Xenobiotic-mediated production of superoxide by primary cultures of rat cerebral endothelial cells, astrocytes, and neurones

Antioxidant nanozymes as next-generation therapeutics to free radical-mediated inflammatory diseases: A comprehensive review

Recent developments in exploring the biological enzyme mimicking properties in nanozymes have opened a separate avenue, which provides a suitable alternative to the natural antioxidants and enzymes. Due to high and tunable catalytic activity, low cost of synthesis, easy surface modification, and good biocompatibility, nanozymes have garnered significant research interest globally. Several inorganic nanomaterials have been investigated to exhibit catalytic activities of some of the key natural enzymes, including superoxide dismutase (SOD), catalase, glutathione peroxidase, peroxidase, and oxidase, etc. These nanozymes are used for diverse biomedical applications including therapeutics, imaging, and biosensing in various cells/tissues and animal models. In particular, inflammation-related diseases are closely associated with reactive oxygen and reactive nitrogen species, and therefore effective antioxidants could be excellent therapeutics due to their free radical scavenging ability. Although biological enzymes and other artificial antioxidants could perform well in scavenging the reactive oxygen and nitrogen species, however, suffer from several drawbacks such as the requirement of strict physiological conditions for enzymatic activity, limited stability in the environment beyond their optimum pH and temperature, and high cost of synthesis, purification, and storage make then unattractive for broad-spectrum applications. Therefore, this review systematically and comprehensively presents the free radical-mediated evolution of various inflammatory diseases (inflammatory bowel disease, mammary gland fibrosis, and inflammation, acute injury of the liver and kidney, mammary fibrosis, and cerebral ischemic stroke reperfusion) and their mitigation by various antioxidant nanozymes in the biological system. The mechanism of free radical scavenging by antioxidant nanozymes under in vitro and in vivo experimental models and catalytic efficiency comparison with corresponding natural enzymes has also been presented.

Exposure of Cultured Astrocytes to Menadione Triggers Rapid Radical Formation, Glutathione Oxidation and Mrp1-Mediated Export of Glutathione Disulfide

Menadione (2-methyl-1,4-naphthoquinone) is a synthetic derivative of vitamin K that allows rapid redox cycling in cells and thereby generates reactive oxygen species (ROS). To test for the consequences of a treatment of brain astrocytes with menadione, we incubated primary astrocyte cultures with this compound. Incubation with menadione in concentrations of up to 30 µM did not affect cell viability. In contrast, exposure of astrocytes to 100 µM menadione caused a time-dependent impairment of cellular metabolism and cell functions as demonstrated by impaired glycolytic lactate production and strong increases in the activity of extracellular lactate dehydrogenase and in the number of propidium iodide-positive cells within 4 h of incubation. In addition, already 5 min after exposure of astrocytes to menadione a concentration-dependent increase in the number of ROS-positive cells as well as a concentration-dependent and transient accumulation of cellular glutathione disulfide (GSSG) were observed. The rapid intracellular GSSG accumulation was followed by an export of GSSG that was prevented in the presence of MK571, an inhibitor of the multidrug resistance protein 1 (Mrp1). Menadione-induced glutathione (GSH) oxidation and ROS formation were found accelerated after glucose-deprivation, while the presence of dicoumarol, an inhibitor of the menadione-reducing enzyme NQO1, did not affect the menadione-dependent GSSG accumulation. Our study demonstrates that menadione rapidly depletes cultured astrocytes of GSH via ROS-induced oxidation to GSSG that is subsequently exported via Mrp1.

