Paramount levels of ergothioneine transporter SLC22A4 mRNA in boar seminal vesicles and cross-species analysis of ergothioneine and glutathione in seminal plasma

Ergothioneine (ET) is a unique natural antioxidant which mammalia acquire exclusively from their food. Recently, we have discovered an ET transporter (ETT; gene symbol SLC22A4). The existence of a specific transporter suggests a beneficial role for ET; however, the precise physiological purpose of ET is still unclear. A conspicuous site of high extracellular ET accumulation is boar seminal plasma. Here, we have investigated whether ETT is responsible for specific accumulation of ET in the boar reproductive tract. The putative ETT from pig (ETTp) was cloned and validated by functional expression in 293 cells. The highest levels of ETTp mRNA were detected by real-time RT-PCR in seminal vesicles, eye, and kidney; much less was present in bulbourethral gland, testis, and prostate. By contrast, there was virtually no ETT mRNA in rat seminal vesicles. ET content in boar reproductive tissues, determined by LC-MS/MS, closely matched the ETT expression profile. Thus, strong and specific expression of ETTp in boar seminal vesicles explains high accumulation of ET in this gland and hence also in seminal plasma. Previous reports suggest that the glutathione (GSH) content of seminal plasma correlates directly with ET content; however, a comprehensive analysis across several species is not available. We have measured ET and GSH in seminal plasma from human, boar, bull, stallion, and rabbit by LC-MS/MS. GSH levels in seminal plasma do not correlate with ET levels. This suggests that the function of ET, at least in this extracellular context, does not depend on redox cycling with GSH.

Effects of ergothioneine from mushrooms (Flammulina velutipes) on melanosis and lipid oxidation of kuruma shrimp (Marsupenaeus japonicus)

The antimelanosic and antioxidative properties of a hot water extract prepared from the fruiting body of the edible mushroom (Flammulina velutipes) were evaluated by dietary supplementation in Kuruma shrimp (Marsupenaeus japonicus) for possible aquaculture application. The extract contained ergothioneine (ERT) at a level of 2.05 mg/mL. A commercial standard of l-ergothioneine (l-ERT) and the mushroom extract showed inhibitory activity against mushroom polyphenoloxidase (PPO). Feeding of the extract had no adverse effects on the immune systems of the shrimp under the present experimental conditions. Supplementation of the extract in the diet significantly suppressed PPO activities in the hemolymphs of the shrimp. Expression of the prophenoloxidase (proPO) gene decreased in the hemocyte of the Kuruma shrimp fed with the mushroom extract. Consequently, development of melanosis was significantly suppressed in the supplement fed shrimp during ice storage. Lipid oxidation was also effectively controlled in the supplement fed group throughout the storage period. In vitro experiments showed that l-ERT effectively inhibited the activation of proPO in the hemocyte lysate supernatant (HLS). The transcript of the proPO gene in the hemocyte showed lower expression in the l-ERT-treated HLS. It was concluded that dietary supplementation of the mushroom extract in shrimp could be a promising approach to control post mortem development of melanosis and lipid oxidation in shrimp muscles.

Probing the substrate specificity of the ergothioneine transporter with methimazole, hercynine, and organic cations

Recently, we have identified the ergothioneine (ET) transporter ETT (gene symbol SLC22A4). Much interest in human ETT has been generated by case-control studies that suggest an association of polymorphisms in the SLC22A4 gene with susceptibility to chronic inflammatory diseases. ETT was originally designated a multispecific novel organic cation transporter (OCTN1). Here we reinvestigated, based on stably transfected 293 cells and with ET as reference substrate, uptake of quinidine, verapamil, and pyrilamine. ETT from human robustly catalyzed transport of ET (68micfrol/(minmgprotein)), but no transport of organic cations was discernible. With ET as substrate, ETT was relatively resistant to inhibition by selected drugs; the most potent inhibitor was verapamil (K(i)=11micromol/l). The natural compound hercynine and antithyroid drug methimazole are related in structure to ET. However, efficiency of ETT-mediated transport of methimazole (K(i)=7.5mmol/l) was 130-fold lower, and transport of hercynine (K(i)=1.4mmol/l) was 25-fold lower than transport of ET. ETT from mouse, upon expression in 293 cells, catalyzed high affinity, sodium-driven uptake of ET very similar to ETT from human. Additional real-time PCR experiments based on 16 human tissues revealed ETT mRNA levels considerably lower than in bone marrow. Our experiments establish that ETT is highly specific for its physiological substrate ergothioneine. ETT is not a cationic drug transporter, and it does not have high affinity for organic cation inhibitors. Detection of ETT mRNA or protein can therefore be utilized as a specific molecular marker of intracellular ET activity.

