The evolving concept of physiological ischemia training vs. ischemia preconditioning

Ischemic heart diseases are the leading cause of death with increasing numbers of patients worldwide. Despite advances in revascularization techniques, angiogenic therapies remain highly attractive. Physiological ischemia train- ing, which is first proposed in our laboratory, refers to reversible ischemia training of normal skeletal muscles by using a tourniquet or isometric contraction to cause physiologic ischemia for about 4 weeks for the sake of triggering mole- cular and cellular mechanisms to promote angiogenesis and formation of collateral vessels and protect remote ische- mia areas. Physiological ischemia training therapy augments angiogenesis in the ischemic myocardium by inducing differential expression of proteins involved in energy metabolism, cell migration, protein folding, and generation. It upregulates the expressions of vascular endothelial growth factor, and induces angiogenesis, protects the myocardium when infarction occurs by increasing circulating endothelial progenitor cells and enhancing their migration, which is in accordance with physical training in heart disease rehabilitation. These findings may lead to a new approach of ther- apeutic angiogenesis for patients with ischemic heart diseases. On the basis of the promising results in animal studies, studies were also conducted in patients with coronary artery disease without any adverse effect in vivo, indicating that physiological ischemia training therapy is a safe, effective and non-invasive angiogenic approach for cardiovascular rehabilitation. Preconditioning is considered to be the most protective intervention against myocardial ischemia-reper- fusion injury to date. Physiological ischemia training is different from preconditioning. This review summarizes the preclinical and clinical data of physiological ischemia training and its difference from preconditioning.

Desferoxamine preconditioning protects against cerebral ischemia in rats by inducing expressions of hypoxia inducible factor 1α and erythropoietin

Objective To investigate whether desferoxamine （DFO） preconditioning can induce tolerance against cerebral ischemia and its effect on the expression of hypoxia inducible factor 1 α （HIF- 1α） and erythropoietin （EPO） in vivo and in vitro. Methods Rat model of cerebral ischemia was established by middle cerebral artery occlusion with or without DFO administration. Infarct size was examined by TTC staining, and the neurological severity score was evaluated according to published method. Cortical neurons were cultured under ischemia stress which was mimicked by oxygen-glucose deprivation （OGD）, and the neuron damage was assessed by MTT assay. Immunofluorescent staining was employed to detect the expressions of HIF-1 and EPO. Results The protective effect induced by DFO （decreasing the infarction volume and ameliorating the neurological function） appeared at 2 d after administration ofDFO （post-DFO）, lasted until 7 d and disappeared at 14 d （P 〈 0.05）; the most effective action was observed at 3 d post-DFO. DFO induced tolerance of cultured neurons against OGD： neuronal viability was increased 23%, 34%, 40%, 48% and 56% at 8 h, 12 h, 24 h, 36 h, and 48 h, respectively, post-DFO （P 〈 0.05）. Immunofluorescent staining found that HIF-1 α and EPO were upregulated in the neurons of rat brain at 3 d and 7 d post-DFO; increase of HIF-1 α and EPO appeared in cultured cortex neurons at 36 h and 48 h post-DFO. Conclusion DFO induced tolerance against focal cerebral ischemia in rats, and exerted protective effect on OGD cultured cortical neurons. DFO significant induced the expression of HIF- 1 α and EPO both in vivo and in vitro. DFO preconditioning can protect against cerebral ischemia, which may be associated with the synthesis of HIF- 1 α and EPO.

Effect of Autophagy Inhibition on the Protection of Ischemia Preconditioning against Myocardial Ischemia/Reperfusion Injury in Diabetic Rats

Background： Ischemia preconditioning （IPC） remains the most powerful intervention of protection against myocardial ischemiaJreperfusion injury （IRI）, but diabetes can weaken or eliminate its cardioprotective effect and detailed mechanisms remain unclear. In this study, we aimed to explore whether changes of autophagy in the diabetic condition are attributable to the decreased cardioprotective effect of I PC. Methods： Sixty diabetic male Sprague-Dawley rats were randomly divided into the control （C）, IRI, rapamycin （R）, wortmannin （W）, rapamycin ＋ IPC （R ＋ IPC）, and wortmannin ＋ IPC （W ＋ IPC） groups. The in vivo rat model of myocardial IRI was established by ligaturing and opening the left anterior descending coronary artery via the left thoracotomy. Durations of ischemia and reperfusion are 30 min and 120 min, respectively. Blood samples were taken at 120 min of reperfusion for measuring serum concentrations of troponin I （TnI） and creatine kinase isoenzyme MB （CK-MB） using the enzyme-linked immunosorbent assay. The infarct size was assessed by Evans blue and triphenyltetrazolium chloride staining. The expressions ofLC3-11, beclin- 1, phosphoinositide 3-kinase （PI3K）, naammalian target of rapamycin （mTOR）, and P-Akt/Akt ratio in the ischemic myocardium were assessed by Western blotting. Results： Compared to the IRI group, infarct size （56.1% ± 6.1% vs. 75.4 ± 7.1%, P 〈 0.05）, serum cTnl （0.61 ± 0.21 vs. 0.95 ±0.26 ng/ml, P 〈 0.05）, and CK-MB levels （6.70 ± 1.25 vs. 11.51 ±2.35 ng/ml, P 〈 0.05） obviously decreased in the W ＋ IPC group. Compared with the C group, myocardial expressions of LC3-11 （0.46 ± 0.04 and 0.56 ± 0.04 vs. 0.36 ± 0.04, P 〈 0.05） and beclin- 1 （0.34 ± 0.08 and 0.38 ± 0.07 vs. 0.24 ±0.03, P 〈 0.05） evidently increased, and myocardial expressions of mTOR （0.26 ± 0.08 and 0.25 ± 0.07 vs. 0.38 ± 0.06, P 〈 0.05）, PI3K （0.29 ± 0.04 and 0.30 ±0.03 vs. 0.38 ± 0.02, P 〈 0.05）, and P-Akt/Akt ratio （0.49 ± 0.10 and 0.48 ± 0.06 vs. 0.72 ± 0.07, P 〈 0.05） markedly decreased in the IRI and R groups, indicating an increased autophagy. Compared with the IRI group, myocardial expression ofbeclin- 1 （0.26 ± 0.03 vs. 0.34 ± 0.08, P 〈 0.05） significantly decreased, and myocardial expressions of mTOR （0.36 ± 0.04 vs. 0.26 ± 0.08, P 〈 0.05）, PI3K （0.37 ± 0.03 vs. 0.29 ± 0.04, P 〈 0.05）, and P-Akt/Akt ratio （0.68 ± 0.05 vs. 0.49 ± 0.10, P 〈 0.05） increased obviously in the W ＋ IPC group, indicating a decreased autophagy. Conclusions： Increased autophagy in the diabetic myocardium is attributable to decreased cardioprotection of IPC, and autophagy inhibited by activating the PI3K-Akt-mTOR signaling pathway can result in an improved protection of IPC against diabetic myocardial IRI.

