APE/Ref-1 responses to oxidative stress in aged rats

APE1: A critical focus in neurodegenerative conditions

The global growth of the aging population has resulted in an increased prevalence of neurodegenerative diseases, characterized by the progressive loss of central nervous system (CNS) structure and function. Given the high incidence and debilitating nature of neurodegenerative diseases, there is an urgent need to identify potential biomarkers and novel therapeutic targets thereof. Apurinic/apyrimidinic endonuclease 1 (APE1), has been implicated in several neurodegenerative diseases, as having a significant role. Abnormal APE1 expression has been observed in conditions including Alzheimer's disease, stroke, amyotrophic lateral sclerosis, Parkinson's disease, Huntington's disease, and epilepsy. However, whether this dysregulation is protective or harmful remains unclear. This review aims to comprehensively review the current understanding of the involvement of APE1 in neurodegenerative diseases.

DNA damage and repair following traumatic brain injury

Traumatic brain injury (TBI) is known to promote significant DNA damage irrespective of age, sex, and species. Chemical as well as structural DNA modification start within minutes and persist for days after TBI. Although several DNA repair pathways are induced following TBI, the simultaneous downregulation of some of the genes and proteins of these pathways leads to an aberrant overall DNA repair process. In many instances, DNA damages escape even the most robust repair mechanisms, especially when the repair process becomes overwhelmed or becomes inefficient by severe or repeated injuries. The persisting DNA damage and/or lack of DNA repair contributes to long-term functional deficits. In this review, we discuss the mechanisms of TBI-induced DNA damage and repair. We further discussed the putative experimental therapies that target the members of the DNA repair process for improved outcome following TBI.

The DNA damage response (DDR) is induced by the C9orf72 repeat expansion in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a rapidly progressing neurodegenerative disease affecting motor neurons. Hexanucleotide (GGGGCC) repeat expansions in a non-coding region of C9orf72 are the major cause of familial ALS and frontotemporal dementia (FTD) worldwide. The C9orf72 repeat expansion undergoes repeat-associated non-ATG (RAN) translation to produce five dipeptide repeat proteins (DRPs), including poly(GR) and poly(PR). Whilst it remains unclear how mutations in C9orf72 lead to neurodegeneration in ALS/FTD, dysfunction to the nucleolus and R loop formation are implicated as pathogenic mechanisms. These events can damage DNA and hence genome integrity. Cells activate the DNA damage response (DDR) with the aim of repairing this damage. However, if the damage cannot be repaired, apoptosis is triggered. In lumbar motor neurons from C9orf72-positive ALS patients, we demonstrate significant up-regulation of markers of the DDR compared to controls: phosphorylated histone 2AX (γ-H2AX), phosphorylated ataxia telangiectasia mutated (p-ATM), cleaved poly (ADP-Ribose) polymerase 1 (PARP-1) and tumour suppressor p53-binding protein (53BP1). Similarly, significant up-regulation of γ-H2AX and p-ATM was detected in neuronal cells expressing poly(GR)100 and poly(PR)100 compared to controls, revealing that DNA damage is triggered by the DRPs. Nucleophosmin (NPM1) is a histone chaperone induced during the DDR, which interacts with APE1 to enhance DNA repair. We also demonstrate that more NPM1 precipitates with APE1 in C9orf72 patients compared to controls. Furthermore, overexpression of NPM1 inhibits apoptosis in cells expressing poly(GR)100 and poly(PR)100. This study therefore demonstrates that DNA damage is activated by the C9orf72 repeat expansion in ALS.

Aging related changes in circulating reactive oxygen species (ROS) and protein carbonyls are indicative of liver oxidative injury

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Circulating ROS and protein carbonyls increase as early as middle age.

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Oxidative DNA damage is increased in the liver of middle age rats.

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DNA damage repairing capacity is reduced in the liver of middle age rats.

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Circulating protein carbonyls are indicative of oxidative liver injury.

Oxidative stress, defined as an imbalance between the production of reactive oxygen species (ROS) and antioxidant defense mechanisms, plays a major role in inducing oxidative damage and cellular impairment, resulting in a general decline of the physiological functions. The aim of this work was to evaluate age-related changes in circulating ROS levels and plasma protein carbonyls, in very young (2 months aged), young (8 months aged) and in middle age (15 months aged) F344 rats. In addition, the DNA oxidative marker 8-hydroxy-2′-deoxyguanosine (8-OHdG) and the expression of the DNA repair enzymes APE1, OGG1 and UNG genes were also measured in the liver of these animals. We also determined whether systemic oxidative stress reflects oxidative injury at organ level. Our results demonstrate that the increase in circulating ROS and protein carbonyl content occurs as early as middle age. Moreover, increased 8-OHdG in the liver of 15-month-old rats was at least in part associated with a reduced DNA damage repairing capacity as suggested by the down-regulation of APE1 gene expression. In addition, we demonstrated for the first time, that plasma carbonyls and liver 8-OHdG are well correlated, suggesting that plasma protein carbonyls may be used as a surrogate marker of oxidative injury in target organs.

Curcumin revitalizes Amyloid beta (25-35)-induced and organophosphate pesticides pestered neurotoxicity in SH-SY5Y and IMR-32 cells via activation of APE1 and Nrf2

Amyloid beta (Aβ) peptide deposition is the primary cause of neurodegeneration in Alzheimer's disease (AD) pathogenesis. Several reports point towards the role of pesticides in the AD pathogenesis, especially organophosphate pesticides (OPPs). Monocrotophos (MCP) and Chlorpyrifos (CP) are the most widely used OPPs. In this study, the role of MCP and CP in augmenting the Aβ-induced oxidative stress associated with the neurodegeneration in AD has been assessed in human neuroblastoma IMR-32 and SH-SY5Y cell lines. From the cell survival assay, it was observed that MCP and CP reduced cell survival both dose- and time-dependently. Nitro blue tetrazolium (NBT) based assay for determination of intracellular reactive oxygen species (ROS) demonstrated that Aβ(25-35), MCP or CP produce significant oxidative stress alone or synergistically in IMR-32 and SH-SY5Y cells, while pretreatment of curcumin reduced ROS levels significantly in all treatment combinations. In this study, we also demonstrate that treatment of Aβ(25-35) and MCP upregulated inducible nitric oxide synthase (iNOS/NOS2) whereas, no change was observed in neuronal nitric oxide synthase (nNOS/NOS1), but down-regulation of the nuclear factor erythroid 2-related factor 2 (Nrf2) level was observed. While curcumin pretreatment resulted in upregulation of iNOS and Nrf2 proteins. Also, the expression of key DNA repair enzymes APE1, DNA polymerase beta (Pol β), and PARP1 were found to be downregulated upon treatment with MCP, Aβ(25-35) and their combinations at 24 h and 48 h time points. In this study, pretreatment of curcumin to the SH-SY5Y cells enhanced the expression of DNA repair enzymes APE1, pol β, and PARP1 enzymes to counter the oxidative DNA base damage via base excision repair (BER) pathway, and also activated the antioxidant element (ARE) via Nrf2 upregulation. Furthermore, the immunofluorescent confocal imaging studies in SH-SY5Y and IMR-32 cells treated with Aβ(25-35) and MCP-mediated oxidative stress and their combinations at different time periods suggesting for cross-talk between the two proteins APE1 and Nrf2. The APE1's association with Nrf2 might be associated with the redox function of APE1 that might be directly regulating the ARE-mediated neuronal survival mechanisms.

