Calcium antagonists and endothelial function: focus on nitric oxide and endothelin

Discovery and Development of Calcium Channel Blockers

In the mid 1960s, experimental work on molecules under screening as coronary dilators allowed the discovery of the mechanism of calcium entry blockade by drugs later named calcium channel blockers. This paper summarizes scientific research on these small molecules interacting directly with L-type voltage-operated calcium channels. It also reports on experimental approaches translated into understanding of their therapeutic actions. The importance of calcium in muscle contraction was discovered by Sidney Ringer who reported this fact in 1883. Interest in the intracellular role of calcium arose 60 years later out of Kamada (Japan) and Heibrunn (USA) experiments in the early 1940s. Studies on pharmacology of calcium function were initiated in the mid 1960s and their therapeutic applications globally occurred in the the 1980s. The first part of this report deals with basic pharmacology in the cardiovascular system particularly in isolated arteries. In the section entitled from calcium antagonists to calcium channel blockers, it is recalled that drugs of a series of diphenylpiperazines screened in vivo on coronary bed precontracted by angiotensin were initially named calcium antagonists on the basis of their effect in depolarized arteries contracted by calcium. Studies on arteries contracted by catecholamines showed that the vasorelaxation resulted from blockade of calcium entry. Radiochemical and electrophysiological studies performed with dihydropyridines allowed their cellular targets to be identified with L-type voltage-operated calcium channels. The modulated receptor theory helped the understanding of their variation in affinity dependent on arterial cell membrane potential and promoted the terminology calcium channel blocker (CCB) of which the various chemical families are introduced in the paper. In the section entitled tissue selectivity of CCBs, it is shown that characteristics of the drug, properties of the tissue, and of the stimuli are important factors of their action. The high sensitivity of hypertensive animals is explained by the partial depolarization of their arteries. It is noted that they are arteriolar dilators and that they cannot be simply considered as vasodilators. The second part of this report provides key information about clinical usefulness of CCBs. A section is devoted to the controversy on their safety closed by the Allhat trial (2002). Sections are dedicated to their effect in cardiac ischemia, in cardiac arrhythmias, in atherosclerosis, in hypertension, and its complications. CCBs appear as the most commonly used for the treatment of cardiovascular diseases. As far as hypertension is concerned, globally the prevalence in adults aged 25 years and over was around 40% in 2008. Usefulness of CCBs is discussed on the basis of large clinical trials. At therapeutic dosage, they reduce the elevated blood pressure of hypertensive patients but don't change blood pressure of normotensive subjects, as was observed in animals. Those active on both L- and T-type channels are efficient in nephropathy. Alteration of cognitive function is a complication of hypertension recognized nowadays as eventually leading to dementia. This question is discussed together with the efficacy of CCBs in cognitive pathology. In the section entitled beyond the cardiovascular system, CCBs actions in migraine, neuropathic pain, and subarachnoid hemorrhage are reported. The final conclusions refer to long-term effects discovered in experimental animals that have not yet been clearly reported as being important in human pharmacotherapy.

Pathophysiological Mechanisms and Correlates of Therapeutic Pharmacological Interventions in Essential Arterial Hypertension

Treating arterial hypertension (HT) remains a hard task. The hypertensive patient is often a subject with several comorbidities and metabolic abnormalities. Clinicians everyday have to choose the right drug for the single patient among the different classes of antihypertensives. Apart from lowering blood pressure, a main therapeutic target should be that of counteracting all the possible pathophysiological mechanisms involved in HT itself and in existing/potential comorbidities. All the ancillary positive and negative effects of the administered drugs should be considered: in particular, since hypertensive patients are often glucose intolerant/diabetic, carrier of serum lipids disorder, have already developed atherosclerotic diseases and endothelial dysfunction, they should not be treated with drugs negatively interfering with these conditions but with molecules that, if possible, improve them. The main pathophysiological mechanisms and correlates of therapeutic pharmacological interventions in essential HT are reviewed here.

