Effects of diuretic therapy on the development of tolerance to nitroglycerin and exercise capacity in patients with chronic stable angina

Recent Advances in Understanding the Pathogenesis of Cardiovascular Diseases and Development of Treatment Modalities

Cardiovascular Diseases (CVDs) are a leading cause of morbidity and mortality worldwide. The underlying pathology for cardiovascular disease is largely atherosclerotic in nature and the steps include fatty streak formation, plaque progression and plaque rupture. While there is optimal drug therapy available for patients with CVD, there are also underlying drug delivery obstacles that must be addressed. Challenges in drug delivery warrant further studies for the development of novel and more efficacious medical therapies. An extensive understanding of the molecular mechanisms of disease in combination with current challenges in drug delivery serves as a platform for the development of novel drug therapeutic targets for CVD. The objective of this article is to review the pathogenesis of atherosclerosis, first-line medical treatment for CVD, and key obstacles in an efficient drug delivery.

Challenges with nitrate therapy and nitrate tolerance: prevalence, prevention, and clinical relevance

Nitrate therapy has been an effective treatment for ischemic heart disease for over 100 years. The anti-ischemic and exercise-promoting benefits of sublingually administered nitrates are well established. Nitroglycerin is indicated for the relief of an established attack of angina and for prophylactic use, but its effects are short lived. In an effort to increase the duration of beneficial effects, long-acting orally administered and topical applications of nitrates have been developed; however, following their continued or frequent daily use, patients soon develop tolerance to these long-acting nitrate preparations. Once tolerance develops, patients begin losing the protective effects of the long-acting nitrate therapy. By providing a nitrate-free interval, or declining nitrate levels at night, one can overcome or reduce the development of tolerance, but cannot provide 24-h anti-anginal and anti-ischemic protection. In addition, patients may be vulnerable to occurrence of rebound angina and myocardial ischemia during periods of absent nitrate levels at night and early hours of the morning, and worsening of exercise capacity prior to the morning dose of the medication. This has been a concern with nitroglycerin patches but not with oral formulations of isosorbide-5 mononitrates, and has not been adequately studied with isosorbide dinitrate. This paper describes problems associated with nitrate tolerance, reviews mechanisms by which nitrate tolerance and loss of efficacy develop, and presents strategies to avoid nitrate tolerance and maintain efficacy when using long-acting nitrate formulations.

The acute administration of either amiloride or captopril does not prevent endothelial dysfunction induced by ischemia and reperfusion in the human forearm vasculature

Animal studies have demonstrated the ability of both sodium–hydrogen exchange inhibitors and angiotensin-converting enzyme inhibitors to reduce infarct size and preserve postischemic ventricular function following ischemia and reperfusion (IR) injury. Whether these interventions can also prevent IR-induced impairment of endothelial function in humans has not been investigated. We performed 2 separate double-blind, placebo-controlled, crossover studies. In the first study, 10 healthy volunteers were randomized to receive oral amiloride (10 mg) or a placebo. In a separate study, another group of volunteers (n = 10) was randomized to receive oral captopril (50 mg) or a placebo. At the time of the peak hemodynamic effect of the drug (3 and 1.5 h after administration of amiloride and captopril, respectively), endothelium-dependent, flow-mediated dilatation of the radial artery was measured before and after IR. IR significantly blunted flow-mediated dilatation in all groups (placebo: pre-IR: 6.8% ± 0.7%; post-IR: 2.9% ± 0.9%; P < 0.01; amiloride: pre-IR: 5.9% ± 0.6%; post-IR: 2.1% ± 1.3%; P = 0.01; captopril: pre-IR: 6.0% ± 0.5%; post-IR: 2.0% ± 0.6%; P < 0.01). In humans, neither 10 mg of oral amiloride nor 50 mg of oral captopril was able to provide protection against IR-induced endothelial dysfunction in the peripheral vasculature.

Effect of Diuretic Therapy on Exercise Capacity in Patients With Chronic Angina and Preserved Left Ventricular Function

AIM

This study was designed to determine whether therapy with a diuretic has antianginal effects in patients with stable angina who are already treated with a traditional antianginal regimen.

METHODS AND RESULTS

Forty patients with chronic stable angina and normal left ventricular function were randomized in a double-blind, placebo-controlled study. Background antianginal therapy included beta blockers (n = 27), calcium channel antagonists (n = 18), and long-acting nitrates (n = 24). Of the patients 30% had diabetes and 75% had a history of hypertension. Patients were treated with a diuretic (hydrochlorothiazide 25 mg plus amiloride 5 mg) or placebo for 21 days. All patients underwent a treadmill exercise test before randomization and at day 21. The primary end point was the change in treadmill walking time until moderate angina. Diuretic therapy was associated with an increase in treadmill walking time of 63 +/- 17 seconds versus 19 +/- 9 seconds in the placebo group (P = 0.026) and reduced ST-segment depression (0.6 +/- 0.2 mm versus 0.1 +/- 0.2 mm (P = 0.03). There was a 25% increase in walking time in 8 patients (40%) treated with diuretic versus 1 patient (5%) in the placebo group (P = 0.02). The increases did not depend on changes in blood pressure or heart rate.

