Oxygen therapy for ischemic stroke remains controversial. Too much oxygen may lead to oxidative stress and free radical damage while too little oxygen will have minimal therapeutic effect. In vivo electron paramagnetic resonance (EPR) oximetry, which can measure localized interstitial partial oxygen (pO2), can monitor penumbral changes of pO2. Therefore, we used EPR to study the effects of oxygen therapy in a rat model of 90-mins middle cerebral artery occlusion (MCAO). We found that 95% normobaric O2 given during ischemia was able to maintain penumbral interstitial pO2 levels close to the preischemic value while it may cause a two-fold increase in penumbral pO2 level if given during reperfusion. Elevation of the penumbra pO2 to preischemic physiologic level during MCAO significantly reduced infarction volume, improved neurologic function, decreased the generation of reactive oxygen species (ROS), and reduced matrix metalloproteinase (MMP)-9 expression and caspase-8 cleavage in the penumbra tissue of rats brain treated with oxygen. These results suggest that maintaining penumbral oxygenation by normobaric oxygen treatment during ischemia lead to neuroprotection, which is further reflected by the decreased production of ROS, MMP-9, and caspase-8.

Arsenic enhances skin tumor formation when combined with other carcinogens, including UV radiation (UVR). In this study we report that low micromolar concentrations of arsenite synergistically increases UVR-induced oxidative DNA damage in human keratinocytes as detected by 8-hydroxyl-2-deoxyguanine (8-OHdG) formation. Poly(ADP-ribose) polymerase-1 (PARP-1) is involved in base excision repair, a process that repairs 8-OHdG lesions. Arsenite suppresses UVR-induced PARP-1 activation in a concentration-dependent manner. Inhibition of PARP-1 activity by 3-aminobenzamide or small interfering RNA silencing of PARP-1 expression significantly increases UVR-induced 8-OHdG formation, suggesting that inhibition of PARP-1 activity by arsenite contributes to oxidative DNA damage. PARP-1 is a zinc finger protein, and mass spectrometry analysis reveals that arsenite can occupy a synthetic apopeptide representing the first zinc finger of PARP-1 (PARPzf). When the PARPzf peptide is preincubated with Zn(II) followed by incubation with increasing concentrations of arsenite, the ZnPARPzf signal is decreased while the AsPARPzf signal intensity is increased as a function of arsenite dose, suggesting a competition between zinc and arsenite for the same binding site. Addition of Zn(II) abolished arsenite enhancement of UVR-stimulated 8-OHdG generation and restored PARP-1 activity. Our findings demonstrate that arsenite inhibits oxidative DNA damage repair and suggest that interaction of arsenite with the PARP-1 zinc finger domain contributes to the inhibition of PARP-1 activity by arsenite. Arsenite inhibition of poly-(ADP-ribosyl)ation is one likely mechanism for the reported cocarcinogenic activities of arsenic in UVR-induced skin carcinogenesis.Arsenic is a naturally occurring element that is present in food, soil, and water (1, 2). Environmental or occupational exposures to arsenic are associated with both acute and chronic toxic effects in humans, including increased incidence of skin, lung, liver, and urinary tract cancers (3). Although human epidemiological data link inorganic arsenic in drinking water with an elevated risk of non-melanoma skin cancer (4), arsenic as a sole agent is not an effective skin carcinogen in animal models (5). However, arsenite enhances tumor development in animals pretreated with other carcinogens (6), chronically stimulated by growth factors (7), or co-treated with UV radiation (UVR) 2 (8). It has been reported that sodium arsenite concentration as low as 1.25 mg/liter (10 M) in drinking water enhances UVRinduced tumorigenicity in mice (8), but the mechanisms underlying this observation are not fully understood.Arsenite exposure generates reactive oxygen species (ROS), and we have directly demonstrated that the production of O 2. , H 2 O 2 , and ⅐ OH in arsenite-exposed keratinocytes is associated with DNA damage (9, 10). Similarly UVR, particularly UVA, generates ROS in the skin also leading to oxidative DNA damage (11). Oxidative stress plays a significant role in UVR-induced skin carcinogenesis (12...

Arsenic is a naturally occurring element that is present in food, soil, and water. Inorganic arsenic can accumulate in human skin and is associated with increased risk of skin cancer. Oxidative stress due to arsenic exposure is proposed as one potential mode of carcinogenic action. The purpose of this study is to investigate the specific reactive oxygen and nitrogen species that are responsible for the arsenic-induced oxidative damage to DNA and protein. Our results demonstrated that exposure of human keratinocytes to trivalent arsenite caused the generation of 8-hydroxyl-2'-deoxyguanine (8-OHdG) and 3-nitrotyrosine (3-NT) in a concentration- and time-dependent manner. Pentavalent arsenate had similar effects, but to a significantly less extent. The observed oxidative damage can be suppressed by pre-treating cells with specific antioxidants. Furthermore, we found that pre-treating cells with Nomega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase (NOS), or with 5,10,15,20-tetrakis (N-methyl-4'-pyridyl) porphinato iron (III) chloride (FeTMPyP), a decomposition catalyst of peroxynitrite, suppressed the generation of both 8-OHdG and 3-NT, which indicated that peroxynitrite, a product of the reaction of nitric oxide and superoxide, played an important role in arsenic-induced oxidative damage to both DNA and protein. These findings highlight the involvement of peroxynitrite in the molecular mechanism underlying arsenic-induced human skin carcinogenesis.

Arsenic is an environmental and occupational toxin. Dermatologic toxicities due to arsenic exposure are well-documented and include basal cell and squamous cell carcinomas. However, the mechanism of arsenic-induced skin cancer is not well-understood. Recent studies indicate that arsenic exposure results in the generation of reactive oxygen species (ROS) and oxidative stress. Here, we examined the chemical nature of the specific ROS, studied the interrelationship among these species, and identified the specific species that is responsible for the subsequent DNA damage in a spontaneously immortalized keratinocyte cell line. We detected the formation of O(2)(*)(-) and H(2)O(2) in keratinocytes incubated with arsenite [As(III)] but not with arsenate. As(III)-induced DNA damage was detected in a concentration-dependent manner and evident at low micromolar concentrations. Catalase, an H(2)O(2) scavenger, eliminated H(2)O(2) and reduced the As(III)-mediated DNA damage. Superoxide dismutase, by enhancing the production of H(2)O(2) and (*)OH, significantly increased the As(III)-mediated DNA damage. Sodium formate, a competitive scavenger for (*)OH, and deferoxamine, a metal chelator, both reduced the DNA damage. These results suggest that exposure to arsenite generates O(2)(*)(-) and H(2)O(2), and (*)OH, derived from H(2)O(2), is responsible, at least in part, for the observed DNA damage. These findings demonstrate arsenic-induced formation of specific ROS and provide the direct evidence of (*)OH-mediated DNA damage in keratinocytes, which may play an important role in the mechanism for arsenic-induced skin carcinogenicity.