Vanillin-coumarin hybrid molecule as an efficient fluorescent probe for trace level determination of Hg(II) and its application in cell imaging.

An efficient Hg(2+) selective fluorescent probe (vanillin azo coumarin, VAC) was synthesized by blending vanillin with coumarin. VAC and its Hg(2+) complex were well characterized by different spectroscopic techniques like (1)H NMR, QTOF-MS ES(+), FTIR and elemental analysis as well. VAC could detect up to 1.25 µM Hg(2+) in aqueous methanol solution through fluorescence enhancement. The method was linear up to 16 µM of Hg(2+). Negative interferences from Cu(2+), Ni(2+), Fe(3+), and Zn(2+) were eliminated using EDTA as a masking agent. VAC showed a strong binding to Hg(2+) ion as evident from its binding constant value (2.2×10(5)), estimated using Benesi-Hildebrand equation. Mercuration assisted restricted rotation of the vanillin moiety and inhibited photoinduced electron transfer from the O, N-donor sites to the coumarin unit are responsible for the enhancement of fluorescence upon mercuration of VAC. VAC was used for imaging the accumulation of Hg(2+) ions in Candida albicans cells.

Antiradical, chelating and antioxidant activities of hydroxamic acids and hydroxyureas.

Reactive oxygen species, along with reactive nitrogen species, may play an important role in the pathogenesis and progress of many diseases, including cancer, diabetes and sickle cell disease. It has been postulated that hydroxyurea, one of the main treatments in sickle cell disease, achieves its activity partly also through its antioxidant properties. A series of hydroxyurea derivatives of L- and D-amino acid amides and cycloalkyl-N-aryl-hydroxamic acids was synthesized and investigated for their radical scavenging activity, chelating properties and antioxidant activity. All the compounds showed exceptional antiradical activities. For example, free radical scavenging activities of investigated hydroxyureas were higher than the activity of standard antioxidant, butylated hydroxyanisole (BHA). Moreover, most of the investigated hydroxamic acids were stronger Fe²âº ion chelators than quercetin. In addition, the investigated compounds, especially hydroxamic acids, were proven to be excellent antioxidants. They were as effective as BHA in inhibiting ß-carotene-linoleic acid coupled oxidation. It is reasonable to assume that the antioxidant activity of the investigated compounds could contribute to their previously proven biological properties as cytostatic and antiviral agents.

Iron deficiency enhances bioactive phenolics in lemon juice.

BACKGROUND: This study was designed to describe the phenolic status of lemon juice obtained from fruits of lemon trees differing in iron (Fe) nutritional status. Three types of Fe(III) compound were used in the experiment, namely a synthetic chelate and two complexes derived from natural polymers of humic and lignine nature. RESULTS: All three Fe(III) compounds were able to improve the Fe nutritional status of lemon trees, though to different degrees. This Fe(III) compound effect led to changes in the polyphenol content of lemon juice. Total phenolics were decreased (∼33% average decrease) and, in particular, flavanones, flavones and flavonols were affected similarly. CONCLUSION: Iron-deficient trees showed higher phenolic contents than Fe(III) compound-treated trees, though Fe deficiency had negative effects on the yield and visual quality of fruits. However, from a human nutritional point of view and owing to the health-beneficial properties of their bioavailable phenolic compounds, the nutritional quality of fruits of Fe-deficient lemon trees in terms of phenolics was higher than that of fruits of Fe(III) compound-treated lemon trees. Moreover, diosmetin-6,8-di-C-glucoside in lemon juice can be used as a marker for correction of Fe deficiency in lemon trees.

Iron chelators of the di-2-pyridylketone thiosemicarbazone and 2-benzoylpyridine thiosemicarbazone series inhibit HIV-1 transcription: identification of novel cellular targets--iron, cyclin-dependent kinase (CDK) 2, and CDK9.

