Angiotensin II Receptor Blocker Reduces Oxidative Stress and Attenuates Hypoxia-Induced Left Ventricular Remodeling in Apolipoprotein E–Knockout Mice

1219 Hypertens Res Vol.30 (2007) No.12 p.1219-1230 Original Article Angiotensin II Receptor Blocker Reduces Oxidative Stress and Attenuates HypoxiaInduced Left Ventricular Remodeling in Apolipoprotein E–Knockout Mice Chika YAMASHITA1), Tetsuya HAYASHI2), Tatsuhiko MORI2), Naoko TAZAWA1), Chol-Jun KWAK1), Daisuke NAKANO1), Koichi SOHMIYA2), Yoshikatsu OKADA3), Yasushi KITAURA2), and Yasuo MATSUMURA1) Elevated superoxide formation in cardiac extracts of apolipoprotein E–knockout (apoE-KO) mice has been reported. In addition, we previously reported that hypoxia increased oxidative stress in the aortas of apoEKO mice, although we did not examine the effect of hypoxia on the heart. The aim of this study was to investigate the effect of chronic hypoxia on the left ventricular (LV) remodeling in apoE-KO mice treated with or without an angiotensin II receptor blocker. Male apoE-KO mice (n = 83) and wild-type mice (n = 34) at 15 weeks of age were kept under hypoxic conditions (oxygen, 10.0 ± 0.5%) and treated with olmesartan (3 mg/ kg/day) or vehicle for 3 weeks. Although LV pressure was not changed, hypoxia caused hypertrophy of cardiomyocytes and increased interstitial fibrosis in the LV myocardium. Furthermore, nuclear factor-κB (NF-κB) and matrix metalloproteinase (MMP)-9 activities were increased in apoE-KO mice exposed to chronic hypoxia. Olmesartan effectively suppressed the 4-hydroxy-2-nonenal protein expression and NF-κB and MMP-9 activities, and preserved the fine structure of the LV myocardium without affecting the LV pressure. In conclusion, olmesartan reduced oxidative stress, and attenuated the hypoxia-induced LV remodeling, in part through the inhibition of NF-κB and MMP-9 activities, in apoE-KO mice. (Hypertens Res 2007; 30: 1219–1230) Key Words: hypoxia, oxidative stress, apolipoprotein E, heart, angiotensin II receptor blocker Introduction Hypoxic stress can be induced by chronic obstructive pulmonary disease (COPD) and sleep apnea syndrome. Both COPD and sleep apnea have been known to increase the risk of cardiovascular disease (1, 2). In addition, several studies have shown that intermittent hypoxia due to sleep apnea has an association with left ventricular (LV) dysfunction (3, 4). The LV remodeling, accompanied by hypertrophy of cardiomyo- cytes and interstitial fibrosis, is a contributory factor in the progression to heart failure (5). On the other hand, sleep apnea has been reported to contribute to hypercholesterolemia (6–8), and abnormalities in lipid regulation that occur in response to hypoxia may also act to increase the cardiovascular risk. Recently, several studies have explored the relation of the apolipoprotein E (apoE) genotype to obstructive sleep apnea, with conflicting results. Among the middle-aged adult patients in the Wisconsin Sleep Cohort Study and the Sleep From the 1)Osaka University of Pharmaceutical Sciences, Takatsuki, Japan; and 2)Department of Internal Medicine III and 3)Department of Pathology, Osaka Medical College, Takatsuki, Japan. Address for Reprints: Tetsuya Hayashi, M.D., Ph.D., Department of Internal Medicine III, Osaka Medical College, 2–7 Daigakumachi, Takatsuki 569– 8686, Japan. E-mail: Received February 14, 2007; Accepted in revised form June 29, 2007. Hypertens Res Vol. 30, No. 12 (2007) A B Body Weight (g) 30 ** 25 ** 20 15 10 5 0 (8) (9) (17) (20) (20) ARB Heart / Body Weight (mg/g) 