Effect of 3,4-dihydroxyphenylalanine on Cu(2+)-induced inactivation of HDL-associated paraoxonasel and oxidation of HDL; inactivation of paraoxonasel activity independent of HDL lipid oxidation

Paraoxonase1 (PON1), one of HDL-asssociated antioxidant proteins, is known to be sensitive to oxidative stress. Here, the effect of endogenous reducing compounds on Cu²⁺-mediated inactivation of PON1 was examined. Cu²⁺-mediated inactivation of PON1 was enhanced remarkably by catecholamines, but not by uric acid or homocysteine. Furthermore, catecholamines such as 3,4-dihydroxyphenylalanine (DOPA), dopamine or norepinephrine were more effective than caffeic acid or pyrocatechol in promoting Cu²⁺-mediated inactivation of PON1, suggesting the importance of dihydroxybenzene group as well as amino group. DOPA at relatively low concentrations showed a concentration-dependent inactivation of PON1 in a concert with Cu²⁺, but not Fe²⁺. The DOPA/Cu²⁺-induced inactivation of PON1 was prevented by catalase, but not hydroxyl radical scavengers, consistent with Cu²⁺-catalyzed oxidation. A similar result was also observed when HDL-associated PON1 (HDL-PON1) was exposed to DOPA/Cu²⁺. Separately, it was found that DOPA at low concentrations (1-6 μM) acted as a pro-oxidant by enhancing Cu²⁺-induced oxidation of HDL, while it exhibited an antioxidant action at ≥10 μM. In addition, Cu²⁺-oxidized HDL lost the antioxidant action against LDL oxidation. Meanwhile, the role of DOPA/Cu²⁺-oxidized HDL differed according to DOPA concentration; HDL oxidized with Cu²⁺ in the presence of DOPA (60 or 120 μM) maintained antioxidant activity of native HDL, in contrast to an adverse effect of DOPA at 3 or 6 μM. These data indicate that DOPA at micromolar level may act as a pro-oxidant in Cu²⁺-induced inactivation of PON1 as well as oxidation of HDL. Also, it is proposed that the oxidative inactivation of HDL-PON1 is independent of HDL oxidation.     

Effect of 3,4-dihydroxyphenylalanine on Cu2+-induced Inactivation of HDL-associated Paraoxonase1 and Oxidation of HDL; Inactivation of Paraoxonase1 Activity Independent of HDL Lipid Oxidation

Paraoxonase1 (PON1), one of HDL-asssociated antioxidant proteins, is known to be sensitive to oxidative stress. Here, the effect of endogenous reducing compounds on Cu²⁺-mediated inactivation of PON1 was examined. Cu²⁺-mediated inactivation of PON1 was enhanced remarkably by catecholamines, but not by uric acid or homocysteine. Furthermore, catecholamines such as 3,4-dihydroxyphenylalanine (DOPA), dopamine or norepinephrine were more effective than caffeic acid or pyrocatechol in promoting Cu²⁺-mediated inactivation of PON1, suggesting the importance of dihydroxybenzene group as well as amino group. DOPA at relatively low concentrations showed a concentration-dependent inactivation of PON1 in a concert with Cu²⁺, but not Fe²⁺. The DOPA/Cu²⁺-induced inactivation of PON1 was prevented by catalase, but not hydroxyl radical scavengers, consistent with Cu²⁺-catalyzed oxidation. A similar result was also observed when HDL-associated PON1 (HDL-PON1) was exposed to DOPA/Cu²⁺. Separately, it was found that DOPA at low concentrations (1-6 μM) acted as a pro-oxidant by enhancing Cu²⁺-induced oxidation of HDL, while it exhibited an antioxidant action at ≥10 μM. In addition, Cu²⁺-oxidized HDL lost the antioxidant action against LDL oxidation. Meanwhile, the role of DOPA/Cu²⁺-oxidized HDL differed according to DOPA concentration; HDL oxidized with Cu²⁺ in the presence of DOPA (60 or 120 μM) maintained antioxidant activity of native HDL, in contrast to an adverse effect of DOPA at 3 or 6 μM. These data indicate that DOPA at micromolar level may act as a pro-oxidant in Cu²⁺-induced inactivation of PON1 as well as oxidation of HDL. Also, it is proposed that the oxidative inactivation of HDL-PON1 is independent of HDL oxidation.     

