The ability of denbufylline to inhibit cyclic nucleotide phosphodiesterase and its affinity for adenosine receptors and the adenosine re-uptake site

Emerging phosphodiesterase inhibitors for treatment of neurodegenerative diseases

Neurodegenerative diseases (NDs) cause progressive loss of neuron structure and ultimately lead to neuronal cell death. Since the available drugs show only limited symptomatic relief, NDs are currently considered as incurable. This review will illustrate the principal roles of the signaling systems of cyclic adenosine and guanosine 3',5'-monophosphates (cAMP and cGMP) in the neuronal functions, and summarize expression/activity changes of the associated enzymes in the ND patients, including cyclases, protein kinases, and phosphodiesterases (PDEs). As the sole enzymes hydrolyzing cAMP and cGMP, PDEs are logical targets for modification of neurodegeneration. We will focus on PDE inhibitors and their potentials as disease-modifying therapeutics for the treatment of Alzheimer's disease, Parkinson's disease, and Huntington's disease. For the overlapped but distinct contributions of cAMP and cGMP to NDs, we hypothesize that dual PDE inhibitors, which simultaneously regulate both cAMP and cGMP signaling pathways, may have complementary and synergistic effects on modifying neurodegeneration and thus represent a new direction on the discovery of ND drugs.

The Complexity and Multiplicity of the Specific cAMP Phosphodiesterase Family: PDE4, Open New Adapted Therapeutic Approaches

Cyclic nucleotides (cAMP, cGMP) play a major role in normal and pathologic signaling. Beyond receptors, cyclic nucleotide phosphodiesterases; (PDEs) rapidly convert the cyclic nucleotide in its respective 5'-nucleotide to control intracellular cAMP and/or cGMP levels to maintain a normal physiological state. However, in many pathologies, dysregulations of various PDEs (PDE1-PDE11) contribute mainly to organs and tissue failures related to uncontrolled phosphorylation cascade. Among these, PDE4 represents the greatest family, since it is constituted by 4 genes with multiple variants differently distributed at tissue, cellular and subcellular levels, allowing different fine-tuned regulations. Since the 1980s, pharmaceutical companies have developed PDE4 inhibitors (PDE4-I) to overcome cardiovascular diseases. Since, they have encountered many undesired problems, (emesis), they focused their research on other PDEs. Today, increases in the knowledge of complex PDE4 regulations in various tissues and pathologies, and the evolution in drug design, resulted in a renewal of PDE4-I development. The present review describes the recent PDE4-I development targeting cardiovascular diseases, obesity, diabetes, ulcerative colitis, and Crohn's disease, malignancies, fatty liver disease, osteoporosis, depression, as well as COVID-19. Today, the direct therapeutic approach of PDE4 is extended by developing allosteric inhibitors and protein/protein interactions allowing to act on the PDE interactome.

Cu-Catalyzed C–H Activation Reaction: One-Pot Direct Synthesis of Xanthine and Uric Acid Derivatives from 5-Bromouracil

A one-pot direct synthesis of xanthine and uric acid derivates is reported. This simple yet efficient methodology illustrates concurrent formation of two C–N bonds using CuBr2 as catalyst and one of those C–N bonds is formed by uracil C6–H bond activation.

Pharmacological potential of methylxanthines: Retrospective analysis and future expectations

Methylated xanthines (methylxanthines) are available from a significant number of different botanical species. They are ordinarily included in daily diet, in many extremely common beverages and foods. Caffeine, theophylline and theobromine are the main methylxanthines available from natural sources. The supposedly relatively low toxicity of methylxanthines, combined with the many beneficial effects that have been attributed to these compounds through time, generated a justified attention and a very prolific ground for dedicated scientific reports. Methylxanthines have been widely used as therapeutical tools, in an intriguing range of medicinal scopes. In fact, methylxanthines have been/were medically used as Central Nervous System stimulants, bronchodilators, coronary dilators, diuretics and anti-cancer adjuvant treatments. Other than these applications, methylxanthines have also been hinted to hold other beneficial health effects, namely regarding neurodegenerative diseases, cardioprotection, diabetes and fertility. However, it seems now consensual that toxicity concerns related to methylxanthine consumption and/or therapeutic use should not be dismissed. Taking all the knowledge and expectations on the potential of methylxanthines into account, we propose a systematic look at the past and future of methylxanthine pharmacologic applications, discussing all the promise and anticipating possible constraints. Anyways, methylxanthines will still substantiate considerable meaningful research and discussion for years to come.

Pharmacological Profile of GPD-1116, an Inhibitor of Phosphodiesterase 4

We have previously reported that GPD-1116, an inhibitor of phosphodiesterase (PDE) 4, exhibits anti-inflammatory effects in a model of cigarette smoke-induced emphysema in senescence-accelerated P1 mice. In the present study, we further characterized the pharmacological profile of GPD-1116 in several experiments in vitro and in vivo. GPD-1116 and its metabolite GPD-1133 predominantly inhibited not only human PDE4, but also human PDE1 in vitro. Moreover, GPD-1116 was effective in several disease models in animals, including acute lung injury, chronic obstructive pulmonary disease (COPD), asthma and pulmonary hypertension; the effective doses of GPD-1116 were estimated to be 0.3-2 mg/kg in these models. With regard to undesirable effects known as class effects of PDE4 inhibitors, GPD-1116 showed suppression of gastric emptying in rats and induction of emesis in dogs, but showed no such suppression of rectal temperature in rats, and these side effects of GPD-1116 seemed to be less potent than those of roflumilast. These results suggested that GPD-1116 could be a promising therapeutic agent for the treatment of inflammatory pulmonary diseases. Furthermore, the inhibitory effects of GPD-1116 for PDE1 might be associated with its excellent pharmacological profile. However, the mechanisms through which PDE1 inhibition contributes to these effects should be determined in future studies.

Structure-Bioactivity Relationships of Methylxanthines: Trying to Make Sense of All the Promises and the Drawbacks

Methylxanthines are a group of phytochemicals derived from the purine base xanthine and obtained from plant secondary metabolism. They are unobtrusively included in daily diet in common products as coffee, tea, energetic drinks, or chocolate. Caffeine is by far the most studied methylxanthine either in animal or epidemiologic studies. Theophylline and theobromine are other relevant methylxanthines also commonly available in the aforementioned sources. There are many disseminated myths about methylxanthines but there is increased scientific knowledge to discuss all the controversy and promise shown by these intriguing phytochemicals. In fact, many beneficial physiologic outcomes have been suggested for methylxanthines in areas as important and diverse as neurodegenerative and respiratory diseases, diabetes or cancer. However, there have always been toxicity concerns with methylxanthine (over)consumption and pharmacologic applications. Herein, we explore the structure-bioactivity relationships to bring light those enumerated effects. The potential shown by methylxanthines in such a wide range of conditions should substantiate many other scientific endeavors that may highlight their adequacy as adjuvant therapy agents and may contribute to the advent of functional foods. Newly designed targeted molecules based on methylxanthine structure may originate more specific and effective outcomes.

Guidelines for translational research in heart failure

Heart failure (HF) remains a major cause of death and hospitalization worldwide. Despite medical advances, the prognosis of HF remains poor and new therapeutic approaches are urgently needed. The development of new therapies for HF is hindered by inappropriate or incomplete preclinical studies. In these guidelines, we present a number of recommendations to enhance similarity between HF animal models and the human condition in order to reduce the chances of failure in subsequent clinical trials. We propose different approaches to address safety as well as efficacy of new therapeutic products. We also propose that good practice rules are followed from the outset so that the chances of eventual approval by regulatory agencies increase. We hope that these guidelines will help improve the translation of results from animal models to humans and thereby contribute to more successful clinical trials and development of new therapies for HF.

