Neurodegeneration and early lethality in superoxide dismutase 2-deficient mice: a comprehensive analysis of the central and peripheral nervous systems

Role of oxidative stress in neurodegenerative disorders: a review of reactive oxygen species and prevention by antioxidants

Neurological disorders include a variety of conditions, including Alzheimer's disease, motor neuron disease and Parkinson's disease, affecting longevity and quality of life, and their pathogenesis is associated with oxidative stress. Several of the chronic neurodegenerative pathologies of the CNS share some common features, such as oxidative stress, inflammation, synapse dysfunctions, protein misfolding and defective autophagia. Neuroinflammation can involve the activation of mast cells, contributing to oxidative stress, in addition to other sources of reactive oxygen species. Antioxidants can powerfully neutralize reactive oxygen species and free radicals, decreasing oxidative damage. Antioxidant genes, like the manganese superoxide dismutase enzyme, can undergo epigenetic changes that reduce their expression, thus increasing oxidative stress in tissue. Alternatively, DNA can be altered by free radical damage. The epigenetic landscape of these genes can change antioxidant function and may result in neurodegenerative disease. This imbalance of free radical production and antioxidant function increases the reactive oxygen species that cause cell damage in neurons and is often observed as an age-related event. Increased antioxidant expression in mice is protective against reactive oxygen species in neurons as is the exogenous supplementation of antioxidants. Manganese superoxide dismutase requires manganese for its enzymic function. Antioxidant therapy is considered for age-related neurodegenerative diseases, and a new mimetic of a manganese superoxide dismutase, avasopasem manganese, is described and suggested as a putative treatment to reduce the oxidative stress that causes neurodegenerative disease. The aim of this narrative review is to explore the evidence that oxidative stress causes neurodegenerative damage and the role of antioxidant genes in inhibiting reactive oxygen species damage. Can the neuronal environment of oxidative stress, causing neuroinflammation and neurodegeneration, be reduced or reversed?

Tenuifolin in the prevention of Alzheimer's disease-like phenotypes: Investigation of the mechanisms from the perspectives of calpain system, ferroptosis, and apoptosis

Polygala tenuifolia was documented to calm the mind and promote wisdom. However, its underlying mechanisms are still unclear. This study aimed to investigate the mechanisms underlying the effects of tenuifolin (Ten) on Alzheimer's disease (AD)-like phenotypes. We first applied bioinformatics methods to screen the mechanisms of P. tenuifolia in the treatment of AD. Thereafter, the d-galactose combined with Aβ1-42 (GCA) was applied to model AD-like behaviors and investigate the action mechanisms of Ten, one active component of P. tenuifolia. The data showed that P. tenuifolia actioned through multi-targets and multi-pathways, including regulation of synaptic plasticity, apoptosis, and calcium signaling, and so forth. Furthermore, in vitro experiments demonstrated that Ten prevented intracellular calcium overload, abnormal calpain system, and down-regulation of BDNF/TrkB signaling induced by GCA. Moreover, Ten suppressed oxidative stress and ferroptosis in HT-22 cells induced by GCA. Calpeptin and ferroptosis inhibitor prevented the decrease of cell viability induced by GCA. Interestingly, calpeptin did not interrupt GCA-induced ferroptosis in HT-22 cells but blocked the apoptosis. Animal experiments further demonstrated that Ten prevented GCA-induced memory impairment in mice and increased synaptic protein expression while reducing m-calpain expression. Ten prevents AD-like phenotypes through multiple signaling by inhibiting oxidative stress and ferroptosis, maintaining the stability of calpain system, and suppressing neuronal apoptosis.

