Hypoxic Preconditioning with Cobalt Attenuates Hypobaric Hypoxia-Induced Oxidative Damage in Rat Lungs

Protective effects of Tanshinone IIA preconditioning against hypobaric hypoxia-induced lung injury in a rat model

Tanshinone IIA (Tan-IIA), derived from Salvia miltiorrhiza, has been used in traditional Chinese medicine to treat cardiovascular diseases and pulmonary hypertension. This study investigates the potential of Tan-IIA preconditioning as a protective strategy against hypoxia-induced lung injury. Male Sprague-Dawley rats (200 ± 25 g) were divided into four groups: normoxia, normoxia with Tan-IIA, hypobaric hypoxia, and hypobaric hypoxia with Tan-IIA. Tan-IIA was administered intraperitoneally at doses of 10, 20, and 40 mg/kg body weight one hour before exposure to hypobaric hypoxia (simulated altitude of 25,000 feet for 48 h). Pulmonary edema was assessed by measuring transvacuolar leakage of sodium fluorescein dye and lung water content. Exposure to hypoxia triggered redox imbalances, inflammation, and changes in levels of nitric oxide (NOx), endothelin- 1, and Na/K ATPase, which contributed to pulmonary edema. Tan-IIA preconditioning, particularly at 20 mg/kg, was effective in reversing these disturbances. Tan-IIA modulated the expression of key signaling molecules, including c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38, as well as downstream activator protein- 1 (AP- 1) subunits (Jun and Fos), thus reducing inflammation. Its protective effects were partly due to increased NO levels and decreased endothelin, which lowered pulmonary vasoconstriction and permeability, respectively. Additionally, enhanced Na/K ATPase expression via hypoxia-inducible factor- 1 (HIF- 1) and AP- 1 pathways promoted alveolar fluid clearance, while interactions between nuclear factor erythroid 2-related factor 2 (Nrf2) and c-Jun highlighted the anti-oxidative properties of Tanshinone IIA. These findings demonstrate that Tanshinone IIA preconditioning protects against hypoxia-induced lung injury by mitigating pulmonary leakage. This highlights its potential therapeutic application in hypoxic lung conditions.

Oxidative stress and expression of inflammatory factors in lung tissue of acute mountain sickness rats

The aim of the present study was to investigate the changes in lung histomorphology and oxidative stress, as well as the expression of interleukin (IL)-17C and other inflammatory factors during acute mountain sickness (AMS) in male Sprague-Dawley rats and to explore the underlying mechanism. Rats were randomly divided into a control group (0 h) and three hypoxia stress groups, exposed to low-pressure oxygen storage at a simulated altitude of 6,000 m for 24, 48 and 72 h, respectively. Morphological changes in lung tissue were observed by hematoxylin and eosin staining under light microscopy and transmission electron microscopy. The expression of inflammatory factors IL-17C, nuclear factor-κB (NF-κB), IL-1β, IL-6 and tumor necrosis factor-α (TNF-α) in lung tissue was assessed by RNA sequencing and verified by reverse transcription-quantitative PCR (RT-qPCR) and western blotting (WB). Superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) enzyme activity and malondialdehyde (MDA) expression were also measured. Experimental groups were compared to the control group following 24, 48 and 72 h of hypoxic stress. Lung tissue suffered from different degrees of injury, and the damage was the most severe after 48 h of hypoxic stress. RNA sequencing data from the lung tissue of rats from each group suggested that the expression of IL-17C, NF-κB, IL-1β, IL-6, and TNF-α increased significantly after hypoxic stress. RT-qPCR and WB demonstrated that the expression of IL-17C and NF-κB increased significantly after hypoxia lasting 48 and 72 h. IL-1β expression increased significantly after hypoxia stress lasting 24 and 48 h, and the expressions of TNF-α and IL-6 increased significantly after hypoxia stress lasting 24, 48 and 72 h (P<0.01). The enzyme activity of SOD and GSH-Px decreased significantly after lasting 24, 48 and 72 h of hypoxia (P<0.01), and MDA increased significantly after hypoxic stress lasting 48 and 72 h (P<0.01). In conclusion, under hypoxic stress, rats quickly initiate oxidative stress and immune responses. However, with prolonged hypoxic stress time, excessive oxidative stress can further stimulate the immune system in vivo, and release a large quantity of inflammatory factors accumulating in the body. This, in turn, may lead to the occurrence of inflammatory storms and further damage the lung tissue resulting in AMS.

