Attenuation of hypertension and heart hypertrophy by adeno-associated virus delivering angiotensinogen antisense

Angiotensinogen: More Than its Downstream Products: Evidence From Population Studies and Novel Therapeutics

The renin-angiotensin-aldosterone system (RAAS) is a well-defined pathway playing a key role in maintaining circulatory homeostasis. Abnormal activation of RAAS contributes to development of cardiovascular disease, including heart failure, cardiac hypertrophy, hypertension, and atherosclerosis. Although several key RAAS enzymes and peptide hormones have been thoroughly investigated, the role of angiotensinogen-the precursor substrate of the RAAS pathway-remains less understood. The study of angiotensinogen single-nucleotide polymorphisms (SNPs) has provided insight into associations between angiotensinogen and hypertension, congestive heart failure, and atherosclerotic cardiovascular disease. Targeted drug therapy of RAAS has dramatically improved clinical outcomes for patients with heart failure, myocardial infarction, and hypertension. However, all such therapeutics block RAAS components downstream of angiotensinogen and elicit compensatory pathways that limit their therapeutic efficacy as monotherapy. Upstream RAAS targeting by an angiotensinogen inhibitor has the potential to be more efficacious in patients with suboptimal RAAS inhibition and has a better safety profile than multiagent RAAS blockade. Newly developed therapeutics that target angiotensinogen through antisense oligonucleotides or silencer RNA technologies are providing a novel perspective into the pathobiology of angiotensinogen and show promise as the next frontier in the treatment of cardiovascular disease.

Aging impairs arterial compliance via Klotho-mediated downregulation of B-cell population and IgG levels

OBJECTIVE

Aging is associated with compromised immune function and arterial remodeling and stiffness. The purpose of this study is to investigate whether in vivo AAV-based delivery of secreted Klotho (SKL) gene (AAV-SKL) improves aging- and senescence-associated immune dysfunction and arterial stiffness.

METHODS AND RESULTS

Senescence-accelerated mice prone strain 1 (SAMP1, 10 months) and old mice (20 months) were used. Serum SKL levels, B-cell population and serum IgG levels were markedly decreased in SAMP1 and old mice. Rescue of downregulation of serum SKL levels by in vivo AAV2-based delivery of SKL gene (AAV-SKL) increased B-cell population and serum IgG levels and attenuated arterial stiffness in SAMP1 and old mice. Thus, Klotho deficiency may play a role in senescence- and aging-associated humoral immune dysfunction and arterial stiffness. Vascular infiltration of inflammatory cells and expression of TGFβ1, collagen 1, scleraxis, MMP-2 and MMP-9 were increased while the elastin level was decreased in aortas of SAMP1 and old mice which can be rescued by AAV-SKL. Interestingly, treatment with IgG effectively rescued arterial inflammation and remodeling and attenuated arterial stiffness and hypertension in aging mice. In cultured B-lymphoblast cells, we further showed that SKL regulates B-cell proliferation and maturation partly via the NFkB pathway.

CONCLUSION

Aging-associated arterial stiffening may be largely attributed to downregulation of B-cell population and serum IgG levels. AAV-SKL attenuates arterial stiffness in aging mice partly via restoring B-cell population and serum IgG levels which attenuates aging-associated vascular inflammation and arterial remodeling.

Effects of Angiotensin II type I receptor shRNA on blood pressure and left ventricular remodeling in spontaneously hypertensive rats

This study was designed to investigate the effects of the Angiotensin II type I receptor (AT1R) shRNA on blood pressure and left ventricular remodeling in spontaneously hypertensive rats. Ten Wistar Kyoto (WKY) rats were used as a normal blood pressure control group, and 20 spontaneously hypertensive rats (SHR) were randomly divided into the experimental and hypertension control groups. The rats in the experimental group were injected with AT1R shRNA recombinant adenovirus (Ad5-AT1R-shRNA) via a tail vein, and the rats in the other two groups were injected with recombinant adenovirus (Ad5-EGFP). The systolic blood pressure (SBP) at rat arteria caudalis was measured before and after the injection, and the heart, kidney, aorta, and adrenal tissues were obtained two days after repeated injection to observe the distribution of Ad5-AT1R-shRNA under a fluorescence microscope. Before the injection of Ad5-AT1R-shRNA, the blood pressure of the experimental group and the hypertension control group was significantly higher than that of the normal blood pressure control group (P<0.01). After two injections, the blood pressure in the experimental group decreased significantly, and the duration of blood pressure reduction reached 19 days. In the experimental group, the kidney, heart, aorta, and adrenal gland tissues showed vigorous fluorescence expression under the fluorescence microscope. Repeated administration of Ad5-AT1R-shRNA has a long-lasting hypotensive effect on SHR and can significantly improve ventricular remodeling.

