Possible Role of JAK-2 in Attenuated Cardioprotective Effect of Ischemic Preconditioning in Hyperhomocysteinemic Rat Hearts

Abstract

The present study investigated the possible role of Janus kinase-2 (JAK-2) in hyperhomocysteinemia-induced attenuation of the cardioprotective eŠects of ischemic preconditioning (IPC). Rats were administered L-methionine (1.7 g/kg/day, p.o.) for 4 weeks to produce hyperhomocysteinemia. Isolated LangendorŠ's perfused normal and hyperhomocysteinemic rat hearts were subjected to global ischemia for 30 min, followed by reperfusion for 120 min. Myocardial infarct size was assessed macroscopically using triphenyltetrazolium chloride staining. Coronary eOEuent was analyzed for lactate dehydrogenase (LDH) and creatine kinase (CK) release to assess the extent of cardiac injury. The oxidative stress in the heart was assessed by measuring thiobarbituric acid-reactive substances (TBARS), superoxide anion generation and the reduced form of glutathione. Ischemia-reperfusion (I/R) induced oxidative stress by increasing TBARS, superoxide anion generation and decreasing reduced form of glutathione in normal and hyperhomocystenemic rat hearts. Moreover, I/R produced myocardial injury, which was assessed in terms of the increase in myocardial infarct size, LDH and CK release in coronary eOEuent, and decrease in coronary ‰ow rate in normal and hyperhomocysteinemic rat hearts. The hyperhomocysteinemic rat hearts showed enhanced I/R-induced myocardial injury with a high degree of oxidative stress as compared with normal rat hearts subjected to I/R. Four episodes of IPC (5 min each) aŠorded cardioprotection against I/R-induced myocardial injury in normal rat hearts as assessed in terms of improvement in coronary ‰ow rate and reduction in myocardial infarct size, levels of LDH, CK, and oxidative stress. On the other hand, IPC-mediated myocardial protection against I/R-injury was abolished in hyperhomocysteinemic rat hearts. Tyrphostin AG490 (5 mM), a selective inhibitor of JAK-2, did not aŠect the cardioprotective eŠects of IPC in normal rat hearts, but its administration markedly restored the cardioprotective potential of IPC in hyperhomocysteinemic rat hearts. Administration of diazoxide (30 mM), an ATP-sensitive potassium (K ATP ) channel opener, also restored the cardioprotective eŠects of IPC in hyperhomocysteinemic rat hearts. In conclusion, it is suggested that the high degree of oxidative stress produced in hyperhomocysteinemic rat hearts during reperfusion and consequent activation of JAK-2 and closure of K ATP channels may be responsible for abolishing the cardioprotective potential of IPC against I/Rinduced myocardial injury.

Effects of Losartan and Vanillic Acid Co-Administration on Ischemia-Reperfusion-Induced Oxidative Stress in Isolated Rat Heart

“…The extent of CK-MB elevation strongly correlates with infarct size; moreover, LDH raises in myocardial infarction after reperfusion, which may be due to sustained ischemic injury (7). In the present study, 30 minutes ischemia followed by 60 min reperfusion produced myocardial injury as shown by elevated levels of CPK, CK-MB, and LDH in the coronary effluent, which was consistent with the earlier reports (21, 22).…”

“…In this process, free radicals steal electron from the lipids in cell membrane and result in cell damage (7). TBARS are low-molecular end products, the major component of which is MDA, that are made during the decomposition of lipid peroxidation product.…”

“…Creatine kinase (CK) is an intramuscular enzyme that has two subunits, namely, M (muscle) and B (brain), which combine to produce isoenzymes CK-MM (muscular), CK-BB (brain), and CK-MB (myocardial). CK and CKMB levels increase with myocardial damage (7). The renin-angiotensin system (RAS) is upregulated during myocardial infarction and I/R injury (8, 9).…”

Myocardial postconditioning: Next step to cardioprotection

“…Recently, we showed that the cardioprotective potential of IPost did not occur in hearts from hyperhomocysteinemic rats (Dreiseitel et al, 2009;Rohilla and Balakumar, 2009;Singh et al, 2009;Rohilla et al, 2010). Mechanistically, a high degree of oxidative stress in hyperhomocysteinemic rat hearts in response to I/R injury may be responsible for the attenuated effects of IPost (Dreiseitel et al, 2009;Rohilla and Balakumar, 2009;Singh et al, 2009;Rohilla et al, 2010). Clearly, further studies are waranted to understand the modulatory role of various metabolic disorders in postconditioning-mediated myocardial protection.…”

Abrogated cardio protective effect of ischemic preconditioning in hyperhomocysteinemia and hypertrophy

“…In conclusion it is reported that closure of K ATP channel and activation of JAK-2 may be responsible for abrogated cardio protective potential of IPC against I/R induced myocardial injury. 64 …”