Nasal nitric oxide levels do not allow for discrimination between olfactory loss due to various etiologies

Nasal Nitric Oxide as a Biomarker in the Diagnosis and Treatment of Sinonasal Inflammatory Diseases: A Review of the Literature

OBJECTIVE

To critically review the literature on nasal nitric oxide (nNO) and its current clinical and research applicability in the diagnosis and treatment of different sinonasal inflammatory diseases, including acute bacterial rhinosinusitis (ABRS), allergic rhinitis (AR), and chronic rhinosinusitis (CRS).

METHODS

A search of the PubMed database was conducted to include articles on nNO and sinonasal diseases from January 2003 to January 2020. All article titles and abstracts were reviewed to assess their relevance to nNO and ABRS, AR, or CRS. After selection of the manuscripts, full-text reviews were performed to synthesize current understandings of nNO and its applications to the various sinonasal inflammatory diseases.

RESULTS

A total of 79 relevant studies from an initial 559 articles were identified using our focused search and review criteria. nNO has been consistently shown to be decreased in ABRS and CRS, especially in cases with nasal polyps. While AR is associated with elevations in nNO, nNO levels have also been found to be lower in AR cases with higher symptom severity. The obstruction of the paranasal sinuses is speculated to be an important variable in the relationship between nNO and the sinonasal diseases. Treatment of these diseases appears to affect nNO through the reduction of inflammatory disease burden and also mitigation of sinus obstruction.

CONCLUSION

nNO has been of increasing interest to researchers and clinicians over the last decade. The most compelling data for nNO as a clinical tool involve CRS. nNO can be used as a marker of ostiomeatal complex patency. Variations in measurement techniques and technology continue to impede standardized interpretation and implementation of nNO as a biomarker for sinonasal inflammatory diseases.

Decreased nasal nitric oxide levels: A potential marker of decreased olfactory discrimination in chronic rhinosinusitis

Objective

This study aimed to investigate the association of nasal nitric oxide and olfactory function.

Method

A cross-sectional study was performed in 117 adults, including 91 patients with chronic rhinosinusitis and 26 healthy controls. Scores on the 22-item Sino-Nasal Outcomes Test, Lund-Mackay scale and Lund-Kennedy scale were recorded to assess severity of disease. All participants were screened for common inhaled and food allergens. Nasal nitric oxide and fractional exhaled nitric oxide testing, acoustic rhinometry and anterior rhinomanometry testing were performed to measure nasal function. The validated Sniffin’ Sticks test battery was used to assess olfactory function.

Results

Higher nasal nitric oxide was an independent protective factor for odour discrimination and odour threshold in participants with chronic rhinosinusitis after adjusting for age, gender, drinking, smoking, 22-item Sino-Nasal Outcomes Test, Lund-Mackay score, Lund-Kennedy score, immunoglobulin E and the second minimal cross-sectional area by acoustic rhinometry. Nasal nitric oxide also showed high discrimination in predicting impaired odour discrimination. In addition, nasal nitric oxide was lower in older participants, those with higher Lund-Mackay or Lund-Kennedy scores and higher with elevated total serum immunoglobulin E concentrations above a threshold of 0.35 kU/l.

Conclusion

Higher nasal nitric oxide is associated with better odour discrimination in chronic rhinosinusitis and is modulated by age, degree of allergy and severity of chronic rhinosinusitis.

In healthy subjects nasal nitric oxide does not correlate with olfactory sensitivity, trigeminal sensitivity, and nasal airflow

OBJECTIVE

The aim of the study was to determine the relationship between nasal nitric oxide (nNO) and olfactory sensitivity, trigeminal sensitivity and nasal airflow in healthy subjects.

STUDY DESIGN

This is a correlational study.

SETTING

This study was carried out in a tertiary referral centre.

PARTICIPANTS

Forty healthy participants were recruited.

MAIN OUTCOME MEASURES

nNO was measured using a chemiluminescence analyser (Niox Vero^® , Circassia AB, Uppsala, Sweden), olfactory sensitivity was determined using phenyl ethyl alcohol odour thresholds using the 'Sniffin' Sticks', trigeminal sensitivity was assessed with carbon dioxide delivered by an automated device, and nasal airflow was measured using the peak nasal inspiratory flow (PNIF).

RESULTS

The median nNO was 518 ppb (IQR =333) in the right nostril, and it was 567 ppb (IQR = 314) in the left nostril. The median odour threshold was 7.1 (IQR = 4.4), the median CO₂ threshold was 919 ms (IQR = 1297) and the mean PNIF was 108 L/min (SEM = 4.9). nNO did not correlate significantly with odour threshold, CO₂ threshold or PNIF (Spearman's |ρ|  <0.15, p > .18).

CONCLUSION

In healthy subjects, nNO does not appear to be associated with olfactory sensitivity, trigeminal sensitivity and PNIF.

