(Hypertension. 2002;39:969.)
© 2002 American Heart Association, Inc.
Scientific Contributions |
From the Hypertension Center, Wake Forest University School of Medicine (C.M.F., D.M.D.), Winston-Salem, NC; Department of Pharmacodynamics, College of Pharmacy (A.S.P., M.J.K.), and Department of Physiology and Functional Genomics, College of Medicine (M.T.N., M.K.R.), University of Florida, Gainesville, Fla.
Correspondence to Mohan K. Raizada, PhD, Department of Physiology and Functional Genomics, PO Box 100274, University of Florida, College of Medicine, Gainesville, FL 32610. E-mail mraizada{at}phys.med.ufl.edu
| Abstract |
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Key Words: antisense elements rat, transgenic renin-angiotensin system hypertension, essential genes
| Introduction |
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Recent clinical and experimental studies have demonstrated that pharmacological agents, such as angiotensin converting enzyme (ACE) inhibitors can reduce LVH independently of a reduction in BP.8,9 This evidence implicates the role of the tissue-based renin-angiotensin system (RAS) in the development of end-organ damage and demonstrates that the pathophysiology may be independent of high BP. However, it has not been established whether the end-organ damage observed in hypertension is a result of high BP or due to an inherently hyperactive RAS.
The renin-transgenic rat (TGR mRen2) has been developed as an animal model of hypertension that exhibits fulminant hypertension and displays cardiac and vascular hypertrophy because of an overexertion of renin in various tissues.10,11 However the plasma levels of renin and Ang II range from low to normal in this model. These characteristics make this animal an excellent model for studying the participation of tissue RAS in the development and maintenance of hypertension.
We have previously shown that a single intracardiac injection of a retroviral vector containing angiotensin II type I receptor antisense gene (AT1R-AS) prevented the development of high BP and associated cardiac and vascular pathophysiology in spontaneously hypertensive rats (SHR).12,13 These observations support our view that genetic targeting of the RAS is a conceptually viable strategy for long-term control of hypertension. However, by using the SHR model, we were not able to conclude whether normalization of cardiac and vascular pathophysiology was due to a direct effect of the antisense gene on the blockade of tissue RAS or was a result of decreased BP. Thus, the present study was designed to validate the efficacy of AT1R-AS gene therapy in preventing the development of cardiac hypertrophy (CH) and BP in the TGR model of hypertension.
| Methods |
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Physiological and Pathological Measurements
Five animals from each group were euthanized at 12, 19, and 26 days of age. Their hearts were removed, blotted, and weighed. In addition, hearts from a 16-day-old group were perfusion-fixed with 4% paraformaldehyde for histology. In another group of animals, indirect BPs were monitored by the tail-cuff method starting at 3 weeks of age and continuing until 12 weeks of age.
Echocardiographic Studies
Rats of 12 to 14 weeks of age were lightly anesthetized with methoxyflurane and placed on a heating pad for the echocardiographic studies. A Hewlett Packard Sonos Model 5500 with a 12-Hz transducer was used with a focal zone of 2 cm, depth of 2 cm, and a pulse wave Doppler gate length of 0.06 cm. Measurements obtained by echocardiography include left ventricular end diastolic diameter (LVED), left ventricular posterior wall thickness (LVPW), left ventricular free wall thickness (LVFW), interventricular septum thickness during diastole, LV mass, and LV stroke volume. The shortening fraction was calculated as follows: (LVED-LVES)/LVED x 1/100. Left ventricular mass measurements were calculated from the bullet method as follows: 1.05(5/6 A1 [L + T]) (5/6 A2 L), where A1 is the outer diameter of left ventricle; A1, the inner diameter of left ventricle; L, the length of the left ventricle lumen as viewed in a long axis echocardiogram; and T, thickness.
