Gadolinium limits myocardial infarction in the rat: dose-response, temporal relations and mechanisms

Abstract

The lanthanide cation, gadolinium (Gd) attenuates post-ischemic myocardial stunning. This study tests the hypothesis that Gd also preconditions the myocardium against infarction following ischemia-reperfusion (IR) and explores potential mechanisms underlying Gd-induced cardioprotection. Regional myocardial infarction was induced in rats by occluding the left anterior descending artery for 30 min and reperfusing for 120 min. Rats (n=6/group) were administered intravenous Gd (1 to 100 micromol/kg) 15 min prior to ischemia. Hearts were excised after reperfusion to determine infarct size (IS) and area at risk (AAR). The ratio IS/AAR (%) was reduced by Gd in a "U"-shaped, dose-dependent manner. The minimum dose that reduced IS/AAR was 5 micromol/kg (52+/-5% vs. 64+/-4%), while the dose that reduced IS/AAR maximally was 20 micromol/kg (44+/-4%). Gd also reduced IS/AAR when given 1 min before reperfusion (47+/-3%) but not when given 10 s after reperfusion (60+/-3%). Cardioprotection was maintained if IR was delayed 24-72 h after Gd administration. Cardioprotection by Gd was abolished by inhibition of JAK-2 with AG-490, of p42/44 MAPK with PD98059 or of K(ATP) channels with glibenclamide. None of these agents given alone altered IS/AAR compared with controls. Inhibition of JAK-2 also blocked Gd-induced delayed cardioprotection. Gd may have broad potential roles in IR, as it conferred immediate cardioprotection when given prior to ischemia or prior to reperfusion and delayed cardioprotection for up to 72 h after administration. The mechanism underlying Gd-induced preconditioning appears to be multi-factorial, involving JAK-2, STAT-3 and p44 MAPK pathways, as well as K(ATP) channels.

Figure 1

A. Dose-response studies of Gd immediate ischemic cardio-protection. Rats received Gd (1 to 100 μmol/kg IV) 15 minutes before ischemia. Infarct size was determined after 30 minutes of regional ischemia and 120 minutes of reperfusion. B. Phase of action of Gd. AAR, area at risk; IS, infarct size. Data are mean ± SD, n = 6/group. * = P < 0.05, Gd vs drug-free control.

Figure 2

Gd confers delayed ischemic cardio-protection. Rats (n = 6 per group) were treated with a single dose of Gd (20 μmol/kg) via the tail vein and allowed to recover 24–120 hours. Hearts were then isolated and subjected to 30 minutes regional myocardial ischemia and 180 minutes reperfusion with Gd excluded from the coronary perfusate. Open bars represent data from saline treated rats. Solid bars represent data from Gd treated rats. LVDP, left ventricular developed pressure. Bar graphs represent the mean ± SD. * P < 0.05, Gd vs saline-treated.

Figure 3

JAK-2 is required for immediate Gd ischemic cardio-protection. Rats were untreated or were administered Gd (20 μmol/kg) alone or in the presence of AG-490 (3 mg/kg) or received the inhibitor alone. Infarct size was determined after 30 minutes of regional ischemia and 120 minutes of reperfusion. Values are mean ± SD. * = P < 0.05 vs drug-free control.

Figure 4

Role of STAT in mediating protection by Gd. Western analysis of cell lysates from hearts demonstrates that Gd (20 μmol/kg) given before ischemia (Perfusion plus Gd) causes phosphorylation of STAT-3. Reperfusion in the absence of Gd (Reperfusion) also induces phosphorylation of STAT-3 (Tyr-705). Pre-ischemic treatment with Gd does not further increase reperfusion-induced phosphorylation of STAT-3 (Reperfusion plus Gd). Total STAT-3 results shown in lower panel. Bar graphs represent the mean ± SD. * P < 0.05, vs perfusion.

Figure 5

Involvement of JAK-2 in triggering delayed cardioprotection by Gd. Rats were pretreated with the JAK inhibitor AG-490 (3 mg/kg) or saline 15 min before Gd treatment (20 μmol/kg) and resistance to injury from IR determined 24–120 hours later. Infarct size and recovery of post-ischemic left ventricular developed pressure was determined after 30 minutes of regional ischemia and 120 minutes of reperfusion. Values are mean ± SD. * = P < 0.05 vs drug-free control.

Figure 6

Involvement of p42/44 MAPK in mediating protection by Gd. Rats were untreated or were administered Gd (20 μmol/kg) alone or in the presence of PD90859 (1mg/kg) or received the inhibitor alone. Infarct size was determined after 30 minutes of regional ischemia and 120 minutes of reperfusion. Values are mean ± SD. * = P < 0.05 vs untreated. Western analysis of cell lysates from hearts demonstrates that Gd (20 μmol/kg) does not increase phosphorylation of p42/44 MAPK before ischemia (Perfusion plus Gd). Reperfusion in the absence of Gd induces phosphorylation of p42/44 MAPK (Reperfusion). Gd further increases phosphorylation of p42/p44 MAPK during reperfusion (Reperfusion plus Gd). Total p42/44 MAPK results shown in lower panel. Bar graphs represent the mean ± SD. * P < 0.05, perfusion plus Gd vs perfusion. + P < 0.05, reperfusion plus Gd vs reperfusion.

Figure 7

Involvement of K_ATP channels in mediating protection by Gd. Rats were untreated or were administered Gd (20 μmol/kg) alone or in the presence of the K_ATP channel blocker glibenclamide (3 mg/kg) or received inhibitor alone. Infarct size was determined following 30 minutes of regional ischemia and 120 minutes of reperfusion. Values are mean ± SD. * P < 0.05 vs drug-free control.