Hydrogen peroxide causes significant mitochondrial DNA damage in human RPE cells

Effects of Bevacizumab on Bcl-2 Expression and Apoptosis in Retinal Pigment Epithelial Cells under Oxidative Stress

Purpose

To evaluate the effects of bevacizumab on expression of B-cell leukemia/lymphoma (Bcl)-2 and apoptosis in retinal pigment epithelial (RPE) cells under oxidative stress conditions.

Methods

RPE cells were treated with H₂O₂ (0, 100, 200, 300, and 400 µM) and bevacizumab at or above the doses normally used in clinical practice (0, 0.33, 0.67, 1.33, and 2.67 mg/mL). Cell apoptosis was measured using flow cytometry with annexin V-fluorescein isothiocyanate. The expression of Bcl-2 mRNA was determined using reverse transcription polymerase chain reaction.

Results

Under low oxidative stress conditions (H₂O₂ 100 µM), cell apoptosis was not significantly different at any concentration of bevacizumab, but Bcl-2 mRNA expression decreased with increasing concentration of bevacizumab (0.33, 0.67, 1.33, and 2.67 mg/mL). Under moderate oxidative stress conditions (H₂O₂ 200 µM), Bcl-2 mRNA expression decreased with increasing concentration of bevacizumab (0.33, 0.67, 1.33, and 2.67 mg/mL), but cell apoptosis increased only at 2.67 mg/mL of bevacizumab. Under high oxidative stress (300 µM) conditions, cell apoptosis increased at high concentrations of bevacizumab (1.33 and 2.67 mg/mL), but it did not correlate with Bcl-2 expression.

Conclusions

Withdrawal of vascular endothelial growth factor can lead to RPE cell apoptosis and influences the expression of anti-apoptotic genes such as Bcl-2 under oxidative stress conditions. Since oxidative stress levels of each patient are unknown, repeated injections of intravitreal bevacizumab, as in eyes with age-related macular degeneration, might influence RPE cell survival.

Reactive Oxygen Species and Mitochondrial DNA Damage and Repair in BCR-ABL1 Cells Resistant to Imatinib

Imatinib revolutionized the therapy of chronic myeloid leukemia (CML), but the resistance to it became an emerging problem. We reported previously that CML cells expressing the BCR/ABL1 fusion gene, accumulated a high level of reactive oxygen species (ROS) due to deregulated mitochondrial electron transport chain, which in turn led to genomic instability, resulting in imatinib resistance. In the present work, we hypothesize that imatinib-resistant cells may show higher instability of mitochondrial DNA (mtDNA) than their sensitive counterparts. To verify this hypothesis, we checked the ROS level and mtDNA damage and repair in model CML cells sensitive and resistant to imatinib and exposed to doxorubicin (DOX), a DNA-damaging agent. The extent of endogenous ROS in imatinib-resistant cells was higher than in their sensitive counterparts and DOX potentiated this relationship. ROS level in cells with primary resistance, which resulted from the T315I mutation in BCR/ABL1, was higher than in cells with acquired resistance. DOX-induced mtDNA damage in T315I imatinib-resistant cells was more pronounced than in imatinib-sensitive cells. All kinds of cells were repairing mtDNA damage with similar kinetics. In conclusion, imatinib-resistant cells can show increased instability of mtDNA, which can result from increased ROS production.

Bioenergetic programming of macrophages by the apolipoprotein A-I mimetic peptide 4F

The apoA-I (apolipoprotein A-I) mimetic peptide 4F favours the differentiation of human monocytes to an alternatively activated M2 phenotype. The goal of the present study was to test whether the 4F-mediated differentiation of MDMs (monocyte-derived macrophages) requires the induction of an oxidative metabolic programme. 4F treatment induced several genes in MDMs that play an important role in lipid metabolism, including PPARγ (peroxisome-proliferator-activated receptor γ) and CD36. Addition of 4F was associated with a significant increase in FA (fatty acid) uptake and oxidation compared with vehicle treatment. Mitochondrial respiration was assessed by measurement of the OCR (oxygen-consumption rate). 4F increased basal and ATP-linked OCR as well as maximal uncoupled mitochondrial respiration. These changes were associated with a significant increase in ΔΨm (mitochondrial membrane potential). The increase in metabolic activity in 4F-treated MDMs was attenuated by etomoxir, an inhibitor of mitochondrial FA uptake. Finally, addition of the PPARγ antagonist T0070907 to 4F-treated MDMs reduced the expression of CD163 and CD36, cell-surface markers for M2 macrophages, and reduced basal and ATP-linked OCR. These results support our hypothesis that the 4F-mediated differentiation of MDMs to an anti-inflammatory phenotype is due, in part, to an increase in FA uptake and mitochondrial oxidative metabolism.

Salvianolic acid A protects RPE cells against oxidative stress through activation of Nrf2/HO-1 signaling

Reactive oxygen species (ROS) impair the physiological functions of retinal pigment epithelial (RPE) cells, which is known as one major cause of age-related macular degeneration. Salvianolic acid A (Sal A) is the main effective aqueous extract of Salvia miltiorrhiza. The aim of this study was to test the potential role of Sal A against oxidative stress in cultured RPE cells and to investigate the underlying mechanistic signaling pathways. We observed that Sal A significantly inhibited hydrogen peroxide (H2O2)-induced primary and transformed RPE cell death and apoptosis. H2O2-stimulated mitogen-activated protein kinase activation, ROS production, and subsequent proapoptotic AMP-activated protein kinase activation were largely inhibited by Sal A. Further, Sal A stimulation resulted in a fast and dramatic activation of Akt/mammalian target of rapamycin complex 1 (mTORC1) signaling, followed by phosphorylation, accumulation, and nuclear translocation of the NF-E2-related factor 2 (Nrf2), along with increased expression of the antioxidant-response element-dependent gene heme oxygenase-1 (HO-1). Both Nrf2 and HO-1 were required for Sal A-mediated cytoprotective effect, as Nrf2/HO-1 inhibition abolished Sal A-induced beneficial effects against H2O2. Meanwhile, the PI3K/Akt/mTORC1 chemical inhibitors not only suppressed Sal A-induced Nrf2/HO-1 activation, but also eliminated its cytoprotective effect in RPE cells. These observations suggest that Sal A activates the Nrf2/HO-1 axis in RPE cells and protects against oxidative stress via activation of Akt/mTORC1 signaling.

The effects of bioactive compounds from plant foods on mitochondrial function: a focus on apoptotic mechanisms

Mitochondria are essential organelles for cellular integrity and functionality maintenance and their imparement is implicated in the development of a wide range of diseases, including metabolic, cardiovascular, degenerative and hyperproliferative pathologies. The identification of different compounds able to interact with mitochondria for therapeutic purposes is currently becoming of primary importance. Indeed, it is well known that foods, particularly those of vegetable origin, present several constituents with beneficial effects on health. This review summarizes and updates the most recent findings concerning the mechanisms through which different dietary compounds from plant foods affect mitochondria functionality in healthy and pathological in vitro and in vivo models, paying particular attention to the pathways involved in mitochondrial biogenesis and apoptosis.

