-eight hours later, animals were sacrificed and lumbar spinal cord segments were dissected and used for biochemical analyses. The results show that calpain and proteasome activity is specifically, but partially, inhibited with calpeptin and epoxomicin, respectively. Calpain inhibition causes an increase in total protein carbonylation and in the amount of neurofilament proteins (NFPs), β-tubulin and β-actin that were spared from degradation, but no changes are seen in the oxidation of any of three NFPs. By contrast, proteasome inhibition has no effect on total protein carbonylation or cytoskeletal protein degradation but increases the amount of oxidized NFH and NFM. These results suggest that while the proteasome may contribute to removal of oxidized NFPs, calpain is the main protease involved in degradation of neuronal cytoskeleton and does not preferentially targets oxidized NFPs species in acute EAE. Different results were obtained in a cell-free system, where calpain inhibition rises the amount of oxidized NFH, and proteasome inhibition fails to change the oxidation state of the NFPs. The later finding suggests that the preferential degradation of oxidized NFH and NFM in vivo by the proteasome occurs via the 26S and not the 20S particle.

Reduced primary cilia length and altered Arl13b expression are associated with deregulated chondrocyte Hedgehog signaling in alkaptonuria

Alkaptonuria (AKU) is a rare inherited disease resulting from a deficiency of the enzyme homogentisate 1,2-dioxygenase which leads to the accumulation of homogentisic acid (HGA). AKU is characterized by severe cartilage degeneration, similar to that observed in osteoarthritis. Previous studies suggest that AKU is associated with alterations in cytoskeletal organization which could modulate primary cilia structure/function. This study investigated whether AKU is associated with changes in chondrocyte primary cilia and associated Hedgehog signaling which mediates cartilage degradation in osteoarthritis. Human articular chondrocytes were obtained from healthy and AKU donors. Additionally, healthy chondrocytes were treated with HGA to replicate AKU pathology (+HGA). Diseased cells exhibited shorter cilia with length reductions of 36% and 16% in AKU and +HGA chondrocytes respectively, when compared to healthy controls. Both AKU and +HGA chondrocytes demonstrated disruption of the usual cilia length regulation by actin contractility. Furthermore, the proportion of cilia with axoneme breaks and bulbous tips was increased in AKU chondrocytes consistent with defective regulation of ciliary trafficking. Distribution of the Hedgehog-related protein Arl13b along the ciliary axoneme was altered such that its localization was increased at the distal tip in AKU and +HGA chondrocytes. These changes in cilia structure/trafficking in AKU and +HGA chondrocytes were associated with a complete inability to activate Hedgehog signaling in response to exogenous ligand. Thus, we suggest that altered responsiveness to Hedgehog, as a consequence of cilia dysfunction, may be a contributing factor in the development of arthropathy highlighting the cilium as a novel target in AKU.

Inhibition of cytoskeletal protein carbonylation may protect against oxidative damage in traumatic brain injury

Oxidative stress is the principal factor in traumatic brain injury (TBI) that initiates protracted neuronal dysfunction and remodeling. Cytoskeletal proteins are known to be carbonylated under oxidative stress; however, the complex molecular and cellular mechanisms of cytoskeletal protein carbonylation remain poorly understood. In the present study, the expression levels of glutathione (GSH) and thiobarbituric acid reactive substances (TBARS) were investigated in PC12 cells treated with H₂O₂. Western blot analysis was used to monitor the carbonylation levels of β-actin and β-tubulin. The results indicated that oxidative stress was increased in PC12 cells that were treated with H₂O₂ for 24 or 48 h. In addition, increased carbonylation levels of β-actin and β-tubulin were detected in H₂O₂-treated cells. However, these carbonylation levels were reduced by pretreatment with aminoguanidine, a type of reactive carbonyl species chelating agent, and a similar trend was observed following overexpression of proteasome β5 via transgenic technology. In conclusion, the present study results suggested that the development of TBI may cause carbonylation of cytoskeletal proteins, which would then undermine the stability of cytoskeletal proteins. Thus, the development of TBI may be improved via the inhibition of cytoskeletal protein carbonylation.

Aminochrome Toxicity is Mediated by Inhibition of Microtubules Polymerization Through the Formation of Adducts with Tubulin

In this study, we investigated the role of adducts formation between aminochrome and tubulin and its interference in microtubules assembly and stability in aminochrome-induced toxicity in SH-SY5Y cells. We also investigated whether changes in the microtubules structures are an early event that could affect tubulin expression. We demonstrated in vitro that aminochrome tubulin adducts inhibit tubulin polymerization and that aminochrome induces microtubules disassembly. Moreover, when the SH-SY5Y cells were incubated with aminochrome, we observed an increase in soluble tubulin, indicating depolymerization of microtubules. Aminochrome generates disruption of the microtubules network, leading to changes in the morphology of the cells inducing cell death, in a dose- and time-dependent manner. Interestingly, these changes preceded cell death and were partly inhibited by paclitaxel, a microtubule-stabilizing agent. Furthermore, we observed that aminochrome increased early tubulin expression before significant cell death occurred. Consequently, all these antecedents suggest that aminochrome toxicity is mediated by early disruption of microtubules network, where the adduct formation between aminochrome and tubulin could be responsible for the inhibition in the assembly microtubules and the loss of microtubules stability. Possibly, the early changes in tubulin expression could correspond to compensatory mechanisms against the toxic effects of aminochrome.

