Abstract 556: ACE2-Independent Effect of XNT in Ang II-Induced Hypertension

Previous studies using XNT have suggested that the molecule has a unique role as a hypotensive and antifibrotic agent within the RAS acting primarily as an activator of the ACE2. In this study, we assessed the hypothesis that XNT attenuates hypertension by an ACE2-independent mechanism.

Studies were performed in C57BL6 WT and ACE2KO mice. BP was monitored continuously for a period of 25 min following a bolus of Ang II infusion after either XNT or recombinant (r)ACE2 was administered.

Ang peptides were examined in plasma ex-vivo using MAS spectrometry analysis (RAS-fingerprint). ACE2 activity in serum was measured after XNT and/or Ang II infusion, in order to investigate a potential effect of XNT on serum ACE2.

With regard to blood pressure, both XNT (n=11) and rACE2 (n=11) were able to markedly attenuate Ang II -induced hypertension in WT mice. However, a similar decline in BP caused by XNT was also seen in ACE2KO mice (n=14), indicating that the BP-lowering effect of XNT was ACE2-independent. This was additionally evidenced by serum ACE2 activity measurements in WT mice performed 5 minutes after Ang II infusion, showing no significant variation between XNT (0.351±0.06 RFU/ul/hr) and control group (0.393±0.04 RFU/ul/hr). Moreover, results from MAS spectrometry analysis showed that the presence of XNT did not alter plasma Ang II, Ang (1-7) or Ang (1-5) levels, whereas rACE2, without XNT addition, significantly increased Ang (1-7) and Ang(1-5) levels as a result of enhanced Ang II degradation.

XNT has a potent BP-lowering effect in AngII-dependent hypertension but this action is ACE2-independent and unrelated to Ang II or Ang (1-7).

Abstract 57: Angiotensin-converting Enzyme 2(ACE2) Activator, Diminazene Aceturate (DIZE), Improves Endothelial Progenitor Cell (EPC) Function and Attenuates Ischemia-induced Cardiac Pathophysiology

Background: ACE2 [vasoprotective axis of the renin angiotensin system (RAS)], plays a protective role in cardiovascular diseases. In addition, the number and function of EPCs is impaired in heart failure. These observations led us to hypothesize that DIZE would protect against myocardial infarction (MI) and improve EPC function.

Methods: DIZE treatment (15 mg/kg/day, s.c.) was initiated in 8-week-old SD rats two days prior to MI surgery and continued throughout the study-period. Cardiac function was measured four weeks post-MI. The number of circulating rat EPCs (CD4 - /CD5 - /CD8 - /CD90 + ) was quantified via flow cytometry. EPCs were isolated from spleen mononuclear cells and function was assessed by ability to migrate towards SDF-1.

Results: MI rats showed a 58% decrease in fractional shortening (FS,%) [control (C): 54.6 ± 3.0; DIZE alone (D) : 52.5± 4.8; MI: 22.5± 3.7], a 50% decrease in contractility (dP/dt max mmHg/s) (C: 9480 ± 425.3; D: 9585 ± 597.4; MI: 4716 ± 724.9), and a 27% increase in ventricular hypertrophy (VH, mg/mm) (C: 26.5 ± 1.5; D: 26.9 ± 1.4; MI: 33.4± 1.1). This was associated with 40% decrease in cardiac ACE2 activity (C: 246.2 ± 25.1; D: 254.2 ± 20.6; MI: 148.9 ± 29.2, RFU/min). There was a 23% decrease in the number of circulating EPCs (C: 4.3 ± 0.1%; D: 4.2 ± 0.2%; MI: 3.3 ± 0.1%) and 12% decrease in their migratory ability (MI: 20.0%). DIZE resulted in a 2.5 fold increase in ACE2 activity in MI heart, attenuated the MI-induced decrease in FS by 49%, improved dP/dt max by 49%, and reversed VH by 21%. In addition, DIZE increased the number of EPCs by 21% and improved their migratory ability by 9% in the MI rats. Furthermore, immunostaining for Islet-1, a marker for cardiac progenitor cells (CPCs) demonstrated that DIZE increased CPC number and decreased infiltration of macrophages in the peri-infarct area of the ischemic heart. All these beneficial effects were abolished by C-16, an ACE2 inhibitor.

