Possible involvement of caveolin in attenuation of cardioprotective effect of ischemic preconditioning in diabetic rat heart

BMC Cardiovascular Disorders Possible involvement of caveolin in attenuation of cardioprotective effect of ischemic preconditioning in diabetic rat heart Preeti Ajmani 0 Harlokesh N Yadav 0 Manjeet Singh 0 Pyare L Sharma 0 0 Department of Pharmacology, Indo-Soviet College of Pharmacy , Moga 142- 001, Punjab , India Background: Nitric oxide (NO) has been noted to produce ischemic preconditioning (IPC)-mediated cardioprotection. Caveolin is a negative regulator of NO, which inhibits endothelial nitric oxide synthase (eNOS) by making caveolin-eNOS complex. The expression of caveolin is increased during diabetes mellitus (DM). The present study was designed to investigate the involvement of caveolin in attenuation of the cardioprotective effect of IPC during DM in rat. Methods: Experimental DM was induced by single dose of streptozotocin (50 mg/Kg, i.p,) and animals were used for experiments four weeks later. Isolated heart was mounted on Langendorff's apparatus, and was subjected to 30 min of global ischemia and 120 min of reperfusion. IPC was given by four cycles of 5 min of ischemia and 5 min of reperfusion with Kreb's-Henseleit solution (K-H). Extent of injury was measured in terms of infarct size by triphenyltetrazolium chloride (TTC) staining, and release of lactate dehydrogenase (LDH) and creatin kinase-MB (CKMB) in coronary effluent. The cardiac release of NO was noted by measuring the level of nitrite in coronary effluent. Results: IPC- induced cardioprotection and release of NO was significantly decreased in diabetic rat heart. Pretreatment of diabetic rat with daidzein (DDZ) a caveolin inhibitor (0.2 mg/Kg/s.c), for one week, significantly increased the release of NO and restored the attenuated cardioprotective effect of IPC. Also perfusion of sodium nitrite (10 M/L), a precursor of NO, significantly restored the lost effect of IPC, similar to daidzein in diabetic rat. Administration of 5-hydroxy deaconate (5-HD), a mito KATP channel blocker, significantly abolished the observed IPC-induced cardioprotection in normal rat or daidzein and sodium nitrite perfused diabetic rat heart alone or in combination. Conclusions: Thus, it is suggested that attenuation of the cardioprotection in diabetic heart may be due to decrease the IPC mediated release of NO in the diabetic myocardium, which may be due to up -regulation of caveolin and subsequently decreased activity of eNOS. - Background Ischemic heart disease is a leading cause of morbidity and mortality worldwide [1]. Reperfusion of an ischemic myocardium is a requisite, for the restoration of the normal functioning of the myocardium [2]. However, abrupt reperfusion of an ischemic myocardium is not without hazard; it produces further damage of myocardium, described as ischemia-reperfusion (I/R) injury [3,4]. Moreover, it has been documented that controlled reperfusion avoids further injury, both in myocardium and in peripheral tissues [5-8]. Brief episodes of ischemia followed by reperfusion of myocardium, increase the resistance against sustained ischemia of longer duration; this phenomenon is termed as ischemic preconditioning (IPC) [9]. IPC produces cardioprotection by PI-3K/Akt [10,11], phosphorylation of eNOS and by generation of nitric oxide (NO) and by opening of mito KATP channel [12,13]. However, the cardioprotective effect of IPC is attenuated in conditions such as heart failure [14,15] aging [16,17] hypertension ([18,19] obesity [20] hyperlipidemia [21-23]and diabetes mellitus [24-26]. Diabetes mellitus is a one of the major risk factor for ischemic heart disease. Caveolin is the caveolar membrane protein, invaginated on the plasma membrane that serves as signalling platform for many of the G-protein coupled receptors (GPCR) [27-29]. IPC exerts cardioprotection by impairing the death signalling components p38MAPKa and JNK [30], by increase its association with caveolin. It has been well documented that caveolin is a negative regulator of eNOS, it interacts and inhibits the activity of eNOS by making caveolin-eNOS complex [31,32]. IPC increases the activity of eNOS by disrupting the complex of caveolin and eNOS in rat heart [32]. Moreover, it has been documented that NO produces cardioprotection by opening of KATP channel during IPC, and caveolin facilitates the interaction of NO with KATP channel by forming a suitable signaling platform [33]. Caveolin maintains eNOS in inactivated state and thereby limits NO production [34,35] and on agonist stimulation leads to activation of eNOS through increased disruption of caveolin/eNOS complex [31]. In diabetic rat heart, expression of caveolin increases [36-38] which enhances the binding of eNOS to caveolin and decreases the release of NO [31]. Therefore, the present study was undertaken to elucidate whether or not the diminished eNOS/NO signaling in diabetic myocardium is responsible for loss of cardioprotective effect of IPC. Methods The experimental protocol used in the present study was approv (...truncated)