HIV-1 transcription is activated by HIV-1 Tat protein, which recruits cyclin-dependent kinase 9 (CDK9)/cyclin T1 and other host transcriptional coactivators to the HIV-1 promoter. Tat itself is phosphorylated by CDK2, and inhibition of CDK2 by small interfering RNA, the iron chelator 2-hydroxy-1-naphthylaldehyde isonicotinoyl hydrazone (311), and the iron chelator deferasirox (ICL670) inhibits HIV-1 transcription. Here we have analyzed a group of novel di-2-pyridylketone thiosemicarbazone- and 2-benzoylpyridine thiosemicarbazone-based iron chelators that exhibit marked anticancer activity in vitro and in vivo (Proc Natl Acad Sci USA 103:7670-7675, 2006; J Med Chem 50:3716-3729, 2007). Several of these iron chelators, in particular 2-benzoylpyridine 4-allyl-3-thiosemicarbazone (Bp4aT) and 2-benzoylpyridine 4-ethyl-3-thiosemicarbazone (Bp4eT), inhibited HIV-1 transcription and replication at much lower concentrations than did 311 and ICL670. Neither Bp4aT nor Bp4eT were toxic after a 24-h incubation. However, longer incubations for 48 h or 72 h resulted in cytotoxicity. Analysis of the molecular mechanism of HIV-1 inhibition showed that the novel iron chelators inhibited basal HIV-1 transcription, but not the nuclear factor-κB-dependent transcription or transcription from an HIV-1 promoter with inactivated SP1 sites. The chelators inhibited the activities of CDK2 and CDK9/cyclin T1, suggesting that inhibition of CDK9 may contribute to the inhibition of HIV-1 transcription. Our study suggests the potential usefulness of Bp4aT or Bp4eT in antiretroviral regimens, particularly where resistance to standard treatment occurs.

Anti-inflammatory effects of pioglitazone on iron-induced oxidative injury in the nigrostriatal dopaminergic system.

AIMS: Transition metals, oxidative stress and neuroinflammation have been proposed as part of a vicious cycle in central nervous system neurodegeneration. Our aim was to study the anti-inflammatory effect of pioglitazone, a peroxisome proliferative activated receptor-γ agonist, on iron-induced oxidative injury in rat brain. METHODS: Intranigral infusion of ferrous citrate (iron) was performed on anaesthetized rats. Pioglitazone (20 mg/kg) was orally administered. Oxidative injury was investigated by measuring lipid peroxidation in the substantia nigra (SN) and dopamine content in the striatum. Western blot assay and DNA fragmentation were employed to study the involvement of α-synuclein aggregation, neuroinflammation as well as activation of endoplasmic reticulum (ER) and mitochondrial pathways in iron-induced apoptosis. RESULTS: Intranigral infusion of iron time-dependently increased α-synuclein aggregation and haem oxygenase-1 levels. Furthermore, apoptosis was demonstrated by TUNEL-positive cells and DNA fragmentation in the iron-infused SN. Systemic pioglitazone was found to potentiate iron-induced elevation in nuclear peroxisome proliferative activated receptor-γ levels. However, pioglitazone inhibited iron-induced α-synuclein aggregation, elevations in interleukin-1ß and interleukin-6 mRNA levels as well as increases in oxygenase-1, cyclo-oxygenase II, nitric oxide synthase and ED-1 protein levels, an indicator of activated microglia. Moreover, iron-induced DNA laddering as well as activation of ER and mitochondrial pathways were attenuated by pioglitazone. In addition, pioglitazone decreased iron-induced elevation in lipid peroxidation in the infused SN and depletion in striatal dopamine level. CONCLUSIONS: Our results suggest that pioglitazone prevents iron-induced apoptosis via both ER and mitochondrial pathways. Furthermore, inhibition of α-synuclein aggregation and neuroinflammation may contribute to the pioglitazone-induced neuroprotection in central nervous system.

