Effects of olmesartan medoxomil as an angiotensin II-receptor blocker in chronic hypoxic rats

Neurohormonal modulation in pulmonary arterial hypertension

Pulmonary hypertension is a fatal condition of elevated pulmonary pressures, complicated by right heart failure. Pulmonary hypertension appears in various forms; one of those is pulmonary arterial hypertension (PAH) and is particularly characterised by progressive remodelling and obstruction of the smaller pulmonary vessels. Neurohormonal imbalance in PAH patients is associated with worse prognosis and survival. In this back-to-basics article on neurohormonal modulation in PAH, we provide an overview of the pharmacological and nonpharmacological strategies that have been tested pre-clinically and clinically. The benefit of neurohormonal modulation strategies in PAH patients has been limited by lack of insight into how the neurohormonal system is changed throughout the disease and difficulties in translation from animal models to human trials. We propose that longitudinal and individual assessments of neurohormonal status are required to improve the timing and specificity of neurohormonal modulation strategies. Ongoing developments in imaging techniques such as positron emission tomography may become helpful to determine neurohormonal status in PAH patients in different disease stages and optimise individual treatment responses.

Use of olmesartan and enteropathy outcomes: a multi-database study

BACKGROUND

Multiple case reports suggest that olmesartan may be linked to sprue-like enteropathy; however, few epidemiological studies have examined this association and results have been mixed.

AIM

To assess whether olmesartan is associated with a higher rate of enteropathy vs other angiotensin II receptor blockers (ARBs).

METHODS

We conducted a cohort study among ARB initiators in 5 US claims databases representing different health insurance programmes. Cox regression models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for enteropathy-related outcomes, including coeliac disease, malabsorption, concomitant diagnoses of diarrhoea and weight loss, and non-infectious enteropathy, comparing olmesartan initiators to initiators of other ARBs after propensity score (PS) matching.

RESULTS

We identified 1 928 469 eligible patients. The unadjusted incidence rates were 0.82, 1.41, 1.66 and 29.20 per 1000 person-years for coeliac disease, malabsorption, concomitant diagnoses of diarrhoea and weight loss, and non-infectious enteropathy respectively. HRs after PS matching comparing olmesartan to other ARBs were 1.21 (95% CI, 1.05-1.40), 1.00 (95% CI, 0.88-1.13), 1.22 (95% CI, 1.10-1.36) and 1.04 (95% CI, 1.01-1.07) for each outcome. HRs were larger for patients aged 65 years and older (eg for coeliac disease, 1.57 [95% CI, 1.20-2.05]), for patients receiving treatment for more than 1 year (1.62 [95% CI, 1.24-2.12]), and for patients receiving higher cumulative olmesartan doses (1.78 [95% CI, 1.33-2.37]).

CONCLUSIONS

This large-scale, multi-database study found a higher rate of enteropathy in olmesartan initiators as compared to initiators of other ARBs, although the absolute incidence rate was low in both groups.

Endothelial actions of atrial natriuretic peptide prevent pulmonary hypertension in mice

