Evidence that nitric oxide regulates AT1-receptor agonist and antagonist efficacy in rat injured carotid artery

RGS5, RGS4, and RGS2 expression and aortic contractibility are dynamically co-regulated during aortic banding-induced hypertrophy

Overexpression of regulator of G protein signaling 5 (RGS5) in arteries over veins is the most striking difference observed using microarray analysis. The obvious question is what arterial function might require RGS5. Based on functions of homologous proteins in regulating cardiac mass and G-protein-coupled receptor (GPCR) signaling, we proposed that RGS5 and vascular expressed RGS2 and RGS4 could participate in regulating arterial hypertrophy. We used the suprarenal abdominal aorta banding model to induce hypertension and hypertrophy. All 3 RGS messages were expressed in unmanipulated aorta with RGS5 predominating. After 2 days, thoracic aorta lost expression of RGS5, 4, and 2. At 1 week, all three returned to normal, and at 28 days, they increased many fold above normal. Valsartan blockade of angiotensin II (angII)/angII type 1 receptor signaling prevented upregulation of RGS messages but only delayed mass increases, implying wall mass regulation involves both angII-dependent and angII-independent pathways. The abdominal aorta showed less dramatic expression changes in RGS5 and 4, but not 2. Again, those changes were delayed by valsartan treatment with no mass changes. Thoracic aorta contraction to GPCR agonists was examined in aortic explant rings to identify vessel wall physiological changes. In 2-day aorta, the response to Galphaq/i agonists increased above normal, while 28-day aorta had attenuated induced contraction via Galphaq/i agonist, implicating a connection between RGS message levels and changes in GPCR-induced contraction. In vitro overexpression studies showed RGS5 inhibits angII-induced signaling in smooth muscle cells. This study is the first experimental evidence that changes in RGS expression and function correlate with vascular remodeling.

Design and synthesis of new tetrazolyl- and carboxy-biphenylylmethyl-quinazolin-4-one derivatives as angiotensin II AT1 receptor antagonists

A series of novel quinazolin-4-ones was designed and their molecular modeling simulation fitting to a new HipHop 3D pharmacophore model using CATALYST was examined. Several compounds showed significant high simulation fit values. The designed compounds were synthesized and eight of them were biologically evaluated in vitro using an AT1 receptor binding assay, where compound XX competed weakly against radiolabeled Sar1Ile8-angiotensin II (Ang II) binding, compounds XIV and XXII showed moderate competition, and compound XXV showed almost equal ability to displace radiolabeled Sar1Ile8-Ang II binding to AT1 receptors as losartan. In vivo biological evaluation study of compounds XIV, XXII, and XXV on both normotensive and hypertensive rats revealed that compound XXV demonstrated higher hypotensive and antihypertensive activity than the reference compound losartan. To obtain a highly active compound from a candidate set of only eight tested compounds illustrates the power and utility of our pharmacophore model.

Importance of timing of antiaggregant treatment in the prevention of radiation induced enteropathy

Chronic radiation enteropathy (CRE) is an undesirable radiation-induced toxicity and a common health problem in patients with pelvic or abdominal malignancies. Damage to microvascular endothelial cells and connective tissue is blamed to cause this adverse effect. It is shown that platelets are the first cellular elements that initiate the homeostatic and inflammatory responses and release of several proinflammatory and fibrinogenic mediators. Antiplatelet agents such as ticlopidine and clopidogrel were shown to prevent CRE and this effect is believed to be directed by their activities against thrombocytes. However, recent studies have shown that these drugs also induce apoptosis in endothelial cells and may lead to decreased expression of endothelial prostacyclin and thrombomodulin (TM) and increased release of von Willebrand factor which are shown to be major contributors of coagulation process. Assuming that radiation induced apoptosis occur 6-10h after irradiation, we think that timing of these antiaggregant drugs with irradiation is important and a 6-10h interval between these may be beneficial to avoid this adverse interaction.

Synergistic interaction between enalapril, L-arginine and tetrahydrobiopterin in smooth muscle cell apoptosis and aortic remodeling induction in SHR

Smooth muscle cell (SMC) apoptosis occurs at the onset of enalapril-induced regression of aortic hypertrophy in SHR. A potential mechanism is the correction of endothelial dysfunction (ED) leading to reduced production of reactive oxygen species and enhanced bioavailability of nitric oxide (NO), a potent apoptosis inducer. Stimulants of NO include the precursor L-arginine and the NO synthase cofactor tetrahydrobiopterin (BH(4)), which correct ED in several models. The objective was to examine the relationships between ED and the cell growth/death balance during vascular remodeling induced by enalapril in SHR. SHR, 10-week-old, received enalapril (ENA: 30 mg x kg(-1) x day(-1) p.o.) for 1 or 2 weeks, or a co-treatment of L-arginine (2.0 g x kg(-1) x day(-1) p.o.) and BH(4) (5.4 mg x kg(-1) x day(-1) i.p. twice daily) administered alone (group: LB) or in combination with enalapril (ENA+LB) for 1 week. Controls received vehicle. After 1 week, ED was completely corrected with LB but not affected significantly by ENA, whereas both treatments failed to induce SMC apoptosis or aortic remodeling. The correction of ED and the induction of SMC apoptosis (3.3-fold increase in TUNEL labeling) required 2 weeks of ENA treatment. The combination of LB with ENA for 1 week, however, was additive for the reduction of SMC proliferation, and synergistic for the induction of apoptosis and regression of vascular hypertrophy. These interactions were independent of blood pressure regulation. Our results suggest that the correction of ED is not sufficient to induce SMC apoptosis and vascular remodeling, although it facilitates these responses during enalapril treatment.

