(Hypertension. 2004;43:1214.)
© 2004 American Heart Association, Inc.
Scientific Contributions |
From the Departments of Cardiovascular Medicine (M.S., K.T., N.I.,Y.H, R.N.), Urology (H.N.), Metabolic Diseases (J.O., S.I.), University of Tokyo Graduate School of Medicine, Japan; Division of Endocrinology and Metabolism (S.I.), Department of Medicine, Jichi Medical School, Tochigi, Japan; and PRESTO (M.S.), Japan Science and Technology Agency, Kawaguchi, Saitama, Japan.
Correspondence to Dr Masataka Sata, Department of Cardiovascular Medicine, University of Tokyo Graduate School of Medicine, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. E-mail msata-circ{at}umin.ac.jp
| Abstract |
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Key Words: cholesterol atherosclerosis nitric oxide circulation
| Introduction |
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3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors, or statins, are widely used to lower cholesterol levels. Large trials have demonstrated that statins reduce the mortality and the incidence of cardiovascular events.4 Statins possess lipid-independent benefits, including improvement of endothelial function, inhibition of inflammation, and reduction of myocardial or cerebral infarction size.5 It is reported that statins promote angiogenesis in response to ischemia in normocholesterolemic animals.6,7 Although these studies raised clinical enthusiasm because statins could be used for therapeutic angiogenesis, there remains a concern that statins may promote tumors, diabetic retinopathy, and atherosclerosis by stimulating neovascularization.2 Therefore, our studies were designed to examine the effects of stains on physiological and pathological angiogenesis in the same animal.
| Methods |
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Tumor Implantation Model
The 2x107 murine syngeneic colon cancer cells (CMT93, American Type Culture Collection, Rockville, Md) were inoculated into the left flank fold of C57BL/6J mice, whose right femoral arteries had been excised on the same day.9 Blood perfusion of the tumor was assessed using an LDPI system and expressed as the ratio of perfusion in the tumor versus that in the navel. At 5 weeks, tumors were excised and fixed in methanol. Capillaries were identified by positive staining for CD31 and morphology.7
Cell Proliferation Assay In Vitro
CMT93 cells were maintained in Dulbecco modified eagle medium and synchronized in 0.1% fetal bovine serum (FBS) for 72 hours. Cells were then stimulated to proliferate for 36 hours with 10% FBS in the presence of cerivastatin as indicated. DNA content was analyzed by flow cytometry (EPICS XL; Beckman Coulter, Fullerton).10 MTS assay was performed as described.11
Analysis of Atherosclerotic Lesions
ApoE/ mice were fed a western-type diet (0.15% cholesterol, 15% butter) for 5 weeks after induction of hind limb ischemia. Lipid deposition was quantified by en face aorta analysis as previously described.12 The effect of statins on endothelium-dependent vasodilatation of atherosclerotic lesions was evaluated by relaxation of aortic rings in response to acetylcholine.7 Eighteen-week-old wild-type or ApoE/ mice were treated with either saline or cerivastatin (6 mg/kg per day, subcutaneous) for 7 days, and the thoracic aortas were excised. Relaxation of the aortic rings in response to acetylcholine was monitored.7
Statistics
All data are expressed as the mean value±SEM. Statistical comparisons of means were performed by ANOVA followed by Student t test. P<0.05 was considered to be statistically significant.
| Results |
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To elucidate the mechanism by which cerivastatin inhibits tumor growth without affecting tumor-associated angiogenesis, direct effect of statins on cancer cell proliferation was investigated in vitro. When the cancer cells were stimulated to proliferate in the presence of high serum, DNA content analysis revealed that cerivastatin decreased the number of cells in S or G2/M phase (control, G1: 44.6%±0.5%, S: 31.05±3.8%, G2/M: 24.4%±3.6%; 10 µmol/L cerivastatin, G1: 63.3%±3.9%, S: 13.3%±2.6%, G2/M: 23.4%±6.3%) (Figure 2A). Cerivastatin also inhibited proliferation of CMT93 cells in a dose-dependent manner as determined by total cell number (Figure 2B) and MTS assay (Figure 2C). These results suggest that direct inhibitory effects of statins on cell proliferation may mediate, at least in part, their antitumor effects.
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Effects of Statins on Collateral Growth and Atherosclerotic Lesion Progression in Hyperlipidemic Mice
Eight-week-old ApoE/ male mice were fed a western-type diet and treated with saline or cerivastatin. After 1 week, we generated hind limb ischemia in the mice. Cerivastatin significantly enhanced recovery of blood flow after acute ischemia (Figure 3A). Although there was no significant difference in the number of angiographically visible collateral vessels at 5 weeks (Figure 3B), anti-CD31 immunostaining revealed that cerivastatin significantly increased the density of histologically detectable capillaries in the ischemic leg (saline, 464±68/mm2; cerivastatin, 630±287/mm2) (Figure 3C). Consistent with previous reports,13 there was no significant difference in the lipid profile between the mice treated with saline and those treated with cerivastatin (total cholesterol, 630±64 versus 470±53 mg/dL; triglycerides, 84±17 versus 51±11 mg/dL; HDL cholesterol, 15±2 versus 11±1 mg/dL). However, cerivastatin markedly inhibited atherosclerotic progression (Figure 3D). The number of vessels in atherosclerotic lesions at the aortic root (Figure 3E) was significantly smaller in the mice treated with cerivastatin than that in the mice treated with saline (saline, 44.6±7.0/mm2; cerivastatin, 31.3±3.5/mm2) (Figure 3F).
