Cyclic Nucleotide Phosphodiesterase Activity Research Articles

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.

Changes in cAMP phosphodiesterase activity and cAMP concentration during mouse preimplantation development.

Cyclic nucleotide phosphodiesterase (PDE) activity and cAMP amounts were measured in mouse preimplantation embryos at the 1-cell, 2-cell, 8-cell/morula, and mid-blastocyst stages. PDE activity remained constant between the 1-cell and 2-cell stages. It decreased by the 8-cell stage and continued to decrease by the mid blastocyst stage to about 14% of the 1- and 2-cell values. By contrast, cAMP amounts remained essentially constant at 0.05 fmole/embryo (0.3 microM) from the 1-cell to the blastocyst stage and increased to 0.175 fmole in the fully expanded blastocyst that was close to hatching. Measurements of embryo volume indicated that intracellular volume remained essentially constant up to the blastocyst stage. The morphological changes in cell shape that accompany differentiation of the trophectoderm and that are coupled with blastocoel expansion decreased the intracellular volume. This decrease resulted in an increase in the cAMP concentration to about 0.4 microM by the mid-blastocyst stage. Previous studies indicate that either cAMP or TGF-alpha/EGF can stimulate the rate of blastocoel expansion. Although TGF-alpha/EGF can elevate cAMP levels in other cell types, TGF-alpha, at a concentration that maximally stimulates the rate of blastocoel expansion, did not elevate cAMP in blastocysts. Thus, it was unlikely that elevation of cAMP is the mechanism by which TGF-alpha stimulates the rate of blastocoel expansion.

Mechanism for ganglioside-mediated modulation of a calmodulin-dependent enzyme. Modulation of calmodulin-dependent cyclic nucleotide phosphodiesterase activity through binding of gangliosides to calmodulin and the enzyme.

Gangliosides were recently shown to bind to calmodulin (Higashi, H., Omori, A., and Yamagata, T. (1992) J. Biol. Chem. 267, 9831-9838). This prompted us to investigate the effects of gangliosides on the calmodulin-dependent enzyme, cyclic nucleotide phosphodiesterase. Several species of gangliosides competitively inhibited calmodulin-stimulated phosphodiesterase activity, with GD1b, GT1b, and GD1a being noted to do so particularly (group 1). GM1, GQ1b, and GM2 (group 2) were less inhibitory, and GM3, GM3(NeuGc), GalCer, sulfatide, GgOse4Cer, and oligosaccharide portions of inhibitory gangliosides showed no inhibition in accordance with the binding specificity of calmodulin to gangliosides. Trypsin-activated phosphodiesterase was inhibited by gangliosides with similar specificity, indicating interactions of gangliosides with the enzyme. Inhibition, however, was less than that of calmodulin-dependent activity by these compounds and, in both cases, was eliminated by excess calmodulin. In the absence of calmodulin, group 1 gangliosides at lower concentrations activated the intact enzyme but inhibited it over a certain range of increase in concentration. Ganglioside-dependent modulation of calmodulin-dependent phosphodiesterase activity is thus shown to be due to interactions of gangliosides with both calmodulin and the enzyme, and consequently, ganglioside-calmodulin binding is likely the mechanism for regulation of the enzyme.

Cytosolic and membrane-bound cyclic nucleotide phosphodiesterases from guinea pig cardiac ventricles

Cyclic nucleotide phosphodiesterase (PDE) activities were characterized in the cytosolic and post-nuclear membrane preparations of guinea pig cardiac ventricles. The cytosolic PDE activities were stimulated 5-fold by calmodulin (CaM) on both substrates (1 μM) and 1.2-fold by cGMP (5 μM) on cAMP hydrolysis. Conversely, in the membrane preparation, CaM only stimulated PDE activities 1.2- to 1.4-fold, but cGMP induced a 3-fold increase of the hydrolysis of cAMP. In both the cytosolic and the membrane preparations, the hydrolysis of cAMP was inhibited by 100 μM of either the PDE III inhibitor SK & F 94120 (27% and 31% respectively) or the PDE IV inhibitor rolipram (14% and 23% respectively). Four peaks were resolved from the cytosolic preparation by chromatography. Peak A and peak B hydrolyzed both cAMP and cGMP and were stimulated respectively by CaM and cGMP. Peak C and peak D selectively hydrolyzed cAMP. Peak C had an apparent K m value for cAMP of 3.3 μM and was inhibited by PDE IV inhibitors. Peak D showed an apparent K m value for cAMP of 0.43 μM and was inhibited by cGMP and by cardiotonic inhibitors of PDE III. Similar potencies of these inhibitors were observed in the membrane preparation. These results suggest that in guinea pig cardiac ventricles: (1) PDE I (CaM-activated) is almost exclusively cytosolic; (2) PDE II (cGMP-stimulated), PDE III (cGMP-inhibited and cardiotonic-sensitive) and PDE IV (rolipram-sensitive) are present in cytosolic and membrane preparations; (3) PDE III and PDE IV differ in their apparent K m values for cAMP. The latter observation could explain the differential effects of PDE III and PDE IV inhibitors in the regulation of cardiac contraction.

