Hiroyuki Yaoita

Attenuation of Ischemia/Reperfusion Injury in Rats by a Caspase Inhibitor

BACKGROUND Z-Val-Ala-Asp(OMe)-CH2F (ZVAD-fmk), a tripeptide inhibitor of the caspase interleukin-1beta-converting enzyme family of cysteine proteases, may reduce myocardial reperfusion injury in vivo by attenuating cardiomyocyte apoptosis within the ischemic area at risk. METHODS AND RESULTS Sprague-Dawley rats were subjected to a 30-minute coronary occlusion followed by a 24-hour reperfusion. An inert vehicle (dimethylsulfoxide; group 1, n=8) or ZVAD-fmk, at a total dose of 3.3 mg/kg (group 2, n=8), was administered intravenously every 6 hours starting at 30 minutes before coronary occlusion until 24 hours of reperfusion. At this 24-hour point, hemodynamics were assessed by means of cardiac catheterization; then, the rats were killed, and the left ventricle was excised and sliced. The myocardial infarct size/ischemic area at risk and the count of presumed apoptotic cardiomyocytes (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling [TUNEL]-positive cells) within the ischemic area at risk were assessed through triphenyltetrazolium chloride staining and TUNEL methods, respectively. Peak positive left ventricular dP/dt was higher (P=.02) and left ventricular end-diastolic pressure was lower (P=.04) in group 2 than in group 1. The infarct size/ischemic area at risk of group 2 (52.4+/-4.0%) was smaller (P=.02) than that of group 1 (66.6+/-3.7%), and TUNEL-positive cells were fewer (P=.0002) (group 2, 3.1+/-0.9%; group 1, 11.1+/-1.0%). Agarose gel electrophoresis revealed DNA laddering in the border zone myocardium of group 1, but DNA ladder formation was attenuated in group 2. CONCLUSIONS ZVAD-fmk was effective in reducing myocardial reperfusion injury, which could at least be partially attributed to the attenuation of cardiomyocyte apoptosis.

Apoptosis in relevant clinical situations: contribution of apoptosis in myocardial infarction.

Myocardial infarction is associated with increased TUNEL-positivity in cardiac resident and infiltrated cells. Apoptosis of proliferated interstitial myofibroblasts and infiltrated inflammatory cells may have a role in terminating tissue repair processes after infarction. Lateral and endocardial border zones of infarction within the risk area have frequent appearance of TUNEL-positive cardiomyocytes. Although the typical ultrastructural morphology of apoptosis has rarely been detected in ischaemic cardiomyocytes, there are many reports in which the TUNEL method was used for assessment of cardiomyocyte apoptosis. It has become evident that TUNEL-positivity reflects a wide range of cellular conditions; viable cells undergoing DNA repair, apoptosis, and necrosis. Therefore, it is controversial whether TUNEL-positive cardiomyocytes in infarcted myocardium are all apoptotic. Methods which will be more specific for identifying apoptosis are required for future study. TUNEL-positivity can be attenuated by anti-apoptotic interventions such as inhibition of caspases, mitochondrial protection, free radical scavenging, and some conventional pharmacotherapies. However, it remains to be determined whether anti-apoptotic interventions result in satisfactory reduction of infarct size. The injurious impact of myocardial ischaemia comes from a mixture of pro-apoptotic and necrosis-promoting signals, and the target of both signals is mitochondria. Through a common pathway they may cause permeability transition. Interventions which act only at the post-mitochondrial stage of apoptosis may fail to reduce infarct size, whereas those acting at pre-mitochondrial and mitochondrial stages may reduce infarct size. Progress in investigating the basic mechanisms of apoptosis and recognition of the modes of cardiomyocytes death will contribute to advances in cardioprotective therapy in myocardial infarction.

Effects of antioxidants on coronary microvascular spasm induced by epicardial coronary artery endothelial injury in pigs.

