Aim: Trimethylamine N-oxide (TMAO) is a gut microbiota-derived metabolite synthesized in host organisms from specific food constituents, such as choline, carnitine and betaine. During the last decade, elevated TMAO levels have been proposed as biomarkers to estimate the risk of cardiometabolic diseases. However, there is still no consensus about the role of TMAO in the pathogenesis of cardiovascular disease since regular consumption of TMAO-rich seafood (i.e., a Mediterranean diet) is considered to be beneficial for the primary prevention of cardiovascular events. Therefore, the aim of this study was to investigate the effects of long-term TMAO administration on mitochondrial energy metabolism in an experimental model of right ventricle heart failure.Methods: TMAO was administered to rats at a dose of 120 mg/kg in their drinking water for 10 weeks. Then, a single subcutaneous injection of monocrotaline (MCT) (60 mg/kg) was administered to induce right ventricular dysfunction, and treatment with TMAO was continued (experimental groups: Control; TMAO; MCT; TMAO+MCT). After 4 weeks, right ventricle functionality was assessed by echocardiography, mitochondrial function and heart failure-related gene and protein expression was determined.Results: Compared to the control treatment, the administration of TMAO (120 mg/kg) for 14 weeks increased the TMAO concentration in cardiac tissues up to 14 times. MCT treatment led to impaired mitochondrial function and decreased right ventricular functional parameters. Although TMAO treatment itself decreased mitochondrial fatty acid oxidation-dependent respiration, no effect on cardiac functionality was observed. Long-term TMAO administration prevented MCT-impaired mitochondrial energy metabolism by preserving fatty acid oxidation and subsequently decreasing pyruvate metabolism. In the experimental model of right ventricle heart failure, the impact of TMAO on energy metabolism resulted in a tendency to restore right ventricular function, as indicated by echocardiographic parameters and normalized organ-to-body weight indexes. Similarly, the expression of a marker of heart failure severity, brain natriuretic peptide, was substantially increased in the MCT group but tended to be restored to control levels in the TMAO+MCT group.Conclusion: Elevated TMAO levels preserve mitochondrial energy metabolism and cardiac functionality in an experimental model of right ventricular heart failure, suggesting that under specific conditions TMAO promotes metabolic preconditioning-like effects.

Significant impairments in mitochondrial function are associated with the development of multi-organ failure in sepsis/endotoxaemia, but the data on the dynamics of simultaneous mitochondrial impairment in multiple organs are limited. The aim of this study was to evaluate the changes in heart, brain and kidney mitochondrial function in an experimental model of lipopolysaccharide (LPS)-induced endotoxaemia. Samples were collected 4 and 24 h after single injection of LPS (10 mg/kg) in mice. Marked increases in inflammation-related gene expression were observed in all studied tissues 4 h after LPS administration. At 24 h post LPS administration, this expression of inflammation-related genes remained upregulated only in kidneys. Significantly increased concentrations of kidney function markers confirmed that kidneys were severely damaged. Echocardiographic measurements showed that the ejection fraction and fractional shortening were significantly reduced 4 h after LPS administration, whereas 24 h after LPS administration, the cardiac function was restored to baseline. A two-fold decrease in mitochondrial oxidative phosphorylation (OXPHOS) capacity in the kidney was observed 4 and 24 h after LPS administration. Significant decrease in mitochondrial fatty acid oxidation was observed in heart 4 h after LPS administration. Furthermore, 24 h after LPS administration, the respiration rates in cardiac fibers at OXPHOS and electron transport (ET) states were significantly increased, which resulted in increased ET coupling efficiency in the LPS-treated group, whereas four-fold increases in the H2O2 production rate and H2O2/O ratio were observed. The brain mitochondria demonstrated a slightly impaired mitochondrial functionality just 24 h after the induction of endotoxaemia. In conclusion, among studied tissues kidney mitochondria are the most sensitive to endotoxaemia and do not recover from LPS-induced damage, whereas in brain, mitochondrial function was not significantly altered. In heart, endotoxaemia induces a decrease in the mitochondrial fatty acid oxidation capacity, but during the phase of suppressed inflammatory response, the ET efficiency is improved despite the marked increase in reactive oxygen species production.

