Effect of MCI-154, a calcium sensitizer, on calcium sensitivity of myocardial fibers in endotoxic shock rats

[Septic cardiomyopathy: pathophysiology and potential new therapeutic approaches]

Sepsis is the leading cause of death in critically ill patients, and its incidence continues to rise. Sepsis was defined as a systemic inflammatory response syndrome with an identifiable focus of infection, but therapeutic strategies aimed at eliminating the inflammatory response have only modest clinical benefit. The development of a failure of one or more organs poses a major threat to the survival of patients with sepsis, and mortality in sepsis is most often attributed to multiple organ dysfunction. Accordingly, sepsis has been recently redefined as life-threatening organ dysfunction due to a dysregulated host response to infection. Cardiac dysfunction is a well-recognized important component of septic multiple organ failure and can compromise the balance between oxygen supply and demand, ultimately leading to the development of multiple organ failure. The existence of cardiac dysfunction in sepsis is associated with much higher mortality when compared with septic patients without heart problems. Dobutamine, a β₁-selective adrenoceptor agonist, has been used in septic shock for many years as an only inotrope, but limited clinical outcome measures have been provided as to advisability of the usefulness of dobutamine in septic shock management. Here we provide an overview on the possible mechanisms underlying intrinsic myocardial depression during sepsis and discuss the perspective of several inotropes for sepsis-associated cardiac dysfunction.

Cardioprotective and functional effects of levosimendan and milrinone in mice with cecal ligation and puncture-induced sepsis

Levosimendan and milrinone may be used in place of dobutamine to increase cardiac output in septic patients with a low cardiac output due to impaired cardiac function. The effects of the two inotropic agents on cardiac inflammation and left ventricular (LV) performance were examined in mice with cecal ligation and puncture (CLP)-induced sepsis. CLP mice displayed significant cardiac inflammation, as indicated by highly increased pro-inflammatory cytokines and neutrophil infiltration in myocardial tissues. When continuously given, levosimendan prevented but milrinone exaggerated cardiac inflammation, but they significantly reduced the elevations in plasma cardiac troponin-I and heart-type fatty acid-binding protein, clinical markers of cardiac injury. Echocardiographic assessment of cardiac function showed that the effect of levosimendan, given by an intravenous bolus injection, on LV performance was impaired in CLP mice, whereas milrinone produced inotropic responses equally in sham-operated and CLP mice. A lesser effect of levosimendan on LV performance after CLP was also found in spontaneously beating Langendorff-perfused hearts. In ventricular myocytes isolated from control and CLP mice, levosimendan, but not milrinone, caused a large increase in the L-type calcium current. This study represents that levosimendan and milrinone have cardioprotective properties but provide different advantages and drawbacks to cardiac inflammation/dysfunction in sepsis.

Hemodynamic consequences of severe lactic acidosis in shock states: from bench to bedside

Lactic acidosis is a very common biological issue for shock patients. Experimental data clearly demonstrate that metabolic acidosis, including lactic acidosis, participates in the reduction of cardiac contractility and in the vascular hyporesponsiveness to vasopressors through various mechanisms. However, the contributions of each mechanism responsible for these deleterious effects have not been fully determined and their respective consequences on organ failure are still poorly defined, particularly in humans. Despite some convincing experimental data, no clinical trial has established the level at which pH becomes deleterious for hemodynamics. Consequently, the essential treatment for lactic acidosis in shock patients is to correct the cause. It is unknown, however, whether symptomatic pH correction is beneficial in shock patients. The latest Surviving Sepsis Campaign guidelines recommend against the use of buffer therapy with pH ≥7.15 and issue no recommendation for pH levels <7.15. Furthermore, based on strong experimental and clinical evidence, sodium bicarbonate infusion alone is not recommended for restoring pH. Indeed, bicarbonate induces carbon dioxide generation and hypocalcemia, both cardiovascular depressant factors. This review addresses the principal hemodynamic consequences of shock-associated lactic acidosis. Despite the lack of formal evidence, this review also highlights the various adapted supportive therapy options that could be putatively added to causal treatment in attempting to reverse the hemodynamic consequences of shock-associated lactic acidosis.

