Effects And Mechanisms Of Olmesartan And Remote Ischemic Perconditioning/Postconditioning On Myocardial Ischemia Reperfusion Injury In Spontaneously Hypertensive Rats

BackgroundsIschemic heart disease is the leading cause of mortality worldwide. The main treatment strategy of ischemic heart disease is the early reperfusion and restoration of blood flow. However, reperfusion itself contributes to the final myocardial injury via a complex series of event. Therefore, investigating pharmacologic or surgical strategies to lessen ischemia reperfusion injury has great clinical significance.Hypertension, as a common cardiovascular risk factor, increases myocardial load/mechanical stress, and thereby may exacerbate the outcome of an ischemia reperfusion insult to the heart. Angiotensin II receptor blocker is a class of drugs with increasing use in treating hypertension. Olmesartan, as a new angiotensin II receptor blocker, has shown its beneficial effect beyond blood pressure lowing. However, the effect of olmesartan on myocardial ischemia reperfusion injury in spontaneously hypertensive rats has not been investigated. Therefore, we discussed the protective effect of olmesartan against cardiac ischemia reperfusion injury in spontaneously hypertensive rats in Part I.Remote ischemic conditioning is the new protective strategy to reduce ischemia reperfusion injury. This strategy can be applied before the myocardial ischemia, during the myocardial ischemia and after the myocardial ischemia. Compared with remote ischemic preconditioning (RIPC), remote ischemic perconditioning (RIPER) and remote ischemic postconditioning (RIPOST) can be applied to wider range of clinical situations. However, the explanation for RIPER and RIPOST is not clear. The effect of RIPER and RIPOST on myocardial ischemia reperfusion injury in spontaneously hypertensive rats has not been investigated. Therefore, we discussed the effect of RIPER, RIPOST and the combination of the two strategies and investigated olmesartan’s effect on these conditioning strategies respectively in Part II, Part III and Part Ⅳ. We also attached a review which summarizes the available literature on RIPER and RIPOST and discussed the model, algorithms, mechanisms and clinical applications on RIPER and RIPOST respectively.PartⅠThe effect of olmesartan against myocardial ischemia reperfusion injury in spontaneously hypertensive ratsOBJECTIVES:Olmesartan is a new angiotensin II receptor blocker with increasing use in treating hypertension. Olmesartan has shown beneficial effect on cardiovascular diseases besides lowing blood pressure. However, its effect on ischemia reperfusion (IR) injury in spontaneously hypertensive rats (SHRs) has not been investigated. The aim of the study was to examine the effect of olmesartan on IR injury in SHRs and to examine the effect of olmesartan on HMGB1 and HIF-1α mRNA expression.METHODS:Forty SHRs were randomly divided into two groups:Vehicle group and Olmesartan group. In the vehicle group, SHRs received four-week-treatment of vehicle besides normal feed. In the Olmesartan group, SHRs received four-week-treatment of Olmesartan besides normal feed. Two groups of animals were then assigned to one of the two subgroups: sham group and IR group. In the sham group, the suture passed under the left anterior descending coronary artery (LAD) without being tightened. In the IR group, the LAD was ligated for 40 min followed by a 180 min reperfusion.Left ventricular mass index (LVMI), creatine kinase (CK) concentration, heart rate during ischemia and reperfusion, arrhythmia score, infarct size, HMGB1 protein expression and HIF-la mRNA expression were measured.RESULTS:Compared with the vehicle-treated SHRs, Olmesartan significantly reduced blood pressure and ameliorated left ventricular hypertrophy in Olmesartan-treated SHRs. Compared with the Vehicle-sham group, HMGB1 expression and HIF-1α expression was significantly decreased in the Olmesartan-sham group. Compared with the Vehicle-IR group, infarct size, CK concentration and HMGB1 expression was significantly reduced in the Olmesartan-IR group. The proportional increase in HIF-1α expression due to IR was greater in the Olmesartan-treated SHRs compared with the vehicle-treated SHRs.CONCLUSION:Our experiment demonstrates for the first time that: 1) Olmesartan ameliorate left ventricular hypertrophy and protects against IR injury in SHRs besides lowing blood pressure,2) Olmesartan reduces HMGB 1 expression and down-regulates HIF-1α expression, and 3) the protective effect of Olmesartan is due to its anti-oxidative and anti-inflammatory propertiesPart IIThe effect of remote ischemic perconditioning against myocardial ischemia reperfusion injury in spontaneously hypertensive ratsOBJECTIVES:Remote ischemic perconditioning (RIPER) is a new technique to lessen ischemia reperfusion (IR) injury. However, its effect in spontaneously hypertensive rats (SHRs) has not been investigated. The aim of the study was to examine the effect of RIPER in SHRs, to determine whether chronic treatment with Olmesartan could influence the effect of RIPER, and to examine whether the protective effect is related to HIF-1α, miR-21 and miR-210 expression.METHODS:Sixty SHRs were randomly divided into two groups:Vehicle group and Olmesartan group. In the vehicle group, SHRs received