Aging is not a disease: distinguishing age-related macular degeneration from aging

Age-related macular degeneration (AMD) is a disease of the outer retina, characterized most significantly by atrophy of photoreceptors and retinal pigment epithelium accompanied with or without choroidal neovascularization. Development of AMD has been recognized as contingent on environmental and genetic risk factors, the strongest being advanced age. In this review, we highlight pathogenic changes that destabilize ocular homeostasis and promote AMD development. With normal aging, photoreceptors are steadily lost, Bruch's membrane thickens, the choroid thins, and hard drusen may form in the periphery. In AMD, many of these changes are exacerbated in addition to the development of disease-specific factors such as soft macular drusen. Para-inflammation, which can be thought of as an intermediate between basal and robust levels of inflammation, develops within the retina in an attempt to maintain ocular homeostasis, reflected by increased expression of the anti-inflammatory cytokine IL-10 coupled with shifts in macrophage plasticity from the pro-inflammatory M1 to the anti-inflammatory M2 polarization. In AMD, imbalances in the M1 and M2 populations together with activation of retinal microglia are observed and potentially contribute to tissue degeneration. Nonetheless, the retina persists in a state of chronic inflammation and increased expression of certain cytokines and inflammasomes is observed. Since not everyone develops AMD, the vital question to ask is how the body establishes a balance between normal age-related changes and the pathological phenotypes in AMD.

Prolonged cigarette smoke exposure alters mitochondrial structure and function in airway epithelial cells

BACKGROUND

Cigarette smoking is the major risk factor for COPD, leading to chronic airway inflammation. We hypothesized that cigarette smoke induces structural and functional changes of airway epithelial mitochondria, with important implications for lung inflammation and COPD pathogenesis.

METHODS

We studied changes in mitochondrial morphology and in expression of markers for mitochondrial capacity, damage/biogenesis and fission/fusion in the human bronchial epithelial cell line BEAS-2B upon 6-months from ex-smoking COPD GOLD stage IV patients to age-matched smoking and never-smoking controls.

RESULTS

We observed that long-term CSE exposure induces robust changes in mitochondrial structure, including fragmentation, branching and quantity of cristae. The majority of these changes were persistent upon CSE depletion. Furthermore, long-term CSE exposure significantly increased the expression of specific fission/fusion markers (Fis1, Mfn1, Mfn2, Drp1 and Opa1), oxidative phosphorylation (OXPHOS) proteins (Complex II, III and V), and oxidative stress (Mn-SOD) markers. These changes were accompanied by increased levels of the pro-inflammatory mediators IL-6, IL-8, and IL-1β. Importantly, COPD primary bronchial epithelial cells (PBECs) displayed similar changes in mitochondrial morphology as observed in long-term CSE-exposure BEAS-2B cells. Moreover, expression of specific OXPHOS proteins was higher in PBECs from COPD patients than control smokers, as was the expression of mitochondrial stress marker PINK1.

CONCLUSION

The observed mitochondrial changes in COPD epithelium are potentially the consequence of long-term exposure to cigarette smoke, leading to impaired mitochondrial function and may play a role in the pathogenesis of COPD.

Role of antioxidant enzymes and small molecular weight antioxidants in the pathogenesis of age-related macular degeneration (AMD)

Cells in aerobic condition are constantly exposed to reactive oxygen species (ROS), which may induce damage to biomolecules, including proteins, nucleic acids and lipids. In normal circumstances, the amount of ROS is counterbalanced by cellular antioxidant defence, with its main components—antioxidant enzymes, DNA repair and small molecular weight antioxidants. An imbalance between the production and neutralization of ROS by antioxidant defence is associated with oxidative stress, which plays an important role in the pathogenesis of many age-related and degenerative diseases, including age-related macular degeneration (AMD), affecting the macula—the central part of the retina. The retina is especially prone to oxidative stress due to high oxygen pressure and exposure to UV and blue light promoting ROS generation. Because oxidative stress has an established role in AMD pathogenesis, proper functioning of antioxidant defence may be crucial for the occurrence and progression of this disease. Antioxidant enzymes play a major role in ROS scavenging and changes of their expression or/and activity are reported to be associated with AMD. Therefore, the enzymes in the retina along with their genes may constitute a perspective target in AMD prevention and therapy.

The maintenance of mitochondrial DNA integrity--critical analysis and update

DNA molecules in mitochondria, just like those in the nucleus of eukaryotic cells, are constantly damaged by noxious agents. Eukaryotic cells have developed efficient mechanisms to deal with this assault. The process of DNA repair in mitochondria, initially believed nonexistent, has now evolved into a mature area of research. In recent years, it has become increasingly appreciated that mitochondria possess many of the same DNA repair pathways that the nucleus does. Moreover, a unique pathway that is enabled by high redundancy of the mitochondrial DNA and allows for the disposal of damaged DNA molecules operates in this organelle. In this review, we attempt to present a unified view of our current understanding of the process of DNA repair in mitochondria with an emphasis on issues that appear controversial.

Photosensitized oxidative stress to ARPE-19 cells decreases protein receptors that mediate photoreceptor outer segment phagocytosis

PURPOSE

To determine whether previously shown photodynamic (PD)-induced inhibition of specific photoreceptor outer segment (POS) phagocytosis by ARPE-19 cells is associated with reductions in receptor proteins mediating POS phagocytosis, and if PD treatment with merocyanine-540 (MC-540) produces additional effects leading to its inhibition of nonspecific phagocytosis.

METHODS

ARPE-19 cells preloaded with MC-540 or rose bengal (RB) were sublethally irradiated with green light. Phagocytosis of POS was measured by flow cytometry and POS receptor proteins (Mer tyrosine kinase receptor [MerTK] and integrin subunits αv and β5) and β-actin were quantified by Western blotting at 0.5 and 24 hours after irradiation, with comparison to samples from nonsensitized control cultures. The intact integrin heterodimer αvβ5 was quantified by immunoprecipitation followed by blotting. The distribution of N-cadherin, ZO-1, and F-actin was visualized by fluorescence microscopy.

RESULTS

Mild PD stress mediated by both photosensitizers that elicits no significant morphologic changes produces transient and recoverable reductions in MerTK. The individual αv and β5 integrin subunits are also reduced but only partially recover. However, there is sufficient recovery to support full recovery of the functional heterodimer. Light stress mediated by MC-540 also reduced levels of actin, which is known to participate in the internalization of particles regardless of type.

CONCLUSIONS

After PD treatment POS receptor protein abundance and phagocytosis show a coincident in time reduction then recovery suggesting that diminution in receptor proteins contributes to the phagocytic defect. The additional inhibition of nonspecific phagocytosis by MC-540-mediated stress may result from more widespread effects on cytosolic proteins. The data imply that phagocytosis receptors in RPE cells are sensitive to oxidative modification, raising the possibility that chronic oxidative stress in situ may reduce the efficiency of the RPE's role in photoreceptor turnover, thereby contributing to retinal degenerations.

