Hypoxia depresses nitric oxide output in the human nasal airways

Airway microenvironment alterations and pathogen growth in cystic fibrosis

Cystic Fibrosis Transmembrane Regulator (CFTR) dysfunction is associated with epithelial cell vulnerability and with dysregulation of the local inflammatory responses resulting in excessive airway neutrophilic inflammation and pathogen growth. In combination with impaired mucociliary clearance, and dysregulation of defense function, bacterial infection follows with eventual airway damage and remodeling. Because of these inherent vulnerabilities, viral infections are also more severe and prolonged and appear to render the airway even more prone to bacterial infection. Airway acidity, deficient nitric oxide production and increased iron concentrations, further enhance the airway milieu's susceptibility to infection. Novel diagnostic techniques of the airway microbiome elucidate the coexistence of an array of non-virulent taxa beyond the recognized virulent organisms, predominantly Pseudomonas aeruginosa. The complex interplay between these two bacterial populations, including upregulation of virulence genes and utilization of mucin as a nutrient source, modulates the action of pathogens, modifies the CF airway milieu and contributes to the processes leading to airway derangement. The review provides an update on recent advances of the complex mechanisms that render the CF airway vulnerable to inflammation, infection and ultimately structural damage, the key pathogenetic elements of CF. The recent contributions on CF pathogenesis will hopefully help in identifying new prophylactic measures and therapeutic targets for this highly destructive disorder.

[The paranasal sinuses as the nitric oxide depot]

This paper was designed to report the currently available data on physiology of the nasal cavity and paranasal sinuses together with the results of national and international investigations on the computer modeling of the air flow in these structures. Also discussed are the gas composition in the paranasal sinuses and the potential factors responsible for the changes in the concentration of nitric oxide with the chemical formula of NO in the nasal cavity and paranasal sinuses.

Paranasal sinus nitric oxide and migraine: a new hypothesis on the sino rhinogenic theory

Migraine is a debilitating illness that has no exact bio molecule to explain its pathology. After reviewing the neurophysiological and biochemical basis of the research findings of nitric oxide and migraine, I present to the best of my knowledge the first para sinus nitric oxide mediated neurobiophysiological hypothesis for migraine of sino rhinogenic origin. The diffused paranasal sinus nitric oxide in the nasal mucosa could be the primary molecule that initiates migraine and is termed Sinus Hypoxic Nitric Oxide Theory. This hypothesis regards repetitive or intermittent activation of the trigeminal sensory nerve and blood vessels in the nasal mucosa. Production of paranasal sinus nitric oxide is mainly induced by hypoxia due to several independent factors and the diffusion of paranasal sinus nitric oxide depends on the vulnerable surface area in the nasal cavity. Apart from the known trigeminal nociceptive impulse in the migraine, two main peripheral trigeminal nerve activating mechanisms may induce migraine. First the nerve endings of the nasal mucosa which are directly stimulated by diffused paranasal sinus nitric oxide are indirectly stimulated by vasoactive substances released by antidromic activation of the nerve, parasympathetic efferent of the nerve and sterile neurogenic inflammation. Secondly, the perivascular nerve of nasal mucosal and the meningial blood vessels are directly stimulated by either diffused paranasal sinus nitric oxide or by shear stress mediation. The nerve impulses of the trigeminal sensory nerve, projected at trigeminal nucleus caudalis to the central nerve system and low plasma magnesium due to the consequence of shear stress gives rise to the symptoms of migraine. Moreover sino rhinogenic impulses may mediate to disruption of inhibitory sensitization modulated of sensory input and cause sensory hiperexcitability. In addition neuronal stimulation proposed by some migraine hypotheses could also give rise to migraine headache when the sino rhinogenic vulnerable factors induce the migraine pathophysiology. Indeed this article explains a new pathophysiological initiation between sino rhinogenic nitric oxide effects and migraine and provides an initial step for the obscured or neglected etiologically important neuro vascular impulse generating pathway. The patients who are clinically suspected of having headaches should receive comprehensive sino rhinological examination and evaluation based on the sinus hypoxic nitric oxide theory. A standard surgical and medical management of migraine that links with the sinus hypoxic nitric oxide theory may restore the hypoxic state or reduce or remove the paranasal sinus nitric oxide diffusing surface. It warrants clinical testing.