Serum Inflammatory Factor Profiles in the Pathogenesis of High-Altitude Polycythemia and Mechanisms of Acclimation to High Altitudes

High-altitude polycythemia (HAPC) is a common aspect of chronic mountain sickness (CMS) caused by hypoxia and is the main cause of other symptoms associated with CMS. However, its pathogenesis and the mechanisms of high-altitude acclimation have not been fully elucidated. Exposure to high altitude is associated with elevated inflammatory mediators. In this study, the subjects were recruited and placed into a plain control (PC) group, plateau control (PUC) group, early HAPC (eHAPC) group, or a confirmed HAPC (cHAPC) group. Serum samples were collected, and inflammatory factors were measured by a novel antibody array methodology. The serum levels of interleukin-2 (IL-2), interleukin-3 (IL-3), and macrophage chemoattractant protein-1 (MCP-1) in the eHAPC group and the levels of interleukin-1 beta (IL-1 beta), IL-2, IL-3, tumor necrosis factor-alpha (TNF-alpha), MCP-1, and interleukin-16 (IL-16) in the cHAPC group were higher than those in the PUC group. More interestingly, the expression of IL-1 beta, IL-2, IL-3, TNF-alpha, MCP-1, and IL-16 in the PUC group showed a remarkable lower value than that in the PC group. These results suggest that these six factors might be involved in the pathogenesis of HAPC as well as acclimation to high altitudes. Altered inflammatory factors might be new biomarkers for HAPC and for high-altitude acclimation.

Polysaccharide from Potentilla anserina L ameliorate pulmonary edema induced by hypobaric hypoxia in rats

High-altitude pulmonary edema (HAPE) is a life-threatening disease occurs in hypobaric hypoxia (HH) environment, which could be treated by Dexamethasone, but might cause side-effects. Potentilla anserina L polysaccharide (PAP) holds promising physiological and pharmacological properties which could be beneficial for HAPE treatment. In our study, the anti-hypoxia effect of PAP was firstly investigated through anti-normobaric hypoxia test and anti-acute hypoxia test. Then we established a model of HAPE and measured the lung water content, pathological changes and MDA, NO, SOD, GSH concentrations in lung tissues. We also evaluated the protein and mRNA levels of pro-inflammatory cytokines (IL-1β, IL-6, TNF-α, VEGF, NF-κB and HIF-1α) by ELISA kits, RT-PCR and Western blotting. As expected, PAP could dramatically reduce the lung water content, alleviate lung tissue injury, and inhibit MDA and NO production, it also promote SOD activity and GSH expression. In addition, it has been found that PAP blocked the NF-κB and HIF-1α signaling pathway activation, inhibited the generation of downstream pro-inflammatory cytokines. Therefore, PAP provides great potential in HAPE treatment mainly through suppression of oxidative stress and inflammatory suppression.

Hypoxia, HIF-1α, and COVID-19: from pathogenic factors to potential therapeutic targets

The pandemic of coronavirus disease 2019 (COVID-19) and its pathogen, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) have become the greatest current threat to global public health. The highly infectious SARS-CoV-2 virus primarily attacks pulmonary tissues and impairs gas exchange leading to acute respiratory distress syndrome (ARDS) and systemic hypoxia. The current pharmacotherapies for COVID-19 largely rely on supportive and anti-thrombi treatment and the repurposing of antimalarial and antiviral drugs such as hydroxychloroquine and remdesivir. For a better mechanistic understanding of COVID-19, our present review focuses on its primary pathophysiologic features: hypoxia and cytokine storm, which are a prelude to multiple organ failure and lethality. We discussed a possible link between the activation of hypoxia inducible factor 1α (HIF-1α) and cell entry of SARS-CoV-2, since HIF-1α is shown to suppress the angiotensin-converting enzyme 2 (ACE2) receptor and transmembrane protease serine 2 (TMPRSS2) and upregulate disintegrin and metalloproteinase domain-containing protein 17 (ADAM17). In addition, the protein targets of HIF-1α are involved with the activation of pro-inflammatory cytokine expression and the subsequent inflammatory process. Furthermore, we hypothesized a potential utility of so-called "hypoxic conditioning" to activate HIF-1α-induced cytoprotective signaling for reduction of illness severity and improvement of vital organ function in patients with COVID-19. Taken together, we would propose further investigations into the hypoxia-related molecular mechanisms, from which novel targeted therapies can be developed for the improved management of COVID-19.

Downregulated Recycling Process but Not De Novo Synthesis of Glutathione Limits Antioxidant Capacity of Erythrocytes in Hypoxia

Red blood cells (RBCs) are susceptible to sustained free radical damage during circulation, while the changes of antioxidant capacity and regulatory mechanism of RBCs under different oxygen gradients remain unclear. Here, we investigated the changes of oxidative damage and antioxidant capacity of RBCs in different oxygen gradients and identified the underlying mechanisms using an in vitro model of the hypoxanthine/xanthine oxidase (HX/XO) system. In the present study, we reported that the hypoxic RBCs showed much higher oxidative stress injury and lower antioxidant capacity compared with normoxic RBCs. In addition, we found that the disturbance of the recycling process, but not de novo synthesis of glutathione (GSH), accounted for the significantly decreased antioxidant capacity of hypoxic RBCs compared to normoxic RBCs. We further elucidated the underlying molecular mechanism by which oxidative phosphorylation of Band 3 blocked the hexose monophosphate pathway (HMP) and decreased NADPH production aggravating the dysfunction of GSH synthesis in hypoxic RBCs under oxidative conditions.

