Amlodipine-induced reduction of oxidative stress in the brain is associated with sympatho-inhibitory effects in stroke-prone spontaneously hypertensive rats

Effects of L-Type Voltage-Gated Calcium Channel (LTCC) Inhibition on Hippocampal Neuronal Death after Pilocarpine-Induced Seizure

Epilepsy, marked by abnormal and excessive brain neuronal activity, is linked to the activation of L-type voltage-gated calcium channels (LTCCs) in neuronal membranes. LTCCs facilitate the entry of calcium (Ca2+) and other metal ions, such as zinc (Zn2+) and magnesium (Mg2+), into the cytosol. This Ca2+ influx at the presynaptic terminal triggers the release of Zn2+ and glutamate to the postsynaptic terminal. Zn2+ is then transported to the postsynaptic neuron via LTCCs. The resulting Zn2+ accumulation in neurons significantly increases the expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits, contributing to reactive oxygen species (ROS) generation and neuronal death. Amlodipine (AML), typically used for hypertension and coronary artery disease, works by inhibiting LTCCs. We explored whether AML could mitigate Zn2+ translocation and accumulation in neurons, potentially offering protection against seizure-induced hippocampal neuronal death. We tested this by establishing a rat epilepsy model with pilocarpine and administering AML (10 mg/kg, orally, daily for 7 days) post-epilepsy onset. We assessed cognitive function through behavioral tests and conducted histological analyses for Zn2+ accumulation, oxidative stress, and neuronal death. Our findings show that AML's LTCC inhibition decreased excessive Zn2+ accumulation, reactive oxygen species (ROS) production, and hippocampal neuronal death following seizures. These results suggest amlodipine's potential as a therapeutic agent in seizure management and mitigating seizures' detrimental effects.

Clarification of hypertension mechanisms provided by the research of central circulatory regulation

Sympathoexcitation, under the regulatory control of the brain, plays a pivotal role in the etiology of hypertension. Within the brainstem, significant structures involved in the modulation of sympathetic nerve activity include the rostral ventrolateral medulla (RVLM), caudal ventrolateral medulla (CVLM), nucleus tractus solitarius (NTS), and paraventricular nucleus (paraventricular). The RVLM, in particular, is recognized as the vasomotor center. Over the past five decades, fundamental investigations on central circulatory regulation have underscored the involvement of nitric oxide (NO), oxidative stress, the renin-angiotensin system, and brain inflammation in regulating the sympathetic nervous system. Notably, numerous significant findings have come to light through chronic experiments conducted in conscious subjects employing radio-telemetry systems, gene transfer techniques, and knockout methodologies. Our research has centered on elucidating the role of NO and angiotensin II type 1 (AT1) receptor-induced oxidative stress within the RVLM and NTS in regulating the sympathetic nervous system. Additionally, we have observed that various orally administered AT1 receptor blockers effectively induce sympathoinhibition by reducing oxidative stress via blockade of the AT1 receptor in the RVLM of hypertensive rats. Recent advances have witnessed the development of several clinical interventions targeting brain mechanisms. Nonetheless, Future and further basic and clinical research are needed.

Estrogen Dampens Central Cannabinoid Receptor 1-mediated Neuroexcitation and Pressor Response in Conscious Female Rats

Activation of the rostral ventrolateral medulla (RVLM) cannabinoid receptor-1 (CB₁R) causes nNOS-dependent increases in sympathetic activity, blood pressure (BP) and heart rate (HR) in male rats. However, it remains unknown if the CB₁R-mediated neurochemical and cardiovascular responses are influenced by the ovarian sex hormones, particularly estrogen (E₂). Therefore, we studied the effects of intra-RVLM CB₁R activation (WIN 55,212-2) on BP and HR in conscious female rats under the following hormonal states: (1) highest E₂ level (proestrus sham-operated, SO); (2) E₂-deprivation (ovariectomized, OVX); (3) OVX with E₂ replacement (OVXE2). Intra-RVLM WIN55,212-2 elicited dose (100-400 pmol) dependent pressor and tachycardic responses, in OVX rats, which replicated the reported responses in male rats. However, in SO and OVXE2 rats, the CB₁R-mediated pressor response was attenuated and the tachycardic response reverted to bradycardic response. The neurochemical findings suggested a key role for the upregulated RVLM sympathoexcitatory molecules phosphorated protein kinase B, phosphorated neuronal nitric oxide synthase and reactive oxygen species in the exaggerated CB₁R-mediated BP and HR responses in OVX rats, and an E₂-dependent dampening of these responses. The intra-RVLM WIN55212-2-evoked cardiovascular and neurochemical responses were CB₁R-mediated because they were attenuated by prior CB₁R blockade (AM251). Our findings suggest that attenuation of RVLM neuroexcitation and oxidative stress underlies the protection conferred by E₂, in female rats, against the CB₁R-mediated adverse cardiovascular effects.