Insights into Manganese Superoxide Dismutase and Human Diseases

Redox equilibria and the modulation of redox signalling play crucial roles in physiological processes. Overproduction of reactive oxygen species (ROS) disrupts the body's antioxidant defence, compromising redox homeostasis and increasing oxidative stress, leading to the development of several diseases. Manganese superoxide dismutase (MnSOD) is a principal antioxidant enzyme that protects cells from oxidative damage by converting superoxide anion radicals to hydrogen peroxide and oxygen in mitochondria. Systematic studies have demonstrated that MnSOD plays an indispensable role in multiple diseases. This review focuses on preclinical evidence that describes the mechanisms of MnSOD in diseases accompanied with an imbalanced redox status, including fibrotic diseases, inflammation, diabetes, vascular diseases, neurodegenerative diseases, and cancer. The potential therapeutic effects of MnSOD activators and MnSOD mimetics are also discussed. Targeting this specific superoxide anion radical scavenger may be a clinically beneficial strategy, and understanding the therapeutic role of MnSOD may provide a positive insight into preventing and treating related diseases.

Antioxidant Role and Cardiolipin Remodeling by Redox-Activated Mitochondrial Ca2+-Independent Phospholipase A2γ in the Brain

Mitochondrial Ca²⁺-independent phospholipase A₂γ (iPLA₂γ/PNPLA8) was previously shown to be directly activated by H₂O₂ and release free fatty acids (FAs) for FA-dependent H⁺ transport mediated by the adenine nucleotide translocase (ANT) or uncoupling protein 2 (UCP2). The resulting mild mitochondrial uncoupling and consequent partial attenuation of mitochondrial superoxide production lead to an antioxidant effect. However, the antioxidant role of iPLA₂γ in the brain is not completely understood. Here, using wild-type and iPLA₂γ-KO mice, we demonstrate the ability of tert-butylhydroperoxide (TBHP) to activate iPLA₂γ in isolated brain mitochondria, with consequent liberation of FAs and lysophospholipids. The liberated FA caused an increase in respiratory rate, which was fully inhibited by carboxyatractyloside (CATR), a specific inhibitor of ANT. Employing detailed lipidomic analysis, we also demonstrate a typical cleavage pattern for TBHP-activated iPLA₂γ, reflecting cleavage of glycerophospholipids from both sn-1 and sn-2 positions releasing saturated FAs, monoenoic FAs, and predominant polyunsaturated FAs. The acute antioxidant role of iPLA₂γ-released FAs is supported by monitoring both intramitochondrial superoxide and extramitochondrial H₂O₂ release. We also show that iPLA₂γ-KO mice were more sensitive to stimulation by pro-inflammatory lipopolysaccharide, as reflected by the concomitant increase in protein carbonyls in the brain and pro-inflammatory IL-6 release in the serum. These data support the antioxidant and anti-inflammatory role of iPLA₂γ in vivo. Our data also reveal a substantial decrease of several high molecular weight cardiolipin (CL) species and accumulation of low molecular weight CL species in brain mitochondria of iPLA₂γ-KO mice. Collectively, our results support a key role of iPLA₂γ in the remodeling of lower molecular weight immature cardiolipins with predominantly saturated acyl chains to high molecular weight mature cardiolipins with highly unsaturated PUFA acyl chains, typical for the brain.

Epigenetic Blockade of Hippocampal SOD2 Via DNMT3b-Mediated DNA Methylation: Implications in Mild Traumatic Brain Injury-Induced Persistent Oxidative Damage