Early increase in lymphocyte cyclic nucleotide phosphodiesterase activity upon mitogenic activation of human peripheral blood mononuclear cells.

Cyclic nucleotide phosphodiesterase activity of human peripheral blood mononuclear cells was significantly increased following a short (30 min) incubation with the mitogenic lectin Concanavalin A. Con A stimulated phosphodiesterase activity to the same extent whatever the subcellular compartment (homogenate, cytosol or pellet). Further separation of the Con A-activated mononuclear cells into lymphocyte-enriched and monocyte-enriched populations showed that the Con A-induced increase of phosphodiesterase activity exclusively affected the lymphocyte-enriched population. In lymphocytes, cyclic GMP phosphodiesterase activity was more importantly enhanced by Con A (+275%) than cyclic AMP phosphodiesterase activity (+75%). The increase of both activities occurred as early as from 10 min of Con A incubation and proved to be maximal with Con A doses of 2.5 and 5 micrograms per 10(6) cells, lower and higher doses being less effective. Inhibition experiments with reference inhibitors suggested that, among the high affinity phosphodiesterase isoforms, the cyclic GMP-inhibited enzyme might be more selectively enhanced by Con A than the cyclic AMP-specific, Rolipram-sensitive one. The non-mitogenic lectin Helix pomatia hemagglutinin, was not able to enhance cyclic nucleotide phosphodiesterase activity of human mononuclear cells whereas anti-CD3 monoclonal antibody, although being less effective than Con A, exhibited a significant stimulatory effect. Putting together these results suggest that the early increase in phosphodiesterase activity might be a normal step involved in the mitogenic activation of human lymphocyte.

Low Copper Status of Rats Affects Polyunsaturated Fatty Acid Composition of Brain Phospholipids, Unrelated to Neuropathology ,

To determine the molecular basis of the neuropathology of copper deficiency, brain lipid composition was determined in second–generation copper–deficient rats. Non–parous female rats were fed a low copper diet (0.5 mg Cu/kg) or a control diet (10 mg Cu/kg) during gestation and lactation, and the offspring were continued on the respective diets to ∼8 wk of age. In one experiment the source of carbohydrate was 15% starch and 52.6% sucrose, and in another experiment sucrose and glucose were compared in a factorial design. The source of carbohydrate had no effect on copper status. Myelin concentration was estimated by isolation, by 2´,3´–cyclic nucleotide phosphodiesterase activity, and by concentration of 20:1 (n–9). Fatty acid compositions of the phospholipid fractions of brain parts and of myelin were determined. Copper deficiency reduced myelin concentration slightly in the midbrain region and increased the proportion of linoleic acid [18:2(n–6)] in both brain and isolated myelin. In the cerebellum the long–chain polyunsaturated fatty acids, particularly 22:6(n–3), were lower. Approximately one–half of the copper–deficient rats developed Parkinson–like signs and had low striatal dopamine, but neither myelin content nor brain fatty acid composition was associated with the neuropathology.