Manifestation of renin angiotensin system modulation in traumatic brain injury

Traumatic brain injury (TBI) alters brain function and is a crucial public health concern worldwide. TBI triggers the release of inflammatory mediators (cytokines) that aggravate cerebral damage, thereby affecting clinical prognosis. The renin angiotensin system (RAS) plays a critical role in TBI pathophysiology. RAS is widely expressed in many organs including the brain. Modulation of the RAS in the brain via angiotensin type 1 (AT₁) and type 2 (AT₂) receptor signaling affects many pathophysiological processes, including TBI. AT₁R is highly expressed in neurons and astrocytes. The upregulation of AT₁R mediates the effects of angiotensin II (ANG II) including release of proinflammatory cytokines, cell death, oxidative stress, and vasoconstriction. The AT₂R, mainly expressed in the fetal brain during development, is also related to cognitive function. Activation of this receptor pathway decreases neuroinflammation and oxidative stress and improves overall cell survival. Numerous studies have illustrated the therapeutic potential of inhibiting AT₁R and activating AT₂R for treatment of TBI with variable outcomes. In this review, we summarize studies that describe the role of brain RAS signaling, through AT₁R and AT₂R in TBI, and its modulation with pharmacological approaches.

Losartan Treatment Could Improve the Outcome of TBI Mice

Traumatic brain injury frequently leads to serious mortality and physical disability, yet effective treatments remains insufficient. TBI always leads to a series of secondary brain injuries including neuronal apoptosis, continuous inflammation, endoplasmic reticulum stress, and disruption of the blood-brain barrier. Sartans that block angiotensin II type 1 receptors are strongly neuroprotective, neurorestorative and anti-inflammatory. However, whether losartan, a FDA-approved and widely used drug for regulating blood pressure, is beneficial for improving the prognosis of TBI need more evidence. Through a controlled cortical impact injury mice model, we confirmed that losartan treatment could ameliorate CCI-induced secondary brain injury. We found that losartan treatment decreased brain lesion volume, neuronal apoptosis and ER stress protein ATF4 and eIF2α. Moreover, our results showed that losartan also improved neurological and motor function. It is worth pointing out that losartan increased the expression of tight junction proteins ZO-1 and alleviated brain edema and blood brain barrier leakage. Additionally, losartan inhibited pro-inflammatory factor TNF-α and improve anti-inflammatory factor IL-10. Taken together, our data demonstrated that losartan could improve the prognosis of TBI and may be a promising therapeutic method for mitigating TBI.

Therapeutic Potential of Dihydropyridine Calcium Channel Blockers on Oxidative Injury Caused by Organophosphates in Cortex and Cerebellum: An In Vivo Study

This study was designed to investigate the effects of amlodipine (AM), a dihydropyridine calcium channel blocker, on the oxidative damage induced by diazinon (DZN) in the rat cortex and cerebellum. Forty-two rats were randomly divided into six groups. The rats were treated intraperitoneally with normal saline (group 1), AM (9 mg/kg; group 2), DZN (32 mg/kg; group 3) and different doses of AM (3, 6, and 9 mg/kg; groups 4, 5, and 6, respectively) with DZN. After 14 days, the cerebellum and cortex tissues were removed for biochemical and histological experiments. DZN significantly decreased acetylcholinesterase activity (AChE; 57%, p < 0.001 and 39.1%, p < 0.05), depleted total antioxidant capacity (TAC; 46.2%, p < 0.01 and 44.7%, p < 0.05), and increased lactate dehydrogenase activity (LDH; 96%, p < 0.001 and 202%, p < 0.001), nitric oxide (NO; 130%, p < 0.001 and 74.4%, p < 0.001), and lipid peroxidation levels (LPO; 35.6%, p < 0.001 and 128.7%, p < 0.001), in the cerebellum and cortex tissues, respectively. In addition, DZN induced structural alterations in the cerebellum and cortex. Following AM administration, a remarkable improvement was observed in LDH activity and some of the oxidative markers, such as NO and LPO; however, no significant changes were found in AChE activity when the DZN group was compared with the AM-treated groups. This study suggests that AM may prevent DZN-induced neurotoxicity via improvement of the oxidative/antioxidant balance in the cerebellum and cortex tissues.

Differential impacts of brain stem oxidative stress and nitrosative stress on sympathetic vasomotor tone

Based on work-done in the rostral ventrolateral medulla (RVLM), this review presents four lessons learnt from studying the differential impacts of oxidative stress and nitrosative stress on sympathetic vasomotor tone and their clinical and therapeutic implications. The first lesson is that an increase in sympathetic vasomotor tone because of augmented oxidative stress in the RVLM is responsible for the generation of neurogenic hypertension. On the other hand, a shift from oxidative stress to nitrosative stress in the RVLM underpins the succession of increase to decrease in sympathetic vasomotor tone during the progression towards brain stem death. The second lesson is that, by having different cellular sources, regulatory mechanisms on synthesis and degradation, kinetics of chemical reactions, and downstream signaling pathways, reactive oxygen species and reactive nitrogen species should not be regarded as a singular moiety. The third lesson is that well-defined differential roles of oxidative stress and nitrosative stress with distinct regulatory mechanisms in the RVLM during neurogenic hypertension and brain stem death clearly denote that they are not interchangeable phenomena with unified cellular actions. Special attention must be paid to their beneficial or detrimental roles under a specific disease or a particular time-window of that disease. The fourth lesson is that, to be successful, future antioxidant therapies against neurogenic hypertension must take into consideration the much more complicated picture than that presented in this review on the generation, maintenance, regulation or modulation of the sympathetic vasomotor tone. The identification that the progression towards brain stem death entails a shift from oxidative stress to nitrosative stress in the RVLM may open a new vista for therapeutic intervention to slow down this transition.

