Angiotensin II increases plasminogen activator inhibitor type 1 and tissue-type plasminogen activator messenger RNA in cultured rat aortic smooth muscle cells

Is the effect of antihypertensive drugs on platelet aggregability and fibrinolysis clinically relevant?

Hypertension is associated with decreased fibrinolytic potential, mainly expressed as elevated plasma plasminogen activator inhibitor type 1 (PAI-1) levels, and increased platelet aggregability, which may account in part for the increased risk of atherosclerosis and its clinical complications in hypertensive patients. The effects of antihypertensive drugs on this prothrombotic state have been investigated and controversial findings have been reported, possibly because of differences in study designs, patients selected, and methodology used. Scarce and conflicting data exist about the effects of diuretics and beta-adrenoceptor antagonists on the fibrinolytic system, whereas ACE inhibitors have generally been reported to improve the fibrinolytic balance by decreasing plasma PAI-1 levels, calcium channel antagonists have been shown to increase tissue plasminogen activator (tPA) activity, and angiotensin II type 1 (AT(1)) receptor antagonists seem to exert neutral effects. beta-Adrenoceptor antagonists, calcium channel antagonists, and AT(1)-receptor antagonists have been reported to exert anti-aggregatory effects on platelets, while contrasting data exist about the influence of ACE inhibitors. Clinical implications of the changes induced by antihypertensive drugs on the fibrinolytic balance and platelet function are still debated. In particular, the question of whether these changes may translate into different degrees of cardiovascular protection in hypertensive patients remains unanswered. While awaiting more information from clinical trials, the choice of antihypertensive drugs, particularly in high-risk patients, should take into account effects beyond their BP-lowering efficacy. Selected agents should have a favorable, or at least neutral, impact on fibrinolytic function and platelet activity.

Short-term effects of exogenous angiotensin II on plasma fibrinolytic balance in normal subjects

OBJECTIVE

Numerous studies have provided evidence for a direct functional link between the renin-angiotensin-aldosterone system and the fibrinolytic system. Angiotensin II has been suggested to mediate this interrelationship because this peptide was shown to stimulate plasminogen activator inhibitor-1 (PAI-1) in experimental settings. However, evidence from studies in man regarding effects of Angiotensin II on fibrinolytic function remains controversial.

METHODS

In the present study, we have therefore infused Angiotensin II at doses of 1, 3 and 10 ng kg(-1) min(-1), each over 45 min, in 9 healthy volunteer subjects without and with pretreatment with a single dose of the Angiotensin II (type 1) (AT1)-receptor antagonist valsartan (160 mg).

RESULTS

Angiotensin II infusion dose-dependently increased plasma Angiotensin II concentrations and systolic/diastolic arterial blood pressure from 121 +/- 2/70 +/- 2 mmHg to 146 +/- 2/97 +/- 1 mmHg (p < 0.001). The maximum increase in blood pressure was completely abolished (118 +/- 3/72 +/- 1 mmHg) when Angiotensin II was infused in volunteers pretreated with valsartan. In spite of the marked hemodynamic changes seen with the Angiotensin II infusion, no effect could be demonstrated on the activity and antigen concentration of PAI-1. Furthermore, pretreatment of the volunteers with valsartan markedly blunted the increase in arterial blood pressure but was not associated with changes in PAI-1.

CONCLUSION

In conclusion, in healthy volunteer subjects, short-term infusion of Angiotensin II without and with concomitant administration of an AT1-receptor antagonist has no effect on PAI-1 activities and plasma concentrations.

Spironolactone prevents early renal injury in streptozotocin-induced diabetic rats

BACKGROUND

Glomerular and tubulointerstitial injury leads to chronic impairment of renal function, and thus, reversal of the injury may improve renal function and survival. The present study investigated whether and how mineralocorticoid receptor antagonist spironolactone ameliorates early renal injury in streptozotocin-induced diabetic rats.

METHODS

Streptozotocin (65 mg/kg, single intraperitoneal injection)- or vehicle-administered rats were used as diabetic or control rats, respectively. The streptozotocin-administered rats were treated with spironolactone (50 mg/kg/day sc) for 3 weeks. Among the 3 groups of rats, we compared renal fibrosis and renal hypertrophy, using picro-sirius red staining and immunohistochemistry of ED-1 macrophage marker, plasminogen activator inhibitor-1 (PAI-1), and transforming growth factor (TGF)-beta1.

RESULTS

Three weeks after administration of streptozotocin, rats exhibited increased collagen deposition in glomerular, tubulointerstitial, and perivascular areas in the kidney, which was completely attenuated by spironolactone treatment. In rats given streptozotocin alone, there were increases in ED-1-positive cell, PAI-1 expression, and TGF-beta1 expression in glomeruli and tubulointerstitiums, which were also suppressed by spironolactone treatment. Maximal glomerular and proximal tubular areas were not significantly different among the 3 groups. Rats given streptozotocin alone revealed an increase in proximal tubule wall-to-lumen ratio that was not influenced by treatment with spironolactone.

CONCLUSION

Streptozotocin-induced renal fibrosis, PAI-1 expression, TGF-beta1 expression, and macrophage infiltration occur via mineralocorticoid receptor, and spironolactone ameliorates renal fibrosis presumably via the inhibition of macrophage infiltration, PAI-1 expression, and TGF-beta1 expression in streptozotocin-induced early diabetic injury.

Effect of plasminogen activator inhibitor-1 in diabetes mellitus and cardiovascular disease

Concentrations of plasminogen activator inhibitor-1 (PAI-1) are elevated beginning at the stage of impaired glucose tolerance and continuing through the development of diabetes mellitus and the metabolic syndrome. Evolving evidence of the central role of PAI-1 in mediating fibrosis and thrombosis increasingly supports the theory that it is a significant risk factor for macrovascular complications and cardiovascular disease, particularly in patients with diabetes. Several clinical studies have demonstrated a strong correlation between circulating PAI-1 levels and cardiovascular events and mortality. With the potentially severe effects of elevated PAI-1 levels becoming evident, there is increased interest in developing therapies targeted at reducing PAI-1 expression or circulating concentrations. Thus far, weight loss, inhibitors of the renin-angiotensin system, and insulin sensitization through use of thiazolidinediones (TZDs) appear to be the most promising strategies for managing elevated PAI-1 levels. Of these, TZD therapy is the only one that provides the benefits of both long-term glycemic control and improved cardiovascular risk profile. This article reviews the regulation of PAI-1, its activity in various disease states, and available treatment options.

Pericellular plasmin induces smooth muscle cell anoikis

Smooth muscle cell (SMC) rarefaction is involved in the development of several vascular pathologies. We suggest that the plasminogen activation system is a potential extracellular signal that can induce pericellular proteolysis and apoptosis of vascular SMCs. Using primary cultures of arterial SMCs, we show that plasmin generated from plasminogen on the cell surface induces cell retraction and fibronectin fragmentation, leading to detachment and morphological/biochemical changes characteristic of apoptosis (also called anoikis). The generation of cell-bound plasmin mediated by tissue-type plasminogen activator (t-PA), constitutively expressed by VSMCs, requires binding of plasminogen to the cell surface and is inhibited by epsilon-aminocaproic acid (IC50=0.9+/-0.2 mM), a competitor of plasminogen binding to membrane glycoproteins. Conversely, addition of alpha2-antiplasmin, which blocks free plasmin in the cell supernatant, could not fully prevent anoikis. Finally, an MMP inhibitor failed to prevent VSMC anoikis, arguing for a direct involvement of plasmin in this phenomenon. Indeed, similar changes are induced by plasmin directly added to VSMCs or to arterial rings, ex-vivo. We show for the first time that pathological anoikis can be triggered by a process that requires functional assembly of the plasminogen activation system on the surface of VSMCs.

Circadian gene expression of clock genes and plasminogen activator inhibitor-1 in heart and aorta of spontaneously hypertensive and Wistar-Kyoto rats

OBJECTIVE

Heart and aorta possess biologic clocks, but their involvement in genetic hypertension has been unknown. Plasminogen activator inhibitor-1 (PAI-1) expression is directly regulated by clock genes, while angiotensin II modulates both PAI-1 and clock gene expression. We therefore examined circadian expression of PAI-1 and clock genes, and effects of angiotensin type 1 (AT1) receptor antagonism, in heart and aorta of spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats.

METHODS

We examined cardiac and aortic mRNA expression for PAI-1 and clock genes (Per2, Bmal1, Clock, and Dbp) every 4 h throughout the day by quantitative reverse transcription-polymerase chain reaction, and intervention with the AT1 receptor antagonist candesartan and equihypotensive hydralazine.

RESULTS

Cardiac PAI-1 expression was high in the dark, while aortic PAI-1 expression was high in the light. Both cardiac and aortic PAI-1 expression were greater in SHR than in WKY rats. Candesartan treatment decreased cardiac PAI-1 expression only in the dark in WKY rats but throughout the day in SHR. Candesartan but not hydralazine strongly attenuated circadian fluctuation of aortic PAI-1 mRNA in SHR and WKY rats. Clock genes oscillated synchronously in heart and aorta of SHR and WKY rats. Clock gene expression was increased in heart but not aorta of SHR. Candesartan did not affect clock gene expression.

