MiniReview |
From the Department of Physiology, College of Medicine (C.H.G., M.K.R.) and Department of Pharmacodynamics, College of Pharmacy (M.J.K.), University of Florida, Gainesville, Fla.
Correspondence to Craig H. Gelband, PhD, Department of Physiology, University of Florida College of Medicine, PO Box 100274, Gainesville, FL 32610-0274. E-mail gelband{at}phys.med.ufl.edu
| Abstract |
|---|
|
|
|---|
Key Words: antisense gene therapy hypertension renal and cardiac pathophysiology renin-angiotensin system
| Introduction |
|---|
|
|
|---|
Traditional agents such as diuretics, ß-blockers, and calcium-channel antagonists have been used to treat systemic hypertension. Recently, a group of antihypertensive agents targeting the RAS that act by inhibiting either the formation of angiotensin II (Ang II) or the actions of Ang II have been used. These agents are reliable and affordable, and their short duration of action makes them an excellent choice for reversible drugs. However, they are not without limitations and disadvantages. As with most antihypertensive drugs, their effects are short-lived, have to be administered on a regular basis, and produce significant side effects. These limitations have often led to problems with compliance with some patients. Finally, all of the therapeutic agents are excellent in the control of blood pressure but hold little promise in a cure, because discontinuing the drugs results in the reappearance of high blood pressure and related cardiovascular pathophysiological symptoms of the disease.
In addition to systemic hypertension, pulmonary hypertension is a cardiovascular disease with significant morbidity and mortality. In pulmonary hypertension, the mean pulmonary arterial pressure is >20 mm Hg at rest. This disorder occurs in 3 distinct forms: primary pulmonary hypertension, pulmonary hypertension of the newborn, and secondary pulmonary hypertension.16 The cellular and physiological mechanisms of this form of hypertension are poorly defined; thus, there are few effective pharmacological agents that are used clinically. The drugs presently in use are anticoagulants, calcium-channel antagonists, intravenous prostacyclin, and inhaled nitric oxide; however, none of these agents has significantly reduced the mortality attributable to pulmonary hypertension. From the discussion above it can be concluded that pharmacological regimens have reached a conceptual plateau for the treatment and long-term prevention of hypertension and that a cure for either systemic or pulmonary hypertension is not on the horizon.
For this reason, many investigators have turned their attention to explore a gene therapy strategy.17 18 They have argued that genetic manipulation may induce a permanent correction, resulting in a possible cure for hypertension. On a conceptual level, such an approach could offer major advantages over pharmacological therapy. It could essentially eliminate the compliance and side-effect issues when using conventional therapy. In addition, a genetic strategy could lead to a permanent control of hypertension if appropriate target genes controlling hypertension could be identified and their expression could be regulated.
| Gene Therapy for Systemic Hypertension |
|---|
|
|
|---|
Antisense Knockdown of the RAS
The use of antisense gene therapy to target
vasoconstrictor pathways has been quite successful in lowering blood
pressure and preventing or reversing the associated cardiovascular
pathophysiology of hypertension on a long-term basis. The RAS has been
the target of choice for antisense gene therapy in the treatment of
systemic hypertension. There are multiple reasons for this. First, the
role of the RAS in hypertension is well understood. Second, the RAS
provides an ideal target for gene delivery, because it is widely
distributed. Third, pharmacological agents that target the RAS exert
antihypertensive effects at multiple levels (vasodilator mechanisms and
fibrinolytic and oxidative stress pathways) in addition to their
actions on Ang
II.17
Conceptual support that antisense targeting of the RAS would
be effective in treating hypertension was derived from the use of
antisense
oligonucleotides.24 25 26
Studies demonstrated that the central or peripheral injection of
antisense oligonucleotides to the RAS (angiotensinogen or angiotensin
II type 1 receptor [AT1R]) resulted in a
transient, short-term (days), and modest, but significant, effect on
lowering blood pressure in the SHR. The amount (
23 mm Hg) and
duration (9 weeks) of the blood pressurelowering effect were
prolonged to weeks with the use of an adeno-associated virus
viral vector delivery
system.27
Our research group has used these studies as a basis to
determine if retroviral-vectormediated delivery of antisense
targeting the AT1R and angiotensin-converting
enzyme (ACE) would prevent hypertension (high blood pressure)
and cardiovascular pathophysiology associated with hypertension for
longer time
periods.17 28 29 30
A single intracardiac administration of retroviral particles containing
AT1R antisense (AT1R-AS)
into 5-day-old SHR results in attenuation of high blood pressure and
long-term expression of the AT1R-AS for at least
210 days. This attenuation of blood pressure is similar to that seen
for AT1R antagonists. This was associated with
complete attenuation of cardiac hypertrophy, arterial wall thickness,
and perivascular and myocardial fibrosis.