The cardiac hormone atrial natriuretic peptide (ANP) regulates systemic and pulmonary arterial blood pressure by activation of its cyclic GMP-producing guanylyl cyclase-A (GC-A) receptor. In the lung, these hypotensive effects were mainly attributed to smooth muscle-mediated vasodilatation. It is unknown whether pulmonary endothelial cells participate in the homeostatic actions of ANP. Therefore, we analyzed GC-A/cGMP signalling in lung endothelial cells and the cause and functional impact of lung endothelial GC-A dysfunction. Western blot and cGMP determinations showed that cultured human and murine pulmonary endothelial cells exhibit prominent GC-A expression and activity which were markedly blunted by hypoxia, a condition known to trigger pulmonary hypertension (PH). To elucidate the consequences of impaired endothelial ANP signalling, we studied mice with genetic endothelial cell-restricted ablation of the GC-A receptor (EC GC-A KO). Notably, EC GC-A KO mice exhibit PH already under resting, normoxic conditions, with enhanced muscularization of small arteries and perivascular infiltration of inflammatory cells. These alterations were aggravated on exposure of mice to chronic hypoxia. Lung endothelial GC-A dysfunction was associated with enhanced expression of angiotensin converting enzyme (ACE) and increased pulmonary levels of Angiotensin II. Angiotensin II/AT1-blockade with losartan reversed pulmonary vascular remodelling and perivascular inflammation of EC GC-A KO mice, and prevented their increment by chronic hypoxia. This experimental study indicates that endothelial effects of ANP are critical to prevent pulmonary vascular remodelling and PH. Chronic endothelial ANP/GC-A dysfunction, e.g. provoked by hypoxia, is associated with activation of the ACE-angiotensin pathway in the lung and PH.

The role of local renin-angiotensin system in arterial chemoreceptors in sleep-breathing disorders

The renin-angiotensin system (RAS) plays pivotal roles in the regulation of cardiovascular and renal functions to maintain the fluid and electrolyte homeostasis. Experimental studies have demonstrated a locally expressed RAS in the carotid body, which is functional significant in the effect of angiotensin peptides on the regulation of the activity of peripheral chemoreceptors and the chemoreflex. The physiological and pathophysiological implications of the RAS in the carotid body have been proposed upon recent studies showing a significant upregulation of the RAS expression under hypoxic conditions relevant to altitude acclimation and sleep apnea and also in animal model of heart failure. Specifically, the increased expression of angiotensinogen, angiotensin-converting enzyme and angiotensin AT₁ receptors plays significant roles in the augmented carotid chemoreceptor activity and inflammation of the carotid body. This review aims to summarize these results with highlights on the pathophysiological function of the RAS under hypoxic conditions. It is concluded that the maladaptive changes of the RAS in the carotid body plays a pathogenic role in sleep apnea and heart failure, which could potentially be a therapeutic target for the treatment of the pathophysiological consequence of sleep apnea.

Angiotensin II type 1 receptor blockade partially attenuates hypoxia-induced pulmonary hypertension in newborn piglets: relationship with the nitrergic system

The objective of this study was to observe possible interactions between the renin-angiotensin and nitrergic systems in chronic hypoxia-induced pulmonary hypertension in newborn piglets. Thirteen chronically instrumented newborn piglets (6.3 ± 0.9 days; 2369 ± 491 g) were randomly assigned to receive saline (placebo, P) or the AT₁ receptor (AT₁-R) blocker L-158,809 (L) during 6 days of hypoxia (FiO₂ = 0.12). During hypoxia, pulmonary arterial pressure (Ppa; P < 0.0001), pulmonary vascular resistance (PVR; P < 0.02) and the pulmonary to systemic vascular resistance ratio (PVR/SVR; P < 0.05) were significantly attenuated in the L (N = 7) group compared to the P group (N = 6). Western blot analysis of lung proteins showed a significant decrease of endothelial NOS (eNOS) in both P and L animals, and of AT₁-R in P animals during hypoxia compared to normoxic animals (C group, N = 5; P < 0.01 for all groups). AT₁-R tended to decrease in L animals. Inducible NOS (iNOS) did not differ among P, L, and C animals and iNOS immunohistochemical staining in macrophages was significantly more intense in L than in P animals (P < 0.01). The vascular endothelium showed moderate or strong eNOS and AT₁-R staining. Macrophages and pneumocytes showed moderate or strong iNOS and AT₁-R staining, but C animals showed weak iNOS and AT₁-R staining. Macrophages of L and P animals showed moderate and weak AT₂-R staining, respectively, but the endothelium of all groups only showed weak staining. In conclusion, pulmonary hypertension induced by chronic hypoxia in newborn piglets is partially attenuated by AT₁-R blockade. We suggest that AT₁-R blockade might act through AT₂-R and/or Mas receptors and the nitrergic system in the lungs of hypoxemic newborn piglets.

