The Renin-Angiotensin and fibrinolytic systems co-conspirators in the pathogenesis of ischemic cardiovascular disease

Role of plasminogen activated inhibitor-1 in the pathogenesis of anticoagulant related nephropathy

Anticoagulant related nephropathy (ARN) is the result of glomerular hemorrhage in patients on systemic anticoagulation therapy or underlying coagulopathy. Red blood cells (RBC) that passed through the glomerular filtration barrier form RBC casts in the tubules, increase oxidative stress and result in acute tubular necrosis (ATN). The mechanisms of ARN still not completely discovered. Plasminogen activator inhibitor-1 (PAI-1) plays a significant role in the maintenance of coagulation homeostasis. We developed an animal model to study ARN in 5/6 nephrectomy (5/6NE) rats. The aim of this study was to elucidate the role of PAI-1 in the ARN pathogenesis. 5/6NE rats were treated per os with warfarin (0.75 mg/kg/day) or dabigatran (150 mg/kg/day) alone or in combination with PAI-1 antagonist TM5441 (2.5, 5.0 and 10 mg/kg/day). TM5441 in a dose dependent manner ameliorated anticoagulant-induced increase in serum creatinine in 5/6NE rats. Anticoagulant-associated increase in hematuria was no affected by TM5441. The levels of reactive oxygen species (ROS) in the kidneys were in a dose-dependent manner decreased in 5/6NE rats treated with an anticoagulant and TM5441. Our data demonstrates that PAI-1 may reduce ARN by decreasing ROS in the kidneys. Glomerular hemorrhage is not affected by anti-PAI-1 treatment. These findings indicate that while symptoms of ARN can be reduced by PAI-1 inhibition, the main pathogenesis of ARN - glomerular hemorrhage - cannot be prevented.

Anti-platelet therapy with clopidogrel prevents endothelial dysfunction and vascular remodeling in aortas from hypertensive rats

The aim was to investigate the beneficial effects of clopidogrel in thoracic aorta function and structure and to characterize if P2Y₁₂ receptors contribute to these effects. Male Sprague Dawley rats were infused with angiotensin II [(Ang II) 60 ng.min⁻¹, 14 days] or saline (control rats) and were simultaneously treated with clopidogrel (10 mg.kg⁻¹.day⁻¹) or vehicle. After 14 days, systolic blood pressure (mmHg) was similar in Ang II-hypertensive rats treated with clopidogrel or vehicle (199±9 vs. 190±11, respectively). Systolic blood pressure in control rats was not altered by clopidogrel treatment (128±1 vs. vehicle, 134±2). Endothelium-dependent relaxation induced by 2-MeS-ADP was decreased in aortas from vehicle-treated Ang II-hypertensive rats, compared to vehicle-treated control rats. This response was elicited via activation of P2Y₁ and P2Y₁₂ receptors. In the presence of L-NAME and indomethacin, 2-MeS-ADP induced contraction and this response was augmented in vehicle-treated Ang II-hypertensive rats, compared to vehicle-treated control rats. The contraction to 2-MeS-ADP was evoked by P2Y₁₃ and P2Y₁₂ receptor activation. Clopidogrel-treatment did not normalize relaxation or contractile responses induced by 2-MeS-ADP in aortas from Ang II-hypertensive rats. P2Y₁ and P2Y₁₂ protein expression was increased, whereas P2Y₁₃ receptor expression was reduced in aorta from vehicle-treated Ang II-hypertensive rats. Endothelium-dependent relaxation upon acetylcholine-stimulation was reduced in vehicle-treated Ang II-hypertensive rats, and clopidogrel treatment was effective in improving endothelial function. Clopidogrel also prevented vascular remodeling, evidenced by augmented media thickness in aortas from Ang II-hypertensive rats. Clopidogrel has beneficial effects on the aortic endothelium of Ang II-hypertensive rats, but its effects do not seem to be directly related to the presence of P2Y₁₂ receptors in this vessel.

Are polymorphisms in the ACE and PAI-1 genes associated with recurrent spontaneous miscarriages?

PROBLEM

To determine whether the ACE D/D genotype or the combination of PAI-1 4G/4G and ACE D/D genotypes may serve as a risk factor for recurrent pregnancy loss.

METHOD OF STUDY

Buccal swabs were obtained from 120 women experiencing recurrent pregnancy loss and from 84 fertile control women. DNA was extracted from the buccal swab samples using the Qiagen DNA Mini Kit (Qiagen), followed by multiplex polymerase chain reaction (PCR). PCR products were analyzed for the ACE gene polymorphism, which consists of the insertion or deletion (I/D) of a 287-bp fragment in intron 16, and the PAI-1 4G/4G genotype.