Cardiac Cell Senescence and Redox Signaling

Aging is characterized by a progressive loss of the ability of the organism to cope with stressors and to repair tissue damage. As a result, chronic diseases, including cardiovascular disease, increase their prevalence with aging, underlining the existence of common mechanisms that lead to frailty and age-related diseases. In this frame, the progressive decline of the homeostatic and reparative function of primitive cells has been hypothesized to play a major role in the evolution of cardiac pathology to heart failure. Although initially it was believed that reactive oxygen species (ROS) were produced in an unregulated manner as a byproduct of cellular metabolism, causing macromolecular damage and aging, accumulating evidence indicate the major role played by redox signaling in physiology. Aim of this review is to critically revise evidence linking ROS to cell senescence and aging and to provide evidence of the primary role played by redox signaling, with a particular emphasis on the multifunctional protein APE1/Ref in stem cell biology. Finally, we will discuss evidence supporting the role of redox signaling in cardiovascular cells.

Association between Single-Nucleotide Polymorphisms of the hOGG1,NEIL1,APEX1, FEN1,LIG1, and LIG3 Genes and Alzheimer's Disease Risk

BACKGROUND

One of the factors that contribute to Alzheimer's disease (AD) is the DNA damage caused by oxidative stress and inflammation that occurs in nerve cells. It has been suggested that the risk of AD may be associated with an age-dependent reduction of the DNA repair efficiency. Base excision repair (BER) is, among other things, a main repair system of oxidative DNA damage. One of the reasons for the reduced efficiency of this system may be single-nucleotide polymorphisms (SNP) of the genes encoding its proteins.

METHODS

DNA for genotyping was obtained from the peripheral blood of 281 patients and 150 controls. In the present study, we evaluated the impact of 8 polymorphisms of 6 BER genes on the AD risk. We analyzed the following SNP: c.-468T>G and c.444T>G of APEX1, c.*50C>T and c.*83A>C of LIG3, c.977C>G of OGG1, c.*283C>G of NEIL1, c.-441G>A of FEN1, and c.-7C>T of LIG1.

RESULTS

We showed that the LIG1 c.-7C>T A/A and LIG3 c.*83A>C A/C variants increased, while the APEX1 c.444T>G G/T, LIG1 c.-7C>T G/, LIG3 c.*83A>C C/C variants reduced, the AD risk. We also evaluated the relation between gene-gene interactions and the AD risk. We showed that combinations of certain BER gene variants such as c.977C>G×c.*50C>T CC/CT, c.444T>G×c.*50C>T GG/CT, c.-468T>G×c.*50C>T GG/CT, c.-441G>Ac.*50C>T×c.*50C>T GG/CT, c.*83A>C× c.*50C>T CT/AC, and c.-7C>T×c.*50C>T CT/GG can substantially positively modulate the risk of AD.

CONCLUSIONS

In conclusion, we revealed that polymorphisms of BER genes may have a significant effect on the AD risk, and the presence of polymorphic variants may be an important marker for AD.

Ginkgolide B revamps neuroprotective role of apurinic/apyrimidinic endonuclease 1 and mitochondrial oxidative phosphorylation against Aβ25-35 -induced neurotoxicity in human neuroblastoma cells

Accumulating evidence points to roles for oxidative stress, amyloid beta (Aβ), and mitochondrial dysfunction in the pathogenesis of Alzheimer's disease (AD). In neurons, the base excision repair pathway is the predominant DNA repair (BER) pathway for repairing oxidized base lesions. Apurinic/apyrimidinic endonuclease 1 (APE1), a multifunctional enzyme with DNA repair and reduction-oxidation activities, has been shown to enhance neuronal survival after oxidative stress. This study seeks to determine 1) the effect of Aβ25-35 on reactive oxygen species (ROS)/reactive nitrogen species (RNS) levels, 2) the activities of respiratory complexes (I, III, and IV), 3) the role of APE1 by ectopic expression, and 4) the neuromodulatory role of ginkgolide B (GB; from the leaves of Ginkgo biloba). The pro-oxidant Aβ25-35 peptide treatment increased the levels of ROS/RNS in human neuroblastoma IMR-32 and SH-SY5Y cells, which were decreased after pretreatment with GB. Furthermore, the mitochondrial APE1 level was found to be decreased after treatment with Aβ25-35 up to 48 hr, and the level was increased significantly in cells pretreated with GB. The oxidative phosphorylation (OXPHOS; activities of complexes I, III, and IV) indicated that Aβ25-35 treatment decreased activities of complexes I and IV, and pretreatment with GB and ectopic APE1 expression enhanced these activities significantly compared with Aβ25-35 treatment. Our results indicate that ectopic expression of APE1 potentiates neuronal cells to overcome the oxidative damage caused by Aβ25-35 . In addition, GB has been shown to modulate the mitochondrial OXPHOS against Aβ25-35 -induced oxidative stress and also to regulate the levels of ROS/RNS in the presence of ectopic APE1. This study presents findings from a new point of view to improve therapeutic potential for AD via the synergistic neuroprotective role played by APE1 in combination with the phytochemical GB.

Down-regulation of apurinic/apyrimidinic endonuclease 1 (APE1) in spinal motor neurones under oxidative stress

AIM

Apurinic/apyrimidinic endonuclease 1 (APE1) is an intermediate enzyme in base excision repair which is important for removing damaged nucleotides under normal and pathological conditions. Accumulation of damaged bases causes genome instability and jeopardizes cell survival. Our study is to examine APE1 regulation under oxidative stress in spinal motor neurones which are vulnerable to oxidative insult.

METHODS

We challenged the motor neurone-like cell line NSC-34 with hydrogen peroxide and delineated APE1 function by applying various inhibitors. We also examined the expression of APE1 in spinal motor neurones after spinal root avulsion in adult rats.

RESULTS

We showed that hydrogen peroxide induced APE1 down-regulation and cell death in a differentiated motor neurone-like cell line. Inhibiting the two functional domains of APE1, namely, DNA repair and redox domains potentiated hydrogen peroxide induced cell death. We further showed that p53 phosphorylation early after hydrogen peroxide treatment might contribute to the down-regulation of APE1. Our in vivo results similarly showed that APE1 was down-regulated after root avulsion injury in spinal motor neurones. Delay of motor neurone death suggested that APE1 might not cause immediate cell death but render motor neurones vulnerable to further oxidative insults.

CONCLUSION

We conclude that spinal motor neurones down-regulate APE1 upon oxidative stress. This property renders motor neurones susceptible to continuous challenge of oxidative stress in pathological conditions.

The impact of base excision DNA repair in age-related neurodegenerative diseases

The aging process and several age-related neurodegenerative disorders have been linked to elevated levels of DNA damage induced by ROS and deficiency in DNA repair mechanisms. DNA damage induced by ROS is a byproduct of cellular respiration and accumulation of damage over time, is a fundamental aspect of a main theory of aging. Mitochondria have a pivotal role in generating cellular oxidative stress, and mitochondrial dysfunction has been associated with several diseases. DNA base excision repair is considered the major pathway for repair of oxidized bases in DNA both in the nuclei and in mitochondria, and in neurons this mechanism is particularly important because non-diving cells have limited back-up DNA repair mechanisms. An association between elevated oxidative stress and a decrease in BER is strongly related to the aging process and has special relevance in age-related neurodegenerative diseases. Here, we review the role of DNA repair in aging, focusing on the implications of the DNA base excision repair pathways and how alterations in expression of these DNA repair proteins are related to the aging process and to age-related neurodegenerative diseases.

Base excision repair in the mammalian brain: implication for age related neurodegeneration

The repair of damaged DNA is essential to maintain longevity of an organism. The brain is a matrix of different neural cell types including proliferative astrocytes and post-mitotic neurons. Post-mitotic DNA repair is a version of proliferative DNA repair, with a reduced number of available pathways and most of these attenuated. Base excision repair (BER) is one pathway that remains robust in neurons; it is this pathway that resolves the damage due to oxidative stress. This oxidative damage is an unavoidable byproduct of respiration, and considering the high metabolic activity of neurons this type of damage is particularly pertinent in the brain. The accumulation of oxidative DNA damage over time is a central aspect of the theory of aging and repair of such chronic damage is of the highest importance. We review research conducted in BER mouse models to clarify the role of this pathway in the neural system. The requirement for BER in proliferating cells also correlates with high levels of many of the BER enzymes in neurogenesis after DNA damage. However, the pathway is also necessary for normal neural maintenance as larger infarct volumes after ischemic stroke are seen in some glycosylase deficient animals. Further, the requirement for DNA polymerase β in post-mitotic BER is potentially more important than in proliferating cells due to reduced levels of replicative polymerases. The BER response may have particular relevance for the onset and progression of many neurodegenerative diseases associated with an increase in oxidative stress including Alzheimer's.