CONCLUSIONS

Enhanced expression of clock genes may increase PAI-1 expression in concert with activated renin-angiotensin system in SHR heart. Rather than clock genes, the renin-angiotensin system induces daily fluctuation and increased expression of aortic PAI-1 mRNA in SHR.

ANG II increases TIMP-1 expression in rat aortic smooth muscle cells in vivo

Matrix metalloproteinases (MMPs) and their tissue inhibitors (TIMPs) are involved in tissue remodeling processes. TIMP-1 is the main native inhibitor of MMPs and it contributes to the development of tissue fibrosis. It is known that ANG II plays a fundamental role in vascular remodeling. In this study, we investigated whether ANG II modulates TIMP-1 expression in rat aortic smooth muscle cells. In vitro, ANG II induces TIMP-1 mRNA expression in a dose-dependent manner. The maximal increase in TIMP-1 expression was present after 3 h of ANG II stimulation. The ANG II increase in TIMP-1 expression was mediated by the ANG type 1 receptors because it was blocked by losartan. The increase in TIMP-1 expression was present after the first ANG II treatment, whereas repeated treatments (3 and 5 times) did not modify TIMP-1 expression. In vivo, exogenous ANG II was administered to Sprague-Dawley rats (200 ng. kg(-1). min(-1) sc) for 6 and 25 days. Control rats received physiological saline. After treatment, systolic blood pressure was significantly higher (P < 0.01), whereas plasma renin activity was suppressed (P < 0.01), in ANG II-treated rats. ANG II increased TIMP-1 expression in the aorta of ANG II-treated rats both at the mRNA (P < 0.05) and protein levels as evaluated by Western blotting (P < 0.05) and/or immunohistochemistry. Neither histological modifications at the vascular wall nor differences in collagen content in the tunica media were present in both the ANG II- and saline-treated groups. Our data demonstrate that ANG II increases TIMP-1 expression in rat aortic smooth muscle cells. In vivo, both short- and long-term chronic ANG II treatments increase TIMP-1 expression in the rat aorta. TIMP-1 induction by ANG II in aortic smooth muscle cells occurs in the absence of histological changes at the vascular wall.

Effects of Losartan and Delapril on the Fibrinolytic System in Patients with Mild to Moderate Hypertension

BACKGROUND AND OBJECTIVES

Angiotensin-converting enzyme (ACE) probably influences the fibrinolytic system at a central point by converting angiotensin I to angiotensin II, which increases plasminogen activator inhibitor-1 (PAI-1) activity. This effect appears to be mediated in humans via the angiotensin II type 1 (AT(1)) receptor. The objective of this study was to evaluate, in patients with mild to moderate hypertension, the change in tissue plasminogen activator (t-PA) and PAI-1 plasma levels after treatment with an AT(1)-receptor blocker (losartan 50 mg/day) or an ACE inhibitor (delapril 60 mg/day).

PATIENTS AND METHODS

30 hypertensive patients and 15 controls were enrolled. Essential hypertension was established by a medical history, physical examination and the absence of clinical findings suggestive of a secondary form of hypertension. Preliminary investigations, routine biochemical tests (including clearance of creatinine and oral glucose tolerance test), chest x-ray, standard and 24-hour ECG monitoring, M- and B-mode echocardiography and fundus oculi examinations were performed. No patients had previously received ACE inhibitors or AT(1)-receptor blockers. After a 14-day run-in period with placebo, patients were randomised in a double-blind fashion into two groups: 15 patients were randomised to losartan 50 mg/day (group 1), 15 patients were randomised to delapril 60 mg/day (group 2), and 15 healthy subjects were used as controls (group 3). Plasma PAI-1 and t-PA antigen were determined by enzyme-linked immunosorbent assay and a photometric method at the end of the run-in period and after 6 months of treatment.

RESULTS

There were no significant differences among the three groups regarding age, sex, body mass index and smoking. After 6 months, both groups of patients showed a reduction in blood pressure values. The losartan group did not demonstrate significant changes in PAI-1 levels (96.52 +/- 23.73 and 99.89 +/- 22.18 mug/L, pre- and post-treatment, respectively) or in t-PA antigen levels (26.17 +/- 6.18 and 27.32 +/- 5.91 mug/L, pre- and post-treatment, respectively). The delapril group showed no significant changes in PAI-1 levels (97.73 +/- 25.75 and 86.12 +/- 13.12 mug/L, pre- and post-treatment, respectively), but did show a statistically significant difference (p < 0.005) in t-PA antigen levels (25.71 +/- 6.40 and 32.24 +/- 5.31 mug/L, pre- and post-treatment, respectively). The losartan group demonstrated significantly higher post-treatment PAI-1 values than the delapril group (p = 0.048).

CONCLUSION

The study showed that losartan does not affect fibrinolytic parameters, while delapril resulted in an insignificant reduction in PAI-1 and a significant increase in t-PA levels. Further studies are clearly required in order to establish whether these different effects on the fibrinolytic system between ACE inhibitors and AT(1)-receptor blockers may have clinical relevance.

Regulation of plasminogen activator inhibitor-1 secretion by growth factors in smooth muscle cells

Epithelioid-type vascular smooth muscle cells are metabolically active and secrete many proteases and protease inhibitors. We have previously cloned epithelioid-type smooth muscle cells from rat carotid arteries, and showed that polypeptide growth factors basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF) could dose-dependently induce plasminogen activator inhibitor-1 (PAI-1) secretion from these cells. In the present study, we have used these cells to investigate the growth factor-induced signal transduction pathways leading to PAI-1 secretion. We report here that PAI-1 induction was dependent on protein kinase C (PKC) and tyrosine kinase but not on protein kinase A (PKA), ras and phosphoinositol-3-kinase inhibitor. Induction of PAI-1 by bFGF and PDGF was also accompanied by activation of a mitogen-activated protein kinase pathway involving Raf/Mek/Erk1/2, and the family non-receptor tyrosine kinases., another non-receptor tyrosine kinase, on the contrary, behaved differently from in that it was part of a pathway leading to PAI-1 induction by bFGF, but not when PDGF was used as the stimulating reagent. Activation of a PKA-dependent pathway(s) opposed PAI-1 induction. One mechanism for PKA activators to inhibit PAI-1 secretion was that they markedly inhibited the phosphorylations of Mek and mitogen-activated protein kinase that were up-regulated in the presence of bFGF and PDGF.

The renin-angiotensin-aldosterone system and fibrinolysis in progressive renal disease

Renal glomerular and interstitial fibrosis is widely viewed as the final common pathway to renal failure, regardless of the initiating injury. Similarly, the renin-angiotensin-aldosterone system (RAAS) plays an important role in the progression of renal disease. This review explores the hypothesis that the RAAS causes injury and fibrosis, in part, through effects on plasminogen activator inhibitor-1 (PAI-1), the major physiologic inhibitor of plasminogen activators in vivo. PAI-1, by inhibiting the production of plasmin from plasminogen, tips the balance in favor of extracellular matrix accumulation and promotes fibrosis. Interruption of the RAAS decreases both PAI-1 expression and fibrosis in animal models. These findings have implications for the clinical management of renal disease.

PAI-1 in human hypertension: relation to hypertensive groups

BACKGROUND

Although the renin-angiotensin system and insulin resistance (IR) have been identified as major regulators of plasminogen activator inhibitor type-1 (PAI-1), their roles in hypertensive subjects is not clearly defined.

METHODS

We examined the effect of dietary salt restriction on PAI-1 levels in 239 hypertensive subjects from three centers. Subjects were placed on a 200 and 10 mmol/day sodium diets for 1-week periods. Plasma renin activity (PRA) and PAI-1 levels were measured on the last day of both diets and fasting insulin, glucose, and aldosterone (ALDO) levels, only on the low salt diet.

RESULTS

Sodium restriction increased PAI-1 levels from 32.1 +/- 2.5 ng/mL to 39.8 +/- 3.2 ng/mL (P = .009). There was a strong positive correlation between PAI-1 levels and PRA (r = 0.228, P = .0004), IR (r = 0.222, P = .001), triglycerides (r = 0.275, P < .001), and ALDO (P = .018 for linear trend). The patients were divided into low renin (low IR and ALDO levels), nonmodulators (normal PRA, high IR, and low ALDO levels), and modulators (normal PRA, intermediate IR, and normal ALDO levels) groups to assess the relative contribution of each factor to PAI-1 levels. Modulators had significantly (P = .019) higher PAI-1 levels compared to the low renin and nonmodulators who had similar PAI-1 levels.

CONCLUSIONS

Plasma renin activity, IR, and ALDO all correlate with PAI-1 levels in the hypertensive subjects. However, the data suggest that ALDO may be an important factor contributing to the variability of PAI-1 levels in individual hypertensive subjects.