Effects of olmesartan medoxomil, an angiotensin II type 1 receptor antagonist, on plasma concentration of B-type natriuretic peptide, in hypertensive patients with type 2 diabetes mellitus: a preliminary, observational, open-label study

BACKGROUND AND OBJECTIVE

Angiotensin II type 1 (AT1) receptor antagonists (angiotensin receptor blockers [ARBs]) are widely used for the treatment of not only hypertension but also cardiac dysfunction. B-type natriuretic peptide (BNP) is secreted mainly by the cardiac ventricle and plays an important role in the regulation of blood pressure (BP) and body fluid. It has been established that the plasma level of BNP is increased in patients with chronic heart failure in proportion to the severity of cardiac dysfunction. Because cardiac dysfunction is closely associated with a high risk of mortality in patients with diabetes mellitus, early identification and prevention of cardiac dysfunction are important. The objective of this study was to determine the effects of olmesartan medoxomil, a novel ARB, on the plasma level of BNP in hypertensive patients with type 2 diabetes.

METHODS

This was a preliminary, prospective, observational, open-label study. Sixty-eight type 2 diabetic patients with hypertension (systolic BP [SBP]≥140 mmHg or diastolic BP [DBP]≥90 mmHg) received olmesartan medoxomil 10–20 mg/day for 24 weeks. Plasma levels of BNP, as well as several clinical parameters of glycaemic control and lipid metabolism, were compared before and after 24 weeks of treatment. Another group consisting of 22 age- and body mass index-matched subjects not treated with olmesartan medoxomil was observed for reference purposes.

RESULTS

In the olmesartan medoxomil group, mean±SD SBP decreased from 152.8±16.4 at baseline to 146.8±14.4 mmHg after 24 weeks' treatment (p<0.05); similarly, mean±SD DBP decreased from 85.6±10.5 to 81.3±11.6 mmHg (p<0.05). In 53 subjects in whom plasma levels of BNP could be measured both before and after treatment, mean±SD BNP decreased from 41.3±49.9 to 32.5±36.3 pg/mL (p<0.05). Change in plasma BNP level over the 24-week treatment period in the olmesartan medoxomil group was not correlated with change in SBP or DBP. Multiple regression analysis revealed that change in plasma BNP level was not correlated with baseline value of or change in any other parameters. No other parameters in the olmesartan medoxomil group, and no parameters in the non-olmesartan medoxomil reference group, showed significant changes.

CONCLUSION

The current preliminary study showed that olmesartan medoxomil treatment might decrease plasma BNP levels, independent of its BP-lowering effect, in hypertensive patients with type 2 diabetes.

Effects of telmisartan on right ventricular remodeling induced by monocrotaline in rats

The present study investigated whether telmisartan, an angiotensin II type 1 receptor antagonist, has cardioprotective effects on monocrotaline-induced right ventricular (RV) remodeling in rats. Six-week-old male Wistar rats were divided into control group (CONT), monocrotaline (60 mg/kg, i.p.)-treated group (MCT), monocrotaline (60 mg/kg, i.p.) + telmisartan (3 mg/kg per day, p.o.)-treated group (MCT+TEL), and telmisartan (3 mg/kg per day, p.o.) alone-treated group (TEL). Hearts were excised after echocardiography examinations at day 25. Significant increase in RV weight and histologically remarkable fibrosis in RV sections were observed in MCT. Tricuspid annular plane systolic excursion, a parameter for RV systolic function, significantly decreased in MCT. These RV hypertrophy, fibrosis, and dysfunction were inhibited in MCT+TEL. In MCT, the acceleration time/ejection time ratio of pulmonary artery flow velocity, an index of pulmonary hypertension, significantly decreased. This decrease was not affected in MCT+TEL. In MCT, expressions and activities of matrix metalloproteinase (MMP)-2 and MMP-9, which play a critical role in cardiac remodeling, significantly increased in the RV. In MCT+TEL, these increases in expressions and activities were inhibited. MCT showed about 2-fold increase in transforming growth factor-beta1 expression compared with CONT, and such an increase was not decreased in MCT+TEL. There were no significant changes of these parameters in TEL compared with CONT. These results suggest that telmisartan could attenuate the monocrotaline-induced RV remodeling through improvements of RV hypertrophy, fibrosis, dysfunction, and inhibition of MMPs.