Ceric ammonium nitrate (CAN): an efficient and eco-friendly catalyst for the one-pot synthesis of alkyl/aryl/heteroaryl-substituted bis(6-aminouracil-5-yl)methanes at room temperature

Ceric ammonium nitrate (CAN)-catalyzed one-pot synthesis of alkyl/aryl/heteroaryl-substituted bis(6-aminouracil-5-yl)methane scaffolds (3a–3u) has been developed via a pseudo three-component reaction in aqueous ethanol at room temperature.

Phosphodiesterase inhibitors: history of pharmacology

The first pharmacological investigations of phosphodiesterase (PDE) inhibitors were developed with the clinical efficacies of drugs isolated from coffee, cacao and tea but only later their relevant ingredients were identified as xanthines that act as PDE. With its diuretic, inotropic and bronchodilating clinical efficacy, use of theophylline anticipated the clinical goals, which were later approached with the first-generation of weakly selective PDE inhibitors in the period from 1980 to 1990. Pharmacological and clinical research with these early compounds provided a vast pool of information regarding desired and adverse actions - although most of these new drugs had to be discontinued due to severe adverse effects. The pharmacological models for cardiac, vascular and respiratory indications were analysed for their PDE isoenzyme profiles, and when biochemical and molecular biological approaches expanded our knowledge of the PDE superfamily, the purified isoenzymes that were now available opened the door for more systematic studies of inhibitors and for generation of highly selective isoenzyme-specific drugs. The development of simple screening models and clinically relevant indication models reflecting the growing knowledge about pathomechanisms of disease are summarised here for today's successful application of highly selective PDE3, PDE4 and PDE5 inhibitors. The interplay of serendipitous discoveries, the establishment of intelligent pharmacological models and the knowledge gain by research results with new substances is reviewed. The broad efficacies of new substances in vitro, the enormous biodiversity of the PDE isoenzyme family and the sophisticated biochemical pharmacology enabled Viagra to be the first success story in the field of PDE inhibitor drug development, but probably more success stories will follow.

ASP3258, an orally active potent phosphodiesterase 4 inhibitor with low emetic activity

We investigated the pharmacology of a novel phosphodiesterase (PDE) 4 inhibitor, ASP3258 (3-[4-(3-chlorophenyl)-1-ethyl-7-methyl-2-oxo-1,2-dihydro-1,8-naphthyridin-3-yl] propanoic acid), comparing its potency with that of the most advanced PDE4 inhibitors, roflumilast and cilomilast. PDE4 inhibition by ASP3258 (IC(50)=0.28nM) was as potent as that achieved with roflumilast. ASP3258 inhibited lipopolysaccharide-induced tumor necrosis factor (TNF)-α production in rat whole blood cells (IC(50)=8.8 nM) and rat alveolar macrophages (IC(50)=2.6 nM). Orally administered ASP3258, roflumilast, and cilomilast dose-dependently inhibited production of interleukin-4, TNF-α, and cysteinyl leukotrienes, as well as leukocyte infiltration in bronchoalveolar lavage fluid from the airways of ovalbumin-sensitized Brown Norway rats, and these compounds showed almost complete inhibition at doses of 3, 3, and 30 mg/kg, respectively. PDE4 inhibitors induce emesis by mimicking the pharmacological action of α(2)-adrenoceptor antagonist. However, orally administered roflumilast (3mg/kg) and cilomilast (10mg/kg), but not ASP3258 (3mg/kg), inhibited α(2)-adrenoceptor agonist-induced anesthesia in rats and induced emesis in ferrets. Although ASP3258 (3mg/kg) inhibited airway inflammation completely, it had no emetic activity. As such, this compound may be useful in treating airway inflammatory diseases such as asthma and COPD.

Changes in phosphodiesterase activity in the developing rat submandibular gland

Developmental changes (from 2 to 26 weeks) in phosphodiesterase (PDE) activity in the rat submandibular gland were investigated. Major activities for both cAMP- and cGMP-PDE were present in the 100000 x g supernatant fractions (70-90% of total activities), but not in the pellet fractions, during development. The effects of stimulators (Ca(2+)/calmodulin and cGMP) and inhibitors (cGMP, cilostamide, rolipram and zaprinast) were investigated in the supernatant fractions. During development, PDE4 (cAMP-specific PDE) was a major PDE, indicating that the majority of cAMP is hydrolysed by PDE4. In the young rat, PDE1 hydrolysed cGMP three-fold more than the control, and PDE2 (cGMP-stimulated PDE) was present, indicating that the concentration of intracellular cGMP may be enhanced, and cGMP may function in the growth pathway in the submandibular gland. Chromatograms eluted on a Mono Q HR5/5 ion-exchange column supported the results of the inhibition studies: PDE1, PDE2, PDE3, PDE4 and PDE5 were present in the young submandibular gland, and PDE1, PDE3, PDE4 and PDE5 in the adult gland. Expression of PDE5 was detected by inhibition studies, reverse transcriptase-polymerase chain reaction and Western blotting in the submandibular gland.

Synthesis and biological evaluation of novel pyrazoles and indazoles as activators of the nitric oxide receptor, soluble guanylate cyclase

Database searching and compound screening identified 1-benzyl-3-(3-dimethylaminopropyloxy)indazole (benzydamine, 3) as a potent activator of the nitric oxide receptor, soluble guanylate cyclase. A comprehensive structure-activity relationship study surrounding 3 clearly showed that the indazole C-3 dimethylaminopropyloxy substituent was critical for enzyme activity. However replacement of the indazole ring of 3 by appropriately substituted pyrazoles maintained enzyme activity. Compounds were evaluated for inhibition of platelet aggregation and showed a general lipophilicity requirement. Aryl-substituted pyrazoles 32, 34, and 43 demonstrated potent activation of soluble guanylate cyclase and potent inhibition of platelet aggregation. Pharmacokinetic studies in rats showed that compound 32 exhibits modest oral bioavailability (12%). Furthermore 32 has an excellent selectivity profile notably showing no significant inhibition of phosphodiesterases or nitric oxide synthases.

Role of cGMP-inhibited phosphodiesterase and sarcoplasmic calcium in mediating the increase in basal heart rate with nitric oxide donors

Nitric oxide (NO) donors increase heart rate (HR) through a guanylyl cyclase-dependent stimulation of the pacemaker current I(f), without affecting basal I(Ca-L). The activity of I(f)is known to be enhanced by cyclic nucleotides and by an increase in cytosolic Ca(2+). We examined the role of cGMP-dependent signaling pathways and intracellular Ca(2+)stores in mediating the positive chronotropic effect of NO donors. In isolated guinea pig atria, the increase in HR in response to 1-100 micromol/l 3-morpholino-sydnonimine (SIN-1; with superoxide dismutase, n=6) or diethylamine-NO (DEA-NO, n=8) was significantly attenuated by blockers of the cGMP-inhibited phosphodiesterase (PDE3; trequinsin, milrinone or Ro-13-6438, n=22). In addition, the rate response to DEA-NO or sodium nitroprusside (SNP) was significantly reduced following inhibition of PKA (KT5720 or H-89, n=15) but not PKG (KT5728 or Rp-8-pCPT-cGMPs, n=16). Suppression of sarcoplasmic (SR) Ca(2+)release by pretreatment of isolated atria with ryanodine or cyclopiazonic acid (2 micromol/l and 60 micromol/l, n=16) significantly reduced the chronotropic response to 1-100 micromol/l SIN-1 or DEA-NO. Moreover, in isolated guinea pig sinoatrial node cells 5 micromol/l SNP significantly increased diastolic and peak Ca(2+)fluorescence (+13+/-1% and +28+/-1%, n=6, P<0.05). Our findings are consistent with a functionally significant role of cAMP/PKA signaling (via cGMP inhibition of PDE3) and SR Ca(2+)in mediating the positive chronotropic effect of NO donors.

