Dityrosine Formation Research Articles

Abstract 14677: Oxidative Damage in Failed Clinical Bioprosthetic Heart Valve Explants

Introduction: Bioprosthetic heart valves (BHVs), fabricated from glutaraldehyde-fixed bovine pericardium or porcine aortic valves, have been widely used in valve replacement surgery. However, BHVs fail over time due to structural degeneration. Despite frequent observations of calcification-associated BHV failure, more than 25% of BHV structural failures occur without calcification. Previously, we reported that oxidative stress may have a pivotal role in noncalcific BHV failure. Moreover, oxidation-induced formation of dityrosine (DT) crosslinks via hydroxyl- and tyrosyl-radical mediated pathways was only detected in clinical BHV explants. Yet the mechanism of DT formation and its role in structural degeneration of clinical BHV is incompletely understood. Hypothesis: Oxidative damage to BHV is due to a specific spatial localization of DT crosslink formation mediated by myeloperoxidase (MPO) and/or iron (Fe) deposition in clinical BHV explants Method & Results: BHVs from 7 human subjects were collected and subjected to mass spectrometry to measure DT in paraffin sections of BHV. 4 different regions of each BHV leaflet (free edge, sewing cushion, commissure, and middle region) were sampled as well as entire cross-sections of each cusp. DT was only detected in the mid–cusp (137.37±49.96 μmol/mol) and was not significantly different from DT quantitated in the cross-sections (191.29±65.98 μmol/mol). DT was not detected in other regions, implying a specific spatial localization of oxidative stress in BHV. MPO, a neutrophil derived enzyme, is responsible for reactive oxygen species (ROS) generation. Immunofluoresence microscopy demonstrated significant presence of MPO in the BHV, implying that MPO may be responsible for the DT formation in BHV. Fe deposition due to intracuspal hematomas and/or Fe-association with calcific deposits can also be responsible for ROS and DT formation. Fe was shown to be present in histology sections in failed BHV by Prussian Blue staining, indicating that Fe deposits may also in part be responsible for the observed DT formation. Conclusion: These results demonstrated a mid-leaflet localization of DT formation in clinically failed BHV explants. This may in part be mediated by MPO and/or Fe-deposits in clinical BHV.

Urinary biomarkers of oxidative stress and plasmatic inflammatory profile in phenylketonuric treated patients

Oxidative stress has been proposed as an important pathophysiologic feature of various inborn errors of metabolism, including phenylketonuria (PKU). Considering that there are few studies relating oxidative stress and inflammation directly in PKU disease, the aim of this study was to evaluate and correlate oxidative damage to biomolecules, antioxidant defenses, pro-inflammatory cytokines, phenylalanine (Phe) and its metabolites (phenyllactic acid—PLA and phenylacetic acid—PAA) levels in urine and plasma from patients with PKU under dietary treatment. We observed a marked increase of isoprostanes, which is a lipid peroxidation biomarker, in urine from these treated patients. Next, we demonstrated that protein oxidative damage, measured by di-tyrosine formation, was significantly increased in urine from PKU treated patients and that decreased urinary antioxidant capacity was also observed. Our findings concerning to the inflammatory cytokines interleukin-6 and interleukin-1β, both significantly increased in these patients, provide evidence that the pro-inflammatory state occurs. Besides, interleukin-1β was positively correlated with isoprostanes. We observed a negative correlation between interleukin-6 and interleukin-10, an anti-inflammatory cytokine. Di-tyrosine was positively correlated with Phe, which indicates oxidative damage to proteins, as well as with PAA. These findings may suggest that the protein damage may be induced by Phe and its metabolite PAA in PKU. Our results indicate that pro-oxidant and pro-inflammatory states occur and are, in part, correlated and protein oxidation seems to be induced by Phe and PPA in PKU patients.

Protein Cross-Linking and Oligomerization through Dityrosine Formation upon Exposure to Ozone.