Deferasirox is a powerful NF-kappaB inhibitor in myelodysplastic cells and in leukemia cell lines acting independently from cell iron deprivation by chelation and reactive oxygen species scavenging.

BACKGROUND: Usefulness of iron chelation therapy in myelodysplastic patients is still under debate but many authors suggest its possible role in improving survival of low-risk myelodysplastic patients. Several reports have described an unexpected effect of iron chelators, such as an improvement in hemoglobin levels, in patients affected by myelodysplastic syndromes. Furthermore, the novel chelator deferasirox induces a similar improvement more rapidly. Nuclear factor-kappaB is a key regulator of many cellular processes and its impaired activity has been described in different myeloid malignancies including myelodysplastic syndromes. DESIGN AND METHODS: We evaluated deferasirox activity on nuclear factor-kappaB in myelodysplastic syndromes as a possible mechanism involved in hemoglobin improvement during in vivo treatment. Forty peripheral blood samples collected from myelodysplastic syndrome patients were incubated with 50 muM deferasirox for 18h. RESULTS: Nuclear factor-kappaB activity dramatically decreased in samples showing high basal activity as well as in cell lines, whereas no similar behavior was observed with other iron chelators despite a similar reduction in reactive oxygen species levels. Additionally, ferric hydroxyquinoline incubation did not decrease deferasirox activity in K562 cells suggesting the mechanism of action of the drug is independent from cell iron deprivation by chelation. Finally, incubation with both etoposide and deferasirox induced an increase in K562 apoptotic rate. CONCLUSIONS: Nuclear factor-kappaB inhibition by deferasirox is not seen from other chelators and is iron and reactive oxygen species scavenging independent. This could explain the hemoglobin improvement after in vivo treatment, such that our hypothesis needs to be validated in further prospective studies.

The effect of iron(III) on the activity of selenoenzymes and oxidative damage in the liver of rats. Interaction with natural antioxidants and deferiprone.

Iron is an essential element which, under certain conditions, can have prooxidant and cancerogenic effects. The effect of iron and iron chelators on the activity of selenoenzymes has been studied. Acute experiments in male Wistar rats demonstrated the prooxidant effect of iron on the selenoenzymes thioredoxin reductase (TrxR) and glutathione peroxidase (GPx). These enzymes represent an important part of the antioxidant defense system. Deferiprone (L1) has been shown to abolish the stimulating effect of iron on lipid peroxidation and reduced glutathione (GSH) levels, and also to inhibit the influence of iron on the activity of TrxR and GPx. Similarly, the flavonoid quercetin abolished the influence of iron on the activity of TrxR. The activity of both selenoenzymes has also been shown to be stimulated using L1, naringin (NAR), quercetin (QUE) and myricetin (MYR) in the absence of iron. Further studies including the combination of synthetic and natural compounds (e.g., flavonoids) are being considered for their possible development and clinical use in antioxidant therapies.

Abolition of biofilm formation in urinary tract Escherichia coli and Klebsiella isolates by metal interference through competition for fur.

Bacterial biofilms are associated with a large number of persistent and chronic infections. Biofilm-dwelling bacteria are particularly resistant to antibiotics and immune defenses, which makes it hard if not impossible to eradicate biofilm-associated infections. In the urinary tract, free iron is strictly limited but is critical for bacterial growth. Biofilm-associated Escherichia coli cells are particularly desperate for iron. An attractive way of inhibiting biofilm formation is to fool the bacterial regulatory system for iron uptake. Here, we demonstrate that biofilm formation can be impaired by the addition of divalent metal ions, such as Zn(II) and Co(II), which inhibit iron uptake by virtue of their higher-than-iron affinity for the master controller protein of iron uptake, Fur. Reduced biofilm formation of urinary tract-infectious E. coli strains in the presence of Zn(II) was observed in microtiter plates and flow chambers as well as on urinary catheters. These results further support that iron uptake is indeed crucial for biofilm formation, and thereby, targeting these uptake systems might be an effective way to eradicate biofilms caused by infectious strains.