Intra-adrenal interactions in fish: catecholamine stimulated cortisol release in sea bass (Dicentrarchus labrax L.)

The effect of the catecholamines, adrenaline and noradrenaline, on sea bass (Dicentrarchus labrax) and sea bream (Sparus auratus) interrenal cortisol production was studied in vitro using a dynamic superfusion system technique. Increasing concentrations of catecholamines (10(-6), 10(-8) and 10(-10) M) stimulated cortisol production in a dose-dependent manner, in sea bass only. The increase in cortisol production stimulated by adrenaline (10(-6) M) and noradrenaline (10(-6) M) was inhibited by sotalol (2 x 10(-5) M), but not by prazosin suggesting that catecholamines stimulate cortisol release through the beta-receptor subtype. To evaluate catecholamine-induced signal transduction in head kidney cells, measurements of cAMP production and [H3]myo-inositol incorporation were determined in head kidney cell suspensions. Adrenaline and noradrenaline (10(-6) M) increased cAMP production, but had no effect on total inositol phosphate accumulation. These results indicate that catecholamines released from the chromaffin cells within the interrenal tissue may act as a paracrine factor to stimulate interrenal steroidogenesis in the sea bass.     

Transthyretin is involved in depression-like behaviour and exploratory activity

Transthyretin (TTR), the major transporter of thyroid hormones and vitamin A in cerebrospinal fluid (CSF), binds the Alzheimer beta-peptide and thus might confer protection against neurodegeneration. In addition, altered TTR levels have been described in the CSF of patients with psychiatric disorders, yet its function in the CNS is far from understood. To determine the role of TTR in behaviour we evaluated the performance of TTR-null mice in standardized tasks described to assess depression, exploratory activity and anxiety. We show that the absence of TTR is associated with increased exploratory activity and reduced signs of depressive-like behaviour. In order to investigate the mechanism underlying these alterations, we measured the levels of catecholamines. We found that the levels of noradrenaline were significantly increased in the limbic forebrain of TTR-null mice. This report represents the first clear indication that TTR plays a role in behaviour, probably by modulation of the noradrenergic system.     

Redox reactions of neurotransmitters possibly involved in the progression of Parkinson's Disease

In Parkinson's Disease the neuromelanin in the substania nigra is known to contain considerably increased amounts of iron suggesting the presence of free, unprotected iron ions during its formation. Iron(II) is known to interact with peroxide via Fenton's reaction producing OH-radicals or ferryl (Fe(IV)) species. This can readily oxidize the neurotransmitter dopamine to the neurotoxic 6-hydroxydopamine (6-OHDA) which is a strong reducing agent. The produced 6-OHDA is, in turn, able to reduce and possibly release iron, as iron(II), from the iron storage protein ferritin. This cycle of events could well explain the development of Parkinson's Disease due to a continuous production of cell damaging species. The contrasting behaviour of 6-OHDA with some other important catecholamines is discussed.     

Antioxidant activity of L-adrenaline: a structure-activity insight

L-adrenaline belongs to a group of the compounds known as catecholamines, which play an important role in the regulation of physiological process in living organisms. The antioxidant activity and antioxidant mechanism of L-adrenaline was clarified using various in vitro antioxidant assays including 1,1-diphenyl-2-picryl-hydrazyl (DPPH), 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), N,N-dimethyl-p-phenylenediamine (DMPD(+)), and superoxide anion radicals (O(2)(-)) scavenging activity, hydrogen peroxide (H(2)O(2)), total antioxidant activity, ferric ions (Fe(3+)) and cupric ions (Cu(2+)) reducing ability, ferrous ions (Fe(2+)) chelating activity. L-adrenaline inhibited 74.2% lipid peroxidation of a linoleic acid emulsion at 30 microg/mL concentration. On the other hand, butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), alpha-tocopherol and trolox displayed 83.3, 82.1, 68.1 and 81.3% inhibition on the peroxidation of linoleic acid emulsion at the same concentration, respectively. BHA, BHT, alpha-tocopherol and trolox were used as reference antioxidants and radical scavenger compounds. Moreover, this study will bring an innovation for further studies related to antioxidant properties of L-adrenaline. According to present study, L-adrenaline had effective in vitro antioxidant and radical scavenging activity.     

