Ondrej Szarszoi

Effects of mitochondrial KATP modulators on cardioprotection induced by chronic high altitude hypoxia in rats

OBJECTIVES Adaptation of rats to intermittent high altitude hypoxia increases the tolerance of their hearts to acute ischemia/reperfusion injury. Our aim was to examine the role of mitochondrial ATP-sensitive potassium channels (K(ATP)) in this form of protection. METHODS Adult male Wistar rats were exposed to hypoxia of 5000 m in a barochamber for 8 h/day, 5 days a week; the total number of exposures was 24-32. A control group was kept under normoxic conditions (200 m). Infarct size (tetrazolium staining) was measured in anesthetized open-chest animals subjected to 20-min regional ischemia (coronary artery occlusion) and 4-h reperfusion. Isolated perfused hearts were used to assess the recovery of contractile function following 20-min global ischemia and 40-min reperfusion. In the open-chest study, a selective mitochondrial K(ATP) blocker, 5-hydroxydecanoate (5 mg/kg), or openers, diazoxide (10 mg/kg) or BMS-191095 (10 mg/kg), were administered into the jugular vein 5 and 10 min before occlusion, respectively. In the isolated heart study, 5-hydroxydecanoate (250 micromol/l) or diazoxide (50 micromol/l) were added to the perfusion medium 5 or 10 min before ischemia, respectively. RESULTS In the control normoxic group, infarct size occupied 62.2+/-2.0% of the area at risk as compared with 52.7+/-2.5% in the chronically hypoxic group (P<0.05). Post-ischemic recovery of contractile function (dP/dt) reached 60.0+/-3.9% of the pre-ischemic value and it was improved to 72.4+/-1.2% by adaptation to hypoxia (P<0.05). While 5-hydroxydecanoate completely abolished these protective effects of chronic hypoxia, it had no appreciable influence in normoxic groups. In contrast, diazoxide significantly increased the recovery of contractile function and reduced infarct size in normoxic groups only. The later effect was also observed following treatment with BMS-191095. CONCLUSION The results suggest that opening of mitochondrial K(ATP) channels is involved in the cardioprotective mechanism conferred by long-term adaptation to intermittent high altitude hypoxia.

Effects of melatonin on ischemia and reperfusion injury of the rat heart.

Effects of melatonin on various manifestations of ischemia/reperfusion injury of the isolated perfused rat heart were examined. Ischemia- and reperfusion-induced ventricular arrhythmias were studied under constant flow in hearts subjected to 10, 15 or 25 min of regional ischemia (induced by LAD coronary artery occlusion) and 10-min reperfusion. Melatonin was added to the perfusion medium 5 min before ischemia at concentrations of 10 μmol/l or 10 nmol/l and was present throughout the experiment. Recovery of the contractile function was evaluated under constant perfusion pressure after 20-min global ischemia followed by 40-min reperfusion. Hearts were treated with melatonin at a high concentration (10 μmol/l) either 5 min before ischemia only (M1) or 5 min before ischemia and during reperfusion (M2) or only during reperfusion (M3). At the high concentration, melatonin significantly reduced the incidence of reperfusion-induced ventricular fibrillation and decreased arrhythmia score (10% and 2.2 ± 0.3, respectively) as compared with the corresponding untreated group (62% and 4.1 ± 0.3, respectively); the low concentration had no effect. This substance did not affect the incidence and severity of ischemic arrhythmias. Melatonin (M2, M3) significantly improved the recovery of the contractile function as compared with the untreated group; this protection did not appear if melatonin was absent in the medium during reperfusion (M1). Our results show that melatonin, in accordance with its potent antioxidant properties, effectively protects the rat heart against injury associated with reperfusion. It appears unlikely that melatonin is cardioprotective at physiological concentrations.

Effect of perinatal hypoxia on cardiac tolerance to acute ischaemia in adult male and female rats