CONCLUSION

Therapy with hydrochlorothiazide plus amiloride has potent antianginal effects in patients with stable angina and preserved left ventricular function under treatment with standard antianginal therapy. Because most of the study patients had a history of hypertension the extrapolation of these findings to patients who did not have hypertension requires further investigation.

Simultaneous determination of amiloride and hydrochlorothiazide in human plasma by liquid chromatography/tandem mass spectrometry with positive/negative ion-switching electrospray ionisation

A new method for simultaneous determination of amiloride and hydrochlorothiazide by liquid chromatography/electrospray tandem mass spectrometry (LC/MS/MS) operated in positive and negative ionization switching mode was developed and validated. Protein precipitation with acetonitrile was selected for sample preparation. The analytes were separated on a Phenomenex Curosil-PFP (250x4.6 mm, 5 microm) column by a gradient elution with a mobile phase consisting of 0.15% formic acid solution containing 0.23% ammonium acetate and methanol pumped at a flow rate of 1.0 mL.min(-1). Rizatriptan was used as the internal standard (IS) for quantification. The determination was carried out on a Waters Quattro-micro triple-quadrupole mass spectrometer operated in multiple reaction monitoring (MRM) mode using the following transitions monitored simultaneously: positive m/z 230-->171 for amiloride, m/z 270-->158 for rizatriptan, and negative m/z 296-->205 for hydrochlorothiazide. The lower limits of quantification (LLOQs) were 0.1 and 1.0 ng.mL(-1) for amiloride and hydrochlorothiazide, respectively, which were lower than other published methods by using ultraviolet (UV), fluorimetric or mass spectrometric detection. The intra- and inter-day precision and accuracy were studied at three different concentration levels and were always better than 15% (n=5). This simple and robust LC/MS/MS method was successfully applied to the pharmacokinetic study of compound amiloride and hydrochlorothiazide tablets in healthy male Chinese volunteers.

Simultaneous determination of amiloride hydrochloride and hydrochlorothiazide in synthetic samples and pharmaceutical formulations by multivariate analysis of spectrophotometric data

The use of multivariate spectrophotometric calibration for the simultaneous analysis of synthetic samples and commercial tablet preparations containing hydrochlorothiazide (HCT) and amiloride hydrochloride (AMH) is reported. Partial least squares (PLS-1) analysis of electronic absorption spectral data allowed the rapid and accurate resolution of mixtures in which the analyte ratios were approximately 10:1, without the need of a previous separation step and without interference from other sample constituents. The method, validated by the analysis of synthetic mixtures of both drugs, where accuracy over the linear working range as well as inter- and intra-assay precision were determined, was used in the concentration ranges of 21.7-30.4 mg l(-1) for HCT and 1.8-3.0 mg l(-1) for AMH. The proposed method was successfully applied to the evaluation of the stability of the stock solutions of the analytes in MeOH-H(2)O and to the elaboration of drug dissolution profiles of commercial tablets, results being concordant with those furnished by the USP technique. The method was also employed for the determination of drug content in two different pharmaceutical formulations, providing results that were in excellent agreement with those obtained by HPLC.

Clinical comparison of antiischemic efficacy of isosorbide dinitrate and molsidomine

In 16 patients with documented coronary artery disease, the extent and duration of acute antiischemic and hemodynamic effects of monotherapies with 120 mg of sustained-release isosorbide dinitrate once daily and 8 mg of sustained-release molsidomine 3 times daily were compared according to a randomized, double-blind, cross-over and placebo-controlled protocol including exercise testing for assessment of ST-segment depression (ST) at an identical workload and determination of plasma concentrations of both substances. Up to 8 h after dosing in the morning, more marked and sustained effects were observed with the nitrate (ST at 2 h, -82%; p < 0.001; at 8 h, -64%; p < 0.01) than with molsidomine (2 h, -68%; p < 0.001; at 8 h, -9%; NS). At 12 h, no more meaningful actions were detectable with isosorbide dinitrate (-13%, NS) despite plasma concentrations still within a range otherwise considered therapeutically effective, whereas with molsidomine, at 4 h after renewed dosing, this parameter was reduced by 38% (p < 0.01). However, therapeutic coverage over a 24-h period could be demonstrated on neither regimen, in the case of the nitrate because of the development of early tolerance, and in the case of molsidomine with its meaningfully shorter half-life because of the necessity of increasing the dosing frequency even further. No meaningful adverse effects were observed with either regimen. Nonresponders, overall a minority on one treatment, responded completely to the alternative regimen and vice versa.

