A Rhodanese-Like Enzyme that Catalyzes Desulfination of Ergothioneine Sulfinic Acid

Many actinobacterial species contain structural genes for iron-dependent enzymes that consume ergothioneine by way of O2-dependent dioxygenation. The resulting product ergothioneine sulfinic acid is stable under physiological conditions unless cleavage to sulfur dioxide and trimethyl histidine is catalyzed by a dedicated desulfinase. This report documents that two types of ergothioneine sulfinic desulfinases have evolved by convergent evolution. One type is related to metal-dependent decarboxylases while the other belongs to the superfamily of rhodanese-like enzymes. Pairs of ergothioneine dioxygenases (ETDO) and ergothioneine sulfinic acid desulfinase (ETSD) occur in thousands of sequenced actinobacteria, suggesting that oxidative ergothioneine degradation is a common activity in this phylum.

Uncovering the roles of Mycobacterium tuberculosis melH in redox and bioenergetic homeostasis: implications for antitubercular therapy

Mycobacterium tuberculosis (Mtb), the pathogenic bacterium that causes tuberculosis, has evolved sophisticated defense mechanisms to counteract the cytotoxicity of reactive oxygen species (ROS) generated within host macrophages during infection. The melH gene in Mtb and Mycobacterium marinum (Mm) plays a crucial role in defense mechanisms against ROS generated during infection. We demonstrate that melH encodes an epoxide hydrolase and contributes to ROS detoxification. Deletion of melH in Mm resulted in a mutant with increased sensitivity to oxidative stress, increased accumulation of aldehyde species, and decreased production of mycothiol and ergothioneine. This heightened vulnerability is attributed to the increased expression of whiB3, a universal stress sensor. The absence of melH also resulted in reduced intracellular levels of NAD+, NADH, and ATP. Bacterial growth was impaired, even in the absence of external stressors, and the impairment was carbon source dependent. Initial MelH substrate specificity studies demonstrate a preference for epoxides with a single aromatic substituent. Taken together, these results highlight the role of melH in mycobacterial bioenergetic metabolism and provide new insights into the complex interplay between redox homeostasis and generation of reactive aldehyde species in mycobacteria.

IMPORTANCE

This study unveils the pivotal role played by the melH gene in Mycobacterium tuberculosis and in Mycobacterium marinum in combatting the detrimental impact of oxidative conditions during infection. This investigation revealed notable alterations in the level of cytokinin-associated aldehyde, para-hydroxybenzaldehyde, as well as the redox buffer ergothioneine, upon deletion of melH. Moreover, changes in crucial cofactors responsible for electron transfer highlighted melH's crucial function in maintaining a delicate equilibrium of redox and bioenergetic processes. MelH prefers epoxide small substrates with a phenyl substituted substrate. These findings collectively emphasize the potential of melH as an attractive target for the development of novel antitubercular therapies that sensitize mycobacteria to host stress, offering new avenues for combating tuberculosis.

Co-augmentation of a transport gene mfsT1 in Mycolicibacterium neoaurum with genome engineering to enhance ergothioneine production

Ergothioneine (EGT) is a rare thiohistidine derivative with exceptional antioxidant properties. The blood level of EGT is considered highly reliable predictors for cardiovascular diseases and mortality, yet animals lack the ability to synthesize this compound. Free plasmids have been previously used to overexpress genes involved in the EGT biosynthetic pathway of Mycolicibacterium neoaurum. Here, we tentatively introduced a putative transporter gene mfsT1 into high-copy plasmids and sharply increased the ratio of extracellular EGT concentration from 18.7% to 44.9%. Subsequently, an additional copy of egtABCDE, hisG, and mfsT1 was inserted into the genome with a site-specific genomic integration tool of M. neoaurum, leading a 2.7 times increase in EGT production. Co-enhancing the S-adenosyl-L-methionine regeneration pathway, or alternatively, the integration of three copies of egtABCDE, hisG and mfsT1 into the genome further increased the total EGT yield by 16.1% (64.6 mg/L) and 21.7% (67.7 mg/L), respectively. After 168-h cultivation, the highest titer reached 85.9 mg/L in the latter strain with three inserted copies. This study provided a solid foundation for genome engineering to increase the production of EGT in M. neoaurum.

