Extracellular cyclic-amp phosphodiesterase regulation in agar plate cultures of Dictyostelium discoideum

Extracellular cyclic-AMP phosphodiesterase and the inhibitor of this enzyme is tested in agar plate cultures of two Dictyostelium discoideum wild-type strains and in a mutant which lacks the inhibitor. Under the conditions used, the phosphodiesterase inhibitor is formed in both wild-type strains either before or in an early stage of cell aggregation. During aggregation of one strain the phosphodiesterase activity is extremely low, excluding a necessary function of the enzyme in the aggregation process.

Inhibition of separated forms of phosphodiesterases from pig coronary arteries by uracils and by 7-substituted derivatives of 1-methyl-3-isobutylxanthine

A series of 7-substituted 1-methyl-3-isobutylxanthines was designed in an attempt to increade the specificity of the 1-methyl-3-isobutylxanthine (MIX) structure for one of the two cyclic nucleotide phosphodiesterase peaks isolated by DEAE-cellulose chromatography of the soluble fraction of the intima + media layer of pig coronary arteries. A series of 1,3-dialkyluracils was of low potency as inhibitors of either peak I or peak II. The 7-substituted xanthines were prepared by alkylation of MIX with the corresponding alkyl or aralkyl halide in DMF containing K2CO3. These compounds were, in general, much less potent inhibitors of peak II activity than was MIX, but some of them retained the potency of MIX as inhibitors of peak I and, therefore, were relatively specific for inhibition of peak I. 7-Bzl-MIX was the most selective compound tested; it was a potent inhibitor of peak I activity but was much less effective as an inhibitor of peak II activity. Substitution of either electron-withdrawing (nitro) or electron-donating (methoxy) groups on the 7-benzyl moiety reduced the effectiveness of the 7-benzyl compounds as inhibitors of peak I. Chlorobenzyl substitution increased the potency slightly over the benzyl but not the selectivity between peaks.

[Adenyl cyclase and adenosine-3',5'-monophosphate phosphodiesteraze: their nature, properties and regulation]

Modern data on the nature, properties and pathways of regulation enzymes, participated metabolism of cyclic, adenosine-3',5'-monophosphate, are described. Much consideration is being given to the problem of regulation of the phosphodiesterase activity due to the effect of Ca2+-binding proteins.

Effects of imipramine, nomifensine and d-amphetamine on type B monoamine oxidase, cyclic AMP phosphodiesterase and dopamine-beta-hydroxylase

The three dissimilar structural antidepressant drugs, imipramine, nomifensine and d-amphetamine, were compared for their effects on type B monoamine oxidase, cyclic AMP phosphodiesterase and dopamine-beta-hydroxylase. Three antidepressant drugs caused a dose-dependent inhibition on type B monoamine oxidase. Of the three drugs, imipramine had a most potent effect. Unlike d-amphetamine, both imipramine and nomifensine inhibited the cyclic AMP phosphodiesterase activity at concentrations more than 10(-4)M. No effect was observed below this concentration. All drugs seemed to have little or no effects on the partially purified dopamine-beta-hydroxylase activity. The weak inhibitory effects of nomifensine on these three enzymes may not be attributable to its antidepressant properties. Morphine had no effect on the three enzyme activities.

Modifications in the release of rat growth hormone in vitro and the morphology of rat anterior pituitaries incubated in various ionophores

The ionophore A23187 increased the release of rat growth hormone in the presence of a phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine; a second ionophore X537A inhibited growth hormone release induced by the methylxanthine. A23187 did not alter rat growth hormone release in the absence of 3-isobutyl-1-methylxanthine, but X537A enhanced hormone release in the absence of calcium or in the presence or somatostatin. These findings provide further evidence that both calcium and cyclic AMP are important in the regulation of growth hormone release. Tissue incubated in X537A combined electronlucent vesicles apparently derived from the Golgi apparatus, swollen granules and mitochondria with dense matrices. Tissue incubated in the presence of valinomycin or A23187 did not show altered morphology of either secretory granules or the Golgi complex. Possible mechanisms of these changes are discussed.