Training-Induced Deactivation of the AT1 Receptor Pathway Drives Autonomic Control and Heart Remodeling During the Transition From the Pre- to Hypertensive Phase in Spontaneously Hypertensive Rats

BACKGROUND

The effects of hypertension and exercise training (T) on the sequential interplay between renin-angiotensin system (RAS), autonomic control and heart remodeling during the development of hypertension in spontaneously hypertensive rats (SHR), was evaluated.

METHODS AND RESULTS

Time course changes of these parameters were recorded in 4-week-old SHR submitted to a T or sedentary (S) protocol. Wistar Kyoto rats served as controls. Hemodynamic recordings were obtained in conscious rats at experimental weeks 0, 1, 2, 4, and 8. The left ventricle (LV) was collected to evaluate RAS gene and protein expression, cardiomyocytes' hypertrophy and collagen accumulation. Pre-hypertensive SHR exhibited augmented AT1R gene expression; at 5 weeks, they presented with elevated pressure, increased LV angiotensinogen and ACE mRNA expression, followed by sympathoexcitation (from the 8thweek onwards). Marked AT1R protein content, myocytes's hypertrophy, collagen deposition and increased pressure variability were observed in 12-week-old sedentary SHR. In addition to attenuating all these effects, T activated Mas receptor expression augmented parasympathetic modulation of the heart, and delayed the onset and reduced the magnitude, but did not block the development of genetic hypertension.

CONCLUSIONS

The close temporal relationship between changes in the LV ACE-Ang II-AT1R axis, autonomic control and cardiac remodeling at both the establishment of hypertension and during exercise training reveals the essential role played by the AT1R pathway in driving cardiac remodeling and autonomic modulation during the transition from the pre- to hypertensive phase.

The emerging role of angiotensinogen in cardiovascular diseases

Angiotensinogen (AGT) is the unique precursor of all angiotensin peptides. Many of the basic understandings of AGT in cardiovascular diseases have come from research efforts to define its effects on blood pressure regulation. The development of novel techniques targeting AGT manipulation such as genetic animal models, adeno-associated viral approaches, and antisense oligonucleotides made it possible to deeply investigate the relationship between AGT and cardiovascular diseases. In this brief review, we provide contemporary insights into the emerging role of AGT in cardiovascular diseases. In light of the recent progress, we emphasize some newly recognized features and mechanisms of AGT in heart failure, hypertension, atherosclerosis, and cardiovascular risk factors.

Antisense oligonucleotides targeting angiotensinogen: insights from animal studies

Angiotensinogen (AGT) is the unique substrate of all angiotensin peptides. We review the recent preclinical research of AGT antisense oligonucleotides (ASOs), a rapidly evolving therapeutic approach. The scope of the research findings not only opens doors for potentially new therapeutics of hypertension and many other diseases, but also provides insights into understanding critical physiological and pathophysiological roles mediated by AGT.

Preservation of cardiac function in left ventricle cardiac hypertrophy using an AAV vector which provides VEGF-A expression in response to p53

Here we present the application of our adeno-associated virus (AAV2) vector where transgene expression is driven by a synthetic, p53-responsive promoter, termed PG, used to supply human vascular endothelial growth factor-A165 (VEGF-A). Thus, p53 is harnessed to promote the beneficial expression of VEGF-A encoded by the AAVPG vector, bypassing the negative effect of p53 on HIF-1α which occurs during cardiac hypertrophy. Wistar rats were submitted to pressure overload induced by thoracic aorta coarctation (TAC) with or without concomitant gene therapy (intramuscular delivery in the left ventricle). After 12 weeks, rats receiving AAVPG-VEGF gene therapy were compared to those that did not, revealing significantly improved cardiac function under hemodynamic stress, lack of fibrosis and reversal of capillary rarefaction. With these functional assays, we have demonstrated that application of the AAVPG-VEGF vector under physiologic conditions known to stimulate p53 resulted in the preservation of cardiac performance.

Caveolin and β1-integrin coordinate angiotensinogen expression in cardiac myocytes

BACKGROUND

The cardiac renin-angiotensin system (RAS) has been implicated in mediating myocyte hypertrophy and remodeling, although the biochemical mechanisms responsible for regulating the local RAS are poorly understood. Caveolin-1 (Cav-1)/Cav-3 double-knockout mice display cardiac hypertrophy, and in vitro disruption of lipid rafts/caveolae using methyl-β-cyclodextrin (MβCD) abolishes cardiac protection.