Inflammation and Organic Cation Transporters Novel (OCTNs)

Inflammation is a physiological condition characterized by a complex interplay between different cells handled by metabolites and specific inflammatory-related molecules. In some pathological situations, inflammation persists underlying and worsening the pathological state. Over the years, two membrane transporters namely OCTN1 (SLC22A4) and OCTN2 (SLC22A5) have been shown to play specific roles in inflammation. These transporters form the OCTN subfamily within the larger SLC22 family. The link between these proteins and inflammation has been proposed based on their link to some chronic inflammatory diseases such as asthma, Crohn's disease (CD), and rheumatoid arthritis (RA). Moreover, the two transporters show the ability to mediate the transport of several compounds including carnitine, carnitine derivatives, acetylcholine, ergothioneine, and gut microbiota by-products, which have been specifically associated with inflammation for their anti- or proinflammatory action. Therefore, the absorption and distribution of these molecules rely on the presence of OCTN1 and OCTN2, whose expression is modulated by inflammatory cytokines and transcription factors typically activated by inflammation. In the present review, we wish to provide a state of the art on OCTN1 and OCTN2 transport function and regulation in relationships with inflammation and inflammatory diseases focusing on the metabolic signature collected in different body districts and gene polymorphisms related to inflammatory diseases.

Enzyme-Catalyzed Oxidative Degradation of Ergothioneine

Ergothioneine is a sulfur-containing metabolite that is produced by bacteria and fungi, and is absorbed by plants and animals as a micronutrient. Ergothioneine reacts with harmful oxidants, including singlet oxygen and hydrogen peroxide, and may therefore protect cells against oxidative stress. Herein we describe two enzymes from actinobacteria that cooperate in the specific oxidative degradation of ergothioneine. The first enzyme is an iron-dependent thiol dioxygenase that produces ergothioneine sulfinic acid. A crystal structure of ergothioneine dioxygenase from Thermocatellispora tengchongensis reveals many similarities with cysteine dioxygenases, suggesting that the two enzymes share a common mechanism. The second enzyme is a metal-dependent ergothioneine sulfinic acid desulfinase that produces Nα-trimethylhistidine and SO2 . The discovery that certain actinobacteria contain the enzymatic machinery for O2 -dependent biosynthesis and O2 -dependent degradation of ergothioneine indicates that these organisms may actively manage their ergothioneine content.

L-ergothioneine reduces mitochondrial-driven NLRP3 activation in gestational diabetes mellitus

BACKGROUND

Maternal hyperglycaemia has a significant impact on placental metabolism and mitochondrial function. The NLRP3 inflammasome is responsive to endogenous signals of mitochondrial dysfunction. We tested our hypothesis that mitochondrial dysfunction orchestrates activation of the NLRP3 inflammasome and contributes to inflammation in gestational diabetes mellitus (GDM).

METHODS

Fasting blood, omental and placental tissue were collected on the day of caesarean section from nulliparous women with normal glucose tolerant (NGT) (n = 30) and GDM (n = 27) pregnancies. Cell-free mitochondrial DNA (cf-mtDNA) copy number was quantified by real-time PCR. M1-like (CD14+CD86+CD206-) and M2-like (CD14+CD86+CD206+) macrophage populations were characterized by flow cytometry. Immunoblotting for protein expression of NLRP3, ASC and caspase-1 was performed in maternal BMI and age-matched tissue samples. IL-1β and IL-18 were measured by multiplex ELISA. Placental explants from GDM participants were cultured for 24 h with 1 mM L-ergothioneine (antioxidant) and 1 µM MCC950 (NLRP3 inhibitor).

RESULTS

Cf-mtDNA copy numbers were significantly higher in GDM compared to NGT participants (p = 0.002). Placental populations of CD14+ (p = 0.02) and CD14+CD86+CD206- (p = 0.03) macrophages produced significantly increased levels of mitochondrial superoxide in GDM compared to NGT participants. Placental production of IL-18 (p = 0.04) was significantly increased in GDM. This increase in placental IL-18 was attenuated by treatment with 1 µM MCC950 (p = 0.0005), and 1 mM L-ergothioneine (p = 0.007).

CONCLUSION

Placental inflammation is significantly increased in women with GDM. Furthermore, this increase may be initiated by elevated production of mitochondrial superoxide by macrophage subpopulations and orchestrated by the NLRP3 inflammasome. The mitochondrial antioxidant, L-ergothioneine, ameliorates NLRP3-induced placental inflammation in GDM, identifying a potential therapeutic role.

Effect of Selected Antioxidants on the In Vitro Aging of Human Fibroblasts

The modification of the replicative lifespan (RLS) of fibroblasts is of interest both from a knowledge point of view and for the attenuation of skin aging. The effect of six antioxidants at a concentration of 1 μM on the replicative lifespan of human dermal fibroblasts was studied. The nitroxide 4-hydroxy-TEMPO (TEMPOL), ergothioneine, and Trolox extended the replicative lifespan (RLS) (40 ± 1 population doublings (PD)) by 7 ± 2, 4 ± 1, and 3 ± 1 PD and lowered the expression of p21 at late passages. Coumaric acid, curcumin and resveratrol did not affect the RLS . The level of reactive oxygen species (ROS) was decreased or not affected by the antioxidants although TEMPOL and coumaric acid decreased the level of glutathione. Only ergothioneine and resveratrol decreased the level of protein carbonylation. The antioxidants that could prolong the RLS elevated the mitochondrial membrane potential. Protecting the activity of mitochondria seems to be important for maintaining the replicative capacity of fibroblasts.

Ergothioneine Prevents Neuronal Cell Death Caused by the Neurotoxin 6-Hydroxydopamine

Neuronal cell death is a key mechanism involved in the development and exacerbation of Parkinson's disease (PD). The excessive production of reactive oxygen species (ROS) is a major cause leading to neuronal death; therefore, compounds that prevent oxidative stress-dependent neuronal death may be promising as a preventive method for PD. Ergothioneine is a natural amino acid with antioxidant properties, and its protective functions in the body are attracting attention. However, there has been no investigation into the protective functions of ergothioneine using in vivo and in vitro PD models. Thus, in this study, we analyzed the efficacy of ergothioneine against 6-hydroxydopamine (6-OHDA)-dependent neuronal cell death using immortalized hypothalamic neurons (GT1-7 cells). First, we found that ergothioneine prevents 6-OHDA-dependent neuronal cell death by suppressing ROS overproduction in GT1-7 cells. The cytoprotective effect of ergothioneine was partially abolished by verapamil, an inhibitor of OCTN1, which is involved in ergothioneine uptake. Furthermore, ergothioneine-rich Rice-koji (Ergo-koji) showed cytoprotective and antioxidant effects similar to those of ergothioneine. Taken together, these results suggest that ergothioneine or foods containing ergothioneine may be an effective method for preventing the development and progression of PD.

Structural insights into a novel nonheme iron-dependent oxygenase in selenoneine biosynthesis

Selenoneine (SEN) is a natural histidine derivative with radical-scavenging activity and shows higher antioxidant potential than its sulfur-containing isolog ergothioneine (EGT). Recently, the SEN biosynthetic pathway in Variovorax paradoxus was reported. Resembling EGT biosynthesis, the committed step of SEN synthesis is catalyzed by a nonheme Fe-dependent oxygenase termed SenA. This enzyme catalyzes oxidative carbon‑selenium (C-Se) bond formation to conjugate N-α-trimethyl histidine (TMH) and selenosugar to yield selenoxide; the process parallels the EGT biosynthetic route, in which sulfoxide synthases known as EgtB members catalyze the conjugation of TMH and cysteine or γ-glutamylcysteine to afford sulfoxides. Here, we report the crystal structures of SenA and its complex with TMH and thioglucose (SGlc), an analog of selenoglucose (SeGlc) at high resolution. The overall structure of SenA adopts the archetypical fold of EgtB, which comprises a DinB-like domain and an FGE-like domain. While the TMH-binding site is highly conserved to that of EgtB, a various substrate-enzyme interaction network in the selenosugar-binding site of SenA features a number of water-mediated hydrogen bonds. The obtained structural information is beneficial for understanding the mechanism of SenA-mediated C-Se bond formation.

Structure of mycobacterial ergothioneine-biosynthesis C-S lyase EgtE

L-ergothioneine is widely distributed among various microbes to regulate their physiology and pathogenicity within complex environments. One of the key steps in the ergothioneine-biosynthesis pathway, the C-S bond cleavage reaction, uses the pyridoxal 5'-phosphate dependent C-S lyase to produce the final product L-ergothioneine. Here, we present the crystallographic structure of the ergothioneine-biosynthesis C-S lyase EgtE from Mycobacterium smegmatis (MsEgtE) represents the first published structure of ergothioneine-biosynthesis C-S lyases in bacteria and shows the effects of active site residues on the enzymatic reaction. The MsEgtE and the previously reported ergothioneine-biosynthesis C-S lyase Egt2 from Neurospora crassa (NcEgt2) fold similarly. However, discrepancies arise in terms of substrate recognition, as observed through sequence and structure comparison of MsEgtE and NcEgt2. The structural-based sequence alignment of the ergothioneine-biosynthesis C-S lyase from fungi and bacteria shows clear distinctions among the recognized substrate residues, but Arg348 is critical and an extremely conserved residue for substrate recognition. The α14 helix is exclusively found in the bacteria EgtE, which represent the most significant difference between bacteria EgtE and fungi Egt2, possibly resulting from the convergent evolution of bacteria and fungi.

Ergothioneine: an underrecognised dietary micronutrient required for healthy ageing?

Ergothioneine is a naturally occurring amino acid and thiol antioxidant found in high amounts in mushrooms and fermented foods. Humans and animals acquire ergothioneine from the diet through the pH-dependent activity of a membrane transporter, the large solute carrier 22A member 4 (SLC22A4), expressed on the apical membrane of the small intestine. The SLC22A4 transporter also functions in the renal reabsorption of ergothioneine in the kidney, with avid absorption and retention of ergothioneine from the diet observed in both animals and humans. Ergothioneine is capable of scavenging a diverse range of reactive oxygen and nitrogen species, has metal chelation properties, and is predicted to directly regulate nuclear factor erythroid 2-related factor 2 (Nrf2) activity. Although not lethal, the genetic knockout of the SLC22A4 gene in multiple organisms increases susceptibility to oxidative stress, damage and inflammation; in agreement with a large body of preclinical data suggesting the physiological function of ergothioneine is as a cellular antioxidant and cytoprotectant agent. In humans, blood levels of ergothioneine decline after the age of 60 years, and lower levels of ergothioneine are associated with more rapid cognitive decline. Conversely, high plasma ergothioneine levels have been associated with significantly reduced cardiovascular mortality and overall mortality risks. In this horizon’s manuscript, we review evidence suggesting critical roles for dietary ergothioneine in healthy ageing and the prevention of cardiometabolic disease. We comment on some of the outstanding research questions in the field and consider the question of whether or not ergothioneine should be considered a conditionally essential micronutrient.