Anthraquinone-2-sulfonic acid (AQ2S) is a novel neurotherapeutic agent

Anthraquinone derivatives such as emodin have recently been shown to protect in models of beta amyloid β (Aβ) and tau aggregation-induced cell death. The mechanisms of action possibly involve preconditioning effects, anti-aggregation properties, and/or enhancing the phosphatidylinositol-3-kinase (PI3K)/AKT survival mechanism. We studied several natural (emodin, rhein, and aloin) and synthetic (AQ2S) anthraquinones, to screen for post-treatment therapeutic benefit in two models of neuronal death, namely hydrogen peroxide (H(2)O(2)) and staurosporine (STS)-induced injury. Treatment with emodin, rhein, or aloin failed to reduce H(2)O(2) injury. Moreover, consistent with emodin behaving like a mild toxin, it exacerbated oxidative injury at the highest concentration used (50 μM) in our post-treatment paradigm, and potently inhibited AKT. In contrast, AQ2S was neuroprotective. It reduced H(2)O(2) injury at 50 and 75 μM. In addition, AQ2S potently inhibited staurosporine (STS)-induced injury. The mechanisms of action involve caspase inhibition and AKT activation. However, blockade of AKT signaling with LY294002 failed to abolish AQ2S-mediated protection on the STS assay. This is the first study to report that AQ2S is a new neuroprotective compound and a novel caspase inhibitor.

Molecular mechanisms of pesticide-induced neurotoxicity: Relevance to Parkinson's disease

Pesticides are widely used in agricultural and other settings, resulting in continued human exposure. Pesticide toxicity has been clearly demonstrated to alter a variety of neurological functions. Particularly, there is strong evidence suggesting that pesticide exposure predisposes to neurodegenerative diseases. Epidemiological data have suggested a relationship between pesticide exposure and brain neurodegeneration. However, an increasing debate has aroused regarding this issue. Paraquat is a highly toxic quaternary nitrogen herbicide which has been largely studied as a model for Parkinson's disease providing valuable insight into the molecular mechanisms involved in the toxic effects of pesticides and their role in the progression of neurodegenerative diseases. In this work, we review the molecular mechanisms involved in the neurotoxic action of pesticides, with emphasis on the mechanisms associated with the induction of neuronal cell death by paraquat as a model for Parkinsonian neurodegeneration.

Pharmacophore mapping of arylamino-substituted benzo[b]thiophenes as free radical scavengers

Predictive pharmacophore models have been developed for a series of arylamino-substituted benzo[b]thiophenes exhibiting free radical scavenging activity. 3D pharmacophore models were generated using a set of 20 training set compounds and subsequently validated by mapping 6 test set compounds using Discovery Studio 2.1 software. Further model validation was performed by randomizing the data using Fischer's validation technique at the 95% confidence level. The most predictive pharmacophore model developed using the conformers obtained from the BEST method showed a correlation coefficient (r) of 0.942 and consisted of three features: hydrogen bond donor, hydrogen bond acceptor and aromatic ring. Acceptable values of external validation parameters, like R2pred (0.853) and r2m(test) (0.844), also implied that the external predictivity of the model was significant. The development of further pharmacophore models using conformers obtained from the FAST method yielded a few models with good predictivity, with the best one (r=0.904) consisting of two features: hydrogen bond donor and hydrogen bond acceptor. Significant values of external validation parameters, R2pred (0.913) and r2m(test) (0.821), also reflect the high predictive ability of the model. Again, Fischer validation results implied that the models developed were robust enough and their good results were not based on mere chance. These validation approaches indicate the reliability of the predictive abilities of the 3D pharmacophore models developed here, which may thus be further utilized as a 3D query tool in the virtual screening of new chemical entities with potent antioxidant activities.

The X-Linked Adrenoleukodystrophy (X-ALD) and Oxidative Stress

Most of the studies indicate that there is as yet no complete cure for X-ALD. However, methods of the treatment seem to slow rather than treat the disease. One method is the use of Lorenzo's oil in conjunction with a low fat diet, which may help in cerebral X-ALD. X-ALD is in very close resemblance to another neurodegenerative disease, amyotrophic lateral sclerosis (ALS). One of the believed pathomechanisms of ALS is oxidative stress; therefore, this article's emphasis on the role of reactive oxygen species in X-ALD. The aim of the present study was to review the literature concerning the advances in the treatment of X-adrenoleukodystrophy (X-ALD, OMIM # 300100) in the last two decades and to shed more light on the link between oxidative stress and X-ALD. This review article may point to a deficit in reactive oxygen species (ROS) scavenging and/or ROS overproduction being involved in the aetiopathology of these neurodegenerative diseases. Consequently, one of the useful neuronal rescue strategies could be the treatment with antioxidant agents.

cis- and trans-Resveratrol are glucuronidated in rat brain, olfactory mucosa and cultured astrocytes

BACKGROUND/AIMS

Glucuronidation of cis- and trans-resveratrol (3,5,4'-trihydroxy-trans-stilbene), which is a naturally occurring phytoalexin known to exert a number of beneficial health effects, was investigated in rat brain, cultured astrocytes and olfactory mucosa.

METHODS

The isomers were incubated with tissue homogenates, microsomes, or rat liver recombinant UDP-glucuronosyltransferases in the presence of UDP-glucuronic acid. The glucuronides were separated by HPLC and quantitated. Astrocytes were exposed to lipopolysaccharide to promote inflammatory conditions.

RESULTS

All tissues were able to form resveratrol glucuronides although at a lower extent, when compared to the liver. The reaction was stereo- and regioselective. In brain tissue, trans-resveratrol 3-O-glucuronide was mainly formed, whereas the cis-isomer was glucuronidated at a lower rate on that position. No 4'-O-glucuronide was detected in brain. In olfactory mucosa homogenates, the cis 3-O-glucuronide was mainly formed, whereas the trans-isomer was glucuronidated only on the 3-position. In astrocytes, 3-O-glucuronides of the cis- and trans-resveratrol were only detected. The rat recombinant UGT1A6 and UGT2B1 isoforms were able to glucuronidate cis- and trans-resveratrol. Finally, in inflammatory conditions, trans-resveratrol glucuronidation was enhanced in astrocytes.

CONCLUSION

Brain tissues are effective in the glucuronidation of resveratrol isomers. This metabolism pathway is likely to modulate the concentration of these biologically active substances.

Cytochrome P4501A is induced in endothelial cell lines from the kidney and lung of the bottlenose dolphin, Tursiops truncatus

Marine mammals respond to the presence of polycyclic and planar halogenated aromatic hydrocarbons (PAH or PHAH) with the induced expression in endothelium of cytochrome P4501A1, regulated through the aryl hydrocarbon receptor (AHR) transcription factor. Physiological responses in other animals, such as edema and inflammation indicate that the endothelium may be compromised by exposure to AHR agonists, which are ubiquitous in the marine environment. In other mammals and fish the cellular and molecular consequences of exposure to AHR agonists have been elucidated in cultured endothelial cells. We have cultured and characterized cetacean endothelial cells (EC) and used them in induction studies. Endothelial cells were cultured from the lung and kidney of the bottlenose dolphin, Tursiops truncates, and exposed to the AHR agonists beta-naphthoflavone (betaNF) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). betaNF (1-3 microM) induced significant increases in CYP1A1 (O-deethylation of 7-ethoxyresorufin to resorufin; EROD) activity to 3.6 and 0.92 pmol/mg/min in lung and kidney EC, respectively. TCDD was more potent than betaNF, and more efficacious, with maximum induction of CYP1A1 activity of 10.1 and 15.2 pmol/mg/min in lung and kidney EC at 3-10 nM TCDD. The differential response indicates that the lung and kidney endothelial cells in culture retain the ability to respond in a selective manner to specific stimuli. Both the molecular mechanisms of induction and the physiological consequences, especially in the vasculature, of toxicant exposure can be studied in this system.