Angiotensin II-mediated signal transduction pathways

The renin-angiotensin system is one of the major cardiovascular systems that controls blood volume, peripheral vascular tone, and blood pressure. Recent studies indicate important roles for angiotensin II in inflammation, atherosclerosis, and congestive heart failure as well. It is gradually becoming clear that angiotensin II exerts effects on the cardiovascular system through several unique mechanisms, including the availability of two different angiotensin II receptors, recruitment of protein tyrosine kinase activity, and receptor tyrosine kinase transactivation. This review discusses the diverse mechanisms of angiotensin II-mediated signal transduction pathways and the various effects of angiotensin II on the cardiovascular system.

L-158,809 and (D-Ala(7))-angiotensin I/II (1-7) decrease PAI-1 release from human umbilical vein endothelial cells

The endothelium is a major source of plasminogen activator inhibitor-1 (PAI-1), which plays a critical role in the regulation of fibrinolysis. There are many reports on the increase in the expression of PAI-1 by angiotensin II (Ang II). In the present study, we investigated the effects of angiotensin-related substances on the release of PAI-1 from human umbilical vein endothelial cells (HUVECs). Ang II increased PAI-1 and tissue plasminogen activator (t-PA) release, while its metabolite angiotensin-(1-7) (Ang-(1-7)) amino acid fragment decreased them. Angiotensin Type 1 (AT1) receptor antagonist, L-158,809 (L-1), and Ang-(1-7) receptor antagonist, (D-Ala(7))-angiotensin I/II (1-7) (D-Ala), decreased PAI-1 and t-PA release; angiotensin Type 2 (AT2) antagonist, PD123,319 (PD), however, did not have any effects on the release of PAI-1 and t-PA. The addition of the equal concentration or 10-times-higher concentration of L-1 to Ang II did not change PAI-1 release compared to that by Ang II. Although Ang-(1-7) and L-1 decreased PAI-1 release, there were no additional effects on the decrease of the amounts of PAI-1 by the mixture of Ang-(1-7) and the equal concentration or 10-times-higher concentration of L-1 compared to those by Ang-(1-7). The equal concentration of D-Ala to Ang II did not change the amounts of PAI-1, but the addition of the 10-times-higher concentration of D-Ala to Ang II resulted in significant decrease of the amounts of PAI-1 compared to those by Ang II. The addition of equal concentration or 10-times-higher concentration of D-Ala to Ang-(1-7) showed the significant decrease of the amounts of PAI-1 compared to those by Ang-(1-7). In conclusion, L-158,809 and (D-Ala(7))-angiotensin I/III (1-7) may be used as profibrinolytic drugs.

Achieving maximal renal protection in nondiabetic chronic renal disease

A rapid global increase in the number of patients requiring renal replacement therapy necessitates that effective strategies for renal protection are developed and applied widely. We review the experimental and clinical evidence in support of individual renoprotective interventions, including angiotensin-converting enzyme therapy, control of systemic hypertension, dietary protein restriction, reduction of proteinuria, treatment of hyperlipidemia, and smoking cessation. We also consider potential future renoprotective therapies. To achieve maximal renal protection, a comprehensive strategy employing all of these elements is required. This strategy should be directed at normalizing clinical markers of renal disease to induce a state of remission.

Losartan inhibits the angiotensin II-induced modifications on fibrinolysis and matrix deposition by primary human vascular smooth muscle cells

Disorders in the fibrinolytic and renin-angiotensin-aldosterone systems and excessive extracellular matrix (ECM) deposition are determinant factors in several pathologic manifestations of vascular and cardiac tissue. We used primary human vascular smooth muscle cells (VSMC) and studied the effects of losartan on angiotensin II (Ang II)-mediated (a) DNA synthesis, (b) secretion of tissue-type plasminogen activator (tPA) and plasminogen activator inhibitor-1 (PAI-1), (c) secretion of matrix metalloprotease-2 (MMP-2) activity and tissue inhibitors of MMPs (TIMPs), and (d) synthesis of glycosaminoglycans. VSMC cultures, established from human pulmonary arteries, were treated with Ang II (0.1 nM -1 microM ) and/or losartan (0.1-10 microM ), for 24 or 48 h. DNA synthesis was assessed by incorporation of 3 H-thymidine into VSMC, secreted tPA, PAI-1, and TIMPs by enzyme-linked immunosorbent assay, MMP-2 activity by gelatin zymography, and glycosaminoglycan synthesis by 3 H-glucosamine incorporation. Ang II (1 microM ) enhanced DNA synthesis and secretion of PAI-1 and glycosaminoglycans and decreased secretion of MMP-2 activity and tPA, whereas it had no effect on secretion of TIMPs and glycosaminoglycans associated with cell layers. The Ang II-mediated effects were reversed by losartan, in a concentration-dependent manner. Losartan alone increased secretion of tPA, MMP-2 activity, and TIMPs and decreased secretion of PAI-1. These results indicate that AT 1 receptors are implicated in Ang II-mediated disorders of fibrinolysis and excessive ECM deposition by VSMC.

Plasminogen activator inhibitor type-1 in cardiovascular disease. Status report 2001

Plasminogen activator inhibitor type-1 (PAI-1) is known to contribute to thrombus formation and to the development and the clinical course of acute and chronic cardiovascular disease, as well as of other arterial and venous thromboembolic diseases. Recently, an important role of elevated pretreatment levels of PAI-1 for failure of thrombolytic therapy of acute myocardial infarction has been discussed. PAI-1 plasma levels depend on the one hand on gene regulation but are related on the other hand to known risk factors of atherosclerosis like insulin resistance, diabetes or hypertriglyceridemia, respectively. Furthermore, an activated renin-angiotensin-aldosterone system (RAAS) significantly contributes to the upregulation of PAI-1 concentration via a receptor-mediated mechanism. In accordance to the known mechanisms of regulation of PAI-1 plasma levels, the use of specific agents like antidiabetic drugs, fibrates, statins, ACE inhibitors and angiotensin II type-1 receptor-blockers may contribute to the downregulation of circulating PAI-1 and, therefore, increase the fibrinolytic capacity and consecutively counteract the thrombotic tendency. To further improve the efficacy of thrombolytic therapy, a PAI-1 resistant variant of t-PA, TNK-t-PA, has been developed and is now available for acute myocardial infarction.

Angiotensin converting enzyme DD genotype affects the changes of plasma plasminogen activator inhibitor-1 activity after primary percutaneous transluminal coronary angioplasty in acute myocardial infarction patients

Angiotensin converting enzyme (ACE) DD genotype, and plasminogen activator inhibitor (PAI-1) 4G/4G genotype have been reported to affect PAI-1 activity in control subjects and atherosclerotic patients, but no data are available on the influence of angiotensin II type 1 receptor (AT1R) A1166C polymorphism on the inhibitor levels. The degree of fibrinolytic activation after percutaneous transluminal coronary angioplasty (PTCA) has been found to affect the risk of restenosis. The aim of this study was to investigate the possible influence of ACE I/D, AT1R A1166C, and PAI-1 4G/5G polymorphisms on the changes of PAI-1 activity after primary successful percutaneous transluminal angioplasty. In 29 consecutive acute myocardial infarction patients, undergoing primary successful angioplasty, genotyping of ACE I/D, AT1R A1166C, and PAI-1 4G/5G polymorphisms was performed by polymerase chain reaction and restriction fragment length polymorphism analysis, and PAI-1 plasma activity (chromogenic method) was assessed before and after angioplasty. Following angioplasty, PAI-1 activity increased in 10 of 29 patients and decreased or remained unchanged in 19 of 29. ACE DD genotype was significantly (P = 0.04) associated with an increase of PAI-1 activity post angioplasty (OR DD/ID+II = 6.5, CI 95% 4.83-8.22). Whereas no effect of PAI-1 4G/5G and AT1R A1166C polymorphisms on PAI-1 response to angioplasty was demonstrated, these data suggest that renin-angiotensin system genes are involved in the regulation of the fibrinolytic response to balloon injury, possibly affecting angiotensin converting enzyme activity. This interaction between the renin-angiotensin system and hemostasis may be a mechanism by which ACE DD genotype affects the risk of restenosis after percutaneous transluminal angioplasty.

Evolving strategies for renoprotection: non-diabetic chronic renal disease

Experimental and clinical studies over the past two decades have identified several interventions for slowing the progression of chronic renal disease towards end-stage renal failure. In this paper we review the experimental and clinical evidence in support of dietary protein restriction, angiotensin-converting enzyme inhibitor therapy, control of systemic hypertension, reduction of proteinuria, treatment of hyperlipidemia and smoking cessation. We also consider potential future renoprotective therapies. Finally we propose a comprehensive strategy for achieving maximal renoprotection with available interventions and monitoring.

