Is gene therapy for hypertension possible?

Antisense oligonucleotides for the arterial hypertension mechanisms study and therapy

Arterial hypertension is one of the most common chronic diseases in adults all over the world. This pathology can not only reduce patients’ life quality, but can also be accompanied by a number of complications. Despite the fact that there is a large group of antihypertensive drugs on the market, mainly representing different combinations of inhibitors of the renin-angiotensin system, adrenoreceptor blockers in combination with diuretics, there is no generally accepted “gold standard” for drugs that would not have side effects. The review discusses the main aspects of antisense oligonucleotides use in the context of arterial hypertension. It is well known that the medical implementation of antisense oligonucleotides aims to block the expression of particular genes involved in the pathology development, and a key advantage of this technique is a high selectivity of the effect. However, with the undoubted advantages of the method, there are difficulties in its application, related both to the properties of the oligonucleotides themselves (insufficient stability and poor penetration into cells), and to the variety of mechanisms of the origin of a particular pathology, arterial hypertension, in our case. The review provides a brief description of the main molecular targets for antisense treatment of hypertensive disease. The newest targets for therapy with oligonucleotides – microRNAs – are discussed. The main modifications of antisense nucleotides, designed to increase the duration of their effects and simplify the delivery of this type of drugs to the targets are discussed, in particular, combining antisense oligonucleotides with adenovirus-based expression vectors. Particular attention is given to antisense oligonucleotides in the complex with nanoparticles. The review discusses the results of the use of titanium dioxide (TiO2) containing antisense nanocomposites for the angiotensin converting enzyme in rats with stress induced arterial hypertension (ISIAH). It was shown that the use of antisense oligonucleotides continues to be a promising technique for studying the mechanisms of various forms of hypertensive disease and has a high potential for therapeutic use.

Overexpression of eNOS prevents the development of renovascular hypertension in mice

Gene therapy has become an important tool for understanding several cardiovascular diseases. In the present study we investigated the effects of endothelial nitric oxide synthase (eNOS) overexpression on renovascular hypertension. Experiments were carried out in C57BL/6 mice randomly assigned to either a two-kidney one-clip (2K1C) hypertension group or a sham-operated group. At the same time surgery was carried out, both 2K1C and sham mice received an intravenous injection of recombinant adenovirus expressing the functional gene eNOS or the reporter gene beta-galactosidase (beta-gal). Fourteen days later, arterial pressure, baroreflex sensitivity, and cardiac sympathetic and parasympathetic tone were evaluated in conscious mice. Measurement of mean arterial pressure showed arterial hypertension in 2K1C-betagal mice compared with sham-betagal mice (121 +/- 3 vs. 96 +/- 2 mm Hg, p < 0.01), which was prevented by eNOS overexpression (2K1C-eNOS 100 +/- 4 vs. sham-eNOS 99 +/- 3 mm Hg). Linear regression analysis of the reflex tachycardia response to sodium nitroprusside-induced hypotension showed that baroreflex sensitivity was significantly attenuated in 2K1C-betagal mice (5.8 +/- 0.5 vs. sham-betagal 8.0 +/- 0.8 beats.min-1 x mm Hg-1, p < 0.05), but this decrease was not prevented by eNOS overexpression (2K1C-eNOS 7.2 +/- 0.5 vs. sham-eNOS 8.8 +/- 0.7 beats x min-1 x mm Hg-1, p < 0.05). The cardiac sympathetic tone was augmented and the vagal tone was reduced in 2K1C-betagal (152 +/- 17 and 45 +/- 12 beats.min-1, respectively) compared with sham-betagal mice (112 +/- 6 and 89 +/- 7 beats.min-1, respectively), and similar results were observed in 2K1C-eNOS mice compared with sham-eNOS. The data indicate that eNOS overexpression was able to prevent the development of 2K1C renovascular hypertension in mice, without affecting other characteristic cardiovascular dysfunctions.