Glutathione peroxidases and redox-regulated transcription factors

Analysis of the selenoproteome identified five glutathione peroxidases (GPxs) in mammals: cytosolic GPx (cGPx, GPx1), phospholipid hydroperoxide GPx (PHGPX, GPx4), plasma GPx (pGPX, GPx3), gastrointestinal GPx (GI-GPx, GPx2) and, in humans, GPx6, which is restricted to the olfactory system. GPxs reduce hydroperoxides to the corresponding alcohols by means of glutathione (GSH). They have long been considered to only act as antioxidant enzymes. Increasing evidence, however, suggests that nature has not created redundant GPxs just to detoxify hydroperoxides. cGPx clearly acts as an antioxidant, as convincingly demonstrated in GPx1-knockout mice. PHGPx specifically interferes with NF-kappaB activation by interleukin-1, reduces leukotriene and prostanoid biosynthesis, prevents COX-2 expression, and is indispensable for sperm maturation and embryogenesis. GI-GPx, which is not exclusively expressed in the gastrointestinal system, is upregulated in colon and skin cancers and in certain cultured cancer cells. GI-GPx is a target for Nrf2, and thus is part of the adaptive response by itself, while PHGPx might prevent cancer by interfering with inflammatory pathways. In conclusion, cGPx, PHGPx and GI-GPx have distinct roles, particularly in cellular defence mechanisms. Redox sensing and redox regulation of metabolic events have become attractive paradigms to unravel the specific and in part still enigmatic roles of GPxs.     

N-Acetylcysteine as an antioxidant and disulphide breaking agent: the reasons why

The main molecular mechanisms explaining the well-established antioxidant and reducing activity of N-acetylcysteine (NAC), the N-acetyl derivative of the natural amino acid l-cysteine, are summarised and critically reviewed. The antioxidant effect is due to the ability of NAC to act as a reduced glutathione (GSH) precursor; GSH is a well-known direct antioxidant and a substrate of several antioxidant enzymes. Moreover, in some conditions where a significant depletion of endogenous Cys and GSH occurs, NAC can act as a direct antioxidant for some oxidant species such as NO₂ and HOX. The antioxidant activity of NAC could also be due to its effect in breaking thiolated proteins, thus releasing free thiols as well as reduced proteins, which in some cases, such as for mercaptoalbumin, have important direct antioxidant activity. As well as being involved in the antioxidant mechanism, the disulphide breaking activity of NAC also explains its mucolytic activity which is due to its effect in reducing heavily cross-linked mucus glycoproteins. Chemical features explaining the efficient disulphide breaking activity of NAC are also explained.     

Nitric oxide stimulates the erythrocyte for ascorbate recycling.

S-Nitrosothiols act as carrier and reservoir of nitric oxide (NO), and release NO under stimulation of ascorbate (Asc). Erythrocyte can regenerate Asc from its oxidised products, thus saving this powerful antioxidant. In this paper the effect of donors of NO, superoxide, and peroxynitrite (SpNONOate, KO(2), and SIN-1, respectively) on the erythrocyte production of Asc was investigated. We report here that NO stimulated, while superoxide and peroxynitrite decreased, the Asc recycling. The NO-stimulating effect on the erythrocyte production of Asc was confirmed by using GSNO, a natural occurring S-nitrosothiol, as NO donor. These data highlight a new property of NO, that is the stimulation of erythrocytes for their Asc recycling. Such a property might contribute to regenerate Asc from its oxidised forms, thus preventing its depletion in the circulation. Temperature and pH significantly affected, both in absence and presence of NO, the recycling of Asc by erythrocytes. We propose that a positive feedback, involving the reciprocal stimulation between Asc and S-nitrosothiols, might enhance productions of Asc by erythrocytes and NO release by circulating S-nitrosothiols.     