METHODS

In this study, neonatal rat ventricular myocytes (NRVM) were used to determine whether lipid rafts/caveolae may be involved in the regulation of angiotensinogen (Ao) gene expression, a substrate of the RAS system.

RESULTS

Treatment with MβCD caused a time-dependent upregulation of Ao gene expression, which was associated with differential regulation of mitogen-activated protein (MAP) kinases ERK1/2, p38 and JNK phosphorylation. JNK was highly phosphorylated shortly after MβCD treatment (2-30 min), whereas marked activation of ERK1/2 and p38 occurred much later (2-4h). β1D-Integrin was required for MβCD-induced activation of the MAP kinases. Pharmacologic inhibition of ERK1/2 and JNK enhanced MβCD-induced Ao gene expression, whereas p38 blockade inhibited this response. Adenovirus-mediated expression of wild-type p38α enhanced MβCD-induced Ao gene expression; conversely expression of dominant negative p38α blocked the stimulatory effects of MβCD. Expression of Cav-3 siRNA stimulated Ao gene expression, whereas overexpression of Cav-3 was inhibitory. Cav-1 and Cav-3 expression levels were found to be positively regulated by p38, but unaffected by ERK1/2 and JNK.

CONCLUSION

Collectively, these studies indicate that lipid rafts/caveolae couple to Ao gene expression through a mechanism that involves β1-integrin and the differential actions of MAP kinase family members.

The effects of repeated delivery of angiotensin II AT(1) receptor antisense on distinct vasoactive systems in Ren-2 transgenic rats: young vs. adult animals

Although Ren-2 transgenic rat (TGR) is defined as a model of angiotensin II-dependent hypertension, we studied whether the renin-angiotensin system (RAS) is really the main contributor to blood pressure (BP) elevation in hetero- and homozygous TGRs. Moreover, we examined whether repeated antisense (AS) therapy against AT(1) receptors would have a similar effect on the BP and the contribution of the principle vasoconstrictor/vasodilator systems to BP regulation in young and adult TGRs. From the age of 30 (young) and 100 (adult) days, rats were injected with AS for 40 days in 10-day intervals. After 10 and 40 days of AS therapy, the basal BP and acute BP responses to the sequential blockade of the RAS, sympathetic nervous (SNS) and nitric oxide systems were determined in conscious rats. The RAS system was the major system maintaining elevated BP in young homozygous animals, whereas there was an increasing contribution of the SNS in heterozygous TGR with age. The AS therapy in the young TGR had a transient BP-lowering effect that was associated with reduced cardiac hypertrophy; the AS therapy was most effective in young homozygous TGR, causing a substantial reduction of angiotensin-dependent vasoconstriction. In heterozygous rats, AS therapy at earlier stages was related to an inhibition of sympathetic vasoconstriction, whereas to RAS inhibition in established hypertension. In conclusion, repeated AS therapy had transient antihypertensive effects exclusively in young TGR. The contribution of the RAS to BP maintenance is highly important only in homozygous TGRs, whereas it is surpassed by SNS in heterozygous TGR.

Ribonucleic acid interference knockdown of interleukin 6 attenuates cold-induced hypertension

The purpose of this study was to determine the role of the proinflammatory cytokine interleukin (IL) 6 in cold-induced hypertension. Four groups of male Sprague-Dawley rats were used (6 rats per group). After blood pressure was stabilized, 3 groups received intravenous delivery of adenoassociated virus carrying IL-6 small hairpin RNA (shRNA), adenoassociated virus carrying scrambled shRNA, and PBS, respectively, before exposure to a cold environment (5 degrees C). The last group received PBS and was kept at room temperature (25 degrees C, warm) as a control. Adenoassociated virus delivery of IL-6 shRNA significantly attenuated cold-induced elevation of systolic blood pressure and kept it at the control level for < or =7 weeks (length of the study). Chronic exposure to cold upregulated IL-6 expression in aorta, heart, and kidneys and increased macrophage and T-cell infiltration in kidneys, suggesting that cold exposure increases inflammation. IL-6 shRNA delivery abolished the cold-induced upregulation of IL-6, indicating effective silence of IL-6. Interestingly, RNA interference knockdown of IL-6 prevented cold-induced inflammation, as evidenced by a complete inhibition of tumor necrosis factor-alpha expression and leukocyte infiltration by IL-6 shRNA. RNA interference knockdown of IL-6 significantly decreased the cold-induced increase in vascular superoxide production. It is noted that IL-6 shRNA abolished the cold-induced increase in collagen deposition in the heart, suggesting that inflammation is involved in cold-induced cardiac remodeling. Cold exposure caused glomerular collapses, which could be prevented by knockdown of IL-6, suggesting an important role of inflammation in cold-induced renal damage. In conclusion, cold exposure increased IL-6 expression and inflammation, which play critical roles in the pathogenesis of cold-induced hypertension and cardiac and renal damage.