Molecular and Cellular Response of Co-cultured Cells toward Cobalt Chloride (CoCl2)-Induced Hypoxia

Cobalt chloride (CoCl₂) is a well-known hypoxia mimetic mediator that induces hypoxia-like responses. CoCl₂, a mediator confirmed to alleviate hypoxia-inducible factor-1 (HIF-1), has been associated with a variety of hypoxic responses. HIF-1 is the foremost transcriptionfactor that is particularly activated during hypoxia and regulates various genes. Therefore, this study aimed to investigate the cellular and molecular responses of the co-cultured cells under the influence of the CoCl₂-induced hypoxic condition. Mono- and co-cultured C2C12 and 3T3-L1 cells were exposed to CoCl₂, and a significant induction in HIF-1, reactive oxygen species and lipid peroxidase and a reduction in glutathione and catalase were observed. The expressions of proapoptotic genes like Bax, p53, caspase-9, and caspase-3 were notably increased, whereas the antiapoptotic gene, i.e., Bcl2, was downregulated during hypoxia in mono- as well as co-cultured C2C12 cells. However, the co-cultured C2C12 cells show significantly lower induction in oxidative stress and expression of apoptotic genes in comparison to monocultured C2C12 cells. Whereas, the co-cultured 3T3-L1 cells show comparatively higher oxidative stress and apoptotic event in comparison to monocultured 3T3-L1 cells. The reason may be the communication between the cells and some soluble factors that help in cell survival/death from hypoxia. Moreover, it may also be due to the fact that fat and muscle cells interact and communicate via proximity and mutual ability when growing together. Therefore, the co-culture system provides a unique approach to intercellular communication between the two different cell types.

Aβ1-42 increases the expression of neural KATP subunits Kir6.2/SUR1 via the NF-κB, p38 MAPK and PKC signal pathways in rat primary cholinergic neurons

ATP-sensitive potassium channels (KATP) may mediate a potential neuroprotective role in Alzheimer's disease (AD). Given that exposure to Aβ1-42 in cultured primary cholinergic neurons for 72 h significantly upregulates the expression of KATP subunits Kir6.2/SUR1, we aim to study the underlying signal transduction mechanisms that are involved in Aβ_1-42-induced upregulation of KATP subunits Kir6.2/SUR1. In the present study, we first identified the primary cultured rat cortical and hippocampal neurons using immunocytochemistry. 0.5 μM NF-κB inhibitor SN-50, 2 μM p38MAPK inhibitor SB203580 or 2 μM PKC inhibitor Chelerythrine chloride (CTC) were then added in three separate groups, followed by 2 μM Aβ_1-42 30 min later in all 3 groups. Western Blot was performed 72 h later to detect the expression of KATP subunits Kir6.2/SUR1. We found that Aβ_1-42 significantly increased the level of KATP subunits Kir6.2/SUR1 expression at 72 h when compared with the control group ( p < 0.05). However, when compared with the Aβ_1-42 group, the level of KATP subunits Kir6.2/SUR1 expression at 72 h significantly decreased in the SN50 + Aβ_1-42 group, SB203580 + Aβ_1-42 group, and the CTC + Aβ_1-42 group ( p < 0.05). Our findings suggest that the NF-κB, p38 MAPK, and PKC signal pathways are partially involved in the upregulation of KATP subunits Kir6.2/SUR1 expression induced by Aβ_1-42 cytotoxicity in neurons, which supports a potential theoretical basis of targeting these signal pathways in the treatment of AD.

Dependence of the severity of the systemic inflammatory response on resistance to hypoxia in male Wistar rats

Purpose

The aim of the study was to characterize the severity of the systemic inflammatory response induced by lipopolysaccharide (LPS) in animals with different resistance levels to hypoxia.

Materials and methods

Two to three months old male Wistar rats (220–240 g) were divided according to hypoxia tolerance in a hypobaric chamber. After a month, they were injected intraperitoneally with Escherichia coli LPS at a dose of 1.5 mg/kg. After 3, 6 and 24 hours of LPS injection, we studied the levels of IL-1β, C-reactive protein (CRP) and TGF-β in the serum, the expression of Hif-1α and Nf-kb in the liver, morphological disorders in the lung and ex vivo production of IL-10 by splenic cells activated by ConA.

Results

In the early periods after the injection of LPS, increase in Nf-kb expression in the liver was observed only in the rats susceptible to hypoxia. After 6 hours of LPS injection, the number of neutrophils in the interalveolar septa of the lungs of rats susceptible to hypoxia was higher than in tolerant rats. This points to the development of more pronounced LPS-induced inflammation in the rats susceptible to hypoxia and is accompanied by increased expression of Hif-1α in the liver after 6 hours of LPS administration, serum IL-1β level after 3 hours and CRP level after 24 hours. The production of the anti-inflammatory cytokine IL-10 by the spleen was significantly decreased after 6 hours of LPS injection only in the animals tolerant to hypoxia. After 24 hours of LPS injection, a significant decrease in serum TGF-β level occurred in the rats tolerant to hypoxia in comparison with the control group, which improved the survival rates of the animals.