Different redox states of metallothionein/thionein in biological tissue

Mammalian metallothioneins are redox-active metalloproteins. In the case of zinc metallothioneins, the redox activity resides in the cysteine sulfur ligands of zinc. Oxidation releases zinc, whereas reduction re-generates zinc-binding capacity. Attempts to demonstrate the presence of the apoprotein (thionein) and the oxidized protein (thionin) in tissues posed tremendous analytical challenges. One emerging strategy is differential chemical modification of cysteine residues in the protein. Chemical modification distinguishes three states of the cysteine ligands (reduced, oxidized and metal-bound) based on (i) quenched reactivity of the thiolates when bound to metal ions and restoration of thiol reactivity in the presence of metal-ion-chelating agents, and (ii) modification of free thiols with alkylating agents and subsequent reduction of disulfides to yield reactive thiols. Under normal physiological conditions, metallothionein exists in three states in rat liver and in cell lines. Ras-mediated oncogenic transformation of normal HOSE (human ovarian surface epithelial) cells induces oxidative stress and increases the amount of thionin and the availability of cellular zinc. These experiments support the notion that metallothionein is a dynamic protein in terms of its redox state and metal content and functions at a juncture of redox and zinc metabolism. Thus redox control of zinc availability from this protein establishes multiple methods of zinc-dependent cellular regulation, while the presence of both oxidized and reduced states of the apoprotein suggest that they serve as a redox couple, the generation of which is controlled by metal ion release from metallothionein.

Zinc-buffering capacity of a eukaryotic cell at physiological pZn

In spite of the paramount importance of zinc in biology, dynamic aspects of cellular zinc metabolism remain poorly defined at the molecular level. Investigations with human colon cancer (HT-29) cells establish a total cellular zinc concentration of 264 microM. Remarkably, about 10% of the potential high-affinity zinc-binding sites are not occupied by zinc, resulting in a surplus of 28 muM ligands (average Kd(c) = 83 pM) that ascertain cellular zinc-buffering capacity and maintain the "free" zinc concentration in proliferating cells at picomolar levels (784 pM, pZn = 9.1). This zinc-buffering capacity allows zinc to fluctuate only with relatively small amplitudes (DeltapZn = 0.3; below 1 nM) without significantly perturbing physiological pZn. Thus, the "free" zinc concentrations in resting and differentiated HT-29 cells are 614 pM and 1.25 nM, respectively. The calculation of these "free" zinc concentrations is based on measurements at different concentrations of the fluorogenic zinc-chelating agent and extrapolation to a zero concentration of the agent. It depends on the state of the cell, its buffering capacity, and the zinc dissociation constant of the chelating agent. Zinc induction of thionein (apometallothionein) ensures a surplus of unbound ligands, increases zinc-buffering capacity and the availability of zinc (DeltapZn = 0.8), but preserves the zinc-buffering capacity of the unoccupied high-affinity zinc-binding sites, perhaps for crucial physiological functions. Jointly, metallothionein and thionein function as the major zinc buffer under conditions of increased cellular zinc.