A microbial transporter of the dietary antioxidant ergothioneine

Low-molecular-weight (LMW) thiols are small-molecule antioxidants required for the maintenance of intracellular redox homeostasis. However, many host-associated microbes, including the gastric pathogen Helicobacter pylori, unexpectedly lack LMW-thiol biosynthetic pathways. Using reactivity-guided metabolomics, we identified the unusual LMW thiol ergothioneine (EGT) in H. pylori. Dietary EGT accumulates to millimolar levels in human tissues and has been broadly implicated in mitigating disease risk. Although certain microorganisms synthesize EGT, we discovered that H. pylori acquires this LMW thiol from the host environment using a highly selective ATP-binding cassette transporter-EgtUV. EgtUV confers a competitive colonization advantage in vivo and is widely conserved in gastrointestinal microbes. Furthermore, we found that human fecal bacteria metabolize EGT, which may contribute to production of the disease-associated metabolite trimethylamine N-oxide. Collectively, our findings illustrate a previously unappreciated mechanism of microbial redox regulation in the gut and suggest that inter-kingdom competition for dietary EGT may broadly impact human health.

First evidence of dermo-protective activity of marine sulfur-containing histidine compounds

Among natural products, ovothiol (ovo), produced by marine invertebrates, bacteria, and microalgae, is receiving increasing interest for its unique antioxidant properties. Recently, ovo has been shown to exhibit anti-inflammatory activity in an in vitro model of endothelial dysfunction and in an in vivo model of liver fibrosis. The aim of this study was to evaluate the effect of ovo and its precursor 5-thiohistidine (5-thio) in comparison with ergothioneine (erg), in human skin cells and tissues upon inflammation. We used both an in vitro and ex vivo model of human skin, represented by a keratinocytes cell line (HaCaT) and skin biopsies, respectively. We observed that ovo, 5-thio, and erg were not cytotoxic in HaCaT cells, but instead exerted a protective function against TNF-α -induced inflammation. In order to get insights on their mechanism of action, we performed western blot analysis of ERK and JNK, as well as sub-cellular localization of Nrf2, a key mediator of the anti-inflammatory response. The results indicated that the pre-treatment with ovo, 5-thio, and erg differently affected the phosphorylation of ERK and JNK. However, all the three molecules promoted the accumulation of Nrf2 in the nucleus of HaCaT cells. In addition, gene expression analysis by RTqPCR and ELISA assays performed in ex vivo human skin tissues pre-treated with thiohistidines and then inflamed with IL-1β revealed a significant downregulation of IL-8, TNF-α and COX-2 genes and a concomitant significant decrease in the cytokines IL-6, IL-8 and TNF-α production. Moreover, the protective action of ovo and 5-thio resulted to be stronger when compared with dexamethasone, a corticosteroid drug currently used to treat skin inflammatory conditions. Our findings suggest that ovo and 5-thio can ameliorate skin damage and may be used to develop natural skin care products to prevent the inflammatory status induced by environmental stressors and aging.

[Recent progress in ergothioneine biosynthesis: a review]

Ergothioneine is a multifunctional physiological cytoprotector, with broad application in foods, beverage, medicine, cosmetics and so on. Biosynthesis is an increasingly favored method in the production of ergothioneine. This paper summarizes the new progress in the identification of key pathways, the mining of key enzymes, and the development of natural edible mushroom species and high-yield engineering strains for ergothioneine biosynthesis in recent years. Through this review, we aim to reveal the molecular mechanism of ergothioneine biosynthesis and then employ the methods of fermentation engineering, metabolic engineering, and synthetic biology to greatly increase the yield of ergothioneine.