RESULTS

No significant differences in specific ACE gene mutations were observed when patients experiencing recurrent miscarriage were compared with control women. When the frequencies of homozygous mutations for ACE D/D and PAI-I 4G/4G were compared between recurrent aborters and controls, again no significant differences in the prevalence of the combination of these gene mutations were noted.

CONCLUSION

Homozygosity for the D allele of the ACE gene and the combination of the D/D genotype with two 4G alleles of the PAI-1 promoter gene are not associated with a significant increase in the risk of recurrent miscarriage.

Evaluation of angiotensin-converting enzyme (ACE), its homologue ACE2 and neprilysin in angiotensin peptide metabolism

In the RAS (renin-angiotensin system), Ang I (angiotensin I) is cleaved by ACE (angiotensin-converting enzyme) to form Ang II (angiotensin II), which has effects on blood pressure, fluid and electrolyte homoeostasis. We have examined the kinetics of angiotensin peptide cleavage by full-length human ACE, the separate N- and C-domains of ACE, the homologue of ACE, ACE2, and NEP (neprilysin). The activity of the enzyme preparations was determined by active-site titrations using competitive tight-binding inhibitors and fluorogenic substrates. Ang I was effectively cleaved by NEP to Ang (1-7) (kcat/K(m) of 6.2x10(5) M(-1) x s(-1)), but was a poor substrate for ACE2 (kcat/K(m) of 3.3x10(4) M(-1) x s(-1)). Ang (1-9) was a better substrate for NEP than ACE (kcat/K(m) of 3.7x10(5) M(-1) x s(-1) compared with kcat/K(m) of 6.8x10(4) M(-1) x s(-1)). Ang II was cleaved efficiently by ACE2 to Ang (1-7) (kcat/K(m) of 2.2x10(6) M(-1) x s(-1)) and was cleaved by NEP (kcat/K(m) of 2.2x10(5) M(-1) x s(-1)) to several degradation products. In contrast with a previous report, Ang (1-7), like Ang I and Ang (1-9), was cleaved with a similar efficiency by both the N- and C-domains of ACE (kcat/K(m) of 3.6x10(5) M(-1) x s(-1) compared with kcat/K(m) of 3.3x10(5) M(-1) x s(-1)). The two active sites of ACE exhibited negative co-operativity when either Ang I or Ang (1-7) was the substrate. In addition, a range of ACE inhibitors failed to inhibit ACE2. These kinetic data highlight that the flux of peptides through the RAS is complex, with the levels of ACE, ACE2 and NEP dictating whether vasoconstriction or vasodilation will predominate.

Angiotensin II AT1 receptor antagonists inhibit platelet adhesion and aggregation by nitric oxide release

This study investigated the process of nitric oxide (NO) release from platelets after stimulation with different angiotensin II type 1 (AT1)-receptor antagonists and its effect on platelet adhesion and aggregation. Angiotensin II AT1-receptor antagonist-stimulated NO release in platelets was compared with that in human umbilical vein endothelial cells by using a highly sensitive porphyrinic microsensor. In vitro and ex vivo effects of angiotensin II AT1-receptor antagonists on platelet adhesion to collagen and thromboxane A2 analog U46619-induced aggregation were evaluated. Losartan, EXP3174, and valsartan alone caused NO release from platelets and endothelial cells in a dose-dependent manner in the range of 0.01 to 100 micro mol/L, which was attenuated by NO synthase inhibitor N(G)-nitro-L-arginine methyl ester. The angiotensin II AT1-receptor antagonists had more than 70% greater potency in NO release in platelets than in endothelial cells. The degree of inhibition of platelet adhesion (collagen-stimulated) and aggregation (U46619-stimulated) elicited by losartan, EXP3174, and valsartan, either in vitro or ex vivo, closely correlated with the NO levels produced by each of these drugs alone. The inhibiting effects of angiotensin II AT1-receptor antagonists on collagen-stimulated adhesion and U46619-stimulated aggregation of platelets were significantly reduced by pretreatment with N(G)-nitro-L-arginine methyl ester. Neither the AT2 receptor antagonist PD123319, the cyclooxygenase synthase inhibitor indomethacin, nor the selective thromboxane A2/prostaglandin H2 receptor antagonist SQ29,548 had any effect on angiotensin II AT1-receptor antagonist-stimulated NO release in platelets and endothelial cells. The presented studies clearly indicate a crucial role of NO in the arterial antithrombotic effects of angiotensin II AT1-receptor antagonists.

