Cardiovascular and adenylate cyclase stimulant properties of NKH477, a novel water-soluble forskolin derivative

Structural insights into membrane adenylyl cyclases, initiators of cAMP signaling

Membrane adenylyl cyclases (ACs) catalyze the conversion of ATP to the ubiquitous second messenger cAMP. As effector proteins of G protein-coupled receptors and other signaling pathways, ACs receive and amplify signals from the cell surface, translating them into biochemical reactions in the intracellular space and integrating different signaling pathways. Despite their importance in signal transduction and physiology, our knowledge about the structure, function, regulation, and molecular interactions of ACs remains relatively scarce. In this review, we summarize recent advances in our understanding of these membrane enzymes.

Diagnosis and prevention of the vasodepressor type of neurally mediated syncope in Japanese patients

We investigated circulatory dynamics in patients with vasodepressor type neurally mediated syncope (VT-NMS) by performing high-resolution Holter electrocardiography and a correlation analysis of changes in adenylate cyclase activity, blood pressure, and pulse during the head-up tilt test. Holter electrocardiography was performed for 30 patients. Adenylate cyclase activity was evaluated in lymphocytes from blood samples taken at rest and during the head-up tilt test. There was no change in autonomic nerve fluctuation during electrocardiography in VT-NMS patients, but our results showed a significant difference in blood pressure and adenylate cyclase activity between VT-NMS patients and healthy volunteers; the systolic blood pressure of VT-NMS patients decreased after 5 min, while at 10 min, the adenylate cyclase activity was the highest (0.53%) and the systolic blood pressure was the lowest (111.8 mm Hg). Pulse rates increased after 10 min. VT-NMS patients showed higher blood pressure, pulse rate, and adenylate cyclase activity during the tilt test than did healthy volunteers. In patients with syncope, standing for longer than 10 minutes may increase the risk of VT-NMS. From our results, we consider it likely that high systolic blood pressure and adenylate cyclase activity at rest cause fainting in VT-NMS patients. Our findings may be helpful for identifying individuals with a high risk of developing NMS in the healthy population.

Dopamine increases HIV entry into macrophages by increasing calcium release via an alternative signaling pathway

Dopaminergic dysfunction has long been connected to the development of HIV infection in the CNS. Our previous data showed that dopamine increases HIV infection in human macrophages by increasing the susceptibility of primary human macrophages to HIV entry through stimulation of both D1-like and D2-like receptors. These data suggest that, in macrophages, both dopamine receptor subtypes may act through a common signaling mechanism. To define better the mechanism(s) underlying this effect, this study examines the specific signaling processes activated by dopamine in primary human monocyte-derived macrophages (hMDM). In addition to confirming that the increase in entry is unique to dopamine, these studies show that dopamine increases HIV entry through a PKA insensitive, Ca²⁺ dependent pathway. Further examination demonstrated that dopamine can signal through a previously defined, non-canonical pathway in human macrophages. This pathway involves both Ca²⁺ release and PKC phosphorylation, and these data show that dopamine mediates both of these effects and that both were partially inhibited by the G_q/11 specific inhibitor YM-254890. Studies have shown that G_q/11 preferentially couples to the D1-like receptor D5, indicating an important role of the D1-like receptors in mediating these effects. These data indicate a role for Ca²⁺ flux in the HIV entry process, and suggest a distinct signaling mechanism mediating some of the effects of dopamine in macrophages. Together, the data indicate that targeting this alternative dopamine signaling pathway might provide new therapeutic options for individuals with elevated CNS dopamine suffering from NeuroHIV.

Neurally mediated syncope diagnosis based on adenylate cyclase activity in Japanese patients

The study aims to clarify the mechanism in patients with neurally mediated syncope (NMS), focusing on the adenylate cyclase (AC) activity level in lymphocytes. This study included 40 subjects: 22 healthy volunteers and 18 NMS patients. We investigated the changes in AC activity that occur during of syncope at rest and during the head-up tilt (HUT) test. We obtained 8 mL of blood at rest time and four times during the HUT test. Then, we measured the AC activity and the test reagent was added to the lymphocytes (10,000) and reacted for 30 min at room temperature. We were able to determine the standard value of AC activity when adrenaline (AD) and isoproterenol (IP) were added to lymphocytes. The results of our study showed one of the causes of NMS has a difference in AC activity level and classification of the patients into two different types of NMS was possible: either the vasodepressor type (VT) or mixed type (MT). At rest time, VT patients showed significantly higher AC activity (AD; 100 μM: p = 0.005, IP; 50 μM: p = 0.02) and MT patients showed significantly lower AC activity (AD; 10 μM: p = 0.02, IP; 50 μM: p = 0.004) than the average AC activity in healthy volunteers. Moreover, VT patients had significantly higher AC activity than healthy volunteers at the four points of the HUT test. MT patients had significantly lower AC activity (AD: p = 0.04 and IP: p = 0.04) than healthy volunteers at the rest time of HUT. Our study showed a significant difference in AC activities between NMS patients and healthy volunteers at rest. Therefore, a detailed NMS diagnosis can be made by examining AC activity levels in blood taken at rest time.

Natural products as modulators of the cyclic-AMP pathway: evaluation and synthesis of lead compounds

It is now well recognized that the normal cellular response in mammalian cells is critically regulated by the cyclic-AMP (cAMP) pathway through the appropriate balance of adenylyl cyclase (AC) and phosphodiesterase-4 (PDE4) activities. Dysfunctions in the cAMP pathway have major implications in various diseases like CNS disorders, inflammation and cardiac syndromes and, hence, the modulation of cAMP signalling through appropriate intervention of AC/PDE4 activities has emerged as a promising new drug discovery strategy of current interest. In this context, synthetic small molecules have had limited success so far and therefore parallel efforts on natural product leads have been actively pursued. The early promise of using the diterpene forskolin and its semi-synthetic analogs as AC activators has given way to new leads in the last decade from novel natural products like the marine sesterterpenoids alotaketals and ansellones and the 9,9'-diarylfluorenone cored selaginpulvilins, etc. and their synthesis has drawn much attention. This review captures these contemporary developments, particularly total synthesis campaigns and structure-guided analog design in the context of AC and PDE-4 modulating attributes and the scope for future possibilities.

Shedding light on the role of cAMP in mammalian sperm physiology

Mammalian fertilization relies on sperm finding the egg and penetrating the egg vestments. All steps in a sperm's lifetime crucially rely on changes in the second messenger cAMP (cyclic adenosine monophosphate). In recent years, it has become clear that signal transduction in sperm is not a continuum, but rather organized in subcellular domains, e.g. the sperm head and the sperm flagellum, with the latter being further separated into the midpiece, principal piece, and endpiece. To understand the underlying signaling pathways controlling sperm function in more detail, experimental approaches are needed that allow to study sperm signaling with spatial and temporal precision. Here, we will give a comprehensive overview on cAMP signaling in mammalian sperm, describing the molecular players involved in these pathways and the sperm functions that are controlled by cAMP. Furthermore, we will highlight recent advances in analyzing and manipulating sperm signaling with spatio-temporal precision using light.

A novel biosensor to study cAMP dynamics in cilia and flagella

The cellular messenger cAMP regulates multiple cellular functions, including signaling in cilia and flagella. The cAMP dynamics in these subcellular compartments are ill-defined. We introduce a novel FRET-based cAMP biosensor with nanomolar sensitivity that is out of reach for other sensors. To measure cAMP dynamics in the sperm flagellum, we generated transgenic mice and reveal that the hitherto methods determining total cAMP levels do not reflect changes in free cAMP levels. Moreover, cAMP dynamics in the midpiece and principal piece of the flagellum are distinctively different. The sole cAMP source in the flagellum is the soluble adenylate cyclase (SACY). Although bicarbonate-dependent SACY activity requires Ca²⁺, basal SACY activity is suppressed by Ca²⁺. Finally, we also applied the sensor to primary cilia. Our new cAMP biosensor features unique characteristics that allow gaining new insights into cAMP signaling and unravel the molecular mechanisms underlying ciliary function in vitro and in vivo.

DOI:http://dx.doi.org/10.7554/eLife.14052.001

Cells can change the way they grow, move or develop in response to information from their environment. This information is first detected at the surface of the cell and then the information is relayed around the interior of the cell by signaling molecules known as “second messengers”. A molecule called cAMP is a well-known second messenger that is involved in many different signaling pathways. Therefore, the levels of cAMP in specific areas of the cell need to be precisely regulated to enable different signaling pathways to be activated at specific times and locations.

