No abstract

Echocardiography is a reliable and reproducible method to assess non-invasively cardiac function in clinical and experimental research. Significant progress in the development of echocardiographic equipment and transducers has led to the successful translation of this methodology from humans to rodents, allowing for the scoring of disease severity and progression, testing of new drugs, and monitoring cardiac function in genetically modified or pharmacologically treated animals. However, as yet, there is no standardization in the procedure to acquire echocardiographic measurements in small animals. This position paper focuses on the appropriate acquisition and analysis of echocardiographic parameters in adult mice and rats, and provides reference values, representative images, and videos for the accurate and reproducible quantification of left ventricular function in healthy and pathological conditions.

Aim Calcium ions play a pivotal role in matching energy supply and demand in cardiac muscle. Mitochondrial calcium concentration is lower in animal models of heart failure with reduced ejection fraction (HFrEF), but limited information is available about mitochondrial calcium handling in heart failure with preserved ejection fraction (HFpEF). Methods We assessed mitochondrial Ca2+ handling in intact cardiomyocytes from Zucker/fatty Spontaneously hypertensive F1 hybrid (ZSF1)‐lean (control) and ZSF1‐obese rats, a metabolic risk‐related model of HFpEF. A mitochondrially targeted Ca2+ indicator (MitoCam) was expressed in cultured adult rat cardiomyocytes. Cytosolic and mitochondrial Ca2+ transients were measured at different stimulation frequencies. Mitochondrial respiration and swelling, and expression of key proteins were determined ex vivo. Results At rest, mitochondrial Ca2+ concentration in ZSF1‐obese was larger than in ZSF1‐lean. The diastolic and systolic mitochondrial Ca2+ concentrations increased with stimulation frequency, but the steady‐state levels were larger in ZSF1‐obese. The half‐widths of the contractile responses, the resting cytosolic Ca2+ concentration and the decay half‐times of the cytosolic Ca2+ transients were higher in ZSF1‐obese, likely because of a lower SERCA2a/phospholamban ratio. Mitochondrial respiration was lower, particularly with nicotinamide adenine dinucleotide (NADH) (complex I) substrates, and mitochondrial swelling was larger in ZSF1‐obese. Conclusion The free mitochondrial calcium concentration is higher in HFpEF owing to alterations in mitochondrial and cytosolic Ca2+ handling. This coupling between cytosolic and mitochondrial Ca2+ levels may compensate for myocardial ATP supply in vivo under conditions of mild mitochondrial dysfunction. However, if mitochondrial Ca2+ concentration is sustainedly increased, it might trigger mitochondrial permeability transition pore opening.