Hepatitis C virus core protein compromises iron-induced activation of antioxidants in mice and HepG2 cells.

One of the characteristics of hepatitis C virus (HCV) infection is the unusual augmentation of oxidative stress, which is exacerbated by iron accumulation in the liver, as observed frequently in hepatitis C patients. Using a transgenic mouse model, the core protein of HCV was shown previously to induce the overproduction of reactive oxygen species (ROS) in the liver. In the present study, the impact of iron overloading on the oxidant/antioxidant system was examined using this mouse model and cultured cells. Iron overloading caused the induction of ROS as well as antioxidants. However, the augmentation of some antioxidants, including heme oxygenase-1 and NADH dehydrogenase, quinone 1, was compromised by the presence of the core protein. The attenuation of iron-induced augmentation of heme oxygenase-1 was also confirmed in HepG2 cells expressing the core protein. This attenuation was not dependent on the Nrf2 transcription factor. Thus, HCV infection not only induces oxidative stress but also hampers the iron-induced antioxidant activation in the liver, thereby exacerbating oxidative stress that would facilitate hepatocarcinogenesis.

Lunasin peptide purified from Solanum nigrum L. protects DNA from oxidative damage by suppressing the generation of hydroxyl radical via blocking fenton reaction.

Oxidative DNA damage is the most critical factor implicated in carcinogenesis and other disorders. However, the protective effects of lunasin against oxidative DNA damage have not yet reported. In this study, we report here the protective effect of lunasin purified from Solanum nigrum L. against oxidative DNA. Lunasin protected DNA from the oxidative damage induced by Fe(2+) ion and hydroxyl radical. To better understand the mechanism for the protective effect of lunasin against DNA damage, the abilities to chelate Fe(2+), scavenge the generated hydroxyl radical and block the generation of hydroxyl radical were evaluated. Although it did not scavenge generated hydroxyl radical, lunasin blocked the generation of hydroxyl radical by chelating Fe(2+) ion. We conclude that lunasin protects DNA from oxidation by blocking fenton reaction between Fe(2+) and H(2)O(2) by chelating Fe(2+) and that consumption of lunasin may play an important role in the chemoprevention for the oxidative carcinogenesis.

Biological activity of novel synthetic derivatives of carnosine.

Two novel derivatives of carnosine--(S)-trolox-L-carnosine (STC) and (R)-trolox-L-carnosine (RTC) are characterized in terms of their antioxidant and membrane-stabilizing activities as well as their resistance to serum carnosinase. STC and RTC were synthesized by N-acylation of L-carnosine with (S)- and (R)-trolox, respectively. STC and RTC were found to react more efficiently with 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) and protect serum lipoproteins from Fe(2+)-induced oxidation more successfully than carnosine and trolox. At the same time, STC, RTC and trolox suppressed oxidative hemolysis of red blood cells (RBC) less efficiently than carnosine taken in the same concentration. When oxidative stress was induced in suspension of cerebellum granule cells by their incubation with N-methyl-D-aspartate (NMDA), or hydrogen peroxide (H(2)O(2)), both STC and RTC more efficiently decreased accumulation of reactive oxygen species (ROS) than carnosine and trolox. Both STC and RTC were resistant toward hydrolytic degradation by human serum carnosinase. STC and RTC were concluded to demonstrate higher antioxidant capacity and better ability to prevent cerebellar neurons from ROS accumulation than their precursors, carnosine and trolox.

Alpha-tocopherol decreases iron-induced hippocampal and nigral neuron loss.

