Angiotensin II-Receptor Antagonist Losartan Does not Prevent Nitroglycerin Tolerance in Patients with Coronary Artery Disease

Impact of an Innovative Educational Strategy on Medication Appropriate Use and Length of Stay in Elderly Patients

To evaluate the impact of an educational strategy on potentially inappropriate medications (PIMs) and length of stay in hospitalized elderly patients.

DESIGN

An open study, with two cross-sectional surveys interspersed with an educational program (PRE phase and POST phase), has been performed in order to compare the PIMs number before and after the introduction of an educational strategy. The study included 2 phases: PRE, in which patients were enrolled as control group; POST, in which an educational strategy on the PIMs use was introduced among physicians, and patients were enrolled as intervention group.

SETTING

Italian residential rehabilitation Centre. Inclusion criteria were ≥ 2 active chronic diseases and the current use of ≥ 4 medications. The educational strategy consisted of a 3-day course on strategies to prevent PIMs and a computerized tool running on a Personal Digital Assistant (PDA) device to check for PIMs.

OUTCOMES

The primary was the PIMs number, the secondary the length of stay.

RESULTS

A total of 790 patients, 450 controls and 340 cases, were enrolled. According to the Beers criteria, 52.3% of the study population received ≥ 1 PIMs, 18.73% ≥ 2, and 2.4% ≥ 4 PIMs. A significant reduction of PIMs (P = 0.020) and length of stay (P < 0.0001) were seen in the intervention group. At multivariate analysis, PIMs significantly correlated with age, drugs number, and the intervention, and the length of stay significantly correlated with disease count, comorbidities, and intervention. These data suggest that our educative instrument may be useful in reducing the PIMs number and length of hospitalization in elderly with a high number of drugs and comorbidities.

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.

Nitroglycerin-induced endothelial dysfunction and tolerance involve adverse phosphorylation and S-Glutathionylation of endothelial nitric oxide synthase: beneficial effects of therapy with the AT1 receptor blocker telmisartan

OBJECTIVE

Continuous administration of nitroglycerin (GTN) causes tolerance and endothelial dysfunction by inducing reactive oxygen species (ROS) production from various enzymatic sources, such as mitochondria, NADPH oxidase, and an uncoupled endothelial nitric oxide synthase (eNOS). In the present study, we tested the effects of type 1 angiotensin (AT(1))-receptor blockade with telmisartan on GTN-induced endothelial dysfunction in particular on eNOS phosphorylation and S-glutathionylation sites and the eNOS cofactor synthesizing enzyme GTP-cyclohydrolase I.

METHODS AND RESULTS

Wistar rats were treated with telmisartan (2.7 or 8 mg/kg per day PO for 10 days) and with GTN (50 mg/kg per day SC for 3 days). Aortic eNOS phosphorylation and S-glutathionylation were assessed using antibodies against phospho-Thr495 and Ser1177 or protein-bound glutathione, which regulate eNOS activity and eNOS-dependent superoxide production (uncoupling). Expression of mitochondrial aldehyde dehydrogenase was determined by Western blotting. Formation of aortic and cardiac ROS was assessed by fluorescence, chemiluminescence, and 3-nitrotyrosine/malondialdehyde-positive protein content. Telmisartan prevented endothelial dysfunction and partially improved nitrate tolerance. Vascular, cardiac, mitochondrial, and white blood cell ROS formation were significantly increased by GTN treatment and inhibited by telmisartan. GTN-induced decrease in Ser1177, increase in Thr495 phosphorylation or S-glutathionylation of eNOS, and decrease in mitochondrial aldehyde dehydrogenase expression were normalized by telmisartan.

CONCLUSIONS

These data identify modification of eNOS phosphorylation as an important component of GTN-induced endothelial dysfunction. Via its pleiotropic "antioxidant" properties, telmisartan prevents, at least in part, GTN-induced oxidative stress, nitrate tolerance, and endothelial dysfunction.

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.

Redox signaling (cross-talk) from and to mitochondria involves mitochondrial pores and reactive oxygen species

This review highlights the important role of redox signaling between mitochondria and NADPH oxidases. Besides the definition and general importance of redox signaling, the cross-talk between mitochondrial and Nox-derived reactive oxygen species (ROS) is discussed on the basis of 4 different examples. In the first model, angiotensin-II is discussed as a trigger for NADPH oxidase activation with subsequent ROS-dependent opening of mitochondrial ATP-sensitive potassium channels leading to depolarization of mitochondrial membrane potential followed by mitochondrial ROS formation and respiratory dysfunction. This concept was supported by observations that ethidium bromide-induced mitochondrial damage suppressed angiotensin-II-dependent increase in Nox1 and oxidative stress. In another example hypoxia was used as a stimulator of mitochondrial ROS formation and by using pharmacological and genetic inhibitors, a role of mitochondrial ROS for the induction of NADPH oxidase via PKCvarepsilon was demonstrated. The third model was based on cell death by serum withdrawal that promotes the production of ROS in human 293T cells by stimulating both the mitochondria and Nox1. By superior molecular biological methods the authors showed that mitochondria were responsible for the fast onset of ROS formation followed by a slower but long-lasting oxidative stress condition based on the activation of an NADPH oxidase (Nox1) in response to the fast mitochondrial ROS formation. Finally, a cross-talk between mitochondria and NADPH oxidases (Nox2) was shown in nitroglycerin-induced tolerance involving the mitochondrial permeability transition pore and ATP-sensitive potassium channels. The use of these redox signaling pathways as pharmacological targets is briefly discussed.