An action of disodium cromoglycate: inhibition of cyclic 3',5'-AMP phosphodiesterase

Disodium cromoglycate (DSCG) prevents allergic asthma by inhibiting the release of chemical mediators of immediate-type allergic reactions. The mechanism of this action is unclear and prompted us to examine the effect of DSCG on cyclic adenosine 3',5'-monophosphate (cAMP), the implicated regulator of IgE-mediated reactions. We used the peripheral blood lymphocyte as a model to mirror the biochemical events occurring in the allergic shock organs. Isolated peripheral blood lymphocytes from perennial allergic asthmatic children receiving only DSCG had significantly (p less than 0.005) lower phosphodiesterase (PDE) activity (mean 1.05 +/- 0.17 SE per 10(6) cells) than normal individuals (2.93 +/- 0.14) and allergic children receiving methylxanthines (4.08 +/- 0.28) or no medications (3.58 +/- 0.2). DSCG (10 mug/ml) significantly lowered PDE activity in normal lymphocytes (p less than 0.005) in a beef heart extract (p less than 0.001), and 100 mug/ml lowered PDE activity in fetal rabbit lung homogenates (p less than 0.001). DSCG (10 mug/ml) significantly elevated (p less than 0.01) cAMP concentration in normal human lymphocytes (118 +/- 38 vs 30 +/- 10 picomoles cAMP/10(6) lymphocytes). Thus, DSCG appears to inhibit chemical mediator release by increasing intracellular cAMP through the inhibition of cAMP PDE.

[Inhibition of 3', 5'-cyclic AMP phosphodiesterase in the guinea pig lung by a new anti-allergic: 10-(3-quinuclidinylmethyl) phenothiazine (LM 209)]

The action of a new antiallergic agent, 10-(3-quinuclidinylmethyl) phenothiazine or LM 209, on cAMP phosphodiesterase (PDE) was studied on a guinea-pig lung preparation and compared with that of other compounds such as cromoglycate (I), dexamethasone (II), dexchlorpheniramine (III), promethazine (IV) and theophylline (V). Compounds I, IV and V are competitive inhibitors whereas LM 209 and compound III are non competitive inhibitors of PDE. Compound II is practically inactive on the enzyme. Compounds III and V produce an inhibition of equal intensity, independently of the substrate concentration. Compounds I and IV are more active on PDE with low affinity than on PDE with strong affinity, whereas it is the contrary with LM 209. The mechanism of action of LM 209 at the pulmonary level is discussed in the light of these findings.

Circadian periodicity a neurospora: alteration by inhibitors of cyclic AMP phosphodiesterase

Three methyl xanthine inhibitors of adenosine 3',5'-monophosphate phosphodiesterase-theophylline, aminophyline, and caffeine-lengthen the period of the circadian conidiation rhythm of Neurospora. The effect are seen in wild-type strains and in three mutant strains with genetically altered period lengths. These results suggest the possible involvement of adenosine 3', 5'-monophosphate in the control of circadian rhythmicity.

Prazosin: biochemistry and structure-activity studies

Prazosin, a structurally and mechanistically novel antihypertensive agent, is the culmination of a systematic synthesis and pharmacologic developmental effort which had as its goal the development of an agent that would lower blood pressure by direct vasodilation. Pharmacologic studies have demonstrated that the vasodilator action of prazosin is confined primarily to the arterioles and that antihypertensive effects are unaccompanied by excessive increases in heart rate. Evidence is presented rationalizing these observations on a biochemical basis. Results of inhibitory studies with isolated cyclic nucleotide phosphodiesterases are consistent with the hypothesis that prazosin elicits its therapeutic effects by increasing intracellular levels of cyclic AMP at vascular sites and intracellular levels of cyclic GMP at cholinergic receptor sites in the heart. Tissue distribution studies with radioactive prazosin-2-14C are in accord with this rationale and further support the mechanistic conclusions reached on the basis of pharmacologic observations. Pharmacokinetic and biotransformation studies indicate that prazosin is well absorbed and is excreted principally in metabolized form with biliary excretion being the major route of elimination. A high margin of safety for prazosin has been established in safety evaluation studies in a variety of animal species.