Microangiopathic injury and augmented PAI-1 in human diabetic nephropathy

BACKGROUND

Microvascular injury and mesangial dysfunction contribute to the pathogenesis of diabetic glomerulosclerosis. We investigated the extent of microvascular injury characterized by fragmented red blood cells (RBCs) in the mesangium of glomeruli in diabetic nephropathy, and its clinicopathologic significance. We also investigated the possible contributions of plasminogen activator inhibitor-1 (PAI-1), which has been implicated in thrombosis and sclerosis, and the novel steroid receptor superfamily member, peroxisome proliferator-activated receptorgamma (PPARgamma), implicated in monocyte-foamy macrophage transformation in atherosclerosis and improved insulin responsiveness in diabetes.

METHODS

Sixty-four diabetic nephropathy (DN) cases in our renal biopsy files at VUMC, diagnosed between 1997 and 1999, were reviewed. Patients were classified based on the presence or absence of fragmented RBCs in the mesangium (M+, M-). PAI-1 and PPARgamma immunostaining was performed with double staining for the macrophage marker CD68.

RESULTS

M+ lesions were present in 21.9% of cases, and in positive cases, involved on average 10.2 +/- 2.1% of glomeruli. M+ patients were 40- to 78-years-old (mean +/- SD, 60.4 +/- 9.8), the female/male ratio was 2.5, and the white/black ratio was 6. In M-, the patients' ages ranged from 29 to 81 years (57.6 +/- 13.3, P = NS vs. M+), the female/male ratio was 0.5 (P < 0.05 vs. M+), and the white/black ratio was 2.3 (P = 0.1 vs. M+). Mean 24-hour urine protein in M+ was 9.9 +/- 13.6 g/24 h, versus 4.0 +/- 2.8 g/24 h in M- (P < 0.05). The fragmented RBCs in M+ cases localized exclusively within Kimmelstiel-Wilson nodules. PAI-1 and PPARgamma immunostaining was increased in areas of sclerosis in arteries and glomeruli, with expression of both in glomerular mesangial, parietal and visceral epithelial cells. Infiltrating macrophages in glomeruli were PPARgamma negative, contrasting positivity in macrophages in control cases of carotid artery plaque and in renal interstitial macrophages. The Kimmelstiel-Wilson nodules in M+ patients showed increased PAI-1 staining.

CONCLUSIONS

Mesangial RBC fragments are indicative of microvascular injury and mesangiolysis in DN and are associated with worse proteinuria, and possible worse prognosis. Possible pathogenic mechanisms involve the fibrinolytic/proteolytic system and locally activated PAI-1.

Inhibition of platelet aggregability by losartan in essential hypertension

Most clinical events associated with hypertension have a thrombotic component. Losartan is a selective, competitive antagonist of the thromboxane A2 receptor in experiments performed in isolated vascular strips and in human and rat platelet-enriched plasma. In this study, we investigated for the first time whether losartan at therapeutic doses has an effect on platelet aggregability and indexes of fibrinolysis in essential hypertensive subjects. Changes in the dose-response curve to platelet aggregation induced by the thrombin receptor-activating peptide SFLRRN-NH2 were determined in 9 patients (56% men, 72% white; mean age 52.8 years) with stage I or II essential hypertension and in 9 untreated healthy volunteers. After a 4-week washout period, hypertensive subjects received 2 weeks of placebo followed by 4 weeks of losartan 50 mg/day. Both subjects and end points were blinded for treatment assignment. In addition, plasminogen activator inhibitor type 1 antigen and von Willebrand antigen were studied in all patients and controls. Four weeks of losartan produced a statistically significant (p <0.05) increase in the concentration of SFLRRN-NH2 required to induce a half-maximal response in platelet aggregation extent and rate 4 weeks after initiation of treatment. The decrease in platelet aggregability was independent of blood pressure control and the effects of gender and age. Losartan had no effect on plasma concentrations of plasminogen activator inhibitor-1 and von Willebrand factor in hypertensive subjects. These data demonstrate for the first time a novel antiplatelet effect of losartan at therapeutic doses, which was independent of changes in blood pressure, plasma markers of fibrinolytic activity, and endothelial perturbation.

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.

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.

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.

