Statin mediated protection of the ischemic myocardium

Acute effects of statin on reduction of angiopoietin-like 2 and glyceraldehyde-derived advanced glycation end-products levels in patients with acute myocardial infarction: a message from SAMIT (Statin for Acute Myocardial Infarction Trial)

Experimental ischemia-reperfusion models have shown that 3-hydroxy-3methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, statins, have cardioprotective effects. SAMIT (Statin Acute Myocardial Infarction Trial) is a multicenter prospective open randomized trial, designed to evaluate the effects of statin treatment from the earliest stage on cardioprotection in patients with acute myocardial infarction (AMI). Patients were randomly assigned to receive atorvastatin (initial dose of 40 mg at admission followed by the maintenance dose of 10 mg/day for 30 days) or not (control), and then immediately underwent percutaneous coronary intervention (PCI) for the culprit lesion. The primary endpoints were infarct size and left ventricular function. The secondary endpoints were major adverse cardiac and cerebrovascular events (MACCE) and various biomarkers. There were no significant differences in baseline characteristics between 2 groups of the statin treatment group and the control group. The left ventricular ejection fraction increased at 6 months after the onset of AMI, compared with the baseline level in the atorvastatin group (P < 0.05), while it did not change in the control group. Although there were no significant differences in the MACCE, the changes in the levels of angiopoietin-like protein 2 (ANGPTL2) (P < 0.05), and glyceraldehyde-derived advanced glycation end-products, (TAGE) (P < 0.01) were suppressed at 2 weeks in the atorvastatin group, compared with the control group. Statin therapy started early after the onset reduced the levels of ANGPTL2 and TAGE, and thus, might have cardioprotective effects in patients with AMI.

Atorvastatin at reperfusion reduces myocardial infarct size in mice by activating eNOS in bone marrow-derived cells

Background

The current study was designed to test our hypothesis that atorvastatin could reduce infarct size in intact mice by activating eNOS, specifically the eNOS in bone marrow-derived cells. C57BL/6J mice (B6) and congenic eNOS knockout (KO) mice underwent 45 min LAD occlusion and 60 min reperfusion. Chimeric mice, created by bone marrow transplantation between B6 and eNOS KO mice, underwent 40 min LAD occlusion and 60 min reperfusion. Mice were treated either with vehicle or atorvastatin in 5% ethanol at a dose of 10 mg/kg IV 5 min before initiating reperfusion. Infarct size was evaluated by TTC and Phthalo blue staining.

Results

Atorvastatin treatment reduced infarct size in B6 mice by 19% (p<0.05). In eNOS KO vehicle-control mice, infarct size was comparable to that of B6 vehicle-control mice (p = NS). Atorvastatin treatment had no effect on infarct size in eNOS KO mice (p = NS). In chimeras, atorvastatin significantly reduced infarct size in B6/B6 (donor/recipient) mice and B6/KO mice (p<0.05), but not in KO/KO mice or KO/B6 mice (p = NS).

Conclusions

The results demonstrate that acute administration of atorvastatin significantly reduces myocardial ischemia/reperfusion injury in an eNOS-dependent manner, probably through the post-transcriptional activation of eNOS in bone marrow-derived cells.

Effects of statins on ischemia-reperfusion complications in breast free flaps

BACKGROUND

Administration of statins or other cardiovascular medications (CVMs) could potentially protect against the development of ischemia-reperfusion (I/R) injury in free flap reconstruction. The aim of this study was to examine whether the use of statins and other CVMs decreased the rate of I/R injury in autologous free flap breast reconstruction.

METHODS

Retrospective chart review was performed on women who had undergone mastectomy and autologous free flap breast reconstruction between 2004 and 2010. Patient characteristics, use of statin and/or CVMs, and I/R-related complications were ascertained. Multivariable logistic regression was used to identify associations between independent risk factors and specific complications.

