Cardioprotection of ischaemic preconditioning is associated with inhibition of translocation of MLKL within the plasma membrane.

Necroptosis, a form of cell loss involving the RIP1-RIP3-MLKL axis, has been identified in cardiac pathologies while its inhibition is cardioprotective. We investigated whether the improvement of heart function because of ischaemic preconditioning is associated with mitigation of necroptotic signaling, and these effects were compared with a pharmacological antinecroptotic approach targeting RIP1. Langendorff-perfused rat hearts were subjected to ischaemic preconditioning with or without a RIP1 inhibitor (Nec-1s). Necroptotic signaling and the assessment of oxidative damage and a putative involvement of CaMKII in this process were analysed in whole tissue and subcellular fractions. Ischaemic preconditioning, Nec-1s and their combination improved postischaemic heart function recovery and reduced infarct size to a similar degree what was in line with the prevention of MLKL oligomerization and translocation to the membrane. On the other hand, membrane peroxidation and apoptosis were unchanged by either approach. Ischaemic preconditioning failed to ameliorate ischaemia-reperfusion-induced increase in RIP1 and RIP3 while pSer229-RIP3 levels were reduced only by Nec-1s. In spite of the additive phosphorylation of CaMKII and PLN because of ditherapy, the postischaemic contractile force and relaxation was comparably improved in all the intervention groups while antiarrhythmic effects were observed in the ischaemic preconditioning group only. Necroptosis inhibition seems to be involved in cardioprotection of ischaemic preconditioning and is comparable but not intensified by an anti-RIP1 agent. Changes in oxidative stress nor CaMKII signaling are unlikely to explain the beneficial effects.

Evidence of necroptosis in hearts subjected to various forms of ischemic insults.

Long-lasting ischemia can result in cell loss; however, repeated episodes of brief ischemia increase the resistance of the heart against deleterious effects of subsequent prolonged ischemic insult and promote cell survival. Traditionally, it is believed that the supply of blood to the ischemic heart is associated with release of cytokines, activation of inflammatory response, and induction of necrotic cell death. In the past few years, this paradigm of passive necrosis as an uncontrolled cell death has been re-examined and the existence of a strictly regulated form of necrotic cell death, necroptosis, has been documented. This controlled cell death modality, resembling all morphological features of necrosis, has been investigated in different types of ischemia-associated heart injuries. The process of necroptosis has been found to be dependent on the activation of RIP1-RIP3-MLKL axis, which induces changes leading to the rupture of cell membrane. This pathway is activated by TNF-α, which has also been implicated in the cardioprotective signaling pathway of ischemic preconditioning. Thus, this review is intended to describe the TNF-α-mediated signaling leading to either cell survival or necroptotic cell death. In addition, some experimental data suggesting a link between heart dysfunction and the cellular loss due to necroptosis are discussed in various conditions of myocardial ischemia.

Molecular hydrogen potentiates beneficial anti-infarct effect of hypoxic postconditioning in isolated rat hearts: a novel cardioprotective intervention.

Generation of free radicals through incomplete reduction of oxygen during ischemia-reperfusion (I/R) is well described. On the other hand, molecular hydrogen (H2) reduces oxidative stress due to its ability to react with strong oxidants and easily penetrate cells by diffusion, without disturbing metabolic redox reactions. This study was designed to explore cardioprotective potential of hypoxic postconditioning (HpostC) against I/R (30 min global I - 120 min R) in isolated rat hearts using oxygen-free Krebs-Henseleit buffer (KHB). Furthermore, the possibility to potentiate the effect of HpostC by H2 using oxygen-free KHB saturated with H2 (H2 + HpostC) was tested. HPostC was induced by 4 cycles of 1-minute perfusion with oxygen-free KHB intercepted by 1-minute perfusion with normal KHB, at the onset of reperfusion. H2 + HPostC was applied in a similar manner using H2-enriched oxygen-free KHB. Cardioprotective effects were evaluated on the basis of infarct size (IS, in % of area at risk, AR) reduction, post-I/R recovery of heart function, and occurrence of reperfusion arrhythmias. HPostC significantly reduced IS/AR compared with non-conditioned controls. H2 present in KHB during HPostC further decreased IS/AR compared with the effect of HPostC, attenuated severe arrhythmias, and significantly restored heart function (vs. controls). Cardioprotection by HpostC can be augmented by molecular hydrogen infusion.

Comparison of different osmotic therapies in a mouse model of traumatic brain injury.

BACKGROUND: Inflammation in the affected region, increased intracranial pressure, consequent oedema and congestion contribute to the negative outcome of traumatic brain injury. Osmotic therapies are recommended for improvement in cognitive and motor functions. Aim of the present study was to evaluate the effect of osmotic therapies in a mice model of traumatic brain injury. METHODS: Experimental closed head injury was performed in adult Swiss albino mice by the weight-drop method. Different group of animals were treated with normal saline (G1), mannitol (G2), mannitol+glycerin (G3) and Neurotol (G4). Neurological Severity Score (NSS) was recorded at different time-points upto a period of six days. Effect of treatments on cerebral oedema, learning and memory function, motor function and co-ordination were evaluated by gravimetry, Morris water maze and beam walk test respectively. Histopathology was performed to evaluate the treatment effects on microscopic complications arising from primary closed head injury (CHI). RESULTS: All the treatments showed a marked improvement in the evaluated parameters as compared with the vehicle control group. It was evident that G3 and G4 had a distinct advantage over mannitol therapy. Based on the NSS score, Neurotol proved to be comparatively safe and more efficacious than either mannitol or a combination of mannitol+glycerol. The effect of Neurotol could have been enhanced by the presence of VRP011 (a Mg+2 salt). CONCLUSIONS: Neurotol is safe and exhibits better efficacy as compared with other treatments for the management of traumatic brain injury.

