Factors that modulate olfactory dysfunction

ACKR3 in olfactory glia cells shapes the immune defense of the olfactory mucosa

Barrier-forming olfactory glia cells, termed sustentacular cells, play important roles for immune defense of the olfactory mucosa, for example as entry sites for SARS-CoV-2 and subsequent development of inflammation-induced smell loss. Here we demonstrate that sustentacular cells express ACKR3, a chemokine receptor that functions both as a scavenger of the chemokine CXCL12 and as an activator of alternative signaling pathways. Differential gene expression analysis of bulk RNA sequencing data obtained from WT and ACKR3 conditional knockout mice revealed upregulation of genes involved in immune defense. To map the regulated genes to the different cell types of the olfactory mucosa, we employed biocomputational methods utilizing a single-cell reference atlas. Transcriptome analysis, PCR and immunofluorescence identified up-regulation of NF-κB-related genes, known to amplify inflammatory signaling and to facilitate leukocyte transmigration, in the gliogenic lineage. Accordingly, we found a marked increase in leukocyte-expressed genes and confirmed leukocyte infiltration into the olfactory mucosa. In addition, lack of ACKR3 led to enhanced expression and secretion of early mediators of immune defense by Bowman's glands. As a result, the number of apoptotic cells in the epithelium was decreased. In conclusion, our research underlines the importance of sustentacular cells in immune defense of the olfactory mucosa. Moreover, it identifies ACKR3, a druggable G protein-coupled receptor, as a promising target for modulation of inflammation-associated anosmia.

Reduced olfactory performance is associated with changed microbial diversity, oralization, and accumulation of dead biomaterial in the nasal olfactory area

The partial or complete loss of the sense of smell, which affects about 20% of the population, impairs the quality of life in many ways. Dysosmia and anosmia are mainly caused by aging, trauma, infections, or even neurodegenerative disease. Recently, the olfactory area-a site containing the olfactory receptor cells responsible for odor perception-was shown to harbor a complex microbiome that reflects the state of olfactory function. This initially observed correlation between microbiome composition and olfactory performance needed to be confirmed using a larger study cohort and additional analyses. A total of 120 participants (middle-aged, no neurodegenerative disease) were enrolled in the study to further analyze the microbial role in human olfactory function. Olfactory performance was assessed using the Sniffin' Stick battery, and participants were grouped accordingly (normosmia: n = 93, dysosmia: n = 27). The olfactory microbiome was analyzed by 16S rRNA gene amplicon sequencing and supplemented by metatranscriptomics in a subset (Nose 2.0). Propidium monoazide (PMA) treatment was performed to distinguish between intact and non-intact microbiome components. The gastrointestinal microbiome of these participants was also characterized by amplicon sequencing and metabolomics and then correlated with food intake. Our results confirm that normosmics and dysosmics indeed possess a distinguishable olfactory microbiome. Alpha diversity (i.e., richness) was significantly increased in dysosmics, reflected by an increase in the number of specific taxa (e.g., Rickettsia, Spiroplasma, and Brachybacterium). Lower olfactory performance was associated with microbial signatures from the oral cavity and periodontitis (Fusobacterium, Porphyromonas, and Selenomonas). However, PMA treatment revealed a higher accumulation of dead microbial material in dysosmic subjects. The gastrointestinal microbiome partially overlapped with the nasal microbiome but did not show substantial variation with respect to olfactory performance, although the diet of dysosmic individuals was shifted toward a higher meat intake. Dysosmia is associated with a higher burden of dead microbial material in the olfactory area, indicating an impaired clearance mechanism. As the microbial community of dysosmics (hyposmics and anosmics) appears to be influenced by the oral microbiome, further studies should investigate the microbial oral-nasal interplay in individuals with partial or complete olfactory loss.IMPORTANCEThe loss of the sense of smell is an incisive event that is becoming increasingly common in today's world due to infections such as COVID-19. Although this loss usually recovers a few weeks after infection, in some cases, it becomes permanent-why is yet to be answered. Since this condition often represents a psychological burden in the long term, there is a need for therapeutic approaches. However, treatment options are limited or even not existing. Understanding the role of the microbiome in the impairment of olfaction may enable the prediction of olfactory disorders and/or could serve as a possible target for therapeutic interventions.

Patient Insights into the Diagnosis of Smell and Taste Disorders in the United States

OBJECTIVES

Diagnosis of smell/taste dysfunction is necessary for appropriate medical care. This study examines factors affecting testing and diagnosis of smell/taste disorders .

