11C-Radiosynthesis and preliminary human evaluation of the disposition of the ACE inhibitor [11C]zofenoprilat

Efficacy of Zofenopril Alone or in Combination with Hydrochlorothiazide in Patients with Kidney Dysfunction

Hypertension and kidney disease often coexist, further increasing the risk of future cardiovascular events. Treatment of hypertensive adults with an angiotensin converting enzyme inhibitor in case of concomitant kidney disease may slow disease progression. The third-generation liphophilic angiotensin converting enzyme inhibitor zofenopril, administered alone or combined with a thiazide diuretic, has proved to be effective in lowering blood pressure in hypertensive patients and to reduce the risk of fatal and non-fatal events in post-acute myocardial infarction and heart failure. In almost three-hundred hypertensive patients with kidney impairment zofenopril administered for 12 weeks showed a similar blood pressure-lowering effect irrespective of the stage of the disease, with larger effects in combination with a thiazide diuretic, particularly in patients with slightly or moderately impaired kidney function. In animal models, zofenopril produced a significant and long-lasting inhibition of kidney angiotensin converting enzyme inhibitor and prevented kidney morphological and functional alterations following kidney ischemia-reperfusion injury. Treatment of hypertensive patients for 18 weeks with a combination of zofenopril 30 mg and hydrochlorothiazide 12.5 mg resulted in a reduction in albumin creatinine ratio of 8.4 mg/g (49.6% reduction from baseline values) and no changes in glomerular filtration rate, variations in line with those obtained in the control group treated with a combination of irbesartan 150 mg and hydrochlorothiazide 12.5 mg. Thus, some preliminary evidence exists to support that relatively long-term treatment with the angiotensin converting enzyme inhibitor zofenopril alone or combined with hydrochlorothiazide is effective in controlling blood pressure and may confer some kidney protection due to ACE inhibition properties.

Molecular imaging of cardiac remodelling after myocardial infarction

Myocardial infarction and subsequent heart failure is a major health burden associated with significant mortality and morbidity in western societies. The ability of cardiac tissue to recover after myocardial infarction is affected by numerous complex cellular and molecular pathways. Unbalance or failure of these pathways can lead to adverse remodelling of the heart and poor prognosis. Current clinical cardiac imaging modalities assess anatomy, perfusion, function, and viability of the myocardium, yet do not offer any insight into the specific molecular pathways involved in the repair process. Novel imaging techniques allow visualisation of these molecular processes and may have significant diagnostic and prognostic values, which could aid clinical management. Single photon-emission tomography, positron-emission tomography, and magnetic resonance imaging are used to visualise various aspects of these molecular processes. Imaging probes are usually attached to radioisotopes or paramagnetic nanoparticles to specifically target biological processes such as: apoptosis, necrosis, inflammation, angiogenesis, and scar formation. Although the results from preclinical studies are promising, translating this work to a clinical environment in a valuable and cost-effective way is extremely challenging. Extensive evaluation evidence of diagnostic and prognostic values in multi-centre clinical trials is still required.

Cardiac molecular imaging to track left ventricular remodeling in heart failure

Cardiac left ventricular (LV) remodeling is the final common pathway of most primary cardiovascular diseases that manifest clinically as heart failure (HF). The more advanced the systolic HF and LV dysfunction, the worse the prognosis. The knowledge of the molecular, cellular, and neurohormonal mechanisms that lead to myocardial dysfunction and symptomatic HF has expanded rapidly and has allowed sophisticated approaches to understanding and management of the disease. New therapeutic targets for pharmacologic intervention in HF have also been identified through discovery of novel cellular and molecular components of membrane-bound receptor-mediated intracellular signal transduction cascades. Despite all advances, however, the prognosis of systolic HF has remained poor in general. This is, at least in part, related to the (1) relatively late institution of treatment due to reliance on gross functional and structural abnormalities that define the "heart failure phenotype" clinically; (2) remarkable genetic-based interindividual variations in the contribution of each of the many molecular components of cardiac remodeling; and (3) inability to monitor the activity of individual pathways to cardiac remodeling in order to estimate the potential benefits of pharmacologic agents, monitor the need for dose titration, and minimize side effects. Imaging of the recognized ultrastructural components of cardiac remodeling can allow redefinition of heart failure based on its "molecular phenotype," and provide a guide to implementation of "personalized" and "evidence-based" evaluation, treatment, and longitudinal monitoring of the disease beyond what is currently available through randomized controlled clinical trials.