Alkylxanthines as research tools

(1) The methylxanthine caffeine has many pharmacological effects, most of which can be linked to blockade of adenosine receptors, inhibition of phosphodiesterases, and augmentation of calcium-dependent release of calcium from intracellular stores. (2) A variety of xanthines have been developed as potent and/or selective antagonists for adenosine receptors. (3) Several xanthines have been developed that are more potent and more selective inhibitors of cyclic nucleotide phosphodiesterase than caffeine or theophylline. (4) Caffeine remains the xanthine of choice for activation of intracellular calcium-sensitive calcium release channels although millimolar concentrations are required, which can have effects on other aspects of calcium regulation.

Phosphodiesterase 4 inhibitors, structurally unrelated to rolipram, as promising agents for the treatment of asthma and other pathologies

An increase of cyclic adenosine and guanosine monophosphate (cAMP and cGMP) level can be achieved by inhibition of phosphodiesterases (PDEs), which are the enzymes responsible for the conversion of these second messengers into the corresponding 5-monophosphate inactive counterparts. The high heterogeneity in PDE families and in their tissue distribution, as well as their different functional role, make these enzymes very attractive targets for medicinal chemists. The PDE 4 family is particularly abundant in immunocompetent cells, where an increase of cAMP leads to the inhibition of the synthesis and release of pro-inflammatory mediators, cytokines and active oxygen species. Moreover PDE 4 inhibitors are able to reduce bronchial smooth muscle tone in vitro and show bronchodilatory effects in vivo. Thus, the current therapy for asthma, which is based on a combination of beta(2) agonists and corticosteroids, could be replaced by treatment with PDE 4 inhibitors. This review mainly covers PDE 4 inhibitors structurally related to xanthines and Nitraquazone, which appear to be very attractive models for the synthesis of novel PDE 4 inhibitors potentially useful for the treatment of asthma, chronic pulmonary obstructive disease and some autoimmune diseases. These compounds could be devoid of the central side-effects (nausea, vomiting, headache) of the archetypal Rolipram, which hampered its development as a drug. The review also highlights the novel structural classes of PDE 4 inhibitors recently reported in the literature.

Novel and selective calcitonin-inducing agents

A series of xanthine sulfonamides is presented as a class of calcitonin (CT) inducers - a potentially new method for treating diseases associated with postmenopausal bone loss such as osteoporosis. We have found that certain di-n-butylxanthine sulfonamides 4 upregulate CT transcription in a CT-luciferase reporter gene assay (CT-luci) and increase the production and release of CT in a CT secretion/RIA assay (CTS). In addition, these compounds do not have potent PDE4 inhibitory activity as do the related xanthine methylene ketones such as denbufyllene (2). One compound in particular (9) shows a transcription activation ratio (TAR) of 2.1 in CT-luci, a CTS increase of 3.6-fold, and a PDE4 (phosphodiesterase type IV) IC(50) = 4.1 microM. In addition, this compound showed a statistically significant 47% trabecular bone protection in ovariectomized-induced osteopenia (OVX) rats as determined by assay when administered for 4 weeks at 30 mg/kg/day, i. p. by quantitative computed tomography (QCT). When administered p.o., compound 9 shows 50% trabecular bone protection when administered for 3 weeks at 50 mg/kg/day, i.p. This compared with salmon CT which shows 62% trabecular bone protection when administered at 50 IU/kg/day for 4 weeks.

Effects of noradrenergic lesions on the development of rolipram-sensitive, low-K(m), cyclic AMP specific phosphodiesterase in rat brain

Rolipram-sensitive, low-K(m)80% loss of norepinephrine in cerebral cortex) without affecting dopaminergic systems. The lesions resulted in temporary reduction of PDE4 activity in cerebral cortex, cerebellum and brainstem. Lesions in the adult rats, on the other hand, did not alter PDE4 activity. Decreased PDE4 activity by neonatal noradrenergic lesions was due to a decrease in the V(max) of cAMP hydrolysis by PDE4, and not a change in the K(m) values. Immunoblot analysis showed that decreased PDE4 activity in cerebellum was associated with reduced expression of PDE4A5, PDE4A1, and several PDE4B variants. No change in the expression of any PDE4 subtype in cerebral cortex was detected with the antibodies used in this study. Neither the permanent loss of noradrenergic innervation in cerebral cortex, nor the permanent noradrenergic hyperinnervation in brainstem was accompanied by any permanent change in PDE4 activity. Decreasing PDE4 activity early after neonatal noradrenergic lesions might be important in maintaining constant concentrations of cAMP, which is critical for the cellular proliferation and differentiation that is active during this period.

Ontogeny of rolipram-sensitive, low-K(m), cyclic AMP-specific phosphodiesterase in rat brain

The postnatal development of rolipram-sensitive, low-K(m), cyclic AMP-specific phosphodiesterase (PDE4) was investigated in discrete regions of rat brain using a PDE4 activity assay and immunoblot analyses with K116, a PDE4 antibody. The Vmax for cyclic AMP hydrolysis by PDE4 was lower at birth when compared to adult levels in cerebral cortex, cerebellum, and neostriatum. K(m) values for cyclic AMP hydrolysis by PDE4, in contrast, did not change throughout the observed period in any brain region tested. The developmental patterns for PDE4 were significantly different among the examined brain regions. PDE4 activity in olfactory bulb and hippocampus also was found to be lower at birth in comparison to adult levels. Immunoblot analyses showed that developmental patterns of PDE4 were significantly different for the various subtypes, and also varied substantially across brain regions. The results suggest that PDE4 might be differentially regulated by different ontogenetic events.

Evidence for the activity of five adenosine-3',5'-monophosphate-degrading phosphodiesterase isozymes in the adult rat neocortex

In the present study, the expression of the activity of adenosine-3',5'-monophosphate-degrading phosphodiesterases (cAMP-PDEs) was analyzed in rat neocortex homogenates. Following separation by anion-exchange chromatography, the isozymes were characterized by their sensitivity to modulators and by their kinetic properties. We identified the activity of five distinct cAMP-PDE isozymes: two calcium/calmodulin-dependent forms (PDE 1), one PDE 2 isozyme stimulated by guanosine-3',5'-monophosphate (cGMP), one cGMP-inhibited form (PDE 3) and a cAMP-specific, rolipram-sensitive form (PDE 4). Our study provides, for the first time, evidence for the existence of PDE 3 enzyme activity in rat neocortex and predicts the expression of at least two isoforms (splice variants) of PDE 1A in this brain area. The existence of different cAMP-degrading phosphodiesterases modulated by different intracellular second messengers (calcium and cGMP) suggests that the activity of neocortical neurons and glia cells is regulated, inter alia, by a 'crosstalk' between calcium-, cGMP- and cAMP-dependent second messenger pathways.