Plasminogen activator inhibitor type-1 (part one): basic mechanisms, regulation, and role for thromboembolic disease

Plasminogen activator inhibitor type-1 (PAI-1) is a rapid inhibitor of tissue plasminogen activator (tPA) in circulation. Evidence suggests that the PAI-1 concentration is responsible for the regulation of the endogenous fibrinolytic system through its tPA/PAI-1 interactions. Accordingly, increased levels of PAI-1 have emerged as a masker for an increased thrombolic risk. This article represents a status report of mechanism of action, regulation of plasma levels, as well as the role of PAI-1 in arterial and venous thromboembolic disease.

Angiotensin, fibrinolysis, and vascular homeostasis

There is strong evidence that imbalance of the fibrinolytic system is involved in the pathogenesis of ischemic cardiovascular events. A reduction in fibrinolytic function may also mediate part of the adverse response of the vasculature to conditions of low nitric oxide production. Because reduced nitric oxide activity predisposes to the development of atherosclerosis, imbalance of the fibrinolytic system is heavily implicated in the development of cardiovascular pathology. The renin-angiotensin system exerts substantial control over the fibrinolytic system, and pharmacologic interventions that reduce the activity of angiotensin II also have favorable effects on fibrinolytic balance and on the incidence of adverse cardiovascular events. This review summarizes the evidence for a link between activation of the renin-angiotensin system, fibrinolytic imbalance, and cardiovascular pathology.

Plasminogen activator and plasminogen activator inhibitor gene expression in human saphenous vein organ culture

We describe the expression of tissue-type plasminogen activator (t-PA) and plasminogen activator inhibitor (PAI-1) in saphenous vein culture. Smooth muscle cells (SMC) are quiescent in fresh tissue, whereas these cells acquire a proliferating phenotype when venous segments are cultured in the presence of serum. t-PA and PAI-1 were localized immunohistochemically and quantified using biochemical techniques. t-PA and PAI-1 mRNA was quantified by reverse transcription polymerase chain reaction (RT--PCR) assay. Immunostaining showed an increase in the positivity of proliferating cell nuclear antigen (PCNA) from 10-day tissue culture. Tissue sections from fresh vein showed minimal t-PA and maximal PAI-1 immunostaining. In contrast, 10-day cultures showed an increase in t-PA and a decline in PAI-1 staining. Biochemical analysis revealed a 118% increase in t-PA and a 50% decrease in PAI-1 antigen levels from 10-day tissue cultures. RT--PCR demonstrated that the mRNA encoding t-PA increased, while PAI-1 decreased after 10 days of culture. In conclusion, venous culture showed an up-regulation of t-PA and a repression of PAI-1 gene expression during SMC proliferation in the vessel wall. The PAI-1 repression observed in venous culture is in contrast to the situation observed in human atheroma. A shift in the t-PA/PAI-1 balance may have a role in vascular remodeling.

Effect of valsartan and captopril in rabbit carotid injury. Possible involvement of bradykinin in the antiproliferative action of the renin-angiotensin blockade

The effects of the specific angiotensin II (Ang II) AT1-receptor blocker valsartan on events related to restenosis were investigated in rabbits after common carotid balloon injury. Six animals were given valsartan from two days prior to injury until 14 days post-injury. Three control groups (n=6 in each group) were either sham-operated, untreated or treated with the angiotensin-converting enzyme (ACE) inhibitor,captopril. Both ACE inhibition and AT,-receptor blockade had marked effects on plasma levels of endothelin ET1, thromboxane TXB2 and 6-keto-PGF1-alpha. The most dramatic effects on ET, levels were seen in rabbits treated with valsartan, where levels were reduced to values close to those for sham-operated animals (96.85 vs. 86.45 pg/ml). Captopril treatment led to a statistically significant (p<0.01) reduction in ET1 levels compared with untreated animals, but the reduction was only about half that seen with AT1-receptor blockade. TXB2 levels doubled (202.58 vs.413.28 pg/ml) upon arterial injury in control animals but rose by only 20-35% in rabbits treated with captopril (246.45 pg/ml) or valsartan (268.13). In untreated animals, 6-keto-PGF1-alpha levels decreased slightly after injury, but for both the captopril and valsartan groups, there were significant increases in levels of this prostaglandin derivative, effects attributed to the action of bradykinins. Levels were highest in the captopril-treated animals. Valsartan and captopril treatment led to a significant reduction in neointimal thickness and the extent of lumen stenosis compared with untreated animals. Both treatments were effective in reducing neointimal area and significantly (p<0.05)reduced cell proliferation. The differences between treatments can be attributed to the different actions of the agents, as valsartan leaves the AT2-receptor unblocked, while captopril, through inhibition of Ang II synthesis, prevents stimulation of both receptors.A combination of both treatments may be a possible way forward in the clinical prevention of restenosis.

The multiple actions of angiotensin II in atherosclerosis

Angiotensin II (Ang II), the effector peptide of the renin-angiotensin system, has been implied in the pathogenesis of atherosclerosis on various levels. There is abundant experimental evidence that pharmacological antagonism of Ang II formation by angiotensin converting enzyme inhibition or blockade of the cellular effects of Ang II by angiotensin type 1 receptor blockade inhibits formation and progression of atherosclerotic lesions. Angiotensin promotes generation of oxidative stress in the vasculature, which appears to be a key mediator of Ang II-induced endothelial dysfunction, endothelial cell apoptosis, and lipoprotein peroxidation. Ang II also induces cellular adhesion molecules, chemotactic and proinflammatory cytokines, all of which participate in the induction of an inflammatory response in the vessel wall. In addition, Ang II triggers responses in vascular smooth muscle cells that lead to proliferation, migration, and a phenotypic modulation resulting in production of growth factors and extracellular matrix. While all of these effects contribute to neointima formation and development of atherosclerotic lesions, Ang II may also be involved in acute complications of atherosclerosis by promoting plaque rupture and a hyperthrombotic state. Accordingly, Ang II appears to have a central role in the pathophysiology of atherosclerosis.

Lack of association between the angiotensin-converting enzyme insertion/deletion polymorphism and plasminogen activator inhibitor-1 antigen levels in the National Heart, Lung, and Blood Institute Family Heart Study

Experimental and clinical research supports a direct link between activation of the renin-angiotensin system and production of plasminogen activator inhibitor-1 (PAI-1), the primary physiologic inhibitor of tissue plasminogen activator. Several studies have reported higher PAI-1 levels in individuals carrying the deletion (D) allele of the angiotensin-converting enzyme (ACE) gene. We investigated the association between ACE genotypes and plasma PAI-1 levels in a family study of 577 women and 428 men from four US communities. Participants were between 25 and 84 years of age without evidence of coronary heart disease (CHD). Mean geometric plasma PAI-1 levels adjusted for ethnicity were 17.4, 17.9, and 18.1 ng/ml in participants with the DD, insertion-deletion (ID), and II genotypes, respectively (P = 0.89 for difference). We found no associations between ACE I/D genotypes and plasma PAI-1 antigen concentrations in a subset of participants without major CHD risk factors (hypertension, hypercholesterolemia, overweight, smoking, diabetes) or in a small sample of African-Americans. Our findings suggest that the ACE insertion/deletion polymorphism has relatively little, if any, influence on circulating PAI-1 levels in the population at large.

Aldosterone modulates plasminogen activator inhibitor-1 and glomerulosclerosis in vivo

BACKGROUND

Aldosterone promotes nephrosclerosis in several rat models, whereas aldosterone receptor antagonism blunts the effect of activation of the renin-angiotensin-aldosterone system (RAAS) on nephrosclerosis, independent of effects on blood pressure. Based on recent findings linking activation of the RAAS with impaired fibrinolytic balance, we hypothesized that aldosterone induces sclerosis through effects on plasminogen activator inhibitor-1 (PAI-1), the major physiological inhibitor of plasminogen activation.

METHODS

We examined the effect of aldosterone antagonism on the development of sclerosis and on renal PAI-1 expression following radiation injury in the rat. Following a single dose of 12 Gy to the kidneys, male Sprague-Dawley rats were treated with placebo, the aldosterone antagonist spironolactone (4.5 mg/day by time-release subcutaneous pellet), the angiotensin type 1 receptor antagonist L158-809 (AT1RA; 80 mg/L drinking water), or combined spironolactone and AT1RA.

RESULTS

Rats treated with placebo developed significant proteinuria and nephrosclerosis 12 weeks following radiation associated with hypertension. Kidney PAI-1 mRNA expression was increased eightfold (P < 0.001 vs. nonradiated controls). Spironolactone alone had no effect on blood pressure (systolic blood pressure 149.0 +/- 5.4 mm Hg) compared with placebo (151.6 +/- 11.2 mm Hg, P = NS), whereas AT1RA alone (107.7 +/- 8.9 mm Hg, P = 0.013 vs. placebo) or in combination therapy (102.1 +/- 6.2 mm Hg, P = 0.001 vs. placebo) lowered blood pressure. Both the AT1RA and spironolactone decreased proteinuria following radiation (P < 0.001 vs. placebo for either drug), and the combination of AT1RA + spironolactone had a greater effect on proteinuria than spironolactone alone (P = 0.003). Aldosterone antagonism significantly decreased (P = 0.016 vs. placebo) and AT1RA virtually abolished (P = 0.001 vs. placebo) the development of sclerosis. Spironolactone significantly decreased PAI-1 mRNA expression in the kidneys of radiated animals (PAI-1 mRNA/GAPDH ratio 0.39 +/- 0.13 vs. placebo 0.84 +/- 0.05, P = 0.006), and there was a significant correlation between the degree of sclerosis and the level of PAI-1 immunostaining within individual rats (R2 = 0.97, P < 0.0001).