Some cells have hair-like structures called cilia or flagella on their surface. Cilia and flagella are able to move the fluid that surrounds the cells or even move the cells themselves. The second messenger cAMP plays an essential role in making cilia move, but it is challenging to analyze the dynamics of cAMP – that this, how the levels of this molecule change over time – in these structures. The levels of cAMP in live cells can only be measured using fluorescent biosensors. Introducing these biosensors into specific cell structures is difficult and they are not sensitive enough to respond to low levels of cAMP. Furthermore, it is difficult to measure cAMP activity inside such tiny structures using these biosensors.

Mukherjee, Jansen, Jikeli et al. now address some of these challenges by creating a new cAMP biosensor that has several unique features. Most importantly, it can respond to very low levels of cAMP, making it more sensitive than previous biosensors. Mukherjee et al. test this new biosensor in the flagella of sperm cells from mice, which reveals how the production of cAMP is regulated in the flagellum. The new biosensor also shows that different parts of the flagellum can have different cAMP dynamics. In the future, this new biosensor could be used to study cAMP in other structures and compartments within cells.

DOI:http://dx.doi.org/10.7554/eLife.14052.002

Highly selective one pot synthesis and biological evaluation of novel 3-(allyloxy)-propylidene acetals of some natural terpenoids

Synthesis, in vitro antiproliferative and α-glucosidase inhibitory activities of novel 3-(allyloxy)-propylidene acetals of some natural terpenoids.

Influence of acidosis on cardiotonic effects of colforsin and epinephrine: a dose-response study

OBJECTIVE

Acidosis produces a negative inotropic effect on cardiac muscle against which catecholamines and phosphodiesterase III inhibitors have limited therapeutic effects. This study evaluated the effects of colforsin, which directly activates adenylate cyclase without β-adrenergic receptor activation, in isolated Langendorff rat hearts in a pH- and concentration-dependent manner.

DESIGN

Experimental animal study.

SETTING

A university laboratory.

PARTICIPANTS

Sprague-Dawley rats.

INTERVENTIONS

Hearts were isolated and perfused with 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid/Tyrode solution (pH 7.4) in the Langendorff preparation. The hearts were assigned randomly to the control (pH 7.4), mild acidosis (pH 7.0), or severe acidosis (pH 6.6) group (n = 8 per group) and were perfused continuously with colforsin 10(-7), 10(-6), and 10(-5) mol/L.

MEASUREMENTS AND MAIN RESULTS

Maximum dP/dt was determined, and the concentration-response relation was evaluated at each pH. Colforsin at 10(-6) mol/L increased the maximum dP/dt from 2,592 ± 557 to 5,189 ± 721 mmHg/s (p < 0.001) and from 1,942 ± 325 to 3,399 ± 608 mmHg/s (p < 0.001) in the control and mild acidosis groups, respectively; whereas colforsin, 10(-5) mol/L, significantly increased the maximum dP/dt even in the severe acidosis group. No significant difference was seen in maximum dP/dt among the 3 groups after infusion with colforsin 10(-5) mol/L.

CONCLUSIONS

In contrast to catecholamines and other inodilators, colforsin at a high concentration restores decreased cardiac contractility against severe acidosis to an extent similar to physiologic pH.

Intra-arterial colforsin daropate for the treatment of cerebral vasospasm after aneurysmal subarachnoid hemorrhage

INTRODUCTION

Cerebral vasospasm (CV) remains a major cause of mortality and morbidity in patients with subarachnoid hemorrhage (SAH). Here, we examined the effectiveness and safety of intra-arterial injection of colforsin daropate hydrochloride (CDH).

METHODS

A consecutive series of 29 patients with angiographically confirmed CV received intra-arterial CDH (IAC) therapy. Angiographic changes in spastic vessels and the cerebral circulation time (CCT) were assessed before and after IAC treatment, together with the change in clinical status.

RESULTS

IAC treatment was performed in 53 procedures in 29 patients. Angiographic improvement was observed following all procedures (100%), and clinical improvement was observed following 36 of 42 procedures (86%) in symptomatic cases. CCT improved significantly. At the 3-month follow-up, 19 patients (66%) showed good recovery or moderate disability on the Glasgow Outcome Scale. Major adverse effects were headache and increased heart rate.

CONCLUSIONS

IAC treatment was effective and safe for the treatment of CV after SAH.

Adenylyl cyclases as innovative therapeutic goals

Pharmacological modulation of intracellular cyclic AMP (cAMP) signalling could provide new therapeutic and experimental tools. Although drugs interfering with this pathway have traditionally targeted membrane receptors, the effector enzyme adenylyl cyclase (AC), which functions as a signalling catalyst, also presents an interesting target. Thus, development of isoform-selective stimulator and/or inhibitor compounds for AC could lead to organ-specific pharmacotherapeutics for treating heart failure, cancer and neurodegenerative diseases. In this review, the potential of AC as the object of drug therapy is discussed.

Chronic direct stimulation of adenylyl cyclase induces cardiac desensitization to catecholamine and beta-adrenergic receptor downregulation in rabbits

Chronic stimulation of beta-adrenergic receptors (betaARs) induces betaAR downregulation. However, it is not known whether continuous activation of adenylyl cyclase without direct stimulation of betaARs leads to receptor downregulation. This study investigated the effects of chronic stimulation of adenylyl cyclase with colforsin, on hemodynamic variables, and on myocardial betaAR density. In all, 55 rabbits received intravenous colforsin (1.6 microg/kg/min, n = 20), isoproterenol (ISO; 0.4 microg/kg/min, n = 16), or saline (n = 19) for two weeks. After chronic drug administration, responses of systolic (Delta% peak LV +dP/dt) and diastolic function (Delta% peak LV -dP/dt), and heart rate (Delta% heart rate), to acute administration of ISO (0.05 to 0.2 microg/kg/min) or colforsin (5 to 20 nmol/kg/min) were decreased compared to those before chronic administration. betaAR density in the colforsin group (69.8 +/- 13.8 fmol/ml protein) was less than that in the saline group (79.8 +/- 15.0 fmol/ml protein, P < 0.05), but was greater than that in the ISO group (56.3 +/- 8.4 fmol/ml protein, P < 0.05). Thus, chronic direct stimulation of adenylyl cyclase elicited systolic and diastolic functional desensitization to betaAR stimulation or adenylyl cyclase stimulation, and myocardial betaAR downregulation.

Regulatory properties of adenylate cyclases type 5 and 6: A progress report

Adenylate cyclases (AC) type 5 and 6 comprise the calcium-inhibited family of adenylate cyclase isoforms. Here we review recent discoveries in the regulation of AC5 and AC6 with a focus on posttranslational modifications including glycosylation, nitrosylation, and phosphorylation by the cyclic AMP-dependent protein kinase (PKA), protein kinase C (PKC), and Raf1. We also describe novel signaling interactions such as Galpha(q)-mediated potentiation of AC6 activation. Novel regulators of AC5 and AC6, including small molecules and proteins that physically interact with AC5 and AC6 such as snapin, regulator of G protein signaling 2 (RGS2), protein associated with myc (PAM), and caveolin peptides are discussed. We also describe several recent studies that demonstrate the usefulness of transgenic or adenoviral overexpression of AC5 and AC6 in models for disease states such as cardiovascular hypertrophy. The discovery of novel regulatory mechanisms for AC5 and AC6 and their potential role in crucial physiological processes provide new avenues for research into therapeutic interventions targeting the cyclic AMP pathway.

Antiproliferative effects of NKH477, a forskolin derivative, on cytokine profile in rat lung allografts

OBJECTIVE

NKH477 was recently identified as a water-soluble forskolin derivative and was reported to prolong survival of murine cardiac allografts. However, the mechanism of the efficacy is not clear in vivo. The aim of this study was to investigate the immunosuppressive effects of NKH477 on acute lung allograft rejection in the rat model and its mechanism of action in vivo.

METHODS

Left lungs were transplanted orthotopically from Brown-Norway donors to Lewis recipients. Recipient rats were untreated or treated daily with different doses of NKH477. Grafts were excised on Day 3 or Day 5 to determine histopathological rejection and expressions of interleukin (IL)-2, IL-4, IL-10, and interferon (IFN)-gamma by enzyme-linked immunosorbent assay. The cytokine expression at Day 3 or Day 5 was also evaluated in recipient spleens by immunohistochemistry. Furthermore, mesenteric lymph node cells from recipients at Day 5 were cultured alone or stimulated with donor antigens for 72 hours to determine cell proliferation by means of thymidine incorporation.

RESULTS

NKH477 significantly extended allograft survival time in a dose-dependent manner and reduced histopathological rejection. Treatment with NKH477 inhibited IFN-gamma and IL-10 expression, whereas expression of these cytokines were markedly upregulated in the untreated allografts. Expression of IL-2 and IL-10 also increased in the spleen of untreated allorecipients. NKH477 suppressed expression of both cytokines in the spleen. In addition, lymphocyte proliferation was inhibited in NKH477-treated recipients as compared with untreated recipients.

