Characterization of oxidative pathways in chronic rhinosinusitis and sinonasal polyposis

Peroxidasin mediates bromination of tyrosine residues in the extracellular matrix

Peroxidasin is a heme peroxidase that oxidizes bromide to hypobromous acid (HOBr), a powerful oxidant that promotes the formation of the sulfilimine crosslink in collagen IV in basement membranes. We investigated whether HOBr released by peroxidasin leads to other oxidative modifications of proteins, particularly bromination of tyrosine residues, in peroxidasin-expressing PFHR9 cells. Using stable isotope dilution LC-MS/MS, we detected the formation of 3-bromotyrosine, a specific biomarker of HOBr-mediated protein modification. The level of 3-bromotyrosine in extracellular matrix proteins from normally cultured cells was 1.1 mmol/mol tyrosine and decreased significantly in the presence of the peroxidasin inhibitor, phloroglucinol. A negligible amount of 3-bromotyrosine was detected in peroxidasin-knockout cells. 3-Bromotyrosine formed both during cell growth in culture and in the isolated decellularized extracellular matrix when embedded peroxidasin was supplied with hydrogen peroxide and bromide. The level of 3-bromotyrosine was significantly higher in extracellular matrix than intracellular proteins, although a low amount was detected intracellularly. 3-Bromotyrosine levels increased with higher bromide concentrations and decreased in the presence of physiological concentrations of thiocyanate and urate. However, these peroxidase substrates showed moderate to minimal inhibition of collagen IV crosslinking. Our findings provide evidence that peroxidasin promotes the formation of 3-bromotyrosine in proteins. They show that HOBr produced by peroxidasin is selective for, but not limited to, the crosslinking of collagen IV. Based on our findings, the use of 3-bromotyrosine as a specific biomarker of oxidative damage by HOBr warrants further investigation in clinical conditions linked to high peroxidasin expression.

The role of endogenous bromotyrosine in health and disease

Bromotyrosine is a stable by-product of eosinophil peroxidase activity, a result of eosinophil activation during an inflammatory immune response. The elevated presence of bromotyrosine in tissue, blood, and urine in medical conditions involving eosinophil activation has highlighted the potential role of bromotyrosine as a medical biomarker. This is highly beneficial in a paediatric setting as a urinary noninvasive biomarker. However, bromotyrosine and its derivatives may exert biological effects, such as protective effects in the brain and pathogenic effects in the thyroid. Understanding these pathways may yield therapeutic advancements in medicine. In this review, we summarize the existing evidence present in literature relating to bromotyrosine formation and metabolism, identify the biological actions of bromotyrosine and evaluate the feasibility of bromotyrosine as a medical biomarker.

Calcification and Oxidative Modifications Are Associated With Progressive Bioprosthetic Heart Valve Dysfunction

Background

Bioprosthetic heart valves (BHVs), fabricated from glutaraldehyde‐pretreated bovine pericardium or porcine aortic valves, are widely used for the surgical or interventional treatment of heart valve disease. Reoperation becomes increasingly necessary over time because of BHV dysfunction.

Methods and Results

Forty‐seven explanted BHV aortic valve replacements were retrieved at reoperation for clinically severe BHV dysfunction over the period 2010–2016. Clinical explant analyses of BHV leaflets for calcium (atomic absorption spectroscopy) and oxidized amino acids, per mass spectroscopy, were primary end points. Comorbidities for earlier BHV explant included diabetes mellitus and coronary artery bypass grafting. Mean calcium levels in BHV leaflets were significantly increased compared with unimplanted BHV (P<0.001); however, time to reoperation did not differ comparing calcified and noncalcified BHV. BHV dityrosine, an oxidized amino acid cross‐link, was significantly increased in the explants (227.55±33.27 μmol/mol [dityrosine/tyrosine]) but was undetectable in unimplanted leaflets (P<0.001). BHV regional analyses revealed that dityrosine, ranging from 57.5 to 227.8 μmol/mol (dityrosine/tyrosine), was detectable only in the midleaflet samples, indicating the site‐specific nature of dityrosine formation. 3‐Chlorotyrosine, an oxidized amino acid formed by myeloperoxidase‐catalyzed chlorinating oxidants, correlated with BHV calcium content in leaflet explant analyses from coronary artery bypass graft patients (r=0.62, P=0.01) but was not significantly correlated with calcification in non–coronary artery bypass graft explanted BHV.

