Christiane Neuhof

Interplay between Ca2+ cycling and mitochondrial permeability transition pores promotes reperfusion-induced injury of cardiac myocytes

Uncontrolled release of Ca2+ from the sarcoplasmic reticulum (SR) contributes to the reperfusion‐induced cardiomyocyte injury, e.g. hypercontracture and necrosis. To find out the underlying cellular mechanisms of this phenomenon, we investigated whether the opening of mitochondrial permeability transition pores (MPTP), resulting in ATP depletion and reactive oxygen species (ROS) formation, may be involved. For this purpose, isolated cardiac myocytes from adult rats were subjected to simulated ischemia and reperfusion. MPTP opening was detected by calcein release and by monitoring the ΔΨm. Fura‐2 was used to monitor cytosolic [Ca2+]i or mitochondrial calcium [Ca2+]m, after quenching the cytosolic compartment with MnCl2. Mitochondrial ROS [ROS]m production was detected with MitoSOX Red and mag‐fura‐2 was used to monitor Mg2+ concentration, which reflects changes in cellular ATP. Necrosis was determined by propidium iodide staining. Reperfusion led to a calcein release from mitochondria, ΔΨm collapse and disturbance of ATP recovery. Simultaneously, Ca2+ oscillations occurred, [Ca2+]m and [ROS]m increased, cells developed hypercontracture and underwent necrosis. Inhibition of the SR‐driven Ca2+ cycling with thapsigargine or ryanodine prevented mitochondrial dysfunction, ROS formation and MPTP opening. Suppression of the mitochondrial Ca2+ uptake (Ru360) or MPTP (cyclosporine A) significantly attenuated Ca2+ cycling, hypercontracture and necrosis. ROS scavengers (2‐mercaptopropionyl glycine or N‐acetylcysteine) had no effect on these parameters, but reduced [ROS]m. In conclusion, MPTP opening occurs early during reperfusion and is due to the Ca2+ oscillations originating primarily from the SR and supported by MPTP. The interplay between Ca2+ cycling and MPTP promotes the reperfusion‐induced cardiomyocyte hypercontracture and necrosis. Mitochondrial ROS formation is a result rather than a cause of MPTP opening.

Mitochondrial dysfunction in sepsis: evidence from bacteraemic baboons and endotoxaemic rabbits.

Mitochondria, that provide most of the ATP needed for cell work, and that play numerous specific functions in biosyntheses and degradations, as well as contributing to Ca2+; signaling, also play a key role in the pathway to cell death. Impairment of mitochondrial functions caused by mutations of mt-genome, and by acute processes, are responsible for numerous diseases.The involvement of impaired mitochondria in the pathogenesis of sepsis is discussed. By means of the skinned fiber technique and high resolution respirometry, we have detected significantly reduced rates of mitochondrial respiration in heart and skeletal muscle of endotoxaemic rabbits. Mitochondria from heart were more affected than those from skeletal muscle. Decreased respiration rates were accompanied by reduced activities of complex I+III of the respiratory chain. Endotoxin-caused impairment was also detectable at the level of the Langendorff perfused heart, where the coronary vascular resistance was significantly increased.For an investigation of the influence of bacteraemia on the mitochondrial respiratory chain, baboons were made septic by infusion of high and low amounts of E. coli. For complex I+III and II+III, a clear dose-dependent decrease was detectable and in animals which died in septic shock, a further decrease of enzyme activities in comparison to the controls were found.These results are discussed in the light of current knowledge on the role of mitochondria in cell pathology in respect to sepsis.In conclusion, we present evidence that mitochondrial function is disturbed during sepsis. Besides ischaemic and poison-induced disturbances of mitochondrial function, sepsis is a further example of an acute disease where impaired mitochondria have to be taken into account.

Calpain system and its involvement in myocardial ischemia and reperfusion injury.

Calpains are ubiquitous non-lysosomal Ca(2+)-dependent cysteine proteases also present in myocardial cytosol and mitochondria. Numerous experimental studies reveal an essential role of the calpain system in myocardial injury during ischemia, reperfusion and postischemic structural remodelling. The increasing Ca(2+)-content and Ca(2+)-overload in myocardial cytosol and mitochondria during ischemia and reperfusion causes an activation of calpains. Upon activation they are able to injure the contractile apparatus and impair the energy production by cleaving structural and functional proteins of myocytes and mitochondria. Besides their causal involvement in acute myocardial dysfunction they are also involved in structural remodelling after myocardial infarction by the generation and release of proapoptotic factors from mitochondria. Calpain inhibition can prevent or attenuate myocardial injury during ischemia, reperfusion, and in later stages of myocardial infarction.