Mitochondrial and nuclear DNA damage and repair in age-related macular degeneration

Aging and oxidative stress seem to be the most important factors in the pathogenesis of age-related macular degeneration (AMD), a condition affecting many elderly people in the developed world. However, aging is associated with the accumulation of oxidative damage in many biomolecules, including DNA. Furthermore, mitochondria may be especially important in this process because the reactive oxygen species produced in their electron transport chain can damage cellular components. Therefore, the cellular response to DNA damage, expressed mainly through DNA repair, may play an important role in AMD etiology. In several studies the increase in mitochondrial DNA (mtDNA) damage and mutations, and the decrease in the efficacy of DNA repair have been correlated with the occurrence and the stage of AMD. It has also been shown that mitochondrial DNA accumulates more DNA lesions than nuclear DNA in AMD. However, the DNA damage response in mitochondria is executed by nucleus-encoded proteins, and thus mutagenesis in nuclear DNA (nDNA) may affect the ability to respond to mutagenesis in its mitochondrial counterpart. We reported that lymphocytes from AMD patients displayed a higher amount of total endogenous basal and oxidative DNA damage, exhibited a higher sensitivity to hydrogen peroxide and UV radiation, and repaired the lesions induced by these factors less effectively than did cells from control individuals. We postulate that poor efficacy of DNA repair (i.e., is impaired above average for a particular age) when combined with the enhanced sensitivity of retinal pigment epithelium cells to environmental stress factors, contributes to the pathogenesis of AMD. Collectively, these data suggest that the cellular response to both mitochondrial and nuclear DNA damage may play an important role in AMD pathogenesis.

Oxidative stress increases HO-1 expression in ARPE-19 cells, but melanosomes suppress the increase when light is the stressor

PURPOSE

Phagocytized melanosomes in ARPE-19 cells were previously shown to decrease susceptibility to oxidative stress induced by hydrogen peroxide treatment and increase stress due to light irradiation relative to cells containing control black latex beads. Here we asked whether differential expression of antioxidant enzymes in cells containing pigment granules could explain the outcomes.

METHODS

ARPE-19 cells were loaded by phagocytosis with porcine RPE melanosomes or black latex beads (control particles). Heme oxygenase-1 (HO-1), HO-2, glutathione peroxidase (GPx), and catalase were quantified by Western blot analysis before and after treatment with sublethal hydrogen peroxide or blue light (400-450 nm). The stress was confirmed as sublethal by cell survival analysis using real-time quantification of propidium iodide fluorescence.

RESULTS

Phagocytosis itself produced transient changes in protein levels of some antioxidant enzymes, but steady-state levels (7 days after phagocytosis) did not differ in cells containing melanosomes versus beads. Sublethal stress, induced by either hydrogen peroxide or light, had no effect on catalase or HO-2 in either particle-free or particle-loaded cells. In contrast, HO-1 protein was upregulated by treatment with both hydrogen peroxide and light. Particle content did not affect the HO-1 increase induced by hydrogen peroxide, but the increase induced by blue light irradiation was partially blocked in cells containing black beads and blocked even more in cells containing melanosomes.

CONCLUSIONS

The results do not implicate differential antioxidant enzyme levels in stress protection by melanosomes against hydrogen peroxide, but they suggest a multifaceted role for melanosomes in regulating light stress susceptibility in RPE cells.

Assessment of mitochondrial damage in retinal cells and tissues using quantitative polymerase chain reaction for mitochondrial DNA damage and extracellular flux assay for mitochondrial respiration activity

Mitochondrial dysfunction and genomic instability are associated with a number of retinal pathologies including age-related macular degeneration, diabetic retinopathy, and glaucoma. Consequences of mitochondrial dysfunction within cells include elevation of the rate of ROS production due to damage of electron transport chain proteins, mitochondrial DNA (mtDNA) damage, and loss of metabolic capacity. Here we introduce the quantitative polymerase chain reaction assay (QPCR) and extracellular flux assay (XF) as powerful techniques to study mitochondrial behavior. The QPCR technique is a gene-specific assay developed to analyze the DNA damage repair response in mitochondrial and nuclear genomes. QPCR has proved particularly valuable for the measurement of oxidative-induced mtDNA damage and kinetics of mtDNA repair. To assess the functional consequence of mitochondrial oxidative damage, real-time changes in cellular bioenergetics of cell monolayers can be measured with a Seahorse Biosciences XF24 analyzer. The advantages and limitations of these procedures will be discussed and detailed methodologies provided with particular emphasis on retinal oxidative stress.

MicroRNA-30b-mediated regulation of catalase expression in human ARPE-19 cells

BACKGROUND

Oxidative injury to retinal pigment epithelium (RPE) and retinal photoreceptors has been linked to a number of retinal diseases, including age-related macular degeneration (AMD). Reactive oxygen species (ROS)-mediated gene expression has been extensively studied at transcriptional levels. Also, the post-transcriptional control of gene expression at the level of translational regulation has been recently reported. However, the microRNA (miRNA/miR)-mediated post-transcriptional regulation in human RPE cells has not been thoroughly looked at. Increasing evidence points to a potential role of miRNAs in diverse physiological processes.

METHODOLOGY/PRINCIPAL FINDINGS

We demonstrated for the first time in a human retinal pigment epithelial cell line (ARPE-19) that the post-transcriptional control of gene expression via miRNA modulation regulates human catalase, an important and potent component of cell's antioxidant defensive network, which detoxifies hydrogen peroxide (H(2)O(2)) radicals. Exposure to several stress-inducing agents including H(2)O(2) has been reported to alter miRNA expression profile. Here, we demonstrated that a sublethal dose of H(2)O(2) (200 µM) up-regulated the expression of miR-30b, a member of the miR-30 family, which inhibited the expression of endogenous catalase both at the transcript and protein levels. However, antisense (antagomirs) of miR-30b was not only found to suppress the miR-30b mimics-mediated inhibitions, but also to dramatically increase the expression of catalase even under an oxidant environment.

CONCLUSIONS/SIGNIFICANCE

We propose that a microRNA antisense approach could enhance cytoprotective mechanisms against oxidative stress by increasing the antioxidant defense system.

Noninvasive imaging of mitochondrial dysfunction in dry age-related macular degeneration

BACKGROUND AND OBJECTIVE

Oxidative stress and mitochondrial dysfunction are implicated in the pathogenesis of age-related macular degeneration (AMD). Because increased flavoprotein fluorescence (FPF) is indicative of mitochondrial dysfunction, the authors attempted to detect mitochondrial dysfunction in eyes with AMD using FPF.

PATIENTS AND METHODS

Six nonexudative eyes with AMD, including three with geographic atrophy (GA), and age-matched control eyes were imaged with a FPF device. Qualitative and quantitative analyses were conducted on the FPF images.

RESULTS

Five eyes with AMD, including all three eyes with GA, showed qualitative and/or quantitative FPF heterogeneity that was not present in control eyes. Mean FPF average intensities of eyes with AMD with (P = .044) and without (P = .00060) GA were significantly greater than those of control eyes. The standard deviations of FPF images were greater in eyes with AMD (P = .020).

CONCLUSION

In this small cluster of patients with AMD, retinal FPF is increased, suggesting elevated mitochondrial dysfunction. FPF heterogeneity indicates that an increased variability in mitochondrial dysfunction seems to be present in eyes with advanced disease.