Chronic pressure-overload and diabetes mellitus are two frequent disorders affecting the heart. We aimed to characterize myocardial structural and functional changes induced by both conditions. Pressure-overload was established in Wistar-han male rats by supra-renal aortic banding. Six-weeks later, diabetes was induced by streptozotocin (65 mg/kg,ip), resulting in four groups: SHAM, banding (BA), diabetic (DM) and diabetic-banding (DB). Six-weeks later, pressure-volume loops were obtained and left ventricular samples were collected to evaluate alterations in insulin signalling pathways, extracellular matrix as well as myofilament function and phosphorylation. Pressure-overload increased cardiomyocyte diameter (BA 22.0 ± 0.4 lm, SHAM 18.2 ± 0.3 lm) and myofilament maximal force (BA 25.7 ± 3.6 kN/m 2 , SHAM 18.6 ± 1.4 kN/m 2 ), Ca 2? sensitivity (BA 5.56 ± 0.02, SHAM 5.50 ± 0.02) as well as MyBP-C, Akt and Erk phosphorylation, while decreasing rate of force redevelopment (K tr ; BA 14.9 ± 1.1 s -1 , SHAM 25.2 ± 1.5 s -1 ). At the extracellular matrix level, fibrosis (BA 10.8 ± 0.9%, SHAM 5.3 ± 0.6%), pro-MMP-2 and MMP-9 activities increased and, in vivo, relaxation was impaired (s; BA 14.0 ± 0.9 ms, SHAM 12.9 ± 0.4 ms). Diabetes increased cardiomyocyte diameter, fibrosis (DM 21.4 ± 0.4 lm, 13.9 ± 1.8%, DB 20.6 ± 0.4 lm, 13.8 ± 0.8%, respectively), myofilament Ca 2? sensitivity (DM 5.57 ± 0.02, DB 5.57 ± 0.01), advanced glycation end-product deposition (DM 4.9 ± 0.6 score/mm 2 , DB 5.1 ± 0.4 score/mm 2 , SHAM 2.1 ± 0.3 score/mm 2 ), and apoptosis, while decreasing K tr (DM 13.5 ± 1.9 s -1 , DB 15.2 ± 1.4 s -1 ), Akt phosphorylation and MMP-9/TIMP-1 and MMP-1/ TIMP-1 ratios. Diabetic hearts were stiffer (higher enddiastolic-pressure: DM 7.0 ± 1.2 mmHg, DB 6.7 ± 0.7 mmHg, SHAM 5.3 ± 0.4 mmHg, steeper end-diastolicpressure-volume relation: DM 0.59 ± 0.18, DB 0.83 ± 0.17, SHAM 0.41 ± 0.10), and hypo-contractile (decreased end-systolic-pressure-volume-relation). DB animals presented further pulmonary congestion (Lungs/ body-weight: DB 5.23 ± 0.21 g/kg, SHAM 3.80 ± 0.14 g/kg) as this group combined overload-induced relaxation abnormalities and diabetes-induced stiffness. Diabetes mellitus and pressure overload led to distinct diastolic dysfunction phenotypes: while diabetes promoted myocardial stiffening, pressure overload impaired relaxation. The association of these damages accelerates the progression of diastolic heart failure progression in diabeticbanded animals.

PurposeAlthough increased oxidative stress is a major component of diabetic hypertensive cardiomyopathy, research into the effects of antioxidants on cardiac remodeling remains scarce. The actions of antioxidant apocynin include inhibiting reactive oxygen species (ROS) generation by nicotinamide adenine dinucleotide phosphate (NADPH) oxidases and ROS scavenging. We evaluated the effects of apocynin on cardiac remodeling in spontaneously hypertensive rats (SHR) with diabetes mellitus (DM).MethodsMale SHR were divided into four groups: control (SHR, n = 16); SHR treated with apocynin (SHR-APO; 16 mg/kg/day, added to drinking water; n = 16); diabetic SHR (SHR-DM, n = 13); and SHR-DM treated with apocynin (SHR-DM-APO, n = 14), for eight weeks. DM was induced by streptozotocin (40 mg/kg, single dose). Statistical analyzes: ANOVA and Tukey or Mann–Whitney.ResultsEchocardiogram in diabetic groups showed higher left ventricular and left atrium diameters indexed for body weight, and higher isovolumetric relaxation time than normoglycemic rats; systolic function did not differ between groups. Isolated papillary muscle showed impaired contractile and relaxation function in diabetic groups. Developed tension was lower in SHR-APO than SHR. Myocardial hydroxyproline concentration was higher in SHR-DM than SHR, interstitial collagen fraction was higher in SHR-DM-APO than SHR-APO, and type III collagen protein expression was lower in SHR-DM and SHR-DM-APO than their controls. Type I collagen and lysyl oxidase expression did not differ between groups. Apocynin did not change collagen tissue. Myocardial lipid hydroperoxide concentration was higher in SHR-DM than SHR and SHR-DM-APO. Glutathione peroxidase activity was lower and catalase higher in SHR-DM than SHR. Apocynin attenuated antioxidant enzyme activity changes in SHR-DM-APO. Advanced glycation end-products and NADPH oxidase activity did not differ between groups.ConclusionApocynin reduces oxidative stress independently of NADPH oxidase activity and does not change ventricular or myocardial function in spontaneously hypertensive rats with diabetes mellitus. The apocynin-induced myocardial functional impairment in SHR shows that apocynin actions need to be clarified during sustained chronic pressure overload.