Calcium channel blockers in cardiovascular pharmacotherapy

This paper summarizes the pharmacological properties of calcium channel blockers (CCBs), their established therapeutic uses for cardiovascular disorders and the current improvement of their clinical effects through drug combinations. Their identification resulted from study of small molecules including coronary dilators, which were named calcium antagonists. Further experiments showed that they reduced contraction of arteries by inhibiting calcium entry and by interacting with binding sites identified on voltage-dependent calcium channels. This led to the denomination calcium channel blockers. In short-term studies, by decreasing total peripheral resistance, CCBs lower arterial pressure. By unloading the heart and increasing coronary blood flow, CCBs improve myocardial oxygenation. In long-term treatment, the decrease in blood pressure is more pronounced in hypertensive than in normotensive patients. A controversy on the safety of CCBs ended after a large antihypertensive trial (ALLHAT) sponsored by the National Heart, Lung, and Blood Institute. There are two main types of CCBs: dihydopyridine and non-dihydropyridine; the first type is vascular selective. Dihydropyrines are indicated for hypertension, chronic, stable and vasospastic angina. Non-dihydropyridines have the same indications plus antiarrythmic effects in atrial fibrillation or flutter and paroxysmal supraventricular tachycardia. In addition, CCBs reduced newly formed coronary lesions in atherosclerosis. In order to reach recommended blood pressure goals, there is a recent therapeutic move by combination of CCBs with other antihypertensive agents particularly with inhibitors acting at the level of the renin-angiotensin system. They are also combined with statins. Prevention of dementia has been reported in hypertensive patients treated with nitrendipine, opening a way for further studies on CCBs' beneficial effect in cognitive deterioration associated with aging.

End organ protection by calcium-channel blockers

In recent years, much attention has been given to end organ protection by antihypertensive, anti-heart failure, and anti-ischemic medications. This review describes the available information on end organ protection by calcium-channel blockers (CCBs). In normotensive patients and patients with hypertension treated with long-acting dihydropyridines, medial thickness was thinner than in patients treated with atenolol or in untreated hypertensive patients. Long-term treatment was associated with significant reduction in left ventricular mass. Calcium-channel blockers also improved endothelial-dependent relaxation and reversed the vasoconstrictive response to nitric oxide inhibitors. In diabetic patients, CCBs were effective in preserving kidney function and microalbuminurea. The combination of angiotensin-converting enzyme (ACE) inhibitors and CCBs was more effective than ACE inhibitors alone in preserving kidney function. In animal experiments, CCBs prevented development of coronary atheroschlerosis; however, in humans only limited data are available on their antiatherogenic effect. Some studies suggest that CCBs exert antiplatelets properties and may therefore be beneficial in patients with coronary artery disease.

Calcium-channel modulators for cardiovascular disease

It is generally accepted that hypertension doubles the risk of cardiovascular disease, of which coronary heart disease is the most common and lethal. Hypertension is a predisposing factor for the development of stroke, peripheral arterial disease, heart failure and end-state renal disease. Atherosclerosis-causing coronary heart disease is related to the severity of hypertension. Inhibition of calcium entry reduces the active tone of vascular smooth muscle and produces vasodilatation. This pharmacological action has been the basis for the use of calcium-channel blockers (CCBs) for the management of hypertension. Other drug families may achieve this: diuretics, beta-blockers, angiotensin-converting enzyme inhibitors, angiotensin-receptor antagonists. Cardiovascular hypertrophy and atherosclerosis are major complications related to high blood pressure. Cardiac hypertrophy is considered as an independent risk factor associated with abnormalities of diastolic function and can result in heart failure. Atherosclerosis is associated with activation of innate immunity. Atherosclerosis is expressing itself not only as coronary heart disease, but as a cerebrovascular and peripheral arterial disease. By impairing physiological vasomotor function, atherosclerosis includes ultimately necrosis of myocardium. CCBs reduce blood pressure. Do they prevent the progress of the main complications of hypertension? This major question is the matter of the present paper.

Circulating levels of endothelin-1 in a homogenous Gulf Arab population with untreated essential hypertension

BACKGROUND

Racial variations are reported in the natural history of hypertension. For example, hypertension is significantly more prevalent in blacks than whites. Endothelial cells are important regulators of vascular tone and homeostasis, in part through secretions of vasoactive substances including endothelin-1 (ET-1), a small peptide with potent vasopressor actions. In black hypertensives, ET-1 levels are higher than in normotensive blacks and in both hypertensive and normotensive whites. Since ET-1 might play a significant role in the development and severity of hypertension in the indigenous Arab population of the United Arab Emirates, we investigated the circulating levels of ET-1 in this homogenous population.

PATIENTS AND METHODS

ET-1 levels were measured in plasma samples from 60 untreated hypertensive Arabs and compared with 60 age- and sex-matched normotensive controls.

RESULTS

ET-1 levels were significantly higher in hypertensives (mean 10.1 +/- 1 pmol/L) than normotensives (mean 2.2 +/- 0.5 pmol/L). Body mass index (BMI) was slightly higher among the hypertensives. For all subjects these levels significantly (P < 0.001) correlated with systolic blood pressure and less significantly (P < 0.05) with diastolic blood pressure and body weight. The correlation between ET-1 and both systolic and diastolic blood pressure was persistently significant after adjusting for BMI.