Inhibition of Human Platelet Aggregation by Ibudilast (3-isobutyryl-2-isopropylpyrazolo [1, 5-a] pyridine, KC-404)

The effect of a novel compound, 3-isobutyryl-2-isopropylpyrazolo [1, 5-a] pyridine (ibudilast, KC-404), on human platelet aggregation and its mechanism of action were investigated.In vitro, KC-404 inhibited human platelet aggregation induced by ADP, collagen, adrenalin, platelet activating factor and arachidonic acid but not by ristocetin. Together, KC-404 and agents which increased cAMP (prostaglandin I2, prostaglandin E1 (PGE1), forskolin) or cGMP (3-morpholinosydnonimine (SIN-1)) produced synergistic inhibitory effects on platelet aggregation.KC-404 inhibited human platelet cAMP phosphodiesterase (PDE) (IC50: 50μM) and cGMP-PDE (IC50: 5.2μM) activities. cAMP and cGMP concentration of human platelets were not increased by KC-404 itself. PGE1, an adenylate cyclase stimulator, increased cAMP content; KC-404 enhanced the effect of PGE1 on cAMP accumulation. SIN-1, which stimulates guanylate cyclase, increased cGMP content; KC-404 enhanced the effect of SIN-1 on cGMP accumulation.These results suggest that effects of KC-404 on accumulation of cyclic nucleotides and inhibition of platelet aggregation are mediated via inhibition of platelet cyclic nucleotide phosphodiesterase activities.

Dietary Polyunsaturated Fatty Acids Modulate Fatty Acid Composition and Early Activation Steps of Concanavalin A-Stimulated Rat Thymocytes

The early biochemical responses to concanavalin A (Con A) of thymocytes from rats fed a saturated (coconut oil), (n-6) (sunflower oil) or (n-3) (fish oil) fatty acid-enriched diet for 3 wk were investigated. Fish oil feeding resulted in greater (n-3) polyunsaturated fatty acid level (PUFA) at the expense of (n-6) PUFA in total and individual thymocyte phospholipids. Such alterations of the fatty acid composition did not affect basal ornithine decarboxylase (ODC), cyclic nucleotide phosphodiesterase (PDE) or gamma-glutamyl transferase activities. However, the fish oil-enriched diet impaired some of the early thymocyte responses to Con A, such as the rapid induction (30 min) of soluble ODC and PDE activities. Synthesis of [3H]20:4(n-6) oxygenated metabolites was not different between the dietary groups; however, the uptake of [3H]20:4(n-6) into phospholipid classes was significantly lower in phosphatidylcholine and greater in phosphatidylethanolamine and phosphatidylinositol after fish oil feeding. Similarly, the Con A-induced remodeling of the [3H]20:4(n-6) esterification in phospholipids differed in sunflower oil- vs. fish oil-fed rats, suggesting a modulation of acyl CoA synthase and/or acyl CoA transferase activities. Thus, the modulation of Con A-induced ODC and PDE stimulation upon in vivo changes of membrane phospholipid fatty acid composition is not related to eicosanoid formation, but rather to the modification of the fatty acid acylation processes, altering phospholipid composition and signal transduction.

Characterisation of cyclic nucleotide phosphodiesterases from rat mesenteric artery

Four cyclic nucleotide phosphodiesterase activities (PDEs) could be resolved from rat mesenteric artery by DEAE-Sephacel chromatography: a calipodulin-activated fraction, a cyclic GMP-inhibited fraction, a cyclic AMP-specific rolipram-sensitive fraction and a cyclic GMP-specific fraction containing PDE I, III, IV and V. Cardiotonic drugs (CI 930 and LY 195115) selectively inhibited PDE III; rolipram and zaprinast selectively inhibited PDE IV and PDE V, respectively. These results show that the rat mesenteric artery contains the same PDEs as previously found in the aorta, and suggest that these PDEs may be implicated in the regulation of arterial contraction.

Inhibitory effect of calcium-binding protein regucalcin on Ca2+/calmodulin-dependent cyclic nucleotide phosphodiesterase activity in rat liver cytosol

The effect of regucalcin, a calcium-binding protein isolated from rat liver cytosol, on Ca2+/calmodulin-dependent cyclic nucleotide (AMP) phosphodiesterase activity in rat liver cytosol was investigated. The addition of Ca2+ (50 microM) and calmodulin 160 U/ml in the enzyme reaction mixture caused a significant increase in cyclic AMP phosphodiesterase activity. This increase was inhibited by the presence of regucalcin (0.5-3.0 microM); the inhibitory effect was complete at 1.0 microM. Regucalcin (1.0 microM) did not have an appreciable effect on basal activity without Ca2+ and calmodulin. The inhibitory effect of regucalcin was still evident even at several fold higher concentrations of calmodulin (160-480 U/ml). However, regucalcin (1.0 microM) did not inhibit Ca2+/calmodulin-dependent cyclic AMP phosphodiesterase activity in the presence of 100 and 200 microM Ca2+ added. Meanwhile, Cd2+ (25-100 microM)-induced decrease in Ca2+/calmodulin-dependent cyclic AMP phosphodiesterase activity was not reversed by the presence of regucalcin (1.0 microM). The present results suggest that regucalcin can regulate Ca2+/calmodulin-dependent cyclic AMP phosphodiesterase activity due to binding Ca2+ in liver cells.