Interferon γ stimulates accumulation of gas phase nitric oxide in differentiated cultures of normal and cystic fibrosis airway epithelial cells

BACKGROUND

Exhaled nitric oxide (NO) levels have been reported to be lower in patients with cystic fibrosis (CF) than in controls; however the mechanism(s) responsible and the effect on pathogenesis are unclear. The objective of these studies was to determine if the low levels of gas phase NO (gNO) could be reproduced in well-differentiated air-liquid interface (ALI) cultures of normal and CF cells.

METHODS

Human bronchial epithelial (HBE) cells from CF and control tissues were cultured under ALI conditions that promote differentiation into a mostly ciliated, pseudostratified epithelium similar to that of the in vivo airway. Cultures were incubated in gas tight chambers and the concentration of gNO was measured using a Sievers nitric oxide analyzer.

RESULTS

In CF and control cultures the level of accumulated gNO under baseline conditions was low (<20 ppb). Treatment with interferon gamma (IFNγ) induced iNOS expression and increased gNO significantly in differentiated cultures, while having no significant effect on undifferentiated cultures. Submersion of the apical surface with fluid drastically reduced the level of gNO. Importantly, the average level of gNO measured after IFNγ treatment of control cells (576 ppb) was threefold greater than that from CF cells (192 ppb).

CONCLUSIONS

The results demonstrate that the lower level of exhaled NO observed in CF patients is reproduced in well-differentiated primary cultures of HBE cells treated with IFNγ, supporting the hypothesis that the regulation of NO production is altered in CF. The results also demonstrate that IFNγ treatment of differentiated cells results in higher levels of gNO than treatment of undifferentiated cells, and that a layer of fluid on the apical surface drastically reduces the amount of gNO, possibly by limiting the availability of oxygen.

Physical and computational modeling of ventilation of the maxillary sinus

Objective. Sinus ventilation is often associated with sinusitis, a common condition causing significant pain and reduced quality of life. Clinical implications of the diverse anatomy of ostia connecting sinus to nose and the efficacy of surgical intervention in chronic sinusitis are poorly understood. This study aimed to measure sinus ventilation and explore variables in physical and mathematical models.

Study Design. γ-Scintigraphy of krypton 81m (81mKr) was carried out in a stylized physical model of a human maxillary sinus. Computational simulations matched this model for validation and extrapolated to combinations of variables not possible experimentally for evaluation of transport mechanisms.

Setting. Research laboratory in Department of Aeronautics. Imperial College London, and Department of Nuclear Medicine, Hammersmith Hospital, London.

Methods. 81mKr distribution was measured with both single- and double-ostia sinuses. Computational simulations matched and extended the physical measurements and enabled separate identification and evaluation of transport mechanisms.

Results. The presence of an additional ostium resulted in a 50-fold increase in the effective volume flow rate of gas replacement in the sinus. In the case of a single ostium, doubling the ostial diameter doubled the effective volume flow rate of gas exchange.

Conclusion. γ-Scintigraphy of 81mKr enables quantitative assessment of effective volume flow rate in physical model sinuses. These flow rates obtained experimentally for single- and double-ostium sinuses match the computational predictions of matching geometries. The increased ventilation seen with an additional ostium or increased ostial diameters may not be clinically beneficial, because it could reduce nitric oxide concentration in the sinus.

Exhaled nasal nitric oxide output is reduced in humans at night during the sleep period

The physiologic function of nasal nitric oxide (NO) release is unknown. In prior experiments, topical NG-nitro-L-arginine methyl ester (L-NAME) on nasal mucosa reduced exhaled nasal NO output and caused daytime sleepiness. We hypothesized that nasal NO output is reduced at night during the sleep period. We measured exhaled nasal NO concentration and minute ventilation and calculated nasal NO output in humans over 24 h. Daytime awake NO output was greater than NO output at night during sleep or transient wakefulness. Exhaled NO concentration decreased during sleep along with minute ventilation. A daytime voluntary reduction in minute ventilation also decreased nasal NO output but exhaled NO concentration increased. Nasal NO output was not changed by body position. We conclude that exhaled nasal NO output is decreased at night due to decreased mass flow of NO into nasal air in addition to decreased minute ventilation. Our findings suggest a role of nasal NO in sleep or in the physiologic processes accompanying sleep.

A novel method of measuring gas phase nitric oxide concentration in cell cultures

This is the first report on the measurement of nitric oxide (NO) concentrations in the gas phase in a squamous cell culture. The technique may permit the assessment of NO output under conditions that aim to mimic facets of pathology in relatively inaccessible tissues. The primary aim of this study was to devise a method to detect the NO concentration produced by cell cultures in the gas phase of a culture flask. A secondary aim was to determine whether the effect of hypoxia or radiation on NO production in a human squamous cell carcinoma cell culture would be detectable with this technique. The NO concentration was measured off-line using a rapid-response chemiluminescent analyzer. The gas samples were aspirated from cell culture flasks (i) under normal culture conditions, (ii) under conditions of hypoxia and (iii) following radiation of human head and neck squamous cell carcinoma cell line cultures. Elevated levels of the gas phase NO concentration were consistently obtained from the cell culture flasks using this experimental set-up. Hypoxia and radiation diminished NO production.

A comparison between nitric oxide output in the nose and sinuses: A pilot study in one volunteer

From a study of nitric oxide (NO) output in the nose and sinuses it seems that: (i) the results obtained regarding the regulation of NO output in the nose do not necessarily apply to the sinuses; (ii) the results obtained for one group of sinuses may not apply to another; and (iii) NO output in the sinuses does not behave as one would expect if it serves to protect against infection.A pilot study was undertaken in one subject to determine whether the control of NO output in the nose differs from that in the sinuses.NO output was measured by aspirating different gaseous concentrations of oxygen (and/or carbon dioxide) through the nasal airways or punctured maxillary and frontal sinuses before and after i.v. administration of L-arginine (20 mg/kg). In the absence of gaseous oxygen in the nose or maxillary antrum, the effect of L-arginine on NO output was the same as that in the presence of oxygen. In the frontal sinus, the effect of L-arginine on NO output was blocked by the absence of gaseous oxygen. NO output in the nose and frontal sinus showed similar changes after either i.v. administration of L-arginine or removal of oxygen from the air. NO output in the maxillary antrum was virtually unaffected by either procedure. NO output in the nose was largely unaffected by the gaseous carbon dioxide content but that in the frontal and maxillary sinuses was profoundly inhibited by it. In both sinuses, suppression of NO output by carbon dioxide was countered by oxygen. Alterations in the oxygen or carbon dioxide content of the maxillary antrum did not alter NO output in the frontal sinus, or vice versa. After i.v. infusion of L-arginine, nasal NO output remained elevated for >1 h.

Current value of nasal nitric oxide measurement in rhinology

PURPOSE OF REVIEW

Since the first description of nitric oxide in the exhaled breath of humans by Gustafsson et al., there has been enormous interest in the study of nitric oxide and its role in the nose and paranasal sinuses. The aim of this review is to present the current knowledge about nasal NO: its physiology, novel methods of detection and measurement, and implications in sinonasal disease, focusing on the recent data from the literature.

RECENT FINDINGS

Nitric oxide production is known to be produced in the nose at the apical tip of the ciliated respiratory mucosa. A new study has localized nitric oxide production in the pericytes and osteocytes of nasal turbinates. Studies have also discovered the efficacy of offline measurement techniques showing high correlation between standard online measurements with offline techniques. In an interesting study examining the influence of maxillary ostium size and nasal nitric oxide levels, decreased nitric oxide levels found with larger size ostia may eventually influence our approach to sinus surgery.

SUMMARY

Nasal nitric oxide has been an ever-increasing topic of interest to both the allergist and the head and neck surgeon. The recent advances in the study of nasal nitric oxide as it relates to sinonasal disease and nasal physiology are discussed and important new findings are highlighted.

Nitric oxide (NO) and obstructive sleep apnea (OSA)

Nitric oxide (NO) and obstructive sleep apnea are inseparable. Obstructive sleep apnea could be described as the intermittent failure to transport the full complement of nasal NO to the lung with each breath. There NO matches perfusion to ventilation. NO is utilized by the efferent pathways that control the unequal, inspiratory battle between the pharyngeal dilators and the closing negative pressures induced by the thoracic musculature. Recurrent cortical arousals are a major short-term complication, and the return to sleep after each arousal uses NO. The long-term complications, namely hypertension, myocardial infarction, and stroke, might be due to the repeated temporary dearth of NO in the tissues, secondary to a lack of oxygen, one of NO's two essential substrates.