Biochemical Measurements
Polymerase chain reaction (PCR) and reverse transcription-polymerase chain reaction (RT-PCR) were performed to measure the incorporation and expression of AT1R-AS in 10 and 120-day old animals, respectively, as previously described.12 PCR was performed using different numbers of PCR cycles and was logarithmically linear between 20 and 30 cycles. RT-PCR was also used to measure changes in gene expression of
-actin and atrial natriuretic peptide (ANP) in the ventricles from adult SD, LNSV-TGR, and LNSV-AT1R-AStreated TGR. Total RNA was isolated by the Trizol method (GIBCO) and was converted to cDNA in the reverse transcription (RT) reaction according to manufacturers protocol. This cDNA was then used in the PCR reaction using the primers as follows: ANP (forward): 5' -ATCTGATGGATTTCAAGAACC-3'; ANP (reverse): 5' -GCTCCAATCCTGTCAATCCTAC-3';
-actin: (forward): 5' -ACCAGGGTGTCATGG-3';
-actin (reverse): 5' -GTG-AGCAGGGTCGGG-3'; GAPDH (forward): 5' -CCCTTCATTG-ACCTCAACTACATGG-3'; GAPDH (reverse): 5' -GAGGGGCCAT-CCACAGTCTTCTG-3'. Annealing temperatures for the primers were as follows: ANP 62°C;
-actin 60°C; GAPDH 60°C. Relative absorbency was measured by densitometry, and values were normalized to GAPDH, which served as the internal control.
Statistics
All results were expressed as mean±SE. Indirect BP was analyzed by repeated measures ANOVA. Direct mean BPs were analyzed by ANOVA. Values of P<0.05 were considered statistically significant. All experiments had at least 7 animals per group unless stated otherwise.
| Results |
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Indirect BP was significantly elevated in the TGR compared with their age-matched SD controls at 8 to 12 weeks of age (Figure 2A). At 12 weeks of age, TGR showed 90 mm Hg higher BP compared with SD controls (220±3 versus 130±3 mm Hg, n=9). Whereas LNSV treatment in the TGR showed no significant effect on BP compared with their saline-treated controls, a modest, but significant, reduction in BP was observed in the LNSV-AT1R-AStreated TGR compared with the LNSV-treated TGR (220±3 versus 190±6 mm Hg, n=9). Direct basal systolic BP (SBP, Figure 2B) measured at 12 weeks of age confirmed this and showed an average of 23 mm Hg decrease in BP in the LNSV-AT1R-AStreated TGR compared with the LNSV-TGR. There was a similar decrease in diastolic BP (25 mm Hg) and a reduction in heart rate (403±8 versus 316±31 beats per minute [bpm]) between LNSV-TGR and LNSV-AT1R-AStreated TGR. Despite this decrease in BP, the AT1R-AS treated TGR still maintained significantly higher BP than that observed in the control SD rats. Antisense treatment was without effect on BP and heart rate (HR) in the control SD animals (data not shown).
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Effect of AT1R-AS Treatment on Cardiac Pathophysiology
At 12 weeks of age, control and LNSV-AT1R-AS rats were subjected to echocardiography to characterize hypertension-induced cardiac pathophysiology and to determine the effects of AT1R-AS expression on vascular wall thickness. LVFW thickness was significantly increased in TGR compared with SD rats (5.02±1.2 versus 2.8±0.3 mm, P<0.001). This was fully corrected in the AT1R-AStreated TGR (Figures 3A through 3D). Other parameters such as LVPW thickness, shortening fraction, and stroke volume were not statically different between the SD and TGR and were not affected by the AT1R-AS treatment. Heart-weight/body-weight ratio (HW/BW) of LNSV-treated TGR controls (3.8±0.6 g/kg) was similar to that of the untreated TGR (3.3±0.13 g/kg). This was 48% higher than the SD controls (Figure 3E). LNSV-AT1R-AS transduction significantly reduced this ratio in the TGR (2.6±0.8 g/kg) and restored the value to that observed in the control SD rats (2.3±0.1 g/kg) (Figure 3E). We also observed the presence of pericardial effusion in untreated and LNSV-treated transgenic rats, which was not present in either SD or LNSV-AT1R-AStreated TGR (5/6 for LNSV versus 1/6 for LNSV-AT1R-AS).
