Effects of GIP on regional blood flow during normoglycemia and hyperglycemia in anesthetized rats

Renal effects of GLP-1 receptor agonists and tirzepatide in individuals with type 2 diabetes: seeds of a promising future

PURPOSE

Chronic kidney disease (CKD) is one of the most common complications of type 2 diabetes (T2D), and CKD-related disability and mortality are increasing despite the recent advances in diabetes management. The dual GIP/GLP-1 receptor agonist tirzepatide is among the furthest developed multi-agonists for diabetes care and has so far displayed promising nephroprotective effects. This review aims to summarize the evidence regarding the nephroprotective effects of glucagon-like peptide-1 receptor agonists (GLP-1RA) and tirzepatide and the putative mechanisms underlying the favorable renal profile of tirzepatide.

METHODS

A comprehensive literature search was performed from inception to July 31st 2023 to select research papers addressing the renal effects of GLP-1RA and tirzepatide.

RESULTS

The pathogenesis of CKD in patients with T2D likely involves many contributors besides hyperglycemia, such as hypertension, obesity, insulin resistance and glomerular atherosclerosis, exerting kidney damage through metabolic, fibrotic, inflammatory, and hemodynamic mechanisms. Tirzepatide displayed an unprecedented glucose and body weight lowering potential, presenting also with the ability to increase insulin sensitivity, reduce systolic blood pressure and inflammation and ameliorate dyslipidemia, particularly by reducing triglycerides levels.

CONCLUSION

Tirzepatide is likely to counteract most of the pathogenetic factors contributing to CKD in T2D, potentially representing a step forward in incretin-based therapy towards nephroprotection. Further evidence is needed to understand its role in renal hemodynamics, fibrosis, cell damage and atherosclerosis, as well as to conclusively show reduction of hard renal outcomes.

Effects on pancreatic Beta and other Islet cells of the glucose-dependent insulinotropic polypeptide

Glucose-dependent insulinotropic polypeptide (GIP) is a gut-derived incretin that, in common with glucagon-like peptide-1 (GLP-1), has both insulin releasing and extra-pancreatic glucoregulatory actions. GIP is released in response to glucose or fat absorption and acts on the GIP receptor (GIPR) to potentiate insulin release from pancreatic beta cells. GIP has also been shown to promote beta cell survival and stimulate the release of GLP-1 from islet alpha cells. There is now evidence to suggest that low levels of GIP are secreted from alpha cells and may act in a paracrine manner to prime neighboring beta cells for insulin release. In addition, GIP acts on adipocytes to stimulate fat storage and can exert anorexigenic effects via actions in the hypothalamus. Contrary to GLP-1, the development of effective GIP-based T2D treatments has been hindered by poor bioavailability and attenuation of beta cell responses to GIP in some patients with sub-optimally controlled T2D. Recently, longer-acting GIP agonists that exhibit enzymatic stability, as well as dual GLP-1/GIP agonists which provide simultaneous improvement in glucose and weight control have been generated and successfully tested in animal T2D models. This, together with reports on GIP antagonists that may protect against obesity, has revived the interest on the GIP/GIPR axis as a potential anti-diabetic pathway. In this review, we summarize the known aspects of the effects of GIP on beta and other islet cells and discuss the most recent developments on GIP-based therapeutic agents for the improvement of beta cell function in T2D patients.