Role of cyclic AMP in differentiation of human neuroblastoma cells in culture

The inhibitors of cyclic AMP phosphodiesterase (papaverine and 4-(-3-butoxy-4-methoxybenzyl)-2-imidazolidinone), serum-free medium, and x irradiation caused cell death and neurite formation in human neuroblastoma cells in culture (IMR-32), whereas theophylline was ineffective. Prostaglandin (PG) E1, N6O'2-dibutyryl adenosine 3',5'-cyclic monophosphate (dbcAMP) induced neurites without causing cell lethality. Inhibitors of phosphodiesterase and PGE1 increased the intracellular level of cAMP by about 2- and 4-fold respectively, whereas serum-free medium and x irradiation did not. The combination of PGE1 and phosphodiesterase inhibitor was more effective in causing morphological differentiation and in increasing the cAMP level than the individual agent. Sodium butyrate induced cell death and neurites, probably in part by increasing the cAMP level. cAMP, guanosine 3',5'-cyclic monophosphate, and adenosine had no detectable effect on the growth or morphology of neuroblastoma cells in culture. Adenosine 5'-monophosphate produced cell death without causing neurite formation. DbcAMP, and to a much lesser degree, sodium butyrate increased the tyrosine hydroxylase activity.

8-Substituted derivatives of adenosine 3',5'-cyclic phosphate require an unsubstituted 2'-hydroxyl group in the ribo configuration for biological activity

Derivatives of adenosine 3',5'-cyclic phosphate (cAMP) with modifications in both the 2' and the 8 positions were synthesized and their enzymic activities as activators of cAMP-dependent protein kinase and as substrates for and inhibitors of cAMP phosphodiesterases were determined. Three types of derivatives were investigated: 8-substituted derivatives of O2'-Bt-cAMP, 8-substituted derivatives of 9-beta-D-arabinofuranosyladenine 3',5'-cyclic phosphate (ara-cAMP), and 8-substituted derivatives of 8,2'-anhydro-9-beta-D-arabinofuranosyladenine 3,'5'-cyclic phosphate (8,2'-anhydro-cAMP). The 8-substituted O2'-Bt-cAMP derivatives were synthesized by acylation of the preformed 8-substituted cAMP (8-HS-cAMP, 8-MeS-cAMP, and 8-PhCH2S-cAMP). 8-Br-O2'-tosyl-cAMP was sued as an intermediate for the preparation of 8,2'-anhydro-cAMP derivatives (8-HO-, 8-SH-, 8-H2N-, and 8-H3 CHN derivatives of 8,2'-anhydro-cAMP). 8-Substituted ara-cAMP derivatives were obtained by ring opening of 8-HO-8,2'-anhydro-cAMP with H+/H2O, NH3/MeOH, or MeONa/MeOH (to yield the 8-HO-, 8-H2N-, and 8-MeO-ara-cAMP derivatives). All of these doubly modified derivatives of cAMP are less than one-hundredth as active as cAMP at activating protein kinase and did not serve as substrates for the phosphodiesterase. These data show that the general inactivity of 2' derivatives of cAMP with kinase was not overcome by addition of an 8-substituent, even though many 8-substituted derivatives of cAMP activate the kinase more efficiently than does cAMP itself. In addition they show that while 2'-modification were tolerated by the phosphodiesterase, addition of an 8-substituent countermanded the allowable 2'-modification. The 8-substituted derivates of 02'-Bt-cAMP were found in general to be slightly better inhibitors of phosphodiesterase than the parent compounds containing no o2'-Bt substitution. As a group, the 8-substituted ara-cAMP derivatives were poorer inhibitors of phosphodiesterase than 8-substituted cAMP derivatives while the 8,2'-anhydro-cAMP derivatives were much poorer inhibitors than the 8-substituted ara-cAMP derivatives.

3':5'-cyclic-nucleotide phosphodiesterases of mammalian sera

Cyclic AMP and cyclic GMP phosphodiesterases (3':5'-cyclic-nucleotide 5'-nucleotidohydrolase EC 3.1.4.17) were found in the sera of human, dog, rabbit and rat. The formed elements of blood were not present in sera and thus not the source of the phosphodiesterase. More rapid hydrolysis of cyclic GMP than cyclic AMP is observed in the sera of these four species when 0.4 muM of cyclic AMP or cyclic GMP is used as the substrate. Protein activator of the phosphodiesterase is not detectable in the sera of these four species. Serum cyclic AMP and cyclic GMP phosphodiesterase activities are not stimulated by protein activator prepared from bovine brain. The serum phosphodiesterases of these four species are purified through Sepharose 6B column chromatography. Cyclic AMP phosphodiesterase are found in a broad area corresponding to molecular weights ranging from approximately 150 000 to 340 000 with 2 to 3 peaks in all animals tested. Cyclic GMP hosphodiesterase is found in a single area corresponding to molecular weights of 230 000 (rabbit and rat) and 270 000 (human and dog). Serum cyclic AMP and cyclic GMP hosphodiesterase activities of these four species have pH optimum of 7.5-8.5. Optimal concentration of Mg-2+ is about 5 mM for cyclic GMP phosphodiesterase activities of these four species as well as for cyclic AMP phosphodiesterase activities except rabbit. Rabbit serum cyclic AMP phosphodiesterase requires higher concentration of Mg-2+ (50 mM) for its optimal activity. The double reciprocal plots are non-linear for cyclic AMP phosphodiesterases of all animals and cyclic GMP phosphodiesterases of human, dog and rat. Rabbit cyclic GMP phosphodiesterase exhibits a linear reciprocal plot. Cyclic GMP is inhibitor of serum cyclic AM phosphodiesterase. Rabbit enzyme was most effectively inhibited by cyclic GMP.

Characterisation of cyclic adenosine 3':5'-monophosphate phospodiesterase from Walker carcinoma sensitive and resistant to bifunctional alkylating agents

Walker carcinoma cell lines sensitive or resistant to bifunctional alkylating agents have been found to contain multiple forms of cyclic AMP phosphodiesterase (3':5'-cyclic AMP 5'-nucleotidohydrolase, EC 3.1.4.17). These activities have been resolved using Sepharose 6B gel filtration and their apparent molecular weights have been estimated. The enzyme appears to occur in four active forms of apparent mol. wts of greater than 1 000 000, 430 000, 350 000 and 225 000, when assayed at low substrate concentrations. Evidence has been obtained which suggests that all four forms of the enzyme are composed of subunits of mol. wt of approximately 15 000 and are interconvertible. While the ionic strength of the buffer affected the predominance of the different forms, the presence of cyclic AMP at 10(-6) M had no effect on aggregation or dissociation of the enzyme. An activity shift from high molecular weight forms of the enzyme to low molecular weight forms has been found in the resistant tumour at low substrate concentration. No change in elution profile between sensitive and resistant tumours was observed for the low affinity form of the enzyme. The pH optima of the enzymes with both high and low affinity for the substrate was found to be pH 8.0 in the sensitive line. In the resistant tumour the pH optima of the high affinity form is shifted to pH 8.4 while the low affinity form remains at pH 8.0. The high affinity forms of the phosphodiesterase in the sensitive and resistant tumour also differed in their inhibition by theophylline. In both cases inhibition was of the competitive type with Ki values for the sensitive and resistant lines being 2.35 and 0.32 mM, respectively. There was no significant difference in the inhibition of the low affinity form between the sensitive and resistant tumour.

Differences and similarities between guanosine 3',5'-cyclic monophosphate phosphodiesterase and adenosine 3',5'-cyclic monophosphate phosphodiesterase activities in neuroblastoma cells in culture

There are phosphodiesterase activities in both particulate and supernatant fractions which hydrolyze guanosine 3',5'-cyclic monophosphate (cGMP) and adenosine 3',5'-cyclic monophosphate (cAMP) with an apparent Km of 2-8 muM and with an apparent Km of 44-222 muM. 4-(3-Butoxy-4-methoxybenzyl-2-imidazolidinone (RO20-1724) did not inhibit cGMP phosphodiesterase activity in homogenates of mouse neuroblastoma cells, but markedly inhibited cAMP phosphodiesterase activity. Papaverine and theophylline inhibited both cGMP and cAMP phosphodiesterase activities to about the same extent. The former was more potent than the latter. The specific activity of cGMP phosphodiesterase as a function of protein concentrations first increased and then decreased. The specific activity of cAMP phosphodiesterase decreased under a similar experimental condition.

Cyclic 3',5'-nucleotide phosphodiesterase in rat skin. II. Biochemical characterization

The biochemical characteristics of cyclic 3',5'-nucleotide phosphodiesterase were studied in homogenates of male albino rat skin using preparations which were predominantly epidermal. Enzymatic activity was detected in both the particulate and soluble fractions of these skin homogenates. Two kinetically distinct phosphodiesterase (PDE) activities were detected in the soluble fraction (100,000 times g supernatant). This 100,000 times g supernatant contains at least two distinct protein bands that hydrolyze cyclic AMP as demonstrated by gel electrophoresis. Divalent cations (Mg-++ or Mn-++) and 2-mercaptoethanol were required for maximal enzymatic activity. Epinephrine, dibutyryl cyclic AMP, and methylxanthines inhibited while imidazole and histamine phosphate stimulated the cyclic AMP phosphodiesterase activity at high and low cyclic AMP concentrations. Cyclic GMP competitively inhibited hydrolysis of low, but not high, concentrations of cyclic AMP. Hydrocortisone phosphate in pharmacologic concentrations blocked PDE denaturation by heat. These studies indicate that there are complex interrelationships between cyclic nucleotides and PDE in rat skin.

Stimulation of ion transport by ascorbic acid through inhibition of 3':5'-cyclic-AMP phosphodiesterase in the corneal epithelium and other tissues

Ascorbic acid stimulates active transport of Cl-minus by the isolated intact cornea. The effect is not present in corneas previously stimulated by the theophylline, an inhibitor of 3':5"-cyclic-AMP phosphodiesterase (EC 3.1.4.17), and vice versa, theophylline has no action after stimulation with ascorbic acid. This indicated inhibition of 3':5'-cyclic-AMP phosphodiesterase by ascorbic acid. Assay of phosphodiesterase using 3-H-labeled cyclid AMP of frog and rabbit corneal epithelial homogenates showed an inhibitory effect of ascorbic acid. Concentration of 5 mM produced 16% inhibition with 20 mM producing 46%. This compares with 58% inhibition by theophylline at 5 mM. Phosphodiesterase activity is mostly soluble in frog corneal epithelium but in rabbit 45% is particulate. Soluble and particulate fractions are inhibited by ascorbate, but in rabbits greater inhibition (50%) was observed in the particulate fraction than in the soluble fraction. Other tissues showed inhibition also: frog retina 12%, rat brain (caudate nucleus) 48%, rabbit brain 14%, rabbit liver 16%. It is concluded that ascorbate produces an increase in cyclic AMP content of corneal epithelium and other tissues by inhibition of 3':5'-cyclic-AMP phosphodiesterase. This action may be one of the main functions of the high ascorbic acid content of ocular tissues and explain some of the effects of high dosis of ascorbate in other systems.

Synthesis and antitumor activity of 5'-phosphates and cyclic 3',5'-phosphates derived from biologically active nucleosides

Syntheses and biological activities of 12 N6-substituted adenosine 5'-phosphates and 15 cyclic 3',5'-phosphates are described. Included among these are the cyclic phosphates of the naturally occurring anticodon adjacent modified nucleosides, N6-(delta2-isopentenyl)adenosine and N-(purin-6-ylcarbamoyl)-L-threonine ribonucleoside. Also reported in this paper are the 5'-phosphates and cyclic phosphates of the cytokinins, N6-benzyladenosine, kinetin ribonucleoside, 3-(chloro-trans-2-buten-2-yl)adenosine,6-o-chlorophenylureidopurine ribonucleoside, and 6-allylureidopurine ribonucleoside. The 5'-nucleotides were prepared by direct phosphorylation of the corresponding ribonucleosides with POCl3 and triethyl phosphate. These compounds were converted to the cyclic 3',5'-phosphates by cyclization of the corresponding 5'-nucleotides with dicyclohexylcarbodiimide. Comparison of the cytotoxicity of the ribonucleosides with their 5'-nucleotides and cyclic 3',5'-nucleotides showed that some of the 5'-phosphates and cyclic phosphates were almost as active as the parent nucleosides. The 5'-nucleotides and the cyclic phosphates were more soluble than the parent nucleosides. The cyclic 3',5'-nucleotides were examined as alternate activators of cAMP-dependent protein kinase from beef heart. While all of the analogs studied showed some activity toward this enzyme, several compounds were more effective than cAMP itself. The analogs were also tested as substrates for cyclic 3',5'-nucleotide phosphodiesterase from beef heart. The N6-alkyl-cAMP analogs were poor substrates for the enzyme, while N6-carbamoyl-cAMP derivatives were inert toward this enzyme. These compounds did not inhibit the phosphodiesterase. Some of the cyclic phosphates exhibited marginal effect in the inhibition of glycogen synthesis in skin slices.

Inhibition of platelet cyclic 3',5'-adenosine-monophosphate phosphodiesterases by pentifylline

Pentifylline (1-hexyl-3,7-dimethylxanthine equals SK 7, the main active principle in Cosaldon) inhibits the soluble and the particulate cyclic AMP phosphodiesterases (PDE I and PDE II) from bovine platelets. I50 PDE I equals 2.0 x 10(-3)M; I50 PDE II equals 8.1 x 10(-4)M. The type of inhibition of both PDE's was non-competitive.

Adenosine cyclic 3',5',-monophosphate phosphodiesterasr inhibitors. 2.3-Substituted 5,7-dialkylpyrazolo [1,5-a]pyrimidines

A number of 3-bromo-, 3-nitro-, and 3-ethoxycarbonyl-5,7-dialkylpyrazolo[1,5-a]pyrimidines were synthesized and screened as in vitro cAMP phosphodiesterase inhibitors. The condensation of 3-aminopyrazole with symmetrical beta-diketones (acetylacetone, heptane-3,5-dione, etc.) afforded symmetrical dialkylpyrazolo[1,5-a]pyrimidines (5). The reaction of 3-aminopyrazole with unsymmetrical beta-diketones (hexane-2,4-dione, heptane-3,5-dione, etc.) gave a mixture of 5-methyl-7-alkylpyrazolo[1,5-a]pyrimidine (3) and 5-alkyl-7-methylpyrazolo[1,5-a]pyrimidines (4). The technique for the separation of 3 from 4 is described. The inhibition constants, alpha (the ratio of the molar I50 of theophylline to the molar I50 of the test compounds), were subjected to a Hansch correlation analysis. The results indicated that PDE isolated from beef heart tissue was most sensitive to changes in the length of the alkyl group in the 5 position of the pyrazolo[1,5-a]pyrimidine ring, whereas the PDE isolated from rabbit lung tissue was more sensitive to changes in the length of the 7-alkyl group. Experimentally and theoretically, the n-propyl group was found to approximate the ideal size for the alkyl group in both the 5 and 7 positions;5,7-di-n-propyl-3-ethoxycarbonylpyrazolo[1,5-a]pyrimidine (5e) was the most potent inhibitor of both lung and heart PDE.