The recurrent events of mild trauma exacerbate the vulnerability for post-traumatic stress disorder; however, the underlying molecular mechanisms are scarcely known. The repeated mild traumatic brain injury (rMTBI) perturbs redox homeostasis which is primarily managed by superoxide dismutase 2 (SOD2). The current study investigates the role of DNA methylation in SOD2 gene regulation and its involvement in rMTBI-induced persistent neuropathology inflicted by weight drop injury paradigm. The oxidative damage, neurodegenerative indicators, and SOD2 function and its regulation in the hippocampus were analyzed after 48 h and 30 days of rMTBI. The temporal and episodic increase in ROS levels (oxidative stress) heightened 8-hydroxyguanosine levels indicating oxidative damage after rMTBI that was concomitant with decline in SOD2 function. In parallel, occupancy of DNMT3b at SOD2 promoter was higher post 30 days of the first episode of rMTBI causing hypermethylation at SOD2 promoter. This epigenetic silencing of SOD2 promoter was sustained after the second episode of rMTBI causing permanent blockade in SOD2 response. The resultant oxidative stress further culminated into the increasing number of degenerating neurons. The treatment with 5-azacytidine, a pan DNMT inhibitor, normalized DNA methylation levels and revived SOD2 function after the second episode of rMTBI. The release of blockade in SOD2 expression by DNMT inhibition also normalized the post-traumatic oxidative consequences and relieved the neurodegeneration and deficits in learning and memory as measured by novel object recognition test. In conclusion, DNMT3b-mediated DNA methylation plays a critical role in SOD2 gene regulation in the hippocampus, and the perturbations therein post rMTBI are detrimental to redox homeostasis manifesting into neurological consequences.

Mitochondrial Superoxide Dismutase Specifies Early Neural Commitment by Modulating Mitochondrial Dynamics

Studies revealing molecular mechanisms underlying neural specification have majorly focused on the role played by different transcription factors, but less on non-nuclear components. Earlier, we reported mitochondrial superoxide dismutase (SOD2) to be essential for self-renewal and pluripotency of mouse embryonic stem cells (mESCs). In the present study, we found SOD2 to be specifically required for neural lineage, but not the meso- or endoderm specification. Temporally, SOD2 regulated early neural genes, but not the matured genes, by modulating mitochondrial dynamics—specifically by enhancing the mitochondrial fusion protein Mitofusin 2 (MFN2). Bio-complementation strategy further confirmed SOD2 to enhance mitochondrial fusion process independent of its antioxidant activity. Over-expression of SOD2 along with OCT4, but neither alone, transdifferentiated mouse fibroblasts to neural progenitor-like colonies, conclusively proving the neurogenic potential of SOD2. In conclusion, our findings accredit a novel role for SOD2 in early neural lineage specification.

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SOD2 is essential for early neural differentiation of mESCs

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Up-regulation of MFN2, but not MFN1, underlies SOD2-mediated neurogenesis

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Antioxidant enzymatic activity of SOD2 is dispensable for mitochondrial fusion

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Overexpression of SOD2 with OCT4 transdifferentiate MEFs to iNPLCs

Tart Cherry Increases Lifespan in Caenorhabditis elegans by Altering Metabolic Signaling Pathways

Aging and healthspan are determined by both environmental and genetic factors. The insulin/insulin-like growth factor-1(IGF-1) pathway is a key mediator of aging in Caenorhabditis elegans and mammals. Specifically, DAF-2 signaling, an ortholog of human IGF, controls DAF-16/FOXO transcription factor, a master regulator of metabolism and longevity. Moreover, mitochondrial dysfunction and oxidative stress are both linked to aging. We propose that daily supplementation of tart cherry extract (TCE), rich in anthocyanins with antioxidant properties may exert dual benefits for mitochondrial function and oxidative stress, resulting in beneficial effects on aging in C. elegans. We found that TCE supplementation at 6 μg or 12 μg/mL, increased (p < 0.05) the mean lifespan of wild type N2 worms, respectively, when compared to untreated control worms. Consistent with these findings, TCE upregulated (p < 0.05) expression of longevity-related genes such as daf-16 and aak-2 (but not daf-2 or akt-1 genes) and genes related to oxidative stress such as sod-2. Further, we showed that TCE supplementation increased spare respiration in N2 worms. However, TCE did not change the mean lifespan of daf-16 and aak-2 mutant worms. In conclusion, our findings indicate that TCE confers healthspan benefits in C. elegans through enhanced mitochondrial function and reduced oxidative stress, mainly via the DAF-16 pathway.

