Superoxide radical scavenging and attenuation of hypoxia-reoxygenation injury by neurotransmitter ferric complexes in isolated rat hepatocytes

Opportunistic use of catecholamine neurotransmitters as siderophores to access iron by Pseudomonas aeruginosa

Iron is an essential nutrient for bacterial growth and the cause of a fierce battle between the pathogen and host during infection. Bacteria have developed several strategies to access iron from the host, the most common being the production of siderophores, small iron-chelating molecules secreted into the bacterial environment. The opportunist pathogen Pseudomonas aeruginosa produces two siderophores, pyoverdine and pyochelin, and is also able to use a wide panoply of xenosiderophores, siderophores produced by other microorganisms. Here, we demonstrate that catecholamine neurotransmitters (dopamine, l-DOPA, epinephrine and norepinephrine) are able to chelate iron and efficiently bring iron into P. aeruginosa cells via TonB-dependent transporters (TBDTs). Bacterial growth assays under strong iron-restricted conditions and with numerous mutants showed that the TBDTs involved are PiuA and PirA. PiuA exhibited more pronounced specificity for dopamine uptake than for norepinephrine, epinephrine and l-DOPA, whereas PirA specificity appeared to be higher for l-DOPA and norepinephrine. Proteomic and qRT-PCR approaches showed pirA transcription and expression to be induced in the presence of all four catecholamines. Finally, the oxidative properties of catecholamines enable them to reduce iron, and we observed ferrous iron uptake via the FeoABC system in the presence of l-DOPA.

Interactions of iron, dopamine and neuromelanin pathways in brain aging and Parkinson's disease

There are several interrelated mechanisms involving iron, dopamine, and neuromelanin in neurons. Neuromelanin accumulates during aging and is the catecholamine-derived pigment of the dopamine neurons of the substantia nigra and norepinephrine neurons of the locus coeruleus, the two neuronal populations most targeted in Parkinson's disease. Many cellular redox reactions rely on iron, however an altered distribution of reactive iron is cytotoxic. In fact, increased levels of iron in the brain of Parkinson's disease patients are present. Dopamine accumulation can induce neuronal death; however, excess dopamine can be removed by converting it into a stable compound like neuromelanin, and this process rescues the cell. Interestingly, the main iron compound in dopamine and norepinephrine neurons is the neuromelanin-iron complex, since neuromelanin is an effective metal chelator. Neuromelanin serves to trap iron and provide neuronal protection from oxidative stress. This equilibrium between iron, dopamine, and neuromelanin is crucial for cell homeostasis and in some cellular circumstances can be disrupted. Indeed, when neuromelanin-containing organelles accumulate high load of toxins and iron during aging a neurodegenerative process can be triggered. In addition, neuromelanin released by degenerating neurons activates microglia and the latter cause neurons death with further release of neuromelanin, then starting a self-propelling mechanism of neuroinflammation and neurodegeneration. Considering the above issues, age-related accumulation of neuromelanin in dopamine neurons shows an interesting link between aging and neurodegeneration.

The biology of the PmrA/PmrB two-component system: the major regulator of lipopolysaccharide modifications

The ability of gram-negative bacteria to resist killing by antimicrobial agents and to avoid detection by host immune systems often entails modification to the lipopolysaccharide (LPS) in their outer membrane. In this review, we examine the biology of the PmrA/PmrB two-component system, the major regulator of LPS modifications in the enteric pathogen Salmonella enterica. We examine the signals that activate the sensor PmrB and the targets controlled by the transcriptional regulator PmrA. We discuss the PmrA/PmrB-dependent chemical decorations of the LPS and their role in resistance to antibacterial agents. We analyze the feedback mechanisms that modulate the activity and thus output of the PmrA/PmrB system, dictating when, where, and to what extent bacteria modify their LPS. Finally, we explore the qualitative and quantitative differences in gene expression outputs resulting from the distinct PmrA/PmrB circuit architectures in closely related bacteria, which may account for their differential survival in various ecological niches.