Air pollution is a potential driver for the increasing prevalence of allergic disease, and post-translational modification by air pollutants can enhance the allergenic potential of proteins. Here, the kinetics and mechanism of protein oligomerization upon ozone (O3) exposure were studied in coated-wall flow tube experiments at environmentally relevant O3 concentrations, relative humidities and protein phase states (amorphous solid, semisolid, and liquid). We observed the formation of protein dimers, trimers, and higher oligomers, and attribute the cross-linking to the formation of covalent intermolecular dityrosine species. The oligomerization proceeds fast on the surface of protein films. In the bulk material, reaction rates are limited by diffusion depending on phase state and humidity. From the experimental data, we derive a chemical mechanism and rate equations for a kinetic multilayer model of surface and bulk reaction enabling the prediction of oligomer formation. Increasing levels of tropospheric O3 in the Anthropocene may promote the formation of protein oligomers with enhanced allergenicity and may thus contribute to the increasing prevalence of allergies.

Streptozotocin Stimulates the Ion Channel TRPA1 Directly: INVOLVEMENT OF PEROXYNITRITE

Streptozotocin (STZ)-induced diabetes is the most commonly used animal model of diabetes. Here, we have demonstrated that intraplantar injections of low dose STZ evoked acute polymodal hypersensitivities in mice. These hypersensitivities were inhibited by a TRPA1 antagonist and were absent in TRPA1-null mice. In wild type mice, systemic STZ treatment (180 mg/kg) evoked a loss of cold and mechanical sensitivity within an hour of injection, which lasted for at least 10 days. In contrast, Trpa1(-/-) mice developed mechanical, cold, and heat hypersensitivity 24 h after STZ. The TRPA1-dependent sensory loss produced by STZ occurs before the onset of diabetes and may thus not be readily distinguished from the similar sensory abnormalities produced by the ensuing diabetic neuropathy. In vitro, STZ activated TRPA1 in isolated sensory neurons, TRPA1 cell lines, and membrane patches. Mass spectrometry studies revealed that STZ oxidizes TRPA1 cysteines to disulfides and sulfenic acids. Furthermore, incubation of tyrosine with STZ resulted in formation of dityrosine, suggesting formation of peroxynitrite. Functional analysis of TRPA1 mutants showed that cysteine residues that were oxidized by STZ were important for TRPA1 responsiveness to STZ. Our results have identified oxidation of TRPA1 cysteine residues, most likely by peroxynitrite, as a novel mechanism of action of STZ. Direct stimulation of TRPA1 complicates the interpretation of results from STZ models of diabetic sensory neuropathy and strongly argues that more refined models of diabetic neuropathy should replace the use of STZ.

Thermal and Photochemical Effects on the Fluorescence Properties of Type I Calf Skin Collagen Solutions at Physiological pH

Mammalian collagens exhibit weak intrinsic UV fluorescence that depends on the age and previous history of the sample. Post-translational modifications result in additional fluorescent products (e.g. DOPA, dityrosine, and advanced glycation end products (AGE)). UV radiation can cause longer wavelength fluorescent oxidative bands. These alterations can assess the extent of photolysis. We describe the ground- and excited-state oxidative transformations of newly-purchased type I calf skin collagens (samples #092014 and #072012) and a 7-year-old sample (#072005). We compare the effects of UV radiation (mainly 254 nm) and age on the photochemical reaction kinetics and fluorescence spectral distribution of type I calf skin collagen at pH 7.4. The fluorescence spectra of samples #072012 and #092014 were similar but not identical to pure tyrosine, whereas #072005 indicated significant “dark” oxidation at the expense of tyrosine. Fading of oxidized product(s) at 270/360 nm is second-order. Build-up of 325/400 nm (dityrosine) fluorescence is linear with time. Rate parameters r2 and r1 were respectively proportional to second order disappearance of ground state oxidation products and the quasi–first-order photochemical formation of dityrosine. There is a reciprocal relationship between the rates of decrease in the 270/360 nm fluorescence and concomitant increase in 325/400 nm fluorescence. Their relative rates depend on the age of the collagen sample. There is a reciprocal relationship between r1 and r2. This relationship results because both ground state autoxidation and excited state photo-dimerization proceed via a common tyrosyl radical intermediate. Water of hydration appears to play a role in generating tyrosyl radical.

