Sildenafil citrate (viagra) induces cardioprotective effects after ischemia/reperfusion injury in infant rabbits

Protective or Inhibitory Effect of Pharmacological Therapy on Cardiac Ischemic Preconditioning: A Literature Review

Ischemic preconditioning (IP) is an innate phenomenon, triggered by brief, non-lethal cycles of ischemia/reperfusion applied to a tissue or organ that confers tolerance to a subsequent more prolonged ischemic event. Once started, it can reduce the severity of myocardial ischemia associated with some clinical situations, such as percutaneous coronary intervention (PCI) and intermittent aortic clamping during coronary artery bypass graft surgery (CABG). Although the mechanisms underlying IP have not been completely elucidated, several studies have shown that this phenomenon involves the participation of cell triggers, intracellular signaling pathways, and end-effectors. Understanding this mechanism enables the development of preconditioning mimetic agents. It is known that a range of medications that activate the signaling cascades at different cellular levels can interfere with both the stimulation and the blockade of IP. Investigations of signaling pathways underlying ischemic conditioning have identified a number of therapeutic targets for pharmacological manipulation. This review aims to present and discuss the effects of several medications on myocardial IP.

Pulmonary vascular resistance as a potential marker of reactive pulmonary hypertension reduction following sildenafil therapy in patients disqualified from orthotopic heart transplantation

PURPOSE

We sought to determine the predictors of restoration of heart transplantation (HTx) candidacy in patients with systolic heart failure (HF) and reactive fixed pulmonary hypertension (RFPH) defined as pulmonary vascular resistance (PVR) > 2.5 Wood units (WU), transpulmonary gradient (TPG) > 12 mmHg or ≤2.5 WU with systolic arterial pressure ≤85 mmHg during vasoreactivity test, following sildenafil therapy.

MATERIAL AND METHODS

Between 2007 and 2018 1136 patients were evaluated at our department as candidates for HTx. Thirty-five of them, who presented with systolic HF and were not eligible for HTx due to RFPH, were included in the study (31 men aged 55.1 ± 7.4 years). In all the patients sildenafil was introduced and up-titrated to a maximal tolerated dose in addition to optimal medical therapy. Patients were assessed at 3-6 months intervals.

RESULTS

During median 11 months (interquartile range 6-18 months) reduction of RFPH enabling qualification for HTx was observed in 62.9% patients. Higher baseline PVR (OR 0.32; 95% CI (0.14-0.74) p < 0.001), pulmonary artery systolic pressure (PASP) (OR 0.94, 95% CI (0.88-0.99) p = 0.05), mean artery pulmonary pressure (mPAP) (OR 0.87, 95% CI (0.77-0.98) p = 0.02) and TPG (OR 082, 95% CI (0.70-0.96) p = 0.003) were negative predictors of RFPH reduction with sildenafil therapy. In multivariable analysis, lower PVR (p = 0.02) was identified as an independent predictor of RFPH reduction following sildenafil therapy.

CONCLUSION

Sildenafil therapy can support PH reduction in systolic HF patients uneligible for HTx due to RFPH. Lower baseline PVR was identified as an independent predictor of PH reversibility with sildenafil enabling restoration of HTx candidacy.

Phosphodiesterase Type 5 Inhibitor Sildenafil Decreases the Proinflammatory Chemokine CXCL10 in Human Cardiomyocytes and in Subjects with Diabetic Cardiomyopathy

T helper 1 (Th1) type cytokines and chemokines are bioactive mediators in inflammation underling several diseases and co-morbid conditions, such as cardiovascular and metabolic disorders. Th1 chemokine CXCL10 participates in heart damage initiation/progression; cardioprotection has been recently associated with sildenafil, a type 5 phosphodiesterase inhibitor. We aimed to evaluate the effect of sildenafil on CXCL10 in inflammatory conditions associated with diabetic cardiomyopathy. We analyzed: CXCL10 gene and protein in human cardiac, endothelial, and immune cells challenged by pro-inflammatory stimuli with and without sildenafil; serum CXCL10 in diabetic subjects at cardiomyopathy onset, before and after 3 months of treatment with sildenafil vs. placebo. Sildenafil significantly decreased CXCL10 protein secretion (IC₅₀ = 2.6 × 10⁻⁷) and gene expression in human cardiomyocytes and significantly decreased circulating CXCL10 in subjects with chemokine basal level ≥ 930 pg/ml, the cut-off value as assessed by ROC analysis. In conclusion, sildenafil could be a pharmacologic tool to control CXCL10-associated inflammation in diabetic cardiomyopathy.

Genetic Understanding of Stroke Treatment: Potential Role for Phosphodiesterase Inhibitors

Phosphodiesterase (PDE) gene family is a large family having at least 21 genes and multiple versions (isoforms) of the phosphodiesterase enzymes. These enzymes catalyze the inactivation of intracellular mediators of signal transduction such as cAMP and cGMP and therefore, play a pivotal role in various cellular functions. PDE inhibitors (PDEI) are drugs that block one or more of the five subtypes of the PDE family and thereby prevent inactivation of the intracellular cAMP and cGMP by the respective PDE-subtypes. The first clinical use of PDEI was reported almost three decades ago. Studies later found the ability of these compounds to increase the levels of ubiquitous secondary messenger molecules that can cause changes in vascular tone, cardiac function and other cellular events and thus these findings paved the way for their use in various medical emergencies. PDEs are found to be distributed in many tissues including brain. Therefore, new therapeutic agents in the form of PDEI are being explored in neurodegenerative diseases including stroke. Although studies have revealed their use in cerebral infarction prevention, their full-fledged application in times of neurological emergency or stroke in specific has been very limited so far. Nevertheless, recent investigations suggest PDE4 and PDE5 inhibitors to play a vital role in mitigating stroke symptoms by modulating signaling mechanisms in PDE pathway. Further, extensive research in terms of their pharmacological properties like dosing, drug specific activities, use of simultaneous medications, ancillary properties of these compounds and studies on adverse drug reactions needs to be carried out to set them as standard drugs of use in stroke.