Conclusions: Collectively, our observations demonstrate that activation of endogenous ACE2 improves cardiac function and attenuates LV remodeling post-MI, increases EPC number and function, increases engraftment of CPCs and decreases inflammatory cells in peri-infarct cardiac regions. Thus, DIZE may represent a promising therapeutic strategy for treating MI.

Abstract 569: Both Young and Old ACE2-transgenic Mice are More Resistant to Cardiac Dysfunction Induced by Myocardial Infarction

Background: Increased activity of the classic renin-angiotensin system (RAS) is associated with cardiovascular diseases (CVD) such as heart failure and hypertension. Angiotensin-converting enzyme 2 (ACE2) is reported to provide a protective role in CVD. In addition, there is a shift in the balance of the ACE2/Angiotensin-(1-7) axis towards the ACE/Angiotensin II axis during aging, making the cardiovascular system more vulnerable to damages. We hypothesized that global ACE2-overexpression could correct the imbalance between the two axes by providing a cardiovascular protective role against heart failure both in young and aged mice.

Methods: Both young (10 weeks old) and old (12 months old) ACE2-transgenic and wild type (WT) mice underwent myocardial infarction surgery. Cardiac function was measured using echocardiography four weeks after MI. The number of circulating inflammatory cells (CD11b) in the blood for these animals was also measured using flow cytometry.

Results: In the MI animals, the WT-old mice had a significant reduction in ejection fraction (47.67±4.23%: from 72.63±8.52% to 24.96±4.29%). However, the reduction in EF for ACE2-old mice was 37% lower (26.26±1.90%: from 60.06±7.56% to 29.18±5.66%) than that of WT-old mice. Meanwhile, the MI-induced decrease in EF of 14.60±1.56% for ACE2-young mice (from 59.09±8.38% to 44.49±6.82%) also was significantly less than the 26.97±1.21% reduction observed in WT-young mice (from 53.23±7.67% to 26.26±6.46%). Thus, ACE2 overexpression provides some protection of cardiac function from ischemia-induced injury in both young and old animals. Moreover, the circulating monocytes and macrophages in the blood of ACE2-young MI mice (22.65±6.86%) was also less than which observed in the WT control (31.37±4.90%), suggesting that there is less cardiac damage in these animals.

Conclusions: Collectively, our observation suggests that global ACE2 overexpression has a consistent cardiac protection both in the young and old and as a result, the heart may be more resistant to heart failure damage during aging. This protective effect may be partly due to its systematic anti-inflammatory effect.

Abstract 609: Potential Role Of Adipose Derived Stem Cells In Attenuating Pulmonary Hypertension

Pulmonary hypertension (PH) is a devastating cardiopulmonary

disorder, which often results in right heart failure. In spite of recent

advancements in the pharmacotherapy of pulmonary hypertension, the mortality

rate has not been significantly reduced. Recently stem cell therapy has gained

more attention for the treatment of cardiopulmonary diseases. Despite the

promising results shown by bone marrow derived stem cells in attenuating right heart

failure in PH, it remains a highly invasive and laborious procedure. On the contrary, adipose derived stem cell

(ADSC) presents a less complicated option. Therefore, we proposed to use ADSC in

attenuating the progression of PH. Monocrotaline

(MCT) at a 50 mg/kg dose was injected to eight-week old male Sprague-Dawley

rats to induce PH. Four weeks post MCT injection; animals developed PH with

elevated right ventricular systolic pressure (RVSP, Control: 28.65±0.40; MCT:

78.06±6.4 mmHg; n=6-8), and right ventricular hypertrophy (RVH, Control;

0.22±0.005; MCT: 0.48±0.054 [ratio, AU]; n=6-8). ADSC (isolated from inguinal fat of healthy male

rat) were characterized using flow cytometry (CD44 + , CD90 + ,

CD34 - and CD45 - ) and their differentiation to adipocyte

was confirmed by Oil Red O staining. ADSCs

(1x10 6 ; passage 2-4) were injected through the jugular vein, 14 days

post MCT injection. After 2 weeks following

ADSC therapy, RVSP (MCT+ADSC: 55.67±8.99 mmHg; n=6-8) and RVH (MCT+ADSC:

0.32±0.062 [AU]; n=6-8) was significantly reduced. Moreover, the elevated right ventricular end

diastolic pressure (RVEDP) and ±dP/dT associated with PH were attenuated

significantly in ADSC treated MCT animals. An additional group of animals received only

the ADSC conditioned media (CM) from 1x10 6 cells. After 2 weeks of CM administration, RVSP

(MCT+CM: 42.11±4.66 mmHg; n=5) and RVH (MCT+CM: 0.29±0.020 [AU]; n=5) was

significantly reduced. Further, the RVEDP

and ± dP/dT were also significantly reduced in CM treated MCT animals. Collectively, either ADSC or conditioned media

alone can attenuate the progression of PH, which suggest that paracrine-like substances

may be responsible for the beneficial effects observed and may be considered as

a potential therapeutic alternative for the treatment of right heart failure.

Discovery and characterization of alamandine: a novel component of the renin-angiotensin system

RATIONALE

The renin-angiotensin system (RAS) is a key regulator of the cardiovascular system, electrolyte, and water balance. Here, we report identification and characterization of alamandine, a new heptapeptide generated by catalytic action of angiotensin-converting enzyme-2 angiotensin A or directly from angiotensin-(1-7).

OBJECTIVE

To characterize a novel component of the RAS, alamandine.

METHODS AND RESULTS

Using mass spectrometry we observed that alamandine circulates in human blood and can be formed from angiotensin-(1-7) in the heart. Alamandine produces several physiological actions that resemble those produced by angiotensin-(1-7), including vasodilation, antifibrosis, antihypertensive, and central effects. Interestingly, our data reveal that its actions are independent of the known vasodilator receptors of the RAS, Mas, and angiotensin II type 2 receptor. Rather, we demonstrate that alamandine acts through the Mas-related G-protein-coupled receptor, member D. Binding of alamandine to Mas-related G-protein-coupled receptor, member D is blocked by D-Pro(7)-angiotensin-(1-7), the Mas-related G-protein-coupled receptor, member D ligand β-alanine and PD123319, but not by the Mas antagonist A-779. In addition, oral administration of an inclusion compound of alamandine/β-hydroxypropyl cyclodextrin produced a long-term antihypertensive effect in spontaneously hypertensive rats and antifibrotic effects in isoproterenol-treated rats. Alamandine had no noticeable proliferative or antiproliferative effect in human tumoral cell lines.

CONCLUSIONS

The identification of these 2 novel components of the RAS, alamandine and its receptor, provides new insights for the understanding of the physiological and pathophysiological role of the RAS and may help to develop new therapeutic strategies for treating human cardiovascular diseases and other related disorders.

C1 catecholamine neurons form local circuit synaptic connections within the rostroventrolateral medulla of rat

C1 catecholamine neurons reside within the rostroventrolateral medulla (RVLM), an area that plays an integral role in blood pressure regulation through reticulospinal projections to sympathetic preganglionic neurons in the thoracic spinal cord. In a previous investigation we mapped the efferent projections of C1 neurons, documenting supraspinal projections to cell groups in the preautonomic network that contribute to the control of cardiovascular function. Light microscopic study also revealed putative local circuit connections within RVLM. In this investigation we tested the hypothesis that RVLM C1 neurons elaborate a local circuit synaptic network that permits communication between C1 neurons giving rise to supraspinal and reticulospinal projections. A replication defective lentivirus vector that expresses enhanced green fluorescent protein (EGFP) under the control of a synthetic dopamine beta hydroxylase (DβH) promoter was used to label C1 neurons and their processes. Confocal fluorescence microscopy demonstrated thin varicose axons immunopositive for EGFP and tyrosine hydroxylase that formed close appositions to C1 somata and dendrites throughout the rostrocaudal extent of the C1 area. Dual-labeled electron microscopic analysis revealed axosomatic, axodendritic and axospinous synaptic contacts with C1 and non-C1 neurons with a distribution recapitulating that observed in the light microscopic analysis. Labeled boutons were large, contained light axoplasm, lucent spherical vesicles, and formed asymmetric synaptic contacts. Collectively these data demonstrate that C1 neurons form a synaptic network within the C1 area that may function to coordinate activity among projection-specific subpopulations of neurons. The data also suggest that the boundaries of RVLM should be defined on the basis of function criteria rather than the C1 phenotype of neurons.