The effects of the covalent attachment of 3-(4-hydroxy-3,5-di-tert-butylphenyl) propyl amine to glutaraldehyde pretreated bovine pericardium on structural degeneration, oxidative modification, and calcification of rat subdermal implants.

Bioprosthetic heart valves (BHV) fabricated from glutaraldehyde pretreated heterograft materials, porcine aortic valves or bovine pericardium (BP), are widely used in cardiac surgery. BHV progressively fail in clinical use due to structural degeneration. Previously we reported that dityrosine, an oxidized amino acid, was present in failed clinical BP-BHV explants; unimplanted BP had no detectable dityrosine. In the same studies BP were demonstrated in vitro to be susceptible to oxidative damage, that could be mitigated with BP covalently modified with the antioxidant, 3-(4-hydroxy-3,5-di-tert-butylphenyl)propyl amine (DBP). The present studies compared in rat subdermal implants glutaraldehyde pretreated BP to BP modified with either DBP or the chemical reactions used to link DBP. All BP explants regardless of DBP demonstrated reduced hydroxyproline and increased digestibility by collagenase. However, the DBP-BP explants showed significant inhibition of reduced explant shrink temperatures (an index of crosslinking) as compared with control BP. Significant mitigation of calcification was observed in both the BP-DBP and chemically modified explants as compared with BP. Dityrosine was not detectable in the 90 day explants. It is concluded that rat subdermal BP implants undergo both calcific and noncalcific structural degeneration, but without the formation of dityrosine, unlike clinical BP explants.

Elevated Plasma Dityrosine in Patients with Hyperlipidemia Compared to Healthy Individuals

Background: Dityrosine, the modification of tyrosine residues, may contribute to metabolic disorders. This study was undertaken to investigate plasma dityrosine concentrations in patients with hyperlipidemia and to examine the correlation between dityrosine and lipid profiles. Methods: Fluorescence spectrophotometry was used to measure dityrosine in the plasma of healthy subjects (n = 203) and dyslipidemic subjects, which included patients with mild hyperlipidemia (n = 246) and hyperlipidemia (n = 179). Advanced oxidation protein products (AOPP) and malondialdehyde (MDA) were also assayed in all subjects. Results: Dityrosine levels were higher by 9.3 and 22.9% in mildly hyperlipidemic and hyperlipidemic patients, respectively, compared to controls after adjustment for age, gender, and BMI. AOPP and MDA levels showed similar trends. The levels of dityrosine related positively (p < 0.05) to total cholesterol (r = 0.362), triglycerides (r = 0.449), and low-density lipoprotein cholesterol (r = 0.359). Moreover, plasma dityrosine (r = 0.408), AOPP (r = 0.488), and MDA (r = 0.181) levels were elevated with an increase in the atherosclerosis index in the subjects. Conclusions: These findings suggest that dityrosine formation may be an early event in the pathological process of hyperlipidemia. Dityrosine as a biomarker detected by fluorescence spectrophotometry might be a useful tool to evaluate the plasma redox state in hyperlipidemia.

A central role for intermolecular dityrosine cross-linking of fibrinogen in high molecular weight advanced oxidation protein product (AOPP) formation