CONCLUSION

Plasma concentrations of ET-1 are significantly higher in hypertensive Gulf Arabs as compared with reported levels in white hypertensives and ET-1 could be a risk factor for cardiovascular diseases in this population. The endothelial system might be particularly important with respect to hypertension in this racial group and merits further study.

The effect of combined Angiotensin-converting enzyme inhibition and calcium antagonism on allograft coronary vasculopathy validated by intravascular ultrasound

BACKGROUND

Hypertension is a potential risk factor for allograft coronary vasculopathy. We evaluated the efficacy of angiotensin-converting enzyme (ACE) inhibitors and calcium antagonists, and their combined use, on the development of coronary vasculopathy in hypertensive heart transplant recipients.

METHODS

Eighty-two heart transplant recipients underwent serial intravascular ultrasound (IVUS) analysis at baseline (within 1 month) and at 1 year after transplantation and were evaluated for the development of coronary vasculopathy. Patients were divided into 4 groups. Nineteen normotensive recipients received no treatment, control (Group A). Hypertensive patients were treated with either ACE inhibitors (Group B, n = 37), calcium antagonists (Group C, n = 16), or both (Group D, n = 10).

RESULTS

We found a significant reduction in IVUS indices of coronary vasculopathy in heart transplant recipients who used a combination of an ACE inhibitor and a calcium antagonist compared with recipients who used either drug alone (p < 0.05). This synergistic efficacy was independent of the baseline indices evaluated in a multivariate regression analysis model and was noted despite comparable mean arterial pressure among the 3 hypertensive groups at 1 year, thus suggesting the presence of a synergistic anti-proliferative effect beyond the anti-hypertensive efficacy.

CONCLUSIONS

The combined use of an ACE inhibitor and a calcium antagonist is more effective than the individual use of either drug alone on the development of coronary vasculopathy in cardiac transplant recipients. Large randomized clinical trials are warranted to evaluate such a synergistic efficacy.

The vasorelaxing action of labedipinedilol-A involves endothelial cell-derived NO and eNOS expression caused by calcium influx

Labedipinedilol-A, a novel dihydropyridine-type calcium antagonist, has been shown to induce hypotension and vasorelaxation. The objective of the present study was to investigate the effect of labedipinedilol-A on vascular function of rat aortic rings and cultured human umbilical vein endothelial cells (HUVECs). Labedipinedilol-A induced vasorelaxation in rat aortic rings that had been precontracted with phenylephrine in a concentration-dependent manner. This labedipinedilol-A-induced relaxation was significantly reduced by endothelium removal and by exposure to L-NG-nitroarginine methyl ester (L-NAME), methylene blue, or 1H-[1,2,4]oxadiazolol[4,3,a]quinoxalin-1-one (ODQ). In addition, the cyclic GMP content was significantly increased by labedipinedilol-A, which was inhibited by L-NAME in aorta. In cultured HUVECs, labedipinedilol-A induced concentration-dependent formation of NO and Ca2+ influx, and it increased the abundance of endothelial NO synthase (eNOS) protein. Furthermore, labedipinedilol-A suppressed basal, 10% FBS- and thrombin-stimulated endothelin-1 production, which were reversed by pretreatment with L-NAME, demonstrating that NO was able to inhibit production of ET-1 in HUVECs. Labedipinedilol-A significantly protected cultured HUVECs against dihydroxyfumarate/iron ion-induced decrease of glutathione and cell death. Moreover, labedipinedilol-A also inhibited iron-induced lipid peroxidation in rat brain homogenate and scavenged 2,2'-azobis (2-amidinopropane) dihydrochloride-derived peroxy radicals. Labedipinedilol-A acts as lacidipine with additional antioxidant effects and can protect endothelial cells against free radical-induced lipid peroxidation and cell injury. Our results indicate that the endothelium-dependent vasorelaxation by labedipinedilol-A is mediated through Ca2+-dependent activation of NO synthase and stimulation of NO/cyclic GMP pathway.

Evidence that lacidipine at nonsustained antihypertensive doses activates nitrogen monoxide system in the endothelium of salt-loaded Dahl-S rats

Lacidipine is a clinically active, antihypertensive calcium antagonist of the 1,4 dihydropyridine (DHP) class. It is also capable of vascular protection when administered (prophylactically and therapeutically) at nonsustained antihypertensive doses to salt-sensitive Dahl-S rats: useful animal models for studying the vasoprotective effect of calcium antagonists. In our previous work using voltammetry with selective biosensors, we observed that lacidipine implements endothelial nitrogen monoxide (NO) in normal rats. These experiments, performed in aortic rings obtained from Dahl-S rats analyzed with voltammetry and specific biosensors, further demonstrate that lacidipine, given at doses that do not control the development of hypertension (1 mg/kg), enhance endothelial NO activity. Taken together with the observation that 1 mg/kg lacidipine, and not its vehicle, is able to prevent vascular damage and concomitant increases in mortality (accelerated by a salt diet), this voltametric data suggest that NO acts as a component of positive influence of this DHP on vascular structure and function.

