Preventive effects of angiotensin-converting enzyme inhibitors on nitrate tolerance during continuous transdermal application of nitroglycerin in patients with chronic heart failure

Can Nitric Oxide-Based Therapy Be Improved for the Treatment of Cancers? A Perspective

Since the early observations that nitric oxide (•NO) at high concentrations is cytotoxic to cancer cells and that it may play an important role in the treatment of human cancers, a significant number of compounds (NO-donors) have been prepared to deliver •NO to tumors. •NO also sensitizes various clinically active anticancer drugs and has been shown to induce the reversal of multi-drug resistance in tumor cells expressing ATP-binding cassette-transporter proteins. For the successful treatment of cancers, •NO needs to be delivered precisely to tumors, and its adverse toxicity must be limited. Like other chemotherapeutics, the precise delivery of drugs has been a problem and various attempts have been made, such as the encapsulation of drugs in lipid polymers, to overcome this. This prospective study examines the use of various strategies for delivering •NO (using NO-donors) for the treatment of cancers. Finding and utilizing such a delivery system is an important step in delivering cytotoxic concentrations of •NO to tumors without adverse reactions, leading to a successful clinical outcome for patient management.

Nitrate therapy for heart failure: benefits and strategies to overcome tolerance

Combination therapy with hydralazine and nitrates can improve outcomes in patients with heart failure and low ejection fraction. However, this combination is underused in clinical practice for several reasons, including side effects related to hydralazine and polypharmacy. Some of the benefits seen with hydralazine, including afterload reduction and attenuation of nitrate tolerance, have also been observed with angiotensin-converting enzyme inhibitors. Demonstrating similar clinical benefits with nitrates plus angiotensin-converting enzyme inhibitor therapy alone, in the absence of hydralazine, may represent an opportunity to improve heart failure care by increasing the use of nitrates. In this paper, we summarize data that support studying such an approach.

Nitroglycerin use in myocardial infarction patients

Acute myocardial infarction (MI) and its sequelae are leading causes of morbidity and mortality worldwide. Nitroglycerin (glyceryl trinitrate [GTN]) remains a first-line treatment for angina pectoris and acute MI. Nitroglycerin achieves its benefit by giving rise to nitric oxide (NO), which causes vasodilation and increases blood flow to the myocardium. However, continuous delivery of GTN results in tolerance, limiting the use of this drug. Nitroglycerin tolerance is caused, at least in part, by inactivation of aldehyde dehydrogenase 2 (ALDH2), an enzyme that converts GTN to the vasodilator, NO. We recently found that in a MI model in animals, in addition to GTN's effect on the vasculature, sustained treatment negatively affected cardiomyocyte viability following ischemia, thus resulting in increased infarct size. Coadministration of Alda-1, an activator of ALDH2, with GTN improves metabolism of reactive aldehyde adducts and prevents the GTN-induced increase in cardiac dysfunction following MI. In this review, we describe the molecular mechanisms associated with the benefits and risks of GTN administration in MI.

Organic nitrates and nitrate resistance in diabetes: the role of vascular dysfunction and oxidative stress with emphasis on antioxidant properties of pentaerithrityl tetranitrate

Organic nitrates represent a class of drugs which are clinically used for treatment of ischemic symptoms of angina as well as for congestive heart failure based on the idea to overcome the impaired NO bioavailability by “NO” replacement therapy. The present paper is focused on parallels between diabetes mellitus and nitrate tolerance, and aims to discuss the mechanisms underlying nitrate resistance in the setting of diabetes. Since oxidative stress was identified as an important factor in the development of tolerance to organic nitrates, but also represents a hallmark of diabetic complications, this may represent a common principle for both disorders where therapeutic intervention should start. This paper examines the evidence supporting the hypothesis that pentaerithrityl tetranitrate may represent a nitrate for treatment of ischemia in diabetic patients. This evidence is based on the considerations of parallels between diabetes mellitus and nitrate tolerance as well as on preliminary data from experimental diabetes studies.

Coadministration of carvedilol attenuates nitrate tolerance by preventing cytochrome p450 depletion

BACKGROUND

Long-term administration of nitroglycerin (NTG) causes tolerance secondary to increased vascular formation of reactive oxygen species. Carvedilol, which has potent antioxidant activity in addition to functioning as an adrenergic blocker, prevents nitrate tolerance by a still to be elucidated mechanism. The present study investigated how carvedilol attenuates nitrate tolerance, particularly with reference to cytochrome P450 (CYP), an enzyme involved in the development of tolerance.

METHODS AND RESULTS

Male Wistar rats were subjected to 48-h continuous infusion of NTG alone (0.5 mg/h) or NTG with concomitant carvedilol (20 or 100 microg/h), and then compared with vehicle-treated rats (4 groups; n=6 in each group). Following the continuous administration, nitrate tolerance, assessed by bolus NTG injections, was hemodynamically prevented by coadministration of carvedilol. Levels of CYP1A1/1A2, superoxide production, and phosphorylated vasodilator-stimulated phosphoprotein at serine 239 (P-VASP) were examined in the aortic wall and heart tissue. When NTG alone was continuously administered, vascular superoxide was produced, there was a decrease in the cardiac CYP1A1/1A2 level, and depletion of P-VASP. However, each of these changes induced by continuous NTG administration was significantly attenuated by coadministration of carvedilol and the extent of attenuation was more pronounced at the higher dose (100 microg/h).

CONCLUSIONS

Coadministration of carvedilol attenuates nitrate tolerance through maintenance of NO/cGMP pathway activity by preventing free radical generation and CYP depletion.

Attenuation of nitrate tolerance and oxidative stress by an angiotensin II receptor blocker in patients with coronary spastic angina

BACKGROUND

Nitrates are widely used to treat coronary artery disease, but their therapeutic value is compromised by the rapid development of tolerance. Recently, the renin-angiotensin system has been suggested to play an important role in the development of nitrate tolerance.

METHODS AND RESULTS

Sixty-four patients with coronary spastic angina were investigated to clarify the effect of angiotensin II type 1 receptor blocker (ARB) therapy on nitrate tolerance. Transdermal nitroglycerin (10 mg/d) and an ARB (candesartan, 8 mg/d) were administered to 21 patients (GTN+ARB group) for 3 days, whereas transdermal nitroglycerin and placebo were administered to 19 patients (GTN group). Another 18 patients were treated with placebo skin patches and placebo tablets for 3 days (control group). The brachial artery response to incremental doses of intravenous nitroglycerin (0.01, 0.1, and 1.0 micro;g/kg) was measured by ultrasound before and after transdermal nitroglycerin therapy. Before treatment, the arterial diameter was increased by nitroglycerin injection in each group. After treatment, the increase of arterial diameter was significantly suppressed in the GTN group but not in the control or GTN+ARB groups. The plasma level of thioredoxin (a marker of oxidative stress) was increased in the GTN group after treatment (P<0.01) but not in the control or GTN+ARB groups.

CONCLUSIONS

An ARB suppressed the development of nitrate tolerance during transdermal nitroglycerin therapy. These results suggest that increased oxidative stress induced by activation of angiotensin II may play an important role in the development of nitrate tolerance.