BackgroundAdvanced oxidation protein products (AOPPs) are dityrosine cross-linked and carbonyl-containing protein products formed by the reaction of plasma proteins with chlorinated oxidants, such as hypochlorous acid (HOCl). Most studies consider human serum albumin (HSA) as the main protein responsible for AOPP formation, although the molecular composition of AOPPs has not yet been elucidated. Here, we investigated the relative contribution of HSA and fibrinogen to generation of AOPPs. MethodsAOPP formation was explored by SDS-PAGE, under both reducing and non-reducing conditions, as well as by analytical gel filtration HPLC coupled to fluorescence detection to determine dityrosine and pentosidine formation. ResultsFollowing exposure to different concentrations of HOCl, HSA resulted to be carbonylated but did not form dityrosine cross-linked high molecular weight aggregates. Differently, incubation of fibrinogen or HSA/fibrinogen mixtures with HOCl at concentrations higher than 150μM induced the formation of pentosidine and high molecular weight (HMW)-AOPPs (>200kDa), resulting from intermolecular dityrosine cross-linking. Dityrosine fluorescence increased in parallel with increasing HMW-AOPP formation and increasing fibrinogen concentration in HSA/fibrinogen mixtures exposed to HOCl. This conclusion is corroborated by experiments where dityrosine fluorescence was measured in HOCl-treated human plasma samples containing physiological or supra-physiological fibrinogen concentrations or selectively depleted of fibrinogen, which highlighted that fibrinogen is responsible for the highest fluorescence from dityrosine. ConclusionsA central role for intermolecular dityrosine cross-linking of fibrinogen in HMW-AOPP formation is shown. General significanceThese results highlight that oxidized fibrinogen, instead of HSA, is the key protein for intermolecular dityrosine formation in human plasma.

P78 - Polyphenols protect against protein glycoxidation

Glycoxidation belongs to posttranslational protein modifications which underlie pathological sequelae of diabetes and other diseases, and contribute to aging. Search for efficient inhibitors of glycoxidation is therefore of considerable importance. We studied the effect of various polyphenols on the glycoxidation of bovine serum albumin (90 uM) incubated in vitro with glucose, fructose or ribose (100mM) for 6 days in 0.1M phosphate buffer, pH 7.4. Polyphenols have multiple biological actions including antioxidant activity and chelation of transition metal ions. The extent of glycoxidation was evaluated using fluorimetic parameters reflecting formation of Advanced Glycoxidation End Products (AGEs: 325/440nm), dityrosine (330/415nm), formylkynurenine (325/434nm) and kynurenine (365/480nm) and confirmed by estimation of AGEs using an ELISA kit. The results confirmed reliability of easily measurable fluorimetric parameters such as AGEs, dityrosine and formylkynurenine level for estimation of the extent of glycoxidation.All the polyphenols used (caffeic acid, ferulic acid, gallic acid, genistein, naringin, propyl gallate, quercitrin and rutin) decreased the extent of albumin glycoxidation. The extent of protection varied for different sugars (e. g. 1mM genistein: 24.4±1.7 for glucose, 44.5±0.2 for fructose 51.4±0.3 for ribose) The sequence of protective effect was: ferulic acid>caffeic acid>propyl gallate>naringin>quercitrin>genistein for glucose, caffeic acid>ferulic acid>propyl gallate>genistein>quercitrin>rutin>naringin for fructose and genistein>ferulic acid>caffeic acid>rutin>propyl gallate>naringin>quercitrin>gallic acid. These results confirm that polyphenols, natural components of human diet, protect against protein glycation in a model in vitro system.This study was performed within the framework of COSTCM1001 action and was sponsored by Grant 2011/01/M/N23-02065 of the National Science Center of Poland.

P428Cholesterol-enriched diet inhibits cardioprotection by ATP-sensitive K+-channel activators cromakalim and diazoxide

