Pharmacological Modulation by Low Molecular Weight Heparin of Purinergic Signaling in Cardiac Cells Prevents Arrhythmia and Lethality Induced by Myocardial Infarction

Figure 1. (A) ECG recording of animals submitted to the CIR without treatment with ENOX; (B) ECG recording of animals submitted to the CIR under treatment with ENOX, intravenously, immediately before performing cardiac ischemia due to occlusion of the left descending coronary artery. AV = Ventricular arrhythmia; AVB = Atrioventricular block; CIR = Cardiac ischemia and reperfusion.

Figure 2. Incidence of (A) ventricular arrhythmias (VA); (B) atrioventricular block (AVB) and (C) lethality (LET) in the SHAM, CIR + SS, CIR + ENOX, CIR + PROB, CIR + PROB + ENOX, and CIR + DPCPX + ENOX groups. The results are expressed as percentage frequencies and compared with Fisher’s exact test (* p < 0.05). VA, AVB, and LET were not observed in the SHAM group. ENOX did not reduce the incidence of VA when compared with the control CIR + SS group but did significantly reduce AVB and LET incidence. Disruption of the extracellular cAMP-ADO pathway with either PROB or DPCPX abolished the cardioprotective effect of ENOX on AVB and LET. Treatment with either PROB or DPCPX alone had no effect on mortality. CIR + SS = cardiac ischemia and reperfusion group treated with saline solution; CIR + ENOX = cardiac ischemia and reperfusion group treated with enoxaparin; CIR + PROB = cardiac ischemia and reperfusion group treated with probenecid 5 min before CIR; CIR + PROB + ENOX = cardiac ischemia and reperfusion group treated with probenecid 5 min before treatment with enoxaparin, administered immediately before CIR; CIR + DPCPX + ENOX = cardiac ischemia and reperfusion group treated with DPCPX 5…

Figure 3. Serum concentration of CPK (A), and CK-MB (B) in the CIR + SS, CIR + ENOX, CIR + PROB, CIR + PROB + ENOX, and CIR + DPCPX + ENOX groups. The results are expressed as mean ± standard deviation of the mean, and analysis of variance (ANOVA) was applied, followed by the Tukey post-test (* p < 0.05). Serum levels of biochemical markers of cardiac injury in the SHAM group were lower than in the other groups, both CPK and CK-MB. CIR + SS = cardiac ischemia and reperfusion group treated with saline solution; CIR + ENOX = cardiac ischemia and reperfusion group treated with enoxaparin; CIR + PROB = cardiac ischemia and reperfusion group treated with probenecid 5 min before induction of CIR; CIR + PROB + ENOX = cardiac ischemia and reperfusion group treated with probenecid 5 min before treatment with enoxaparin, administered immediately before induction of CIR; CIR + DPCPX + ENOX = cardiac ischemia and reperfusion group treated with DPCPX 5 min before treatment with enoxaparin, administered immediately before induction of CIR.

Figure 4. Molecular mechanisms involved in enoxaparin (ENOX) regulation of cardiac cell function. ENOX acts on the intracellular production and efflux of second-messenger cAMP, which is later transformed by extracellular enzymes into adenosine (ADO), which in turn is an antiarrhythmic through the activation of A1R receptors. ENOX stimulates the Na+-Ca2+ exchanger (NCX) and, therefore, reduces cytosolic calcium in cardiac cells. In addition, ENOX is also able to block voltage-gated calcium channels, which also causes a decrease in cytosolic calcium. This reduction in cytosolic calcium in cardiomyocytes increases intracellular levels of cAMP through the activation of adenylate cyclase (AC), a membrane enzyme. cAMP activates PKA, which phosphorylates L-type Cav (L-Cav), resulting in increased Ca2+ influx with positive chronotropic and inotropic responses. The increase in intracellular cAMP stimulates the transport of cAMP to the extracellular medium through the MRP4 ABC transporter. In the extracellular environment, cAMP is converted to ADO due to the enzymatic action of ectophosphodiesterases (EPDE) and ectonucleotidaeses (ENT). This purinergic signaling involves the action of ADO on A1R…