Base excision repair in physiology and pathology of the central nervous system

Relatively low levels of antioxidant enzymes and high oxygen metabolism result in formation of numerous oxidized DNA lesions in the tissues of the central nervous system. Accumulation of damage in the DNA, due to continuous genotoxic stress, has been linked to both aging and the development of various neurodegenerative disorders. Different DNA repair pathways have evolved to successfully act on damaged DNA and prevent genomic instability. The predominant and essential DNA repair pathway for the removal of small DNA base lesions is base excision repair (BER). In this review we will discuss the current knowledge on the involvement of BER proteins in the maintenance of genetic stability in different brain regions and how changes in the levels of these proteins contribute to aging and the onset of neurodegenerative disorders.

Time course of neuroprotection induced by normobaric hyperoxia in focal cerebral ischemia

BACKGROUND

The purpose of this study was to determine if normobaric hyperoxia (HO) preconditioning offers durable neuroprotection against cerebral ischemia and the role of reactive oxygen species in the ischemic tolerance mechanism.

MATERIALS AND METHODS

Rats were divided into four experimental main groups. First main group which was comprised four subgroups, were exposed to 90% HO for 6 days, 4 hours per day and subjected to 60 minutes of right middle cerebral artery occlusion (MCAO) after 2, 5, 10, and 15 days. Second group acted as control, was exposed to 21% oxygen (RA; room air) in the same chamber, and subjected to 60 minutes of right MCAO. Third main group comprised two subgroups, were exposed to 90% HO for 6 days, 4 hours per day, received normal saline (NS; 2HO+NS) and dimethylthiourea (DT) just before inhaling 90% HO (2HO+DT). Forth main group was exposed to 21% oxygen (2RA) in the same chamber and received normal saline (2RA+NS) and DT just before inhaling 21% oxygen (2RA+DT). Last two main groups were subjected to 60 minutes of right MCAO after 2 days. After 24-hour reperfusion, neurological deficit score (NDS), infarct volume, brain water content, and Evans blue extravasations were assessed in all animals.

RESULTS

First main group compared with the RA group, NDS, infarct volume, Brain water content, and Evans blue extravasations were reduced in 2, 5, and 10 days significantly, whereas there was no difference among groups 2HO+DT, 2RA+DT, and 2RA+NS.

CONCLUSIONS

In the model of transient focal cerebral ischemia, hyperoxia preconditioning induced effective but transient neuroprotective effects.

Proteomic study of amyloid beta (25-35) peptide exposure to neuronal cells: Impact on APE1/Ref-1's protein-protein interaction

The genotoxic, extracellular accumulation of amyloid β (Aβ) protein and subsequent neuronal cell death are associated with Alzheimer's disease (AD). APE1/Ref-1, the predominant apurinic/apyrimidinic (AP) endonuclease and essential in eukaryotic cells, plays a central role in the base excision repair (BER) pathway for repairing oxidized and alkylated bases and single-strand breaks (SSBs) in DNA. APE1/Ref-1 is also involved in the redox activation of several trans-acting factors (TFs) in various cell types, but little is known about its role in neuronal functions. There is emerging evidence for APE1/Ref-1's role in neuronal cells vulnerable in AD and other neurodegenerative disorders, as reflected in its nuclear accumulation in AD brains. An increase in APE1/Ref-1 has been shown to enhance neuronal survival after oxidative stress. To address whether APE1/Ref-1 level or its association with other proteins is responsible for this protective effect, we used 2-D proteomic analyses and identified cytoskeleton elements (i.e., tropomodulin 3, tropomyosin alpha-3 chain), enzymes involved in energy metabolism (i.e., pyruvate kinase M2, N-acetyl transferase, sulfotransferase 1c), proteins involved in stress response (i.e., leucine-rich and death domain, anti-NGF30), and heterogeneous nuclear ribonucleoprotien-H (hnRNP-H) as being associated with APE1/Ref-1 in Aβ(25-35)-treated rat pheochromocytoma PC12 and human neuroblastoma SH-SY5Y cell lines, two common neuronal precursor lines used in Aβ neurotoxicity studies. Because the levels of some of these proteins are affected in the brains of AD patients, our study suggests a neuroprotective role for APE1/Ref-1 via its association with those proteins and modulating their cellular functions during Aβ-mediated neurotoxicity.

Oxidative genome damage and its repair: implications in aging and neurodegenerative diseases

Reactive oxygen species (ROS), generated endogenously during respiration or exogenously by genotoxic agents, induce oxidized bases and single-strand breaks (SSBs) in DNA that are repaired via the base excision/SSB repair (BER/SSBR) pathway in both the nucleus and mitochondria. Tightly regulated BER/SSBR with multiple sub-pathways is highly complex, and is linked to the replication and transcription. The repair-initiating DNA glycosylases (DGs) or AP-endonuclease (APE1) control the sub-pathway by stably interacting with downstream proteins usually via their common interacting domain (CID). A nonconserved CID with disordered structure usually located at one of the termini includes the sequences for covalent modifications and/or organelle targeting. While the DGs are individually dispensable, the SSBR-initiating APE1 and polynucleotide kinase 3' phosphatase (PNKP) are essential. BER/SSBR of mammalian nuclear and mitochondrial genomes share the same early enzymes. Accumulation of oxidative damage in nuclear and mitochondrial genomes has been implicated in aging and various neurological disorders. While defects in BER/SSBR proteins have been linked to hereditary neurodegenerative diseases, our recent studies implicated transition metal-induced inhibition of NEIL family DGs in sporadic diseases. This review focuses on the recent advances in repair of oxidatively damages in mammalian genomes and their linkage to aging and neurological disorders.

Oxidative stress and its role in the pathogenesis of ischaemic stroke

Stroke is one of the leading causes of mortality and morbidity, with astronomical financial repercussions on health systems worldwide. Ischaemic stroke accounts for approximately 80-85% of all cases and is characterised by the disruption of cerebral blood flow and lack of oxygen to the affected area. Oxidative stress culminates due to an imbalance between pro-oxidants and antioxidants and consequent excessive production of reactive oxygen species. Reactive oxygen species are biphasic, playing a role in normal physiological processes and are also implicated in a number of disease processes, whereby they mediate damage to cell structures, including lipids, membranes, proteins, and DNA. The cerebral vasculature is a major target of oxidative stress playing a critical role in the pathogenesis of ischaemic brain injury following a cerebrovascular attack. Superoxide, the primary reactive oxygen species, and its derivatives have been shown to cause vasodilatation via the opening of potassium channels and altered vascular reactivity, breakdown of the blood-brain barrier and focal destructive lesions in animal models of ischaemic stroke. However, reactive oxygen species are involved in normal physiological processes including cell signalling, induction of mitogenesis, and immune defence. Primarily, this review will focus on the cellular and vascular aspects of reactive oxygen and nitrogen species generation and their role in the pathogenesis of ischaemia-reperfusion phenomena. Secondly, the proposed mechanisms of oxidative stress-related neuronal death will be reflected upon and in summation specific targeted neuroprotective therapies targetting oxidative stress and their role in the pathogenesis of stroke will be discussed.

