Free radical scavengers: chemical concepts and clinical relevance

Catechol-derived Mannich bases: radical regulatory properties, cytotoxicity and interaction with biomolecules

Free radicals are ubiquitous in biological systems, being responsible for pathogenesis of degenerative diseases and participating in vitally important biochemical processes, which are mediated by radical regulatory agents. The effects of the aliphatic amine substituents in the catechol-derived Mannich bases on their antioxidant and pro-oxidant activity were investigated. It has been found that the presence of catechol moiety in the structure of Mannich bases allows them to act as Cu(II) reductants, efficient Fe(II) chelators and potent DPPH radical scavengers. It has been found that the plausible mechanism of the DPPH radical scavenging proceeds via quinone formation, followed by their interaction with ethanol via the Michael addition reaction. In the neutrophil respiratory burst assay, several compounds have demonstrated a weak antioxidant activity at the micromolar level (0.1-10 µM), whereas at the millimolar level (0.1 mМ) a strong pro-oxidant effect has been observed. Additionally, at the highest used concentrations a pronounced cytotoxicity against dermal fibroblasts DF-2 and an immunosuppressive effect against T-lymphocytes have been observed for all the synthesized compounds. It has been demonstrated that the oxidation of catechols in the presence of low-molecular thiols results in the formation of covalent adducts, which provides an insight into their cytotoxicity and detoxification pathways.

Discovery of New Phenyltetrazolium Derivatives as Ferroptosis Inhibitors for Treating Ischemic Stroke: An Example Development from Free Radical Scavengers

Ferroptosis is a promising therapeutic target for injury-related diseases, yet diversity in ferroptosis inhibitors remains limited. In this study, initial structure optimization led us to focus on the bond dissociation enthalpy (BDE) of the N-H bond and the residency time of radical scavengers in a phospholipid bilayer, which may play an important role in ferroptosis inhibition potency. This led to the discovery of compound D1, exhibiting potent ferroptosis inhibition, high radical scavenging, and moderate membrane permeability. D1 demonstrated significant neuroprotection in an oxygen glucose deprivation/reoxygenation (OGD/R) model and reduced infarct volume in an in vivo stroke model upon intravenous treatment. Further screening based on this strategy identified NecroX-7 and Eriodictyol-7-O-glucoside as novel ferroptosis inhibitors with highly polar structural characteristics. This approach bridges the gap between free radical scavengers and ferroptosis inhibitors, providing a foundation for research and insights into novel ferroptosis inhibitor development.

Antioxidant Chimeric Molecules: Are Chemical Motifs Additive? The Case of a Selenium-Based Ligand

We set up an in silico experiment and designed a chimeric compound integrating molecular features from different efficient ROS (Reactive Oxygen Species) scavengers, with the purpose of investigating potential relationships between molecular structure and antioxidant activity. Furthermore, a selenium centre was inserted due to its known capacity to reduce hydroperoxides, acting as a molecular mimic of glutathione peroxidase; finally, since this organoselenide is a precursor of a N-heterocyclic carbene ligand, its Au(I) carbene complex was designed and examined. A validated protocol based on DFT (Density Functional Theory) was employed to investigate the radical scavenging activity of available sites on the organoselenide precursor ((SMD)-M06-2X/6-311+G(d,p)//M06-2X/6-31G(d)), as well as on the organometallic complex ((SMD)-M06-2X/SDD (Au), 6-311+G(d,p)//ZORA-BLYP-D3(BJ)/TZ2P), considering HAT (Hydrogen Atom Transfer) and RAF (Radical Adduct Formation) regarding five different radicals. The results of this case study suggest that the antioxidant potential of chemical motifs should not be considered as an additive property when designing a chimeric compound, but rather that the relevance of a molecular topology is derived from a chemical motif combined with an opportune chemical space of the molecule. Thus, the direct contributions of single functional groups which are generally thought of as antioxidants per se do not guarantee the efficient radical scavenging potential of a molecular species.

Antioxidant properties of flavonoid derivatives and their hepatoprotective effects on CCl4 induced acute liver injury in mice

Excessive accumulation of free radicals in the body can cause liver damage, aging, cancer, stroke, and myocardial infarction. Anastatin B, a skeletal flavonoid, was reported to have antioxidant and hepatoprotective effects. Anastatin B derivatives, compound 1 and 2, were synthesized by our group previously. In this study, their antioxidant activity and hepatoprotective mechanism were studied using chemical evaluation methods, a cellular model of hydrogen peroxide (H2O2)-induced oxidative damage, and a mouse model of carbon tetrachloride (CCl4)-induced liver injury. Results from the chemical evaluation suggested that both compounds had good antioxidant power and radical scavenging ability in vitro. MTT assay showed that both compounds had cytoprotective activity in H2O2-treated PC12 cells. Moreover, their hepatoprotective activities evaluated using a mouse model of CCl4-induced liver injury that compared with the model group, pretreatment with compound 1 and 2 significantly decreased alanine transaminase (ALT), aspartate transaminase (AST), lactate dehydrogenase (LDH), and malondialdehyde (MDA) levels; reduced the liver tissue damage; and increased glutathione content. However, compound 2 was a more effective hepatoprotectant than compound 1 was. Finally, the amount of TNF-α and cytochrome P450 2E1 (CYP2E1) were significantly downregulated in compound 1 and 2 pretreatment groups. Collectively, our findings demonstrate that both compounds have potential antioxidant activity and hepatoprotective effect in vitro and in vivo. Further chemo-biological study and investigation of the compounds' enzymatic targets are ongoing.