Angiotensin II Causes Neuronal Damage in Stretch-Injured Neurons: Protective Effects of Losartan, an Angiotensin T1 Receptor Blocker

Angiotensin II (Ang II) is a mediator of oxidative stress via activation/induction of reactive oxygen and nitrogen species-generating enzymes, NADPH oxidase (NOX) and inducible nitric oxide synthase (iNOS). We investigated the hypothesis that overproduction of Ang II during traumatic brain injury (TBI) induces the activation of the oxidative stress, which triggers neuroinflammation and cell apoptosis in a cell culture model of neuronal stretch injury. We first established that stretch injury causes a rapid increase in the level of Ang II, which causes the release of pro-inflammatory cytokines, IL-1β and TNF-α, via the induction of oxidative stress. Since angiotensin-converting enzyme (ACE) mediates the production of Ang II via the conversion of Ang I into Ang II, we analyzed the expression of ACE by western blotting. Further, we analyzed caspase-3-mediated apoptosis by TUNEL staining and annexin V western blotting. Angiotensin type I (AT₁) receptor antagonist losartan attenuated Ang II-induced oxidative stress and associated neuroinflammation and cell death in cultured neurons. Remarkably, we noticed that the expression of Ang II type 1 receptor (AngT₁R) upregulated in neuronal stretch injury; losartan mitigates this upregulation. Findings from this study significantly extend our understanding of the pathophysiology of TBI and may have significant implications for developing therapeutic strategies for TBI-associated brain dysfunctions.

Amlodipine and enalapril promote distinct effects on cardiovascular autonomic control in spontaneously hypertensive rats: the role of aerobic physical training

BACKGROUND

We compared the autonomic and hemodynamic cardiovascular effects of amlodipine and enalapril treatment associated with an aerobic physical training program on spontaneously hypertensive rats.

METHODS

Eighteen-week-old (n = 48) spontaneously hypertensive rats were assigned to one of two groups: sedentary (n = 24) and trained (n = 24) through a 10-week swimming training program. Each group was subdivided into three groups (n = 8): control (vehicle group), amlodipine (amlodipine group; 10 mg/kg per day) and enalapril (enalapril group; 10 mg/kg per day) (both for 10 weeks). We cannulated the femoral artery and vein of all animals for recording arterial pressure and injecting drugs, respectively. Autonomic assessment was performed by double blockade with propranolol and atropine, analysis of heart rate variability (HRV), systolic arterial pressure variability and baroflex sensitivity.

RESULTS

Arterial pressure reduction was more prominent in the sedentary and trained enalapril groups. Amlodipine sedentary group presented important autonomic adjustments characterized by a predominance of vagal tone in cardiac autonomic balance, increased HRV associated with sympathetic autonomic modulation reduction and increased vagal autonomic modulation, and increased baroflex sensitivity. All findings were not potentialized by physical training. In turn, the enalapril trained group, but not its sedentary counterpart, also had vagal tone prevalence in cardiac autonomic balance, increased HRV, increased baroflex sensitivity and decreased low-frequency band in systolic arterial pressure variability.

CONCLUSION

Amlodipine was more effective in promoting beneficial autonomic cardiovascular adaptations in sedentary animals. In contrast, enalapril achieved better autonomic results only when combined with aerobic physical training.

1,4-Dihydropyridine Derivatives: Dihydronicotinamide Analogues-Model Compounds Targeting Oxidative Stress

Many 1,4-dihydropyridines (DHPs) possess redox properties. In this review DHPs are surveyed as protectors against oxidative stress (OS) and related disorders, considering the DHPs as specific group of potential antioxidants with bioprotective capacities. They have several peculiarities related to antioxidant activity (AOA). Several commercially available calcium antagonist, 1,4-DHP drugs, their metabolites, and calcium agonists were shown to express AOA. Synthesis, hydrogen donor properties, AOA, and methods and approaches used to reveal biological activities of various groups of 1,4-DHPs are presented. Examples of DHPs antioxidant activities and protective effects of DHPs against OS induced damage in low density lipoproteins (LDL), mitochondria, microsomes, isolated cells, and cell cultures are highlighted. Comparison of the AOA of different DHPs and other antioxidants is also given. According to the data presented, the DHPs might be considered as bellwether among synthetic compounds targeting OS and potential pharmacological model compounds targeting oxidative stress important for medicinal chemistry.