Stretch-induced regulation of angiotensinogen gene expression in cardiac myocytes and fibroblasts: opposing roles of JNK1/2 and p38alpha MAP kinases

The cardiac renin-angiotensin system (RAS) has been implicated in mediating myocyte hypertrophy, remodeling, and fibroblast proliferation in the hemodynamically overloaded heart. However, the intracellular signaling mechanisms responsible for regulation of angiotensinogen (Ao), a substrate of the RAS system, are largely unknown. Here we report the identification of JNK1/2 as a negative, and p38alpha as a major positive regulator of Ao gene expression. Isolated neonatal rat ventricular myocytes (NRVM) and fibroblasts (NRFB) plated on deformable membranes coated with collagen IV, were exposed to 20% equiaxial static-stretch (0-24 h). Mechanical stretch initially depressed Ao gene expression (4 h), whereas after 8 h, Ao gene expression increased in a time-dependent manner. Blockade of JNK1/2 with SP600125 increased basal Ao gene expression in NRVM (10.52+/-1.98 fold, P<0.001) and NRFB (13.32+/-2.07 fold, P<0.001). Adenovirus-mediated expression of wild-type JNK1 significantly inhibited, whereas expression of dominant-negative JNK1 and JNK2 increased basal and stretch-mediated (24 h) Ao gene expression, showing both JNK1 and JNK2 to be negative regulators of Ao gene expression in NRVM and NRFB. Blockade of p38alpha/beta by SB202190 or p38alpha by SB203580 significantly inhibited stretch-induced (24 h) Ao gene expression, whereas expression of wild-type p38alpha increased stretch-induced Ao gene expression in both NRVM (8.41+/-1.50 fold, P<0.001) and NRFB (3.39+/-0.74 fold, P<0.001). Conversely, expression of dominant-negative p38alpha significantly inhibited stretch response. Moreover, expression of constitutively active MKK6b (E) significantly stimulated Ao gene expression in the absence of stretch, indicating that p38 activation alone is sufficient to induce Ao gene expression. Taken together p38alpha was demonstrated to be a positive regulator, whereas JNK1/2 was found to be a negative regulator of Ao gene expression. Prolonged stretch diminished JNK1/2 activation, which was accompanied by a reciprocal increase in p38 activation and Ao gene expression. This suggests that a balance in JNK1/2 and p38alpha activation determines the level of Ao gene expression in myocardial cells.

AAV vectors for RNA-based modulation of gene expression

At the post-transcriptional level, gene expression is largely regulated through a network of molecular machines that regulate pre-mRNA maturation integrity, transport, translation and degradation. These processes are based on the formation of nucleoprotein complexes and require the recognition of sequence motifs on the RNA. By masking these targets with complementary RNA sequences forming Watson-Crick base pairing, it is possible to efficiently and specifically impact on the cell phenotype, or to compensate the deleterious effect of mutations. Here we review how the adeno-associated virus technology is being exploited for expressing non-coding RNAs in tissues such as the brain, muscle or liver, in functional genomic studies as well as for the development of novel therapeutic strategies.

Genetic modification of stem cells for transplantation

Gene modification of cells prior to their transplantation, especially stem cells, enhances their survival and increases their function in cell therapy. Like the Trojan horse, the gene-modified cell has to gain entrance inside the host's walls and survive and deliver its transgene products. Using cellular, molecular and gene manipulation techniques the transplanted cell can be protected in a hostile environment from immune rejection, inflammation, hypoxia and apoptosis. Genetic engineering to modify cells involves constructing modules of functional gene sequences. They can be simple reporter genes or complex cassettes with gene switches, cell specific promoters and multiple transgenes. We discuss methods to deliver and construct gene cassettes with viral and non-viral delivery, siRNA, and conditional Cre/Lox P. We review the current uses of gene-modified stem cells in cardiovascular disease, diabetes, neurological diseases, (including Parkinson's, Alzheimer's and spinal cord injury repair), bone defects, hemophilia, and cancer.

Recombinant adeno-associated virus-mediated delivery of antisense angiotensin II receptor 1 gene attenuates hypertension development

AIM

The renin-angiotensin system plays a crucial role in the development and establishment of hypertension, and the pharmacological blockade of the system results in a reduction in blood pressure. In the present study, we investigated whether the effects of a novel, double-stranded, recombinant adeno-associated virus vector (rAAV)-mediated antisense angiotensin II receptor 1 (AT1R) gene efficiently prevents the development of hypertension induced by a high-salt diet in adult, male Sprague-Dawley (SD) rats.

