Metabolic hormones in saliva: origins and functions

Abstract

The salivary proteome consists of thousands of proteins, which include, among others, hormonal modulators of energy intake and output. Although the functions of this prominent category of hormones in whole body energy metabolism are well characterized, their functions in the oral cavity, whether as a salivary component, or when expressed in taste cells, are less studied and poorly understood. The respective receptors for the majority of salivary metabolic hormones have been also shown to be expressed in salivary glands, taste cells, or other cells in the oral mucosa. This review provides a comprehensive account of the gastrointestinal hormones, adipokines, and neuropeptides identified in saliva, salivary glands, or lingual epithelium, as well as their respective cognate receptors expressed in the oral cavity. Surprisingly, few functions are assigned to salivary metabolic hormones, and these functions are mostly associated with the modulation of taste perception. Because of the well-characterized correlation between impaired oral nutrient sensing and increased energy intake and body mass index, a conceptually provocative point of view is introduced, whereupon it is argued that targeted changes in the composition of saliva could affect whole body metabolism in response to the activation of cognate receptors expressed locally in the oral mucosa.

Dipeptidyl Peptidase-IV Activity and Neuropeptide Y in the Mouth: The Relationship with Body Composition and the Impact of Carbohydrates

“…This is in contrast with what was expected, as this is an important enzyme and substrate in the regulation of satiety [7]. However, we measured the total amount of full length NPY in the saliva.…”

“…The hypothesis for this study was the enzymatic activity of DPP-IV in the plasma would correlate with the DPP-IV enzymatic activity in the saliva [7]. However, no significant correlation was found between the two pools of DPP-IV at the fasted state.…”

“…Two possible sources of DPP-IV in the mouth are exosomes released by the salivary glands [2,3] and/ or by transport from capillaries or secretion into the gingival cervicular fluid [4]. Although controversial, some research posits that changes in proteins in the saliva may mirror the blood [5][6][7][8]. As a result, salivary DPP-IV may, in part, mirror the plasma activity levels of DPP-IV, especially at resting conditions when the modulation of its hormonal substrates is limited due to homeostatic maintenance.…”

Taste of Fat: A Sixth Taste Modality?

“…A decreased response to sour and salty tastants was observed in GHSR-null mice (195). In brief, all taste modalities appear to be under endocrine control (234). Hormones produced by taste buds mainly play a role in modulating taste sensitivity.…”

Role of Saliva in Oral Food Perception

“…In a recent article, Zolotukhin [16] reviewed the different metabolic hormones present in saliva and their functions. Quite a few play a direct role in taste perception (often by modulating taste receptors); although most of these studies were performed in animal models, some of these hormones were also found in human saliva, such as glucagon [17], insulin [18], leptin [19,20], oxytocin [21] and ghrelin [20].…”