Brain stem NOS and ROS in neural mechanisms of hypertension

SIGNIFICANCE

There is now compelling evidence to substantiate the notion that by depressing baroreflex regulation of blood pressure and augmenting central sympathetic outflow through their actions on the nucleus tractus solitarii (NTS) and rostral ventrolateral medulla (RVLM), brain stem nitric oxide synthase (NOS) and reactive oxygen species (ROS) are important contributing factors to neural mechanisms of hypertension. This review summarizes our contemporary views on the impact of NOS and ROS in the NTS and RVLM on neurogenic hypertension, and presents potential antihypertensive strategies that target brain stem NOS/ROS signaling.

RECENT ADVANCES

NO signaling in the brain stem may be pro- or antihypertensive depending on the NOS isoform that generates this gaseous moiety and the site of action. Elevation of the ROS level when its production overbalances its degradation in the NTS and RVLM underlies neurogenic hypertension. Interventional strategies with emphases on alleviating the adverse actions of these molecules on blood pressure regulation have been investigated.

CRITICAL ISSUES

The pathological roles of NOS in the RVLM and NTS in neural mechanisms of hypertension are highly complex. Likewise, multiple signaling pathways underlie the deleterious roles of brain-stem ROS in neurogenic hypertension. There are recent indications that interactions between brain stem ROS and NOS may play a contributory role.

FUTURE DIRECTIONS

Given the complicity of action mechanisms of brain-stem NOS and ROS in neural mechanisms of hypertension, additional studies are needed to identify the most crucial therapeutic target that is applicable not only in animal models but also in patients suffering from neurogenic hypertension.

Essential hypertension: an approach to its etiology and neurogenic pathophysiology

Essential hypertension, a rise in blood pressure of undetermined cause, includes 90% of all hypertensive cases and is a highly important public health challenge that remains, however, a major modifiable cause of morbidity and mortality. This review emphasizes that, from an evolutionary point of view, we are adapted to ingest and excrete <1 g of sodium (2.5 g of salt) per day and that essential hypertension develops when the kidneys become unable to excrete the amount of sodium ingested, unless blood pressure is increased. The renal-mean arterial pressure set-point model is briefly described to explain that a shift of the pressure natriuresis relationship toward abnormally high pressure levels is a pathophysiological characteristic of essential hypertension. Evidence indicating that this anomaly in the pressure natriuresis relationship arises from a sympathetic nervous system dysfunction is briefly formulated, and the most widely accepted pathophysiologic proposal to explain the development of this sympathetic dysfunction is described, with commentaries about novel action mechanisms of some drugs currently used in essential hypertension treatment.

Statins and the autonomic nervous system

Statins (3-hydroxy-3-methylglutaryl-CoA reductase inhibitors) reduce plasma cholesterol and improve endothelium-dependent vasodilation, inflammation and oxidative stress. A ‘pleiotropic’ property of statins receiving less attention is their effect on the autonomic nervous system. Increased central sympathetic outflow and diminished cardiac vagal tone are disturbances characteristic of a range of cardiovascular conditions for which statins are now prescribed routinely to reduce cardiovascular events: following myocardial infarction, and in hypertension, chronic kidney disease, heart failure and diabetes. The purpose of the present review is to synthesize contemporary evidence that statins can improve autonomic circulatory regulation. In experimental preparations, high-dose lipophilic statins have been shown to reduce adrenergic outflow by attenuating oxidative stress in central brain regions involved in sympathetic and parasympathetic discharge induction and modulation. In patients with hypertension, chronic kidney disease and heart failure, lipophilic statins, such as simvastatin or atorvastatin, have been shown to reduce MNSA (muscle sympathetic nerve activity) by 12–30%. Reports concerning the effect of statin therapy on HRV (heart rate variability) are less consistent. Because of their implications for BP (blood pressure) control, insulin sensitivity, arrhythmogenesis and sudden cardiac death, these autonomic nervous system actions should be considered additional mechanisms by which statins lower cardiovascular risk.

Amlodipine prevents apoptotic cell death by correction of elevated intracellular calcium in a primary neuronal model of Batten disease (CLN3 disease)

CLN3 disease (Spielmeyer-Vogt-Sjogren-Batten disease) is a severe pediatric neurodegenerative disorder for which there is currently no effective treatment. The disease is characterized by progressive neuronal death, which may be triggered by abnormal intracellular calcium levels leading to neuronal apoptosis. Previously, we demonstrated reversal of the calcium effect in a neuroblastoma cell line using amlodipine and other calcium channel antagonists. In the present studies, we developed a CLN3 siRNA-inhibited primary rat neuron model to further study etoposide-induced calcium changes and apoptosis in CLN3 disease followed by recovery experiments with amlodipine. Our results show that intracellular calcium is significantly elevated in siRNA-inhibited cortical neurons after potassium chloride-induced depolarization. We were also able to show that amlodipine, a predominantly L-type dihydropyrimidine calcium channel antagonist can reverse the aberrant calcium elevations in this model of the disease. We performed an in situ TUNEL assay following etoposide-exposure to siRNA inhibited primary neurons, and apoptotic nuclei were detected providing additional evidence that increased neuronal apoptosis is associated with increased calcium levels. Amlodipine also reduced the absolute number of apoptotic cells in this experimental model.