RESULTS

There were 702 free flap breast reconstructions included in this study; 45 performed in patients on statins, 70 in patients on CVMs, and 38 in patients on both. Overall complication rate in patients on statins and patients on CVMs was significantly higher than those not on any medication (46.7% versus 31.5%, P=0.037 and 45.7% versus 31.5%, P=0.017, respectively). When I/R complications were pooled, there were no significant differences between patients not on any medications and those on statins (P=0.26), CVMs (P=0.18), and both (P=0.83.)

CONCLUSIONS

Although there may be theoretical pharmacologic benefits of statins and/or CVMs to reduce the incidence of IR injury in autologous free flap breast reconstruction, the results of this study showed no clear advantages when these drugs were used.

The Effect of Statins and Other Cardiovascular Medication on Ischemia-Reperfusion Damage in a Human DIEP Flap Model: Theoretical and Epidemiological Considerations

Background. Statins and other cardiovascular medication possess antioxidant capacity. It was examined whether chronic use of these medications protects from the development of ischemia-reperfusion (I/R) related complications after DIEP (Deep Inferior Epigastric Perforator Free Flap) surgery. This paper contains a literature study on the antioxidant working mechanisms of these drugs. Methods. Medical information of 134 DIEP patients (173 flaps) was studied from their medical files. Patient and operative characteristics were registered, as well as I/R related complications. Results. Of the group that didnot use statins, 16.3% developed complications versus 30.8% amongst patients that did use these drugs (P = 0.29). Amongst patients that chronically use other cardiovascular medication, 26.8% developed I/R related complications versus 14.4% of the patients without medication (P = 0.10). Conclusions. Chronic use of statins or other cardiovascular medication didnot decrease the occurrence of I/R related complications after DIEP surgery. Therefore, research should be aimed at evaluating short-term pre-treatment with statins.

Observational Study on the Beneficial Effect of Preoperative Statins in Reducing Atrial Fibrillation After Coronary Surgery

BACKGROUND

Recent evidence supports the important role of inflammation in atrial fibrillation (AF) after coronary artery bypass grafting (CABG) and there is growing evidence that statin has cardiac antiarrhythmic effects. The aim of this study was to assess the efficacy of preoperative statins in preventing AF after CABG in a longitudinal observational study.

METHODS

Over a two-year period, 405 consecutive patients underwent isolated CABG procedures. Univariate analysis was performed exploring the relationship regarding statin use and AF development. A propensity score for treatment with statins was obtained from core patient characteristics. The role of statin therapy on postoperative AF was assessed by means of a conditional logistic model, while stratifying on the quintiles of the propensity score. All analysis was performed retrospectively.

RESULTS

Postoperative AF occurred in 29.5% of the patients with preoperative statin therapy compared with 40.9% of those patients without it (p = 0.021). No statistical differences among development of AF and type, dose, or duration of preoperative statin therapy were observed. Preoperative statins were associated with a 42% reduction in risk of AF development after CABG surgery (odds ratio [OR] 0.58, 95% confidence interval [CI] 0.37 to 0.91, p = 0.017, while stratifying on the propensity score). No different effect of statins on AF was observed with respect to age groups (< or = 70 and > 70 years) (interaction p = 0.711).

CONCLUSIONS

Preoperative statins may reduce postoperative AF after CABG. Patients undergoing elective revascularization may benefit from a preventive statin approach.

Pharmacologic therapeutics for cardiac reperfusion injury

Cardiovascular disease is the leading cause of morbidity and mortality in industrial societies, with myocardial infarction as the primary assassin. Pharmacologic agents, including the myocardial cell membrane receptor agonists adenosine, bradykinin/angiotensin-converting enzyme inhibitors, opioids and erythropoietin or the mixed cell membrane and intracellular agonists, glucose insulin potassium, and volatile anesthetics, either clinically or experimentally reduce the extent of myocardial injury when administered just prior to reperfusion. Agents that specifically target proteins, transcription factors or ion channels, including PKC agonists/antagonists, PPAR, Phosphodiesterase-5 inhibitors, 3-Hydroxy-3-methyl glutaryl coenzyme A reductase and the ATP-dependent potassium channel are also promising. However, no agent has been specifically approved to reduce reperfusion injury clinically. In this review, we will discuss the advantages and limitations of agents to combat reperfusion injury, their market development status and findings reported in both clinical and preclinical studies. The molecular pathways activated by these agents that preserve myocardium from reperfusion injury, which appear to commonly involve glycogen synthase kinase 3beta and mitochondrial permeability transition pore inhibition, are also described.