Vascular pro-oxidant effects related to the autoxidation of dopamine

Dopamine autoxidation in an oxygenated physiological salt solution (37 degrees C, pH=7.4) mostly occurred in a 2.5 h time period. H(2)O(2) and dopamine quinones were produced during dopamine autoxidation. In partially pre-contracted rat aortic rings, 10-100 microm dopamine induced endothelium-independent contractions and 0.3-1 mm dopamine induced complete, slow-developing endothelium-independent relaxations. Indomethacin and catalase suppressed the endothelium-independent dopamine contractions. Catalase strongly reduced the endothelium-independent dopamine relaxations. Furthermore, 1 mm dopamine for 60 min followed by a 90 min washout period induced the release of lactate dehydrogenase and the complete impairment of ring reactivity to phenylephrine and KCl. Pre-treatment with catalase or glutathione prevented dopamine-induced deleterious effects so that further concentration-response curves to phenylephrine and KCl could be obtained. The phenylephrine potency was maintained in rings pre-treated with glutathione but not in rings pre-treated with catalase.

IN CONCLUSION

(1) dopamine is rapidly and non-enzymatically oxidized in physiological solutions, generating H(2)O(2) and quinones; (2) low H(2)O(2) levels increase vascular tone by activating cyclooxygenase; (3) high H(2)O(2) levels cause irreversible relaxations due to unspecific cellular damage; and (4) dopamine quinones cause a specific alteration in the phenylephrine response.

Norepinephrine mediates acquisition of transferrin-iron in Bordetella bronchiseptica

Previous research demonstrated that the sympathoadrenal catecholamine norepinephrine could promote the growth of Bordetella bronchiseptica in iron-restricted medium containing serum. In this study, norepinephrine was demonstrated to stimulate growth of this organism in the presence of partially iron-saturated transferrin but not lactoferrin. Although norepinephrine is known to induce transcription of the Bordetella bfeA enterobactin catechol xenosiderophore receptor gene, neither a bfeA mutant nor a bfeR regulator mutant was defective in growth responsiveness to norepinephrine. However, growth of a tonB mutant strain was not enhanced by norepinephrine, indicating that the response to this catecholamine was the result of high-affinity outer membrane transport. The B. bronchiseptica genome encodes a total of 19 known and predicted iron transport receptor genes, none of which, when mutated individually, were found to confer a defect in norepinephrine-mediated growth stimulation in the presence of transferrin. Labeling experiments demonstrated a TonB-dependent increase in cell-associated iron levels when bacteria grown in the presence of (55)Fe-transferrin were exposed to norepinephrine. In addition, TonB was required for maximum levels of cell-associated norepinephrine. Together, these results demonstrate that norepinephrine facilitates B. bronchiseptica iron acquisition from the iron carrier protein transferrin and this process may represent a mechanism by which some bacterial pathogens obtain this essential nutrient in the host environment.

Interaction of Vimang (Mangifera indica L. extract) with Fe(III) improves its antioxidant and cytoprotecting activity

A standard aqueous stem bark extract from selected species of Mangifera indica L. (Anacardiaceae)--Vimang, whose major polyphenolic component is mangiferin, displays potent in vitro and in vivo antioxidant activity. The present study provides evidence that the Vimang-Fe(III) mixture is more effective at scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH) and superoxide radicals, as well as in protecting against t-butyl hydroperoxide-induced mitochondrial lipid peroxidation and hypoxia/reoxygenation-induced hepatocytes injury, compared to Vimang alone. Voltammetric assays demonstrated that Vimang, in line with the high mangiferin content of the extract, behaves electrochemically like mangiferin, as well as interacts with Fe(III) in close similarity with mangiferin's interaction with the cation. These results justify the high efficiency of Vimang as an agent protecting from iron-induced oxidative damage. We propose Vimang as a potential therapy against the deleterious action of reactive oxygen species generated during iron-overload, such as that occurring in diseases like beta-thalassemia, Friedreich's ataxia and haemochromatosis.

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.