Conclusion

We have demonstrated the differences in the severity of the LPS-induced inflammatory response in male Wistar rats with different resistance levels to hypoxia. Rats susceptible to hypoxia are characterized by a more pronounced inflammatory response induced by LPS.

Cobalt-containing bioactive glasses reduce human mesenchymal stem cell chondrogenic differentiation despite HIF-1α stabilisation

Bioactive glasses (BGs) are excellent delivery systems for the sustained release of therapeutic ions and have been extensively studied in the context of bone tissue engineering. More recently, due to their osteogenic properties and expanding application to soft tissue repair, BGs have been proposed as promising materials for use at the osteochondral interface. Since hypoxia plays a critical role during cartilage formation, we sought to investigate the influence of BGs releasing the hypoxia-mimicking agent cobalt (CoBGs) on human mesenchymal stem cell (hMSC) chondrogenesis, as a novel approach that may guide future osteochondral scaffold design. The CoBG dissolution products significantly increased the level of hypoxia-inducible factor-1 alpha in hMSCs in a cobalt dose-dependent manner. Continued exposure to the cobalt-containing BG extracts significantly reduced hMSC proliferation and metabolic activity, as well as chondrogenic differentiation. Overall, this study demonstrates that prolonged exposure to cobalt warrants careful consideration for cartilage repair applications.

S1P prophylaxis mitigates acute hypobaric hypoxia-induced molecular, biochemical, and metabolic disturbances: A preclinical report

Sphingosine-1-phosphate (S1P) is emerging to have hypoxic preconditioning potential in various preclinical studies. The study aims to evaluate the preclinical preconditioning efficacy of exogenously administered S1P against acute hypobaric hypoxia (HH)-induced pathological disturbances. Male Sprague Dawley rats (200 ± 20 g) were preconditioned with 1, 10, and 100 μg/kg body weight (b.w.) S1P (i.v.) for three consecutive days. On the third day, S1P preconditioned animals, along with hypoxia control animals, were exposed to HH equivalent to 7,620 m (280 mm Hg) for 6 h. Postexposure status of cardiac energy production, circulatory vasoactive mediators, pulmonary and cerebral oxidative damage, and inflammation were assessed. HH exposure led to cardiac energy deficit indicated by low ATP levels and pronounced AMPK activation levels, raised circulatory levels of brain natriuretic peptide and endothelin-1 with respect to total nitrate (NOx), redox imbalance, inflammation, and alterations in NOx levels in the pulmonary and cerebral tissues. These pathological precursors have been routinely reported to be coincident with high-altitude diseases. Preconditioning with S1P, especially 1 µg/kg b.w. dose, was seen to reverse the manifestation of these pathological disturbances. The protective efficacy could be attributed, at least in part, to enhanced activity of cardioprotective protein kinase C and activation of small GTPase Rac1, which led to further induction of hypoxia-adaptive molecular mediators: hypoxia-inducible factor (HIF)-1α and Hsp70. This is a first such report, to the best of our knowledge, elucidating the mechanism of exogenous S1P-mediated HIF-1α/Hsp70 induction. Conclusively, systemic preconditioning with 1 μg/kg b.w. S1P in rats protects against acute HH-induced pathological disturbances. © 2016 IUBMB Life 68(5):365-375, 2016.

Ω3 Supplementation and intermittent hypobaric hypoxia induce cardioprotection enhancing antioxidant mechanisms in adult rats

Intermittent hypobaric hypoxia (IH) is linked with oxidative stress, impairing cardiac function. However, early IH also activate cardio-protective mechanisms. Omega 3 fatty acids (Ω3) induce cardioprotection by reducing infarct size and reinforcing antioxidant defenses. The aim of this work was to determine the combined effects of IH and Ω3 on cardiac function; oxidative balance and inflammatory state. Twenty-eight rats were randomly divided into four groups: normobaric normoxia (N); N + Ω3 (0.3 g·kg⁻¹·day⁻¹); IH; and IH + Ω3. IH was induced by 4 intercalate periods of hypoxia (4 days)—normoxia (4 days) in a hypobaric chamber during 32 days. At the end of the exposure, hearts were mounted in a Langendorff system and subjected to 30 min of ischemia followed by 120 min of reperfusion. In addition, we determined HIF-1α and ATP levels, as well as oxidative stress by malondialdehyde and nitrotyrosine quantification. Further, the expression of the antioxidant enzymes superoxide dismutase, catalase, and glutathione peroxidase was determined. NF-kappaB and myeloperoxidase levels were assessed in the hearts. Relative to N hearts, IH improved left ventricular function (Left ventricular developed pressure: N; 21.8 ± 3.4 vs. IH; 42.8 ± 7.1 mmHg; p < 0.05); reduced oxidative stress (Malondialdehyde: N; 14.4 ± 1.8 vs. IH; 7.3 ± 2.1 μmol/mg prot.; p < 0.05); and increased antioxidant enzymes expression. Supplementation with Ω3 induces similar responses as IH group. Our findings suggest that both, IH and Ω3 in an independent manner, induce functional improvement by antioxidant and anti-inflammatory mechanisms, establishing cardio-protection.