Carnosine and related dipeptides protect human ceruloplasmin against peroxyl radical-mediated modification

Ceruloplasmin (CP) is the major plasma antioxidant and copper transport protein. In a previous study, we showed that the aggregation of human ceruloplasmin was induced by peroxyl radicals. We investigated the effects of antioxidant dipeptides carnosine, homocarnosine and anserine on peroxyl radical-mediated ceruloplasmin modification. Carnosine, homocarnosine and anserine significantly inhibited the aggregation of CP induced by peroxyl radicals. When CP was incubated with peroxyl radicals in the presence of three compounds, ferroxidase activity, as measured by the activity staining method, was protected. All three compounds also inhibited the formation of dityrosine in peroxyl radicals-treated CP. The results suggest that carnosine and related compounds act as peroxyl radical scavenger to protect the protein modification. It is proposed that carnosine and related peptides might be explored as potential therapeutic agents for pathologies that involve CP modification mediated by peroxyl radicals generated in the lipid peroxidation.     

Do spin traps also act as classical chain-breaking antioxidants? A quantitative kinetic study of phenyl tert-butylnitrone (PBN) in solution and in liposomes

Free radical spin traps such as phenyl tert-butylnitrone (PBN) are often reported to provide protection of the central nervous system of animal models against free radical damage, and the effects are attributed to its "antioxidant activity." The effects of PBN and p-CH(3)O-PBN were compared with known antioxidants, alpha-tocopherol and 2,2,5,7,8-pentamethyl-6-hydroxychroman (PMHC), in quantitative kinetic studies of lipid peroxidation thermally initiated under controlled conditions. Results obtained on the spin traps in organic solvents and in dilinoleoyl phosphatidylcholine (DLPC) bilayers indicated that the spin traps do not act as peroxyl radical trapping antioxidants but rather act only as moderate "retarders" of oxygen uptake at relatively high concentration. At low oxygen partial pressures, e.g., 14 torr, which better reflect oxygen partial pressures in biological systems, PBN provides a more significant reduction in oxygen uptake (up to 50%) by DLPC bilayers but still did not act as a typical antioxidant. However, at low partial pressures, PBN does act cooperatively with PMHC. It is suggested that its role in biological fluids and tissues may be to extend the suppressed oxidation by natural antioxidants expected to be present. The combination of antioxidant/spin trap, alpha-(3, 5-di-tert-butyl-4-hydroxyphenyl)-N-tert-butylnitrone did not exhibit any enhanced antioxidant efficiency compared with the related hindered phenol, 2,6-di-tert-butyl-4-methoxyphenol.     

Synaptosomal response to oxidative stress: effect of vinpocetine

It has been suggested that reactive oxygen species (ROS) play a role in the neuronal damage occurring in ischemic injury and neurodegenerative disorders and that their neutralization by antioxidant drugs may delay or minimize neurodegeneration. In the present study we examine whether vinpocetine can act as an antioxidant and prevent the formation of ROS and lipid peroxidation in rat brain synaptosomes. After ascorbate/Fe²⁺ treatment a significant increase in oxygen consumption (about 5-fold) and thiobarbituric acid reactive substances (TBARS) formation (about 7-fold) occurred as compared to control conditions. Vinpocetine inhibited the ascorbate/Fe²⁺ stimulated consumption of oxygen and TBARS accumulation, an indicator of lipid peroxidation, in a concentration-dependent manner. The ROS formation was also prevented by vinpocetine. Oxidative stress increased significantly the fluorescence of the probes 2',7'-dichlorodihydrofluorescein (DCFH₂-DA) (about 6-fold) and dihydrorhodamine (DHR) 123 (about 10-fold), which is indicative of intrasynaptosomal ROS generation. Vinpocetine at 100 μM concentration decreased the fluorescence of DCFH₂-DA and DHR 123 by about 50% and 83%, respectively. We conclude that the antioxidant effect of vinpocetine might contribute to the protective role exerted by the drug in reducing neuronal damage in pathological situations.     