Abstract 72: Potentiation of Reparative Capacity of Cardiac Progenitor Cells (cpcs, Islet-1+) by Angiotensin-(1-7) in Myocardial Infarction (MI)-induced Cardiac Damage

Background: Endogenous myocardial regeneration is insufficient to fully rescue hemodynamic functions following MI. Stem cell therapy has been attempted to provide exogenous reparative support to ameliorate cardiac regeneration with limited success. We evaluated the hypothesis that transduction of CPCs with Ang-(1-7) would improve their reparative capacity, since this vasoprotective axis of the renin angiotensin system is implicated in progenitor cell functions.

Methods: CPCs were isolated from adult rats, characterized by the presence of Islet-1 in the nuclei and expression of GATA4 and Nkx2-5. Their transduction with Lenti-Ang-(1-7) resulted in a 20-fold increase in Ang-(1-7) production. 4 × 10 6 of CPCs, or lenti-Ang-(1-7) transduced CPCs, were injected via the jugular vein three days after permanent left anterior descending coronary artery ligation. Echocardiography, hemodynamic, histological parameters, and capillary vessel density were measured to assess cardiac function and effects of cell transplantation four weeks thereafter.

Results: First we determined if Ang-(1-7) improves CPC functions in vitro . Hypoxia inhibited the migration of CPCs, whereas Ang-(1-7) protected CPCs from hypoxia induced inhibition of migration. Results from the in vivo studies demonstrated that MI significantly reduced fractional shortening (FS, 33.0% ± 1.5 vs 59.5% ± 1.9 for control), increased ventricular hypertrophy (VH, 3.6 ± 0.1 vs 2.7 ± 0.1 for control, (g/kg)), and decreased dP/dt max (7235 ± 271.9 vs 10394 ± 326.3 for control, mmHg/sec). In comparison to MI, CPCs alone restored FS by 22%, reversed VH by 11%, and improved dP/dt max by 23%. Remarkably, Ang-(1-7) expressing CPCs further improved FS by 44%, decreased VH by 15%, and attenuated the reduction in dP/dt max by 42%. Finally, capillary density in the peri-infarct myocardium was increased by 59% with CPCs alone and this capillary density was further increased by 139% with Ang-(1-7) expressing CPCs.

Conclusions: These observations, for the first time, demonstrate that Ang-(1-7) enhances CPC capacities to improve cardiac hemodynamic and circulation following MI. They suggest that Ang-(1-7) transduced CPC could be an improved stem cell therapy strategy for the treatment of ischemic heart disease.

Abstract 3: Angiotensin II Affects Hematopoietic Stem/progenitor Cell Engraftment and Mobilization

Evidence indicates that Angiotensin II (Ang II) induces proliferation of the hematopoietic stem/progenitor cells (HSPCs). However, the mechanism of its action in vivo at the level of bone marrow (BM) remains poorly understood. In the present study, we have used an innovative in vivo imaging technique to visualize mouse tibia bone so that we can elucidate the effect of Ang II on HSPC in the BM. Sca-1+, c-Kit+, Lin- (SKL) HSPCs from GFP mice were isolated and 6-10X10^3 SKL cells were injected into the lethally irradiated C57BL6 mice. SKL cells engrafted in the tibia bone were visualized in real time with the use of tibia window technique. The effect of Ang II on GFP+ SKL cells was studied by chronic infusion of Ang II osmotic minipumps (1000ng/kg/min). We observed a significant delay in the homing of GFP+ SKL cells by Ang II infusion for 7 days. In addition, the SKL cells failed to efficiently engraft to the osteoblastic niche. Consistent with this observation, colony formation unit-Spleen (CFU-S) analysis showed that extramedullary hematopoiesis was drastically reduced in Ang II treated mice. Furthermore, CX3CR1+/Gr-1+ inflammatory monocytes in the peripheral blood were increased by 47% following 2 weeks of Ang II infusion. This was associated with the significant increase of Sca-1+ CX3CR1+ cells in the BM indicating that Ang II also affects monocyte progenitor cells in the BM. Finally, we observed an increased number of BM derived monocytes in the paraventricular nucleus (PVN) of the hypothalamus in Ang II treated mice. These data demonstrate that chronic Ang II infusion inhibits homing of HSPC, prevents their engraftment into the functional BM niche and increases mobilization of monocyte progenitors into the PVN. They suggest that monocyte progenitors derived from the BM may contribute to an increase in the number of activated microglia in the PVN of hypertensive animals.