CONCLUSION

This study is, to our knowledge, the first to demonstrate that aldosterone regulates PAI-1 expression in vivo, and supports the hypothesis that aldosterone induces renal injury through its effects on PAI-1 expression.

The renin-angiotensin-aldosterone system and fibrinolysis

Activation of the RAAS has been linked with an increased risk of myocardial infarction and stroke,(1,2,37,38) and recently these beneficial effects have, in part, been attributed to the effects of the RAAS on the fibrinolytic system. Indeed, ACE seems to occupy a central position in modulating the fibrinolytic balance, where an angiotensin II-mediated increase of PAI-1 plays a major role. By contrast, the effect on bradykinin stimulated t-PA release may be of lesser importance, although the data are conflicting. Importantly, the impact of the RAAS on the fibrinolytic balance may also contribute to the favourable effects of ACE inhibition and AT1-receptor antagonists on cardiovascular events, particularly when considering the activation of the RAAS in hypertension and heart failure. More work is clearly required in this area to elucidate potential therapeutic targets.

Plasminogen activator inhibitor-1 expression is regulated by the angiotensin type 1 receptor in vivo

BACKGROUND

The fibrinolytic system plays an important role in degrading fibrin-rich thrombi and in vascular and tissue remodeling. Elevated levels of plasminogen activator inhibitor-1 (PAI-1) can reduce the efficiency of the endogenous fibrinolytic system. Angiotensin (Ang) has been shown to regulate PAI-1 expression via the Ang type 1 (AT1) receptor in some tissues and via the AT4 receptor in cultured endothelium. The purpose of this study was to examine the tissue-specific pattern of PAI-1 expression in response to infusion of Ang II in vivo.

METHODS

Adult male Sprague-Dawley rats (N = 5 in each group) were treated with four hours of intravenous infusions of Ang II or vehicle control while mean arterial pressure (MAP) was monitored: group 1, 600 ng/kg/min Ang II; group 2, Ang II + 10 mg/kg of the AT1 receptor antagonist (AT1RA) L158-809 q2 hour; group 3, Ang II + 0.01 to 0.1 mg/kg hydralazine as required to maintain normal blood pressure; and group 4, saline-infused controls. After infusion, tissue was harvested for Northern blotting, immunohistochemical analysis, and in situ hybridization.

RESULTS

In group 1, Ang II infusion increased MAP from 105 +/- 8 to 160 +/- 9 mm Hg (mean +/- SE, P < 0. 01). Ang II induced increased expression of PAI-1 mRNA in all tissues examined from 5.1-fold in the heart, 9.7-fold in the kidney, 10.0-fold in the aorta, and up to 30.0-fold in the liver (all P < 0. 01 vs. control). While both AT1RA (group 3) and hydralazine (group 4) prevented Ang II-induced elevation in blood pressure, the Ang II-dependent expression of PAI-1 mRNA was reduced by only AT1 receptor blockade.

CONCLUSIONS

We conclude that in the rat, PAI-1 is induced in a variety of tissues by Ang II directly through the AT1 receptor, independent of its effects on blood pressure.

Differential effects of imidapril and candesartan cilexetil on plasminogen activator inhibitor-1 expression induced by prolonged inhibition of nitric oxide synthesis in rat hearts

We investigated effects of the angiotensin-converting enzyme (ACE) inhibitor imidapril and the angiotensin II type 1 (AT1) antagonist candesartan cilexetil on cardiac plasminogen activator inhibitor-1 (PAI-1) expression in rats. Cardiac PAI-1 mRNA levels were increased after a 7-day treatment with the nitric oxide (NO) synthesis inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME). PAI-1 immunoreactivity was increased in the coronary arteries. Treatment with imidapril significantly prevented the L-NAME-induced increase in the gene expression and immunoreactivity of PAI-1, but candesartan cilexetil showed no such effect. This study provides the first evidence of differential effects of ACE inhibition and AT1 antagonism on cardiac PAI-1 expression in vivo.

Renoprotective benefits of RAS inhibition: from ACEI to angiotensin II antagonists

In landmark clinical trials, pharmacological inhibition of the renin-angiotensin system (RAS) with angiotensin-converting enzyme inhibitors (ACEIs) attenuated the decline in renal function associated with chronic renal disease (CRD). Hemodynamic and nonhemodynamic effects of angiotensin II (Ang II) attest to its central role in the pathogenesis of CRD. Angiotensin II subtype 1 receptor antagonists (AT1RA) differ from ACEI in their effects on the RAS and on bradykinin metabolism. Elevations in bradykinin levels associated with ACEI and stimulation of angiotensin subtype 2 receptors resulting from AT1RA may produce therapeutic effects unique to each class of drug. Nevertheless, in animal models of CRD, ACEI and AT1RA exert equivalent renoprotection, implying that their renoprotective effects result primarily from inhibition of Ang II-mediated stimulation of angiotensin subtype 1 receptors. Clinical data comparing ACEI and AT1RA therapy in renal disease are limited to short-term studies, which indicate that AT1RAs have equivalent effects to ACEI on the major determinants of CRD progression, namely blood pressure and proteinuria. AT1RAs were well tolerated, with side-effect profiles similar to placebo. Taken together, available evidence suggests that AT1RAs will share the renoprotective properties of ACEI in human CRD. Nevertheless, the results of long-term clinical trials are required before AT1RA can be recommended as an alternative to ACEI in renoprotective therapy.

The role of angiotensin II and plasminogen activator inhibitor-1 in progressive glomerulosclerosis

Regardless of the primary cause, progressive renal deterioration with sclerosis is a hallmark of many renal diseases. Several studies have shown the superiority of angiotensin-converting enzyme inhibitors compared with other antihypertensive agents in providing protection from progressive renal deterioration. Furthermore, animal studies have shown that angiotensin II antagonists in excess of antihypertensive doses can also ameliorate or reverse glomerulosclerosis, leading to the hypothesis that angiotensin II has nonhemodynamic effects that mediate the renoprotective effects shown in these investigations. Although historically angiotensin II has been associated with salt and fluid homeostasis, recent data show that angiotensin II induces cell growth and matrix accumulation in glomerular cells. Plasminogen activator inhibitor-1 has been shown to be the major inhibitor of tissue plasminogen activator and urokinase-like plasminogen activator, with potentially important effects not only on thrombosis/fibrinolysis, but also on matrix degradation because of the proteolytic actions of these substances. Angiotensin II has been shown to influence the actions of plasminogen activator inhibitor-1 and, consequently, its thrombotic and sclerotic effects. Various studies, both in vitro and in vivo, have shown that direct hemodynamic actions, modulation of endothelial injury, and growth factor actions also may be important in the development of sclerosis. These factors can be directly modulated by angiotensin II inhibition. Sclerosis may even be reversed when therapies augment matrix degradation processes, both by directly increasing proteolytic activity and by downregulating inhibitors of matrix degradation. These observations indicate that angiotensin II is important in fibrotic as well as thrombotic renal injuries that lead to progressive renal disease and also in the development of therapies such as specific angiotensin receptor antagonists to prevent or reverse these conditions.

Angiotensin-converting enzyme inhibitor prevents plasminogen activator inhibitor-1 expression in a rat model with cardiovascular remodeling induced by chronic inhibition of nitric oxide synthesis

Plasminogen activator inhibitor-1 (PAI-1) may participate in the development of cardiovascular remodeling by inhibiting extracellular matrix turnover and fibrinolysis. However, little is known about physiological regulators of PAI-1 in vivo. Angiotensin II has been shown to stimulate PAI-1 in vitro. We previously reported that long-term inhibition of nitric oxide (NO) synthesis with Nomega-nitro-L-arginine methyl ester (L-NAME) causes cardiovascular remodeling (vascular medial thickening and fibrosis) associated with increased tissue angiotensin-converting enzyme (ACE) activity. In the present study, we examined whether treatment with an ACE inhibitor modulates the cardiovascular PAI-1 expression in this model in vivo. Wistar-Kyoto rats were treated with either no drugs, L-NAME (100 mg/kg x day), or L-NAME plus the ACE inhibitor imidapril (20 mg/kg day). Marked increases in PAI-1 mRNA and protein levels in the aorta and left ventricle were observed after the first and fourth weeks of PAI-1 treatment. PAI-1 immunoreactivity was increased in the endothelium and the media of the aorta and coronary arteries after treatment of L-NAME. This increase in PAI-1 levels was associated with an increase in ACE activity of the aorta and left ventricle. ACE inhibition with imidapril significantly prevented both the increases in PAI-1 levels and the development of cardiovascular remodeling. These findings suggest that the local renin-angiotensin system regulates PAI-1 expression, and that the increased PAI-1 levels may contribute to the cardiovascular remodeling in this model.

