Background. In patients with obesity or diabetes, agonists of the anorexic Glucagon like peptide 1 receptor (GLP-1R), such as semaglutide (sema), efficiently reduce body weight and improve cardiovascular outcomes, with a modest effect also on hospitalization for heart failure (by 11% in meta-analysis). Obesity is an important risk factor also for heart failure, where defects in excitation-contraction coupling and mitochondria energetics occur. Since it is currently evaluated in clinical trials whether GLP-1R agonists improve outcome of patients with heart failure and obesity, we evaluated the impact of sema on mechano-energetic coupling in cardiac myocytes from obese rats treated with sema.

Methods and results. Male Wistar rats were fed a high fat, high fructose diet (HFD) for 8 weeks to induce obesity. Rats were then randomly assigned to receive sema (120μg/kg s.c.) or saline s.c. (CO) for 8 weeks, leading to a body weight change of -10% (sema) vs. +8% (CO). Rats could choose between HFD and low-fat diet ad libitum while receiving therapy. After 16 weeks, cardiac ventricular myocytes (from n=3 CO and n=5 sema rats) and mitochondria (from n=6 rats per group) were isolated. Sarcomere length, cytosolic Ca²⁺ (Indo1, AM), mitochondrial redox state (autofluorescence of NAD(P)H and FAD), membrane potential (TMRM) and ROS (DCF) were measured in myocytes with an automatic Ionoptix fluorescence setup. Pacing at 0.3 Hz, followed by β-adrenergic stimulation and increasing stimulation rate at 3 Hz for 3 minutes, was used to subject cardiac myocytes to a physiological stress regimen. Sema treatment in vivo lowered systolic and diastolic [Ca²⁺]_i and Ca²⁺-transient amplitude (n=100 cells) compared to CO (n=70), which led to longer sarcomere lengths at both systole and diastole in sema (n=120) vs. CO (n=100), but without altering fractional sarcomere shortening. Mitochondrial redox state (n=46/82 CO/sema) remained unaltered, but membrane potential was diminished in sema by approx. 3% during the protocol and about 50% overall (n=120) vs. CO (n=69), and ROS generation was enhanced in sema  by approx. 10%(n=33) vs. CO (n=56). Mitochondrial respiration was measured in isolated mitochondria. Ca²⁺-retention capacity using Calcium-Green, mitochondrial membrane potential using TMRM, and NAD(P)H levels were determined. While pyruvate/malate (P/M, Complex I)- and succinate (Complex II)-supported state 3 respiration (in the presence of ADP) was unchanged, fatty acid-supported state 3 respiration was increased. In contrast, Ca²⁺-retention capacity, mitochondrial membrane potential, and NAD(P)H levels remained unaltered.

Conclusion. In rats with diet-induced obesity, semaglutide substantially reduced body weight and boosted fatty acid-supported respiration of cardiac mitochondria. In cardiac myocytes, cytosolic Ca²⁺ concentrations were lowered without compromising fractional sarcomere shortening. However, since sema in vivo treatment also lowered mitochondrial membrane potential but increased ROS, further studies are required to resolve the underlying mechanisms.