Plasma catecholamines in rats during rewarming from induced hypothermia

The present study sought to quantitate the levels of plasma catecholamines [norepinephrine (NE), epinephrine (E), and dopamine (DA)] during induction and rewarming from hypothermia. Male rats (317 +/- 8 g) were made hypothermic by exposure to 0.9% halothane at -10 to -15 degrees C while blood pressure (carotid artery), heart rate, and colonic temperature (Tc) were monitored. Anesthesia was discontinued when Tc reached 28 degrees C. Tc continued to fall but was held at 20-20.5 degrees C for 30 min. Rewarming was then initiated by raising ambient temperature to 22 degrees C. Arterial blood samples were taken 1) before cooling, 2) just before rewarming, 3) when Tc reached 22 degrees C during rewarming, and 4) when Tc reached 27 degrees C during rewarming. Plasma was assayed radioenzymatically for catecholamines using both phenylethanolamine-N-methyltransferase and catechol-O-methyltransferase procedures, and hypothermic induction resulted in significant increases in NE, E, and DA above control levels (P less than 0.01). With rewarming to Tc = 22 degrees C, all catecholamines increased above the level observed during hypothermia (P less than 0.01), and NE and DA increased still further (P less than 0.01) when Tc reached 27 degrees C. The levels of plasma catecholamines observed during hypothermia and during the rewarming phase indicate a role of the sympathoadrenal medullary system in the metabolic adjustments associated with hypothermia and recovery. During rewarming, the levels of E and NE attained exceed those at which both substances may be expected to act as circulating hormones.     

Fibrinogen is an efficient antioxidant

Fibrinogen has been included among the risk factors for vascular disease. Fibrinogen belongs with albumin, ceruloplasmin and transferrin to an acute phase protein group in the plasma. Albumin, ceruloplasmin and transferrin are already recognized as natural antioxidants. In the present study we used three different oxygen generating systems in order to test whether fibrinogen is able to act as an antioxidant in an in vitro system. We used 1) pyrogallol auto-oxidation, 2) the reaction catalysed by xanthine oxidase coupled with the reduction of ferricytochrome c and 3) chemiluminescence. We found that in a dose-dependent manner fibrinogen inhibited superoxide generation (pyrogallol and xanthine-xanthine oxidase reactions), ferrous ion oxidation and hydroxyl radical dependent degradation (of deoxyribose). Fibrinogen also inhibited LDL oxidation (copper and azo compound-induced), hydrogen peroxide oxidation and chemiluminescence produced by polymorphonuclear leukocytes. Fibrinogen, albumin, ceruloplasmin and transferrin act as a supplementary antioxidant defense mechanism against oxidative stress arising from inflammatory conditions.     

A new screening method to detect water-soluble antioxidants: acetaminophen (tylenol®) and other phenols react as antioxidants and destroy peroxynitrite-based luminol-dependent chemiluminescence

