Effects of a long-acting secretin peptide analog alone and in combination with a GLP-1R agonist in a diet-induced obesity mouse model.

OBJECTIVE: Obesity is a major global health problem which can be targeted with new mechanistic diverse pharmacological interventions. Here we evaluate a new long-acting secretin receptor agonist as a potential treatment for obesity. METHODS: BI-3434 was designed as a secretin analog with stabilized peptide backbone and attached fatty acid-based half-life extension group. The peptide was evaluated in vitro for its ability to stimulate cAMP accumulation in a cell line stably expressing recombinant secretin receptor. On the functional level, stimulation of lipolysis in primary adipocytes after treatment with BI-3434 was determined. The ability of BI-3434 to activate secretin receptor in vivo was assessed in a cAMP reporter CRE-Luc mouse model. Furthermore, a diet-induced obesity mouse model was used to test the effects of BI-3434 on body weight and food intake following repeated daily subcutaneous administration alone and in combination with a GLP-1R agonist. RESULTS: BI-3434 potently activated human secretin receptor. However, lipolysis was only weakly induced in primary murine adipocytes. BI-3434 had an extended half-life compared to endogenous secretin and activated target tissues like pancreas, adipose tissue, and stomach in vivo. BI-3434 did not lower food intake in lean or diet-induced obese mice, but it increased energy expenditure after daily administration. This led to a loss of fat mass, which did not translate in a significant effect on body weight. However, treatment in combination with a GLP-1R agonist led to a synergistic effect on body weight loss. CONCLUSIONS: BI-3434 is a highly potent and selective agonist of secretin receptor with an extended pharmacokinetic (PK) profile. Increased energy expenditure after daily treatment with BI-3434 suggests that secretin receptor is involved in metabolic regulation and energy homeostasis. Targeting secretin receptor alone may not be an efficient anti-obesity treatment, but could be combined with anorectic principles like GLP-1R agonists.

Ndrg1 promotes adipocyte differentiation and sustains their function.

Adipocytes play a central role in maintaining metabolic homeostasis in the body. Differentiation of adipocyte precursor cells requires the transcriptional activity of peroxisome proliferator-activated receptor-γ (Pparγ) and CCAAT/enhancer binding proteins (C/Ebps). Transcriptional activity is regulated by signaling modules activated by a plethora of hormones and nutrients. Mechanistic target of rapamacin complexes (mTORC) 1 and 2 are central for the coordination of hormonal and nutritional inputs in cells and are essential for adipogenesis. Serum glucocorticoid kinase 1 (Sgk1)-dependent phosphorylation of N-Myc downstream-regulated gene 1 (Ndrg1) is a hallmark of mTORC2 activation in cells. Moreover, Pparγ activation promotes Ndrg1 expression. However, the impact of Ndrg1 on adipocyte differentiation and function has not yet been defined. Here, we show that Ndrg1 expression and its Sgk1-dependent phosphorylation are induced during adipogenesis. Consistently, we demonstrate that Ndrg1 promotes adipocyte differentiation and function by inducing Pparγ expression. Additionally, our results indicate that Ndrg1 is required for C/Ebpα phosphorylation. Moreover, we found that Ndrg1 phosphorylation by Sgk1 promotes adipocyte formation. Taken together, we show that induction of Ndrg1 expression by Pparγ and its phosphorylation by Sgk1 kinase are required for the acquisition of adipocyte characteristics by precursor cells.