OCTN1: A Widely Studied but Still Enigmatic Organic Cation Transporter Linked to Human Pathology and Drug Interactions

The Novel Organic Cation Transporter, OCTN1, is the first member of the OCTN subfamily; it belongs to the wider Solute Carrier family SLC22, which counts many members including cation and anion organic transporters. The tertiary structure has not been resolved for any cation organic transporter. The functional role of OCNT1 is still not well assessed despite the many functional studies so far conducted. The lack of a definitive identification of OCTN1 function can be attributed to the different experimental systems and methodologies adopted for studying each of the proposed ligands. Apart from the contradictory data, the international scientific community agrees on a role of OCTN1 in protecting cells and tissues from oxidative and/or inflammatory damage. Moreover, the involvement of this transporter in drug interactions and delivery has been well clarified, even though the exact profile of the transported/interacting molecules is still somehow confusing. Therefore, OCTN1 continues to be a hot topic in terms of its functional role and structure. This review focuses on the most recent advances on OCTN1 in terms of functional aspects, physiological roles, substrate specificity, drug interactions, tissue expression, and relationships with pathology.

Functional identification of ergothioneine transporter in rainbow trout (Oncorhynchus mykiss)

(2S)-3-(2-sulfanylidene-1,3-dihydroimidazol-4-yl)-2-(trimethylazaniumyl)propanoate (ergothioneine, ET) is hydrophilic antioxidant produced only by certain low-level organisms, but has been reported in the organs of some animals upon dietary intake, facilitated by the ergothioneine transporter (ETT). In this study, it was hypothesised that ETT is involved in the uptake of ET from diet in salmonids. The mechanism of ET uptake was evaluated through knockdown of candidate gene encoding ETT in a cell line (RTG-2) from rainbow trout (Oncorhynchus mykiss). ETT gene expression in blood cells and certain tissues from rainbow trout was also investigated as ET from the diet is expected to be carried over to the muscle. Knockdown of an ETT candidate (E1) in RTG-2 cells resulted in a remarkable decrease in E1 mRNA expression; uptake of ET was lower in the knocked group than in the control group suggesting that E1 functions as an ETT for rainbow trout. Furthermore, the expression of ETT gene in different tissues including the muscle points to ET uptake from the diet to the muscle of salmonids. In conclusion, this study partly reveals the possible pathway underlying ET uptake from the diet and its deposition in the muscle of edible fish species.

Carnitine/organic cation transporter 1 precipitates the progression of interstitial fibrosis through oxidative stress in diabetic nephropathy in mice

Carnitine/organic cation transporter 1 (OCTN1) is the only known uptake transporter for ergothioneine which is a food-derived strong antioxidant amino acid that is absorbed by OCTN1. We previously reported the roles of OCTN1/ergothioneine in the progression of kidney fibrosis in ischemic kidney disease. In this study, we evaluated the roles of OCTN1 in the progression of diabetic kidney disease. A diabetic kidney disease model was induced in octn1 knockout and wild-type mice by streptozotocin (STZ). Oxidative stress, represented by urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), were higher in the octn1 knockout mice. Azan- and Sirius red-positive areas increased significantly in the octn1 knockout mice. Gene expression was evaluated by cluster analysis, and shown to be different in the octn1 knockout mice compared with the wild-type mice. In a pathway analysis, the pathway associated with the cytoskeleton and cell adhesion increased. In accordance with interstitial fibrosis in octn1 knockout mice, gene expression of moesin in the injured kidney, known as an associated protein of cytoskeleton and cell membranes, was doubled 28 weeks after STZ injection. In addition, the moesin protein was expressed in a part of α-SMA-positive renal tubular epithelial cells. These findings were confirmed by cultured murine proximal tubular epithelial cells: The expression of moesin was induced under oxidative stress with hydrogen peroxide. These data indicate that OCTN1 would play some roles in progression of interstitial fibrosis under oxidative stress via moesin expression in diabetic kidney disease.