Ape1/Ref-1 Stimulates GDNF/GFRalpha1-mediated Downstream Signaling and Neuroblastoma Proliferation

We previously reported that glial cell line-derived neurotropic factor (GDNF) receptor alpha1 (GFRalpha1) is a direct target of apurinic/apyrimidinic endonuclease 1 (Ape1/Ref-1). In the present study, we further analyzed the physiological roles of Ape1/Ref-1-induced GFRalpha1 expression in Neuro2a mouse neuroblastoma cells. Ape1/Ref-1 expression caused the clustering of GFRalpha1 immunoreactivity in lipid rafts in response to GDNF. We also found that Ret, a downstream target of GFRalpha1, was functionally activated by GDNF in Ape1/Ref-1-expressing cells. Moreover, GDNF promoted the proliferation of Ape1/Ref-1-expressing Neuro2a cells. Furthermore, GFRalpha1-specific RNA experiments demonstrated that the downregulation of GFRalpha1 by siRNA in Ape1/Ref-1-expressing cells impaired the ability of GDNF to phosphorylate Akt and PLCgamma-1 and to stimulate cellular proliferation. These results show an association between Ape1/Ref-1 and GDNF/GFRalpha signaling, and suggest a potential molecular mechanism for the involvement of Ape1/Ref-1 in neuronal proliferation.

Transcriptional regulatory functions of mammalian AP-endonuclease (APE1/Ref-1), an essential multifunctional protein

The mammalian AP-endonuclease (APE1/Ref-1) plays a central role in the repair of oxidized and alkylated bases in mammalian genomes via the base excision repair (BER) pathway. However, APE1, unlike its E. coli prototype Xth, has two unique and apparently distinct transcriptional regulatory activities. APE1 functions as a redox effector factor (Ref-1) for several transcription factors including AP-1, HIF1-alpha, and p53. APE1 was also identified as a direct trans-acting factor for repressing human parathyroid hormone (PTH) and renin genes by binding to the negative calcium-response element (nCaRE) in their promoters. We have characterized APE1's post-translational modification, namely, acetylation which modulates its transcriptional regulatory function. Furthermore, stable interaction of APE1 with several other trans-acting factors including HIF-1alpha, STAT3, YB-1, HDAC1, and CBP/p300 and formation of distinct trans-acting complexes support APE1's direct regulatory function for diverse genes. Multiple functions of mammalian APE1, both in DNA repair and gene regulation, warrant extensive analysis of its own regulation and dissection of the mechanisms. In this review, we have discussed APE1's own regulation and its role as a transcriptional coactivator or corepressor by both redox-dependent and redox-independent (acetylation-mediated) mechanisms, and explore the potential utility of targeting these functions for enhancing drug sensitivity of cancer cells.

Ape1/Ref-1 induces glial cell-derived neurotropic factor (GDNF) responsiveness by upregulating GDNF receptor alpha1 expression

Apurinic/apyrimidinic endonuclease 1 (Ape1/Ref-1) dysregulation has been identified in several human tumors and in patients with a variety of neurodegenerative diseases. However, the function of Ape1/Ref-1 is unclear. We show here that Ape1/Ref-1 increases the expression of glial cell-derived neurotropic factor (GDNF) receptor alpha1 (GFRalpha1), a key receptor for GDNF. Expression of Ape1/Ref-1 led to an increase in the GDNF responsiveness in human fibroblast. Ape1/Ref-1 induced GFRalpha1 transcription through enhanced binding of NF-kappaB complexes to the GFRalpha1 promoter. GFRalpha1 levels correlate proportionally with Ape1/Ref-1 in cancer cells. The knockdown of endogenous Ape1/Ref-1 in pancreatic cancer cells markedly suppressed GFRalpha1 expression and invasion in response to GNDF, while overexpression of GFRalpha1 restored invasion. In neuronal cells, the Ape1/Ref-1-mediated increase in GDNF responsiveness not only stimulated neurite outgrowth but also protected the cells from beta-amyloid peptide and oxidative stress. Our results show that Ape1/Ref-1 is a novel physiological regulator of GDNF responsiveness, and they also suggest that Ape1/Ref-1-induced GFRalpha1 expression may play important roles in pancreatic cancer progression and neuronal cell survival.

Resveratrol, a unique phytoalexin present in red wine, delivers either survival signal or death signal to the ischemic myocardium depending on dose

Recent studies have demonstrated the cardioprotective abilities of resveratrol, a polyphenolic antioxidant present in red wine. Resveratrol can also kill cancer cells at relatively higher doses by exerting a death signal. We reasoned that resveratrol might possess the ability to protect the cells at lower doses as observed during pharmacological preconditioning of the heart, while at higher doses cause cell death as found for cancer cells. To test this hypothesis, rats were randomly fed for 14 days by gavaging any of the four doses of resveratrol - 2.5, 5.0, 25 or 50 mg/kg - while vehicle-fed animals served as placebo control. After 14 days, isolated working hearts were prepared from both experimental and control animals, and the hearts were subjected to 30-min global ischemia followed by 2 h of reperfusion. The rats fed either 2.5 or 5 mg/kg dose of resveratrol for 14 days provided cardioprotection as evidenced by improved post-ischemic ventricular recovery and reduction of myocardial infarct size and cardiomyocyte apoptosis compared to control. In contrast, the hearts fed either 25 or 50 mg/kg dose of resveratrol depressed cardiac function and increased myocardial infarct size and number of apoptotic cells. The results for Western blots and RT-PCR demonstrated an increase of protein and RNA transcripts of redox proteins including thioredoxin (Trx)-1, Trx-2, glutaredoxin (Grx)-1, Grx-2, redox factor Ref-1 as well as redox-sensitive transcription factor NFkappaB, and survival factors such as phosphorylated-Akt (p-Akt), and Bcl-2 in the animals fed lower doses (2.5 and 5 mg/kg) of resveratrol, while the reverse was true for the animals fed higher doses (25 and 50 mg/kg) of resveratrol. The results thus indicate that at lower doses (2.5 or 5 mg/kg), resveratrol exerts survival signal by up-regulating anti-apoptotic and redox proteins Akt and Bcl-2, while at higher doses (>25 mg/kg), it potentiates a death signal by down-regulating redox proteins and up-regulating pro-apoptotic proteins.

Normobaric hyperoxia induces ischemic tolerance and upregulation of glutamate transporters in the rat brain and serum TNF-alpha level

Recent studies suggest that intermittent and prolonged normobaric hyperoxia (HO) results in ischemic tolerance to reduce ischemic brain injury. In this research, we attempted to see changes in excitatory amino acid transporters (EAATs) and TNF-alpha levels following prolonged and intermittent hyperoxia preconditioning. Rats were divided into four experimental groups, each of 21 animals. The first two were exposed to 95% inspired HO for 4 h/day for 6 consecutive days (intermittent HO, InHO) or for 24 continuous hours (prolonged HO, PrHO). The second two groups acted as controls, and were exposed to 21% oxygen in the same chamber. Each main group was subdivided to middle cerebral artery occlusion (MCAO-operated), sham-operated (without MCAO), and intact (without any surgery) subgroups. After 24 h from pretreatment, MCAO-operated subgroups were subjected to 60 min of right MCAO. After 24 h reperfusion, neurologic deficit score (NDS) and infarct volume were measured in MCAO-operated subgroups. EAATs expression and serum TNF-alpha levels were assessed in sham-operated and intact subgroups. Preconditioning with prolonged and intermittent HO decreased NDS and upregulated EAAT1, EAAT2, and EAAT3 and increased serum TNF-alpha levels significantly. Although further studies are needed to clarify the mechanisms of ischemic tolerance, the intermittent and prolonged HO seems to partly exert their effects via increase serum TNF-alpha levels and upregulation of EAATs.

