key: cord-0877618-ygvwk0sa
authors: Sayin, Ibrahim; Yazici, Zahide Mine
title: Taste and Smell Impairment in SARS-CoV-2 Recovers Early and Spontaneously: Experimental Data Strongly Linked to Clinical Data
date: 2020-06-15
journal: ACS Chem Neurosci
DOI: 10.1021/acschemneuro.0c00296
sha: 350fb809284685161e6466a97c2ec9025659aa57
doc_id: 877618
cord_uid: ygvwk0sa

[Image: see text] A growing body of literature indicates that smell and taste impairment has frequently occurred during the Severe Acute Respiratory Syndrome (SARS)-like Coronavirus (SARS-CoV-2) outbreak. Experimental studies have mostly found that non-neural-type cells are responsible for SARS-CoV-2-related taste and smell impairment. If this is the case, smell/taste impairment needs to recover early. Literature data from clinical studies indicated a strong correlation between experimental and clinical findings. This article presents clinical studies related to SARS-CoV-2-induced smell/taste impairment that reported recovery rates. Experimental researchers may use these data to observe the dynamics of smell impairment and implement these findings in their research (e.g., correct timing of sampling) to perform further studies.

T wo articles recently appeared in ACS Chemical Neuroscience that need attention. 1, 2 The article published by Bilinska et al. indicated that sustentacular cells are responsible for Severe Acute Respiratory Syndrome (SARS)-like Coronavirus (SARS-CoV-2) entry and related smell impairment. 1 Bilinska et al. also reported that non-neuronal cells of the olfactory epithelium (OE) are more likely to be the entry point of SARS-CoV-2 virus rather than olfactory receptor neurons (ORNs). 1 In the second report, Butowt and Bilinska highlighted the need for OE-oriented experimental studies to clarify various points related to SARS-CoV-2 virus and the continuous need for clinical data related to SARS-CoV-2 and related smell loss. 2 Brann et al. reported that direct involvement of olfactory sensory neurons (OSNs) may not occur in SARS-CoV-2 infection since OSNs did not express ACE2. Non-neural cell types (e.g., stem cells, TMPRSS2 support cells, and perivascular cells) express ACE2, and they are responsible for related smell impairment. 3 Brann et al. hypothesized that inflammation, deteriorated signaling, and diffuse architectural damage of the OE may be the mechanisms for smell impairment.

On the basis of these experimental studies, in the clinical setting smell impairment needs to be resolved early and spontaneously because in the majority of the cases direct involvement of OSNs did not widely occur. In order to evaluate the consistency between experimental and clinical findings, we systematically reviewed clinical studies that reported resolution rates in SARS-CoV-2-related smell impairment. 4−14 The results are presented in Table 1 . Published studies indicated that smell impairment in SAR-CoV-2 recovered early. At present, no treatment for SARS-CoV-2-related smell impairment exists. In two studies, some treatments, including nasal saline irrigation, intranasal corticosteroids, systemic corticosteroids, dietary supplements, vitamin A, and olfactory training, on limited number of the subjects were reported. 7, 11 However, no definite conclusion could be made concerning the effect of treatment on recovery rates. Smell loss mostly recovered in a few weeks after the infection and seemed to reduce with time.

The present report has some limitations. This report's knowledge was limited to published data to date. The reviewed articles were mostly observational and questionnaire-based. Among the rewieved articles for this report; only one study used objective testing methods and reported outcomes. 14 Literature data point out that there will be an inconsistency between patient-reported and objective-testing-determined smell/taste impairment. However, nasal procedures, detailed examinations, and close contact with subjects were avoided during the pandemic, which resulted in a limited number of studies that reported objective outcomes. Besides, the studies single-arm descriptive 345 subjects underwent objective chemosensitive evaluation RT-PCR 65% for OD and 67.8% for GD complete resolution for OD and GD were 31.3% and 50.4%, respectively, at the time of the study; improvement was evident in the first and second weeks of disease a regarding smell/taste impairment were mostly cross-sectional single-arm studies. Comparative studies with SARS-CoV-2 (−) subjects and comparative studies with other upper respiratory tract infection causes were limited in number. Even for the studies that presented followup, the followup period was limited to weeks. Larger studies with objective testing methods and longer followup periods will deepen our knowledge about SARS-CoV-2-related taste/smell impairment.

These findings represent a well-linked relation between experimental studies and clinical studies. Experimental researchers may use these data to observe the dynamics of smell impairment and implement these findings in their researches (e.g., correct timing of sampling) to perform further studies. 

The authors declare no competing financial interest.

Expression of the SARS-CoV-2 Entry Proteins, ACE2 and TMPRSS2, in Cells of the Olfactory Epithelium: Identification of Cell Types and Trends with Age

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