Spectroscopic investigation on the binding of bioactive pyridazinone derivative to human serum albumin and molecular modeling

The interaction between a novel promising pyridazinone derivative (5-chloro-2-nitro-N-(4-(6-oxo-1,4,5,6-tetrahydropyridazin-3-yl)phenyl)benzamide (CNPB)) and human serum albumin (HSA) under physiological conditions has been investigated systematically by fluorescence spectroscopy, UV absorption spectroscopy, circular dichroism (CD) and molecular modeling. From the spectra obtained, it was observed that CNPB had a strong ability to quench the intrinsic fluorescence of HSA through a static quenching procedure. The site binding constants (K(b)) were 4.22 x 10(4) and 3.32 x 10(4)M(-1) at 290 and 300 K, respectively. The alterations of protein secondary structure in the presence of CNPB were qualitative and quantitative calculated by the results from CD and synchronous fluorescence. In addition, the thermodynamic standard enthalpy (DeltaH) and standard entropy (DeltaS) for the reaction were calculated to be -17.35 kJ mol(-1) and 9.57 J mol(-1)K(-1), respectively. These results showed that the binding of CNPB to HSA was mainly of hydrophobic interaction, but the hydrogen bonding and electrostatic interaction could not be excluded. Furthermore, the study of molecular modeling also indicated that CNPB could strongly bind to the site I (subdomain IIA) of HSA mainly by hydrophobic interaction and there were hydrogen bond interactions between CNPB and the residue His242.

Molecular characterization and immunohistochemical localization of a novel troponin C during silkworm development

We have cloned and sequenced a novel Bombyx mori gene that encodes a protein having a high degree of homology with other known troponin C (TnC) proteins. The amino acid sequence, DX[DN]X[DSG]X(6)E, a highly conserved putative Ca(2+) -binding motif found in loops within the globular domains of previously identified TnC proteins, is also present in BmTnC. We have expressed and purified to homogeneity a His-tagged BmTnC fusion protein having a molecular weight of approximately 21.6 kDa. We have used this purified fusion protein to produce polyclonal antibodies against BmTnC for Western blot analyses. These analyses have revealed that BmTnC is expressed in the larval head, the Malpighian tubule, the epidermis, the testis, and the gut, as has been confirmed by immunohistochemistry. In addition, real-time reverse transcription/polymerase chain reaction has shown that BmTnC mRNA levels differ substantially among these tissues. Our findings indicate that BmTnC is selectively expressed in the muscular tissues of the silkworm, including portions of the head, the Malpighian tubule, the body wall, and the gut.

Activation of peroxisome proliferator-activated receptor-alpha by fenofibrate prevents myocardial dysfunction during endotoxemia in rats

OBJECTIVE

To investigate the effects of fenofibrate, an activator of peroxisome proliferator-activated receptor-alpha, on cardiac function in a rat endotoxemia model.

DESIGN

Prospective, randomized, controlled study.

SETTING

University research laboratory.

SUBJECTS

Three-month-old male Wistar rats.

INTERVENTIONS

Animals were fed with standard diet containing no drug or fenofibrate (0.2%) for 14 days. They were then injected intravenously with either 5 mg/kg lipopolysaccharide (LPS and fenofibrate + LPS groups) or saline (control and fenofibrate groups).

MEASUREMENTS AND MAIN RESULTS

In the LPS group, body weight loss, metabolic acidosis, and thrombocytopenia confirmed presence of systemic endotoxemia. LPS administration resulted in an early peak in plasma tumor necrosis factor-alpha, decreased cardiac contractility (isolated and perfused heart), reduced myofilament Ca2+ sensitivity (Triton-skinned cardiac fibers), and increased left ventricular nitric oxide (NO) end-oxidation products (NO(x) and NO2), without evidence of myocardial oxidative stress (thiobarbituric acid-reactive substances and antioxidant enzyme activities). Fenofibrate pretreatment (fenofibrate + LPS group) did not alter signs of endotoxemia but prevented reductions in both cardiac contractility and myofilament Ca2+ sensitivity. The peak of plasma tumor necrosis factor-alpha was attenuated, whereas myocardial NO(x) and NO2 remained similar to the LPS group. Oxidative stress was suggested from moderate increase in cardiac thiobarbituric acid-reactive substances and reduced glutathione peroxidase activity.

CONCLUSION

Fenofibrate, an activator of peroxisome proliferator-activated receptor-alpha, may prevent endotoxemia-induced cardiac dysfunction and reduction in myofilament Ca2+ sensitivity. Our data also suggest a mediating role for early peak plasma tumor necrosis factor-alpha, but not for myocardial NO production or oxidative stress.