ObjectivesThe effect of oxidative stress on coronary microvascular disease is unknown. We investigated whether chronic administration of ascorbic acid (ASC) or glutathione (GSH) prevents microvascular dysfunction and remodeling induced by upstream repeated coronary artery endothelial injury. MethodsBalloon endothelial injury was repeated at the left anterior descending coronary artery (LAD), just distal to an implanted flow meter, every 2 weeks for 6 weeks in pigs. Changes in LAD blood flow induced by acetylcholine (ACh) and 5-hydroxytryptamine were assessed before each endothelial injury and at 8 weeks after the first endothelial injury in pigs without treatment (endothelial injury group, n=12) and in pigs treated with oral ASC (3 g/day) (ASC group, n=12) and ASC (3 g/day) plus GSH (1 g/day) (ASC+GSH group, n=12). ResultsIn the endothelial injury group, reduced blood flow in response to ACh was augmented from a decrease of 18±17% to a decrease of 100% (that is, zero flow, 8 weeks, P<0.01), accompanied by an increase of ascorbyl free radicals (AFRs) in coronary sinus blood. In contrast, in the ASC+GSH group, blood flow response to ACh was altered to a decrease of 45±17% (8 weeks, P<0.01 compared with the endothelial injury group), coronary sinus blood AFRs did not change (8 weeks, 21.4±12.5 signal intensities, P<0.01 compared with the endothelial injury group) and the rate of platelet aggregation induced by adenosine diphosphate was small (8 weeks, 56±17%, P<0.01 compared with the endothelial injury group). ConclusionsChronic administration of antioxidants suppressed microvascular hypercontraction, suggesting that it may be a promising therapeutic strategy for treating coronary microvessel disorders, including microvascular angina.

Intervention for apoptosis in cardiomyopathy

Apoptosis plays an important role in pathogenesis of primary and secondary cardiomyopathies. It is proposed that antiapoptotic interventions may constitute an effective strategy for these diseases. Some of the antiapoptotic interventions are “old wine in a new bottle” measures already included in the conventional pharmacotherapy. As specific antiapoptotic treatment, caspase inhibitors and anti-TNF-α antibody are in early phases of clinical trials in non-cardiac diseases or being contemplated for clinical studies. Non-pharmacotherapies such as cardiac resynchronization and left ventricular assist device also exert cardioprotection partly by antiapoptotic mechanisms. In the field of regenerative medicine, myocardial transplantation of bone marrow-derived stem cells has been performed. Although it is controversial whether it is a true regenerative medicine or the cytokine therapy, antiapoptotic effect of transplanted cells may also have a role in cardioprotection. Moreover, apoptosis may develop despite efforts for cardioprotection in some severe situations of heart failure. Cardiac repair and regeneration by cardiac stem cells may compensate a loss of cardiomyocytes avoiding a deleterious situation. Therefore, protection and/or potentiation of such effects by cardiac stem cells appear to be promising therapeutic strategy in the future. In this review, we discuss about the antiapoptotic interventions for cardiomyopathies in the “real world” and the future of clinical cardiology.

Characteristics of death of neonatal rat cardiomyocytes following hypoxia or hypoxia–reoxygenation: the association of apoptosis and cell membrane disintegrity

Abstract. Irreversibly injured cardiomyocytes are positive for terminal deoxynucleotidyl transferase nick end-labeling (TUNEL), making it controversial as to whether TUNEL-positive cardiomyocytes induced by hypoxia–reoxygenation are apoptotic (secondarily necrotic) or primarily necrotic. We investigated the relationship between plasma membrane integrity and DNA fragmentation in hypoxic-reoxygenated cardiomyocytes. Cardiomyocytes were prepared from neonatal rat heart and exposed to hypoxia. The plasma membrane integrity was assessed by propidium iodide (PI) staining. The mode of DNA fragmentation was assessed by TUNEL and in situ polymerase chain reaction ligation assay. Furthermore, caspase-3 activity was measured in hypoxic-reoxygenated cardiomyocytes. Reoxygenation for 24 h after 3–8 h of hypoxia increased TUNEL positivity. However, the appearance of PI-positivity preceded that of TUNEL at various time points following reoxygenation. In contrast, TUNEL-positive but PI-negative cells were rarely found. In the hypoxic-reoxygenated cells, caspase-3 activity was increased, and PI- and TUNEL-positive cardiomyocytes possessed a sufficient number of double-strand DNA breaks with single-base 3′-OH terminals. In cardiomyocytes subjected to hypoxia–reoxygenation, the appearance of TUNEL positivity was delayed in comparison to membrane disintegrity, but in these cells caspase-3 has been activated and the mode of DNA fragmentation was apoptosis-specific. Thus, hypoxia–reoxygenation induces apoptosis associated with cell membrane disintegrity in cardiomyocytes.