Identification of protein succination as a novel modification of tubulin

Protein succination is a stable post-translational modification that occurs when fumarate reacts with cysteine residues to generate 2SC [S-(2-succino)cysteine]. We demonstrate that both α- and β-tubulin are increasingly modified by succination in 3T3-L1 adipocytes and in the adipose tissue of db/db mice. Incubation of purified tubulin from porcine brain with fumarate (50 mM) or the pharmacological compound DMF (dimethylfumarate, 500 μM) inhibited polymerization up to 35% and 59% respectively. Using MS we identified Cys347α, Cys376α, Cys12β and Cys303β as sites of succination in porcine brain tubulin and the relative abundance of succination at these cysteine residues increased in association with fumarate concentration. The increase in succination after incubation with fumarate altered tubulin recognition by an anti-α-tubulin antibody. Succinated tubulin in adipocytes cultured in high glucose compared with normal glucose also had reduced reactivity with the anti-α-tubulin antibody; suggesting that succination may interfere with tubulin-protein interactions. DMF reacted rapidly with 11 of the 20 cysteine residues in the αβ-tubulin dimer, decreased the number of free thiols and inhibited the proliferation of 3T3-L1 fibroblasts. Our data suggest that inhibition of tubulin polymerization is an important undocumented mechanism of action of DMF. Taken together, our results demonstrate that succination is a novel post-translational modification of tubulin and suggest that extensive modification by fumarate, either physiologically or pharmacologically, may alter microtubule dynamics.

Microtubules and their role in cellular stress in cancer

Microtubules are highly dynamic structures, which consist of α- and β-tubulin heterodimers, and are involved in cell movement, intracellular trafficking, and mitosis. In the context of cancer, the tubulin family of proteins is recognized as the target of the tubulin-binding chemotherapeutics, which suppress the dynamics of the mitotic spindle to cause mitotic arrest and cell death. Importantly, changes in microtubule stability and the expression of different tubulin isotypes as well as altered post-translational modifications have been reported for a range of cancers. These changes have been correlated with poor prognosis and chemotherapy resistance in solid and hematological cancers. However, the mechanisms underlying these observations have remained poorly understood. Emerging evidence suggests that tubulins and microtubule-associated proteins may play a role in a range of cellular stress responses, thus conferring survival advantage to cancer cells. This review will focus on the importance of the microtubule-protein network in regulating critical cellular processes in response to stress. Understanding the role of microtubules in this context may offer novel therapeutic approaches for the treatment of cancer.

Evidence in support of potential applications of lipid peroxidation products in cancer treatment

Cancer cells generate reactive oxygen species (ROS) resulting from mitochondrial dysfunction, stimulation of oncogenes, abnormal metabolism, and aggravated inflammatory activities. Available evidence also suggests that cancer cells depend on intrinsic ROS level for proliferation and survival. Both physiological and pathophysiological roles have been ascribed to ROS which cause lipid peroxidation. In spite of their injurious effects, the ROS and the resulting lipid peroxidation products could be beneficial in cancer treatment. This review presents research findings suggesting that ROS and the resulting lipid peroxidation products could be utilized to inhibit cancer growth or induce cancer cell death. It also underscores the potential of lipid peroxidation products to potentiate the antitumor effect of other anticancer agents. The review also highlights evidence demonstrating other potential applications of lipid peroxidation products in cancer treatment. These include the prospect of lipid peroxidation products as a diagnostic tool to predict the chances of cancer recurrence, to monitor treatment progress or how well cancer patients respond to therapy. Further and detailed research is required on how best to successfully, effectively, and selectively target cancer cells in humans using lipid peroxidation products. This may prove to be an important strategy to complement current treatment regimens for cancer patients.

Cyclooxygenase-2 generates the endogenous mutagen trans-4-hydroxy-2-nonenal in Enterococcus faecalis-infected macrophages

Infection of macrophages by the human intestinal commensal Enterococcus faecalis generates DNA damage and chromosomal instability in mammalian cells through bystander effects. These effects are characterized by clastogenesis and damage to mitotic spindles in target cells and are mediated, in part, by trans-4-hydroxy-2-nonenal (4-HNE). In this study, we investigated the role of COX and lipoxygenase (LOX) in producing this reactive aldehyde using E. faecalis-infected macrophages and interleukin (IL)-10-knockout mice colonized with this commensal. 4-HNE production by E. faecalis-infected macrophages was significantly reduced by COX and LOX inhibitors. The infection of macrophages led to decreased Cox1 and Alox5 expression whereas COX-2 and 4-HNE increased. Silencing Alox5 and Cox1 with gene-specific siRNAs had no effect on 4-HNE production. In contrast, silencing Cox2 significantly decreased 4-HNE production by E. faecalis-infected macrophages. Depleting intracellular glutathione increased 4-HNE production by these cells. Next, to confirm COX-2 as a source for 4-HNE, we assayed the products generated by recombinant human COX-2 and found 4-HNE in a concentration-dependent manner using arachidonic acid as a substrate. Finally, tissue macrophages in colon biopsies from IL-10-knockout mice colonized with E. faecalis were positive for COX-2 by immunohistochemical staining. This was associated with increased staining for 4-HNE protein adducts in surrounding stroma. These data show that E. faecalis, a human intestinal commensal, can trigger macrophages to produce 4-HNE through COX-2. Importantly, it reinforces the concept of COX-2 as a procarcinogenic enzyme capable of damaging DNA in target cells through bystander effects that contribute to colorectal carcinogenesis.

4-Hydroxy-2-nonenal, a reactive product of lipid peroxidation, and neurodegenerative diseases: a toxic combination illuminated by redox proteomics studies

SIGNIFICANCE

Among different forms of oxidative stress, lipid peroxidation comprises the interaction of free radicals with polyunsaturated fatty acids, which in turn leads to the formation of highly reactive electrophilic aldehydes. Among these, the most abundant aldehydes are 4-hydroxy-2-nonenal (HNE) and malondialdehyde, while acrolein is the most reactive. HNE is considered a robust marker of oxidative stress and a toxic compound for several cell types. Proteins are particularly susceptible to modification caused by HNE, and adduct formation plays a critical role in multiple cellular processes.

