Effect of non-nutritive sweeteners on vascular function: deciphering the role of the T1R sweet-taste receptors – SOSweet

First, we will explore the effects of chronic sweetener consumption in mice on vascular and gastrointestinal function: microvascular reactivity in vivo and macrovascular reactivity ex vivo and gastrointestinal contractility ex and in vivo. Pharmacological inhibition of T1Rs or the use of T1Rs knockout mice will allow us to explore the mechanisms involved. We will then conduct a randomised, placebo-controlled clinical trial to study (1) the effects of sweetener consumption on macro- and microvascular function in healthy volunteers. Speckle contrast imaging coupled with intra-dermal microdialysis will be used to dissect the role of the T1R pathway in these vascular effects; (2) to understand how oral and/or intestinal T1Rs are involved in metabolic responses and the consequences for vascular function We will also study in humans and animals the direct effect of sweeteners on the vessel via activation of T1Rs present in vascular cells. Finally, since these sweeteners can have an action on the metabolic response or on the control of food intake, we will dissect in vivo in a healthy or knock out T1Rs mouse model, and by pharmacological modulation, the cerebral projections from the numerous nervous afferent pathways of the digestive tract. The direct effect of sweeteners on brain T1Rs will also be studied. These neural pathways could, in turn, affect the neural regulation of vascular tone.

Our first results showed that there is probably a specific effect of each sweetener on vascular function, thus providing a new working hypothesis. The artificial molecule sucralose, proposed in this project, could have protective effects on cardiometabolic risk, contrary to other molecules such as acesulfame potassium (Ace K). Our initial results also suggest that it is interesting, in parallel to our healthy populations, to propose models with cardiovascular or metabolic disorders. These data could help to better understand the very long-term effects of sweetener consumption.
In this context, these sweeteners are also suspected to act on the control of food intake through a direct action on brain T1Rs, so we performed a test of food intake after a 10-hour fast. The animals received either an IP injection of NaCl (control), glucose (satiety) or sweeteners (20 mg/kg sucralose or 100 mg/kg Ace K). Measurement of food intake shows that the sucralose group ate significantly more than the glucose group, whereas the Ace K group ate significantly less than all other groups, suggesting a satiety-inducing effect of this sweetener. Collectively, these preliminary results indicate that sweeteners interfere at the brain level with the control of autonomic function and food intake. We also confirm in this section the importance of studying the effects of each molecule in isolation.
Concerning the clinical part, the submission and the administrative authorisations were strongly impacted by the health crisis, since all the research projects except Covid were suspended at the CIC of the Grenoble Alpes University Hospital. However, we obtained a favourable opinion from the Comité de Protection des Personnes on july 13th 2021. Inclusions should start at the end of 2021.

It is now a question of unravelling the involvement of T1Rs in these observed vascular and cerebral responses and better understanding which molecular targets are impacted. These observations are awaiting confirmation in humans in a forthcoming clinical study.

Risdon S*, Battault S*, Romo-Romo A*, Roustit M, Briand L, Meyer G, Almeda-Valdes P, Walther G. Sucralose and cardiometabolic health: current understanding from receptors to clinical investigations. Adv Nutr. 2021 Feb 12:nmaa185. doi: 10.1093/advances/nmaa185

Habitual excess sugar consumption, such as that via soda-like drinks, contributes to the risk of developing metabolic diseases (obesity, type 2 diabetes) and increases the risk of developing cardiovascular diseases. In an effort to address this, synthetic or natural non-caloric sweeteners (e.g. aspartame, sucralose, acesulfame K, stevia etc.) are commonly used in commercial products, providing consumers with a similar sweet savor to that of sugar, but without the high-caloric content and, subsequent, hyperglycemic peak. These non-nutritive sweeteners are validated by the American Academy of Nutrition and Dietetics, as well as the European Food Safety Agency; and are often promoted as a healthy alternative to added sugars. However, very recent research demonstrates an association between the consumption of products containing non-nutritive sweeteners and increased risk of mortality, including that of cardiovascular origin. Additionally, research has indicated that these sweeteners have adverse effects on glucose metabolism, gut microbiota and/or the control of appetite. Thus, sweeteners may not be biologically inert, but the underlying mechanisms explaining its consequences to human health are not known. Recent work has identified the presence of sweet taste receptors (T1Rs), which are activated by sweeteners, in the pancreas and intestine; and, more surprisingly, in the brain and endothelial cells. In addition, our preliminary results demonstrate impaired vascular function in rats consuming non-nutritive sweeteners within the limit of an acceptable daily intake. Indeed, vascular endothelial dysfunction is well recognized for its early role in the development of atherosclerosis, as well as an early and sensitive marker in the development of obesity and insulin resistance. Thus, we hypothesize that these sweetener-activated T1Rs are involved directly (at the blood vessel level) and indirectly (via brain integration or metabolic modulation) in the disruption of vascular reactivity. This translational research will combine studies in humans and animals with respect to ethical guidelines and the protection of people. First, we will explore, in mice, the effects of habitual non-nutritive sweetener consumption on vascular and gastrointestinal function; in vivo and ex-vivo macrovascular and microvascular reactivity respectively, as well as in vivo and ex-vivo gastrointestinal contractility. A pharmacological modulation of T1Rs and the use of T1Rs knock-out mice will make it possible to explore the mechanisms involved. We will then conduct a randomized, placebo-controlled clinical trial to investigate (1) the effects of consuming non-nutritive sweeteners on macro- and microvascular function in healthy volunteers, using speckle contrast imaging coupled with intradermal microdialysis to determine the influence of the T1R pathway on vascular reactivity; and (2) to understand how oral and/or gastro-intestinal T1Rs are involved in metabolic responses and consequences for vascular function. We will also study the direct effect of sweeteners on blood vessels via activation of T1Rs present in vascular cells in humans and animals. Finally, since non-nutritive sweeteners can act on the metabolic responses or on the control of food intake, we will assess, in vivo, in a model of healthy mice and T1Rs knock-out mice, as well as by pharmacological methodologies, afferent nerve pathways originating from the digestive tract and projecting to the brain. The direct effect of sweeteners on brain T1Rs will also be studied. These neural pathways may, in turn, affect nerve regulation of vascular tone.