Should a statin be prescribed to every patient with heart failure?

Chronic heart failure (HF) represents an emerging epidemic since its prevalence is continuously increasing despite advances in treatment. Many recent clinical studies have clearly demonstrated that statin therapy is associated with improved outcomes in HF irrespective of aetiology (ischaemic or not) or baseline cholesterol levels. Indeed, most of the conducted large statin trials and trials in HF have demonstrated a positive effect of statins in HF patients. Furthermore, the use of statins in HF seems to be safe as none of the recent trials has resulted in worse outcomes for HF patients treated with statins. Potential mechanisms through which statins could benefit the failing myocardium include non-sterol effects of statins, as well as effects on nitric oxide and endothelial function, inflammation and adhesion molecules, apoptosis and myocardial remodelling and neurohormonal activation. This review discusses the pathophysiological basis of statin effects on HF and focuses on clinical data for the benefit from statin use in this setting. Until today there are no official recommendations in both the American and the European guidelines regarding the use of statins in HF patients, as the available data come from small observational or larger but retrospective, non-randomised studies. Therefore, HF patients should be treated according to current lipid guidelines. Large randomised clinical trials are underway and will further delineate the role of statin therapy in HF patients. Until more data are available, we could not recommend statin use to every patient with HF irrespective of HF aetiology and baseline cholesterol levels.

The myocardial infarct size-limiting and antiarrhythmic effects of acyl-CoA:cholesterol acyltransferase inhibitor VULM 1457 protect the hearts of diabetic-hypercholesterolaemic rats against ischaemia/reperfusion injury both in vitro and in vivo

The study was designed to characterise the influence of a novel acyl-CoA:cholesterol acyltransferase inhibitor, VULM 1457, on the severity of myocardial ischaemia-reperfusion injury in a model of diabetes mellitus and hypercholesterolaemia induced by co-administration of streptozotocin and a high fat-cholesterol diet. We used Langendorff-perfused rat hearts to measure the size of myocardial infarction after 30 min of regional ischaemia, followed by a 2-h reperfusion period, and open-chest rats were exposed to 6 min of ischaemia and 10 min of reperfusion to analyse ventricular arrhythmias. In addition to the high fat-cholesterol diet, VULM 1457 was administered to the diabetic-hypercholesterolaemic rats for 5 days. Decreased plasma and liver cholesterol levels and a significantly reduced occurrence of ventricular fibrillation (29% vs. 100%, P<0.01), determined via the mean number and duration of episodes (0.6+/-0.4 and 2.1+/-1.4 s vs. 2.8+/-0.8 and 53.5+/-14.4 s in diabetic-hypercholesterolaemic rats, both P<0.01), were observed in these animals. Lethal ventricular fibrillation was suppressed, and arrhythmia severity was also significantly decreased in these animals as compared to the non-treated animals (2.9+/-0.6 vs. 4.9+/-0.2; P<0.05). A smaller infarct size, normalised to the size of area at risk, was observed in the treated diabetic-hypercholesterolaemic group as compared to the non-treated group (16.3+/-1.9% vs. 37.3+/-3.1%; P<0.01). Aside from remarkable hypolipidaemic activity, VULM 1457 improved the overall myocardial ischaemia-reperfusion injury outcomes in the diabetic-hypercholesterolaemic rats by suppressing arrhythmogenesis as well as by reducing myocardial necrosis.

Beneficial effects of statins on perioperative cardiovascular outcome

PURPOSE OF REVIEW

This review evaluates clinical and experimental articles that have recently been published on the cardioprotective effect of perioperative statin therapy.