Oxidants and not alkylating agents induce rapid mtDNA loss and mitochondrial dysfunction

Mitochondrial DNA (mtDNA) is essential for proper mitochondrial function and encodes 22 tRNAs, 2 rRNAs and 13 polypeptides that make up subunits of complex I, III, IV, in the electron transport chain and complex V, the ATP synthase. Although mitochondrial dysfunction has been implicated in processes such as premature aging, neurodegeneration, and cancer, it has not been shown whether persistent mtDNA damage causes a loss of oxidative phosphorylation. We addressed this question by treating mouse embryonic fibroblasts with either hydrogen peroxide (H(2)O(2)) or the alkylating agent methyl methanesulfonate (MMS) and measuring several endpoints, including mtDNA damage and repair rates using QPCR, levels of mitochondrial- and nuclear-encoded proteins using antibody analysis, and a pharmacologic profile of mitochondria using the Seahorse Extracellular Flux Analyzer. We show that a 60min treatment with H(2)O(2) causes persistent mtDNA lesions, mtDNA loss, decreased levels of a nuclear-encoded mitochondrial subunit, a loss of ATP-linked oxidative phosphorylation and a loss of total reserve capacity. Conversely, a 60min treatment with 2mM MMS causes persistent mtDNA lesions but no mtDNA loss, no decrease in levels of a nuclear-encoded mitochondrial subunit, and no mitochondrial dysfunction. These results suggest that persistent mtDNA damage is not sufficient to cause mitochondrial dysfunction.

Analysis of DNA damage and repair in nuclear and mitochondrial DNA of animal cells using quantitative PCR

This chapter was written as a guide to using the long-amplicon quantitative PCR (QPCR) assay for the measurement of DNA damage in mammalian as well as nonmammalian species such as Caenorhabditis elegans (nematodes), Drosophila melanogaster (fruit flies), and two species of fish (Fundulus heteroclitus and Danio rerio). Since its development in the early 1990s (Kalinowski et al., Nucleic Acids Res 20:3485-3494, 1992; Salazar and Van Houten, Mutat Res 385:139-149, 1997; Yakes and Van Houten, Proc Natl Acad Sci USA 94:514-519, 1997), the QPCR assay has been widely used to measure DNA damage and repair kinetics in nuclear and mitochondrial genomes after genotoxin exposure (Yakes and Van Houten, Proc Natl Acad Sci USA 94:514-519, 1997; Santos et al., J Biol Chem 278:1728-1734, 2003; Mandavilli et al., Mol Brain Res 133:215-223, 2005). One of the main strengths of the assay is that the labor-intensive and artifact-generating step of mitochondrial isolation is not needed for the accurate measurement of mitochondrial DNA copy number and damage. Below we present the advantages and limitations of using QPCR to assay DNA damage in animal cells and provide a detailed protocol of the QPCR assay that integrates its usage in newly developed animal systems.

The MFN2 gene is responsible for mitochondrial DNA instability and optic atrophy 'plus' phenotype

MFN2 and OPA1 genes encode two dynamin-like GTPase proteins involved in the fusion of the mitochondrial membrane. They have been associated with Charcot-Marie-Tooth disease type 2A and autosomal dominant optic atrophy, respectively. We report a large family with optic atrophy beginning in early childhood, associated with axonal neuropathy and mitochondrial myopathy in adult life. The clinical presentation looks like the autosomal dominant optic atrophy 'plus' phenotype linked to OPA1 mutations but is associated with a novel MFN2 missense mutation (c.629A>T, p.D210V). Multiple mitochondrial DNA deletions were found in skeletal muscle and this observation makes MFN2 a novel gene associated with 'mitochondrial DNA breakage' syndrome. Contrary to previous studies in patients with Charcot-Marie-Tooth disease type 2A, fibroblasts carrying the MFN2 mutation present with a respiratory chain deficiency, a fragmentation of the mitochondrial network and a significant reduction of MFN2 protein expression. Furthermore, we show for the first time that impaired mitochondrial fusion is responsible for a deficiency to repair stress-induced mitochondrial DNA damage. It is likely that defect in mitochondrial DNA repair is due to variability in repair protein content across the mitochondrial population and is at least partially responsible for mitochondrial DNA instability.

Erythrocyte antioxidant defenses as a potential biomarker of liver mitochondrial status in different oxidative conditions

The need for minimally invasive biomarkers to predict the progression of non-alcoholic fatty liver disease to non-alcoholic steatohepatitis is a priority. Oxidative stress and mitochondrial dysfunction contribute in this physiopathological process. The aim of this study was to analyze the potential role of erythrocytes as surrogate biomarkers of hepatic mitochondrial oxidative status in an animal model under different dietary oxidative conditions. Interestingly, we found that erythrocyte antioxidant status correlated with triglyceride content (p < 0.05-p < 0.001), thiobarbituric acid reactive species levels (p < 0.001) and with liver mitochondrial antioxidant levels (p < 0.001). These data suggest that erythrocyte antioxidant defenses could be used as sensitive and minimally invasive biomarkers of mitochondrial status in diverse oxidative conditions.

Mitochondrial dysfunction in retinal diseases

The mitochondrion is a vital intracellular organelle for retinal cell function and survival. There is growing confirmation to support an association between mitochondrial dysfunction and a number of retinal degenerations. Investigations have also unveiled mitochondrial genomic instability as one of the contributing factors for age-related retinal pathophysiology. This review highlights the role of mitochondrial dysfunction originating from oxidative stress in the etiology of retinal diseases including diabetic retinopathy, glaucoma and age-related macular degeneration (AMD). Moreover, mitochondrial DNA (mtDNA) damage associated with AMD due to susceptibility of mtDNA to oxidative damage and failure of mtDNA repair pathways is also highlighted in this review. The susceptibility of neural retina and retinal pigment epithelium (RPE) mitochondria to oxidative damage with ageing appears to be a major factor in retinal degeneration. It thus appears that the mitochondrion is a weak link in the antioxidant defenses of retinal cells. In addition, failure of mtDNA repair pathways can also specifically contribute towards pathogenesis of AMD. This review will further summarize the prospective role of mitochondria targeting therapeutic agents for the treatment of retinal disease. Mitochondria based drug targeting to diminish oxidative stress or promote repair of mtDNA damage may offer potential alternatives for the treatment of various retinal degenerative diseases.

