Investigating taste function in the ageing population

• Main Author: Pushpass, Rose-Anna Grace
• Other Authors: Proctor, Gordon Burgess ; Kelly, Charles George
• Published: King's College London (University of London) 2018
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.762409

The diet of the ageing population is known to deteriorate which is in part due to loss of taste sensation. Lack of interest in food leads to nutritional deficiencies, dehydration and reduced quality of life. The maintenance of taste function is dependent on the presence and function of saliva. Saliva bathes the taste buds and coats the oral mucosa to enable processing of foods and to provide a trophic stimulus for taste bud function. In the ageing population salivary flows tend to decrease for several reasons including disease, reduced water intake and the side-effects of some medications. This project firstly established the connection between quantity or alteration in quality of saliva and loss of taste sensitivity by comparing taste perception and physicochemical properties of saliva in older (60-90 years) and younger (18-30 years) groups. Saliva samples were collected in response to taste stimulation and rheological properties, viscoelasticity and viscosity, were assessed as well as composition particularly of proteins including mucins, cystatin S and carbonic anhydrase VI (CAVI). The second part of this study was to develop in vitro cellular models to investigate saliva-mediated modulation of specific taste receptor responses. Transfected TR146 cells over-expressing the TAS2R38 receptor and the SCC090 cell line that endogenously expresses TAS2R10 were used to measure intracellular calcium responses to bitter taste compounds. Models were tested using a fluorophore and confocal microscopy as well as a florescent plate reader. Saliva samples collected during the volunteer study were used to create a salivary layer over a confluent epithelial cell monolayer and the effects of saliva from older and younger groups were compared with regard to tastant diffusion and receptor activation. Reduced calcium responses to bitter taste compounds were observed when saliva from older adults was added to the confluent cells compared to saliva from younger adults. Responses to bitter tastants in vivo could be correlated to the calcium response in the in vitro model in the presence of saliva from younger subjects but not with saliva from older subjects. Levels of certain salivary proteins including mucins and the viscoelasticity of saliva samples correlated with taste receptor activation in the cell models and as such, the effect of physical properties of saliva on taste function was demonstrated in vitro.