METHODS

The online USA Smell and Taste Patient Survey was made available to US patients with smell/taste disorders between April 6-20, 2022. 4,728 respondents were included.

RESULTS

1,791 (38%) patients reported a documented diagnosis. Patients most often saw family practitioners (34%), otolaryngologists (20%), and Taste/Smell clinics (6%) for smell/taste dysfunction. 64% of patients who went to Taste/Smell clinics received smell testing, followed by 39% of patients who saw otolaryngologists, and 31% of patients who saw family practitioners. Factors associated with increased odds of diagnosis included age (25-39 years (OR 2.97, 95% CI [2.25, 3.95]), 40-60 (OR 3.3, 95% CI [2.56, 4.52]), and >60 (OR 4.25, 95% CI [3.21, 5.67]) vs. 18-24 years), male gender (OR 1.26, 95% CI [1.07, 1.48]), insurance status (private (OR 1.61, 95% CI [1.15, 2.30]) or public (OR 2.03, 95% CI [1.42, 2.95]) vs. uninsured), perception of their family practitioner to be knowledgeable (OR 2.12, 95% CI [1.16, 3.90]), otolaryngologic evaluation (OR 6.17, 95% CI [5.16, 7.38]), and psychophysical smell testing (OR 1.77, 95% CI [1.42, 2.22]).

CONCLUSION

Psychophysical testing, otolaryngologic evaluation, patient assessment of family practitioner knowledge level, insurance, age, and gender are significant factors in obtaining smell/taste dysfunction diagnosis. This study identifies barriers to diagnosis including lack of insurance or access to specialist evaluation and highlights the importance of educating family practitioners in diagnosis and management of patients with smell/taste disorders.

Olfactory Dysfunction following COVID-19 and the Potential Benefits of Olfactory Training

COVID-19 is associated with a common symptom of olfactory dysfunction, which may persist even after the infection is resolved. Olfactory training (OT) has emerged as the most effective intervention for post-viral olfactory dysfunction. OT involves daily exposure of the olfactory system to various odors. The current study aims to explore olfactory dysfunction following COVID-19 and the potential benefits of olfactory training.

METHODS

This is a cross-sectional study conducted among adults aged 18-60 living in Alahssa, Saudi Arabia. An online questionnaire containing an informed consent form and a survey to collect demographic data, vaccination status, level of loss of smell and taste, and the level of awareness about olfactory training (OT) was distributed among all participants who agreed to participate in this study.

RESULTS

The study included 524 participants and presented their baseline characteristics, including age, gender, COVID-19 infection status, and complaints. Most patients were female (66.0%), and 46.2% had previously been infected with COVID-19. About 54.8% of participants reported chemosensory dysfunction, while 286 had olfactory dysfunction. Of those, 29.8% had anosmia, 16.8% had hyposmia, and 8.0% had parosmia. Results suggest that being fully or partially vaccinated may offer some protection against olfactory dysfunction compared to being unvaccinated. Adherence to olfactory training was associated with improvement in the sense of smell.

CONCLUSIONS

The study highlights the importance of awareness and adherence to olfactory training, which may improve the sense of smell in individuals with chemosensory dysfunction. The findings of this study can inform public health policies and interventions aimed at reducing the burden of olfactory dysfunction associated with COVID-19 vaccination.

Wearing N95 masks decreases the odor discrimination ability of healthcare workers: a self-controlled before-after study

Objective

During the coronavirus disease 2019 (COVID-19) pandemic, the N95 mask is an essential piece of protective equipment for healthcare workers. However, the N95 mask may inhibit air exchange and odor penetration. Our study aimed to determine whether the use of N95 masks affects the odor discrimination ability of healthcare workers.

Methods

In our study, all the participants were asked to complete three olfactory tests. Each test involved 12 different odors. The participants completed the test while wearing an N95 mask, a surgical mask, and no mask. The score for each olfactory test was documented.

Results

The olfactory test score was significantly lower when the participants wore N95 masks than when they did not wear a mask (7 vs. 10, p < 0.01). The score was also lower when the participants wore N95 masks than surgical masks (7 vs. 8, p < 0.01).

Conclusion

Wearing N95 masks decreases the odor discrimination ability of healthcare workers. Therefore, we suggest that healthcare workers seek other clues when diagnosing disease with a characteristic odor.

