Dityrosine, a specific marker of oxidation, is synthesized by the myeloperoxidase-hydrogen peroxide system of human neutrophils and macrophages

Chiral Polar Bifunctional Polyimide Enantiomers for Asymmetric Photo- and Piezo-Catalysis

Chiral catalysts for asymmetric catalysis represent a crucial research focus in chemistry and materials science. However, a few cases about chiral-dependent photocatalysts primarily focus on plasmonic noble metals. Particularly, developing chiral nano-catalysts that can be driven by mechanical energy remains in the blank stage. Herein, organic polymer-based enantiomers, chiral polar polyimide (PI) microspheric nano-assembly are synthesized as novel bifunctional catalysts for asymmetric photocatalysis and piezocatalysis. The PI catalyst enantiomers present enantioselectivity towards left- and right-circularly polarized light, demonstrating chiral-dependent H2O2 photoproduction. Interestingly, enantioselectivity of the catalyst reverses under irradiation of different bands, presenting tunability in the interaction between chiral catalysts and circularly polarized light. For the first time, enantioselective piezocatalytic behavior is demonstrated by the chiral polar PI catalysts. They show remarkable chiral preference for asymmetric Diels-Alder reaction and enantioselective conversion of tyrosine substrates under ultrasonic vibration. The findings provide a new perspective into exploring metal-free chiral catalysts and their asymmetric catalysis applications across multiple energy forms.

Postmortem Immunohistochemical Findings in Early Acute Myocardial Infarction: A Systematic Review

The diagnosis of early acute myocardial infarction is of particular importance in forensic practice considering the frequency of sudden cardiac death and the difficulty of positively identifying it through classical histological methods if survival is less than 6 h. This article aims to analyze potential immunohistochemical markers that could be useful in diagnosing acute myocardial infarction within the first 6 h of its onset. We conducted an extensive evaluation of the literature according to the PRISMA guidelines for reporting systematic literature reviews. We searched the Web of Science and PubMed databases from their inception to 2023 using the following keywords: "myocardial infarction" and "immunohistochemistry". Fifteen studies met the inclusion criteria. Immunohistochemical markers as complement factors and CD59, myoglobin, fibrinogen, desmin, tumor necrosis factor alpha (TNF-α), P-38, JNK (Jun N Terminal Kinase), transforming growth factor β1 (TGF-β1), cardiac troponins, fibronectin, H-FABP (heart fatty acid binding protein), dityrosine, fibronectin, CD15, IL-1β, IL-6, IL-15, IL-8, MCP-1, ICAM-1, CD18, and tryptase can be used to identify the first six hours of acute myocardial infarction. These markers are mostly studied in experimental animal models. It is necessary to conduct extensive studies on human myocardial tissue fragments, which will involve the analysis of several immunohistochemical markers and careful analysis of the available data on perimortem events, resuscitation, and postmortem intervals in the context of a uniform laboratory methodology.

Horseradish Peroxidase-Mediated Bioprinting via Bioink Gelation by Alternately Extruded Support Material

Horseradish peroxidase (HRP)-mediated extrusion bioprinting has a significant potential in tissue engineering and regenerative medicine. However, they often face challenges in terms of printing fidelity and structural integrity when using low-viscosity inks. To address this issue, a method that alternately extrudes bioinks and support material was developed in this study. The bioinks consisting of cells, HRP, and phenolated polymers, and the support material contained hydrogen peroxide (H2O2). The support material not only prevented the collapse of the constructs but also supplied H2O2 to facilitate the enzymatic reaction. 3D constructs with tall and complex shapes were successfully printed from a low-viscosity ink containing 10 U/mL HRP and 1.0% w/v phenolated hyaluronic acid (HA-Ph), with a support material containing 10 mM H2O2. Over 90% viability of mouse fibroblasts (10T1/2) was achieved following the printing process, along with a morphology and proliferation rate similar to that of nontreated cells. Furthermore, human hepatoblastoma (HepG2) cells showed an increased spheroid size over 14 days in the printed constructs. The 10T1/2 cells adhered and proliferated on the constructs printed from inks containing both phenolated gelatin and HA-Ph. These results demonstrate the great potential of this HRP-mediated extrusion bioprinting technique for tissue engineering applications.

Methods to Evaluate Changes in Mitochondrial Structure and Function in Cancer

Mitochondria are regulators of key cellular processes, including energy production and redox homeostasis. Mitochondrial dysfunction is associated with various human diseases, including cancer. Importantly, both structural and functional changes can alter mitochondrial function. Morphologic and quantifiable changes in mitochondria can affect their function and contribute to disease. Structural mitochondrial changes include alterations in cristae morphology, mitochondrial DNA integrity and quantity, and dynamics, such as fission and fusion. Functional parameters related to mitochondrial biology include the production of reactive oxygen species, bioenergetic capacity, calcium retention, and membrane potential. Although these parameters can occur independently of one another, changes in mitochondrial structure and function are often interrelated. Thus, evaluating changes in both mitochondrial structure and function is crucial to understanding the molecular events involved in disease onset and progression. This review focuses on the relationship between alterations in mitochondrial structure and function and cancer, with a particular emphasis on gynecologic malignancies. Selecting methods with tractable parameters may be critical to identifying and targeting mitochondria-related therapeutic options. Methods to measure changes in mitochondrial structure and function, with the associated benefits and limitations, are summarized.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

PINK1/Parkin-mediated mitophagy inhibits osteoblast apoptosis induced by advanced oxidation protein products

Osteoblast apoptosis plays an important role in age-related bone loss and osteoporosis. Our previous study revealed that advanced oxidation protein products (AOPPs) could induce nicotinamide adenine dinucleotide phosphate oxidase (NOX)-derived reactive oxygen species (ROS) production, cause mitochondrial membrane potential (ΔΨm) depolarization, trigger the mitochondria-dependent intrinsic apoptosis pathway, and lead to osteoblast apoptosis and ultimately osteopenia and bone microstructural destruction. In this study, we found that AOPPs also induced mitochondrial ROS (mtROS) generation in osteoblastic MC3T3-E1 cells, which was closely related to NOX-derived ROS, and aggravated the oxidative stress condition, thereby further promoting apoptosis. Removing excessive ROS and damaged mitochondria is the key factor in reversing AOPP-induced apoptosis. Here, by in vitro studies, we showed that rapamycin further activated PINK1/Parkin-mediated mitophagy in AOPP-stimulated MC3T3-E1 cells and significantly alleviated AOPP-induced cell apoptosis by eliminating ROS and damaged mitochondria. Our in vivo studies revealed that PINK1/Parkin-mediated mitophagy could decrease the plasma AOPP concentration and inhibit AOPP-induced osteoblast apoptosis, thus ameliorating AOPP accumulation-related bone loss, bone microstructural destruction and bone mineral density (BMD) loss. Together, our study indicated that therapeutic strategies aimed at upregulating osteoblast mitophagy and preserving mitochondrial function might have potential for treating age-related osteoporosis.

