Methods and Results: HFpEF was induced by a combination of high fat diet (HFD) and endothelial NO synthase (eNOS) inhibition with L-NAME for 15 weeks in C57BL/6N mice. At week 11, mice received either NO₂-OA or vehicle via mini-osmotic pumps for 4 weeks. As previously reported, treatment with NO₂-OA significantly improved LV diastolic function. Echocardiographic analysis of RV function now revealed, that tricuspid annular plane systolic excursion (TAPSE) in the HFpEF mouse model at 15 weeks was significantly decreased compared to mice receiving normal chow (TAPSE, mean ± SD; chow: 1.17 ± 0.13; HFD+L-NAME: 0.91 ± 018; N=10, p<0.01). Whereas treatment with NO₂-OA significantly alleviated diastolic LV dysfunction, RV function was not changed by NO₂-OA administration (TAPSE, mean ± SD; HFD+L-NAME: 0.91 ± 018; HFD+L-NAME NO₂-OA: 0.97 ± 0.20; N=10/11, p>0.99). While we on the one hand cannot rule out that RV dysfunction might be diminished after longer time periods of treatment at the moment, it might on the other hand point towards intraventricular differences in the underlying pathomechanisms. To unravel these potential differences, we analysed superoxide dismutases (SOD) as important mediators of redox regulation and markers of oxidative stress in RV and LV, given that NO₂-OA is known to have antioxidative properties. In HFpEF vehicle-treated mice, mRNA expression of the SOD isoform 1, which is mainly expressed in the cytoplasm, was significantly upregulated in the LV (p<0.01), but not in RV tissue compared to mice fed with normal chow. In contrast, SOD2, an isoform exclusively located to mitochondria, was significantly upregulated in RV (p<0.05) but not in LV tissue. Interestingly, treatment with NO₂-OA blunted the SOD1 upregulation in the LV, but had no effect on SOD2 expression in RV tissue. Differences in redox regulation in RV and LV myocardium were also disclosed in experiments with Langendorff-perfused mouse hearts with hydrogen peroxide. In RV myocardium the extent of hyperoxidized peroxiredoxin, a marker of oxidative stress, was higher compared to LV myocardium.

Conclusion: RV dysfunction, an important determinant of mortality in HFpEF patients, was observed in a mouse model of HFpEF induced by a combination of HFD and eNOS inhibition. Treatment with NO₂-OA, a cardioprotective and antioxidative agent, ameliorated LV diastolic function, but could not target RV dysfunction, which might be related to differential regulations of oxidative stress. Antioxidative strategies directly targeting mitochondrial integrity might by a promising approach to prevent RV dysfunction in HFpEF.