The calcium-channel blocker, azelnidipine, enhances the inhibitory action of AT1 receptor blockade on ischemic brain damage

The Effect of Candesartan Alone and Its Combination With Estrogen on Post-traumatic Brain Injury Outcomes in Female Rats

Aim: The aim of this study was to evaluate the effect of candesartan (angiotensin II type I receptor blocker) alone and its combination with estrogen on the changes in brain edema, intracranial pressure (ICP), and cerebral perfusion pressure (CPP) following diffuse traumatic brain injury (TBI) in female rats.

Methods: TBI was induced in ovariectomized female rats using Marmarou's method. The treatment groups received low-dose (LC) and high-dose (HC) candesartan, estrogen (E2), a combination of estrogen vehicle and candesartan vehicle (oil + vehicle), or a combination of estrogen with low-dose (E2 + LC), or with high-dose (E2 + HC) candesartan. ICP and CPP were measured before and several times after TBI, and the brain water content (brain edema) was measured 24 h after TBI.

Results: After the TBI, brain edema and ICP in the estrogen group were lower than in the vehicle and TBI groups. Brain edema and ICP in the HC group were lower than in the vehicle group after TBI. Although there was no significant difference in brain edema and ICP between the LC and vehicle groups, significant differences in these variables were observed when the E2 + LC and E2 + HC groups were compared with the oil + vehicle group after TBI. A significant increase in CPP was observed in the estrogen group 4 and 24 h post-TBI, while this increase was found in the HC and E2 + LC groups 24 h post-TBI.

Conclusions: A low dose of candesartan did not exert a protective effect on TBI outcomes, but such an effect did appear after combination with estrogen. This finding suggests that interaction between low-dose candesartan and estrogen improves TBI-induced consequences.

Calcium channel blocker enhances beneficial effects of an angiotensin II AT1 receptor blocker against cerebrovascular-renal injury in type 2 diabetic mice

Recent clinical trials have demonstrated that combination therapy with renin-angiotensin system inhibitors plus calcium channel blockers (CCBs) elicits beneficial effects on cardiovascular and renal events in hypertensive patients with high cardiovascular risks. In the present study, we hypothesized that CCB enhances the protective effects of an angiotensin II type 1 receptor blocker (ARB) against diabetic cerebrovascular-renal injury. Saline-drinking type 2 diabetic KK-A^y mice developed hypertension and exhibited impaired cognitive function, blood-brain barrier (BBB) disruption, albuminuria, glomerular sclerosis and podocyte injury. These brain and renal injuries were associated with increased gene expression of NADPH oxidase components, NADPH oxidase activity and oxidative stress in brain and kidney tissues as well as systemic oxidative stress. Treatment with the ARB, olmesartan (10 mg/kg/day) reduced blood pressure in saline-drinking KK-A^y mice and attenuated cognitive decline, BBB disruption, glomerular injury and albuminuria, which were associated with a reduction of NADPH oxidase activity and oxidative stress in brain and kidney tissues as well as systemic oxidative stress. Furthermore, a suppressive dose of azelnidipine (3 mg/kg/day) exaggerated these beneficial effects of olmesartan. These data support the hypothesis that a CCB enhances ARB-associated cerebrovascular-renal protective effects through suppression of NADPH oxidase-dependent oxidative stress in type 2 diabetes.

A systematic comparison of the properties of clinically used angiotensin II type 1 receptor antagonists

Angiotensin II type 1 receptor antagonists (ARBs) have become an important drug class in the treatment of hypertension and heart failure and the protection from diabetic nephropathy. Eight ARBs are clinically available [azilsartan, candesartan, eprosartan, irbesartan, losartan, olmesartan, telmisartan, valsartan]. Azilsartan (in some countries), candesartan, and olmesartan are orally administered as prodrugs, whereas the blocking action of some is mediated through active metabolites. On the basis of their chemical structures, ARBs use different binding pockets in the receptor, which are associated with differences in dissociation times and, in most cases, apparently insurmountable antagonism. The physicochemical differences between ARBs also manifest in different tissue penetration, including passage through the blood-brain barrier. Differences in binding mode and tissue penetration are also associated with differences in pharmacokinetic profile, particularly duration of action. Although generally highly specific for angiotensin II type 1 receptors, some ARBs, particularly telmisartan, are partial agonists at peroxisome proliferator-activated receptor-γ. All of these properties are comprehensively reviewed in this article. Although there is general consensus that a continuous receptor blockade over a 24-hour period is desirable, the clinical relevance of other pharmacological differences between individual ARBs remains to be assessed.