This study is based on a simple chemical interaction of peroxynitrite (ON O O⁻) and luminol, which produces blue light upon oxidation. Since peroxynitrite has a half-life of about 1 s, a drug known as linsidomine (SIN-1) is used as a peroxynitrite generator. Peroxynitrite can oxidize lipids, proteins and nucleic acids. Upon the stimulation of inflammation and/or infection, macrophages and neutrophils can be induced to produce large amounts of peroxynitrite, which can oxidize phenols and sulphhydryl-containing compounds. Therefore, phenols and sulphhydryls eliminate peroxynitrite. This is an example of the Yin–Yang hypothesis e.g. oxidation–reduction. Acetaminophen (Tylenol®) can inhibit fever and some types of pain without being a particularly effective anti-inflammatory. Since it is a phenol, it could act as a nitration target for peroxynitrite. Then peroxynitrite, the possible cause of pain and elevated temperature, might be destroyed in the reaction. Acetaminophen is a phenolic compound which produces a clear inhibitory dose–response curve with peroxynitrite in its range of clinical effectiveness. Whether acetaminophen actually works as we suggest is to be proven. Three different types of reaction could decrease the amount of peroxynitrite: (a) interference with base-catalysed opening of the SIN-1 molecule; (b) destruction of one or both substances needed to form it— superoxide and/or nitric oxide; when the SIN-1 degrades to superoxide and nitric oxide, the former may be destroyed by superoxide dismutase (SOD); (c) peroxynitrite may react directly with phenols (mono-, di-, tri- and tetraphenols), possibly by nitration. Nordihydroguaiaretic acid and 2-hydroxyestradiol (catechol estrogen) are potent inhibitors of luminol light emission. Epineprine, isoproterenol, pyrogallol, catechol and ascorbic acid (a classic antioxidant) are all inhibitors of luminol chemiluminescence. Isoproterenol, norepinephrine/and epinephrine first inhibit light but overall stimulate the light production. Initially, SIN-1 degrades to produce peroxynitrite, which reacts with luminol to produce blue light. If any of three catecholamines are present with the reaction that produces light, there is an initial inhibition of light production, and then a marked stimulation. A possible reason for this is that these catechols are oxidized and the metabolized phenol stimulates the production of light from luminol. Also, during oxidation of catecholamines superoxide is sometimes formed, which could stimulate production of peroxynitrite. This simple screening system is introduced to find useful antioxidants against peroxynitrite. © 1998 John Wiley & Sons, Ltd.     

Microbial and host cells acquire enhanced oxidant-scavenging abilities by binding polyphenols

The dilemma whether supplementations of dietary antioxidants might prevent the adverse consequences of oxidative stress, the inadequacy of the analytical methods employed to quantify oxidant scavenging ability (OSA) levels in whole blood and the distribution and fate of polyphenols and their metabolites in various body compartments following oral consumption are discussed. While none-metabolized polyphenols might exert their antioxidant effects mainly in the oral cavity, metabolized polyphenols might be beneficial in the gastrointestinal tract to counteract the toxicity of oxidants and also of the sequelae of inflammatory processes. Although only micromolar amounts of polyphenols and their metabolites eventually reach the blood circulation, these may nevertheless still be highly effective as scavengers of reactive oxygen and nitrogen species because of their ability to synergize with plasma low molecular-weight antioxidants and with albumin. Polyphenols can avidly bind to surfaces of microorganisms and of blood cells to markedly enhance their OSA, therefore the routine quantifications of antioxidant levels conducted in clinical settings should always use catalase-rich whole blood but not as customary, plasma alone. In addition to their antioxidant and metal chelating properties, polyphenols may also act as signaling agents capable of affecting metabolic, inflammatory, autoimmune, carcinogenic and aging processes.     

Synaptosomal response to oxidative stress: Effect of vinpocetine

It has been suggested that reactive oxygen species (ROS) play a role in the neuronal damage occurring in ischemic injury and neurodegenerative disorders and that their neutralization by antioxidant drugs may delay or minimize neurodegeneration. In the present study we examine whether vinpocetine can act as an antioxidant and prevent the formation of ROS and lipid peroxidation in rat brain synaptosomes. After ascorbate/Fe²⁺ treatment a significant increase in oxygen consumption (about 5-fold) and thiobarbituric acid reactive substances (TBARS) formation (about 7-fold) occurred as compared to control conditions. Vinpocetine inhibited the ascorbate/Fe²⁺ stimulated consumption of oxygen and TBARS accumulation, an indicator of lipid peroxidation, in a concentration-dependent manner. The ROS formation was also prevented by vinpocetine. Oxidative stress increased significantly the fluorescence of the probes 2′,7′-dichlorodihydrofluorescein (DCFH₂-DA) (about 6-fold) and dihydrorhodamine (DHR) 123 (about 10-fold), which is indicative of intrasynaptosomal ROS generation. Vinpocetine at 100 μM concentration decreased the fluorescence of DCFH₂-DA and DHR 123 by about 50% and 83%, respectively. We conclude that the antioxidant effect of vinpocetine might contribute to the protective role exerted by the drug in reducing neuronal damage in pathological situations.     