Aryl hydrocarbon receptors in osteoclast lineage cells are a negative regulator of bone mass

Aryl hydrocarbon receptors (AhRs) play a critical role in various pathological and physiological processes. Although recent research has identified AhRs as a key contributor to bone metabolism following studies in systemic AhR knockout (KO) or transgenic mice, the cellular and molecular mechanism(s) in this process remain unclear. In this study, we explored the function of AhR in bone metabolism using AhR^{RANKΔOc/ΔOc} (RANK^Cre/+;AhR^flox/flox) mice. We observed enhanced bone mass together with decreased resorption in both male and female 12 and 24-week-old AhR^{RANKΔOc/ΔOc} mice. Control mice treated with 3-methylcholanthrene (3MC), an AhR agonist, exhibited decreased bone mass and increased bone resorption, whereas AhR^{CtskΔOc/ΔOc} (Ctsk^Cre/+;AhR^flox/flox) mice injected with 3MC appeared to have a normal bone phenotype. In vitro, bone marrow-derived macrophages (BMDMs) from AhR^{RANKΔOc/ΔOc} mice exhibited impaired osteoclastogenesis and repressed differentiation with downregulated expression of B lymphocyte-induced maturation protein 1 (Blimp1), and cytochrome P450 genes Cyp1b1 and Cyp1a2. Collectively, our results not only demonstrated that AhR in osteoclast lineage cells is a physiologically relevant regulator of bone resorption, but also highlighted the need for further studies on the skeletal actions of AhR inhibitors in osteoclast lineage cells commonly associated with bone diseases, especially diseases linked to environmental pollutants known to induce bone loss.

Effect of subchronic hypobaric hypoxia on oxidative stress in rat heart

We examined the effect of subchronic hypobaric hypoxia in rat heart. Adult male Sprague-Dawley rats were exposed at 25,000 ft for different time periods (2 and 5 days). Susceptibility of their hearts to oxidative stress as well as modulation in gene expression was evaluated. The results showed a crosstalk between reactive oxygen species (ROS) and nitric oxide (NO), initial response was accompanied by increase in ROS generation and development of oxidative stress as confirmed by increased lipid peroxidation, protein oxidation and accumulation of 2, 4-dinitrophenyl hydrazine and 4-hydroxy-2-nonenal adducts. At the same time, glutathione activity decreased; however, antioxidant enzymatic activities of superoxide dismutases, glutathione-S-transferase, and glutathione peroxidase rose in response to 5-days hypoxia. Interestingly, NO level increased till 5 days, however ROS decreased after 5 days; this observation suggests that ROS/NO balance plays an important role in cardioprotection. This observation is further supported by upregulation of antioxidant genes hemeoxygenase (HO-1) and metallothionein (MT). In addition, hypoxia also induces gradual upregulation of hypoxia-inducible transcription factor (HIF-1α), which in turn induces the expression of adaptive genes erythropoiesis, vascular endothelial growth factor, glucose transporter-1, nitric oxide synthase. Collectively, our data suggests a reciprocal regulation of ROS and NO and this effect is mediated by the increase in antioxidant proteins HO-1 and MT. Along with this HIF-1-mediated induction of various cardioprotective genes also plays an important role in acclimatization.

Radioprotective effect on HepG2 cells of low concentrations of cobalt chloride: induction of hypoxia-inducible factor-1 alpha and clearance of reactive oxygen species

It has been found that low doses of certain toxicants might generate a protective response to cellular damage. Previous data have shown that elevated doses of cobalt (Co) induce injury to cells and organisms or result in radiological combined toxicity. Whether low doses of Co generate a protective effect or not, however, remains controversial. In this study, we investigated the effect and mechanism of action of low dose cobalt chloride (CoCl2, 100 μM) on the viability of irradiated cells. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay was used to observe the radio-sensitivity of HepG2 cells under different pretreatments. The alteration of intracellular DNA damage was further measured using micronucleus (MN) assay. Levels of hypoxia inducible factor-1α (HIF-1α) expression and its target gene, EPO, were monitored by western blot and reverse transcription polymerase chain reaction (RT-PCR), respectively, and intracellular reactive oxygen species (ROS) content was determined by 2',7'-dichlorofluorescein diacetate (DCFH-DA) probe staining. Our results show that low dose CoCl2does not influence HepG2 cell viability, but induces the expression of HIF-1α, followed by increased radio-resistance. Additionally, cells treated with HIF-1α siRNA retained a partial refractory response to irradiation concomitant with a marked reduction in intracellular ROS. The change of MN further indicated that the reduction of DNA damage was confirmed with the alteration of ROS. Our results demonstrate that low dose CoCl2may protect cells against irradiative harm by two mechanisms, namely HIF-1α expression and ROS clearance.