Effect of angiotensin II type 2 receptor on stroke, cognitive impairment and neurodegenerative diseases

Here, we briefly review the role of the renin-angiotensin system (RAS) in cognitive impairment and neurodegenerative disease, mainly discussing our experimental studies on the angiotensin II type 2 (AT(2)) receptor. Ischemic brain damage is enhanced in mice with overexpression of angiotensin II, with reduced cerebral blood flow in the penumbra and an increase in oxidative stress in the ischemic area. Angiotensin II binds two types of receptors, type 1 (AT(1)) and type 2 (AT(2)). Our previous experiments showed that AT(1) receptor signaling has a harmful effect, and AT(2) receptor signaling has a protective effect on the brain after stroke. AT(2) receptor signaling in bone marrow stromal cells or hematopoietic cells was shown to prevent ischemic brain damage after middle cerebral artery occlusion. In contrast, AT(2) receptor signaling also affects cognitive function. We showed that direct stimulation of the AT(2) receptor by a newly generated direct AT(2) receptor agonist, Compound 21 (C21), enhanced cognitive function in wild-type (C57BL6) mice and an Alzheimer's disease mouse model with intracerebroventricular injection of amyloid β (1-40). Finally, we carried out clinical research by investigating the levels of RAS components in patients with neurodegenerative diseases. We observed a reduction of angiotensin II and angiotensin converting enzyme (ACE) 2 levels, and an increase in ACE level in cerebrospinal fluid from patients with multiple sclerosis. These results suggest that RAS is also involved in neurodegenerative disease. Therefore, regulation of RAS might be a new therapeutic target to protect neurons from neural diseases.

Nifedipine, a calcium-channel blocker, attenuated glucose intolerance and white adipose tissue dysfunction in type 2 diabetic KK-A(y) mice

BACKGROUND

To explore the metabolic actions of nifedipine on diabetes, we examined glucose intolerance and white adipose tissue changes in type 2 diabetic KK-A(y) mice.

METHODS

Male KK-A(y) mice were treated with nifedipine (1.5 mg/kg/day in lab chow) for 5 weeks, which did not affect blood pressure or feeding of KK-A(y) mice.

RESULTS

After treatment with nifedipine, body weight tended to decrease and the weight of white adipose tissue was reduced. Without food restriction, nifedipine decreased plasma insulin level, while plasma glucose level tended to decrease. In oral glucose tolerance test, nifedipine suppressed the increase in glucose level after a glucose load without affecting plasma insulin concentration. Nifedipine also improved the result of insulin tolerance test. In white adipose tissue, nifedipine increased adipocyte number and the expression of peroxisome proliferator-activated receptor-γ (PPARγ) and adipocyte fatty acid-binding protein related to adipocyte differentiation. In addition, expression of adiponectin, insulin receptor, insulin receptor substrate-1, and glucose transporter type-4 was also increased by nifedipine. Nifedipine also increased the expression of NO synthase in white adipose tissue. Nifedipine did not affect expression of angiotensin II type 1 (AT₁) and type 2 (AT₂) receptors in white adipose tissue. Such changes in white adipose tissue were apparent in retroperitoneal adipose tissue. Nifedipine did not change the expression of angiotensin receptors, renin receptor, and angiotensinogen in white adipose tissue. Moreover, nifedipine attenuated nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity and increased superoxide dismutase (SOD) activity in white adipose tissue.

CONCLUSION

These results suggest that nifedipine can enhance insulin sensitivity and reduce white adipose tissue, possibly related to stimulation of adipocyte differentiation.