Thionein can serve as a reducing agent for the methionine sulfoxide reductases

It has been generally accepted, primarily from studies on methionine sulfoxide reductase (Msr) A, that the biological reducing agent for the members of the Msr family is reduced thioredoxin (Trx), although high levels of DTT can be used as the reductant in vitro. Preliminary experiments using both human recombinant MsrB2 (hMsrB2) and MsrB3 (hMsrB3) showed that although DTT can function in vitro as the reducing agent, Trx works very poorly, prompting a more careful comparison of the ability of DTT and Trx to function as reducing agents with the various members of the Msr family. Escherichia coli MsrA and MsrB and bovine MsrA efficiently use either Trx or DTT as reducing agents. In contrast, hMsrB2 and hMsrB3 show <10% of the activity with Trx as compared with DTT, raising the possibility that, in animal cells, Trx may not be the direct hydrogen donor or that there may be a Trx-independent reducing system required for MsrB2 and MsrB3 activity. A heat-stable protein has been detected in bovine liver that, in the presence of EDTA, can support the Msr reaction in the absence of either Trx or DTT. This protein has been identified as a zinc-containing metallothionein (Zn-MT). The results indicate that thionein (T), which is formed when the zinc is removed from Zn-MT, can function as a reducing system for the Msr proteins because of its high content of cysteine residues and that Trx can reduce oxidized T.

Domain-specific fluorescence resonance energy transfer (FRET) sensors of metallothionein/thionein

Each of the two domains of mammalian metallothioneins contains a zinc-thiolate cluster. Employing site-directed mutagenesis and chemical modification, fluorescent probes were introduced into human metallothionein (isoform 2) with minimal perturbations of the structures of these clusters. The resulting FRET (fluorescence resonance energy transfer) sensors are specific for each domain. The design and construction of a sensor for the alpha-domain cluster is based on a FRET pair where a C-terminally added tryptophan serves as the donor for a fluorescence acceptor attached to a free cysteine in the linker region between the two domains. Molecular modeling studies and steady-state fluorescence polarization anisotropy measurements suggest unrestricted motion of the tryptophan donor, but limited motion of the AEDANS ([[(amino)ethyl]amino]naphthalene-1-sulfonic acid) acceptor, putting constraints on the use of the alpha-domain sensor with this FRET pair as a spectroscopic ruler. The fluorescent metallothioneins allow distance measurements during binding and removal of metals in the individual domains. The overall dimensions of the apoprotein, thionein, for which no structural information is available, do not seem to be significantly different from those of the holoprotein. The single- and double-labeled fluorescent metallothioneins overcome a longstanding impediment in studies of the function of this protein, namely its lack of intrinsic probe characteristics.

Discovery of the ergothioneine transporter

Variants of the SLC22A4 gene are associated with susceptibility to rheumatoid arthritis and Crohn's disease. SLC22A4 codes for an integral membrane protein, OCTN1, that has been presumed to carry organic cations like tetraethylammonium across the plasma membrane. Here, we show that the key substrate of this transporter is in fact ergothioneine (ET). Human OCTN1 was expressed in 293 cells. A substrate lead, stachydrine (alias proline betaine), was identified by liquid chromatography MS difference shading, a new substrate search strategy. Analysis of transport efficiency of stachydrine-related solutes, affinity, and Na+ dependence indicates that the physiological substrate is ET. Efficiency of transport of ET was as high as 195 microl per min per mg of protein. By contrast, the carnitine transporter OCTN2 from rat did not transport ET at all. Because ET is transported >100 times more efficiently than tetraethylammonium and carnitine, we propose the functional name ETT (ET transporter) instead of OCTN1. ET, all of which is absorbed from food, is an intracellular antioxidant with metal ion affinity. Its particular purpose is unresolved. Cells with expression of ETT accumulate ET to high levels and avidly retain it. By contrast, cells lacking ETT do not accumulate ET, because their plasma membrane is virtually impermeable for this compound. The real-time PCR expression profile of human ETT, with strong expression in CD71+ cells, is consistent with a pivotal function of ET in erythrocytes. Moreover, prominent expression of ETT in monocytes and SLC22A4 polymorphism associations suggest a protective role of ET in chronic inflammatory disorders.

