Makaronidis, Janine Maria; (2021) Chemosensory dysfunction as a marker of global disease: Investigating the role of taste and smell signalling in obesity and COVID-19. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

The work in this thesis examines chemosensory dysfunction related to obesity and COVID-19, two global pandemics markedly impacting on health. Following the COVID-19 outbreak, reports emerged that loss of smell and/or taste may be caused by SARS-CoV-2. The work in Chapter 2 was undertaken before loss of smell and/or taste were recognised COVID-19 symptoms and aimed to determine the seroprevalence of SARS-CoV-2 antibodies in people with acute taste and/or smell loss, characterise the loss of chemosensory function and identify factors affecting their recovery. Overall, 78% of people with taste and/or smell loss had positive SARS-CoV-2 IgG/IgM antibodies. Female sex and altered smell/taste perceptions were identified as predictors for persistent loss of sense of taste and/or smell and long COVID. Furthermore, objective smell testing and quantitative MRI brain imaging were undertaken to investigate the underlying pathophysiology. Early results suggest ongoing neuroinflammation in people with persistent smell loss. Obesity, a chronic disease with multiple associated co-morbidities, is associated with chemosensory dysfunction, particularly toward dietary fat. The obesity section of this thesis used different modalities, including functional taste assessment, salivary and circulating biomarkers and functional brain imaging to characterise chemosensory dysfunction in obesity. Findings from these studies demonstrated a reduced ability to taste fat in the fed state, as well as increased taste-stimulated activity in reward-related brain regions in people with obesity. Altered adipocytokines and inflammation are postulated to underlie the increased risk of critical illness from COVID-19 in people living with obesity. In Chapter 6 inflammatory adipocytokines and metabolomic markers were measured in people with obesity before and after bariatric surgery. A substantial inter-individual variability was identified in circulating levels of these markers, which may underlie some of the susceptibility to infection-induced critical illness. Importantly, the results indicated improvement in inflammation markers following bariatric surgery, suggesting the potential for reducing obesity-associated risks.

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