Olmesartan, an angiotensin II receptor blocker, restores cerebral hypoperfusion in elderly patients with hypertension

We evaluated the effects of olmesartan, an angiotensin II receptor blocker (ARB), on cerebral blood flow (CBF) in elderly and hypertensive subjects. Ten subjects with first- or second-degree essential hypertension (mean age, 70.5 years) underwent brain single-photon emission tomography (SPECT) scanning with (99m)Tc-ethyl cysteinate dimer before and after a 24-week course of olmesartan. Mean systolic blood pressure (SBP) was 156.2+/-9.9 mm Hg, and mean diastolic blood pressure (DBP) was 89.1+/-5.5mm Hg. No subject had any abnormalities on neurologic examination or previous history of stroke or cardiovascular disease. Before olmesartan administration, the hypertensive subjects had approximately 15% less whole brain CBF compared with age-matched normotensive controls. Regional CBF was decreased by 11%-20% in the frontal, parietal, temporal, and posterior lobes. Olmesartan treatment significantly decreased SBP to 130.4+/-4.2mm Hg (P < .001) and DBP to 78.2+/-7.0mm Hg (P < .001). After 24 weeks of olmesartan treatment, CBF of whole brain and regional CBF of the frontal, parietal, and temporal lobe were similar to those of control subjects. Our brain SPECT data indicate that olmesartan restores brain hypoperfusion in elderly and hypertensive patients without organic damage. This ARB may have a favorable potential for cerebrovascular circulation, in addition to a blood pressure-lowering effect.

Improvement of glucose intolerance by combination of pravastatin and olmesartan in type II diabetic KK-A(y) mice

The effects of the coadministration of pravastatin and an angiotensin type 1 (AT(1)) receptor blocker, olmesartan, on glucose intolerance were examined using type II diabetic mice. Male KK-A(y) mice (8 weeks of age) were treated with pravastatin and/or olmesartan for 2 weeks. An oral glucose tolerance test (OGTT) was performed with an administration of 2 g kg(-1) glucose. Tissue glucose uptake was determined using 2-[(3)H]deoxyglucose. The treatment of mice with pravastatin attenuated the increase in the plasma glucose level during OGTT in a dose-dependent manner, without affecting the plasma insulin level. Pravastatin increased glucose uptake in insulin-sensitive tissue such as the skeletal muscle and adipose tissue after treatment at 5-20 mg kg(-1) day(-1) for 2 weeks, but not at 1 mg kg(-1) day(-1). The combination of a noneffective dose of pravastatin (1 mg kg(-1) day(-1)) and a noneffective dose of olmesartan (0.5 mg kg(-1) day(-1)) synergistically improved OGTT without affecting the plasma insulin level. This combination also increased 2-[(3)H]deoxyglucose uptake in the skeletal muscle and adipose tissue. The effects of pravastatin or olmesartan on OGTT and tissue 2-[(3)H]deoxyglucose uptake were significantly enhanced by an antioxidant, tempol, whereas the effects of a pravastatin-olmesartan combination were not further enhanced by tempol. These results indicate that the combination of pravastatin and olmesartan synergistically improves glucose intolerance through an increase in tissue glucose uptake. The effects seem to be mediated by an increase in insulin sensitivity through the inhibition of oxidative stress.

Protective effect of candesartan in experimental ischemic stroke in the rat mediated by AT2 and AT4 receptors

OBJECTIVES

The contribution of the AT2 and AT4 angiotensin receptors to the protective role of the AT1 receptor blocker candesartan in acute ischemic stroke was investigated.

METHODS

Embolic stroke was induced by injection of calibrated microspheres (50 microm) in the right internal carotid in Sprague-Dawley rats.

