Hydrogen peroxide-induced epithelial damage increases terbutaline transport in guinea-pig tracheal wall: implications for drug delivery

The effects of acute hydrogen peroxide exposure on respiratory cilia motility and viability

COVID-19 has seen the propagation of alternative remedies to treat respiratory disease, such as nebulization of hydrogen peroxide (H₂O₂). As H₂O₂ has known cytotoxicity, it was hypothesised that H₂O₂ inhalation would negatively impact respiratory cilia function. To test this hypothesis, mouse tracheal samples were incubated with different H₂O₂ concentrations (0.1-1%) then cilia motility, cilia generated flow, and cell death was assessed 0-120 min following H₂O₂ treatment. 0.1-0.2% H₂O₂ caused immediate depression of cilia motility and complete cessation of cilia generated flow. Higher H₂O₂ concentrations (≥0.5%) caused immediate complete cessation of cilia motility and cilia generated flow. Cilia motility and flow was restored 30 min after 0.1% H₂O₂ treatment. Cilia motility and flow remained depressed 120 min after 0.2-0.5% H₂O₂ treatment. No recovery was seen 120 min after treatment with ≥1% H₂O₂. Live/dead staining revealed that H₂O₂ treatment caused preferential cell death of ciliated respiratory epithelia over non-ciliated epithelia, with 1% H₂O₂ causing 35.3 ± 7.0% of the ciliated epithelia cells to die 120 min following initial treatment. This study shows that H₂O₂ treatment significantly impacts respiratory cilia motility and cilia generated flow, characterised by a significant impairment in cilia motility even at low concentrations, the complete cessation of cilia motility at higher doses, and a significant cytotoxic effect on ciliated respiratory epithelial cells by promoting cell death. While this data needs further study using in vivo models, it suggests that extreme care should be taken when considering treating respiratory diseases with nebulised H₂O₂.

Acute stress to excised vocal fold epithelium from reactive oxygen species

OBJECTIVES/HYPOTHESIS

Vocal fold epithelium is exposed to reactive oxygen species from the inhaled environment and from tissue inflammation. The objective of this study was to explore the functional and structural consequences of reactive oxygen species exposure on vocal fold epithelium.

STUDY DESIGN

In vitro, prospective study design.

METHODS

Hydrogen peroxide (H(2)O(2)), a common reactive oxygen species, was utilized in this study. Freshly excised, viable porcine vocal fold epithelia (N = 32) were exposed to H(2) O(2) or sham challenge for 2 hours. Electrophysiology, western blotting, and light microscopy were used to quantify the functional and structural effects of reactive oxygen species on vocal fold epithelia.

RESULTS

Exposure to reactive oxygen species did not significantly alter transepithelial resistance. There was a small, nonsignificant trend for decreased concentration of epithelial junctional complex protein with reactive oxygen species challenge. Minimal changes to the gross structural appearance of vocal fold epithelia were also noted.

CONCLUSIONS

The stratified squamous epithelia of the vocal folds effectively defend against an acute reactive oxygen species challenge. The current study lays the groundwork for future investigations on the effects of reactive oxygen species on vocal fold epithelia that are compromised from phonotrauma.

Functional, structural, and chemical changes in myosin associated with hydrogen peroxide treatment of skeletal muscle fibers

To understand the molecular mechanism of oxidation-induced inhibition of muscle contractility, we have studied the effects of hydrogen peroxide on permeabilized rabbit psoas muscle fibers, focusing on changes in myosin purified from these fibers. Oxidation by 5 mM peroxide decreased fiber contractility (isometric force and shortening velocity) without significant changes in the enzymatic activity of myofibrils and isolated myosin. The inhibitory effects were reversed by treating fibers with dithiothreitol. Oxidation by 50 mM peroxide had a more pronounced and irreversible inhibitory effect on fiber contractility and also affected enzymatic activity of myofibrils, myosin, and actomyosin. Peroxide treatment also affected regulation of contractility, resulting in fiber activation in the absence of calcium. Electron paramagnetic resonance of spin-labeled myosin in muscle fibers showed that oxidation increased the fraction of myosin heads in the strong-binding structural state under relaxing conditions (low calcium) but had no effect under activating conditions (high calcium). This change in the distribution of structural states of myosin provides a plausible explanation for the observed changes in both contractile and regulatory functions. Mass spectroscopy analysis showed that 50 mM but not 5 mM peroxide induced oxidative modifications in both isoforms of the essential light chains and in the heavy chain of myosin subfragment 1 by targeting multiple methionine residues. We conclude that 1) inhibition of muscle fiber contractility via oxidation of myosin occurs at high but not low concentrations of peroxide and 2) the inhibitory effects of oxidation suggest a critical and previously unknown role of methionines in myosin function.

