Protective signalling effect of manganese superoxide dismutase in hypoxia-reoxygenation of hepatocytes

Radiotherapy induces an increase in serum antioxidant capacity reflecting tumor response

Background and purpose

Radiotherapy (RT) is a mainstay component of treatment for patients with head and neck squamous cell carcinoma (HNSCC), but responses vary. As RT relies upon oxidative damage, antioxidant expression in response to RT-induced reactive oxygen species (ROS) could compromise treatment response. We aimed to examine local and systemic antioxidant responses to increased RT-induced ROS in relation to treatment success.

Materials and methods

Nuclear factor erythroid 2-related factor 2 (NRF2), the main antioxidant transcription factor, was immunofluorescently stained in FaDu cells and in tumor biopsies of patients with oral cavity/oropharynx HNSCC before and after five fractions of RT. Besides, total antioxidant capacity (TAC) was analyzed in HNSCC tumor cells in vitro and in serum of HNSCC patients before, during, and after RT.

Results

Data revealed an increase in NRF2 expression and TAC in head and neck cancer cells in vitro over the course of 5 daily fractions of 2 Gy. In accordance, also in patients' tumors NRF2 expression increased, which was associated with increased serum TAC during RT. Increasing serum TAC was related to impaired local tumor control.

Conclusion

Radiation induced NRF2 expression and upregulated TAC, which may compromise the effect of RT-induced ROS. Changes in serum TAC during RT could serve as a novel predictor of treatment outcome in HNSCC patients.Medical Ethics Review Committee (CMO) approval - CMO number: 2007/104.

A hypothesis for the pathogenesis of radiation-induced oral mucositis: when biological challenges exceed physiologic protective mechanisms. Implications for pharmacological prevention and treatment

Oral mucositis (OM) remains a significant unmet need for patients being treated with standard concomitant chemoradiation (CRT) regimens for head and neck cancers (HNC). OM's pathogenesis is complex and includes both direct and indirect damage pathways. In this paper, the field is reviewed with emphasis on the initiating and sustaining role of oxidative stress on OM's pathobiology. A hypothesis is presented which suggests that based on OM's clinical and biological trajectory, mucosal damage is largely the consequence of cumulative CRT-induced biological changes overwhelming physiologic self-protective mechanisms. Furthermore, an individual's ability to mount and maintain a protective response is dependent on interacting pathways which are primarily determined by a multiplex consisting of genomics, epigenomics, and microbiomics. Effective biologic or pharmacologic OM interventions are likely to supplement or stimulate existing physiologic damage-control mechanisms.

Cholesterol Prevents Hypoxia-Induced Hypoglycemia by Regulation of a Metabolic Ketogenic Shift

Blood cholesterol levels have been connected to high-altitude adaptation. In the present study, we treated mice with high-cholesterol diets following exposure to acute hypoxic stress and evaluated the effects of the diets on whole-body, liver glucose, and liver fat metabolism. For rapid cholesterol liver uptake, 6-week-old male C57BL/J6 mice were fed with high-cholesterol/cholic acid (CH) diet for 6 weeks and then were exposed to gradual oxygen level reduction for 1 h and hypoxia at 7% oxygen for additional 1 hour using a hypoxic chamber. Animals were than sacrificed, and metabolic markers were evaluated. Hypoxic treatment had a strong hypoglycemic effect that was completely blunted by CH treatment. Decreases in gluconeogenesis and glycogenolysis as well as an increase in ketone body formation were observed. Such changes indicate a metabolic shift from glucose to fat utilization due to activation of the inducible nitric oxide synthase/AMPK axis in the CH-treated animals. Increased ketogenesis was also observed in vitro in hepatocytes after cholesterol treatment. In conclusion, our results show for the first time that cholesterol contributes to metabolic shift and adaptation to hypoxia in vivo and in vitro through induction of HIF-1α and iNOS expression.