Inhibitory effects of rolipram on partially purified phosphodiesterase 4 from rat brains

Several previous studies have demonstrated that the phosphodiesterase 4 selective inhibitor rolipram affects cellular function at a much lower concentration than the reported Ki value for phosphodiesterase 4 inhibition. In this study, we examined the inhibitory effect of rolipram on rat brain phosphodiesterase 4 to determine the heterogeneity of the enzyme activity. Partial purification of various phosphodiesterases from the rat brain was performed by anion-exchange chromatography. The eluant was pooled into four fractions, two of which manifested cAMP-selective phosphodiesterase activity that was blocked by 10 microM of rolipram, indicating the presence of phosphodiesterase 4 in these fractions. The IC50 of rolipram (racemate) of these two fractions was 492 and 79 nM, respectively. The R-(-)-enantiomer of rolipram inhibited the cAMP-phosphodiesterase activity in the latter fraction 10 times more than did S-(+)-rolipram, and the inhibition of the former fraction was less stereospecific. Dixon plot analysis revealed that the rolipram enantiomers inhibited the cAMP-phosphodiesterase in the latter fraction in a multiphasic manner, with two Ki values, one at the micromolar level and the other at the sub-micromolar level, respectively, for both of the enantiomers. These results suggest that there is a heterogeneity for phosphodiesterase 4 in the rat brain, and some of the phosphodiesterase forms are sensitive to rolipram.

Role of phosphodiesterase 4 isoenzyme in alkaline phosphatase activation by calcitonin in porcine kidney LLC-PK1 cells

To confirm the intracellular signal transduction in regulation of alkaline phosphatase (ALP) activity by calcitonin in kidney tubular cells, effects of several inhibitors of cyclic nucleotide phosphodiesterase (PDE) isoenzymes and cyclic AMP-dependent protein kinase (PKA) on the action of salmon calcitonin in porcine kidney tubular epithelial cells LLC-PK1 were examined. A confluent culture of LLC-PK1 cells was treated with calcitonin and inhibitors in Dulbecco's modified Eagle's medium supplemented with 0.1% bovine serum albumin, and intracellular cyclic AMP content and ALP activity were measured after incubation for 30 min and 48 hr, respectively. Calcitonin and PDE 4 inhibitors increased cyclic AMP level and ALP activity in the cells, and PDE 4 inhibitors synergistically potentiated the effects of calcitonin. Calcitonin induced ALP activation by treatment for the first 1 hr, as well as continuous treatment for 48 hr, while it never increased the enzyme activity just after 1-hr exposure. Rolipram, an inhibitor of PDE 4 isoenzyme, induced ALP activation by itself and in combination with calcitonin by only a long term treatment (48 hr). The activation of ALP by calcitonin and rolipram each alone and in combination was completely abolished by a PKA inhibitor, H-89. These results confirm that calcitonin induces ALP activation through the cyclic AMP-PKA pathway and that PDE 4 isoenzyme is closely associated with the calcitonin-receptor system and plays a major role in hydrolysis of cyclic AMP produced in the kidney tubular cells.

Selective inhibitors of cyclic AMP-specific phosphodiesterase: heterocycle-condensed purines

To reverse the adverse reactions of alkylxanthines and to develop novel inhibitors of cyclic AMP-specific phosphodiesterase (PDE IV), a series of heterocycle-condensed purines were designed and synthesized. Some of these new compounds had similar or more potent and selective inhibitory activity against PDE IV than known PDE IV inhibitors. The tracheal-relaxant activity of these compounds was closely correlated with their PDE IV-inhibitory activity. Moreover, these purine analogues did not have any positive-chronotropic action or adenosine-antagonistic action on isolated heart preparations, which are the particular adverse reactions of alkylxanthines. Among them, 3,4-dipropyl-4,5,7,8-tetrahydro-3H-imidazo[1,2-i]-purin-5-one (1c), which was the most selective and potent PDE IV inhibitor, did not cause emesis in Suncus murinus at a dosage range of 10-100 mg/kg (po), while an imidazole analogue of 1c (4c) and known PDE IV inhibitors such as rolipram and denbufylline caused emesis even at 10 or 30 mg/kg.

Reduction of bone loss by denbufylline, an inhibitor of phosphodiesterase 4

The effects of denbufylline, a xanthine derivative with selective inhibitory activity on the phosphodiesterase (PDE) 4 isoenzyme, on bone loss in Walker 256/S-bearing rats and on mineralized nodule formation and osteoclastlike cell formation in bone marrow culture systems were examined. Serial oral administrations of denbufylline inhibited the decrease in the bone mineral density of femurs from Walker 256/S-bearing rats, without influence on the healthy rats. Denbufylline restored the bone mass and the number of osteoclasts and osteoblasts per trabecular surface in the femur metaphysis. Among PDE inhibitors, only PDE4-selective inhibitors increased the number of mineralized nodules and decreased the number of osteoclastlike cells in the in vitro bone marrow culture systems, and dibutyryl cyclic AMP mimicked these effects in the in vitro systems. These results suggest that the PDE4 isoenzyme may play an important role in bone turnover through cyclic AMP and that its inhibitors are candidates for therapeutic drugs for the bone loss diseases.

Stimulation of the hypothalamo-pituitary-adrenal axis in the rat by three selective type-4 phosphodiesterase inhibitors: in vitro and in vivo studies