Biomarkers of oxidative stress and DNA damage in agricultural workers: a pilot study

Oxidative stress and DNA damage have been proposed as mechanisms linking pesticide exposure to health effects such as cancer and neurological diseases. A study of pesticide applicators and farmworkers was conducted to examine the relationship between organophosphate pesticide exposure and biomarkers of oxidative stress and DNA damage. Urine samples were analyzed for OP metabolites and 8-hydroxy-2'-deoxyguanosine (8-OH-dG). Lymphocytes were analyzed for oxidative DNA repair activity and DNA damage (Comet assay), and serum was analyzed for lipid peroxides (i.e., malondialdehyde, MDA). Cellular damage in agricultural workers was validated using lymphocyte cell cultures. Urinary OP metabolites were significantly higher in farmworkers and applicators (p<0.001) when compared to controls. 8-OH-dG levels were 8.5 times and 2.3 times higher in farmworkers or applicators (respectively) than in controls. Serum MDA levels were 4.9 times and 24 times higher in farmworkers or applicators (respectively) than in controls. DNA damage (Comet assay) and oxidative DNA repair were significantly greater in lymphocytes from applicators and farmworkers when compared with controls. Markers of oxidative stress (i.e., increased reactive oxygen species and reduced glutathione levels) and DNA damage were also observed in lymphocyte cell cultures treated with an OP. The findings from these in vivo and in vitro studies indicate that organophosphate pesticides induce oxidative stress and DNA damage in agricultural workers. These biomarkers may be useful for increasing our understanding of the link between pesticides and a number of health effects.

Altered intracellular redox status in Gaucher disease fibroblasts and impairment of adaptive response against oxidative stress

Gaucher disease (GD) is a lysosomal storage disorder, due to glucosylceramide (GlcCer) accumulation in several body tissues, which causes cellular failure by yet unidentified mechanisms. Several evidence indicates that GD pathogenesis is associated to an impairment in intracellular redox state. In fibroblast primary cultures, reactive oxygen species (ROS) levels and protein carbonyl content resulted significantly increased in GD patients compared to healthy donors, suggesting that GD cells, facing a condition of chronic oxidative stress, have evolved an adaptive response to survive. The ROS rise is probably due to NAD(P)H oxidase activity, being inhibited by the treatment with diphenylene iodonium chloride. Interestingly, GD cells are more sensitive to H(2)O(2) induced cell death, suggesting a dysregulation in the adaptive response to oxidative stress in which APE1/Ref-1 plays a central role. We found that the cytoplasmic amounts of APE1/Ref-1 protein were significantly higher in GD fibroblasts with respect to controls, and that GD cells failed to upregulate its expression upon H(2)O(2) treatment. Both ROS and APE1/Ref-1 increases are due to GlcCer accumulation, being prevented by treatment of GD fibroblasts with Cerezyme and induced in healthy fibroblasts treated with conduritol-beta-epoxide. These data, suggesting that GD cells display an impairment in the cellular redox state and in the adaptive cellular response to oxidative stress, may open new perspectives in the comprehension of GD pathogenesis.

DNA repair in neurons: so if they don't divide what's to repair?

Neuronal DNA repair remains one of the most exciting areas for investigation, particularly as a means to compare the DNA repair response in mitotic (cancer) vs. post-mitotic (neuronal) cells. In addition, the role of DNA repair in neuronal cell survival and response to aging and environmental insults is of particular interest. DNA damage caused by reactive oxygen species (ROS) such as generated by mitochondrial respiration includes altered bases, abasic sites, and single- and double-strand breaks which can be prevented by the DNA base excision repair (BER) pathway. Oxidative stress accumulates in the DNA of the human brain over time especially in the mitochondrial DNA (mtDNA) and is proposed to play a critical role in aging and in the pathogenesis of several neurological disorders including Parkinson's disease, ALS, and Alzheimer's diseases. Because DNA damage accumulates in the mtDNA more than nuclear DNA, there is increased interest in DNA repair pathways and the consequence of DNA damage in the mitochondria of neurons. The type of damage that is most likely to occur in neuronal cells is oxidative DNA damage which is primarily removed by the BER pathway. Following the notion that the bulk of neuronal DNA damage is acquired by oxidative DNA damage and ROS, the BER pathway is a likely area of focus for neuronal studies of DNA repair. BER variations in brain aging and pathology in various brain regions and tissues are presented. Therefore, the BER pathway is discussed in greater detail in this review than other repair pathways. Other repair pathways including direct reversal, nucleotide excision repair (NER), mismatch repair (MMR), homologous recombination and non-homologous end joining are also discussed. Finally, there is a growing interest in the role that DNA repair pathways play in the clinical arena as they relate to the neurotoxicity and neuropathy associated with cancer treatments. Among the numerous side effects of cancer treatments, major clinical effects include neurocognitive dysfunction and peripheral neuropathy. These symptoms occur frequently and have not been effectively studied at the cellular or molecular level. Studies of DNA repair may help our understanding of how those cells that are not dividing could succumb to neurotoxicity with the clinical manifestations discussed in the following article.

Neuroanatomical mapping of DNA repair and antioxidative responses in mouse brain: Effects of a single dose of MPTP

The primary objective of this study was to map the normal distribution of the base excision enzyme oxyguanosine glycosylase (OGG1) across mouse-brain regions as a prelude to assessing the effects of various neurotoxicants, ranging from highly selective molecules like MPTP to more global toxic agents. This research is based on the hypothesis that regional brain vulnerability to a toxicant is determined, in part, by variation in the intrinsic capacity of cellular populations to successfully repair oxidative DNA damage. After mapping the normal distributions of OGG1 and superoxide dismutase (SOD) across 44 loci dissected from mouse brain, MPTP, a mitochondrial toxicant with selective dopamine (DA) neuron cytotoxicity was used to elicit focal oxidative stress and DNA repair responses. A single dose of MPTP (20mg/kg, i.p.) elicited time- and region-dependent changes in both SOD and OGG1, with early increases in DNA repair and anti-oxidant activities throughout all regions of brain. In some sampled loci, notably the substantia nigra (SN) and hippocampus, the heightened DNA repair and antioxidant responses were not maintained beyond 48h. Other loci from cerebellum, cerebral cortex and pons maintained high levels of activity up to 72h. Levels of dopamine (DA) were decreased significantly at all time points and remained below control levels in nigro-striatal and mesolimbic systems (ventral tegmental area and nucleus accumbens). Assessment of apoptosis by TUNEL staining revealed a significant increase in number of apoptotic nuclei in the substantia nigra at 72h and not in other loci. The marked degree of apoptosis that became evident in SN at 72h was associated with large decreases in SOD and DNA repair activity at that locus. In conclusion, MPTP elicited global effects on DNA repair and antioxidant activity in all regions of brain, but the most vulnerable loci were unable to maintain elevated DNA repair and antioxidant responses.

Effect of aging on intracellular distribution of abasic (AP) endonuclease 1 in the mouse liver

The abasic (AP) endonuclease (APE1) plays a central role in the base excision repair (BER) pathway for repairing oxidatively damaged bases and abasic sites in mammalian genomes. We have investigated age-dependent changes in APE activity, contributed primarily by APE1, in total extracts as well as in nuclear, mitochondrial, and cytoplasmic compartments of mouse hepatocytes. The APE1 protein and mRNA levels did not differ significantly between the livers of 4-mo (young), 10-mo (middle-aged), and 20-mo (old) mice, and corresponds with similar APE activity. However, we observed a 2-fold increase in specific activity of APE1 in the nucleus, a 2-fold decrease in the cytoplasm, and a 6-fold increase in the mitochondrial matrix of hepatocytes of the old relative to the young animals. Surprisingly, in the middle-age animals we observed 30% increase in APE activity in the nucleus but 6-fold in the mitochondrial matrix. These results indicate age-dependent accumulation of APE1 in the nucleus and mitochondria. Such redistribution occurred early in the mitochondria during the aging process and preferential accumulation of APE in the nucleus was more gradual which may reflect distinct levels of oxidative stress in these organelles.