A new method to denude the endothelium without damage to media: structural, functional, and biomechanical validation

The intimial thickening that occurs in human and animal atherogenesis can be induced by mechanical injury to the endothelium. The objective of the present study was to develop a new method to induce arterial endothelial injury without damage to the media for future investigations of mechanisms of intimal thickening and atherogenesis. A specifically designed catheter was inserted into the common femoral artery of Wistar rats (n = 9) through an arteriotomic mouth. After application of Tyrode solution containing 0.14 M KCl on the surface of the vessel, the vessel contracted onto the catheter. The catheter was then moved back and forth to scrape away the endothelium. The left common femoral artery of the same rat was subjected to the standard balloon injury model. The two models were evaluated structurally, functionally, and biomechanically. Structurally, we verified that both techniques remove the endothelium, but the balloon method damages the media. Functionally, we examined the contractile response of the artery to [K+] and norepinephrine 2 days after the denudation. We found that the right femoral artery underwent contraction in response to [K+], whereas the left artery did not. Furthermore, neither artery responded to norepinephrine. Biomechanically, we measured the pressure-diameter relationship and the zero-stress state of the vessel and computed the stress-strain relation. The circumferential stretch ratios at 120 mmHg were 1.38 +/- 0.08 for the control, 1.41 +/- 0.08 (P > 0.05) for the new method, and 1.56 +/- 0.09 for the balloon injury (P < 0.05). The opening angles at the zero-stress state were 113 +/- 21 degrees for the control, 102 +/- 18 degrees for the new method (P > 0.05), and 8 +/- 13 degrees for the balloon injury (P < 0.001). In conclusion, the new method removes the endothelium while maintaining the structure, contractile function, and biomechanical properties of the vessel.

Angiotensin II and nitric oxide interaction

Nitric oxide degradation linked to endothelial dysfunction plays a central role in cardiovascular diseases. Superoxide producing enzymes such as NADPH oxidase and xanthine oxidase are responsible for NO degradation as they generate a variety of reactive oxygen species (ROS). Moreover, superoxide is rapidly degraded by superoxide dismutase to produce hydrogen peroxide leading to the uncoupling of NO synthase and production of increased amount of superoxide. Angiotensin II is an important stimulus of NADPH oxidase. Through its AT(1) receptor, Ang II stimulates the long-term increase of several membrane component of NADPH oxidase such as P(22) phox or nox-1 and causes an increased activity of NADPH oxidase with inactivation of NO leading to impaired endothelium-dependent vasorelaxation, vascular smooth muscle cell hypertrophy, proliferation and migration, extracellular matrix formation, thrombosis, cellular infiltration and inflammatory reaction. Several preclinical and clinical studies have now confirmed the involvement of the AT(1) receptor in endothelial dysfunction. It is proposed that the AT(2) receptor counterbalances the deleterious effect of the Ang II-induced AT(1) receptor stimulation through bradykinin and NOS stimulation. This mechanism could be especially relevant in pathological cases when the NADPH oxidase activity is blocked with an AT(1) receptor antagonist.

Local nitric oxide release does not affect tachyphylaxis to angiotensin II in dorsal hand veins in man in the presence of prostaglandin synthesis inhibition

AIMS

Local prostaglandin (PG) production contributes to tachyphylaxis to angiotensin II (ANGII) in veins. Our aim was to assess the hypothesis that local nitric oxide (NO) generation is also, in part, responsible for tachyphylaxis to ANGII in veins, using the Aellig dorsal hand vein technique.

METHODS

Eight healthy male volunteers received 600 mg of aspirin (orally) to inhibit PG production. The venoconstrictor effects of ANGII and noradrenaline (NA) were then compared in dorsal hand veins during co-infusion of the NO synthase inhibitor L-NMMA or saline, on separate occasions.

RESULTS

ANGII and NA produced a similar degree of initial venoconstriction. However, the response to ANGII was significantly attenuated by 12 min compared with NA (AUC 147 +/- 38 vs 196 +/- 40, respectively; [95% confidence interval for difference: 7, 92], P = 0.02). Infusion of L-NMMA did not influence the response to ANGII or NA (P = 0.2 and P = 0.3, respectively).

CONCLUSIONS

Tachyphylaxis to ANGII in dorsal hand veins is not dependent on local NO release.

Therapeutic potential of angiotensin II receptor antagonists

The circulating renin-angiotensin system plays an important role in cardiovascular homeostasis. More importantly, the local tissue renin angiotensin plays a pivotal role in cell growth and remodelling of cardiomyocytes and on the peripheral arterial vasculature. In addition, the renin angiotensin system is related to apoptosis, control of baroreflex and autonomic responses, vascular remodelling and regulation of coagulation, inflammation and oxidation. The cardioprotective and vascular protective effects of the angiotensin receptive blockade appears to be related to selective blockade of the angiotensin II (A-II) Type I (AT(1)) receptors. However, there is now growing evidence showing that some of the effects of AT-II receptor blockers (ARBs) are related to the activation of the kinin pathways. This paper will review some of the recent mechanisms related to the cardiovascular effects of angiotensin and more specifically of ARBs. This paper will present the novel data on the role of ARB in the development of atherosclerosis, vascular remodelling, coagulation balance and autonomic regulation. Finally, the role of ARBs, used alone or in combination with ACE inhibitor in patients with heart failure, will be discussed.