Induction of UGT1A6 isoform by inflammatory conditions in rat astrocytes

Alteration of drug metabolism under diseased conditions is of clinical importance. We have investigated the effects of inflammatory conditions on phase II drug-metabolizing enzyme activity in rat cultured astrocytes. Lipopolysaccharide (LPS) treatment was used to promote inflammatory conditions. Thus, we reported that LPS initiates an inflammatory response, which is mediated by pro-inflammatory mediators and free radical generation. An increase in astrocyte glucuronidation activity was observed after a 48-h LPS treatment. This increase in glucuronidation activity was associated with an up-regulation of the UGT1A6 isoform mRNA level as shown by RT-PCR and gene reporter assay. Moreover, this endotoxin-induced increase in UGT1A6 expression level was blocked by actinomycin D and cycloheximide, indicating the requirement for RNA and protein synthesis. The UGT1A6 expression enhancement could be prevented by anti-inflammatory drugs (dexamethasone and NS398) or nitric oxide synthase inhibitors (L-NAME and L-NMMA). Moreover, gel shift assay revealed increased activator protein-1 (AP-1) binding activity after LPS treatment. We propose, based on the data presented, that the action of LPS to induce UGT1A6 isoform up-regulation may be mediated by pro-inflammatory mediator accumulation, and AP-1 binding activity increase.

Menadione reduces rotenone-induced cell death in cerebellar granule neurons

Oxidative stress has been implicated in neuronal death caused by cerebral ischemia or some neurologic disorders. Chemical hypoxia (term defining the simulation by using respiratory inhibitors) chosen as in vitro ischemic model, was induced in primary cultures of rat cerebellar granule neurons by inhibitors of mitochondrial electron transport such as rotenone or paraquat (complex I), 3-nitropropionic acid (3-NPA, complex II), antimycin A (complex III), or sodium azide (complex IV). All compounds caused neuronal death determined by trypan blue staining and MTT-test. On the other hand, neurotoxicity of rotenone and paraquat but not of 3-NPA, antimycin or azide was significantly abolished by menadione (vitamin K3, 2-methyl-1,4-naphthoquinone). This neuroprotective effect of menadione was associated with a decrease of rotenone-induced free radical production.

CYTOCHROME P4501A INDUCED DIFFERENTIALLY IN ENDOTHELIAL CELLS CULTURED FROM DIFFERENT ORGANS OF ANGUILLA ROSTRATA

Endothelial cells are a structural barrier and an active regulator of many bodily processes. Cytochrome P4501A (CYP1A) activity is induced in the endothelium of teleosts and mammals exposed to lipophilic xenobiotics, such as polycyclic aromatic hydrocarbons, and can have significant consequences for endothelial functions. We exposed cultures of characterized endothelial cells from the heart, kidney, and rete mirabile of the eel, Anguilla rostrata, to aryl hydrocarbon receptor (AhR) agonists. In heart endothelial cells, the maximum response (based on O-deethylation of 7-ethoxyresorufin to resorufin [EROD] activity) to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 113 pmol/mg/min, was at 1 nM TCDD and the peak response to beta-napthoflavone (betaNF), 135 pmol/mg/min, was at 3 microM betaNF. The maximum response to TCDD in the kidney endothelial cells is 12 pmol/mg/min at 0.3 nM TCDD. The rete mirabile capillary endothelial cells responded minimally or not at all to exposure to TCDD and betaNF. Both the heart and kidney endothelial cells (but not the rete mirabile capillary cells) have a low level of EROD activity (12.7 and 5.2 pmol/mg/min, respectively) in untreated or dimethylsulfoxide-treated cells. The robust response of the heart endothelial cells to induction and the lack of response in the rete mirabile capillary endothelial cells indicate that these cells are a good resource to use to investigate the physiological consequences of AhR agonist exposure and CYP1A induction in different areas of the vasculature.

