Bullard A J, Govewalla P, Yellon D M
The Hatter Institute and centre for Cardiology, University College London Hospital and Medical School, Grafton Way, London WC1E 6DB, UK.
Basic Res Cardiol. 2005 Sep;100(5):397-403. doi: 10.1007/s00395-005-0537-4. Epub 2005 Jun 10.
Erythropoietin (EPO) is a hormone that is currently used to treat patients with renal failure and anaemia. However, it has also been shown to protect against ischaemia/reperfusion injury; this protection occurring via activation of the ERK 1/2 and PI3K pathways. Since we have previously shown activation of ERK 1/2 and PI3K to be important for protection against reperfusion-induced injury in the myocardium, this study was designed to investigate its effect in the myocardium using both an isolated perfused rat heart and an in vivo rat recovery model of ischaemia-reperfusion.
Using an in vitro isolated rat heart model of 35 minutes ischaemia and 2 hours reperfusion, EPO (50 ng/ml) was administered to the rat myocardium 5 minutes prior to reperfusion for 20 minutes. The in vivo open-chest rat model consisted of 40 minutes ischaemia followed by 24 hours reperfusion with EPO (5000 U/kg) being administered at the point of reperfusion.
In the isolated perfused heart studies 50 ng/ml EPO was found to provide protection with a % I/R of 22.9% +/- 6.4 vs 54.5% +/- 7.4 for the ischaemic control group. To examine the mechanistic pathways involved in EPO-mediated protection, we co-administered the ERK 1/2 inhibitor, U0126 (10 uM) or the PI3K inhibitors, wortmannin, (100 nM) and LY294002 (15 microM) at reperfusion. U0126, wortmannin and LY294002 all abrogated EPO-mediated protection (% I/R 49.2% +/- 5.6, 46.1% +/- 5.5 and 49.9% +/- 6.1 respectively, p < 0.05). In the in vivo open-chest rat model, the % I/R was significantly attenuated in EPO-treated animals from 53.6 % +/- 3.7 in the control to 32.5% +/- 2.9 (p < 0.05). Likewise, wortmannin abrogated EPO-mediated protection (% I/R 50.7 +/- 2.3 v EPO 32.5% +/- 2.9, p < 0.05).
We demonstrate that EPO, administered at the point of reperfusion, reduced infarct size in an isolated perfused rat heart, in an ERK and PI3K dependent manner; in addition the mechanism was also confirmed in a whole animal model of ischaemia-reperfusion. These results suggest that EPO may be able to directly protect the myocardium against lethal reperfusion-induced injury and so offer the myocardium an additional clinical advantage over and above its ability to improve the oxygen carrying capacity of the blood.
促红细胞生成素（EPO）是一种目前用于治疗肾衰竭和贫血患者的激素。然而，它也已被证明可预防缺血/再灌注损伤；这种保护作用是通过激活ERK 1/2和PI3K信号通路实现的。由于我们之前已表明ERK 1/2和PI3K的激活对于保护心肌免受再灌注诱导的损伤很重要，因此本研究旨在使用离体灌注大鼠心脏和缺血-再灌注的体内大鼠恢复模型来研究其在心肌中的作用。
使用离体大鼠心脏模型，进行35分钟缺血和2小时再灌注，在再灌注前5分钟向大鼠心肌给予EPO（50 ng/ml），持续20分钟。体内开胸大鼠模型包括40分钟缺血，随后24小时再灌注，在再灌注时给予EPO（5000 U/kg）。
在离体灌注心脏研究中，发现50 ng/ml EPO可提供保护，缺血/再灌注损伤百分比为22.9%±6.4，而缺血对照组为54.5%±7.4。为了研究EPO介导的保护作用所涉及的机制途径，我们在再灌注时联合给予ERK 1/2抑制剂U0126（10 μM）或PI3K抑制剂渥曼青霉素（100 nM）和LY294002（15 μM）。U0126、渥曼青霉素和LY294002均消除了EPO介导的保护作用（缺血/再灌注损伤百分比分别为49.2%±5.6、46.1%±5.5和49.9%±6.1，p<0.05）。在体内开胸大鼠模型中，EPO治疗组的缺血/再灌注损伤百分比从对照组的53.6%±3.7显著降低至32.5%±2.9（p<0.05）。同样，渥曼青霉素消除了EPO介导的保护作用（缺血/再灌注损伤百分比为50.7±2.3，而EPO组为32.5%±2.9，p<0.05）。
我们证明，在再灌注时给予EPO可使离体灌注大鼠心脏的梗死面积减小，呈ERK和PI3K依赖性；此外，该机制在缺血-再灌注的整体动物模型中也得到了证实。这些结果表明，EPO可能能够直接保护心肌免受致命的再灌注诱导的损伤，因此除了其改善血液携氧能力的能力之外，还为心肌提供了额外的临床优势。
