Human saliva and model saliva at bulk to adsorbed phases – similarities and differences

Salivary lubricity (ex vivo) enhances upon moderate exercise: A pilot study

“…2 A demonstrates a perfect overlap between the saliva from the participants in the Control and Exercise procedures since at time point S 0 , saliva was collected before the exercise intervention commenced. This confirms feasibility of the soft tribology approach to measure salivary lubricity in line with previous reports ( Bongaerts et al, 2007 ; Sarkar, Xu et al, 2019 ; Torres et al, 2019 ; Xu et al, 2020 ). Frictional forces in the Control and Experimental procedure for the saliva boundary (0.003 m/s) and mixed regimes (0.1 m/s) can be seen in Fig.…”

“…Such increase in salivary lubricity can be associated with the increase in overall protein content on exercise as observed in this study and in line with previous results by Ligtenberg et al (2015) . Although the protein content of saliva in this study was at the lower end of the range typically found in whole human saliva possibly due to measurements in the morning in the present study ( Crosley et al, 2009 ; Sarkar, Xu et al, 2019 ), the relative increase of total salivary protein upon exercise was 38 %, which lies in between the range of increase observed for saliva collected from participants subjected to moderate to high intensity exercise procedures by Ligtenberg et al (2015) . Such increase of exercise-induced salivary protein content might be attributed to the direct sympathetic stimulation of the salivary glands by plasma catecholamines that can increase significantly above the anaerobic threshold (which denotes the point at which significant blood lactate accumulation is seen with increasing exercise intensity) ( Brooks, 1985 ; Proctor & Carpenter, 2014 ).…”

“…sprays, hydrogels) such as carboxymethyl cellulose, xanthan gum ( Nieuw Amerongen & Veerman, 2003 ; Oh, Lee, Kim, & Kho, 2008 ), that are far from the composition of real human saliva bring only limited symptomatic relief and any benefits are often short-lived ( Vinke, Kaper, Vissink, & Sharma, 2018 ). This is in part because, in designing most substitutes, rheology (resistance to flow or viscosity) has been considered as the “gold standard” characteristic with the goal to match the viscosity of human saliva ( Sarkar, Xu, & Lee, 2019 ; Xu et al, 2020 ), but fails to consider the tribological (lubrication) aspects of saliva, which is the main focus of this paper.…”

“…Although saliva is largely an aqueous fluid containing 99 % water, it is the proteins ( i.e. mucins (MUC5B) and other low molecular weight proteins) and ions contributing to the rest of the salivary composition that renders saliva its unique rheological (viscosity, elasticity, stickiness) and lubrication properties ( Humphrey & Williamson, 2001 ; Sarkar, Kanti, Gulotta, Murray, & Zhang, 2017 ; Sarkar, Ye, & Singh, 2017 ; Sarkar, Xu et al, 2019 ). Physiologically, the secretion of saliva can be controlled through two separate pathways: the sympathetic and parasympathetic nervous systems, producing varying compositional characteristics in saliva ( Garrett, 1987 ; Proctor & Carpenter, 2014 ).…”

N-Glycan Modifications with Negative Charge in a Natural Polymer Mucin from Bovine Submaxillary Glands, and Their Structural Role

“…The C-terminal Cys-rich part (including the Cys knot) of mucin forms disulfidebonded mucin dimers and multimers [36]. The present results suggest that the physicochemical characterization (e.g., pH sensitivity and stability) of BSM is derived from the sulfate (pKa = 1) groups in N-glycans as well as the reported sialic acid (pKa = 2.6) with some sulfate groups in O-glycans and charged amino acids [37]. Finally, sulfated N-glycans may structurally affect mucin mobility due to inter-and intramolecular electrostatic interactions, and associative polymer networks through self-association could form and stabilize together with hydrogen bonding ( Figure 4B).…”