Alzheimer's disease beta-secretase BACE1 is not a neuron-specific enzyme

The brains of Alzheimer's disease (AD) patients are morphologically characterized by neurofibrillar abnormalities and by parenchymal and cerebrovascular deposits of beta-amyloid peptides. The generation of beta-amyloid peptides by proteolytical processing of the amyloid precursor protein (APP) requires the enzymatic activity of the beta-site APP cleaving enzyme 1 (BACE1). The expression of this enzyme has been localized to the brain, in particular to neurons, indicating that neurons are the major source of beta-amyloid peptides in brain. Astrocytes, on the contrary, are known to be important for beta-amyloid clearance and degradation, for providing trophic support to neurons, and for forming a protective barrier between beta-amyloid deposits and neurons. However, under certain conditions related to chronic stress, the role of astrocytes may not be beneficial. Here we present evidence demonstrating that astrocytes are an alternative source of BACE1 and therefore may contribute to beta-amyloid plaque formation. While resting astroyctes in brain do not express BACE1 at detectable levels, cultured astrocytes display BACE1 promoter activity and express BACE1 mRNA and enzymatically active BACE1 protein. Additionally, in animal models of chronic gliosis and in brains of AD patients, there is BACE1 expression in reactive astrocytes. This would suggest that the mechanism for astrocyte activation plays a role in the development of AD and that therapeutic strategies that target astrocyte activation in brain may be beneficial for the treatment of AD. Also, there are differences in responses to chronic versus acute stress, suggesting that one consequence of chronic stress is an incremental shift to different phenotypic cellular states.

Reactive oxygen species and synaptic plasticity in the aging hippocampus

Aging is associated with a general decline in physiological functions including cognitive functions. Given that the hippocampus is known to be critical for certain forms of learning and memory, it is not surprising that a number of neuronal processes in this brain area appear to be particularly vulnerable to the aging process. Long-term potentiation (LTP), a form of synaptic plasticity that has been proposed as a biological substrate for learning and memory, has been used to examine age-related changes in hippocampal synaptic plasticity. A current hypothesis states that oxidative stress contributes to age-related impairment in learning and memory. This is supported by a correlation between age, memory impairment, and the accumulation of oxidative damage to cellular macromolecules. However, it also has been demonstrated that ROS are necessary components of signal transduction cascades during normal physiological processes. This review discusses the evidence supporting the dual role of reactive oxygen species (ROS) as cellular messenger molecules in normal LTP, as well their role as damaging toxic molecules in the age-related impairment of LTP. In addition, we will discuss parallel analyses of LTP and behavioral tests in mice that overexpress antioxidant enzymes and how the role of antioxidant enzymes and ROS in modulating these processes may vary over the lifespan of an animal.

Senescence-enhanced oxidative stress is associated with deficiency of mitochondrial cytochrome c oxidase in vascular endothelial cells

Cellular senescence-elevated oxidative stress plays a critical role in age-associated vascular endothelial dysfunction. We investigated whether deficiency of mitochondrial cytochrome c oxidase (complex IV) is causally linked to increased oxidant generation during cellular aging using senescent (passage 45) and young (passage 3) pulmonary artery endothelial cells (PAEC). In senescent PAEC, levels of O2- and H2O2 were elevated onefold, respectively, compared to those in young cells. Lipid peroxidation and protein carbonyl contents in aged cells were increased more than twofold compared to young cells. To determine whether lack of complex IV in senescent cells contributed to the increased oxidant generation, complex IV activity in young cells was specifically inhibited using antisense oligonucleotides directed against the mRNA of complex IV subunits. Levels of O2- and H2O2 in PAEC treated with antisense oligonucleotides were elevated onefold, respectively, which correlated with a similar increase in lipid (110%) and protein (20%) oxidation, compared to control oligonucleotides-transfected cells. Moreover, levels of nitrosylated proteins in antisense-transfected cells were increased 30%, compared to controls. These data demonstrate that deficiency of complex IV in senescent cells enhances oxidative and nitrosative stress, which may be responsible for senescence-induced endothelial cell loss and dysfunction.

Decline of nuclear and mitochondrial oxidative base excision repair activity in late passage human diploid fibroblasts

There are numerous studies documenting the increase of oxidative DNA damage in the nuclei and mitochondria of senescing cells as well as in tissues of aging animals. Here, we show that in IMR 90 human diploid fibroblasts, DNA repair activity is robust in both nuclear and mitochondrial extracts, however, the levels of activity differed against the three substrates tested. In extracts, cleavage of the 8-oxoguanine substrate, and to a lesser extent the dihydrouracil-containing substrate, occurred in a concerted reaction between the DNA glycosylases and the second enzyme in the reaction, hAPE. Cleavage of both the furan and the dihydrouracil-containing substrates was unchanged when nuclear extracts from early and late passage cells were compared. However, cleavage of the 8-oxoguanine substrate was substantially reduced in the nuclear extracts from late passage cells and significantly reduced transcription from the hOGG1 gene was observed. When mitochondrial extracts were examined, activity on all three substrates was significantly reduced, with the reduction in hAPE activity being the most marked. The reduction in cleavage of the furan substrate was not simply due to inactive mitochondrial AP endonuclease but a substantially reduced amount of hAPE protein; transcription from the hAPE gene was also reduced. Confocal microscopic analysis confirmed that hAPE was present in the mitochondria of early passage cells but greatly reduced in the mitochondria of late passage cells. Cytoplasmic extracts from late passage fibroblasts also showed reduced activity with all three substrates suggesting that the residual hAPE, and activities that recognized dihydrouracil, were preferentially targeted to the nuclei. Taken together the data support the concept that the increase in oxidative damage in the mitochondrial DNA of senescing cells and tissues from aging animals is due to reduced base excision repair activity.

Oxygen supply modulates MCP-1 release in monocytes from young and aged rats: decrease of MCP-1 transcription and translation is age-related

Hyper or hypoxia may affect the immune system's chemokine production. Monocyte chemotactic protein-1 (MCP-1), an important chemotactic cytokine can be activated by active oxygen species. Groups of rats were exposed to hypoxic and hyperoxic environmental conditions for 60 h and MCP-1 was determined in their peripheral blood mononuclear cells by Elisa and Reverse Transcriptase Polymerase Chain Reaction (RT-PCR). In this study we evaluated if the ability of monocytes to produce MCP-1 under basal conditions or after stimulation with lipopolysaccharide (LPS) or phytohaemagglutinin (PHA) was differently affected by exposure to hyper or hypoxic conditions in young and aged rats. MCP-1 expression and production in monocyte/macrophages from rats at normoxic conditions was reduced in aged subjects. However, spontaneous, LPS or PHA-induced MCP-1 production was up-regulated by exposure to hyperoxic conditions in both young (62 +/- 8, 99 +/- 7, 102 +/- 8 pg/ml, respectively) and aged rats (79 +/- 4, 112 +/- 9, 117 +/- 10 pg/ ml, respectively). We conclude that hyperoxia is an important regulator of MCP-1 release and support the hypothesis that increased % of O2 may serve to initiate MCP-1 production which then serves to recruit and regulate the distribution of mononuclear cells to the sites of inflammation.