Oxidative stress in the brain causes hypertension via sympathoexcitation

Activation of the sympathetic nervous system (SNS) has an important role in the pathogenesis of hypertension, and is determined by the brain. Previous many studies have demonstrated that oxidative stress, mainly produced by angiotensin II type 1 (AT(1)) receptor and nicotinamide adenine dinucleotide phosphate (NAD (P) H) oxidase, in the autonomic brain regions was involved in the activation of the SNS of hypertension. In this concept, we have investigated the role of oxidative stress in the rostral ventrolateral medulla (RVLM), which is known as the cardiovascular center in the brainstem, in the activation of the SNS, and demonstrated that AT(1) receptor and NAD (P) H oxidase-induced oxidative stress in the RVLM causes sympathoexcitation in hypertensive rats. The mechanisms in which brain oxidative stress causes sympathoexcitation have been investigated, such as the interactions with nitric oxide (NO), effects on the signal transduction, or inflammations. Interestingly, the environmental factors of high salt intake and high calorie diet may also increase the oxidative stress in the brain, particularly in the RVLM, thereby activating the central sympathetic outflow and increasing the risk of hypertension. Furthermore, several orally administered AT(1) receptor blockers have been found to cause sympathoinhibition via reduction of oxidative stress through the inhibition of central AT(1) receptor. In conclusion, we must consider that AT(1) receptor and the related oxidative stress production in the brain cause the activation of SNS in hypertension, and that AT(1) receptor in the brain could be novel therapeutic target of the treatments for hypertension.

The effects of catalase inhibition into the fourth cerebral ventricle on the Bezold-Jarisch reflex in spontaneously hypertensive rats

Many studies have investigated the role of oxidative stress on cardiovascular system in the brainstem of spontaneously hypertensive rats (SHR). However, we do not know yet if catalase inhibition influences cardiopulmonary reflex (Bezol-Jarisch reflex). Thus, we aimed to evaluate the effects of central catalase inhibition on cardiopulmonary reflex in SHR. Males Wistar Kyoto (WKY) rats and SHR were implanted with a stainless steel guide cannula into the fourth cerebral ventricle (4th V). The femoral artery and vein were cannulated for mean arterial pressure (MAP) and heart rate (HR) measurement and drug infusion, respectively. The cardiopulmonary reflex was tested with phenylbiguanide (PBG, 8 μg/kg, bolus, i.v.). Cardiopulmonary reflex was evaluated before and 15 minutes after 3-amino-1,2,4-triazole (ATZ, 0.01 g/100 μL) injection into the 4th V. Vehicle treatment did not change basal MAP and HR and cardiopulmonary reflex responses in SHR and WKY rats. Central ATZ increased hypotensive (p=0.038) responses without influencing the bradycardic reflex (p=0.287) in WKY rats. In SHR, ATZ increased hypotension (p=0.0004) and bradycardic (p=0.04) responses to i.v. PBG. No changes were observed regarding basal MAP and HR after ATZ injection in SHR and WKY rats. We suggest central catalase inhibition affects cardiopulmonary reflex with more intensity in SHR compared to WKY rats.

Combination therapy of olmesartan and azelnidipine inhibits sympathetic activity associated with reducing oxidative stress in the brain of hypertensive rats

It has been demonstrated that the antihypertensive drugs with the antioxidant action on the brainstem inhibit the sympathetic activity and consequently decrease blood pressure and heart rate (HR) in hypertensive rats. Combination drugs of the angiotensin receptor blocker and calcium channel blocker, such as olmesartan (OLM)/azelnidipine (AZ) and candesartan (CAN)/amlodipine (AM), are widely used for treating hypertension in Japan. In this study, it was investigated whether there are differences in the antioxidant effect in the brain and the sympathoinhibitory effect between OLM/AZ and CAN/AM combination therapies in stroke-prone spontaneously hypertensive rats (SHRSP). OLM/AZ (10/8 mg kg(-1) day(-1)), CAN/AM (4/2.5 mg kg(-1) day(-1)), or vehicle was orally administered for 30 days to SHRSP. OLM/AZ and CAN/AM markedly decreased systolic blood pressure to the same extent. OLM/AZ decreased HR to a greater extent than CAN/AM. Urinary norepinephrine excretion as a marker of sympathetic activity was unchanged in the CAN/AM group, but reduced in the OLM/AZ group. Oxidative stress in the whole brain assessed using the in vivo electron spin resonance method was similarly decreased in both OLM/AZ and CAN/AM groups. Importantly, thiobarbituric acid reactive substance levels in the brainstem were significantly lower in the OLM/AZ group, but not in the CAN/AM group, than in the vehicle group. These results suggest that combination therapy of either OLM/AZ or CAN/AM does not induce reflex-mediated sympathetic activation despite the marked blood pressure reduction, which is associated with an antioxidant effect in the brain regions affecting the sympathetic activity. Furthermore, the antioxidant effect in the brainstem and the sympathoinhibitory effect of OLM/AZ combination may be greater than those of CAN/AM combination treatment.