Regeneration of ergothioneine after reaction with singlet oxygen

Ergothioneine (ET), an imidazole-2-thione derivative of histidine betaine, is generally considered an antioxidant. Important antioxidants are typically regenerated from their oxidized products, to prevent the interceptors from being lost after a single chemical reaction with a reactive oxygen species. However, no mechanism for the complete regeneration of ET has yet been uncovered. Here we define a non-enzymatic multi-step cycle for the regeneration of ET after reaction with singlet oxygen (¹O₂). All reaction steps were verified by density functional theory computations. Four molecules of GSH are used per turn to detoxify ¹O₂ to water. Pure ¹O₂ was generated by thermolysis at 37 °C of the endoperoxide DHPNO₂. Addition of 1 mM ET to 10 mM DHPNO₂ and 10 mM GSH increased the production of oxidized GSH (GSSG), measured by LC-MS/MS, by a factor of 26 (water) and 28 (D₂O), respectively. In the same assay, the ring of ET alone was able to drive the cycle at equal speed; thus, the zwitterionic amino acid backbone was not involved. Our data suggest that ET reacts at least 4-fold faster with ¹O₂ than ascorbic acid. ET must now be viewed as tightly linked with the GSH/GSSG redox couple. The necessary thiol foundation is present in all mammalian and vertebrate cells, and also in all species that generate ET, such as cyanobacteria, mycobacteria, and fungi. Regeneration provides a decisive advantage for ET over other reactive, but non-recoverable, compounds. Our findings substantiate the importance of ET for the eradication of noxious ¹O₂.

Knockout of the ergothioneine transporter ETT in zebrafish results in increased 8-oxoguanine levels

Ergothioneine (ET) is a natural compound that humans and other vertebrates must absorb from dietary sources. In general, ET is considered an intracellular antioxidant. However, the precise physiological purpose of ET and the consequences of ET deficiency are still unclear. The ergothioneine transporter ETT (human gene symbol SLC22A4) is a highly specific transporter for the uptake of ET. Here, we sought to identify and knock out ETT from zebrafish (Danio rerio) to determine the function of ET. We cloned and assayed three related proteins from zebrafish, only one of which catalyzed the uptake of ET. RT-PCR analysis revealed that the protein is strongly expressed in the skin, brain, kidney, intestine, and eye. In ETT-knockout animals generated by retroviral insertion into exon 1, ET content was reduced by more than 1000-fold compared to the wild type. Thus, ETT is the sole transporter responsible for uptake of ET into zebrafish. ETT-knockout fish did not exhibit obvious differences in morphology or behavior. In whole-fish homogenates, an increase in 4-hydroxy-2,3-trans-nonenal and malondialdehyde was observed, but only after stress caused by incubation with Pb(2+) or Cu(2+). Comparison of unstressed fish at the level of small molecules by LC-MS difference shading revealed a 3.8-fold increase in 8-oxoguanine (8-oxo-7,8-dihydroguanine) in the skin of ETT-knockout animals. Our knockout represents a new model for examining the consequences of complete absence of ET. Based on the phenotype observed here, we hypothesize that the specific purpose of ET could be to eliminate singlet oxygen.

Bioinformatic and biochemical characterizations of C-S bond formation and cleavage enzymes in the fungus Neurospora crassa ergothioneine biosynthetic pathway

Ergothioneine is a histidine thiol derivative. Its mycobacterial biosynthetic pathway has five steps (EgtA-E catalysis) with two novel reactions: a mononuclear nonheme iron enzyme (EgtB) catalyzed oxidative C-S bond formation and a PLP-mediated C-S lyase (EgtE) reaction. Our bioinformatic and biochemical analyses indicate that the fungus Neurospora crassa has a more concise ergothioneine biosynthetic pathway because its nonheme iron enzyme, Egt1, makes use of cysteine instead of γ-Glu-Cys as the substrate. Such a change of substrate preference eliminates the competition between ergothioneine and glutathione biosyntheses. In addition, we have identified the N. crassa C-S lyase (NCU11365) and reconstituted its activity in vitro, which makes the future ergothioneine production through metabolic engineering feasible.