Mitochondrial Superoxide Dismutase: What the Established, the Intriguing, and the Novel Reveal About a Key Cellular Redox Switch

Significance: Reactive oxygen species (ROS) are now widely recognized as central mediators of cell signaling. Mitochondria are major sources of ROS. Recent Advances: It is now clear that mitochondrial ROS are essential to activate responses to cellular microenvironmental stressors. Mediators of these responses reside in large part in the cytosol. Critical Issues: The primary form of ROS produced by mitochondria is the superoxide radical anion. As a charged radical anion, superoxide is restricted in its capacity to diffuse and convey redox messages outside of mitochondria. In addition, superoxide is a reductant and not particularly efficient at oxidizing targets. Because there are many opportunities for superoxide to be neutralized in mitochondria, it is not completely clear how redox cues generated in mitochondria are converted into diffusible signals that produce transient oxidative modifications in the cytosol or nucleus. Future Directions: To efficiently intervene at the level of cellular redox signaling, it seems that understanding how the generation of superoxide radicals in mitochondria is coupled with the propagation of redox messages is essential. We propose that mitochondrial superoxide dismutase (SOD2) is a major system converting diffusion-restricted superoxide radicals derived from the electron transport chain into highly diffusible hydrogen peroxide (H₂O₂). This enables the coupling of metabolic changes resulting in increased superoxide to the production of H₂O₂, a diffusible secondary messenger. As such, to determine whether there are other systems coupling metabolic changes to redox messaging in mitochondria as well as how these systems are regulated is essential.

Amelioration of Huntington's disease phenotype in astrocytes derived from iPSC-derived neural progenitor cells of Huntington's disease monkeys

Huntington’s disease (HD) is a devastating monogenic, dominant, hereditary, neurodegenerative disease. HD is caused by the expansion of CAG repeats in exon 1 of the huntingtin (HTT) gene, IT15, resulting in an expanded polyglutamine (polyQ) residue in the N-terminus of the HTT protein. HD is characterized by the accumulation of mutant HTT (mHTT) in neural and somatic cells. Progressive brain atrophy occurs initially in the striatum and extends to different brain regions with progressive decline in cognitive, behavioral and motor functions. Astrocytes are the most abundant cell type in the brain and play an essential role in neural development and maintaining homeostasis in the central nervous system (CNS). There is increasing evidence supporting the involvement of astrocytes in the development of neurodegenerative diseases such as Parkinson’s disease (PD), Huntington’s disease (HD), Alzheimer’s disease (AD), and amyotrophic lateral sclerosis (ALS). We have generated neural progenitor cells (NPCs) from induced pluripotent stem cells (iPSCs) of transgenic HD monkeys as a model for studying HD pathogenesis. We have reported that NPCs can be differentiated in vitro into mature neural cells, such as neurons and glial cells, and are an excellent tool to study the pathogenesis of HD. To better understand the role of astrocytes in HD pathogenesis and discover new therapies to treat HD, we have developed an astrocyte differentiation protocol and evaluated the efficacy of RNAi to ameliorate HD phenotypes in astrocytes. The resultant astrocytes expressed canonical astrocyte-specific markers examined by immunostaining and real-time PCR. Flow cytometry (FACS) analysis showed that the majority of the differentiated NPCs (95.7%) were positive for an astrocyte specific marker, glial fibrillary acidic protein (GFAP). Functionalities of astrocytes were evaluated by glutamate uptake assay and electrophysiology. Expression of mHTT in differentiated astrocytes induced cytosolic mHTT aggregates and nuclear inclusions, suppressed the expression of SOD2 and PGC1, reduced ability to uptake glutamate, decreased 4-aminopyridine (4-AP) response, and shifted I/V plot measured by electrophysiology, which are consistent with previous reports on HD astrocytes and patient brain samples. However, expression of small-hairpin RNA against HTT (shHD) ameliorated and reversed aforementioned HD phenotypes in astrocytes. This represents a demonstration of a novel non-human primate (NHP) astrocyte model for studying HD pathogenesis and a platform for discovering novel HD treatments.