Electrochemical evidence that lacidipine stimulates release of nitrogen monoxide in rat aorta

Dihidropyridines (DHPs) such as amlodipine, lercanidipine and lacidipine, are compounds capable of vascular protection via their calcium antagonist activity. In addition, they present vascular dilatation function, which has been related to an anti endothelin efficacy, particularly for lacidipine. Recent works have suggested that DHPs modulate vascular relaxation via increase in the release of nitrogen monoxide (NO). Using voltammetry with selective biosensors the present experiments performed in rat aortic rings demonstrate the capability of DHPs to implement endothelial NO at 'useful' and not toxic nanomolar levels, with a maximum efficacy for lacidipine. This activity joins the already described positive effects of these compounds upon vascular functions.

Lipophilic calcium antagonists in antiatherosclerotic therapy

Two key events in atherosclerotic plaque formation are the deposition of lipids in cells of the vascular wall, and migration and proliferation of arterial smooth muscle cells from the tunica intima toward the media. It has been shown that various calcium-channel antagonists may delay plaque formation in animal models. Among these, the new and highly lipophilic calcium antagonists, such as lacidipine and lercanidipine, display the most promising antiatherosclerotic activities. This paper will review and discuss these beneficial effects.

Lacidipine reduces high blood pressure and the target organ damage induced by high fructose diet in rats

OBJECTIVE

Normotensive rats fed a high fructose diet (HFD) develop hypertriglyceridemia, hyperinsulinemia and hypertension. The glomerular changes observed in the kidneys of these animals are similar to those observed in diabetic rats. The aim of this study was to evaluate whether lacidipine could be effective not only in preventing, but also in inducing the regression of hypertension, and renal and cardiac damage in rats fed HFD.

METHODS

Thirty male Wistar-Kyoto (WKY) rats received HFD for 1 month; thereafter, five rats were sacrificed (Group 1) and the other 25 rats were divided into three groups: Group 2 (five rats) received HFD plus placebo, Group 3 (10 rats) HFD plus lacidipine 3 mg/kg per day, and Group 4 (10 rats) HFD plus hydralazine 10 mg/kg per day. At the end of the second month all animals were sacrificed. Kidneys and hearts were immediately removed. Renal deposits of collagen I, collagen IV, fibronectin and cardiac deposits of collagen III were assessed by means of immunohistochemistry.

RESULTS

In the rats receiving HFD plus placebo, blood pressure was increased after the first and the second month of diet. This increase was reversed by lacidipine and hydralazine but, although both drugs normalized blood pressure, only lacidipine was effective in reducing renal and cardiac damage.

CONCLUSIONS

These data suggest that lacidipine is effective in reversing hypertension and reducing target organ damage induced by HFD. Moreover, this protective effect on target organs appears to be not simply a consequence of blood pressure reduction, but seems to be connected to the type of hypotensive drug administered.

Lacidipine prevents the hypertension and renal and cardiac changes induced by high-fructose diet in WKY rats

Normotensive rats fed a high-fructose diet (HFD) develop hypertriglyceridemia, hyperinsulinemia, and hypertension. The glomerular changes observed in the kidneys of these animals are similar to those observed in diabetic rats. The aim of this study was to evaluate whether lacidipine, a calcium antagonist, could have a protective effect with this animal model. Forty male Wistar-Kyoto (WKY) rats were divided into four groups treated with HFD + placebo; HFD + lacidipine, 0.3 mg/kg/day; HFD + lacidipine, 3 mg/kg/day; or standard diet + placebo for 4 weeks. Urinary excretion of the stable metabolic products of nitric oxide (NO) was determined, because this vasoactive agent has been found to cause hemodynamic changes in the diabetic kidney. Glomerular size was determined by means of morphometric analysis. The results of this study show that lacidipine prevents (a) the HFD-induced increase in blood pressure in a dose-dependent manner; (b) the HFD-induced increase in glomerular size and fibronectin synthesis; and (c) the increase of collagen III synthesis in the heart. The drug had no effect on the increased urinary excretion of the stable metabolic products of NO. These data suggest that lacidipine might be useful in preventing the renal and cardiac damage caused by hypertension and non-insulin-dependent diabetes mellitus.