The unintended mitochondrial uncoupling effects of the FDA-approved anti-helminth drug nitazoxanide mitigates experimental parkinsonism in mice

Mitochondria play a primary role in the pathophysiology of Parkinson's disease (PD), and small molecules that counteract the initial stages of disease may offer therapeutic benefit. In this regard, we have examined whether the off-target effects of the Food and Drug Administration (FDA)-approved anti-helminth drug nitazoxanide (NTZ) on mitochondrial respiration could possess any therapeutic potential for PD. Results indicate that MPP⁺-induced loss in oxygen consumption rate (OCR) and ATP production by mitochondria were ameliorated by NTZ in real time by virtue of its mild uncoupling effect. Pretreatment of cells with NTZ mitigated MPP⁺-induced loss in mitochondrial OCR and reactive oxygen species (ROS). Similarly, addition of NTZ to cells pretreated with MPP⁺ could reverse block in mitochondrial OCR and reactive oxygen species induced by MPP⁺ in real time. The observed effects of NTZ were found to be transient and reversible as removal of NTZ from incubation medium restored the mitochondrial respiration to that of controls. Apoptosis induced by MPP⁺ was ameliorated by NTZ in a dose-dependent manner. In vivo results demonstrated that oral administration of NTZ (50 mg/kg) in an acute MPTP mouse model of PD conferred significant protection against the loss of tyrosine hydroxylase (TH)-positive neurons of substantia nigra. Based on the above observations we believe that repurposing of NTZ for PD may offer therapeutic benefit.

Potential neuroprotective properties of epigallocatechin-3-gallate (EGCG)

Neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD) enforce an overwhelming social and economic burden on society. They are primarily characterized through the accumulation of modified proteins, which further trigger biological responses such as inflammation, oxidative stress, excitotoxicity and modulation of signalling pathways. In a hope for cure, these diseases have been studied extensively over the last decade to successfully develop symptom-oriented therapies. However, so far no definite cure has been found. Therefore, there is a need to identify a class of drug capable of reversing neural damage and preventing further neural death. This review therefore assesses the reliability of the neuroprotective benefits of epigallocatechin-gallate (EGCG) by shedding light on their biological, pharmacological, antioxidant and metal chelation properties, with emphasis on their ability to invoke a range of cellular mechanisms in the brain. It also discusses the possible use of nanotechnology to enhance the neuroprotective benefits of EGCG.

Oxidative Stress-Induced Response of Some Endogenous Antioxidants in Schizophrenia

Reactive oxygen species (ROS) formed in various metabolic reactions cause unlimited damage by attacking and oxidizing the macromolecules. An arsenal of antioxidant substances neutralizes these ROS at various sites of their metabolic cascade, and if disequilibrium exists between the pro and antioxidant system, oxidative stress persists. The present study was undertaken in schizophrenia, to highlight the response and role of some endogenous antioxidants viz. reduced glutathione (GSH), bilirubin, total proteins, albumin and uric acid in scavenging the ROS. The effect of severity of disease, age factor, and substance abuse was also studied. In all, 50 schizophrenics and 50 age and sex-matched controls were enrolled in the present study. Fasting blood samples were drawn for estimating malondialdehyde (MDA), GSH, bilirubin, total proteins, albumin and uric acid in both the groups. The results were statistically analyzed by Z-test and correlated using correlation coefficient (r). The study shows reduction in MDA levels and decline in the level of endogenous antioxidants, but within the normal range. Chronic schizophrenics were at a higher risk of oxidative stress and age and substance abuse seems to worsen the situation.

Mechanisms underlying the protective effects of myricetin and quercetin following oxygen-glucose deprivation-induced cell swelling and the reduction in glutamate uptake in glial cells

The protective effects of the flavonoid polyphenols, myricetin and quercetin, were investigated on key features of ischemic injury in cultures including cell swelling and the reduction in glutamate uptake. C6 glial cells were exposed to oxygen-glucose deprivation (OGD) for 5 h and cell swelling was determined 90 min after the end of OGD. OGD-induced swelling was significantly blocked by both quercetin and myricetin although higher concentrations were required for quercetin. OGD-induced free radical production, a contributing factor in cell swelling, was significantly reduced by both myricetin and quercetin. However, depolarization of the inner mitochondrial membrane potential (ΔΨ(m)), the blockade of which generally reduces swelling, was significantly diminished by myricetin, but not quercetin. This indicated that quercetin could reduce swelling despite its inability to prevent depolarization of ΔΨ(m) possibly through other signaling pathways. Increased intracellular calcium ([Ca²+](i)) is an important characteristic of ischemic injury and is implicated in swelling. Both myricetin and quercetin attenuated the increase in [Ca²+](i). Further, a reduction in [Ca²+](i), through the use of nifedipine, nimodipine, verapamil, dantrolene, or BAPTA-AM, significantly reduced OGD-induced cell swelling indicating that one possible mechanism by which such flavonoids attenuate cell swelling may be through regulating [Ca²+](i). OGD-induced decrease in glutamate uptake was attenuated by myricetin, but not quercetin. Cyclosporin A, a blocker of the mitochondrial permeability transition (mPT) pore, but not FK506 (that does not block the mPT), attenuated the decline in glutamate uptake after OGD, indicating the involvement of the mPT in glutamate uptake. Our results indicated that while blockade of ΔΨ(m) may be sufficient to reduce swelling, it may not be a necessary factor, and that flavonoids reduce cell swelling by regulating [Ca²+](i). The differential effects of myricetin and quercetin on OGD-induced reduction on glutamate uptake may be due to their differential effects on mitochondria.

Protective effects of ellagic and chlorogenic acids against oxidative stress in PC12 cells

Following exposure of differentiated neuronal PC12 cells to either t-BHP, hydrogen peroxide (H2O2) or FeSO4 various kinds of reactive oxygen species (ROS) are generated leading to oxidative injury. The protective effects of two plant polyphenols, ellagic (EC) and chlorogenic acid (CGA), as well as of two metabolites, caffeic acid (CA) and ferulic acid (FA), were investigated in preincubation and coincubation experiments with respect to the following parameters: prevention of cell death, GSH depletion, lipid peroxidation and ROS formation. The polyphenols more efficiently suppressed cytotoxicity and loss of GSH caused by peroxides than by iron, particularly in preincubation. Lipid peroxidation which increased much stronger in response to FeSO4 was counteracted completely by the polyphenols. In case of iron, however, only coincubation was effective. EA and CGA and the metabolites CA and FA showed excellent elimination of ROS induced by all stressors. These findings suggest that two dietary antioxidants, EA and CGA, may have protective properties against oxidative stress induced in CNS.