Hepatic expression of polymerase beta, Ref-1, PCNA, and Bax in WY 14,643-exposed rats and hamsters

The hepatic levels of three protein markers of oxidative stress, polymerase beta, Ref-1, and PCNA, and of the pro-apoptotic protein, Bax, were quantitated after exposure to WY 14,643 (500 ppm in the feed) for 6 or 34 days in a rodent that is susceptible peroxisome proliferator (PP)-induced liver tumors (the Sprague Dawley rat) and in a rodent that is relatively resistant PP-induced liver tumors (the Syrian hamster). The analysis of detergent-extracted whole liver homogenates by immunoblotting showed a marked increase in the abundance of a 45-kDa variant of polymerase beta immunoreactivity and significant increases in the expression of Ref-1 and PCNA in WY 14,643-exposed rats. In contrast. WY 14,643-exposed hamsters expressed only trace levels of the polymerase beta variant and showed significant decreases in the expression of Ref-1 and PCNA. Long-term WY 14,643 exposure was associated with marked decreases in Bax expression in both species. Dose-response studies in the rat showed that the hepatic expression of the polymerase beta and Ref-1 were significantly increased after 6 days of exposure to WY 14,643 at levels of 5 and 50 ppm, respectively. The analysis of subcellular fractions of rat liver showed that the pathological increases in the levels of polymerase beta, Ref-1, and PCNA were especially prominent in mitochondria-enriched particulate liver subfractions. These results indicate that WY 14,643 exposure is associated with an increase in oxidative stress to the liver and that liver mitochondria are a major target of WY 14,643-associated liver damage. Our data are consistent with the hypothesis that the chronic overexpression of mutagenic or oncogenic effectors like polymerase beta and Ref-1 in a setting of increased hepatocyte proliferation and decreased apoptosis may facilitate peroxisome proliferator-induced hepatocellular carcinoma in the rat.

Attenuated transcriptional responses to oxidative stress in the aged rat brain

The aged nervous system displays impaired cognitive functions, and these impairments are exacerbated in several neurodegenerative diseases. A role for oxidative stress has been suggested for several of these age-associated dysfunctions. In addition, recovery from more acute traumatic insults that also generate oxidative stress is impaired in the aged. Here we examine the response of aged rat hippocampi to normobaric hyperoxia treatments and demonstrate an attenuation in the DNA binding activity of the AP-1 and nuclear factor-kappa B transcription factors, which are important components of stress response signal transduction pathways and can determine shifts in cellular commitments to necrosis, apoptosis, or functional recovery in the central nervous system.

Early decrease of redox factor-1 in spinal motor neurons of presymptomatic transgenic mice with a mutant SOD1 gene

Oxidative stress has been proposed to play a pivotal role in pathogenesis of both sporadic and familial amyotrophic lateral sclerosis (ALS). Expression of DNA repair enzyme redox factor-1 (Ref-1) protein was examined in the spinal cord of transgenic mice with an ALS-linked mutant Cu/Zn superoxide dismutase (SOD1) gene. Immunoblotting and immunocytochemical analyses showed that the most spinal motor neurons lost the immunoreactivity for Ref-1 in the early presymptomatic stage that preceded significant loss of the neurons. The present result suggests that an early impairment of DNA repair in the spinal motor neurons may account for the mutant SOD1-mediated motor neuronal death in this model.

Inhibition of neuronal nitric oxide synthase results in neurodegenerative changes in the axotomised dorsal root ganglion neurons: evidence for a neuroprotective role of nitric oxide in vivo

In axotomised adult rat dorsal root ganglion (DRG), many neurons show a marked increase in expression of neuronal nitric oxide synthase (nNOS). It has been established that NO functions as a neuron-glial signalling molecule by generating cGMP in glia cells that surround the neuron in DRG. Furthermore, in cultures of dissociated DRG deprived of nerve growth factor, many neurons expressed nNOS and cGMP and subsequently died if either enzyme's activity was inhibited suggesting that NO-cGMP pathway could be neuroprotective in stressed DRG neurons. This has now been tested in vivo. It was found, 10 days after sciatic axotomy that nNOS was expressed in 36% of DRG neurons in the L5 and L6 ganglia giving rise to the damaged nerve, compared with 6% in contralateral ganglia. Almost all nNOS neurons and 24% of non-nNOS neurons expressed c-Jun in their nuclei. Ten days following axotomy, treatment with the relatively selective nNOS-blocker, 1-(2-trifluoromethylphenyl) imidazole (TRIM), caused morphology changes in approximately 50% of neurons that consisted of vacuolations, blebbing and highly irregular cell boundaries. Sham operated, TRIM treated, nerve-sectioned, vehicle treated, and controls did not show these changes. These observations further support the view that NO could be neuroprotective in some injured/stressed primary sensory neurons.

Age-related changes in oxidative damage to lipids and DNA in rat skin

Skin is a tissue exposed most frequently to oxidative stress from the environment in daily life. Age-related changes of oxidative damage and antioxidant enzyme activity in the skin were examined in male Fischer 344 rats aged 6 to 30 months. The contents of phosphatidylcholine hydroperoxide (PCOOH) and thiobarbituric acid-reacting substances (TBARS) increased linearly with age. The content of cholesterol hydroperoxide increased until 24 months of age and then decreased. The content of 8-oxo-2'-deoxyguanosine (8-oxodG) increased gradually with age, and was significantly higher at 30 months of age than at 6 months of age. Superoxide dismutase activity tended to decrease with age. The activities of catalase and glutathione peroxidase showed no changes with age. We examined the effect of dietary restriction on the accumulation of oxidative damage in rat skin. The increase in PCOOH content in the skin of dietary-restricted rats was suppressed until 30 months of age. The TBARS and cholesterol hydroperoxide contents in the skin of dietary-restricted rats were significantly lower than in the skin of ad libitum-fed rats, while the 8-oxodG content was somewhat lower in the dietary-restricted rats than the ad libitum-fed rats. These results indicate that oxidative damage to the lipids and DNA in rat skin increases with age and that dietary restriction delays the accumulation of oxidative damage in skin.

Effects of N-acetylcysteine and ambroxol on the production of IL-12 and IL-10 in human alveolar macrophages

BACKGROUND

N-acetylcysteine (NAC) and ambroxol (AMB) have recently been proposed as possible therapeutic agents in the treatment of pulmonary disorders. IL-12 plays an important role in host resistance to infection and the development of Th-1 cells. In contrast, IL-10 is involved in anti-inflammatory and immunoregulatory mechanisms.

OBJECTIVE

We investigated the effects of NAC and AMB on secretions of IL-12 and IL-10 from human alveolar macrophages.

METHODS

Alveolar macrophages were obtained from 7 healthy nonsmokers by bronchoalveolar lavage. The cells were first incubated with either NAC or AMB for 2 h and then cultured in lipopolysaccharide (LPS) solution for 24 h. IL-12 and IL-10 secretions were measured by ELISA.

RESULT

Both NAC and AMB enhanced LPS-induced secretion of IL-12. NAC also enhanced LPS-induced IL-10 secretion, while AMB did not. The ratio IL-12/IL-10 secretion was increased by AMB, but NAC did not affect it.

CONCLUSIONS

The results suggest that NAC enhances inflammatory and immune responses and prevents excessive responses reciprocally, through keeping local balance of IL-12 and IL-10 production in alveolar macrophages at inflammatory sites of bacterial pneumonia. AMB appears to strengthen inflammatory responses and cell-mediated immunity, facilitating the development of Th-1 cells, through shifting the local balance to IL-12 dominance.

Tissue biology of apoptosis. Ref-1 and cell differentiation in the developing retina

Programmed cell death by apoptosis plays a major role in neurogenesis. The sensitivity to apoptosis in developing nervous tissue is strongly dependent on cell interactions taking place within a highly structured environment, composed of various cell types at distinct stages of differentiation. In this article, we review evidence gathered both in vivo and in a histotypical retinal explant preparation in vitro that the bifunctional AP endonuclease/redox factor Ref-1 (HAP1, APE, APEX) may be an anti-apoptotic protein associated with cell differentiation in the developing retina.