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Nine-week-old male ApoE/ mice were treated with vehicle or pitavastatin (1 mg/kg per day or 10 mg/kg per day) every day by gavage and fed a western-type diet. After 3 weeks, hind limb ischemia was generated. There was no significant difference in the lipid profile among the mice treated with vehicle or pitavastatin (Table). Low-dose pitavastatin (1 mg/kg per day), but not high-dose pitavastatin (10 mg/kg per day), significantly accelerated recovery of blood flow in the ischemic hind limb (Figure 4A). Histological examination revealed that low-dose pitavastatin increased capillary density in the ischemic muscle at 5 weeks (Figure 4B). En face aorta analysis revealed that pitavastatin significantly inhibited atherosclerotic lesion progression (Figure 4C). Interestingly, beneficial effects of pitavastatin on both collateral growth and atherosclerosis were attenuated at a higher dose.
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Dose-dependent effect of statins on ischemia-induced collateral formation was also investigated by oral administration of fluvastatin, one of the wildly prescribed statins. Adult male 24- to 36-week-old C57/BL6J mice were treated with vehicle or fluvastatin (5 mg/kg per day or 20 mg/kg per day) every day by gavage. After 3 weeks, hind limb ischemia was generated. Histological examination revealed that fluvastatin increased capillary density in the ischemic muscle at 5 weeks (Figure 5A). Consistent with the findings with pitavastatin, lower-dose fluvastatin (5 mg/kg per day) was more effective than high-dose fluvastatin (20 mg/kg per day) in promoting neovascularization. Next, atheroprotective effect of low-dose fluvastatin was evaluated in 8-week-old female ApoE/ mice. After 16 weeks, en face aorta analysis revealed that low-dose fluvastatin significantly inhibited atherosclerotic lesion formation (Figure 5B). Taken together, these results suggest that statins can inhibit atherosclerotic lesion formation at low doses that promote ischemia-induced collateral vessel growth.
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Effect of Statins on Endothelium-Dependent Relaxation of Atherosclerotic Lesions
To obtain insights into the mechanism by which statins augment collateral growth in response to ischemia without accelerating the development of cancer and atherosclerosis, we evaluated the effect of statins on endothelium-dependent vasodilatation of atherosclerotic lesions (Figure 6). Compared with the aortas taken from age-matched wild-type C57BL/6 mice, endothelium-dependent vasorelaxation was markedly impaired in aortas of ApoE/ mice treated with saline. Cerivastatin treatment partially restored the endothelium-dependent relaxation of atherosclerotic aortas.
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| Discussion |
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There is a large body of clinical evidence that statin therapy suppresses atherosclerotic lesion progression, even in patients with normal cholesterol level.4 In this study, statins inhibited atherosclerotic lesion progression without significantly affecting circulating cholesterol level. Neovascularization in atheroma was significantly inhibited, whereas collateral vessel development was enhanced by statins in the ischemic muscles of the same animal. Statin therapy partially restored impaired endothelial function of atherosclerotic vessel wall. Most likely, statins inhibit atherosclerotic lesion development by their pleiotropic effects.4 The decrease in capillary density in atheroma appears to be secondary to inhibition of lesion formation by statin therapy.
To explain the puzzling effects of statins on physiological and pathological angiogenesis, it was proposed that stains have a biphasic dose-dependent effect on angiogenesis, ie, proangiogenic at low therapeutic doses (0.5 mg/kg per day of cerivastatin) but angiostatic at high doses (2.5 mg/kg per day),18 based on their observations in mouse models of inflammation and tumor-induced angiogenesis. In this study, cerivastatin augmented collateral vessel growth in response to acute ischemia at even a higher dose (6 mg/kg per day),
1000-fold that for human use.7 It might be plausible that proangiogenic or antiangiogenic effects of statins might also depend on distinct mechanisms of angiogenesis associated with cancer, tissue ischemia, or inflammation. Statins probably function to promote collateral vessel growth only in ischemic tissues without having significant proangiogenic effects in atherosclerosis, tumor, and diabetic retinopathy. Statins may inhibit the development of atherosclerosis and cancer through their pleiotropic effects.4 Consistent with this notion, a low dose (1 mg/kg per day) of pitavastatin was more effective than a high dose (10 mg/kg per day) in increasing blood flow to ischemic tissue and inhibiting atherosclerotic lesion formation.
Although cerivastatin significantly augmented recovery of blood flow in both wild-type mice and ApoE/ mice, we detected significant increase in capillary density only in ApoE/ mice. It is likely that statins may be more effective in hyperlipidemic mice with impaired endothelial function than in normocholesterolemic mice.
Perspectives
Our findings suggest that statins may not promote cancer and atherosclerosis by stimulating pathological angiogenesis at doses that increase collateral blood flow in ischemic tissue. Statin therapy may be advantageous in patients with ischemic diseases, although it remains to be determined whether statins can achieve angiogenic effects as potently as conventional growth factors in patients.
| Acknowledgments |
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Received December 11, 2003; first decision January 6, 2004; accepted February 5, 2004.
| References |
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