Effects of hydrogen peroxide on the guinea-pig tracheobronchial mucosa in vivo

Lumenal entry of plasma (mucosal exudation) is a key feature of airway inflammation. In airways challenged with histamine-type mediators and allergen the mucosal exudation response occurs without causing epithelial derangement and without increased airway absorption. In contrast, reactive oxygen metabolites may cause mucosal damage. In this study, involving guinea-pig airways, we have examined effects of H2O2 on airway exudation and absorption in vivo. Vehicle or H2O2 (0.1 and 0.5 M) was superfused onto the tracheobronchial mucosal surface through an oro-tracheal catheter. 125I-albumin, given intravenously, was determined in tracheobronchial tissue and in lavage fluids 10 min after challenge as an index of mucosal exudation of plasma. The tracheobronchial mucosa was also examined by scanning electron microscopy. In separate animals, 99mTc-DTPA was superfused 20 min after vehicle or H2O2 (0.1 and 0.5 M) had been given. A gamma camera determined the disappearance rate of 99mTc-DTPA from the airways as an index of airway absorption. The high dose of H2O2 (0.5 M) produced epithelial damage, increased the absorption of 99mTc-DTPA (P < 0.001), and increased the exudation of plasma (P < 0.001). Notably, it appeared that all extravasated plasma had entered the airway lumen within 10 min. These data demonstrate that H2O2 differs from exudative autacoids such as histamine by causing both epithelial damage and plasma exudation responses. These data also agree with the view that the epithelial lining determines the rate of absorption and is responsible for the valve-like function that allows lumenal entry of extravasated bulk plasma without any increased inward perviousness.

H2O2 increases sheep tracheal blood flow, permeability, and vascular response to luminal capsaicin

Exogenous hydrogen peroxide (H2O2) causes airway epithelial damage in vitro. We have studied the effects of luminal H2O2 in the sheep trachea in vivo on tracheal permeability to low-molecular-weight hydrophilic (technetium-99m-labeled diethylenetriamine pentaacetic acid; 99mTc-DTPA) and lipophilic ([14C]antipyrine; [14C]AP) tracers and on the tracheal vascular response to luminal capsaicin, which stimulates afferent nerve endings. A tracheal artery was perfused, and tracheal venous blood was collected. H2O2 exposure (10 mM) reduced tracheal potential difference (-42.0 +/- 6.4 mV) to zero. It increased arterial and venous flows (56.7 +/- 6.1 and 57.3 +/- 10.0%, respectively; n = 5, P < 0.01, paired t-test) but not tracheal lymph flow (unstimulated flow 5.0 +/- 1.2 microliters.min-1.cm-1, n = 4). During H2O2 exposure, permeability to 99mTc-DTPA increased from -2.6 to -89.7 x 10(-7) cm/s (n = 5, P < 0.05), whereas permeability to [14C]AP (-3,312.6 x 10(-7) cm/s, n = 4) was not altered significantly (-2,565 x 10(-7) cm/s). Luminal capsaicin (10 microM) increased tracheal blood flow (10.1 +/- 4.1%, n = 5) and decreased venous 99mTc-DTPA concentration (-19.7 +/- 4.0, P < 0.01), and these effects were significantly greater after epithelial damage (28.1 +/- 6.0 and -45.7 +/- 4.3%, respectively, P < 0.05, unpaired t-test). Thus H2O2 increases the penetration of a hydrophilic tracer into tracheal blood and lymph but has less effect on a lipophilic tracer. It also enhances the effects of luminal capsaicin on blood flow and tracer uptake.

