Goodbye gavage – Replacing oral gavage for mouse glucose tolerance testing

Across the world, metabolic disease is a leading cause of ill-health and death. Alterations in blood sugar (glucose) control are a key feature of many metabolic diseases, including type-2 diabetes (T2D), which impacts >3.4 million people in the UK. Studies in mice and rats have been fundamental for advancing understanding the biological basis of metabolic disease and are critical for drug development, including the recent high-profile medicines like semaglutide (Ozempic/Wegovy) for the treatment of obesity and T2D. An oral glucose tolerance test (oGTT) is a routinely used medical test for diagnosis of T2D. A GTT measures the ability of a person (or animal) to clear excess glucose from their blood, in a specified period, after a large bolus treatment. In contrast to humans when glucose is drunk voluntarily, oral gavage and (more commonly) intraperitoneal injection are typically used to administer the glucose bolus in the mouse GTT. Although used less frequently, the former is the more physiologically relevant as it integrates the digestive tract, including associated release of key hormones. However, oral gavage is also not without its limitations: gavaging glucose straight into the stomach bypasses potentially critical early glucose-sensing via the mouth, it is highly invasive for the animals and requires significant investigator skill to perform correctly. We are committed to refining the mouse oGTT, making it more representative of the human test, improving animal welfare and investigator experience. Mission: To make voluntary oral consumption via micropipette-guided dosing/administration (MDA) the field standard glucose dosing method for mouse GTT. In 2022 we received funding via the NC3Rs Skills, knowledge and transfer scheme to refine mouse oGTT to make it more like the human test and improve animal experience through validation of a simple non-invasive MDA method to replace oral gavage. We have successfully created and validated a MDA-oGTT protocol where mice voluntarily drink the glucose and experimentally confirmed is as effective as oral gavage as a dosing method while being much less stressful for the mice. This method has independently been verified by a research facility in the USA. A paper on our findings is openly available online. Through our ongoing programme of outreach activities, we have developed additional partnerships that underpin this application. Building on this success, the goal of the proposed work is to further refine mouse MDA-oGTT for both animal and investigator experience. We will incorporate handling-free habituation methods developed by Prof Robinson of the University of Bristol (“developer”) through prior NC3Rs funding (objective 1). This should reduce the mouse habituation time needed, which we have identified as a barrier to wider adoption of our MDA-oGTT approach. A comprehensive programme of dissemination and outreach activities (objective 2) will be conducted, including partnerships with a diverse world-leading international “end-user group” who will provide external experimental validation in a variety of contexts, including pregnancy-associated diabetes which is currently poorly understood. A database search revealed that GTTs have been used in 5,617 published medical research studies, 149 in 2023. We estimate that if 50% of the studies from 2023 adopted our more refined method, then this would have improved the experience of 2,384 mice worldwide. As such, our refinement has potential wide-ranging impact.