Ergothioneine inhibits oxidative stress- and TNF-alpha-induced NF-kappa B activation and interleukin-8 release in alveolar epithelial cells

Oxidants and inflammatory mediators such as tumour necrosis factor-alpha (TNF-alpha) activate transcription factors such as NF-kappa B. Interleukin-8 (IL-8) is a ubiquitous inflammatory chemokine that mediates a multitude of inflammatory events in the lung. Ergothioneine is a naturally occurring thiol compound, which possesses antioxidant property. The aim of this study was to determine whether ergothioneine can inhibit the hydrogen peroxide (H(2)O(2))- and TNF-alpha-mediated activation of NF-kappa B and the release of IL-8 in human alveolar epithelial cells (A549). Treatment of A549 cells with H(2)O(2) (100 microM) and TNF-alpha (10 ng/ml) significantly increased NF-kappa B activation using a reporter assay. Ergothioneine inhibited both H(2)O(2)- and TNF-alpha-mediated activation of NF-kappa B. Both H(2)O(2) and TNF-alpha significantly increased IL-8 release, which was inhibited by pre-treatment of A549 cells with ergothioneine compared to the control untreated cells. Ergothioneine also abolished the transcriptional activation of IL-8 in an IL-8-chloramphenicol acetyltransferase (CAT) reporter system, transfected into A549 cells. This indicates a molecular mechanism for the anti-inflammatory effects of ergothioneine.

Nitric oxide-induced changes in intracellular zinc homeostasis are mediated by metallothionein/thionein

We hypothesized that metallothionein (MT), a cysteine-rich protein with a strong affinity for Zn(2+), plays a role in nitric oxide (NO) signaling events via sequestration or release of Zn(2+) by the unique thiolate clusters of the protein. Exposing mouse lung fibroblasts (MLF) to the NO donor S-nitrosocysteine resulted in 20-30% increases in fluorescence of the Zn(2+)-specific fluorophore Zinquin that were rapidly reversed by the Zn(2+) chelator N,N,N',N'-tetrakis-(2-pyridylmethyl)ethylenediamine. The absence of a NO-mediated increase in labile Zn(2+) in MLF from MT knockouts and its restoration after MT complementation by adenoviral gene transfer inferred a critical role for MT in the regulation of Zn(2+) homeostasis by NO. Additional data obtained in sheep pulmonary artery endothelial cells suggested a role for the apo form of MT, thionein (T), as a Zn(2+)-binding protein in intact cells, as overexpression of MT caused inhibition of NO-induced changes in labile Zn(2+) that were reversed by Zn(2+) supplementation. Furthermore, fluorescence-resonance energy-transfer data showed that overexpression of green fluorescent protein-modified MT prevented NO-induced conformational changes, which are indicative of Zn(2+) release from thiolate clusters. This effect was restored by Zn(2+) supplementation. Collectively, these data show that MT mediates NO-induced changes in intracellular Zn(2+) and suggest that the ratio of MT to T can regulate Zn(2+) homeostasis in response to nitrosative stress.

Novel thiols of prokaryotes

Glutathione metabolism is associated with oxygenic cyanobacteria and the oxygen-utilizing purple bacteria, but is absent in many other prokaryotes. This review focuses on novel thiols found in those bacteria lacking glutathione. Included are glutathione amide and its perthiol, produced by phototrophic purple sulfur bacteria and apparently involved in their sulfide metabolism. Among archaebacteria, coenzyme M (2-mercaptoethanesulfonic acid) and coenzyme B (7-mercaptoheptanoylthreonine phosphate) play central roles in the anaerobic production of CH4 and associated energy conversion by methanogens, whereas the major thiol in the aerobic phototrophic halobacteria is gamma-glutamylcysteine. The highly aerobic actinomycetes produce mycothiol, a conjugate of N-acetylcysteine with a pseudodisaccharide of glucosamine and myo-inositol, AcCys-GlcNalpha(1 --> 1)Ins, which appears to play an antioxidant role similar to glutathione. Ergothioneine, also produced by actinomycetes, remains a mystery despite many years of study. Available data on the biosynthesis and metabolism of these and other novel thiols is summarized and key areas for additional study are identified.