Lead bone toxicity in growing rats exposed to chronic intermittent hypoxia

Lead chronic intoxication under hypoxic conditions revealed growth retardation in growing rats and damages on femoral and mandibular bones that predispose to fractures. These findings aimed us to investigate if bone material and geometric properties, bone mass in terms of histomorphometry or antioxidant capacity are also impaired in such experimental model. Combined treatments significantly reduced hemimandible cross sectional geometry and intrinsic stiffness (-16% and -34%); tibia and hemimandible bone volume (-45% and -40%) and growth plate cartilage thickness (-19%). These results show a previously unreported toxic effect of lead on mandible however, longer studies should be necessary to evaluate if an adaptation of bone architecture to maintain structural properties may occur and if the oxidative stress can be identified as the primary contributory agent in the pathogenesis of lead poisoning.

Augmentation of aerobic respiration and mitochondrial biogenesis in skeletal muscle by hypoxia preconditioning with cobalt chloride

High altitude/hypoxia training is known to improve physical performance in athletes. Hypoxia induces hypoxia inducible factor-1 (HIF-1) and its downstream genes that facilitate hypoxia adaptation in muscle to increase physical performance. Cobalt chloride (CoCl₂), a hypoxia mimetic, stabilizes HIF-1, which otherwise is degraded in normoxic conditions. We studied the effects of hypoxia preconditioning by CoCl₂ supplementation on physical performance, glucose metabolism, and mitochondrial biogenesis using rodent model. The results showed significant increase in physical performance in cobalt supplemented rats without (two times) or with training (3.3 times) as compared to control animals. CoCl₂ supplementation in rats augmented the biological activities of enzymes of TCA cycle, glycolysis and cytochrome c oxidase (COX); and increased the expression of glucose transporter-1 (Glut-1) in muscle showing increased glucose metabolism by aerobic respiration. There was also an increase in mitochondrial biogenesis in skeletal muscle observed by increased mRNA expressions of mitochondrial biogenesis markers which was further confirmed by electron microscopy. Moreover, nitric oxide production increased in skeletal muscle in cobalt supplemented rats, which seems to be the major reason for peroxisome proliferator activated receptor-gamma coactivator-1α (PGC-1α) induction and mitochondrial biogenesis. Thus, in conclusion, we state that hypoxia preconditioning by CoCl₂ supplementation in rats increases mitochondrial biogenesis, glucose uptake and metabolism by aerobic respiration in skeletal muscle, which leads to increased physical performance. The significance of this study lies in understanding the molecular mechanism of hypoxia adaptation and improvement of work performance in normal as well as extreme conditions like hypoxia via hypoxia preconditioning.

Lung oxidative damage by hypoxia

One of the most important functions of lungs is to maintain an adequate oxygenation in the organism. This organ can be affected by hypoxia facing both physiological and pathological situations. Exposure to this condition favors the increase of reactive oxygen species from mitochondria, as from NADPH oxidase, xanthine oxidase/reductase, and nitric oxide synthase enzymes, as well as establishing an inflammatory process. In lungs, hypoxia also modifies the levels of antioxidant substances causing pulmonary oxidative damage. Imbalance of redox state in lungs induced by hypoxia has been suggested as a participant in the changes observed in lung function in the hypoxic context, such as hypoxic vasoconstriction and pulmonary edema, in addition to vascular remodeling and chronic pulmonary hypertension. In this work, experimental evidence that shows the implied mechanisms in pulmonary redox state by hypoxia is reviewed. Herein, studies of cultures of different lung cells and complete isolated lung and tests conducted in vivo in the different forms of hypoxia, conducted in both animal models and humans, are described.

Oxidative stress and metal carcinogenesis

Occupational and environmental exposures to metals are closely associated with an increased risk of various cancers. Although carcinogenesis caused by metals has been intensively investigated, the exact mechanisms of action are still unclear. Accumulating evidence indicates that reactive oxygen species (ROS) generated by metals play important roles in the etiology of degenerative and chronic diseases. This review covers recent advances in (1) metal-induced generation of ROS and the related mechanisms; (2) the relationship between metal-mediated ROS generation and carcinogenesis; and (3) the signaling proteins involved in metal-induced carcinogenesis, especially intracellular reduction-oxidation-sensitive molecules.

