Ergothioneine-Sodium Hyaluronate Dressing: A Promising Approach for Protecting against Radiation-Induced Skin Injury

Radiotherapy commonly causes damage to healthy tissues, particularly radiation-induced skin injury (RISI) that affects a significant majority of patients undergoing radiotherapy. Effective treatments for RISI are lacking. This study focuses on the pathogenesis of RISI, which primarily involves oxidative stress. Excessive reactive oxygen species (ROS) generation during radiation induces damage to biological macromolecules, triggering oxidative stress and inflammation. To address this, ergothioneine (EGT), a natural and biocompatibile thiol compound with excellent antioxidant activity, is explored as a potential radiation-protective agent. By utilizing its specific transport and absorption in the skin tissue, as well as its efficient and stable clearance of radiation-induced "ROS storm", EGT is combined with sodium hyaluronate (NaHA) to develop a novel radiation protective dressing suitable for the skin. This EGT-NaHA dressing demonstrates an effective ability to scavenge free radicals and reduce oxidative stress in vitro and in vivo, reducing cellular apoptosis and inflammation. These results demonstrate the protective properties of EGT against RISI, with far-reaching implications for research and development in the field of radioprotection.

Hydrogen Bonding Shuts Down Tunneling in Hydroxycarbenes: A Gas-Phase Study by Tandem-Mass Spectrometry, Infrared Ion Spectroscopy, and Theory

Hydroxycarbenes can be generated and structurally characterized in the gas phase by collision-induced decarboxylation of α-keto carboxylic acids, followed by infrared ion spectroscopy. Using this approach, we have shown earlier that quantum-mechanical hydrogen tunneling (QMHT) accounts for the isomerization of a charge-tagged phenylhydroxycarbene to the corresponding aldehyde in the gas phase and above room temperature. Herein, we report the results of our current study on aliphatic trialkylammonio-tagged systems. Quite unexpectedly, the flexible 3-(trimethylammonio)propylhydroxycarbene turned out to be stable─no H-shift to either aldehyde or enol occurred. As supported by density functional theory calculations, this novel QMHT inhibition is due to intramolecular H-bonding of a mildly acidic α-ammonio C-H bonds to the hydroxyl carbene's C-atom (C:···H-C). To further support this hypothesis, (4-quinuclidinyl)hydroxycarbenes were synthesized, whose rigid structure prevents this intramolecular H-bonding. The latter hydroxycarbenes underwent "regular" QMHT to the aldehyde at rates comparable to, e.g., methylhydroxycarbene studied by Schreiner et al. While QMHT has been shown for a number of biological H-shift processes, its inhibition by H-bonding disclosed here may serve for the stabilization of highly reactive intermediates such as carbenes, even as a mechanism for biasing intrinsic selectivity patterns.

Isotope-labeled ergothioneine clarifies the mechanism of reaction with singlet oxygen

Recently we have uncovered a non-enzymatic multi-step cycle for the regeneration of ergothioneine (ET), after reaction with noxious singlet oxygen (¹O₂), by glutathione (GSH). When living cells were loaded with ET labeled with deuterium and N-15 atoms (D5-ET) and exposed to light in the presence of a photosensitizer, no loss of deuterium at position 5 of the imidazole ring was observed, in contradiction to our previous mechanistic proposal. Therefore, it was necessary to reexamine the in vitro products of ET and ¹O₂ by liquid chromatography coupled to high resolution mass spectrometry. Pure ¹O₂ was generated by thermolysis at 37 °C of the endoperoxide DHPNO₂. The use of D5-ET enabled us to revise and extend the reaction scheme. On the main pathway, ¹O₂ attacks the imidazole ring, and the hydroperoxide intermediates are reduced rapidly by ET or GSH via different mechanisms. The intramolecular water elimination from the 5-hydroperoxide described previously is slower and not a part of the cycle. On another side path, ¹O₂ attacks the sulfur of ET to form a sulfine (S-oxide). The reduction of the sulfine also allows for the complete regeneration of ET. Experiments with methanol instead of water as solvent revealed that, in the absence of GSH, ET was attacked 6 times more frequently at the ring than at the sulfur. In the presence of 1 mM GSH or higher, both side paths were abandoned. ET efficiently captures ¹O₂ with its ring and can then be regenerated to a large extent by GSH, without enzyme involvement.

Safe and Effective Antioxidant: The Biological Mechanism and Potential Pathways of Ergothioneine in the Skin

Ergothioneine, a sulfur-containing micromolecular histidine derivative, has attracted increasing attention from scholars since it was confirmed in the human body. In the human body, ergothioneine is transported and accumulated specifically through OCTN-1, especially in the mitochondria and nucleus, suggesting that it can target damaged cells and tissues as an antioxidant. It shows excellent antioxidant, anti-inflammatory effects, and anti-aging properties, and inhibits melanin production. It is a mega antioxidant that may participate in the antioxidant network system and promote the reducing glutathione regeneration cycle. This review summarizes studies on the antioxidant effects of ergothioneine on various free radicals in vitro to date and systematically introduces its biological activities and potential mechanisms, mostly in dermatology. Additionally, the application of ergothioneine in cosmetics is briefly summarized. Lastly, we propose some problems that require solutions to understand the mechanism of action of ergothioneine. We believe that ergothioneine has good prospects in the food and cosmetics industries, and can thus meet some needs of the health and beauty industry.