[ENERGETIC AND ANTIOXIDANT STATUS OF RAT LIVER MITOCHONDRIA DURING HYPOXIA-REOXYGENATION OF DIFFERENT DURATION]

Dynamics of changes in activity and protein expression of antiradical (MnSOD), glutathione-dependent (glutathione peroxidase, glutathione reductase) and NADP⁺-generated (isocitrate dehydrogenase) enzymes as well as in the energy metabolism indeces in rat liver mitochondria under hypoxia- reoxygenation of different duration (1, 3, 7 14 days) were studied. Prolonged hypoxia-reoxygenation was characterized by phase changes of the corticosterone concentration in rat blood, which corresponded to the changes in energy metabolism as well as in pro- and antioxidant balance in rat liver mitochondria. It has been shown that short-term (1 day) hypoxia-reoxygenation (5% O2 in the gas mixture) led to an increase in the blood corticosterone concentration and a significant activation of oxidative processes and energy metabolism in rat liver mitochondria, the intensity of which was reduced to 3rd day. Long- term hypoxia--reoxygenation (7-14th days) led to the gradual depletion of the organism adaptive capabilities, as evidenced by a significant decline in the blood corticosterone concentration, an increase in the content of secondary products of lipid peroxidation, an imbalance in pro- and antioxidant reactions and reduction of energy capacity in liver cells mitochondria. It has been shown that the glutathione peroxidase protein expression and enzymatic activity increased constantly during the whole experimental period and correlated positively with the level of H₂O₂. The amount of Mn-SOD protein as well as it's enzymatic activity was lower in the first seven days of experiment, and it was increased in consequent days up to the control level on 14thday. Increased activity of glutathione peroxidase, glutathione reductase and NADP+⁺dependent isocitrate dehydrogenase during prolonged hypoxia - eoxygenation indicates that glutathione- and NADPH-generating enzymes, were actively involved in the antioxidant protect.

Molecular hydrogen attenuates hypoxia/reoxygenation injury of intrahepatic cholangiocytes by activating Nrf2 expression

Hypoxia/reoxygenation (H/R) injury of cholangiocytes causes serious biliary complications during hepatobiliary surgeries. Molecular hydrogen (H2) has been shown to be effective in protecting various cells and organs against oxidative stress injury. Human liver cholangiocytes were used to determine the potential protective effects of hydrogen against cholangiocyte H/R injury and explore the underlying mechanisms. We found that H2 ameliorated H/R-induced cholangiocytes apoptosis. Our study revealed that H2 activated NF-E2-related factor 2 (Nrf2) and downstream cytoprotective protein expression. However, the protective function of H2 was abolished when Nrf2 was silenced. Apoptosis in cholangiocytes isolated from a rat model of liver ischemia/reperfusion injury indicated that H2 significantly attenuates ischemia/reperfusion cholangiocyte injury in vivo. In conclusion, our study shows that H2 protects intrahepatic cholangiocytes from hypoxia/reoxygenation-induced apoptosis in vitro or in vivo, and this phenomenon may depend on activating Nrf2 expression.

Manganese superoxide dismutase in carcinogenesis: friend or foe?

Superoxide and its derived ROS (reactive oxygen species) have been considered for a long time to be generated as toxic by-products of metabolic events. Although ROS generated in low amounts are able to act as signalling molecules, ROS appear to also play a major role in aging and in the pathogenesis of diseases such as inflammation, diabetes and cancer. Since superoxide formation, in particular in mitochondria, is often considered to be an initial step in the pathogenesis of these diseases, improper function of the MnSOD (mitochondrial superoxide dismutase; SOD2) may be critical for tissue homoeostasis. However, the underlying regulatory mechanisms appear to be multiple and this article summarizes current aspects by which MnSOD can regulate carcinogenesis under various conditions.

The effect of black raspberry extracts on MnSOD activity in protection against concanavalin A induced liver injury

Inflammation and oxidative stress are the key events in carcinogenetic transformation. Black raspberries (BRB) have been demonstrated to have antioxidant, antiinflammatory and anticancer bioactivities. In this study, a concanavalin A induced hepatitis mouse model is used to examine the effect of BRB extract on hepatic injury. Three BRB extracts, including ethanol/H2O extracts (both anthocyanin-contained fraction and nonanthocyanin-contained fraction) and hexane extract were used. The alterations in hepatic histology, apoptosis, and oxidative stress were observed in the animals pretreated with BRB extracts and then challenged by concanavalin A. Results indicate that ethanol/H2O extracts can inhibit Con A induced liver injury. The hepatic protection by the ethanol/H2O BRB extracts is associated with decreases of lipid peroxidation and NDA oxidative damage. Importantly, the BRB extracts increase manganese superoxide dismutase (MnSOD) activity but not the CuZnSOD. The preservation of MnSOD by BRB extracts is associated with the protective action in the liver challenged by Con A. Ethanol/H2O BRB extracts function as antioxidants, thus demonstrating the critical role of oxidative stress in the Con A induced liver injury, and providing evidence that the protective effects of ethanol/H2O BRB extracts result, at least in part, from their antioxidant action.