1. Previous studies in our laboratory have shown that the synthetic xanthine analogue denbufylline, a selective type 4 phosphodiesterase (PDE-4) inhibitor, is a potent activator of the hypothalamo-pituitary-adrenal (HPA) axis when given orally or intraperitoneally (i.p.) to adult male rats. This paper describes the results of experiments in which well established in vivo and in vitro methods were used to compare the effects of denbufylline on HPA function with those of two other selective PDE-4 inhibitors, rolipram and BRL 61063 (1,3-dicyclopropylmethyl-8-amino-xanthine). For comparison, parallel measurements of the immunoreactive- (ir-) luteinising hormone (LH) were made where appropriate. 2. When injected intraperitoneally, rolipram (40 and 200 micrograms kg-1, P < 0.005), denbufylline (0.07-0.6 microgram kg-1, P < 0.05) and BRL 61063 (30 micrograms kg-1, P < 0.005) each produced marked rises in the serum ir-corticosterone concentrations. However, lower doses of rolipram (1.6 and 8 micrograms kg-1) and BRL 61063 (0.25-6 micrograms kg-1) were without effect (P > 0.05). By contrast, intracerebroventricular (i.c.v.) injection of rolipram (8 ng-1 micrograms kg-1) or denbufylline (50 ng-1 microgram kg-1) failed to influence the serum ir-corticosterone concentration. BRL 61063 (8-120 ng kg-1, i.c.v.) was also ineffective in this regard although at a higher dose (1 microgram kg-1, i.c.v.) it produced a small but significant (P < 0.05) increase in ir-corticosterone release. Denbufylline also increased the serum ir-LH concentration when given peripherally (0.2-0.6 microgram kg-1, i.p., P < 0.05) or centrally (100 ng kg-1, i.c.v., P < 0.05) but rolipram (1.6-200 micrograms kg-1, i.p. or 8 ng-1 microgram kg-1, i.c.v.) and BRL 61063 (0.25-30 micrograms kg-1, i.p. or 1 ng-1 microgram kg-1, i.c.v.) did not (P > 0.05). 3. In vitro rolipram (10 microM, P < 0.01), denbufylline (1 mM, P < 0.001) and BRL 61063 (1 and 10 microM, P < 0.05) stimulated the release of corticotrophin releasing hormone (ir-CRH-41) but lower concentrations of the drugs were without effect as also was BRL 61063 at 100 microM (P > 0.05); the rank order of potency was thus BRL 61063 > rolipram > denbufylline. The adenylyl cyclase activator forskolin (100 microM, P < 0.01) also stimulated the release of ir-CRH-41, producing effects which were additive with those of rolipram and denbufylline but not with those of BRL 61063. The secretory responses to forskolin (100 microM) were accompanied by a highly significant increase in the cyclic AMP content of the hypothalamic tissue (P < 0.005). Rolipram (10 microM) also significantly (P < 0.05) elevated the hypothalamic cyclic AMP but denbufylline (10 mM) and BRL 61063 (10 microM) did not. However, all three PDE-inhibitors potentiated the rise in cyclic AMP induced by forskolin (P < 0.05). None of the drugs tested, alone or in combination, modified the release of arginine vasopressin (ir-AVP) from the hypothalamus. 4. Rolipram (100 microM), denbufylline (100 microM) and BRL 61063 (100 microM) stimulated the release of corticotrophin (ir-ACTH) from pituitary tissue in vitro (P < 0.05) but in lower concentrations they were without significant effect. In addition, rolipram (10 microM, P < 0.05), denbufylline (0.1 microM, P < 0.05) and BRL 61063 (10 microM, P < 0.05) potentiated the significant (P < 0.05) rises in ir-ACTH secretion induced by forskolin (100 microM). Forskolin (100 microM) also produced a highly significant increase (P < 0.01) in the tissue cyclic AMP content which was further potentiated by rolipram (10 microM), denbufylline (10 microM) and BRL 61063 (10 microM) which, alone did not affect the cyclic AMP content of the tissue. 5. Since both denbufylline and BRL 61063 possess significant adenosine A1 receptor blocking activity, further studies examined the potential influence of these receptors on the secretion in vitro of CRH-41, AVP and ACTH. The release of ir-CRH-41 was increased significantly by adenosine deaminase (ADA, 5microml-1, P<0.05) and the A1-receptor antagonist, 1,3-dicyclopropyl-8-cyclopentylxanthine (DPCPX, 0.1-10nM, P<0.05). The responses to ADA were abolished by the A1 receptor agonist N6-cyclo-hexyladenosine (CHA, 100nM, P<0.05) which alone had no significant effect on ir-CRH-41 release. ADA (0.1-10microml-1) and DPCPX (1nM) had weak stimulant and inhibitory effects, respectively, on the release of ir-ACTH from the pituitary gland while CHA (0.1-10nM) was without effect. Ligand binding studies with [3H]-DPCPX as a probe demonstrated the presence of specific high affinity A1 binding sites in the hypothalamus (Kd=0.7nM; Bmax=367+/-32fmolmg-1 protein) and in the hippocampus (Kd=1nM; Bmax=1165 +/-145fmolmg-1 protein). In both tissues binding of the ligand was displaced by CHA (IC50=1nM (hypothalamus) and 2nM (hippocampus)), BRL 61063 (IC50=80nM (hypothalamus) and 100nM (hippocampus)) and denbufylline (IC50=5microM (hypothalamus) and 9microM(hippocampus)) but not by rolipram. 6.The results suggest that rolipram, denblufylline and BRL 61063 stimulate the HPA axis in the rat, acting at the levels of both the hypothalamus and the pituitary gland. Their actions may be explained, at least in part, by inhibition of PDE-4 but additional actions including blockade of hypothalamic adenosine A1 receptors by denbufylline and BRL 61063 cannot be excluded.

Compartmentalization of cAMP signaling in mesangial cells by phosphodiesterase isozymes PDE3 and PDE4. Regulation of superoxidation and mitogenesis

Some major pathobiologic processes in renal mesangial cells, elicited in response to immunoinflammatory stimuli, are modulated via cAMP-protein kinase A (PKA) signaling pathways; namely, generation of reactive oxygen metabolites (ROM) and accelerated proliferation of mesangial cells. We investigated the role of cAMP phosphodiesterase (PDE) isozymes in these regulatory mechanisms. Generation of ROM in cultured rat mesangial cells was inhibited by selective inhibitors of PDE4, rolipram and denbufylline, whereas PDE3 inhibitors, cilostamide and lixazinone, had no effect. Conversely, cilostamide or lixazinone suppressed mitogenic synthesis of DNA in mesangial cells, but 1 microM rolipram or 1 microM denbufylline showed no inhibitory effect. The efficacy of PDE isozyme inhibitors (IC50) to suppress [3H]thymidine incorporation or ROM generation paralleled IC50 values for inhibition of cAMP PDE. Incubation of mesangial cells with either rolipram alone or with cilostamide alone increased significantly in situ activity of PKA in mesangial cells, assessed by (-cAMP/+cAMP) PKA activity ratio, and the stimulatory effects were additive. Results indicate that in mesangial cells a cAMP pool that is metabolized by PDE4 activates PKA and thereby inhibits ROM generation; another cAMP pool that is metabolized by PDE3 activates another PKA (isozyme or pool) which suppresses proliferation of mesangial cells. We propose that in mesangial cells, a cAMP-PKA pathway that regulates mitogenesis is determined by activity of PDE3, whereas another cAMP-PKA pathway is directed by activity of PDE4 and controls ROM generation. Therefore, two PDE isozymes within one cell type compartmentalize distinct cAMP signaling pathways.

Ca2+/calmodulin-dependent cyclic GMP phosphodiesterase activity in granule neurons and astrocytes from rat cerebellum

Cyclic GMP (cGMP) formation induced by agonist stimulation of Ca2+/calmodulin-dependent nitric oxide (NO) synthase type I is known to occur in both granule cell and astrocyte cultures from rat cerebellum. Here we show that in these same cells cGMP is predominantly hydrolyzed by a Ca2+/calmodulin-dependent phosphodiesterase. At 10 microM cGMP, Ca2+ (25 microM) stimulated basal (Ca(2+)-independent) phosphodiesterase activity about 6 times in granular neurons and 15 times in astrocytes. The calmodulin antagonist calmidazolium blocked the Ca(2+)-dependent phosphodiesterase activity and exogenous calmodulin increased 3-4-fold the stimulatory potency of Ca2+ in both cell types (EC50 values 1.26 +/- 0.20 and 1.50 +/- 0.42 microM in the absence and 0.38 +/- 0.11 and 0.39 +/- 0.14 microM in the presence of 1 microM calmodulin, for neurons and astrocytes, respectively). In both cell types K(m) values for cGMP at 25 microM Ca2+ were similar (1.72 +/- 0.20 and 1.92 +/- 0.09 microM) and phosphodiesterase activities were inhibited by isozyme-selective phosphodiesterase inhibitors with potencies analogous to those described for Ca2+/calmodulin-phosphodiesterases or phosphodiesterase type 1 isoforms in other preparations. The nonselective phosphodiesterase inhibitor 3-isobutyl-1-methylxantine (IBMX) effectively blocked the Ca2+/calmodulin-phosphodiesterase activity in granule cell and astrocyte extracts (IC50 values at 1 microM cGMP: 31 +/- 10 microM and 46 +/- 6 microM, respectively), in contrast to the apparent inability of this compound to inhibit the Ca(2+)-dependent activity reported in whole brain extracts. These results demonstrate that comparable phosphodiesterase type 1 activities are found in the cytosols of cerebellar granule cells and astrocytes and suggest that these activities may play an important role in controlling cGMP levels in cells where the Ca(2+)-dependent NO synthase type I is stimulated.