Comparative (13)C and (31)P NMR studies of the ligand exchange reactions of auranofin with ergothionine, imidazolidine-2-thione and diazinane-2-thione

The interaction of auranofin (Et(3)PAuSATg) with ergothionine (ErS), imidazolidine-2-thione (Imt) and diazinane-2-thione (Diaz) has been studied using (13)C and (31)P NMR spectroscopy. It is observed that these thiones are able to replace both Et(3)P and SATg(-) ligands simultaneously from gold(I) in auranofin forming >C [double bond] S-Au-SATg and [Et(3)P-Au-S [double bond] C<](+) type complexes. The displaced SATg(-) is oxidized to its disulfide (SATg)(2). However, some of the displaced Et(3)P is oxidized to Et(3)PO while the remaining reacts with thiones to form Et(3)P-S [double bond] C< species characterized by delta (31)P NMR of 1.0-1.5 ppm. The Et(3)PO resonance appeared in the 31P NMR spectrum, after 10 days of the addition of ErS, after 19 days of the addition of Imt and after 6 days of the addition of Diaz, to auranofin solution showing that the thiones react with auranofin very slowly.

Role of ergothioneine on S-nitrosoglutathione catabolism

Ergothioneine (ESH) is a low-molecular-mass thiol present in millimolar concentrations in a limited number of tissues, including erythrocytes, kidney, seminal fluid and liver; however, its biological function is still unclear. In the present study we investigated the role of ESH in the catabolism of S-nitrosoglutathione (GSNO). The results show that: (1) GSNO decomposition is strongly influenced by ESH (k"=0.178+/-0.032 M(-1) x s(-1)); (2) ammonia is the main nitrogen-containing compound generated by the reaction; and (3) nitrite is practically absent under both aerobic and anaerobic conditions. These findings are markedly different from those reported for the GSH-induced decomposition of GSNO, in which the nitrogen-containing end products are nitrite, ammonia and nitrous oxide (N(2)O) under aerobic conditions but nitrite, ammonia, nitric oxide (NO) and small quantities of hydroxylamine under anaerobic conditions. Considering the high concentration of ESH in specific cells, the reaction with GSNO should be considered as an important molecular event occurring in the cell.

Molecular crowding and viscosity as determinants of translational diffusion of metabolites in subcellular organelles

The role of molecular crowding and viscosity on the apparent translational diffusion coefficient (ADC) of small metabolites was investigated in different subcellular organelles using the pulse-field gradient spin-echo 1H NMR technique. ADCs of metabolites with increasing radius of gyration (0.7 A < RG < 4.5 A) were measured in the cytoplasm of rat or chicken erythrocytes, in the nucleus of chicken erythrocytes, and in isolated rat liver mitochondria. Metabolite ADCs in these systems were compared with the corresponding ADCs determined in model solutions of increasing bulk viscosity but different molecular crowding. For solutions having the same viscosity, metabolite ADCs decreased with increasing concentration of cosolutes. This effect is adequately described by the modified Stokes-Einstein relationship, ADC = k/RG (1 + 2.5Phi), where k is a constant for a given temperature and Phi is an obstruction factor reporting the fractional volume of solution occupied by cosolutes, a measure of the molecular crowding in the solution. Cytoplasmic values of Phi for metabolites of different sizes did not depend exclusively on metabolite RG but on additional factors including the chemical nature of the metabolite, the presence of diffusional barriers, and metabolite-specific binding sites. In the case of water, nuclear Phi values approached those of the extracellular space while mitochondrial Phi values were significantly higher than those of the cytoplasm. Taken together, these results reveal important differences in molecular crowding within the different subcellular compartments, suggesting considerable diffusional heterogeneity for small metabolites within the different intracellular organelles.