Characterization of guinea-pig eosinophil phosphodiesterase activity: Assessment of its involvement in regulating superoxide generation

Experiments have been performed to characterize guinea-pig peritoneal eosinophil cyclic nucleotide phosphodiesterase (PDE) activity and establish whether it is involved in regulating superoxide (.O − 2) generation. Eosinophils were found to contain a predominantly membrane-bound cAMP PDE(s) (92.5 ± 2.4% of total activity) which was resistant to solubilization with Triton X-100 (1%). This particulate PDE exhibited complex kinetics ( K m = 1.3 and 31.4 μM) and was unaffected by cGMP ( ic 50 > 100 μ M) or CaCl 2 (2 mM) + calmodulin (10 units/mL). Little cGMP PDE activity was detected in either the soluble or particulate fractions. Inhibitors of the Ro-20-1724-inhibited (Type IV) cAMP PDE, namely Ro-20-1724 ( ic 50 = 0.92 ± 0.43 μ M) , rolipram ( ic 50 = 0.20 ± 0.04 μ M) and denbufylline ( ic 50 = 0.20 ± 0.01 μ M) , potently inhibited the particulate cAMP PDE, as did the non-selective inhibitors trequinsin ( ic 50 = 0.11 ± 0.02 μ M) and AH-21-132 ( ic 50 = 2.57 ± 0.02 μ M) . Eosinophil cAMP PDE was resistant to SK&F 94120 ( ic 50 > 1000 μM), the cGMP-inhibited (Type III) cAMP PDE inhibitor, and the cGMP PDE (Type I) inhibitor, zaprinast, was only weakly active ( ic 50 = 35.33 ± 10.74 μ M) . O − 2 release from resting cells was potently inhibited by rolipram ( ic 50 = 0.05 ± 0.03 μ M) and denbufylline ( ic 50 = 0.06 ± 0.04 μ M) but surprisingly, in view of its potent cAMP PDE inhibitory activity, was only weakly decreased by trequinsin ( ic 50 = 8.0 ± 2.7 μ M) . AH-21-132 ( ic 50 > 10 μ M) , SK&F 94120 ( ic 50 > 10 μ M) and zaprinast ( ic 50 > 10 μ M) were without effect. Rolipram and denbufylline alone exerted little effect on cAMP in intact cells but, in the presence of 10 μM isoprenaline, potently increased intracellular accumulation ( ec 50 = 0.45 ± 0.16 and 0.28 ± 0.08 μ M , respectively). Trequinsin and AH21–132 only weakly enhanced isoprenaline-stimulated cAMP accumulation. Although it induced a marked rise in cAMP only in the presence of isoprenaline, rolipram (50 μM) alone was able to increase the activity ratio of cAMP-dependent protein kinase from 0.24 to 0.84. The results suggest that Ro-201724-inhibited cAMP PDE plays a role in regulating eosinophil. O − 2 generation. The poor correlation between the PDE inhibitory actions of certain compounds and their effectiveness in elevating cAMP and inhibiting. O − 2 suggests the existence of a barrier impeding access to the enzyme.

Inhibition of eosinophil cyclic nucleotide PDE activity and opsonised zymosan-stimulated respiratory burst by 'type IV'-selective PDE inhibitors.

1. The cyclic nucleotide phosphodiesterase (PDE) of guinea-pig eosinophils was partially characterized and the effects of selective inhibitors of PDE isoenzymes upon opsonized zymosan (OZ)-stimulated respiratory burst were studied. 2. PDE activity in eosinophil lysates appeared to be membrane-associated, displayed substrate specificity for adenosine 3':5' cyclic monophosphate (cyclic AMP) versus guanosine 3':5' cyclic monophosphate (cyclic GMP) and was insensitive to cyclic GMP or Ca2+ and calmodulin. 3. The non-selective PDE inhibitor, 3-isobutyl-1-methylxanthine caused a concentration-dependent inhibition of both OZ-stimulated hydrogen peroxide (H2O2) generation and cyclic AMP hydrolysis. The type IV-selective PDE inhibitors, rolipram and denbufylline, also inhibited H2O2 generation and cyclic AMP hydrolysis in a concentration-dependent manner whilst SK&F 94120 and Org 9935 (type III-selective) and zaprinast (type Ia or V-selective) were ineffective. 4. Dibutyryl cyclic AMP, a cell-permeable, non-hydrolysable analogue of cyclic AMP, caused a concentration-dependent inhibition of H2O2 generation stimulated by OZ. Dibutyryl cyclic GMP was ineffective. 5. It is concluded that eosinophil respiratory burst activity induced by OZ can be regulated by intracellular cyclic AMP and that the levels of cyclic AMP are controlled exclusively by a rolipram- and denbufylline-sensitive PDE isoenzyme that resembles a type IV species.

