In vivo interaction of prostacyclin with an inhibitor of cyclic nucleotide phosphodiesterase, HL 725.

Prostacyclin (PGI2) inactivates platelets by stimulation of adenylate cyclase, and its effect can be potentiated in vitro by simultaneous inhibition of cyclic AMP phosphodiesterase. The interaction of synthetic PGI2 and the potent phosphodiesterase inhibitor HL 725 was studied in a model of systemic platelet activation by intravenous injection of collagen. Platelet aggregate formation was evaluated by continuous on-line measurement of the circulating platelet count. Collagen injection in rabbits receiving vehicle caused a 30 +/- 3% decrease in the circulating platelet count. Infusion of PGI2 (0.05, 0.1 and 0.75 micrograms kg-1 min-1) dose-dependently inhibited this decrease. HL 725 (0.5, 1 and 3 micrograms kg-1 min-1) caused a slight but significant effect. Combinations of PGI2 and HL 725, respectively, at 0.25 + 1.0 and 0.1 + 0.5 micrograms kg-1 min-1 inhibited platelet aggregate formation to a greater extent than when either substance was used alone and produced a comparable inhibition to PGI2 at 0.75 micrograms kg-1 min-1. Collagen induced an acute fall in the mean arterial blood pressure (MABP) which also was inhibited by PGI2, HL 725 and their combinations. The infusion of a combination of PGI2 and HL 725 before collagen produced a decrease in the MABP which was greater than when either compound was used on its own. Thus, PGI2 and the phosphodiesterase inhibitor HL 725 interact in vivo to inhibit platelet aggregation and lower MABP.     

KF31327, a new potent and selective inhibitor of cyclic nucleotide phosphodiesterase 5.

The effects of KF31327 (3-ethyl-8-[2-(4-hydroxymethylpiperidino)benzylamino]-2,3-dihydro-1H-imidazo[4,5-g]quinazoline-2-thione dihydrochloride) on phosphodiesterase 5 (cyclic GMP-specific phosphodiesterase) activity and platelet aggregation were investigated and compared with those of sildenafil, a well-known phosphodiesterase 5 inhibitor. KF31327 inhibited phosphodiesterase 5 from canine trachea (K(i)=0.16 nM) more potently than sildenafil (K(i)=7.2 nM). The kinetic analysis revealed that KF31327 was a non-competitive inhibitor. In the presence of nitroglycerin (nitric oxide generator), both compounds inhibited the collagen-induced aggregation of rabbit platelets at less than 0.1 microM, augmenting intracellular cyclic GMP level without affecting cyclic AMP. In contrast, in the absence of nitroglycerin, a higher concentration (10 microM) of KF31327 was required to inhibit platelet aggregation and increased both cyclic nucleotide levels. However, 10 microM sildenafil did not affect aggregation despite elevation of cyclic GMP comparable to that in the presence of nitroglycerin. These results indicate that in the presence of nitroglycerin, the inhibition of platelet aggregation by KF31327 is due to the elevation of cyclic GMP, whereas the mechanism underlying the inhibition without nitroglycerin might be related to a rise in intracellular cyclic AMP.     

Effects of SK&F 94120, an inhibitor of cyclic nucleotide phosphodiesterase type III, on human platelets