Alterations in Sod2-Induced Oxidative Stress Affect Endocrine Cancer Progression

CONTEXT

Although important advances have been made in understanding the genetics of endocrine tumors, cellular physiology is relatively understudied as a determinant of tumor behavior. Oxidative stress and reactive oxygen species are metabolic factors that may affect tumor behavior, and these are, in part, controlled by manganese-dependent superoxide dismutase (MnSod), the mitochondrial superoxide dismutase (encoded by SOD2).

OBJECTIVE

We sought to understand the role of MnSod in the prognosis of aggressive human endocrine cancers and directly assessed the effect of MnSod under- or overexpression on tumor behavior, using established mouse thyroid cancer models.

METHODS

We performed transcriptome analysis of human and mouse models of endocrine cancer. To address the role of Sod2 in endocrine tumors, we introduced a Sod2 null allele or a transgenic Sod2 overexpression allele into mouse models of benign thyroid follicular neoplasia or aggressive, metastatic follicular thyroid cancer (FTC) and monitored phenotypic changes in tumor initiation and progression.

RESULTS

In the thyroid, SOD2/Sod2 was downregulated in FTC but not papillary thyroid cancer. Reduced expression of SOD2 was correlated with poorer survival of patients with aggressive thyroid or adrenal cancers. In mice with benign thyroid tumors, Sod2 overexpression increased tumor burden. In contrast, in mice with aggressive FTC, overexpression of Sod2 reduced tumor proliferation and improved mortality rates, whereas its deficiency enhanced tumor growth.

CONCLUSION

Overall, our results indicate that SOD2 has dichotomous roles in cancer progression and acts in a context-specific manner.

The α-lipoic acid improves high-fat diet-induced cerebral damage through inhibition of oxidative stress and inflammatory reaction

This study is to clarify the protective role of α-lipoic acid in high-fat diet-induced cerebral damage mice. The mice were divided into 5 groups: normal control group, high-fat diet (HFD) group, low-dose α-lipoic acid group for prevention, high-dose α-lipoic acid group for prevention, and high-dose α-lipoic acid group for treatment. The groups' weights and blood glucose changes were monitored. We used HE staining to observe morphological changes in the cerebral cortex. The expression levels of the oxidative stress proteins SOD2, catalase, and the inflammatory pathway proteins p-JNK, p-ERK were measured by western blot and immunochemistry. Compared with the control group, the quantity of cortical neurons in the HFD group was decreased, and the samples exhibited retrogression. However, the lipoic acid significantly protected and promoted the cortical neurons survival. Moreover, compared with the HFD group, the expression levels of SOD2 and catalase in the three α-lipoic acid obtained groups were significantly increased. However, the expression levels of the inflammatory pathway proteins p-JNK and p-ERK were significantly decreased. These results indicate that theα-lipoic acid greatly protects the cortical neurons, and inhibited the oxidative stress and inflammatory reactions in the high-fat diet mice.

On the Origin of Superoxide Dismutase: An Evolutionary Perspective of Superoxide-Mediated Redox Signaling

The field of free radical biology originated with the discovery of superoxide dismutase (SOD) in 1969. Over the last 5 decades, a plethora of research has been performed in species ranging from bacteria to mammals that has elucidated the molecular reaction, subcellular location, and specific isoforms of SOD. However, while humans have only begun to study this class of enzymes over the past 50 years, it has been estimated that these enzymes have existed for billions of years, and may be some of the original enzymes found in primitive life. As life evolved over this expanse of time, these enzymes have taken on new and different functional roles potentially in contrast to how they were originally derived. Herein, examination of the evolutionary history of these enzymes provides both an explanation and further inquiries into the modern-day role of SOD in physiology and disease.

