Phosphodiesterase inhibition by new cardiotonic agents: mechanism of action and possible clinical relevance in the therapy of congestive heart failure

Adverse drug reactions in patients with cardiovascular disease

Adverse drug reactions (ADRs) occur frequently in modern medical practice, increasing morbidity and mortality and inflating the cost of care. Patients with cardiovascular disease are particularly vulnerable to ADRs due to their advanced age, polypharmacy, and the influence of heart disease on drug metabolism. The ADR potential for a particular cardiovascular drug varies with the individual, the disease being treated, and the extent of exposure to other drugs. Knowledge of this complex interplay between patient, drug, and disease is a critical component of safe and effective cardiovascular disease management. The majority of significant ADRs involving cardiovascular drugs are predictable and therefore preventable. Better patient education, avoidance of polypharmacy, and clear communication between physicians, pharmacists, and patients, particularly during the transition between the inpatient to outpatient settings, can substantially reduce ADR risk.

Effects of cAMP modulators on long-chain fatty-acid uptake and utilization by electrically stimulated rat cardiac myocytes

Recently, we established that cellular contractions increase long-chain fatty-acid (FA) uptake by cardiac myocytes. This increase is dependent on the transport function of an 88 kDa membrane FA transporter, FA translocase (FAT/CD36), and, in analogy to skeletal muscle, is likely to involve its translocation from an intracellular pool to the sarcolemma. In the present study, we investigated whether cAMP-dependent signalling is involved in this translocation process. Isoproterenol, dibutyryl-cAMP and the phosphodiesterase (PDE) inhibitor, amrinone, which markedly raised the intracellular cAMP level, did not affect cellular FA uptake, but influenced the fate of intracellular FAs by directing these to mitochondrial oxidation in electrostimulated cardiac myocytes. The PDE inhibitors 3-isobutyl-1-methylxanthine, milrinone and dipyridamole each significantly stimulated FA uptake as well as intracellular cAMP levels, but these effects were quantitatively unrelated. The stimulatory effects of these PDE inhibitors were antagonized by sulpho- N -succinimidylpalmitate, indicating the involvement of FAT/CD36, albeit that the different PDE inhibitors use different molecular mechanisms to stimulate FAT/CD36-mediated FA uptake. Notably, 3-isobutyl-1-methylxanthine and milrinone increased the intrinsic activity of FAT/CD36, possibly through its covalent modification, and dipyridamole induces translocation of FAT/CD36 to the sarcolemma. Elevation of intracellular cGMP, but not of cAMP, by the PDE inhibitor zaprinast did not have any effect on FA uptake and metabolism by cardiac myocytes. The stimulatory effects of PDE inhibitors on cardiac FA uptake should be considered when applying these agents in clinical medicine.

Acute enoximone effect on systemic and renal hemodynamics in patients with heart failure

Patients with heart failure generally show improvement in their clinical condition after enoximone infusion over the period of treatment; this effect cannot be ascribed only to the known hemodynamic action of this drug. Thirty-six patients (age range 44-82 years) with heart failure (NYHA class II-IV) underwent 48-hour enoximone infusion to study whether this prolonged improvement might depend on changes in systemic or renal hemodynamics or in neurohormonal balance. All patients underwent Swan-Ganz hemodynamic monitoring; renal plasma flow, glomerular filtration rate, plasma atrial natriuretic factor (ANF), and plasma renin activity (PRA) were all measured at baseline, at the peak of the enoximone action, and 48 hours after drug discontinuation. The main hemodynamic parameters were significantly improved during enoximone infusion and after drug discontinuation. The cardiac index basal value of 2.2 +/- 0.1 l/min/m2 increased to 3.1 +/- 0.1 l/min/m2 after 24-hour therapy (p < 0.01); similarly, pulmonary wedge pressure, mean pulmonary arterial pressure, and right atrial pressure decreased markedly (p < 0.01). Beneficial effects were also observed in renal hemodynamics; indeed, renal plasma flow (basal value 485 +/- 39 ml/min) increased significantly after 24-hour enoximone infusion (575 +/- 35 ml/min; p < 0.01), and this tendency was also observed 48 hours after drug discontinuation. No significant modifications were observed in plasma hormone data; however, the PRA plasma level had a tendency to decrease. We conclude that in patients with heart failure, enoximone infusion has a less marked effect on renal hemodynamics, but this is more lasting than systemic hemodynamic effects. The tendency of PRA to decrease (although not statistically significant), still detectable 2 days after treatment in the presence of steady high plasma ANF concentrations, may also contribute to the paradoxical longlasting benefit despite the short-lived improvement in systemic hemodynamics after brief cycles of enoximone infusion.