RECENT FINDINGS

Perioperative statin therapy improves short and long-term cardiac outcome following noncardiac surgery. This cardiovascular protection has been attributed to the so-called pleiotropic effects, which have a positive effect on plaque stability. With no clinical studies reporting an increased incidence of adverse effects of perioperative statin use, it appears to be a safe and helpful therapeutic option.

SUMMARY

Perioperative statin therapy may stabilize coronary plaques due to pleiotropic effects and results in a reduction of perioperative cardiovascular complications.

The protective effect of HMG-CoA reductase inhibitors against monocrotaline-induced pulmonary hypertension in the rat might not be a class effect: comparison of pravastatin and atorvastatin

Hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, so called statins, improve endothelial function and exert antiproliferative effects on vascular smooth muscle cells of systemic vessels. This study aimed at comparing the protective effects of two statins, pravastatin and atorvastatin, against monocrotaline (MC)-induced pulmonary hypertension in rats. Pravastatin or atorvastatin (PS or AS, 10 mg/kg per day) or vehicle were given orally for 28 days to Wistar male rats injected or not with MC (60 mg/kg intraperitoneally). At 4 weeks, MC-injected rats developed severe pulmonary hypertension, with an increase in right ventricular pressure (RVP) and right ventricle/left ventricle + septum weight ratio associated with a decrease in acetylcholine- or sodium-nitroprusside-induced pulmonary artery dilation observed in vitro. Hypertensive pulmonary arteries exhibited an increase in medial thickness and endothelial cell apoptosis and a decrease of endothelial nitric oxide synthase (eNOS) expression. MC-rat lungs showed a significant decrease of eNOS (P < 0.01) and increase of cleaved caspase-3 (P < 0.05) expression determined by Western blotting. PS (P = 0.02) but not AS (P = 0.30) significantly limited the development of pulmonary hypertension (RVP in mmHg: 30 +/- 3, 36 +/- 4 vs. 45 +/- 4 and 14 +/- 1 for MC + PS, MC + AS, MC, and control groups, respectively). Both statins significantly reduced MC-induced right ventricle hypertrophy [RV/left ventricular (LV) + S, in mg/g: 0.46 +/- 0.04, 0.39 +/- 0.03, 0.62 +/- 0.05 and 0.29 +/- 0.01 for MC + PS, MC + AS, MC, and control groups, respectively; P < 0.05),and reduced MC-induced thickening (61 +/- 6 microm, 82 +/- 5 microm, 154 +/- 4 microm, and 59 +/- 2 microm for MC + PS, MC + AS, MC, and control groups, respectively; P = 0.01) of small intrapulmonary artery medial wall, with MC + AS still being different from the control group. PS but not AS partially restored acetylcholine-induced pulmonary artery vasodilation in MC rats (E(max)=65 +/- 5%, 49 +/- 6%, 46 +/- 3%, and 76 +/- 4% for MC + PS, MC + AS, MC, and control groups, respectively; P < 0.05 for MC + PS vs. other groups). Both statins prevented apoptosis and restored eNOS expression of pulmonary artery endothelial cells as well as in the whole lung with a more pronounced effect with PS compared with AS. In conclusion, despite its effects on eNOS expression, apoptosis, and medial wall thickening, AS was unable to significantly reduce pulmonary hypertension and to restore endothelium-dependent relaxation, suggesting intermolecular differences between the two HMG-CoA reductase inhibitors in the protection against MC-induced hypertension.

Randomized Trial of Atorvastatin for Reduction of Postoperative Atrial Fibrillation in Patients Undergoing Cardiac Surgery

Background— Atrial fibrillation (AF) after cardiac surgery is associated with increased risk of complications, length of stay, and cost of care. Observational evidence suggests that patients who have undergone previous statin therapy have a lower incidence of postoperative AF. We tested this observation in a randomized, controlled trial.

Methods and Results— Two hundred patients undergoing elective cardiac surgery with cardiopulmonary bypass, without previous statin treatment or history of AF, were enrolled. Patients were randomized to atorvastatin (40 mg/d, n=101) or placebo (n=99) starting 7 days before operation. The primary end point was incidence of postoperative AF; secondary end points were length of stay, 30-day major adverse cardiac and cerebrovascular events, and postoperative C-reactive protein (CRP) variations. Atorvastatin significantly reduced the incidence of AF versus placebo (35% versus 57%, P =0.003). Accordingly, length of stay was longer in the placebo versus atorvastatin arm (6.9±1.4 versus 6.3±1.2 days, P =0.001). Peak CRP levels were lower in patients without AF ( P =0.01), irrespective of randomization assignment. Multivariable analysis showed that atorvastatin treatment conferred a 61% reduction in risk of AF (odds ratio 0.39, 95% confidence interval 0.18 to 0.85, P =0.017), whereas high postoperative CRP levels were associated with increased risk (odds ratio 2.0, 95% confidence interval 1.2 to 7.0, P =0.01). The incidence of major adverse cardiac and cerebrovascular events at 30 days was similar in the 2 arms.

Conclusions— Treatment with atorvastatin 40 mg/d, initiated 7 days before surgery, significantly reduces the incidence of postoperative AF after elective cardiac surgery with cardiopulmonary bypass and shortens hospital stay. These results may influence practice patterns with regard to adjuvant pharmacological therapy before cardiac surgery.

Coronary Artery Bypass Grafting is Superior to Percutaneous Coronary Intervention in Prevention of Perioperative Myocardial Infarctions During Subsequent Vascular Surgery

BACKGROUND

Among patients in need of coronary revascularization before an elective vascular operation, the value of coronary artery bypass grafting (CABG) versus percutaneous coronary intervention (PCI) in preventing perioperative myocardial infarctions is uncertain. We hypothesized that more complete revascularization would improve outcomes after vascular surgery.

METHODS

In this Veterans Affairs Cooperative trial involving 18 medical centers, 222 patients underwent elective vascular surgery after coronary revascularization. The mode of coronary revascularization was selected at each site by the local investigators (CABG in 91 patients and PCI in 131 patients). The vascular surgical indications were similar in both groups.

RESULTS

There were 2 deaths in the CABG group (2.2%) and 5 deaths in the PCI group (3.8%; p = 0.497) after the vascular procedure. There were fewer perioperative myocardial infarctions after the vascular operation in CABG patients (6.6%) than in PCI patients (16.8%; p = 0.024), despite more diseased vessels in the CABG group (3.0 +/- 1.3 versus 2.2 +/- 1.4, respectively; p < 0.001). The completeness of revascularization (defined as the number of coronary artery vessels revascularized relative to the total number of vessels with a stenosis > or = 70%) in patients in the CABG and PCI groups was 117% +/- 63% and 81% +/- 57%, respectively (p < 0.001). Hospital length of stay in CABG versus PCI patients was 6 (4, 8) and 7 (4, 10) days, respectively (p = 0.078).

CONCLUSIONS

Among patients receiving multivessel coronary artery revascularization as prophylaxis for elective vascular surgery, patients having a CABG had fewer myocardial infarctions and tended to spend less time in the hospital after the vascular operation than patients having a PCI. More complete revascularization accounted for the intergroup differences.

Cardioprotection mediated by rosiglitazone, a peroxisome proliferator-activated receptor gamma ligand, in relation to nitric oxide

Activation of peroxisome proliferator-activated receptor (PPAR) gamma protects from myocardial ischemia/reperfusion injury. The aim of the study was to investigate whether the cardioprotective effect of PPARgamma is related to nitric oxide (NO).