Paradoxical Roles of Antioxidant Enzymes: Basic Mechanisms and Health Implications

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated from aerobic metabolism, as a result of accidental electron leakage as well as regulated enzymatic processes. Because ROS/RNS can induce oxidative injury and act in redox signaling, enzymes metabolizing them will inherently promote either health or disease, depending on the physiological context. It is thus misleading to consider conventionally called antioxidant enzymes to be largely, if not exclusively, health protective. Because such a notion is nonetheless common, we herein attempt to rationalize why this simplistic view should be avoided. First we give an updated summary of physiological phenotypes triggered in mouse models of overexpression or knockout of major antioxidant enzymes. Subsequently, we focus on a series of striking cases that demonstrate "paradoxical" outcomes, i.e., increased fitness upon deletion of antioxidant enzymes or disease triggered by their overexpression. We elaborate mechanisms by which these phenotypes are mediated via chemical, biological, and metabolic interactions of the antioxidant enzymes with their substrates, downstream events, and cellular context. Furthermore, we propose that novel treatments of antioxidant enzyme-related human diseases may be enabled by deliberate targeting of dual roles of the pertaining enzymes. We also discuss the potential of "antioxidant" nutrients and phytochemicals, via regulating the expression or function of antioxidant enzymes, in preventing, treating, or aggravating chronic diseases. We conclude that "paradoxical" roles of antioxidant enzymes in physiology, health, and disease derive from sophisticated molecular mechanisms of redox biology and metabolic homeostasis. Simply viewing antioxidant enzymes as always being beneficial is not only conceptually misleading but also clinically hazardous if such notions underpin medical treatment protocols based on modulation of redox pathways.

SOD2 targeted gene editing by CRISPR/Cas9 yields Human cells devoid of MnSOD

To date no models exist to study MnSOD deficiency in human cells. To address this deficiency, we created a SOD2-null human cell line that is completely devoid of detectable MnSOD protein expression and enzyme activity. We utilized the CRISPR/Cas9 system to generate biallelic SOD2 disruption in HEK293T cells. These SOD2-null cells exhibit impaired clonogenic activity, which was rescued by either treatment with GC4419, a pharmacological small-molecule mimic of SOD, or growth in hypoxia. The phenotype of these cells is primarily characterized by impaired mitochondrial bioenergetics. The SOD2-null cells displayed perturbations in their mitochondrial ultrastructure and preferred glycolysis as opposed to oxidative phosphorylation to generate ATP. The activities of mitochondrial complex I and II were both significantly impaired by the absence of MnSOD activity, presumably from disruption of the Fe/S centers in NADH dehydrogenase and succinate dehydrogenase subunit B by the aberrant redox state in the mitochondrial matrix of SOD2-null cells. By creating this model we provide a novel tool with which to study the consequences of lack of MnSOD activity in human cells.

Mechanism of Tang Luo Ning effect on attenuating of oxidative stress in sciatic nerve of STZ-induced diabetic rats

ETHNOPHARMACOLOGICAL RELEVANCE

Tang Luo Ning recipe (TLN), a traditional Chinese herbal medicine based on Huangqi Guizhi Wuwu decoction, has been used clinically to treat diabetic peripheral neuropathy in China. However, the effect of TLN on diabetic peripheral neuropathy is unclear. The objective of this study was to determine the main components in TLN and to investigate the effects of TLN on oxidative stress in diabetic peripheral neuropathy rats.

MATERIALS AND METHODS

The effect of TLN on oxidative stress was investigated in streptozocin (STZ)-induced diabetic rats. Fasting blood glucose, body weight, thermal perception threshold test and motor and sensory nerve conduction velocity of sciatic nerve were measured. Sciatic nerve morphology was observed by Haematoxylin and eosin staining and under transmission electron microscope. T-AOC was measured by colorimetric assay. ROS were measured using enzyme-linked immunosorbent assay. Nrf2 and γGCS protein levels were measured by Western blot analysis. The expression of Bcl2, Bax and Cyto C were examined by immunohistochemistry.