It has been previously shown that hyperlipidemia interferes with cardioprotective mechanisms. Here, we investigated the interaction of hyperlipidemia with cardioprotection induced by pharmacological activators of ATP-sensitive K+- (KATP) channels. Hearts isolated from rats fed a 2% cholesterol-enriched diet or normal diet for 8 wk were subjected to 30 min of global ischemia and 120 min of reperfusion in the presence or absence of KATP modulators. In normal diet-fed rats, either the nonselective KATP activator cromakalim at 10-5 M or the selective mitochondrial (mito)KATP opener diazoxide at 3 x 10-5 M significantly decreased infarct size compared with vehicle-treated control rats. Their cardioprotective effect was abolished by coadministration of the nonselective KATP blocker glibenclamide or the selective mitoKATP blocker 5-hydroxydecanoate, respectively. However, in cholesterol-fed rats, the cardioprotective effect of cromakalim or diazoxide was not observed. Therefore, we further investigated how cholesterol-enriched diet influences cardiac KATP channels. Cardiac expression of a KATP subunit gene (Kir6.1) was significantly downregulated in cholesterol-fed rats; however, protein levels of Kir6.1 and Kir6.2 were not changed. The cholesterol diet significantly decreased cardiac ATP, increased lactate content, and enhanced myocardial oxidative stress, as shown by increased cardiac superoxide and dityrosine formation. This is the first demonstration that cardioprotection by KATP channel activators is impaired in cholesterol-enriched dietinduced hyperlipidemia. The background mechanism may include hyperlipidemia-induced attenuation of mitoKATP function by altered energy metabolism and increased oxidative stress in the heart.

Age-related NADH oxidase (arNOX)-catalyzed oxidative damage to skin proteins.

Age-related NADH oxidase (arNOX), a cell surface-located hydroquinone oxidase capable of superoxide generation, appears at age 30 and increases with age thereafter. The ectodomain of arNOX is shed from the cell surface into body fluids including sera and saliva where its activity was measured spectrophotometrically using a reduction of ferricytochrome c as a measure of superoxide generation. The autofluorescence of advanced glycation end products correlates with epidermal arNOX activity as well. To demonstrate protein cross-linking, a fluorescence-labeled analog of tyrosine, tyramine, that would react with proteins carrying arNOX-generated tyrosyl radicals was used. The assay demonstrated the potential for arNOX-induced oxidative damage (dityrosine formation) to human collagen and elastin and to other surface proteins of intact human embryo fibroblasts and frozen sections from epidermal punch biopsies. The findings support a role for arNOX as a major source of oxidative damage leading to cross-linking of skin proteins.

Original article Assessment of antioxidative activity of alkaloids from Huperzia selago and Diphasiastrum complanatum using in vitro systems

Free radical-induced oxidative damage is implicated in the pathogenesis of neurodegenerative disorders, and antioxidants are presumably of therapeutic value in such diseases. Our previous data indicated that free radicals are strongly associated with brain aging and also play an important role in cytotoxicity of amyloidogenic proteins including -synuclein and amyloid , which accumulate in brains during Parkinson's and Alzheimer's diseases. Disruption of the equilibrium of pro-oxidants and antioxidants results in oxidative stress that leads to the modification of DNA, proteins, carbohydrates, and lipids. It is widely accepted that antioxidants acting as radical scavengers protect the brain against oxidative damage in neurodegenerative diseases. Plant products are rich sources of phytochemicals and have been found to possess a variety of biological activities, including antioxidative potential. The aim of this study was to analyse the antioxidative potential of alkaloid fractions from Huperzia selago and Diphasiastrum complanatum to protect macromolecules against oxidative damage. Thin layer chromatography (TLC) and high-performance liquid chromatography with diode array (HPLC-DAD) and electrospray ionisation mass spectrometric detection (ESI-MS/MS) were used to carry out a comprehensive characterization of alkaloids isolated from the plant material. The effect of the tested compounds on iron/ascorbate-induced lipid peroxidation and carbonyl group formation was analysed in the rat brain homogenate. Direct free radical scavenging (DPPH assay) and the effect on dityrosine formation were measured in cell-free systems. Our results indicated that a number of alkaloid extracts at concentration of 25 µg/ml exhibited antioxidant activity as indicated by DPPH radical scavenging potential (up to 59% inhibition) and inhibition of dityrosine formation. Selected alkaloid fractions provided significant protection against lipid peroxidation and protein oxidation in rat brain tissue homogenate, reducing iron/ascorbate-induced damage by about 20% and 76%, respectively. Overall, the results indicated that selected alkaloids isolated from Huperzia selago effectively protect macromolecules from oxidative stress injury, which will give us an insight into the potential of alkaloids in terms of opening up a new therapeutic approach for oxidative stress-dependent disorders.