Organic cation transporter-mediated ergothioneine uptake in mouse neural progenitor cells suppresses proliferation and promotes differentiation into neurons

The aim of the present study is to clarify the functional expression and physiological role in neural progenitor cells (NPCs) of carnitine/organic cation transporter OCTN1/SLC22A4, which accepts the naturally occurring food-derived antioxidant ergothioneine (ERGO) as a substrate in vivo. Real-time PCR analysis revealed that mRNA expression of OCTN1 was much higher than that of other organic cation transporters in mouse cultured cortical NPCs. Immunocytochemical analysis showed colocalization of OCTN1 with the NPC marker nestin in cultured NPCs and mouse embryonic carcinoma P19 cells differentiated into neural progenitor-like cells (P19-NPCs). These cells exhibited time-dependent [³H]ERGO uptake. These results demonstrate that OCTN1 is functionally expressed in murine NPCs. Cultured NPCs and P19-NPCs formed neurospheres from clusters of proliferating cells in a culture time-dependent manner. Exposure of cultured NPCs to ERGO or other antioxidants (edaravone and ascorbic acid) led to a significant decrease in the area of neurospheres with concomitant elimination of intracellular reactive oxygen species. Transfection of P19-NPCs with small interfering RNA for OCTN1 markedly promoted formation of neurospheres with a concomitant decrease of [³H]ERGO uptake. On the other hand, exposure of cultured NPCs to ERGO markedly increased the number of cells immunoreactive for the neuronal marker βIII-tubulin, but decreased the number immunoreactive for the astroglial marker glial fibrillary acidic protein (GFAP), with concomitant up-regulation of neuronal differentiation activator gene Math1. Interestingly, edaravone and ascorbic acid did not affect such differentiation of NPCs, in contrast to the case of proliferation. Knockdown of OCTN1 increased the number of cells immunoreactive for GFAP, but decreased the number immunoreactive for βIII-tubulin, with concomitant down-regulation of Math1 in P19-NPCs. Thus, OCTN1-mediated uptake of ERGO in NPCs inhibits cellular proliferation via regulation of oxidative stress, and also promotes cellular differentiation by modulating the expression of basic helix-loop-helix transcription factors via an unidentified mechanism different from antioxidant action.

Regioselectivity of the oxidative C-S bond formation in ergothioneine and ovothiol biosyntheses

Ergothioneine (5) and ovothiol (8) are two novel thiol-containing natural products. Their C-S bonds are formed by oxidative coupling reactions catalyzed by EgtB and OvoA enzymes, respectively. In this work, it was discovered that in addition to catalyzing the oxidative coupling between histidine and cysteine (1 → 6 conversion), OvoA can also catalyze a direct oxidative coupling between hercynine (2) and cysteine (2 → 4 conversion), which can shorten the ergothioneine biosynthetic pathway by two steps.

Metabolic effect of an exogenous gene on transgenic Beauveria bassiana using liquid chromatography-mass spectrometry-based metabolomics

Genetic modification of Beauveria bassiana with the scorpion neurotoxin aaIT gene can distinctly increase its insecticidal activity, whereas the effect of this exogenous gene on the metabolism of B. bassiana is unknown until now. Thus, we investigate the global metabolic profiling of mycelia and conidia of transgenic and wild-type B. bassiana by liquid chromatography-mass spectrometry (LC-MS). Principal component analysis (PCA) and orthogonal projection to latent structure discriminant analysis (OPLS-DA) reveal clear discrimination of wild-type mycelia and conidia from transgenic mycelia and conidia. The decrease of glycerophospholipids, carnitine, and fatty acids and the increase of oxylipins, glyoxylate, pyruvic acid, acetylcarnitine, fumarate, ergothioneine, and trehalose in transgenic mycelia indicate the enhanced oxidative reactions. In contrast, most metabolites related to oxidative stress are not altered significantly in conidia, which implies that there will be no significant oxidative stress reaction when the aaIT gene is quiescent in cells.

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.