Dityrosine cross-linking and its potential roles in Alzheimer's disease

Oxidative stress is a significant source of damage that accumulates during aging and contributes to Alzheimer's disease (AD) pathogenesis. Oxidation of proteins can give rise to covalent links between adjacent tyrosines known as dityrosine (DiY) cross-linking, amongst other modifications, and this observation suggests that DiY could serve as a biomarker of accumulated oxidative stress over the lifespan. Many studies have focused on understanding the contribution of DiY to AD pathogenesis and have revealed that DiY crosslinks can be found in both Aβ and tau deposits - the two key proteins involved in the formation of amyloid plaques and tau tangles, respectively. However, there is no consensus yet in the field on the impact of DiY on Aβ and tau function, aggregation, and toxicity. Here we review the current understanding of the role of DiY on Aβ and tau gathered over the last 20 years since the first observation, and discuss the effect of this modification for Aβ and tau aggregation, and its potential as a biomarker for AD.

Effects of Synthetic Short Cationic Antimicrobial Peptides on the Catalytic Activity of Myeloperoxidase, Reducing Its Oxidative Capacity

Cationic antimicrobial peptides (CAMPs) have gained attention as promising antimicrobial therapeutics causing lower or no bacterial resistance. Considerable achievements have been made in designing new CAMPs that are highly active as antimicrobials. However, there is a lack of research on their interaction with biologically important proteins. This study focused on CAMPs' effects on myeloperoxidase (MPO), an enzyme which is microbicidal and concomitantly damaging to host biomolecules and cells due to its ability to produce reactive oxygen and halogen species (ROS/RHS). Four CAMPs designed by us were employed. MPO catalytic activity was assessed by an absorbance spectra analysis and by measuring enzymatic activity using Amplex Red- and Celestine Blue B-based assays. The peptide Hm-AMP2 accelerated MPO turnover. Pept_1545 and Hm-AMP8 inhibited both the MPO chlorinating and peroxidase activities, with components of different inhibition types. Hm-AMP8 was a stronger inhibitor. Its K_i towards H₂O₂ and Cl^- was 0.3-0.4 μM vs. 11-20 μM for pept_1545. Peptide tyrosine and cysteine residues were involved in the mechanisms of the observed effects. The results propose a possible dual role of CAMPs as both antimicrobial agents and agents that downregulate MPO activation, and suggest CAMPs as prototypes for the development of antioxidant compounds to prevent MPO-mediated ROS/RHS overproduction.

An activatable Mn(II) MRI probe for detecting peroxidase activity in vitro and in vivo

Myeloperoxidase (MPO), a hallmark of the function and activation of innate immune cells, can act as a 'double-edged sword', contributing to clear infection as well as causing tissue oxidizing damage in various inflammatory diseases. In this study, an activatable Mn(II) chelate-based magnetic resonance imaging (MRI) contrast agent (CA), Mn-TyEDTA (TyEDTA = tyrosine derived ethylenediaminetetraacetic acid) structurally featuring a phenol group as the electron-donor, was developed to sense the activity of peroxidase in vitro and in vivo. Mn-TyEDTA demonstrated a peroxidase activity-dependent relaxivity in the presence of horseradish peroxidase (HRP)/H₂O₂ with more than a 2.6-fold increase in water proton relaxivity produced (HRP, 500 U; H₂O₂, 4.5 eq). A mechanism of peroxidase-mediated Mn(II) monomer radical polymerization was confirmed with those oligomers of Mn-TyEDTA such as dimer, trimer and tetramer were found in the LC-MS study. Dynamic MR imaging of normal mice revealed rapid blood clearance and mixed renal and hepatobiliary elimination of Mn-TyEDTA. Furthermore, compared to liver-specific and non-specific extracellular contrast agents (Mn-BnO-TyEDTA (BnO-TyEDTA = benzyl tyrosine-derived ethylenediaminetetraacetic acid) and Gd-DTPA (DTPA = diethylene triamine penta-acetic acid)), MRI on a monosodium urate (MSU) crystal-induced acute mice model of arthritis showed that inflamed tissues could be selectively enhanced by Mn-TyEDTA, suggesting that this peroxidase-activatable Mn(II) MRI probe could potentially be used for noninvasive detection of MPO activity in vivo.

Group II truncated haemoglobin YjbI prevents reactive oxygen species-induced protein aggregation in Bacillus subtilis

Oxidative stress-mediated formation of protein hydroperoxides can induce irreversible fragmentation of the peptide backbone and accumulation of cross-linked protein aggregates, leading to cellular toxicity, dysfunction, and death. However, how bacteria protect themselves from damages caused by protein hydroperoxidation is unknown. Here, we show that YjbI, a group II truncated haemoglobin from Bacillus subtilis, prevents oxidative aggregation of cell-surface proteins by its protein hydroperoxide peroxidase-like activity, which removes hydroperoxide groups from oxidised proteins. Disruption of the yjbI gene in B. subtilis lowered biofilm water repellence, which associated with the cross-linked aggregation of the biofilm matrix protein TasA. YjbI was localised to the cell surface or the biofilm matrix, and the sensitivity of planktonically grown cells to generators of reactive oxygen species was significantly increased upon yjbI disruption, suggesting that YjbI pleiotropically protects labile cell-surface proteins from oxidative damage. YjbI removed hydroperoxide residues from the model oxidised protein substrate bovine serum albumin and biofilm component TasA, preventing oxidative aggregation in vitro. Furthermore, the replacement of Tyr⁶³ near the haem of YjbI with phenylalanine resulted in the loss of its protein peroxidase-like activity, and the mutant gene failed to rescue biofilm water repellency and resistance to oxidative stress induced by hypochlorous acid in the yjbI-deficient strain. These findings provide new insights into the role of truncated haemoglobin and the importance of hydroperoxide removal from proteins in the survival of aerobic bacteria.

Association of Vegetable and Fruit Consumption with Urinary Oxidative Biomarkers in Teenaged Girls: A School-Based Pilot Study in Japan

Hexanoyl-lysine (HEL), 8-hydroxy-2'deoxyguanosine (8-OHdG), and dityrosine (DT) have served as potential biomarkers for detecting oxidative modified lipids, DNA, and proteins in biological samples, respectively. Whether regular higher levels of consumption of vegetables/fruit (V/F) would decrease oxidative modification of these biomolecules in the body remain unelucidated. To examine the association of regular V/F consumption with the generation of these reactive oxygen species-induced biomarkers, this study evaluated V/F consumption in a school-based sample of teenaged girls (mean age 15.6 ± 1.7 years, n = 103), and quantified the formation of oxidative stress biomarkers in their urine. Only 19.4% and 23.3% of participants reported that they consumed the recommended daily amount of vegetables and fruits, respectively. Individuals who consumed lower levels of fruit (<100g/day) or vegetables (<250g/day) had significantly higher HEL excretion in their urine than those who consumed higher levels of fruit (≥100g/day) (p < 0.05) or vegetables (≥250g/day) (p = 0.057). The results of a multiple regression analysis showed that vegetable consumption was an important inhibiting factor of early lipid peroxidation measured as HEL in urine, independent of various confounders (β = - 0.332, p < 0.05). The findings suggest that relatively higher consumption of vegetables would help in the prevention of early lipid peroxidation in adolescents.