Antioxidant action of ergothioneine: assessment of its ability to scavenge peroxynitrite

The superoxide radical (O.2-) and nitric oxide (NO.) combine very rapidly to form peroxynitrite (ONOO-), a reactive tissue damaging nitrogen species thought to be involved in the pathology of several chronic diseases. The natural product ergothioneine protects against the nitration of tyrosine and the inactivation of alpha 1-antiproteinase by ONOO-. Ergothioneine merits further investigation as a biological and therapeutic antioxidant agent.

One-electron oxidation of ergothioneine and analogues investigated by pulse radiolysis: redox reaction involving ergothioneine and vitamin C

Redox reactions of endogenous and exogenous sulphur-containing compounds are involved in protection against oxidative damage arising from the incidence and/or treatment of many diseases, including cancer. We have investigated, via pulse radiolysis, the one-electron oxidation of ergothioneine, a molecule with antioxidant properties which is detected at millimolar concentrations in certain tissues and fluids subject to oxidative stress, including erythrocytes and plasma. The spectrum of the transient species, assigned to the product of one-electron oxidation, observed after reaction of ergothioneine with the oxidizing radicals OH., N3. and CCl3O2. has a maximum absorption at 520 nm and is very similar to that obtained by oxidation of analogous molecules such as 2-mercaptoimidazole, 1-methyl-2-mercaptoimidazole, S-methyl- and S,N-dimethyl-ergothioneine. In the presence of vitamin C, the oxidized form of ergothioneine is repaired by a rapid reduction (k = 6.3 x 10(8) M(-1).s(-1)) producing ascorbyl radicals. This co-operative interaction between ergothionine and ascorbate, similar to that previously observed between vitamin E and ascorbate, may contribute to essential biological redox protection.

Stability and nonreactivity of ergothioneine in human erythrocytes studied by 1H NMR

The N(CH3)3 resonance of ergothioneine in 1H spin-echo Fourier transform (SEFT) NMR spectra of red blood cells is usually a large singlet and it has been common practice to use this apparently unchanging resonance as an intensity reference. Recently, Reglinski et al. (Magn. Reson. Med. 6, 217-223 (1988)) have questioned this practice, reporting changes seen in the resonance in response to oxidative stress induced by arsenicals. We propose that the changes in the ergothioneine resonance that were reported are artifacts due to alterations in osmolality and magnetic susceptibility induced by the addition of nonisotonic solutions to red blood cell suspensions. These factors change the specific intensity of the intracellular resonances of all compounds. Ergothioneine was observed not to take part in any chemical reactions with arsenicals in free solution or in intact erythrocytes, and we conclude that ergothioneine may still be used as an internal intensity reference in 1H SEFT NMR spectra, bearing in mind the above physical factors.

Reduction of sperm whale ferrylmyoglobin by endogenous reducing agents: potential reducible loci of ferrylmyoglobin

The reactivity of the endogenous antioxidants ascorbate, ergothioneine, and urate toward the high oxidation state of sperm whale myoglobin, ferrylmyoglobin-formed upon oxidation of metmyoglobin by H2O2--was evaluated by optical spectroscopy and SDS-PAGE analysis. Depending on whether these antioxidants were present in the reaction mixture before or after the addition of H2O2 to a metmyoglobin suspension, two different effects were observed: (a) In the former instances, ascorbate, ergothioneine, and urate reduced efficiently the oxoferryl moiety in ferrylmyoglobin to metmyoglobin and prevented dimer formation, a process which requires intermolecular cross-link involving specific tyrosyl residues. In addition, all the reducing compounds inhibited--albeit with different efficiencies--dityorosine-dependent fluorescence build up produced via dimerization of photogenerated tyrosyl radicals. (b) In the latter instances, the antioxidants reduced the preformed sperm whale ferrylmyoglobin to a modified metmyoglobin, the spectral profile of which was characterized by a blue shift of the typical 633 nm absorbance of native metmyoglobin. In addition, under these experimental conditions, the antioxidants did not affect dimer formation, thus indicating the irreversible character of the process. The dimeric form of sperm whale myoglobin--separated from the monomeric form by gel electrophoresis of a solution in which ergothioneine was added to preformed ferrylmyoglobin--revealed optical spectral properties in the visible region identical to that of the modified myoglobin. This suggests that the dimeric form of the hemoprotein is redox active, inasmuch as the oxoferryl complex can be reduced to its ferric form. These results are discussed in terms of the potential reactivity of these endogenous antioxidants toward the reducible loci of ferrylmyoglobin, the oxoferryl moiety, and the apoprotein radical.