Elevation of cyclic AMP concentrations in platelets inhibits agonist-induced responses. Pharmacological interventions which could increase the levels of platelet cyclic AMP include activation of the synthesis of cyclic AMP or inhibition of its breakdown. In this study we have investigated the effects of SK&F 94120 on human platelet phosphodiesterase (PDE) activities separated by ion-exchange chromatography, and studied the effects of this agent on platelet responses caused by the agonists collagen, U44069 and ADP. Four PDE activities were identified from human platelet preparations. The PDE activities found comprised a cyclic GMP selective PDE, a Ca2+/calmodulin stimulated PDE, a cyclic GMP stimulated PDE and a "low Km" PDE activity called PDE III by analogy with activities described in other tissues. SK&F 94120 was found selectively to inhibit the "low Km" PDE III activity with an IC50 of 10.8 microM, which is consistent with the effects of this compound on cardiac ventricle PDE activities. Exposure of human platelets to SK&F 94120 produced concentration dependent increases in cyclic AMP, showing that inhibition of PDE III activity alone can cause an increase in the level of platelet cyclic AMP. SK&F 94120 also caused an inhibition of platelet responses to collagen, U44069 and ADP. However, SK&F 94120 was much less effective as an inhibitor of aggregation induced by ADP (IC50 greater than 100 microM) than by collagen (IC50 = 24.1 microM) or by U44069 (IC50 = 1.7 microM). Isobutylmethylxanthine (IBMX), a non-selective PDE inhibitor, was less effective than SK&F 94120 as an inhibitor of platelet responses for the same measured increase in cyclic AMP levels. M&B 22948 and rolipram, inhibitors of PDE I and PDE IV respectively, had no significant effect on platelet responses. These data suggest that selective inhibition of PDE III is the primary mechanism of action of SK&F 94120 as an inhibitor of agonist-induced platelet responses, and that increased cyclic AMP in the pool controlled by PDE III has important consequences on platelet responses. Moreover, these data suggest that some form of compartmentalization of cyclic AMP and/or PDE activity exists in human platelets.     

Structure of a novel Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase inhibitor KS-619-1

The structure of KS-619-1, a potent inhibitor of Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase, was determined to be 8,13-dioxo-3-(2-oxopropyl)-5,6,8,13-tetrahydro-1,7,9,11- tetrahydroxybenz[a]naphtacene-2-carboxylic acid by spectral studies of KS-619-1 and its methyl derivative.     

Functional and biochemical evidence for diazepam as a cyclic nucleotide phosphodiesterase type 4 inhibitor

1. The responses of the electrically-driven right ventricle strip of the guinea-pig heart to diazepam were recorded in the absence and in the presence of different selective cyclic nucleotide phosphodiesterase (PDE) inhibitors.
2. Diazepam, at concentrations ranging from 1 μM to 100 μM, was devoid of effect on the contractile force in this preparation.
3. Conversely, diazepam (5 μM–100 μM) produced a consistent positive inotropic response in the presence of a concentration (1 μM), that was without effect in the absence of diazepam, of either of the selective PDE 3 inhibitors milrinone or SK&F 94120, but not in the presence of the selective PDE 4 inhibitor rolipram.
4. This effect of diazepam was not γ-aminobutyric acid (GABA)-dependent, since it was neither mimicked nor potentiated by GABA, and was not affected by either a high concentration (5 μM) of the antagonists of the benzodiazepine/GABA/channel chloride receptor complex, picrotoxin, flumazenil and β-carboline-3-carboxylic acid methyl ester (βCCMe), or by the inverse agonists, β-carboline-3-carboxylic acid N-methylamide (βCCMa) and methyl 6,7-dimethoxy-4-ethyl-β-carboline-3-carboxylate (DMCM, 0.1 μM). Furthermore, a specific antagonist of the peripheral benzodiazepine receptors, PK 11195 (5 μM), did not influence the effect of diazepam.
5. Biochemical studies with isolated PDEs, confirmed that diazepam selectively inhibits type 4 PDE from guinea-pig right ventricle rather than the other PDEs present in that tissue. The compound inhibited this enzyme in a non-competitive manner. Diazepam was also able to inhibit PDE 5, the cyclic GMP specific PDE absent from cardiac muscle, with a potency close to that shown for PDE 4.
6. Diazepam displaced the selective type 4 PDE inhibitor, rolipram from its high affinity binding site in rat brain cortex membranes, and also potentiated the rise in cyclic AMP levels induced by isoprenaline in guinea-pig eosinophils, where only type 4 PDE is present.
7. The PDE inhibitory properties of diazepam were shared, although with lower potency, by other structurally-related benzodiazepines, that also displaced [³H]-rolipram from its high affinity binding site. The order of potency found for these compounds in these assays was not related to their potencies as modulators of the GABA receptor through its benzodiazepine binding site.
8. The pharmacological and biochemical data presented in this study indicate that diazepam behaves as a selective type 4 PDE inhibitor in cardiac tissue and this effect seems neither to be mediated by the benzodiazepine/GABA/channel chloride receptor complex nor by peripheral type benzodiazepine receptors.