Cardiovascular consequences of cortisol excess

Cushing's syndrome is a consequence of primary or, more commonly, secondary oversecretion of cortisol. Cardiovascular disease is the major cause of morbidity and mortality in Cushing's syndrome, and excess risk remains even in effectively treated patients. The cardiovascular consequences of cortisol excess are protean and include, inter alia, elevation of blood pressure, truncal obesity, hyperinsulinemia, hyperglycemia, insulin resistance, and dyslipidemia. This review analyses the relationship of cortisol excess, both locally and at tissue level, to these cardiovascular risk factors, and to putative mechanisms for hypertension. Previous studies have examined correlations between cortisol, blood pressure, and other parameters in the general population and in Cushing's syndrome. This review also details changes induced by short-term cortisol administration in normotensive healthy men.

Gene-based therapy for hypertension--do preclinical data suggest a promising future?

Many experimental studies have obtained a prolonged control of blood pressure through gene treatment. This consists in the administration of genes coding for vasodilator proteins (the 'sense' approach), or of nucleotide sequences that are complementary to the mRNA of vasoconstrictor proteins, which are consequently synthesized in smaller amounts (the 'antisense' approach). Examples of the sense approach include the genes encoding endothelial nitric oxide synthase and kallikrein. Examples of the second type of approach are the antisense oligodeoxynucleotides to angiotensin-converting enzyme and endothelin-1. Also, RNA molecules, such as ribozymes and small interfering RNAs, are capable to inhibit RNA function. Whole sense genes are usually administered through viral vectors, while antisense oligonucleotides may be administered with plasmids or liposomes. Both viral and non-viral vectors have advantages and disadvantages. Despite the still persisting limitations, the possibility exists that in the future some forms of genetic treatment will be extended to the clinical setting, allowing a prolonged control of essential hypertension and its end-organ sequelae.

Gene therapy for vascular disease

It is now feasible to transfer genes to blood vessels to alter vascular function. An alternative approach is to transfer genes to liver or skeletal muscle, so that the transgene releases a protein into blood, and the protein binds to blood vessels to alter vascular function. Gene therapy is being tested for treatment of diseases, such as ischemia in patient with peripheral vascular disease, which cannot be treated with medications. Common diseases, such as hypertension and hypercholesterolemia, also may be targets for gene therapy. Periodic intravenous injection of a vector for gene transfer has the potential for circumventing poor compliance in taking daily medications for these diseases. The key obstacle to widespread use of gene therapy is that a safe and efficient vector for delivery of genes has not yet been developed.

Prolonged attenuation of cold-induced hypertension by adenoviral delivery of renin antisense

BACKGROUND

Renin has been linked to the pathogenesis of some forms of hypertension, including cold-induced hypertension (CIH). Although several antihypertensive drugs that inhibit angiotensin-converting enzyme (ACE) and angiotensin II (Ang II) type 1 (AT(1)) receptors are available, they are short-lasting and have side effects. Inhibition of renin [the first and rate-limiting step of the renin-angiotensin system (RAS)] would provide an inhibition of the entire RAS. Thus, we developed an antisense approach for specific inhibition of renin based on the genetic design. The objective of this study was to test our hypothesis that adenoviral delivery of renin antisense inhibits renin and attenuates CIH.

METHODS

Recombinant adenoviruses carrying rat renin antisense (rAdv.RRA) and LacZ reporter gene (rAdv.LacZ) were constructed and used for in vivo gene transfer via intravenous injection. Four groups of rats were used (six rats/group). Blood pressure did not differ among the four groups during the control period at room temperature (25 degrees C). Two groups of rats received rAdv.RRA (2.5 x 10(9) pfu/rat, intravenously), while the other two groups received the same dose of rAdv.LacZ and served as controls. After gene delivery, one rAdv.LacZ-treated and one rAdv.RRA-treated group were exposed to cold (5 degrees C), while the remaining groups were kept at 25 degrees C. Blood pressure was monitored weekly during cold exposure. A 24-hour urine sample was collected during weeks 1, 3, and 5 for measuring urinary aldosterone excretion. At the end of week 5, all animals were killed and blood was collected for measurement of plasma renin activity (PRA), total plasma renin, plasma active renin, and plasma aldosterone. Vascular Ang II contents were measured in all rats.