Endotoxemia and cytokine generation in cardiac surgery in relation to flow mode and duration of cardiopulmonary bypass.

ABSTRACT We investigated whether pulsatile flow in cardiopulmonary bypass (CPB), which has been shown to improve intestinal perfusion, reduces endotoxin translocation from the gut and, in consequence, decreases cytokine generation. The study population consisted of 48 adult patients who underwent elective CPB surgery. Pulsatile flow was used during aortic cross‐clamping in 24 patients and nonpulsatile flow in 24 patients. Plasma endotoxin concentration increased in all patients during CPB. Significantly (P < 0.05) lower peak levels of 8.25 ± 1.17 (SEM) pg/mL were reached 30 min after CPB in patients with pulsatile flow in contrast to 11.26 ± 1.42 pg/mL in patients with nonpulsatile flow. The extent of endotox‐ emia was not related to the duration of CPB. Following the increase of plasma endotoxin, the concentrations of IL‐6 and IL‐8 increased with delay of approximately 1 h. The peak levels of these cytokines corresponded significantly (P < 0.005 and P < 0.01, respectively) with duration of CPB, but not with flow mode. Thus, in patients with CPB of more than 97 min (median), IL‐6 reached a peak of 335.5 ± 48.87 pg/mL and IL‐8 of 64.86 ± 24.79 pg/mL in contrast to 210.9 ± 18.45 pg/mL and 21.2 ± 10.19 pg/mL, respectively, with bypass times of less than 97 min. The degree of endotoxemia in CPB mainly depends on the quality of tissue perfusion. Cytokine generation, however, is not triggered exclusively by endotoxin, but rather by the trauma of CPB and surgery.

Reduction of myocardial infarction by calpain inhibitors A-705239 and A-705253 in isolated perfused rabbit hearts

Abstract Two novel calpain inhibitors (A-705239 and A-705253) were studied in isolated perfused rabbit hearts subjected to 60-min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid in various final concentrations from the beginning of the experiments before the coronary artery was blocked. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were carried out. Myocardial infarct size and the area at risk (transiently non-perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 77.9±2.3% of the area at risk in untreated controls (n=12). The infarct size was significantly reduced in the presence of both calpain inhibitors. The best effect was achieved with 10-8 M A-705253 (n=8), which reduced (p<0.001) the infarcted area to 49.3±3.9% of the area at risk, corresponding to an infarct reduction of 61.8%. No statistical difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, and in the release of lactate dehydrogenase and creatine kinase from heart muscle.

A novel water-soluble and cell-permeable calpain inhibitor protects myocardial and mitochondrial function in postischemic reperfusion.

Abstract The effects of the novel calpain inhibitor A-705239 were studied in isolated perfused rabbit hearts subjected to 45 min of global ischemia, followed by 60 min of reperfusion. During 15 min of perfusion the inhibitor accumulated in myocardial tissue up to 16 times the concentration in the perfusate. Almost complete recovery and survival of heart function (90%) was seen with an inhibitor concentration of 10 8 M in the perfusion fluid when the compound was administered prior to ischemia. Left ventricular pressure amplitude and coronary flow showed significantly higher values during reperfusion in the presence of the inhibitor. A-705239 significantly reduced the release of creatine kinase, from 166±49 U/l in untreated hearts to 44±10 U/l, and diminished the release of lactate dehydrogenase from 118±20 U/l in untreated hearts to 63±4 U/l. Mitochondrial dysfunction following ischemia and reperfusion was markedly attenuated by the inhibitor. Thus, the state 3 respiration rate only decreased to 4.2 in contrast to 2.6 nmol O2/(min×mg s.w.) in untreated hearts, reflecting a reduced damage of oxidative phosphorylation. Furthermore, in the presence of the inhibitor the inner mitochondrial membranes became less permeable as indicated by a smaller leak respiration. The excellent properties of A-705239 should make this compound a valuable tool for further pharmacological studies.

Reduction of myocardial infarction by postischemic administration of the calpain inhibitor A-705253 in comparison to the Na(+)/H(+) exchange inhibitor Cariporide in isolated perfused rabbit hearts.