Abstract 68: Diminazene, an Angiotensin Converting Enzyme2 (ACE2) Activator, Improves Right Heart Function in Experimental Models of Pressure Overload

BACKGROUND: Right ventricular (RV) failure due to pressure overload is a major cause of morbidity and mortality in pulmonary hypertensive patients. We and others have shown that ACE2 exerts cardiopulmonary protection against lung diseases. This has led us to hypothesize that activation of ACE2 would improve RV hemodynamics and attenuate cardiac remodeling in animal models of pressure-overload.

Methods: Hypoxia and Monocrotaline (MCT) models of pressure-overload were employed to evaluate the effects of Diminazene (DIZE), an ACE2 activator. Rats were exposed to hypoxia for 28 days with simultaneous DIZE treatment (15mg/Kg). In the other model, rats were challenged with MCT (50mg/Kg).Both prevention and reversal protocols were studied in this model. In the prevention protocol, rats were co-treated with DIZE for 4-weeks, while for the reversal protocol, DIZE was injected after 3-weeks of MCT-challenge and the drug treatment continued for additional 2-weeks.

Results: Hypoxia exposed rats exhibited increased ratio of right ventricular to left ventricular plus septum weights, an index of RV hypertrophy (Con:0.26+0.01; Hypoxia: 0.48+0.03), along with cardiac dysfunction in terms of higher right ventricular end diastolic pressure (RVEDP; Con:3.28+0.65; Hypoxia:9.08+0.72mmHg), elevated +dP/dt (Con:2039+230; Hypoxia:2815+156mmHg/s) and increased -dP/dt (Con:-1476+98; Hypoxia:-2663+150mmHg/s). However, DIZE improved all these cardiovascular alterations (RVH:0.38+0.01; RVEDP:7.03+0.3mmHg; +dP/dt:2086+137mmHg/s;-dP/dt: -1945+100mmHg/s). Likewise, MCT injection induced RV hypertrophy (Con:0.27+0.01; MCT:0.50+0.03) and cardiac dysfunction (RVEDP; Con:3.98+0.46; MCT: 8.54+0.56mmHg; +dP/dt; Con:2107+189; MCT:3718+222mmHg/s; -dP/dt; Con:-1545+95; MCT:-2918+238mmHg/s), which was prevented by DIZE (RVH:0.29+0.02; RVEDP:4.76+0.44mmHg; +dP/dt:2525+122mmHg/s; -dP/dt:-2076+150mmHg/s). Furthermore, MCT caused a 3-fold increase in myocardial fibrosis, which was reduced by DIZE. In the reversal protocol, DIZE attenuated RV hypertrophy and improved cardiac hemodynamics.

CONCLUSIONS: Collectively, our results identify a therapeutic potential of DIZE for RV dysfunction induced by pulmonary pressure-overload.