Interactions of calmodulin antagonists with calcium antagonists binding sites

Calmodulin antagonists have calcium entry blocking properties. In order to quantitatively investigate the interactions of these drugs with calcium channels, their effect on [ 3H]nitrendipine and [ 3H]d-cis-diltiazem binding to rat cerebral cortex membrane preparations was compared to their inhibitory effect on the activation of cyclic nucleotide phosphodiesterase by calmodulin. The potency of most antagonists to inhibit [ 3H]nitrendipine binding was correlated with their calmodulin inhibitory potency. However, bepridil (K 0.5 = 280 nM), chlorpromazine (K 0.5 = 3 μM), triflupromazine (K 0.5 = 1.5 μM), imipramine (K 0.5 = 3 μM) and propranolol (K 0.5 = 14 μM) were much more active on [ 3H]d-cis-diltiazem binding than on either [ 3H]nitrendipine binding or calmodulin, suggesting that these compounds bind to higher affinity sites on the calcium antagonist target proitein. Moreover, the potencies of these compounds to compete with [ 3H]d-cis-diltiazem and to inhibit calcium-induced contractions in depolarized smooth muscle were correlated (R = 0.76, p < 0.02). These data suggest that love concentrations of these hydrophobic drugs which have calcium and calmodulin antagonistic properties inhibit smooth muscle contraction through calcium entry blockade, not calmodulin antagonism.

Enhancement of amrinone-induced positive inotropy in rabbit papillary muscles with depressed contractile function: effects on cyclic nucleotide levels and phosphodiesterase isoenzymes.

The inotropic activity of amrinone and its effects on cyclic nucleotide levels in rabbit papillary muscles with normal and depressed contractile function have been compared. The effects of amrinone on the cyclic (c) AMP hydrolytic activity of cyclic nucleotide phosphodiesterase (PDE) isoenzymes were also examined. Amrinone (2.4 x 10(-4) - 1.2 x 10(-3) M) produced a relatively weak (maximal increase 11%) positive inotropic effect in papillary muscles stimulated at the near optimal stimulation frequency of 1 Hz. In contrast, large positive inotropic responses (maximal 138-200%) were obtained with amrinone in papillary muscles in which contractile force had been depressed by: (a) lowering stimulation frequency to 0.4 Hz, (b) reducing extracellular Ca2+ concentration from 2.5 x 10(-3) M to 6.3 x 10(-4) M, (c) prior addition of sodium pentobarbitone (6.5 x 10(-4) M). The EC50 values for amrinone under conditions (a), (b), and (c) were 3.0 x 10(-3), 2.6 x 10(-3), and 2.8 x 10(-3) M, respectively. Force-frequency curves in rabbit papillary muscles were compared at normal (2.5 x 10(-3) M) and low (6.3 x 10(-4) M) extracellular Ca2+ concentration. Contractions at low frequencies of stimulation (less than 0.4 Hz) were less sensitive to removal of extracellular Ca2+ than higher stimulation rates indicating that in the former situation, recycling of intracellular Ca2+ is more important for maintaining contractile force.(ABSTRACT TRUNCATED AT 250 WORDS)

Desensitization of atriopeptin stimulated accumulation and extrusion of cyclic GMP from a kidney epithelial cell line (MDCK)