A three-factor benefits framework for understanding consumer preference for scented household products: psychological interactions and implications for future development

Humans have deliberately scented their environment for purpose or pleasure for millennia. In the contemporary marketplace most consumers prefer and purchase scented versions of common household products. However, the drivers of this consumer preference have not been elucidated. To explain the attraction to scent in household products we propose a novel three-factor framework, comprising functional benefits (malodor mitigation, base odor coverage, freshening), in-use experience benefits (cleanliness, efficacy, pleasure), and emotional benefits (increasing in confidence, mood and nostalgia). To support this framework, we present new data from a market research survey on US consumer purchasing habits and attitudes towards home cleaning, laundry, and air freshening products. Further substantiating our framework, a focused review of olfactory psychological science illustrating the central role of scent in cognition, wellbeing, motivated behavior, and social behavior, as well as sensory marketing research highlights the benefits and implications of scent in consumer household products. Based on our three-factor framework we go on to discuss the potential for scent to influence health and raise issues to consider (such as potential negative responding to fragranced products). We conclude by showcasing new opportunities for future research in olfactory science and on scented household products that can advance the positive impacts of scent.

Association between Administration of Systemic Corticosteroids and the Recovery of Olfactory and/or Gustatory Functions in Patients with COVID-19: A Prospective Cohort Study

AIM: This study is a prospective cohort study aimed to assess the effect of systemic corticosteroids administration time in the recovery of gustatory and olfactory sensations dysfunction (ageusia and anosmia) in COVID-19 patients. MATERIALS AND METHODS: Sixty-seven COVID-19 patients with symptoms of ageusia and anosmia were recruited (that their COVID infection was confirmed using polymerase chain reaction). Daily 10 mg of systemic corticosteroids were prescribed in the 1st week and then reduced to 5 mg in the 2nd week to all the patients to observe taste and smell sensation recovery. All data were recorded and then analyzed. Patients were then grouped into two groups (early and late groups) according to the duration of their taste and smell dysfunction. RESULTS: Regression analysis showed that early corticosteroid administration resulted in a significant decrease in recovery time of ageusia and anosmia (0.27 [0.2–0.35], p < 0.001). Patients in the early administration group (<1 week) showed faster improvement in regaining taste and smell functions than in the late administration group (>1 week) with significant difference (p < 0.001). CONCLUSIONS: The use of systemic corticosteroids in early phases of covid-19 infection help in faster recovery of ageusia and anosmia.

The Pattern of Anosmia in Non-hospitalized Patients in the COVID-19 Pandemic: A Cross-sectional Study

Introduction  It is now evident that the loss of smell and/or taste may be consistent accompanying symptoms of the SARS-CoV-2 infection. Objective  To estimate the social behavior of recent anosmic non-hospitalized patients in the COVID-19 pandemic and to try to obtain the natural pattern in society in a cross-sectional study. Methods  A cross-sectional study conducted on 4,860 patients with anosmia complaints during the COVID-19 pandemic. Patients who needed a consultation for an anosmia complaint confirmed that they had completed the survey regarding age, gender, history of general diseases, history of nasal disease, associated COVID-19 symptoms, smoking, blood group, and risk factors. Results  A total of 4,860 patients with a mean age of 34.26 ± 11.91 years completed the study. There was a predominance of female patients: 3,150 (58.9%). Most patients (4,083 patients; 83%) developed sudden anosmia. In 85% (4131 patients) of the patients, a previous history of contact with anosmic patients was present. The most prevalent blood group was O (39%). In total, 67.4% of the patients underwent medical treatment. A history of unusual influenza attacks in December 2020 was reported by by 27% (1312 patients) of the patients. Conclusion  Despite large diversity of behaviors among anosmic patients in the COVID-19 pandemic, we can observe a great similarity in the pattern of anosmia in non-hospitalized patients, especially in the way it spreads, the predisposing factors, and the individual recovery.

Modulation of olfactory signal detection in the olfactory epithelium: focus on the internal and external environment, and the emerging role of the immune system

Detection and discrimination of odorants by the olfactory system plays a pivotal role in animal survival. Olfactory-based behaviors must be adapted to an ever-changing environment. Part of these adaptations includes changes of odorant detection by olfactory sensory neurons localized in the olfactory epithelium. It is now well established that internal signals such as hormones, neurotransmitters, or paracrine signals directly affect the electric activity of olfactory neurons. Furthermore, recent data have shown that activity-dependent survival of olfactory neurons is important in the olfactory epithelium. Finally, as olfactory neurons are directly exposed to environmental toxicants and pathogens, the olfactory epithelium also interacts closely with the immune system leading to neuroimmune modulations. Here, we review how detection of odorants can be modulated in the vertebrate olfactory epithelium. We choose to focus on three cellular types of the olfactory epithelium (the olfactory sensory neuron, the sustentacular and microvillar cells) to present the diversity of modulation of the detection of odorant in the olfactory epithelium. We also present some of the growing literature on the importance of immune cells in the functioning of the olfactory epithelium, although their impact on odorant detection is only just beginning to be unravelled.