Lack of cross-tolerance to short-term linsidomine in forearm resistance vessels and dorsal hand veins in subjects with nitroglycerin tolerance

BACKGROUND

Therapy with nitroglycerin is widely used in the treatment of angina pectoris, but development of tolerance is a major problem. Nitrovasodilators other than nitroglycerin may be less prone to induce vascular tolerance. This investigation was designed to test whether the alternative nitric oxide donor linsidomine maintains its vasodilator effects in the presence of nitroglycerin tolerance.

METHODS

We tested the vascular effects of nitroglycerin and linsidomine (SIN-1) in forearm resistance arteries (venous occlusion plethysmography) and hand veins (venous compliance technique) using a randomized, double-blind placebo-controlled regimen in 33 healthy subjects (age range, 22 to 38 years; mean age, 26 years) before and after 7 days of assignment to either 1 week of nitroglycerin administration (0.83 mg/hr) for induction of tolerance or placebo administration.

RESULTS

Vascular responses of both vascular beds to nitroglycerin (in veins: mean difference, 42.3%; confidence interval [CI], 3% to 81.7%; p < 0.05; in arteries: mean difference, 65.0%; CI, 38.9% to 91.1%; p < 0.01) but not to linsidomine (in veins: mean difference, -13.8%; CI, -53.5 to 25.8%; not significant; in arteries: -19.7%; CI, -33.7% to -5.6%; not significant) were attenuated in the nitroglycerin patch group, whereas the placebo group showed no differences to either nitroglycerin (in arteries: mean difference, -7.5%; CI, -44.6% to 29.6%; in veins: -10.6%; CI, -58.2% to 36.9%) or linsidomine (in arteries: 4.5%; CI, -12.8% to 21.7%; in veins: -13.1%; CI, -4.5% to 29.8%).

CONCLUSION

These results suggest that short-term administration of sydnonimines can overcome the loss of vascular relaxation associated with long-term nitroglycerin therapy.

Refractory angina pectoris in end-stage coronary artery disease: evolving therapeutic concepts

Refractory angina pectoris in coronary artery disease is defined as the persistence of severe anginal symptoms despite maximal conventional antianginal combination therapy. Further, the option to use an invasive revascularization procedure such as percutaneous coronary balloon angioplasty or aortocoronary bypass grafting must be excluded on the basis of a recent coronary angiogram. This coronary syndrome, which represents end-stage coronary artery disease, is characterized by severe coronary insufficiency but only moderately impaired left ventricular function. Almost all patients demonstrated severe coronary triple-vessel disease with diffuse coronary atherosclerosis, had had one or more myocardial infarctions, and had undergone aortocoronary bypass grafting (70% of cases). We present three new approaches with antiischemic properties: long-term intermittent urokinase therapy, transcutaneous and spinal cord electrical nerve stimulation, and transmyocardial laser revascularization.

[Conservative therapeutic approaches in terminal coronary heart disease. Chronic intermittent urokinase therapy]

Despite progress in the invasive revascularization procedures and even though conventional antianginal treatment has improved the quality of life in patients with symptomatic coronary artery disease considerably, an increasing number of patients suffers from end-stage coronary artery disease and refractory angina pectoris. For these refractory patients long-term intermittent urokinase therapy was developed as an antithrombotic intervention, which is based on its capacity to enhance thrombolysis and blood rheology, and may possibly lead to plaque regression. The coronary syndrome of refractory angina pectoris is characterized by a mismatch of severe coronary insufficiency and a relatively large amount of viable myocardium as indicated by an only moderately impaired left ventricular function. Prior to initiation of long-term intermittent urokinase therapy all potential measures to improve myocardial perfusion have to be considered in each patient. These supportive measures include rigorous reduction of LDL-cholesterol, which has proven antiischemic properties due to an improved endothelial function of epicardial conductance vessels possibly resulting in an antianginal effect. Apart from the proven antiischemic properties of long-term intermittent urokinase therapy in patients with refractory angina pectoris, objective signs of ischemic myocardial heart failure improve. Follow-up studies demonstrated a significant increase of left ventricular ejection fraction as evaluated with multi-gated blood pool analysis. Furthermore, left ventricular diastolic function normalized after a treatment period of 12 weeks. As the clinical effects last well beyond the actual treatment period and as they are accompanied by a remarkable increase in the quality of life, a complex approach as this one is justified in this highly symptomatic patient group.