Atriopeptin caused dose- ( ec 50 ca. 2 × 10 −8 M ) and time-dependent increases in the intracellular concentration of cyclic GMP in the MDCK kidney epithelial cell line; an effect potentiated by the phosphodiesterase inhibitor, IBMX. The atriopeptin-catalysed increase in cyclic GMP was transient and reached a maximum some 10–20 min after challenge of cells with atriopeptin. The basis for the transience of this increase was shown to be due to the densensitization of guanylate cyclase coupled with extrusion of cyclic GMP from the cells and the degradation of cyclic GMP by phosphodiesterase activity. Atriopeptin-catalysed extrusion of cyclic GMP was time- and dose-( ec 50 ca. 1.5 × 10 −8 M ) dependent and was inhibited by probenecid but not by high external cyclic GMP concentrations. The extrusion process underwent apparent desensitization as did guanylate cyclase with similar half lives ( T 1 2 of ca. 20 min ). Desensitization was dose-dependent upon atriopeptin and did not appear to be mediated by elevated cyclic GMP concentrations as pre-incubation with 8-bromo cyclic GMP did not cause desensitization and the half-times for desensitization were similar whether or not IBMX was present. The majority of the cyclic nucleotide phosphodiesterase activity was found in the cytosol fraction of the cells and could be separated into two cyclic AMP specific forms and two cyclic GMP preferring forms.

The isoenzyme selectivity of AH 21-132 as an inhibitor of cyclic nucleotide phosphodiesterase activity.

The smooth muscle relaxant, AH 21-132, was tested for its inhibitory effect on the cyclic nucleotide phosphodiesterase (PDE) activities fractionated from guinea-pig cardiac ventricle and bovine trachealis muscle. Both tissues yielded significant PDE-I and PDE-II activities. The cardiac ventricle also contained a significant amount of PDE-III whilst the trachealis contained PDE-IV. AH 21-132 inhibited PDE-III and PDE-IV selectively (Ki values 0.30-0.55 microM) compared with PDE-I and PDE-II (Ki values 20-140 microM).

Pharmacologic and pharmacokinetic profile of SK&F S-106203, a potent, orally active peptidoleukotriene receptor antagonist, in guinea-pig

In this report the pharmacologic and pharmacokinetic profile of the leukotriene receptor antagonist 3(S)-1(2-carboxyethyl)thio]-3-12-(8-phenyloctyl)phenyl] propanoic acid (SK&F S-106203) in guinea-pigs is described. In isolated guinea-pig tracheae SK&F S-106203 was a potent, competitive antagonist of leukotriene (LT) D 4-induced contractions (pA 2 = 7.6). SK&F S-106203 was also a potent antagonist of LTE 4-induced contractions (pK B = 7.3), but had little effect on those elicited by LTC 4 (pK B = 5.5). SK&F S-106203 (10 μM) had no effect on contractions produced by histamine, carbachol, KCI, U-44069, PGF 2α or PGD 2. In addition, SK&F S-106203 (10 μM) did not inhibit cyclic nucleotide phosphodiesterase (PDE) activity of several PDE isozymes. In guinea-pig lung membrane preparations, SK&F S-106203 was a potent antagonist of 3H-LTD 4 binding with a K i = 19.4 ± 2.1 nM (n = 5). The pharmacokinetic profile of SK&F S-106203 was determined in unanesthetized guinea-pigs. Following an i.v. (bolus) dose (25 mg/kg), SK&F S-106203 disappeared from plasma in a biphasic fashion with half-lives of 0.1 h (50% of the area under the plasma concentration-time curve, AUC) and 11 h. The AUC obtained for SK&F S-106203 following i.v. administration was 87.3 ± 7.5 μg-h/ml. Following an oral dose of SK&F S-106203 (100 mg/kg), the maximal plasma concentration (C max) and the time C max was achieved (T max were 21.62 ± 2.26 kg/ml and 4 ± 1 h, respectively; the AUC was 279.9 ± 41.8 μg-h/ml. Studies examining the effects of i.v. infusion of SK&F S-106203 revealed that marked inhibition of LTD 4-induced bronchospasm was produced with steady-state plasma levels of SK&F S-106203 < 1 μg/ml (< 2 μM). Oral (p.o.) pretreatment with 100 μmol/kg SK&F S-106203 for up to 24 h essentially abolished LTD 4-induced bronchospasm; this correlated with sustained plasma concentrations of > 2 μg/ml. The results indicate that in guinea-pig airways, SK&F S-106203 is a potent and selective LT receptor antagonist that is active via aerosol, oral and i.v. routes of administration. When given orally, SK&F S-106203 is highly bioavailable and has a very long duration of action which correlates with the pharmacokinetic profile of the compound. SK&F S-106203 may be useful therapy in asthma and other disorders in which the Us are thought to play a prominent pathophysiological role.