RECENT ADVANCES

With the outstanding progress of proteomics, the identification of putative biomarkers for neurodegenerative disorders has been the main focus of several studies and will continue to be a difficult task.

CRITICAL ISSUES

The present review focuses on the role of lipid peroxidation, particularly of HNE-induced protein modification, in neurodegenerative diseases. By comparing results obtained in different neurodegenerative diseases, it may be possible to identify both similarities and specific differences in addition to better characterize selective neurodegenerative phenomena associated with protein dysfunction. Results obtained in our laboratory and others support the common deregulation of energy metabolism and mitochondrial function in neurodegeneration.

FUTURE DIRECTIONS

Research towards a better understanding of the molecular mechanisms involved in neurodegeneration together with identification of specific targets of oxidative damage is urgently required. Redox proteomics will contribute to broaden the knowledge in regard to potential biomarkers for disease diagnosis and may also provide insight into damaged metabolic networks and potential targets for modulation of disease progression.

Redox proteomics in selected neurodegenerative disorders: from its infancy to future applications

Several studies demonstrated that oxidative damage is a characteristic feature of many neurodegenerative diseases. The accumulation of oxidatively modified proteins may disrupt cellular functions by affecting protein expression, protein turnover, cell signaling, and induction of apoptosis and necrosis, suggesting that protein oxidation could have both physiological and pathological significance. For nearly two decades, our laboratory focused particular attention on studying oxidative damage of proteins and how their chemical modifications induced by reactive oxygen species/reactive nitrogen species correlate with pathology, biochemical alterations, and clinical presentations of Alzheimer's disease. This comprehensive article outlines basic knowledge of oxidative modification of proteins and lipids, followed by the principles of redox proteomics analysis, which also involve recent advances of mass spectrometry technology, and its application to selected age-related neurodegenerative diseases. Redox proteomics results obtained in different diseases and animal models thereof may provide new insights into the main mechanisms involved in the pathogenesis and progression of oxidative-stress-related neurodegenerative disorders. Redox proteomics can be considered a multifaceted approach that has the potential to provide insights into the molecular mechanisms of a disease, to find disease markers, as well as to identify potential targets for drug therapy. Considering the importance of a better understanding of the cause/effect of protein dysfunction in the pathogenesis and progression of neurodegenerative disorders, this article provides an overview of the intrinsic power of the redox proteomics approach together with the most significant results obtained by our laboratory and others during almost 10 years of research on neurodegenerative disorders since we initiated the field of redox proteomics.

Neuroprotective effects of phlorotannins isolated from a brown alga, Ecklonia cava, against H2O2-induced oxidative stress in murine hippocampal HT22 cells

Exposure of neurons to hydrogen peroxide (H(2)O(2)) results in oxidative stress and the activation of a cascade of intracellular toxic events resulting in oxidation, lipid peroxidation, and Ca(2+) elevation, ultimately resulting in cell death. In this study, we attempted to characterize the neuroprotective effects of phlorotannins isolated from Ecklonia cava, including phloroglucinol, eckol, triphloroethol A, eckstolonol, and dieckol, against H(2)O(2)-induced cell damage in murine hippocampus neuronal (HT22) cells. We measured the reactive oxygen species (ROS) and lipid peroxidation levels and evaluated the resultant cell death and alterations in Ca(2+)-concentrations. All phlorotannins were to scavenge intracellular ROS and repress ROS accumulation, thus preventing lipid peroxidation. Consquently, all phlorotannins reduced H(2)O(2)-induced cell death in HT22 cells. Moreover, phlorotannins inhibited H(2)O(2)-induced Ca(2+) release. This study provides a new useful strategy for preventing neuronal H(2)O(2)-induced oxidative stress.

Lipid peroxidation and neurodegenerative disease

Lipid peroxidation is a complex process involving the interaction of oxygen-derived free radicals with polyunsaturated fatty acids, resulting in a variety of highly reactive electrophilic aldehydes. Since 1975, lipid peroxidation has been extensively studied in a variety of organisms. As neurodegenerative diseases became better understood, research establishing a link between this form of oxidative damage, neurodegeneration, and disease has provided a wealth of knowledge to the scientific community. With the advent of proteomics in 1995, the identification of biomarkers for neurodegenerative disorders became of paramount importance to better understand disease pathogenesis and develop potential therapeutic strategies. This review focuses on the relationship between lipid peroxidation and neurodegenerative diseases. It also demonstrates how findings in current research support the common themes of altered energy metabolism and mitochondrial dysfunction in neurodegenerative disorders.

Modulation of lipid peroxidation and mitochondrial function improves neuropathology in Huntington's disease mice

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder. Oxidative damage has been associated with pathological neuronal loss in HD. The therapeutic modulation of oxidative stress and mitochondrial function using low molecular weight compounds may be an important strategy for delaying the onset and slowing the progression of HD. In the present study, we found a marked increase of 4-hydroxy-2-nonenal (4-HNE) adducts, a lipid peroxidation marker, in the caudate and putamen of HD brains and in the striatum of HD mice. Notably, 4-HNE immunoreactivity was colocalized with mutant huntingtin inclusions in the striatal neurons of R6/2 HD mice. Administration of nordihydroguaiaretic acid (NDGA), an antioxidant that functions by inhibiting lipid peroxidation, markedly reduced 4-HNE adduct formation in the nuclear inclusions of R6/2 striatal neurons. NDGA also protected cultured neurons against oxidative stress-induced cell death by improving ATP generation and mitochondrial morphology and function. In addition, NDGA restored mitochondrial membrane potential, mitochondrial structure, and synapse structure in the striatum of R6/2 mice and increased their lifespan. The present findings suggest that further therapeutic studies using NDGA are warranted in HD and other neurodegenerative diseases characterized by increased oxidative stress and altered mitochondrial function.