RESULTS

Inhibition of production of endogenous angiotensins by pretreatment for 24 h with lisinopril significantly increased mortality and infarct volume, whereas candesartan for 24 h reduced blood pressure to the same extent but had no deleterious effect. A more sustained pretreatment with candesartan for 5 days significantly decreased mortality, neurological deficit and infarct size. The AT2 receptor antagonist PD123319 and the AT4 receptor antagonist divalinal abolished the protective effect of 5 days' AT1 blockade. Combined blockade of AT2 and AT4 in candesartan pretreated rats resulted in an increased mortality, neurological deficit and infarct volume of similar magnitude to lisinopril pretreatment. Coadministration of lisinopril 24 h before surgery completely blunted the protective effect of candesartan pretreatment. Administration of exogenous angiotensin IV (1 nmol) reversed the deleterious effect of lisinopril pretreatment.

CONCLUSION

Protection against acute cerebral ischemia induced by AT1 blockade for 5 days is blood pressure independent and mediated by both AT2 and AT4 angiotensin receptors.

Mebudipine and dibudipine protect PC12 cells against oxygen-glucose deprivation and glutamate-induced cell death

The protective effect of two new L-type calcium-channel blockers, mebudipine and dibudipine on neurotoxic effects induced by glutamate and oxygen-glucose deprivation (OGD) in PC12 cells was investigated. PC12 cells were intoxicated with two different methods. First, the cells were incubated with glutamate (10muM/L), glutamate and mebudipine (10muM/L), dibudipine (10muM/L) or nimodipine (10muM/L), on three different treatment schedules (concurrently, pre-3h and pre-24h). In the second method PC12 cells were exposed to in vitro oxygen-glucose deprivation for 30min and 60min alone or with the drugs in the same time schedules described above. Cellular viability was assessed by MTT assay. Glutamate-induced cell death and OGD-induced cell injury were attenuated significantly by mebudipine, dibudipine in comparison with nimodipine in all three different treatment schedules. Application of MK801 (10muM/L), an antagonist of NMDA glutamate receptors inhibited PC12 cell death in both methods. Our study suggests that mebudipine and dibudipine, like nimodipine, may have protective effects against glutamate and oxygen-glucose deprivation-induced neurotoxicity.

Olmesartan medoxomil: a review of its use in the management of hypertension

Olmesartan medoxomil (Olmetec, Benicar) is an angiotensin II type 1 (AT(1)) receptor antagonist (angiotensin receptor blocker [ARB]) that inhibits the actions of angiotensin II on the renin-angiotensin-aldosterone system, which plays a key role in the pathogenesis of hypertension. Oral olmesartan medoxomil 10-40 mg once daily is recommended for the treatment of adult patients with hypertension. In those with inadequate BP control using monotherapy, fixed-dose olmesartan medoxomil/hydrochlorothiazide (HCTZ) [Olmetec plus, Benicar-HCT] combination therapy may be initiated. Extensive clinical evidence from several large well designed trials and the clinical practice setting has confirmed the antihypertensive efficacy and good tolerability profile of oral olmesartan medoxomil, as monotherapy or in combination with HCTZ, in patients with hypertension, including elderly patients with isolated systolic hypertension (ISH). Notably, BP control is sustained throughout the 24-hour dosage interval, including during the last 4 hours of this period. In clinical trials, olmesartan medoxomil monotherapy provided better antihypertensive efficacy than losartan, candesartan cilexetil or irbesartan monotherapy, and was at least as effective as valsartan treatment, with a faster onset of action than other ARBs in terms of reductions from baseline in diastolic BP (DBP) and, in most instances, systolic BP (SBP). Combination therapy with olmesartan medoxomil plus HCTZ was superior to that with benazepril plus amlodipine, as effective as that with losartan plus HCTZ, noninferior to that with atenolol plus HCTZ, but less effective than that with telmisartan plus HCTZ, in individual trials. Data from ongoing clinical outcome trials are required to more fully determine the relative position of olmesartan medoxomil therapy in the management of hypertension. In the meantime, the consistent antihypertensive efficacy during the entire 24-hour dosage interval and good tolerability profile of olmesartan medoxomil, with or without HCTZ, make it a valuable option for the treatment of adult patients with hypertension, including the elderly.