Redox state alteration modulates astrocyte glucuronidation

We have investigated the effects of mild oxidative conditions on drug-metabolizing enzyme activity in rat cultured astrocytes. These experimental conditions promoting an oxidative environment were obtained by short exposure to a low concentration of menadione (5 microM) for a short duration (15 min). This resulted in the rapid and transient production of reactive oxygen species (+130%), associated with a decrease in GSH cellular content (-24%), and an increase in total protein oxidation (+26%), but promoted neither PGE(2) nor NO production. This treatment induced a rapid and persistent decrease in astrocyte glucuronidation activities, which was totally prevented by N-acetyl-l-cysteine. These oxidative conditions also affected the specific UGT1A6 activity measured in transfected V79-1A6 cells. Finally, the subsequent recovery of astrocyte glucuronidation activity may result from upregulation of UGT1A6 expression (+62%) as shown by RT-PCR and gene reporter assay. These results show that the catalytic properties and expression of cerebral UGT1A6 are highly sensitive to the redox environment. The protective effect of N-acetyl-l-cysteine suggests both a direct action of reactive oxygen species on the protein and a more delayed action on the transcriptional regulation of UGT1A6. These results suggest that cerebral metabolism can be altered by physiological or pathological redox modifications.

Modulation of mitochondrial membrane potential and reactive oxygen species production by copper in astrocytes

In monolayers of cultured rat astrocytes a number of agents that induce oxidative stress act synergistically with exposure to copper leading to rapid depolarization of the mitochondrial membrane potential (Psi m) and increased reactive oxygen species (ROS) production. Copper sensitized astrocytes to the action of menadione, an intracellular generator of superoxide anion radical, exogenous hydrogen peroxide (H2O2) and rotenone, an inhibitor of mitochondrial electron transport chain complex I. However, significant differences were observed in the ability to modulate the copper-enhanced oxidative stress depending on which stressor was used. The inhibitor of mitochondrial permeability transition cyclosporin A attenuated the effect of copper and rotenone, but had no protective action in the case of H2O2/copper and menadione/copper combinations. The H2O2 scavenger pyruvate was effective at protecting mitochondria against damage associated with the combined exposure to H2O2/copper and menadione/copper but not to the rotenone/copper combination. The antioxidant Trolox was ineffective at protecting against any of these actions and indeed had a damaging effect when combined with copper. The membrane-permeable copper chelator neocuproine combined with sensitizing concentrations of menadione caused a decrease in Psi m, mimicking the action of copper. Penicillamine, a membrane-impermeable copper chelator, was effective at reducing copper sensitization. Endogenous copper, mobilized during periods of oxidative stress, may play a role in the pathophysiology of brain injury. Our results suggest that this might be particularly dangerous in dysfunctional conditions in which the mitochondrial electron transport chain is compromised.

The effect of exposure to high flux density static and pulsed magnetic fields on lymphocyte function

We investigated whether a combination of static electromagnetic field (EMF) at a flux density of 4.75 T together with pulsed EMF at a flux density of 0.7 mT generated by an NMR apparatus (NMRF), could promote movements of Ca(2+), cell proliferation, and the eventual production of proinflammatory cytokines in human lymphocytes as well as in Jurkat cells, after exposure to the field for 1 h. The same study was also performed after activation of cells with 5 micro g/ml phytohaemagglutinin (PHA) immediately before the exposure period. Our results clearly demonstrate that NMRF exposure increases the [Ca(2+)](i), without any proliferative, or activating, or proinflammatory effect on both normal and PHA stimulated lymphocytes. Accordingly, the levels of interferon gamma, tumor necrosis factor alpha, interleukin-1beta, interleukin-2, and interleukin-6 remained unvaried after exposure. Exposure of Jurkat cells statistically decreased the [Ca(2+)](i) and the proliferation. This is consistent with the low levels of IL-2 measured in supernatants of these cells after exposure. On the whole our data suggest that static and pulsed NMRF exposure contribute synergistically in the increase of the [Ca(2+)](i) without any activating or proinflammatory effect either in normal or in PHA challenged lymphocytes. In Jurkat cells, by changing the properties of cell membranes, NMRF exposure can influence Ca(2+) transport processes and hence Ca(2+) homeostasis, causing a marked decrease of proliferation.