Mefloquine neurotoxicity is mediated by non-receptor tyrosine kinase

Among several available antimalarial drugs, mefloquine has proven to be effective against drug-resistant Plasmodium falciparum and remains the drug of choice for both therapy and chemoprophylaxis. However, mefloquine is known to cause adverse neurological and/or psychiatric symptoms, which offset its therapeutic advantage. The exact mechanisms leading to the adverse neurological effects of mefloquine are poorly defined. Alterations in neurotransmitter release and calcium homeostasis, the inhibition of cholinesterases and the interaction with adenosine A(2A) receptors have been hypothesized to play prominent roles in mediating the deleterious effects of this drug. Our recent data have established that mefloquine can also trigger oxidative damage and subsequent neurodegeneration in rat cortical primary neurons. Furthermore, we have utilized a system biology-centered approach and have constructed a pathway model of cellular responses to mefloquine, identifying non-receptor tyrosine kinase 2 (Pyk2) as a critical target in mediating mefloquine neurotoxicity. In this study, we sought to establish an experimental validation of Pyk2 using gene-silencing techniques (siRNA). We have examined whether the downregulation of Pyk2 in primary rat cortical neurons alters mefloquine neurotoxicity by evaluating cell viability, apoptosis and oxidative stress. Results from our study have confirmed that mefloquine neurotoxicity is associated with apoptotic response and oxidative injury, and we have demonstrated that mefloquine affects primary rat cortical neurons, at least in part, via Pyk2. The implication of these findings may prove beneficial in suppressing the neurological side effects of mefloquine and developing effective therapeutic modalities to offset its adverse effects.

Roles of 3-nitrotyrosine- and 4-hydroxynonenal-modified brain proteins in the progression and pathogenesis of Alzheimer's disease

Proteins play an important role in normal structure and function of the cells. Oxidative modification of proteins may greatly alter the structure and may subsequently lead to loss of normal physiological cell functions and may lead to abnormal function of cell and eventually to cell death. These modifications may be reversible or irreversible. Reversible protein modifications, such as phosphorylation, can be overcome by specific enzymes that cause a protein to 'revert' back to its original protein structure, while irreversible protein modifications cannot. Several important irreversible protein modifications include protein nitration and HNE modification, both which have been extensively investigated in research on the progression of Alzheimer's disease (AD). From the earliest stage of AD throughout the advancement of the disorder there is evidence of increased protein nitration and HNE modification. These protein modifications lead to decreased enzymatic activity, which correlates directly to protein efficacy and provides support for several common themes in AD pathology, namely altered energy metabolism, mitochondrial dysfunction and reduced cholinergic neurotransmission. The current review summarized some of the findings on protein oxidation related to different stages of Alzheimer's disease (AD) that will be helpful in understanding the role of protein oxidation in the progression and pathogenesis of AD.

Cell cycle sensing of oxidative stress in Saccharomyces cerevisiae by oxidation of a specific cysteine residue in the transcription factor Swi6p

Yeast cells begin to bud and enter the S phase when growth conditions are favorable during the G(1) phase. When subjected to some oxidative stresses, cells delay entry at G(1), allowing repair of cellular damage. Hence, oxidative stress sensing is coordinated with the regulation of cell cycle. We identified a novel function of the cell cycle regulator of Saccharomyces cerevisiae, Swi6p, as a redox sensor through its cysteine residue at position 404. When alanine was substituted at this position, the resultant mutant, C404A, was sensitive to several reactive oxygen species and oxidants including linoleic acid hydroperoxide, the superoxide anion, and diamide. This mutant lost the ability to arrest in G(1) phase upon treatment with lipid hydroperoxide. The Cys-404 residue of Swi6p in wild-type cells was oxidized to a sulfenic acid when cells were subjected to linoleic acid hydroperoxide. Mutation of Cys-404 to Ala abolished the down-regulation of expression of the G(1) cyclin genes CLN1, CLN2, PCL1, and PCL2 that occurred when cells of the wild type were exposed to the lipid hydroperoxide. In conclusion, oxidative stress signaling for cell cycle regulation occurs through oxidation of the G(1)/S-specific transcription factor Swi6p and consequently leads to suppression of the expression of G(1) cyclins and a delay in cells entering the cell cycle.

Accumulation of protein carbonyls within cerebellar astrocytes in murine experimental autoimmune encephalomyelitis

Recent work from our laboratory has implicated protein carbonylation in the pathophysiology of multiple sclerosis (MS) and experimental autoimmune encephalomyelitis (EAE). The present study was designed to determine the changes in protein carbonylation during disease progression and to identify the target cells and modified proteins in the cerebellum of EAE animals, prepared by active immunization of C57/BL6 mice with MOG(35-55) peptide. In this model, protein carbonylation was maximal at the peak of the disease (acute phase), to decrease thereafter (chronic phase). Double-immunofluorescence microscopy of affected cerebella showed that carbonyls accumulate in white matter astrocytes and to a lesser extent in microglia/macrophages, in both the acute and the chronic phase. Surprisingly, T cells, oligodendrocytes, and neurons were barely stained. By 2D oxyblot and mass spectrometry, β-actin, β-tubulin, GFAP, and HSC-71 were identified as the major targets of carbonylation throughout the disease. Using a pull-down/Western blot method, we found a significant increase in the proportion of carbonylated β-actin, β-tubulin, and GFAP in the chronic phase but not in the acute phase. These results suggest that as disease progresses from the inflammatory to the neurodegenerative phase there may be an inappropriate removal of oxidized cytoskeletal proteins. Additionally, the extensive accumulation of carbonylated GFAP in the chronic phase of EAE may be responsible for the abnormal shape of astrocytes observed at this stage.