Retinal flavoprotein fluorescence correlates with mitochondrial stress, apoptosis, and chemokine expression

Oxidative stress and mitochondrial dysfunction occur before apoptosis in many retinal diseases. Under these conditions, a larger fraction of flavoproteins become oxidized and, when excited by blue-light, emit green flavoprotein fluorescence (FPF). In this study, we evaluated the utility of FPF as an early indicator of mitochondrial stress, pre-apoptotic cellular instability, and apoptosis of human retinal pigment epithelial (HRPE) cells subjected to hydrogen peroxide (H(2)O(2)) or monocytes (unstimulated or interferon-γ-stimulated) in vitro and of freshly-isolated pieces of human and rat neural retina subjected to H(2)O(2)ex vivo. Increased FPF of HRPE cells exposed to H(2)O(2) correlated with reduced mitochondrial membrane potential (ΔΨm) and increased apoptosis in a time- and dose-dependent manner. HRPE cells co-cultured with monocytes had increased FPF that correlated in a time-dependent manner with reduced ΔΨm, increased apoptosis, and early expression of pro-inflammatory chemokines, interleukin-8 (IL8) and monocyte chemotactic factor-1 (MCP1), which are known to be induced by oxidative stress. Increased FPF, reduced ΔΨm, and upregulation of IL8 and MCP1 occurred as early as 1-2 h after exposure to stressors, while apoptosis did not occur in HRPE cells until later time points. The antioxidant, N-acetyl-cysteine (NAC), inhibited increased FPF and apoptosis of HRPE cells subjected to H(2)O(2). Increased FPF of human and rat neural retina also correlated with increased apoptosis. This study suggests that FPF is a useful measure of mitochondrial function in retinal cells and tissues and can detect early mitochondrial dysfunction that may precede apoptosis.

The role of Bcl-xL in mouse RPE cell survival

PURPOSE. Retinal pigment epithelial (RPE) cell survival plays a critical role in normal physiology and in retinal diseases, such as age-related macular degeneration (AMD) and proliferative vitreoretinopathy (PVR). We have previously demonstrated that Bcl-x(L) is an important cell survival protein in human RPE (hRPE) cells. Herein, we determined the role of Bcl-x(L) as a survival protein in mouse RPE (mRPE) cells. METHODS. Survival factor gene expression and Bcl-x(L) protein distribution were determined using qRT-PCR and immunohistochemistry, respectively. Cultured mRPE cells were transfected with two modified 2'-O-methoxyethoxy antisense oligonucleotides (ASOs): Bcl-x(L)-mismatched control and Bcl-x(L)-specific. Bcl-x(L) protein levels were analyzed using Western blot. To determine the effects of survival factor regulation in mRPE cells, cultured cells were treated for 24 hours with mouse TNF-α, human IL-1β, and human TNF-α. RESULTS. Bcl-x(L) was the most highly expressed survival factor in both mouse eyecup and cultured mRPE cells, whereas Bax was the most highly expressed antisurvival factor. Bcl-x(L) was expressed in the RPE layer, and the distribution among the retinal layers was similar to that observed in human eyecups. IL-1β and TNF-α had minimal effect on Bcl-x(L) and Bax expression and strongly upregulated Traf-1. Transfection with Bcl-x(L)-specific ASO resulted in markedly diminished Bcl-x(L) gene expression, Bcl-x(L) protein levels, and cell number. CONCLUSIONS. Bcl-x(L) is the most highly expressed survival gene in mRPE cells and is essential for mRPE cell survival. Our data suggest that mouse tissue is an appropriate model for investigations of RPE survival factor genes.

Mitochondrial DNA damage and repair in RPE associated with aging and age-related macular degeneration

PURPOSE

Mitochondrial DNA (mtDNA) damage may be associated with age-related diseases, such as age-related macular degeneration (AMD). The present study was designed to test whether the frequency of mtDNA damage, heteroplasmic mtDNA mutations, and repair capacity correlate with progression of AMD.

METHODS

Macular and peripheral RPE cells were isolated and cultured from human donor eyes with and without AMD. The stages of AMD were graded according to the Minnesota Grading System. Confluent primary RPE cells were used to test the frequency of endogenous mtDNA damage by quantitative PCR. Mutation detection kits were used to detect heteroplasmic mtDNA mutation. To test the mtDNA repair capacity, cultured RPE cells were allowed to recover for 3 and 6 hours after exposure to H(2)O(2), and repair was assessed by quantitative PCR. The levels of human OGG1 protein, which is associated with mtDNA repair, were analyzed by Western blot.

RESULTS

This study showed that mtDNA damage increased with aging and that more lesions occurred in RPE cells from the macular region than the periphery. Furthermore, mtDNA repair capacity decreased with aging, with less mtDNA repair capacity in the macular region compared with the periphery in samples from aged subjects. Most interestingly, the mtDNA damage was positively correlated with the grading level of AMD, whereas repair capacity was negatively correlated. In addition, more mitochondrial heteroplasmic mutations were detected in eyes with AMD.

CONCLUSIONS

These data show macula-specific increases in mtDNA damage, heteroplasmic mutations, and diminished repair that are associated with aging and AMD severity.

Mitochondrial oxidative stress significantly influences atherogenic risk and cytokine-induced oxidant production

BACKGROUND

Oxidative stress associated with cardiovascular disease (CVD) risk factors contributes to disease development. However, less is known whether specific subcellular components play a role in disease susceptibility. In this regard, it has been previously reported that vascular mitochondrial damage and dysfunction are associated with atherosclerosis. However, no studies have determined whether altered mitochondrial oxidant production directly influences atherogenic susceptibility and response in primary cells to atherogenic factors such as tumor necrosis factor-α (TNF-α).

OBJECTIVES

We undertook this study to determine whether increased mitochondrial oxidant production affects atherosclerotic lesion development associated with CVD risk factor exposure and endothelial cell response to TNF-α.

METHODS

We assessed atherosclerotic lesion formation, oxidant stress, and mitochondrial DNA damage in male apolipoprotein E (apoE)-null mice with normal and decreased levels of mitochondrial superoxide dismutase-2 (SOD2; apoE(-/-) and apoE(-/-), SOD2(+/-), respectively) exposed to environmental tobacco smoke or filtered air.

RESULTS

Atherogenesis, oxidative stress, and mitochondrial damage were significantly higher in apoE(-/-), SOD2(+/-) mice than in apoE(-/-) controls. Furthermore, experiments with small interfering RNA in endothelial cells revealed that decreased SOD2 activity increased TNF-α-mediated cellular oxidant levels compared with controls.

CONCLUSIONS

Endogenous mitochondrial oxidative stress is an important CVD risk factor that can modulate atherogenesis and cytokine-induced endothelial cell oxidant generation. Consequently, CVD risk factors that induce mitochondrial damage alter cellular response to endogenous atherogenic factors, increasing disease susceptibility.

Risk factors of ocular involvement in children with mitochondrial respiratory chain complex defect

Purpose

Mitochondrial dysfunction can present with various symptoms depending on the organ it has affected. This research tried to analyze the ophthalmologic symptoms and ophthalmologic examination (OE) results in patients with mitochondrial disease (MD).

Methods

Seventy-four patients diagnosed with mitochondrial respiratory chain complex defect with biochemical enzyme assay were included in the study. They were divided into 2 groups based on the OE results by funduscopy and were analyzed on the basis of their clinical features, biochemical test results, morphological analysis, and neuroimaging findings.

Results

Thirty-seven (50%) of the 74 MD patients developed ophthalmologic symptoms. Abnormal findings were observed in 36 (48.6%) patients during an OE, and 16 (21.6%) of them had no ocular symptoms. Significantly higher rates of prematurity, clinical history of epilepsy or frequent apnea events, abnormal light microscopic findings in muscle pathology, diffuse cerebral atrophy in magnetic resonance imaging, and brainstem hyperintensity and lactate peaks in magnetic resonance spectroscopy were noted in the group with abnormal OE results.