Monocarboxylate transporter 4 plays a significant role in the neuroprotective mechanism of ischemic preconditioning in transient cerebral ischemia

Monocarboxylate transporters（MCTs）, which carry monocarboxylates such as lactate across biological membranes, have been associated with cerebral ischemia/reperfusion process. In this study, we studied the effect of ischemic preconditioning（IPC） on MCT4 immunoreactivity after 5 minutes of transient cerebral ischemia in the gerbil. Animals were randomly designated to four groups（sham-operated group, ischemia only group, IPC ＋ sham-operated group and IPC ＋ ischemia group）. A serious loss of neuron was found in the stratum pyramidale of the hippocampal CA1 region（CA1）, not CA2/3, of the ischemia-only group at 5 days post-ischemia; however, in the IPC ＋ ischemia groups, neurons in the stratum pyramidale of the CA1 were well protected. Weak MCT4 immunoreactivity was found in the stratum pyramidale of the CA1 in the sham-operated group. MCT4 immunoreactivity in the stratum pyramidale began to decrease at 2 days post-ischemia and was hardly detected at 5 days post-ischemia; at this time point, MCT4 immunoreactivity was newly expressed in astrocytes. In the IPC ＋ sham-operated group, MCT4 immunoreactivity in the stratum pyramidale of the CA1 was increased compared with the sham-operated group, and, in the IPC ＋ ischemia group, MCT4 immunoreactivity was also increased in the stratum pyramidale compared with the ischemia only group. Briefly, present findings show that IPC apparently protected CA1 pyramidal neurons and increased or maintained MCT4 expression in the stratum pyramidale of the CA1 after transient cerebral ischemia. Our findings suggest that MCT4 appears to play a significant role in the neuroprotective mechanism of IPC in the gerbil with transient cerebral ischemia.

Ischemic preconditioning produces more powerful anti- inflammatory and cardioprotective effects than limb remote ischemic postconditioning in rats with myocardial ischemia-reperfusion injury

Background Both ischemic preconditioning （IPC） and limb remote ischemic postconditioning （LRIPOC） have been shown to possess significantly different cardioprotective effects against the myocardial ischemia reperfusion injury （IRI）, but no study has compared the anti-inflammatory effects of IPC and LRIPOC during myocardial IRI process. We hypothesized that IPC and LRIPOC would produce different anti-inflammatory effects in an in vivo rat model with myocardial IRI.

Remote ischemia conditioning-an endogenous cardioprotective strategy from outside the heart

Objective A general review was made of studies involving： （1） The experimental evidence of remote ischemic preconditioning （RIPC） and relative clinical studies, （2） The experimental and clinical evidences of remote ischemic postconditioning （RIPOC）, （3） The potential mechanistic pathways underlying their protective effects.Data sources The data used in this review were mainly from manuscripts listed in PubMed that were published in English from 1986 to 2010. The search terms were ＂myocardial ischemia reperfusion injury＂, ＂ischemia preconditioning＂,＂ischemia postconditioning＂, ＂remote preconditioning＂ and ＂remote postconditioning＂.Study selection （1） Clinical and experimental evidence that both RIPC and RIPOC produce preservation of ischemia reperfusion injury （IRI） of myocardium and other organs, （2） Studies related to the potential mechanisms, by which remote ischemic conditioning protects myocardium against IRI.Results Both RIPC and RIOPC have been shown to attenuate myocardial IRI in laboratory animals. Also, their cardioprotective effects have appeared in some clinical studies. Except the external, the detailed internal mechanisms of remote ischemic conditioning have been generally described. Through these descriptions better protocols can be developed to provide improved cardioprotective procedures.Conclusions Remote ischemic conditioning is an endogenous cardioprotective mechanism from outside the heart that protects against myocardial IRI and represents a general form of inter-organ protection. Remote ischemic conditioning may have an immense impact on clinical practice in the near future.