Clovamide and rosmarinic acid induce neuroprotective effects in in vitro models of neuronal death

BACKGROUND AND PURPOSE

Phenolic compounds exert cytoprotective effects; our purpose was to investigate whether the isosteric polyphenolic compounds clovamide and rosmarinic acid are neuroprotective.

EXPERIMENTAL APPROACH

Three in vitro models of neuronal death were selected: (i) differentiated SH-SY5Y human neuroblastoma cells exposed to tert-butylhydroperoxide (t-BOOH), for oxidative stress; (ii) differentiated SK-N-BE(2) human neuroblastoma cells treated with L-glutamate, for excitotoxicity; and (iii) differentiated SH-SY5Y human neuroblastoma cells exposed to oxygen-glucose deprivation/reoxygenation, for ischaemia-reperfusion. Cell death was evaluated by lactate dehydrogenase measurements in the cell media, while the mechanisms underlying the effects by measuring: (i) t-BOOH-induced glutathione depletion and increase in lipoperoxidation; and (ii) L-glutamate-induced intracellular Ca(2+) overload (fura-2 method) and inducible gene expression (c-fos, c-jun), by reverse transcriptase-PCR. The ability of compounds to modulate nuclear factor-kappaB and peroxisome proliferator-activated receptor-gamma activation was evaluated by Western blot in SH-SY5Y cells not exposed to harmful stimuli.

KEY RESULTS

Both clovamide and rosmarinic acid (10-100 micromol x L(-1)) significantly protected neurons against insults with similar potencies and efficacies. The EC(50) values were in the low micromolar range (0.9-3.7 micromol x L(-1)), while the maximal effects ranged from 40% to -60% protection from cell death over untreated control at 100 micromol x L(-1). These effects are mediated by the prevention of oxidative stress, intracellular Ca(2+) overload and c-fos expression. In addition, rosmarinic acids inhibited nuclear factor-kappaB translocation and increased peroxisome proliferator-activated receptor-gamma expression in SH-SY5Y cells not exposed to harmful stimuli.

CONCLUSION AND IMPLICATIONS

Clovamide and rosmarinic acid are neuroprotective compounds of potential use at the nutritional/pharmaceutical interface.

Glycyrrhizic acid modulates t-BHP induced apoptosis in primary rat hepatocytes

Glycyrrhizic acid (GA) is the main bioactive ingredient of licorice (Glycyrrhiza glabra). The object of this study was to evaluate the protective effects of GA on tert-butyl hydroperoxide (t-BHP) induced oxidative injury leading to apoptosis in cultured primary rat hepatocytes. Throughout the study silymarin was used as positive control. Molecular mechanisms involved in apoptotic pathways induced in hepatocytes by t-BHP at 250 microM were explored in detail. DNA fragmentation, activation of caspases and cytochrome c release were demonstrated. In addition, changes in the mitochondrial membrane potential and ROS generation were detected confirming involvement of mitochondrial pathway. Pre-treatment with GA (4 microg) protected the hepatocytes against t-BHP induced oxidative injury and the results were comparable to the pre-treatment with positive control, i.e. silymarin. The protective potential against cell death was achieved mainly by preventing intracellular GSH depletion, decrease in ROS formation as well as inhibition of mitochondrial membrane depolarization. GA was found to modulate critical end points of oxidative stress induced apoptosis and could be beneficial against liver diseases where oxidative stress is known to play a crucial role.

Protective effects of antioxidants on micronuclei induced by irradiated 9-fluorenone/N,N-dimethyl-p-toluidine in CHO cells

9-Fluorenone (9F), the aromatic photosensitizer, is widely used as an initiator in visible-light (VL) cured resin systems. There is growing concern that 9F may produce genetic damage by inducing mutation. In this study, 9F in the presence or absence of reducing agent N,N-dimethyl-p-toluidine (DMT) with or without VL irradiation was analyzed for the induction of chromosomal aberrations indicated by micronuclei (MN) induced in CHO cells. Our data demonstrated that a dose-related increase in the frequency of MN and prolonged cell cycles in 9F with or without DMT in the presence or absence of VL irradiation (p < 0.05). The rank orders with respect to genotoxicity and cytotoxicity were found to be as follows: 9F/DMT +VL > 9F/DMT = 9F + VL > 9F. To determine whether oxidative stress could modulate MN induced by 9F/DMT with or without VL irradiation in CHO cells, cells were pretreated with N-acetyl-L-cysteine (NAC), ascorbic acid, and alpha-tocopherol. The pretreatment with antioxidants could diminish not only the prolonged cell cycle but also the decreased frequency of MN which is induced by 9F with or without DMT in the presence or absence of VL irradiation in CHO cells (p < 0.05). Our findings provide the evidences for the induction of MN by 9F in the presence or absence of DMT with or without VL irradiation in CHO cells, indicating clastogenic activity of 9F/DMT in vitro. These antioxidants act as the antagonists against the genotoxicity and cytotoxicity of 9F/DMT. Thus, leaching photoinitiator and reducing agent might be contributing the sources of oxidative stress.

The differential effects of superoxide anion, hydrogen peroxide and hydroxyl radical on cardiac mitochondrial oxidative phosphorylation

The involvement of reactive oxygen species (ROS) in cardiac ischemia-reperfusion injuries is well-established, but the deleterious effects of hydrogen peroxide (H(2)O(2)), hydroxyl radical (HO*) or superoxide anion (O(2)*(-) ) on mitochondrial function are poorly understood. Here, we report that incubation of rat heart mitochondria with each of these three species resulted in a decline of the ADP-stimulated respiratory rate but not substrate-dependent respiration. These three species reduced oxygen consumption induced by an uncoupler without alteration of the respiratory chain complexes, but did not modify mitochondrial membrane permeability. HO* slightly decreased F1F0-ATPase activity and HO* and O(2)*(-) partially inhibited the activity of adenine nucleotide translocase; H(2)O(2) failed to alter these targets. They inhibited NADH production by acting specifically on aconitase for O(2)*(-) and alpha-ketoglutarate dehydrogenase for H(2)O(2) and HO*. Our results show that O(2)*(-), H(2)O(2) and HO* act on different mitochondrial targets to alter ATP synthesis, mostly through inhibition of NADH production.

