Regulation of the brain's vascular responses to oxygen

Oxidative Stress and Cerebral Vascular Tone: The Role of Reactive Oxygen and Nitrogen Species

The brain's unique characteristics make it exceptionally susceptible to oxidative stress, which arises from an imbalance between reactive oxygen species (ROS) production, reactive nitrogen species (RNS) production, and antioxidant defense mechanisms. This review explores the factors contributing to the brain's vascular tone's vulnerability in the presence of oxidative damage, which can be of clinical interest in critically ill patients or those presenting acute brain injuries. The brain's high metabolic rate and inefficient electron transport chain in mitochondria lead to significant ROS generation. Moreover, non-replicating neuronal cells and low repair capacity increase susceptibility to oxidative insult. ROS can influence cerebral vascular tone and permeability, potentially impacting cerebral autoregulation. Different ROS species, including superoxide and hydrogen peroxide, exhibit vasodilatory or vasoconstrictive effects on cerebral blood vessels. RNS, particularly NO and peroxynitrite, also exert vasoactive effects. This review further investigates the neuroprotective effects of antioxidants, including superoxide dismutase (SOD), vitamin C, vitamin E, and the glutathione redox system. Various studies suggest that these antioxidants could be used as adjunct therapies to protect the cerebral vascular tone under conditions of high oxidative stress. Nevertheless, more extensive research is required to comprehensively grasp the relationship between oxidative stress and cerebrovascular tone, and explore the potential benefits of antioxidants as adjunctive therapies in critical illnesses and acute brain injuries.

Abnormalities in Copper Status Associated with an Elevated Risk of Parkinson's Phenotype Development

In the last 15 years, among the many reasons given for the development of idiopathic forms of Parkinson's disease (PD), copper imbalance has been identified as a factor, and PD is often referred to as a copper-mediated disorder. More than 640 papers have been devoted to the relationship between PD and copper status in the blood, which include the following markers: total copper concentration, enzymatic ceruloplasmin (Cp) concentration, Cp protein level, and non-ceruloplasmin copper level. Most studies measure only one of these markers. Therefore, the existence of a correlation between copper status and the development of PD is still debated. Based on data from the published literature, meta-analysis, and our own research, it is clear that there is a connection between the development of PD symptoms and the number of copper atoms, which are weakly associated with the ceruloplasmin molecule. In this work, the link between the risk of developing PD and various inborn errors related to copper metabolism, leading to decreased levels of oxidase ceruloplasmin in the circulation and cerebrospinal fluid, is discussed.

Hyperoxia evokes pericyte-mediated capillary constriction

Oxygen supplementation is regularly prescribed to patients to treat or prevent hypoxia. However, excess oxygenation can lead to reduced cerebral blood flow (CBF) in healthy subjects and worsen the neurological outcome of critically ill patients. Most studies on the vascular effects of hyperoxia focus on arteries but there is no research on the effects on cerebral capillary pericytes, which are major regulators of CBF. Here, we used bright-field imaging of cerebral capillaries and modeling of CBF to show that hyperoxia (95% superfused O₂) led to an increase in intracellular calcium level in pericytes and a significant capillary constriction, sufficient to cause an estimated 25% decrease in CBF. Although hyperoxia is reported to cause vascular smooth muscle cell contraction via generation of reactive oxygen species (ROS), endothelin-1 and 20-HETE, we found that increased cytosolic and mitochondrial ROS levels and endothelin release were not involved in the pericyte-mediated capillary constriction. However, a 20-HETE synthesis blocker greatly reduced the hyperoxia-evoked capillary constriction. Our findings establish pericytes as regulators of CBF in hyperoxia and 20-HETE synthesis as an oxygen sensor in CBF regulation. The results also provide a mechanism by which clinically administered oxygen can lead to a worse neurological outcome.

SOD3 Expression in Tumor Stroma Provides the Tumor Vessel Maturity in Oral Squamous Cell Carcinoma

Tumor angiogenesis is one of the hallmarks of solid tumor development. The progressive tumor cells produce the angiogenic factors and promote tumor angiogenesis. However, how the tumor stromal cells influence tumor vascularization is still unclear. In the present study, we evaluated the effects of oral squamous cell carcinoma (OSCC) stromal cells on tumor vascularization. The tumor stromal cells were isolated from two OSCC patients with different subtypes: low invasive verrucous squamous carcinoma (VSCC) and highly invasive squamous cell carcinoma (SCC) and co-xenografted with the human OSCC cell line (HSC-2) on nude mice. In comparison, the CD34+ vessels in HSC-2+VSCC were larger than in HSC-2+SCC. Interestingly, the vessels in the HSC-2+VSCC expressed vascular endothelial cadherin (VE-cadherin), indicating well-formed vascularization. Our microarray data revealed that the expression of extracellular superoxide dismutase, SOD3 mRNA is higher in VSCC stromal cells than in SCC stromal cells. Moreover, we observed that SOD3 colocalized with VE-cadherin on endothelial cells of low invasive stroma xenograft. These data suggested that SOD3 expression in stromal cells may potentially regulate tumor vascularization in OSCC. Thus, our study suggests the potential interest in SOD3-related vascular integrity for a better OSCC therapeutic strategy.

Cerebral Oxygen Delivery and Consumption in Brain-Injured Patients

Organism survival depends on oxygen delivery and utilization to maintain the balance of energy and toxic oxidants production. This regulation is crucial to the brain, especially after acute injuries. Secondary insults after brain damage may include impaired cerebral metabolism, ischemia, intracranial hypertension and oxygen concentration disturbances such as hypoxia or hyperoxia. Recent data highlight the important role of clinical protocols in improving oxygen delivery and resulting in lower mortality in brain-injured patients. Clinical protocols guide the rules for oxygen supplementation based on physiological processes such as elevation of oxygen supply (by mean arterial pressure (MAP) and intracranial pressure (ICP) modulation, cerebral vasoreactivity, oxygen capacity) and reduction of oxygen demand (by pharmacological sedation and coma or hypothermia). The aim of this review is to discuss oxygen metabolism in the brain under different conditions.

Assessing the effect of anesthetic gas mixtures on hyperpolarized 13 C pyruvate metabolism in the rat brain

PURPOSE

To determine the effect of altering anesthetic oxygen protocols on measurements of cerebral perfusion and metabolism in the rodent brain.

METHODS

Seven rats were anesthetized and underwent serial MRI scans with hyperpolarized [1-¹³ C]pyruvate and perfusion weighted imaging. The anesthetic carrier gas protocol used varied from 100:0% to 90:10% to 60:40% O₂ :N₂ O. Spectra were quantified with AMARES and perfusion imaging was processed using model-free deconvolution. A 1-way ANOVA was used to compare results across groups, with pairwise t tests performed with correction for multiple comparisons. Spearman's correlation analysis was performed between O₂ % and MR measurements.

RESULTS

There was a significant increase in bicarbonate:total ¹³ C carbon and bicarbonate:¹³ C pyruvate when moving between 100:0 to 90:10 and 100:0 to 60:40 O₂ :N₂ O % (0.02 ± 0.01 vs. 0.019 ± 0.005 and 0.02 ± 0.01 vs. 0.05 ± 0.02, respectively) and (0.04 ± 0.01 vs. 0.03 ± 0.01 and 0.04 ± 0.01 vs. 0.08 ± 0.02, respectively). There was a significant difference in ¹³ C pyruvate time to peak when moving between 100:0 to 90:10 and 100:0 to 60:40 O₂ :N₂ O % (13 ± 2 vs. 10 ± 1 and 13 ± 2 vs. 7.5 ± 0.5 s, respectively) as well as significant differences in cerebral blood flow (CBF) between gas protocols. Significant correlations between bicarbonate:¹³ C pyruvate and gas protocol (ρ = -0.47), mean transit time and gas protocol (ρ = 0.41) and ¹³ C pyruvate time-to-peak and cerebral blood flow (ρ = -0.54) were also observed.

CONCLUSIONS

These results demonstrate that the detection and quantification of cerebral metabolism and perfusion is dependent on the oxygen protocol used in the anesthetized rodent brain.