     

A sensitive assay of human blood platelet cyclic nucleotide phosphodiesterase activity by HPLC using fluorescence derivatization and its application to assessment of cyclic nucleotide phosphodiesterase inhibitors

A selective and sensitive HPLC measurement of 3',5'-cyclic nucleotide phosphodiesterase (PDE) activity in human platelets using (3,4-dimethoxyphenyl)glyoxal (DMPG) as a fluorogenic reagent for guanine and its nucleosides and nucleotides is described. cGMP, a substrate for PDE, and GMP, which was produced by the enzyme reaction, are selectively converted by the reaction with DMPG to the fluorescent derivatives. The derivatives were separated by reversed-phase HPLC. Human platelet PDE activity was measured and the inhibitory effects of several compounds were investigated.     

选择性磷酸二酯酶抑制剂研究进展

磷酸二酯酶 (PDEs)迄今已报道有 9个基因家族 ,每个家族又包括多个亚家族。PDEs分布于多个组织中 ,其抑制剂具有广泛的生理作用。其中 ,PDE 4抑制剂被认为是作用于细胞内靶点的新型免疫调节、抗炎药物。新型PDE 5抑制剂sildenafil通过NO/cGMP通路舒张海绵体血管及平滑肌 ,应用于阳痿治疗取得了较好的临床效果。该文简要综述选择性PDEs抑制剂近年研究进展。     

Role of cyclic nucleotide phosphodiesterase isozymes in intact canine trachealis.

The role of individual cyclic nucleotide phosphodiesterase (PDE) isozymes in regulating cAMP and cGMP content in intact canine trachealis was examined using isozyme-selective and nonselective PDE inhibitors. The inhibitors used in this study were characterized previously [Mol. Pharmacol. 37:206-214 (1990)] and included: 1) zaprinast, an inhibitor (Ki = 0.1 microM) of the cGMP-specific PDE (cAMP Km = 135 microM; cGMP Km = 4 microM); 2) SK&F 94120, an inhibitor (Ki = 7 microM) of the cGMP-inhibited PDE (cAMP Km = 0.3 microM; cGMP Km = 8 microM); 3) Ro 20-1724, an inhibitor (Ki = 5 microM) of the cAMP-specific PDE (cAMP Km = 4 microM; cGMP Km = 40 microM); and 4) 3-isobutyl-1-methylxanthine (IBMX), a nonselective PDE inhibitor (IC50 = 1-30 microM). In addition to the aforementioned isozymes, canine trachealis contains a Ca2+/calmodulin-stimulated PDE (cAMP Km = 1 microM; cGMP Km = 2 microM) and a GMP-stimulated PDE (cAMP Km = 93 microM; cGMP Km = 60 microM), for which selective inhibitors are not available. Isolated canine trachealis strips were contracted with methacholine and exposed to various concentrations of PDE inhibitors, before being relaxed by the cumulative addition of isoproterenol, an adenylate cyclase activator, or sodium nitroprusside, a guanylate cyclase activator. At the completion of the concentration-response studies, tissues were flash-frozen and assayed for cyclic nucleotide content. Neither isoproterenol-induced relaxation nor cAMP accumulation was altered by zaprinast, but both of these responses were potentiated by pretreatment of tissues with either SK&F 94120 or Ro 20-1724. The effects of SK&F 94120 and Ro 20-1724 were additive, and the combination of SK&F 94120, Ro-1724, and IBMX had no greater effect on the responses to isoproperenol than did either IBMX alone or the combination of SK&F 94120 plus Ro 20-1724. In contrast, zaprinast potentiated sodium nitroprusside-induced relaxation and cGMP accumulation, whereas neither SK&F 94120 nor Ro 20-1724 altered these responses. IBMX produced a greater potentiation than did zaprinast, and the combination of zaprinast and IBMX had a greater effect than either agent alone. The results of this study suggest that the cGMP-inhibited and cAMP-specific PDEs are responsible for cAMP hydrolysis in intact canine trachealis, whereas cGMP hydrolysis is mediated by the cGMP-specific PDE as well as the Ca2+/calmodulin-stimulated PDE and/or the cGMP-stimulated PDE.     