RESULTS

Blood pressure of the rAdv.LacZ-treated group rose significantly within 2 weeks of exposure to cold and reached 158.2 +/- 6.4 mm Hg by week 5. In contrast, blood pressure (117.1 +/- 5.3 mm Hg) of the cold-exposed group treated with rAdv.RRA did not increase until 5 weeks after exposure to cold. Thus, a single dose of rAdv.RRA prevented CIH for at least 5 weeks. rAdv.RRA abolished the cold-induced increases in PRA, total plasma renin, plasma active renin, vascular Ang II, and plasma and urine aldosterone, indicating effective inhibition of the entire RAS.

CONCLUSION

rAdv.RRA effectively inhibited the entire RAS and produced prolonged attenuation of CIH. Antisense inhibition of renin may be a novel and ideal approach for long-term control of hypertension.

Regulatable atrial natriuretic peptide gene therapy for hypertension

Hypertension (HTN) is a disease that begins with dysfunctional renal-sodium excretion and progresses to a syndrome of highly elevated systolic, diastolic, and mean arterial pressures. Inadequacies in the therapy of HTN have led to the investigation of the gene therapy of this disease by using systemic overproduction of vasodilatory peptides, such as atrial natriuretic peptide (ANP). However, gene-therapy approaches to HTN using ANP are limited by the need for long-term ANP gene expression and, most important, control of ANP gene expression. Here, we introduce a helper-dependent adenoviral vector carrying the mifepristone (Mfp)-inducible gene-regulatory system to control in vivo ANP expression. In the BPH/2 mouse model of HTN, Mfp-inducible ANP expression was seen for a period of >120 days after administration of vector. Physiological effects of ANP, including decreased systolic blood pressure, increased urinary cGMP output, and decreases in heart weight as a percentage of body weight were also under the control of Mfp. Given these capabilities, this vector represents a paradigm for the gene therapy of HTN.

Human eNOS gene delivery attenuates cold-induced elevation of blood pressure in rats

We previously showed that chronic cold exposure inhibits endothelial nitric oxide synthase (eNOS) expression and decreases nitric oxide (NO) production. The aim of the present study was to evaluate the possible role of the NO system in the development of cold-induced hypertension (CIH) by testing the hypothesis that adenoviral delivery of human eNOS gene increases NO production and attenuates CIH in rats. The effect of in vivo delivery of adenovirus carrying human eNOS full-length cDNA (rAdv.heNOS) on CIH was tested using four groups of Sprague-Dawley rats (6 rats/group). Blood pressure (BP) did not differ among the four groups during the control period at room temperature (24 degrees C). Two groups of rats received intravenous injection of rAdv.heNOS (1 x 10(9) plaque-forming units/rat), and the other two groups received the same dose of rAdv.LacZ to serve as controls. After gene delivery, one rAdv.heNOS-treated group and one rAdv.LacZ-treated group were exposed to cold (6 degrees C) while the remaining groups were kept at 24 degrees C. We found that the BP of the rAdv.LacZ group increased significantly within 1 wk of exposure to cold and reached a peak level at week 5 (152.2 +/- 6.4 mmHg). In contrast, BP (118.7 +/- 8.4 mmHg) of the cold-exposed rAdv.heNOS group did not increase until 5 wk after exposure to cold. The rAdv.heNOS increased plasma and urine levels of NO significantly in cold-exposed rats, which indicates that eNOS gene transfer increased NO production. Notably, rAdv.heNOS decreased plasma levels of norepinephrine and plasma renin activity in cold-exposed rats, which suggests that eNOS gene transfer may decrease the activities of the sympathetic nervous system and the renin-angiotensin system. Immunohistochemical analysis showed that the transferred human eNOS was expressed in both endothelium and adventitia of mesenteric arteries. We conclude that 1) eNOS gene transfer attenuates CIH by increasing NO production and inhibiting the sympathetic nervous system and the renin-angiotensin system; and 2) the NO system appears to mediate this nongenetic, nonpharmacological, nonsurgical model of hypertension.