Abstract The calpain inhibitor A-705253 and the Na+/H+-exchange inhibitor Cariporide® were studied in isolated perfused rabbit hearts subjected to 60 min occlusion of the ramus interventricularis of the left coronary artery (below the origin of the first diagonal branch), followed by 120 min of reperfusion. The inhibitors were added to the perfusion fluid solely or in combination at the beginning of reperfusion. Hemodynamic monitoring and biochemical analysis of perfusion fluid from the coronary outflow were performed. Myocardial infarct size and area at risk (transiently not perfused myocardium) were determined from left ventricular slices after a special staining procedure with Evans blue and 2,3,5-triphenyltetrazolium chloride. The infarcted area (dead myocardium) was 72.7±4.0% of the area at risk in untreated controls, but was significantly smaller in the presence of the inhibitors. The largest effect was observed with 10-6 M A-705253, which reduced the infarcted area to 49.2±4.1% of the area at risk, corresponding to a reduction of 33.6%. Cariporide® at 10-6 M reduced the infarct size to the same extent. The combination of both inhibitors, however, did not further improve cardioprotection. No significant difference was observed between the experimental groups in coronary perfusion, left ventricular pressure, heart rate, or in the release of lactate dehydrogenase and creatine kinase from heart muscle.

Visualisation of tissue kallikrein, kininogen and kinin receptors in human skin following trauma and in dermal diseases

Abstract During dermal injury and inflammation the serine proteases kallikreins cleave endogenous, multifunctional substrates (kininogens) to form bradykinin and kallidin. The actions of kinins are mediated by preferential binding to constitutively expressed kinin-B2 receptors or inducible kinin-B1 receptors. A feature of the kinin-B1 receptors is that they show low levels of expression, but are distinctly upregulated following tissue injury and inflammation. Because recent evidence suggested that kinin-B1 receptors may perform a protective role during inflammation, we investigated the specific occurrence of the kallikrein-kinin components in skin biopsies obtained from normal skin, patients undergoing surgery, basalioma, lichenificated atopic eczema, and psoriasis. The tissue was immunolabelled in order to determine the localisation of tissue pro-kallikrein, kallikrein, kininogen and kinin receptors. The kinin components were visualised in normal, diseased and traumatised skin, except that no labelling was observed for kininogen in normal skin. Of the five types of tissue examined, upregulation of kinin-B1 receptors was observed only in skin biopsies obtained following surgery. In essence, the expression of kinin-B1 receptors did not appear to be enhanced in the other biopsies. Within the multiple steps of the inflammatory cascade in wound healing, our results suggest an important regulatory role for kinin-B1 receptors during the first phase of inflammation following injury.

Omega-3 Fatty acids and vitamin d in cardiology.

Dietary modification and supplementation play an increasingly important role in the conservative treatment of cardiovascular disease. Current interest has focused on n-3 polyunsaturated fatty acids (PUFA) and vitamin D. Clinical trial results on this subject are contradictory in many aspects. Several studies indicate that n-3 PUFA consumption improves vascular and cardiac hemodynamics, triglycerides, and possibly endothelial function, autonomic control, inflammation, thrombosis, and arrhythmia. Experimental studies show effects on membrane structure and associated functions, ion channel properties, genetic regulation, and production of anti-inflammatory mediators. Clinical trials evaluating a possible reduction in cardiovascular disease by n-3 PUFA have shown different results. Supplementation of vitamin D is common regarding prevention and treatment of osteoporosis. But vitamin D also seems to have several effects on the cardiovascular system. Vitamin D deficiency appears to be related to an increase in parathyroid hormone levels and can predispose to essential hypertension and left ventricular hypertrophy, increased insulin resistance, and eventually to atherosclerosis and adverse cardiovascular events. Randomized prospective clinical trials are needed to determine whether vitamin D and omega-3 FA supplementation therapy should be recommended as a routine therapy for primary or secondary prevention of cardiovascular disease.

Randomized Comparison of Multipolar, Duty-Cycled, Bipolar-Unipolar Radiofrequency Versus Conventional Catheter Ablation for Treatment of Common Atrial Flutter

Comparison of Radiofrequency Versus Conventional Catheter Ablation. Introduction: Radiofrequency (RF) catheter ablation has been established as an effective and curative treatment for atrial flutter (AFL). Approved methods include a drag‐and‐drop method, as well as a point‐by‐point ablation technique. The aim of this study was to compare the acute efficacy and procedural efficiency of a multipolar linear ablation catheter with simultaneous energy delivery to multiple catheter electrodes against conventional RF for treatment of AFL.