The chronological characteristics of SOD1 activity and inflammatory response in the hippocampi of STZ-induced type 1 diabetic rats

Because it appears that oxidative stress and inflammation are implicated with disease pathogenesis in the diabetic brain, many researchers have used streptozotocin (STZ)-induced diabetic animals to study superoxide production and the effects of superoxide scavengers like Cu,Zn-superoxide dismutase (SOD1). However, many studies have been conducted without considering temporal changes after STZ injection. Interestingly, though SOD activities were not significantly different among the groups, SOD1 and 4-hydroxy-2-nonenal (4-HNE) immunoreactivities were significantly enhanced at 3 weeks after an STZ injection (STZ3w) versus only marginal levels in sham controls, whereas microglial activity was remarkably reduced in injected rats at this time. However, SOD1 immunoreactivity and microglial activities were only at the sham level at STZ4w. The present study provides important information concerning cell damage by ROS generated by STZ. Microglial response was found to be inactivated at STZ3w and neuronal cells (NeuN) showed a non-significant tendency to be reduced in number at STZ4w except in the dentate gyrus. We speculated that the above oxidative stress-related events should be accomplished at STZ3w in the brains of STZ-induced diabetes animal models. Therefore, the aim of the present study was to investigate chronological changes in SOD1 immunoreactivity associated with lipid peroxidation and inflammatory responses in the hippocampi of STZ-induced type I diabetic rats.

NGF induced differentiated PC12 cells as in vitro tool to study 4-hydroxynonenal induced cellular damage

Investigations were carried out to examine the suitability of PC12 cells as an in vitro tool to examine 4-hydroxynonenal (4-HNE)-induced toxicity in nervous tissue. On day 8 of differentiation, markers of neural effects and oxidative stress were measured following exposure of PC12 cells to 1-50 microM 4-HNE for 1-8h. Endpoints included dopamine DA-D(2) receptor and glutathione S-transferase (GSTP1-1) protein levels, 4-HNE-protein binding, glutathione (GSH) concentrations and intracellular calcium levels. GSH levels were maximally depleted after 4h. 4-HNE also induced depletion of GSTP1-1 and increased intracellular Ca(++), with the latter seen as early as 1h after exposure. Responses at 8h were not greater than responses at earlier times. The experiments suggest that PC12 cells could be an in vitro tool for understanding toxicant-cell interactions, especially those that result in oxidative stress.

Oxidative stress in diabetes and Alzheimer's disease

Oxidative stress plays a major role in diabetes as well as in Alzheimer's disease and other related neurological diseases. Intracellular oxidative stress arises due to the imbalance in the production of reactive oxygen/reactive nitrogen species and cellular antioxidant defense mechanisms. In turn, the excess reactive oxygen/reactive nitrogen species mediate the damage of proteins and nucleic acids, which have been shown to have direct and deleterious consequences in diabetes and Alzheimer's disease. Oxidative stress also contributes to the production of advanced glycation end products through glycoxidation and lipid peroxidation. The advanced glycation end products and lipid peroxidation products are ubiquitous to diabetes and Alzheimer's disease and serve as markers of disease progression in both disorders. Antioxidants and advanced glycation end products inhibitors, either induced endogenously or exogenously introduced, may counteract with the deleterious effects of the reactive oxygen/reactive nitrogen species and thereby, in prevention or treatment paradigms, attenuate or substantially delay the onset of these devastating pathologies.

Redox proteomics identification of 4-hydroxynonenal-modified brain proteins in Alzheimer's disease: Role of lipid peroxidation in Alzheimer's disease pathogenesis

Numerous studies have shown that neuronal lipids are highly susceptible to oxidative stress including in those brain areas directly involved in the neurodegenerative process of Alzheimer's disease (AD). Lipid peroxidation directly damages membranes and also generates a number of secondary biologically active products (toxic aldehydes)that are capable of easily attacking lipids, proteins, and DNA. Accumulating evidence has demonstrated regionally increased brain lipid peroxidation in patients with AD; however, extensive studies on specific targets of lipid peroxidation-induced damage are still missing. The present study represents a further step in understanding the relationship between oxidative modification of protein and neuronal death associated with AD. We used a proteomics approach to determine specific targets of lipid peroxidation in AD brain, both in hippocampus and inferior parietal lobule, by coupling immunochemical detection of 4-hydroxynonenal-bound proteins with 2-D polyacrylamide gel electrophoresis and MS analysis. We identified 4-hydroxynonenal-bound proteins in the hippocampus and inferior parietal lobule brain regions of subjects with AD. The identified proteins play different biological functions including energy metabolism, antioxidant system, and structural proteins, thus impairing multiple molecular pathways. Our results provide further evidence for the role of lipid peroxidation in the pathogenesis of AD.