Conclusion

Although the ophthalmologic symptoms are not very remarkable in MD patients, an OE is required. When the risk factors mentioned above are observed, a more active approach should be taken in the OE because a higher frequency of ocular involvement can be expected.

Perinatal tobacco smoke exposure increases vascular oxidative stress and mitochondrial damage in non-human primates

Epidemiological studies suggest that events occurring during fetal and early childhood development influence disease susceptibility. Similarly, molecular studies in mice have shown that in utero exposure to cardiovascular disease (CVD) risk factors such as environmental tobacco smoke (ETS) increased adult atherogenic susceptibility and mitochondrial damage; however, the molecular effects of similar exposures in primates are not yet known. To determine whether perinatal ETS exposure increased mitochondrial damage, dysfunction and oxidant stress in primates, archived tissues from the non-human primate model Macaca mulatta (M. mulatta) were utilized. M. mulatta were exposed to low levels of ETS (1 mg/m³ total suspended particulates) from gestation (day 40) to early childhood (1 year), and aortic tissues were assessed for oxidized proteins (protein carbonyls), antioxidant activity (SOD), mitochondrial function (cytochrome oxidase), and mitochondrial damage (mitochondrial DNA damage). Results revealed that perinatal ETS exposure resulted in significantly increased oxidative stress, mitochondrial dysfunction and damage which were accompanied by significantly decreased mitochondrial antioxidant capacity and mitochondrial copy number in vascular tissue. Increased mitochondrial damage was also detected in buffy coat tissues in exposed M. mulatta. These studies suggest that perinatal tobacco smoke exposure increases vascular oxidative stress and mitochondrial damage in primates, potentially increasing adult disease susceptibility.

Early biosignature of oxidative stress in the retinal pigment epithelium

The retinal pigment epithelium (RPE) is essential for retinoid recycling and phagocytosis of photoreceptors. Understanding of proteome changes that mediate oxidative stress-induced degeneration of RPE cells may provide further insight into the molecular mechanisms of retinal diseases. In the current study, comparative proteomics has been applied to investigate global changes of RPE proteins under oxidative stress. Proteomic techniques, including 2D SDS-PAGE, differential gel electrophoresis (DIGE), and tandem time-of-flight (TOF-TOF) mass spectrometry, were used to identify early protein markers of oxidative stress in the RPE. Two biological models of RPE cells revealed several differentially expressed proteins that are involved in key cellular processes such as energy metabolism, protein folding, redox homeostasis, cell differentiation, and retinoid metabolism. Our results provide a new perspective on early signaling molecules of redox imbalance in the RPE and putative therapeutic target proteins of RPE diseases caused by oxidative stress.

Mitochondrial DNA damage as a potential mechanism for age-related macular degeneration

PURPOSE

Increasing evidence suggests a central role for mitochondrial (mt) dysfunction in age-related macular degeneration (AMD). Previous proteomic data from the retinal pigment epithelium (RPE) revealed significant changes to mt proteins, suggesting potential functional defects and damage to mitochondrial DNA (mtDNA) with AMD progression. The present study tests the hypothesis that mtDNA damage increases with aging and AMD.

METHODS

Genomic DNA was isolated from the macular region of human donor RPE graded for stages of AMD (Minnesota Grading System [MGS] 1-4). Region-specific mtDNA damage with normal aging was evaluated in 45 control subjects (ages 34-88 years, MGS 1) and AMD-associated damage in diseased subjects (n = 46), compared with that in age-matched control subjects (n = 26). Lesions per 10 kb per genome in the mtDNA and nuclear DNA were measured with long-extension polymerase chain reaction (LX PCR). The level of deleted mtDNA in each donor was measured with quantitative real-time PCR (qPCR).

RESULTS

With aging, an increase in mtDNA damage was observed only in the common deletion region of the mt genome. In contrast, with AMD, mtDNA lesions increased significantly in all regions of the mt genome beyond levels found in age-matched control subjects. mtDNA accumulated more lesions than did two nuclear genes, with total damage of the mt genome estimated to be eight times higher.

CONCLUSIONS

Collectively, the data indicate that mtDNA is preferentially damaged with AMD progression. These results suggest a potential link between mt dysfunction due to increased mtDNA lesions and AMD.

Oxidation and age-related macular degeneration: insights from molecular biology

Age-related macular degeneration (AMD) is the leading cause of blindness in the developed world. It is a multifactorial disease, and current therapy predominantly limits damage only when it has already occurred. The macula is a source of high metabolic activity, and is therefore exposed to correspondingly high levels of reactive oxygen species (ROS). With age, the balance between production of ROS and local antioxidant levels is shifted, and damage ensues. Systemic ROS and antioxidant levels in AMD reflect these local processes. Genetic studies investigating mutations in antioxidant genes in AMD are inconclusive and further studies are indicated, especially to determine the role of mitochondria. Oral antioxidant supplements could be beneficial, and diet modification may help. Future treatments might either increase antioxidant capacity or reduce the production of ROS, using methods such as genetic manipulation. This article reviews the role of oxidative stress in AMD and the potential therapies that might have a role in preventing the blindness resulting from this disease.

Resveratrol protects human retinal pigment epithelial cells from acrolein-induced damage

PURPOSE

Although the exact pathogenesis of age-related macular degeneration (AMD) is not clear, most studies indicate a role for retinal pigment epithelial (RPE) cell damage and death caused by oxidative stress. The purpose of this study was to examine the potential protective effects of lutein, zeaxanthin, meclofenamic acid, and resveratrol on the acrolein-induced oxidative stress in human RPE cells.

METHODS

Cultured human RPE R-50 cells were treated with acrolein at different concentrations and treatment times. The protective effects of lutein (100 microM), zeaxanthin (100 microM), meclofenamic acid (30 microM), and resveratrol (10 microM) were investigated by pretreatment with the above agents before toxicant exposure in acute toxicity models and cotreatment with the toxicant in chronic toxicity models. The synergistic effects of acrolein and hydrogen peroxide exposure were also studied. Fluorescent latex beads were used to assess the phagocytic function of the cells.

RESULTS

Acrolein inhibited the phagocytic function of human RPE R-50 cells, and the inhibitory effects were time dependent. Pretreatment with lutein, zeaxanthin, meclofenamic acid, or resveratrol alleviated the inhibition of phagocytosis in the acute acrolein and combined acrolein/hydrogen peroxide toxicity models. Synergistic effects were seen between zeaxanthin and resveratrol or meclofenamic acid. Cotreatment with lutein, zeaxanthin, meclofenamic acid, or resveratrol showed a protective effect against the damage caused by 7-day acrolein exposure followed by hydrogen peroxide treatment.

CONCLUSIONS

Our results indicated an inhibitory effect of compounds found in cigarette smoke on human RPE phagocytosis, and lutein, zeaxanthin, meclofenamic acid, and resveratrol each offered protection against this inhibition. Therefore, red wine polyphenol, resveratrol, might ameliorate acrolein-induced or age-related RPE degeneration, such as AMD.