Advances in carcinogenic metal toxicity and potential molecular markers

Metal compounds such as arsenic, cadmium, chromium, cobalt, lead, mercury, and nickel are classified as carcinogens affecting human health through occupational and environmental exposure. However, the underlying mechanisms involved in tumor formation are not well clarified. Interference of metal homeostasis may result in oxidative stress which represents an imbalance between production of free radicals and the system's ability to readily detoxify reactive intermediates. This event consequently causes DNA damage, lipid peroxidation, protein modification, and possibly symptomatic effects for various diseases including cancer. This review discusses predominant modes of action and numerous molecular markers. Attention is paid to metal-induced generation of free radicals, the phenomenon of oxidative stress, damage to DNA, lipid, and proteins, responsive signal transduction pathways with major roles in cell growth and development, and roles of antioxidant enzymatic and DNA repair systems. Interaction of non-enzymatic antioxidants (carotenoids, flavonoids, glutathione, selenium, vitamin C, vitamin E, and others) with cellular oxidative stress markers (catalase, glutathione peroxidase, and superoxide dismutase) as well as certain regulatory factors, including AP-1, NF-κB, Ref-1, and p53 is also reviewed. Dysregulation of protective pathways, including cellular antioxidant network against free radicals as well as DNA repair deficiency is related to oncogenic stimulation. These observations provide evidence that emerging oxidative stress-responsive regulatory factors and DNA repair proteins are putative predictive factors for tumor initiation and progression.

Tetramethylpyrazine inhibits hypoxia-induced pulmonary vascular leakage in rats via the ROS-HIF-VEGF pathway

Tetramethylpyrazine (TMP) is a reactive oxygen species (ROS) antagonist that has potent properties for the treatment of a variety of vascular diseases, such as ischemic stroke and pulmonary hypertension secondary to chronic obstructive pulmonary diseases. However, there are few data about the role of TMP in hypoxia-induced pulmonary vascular leakage. This study examined the effect of TMP on hypoxia-induced pulmonary vascular leakage and the underlying mechanisms. Rat pulmonary microvascular endothelial cells (RPMVECs) treated with TMP or not were subjected to hypoxic or normoxic conditions for 24 h, and the monolayer permeability, intracellular ROS, hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) proteins levels were determined. Additionally, rats administrated TMP were exposed to hypobaric hypoxia to evaluate the effect of TMP in vivo by measuring lung water content, pulmonary vascular leakage into the lungs and immunohistochemistry for HIF-1α and VEGF. Hypoxia was found to cause a significant increase in RPMVEC monolayer permeability and intracellular ROS, HIF-1α and VEGF protein levels. Treatment with TMP decreased the hypoxia-induced RPMVEC monolayer permeability and attenuated the elevation of ROS, HIF-1α and VEGF protein levels. TMP-treated animals showed less pulmonary vascular leakage and HIF-1α and VEGF expression compared with those exposed to hypoxia alone. These observations supported that TMP inhibited the increase in pulmonary vascular permeability induced by hypoxia. The underlying mechanisms may be related to the scavenging of intracellular ROS and the suppression of hypoxia-induced upregulation of HIF-1α and VEGF proteins.

Advances in metal-induced oxidative stress and human disease

Detailed studies in the past two decades have shown that redox active metals like iron (Fe), copper (Cu), chromium (Cr), cobalt (Co) and other metals undergo redox cycling reactions and possess the ability to produce reactive radicals such as superoxide anion radical and nitric oxide in biological systems. Disruption of metal ion homeostasis may lead to oxidative stress, a state where increased formation of reactive oxygen species (ROS) overwhelms body antioxidant protection and subsequently induces DNA damage, lipid peroxidation, protein modification and other effects, all symptomatic for numerous diseases, involving cancer, cardiovascular disease, diabetes, atherosclerosis, neurological disorders (Alzheimer's disease, Parkinson's disease), chronic inflammation and others. The underlying mechanism of action for all these metals involves formation of the superoxide radical, hydroxyl radical (mainly via Fenton reaction) and other ROS, finally producing mutagenic and carcinogenic malondialdehyde (MDA), 4-hydroxynonenal (HNE) and other exocyclic DNA adducts. On the other hand, the redox inactive metals, such as cadmium (Cd), arsenic (As) and lead (Pb) show their toxic effects via bonding to sulphydryl groups of proteins and depletion of glutathione. Interestingly, for arsenic an alternative mechanism of action based on the formation of hydrogen peroxide under physiological conditions has been proposed. A special position among metals is occupied by the redox inert metal zinc (Zn). Zn is an essential component of numerous proteins involved in the defense against oxidative stress. It has been shown, that depletion of Zn may enhance DNA damage via impairments of DNA repair mechanisms. In addition, Zn has an impact on the immune system and possesses neuroprotective properties. The mechanism of metal-induced formation of free radicals is tightly influenced by the action of cellular antioxidants. Many low-molecular weight antioxidants (ascorbic acid (vitamin C), alpha-tocopherol (vitamin E), glutathione (GSH), carotenoids, flavonoids, and other antioxidants) are capable of chelating metal ions reducing thus their catalytic activity to form ROS. A novel therapeutic approach to suppress oxidative stress is based on the development of dual function antioxidants comprising not only chelating, but also scavenging components. Parodoxically, two major antioxidant enzymes, superoxide dismutase (SOD) and catalase contain as an integral part of their active sites metal ions to battle against toxic effects of metal-induced free radicals. The aim of this review is to provide an overview of redox and non-redox metal-induced formation of free radicals and the role of oxidative stress in toxic action of metals.