Identification, characterization, and functional role of phosphodiesterase type IV in cerebral vessels: effects of selective phosphodiesterase inhibitors

The role of the phosphodiesterase type IV isozyme (PDE IV) in the regulation of cerebrovascular tone was investigated in the canine basilar artery in vitro and in vivo. The PDE isozymes extracted from the canine basilar artery were isolated by diethylaminoethanol (DEAE)-Sepharose affinity chromatography and identified based on sensitivity to isozyme-selective PDE inhibitors. [3H]cAMP hydrolysis was observed in one major and one minor peak of activity. The predominant peak was inhibited by the addition of cGMP (25%), siguazodan (26%), rolipram (39%), and the combination of siguazodan and rolipram (95%). Selective PDE IV inhibitors BRL 61063, rolipram, and denbufylline were equieffective inhibitors of [3H]-ccAMP hydrolysis mediated by PDE IV isolated from the canine basilar artery [concentrations producing 50% inhibition (IC50S) = 0.21 +/- 0.05 microM, 0.67 +/- 0.23 microM, and 0.73 +/- 0.16 microM, respectively]. In precontracted isolated ring segments of the canine basilar artery, selective PDE IV inhibitors produced potent and complete relaxation (IC50S < 150 nM). In contrast, zaprinast (a selective PDE V inhibitor) and siguazodan (a selective PDE III inhibitor) produced only weak relaxation of the basilar artery (IC50S = 4.5 microM and > 10 microM, respectively). Vasorelaxation produced by PDE IV inhibitors was not altered by removing the endothelium, 1-NAME, or adenosine receptor antagonism. In a canine model of acute cerebral vasospasm, all three selective PDE IV inhibitors reversed basilar artery spasm produced by autologous blood without altering mean arterial blood pressure. In contrast, prolonged treatment with BRL 61063 failed to alter the development of basilar spasm in the two hemorrhage canine models of chronic cerebral vasospasm. Denbufylline-induced relaxation in vitro was also significantly impaired in basilar arteries obtained from the model of chronic vasospasm. In conclusion, PDE IV appears to be the predominant isozyme regulating vascular tone mediated by cAMP hydrolysis in cerebral vessels. In addition, vasorelaxation modulated by PDE IV is compromised in chronic cerebral vasospasm associated with subarachnoid hemorrhage.

Stimulation of the hypothalamo-pituitary-adrenal axis in the rat by the type 4 phosphodiesterase (PDE-4) inhibitor, denbufylline

1. Preliminary studies in our laboratories showed that the synthetic xanthine analogue denbufylline, a selective type 4 phosphodiesterase (PDE-4) inhibitor, is a potent activator of the hypothalamo-pituitary-adrenal (HPA) axis when given orally to adult male rats. This paper describes the results of experiments in which well established in vivo and in vitro models were used to (a) examine further the effects of denbufylline on HPA function and (b) identify the site and mode of action of the drug within the axis. 2. In vivo, administration of denbufylline (0.1-2.5 mg kg-1, i.p.) produced a significant increase in the serum corticosterone concentration; maximal responses were attained at a dose of 1.0 mg kg-1 (P < 0.01 vs. vehicle control, Scheffe's test). However, when denbufylline was administered by intracerebroventricular injection (0.05-1 micrograms kg-1) it failed to influence significantly the serum corticosterone concentration (P > 0.05 vs. vehicle control, Scheffe's test). The adrenocortical responses to peripheral injections of denbufylline (1 mg kg-1, i.p.) were reduced in rats in which the secretion of endogenous corticotrophin releasing factors (CRFs) from the hypothalamus was blocked pharmacologically (P < 0.01 vs. controls, Scheffe's test). However, denbufylline (0.1 mg kg-1, i.p.) potentiated the significant (P < 0.01) increases in serum corticosterone concentration provoked in "CRF blocked rats' by hypothalamic extract (5 hypothalamic extracts kg-1, i.v.) although it failed to influence (P > 0.05) the relatively moderate increases in corticosterone secretion evoked by CRH-41 (2 mg kg-1, i.v.). 3. In vitro, denbufylline (0.01-1 mM) evoked small but significant (P < 0.05) increases in the release of ACTH from rat anterior pituitary segments; furthermore, at these and lower concentrations (0.01 microM-1 mM), it potentiated the adrenocorticotrophic responses to sub-maximal concentrations of hypothalamic extract (P < 0.01) and forskolin (0.1 mM, P < 0.01) but not those to CRH-41 (10 nM) or 8-bromo-cyclic AMP (1-100 microM). In addition, denbufyline (0.1 mM) increased the anterior pituitary cyclic AMP content (P < 0.05) and potentiated the rises in tissue content of the cyclic nucleotide induced by hypothalamic extract (0.1 hypothalamic equivalents ml-1, P < 0.01) and forskolin (0.1 mM, P < 0.01) but not by CRH-41 (10 nM, P < 0.05). By contrast, denbufylline (1 microM-1 mM) failed to influence the release of AVP from rat isolated hypothalami and stimulated the secretion of CRH-41 (P < 0.01) release only at the highest concentration tested (1 mM). 4. The results suggest that the stimulatory actions of denbufylline on the hypothalamo-pituitary-adrenocortical axis are exerted predominantly at the level of the anterior pituitary gland and that they may be attributed, at least in part, to inhibition of type 4 phosphodiesterase enzymes.

Effects of SCA40 on human isolated bronchus and human polymorphonuclear leukocytes: comparison with rolipram, SKF94120 and levcromakalim

1. SCA40 (0.1 nM-0.1 mM) produced concentration-dependent suppression of the spontaneous tone of human isolated bronchus (-log EC50 = 6.85 +/- 0.09; n = 10) and reached a maximal relaxation similar to that of theophylline (3 mM). The potency (-log EC50 values) of SCA40 compared to other relaxants was rolipram (7.44 +/- 0.12; n = 9) > SCA40 > or = levcromakalim (6.49 +/- 0.04; n = 6) > SKF94120 (5.87 +/- 0.10; n = 9). 2. When tested against the activity of the isoenzymes of cyclic nucleotide phosphodiesterase (PDE) isolated from human bronchus, SCA40 proved highly potent against PDE III (-log IC50 = 6.47 +/- 0.16; n = 4). It was markedly less potent against PDE IV (4.82 +/- 0.18; n = 4) and PDE V (4.32 +/- 0.11; n = 4). 3. Human polymorphonuclear leukocytes (PMNs) stimulated with N-formylmethionyl-leucyl-phenylalanine (FMLP) produced a concentration-dependent superoxide anion generation and elastase release. SCA40 (1 nM-10 microM) produced a concentration-related inhibition of FMLP (30 nM approximately EC50)-induced superoxide production (-log IC50 = 5.48 +/- 0.10; n = 6) and elastase release (-log IC50 = 5.50 +/- 0.26; n = 6). Rolipram was an effective inhibitor of superoxide generation and elastase release (-log IC50 values approximately 8) while SKF94120 and levcromakalim were scarcely effective. 4. FMLP (30 nM) and thimerosal (20 microM) induced leukotriene B4 production and elevation of intracellular calcium concentration in human PMNs. The production of leukotriene B4 was inhibited by SCA40 in a concentration-related manner (-log IC50 = 5.94 +/- 0.22; n = 6) but SCA40 was less effective against the elevation of intracellular calcium. Rolipram was an effective inhibitor of leukotriene B4 synthesis (-log IC50 approximately 7) and intracellular calcium elevation (-log IC50 approximately 6) while SKF94120 and levcromakalim were scarcely effective. 5. It is concluded that SCA40 is an effective inhibitor of the inherent tone of human isolated bronchus. The bronchodilatation produced by SCA40 appears mainly related to PDE inhibition since the potency of SCA40 as a relaxant of human isolated bronchus was found to be close to its potency as inhibitor of PDE III activity isolated from human bronchus. In addition, SCA40 exhibited inhibitory effects on human PMN function stimulated by FMLP. These effects may be related to the ability of SCA40 to inhibit PDE IV from human PMNs while the contribution of PDE V inhibition is uncertain. We found no evidence of a role for levcromakalim-sensitive plasmalemmal K+-channels in human PMNs.