Role of HIF-1alpha in the regulation ACE and ACE2 expression in hypoxic human pulmonary artery smooth muscle cells

Angiotensin-converting enzyme (ACE) enhances the proliferation and migration of pulmonary artery smooth muscle cells (PASMCs), which contribute to the pathogenesis of hypoxic pulmonary hypertension (HPH). Previous reports have demonstrated that hypoxia upregulates ACE expression, but the underlying mechanism is unknown. Here, we found that ACE is persistently upregulated in PASMCs on the transcriptional level during hypoxia. Hypoxia-inducible factor 1alpha (HIF-1alpha), a key transcription factor activated during hypoxia, was able to upregulate ACE protein expression under normoxia, whereas knockdown of HIF-1alpha expression in PASMCs inhibited hypoxia-induced ACE upregulation. Furthermore, HIF-1alpha can bind and transactivate the ACE promoter directly. Therefore, we report that ACE is a novel target of HIF-1alpha. Recently, a homolog of ACE, ACE2, was reported to counterbalance the function of ACE. In contrast to ACE, we found that ACE2 mRNA and protein levels increased during the early stages of hypoxia and decreased to near-baseline levels at the later stages after HIF-1alpha accumulation. Thus HIF-1alpha inhibited ACE2 expression, and the accumulated ANG II catalyzed by ACE is a key mediator in the downregulation of ACE2 by HIF-1alpha. Moreover, a reduction of ACE2 expression in PASMCs by RNA interference was accompanied by significantly enhanced proliferation and migration during hypoxia. We conclude that ACE is directly regulated by HIF-1alpha, whereas ACE2 is regulated in a bidirectional way during hypoxia and may play a protective role during the development of HPH. In sum, these findings contribute to the understanding of the pathogenesis of HPH.

Evaluation of olmesartan medoxomil in the rat monocrotaline model of pulmonary hypertension

It is suggested that angiotensin II is involved in the pathogenesis of pulmonary hypertension and subsequent right ventricular hypertrophy; therefore, an angiotensin AT1 receptor antagonist could be beneficial for the treatment of this disease. We tested the effect of the new AT1 receptor antagonist olmesartan medoxomil on monocrotaline-induced pulmonary hypertension in rats. At 3 weeks after a single subcutaneous injection of monocrotaline (50 mg/kg), the lung/body weight ratio, the right ventricle/(left ventricle plus septum) weight ratio [RV/(LV+S)], and right ventricular systolic pressure were increased, indicating establishment of pulmonary hypertension and right ventricular hypertrophy. Oral administration of olmesartan medoxomil (2 or 5 mg/kg/day for 3 weeks) restored RV/(LV+S) and right ventricular systolic pressure, and a higher dose (5 mg/kg/day) improved the lung/body weight ratio. Pulmonary arteries isolated from monocrotaline-treated rats exhibited an increase in basal tone in the resting state, indicating that they had intrinsic tone. Three weeks of treatment with olmesartan decreased this intrinsic tone. These data suggest that long-term treatment with olmesartan has beneficial effects on monocrotaline-induced pulmonary hypertension and subsequent right ventricular hypertrophy.