METHODS

Wild type (WT) and endothelial NO synthase (eNOS) knockout (KO) mice received 3 mg/kg of the PPARgamma agonist rosiglitazone or vehicle (n = 6-9 in each group) i. p. 45 min before anesthesia. The hearts were isolated, perfused in a Langendorff mode and subjected to global ischemia and 30 min reperfusion. The hearts of another two groups of WT mice received the NOS inhibitor L-NNA (100 micromol/l) or vehicle in addition to pre-treatment with vehicle or rosiglitazone.

RESULTS

In the WT heart, rosiglitazone increased the recovery of left ventricular function and coronary flow following ischemia in comparison with the vehicle group.L-NNA did not affect recovery per se but significantly blunted the improvement in the recovery of left ventricular function induced by rosiglitazone. In the KO group rosiglitazone suppressed the recovery of myocardial function following ischemia. Expression of eNOS was not affected, but phosphorylated eNOS was significantly increased by rosiglitazone in the WT hearts (P < 0.05).

CONCLUSION

These results suggest that the cardioprotective effect of the PPARgamma agonist rosiglitazone is mediated via NO by phosphorylation of eNOS.

The HMG-CoA reductase inhibitor, pravastatin, prevents the development of monocrotaline-induced pulmonary hypertension in the rat through reduction of endothelial cell apoptosis and overexpression of eNOS

HMG-CoA reductase inhibitors improve endothelial function and exert antiproliferative effects on vascular smooth muscle cells of systemic vessels. This study was aimed to assess the protective effects of pravastatin (an HMG-CoA reductase inhibitor) against monocrotaline-induced pulmonary hypertension in rats. Pravastatin (PS, 10 mg/kg/day) or vehicle were given orally for 28 days to Wistar male rats injected or not with monocrotaline (MC, 60 mg/kg intraperitonealy) and treated or not by N(omega)-nitro-L-arginine methyl ester (L-NAME) 15 mg/kg/day. At 4 weeks, monocrotaline-injected rats developed severe pulmonary hypertension, with an increase in right ventricular pressure (RVP) and right ventricle/left ventricle+septum weight ratio (RV/LV+S), associated with a decrease in pulmonary artery dilation induced either by acetylcholine or sodium nitroprusside. Hypertensive pulmonary arteries exhibited an increase in medial thickness, medial wall area, endothelial cell apoptosis, and a decrease of endothelial nitric oxide synthase (eNOS) expression. Monocrotaline-rat lungs showed a significant decrease of eNOS expression (4080+/-27 vs 12189+/-761 arbitrary density units [ADU] for MC and control groups respectively, P<0.01) and a significant increase of cleaved caspase-3 expression by western blotting (Control=11628+/-2395 vs MC=2326+/-2243 ADU, P<0.05). A non-significant trend toward a reduced mortality was observed with pravastatin (relative risk of death = 0.33; 95% confidence interval [0.08-1.30], P= 0.12 for MC+PS vs MC groups). Pravastatine induced a protection against the development of the pulmonary hypertension (RVP in mmHg: 30+/-3 vs 45+/-4 and RV/LV+S: 0.46+/-0.04 vs 0.62+/-0.05 for MC+PS and MC groups respectively, P<0.05) and was associated with a significant reduction of MC-induced thickening (61+/-6 mum vs 81+/-3 mum for MC+PS and MC groups respectively, P= 0.01) of the medial wall of the small intrapulmonary arteries. Pravastatin partially restored acetylcholine-induced pulmonary artery vasodilation in MC rats (Emax=65+/-5% and 46+/-3% for MC+PS and MC group respectively, P<0.05) but had no effect on acetylcholine-induced pulmonary artery vasodilation in MC+L-NAME rats. It also prevented apoptosis and restored eNOS expression of pulmonary artery endothelial cells, as well as in the whole lung. Pravastatin reduces the development of monocrotaline-induced pulmonary hypertension and improves endothelium-dependent pulmonary artery relaxation, probably through a reduced apoptosis and a restored eNOS expression of endothelial cells.

Increased superoxide anion production is associated with early atherosclerosis and cardiovascular dysfunctions in a rabbit model

OBJECTIVE

Hypercholesterolemia (HC) has been associated with impairment of vascular and myocardial functions. As HC could generate an alteration in the oxidative status, we studied the effects of a 1-month cholesterol diet on cardiovascular oxidative stress.