Role of mitochondrial DNA damage in the development of diabetic retinopathy, and the metabolic memory phenomenon associated with its progression

Diabetic retinopathy does not halt after hyperglycemia is terminated; the retina continues to experience increased oxidative stress, suggesting a memory phenomenon. Mitochondrial DNA (mtDNA) is highly sensitive to oxidative damage. The goal is to investigate the role of mtDNA damage in the development of diabetic retinopathy, and in the metabolic memory. mtDNA damage and its functional consequences on electron transport chain (ETC) were analyzed in the retina from streptozotocin-diabetic rats maintained in poor control (PC, glycated hemoglobin >11%) for 12 months or PC for 6 months followed by good control (GC, GHb < 6.5%) for 6 months. Diabetes damaged retinal mtDNA and elevated DNA repair enzymes (glycosylase). ETC proteins that were encoded by the mitochondrial genome and the glycosylases were compromised in the mitochondria. Re-institution of GC after 6 months of PC failed to protect mtDNA damage, and ETC proteins remained subnormal. Thus, mtDNA continues to be damaged even after PC is terminated. Although the retina tries to overcome mtDNA damage by inducing glycosylase, they remain deficient in the mitochondria with a compromised ETC system. The process is further exacerbated by subsequent increased mtDNA damage providing no relief to the retina from a continuous cycle of damage, and termination of hyperglycemia fails to arrest the progression of retinopathy.

The importance of mitochondria in age-related and inherited eye disorders

Mitochondria are critical for ocular function as they represent the major source of a cell's supply of energy and play an important role in cell differentiation and survival. Mitochondrial dysfunction can occur as a result of inherited mitochondrial mutations (e.g. Leber's hereditary optic neuropathy and chronic progressive external ophthalmoplegia) or stochastic oxidative damage which leads to cumulative mitochondrial damage and is an important factor in age-related disorders (e.g. age-related macular degeneration, cataract and diabetic retinopathy). Mitochondrial DNA (mtDNA) instability is an important factor in mitochondrial impairment culminating in age-related changes and pathology, and in all regions of the eye mtDNA damage is increased as a consequence of aging and age-related disease. It is now apparent that the mitochondrial genome is a weak link in the defenses of ocular cells since it is susceptible to oxidative damage and it lacks some of the systems that protect the nuclear genome, such as nucleotide excision repair. Accumulation of mitochondrial mutations leads to cellular dysfunction and increased susceptibility to adverse events which contribute to the pathogenesis of numerous sporadic and chronic disorders in the eye.

The effects of quercetin in cultured human RPE cells under oxidative stress and in Ccl2/Cx3cr1 double deficient mice

Quercetin, a member of the flavonoid family, is one of the most prominent dietary antioxidants. This study investigates the mechanisms for the effects of quercetin on cultured human RPE cells and in Ccl2/Cx3cr1 double knock-out (DKO) mice, which spontaneously develop progressive retinal lesions mimicking age-related macular degeneration (AMD). In the in vitro experiment, cultured ARPE-19 cells were exposed to 1 mM H(2)O(2) with or without 50 muM quercetin for 2 h. Cellular viability, mitochondrial function, and apoptosis were assessed using crystal violet staining, MTT assay, and comet assay, respectively. Apoptotic molecular transcripts of BCL-2, BAX, FADD, CASPASE-3 and CASPASE-9 were measured by RQ-PCR. COX activity and nitric oxide (NO) level were determined in the supernatant of the culture medium. Quercetin treatment protected ARPE-19 cells from H(2)O(2)-induced oxidative injury, enhanced BCL-2 transcript levels, increased the BCL-2/BAX ratio, suppressed the transcription of pro-apoptotic factors such as BAX, FADD, CASPASE-3 and CASPASE-9, inhibited the transcription of inflammatory factors such as TNF-alpha, COX-2 and INOS, and decreased the levels of COX and NO in the culture medium. In the in vivo experiment, DKO and C57/B6 mice were treated with 25 mg/kg/day quercetin by intraperitoneal injection daily for two months. Funduscopy was performed monthly. After two months, serum was collected to measure NADP(+)/NADPH, COX, PGE-2, and NO levels. The eyes were harvested for histology and A2E measurement. Ocular transcripts of Bcl-2, Bax, Cox-2, Inos, Tnf-alpha, Fas, FasL and Caspase-3 were detected by RQ-PCR. Quercetin treatment did not reverse the progression of retinal lesions in DKO mice funduscopically or histologically. Although quercetin treatment could recover systemic anti-oxidative capacity, suppress the systemic expression of NO, COX and PGE-2, and decrease ocular A2E levels, it could not effectively suppress the transcripts of the ocular inflammatory factors Tnf-alpha, Cox-2 and Inos, or the pro-apoptotic factors Fas, FasL and Caspase-3 in DKO mice. Our data demonstrate that quercetin can protect human RPE cells from oxidative stress in vitro via inhibition of pro-inflammatory molecules and direct inhibition of the intrinsic apoptosis pathway. However, quercetin (25 mg/kg/day) does not improve the retinal AMD-like lesions in the Ccl2(-/-)/Cx3cr1(-/-) mice, likely due to its insufficient suppression of the inflammatory and apoptosis pathways in the eye.

Mitochondrial dysfunction in neurodegenerative diseases and cancer

Mitochondria are important integrators of cellular function and therefore affect the homeostatic balance of the cell. Besides their important role in producing adenosine triphosphate through oxidative phosphorylation, mitochondria are involved in the control of cytosolic calcium concentration, metabolism of key cellular intermediates, and Fe/S cluster biogenesis and contributed to programmed cell death. Mitochondria are also one of the major cellular producers of reactive oxygen species (ROS). Several human pathologies, including neurodegenerative diseases and cancer, are associated with mitochondrial dysfunction and increased ROS damage. This article reviews how dysfunctional mitochondria contribute to Alzheimer's disease, Parkinson's disease, Huntington's disease, and several human cancers.

Dynamics of H2O2 availability to ARPE-19 cultures in models of oxidative stress

Oxidative injury to cells such as the retinal pigment epithelium (RPE) is often modeled using H(2)O(2)-treated cultures, but H(2)O(2) concentrations are not sustained in culture medium. Here medium levels of H(2)O(2) and cytotoxicity were analyzed in ARPE-19 cultures after H(2)O(2) delivery as a single pulse or with continuous generation using glucose oxidase (GOx). When added as a pulse, H(2)O(2) is rapidly depleted (within 2 h); cytotoxicity at 24 h, determined by the MTT assay for mitochondrial function, is unaffected by medium replacement at 2 h. Continuous generation of H(2)O(2) produces complex outcomes. At low GOx concentrations, H(2)O(2) levels are sustained by conditions under which generation matches depletion, but when GOx concentrations produce cytotoxic levels of H(2)O(2), oxidant depletion accelerates. Acceleration results partly from the release of contents from oxidant-damaged cells as indicated by testing depletion after controlled membrane disruption with detergents. Cytotoxicity analyses show that cells can tolerate short exposure to high H(2)O(2) doses delivered as a pulse but are susceptible to lower chronic doses. The results provide broadly applicable guidance for using GOx to produce sustained H(2)O(2) levels in cultured cells. This approach will be specifically useful for modeling chronic stress relevant to RPE aging and have a wider value for studying cellular effects of sublethal oxidant injury and for evaluating antioxidants that may protect significantly against mild but not lethal stress.