Cholesterol-enriched diet inhibits cardioprotection by ATP-sensitive K+channel activators cromakalim and diazoxide

It has been previously shown that hyperlipidemia interferes with cardioprotective mechanisms. Here, we investigated the interaction of hyperlipidemia with cardioprotection induced by pharmacological activators of ATP-sensitive K(+) (KATP) channels. Hearts isolated from rats fed a 2% cholesterol-enriched diet or normal diet for 8 wk were subjected to 30 min of global ischemia and 120 min of reperfusion in the presence or absence of KATP modulators. In normal diet-fed rats, either the nonselective KATP activator cromakalim at 10(-5) M or the selective mitochondrial (mito)KATP opener diazoxide at 3 × 10(-5) M significantly decreased infarct size compared with vehicle-treated control rats. Their cardioprotective effect was abolished by coadministration of the nonselective KATP blocker glibenclamide or the selective mitoKATP blocker 5-hydroxydecanoate, respectively. However, in cholesterol-fed rats, the cardioprotective effect of cromakalim or diazoxide was not observed. Therefore, we further investigated how cholesterol-enriched diet influences cardiac KATP channels. Cardiac expression of a KATP subunit gene (Kir6.1) was significantly downregulated in cholesterol-fed rats; however, protein levels of Kir6.1 and Kir6.2 were not changed. The cholesterol diet significantly decreased cardiac ATP, increased lactate content, and enhanced myocardial oxidative stress, as shown by increased cardiac superoxide and dityrosine formation. This is the first demonstration that cardioprotection by KATP channel activators is impaired in cholesterol-enriched diet-induced hyperlipidemia. The background mechanism may include hyperlipidemia-induced attenuation of mitoKATP function by altered energy metabolism and increased oxidative stress in the heart.

Intermolecular interactions and conformation of antibody dimers present in IgG1 biopharmaceuticals

Intermolecular interactions and conformation in dimer species of Palivizumab, a monoclonal antibody (IgG1), were investigated to elucidate the physical and chemical properties of the dimerized antibody. Palivizumab solution contains ∼1% dimer and 99% monomer. The dimer species was isolated by size-exclusion chromatography and analysed by a number of methods including analytical ultracentrifugation-sedimantetion velocity (AUC-SV). AUC-SV in the presence of sodium dodecyl sulphate indicated that approximately half of the dimer fraction was non-covalently associated, whereas the other half was dimerized by covalent bond. Disulphide bond and dityrosine formation were likely to be involved in the covalent dimerization. Limited proteolysis of the isolated dimer by Lys-C and mass spectrometry for the resultant products indicated that the dimer species were formed by Fab-Fc or Fab-Fab interactions, whereas Fc-Fc interactions were not found. It is thus likely that the dimerization occurs mainly via the Fab region. With regard to the conformation of the dimer species, the secondary and tertiary structures were shown to be almost identical to those of the monomer. Furthermore, the thermal stability turned out also to be very similar between the dimer and monomer.

Identification of Oxidation Sites and Covalent Cross-Links in Metal Catalyzed Oxidized Interferon Beta-1a: Potential Implications for Protein Aggregation and Immunogenicity