Recombinant adeno-associated virus-mediated kallikrein gene therapy reduces hypertension and attenuates its cardiovascular injuries

Gene therapy of hypertension requires long-term expression of a therapeutic gene to achieve stable reduction of blood pressure. Human tissue kallikrein (HK) cleaves kininogen to produce a potent vasoactive peptide kinin, which plays an important role in the regulation of the cardiovascular and renal functions. In the present study, we have delivered human kallikrein cDNA with an rAAV vector to explore the potential therapeutic effects of kallikrein on hypertension and related secondary complications. A single tail vein injection of the rAAV-HK vector into the adult spontaneously hypertensive rats resulted in a significant reduction (12.0+/-2.55 mmHg, P<0.05, n=6, ANOVA) of the systolic blood pressure from 2 weeks after vector injection, when compared with the control rAAV-lacZ vector-injected rats. Weekly blood pressure monitoring showed stable hypertension-reduction effect throughout the course of the 20-week experiments. In addition, total urine microalbumin contents decreased as a result of rAAV-HK treatment. Histological analysis of various tissues showed remarkable amelioration of cardiovascular hypertrophy, renal injury and collagen depositions in the rAAV-treated group. Finally, persistent expression of the transgene product HK was confirmed by the enzyme-linked immunosorbent assay and reverse transcription-polymerase chain reaction. We conclude that rAAV-mediated HK delivery rendered a long-term and stable reduction of hypertension and protected against renal injury, cardiac remodeling in the spontaneously hypertensive rat model. Further studies are warranted for the development of a gene therapy strategy for human hypertension.

Central alpha2B-adrenergic receptor antisense in plasmid vector prolongs reversal of salt-dependent hypertension

OBJECTIVE

Previous studies have shown that a fully functional alpha(2B)-adrenergic receptor (AR) is necessary for the development of salt-induced hypertension. The current studies were designed to explore the effect of prolonged inhibition of central alpha(2B)-AR gene expression by antisense (AS) DNA on this hypertension.

METHODS

We developed a plasmid vector driven by a cytomegalovirus promoter, containing a green fluorescent protein reporter gene and AS for rat alpha(2B)-AR protein. Subtotally nephrectomized, salt-loaded hypertensive rats received intracerebroventricular injection of 500 microg of either the AS plasmid (n = 9) or sense plasmid (containing cDNA for alpha(2B)-AR), as control (n = 7).

RESULTS

The AS injection produced a fall in SBP from 201 +/- 4 to 171 +/- 5 mmHg within 12 h. The level of BP in the 3 days post-injection was 174 +/- 6, 181 +/- 4 and 184 +/- 6 mmHg on day 1, day 2 and day 3, respectively (P < 0.05), and returned gradually towards baseline in subsequent days, although it remained significantly lower for the 8 days of observation. The control sense plasmid injections produced no significant changes in blood pressure (BP). Neither group had histological evidence of neural tissue disruption.

CONCLUSIONS

These results indicate that protracted translational inhibition of the alpha(2B)-AR gene in the central nervous system can be obtained by AS DNA delivered via plasmid vector and lead to decreased generation of alpha(2B)-AR protein, which can partly reverse salt-induced hypertension for several days.

Gene Therapy for Cardiovascular Disease

The last decade has seen substantial advances in the development of gene therapy strategies and vector technology for the treatment of a diverse number of diseases, with a view to translating the successes observed in animal models into the clinic. Perhaps the overwhelming drive for the increase in vascular gene transfer studies is the current lack of successful long-term pharmacological treatments for complex cardiovascular diseases. The increase in cardiovascular disease to epidemic proportions has also led many to conclude that drug therapy may have reached a plateau in its efficacy and that gene therapy may represent a realistic solution to a long-term problem. Here, we discuss gene delivery approaches and target diseases.