There are many studies about iron-induced neuronal hyperactivity and oxidative stress. Some reports also showed that iron levels rise in the brain in some neurodegenerative diseases such as Parkinson's (PD) and Alzheimer's disease (AD). It has been suggested that excessive iron level increases oxidative stress and causes neuronal death. Tocopherols act as a free radical scavenger when phenoxylic head group encounters a free radical. We have aimed to identify the effect of alpha-tocopherol (Vitamin E) on iron-induced neurotoxicity. For this reason, rats were divided into three groups as control, iron, and iron + alpha-tocopherol groups. Iron chloride (200 mM in 2.5 microl volume) was injected into brain ventricle of iron and iron + alpha-tocopherol group rats. Same volume of saline (2.5 microl) was given to the rats belonging to control group. Rats of iron + alpha-tocopherol group received intraperitoneally (i.p.) alpha-tocopherol (100 mg/kg/day) for 10 days. After 10 days, rats were perfused intracardially under deep urethane anesthesia. Removed brains were processed using standard histological techniques. The numbers of neurons in hippocampus and substantia nigra of all rats were estimated by stereological techniques. Results of present study show that alpha-tocopherol decreased hippocampal and nigral neuron loss from 51.7 to 12.1% and 41.6 to 17.8%, respectively. Findings of the present study suggest that alpha-tocopherol may have neuroprotective effects against iron-induced hippocampal and nigral neurotoxicity and it may have a therapeutic significance for neurodegenerative diseases involved iron.

Failure of deferoxamine, an iron chelator, to improve outcome after collagenase-induced intracerebral hemorrhage in rats.

Intracerebral hemorrhage (ICH) is a devastating stroke with no clinically proven treatment. Deferoxamine (DFX), an iron chelator, is a promising therapy that lessens edema, mitigates peri-hematoma cell death, and improves behavioral recovery after whole-blood-induced ICH in rodents. In this model, blood is directly injected into the brain, usually into the striatum. This mimics many but not all clinical features of ICH (e.g., there is no spontaneous bleed). Thus, we tested whether DFX improves outcome after collagenase-induced striatal ICH in rats. In the first experiment, 3- and 7-day DFX regimens (100 mg/kg twice per day starting 6 h after ICH), similar to those shown effective in the whole-blood model, were compared to saline treatment. Functional recovery was evaluated from 3 to 28 days with several behavioral tests. Except for one instance, DFX failed to lessen ICH-induced behavioral impairments and it did not lessen brain injury, which averaged 43.5 mm(3) at a 28-day survival. In the second experiment, 3 days of DFX treatment were given starting 0 or 6 h after collagenase infusion. Striatal edema occurred, but it was not affected by either DFX treatment (vs. saline treatment). Therefore, in contrast to studies using the whole-blood model, DFX treatment did not improve outcome in the collagenase model. Our findings, when compared to others, suggest that there are critical differences between these ICH models. Perhaps, the current clinical work with DFX will help identify the more clinically predictive model for future neuroprotection studies.

Iron-limited condition modulates biofilm formation and interaction with human epithelial cells of enteroaggregative Escherichia coli (EAEC).

AIMS: The aim of this study was to investigate the influence of low iron availability on biofilm formation and adherence to HEp-2 cells of enteroaggregative Escherichia coli (EAEC) strains isolated from diarrhoea cases. METHODS AND RESULTS: The ability of EAEC to form biofilm on a plastic surface was evaluated quantitatively and qualitatively after 3 and 18 h of incubation of strains with or without the iron chelator 2,2-dipyridyl. When submitted to low iron conditions, prototype EAEC 042 strain showed a decrease in biofilm formation. Conversely, an increase in biofilm formation was observed for the clinical EAEC strains cultured in restricted iron condition. Moreover, the reduction of iron concentration inhibited the aggregative adherence to HEp-2 cells of all EAEC strains tested. However, all effects promoted by iron chelation were suppressed by thiourea. CONCLUSIONS: Low iron availability may modulate biofilm formation and adhesive properties of EAEC strains to HEp-2 cells. SIGNIFICANCE AND IMPACT OF THE STUDY: The data obtained in this study provide useful insights on the influence of low iron conditions possibly associated with redox stress on the pathogenesis of EAEC strains.