Beneficial effect of amrinone on murine cardiac allograft survival

Amrinone is a non-glycoside positive inotropic agent with an inhibitory effect on a cyclic adenosine monophosphate (AMP) phosphodiesterase isoenzyme. In the present study, we examined the immunosuppressive action of amrinone, since several other cyclic AMP-elevating agents have been shown to suppress T lymphocyte activation. First, the in vivo effects of amrinone were investigated. Oral amrinone treatment, at 40 mg/kg per day, significantly prolonged median cardiac allograft survival compared with non-treated controls (22.0 days versus 10.5 days, P < 0.01) when DBA/2 mouse hearts (H-2d) were heterotopically transplanted into C57B1/6 mice (H-2b). Histopathological examination showed that there was less prominent cellular infiltration in the amrinone-treated than in the non-treated allografts. Plasma amrinone concentrations of mice after a single oral dose of 40 mg/kg were within the range of clinical relevance. To clarify the mechanism of action, in vitro studies were done. The generation of specific cytotoxic T lymphocytes after mixed lymphocyte culture was significantly suppressed by addition of amrinone to the culture medium at 5 micrograms/ml. The production of IL-2 and the interferon-gamma during mixed lymphocyte culture was also suppressed by amrinone at 5 micrograms/ml. However, the level of intracellular cyclic AMP in mouse splenic lymphocytes was not affected significantly by the same dose of amrinone. In conclusion, amrinone has immunosuppressive actions at the therapeutic doses, and it may be a beneficial agent for therapy against acute cardiac allograft rejection.

Direct depressant effect of phosphodiesterase inhibitors on ATPase activity of rat cardiac myofibrils

The aim of this study was to determine (i) whether phosphodiesterase inhibitors influenced ATPase activity of maximally calcium activated cardiac myofibrils and (ii) whether this effect varied in relation to isomyosin composition. Myofibrils were prepared from ventricular myocardium of 2- to 3-month-old rats. ATPase activity was determined at low ionic strength at high (> 7.5) and low (4.4) pCa. Five compounds (amrinone, milrinone, enoximone, piroximone, and rolipram) were examined at concentrations between 10 microM and 1 mM. The results obtained showed that only milrinone and amrinone inhibited ATPase activity; inhibition was dose dependent, and milrinone was more potent than amrinone. To assess whether isomyosin composition might influence the responsiveness of myofibrils to phosphodiesterase inhibitors, the effect of 1 mM milrinone was also determined in myofibrils from hypothyroid rats. According to previous observations hypothyroidism caused an isomyosin shift from V1 to V3 in rat ventricular myocardium. The inhibitory effect of milrinone was lower in myofibrils prepared from hypothyroid rats than in myofibrils from euthyroid rats.

Differential effects of phosphodiesterase inhibitors on accumulation of cyclic AMP in isolated ventricular cardiomyocytes