CONCLUSION

These results suggest that NKH477 exerts an antiproliferative effect on lymphocytes in vivo with an altered cytokine profile in rat recipients of lung allografts.

Direct inhibition of type 5 adenylyl cyclase prevents myocardial apoptosis without functional deterioration

Adenylyl cyclase, a major target enzyme of beta-adrenergic receptor signals, is potently and directly inhibited by P-site inhibitors, classic inhibitors of this enzyme, when the enzyme catalytic activity is high. Unlike beta-adrenergic receptor antagonists, this is a non- or uncompetitive inhibition with respect to ATP. We have examined whether we can utilize this enzymatic property to regulate the effects of beta-adrenergic receptor stimulation differentially. After screening multiple new and classic compounds, we found that some compounds, including 1R,4R-3-(6-aminopurin-9-yl)-cyclopentanecarboxylic acid hydroxyamide, potently inhibited type 5 adenylyl cyclase, the major cardiac isoform, but not other isoforms. In normal mouse cardiac myocytes, contraction induced by low beta-adrenergic receptor stimulation was poorly inhibited with this compound, but the induction of cardiac myocyte apoptosis by high beta-adrenergic receptor stimulation was effectively prevented by type 5 adenylyl cyclase inhibitors. In contrast, when cardiac myocytes from type 5 adenylyl cyclase knock-out mice were examined, beta-adrenergic stimulation poorly induced apoptosis. Our data suggest that the inhibition of beta-adrenergic signaling at the level of the type 5 adenylyl cyclase isoform by P-site inhibitors may serve as an effective method to prevent cardiac myocyte apoptosis induced by excessive beta-adrenergic stimulation without deleterious effect on cardiac myocyte contraction.

Pharmacokinetics and a simulation model of colforsin daropate, new forskolin derivative inotropic vasodilator, in patients undergoing coronary artery bypass grafting

Colforsin daropate, a water-soluble forskolin derivative, is an adenyl cyclase activator with positive inotropic and vasodilatory effects that are useful in the treatment of ventricular dysfunction. We investigated the pharmacokinetics of colforsin daropate in cardiac surgery patients and performed simulations to determine the dosage necessary to maintain an effective plasma concentration following cardiopulmonary bypass. In six patients undergoing coronary artery bypass graft, colforsin daropate (0.01mgkg(-1)) was administered immediately after separation from cardiopulmonary bypass. Arterial blood was sampled over the next 16h and plasma concentrations of colforsin daropate and its initial active metabolite were determined by gas-chromatography. Extended nonlinear least-squares regression was used to fit a three-compartment model to each patient's data. Distribution half-life (t(1/2alpha)) was 3.9+/-1.1min, metabolic half-life (t(1/2beta)) was 1.9+/-0.7h, and elimination half-life (t(1/2gamma)) was 95.3+/-15.2h. Central-compartment volume was 591.0+/-42.8mlkg(-1), volume distribution was 2689.2+/-450.6mlkg(-1), and elimination clearance was 27.7+/-14.7mlkg(-1)min(-1). In the pharmacokinetic simulation model, 0.5, 0.75, and 1.0microgkg(-1)min(-1) continuous infusion of colforsin daropate produce effective concentration (5-10ngml(-1)) within 30, 20, and 10min, respectively following administration. An initial active metabolite of decreased rapidly to less than 1.0ngml(-1) within the first 10min.A colforsin daropate infusion of 0.7-1.0microgkg(-1)min(-1) for 10-20min followed by 0.5microgkg(-1)min(-1) continuous infusion is recommended to produce an effective concentration (5-10ngml(-1)) within 10-20min and to maintain a therapeutic concentration throughout the administration period after cardiopulmonary bypass.

Microvascular Inflammatory Response in Cardiac Surgery

Cardiac surgical procedures, with or without cardiopulmonary bypass, elicit a systemic inflammatory response in patients that induces the elaboration of multiple cytokines, chemokines, adhesion molecules, and destructive enzymes. This inflammatory reaction involves multiple interdependent and redundant cell types and humoral cascades, which allows for amplification and positive feedback at numerous steps. This systemic inflammatory response ultimately results in a broad spectrum of clinical manifestations, with multiple organ failure being the most severe form. Investigative efforts have focused on understanding the mechanism of this systemic inflammatory response syndrome in order to develop potential therapeutic targets to inhibit it, thereby possibly decreasing postoperative morbidity and mortality. Multiple therapeutic methods have been investigated, including pharmacologic inhibitors and modifications of surgical technique and the cardiopulmonary bypass circuit. Although studies have demonstrated that the use of these therapies in experimental and clinical settings has attenuated the systemic inflammatory response, they have failed to conclusively show clinical benefit from these therapies. These therapies may be too specific to minimize the deleterious effects of a systemic inflammatory response that results from the activation of multiple, interdependent, and redundant inflammatory cascades and cell types. Hence, further studies that investigate the molecular and cellular events underlying the systemic inflammatory response syndrome and the resultant effects of anti-inflammatory therapies are warranted to ultimately achieve improvements in clinical outcome after cardiac surgical procedures.

Elevated cyclic adenosine monophosphate ameliorates ischemia-reperfusion injury in rat cardiac allografts

BACKGROUND

Oxidative stress after ischemia and reperfusion leads to leukocyte activation, the production of injurious cytokines, and increased expression of inflammatory adhesion molecules. This initial event is one of the most important alloantigen-independent factors associated with graft coronary artery disease (GCAD). Cyclic adenosine monophosphate (cAMP) is an important second messenger that inhibits the expression of tumor necrosis factor alpha (TNF-alpha), vascular cell adhesion molecule 1 (VCAM-1), and endothelial leukocyte adhesion molecule 1 (ELAM-1) in vitro. Its levels decrease during organ preservation. We hypothesized that augmenting allograft cAMP levels with the water-soluble adenylate cyclase activator, NKH477, could decrease ischemia-reperfusion injury and inhibit the progression of GCAD.

METHODS

PVG to ACI rat heterotopic cardiac allografts, treated with NKH477 solution or vehicle, were reperfused for 4 hours or 90 days after 60 minutes of ischemia. We analyzed grafts for intracellular adhesion molecule 1 (ICAM-1), VCAM-1, and ELAM-1 mRNA expression; TNF-alpha and interleukin-6 (IL-6) protein expression; and myeloperoxidase activity. We also performed immunohistochemical analysis for ICAM-1 and VCAM-1 protein expression. At post-operative Day 90, the progression of GCAD had increased morphometrically.

RESULTS

NKH477-treated grafts had significantly decreased levels of myeloperoxidase activity compared with controls. In this group, TNF-alpha, IL-6, and VCAM-1 protein expression was inhibited; however, ICAM-1 and ELAM-1 expression did not alter. We found no differences in the degree of development of GCAD between groups.

CONCLUSION

Although augmented intracellular cAMP prevented acute reperfusion injury, it was insufficient to prevent the development of GCAD. Intracellular adhesion molecule 1 and ELAM-1, whose expression NKH477 does not inhibit, may play important roles in the development of GCAD.

Isoform-specific regulation of adenylyl cyclase: a potential target in future pharmacotherapy

Adenylyl cyclase (AC) is a target enzyme of multiple G-protein-coupled receptors (GPCRs). In the past decade, the cloning, structure and biochemical properties of nine AC isoforms were reported, and each isoform of AC shows distinct patterns of tissue distribution and biochemical/pharmacological properties. In addition to the conventional regulators of this enzyme, such as calmodulin (CaM) or PKC, novel regulators, for example, caveolin, have been identified. Most importantly, these regulators work on AC in an isoform dependent manner. Recent studies have demonstrated that certain classic AC inhibitors, i.e., P-site inhibitors, show an isoform-dependent inhibition of AC. The side chain modifications of forskolin, a diterpene extract from Coleus forskolii, markedly enhance its isoform selectivity. When taken together, these findings suggest that it is feasible to develop new pharmacotherapeutic agents that target AC isoforms to regulate various neurohormonal signals in a highly tissue-/organ-specific manner.

The therapeutic potential of novel cardiotonic agents

During the course of treatment of heart failure patients, cardiotonic agents are inevitable for improvement of myocardial dysfunction. Clinically available agents, such as beta-adrenoceptor agonists and selective phosphodiesterase 3 inhibitors, act mainly via cyclic AMP/protein kinase A-mediated facilitation of Ca(2+) mobilisation (upstream mechanism). These agents are associated with the risk of Ca(2+) overload leading to arrhythmias, myocardial cell injury and premature cell death. In addition, they are energetically disadvantageous because of an increase in activation energy and metabolic effects. Cardiac glycosides act also via an upstream mechanism and readily elicit Ca(2+) overload with a narrow safety margin. No currently available agents act primarily via an increase in the myofilament sensitivity to Ca(2+) ions (central and/or downstream mechanisms). Novel Ca(2+) sensitisers under basic research may deserve clinical trials to examine the therapeutic potential to replace currently employed agents in acute and chronic heart failure patients. Molecular mechanisms of action of Ca(2+) sensitisers are divergent. In addition, they show a wide range of discrete pharmacological profiles due to additional actions associated with individual compounds. Therefore, the outcome of clinical trials has to be explained carefully based on these mechanisms of actions.

Cardiovascular and adenylate cyclase stimulating effects of colforsin daropate, a water-soluble forskolin derivative, compared with those of isoproterenol, dopamine and dobutamine

Colforsin daropate is a recently developed water-soluble derivative of forskolin that directly stimulates adenylate cyclase, unlike the catecholamines. The chronotropic, inotropic and coronary vasodilator actions of colforsin daropate were compared with those of isoproterenol, dopamine and dobutamine, using canine isolated, blood-perfused heart preparations. The stimulating effect of each drug on adenylate cyclase activity was also assessed. Colforsin daropate, as well as each of the catecholamines, exerted positive chronotropic, inotropic and coronary vasodilator actions. The order of selectivity for the cardiovascular variables of colforsin daropate was coronary vasodilation >> positive inotropy > positive chronotropy; whereas that of isoproterenol, dopamine and dobutamine was positive inotropy >> coronary vasodilation > positive chronotropy. Thus, a marked characteristic of colforsin daropate is its potent coronary vasodilator action. On the other hand, each drug significantly increased the adenylate cyclase activity in a dose-related manner: colforsin daropate >> isoproterenol > dopamine = dobutamine. These results suggest that colforsin daropate may be preferable in the treatment of severe heart failure where the coronary blood flow is reduced and beta-adrenoceptor-dependent signal transduction pathway is down-regulated.

Comparison of the cardiovascular effects of intracellular cyclic adenosine 3',5'-monophosphate (cAMP)-modulating agents in isoflurane-anesthetized cats

The inotropic, chronotropic, and vasodilatory effects of five commonly used cyclic adenosine 3',5'-monophosphate (cAMP)-modulating agents were evaluated. Hemodynamic functions were measured continuously in isoflurane-anesthetized cats during infusion of the following: dobutamine (DOB; 2.5, 5 and 10 microg/kg/min; n=8), dopamine (DOP; 1.25, 2.5, 5 and 10 microg/kg/min; n=5), milrinone (MIL; 2.5, 5 and 10 microg/kg/min; n=8), 6-(3-dimethyl-aminopropionyl) forskolin hydrochloride (COL; 0.2, 0.4, 0.8, and 1.6 microg/kg/min; n=7), and bucladesine sodium (BUC; 10, 20, and 40 microg/kg/min; n=9). At the highest infusion rate, DOB and DOP produced the greatest positive inotropic (increase in left ventricular (LV) dP/dt = 89 +/- 4% and 75 +/- 6%, respectively) and chronotropic (increase in heart rate (HR) = 42 +/- 4% and 22 +/- 6%, respectively) effects. MIL and COL produced similar albeit less pronounced positive inotropic (increase in LV dP/dt = 18 +/- 3% and 22 +/- 6%, respectively) and chronotropic (increase in HR = 13 +/- 4% and 21 +/- 4%, respectively) effects. Both also had significant vasodilatory effects (decrease in peripheral resistance (PR) = -30 +/- 2% and -35 +/- 7%, respectively). In contrast, BUC produced only vasodilatation (decrease in PR = -33 +/- 6%). Hence, MIL, COL, and BUC had significant vasodilatory effects and less-pronounced inotropic effects than the catecholamines DOB and DOP. The vasodilatory effects of non-catecholamine drugs for treatment of congestive heart failure should translate into beneficial decreases in both pre-load and after-load. In contrast, the strong inotropic effects of DOB and DOP should be beneficial in the treatment of acute heart failure and anesthetic crisis.

Mechanisms of action of novel cardiotonic agents

Regulation of myocardial contractility by cardiotonic agents is achieved by an increase in intracellular Ca2+ mobilization (upstream mechanism), an increase in Ca2+ binding affinity to troponin C (central mechanism), or facilitation of the process subsequent to Ca2+ binding to troponin C (downstream mechanism). cAMP mediates the regulation induced by Ca2+ mobilizers such as beta-adrenoceptor agonists and selective phosphodiesterase III inhibitors acting through the upstream mechanism. These agents act likewise on the central mechanism to decrease Ca2+ sensitivity of troponin C in association with the cAMP-mediated phosphorylation of troponin I. In addition to such a well-known action of cAMP, recent experimental findings have revealed that Ca2+ sensitizers, such as levosimendan, OR-1896, and UD-CG 212 Cl, require the cAMP-mediated signaling for induction of Ca2+ sensitizing effect. These agents shift the [Ca2+] -force relationship to the left, but their positive inotropic effect (PIE) is inhibited by carbachol, which suppresses selectively the cAMP-mediated PIE. These findings imply that cAMP may play a crucial role in increasing the myofilament Ca2+ sensitivity by cross-talk with the action of individual cardiotonic agents. No clinically available cardiotonic agents act primarily via Ca2+ sensitization, but the PIE of pimobendan and levosimendan is partly mediated by an increase in myofilament Ca2+ sensitivity. Evidence is accumulating that cardiotonic agents with Ca2+ sensitizing action are more effective than agents that act purely via the upstream mechanism in clinical settings. Further clinical trials are required to establish the effectiveness of Ca2+ sensitizers in long-term therapy for congestive heart failure patients.

Influence of colforsin daropate hydrochloride on internal mammary artery grafts

The effect of colforsin daropate hydrochloride (colforsin), a water-soluble forskolin derivative, on blood flow in internal mammary artery (IMA) grafts was evaluated in a prospective randomized study of 26 patients undergoing coronary artery bypass grafting. Patients were randomized to receive either colforsin treatment (colforsin; n=14) or no colforsin treatment (control; n=14). Administration of colforsin (0.5mg x kg(-1) min(-1)) was started after induction of anesthesia and was continued for 6 h. IMA blood flow and hemodynamic measurements were assessed perioperatively. During cardiopoulmonary bypass (CPB), perfusion flow was adjusted to 2.5 L/m2 and IMA free blood flow was measured. IMA blood flow was also measured 1 h after CPB by an ultrasonic flow meter. Systemic vascular resistance was significantly lower in the colforsin group during and after CPB. IMA blood flow was significantly greater in the colforsin group than in the control group during (44 +/- 2 vs 33 +/- 3 ml min-1 x m(-2), p=0.02) and after CPB (38 +/- 6 vs 20 +/- 3ml x min(-1) m(-2), p=0.01). IMA blood flow 1 h after CPB correlated inversely with concurrent systemic vascular resistance (r=-0.61, p=0.001). Intraoperative administration of colforsin daropate hydrochloride caused potent vasodilation, resulting in an increase in IMA blood flow. The results indicate that the regimen can be used perioperatively in patients undergoing coronary artery bypass grafting.

Spasmolytic effects of colforsin daropate on serotonin-induced pulmonary hypertension and bronchoconstriction in dogs

BACKGROUND

We have previously found that agents increasing intracellular cAMP levels of smooth muscles, such as PDE3 inhibitors, aminophylline and prostaglandin E1, produce both bronchodilation and pulmonary vasodilation in serotonin-induced pulmonary hypertension and bronchoconstriction models. In the present study we have simultaneously evaluated the spasmolytic effects of colforsin daropate, a novel forskolin derivative, on serotonin-induced pulmonary hypertension and bronchoconstriction.

METHODS

Ten mongrel dogs were anesthetized with pentobarbital. The pulmonary hypertension and bronchoconstriction were elicited with serotonin (10 microg/kg + 1 mg x kg(-1) x h(-1)) and assessed as percentage changes in pulmonary vascular resistance (PVR) and bronchial cross-sectional area (BCA) (basal = 100%). Initially, the relaxant effects of colforsin daropate (0-300 microg/kg) were determined. The PVR and BCA were assessed before and 30 min after serotonin infusion began and 5 min after each dose of colforsin daropate. To determine whether colforsin daropate-induced relaxation is independent of plasma catecholamine, propranolol 0.4 mg/kg was given following colforsin daropate 300 microg/kg i.v.

RESULTS

Colforsin daropate reversed both pulmonary hypertension and bronchoconstriction dose-dependently: -logED50 (95% confidence intervals, mean ED50) for pulmonary hypertension and bronchoconstriction 5.44 (5.08-5.80, 3.6 microg/kg) and 4.90 (4.06-5.20, 12.5 microg/kg), respectively. However, colforsin daropate (>or= 30 microg/kg) produced a more pronounced systemic than pulmonary vasodilation. Although colforsin daropate (>or= 30 microg/kg) significantly increased plasma catecholamines, propranolol did not reverse the relaxant effects.

CONCLUSIONS

Colforsin daropate may attenuate bronchoconstriction and pulmonary hypertension. In addition, as beta-blockade did not change the attenuation, the relaxant effects may be independent of plasma catecholamines.

Type-specific regulation of adenylyl cyclase. Selective pharmacological stimulation and inhibition of adenylyl cyclase isoforms

Crystallographic studies have elucidated the binding mechanism of forskolin and P-site inhibitors to adenylyl cyclase. Accordingly, computer-assisted drug design has enabled us to identify isoform-selective regulators of adenylyl cyclase. After examining more than 200 newly synthesized derivatives of forskolin, we found that the modification at the positions of C6 and C7, in general, enhances isoform selectivity. The 6-(3-dimethylaminopropionyl) modification led to an enhanced selectivity for type V, whereas 6-[N-(2-isothiocyanatoethyl) aminocarbonyl] and 6-(4-acrylbutyryl) modification led to an enhanced selectivity for type II. In contrast, 2'-deoxyadenosine 3'-monophosphate, a classical and 3'-phosphate-substituted P-site inhibitor, demonstrated a 27-fold selectivity for inhibiting type V relative to type II, whereas 9-(tetrahydro-2-furyl) adenine, a ribose-substituted P-site ligand, showed a markedly increased, 130-fold selectivity for inhibiting type V. Consequently, on the basis of the pharmacophore analysis of 9-(tetrahydro-2-furyl) adenine and adenylyl cyclase, a novel non-nucleoside inhibitor, 2-amino-7-(2-furanyl)-7,8-dihydro-5(6H)-quinazolinone (NKY80), was identified after virtual screening of more than 850,000 compounds. NKY80 demonstrated a 210-fold selectivity for inhibiting type V relative to type II. More importantly, the combination of a type III-selective forskolin derivative and 9-(tetrahydro-2-furyl) adenine or NKY80 demonstrated a further enhanced selectivity for type III stimulation over other isoforms. Our data suggest the feasibility of adenylyl cyclase isoform-targeted regulation of cyclic AMP signaling by pharmacological reagents, either alone or in combination.

Antiinflammatory effects of colforsin daropate hydrochloride, a novel water-soluble forskolin derivative

BACKGROUND

To evaluate the effects of colforsin daropate hydrochloride (colforsin), a water-soluble forskolin derivative, on hemodynamics and systemic inflammatory response after cardiopulmonary bypass, we conducted a prospective randomized study.

METHODS

Twenty-nine patients undergoing coronary artery bypass grafting were randomized to receive either colforsin treatment (colforsin; n = 14) or no colforsin treatment (control; n = 15). Administration of colforsin (0.5 microg.kg(-1).min(-1)) was started after induction of anesthesia and was continued for 6 hours. Perioperative cytokine and cyclic adenosine monophosphate levels, hemodynamics, and respiratory function were measured serially.

RESULTS

Marked positive inotropic and vasodilatory effects were observed in patients receiving colforsin. Interleukin 1beta, interleukin 6, and interleukin 8 levels after cardiopulmonary bypass were significantly (p < 0.05) lower in the colforsin group. Plasma levels of cyclic adenosine monophosphate increased significantly (p < 0.05) in the colforsin group, and the levels correlated inversely (r = -0.56, p = 0.002) with the respiratory index after cardiopulmonary bypass.

CONCLUSIONS

Intraoperative administration of colforsin daropate hydrochloride had potent inotropic and vasodilatory activity and attenuated cytokine production and respiratory dysfunction after cardiopulmonary bypass. The results indicate that the technique can be a novel therapeutic strategy for the systemic inflammatory response associated with cardiopulmonary bypass.

Two possible mechanisms underlying nitrate tolerance in monkey coronary arteries

1. Previous studies using isolated arteries have demonstrated cross-tolerance between nitric oxide (NO) donors such as nitroglycerin (NTG) and sodium nitroprusside (SNP). However, it remains unclear whether the vasorelaxing effect of atrial natriuretic peptide (ANP), an activator of particulate guanylate cyclase, is affected by treatment with NO donors. To investigate the cross-tolerance and interactions between NTG and ANP in coronary vasorelaxant responses, we used two models of monkey coronary arterial strips (Macaca fuscata). 2. In one model, which was induced by a 1 h treatment with 4.4 x 10(-4) mol/L NTG followed by washout of the agent for 1 h, the vasorelaxing effects of subsequent NTG were markedly attenuated, whereas those of ANP and NO were not affected. These findings suggest that the development of NTG tolerance is associated with a biotransformation process from NTG to NO. In the other model, which did not include washout after exposure to 3 x 10(-6) mol/L NTG, the vasorelaxant responses to 10(-8) mol/L ANP (31.1+/-5.4 vs 5.1+/-2.1%, respectively; P < 0.001), 10(-6) mol/L NO (61.5+/-2.4 vs 29.5+/-8.5%, respectively; P < 0.001) and 10(-8) mol/L SNP (49.4+/-6.4 vs 8.0+/-2.0%, respectively; P < 0.001) were significantly attenuated. The concentration- response curve for 8-bromo-cGMP (8-Br-cGMP) was shifted to the right, whereas responses to papaverine and forskolin were unchanged. These findings suggest that an intracellular process that occurs after the synthesis of cGMP is responsible for this interaction. 3. As a mechanism of NTG tolerance, two possible processes may be impaired: (i) biotransformation from NTG to NO; and (ii) an intracellular process that occurs after the synthesis of cGMP.

In vivo changes in free choline level induced by autonomic agonists in mouse organs, including three major salivary glands

Whether free choline levels are changeable in vivo in response to different types of autonomic agonists was examined in several mouse organs. Upon one subcutaneous injection of isoproterenol, phenylephrine and pilocarpine, choline levels in whole organ decreased, increased and decreased, respectively, in various organs within 30 min and returned to initial levels in a day. In the three major salivary glands, a delayed choline elevation also appeared on day 2 after one isoproterenol injection and subsided by day 6. Only in the three salivary glands more choline was accumulated after 10 once-a-day injections of isoproterenol than after one isoproterenol injection. Neither phenylephrine nor pilocarpine induced comparable choline accumulation in any organs examined. Isoproterenol injection repeated at a 2-day interval augmented the subsequent, delayed choline elevation. Examination with dobutamine and the adenylyl cyclase activator 6-(3-dimethylaminopropionyl)forskolin suggested that isoproterenol-induced immediate choline lowering was down-stream of cAMP synthesis and linked to cAMP more tightly than the choline accumulation, though both choline changes occurred via beta1-adrenergic receptors. Choline levels in the salivary glands also changed depending on the form of diet given and particularly in the parotid gland in parallel with gland weights. These results provide the first evidence for the autonomic control of intracellular choline levels; intracellular choline levels might be an integral part of the autonomic signalling pathway.

Age-related endothelium-dependent vascular relaxation in rat thoracic aorta in response to colforsin

BACKGROUND

Colforsin, a novel water-soluble forskolin derivative, increases intracellular cyclic AMP by direct stimulation of adenylate cyclase and has strong positive inotropic and vasodilative effects. However, it is not known whether colforsin causes nitric oxide (NO) release and enhances endothelium-dependent vascular relaxation.

METHODS

We studied NO production and relaxation on exposure to colforsin in thoracic aorta from rats aged 4, 12 and 60 weeks.

RESULTS

When a low concentration of colforsin was added to a solution bathing ring segments of aorta from 12-week-old rats, relaxation was greater in the ring segments with intact endothelium than in those from which the endothelium had been removed. A high concentration of colforsin induced the same degree of relaxation of ring segments with or without endothelium, probably by a direct effect on vascular smooth muscle cells. Production of NO in response to colforsin by cultured endothelial cells from 12-week-old rat aorta was demonstrated by the electron paramagnetic resonance spin trapping method. A low concentration of colforsin relaxed aortic segments with intact endothelium from 4-week-old rats more than those from 12-week-old or 60-week-old rats. Reversal of relaxation by NG-nitro L-arginine, an NO synthesis inhibitor, was most significant in arteries from 4-week-old rats. Production of NO after exposure to colforsin was greater in aortic segments from 4-week-old rats than older rats, as detected by an NO-selective electrode.

CONCLUSIONS

Colforsin induces vasodilation in part by releasing NO from the endothelium in rat thoracic aorta. In addition to a direct vasodilative effect on the vascular smooth muscle cells, an endothelium-dependent vasodilative effect is also important in younger arteries.

Effects of NKH477 on renal nerve stimulation-induced responses in anesthetized dogs

We evaluated the effects of an adenylate cyclase activator, N, N-dimetyl-beta-alanine[3R-(3alpha,4alphabeta,5beta+ ++,6beta,6aalpha, 10alpha,10abeta,10balpha)]-5(acetyloxy)-3-eth enyldodecahydro-10, 10b-dihydroxy-3,4a,7,7,10a-pentamethyl-1-oxo-1H-naphtho[2, 1-b]pyran-6-yl ester hydrochloride (NKH477), on neural control of renal functions in anesthetized dogs. Renal nerve stimulation (2 Hz) increased renal norepinephrine efflux and reduced renal blood flow, glomerular filtration rate, urine flow rate, urinary Na(+) excretion and fractional Na(+) excretion. Intrarenal arterial infusion of NKH477 (300 ng/kg/min) suppressed the stimulation-induced reductions in renal blood flow and glomerular filtration rate and attenuated the reductions in urine flow rate and urinary Na(+) excretion but not the changes in renal norepinephrine efflux and fractional Na(+) excretion. Infusion of NKH477 did not affect the urinary responses induced by renal nerve stimulation at a lower frequency (0.5-1 Hz) which had little influence on renal blood flow and glomerular filtration rate. The present results demonstrate that NKH477 inhibits renal vasoconstriction and hypofiltration but not the enhanced tubular Na(+) reabsorption during activation of the renal sympathetic nervous system.

Effects of NKH477 on renal functions and cyclic AMP production in anesthetized dogs

The present study was undertaken to evaluate the effects of an adenylate cyclase activator N,N-dimethyl-beta-alanine[3R-(3alpha, 4alphabeta, 5beta, 6beta, 6aalpha, 10alpha, 10abeta, 10balpha)]-5(acetyloxy)-3-ethenyldodecahydro-10, 10b-dihydroxy-3, 4a, 7, 7, 10a-pentamethyl-1-oxo-1H-naphtho [2,1-b] pyran-6-yl ester hydrochloride (NKH477) on renal functions and cyclic AMP production in the dog kidney. The intrarenal arterial infusion of NKH477 (30, 100 and 300 ng kg(-1) min(-1)) increased renal blood flow, glomerular filtration rate, urine flow rate, urinary Na+ and cyclic AMP excretion, fractional Na+ excretion and arterial and renal venous plasma cyclic AMP concentrations in a dose-dependent manner. The intrarenal arterial infusion of rolipram (0.3 microg kg(-1) min(-1)), a cyclic AMP-specific phosphodiesterase inhibitor, also caused the same renal responses as NKH477. The increasing effects of NKH477 on renal blood flow, fractional Na+ excretion and renal venous plasma cyclic AMP concentration were facilitated in the presence of rolipram. NKH477 reduced glomerular filtration rate and filtration fraction in the presence of rolipram. The increasing effects of NKH477 on urine flow rate and urinary Na+ excretion were not affected by rolipram. The present results suggest that NKH477 increases glomerular filtration and suppresses tubular sodium reabsorption through activation of cyclic AMP production, and thereby induces natriuresis. The results also demonstrate that renal cyclic AMP level during the activation of adenylate cyclase is regulated by phosphodiesterase IV in both the vascular and tubular sites.

Stimulation of adenylyl cyclase and induction of brain-derived neurotrophic factor and TrkB mRNA by NKH477, a novel and potent forskolin derivative

The present study was undertaken to examine whether NKH477, a novel and potent water-soluble forskolin derivative, stimulates adenylyl cyclase and regulates brain-derived neurotrophic factor (BDNF) and TrkB expression in the rat brain. Administration of NKH477 at a dose of 1.0 mg/kg, but not 0.1 mg/kg, increased levels of cyclic AMP (cAMP) in a time-dependent manner in frontal cortex and hippocampus. Repeated administration of NKH477 (1.0 mg/kg) for 7 or 14 days also increased levels of cAMP in these two brain regions, indicating that the response does not desensitize with chronic treatment. In addition, administration of NKH477 at the 1 mg/kg dose increased the expression of BDNF and TrkB mRNA in frontal cortex and hippocampus. This effect was observed after single, as well as repeated (7 or 14 days), administration of NKH477. These results demonstrate that NKH477 administration rapidly increases cAMP levels in brain and provides evidence that stimulation of this second messenger system increases the expression of BDNF and TrkB mRNA.

Characterization of positive inotropic effect of colforsin dapropate hydrochloride, a water-soluble forskolin derivative, in isolated adult rat cardiomyocytes

The present study was undertaken to characterize the positive inotropic action of colforsin dapropate hydrochloride (NKH477), a novel water-soluble forskolin derivative, on isolated cardiomyocytes of adult rats. Simultaneous measurements of cellular contraction and intracellular calcium concentration ([Ca2+]i) were carried out. The effects of isoprenaline and ouabain on these parameters were also determined for comparison. The contraction and maximum [Ca2+]i of NKH477-, isoprenaline-, or ouabain-treated cells were increased concentration dependently. Peak shortening of NKH477-treated cells was positively correlated with the shortening velocity and inversely with the time to peak shortening. Maximum, but not minimum, [Ca2+]i in NKH477-treated cells was correlated with the rate of increase in [Ca2+]i and inversely with the time to maximum [Ca2+]i. Similar results were obtained with isoprenaline. In contrast, ouabain increased both maximum and minimum [Ca2+]i. Treatment with either NKH477 or isoprenaline increased cellular cAMP content, but treatment with ouabain did not. These results suggest that the positive inotropic action of NKH477 is associated with an increase in [Ca2+]i and acceleration of its kinetics.Key words: adenylate cyclase, calcium transient, colforsin dapropate, isoprenaline, ouabain.

Relaxant effects of NKH477, a new water-soluble forskolin derivative, on guinea-pig tracheal smooth muscle: the role of Ca2+-activated K+ channels

1. Mechanisms underlying the bronchorelaxant action of NKH477, a newly developed water-soluble forskolin derivative, were investigated in guinea-pig isolated tracheal smooth muscle. 2. In muscles precontracted with 3 microM histamine, NKH477 (1 nM-1 microM) caused a concentration-dependent decrease of isometric tension, resulting in a complete relaxation at 300 nM. The EC550 for the relaxation was 32.6+/-4.3 nM (n=6). 3. In the presence of 30 or 90 nM iberiotoxin (IbTX), a selective blocker of the large-conductance Ca2+-activated K+ (BK(Ca)) channel, the relaxing action of NKH477 on the histamine-induced contraction was inhibited, giving rise to a parallel shift of the concentration-response curves; the EC50 of NKH477 was increased to 131.4+/-20.4 nM at 30 nM IbTX (n=4), and 125.3+/-12.2 nM at 90 nM IbTX (n=4). 4. Pretreatment of muscles with 30 mM tetraethylammonium (TEA) caused a similar rightward shift of the concentration-response curve to NKH477 with an increase of the EC50 to 139.8+/-18.4 nM (n=5). In contrast, the relaxing action of NKH477 was unaffected by 10 microM glibenclamide, an ATP-sensitive K channel blocker, or by 100 nM apamin, a blocker of small conductance Ca2+-activated K+ channels. 5. In muscles pretreated with 1 microM nifedipine, a blocker of the voltage-dependent Ca2+ channel (VDC), 30-90 nM IbTX did not affect the relaxant effects of NKH477 on the histamine-induced contraction. 6. In muscles precontracted by a K+-rich (40 mM) solution, NKH477 caused only minimal relaxation (19.8+/-1.7%, n=4) even at the highest concentration (1 microM). 7. In experiments to measure the ratio of fura-2 fluorescence signals (R(340/380)) as an index of the intracellular Ca2+ concentration ([Ca2+]i), the application of 100 nM NKH477 or 200 nM isoprenaline to the preparation precontracted by 3 microM histamine resulted in a decrease in [Ca2+]i in association with a decrease in tension. The reduction of [Ca2+]i and tension by NKH477 was 47.0+/-5.6% and 62.8+/-7.0%, respectively (n=5), and that with isoprenaline 60.6+/-7.4% and 67.4+/-6.4%, respectively (n=5). These effects of NKH477 and isoprenaline on [Ca2+]i and tension were inhibited by 30 nM IbTX. The inhibitory action of IbTX was abolished in the presence of 1 microM nifedipine. 8. These results suggest that the bronchorelaxant action of NKH477 may result, at least in part, from activation of BK(Ca) channels, which may cause a hyperpolarization of smooth muscle cell membranes and a secondary decrease in Ca2+ influx through VDCs, leading to a decrease in [Ca2+]i.

Effects of NKH477, a forskolin derivative, and dibutyryl-cyclic AMP on adrenal catecholamine release in response to splanchnic nerve stimulation, acetylcholine, DMPP and muscarine in anesthetized dogs

The effects of NKH477, a water-soluble forskolin derivative, and dibutyryl-cyclic adenosine monophosphate (dbcAMP) on the release of adrenal catecholamines (CAs) in response to splanchnic nerve stimulation (SNS), acetylcholine (ACh), the nicotinic receptor stimulant 1,1-dimethyl-4-phenyl-piperazinium iodide (DMPP) and muscarine were examined in anesthetized dogs. NKH477, dbcAMP and the cholinergic agonists were infused and injected, respectively, into the adrenal gland intra-arterially. SNS (3 Hz) or injections of ACh (3 micrograms), DMPP (2 micrograms) and muscarine (2 micrograms) produced increases in CA output determined from adrenal venous blood. Both NKH477 infusion (0.3, 1 and 3 micrograms/min) and dbcAMP infusion (0.1, 0.3 and 1 mg/min) caused dose-dependent enhancement of the SNS-, ACh- and DMPP-induced increases in CA output, whereas they failed to affect the muscarine-induced increases in CA output. Neither NKH477 nor dbcAMP affected basal CA output. Cyclic AMP (cAMP) overflow determined from adrenal venous blood increased during NKH477 infusion. These results indicate that NKH477 and dbcAMP have facilitatory effects on adrenal CA release mediated by nicotinic receptors, but not by muscarinic receptors in the dog, and suggest the selective action of cAMP on nicotinic mechanism.

Potential antidepressant properties of forskolin and a novel water-soluble forskolin (NKH477) in the forced swimming test

The mechanisms of the antidepressant activity of forskolin and a novel water soluble forskolin analog (NKH477) were studied using the forced swimming method in rats. Forskolin (0.01-0.1 mg/kg) and NKH477 (0.01-0.1 mg/kg) dose-dependently decreased ratings of immobility, with effects similar to those of amitriptyline treatment. The maximum effects of forskolin and NKH477 were observed at 0.01 mg/kg dose which is 150 more times potent than that (15 mg/kg) of amitriptyline. At a high dose (1.0 mg/kg) of forskolin and NKH477, the duration of immobility was returned to control levels. Forskolin and NKH477 did not influence the spontaneous locomotor activity at intraperitoneal injection doses from 0.01 to 1 mg/kg. Furthermore chronic administration with NKH477 at oral dose from 0.5 to 1.5 mg/kg significantly decreases the duration of immobility. These data indicate that both forskolin and NKH477 have strong antidepressive potency, consistent with the hypothesis that elevation of the cAMP cascade system may have an important role in antidepressive effects.

Zatebradine inhibits tachycardia induced by bronchodilators without affecting respiratory resistance in dogs

Bronchodilators used for bronchial asthma reduce respiratory resistance but also increase heart rate to some extent. It is often difficult to use such bronchodilators with elderly patients and patients with heart disease. The object of our study was to investigate whether a specific bradycardic agent, zatebradine, inhibited the heart rate increased by bronchodilators without affecting respiratory resistance. We evaluated the effects of zatebradine on the increases in heart rate and inhibition of the respiratory resistance in response to the bronchodilators, isoproterenol, procaterol (a beta 2-adrenoceptor agonist), 6-(3-dimethylaminopropionyl)-forskolin, NKH 477 (an adenylyl cyclase activator) and aminophylline in the anesthetized and artificially ventilated dog. When zatebradine in doses of 0.05-1.5 mg/kg i.v. decreased heart rate without affecting arterial blood pressure, it dose dependently attenuated the increase in heart rate in response to isoproterenol, procaterol, NKH 477 and aminophylline but did not affect the inhibition by these substances of the increase in respiratory resistance induced by histamine. Propranolol (0.01-0.3 mg/kg i.v.) dose dependently inhibited not only the increase in heart rate but also the inhibition of the respiratory resistance induced by isoproterenol and procaterol. The present results indicate that zatebradine selectively inhibits the increase in heart rate in response to cyclic AMP-dependent bronchodilators without affecting their bronchodilator effects in anesthetized dogs and suggest that zatebradine may be a useful drug for prevention of the tachycardia induced by bronchodilators used for patients with bronchial asthma.

Forskolin carbamates: binding and activation studies with type I adenylyl cyclase

Three series of analogs were regioselectively prepared from a protected forskolin precursor to afford 7-carbamoyl-7-desacetylforskolins (series 1), 6-carbamoyl-7-desacetylforskolins (series 2), and 6-carbamoylforskolins (series 3). The analogs were pharmacologically evaluated for binding (IC50) to and activation (EC50) of type I adenylyl cyclase in membranes from stably transfected Sf9 cell lines expressing a single adenylate cyclase subtype. The following ranges were determined for the IC50's and EC50's of each individual series: series 1, IC50 = 43-1600 nM, EC50 = 0.5-9.6 microM; series 2, IC50 = 65-680 nM, EC50 = 0.63-6.5 microM; series 3, IC50 = 21-271 nM, EC50 = 0.5-8.1 microM (forskolin IC50 = 41 nM and EC50 = 0.5 microM). Activation paralleled binding; however, some analogs exhibited poor binding and good activation whereas others demonstrated good binding but poor activation. Steric bulk tended to diminish binding and activation when at the 6- or 7-position, although bulk was accommodated at the 6-position if the 7-site was reacetylated. Acylation of the 7-position by the carbamoyl linker or acetyl was important for obtaining good binding and activation; however, the effect was more pronounced with binding. For both binding and activation, small, linear, lipophilic substituents (propyl, allyl, isopropyl) are well tolerated at the 7-position but less so in the 6-position, even when the 7-site is reacetylated. Planar aromatic moieties (phenyl and 2-pyridinyl) demonstrated moderate to good potency for binding and activation when located at either the 6- or 7-positions. There is an overall trend toward increasing potency for both binding and activation with polar substituents.

Effect of ischemic preconditioning of the myocardium on cAMP

Reduction of cAMP has been implicated in the protection of ischemic preconditioning (IP), but until now, this possibility has not been directly addressed. In this study, we found that in the in vivo rabbit heart 10 to 30 minutes of sustained regional ischemia was accompanied by a nearly twofold rise in cAMP levels. This increase in cAMP was attenuated when sustained ischemia was preceded by IP induced with a single cycle of transient ischemia and reperfusion (TI/R) and prevented when ischemia was preceded by three cycles of TI/R. The mechanism of cAMP reduction by IP does not involve activation of protein kinase C (PKC), since the PKC inhibitor polymyxin B (24 mg/kg) did not raise cAMP levels during sustained ischemia in IP hearts. Furthermore, this effect is also not mediated by reduced responsiveness of the beta-adrenergic effector pathway, since both nonischemic hearts and hearts subjected to three cycles of TI/R exhibited similar increases in cAMP in response to 5 micrograms/kg isoproterenol. However, propranolol (0.75 mg/kg) abolished the rise in cAMP levels observed during sustained ischemia in control hearts but did not reduce cAMP levels further in IP hearts. These data indicate that the ischemia-induced rise in cAMP levels in control hearts was mediated by activation of the beta-adrenergic receptor. Taken together with data demonstrating that beta-adrenergic responsiveness was not affected by IP, these data support the conclusion that the lack of elevation in cAMP levels observed during sustained ischemia in IP hearts is mediated by an attenuation of norepinephrine release. To examine whether the protection of IP against necrosis was mediated by the lack of elevation in cAmp levels, we determined whether the infarct size-limiting effect of IP could be blocked by NKH477, an activator of adenylyl cyclase. Four groups or rabbits were subjected to 30 minutes of in vivo regional ischemia and 90 minutes of reperfusion. Control hearts (n = 10) had 53.6 +/- 5.5% infarction of the area at risk. IP with three cycles of transient ischemia limited infarct size to 3.2 +/- 1.3% (N = 13, p < .0001). NKH477 (45 micrograms/kg) increased average cAMP levels in IP hearts during sustained ischemia to levels similar to those in untreated control hearts. However, NKH477 did not block IP (50.2 +/- 7.7% of the area at risk was infarcted in the control +NKH477 group [n = 10] versus 10.0 +/- 5.9% in the IP + NKH477 group [n = 7], P < .05). Therefore, we conclude that although IP lowers cAMP levels during sustained ischemia, this effect is not necessary for its protection against necrosis, since raising cAMP does not block this protection of IP.

Inotropic agent vesnarinone inhibits cytokine production and E-selectin expression in human umbilical vein endothelial cells

The cytokine modulating effects of inotropic agents on human umbilical vein endothelial cells (HUVEC) were investigated. Confluent HUVEC in 24-well plates were treated with inotropic agents and then stimulated with 10 ng/ml of human interleukin (IL)-1 beta. After 24 h of incubation, the cytokine levels in the culture supernatants were determined by specific enzyme-linked immunosorbent assay (ELISA) kits. Vesnarinone [OPC-8212; 3,4-dihydro-6-(4-(3,4-dimethoxybenzoil)-1-piperazinyl)-2(1H)- quinolinone] at 26 mumol/l significantly suppressed the production of IL-6, granulocyte macrophage colony stimulating factor (GM-CSF) and granulocyte colony stimulating factor (G-CSF) induced by IL-1 beta. Although 8 bromoadenosine 3'5' cyclic monophosphate (8Br-cAMP) at 100 mumol/l also inhibited the production of these cytokines, the inhibitory effect was less marked than that of vesnarinone. Amrinone at 26 mumol/l and NKH477 at 10 nmol/l also had a less marked inhibitory effect against the production of IL-6. Next, the inhibitory effect of inotropic agents against the expression of the adhesion molecules of HUVEC was measured by a cell ELISA method. Vesnarinone at 26 mumol/l and NKH477 at 10 mumol/l, a water soluble forskolin derivative used as a positive control, both significantly inhibited the expression of E-selectin induced by 10 ng/ml of human tumor necrosis factor (TNF)-alpha. Amrinone at 26 mumol/l did not inhibit the expression of E-selectin. The level of HUVEC cAMP induced by vesnarinone at 26 mumol/l was much lower than that induced by NKH477 at 10 mumol/l. Moreover, according to a 3-(4,5-dimethyl-thiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) cell viability assay, vesnarinone did not affect the viability of HUVEC. The immunosuppressive effects of vesnarinone described above are not derived from either a cAMP elevating effect or a cytotoxic effect against HUVEC. Although the cytokine network in heart failure has not yet been elucidated, patients with congestive heart failure might benefit from the immunomodulating effects of inotropic agents.

Bronchodilator and cardiovascular effects of NKH477, a novel water-soluble forskolin derivative, in guinea pigs

The bronchodilator and cardiovascular effects of NKH477 (6-(3-dimethylaminopropionyl)forskolin hydrochloride) were evaluated. In anesthetized guinea pigs, i.v. bolus injections of NKH477 (1-100 micrograms/kg) inhibited the bronchoconstriction induced by inhaled leukotriene D4, increased the heart rate (HR) and decreased the diastolic arterial blood pressure (DBP) in a dose-dependent manner. The bronchodilator effect of NKH477 was 1500 times more potent than that of aminophylline and 17 times less potent than that of isoproterenol. The selectivity of NKH477 for bronchodilation vs an increase in HR was 15 times higher than that of isoproterenol and similar to that of aminophylline; and vs a decrease in DBP, the selectivity was 4 times higher than that of aminophylline and similar to that of isoproterenol. I.v. infusion of NKH477 (0.1-3 micrograms/kg/min) for 2 hr dose-dependently inhibited the bronchoconstriction induced by i.v. histamine. Isoproterenol (0.1 microgram/kg/min, i.v.) enhanced the bronchoconstriction after termination of the infusion, whereas NKH477 did not. In conscious guinea pigs, inhalation of NKH477 (0.1-5 mg/ml) concentration-dependently inhibited the bronchoconstriction induced by inhaled histamine, and a high concentration of NKH477 (35.4 mg/ml) increased the HR. The bronchodilator effect of inhaled NKH477 was 15 times less potent than that of isoproterenol. The selectivity of inhaled NKH477 was similar to that of isoproterenol. These results indicate that NKH477 may be useful as a bronchodilator.

Zatebradine attenuates cyclic AMP-related positive chronotropic but not inotropic responses in isolated, perfused right atria of the dog

1. Inhibition of I(f) or ICa by zatebradine has been reported in mammalian SA nodal cells. We thus investigated whether zatebradine differentially attenuates the positive chronotropic and inotropic responses to norepinephrine, isoproterenol, NKH 477 (an adenylyl cyclase activator), 3-isobutyl-1-methylxanthine (IBMX) and Bay k 8644 (a calcium channel agonist) in the isolated, blood-perfused dog atrium. 2. When zatebradine (0.03-1 mumol) decreased sinus rate from 104 +/- 4.5 to 73 +/- 4.9 beats/min dose-dependently, it selectively attenuated the positive chronotropic but not inotropic responses to norepinephrine in a dose-related manner. Zatebradine decreased the norepinephrine-induced tachycardia (by approximately 80% from the control) more effectively than the spontaneous sinus rate (by approximately 30% from the control). 3. Zatebradine similarly attenuated the positive chronotropic but not inotropic responses to isoproterenol, NKH 477 and IBMX. Fifty per cent inhibition doses of zatebradine (0.10-0.18 mumol) for the chronotropic responses to each substance were not significantly different. 4. On the other hand, zatebradine attenuated neither positive chronotropic nor inotropic responses to Bay k 8644. 5. We therefore suggest that zatebradine selectively attenuates the positive chronotropic but not inotropic responses to cyclic AMP-related substances due to inhibition of I(f) but not ICa in the dog heart.

Phosphorylation of focal adhesion vasodilator-stimulated phosphoprotein at Ser157 in intact human platelets correlates with fibrinogen receptor inhibition

Integrins and other adhesion receptors are essential components for outside-in and inside-out signaling through the cell membrane. The platelet glycoprotein IIb-IIIa (also known as fibrinogen receptor or integrin alpha IIb beta 3) is activated by platelet agonists, inhibited by cyclic-nucleotide-elevating agents, and is involved in the activation of protein tyrosine kinases including the 125-kDa focal adhesion kinase (pp125FAK). However, the molecular details of glycoprotein IIb-IIIa regulation are not well understood. Here we report that in ADP-activated human platelets cAMP- and cGMP-dependent protein-kinase-mediated phosphorylation of the focal adhesion vasodilator-stimulated phosphoprotein (VASP) at Ser157 correlates well with glycoprotein IIb-IIIa inhibition. Human platelets contain similar concentrations of glycoprotein IIb-IIIa complexes (fibrinogen binding sites) and VASP. Using gel-filtered platelets, cAMP-elevating agents [e.g. prostaglandin E1 and the forskolin analog 6-(3-dimethylaminopropionyl)forskolin (NKH 477)] caused VASP Ser157 phosphorylation and inhibited glycoprotein IIb-IIIa activation up to 70-100%. NO-generating, cGMP-elevating agents [e.g. 3-morpholinosydnonimine hydrochloride (SIN1) and sodium nitroprusside] stimulated VASP Ser157 phosphorylation and inhibited glycoprotein IIb-IIIa activation up to a maximal extent of 30-50%. The effects of cAMP- and cGMP-elevating agents on VASP phosphorylation and fibrinogen binding were reversible and could be mimicked by membrane-permeant selective activators of platelet cAMP- or cGMP-dependent protein kinase, respectively. Using threshold concentrations, the nitrovasodilator SIN 1 potentiated the effects of the forskolin analog NKH 477 with respect to inhibition of platelet aggregation, VASP phosphorylation and glycoprotein IIb-IIIa inhibition. It is proposed that the inhibition of glycoprotein IIb-IIIa induced by cyclic nucleotide involves cAMP-and cGMP-dependent protein-kinase-mediated VASP phosphorylation at Ser157.

Adenylate cyclase activation promotes the recruitment of coronary vasodilator reserve and improves subendocardial contractility during coronary hypoperfusion

This study was designed to examine the effects of an adenylate cyclase activator, NKH477, on epicardial and endocardial contraction and coronary blood flow (CoF) in the presence or absence of ischemia and to compare it to those of adenosine. We measured coronary pressures (CoP), coronary blood flow, epicardial and endocardial wall thickening (i.e., %EPWT and %ENWT, respectively, by sonomicrometry) in 18 anesthetized dogs. The left circumflex coronary artery was perfused with arterial blood using a pressure controlled servo pump. Propranolol (0.5 mg/kg) and atropine (0.25 mg) were used to minimize the neurogenic effects. CoP decreased from 100 mm Hg to 40 mm Hg with and without drugs. At CoP of 100 mm Hg, intracoronary infusion of NKH477 (10(-8) M/kg/min) produced a two-fold increase in CoF, but there were no changes in either the %EPWT or the %ENWT. During coronary hypofusion at coronary pressures equal to 40 mm Hg, NKH477 increased CoF from 16 +/- 2 to 28 +/- 4 mL/min (p < 0.05) and improved %ENWT significantly from 6 +/- 7 to 23 +/- 7% (p < 0.05). However %EPWT was not improved by NKH477. On the other hand, the intracoronary infusion of adenosine (10 micrograms/kg/min) increased CoF from 16 +/- 5 to 21 +/- 6 mL/min (p < 0.05) at CoP of 40 mm Hg. However, this dose of adenosine failed to improve %ENWT (16 +/- 10% vs. 14 +/- 10%, n.s.). Thus, the improvement of subendocardial function by NKH477 might be related to the improvement of subendocardial perfusion which could be induced by the potentiation of endogenously released adenosine as well as the direct vasodilator effect. This contrasts with the effects of exogenously administered adenosine, which failed to improve subendocardial contractility.