Gene therapy for hypertension: the preclinical data

In spite of several drugs for the treatment of hypertension, there are many patients with poorly controlled high blood pressure. This is partly due to the fact that all available drugs are short-lasting (24 hr or less), have side effects, and are not highly specific. Gene therapy offers the possibility of producing longer-lasting effects with precise specificity from the genetic design. Preclinical studies on gene therapy for hypertension have taken two approaches. Chao et al. have carried out extensive studies on gene transfer to increase vasodilator proteins. They have transferred kallikrein, atrial natriuretic peptide, adrenomedullin, and endothelin nitric oxide synthase into different rat models. Their results show that blood pressure can be lowered for 3-12 weeks with the expression of these genes. The antisense approach, which we began by targeting angiotensinogen and the angiotensin type 1 receptor, has now been tested independently by several different groups in multiple models of hypertension. Other genes targeted include the beta 1-adrenoceptor, TRH, angiotensin gene activating elements, carboxypeptidase Y, c-fos, and CYP4A1. There have been two methods of delivery antisense; one is short oligodeoxynucleotides, and the other is full-length DNA in viral vectors. All the studies show a decrease in blood pressure lasting several days to weeks or months. Oligonucleotides are safe and nontoxic. The adeno-associated virus delivery antisense to AT1 receptors is systemic and in adult rodents decreases hypertension for up to 6 months. We conclude that there is sufficient preclinical data to give serious consideration to Phase I trials for testing the antisense ODNs, first and later the AAV.

The alpha2 -adrenergic receptors in hypertension and heart failure: experimental and clinical studies

This is a brief overview of experimental and clinical studies exploring the hemodynamic functions of the alpha2A and alpha2B adrenergic receptor (AR) subtypes in animals submitted to genetic manipulations or gene treatment, as well as the clinical effects of central sympathetic suppression with the alpha2-AR agonist clonidine in patients with ischemic heart disease and/or heart failure. The animal experiments have led us to conclude that the sympathetic outflow is regulated by activation of the presynaptic alpha2A-AR subtype, which is the predominant alpha2-AR subtype in the central nervous system and exerts a sympathoinhibitory (hypotensive) action; on the contrary, activation of the central alpha2B-AR elicits a sympathoexcitatory response (such as seen in salt-induced hypertension, which requires functionally intact alpha2B-AR). Since there are no selective pharmacologic agents yet capable of discriminating among alpha2-AR subtypes, clinical studies utilize clonidine, the central sympathetic suppressant effect of which has been used for 35 years to treat hypertension. In small clinical trials, clonidine was used successfully for treatment of acute or chronic heart failure, acute myocardial infarct or hypertensive cardiomyopathy with subclinical diastolic dysfunction. We speculate that future development of agents capable of selectively activating the alpha2A-AR or blocking the alpha2B-AR may further improve our capability to treat hypertension, ischemic heart disease and heart failure.

Tyrosine hydroxylase antisense gene therapy causes hypotensive effects in the spontaneously hypertensive rats

We investigated the effect of antisense oligodeoxynucleotides (AS ODN) against tyrosine hydroxylase (TH) on hypertension and sympathetic nervous system activity in spontaneously hypertensive rats (SHR). Systolic blood pressure (SBP) in SHR treated with TH AS ODN (50, 200 microg/rat, i.v.) was significantly lower than that of control SHR. Epinephrine and norepinephrine levels, TH activity, and TH protein levels in the adrenal medulla of SHR were reduced concomitant with TH AS ODN treatment-induced changes in SBP. In contrast, TH AS ODN (200 microg/rat) had no effect on SBP in Wistar-Kyoto rats (WKY), despite significantly decreased catecholamine levels, TH activity, and TH protein levels. These findings suggest that peripheral systemic injection of TH AS ODN may be effective as hypotensive therapy in SHR.

Gene therapy for hypertension: sense and antisense strategies

Gene therapy for hypertension is needed for the next generation of antihypertensive drugs. Current drugs, although effective, have poor compliance, are expensive and short-lasting (hours or one day). Gene therapy offers a way to produce long-lasting antihypertensive effects (weeks, months or years). We are currently using two strategies: antisense oligodeoxynucleotides (AS-ODN), an dantisense DNA delivered in viral vectors, to inhibit genes associated with vasoconstrictive properties. It is not necessary to know all the genes involved in hypertension, since many years of experience with drugs show which genes need to be controlled. AS-ODNs are short, single-stranded DNA that can be injected in naked form or in liposomes. AS-ODNs, targeted to AT1 receptors (AT1R), angiotensinogen (AGT), angiotensin converting enzyme (ACE) and beta 1-adrenergic receptors effectively reduce hypertension in rat models (SHR, 2K-1C and cold-induced) hypertension. The effects can last up to one month when delivered with liposomes. No side effects or toxic effects have been detected and repeated injections can be given. For the vector, adeno-associated virus (AAV) is used with a construct to include a CMV promoter, antisense DNA to AGT or AT1R and a reporter gene. Results in SHR demonstrate reduction and slowing of hypertension development with a single dose administration. Left ventricular hypertrophy is also reduced by AAV-AS-AGT treatment. Double transgenic mice (human renin plus human AGT) with high angiotensin II (Ang II) causing high blood pressure, treated with AAV-AT1R-AS, show a normalisation of blood pressure for over 6 months with a single injection of vector. We conclude that ODNs will probably be developed first because they can be treated like drugs for the treatment of hypertension with long-term effects. Viral vector delivery needs more engineering to be certain of its safety but one day may be used for a very prolonged control of blood pressure.