Endotoxin-induced myocardial dysfunction in senescent rats

Introduction

Aging is associated with a decline in cardiac contractility and altered immune function. The aim of this study was to determine whether aging alters endotoxin-induced myocardial dysfunction.

Methods

Senescent (24 month) and young adult (3 month) male Wistar rats were treated with intravenous lipopolysaccharide (LPS) (0.5 mg/kg (senescent and young rats) or 5 mg/kg (young rats only)), or saline (senescent and young control groups). Twelve hours after injection, cardiac contractility (isolated perfused hearts), myofilament Ca²⁺ sensitivity (skinned fibers), left ventricular nitric oxide end-oxidation products (NOx and NO₂) and markers of oxidative stress (thiobarbituric acid reactive species (TBARS) and antioxidant enzymes) were investigated.

Results

LPS (0.5 mg/kg) administration resulted in decreased contractility in senescent rats (left ventricular developed pressure (LVDP), 25 ± 4 vs 53 ± 4 mmHg/g heart weight in control; P < 0.05) of amplitude similar to that in young rats with LPS 5 mg/kg (LVDP, 48 ± 7 vs 100 ± 7 mmHg/g heart weight in control; P < 0.05). In contrast to young LPS rats (0.5 and 5 mg/kg LPS), myofilament Ca²⁺ sensitivity was unaltered in senescent LPS hearts. Myocardial NOx and NO₂ were increased in a similar fashion by LPS in young (both LPS doses) and senescent rats. TBARS and antioxidant enzyme activities were unaltered by sepsis whatever the age of animals.

Conclusion

Low dose of LPS induced a severe myocardial dysfunction in senescent rats. Ca²⁺ myofilament responsiveness, which is typically reduced in myocardium of young adult septic rats, however, was unaltered in senescent rats. If these results are confirmed in in vivo conditions, they may provide a cellular explanation for the divergent reports on ventricular diastolic function in septic shock. In addition, Ca²⁺-sensitizing agents may not be as effective in aged subjects as in younger subjects.

CHANGES OF RHO KINASE ACTIVITY AFTER HEMORRHAGIC SHOCK AND ITS ROLE IN SHOCK-INDUCED BIPHASIC RESPONSE OF VASCULAR REACTIVITY AND CALCIUM SENSITIVITY

The purpose of the present study is to investigate the changes of Rho kinase activity and its role in biphasic response of vascular reactivity and calcium sensitivity after hemorrhagic shock. The vascular reactivity and calcium sensitivity of superior mesenteric artery (SMA) from hemorrhagic shock rats were determined via observing the contraction initiated by norepinephrine (NE) and Ca under depolarizing conditions (120 mmol/L K) with isolated organ perfusion system. At same time, Rho kinase activity in mesenteric artery was measured, and the effects of Rho kinase activity-regulating agents, angiotensin II (Ang-II), insulin, and Y-27632, on vascular reactivity and calcium sensitivity were also observed. The results indicated that the vascular reactivity and calcium sensitivity were increased at early shock (immediate and 30 min after shock) and decreased at late shock (1 and 2 h after shock). The maximal contractions of NE and Ca were significantly increased (P < 0.05 or P < 0.01) at early shock. But they were significantly decreased at late shock (P < 0.05 or P < 0.01). Rho kinase activity was significantly increased at early shock (immediate after shock) (P < 0.05) but significantly decreased at 1 and 2 h after shock (P < 0.05 or P < 0.01). It was positively correlated with the changes of vascular reactivity and calcium sensitivity. Insulin decreased the increased contractile response of SMA to NE and Caat early shock (P < 0.05 or P < 0.01). Angiotensin II increased the decreased contractile response of SMA to NE and Ca at 2-h shock (P < 0.05 or P < 0.01); Y-27632, Rho kinase-specific antagonist, decreased the contractile response of SMA to NE and Ca at 2-h shock, and abolished Ang-II induced the increase of vascular reactivity and calcium sensitivity. The results suggest that Rho kinase may be involved in the biphasic change of vascular reactivity and calcium sensitivity after hemorrhagic shock. Rho kinase may regulate vascular reactivity through the regulation of calcium sensitivity. Rho kinase-regulating agents may have some beneficial effects on shock-induced vascular hyporeactivity.

