Objective: To investigate the effects of mitochondrion-targeted cyanine fluorescent small molecule IR-61 on cardiac injury induced by exhaustive exercise in rats.
Methods: Thirty-six adult male SD rats were randomly divided into 3 groups(n=12),control group (Ctrl), exhaustive exercise group (EE) and IR-61+ exhaustive exercise group (IR-61+EE). IR-61+EE group were intraperitoneally injected with 2 mg/kg IR-61 at the same time on day 1, 4 and 7. One hour after the end of the last drug administration, the two exhaustive exercise groups were subjected to exhaustive exercise modeling. The rats were placed on an animal treadmill with a slope of 0° at a speed of 10~15 m/min to coordinate their limbs running posture, and then ran at a speed of 25~30 m/min until exhaustion about 15 minutes later. After the animal models established, ECG was recorded by physiological recorder, myocardial injury was observed by light microscope, mitochondrial injury was observed by transmission electron microscope, myocardial cell apoptosis was detected by TUNEL method, markers of myocardial injury were detected by ELISA, and myocardial mitochondrial respiration rate was measured by high-resolution Oxygraph-2K mitochondrial instrument.
Results: ① Compared with Ctrl group, heart rate was increased, PR interval was shortened, QRS interval was prolonged, QTc was prolonged and ST segment was depressed significantly in EE group (P＜0.05). In EE group, myocardial fiber fracture and mitochondrial inner chamber swelling were obvious, mitochondrial crest was fuzzy, mitochondrial outer membrane was incomplete, and a large number of mitochondrial rupture and fusion were visible. In EE group, TUNEL staining cells were abundant, chromatin concentration and marginalization, nuclear membrane lysis, chromatin fragmentation into massive apoptotic bodies, apoptosis score increased (P＜0.05). The levels of creatine kinase isoenzyme-MB (CK-MB), cardiac troponin I(cTn-I) and N-terminal B-type natriuretic peptide (NT-proBNP) were increased in EE group (P＜0.05). Basal respiration rate, oxidative respiration rate of fatty acids and respiration rate of complex Ⅰ, Ⅱ and Ⅳ were all decreased (P＜ 0.05). ② Compared with EE group, the heart rate in IR-61+EE group was increased, PR interval was prolonged, QRS interval was shortened, QTc was shortened, ST segment was not significantly depressed (P＜0.05). In IR-61+EE group, myocardial fiber arrangement was loose, no obvious fracture was observed, mitochondrial inner ventricle was swelling, mitochondrial outer membrane was intact, TUNEL stained cells and unstained cells were observed, the overall morphology was more similar to Ctrl group. Apoptosis index was decreased (P＜0.05), the levels of CK-MB and cTn-I were decreased in IR-61+EE group (P＜0.05). The oxidative respiration rate of fatty acids and the respiration rate of complex Ⅱ and Ⅳ were increased (P＜0.05).
Conclusion: Mitochondrion-targeted cyanine fluorescent small molecule IR-61 can improve cardiac electrical activity, reduce myocardial cell injury and mitochondrial injury, reduce myocardial cell apoptosis, and improve the myocardial mitochondrial energy metabolism condition in exhausted rats.
目的: 研究线粒体靶向七甲川花菁类荧光小分子IR-61对力竭性运动大鼠心脏损伤的影响。方法: 清洁级成年雄性SD大鼠36只,随机分为3组(n=12):对照组(Ctrl组)、力竭组(EE组)、IR-61+力竭组(IR-61+EE组)。IR-61+EE组在第1、4、7日同一时间腹腔注射2 mg/kg IR-61;最后一次给药结束1 h后,两个力竭运动组进行力竭造模,在坡度为0°的动物跑步机上,先以10～15 m/min的速度令大鼠协调四肢跑步姿势,约15 min后以 25～30 m/min 的速度一次性跑步至力竭。以生理记录仪描记大鼠心电图,取大鼠的心肌样品,光镜观察心肌细胞损伤、透射电镜观察线粒体损伤,TUNEL法检测心肌细胞凋亡情况,ELISA法检测心肌损伤标志物,高分辨率线粒体呼吸仪测定心肌线粒体呼吸速率。结果: ① 与Ctrl组相比,EE组的心率增加、PR间期缩短、QRS间期延长、QTc延长、ST段明显压低(P＜0.05);心肌纤维断裂明显,线粒体内室肿胀明显,线粒体嵴模糊,线粒体外膜不完整,可见大量线粒体破裂及融合;可见TUNEL染色细胞较多,呈现染色质浓缩、边缘化,核膜裂解,染色质分割成块状凋亡小体,凋亡评分增加(P＜0.05);CK-MB升高、cTn-I升高、NT-proBNP升高(P＜0.05);基础呼吸速率、脂肪酸氧化呼吸速率、复合物Ⅰ、Ⅱ、Ⅳ呼吸速率均有下降(P＜0.05)。② 与EE组相比,IR-61+EE组的心率增加、PR间期延长、QRS间期缩短、QTc缩短、ST段未见明显压低(P＜0.05),心肌纤维排列疏松,未见明显断裂,线粒体内室肿胀,线粒体外膜完整,可见TUNEL染色细胞与未染色细胞,整体形态更接近Ctrl组,凋亡评分下降(P＜0.05), CK-MB下降,cTn-I下降(P＜0.05);脂肪酸氧化呼吸速率及复合物Ⅱ、Ⅳ呼吸速率均有提高(P＜0.05)。结论: 线粒体靶向七甲川花菁类荧光小分子IR-61可改善力竭运动大鼠的心电活动,减轻心肌细胞及线粒体损伤,减少心肌细胞凋亡,提高心肌线粒体能量代谢水平。.
Keywords: cardiac injury; cyanine; exhaustive exercise; fluorescent small molecule IR-61; myocardial mitochondrial energy metabolism; rats.