Zinc transfer from transcription factor IIIA fingers to thionein clusters

The rapid induction of thionein (apometallothionein) by many endogenous stimuli such as steroid hormones, cytokines, and second messengers suggests that this cysteine-rich, metal binding protein participates in an as yet undefined role in cellular regulatory processes. This study demonstrates with DNA and RNA binding assays and in vitro transcription measurements that thionein suppresses the binding of the Xenopus laevis zinc finger transcription factor IIIA (TFIIIA) to 5S RNA and to the 5S RNA gene and abrogates the capacity of TFIIIA to initiate the RNA polymerase III-catalyzed synthesis of 5S RNA. The effect is reversed by the addition of zinc and is not observed in the TFIIIA-independent transcription of a tRNA gene by the same RNA polymerase. In view of the strong tendency of thionein to complex posttransition metals such as zinc, one effect of its enhanced synthesis in vivo could be to reduce the intracellular disposability of zinc and thus modulate the actions of zinc-dependent enzymes and proteins, most notably those of the zinc finger transcription factors.

The antioxidant action of ergothioneine

Ergothioneine is a product of plant origin that accumulates in animal tissues. Its suggested ability to act as an antioxidant has been evaluated. Ergothioneine is a powerful scavenger of hydroxyl radicals (.OH) and an inhibitor of iron or copper ion-dependent generation of .OH from hydrogen peroxide (H2O2). It is also an inhibitor of copper ion-dependent oxidation of oxyhaemoglobin, and of arachidonic acid peroxidation promoted by mixtures of myoglobin (or haemoglobin) and H2O2. Ergothioneine is a powerful scavenger of hypochlorous acid, being able to protect alpha 1-antiproteinase against inactivation by this molecule. By contrast, it does not react rapidly with superoxide (O2-) or hydrogen peroxide (H2O2) and it does not inhibit microsomal lipid peroxidation in the presence of iron ions. Overall, our results show that ergothioneine at the concentrations present in vivo could act as an antioxidant.

The reduction of ferryl myoglobin by ergothioneine: a novel function for ergothioneine

In this paper, we demonstrate that ergothioneine (ES), a naturally occurring thiolhistidine, reduces ferrylmyoglobin (MbIV) to MbIII when the former (ferryl species) is produced by exposing either deoxy MbII or MbIII to H2O2. The reduction of MbIV to MbIII by ES yields the disulfide of ES which the addition of GSH promptly reduces back to ES. The addition of ES (100 microM) in the perfusion buffer of Langendorff rat heart preparations exposed to a brief period of ischemia prevents the myocardial damage (lactate dehydrogenase release) which accompanies reperfusion. The results of these experiments support a view that ES and its redox couple GSH might function in a Mb redox cycle.

Spin-echo 1H NMR detected response of ergothioneine to oxidative stress in the intact human erythrocyte

Human erythrocytes were subjected to oxidative stress using arsenicals. The study is a model for thiol-related redox processes observed in the etiology of diseases such as rheumatoid arthritis. Spin-echo NMR spectroscopy of the living cell was used to monitor the cellular biochemistry. Oxidation of glutathione and the first demonstrated response of ergothioneine to a chemical stimulus in a cell were observed. The reversible nature of the ergothioneine response is interpreted as an environmental rather than a chemical change.