Conclusions

Both increased BHV leaflet calcium levels and elevated oxidized amino acids were associated with bioprosthesis dysfunction necessitating reoperation; however, BHV calcium levels were not a determinant of implant duration, indicating a potentially important role for oxidized amino acid formation in BHV dysfunction.

Eosinophil Peroxidase Catalyzed Protein Carbamylation Participates in Asthma

The biochemical mechanisms through which eosinophils contribute to asthma pathogenesis are unclear. Here we show eosinophil peroxidase (EPO), an abundant granule protein released by activated eosinophils, contributes to characteristic asthma-related phenotypes through oxidative posttranslational modification (PTM) of proteins in asthmatic airways through a process called carbamylation. Using a combination of studies we now show EPO uses plasma levels of the pseudohalide thiocyanate (SCN^-) as substrate to catalyze protein carbamylation, as monitored by PTM of protein lysine residues into N^ϵ-carbamyllysine (homocitrulline), and contributes to the pathophysiological sequelae of eosinophil activation. Studies using EPO-deficient mice confirm EPO serves as a major enzymatic source for protein carbamylation during eosinophilic inflammatory models, including aeroallergen challenge. Clinical studies similarly revealed significant enrichment in carbamylation of airway proteins recovered from atopic asthmatics versus healthy controls in response to segmental allergen challenge. Protein-bound homocitrulline is shown to be co-localized with EPO within human asthmatic airways. Moreover, pathophysiologically relevant levels of carbamylated protein either incubated with cultured human airway epithelial cells in vitro, or provided as an aerosolized exposure in non-sensitized mice, induced multiple asthma-associated phenotypes including induction of mucin, Th2 cytokines, IFNγ, TGFβ, and epithelial cell apoptosis. Studies with scavenger receptor-A1 null mice reveal reduced IL-13 generation following exposure to aerosolized carbamylated protein, but no changes in other asthma-related phenotypes. In summary, EPO-mediated protein carbamylation is promoted during allergen-induced asthma exacerbation, and can both modulate immune responses and trigger a cascade of many of the inflammatory signals present in asthma.

Oxidation increases mucin polymer cross-links to stiffen airway mucus gels

Airway mucus in cystic fibrosis (CF) is highly elastic, but the mechanism behind this pathology is unclear. We hypothesized that the biophysical properties of CF mucus are altered because of neutrophilic oxidative stress. Using confocal imaging, rheology, and biochemical measures of inflammation and oxidation, we found that CF airway mucus gels have a molecular architecture characterized by a core of mucin covered by a web of DNA and a rheological profile characterized by high elasticity that can be normalized by chemical reduction. We also found that high levels of reactive oxygen species in CF mucus correlated positively and significantly with high concentrations of the oxidized products of cysteine (disulfide cross-links). To directly determine whether oxidation can cross-link mucins to increase mucus elasticity, we exposed induced sputum from healthy subjects to oxidizing stimuli and found a marked and thiol-dependent increase in sputum elasticity. Targeting mucin disulfide cross-links using current thiol-amino structures such as N-acetylcysteine (NAC) requires high drug concentrations to have mucolytic effects. We therefore synthesized a thiol-carbohydrate structure (methyl 6-thio-6-deoxy-α-D-galactopyranoside) and found that it had stronger reducing activity than NAC and more potent and fast-acting mucolytic activity in CF sputum. Thus, oxidation arising from airway inflammation or environmental exposure contributes to pathologic mucus gel formation in the lung, which suggests that it can be targeted by thiol-modified carbohydrates.

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.

Hypohalous acid-modified human serum albumin induces neutrophil NADPH oxidase activation, degranulation, and shape change