Spontaneous and Ionizing Radiation-Induced Aggregation of Human Serum Albumin: Dityrosine as a Fluorescent Probe

The use of spectroscopic techniques has shown that human serum albumin (HSA) undergoes reversible self-aggregation through protein−protein interactions. It ensures the subsequent overlapping of electron clouds along with the stiffening of the conformation of the interpenetrating network of amino acids of adjacent HSA molecules. The HSA oxidation process related to the transfer of one electron was investigated by pulse radiolysis and photochemical methods. It has been shown that the irradiation of HSA solutions under oxidative stress conditions results in the formation of stable protein aggregates. The HSA aggregates induced by ionizing radiation are characterized by specific fluorescence compared to the emission of non-irradiated solutions. We assume that HSA dimers are mainly responsible for the new emission. Dityrosine produced by the intermolecular recombination of protein tyrosine radicals as a result of radiolysis of an aqueous solution of the protein is the main cause of HSA aggregation by cross-linking. Analysis of the oxidation process of HSA confirmed that the reaction of mild oxidants (Br2•−, N3•, SO4•−) with albumin leads to the formation of covalent bonds between tyrosine residues. In the case of •OH radicals and partly, Cl2•−, species other than DT are formed. The light emission of this species is similar to the emission of self-associated HSA.

Second Sphere Interactions in Amyloidogenic Diseases

Amyloids are protein aggregates bearing a highly ordered cross β structural motif, which may be functional but are mostly pathogenic. Their formation, deposition in tissues and consequent organ dysfunction is the central event in amyloidogenic diseases. Such protein aggregation may be brought about by conformational changes, and much attention has been directed toward factors like metal binding, post-translational modifications, mutations of protein etc., which eventually affect the reactivity and cytotoxicity of the associated proteins. Over the past decade, a global effort from different groups working on these misfolded/unfolded proteins/peptides has revealed that the amino acid residues in the second coordination sphere of the active sites of amyloidogenic proteins/peptides cause changes in H-bonding pattern or protein-protein interactions, which dramatically alter the structure and reactivity of these proteins/peptides. These second sphere effects not only determine the binding of transition metals and cofactors, which define the pathology of some of these diseases, but also change the mechanism of redox reactions catalyzed by these proteins/peptides and form the basis of oxidative damage associated with these amyloidogenic diseases. The present review seeks to discuss such second sphere modifications and their ramifications in the etiopathology of some representative amyloidogenic diseases like Alzheimer's disease (AD), type 2 diabetes mellitus (T2Dm), Parkinson's disease (PD), Huntington's disease (HD), and prion diseases.

A Novel Role for Plasminogen Activator Inhibitor Type-2 as a Hypochlorite-Resistant Serine Protease Inhibitor and Holdase Chaperone

Plasminogen activator inhibitor type-2 (PAI-2), a member of the serpin family, is dramatically upregulated during pregnancy and in response to inflammation. Although PAI-2 exists in glycosylated and non-glycosylated forms in vivo, the majority of in vitro studies of PAI-2 have exclusively involved the intracellular non-glycosylated form. This study shows that exposure to inflammation-associated hypochlorite induces the oligomerisation of PAI-2 via a mechanism involving dityrosine formation. Compared to plasminogen activator inhibitor type-1 (PAI-1), both forms of PAI-2 are more resistant to hypochlorite-induced inactivation of its protease inhibitory activity. Holdase-type extracellular chaperone activity plays a putative non-canonical role for PAI-2. Our data demonstrate that glycosylated PAI-2 more efficiently inhibits the aggregation of Alzheimer’s disease and preeclampsia-associated amyloid beta peptide (Aβ), compared to non-glycosylated PAI-2 in vitro. However, hypochlorite-induced modification of non-glycosylated PAI-2 dramatically enhances its holdase activity by promoting the formation of very high-molecular-mass chaperone-active PAI-2 oligomers. Both PAI-2 forms protect against Aβ-induced cytotoxicity in the SH-SY5Y neuroblastoma cell line in vitro. In the villous placenta, PAI-2 is localised primarily to syncytiotrophoblast with wide interpersonal variation in women with preeclampsia and in gestational-age-matched controls. Although intracellular PAI-2 and Aβ staining localised to different placental cell types, some PAI-2 co-localised with Aβ in the extracellular plaque-like aggregated deposits abundant in preeclamptic placenta. Thus, PAI-2 potentially contributes to controlling aberrant fibrinolysis and the accumulation of misfolded proteins in states characterised by oxidative and proteostasis stress, such as in Alzheimer’s disease and preeclampsia.

Mammalian peroxidasin (PXDN): From physiology to pathology

Heme-containing peroxidases catalyze the oxidation of a variety of substrates by consuming hydrogen peroxide (H2O2), and play diversified roles in physiology and pathology including innate immunity, the synthesis of thyroid hormone and the extracellular matrix, as well as the pathogenesis of several inflammatory diseases. Peroxidasin (PXDN), also known as Vascular Peroxidase-1 (VPO1), is a newly identified peroxidase and expresses in multiple cells and tissues including cardiovascular system and the lung. Recent studies imply its roles in the innate immunity, cardiovascular physiology and diseases, and extracellular matrix formation. Studies on the role of PXDN in human diseases are entering a new and exciting stage, and this review provides the insights into this emerging field of PXDN.

Relationship between the Structure and Chaperone Activity of Human αA-Crystallin after Its Modification with Diabetes-Associated Oxidative Agents and Protective Role of Antioxidant Compounds

The study was aimed to evaluate the impact of peroxynitrite (PON, oxidative stress agent in diabetes), methylglyoxal (MGO, diabetes-associated reactive carbonyl compound), and their simultaneous application on the structural and functional features of human αA-crystallin (αA-Cry) using various spectroscopy techniques. Additionally, the surface tension and oligomer size distribution of the treated and untreated protein were tested using tensiometric analysis and dynamic light scattering, respectively. Our results indicated that the reaction of PON and MGO with human αA-Cry leads to the formation of new chromophores, alterations in the secondary to quaternary protein structure, reduction in the size of protein oligomers, and significant enhancement in the chaperone activity of αA-Cry. To reverse the effects of the tested compounds, ascorbic acid and glutathione (main components of lens antioxidant defense system) were applied. As expected, the two antioxidant compounds significantly prevented formation of high molecular weight aggregates of αA-Cry (according to SDS-PAGE). Our results suggest that the lens antioxidant defense system, in particular, glutathione, may provide a strong protection against rapid incidence and progression of diabetic cataract by preventing the destructive reactions of highly reactive DM-associated metabolites.