Protective effects of antioxidants on micronuclei induced by camphorquinone/N,N-dimethyl-p-toluidine employing in vitro mammalian test system

Camphorquinone (CQ) is widely used as an initiator in modern visible-light (VL) cured resin systems. CQ is also characterized as a potential allergenic compound. To date, there is growing concern that CQ may produce genetic damage by inducing mutation. In this study, CQ in the presence of reducing agent N,N-dimethyl-p-toluidine (DMT) with or without VL irradiation was analyzed for the induction of chromosomal aberrations indicated by micronuclei (MN) induced in CHO cells. Our data demonstrated that an increase in the numbers of MN was observed with CQ/DMT with or without VL irradiation (p < 0.05). Significant prolongation of cell cycles was observed by the treatment with CQ/DMT with or without VL irradiation (p < 0.05). In addition, VL irradiated CQ/DMT was found to exhibit significantly genotoxic and cytotoxic effects as compared with CQ/DMT alone (p < 0.05). Furthermore, to determine whether oxidative stress could modulate the MN induced by CQ/DMT with or without VL irradiation in CHO cells, cells were pre-treated with various antioxidants 10 mM N-acetyl-L-cysteine (NAC), 2 mM ascorbic acid, and 2 mM alpha-tocopherol. The pre-treatment with antioxidants could antagonize not only the increased MN cells but also the prolonged cell cycle induced by CQ/DMT with or without VL irradiation in CHO cells (p < 0.05). Our findings provide the evidences for the induction of MN by CQ/DMT employing mammalian test system, indicating clastogenic activity of CQ/DMT with or without VL irradiation in vitro. In addition, VL irradiated CQ/DMT exhibits higher genotoxic and cytotoxic effects than CQ/DMT alone. Moreover, NAC, ascorbic acid, and alpha-tocopherol act as the antagonists against the genotoxicity and cytotoxicity of CQ/DMT with or without VL irradiation.

Effect of dopamine on rat diaphragm apoptosis and muscle performance

The purpose of this study was to determine whether dopamine (DA) decreases diaphragm apoptosis and attenuates the decline in diaphragmatic contractile performance associated with repetitive isometric contraction using an in vitro diaphragm preparation. Strenuous diaphragm contractions produce free radicals and muscle apoptosis. Dopamine is a free radical scavenger and, at higher concentrations, increases muscle contractility by simulating beta2-adrenoreceptors. A total of 47 male Sprague-Dawley rats weighing 330-450 g were used in a prospective, randomized, controlled in vitro study. Following animal anaesthetization, diaphragms were excised, and muscle strips prepared and placed in a temperature-controlled isolated tissue bath containing Krebs-Ringer solution (KR) or KR plus 100 microm DA. The solutions were equilibrated with oxygen (O2) at 10, 21 or 95% and 5% carbon dioxide, with the balance being nitrogen. Diaphragm isometric twitch and subtetanic contractions were measured intermittently over 65 min. The diaphragms were then removed and, using a nuclear differential dye uptake method, the percentages of normal, apoptotic and necrotic nuclei were determined using fluorescent microscopy. There were significantly fewer apoptotic nuclei in the DA group diaphragms than in the KR-only group diaphragms in 10 and 21% O2 following either twitch or subtetanic contractions. Dopamine at 100 microm produced only modest increases in muscle performance in both 10 and 21% O2. The attenuation of apoptosis by DA was markedly greater than the effect of DA on muscle performance. Dopamine decreased diaphragmatic apoptosis, perhaps by preventing the activation of intricate apoptotic pathways, stimulating antiapoptotic mechanisms and/or scavenging free radicals.

Apomorphine-induced myocardial protection is due to antioxidant and not adrenergic/dopaminergic effects

Apomorphine (Apo), a dopaminergic agonist used for treatment of Parkinson disease, is a potent antioxidant. In addition to its antioxidative effects, the dopaminergic and adrenergic effects of Apo were studied. Isolated perfused rat hearts were exposed to 25 min of no-flow global ischemia (37 degrees C) and 60 min of reperfusion (I/R, control). Drugs were introduced for the first 20 min of reperfusion. The LVDP of the control group recovered to 54.6 +/- 3.3%. Apo-treated hearts had significantly improved recovery (61.6 +/- 5%, p < 0.05). The recovery of the work index LVDP x HR was even bigger: 67.8 +/- 3.7% (Apo treatment) vs 41.7 +/- 4.6% (control, p < 0.001). Haloperidol, a dopaminergic antagonist, did not affect the recovery with Apo. Propranolol, a beta-adrenergic blocker, initially inhibited the effect of Apo. However, the recovery of the combined group (Apo + propranolol) increased and reached significance (LVDP, p < 0.05 vs control group) after cessation of propranolol perfusion. At 60 min of reperfusion this group was superior to Apo-treated hearts (LVDP, p < 0.05). Propranolol (without Apo) did not improve the hemodynamic recovery. The same pattern of recovery applies also to the recovery of the +dP/dt during the reperfusion. L-DOPA was less effective than Apo. I/R caused significant increase in carbonylation of proteins. Apomorphine inhibited the increase in carbonylation. Haloperidol did not affect this beneficial effect of Apo. L-DOPA significantly decreased the carbonylation of proteins. We conclude that the antioxidative effect of Apo is its main mechanism of cardioprotection.

