Loss of bacterial diversity in the sinuses is associated with lower smell discrimination scores

Nature and human well-being: The olfactory pathway

The world is undergoing massive atmospheric and ecological change, driving unprecedented challenges to human well-being. Olfaction is a key sensory system through which these impacts occur. The sense of smell influences quality of and satisfaction with life, emotion, emotion regulation, cognitive function, social interactions, dietary choices, stress, and depressive symptoms. Exposures via the olfactory pathway can also lead to (anti-)inflammatory outcomes. Increased understanding is needed regarding the ways in which odorants generated by nature (i.e., natural olfactory environments) affect human well-being. With perspectives from a range of health, social, and natural sciences, we provide an overview of this unique sensory system, four consensus statements regarding olfaction and the environment, and a conceptual framework that integrates the olfactory pathway into an understanding of the effects of natural environments on human well-being. We then discuss how this framework can contribute to better accounting of the impacts of policy and land-use decision-making on natural olfactory environments and, in turn, on planetary health.

Olfactory Loss in Rhinosinusitis: Mechanisms of Loss and Recovery

Chronic rhinosinusitis (CRS) is a highly prevalent disease and up to 83% of CRS patients suffer from olfactory dysfunction (OD). Because OD is specifically seen in those CRS patients that present with a type 2 eosinophilic inflammation, it is believed that type 2 inflammatory mediators at the level of the olfactory epithelium are involved in the development of this olfactory loss. However, due to the difficulties in obtaining tissue from the olfactory epithelium, little is known about the true mechanisms of inflammatory OD. Thanks to the COVID-19 pandemic, interest in olfaction has been growing rapidly and several studies have been focusing on disease mechanisms of OD in inflammatory conditions. In this paper, we summarize the most recent data exploring the pathophysiological mechanisms underlying OD in CRS. We also review what is known about the potential capacity of olfactory recovery of the currently available treatments in those patients.

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.

Mammalian odorant-binding proteins are prone to form amorphous aggregates and amyloid fibrils

Odorant-binding proteins are involved in perceiving smell by capturing odorants within the protein's β-barrel. On the example of bovine odorant-binding protein (bOBP), the structural organization of such proteins and their ability to bind ligands under various conditions in vitro were examined. We found a tendency of bOBP to form oligomers and small amorphous aggregates without disturbing the integrity of protein monomers at physiological conditions. Changes in environmental parameters (increased temperature and pH) favored the formation of larger and dense supramolecular complexes that significantly reduce the binding of ligands by bOBP. The ability of bOBP to form fibrillar aggregates with the properties of amyloids, including high cytotoxicity, was revealed at sample stirring (even at physiological temperature and pH), at medium acidification or pre-solubilization with hexafluoroisopropanol. Fibrillogenesis of bOBP was initiated by the dissociation of the protein's supramolecular complexes into monomers and the destabilization of the protein's β-barrels without a significant destruction of its native β-strands.

Nasal Microbiome in COVID-19: A Potential Role of Corynebacterium in Anosmia

The evolution and the development of the symptoms of Coronavirus disease 19 (COVID-19) are due to different factors, where the microbiome plays a relevant role. The possible relationships between the gut, lung, nasopharyngeal, and oral microbiome with COVID-19 have been investigated. We analyzed the nasal microbiome of both positive and negative SARS-CoV-2 individuals, showing differences in terms of bacterial composition in this niche of respiratory tract. The microbiota solution A (Arrow Diagnostics) was used to cover the hypervariable V1-V3 regions of the bacterial 16S rRNA gene. MicrobAT Suite and MicrobiomeAnalyst program were used to identify the operational taxonomic units (OTUs) and to perform the statistical analysis, respectively. The main taxa identified in nasal microbiome of COVID-19 patients and in Healthy Control subjects belonged to three distinct phyla: Proteobacteria (HC = 14%, Cov19 = 35.8%), Firmicutes (HC = 28.8%, Cov19 = 30.6%), and Actinobacteria (HC = 56.7%, Cov19 = 14.4%) with a relative abundance > 1% in all groups. A significant reduction of Actinobacteria in Cov19 group compared to controls (P < 0.001, FDR = 0.01) was found. The significant reduction of Actinobacteria was identified in all taxonomic levels down to the genus (P < 0.01) using the ANOVA test. Indeed, a significantly reduced relative abundance of Corynebacterium was found in the patients compared to healthy controls (P = 0.001). Reduced abundance of Corynebacterium has been widely associated with anosmia, a common symptom of COVID-19 as suffered from our patients. Contrastingly, the Corynebacterium genus was highly represented in the nasal mucosa of healthy subjects. Further investigations on larger cohorts are necessary to establish functional relationships between nasal microbiota content and clinical features of COVID-19.

Olfactory Evaluation in Clinical Medical Practice

The subjective and demanding nature of olfactory testing means that it is often neglected in clinic despite loss of smell leading to significant limitations in everyday life. The list of diseases associated with loss of olfaction far exceeds the field of otorhinolaryngology and can also be seen in neurodegenerative disorders. Knowledge of possible clinical testing is essential to determine a proper differential diagnosis for the loss of olfactory sense. Causes of olfactory impairment can be divided into either failure in transferring odour to the organ of perception or damage to the olfactory pathway structure itself. Examination should therefore include methods evaluating cross-sectional area and patency of the nasal cavity as well as subjective or objective assessment of olfactory function. In this report we summarize several articles, studies, and our own experiences to provide a comprehensive review of their current clinical usage including their benefits, limitations, and possible outcomes. We also discuss the mechanism of olfaction step by step to provide a full understanding of the possible errors depending on the localization in the pathway and the methods designed for their detection. We discuss the correlation of the microbiome in nasal polyposis and chronic rhinitis with olfactory impairment using objective olfactometry. The topic of objective olfactometry and the examination of olfactory event-related potentials (OERP) is commented upon in detail.

The Influence of Common Noncommunicable Diseases on Chemosensory Perception and Clinical Implications in Children and Adolescents

An increased incidence of noninfectious chronic diseases, such as obesity, diabetes, and allergies, has been noted in the last century, especially in the last 2 to 3 generations. Evidence suggested that the interrelation among these chronic conditions in pediatric age (e.g., children and adolescents aged 4-16 y) is complex and still unknown, reinforcing the interest of pediatricians in these diseases. Of interest is the need to better understand the link between these pathologies and sensory perception, since the chemical senses of taste and smell, together with chemesthesis, are reported to have a role in food choices and may provide a novel target for intervention in the treatment of these pathologies. This review aims to explore the current evidence on the link between these chronic conditions and chemosensory perception (i.e., taste and smell). In addition, the putative role that chemosensory perception may have on food choices and eating behavior of children and adolescents affected by these diseases are highlighted. Furthermore, the review addresses the unexplored issues that need to be investigated in this area. The literature data search suggested that no clear relation between taste and smell perception and the aforementioned diseases in young population yet exists. However, some possible trends have been highlighted in the adult population, in whom the duration of disease might have affected the relation. There is a need for further, high-quality, hypothesis-led research, with robust measures of taste and smell functions as the primary outcomes, to strengthen or deny this evidence.