Structural and functional analysis of broad pH and thermal stable protease from Penicillium aurantiogriseum URM 4622

This study aimed to better characterize a recently purified stable extracellular alkaline peptidase produced by Penicillium aurantiogriseum (URM 4622) through fluorescence spectroscopy, far-UV circular dichroism, kinetic and thermodynamic models to understand its' structure-activity and denaturation. Fluorescence data showed that changing pH leads to tryptophan residues exposure to more hydrophilic environments at optimum activity pH 9.0 and 10.0. When thermally treated, it displayed less unfolding at these pH values, along with 4-fold less photoproducts formation than at neutral pH. Different pH CD spectra showed more β-sheet (21.5-43.0%) than α-helix (1-6.2%). At pH9.0, more than 2-fold higher α-helix content than any other pH. The melting temperature (T_m) was observed between 50 and 60 °C at all pH studied, with lower T_m at pH 9.0-11.0 (54.9-50.3 °C). The protease displayed two phase transition, with two energies of denaturation, and a 4-fold higher thermal stability (ΔH°_m) than reports for other microorganism's proteases. An irreversible folding transition occurs between 50 and 60 °C. It displayed energies of denaturation suggesting higher thermal stability than reported for other microorganism's proteases. These results help elucidating the applicability of this new stable protease.

Role of myeloperoxidase and oxidant formation in the extracellular environment in inflammation-induced tissue damage

The heme peroxidase family generates a battery of oxidants both for synthetic purposes, and in the innate immune defence against pathogens. Myeloperoxidase (MPO) is the most promiscuous family member, generating powerful oxidizing species including hypochlorous acid (HOCl). Whilst HOCl formation is important in pathogen removal, this species is also implicated in host tissue damage and multiple inflammatory diseases. Significant oxidant formation and damage occurs extracellularly as a result of MPO release via phagolysosomal leakage, cell lysis, extracellular trap formation, and inappropriate trafficking. MPO binds strongly to extracellular biomolecules including polyanionic glycosaminoglycans, proteoglycans, proteins, and DNA. This localizes MPO and subsequent damage, at least partly, to specific sites and species, including extracellular matrix (ECM) components and plasma proteins/lipoproteins. Biopolymer-bound MPO retains, or has enhanced, catalytic activity, though evidence is also available for non-catalytic effects. These interactions, particularly at cell surfaces and with the ECM/glycocalyx induce cellular dysfunction and altered gene expression. MPO binds with higher affinity to some damaged ECM components, rationalizing its accumulation at sites of inflammation. MPO-damaged biomolecules and fragments act as chemo-attractants and cell activators, and can modulate gene and protein expression in naïve cells, consistent with an increasing cycle of MPO adhesion, activity, damage, and altered cell function at sites of leukocyte infiltration and activation, with subsequent tissue damage and dysfunction. MPO levels are used clinically both diagnostically and prognostically, and there is increasing interest in strategies to prevent MPO-mediated damage; therapeutic aspects are not discussed as these have been reviewed elsewhere.

Selective and sensitive UHPLC-ESI-Orbitrap MS method to quantify protein oxidation markers

A targeted UHPLC-MS/MS isotopic dilution method has been developed for the simultaneous quantification of 18 different free and protein-bound aromatic amino acid oxidation products in food and biological matrices. All analytes, including critical isomeric pairs of Tyr, o-Tyr, m-Tyr, and dioxyindolylalanine diastereomers were chromatographically resolved to obtain high selectivity, without the need for derivatizing or ion pairing agents. The results of method validation showed adequate retention time reproducibility [0.1-0.6% coefficient of variation (CV) for over 224 injections], accuracy (within ±1-20% of the nominal concentration), and precision (1-17% CV) for all target analytes. The lower limit of quantification was calculated in different matrices using both the Hubaux-Vos approach and accuracy and precision data showing values in the range of 0.2-15 ng/mL. Use of stable isotope-labelled internal standards compensated errors due to matrix effects and artefactual degradation of analytes. Both acid and enzymatic hydrolyses were tested to obtain the best possible results for the quantification of protein oxidation products, demonstrating the stability of target analytes under hydrolytic conditions. The method was successfully applied to quantify target analytes in serum, tissue, milk, infant formula, pork liver pâté, chicken meat and fish. The method was also applied to assess the role of Fenton's reagent in oxidizing Trp, Phe and Tyr residues in different proteins, with results showing o-Tyr, dioxyindolylalanine diastereomers, kynurenine, dityrosine being the main oxidation products. The Fenton chemistry favored the formation of o-Tyr over m-Tyr from Phe with 2-36 folds higher yields. 3-Nitrotyrosine, a marker of protein nitration, was also detected in samples treated with Fenton's reagent.

Hypochlorous acid-modified human serum albumin suppresses MHC class II - dependent antigen presentation in pro-inflammatory macrophages

Macrophages are innate immune cells that internalize and present exogenous antigens to T cells via MHC class II proteins. They operate at sites of infection in a highly inflammatory environment, generated in part by reactive oxygen species, in particular the strong oxidant hypochlorous acid (HOCl) produced in the neutrophil respiratory burst. HOCl effectively kills a broad range of pathogens but can also contribute to host tissue damage at sites of inflammation. To prevent tissue injury, HOCl is scavenged by human serum albumin (HSA) and other plasma proteins in interstitial fluids, leading to the formation of variously modified advanced oxidation products (AOPPs) with pro-inflammatory properties. Previously, we showed that HOCl-mediated N-chlorination converts HSA and other plasma proteins into efficient activators of the phagocyte respiratory burst, but the role of these AOPPs in antigen presentation by macrophages remained unclear. Here, we show that physiologically relevant amounts of N-chlorinated HSA can strongly impair the capacity of THP-1-derived macrophages to present antigens to antigen-specific T cells via MHC class II proteins at multiple stages. Initially, N-chlorinated HSA inhibits antigen internalization by converting antigens into scavenger receptor (SR) ligands and competing with the modified antigens for binding to SR CD36. Later steps of antigen presentation, such as intracellular antigen processing and MHC class II expression are negatively affected, as well. We propose that impaired processing of pathogens or exogenous antigens by immune cells at an initial stage of infection prevents antigen presentation in an environment potentially hostile to cells of the adaptive immune response, possibly shifting it towards locations removed from the actual insult, like the lymph nodes. On the flip side, excessive retardation or complete inhibition of antigen presentation by N-chlorinated plasma proteins could contribute to chronic infection and inflammation.