The influence of very low doses of N-nitrosodimethylamine (NDMA) on the apoptosis of rat neutrophils in vivo. The role of reactive oxygen species

N-nitrosodimethylamine (NDMA) causes the apoptosis of neutrophils in vitro experiments. This compound also has the ability to stimulate neutrophils for the production of reactive oxygen species. It has been decided to examine more closely whether the apoptosis of neutrophils by NDMA is caused by the influence of the radicals produced by these cells and whether the stimulation to undergo apoptosis of neutrophils is caused by NDMA in either the original form or by its metabolites. The experiment was conducted on rats. The animals were administered a one-time dose of NDMA intragastrically, 1.5 mg/kg. The research was conducted 1,2,4,12 h consecutively following NDMA administration. The concentration of NDMA in blood was evaluated by means of the gas chromatography method. The neutrophils were isolated from blood by means of differential centrifugation. Respiratory burst was assessed in cells, by means of the cytochrome c reduction method. The percentage of cells revealing morphological properties of apoptosis was determined under the fluorescent microscope. It has been observed that the activation of the respiratory burst is caused mainly by non-metabolised NDMA. Probably the non-metabolised molecules of this compound also have a decisive role in the initiation of apoptosis of neutrophils. It can be assumed that the main factor responsible for the apoptosis of neutrophil rats following a one-time NDMA administration is the induction of respiratory burst in neutrophils by this compound.

Inhibition of rat brain microsomal cytochrome P450-dependent dealkylation activities by an oxidative stress

There is increasing evidence that an oxidative stress not only alters cellular lipids and nucleic acids, but also numerous proteins. This oxidation results in alterations of some cellular functions, either by reversible modifications allowing a post-transcriptional regulation of enzyme activities or receptor affinities, or by irreversible modifications of the protein, triggering its inactivation and destruction. In the present work, we examined the effects of an experimental oxidative stress on rat brain microsomal cytochrome P450-dependent dealkylation activities. For that purpose, superoxide anions were produced either by the NADPH-dependent redox cycling of a quinine, menadione, or by the addition of apomorphine, which produces by autoxidation both superoxide anions and apomorphine-derived quinones. The inhibition of brain cytochrome P450-dependent alkoxyresorufin O-dealkylase activities was dependent on both menadione or apomorphine concentrations. Simultaneously, an increase of microsomal carbonyl groups was recorded. Immunoblotting characterization of brain microsomal oxidized protein was carried out, using antibodies raised against 2,4-dinitrophenylhydrazine as a reagent of protein carbonyl groups, and a revelation by a chemiluminescence method. We observed an increase in cerebral CYP1A protein oxidation, related to menadione concentration, suggesting that oxidation of cytochrome P450 protein may result in its catalytic inactivation.

The effect of pulsed electromagnetic fields on the physiologic behaviour of a human astrocytoma cell line

We evaluated the effects of 50 Hz pulsed electromagnetic fields (EMFs) with a peak magnetic field of 3 mT on human astrocytoma cells. Our results clearly demonstrate that, after the cells were exposed to EMFs for 24 h, the basal [Ca(2+)](i) levels increased significantly from 124+/-51 nM to 200+/-79 nM. Pretreatment of the cells with 1.2 microM substance P increased the [Ca(2+)](i) to 555+/-278 nM, while EMF exposure caused a significant drop in [Ca(2+)](i) to 327+/-146 nM. The overall effect of EMFs probably depends on the prevailing Ca(2+) conditions of the cells. After exposure, the proliferative responses of both normal and substance P-pretreated cells increased slightly from 1.03 to 1.07 and 1.04 to 1.06, respectively. U-373 MG cells spontaneously released about 10 pg/ml of interleukin-6 which was significantly increased after the addition of substance P. Moreover, immediately after EMF exposure and 24 h thereafter, the interleukin-6 levels were more elevated (about 40%) than in controls. On the whole, our data suggest that, by changing the properties of cell membranes, EMFs can influence Ca(2+) transport processes and hence Ca(2+) homeostasis. The increased levels of interleukin-6 after 24 h of EMF exposure may confirm the complex connection between Ca(2+) levels, substance P and the cytokine network.