The current status of antihypertensive treatments: into the new millennium

In this short review, we present a historical perspective of the treatment of hypertension, highlight some current issues and look to the possible future of antihypertensive therapy. The distribution of blood pressure within the population adopts a continuous, albeit somewhat skewed, distribution, so what constitutes hypertension? Conventionally, the disease has been defined as a level of blood pressure >> 140/90 mmHg. Accepting this 'arbitrary' definition infers that approximately one quarter of the adult population in the US are hypertensive [1]. This has significant implications in terms of the impact upon public health. We know that treatment of hypertension can prevent the serious consequences of cardiovascular disease: stroke, myocardial infarction (MI), heart failure and renal disease. Thus, it is important that raised blood pressure is both detected and effectively lowered. To what level should blood pressure be reduced. Conventionally, a level of 120/80 mmHg has been used to define normotension but there are indications that under certain circumstances this should not be the target. The question also arises as to whether it matters how blood pressure is treated. The choice of agent may ultimately depend upon the presence of any concomitant condition and risk factors. Recent trial evidence has concluded that therapy selected to treat raised blood pressure should take into account the overall cardiovascular risk profile of the patient [2].

Recent developments in gene therapy for cardiac disease

Cardiovascular[TRACE;del] disease is the leading cause of death in the US and world-wide. Advances in molecular biology and the human genome project have revealed opportunities for novel strategies for cardiac gene therapy. This review discusses general and specific aspects of gene transfer strategies in cardiac tissues. These include 1) the selection and/or optimization of the vector for gene transfer; 2) the identification of the target gene(s); 3) the use of cardiac-specific promoters; and 4) the use of an appropriate delivery system for administration. Currently, several vectors (e.g., viral and nonviral vectors) have been developed and many target genes have been identified (e.g., VEGF, FGF, beta-AR, etc.). Many investigations have provided experimental models for gene delivery systems but the most efficient cardiac gene transfer was obtained from intramyocardial injection or perfusion of explanted myocardium. The data available thus far have suggested favorable immediate effects following gene transfer, but long-term value of cardiac gene therapy has not been proven. Further refinements in appropriate vectors that provide cell or tissue selectivity and long-lasting effects are necessary as well as the development of minimally invasive procedures for gene transfer.

Gene therapy for atherosclerotic cardiovascular disease: a time for optimism and caution

Cardiovascular disease is the leading cause of death in the Western world, and gene therapy approaches to several cardiovascular disorders have been proposed. One of the major stumbling blocks to be overcome before widespread clinical use of this technology is how to deliver DNA efficiently and safely to cells in vivo. While delivery of DNA alone is inefficient, use of viral vectors may overcome this problem. Adenoviral vectors are most commonly used in cardiovascular gene delivery, but toxicity related to these vectors remains a concern. In addition, duration of gene expression with use of these vectors is limited, which may be advantageous in settings in which transient expression is satisfactory to obtain a therapeutic effect. Gene therapy has been suggested as an approach to multiple conditions, including restenosis after angioplasty, therapeutic neovascularization, and bypass graft restenosis. Phase 1 clinical trials were recently reported. While proof of principle has been established in preclinical animal models, convincing efficacy data in humans do not yet exist. Improvements in vector technology and methods of catheter-mediated vascular gene delivery are needed before widespread clinical application of this therapy.