Role of Small Moiety of a Large Ligand: Tyrosine Templated Copper Nanoclusters

To explore the underlying formation mechanism of luminescent metal nanoclusters (NCs) using a small moiety such as amino acids (outside the milieu of a protein environment) as templates, herein we report blue-emitting copper nanoclusters (CuNCs) using l-tyrosine (l-Tyr) as a capping agent as well as a reducing agent. We also demonstrate the effect of an in situ fibrillation of Tyr on the luminescence and structural properties of NCs. Fluorescence studies along with microscopic imaging revealed the rapid formation of a dityrosine (di-Tyr) moiety in an alkaline medium followed by an aggregated "Tamarix dioica leaf"-like fibrillar pattern along with CuNCs. Our present investigation delineates the role played by π-π interactions in the formation of the fibrillar structures. We substantiated the fundamentals of using a small molecule of a large ligand that can serve as a template and also show how these NCs once formed destroy the fibrils of di-Tyr as a function of time.

Microbial Biofilms in the Food Industry-A Comprehensive Review

Biofilms, present as microorganisms and surviving on surfaces, can increase food cross-contamination, leading to changes in the food industry’s cleaning and disinfection dynamics. Biofilm is an association of microorganisms that is irreversibly linked with a surface, contained in an extracellular polymeric substance matrix, which poses a formidable challenge for food industries. To avoid biofilms from forming, and to eliminate them from reversible attachment and irreversible stages, where attached microorganisms improve surface adhesion, a strong disinfectant is required to eliminate bacterial attachments. This review paper tackles biofilm problems from all perspectives, including biofilm-forming pathogens in the food industry, disinfectant resistance of biofilm, and identification methods. As biofilms are largely responsible for food spoilage and outbreaks, they are also considered responsible for damage to food processing equipment. Hence the need to gain good knowledge about all of the factors favouring their development or growth, such as the attachment surface, food matrix components, environmental conditions, the bacterial cells involved, and electrostatic charging of surfaces. Overall, this review study shows the real threat of biofilms in the food industry due to the resistance of disinfectants and the mechanisms developed for their survival, including the intercellular signalling system, the cyclic nucleotide second messenger, and biofilm-associated proteins.

Iron Complexes of Flavonoids-Antioxidant Capacity and Beyond

Flavonoids are common plant natural products able to suppress ROS-related damage and alleviate oxidative stress. One of key mechanisms, involved in this phenomenon is chelation of transition metal ions. From a physiological perspective, iron is the most significant transition metal, because of its abundance in living organisms and ubiquitous involvement in redox processes. The chemical, pharmaceutical, and biological properties of flavonoids can be significantly affected by their interaction with transition metal ions, mainly iron. In this review, we explain the interaction of various flavonoid structures with Fe(II) and Fe(III) ions and critically discuss the influence of chelated ions on the flavonoid biochemical properties. In addition, specific biological effects of their iron metallocomplexes, such as the inhibition of iron-containing enzymes, have been included in this review.

The effects of neutrophil-generated hypochlorous acid and other hypohalous acids on host and pathogens

Neutrophils are predominant immune cells that protect the human body against infections by deploying sophisticated antimicrobial strategies including phagocytosis of bacteria and neutrophil extracellular trap (NET) formation. Here, we provide an overview of the mechanisms by which neutrophils kill exogenous pathogens before we focus on one particular weapon in their arsenal: the generation of the oxidizing hypohalous acids HOCl, HOBr and HOSCN during the so-called oxidative burst by the enzyme myeloperoxidase. We look at the effects of these hypohalous acids on biological systems in general and proteins in particular and turn our attention to bacterial strategies to survive HOCl stress. HOCl is a strong inducer of protein aggregation, which bacteria can counteract by chaperone-like holdases that bind unfolding proteins without the need for energy in the form of ATP. These chaperones are activated by HOCl through thiol oxidation (Hsp33) or N-chlorination of basic amino acid side-chains (RidA and CnoX) and contribute to bacterial survival during HOCl stress. However, neutrophil-generated hypohalous acids also affect the host system. Recent studies have shown that plasma proteins act not only as sinks for HOCl, but get actively transformed into modulators of the cellular immune response through N-chlorination. N-chlorinated serum albumin can prevent aggregation of proteins, stimulate immune cells, and act as a pro-survival factor for immune cells in the presence of cytotoxic antigens. Finally, we take a look at the emerging role of HOCl as a potential signaling molecule, particularly its role in neutrophil extracellular trap formation.

3-Nitrotyrosine and related derivatives in proteins: precursors, radical intermediates and impact in function

Oxidative post-translational modification of proteins by molecular oxygen (O2)- and nitric oxide (•NO)-derived reactive species is a usual process that occurs in mammalian tissues under both physiological and pathological conditions and can exert either regulatory or cytotoxic effects. Although the side chain of several amino acids is prone to experience oxidative modifications, tyrosine residues are one of the preferred targets of one-electron oxidants, given the ability of their phenolic side chain to undergo reversible one-electron oxidation to the relatively stable tyrosyl radical. Naturally occurring as reversible catalytic intermediates at the active site of a variety of enzymes, tyrosyl radicals can also lead to the formation of several stable oxidative products through radical-radical reactions, as is the case of 3-nitrotyrosine (NO2Tyr). The formation of NO2Tyr mainly occurs through the fast reaction between the tyrosyl radical and nitrogen dioxide (•NO2). One of the key endogenous nitrating agents is peroxynitrite (ONOO-), the product of the reaction of superoxide radical (O2•-) with •NO, but ONOO--independent mechanisms of nitration have been also disclosed. This chemical modification notably affects the physicochemical properties of tyrosine residues and because of this, it can have a remarkable impact on protein structure and function, both in vitro and in vivo. Although low amounts of NO2Tyr are detected under basal conditions, significantly increased levels are found at pathological states related with an overproduction of reactive species, such as cardiovascular and neurodegenerative diseases, inflammation and aging. While NO2Tyr is a well-established stable oxidative stress biomarker and a good predictor of disease progression, its role as a pathogenic mediator has been laboriously defined for just a small number of nitrated proteins and awaits further studies.

Photoluminescence Response in Carbon Nanomaterials to Enzymatic Degradation

Myeloperoxidase (MPO), a key enzyme released by neutrophils during inflammation, has been shown to catalyze the biodegradation of carbon nanomaterials. In this work, we perform photoluminescence studies on the MPO-catalyzed oxidation of graphene oxide (GO) and surfactant-coated pristine (6,5) single-walled carbon nanotubes (SWCNTs). The enzymatic degradation mechanism involves the introduction of defects, which promotes further degradation. Interestingly, the photoluminescence responses of GO and SWCNTs to enzymatic degradation are counterposed. Although the near-infrared (NIR) fluorescence intensity of SWCNTs at 998 nm is either unchanged or decreases depending on the surfactant identity, the blue fluorescence intensity of GO at 440 nm increases with the progression of oxidation by MPO/H₂O₂/Cl^- due to the formation of graphene quantum dots (GQDs). Turn-on GO fluorescence is also observed with neutrophil-like HL-60 cells, indicative of potential applications of GO for imaging MPO activity in live cells. Based on these results, we further construct two ratiometric sensors using SWCNT/GO nanoscrolls by incorporating surfactant-wrapped pristine SWCNTs as the internal either turn-off (with sodium cholate (SC)) or reference (with carboxymethylcellulose (CMC)) sensor. The ratiometric approach enables the sensors to be more stable to external noise by providing response invariant to the absolute intensity emitted from the sensors. Our sensors show linear response to MPO oxidative machinery and hold the promise to be used as self-calibrating carbon nanomaterial-based MPO activity indicators.