A Single Aspergillus fumigatus Gene Enables Ergothioneine Biosynthesis and Secretion by Saccharomyces cerevisiae

The naturally occurring sulphur-containing histidine derivative, ergothioneine (EGT), exhibits potent antioxidant properties and has been proposed to confer human health benefits. Although it is only produced by select fungi and prokaryotes, likely to protect against environmental stress, the GRAS organism Saccharomyces cerevisiae does not produce EGT naturally. Herein, it is demonstrated that the recombinant expression of a single gene, Aspergillus fumigatus egtA, in S. cerevisiae results in EgtA protein presence which unexpectedly confers complete EGT biosynthetic capacity. Both High Performance Liquid Chromatography (HPLC) and LC−mass spectrometry (MS) analysis were deployed to detect and confirm EGT production in S. cerevisiae. The localisation and quantification of the resultant EGT revealed a significantly (p < 0.0001) larger quantity of EGT was extracellularly present in culture supernatants than intracellularly accumulated in 96 h yeast cultures. Methionine addition to cultures improved EGT production. The additional expression of two candidate cysteine desulfurases from A. fumigatus was thought to be required to complete EGT biosynthesis, namely AFUA_2G13295 and AFUA_3G14240, termed egt2a and egt2b in this study. However, the co-expression of egtA and egt2a in S. cerevisiae resulted in a significant decrease in the observed EGT levels (p < 0.05). The AlphaFold prediction of A. fumigatus EgtA 3-Dimensional structure illuminates the bidomain structure of the enzyme and the opposing locations of both active sites. Overall, we clearly show that recombinant S. cerevisiae can biosynthesise and secrete EGT in an EgtA-dependent manner which presents a facile means of producing EGT for biotechnological and biomedical use.

Matching chemical properties to molecular biological activities opens a new perspective on L-ergothioneine

L-ergothioneine is a low-molecular weight natural product, the chemical structure of which comprises oxygen-, nitrogen- and sulfur-containing functional groups. This gives L-ergothioneine specific physicochemical properties and allows to better understanding its chemical reactivity, which is primarily due to the 2-thio-imidazole group. Here, I review how different modes of chemical reactivity account for the reported molecular biological activities of L-ergothioneine. By matching the physicochemical properties to the biological properties of L-ergothioneine, a new perspective of the function and the mode of action of this enigmatic molecule emerges into the limelight.

From QCEIMS to QCxMS: A Tool to Routinely Calculate CID Mass Spectra Using Molecular Dynamics

Mass spectrometry (MS) is a powerful tool in chemical research and substance identification. For the computational modeling of electron ionization MS, we have developed the quantum-chemical electron ionization mass spectra (QCEIMS) program. Here, we present an extension of QCEIMS to calculate collision-induced dissociation (CID) spectra. The more general applicability is accounted for by the new name QCxMS, where "x" refers to EI or CID. To this end, fragmentation and rearrangement reactions are computed "on-the-fly" in Born-Oppenheimer molecular dynamics (MD) simulations with the semiempirical GFN2-xTB Hamiltonian, which provides an efficient quantum mechanical description of all elements up to Z = 86 (Rn). Through the explicit modeling of multicollision processes between precursor ions and neutral gas atoms as well as temperature-induced decomposition reactions, QCxMS provides detailed insight into the collision kinetics and fragmentation pathways. In combination with the CREST program to determine the preferential protonation sites, QCxMS becomes the first standalone MD-based program that can predict mass spectra based solely on molecular structures as input. We demonstrate this for six organic molecules with masses ranging from 159 to 296 Da, for which QCxMS yields CID spectra in reasonable agreement with experiments.

Breslow Intermediates (Amino Enols) and Their Keto Tautomers: First Gas-Phase Characterization by IR Ion Spectroscopy

Breslow intermediates (BIs) are the crucial nucleophilic amino enol intermediates formed from electrophilic aldehydes in the course of N-heterocyclic carbene (NHC)-catalyzed umpolung reactions. Both in organocatalytic and enzymatic umpolung, the question whether the Breslow intermediate exists as the nucleophilic enol or in the form of its electrophilic keto tautomer is of utmost importance for its reactivity and function. Herein, the preparation of charge-tagged Breslow intermediates/keto tautomers derived from three different types of NHCs (imidazolidin-2-ylidenes, 1,2,4-triazolin-5-ylidenes, thiazolin-2-ylidenes) and aldehydes is reported. An ammonium charge tag is introduced through the aldehyde unit or the NHC. ESI-MS IR ion spectroscopy allowed the unambiguous conclusion that in the gas phase, the imidazolidin-2-ylidene-derived BI indeed exists as a diamino enol, while both 1,2,4-triazolin-5-ylidenes and thiazolin-2-ylidenes give the keto tautomer. This result coincides with the tautomeric states observed for the BIs in solution (NMR) and in the crystalline state (XRD), and is in line with our earlier calculations on the energetics of BI keto-enol equilibria.