Efferent projections of rat rostroventrolateral medulla C1 catecholamine neurons: Implications for the central control of cardiovascular regulation

A replication-defective lentivirus vector that expresses enhanced green fluorescent protein (EGFP) under the control of a synthetic dopamine-beta-hydroxylase (DbetaH) promoter was used to define efferent projections of C1 catecholamine neurons in rat rostral ventrolateral medulla (RVLM). EGFP expression was restricted to C1 neurons and filled their somatodendritic compartments and efferent axons 7-28 days after vector injection. This included the descending projections to thoracic spinal cord and a network in brainstem, midbrain, and diencephalon. In caudal brainstem, restricted terminal fields were present in the dorsal motor vagal complex, A1, raphe pallidus and obscurus, and marginal layer of ventrolateral medulla. Innervation of raphe nuclei was most dense at the level of RVLM, but rostral levels of pallidus were devoid of innervation. A sparse commissural projection to contralateral RVLM was observed, and pericellular arbors were present in the dorsal reticular formation among the projection pathway of catecholamine axons. Rostral brainstem contained a dense innervation of locus coeruleus and the nucleus subcoeruleus. A restricted innervation of the ventrolateral column of the periaqueductal gray distinguished the midbrain. Forebrain labeling was restricted to the diencephalon, where distinctive terminal fields were observed in the paraventricular thalamic nucleus; the lateral hypothalamic area; and the paraventricular, dorsomedial, supraoptic, and median preoptic nuclei of hypothalamus. Projection fibers also coursed through the tuberal hypothalamus into the median eminence. Collectively, these data demonstrate that RVLM C1 neurons modulate the activity of other central cell groups known to participate in the regulation of cardiovascular and autonomic function.

Effects of early perturbation of the renin–angiotensin system on cardiovascular remodeling in spontaneously hypertensive rats

RATIONALE

The goal of this study was to analyze cardiovascular (CV) remodeling in early, short-term CAP treated SHR and their offspring.

METHODS

We treated SHR with Captopril (CAP, 100 mg/kg) from in utero to 1 month of age (OCAP). Some of these rats were mated at 3-4 months of age and we used their offspring (2nd G). Controls were untreated SHR, normotensive Wistar Kyoto rats (WKY) and SHR maintained on CAP (SCAP). At 12-14 months of age, rats were cannulated for mean arterial blood pressure (MAP) measurements. An image analysis system was used to quantitate changes in cardiac and vascular (wall-to-lumen ratios, w/l) morphology and fibrosis.

RESULTS

Early, short-term CAP treatment prevented the full expression of hypertension in treated rats and their offspring. MAPs were: SHR (180+/-2.2 mm Hg); WKY 125+/-3 mm Hg); SCAP 112+/-2.5mm Hg; OCAP 138+/-2.3 mm Hg; and 2nd G (145+/-2.0 mm Hg). There were significant decreases in heart weight/body weight ratios, large and small vessel morphology, and interstitial and perivascular fibrosis in CAP-treated animals and their offspring in comparison to untreated SHR.

CONCLUSIONS

The CV protective properties of early, short-term CAP treatment were not solely due to a reduction in MAP. Although MAP was higher in OCAP and 2nd G, CV structure resembled that found in WKY and SCAP. The effects of our early treatment appear to be due to chronic blockade of the renin-angiotensin system and its effects on growth of CV tissues and the development of fibrosis.

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.

The independent stage-specific expression of the 18-kDa heat shock protein genes during microsporogenesis in Zea mays L

The small (18-kDa) heat shock proteins (hsps) of maize are encoded by a complex multigene family. In a previous report, we described the genetic information from cDNAs encoding two different members of the family. In this communication, we report the isolation and characterization of cDNA and genomic clones encoding information for a third member of this hsp family (c/gMHSP18-1). DNA fragments containing nucleotide sequences common to, or specific for, each of these characterized 18-kDa genes were prepared and used as probes to assess the expression of these genes during microsporogenesis and development of the gametophyte in an inbred line of maize (Oh43). Our results demonstrate (1) that mRNA transcripts encoding the 18-kDa hsps are expressed and/or accumulate during microsporogenesis, and (2) that genes encoding two of the characterized 18-kDa hsps are expressed and/or accumulate independently, in a stage-specific manner during microsporogenesis. These observations imply that the stage-specific expression of particular 18-kDa hsp genes results from gene-specific regulation during microsporogenesis and gametophyte development rather than from an overall activation of the heat shock or stress response.