Insulin-like growth factor 1 (IGF1) is an anabolic hormone that controls the growth and metabolism of many cell types. However, IGF1 also mediates cardio-protective effects after acute myocardial infarction (AMI), but the underlying mechanisms and cellular targets are not fully understood. Here we demonstrate that short-term IGF1 treatment for 3 days after AMI improved cardiac function after 1 and 4 weeks. Regional wall motion was improved in ischemic segments, scar size was reduced, and capillary density increased in the infarcted area and the border zone. Unexpectedly, inducible inactivation of the IGF1 receptor (IGF1R) in cardiomyocytes did not attenuate the protective effect of IGF1. Sequential cardiac transcriptomic analysis indicated an altered myeloid cell response in the acute phase after AMI, and, notably, myeloid-cell Igf1r-/- mice lost the protective IGF1 function after I/R. In addition, IGF1 induced an M2-like anti-inflammatory phenotype in bone marrow-derived macrophages and enhanced the number of anti-inflammatory macrophages in heart tissue on day 3 after AMI in vivo. In summary, modulation of the acute inflammatory phase after AMI by IGF1 represents an effective mechanism to preserve cardiac function after I/R.

Myoglobin knockout mice (myo−/−) adapt to the loss of myoglobin by the activation of a variety of compensatory mechanisms acting on the structural and functional level. To analyze to what extent myo−/− mice would tolerate cardiac stress we used the model of chronic isoproterenol application to induce cardiac hypertrophy in myo−/− mice and wild-type (WT) controls. After 14 days of isoproterenol infusion cardiac hypertrophy in WT and myo−/− mice reached a similar level. WT mice developed lung edema and left ventricular dilatation suggesting the development of heart failure. In contrast, myo−/− mice displayed conserved cardiac function and no signs of left ventricular dilatation. Analysis of the cardiac gene expression profiles using 40K mouse oligonucleotide arrays showed that isoproterenol affected the expression of 180 genes in WT but only 92 genes of myo−/− hearts. Only 40 of these genes were regulated in WT as well as in myo−/− hearts. In WT hearts a pronounced induction of genes of the extracellular matrix occurred suggesting a higher level of cardiac remodeling. myo−/− hearts showed altered transcription of genes involved in carbon metabolism, inhibition of apoptosis and muscular repair. Interestingly, a subset of genes that was altered in myo−/− mice already under basal conditions was differentially expressed in WT hearts under isoproterenol treatment. In summary, our data show a high capacity of myoglobin-deficient mice to adapt to catecholamine induced cardiac stress which is associated with activation of a distinct cardiac gene expression program.

Remote ischemic preconditioning (RIPC) is a practicable and noninvasive method to protect the heart against ischemia reperfusion injury. Unfortunately results from clinical studies are not convincing. Propofol is suggested to be an inhibiting factor of cardioprotection by RIPC, but the underlying mechanism is still unknown. We investigated whether after RIPC the release of humoral factors and/or the direct cardioprotective effect at the myocardium is inhibited by propofol. Randomized, prospective, blinded laboratory investigation. Experimental laboratory. Male Wistar rats. Repetitive hind limb ischemia in rats—blood plasma transfers to isolated rat heart. In male Wistar rats (six groups, each n = 6/group), RIPC was induced by four cycles of 5 minutes bilateral hind limb ischemia alternately with 5 minutes of reperfusion. Blood samples were taken with (RIPC) and without RIPC (Con). Rats received continuous anesthesia with pentobarbital (Pento, 40 mg/kg body weight/hr) or propofol (Prop, 12 mg/kg body weight/hr), respectively. Cardioprotective properties of the blood plasma was investigated in the rat heart in vitro (six groups, each n = 6/group) perfused with Krebs-Henseleit buffer alone or with propofol (10 µM). Plasma was administered over 10 minutes before myocardial ischemia. All hearts underwent 33 minutes of global ischemia followed by 1 hour of reperfusion. At the end of the experiments, infarct size was determined by triphenyl-tetrazolium-chloride staining. RIPC plasma from pentobarbital anesthetized rats (Pento-RIPC) reduced infarct size from 64% (62–71%) (Pento-Con) to 34% (30–39%) (p < 0.0001). Infarct size with control plasma from propofol anesthetized rats was 59% (58–64%) (Prop-Con). RIPC plasma could not induce cardioprotection (Prop-RIPC: 63% [56–70%] ns vs Prop-Con). In contrast, RIPC plasma from pentobarbital anesthetized rats induced a significant infarct size reduction under propofol perfusion (Pento-RIPC: 34% [30–42%] vs Pento-Con: 54% [53–63%]; p < 0.0001). Loss of cardioprotection by RIPC during propofol anesthesia depends on inhibition of release of humoral factors.