AT1R-AS expression also resulted in significant
reduction in the amount of neointimal formation after carotid artery
balloon injury in the SHR
(Figure
).
AT1R-AS prevented alterations in vascular
reactivity, endothelial dysfunction, Ca2+
handling, and ion channel dysfunction in renal arterioles. These
studies established that AT1R-AS will abolish
the development of hypertension in the SHR on a long-term
basis.
|
Intracardiac injection of virus particles containing AT1R-AS into the adult SHR resulted in a 30- to 60-mm Hg reduction in blood pressure that was maintained for up to 36 days compared with the SHR treated with virus alone.31 This was accompanied by a reversal of the increase in vasoreactivity and the gain of endothelial function in renal resistance arterioles. These observations are consistent with studies that have previously shown a similar transient reversal of high blood pressure by antisense in the adult rat.24 25 26 27 Collectively, these data demonstrate that virally mediated gene delivery of AT1R-AS can effectively reduce blood pressure and reverse renovascular pathophysiology associated with hypertension in the adult SHR. However, the transient nature of the antihypertensive effect in the adult remains to be addressed and must be improved on.
Also relevant would be determining if antisense gene targeting could clarify the role of the tissue RAS in cardiovascular pathophysiology. This is clinically relevant in view of the recent results from the Heart Outcomes Prevention Evaluation clinical study.32 This study showed that ramipril, an ACE inhibitor, produced a significant improvement in outcomes and reduction in deaths attributable to cardiovascular causes without a significant change in blood pressure. Introduction of ACE antisense (ACE-AS) by a retroviral vector resulted in a modest (15 to 18 mm Hg) but significant attenuation of high blood pressure exclusively in the SHR for 100 days.33 34 In spite of this modest decrease in blood pressure, ACE-AS resulted in complete attenuation of ventricular hypertrophy and prevention of altered endothelial function, vascular reactivity, [Ca2+]i, and ion channel dysfunction. The data provide support for the importance of the tissue RAS emphasized in the results of the Heart Outcomes Prevention Evaluation trial.
In summary, the above data illustrate that an interruption of the RAS activity at a genetic level could prevent hypertension on a long-term basis. Support for this hypothesis is provided by several experiments. The F1 and F2 generation offspring of the AT1R-AStreated SHRs expressed a persistently lower blood pressure, decreased cardiac hypertrophy and fibrosis, decreased medial thickness, and normalization of renal artery excitation-contraction coupling, Ca2+ current, membrane potential, Kv current, and [Ca2+]i compared with offspring derived from the virus-treated SHRs.30 In addition, AT1R-AS was found in the genomic DNA and was expressed in cardiovascularly relevant tissue of the F1 and F2 offspring. The transmission of antihypertensive phenotypes to the offspring was also seen in the ACE-AStreated SHRs.33 34 The mechanism of transmission of this antihypertensive phenotype to the offspring is unknown at the present time but might involve germ line transmission of the antisense, parental environment, transmission of a humoral factor through the breast milk, or expression at a critical stage of SHR development.35 36 37 38 39 For example, cross studies have shown that SHR babies parented by WKY mothers express a significantly lower blood pressure, while WKY babies parented by SHR mothers are hypertensive.36 37
Antisense Knockdown of the
ß1-Adrenergic Receptors
Zhang et
al40 have used antisense
oligonucleotides to the ß1 receptor to provide
additional conceptual support for gene therapy in hypertension. A
single intravenous injection of ß1 receptor
antisense in cationic liposomes decreased cardiac
ß1 receptor density by 30% to 50%,
attenuated the ß1 receptormediated positive
inotropic response in isolated perfused hearts, and decreased blood
pressure by
38 mm Hg in the SHR. The effect lasted 2 to 3 weeks
and, interestingly, had no significant effect on heart rate. In
addition, a 35% reduction in the renal ß1 but
not ß2 receptor density was observed. Finally,
4 days after administration, ß1 receptor
antisense decreased preprorenin mRNA levels in the renal cortex by
37%, which was accompanied by a marked diminution of plasma renin
activity and plasma Ang II levels by day
10.41
| Gene Therapy for Pulmonary Hypertension |
|---|
|
|
|---|
than controls, and, after exposure to chronic hypobaric hypoxia, the
PGIS-overexpressing mice showed a lower right ventricular systolic
pressure than controls. Histological examination of the lungs revealed
nearly normal arteriolar vessels in the PGIS-expressing mice in
comparison with vessel-wall hypertrophy in the control mice. These
studies demonstrate that overexpression of PGIS in the lung protected
mice from the development of pulmonary hypertension after exposure to
chronic hypoxia.
