Effects of semaglutide in a rat model of heart failure with preserved ejection fraction: Focus on excitation-contraction coupling and mitochondrial function

Background. In the treatment of obesity and diabetes, agonists of the anorexic Glucagon like peptide 1 receptor (GLP-1R) are well-established, with semaglutide (SEMA) having the strongest weight reducing effects. SEMA has proven beneficial effects on cardiovascular outcomes, especially on heart failure with preserved ejection fraction (HFpEF). However, exact effects on a cardiomyocyte level are still not fully elucidated.

Methods and Results Male Wistar rats were fed standard chow (CO) or high fat/fructose (HFD) diet combined with L-Name (0.25mg/ml) via drinking water for 8-weeks to induce obesity and HFpEF.  HFD fed rats were then randomly assigned to receive SEMA (HF+SEMA) (120μg/kg/day s.c.) or the same volume of saline s.c. (HF) for 8 weeks. Under treatment, rats of the HF and HF+SEMA group were allowed to choose between HFD and low-fat diet ad libitum. After eight weeks, cardiac ventricular myocytes (n=3 per group, min. 33 cardiac myocytes) and mitochondria (n=6-8 per group) were isolated. Sarcomere length, cytosolic Ca²⁺ (Indo1, AM) and mitochondrial redox state (auto fluorescents NAD(P)H and FAD+), membrane potential (TMRM), and ROS (DCF) in myocytes were measured using 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.

The HF group showed a significantly shorter diastolic sarcomere length and increased diastolic & systolic [Ca²⁺] compared to CO. Fractional shortening was comparable, while Ca-transient amplitude was increased in HF. The mitochondrial redox status was more oxidized in the HF compare to the CO group, but mitochondrial membrane potential was more negative and more stable, furthermore ROS production was reduced. BNP blood levels were significantly increased in HF compared to CO. Treatment with SEMA rescued diastolic sarcomere length and Ca-transient amplitude to CO levels, but not diastolic and systolic [Ca2+]. Mitochondrial redox status was unaffected and ROS production was lower in HF+SEMA compared to CO. Interestingly, mitochondrial membrane potential was more negative and stable in HF vs. HF+SEMA. In isolated mitochondria, mitochondrial respiration, Ca²⁺-retention capacity using Calcium-Green, mitochondrial membrane potential using TMRM and H₂O₂ production using AmplexRed was examined. SEMA rescued mitochondrial respiration with pyruvate/malate and succinate as substrates to CO levels, while mitochondrial respiration could partially be rescued in the presence of fatty acid mix as substrates. Mitochondrial membrane potential was unchanged, Ca²⁺-retention capacity was lowered in SEMA compared to CO. H₂O₂ production was unchanged by SEMA, independent of the given substrate.

Conclusions The combined treatment of rats with HFD and L-Name is sufficient to generate calcium mishandling and mitochondrial dysfunction typical for HFpEF. A therapy with SEMA is able to partially rescue these typical HFpEF findings and furthermore reduce ROS burden. This is in line with clinical studies showing beneficial effects of SEMA in HFpEF patients.