Ascorbic acid in nasal and tracheobronchial airway lining fluids

Protective effects of inhaled antioxidants against air pollution-induced pathological responses

As the public health burden of air pollution continues to increase, new strategies to mitigate harmful health effects are needed. Dietary antioxidants have previously been explored to protect against air pollution-induced lung injury producing inconclusive results. Inhaled (pulmonary or nasal) administration of antioxidants presents a more promising approach as it could directly increase antioxidant levels in the airway surface liquid (ASL), providing protection against oxidative damage from air pollution. Several antioxidants have been shown to exhibit antioxidant, anti-inflammatory, and anti-microbial properties in in vitro and in vivo models of air pollution exposure; however, little work has been done to translate these basic research findings into practice. This narrative review summarizes these findings and data from human studies using inhaled antioxidants in response to air pollution, which have produced positive results, indicating further investigation is warranted. In addition to human studies, cell and murine studies should be conducted using more relevant models of exposure such as air-liquid interface (ALI) cultures of primary cells and non-aqueous apical delivery of antioxidants and pollutants. Inhalation of antioxidants shows promise as a protective intervention to prevent air pollution-induced lung injury and exacerbation of existing lung disease.

Integration of Epigenetic Mechanisms into Non-Genotoxic Carcinogenicity Hazard Assessment: Focus on DNA Methylation and Histone Modifications

Epigenetics involves a series of mechanisms that entail histone and DNA covalent modifications and non-coding RNAs, and that collectively contribute to programing cell functions and differentiation. Epigenetic anomalies and DNA mutations are co-drivers of cellular dysfunctions, including carcinogenesis. Alterations of the epigenetic system occur in cancers whether the initial carcinogenic events are from genotoxic (GTxC) or non-genotoxic (NGTxC) carcinogens. NGTxC are not inherently DNA reactive, they do not have a unifying mode of action and as yet there are no regulatory test guidelines addressing mechanisms of NGTxC. To fil this gap, the Test Guideline Programme of the Organisation for Economic Cooperation and Development is developing a framework for an integrated approach for the testing and assessment (IATA) of NGTxC and is considering assays that address key events of cancer hallmarks. Here, with the intent of better understanding the applicability of epigenetic assays in chemical carcinogenicity assessment, we focus on DNA methylation and histone modifications and review: (1) epigenetic mechanisms contributing to carcinogenesis, (2) epigenetic mechanisms altered following exposure to arsenic, nickel, or phenobarbital in order to identify common carcinogen-specific mechanisms, (3) characteristics of a series of epigenetic assay types, and (4) epigenetic assay validation needs in the context of chemical hazard assessment. As a key component of numerous NGTxC mechanisms of action, epigenetic assays included in IATA assay combinations can contribute to improved chemical carcinogen identification for the better protection of public health.

Vitamin C: the known and the unknown and Goldilocks

Vitamin C (Ascorbic Acid), the antiscorbutic vitamin, cannot be synthesized by humans and other primates, and has to be obtained from diet. Ascorbic acid is an electron donor and acts as a cofactor for fifteen mammalian enzymes. Two sodium-dependent transporters are specific for ascorbic acid, and its oxidation product dehydroascorbic acid is transported by glucose transporters. Ascorbic acid is differentially accumulated by most tissues and body fluids. Plasma and tissue vitamin C concentrations are dependent on amount consumed, bioavailability, renal excretion, and utilization. To be biologically meaningful or to be clinically relevant, in vitro and in vivo studies of vitamin C actions have to take into account physiologic concentrations of the vitamin. In this paper, we review vitamin C physiology; the many phenomena involving vitamin C where new knowledge has accrued or where understanding remains limited; raise questions about the vitamin that remain to be answered; and explore lines of investigations that are likely to be fruitful.