The intracellular actions of phosphodiesterase (PDE) inhibitors on the accumulation of cyclic nucleotides were studied in isolated ventricular cardiomyocytes from adult Sprague-Dawley rats. Elevated levels of cyclic AMP, due to the effects of selective PDE inhibitors, were detected only when the levels of cyclic nucleotide were enhanced with forskolin (10 microM). The time course for the elevation of cyclic AMP levels was similar for all the PDE inhibitors tested, following the pattern of an initial rise in the first 2-4 min, proceeded by a steady state at 67 +/- 6% of the maximum stimulation. HN-10200 (2-[3-methoxy-5-methylsulfinyl-2-thienyl]-1H-imidazo-[4,5-c]- pyridine hydrochloride), a new imidazopyridine derivative, had a similar concentration-dependent profile to the structurally related compound, sulmazole (AR-L 115 BS, 2-[2-methoxy-4-methylsulfinyl)phenyl]-1H- imidazo-[4,5-b]-pyridine). Both the non-selective inhibitor, 3-isobutyl-1-methylxanthine (IBMX), and the selective PDE IV inhibitor, Ro 20-1724 (4-[(3-butoxy-4-methoxyphenyl)methyl]-2- imidazolidinone), potentiated the forskolin-stimulated levels of cyclic AMP with a much greater efficacy than sulmazole or HN-10200. The concentrations of forskolin required by IBMX, sulmazole and HN-10200 (10(-3) M) to increase levels of cyclic AMP by 4 pmol/mg protein were 3.2 x 10(-6) M, 1.32 x 10(-5) M and 1.46 x 10(-5) M, respectively. Enoximone failed to cause an increase in the levels of cyclic AMP, even when stimulated with maximal concentrations of forskolin. Furthermore, in the presence of forskolin, enoximone attenuated the response of Ro 20-1724 and IBMX in a concentration-dependent manner. Enoximone, similarly to HN-10200, sulmazole, Ro 20-1724 and IBMX did not produce any significant effect on levels of cyclic GMP under elevated conditions in the presence of sodium nitroprusside. The combined action of Ro 20-1724, with either HN-10200, sulmazole, or IBMX (10(-4) M), on intracellular levels of cyclic AMP, was not greater than the response to Ro 20-1724 alone. These data demonstrate the differential actions of PDE III and PDE IV inhibitors in rat ventricular cardiomyocytes. It is suggested that enoximone has a high selectivity for the PDE III isoenzyme so that hydrolysis of cyclic AMP by the PDE IV isoenzyme is not inhibited, in accordance with the lack of increase in cyclic AMP by enoximone in rat cardiomyocytes. HN-10200 and sulmazole, producing small increases in intracellular levels of cyclic AMP, are less selective PDE III inhibitors than enoximone.(ABSTRACT TRUNCATED AT 400 WORDS)

The inotropic mechanism of the phosphodiesterase inhibitor OPC 3911 alone and in combination with rolipram, studied in papillary muscles of ferret and guinea-pig and isolated myocytes of guinea-pig ventricular muscle

OPC 3911 is a potent inhibitor and PDE III is a specific inhibitor in cardiac muscle. The effects of the drug alone and in combination with the non-inotropic PDE IV inhibitor rolipram were analysed using hearts from guinea-pigs and ferrets. OPC 3911 had an EC50 value of 0.1 microM. At 0.1 microM peak force was increased by 50.7 +/- 7.6% (n = 6, P < 0.001), time to peak tension (TPT) reduced by 18.7 +/- 5.6% (n = 6, P < 0.05). Time to half relaxation (THR) was prolonged by 19 +/- 4.2% (n = 6, P < 0.001). After addition of rolipram (30 microM), there was a potentiation of peak force at all concentrations of OPC 3911. At 0.1 microM OPC rolipram increased peak force by 82.8 +/- 8.9% (n = 6, P < 0.001), reduced TPT by 73 +/- 6% (n = 6, P < 0.005) and increased THR by 27 +/- 5% (P < 0.01). OPC 3911 shortened action potential duration (APD) at 50% repolarization by 5.3 +/- 2.5% (n = 6, P < 0.05). Addition of rolipram prolonged APD by 3.7 +/- 2.5% (n = 6, P < 0.05). Second inward current (Isi) was increased at 3 microM OPC 3911 by 46 +/- 6% (n = 6, P < 0.05). The combination of OPC 3911 and rolipram intensified the Isi to 101 +/- 5% (n = 3). Rolipram slowed the rate of restitution and the onset of restitution was prolonged. Relative maximum post-extrasystolic potentiation was reduced in the presence of OPC 3911 from 67 +/- 5% to 45 +/- 6%. Adding rolipram caused potentiation of 55 +/- 6%. OPC 3911 increased the recirculation fraction of activator calcium from 0.36 to 0.42 (n = 10, P < 0.05). After addition of rolipram the recirculation fraction was 0.41 +/- 0.04 (n = 10, P < 0.05). The results suggest that rolipram exerts its potentiating effect on OPC 3911 via an increased Isi.

The contractile and electrophysiological effects of rolipram in guinea-pig papillary muscles and isolated ventricular myocytes

