Differential effects of various phosphodiesterase inhibitors, pyrimidine and purine compounds, and inorganic phosphates on cyclic CMP, cyclic AMP and cyclic GMP phosphodiesterases

The quantitative analysis of the mechanism involved in pertussis toxin-mediated cell clustering and its implications in the in vitro quality control of diphtheria tetanus and whole cell pertussis vaccines

Some of the adverse side-effects such as leukocytosis, hyperinsulinemia, hypoglycemia and sensitization to histamine, caused by diphtheria, tetanus and whole cell pertussis (DTwP) vaccines are related to the presence of non-inactivated pertussis toxin (PTx) residues (NiPTxR). The CHO cell clustering assay is an in vitro assay to measure NiPTxR in DTwP vaccines based on the ability of active PTx to cause cellular clustering. To study the biochemical mechanism involved in the clustering effect in CHO cells induced by PTx and by two DTwP vaccines, the levels of total cyclic cAMP were measured and compared to those obtained after treatment with cholera toxin (CTx) able to induce CHO cells elongation instead of cell clustering. Our results showed an increment of cAMP levels by CTx and total cell elongation in CHO cells. However, changes in cAMP levels were not associated with the total clustering induced by PTx or by DTwP vaccines. The high correlation seen between the levels of NiPTxR in the DTwP vaccines determined by the in vivo lethal histamine sensitization (HIST) assay and the in vitro CHO cell clustering assay indicated that the latter could be a suitable alternative test to HIST assay for the toxicological approval and release of batches of DTwP vaccines in their final formulation for human use in accordance with the application of the 3R's principle.

Inactivation of Non-canonical Cyclic Nucleotides: Hydrolysis and Transport

This chapter addresses cNMP hydrolysis by phosphodiesterases (PDEs) and export by multidrug resistance associated proteins (MRPs). Both mechanisms are well-established for the canonical cNMPs, cAMP, and cGMP. Increasing evidence shows that non-canonical cNMPs (specifically cCMP, cUMP) are also PDE and MRP substrates. Hydrolysis of cUMP is achieved by PDE 3A, 3B, and 9A, which possibly explains the cUMP-degrading activities previously reported for heart, adipose tissue, and brain. Regarding cCMP, the only known "conventional" (class I) PDE that hydrolyzes cCMP is PDE7A. Older reports describe cCMP-degrading PDE-like activities in mammalian tissues, bacteria, and plants, but the molecular identity of these enzymes is not clear. High K _M and V _max values, insensitivity to common inhibitors, and unusually broad substrate specificities indicate that these activities probably do not represent class I PDEs. Moreover, the older results have to be interpreted with caution, since the historical analytical methods were not as reliable as modern highly sensitive and specific techniques like HPLC-MS/MS. Besides PDEs, the transporters MRP4 and 5 are of major importance for cAMP and cGMP disposal. Additionally, both MRPs also export cUMP, while cCMP is only exported by MRP5. Much less data are available for the non-canonical cNMPs, cIMP, cXMP, and cTMP. None of these cNMPs has been examined as MRP substrate. It was shown, however, that they are hydrolyzed by several conventional class I PDEs. Finally, this chapter reveals that there are still large gaps in our knowledge about PDE and MRP activities for canonical and non-canonical cNMPs. Future research should perform a comprehensive characterization of the known PDEs and MRPs with the physiologically most important cNMP substrates.

From canonical to non-canonical cyclic nucleotides as second messengers: pharmacological implications