1220 7 ** 6 ## 5 4 3 2 1 0 (8) (9) (17) (20) (20) ARB ia xia xia xia ox mo po po rm r y y o o h h n n ia xia xia xia ox mo po po r rm y y o o h h n n Wild-type Wild-type ApoE-KO ApoE-KO Fig. 1. Effect of hypoxia on the body weight and the ratio of heart weight to body weight (Hw/Bw). A: Hypoxia significantly decreased the body weight in both wild-type and apolipoprotein E–knockout (apoE-KO) mice. Treatment with an angiotensin II receptor blocker (ARB) had no effect on body weight. B: Hypoxia did not change the Hw/Bw in wild-type mice. However, the Hw/Bw was significantly increased in apoE-KO mice exposed to hypoxia, and this increase was suppressed by treatment with an ARB. Columns and bars represent the mean ± SEM. †p< 0.05, and ††p< 0.01 vs. normoxic wild-type mice. §§p< 0.01 vs. hypoxic wild-type mice. **p< 0.01, and ##p< 0.01 vs. normoxic and hypoxic apoE-KO mice, respectively. Table 1. Effect of Hypoxia on Right and Left Ventricular Systolic Pressure and Plasma Low-Density Lipoprotein (LDL) Wild-type apoE-KO Normoxia Hypoxia Normoxia Hypoxia Hypoxia+ARB n RVsys (mmHg) LVsys (mmHg) 6 22 ± 2 99 ± 4 6 72 ± 5†† 95 ± 3 6 23 ± 2§§ 96 ± 4 10 59 ± 8††,** 98 ± 3 5 40 ± 3§ 95 ± 9 n LDL (mg/dL) 10 6.6 ± 0.3 10 14.1 ± 1.3 16 87.7 ± 8.6††,§§ 15 148.5 ± 13.4††,§§,** 13 106.2 ± 22.3††,§§ Values are means ± SEM. RVsys and LVsys, right and left ventricular systolic pressure respectively. ††p < 0.01 vs. normoxic wild-type mice. §p < 0.05, §§p < 0.01 vs. hypoxic wild-type mice. **p < 0.01 vs. normoxic apoE-KO mice. Heart Health Study, the presence of an apoE ε4 allele was associated with increased risk of obstructive sleep apnea, although no such association was observed in a group of Finnish sleep apnea patients (9–11). On the other hand, the Cleveland Family Study found evidence suggesting a linkage to the apnea-hypopnea index in a region of chromosome 19 that includes the apoE gene (12). We previously reported that chronic hypoxia accelerated the progression of atherosclerosis in apoE-knockout (apoEKO) mice (13), accompanied by significant increases of oxidative stress and matrix metalloproteinase (MMP)-9 activity in aortic tissues. However, the effect of hypoxia on the heart was not examined, and the role of apoE in cardiac function remains obscure. Wu et al. have suggested that apoE might play an important role in modulating LV hypertrophy (14). In addition, the ratio of heart weight to body weight (Hw/Bw) is significantly increased, and superoxide formation, which might induce cardiac remodeling, is elevated in cardiac extracts in apoE-KO mice (15, 16). On the other hand, increased MMP activities as well as oxidative stress might contribute to the development of LV remodeling. MMP activities are regulated through a number of pathways, including reactive oxygen species (ROS) (17) and nuclear factor-κB (NF-κB) (18). NF-κB activation plays an important role in the hypertrophic response of cardiomyocytes (19, 20). Angiotensin II receptor blockers (ARBs) are widely known to exert protective effects against heart failure. Harada et al. demonstrated that angiotensin II type 1 (AT1) receptor signal- Yamashita et al: Hypoxia-Induced Remodeling in ApoE-KO Mice 1221 Fig. 2. Representative light micrographs of the left ventricular (LV) myocardium in wild-type (A, B, a, b) and apolipoprotein E– knockout (apoE-KO) mice (C–E, c–e). The histology of wild-type and apoE-KO mice kept under normoxia looks normal (A, C, a, c). Although hypoxia showed little effect on wild-type mice (B, b), disarran (...truncated)