GSH Induced Controlled Release of Levofloxacin from a Purpose-Built Prodrug: Luminescence Response for Probing the Drug Release in Escherichia coli and Staphylococcus aureus

Fluoroquinolones are third-generation broad spectrum bactericidal antibiotics and work against both Gram-positive and Gram-negative bacteria. Levofloxacin (L), a fluoroquinolone, is widely used in anti-infective chemotherapy and treatment of urinary tract infection and pneumonia. The main pathogen for urinary tract infections is Escherichia coli, and Streptococcus pneumoniae is responsible for pneumonia, predominantly a lower respiratory tract infection. Poor permeability of L leads to the use of higher dose of this drug and excess drug in the outer cellular fluid leads to central nervous system (CNS) abnormality. One way to counter this is to improve the lipophilicity of the drug molecule, and accordingly, we have synthesized two new Levofloxacin derivatives, which participated in the spatiotemporal release of drug via disulfide bond cleavage induced by glutathione (GSH). Recent studies with Streptococcus mutants suggest that it is localized in epithelial lining fluid (ELF) of the normal lower respiratory tract and the effective [GSH] in ELF is ∼430 μM. E. coli typically cause urinary tract infections and the concentration of GSH in porcine bladder epithelium is reported as 0.6 mM for a healthy human. Thus, for the present study we have chosen two important bacteria (Gram + ve and Gram - ve), which are operational in regions having high extracellular GSH concentration. Interestingly, this supports our design of new lipophilic Levofloxacin based prodrugs, which released effective drug on reaction with GSH. Higher lipophilicity favored improved uptake of the prodrugs. Site specific release of the drug (L) could be achieved following a glutathione mediated biochemical transformation process through cleavage of a disulfide bond of these purpose-built prodrugs. Further, appropriate design helped us to demonstrate that it is possible also to control the kinetics of the drug release from respective prodrugs. Associated luminescence enhancement helps in probing the release of the drug from the prodrug in bacteria and helps in elucidating the mechanistic pathway of the transformation. Such an example is scarce in the contemporary literature.

Bacterial Metabolism in the Host Environment: Pathogen Growth and Nutrient Assimilation in the Mammalian Upper Respiratory Tract

Pathogens evolve in specific host niches and microenvironments that provide the physical and nutritional requirements conducive to their growth. In addition to using the host as a source of food, bacterial pathogens must avoid the immune response to their presence. The mammalian upper respiratory tract is a site that is exposed to the external environment, and is readily colonized by bacteria that live as resident flora or as pathogens. These bacteria can remain localized, descend to the lower respiratory tract, or traverse the epithelium to disseminate throughout the body. By virtue of their successful colonization of the respiratory epithelium, these bacteria obtain the nutrients needed for growth, either directly from host resources or from other microbes. This chapter describes the upper respiratory tract environment, including its tissue and mucosal structure, prokaryotic biota, and biochemical composition that would support microbial life. Neisseria meningitidis and the Bordetella species are discussed as examples of bacteria that have no known external reservoirs but have evolved to obligately colonize the mammalian upper respiratory tract.

Identification of vitamin C transporters in the human airways: a cross-sectional in vivo study

OBJECTIVES

Vitamin C is an important low-molecular weight antioxidant at the air-lung interface. Despite its critical role as a sacrificial antioxidant, little is known about its transport into the respiratory tract lining fluid (RTLF), or the underlying airway epithelial cells. While several vitamin C transporters have been identified, such as sodium-ascorbate cotransporters (SVCT1/2) and glucose transporters (GLUTs), the latter transporting dehydroascorbate, knowledge of their protein distribution within the human lung is limited, in the case of GLUTs or unknown for SVCTs.

SETTING AND PARTICIPANTS

Protein expression of vitamin C transporters (SVCT1/2 and GLUT1-4) was examined by immunohistochemistry in endobronchial biopsies, and by FACS in airway leucocytes from lavage fluid, obtained from 32 volunteers; 16 healthy and 16 mild asthmatic subjects. In addition, antioxidant concentrations were determined in RTLF. The study was performed at one Swedish centre.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary outcome measure was to establish the location of vitamin C transporters in the human airways. As secondary outcome measures, RTLF vitamin C concentration was measured and related to transporter expression, as well as bronchial epithelial inflammatory and goblet cells numbers.

RESULTS

Positive staining was identified for SVCT1 and 2 in the vascular endothelium. SVCT2 and GLUT2 were present in the apical bronchial epithelium, where SVCT2 staining was predominately localised to goblet cells and inversely related to RTLF vitamin C concentrations.

CONCLUSIONS

This experimental study is the first to demonstrate protein expression of GLUT2 and SVCT2 in the human bronchial epithelium. A negative correlation between SVCT2-positive goblet cells and bronchial RTLF vitamin C concentrations suggests a possible role for goblet cells in regulating the extracellular vitamin C pool.