Dopaminergic drugs may counteract behavioral and biochemical changes induced by models of brain injury

The dopaminergic drugs, bromocriptine, cabergoline, dihydroergocryptine, pergolide and ropinirole were injected subcutaneously (s.c.) at the dose of 0.1, 0.5 and 1 mg/kg/day for 7 days into male rats of the Sprague-Dawley strain. The drug pre-treatment reverted amnesia induced in rats by hypobaric hypopxia and tested in active and passive avoidance tasks. A restoration of memory retention, as assessed in a step-through passive avoidance task, was found in animals with a 2-month brain occlusive ischemia and exposed to dopaminergic drugs for 7 days. For behavioral effects in both active and passive avoidance tests in both experimental models, the rank of relative potency was ropirinole>bromocriptine=cabergoline>pergolide>dihydroergocryptine. Spontaneous ambulation of animals with brain occlusive ischemia was increased by the higher doses of drugs. All dopaminergic drugs reduced kainate mortality rate. The rank of relative potency for this effect was ropirinole=bromocriptine=cabergoline>pergolide=dihydroergocryptine. However, no change was found in other seizure parameters (latency to first convulsion and total number of convulsions) after drug treatment. A biochemical analysis of glutathione redox index (glutathione reduced/glutathione oxidized ratio) in discrete brain areas revealed that exposure to dopaminergic drugs increased this parameter in frontal cortex, striatum and hippocampus of animals subject to hypobaric hypoxia and brain occlusive ischemia. For this effect, the relative potency rank was ropirinole>bromocriptine=cabergoline>>pergolide=dihydroergocryptine. These behavioral and biochemical findings suggest that dopaminergic drugs may counteract either behavioral or biochemical changes induced by experimental models of brain injury. This activity was found after protective activity (as found in animals pre-treated with these drugs and exposed to hypobaric hypoxia) or reversal of brain injury (as found in animals treated after 2-month occlusive brain ischemia). Their neuroprotective activity probably involves the reduction/oxidation balance of the glutathione system in the brain.

Dopamine D3 receptor-preferring agonists induce neurotrophic effects on mesencephalic dopamine neurons

Anti-parkinsonian agents, pramipexole (PPX) and ropinirole (ROP), have been reported to possess neuroprotective properties, both in vitro and in vivo. The mechanisms underlying neuroprotection afforded by the D3-preferring receptor agonists remain poorly understood. The present study demonstrates that incubation of primary mesencephalic cultures with PPX and ROP or the conditioned medium from PPX- or ROP-treated primary cultures induced a marked increase in the number of dopamine (DA) neurons in the cultures. Similar effects can be observed after incubating with the conditioned medium derived from PPX- and ROP-treated substantia nigra astroglia. Meanwhile, PPX and ROP can protect the primary cells from insult of 1-methyl-4-phenylpyridinium (MPP+), the active metabolite of the neurotoxin 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine (MPTP). Furthermore, the neurotrophic effects of PPX and ROP on mesencephalic dopamine neurons could be significantly blocked by D3 receptor antagonist, but not by D2 receptor antagonist. Moreover, we found that the levels of glial cell line-derived neurotrophic factor (GDNF) and brain-derived neurotrophic factor (BDNF) in the conditioned medium of mesencephalic cultures treated with PPX and ROP were significantly increased. Blocking GDNF and BDNF with the neutralizing antibodies, the neurotrophic effects of PPX and ROP were greatly diminished. These results suggest that D3 dopamine receptor-preferring agonists, PPX and ROP, exert neurotrophic effects on cultured DA neurons by modulating the production of endogenous GDNF and BDNF, which may participate in their neuroprotection.

Neurological mechanisms of green tea polyphenols in Alzheimer's and Parkinson's diseases

Tea consumption is varying its status from a mere ancient beverage and a lifestyle habit, to a nutrient endowed with possible prospective neurobiological-pharmacological actions beneficial to human health. Accumulating evidence suggest that oxidative stress resulting in reactive oxygen species generation and inflammation play a pivotal role in neurodegenerative diseases, supporting the implementation of radical scavengers, transition metal (e.g., iron and copper) chelators, and nonvitamin natural antioxidant polyphenols in the clinic. These observations are in line with the current view that polyphenolic dietary supplementation may have an impact on cognitive deficits in individuals of advanced age. As a consequence, green tea polyphenols are now being considered as therapeutic agents in well controlled epidemiological studies, aimed to alter brain aging processes and to serve as possible neuroprotective agents in progressive neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. In particular, literature on the putative novel neuroprotective mechanism of the major green tea polyphenol, (-)-epigallocatechin-3-gallate, are examined and discussed in this review.

On the neurotoxicity mechanism of leukoaminochrome o-semiquinone radical derived from dopamine oxidation: mitochondria damage, necrosis, and hydroxyl radical formation

Leukoaminochrome o-semiquinone radical is generated during one-electron reduction of dopamine oxidation product aminochrome when DT-diaphorase is inhibited. Incubation of 100 microM aminochrome with 100 microM dicoumarol, an inhibitor of DT-diaphorase during 2 h, induces 56% cell death (P < 0.001) with concomitant formation of (i) intracellular hydroperoxides (4.2-fold increase compared to control; P < 0.001); (ii) hydroxyl radicals, detected with ESR and spin trapping agents (2.4-fold increase when cells were incubated with aminochrome in the presence of dicoumarol compared to aminochrome alone); (iii) intracellular edema, and cell membrane deterioration determined by transmission electron microscopy; (iv) absence of apoptosis, supported by using anexin-V with flow cytometry; (v) a strong decrease of mitochondrial membrane potential determined by the fluorescent dye 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolylcarbocyanineiodide (P < 0.01); (vi) swelling and disruption of outer and inner mitochondrial membranes determined by transmission electron microscopy. These results support the proposed role of leukoaminochrome o-semiquinone radical as neurotoxin in Parkinson's disease neurodegeneration and DT-diaphorase as neuroprotective enzyme.

