Inhibition of arterial thrombogenesis by quinapril but not losartan

Angiotensin IV does not exert prothrombotic effects in vivo

Thrombosis and thromboembolism are serious clinical complications of cardiovascular diseases and are among the leading causes of mortality worldwide. Dysregulation of the renin-angiotensin system is associated with an increased incidence of thrombotic events. Angiotensin II (AngII) is known to enhance platelet aggregation, contributing to a prothrombotic state in patients. Important biological roles of other angiotensin peptides and their receptors have been shown, but their specific role in thrombus formation remains unclear. Recent evidence suggests a prothrombotic role of angiotensin IV (AngIV). To confirm the prothrombotic effects of AngIV and to further investigate AngIV-mediated mechanisms, we utilized osmotic minipumps to administer AngIV in mice continuously over 4 weeks. AngIV treatment did not induce thrombus formation in the heart, did not affect platelet numbers, and did not enhance platelet aggregation. HGF, c-MET, or PAI-1 expression levels in the heart were not affected by AngIV treatment in mice. Furthermore, we did not observe altered platelet aggregation of human platelets incubated with HGF. These findings indicate that AngIV does not regulate key prothrombotic mechanisms.

Ebelactone B, an Inhibitor of Extracellular Cathepsin A-Type Enzyme, Suppresses Platelet Aggregation Ex Vivo in Renovascular Hypertensive Rats

The present study was undertaken to investigate whether ebelactone B, an inhibitor of bradykinin and angiotensin I hydrolysis by serine carboxypeptidase Y-like enzymes, could influence platelet aggregation ex vivo in renovascular hypertensive rats (2-kidney, 1-clip Goldblatt model, 2K1C). We found that ebelactone B (5 mg/kg) administrated subcutaneously once a day for 5 days, 5 weeks after the development of hypertension, or a single dose of ebelactone B (0.5 mg/kg) injected intravenously into 2K1C hypertensive rats before the induction of arterial thrombosis, both markedly suppressed collagen-induced platelet aggregation in whole blood. In contrast, inhibition of collagen-induced platelet aggregation was not evident in vitro after pretreatment of the blood with ebelactone B, indicating that ex vivo the antiaggregatory action of this compound can proceed through an indirect mechanism. The injection of ebelactone B did not affect the mean blood pressure of 2K1C hypertensive rats but lowered an elevated extracellular serine carboxypeptidase cathepsin A-like activity. Thus, the data indicate that ebelactone B may be a promising antiaggregatory agent in renovascular hypertension and suggest that 1 of the possible mechanisms through which it exerts this effect may be related to the suppression of cathepsin A-like activity released locally during the development of renovascular hypertension.

Use of calcium antagonists and worsening renal function in patients receiving angiotensin-converting-enzyme inhibitors

OBJECTIVE

The objective of this study was to assess whether calcium antagonists, which have been proven to dilate the afferent glomerular arteriole, might prevent increases in serum creatinine levels among older subjects who started treatment with angiotensin-converting enzyme (ACE) inhibitors.

METHODS

We explored the association between use of calcium antagonists and incident increases in serum creatinine in 780 elderly patients with baseline creatinine levels <1.2 mg/dL (106.19 micromol/L), who were enrolled in a multicenter pharmacoepidemiology study, and who started using ACE inhibitors during their hospital stay. Among these participants, 279 also started using calcium antagonists. Demographic variables, comorbid conditions, medications, and objective tests, which were associated with increasing serum creatinine levels in separate regression models, were examined as potential confounders in a summary model.

RESULTS

Among patients receiving ACE inhibitors, serum creatinine levels increased in 22% of participants who were dispensed calcium antagonists, and in 31% of other patients (P=0.005). In the summary regression model, use of calcium antagonists was associated with a decreased risk of worsening renal function (RR 0.56, 95% CI 0.37-0.84). The adjusted risk of increasing serum creatinine was lower (RR 0.25, 95% CI 0.05-0.95) in participants receiving higher calcium antagonists dosages than in those taking lower dosages. This protective effect of calcium antagonists was not detected in patients not dispensed ACE inhibitors.

CONCLUSION

ACE inhibitors are underused in older subjects, mainly because of the higher incidence of renal damage among geriatric populations. Our results indicate that among elderly patients receiving ACE inhibitors, the use of calcium antagonists is associated with a reduced risk of worsening renal function. Thus, these results warrant trials aiming at establishing whether combined treatment with calcium antagonists might allow the use of ACE inhibitors in clinical practice to be expanded to the elderly population.

Angiotensin II and IV stimulate expression and release of plasminogen activator inhibitor-1 in cultured human coronary artery endothelial cells

There is increasing evidence that angiotensin II influences thrombogenesis by regulating the expression of plasminogen activator inhibitor-1 (PAI-1). In this study, the effects of angiotensin II and its receptors on the expression and release of PAI-1 and tissue-type plasminogen activator (t-PA) were examined in human coronary artery endothelial cells (HCAECs). As control, cells were treated with angiotensin IV. HCAECs incubated with angiotensin II increased the expression of PAI-1 mRNA in a concentration (10-9-10-5 M)- and time (6-24 h)-dependent manner. PAI-1 protein release was also increased in the culture medium of HCAECs treated with angiotensin II. The effects of angiotensin II (10-6 M) were blocked completely by the AT1 receptor blocker losartan (10-6 M) but not by the AT2 receptor blocker PD123319 (10-6 M). Angiotensin II pretreatment also slightly, but significantly, increased t-PA mRNA expression. This effect of angiotensin II on t-PA mRNA was blocked by losartan but not by PD123319. HCAECS treated with angiotensin II revealed large amounts of the lipid peroxidation product, malonaldehyde (MDA). The effects of angiotensin II on PAI-1 expression and MDA release were blocked by pretreatment of cells with alpha-tocopherol (10-5 M). In control experiments, treatment of HCAECs with angiotensin IV markedly increased PAI-1 mRNA expression and protein release. This effect of angiotensin IV was blocked by the AT4 receptor blocker divalinal (10-6 M). These observations indicate that AT1 receptor activation plays an important role in the stimulation of PAI-1 expression and release in response to angiotensin II. Upregulation of t-PA gene may reflect autoregulation in response to PAI-1 release. Angiotensin II-mediated activation of oxidation pathways may relate to uupregulation of PAI-1. This study also confirms that angiotensin IV upregulates PAI-1 expression in HCAECs.