Arousal influences olfactory abilities in adults with different degree of food neophobia

Food neophobia, i.e., the aversion to novel foods, and olfaction are both factors strongly affecting food choices. Mounting evidence suggests a higher arousal towards food as a key factor underlying the reluctance to eat what is unfamiliar to us. As the role of olfaction behind this phenomenon is poorly understood, we explored the associations between food neophobia and trait anxiety, olfactory functions (odor threshold, discrimination and identification) and retronasal aroma release from a reference food in a healthy cohort of 83 adult volunteers. We grouped participants in Low-Neophobics or neophilics (n = 35), Medium-Neophobics (n = 32) and High-Neophobics (n = 16) according to the widely recognized Food Neophobia Scale. Participants with higher neophobic tendencies were found to have marginally higher trait anxiety levels than neophilics (p = 0.10). A lower global olfactory functioning and odor discrimination abilities characterized High-Neophobics, while Medium-Neophobics showed a higher odor sensitiveness than Low-Neophobics. Lastly, High-Neophobics showed a lower extent of retronasal aroma release, likely due to a shorter duration of oral processing and higher anxiety-related physiological responses (such as breathing rate). In summary, this study supports the assumption that the conflicting relationship that neophobics have with food may be led by higher levels of arousal toward foods, rather than different chemosensory functions.

Anosmia in the course of COVID-19: A case report

RATIONALE

A sudden onset of anosmia has been recently recognized as a symptom of coronavirus disease (COVID-19).

PATIENT CONCERNS

Here, we describe a case of complete anosmia in a young male with COVID-19. Although he had fever and odynophagia, no abnormalities were observed in his nasopharyngeal mucosa, suggesting that his anosmia resulted from olfactory neuropathy.

DIAGNOSES

COVID-19 was confirmed by RNA detection in nasopharyngeal swab specimen.

INTERVENTIONS

The patient received olfactory training and B complex vitamins.

OUTCOMES

On day 30, the patient reported complete recovery of his sense of smell.

LESSONS

As early diagnosis is fundamental to control the spread of COVID-19 infection, we emphasize that anosmia identified in febrile cases during the COVID-19 epidemic may be a symptom indicative of the disease. Moreover, COVID-19-related anosmia can be completely reversible.

Combination of olfactory ensheathing cells and human umbilical cord mesenchymal stem cell-derived exosomes promotes sciatic nerve regeneration

Olfactory ensheathing cells (OECs) are promising seed cells for nerve regeneration. However, their application is limited by the hypoxic environment usually present at the site of injury. Exosomes derived from human umbilical cord mesenchymal stem cells have the potential to regulate the pathological processes that occur in response to hypoxia. The ability of OECs to migrate is unknown, especially in hypoxic conditions, and the effect of OECs combined with exosomes on peripheral nerve repair is not clear. Better understanding of these issues will enable the potential of OECs for the treatment of nerve injury to be addressed. In this study, OECs were acquired from the olfactory bulb of Sprague Dawley rats. Human umbilical cord mesenchymal stem cell-derived exosomes (0–400 μg/mL) were cultured with OECs for 12–48 hours. After culture with 400 μg/mL exosomes for 24 hours, the viability and proliferation of OECs were significantly increased. We observed changes to OECs subjected to hypoxia for 24 hours and treatment with exosomes. Exosomes significantly promoted the survival and migration of OECs in hypoxic conditions, and effectively increased brain-derived neurotrophic factor gene expression, protein levels and secretion. Finally, using a 12 mm left sciatic nerve defect rat model, we confirmed that OECs and exosomes can synergistically promote motor and sensory function of the injured sciatic nerve. These findings show that application of OECs and exosomes can promote nerve regeneration and functional recovery. This study was approved by the Institutional Ethical Committee of the Air Force Medical University, China (approval No. IACUC-20181004) on October 7, 2018; and collection and use of human umbilical cord specimens was approved by the Ethics Committee of the Linyi People’s Hospital, China (approval No. 30054) on May 20, 2019.