Halogenated lipids, proteins, and lipoproteins formed in reactions with myeloperoxidase (MPO)-derived hypochlorous acid (HOCl) and hypobromous acid (HOBr) can contribute to the regulation of functional activity of cells and serve as mediators of inflammation. Human serum albumin (HSA) is the major plasma protein target of hypohalous acids. This study was performed to assess the potency of HSA modified by HOCl (HSA-Cl) and HOBr (HSA-Br) to elicit selected neutrophil responses. HSA-Cl/Br were found to induce neutrophil degranulation, generation of reactive oxygen intermediates, shape change, and actin cytoskeleton reorganization. Thus HSA-Cl/Br can initially act as a switch and then as a feeder of the "inflammatory loop" under oxidative stress. In HSA-Cl/Br-treated neutrophils, monoclonal antibodies against CD18, the β subunit of β2 integrins, reduced the production of superoxide anion radicals and hydrogen peroxide as well as MPO exocytosis, suggesting that CD18 contributed to neutrophil activation. HSA-Cl/Br-induced neutrophil responses were also inhibited by genistein, a broad-specificity tyrosine kinase inhibitor, and wortmannin, a phosphoinositide 3-kinase (PI3K) inhibitor, supporting the notion that activation of both tyrosine kinase and PI3K may play a role in neutrophil activation by HSA modified in MPO-dependent reactions. These results confirm the hypothesis that halogenated molecules formed in vivo via MPO-dependent reactions can be considered as a new class of biologically active substances potentially able to contribute to activation of myeloid cells in sites of inflammation and serve as inflammatory response modulators.

The susceptibility of bioprosthetic heart valve leaflets to oxidation

The clinical use of bioprosthetic heart valves (BHV) is limited due to device failure caused by structural degeneration of BHV leaflets. In this study we investigated the hypothesis that oxidative stress contributes to this process. Fifteen clinical BHV that had been removed for device failure were analyzed for oxidized amino acids using mass spectrometry. Significantly increased levels of ortho-tyrosine, meta-tyrosine and dityrosine were present in clinical BHV explants as compared to the non-implanted BHV material glutaraldehyde treated bovine pericardium (BP). BP was exposed in vitro to oxidizing conditions (FeSO4/H2O2) to assess the effects of oxidation on structural degeneration. Exposure to oxidizing conditions resulted in significant collagen deterioration, loss of glutaraldehyde cross-links, and increased susceptibility to collagenase degradation. BP modified through covalent attachment of the oxidant scavenger 3-(4-hydroxy-3,5-di-tert-butylphenyl) propyl amine (DBP) was resistant to all of the monitored parameters of structural damage induced by oxidation. These results indicate that oxidative stress, particularly via hydroxyl radical and tyrosyl radical mediated pathways, may be involved in the structural degeneration of BHV, and that this mechanism may be attenuated through local delivery of antioxidants such as DBP.

The Histopathological Effect of Thymoquinone on Experimentally Induced Rhinosinusitis in Rats

Background

Rhinosinusitis is a common disorder and its treatment includes a variety of topical and systemic drugs. This study was designed to determine the histopathological effect of thymoquinone on experimentally induced rhinosinusitis in rats.

Methods

Sixty rats were randomly allocated into 3 test and 2 control groups, each of which consisted of 12 animals. The rhinosinusitis model was induced using intranasal application of platelet-activating factor. In test groups, the animals were separated into groups: (1) rhinosinusitis-antibiotherapy, (2) rhinosinusitis-thymoquinone, (3) rhinosinusitis-combination therapy. The positive and negative control groups were defined: rhinosinusitis group without any treatment and the group without rhinosinusitis, respectively. The histopathological features (vascular congestion, inflammation, and epithelial injury) in nasal respiratory and olfactory mucosa of animals were examined and graded according to their severity. A quantitative and statistical analysis of histopathological features was performed.

Results

All histopathological features showed statistically significant differences between negative and positive control groups, respectively. Conversely, neither the group with rhinosinusitis-antibiotherapy nor the group with rhinosinusitis-thymoquinone had a statistically significant difference with the negative control group. Moreover, none of the histopathological features showed a statistically significant difference, when the group with rhinosinusitis-antibiotherapy and the group with rhinosinusitis-thymoquinone were compared. A statistically significant difference was not determined when the group with rhinosinusitis-combination therapy was compared with the group with rhinosinusitis-thymoquinone. The histopathological features did not show a statistically significant difference between the group with combination therapy and the negative control

Conclusion

Thymoquinone is a promising bioactive agent for the treatment of rhinosinusitis, and its histopathological effect is as equivalent as an antibiotic.

Epigenetics of chronic rhinosinusitis and the role of the eosinophil

BACKGROUND

One theory for the pathogenesis of chronic rhinosinusitis with nasal polyps (CRSwNP) involves aberration in the expression of genes that maintain the sinonasal innate immune system. We propose that the alteration in gene expression seen in CRSwNP is a result of oxidative byproducts of eosinophils. Activated eosinophils and neutrophils may lead to the production of hypobromous acid (HOBr) and hypochlorous acid (HOCL) and the posttranslational modification products 5-bromocytosine (5BrC) and 5-chlorocytosine (5ClC), respectively. 5BrC and 5ClC may cause aberrant methylation of cytosine during DNA replication and mimic the endogenous methylation signal associated with gene silencing. We propose to use gas chromatography-mass spectrometry (GC-MS) to identify the presence of 5BrC and 5ClC in CRSwNP patients.