Comparison of cyclic nucleotide phosphodiesterase isoenzymes in rat and rabbit ventricular myocardium: positive inotropic and phosphodiesterase inhibitory effects of Org 30029, milrinone and rolipram

The species dependent variation in the cardiotonic activity of selective cyclic nucleotide phosphodiesterase (PDE) isoenzyme inhibitors was examined by comparing the inotropic and PDE inhibitory effects of Org 30029 (N-hydroxy-5,6-dimethoxy-benzo[b]thiophene-2-carboximidamide HCl), 3-isobutyl-1-methyl-xanthine (IBMX), milrinone and rolipram in rat and rabbit ventricular myocardium. The relative activities of PDE isoenzymes in rat and rabbit cardiac ventricle were also examined to assess the role of the different PDE subtypes in modulating contractile force in the two species. In rabbit papillary muscles, IBMX, Org 30029 and milrinone increased contractile force whilst rolipram was inactive. The rank order of potency of the active compounds was Org 30029 greater than IBMX greater than milrinone. Only Org 30029 and IBMX produced significant positive inotropic responses in rat papillary muscles, milrinone and rolipram being inactive. However, large positive inotropic responses were obtained in rat papillary muscles when milrinone and rolipram were tested in combination. In rabbit papillary muscles, the positive inotropic action of milrinone was markedly potentiated by rolipram. Four main types of PDE (I, II, III, IV) isoenzymes were resolved, by DEAE-sepharose or Mono-Q ion-exchange chromatography, from both rat and rabbit cardiac ventricular tissue. In rabbit, Ca2+/calmodulin dependent PDE (PDE I) and cyclic GMP inhibited PDE (PDE III) were the dominant cAMP activities. In contrast, cyclic GMP stimulated PDE (PDE II), PDE III and cGMP insensitive PDE (PDE IV) represented the main cAMP activities in rat cardiac ventricle. The inhibitory effects of Org 30029, IBMX, milrinone and rolipram on PDE isoenzymes from rat and rabbit cardiac ventricle were essentially similar.(ABSTRACT TRUNCATED AT 250 WORDS)

Calcium depletion of Dictyostelium cells selectively inhibits cyclic nucleotide phosphodiesterase synthesis at a post-transcriptional step

ABSTRACT We reported previously that Ca2+ deprivation of Dictyostelium discoideum amoebae inhibits both the induction by cyclic AMP of soluble cyclic nucleotide phosphodiesterase (PD) activity in wild-type cells and the constitutive production of this activity in mutant HC35 cells. In this study, the mutant strain has been used to characterize this phenomenon further and to attempt to identify the Ca2+-dependent step(s) in PD production. Incubation of HC35 cells with 0.9 mM EGTA increased the rate of 4SCa2+ efflux from preloaded cells and partially inhibited PD production. The effect of EGTA on both processes was enhanced considerably by the presence of 1 fiM A23187. This concentration of ionophore alone had little effect on either Ca2+ efflux or PD production. Addition of 1 pM free extracellular Ca2+ to amoebae incubated with EGTA and A23187 increased PD production two-to sixfold. Ca2+ depletion did not appreciably inhibit total protein synthesis or total protein glycosylation as determined by the incorporation of [3H]leucine or [3H]mannose, respectively. Also, the abundance of PD mRNAs was approximately the same in Ca2+-depleted and control cells. In contrast, immunoblot analysis of extracellular fluids and intracellular extracts of these cells revealed a dramatic reduction (up to 85%) in the levels of PD-related polypeptides associated with the Ca2+-depleted cells. These results suggest that Ca2+ deprivation selectively inhibits PD production by impairing a post-transcriptional process.

Decreased Cyclic Nucleotide Phosphodiesterase Activity in Human Peripheral Blood Mononuclear Cells from Elderly Women

1. Both adenosine 3':5'-cyclic monophosphate and guanosine 3':5'-cyclic monophosphate phosphodiesterase activities of peripheral blood mononuclear cells were markedly decreased in elderly women as compared with young control women. 2. In contrast, the ability of these cells to bind guanosine 5'-[beta, gamma-imido]triphosphate, a non-hydrolysable analogue of guanosine 5'-triphosphate, was the same in both groups. 3. These findings are discussed in the context of the decline in immune function which occurs with increasing age.