Department of Anesthesiology, Medical Faculty and University Hospital Duesseldorf, Heinrich-Heine-University Duesseldorf, Moorenstr. 5, 40225 Duesseldorf, Germany.
Institute of Cardiovascular Physiology, Medical Faculty and University Hospital Duesseldorf, Heinrich-Heine-University Duesseldorf, Universitaetsstr. 1, 40225 Duesseldorf, Germany.
Int J Mol Sci. 2021 Nov 19;22(22):12471. doi: 10.3390/ijms222212471.
The osmodiuretic agent Mannitol exerts cardioprotection against ischemia and reperfusion (I/R) injury when applied as a pre- and/or postconditioning stimulus. Previously, we demonstrated that these properties are mediated via the activation of mitochondrial ATP-sensitive potassium (mK) channels. However, considering Mannitol remains in the extracellular compartment, the question arises as to which receptor and intracellular signaling cascades are involved in myocardial protection by the osmodiuretic substance. Protein kinase B (Akt) and G (PKG), as part of the reperfusion injury salvage kinase (RISK) and/or endothelial nitric oxide (eNOS)/PKG pathway, are two well-investigated intracellular targets conferring myocardial protection upstream of mitochondrial potassium channels. Adenosine receptor subtypes have been shown to trigger different cardioprotective pathways, for example, the reperfusion injury. Further, Mannitol induces an increased activation of the adenosine 1 receptor (A1R) in renal cells conferring its nephroprotective properties. Therefore, we investigated whether (1) Akt and PKG are possible signaling targets involved in Mannitol-induced conditioning upstream of the mK channel and/or whether (2) cardioprotection by Mannitol is mediated via activation of the A1R. All experiments were performed on male Wistar rats in vitro employing the Langendorff isolated heart perfusion technique with infarct size determination as the primary endpoint. To unravel possible protein kinase activation, Mannitol was applied in combination with the Akt (MK2206) or PKG (KT5823) inhibitor. In further groups, an A1R blocker (DPCPX) was given with or without Mannitol. Preconditioning with Mannitol (Man) significantly reduced the infarct size compared to the control group. Co-administration of the A1R blocker DPXPC fully abolished myocardial protection of Mannitol. Interestingly and in contrast to the initial hypothesis, neither administration of the Akt nor the PKG blocker had any impact on the cardioprotective properties of Mannitol-induced preconditioning. These results are quite unexpected and show that the protein kinases Akt and PKG-as possible targets of known protective signaling cascades-are not involved in Mannitol-induced preconditioning. However, the cardioprotective effects of Mannitol are mediated via the A1R.
渗透利尿剂甘露醇在缺血再灌注（I/R）损伤时作为预处理和/或后处理刺激发挥心脏保护作用。以前，我们证明这些特性是通过激活线粒体 ATP 敏感性钾 (mK) 通道介导的。然而，考虑到甘露醇仍存在于细胞外间隙，问题是渗透利尿剂物质通过哪种受体和细胞内信号级联发挥心肌保护作用。蛋白激酶 B (Akt) 和 G (PKG) 作为再灌注损伤挽救激酶 (RISK) 和/或内皮型一氧化氮合酶 (eNOS)/PKG 途径的一部分，是两个经过充分研究的细胞内靶点，在 mK 通道上游赋予心肌保护作用。已经表明，腺苷受体亚型可以触发不同的心脏保护途径，例如再灌注损伤。此外，甘露醇诱导肾细胞中腺苷 1 受体 (A1R) 的激活增加，从而发挥其肾脏保护特性。因此，我们研究了（1）Akt 和 PKG 是否是 mK 通道上游甘露醇诱导的调节的可能信号靶标，以及（2）甘露醇的心脏保护作用是否通过激活 A1R 介导。所有实验均在雄性 Wistar 大鼠体外进行，采用 Langendorff 离体心脏灌注技术，以梗死面积测定作为主要终点。为了揭示可能的蛋白激酶激活，将甘露醇与 Akt（MK2206）或 PKG（KT5823）抑制剂联合应用。在进一步的组中，给予 A1R 阻滞剂（DPCPX），并与或不与甘露醇一起给予。与对照组相比，甘露醇预处理显著减少了梗死面积。A1R 阻滞剂 DPXPC 的共同给药完全消除了甘露醇的心肌保护作用。有趣的是，与最初的假设相反，Akt 或 PKG 阻滞剂的给药对甘露醇诱导的预处理的心脏保护特性没有任何影响。这些结果出人意料，表明蛋白激酶 Akt 和 PKG——作为已知保护信号级联的可能靶标——不参与甘露醇诱导的预处理。然而，甘露醇的心脏保护作用是通过 A1R 介导的。