Inhibitory effect of Agaricu blazei Murill components on abnormal collagen fiber formation in human hepatocarcinoma cells

Hot-water extracts of the mycelial culture and fruiting bodies of Agaricus blazei Murill were fractionated by ethanol precipitation, using various ethanol concentrations. The mycelial fraction (A-4) inhibited abnormal collagen fiber formation, and fractions A-1 to A-3 showed a small inhibitory effect. The strongest inhibition was obtained by fraction A-4, and no significant inhibition was observed with fractions A-5 and A-6. With the fruiting bodies, fractions B-1 to B-6 showed no inhibitory effects on collagen fiber formation in HCC. The reverse transcription-polymerase chain reaction (RT-PCR) demonstrates that Agaricus blazei mycelial fraction A-4 did not inhibit the type I, II or III procollagen gene expression.

Pulmonary arterial hypertension: current therapeutic strategies

The treatment of pulmonary arterial hypertension--once a lethal condition--has evolved considerably over the past few years as the number of therapeutic options available to treat this disease has increased. In this Review we attempt to summarize the current knowledge of the pathogenesis of pulmonary hypertension, in relation to the therapies presently available and those that could become available in the near future. The use of prostacyclin and its analogs, calcium-channel blockers, endothelin-receptor antagonists and phosphodiesterase type 5 inhibitors is reviewed. Newer concepts, such as the use of combination therapy, and the potential for long-term disease amelioration and improvement of outcomes, are also discussed. The role of supportive care and medications not specific to pulmonary hypertension is also examined. In addition, we review the novel emerging therapies, such as imatinib, fasudil, simvastatin, ghrelin and vasoactive intestinal peptide, which hold therapeutic potential for disease modification as well as treatment of symptoms.

Effects of olmesartan, an AT1 receptor antagonist, on hypoxia-induced activation of ERK1/2 and pro-inflammatory signals in the mouse lung

The present study aimed to investigate the effects of olmesartan, an antagonist for angiotensin II receptor type 1(AT1), on the activation of extracellular signal-regulated kinases (ERK)1/2, tissue remodeling, and pro-inflammatory signals in the right ventricle and lung of mice during the early phase of hypobaric hypoxia. Phosphorylation of ERK1/2 in both tissue types in response to hypoxia peaked at 1-3 days, and declined rapidly in the right ventricle, whereas in the lung it was sustained for at least 8 days. Upregulation of angiotensinogen mRNA was observed in the hypoxic lung at 4-9 days, but not in the hypoxic right ventricle and pulmonary artery. Olmesartan inhibited the hypoxia-induced phosphorylation of ERK1/2 in the lung, but not in the right ventricle. Neither right ventricular hypertrophy nor the thickening of the intrapulmonary arterial wall was ameliorated by olmesartan. However, this drug inhibited the expression of the mRNA for angiotensinogen and several pro-inflammatory factors, including interleukin-6 and inducible nitric oxide synthase in the hypoxic lung. These results suggest that olmesartan blocks a potential positive feedback loop of the angiotensin II-AT1 receptor system, which may lead to attenuate pro-inflammatory signals in the mouse lung, that are associated with hypoxic pulmonary hypertension, without inducing any appreciable effects on the compensatory cardiopulmonary hypertrophy at an early phase of exposure to a hypobaric hypoxic environment.

How valid are animal models to evaluate treatments for pulmonary hypertension?

Various animal models of pulmonary hypertension (PH) exist, among which injection of monocrotaline (MCT) and exposure to hypoxia are used most frequently. These animal models have not only been used to characterize the pathophysiology of PH and its sequelae such as right ventricular hypertrophy and failure, but also to test novel therapeutic strategies. This manuscript summarizes the available treatment studies in animal models of PH, and compares the findings to those obtained in patients with PH. The analysis shows that all approaches which have proven successful in patients, most notably prostacyclin and its analogs and endothelin receptor antagonists, are also effective in various animal models. However, the opposite it not always true. Therefore, promising results in animals have to be interpreted carefully until confirmed in clinical studies.