Isometric force, action potentials and in voltage-clamp Isi (second inward current) and its current voltage relation were recorded in papillary muscles from guinea-pigs and from guinea-pig isolated ventricular myocytes (35-37 degrees C, 0.5-1 Hz). Rolipram (1-100 microM) had no significant effect on peak isometric twitch. The rate of rise of force and time to peak tension (TPT) was likewise unaffected. Time to half relaxation (THR) was increased in a dose-dependent manner and at 30 microM THR was prolonged by 25.3 +/- 6% (n = 10, P < 0.001). The effect of 30 microM rolipram on isometric force was frequency dependent. At 0.25 Hz peak force was increased by 6.3 +/- 3.1% (n = 7, P < 0.05). At 2 Hz rolipram exhibited a negative inotropic effect of 9.8 +/- 3.3% (n = 5, P < 0.02). Action potential duration at 90% repolarization was prolonged by 13 +/- 6 ms (n = 7, P < 0.05), and there was usually no effect on resting potential or action potential amplitude. Sometimes, however, a depressed plateau was recorded. Rolipram was without effect on Isi and its current-voltage relations. Time to full mechanical restitution after a test interval was not changed but the shape of the restitution curve was altered. The restitution process was much slower in the presence of rolipram. Hence, peak force was lower at test intervals shorter than 800 ms. Likewise, the shape of the curve relating postextrasystolic potentiation to test interval was altered by rolipram.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiac effects of R 79595 and its isomers (R 80122 and R 80123) in an acute heart failure model. A new class of cardiotonic agents with highly selective phosphodiesterase III inhibitory properties

R 79595 (N-cyclohexyl-N-methyl-2-[[[phenyl (1,2,3,5-tetrahydro-2 oxoimidazo [2,1-b]-quinazolin-7-yl) methylene] amin] oxy] acetamide) and its isomers represent a novel class of compounds with phosphodiesterase (PDE) inhibitory and cardiotonic (positive inotropic) actions. The cardiac effects of this class of compounds were investigated in the hexobarbital-depressed heart-lung preparation of the guinea-pig. After induction of heart failure (reduction of cardiac output to 25% of the initial value) cumulative addition of R 79595 or its isomers R 80122 (E-isomer) and R 80123 (Z-isomer) concentration-dependently reversed the cardiac depressant effects of hexobarbitone-Na. With regard to reconstitution of contractility and cardiac function R 80122 (E-isomer) was 10 fold more potent than R 79595 (1:1 mixture of the isomers) and nearly 100 fold more potent than R 80123 (Z-isomer). Furthermore, the cardiotonic action of the most potent isomer (R 80122) was compared to the effects of several positive inotropic reference compounds. The order of cardiotonic potency was as follows: (-)-adrenaline > R 80122 = adibendan > digitoxin > milrinone = enoximone > theophylline. Adibendan (EC50 value: 6.7 +/- 1.8 x 10.-8 mol/l), which showed cardiotonic effects in the same concentration range as R 80122 (EC50 value: 6.1 +/- 1.3 x 10(-8) mol/l), was significantly (p < 0.01) less effective than R 80122 with respect to the maximally induceable increase in cardiac output (CO). The cardiotonic effects of R 80122 could be observed in the low concentration range of 3 x 10(-8) to 1 x 10(-6) mol/l, whereas enoximone (EC50 value: 1.2 +/- 0.1 x 10(-5) mol/l) and milrinone (EC50 value: 8.9 +/- 3.5 x 10(-6) mol/l) elicited positive inotropic effects at 100 fold higher concentrations. Digitoxin was 10 fold less and theophylline was 300 fold less potent than R 80122 with regard to reconstitution of heart function. The cardiotonic effects of R 80122 were not accompanied by an increase in heart rate as found with milrinone, theophylline or (-)-adrenaline in this model. Furthermore, the PDE inhibitory effect of R 79595 and its E-isomer R 80122 were investigated in partially purified isoenzymes from guinea-pig ventricles. The IC50 values of R 79595 and R 80122 on PDE I-IV were compared to the IC50 values of adibendan, milrinone, enoximone and theophylline. The selectivity of an inhibitor for PDE III was evaluated by division of its IC50 values on PDE I, II and IV by the IC50 value on PDE III. R 80122 was the most potent and selective PDE III inhibitor.(ABSTRACT TRUNCATED AT 400 WORDS)

Phosphodiesterase inhibition in ventricular cardiomyocytes from guinea-pig hearts