Insulin-like growth factor (IGF-I) signaling has been implicated to play an important role in regulation of cardiac growth, hypertrophy, and contractile function and has been linked to the development of age-related congestive heart failure. Here, we address the question to what extent cardiomyocyte-specific IGF-I signaling is essential for maintenance of the structural and functional integrity of the adult murine heart. To investigate the effects of IGF-I signaling in the adult heart without confounding effects due to IGF-I overexpression or adaptation during embryonic and early postnatal development, we inactivated the IGF-I receptor (IGF-IR) by a 4-hydroxytamoxifen-inducible Cre recombinase in adult cardiac myocytes. Efficient inactivation of the IGF-IR (iCMIGF-IRKO) as assessed by Western analysis and real-time PCR went along with reduced IGF-I-dependent Akt and GSK3β phosphorylation. Functional analysis by conductance manometry and MRI revealed no functional alterations in young adult iCMIGF-IRKO mice (age 3 mo). However, when induced in aging mice (11 mo) diastolic cardiac function was depressed. To address the question whether insulin signaling might compensate for the defective IGF-IR signaling, we inactivated β-cells by streptozotocin. However, the diabetes-associated functional depression was similar in control and iCMIGF-IRKO mice. Similarly, analysis of the cardiac gene expression profile on 44K microarrays did not reveal activation of overt adaptive processes. Endogenous IGF-IR signaling is required for conservation of cardiac function of the aging heart, but not for the integrity of cardiac structure and function of young hearts.

Activation of melatonin receptors induces cardioprotection. Mitochondrial potassium channels (mK_Ca and mK_ATP) are involved in the signaling cascade of preconditioning. The melatonin receptor agonist ramelteon is an approved oral medication for treatment of insomnia, but nothing is known about possible cardioprotective properties. We investigated whether (1) ramelteon induces cardioprotection mediated by the melatonin receptor; (2) this effect is concentration-dependent; and (3) mK_Ca and/or mK_ATP channels are critically involved in ramelteon-induced cardioprotection. Hearts of male Wistar rats were randomized and placed on a Langendorff system, perfused with Krebs–Henseleit buffer at a constant pressure of 80 mm Hg. All hearts were subjected to 33 minutes of global ischemia and 60 minutes of reperfusion. Before, ischemic hearts were perfused with different concentrations of ramelteon (0.01–5 μM) for determination of a concentration–effect curve. In subsequent experiments, the lowest protective concentration of ramelteon was administered together with paxilline (mK_Ca channel inhibitor) and 5-hydroxydecanoate (mK_ATP channel inhibitor). To determine whether the reduction of ischemia and reperfusion injury by ramelteon is mediated by melatonin receptor, we combined ramelteon with luzindole, a melatonin receptor antagonist. Infarct size was determined by triphenyltetrazolium chloride staining. In control animals, infarct size was 58% ± 6%. Ramelteon in a concentration of 0.03 µM reduced infarct size to 28% ± 4% (P < 0.0001 vs. Con). A lower concentration of ramelteon did not initiate cardioprotection, and higher concentrations did not further decrease infarct size. Paxilline, 5-hydroxydecanoate, and luzindole completely blocked the ramelteon-induced cardioprotection. This study shows for the first time that (1) ramelteon induces cardioprotection through melatonin receptor; (2) the effect is not concentration-dependent; and (3) activation of mK_Ca and mK_ATP channels is involved.

Microcirculatory and mitochondrial dysfunction are considered the main mechanisms of septic shock. Studies suggest that statins modulate inflammatory response, microcirculation, and mitochondrial function, possibly through their action on peroxisome proliferator-activated receptor alpha (PPAR-α). The aim of this study was to examine the effects of pravastatin on microcirculation and mitochondrial function in the liver and colon and the role of PPAR-α under septic conditions. This study was performed with the approval of the local animal care and use committee. Forty Wistar rats were randomly divided into 4 groups: sepsis (colon ascendens stent peritonitis, CASP) without treatment as control, sepsis + pravastatin, sepsis + PPAR-α-blocker GW6471, and sepsis + pravastatin + GW6471. Pravastatin (200 µg/kg s.c.) and GW6471 (1 mg/kg) were applied 18 h before CASP-operation. 24 h after initial surgery, a relaparotomy was performed, followed by a 90 min observation period for assessment of microcirculatory oxygenation (μHbO₂) of the liver and colon. At the end of the experiments, animals were euthanized, and the colon and liver were harvested. Mitochondrial function was measured in tissue homogenates using oximetry. The ADP/O ratio and respiratory control index (RCI) for complexes I and II were calculated. Reactive oxygen species (ROS) production was assessed using the malondialdehyde (MDA)-Assay. Statistics: two-way analysis of variance (ANOVA) + Tukey’s/Dunnett’s post hoc test for microcirculatory data, Kruskal–Wallis test + Dunn’s post hoc test for all other data. In control septic animals µHbO₂ in liver and colon deteriorated over time (µHbO₂: −9.8 ± 7.5%* and −7.6 ± 3.3%* vs. baseline, respectively), whereas after pravastatin and pravastatin + GW6471 treatment μHbO₂ remained constant (liver: µHbO₂ pravastatin: −4.21 ± 11.7%, pravastatin + GW6471: −0.08 ± 10.3%; colon: µHbO₂ pravastatin: −0.13 ± 7.6%, pravastatin + GW6471: −3.00 ± 11.24%). In both organs, RCI and ADP/O were similar across all groups. The MDA concentration remained unchanged in all groups. Therefore, we conclude that under septic conditions pravastatin improves microcirculation in the colon and liver, and this seems independent of PPAR-α and without affecting mitochondrial function.