Antioxidant and Cardioprotective Properties of the Sulphydryl Angiotensinconverting Enzyme Inhibitor Zofenopril

Zofenopril, a new potent sulphydryl angiotensin-converting enzyme (ACE) inhibitor, is characterized by high lipophilicity, selective cardiac ACE inhibition, and antioxidant and tissue protective activities. In vitro and in vivo experiments suggest that zofenopril exerts antioxidant properties at clinically achievable tissue concentrations. In endothelial cells, zofenopril enhances nitric oxide production, attenuates atherosclerotic lesion development and inhibits adhesion molecule expression by reducing reactive oxygen species. These peculiar characteristics are reflected in the drug's cardioprotective activity, which has been shown to be greater than that of non-sulphydryl ACE inhibitors. Cardiac hypertrophy was also reduced by chronic zofenopril administration, independently of its blood pressure-reducing effect. ACE inhibitors with a sulphydryl group could have an advantage in improving vascular function and reducing cardiac impairment compared with non-sulphydryl-containing ACE inhibitors. This could explain zofenopril's remarkable clinical efficacy post-infarction, and potentially beneficial use in prevention and therapy of cardiovascular diseases, such as atherosclerosis, thrombosis and heart failure.

Utility of positron emission tomography for drug development for heart failure

Only about 1 in 5,000 investigational agents in a preclinical stage acquires Food and Drug Administration approval. Among many reasons for this includes an inefficient transition from preclinical to clinical phases, which exponentially increase the cost and the delays the process of drug development. Positron emission tomography (PET) is a nuclear imaging technique that has been used for the diagnosis, risk stratification, and guidance of therapy. However, lately with the advance of radiochemistry and of molecular imaging technology, it became evident that PET could help novel drug development process. By using a PET radioligand to report on receptor occupancy during novel agent therapy, it may help assess the effectiveness, efficacy, and safety of such a new medication in an early preclinical stage and help design successful clinical trials even at a later phase. In this article, we explore the potential implications of PET in the development of new heart failure therapies and review PET's application in the respective pathophysiologic pathways such as myocardial perfusion, metabolism, innervation, inflammation, apoptosis, and cardiac remodeling.

Radionuclide imaging of neurohormonal system of the heart

Heart failure is one of the growing causes of death especially in developed countries due to longer life expectancy. Although many pharmacological and instrumental therapeutic approaches have been introduced for prevention and treatment of heart failure, there are still limitations and challenges. Nuclear cardiology has experienced rapid growth in the last few decades, in particular the application of single photon emission computed tomography (SPECT) and positron emission tomography (PET), which allow non-invasive functional assessment of cardiac condition including neurohormonal systems involved in heart failure; its application has dramatically improved the capacity for fundamental research and clinical diagnosis. In this article, we review the current status of applying radionuclide technology in non-invasive imaging of neurohormonal system in the heart, especially focusing on the tracers that are currently available. A short discussion about disadvantages and perspectives is also included.

Novel molecular angiotensin converting enzyme and angiotensin receptor imaging techniques

Angiotensin II (AII), an octapeptide member of the renin-angiotensin system (RAS), is formed by the enzyme angiotensin converting enzyme (ACE) and exerts adverse cellular effects through an interaction with its type 1 receptor (AT1R). Both ACE inhibitors and angiotensin receptor blockers (ARB) mitigate the vasoconstrictive, proliferative, proinflammatory, proapoptotic, and profibrotic effects of AII and are widely used as effective anti-remodeling agents in clinical practice. Prediction of individual response to these agents, however, remains problematic and is influenced by many factors including race, gender, and genotype. In addition, systemic and tissue RAS activity do not correlate closely. This report summarizes the results of on-going attempts to noninvasively determine tissue ACE activity and AT1R expression using novel nuclear tracers. It is hoped that the availability of such imaging techniques improve treatment of heart failure through more selective pharmacologic intervention and better dose titration of available drugs.