The potential role of antisense oligodeoxynucleotide therapy for cardiovascular disease

Current drugs used in the treatment of cardiovascular disease are effective but compliance is poor and they are short acting (hours or one day). Gene therapy offers a way to produce long-lasting effects (weeks, months or years). Antisense inhibition is being developed for the treatment of hypertension, myocardial ischaemia and improved allograft survival in human vascular bypass grafts. We are currently using 2 strategies: (i) antisense oligodeoxynucleotides (AS-ODNs) which are delivered nonvirally and (ii) antisense DNA delivered in viral vectors to inhibit genes associated with vasoconstrictive properties. It is not necessary to know all the genes involved in hypertension, since many years of experience with drugs show which genes need to be controlled. AS-ODN are short, single-stranded DNA that can be injected in naked form or in liposomes. AS-ODN targeted to angiotensin type 1 (AT1) receptors, angiotensinogen (ATG), angiotensin converting enzyme (ACE) and beta1 adrenoceptors effectively reduce hypertension in rat models. A single dose is effective for up to one month when delivered with liposomes. No adverse or toxic effects have been detected, and repeated injections are effective. For viral delivery, adeno-associated virus (AAV) is used with a construct to include a cytomegalovirus or tissue-specific promoter, antisense DNA to ATG, ACE or AT1 receptors and a reporter gene. Results in rats and transgenic mice show significant prolonged reduction of hypertension, with a single dose administration of AAV-AS. Left ventricular hypertrophy is also reduced by antisense treatment. AS-ODNs to AT1 receptors, ATG and beta1 adrenoceptors provide cardioprotection from the effects of myocardial ischaemia. The AT1 receptor is more protective than losartan and does not increase plasma angiotensin as losartan does.

Somatic gene therapy for hypertension

Gene therapy for hypertension is needed for the next generation of antihypertensive drugs. Current drugs, although effective, have poor compliance, are expensive and short-lasting (hours or one day). Gene therapy offers a way to produce long-lasting antihypertensive effects (weeks, months or years). We are currently using two strategies: a) antisense oligodeoxynucleotides (AS-ODN) and b) antisense DNA delivered in viral vectors to inhibit genes associated with vasoconstrictive properties. It is not necessary to know all the genes involved in hypertension, since many years of experience with drugs show which genes need to be controlled. AS-ODN are short, single-stranded DNA that can be injected in naked form or in liposomes. AS-ODN, targeted to angiotensin type 1 receptors (AT1-R), angiotensinogen (AGT), angiotensin converting enzyme, and ss1-adrenergic receptors effectively reduce hypertension in rat models (SHR, 2K-1C) and cold-induced hypertension. A single dose is effective up to one month when delivered with liposomes. No side effects or toxic effects have been detected, and repeated injections can be given. For the vector, adeno-associated virus (AAV) is used with a construct to include a CMV promoter, antisense DNA to AGT or AT1-R and a reporter gene. Results in SHR demonstrate reduction and slowing of development of hypertension, with a single dose administration. Left ventricular hypertrophy is also reduced by AAV-AGT-AS treatment. Double transgenic mice (human renin plus human AGT) with high angiotensin II causing high blood pressure, treated with AAV-AT1-R-AS, show a normalization of blood pressure for over six months with a single injection of vector. We conclude that ODNs will probably be developed first because they can be treated like drugs for the treatment of hypertension with long-term effects. Viral vector delivery needs more engineering to be certain of its safety, but one day may be used for a very prolonged control of blood pressure.

Gene therapy of hypertensive vascular injury

Hypertension and vascular injury usually require prolonged treatment, and compliance is a key to efficacy for pharmacologically-based antihypertensive therapy. Gene therapy has the potential to be long lasting, with few side effects. Recent studies have provided promising results, in which hypertension can be treated by either augmentation of vasodilation or inhibition of vasoconstriction through gene transfer in experimental models. Gene transfer is also becoming useful for the study of mechanisms of physiologic and pathophysiologic conditions, including hypertension. In this mini-review, we summarize some recent studies in this area of research, and suggest some areas where progress is needed to advance the research toward gene therapy.