Azelnidipine attenuates glomerular damage in Dahl salt-sensitive rats by suppressing sympathetic nerve activity

Dihydropyridine-type calcium channel blockers (CCBs) exert potent antihypertensive effects. The CCB azelnidipine decreases heart rate by suppressing sympathetic nerve activity, which affects afferent and efferent arterioles in the glomeruli. We examined whether azelnidipine can improve progressive glomerular injury in comparison with amlodipine by suppressing renal sympathetic nerve activity in Dahl salt-sensitive rats. Glomerular circulation in Dahl salt-sensitive rats was monitored with a charge-coupled device camera before and after administration of amlodipine (0.5 mg kg(-1), bolus injection) or azelnidipine (0.1 mg kg(-1), bolus injection). Systemic sympathetic nerve activity was also compared by analysis of heart rate variability with a telemetry blood pressure monitoring system after crossover administration of amlodipine (1.0 mg kg(-1) per day) and azelnidipine (3.0 mg kg(-1) per day) for 1 week. To investigate renoprotective effects, rats were treated with amlodipine (1.0 mg kg(-1) per day) or azelnidipine (3.0 mg kg(-1) per day) for 3 weeks with or without renal denervation. The efferent arteriole contracted in response to acute amlodipine but not azelnidipine treatment. The low frequency/high frequency ratio, an index of parasympathetic nerve activity, decreased in response to azelnidipine but not amlodipine treatment. In response to chronic treatment, proteinuria and glomerular injury improved to a greater extent with azelnidipine compared with amlodipine. The renoprotective effects of azelnidipine were diminished by renal denervation. Azelnidipine decreased glomerular damage in Dahl salt-sensitive rats to a greater extent than amlodipine. Azelnidipine appeared to decrease intraglomerular pressure by suppressing sympathetic nerve activity.

Inflammation and therapy for hypertension

It is currently accepted that hypertension, atherosclerosis, and diabetes are disorders with subtle or overt activation of inflammatory mediators. Therefore, it has become increasingly important to ascertain whether current antihypertensive drug families have proinflammatory or anti-inflammatory actions that modify the outcomes of their hemodynamic effects on blood pressure. We review the current state of knowledge about the effects of the major classes of available antihypertensive agents on inflammation and speculate on the possible contribution of these effects to observations in clinical trials. We suggest that a strategy of drug development specifically addressing inflammation in hypertension may provide increased benefit in terms of target organ damage, and we describe some examples of these promising developments.

Imbalance of central nitric oxide and reactive oxygen species in the regulation of sympathetic activity and neural mechanisms of hypertension

Nitric oxide (NO) and reactive oxygen species (ROS) play important roles in blood pressure regulation via the modulation of the autonomic nervous system, particularly in the central nervous system (CNS). In general, accumulating evidence suggests that NO inhibits, but ROS activates, the sympathetic nervous system. NO and ROS, however, interact with each other. Our consecutive studies and those of others strongly indicate that an imbalance between NO bioavailability and ROS generation in the CNS, including the brain stem, activates the sympathetic nervous system, and this mechanism is involved in the pathogenesis of neurogenic aspects of hypertension. In this review, we focus on the role of NO and ROS in the regulation of the sympathetic nervous system within the brain stem and subsequent cardiovascular control. Multiple mechanisms are proposed, including modulation of neurotransmitter release, inhibition of receptors, and alterations of intracellular signaling pathways. Together, the evidence indicates that an imbalance of NO and ROS in the CNS plays a pivotal role in the pathogenesis of hypertension.

L/N-type calcium channel blocker cilnidipine ameliorates proteinuria and inhibits the renal renin-angiotensin-aldosterone system in deoxycorticosterone acetate-salt hypertensive rats

Cilnidipine, an N/L-type calcium channel blocker, has been reported to inhibit sympathetic nerve activity and has a greater renoprotective effect than L-type calcium channel blockers. To investigate the hypothesis that cilnidipine might ameliorate advanced hypertensive nephropathy and inhibit the renal renin-angiotensin-aldosterone system, cilnidipine (1 mg per kg per day) or amlodipine (1 mg per kg per day) was administered to uninephrectomized deoxycorticosterone (DOCA)-salt hypertensive rats (DOCA-salt) for 4 weeks by gavage. Although the blood pressure in the DOCA-salt group was higher than that of control, neither cilnidipine nor amlodipine had any effect on the increase in blood pressure in the DOCA-salt group. The DOCA (40 mg per kg per week, subcutaneously (s.c.)) and salt (1% NaCl in drinking water) treatment significantly aggravated the levels of urinary protein excretion and creatinine clearance and increased glomerulosclerosis and collagen deposition in the tubulointerstitial area of the kidney. These effects were attenuated by cilnidipine treatment. Reverse transcription-polymerase chain reaction analysis revealed that the renal expression of mRNA for collagen I/IV and transforming growth factor-β was enhanced in the DOCA-salt group and that the overexpression of these molecules was suppressed by cilnidipine. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-derived superoxide production in the kidney and urinary norepinephrine excretion, which were enhanced in the DOCA-salt group, were suppressed by cilnidipine. Cilnidipine also decreased the activity and expression of angiotensin-converting enzyme (ACE) and the aldosterone concentration in the renal homogenate. Although neither cilnidipine nor amlodipine had any effect on the increased blood pressure in the DOCA-salt group, these renal changes were not induced by treatment with amlodipine. In conclusion, cilnidipine inhibited renal dysfunction, sympathetic nerve activity and renal renin-angiotensin-aldosterone system in the DOCA-salt group.