Myeloperoxidase-derived damage to human plasma fibronectin: Modulation by protein binding and thiocyanate ions (SCN-)

Endothelial cell dysfunction is an early event in cardiovascular disease and atherosclerosis. The origin of this dysfunction is unresolved, but accumulating evidence implicates damaging oxidants, including hypochlorous acid (HOCl), a major oxidant produced by myeloperoxidase (MPO), during chronic inflammation. MPO is released extracellularly by activated leukocytes and binds to extracellular molecules including fibronectin, a major matrix glycoprotein involved in endothelial cell binding. We hypothesized that MPO binding might influence the modifications induced on fibronectin, when compared to reagent HOCl, with this including alterations to the extent of damage to protein side-chains, modified structural integrity, changes to functional domains, and impact on naïve human coronary artery endothelial cell (HCAEC) adhesion and metabolic activity. The effect of increasing concentrations of the alternative MPO substrate thiocyanate (SCN-), which might decrease HOCl formation were also examined. Exposure of fibronectin to MPO/H2O2/Cl- is shown to result in damage to the functionally important cell-binding and heparin-binding fragments, gross structural changes to the protein, and altered HCAEC adhesion and activity. Differences were observed between stoichiometric, and above-stoichiometric MPO concentrations consistent with an effect of MPO binding to fibronectin. In contrast, MPO/H2O2/SCN- induced much less marked changes and limited protein damage. Addition of increasing SCN- concentrations to the MPO/H2O2/Cl- system provided protection, with 20 μM of this anion rescuing damage to functionally-important domains, decreasing chemical modification, and maintaining normal HCAEC behavior. Modulating MPO binding to fibronectin, or enhancing SCN- levels at sites of inflammation may therefore limit MPO-mediated damage, and be of therapeutic value.

Hopane-type triterpenes from Cnidoscolus spinosus and their bioactivities

Chemical investigation of the aerial parts of Cnidoscolus spinosus resulted in the isolation of relatively infrequent hopane-type triterpenes, 3β-acetoxy-hop-22(29)-ene (1), first reported here as natural product, together with 3-oxo-hop-22(29)-ene (2), and 3β-hydroxy-hop-22(29)-ene (3). β-Amyrin palmitate and three phytosterols were also characterized. The structures of the compounds were established using spectroscopic methods, and those of 1 and 2 were confirmed by crystallographic analysis. Selected biological activities for the isolated hopane-type triterpenes were tested through a series of assays for determining the cytotoxic, anti-inflammatory, α-glucosidase inhibition and antiparasitic activities. Compounds 1-3 did not show cytotoxic activity, compound 1 displayed an important inhibitory effect in the mouse ear induced inflammation assay, and significantly inhibited the yeast α-glucosidase activity in vitro and in silico. Additionally, compounds 2 and 3 showed marginal activities against Trypanosoma cruzi and Leishmania mexicana. Therefore, the bioactivities of hopane-type triterpenes deserve further investigation, particularly their anti-inflammatory properties.

Peroxidase activity of heme bound amyloid β peptides associated with Alzheimer's disease

The amyloid cascade hypothesis attributes the neurodegeneration observed in Alzheimer's disease (AD) to the deposition of the amyloid β (Aβ) peptide into plaques and fibrils in the AD brain. The metal ion hypothesis which implicates several metal ions, viz. Zn²⁺, Cu²⁺ and Fe³⁺, in the AD pathology on account of their abnormal accumulation in the Aβ plaques along with an overall dyshomeostasis of these metals in the AD brain was proposed a while back. Metal ion chelators and ionophores, put forward as possible drug candidates for AD, are yet to succeed in clinical trials. Heme, which is widely distributed in the mammalian body as the prosthetic group of several important proteins and enzymes, has been thought to be associated with AD by virtue of its colocalization in the Aβ plaques along with the similarity of several heme deficiency symptoms with those of AD and most importantly, due to its ability to bind Aβ. This feature article illustrates the active site environment of heme-Aβ which resembles those of peroxidases. It also discusses the peroxidase activity of heme-Aβ, its ability to effect oxidative degradation of neurotransmitters like serotonin and also the identification of the highly reactive high-valent intermediate, compound I. The effect of second sphere residues on the formation and peroxidase activity of heme-Aβ along with the generation and decay of compound I is highlighted throughout the article. The reactivities of heme bound Aβ peptides give an alternative theory to understand the possible cause of this disease.

Effects of Post-Translational Modifications of Fibrinogen on Clot Formation, Clot Structure, and Fibrinolysis: A Systematic Review

Supplemental Digital Content is available in the text.

Post-translational modifications of fibrinogen influence the occurrence and progression of thrombotic diseases. In this systematic review, we assessed the current literature on post-translational modifications of fibrinogen and their effects on fibrin formation and clot characteristics.

Enzyme production ofd-gluconic acid and glucose oxidase: successful tales of cascade reactions

This review mainly focuses on the use of glucose oxidase in the production ofd-gluconic acid, which is a reactant of undoubtable interest in different industrial areas. As example of diverse enzymatic cascade reactions.

Hypochlorous acid-mediated modification of proteins and its consequences

Myeloperoxidase (MPO) is a mammalian heme peroxidase released by activated immune cells, which forms chemical oxidants, including hypochlorous acid (HOCl), to kill bacteria and other invading pathogens. In addition to this important role in the innate immune system, there is significant evidence from numerous chronic inflammatory pathologies for the elevated production of HOCl and associated oxidative modification of proteins and damage to host tissue. Proteins are major targets for HOCl in biological systems, owing to their abundance and the high reactivity of several amino acid side-chains with this oxidant. As such, there is significant interest in understanding the molecular mechanisms involved in HOCl-mediated protein damage and defining the consequences of these reactions. Exposure of proteins to HOCl results in a wide range of oxidative modifications and the formation of chlorinated products, which alter protein structure and enzyme activity, and impact the function of biological systems. This review describes the reactivity of HOCl with proteins, including the specific pathways involved in side-chain modification, backbone fragmentation and aggregation, and outlines examples of some of the biological consequences of these reactions, particularly in relation to the development of chronic inflammatory disease.