METHODS AND RESULTS

New Zealand rabbits received cholesterol (1%) or normal chow for 1 month. At 30 days, superoxide anion levels, assessed by ESR spectroscopy, NAD(P)H oxidase (NOX) activity, and dihydroethidium (DHE) staining of aortas were higher in the cholesterol-fed (CF) group compared with control (respectively, 4.0 +/- 0.6 Arbitrary Units/mg (AU/mg) vs. 2.6 +/- 0.3, p < 0.05; 4231 +/- 433 vs. 2931 +/- 373 AU/mg, p<0.05; 21.4 +/- 1.2 vs. 12.9 +/- 1.7% fluorescence/mm2, p < 0.001). NOX gp91 phox and p67 phox expression in the aortas were higher in the CF group vs. control (1.5 +/- 0.2 vs. 0.5 +/- 0.2, p < 0.001; 0.9 +/- 0.2 vs. 0.3 +/- 0.2, p<0.05). The endothelium-dependent relaxation evaluated on the iliac arteries was higher in control than in the CF group (64.8 +/- 10.1 vs. 13.1 +/- 3.70%, p<0.001). The cardiac diastolic pressure estimated on isolated hearts was higher in the CF group than in control (21.1 +/- 4.1 vs. 10.3 +/- 1.4 mmHg, p<0.05) after 60 min of ischemia.

CONCLUSIONS

Hypercholesterolemia induced increased levels of superoxide in the aortas and a higher expression of NOX subunits, associated with altered vasorelaxation. The increased diastolic pressure observed in hearts, consistent with a post-ischemic contractile dysfunction might be mediated by the production of superoxide.

Protection of adult rat cardiac myocytes from ischemic cell death: role of caveolar microdomains and delta-opioid receptors

The role of caveolae, membrane microenvironments enriched in signaling molecules, in myocardial ischemia is poorly defined. In the current study, we used cardiac myocytes prepared from adult rats to test the hypothesis that opioid receptors (OR), which are capable of producing cardiac protection in vivo, promote cardiac protection in cardiac myocytes in a caveolae-dependent manner. We determined protein expression and localization of delta-OR (DOR) using coimmunohistochemistry, caveolar fractionation, and immunoprecipitations. DOR colocalized in fractions with caveolin-3 (Cav-3), a structural component of caveolae in muscle cells, and could be immunoprecipitated by a Cav-3 antibody. Immunohistochemistry confirmed plasma membrane colocalization of DOR with Cav-3. Cardiac myocytes were subjected to simulated ischemia (2 h) or an ischemic preconditioning (IPC) protocol (10 min ischemia, 30 min recovery, 2 h ischemia) in the presence and absence of methyl-beta-cyclodextrin (MbetaCD, 2 mM), which binds cholesterol and disrupts caveolae. We also assessed the cardiac protective effects of SNC-121 (SNC), a selective DOR agonist, on cardiac myocytes with or without MbetaCD and MbetaCD preloaded with cholesterol. Ischemia, simulated by mineral oil layering to inhibit gas exchange, promoted cardiac myocyte cell death (trypan blue staining), a response blunted by SNC (37 +/- 3 vs. 59 +/- 3% dead cells in the presence and absence of 1 muM SNC, respectively, P < 0.01) or by use of the IPC protocol (35 +/- 4 vs. 62 +/- 3% dead cells, P < 0.01). MbetaCD treatment, which disrupted caveolae (as detected by electron microscopy), fully attenuated the protective effects of IPC or SNC, resulting in cell death comparable to that of the ischemic group. By contrast, SNC-induced protection was not abrogated in cells incubated with cholesterol-saturated MbetaCD, which maintained caveolae structure and function. These findings suggest a key role for caveolae, perhaps through enrichment of signaling molecules, in contributing to protection of cardiac myocytes from ischemic damage.