METHODS

A rAAV was prepared with a cassette containing a cytomegalovirus promoter and partial cDNA (660 base pairs) for the AT1R inserted in the antisense direction (rAAV-AT1-AS). A single tail vein injection of the rAAV-AT1-AS or rAAV-GFP (green fluorescent protein, a reporter gene) was performed in adult, male SD rats. Two weeks after injection, the animals were fed a diet containing 8% NaCl, and the systolic blood pressure was measured weekly using the tail-cuff method for 12 weeks.

RESULTS

The high-salt diet induced a significant rise in systolic blood pressure in the rAAV-GFP-treated animals; however, the rAAV-AT1-AS treatment attenuated the rise in blood pressure (142.7+/-4.5 mmHg vs 117+/-3.8 mmHg, P<0.01), and the hypotensive effect was maintained until the experiments ended at 12 weeks. In the rAAV-GFP-treated animals AT1 was overexpressed in various tissues, especially in the aorta and kidney at mRNA levels; in contrast, rAAV-AT1-AS treatment markedly attenuated AT1 expression. Furthermore, rAAV-AT1-AS treatment prevented target organ damages from hypertension, including cardiac dysfunction and renal injury compared to the rAAV-GFP group.

CONCLUSION

These results suggest that rAAVmediated anti-AT1 delivery attenuates the development of hypertension and protects against renal injury and cardiac remodeling.

Inhibition of atherogenesis in LDLR knockout mice by systemic delivery of adeno-associated virus type 2-hIL-10

Atherosclerosis is an inflammatory disease of the arteries. Interleukin-10 (IL-10) is known to be an anti-inflammatory cytokine which might be useful for counteracting the development of atherosclerosis. As long-term systemic cytokine delivery is prohibitively expensive, gene therapy might be a suitable approach. To test this idea, low-density lipoprotein receptor (LDLR) knockout mice were injected with recombinant adeno-associated virus type 2 (AAV)/interleukin-10 virus or AAV/granulocyte macrophage-colony stimulating factor (GM-CSF) virus and then put on a high-cholesterol diet. Upon harvesting the animals at 18 weeks, elevated blood lipids could be documented and AAV/IL-10 and AAV/GM-CSF DNA and mRNA could be found in various mouse organs. The mice receiving the AAV/IL-10 virus had significantly lower levels of atherogenesis (Sudan IV-staining and histology) than the untreated or the AAV/GM-CSF-treated animals, dropping from 53% to 17% (p < 0.05). The aortas of the AAV/IL-10-treated animals displayed higher IL-10 expression and lower CD68 and nitrotyrosine expression. These data are similar to those of Yoshioka et al. [Yoshioka, T, Okada, T, Maeda, Y, et al. Adeno-associatedvirus vector-mediated interleukin-10 gene transfer inhibits atherosclerosis in apolipoprotein E-deficient mice. Gene Ther 2004;11:1772-9] in which AAV/IL-10 was delivered into the tibial muscle of ApoE-deficient mice, instead of tail vein injection used here. These data indicate that systemic AAV/IL-10 gene delivery, with resulting inhibition of inflammation and oxidative stress, was able to limit atherogenesis, and suggest that this approach is worthy of further study.

Hypertensive heart disease

Left ventricular hypertrophy (LVH) and diastolic dysfunction (CHF-D) are the early manifestations of cardiovascular target organ damage in patients with arterial hypertension and signify hypertensive heart disease. Identification of hypertensive heart disease is critical, as these individuals are more prone to congestive heart failure, arrhythmias, myocardial infarction and sudden cardiac death. Regression of left ventricular (LV) mass with antihypertensive therapy decreases the risk of future cardiovascular events. The goal of antihypertensive therapy is to both lower blood pressure (BP) and interrupt BP-independent pathophysiologic processes that promote LVH and CHF-D. The purpose of this review is to summarize current and emerging approaches to the pathophysiology and treatment of hypertensive heart disease.

Effects of suppressing intrarenal angiotensinogen on renal transforming growth factor-beta1 expression in acute ureteral obstruction

BACKGROUND

Angiotensin II (Ang II) mediates the up-regulation of fibrogenic factors such as transforming growth factor-beta1 (TGF-beta1) in chronic renal diseases. In addition, it has been proposed that the intrarenal renin-angiotensin system (RAS) is as important as the systemic RAS in kidney disease progression.