METHODS

Patients with CRSwNP undergoing endoscopic sinus surgery were prospectively recruited into this study. Using GC-MS, tissue specimens were analyzed for the presence of 5BrC, 5ClC, and methylated cytosine.

RESULTS

Tissue specimens from 14 patients with CRSwNP and 3 normal controls were processed using GC-MS. CRSwNP specimens demonstrate elevated levels of 5BrC and 5ClC compared to normal controls.

CONCLUSION

Eosinophils, which are predominantly found in CRSwNP, may lead to DNA modification and gene silencing via 5BrC and aberrant methylation patterns and may help explain the pathogenesis of CRSwNP.

Kinetics of 3-chlorotyrosine formation and loss due to hypochlorous acid and chloramines

The persistent activation of innate immune cells in chronic inflammation is gaining recognition as a contributing factor in a number of human diseases. A distinguishing feature of activated leukocytes at sites of inflammation is their production of reactive species such as hypochlorous acid (HOCl). Investigating the role of reactive molecules such as HOCl in inflammation and human disease requires appropriate biomarkers. The preferred biomarker for HOCl, and by extension its synthesizing enzyme myeloperoxidase, is 3-chlorotyrosine. 3-Chlorotyrosine is a chemically stable product formed when HOCl, or an HOCl-generated chloramine, reacts with the tyrosine side chain and is readily measured by sensitive mass spectrometry methods. However, Whiteman and Spencer ((2008) Biochem. Biophys. Res. Commun., 371, 50 - 53.) noted that 3-chlorotyrosine is degraded by HOCl, calling into question its use as a biomarker. The kinetic rate constants for the reaction of 3-chlorotyrosine with HOCl, histidine chloramine, or lysine chloramine to form 3,5-dichlorotyrosine are reported. The kinetics of tyrosine chlorination in the context of a peptide with a nearby lysine residue was also determined and further supports the role of chloramines in the chlorination of protein-bound tyrosine residues. The likelihood of free and protein-bound 3,5-dichlorotyrosine occurring in vivo, given the reported rate constants, is discussed.

Protein modifications as potential biomarkers in breast cancer

A variety of post-translational protein modifications (PTMs) are known to be altered as a result of cancer development. Thus, these PTMs are potentially useful biomarkers for breast cancer. Mass spectrometry, antibody microarrays and immunohistochemistry techniques have shown promise for identifying changes in PTMs. In this review, we summarize the current literature on PTMs identified in the plasma and tumor tissue of breast-cancer patients or in breast cell lines. We also discuss some of the analytical techniques currently being used to evaluate PTMs.

Nitric oxide metabolites as biomarkers for follow-up after chronic rhinosinusitis surgery

BACKGROUND

Nitric oxide (NO) has a variety of effects on the pathophysiology of the nasal cavity and seems to play an important role in inflammation. It is increased in the common cold but decreased in acute and chronic rhinosinusitis (CRS). Exhaled NO increases after endoscopic sinus surgery in CRS. In our previous study we showed that NO metabolite (nitrate and nitrite) levels are increased in the sinus cavity of CRS patients. We hypothesized that NO metabolite levels are increased to normal in the nasal lavage of CRS patients after endoscopic sinus surgery and NO metabolites in the nasal lavage can be used as indicators of the disease status after surgery.

METHODS

This study was performed on 52 patients with CRS who did not respond to medical therapy and who underwent surgery. NO metabolite levels were measured in nasal lavages of the patients before surgery and 2 months after surgery.

RESULTS

NO metabolite levels (mean +/- SEM) were 18.11 +/- 3.08 micromol/L and 35.97 +/- 4.64 micromol/L in nasal lavages of patients before and after surgery, respectively. The levels of NO metabolites were increased significantly (p < 0.01) after surgery in nasal lavages and patients reported significant improvement based on the visual analog scoring after the operation.

CONCLUSION

NO metabolite levels were decreased in nasal lavages of CRS patients and were increased to normal levels after surgery along with improvement of the disease. NO metabolite levels may be used as an indicator for the follow-up of patients after endoscopic sinus surgery.