Single- and multi-component chiral supraparticles as modular enantioselective catalysts

Nanoscale biological assemblies exemplified by exosomes, endosomes and capsids, play crucial roles in all living systems. Supraparticles (SP) from inorganic nanoparticles (NPs) replicate structural characteristics of these bioassemblies, but it is unknown whether they can mimic their biochemical functions. Here, we show that chiral ZnS NPs self-assemble into 70–100 nm SPs that display sub-nanoscale porosity associated with interstitial spaces between constituent NPs. Similarly to photosynthetic bacterial organelles, these SPs can serve as photocatalysts, enantioselectively converting L- or D-tyrosine (Tyr) into dityrosine (diTyr). Experimental data and molecular dynamic simulations indicate that the chiral bias of the photocatalytic reaction is associated with the chiral environment of interstitial spaces and preferential partitioning of enantiomers into SPs, which can be further enhanced by co-assembling ZnS with Au NPs. Besides replicating a specific function of biological nanoassemblies, these findings establish a path to enantioselective oxidative coupling of phenols for biomedical and other needs.

Nanoscale biological assemblies play crucial roles in all living systems and display a variety of chemical functionalities. Here the authors show that it is possible to replicate some of the biochemical functions in similarly-sized assemblies made from inorganic nanoparticles.

The nitroxide 4-methoxy-tempo inhibits the pathogenesis of dextran sodium sulfate-stimulated experimental colitis

Inflammatory bowel disease (IBD) is a chronic condition characterised by leukocyte recruitment to the gut mucosa. Leukocyte myeloperoxidase (MPO) produces the two-electron oxidant hypochlorous acid (HOCl), damaging tissue and playing a role in cellular recruitment, thereby exacerbating gut injury. We tested whether the MPO-inhibitor, 4-Methoxy-TEMPO (MetT), ameliorates experimental IBD. Colitis was induced in C57BL/6 mice by 3% w/v dextran-sodium-sulfate (DSS) in drinking water ad libitum over 9-days with MetT (15 mg/kg; via i. p. injection) or vehicle control (10% v/v DMSO+90% v/v phosphate buffered saline) administered twice daily during DSS challenge. MetT attenuated body-weight loss (50%, p < 0.05, n = 6), improved clinical score (53%, p < 0.05, n = 6) and inhibited serum lipid peroxidation. Histopathological damage decreased markedly in MetT-treated mice, as judged by maintenance of crypt integrity, goblet cell density and decreased cellular infiltrate. Colonic Ly6C⁺, MPO-labelled cells and 3-chlorotyrosine (3-Cl-Tyr) decreased in MetT-treated mice, although biomarkers for nitrosative stress (3-nitro-tyrosine-tyrosine; 3-NO₂-Tyr) and low-molecular weight thiol damage (assessed as glutathione sulfonamide; GSA) were unchanged. Interestingly, MetT did not significantly impact colonic IL-10 and IL-6 levels, suggesting a non-immunomodulatory pathway. Overall, MetT ameliorated the severity of experimental IBD, likely via a mechanism involving the modulation of MPO-mediated damage.

N-chlorination mediates protective and immunomodulatory effects of oxidized human plasma proteins

Hypochlorous acid (HOCl), a powerful antimicrobial oxidant, is produced by neutrophils to fight infections. Here, we show that N-chlorination, induced by HOCl concentrations encountered at sites of inflammation, converts blood plasma proteins into chaperone-like holdases that protect other proteins from aggregation. This chaperone-like conversion was reversible by antioxidants and was abrogated by prior methylation of basic amino acids. Furthermore, reversible N-chlorination of basic amino acid side chains is the major factor that converts plasma proteins into efficient activators of immune cells. Finally, HOCl-modified serum albumin was found to act as a pro-survival molecule that protects neutrophils from cell death induced by highly immunogenic foreign antigens. We propose that activation and enhanced persistence of neutrophils mediated by HOCl-modified plasma proteins, resulting in the increased and prolonged generation of ROS, including HOCl, constitutes a potentially detrimental positive feedback loop that can only be attenuated through the reversible nature of the modification involved.

Oxidation of human plasma fibronectin by inflammatory oxidants perturbs endothelial cell function

Dysfunction of endothelial cells of the artery wall is an early event in cardiovascular disease and atherosclerosis. The cause(s) of this dysfunction are unresolved, but accumulating evidence suggests that oxidants arising from chronic low-grade inflammation are contributory agents, with increasing data implicating myeloperoxidase (MPO, released by activated leukocytes), and the oxidants it generates (e.g. HOCl and HOSCN). As these are formed extracellularly and react rapidly with proteins, we hypothesized that MPO-mediated damage to the matrix glycoprotein fibronectin (FN) would modulate FN structure and function, and its interactions with human coronary artery endothelial cells (HCAEC). Exposure of human plasma FN to HOCl resulted in modifications to FN and its functional epitopes. A dose-dependent loss of methionine and tryptophan residues, together with increasing concentrations of methionine sulfoxide, and modification of the cell-binding fragment (CBF) and heparin-binding fragment (HBF) domains was detected with HOCl, but not HOSCN. FN modification resulted in a loss of HCAEC adhesion, impaired cell spreading and reduced cell proliferation. Exposure to HCAEC to HOCl-treated FN altered the expression of HCAEC genes associated with extracellular matrix (ECM) synthesis and adhesion. Modifications were detected on HCAEC-derived ECM pre-treated with HOCl, but not HOSCN, with a loss of antibody recognition of the CBF, HBF and extra-domain A. Co-localization of epitopes arising from MPO-generated HOCl and cell-derived FN was detected in human atherosclerotic lesions. Damage was also detected on FN extracted from lesions. These data support the hypothesis that HOCl, but not HOSCN, targets and modifies FN resulting in arterial wall endothelial cell dysfunction.

Covalent Modification of Amino Acids and Peptides Induced by Ionizing Radiation from an Electron Beam Linear Accelerator Used in Radiotherapy

To identify modifications to amino acids that are directly induced by ionizing radiation, free amino acids and 3-residue peptides were irradiated using a linear accelerator (Linac) radiotherapy device. Mass spectrometry was performed to detail the relative sensitivity to radiation as well as identify covalent, radiation-dependent adducts. The order of reactivity of the 20 common amino acids was generally in agreement with published literature except for His (most reactive of the 20) and Cys (less reactive). Novel and previously identified modifications on the free amino acids were detected. Amino acids were far less reactive when flanked by glycine residues in a tripeptide. Order of reactivity, with GVG most and GEG least, was substantially altered, as were patterns of modification. Radiation reactivity of amino acids is clearly and strongly affected by conversion of the α-amino and α-carboxyl groups to peptide bonds, and the presence of neighboring amino acid residues.

Thermal Effects on Biochemical Signatures of UHT, Pasteurized and Domestically Boiled Buffalo Milk Detected by Synchronous Fluorescence Spectroscopy

Thermal treatment of milk is performed to limit bacterial growth and make it safe for human consumption. To increase the shelf life of milk, either ultrahigh temperature (UHT) or pasteurization techniques are employed that destroy the microorganisms. In this study, the synchronous front face fluorescence spectroscopy was employed for comparative study of raw, UHT treated, pasteurized and conventionally boiled milk at 93 °C (domestic boiling). Principal Component analysis clearly showed distinct clustering of UHT milk due to formation of Maillard reaction products. Fluorescence emission peak at 410 nm showed irreversible change in peak intensity attributed to conformational changes in protein due to UHT treatment while pasteurization and domestic boiling showed reversible changes when milk was cooled down to 10 °C. Furthermore, fluorescence emission peaks at 410 nm previously assigned to vitamin A has also been discussed.