Purpose. Sodium-glucose cotransporter 2 (SGLT2) inhibitors prevent heart failure and decrease cardiovascular mortality in patients with type 2 diabetes. Heart failure is associated with detrimental changes in energy metabolism, and the preservation of cardiac mitochondrial function is crucial for the failing heart. However, to date, there are no data to support the hypothesis that treatment with a SGLT2 inhibitor might alter mitochondrial bioenergetics in diabetic failing hearts. Thus, the aim of this study was to investigate the protective effects of empagliflozin on mitochondrial fatty acid metabolism.Methods. Mitochondrial dysfunction was induced by 18 weeks of high-fat diet (HFD)induced lipid overload. Empagliflozin was administered at a dose of 10 mg/kg in a chow for 18 weeks. Palmitate metabolism in vivo, cardiac mitochondrial functionality and biochemical parameters were measured. Results.In HFD-fed mice, the palmitate uptake was 1.7, 2.3, and 1.9 times lower in the heart, liver and kidneys, respectively, compared to that of the normal chow control group.Treatment with empagliflozin increased palmitate uptake and decreased the accumulation of metabolites of incomplete fatty acid oxidation (FAO) in cardiac tissues, but not other tissues, compared to those of the HFD control group. Moreover, empagliflozin treatment resulted in fully restored fatty acid oxidation pathway-dependent respiration in permeabilized cardiac fibers. Treatment with empagliflozin did not affect the biochemical parameters related to hyperglycemia or hyperlipidemia Conclusion. Empagliflozin treatment preserves mitochondrial fatty acid oxidation in the heart under conditions of chronic lipid overload.

The suppression of energy metabolism is one of cornerstones of cardiac dysfunction in sepsis/endotoxaemia. To investigate the role of fatty acid oxidation (FAO) in the progression of inflammation‐induced cardiac dysfunction, we compared the effects of FAO‐targeting compounds on mitochondrial and cardiac function in an experimental model of lipopolysaccharide (LPS)‐induced endotoxaemia. In LPS‐treated mice, endotoxaemia‐induced inflammation significantly decreased cardiac FAO and increased pyruvate metabolism, while cardiac mechanical function was decreased. AMP‐activated protein kinase activation by A769662 improved mitochondrial FAO without affecting cardiac function and inflammation‐related gene expression during endotoxaemia. Fatty acid synthase inhibition by C75 restored both cardiac and mitochondrial FAO; however, no effects on inflammation‐related gene expression and cardiac function were observed. In addition, the inhibition of carnitine palmitoyltransferase 2 (CPT2)‐dependent FAO by aminocarnitine resulted in the accumulation of FAO intermediates, long‐chain acylcarnitines, in the heart. As a result, cardiac pyruvate metabolism was inhibited, which further exacerbated inflammation‐induced cardiac dysfunction. In conclusion, although inhibition of CPT2‐dependent FAO is detrimental to cardiac function during endotoxaemia, present findings show that the restoration of cardiac FAO alone is not sufficient to recover cardiac function. Rescue of cardiac FAO should be combined with anti‐inflammatory therapy to ameliorate cardiac dysfunction in endotoxaemia.

Right ventricular (RV) and left ventricular (LV) dysfunction is common in a significant number of hospitalized coronavirus disease 2019 (COVID-19) patients. This study was conducted to assess whether the improved mitochondrial bioenergetics by cardiometabolic drug meldonium can attenuate the development of ventricular dysfunction in experimental RV and LV dysfunction models, which resemble ventricular dysfunction in COVID-19 patients. Effects of meldonium were assessed in rats with pulmonary hypertension-induced RV failure and in mice with inflammation-induced LV dysfunction. Rats with RV failure showed decreased RV fractional area change (RVFAC) and hypertrophy. Treatment with meldonium attenuated the development of RV hypertrophy and increased RVFAC by 50%. Mice with inflammation-induced LV dysfunction had decreased LV ejection fraction (LVEF) by 30%. Treatment with meldonium prevented the decrease in LVEF. A decrease in the mitochondrial fatty acid oxidation with a concomitant increase in pyruvate metabolism was noted in the cardiac fibers of the rats and mice with RV and LV failure, respectively. Meldonium treatment in both models restored mitochondrial bioenergetics. The results show that meldonium treatment prevents the development of RV and LV systolic dysfunction by enhancing mitochondrial function in experimental models of ventricular dysfunction that resembles cardiovascular complications in COVID-19 patients.