Exercise provides direct biphasic cardioprotection via manganese superoxide dismutase activation

Abstract

Epidemiologic investigations have shown that exercise reduces morbidity and mortality from coronary artery disease. In this study, using a rat model, we attempted to determine whether exercise can reduce ischemic injury to the heart and elucidate a mechanism for the cardioprotective effect of exercise. Results showed that exercise significantly reduced the magnitude of a myocardial infarction in biphasic manner. The time course for cardioprotection resembled that of the change in manganese superoxide dismutase (Mn-SOD) activity. The administration of the antisense oligodeoxyribonucleotide to Mn-SOD abolished the expected decrease in infarct size. We showed that the level of tumor necrosis factor alpha (TNF-alpha) and interleukin 1beta (IL-1beta) increased after exercise. The simultaneous administration of the neutralizing antibodies to the cytokines abolished the exercise-induced cardioprotection and the activation of Mn-SOD. Furthermore, TNF-alpha can mimic the biphasic pattern of cardioprotection and activation of Mn-SOD. An antioxidant completely abolished cardioprotection and the activation of Mn-SOD by exercise or the injection of TNF-alpha as well as exercise-induced increase in TNF-alpha and IL-1beta. The production of reactive oxygen species and endogenous TNF-alpha and IL-1beta induced by exercise leads to the activation of Mn-SOD, which plays major roles in the acquisition of biphasic cardioprotection against ischemia/reperfusion injury in rats.

Figure 1

Effect of exercise on the size of the myocardial infarct (top) and the activity (center) and content (bottom) of Mn-SOD. Rats were subjected to occlusion of the LCA followed by reperfusion at 0.5, 3, 24, 36, 48, 60, and 72 h after exercise. C, sham-treated control 0.5 h after sham treatment. Top, the size of the infarct was evaluated 48 h after reperfusion. The size of the area of myocardial infarct (the area without TTC staining) was expressed as a percentage of the ischemic area at risk (the area without Evans blue dye); n = 9–10. Center, Mn-SOD activity in the myocardial tissue was examined between 0.5 and 72 h after one session of exercise. Mn-SOD activity divided by total protein content is shown; n = 3–4. Bottom, Mn-SOD content in myocardial tissue was examined between 0.5 and 72 h after one trial of exercise. Mn-SOD content divided by total protein content is shown; n = 3–4. Data are expressed as mean ± SEM; *P < 0.05 vs. sham-treated control by one-way ANOVA with Bonferroni's post hoc test for multiple comparisons.

Figure 2

Effects of ASODN to Mn-SOD on the size of the myocardial infarct (top) and the activity (center) and content (bottom) of MnSOD. SODN, ASODN, or scrambled ODN to Mn-SOD were injected intraperitoneally into rats just after exercise (EX). In 48 h, rats were subjected to occlusion of the LCA for 20 min, followed by reperfusion for 48 h. The size of the myocardial infarct was measured after reperfusion (n = 6–10). The activity and content of Mn-SOD (n = 4–5) was evaluated 48 h after exercise. C 48h, sham-treated control 48 h after sham treatment. Data are expressed as mean ± SEM; *P < 0.05 vs. sham-treated control; ⁺ P < 0.05 vs. without ASODN by one-way ANOVA with the Bonferroni's post hoc test for multiple comparisons.

Figure 3

Time course of myocardial levels of TNF-α (top) and IL-1β (bottom) after exercise. After exercise, the myocardial levels of TNF-α and IL-1β were measured with an ELISA (○). Increases in TNF-α and IL-1β were neutralized by their respective antibodies (•). MPG abolished the increases in TNF-α and IL-1β related to exercise (▪). C, sham-treated control just after sham treatment. Data are expressed as mean ± SEM; n = 3–4. *P < 0.05 vs. sham-treated control (C); ⁺ P < 0.05 vs. without antibody or MPG by one-way ANOVA with Bonferroni's post hoc test for multiple comparisons.

Figure 4

Effects of anti–TNF-α and anti–IL-1β antibodies on infarct size (top) and Mn-SOD activity (bottom). Anti-murine TNF-α and/or anti-murine IL-1β antibodies were infused intraperitoneally 30 min before exercise. 0.5 or 48 h after exercise (EX), rats were subjected to occlusion of the LCA followed by reperfusion. C 0.5h and C 48h indicate sham-treated control 0.5 and 48 h after sham treatment, respectively. The size of the myocardial infarct was measured 48 h after reperfusion (n = 6–10). The activity of Mn-SOD (n = 4–5) was evaluated 0.5 or 48 h after exercise. Data are expressed as mean ± SEM; *P < 0.05 vs. corresponding sham-treated control; ⁺ P < 0.05 vs. without the antibodies by one-way ANOVA with Bonferroni's post hoc test for multiple comparisons.

Figure 5

Effects of TNF-α on size of myocardial infarct (top) and activity of Mn-SOD (bottom). After the intravenous injection of  rTNF-α, rats were subjected to LCA occlusion followed by reperfusion at the times indicated. Infarct size was evaluated 48 h after reperfusion (n = 7–9). The activity of Mn-SOD was measured at the indicated times after TNF-α administration (n = 4). C, untreated control 0.5 h after vehicle (saline) injection. Data are expressed as mean ± SEM; *P < 0.05 vs. control (C) by one-way ANOVA with Bonferroni's post hoc test for multiple comparisons.

Figure 6

Effects of MPG on size of infarct (top) and activity of Mn-SOD (bottom). MPG was infused intraperitoneally 10 min before a 20-min exercise period or 30 min before the injection of TNF-α. At 30 min and 48 h after exercise (EX) or the injection of TNF-α, rats were subjected to occlusion of the LCA for 20 min, followed by reperfusion for 48 h. The size of the infarct was then evaluated (n = 7–9). The activity of Mn-SOD was measured 0.5 and 48 h after exercise or the injection of TNF-α (n = 4). C 0.5h and C 48h indicate sham-treated control 0.5 and 48 h after sham treatment, respectively. Both controls received vehicle (saline) injection. There were no differences in the size of myocardial infarct or Mn-SOD activity between the untreated and sham-treated control rats. Data are expressed as mean ± SEM; *P < 0.05 vs. corresponding sham-treated control; ⁺ P < 0.05. vs. without MPG by one-way ANOVA with Bonferroni's post hoc test for multiple comparisons.