Chronic intermittent hypobaric hypoxia protects the heart against ischemia/reperfusion injury through upregulation of antioxidant enzymes in adult guinea pigs

Abstract

Aim: To investigate the protection and the anti-oxidative mechanism afforded by chronic intermittent hypobaric hypoxia (CIHH) against ischemia/reperfusion (I/R) injury in guinea pig hearts.

Methods: Adult male guinea pigs were exposed to CIHH by mimicking a 5000 m high altitude (p(B)=404 mmHg, p(O2)=84 mmHg) in a hypobaric chamber for 6 h/day for 28 days. Langendorff-perfused isolated guinea pig hearts were used to measure variables of left ventricular function during baseline perfusion, ischemia and the reperfusion period. The activity and protein expression of antioxidant enzymes in the left myocardium were evaluated using biochemical methods and Western blotting, respectively. Intracellular reactive oxygen species (ROS) were assessed using ROS-sensitive fluorescence.

Results: After 30 min of global no-flow ischemia followed by 60 min of reperfusion, myocardial function had better recovery rates in CIHH guinea pig hearts than in control hearts. The activity and protein expression of superoxide dismutase (SOD) and catalase (CAT) were significantly increased in the myocardium of CIHH guinea pigs. Pretreatment of control hearts with an antioxidant mixture containing SOD and CAT exerted cardioprotective effects similar to CIHH. The irreversible CAT inhibitor aminotriazole (ATZ) abolished the cardioprotection of CIHH. Cardiac contractile dysfunction and oxidative stress induced by exogenous hydrogen peroxide (H(2)O(2)) were attenuated by CIHH and CAT.

Conclusions: These data suggest that CIHH protects the heart against I/R injury through upregulation of antioxidant enzymes in guinea pig.Acta Pharmacologica Sinica (2009) 30: 947-955; doi: 10.1038/aps.2009.57; published online 22 June 2009.

Figure 1

Effects of CIHH on antioxidant enzyme activity and MDA concentration in guinea pig hearts. SOD, superoxide dismutase; CAT, catalase; GPX, glutathione peroxidase; MDA, malondialdehyde; non-CIHH, control group; CIHH, chronic intermittent hypobaric hypoxia group; baseline, pre-ischemia; I/R, 60 min after reperfusion. n=6. Values represent the means±SEM. ^cP<0.01 vs corresponding baseline values; ^fP<0.01 vs the corresponding non-CIHH group.

Figure 2

Effects of CIHH on the protein expression of SOD-1, SOD-2, and CAT in the left ventricle. SOD, superoxide dismutase; CAT, catalase. Top: representative lanes of a Western blot for SOD-1 (A), SOD-2 (B), or CAT (C). Bottom: densitometric analysis of SOD-1, SOD-2, and CAT bands normalized to β-actin. non-CIHH, control group; CIHH, chronic intermittent hypobaric hypoxia group; baseline, pre-ischemia; I/R, 60 min after reperfusion. n=5. Values represent the means±SEM. ^eP<0.05, ^fP<0.01 vs the corresponding non-CIHH group.

Figure 3

Effects of CIHH on H₂O₂-induced oxidative stress in isolated cardiac myocytes. CAT, catalase; ATZ, aminotriazole; CON1, non-CIHH group; CON1+CAT, CON1+CAT group; (3) CON1+ATZ, CON1+ATZ group; CIHH1, CIHH group; CIHH1+ATZ, CIHH1+ATZ group. Myocytes were subjected to H₂O₂-induced injury using a protocol of 10 min baseline perfusion, followed by 10 min of H₂O₂ treatment. The myocytes in the CON1+CAT group were treated with CAT (100 U/mL) for 5 min before and 10 min during H₂O₂ treatment. Aminotriazole was administered intraperitoneally to the guinea pig 1 h before isolation of the heart in the CON1+ATZ and CIHH1+ATZ groups. (A) Fluorescent intensity changes in cardiac myocytes exposed to H₂O₂ (10 min). (B) The bar graph shows the fluorescent intensity that represents the ratio of (FI-FI₀)/FI₀. n=18, from 3–4 different hearts. Values represent the means±SEM. ^cP<0.01 vs the CON1 group; ^fP<0.01 vs the CIHH1 group.