Research links COVID-19 sensory loss to specific tongue receptors, suggesting treatment targets.
Loss of taste and smell is a common symptom associated with SARS-CoV-2, the COVID-19 virus, and can be the first thing individuals infected with the virus notice. In fact, oftentimes, patients don’t regain these sensory processes long after the acute phase has passed, which can have a significant impact on their quality of life.
In a recent study published in Scientific Reports, a team of researchers attempted to get to the root causes of these sensory losses in order to better tailor treatments for infected patients that would protect against the loss and/or allow patients to smell and taste again sooner. The team specifically surmised that they could be linked to changes in the transcriptome of the foliate papillae area of the tongue.
The study involved hospital employees from the university hospital Klinikum rechts der Isar and medical students at the Technical University of Munich (TUM) who were part of the SeCoMRI study. Participants were tested for SARS-CoV-2 immunoglobulin G (IgG) to determine whether they’d contracted the virus. Those with IgG levels ≥ 10 AU/mL were classified as IgG positive (IgG+), while those with levels < 10 AU/mL were classified as IgG negative (IgG-).
From there, a total of 158 participants completed questionnaires on sensory status, and 141 underwent forced choice taste tests to confirm input given. Additionally, 43 participants consented to donate tongue swabs.
Participants were then divided into four groups based on their IgG status and self-reported sensory impairment (SSI). The groups were: IgG+/SSI+, IgG+/SSI-, IgG-/SSI+, and IgG-/SSI-. Sensory testing was performed that focused on sweet, sour, bitter, metallic, and spicy, and participants rated sensory losses on a scale from 0 (no loss) to 10 (the most loss/highest rating). They also completed a questionnaire on changes to their sense of smell and taste, focusing on foods and beverages such as tea, coffee, cheese, and chocolate.
The team found that receptors such as OR1A2, OR2J2, OR1A1, OR5K1, and OR1G1, which are linked to metallic taste, showed a significant reduction in expression suggesting potential role of these receptors in the sensory losses the participants noted.
The study also reported IgG+ participants who couldn’t detect a metallic taste had higher IgG levels compared to those who detected iron gluconate, suggesting IgG titers and sensory impairment are related, and the lower levels of specific smell receptors in the tongue might cause a phantom metal taste. This result raises the question about whether receptors on the tongue, in fact, do play a role in metal sensation and could be targets for sensory losses.
Loss of these functions can have significant implications on an individual’s overall quality of life, disabling the body’s natural processes for detecting when food and beverage items are expired or otherwise no longer edible. This can lead to an uptick on foodborne illnesses, which are sometimes fatal.
However, given the recent findings, researchers now have a better understanding of the mechanisms behind why those who contract the COVID-19 virus lose their sense of taste and smell to begin with. More research is still needed to confirm and further support these findings, but they could have very meaningful implications for the future of COVID treatments. Mainly, linking sensory loss to receptors on the tongue can lead to the development of interventions designed to prevent loss of taste or smell altogether or at least protect patients against long-term sensory dysfunction.
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COVID-19 and metallic taste: Study connects immunoglobulin levels to sensory impairment
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