In vivo brain ischemia-reperfusion model induced by hypoxia-reoxygenation using zebrafish larvae

Cerebral infarct is caused by cerebrovascular occlusion and results in brain damage. Although many rodent models of cerebral infarct exist, there is none based on zebrafish. In this study, we developed a novel ischemia-reperfusion model induced by hypoxic treatment using zebrafish. We first examined the changes in blood flow under hypoxic conditions. Hypoxic treatment interrupted the blood flow in 4 dpf (days post fertilization) zebrafish larvae. To quantify the trunk and cerebral blood flow, we selected the middle mesencephalic central artery (MMCtA) as a cerebral blood vessel and the dorsal aorta (DA) as a blood vessel of the trunk. Interestingly, the interruption of blood flow in MMCtA preceded that in DA. Considering these results, we hypothesized that reoxygenation immediately after hypoxia-induced cerebral ischemia leads to reperfusion. As a result, hypoxia-reoxygenation (H/R) treatment induced ischemia-reperfusion in cerebral vessels. Furthermore, brain cell death was increased 24 h after H/R treatment. Transgenic zebrafish (HuC:kaede), with neuronal cells expressing the kaede fluorescent protein, was used to investigate the effect of H/R on neuronal cells. The H/R treatment reduced the fluorescence intensity of kaede. Besides, glial fibrillary acidic protein immunoreactivity in H/R-treated larvae was significantly increased. In conclusion, H/R-treated zebrafish larvae may provide a novel ischemia-reperfusion model.

Combined signatures of serum proteome and transcriptome in patients with recurrent aphthous ulcer

OBJECTIVES

Recurrent aphthous ulcer (RAU) is a common oral disease with unclear mechanism. This study aimed to explore the serum signatures of RAU patients via proteomic and transcriptomic analysis.

METHODS

This study was based on clinical observation. Part of serum was used for clinical tests, while the rest was processed for isobaric tags for relative and absolute quantitation (ITRAQ) labeling coupled with two-dimensional liquid chromatography-tandem mass spectrometry (2D LC-MS/MS) combined with microRNA (miRNA) microarrays. Bioinformatic analysis was then used to obtain significant signatures, which was verified by ELISA, qRT-PCR, and dual-luciferase reporter gene assays.

RESULTS

Clinical data showed that triglyceride level, white blood cell count, and neutrophils percentage were increased in RAU group, while lymphocytes percentage was decreased. ITRAQ-2D LC-MS/MS identified 22 upregulated and 33 downregulated proteins in RAU group. Simultaneously, miRNA microarrays identified 64 upregulated and 31 downregulated miRNAs. After integrative bioinformatic analysis and verification, three miRNA-protein pairs, mainly involved in oxidative stress and inflammation responses, were obtained. Additionally, the interaction network indicated the crucial role of complement and coagulation cascade pathway in RAU.

CONCLUSIONS

Our study revealed that complement and coagulation cascade pathway, oxidative stress, and inflammation responses may act as vital factors in pathogenesis of RAU.

Superoxide Dismutase Multigene Family from a Primitive Chondrostean Sturgeon, Acipenser baerii: Molecular Characterization, Evolution, and Antioxidant Defense during Development and Pathogen Infection

Three distinct superoxide dismutases (SODs)-copper/zinc-SOD (SOD1), manganese-SOD (SOD2), and extracellular copper/zinc-SOD (SOD3)-were identified from a primitive chondrostean fish, Acipenser baerii, enabling the comparison of their transcriptional regulation patterns during development, prelarval ontogeny, and immune stimulation. Each A. baerii SOD isoform (AbSOD) shared conserved structural features with its vertebrate orthologs; however, phylogenetic analyses hypothesized a different evolutionary history for AbSOD3 relative to AbSOD1 and AbSOD2 in the vertebrate lineage. The AbSOD isoforms showed different tissue distribution patterns; AbSOD1 was predominantly expressed in most tissues. The expression of the AbSOD isoforms showed isoform-dependent dynamic modulation according to embryonic development and prelarval ontogenic behaviors. Prelarval microinjections revealed that lipopolysaccharide only induced AbSOD3 expression, while Aeromonas hydrophila induced the expression of AbSOD2 and AbSOD3. In fingerlings, the transcriptional response of each AbSOD isoform to bacterial infection was highly tissue-specific, and the three isoforms exhibited different response patterns within a given tissue type; AbSOD3 was induced the most sensitively, and its induction was the most pronounced in the kidneys and skin. Collectively, these findings suggest isoform-dependent roles for the multigene SOD family in antioxidant defenses against the oxidative stress associated with development and immune responses in these endangered sturgeon fish.

Rottlerin, a natural polyphenol compound, inhibits upregulation of matrix metalloproteinase-9 and brain astrocytic migration by reducing PKC-δ-dependent ROS signal

Background

Upregulation of matrix metalloproteinase-9 (MMP-9) has been indicated as one of the inflammatory biomarkers. In the central nervous system (CNS), the MMP-9 is induced by several proinflammatory mediators and participates in the CNS disorders, including inflammation and neurodegeneration. In addition, protein kinase Cs (PKCs) has been shown to be involved in regulation of various inflammatory factors like MMP-9 by several stimuli in many cell types. Several phytochemicals are believed to reduce the risk of several inflammatory disorders including the CNS diseases. The rottlerin, a principal phenolic compound of the Kamala plant Mallotus philippinensis, has been shown to possess an array of medicinal properties, including anti-PKC-δ, antitumor, anti-oxidative, and anti-inflammatory activities.

Methods

Herein, we used rat brain astrocytes (RBA) to demonstrate the signaling mechanisms of phorbol 12-myristate 13-acetate (PMA)-induced MMP-9 expression by zymographic, RT-PCR, subcellular isolation, Western blot, ROS detection, and promoter reporter analyses. Then, we evaluate the effects of rottlerin on PMA-induced MMP-9 expression in RBA and its influencing mechanism.

Results

We first demonstrated that PMA stimulated activation of various types of PKC, including PKC-δ in RBA. Subsequently, PMA induced MMP-9 expression via PKCδ-mediated reactive oxygen species (ROS) generation, extracellular signal-regulated kinase 1/2 (ERK1/2) activation, and then induced c-Fos/AP-1 signaling pathway. Finally, upregulation of MMP-9 by PMA via the pathway may promote astrocytic migration, and the event could be attenuated by rottlerin.

Conclusions

These data indicated that rottlerin may have anti-inflammatory activity by reducing these related pathways of PKC-δ-dependent ROS-mediated MMP-9 expression in brain astrocytes.

CNS function and dysfunction during exposure to hyperbaric oxygen in operational and clinical settings

Hyperbaric oxygen (HBO2) is breathed during hyperbaric oxygen therapy and during certain undersea pursuits in diving and submarine operations. What limits exposure to HBO2 in these situations is the acute onset of central nervous system oxygen toxicity (CNS-OT) following a latent period of safe oxygen breathing. CNS-OT presents as various non-convulsive signs and symptoms, many of which appear to be of brainstem origin involving cranial nerve nuclei and autonomic and cardiorespiratory centers, which ultimately spread to higher cortical centers and terminate as generalized tonic-clonic seizures. The initial safe latent period makes the use of HBO2 practical in hyperbaric and undersea medicine; however, the latent period is highly variable between individuals and within the same individual on different days, making it difficult to predict onset of toxic indications. Consequently, currently accepted guidelines for safe HBO2 exposure are highly conservative. This review examines the disorder of CNS-OT and summarizes current ideas on its underlying pathophysiology, including specific areas of the CNS and fundamental neural and redox signaling mechanisms that are thought to be involved in seizure genesis and propagation. In addition, conditions that accelerate the onset of seizures are discussed, as are current mitigation strategies under investigation for neuroprotection against redox stress while breathing HBO2 that extend the latent period, thus enabling safer and longer exposures for diving and medical therapies.

Human brain blood flow and metabolism during isocapnic hyperoxia: the role of reactive oxygen species

KEY POINTS

It is unknown whether excessive reactive oxygen species (ROS) production drives the isocapnic hyperoxia (IH)-induced decline in human cerebral blood flow (CBF) via reduced nitric oxide (NO) bioavailability and leads to disruption of the blood-brain barrier (BBB) or neural-parenchymal damage. Cerebral metabolic rate for oxygen (CMR O 2 ) and transcerebral exchanges of NO end-products, oxidants, antioxidants and neural-parenchymal damage markers were simultaneously quantified under IH with intravenous saline and ascorbic acid infusion. CBF and CMR O 2 were reduced during IH, responses that were followed by increased oxidative stress and reduced NO bioavailability when saline was infused. No indication of neural-parenchymal damage or disruption of the BBB was observed during IH. Antioxidant defences were increased during ascorbic acid infusion, while CBF, CMR O 2 , oxidant and NO bioavailability markers remained unchanged. ROS play a role in the regulation of CBF and metabolism during IH without evidence of BBB disruption or neural-parenchymal damage.