1 The number of adult patients undergoing surgery for congenital cyanotic defects in childhood has increased significantly. Therefore, the aim of the present study was to examine the effect of perinatal hypoxia on the tolerance of the adult myocardium to acute ischaemia–reperfusion injury. 2 Pregnant Wistar rats were exposed to intermittent hypobaric hypoxia 7 days before delivery; pups were born under normoxic conditions and exposed to hypoxia again for 10 postnatal days. After the last hypoxic exposure, all animals were kept for an additional 3 months under normoxic conditions. All experiments were performed on 90‐day‐old rats. 3 Ventricular arrhythmias were assessed on isolated perfused hearts during 30 min occlusion of the left anterior descending coronary artery. Infarct size was measured on isolated hearts (40 min regional ischaemia and 120 min reperfusion) and on open‐chest animals (20 min regional ischaemia and 3 h reperfusion). 4 Perinatal exposure to hypoxia significantly increased cardiac tolerance to ischaemic injury in adult females, as evidenced by the lower incidence and severity of ischaemic ventricular arrhythmias, compared with the normoxic group. The effect of perinatal hypoxia on ischaemic arrhythmias in males was quite the opposite. Myocardial infarct size measured in open‐chest animals only was significantly smaller in normoxic females compared with normoxic males. Perinatal exposure to hypoxia had no effect on infarct size in either setting or sex. 5 The results of the present study support the hypothesis that perinatal hypoxia is a primary programming stimulus in the heart that may lead to sex‐dependent changes in cardiac tolerance to acute ischaemia in later adult life. This would have important implications for patients who have experienced prolonged hypoxaemia in early life.

Perivascular sirolimus-delivery system.

Autologous vein grafts are often used for treating damaged vessels, e.g. arteriovenous fistulas or arterial bypass conduits. Veins have a different histological structure from arteries, which often leads to intimal hyperplasia and graft restenosis. The aim of this study was to develop a perivascular sirolimus-delivery system that would release the antiproliferative drug sirolimus in a controlled manner. Polyester Mesh I was coated with purasorb, i.e. a copolymer of L-lactide and ɛ-caprolactone, with dissolved sirolimus; Mesh II was coated with two copolymer layers; the layer with dissolved sirolimus was overlaid with pure purasorb. This arrangement allowed sirolimus to be released for 6 and 4 weeks, for Mesh I and Mesh II, respectively. Mesh II released sirolimus more homogeneously, without the initial burst effect during the first week. However, the cumulative release curve was steeper at later time points than the curve for Mesh I. Both meshes inhibited proliferation of rat vascular smooth muscle cells during 14-day culture in vitro and preserved excellent cell viability. Newly developed sirolimus-releasing perivascular meshes are promising devices for preventing autologous graft restenosis.

A perivascular system releasing sirolimus prevented intimal hyperplasia in a rabbit model in a medium-term study

The main complication of aortocoronary reconstruction with vein grafts is restenosis in the course of time. The aim was to assess the effect of a periadventitial polyester mesh releasing sirolimus on intimal hyperplasia of autologous grafts. We implanted v. jugularis ext. into a. carotis communis in rabbits. The vein graft was either intact, or was wrapped with a pure polyester mesh, or with a sirolimus-releasing mesh. Three and six weeks after surgery, the veins were subjected to standard histological staining and the thicknesses of the tunica intima, the media and the intima-media complex were measured. Wrapping the vein with a mesh releasing sirolimus or with a pure mesh decreased the thickness of the intima in comparison with a vein graft by 73 ± 11% or 73 ± 8% after 3 weeks, and by 73 ± 9% or 59 ± 12% after 6 weeks, respectively. Sirolimus-releasing meshes reduced the thickness of the media by 65 ± 9% and 20 ± 12% after 3 and 6 weeks. The thickness of the intima-media complex in grafts with sirolimus-releasing meshes decreased by 60 ± 6% and 30 ± 13% in comparison with pure PES meshes, after 3 and 6 weeks, respectively. A periadventitial polyester mesh releasing sirolimus has the potential to become an effective device in preventing vein graft restenosis.

Bridge to transplantation with long-term mechanical assist device in adults after the Mustard procedure.

BACKGROUND There is limited clinical experience with bridging to transplant with a left ventricular assist device (VAD) in patients with previously palliated transposition of great arteries. METHODS Five adult patients presenting with systemic right ventricular failure 30 years after a Mustard operation were implanted with a HeartMate II VAD. The implant was completed using standard procedures with only minor modifications to accommodate right ventricular cannulation. RESULTS All 5 patients were men, with a mean age of 31.5 ± 1.8 years and a median time since Mustard operation of 30 (range 28 to 32) years. All patients had sternal closure on Post-operative Day (POD) 1, and 2 patients required additional re-operation for bleeding. One patient required temporary support of the non-systemic ventricle. The mean duration of VAD support was 284 ± 177 days; 3 patients underwent heart transplant and 2 died on PODs 502 and 34, respectively. Both deaths were due to progressive heart failure and pump thrombosis. Comorbidities, anatomy and mediastinal scarring did not preclude implantation and heart failure symptoms improved in all patients. CONCLUSIONS With the increased prevalence of late post-Mustard heart failure, bridge to transplant with a VAD may be a suitable treatment option for patients who are severely ill.