Effects of MCI-154 on Vascular Reactivity and Its Mechanisms After Hemorrhagic Shock in Rats

The objectives of this study were to investigate the effects of 6-[4-(4'-pyridylamino)phenyl]-4,5-dihydro-3(2H)-pyridazinone hydrochloride trihydrate (MCI-154), a newly developed cardiotonic agent, on vascular reactivity and contractile responses to extracellular Ca2+ ([Ca2+]o) after hemorrhagic shock and primarily explore its mechanism. In vivo, the effects of MCI-154 (0.1, 0.5, 1.0, and 2.0 mg/kg) on the pressor effect of norepinephrine (NE) in rats subjected to hemorrhagic shock (30 mm Hg for 2 h) were observed and in vitro, the effects of MCI-154 (10(-7), 10(-6), 10(-5), 10(-4) mol/L) on vascular reactivity and contractile responses to [Ca2+]o of superior mesenteric artery (SMA) from hemorrhagic shock rats and its relationship to Rho-kinase, protein kinase C (PKC), and protein kinase G (PKG) were observed. The results showed that the NE-induced pressor response after hemorrhagic shock was significantly decreased (P<0.01), and MCI-154 made it decrease further. In vitro, MCI-154 further decreased the contractile responses of SMA to NE and Ca2+ after hemorrhagic shock as compared with untreated hemorrhagic shock group (P<0.01). Angiotensin II (Ang II), with Rho-kinase stimulating action, and PMA, a PKC agonist increased the contractile responses to [Ca2+]o of SMA after hemorrhagic shock. MCI-154 (10(-5) mol/L) partly inhibited Ang II and PMA-induced increase of the contractile responses to [Ca2+]o of SMA (P<0.01). KT-5823, the PKG antagonist, antagonized MCI-154-induced decrease of the contractile responses to [Ca2+]o. Taken together, these results suggested that the vascular reactivity and contractile responses to [Ca2+]o of vascular smooth muscle after hemorrhagic shock were significantly decreased. MCI-154 worsened hemorrhagic shock-induced vascular hyporeactivity and the decrease of contractile responses to [Ca2+]o. These effects were possibly regulated by Rho-kinase, PKC, and PKG, but this needs further confirmation.

Dysfonctionnement myocardique et choc septique

Myocardial dysfunction frequently accompanies severe sepsis and septic shock. It is now clear that such a myocardial depression, as evidenced by biventricular alteration, is present during the early phase of sepsis in most patients. Myocardial depression exists despite a fluid loading-dependent hyperdynamic state and usually recovers within 7 to 10 days in survivors. Myocardial dysfunction does not appear to be due to irreversible structural abnormalities nor to myocardial hypoperfusion, but rather linked to many circulating mediators including cytokines. At a cellular level, reduced myocardial contractility could be related in part to apoptosis and induced by both nitric oxide-dependent and nitric oxide-independent mechanisms. However, whatever the mechanism involved, it leads to calcium homeostasis abnormality. The present review describes both the diagnosis procedure and the molecular and cellular pathways of sepsis-induced myocardial depression.

The role of Ca++-sensitizers for the treatment of heart failure

For increasing myocardial contractility in patients with cardiac failure, catecholamines, phosphodiesterase-III (PDE) inhibitors, and calcium sensitizers are available. Improving myocardial performance with catecholamines and PDE inhibitors leads to increased intracellular calcium concentration as an unavoidable side effect. An increase in intracellular calcium can induce harmful arrhythmias and increases the energetic demands of the myocardium. Long-term trials with PDE inhibitors have raised concerns about the safety of positive inotropic treatment for cardiac failure. Calcium sensitizers are a new class of inotropic drugs. They improve myocardial performance by directly acting on contractile proteins without increasing intracellular calcium load. Thus, they avoid the undesired effects of an increased intracellular calcium load. Calcium sensitizers may enhance myocardial performance without increasing myocardial oxygen consumption and without provoking fatal arrhythmias. Two calcium sensitizers are available for the treatment of cardiac failure in men. Pimobendan is a drug with positive inotropic effects that additionally inhibits the production of proinflammatory cytokines. However, it exerts a significant inhibition of PDE at clinically relevant doses. Levosimendan is a calcium sensitizer with no major inhibition of PDE at clinically relevant doses. It opens ATP-dependent potassium channels and thus has vasodilating and cardioprotective effects. The most important studies of the long-term treatment of stable cardiac failure with pimobendan and on the short-term treatment of unstable cardiac failure with levosimendan are presented.