Molecular imaging of the pulmonary circulation in health and disease

The pulmonary circulation, at the unique crossroads between the left and the right heart, is submitted to large physiologic hemodynamic variations and possesses numerous important metabolic functions mediated through its vast endothelial surface. There are many pathologic conditions that can directly or indirectly affect the pulmonary vasculature and modify its physiology and functions. Pulmonary hypertension, the end result of many of these affections, is unfortunately diagnosed too late in the disease process, meaning that there is a crying need for earlier diagnosis and surrogate markers of disease progression and regression. By targeting endothelial, medial and adventitial targets of the pulmonary vasculature, novel molecular imaging agents could provide early detection of physiologic and biologic perturbation in the pulmonary circulation. This review provides the rationale for the development of molecular imaging agents for the diagnosis and follow-up of disorders of the pulmonary circulation and discusses promising targets for SPECT and positron emission tomographic imaging.

Safety and efficacy of the sulfydryl ACE-inhibitor zofenopril in the management of cardiovascular disease

In the 1970s, pharmacological therapy interrupting the renin-angiotensin system was considered beneficial for patients with high-renin hypertension. Angiotensin-converting enzyme (ACE) inhibitors proved to be effective not only in patients with high renin and elevated blood pressure, but also in many hypertensive patients with normal levels of plasma renin activity. ACE inhibitors are used in a wide range of chronic illnesses such as atherosclerosis, hypertension, myocardial infarction, heart failure, diabetic complications, and stroke. To date, more than ninety controlled clinical trials evaluating the beneficial effects of 14 different ACE inhibitors were conducted. Moreover, data from experimental studies showed that ACE inhibitors can attenuate the development of atherosclerosis, oxidative stress, and vascular inflammation in a wide range of species indicating that ACE inhibition also favourably affects the vasculature. More than fifteen years ago, the bi-sulfydryl ACE-inhibitor zofenopril has shown an excellent clinical safety and efficacy in patients with hypertension and in those with myocardial infarction. More recently, this compound exhibited a potent antioxidant and antiatherosclerotic effect indicating a clinical useful vasoprotective action.

Effects of zofenopril on cardiac sarcoplasmic reticulum calcium handling

Isolated rat hearts were perfused for 120 minutes in the presence or in the absence of 10 microM zofenoprilat, the active metabolite of zofenopril. At the end of perfusion, cardiac tissue was used to assay sarcoplasmic reticulum (SR) (45)Ca uptake and SR calcium release, which was determined by automatized quick filtration technique after SR vesicle loading with (45)Ca. The expression of genes involved in the control of calcium homeostasis was evaluated by polymerase chain reaction after reverse transcription. In chronic experiments, SR (45)Ca uptake and gene expression were measured in hearts derived from rats treated with 15 mg*kg(-1)*day(-1) zofenopril for 15 days. Acute or chronic zofenopril administration did not produce any change in contractile performance. In acute experiments, SR (45)Ca uptake was significantly increased after exposure to zofenoprilat. The rate constant of calcium-induced calcium release was slightly although not significantly higher, and the calcium leak measured under conditions promoting SR channel closure was significantly increased. In the chronic model, significant increase in the rate of SR (45)Ca uptake was confirmed. Gene expression was not modified, except for decreased phospholamban expression, which is observed in the acute but not in the chronic model. In conclusion, zofenopril increases SR calcium cycling and stimulates active calcium uptake into the SR.

Imaging left ventricular remodeling: targeting the neurohumoral axis

Left ventricular remodeling is a key determinant of the clinical course and outcome of systolic heart failure. The myocardial renin-angiotensin system (RAS) has been closely linked to the major maladaptive cellular and molecular changes that accompany left ventricular remodeling. Direct inhibition of various components of the RAS, such as the angiotensin-converting enzyme, angiotensin II type 1 receptor, and aldosterone, has resulted in favorable clinical responses in heart failure. Many questions, however, remain unanswered regarding the timing of initiation, optimum doses, need for simultaneous use of RAS inhibitors, and proper monitoring of RAS blockade. Additionally, significant variation has been noted in individual responses to RAS blockade as a result of genetic differences. Answering these questions requires direct access to the myocardial component of RAS, which is largely independent of its systemic component. Molecular imaging using radiotracers with high affinities for myocardial angiotensin-converting enzyme and angiotensin II type 1 receptors can provide direct access to tissue RAS and thus provide a better understanding of the pathophysiology of left ventricular remodeling in individual patients. This Article briefly reviews the potential for evaluating the tissue expression of angiotensin in heart failure by targeted RAS imaging.

Radiopharmaceuticals for renal positron emission tomography imaging

Radiopharmaceuticals for functional renal imaging, including renal blood flow, renal blood volume, glomerular excretion, and metabolism have been available for some time. This review outlines radiopharmaceuticals for functional renal imaging as well as those that target pertinent molecular constituents of renal injury and repair. The angiotensin and endothelin receptors are particularly appealing molecular targets for renal imaging because of their association with renal physiology and pathology. Other targets such as the vascular endothelial growth factor (VEGF) receptor, integrin, or phosphatidylserine have been investigated at length for cancer imaging, but they are just as important constituents of the renal injury/repair process. Various diseases can involve identical mechanisms, such as angiogenesis and apoptosis, and radiopharmaceuticals developed for these processes in other organs can also be used for renal imaging. The sensitivity and spatial resolution of positron emission tomography makes it an ideal tool for molecular and functional kidney imaging. Radiopharmaceutical development for the kidneys must focus on achieving high target selectivity and binding affinity, stability and slow metabolism in vivo, and minimal nonspecific accumulation and urinary excretion.

The role and regulation of cardiac angiotensin-converting enzyme for noninvasive molecular imaging in heart failure

Congestive heart failure is a pathologic condition characterized by progressive decrease in left ventricular contractility and consequent decline of cardiac output. There is convincing clinical and experimental evidence that the renin-angiotensin system (RAS) and its primary effector peptide, angiotensin II, are linked to the pathophysiology of interstitial fibrosis, cardiac remodeling, and heart failure. In addition to the traditional endocrine or circulating RAS, an active tissue RAS has been characterized. Tissue angiotensin-converting enzyme and locally synthesized angiotensin II, for example, by chymase, exert local trophic effects that modulate gene expression, which regulates growth and proliferation in both myocytes and nonmyocytes. The existence of the tissue RAS offers an opportunity for targeted imaging, which may be of considerable value for guiding medical therapy.

Blood-brain barrier penetration of zolmitriptan--modelling of positron emission tomography data

Positron emission tomography (PET) with the drug radiolabelled allows a direct measurement of brain or other organ kinetics, information which can be essential in drug development. Usually, however, a PET-tracer is administered intravenously (i.v.), whereas the therapeutic drug is mostly given orally or by a different route to the PET-tracer. In such cases, a recalculation is needed to make the PET data representative for the alternative administration route. To investigate the blood-brain barrier penetration of a drug (zolmitriptan) using dynamic PET and by PK modelling quantify the brain concentration of the drug after the nasal administration of a therapeutic dose. [11C]Zolmitriptan at tracer dose was administered as a short i.v. infusion and the brain tissue and venous blood kinetics of [11C]zolmitriptan was measured by PET in 7 healthy volunteers. One PET study was performed before and one 30 min after the administration of 5 mg zolmitriptan as nasal spray. At each of the instances, the brain radioactivity concentration after subtraction of the vascular component was determined up to 90 min after administration and compared to venous plasma radioactivity concentration after correction for radiolabelled metabolites. Convolution methods were used to describe the relationship between arterial and venous tracer concentrations, respectively between brain and arterial tracer concentration. Finally, the impulse response functions derived from the PET studies were applied on plasma PK data to estimate the brain zolmitriptan concentration after a nasal administration of a therapeutic dose. The studies shows that the PET data on brain kinetics could well be described as the convolution of venous tracer kinetics with an impulse response including terms for arterial-to-venous plasma and arterial-to-brain impulse responses. Application of the PET derived impulse responses on the plasma PK from nasal administration demonstrated that brain PK of zolmitriptan increased with time, achieving about 0.5 mg/ml at 30 min and close to a maximum of 1.5 mg/ml after 2 hr. A significant brain concentration was observed already after 5 min. The data support the notation of a rapid brain availability of zolmitriptan after nasal administration.

Future Direction of Renal Positron Emission Tomography

Positron emission tomography (PET) is perfectly suited for quantitative imaging of the kidneys, and the recent improvements in detector technology, computer hardware, and image processing software add to its appeal. Multiple positron emitting radioisotopes can be used for renal imaging. Some, including carbon-11, nitrogen-13, and oxygen-15, can be used at institutions with an on-site cyclotron. Other radioisotopes that may be even more useful in a clinical setting are those that either can be obtained from radionuclide generators (rubidium-82, copper-62) or have a sufficiently long half-life for transportation (fluorine-18). The clinical use of functional renal PET studies (blood flow, glomerular filtration rate) has been slow, in part because of the success of concurrent technologies, including single-photon emission computed tomography (SPECT) and planar gamma camera imaging. Renal blood flow studies can be performed with O-15-labeled water, N-13-labeled ammonia, rubidium-82, and copper-labeled PTSM. With these tracers, renal blood flow can be quantified using a modified microsphere kinetic model. Glomerular filtration can be imaged and quantified with gallium-68 EDTA or cobalt-55 EDTA. Measurements of renal blood flow with PET have potential applications in renovascular disease, in transplant rejection or acute tubular necrosis, in drug-induced nephropathies, ureteral obstruction, before and after revascularization, and before and after the placement of ureteral stents. The most important clinical application for imaging glomerular function with PET would be renovascular hypertension. Molecular imaging of the kidneys with PET is rather limited. At present, research is focused on the investigation of metabolism (acetate), membrane transporters (organic cation and anion transporters, pepT1 and pepT2, GLUT, SGLT), enzymes (ACE), and receptors (AT1R). Because many nephrological and urological disorders are initiated at the molecular and organelle levels and may remain localized at their origin for an extended period of time, new disease-specific molecular probes for PET studies of the kidneys need to be developed. Future applications of molecular renal imaging are likely to involve studies of tissue hypoxia and apoptosis in renovascular renal disease, renal cancer, and obstructive nephropathy, monitoring the molecular signatures of atherosclerotic plaques, measuring endothelial dysfunction and response to balloon revascularization and restenosis, molecular assessment of the nephrotoxic effects of cyclosporine, anticancer drugs, and radiation therapy. New radioligands will enhance the staging and follow-up of renal and prostate cancer. Methods will be developed for investigation of the kinetics of drug-delivery systems and delivery and deposition of prodrugs, reporter gene technology, delivery of gene therapy (nuclear and mitochondrial), assessment of the delivery of cellular, viral, and nonviral vectors (liposomes, polycations, fusion proteins, electroporation, hematopoietic stems cells). Of particular importance will be investigations of stem cell kinetics, including local presence, bloodborne migration, activation, seeding, and its role in renal remodeling (psychological, pathological, and therapy induced). Methods also could be established for investigating the role of receptors and oncoproteins in cellular proliferation, apoptosis, tubular atrophy, and interstitial fibrosis; monitoring ras gene targeting in kidney diseases, assessing cell therapy devices (bioartificial filters, renal tubule assist devices, and bioarticial kidneys), and targeting of signal transduction moleculas with growth factors and cytokines. These potential new approaches are, at best, in an experimental stage, and more research will be needed for their implementation.

Fixed combination of zofenopril plus hydrochlorothiazide in the management of hypertension: a review of available data

Angiotensin-converting enzyme (ACE) inhibitors effectively interfere with the renin-angiotensin system and exert various beneficial actions on vascular structure and function beyond their blood pressure-lowering effects. Zofenopril, a potent sulphydryl ACE inhibitor, is characterized by high lipophilicity, sustained cardiac ACE inhibition, and antioxidant and tissue protective activities. Its ancillary properties, such as antioxidant activity and cardiovascular (CV) protection, make this drug potentially suitable for the treatment and prevention of certain CV diseases. The Survival of Myocardial Infarction Long term Evaluation trials have demonstrated that the early administration of zofenopril to patients with acute myocardial infarction is associated with a significant reduction in the 6-week occurrence of major CV events in high-risk patients with anterior non-thrombolyzed myocardial infarction. The fixed combination of zofenopril-hydrochlorothiazide (HCTZ) 30/12.5 mg/day is approved for the management of mild-to-moderate hypertension in different European countries. In clinical trials comparing zofenopril-HCTZ with each agent administered as monotherapy, combination therapy was clearly more effective in normalizing blood pressure (BP). In addition, combination therapy provided sustained and consistent BP control over the entire 24 hour dosing interval. The efficacy and safety profile of zofenopril-HCTZ highlights that this combination is a potentially useful addition to currently available therapy for patients with BP inadequately controlled by monotherapy, as well as for patients who require more rapid and intensive BP control.