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ANP and
-actin mRNA levels were examined in cardiac tissues as another measure of cardiac hypertrophy (Figures 4A and 4B). mRNA levels for both genes were elevated 25% to 30% in the LNSV-treated TGR compared with SD control rats. LNSV-AT1R-AS transduction resulted in a 50% to 55% decrease in the levels of mRNA for ANP and
-actin.
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Development of Cardiac Hypertrophy and Effect of AT1R-AS
A developmental study was undertaken to determine if the beneficial outcome of the AT1R-AS treatment on CH is independent of normalization of high BP. Five TGR and five SD rats were euthanized at 12, 19, and 26 days of age. A significant increase in HW/BW ratio was observed in untreated TGR compared with untreated SD rats at all the investigated time points (7.4±0.98 versus 4.8±0.14 g/kg, P<0.05; 5.2±0.08 versus 4.2±0.06 g/kg, P<0.01; 4.5±0.15 versus 3.7±0.03 g/kg, P<0.001; Figure 5A). At the same time there was no difference in absolute body weight between the groups (data not shown). Indirect BP was measured in 21-day-old SD and TGR (the earliest time measurements can be made with high degree of reliability) to determine whether the TGR with CH show high BP. No significant difference in elevation of BP was observed in TGR compared with the age-matched control SD rats (Figure 5B).
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CH in the neonatal TGR was further evident by the marked increase in the left ventricle wall thickness in the TGR compared with the SD rat. A representative histological section shown in Figure 6A demonstrates an increased septal (SW), anterior (AW), and lateral (LW) wall thickness in LNSV-TGR (SW 0.762 mm, AW 0.873 mm, LW 1.001 mm) compared with untreated SD rat (SW 0.721 mm, AW 0.698 mm, LW 0.78 mm). This CH was significantly attenuated in the TGR expressing AT1R-AS as early as 16 days of age (Figure 6B).
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| Discussion |
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We had previously established that AT1R-AS gene transduction prevents both cardiac and renovascular pathophysiology in the SHR, along with a profound reduction in high BP.12,13,1719 Therefore, it was not possible to determine whether the observed tissue-protective effects of the antisense gene were mediated via a decrease in BP or by direct effects on the tissue RAS. In the present study, we have attempted to test this hypothesis by using the TGR, an established model of hypertension that exhibits an overactive RAS,10,11 despite low plasma RAS levels.
Severe LVH, measured by both echocardiography and gross measurement of HW/BW ratio, was observed in 12-week-old hypertensive TGR rats. A single intracardiac administration of AT1R-AS blocked the development of CH with only a modest reduction in BP in adult TGR. The LV mass in the adult AT1R-AStreated TGR was similar to that observed in AT1R-AStreated SHR.12,13 The increase in LV mass in TGR was associated with an upregulated expression of fetal and structural genes such as ANP and
-skeletal actin, the levels of which were reduced by 50% and 55%, respectively, in AT1R-AStreated adult TGR.
The observation that CH could be completely prevented in the face of only a 13% decrease in BP illustrates the point that a complete normalization of BP is not necessary for improvement in CH. Additionally, it indicates that an overactive tissue RAS, and not pressure overload, may be primarily responsible for CH in the TGR. This view is further supported by studies using pharmacological strategies.20 This study also demonstrated that our antisense treatment significantly reduced HR in the adult TGR to that observed in the control SD. The relationship between the reduction in HR and CH in this model could not be established because HR was not ascertained in the neonatal TGR.