Diazepam effects on frog skin cyclic nucleotide phosphodiesterase

1. The activities of cAMP phosphodiesterases (cAMP-PDE) have been measured in the homogenate of the skin of Rana esculenta. 2. The tissue possesses two distinct enzymes: a "low" Km PDE (Km = 0.42 x 10(-6) M; Vmax = 16 pmol/mg protein/min) and a "high" Km PDE (Km = 180 x 10(-6) M; Vmax = 2853 pmol/mg prot/min). Only the "high" Km form is stimulated by calcium. 3. Diazepam (1-0.5 mM) significantly inhibits both enzymes, the inhibition being of competitive type.     

KS-619-1, a new inhibitor of Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase from Streptomyces californicus

KS-619-1, a new inhibitor of Ca2+ and calmodulin-dependent cyclic nucleotide phosphodiesterase, was isolated from the cultured broth of Streptomyces californicus. KS-619-1 has an anthraquinone moiety. IC50 values for the effect of KS-619-1 on Ca2+ and calmodulin-stimulated activity of bovine brain and heart enzymes were 2.0 and 1.5 microM, respectively. On the other hand, basal activity (the activity in the presence of ethylene bis(oxyethylenenitrilo)tetraacetic acid (EGTA) instead of Ca2+/calmodulin) of the bovine brain enzyme, calmodulin-independent cyclic nucleotide phosphodiesterase from bovine heart, and protein kinase C from rat brain were inhibited by KS-619-1 to a lesser extent with IC50 values; 12.3, 25.9 and 151 microM, respectively.     

Tissue selective inhibition of cyclic nucleotide phosphodiesterase by denbufylline

The effects of the novel alkylxanthine denbufylline (1,3-d-n-butyl-7-(2'-oxopropyl)-xanthine), theophylline and 3-isobutyl-1-methyl-xanthine (IBMX), on the breakdown of cyclic AMP in homogenates of rat erythrocytes, abdominal aorta, adipocytes and cardiac and skeletal muscle were studied. Theophylline and IBMX inhibited cyclic nucleotide phosphodiesterase in all tissue extracts. In contrast, denbufylline was a tissue selective inhibitor of cyclic nucleotide phosphodiesterase. In skeletal muscle and erythrocytes, denbufylline (10 mumol/l) inhibited cyclic nucleotide phosphodiesterase activity by at least 80%. In these tissues, denbufylline was 10-30 and 100-300fold more potent than IBMX and theophylline, respectively. In adipocytes and cardiac and smooth muscle, denbufylline was not an effective inhibitor of cyclic AMP breakdown. Hofstee analysis of phosphodiesterase activity revealed that denbufylline selectively inhibited high affinity cyclic AMP phosphodiesterase in erythrocytes and skeletal muscle. In adipocytes, cardiac and vascular smooth muscle, denbufylline did not effectively inhibit the composite cyclic nucleotide phosphodiesterase activities either with high or with low affinity for cyclic AMP.     

Silymarin: potent inhibitor of cyclic AMP phosphodiesterase

Silymarin, the active principle of the Milk Thistle (Silybum marianum Gaertner), is a very potent inhibitor of cyclic AMP breakdown in vitro by a commercial beef heart phosphodiesterase preparation. Its main constituents, silybin, silydianin and silychristin, are 12.66 to 52.06 times more active than theophylline and 0.77 to 3.17 times more active than papaverine in this respect. Using a novel HPLC technique, the enzyme kinetical analysis can be performed much faster than by the classical methods.     

API 0134对钙调素非依赖型环核苷酸磷酸二酯酶的影响

采用钙调素非依赖型环核苷酸磷酸二酯酶（ＰＤＥ－Ⅱ）测定方法，观察ＡＰＩ０１３４对ＰＤＥ－Ⅱ的作用。ＡＰＩ０１３４浓度５０ｍｇ·Ｌ－１时明显抑制ＰＤＥ一Ⅱ活性，半效抑制浓度为２１３ｍｇ·Ｌ－１。酶促动力学分析表明：ＡＰＩ０１３４存在时，ＰＤＥ－Ⅱ的Ｋｍ值不变，为１．９２×１０－４ｍｏｌ·Ｌ－１，而Ｖｍａｘ值则随ＡＰＩ０１３４剂量增大而减小，提示ＡＰＩ０１３４为ＰＤＥ－Ⅱ的非竞争性抑制剂。