Synergistic effect of adrenal steroids and angiotensin II on plasminogen activator inhibitor-1 production

Recent data suggest an interaction between the renin-angiotensin-aldosterone system and fibrinolysis. Although previous work has focused on the effect of angiotensin II (Ang II) on plasminogen activator inhibitor (PAI-1) expression, the present study tests the hypothesis that aldosterone contributes to the regulation of PAI-1 expression. To test this hypothesis in vitro, luciferase reporter constructs containing the human PAI-1 promoter were transfected into rat aortic smooth muscle cells. Exposure of the cells to 100 nmol/L Ang II resulted in a 3-fold increase in luciferase activity. Neither 1 micromol/L dexamethasone nor 1 micromol/L aldosterone alone increased PAI-1 expression. However, both dexamethasone and aldosterone enhanced the effect of Ang II in a dose-dependent manner. This effect was abolished by mutation in the region of a putative glucocorticoid-responsive element. A similar interactive effect of Ang II and aldosterone was observed in cultured human umbilical vein endothelial cells. The time course of the effect of aldosterone on Ang II-induced PAI-1 expression was consistent with a classical mineralocorticoid receptor mechanism, and the effect of aldosterone on PAI-1 synthesis was attenuated by spironolactone. To determine whether aldosterone affected PAI-1 expression in vivo, we measured local venous PAI-1 antigen concentrations in six patients with primary hyperaldosteronism undergoing selective adrenal vein sampling. PAI-1 antigen, but not tissue plasminogen activator antigen, concentrations were significantly higher in adrenal venous blood than in peripheral venous blood. Taken together, these data support the hypothesis that aldosterone modulates the effect of Ang II on PAI-1 expression in vitro and in vivo in humans.

Angiotensin IV stimulates plasminogen activator inhibitor-1 expression in proximal tubular epithelial cells

BACKGROUND

Angiotensin II (Ang II) has been shown to be implicated in the development of renal fibrosis in several forms of chronic glomerulonephritides, but the precise mechanisms of its effects remain unclear. It has recently been reported that Ang II stimulates the expression of plasminogen activator inhibitor-1 (PAI-1) in several cell lines. PAI-1 is a major physiological inhibitor of the plasminogen activator/plasmin system, a key regulator of fibrinolysis and extracellular matrix (ECM) turnover. PAI-1 induction by Ang II in endothelial cells seems to be mediated by Ang IV via a receptor that is different from Ang II type 1 and 2 receptors (AT1 and AT2).

METHODS

In this study, we sought to evaluate the effects of Ang IV on PAI-1 gene and protein expression in a well-characterized and immortalized human proximal tubular cell line (HK2) by Northern blot and enzyme-linked immunosorbent assay.

RESULTS

Ang IV stimulated PAI-1 mRNA expression, whereas it did not induce a significant increase in tritiated thymidine uptake after 24 hours of incubation. This effect was dose and time dependent. Ang IV (10 nM) induced a 7.8 +/- 3.3-fold increase in PAI-1 mRNA expression. The PAI-1 antigen level was significantly higher in conditioned media and the ECM of cells treated with Ang II and Ang IV than in control cells (both P < 0.02). Although Ang II induced a 4.2 +/- 2. 1-fold increase in PAI-1 mRNA expression, its effect underwent a dose-dependent reduction when amastatin, a potent inhibitor of the endopeptidases that catalyzes the conversion of Ang II to Ang IV, was added. In contrast, amastatin was not able to prevent the expression of PAI-1 mRNA induced by Ang IV. Finally, pretreatment of HK2 cells with losartan and N-Nicotinoyl-Tyr-N3-(Nalpha-CBZ-Arg)-Lys-His-Pro-Ile, the specific antagonists of AT1 and AT2 receptors, failed to modify PAI-1 mRNA expression as induced by Ang II.

CONCLUSIONS

Our results demonstrate that Ang II stimulates PAI-1 mRNA expression and the production of its protein in human proximal tubular cells. This is mainly-if not exclusively-due to Ang IV, which acts on a receptor that is different than AT1 or AT2. Therefore, it can be hypothesized that the induction of PAI-1 by Ang IV may be implicated in the pathogenesis of renal interstitial fibrosis in several forms of chronic glomerulonephritides.

High salt intake potentiates the renal vascular and glomerular damage caused by low doses of angiotensin II in uni-nephrectomized rats

OBJECTIVE

We recently reported that the renin-angiotensin system plays an important role in the progression of vascular and kidney injuries, even in Dahl salt-sensitive rats with volume-dependent hypertension. In this study, we investigated whether a high-salt diet increases susceptibility to kidney injury induced by angiotensin II in normotensive, uni-nephrectomized Sprague-Dawley rats, which mimics the condition of salt-volume repletion and blunted renin-angiotensin system.

METHODS

The rats were fed either a low-salt (0.3% NaCl) or a high-salt (4% NaCl) diet and divided into five groups: two control groups with a low-salt or a high-salt diet without angiotensin II infusion (saline infusion), and three angiotensin II groups (angiotensin II infusion, 10 or 50 ng/kg per min with high-salt diet, 50 ng/kg per min with low-salt diet, subcutaneously). The rats were kept on these regimes for 8 weeks. The blood pressure was measured every week. Functional and morphological alterations in the kidney were assessed at the end of the experiment

RESULTS

There were no differences in the arterial blood pressures of the five experimental groups. However, angiotensin II infusion increased the weights of the heart and aortic walls in a dose-dependent manner in the high-salt groups. There was also a dose-dependent increase in proteinuria, N-acetyl-beta-D-glucosaminidase activity (NAG) excretion, and additional glomerular and arterial injuries in the kidney, associated with angiotensin II infusion in the high-salt groups. In the rats given a higher dose of angiotensin II, the high-salt diet significantly increased the weights of the heart and aortic walls and exacerbated the renal function and morphological injuries, compared to the low-salt group. High-salt diet alone increased the kidney and heart weights. However, it did not significantly influence the results of the morphological and functional study. On the other hand, angiotensin II infusion on a low-salt diet showed a trend towards glomerular damage; however, the effects were small and not significant. Similarly, there were few effects of angiotensin II infusion on morphology and functional study on a low-salt diet

CONCLUSION

These data clearly show that a high-salt intake increases susceptibility of the kidney to injuries induced by low doses of angiotensin II in normotensive, uni-nephrectomized rats.

Angiotensin-converting enzyme inhibitors and angiotensin II receptor antagonists in the treatment of heart failure caused by left ventricular systolic dysfunction

Activation of the renin-angiotensin-aldosterone system (RAAS) in left ventricular systolic dysfunction is a critically important determinant in the pathophysiologic processes that lead to progression of heart failure and sudden death. Angiotensin II, acting at the specific angiotensin receptor (AT1-R), activates a series of intracellular signaling sequences which are ultimately expressed within the cardiovascular system as vasoconstriction and associated vascular hypertrophy and remodeling. Angiotensin converting enzyme (ACE) inhibition leads to increases in the vasodilatory peptides bradykinin and substance P and at least an initial reduction in angiotensin II concentrations. AT1-R blocking drugs prevent access of angiotensin II to the AT1-R and thus prevent cellular activation. ACE inhibitors have clearly been demonstrated through a large number of clinical trials to increase survival in congestive heart failure, primarily by reducing the rate of progression of left ventricular dilatation and decompensation. However, this beneficial effect diminishes over time. Preliminary short-term clinical studies evaluating the efficacy of AT1-R blocking drugs in the treatment of heart failure have suggested that they elicit similar hemodynamic and neuroendocrine effects as do the ACE inhibitors. The combination ACE inhibitors and AT1-R blocking drugs offer the theoretical advantage of increasing bradykinin while blocking the actions of angiotensin II, and thus possibly show a synergistic effect. Again, preliminary studies have yielded encouraging results that are difficult to interpret because neither ACE inhibitor nor the AT1-R blocking drug doses were titrated to tolerance. Pharmacological manipulation of the RAAS has led to better understanding of its role in heart failure and improved clinical outcomes.