The effect of vitamin C on bronchoconstriction and respiratory symptoms caused by exercise: a review and statistical analysis

Physical activity increases oxidative stress and therefore the antioxidant effects of vitamin C administration might become evident in people undertaking vigorous exercise. Vitamin C is involved in the metabolism of histamine, prostaglandins, and cysteinyl leukotrienes, all of which appear to be mediators in the pathogenesis of exercise-induced bronchoconstriction (EIB). Three studies assessing the effect of vitamin C on patients with EIB were subjected to a meta-analysis and revealed that vitamin C reduced postexercise FEV1 decline by 48% (95% CI: 33% to 64%). The correlation between postexercise FEV1 decline and respiratory symptoms associated with exercise is poor, yet symptoms are the most relevant to patients. Five other studies examined subjects who were under short-term, heavy physical stress and revealed that vitamin C reduced the incidence of respiratory symptoms by 52% (95% CI: 36% to 65%). Another trial reported that vitamin C halved the duration of the respiratory symptoms in male adolescent competitive swimmers. Although FEV1 is the standard outcome for assessing EIB, other outcomes may provide additional information. In particular, the mean postexercise decline of FEF50 is twice the decline of FEV1. Schachter and Schlesinger (1982) reported the effect of vitamin C on exercise-induced FEF60 levels in 12 patients suffering from EIB and their data are analyzed in this paper. The postexercise FEF60 decline was greater than 60% for five participants and such a dramatic decline indicates that the absolute postexercise FEF60 level becomes an important outcome in its own right. Vitamin C increased postexercise FEF60 levels by 50% to 150% in those five participants, but had no significant effect in the other seven participants. Thus, future research on the effects of vitamin C on EIB should not be restricted to measuring only FEV1. Vitamin C is inexpensive and safe, and further study on those people who have EIB or respiratory symptoms associated with exercise is warranted.

Effect of vitamin supplementation on lung injury and running performance in a hot, humid, and ozone-polluted environment

In this study, the effect of vitamin C and E supplementation on lung injury and performance of runners were analyzed. Using a randomized, double-blinded, crossover design, nine runners participated in two experimental trials: a 2-week Vitamin trial (vitamin C = 500  mg/day + vitamin E = 100  IU/day) and a 2-week Placebo trial. At the end of each supplementation period the runners performed an 8-km time-trial run in a hot (31°C), humid (70% rh), and ozone-polluted (0.10  ppm O(3)) environmental chamber. Nasal lavage and blood samples were collected pre-, post-, and 6-h post-exercise to assess antioxidant status and CC16 as lung injury marker. Higher plasma (pre- and post-exercise) and nasal lavage (post-exercise) antioxidant concentration were found for the Vitamin trial. Nevertheless, this did not result in performance differences (Vitamin trial: 31:05  min; Placebo trial: 31:54  min; P = 0.075) even though significant positive correlations were found between antioxidant concentration and improvement in time to complete the run. CC16 was higher post-exercise in the Placebo trial (P < 0.01) in both plasma and nasal lavage. These findings suggest that antioxidant supplementation might help to decrease the lung injury response of runners when exercising in adverse conditions, but has little effect on performance.

Targeting maladaptive glutathione responses in lung disease

The lung is unique being exposed directly to the atmospheric environment containing xenobiotics, pathogens, and other agents which are continuously inhaled on a daily basis. Additionally, the lung is exposed to higher ambient oxygen levels which can promote the formation of a complex number of reactive oxygen and nitrogen species. Due to this constant barrage of potential damaging agents, the lung has developed a high degree of plasticity in dealing with ever changing conditions. In the present commentary, we will focus on glutathione (GSH) as a key antioxidant in the lung airways and discuss mechanisms by which the lung uses GSH to adapt to its rapidly changing environment. We will then examine the evidence on how defective and inadequate adaptive responses can lead to lung injury, inflammation and disease. Lastly, we will examine some of the recent attempts to alter lung GSH levels with therapies in a number of human lung diseases and discuss some of the limitations of such approaches.

