Kaur Kamaldeep, Singh Nirmal, Dhawan R K
Department of Pharmaceutical Sciences and Drug Research, Punjabi University, Patiala.
Department of Pharmacology, Khalsa College of Pharmacy, Amritsar.
Iran J Basic Med Sci. 2019 Dec;22(12):1415-1423. doi: 10.22038/IJBMS.2019.14067.
Reperfusion of ischaemic myocardium results in reduced nitric oxide (NO) biosynthesis by endothelial nitric oxide synthase (eNOS) leading to endothelial dysfunction and subsequent tissue damage. Impaired NO biosynthesis may be partly due to increased levels of asymmetrical dimethylarginine (ADMA), an endogenous inhibitor of eNOS. As dimethylarginine dimethylaminohydrolase (DDAH) is a key enzyme responsible for degradation of ADMA, the present study was designed to explore the role of DDAH/ADMA/NO pathway in cardio-protective mechanism of ischaemic postconditioning.
Isolated rat hearts were subjected to myocardial ischaemia for 30 min followed by reperfusion for 2 hours in control group. Myocardial injury was assessed by measurement of infarct size, left ventricular developed pressure (LVDP), lactate dehydrogenase (LDH) and creatine kinase (CK) enzymes in coronary effluents. The reperfused hearts were homogenised and tissue concentration of nitrite, ADMA level and DDAH enzyme activity was determined.
A significant increase in infarct size, LDH, CK release in coronary effluents and ADMA level in myocardial tissue was observed in control group. The increase in tissue ADMA coincided with reductions of NO tissue concentrations and DDAH activity. Ischaemic postconditioning significantly attenuated ischaemia-reperfusion induced myocardial injury manifested in the terms of decreased infarct size, LDH, CK, tissue ADMA along with increase in NO levels and DDAH enzyme activity. Pretreatment with L-Homocysteine (300 µM), a competitive inhibitor of DDAH, and L-NG-nitroarginine methyl ester (L-NAME; 100 µM), an inhibitor of eNOS, completely abolished ischaemic postconditioning-induced myocardial protection.
Enhancing DDAH activity by postconditioning may be a novel target to reduce ADMA level and increase NO bioavailability to prevent myocardial ischaemia-reperfusion injury.
缺血心肌再灌注会导致内皮型一氧化氮合酶（eNOS）产生的一氧化氮（NO）生物合成减少，进而导致内皮功能障碍及随后的组织损伤。NO生物合成受损可能部分归因于不对称二甲基精氨酸（ADMA）水平升高，ADMA是eNOS的内源性抑制剂。由于二甲基精氨酸二甲胺水解酶（DDAH）是负责降解ADMA的关键酶，本研究旨在探讨DDAH/ADMA/NO途径在缺血后处理心脏保护机制中的作用。
对照组中，将离体大鼠心脏进行30分钟的心肌缺血，随后再灌注2小时。通过测量梗死面积、左心室舒张末压（LVDP）、冠状动脉流出液中的乳酸脱氢酶（LDH）和肌酸激酶（CK）酶来评估心肌损伤。将再灌注后的心脏匀浆，测定组织中亚硝酸盐浓度、ADMA水平和DDAH酶活性。
对照组中观察到梗死面积、冠状动脉流出液中LDH和CK释放以及心肌组织中ADMA水平显著增加。组织中ADMA的增加与NO组织浓度和DDAH活性的降低同时出现。缺血后处理显著减轻了缺血再灌注诱导的心肌损伤，表现为梗死面积、LDH、CK、组织ADMA降低，同时NO水平和DDAH酶活性增加。用DDAH的竞争性抑制剂L-同型半胱氨酸（300μM）和eNOS抑制剂L-NG-硝基精氨酸甲酯（L-NAME；100μM）预处理，完全消除了缺血后处理诱导的心肌保护作用。
通过后处理增强DDAH活性可能是降低ADMA水平和增加NO生物利用度以预防心肌缺血再灌注损伤的新靶点。