Synthesis,Characterization, Molecular Docking,and Biological Activities of Some Natural and Synthetic Urolithin Analogs

Urolithins (that is, hydroxy substituted benzo[c]chromen‐6‐one derivatives) are formed within the gastrointestinal tract following to the exposure to various ellagitannin rich diet, particularly involving pomegranate, nuts, and berries. Regarding the bioavailability deficiency of ellagitannins, the biological activities obtained through the extracts of these dietaries are attributed to the urolithin compounds, since they are bioavailable. Particularly, there are studies indicating the importance of ellagitannin‐rich food for protective and alternative treatment of Alzheimer's Disease (AD). From this perspective, within this study, the major urolithins (that is, urolithins A and B), their methyl ether metabolites, as well as some synthetic urolithin analogs have been synthesized and screened for their biological activities in various enzyme inhibition (acetylcholinesterase, butyrylcholinesterase, monoamine oxidase B, cyclooxygenase 1, and cyclooxygenase 2) and antioxidant (DPPH radical scavenging) assay systems. The results pointed out the potential of urolithins to act as inhibitors on these receptors. Docking studies were also performed to investigate the possible interactions.     

Oxidation of adrenaline and its derivatives by S-nitrosoglutathione.

An oxidizing effect of S-nitrosoglutathione toward adrenaline and its cyclic derivatives (adrenochrome and adrenolutin) is reported. The oxidation was monitored either spectrophotometrically or as oxygen uptake. Adrenaline was first oxidized to adrenochrome that, after isomerization to adrenolutin, was further oxidized to products monitored as fluorescence decrease. To occur to a significant extent, this oxidation requires copper ions that, in addition to a direct effect on the oxidation of the ortho-diphenol moiety, are also able to decompose nitrosothiols, giving rise to nitric oxide. The latter, after interaction with oxygen and superoxide, produces nitrogen oxides and peroxynitrite, respectively, that are important contributors to the oxidative process. In this context, catecholamines might act as regulatory factors toward nitric oxide and its derivatives.     

Antioxidant and pro-oxidant actions of flavonoids: effects on DNA damage induced by nitric oxide, peroxynitrite and nitroxyl anion

Antioxidant and pro-oxidant activities of flavonoids have been reported. We have studied the effects of 18 flavonoids and related phenolic compounds on DNA damage induced by nitric oxide (NO), peroxynitrite, and nitroxyl anion (NO⁻). Similarly to our previous findings with catecholamines and catechol-estrogens, DNA single-strand breakage was induced synergistically when pBR322 plasmid was incubated in the presence of an NO-releasing compound (diethylamine NONOate) and a flavonoid having an ortho-trihydroxyl group in either the B ring (e.g., epigallocatechin gallate) or the A ring (e.g., quercetagetin). Either NO or any of the above flavonoids alone did not induce strand breakage significantly. However, most of the tested flavonoids inhibited the peroxynitrite-mediated formation of 8-nitroguanine in calf-thymus DNA, measured by a new HPLC-electrochemical detection method, as well as the peroxynitrite-induced strand breakage. NO⁻ generated from Angeli’s salt caused DNA strand breakage, which was also inhibited by flavonoids but at only high concentrations. On the basis of these findings, we propose that NO⁻ and/or peroxynitrite could be responsible for DNA strand breakage induced by NO and a flavonoid having an ortho-trihydroxyl group. Our results indicate that flavonoids have antioxidant properties, but some act as pro-oxidants in the presence of NO.