Amlodipine suppressed cardiac gene expression of brain natriuretic peptide, transforming growth factor-β₁ and fibronectin mediated by aldosterone in male stroke-prone spontaneously hypertensive rats

OBJECTIVES

Amlodipine, a calcium channel blocker (CCB), is one of the most common antihypertensive medicines in Japan. We evaluated whether the calcium channel blocker confers cardiac protection through the renin-angiotensin-aldosterone system in male stroke-prone spontaneously hypertensive rats (SHR-SP).

METHODS

Fifteen week-old rats were divided into 2 groups: amlodipine group (3 mg/kg/day, n = 5) and control group (n = 5).

KEY FINDINGS

The CCB lowered systolic blood pressure significantly (P < 0.05). Plasma aldosterone concentration in the amlodipine group was remarkably lower than in the control group (P < 0.05), but plasma renin activity and plasma angiotensin II concentration were not different between the two groups. The CCB also suppressed the mRNA expression of brain natriuretic peptide, transforming growth factor-β₁, and fibronectin extracted from the left ventricle.

CONCLUSIONS

These results suggest that amlodipine attenuates cardiac damage by lowering plasma aldosterone concentration in hypertensive rats with developing arteriosclerosis.

Oxidative stress and central cardiovascular regulation. - Pathogenesis of hypertension and therapeutic aspects -

Oxidative stress is a key factor in the pathogenesis of hypertension and target organ damage, beginning in the earliest stages. Extensive evidence indicates that the pivotal role of oxidative stress in the pathogenesis of hypertension is due to its effects on the vasculature in relation to the development of atherosclerotic processes. It remains unclear, however, whether oxidative stress in the brain, particularly the autonomic nuclei (including the vasomotor center), has an important role in the occurrence and maintenance of hypertension via activation of the sympathetic nervous system. The aim of the present review is to describe the contribution of oxidative stress in the brain to the neural mechanisms that underlie hypertension, and discuss evidence that brain oxidative stress is a potential therapeutic target.

Role of inducible nitric oxide synthase in rostral ventrolateral medulla in blood pressure regulation in spontaneously hypertensive rats

Nitric oxide (NO) in the brainstem modulates blood pressure (BP). Overexpression of inducible NO synthase (iNOS) in the rostral ventrolateral medulla (RVLM) increases BP in normotensive Wistar-Kyoto rats (WKY), but its role in BP regulation in spontaneously hypertensive rats (SHR) is unknown. We examined iNOS expression and the effect of iNOS inhibitors in the RVLM on BP and heart rate in SHR and WKY. iNOS levels in the RVLM were significantly higher in SHR than in WKY. Bilateral microinjection of aminoguanidine into the RVLM dose-dependently decreased BP and heart rate in SHR, but not in WKY. These findings suggest that iNOS expression in the RVLM of SHR contributes to increase BP.

Azelnidipine decreases sympathetic nerve activity via antioxidant effect in the rostral ventrolateral medulla of stroke-prone spontaneously hypertensive rats

The long-acting dihydropyridine calcium channel blocker, azelnidipine, is suggested to inhibit sympathetic nerve activity. We previously demonstrated that oxidative stress in the rostral ventrolateral medulla (RVLM) activates sympathetic nerve activity. The aim of the present study was to determine whether oral administration of azelnidipine inhibits sympathetic nerve activity and if so to determine whether the effect is mediated by antioxidant effect in the RVLM. Azelnidipine, hydralazine, or vehicle was orally administered for 28 days to stroke-prone spontaneously hypertensive rats. Reductions in systolic blood pressure were similar in azelnidipine and hydralazine groups. Heart rate was significantly higher in the hydralazine group than in the control, but not altered in the azelnidipine group. Urinary norepinephrine excretion as an indicator of sympathetic nerve activity was significantly lower in the azelnidipine group, whereas it was significantly higher in the hydralazine group than in the control. Levels of thiobarbituric acid-reactive substances and nicotinamide adenine dinucleotide phosphate oxidase activity were significantly lower in the azelnidipine group than in control. Superoxide dismutase activity was significantly increased in the azelnidipine group more than in the control. These results suggest that azelnidipine decreases an indicator of sympathetic nerve activity by antioxidant effect mediated through inhibition of nicotinamide adenine dinucleotide phosphate oxidase activity and activation of superoxide dismutase in the RVLM of stroke-prone spontaneously hypertensive rats.