Environmentally induced oxidative stress in aquatic animals

Reactive oxygen species (ROS) are an unenviable part of aerobic life. Their steady-state concentration is a balance between production and elimination providing certain steady-state ROS level. The dynamic equilibrium can be disturbed leading to enhanced ROS level and damage to cellular constituents which is called "oxidative stress". This review describes the general processes responsible for ROS generation in aquatic animals and critically analyses used markers for identification of oxidative stress. Changes in temperature, oxygen levels and salinity can cause the stress in natural and artificial conditions via induction of disbalance between ROS production and elimination. Human borne pollutants can also enhance ROS level in hydrobionts. The role of transition metal ions, such as copper, chromium, mercury and arsenic, and pesticides, namely insecticides, herbicides, and fungicides along with oil products in induction of oxidative stress is highlighted. Last years the research in biology of free radicals was refocused from only descriptive works to molecular mechanisms with particular interest to ones enhancing tolerance. The function of some transcription regulators (Keap1-Nrf2 and HIF-1α) in coordination of organisms' response to oxidative stress is discussed. The future directions in the field are related with more accurate description of oxidative stress, the identification of its general characteristics and mechanisms responsible for adaptation to the stress have been also discussed. The last part marks some perspectives in the study of oxidative stress in hydrobionts, which, in addition to classic use, became more and more popular to address general biological questions such as development, aging and pathologies.

Hypoxia preconditioning by cobalt chloride enhances endurance performance and protects skeletal muscles from exercise-induced oxidative damage in rats

AIM

Training under hypoxia has several advantages over normoxic training in terms of enhancing the physical performance. Therefore, we tested the protective effect of hypoxia preconditioning by hypoxia mimetic cobalt chloride against exercise-induced oxidative damage in the skeletal muscles and improvement of physical performance.

METHOD

Male Sprague-Dawley rats were randomly divided into four groups (n=8), namely control, cobalt-supplemented, training and cobalt with training. The red gastrocnemius muscle was examined for all measurements, viz. free radical generation, lipid peroxidation, muscle damage and antioxidative capacity.

RESULTS

Hypoxic preconditioning with cobalt along with training significantly increased physical performance (33%, P<0.01) in rats compared with training-only rats. Cobalt supplementation activated cellular oxygen sensing system in rat skeletal muscle. It also protected against training-induced oxidative damage as observed by an increase in the GSH/GSSG ratio (36%, P<0.001; 28%, P<0.01 respectively) and reduced lipid peroxidation (15%, P<0.01; 31%, P<0.01 respectively) in both trained and untrained rats compared with their respective controls. Cobalt supplementation along with training enhanced the expression of antioxidant proteins haem oxygenase-1 (HO-1; 1.2-fold, P<0.05) and metallothionein (MT; 4.8-fold, P<0.001) compared with training only. A marked reduction was observed in exercise-induced muscle fibre damage as indicated by decreased necrotic muscle fibre, decreased lipofuscin content of muscle and plasma creatine kinase level (16%, P<0.01) in rats preconditioned with cobalt.

CONCLUSION

Our study provides strong evidence that hypoxic preconditioning with cobalt chloride enhances physical performance and protects muscle from exercise-induced oxidative damage via GSH, HO-1 and MT-mediated antioxidative capacity.

Hypoxic preconditioning facilitates acclimatization to hypobaric hypoxia in rat heart

Objectives

Acute systemic hypoxia induces delayed cardioprotection against ischaemia-reperfusion injury in the heart. As cobalt chloride (CoCl2) is known to elicit hypoxia-like –responses, it was hypothesized that this chemical would mimic the preconditioning effect and facilitate acclimatization to hypobaric hypoxia in rat heart.

Methods

Male Sprague-Dawley rats treated with distilled water or cobalt chloride (12.5 mg Co/kg for 7 days) were exposed to simulated altitude at 7622 m for different time periods (1, 2, 3 and 5 days).

Key findings

Hypoxic preconditioning with cobalt appreciably attenuated hypobaric hypoxia-induced oxidative damage as observed by a decrease in free radical (reactive oxygen species) generation, oxidation of lipids and proteins. Interestingly, the observed effect was due to increased expression of the antioxidant proteins hemeoxygenase and metallothionein, as no significant change was observed in antioxidant enzyme activity. Hypoxic preconditioning with cobalt increased hypoxia-inducible factor 1α (HIF-1α) expression as well as HIF-1 DNA binding activity, which further resulted in increased expression of HIF-1 regulated genes such as erythropoietin, vascular endothelial growth factor and glucose transporter. A significant decrease was observed in lactate dehydrogenase activity and lactate levels in the heart of preconditioned animals compared with non-preconditioned animals exposed to hypoxia.

Conclusions

The results showed that hypoxic preconditioning with cobalt induces acclimatization by up-regulation of hemeoxygenase 1 and metallothionein 1 via HIF-1 stabilization.