Olfactory function and nasal nitric oxide

Nitric Oxide: The Missing Factor in COVID-19 Severity?

Coronavirus disease 2019 (COVID-19) is a contagious respiratory and vascular disease that continues to spread among people around the world, mutating into new strains with increased transmission rates, such as the delta variant. The scientific community is struggling to discover the link between negative COVID-19 outcomes in patients with preexisting conditions, as well as identify the cause of the negative clinical patient outcomes (patients who need medical attention, including hospitalization) in what seems like a widespread range of COVID-19 symptoms that manifest atypically to any preexisting respiratory tract infectious diseases known so far. Having successfully developed a nutritional formulation intervention based on nitrate, a nitric oxide precursor, the authors hypothesis is that both the comorbidities associated with negative clinical patient outcomes and symptoms associated with COVID-19 sickness are linked to the depletion of a simple molecule: nitric oxide.

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.

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.

Overexpression of Inducible Nitric Oxide Synthase in Allergic and Nonallergic Nasal Polyp

Sinonasal polyps are very common benign lesions of the nasal mucosa. Most of nasal polyps (NP) are idiopathic, and the pathophysiology of this disease is still incompletely understood. Nitric oxide (NO) is a reactive molecule generated by nitric oxide synthase (NOS). NO has been identified as an important mediator in airway function and pathogenesis of several respiratory system diseases. Histological and genetical expression of iNOS was detected to evaluate the role of NO in the pathogenesis of allergic (ANP) and nonallergic nasal polyps (NANP). Forty patients with nasal polyps (20 allergic and 20 nonallergic) were identified by history, clinical examination, and investigation. NPs were obtained from the middle turbinate (MT) during concha bullosa surgery. Twenty normal MT nasal tissues were taken as the control from patients undergoing concha bullosa surgery, without any evidence of allergy or inflammation. A nasal polyp specimen from each patient was subjected for immune-histochemical study followed by histological examination to detect the expression of iNOS. RT-PCR was used to evaluate the iNOS gene expression in isolated tissues. The expression of iNOS in both epithelial and stromal layers was greater in NP than in MT tissues. The ANP group showed more iNOS expression than those of the NANP group. The relative mRNA levels of iNOS gene were significantly higher in ANP (2.5-fold) compared to the normal (1.02-fold, P < 0.001) and NANP (1.5-fold, P < 0.01) groups. NP exhibited a significantly high expression of iNOS at both histological and genetical levels. NO might be an essential factor in the life history of NP. Further studies in a larger sample size are required to explain the probable mechanisms of NO in pathogenesis of NP.

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

OBJECTIVES/HYPOTHESIS

Nasal nitric oxide (NO) and olfactory function are decreased in patients with chronic inflammatory sinonasal disease, suggesting a link between these two parameters. The aim of the study was to investigate nasal NO levels in patients with olfactory dysfunction due to different causes.

STUDY DESIGN

Prospective study in a university clinic setting (tertiary referral center).

METHODS

Posttraumatic (n = 11), idiopathic (n = 13), and sinonasal-related olfactory-impaired patients (n = 55) were compared with healthy subjects (n = 11). Nasal NO levels, olfactory testing (Sniffin' Sticks), and rhinosinusitis questionnaires (Short-Form 36, Sinonasal Outcome Test 22, Rhinosinusitis Disability Index) were obtained.

RESULTS

No significant difference in nasal NO levels were found between the different olfactory dysfunction causes. Nasal NO correlated negatively with age and positively with overall olfactory function, olfactory discrimination, and identification but not with olfactory thresholds. The more nasal symptoms prevailed in the Rhinosinusitis Disability Index, the lower the nasal NO.

CONCLUSIONS

Nasal NO levels do not allow for discrimination between olfactory loss due to various etiologies based on the present data. Nasal NO production seems to decrease with age and also seems to be associated to overall olfactory function and in particular to central nervous system tasks such as olfactory discrimination and identification but not to olfactory thresholds. These findings raise questions about the link and interaction between olfactory function and nasal NO.

Plasma amino acid levels discriminate between control subjects and mildly depressed elderly women

BACKGROUND AND AIMS

Depression is the most common of all psychiatric disorders and the role of amino acid transmitters in this pathology has been recently studied. We undertook this study to investigate if the plasma levels of L-arginine, L-citrulline, L-glutamic acid, L-glutamine, L-asparagine and other amino acids, the L-citrulline/L-arginine and the L-tyrosine/L-phenylalanine ratios, and the nitrite levels are modified in mildly depressed women and if such changes are related to olfactory dysfunction.

METHODS

Plasma samples were obtained from elderly female subjects (n = 21) with mild depression and (n = 48) controls. Amino acids were analyzed with high-performance liquid chromatography, plasma nitrite levels were measured using the Griess method, and olfactory performance was assessed by the combined testing of odor identification, odor discrimination, odor recognition, and the olfactory threshold.

RESULTS

Compared to controls, depressed patients had a significantly higher concentration of L-arginine and a significantly lower L-citrulline/L-arginine ratio when the effect of other variables is not taken into account. A logistic regression model allowed us to identify two risk factors for mild depression, L-arginine and L-glutamic acid, and two protective factors, L-asparagine and the L-tyrosine/L-phenylalanine ratio. Additionally, a significant increase in nitrite levels in depressed women was found. No significant differences were found between the percentage of depressed and control women that identified the odors.

CONCLUSIONS

We identified that the amino acids L-arginine and L-glutamic acid are risk factors for mild depression, whereas L-asparagine and the L-tyrosine/L-phenylalanine ratio are protective factors.