Cell signaling pathways in the neuroprotective actions of the green tea polyphenol (-)-epigallocatechin-3-gallate: implications for neurodegenerative diseases

Accumulating evidence supports the hypothesis that brain iron misregulation and oxidative stress (OS), resulting in reactive oxygen species (ROS) generation from H2O2 and inflammatory processes, trigger a cascade of events leading to apoptotic/necrotic cell death in neurodegenerative disorders, such as Parkinson's (PD), Alzheimer's (AD) and Huntington's diseases, and amyotrophic lateral sclerosis (ALS). Thus, novel therapeutic approaches aimed at neutralization of OS-induced neurotoxicity, support the application of ROS scavengers, transition metals (e.g. iron and copper) chelators and non-vitamin natural antioxidant polyphenols, in monotherapy, or as part of antioxidant cocktail formulation for these diseases. Both experimental and epidemiological evidence demonstrate that flavonoid polyphenols, particularly from green tea and blueberries, improve age-related cognitive decline and are neuroprotective in models of PD, AD and cerebral ischemia/reperfusion injuries. However, recent studies indicate that the radical scavenger property of green tea polyphenols is unlikely to be the sole explanation for their neuroprotective capacity and in fact, a wide spectrum of cellular signaling events may well account for their biological actions. In this article, the currently established mechanisms involved in the beneficial health action and emerging studies concerning the putative novel molecular neuroprotective activity of green tea and its major polyphenol (-)-epigallocatechin-3-gallate (EGCG), will be reviewed and discussed.

Neuroprotective strategies in Parkinson's disease : an update on progress

In spite of the extensive studies performed on postmortem substantia nigra from Parkinson's disease patients, the aetiology of the disease has not yet been established. Nevertheless, these studies have demonstrated that, at the time of death, a cascade of events had been initiated that may contribute to the demise of the melanin-containing nigro-striatal dopamine neurons. These events include increased levels of iron and monoamine oxidase (MAO)-B activity, oxidative stress, inflammatory processes, glutamatergic excitotoxicity, nitric oxide synthesis, abnormal protein folding and aggregation, reduced expression of trophic factors, depletion of endogenous antioxidants such as reduced glutathione, and altered calcium homeostasis. To a large extent, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and 6-hydroxydopamine (6-OHDA) animal models of Parkinson's disease confirm these findings. Furthermore, neuroprotection can be afforded in these models with iron chelators, radical scavenger antioxidants, MAO-B inhibitors, glutamate antagonists, nitric oxide synthase inhibitors, calcium channel antagonists and trophic factors. Despite the success obtained with animal models, clinical neuroprotection is much more difficult to accomplish. Although the negative studies obtained with the MAO-B inhibitor selegiline (deprenyl) and the antioxidant tocopherol (vitamin E) may have resulted from an inappropriate choice of drug (selegiline) or an inadequate dose (tocopherol), the niggling problem that still remains is why these drugs, and others, do work in animals while they fail in the clinic. One reason for this may be related to the fact that in normal human brains the number of dopaminergic neurons falls by around 3-5% every decade, while in Parkinson's disease this decline is greater. Brain autopsy studies have shown that by the time the disease is identified, some 70-75% of the dopamine-containing neurons have been lost. More sensitive reliable methods and clinical correlative markers are required to discern between confoundable symptomatic effects versus a possible neuroprotective action of drugs, namely, the ability to delay or forestall disease progression by protecting or rescuing the remaining dopamine neurons or even restoring those that have been lost.A number of other possibilities for the clinical failure of potential neuroprotectants also exist. First, the animal models of Parkinson's disease may not be totally reflective of the disease and, therefore, the chemical pathologies established in the animal models may not cause, or contribute to, the progression of the disease clinically. Second, because of the series of events occurring in neurodegeneration and our ignorance about which of these factors constitutes the primary event in the pathogenic process, a single drug may not be adequate to induce neuroprotection and, as a consequence, use of a cocktail of drugs may be more appropriate. The latter concept receives support from recent complementary DNA (cDNA) microarray gene expression studies, which show the existence of a gene cascade of events occurring in the nigrostriatal pathway of MPTP, 6-OHDA and methamphetamine animal models of Parkinson's disease. Even with the advent of powerful new tools such as genomics, proteomics, brain imaging, gene replacement therapy and knockout animal models, the desired end result of neuroprotection is still beyond our current capability.

In vitro effects of ascorbate and Trolox on the biocompatibility of dental restorative materials

Previous in vitro studies on the cytotoxicity of eight dental restorative materials including composites, compomers, resin-modified glass ionomer cements and glass ionomer cements have demonstrated a depletion of intracellular glutathione in gingival fibroblasts incubated with eluates of these materials and a protective effect of N-acetylcysteine. In the present study, we investigate the effects of two other antioxidants: ascorbate and Trolox. It was found that Trolox reduced the cytotoxicity induced by resin-based biomaterial eluates. In contrast, ascorbate increased in a dose-dependent manner the toxic effect of all eluates except for Z100 MP and Tetric flow (composites). The effect of D-mannitol was studied for GC FUJI II and was found to neutralize the additional toxic effect of ascorbate. Ascorbate increased the depletion of intracellular glutathione of these dental material eluates (between 17% and 24%, depending on the material). Quantification of metal ions in the dental material eluates showed the presence of significant amounts of aluminum and iron in GC FUJI II > photac fil > GC FUJI II LC > F2000. The mechanism of this increased cytotoxicity could be explained by the Fenton reaction resulting from the pro-oxidant effect of ascorbate in the presence of iron (transition metal ions) and/or aluminum.