Recent insight into therapy of congestive heart failure: focus on ACE inhibition and angiotensin-II antagonism

One possible intervention to interrupt the deleterious effects of the renin-angiotensin system is suppression of angiotensin II (Ang II) formation by inhibition of angiotensin-converting enzyme (ACE). However, ACE inhibition incompletely suppresses Ang II formation and also leads to accumulation of bradykinin. Angiotensin II type 1 (AT1) receptors are believed to promote the known deleterious effects of Ang II. Therefore, AT1 receptor antagonists have been recently introduced into therapy for hypertension and congestive heart failure (CHF). Although there are significant differences between the effects of AT1 receptor antagonists and ACE inhibitors including the unopposed stimulation of angiotensin II type 2 (AT2) receptors by AT1 receptor antagonists, the discussion of whether ACE inhibitors, AT1 receptor antagonists or the combination of both are superior in the pharmacotherapy of CHF is still largely theoretical. Accordingly, AT1 receptor antagonists are still investigational. Angiotensin-converting enzyme inhibitors remain first line therapy in patients with CHF due to systolic dysfunction. However, in patients not able to tolerate ACE inhibitor induced side effects, in particular cough, AT1 receptor antagonism is a good alternative. In clinical practice, emphasis should be placed on increasing the utilization of ACE inhibitors, as more than 50% of patients with CHF do not receive ACE inhibitors. In addition, the majority of those on ACE inhibitors receive doses lower than the dosage used in the large clinical trials. Although not yet completely proved, it is likely that high doses of ACE inhibition are superior to low doses with respect to prognosis and symptoms.

New insights into the renin-angiotensin system and hypertensive renal disease

The role of the renin-angiotensin system in hypertension and end organ damage has long been recognized. Recent advances in genetic models and newly available pharmacologic tools have allowed dissection of the mechanisms of actions of the renin-angiotensin system in hypertensive kidney disease. The newly cloned AT(2) receptor is now recognized to oppose many of the AT(1) receptor"s actions. The renin-angiotensin system is now recognized to be linked to induction of plasminogen activator inhibitor-1 (PAI-1), possibly via the AT(4) receptor, thus promoting both thrombosis and fibrosis. Interactions of the renin-angiotensin system with aldosterone and bradykinin may have impact on both blood pressure and tissue injury. The effects of angiotensin 1 converting enzyme inhibitors versus those of the newly available AT(1) receptor antagonists on blood pressure and organ damage are undergoing evaluation in clinical trials. Finally, polymorphisms of genes relevant to the renin-angiotensin system appear to affect response to treatment, although this effect varies in different populations.

Polymorphism of angiotensin converting enzyme gene is associated with circulating levels of plasminogen activator inhibitor-1

The deletion (D) allele of the insertion/deletion (I/D) polymorphism of the angiotensin converting enzyme (ACE) gene is strongly associated with an increased level of circulating ACE. The ACE gene polymorphism may influence the production of angiotensin II (Ang II). It has been shown that Ang II modulates fibrinolysis, that is, Ang II increases plasminogen activator inhibitor-1 (PAI-1) mRNA and plasma PAI-1 levels in vitro and in vivo. Considered together, we tested the hypothesis that the deletion allele of the ACE gene might be associated with increased levels of PAI-1. We related the ACE genotype to PAI-1 antigen levels in 603 men and 221 women attending a routine health screening. As a whole, the plasma PAI-1 level was not strongly associated with ACE genotype. Since the PAI-1 level was significantly influenced by well-known risk factors for coronary artery disease (CAD), we further analyzed the data after excluding subjects with major cardiovascular risk factors. In low-risk male subjects, the DD genotype had significantly higher levels of plasma PAI-1 (DD: 20.3 +/- 2.2; DI: 13.9 +/- 1.1; II: 13.6 +/- 1.3 ng/mL, P = .010 by ANOVA). In low-risk female subjects, the DD genotype showed a tendency to a high level of plasma PAI-1 without statistical significance. When analysis was restricted to postmenopausal women (age > or = 55 or FSH > or = 35 ng/mL), the DD genotype showed a significantly higher level of PAI-1 than subjects with the DI and II genotypes (27.7 +/- 6.2 versus 15.6 +/- 1.8 ng/mL, P = .028). The DD polymorphism of the ACE gene is associated with high PAI-1 levels in male and possibly in postmenopausal female subjects who have lower conventional cardiovascular risk factors. These results suggest that the increased ACE activity caused by DD polymorphism may play an important role in elevating the level of plasma PAI-1. Our data support the notion that the genetic variation of ACE contributes to the balance of the fibrinolytic pathway.