Development of a human model for the study of effects of hypoxia, exercise, and sildenafil on cardiac and vascular function in chronic heart failure

Background: Pulmonary hypertension is associated with poor outcome in patients with chronic heart failure (CHF) and may be a therapeutic target. Our aims were to develop a noninvasive model for studying pulmonary vasoreactivity in CHF and characterize sildenafil's acute cardiovascular effects. Methods and Results: In a crossover study, 18 patients with CHF participated 4 times [sildenafil (2 × 20 mg)/or placebo (double-blind) while breathing air or 15% oxygen] at rest and during exercise. Oxygen saturation (SaO2) and systemic vascular resistance were recorded. Left and right ventricular (RV) function and transtricuspid systolic pressure gradient (RVTG) were measured echocardiographically. At rest, hypoxia caused SaO2 (P = 0.001) to fall and RVTG to rise (5 ± 4 mm Hg; P = 0.001). Sildenafil reduced SaO2 (−1 ± 2%; P = 0.043), systemic vascular resistance (−87 ± 156 dyn·s−1·cm−2; P = 0.034), and RVTG (−2 ± 5 mm Hg; P = 0.05). Exercise caused cardiac output (2.1 ± 1.8 L/min; P < 0.001) and RVTG (19 ± 11 mm Hg; P < 0.0001) to rise. The reduction in RVTG with sildenafil was not attenuated by hypoxia. The rise in RVTG with exercise was not substantially reduced by sildenafil. Conclusions: Sildenafil reduces SaO2 at rest while breathing air, this was not exacerbated by hypoxia, suggesting increased ventilation–perfusion mismatching due to pulmonary vasodilation in poorly ventilated lung regions. Sildenafil reduces RVTG at rest and prevents increases caused by hypoxia but not by exercise. This study shows the usefulness of this model to evaluate new therapeutics in pulmonary hypertension

Upregulation of PPARβ/δ Is Associated with Structural and Functional Changes in the Type I Diabetes Rat Diaphragm

Diabetes mellitus is associated with alterations in peripheral striated muscles and cardiomyopathy. We examined diaphragmatic function and fiber composition and identified the role of peroxisome proliferator-activated receptors (PPAR alpha and beta/delta) as a factor involved in diaphragm muscle plasticity in response to type I diabetes.Streptozotocin-treated rats were studied after 8 weeks and compared with their controls. Diaphragmatic strips were stimulated in vitro and mechanical and energetic variables were measured, cross bridge kinetics assessed, and the effects of fatigue and hypoxia evaluated. Morphometry, myosin heavy chain isoforms, PPAR alpha and beta/delta gene and protein expression were also assessed. Diabetes induced a decrease in maximum velocity of shortening (-14%, P<0.05) associated with a decrease in myosin ATPase activity (-49%, P<0.05), and an increase in force (+20%, P<0.05) associated with an increase in the number of cross bridges (+14%, P<0.05). These modifications were in agreement with a shift towards slow myosin heavy chain fibers and were associated with an upregulation of PPARbeta/delta (+314% increase in gene and +190% increase in protein expression, P<0.05). In addition, greater resistances to fatigue and hypoxia were observed in diabetic rats.Type I diabetes induced complex mechanical and energetic changes in the rat diaphragm and was associated with an up-regulation of PPARbeta/delta that could improve resistance to fatigue and hypoxia and favour the shift towards slow myosin heavy chain isoforms

Chapter 15 Determination of PPAR Expression by Western Blot

International audiencePeroxisome proliferator-activated receptors (PPARs) are key nuclear receptors which mediate the regulation of the transcription of many genes, especially those involved in lipid catabolism and inflammation. In mammals, three types of PPARs named PPARa, PPARb (also called PPARd), and PPARg have been identified. Up and down-regulations of one or more of these receptors are encountered during development , physiological adaptations, and in several diseases. Therefore, the ability to accurately measure PPAR expression in cells and tissues is an important aspect of PPAR research. This can be done by Western blot with specific antibodies. In this chapter, we describe the use of our techniques (Cardiovasc Res 84: 83-90, 2009; PLoS One 5: e11494, 2010) to measure PPARs expression, describe the adequate way to extract proteins, the best antibodies currently available and discuss potential misleading results in the absence of appropriate controls

Cyclic AMP Synthesis and Hydrolysis in the Normal and Failing Heart

International audienceCyclic AMP regulates a multitude of cellular responses and orchestrates a network of intracellular events. In the heart, cAMP is the main second messenger of the β-adrenergic receptor (β-AR) pathway producing positive chronotropic, inotropic and lusitropic effects during sympathetic stimulation. Whereas short term stimulation of β-AR/cAMP is beneficial for the heart, chronic activation of this pathway triggers pathological cardiac remodelling which may ultimately lead to heart failure (HF). Cyclic AMP is controlled by two families of enzymes with opposite actions: adenylyl cyclases which control cAMP production and phosphodiesterases which control its degradation. The large number of families and isoforms of these enzymes, their different localization within the cell and their organization in macromolecular complexes leads to a high level of compartmentation, both in space and time, of cAMP signaling in cardiac myocytes. Here, we review the expression level, molecular characteristics, functional properties and roles of the different adenylyl cyclase and phosphodiesterase families expressed in heart muscle and the changes that occur in cardiac hypertrophy and failure