Stimulated eosinophils and proteinases augment the transepithelial flux of albumin in bovine bronchial mucosa

1. The apical to basolateral transmucosal flux of albumin has been measured in isolated sheets of bovine bronchial and tracheal mucosa. Under resting conditions the net unidirectional flux in the bronchial mucosa was not significantly different from that measured previously for the basolateral to apical vector. In contrast, the apical to basolateral flux in the tracheal mucosa was significantly lower than that measured in the opposite direction. 2. Addition of guinea-pig peritoneal eosinophils to the apical side of the tissues had no significant effect on the transmucosal flux of albumin in either the bronchial or tracheal mucosa. 3. When eosinophils were stimulated with the ionophore A23187 or by opsonic adherence to tissues treated with a guinea-pig anti-bovine airway epithelium antibody, the bronchial mucosal sheets that had been exposed showed a significant increase in the transmucosal flux of albumin. However, tissues from the tracheal mucosa were resistant to the effects of stimulated eosinophils. 4. Histologically, sheets of mucosa from bovine main bronchi that had been exposed to stimulated eosinophils were characterized by epithelial injury consisting of loss of columnar epithelium from the underlying basal cell layer and biomatrix. Much less evidence of cellular injury was observed in tracheal tissues. 5. Bacterial collagenases applied to the apical side of the sheets were shown to increase the permeability of the bronchial mucosa to albumin and to produce histological changes that had similarities with the pattern of damage produced by stimulated eosinophils. 6. These observations demonstrate that the ability of eosinophils to injure the bronchial mucosa is independent of the side of the tissue on which they are present. Furthermore, key aspects of the injury process may be reproduced, at least in part, by metalloproteinases.

Leukotriene B4 level in stimulated blood neutrophils and alveolar macrophages from healthy and asthmatic subjects. Effect of beta-2 agonist therapy

Leukotriene B4 levels were measured after stimulation by calcium ionophore A23187: (i) in peripheral, neutrophils (PMN) from allergic asthmatics, rhinitis and healthy subjects; (ii) in macrophages collected by bronchoalveolar lavage. LTB4 levels in PMNs were significantly higher in non-treated allergic asthmatics and non-treated subjects with rhinitis compared to controls. Beta-2 agonist-treated asthmatics showed a significantly decreased LTB4 production which was not different from those of controls. In vitro, LTB4 production decreased significantly after PMN incubation with Salbutamol (10(-6) mol l-1). LTB4 produced by AM collected by BAL was measured in non-treated (n = 5) and treated (n = 11) asthmatics with inhaled beta-2 agonist. AM collected from all controls and non-treated asthmatics produced LTB4. By contrast, no production of LTB4 was observed in the treated group. LTB4 production decreased when normal AM were incubated in vitro with Salbutamol (10(-8) mol l-1). These results suggest that biochemical differences occur in PMN and macrophages from subjects treated with beta-2 agonist, presumably in changing the 5-lipoxygenase pathway.

Epithelial disruption by proteases augments the responsiveness of porcine bronchial segments

1. The effect of disruption to the epithelium of intact porcine bronchi was examined by comparing the responsiveness to agonists applied to the adventitial and luminal surfaces. The development of smooth muscle tone was measured as an increase in pressure in an isovolumic bronchial segment of approximately 2 mm i.d. The reactivity and sensitivity to acetylcholine (ACh) introduced intraluminally was greatly attenuated when compared with adventitial addition. 2. Luminal exposure to K+ and vanadate (VO3-) had little effect compared with strong responses obtained by adventitial application. 3. Intraluminal exposure to trypsin, chymotrypsin and elastase (1 mg/mL) selectively augmented both the sensitivity and the reactivity to the luminal addition of ACh, K+ and carbachol. 4. Mechanical removal of the epithelium produced a 716-fold increase in sensitivity to ACh introduced luminally but had no effect on ACh applied adventitially. 5. The inhibitory effects of luminally introduced isoprenaline on electrical field stimulation responses were also significantly potentiated in segments stripped of epithelium. 6. The evidence presented here indicates that the responsiveness of in vitro airways segments is highly influenced by the epithelial layer, which acts most prominently as a barrier inhibiting the penetration of luminally introduced agonists.