METHODS

We suppressed angiotensinogen (AGT) gene expression in the kidney by transferring recombinant adenoviral vectors carrying a transgene expressing AGT antisense mRNA, and determined the effect of the local inhibition of the RAS on TGF-beta1 synthesis in the kidneys of rats with unilateral ureteral obstruction (UUO). Immediately after UUO, recombinant adenovirus vectors were injected intraparenchymally into the cortex of obstructed kidneys.

RESULTS

beta-galactosidase (beta-gal)-stained kidney sections revealed the efficient transduction of the recombinant adenoviral vectors into tubular epithelial cells. Kidney cortex injected with AGT antisense showed significantly lower native AGT mRNA and protein expressions than control UUO kidneys at 24 hours and 5 days post-UUO. TGF-beta1 was significantly up-regulated in the renal cortex 24 hours and 5 days post-UUO, whereas AGT antisense-injected UUO rats showed significantly reduced TGF-beta1 expression compared to control UUO rats. Both fibronectin and collagen type I expressions were increased 24 hours and 5 days post-UUO, and these augmentations were considerably reduced by AGT antisense RNA treatment.

CONCLUSION

This study demonstrates that the suppression of intrarenal RAS prevents the formation of renal cortical TGF-beta1, and of related fibrogenic factors, in early UUO.

Cloning and characterization of a secreted form of angiotensin-converting enzyme 2

Angiotensin-converting enzyme 2 (ACE2) is a newly discovered, membrane-bound aminopeptidase responsible for the production of vasodilatory peptides such as angiotensin 1-7 (Ang 1-7). Thus, ACE2 is important in counteracting the adverse, vasoconstrictor effects of angiotensin II (Ang II). The objective of the present study was to clone and characterize a constitutively secreted form of ACE2 as a prelude to an investigation into its therapeutic potential in hypertension. A truncated form of ACE2 was cloned into a lentiviral vector behind the human elongation factor 1 alpha promoter (lenti-shACE2). Transfection experiments demonstrated that secreted human ACE2 (shACE2) was secreted constitutively into the medium. The kinetic properties of shACE2 were comparable to the human recombinant enzyme (rACE2). Transduction of human coronary artery endothelial cells and rat cardiomyocytes with lenti-shACE2 showed a significant secretion of the enzyme into the medium compared to its native, membrane-bound homolog (human ACE2 [hACE2]). In addition, systemic administration of lenti-shACE2 into neonatal rats resulted in a eightfold increase in ACE2 activity in the serum above control values. These observations establish that lenti-shACE2 can be used to transduce cardiovascularly relevant cells for the secretion of functional ACE2 enzyme both in vitro and in vivo. Collectively, these results set the stage for the use of these vectors to investigate the consequences of ACE2 over-expression in the pathogenesis of hypertension.

Antihypertensive drugs and the heart

Left ventricular hypertrophy (LVH) and diastolic dysfunction (CHF-D) are early signs of cardiac end-organ damage (hypertensive heart disease) in patients with arterial hypertension. The presence of LVH or CHF-D confers increased risk of cardiovascular morbidity and mortality in patients with hypertension. Regression of left ventricular mass with antihypertensive therapy is associated with reduction in cardiovascular events. Antihypertensive therapy should be geared to both lower blood pressure and specifically reverse the pathophysiologic processes that may be independent of actual blood pressure. This review summarizes current and emerging approaches to the treatment of individuals with hypertensive heart disease.

Elevated blood pressure in normotensive rats produced by ‘knockdown’ of the angiotensin type 2 receptor

Most of our knowledge of the function of the angiotensin type 2 receptor (AT(2)R) has been obtained from transgenic mouse models. The aim of the present study was to investigate the role of the AT(2)R in normotensive Sprague-Dawley (SD) rats by using antisense gene transfer technology to 'knockdown' this specific receptor subtype. A retroviral vector containing full-length AT(2)R antisense cDNA (AT(2)R-AS) was constructed and the effectiveness of the transduction of AT(2)R-AS was studied in vitro. In subsequent in vivo studies, 5-day-old normotensive SD rats received a single intracardiac bolus (25 microl) of AT(2)R-AS viral particles. When animals reached adulthood, direct blood pressure (BP), and both pressor and dipsogenic responses to angiotensin II were investigated. Long-lasting expression of the AT(2)R-AS transcript and a reduction in mRNA and binding of the AT(2)R was observed in vitro. Expression of AT(2)R-AS transcript was maintained for 90 days in heart, kidney, lung and brain, indicating a high degree of transgene transduction in vivo. As adults, systolic BP and the pressor responses to angiotensin were significantly elevated in AT(2)R-AS-treated rats. However, AT(2)R-AS-treated rats displayed significantly reduced dipsogenic responses to both angiotensin and water deprivation. Collectively, these data demonstrate that a single neonatal injection of the retroviral vector containing antisense to the AT(2) receptors in rats results in similar cardiovascular and dipsogenic responses as reported in AT(2)R knockout mice. The actions of the AT(2) receptors appear to be antagonistic to the cardiovascular actions of the AT(1) receptors, whereas AT(1) and AT(2) receptors appear to act synergistically in the regulation of water intake.