Inhibition of lipopolysaccharide-induced bowel erythrocyte extravasation in rats, and of mesenteric hypoperfusion in dogs, by phosphodiesterase inhibitors

Sepsis is intricately associated with mesenteric ischemia. The remote complications of mesenteric ischemia are essentially those of sepsis, whether as a cause or as a consequence. Experimental endotoxic shock induces bowel hypoperfusion, erythrocyte extravasation and intestinal necrosis. The effects of pentoxifylline, rolipram and denbufylline, three phosphodiesterase inhibitors, were studied on endotoxin-induced bowel erythrocyte extravasation and intestinal and renal hypoperfusion, in conscious rats and anaesthetized dogs, respectively. Two hours after lipopolysaccharide i.v. injection in rats, erythrocyte extravasation was evident throughout the intestinal musculature and mucosa, apparently without affecting lungs, heart, kidneys, liver or pancreas. Pretreatment with the non-selective phosphodiesterase inhibitor, pentoxifylline, or selective phosphodiesterase IV inhibitors such as denbufylline or rolipram reduced intestinal haemoconcentration. In the anaesthetized dog, pentoxifylline and denbufylline both inhibited the E. coli lipopolysaccharide-induced mesenteric blood flow fall, without affecting renal blood flow or cardiac index. In conclusion, phosphodiesterase inhibitors protected from intestinal damage and bowel hypoperfusion after lipopolysaccharide challenge. This action may thus play a role in the protective effects against endotoxin-induced lethal toxicity previously described for phosphodiesterase inhibitors.

A xanthine derivative denbufylline inhibits negative inotropic response to verapamil in guinea pig ventricular papillary muscles, independent of its phosphodiesterase inhibitory activity

A phosphodiesterase (PDE) III inhibitor, amrinone, inhibited both the negative inotropic actions of verapamil and nicardipine in guinea pig ventricular papillary muscle; this effect was canceled by the protein kinase A inhibitor H-89. The PDE IV inhibitor 1,3-di-n-butyl-7-(2'-oxopropyl)xanthine (denbufylline), which elicited a negative inotropic action by itself, attenuated the action of verapamil up to 10 microM, without any interaction with nicardipine. The attenuation by denbufylline was not influenced by H-89. This suggests that in the ventricular papillary muscle, denbufylline acts on some verapamil-sensitive site(s) in the membrane and interferes with the calcium channel function without involvement of its PDE inhibitory activity.

Relaxant influence of phosphodiesterase inhibitors in the cat gastric fundus

The breakdown of the relaxation-inducing second messengers cAMP and cGMP is mediated by phosphodiesterases. Inhibitors of functionally present phosphodiesterases can be expected to induce relaxation by increasing the basic amount of cAMP and/or cGMP. In the cat gastric fundus, vinpocetine, which has some selectivity for phosphodiesterase type I, only induced contractions, but the inhibitors of type III [5-(4-acetimidophenyl)pyrazin-(1H)-one; SKF 94120], type IV (rolipram) and type V (zaprinast) phosphodiesterase all caused concentration-dependent relaxation, as did the non-specific phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX). The most potent relaxant agent was rolipram (EC50 9 +/- 5 x 10(-7) M and 3 +/- 1 x 10(-7) M in longitudinal and circular smooth muscle strips, respectively). These results suggest that type III, IV and V phosphodiesterases are functionally present in the cat gastric fundus and are involved in the regulation of tone. The possible influence of the phosphodiesterase inhibitors on non-adrenergic non-cholinergic (NANC) relaxation induced by nitric oxide (NO), vasoactive intestinal polypeptide (VIP) and train and sustained electrical field stimulation was then tested. Rolipram (3 x 10(-8) M), SKF 94120 (10(-5) M) and IBMX (10(-6) M) did not potentiate any of the relaxant stimuli studied. Zaprinast (10(-5) M), the cGMP specific type V phosphodiesterase inhibitor, caused a significant increase of the relaxation induced by exogenous NO and by train electrical field stimulation. These stimuli are thought to induce relaxation via an increase of intracellular cGMP.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of cyclic AMP phosphodiesterase isozymes in rat parotid gland

Cyclic AMP phosphodiesterase (PDE) isozymes were isolated and characterized from the soluble fraction of rat parotid gland. Four main peaks containing PDE activity were obtained by Q-Sepharose Fast Flow column chromatography. The four peaks were identified as PDEs I-IV by kinetic properties, molecular-weight analysis and their responses to effectors and inhibitors.

Comparative cardiac effects of milrinone and sodium nitroprusside in conscious rats

The rat has been shown to be resistant to the inotropic action of milrinone. We compared in conscious rats, the effects of an i.v. infusion of milrinone (0.3 mg/kg/min), a phosphodiesterase (PDE) inhibitor to those of nitroprusside (50 micrograms/kg/min), a pure vasodilator, on blood pressure and dP/dtmax to determine whether or not an inherent positive inotropic effect of milrinone is offset by its powerful hypotensive action. For the first 10 min of infusion, we found no differences in dP/dtmax, (the first derivative of the left ventricular pressure (LVP), an index of contractility) for equihypotensive doses of milrinone or nitroprusside. A second objective of this study was to determine if milrinone-induced ventricular fibrillation (VF) is due to cardiac ischemia which could be associated with the profound hypotension induced by the drug. Milrinone infusion was accompanied by a significant QTc interval (QT corrected for heart rate) prolongation. VF and death occurred in 5/6 rats at total doses varying from 3.6 to 20.1 mg/kg infused over 12 to 67 min respectively. Premature ventricular contractions (PVCs) were noted in all 6 milrinone infused rats during the first min. of infusion. No arrhythmias were noted during the 2 hour i.v. infusion with nitroprusside. A direct action on the heart is postulated to explain, at least partially, the milrinone-induced VF since nitroprusside had a similar hypotensive action but no effect on the ECG. We conclude that the rat, in analogy to patients with severe cardiac failure, might be resistant to the inotropic action of milrinone but is sensitive to its vasodilatory and arrhythmogenic effects.

The role of cyclic nucleotides in the action of peripheral-type benzodiazepine receptor ligands in rat aorta

1. Peripheral-type benzodiazepine ligands (Ro 5-4864, AHN-086, PK 11195 and PK 14105) inhibit, in a concentration-dependent and non-competitive manner, noradrenaline-induced contractions in isolated rat aortic rings (IC50 values: 24 +/- 1.8, 49 +/- 2.5, 15 +/- 1.2, 49 +/- 3.2 microM, respectively). 2. This effect is probably not mediated by peripheral-type benzodiazepine receptors and is not related to the presence of endothelium. 3. All compounds inhibited phosphodiesterase activity in vitro. 4. From the results obtained with nucleotide analogs, calcium antagonists and specific inhibitors of PDE isoenzymes, it can be concluded that the actions of AHN-086 and PK 11195 are related to effects on PDE I, III and IV.

Identification and characterization of isoenzymes of cyclic nucleotide phosphodiesterase in human kidney and heart, and the effects of new cardiotonic agents on these isoenzymes

The present study was done to identify and characterize the isoenzymes of cyclic nucleotide phosphodiesterase (PDE) and to determine their intracellular distribution in human kidney and heart. The in vitro effects of new cardiotonic agents, namely, NSP-805 (4,5-dihydro-5-methyl-6-[4-[(2-methyl-3-oxo-1-cyclopentenyl)amino] phenyl]-3(2H)-pyridazinone), TZC-5665 (6-[4-[2-[3-(5-chloro-2-cyanophenoxy)-2-hydroxypropylamino]- 2 -methylpropylamino]phenyl]-5-methyl-4,5-dihydro-3(2H)-pyridazinone ) and its metabolites, OPC-18790 ((+/-)-6-[3-(3,4-dimethoxybenzylamino)-2 -hydroxypropoxy]-2-(1H)-quinolinone), MS-857 (4-acetyl-1-methyl-7-(4-pyridyl)-5,6,7,8-tetrahydro-3(2H)-isoquinolinone ) and E-1020 (1,2-dihydro-6-methyl-2-oxo-5-(imidazo[1,2-a]pyridin-6-yl)-3-pyridine carbonitrile hydrochloride monohydrate), on these human PDE isoenzymes were also investigated. PDE isoenzymes were separated from cytosolic and particulate fractions of homogenates of human kidney and heart by DEAE-Sepharose chromatography. PDE isoenzymes were identified by their elution characteristics, substrate specificities, sensitivities to regulation by effectors and by the use of isoenzyme-specific inhibitors. In a cytosolic fraction from kidney, Ca2+/calmodulin-dependent PDE (CaM-PDE), cyclic GMP-stimulated PDE (cGS-PDE), cyclic GMP-inhibited PDE (cGI-PDE) and two forms of cyclic AMP-specific PDE (cAMP-PDE) were resolved. One form of cAMP-PDE (cAMP-PDE alpha), which was eluted at a lower ionic strength than cGI-PDE during DEAE-Sepharose chromatography, was newly recognized in human tissues, though the other form (cAMP-PDE beta), which eluted later than cGI-PDE, had been previously isolated.(ABSTRACT TRUNCATED AT 250 WORDS)

Selective tracheal relaxation and phosphodiesterase-IV inhibition by xanthine derivatives

The effects of substitutions in the xanthine nucleus on tracheal relaxant activity, atrium chronotropic activity, adenosine A1 affinity, and inhibitory activities on cyclic AMP-phosphodiesterase isoenzymes in guinea pigs were studied. Substitution with a long alkyl chain at the N1-position of xanthine nucleus increased the tracheal relaxant activity without leading to positive chronotropic action, and long alkyl chains at the N3-position increased both activities. N7-substitutions with n-propyl and 2'-oxopropyl groups, such as in denbufylline, increased bronchoselectivity. N7-substitution decreased the adenosine A1 affinity, but substitution at either the N1- or N3-position increased it. The bronchorelaxant activity of xanthine derivatives was closely correlated with their inhibition of phosphodiesterase-IV, but not with their adenosine A1 affinity; the positive chronotropic effects were related to their inhibition of phosphodiesterase-III. This study confirms that the bronchorelaxation of xanthine derivatives is mediated by inhibition of the isoenzyme phosphodiesterase-IV. The results of structure-activity analysis suggest that substitutions at the N1- and N7-positions should be tried in the development of xanthine derivatives that are selective bronchodilators and phosphodiesterase-IV inhibitors.

Cyclic nucleotide phosphodiesterases in the human lung

Although theophylline has been used in the treatment of lung diseases, particularly bronchial asthma, since the nineteenth century, the mechanisms underlying its effectiveness remained poorly understood until quite recently. The identification of cyclic nucleotide phosphodiesterase (PDE)--the enzyme responsible for breaking down cyclic AMP and cyclic GMP within cells--as a target for methylxanthines such as theophylline led to a research effort that has resulted in the characterization of multiple forms of the PDE enzyme and the development of selective inhibitors for some of these forms. Using these drugs, it has been possible to identify the PDE "isoenzymes" in a number of tissues and cells and to demonstrate the functional effects of the inhibition of different PDEs upon these tissues. Studies on the smooth muscle of human airways and pulmonary arteries have identified isoenzyme-selective PDE inhibitors that are effective broncho- and vasorelaxants in vitro, and it is hoped that these agents may be effective in relieving airway obstruction and pulmonary hypertension in patients. In addition, selective inhibitors of certain PDE isoenzymes suppress the proinflammatory functions of a range of immune cells, including the lung mast cell and the alveolar macrophage. Selective inhibitors of PDE isoenzymes are beginning to undergo clinical trials for the treatment of asthma. The advancing understanding of the PDE distribution in the lung and the ever more precise characterization of distinct enzyme proteins should allow the development of site-selective drugs for the treatment of lung diseases, while minimizing the systemic side effects associated with nonselective PDE inhibitors such as theophylline.

Phosphodiesterase inhibitory profile of some related xanthine derivatives pharmacologically active on the peripheral microcirculation

The cyclic nucleotide phosphodiesterase (PDE) inhibitory profile of four related xanthine derivatives: pentoxifylline (BL 191), propentofylline (HWA 285), torbafylline (HWA 448) and albifylline (HWA 138), pharmacologically active on the peripheral and/or cerebral microcirculation was established using the four main PDE isoforms present in rat heart cytosol. HPLC on a Mono Q ion-exchange column resolved four separate cyclic nucleotide PDE activities: a calmodulin-activated fraction (PDE I), a cGMP-stimulated fraction (PDE II), a cAMP-specific rolipram-sensitive fraction (PDE IV) and a cGMP-inhibited fraction (PDE III). Among the four compounds studies, only torbafylline and pentoxifylline inhibited more efficiently the calcium plus calmodulin-stimulated than the basal activity of PDE I. The four xanthine derivatives inhibited more potently the cGMP-stimulated than the basal activity of the cGMP-stimulatable PDE II, propentofylline being the most inhibitory (IC50: 20 microM). Except for propentofylline, which exhibited a marked selectivity toward the rolipram-sensitive PDE versus the cGMP-inhibited PDE III, the other xanthines modestly (IC50 in the 10(-4) M range) inhibited both cAMP-specific isoforms with similar potency. Propentofylline proved to be the best inhibitor whatever the considered isoform whereas torbafylline exhibited the weakest inhibitory potency with, however, some selectivity for PDE I.

Separation and characterization of a novel isoenzyme of cyclic nucleotide phosphodiesterase from rat cerebrum

Anion-exchange chromatography on a Mono-Q column of the supernatant fraction, after ultracentrifugation, from a homogenate of rat cerebrum, prepared under isotonic conditions in the presence of protease inhibitors, yielded a novel isoenzyme of cyclic nucleotide phosphodiesterase (PDE) with properties unlike those of known PDEs. The isoenzyme was insensitive to stimulation by Ca2+/calmodulin and cyclic GMP, and it hydrolyzed both cyclic AMP and cyclic GMP with KM values of 0.109 +/- 0.008 microM and 1.78 +/- 0.04 microM, respectively. The ratio of Vmax of hydrolysis of cyclic GMP to that of cyclic AMP was 1.90 +/- 0.07. Nicardipine (PDE I inhibitor), SK&F 94120 (PDE III inhibitor), rolipram (PDE IV inhibitor) and zaprinast (PDE V inhibitor) had very weak inhibitory effects on the PDE activity of the isoenzyme. These results suggest that the isoenzyme is a novel and previously unreported species of PDE, which we tentatively designate PDE VIII.