1. The present study compared the cyclic nucleotide phosphodiesterase (PDE) activities in cardiomyocytes and ventricular cardiac tissue from guinea-pigs. The aim of the study was to determine whether PDE activities in ventricular tissue accurately reflect the isoenzymes present in cardiomyocytes. 2. In homogenates of cardiomyocytes and multicellular ventricular tissue, four distinct soluble PDE activities could be separated by DEAE-sepharose chromatography. 3. In multicellular cardiac tissue as well as in cardiomyocyte preparations, adenosine 3':5'-cyclic monophosphate (cyclic AMP) PDE isoenzymes I-IV were comparable in terms of substrate affinities, and inhibition or stimulation by guanosine 3':5'-cyclic monophosphate (cyclic GMP). However, in cardiomyocytes the Vmax values of PDE I-IV were lower by a factor of about 2 to 7 and the basal activities were lower by a factor of about 3 to 5 as compared to multicellular cardiac tissue. 4. To investigate whether the PDE I-IV activities were similarly inhibited by PDE inhibitors in both preparations, we studied the effects of 3-isobutyl-1-methylxanthine (IBMX), UD-CG 212 Cl (2-(4-hydroxy-phenyl)-5-(5-methyl-3-oxo-4, 5-dihydro-2H-6-pyridazinyl)benzimidazole HCl) and rolipram. UD-CG 212 Cl was a selective PDE III inhibitor in cardiomyocytes (IC50 0.3 mumol l-1) and in ventricular tissue (IC50 value 0.1 mumol l-1). Rolipram selectively inhibited PDE IV in cardiomyocytes (IC50 1.4 mumol ml-1) and in ventricular tissue (IC50 1.1 mumol l-1) whereas IBMX was a nonselective PDE inhibitor in both preparations.5. It is concluded that the PDE isoenzymes I-IV from multicellular ventricular tissue can be used as a representative system for investigating PDE inhibiting properties of PDE inhibitors in the myocardium since comparable PDE isoenzymes I-IV exist in guinea-pig ventricular cardiomyocytes and multicellular ventricular tissue.

Selective inhibition of cGMP-inhibited and cGMP-noninhibited cyclic nucleotide phosphodiesterases and relaxation of rat aorta

In the supernatant (50,000 g, 1 hr) fraction from rat aortic smooth muscle homogenates, approximately 50% of total cAMPE PDE activity was inhibited by OPC 3911 (3 microM), while approximately 20% was inhibited by rolipram (30 microM). A cGMP-inhibited cyclic nucleotide phosphodiesterase (cGI-PDE) was further purified using DEAE chromatography followed by affinity chromatography on the N-(2-isothiocyanato)ethyl derivative of cilostamide conjugated to aminoethyl agarose (CIT-agarose). OPC 3911, CI-930, and milrinone, but not rolipram, were potent and selective inhibitors of this enzyme. The PDE-activity in the CIT-agarose flow through fraction (RI-PDE), however, was inhibited potently by rolipram, but not by cGMP, OPC 3911, CI-930 or milrinone. Functional studies showed that OPC 3911, CI-930, and milrinone were potent relaxants of contracted rat aorta. Rolipram had little relaxant effect. When OPC 3911 or milrinone was combined with rolipram more than additive effects on aortic relaxation and cAMP content were obtained. OPC 3911 combined with milrinone had only additive effects. These results demonstrate the presence of a cGI-PDE in rat aortic smooth muscle, and that inhibition of this isozyme may be of primary importance for the relaxant effects of OPC 3911, CI-930, and milrinone. A RI-PDE activity was also found, but it appeared to be less important for modulation of vascular tone unless the cGI-PDE was already inhibited. This may explain the synergistic relaxant effects observed when both PDE-isozymes were inhibited.

Effects of selective phosphodiesterase inhibitors on isolated coronary, lung and renal arteries from man and rat

The relaxant effects of some isozyme-selective phosphodiesterase inhibitors were evaluated in isolated human and rat coronary, lung and renal arteries. Milrinone and OPC 3911, inhibitors of a cGMP-inhibited cAMP phosphodiesterase (cGI-PDE), were shown to have distinct vasodilator actions. These agents were less potent as relaxants in rat lung and renal arteries than in the corresponding human tissues. OPC 3911, the more potent cGMP-inhibited cAMP phosphodiesterase inhibitor, was found to be the more potent vasorelaxant. Rolipram, a selective inhibitor of a cGMP-noninhibited cAMP phosphodiesterase, had small effects on coronary and lung arteries, but produced a slightly more pronounced relaxation of renal arteries from both man and rat. In human preparations contracted by 30 mM K+, milrinone and OPC 3911 had similar relaxant profiles, and were as potent in coronary as in renal arteries. These results do not support the notion that milrinone has reduced effects on renal vessels in man and show that there may be species differences in vascular responsiveness to cGMP-inhibited cAMP phosphodiesterase inhibitors.