CH was studied at various stages of growth to further confirm BP-independent development of CH in TGR. TGR, as young as 12 days of age, exhibited significantly higher HW/BW ratios than normotensive SD rats. This hypertrophy was not dependent on high BP because BPs of 21-day-old TGR were comparable with the normotensive SD rats. These findings were confirmed by histology demonstrating higher lateral, septal, and anterior left ventricle wall thickness in TGR hearts compared with age-matched normotensive SD rats. These observations are consistent with the SHR model of hypertension in which cardiac enlargement and increased DNA synthesis are seen in the newborn SHR hearts when compared with WKY rats.21,22 These results support the hypothesis that CH observed in adult hypertensive rats, whether it is TGR or SHR, occurs during the early stages of growth and thus argue against the role of high BP in the development of hypertension-associated organ pathology.
Other lines of evidence also support a role of the intrinsic cardiac RAS in the regulation of cardiac growth and hypertrophy. These include increased expression of renin in hypertrophied SHR hearts,23 elevated tissue-converting enzyme activity in the SHR,24 and the presence of cardiac hypertrophy in mice overexpressing AT1 receptors in cardiomyocytes without any effect on BP.25 However, studies correlating mRNA levels of components of the RAS during different developmental stages of CH have not been performed, thus leaving to speculation the exact role of tissue RAS in BP-independent hypertrophy.
Collectively, these results demonstrate that development of CH, which is a characteristic of hypertension, can be manifested independently of high BP. We also demonstrate that the induction of CH may actually take place during the perinatal growth period, preceding the onset of high BP, and may be a result of an overactive cardiac RAS.
| Acknowledgments |
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| Footnotes |
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Received September 27, 2001; first decision October 29, 2001; accepted March 27, 2001.
| References |
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2. Dang A, Zheng D, Wang B, Zhang Y, Zhang P, Xu M, Liu G, Liu L. The role of the renin-angiotensin and cardiac sympathetic nervous systems in the development of hypertension and left ventricular hypertrophy in spontaneously hypertensive rats. Hypertens Res. 1999; 22: 217221.[Medline] [Order article via Infotrieve]
3. Cohn JN. Beta blockers in heart failure. Eur Heart J. 1998; 19 (suppl F): F52F55.[Medline] [Order article via Infotrieve]
4.
Barlucchi L, Leri A, Dostal DE, Fiordaliso F, Tada H, Hintze TH, Kajstura J, Nadal-Ginard B, Anversa P. Canine ventricular myocytes possess a renin-angiotensin system that is upregulated with heart failure. Circ Res. 2001; 88: 298304.
5. Yamazaki T, Komuro I, Yazaki Y. Role of the renin-angiotensin system in cardiac hypertrophy. Am J Cardiol. 1999; 83: 53H57H.[CrossRef][Medline] [Order article via Infotrieve]
6. Brilla CG. Aldosterone and myocardial fibrosis in heart failure. Herz. 2000; 25: 299306.[CrossRef][Medline] [Order article via Infotrieve]
7.
Takeda Y, Yoneda T, Demura M, Miyamori I, Mabuchi H. Sodium-induced cardiac aldosterone synthesis causes cardiac hypertrophy. Endocrinology. 2000; 141: 19011904.
8. Schlaich MP, Schmieder RE. Left ventricular hypertrophy and its regression: pathophysiology and therapeutic approach: focus on treatment by antihypertensive agents. Am J Hypertens. 1998; 11(11 Pt 1): 13941404.
9. Roman MJ, Alderman MH, Pickering TG, Pini R, Keating JO, Sealey JE, Devereux RB. Differential effects of angiotensin converting enzyme inhibition and diuretic therapy on reductions in ambulatory blood pressure, left ventricular mass, and vascular hypertrophy. Am J Hypertens. 1998; 11(4 Pt 1): 387396.
10. Engler S, Paul M, Pinto YM. The TGR (mRen2)27 transgenic rat model of hypertension. Regul Pept. 1998; 77: 38.[Medline] [Order article via Infotrieve]
11. Lee MA, Bohm M, Paul M, Bader M, Ganten U, Ganten D. Physiological characterization of the hypertensive transgenic rat TGR(mREN2)27. Am J Physiol. 1996; 270(6 Pt 1): E919E929.