Altered cross-bridge properties in skeletal muscle dystrophies

International audience† Co-first authors. Force and motion generated by skeletal muscle ultimately depends on the cyclical interaction of actin with myosin. This mechanical process is regulated by intracellular Ca 2+ through the thin filament-associated regulatory proteins i.e.; troponins and tropomyosin. Muscular dystrophies are a group of heterogeneous genetic affections characterized by progressive degeneration and weakness of the skeletal muscle as a consequence of loss of muscle tissue which directly reduces the number of potential myosin cross-bridges involved in force production. Mutations in genes responsible for skeletal muscle dystrophies (MDs) have been shown to modify the function of contractile proteins and cross-bridge interactions. Altered gene expression or RNA splicing or post-translational modifications of contractile proteins such as those related to oxidative stress, may affect cross-bridge function by modifying key proteins of the excitation-contraction coupling. Micro-architectural change in myofilament is another mechanism of altered cross-bridge performance. In this review, we provide an overview about changes in cross-bridge performance in skeletal MDs and discuss their ultimate impacts on striated muscle function

Speckle Characterization by Fractional Parameters: preliminary results before application to the discrimination of cardiopathies from echocardiographic images

Congrès sous l’égide de la Société Française de Génie Biologique et Médical (SFGBM).National audienceTo this day, echocardiography does not allow to discriminate certain pathologies such as, Hyper-trophic Cardiomyopathy (HCM) and cardiac amyloido-sis. Therefore, we attempt to define new echographic markers suited for this discrimination purpose. The work presented in this paper concerns the evaluation of the ability of fractal parameters to characterize speckle properties. For this purpose, we carried out an experiment by capturing the transmission of a laser light through a layer of milk thanks to a lensless camera. The obtained images present speckle that can be changed either by modifying the milk temperature or by changing its thickness. Thus, we evaluated how two fractal parameters (Hurst exponent and Fractional Dimension) could take into account these modifications of the speckle properties. This preliminary work leads to good results that we currently adapt in order to discriminate hypertrophic heart diseases on a database of echocardiographic images under development

Patient-specific biomechanical modeling of cardiac amyloidosis – A case study

International audienceWe present a patient-specific biomechanical modeling framework and an initial case study for investigating cardiac amyloidosis (CA). Our patient-specific heartbeat simulations are in good agreement with the data, and our model calibration indicates that the major effect of CA in the biophysical behavior lies in a dramatic increase of the passive stiffness. We also conducted a preliminary trial for predicting the effects of pharmacological treatments – which is an important clinical challenge – based on the model combined with a simple venous return representation. This requires further investigation and validation, albeit provides some valuable preliminary insight

Tempol prevents cardiac oxidative damage and left ventricular dysfunction in the PPAR-α KO mouse

International audienceGuellich A, Damy T, Conti M, Claes V, Samuel JL, Pineau T, Lecarpentier Y, Coirault C. Tempol prevents cardiac oxidative damage and left ventricular dysfunction in the PPAR-␣ KO mouse.oxisome proliferator-activated receptor (PPAR)-␣ deletion induces a profound decrease in MnSOD activity, leading to oxidative stress and left ventricular (LV) dysfunction. We tested the hypothesis that treatment of PPAR-␣ knockout (KO) mice with the SOD mimetic tempol prevents the heart from pathological remodelling and preserves LV function. Twenty PPAR-␣ KO mice and 20 age-matched wild-type mice were randomly treated for 8 wk with vehicle or tempol in the drinking water. LV contractile parameters were determined both in vivo using echocardiography and ex vivo using papillary muscle mechanics. Translational and posttranslational modifications of myo-sin heavy chain protein as well as the expression and activity of major antioxidant enzymes were measured. Tempol treatment did not affect LV function in wild-type mice; however, in PPAR-␣ KO mice, tempol prevented the decrease in LV ejection fraction and restored the contractile parameters of papillary muscle, including maximum shortening velocity, maximum extent of shortening, and total tension. Moreover, compared with untreated PPAR-␣ KO mice, myosin heavy chain tyrosine nitration and anion superoxide production were markedly reduced in PPAR-␣ KO mice after treatment. Tempol also significantly increased glutathione peroxidase and glutathione reduc-tase activities (ϳ 50%) in PPAR-␣ KO mice. In conclusion, these findings demonstrate that treatment with the SOD mimetic tempol can prevent cardiac dysfunction in PPAR-␣ KO mice by reducing the oxidation of contractile proteins. In addition, we show that the beneficial effects of tempol in PPAR-␣ KO mice involve activation of the glutathione peroxidase/glutathione reductase system