Structural determination and antioxidant activity of a polysaccharide from the fruiting bodies of cultured Cordyceps sinensis.

A water-soluble polysaccharide named CPS1 had been isolated from C. sinensis mycelium by hot water extraction, ethanol precipitation, anion-exchange, and gel-permeation chromatography. UV spectra, FTIR spectra, partial acid hydrolysis, PMP precolumn derivation, periodate oxidation and Smith degradation studies were conducted to elucidate its structure. The results indicated that CPS1 was a glucomannogalactan with the monosaccharide composition of glucose: mannose: galactose = 2.8: 2.9: 1. The total carbohydrate content of CPS1 was 99.0%. The weight-average molecular weight was 8.1 x 10(3) Da. The results predicted (1-->2) and (1-->4)-linkage of mannose, (1-->3)-linkage of galactose, (1--> ) and (1-->3, 6)-linkage of glucose composed the backbone of CPS1. CPS1 was also evaluated for its antioxidant activity in vitro, including scavenging effects on the hydroxyl radicals, the reducing power, Fe(2+)-chelating activity, scavenging effect on superoxide radicals, as well as the inhibition of hydrogen peroxide induced haemolysis. CPS1 showed a high antioxidant effect, especially scavenging effect of hydroxyl radicals, the reducing power and Fe(2+)-chelating activity. The results provide scientific support for the antioxidant activity and indicated a connection between antioxidant activity and reparation of renal failure.

[Mechanisms of protective action of bacterial intracellular metabolites for lowering of bactericidal effect of hydroxyl radicals].

AIM: To study mechanisms of attenuation of bactericidal effect of hydroxyl radicals by bacterial intracellular metabolites. MATERIALS AND METHODS: Culture liquids of 16 strains of Lactobacillus spp., 21 strains of Corynebacterium spp., 8 strains of Micrococcus spp. and 17 strains of Staphylococcus spp. and fractions obtained from them were used. Bactericidal effect of hydroxyl radicals on Escherichia coli was measured by survival of the bacteria. RESULTS: High prevalence of ability of bacteria to prevent other microorganisms from bactericidal action of hydroxyl radicals produced in Fenton's reaction was revealed. This effect was accompanied by other two: ability to oxidize Fe2+ in Fe3+ and production of substances with antioxidant properties - extracellular polysaccharides, pigments and lipid-containing compounds. CONCLUSION: It was assumed that defense of microorganisms composing microbiocenosis from toxic effect of hydroxyl radicals realizes through production of bacterial metabolites which inactivate hydroxyl radicals or prevent their formation.

10-undecanhydroxamic acid, a hydroxamate derivative of the undecanoic acid, has strong antimicrobial activity through a mechanism that limits iron availability.

Undecanoic acid (UDA) is a fatty acid with significant antimycotic activity. In this work we have synthesized 10-undecanhydroxamic acid, a hydroxamate derivative of the UDA, and tested its antimicrobial activity on different microorganisms. Our results demonstrate that this compound has higher efficacy than UDA against a variety of fungi and bacteria. Analysis of the intracellular concentration of protein involved in iron transport in Salmonella enterica serovar Typhimurium suggests that its antimicrobial effect actually relies on the ability to chelate iron ions, providing an efficient mechanism to interfere with microbial growth.

Nanoparticle-chelator conjugates as inhibitors of amyloid-beta aggregation and neurotoxicity: a novel therapeutic approach for Alzheimer disease.