Sodium Pentosan Polysulfate Reduced Renal Ischemia-Reperfusion-Induced Oxidative Stress and Inflammatory Responses in an Experimental Animal Model

Acute kidney injury (AKI) remains an independent risk factor for mortality and morbidity after vascular surgery (affecting the renal arteries) or aortic surgery (requiring suprarenal aortic clamping). These types of vascular surgery produce renal ischemia/reperfusion (I/R) injury, a common cause of AKI. The present studies aimed at monitoring the course of renal I/R injury at the cellular level and investigating the efficacy of long-term preoperative and single-shot intraoperative administration of sodium pentosan polysulfate (PPS) to protect renal tissue from acute I/R injury both in native and diabetic kidneys in rats. Western blot analyses of the proapoptotic (bax) and antiapoptotic (bcl-2) signaling pathways, as well as the extent of DNA damage (phospho-p53), were performed. Oxidative stress followed upon the termination of malondialdehyde, reduced glutathione, thiol group, and superoxide dismutase plasma levels. Inflammatory changes were measured by the determination of serum tumor necrosis factor-α and interleukin-1 levels. Morphological changes were detected by histological examinations. Our results showed that the long-term administration of PPS has an advantage in reducing I/R kidney injury in diabetic rats, while high-dose, single-shot parenteral administration of PPS prior to revascularization might be useful in nondiabetic rats.

Preoperative Sildenafil administration in children undergoing cardiac surgery: a randomized controlled preconditioning study

OBJECTIVES

Sildenafil has strong cardiac preconditioning properties in animal studies and has a safe side-effect profile in children. Therefore, we evaluated the application of Sildenafil preconditioning to reduce myocardial ischaemia/reperfusion injury in children undergoing surgical ventricular septal defect (VSD) closure.

METHODS

This is a randomized, double-blind study. Children (1-17 years) undergoing VSD closure were randomized into three groups: placebo (Control group), preconditioning with 0.06 mg/kg (Sild-L group) and 0.6 mg/kg Sildenafil (Sild-H group).

PRIMARY ENDPOINT

troponin release. CK-MB, Troponin I, inflammatory response (IL-6 and TNF-α), bypass and ventilation weaning times, inotropy score and echocardiographic function were assessed. Data expressed as median (range), and a value of P < 0.05 was considered significant.

RESULTS

Thirty-nine patients were studied (13/group). Aortic cross-clamp time was similar [27 (18-85) and 27 (12-39) min] in the Control and Sild-L groups, respectively, but significantly longer [39 (20-96) min] in the Sild-H group when compared with the Control group. Area under the curve of CK-MB release was 1105 (620-1855) h ng/ml in the Control group, 1672 (564-2767) h ng/ml in the Sild-L group and was significantly higher in the Sild-H group [1695 (1252-3377) h ng/ml] when compared with the Control group. There were no significant differences in inflammatory response markers, cardiopulmonary bypass and ventilation weaning times, inotropy scores and echocardiographic function between the groups.

CONCLUSIONS

In this small study, Sildenafil failed to reduce myocardial injury in children undergoing cardiac surgery, nor does it alter cardiac function, inotropic needs or postoperative course. A subclinical increase in cardiac enzyme release after Sildenafil preconditioning cannot be excluded.

CLINICAL TRIALS REGISTRY

CTRI/2014/03/004468.

Tadalafil prevents acute heart failure with reduced ejection fraction in mice

PURPOSE

Phosphodiesterase-5 (PDE5) inhibitors were shown to exert powerful protection in various animal models of cardiomyopathy. Tadalafil is a long-acting and highly specific PDE5 inhibitor, which makes it the most attractive in its class for long-term management of patients with heart failure. We studied the effects of tadalafil in attenuating ischemic cardiomyopathy in mice.

METHODS AND RESULTS

Adult male mice underwent myocardial infarction (MI) by permanent left coronary artery ligation and were treated daily with tadalafil (1 mg/kg; ip) or volume-matched 10% DMSO for 4 weeks. Twenty four hours after coronary ligation, infarct size, measured by TTC staining, was reduced from 70.1 ± 3.1% in DMSO-treated group to 49.3 ± 2.6% with tadalafil (P < 0.05). Similarly, tadalafil treatment yielded a smaller fibrotic area (8.8 ± 2.8% of LV), assessed by Masson's trichrome staining, as compared to DMSO group (21.9 ± 3.9%, P < 0.05). Apoptosis, measured by TUNEL assay, also declined with tadalafil (2.1 ± 0.2%) as compared to DMSO (6.7 ± 0.4%, P < 0.05) at 28 days post MI. Tadalafil also attenuated the increase in cardiac hypertrophy and pulmonary edema following infarction. These parameters reflect diminished left ventricular (LV) adverse remodeling and preserved fractional shortening with tadalafil at 7 and 28 days post infarction.

CONCLUSIONS

Tadalafil attenuates ischemic cardiomyopathy in mice and preserves LV function.

The protective effects of a phosphodiesterase 5 inhibitor, sildenafil, on postresuscitation cardiac dysfunction of cardiac arrest: metabolic evidence from microdialysis

INTRODUCTION

Recent experimental and clinical studies have indicated the cardioprotective role of sildenafil during ischemia/reperfusion injury. The aim of this study was to determine, by obtaining metabolic evidence from microdialysis, if sildenafil could reduce the severity of postresuscitation myocardial dysfunction and lead to cardioprotection through beneficial effects on energy metabolism.

METHODS

Twenty-four male piglets were randomly divided into three groups: sildenafil (n = 8), saline (SA; n = 8) and sham operation (n = 8). Sildenafil pretreatment consisted of 0.5 mg/kg sildenafil administered once intraperitoneally 30 minutes prior to ventricular fibrillation (VF). The myocardial interstitial fluid (ISF) concentrations of glucose, lactate, pyruvate, glutamate and glycerol were determined by microdialysis before VF. Afterward, the piglets were subjected to 8 minutes of untreated VF followed by 15 minutes of open-chest cardiopulmonary resuscitation. ISF was collected continuously, and the experiment was terminated 24 hours after resuscitation.

RESULTS

After 8 minutes of untreated VF, the sildenafil group exhibited higher glucose and pyruvate concentrations of ISF and lower lactate and glutamate levels in comparison with the SA group, and these data reached statistical significance (P < 0.05). Advanced cardiac life support was delivered to both groups, with a 24-hour survival rate showing a promising trend in the sildenafil group (7 of 8 versus 3 of 8 survivors, P < 0.05). Compared with the SA group, the sildenafil group had a better outcome in terms of hemodynamic and oxygen metabolism parameters (P < 0.05). Myocardial tissue analysis revealed a dramatic increase in the contents of ATP, ADP and phosphocreatine in the sildenafil group versus the SA group at 24 hours after return of spontaneous circulation (ROSC; P = 0.03, P = 0.02 and P = 0.02, respectively). Furthermore, 24 hours after ROSC, the sildenafil group had marked elevations in activity of left ventricular Na(+)-K(+)-ATPase and Ca(2+)-ATPase compared with the SA group (P = 0.03, P = 0.04, respectively).

CONCLUSIONS

Sildenafil could reduce the severity of postresuscitation myocardial dysfunction, and it produced better clearance of metabolic waste in the ISF. This work might provide insights into the development of a novel strategy to treat postresuscitation myocardial dysfunction.

PDE5 inhibitors as therapeutics for heart disease, diabetes and cancer

The phosphodiesterase 5 (PDE5) inhibitors, including sildenafil (Viagra™), vardenafil (Levitra™), and tadalafil (Cialis™) have been developed for treatment of erectile dysfunction. Moreover, sildenafil and tadalafil are used for the management of pulmonary arterial hypertension in patients. Since our first report showing the cardioprotective effect of sildenafil in 2002, there has been tremendous growth of preclinical and clinical studies on the use of PDE5 inhibitors for cardiovascular diseases and cancer. Numerous animal studies have demonstrated that PDE5 inhibitors have powerful protective effect against myocardial ischemia/reperfusion (I/R) injury, doxorubicin cardiotoxicity, ischemic and diabetic cardiomyopathy, cardiac hypertrophy, Duchenne muscular dystrophy and the improvement of stem cell efficacy for myocardial repair. Mechanistically, PDE5 inhibitors protect the heart against I/R injury through increased expression of nitric oxide synthases, activation of protein kinase G (PKG), PKG-dependent hydrogen sulfide generation, and phosphorylation of glycogen synthase kinase-3β - a master switch immediately proximal to mitochondrial permeability transition pore and the end effector of cardioprotection. In addition, PDE5 inhibitors enhance the sensitivity of certain types of cancer to standard chemotherapeutic drugs, including doxorubicin. Many clinical trials with PDE5 inhibitors have focused on the potential cardiovascular and anti-cancer benefits. Despite mixed results of these clinical trials, there is a continuing strong interest by basic scientists and clinical investigators in exploring their new clinical uses. It is our hope that future new mechanistic investigations and carefully designed clinical trials would help in reaping additional benefits of PDE5 inhibitors for cardiovascular disease and cancer in patients.

Preconditioning by phosphodiesterase-5 inhibition improves therapeutic efficacy of adipose-derived stem cells following myocardial infarction in mice

The rationale of this article is enhancing the therapeutic potential of stem cells in ischemic microenvironments by novel preconditioning strategies is critical for improving cellular therapy. We tested the hypothesis that inhibition of phosphodiesterase-5 (PDE-5) with sildenafil (Viagra) or knockdown with a silencing vector in adipose-derived stem cells (ASCs) would improve their survival and enhance cardiac function following myocardial implantation in vivo. ASCs were treated with sildenafil or PDE-5 silencing vector short hairpin RNA (shRNA(PDE-5)) and subjected to simulated ischemia/reoxygenation in vitro. Both sildenafil and shRNA(PDE-5) significantly improved viability, decreased necrosis, apoptosis, and enhanced the release of growth factors, vascular endothelial growth factor (VEGF), basic fibroblast growth factor (b-FGF), and insulin-like growth factor. Inhibition of protein kinase G reversed these effects. To show the beneficial effect of preconditioned ASCs in vivo, adult male CD-1 mice underwent myocardial infarction. Preconditioned ASCs (4 × 10(5)) were directly injected intramyocardially. Preconditioned ASC-treated hearts showed consistently superior cardiac function when compared with nonpreconditioned ASCs after 4 weeks of treatment. This was associated with significantly reduced fibrosis, increased vascular density, and decreased resident myocyte apoptosis when compared with mice receiving nonpreconditioned ASCs. VEGF, b-FGF, and Angiopoietin-1 were also significantly elevated 4 weeks after cell therapy with preconditioned ASCs. We conclude that preconditioning by inhibition of PDE-5 can be a powerful novel approach to improve stem cell therapy following myocardial infarction.

Effect of sildenafil in renal ischemia/reperfusion injury in rats

PURPOSE

To evaluate the effect of sildenafil, administered prior to renal ischemia/reperfusion (I/R), by scintigraphy and histopathological evaluation in rats.

METHODS

Twenty-four rats were divided randomly into two groups. They received 0.1 ml of 99mTechnetium-etilenodicisteine intravenous, and a baseline (initial) renal scintigraphy was performed. The rats underwent 60 minutes of ischemia by left renal artery clamping. The right kidney was not manipulated. The sildenafil group (n=12) received orally 1 mg/kg of sildenafil suspension 60 minutes before ischemia. Treatment with saline 0.9% in the control group (n=12). Half of the rats was assessed after 24 hours and half after seven days I/R, with new renal scintigraphy to study differential function. After euthanasia, kidneys were removed and subjected to histopathological examination. For statistical evaluation, Student t and Mann-Whitney tests were used.

RESULTS

In the control group rats, the left kidneys had significant functional deficit, seven days after I/R, whose scintigraphic pattern was consistent with acute tubular necrosis, compared with the initial scintigraphy (p<0.05). Sildenafil treatment resulted in better differential function of the left kidneys 24h after reperfusion, compared with controls. Histopathologically, the left kidney of control rats (24 hours after I/R) showed a higher degree of cellular necrosis when compared with the sildenafil treated rats (p<0.05).

CONCLUSION

Sildenafil had a protective effect in rat kidneys subjected to normothermic I/R, demonstrated by scintigraphy and histomorphometry.

Mammalian Cyclic Nucleotide Phosphodiesterases: Molecular Mechanisms and Physiological Functions

The superfamily of cyclic nucleotide (cN) phosphodiesterases (PDEs) is comprised of 11 families of enzymes. PDEs break down cAMP and/or cGMP and are major determinants of cellular cN levels and, consequently, the actions of cN-signaling pathways. PDEs exhibit a range of catalytic efficiencies for breakdown of cAMP and/or cGMP and are regulated by myriad processes including phosphorylation, cN binding to allosteric GAF domains, changes in expression levels, interaction with regulatory or anchoring proteins, and reversible translocation among subcellular compartments. Selective PDE inhibitors are currently in clinical use for treatment of erectile dysfunction, pulmonary hypertension, intermittent claudication, and chronic pulmonary obstructive disease; many new inhibitors are being developed for treatment of these and other maladies. Recently reported x-ray crystallographic structures have defined features that provide for specificity for cAMP or cGMP in PDE catalytic sites or their GAF domains, as well as mechanisms involved in catalysis, oligomerization, autoinhibition, and interactions with inhibitors. In addition, major advances have been made in understanding the physiological impact and the biochemical basis for selective localization and/or recruitment of specific PDE isoenzymes to particular subcellular compartments. The many recent advances in understanding PDE structures, functions, and physiological actions are discussed in this review.

Comparison of the effects of propofol and midazolam on inflammation and oxidase stress in children with congenital heart disease undergoing cardiac surgery

PURPOSE

To investigate and compare the effects of propofol and midazolam on inflammation and oxidase stress in children with congenital heart disease undergoing cardiac surgery.

MATERIALS AND METHODS

Thirty-two ASA class I-II children with congenital heart disease undergoing cardiac surgery were randomly divided into two groups: propofol combined with low dose fentanyl (PF group, n = 16) and midazolam combined with low dose fentanyl (MF group, n = 16). Tracheal extubation time and length of Intensive Care Unit (ICU) stay were recorded. Blood samples were taken before operation (T₀), at 2 h after release of the aorta cross-clamp (T₃) and at 24 h after operation (T₄) to measure interleukin 6 (IL-6), IL-8, superoxide dismutase (SOD) and malondialdehyde (MDA) levels. Myocardium samples were collected at 10-20 min after aorta cross-clamp (T₁) and at 10-20 min after the release of the aorta cross-clamp (T₂) to detect heme oxygenase-1 (HO-1) expression.

RESULTS

Tracheal extubation time and length of ICU stay in PF group were significantly shorter than those of the MF group (p < 0.05, respectively). After cardiopulmonary bypass, IL-6, IL-8 and MDA levels were significantly increased, and the SOD level was significantly reduced in both two groups, but PF group exhibited lower IL-6, IL-8 and MDA levels and higher SOD levels than the MF group (p < 0.05, respectively). The HO-1 expression in the PF group was significantly higher than that in MF group at the corresponding time points (p < 0.05, respectively).

CONCLUSION

Propofol is superior to midazolam in reducing inflammation and oxidase stress and in improving post-operation recovery in children with congenital heart disease undergoing cardiac surgery.

Sildenafil promotes smooth muscle preservation and ameliorates fibrosis through modulation of extracellular matrix and tissue growth factor gene expression after bilateral cavernosal nerve resection in the rat

INTRODUCTION

It has been shown that phosphodiesterase type 5 (PDE5) inhibitors preserve smooth muscle (SM) content and ameliorate the fibrotic degeneration normally seen in the corpora cavernosa after bilateral cavernosal nerve resection (BCNR). However, the downstream mechanisms by which these drugs protect the corpora cavernosa remain poorly understood.

AIM

To provide insight into the mechanism, we aimed to determine the gene expression profile of angiogenesis-related pathways within the penile tissue after BCNR with or without continuous sildenafil (SIL) treatment.

METHODS

Five-month-old Fisher rats were subjected to BCNR or sham operation and treated with or without SIL (20 mg/kg/BW drinking water) for 3 days or 45 days (N = 8 rats per group). Total RNAs isolated from the denuded penile shaft and prostate were subjected to reverse transcription and to angiogenesis real-time-polymerase chain reaction arrays (84 genes). Changes in protein expression of selected genes such as epiregulin (EREG) and connective tissue growth factor (CTGF) were corroborated by Western blot and immunohistochemistry.

MAIN OUTCOMES MEASURES

Genes modulated by BCNR and SIL treatment.

RESULTS

A decreased expression of genes related to SM growth factors such as EREG, platelet-derived growth factor (PDGF), extracellular matrix regulators such as metalloproteinases 3 and 9, endothelial growth factors, together with an upregulation of pro-fibrotic genes such as CTGF and transforming growth factor beta 2 were found at both time points after BCNR. SIL treatment reversed this process by upregulating endothelial and SM growth factors and downregulating pro-fibrotic factors. SIL did not affect the expression of EREG, VEGF, and PDGF in the ventral prostate of BCNR animals.

CONCLUSIONS

SIL treatment after BCNR activates genes related to SM preservation and downregulates genes related to fibrosis in the corpora cavernosa. These results provide a mechanistic justification for the use of SIL and other PDE5 inhibitors as protective therapy against corporal SM loss and fibrosis after radical prostatectomy.

Phospholemman Ser69 phosphorylation contributes to sildenafil-induced cardioprotection against reperfusion injury

The phosphodiesterase type-5 inhibitor sildenafil has powerful cardioprotective effects against ischemia-reperfusion injury. PKG-mediated signaling has been implicated in this protection, although the mechanism and the downstream targets of this kinase remain to be fully elucidated. In this study we assessed the role of phospholemman (PLM) phosphorylation, which activates the Na⁺/K⁺-ATPase, in cardioprotection afforded by sildenafil administered during reperfusion. Isolated perfused mouse hearts were optimally protected against infarction (indexed by tetrazolium staining) by 0.1 μM sildenafil treatment during the first 10 min of reperfusion. Extended sildenafil treatment (30, 60, or 120 min at reperfusion) did not alter the degree of protection provided. This protection was PKG dependent, since it was blocked by KT-5823. Western blot analysis using phosphospecific antibodies to PLM showed that sildenafil at reperfusion did not modulate PLM Ser63 or Ser68 phosphorylation but significantly increased Ser69 phosphorylation. The treatment of isolated rat ventricular myocytes with sildenafil or 8-bromo-cGMP (PKG agonist) enhanced PLM Ser69 phosphorylation, which was bisindolylmaleimide (PKC inhibitor) sensitive. Patch-clamp studies showed that sildenafil treatment also activated the Na⁺/K⁺-ATPase, which is anticipated in light of PLM Ser69 phosphorylation. Na⁺/K⁺-ATPase activation during reperfusion would attenuate Na⁺ overload at this time, providing a molecular explanation of how sildenafil guards against injury at this time. Indeed, using flame photometry and rubidium uptake into isolated mouse hearts, we found that sildenafil enhanced Na⁺/K⁺-ATPase activity during reperfusion. In this study we provide a molecular explanation of how sildenafil guards against myocardial injury during postischemic reperfusion.

PDE5A suppression of acute beta-adrenergic activation requires modulation of myocyte beta-3 signaling coupled to PKG-mediated troponin I phosphorylation

Phosphodiesterase type 5A (PDE5A) inhibitors acutely suppress beta-adrenergic receptor (beta-AR) stimulation in left ventricular myocytes and hearts. This modulation requires cyclic GMP synthesis via nitric oxide synthase (NOS)-NO stimulation, but upstream and downstream mechanisms remain un-defined. To determine this, adult cardiac myocytes from genetically engineered mice and controls were studied by video microscopy to assess sarcomere shortening (SS) and fura2-AM fluorescence to measure calcium transients (CaT). Enhanced SS from isoproterenol (ISO, 10 nM) was suppressed >or=50% by the PDE5A inhibitor sildenafil (SIL, 1 microM), without altering CaT. This regulation was unaltered despite co-inhibition of either the cGMP-stimulated cAMP-esterase PDE2 (Bay 60-7550), or cGMP-inhibited cAMP-esterase PDE3 (cilostamide). Thus, the SIL response could not be ascribed to cGMP interaction with alternative PDEs. However, genetic deletion (or pharmacologic blockade) of beta3-ARs, which couple to NOS signaling, fully prevented SIL modulation of ISO-stimulated SS. Importantly, both PDE5A protein expression and activity were similar in beta3-AR knockout (beta3-AR(-/-)) myocytes as in controls. Downstream, cGMP stimulates protein kinase G (PKG), and we found contractile modulation by SIL required PKG activation and enhanced TnI phosphorylation at S23, S24. Myocytes expressing the slow skeletal TnI isoform which lacks these sites displayed no modulation of ISO responses by SIL. Non-equilibrium isoelectric focusing gel electrophoresis showed SIL increased TnI phosphorylation above that from concomitant ISO in control but not beta3-AR(-/-) myocytes. These data support a cascade involving beta3-AR stimulation, and subsequent PKG-dependent TnI S23, S24 phosphorylation as primary factors underlying the capacity of acute PDE5A inhibition to blunt myocardial beta-adrenergic stimulation.

Pivotal effects of phosphodiesterase inhibitors on myocyte contractility and viability in normal and ischemic hearts

Phosphodiesterases (PDEs) are enzymes that degrade cellular cAMP and cGMP and are thus essential for regulating the cyclic nucleotides. At least 11 families of PDEs have been identified, each with a distinctive structure, activity, expression, and tissue distribution. The PDE type-3, -4, and -5 (PDE3, PDE4, PDE5) are localized to specific regions of the cardiomyocyte, such as the sarcoplasmic reticulum and Z-disc, where they are likely to influence cAMP/cGMP signaling to the end effectors of contractility. Several PDE inhibitors exhibit remarkable hemodynamic and inotropic properties that may be valuable to clinical practice. In particular, PDE3 inhibitors have potent cardiotonic effects that can be used for short-term inotropic support, especially in situations where adrenergic stimulation is insufficient. Most relevant to this review, PDE inhibitors have also been found to have cytoprotective effects in the heart. For example, PDE3 inhibitors have been shown to be cardioprotective when given before ischemic attack, whereas PDE5 inhibitors, which include three widely used erectile dysfunction drugs (sildenafil, vardenafil and tadalafil), can induce remarkable cardioprotection when administered either prior to ischemia or upon reperfusion. This article provides an overview of the current laboratory and clinical evidence, as well as the cellular mechanisms by which the inhibitors of PDE3, PDE4 and PDE5 exert their beneficial effects on normal and ischemic hearts. It seems that PDE inhibitors hold great promise as clinically applicable agents that can improve cardiac performance and cell survival under critical situations, such as ischemic heart attack, cardiopulmonary bypass surgery, and heart failure.

Validation of brain extracellular glycerol as an indicator of cellular membrane damage due to free radical activity after traumatic brain injury

Following severe traumatic brain injury (TBI), increasing oxygen delivery to the brain has been advocated as a useful strategy to reverse mitochondrial dysfunction and improve neurological outcome. However, this might also promote overproduction of free radicals, responsible for lipid peroxidation and hence brain cell damage. Therefore, a method for monitoring this potential adverse effect in humans is desirable. Glycerol, an end product of phospholipid breakdown, easily detectable in the human brain by means of microdialysis, might represent a reliable indicator of free radical-induced cell membrane damage. Brain microdialysates were collected from 24 adult male Sprague-Dawley rats over a 3-hour period following sham operation (n=6), chemical brain injury via administration of Fenton's reagent (n=6), a powerful hydroxyl radical generator, and lateral fluid percussion injury (FPI; n=12). In the FPI animals, post-traumatic i.v. administration of either normal saline or the free radical scavenger Tempol (10 mg/kg, followed by an infusion of 30 mg/kg/h over 3 h) was carried out to evaluate the effect of blockade of free radical generation. Samples were analyzed for the presence of glycerol and the marker of hydroxyl radical (OH.) by generation of 2,3-DHBA (dihydroxybenzoic acid). Brain tissue staining with TTC (2,3,5-triphenyltetrazoium chloride) was performed for lesion size assessment. Rats subjected to either Fenton's reagent administration or FPI exhibited significantly higher levels of glycerol as compared with shams (p=0.05). However, when the FPI was followed by Tempol administration, concentration of both glycerol and 2,3-DHBA decreased significantly (p=0.05). Furthermore, TCC staining revealed a significant reduction of secondary brain tissue damage in Tempol-treated animals (p=0.05). Our data suggest that injury-induced increases in microdialysate glycerol levels are a valid indicator of free radical activity, and their amelioration following Tempol treatment accords with less histological damage in response to FPI.

Sildenafil-mediated neovascularization and protection against myocardial ischaemia reperfusion injury in rats: role of VEGF/angiopoietin-1

Sildenafil citrate (SC), a drug for erectile dysfunction, is now emerging as a cardiopulmonary drug. Our study aimed to determine a novel role of sildenafil on cardioprotection through stimulating angiogenesis during ischaemia (I) reperfusion (R) at both capillary and arteriolar levels and to examine the role of vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang-1) in this mechanistic effect. Rats were divided into: control sham (CS), sildenafil sham (SS), control + IR (CIR) and sildenafil + IR (SIR). Rats were given 0.7 mg/kg, (i.v) of SC or saline 30 min. before occlusion of left anterior descending artery followed by reperfusion (R). Sildenafil treatment increased capillary and arteriolar density followed by increased blood flow (2-fold) compared to control. Treatment with sildenafil demonstrated increased VEGF and Ang-1 mRNA after early reperfusion. PCR data were validated by Western blot analysis. Significant reduction in infarct size, cardiomyocyte and endothelial apoptosis were observed in SC-treated rats. Increased phosphorylation of Akt, eNOS and expression of anti-apoptotic protein Bcl-2, and thioredoxin, hemeoxygenase-1 were observed in SC-treated rats. Echocardiography demonstrated increased fractional shortening and ejection fraction following 45 days of reperfusion in the treatment group. Stress testing with dobutamine infusion and echocardiogram revealed increased contractile reserve in the treatment group. Our study demonstrated for the first time a strong additional therapeutic potential of sildenafil by up-regulating VEGF and Ang-1 system, probably by stimulating a cascade of events leading to neovascularization and conferring myocardial protection in in vivo I/R rat model.

Sildenafil citrate diminishes microalbuminuria and the percentage of A1c in male patients with type 2 diabetes

Sildenafil citrate has shown to display beneficial cardiovascular effects, suggesting that it may have other systemic benefits involving the endothelium. There is little data regarding the long-term use of this drug and the effects of this on different organs.

OBJECTIVE

The primary aim of this study was to determine whether sildenafil citrate diminishes concentrations of microalbuminuria and percentage of A1c in patients with type 2 diabetes.

DESIGN

A double-blind, randomized, controlled trial in 40 male patients, age 35-50, with type 2 diabetes. Subjects received sildenafil citrate 50 mg daily (n=20) or placebo (n=20) for 30 days. Levels of hs-CRP, microalbuminuria, homocysteine, A1c and erectile function were measured at baseline and to the end of the study.

RESULTS

Men that received sildenafil citrate displayed a significant decrease in the microalbuminuria concentrations (p<0.01) versus baseline, (p=0.02) versus placebo and A1c (p<0.01) versus baseline, (p=0.01) versus placebo. In addition, we observed a significant increase in the total IIEF score after 30 days of treatment (p<0.01) versus baseline, (p<0.01) versus placebo.

CONCLUSIONS

The administration of 50mg of sildenafil citrate for 30 consecutive days diminishes microalbuminuria and the percentage of A1c in patients with type 2 diabetes.

Cyclic GMP and protein kinase-G in myocardial ischaemia-reperfusion: opportunities and obstacles for survival signaling

It is clear that multiple signalling pathways regulate the critical balance between cell death and survival in myocardial ischaemia-reperfusion. Recent attention has focused on the activation of survival or salvage kinases, particularly during reperfusion, as a common mechanism of many cardioprotective interventions. The phosphatidyl inositol 3'-hydroxy kinase/Akt complex (PI3K/Akt) and p42/p44 mitogen-activated protein kinase cascades have been widely promoted in this respect but the cyclic guanosine 3',5'-monophosphate/cGMP-dependent protein kinase (cGMP/PKG) signal transduction cassette has been less systematically investigated as a survival cascade. We propose that activation of the cGMP/PKG signalling pathway, following activation of soluble or particulate guanylate cyclases, may play a pivotal role in survival signalling in ischaemia-reperfusion, especially in the classical preconditioning, delayed preconditioning and postconditioning paradigms. The resurgence of interest in reperfusion injury, largely as a result of postconditioning-related research, has confirmed that the cGMP/PKG pathway is a pivotal salvage mechanism in reperfusion. Numerous studies suggest that the infarct-limiting effects of preconditioning and postconditioning, exogenously donated nitric oxide (NO), natriuretic peptides, phosphodiesterase inhibitors, and other diverse drugs and mediators such as HMG co-A reductase inhibitors (statins), Rho-kinase inhibitors and adrenomedullin, whether given before and during ischaemia, or specifically at the onset of reperfusion, may be mediated by activation or enhancement of the cGMP pathway, either directly or indirectly via endogenous NO generation downstream of PI3K/Akt. Putative mechanisms of protection include PKG regulation of Ca(2+) homeostasis through the modification of sarcoplasmic reticulum Ca(2+) uptake mechanisms, and PKG-induced opening of ATP-sensitive K(+) channels during ischaemia and/or reperfusion. At present, significant technical obstacles in defining the precise roles played by cGMP/PKG signalling include the heavy reliance on pharmacological PKG inhibitors of uncertain selectivity, difficulties in determining PKG activity in intact tissue, and the growing recognition that intracellular compartmentalisation of the cGMP pool may contribute markedly to the nucleotide's biological actions and biochemical determination. Overall, the body of experimental evidence suggests that cGMP/PKG survival signalling ameliorates irreversible injury associated with ischaemia-reperfusion and may be a tractable therapeutic target.

Cardiovascular protection with sildenafil following chronic inhibition of nitric oxide synthase

During the past 18 years, sildenafil has evolved from a potential anti-angina drug to an on-demand treatment for erectile dysfunction and more recently to a new orally active treatment for pulmonary hypertension. Recent studies suggest that the drug has powerful cardioprotective effect against ischemia/reperfusion injury, doxorubicin-induced cardiomyopathy and anti-hypertensive effect induced by chronic inhibition of nitric oxide synthase in animals. Based on several recent basic and clinical studies, it is clear that sildenafil and other clinically approved type-5 phosphodiesterase-5 inhibitors including vardenafil and tadalafil will eventually be developed for several cardiovascular indications including essential hypertension, endothelial dysfunction, ischemia/reperfusion injury, myocardial infarction, ventricular remodeling and heart failure.

Systemic administration of phosphodiesterase V inhibitor, sildenafil citrate, for attenuation of cerebral vasospasm after experimental subarachnoid hemorrhage

OBJECTIVE

One of the phosphodiesterase isoenzymes, Type V (PDE V), specifically hydrolyzes cyclic guanosine monophosphate to cause vasoconstriction. This study analyses the effect of PDE V inhibition with sildenafil citrate (SC) on cerebral vasospasm and its effect on apoptotic changes of the vascular endothelium.

METHODS

Twenty-four rabbits were divided into four groups. The first group was composed of sham-surgery animals. The second group was the subarachnoid hemorrhage (SAH) group, in which cerebral vasospasm was induced. In the third group, sham-surgery rabbits were treated with SC. In the fourth group, animals were treated with SC after SAH. SC was administered for 48 hours, 0.7 mg/kg, three times per day in Groups 3 and 4. Basilar artery lumen circumferences were measured in all groups by computerized image analysis. The terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end-labeling (TUNEL) method was used to evaluate the rate of apoptosis between SAH and SC-treated SAH groups. Results were compared by analysis of variance and paired t tests, and P values less than 0.05 were considered significant.

RESULTS

Basilar artery circumferences between groups were significantly different (P < 0.001). SC (0.7 mg/kg, three times per d) significantly dilated the basilar arteries in both the sham-surgery group (2370 +/- 233 microm; P = 0.039) and the SAH group (2142 +/- 195 microm; P = 0.006) after 48 hours of treatment. The TUNEL method for apoptosis revealed that actual numbers of the apoptotic endothelial cells per cross section after SAH in the control (no treatment) (73 +/- 2) and SC-treated (0.7 mg/kg) groups(76 +/- 3) were not significantly different (P > 0.05).

CONCLUSION

The vasodilatory effect of SC was observed to be significant on normal cerebral vessels and after SAH-induced vasospasm. SC did not prevent apoptosis of the endothelium in our study, which suggests that prevention of apoptosis is not necessary in the treatment of cerebral vasospasm.

Hemodynamic changes during acute elevation of intra-abdominal pressure in rabbits

BACKGROUND

The intra-abdominal pressure (IAP) may be increased during pneumoperitoneum for minimally invasive surgery, after high tension repairs of congenital abdominal wall defects, major abdominal surgery, liver transplantation, abdominal trauma, peritonitis or ileus. The aim of this study was to investigate hemodynamic changes during elevation of IAP using an experimental setting, which mirrors anatomical and physiological conditions of neonates and small infants as closely as possible.

METHODS

In five fasted, anesthetized, mechanically ventilated and multicatheterized New Zealand rabbits, the IAP was gradually increased by intra-abdominal infusion of normal saline (total volume 1000 ml). At baseline and after each infusion of 100 ml normal saline cardiac output (CO, transcardiopulmonary thermodilution), pressure in the superior (SVCP) and inferior vena cava (IVCP), mean arterial pressure (MAP), peak airway pressure (PAP) and IAP was recorded.

RESULTS

During the study, IAP, SVCP and IVCP increased significantly. IVCP was significantly higher than SVCP from timepoint 200 ml to study end. After abdominal decompression IAP, SVCP and IVCP decreased to baseline levels. Changes in MAP were not significant. CO increased significantly from baseline to timepoint 200 ml (peak value), remained nearly constant until timepoint 800 ml and decreased thereafter until the abdominal infusion ceased. After abdominal decompression CO returned to baseline level. SVCP, IVCP and PAP correlated significantly with IAP (SVCP, r = 0.73; IVCP, r = 0.97; PAP, r = 0.94; P < 0.0001).

CONCLUSIONS

The hemodynamic changes caused by increased IAP cannot be recognized by routine monitoring of arterial blood pressure and transcutaneous oxygen saturation. The increase in central venous pressure may be misinterpreted as an elevation of cardiac preload. One major effect of a prolonged increase in IAP is a decreased CO.

Reactive oxygen species and erectile dysfunction: possible role of NADPH oxidase

Erectile dysfunction (ED) is a widespread condition, the incidence of which is increasing globally. ED is also indicative of underlying vasculopathy and represents a predictor of more serious cardiovascular disorders. Understanding the aetiology of ED may therefore provide invaluable pointers to the pathobiology of other cardiovascular diseases (CVDs) and syndromes. It follows, too, that therapeutic interventions that are successful in treating ED may, ipso facto, be effective in treating the early stages of conditions that include atherosclerosis, angina, plaque rupture and diabetic angiopathy. One common pathological denominator in both CVD and ED is oxidative stress, that is, the overproduction of reactive oxygen species (ROS), in particular, superoxide (O(2)(*-)) and hydrogen peroxide (H(2)O(2)). In this review, therefore, we consider the aetiology and pathobiology of O(2)(*-) in promoting ED and focus on NADPH oxidase as an inducible source of O(2)(*-) and H(2)O(2). Therapeutic strategies aimed at reducing oxidative stress to improve erectile function are also discussed.

Cyclic GMP-dependent protein kinase Ialpha attenuates necrosis and apoptosis following ischemia/reoxygenation in adult cardiomyocyte

Cyclic GMP-dependent protein kinases protein kinase G (PKG) Ialpha and PKGIbeta are major mediators of cGMP signaling in the cardiovascular system. PKGIalpha is present in the heart, although its role in protection against ischemia/reperfusion injury is not known. We investigated the direct effect of PKGIalpha against necrosis and apoptosis following simulated ischemia (SI) and reoxygenation (RO) in cardiomyocytes. Adult rat cardiomyocytes were infected with adenoviral vectors containing hPKGIalpha or catalytically inactive mutant hPKGIalphaK390A. After 24 h, the cells were subjected to 90 min of SI and 2 h RO for necrosis (trypan blue exclusion and lactate dehydrogenase release) or 18 h RO for apoptosis studies. To evaluate the role of K(ATP) channels, subgroups of cells were treated with 5-hydroxydecanoate (100 microm), HMR1098 (30 microm), or glibenclamide (50 microm), the respective blockers of mitochondrial, sarcolemmal, or both types of K(ATP) channels prior to SI. The necrosis observed in 33.7 +/- 1.6% of total myocytes in the SI-RO control group was reduced to 18.6 +/- 0.8% by PKGIalpha (mean +/- S.E., n = 7, p < 0.001). The apoptosis observed in 17.9 +/- 1.3% of total myocytes in the SI-RO control group was reduced to 6.0 +/- 0.6% by PKGIalpha (mean +/- S.E., n = 7, p < 0.001). In addition, PKGIalpha inhibited the activation of caspase-3 after SI-RO in myocytes. Myocytes infected with the inactive PKGIalphaK390A mutant showed no protection. PKGIalpha enhanced phosphorylation of Akt, ERK1/2, and JNK, increased Bcl-2, inducible nitric-oxide synthase, endothelial nitric-oxide synthase, and decreased Bax expression. 5-Hydroxydecanoate and glibenclamide abolished PKGIalpha-mediated protection against necrosis and apoptosis. However, HMR1098, had no effect. A scavenger of reactive oxygen species, as well as inhibitors of phosphatidylinositol 3-kinase, ERK, JNK1, and NOS, also blocked PKGIalpha-mediated protection against necrosis and apoptosis. These results show that opening of mitochondrial K(ATP) channels and generation of reactive oxygen species, in association with phosphorylation of Akt, ERK, and JNK, and increased expression of NOS and Bcl-2, play an essential role in the protective effect of PKGIalpha.

Haemodynamic, acid–base and blood volume changes during prolonged low pressure pneumoperitoneum in rabbits

BACKGROUND

The anaesthetic management of small infants during advanced laparoscopic surgery can be complicated by the major pathophysiological effects of increased intra-abdominal pressure. In this study haemodynamic, acid-base and blood volume changes were investigated during pneumoperitoneum in a small animal model.

METHODS

Ten fasted, anaesthetized, mechanically ventilated and multi-catheterized New Zealand rabbits were randomized to carbon dioxide pneumoperitoneum (PP, duration 210 min, pressure 8 mm Hg) or control group. Cardiac index was determined using trans-cardiopulmonary thermodilution and total blood volume was measured by thermal-dye dilution with indocyanine green using a fibreoptic monitor system.

RESULTS

In PP cardiac index (CI), central venous oxygen saturation (Scv(O(2))), total blood volume (TBV) and base excess (BE) decreased significantly during the study whereas all variables remained constant in the control group. After release of PP the measured variables did not return to baseline within 30 min [PP, baseline vs study end: CI 108 (22) vs 85 (14) ml kg(-1) min(-1), Scv(O(2)) 81.4 (8.9) vs 56.7 (9.8)%, TBV 318 (69) vs 181 (54) ml, BE -1.9 (2.7) vs -8.7 (1.8) mmol litre(-1); P<0.01].

CONCLUSION

Our animal model suggests that a decrease in CI, metabolic acidosis and hypovolaemia could occur after prolonged low pressure pneumoperitoneum in small infants, which is possibly not detectable by the standard monitor setting. Therefore, the routine use of an extended monitoring including measurement of central venous oxygen saturation and acid-base parameters should be considered during and soon after operation, when pneumoperitoneum will last longer than 2 h.

Phosphodiesterase type 5 is not upregulated by tadalafil in cultures of human penile cells

OBJECTIVE

Tadalafil, a long-acting phosphodiesterase type 5 (PDE5) inhibitor, improves the erectile response by inhibiting cyclic guanosine monophosphate (cGMP) breakdown. Sustained higher levels of cGMP may hypothetically upregulate PDE5 expression and/or activity and lead to tachyphylaxis. We have investigated whether PDE5 upregulation occurs in vitro in cultures of human penile cells subjected to long-term incubation with increasing concentrations of tadalafil in the presence of a nitric oxide (NO) donor.

METHODS

Human corpora cavernosa smooth muscle cells (CSMC) and tunica albuginea fibroblasts (TAF) primary cultures were characterized by immunocytochemistry and Western blot, and incubated with graded concentrations of tadalafil for 14 days, adding S-nitroso-N-acetyl penicillamine (SNAP) as an NO donor for the last 24 hours or at time zero, and cGMP levels were measured. Incubations were repeated for 7, 10, and 14 days, in the presence of SNAP, and PDE5 was estimated by Western blot, and at 14 days, by immunocytochemistry combined with quantitative image analysis, and by real-time reverse transcriptase polymerase chain reaction (RT-PCR). Constructs of the human PDE5A promoter expressing luciferase were cloned and transfected into CSMC, and promoter activation by 8-deoxybromo-cGMP (8-Br-cGMP) was measured by luminometry.

RESULTS

Incubations of CSMC with SNAP and tadalafil up to 14 days did not upregulate PDE5 mRNA or protein levels. With TAF, PDE5 protein was also not upregulated despite a slight increase in mRNA levels. PDE5 enzyme activity was unaffected by tadalafil in either CSMC or TAF. No upregulation of the PDE5 promoter was observed with up to 2 mM 8-Br-cGMP.

CONCLUSIONS

Long-term incubation of human penile cells with tadalafil at concentrations above the in vitro IC50, and around the in vivo Cmax utilized in the clinical setting, did not upregulate PDE5A expression nor decrease cGMP levels. These data suggest that PDE5 upregulation is unlikely to occur in vivo on long-term tadalafil treatment.

Enhanced Cardioprotection Against Ischemia-Reperfusion Injury with Combining Sildenafil with Low-Dose Atorvastatin

PURPOSE

Both ATV and SL reduce myocardial infarct size (IS) by enhancing expression and activity of NOS isoforms. We investigated whether atorvastatin (ATV) and sildenafil (SL) have synergistic effects on myocardial infarct size (IS) reduction and enhancing nitric oxide synthase (NOS) expression.

METHOD

Rats were randomized to nine groups: ATV-1 (1 mg/kg/d); ATV-10 (10 mg/kg/d); SL-0.7 (0.7 mg/kg); SL-1 (1 mg/kg); ATV-1 + SL-0.7; water alone (controls); 1400W (iNOS inhibitor; 1 mg/kg); ATV-10 + 1400W; and ATV-1 + SL-0.7 + 1400W. ATV was administered orally for 3 days. SL was administered intraperitoneally 18 h before surgery and 1400W intravenously 15 min before surgery. Rats either underwent 30 min ischemia-4 h reperfusion or the hearts were explanted for immunoblotting and enzyme activity tests without being exposed to ischemia.

RESULTS

IS (% risk area, mean +/- SEM) was smaller in the ATV-10 (13 +/- 1%), SL-1 (11 +/- 2%), SL-0.7 (18 +/- 2%) and ATV-1 + SL-0.7 (9 +/- 1%) groups as compared with controls (34 +/- 3%; P < 0.001), whereas ATV-1 had no effect (29 +/- 2%). ATV-1 + SL-0.7 (9 +/- 1%) reduced IS more than SL-0.7 alone (p = 0.012). 1400W abrogated the protective effect of ATV-10 (35 +/- 3%) and ATV-1 + SL-0.7 (34 +/- 1%). SL-0.7 and ATV-10 increased phosphorylated endothelial (P-eNOS; 210 +/- 2.5% and 220 +/- 8%) and inducible (iNOS; 151 +/- 1% and 154 +/- 1%) NOS expression, whereas ATV-1 did not. These changes were significantly enhanced by ATV-1 + SL-0.7 (P-eNOS, 256 +/- 2%, iNOS 195 +/- 1%). SL-1 increased P-eNOS (311 +/- 22%) and iNOS (185 +/- 1%) concentrations.

CONCLUSIONS

Combining low-dose ATV with SL augments the IS limiting effects through enhanced P-eNOS and iNOS expression.

Pharmacological preconditioning with sildenafil: Basic mechanisms and clinical implications

The phosphodiesterase type-5 (PDE5) inhibitor, sildenafil, is the first drug developed for treatment of erectile dysfunction in patients. Experimental data in animals show that sildenafil has a preconditioning-like cardioprotective effect against ischemia/reperfusion injury in the intact heart. Mechanistic studies suggest that sildenafil exerts cardioprotection through NO generated from eNOS/iNOS, activation of protein kinase C/ERK signaling and opening of mitochondrial ATP-sensitive potassium channels. Additional studies show that the drug attenuates cell death resulting from necrosis and apoptosis, and increases the Bcl2/Bax ratio through NO signaling in adult cardiomyocytes. Emerging new data also suggest that sildenafil may be used clinically for treatment of pulmonary arterial hypertension and endothelial dysfunction. Future demonstration of the cardioprotective effect in patients with the relatively safe and effective FDA-approved PDE5 inhibitors such as sildenafil could have an enormous impact on bringing the long-studied phenomenon of ischemic and pharmacologic preconditioning to the clinical forefront.