Organic nitrates and nitrate tolerance--state of the art and future developments

The hemodynamic and antiischemic effects of nitroglycerin (GTN) are lost upon chronic administration due to the rapid development of nitrate tolerance. The mechanism of this phenomenon has puzzled several generations of scientists, but recent findings have led to novel hypotheses. The formation of reactive oxygen and nitrogen species in the mitochondria and the subsequent inhibition of the nitrate-bioactivating enzyme mitochondrial aldehyde dehydrogenase (ALDH-2) appear to play a central role, at least for GTN, that is, bioactivated by ALDH-2. Importantly, these findings provide the opportunity to reconcile the two "traditional" hypotheses of nitrate tolerance, that is, the one postulating a decreased bioactivation and the concurrent one suggesting a role of oxidative stress. Furthermore, recent animal and human experimental studies suggest that the organic nitrates are not a homogeneous group but demonstrate a broad diversity with regard to induction of vascular dysfunction, oxidative stress, and other side effects. In the past, attempts to avoid nitrate-induced side effects have focused on administration schedules that would allow a "nitrate-free interval"; in the future, the role of co-therapies with antioxidant compounds and of activation of endogeneous protective pathways such as the heme oxygenase 1 (HO-1) will need to be explored. However, the development of new nitrates, for example, tolerance-free aminoalkyl nitrates or combination of nitrate groups with established cardiovascular drugs like ACE inhibitors or AT(1)-receptor blockers (hybrid molecules) may be of great clinical interest.

First evidence for a crosstalk between mitochondrial and NADPH oxidase-derived reactive oxygen species in nitroglycerin-triggered vascular dysfunction

Chronic nitroglycerin treatment results in development of nitrate tolerance associated with endothelial dysfunction (ED). We sought to clarify how mitochondria- and NADPH oxidase (Nox)-derived reactive oxygen species (ROS) contribute to nitrate tolerance and nitroglycerin-induced ED. Nitrate tolerance was induced by nitroglycerin infusion in male Wistar rats (100 microg/h/4 day) and in C57/Bl6, p47(phox/) and gp91(phox/) mice (50 microg/h/4 day). Protein and mRNA expression of Nox subunits were unaltered by chronic nitroglycerin treatment. Oxidative stress was determined in vascular rings and mitochondrial fractions of nitroglycerin-treated animals by L-012 enhanced chemiluminescence, revealing a dominant role of mitochondria for nitrate tolerance development. Isometric tension studies revealed that genetic deletion or inhibition (apocynin, 0.35 mg/h/4 day) of Nox improved ED, whereas nitrate tolerance was unaltered. Vice versa, nitrate tolerance was attenuated by co-treatment with the respiratory chain complex I inhibitor rotenone (100 microg/h/4 day) or the mitochondrial permeability transition pore blocker cyclosporine A (50 microg/h/4 day). Both compounds improved ED, suggesting a link between mitochondrial and Nox-derived ROS. Mitochondrial respiratory chain-derived ROS are critical for the development of nitrate tolerance, whereas Nox-derived ROS mediate nitrate tolerance-associated ED. This suggests a crosstalk between mitochondrial and Nox-derived ROS with distinct mechanistic effects and sites for pharmacological intervention.

Dissociation between superoxide accumulation and nitroglycerin-induced tolerance

We hypothesize that superoxide (O(2)(*-)) accumulation is not a crucial causative factor in inducing nitroglycerin (NTG) tolerance. In LLC-PK1 cells, pre-exposure to NTG resulted in increased O(2)(*-) accumulation and reduced cGMP response to NTG versus vehicle control. O(2)(*-) stimulated by NTG was reduced by oxypurinol (100 microM), a xanthine oxidase inhibitor. Exposure to angiotensin II (Ang II) increased O(2)(*-) but did not reduce cGMP response. The O(2)(*-) scavenger tiron reduced Ang II-induced O(2)(*-) production but did not increase NTG-stimulated cGMP production. Using p47(phox-/-) and gp91(phox-/-) mice versus their respective wild-type controls (WT), we showed that aorta from mice null of these critical NADPH oxidase subunits exhibited similar vascular tolerance after NTG dosing (20 mg/kg s.c., t.i.d. for 3 days), as indicated by their ex vivo pEC(50) and cGMP accumulation upon NTG challenge. In vitro aorta O(2)(*-) production was enhanced by NTG incubation in both p47(phox) null and WT mice. Pre-exposure of isolated mice aorta to 100 microM NTG for 1 h resulted in vascular tolerance toward NTG and increased O(2)(*-) accumulation. Oxypurinol (1 mM) reduced O(2)(*-) but did not attenuate vascular tolerance. These results suggest that O(2)(*-) does not initiate either in vitro and in vivo NTG tolerance, and that the p47(phox) and gp91(phox) subunits of NADPH oxidase are not critically required. Increased O(2)(*-) accumulation may be an effect, rather than an initiating cause, of NTG tolerance.