four-week-treatment of vehicle besides normal feed. In the Olmesartan group, SHRs received four-week-treatment of Olmesartan besides normal feed. Two groups of animals were then assigned to one of the three subgroups:sham group, IR group and RIPER group. In the sham group, the suture passed under the left anterior descending coronary artery (LAD) without being tightened. In the IR group, the LAD was ligated for 40 min followed by a 180 min reperfusion. In the RIPER group, SHRs underwent the same procedures as the IR group, with the exception that three cycles of 5 min ischemia/5 min reperfusion were applied on the left hind limb of SHRs using a tourniquet at the beginning of ischemia to induce RIPER.Left ventricular mass index (LVMI), creatine kinase (CK) concentration, heart rate during ischemia and reperfusion, arrhythmia score, infarct size, pathological changes, HIF-la mRNA expression, miR-21 expression and miR-210 expression were measured.RESULTS:Four-week-treatment of Olmesartan markedly reduced blood pressure and ameliorated left ventricular hypertrophy. CK concentration, infarct size and arrhythmia score during ischemia and reperfusion were comparable between the Vehicle-IR group and the Vehicle-RIPER group in vehicle-treated SHRs. The protective effect of RIPER was lost in SHRs.Compared to the Olmesartan-IR group, CK concentration, infarct size and arrhythmia score during reperfusion were significantly reduced in the Olmesartan-RIPER group in Olmesartan-treated SHRs. Olmesartan restored the protective effect of RIPER. Compared to Olmesartan-IR group, HIF-la expression, miR-21 expression and miR-210 expression were significantly elevated in the Olmesartan-RIPER group in Olmesartan-treated SHRs.CONCLUSION:Our experiment demonstrates for the first time that:1) the protective effect of RIPER is lost in SHRs and four-week-treatment of Olmesartan can restore the protective effect of RIPER,2) the recovery of protective effect of RIPER may be related to the upregulation of HIF-la expression and the upregulation of the two apoptosis-related microRNAs (miR-21 and miR-210).Part IIIThe effect of remote ischemic postconditioning against myocardial ischemia reperfusion injury in spontaneously hypertensive ratsOBJECTIVES:Remote ischemic postconditioning (RIPOST) is a new technique to lessen ischemia reperfusion (IR) injury. However, its effect in spontaneously hypertensive rats (SHRs) has not been investigated. The aim of the study was to examine the effect of RIPOST in SHRs, to determine whether chronic treatment with Olmesartan could influence the effect of RIPOST, and to examine whether the protective effect is related to HIF-la, miR-21 and miR-210 expression.METHODS:Sixty SHRs were randomly divided into two groups:Vehicle group and Olmesartan group. In the vehicle group, SHRs received four-week-treatment of vehicle besides normal feed. In the Olmesartan group, SHRs received four-week-treatment of Olmesartan besides normal feed. Two groups of animals were then assigned to one of the three subgroups:sham group, IR group and RIPOST group. In the sham group, the suture passed under the left anterior descending coronary artery (LAD) without being tightened. In the IR group, the LAD was ligated for 40 min followed by a 180 min reperfusion. In the RIPOST group, SHRs underwent the same procedures as the IR group, with the exception that three cycles of 5 min ischemia/5 min reperfusion were applied on the left hind limb of SHRs using a tourniquet at the beginning of reperfusion to induce RIPOST.Left ventricular mass index (LVMI), creatine kinase (CK) concentration, heart rate during ischemia and reperfusion, arrhythmia score, infarct size, pathological changes, HIF-1α mRNA expression, miR-21 expression and miR-210 expression were measured.RESULTS:Four-week-treatment of Olmesartan markedly reduced blood pressure and ameliorated left ventricular hypertrophy. CK concentration, infarct size and arrhythmia score during ischemia and reperfusion were comparable between the Vehicle-IR group and the Vehicle-RIPOST group in vehicle-treated SHRs. The protective effect of RIPOST was lost in SHRs.Compared to Olmesartan-IR group, CK concentration and infarct size were significantly reduced in the Olmesartan-RIPOST group in Olmesartan-treated SHRs. Arrhythmia score was comparable between the Olmesartan-IR group and the Olmesartan-RIPOST group. Compared to the Olmesartan-IR group, HIF-la expression, miR-21 expression and miR-210 expression were significantly elevated in the Olmesartan-RIPOST group in Olmesartan-treated SHRs.CONCLUSION:Our experiment demonstrates for the first time that: 1) the protective effect of RIPOST is lost in SHRs and four-week-treatment of Olmesartan can restore the protective effect of RIPOST, 2) the recovery of protective effect of RIPOST may be related to the upregulation of HIF-1α expression and the upregulation of the two apoptosis-related microRNAs (miR-21 and miR-210).Part IVThe effect of combined remote conditioning therapy against myocardial ischemia reperfusion injury in spontaneously hypertensive ratsOBJECTIVES:Remote ischemic perconditioning (RIPER) and remote ischemic postconditioning (RIPOST) are new techniques to lessen ischemia reperfusion (IR) injury. However, whether the combination of RIPER and RIPOST can protect myocardium against ischemia reperfusion injury