Using adenoviral gene transfer of eNOS to the mouse lung,
Champion et al43 showed the
beneficial effects of this gene on pulmonary hemodynamics. At 21 to 28
days after gene transfer, the pressure-flow relationship in the
pulmonary vascular bed was shifted to the right in animals transfected
with eNOS, and pulmonary pressor responses to endothelin-1, Ang II, and
ventilatory hypoxia were reduced significantly in animals transfected
with the eNOS gene. In preliminary findings, this same group
demonstrated that not only did the eNOS knockout mouse have pulmonary
hypertension (pulmonary artery pressure
25 mm Hg), but when
the eNOS gene was delivered back to the lung of the knockout mouse
using an adenoviral construct, no pulmonary hypertension developed in
the knockout.44 CGRP is also
believed to play an important role in maintaining low pulmonary
vascular resistance and modulating pulmonary vascular responses to
chronic hypoxia. Intratracheal administration of prepro-CGRP with an
adenovirus to the mouse lung, followed by 16 days of chronic hypoxia,
caused an attenuation of the hypoxic-induced increases in pulmonary
vascular resistance, right ventricular mass, pulmonary artery pressure,
and pulmonary vascular
remodeling.45 These recent
findings suggest that the use of gene therapy targeting vasodilator
agents in the lung may be successful in the treatment of pulmonary
hypertension.
| Future Directions and Conclusions |
|---|
|
|
|---|
Second, other gene targets that may be relevant in hypertension must be explored. For example, the targeting of matrix proteins could be a potentially interesting site of gene therapy for hypertension. This is relevant in view of the fact that therapies using secreted molecules may not require as high a degree of transduction as do therapies that require intracellular expression of proteins or antisense. Cowan et al46 showed that progression of pulmonary hypertension is associated with increased serine elastase activity and the proteinase-dependent deposition of tenascin-C. In monocrotaline-treated rats, oral administration of serine elastase inhibitors increased survival and decreased pulmonary artery pressure and muscularization. This was attributable to myocyte apoptosis and loss of extracellular matrix, specifically elastin and tenascin-C. Therefore, it seems plausible that targeting extracellular matrix proteins may also be beneficial in vascular disorders. It would also be interesting to develop a strategy that would target antisense knockdown of Ca2+ channels using a smooth muscle cellspecific promoter. Finally, cell-specific overexpression of signaling molecules that may be vasodilator in nature (ie, protein kinases A and G) would be potential targets for antihypertensive gene therapy.
In conclusion, there is sufficient evidence to indicate that gene therapy may be an important and significant step forward in the long-term treatment and possible cure of both systemic and pulmonary hypertension. It is quite possible that hypertension-relevant genes could be identified in the near future. The establishment of the conceptual basis for gene therapy in the animal models of hypertension coupled with the anticipated advances in the genetic aspects of this disease would make it highly feasible to attempt gene delivery in the control of human hypertension
| Acknowledgments |
|---|
Received June 29, 2000; revision received October 18, 3000; accepted October 18, 2000.
| References |
|---|
|
|
|---|
This article has been cited by other articles:
![]() |
J.-C. Richard, Z. Zhou, D. E. Ponde, C. S. Dence, P. Factor, P. N. Reynolds, G. D. Luker, V. Sharma, T. Ferkol, D. Piwnica-Worms, et al. Imaging Pulmonary Gene Expression with Positron Emission Tomography Am. J. Respir. Crit. Care Med., May 1, 2003; 167(9): 1257 - 1263. [Abstract] [Full Text] [PDF] |
||||
![]() |
Y. Chu, S. Iida, D. D. Lund, R. M. Weiss, G. F. DiBona, Y. Watanabe, F. M. Faraci, and D. D. Heistad Gene Transfer of Extracellular Superoxide Dismutase Reduces Arterial Pressure in Spontaneously Hypertensive Rats: Role of Heparin-Binding Domain Circ. Res., March 7, 2003; 92(4): 461 - 468. [Abstract] [Full Text] [PDF] |
||||
![]() |
K Taylor and J Stein Dyslexia and familial high blood pressure: an observational pilot study Arch. Dis. Child., January 1, 2002; 86(1): 30 - 33. [Abstract] [Full Text] [PDF] |
||||
![]() |
A. S. Pachori, M. J. Huentelman, S. C. Francis, C. H. Gelband, M. J. Katovich, and M. K. Raizada The Future of Hypertension Therapy: Sense, Antisense, or Nonsense? Hypertension, February 1, 2001; 37(2): 357 - 364. [Abstract] [Full Text] [PDF] |
||||
![]() |
S. C. FRANCIS, M. K. RAIZADA, A. A. MANGI, L. G. MELO, V. J. DZAU, P. R. VALE, J. M. ISNER, D. W. LOSORDO, J. CHAO, M. J. KATOVICH, et al. Genetic targeting for cardiovascular therapeutics: are we near the summit or just beginning the climb? Physiol Genomics, December 21, 2001; 7(2): 79 - 94. [Abstract] [Full Text] [PDF] |
||||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Circulation Research Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 2000 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |