Multiplicity within cyclic nucleotide phosphodiesterases

Topical combinations to treat microvascular dysfunction of chronic postischemia pain

BACKGROUND

Growing evidence indicates that patients with complex regional pain syndrome (CRPS) exhibit tissue abnormalities caused by microvascular dysfunction in the blood vessels of skin, muscle, and nerve. We tested whether topical combinations aimed at improving microvascular function would relieve allodynia in an animal model of CRPS. We hypothesized that topical administration of either α2-adrenergic (α2A) receptor agonists or nitric oxide (NO) donors given to increase arterial blood flow, combined with either phosphatidic acid (PA) or phosphodiesterase (PDE) inhibitors to increase capillary blood flow, would effectively reduce allodynia and signs of microvascular dysfunction in the animal model of chronic pain.

METHODS

Mechanical allodynia was induced in the hindpaws of rats with chronic postischemia pain (CPIP). Allodynia was assessed before and after topical application of vehicle, single drugs or combinations of an α2A receptor agonist (apraclonidine) or an NO donor (linsidomine), with PA or PDE inhibitors (lisofylline, pentoxifylline). A topical combination of apraclonidine + lisofylline was also evaluated for its effects on a measure of microvascular function (postocclusive reactive hyperemia) and tissue oxidative capacity (formazan production by tetrazolium reduction) in CPIP rats.

RESULTS

Each of the single topical drugs produced significant dose-dependent antiallodynic effects compared with vehicle in CPIP rats (N = 30), and the antiallodynic dose-response curves of either PA or PDE inhibitors were shifted 5- to 10-fold to the left when combined with nonanalgesic doses of α2A receptor agonists or NO donors (N = 28). The potent antiallodynic effects of ipsilateral treatment with combinations of α2A receptor agonists or NO donors with PA or PDE inhibitors were not reproduced by the same treatment of the contralateral hindpaw (N = 28). Topical combinations produced antiallodynic effects lasting up to 6 hours (N = 15) and were significantly enhanced by low-dose systemic pregabalin in early, but not late, CPIP rats (N = 18). An antiallodynic topical combination of apraclonidine + lisofylline was also found to effectively relieve depressed postocclusive reactive hyperemia in CPIP rats (N = 61) and to increase formazan production in postischemic tissues (skin and muscle) (N = 56).

CONCLUSIONS

The present results support the hypothesis that allodynia in an animal model of CRPS is effectively relieved by topical combinations of α2A receptor agonists or NO donors with PA or PDE inhibitors. This suggests that topical treatments aimed at improving microvascular function by increasing both arterial and capillary blood flow produce effective analgesia for CRPS.

Topical combinations aimed at treating microvascular dysfunction reduce allodynia in rat models of CRPS-I and neuropathic pain

Growing evidence indicates that various chronic pain syndromes exhibit tissue abnormalities caused by microvasculature dysfunction in the blood vessels of skin, muscle, or nerve. We tested whether topical combinations aimed at improving microvascular function would relieve allodynia in animal models of complex regional pain syndrome type I (CRPS-I) and neuropathic pain. We hypothesized that topical administration of either α(2)-adrenergic (α(2)A) receptor agonists or nitric oxide (NO) donors combined with either phosphodiesterase (PDE) or phosphatidic acid (PA) inhibitors would effectively reduce allodynia in these animal models of chronic pain. Single topical agents produced significant dose-dependent antiallodynic effects in rats with chronic postischemia pain, and the antiallodynic dose-response curves of PDE and PA inhibitors were shifted 2.5- to 10-fold leftward when combined with nonanalgesic doses of α(2)A receptor agonists or NO donors. Topical combinations also produced significant antiallodynic effects in rats with sciatic nerve injury, painful diabetic neuropathy, and chemotherapy-induced painful neuropathy. These effects were shown to be produced by a local action, lasted up to 6 hours after acute treatment, and did not produce tolerance over 15 days of chronic daily dosing. The present results support the hypothesis that allodynia in animal models of CRPS-I and neuropathic pain is effectively relieved by topical combinations of α(2)A or NO donors with PDE or PA inhibitors. This suggests that topical treatments aimed at improving microvascular function may reduce allodynia in patients with CRPS-I and neuropathic pain.

PERSPECTIVE

This article presents the synergistic antiallodynic effects of combinations of α(2)A or NO donors with PDE or PA inhibitors in animal models of CRPS-I and neuropathic pain. The data suggest that effective clinical treatment of chronic neuropathic pain may be achieved by therapies that alleviate microvascular dysfunction in affected areas.

Dihydroartemisinin can inhibit calmodulin, calmodulin-dependent phosphodiesterase activity and stimulate cellular immune responses

Calmodulin (CaM) is a ubiquitous, calcium-binding protein that regulates several important aspects of cellular metabolism. A number of enzymes such as phosphodiesterase (PDE-1) are stimulated by CaM. In previous studies, our results showed that artemisinin (ART) is a potent inhibitor of CaM and PDE-1 activity. In this study, the effects of dihydroartemisinin (DHA) that is a semisynthesized agent from the ART on CaM structure were investigated. The result showed that DHA increased fluorescence emission of CaM in higher amounts compared with the ART. Also, the effect of DHA on CaM-dependent PDE-1 activity was studied. Kinetic analysis of the DHA-CaM interaction showed that this agent competitively inhibited the activation of PDE-1 without affecting Vmax. Km values of PDE-1 in the presence of ART and DHA were 10 and 15 microM, respectively; DHA increased Km value in higher amounts compared with the ART. The Ki constants for ART and DHA were 10 microM and 7.3 microM, respectively. As a conclusion, CaM and CaM-dependent PDE-1 were inhibited by DHA more than ART. The data indicated that DHA could stimulate the delayed type hypersensitivity (DTH) against sheep blood cells in Balb/c mice and reduced the tumor growth in vivo against invasive ductal carcinoma in Balb/c mice.

Rolipram attenuates MK-801-induced deficits in latent inhibition

Latent inhibition is used to examine attention and study cognitive deficits associated with schizophrenia. Research using MK-801, an N-methyl-D-aspartate (NMDA) open channel blocker, implicates glutamate receptors in acquisition of latent inhibition of cued fear conditioning. Evidence suggests an important relationship between NMDA-induced increases in cyclic adenosine monophosphate (cAMP) and learning and memory. The authors examine whether amplification of the cAMP signaling pathway by rolipram, a selective Type 4 cAMP phosphodiesterase inhibitor, reverses MK-801-induced impairments in latent inhibition. One day before training, mice were injected with MK-801, rolipram, MK-801 and rolipram, or vehicle and received 20 preexposures or no preexposures to an auditory conditioned stimulus (CS). Training consisted of 2 CS-footshock unconditioned stimulus pairings. Rolipram attenuated the disruptive effect of MK-801 on latent inhibition, which suggests a role for the cAMP signaling pathway in the task and implicates phosphodiesterase inhibition as a target for treating cognitive impairments associated with schizophrenia.

The type IV-specific phosphodiesterase inhibitor rolipram and its effect on hippocampal long-term potentiation and synaptic tagging

We investigated the effects of rolipram, a selective cAMP phosphodiesterase (PDE) inhibitor, on late plastic events during functional CA1 plasticity in vitro in rat hippocampal slices. We present data showing that an early form of long-term potentiation (LTP) (early-LTP) that normally decays within 2-3 hr can be converted to a lasting LTP (late-LTP) if rolipram is applied during tetanization. This rolipram-reinforced LTP (RLTP) was NMDA receptor and protein synthesis dependent. cAMP formation in region CA1 during late-LTP requires dopaminergic receptor activity (Frey et al., 1989, 1990). Thus, we studied whether RLTP was influenced by inhibitors of the D(1)/D(5) receptor. Application of the specific D(1)/D(5) antagonist SCH23390 (0.1 microm) did not prevent RLTP, suggesting that the phosphodiesterase inhibitor acts downstream of the D(1)/D(5) receptors. We also studied whether rolipram can interact with processes of synaptic tagging, because RLTP was also dependent on protein synthesis, similar to late-LTP. Inhibition of PDE and subsequent induction of RLTP in one synaptic population were able to transform early-LTP into late-LTP in a second, independent synaptic population of the same neurons. This supports our hypothesis that cAMP-dependent processes are directly involved in the synthesis of plasticity-related proteins.

Therapeutic efficacy of milrinone in the management of enterovirus 71-induced pulmonary edema

Hand, foot, and mouth disease and herpangina are the major clinical manifestations of enterovirus 71 (EV71) infections. Brain-stem encephalitis and pulmonary edema are severe complications that can lead to death. This study was designed to evaluate the potential therapeutic effect of milrinone, a phosphodiesterase (PDE) inhibitor, in the treatment of patients with EV71-induced pulmonary edema. We conducted a historically controlled trial of 24 children with severe EV71-induced pulmonary edema from April 1998-June 2003 in southern Taiwan. Patients were divided into groups treated before and after the introduction of milrinone therapy. Etiological diagnosis was established by viral cultures and confirmed by specific immunofluorescence and neutralization tests. All 24 patients were below 5 years of age. The mortality was lower in the milrinone-treated vs. nontreated group (36.4% vs. 92.3%, P=0.005). Sympathetic tachycardia was decreased in patients treated with milrinone compared to controls (144 +/- 17/min vs. 206 +/- 26/min, P=0.004). A marked decrease in IL-13 (77 +/- 9 pg/ml vs. 162 +/- 88 pg/ml, P=0.001) was observed in milrinone-treated patients compared to controls. There was a significant reduction in white blood cell (10,838 +/- 4,537/mm3 vs. 19,475 +/- 7,798/mm3, P=0.009) and platelet (257 +/- 45 x 10(3)/mm3 vs. 400 +/- 87 x 10(3)/mm3, P=0.001) counts in milrinone-treated patients compared to controls. These results were associated with improvement in sympathetic regulation and decrease in IL-13 production. Milrinone therapy may provide a useful therapeutic approach for this highly lethal disorder.

Presence of cyclic nucleotide phosphodiesterases PDE1A, existing as a stable complex with calmodulin, and PDE3A in human spermatozoa

Mammalian sperm motility, capacitation, and the acrosome reaction are regulated by signal transduction systems involving cAMP as a second messenger. Levels of cAMP are controlled by two key enzymes, adenylyl cyclase and phosphodiesterases (PDEs), the latter being involved in cAMP degradation. Calmodulin-dependent PDE (PDE1) and cAMP-specific PDE (PDE4) activities were previously identified in spermatozoa via the use of specific inhibitors. Here we report that human sperm PDEs are associated with the plasma membrane (50%-60%) as well as with the particulate fraction (30%-50%) and have more affinity for cAMP than cGMP. Immunocytochemical data indicated that PDE1A, a variant of PDE1, is localized on the equatorial segment of the sperm head as well as on the mid and principal pieces of the flagellum, and that PDE3A is found on the postacrosomal segment of the sperm head. Immunoblotting confirmed the presence of PDE1A and PDE3A isoforms in spermatozoa. Milrinone, a PDE3 inhibitor, increased intracellular levels of cAMP by about 15% but did not affect sperm functions, possibly because PDE3 represents only a small proportion of the sperm total PDE activity (10% and 25% in Triton X-100 soluble and particulate fractions, respectively). PDE1A activity in whole sperm extract or after partial purification by anion-exchange chromatography was not stimulated by calcium + calmodulin. Results obtained with electrophoresis in native conditions indicated that calmodulin is tightly bound to PDE1A. Incubation with EGTA + EDTA, trifluoperazine, or urea did not dissociate the PDE1A-calmodulin complex. These results suggest that PDE1A is permanently activated in human spermatozoa.

Cross-regulation of intracellular cGMP and cAMP in cultured human corpus cavernosum smooth muscle cells

The goal of this study was to assess the potential cross-regulation of cyclic nucleotides in human corpus cavernosum (HCC). Incubation of primary cultures of HCC smooth muscle cells with either the NO donor sodium nitroprusside (SNP, 10 microM) or the phosphodiesterase type 5 (PDE 5) inhibitor sildenafil (50 nM) produced little or no changes in the intracellular cGMP levels. Incubation with both SNP and sildenafil produced marked increases in cGMP. Interestingly, incubation of cells with 10 microM of forskolin or PGE(1) produced significant enhancement of cGMP accumulation. These increases were not further enhanced by the addition of SNP and sildenafil. Kinetic analyses of cGMP hydrolysis by PDE 5 showed that high concentrations of cAMP reversibly inhibited the enzyme with a K(i) of 258 +/- 54 microM. The increase in cGMP levels in response to cAMP generating agents is not due to assay artifact since cAMP did not cross-react with cGMP antibody. Our data suggest that cAMP up-regulates intracellular levels of cGMP, in part, by inhibition of PDE 5. We also noted that cGMP down-regulates cAMP synthesis via a mechanism requiring G-protein coupling of adenylyl cyclase. These observations may have important implications in the utility of pharmacotherapeutic agents targeting cyclic nucleotide metabolism for the treatment of erectile dysfunction.

Additive effects of inhaled nitric oxide and intravenous milrinone in experimental pulmonary hypertension

OBJECTIVE

To determine whether inhaled nitric oxide (IN0) and intravenous milrinone have additive pulmonary vasodilator effects in a rat model of pulmonary hypertension.

DESIGN

Prospective, experimental study.

SETTING

Animal laboratory of a university medical center.

SUBJECTS

Male New Zealand White rabbits.

INTERVENTIONS

Anesthetized rabbits were mechanically ventilated and instrumented for measurement of systemic mean arterial pressure (MAP), pulmonary artery pressure (PAP), left atrial pressure, and cardiac output (CO). After baseline measurements, the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (30 mg/kg iv) was administered. Pulmonary hypertension was produced by the continuous infusion of U46619, a thromboxane A2 mimetic. INO (40 ppm) was added to the inspired gas, and hemodynamic measurements were obtained before and after INO. Milrinone was administered sequentially as a 30-mg/kg bolus followed by a 3-microg/kg/min infusion, a 100-mg/kg bolus followed by a 10-microg/kg/min infusion, and a 300-mg/kg bolus followed by a 30-microg/kg/min infusion (M3). Hemodynamic measurements were obtained with and without INO at each dose of milrinone.

MEASUREMENTS AND MAIN RESULTS

During U46619-induced pulmonary hypertension, INO decreased PAP and pulmonary vascular resistance (PVR) but did not affect MAP, systemic vascular resistance (SVR), or CO. Milrinone dose dependently decreased PAP, PVR, MAP, and SVR and increased CO. At each dose of milrinone, INO further decreased PVR but not SVR. M3 decreased PVR 49%, and the addition of INO decreased PVR an additional 19% so that PAP and PVR decreased to baseline values.

CONCLUSIONS

Milrinone and INO both decrease pulmonary hypertension individually, and the combination produces additive effects. Combination therapy may produce potent and selective pulmonary vasodilation during the treatment of pulmonary hypertension.

Comparison of phosphodiesterase isozymes in rodent parotid glands

We investigated phosphodiesterase (PDE) isozymes, which hydrolyze cAMP, in rodent parotid glands (mouse, hamster and guinea pig) in order to clarify the effects of cGMP and Ca/calmodulin on the regulation of cellular cAMP and compared them with those of the rat. More than 80% of the activities were in the supernatant fractions except for the hamster. The isozymes were fractionated using Mono Q ion-exchange column. The mouse parotid PDEs consisted of PDE1 (Ca/calmodulin-dependent), PDE2 (cGMP-stimulated), PDE3 (cGMP-inhibited) and PDE4 (cAMP-specific) similar to those of the rat. PDE3 was not detected in the hamster, and PDE4 was not detected in the guinea pig. PDE activities in the supernatant of the mouse and the hamster were stimulated by cGMP, and that of the guinea pig was stimulated by Ca/calmodulin. These results suggest that various PDE isozymes are present in the parotid gland of several species of order Rodentia. There seems to be differences among the species with regard to the PDE isozymes.

Identification of inhibitor specificity determinants in a mammalian phosphodiesterase

Mammalian phosphodiesterase types 3 and 4 (PDE3 and PDE4) hydrolyze cAMP and are essential for the regulation of this intracellular second messenger in many cell types. Whereas these enzymes share structural and biochemical similarities, each can be distinguished by its sensitivity to isozyme-specific inhibitors. By using a series of chimeric enzymes, we have localized the region of PDE4 that confers sensitivity to selective inhibitors. This inhibitor specificity domain lies within a short sequence at the carboxyl terminus of the catalytic domain of the protein, consistent with the competitive nature of inhibition by these compounds. Surprisingly, the identified region also includes some of the most highly conserved residues among PDE isoforms. A yeast-based expression system was used for the isolation and characterization of mutations within this area that confer resistance to the PDE4-specific inhibitor rolipram. Analysis of these mutants indicated that both conserved and unique residues are required for isoform-specific inhibitor sensitivity. In some cases, combined point mutations contribute synergistically to the reduction of sensitivity (suppression of IC50). We also report that several mutations display differential sensitivity changes with respect to distinct structural classes of inhibitors.

Rolipram, a type IV-specific phosphodiesterase inhibitor, facilitates the establishment of long-lasting long-term potentiation and improves memory

In an attempt to improve behavioral memory, we devised a strategy to amplify the signal-to-noise ratio of the cAMP pathway, which plays a central role in hippocampal synaptic plasticity and behavioral memory. Multiple high-frequency trains of electrical stimulation induce long-lasting long-term potentiation, a form of synaptic strengthening in hippocampus that is greater in both magnitude and persistence than the short-lasting long-term potentiation generated by a single tetanic train. Studies using pharmacological inhibitors and genetic manipulations have shown that this difference in response depends on the activity of cAMP-dependent protein kinase A. Genetic studies have also indicated that protein kinase A and one of its target transcription factors, cAMP response element binding protein, are important in memory in vivo. These findings suggested that amplification of signals through the cAMP pathway might lower the threshold for generating long-lasting long-term potentiation and increase behavioral memory. We therefore examined the biochemical, physiological, and behavioral effects in mice of partial inhibition of a hippocampal cAMP phosphodiesterase. Concentrations of a type IV-specific phosphodiesterase inhibitor, rolipram, which had no significant effect on basal cAMP concentration, increased the cAMP response of hippocampal slices to stimulation with forskolin and induced persistent long-term potentiation in CA1 after a single tetanic train. In both young and aged mice, rolipram treatment before training increased long- but not short-term retention in freezing to context, a hippocampus-dependent memory task.

Chronic pulmonary hypertension increases fetal lung cGMP phosphodiesterase activity

An experimental ovine fetal model for perinatal pulmonary hypertension of the neonate (PPHN) was characterized by altered pulmonary vasoreactivity and structure. Because past studies had suggested impaired nitric oxide-cGMP cascade in this experimental model, we hypothesized that elevated phosphodiesterase (PDE) activity may contribute to altered vascular reactivity and structure in experimental PPHN. Therefore, we studied the effects of the PDE inhibitors zaprinast and dipyridamole on fetal pulmonary vascular resistance and PDE5 activity, protein, mRNA, and localization in normal and pulmonary hypertensive fetal lambs. Infusion of dipyridamole and zaprinast lowered pulmonary vascular resistance by 55 and 35%, respectively, in hypertensive animals. In comparison with control animals, lung cGMP PDE activity was elevated in hypertensive fetal lambs (150%). Increased PDE5 activity was not associated with either an increased PDE5 protein or mRNA level. Immunocytochemistry demonstrated that PDE5 was localized to vascular smooth muscle. We concluded that PDE5 activity was increased in experimental PPHN, possibly by posttranslational phosphorylation. We speculated that these increases in cGMP PDE activity contributed to altered pulmonary vasoreactivity in experimental perinatal pulmonary hypertension.

Chemotherapeutic potential of phosphodiesterase inhibitors

The application of molecular cloning has revealed the phenomenal diversity and complexity of the phosphodiesterase isoenzyme family. Thus, more than 30 human phosphodiesterases are now known; all are apparently necessary for the seemingly simple task of hydrolysing the 3'-ester bond of either cyclic adenosine monophosphate or cyclic guanosine monophosphate. The availability of phosphodiesterase isoenzymes as pure recombinant proteins has greatly facilitated the identification of potent, selective inhibitors. The potential of these inhibitors to therapeutically exploit the molecular diversity of the phosphodiesterases has progressed significantly. A number of drugs are in clinical trials for asthma, and Viagra has become the first selective phosphodiesterase inhibitor to be approved by the US Food and Drug Administration.

The adrenomedullary venous vasculature as a target for endothelins: comparison of the porcine and bovine central adrenomedullary veins

The functional properties of the isolated porcine and bovine central adrenomedullary veins were compared, with emphasis on the active tension responses to high K+, endothelin-1 (ET-1) and neuropeptide Y (NPY). In the porcine vein, the contraction evoked by ET-1 was 4--5-fold higher than with high K+, as in the bovine vein. The potencies for ET-1 were similar in ring and strip preparations of the porcine vein, with EC50 values 5--7-fold higher than in the bovine vein. In preparations previously exposed to ET-1 the contractions evoked by high K+ and NPY were potentiated and facilitated, respectively,. However, only in the porcine vein was the ET-1 contraction sustained. This contraction was effectively relaxed by milrinone, indicating a role for cGMP inhibited cyclic nucleotide phosphodiesterase in the sustained contraction. Caffeine and forskolin were also effective relaxants of contractions evoked by ET-1 in both veins, suggesting relaxation by elevated levels of cAMP. The K(+)-contracted porcine, but not bovine, vein was relaxed by acetylcholine (ACh) and vasointestinal polypeptide in a concentration-dependent manner, indicating species differences with respect to signal transduction leading to increases in cyclic nucleotides. In conclusion, these results demonstrate that ET-1 is the main constrictor of the porcine central adrenomedullary vein, with significant species differences in mode of contraction and relaxation. These findings suggest roles for the endogeneously released ET-1 and NPY in regulation of venous contractility within the adrenal gland of mammals.

Positive functional effects of milrinone and methylene blue are not additive in control and hypertrophic canine hearts

This study was designed to test whether increased inotropy caused by raising intracellular cAMP would add to the positive inotropy caused by reducing cGMP and whether this relationship was affected by experimental hypertrophy. We used open chest anesthetized dogs with left ventricular hypertrophy (LVH) induced by valvular aortic stenosis and age matched controls (CON). Hearts were instrumented to measure local segment shortening, force, and regional work. Milrinone (MIL), a selective cyclic AMP-phosphodiesterase inhibitor, and methylene blue (MB), a guanylate cyclase inhibitor, were used to alter cAMP and cGMP levels. Ten CON and 11 LVH animals were randomly assigned to receive first either MIL (1 microg/kg/min) or MB (2 mg/kg/min) intracoronary (i.c.) infusion. After 10 min, simultaneous i.c. infusion of the other agent was begun. MIL increased regional minute work (g x mm/min) in both CON (1311 +/- 207 to 2072 +/- 285) and LVH (1052 +/- 136 to 1371 +/- 351) hearts. MB did not increase work significantly, but did increase contractile force. MIL + MB increased work from baseline; however, the combination did not increase work more than either agent alone (1961 +/- 510 CON; 1390 +/- 285 LVH). Myocardial cAMP levels (pmol/g) were significantly increased by MIL in both CON (329 +/- 53 to 437 +/- 13) and LVH hearts (351 +/- 67 to 538 +/- 32), and the addition of MB further raised cAMP (879 +/- 115 CON; 741 +/- 96 LVH). MB resulted in decreased myocardial cGMP (pmol/g) (3.20 +/- 0.61 to 2.16 +/- 0.92 CON; 5.21 +/- 1.15 to 2.46 +/- 0.56 LVH), while MIL increased cGMP (3.20 +/- 0.61 to 6.24 +/- 1.79 CON; 5.21 +/- 1.15 to 6.53 +/- 0.41 LVH). Both MIL and MB caused increases in O2 consumption, with MIL + MB together increasing O2 consumption further. The current findings demonstrate a potentiation of cAMP production in the presence of MIL + MB above either agent alone, but this did not lead to potentiation of positive functional effects. High levels of cGMP caused by milrinone may have limited the positive functional effects of cAMP.

Correlations of PDE-4 inhibition between enzymes of smooth muscle and inflammatory cell sources

The sensitivities of PDE-4 enzymes from smooth muscle and inflammatory cell sources from different species to a range of structurally diverse compounds were compared. All inflammatory cell PDE-4 sources displayed good crosscorrelations in their sensitivity to inhibition by these compounds. Similarly, PDE-4 enzymes from smooth muscle sources were well-correlated; however, there was no crosscorrelation between PDE-4 from smooth muscle sources and those of inflammatory cell sources, possibly reflecting differences in subcellular location of enzymes as well as subtype expression. The present study concludes that PDE-4 preparations from smooth muscle sources as well as those from inflammatory cell sources may be used to model the potential smooth muscle cell relaxing properties and anti-inflammatory properties of a compound in relation to human asthma.

Identification, quantitation, and cellular localization of PDE1 calmodulin-stimulated cyclic nucleotide phosphodiesterases

The calmodulin-stimulated cyclic nucleotide phosphodiesterases (PDE1s) constitute a large gene family and are found in a wide variety of tissues and cells. Because of the functional diversity of PDE1 genes and the observation that these isozymes often make up a major component of the total cyclic nucleotide hydrolytic activity in certain cell types, PDE1s are of growing interest as targets for therapeutic intervention. Here we describe a series of methodologies to identify, quantitate, and determine the cellular expression of PDE1 isozymes. We describe first the resolution of different PDEs using high-performance anion-exchange chromatography and then a Western blotting methodology for identifying or authenticating PDE1 activities. Next we present an immunoprecipitation method that can be used for quantitating specific PDE1 isoforms and describe the use of RNase protection analysis for further identification of PDE1 subtypes. Finally, we provide a simple, immunocytochemical method for determining the cellular expression of PDE1 isozymes. Combined, the above methodologies should allow an investigator to identify, quantitate, and determine the cellular localization of PDE1 isozymes in any tissue with little ambiguity.

Calmodulin-stimulated cyclic nucleotide phosphodiesterase (PDE1C) is induced in human arterial smooth muscle cells of the synthetic, proliferative phenotype

The diversity among cyclic nucleotide phosphodiesterases provides multiple mechanisms for regulation of cAMP and cGMP in the cardiovascular system. Here we report that a calmodulin-stimulated phosphodiesterase (PDE1C) is highly expressed in proliferating human arterial smooth muscle cells (SMCs) in primary culture, but not in the quiescent SMCs of intact human aorta. High levels of PDE1C were found in primary cultures of SMCs derived from explants of human newborn and adult aortas, and in SMCs cultured from severe atherosclerotic lesions. PDE1C was the major cAMP hydrolytic activity in these SMCs. PDE expression patterns in primary SMC cultures from monkey and rat aortas were different from those from human cells. In monkey, high expression of PDE1B was found, whereas PDE1C was not detected. In rat SMCs, PDE1A was the only detectable calmodulin-stimulated PDE. These findings suggest that many of the commonly used animal species may not provide good models for studying the roles of PDEs in proliferation of human SMCs. More importantly, the observation that PDE1C is induced only in proliferating SMCs suggests that it may be both an indicator of proliferation and a possible target for treatment of atherosclerosis or restenosis after angioplasty, conditions in which proliferation of arterial SMCs is negatively modulated by cyclic nucleotides.