Hydrogen peroxide causes mitochondrial DNA damage in corneal epithelial cells

PURPOSE

To study the effects of hydrogen peroxide exposure on mitochondrial DNA (mtDNA) in cultured human corneal epithelial cells. In addition, we compared the integrity of mtDNA found in epithelial cells isolated from keratoconus (KC) and normal (NL) corneas.

METHODS

Telomerase immortalized human corneal epithelial cell line (hTCEpi) were cultured at pH 7.0 or pH 5.0 with or without 200 microM hydrogen peroxide (H2O2). Immunohistochemistry with a marker for oxidative damage, 8-hydroxy-2'-deoxyguanosine (8-OH-dG), was performed on KC and NL corneas (n = 10). Epithelial cells were isolated from KC corneas (n = 5) and NL corneas (n = 7). Total DNA was extracted, and the mtDNA was analyzed by long extension polymerase chain reaction (LX-PCR). The ratios of mtDNA to nuclear DNA were measured by PCR. The mtDNA control regions were PCR amplified and sequenced.

RESULTS

In the epithelial cell cultures, the full-length LX-PCR mtDNA decreased 54% and 44% in the H2O2 + pH7 cultures and H2O2 + pH5 cultures, respectively. 8-OH-dG was present in all layers of KC epithelial cells but only in superficial layers of NL epithelial cells. The isolated KC and NL epithelial cells had comparable levels of full-length LX-PCR mtDNA (16.2 kb) and smaller sized mtDNA bands (4.3 +/- 0.99 vs 4.0 +/- 0.83 bands per individual, respectively). There were no significant differences in the control region nucleotide sequences in KC and NL epithelia.

CONCLUSIONS

Hydrogen peroxide can significantly degrade LX-PCR mtDNA in vitro. Although the KC epithelium showed a higher degree of oxidative damage, the levels of mtDNA damage in NL and KC epithelial cells were similar to each other.

Resveratrol protects against ultraviolet A-mediated inhibition of the phagocytic function of human retinal pigment epithelial cells via large-conductance calcium-activated potassium channels

This study was undertaken to examine the protective effect of resveratrol on human retinal pigment epithelial (RPE) cell phagocytosis against ultraviolet irradiation damage. Cultured RPE cells were exposed to ultraviolet A (UVA, 20 minutes) irradiation, and treated with meclofenamic acid (30 microM, 20 minutes), paxilline (100 nM, 20 minutes) or resveratrol (10 microM, 20 minutes). Meclofenamic acid and resveratrol were given after exposure to UVA. Pretreatment with meclofenamic acid, resveratrol or paxilline before UVA irradiation was also performed. Fluorescent latex beads were then fed for 4 hours and the phagocytotic function was assessed by flow cytometry. UVA irradiation inhibited the phagocytic function of human RPE cells. The large-conductance calcium-activated potassium channel activator meclofenamic acid ameliorated the damage caused by UVA irradiation. Pretreatment with resveratrol acid also provided protection against damage caused by UVA. Posttreatment with meclofenamic acid offered mild protection, whereas resveratrol did not. In conclusion, the red wine flavonoid resveratrol ameliorated UVA-mediated inhibition of human RPE phagocytosis. The underlying mechanism might involve the large-conductance calcium-activated potassium channels.

Association of superoxide anions with retinal pigment epithelial cell apoptosis induced by mononuclear phagocytes

PURPOSE

Oxidative stress of the retinal pigment epithelium by reactive oxygen species and monocytic infiltration have been implicated in age-related macular degeneration. The purpose of this study was to determine the role of superoxide anions (O(2)(-)) in mononuclear phagocyte-induced RPE apoptosis.

METHODS

Mouse RPE cell cultures were established from wild-type and heterozygous superoxide dismutase 2-knockout (Sod2(+/-)) mice. The intracellular reactive oxygen species, O(2)(-) and hydrogen peroxide, were measured by using dihydroethidium assay and 5-(and 6)-chloromethyl-2',7'-dichlorodihydrofluorescence diacetate, acetyl ester assay, respectively. RPE apoptosis was evaluated by Hoechst staining and terminal deoxynucleotidyltransferase dUTP nick-end labeling assay. Changes in mitochondrial membrane potential were detected by 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide dye. Activated caspases and caspase-3 were detected in situ by FITC-VAD-fmk staining and caspase-3 substrate, respectively.

RESULTS

Mononuclear phagocytes and interferon-gamma-activated mononuclear phagocytes induced the production of intracellular RPE O(2)(-), a decrease in RPE mitochondrial membrane potential, caspase activation, and apoptosis of mouse RPE cells. All theses changes were significantly enhanced in the Sod2(+/-) RPE cells. Activated mononuclear phagocytes induced more of these oxidative and apoptotic changes in RPE cells than did unstimulated mononuclear phagocytes.

CONCLUSIONS

The authors have shown that the decreased expression of SOD2 and increased superoxide production correlate with RPE apoptosis induced by unstimulated and activated mononuclear phagocytes. The authors suggest that elevated O(2)(-) levels due to genetic abnormalities of SOD2 or immunologic activation of mononuclear phagocytes lead to greater levels of RPE apoptosis. The present study could serve as a useful model to characterize RPE/phagocyte interaction in AMD and other retinal diseases.

Erythropoietin protects retinal pigment epithelial cells from oxidative damage

Oxidative damage from reactive oxygen species (ROS) has been implicated in many diseases, including age-related macular degeneration, in which the retinal pigment epithelium (RPE) is considered a primary target. The aim of this study was to determine whether erythropoietin (EPO) protects cultured human RPE cells against oxidative damage and to identify the pathways that may mediate protection. EPO (1 IU/ml) significantly increased the viability of oxidant-treated RPE cells, decreased the release of the inflammatory cytokines tumor necrosis factor-alpha and interleukin-1beta, recovered the RPE cells' barrier integrity disrupted by oxidative stress, prevented oxidant-induced cell DNA fragmentation and membrane phosphatidylserine exposure, and also reduced the levels of oxidant-induced intracellular ROS and restored cellular antioxidant potential, total antioxidant capacity, glutathione peroxidase, and superoxide dismutase and decreased malondialdehyde, the end product of lipid peroxidation. EPO inhibited caspase-3-like activity. Protection by EPO was partly dependent on the activation of Akt1 and the maintenance of the mitochondrial membrane potential. No enhanced or synergistic protection was observed during application of Z-DEVD-FMK (caspase-3 inhibitor) combined with EPO compared with cultures exposed to EPO and H(2)O(2) alone. Together, these results suggest that EPO could protect against oxidative injury-induced cell death and mitochondrial dysfunction in RPE cells through modulation of Akt1 phosphorylation, mitochondrial membrane potential, and cysteine protease activity.