Cabergoline prevents necrotic neuronal death in an in vitro model of oxidative stress

To study if cabergoline, a long-lasting specific dopamine D2 receptor agonist, has neuroprotective effects against oxidative stress, we exposed (3 h) SH-SY5Y human neuroblastoma cells to tert-butylhydroperoxide (t-BOOH; 500 microM). t-BOOH caused a 42+/-4% neuronal death, which was prevented by cabergoline (2 h before) in a concentration-dependent manner (EC(50): 1.24 microM). This effect was not antagonised by haloperidol (concentration up to 10 microM), and was associated with an increased availability of intracellular GSH contents (+30+/-11%) and a decrease in the membrane lipid peroxidation (-23+/-9%). Our data suggest that cabergoline has neuroprotective effects useful for Parkinson's disease therapy.

MPTP: insights into parkinsonian neurodegeneration

MPTP burst upon the medical landscape two decades ago, first as a mysterious parkinsonian epidemic, triggering an unparalleled quest for the toxin's identity, and closely followed by an intense pursuit of its cellular mechanisms of action. MPTP treatment created an animal model of many features of Parkinson's disease (PD), used primarily in primates and later in mice. The critical role of oxidative stress damage to vulnerable dopamine neurons, as well as for neurodegenerative diseases in general, emerged from MPTP neurotoxicity. A remarkable cross-fertilization of basic and clinical findings, including genetic and epidemiologic studies, has greatly advanced our understanding of PD and revealed multiple factors contributing to the parkinsonian phenotypes. Brain imaging localizes sites of action and provides potential presymptomatic diagnostic testing. Epidemiologic reports linking PD with pesticide exposure were complimented by supportive evidence from biochemical studies of MPTP and structurally related compounds, especially after low-level, long-term exposure. Genetic studies on the role of risk genes, such as alpha-synuclein or parkin, have been validated by biochemical, anatomical and neurochemical investigations showing factors interacting to produce pathophysiology in the animal model. Focusing on the pivotal role of mitochondria, subcellular pathways participating in cell death have been clarified by unraveling similar sites of action of MPTP. Along the way, compounds antagonizing or potentiating MPTP effects indicated new PD therapies, some of the former achieving clinical trials. The future is encouraging for combating PD and will continue to benefit from the MPTP neurotoxicity model.

Pergolide protects SH-SY5Y cells against neurodegeneration induced by H(2)O(2)

We found that pergolide, a dopamine D1/D2 receptor agonist used in the clinical therapy of Parkinson's disease, protects SH-SY5Y neuroblastoma cells from cell death induced by a brief pulse (15 min) of 1 mM H(2)O(2). Neuroprotection was found when pergolide was added to the culture medium either simultaneously with (EC(50)=60 nM) or 2 h before (EC(50)=40 nM) H(2)O(2) treatment. These effects were not blocked by different dopamine receptor antagonists. Our data suggest that pergolide, independently of dopamine receptor stimulation, may interfere with the early phases of the oxidative stress-induced neurotoxic process.

Green tea polyphenol (-)-epigallocatechin-3-gallate prevents N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced dopaminergic neurodegeneration

In the present study we demonstrate neuroprotective property of green tea extract and (-)-epigallocatechin-3-gallate in N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mice model of Parkinson's disease. N-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxin caused dopamine neuron loss in substantia nigra concomitant with a depletion in striatal dopamine and tyrosine hydroxylase protein levels. Pretreatment of mice with either green tea extract (0.5 and 1 mg/kg) or (-)-epigallocatechin-3-gallate (2 and 10 mg/kg) prevented these effects. In addition, the neurotoxin caused an elevation in striatal antioxidant enzymes superoxide dismutase (240%) and catalase (165%) activities, both effects being prevented by (-)-epigallocatechin-3-gallate. (-)-Epigallocatechin-3-gallate itself also increased the activities of both enzymes in the brain. The neuroprotective effects are not likely to be caused by inhibition of N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine conversion to its active metabolite 1-methyl-4-phenylpyridinium by monoamine oxidase-B, as both green tea and (-)-epigallocatechin-3-gallate are very poor inhibitors of this enzyme in vitro (770 microg/mL and 660 microM, respectively). Brain penetrating property of polyphenols, as well as their antioxidant and iron-chelating properties may make such compounds an important class of drugs to be developed for treatment of neurodegenerative diseases where oxidative stress has been implicated.

Catecholamines inhibit lipid peroxidation in young, aged, and Alzheimer's disease brain

Some catecholamines and indolamines inhibit lipid peroxidation. Recent studies indicate that catecholaminergic inhibition of lipid peroxidation may be receptor mediated in vivo and in cell cultures. Because oxidative stress is one of the hypothesized pathogenic mechanisms for neurodegenerative diseases, including Alzheimer's disease (AD), we hypothesized that catecholaminergic and indolaminergic inhibition of lipid peroxidation would be altered in AD as compared to age-matched non-AD. To test this hypothesis we studied the effect of a variety of neurotransmitters and their antagonists on ascorbate-stimulated lipid peroxidation in membrane fragment preparations derived from postmortem human brain. In this in vitro system, the inhibition of lipid peroxidation by dopamine and serotonin did not appear to be receptor mediated. Further, our findings indicate that there is no apparent effect of age or AD on the inhibition of lipid peroxidation by catecholaminergic and indolaminergic agents.

Oxidative stress and disturbed glutamate transport in hereditary nucleotide repair disorders

Xeroderma pigmentosum group A (XPA) and Cockayne syndrome (CS) are hereditary DNA repair disorders complicated by progressive neurodegeneration. Here we immunohistochemically examine the in situ expression of materials that are produced by oxidative stress and glutamate transporters (which can contribute to prevention of glutamate neurotoxicity) in the brains of 5 autopsied patients each of XPA, CS, and control groups. All oxidative products, including nitrotyrosine, advanced glycation end product, and 4-hydroxy-2-nonenal-modified protein (HNE) were deposited in large amounts in the globus pallidus of CS patients compared to XPA patients. They were frequently recognized in the pseudocalcified foci and free minerals in the neuropil, and more rarely in foamy spheroids. In addition, the deposition of HNE was observed also in hippocampal and cerebellar dentate neurons of both CS and XPA patients. The expression of glial glutamate transporters, EAAT1 and GLT-1, was affected in the globus pallidus in 5 CS patients and 3 XPA patients. They were also altered in the cerebellar cortex in most of the CS patients. These data suggest that oxidative stress and disturbed glutamate transport may be involved in pallidal and/or cerebellar degeneration in hereditary nucleotide repair disorders.