Somato-sympathetic vasoconstriction to intranasal fluid administration with consecutive decrease in nasal nitric oxide

AIM

Patients suffering from non-allergic chronic rhinosinusitis (NACRS) increasingly use intranasal saline sprays. They report better nasal comfort.

METHODS

In order to better understand this phenomenon, we studied intranasal laser Doppler flowmetry (LDF) and nasal nitric oxide (NO) variations evoked by local administration of saline, histamine, N-acetylcysteine (NAC) and lidocaine at room temperature (22 degrees C).

RESULTS

There was a significant (P < 0.05) 14 +/- 3.8% decrease in LDF signal after 30 s, which lasted for 60-90 s, for all the substances applied at 22 degrees C. This pharmaco-independent vasoconstriction was further studied in patients under general anaesthesia (GA), with saline at 37 degrees C and after intranasal adrenaline treatment. While GA did not influence the vasoconstriction, saline at 37 degrees C and adrenaline pre-treatment abolished it. Nasal NO is influenced by vasoconstriction. Therefore we investigated, whether the observed vasoconstriction also changes nasal NO. A significant (P < 0.001) 8.03 +/- 0.59% decrease in nasal NO was recorded 60 s after administration of all the substances, and under GA after 22 degrees C saline application. This NO decrease was absent after intranasal adrenaline pre-treatment. An additional experiment tested the effect of nose blowing on nasal NO concentration. We registered an NO decrease with a similar pattern than observed with the other substances.

CONCLUSIONS

Intranasal fluid nebulization at 22 degrees C induces a sympathetic mediated, transient vasoconstrictor reflex response. This somato-sympathetic vasoconstriction induces a decrease in nasal NO. Both could be related to the subjective comfort experienced by NACRS patients using intranasal saline sprays.

Ambient oxygen regulates epithelial metabolism and nitric oxide production in the human nose

The effects of ambient O(2) tension on epithelial metabolism and nitric oxide (NO) production (VNO) in the nasal airway were examined in nine healthy volunteers. Nasal VNO, O(2) consumption (VO(2)), and CO(2) production (VCO(2)) were measured during normoxia followed by gradual hypoxia from 21 to 0% O(2) concentration. Nasal VO(2), VCO(2), and respiratory quotient during normoxia were determined to be 1.19 +/- 0.04 ml/min, 1.60 +/- 0.04 ml/min, and 1.35 +/- 0.04, respectively. Hypoxia exposure to the nasal cavity significantly decreased both VCO(2) and VNO [VCO(2): 1.60 +/- 0.04 to 0.96 +/- 0.03 ml/min (P < 0.01), VNO: 530 +/- 15 to 336 +/- 9 nl/min (P < 0.01)]. VNO was reduced commensurately with gradual decline in O(2) tension, and the apparent K(m) value for O(2) was determined to be 23.0 microM. These results indicate that the nasal epithelial cells exchange O(2) and CO(2) with ambient air in the course of their metabolism and that nasal epithelial cells can synthesize NO by using ambient O(2) as a substrate. We conclude that air-borne O(2) diffuses into the epithelium where it may be utilized for either cell metabolism or NO synthesis.

Exchange dynamics of nitric oxide in the human nose

Nasal nitric oxide (NO) exchange dynamics are poorly understood but potentially are of importance, inasmuch as they may provide insight into the NO-related physiology of the bronchial tree. In healthy human volunteers, NO output was assessed by isolating the nasal cavity through elevation of the soft palate and application of tight-fitting nasal olives. Mean NO output was 334 nl/min and was a positive function of gas flow. With the use of a mathematical model and the introduction of nonzero concentrations of NO, the diffusing capacity for NO in the nose (DNO) and the mucosal NO concentration (Cw) were determined. DNO ranged from 0.52 to 2.98 x 10(-3) nl x s(-1) x ppb(-1) and Cw from 1,236 to 8,947 ppb. Cw declined with increasing gas flow, while DNO was constant. NO output declined with luminal hypoxia, particularly at oxygen tensions <10%. Measurement of nasal DNO and Cw is easy using this method, and the range of intersubject values of Cw raises the possibility of interindividual differences in NO-dependent nasal physiology.