Oxidative stress and neuronal DNA fragmentation mediate age-dependent vulnerability to the mitochondrial toxin, 3-nitropropionic acid, in the mouse striatum

Oxidative stress is involved in the neuropathology of several neurodegenerative diseases and stroke, all of which are related to excitotoxicity. Age-dependent vulnerability is characteristic of these conditions. It is not clear whether apoptosis-related neuronal death is involved in age-dependent vulnerability to excitotoxicity. We evaluated whether apoptosis-related neuronal death after treatment with 3-nitropropionic acid (3-NP) is age-dependent in the mouse striatum. We have demonstrated that oxidative stress occurs early after 3-NP treatment and even more so in aged mice. DNA fragmentation with terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end labeling staining and gel electrophoresis occurred in an age-dependent fashion. Expression of the DNA repair enzyme, apurinic/apyrimidinic endonuclease, was more attenuated in old mice. Therefore, these results suggest that oxidative stress induces age-dependent neuronal apoptosis in the mouse striatum after 3-NP treatment, which in turn produces an age-dependent vulnerability to 3-NP.

Preconditioning regulation of bcl-2 and p66shc by human NOS1 enhances tolerance to oxidative stress

Preconditioning stress induced by a transient ischemia may increase brain tolerance to oxidative stress, and the underlying neuroprotective mechanisms are not well understood. In a series of experiments, we found that endogenous nitric oxide (NO), S-nitrosoglutathione (GSNO), and antioxidants blocked serum deprivation-induced oxidative stress and apoptosis in human neuroblastoma cells. Similar to nuclear redox factor-1 (Ref-1), mRNA of human neuronal nitric oxide synthase (hNOS1) was maximally up-regulated within 2 h after oxidative stress and down-regulated by NO/GSNO and hydroxyl radical (OH) scavenger. A brief preconditioning stress induced by serum deprivation for 2 h caused a delayed increase in the expression of hNOS1 protein and the associated formation of NO and cGMP, which in turn decreased OH generation and stress-related cell death. In addition to inhibiting caspase-3 through a dithiothreitol-sensitive S-nitrosylation process, preconditioning stress concomitantly up-regulated the expression of the anti-apoptotic bcl-2 protein and down-regulated the p66shc adaptor protein. This beneficial cytoprotective process of preconditioning stress is mediated by newly synthesized NO because it can be suppressed by the inhibition of hNOS1 and guanylyl cyclase. Therefore, the constitutive isoform of hNOS1 is dynamically redox-regulated to meet both functional and compensatory demands of NO for gene regulation, antioxidant defense, and tolerance to oxidative stress.

Going APE over ref-1

The DNA base excision repair (BER) pathway is responsible for the repair of cellular alkylation and oxidative DNA damage. A crucial and the second step in the BER pathway involves the cleavage of baseless sites in DNA by an AP endonuclease. The major AP endonuclease in mammalian cells is Ape1/ref-1. Ape1/ref-1 is a multifunctional protein that is not only responsible for repair of AP sites, but also functions as a reduction-oxidation (redox) factor maintaining transcription factors in an active reduced state. Ape1/ref-1 has been shown to stimulate the DNA binding activity of numerous transcription factors that are involved in cancer promotion and progression such as Fos, Jun, NF(B, PAX, HIF-1(, HLF and p53. Ape1/ref-1 has also been implicated in the activation of bioreductive drugs which require reduction in order to be active and has been shown to interact with a subunit of the Ku antigen to act as a negative regulator of the parathyroid hormone promoter, as well as part of the HREBP transcription factor complex. Ape1/ref-1 levels have been found to be elevated in a number of cancers such as ovarian, cervical, prostate, rhabdomyosarcomas and germ cell tumors and correlated with the radiosensitivity of cervical cancers. In this review, we have attempted to try and assimilated as much data concerning Ape1/ref-1 and incorporate the rapidly growing information on Ape1/ref-1 in a wide variety of functions and systems.

Redox factor-1 in muscle biopsies of patients with inclusion-body myositis

To determine whether redox factor-1 (Ref-1) participates in the pathogenesis of inclusion-body myositis (IBM), we immunolocalized Ref-1 in muscle biopsies of IBM patients by light- and electron-microscopy. Approximately 70-80% of the IBM vacuolated muscle fibers had focal inclusions strongly immunoreactive for Ref-1. By immunoelectronmicroscopy, Ref-1 was localized to paired-helical filaments, 6-10 nm amyloid-like fibrils and amorphous material. Virtually all regenerating and necrotic muscle fibers in various muscle biopsies had diffusely strong Ref-1 immunoreactivity. At all neuromuscular junctions, postsynaptically there was strong Ref-1 immunoreactivity. Our study suggests that Ref-1 plays a role in IBM pathogenesis, and in other pathologic and normal processes of human muscle.

Increased AP-1 DNA-binding activity and nuclear REF-1 accumulation in lead-exposed primary cultures of astrocytes

Pb was shown to perturb neuronal and glial function either directly by interacting with protein thiol groups or indirectly by mimicking Ca(2+) and increasing oxidative stress. In view of the potential action of Pb on cellular redox homeostasis we studied the regulation of activator protein-1 (AP-1) DNA binding. A 1h incubation of astrocyte primary cultures with 10 microM Pb caused a 2.5 fold increase in AP-1 DNA binding. An assessment of how Pb elicited this increase revealed the involvement of 1. transcriptional and 2. posttranslational processes. The first one was documented by an increase of c-jun mRNA content after 15 to 30 min of 10 microM Pb exposure. The second one was suggested by an enhanced nuclear accumulation of redox factor-1 after 30 to 60 min of 10 microM Pb exposure. The Pb-elicited increase of the reduction/oxidation-sensitive AP-1 signal transduction may regulate target genes operative in cell survival or cell death.

Damage and repair of nerve cell DNA in toxic stress

It is generally agreed that ALS/PDC is triggered by a disappearing environmental factor peculiar to the lifestyle of people of the western Pacific (i.e., Guam, Irian Jaya, Indonesia, and the Kii Peninsula of Japan). A strong candidate is the cycad plant genotoxin cycasin, the beta-D-glucoside of methylazoxymethanol (MAM). We propose that prenatal or postnatal exposure to low levels of cycasin/MAM may damage neuronal DNA, compromise DNA repair, perturb neuronal gene expression, and irreversibly alter cell function to precipitate a slowly evolving disease ("slow-toxin" hypothesis). In support of our hypothesis, we have demonstrated the following: 1. DNA from postmitotic rodent central nervous system neurons is particularly sensitive to damage by MAM. 2. MAM reduces DNA repair in human and rodent neurons, whereas DNA-repair inhibitors potentiate MAM-induced DNA damage and toxicity in mature rodent nervous tissue. 3. Human neurons (SY5Y neuroblastoma) that are deficient in DNA repair are susceptible to MAM-induced cytotoxicity and DNA damage, whereas overexpression of DNA repair in similar cells is protective. 4. MAM alters gene expression in SY5Y human neuroblastoma cells and, in the presence of DNA damage and reduced DNA repair, enhances glutamate-modulated expression of tau mRNA in rat primary neurons; the corresponding protein (TAU) is elevated in ALS/PDC and Alzheimer's disease. These findings support a direct relationship between MAM-induced DNA damage and neurotoxicity and suggest the genotoxin may operate in a similar manner in vivo. More broadly, a combination of genotoxin-induced DNA damage (via exogenous and/or endogenous agents) and disturbed DNA repair may be important contributing factors in the slow and progressive degeneration of neurons that is characteristic of sporadic neurodegenerative disease. Preliminary studies demonstrate that DNA repair is reduced in the brain of subjects with western Pacific ALS/PDC, ALS, and Alzheimer's disease, which would increase the susceptibility of brain tissue to DNA damage by endogenous/exogenous genotoxins. Interindividual differences in the extent of prior exposure to DNA-damaging agents and/or the efficiency of its repair might produce population variety in the rate of damage accumulation and explain the susceptibility of certain individuals to sporadic neurodegenerative disease. Studies are underway using DNA-repair proficient and deficient neuronal cell cultures and mutant mice to explore gene-environment interplay with respect to MAM treatment, DNA damage, and DNA repair, and the age-related appearance of neurobehavioral and neuropathological compromise.