This review summarizes our knowledge on the non-canonical cyclic nucleotides cCMP, cUMP, cIMP, cXMP and cTMP. We place the field into a historic context and discuss unresolved questions and future directions of research. We discuss the implications of non-canonical cyclic nucleotides for experimental and clinical pharmacology, focusing on bacterial infections, cardiovascular and neuropsychiatric disorders and reproduction medicine. The canonical cyclic purine nucleotides cAMP and cGMP fulfill the criteria of second messengers. (i) cAMP and cGMP are synthesized by specific generators, i.e. adenylyl and guanylyl cyclases, respectively. (ii) cAMP and cGMP activate specific effector proteins, e.g. protein kinases. (iii) cAMP and cGMP exert specific biological effects. (iv) The biological effects of cAMP and cGMP are terminated by phosphodiesterases and export. The effects of cAMP and cGMP are mimicked by (v) membrane-permeable cyclic nucleotide analogs and (vi) bacterial toxins. For decades, the existence and relevance of cCMP and cUMP have been controversial. Modern mass-spectrometric methods have unequivocally demonstrated the existence of cCMP and cUMP in mammalian cells. For both, cCMP and cUMP, the criteria for second messenger molecules are now fulfilled as well. There are specific patterns by which nucleotidyl cyclases generate cNMPs and how they are degraded and exported, resulting in unique cNMP signatures in biological systems. cNMP signaling systems, specifically at the level of soluble guanylyl cyclase, soluble adenylyl cyclase and ExoY from Pseudomonas aeruginosa are more promiscuous than previously appreciated. cUMP and cCMP are evolutionary new molecules, probably reflecting an adaption to signaling requirements in higher organisms.

Novel protein inhibitor of calmodulin-dependent cyclic nucleotide phosphodiesterase from glioblastoma multiforme

Previous investigations from our laboratory have demonstrated a significant reduction in the catalytic function of the 60 kDa and 63 kDa isozymes of calmodulin-dependent cyclic nucleotide phosphodiesterase (CaMPDE) when comparing human cerebral tissue that was free of tumor and glioblastoma multiforme (GBM) and gliosarcoma [Lal S., Raju R. V. S., Macaulay R. B. J., and Sharma R. K. (1996) Can. J. Neurol. Sci., 23, 245-250]. The results suggested the possibility of an endogenously produced inhibitor of CaMPDE expressed in these tumors. Further investigation has initially characterized the presence of a heat-labile, protein inhibitor of both the 60 kDa and 63 kDa isozymes of CaMPDE. Sephacryl S-200 gel filtration column chromatography indicated that the inhibitor has an apparent molecular weight of 22 kDa and experimental evidence demonstrates that this inhibitor protein may act independently of calmodulin, and is therefore a novel CaMPDE inhibitor. Previous work on non-CNS tumors has shown high levels of CaMPDE activity and absence of an inhibitor. This suggests that a different mechanism may exist for the proliferation of these subsets of tumors.

Conversion of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine to cidofovir by an intracellular cyclic CMP phosphodiesterase

Cidofovir (HPMPC) [1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]-cytosine] is an acyclic nucleotide analog with potent and selective activity against herpesviruses. The prodrug, cyclic HPMPC (cHPMPC) [1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl) methyl]cytosine], has antiviral activity similar to that of the parent compound but exhibits reduced toxicity in animal models. cHPMPC is converted to cidofovir by a cellular cyclic CMP phosphodiesterase (EC 3.1.4.37) which hydrolyzes a variety of substrates, including adenosine 3',5'-cyclic monophosphate (cAMP) and cytidine 3',5'-cyclic monophosphate (cCMP). The K(m) and Vmax values for hydrolysis of cHPMPC by cCMP phosphodiesterase purified from human liver are 250 microM and 0.66 nmol.min-1.unit-1, respectively. These values are similar to the K(m) and Vmax values for cAMP (23 microM and 1.16 nmol.min-1.unit-1, respectively) and cCMP (75 microM and 2.32 nmol.min-1.unit of enzyme-1, respectively). The catalytic efficiency (Vmax/K(m) ratio) of this enzyme for the cHPMPC substrate is only 10- to 20-fold lower than those for the natural cyclic nucleotides, indicating that cHPMPC is a viable intracellular substrate for the human enzyme. Kinetic analysis indicates that cHPMPC, cAMP, and cCMP are competitive with respect to each other and that they are hydrolyzed by the same enzyme. cHPMPC is hydrolyzed to cidofovir in all primary human cell systems tested, including those derived from target organs that might be infected in patients with human cytomegalovirus (HCMV) disease. Importantly, hydrolysis of cHPMPC is not diminished in cells infected with HCMV.