Angiotensin-converting enzyme gene polymorphism is associated with coronary heart disease in non-insulin-dependent diabetic patients evaluated for 9 years

The insertion/deletion (I/D) polymorphism of the human angiotensin-converting enzyme (ACE) gene is a major determinant of circulating ACE levels. Recent studies have found the ACE D allele to be associated with an increased risk for coronary heart disease (CHD) in diabetic and nondiabetic subjects. This association has not been evaluated in prospective studies. We therefore studied the relationship between ACE gene I/D polymorphism and CHD in patients with non-insulin-dependent diabetes mellitus (NIDDM) evaluated for 9 years. The I/D polymorphism was determined by polymerase chain reaction (PCR). Overestimation of the frequency of the DD genotype was eliminated by insertion-specific primers and inclusion of 5% dimethylsulfoxide (DMSO). Eighty-three patients were evaluated for a mean period of 9.1 years (range, 7.4 to 10.5). Among them, 64 patients showed no CHD at entry. During the follow-up period, 21 patients (37.5%) developed CHD. The systolic blood pressure (P = .046), fasting blood glucose (P < .01), and prevalence of hypertension (P < .001) increased, while high-density lipoprotein (HDL) cholesterol (P < .001) decreased. Patients who developed CHD were older than those who did not; the mean age was 59.3 and 53.2 years, respectively (P = .003). The prevalence of albuminuria at follow-up examination was higher in CHD subjects versus non-CHD subjects (61.9% v 20.9%, P = .012). The D allele of the ACE gene was significantly more frequent in subjects with CHD versus those without CHD in both follow-up (P = .028, chi2 test) and cross-sectional (P = .033, chi2 test) settings. No difference could be detected between the three genotypes in age, body mass index (BMI), blood pressure, or plasma lipid levels. In our logistic regression analysis, the best model selected the DD genotype (P = .0105) and age (P = .0407) as significant risk factors for CHD. This model classified 89% of the subjects correctly. In conclusion, this 9-year prospective study supports the hypothesis that the ACE I/D polymorphism is an important and independent risk factor for CHD in patients with NIDDM.

Angiotensin-Converting Enzyme Inhibition Delays Onset of Glucosuria With Regression of Renal Injuries in Genetic Rat Model of Non-Insulin-Dependent Diabetes Mellitus

BACKGROUND: The Otsuka Long-Evans Tokushima Fatty (OLETF) rat is a new genetic model of non-insulin-dependent diabetes mellitus (NIDDM). We investigated whether angiotensin inhibition influences the onset of NIDDM and brings about a regression of renal injury in diabetes mellitus. METHODS AND RESULTS: Six-week-old OLETF rats were treated with the angiotensin-converting enzyme (ACE) inhibitors imidapril or enalapril for 16 weeks. Systolic blood pressure is increased in an age-dependent manner in OLETF rats. In this study, the elevation in systolic blood pressure was dose-dependently reduced by ACE inhibitor treatment. In OLETF rats, plasma concentrations of insulin and glucose increased and the glucosuria occurred at the age of 22 weeks. Simultaneously, OLETF rats exhibited proteinuria and nodular lesions in glomeruli. The ACE inhibitor treatment almost completely reduced glucosuria, and also decreased plasma concentrations of insulin and glucose in OLETF rats. ACE inhibitor treatment lessened the proteinuria and attenuated morphologically the severity of nodular lesions in OLETF rats. Moreover, increases in plasminogen activator inhibitor 1 (PAI-1) in OLETF rats were reduced by the ACE inhibitor treatment, and the improvement of glomerular lesions was related to decreases of PAI-1 and angiotensin II levels in plasma but not to improvement of glucose metabolism. CONCLUSIONS: ACE inhibitors delay onset of NIDDM with attenuation of kidney injury. The regression of kidney lesions is probably due to angiotensin reductions but not to glucose metabolism per se. ACE inhibitor drug therapy may be useful in preventing NIDDM and the subsequent renal injury in patients with NIDDM.

Effects and mechanism of tissue-type plasminogen activator and plasminogen activator inhibitor on vascular smooth muscle cell proliferation

Smooth muscle cell (SMC) proliferation and migration play a pivotal role in restenosis following angioplasty. The expression of tissue-type plasminogen activator (tPA) increased significantly during SMC proliferation and migration in rabbit iliac artery injury model. In this experiment, the relationship of tPA, PAI-1 and vascular SMC proliferation was studied in vitro using human aortic smooth muscle cells cultivated in normal lipid or high lipid serum. The expression of certain oncogenes during the SMC proliferation was detected by Northern blot.

RESULTS

tPA stimulates vascular SMC proliferation in a dose-dependent manner, and the effect is increased significantly in high lipid environment. PAI-1 inhibits the mitogenic effect of tPA to SMC and is dose-dependent. tPA increases oncogene c-myc mRNA level during SMC proliferation, and the level of c-myc mRNA increases significantly in hyperlipidemia. These findings indicate that tPA directly promotes human vascular SMC proliferation in vitro, and may contribute to intimal SMC proliferation after vascular injury by increasing the expression of oncogene c-myc mRNA.

Saralasin-induced inhibition of ovulation in the in vitro perfused rat ovary is not replicated by the angiotensin II type-2 receptor antagonist PD123319

OBJECTIVE

Our aim was to explain the effect of the nonspecific angiotensin II antagonist saralasin and the specific angiotensin II type-2 receptor antagonist PD123319 on ovulation.

STUDY DESIGN

Saralasin, 1 micromol/L (n = 5), and PD123319 10 micromol/L (n = 6), were administered to in vitro perfused rat ovary. Prostaglandin (prostaglandin E2, prostaglandin F2alpha, 6-keto-prostaglandin F1alpha), hydroxy-eicosatetraenoic acid (12-hydroxy-eicosatetraenoic acid, 15-hydroxy-eicosatetraenoic acid), estradiol, and progesterone levels in the perfusate and the ovulation rate were compared (Mann-Whitney U test) with controls.

RESULTS

Saralasin significantly (P < .01) inhibited the ovulation rate (3.0 +/- 1.4) versus control (13.1 +/- 1.0) and reduced prostaglandin E2 (at 3 hours P < .01 and 20 hours P < .05) and 6-keto-prostaglandin F1alpha (at 20 hours P < .05) levels. Saralasin did not alter prostaglandin F2alpha, hydroxy-eicosatetraenoic acids, or steroid levels. PD123319 decreased 15-hydroxy-eicosatetraenoic acid levels at 3 hours (P < .05) but had no effects on other eicosanoids, steroid levels, or the ovulation rate.

CONCLUSION

Angiotensin II plays an important role in ovulation in the rat and is associated with ovarian prostaglandin synthesis. This effect is not selectively regulated via the angiotensin II type-2 receptor.

Combination of ACE inhibitors and calcium antagonists: a logical approach

An increasing body of evidence indicates that impairment of endothelial function is crucially involved in the pathogenesis of cardiovascular disease. Injury to the endothelium precipitates atherosclerosis by causing smooth-muscle cell migration and proliferation, induction of expression of growth factors, and impairment of plasma coagulation and endogenous fibrinolysis. Angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists are widely used in patients with cardiovascular disease and have beneficial vascular effects beyond blood pressure control alone. Both exhibit a synergistic hemodynamic profile. Whereas calcium antagonists dilate large conduit and resistance arteries, ACE inhibitors inhibit the renin-angiotensin system (RAS) and reduce sympathetic outflow. Certain calcium antagonists, such as verapamil and diltiazem, reduce heart rate, whereas dihydropyridines tend to increase it. In the blood vessel wall, the local vascular effects of ACE inhibitors and calcium antagonists are complementary. ACE inhibitors diminish transformation of angiotensin I (Ang I) into angiotensin II (Ang II) and prevent degradation of bradykinin [which stimulates nitric oxide (NO) and prostacyclin formation]. Calcium antagonists inhibit the effects of Ang I and endothelin-1 (ET-1) at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of NO. The resistance circulation is particularly dependent on extracellular Ca2+, thereby explaining why nifedipine and verapamil effectively inhibit ET-induced vasoconstriction in vitro and in vivo. In hypertension, ACE inhibitors and calcium antagonists markedly improve structural changes and increase the media/lumen ratio in resistance arteries. Long-term combination therapy with verapamil and trandolapril is particularly effective in reversing endothelial dysfunction in hypertensive animals. ACE inhibitors substantially reduce morbidity and mortality in patients with left ventricular dysfunction after myocardial infarction (MI). There is a strong trend indicating benefit with verapamil as well, but this is confined to patients with a normal left ventricular ejection fraction. Clinical studies have confirmed that calcium antagonists exhibit antiatherogenic properties. However, the clinical relevance of these findings has recently been disputed because short-acting dihydropyridines are reported to increase risk for MI. Because ACE inhibitors and calcium antagonists exhibit synergistic hemodynamic, antiproliferative, antithrombotic, and antiatherogenic properties, combination therapy provides a promising concept in patients with cardiovascular and renal disease.

Is there a rationale for combining angiotensin-converting enzyme inhibitors and calcium antagonists in cardiovascular disease?