Correlation between nasal nitric oxide and its metabolites, RANTES, IL-5 in allergic rhinitis

There have been two measurement methods for nasal nitric oxide (nNO): direct measurement of nNO and indirect measurement of NO metabolites or the NO synthase enzyme. The aim of this study is to investigate the difference in nNO between allergic rhinitis (AR) patients and the correlation of the direct measurement of nNO and indirect measurement of nNO metabolites, RANTES, and IL-5. Fifteen patients with AR, 15 patients with septal deviation as a control group were enrolled. We measured the nNO level using a chemiluminescence analyzer and the amount of NO metabolites, RANTES, and IL-5 in nasal lavage fluid using the ELISA method. Nasal NO levels were significantly higher in AR than the control (195.7 ± 39.6 vs 159.4 ± 25.8 ppb, P = 0.027). NO metabolites, IL-5, and RANTES levels were higher in AR, but there was no statistically significant difference. There was no significant correlation between nNO and nNO metabolites, RANTES, IL-5, and clinical parameters except for the olfactory test score in AR. There was a negative correlation between nNO and the olfactory test score in AR ( r = −0.590, P = 0.034). Nasal NO concentration increased in AR. However, nNO metabolites and IL-5, RANTES in nasal secretion did not show any correlation with nNO. Direct measurement of nNO could be a potentially useful biomarker of AR compared to indirect measurement of NO metabolites, cytokines, and chemokines in nasal secretion.

Nitric oxide signalling in the brain and its control of bodily functions

Nitric oxide (NO) is a versatile molecule that plays key roles in the development and survival of mammalian species by endowing brain neuronal networks with the ability to make continual adjustments to function in response to moment-to-moment changes in physiological input. Here, we summarize the progress in the field and argue that NO-synthetizing neurons and NO signalling in the brain provide a core hub for integrating sensory- and homeostatic-related cues, control key bodily functions, and provide a potential target for new therapeutic opportunities against several neuroendocrine and behavioural abnormalities.

Nasal Nitric Oxide in Chronic Rhinosinusitis with or without Nasal Polyps: A Systematic Review with Meta-Analysis

Background and Aims: There has been a recent growing interest in the role of nasal nitric oxide (nNO) as a biomarker for osteomeatal complex obstruction in paranasal sinus diseases. By using meta-analysis, we systematically reviewed the literature to establish the possible link between nNO concentration and chronic rhinosinusitis with nasal polyps (CRSwNP) or without (CRSsNP). Methods: We systematically searched the EMBASE, PubMed, Scopus, and Web of Science databases for related studies. Differences between controls and cases were reported as standardized mean difference (SMD), with 95% confidence intervals (95% CI), using the random-effects method. Results: We selected 23 articles for the final analysis: 15 with data on 461 CRSwNP patients and 384 healthy controls, 10 with data on 183 CRSsNP patients and 260 controls, and 14 studies on 372 CRSwNP and 297 CRSsNP patients. CRSwNP patients showed significantly lower nNO values when compared to both healthy controls (SMD: −1.495; 95% CI: −2.135, −0.854; p < 0.0001) and CRSsNP patients (SMD: −1.448; 95% CI: −2.046, −0.850; p < 0.0001). Sensitivity and subgroup analyses confirmed the results, which were further refined by regression models. They showed that an increasing aspiration flow is related to a greater difference in nNO levels between cases and control subjects. We also documented lower nNO levels in CRSsNP patients with respect to controls (SMD: −0.696; 95% CI: −1.189, −0.202; p = 0.006), being this result no longer significant when excluding patients in therapy with intranasal corticosteroids. As shown by regression models, the increased Lund–Mackay score indicates a high effect size. Conclusions: nNO levels are significantly lower in CRSwNP, especially when using higher aspiration flows. Additional studies are needed to define one single standardized method and normal reference values for nNO.

Relationship of Phenylthiocarbamide (PTC) Taster Status to Olfactory and Gustatory Function in Patients with Chemosensory Disturbances

Poor sensitivity to the bitter taste of phenylthiocarbamide (PTC) and related substances has been associated with a number of diseases. We determined, in patients with chemosensory dysfunction from multiple etiologies, whether PTC "tasters" (n = 511) exhibit less smell and taste dysfunction than their non-PTC-tasting counterparts (n = 432) on a comprehensive battery of olfactory and gustatory tests. The proportion of tasters (54%) in our study population was much lower than that calculated from 11 North American population studies (76.5%; P < 0.0001). This taster/nontaster ratio was maintained across a range of etiologic categories. More women (60.7%) than men (45.5%) were PTC tasters (P < 0.0001). Although PTC tasting status was unrelated to scores on the olfactory tests (which included tests of odor identification, detection threshold, and odor memory/discrimination), tasters significantly outperformed nontasters on suprathreshold identification and intensity taste tests employing both bitter (caffeine) and nonbitter (sucrose, citric acid, sodium chloride) tasting stimuli. Regardless of PTC taster status, women outperformed men on the taste tests. Our findings suggest the possibility that the T2R38 gene may protect against significant olfactory dysfunction, but once such dysfunction becomes manifest at a level where professional help is sought, such protection is not evident. However, other hypotheses for this phenomenon are possible. This study demonstrates that patients with chemosensory disturbances who are PTC tasters outperform their non-PTC taster counterparts in both identifying and perceiving the intensity of a range of suprathreshold tastants, including ones that do not taste bitter.