in spontaneously hypertensive rats (SHRs) has not been investigated. The aim of the study was to examine whether the combination of RIPER and RIPOST can protect myocardium against ischemia reperfusion injury in SHRs, to examine whether there are further advantage in combined remote conditioning therapy, and to determine whether four-week-treatment with Olmesartan could influence the effect of the combined conditioning therapy.METHODS:One hundred SHRs were randomly divided into two groups:Vehicle group and Olmesartan group. In the vehicle group, SHRs received four-week-treatment of vehicle besides normal feed. In the Olmesartan group, SHRs received four-week-treatment of Olmesartan besides normal feed. Two groups of animals were then assigned to one of the five subgroups: sham group, IR group, RIPER group, RIPOST group and RIPER+RIPOST group. In the sham group, the suture passed under the left anterior descending coronary artery (LAD) without being tightened. In the IR group, the LAD was ligated for 40 min followed by a 180 min reperfusion. In the RIPER group, SHRs underwent the same procedure as the IR group, with the exception that three cycles of 5 min ischemia/5 min reperfusion were applied on the left hind limb of SHRs using a tourniquet at the beginning of ischemia to induce RIPER. In the RIPOST group, SHRs underwent the same procedure as the IR group, with the exception that three cycles of 5 min ischemia/5 min reperfusion were applied on the left hind limb of SHRs using a tourniquet at the beginning of reperfusion to induce RIPOST. In the RIPER+RIPOST group, SHRs underwent the same procedure as the IR group, with the exception that three cycles of 5 min ischemia/5 min reperfusion were applied on the left hind limb of SHRs using a tourniquet both at the beginning of ischemia and at the beginning of reperfusion to induce combined conditioning.Left ventricular mass index (LVMI), creatine kinase (CK) concentration, heart rate during ischemia and reperfusion, arrhythmia score, infarct size, pathological changes, HIF-1α mRNA expression, miR-21 expression and miR-210 expression were measured.RESULTS:Four-week-treatment of Olmesartan markedly reduced blood pressure and ameliorated left ventricular hypertrophy. CK concentration, infarct size and arrhythmia score during ischemia and reperfusion were comparable between the Vehicle-IR group, the Vehicle-RIPER group, the Vehicle-RIPOST group and the Vehicle-RIPER+RIPOST group in vehicle-treated SHRs. The protective effects of RIPER, RIPOST and RIPER+RIPOST were lost in SHRs.Compared to the Olmesartan-IR group, CK concentration and infarct size were significantly reduced in the Olmesartan-RIPER group, the Olmesartan-RIPOST group and the Olmesartan-RIPER+RIPOST group in Olmesartan-treated SHRs. However, CK concentration and infarct size were comparable between the Olmesartan-RIPER group, the Olmesartan-RIPOST group and the Olmesartan-RIPER+RIPOST group. Compared to the Olmesartan-IR group, HIF-la expression was significantly increased in the Olmesartan-RIPER group, the Olmesartan-RIPOST group and the Olmesartan-RIPER+RIPOST group in Olmesartan-treated SHRs. However, HIF-1α expression was comparable between the Olmesartan-RIPER group, the Olmesartan-RIPOST group and the Olmesartan-RIPER+RIPOST group. This may explain why combined remote conditioning therapy failed to further reduce CK concentration and infarct size in Olmesartan-treated SHRs.Compared to the Olmesartan-IR group, arrhythmia score was significantly reduced in the Olmesartan-RIPER group and the Olmesartan-RIPER+RIPOST group in Olmesartan-treated SHRs. Arrhythmia score was comparable between the Olmesartan-IR group and the Olmesartan-RIPOST group in Olmesartan-treated SHRs. Moreover, arrhythmia score was comparable between the Olmesartan-RIPER group and the Olmesartan-RIPER+RIPOST group. Because RIPOST failed to decrease arrhythmia score, the combined remote conditioning therapy failed to further ameliorate ventricular arrhythmias in Olmesartan-treated SHRs.Compared to the Olmesartan-IR group, miR-21 expression and miR-210 expression were significantly elevated in the Olmesartan-RIPER group, the Olmesartan-RIPOST group and the Olmesartan-RIPER+RIPOST group in Olmesartan-treated SHRs. Further, compared to the Olmesartan-RIPER group and the Olmesartan-RIPOST group, miR-21 expression and miR-210 expression were significantly up-regulated in the Olmesartan-RIPER+RIPOST group. The combined remote conditioning therapy shows its additive effect in inhibiting apoptosis by further regulating the expression of miR-21 and the expression of miR-210 in Olmesartan-treated SHRs.CONCLUSION:Our experiment demonstrates for the first time that:1) the protective effect of the combined remote conditioning therapy is lost in SHR and four-week-treatment of Olmesartan can restore the protective effect of the combined remote conditioning therapy,2) compared to RIPER and RIPOST, the combined remote conditioning therapy can not further decrease CK concentration, reduce infarct size and ameliorate ventricular arrhythmias in Olmesartan-treated SHRs, and 3) compared to RIPER and RIPOST, the combined remote conditioning therapy gains further advantage in inhibiting apoptosis in Olmesartan-treated SHRs, which may be related to the further upregulations of miR-21 expression and miR-210 expression.