Justification for antioxidant preconditioning (or how to protect insulin-mediated actions under oxidative stress)

Insulin resistance is characterized by impaired glucose utilization in the peripheral tissues, accelerated muscle protein degradation, impaired antioxidant defences and extensive cell death. Apparently, both insulin and IGF-1 at physiological concentrations support cell survival by phosphatidylinositol 3 kinase-dependent and independent mechanisms. Postprandial hyperglycemia and hyperinsulinemia are found in insulin resistance, which accompanies the so-called noninsulin dependent diabetes mellitus (diabetes type 2). Evidence also indicates that increased susceptibility of muscle cells and cardiomycoytes to oxidative stress is among the harmful complications of insulin resistance and diabetes. Limited knowledge showing benefits of preconditioning with anti- oxidants (vitamin C, E, a-lipoic acid, N-acetylcysteine) in order to protect insulin action under oxidative stress prompted the author to discuss the theoretical background to this approach. It should be stressed that antioxidant preconditioning is relevant to prevention of both diabetes- and insulin resistance-associated side-effects such as low viability and cell deletion. Furthermore, antioxidant conditioning promises to provide higher efficacy for clinical applications in myoblast transfer therapy and cardiomyoplasty.

Dietary flavonoid iron complexes as cytoprotective superoxide radical scavengers

Superoxide radicals have been implicated in the pathogenesis of ischemia/reperfusion, aging, and inflammatory diseases. In the present work, we have shown that the Fe(3+) complexes of flavonoids (polyphenols) were much more effective than the uncomplexed flavonoids in protecting isolated rat hepatocytes against hypoxia-reoxygenation injury. The 2:1 flavonoid-metal complexes of Cu(2+), Fe(2+), or Fe(3+) were more effective than the parent compounds in scavenging superoxide radicals generated by xanthine oxidase/hypoxanthine (an enzymatic superoxide-generating system). The 2:1 [flavonoid:Fe(3+)] complexes but not the [deferoxamine:Fe(3+)] complex readily scavenged superoxide radicals. These results suggest that the initial step in superoxide radical scavenging (SRS) activity involves a redox-active flavonoid:Fe(3+) complex. Flavonoid:Fe(3+) complexes should, therefore, be tested as a therapy for the treatment of ischemia/reperfusion injury.

Design and characterization of non-phosphopeptide inhibitors for Src family SH2 domains

The development of novel non-phosphopeptide inhibitors for the Src family SH2 domain is described. Several commercially available hydroxyl aromatic acids have been appended off the N-terminus of pYEEIE and the potent phosphopeptide inhibitors of GST-Lck-SH2 were identified via ELISA. The most potent inhibitor, caffeic acid-pYEEIE, exhibited approximately 30-fold more binding activity than Ac-pYEEIE. Non-phosphopeptides were synthesized by replacing phosphotyrosine of caffeic acid-pYEEIE with tyrosine or 3,4-dihydroxyphenylalanine (DOPA). Caffeic acid-DOPA-EEIE that did not contain phosphotyrosine and its isosteres exhibited less than 20 times decreased binding affinity for GST-Lck-SH2 than Ac-pYEEIE. Moreover, it had a similar binding affinity for the GST-Lck-SH2, GST-Src-SH2, and GST-Fyn-SH2 domains. This study showed that the pY-1 positions of the phosphopeptide inhibitors and of the non-phosphopeptide inhibitors played an important role in the binding for the SH2 domain and that the non-phosphopeptide inhibitor must be a new lead in the development of SH2 inhibitors.

Adrenaline (via α1B-adrenoceptors) and ethanol stimulate OH radical production in isolated rat hepatocytes

Adrenaline is able to increase the oxidative damage caused by some xenobiotic agents in the liver. Ethanol produces oxidative changes in hepatic tissue, while an acute intoxication with alcohol increases adrenaline blood levels. The aim of this study was to determine whether adrenaline increases ethanol-induced hydroxyl free radical production in isolated hepatocytes. Adrenaline augmented hydroxyl radicals in a concentration-dependent manner and was blocked by chloroethylclonidine, an alpha(1B)-adrenoceptor antagonist, while adrenaline plus ethanol added their individual effects. It is suggested that adrenaline increases hydroxyl radicals by an alpha(1B)-adrenoceptor-mediated mechanism, while ethanol does so by a receptor-independent mechanism.