Cyclic nucleotide-induced termination of vitellogenin uptake by Hyalophora cecropia follicles

Endocytosis of vitellogenin by isolated follicles of Hyalophora cecropia terminated after membrane-permeable analogs of cAMP or cGMP were added to the culture medium. Depending on the concentration of the analog, a lag period of 30 min to 3 h preceded termination. Forskolin and IBMX both stimulated a rise in endogenous cAMP, and this also induced termination, as did pharmacological activation of the cyclic nucleotide-dependent protein kinases PKA and PKG. Inhibitors of PKA or PKG protected follicles from the corresponding cyclic nucleotide effect. When cAMP or cGMP was added to homogenates of vitellogenic follicles, a 32 kDa polypeptide was phosphorylated; inhibition of PKA, prevented phosphorylation of this protein. The rate of vitellogenin uptake did not accelerate significantly when PKA or PKG was inhibited in culture, which suggests that these kinases are normally inactive or operating below threshold during the several days of vitellogenesis. They seem thus not to be involved in the steady-state modulation of protein uptake. A more likely function of this control pathway in follicle development would be to trigger the termination of vitellogenesis, which normally occurs spontaneously in follicles of this species as they reach a length of 2 mm.

Ocular hypotension induced by topical dopaminergic drugs and phosphodiesterase inhibitors

The aim of this work was to investigate the ocular hypotensive activity of some topically administered cAMP-phosphodiesterase inhibitors alone and in combination with dopaminergic compounds. Experiments were performed with ocular normotensive rabbits and during transitory induced ocular hyper- or hypotension. An ocular hypotensive effect was observed after instillation of aminophylline, dyphylline, pentoxifylline, caffeine, and iso-caffeine, but not following topical hydroxypropyl-1,3-dimethylxanthine. Dopaminergic compounds were also studied in order to be combined with phosphodiesterase inhibitors as ocular anti-hypertensive treatment. Significant ocular hypotensive activity was observed after topical application of trifluperidol, fluphenazine, thiothixene, and the S(-) enantiomer of 3-(3-hydroxyphenyl)-N-n-propylpiperidine (3-PPP). Of the cAMP-phosphodiesterase inhibitors that were tested, pentoxifylline was the most interesting compound, with good ocular tolerance, significant reduction in intra-ocular pressure, and potential retinal microvascular benefits. After allowing adequate time for pentoxifylline to reach its maximal activity, trifluperidol or S(-)-3-PPP was also instilled. A more pronounced ocular hypotensive effect was then observed. The findings of this study may suggest that administration of eye-drops combining drugs acting by separate ways on second messengers involved in the regulation of intra-ocular pressure (e.g. cyclic AMP) could be used to reduce intra-ocular pressure during glaucoma.

Histamine H3-receptor-induced inhibition of duodenal cholinergic transmission is independent of intracellular cyclic AMP and GMP

1. The inhibitory effect of the histamine H3-receptor agonist (R) alpha-methylhistamine on cholinergic neurotransmission was studied in the isolated guinea pig duodenum in the presence of different compounds which alter intracellular levels of cyclic nucleotides and of the G proteins blocker pertussis toxin. 2. The action of (R) alpha-methylhistamine on electrically-evoked contractions was not modified either by forskolin and isobutylmethylxanthine (which increase cyclic AMP) or by zaprinast and methylene blue (which increase and decrease, respectively intracellular cyclic GMP). Drugs affecting cyclic nucleotide levels were also ineffective against the inhibitory effect of the alpha 2 adrenergic agonist clonidine. 3. Pertussis toxin significantly reduced the maximum inhibition induced by (R) alpha-methylhistamine and clonidine, without influencing the effect of low concentrations of the above compounds; conversely it shifted to the right in a parallel way the inhibitory effect of adenosine. 4. These data suggest that H3-receptor-mediated inhibition of cholinergic transmission in the guinea pig duodenum is not linked to intracellular nucleotide changes. Moreover the signal transducing mechanism activated by (R) alpha-methylhistamine involves pertussis toxin both sensitive and insensitive G proteins.

Role of cyclic AMP in prostaglandin-induced modulation of acetylcholine release from the myenteric plexus of guinea pig ileum

Prostaglandins (PGs) have modulatory effects on spontaneous and nicotine-induced release of acetylcholine (ACh) from the myenteric plexus of guinea pig ileum. To determine whether cyclic AMP is involved in the mechanisms of these effects, we studied ACh release under conditions that inhibit PG synthesis. Indomethacin (IND), a cyclooxygenase inhibitor, inhibited ACh release concentration-dependently. The effect of the maximally inhibitory concentration of IND (2.8 microM) on nicotine-induced ACh release were reversed concentration-dependently by PGE2, forskolin, 3-isobutyl-1-methylxanthine (IBMX) and 8-bromo cyclic AMP. These compounds caused concentration-dependent reversal of the inhibition of spontaneous ACh release by IND, but their concentrations for restoration of spontaneous release were higher than those for restoration of nicotine-induced release. The effects of PGE2 and forskolin or IBMX were not additive in reversing the inhibition of nicotine-induced ACh release by IND. Neither forskolin nor 8-bromo cyclic AMP alone had any significant effect on either release. These results showed that increase in the level of cyclic AMP in myenteric cholinergic neurons restored ACh release from the tissue whose PG level had been lowered by IND and indicated that endogenous PGs may modulate the level of intraneuronal cyclic AMP.

Differential modulation by N4, 2'-O-dibutyryl cytidine 3':5'-cyclic monophosphate of neutrophil activation

The cyclic pyrimidine nucleotide, cCMP, is an endogenous substance in mammalian cells but little is known on its functional role. We studied the effects of cCMP, its cell-permeant analogue, N4,2'-O-dibutyryl cytidine 3':5'-cyclic monophosphate (Bt2cCMP), and of butyrate on superoxide (O2-) formation and cytosolic Ca2+ [( Ca2+]i) in human neutrophils. Bt2cCMP inhibited O2- formation and the rise in [Ca2+]i induced by a chemotactic peptide at submaximally effective concentrations. O2- formation induced by platelet-activating factor was potentiated by Bt2cCMP, whereas the cyclic nucleotide had no effect on the rise in [Ca2+]i induced by this agonist. Bt2cCMP enhanced O2- formation induced by tau-hexachlorocyclohexane at a submaximally effective concentration. O2- formation stimulated by complement C5a, concanavalin A, NaF, A 23187, phorbol myristate acetate and arachidonic acid was not affected by Bt2cCMP. cCMP was less effective than Bt2cCMP to inhibit fMet-Leu-Phe-induced O2- formation, and butyrate was without effect on any of the functional parameters studied. Our data show that a cell-permeant analogue of cCMP differentially inhibits and potentiates activation of human neutrophils.

Opioid inhibition of cholinergic transmission in the guinea-pig ileum is independent of intracellular cyclic AMP

This study examined whether the inhibitory actions of opioids in the guinea-pig ileum were influenced by agents which mimic or elevate intracellular cyclic adenosine 3',5'-monophosphate (cyclic AMP) levels. In longitudinal muscle-myenteric plexus preparations, the mu agonist, [D-Ala2,NMePhe4,Gly-ol5]enkephalin (DAGO) and the kappa agonist, dynorphin A-(1-13) depressed contractions of the longitudinal muscle evoked by electrical stimulation of myenteric neurons. Mean IC50 values were 19 and 2.8 nM for DAGO and dynorphin, respectively. Neither forskolin, cholera toxin nor dibutyryl cyclic AMP affected significantly the IC50s for the opioid agonists. The experiments suggest that mu and kappa agonists inhibit excitatory cholinergic transmission to the longitudinal muscle by intracellular effector mechanisms that do not involve cyclic AMP.

Hyperpolarization of myenteric neurons by opioids does not involve cyclic adenosine-3',5'-monophosphate

To investigate the role of cyclic adenosine-3'5'-monophosphate on the inhibitory actions of opioids in guinea-pig ileum, we made intracellular recordings from the two electrophysiologically defined classes of neurons (S and AH) in the myenteric plexus. The selective opioid mu agonist (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin caused a membrane hyperpolarization in 34 out of 67 S neurons but did not affect the membrane potential of AH neurons. The mean amplitude (+/- S.E.M.) of the hyperpolarization was 8.2 +/- 0.8 mV. Forskolin, which activates adenylate cyclase and increases intracellular cyclic adenosine-3',5'-monophosphate levels, caused a membrane depolarization in AH neurons (9.4 +/- 1.9 mV) but did not alter the resting membrane potential of S neurons. Similarly, neither the phosphodiesterase inhibitor, isobutylmethylxanthine, nor the membrane permeable analogue of cyclic adenosine-3',5'-monophosphate, dibutyryl cyclic adenosine-3'-5'-monophosphate, altered the resting membrane properties of S neurons. Furthermore, none of these agents affected significantly the amplitude of the hyperpolarization of S neurons by (D-Ala2,N-Me-Phe4,Gly5-ol)-enkephalin. The experiments indicate that changes in intracellular cyclic adenosine-3',5'-monophosphate are not important in the processes that link occupation of mu receptors to the opening of potassium channels on myenteric neurons.

Prostaglandin E2 induced the cyclic AMP-dependent release of acetylcholine in circular muscles of the isolated guinea pig ileum

Prostaglandin E2 (PGE2) induced a dose-dependent increase in tone of the circular muscles of guinea pig ileum in vitro. These actions of PGE2 were deleted in the cold-stored preparations and blocked by tetrodotoxin. Atropine reduced the effects of PGE2 and physostigmine potentiated the PGE2-induced contractions. The release of acetylcholine (ACh) by PGE2 was responsible for initiating this contraction. The effect of PGE2 was compared with that of an electrical stimulation which also initiated a non-receptor-mediated release of ACh. Hexamethonium abolished the effect of PGE2 but did not influence the actions of the electrical stimulations. Synaptosomal fractions of the circular muscles were prepared to study the release of [14C]ACh. However, PGE2 failed to evoke a marked increase in the efflux of radioactivity, even at the maximal concentration. Damage and/or removal of the myenteric plexus may be responsible for this result because electrical stimulations that exert a powerful spasmogenic effect on longitudinal muscles also induced an insensitive response. Alloxan and ethacrynic acid, inhibitors of adenylate cyclase, reduced the activity of PGE2 at a concentration insufficient to modify either the actions of ACh or the electrical stimulations. 3-Isobutyl-1-methylxanthine (IBMX) potentiated the responses to PGE2 at a dose sufficient to block the activity of phosphodiesterase (PDE). Imidazole, a stimulator of PDE, decreased the actions of PGE2 in a dose-dependent manner. IBMX, like imidazole, failed to modify the activities of both ACh and the electrical stimulations. These results indicate that PGE2 may function as a releaser of ACh in a cyclic AMP-dependent manner in the circular muscles of guinea pig ileum.

Possible role of adenosine in the relaxant effect of amrinone on guinea-pig ileum

In isolated segments of guinea-pig ileum, amrinone (0.3 mM-0.3 M) caused a transient contraction followed by a concentration-dependent relaxation. Theophylline (0.1-0.5 mM) mimicked the effects of amrinone but apparently inhibited relaxation induced by the latter. However the total decrease of muscle tension measured in preparations exposed to amrinone before and after theophylline treatment was quantitatively comparable. Dipyridamole (0.1 microM) potentiated the relaxing effect of amrinone. The stimulatory response of the ileum to high concentrations of adenosine (10-50 mM) was abolished by amrinone. In preparations treated with adenosine deaminase (10 U/ml) the basal tone was decreased and both amrinone and theophylline were ineffective. In rat ileum, amrinone exerted a marked relaxing effect that was abolished by adenosine deaminase. Thus amrinone appears to cause relaxation of intestinal smooth muscle from different species by hindering the stimulatory effect of endogenous adenosine. The possible intracellular localization of the amrinone-adenosine interaction site is discussed.

