Y. Yang1, I. Wang1, M. Turrentine1, M. Wang1 1Indiana University School Of Medicine,Cardiothoracic Surgery/Surgery,Indianapolis, IN, USA
Introduction: Cardioprotection provided by estrogen has been recognized for many years. But most of these studies employ a means of pre-injury application of estrogen in experimental research and the preventive usage in clinical studies. Compared to pretreatment, post-ischemic administration of estrogen will be more practical in treating myocardial ischemia (MI) given its clinical therapeutic potential. On the other hand, defect in circadian clock gene – period2 (PER2) disturbs heart energy homeostasis and aggravates MI-caused heart damage. Although PER2 expression decreases as a consequence of menopause, no information is available regarding the role of PER2 in estrogen-mediated protection following myocardial ischemia/reperfusion (I/R). In this study, we aim to determine: 1) potential improvement of myocardial function by post-ischemic administration of 17b-estradiol (E2) using an in-vivo myocardial I/R model; and 2) whether I/R affects myocardial PER2 expression, and if so, whether this alteration of PER2 can be reversed by E2 treatment.
Methods: Thirty-min ligation of left anterior descending artery (LAD) (a small piece of tubing used for ligation) followed by 24-hr reperfusion (tubing removed for reperfusion) was performed on adult C57BL male mice and ovariectomy female (OVX F) mice. Groups (n=3-6/group) were as follows: 1) SHAM, 2) I/R+Vehicle, and 3) I/R+E2. Vehicle or 0.5mg/kg of E2 was subcutaneously injected right after 30-min ischemia. Following 24-hr reperfusion, myocardial function was determined by a Millar pressure catheter inserted into the left ventricle (LV) with heart rate of 400-500 BPM. Heart tissue was collected for analysis of PER2 by Western blot. P<0.05=statistically significant.
Results: Successful ligation of the LAD was verified by myocardial blanching, abnormal movement of the anterior wall, and elevation of ST by ECG. Reperfusion was confirmed by returning the pink-red color of the LV anterior wall and decreased ST-elevation. I/R significantly impaired LV function (LVDP and +/-dP/dt, p<0.05) in both male (Fig. A1-A3) and OVX F (Fig. B1-B3), whereas post-ischemic treatment of E2 markedly improved I/R-damaged myocardial function (Fig. A and B, p<0.05). Following I/R, a trend of decreased PER2 level was observed in both male hearts and OVX F hearts. Intriguingly, E2 treatment up-regulated myocardial PER2 expression in the I/R hearts (Fig. C).
Conclusion: Our study represent the initial evidence that post-injury administration of E2 effectively improves I/R-damaged myocardial function and this protective effect of E2 may involve up-regulation of PER2. Further clarification of this novel approach and its related mechanisms may lead to clinically feasible therapies for ischemic heart disease.