Free Heme and Amyloid-β: A Fatal Liaison in Alzheimer's Disease

While the etiology of Alzheimer's disease (AD) is still unknown, an increased formation of amyloid-β (Aβ) peptide and oxidative processes are major pathological mechanism of the disease. The interaction of Aβ with free heme leads to the formation of peroxidase-active Aβ-heme complexes. However, enzyme-kinetic data and systematic mutational studies are still missing. These aspects were addressed in this study to evaluate the role of Aβ-heme complexes in AD. The enzyme-kinetic measurements showed peroxidase-specific pH- and H2O2-dependencies. In addition, the enzymatic activity of Aβ-heme complexes constantly increased at higher peptide excess. Moreover, the role of the Aβ sequence for the named enzymatic activity was tested, depicting human-specific R5, Y10, and H13 as essential amino acids. Also by studying Y10 as an endogenous peroxidase substrate for Aβ-heme complexes, ratio-specific effects were observed, showing an optimal dityrosine formation at an about 40-fold peptide excess. As dityrosine formation promotes Aβ fibrillation while free heme disturbs protein aggregation, we also investigated the effect of Aβ-heme complex-derived peroxidase activity on the formation of Aβ fibrils. The fluorescence measurements showed a different fibrillation behavior at strong peroxidase activity, leading also to altered fibril morphologies. The latter was detected by electron microscopy. As illustrated by selected in vivo measurements on a mouse model of AD, the disease is also characterized by Aβ-derived microvessel destructions and hemolytic processes. Thus, thrombo-hemorrhagic events are discussed as a source for free heme in brain tissue. In summary, we suggest the formation and enzymatic activity of Aβ-heme complexes as pathological key features of AD.

Maintaining a Healthy Proteome during Oxidative Stress

Some of the most challenging stress conditions that organisms encounter during their lifetime involve the transient accumulation of reactive oxygen and chlorine species. Extremely reactive to amino acid side chains, these oxidants cause widespread protein unfolding and aggregation. It is therefore not surprising that cells draw on a variety of different strategies to counteract the damage and maintain a healthy proteome. Orchestrated largely by direct changes in the thiol oxidation status of key proteins, the response strategies involve all layers of protein protection. Reprogramming of basic biological functions helps decrease nascent protein synthesis and restore redox homeostasis. Mobilization of oxidative stress-activated chaperones and production of stress-resistant non-proteinaceous chaperones prevent irreversible protein aggregation. Finally, redox-controlled increase in proteasome activity removes any irreversibly damaged proteins. Together, these systems pave the way to restore protein homeostasis and enable organisms to survive stress conditions that are inevitable when living an aerobic lifestyle.

Measurements for Sulfide-Mediated Inhibition of Myeloperoxidase Activity

Oxidative stress-alleviating and inflammation-mediatory functions of hydrogen sulfide were reported to be key features of its biological actions. However, the underlying molecular mechanisms of these biological observations are not fully understood. In conditions where sulfide was proposed to be protective against oxidative stress- or inflammation-induced tissue damage (e.g., reperfusion injury, atherosclerosis, vascular inflammation), the reactive oxidant-producing function of a key neutrophil enzyme, myeloperoxidase, was reported to be a protagonist on the detrimental side. We recently described favorable interactions between sulfide and myeloperoxidase and proposed that the potent inhibition of myeloperoxidase activities could contribute to sulfide's beneficial functions in a number of cardiovascular pathologies. Our chapter is dedicated to aid future studies and drug development endeavors in this area by providing methodological guidance on how to assess the inhibitory potential of sulfide on myeloperoxidase enzymatic activities in isolated protein systems, in neutrophil homogenates, and in live neutrophil preparations.

Silk Molecular Weight Influences the Kinetics of Enzymatically Cross-linked Silk Hydrogel Formation

We transform reconstituted silk solutions into robust hydrogels through covalent dityrosine cross-linking resulting from an enzymatic reaction. The bulk rheological properties and the covalent dityrosine bond formation of these gels are measured during polymerization. We compare the time-resolved bond formation to the mechanical properties, where we find that the gelation process is consistent with a model of percolation. The molecular weight of the protein determines whether a secondary mode of growth postpercolation exists, indicating that molecular weight changes affect the mechanisms by which these gels polymerize.

Peroxidase Activity of Human Hemoproteins: Keeping the Fire under Control

The heme in the active center of peroxidases reacts with hydrogen peroxide to form highly reactive intermediates, which then oxidize simple substances called peroxidase substrates. Human peroxidases can be divided into two groups: (1) True peroxidases are enzymes whose main function is to generate free radicals in the peroxidase cycle and (pseudo)hypohalous acids in the halogenation cycle. The major true peroxidases are myeloperoxidase, eosinophil peroxidase and lactoperoxidase. (2) Pseudo-peroxidases perform various important functions in the body, but under the influence of external conditions they can display peroxidase-like activity. As oxidative intermediates, these peroxidases produce not only active heme compounds, but also protein-based tyrosyl radicals. Hemoglobin, myoglobin, cytochrome c/cardiolipin complexes and cytoglobin are considered as pseudo-peroxidases. Рeroxidases play an important role in innate immunity and in a number of physiologically important processes like apoptosis and cell signaling. Unfavorable excessive peroxidase activity is implicated in oxidative damage of cells and tissues, thereby initiating the variety of human diseases. Hence, regulation of peroxidase activity is of considerable importance. Since peroxidases differ in structure, properties and location, the mechanisms controlling peroxidase activity and the biological effects of peroxidase products are specific for each hemoprotein. This review summarizes the knowledge about the properties, activities, regulations and biological effects of true and pseudo-peroxidases in order to better understand the mechanisms underlying beneficial and adverse effects of this class of enzymes.

Exploring the Inhibitory and Antioxidant Effects of Fullerene and Fullerenol on Ribonuclease A

Fullerene-protein interaction studies have been a key topic of investigation in recent times, but the lower water solubility of fullerene somewhat limits its application in the biological system. In this work, we have compared the activities of fullerene and its water-soluble hydrated form, that is fullerenol, on ribonuclease A (RNase A) under physiological conditions (pH 7.4). The interaction studies of fullerene and fullerenol with protein suggest that the binding depends on the hydrophobic interactions between the protein and the ligand. In addition, fullerene and fullerenol slow down the ribonucleolytic activity of RNase A through noncompetitive and mixed types of inhibition, respectively. This precisely gives the idea about the ligand-binding sites in RNase A, which has further been explored using docking studies. Both these nanoparticles show a reduction in dityrosine formation in RNase A caused due to oxidative stress and also prevent RNase A dimer formation to different extents depending on their concentration.