Hydrogen tunneling avoided: enol-formation from a charge-tagged phenyl pyruvic acid derivative evidenced by tandem-MS, IR ion spectroscopy and theory

A charge-tagged phenyl pyruvic acid derivative was investigated by tandem-MS, infrared (IR) ion spectroscopy and theory. The tailor-made precursor ions efficiently lose CO₂ in collision induced dissociation (CID) experiments, offering access to study the secondary decay reactions of the product ions. IR ion spectroscopy provides evidence for the formation of an enol acid precursor ion structure in the gas phase and indicates the presence of enol products formed after CO₂ loss. Extensive DFT computations however, suggest intermediate generation of hydroxycarbene products, which in turn rearrange in a secondary process to the enol ions detected by IR ion spectroscopy. Quantum mechanical tunneling of the hydroxycarbene can be excluded since no evidence for aldehyde product ion formation could be found. This finding is in contrast to the behavior of methylhydroxycarbene, which cleanly penetrates the energy barrier to form exclusively acetaldehyde at cryogenic temperatures in an argon matrix via quantum mechanical hydrogen tunneling. The results presented here are attributed to the highly excited energy levels of the product ions formed by CID in combination with different barrier heights of the competing reaction channels, which allow exclusive access over one energy barrier leading to the formation of the enol tautomer ions observed.

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.

Selecting and identifying gas-phase protonation isomers of nicotineH+ using combined laser, ion mobility and mass spectrometry techniques

Protonation isomers of gas-phase nicotineH⁺ are separated and assigned using a combination of FAIMS and UV photodissociation action spectroscopy.

Substrate Selectivity Check of the Ergothioneine Transporter

The candidate vitamin ergothioneine (ET) is a unique antioxidant. Expression of the ET transporter (ETT) (gene symbol SLC22A4) in distinct cells is thought to signal intracellular ET activity, since we have previously shown that the ETT is highly selective for ET. Unfortunately, some continue to hold the ETT as a relevant drug transporter, using the misleading functional name OCTN1, novel organic cation transporter. The present study was provoked by two recent reports in which new ETT substrates were declared. Astonishingly, the transport efficiencies (TEs) of ETT for saracatinib and some nucleoside drugs were as high as the TE for ET. Here we examined, based on regulated expression of ETT from human and rat in 293 cells and liquid chromatography-mass spectrometry quantification, the transport of several drugs. With the nucleosides cytarabine, gemcitabine, 2'-deoxycytidine, and 2'-deoxyadenosine, and the drugs saracatinib, ipratropium, metformin, and oxaliplatin, the uptake into cells expressing ETT was not increased over control cells. ETT-mediated uptake of gabapentin was detectable, but the TE was approximately 100-fold lower than the TE for ergothioneine (50-200 µl/min per milligram of protein). In conclusion, the ETT remains highly specific for its physiologic substrate ergothioneine. Our results contradict several reports on additional substrates. The ETT does not provide multiple substrate specificities, and it is not a transporter of cationic drugs. Only compounds that are related to ET in substructure-for example, gabapentin, carnitine, and TEA-can be transported, but with very low efficiency. Thus, ETT persists as a specific molecular indicator of ET activity.

Ergothioneine stands out from hercynine in the reaction with singlet oxygen: Resistance to glutathione and TRIS in the generation of specific products indicates high reactivity

The candidate vitamin ergothioneine (ET), an imidazole-2-thione derivative of histidine betaine, is generally considered an antioxidant. However, the precise physiological role of ET is still unresolved. Here, we investigated in vitro the hypothesis that ET serves specifically to eradicate noxious singlet oxygen (¹O₂). Pure ¹O₂ was generated by thermolysis at 37°C of N,N'-di(2,3-dihydroxypropyl)-1,4-naphthalenedipropanamide 1,4-endoperoxide (DHPNO₂). Assays of DHPNO₂ with ET or hercynine (= ET minus sulfur) at pH 7.4 were analyzed by LC-MS in full scan mode to detect products. Based on accurate mass and product ion scan data, several products were identified and then quantitated as a function of time by selected reaction monitoring. All products of hercynine contained, after a [4+2] cycloaddition of ¹O₂, a carbonyl at position 2 of the imidazole ring. By contrast, because of the doubly bonded sulfur, we infer from the products of ET as the initial intermediates a 4,5-dioxetane (after [2+2] cycloaddition) and hydroperoxides at position 4 and 5 (after Schenck ene reactions). The generation of single products from ET, but not from hercynine, was fully resistant to a large excess of tris(hydroxymethyl)aminomethane (TRIS) or glutathione (GSH). This suggests that ¹O₂ markedly favors ET over GSH (at least 50-fold) and TRIS (at least 250-fold) for the initial reaction. Loss of ET was almost abolished in 5mM GSH, but not in 25mM TRIS. Regeneration of ET seems feasible, since some ET products - by contrast to hercynine products - decomposed easily in the MS collision cell to become aromatic again.