Direct comparison of efficiency and stability of gene transfer into the mammalian heart using adeno-associated virus versus adenovirus vectors

OBJECTIVE

Recent gene therapy strategies have relied on the use of adenovirus or plasmid as vehicles for gene delivery to the heart. These approaches have been limited by low transduction frequencies and transient transgene expression. We sought to determine whether adeno-associated virus produces more stable, higher efficiency gene expression in the rodent heart than did previous conventional methods.

METHODS

Two recombinant viral constructs were made: an adeno-associated virus containing the lacZ gene under the control of the cytomegalovirus promoter (AAV-lacZ) and an adenovirus expressing lacZ under the control of the same promoter (Adeno-lacZ). Twenty rats were injected (into the ventricular apex) with 1 x 10(7-8) genomic particles of each virus. Animals were put to death at serial time points and transgene expression quantitated by beta-galactosidase activity, myocardial staining, and Western blot protein analysis.

RESULTS

Three months after adeno-associated virus gene transfer, animals demonstrated stable beta-galactosidase expression in 60% of cardiomyocytes without evidence of myocardial inflammation/necrosis. The distribution and degree of protein expression and number of positive cells at 3 months were equivalent to transgene expression at 4 weeks. Adeno-associated virus was not detected in organs other than the heart. In contrast, Adeno-lacZ animals displayed transient beta-galactosidase activity in 60% of cardiomyocytes, which was undetectable 4 weeks after gene transfer. Adenovirus-treated animals manifest significant myocardial inflammation and had transgene expression in other organs.

CONCLUSION

Direct intramyocardial injection of an adeno-associated virus vector programs stable, long-term, cardiac-specific transgene expression in the rodent heart for up to 3 months. Our results suggest adeno-associated virus has significant advantages for long-term transgene expression in the heart compared to adenovirus vectors.

Regression of left ventricular hypertrophy: are there preferred drugs?

The presence of left ventricular hypertrophy (LVH) confers markedly increased risk of cardiovascular morbidity and mortality in patients with hypertension. Regression of left ventricular (LV) mass with antihypertensive therapy is associated with reduction in cardiovascular events. In studies based on monotherapy, among the classes of antihypertensive drugs that have been adequately tested, diuretics and angiotensin-converting enzyme inhibitors appear to be the most effective agents for reducing LV mass. New avenues of research, based on combination antihypertensive therapy and on a more sophisticated understanding of the molecular mechanisms of LVH, may yield new pharmacologic approaches to regressing LV mass.

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.

The predominant role of brain angiotensinogen and angiotensin in environmentally induced hypertension

Rats exposed chronically to a cold environment (5 degrees C/4 degrees F) develop hypertension. This cold-induced hypertension (CIH) is a non-genetic, non-pharmacological, non-surgical model of environmentally induced hypertension in rats. The renin-angiotensin system (RAS) appears to play a role in both initiating and/or maintaining the high blood pressure in CIH. The goal of the present study was to evaluate the role of central and peripheral circulating RAS components, angiotensinogen (AGT), angiotensin-converting enzyme (ACE) and angiotensin (Ang) II, in CIH. Seventy-two Sprague-Dawley adult male rats were used. Thirty-six rats were kept in cold room at 5 degrees C while the other 36 were at 24 degrees C as controls for 5 weeks. Systolic blood pressure (SBP) was recorded by tail cuff. The SBP was increased in rats exposed to cold within 1 week, and this increase was significant for the next 2-5 weeks of the cold exposure (p<0.01). Three subgroups of the cold-treated and control rats (n=12) were sacrificed at 1, 3 and 5 weeks. The brain and liver were removed and plasma was saved. The AGT mRNA significantly increased in the hypothalamus and liver in cold-treated rats from the first week of exposure to cold, and was maintained throughout the time of exposure to cold (n=4, p<0.01). The AGT protein levels in the brain, liver and plasma did not differ significantly between cold-treated and control rats (p>0.05, n=4). The hypothalamic Ang II levels were significantly increased, whereas plasma Ang II levels significantly decreased, in the rats of 5 weeks of cold exposure (n=8, p<0.05). Plasma ACE significantly increased in the rats of 1 week of cold exposure (p<0.05, n=12). The results show differential regulation of RAS components, AGT, ACE and Ang II, between brain and periphery in cold-exposed rats. We conclude that the exposure to low temperature initially increases plasma RAS but with continuous exposure to cold, the brain RAS maintains the hypertension, probably by sustained sympathetic activation, which would provide increased metabolism but also vasoconstriction leading to hypertension.