ABSTRACT

To test the hypothesis that isocapnic hyperoxia (IH) affects cerebral blood flow (CBF) and metabolism through exaggerated reactive oxygen species (ROS) production, reduced nitric oxide (NO) bioavailability, disturbances in the blood-brain barrier (BBB) and neural-parenchymal homeostasis, 10 men (24 ± 1 years) were exposed to a 10 min IH trial (100% O₂ ) while receiving intravenous saline and ascorbic acid (AA, 3 g) infusion. Internal carotid artery blood flow (ICABF), vertebral artery blood flow (VABF) and total CBF (tCBF, Doppler ultrasound) were determined. Arterial and right internal jugular venous blood was sampled to quantify the cerebral metabolic rate of oxygen (CMR O 2 ), transcerebral exchanges (TCE) of NO end-products (plasma nitrite), antioxidants (AA and AA plus dehydroascorbic acid (AA+DA)) and oxidant biomarkers (thiobarbituric acid-reactive substances (TBARS) and 8-isoprostane), and an index of BBB disruption and neuronal-parenchymal damage (neuron-specific enolase; NSE). IH reduced ICABF, tCBF and CMR O 2 , while VABF remained unchanged. Arterial 8-isoprostane and nitrite TCE increased, indicating that CBF decline was related to ROS production and reduced NO bioavailability. AA, AA+DA and NSE TCE did not change during IH. AA infusion did not change the resting haemodynamic and metabolic parameters but raised antioxidant defences, as indicated by increased AA/AA+DA concentrations. Negative AA+DA TCE, unchanged nitrite, reductions in arterial and venous 8-isoprostane, and TBARS TCE indicated that AA infusion effectively inhibited ROS production and preserved NO bioavailability. Similarly, AA infusion prevented IH-induced decline in regional and total CBF and re-established CMR O 2 . These findings indicate that ROS play a role in CBF regulation and metabolism during IH without evidence of BBB disruption or neural-parenchymal damage.

Depressed mitochondrial function and electron transport Complex II-mediated H2O2 production in the cortex of type 1 diabetic rodents

AIMS

Abnormalities in mitochondrial function under diabetic conditions can lead to deficits in function of cortical neurons and their support cells exhibiting a pivotal role in the pathogenesis of several neurodegenerative disorders, including Alzheimer's disease. We aimed to assess mitochondrial respiration rates and membrane potential or H2O2 generation simultaneously and expression of proteins involved in mitochondrial dynamics, ROS scavenging and AMPK/SIRT/PGC-1α pathway activity in cortex under diabetic conditions.

METHODS

Cortical mitochondria from streptozotocin (STZ)-induced type 1 diabetic rats or mice, and aged-matched controls were used for simultaneous measurements of mitochondrial respiration rates and mitochondrial membrane potential (mtMP) or H2O2 using OROBOROS oxygraph. Measurements of enzymatic activities of respiratory complexes were performed using spectophotometry. Protein levels in cortical mitochondria and homogenates were determined by Western blotting.

RESULTS

Mitochondrial coupled respiration rates and FCCP-induced uncoupled respiration rates were significantly decreased in mitochondria of cortex of STZ-diabetic rats compared to controls. The mtMP in the presence of ADP was significantly depolarized and succinate-dependent respiration rates and H2O2 were significantly diminished in cortical mitochondria of diabetic animals compared to controls, accompanied with reduced expression of CuZn- and Mn-superoxide dismutase. The enzymatic activities of Complex I, II, and IV and protein levels of certain components of Complex I and II, mitofusin 2 (Mfn2), dynamin-related protein 1 (DRP1), P-AMPK, SIRT2 and PGC-1α were significantly diminished in diabetic cortex.

CONCLUSION

Deficits in mitochondrial function, dynamics, and antioxidant capabilities putatively mediated through sub-optimal AMPK/SIRT/PGC-1α signaling, are involved in the development of early sub-clinical neurodegeneration in the cortex under diabetic conditions.

Neuroprotective Effects of Dehydroepiandrosterone Sulfate Through Inhibiting Expression of Matrix Metalloproteinase-9 from Bradykinin-Challenged Astroglia

Dehydroepiandrosterone sulfate (DHEAS), one of the most important neuroactive steroids, is produced in the adrenals and the brain. DHEAS is believed to play a critical role in modulating different forms of cellular control, including processes associated with human neural systems. Its production rate and level in serum, adrenals, and brain gradually decrease with advancing age. The decline of DHEAS level was associated with age-related neuronal dysfunction and degeneration, most probably because the steroids protect the central nervous system (CNS) neurons against neurotoxic challenges. Moreover, increasing studies show that matrix metalloproteinases (MMPs), MMP-9 especially, are upregulated by proinflammatory mediators in the CNS disorders. The increased MMP-9 as an inflammatory biomarker of several CNS disorders that may participate in the CNS inflammation and neurodegeneration. Herein, we investigate the effects of DHEAS on brain inflammation by the model we have defined of bradykinin (BK)-induced MMP-9 expression in rat brain astrocyte (RBA) and its mechanism. The results showed that DHEAS significantly reduce MMP-9 induced by BK. Pretreatment with DHEAS can inhibit BK-stimulated phosphorylation of c-Src and PYK2. Moreover, DHEAS attenuated BK-stimulated NADPH oxidase (Nox)-derived reactive oxygen species (ROS) production, suggesting that DHEAS has an antioxidative effect. We further demonstrated that DHEAS blocked activation of ERK1/2, Akt, and c-Fos/AP-1 by BK. Finally, DHEAS decreased MMP-9-related events including RBA migration and neuronal apoptosis. The results will provide new insights into the anti-inflammatory action of DHEAS, supporting that DHEAS may have a neuroprotective effect in the improvement of the CNS disorders by reducing neuroinflammation.

SOD3 improves the tumor response to chemotherapy by stabilizing endothelial HIF-2α

One drawback of chemotherapy is poor drug delivery to tumor cells, due in part to hyperpermeability of the tumor vasculature. Extracellular superoxide dismutase (SOD3) is an antioxidant enzyme usually repressed in the tumor milieu. Here we show that specific SOD3 re-expression in tumor-associated endothelial cells (ECs) increases doxorubicin (Doxo) delivery into and chemotherapeutic effect on tumors. Enhanced SOD3 activity fostered perivascular nitric oxide accumulation and reduced vessel leakage by inducing vascular endothelial cadherin (VEC) transcription. SOD3 reduced HIF prolyl hydroxylase domain protein activity, which increased hypoxia-inducible factor-2α (HIF-2α) stability and enhanced its binding to a specific VEC promoter region. EC-specific HIF-2α ablation prevented both the SOD3-mediated increase in VEC transcription and the enhanced Doxo effect. SOD3, VEC, and HIF-2α levels correlated positively in primary colorectal cancers, which suggests a similar interconnection of these proteins in human malignancy.

Tumour vasculature influences drug delivery. Here, the authors show that SOD3 re-expression enhances doxorubicin delivery and effects through normalization of tumour vasculature via the HIF-2a/VE-cadherin pathway.

Oxygen Toxicity and Special Operations Forces Diving: Hidden and Dangerous

In Special Operations Forces (SOF) closed-circuit rebreathers with 100% oxygen are commonly utilized for covert diving operations. Exposure to high partial pressures of oxygen (PO₂) could cause damage to the central nervous system (CNS) and pulmonary system. Longer exposure time and higher PO₂ leads to faster development of more serious pathology. Exposure to a PO₂ above 1.4 ATA can cause CNS toxicity, leading to a wide range of neurologic complaints including convulsions. Pulmonary oxygen toxicity develops over time when exposed to a PO₂ above 0.5 ATA and can lead to inflammation and fibrosis of lung tissue. Oxygen can also be toxic for the ocular system and may have systemic effects on the inflammatory system. Moreover, some of the effects of oxygen toxicity are irreversible. This paper describes the pathophysiology, epidemiology, signs and symptoms, risk factors and prediction models of oxygen toxicity, and their limitations on SOF diving.

Extracellular superoxide dismutase is necessary to maintain renal blood flow during sepsis development

Background

Extracellular superoxide dismutase (ECSOD) protects nitric oxide (NO) bioavailability by decreasing superoxide levels and preventing peroxynitrite generation, which is important in maintaining renal blood flow and in preventing acute kidney injury. However, the profile of ECSOD expression after sepsis is not fully understood. Therefore, we intended to evaluate the content and gene expression of superoxide dismutase (SOD) isoforms in the renal artery and their relation to renal blood flow.

Methods

Sepsis was induced in Wistar rats by caecal ligation and perforation. Several times after sepsis induction, renal blood flow (12, 24 and 48 h); the renal arterial content of SOD isoforms, nitrotyrosine, endothelial and inducible nitric oxide synthase (e-NOS and i-NOS), and phosphorylated vasodilator-stimulated phosphoprotein (pVASP); and SOD activity (3, 6 and 12 h) were measured. The influence of a SOD inhibitor was also evaluated.