Total artificial heart support with two continuous-flow ventricular assist devices in a patient with an infiltrating cardiac sarcoma.

Primary cardiac sarcoma is normally fatal, but cardiac replacement may provide some hope for long-term survival. A 38 year-old man with cardiac sarcoma, involving the interventricular septum and posterior wall with intermittent mitral obstruction, underwent implantation of two HeartMate II ventricular assist devices for total artificial heart support. After cardiectomy, the HeartMate sewing rings were sewn to the right neoatrium and the left atrial remnants. After the outflow grafts were sewn end to end to the pulmonary artery and aorta, the two drivelines were externalized through the abdominal wall, and perfusion started. The postoperative course was complicated by respiratory and renal dysfunction, which resolved. After 6 months of support, the patient has normal organ function and is ambulatory. Follow-up oncologic evaluation of positron emission tomography-computed tomography scan is negative.

Alloimmunosensitization in left ventricular assist device recipients and impact on posttransplantation outcome.

Left ventricular assist devices (LVADs) have become an established surgical therapy for patients with end-stage heart failure who require hemodynamic support as a bridge-to-transplant or destination therapy. However, the anatomic and physiologic consequences of long-term LVAD support have yet to be fully clarified. Despite the clinical success of these devices, it has been reported that many patients bridged to transplantation with mechanical support develop circulating antibodies with potential donor reactivity. Transplanting against existing or historic donor-specific antibodies is associated with increased risk of antibody-mediated rejection, graft dysfunction, and decreased survival. Safe transplantation of allosensitized patients is dependent on using prospective crossmatching and antibody titer reduction techniques (desensitization). Strict protocols requiring a negative prospective crossmatch before transplantation result in a decreased donor pool and a longer duration of support in sensitized LVAD recipients with increased inherent morbidity such as infections and thromboembolic complications. The aim of this review is to present the current state of knowledge of possible immunologic mechanisms involved in alloimmunization of LVAD recipients, outline new methods of antibody detection, compare various desensitization strategies, and present an overview of clinical data assessing the impact of sensitization on posttransplantation outcome.

Impact of Perinatal Chronic Hypoxia on Cardiac Tolerance to Acute Ischemia

Perinatal period is critical for the normal cardiac development, and different interventions imposed on the heart may significantly influence myocardial structure and function. Perinatal hypoxemia, although transient, may thus have serious early and late consequences on the cardiovascular system. Epidemiological and experimental studies have repeatedly suggested a possible link between perinatal hypoxia and increased sensitivity to ischemia/reperfusion (I/R) injury in adults. The mechanisms of this increased susceptibility are not known at present. It has been found that prenatal chronic hypoxia sensitizes the apoptosis pathway in the adult male heart in response to I/R stimulation. In addition, cardiac heat shock proteins (Hsp) 70 expression was significantly lower in prenatal hypoxic hearts than in controls; this fact may play a role in the increased susceptibility of the adult heart to I/R injury. The decreased eNOS levels in adult prenatal hypoxic hearts may also contribute to their increased sensitivity. These studies suggest that chronic hypoxic exposure during early development may cause in utero or neonatal programming of several genes which can play an important role in the increased susceptibility of the adult male heart to I/R injury. Furthermore, it has been observed in the rat model that late myocardial effects of chronic hypoxia, experienced in early life, may be sex-dependent. Unlike in males, perinatal exposure to chronic hypoxia significantly increased cardiac tolerance to acute I/R injury in adult females, expressed as the lower incidence of ischemic arrhythmias, decreased infarct size, decreased cardiac enzyme release, and increased postischemic recovery of left ventricular function. It was suggested that these sex-dependent changes may be due to differences in fetal programming of PKCe gene expression, which play a pivotal role in cardioprotection; down-regulation of PKCe function was observed in the hearts of adult male offspring only. These results would have important clinical implications, since cardiac sensitivity to oxygen deprivation in adult patients may be significantly influenced by perinatal hypoxia in a sex-dependent manner.

Aortic and Mitral Valve Replacement Due to Extensive Inflammatory Immunoglobulin G4-Related Pseudotumor.

A 64-year-old woman with extensive tumorous infiltration of the mitral and aortic valves underwent partial resection of a tumor of the left ventricular outflow tract and replacement of both affected valves. Histology revealed an inflammatory pseudotumor with a significant number of immunoglobulin-G4-positive plasma cells. The histologic and clinical findings suggested immunoglobulin-G4-related disease of the heart.