MnSOD protects against COX1-mediated endothelial dysfunction in chronic heart failure

Abstract

Endothelial function is impaired by oxidative stress in chronic heart failure (HF). Mechanisms that protect against increases in oxidative stress in HF are not clear. The goal of this study was to determine whether manganese superoxide dismutase (MnSOD) plays a key role in protecting against endothelial dysfunction in HF. Endothelial function and gene expression were examined in aorta from wild-type mice (MnSOD(+/+)) and mice deficient in MnSOD (MnSOD(+/-)) 12 wk after ligation of the left coronary artery (LCA). LCA ligation produced similar size myocardial infarctions in MnSOD(+/+) and MnSOD(+/-) mice and reduced ejection fraction to approximately 20% in both groups. Maximal relaxation in response to acetylcholine was 78 +/- 3% (mean +/- SE) and 66 +/- 8% in sham-operated MnSOD(+/+) and MnSOD(+/-) mice, respectively. Expression of antioxidant enzymes increased in MnSOD(+/+) mice with HF, and maximal relaxation to acetylcholine was slightly impaired (68 +/- 4%). Greater endothelial dysfunction was observed in MnSOD(+/-) mice with HF (46 +/- 5%, P < 0.05), which was significantly improved by polyethylene glycol-catalase but not Tempol. Incubation with the nonspecific cyclooxygenase (COX) inhibitor indomethacin or the COX1 inhibitor valeryl salicylate, but not the COX-2 inhibitor NS-398, significantly improved relaxation to acetylcholine in HF mice (maximum relaxation = 74 +/- 5, 91 +/- 1, and 58 +/- 5%). These data suggest that MnSOD plays a key role in protecting against endothelial dysfunction in HF. A novel mechanism was identified whereby chronic increases in oxidative stress, produced by mitochondrial SOD deficiency, impair vascular function via a hydrogen peroxide-dependent, COX1-dependent, endothelium-derived contracting factor.

Fig. 1.

Expression of antioxidant genes (A–F), prooxidant genes (G–I), and nitric oxide synthase (NOS) isoforms (J–L) in wild-type (WT) and manganese superoxide dismutase (MnSOD)-deficient mice with or without heart failure (HF). Note that the compensatory increases in antioxidant enzymes (A–F) that occur in WT mice with HF are abolished in MnSOD-deficient mice with HF. Also, only endothelial nitric oxide synthase (eNOS) was significantly increased in WT mice with HF. Values are means ± SE; n = 7–15 mice/group. *P < 0.05. HET, MnSOD-deficient (+/−) mice; CuZnSOD, copper-zinc superoxide dismutase; ecSOD, extracellular SOD; GPx, glutathione peroxidase; Nox, NAD(P)H oxidase; iNOS, inducible NOS; nNOS, neuronal NOS; CHF, chronic HF.

Fig. 2.

Vasomotor function in WT and MnSOD-deficient (MnSOD^+/−) mice with or without HF. A: responses to acetylcholine (ACh). B: vascular responses to sodium nitroprusside (SNP). C: responses to prostaglandin F_2α (PGF_2α). Note that vasorelaxation in response to acetylcholine is relatively well preserved in WT mice with HF but profoundly impaired in MnSOD-deficient mice. BL, baseline. *P < 0.05 vs. sham-operated MnSOD-deficient mice; n = 7–15 mice/group.

Fig. 3.

Effects of Tempol (an antioxidant) or polyethylene glycol (PEG)-catalase (CAT) on vascular function in WT and MnSOD-deficient mice with or without HF. A and C: effects of Tempol or PEG-catalase on responses to acetylcholine in sham-operated and HF WT mice. B and D: effects of Tempol or PEG-catalase on vascular responses to acetylcholine in sham-operated and HF MnSOD-deficient mice. Tempol did not improve vascular function in vessels from WT mice and only improved relaxation in response to acetylcholine in sham-operated, MnSOD-deficient mice. PEG-catalase significantly improved vascular function only in MnSOD-deficient mice with HF. *P < 0.05 vs. vessels without antioxidants; n = 7–12 mice/group.

Fig. 4.

Effects of indomethacin (INDO; an inhibitor of cyclooxygenase 1 and 2) on responses to acetylcholine in WT (A) and MnSOD-deficient (B) mice with or without HF. Note that preincubation with indomethacin significantly improved responses to acetylcholine only in MnSOD-deficient mice with HF. *P < 0.05 vs. MnSOD-deficient HF group; n = 6–10/group.

Fig. 5.

Effects of valeryl salicylate [VS, a cyclooxygenase (COX) 1 inhibitor; A] or NS-398 (a COX2 inhibitor; B) on responses to acetylcholine in WT or MnSOD-deficient mice with HF. C: expression of cyclooxygenase-1 in WT and MnSOD-deficient mice with and without HF. D: expression of cyclooxygenase-2 in WT and MnSOD-deficient mice with and without HF. Only valeryl salicylate, which blocks cyclooxygenase-1, improved responses to acetylcholine in MnSOD-deficient mice with HF. *P < 0.05 vs. HF + vehicle within each panel; n = 5–7/group.