Coronary artery disease and its sequelae remain the most important cause of morbidity and mortality in Western countries. Because the pathophysiologic characteristics of coronary artery disease are multifactorial, impairment of endothelial function featuring enhanced vasoconstriction, increased platelet vessel wall interaction, adherence of monocytes, migration and proliferation of vascular smooth muscle cells are crucially involved. Endothelial cells release numerous vasoactive substances regulating function of vascular smooth muscle and trafficking blood cells such as nitric oxide (NO), which is a potent vasodilator also inhibiting cellular growth and migration. In addition, NO possesses antiatherogenic and thromboresistant properties by preventing platelet aggregation and cell adhesion. These effects are counterbalanced by endothelial vasoconstrictors such as angiotensin II and endothelin-1. In the blood vessel wall, the local vascular effects of angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists are synergistic. ACE inhibitors diminish the conversion of angiotensin I into angiotensin II and the inactivation of bradykinin. Calcium antagonists counteract angiotensin II and endothelin-1 at the level of vascular smooth muscle by reducing Ca2+ inflow and facilitating the vasodilator effects of NO. In hypertensive animals, long-term combination therapy with verapamil and trandolapril is particularly effective in reversing endothelial dysfunction. Further, ACE inhibitors and calcium antagonists exert beneficial vascular and complementary hemodynamic effects. Whereas ACE inhibitors inhibit the renin-angiotensin system and reduce sympathetic outflow, calcium antagonists dilate large conduit and resistance arteries. Because small vessels appear to be more dependent on extracellular Ca2+ than larger vessels, nifedipine and verapamil effectively inhibit endothelin-induced vasoconstriction in vitro and in vivo in the resistance circulation. Long-term treatment with ACE inhibitors substantially reduces morbidity and mortality rates in patients with left ventricular dysfunction after myocardial infarction; beneficial effects of verapamil in secondary prevention are confined to patients with normal left ventricular ejection fraction. In summary, long-term combination therapy of ACE inhibitors and calcium antagonists might provide beneficial effects in cardiovascular disease because they exert synergistic hemodynamic, antiproliferative, antithrombotic, and antiatherogenic properties.

The integrated effects of angiotensin II

In recent years, a prodigious amount of information has been gathered regarding the relationship between vascular biology and the mechanisms underlying cardiovascular disease. Activation of elements of the reninangiotensin system (RAS) appear to play an important role in the development and progression of conditions such as hypertension, coronary artery disease, and heart failure. Indeed, converging lines of evidence indicate that angiotensin-converting enzyme (ACE) regulates a delicate balance among a multitude of factors responsible for vascular tone, cellular growth promotion and inhibition, and pro- and anti-inflammatory effects. Because angiotensin II inhibits fibronectin, stimulates expression of plasminogen activator inhibitors, and degrades bradykinin, thereby impairing production of nitric oxide, ACE and the RAS are also involved in thrombosis and fibrinolysis. The favorable effects of ACE inhibition on endothelial function and, potentially, on cardiovascular morbidity and mortality are believed to result not only from angiotensin II suppression but also its consequent bradykinin preservation and nitric oxide production.

Modulation of plasminogen activator inhibitor-1 in vivo: a new mechanism for the anti-fibrotic effect of renin-angiotensin inhibition

We examined the potential of in vivo linkage of plasminogen activator inhibitor-1 (PAI-1) and angiotensin II (Ang II) in the setting of endothelial injury and sclerosis following radiation injury in the rat. PAI-1 is a major physiological inhibitor of the plasminogen activator (PA)/plasmin system, a key regulator of fibrinolysis and extracellular matrix (ECM) turnover. PAI-1 mRNA expression in the kidney was markedly increased (9-fold) at 12 weeks after irradiation (P < 1.001 vs. normal control). In situ hybridization revealed significant association of PAI-1 expression with sites of glomerular injury (signal intensity in injured vs. intact glomeruli, P < 0.001). Angiotensin converting enzyme inhibitors (ACEI, captopril or enalapril) or angiotensin II receptor antagonist (AIIRA, L158,809) markedly reduced glomerular lesions (thrombosis, mesangiolysis, and sclerosis; sclerosis index, 0 to 4+ scale, 0.49 +/- 0.20 in untreated vs. 0.05 +/- 0.02, 0.02 +/- 0.01, 0.04 +/- 0.02 in captopril, enalapril and AIIRA, respectively, all P < 0.01 vs untreated). Further, ACEI and AIIRA markedly attenuated increased PAI-1 mRNA expression in the irradiated kidney (36, 19 and 20% expression, respectively, for captopril, enalapril and AIIRA, compared to untreated irradiated kidney, P < 0.05, < 0.01, < 0.01). This effect was selective in that neither tissue-type nor urokinase-type PA mRNA expression was affected by these interventions. Thus, we speculate that inhibition of the renin-angiotensin system may ameliorate injury following radiation by accelerating fibrinolysis and ECM degradation, at least in part, via suppression of PAI-1 expression. In summary, inhibition of Ang II, in addition to its known effects on vascular sclerosis, may also by its novel effect to inhibit PAI-1, lessen fibrosis following endothelial/thrombotic injury.

Identification of a cis-acting sequence in the human plasminogen activator inhibitor type-1 gene that mediates transforming growth factor-beta1 responsiveness in endothelium in vivo

The mechanism of regulation of the plasminogen activator inhibitor type-1 (PAI-1) gene by transforming growth factor-beta1 (TGF-beta1) was studied in vitro and in vivo in endothelial cells. We constructed adenovirus vectors containing PAI-1 5'-flanking sequences driving expression of a beta-galactosidase (beta-gal) reporter gene. Cultured bovine endothelial cells were transduced with the vectors and treated with TGF-beta1. beta-Gal expression was up-regulated 10-20-fold by TGF-beta1 when vectors contained 799-base pair (bp) of 5'-flanking sequence, but only minimally (2-3-fold) from a vector containing only 82-bp of 5' PAI-1 flanking sequence. TGF-beta1 up-regulated beta-gal expression at the mRNA level, congruently with TGF-beta1 up-regulation of expression of the endogenous PAI-1 gene. The constructs were transduced into intact rat carotid endothelium, and TGF-beta1 was injected systemically. In vivo, TGF-beta1 up-regulated endothelium-specific expression of beta-gal 3-fold (p < 0.03) from a vector containing the 799-bp sequence, but did not alter expression from a vector containing the 82-bp sequence. The sequence between -799 and -82 mediates up-regulation of reporter gene expression by TGF-beta1 in endothelial cells in vitro and in vivo. This general method permits the elucidation of mechanisms of gene regulation by physiologic stimuli delivered to the endothelium of intact animals.

The renin-angiotensin system and vascular hypertrophy

In addition to its vasoconstrictor and aldosterone-stimulating action, angiotensin II also drives cell growth and replication in the cardiovascular system, which may result in myocardial hypertrophy and hypertrophy or hyperplasia of conduit and resistance vessels in certain subjects. These actions are mediated through angiotensin II receptors (subtype AT1), which activate the G protein, phospholipase C, diacylglycerol and inositol trisphosphate pathway, to increase the expression of certain protooncogenes (c-fos, c-myc and c-jun) and growth factors (platelet-derived growth factor-A-chain, transforming growth factor-beta 1 and basic fibroblast growth factor). The cellular responses to angiotensin II in vascular smooth muscle have been shown in different hypertensive vessels to be either hypertrophy alone, hypertrophy and DNA synthesis without cell division (polyploidy) or DNA synthesis with cell division (hyperplasia). In genetic hypertension, the altered structure of small arteries is due to either cellular hyperplasia or remodeling, whereas in renovascular hypertension there is hypertrophy of vascular smooth muscle cells. Angiotensin II also increases synthesis of some matrix components, activates blood monocytes and is thrombogenic. Angiotensin-converting enzyme (ACE) inhibitors prevent or reverse vascular hypertrophy in animal models of hypertension; this seems to be a class effect, shared to some extent with calcium channel blocking agents. In human hypertension, ACE inhibitors reduce the increased media/lumen ratio of large and small arteries in hypertension and increase arterial compliance. These properties are also shared by losartan, the first of the new class of angiotensin II receptor (AT1) antagonists. The clinical implications of these findings need to be tested through rigorous and prospective clinical trials.

Prolonging action of imidapril on the lifespan expectancy of cardiomyopathic hamsters

We studied the effect of imidapril, a novel angiotensin-converting enzyme (ACE) inhibitor, on lifespan expectancy of cardiomyopathic (CM) hamsters of BIO 14.6 strain, one of the representative models of congestive heart failure (CHF). Imidapril was consecutively administered to hamsters by mixing it in their diet at a concentration of 480 ppm (approximately 30 mg/kg/day) or 1,600 ppm (approximately 120 mg/kg/day) from age 26 weeks. Only several control hamsters died before age 54 weeks, but their survival rate decreased to 23.7% at age 73 weeks. The survival rates of 480-ppm and 1,600-ppm imidapril groups at age 73 weeks were as high as 75.7 and 68.4%, respectively (p < 0.01 vs. control hamsters). Macroscopic and microscopic pathology in imidapril-treated groups was milder than that in control animals in general, but differences were not statistically significant when animals were divided into survivors and fatalities except for the presence of mural thrombus in the heart. We further studied the effects of imidapril on blood pressure (BP), in vivo cardiac function, cardiac beta-adrenoceptor distribution, and plasma catecholamine levels after dietary treatment with 480 ppm imidapril for 8-10 weeks from age 37 weeks. Imidapril-treated animals showed improved cardiac function under urethane anesthesia. These results indicate that imidapril prolongs lifespan expectancy of CM hamsters and suggest that a hemodynamic effect of imidapril is involved in its beneficial effect.