Obstructive sleep apnea and intermittent hypoxia increase expression of dual specificity phosphatase 1

OBJECTIVE

Dual specificity phosphatase 1 (DUSP1) inhibits mitogen activated protein kinase activity, and is activated by several stimuli such as sustained hypoxia, oxidative stress, and hormones. However, the effect of intermittent hypoxia is not known. The aim of this study was to evaluate the role of intermittent hypoxia on DUSP1 expression, and to validate its role in a human model of intermittent hypoxia, as seen in obstructive sleep apnea (OSA). OSA is characterized by recurrent episodes of hypoxemia/reoxygenation and is a known risk factor for cardiovascular morbidity.

METHODS

In-vitro studies using human coronary artery endothelial cells (HCAEC) and ex-vivo studies using white blood cells isolated from healthy and OSA subjects.

RESULTS

Intermittent hypoxia induced DUSP1 expression in human coronary artery endothelial cells (HCAEC), and in granulocytes isolated from healthy human subjects. Functionally, DUSP1 increased the expression and activity of manganese superoxide dismutase (MnSOD) in HCAEC. Further, significant increases in DUSP1 mRNA from total blood, and in DUSP1 protein in mononuclear cells and granulocytes isolated from OSA subjects, were observed in the early morning hours after one night of intermittent hypoxemia due to untreated OSA. This early-morning OSA-induced augmentation of DUSP1 gene expression was attenuated by continuous positive airway pressure (CPAP) treatment of OSA.

CONCLUSION

Intermittent hypoxia increases MnSOD activity via increased DUSP1 expression in HCAEC. Similarly, overnight intermittent hypoxemia in patients with OSA induces expression of DUSP1, which may mediate increases of MnSOD expression and activity. This may contribute significantly to neutralizing the effects of reactive oxygen species, a consequence of the intermittent hypoxemia/reperfusion elicited by OSA.

Ghrelin protects against cobalt chloride-induced hypoxic injury in cardiac H9c2 cells by inhibiting oxidative stress and inducing autophagy

Ghrelin is a multifunctional peptide that actively protects against cardiovascular ischemic diseases, but the underlying mechanisms are unclear. We used CoCl(2) to mimic hypoxic conditions in cardiac H9c2 cells in order to study the mechanism by which ghrelin protects cardiac myocytes against hypoxic injury by regulating the content of intracellular ROS and autophagy levels. Cell apoptosis and necrosis were evaluated by the flow cytometry assay, Hoechst staining, and LDH activity. Cell viability was detected by the WST-1 assay; ROS levels were assessed using DCFH2-DA; and Nox1, catalase and Mn-SOD were assayed by real-time PCR and activity assays. LC3II was measured by Western blot analysis. We observed that CoCl(2) induced apoptosis and death of H9c2 cells in a dose- and time-dependent manner. This was characterized by an increase in cell apoptosis, LDH activity, ROS content, Nox1 expression, and autophagy levels and a decrease in cell viability, catalase, and Mn-SOD activities. Ghrelin treatment significantly attenuated CoCl(2)-induced hypoxic injury by decreasing cell apoptosis, LDH activity, ROS content, and Nox1 expression and increasing cell viability, autophagy levels, catalase, and Mn-SOD mRNA levels and activities. Further experiments revealed that inhibiting autophagy using 3-MA or AMPK pathway with compound C almost abrogated the induction of ghrelin in autophagy. This was associated with a decrease in cell viability and an increase in LDH activity. Our results indicate that ghrelin protected cardiac myocytes against CoCl(2)-induced hypoxic injury by decreasing Nox1 expression, increasing the expression and activity of endogenous antioxidant enzymes, and inducing protective autophagy in an AMPK-dependent manner.

Moderate intermittent hypoxia/hyperoxia: implication for correction of mitochondrial dysfunction

The purpose of this study was to appreciate the acute hypoxia-induced mitochondrial oxidative damage development and the role of adaptation to hypoxia/hyperoxia (H/H) in correction of mitochondrial dysfunction. It was demonstrated that long-term sessions of moderate H/H [5 cycles of 5 min hypoxia (10% O2 in N2) alternated with 5 min hyperoxia (30% O2 in N2) daily for two weeks]_attenuated basal and Fe2+/ascorbate-induced lipid peroxidation (LPO) as well as production of carbonyl proteins and H2O2 in liver mitochondria of rats exposed to acute severe hypoxia (7% O2 in N2, 60 min) in comparison with untreated animals. It was shown that H/H increases the activity of glutathione peroxidase (GPx), reduces hyperactivation of Mn-SOD, and decreases Cu,Zn-SOD activity as compared with untreated rats. It has been suggested that the induction of Mn-SOD protein expression and the coordinated action of Mn-SOD and GPx could be the mechanisms underlying protective effects of H/H, which promote the correction of the acute hypoxia-induced mitochondrial dysfunction. The increase in Mn-SOD protein synthesis without changes in Mn-SOD mRNA level under H/H pretreatment indicates that the Mn-SOD activity is most likely dependent on its posttranslational modification or on the redox state of liver mitochondria.