Gene therapy for renal disorders: what are the benefits for the elderly?

Chronic renal failure is one of the major health problems for the elderly. Currently, about 50% of all patients receiving chronic dialysis for end-stage renal disease (ESRD) are aged 65 years or older. Their first-year mortality rate is as high as 30%. The leading causes of ESRD in the elderly are diabetic nephropathy, hypertension and large vessel diseases, and glomerulonephritis. The elderly are also prone to developing acute renal failure induced by ischaemic injury or nephrotoxic drugs. Gene transfer in experimental animals have been tested in all of these conditions, as well as in animal kidney transplantation models, with various degrees of success. However, there are many obstacles to be overcome before gene therapy can be tested clinically for renal disorders. In particular, the major challenges include determining how to prolong and control transgene expression or antisense inhibition and how to minimise the adverse effects of viral or nonviral vectors. Once these problems are solved, gene therapy will have a role in treating age-related renal impairment.

Development and use of gene transfer for treatment of cardiovascular disease

Gene therapy holds promise for the treatment of cardiovascular diseases for which effective pharmacological therapies are insufficient or unavailable. Recent studies have suggested that modification of current gene delivery systems combined with the use of efficacious therapeutic genes may ultimately be successful for clinical vascular gene therapy. Although certain applications such as vein-graft failure may be best suited for short-term transient overexpression of therapeutic genes, other disorders including human essential hypertension and atherosclerosis require sustained overexpression of genes. Hence, design and use of vector systems for delivery of genes to the required site in vivo requires careful consideration. Both viral and nonviral gene therapy vectors show low efficiency for gene transfer into vascular cells and demonstrate a lack of selectivity, as vectors have natural tropism for other cells and tissues. Recent work has focused on the design, development, and utility of vascular cell-selective gene therapy vectors for use in distinct and diverse vascular gene therapy scenarios. Using phage display technology we have isolated small peptide ligands that mediate selective binding to either vascular endothelial cells or vascular smooth muscle cells. When engineered into either adenoviral (Ad) or adeno-associated viral (AAV) vectors, candidate peptides enabled the virus to selectively bind to the desired cell type thus generating novel vascular cell-selective gene transfer. As preclinical studies have highlighted both the potential for vascular gene therapy as well as defining the potential pitfalls, the development of disease-selective gene therapeutics will increase safety and efficiency of gene therapy for future clinical use.

Vigilant vectors: adeno-associated virus with a biosensor to switch on amplified therapeutic genes in specific tissues in life-threatening diseases

There are many life-threatening and chronic diseases in which physiological signals could be used to switch on therapeutic protective genes. We are developing a gene therapy approach in which a systemically injected "vigilant vector" waits for these signals and switches on genes to protect specific tissues with high amplification. The concept of a vigilant vector requires four components. The first component is a safe and stable vector that can be administered by systemic injection and express transgenes in a particular organ or tissue. The adeno-associated virus vector is safe and stable for this purpose. The second component is a reversible gene switch which is a biosensor that can detect certain physiological signals. We are developing a hypoxia switch, based on the oxygen-dependent degradation domain of hypoxia-inducible factor. The third component is a tissue-specific promoter, and we have used the myosin light-chain-2V promoter for specific expression in the heart. The fourth component is an amplification system. For this we have developed a double-plasmid/vector system based on the yeast GAL4 and human transcriptional activator p65 to produce a transactivating fusion protein that binds to a GAL4 activation sequence in an activating plasmid that then expresses high levels of cardioprotective genes.

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.

Genetic targeting of the renin-angiotensin system for long-term control of hypertension

Although traditional approaches are effective for the treatment and control of hypertension, they have not succeeded in curing the disease, and have therefore reached a plateau. As a result of the completion of the Human Genome Project and the continuous advancement in gene delivery systems, it is now possible to investigate genetic means for the treatment and possible cure for hypertension. In this review we discuss the potential of genetic targeting of the renin-angiotensin system for the treatment of hypertension. We provide examples of various approaches that have used antisense technology with a high degree of success. We focus on our own research, which targets the use of antisense of the angiotensin type I receptor in various models of hypertension. Finally, we discuss the future of antisense technology in the treatment of human hypertension.

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.