Lipid aldehyde-mediated cross-linking of apolipoprotein B-100 inhibits secretion from HepG2 cells

Hepatic oxidative stress and lipid peroxidation are common features of several prevalent disease states, including alcoholic liver disease (ALD) and non-alcoholic fatty liver disease (NAFLD), a common component of the metabolic syndrome. These conditions are characterized in part by excessive accumulation of lipids within hepatocytes, which can lead to autocatalytic degradation of cellular lipids giving rise to electrophilic end products of lipid peroxidation. The pathobiology of reactive lipid aldehydes remains poorly understood. We therefore sought to investigate the effects of 4-hydroxynonenal (4-HNE) and 4-oxononenal (4-ONE) on the transport and secretion of very low-density lipoprotein using HepG2 cells as a model hepatocyte system. Physiologically relevant concentrations of 4-HNE and 4-ONE rapidly disrupted cellular microtubules in a concentration-dependent manner. Interestingly, 4-ONE reduced apolipoprotein B-100 (ApoB) secretion while 4-HNE did not significantly impair secretion. Both 4-HNE and 4-ONE formed adducts with ApoB protein, but 4-HNE adducts were detectable as mono-adducts, while 4-ONE adducts were present as protein-protein cross-links. These results demonstrate that reactive aldehydes generated by lipid peroxidation can differ in their biological effects, and that these differences can be mechanistically explained by the structures of the protein adducts formed.

Neurotrophic support and oxidative stress: converging effects in the normal and diseased nervous system

Oxidative stress and loss of neurotrophic support play major roles in the development of various diseases of the central and peripheral nervous systems. In disorders of the central nervous system such as Alzheimer's, Parkinson's, and Huntington's diseases, oxidative stress appears inextricably linked to the loss of neurotrophic support. A similar situation is seen in the peripheral nervous system in diseases of olfaction, hearing, and vision. Neurotrophic factors act to up-regulate antioxidant enzymes and promote the expression of antioxidant proteins. On the other hand, oxidative stress can cause down-regulation of neurotrophic factors. We propose that normal functioning of the nervous systems involves a positive feedback loop between antioxidant processes and neurotrophic support. Breakdown of this feedback loop in disease states leads to increased oxidative stress and reduced neurotrophic support.

Proteomic identification of dopamine-conjugated proteins from isolated rat brain mitochondria and SH-SY5Y cells

Dopamine oxidation has been previously demonstrated to cause dysfunction in mitochondrial respiration and membrane permeability, possibly related to covalent modification of critical proteins by the reactive dopamine quinone. However, specific mitochondrial protein targets have not been identified. In this study, we utilized proteomic techniques to identify proteins directly conjugated with (14)C-dopamine from isolated rat brain mitochondria exposed to radiolabeled dopamine quinone (150 microM) and differentiated SH-SY5Y cells treated with (14)C-dopamine (150 microM). We observed a subset of rat brain mitochondrial proteins that were covalently modified by (14)C-dopamine, including chaperonin, ubiquinol-cytochrome c reductase core protein 1, glucose regulated protein 75/mitochondrial HSP70/mortalin, mitofilin, and mitochondrial creatine kinase. We also found the Parkinson's disease associated proteins ubiquitin carboxy-terminal hydrolase L1 and DJ-1 to be covalently modified by dopamine in both brain mitochondrial preparations and SH-SY5Y cells. The susceptibility of the identified proteins to covalent modification by dopamine may carry implications for their role in the vulnerability of dopaminergic neurons in Parkinson's disease pathogenesis.

Cytoskeletal protein carbonylation and degradation in experimental autoimmune encephalomyelitis

Protein carbonylation, the non-enzymatic addition of aldehydes or ketones to specific amino acid residues, has been implicated in the pathophysiology of multiple sclerosis. In this study, we investigated whether protein carbonyls also accumulate in the spinal cord of Lewis rats with acute experimental autoimmune encephalomyelitis (EAE). Western blots analysis after derivatization with dinitrophenyl hydrazine (oxyblot) showed elevated protein carbonylation at the time of maximal clinical disability. During the same period glutathione levels were substantially reduced, suggesting a causal relationship between these two markers. In contrast, lipid peroxidation products accumulated in EAE spinal cord well before the appearance of neurological symptoms. Carbonyl staining was not restricted to inflammatory lesions but present throughout the spinal cord particularly in neuronal cell bodies and axons. By 2-dimensional-oxyblot, we identified several cytoskeletal proteins, including beta-actin, glial acidic fibrillary protein, and the neurofilament proteins as the major targets of carbonylation. These findings were confirmed by pull-down experiments, which also showed an increase in the number of carbonylated beta-actin molecules and a decrease in that of oxidized neurofilament proteins in EAE. These data suggest the possibility that oxidation targets neurofilament proteins for degradation, which may contribute to axonal pathology observed in multiple sclerosis and EAE.

Mechanism of destruction of microtubule structures by 4-hydroxy-2-nonenal

A major end product of lipid peroxidation, 4-hydroxy-2-nonenal (HNE), is an electrophilic alkenal and produces Michael adducts with cellular proteins. It is known that exposure of cultured cells to HNE causes rapid disappearance of microtubule networks. In this study we addressed the mechanism. Immunochemical studies revealed that HNE preferentially modified alpha-tubulin in rat primary neuronal cells, PC12 cells, and rat fibroblast cell line 3Y1 cells. This was morphologically associated with the disappearance of microtubule structures in those cells. In a purified rat brain microtubule fraction, HNE modified unpolymerized tubulin and impaired its polymerizability, with a concomitant increase in insolubilized tubulin. Nevertheless, HNE had a marginal effect on the stability of pre-polymerized microtubules. These results suggest that disruption of microtubule assembly as a result of HNE modification of unpolymerized tubulin, rather than destruction of assembled microtubules, is responsible for the disappearance of microtubule structures in cells exposed to HNE.

Unconjugated bilirubin differentially affects the redox status of neuronal and astroglial cells

We investigated whether nerve cell damage by unconjugated bilirubin (UCB) is mediated by oxidative stress and ascertained the neuronal and astroglial susceptibility to injury. Several oxidative stress biomarkers and cell death were determined following incubation of neurons and astrocytes isolated from rat cortical cerebrum with UCB (0.01-1.0 microM). We show that UCB induces a dose-dependent increase in neuronal death in parallel with the oxidation of cell components and a decrease in the intracellular glutathione content. Comparison of the results obtained in both cell types demonstrates that neurons are more vulnerable than astrocytes to oxidative injury by UCB, for which accounts the lower glutathione stores in neuronal cells. Moreover, neuronal oxidative injury is prevented by supplementation with N-acetylcysteine, a glutathione precursor, whereas astroglial sensitivity to UCB is enhanced by inhibition of glutathione synthesis, using buthionine sulfoximine. Collectively, we demonstrate that oxidative stress is involved in UCB neurotoxicity and depict a new therapeutic approach for UCB-induced oxidative damage.

Residue-specific adduction of tubulin by 4-hydroxynonenal and 4-oxononenal causes cross-linking and inhibits polymerization

The modification of proteins by lipid aldehydes produced in cells undergoing oxidative stress has been proposed as an important event that contributes to the pathology of numerous diseases. In this context, the alpha,beta-unsaturated aldehydes 4-hydroxynonenal (4-HNE) and 4-oxononenal (4-ONE) generated during membrane lipid peroxidation have been shown to adduct and inactivate numerous proteins. We report here that purified bovine brain tubulin modified with physiologically relevant concentrations of 4-HNE or 4-ONE results in significant protein cross-linking and marked inhibition of the functional capacity of tubulin polymerization. Comparative analysis demonstrated that 4-ONE is a much more potent cross-linker and inhibitor of tubulin assembly than 4-HNE. Additional experiments revealed the unique property of 4-ONE, initiation of depolymerization of intact microtubules. LC-MS/MS analysis demonstrated that Cys 347alpha, Cys 376alpha, and Cys 303beta are consistently modified by 4-HNE. The identification of target residues within tubulin modified by 4-ONE was not successful, and this was attributed to the marked tubulin cross-linking that occurred immediately after addition of 4-ONE. The modification of Lys residues by reductive propylation demonstrated that the majority of 4-HNE and 4-ONE adducts involve Lys residues, suggesting that tubulin cross-links are Lys-dependent. Taken together, these data suggest a mechanistic basis for the impairment of tubulin function by 4-HNE and 4-ONE produced as a consequence of diseases associated with chronic oxidative stress.

Lipid Peroxidation Scavengers Prevent the Carbonylation of Cytoskeletal Brain Proteins Induced by Glutathione Depletion

In this study, we investigated the possible link between lipid peroxidation (LPO) and the formation of protein carbonyls (PCOs) during depletion of brain glutathione (GSH). To this end, rat brain slices were incubated with the GSH depletor diethyl maleate (DEM) in the absence or presence of classical LPO scavengers: trolox, caffeic acid phenethyl ester (CAPE), and butylated hydroxytoluene (BHT). All three scavengers reduced DEM-induced lipid oxidation and protein carbonylation, suggesting that intermediates/products of the LPO pathway such as lipid hydroperoxides, 4-hydroxynonenal and/or malondialdehyde are involved in the process. Additional in vitro experiments revealed that, among these products, lipid hydroperoxides are most likely responsible for protein oxidation. Interestingly, BHT prevented the carbonylation of cytoskeletal proteins but not that of soluble proteins, suggesting the existence of different mechanisms of PCO formation during GSH depletion. In pull-down experiments, beta-actin and alpha/beta-tubulin were identified as major carbonylation targets during GSH depletion, although other cytoskeletal proteins such as neurofilament proteins and glial fibrillary acidic protein were also carbonylated. These findings may be important in the context of neurological disorders that exhibit decreased GSH levels and increased protein carbonylation such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis.

Oligomeric alpha-synuclein inhibits tubulin polymerization

Earlier investigations have demonstrated that tubulin co-localizes with alpha-synuclein in Lewy bodies and influences the formation of alpha-synuclein aggregation. However, it is not clear whether aggregated alpha-synuclein has any effects on the function of tubulin, i.e. tubulin polymerization, a critical mechanism by which neurons maintain their morphology and execute functions. In this study, we evaluated the effects of aggregated alpha-synuclein on tubulin polymerization in dopaminergic neurons (MES cells), along with mitochondrial function, cell morphology, and viability. The results indicate that MES cells exposed to extracellular oligomeric alpha-synuclein exhibited decreased tubulin polymerization and mitochondrial function as well as morphological alternation long before cell death. Further investigation showed that internalization of oligomeric alpha-synuclein by neurons appeared to be critical in the process, although direct interaction between tubulin and intracellular oligomeric alpha-synuclein was not necessary. Finally, we demonstrated that neurotoxicity induced by oligomeric alpha-synuclein was largely prevented by overexpressing the neuroprotective protein, DJ-1.

Redox regulation of 4-hydroxy-2-nonenal-mediated endothelial barrier dysfunction by focal adhesion, adherens, and tight junction proteins

4-Hydroxy-2-nonenal (4-HNE), one of the major biologically active aldehydes formed during inflammation and oxidative stress, has been implicated in a number of cardiovascular and pulmonary disorders. 4-HNE has been shown to increase vascular endothelial permeability; however, the underlying mechanisms are unclear. Hence, in the current study, we tested our hypothesis that 4-HNE-induced changes in cellular thiol redox status may contribute to modulation of cell signaling pathways that lead to endothelial barrier dysfunction. Exposure of bovine lung microvascular endothelial cells (BLMVECs) to 4-HNE induced reactive oxygen species generation, depleted intracellular glutathione, and altered cell-cell adhesion as measured by transendothelial electrical resistance. Pretreatment of BLM-VECs with thiol protectants, N-acetylcysteine and mercaptopropionyl glycine, attenuated 4-HNE-induced decrease in transendothelial electrical resistance, reactive oxygen species generation, Michael protein adduct formation, protein tyrosine phosphorylation, activation of ERK, JNK, and p38 MAPK, and actin cytoskeletal rearrangement. Treatment of BLMVECs with 4-HNE resulted in the redistribution of FAK, paxillin, VE-cadherin, beta-catenin, and ZO-1, and intercellular gap formation. Western blot analyses confirmed the formation of 4-HNE-derived Michael adducts with the focal adhesion and adherens junction proteins. Also, 4-HNE decreased tyrosine phosphorylation of FAK without affecting total cellular FAK contents, suggesting the modification of integrins, which are natural FAK receptors. 4-HNE caused a decrease in the surface integrin in a time-dependent manner without altering total alpha5 and beta3 integrins. These results, for the first time, revealed that 4-HNE in redox-dependent fashion affected endothelial cell permeability by modulating cell-cell adhesion through focal adhesion, adherens, and tight junction proteins as well as integrin signal transduction that may lead dramatic alteration in endothelial cell barrier dysfunction during heart infarction, brain stroke, and lung diseases.

Cell-permeable peptide antioxidants as a novel therapeutic approach in a mouse model of amyotrophic lateral sclerosis

Reactive oxygen species (ROS) play a major role in the pathogenesis of neurodegenerative diseases. They are important contributors to necrotic and apoptotic cell death. A major proportion of cellular ROS is generated at the inner mitochondrial membrane by the respiratory chain. In the present study, we investigated a novel peptide antioxidant (SS-31) targeted to the inner mitochondrial membrane for its therapeutic effects both in vitro and in vivo in the G93A mouse model of amyotrophic lateral sclerosis (ALS). SS-31 protected against cell death induced by hydrogen peroxide in vitro in neuronal cells stably transfected with either wild-type or mutant Cu/Zn superoxide dismutase (SOD1). Daily intraperitoneal injections of SS-31 (5 mg/kg), starting at 30 days of age, led to a significant improvement in survival and motor performance. In comparison with vehicle-treated G93A mice, SS-31-treated mice showed a decreased cell loss and a decrease in immunostaining for markers of oxidative stress in the lumbar spinal cord. This further enhances the concept that pharmacological modification of oxidative stress is a therapeutic option for the treatment of ALS.

Selectively increased oxidative modifications mapped to detergent‐insoluble forms of Aβ and β‐III tubulin in Alzheimer's disease

Deleterious post-translational modifications (PTMs) to the neuronal cytoskeleton are a proposed mechanistic link between accumulation of amyloid (A) beta peptides and subsequent abnormalities of tau and neurodegeneration in Alzheimer's disease (AD). Here we tested the hypothesis that PTMs on neuronal tubulins selectively accumulate in a pathological protein fraction in AD. We used new software, P-MOD, to identify comprehensively and map PTMs using mass spectral data from soluble (normal) and detergent-insoluble (pathological) protein fractions from AD, as well as total extracts from controls, for selected proteins: Abeta, tau, apolipoprotein (apo) E, glial fibrillary acidic protein (GFAP), alpha-III tubulin, and beta-III tubulin. Our results confirmed direct observations of others by identifying methionine (M) sulfoxides at Abeta position 35 and numerous sites of tau phosphorylation in detergent-insoluble protein from AD, while no PTMs were enriched on primarily astrocyte-derived apoE or GFAP in this fraction. P-MOD mapped several abundant M sulfoxides to neuron-enriched beta-III tubulin but not its heterodimeric partner, neuron-enriched alpha-III tubulin, a result confirmed by selective suppression of CNBr-mediated cleavage of beta-III tubulin. These findings are the first comprehensive assessment of PTMs in AD and point to oxidative modification of beta-III tubulin as a potential contributor to the neuronal cytoskeletal disruption that is characteristic of AD.

Increased brain levels of 4-hydroxy-2-nonenal glutathione conjugates in severe Alzheimer's disease

In the last decade an important role for the progression of neuronal cell death in Alzheimer's disease (AD) has been ascribed to oxidative stress. trans-4-Hydroxy-2-nonenal, a product of lipid peroxidation, forms conjugates with a variety of nucleophilic groups such as thiols or amino moieties. Here we report for the first time the quantitation of glutathione conjugates of trans-4-hydroxy-2-nonenal (HNEGSH) in the human postmortem brain using the specific and very sensitive method of electrospray ionization triple quadrupole mass spectrometry (ESI-MS-MS). Levels of HNEGSH conjugates calculated as the sum of three chromatographically separated diastereomers were determined in hippocampus, entorhinal cortex, substantia innominata, frontal and temporal cortex, as well as cerebellum from patients with AD and controls matched for age, gender, postmortem delay and storage time. Neither age, nor postmortem delay, nor storage time did correlate with levels of HNEGSH conjugates which ranged between 1 and 500 pmol/g fresh weight in the brain areas examined. The brain specimen from patients with clinically and neuropathologically probable AD diagnosed according to criteria of the consortium to establish a registry for AD (CERAD) show increased levels of HNEGSH in the temporal and frontal cortex, as well as in the substantia innominata. Classification of disease severity according to Braak and Braak, which takes into consideration the amount of neurofibrillary tangles and neuritic plaques, revealed highest levels of HNEGSH in the substantia innominata and the hippocampus, two brain regions known to be preferentially affected in AD. These results substantiate the link between conjugates of glutathione with a product of lipid peroxidation and Alzheimer's disease and justify further studies to evaluate the role of HNE metabolites as potential biomarkers for disease progression in AD.