Sympathetic regulation of the renal functions in rats reciprocally congenic for chromosome 1 blood pressure quantitative trait locus

The role of the chromosome 1 blood pressure quantitative trait locus (QTL) on the sympathorenal interaction was studied using congenic strains. The two reciprocal congenic strains, WKYpch1.0 and SHRSPwch1.0, were respectively constructed by introgressing the stroke-prone spontaneously hypertensive rat (SHRSP)-derived fragment for the QTL into a Wistar-Kyoto rat (WKY) and vice versa. The role of the sympathetic nervous system in the kidney was evaluated by comparing the renal functions between denervated and sham-operated kidneys under anesthesia. The denervation was performed by stripping the adventitia off and applying 10% phenol to the blood vessels at the left renal hilus. Polyfructosan was continuously injected intravenously to determine the renal plasma flow and the glomerular filtration rate. A reciprocal and significant alteration in the renal norepinephrine (NE) content was observed between WKY and WKYpch1.0 and between SHRSP and SHRSPwch1.0. Concomitantly, the renal vascular resistance differed significantly between the congenic and the background parental strains. By contrast, no significant difference was observed in the fractional excretion of sodium, an index of the tubular function. While the denervation elicited a significant decrease of the renal NE content in all of the four strains studied, the significant effects of the denervation on the renal functions were observed only in SHRSP and WKYpch1.0, both of which harbored the SHRSP-derived QTL fragment. These results indicated that the chromosome 1 blood pressure QTL modulated the renal functions through the sympathetic nerve activity in the kidney.

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.

Azelnidipine Attenuates Cardiovascular and Sympathetic Responses to Air-Jet Stress in Genetically Hypertensive Rats

Azelnidipine is a new dihydropyridine calcium channel blocker that causes minimal stimulation of the sympathetic nervous system despite its significant depressor effect. In the present study, we examined the effects of oral or intravenous administration of azelnidipine on cardiovascular and renal sympathetic nerve activity (RSNA) responses to air-jet stress in conscious, unrestrained stroke-prone spontaneously hypertensive rats. Oral administration of high-dose azelnidipine (10 mg/kg per day) or nicardipine (150 mg/kg per day) for 10 days caused a significant and comparable decrease in blood pressure, but low-dose azelnidipine (3 mg/kg per day) did not. Air-jet stress increased mean arterial pressure (MAP), heart rate (HR) and RSNA. High-dose azelnidipine significantly attenuated the increases in MAP, HR and RSNA in response to air-jet stress while nicardipine did not. Low-dose azelnidipine significantly attenuated the pressor response with a trend of decrease in RSNA. Intravenous injection of azelnidipine induced a slowly developing depressor effect. To obtain a similar time course of decrease in MAP by azelnidipine, nicardipine was continuously infused at adjusted doses. Both drugs increased HR and RSNA significantly, while the change in RSNA was smaller in the azelnidipine group. In addition, intravenous administration of azelnidipine attenuated the responses of MAP, HR, and RSNA to air-jet stress; by comparison, the inhibitory actions of nicardipine were weak. In conclusion, oral or intravenous administration of azelnidipine inhibited cardiovascular and sympathetic responses to air-jet stress. This action of azelnidipine may be mediated at least in part by the inhibition of the sympathetic nervous system.

Benidipine Attenuates Glomerular Hypertension and Reduces Albuminuria in Patients with Metabolic Syndrome

Recent studies have shown that metabolic syndrome is associated with an increased risk for chronic kidney disease. We recently found that the prevalence of sodium-sensitive hypertension in patients with metabolic syndrome was significantly higher than that in patients with essential hypertension but without metabolic syndrome. We therefore assessed the effects of benidipine, a long-acting calcium channel blocker, on the sodium sensitivity of blood pressure and renal hemodymamics in 5 patients with metabolic syndrome. Glomerular hemodynamics were assessed using pressure-natriuresis curves, which were constructed by plotting the urinary excretion of sodium as a function of the mean arterial pressure, which was calculated as the mean of 48 values based on 24-h monitoring, during the intake of low (3 g NaCl daily) and relatively high (10 g NaCl daily) sodium diets. Under the relatively high sodium diet condition, benidipine significantly lowered systolic and diastolic blood pressure. The pressure-natriuresis curve was steeper after the administration of benidipine. Benidipine lowered glomerular capillary hydraulic pressure (P(GC)) levels (from 54.4+/-7.5 to 47.0+/-7.0 mmHg, p=0.0152) and reduced both the resistance of the afferent arterioles (from 10,338+/-2,618 to 9,026+/-2,627 dyn.s/cm5, p=0.047) and the resistance of the efferent arterioles (from 4,649+/-2,039 to 2,419+/-2,081 dyn.s/cm(5), p=0.003). The urinary albumin excretion rate also decreased after the administration of benidipine. These findings indicated that benidipine may be effective for reducing the risk of developing chronic kidney disease in patients with metabolic syndrome.