Oxidation via Cu(2+)/ascorbate of recombinant human interferon beta-1a (IFNβ1a) leads to highly immunogenic aggregates, however it is unknown which amino acids are modified and how covalent aggregates are formed. In the present work we mapped oxidized and cross-linked amino acid residues in aggregated IFNβ1a, formed via Cu(2+)/ascorbate catalyzed oxidation. Size exclusion chromatography (SEC) was used to confirm extensive aggregation of oxidized IFNβ1a. Circular dichroism and intrinsic fluorescence spectroscopy indicated substantial loss of secondary and tertiary structure, respectively. Derivatization with 4-(aminomethyl)benzenesulfonic acid was used to demonstrate, by fluorescence in combination with SEC, the presence of tyrosine (Tyr) oxidation products. High performance liquid chromatography coupled to electrospray ionization mass spectrometry of reduced, alkylated, and digested protein was employed to localize chemical degradation products. Oxidation products of methionine, histidine, phenylalanine (Phe), tryptophan, and Tyr residues were identified throughout the primary sequence. Covalent cross-links via 1,4- or 1,6-type addition between primary amines and DOCH (2-amino-3-(3,4-dioxocyclohexa-1,5-dien-1-yl)propanoic acid, an oxidation product of Phe and Tyr) were detected. There was no evidence of disulfide bridge, Schiff base, or dityrosine formation. The chemical cross-links identified in this work are most likely responsible for the formation of covalent aggregates of IFNβ1a induced by oxidation, which have previously been shown to be highly immunogenic.

Nanostructure development during peroxidase catalysed cross-linking of α-lactalbumin

Whereas extensive work has been done on the food functional and chemical aspects of enzymatic protein cross-linking, relatively little is known about the nanostructure and physical-chemical properties of enzymatically cross-linked protein. We investigate how nanostructure develops during enzymatic cross-linking of the 4 tyrosine residues of the globular protein apo α-lactalbumin. Protein cross-linking is catalysed by Horseradish Peroxidase, under the periodic addition of peroxide. We use on-line static and dynamic light scattering, combined with on-line UV-spectroscopy to simultaneously probe the development of nanostructure, the extent of dityrosine formation, and the catalytic state of the enzyme, as a function of the number of peroxide additions. It is found that initially, the rate of dityrosine formation is high, whereas the increase in the solution size of the cross-linked protein is limited. At later stages, the increase in solution size is significant whereas dityrosine formation slows down. Finally, the reaction stops due to enzyme inactivation. Off-line size exclusion chromatography shows that the initial phase corresponds to a fast cross-linking of monomers into small oligomers, followed by a slower joining of oligomers into large protein polymers. Consistent with this, Atomic Force Microscopy shows very heterogeneous polymers, apparently consisting of subunits that we identify with the oligomers formed in the first phase of the reaction. The dependence of the solution size on the molar mass of the cross-linked protein is determined using static and dynamic light scattering on fractionated reaction products. For sizes ranging from 30 nm to 80 nm, the protein polymers consist of 100–1000 α-lactalbumin subunits, and have molar masses of 106–107 g/mol. Apparent internal protein densities of the protein polymers calculated from these numbers are only a few weight percent, indicating a very dilute, open architecture of the cross-linked protein.

Effect of oxidation on the emulsifying properties of soy protein isolate

Soy protein isolate (SPI) was oxidized by peroxyl radicals derived from 2,2′-azobis (2-amidinopropane) dihydrochloride (AAPH) and the structural and emulsifying properties of oxidized SPI were evaluated. Increasing extent of oxidation resulted in gradual carbonyl group generation, free sulfhydryl group degradation and dityrosine formation. Moderate oxidization could generate soluble protein aggregates with more flexible structure while over-oxidization would induce the formation of insoluble aggregates. Compared with the control, emulsions stabilized by moderately oxidized SPI had smaller droplet size and better thermal stability. Results from creaming index and microstructure measurement after 15days indicated that emulsions stabilized by SPI of over-oxidation underwent severe droplet aggregation during storage while moderate oxidation had a positive effect on the emulsion stability.

Peroxynitrite-modified H3 Histone is Highly Immunogenic and Binds Circulating SLE Autoantibodies Better than Native DNA