Effects of adenylate cyclase inhibitors, phosphodiesterase inhibitors, and dibutyryl cyclic AMP on spontaneous and various stimuli-induced acetylcholine release from guinea pig ileum myenteric plexus

In order to examine a possible contribution of cyclic AMP to acetylcholine (ACh) release from guinea pig ileum myenteric plexus, effects of adenylate cyclase inhibitors, phosphodiesterase (PDE) inhibitors and dibutyryl cyclic AMP on the spontaneous and the various stimuli-induced ACh release were investigated. A PDE inhibitor, theophylline (1 mM) increased the ACh release induced by nicotine (6.16 microM) significantly. Another PDE inhibitor, 3-isobutyl-1-methylxanthine (IBMX, 1 mM) and dibutyryl cyclic AMP (4 mM) had no effect. The adenylate cyclase inhibitors dithiobisnitrobenzoic acid (DTNB, 1 mM) and alloxan (4 mM) both decreased the nicotine-induced ACh release remarkably. PDE inhibitors increased and adenylate cyclase inhibitors decreased the high-K+-induced ACh release. Dibutyryl cyclic AMP brought about a slight but significant increase of the high-K+-induced ACh release. All the drugs failed to alter the ACh release induced by electrical field stimulation (EFS) at 10 Hz. Effects of all drugs except dibutyryl cyclic AMP on the spontaneous ACh release were the same as those on the nicotine-induced one. Dibutyryl cyclic AMP decreased it significantly. These results suggest that the cyclic AMP system is involved in the spontaneous, the nicotine-induced and the high-K+-induced ACh release and that the EFS-induced ACh release is independent of cyclic AMP.

The stimulatory effects of caffeine, theophylline, lysine-theophylline and 3-isobutyl-1-methylxanthine on human sperm motility

The potencies of caffeine, theophylline, lysine-theophylline and 3-isobutyl-1-methylxanthine (IBMX) in stimulating sperm motility have been compared, and we have found IBMX to be significantly more potent than the other three compounds, which did not exhibit significant differences in potency from each other.

Comparison of 3-isobutyl-1-methylxanthine-induced accumulation of putrescine in rat pancreas and liver

3-Isobutylmethylxanthine (IBMX), a potent phosphodiesterase inhibitor, causes accumulation of putrescine of same magnitude in rat pancreas and liver. IBMX produces increases of acetyl CoA: polyamine N'-acetyltransferase (PAT) and of ornithine decarboxylase (ODC) activities in both organs. However ODC activity is 300 times higher in liver than in pancreas. In the latter organ, there is a transient increase of N1-acetylspermidine, followed by a decrease of spermidine, alpha-Difluoromethylornithine (DFMO), a potent ODC inhibitor, impairs the accumulation of putrescine in liver but not in pancreas. These results suggest that in pancreas the accumulated putrescine is essentially formed from spermidine, via N1-acetylation and oxidation, while in liver it is formed from decarboxylation of ornithine. A possible involvement of cAMP in the stimulation of the polyamine interconversion pathway is discussed.

Decreased activities of cyclic cytidine 3',5'-monophosphate phosphodiesterase in Morris hepatomas having varying growth rates

1. The activities of cyclic cytidine 3',5'-monophosphate (cCMP) phosphodiesterase in normal rat liver and host liver (bearing hepatoma 5123 t.c.(h)) were compared with those of three Morris hepatomas of varying growth rates. 2. The results show that the order of enzyme activity was as follows: normal liver = host liver greater than 7794A (slow growth rate) greater than 5123 t.c.(h) (intermediate growth rate) greater than 7800 (fast growth rate). 3. The enzyme had a pH optimal value of about 7.0 and an apparent Km for cCMP about 2.8 mM; its activity was slightly affected by the presence of calmodulin (100 micrograms/ml) and/or CaCl2 (100 microM), but showed variable responses to other cations (La3+, Mg2+, Mn2+, Zn2+, Fe2+, Na+ and K+).