The effect of DN (dominant-negative) Ku70 and reoxygenation on hypoxia cell-kill: evidence of hypoxia-induced potentially lethal damage

PURPOSE

To study the effect of DN (dominant-negative) Ku70 and reoxygenation on the hypoxia-induced cell-kill.

MATERIALS AND METHODS

Cell lines were human colorectal carcinoma HCT8 and HT29 cells and their respective derivatives, v-HCT8 and v-HT29 infected with DNKu70-containing adenovirus. Cells were plated in glass tubes and made hypoxic by flushing N(2) gas containing 0, 0.1 or 0.5% O(2). Cell survival was determined by colony formation assay immediately after 0-96 h hypoxia. To reoxygenate medium were replaced fresh following 48 or 72 h in hypoxia and cells were incubated in aerobic environment for 2-24 h before survival assay.

RESULTS

When incubated in hypoxia, cells lost reproductive capability ∼ exponentially as a function of time in hypoxia, and depending on the O(2) concentration. DNKu70 rendered cells more prone to hypoxia-induced cell-kill. Following reoxygenation cell survival increased rapidly but without detectable cell proliferation during first 24 hours. This evinced hypoxia-induced potentially lethal damage (PLD) that was repairable upon reoxygenation. DNKu70 did not significantly inhibit this repair.

CONCLUSION

Hypoxia-induced cell lethality was facilitated by DNKu70, but substantially repaired upon reoxygenation. This may have negative impact on the effect of reoxygenation in cancer therapy.

Autophagy: a cyto-protective mechanism which prevents primary human hepatocyte apoptosis during oxidative stress

The role of autophagy in the response of human hepatocytes to oxidative stress remains unknown. Understanding this process may have important implications for the understanding of basic liver epithelial cell biology and the responses of hepatocytes during liver disease. To address this we isolated primary hepatocytes from human liver tissue and exposed them ex vivo to hypoxia and hypoxia-reoxygenation (H-R). We showed that oxidative stress increased hepatocyte autophagy in a reactive oxygen species (ROS) and class III PtdIns3K-dependent manner. Specifically, mitochondrial ROS and NADPH oxidase were found to be key regulators of autophagy. Autophagy involved the upregulation of BECN1, LC3A, Atg7, Atg5 and Atg 12 during hypoxia and H-R. Autophagy was seen to occur within the mitochondria of the hepatocyte and inhibition of autophagy resulted in the lowering a mitochondrial membrane potential and onset of cell death. Autophagic responses were primarily observed in the large peri-venular (PV) hepatocyte subpopulation. Inhibition of autophagy, using 3-methyladenine, increased apoptosis during H-R. Specifically, PV human hepatocytes were more susceptible to apoptosis after inhibition of autophagy. These findings show for the first time that during oxidative stress autophagy serves as a cell survival mechanism for primary human hepatocytes.

Nrf2 inhibits LXRα-dependent hepatic lipogenesis by competing with FXR for acetylase binding

AIMS

The nuclear receptor liver X receptor-α (LXRα) stimulates lipogenesis, leading to steatosis. Nuclear factor erythroid-2-related factor-2 (Nrf2) contributes to cellular defense mechanism by upregulating antioxidant genes, and may protect the liver from injury inflicted by fat accumulation. However, whether Nrf2 affects LXRα activity is unknown. This study investigated the inhibitory role of Nrf2 in hepatic LXRα activity and the molecular basis.

RESULTS

A deficiency of Nrf2 enhanced the ability of LXRα agonist to promote hepatic steatosis, as mediated by lipogenic gene induction. In hepatocytes, Nrf2 overexpression repressed gene transactivation by LXR-binding site activation. Consistently, treatment of mice with sulforaphane (an Nrf2 activator) suppressed T0901317-induced lipogenesis, as confirmed by the experiments using hepatocytes. Nrf2 activation promoted deacetylation of farnesoid X receptor (FXR) by competing for p300, leading to FXR-dependent induction of small heterodimer partner (SHP), which was responsible for the repression of LXRα-dependent gene transcription. In human steatotic samples, the transcript levels of LXRα and SREBP-1 inversely correlated with those of Nrf2, FXR, and SHP.