Effect of L-ascorbate on chloride transport in freshly excised sinonasal epithelia

BACKGROUND

Chronic rhinosinusitis (CRS) occurs at high frequency in patients with cystic fibrosis, suggesting that the cystic fibrosis transmembrane conductance regulator (CFTR) chloride (Cl) ion channel might be involved in the development of chronic sinusitis in the general population. CFTR Cl ion transport controls the hydration of mucosal surfaces and promotes effective mucociliary clearance. Altered ion transport and, hence, disrupted mucociliary function, could play a role in the pathogenesis of sinus disease. L-ascorbate is a metabolically active component of the nasal and tracheobronchial airway lining fluids and appears to serve as an important biological effector of CFTR-mediated chloride secretion. The purpose of this study was to determine the effects of L-ascorbate on Cl ion transport in freshly excised sinonasal epithelia from normal controls and patients with CRS.

METHODS

Four different types of sinonasal tissue (normal sinus mucosa, sinus mucosa from CRS, normal nasal mucosa, nasal mucosa from CRS) were obtained during endoscopic sinus surgery and mounted on sliders with open areas of 0.03-0.71 cm2 between Ussing hemichambers. Short-circuit current (Isc) was continuously recorded, and a serosa-to-mucosa-directed Cl gradient was applied to increase the electrochemical driving force.

RESULTS

L-ascorbate (500 microM) stimulated Cl currents (DeltaI(Cl), microA/cm2) across sinonasal epithelia from normal and CRS patients. The Cl secretory response to L-ascorbate was effectively blocked by the Cl ion transport inhibitors glibenclamide and bumetanide. A maximal dose of L-ascorbate (at 1 mM) stimulated 53-70% of Cl currents elicited by the cAMP agonist forskolin. CRS sinonasal tissue was characterized by impaired Cl secretory responses to L-ascorbate that were reduced by 33% in sinus epithelial tissue and by 70% in nasal epithelial tissue when compared with normal subjects. In nasal epithelial tissue from normal subjects, Cl secretion was approximately twofold increased when compared with sinus epithelial tissue. In contrast, nasal versus sinus epithelial tissue from CRS patients showed no differences.

CONCLUSION

Topical administration of L-ascorbate to freshly excised sinus and nasal mucosa enhances chloride secretion. Given that decreased CFTR-mediated Cl secretion may contribute to the development of CRS, L-ascorbate may offer potential as a therapeutic agent for the improvement of mucociliary clearance.

Salivary oxidative stress in children during acute asthmatic attack and during remission

BACKGROUND

Patients with asthma generate an increased amount of reactive oxygen species from peripheral blood cells, which may contribute to its pathogenesis. Saliva analysis is non-invasive and friendly to children. We undertook this study to analyze the salivary oxidative profile and composition in children with asthma during attack and remission, and to compare them with the levels of salivary antioxidants of healthy control children.

METHODS

School age (range 6-18 years) children referred to the emergency room for acute asthma were included. Clinical score was assessed, spirometry performed, and saliva samples were collected and analyzed. All measurements were repeated during remission of asthma attack (2-4 weeks after attack). Salivary analysis was performed blindly during asthma attack and the results were compared to those obtained during remission, and to those of the control group.

RESULTS

Statistically significant decreases in levels of salivary peroxidase enzyme activity were observed in asthmatic children during attack compared with healthy controls, with partial recovery during remission of attack. Similarly decreased levels of calcium concentrations were observed in asthmatic children, accompanied by increased phosphate levels.

CONCLUSIONS

Children with acute asthma attacks exhibit a decrease in the activity of the most important salivary antioxidant enzyme-peroxidase, which is accompanied by other salivary composition alterations. Hence, acute asthma is manifested by salivary changes. This implies systemic oxidative stress in asthma, which may be reflected in salivary analysis.

Antioxidants in cystic fibrosis. Conclusions from the CF antioxidant workshop, Bethesda, Maryland, November 11-12, 2003

Although great strides are being made in the care of individuals with cystic fibrosis (CF), this condition remains the most common fatal hereditary disease in North America. Numerous links exist between progression of CF lung disease and oxidative stress. The defect in CF is the loss of function of the transmembrane conductance regulator (CFTR) protein; recent evidence that CFTR expression and function are modulated by oxidative stress suggests that the loss may result in a poor adaptive response to oxidants. Pancreatic insufficiency in CF also increases susceptibility to deficiencies in lipophilic antioxidants. Finally the airway infection and inflammatory processes in the CF lung are potential sources of oxidants that can affect normal airway physiology and contribute to the mechanisms causing characteristic changes associated with bronchiectasis and loss of lung function. These multiple abnormalities in the oxidant/antioxidant balance raise several possibilities for therapeutic interventions that must be carefully assessed.