Protective effect of melatonin against myocardial injury induced by epinephrine.

Epinephrine, in high doses, exhibits cardiotoxicity that is associated with excessive production of free radicals. Melatonin is antioxidant and free radical scavenger with cardioprotective properties. In our study, cardioprotective effects of melatonin against epinephrine cardiotoxicity were explored in the model of isolated rat heart. In the melatonin group, melatonin (50 µmol/l) was present in the perfusion solution during the whole experiment. In the control group, perfusion solution contained no melatonin. In both of the groups, after 30 min of initial perfusion, epinephrine was applied during 2 min directly into the heart and led to its strong stimulation. Changes in the heart function and arrhythmogenesis were evaluated before application of epinephrine and after the decline of its acute effects. No significant differences were observed during the initial perfusion. However, in the 15th and 20th minute after epinephrine application, indexes of ventricular contraction and relaxation were significantly higher in the melatonin group. Likewise, the values of the left ventricular developed pressure were significantly increased in this group in the 15th minute. These differences indicate better preservation of contraction and relaxation in the melatonin-treated group. Parameters of arrhythmogenesis-arrhythmia score, incidence and total duration of severe ventricular arrhythmias, were not significantly different between the experimental groups. However, their markedly lower average values in the melatonin-treated group suggest the reduction of electrical instability by melatonin. In conclusion, the obtained data confirm cardioprotective properties of melatonin and fill in the mosaic of information that can lead to the usage of melatonin as a therapeutic tool.

Oxytocin exerts protective effects on in vitro myocardial injury induced by ischemia and reperfusion.

Among the cardiovascular pathologies, ischemic heart disease is a serious medical problem that can result in cardiac injury and (or) heart failure. The aim of the present study was to test the hypothesis that neuropeptide oxytocin induces cardioprotective effects on ischemia-reperfusion-induced myocardial damage. The functional parameters of isolated Langendorff-perfused rat hearts were recorded before and after global 25 min ischemia and subsequent reperfusion. The infarct size was determined by a computerized planimetric method. The results showed that oxytocin produced negative chronotropic effect even at low concentrations (90-125 nmol/L). Perfusion with oxytocin before ischemia resulted in significant reduction of the infarct size (p<0.01), which was about 66% smaller than that in the control group. To evaluate the functional mechanisms involved, further experiments were performed under conditions of constant heart rate. The lower dose of oxytocin (90 nmol/L), which was ineffective in spontaneously beating hearts, induced a significant decrease of contractility. Elimination of the negative chronotropic effect of oxytocin prevented its cardioprotective action. In conclusion, our results demonstrated an attenuation of the infarct size in oxytocin-treated hearts, indicating a cardioprotective effect of oxytocin. The data suggest that the negative chronotropic action of oxytocin participates in its protective effects on ischemia-reperfusion-induced myocardial injury.

Effect of streptozotocin-induced diabetes on daily expression of per2 and dbp in the heart and liver and melatonin rhythm in the pineal gland of Wistar rat.

The circadian system is a flexible framework allowing a proper adjustment of physiological functions to the regularly changing environment. Pathways that are used to synchronize components of the circadian system have been shown to be susceptible to pathophysiological conditions. In our study, we investigated effects of streptozotocin (STZ)-induced diabetes mellitus on function of the circadian system at the level of melatonin synthesis and expression of per2 and dbp in the heart and liver in 8-week-old Wistar rats. Rhythmic pattern of clock gene per2 and transcription factor dbp in controls and STZ-treated animals was determined. Streptozotocin administration had a more substantial effect on per2 expression in the liver than in the heart. Pronounced phase advance in the rhythm of dbp expression in both the liver and the heart was observed. The melatonin rhythm reflecting the phase of the master clock was not affected by STZ application. Changes in per2 and dbp expression in the heart and liver imply alterations in input pathway or peripheral oscillators with possible consequences on function of analysed organs.

Mitochondrial channels permeable by calcium ions.

The aim of this work was to characterize inner mitochondrial membrane channels permeable to calcium cations (Ca(++)). Mitochondrial membranes isolated from rat heart were incorporated into the bilayer lipid membrane, and single Ca(++) channel currents were measured. The observed channels were selective for Ca(++) and barium cations (Ba(++)) (53 and 50 mM) over Tris(+) (113 mM), but single-channel currents in most cases were noisy and did not show the typical single-channel shape, as it is known, for example, in the ryanodine receptor or in inositol 1,4,5-trisphosphate (IP(3)R) Ca(++)-release channels. The most commonly observed single-channel currents, measured at the 0 mV and 53 mM Ca(++) gradient, were in the range of 1 pA or less. The channels responded to pharmacological modulators. Some of the channels were inhibited by ruthenium red and cyclosporin A, and others were modulated by ryanodine. This may indicate that the observed channels passing Ca(++) may originate from the mitochondrial Ca(++) uniporter, the permeability transition pore, and the ryanodine receptor calcium channel.