Biogerontology research in Israel

The article describes the special features of gerontology research that has been expanding for five decades in Israel, and outlines the research in the biology of aging, covering a wide spectrum of areas and topics. A variety of associations, institutes and centers that have been established over the years play an important role in furthering the research and academic training.

Chromate-induced human erythrocytes haemoglobin oxidation and peroxidation: influence of vitamin E, vitamin C, salicylate, deferoxamine, and N-ethylmaleimide

In order to attenuate or to prevent chromate-induced human erythrocytes injury, the influence of vitamin E, vitamin C, salicylate, deferoxamine, and N-ethylmaleimide on chromate-induced human erythrocytes haemoglobin oxidation and peroxidation were investigated. It was observed that pretreatment of human erythrocytes with vitamin E (20 microM), vitamin C (1 mM), salicylate (3 mM), and deferoxamine (4 mM) significantly increased (P=0.0001) chromate-induced human erythrocytes haemoglobin oxidation in a time dependent manner, while it was significantly decreased (P=0.0001) by pretreatment with N-ethylmaleimide (1 mM). In contrast, pretreatment of human erythrocytes with deferoxamine (4 mM) immediately inhibited (P=0.0001) chromate-induced human erythrocytes peroxidation, while it was significantly increased (P=0.0001) by pretreatment with N-ethylmaleimide (1 mM) during the first 4 h of cells exposition to chromate. For time periods superior to 6 h pretreatment with N-ethylmaleimide (1 mM) significantly decreased (P=0.0001) chromate-induced human erythrocytes peroxidation. It was concluded that care must be taken as these drugs are used to prevent against toxicity induced by chromium(VI) compounds.

The pivotal role of iron in NF-kappa B activation and nigrostriatal dopaminergic neurodegeneration. Prospects for neuroprotection in Parkinson's disease with iron chelators

R-Apomorphine (APO) the catechol-derived dopamine D1-D2 receptor agonist has been shown to be highly potent iron chelator and radical scavenger and inhibitor of membrane lipid peroxidation in vitro, in vivo and in cell culture employing PC12 cells. Its potency has been compared to the prototype iron chelator desferrioxamine (desferal), dopamine, nifedipine and dopamine D2 receptor agonists, bromocriptine, lisuride, pergolide and pramipexole. APO also inhibits brain and mitochondrial protein oxidation. In vivo APO protects against MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)- induced striatal dopaminergic neurodegeneration in C57 black mice with as low as 5 mg/kg. APO is a reversible competitive inhibitor of monoamine oxidase (MAO) A and B with IC50 values of 93 and 214 uM, respectively. The iron chelating and radical scavenging actions of desferal and APO explains their ability to inhibit iron and 6-hydroxydopamine (6-OHDA)-induced neurodegeneration and activation of redox-sensitive transcription factor NF-kappa B and the subsequent transactivation of promoters of genes involved in inflammatory cytokines. Iron is thought to play a pivotal role in neurodegeneration, and APO may be an ideal drug to investigate neuroprotection in Parkinson's disease where iron and oxidative stress have been implicated in the pathogenesis of nigrostriatal dopamine neuron degeneration.

Chronic cerebral hypoperfusion induces transient reversible monoaminergic changes in the rat brain

Chronic restriction of cerebral blood flow in hypoperfused Wistar rats has been proposed as a new model of cerebrovascular-type dementia. Using this model, we have investigated central monoaminergic neuronal systems that are closely related to higher brain function. Monoamine and monoamine-metabolite levels were determined, as relative monoaminergic markers, at 1 day and 1,3,6 and 12 weeks after the bilateral occlusion of common carotid arteries. Dopaminergic changes in the frontal cortex and striatum were observed in hypoperfused rats at 1-3 weeks following occlusion. Serotonergic changes were recognized at four brain regions examined (frontal cortex, hippocampus, striatum and thalamus+midbrain). In particular, the immediate enhancement of serotonin turnover in the striatum appeared to influence the reaction to the acute ischemic attack such as vasoconstriction produced by hypoperfusion. Our findings suggest that chronic cerebral hypoperfusion induces transient reversible changes in central monoaminergic neuronal function within three weeks of ligation of carotid arteries. This time interval seems to represent a turning point in the process of chronic cerebral hypoperfusion-induced progressive brain injury.

Potent neuroprotective and antioxidant activity of apomorphine in MPTP and 6-hydroxydopamine induced neurotoxicity

Apomorphine is a potent radical scavenger and iron chelator. In vitro apomorphine acts as a potent iron chelator and radical scavenger with IC50 of 0.3 microM for iron (2.5 microM) induced lipid peroxidation in rat brain mitochondrial preparation, and it inhibits mice striatal MAO-A and MAO-B activities with IC50 values of 93 microM and 241 microM. Apomorphine (1-10 microM) protects rat pheochromocytoma (PC12) cells from 6-hydroxydopamine (150 microM) and H2O2 (0.6 mM) induced cytotoxicity and cell death. The neuroprotective property of (R)-apomorphine, a dopamine D1-D2 receptor agonist, has been studied in the MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) model of Parkinson's disease. (R)-apomorphine (5-10 mg/kg, s.c.) pretreatment in C57BL mice, protects against MPTP (24 mg/kg, i.p.) induced loss of nigro-striatal dopamine neurons, as indicated by striatal dopamine content, tyrosine hydroxylase content and tyrosine hydroxylase activity. It is suggested that the neuroprotective effect of (R)-apomorphine against MPTP neurotoxicity derives from its radical scavenging and MAO inhibitory actions and not from its agonistic activity, since the mechanism of MPTP dopaminergic neurotoxicity involves the generation of oxygen radical species induced-oxidative stress.