Oxidative stress and amyloid-beta are considered major etiological and pathological factors in the initiation and promotion of neurodegeneration in Alzheimer disease (AD). Insomuch as causes of such oxidative stress, transition metals, such as iron and copper, which are found in high concentrations in the brains of AD patients and accumulate specifically in the pathological lesions, are viewed as key contributors to the altered redox state. Likewise, the aggregation and toxicity of amyloid-beta is dependent upon transition metals. As such, chelating agents that selectively bind to and remove and/or "redox silence" transition metals have long been considered as attractive therapies for AD. However, the blood-brain barrier and neurotoxicity of many traditional metal chelators has limited their utility in AD or other neurodegenerative disorders. To circumvent this, we previously suggested that nanoparticles conjugated to iron chelators may have the potential to deliver chelators into the brain and overcome such issues as chelator bioavailability and toxic side-effects. In this study, we synthesized a prototype nanoparticle-chelator conjugate (Nano-N2PY) and demonstrated its ability to protect human cortical neurons from amyloid-beta-associated oxidative toxicity. Furthermore, Nano-N2PY nanoparticle-chelator conjugates effectively inhibited amyloid-beta aggregate formation. Overall, this study indicates that Nano-N2PY, or other nanoparticles conjugated to metal chelators, may provide a novel therapeutic strategy for AD and other neurodegenerative diseases associated with excess transition metals.

Hypothermic preconditioning of endothelial cells attenuates cold-induced injury by a ferritin-dependent process.

Hypothermia for myocardial protection or storage of vascular grafts may damage the endothelium and impair vascular function upon reperfusion/rewarming. Catalytic iron pools and oxidative stress are important mediators of cold-induced endothelial injury. Because endothelial cells are highly adaptive, we hypothesized that hypothermic preconditioning (HPC) protects cells at 0 degrees C by a heme oxygenase-1 (HO-1) and ferritin-dependent mechanism. Storage of human coronary artery endothelial cells at 0 degrees C caused the release of lactate dehydrogenase, increases in bleomycin-detectible iron (BDI), and increases in the ratio of oxidized/reduced glutathione, signifying oxidative stress. Hypoxia increased injury at 0 degrees C but did not increase BDI or oxidative stress further. HPC at 25 degrees C for 15-72 h attenuated these changes by an amount achievable by pretreating cells with 10-20 microM deferoxamine, an iron chelator, and protected cell viability. Treating cells with hemin chloride at 37 degrees C transiently increased intracellular heme, HO-1, BDI, and ferritin. Elevated heme/iron sensitized cells to 0 degrees C but ferritin was protective. HPC increased iron maximally after 2 h at 25 degrees C and ferritin levels peaked after 15 h. HO-1 was not induced. When HPC-mediated increases in ferritin were blocked by deferoxamine, protection at 0 degrees C was diminished. We conclude that HPC-mediated endothelial protection from hypothermic injury is an iron- and ferritin-dependent process.

Iron-binding and anti-Fenton properties of baicalein and baicalin.

Baicalein and baicalin, the major bioactive compounds found in the Chinese herb Scutellaria baicalensis, have been shown to be effective against cancer, bacterial infections and oxidative stress diseases. However, little is known about their mechanisms of action. To probe whether iron homeostasis modulation may play a role in their bioactivity, we have investigated their iron binding characteristics under physiologically relevant conditions. A 2:1 baicalein-ferrous complex was readily formed in 20mM phosphate buffer, pH 7.2, with a binding constant approximately 2-9 x 10(11)M(-2), whereas a 1:1 baicalein-ferric complex was formed, under the same conditions, with an apparent binding constant approximately 1-3 x 10(6)M(-1). Baicalein appears to bind the ferrous ion more strongly than ferrozine, a well known iron(II) chelator. Using (1) H NMR and Zn(2+) and Ga(3+) as probes, the iron-binding site on baicalein was elucidated to be at the O6/O7 oxygen atoms of the A-ring. No binding was observed for baicalin under the same NMR conditions. Furthermore, baicalein strongly inhibits the Fe-promoted Fenton chemistry via a combination of chelation and radical scavenging mechanism while baicalin can provide only partial protection against radical damage. These results indicate that baicalein is a strong iron chelator under physiological conditions and hence may play a vital role in modulating the body's iron homeostasis. Modulation of metal homeostasis and the inhibition of Fenton chemistry may be one of the possible mechanisms for herbal medicine.