Combination therapy with renin-angiotensin system inhibitors and the calcium channel blocker azelnidipine decreases plasma inflammatory markers and urinary oxidative stress markers in patients with diabetic nephropathy

A calcium channel blocker (CCB), azelnidipine (AZ), is reported to inhibit oxidative stresses, particularly when administered under blockade of the renin-angiotensin system (RAS). The purpose of this study was to investigate whether AZ inhibits oxidative stresses more potently than other CCBs under blockade of RAS and exerts renoprotection in type 2 diabetic nephropathy. Subjects were hypertensive type 2 diabetics with nephropathy, taking RAS inhibitors. The patients were randomly assigned to two groups, an AZ group (n=21, 16 mg/d) and a nifedipine-CR (NF) group (n=17, 40 mg/d). The plasma levels of monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6), high-sensitive C-reactive protein (hsCRP), adiponectin and tumor necrosis factor-alpha (TNF(alpha)), the urinary excretion of 8-epi-prostaglandin F(2alpha) (8-epi-PGF(2alpha)) and 8-hydroxydeoxyguanosine (8-OHdG), and the urinary albumin-to-creatinine ratios (ACR) were determined before and after 16-week treatment. Neither metabolic parameters nor blood pressure levels differed between the two groups not only at baseline but also after the treatment. However, significant decreases in MCP-1, IL-6, hsCRP, TNF(alpha), 8-epi-PGF(2alpha), 8-OHdG and ACR levels, and a significant increase in the plasma adiponectin level were detected in the AZ group, but not in the NF group. The % change in the urinary oxidative stress markers correlated with that in ACR. Our results indicate that, in hypertensive patients with diabetic nephropathy, a combination therapy of RAS inhibitors and AZ is an effective therapeutic modality for decreasing not only blood pressure but also inflammations and oxidative stresses.

Prevention of neuronal damage by calcium channel blockers with antioxidative effects after transient focal ischemia in rats

BACKGROUND

Cerebral ischemia is a major leading cause of death and at the first place cause of disability all over the world. There are a lot of drugs that are in experimental stage for treatment of stroke. Among them are calcium channel blockers (CCBs) that have, in animal models, different effectiveness in healing of ischemic damage in brain. Mechanism of CCBs' action in cerebral ischemia is still unclear, but antioxidative property is supposed to be implicated. In the present study, we investigated antioxidative and neuroprotective properties of two CCBs, azelnidipine and amlodipine.

METHODS

Male Wistar Kyoto rats were subjected to 90 min of transient middle cerebral artery occlusion (MCAO) by a nylon thread. Animals were divided into 3 groups, vehicle, azelnidipine and amlodipine group. In the azelnidipine and amlodipine groups, rats were treated with azelnidipine (1 mg/kg) and amlodipine (1 mg/kg) by gastric gavage for 2 weeks before MCAO. Vehicle group was treated by solution of methyl cellulose for 2 weeks. Rats were killed 24 h after MCAO. Physiological parameters (mean arterial pressure, heart rate, body weight), infarct volume, brain edema index, cerebral blood flow (CBF), oxidative stress markers which are HEL, 4-HNE, AGE and 8-OHdG, and evidence of apoptosis by TUNEL, were investigated.

RESULTS

There were no significant differences among groups in mean arterial pressure, heart rate and body weight. Treatment with azelnidipine and amlodipine reduced infarct volume and brain edema. Azelnidipine treated group showed more marked reduction of infarct volume and cerebral edema than amlodipine group. There was no attenuation of CBF in CCBs groups. The number of HEL, 4-HNE, AGE and 8-OHdG positive cells were significantly decreased in the CCBs treated groups. These molecules were again fewer in the azelnidipine group than in the amlodipine group. In TUNEL staining, the numbers of positive cells was smaller in the CCBs treated groups, especially in the azelnidipine group.

CONCLUSIONS

Pretreatment of azelnidipine and amlodipine had a neuroprotective effect in ischemic brain. Antioxidative property is one of the important profiles of CCBs that is implicated in brain protection.