Peroxynitrite is a bifaceted reactive species. It can oxidize and nitrate proteins/nucleic acids/lipids and is involved in inflammation, apoptosis, cytotoxicity and autoimmune disorders of unknown etiology, including SLE. In this study, H3 histone exposed to peroxynitrite caused loss of tertiary structure, nitration of tyrosine residues and dityrosine formation. Experimentally produced antibodies against peroxynitrite-modified H3 histone showed specificity for the immunogen. However, cross-reactions with other nitrated proteins were also observed. We further investigated the binding of SLE autoantibodies with native DNA, native H3 histone and peroxynitrite-modified H3 histone to explore the possible role of modified-H3 histone in the initiation and/or progression of SLE in a sub-group of patients. The results showed preferential binding of SLE anti-nDNA autoantibodies to peroxynitrite-modified H3 histone. The visual detection of immune complex formation with native and peroxynitrite-modified H3 histone reiterated preferential binding of SLE autoantibodies with modified H3 histone. It may be concluded that anti-histone autoantibodies seen in a subgroup of SLE patients might be due to the immunogenicity of peroxynitrite-modified H3 histone.

Oxidative modification of neurofilament-L and neuronal cell death induced by the catechol neurotoxin, tetrahydropapaveroline

Tetrahydropapaveroline (THP), which is an endogenous neurotoxin, has been suspected to be associated with dopaminergic neurotoxicity of l-DOPA. In this study, we examined oxidative modification of neurofilament-L (NF-L) and neuronal cell death induced by THP. When disassembled NF-L was incubated with THP, protein aggregation was increased in a time- and THP dose-dependent manner. The formation of carbonyl compounds and dityrosine were observed in the THP-mediated NF-L aggregates. Radical scavengers reduced THP-mediated NF-L modification. These results suggest that the modification of NF-L by THP may be due to oxidative damage resulting from the generation of reactive oxygen species (ROS). When THP exposed NF-L was subjected to amino acid analysis, glutamate, proline and lysine residues were found to be particularly sensitive. We also investigated the effects of copper ions on THP-mediated NF-L modification. At a low concentration of THP, copper ions enhanced the modification of NF-L. Treatment of C6 astrocyte cells with THP led to a concentration-dependent reduction in cell viability. When these cells were treated with 100μM THP, the levels of ROS increased 3.5-fold compared with control cells. Furthermore, treatment of cells with THP increased NF-L aggregate formation, suggesting the involvement of NF-L modification in THP-induced cell damage.

UV-Light Exposure of Insulin: Pharmaceutical Implications upon Covalent Insulin Dityrosine Dimerization and Disulphide Bond Photolysis

In this work we report the effects of continuous UV-light (276 nm, ∼2.20 W.m−2) excitation of human insulin on its absorption and fluorescence properties, structure and functionality. Continuous UV-excitation of the peptide hormone in solution leads to the progressive formation of tyrosine photo-product dityrosine, formed upon tyrosine radical cross-linkage. Absorbance, fluorescence emission and excitation data confirm dityrosine formation, leading to covalent insulin dimerization. Furthermore, UV-excitation of insulin induces disulphide bridge breakage. Near- and far-UV-CD spectroscopy shows that UV-excitation of insulin induces secondary and tertiary structure losses. In native insulin, the A and B chains are held together by two disulphide bridges. Disruption of either of these bonds is likely to affect insulin’s structure. The UV-light induced structural changes impair its antibody binding capability and in vitro hormonal function. After 1.5 and 3.5 h of 276 nm excitation there is a 33.7% and 62.1% decrease in concentration of insulin recognized by guinea pig anti-insulin antibodies, respectively. Glucose uptake by human skeletal muscle cells decreases 61.7% when the cells are incubated with pre UV-illuminated insulin during 1.5 h. The observations presented in this work highlight the importance of protecting insulin and other drugs from UV-light exposure, which is of outmost relevance to the pharmaceutical industry. Several drug formulations containing insulin in hexameric, dimeric and monomeric forms can be exposed to natural and artificial UV-light during their production, packaging, storage or administration phases. We can estimate that direct long-term exposure of insulin to sunlight and common light sources for indoors lighting and UV-sterilization in industries can be sufficient to induce irreversible changes to human insulin structure. Routine fluorescence and absorption measurements in laboratory experiments may also induce changes in protein structure. Structural damage includes insulin dimerization via dityrosine cross-linking or disulphide bond disruption, which affects the hormone’s structure and bioactivity.