Cardiovascular gene therapy

Vascular gene transfer potentially offers new treatments for cardiovascular diseases. It can be used to overexpress therapeutically important proteins and correct genetic defects, and to test experimentally the effects of various genes in a local vascular compartment. Vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) gene transfers have improved blood flow and collateral development in ischaemic limb and myocardium. Promising therapeutic effects have been obtained in animal models of restenosis or vein-graft thickening with the transfer of genes coding for VEGF, nitric-oxide synthase, thymidine kinase, retinoblastoma, growth arrest homoeobox, tissue inhibitor of metalloproteinases, cyclin or cyclin-dependent kinase inhibitors, fas ligand and hirudin, and antisense oligonucleotides against transcription factors or cell-cycle regulatory proteins. First experiences of VEGF gene transfer and decoy oligonucleotides in human beings have been reported. However, further developments in gene-transfer vectors, gene-delivery techniques and identification of effective treatment genes will be required before the full therapeutic potential of gene therapy in cardiovascular disease can be assessed.

Vectors for gene therapy of cardiovascular disease

Several phase I/II clinical trials are currently ongoing in gene therapy of cardiovascular disease. Whereas the indications vary, including peripheral artery disease, ischemic heart disease, post-angioplasty restenosis, and vein graft failure, these trials are mostly based on the use of adenoviral vectors and nonviral vectors. Novel vectors aimed at improving the efficacy and safety of gene delivery in target organs, such as heart, skeletal muscle, vasculature, and liver, have been recently generated. Some of them have already been successfully validated in preclinical models of cardiovascular disease. This review focuses on the most recent advances in vector development that could substantially increase the spectrum of cardiovascular pathologies amenable to gene transfer-based treatments.

Intravenous angiotensinogen antisense in AAV-based vector decreases hypertension

Angiotensinogen (AGT) has been linked to hypertension. Because there are no direct inhibitors of AGT, we have developed antisense (AS) inhibition of AGT mRNA delivered in an adeno-associated virus (AAV)-based plasmid vector. This plasmid, driven by the cytomegalovirus promoter, contains a green fluorescent protein reporter gene and AS cDNA for rat AGT. Transfection of the plasmid into rat hepatoma cells brought a strong expression of the transgenes and a significant reduction in the level of AGT. In the in vivo study, naked plasmid DNA was intravenously injected into adult spontaneously hypertensive rats at different doses (0.6, 1.5, and 3 mg/kg). Expression of AGT AS mRNA was present in liver and heart, and it lasted longer in the liver. All three doses produced a significant decrease in blood pressure (BP). BP decreased for 2, 4, and 6 days, respectively. The lowest dose decreased BP by 12 +/- 3.0 mmHg, whereas the higher doses decreased BP by up to 22.5 +/- 5.2 mmHg compared with the control rats injected with saline (P < 0.01). The injection of the plasmid with liposomes produced a more profound and longer reduction (8 days) in BP. Consistent changes in plasma AGT level were observed. Sense plasmid had no effect. No liver toxicity was observed after injection of AS plasmid with or without liposomes. Our results suggest that the systemic delivery of AS against AGT mRNA by AAV-based plasmid vector, especially with liposomes, may have potential for gene therapy of hypertension and that further studies with the plasmid packaged into a recombinant AAV vector for a longer-lasting AS effect are warranted.

Beneficial interactions between pharmacological, pathophysiological and hypertension research

The treatment of essential hypertension continues to be carried out by drugs, combined with the adaptation of life style. The development of various types of antihypertensive drugs has not only greatly improved the management of hypertension, but also offered significant methodological sophistication of the pharmacological and pathophysiological sciences. Antihypertensive drugs and related experimental agents have been widely used in pharmaco-logical and pathophysiological research. The beneficial effects of such agents will be illustrated by means of several examples, emphasizing the sympathetic nervous system, the renin-angiotensin-aldosterone system, and calcium homeostasis as major targets. As pharmacological tools, which are also antihypertensives, we discuss various types of centrally acting antihypertensives, ganglionic and peripheral neuronal blocking agents, alpha- and beta-adrenoceptor antagonists, angiotensin converting enzyme (ACE)-inhibitors, renin-inhibitors, angiotensin II-receptor antagonists (AT1-blockers) and calcium antagonists. Finally, a few remarks will be made concerning the beneficial therapeutic effects of classic and newer antihypertensive drugs, such as beta-blockers, diuretics, calcium antagonists, ACE-inhibitors and AT1-blockers.