Results

An increase in ECSOD content was associated with decreased 3-nitrotyrosine levels. These events were associated with an increase in pVASP content and maintenance of renal blood flow. Moreover, previous treatment with a SOD inhibitor increased nitrotyrosine content and reduced renal blood flow.

Conclusions

ECSOD appears to have a major role in decreasing peroxynitrite formation in the renal artery during the early stages of sepsis development, and its application can be important in renal blood flow control and maintenance during septic insult.

Normobaric hyperoxia stimulates superoxide and nitric oxide production in the caudal solitary complex of rat brain slices

Central CO₂-chemosensitive neurons in the caudal solitary complex (cSC) are stimulated not only by hypercapnic acidosis, but by hyperoxia as well. While a cellular mechanism for the CO₂ response has yet to be isolated, previous data show that a redox-sensitive mechanism underlies neuronal excitability to hyperoxia. However, it remains unknown how changes in Po₂ affect the production of reactive oxygen and nitrogen species (RONS) in the cSC that can lead to increased cellular excitability and, with larger doses, to cellular dysfunction and death. To this end, we used fluorescence microscopy in real time to determine how normobaric hyperoxia increases the production of key RONS in the cSC. Because neurons in the region are CO₂ sensitive, we also examined the potential effects of CO₂ narcosis, used during euthanasia before brain slice harvesting, on RONS production. Our findings show that normobaric hyperoxia (0.4 → 0.95 atmospheres absolute O₂) increases the fluorescence rates of fluorogenic dyes specific to both superoxide and nitric oxide. Interestingly, different results were seen for superoxide fluorescence when CO₂ narcosis was used during euthanasia, suggesting long-lasting changes in superoxide production and/or antioxidant activity subsequent to CO₂ narcosis before brain slicing. Further research needs to distinguish whether the increased levels of RONS reported here are merely increases in oxidative and nitrosative signaling or, alternatively, evidence of redox and nitrosative stress.

Hypoxic mechanisms in primary headaches

Background Hypoxia causes secondary headaches such as high-altitude headache (HAH) and headache due to acute mountain sickness. These secondary headaches mimic primary headaches such as migraine, which suggests a common link. We review and discuss the possible role of hypoxia in migraine and cluster headache. Methods This narrative review investigates the current level of knowledge on the relation of hypoxia in migraine and cluster headache based on epidemiological and experimental studies. Findings Epidemiological studies suggest that living in high-altitude areas increases the risk of migraine and especially migraine with aura. Human provocation models show that hypoxia provokes migraine with and without aura, whereas cluster headache has not been reliably induced by hypoxia. Possible pathophysiological mechanisms include hypoxia-induced release of nitric oxide and calcitonin gene-related peptide, cortical spreading depression and leakage of the blood-brain barrier. Conclusion There is a possible link between hypoxia and migraine and maybe cluster headache, but the exact mechanism is currently unknown. Provocation models of hypoxia have yielded interesting results suggesting a novel approach to study in depth the mechanism underlying hypoxia and primary headaches.

Predictors of cerebral blood flow in patients with and without anemia

Sickle cell disease (SCD) is the most common cause of stroke in childhood and results primarily from a mismatch of cerebral oxygen supply and demand rather than arterial obstruction. However, resting cerebral blood flow (CBF) has not been examined in the general African American population, in whom obesity, hypertension, cerebrovascular disease, and diminished cerebrovascular reserve capacity are common. To better understand the underlying physiological substrate upon which SCD is superimposed, we measured CBF in 32 young (age 28 ± 10 yr), asymptomatic African American subjects with and without sickle cell trait (n= 14). To characterize the effects of chronic anemia, in isolation of sickle hemoglobin we also studied a cohort of 13 subjects with thalassemia major (n= 10), dyserythropoetic anemia (n= 1), or spherocytosis (n= 2). Blood was analyzed for complete blood count, hemoglobin electrophoresis, cell free hemoglobin, and lactate dehydrogenase. Multivariate regression analysis showed that oxygen content was the strongest predictor of CBF (r(2)= 0.33,P< 0.001). CBF declined rapidly in the second and third decades of life, but this drop was explained by reductions in cerebral gray matter. However, age effects persisted after correction for brain composition, possibly representing microvascular impairment. CBF was independent of viscosity, hemoglobin S%, and body mass index. Hyperoxia resulted in reduced CBF by 12.6% (P= 0.0002), and CBF changes were proportional to baseline oxygen content (r(2)= 0.16,P= 0.02). These data suggest that these hemoglobin subtypes do not alter the normal CBF regulation of the balance of oxygen supply and demand.

Cloning, Purification, and Characterization of Recombinant Human Extracellular Superoxide Dismutase in SF9 Insect Cells

A balance between production and degradation of reactive oxygen species (ROS) is critical for maintaining cellular homeostasis. Increased levels of ROS during oxidative stress are associated with disease conditions. Antioxidant enzymes, such as extracellular superoxide dismutase (EC-SOD), in the extracellular matrix (ECM) neutralize the toxicity of superoxide. Recent studies have emphasized the importance of EC-SOD in protecting the brain, lungs, and other tissues from oxidative stress. Therefore, EC-SOD would be an excellent therapeutic drug for treatment of diseases caused by oxidative stress. We cloned both the full length (residues 1-240) and truncated (residues 19-240) forms of human EC-SOD (hEC-SOD) into the donor plasmid pFastBacHTb. After transposition, the bacmid was transfected into the Sf9-baculovirus expression system and the expressed hEC-SOD purified using FLAG-tag. Western blot analysis revealed that hEC-SOD is present both as a monomer (33 kDa) and a dimer (66 kDa), as detected by the FLAG antibody. A water-soluble tetrazolium (WST-1) assay showed that both full length and truncated hEC-SOD proteins were enzymatically active. We showed that a potent superoxide dismutase inhibitor, diethyldithiocarbamate (DDC), inhibits hEC-SOD activity.

Hyperoxia Improves Hemodynamic Status During Head-up Tilt Testing in Healthy Volunteers: A Randomized Study

Head-up tilt test is useful for exploring neurally mediated syncope. Adenosine is an ATP derivative implicated in cardiovascular disturbances that occur during head-up tilt test. The aim of the present study was to investigate the impact of hyperoxia on adenosine plasma level and on hemodynamic changes induced by head-up tilt testing.Seventeen healthy male volunteers (mean age 35 ± 11 years) were included in the study. The experiment consisted of 2 head-up tilt tests, 1 session with subjects breathing, through a mask, medical air (FiO2 = 21%) and 1 session with administration of pure oxygen (FiO2 = 100%) in double-blind manner. Investigations included continuous monitoring of hemodynamic data and measurement of plasma adenosine levels.No presyncope or syncope was found in 15 of the 17 volunteers. In these subjects, a slight decrease in systolic blood pressure was recorded during orthostatic stress performed under medical air exposure. In contrast, hyperoxia led to increased systolic blood pressure during orthostatic stress when compared with medical air. Furthermore, mean adenosine plasma levels decreased during hyperoxic exposure before (0.31 ± 0.08 μM) and during head-up tilt test (0.33 ± 0.09 μM) when compared with baseline (0.6 ± 0.1 μM). Adenosine plasma level was unchanged during medical air exposure at rest (0.6 ± 0.1 μM), and slightly decreased during orthostatic stress. In 2 volunteers, the head-up tilt test induced a loss of consciousness when breathing air. In these subjects, adenosine plasma level increased during orthostatic stress. In contrast, during hyperoxic exposure, the head-up tilt test did not induce presyncope or syncope. In these 2 volunteers, biological study demonstrated a decrease in adenosine plasma level at both baseline and during orthostatic stress for hyperoxic exposure compared with medical air.These results suggest that hyperoxia was able to increase blood pressure during head-up tilt test via a decrease in plasma adenosine concentration. Our results also suggest that adenosine receptor antagonists are worth trying in neurocardiogenic syncope.

Leukemia Inhibitory Factor Protects Neurons from Ischemic Damage via Upregulation of Superoxide Dismutase 3

Leukemia inhibitory factor (LIF) has been shown to protect oligodendrocytes from ischemia by upregulating endogenous antioxidants. The goal of this study was to determine whether LIF protects neurons during stroke by upregulating superoxide dismutase 3 (SOD3). Animals were administered phosphate-buffered saline (PBS) or 125 μg/kg LIF at 6, 24, and 48 h after middle cerebral artery occlusion or sham surgery. Neurons were isolated from rat pups on embryonic day 18 and used between 7 and 15 days in culture. Cells were treated with LIF and/or 10 μM Akt inhibitor IV with PBS and 0.1 % DMSO acting as vehicle controls. Neurons transfected with scrambled or SOD3 small interfering RNA (siRNA) were subjected to 24-h ischemia after PBS or LIF treatment. LIF significantly increased superoxide dismutase activity and SOD3 expression in ipsilateral brain tissue compared to PBS. Following 24-h ischemia, LIF reduced cell death and increased SOD3 messenger RNA (mRNA) in vitro compared to PBS. Adding Akt inhibitor IV with LIF counteracted the decrease in cell death. Partially silencing the expression of SOD3 using siRNA prior to LIF treatment counteracted the protective effect of LIF-alone PBS treatment. These results indicate that LIF protects neurons in vivo and in vitro via upregulation of SOD3.

Hyperoxia and Functional MRI

Oxygen plays a fundamental role in functional magnetic resonance imaging (FMRI). Blood oxygenation level-dependent (BOLD) imaging is the foundation stone of all FMRI and is still the essential workhorse of the vast majority of FMRI procedures. Hemoglobin may provide the magnetic properties that allow the technique to work, but it is oxygen that allows the contrast to effectively be switched on or off, and it is oxygen that we are interested in tracking in order to observe the oxygen metabolism changes. In general the changes in venous oxygen saturation are observed in order to infer changes in the correlated mechanisms, which can include changes in cerebral blood flow, metabolism, and the fraction of inspired oxygen. By independently manipulating the fraction of inspired oxygen it is possible to alter the amount of dissolved oxygen in the plasma, the venous saturation, or even the blood flow. The effects that these changes have on the observed MRI signal can be either a help or a hindrance depending on how well the changes induced are understood. The administration of supplemental inspired oxygen is in a unique position to provide a flexible, noninvasive, inexpensive, patient-friendly addition to the MRI toolkit to enable investigations to look beyond statistics and regions of interest, and actually produce calibrated, targeted measurements of blood flow, metabolism or pathology.

Current and emerging therapies in the management of diabetic foot ulcers

BACKGROUND

Diabetic foot ulcers are one of the major causes of mortality in diabetic patients. Very few drugs and therapies have regulatory approval for this indication and several agents from diverse pharmacological classes are currently in various phases of clinical trials for the management of diabetic foot ulcers.

SCOPE

The purpose of this review is to provide concise information of the drugs and therapies which are approved and present in clinical trials.

REVIEW METHODS

This review was carried out by systematic searches of relevant guidelines, patents, published articles, reviews and abstracts in PubMed/Medline, Web of Science, clinicaltrials.gov, Cochrane Central Register of Controlled Trials, Cochrane Database of Systematic Reviews and Google Scholar of all English language articles up to 1 March 2015. The following search terms were used: diabetes, diabetic foot, diabetic foot ulcer, diabetic wound, diabetic foot infections, wound management, randomized controlled trials, approved treatments, new treatments and clinical trials.

CONCLUSIONS

The various drugs and therapies for the management of diabetic foot ulcers comprise antibiotics, neuropathic drugs, wound dressings, skin substitutes, growth factors and inflammatory modulators. The majority of these therapies target the treatment of diabetic foot ulcers to address the altered biochemical composition of the diabetic wound. However, no single treatment can be definitively recommended for the treatment of diabetic foot ulcers.

Evaluation of Anti-Inflammatory Effects of Helminthostachys zeylanica Extracts via Inhibiting Bradykinin-Induced MMP-9 Expression in Brain Astrocytes

Phytochemicals present in vegetables, fruits, and herbs are believed to reduce the risk of several major diseases including cardiovascular or neurodegenerative disorders. The roots of the fern Helminthostachys zeylanica (L.) Hook. (Ophioglossaceae) have been used for centuries in the treatment of inflammation and as a folk medicine in several countries. The plant has been shown to possess an array of medicinal properties, including antioxidants and anti-inflammatory activities. Moreover, a rising level of matrix metalloproteinase-9 (MMP-9) has been found in blood fluid of these patients suffering from brain inflammatory diseases, which may be considered an inflammatory biomarker in several inflammatory diseases including the central nervous system (CNS) inflammation. Previously, we have demonstrated the signaling mechanisms of bradykinin (BK)-induced MMP-9 expression in brain astrocytes. Herein, we evaluate the effects of H. zeylanica extracts on BK-induced MMP-9 expression in brain astrocytes and its influencing mechanism. The results showed that H. zeylanica extracts, including E0, E1, and E2 significantly reduce MMP-9 induced by BK in brain astrocytes (RBA-1 cells). These H. zeylanica extracts can inhibit BK-stimulated phosphorylation of c-Src, Pyk2, and PKC(α/δ). Moreover, BK-stimulated NADPH oxidase (Nox)-derived reactive oxygen species (ROS) generation has also been attenuated by pretreatment with these extracts, suggesting that the H. zeylanica extracts have an antioxidative activity. We further demonstrated that the H. zeylanica extracts blocked activation of MAPKs (e.g., ERK1/2 and p38 MAPK) by BK. These data indicated that the H. zeylanica extracts may be has anti-inflammatory activity by reducing BK-induced ROS-dependent MMP-9 expression via these related pathways in brain astrocytes.

Alteration of blood glucose levels in the rat following exposure to hyperbaric oxygen

Findings regarding blood glucose level (BGL) on exposure to hyperbaric oxygen (HBO) are contradictory. We investigated the influence of HBO on BGL, and of BGL on latency to central nervous system oxygen toxicity (CNS-OT). The study was conducted on five groups of rats: Group 1, exposure to oxygen at 2.5 atmospheres absolute (ATA), 90 min/day for 7 days; Group 2, exposure to oxygen once a week from 2 to 6 ATA in increments of 1 ATA/wk, for a period of time calculated as 60% of the latency to CNS-OT (no convulsions); Group 3, exposure to 6 ATA breathing a gas mixture with a pO2 of 0.21; Group 4, received 10 U/kg insulin to induce hypoglycemia before exposure to HBO; Group 5, received 33% glucose to induce hyperglycemia before exposure to HBO. Blood samples were drawn before and after exposures for measurement of BGL. No change was observed in BGL after exposure to oxygen at 2.5 ATA, 90 min/day for 7 days. BGL was significantly elevated after exposure to oxygen at 6 ATA until the appearance of convulsions, and following exposure to 4, 5, and 6 ATA without convulsions (P < 0.01). No change was observed in BGL after exposure to 6 ATA breathing a gas mixture with a pO2 of 0.21. Hypoglycemia shortened latency to CNS oxygen toxicity, whereas hyperglycemia had no effect. Our results demonstrate an influence of HBO exposure on elevation of BGL, starting at 4 ATA. This implies that BGL may serve as a marker for the generation of CNS-OT.

Effect of oxygen on neuronal excitability measured by critical flicker fusion frequency is dose dependent

INTRODUCTION

Reactive oxygen species are involved in the functional changes necessary for synaptic plasticity, memory, and cognitive function. It is far from clear whether the increased excitability, and which forms of neuronal excitability, should be considered a part of the learning process or, rather, cellular manifestation of neuronal oxygen poisoning. It is yet to be elucidated whether oxygen (O2)-induced learning and poisoning use the same or distinct cellular pathways.

PURPOSE

We hypothesized that O2-induced neuronal excitability might use the same or an intertwined signaling cascade as the poisoning cellular pathway.

METHOD

Eighty-one healthy, young males, mean age 27.7 ± 4.1 (SD) years, were exposed in the hyperbaric chamber to 0.7 atmosphere absolute (ATA) O2, 1.4 ATA O2, and 2.8 ATA O2. The critical flicker fusion frequency (CFFF), oxyhemoglobin saturation (SiO2), and heart rate (HR) were measured before exposure, after 30 min of oxygen breathing while still at pressure and then after exposure.

RESULTS

Normobaric (0.7 ATA) O2 exposure did not affect CFFF and HR. Medium hyperbaric O2 exposure (1.4 ATA) decreased CFFF but HR remained unchanged. High hyperbaric O2 exposure (2.8 ATA) increased CFFF and diminished HR. SiO2 was similar in all investigated groups. A correlation between CFFF, HR, and SiO2 was observed only at low oxygen (0.7 ATA).

CONCLUSIONS

The effect of O2 on neuronal excitability measured by CFFF in young healthy men was dose dependent: 0.7 ATA O2 did not affect CFFF; CFFF were significantly jeopardized at 1.4 ATA O2, while CFFF recovered at 2.8 ATA. With 2.8 ATA O2, the CFFF and oxygen poisoning transduction pathways seemed to be intertwined.

Overexpression of extracellular superoxide dismutase protects against brain injury induced by chronic hypoxia

Extracellular superoxide dismutase (EC-SOD) is an isoform of SOD normally found both intra- and extra-cellularly and accounting for most SOD activity in blood vessels. Here we explored the role of EC-SOD in protecting against brain damage induced by chronic hypoxia. EC-SOD Transgenic mice, were exposed to hypoxia (FiO2.1%) for 10 days (H-KI) and compared to transgenic animals housed in room air (RA-KI), wild type animals exposed to hypoxia (H-WT or wild type mice housed in room air (RA-WT). Overall brain metabolism evaluated by positron emission tomography (PET) showed that H-WT mice had significantly higher uptake of 18FDG in the brain particularly the hippocampus, hypothalamus, and cerebellum. H-KI mice had comparable uptake to the RA-KI and RA-WT groups. To investigate the functional state of the hippocampus, electrophysiological techniques in ex vivo hippocampal slices were performed and showed that H-KI had normal synaptic plasticity, whereas H-WT were severely affected. Markers of oxidative stress, GFAP, IBA1, MIF, and pAMPK showed similar values in the H-KI and RA-WT groups, but were significantly increased in the H-WT group. Caspase-3 assay and histopathological studies showed significant apoptosis/cell damage in the H-WT group, but no significant difference in the H-KI group compared to the RA groups. The data suggest that EC-SOD has potential prophylactic and therapeutic roles in diseases with compromised brain oxygenation.

Dark chocolate reduces endothelial dysfunction after successive breath-hold dives in cool water

OBJECTIVE

The aim of this study is to observe the effects of dark chocolate on endothelial function after a series of successive apnea dives in non-thermoneutral water.

METHODS

Twenty breath-hold divers were divided into two groups: a control group (8 males and 2 females) and a chocolate group (9 males and 1 female). The control group was asked to perform a series of dives to 20 m adding up to 20 min in the quiet diving pool of Conflans-Ste-Honorine (Paris, France), water temperature was 27 °C. The chocolate group performed the dives 1 h after ingestion of 30 g of dark chocolate. Flow-mediated dilatation (FMD), digital photoplethysmography, nitric oxide (NO), and peroxynitrite ONOO−) levels were measured before and after each series of breath-hold dives.

RESULTS

A significant decrease in FMD was observed in the control group after the dives (95.28 ± 2.9 % of pre-dive values, p < 0.001) while it was increased in the chocolate group (104.1 ± 2.9 % of pre-dive values, p < 0.01). A decrease in the NO level was observed in the control group (86.76 ± 15.57 %, p < 0.05) whereas no difference was shown in the chocolate group (98.44 ± 31.86 %, p > 0.05). No differences in digital photoplethysmography and peroxynitrites were observed between before and after the dives.

CONCLUSION

Antioxidants contained in dark chocolate scavenge free radicals produced during breath-hold diving. Ingestion of 30 g of dark chocolate 1 h before the dive can thus prevent endothelial dysfunction which can be observed after a series of breath-hold dives.

A comparison of factors involved in the development of central nervous system and pulmonary oxygen toxicity in the rat

Central nervous system oxygen toxicity (CNS-OT) can occur in humans at pressures above 2atmospheres absolute (ATA), and above 4.5ATA in the rat. Pulmonary oxygen toxicity appears at pressures above 0.5ATA. We hypothesized that exposure to mild HBO following extreme exposure might provide protection against CNS, but not pulmonary oxygen toxicity. We measured the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX), and nitrotyrosine and nNOS levels in the brain and lung in the following groups: (1) Sham rats, no pressure exposure (SHAM); (2) Exposure to 6ATA oxygen for 60% of latency to CNS-OT (60%LT); (3) Exposure to 6ATA for 60% of latency to CNS-OT, followed by 20min at 2.5ATA for recovery (REC); (4) Exposure to 6ATA for 60% of latency to CNS-OT, followed by 20min at 2.5ATA oxygen and a subsequent increase in pressure to 6ATA until the appearance of convulsions (CONV); (5) Control rats exposed to 6ATA until the appearance of convulsions (C). SOD and CAT activity were reduced in both brain and lung in the REC group. GPX activity was reduced in the hippocampus in the REC group, but not in the cortex or the lung. nNOS levels were reduced in the hippocampus in the REC group. Contrary to our hypothesis, no difference was observed between the brain and the lung for the factors investigated. We suggest that at 2.5ATA and above, CNS and pulmonary oxygen toxicity may share similar mechanisms.

Muscle contraction increases interstitial nitric oxide as predicted by a new model of local blood flow regulation

The prevailing metabolic theory of local blood flow regulation suggests the dilatation of arterioles in response to tissue hypoxia via the emission of multiple metabolic vasodilators by parenchymal cells. We have proposed a mechanism of regulation, built from well-known components, which assumes that arterioles are normally dilated in metabolically active tissues, due to the emission of NO by the endothelium of microvessels. Regulation of local blood flow aims at preventing an excessive supply of oxygen (O2) and glucose to the tissue and thus provides an adequate supply, in contrast to the metabolic regulation theory which requires permanent hypoxia to generate the metabolic vasodilators. The mediator of the restrictive signal is superoxide anion (O2(-)) released by membrane NAD(P)H oxidases into the interstitial space, where it neutralizes NO at a diffusion-limited rate. This model predicts that the onset of muscle contraction will lead to the cessation of O2(-) production, which will cause an elevation of interstitial NO concentration and an increase in fluorescence of the NO probe DAF-FM after its conversion to DAF-T. The time course of DAF-T fluorescence in contracting muscle is predicted by also considering the washout from the muscle of the interstitially loaded NO indicator. Experiments using pulse fluorimetry confirmed an increase in the interstitial concentration of NO available for reaction with DAF-FM during bouts of muscle contraction. The sharp increase in interstitial [NO] is consistent with the hypothesis that the termination of the neutralizing superoxide flow into the interstitium is associated with the activation of mitochondria and a reduction of the interstitial oxygen tension. The advantage of the new model is its ability to explain the interaction of metabolic activity and local blood flow through the adequate delivery of glucose and oxygen.

Oxidative stress in hypertension: role of the kidney

SIGNIFICANCE

Renal oxidative stress can be a cause, a consequence, or more often a potentiating factor for hypertension. Increased reactive oxygen species (ROS) in the kidney have been reported in multiple models of hypertension and related to renal vasoconstriction and alterations of renal function. Nicotinamide adenine dinucleotide phosphate oxidase is the central source of ROS in the hypertensive kidney, but a defective antioxidant system also can contribute.

RECENT ADVANCES

Superoxide has been identified as the principal ROS implicated for vascular and tubular dysfunction, but hydrogen peroxide (H2O2) has been implicated in diminishing preglomerular vascular reactivity, and promoting medullary blood flow and pressure natriuresis in hypertensive animals.

CRITICAL ISSUES AND FUTURE DIRECTIONS

Increased renal ROS have been implicated in renal vasoconstriction, renin release, activation of renal afferent nerves, augmented contraction, and myogenic responses of afferent arterioles, enhanced tubuloglomerular feedback, dysfunction of glomerular cells, and proteinuria. Inhibition of ROS with antioxidants, superoxide dismutase mimetics, or blockers of the renin-angiotensin-aldosterone system or genetic deletion of one of the components of the signaling cascade often attenuates or delays the onset of hypertension and preserves the renal structure and function. Novel approaches are required to dampen the renal oxidative stress pathways to reduced O2(-•) rather than H2O2 selectivity and/or to enhance the endogenous antioxidant pathways to susceptible subjects to prevent the development and renal-damaging effects of hypertension.

Role of redox signaling in neuroinflammation and neurodegenerative diseases

Reactive oxygen species (ROS), a redox signal, are produced by various enzymatic reactions and chemical processes, which are essential for many physiological functions and act as second messengers. However, accumulating evidence has implicated the pathogenesis of several human diseases including neurodegenerative disorders related to increased oxidative stress. Under pathological conditions, increasing ROS production can regulate the expression of diverse inflammatory mediators during brain injury. Elevated levels of several proinflammatory factors including cytokines, peptides, pathogenic structures, and peroxidants in the central nervous system (CNS) have been detected in patients with neurodegenerative diseases such as Alzheimer's disease (AD). These proinflammatory factors act as potent stimuli in brain inflammation through upregulation of diverse inflammatory genes, including matrix metalloproteinases (MMPs), cytosolic phospholipase A₂ (cPLA₂), cyclooxygenase-2 (COX-2), and adhesion molecules. To date, the intracellular signaling mechanisms underlying the expression of target proteins regulated by these factors are elusive. In this review, we discuss the mechanisms underlying the intracellular signaling pathways, especially ROS, involved in the expression of several inflammatory proteins induced by proinflammatory factors in brain resident cells. Understanding redox signaling transduction mechanisms involved in the expression of target proteins and genes may provide useful therapeutic strategies for brain injury, inflammation, and neurodegenerative diseases.

The medical use of oxygen: a time for critical reappraisal

Oxygen treatment has been a cornerstone of acute medical care for numerous pathological states. Initially, this was supported by the assumed need to avoid hypoxaemia and tissue hypoxia. Most acute treatment algorithms, therefore, recommended the liberal use of a high fraction of inspired oxygen, often without first confirming the presence of a hypoxic insult. However, recent physiological research has underlined the vasoconstrictor effects of hyperoxia on normal vasculature and, consequently, the risk of significant blood flow reduction to the at-risk tissue. Positive effects may be claimed simply by relief of an assumed local tissue hypoxia, such as in acute cardiovascular disease, brain ischaemia due to, for example, stroke or shock or carbon monoxide intoxication. However, in most situations, a generalized hypoxia is not the problem and a risk of negative hyperoxaemia-induced local vasoconstriction effects may instead be the reality. In preclinical studies, many important positive anti-inflammatory effects of both normobaric and hyperbaric oxygen have been repeatedly shown, often as surrogate end-points such as increases in gluthatione levels, reduced lipid peroxidation and neutrophil activation thus modifying ischaemia-reperfusion injury and also causing anti-apoptotic effects. However, in parallel, toxic effects of oxygen are also well known, including induced mucosal inflammation, pneumonitis and retrolental fibroplasia. Examining the available 'strong' clinical evidence, such as usually claimed for randomized controlled trials, few positive studies stand up to scrutiny and a number of trials have shown no effect or even been terminated early due to worse outcomes in the oxygen treatment arm. Recently, this has led to less aggressive approaches, even to not providing any supplemental oxygen, in several acute care settings, such as resuscitation of asphyxiated newborns, during acute myocardial infarction or after stroke or cardiac arrest. The safety of more advanced attempts to deliver increased oxygen levels to hypoxic or ischaemic tissues, such as with hyperbaric oxygen therapy, is therefore also being questioned. Here, we provide an overview of the present knowledge of the physiological effects of oxygen in relation to its therapeutic potential for different medical conditions, as well as considering the potential for harm. We conclude that the medical use of oxygen needs to be further examined in search of solid evidence of benefit in many of the current clinical settings in which it is routinely used.

Hyperbaric conditions

Exposure to elevated ambient pressure (hyperbaric conditions) occurs most commonly in underwater diving, during which respired gas density and partial pressures, work of breathing, and physiological dead space are all increased. There is a tendency toward hypercapnia during diving, with several potential causes. Most importantly, there may be reduced responsiveness of the respiratory controller to rising arterial CO₂, leading to hypoventilation and CO₂ retention. Contributory factors may include elevated arterial PO₂, inert gas narcosis and an innate (but variable) tendency of the respiratory controller to sacrifice tight control of arterial CO₂ when work of breathing increases. Oxygen is usually breathed at elevated partial pressure under hyperbaric conditions. Oxygen breathing at modest hyperbaric pressure is used therapeutically in hyperbaric chambers to increase arterial carriage of oxygen and diffusion into tissues. However, to avoid cerebral and pulmonary oxygen toxicity during underwater diving, both the magnitude and duration of oxygen exposure must be managed. Therefore, most underwater diving is conducted breathing mixtures of oxygen and inert gases such as nitrogen or helium, often simply air. At hyperbaric pressure, tissues equilibrate over time with high inspired inert gas partial pressure. Subsequent decompression may reduce ambient pressure below the sum of tissue gas partial pressures (supersaturation) which can result in tissue gas bubble formation and potential injury (decompression sickness). Risk of decompression sickness is minimized by scheduling time at depth and decompression rate to limit tissue supersaturation or size and profusion of bubbles in accord with models of tissue gas kinetics and bubble formation and growth.

Functional imaging of cerebral perfusion

The functional imaging of perfusion enables the study of its properties such as the vasoreactivity to circulating gases, the autoregulation and the neurovascular coupling. Downstream from arterial stenosis, this imaging can estimate the vascular reserve and the risk of ischemia in order to adapt the therapeutic strategy. This method reveals the hemodynamic disorders in patients suffering from Alzheimer's disease or with arteriovenous malformations revealed by epilepsy. Functional MRI of the vasoreactivity also helps to better interpret the functional MRI activation in practice and in clinical research.

Baroreflex-mediated cardiovascular responses to hyperbaric oxygen

The cardiovascular system responds to hyperbaric hyperoxia (HBO2) with vasoconstriction, hypertension, bradycardia, and reduced cardiac output (CO). We tested the hypothesis that these responses are linked by a common mechanism-activation of the arterial baroreflex. Baroreflex function in HBO2 was assessed in anesthetized and conscious rats after deafferentation of aortic or carotid baroreceptors or both. Cardiovascular and autonomic responses to HBO2 in these animals were compared with those in intact animals at 2.5 ATA for conscious rats and at 3 ATA for anesthetized rats. During O2 compression, hypertension was greater after aortic or carotid baroreceptor deafferentation and was significantly more severe if these procedures were combined. Similarly, the hyperoxic bradycardia observed in intact animals was diminished after aortic or carotid baroreceptor deafferentation and replaced by a slight tachycardia after complete baroreceptor deafferentation. We found that hypertension, bradycardia, and reduced CO--the initial cardiovascular responses to moderate levels of HBO2--are coordinated through a baroreflex-mediated mechanism initiated by HBO2-induced vasoconstriction. Furthermore, we have shown that baroreceptor activation in HBO2 inhibits sympathetic outflow and can partially reverse an O2-dependent increase in arterial pressure.

Cu/Zn incorporation during purification of soluble human EC-SOD from E. coli stabilizes proper disulfide bond formation

Extracellular superoxide dismutase (EC-SOD) is the only enzyme that removes superoxide radical in the extracellular space. The reduction of EC-SOD is linked to many diseases, suggesting that the protein may have therapeutic value. EC-SOD is reported to be insoluble and to make inclusion bodies when overexpressed in the cytoplasm of Escherichia coli. The refolding process has the advantage of high yield, but has the disadvantage of frequent aggregation or misfolding during purification. For the first time, this study shows that fusion with maltose-binding protein (MBP), N-utilization substance protein A, and protein disulfide isomerase enabled the soluble overexpression of EC-SOD in the cytoplasm of E. coli. MBP-tagged human EC-SOD (hEC-SOD) was purified by MBP affinity and anion exchange chromatography, and its identity was confirmed by MALDI-TOF MS analysis. The purified protein showed good enzyme activity in vitro; however, there was a difference in metal binding. When copper and zinc were incorporated into hEC-SOD before MBP tag cleavage, the enzymatic activity was higher than when the metal ions were bound to the purified protein after MBP tag cleavage. Therefore, the enzymatic activity of hEC-SOD is associated with metal incorporation and protein folding via disulfide bond.

Multiple factors from bradykinin-challenged astrocytes contribute to the neuronal apoptosis: involvement of astroglial ROS, MMP-9, and HO-1/CO system

Bradykinin (BK) has been shown to induce the expression of several inflammatory mediators, including reactive oxygen species (ROS) and matrix metalloproteinases (MMPs), in brain astrocytes. These mediators may contribute to neuronal dysfunction and death in various neurological disorders. However, the effects of multiple inflammatory mediators released from BK-challenged astrocytes on neuronal cells remain unclear. Here, we found that multiple factors were released from brain astrocytes (RBA-1) exposed to BK in the conditioned culture media (BK-CM), including ROS, MMP-9, and heme oxygenase-1 (HO-1)/carbon monoxide (CO), leading to neuronal cell (SK-N-SH) death. Exposure of SK-N-SH cells to BK-CM or H2O2 reduced cell viability and induced cell apoptosis which were attenuated by N-acetyl cysteine, indicating a role of ROS in these responses. The effect of BK-CM on cell viability and cell apoptosis was also reversed by immunoprecipitation of BK-CM with anti-MMP-9 antibody (MMP-9-IP-CM) or MMP2/9 inhibitor, suggesting the involvement of MMP-9 in BK-CM-mediated responses. Astroglial HO-1/CO in BK-CM induced cell apoptosis and reduced cell viability which was reversed by hemoglobin. Consistently, the involvement of CO in these cellular responses was revealed by incubation with a CO donor CO-RM2 which was reversed by hemoglobin. The role of HO-1 in BK-CM-induced responses was confirmed by overexpression of HO-1 in SK-N-SH infected with Adv-HO-1. BK-CM-induced cell apoptosis was due to the activation of caspase-3 and cleavage of PARP. Together, we demonstrate that BK-induced several neurotoxic factors, including ROS, MMP-9, and CO released from astrocytes, may induce neuronal death through a caspase-3-dependent apoptotic pathway.