RESULTS

TLN markedly improved the neurological function including thermal perception threshold and nerve conduction velocity of DPN rats. Haematoxylin and eosin (HE) and transmission electron microscopy (TEM) staining results showed that TLN attenuated axon atrophy and demyelination in DPN rats. Moreover, TAOC were increased, whereas ROS content was decreased after treatment with TLN in rats with DPN. Furthermore, TLN increased protein levels of Nrf2, γGCS and Bcl2, and decreased Bax and Cyto C expression.

CONCLUSIONS

TLN improved neurological function to prevent diabetic peripheral neuropathy by attenuating oxidative stress through Nrf2 and Bcl2 activation.

Biochemical and Molecular Alterations Following Arsenic-Induced Oxidative Stress and Mitochondrial Dysfunction in Rat Brain

Oxidative stress is associated with the generation of reactive oxygen species (ROS), which is supposed to be one of the mechanisms of arsenic-induced neurodegeneration. Mitochondria, being the major source of ROS generation may present an important target of arsenic-mediated neurotoxicity. Hence, we planned the study to elucidate the possible biochemical and molecular alterations induced by arsenic exposure in rat brain mitochondria. Chronic sodium arsenite treatment (25 ppm for 12 weeks) resulted in decreased activity of mitochondrial complexes I, II, and IV followed by increased ROS generation. There was decrease in mitochondrial superoxide dismutase (MnSOD) activity in arsenic-treated rat brain further showing increased superoxide radical generation in mitochondria. The decrease in MnSOD activity might be responsible for the increased protein and lipid oxidation as observed in our study. Protein and messenger RNA (mRNA) levels of MnSOD and mitochondrial uncoupling protein 2 (UCP-2) were downregulated suggesting decreased removal of ROS in rat brain. Fourier transform infrared (FTIR) spectroscopy analysis revealed significant decrease in amide A, amide I, amide II, and Olefinic = CH stretching band area suggesting molecular alteration in proteins and lipids after arsenic treatment. The results of present study indicate that arsenic-induced disturbed mitochondrial metabolism, decreased removal of ROS, decrease in protein synthesis, and altered membrane lipid polarity and fluidity may be responsible for the mitochondrial oxidative damage in rat brain that may further be implicated as contributing factor in arsenic-induced neurodegeneration.

Revisiting an age-old question regarding oxidative stress

Significant advances in maintaining health throughout life can be made through a clear understanding of the fundamental mechanisms that regulate aging. The Oxidative Stress Theory of Aging (OSTA) is probably the most well studied mechanistic theory of aging and suggests that the rate of aging is controlled by accumulation of oxidative damage. To directly test the OSTA, aging has been measured in several lines of mice with genetic alterations in the expression of enzymatic antioxidants. Under its strictest interpretation, these studies do not support the OSTA, as modulation of antioxidant expression does not generally affect mouse life span. However, the incidence of many age-related diseases and pathologies is altered in these models, suggesting that oxidative stress does significantly influence some aspects of the aging process. Further, oxidative stress may affect aging in disparate patterns among tissues or under various environmental conditions. In this review, we summarize the current literature regarding aging in antioxidant mutant mice and offer several interpretations of their support of the OSTA.

The use of the Cre/loxP system to study oxidative stress in tissue-specific manganese superoxide dismutase knockout models

SIGNIFICANCE

Respiring mitochondria are a significant site for reactions involving reactive oxygen and nitrogen species that contribute to irreversible cellular, structural, and functional damage leading to multiple pathological conditions. Manganese superoxide dismutase (MnSOD) is a critical component of the antioxidant system tasked with protecting the oxidant-sensitive mitochondrial compartment from oxidative stress. Since global knockout of MnSOD results in significant cardiac and neuronal damage leading to early postnatal lethality, this approach has limited use for studying the mechanisms of oxidant stress and the development of disease in specific tissues lacking MnSOD. To circumvent this problem, a number of investigators have employed the Cre/loxP system to precisely knockout MnSOD in individual tissues.