Vitamin supplementation does not protect against symptoms in ozone-responsive subjects

Vitamin supplements have been reported to reduce the magnitude of symptoms in subjects exposed to oxidant air pollution. To confirm whether supplementation with vitamins C and E could reduce lung function decrements, airway inflammation, and epithelial injury in subjects sensitive to ozone, a double-blinded, crossover control study was performed. Fourteen ozone-responsive subjects were randomly exposed to both air and ozone (0.2 ppm for 2 h) after 7 days of either placebo treatment or supplementation with vitamin C (500 mg/day) and E (100 mg/day). Lung function was assessed pre- and immediately postexposure and blood samples were taken at set intervals. Inflammatory, tissue injury, and antioxidant responses were examined in lavage fluid obtained by bronchoscopy 6 h postexposure. Exposure to ozone resulted in significant (P < 0.01) decrements in FEV1 with no protection observed following vitamin supplementation (-8.5%) versus placebo (-7.3%) treatment. Similarly, ozone-induced neutrophilia were of a similar magnitude after both treatments (P < 0.05). This lack of protection was observed despite elevated plasma vitamin C (+60.1%) and vitamin E (+51.4%) concentrations following supplementation, and increased vitamin C concentrations in the airways after supplementation following ozone exposure. These data do not therefore support the contention that acute ozone-induced symptoms can be attenuated through the use of dietary antioxidants in well-nourished individuals.

Apples increase nitric oxide production by human saliva at the acidic pH of the stomach: a new biological function for polyphenols with a catechol group?

Dietary inorganic nitrate is secreted in saliva and reduced to nitrite by bacterial flora. At the acidic pH of the stomach nitrite is present as nitrous acid in equilibrium with nitric oxide (*NO), and other nitrogen oxides with nitrating and nitrosating activity. *NO in the stomach exerts several beneficial effects, but nitrosating/nitrating species have been implicated as a possible cause of epithelial neoplasia at the gastroesophageal junction. We investigated the effects of apple extracts on *NO release by human saliva at pH 2. A water extract obtained from apple homogenate increased *NO release caused by acidification of saliva. Data show that polyphenols were responsible for this activity, with chlorogenic acid and (+)-catechin the most active and concentrated species. However, ferulic acid, a hydroxycinnamic acid with only one aromatic hydroxyl group, did not increase *NO release. Fructose, the most representative sugar in apples, was also inactive. Interestingly, ascorbic acid in saliva induced a SCN(-)-enhanced burst of *NO but, unlike apple, the release was transient. The simultaneous addition of ascorbic acid and apple extract caused a burst of *NO followed by the increased steady-state level characteristic of saliva containing apple extract. Chlorogenic acid and (+)-catechin, but not ferulic acid, formed o-semiquinone radicals and nitrated polyphenols, suggesting the scavenging of *NO(2) by o-semiquinones. Our results propose that some apple polyphenols not only inhibit nitrosation/nitration but also promote *NO bio-availabilty at the gastric level, a previously unappreciated function.

Immunohistochemical study on the distribution of sodium-dependent vitamin C transporters in the respiratory system of adult rat

As vitamin C (L-ascorbic acid, VC) is known to be essential for many enzymatic reactions, the study on the transport mechanism of VC through cytoplasmic membrane is crucial to understanding physiological role of VC in cells and the respiratory system. In this regard, the study on the newly identified sodium-dependent VC transporters (SVCTs), SVCT1 and SVCT2, is required in organs that contain high concentration of VC. We have shown the distribution of SVCT proteins in the respiratory system, which has been reported to be one of the organs with a high concentration of VC, using immunohistochemical techniques. In the present study, intense SVCT immunoreactivities (IRs) were mainly localized in the respiratory system epithelial cells. In the trachea, both SVCT1 and 2 were localized in the psuedostratified ciliated columnar epithelium. In the terminal bronchiole, SVCT1 and 2 IRs were mainly observed in the apical portion of the simple columnar epithelium. In addition, SVCT IRs was localized within the cell membrane of some alveolar cells, even though we could not identify the exact cell types. These results provide the first evidence that intense SVCT1 and 2 IRs were found in the apical portion of the respiratory epithelial cells, suggesting that SVCT proteins in the apical portion could transport the reduced form of VC included in the airway surface liquid into the respiratory epithelial cells.