Hemoglobin: a nitric-oxide dioxygenase

Members of the hemoglobin superfamily efficiently catalyze nitric-oxide dioxygenation, and when paired with native electron donors, function as NO dioxygenases (NODs). Indeed, the NOD function has emerged as a more common and ancient function than the well-known role in O2 transport-storage. Novel hemoglobins possessing a NOD function continue to be discovered in diverse life forms. Unique hemoglobin structures evolved, in part, for catalysis with different electron donors. The mechanism of NOD catalysis by representative single domain hemoglobins and multidomain flavohemoglobin occurs through a multistep mechanism involving O2 migration to the heme pocket, O2 binding-reduction, NO migration, radical-radical coupling, O-atom rearrangement, nitrate release, and heme iron re-reduction. Unraveling the physiological functions of multiple NODs with varying expression in organisms and the complexity of NO as both a poison and signaling molecule remain grand challenges for the NO field. NOD knockout organisms and cells expressing recombinant NODs are helping to advance our understanding of NO actions in microbial infection, plant senescence, cancer, mitochondrial function, iron metabolism, and tissue O2 homeostasis. NOD inhibitors are being pursued for therapeutic applications as antibiotics and antitumor agents. Transgenic NOD-expressing plants, fish, algae, and microbes are being developed for agriculture, aquaculture, and industry.

NADPH oxidase 2-derived reactive oxygen species signal contributes to bradykinin-induced matrix metalloproteinase-9 expression and cell migration in brain astrocytes

Background

Matrix metalloproteinase-9 (MMP-9) plays a crucial role in pathological processes of brain inflammation, injury, and neurodegeneration. Moreover, bradykinin (BK) induces the expression of several inflammatory proteins in brain astrocytes. Recent studies have suggested that increased oxidative stress is implicated in the brain inflammation and injury. However, whether BK induced MMP-9 expression mediated through oxidative stress remains virtually unknown. Herein we investigated the role of redox signals in BK-induced MMP-9 expression in rat brain astrocytes (RBA-1 cells).

Results

In the study, we first demonstrated that reactive oxygen species (ROS) plays a crucial role in BK-induced MMP-9 expression in cultured brain astrocytes (in vitro) and animal brain tissue (in vivo) models. Next, BK-induced MMP-9 expression is mediated through a Ca²⁺-mediated PKC-α linking to p47^phox/NADPH oxidase 2 (Nox2)/ROS signaling pathway. Nox2-dependent ROS generation led to activation and up-regulation of the downstream transcriptional factor AP-1 (i.e. c-Fos and c-Jun), which bound to MMP-9 promoter region, and thereby turned on transcription of MMP-9 gene. Functionally, BK-induced MMP-9 expression enhanced astrocytic migration.

Conclusions

These results demonstrated that in RBA-1 cells, activation of AP-1 (c-Fos/c-Jun) by the PKC-α-mediated Nox2/ROS signals is essential for up-regulation of MMP-9 and cell migration enhanced by BK.

NADPH oxidase-mediated redox signal contributes to lipoteichoic acid-induced MMP-9 upregulation in brain astrocytes

BACKGROUND

Lipoteichoic acid (LTA) is a component of gram-positive bacterial cell walls and may be elevated in the cerebrospinal fluid of patients suffering from meningitis. Among matrix metalloproteinases (MMPs), MMP-9 has been observed in patients with brain inflammatory diseases and may contribute to the pathology of brain diseases. Moreover, several studies have suggested that increased oxidative stress is implicated in the pathogenesis of brain inflammation and injury. However, the molecular mechanisms underlying LTA-induced redox signal and MMP-9 expression in brain astrocytes remain unclear.

OBJECTIVE

Herein we explored whether LTA-induced MMP-9 expression was mediated through redox signals in rat brain astrocytes (RBA-1 cells).

METHODS

Upregulation of MMP-9 by LTA was evaluated by zymographic and RT-PCR analyses. Next, the MMP-9 regulatory pathways were investigated by pretreatment with pharmacological inhibitors or transfection with small interfering RNAs (siRNAs), Western blotting, and chromatin immunoprecipitation (ChIP)-PCR and promoter activity reporter assays. Moreover, we determined the cell functional changes by migration assay.

RESULTS

These results showed that LTA induced MMP-9 expression via a PKC(α)-dependent pathway. We further demonstrated that PKCα stimulated p47phox/NADPH oxidase 2 (Nox2)-dependent reactive oxygen species (ROS) generation and then activated the ATF2/AP-1 signals. The activated-ATF2 bound to the AP-1-binding site of MMP-9 promoter, and thereby turned on MMP-9 gene transcription. Additionally, the co-activator p300 also contributed to these responses. Functionally, LTA-induced MMP-9 expression enhanced astrocytic migration.

CONCLUSION

These results demonstrated that in RBA-1 cells, activation of ATF2/AP-1 by the PKC(α)-mediated Nox(2)/ROS signals is essential for upregulation of MMP-9 and cell migration enhanced by LTA.

Use of normobaric and hyperbaric oxygen in acute focal cerebral ischemia - a preclinical and clinical review

High socioeconomic burden is attributed to acute ischemic stroke, but treatment strategies are still limited. Normobaric (NBO) and hyperbaric oxygen therapy (HBO) were frequently investigated in preclinical studies following acute focal cerebral ischemia with predominantly beneficial effects in different outcome measurements. Best results were achieved in transient cerebral ischemia, starting HBO early after artery occlusion, and by using relatively high pressures. On molecular level, oxygen application leads to blood-brain barrier stabilization, reduction of excitotoxic metabolites, and inhibition of inflammatory processes. Therefore, NBO and HBO appear excessively hopeful in salvaging impaired brain cells during ischemic stroke. However, harmful effects have been noted contributing to damaging properties, for example, vasoconstriction and free oxygen radicals. In the clinical setting, NBO provided positive results in a single clinical trial, but HBO failed to show efficacy in three randomized trials. To date, the translation of numerous evidentiary experimental results into clinical implementation remains open. Recently, oxygen became interesting as an additional therapy to neuroprotective or recanalization drugs to combine positive effects. Further preclinical research is needed exploring interactions between NBO, HBO, and key factors with multiphasic roles in acute damaging and delayed inflammatory processes after cerebral ischemia, for example, matrix-metalloproteinases and hypoxia-inducible factor-1α.

N-acetylcysteine improves hemodynamics and reduces oxidative stress in the brains of newborn piglets with hypoxia-reoxygenation injury

Reactive oxygen species have been implicated in the pathogenesis of hypoxic-ischemic injury. It has been shown previously that treating an animal with N-acetyl-L-cysteine (NAC), a scavenger of free radicals, significantly minimizes hypoxic-ischemic-induced brain injury in various acute models. Using a subacute swine model of neonatal hypoxia-reoxygenation (H-R), we evaluated the long-term beneficial effect of NAC against oxidative stress-induced brain injury. Newborn piglets were randomly assigned to a sham-operated group (without H-R, n = 6), and two H-R experimental groups (n = 8 each), with 2 h normocapnic alveolar hypoxia and 1 h of 100% oxygen reoxygenation followed by 21% oxygen for 47 h. Five minutes after reoxygenation, the H-R piglets received either normal saline (H-R controls) or NAC (150 mg/kg bolus and 20 mg/kg/h IV for 24 h) in a blinded randomized fashion. Treating the piglets with NAC significantly increased both common carotid arterial flow (CCAF) and oxygen delivery during the early phase of rexoygenation, while both CCAF and carotid oxygen delivery of the H-R group remained lower than the sham-operated groups throughout the experimental period. Compared with H-R controls, significantly higher amounts of anesthetic and sedative medications were required to maintain the NAC-treated piglets in stable condition throughout the experimental period, indicating a stronger recovery. Post-resuscitation NAC treatment also significantly attenuated the increase in cortical caspase-3 and lipid hydroperoxide concentrations. Our findings suggest that post-resuscitation administration of NAC reduces cerebral oxidative stress with improved cerebral oxygen delivery, and probably attenuates apoptosis in newborn piglets with H-R insults.