INNOVATION

Our findings offer the mechanism to explain how decrease in Nrf2 activity in hepatic steatosis could contribute to the progression of NAFLD, providing the use of Nrf2 as a molecular biomarker to diagnose NAFLD. As certain antioxidants have the abilities to activate Nrf2, clinicians might utilize the activators of Nrf2 as a new therapeutic approach to prevent and/or treat NAFLD.

CONCLUSION

Nrf2 activation inhibits LXRα activity and LXRα-dependent liver steatosis by competing with FXR for p300, causing FXR activation and FXR-mediated SHP induction. Our findings provide important information on a strategy to prevent and/or treat steatosis.

An oxidative environment promotes growth of Mycobacterium abscessus

Mycobacterium abscessus infections, particularly those causing chronic lung diseases, are becoming more prevalent worldwide. M. abscessus infections are difficult to treat because of antibiotic resistance. Thus, new treatment options are urgently needed. M. abscessus is an intracellular pathogen that primarily infects macrophages and fibroblasts. Because this bacterium has only recently been identified as a separate species, very little is known about M. abscessus-host interactions and how M. abscessus growth is regulated. Oxidative stress has long been shown to inhibit the growth of bacterial organisms. However, some intracellular bacteria, such as Mycobacterium tuberculosis, grow well in oxidizing environments. In this study, we show that M. abscessus infection causes the host cell environment to become more oxidizing. Furthermore, we show that a more oxidizing environment leads to enhanced growth of M. abscessus inside macrophages. In the presence of antioxidants, MnTE-2-PyP (chemical name: manganese(II) meso-tetrakis-(N-methylpyridinium-2-yl) porphyrin) or N-acetyl-l-cysteine, M. abscessus growth is inhibited. These results lead us to postulate that antioxidants may aid in the treatment of M. abscessus infections.

Modifying radiation damage

Radiation leaves a fairly characteristic footprint in biological materials, but this is rapidly all but obliterated by the canonical biological responses to the radiation damage. The innate immune recognition systems that sense "danger" through direct radiation damage and through associated collateral damage set in motion a chain of events that, in a tissue compromised by radiation, often unwittingly result in oscillating waves of molecular and cellular responses as tissues attempt to heal. Understanding "nature's whispers" that inform on these processes will lead to novel forms of intervention targeted more precisely towards modifying them in an appropriate and timely fashion so as to improve the healing process and prevent or mitigate the development of acute and late effects of normal tissue radiation damage, whether it be accidental, as a result of a terrorist incident, or of therapeutic treatment of cancer. Here we attempt to discuss some of the non-free radical scavenging mechanisms that modify radiation responses and comment on where we see them within a conceptual framework of an evolving radiation-induced lesion.

Ionizing radiation activates the Nrf2 antioxidant response

The transcription factor NF-E2-related factor 2 (Nrf2) binds the antioxidant DNA response element (ARE) to activate important cellular cytoprotective defense systems. Recently several types of cancers have been shown to overexpress Nrf2, but its role in the cellular response to radiation therapy has yet to be fully determined. In this study, we report that single doses of ionizing radiation from 2 to 8 Gy activate ARE-dependent transcription in breast cancer cells in a dose-dependent manner, but only after a delay of five days. Clinically relevant daily dose fractions of radiation also increased ARE-dependent transcription, but again only after five days. Downstream activation of Nrf2-ARE-dependent gene and protein markers, such as heme oxygenase-1, occurred, whereas Nrf2-deficient fibroblasts were incapable of these responses. Compared with wild-type fibroblasts, Nrf2-deficient fibroblasts had relatively high basal levels of reactive oxygen species that increased greatly five days after radiation exposure. Further, in vitro clonogenic survival assays and in vivo sublethal whole body irradiation tests showed that Nrf2 deletion increased radiation sensitivity, whereas Nrf2-inducing drugs did not increase radioresistance. Our results indicate that the Nrf2-ARE pathway is important to maintain resistance to irradiation, but that it operates as a second-tier antioxidant adaptive response system activated by radiation only under specific circumstances, including those that may be highly relevant to tumor response during standard clinical dose-fractionated radiation therapy.