12. Iyer SN, Lu D, Katovich MJ, Raizada MK. Chronic control of high blood pressure in the spontaneously hypertensive rat by delivery of angiotensin type 1 receptor antisense. Proc Natl Acad Sci U S A. 996; 93: 99609965.
13. Lu D, Raizada MK, Iyer S, Reaves P, Yang H, Katovich MJ. Losartan versus gene therapy: chronic control of high blood pressure in spontaneously hypertensive rats. Hypertension. 1997; 30(3 Pt 1): 363370.
14.
Yusuf S, Sleight P, Pogue J, Bosch J, Davies R, Dagenais G. Effects of an angiotensin-converting-enzyme inhibitor, ramipril, on cardiovascular events in high-risk patients. The Heart Outcomes Prevention Evaluation Study Investigators. N Engl J Med. 2000; 342: 145153.
15. Smith WH, Ball SG. ACE inhibitors in heart failure: an update. Basic Res Cardiol. 2000; 95 (suppl I): I-8I-14.[Medline] [Order article via Infotrieve]
16. Yamazaki T, Yazaki Y. Role of tissue angiotensin II in myocardial remodeling induced by mechanical stress. J Hum Hypertens. 1999; 13 (suppl 1): S43S47;discussion S49S50.[CrossRef]
17.
Pachori AS, Wang H, Gelband CH, Ferrario CM, Katovich MJ, Raizada MK. Inability to induce hypertension in normotensive rat expressing AT(1) receptor antisense. Circ Res. 2000; 86: 11671172.
18. Martens JR, Reaves PY, Lu D, Katovich MJ, Berecek KH, Bishop SP, Raizada MK, Gelband CH. Prevention of renovascular and cardiac pathophysiological changes in hypertension by angiotensin II type 1 receptor antisense gene therapy. Proc Natl Acad Sci U S A. 998; 95: 26642669.
19. Pachori AS, Huentelman MJ, Francis SC, Gelband CH, Katovich MJ. The future of hypertension therapy: sense, antisense, or nonsense. Hypertension. 2001; 37: 257264.
20. Teisman AC, Pinto YM, Buikema H, Flesch M, Bohm M, Paul M, van Gilst WH. Dissociation of blood pressure reduction from end-organ damage in TGR(mREN2)27 transgenic hypertensive rats. J Hypertens. 1998; 16(12 Pt 1): 17591765.
21. Kunes J, Pang SC, Cantin M, Genest J, Hamet P. Cardiac and renal hyperplasia in newborn spontaneously hypertensive rats. Clin Sci (Colch). 1987; 72: 271275.[Medline] [Order article via Infotrieve]
22. Cutilletta AF, Benjamin M, Culpepper WS, Oparil S. Myocardial hypertrophy and ventricular performance in the absence of hypertension in spontaneously hypertensive rats. J Mol Cell Cardiol. 1978; 10: 689693.[CrossRef][Medline] [Order article via Infotrieve]
23. Passier RC, Smits JF, Verluyten MJ, Daemen MJ. Expression and localization of renin and angiotensinogen in rat heart after myocardial infarction. Am J Physiol. 1996; 271(3 Pt 2): H1040H1048.
24.
Fernandez-Alfonso MS, Kreutz R, Zeh K, Liu Y, Ganten D, Paul M. Differential regulation of vascular angiotensin I-converting enzyme in hypertension. Hypertension. 1994; 24: 280286.
25. Paradis P, Dali-Youcef N, Paradis FW, Thibault G, Nemer M. Overexpression of angiotensin II type I receptor in cardiomyocytes induces cardiac hypertrophy and remodeling. Proc Natl Acad Sci U S A. 000; 97: 931936.
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