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Fridovich identified CuZnSOD in 1969 and manganese superoxide dismutase (MnSOD) in 1973, and proposed ”the Superoxide Theory,” which postulates that superoxide (O2•−) is the origin of most reactive oxygen species (ROS) and that it undergoes a chain reaction in a cell, playing a central role in the ROS producing system. Increased oxidative stress on an organism causes damage to cells, the smallest constituent unit of an organism, which can lead to the onset of a variety of chronic diseases, such as Alzheimer’s, Parkinson’s, amyotrophic lateral sclerosis and other neurological diseases caused by abnormalities in biological defenses or increased intracellular reactive oxygen levels. Oxidative stress also plays a role in aging. Antioxidant systems, including non-enzyme low-molecular-weight antioxidants (such as, vitamins A, C and E, polyphenols, glutathione, and coenzyme Q10) and antioxidant enzymes, fight against oxidants in cells. Superoxide is considered to be a major factor in oxidant toxicity, and mitochondrial MnSOD enzymes constitute an essential defense against superoxide. Mitochondria are the major source of superoxide. The reaction of superoxide generated from mitochondria with nitric oxide is faster than SOD catalyzed reaction, and produces peroxynitrite. Thus, based on research conducted after Fridovich’s seminal studies, we now propose a modified superoxide theory; i.e., superoxide is the origin of reactive oxygen and nitrogen species (RONS) and, as such, causes various redox related diseases and aging.

Microcystin-LR (MCLR) is a potent hepatotoxin. Oxidative stress is thought to be implicated in the cytotoxicity of MCLR, but the mechanisms by which MCLR produces reactive oxygen species (ROS) are still unclear. This study investigated the role and possible sources of ROS generation in MCLR-induced cytogenotoxicity in HepG2, a human hepatoma cell line. MCLR increased DNA strand breaks, 8-hydroxydeoxiguanosine formation, lipid peroxidation, as well as LDH release, all of which were inhibited by ROS scavengers. ROS scavengers partly suppressed MCLR-induced cytotoxicity determined by the MTT assay. MCLR induced the generation of ROS, as confirmed by confocal microscopy with 2-[6-(4'-hydroxy)phenoxy-3H-xanthen-3-on-9-yl]benzoic acid, and upregulated the expression of CYP2E1 mRNA. In addition, CYP2E1 inhibitors chlormethiazole and diallyl dulphide inhibited both ROS generation and cytotoxicity induced by MCLR. The results suggest that ROS contribute to MCLR-induced cytogenotoxicity. CYP2E1 might be a potential source responsible for ROS generation by MCLR.

Tumor invasion is the most important factor to decide patient’s prognosis. The relation between reactive oxygen species and tumor invasion is mainly reported that nicotinamide adenine dinucleotide phosphate oxidase in the cell membrane is a reactive oxygen species producer for formulating an invadopodia. On the other hand, mitochondrion was known as one of the most important reactive oxygen species-producer in the cell via an energy transfer system. However, the relation between mitochondrial reactive oxygen species and the tumor invasion was not well clarified. In this study, we evaluated the relation between mitochondrial reactive oxygen species and tumor invasion using a normal gastric mucosal cell-line (RGM-1) and a cancerous mutant RGM-1 cell-line (RGK-1). Manganese superoxide dismutase-expressing RGK-1 cell-lines were used for a scavenging mitochondrial reactive oxygen species. The cells have been evaluated their movement ability as follows; cellular ruffling frequencies, wound healing assay to evaluate horizontal cellular migration, and invasion assay using matrigel to analyze vertical cellular migration. All cellular movement abilities were inhibited by scavenging mitochondrial reactive oxygen species with manganese superoxide dismutase. Therefore mitochondrial reactive oxygen species was one of factors enhancing the tumor invasion in gastric cancer.

Mitochondria are a major source of intracellular energy and reactive oxygen species in cells, but are also increasingly being recognized as a controller of cell death. Here, we review evidence of signal transduction control by mitochondrial superoxide generation via the nuclear factor-κB (NF-κB) and GATA signaling pathways. We have also reviewed the effects of ROS on the activation of MMP and HIF. There is significant evidence to support the hypothesis that mitochondrial superoxide can initiate signaling pathways following transport into the cytosol. In this study, we provide evidence of TATA signal transductions by mitochondrial superoxide. Oxidative phosphorylation via the electron transfer chain, glycolysis, and generation of superoxide from mitochondria could be important factors in regulating signal transduction, cellular homeostasis, and cell death.

tion. Magnetic resonance imaging revealed bilateral temporal lesions (Figure, B). The lesions slowly expanded to the parieto-occipital region. He developed akinetic mutism and became bedridden. During this course, patient 2 experienced a sudden cardiac arrest in his early 50s. He died of congestive heart failure 2 years later. These patients grew up separately without knowing each other. Their mother and another sibling did not have diabetes, deafness, short stature, or cardiac disease.

The effects of blue light emitter diode (LED) light exposure on retinal pigment epithelial cells (RPE cells) were examined to detect cellular damage or change and to clarify its mechanisms. The RPE cells were cultured and exposed by blue (470 nm) LED at 4.8 mW/cm(2). The cellular viability was determined by XTT assay and cellular injury was determined by the lactate dehydrogenase activity in medium. Intracellular reactive oxygen species (ROS) generation was determined by confocal laser microscope image analysis using dihydrorhodamine 123 and lipid peroxidation was determined by 4-hydroxy-2-nonenal protein-adducts immunofluorescent staining (HNE). At 24 h after 50 J/cm(2) exposures, cellular viability was significantly decreased to 74% and cellular injury was significantly increased to 365% of control. Immediately after the light exposure, ROS generation was significantly increased to 154%, 177%, and 395% of control and HNE intensity was increased to 211%, 359%, and 746% of control by 1, 10, and 50 J/cm(2), respectively. These results suggest, at least in part, that oxidative stress is an early step leading to cellular damage by blue LED exposure and cellular oxidative damage would be caused by the blue light exposure at even lower dose (1, 10 J/cm(2)).

Photodynamic therapy using hematoporphyrin and its derivatives is clinically useful for cancer treatments. It has been reported that cancer cells incorporate hematoporphyrin and its derivatives via heme carrier protein 1, which is a proton-coupled folate transporter. However, the mechanism of this protein expression has not been elucidated. In general, the concentration of reactive oxygen species in cancer cells is higher than that in normal cells. We previously reported that reactive oxygen species from mitochondria involved in the expression of peptide transporter 1 and accelerate the uptake of 5-aminolevulinic acid, which is a precursor of protoporphyrin IX. We suggested mitochondrial reactive oxygen species also regulated the expression of heme carrier protein 1. In this study, we used a rat gastric mucosal cell line RGM1 and its cancer-like mutated cell line RGK1. We clarified the expression of heme carrier protein 1 increased in cancer cells and it decreased in manganese superoxide dismutase expressed cancer cells. In addition, the uptake level of hematoporphyrin and photodynamic therapeutic effect were also decreased in manganese superoxide dismutase expressed cancer cells in comparison with cancer cells. Thus, we concluded that mitochondrial reactive oxygen species regulated heme carrier protein 1 expression and photodynamic therapeutic effect.