RECENT ADVANCES

Multiple tissue and organ-specific Cre-expressing mice have been generated, which greatly enhance the specificity of MnSOD knockout in tissues and organ systems that were once difficult, if not impossible to study.

CRITICAL ISSUES

Evaluating the contribution of MnSOD deficiency to oxidant-mediated mitochondrial damage requires careful consideration of the promoter system used for creating the tissue-specific knockout animal, in addition to the collection and interpretation of multiple indices of oxidative stress and damage.

FUTURE DIRECTIONS

Expanded use of well-characterized tissue-specific promoter elements and inducible systems to drive the Cre/loxP recombinational events will lead to a spectrum of MnSOD tissue knockout models, and a clearer understanding of the role of MnSOD in preventing mitochondrial dysfunction in human disease.

Curcumin ameliorated diabetic neuropathy partially by inhibition of NADPH oxidase mediating oxidative stress in the spinal cord

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases are the main enzymes that produce oxidative stress, which plays an important role in painful diabetic neuropathy. Curcumin has been reported to exert an antinociceptive effect in a rat model of diabetic neuropathy by suppressing oxidative stress in the spinal cord. However, it remains unknown whether the mechanism by which curcumin ameliorates diabetic neuropathy can be attributed to spinal NADPH oxidases. This study was designed to determine the effect of curcumin on diabetic neuropathy and to investigate its precise mechanism in relation to NADPH oxidase-mediating oxidative stress in the spinal cord. Diabetic neuropathy was induced in Sprague-Dawley rats by intraperitoneal injection with 1% streptozotocin (STZ; 60 mg/kg). After the onset of diabetic neuropathy, a subset of the diabetic rats received daily intragastric administrations of curcumin (200mg/kg) or intraperitoneal injections of apocynin (2.5mg/kg) for 14 consecutive days, whereas other diabetic rats received equivalent volumes of normal saline (NS). STZ resulted in diabetic neuropathy with hyperglycemia and a lower paw withdrawal threshold (PWT), accompanied by elevations in the expression of the NADPH oxidase subunits p47(phox) and gp91(phox) and in the levels of hydrogen peroxide (H2O2) and malondialdehyde (MDA) and a reduction in superoxide dismutase (SOD) activity (P<0.05) in the spinal cord. Both curcumin and apocynin ameliorated diabetic neuropathy. In conclusion, curcumin attenuated neuropathic pain in diabetic rats, at least partly by inhibiting NADPH oxidase-mediating oxidative stress in the spinal cord.

SOD2 in mitochondrial dysfunction and neurodegeneration

The brain is a highly metabolically active tissue that critically relies on oxidative phosphorylation as a means for maintaining energy. One result of this process is the production of potentially damaging radicals such as the superoxide anion (O2(-)). Superoxide has the capacity to damage components of the electron transport chain and other cellular constituents. Eukaryotic systems have evolved defenses against such damaging moieties, the chief member of which is superoxide dismutase (SOD2), an enzyme that efficiently converts superoxide to the less reactive hydrogen peroxide (H2O2), which can freely diffuse across the mitochondrial membrane. Loss of SOD2 activity can result in numerous pathological phenotypes in metabolically active tissues, particularly within the central nervous system. We review SOD2's potential involvement in the progression of neurodegenerative diseases such as stroke and Alzheimer and Parkinson diseases, as well as its potential role in "normal" age-related cognitive decline. We also examine in vivo models of endogenous oxidative damage based upon the loss of SOD2 and associated neurological phenotypes in relation to human neurodegenerative disorders.