Interactions of formylmethionyl-leucyl-phenylalanine, adenosine, and phosphodiesterase inhibitors in human monocytes. Effects on superoxide release, inositol phosphates and cAMP

Modulation of TNF and GM-CSF release from dispersed human nasal polyp cells and human whole blood by inhibitors of different PDE isoenzymes and glucocorticoids

The aim of this study was to investigate the role of the inhibitors of different PDE isoenzymes (PDE 1-5) on the production of two pro-inflammatory cytokines - tumor necrosis factor alpha (TNF) and granulocyte-macrophage colony-stimulating factor (GM-CSF). Two in vitro models were used to compare the antiinflammatory properties of PDE inhibitors with that of glucocorticoids. The effect on TNF release from diluted human blood following lipopolysaccharide (LPS from Salmonella abortus equi) stimulation as well as the GM-CSF and TNF release from human nasal polyp cells following allergic stimulation were investigated. Both models proofed to be well suited for the characterisation of the antiinflammatory properties of new chemical entities. In diluted human blood and dispersed human nasal polyp cells the induced TNF release was most potently suppressed by selective PDE4 inhibitors. Amrinone and milrinone, selective PDE3 inhibitors, suppressed TNF secretion to a lesser extent. The effects of theophylline (unspecific PDE inhibitor), vinpocetine (PDE1 inhibitor), EHNA (PDE2 inhibitor) and the PDE5 inhibitors zaprinast and E 4021 were weak. In human blood, the tested glucocorticoids beclomethasone, dexamethasone and fluticasone inhibited the LPS induced TNF release potently in a concentration dependent manner, whereas in dispersed human nasal polyp cells, the effect of the glucocorticoids on allergically induced TNF release, with the exception of dexamethasone, was much less pronounced. Glucocorticoids were the most potent inhibitors of GM-CSF release and the effect correlates well with the affinity to the glucocorticoid receptor. The selective PDE 4 inhibitors, and to a certain extent the PDE3 inhibitors amrinone and milrinone, reduced the GM-CSF release in a concentration dependent manner. In all investigations selective PDE4 inhibitors reduced TNF release to a much higher degree (4-10 fold) than GM-CSF release.

Cyclic nucleotide phosphodiesterases

Cyclic nucleotide second messengers (cAMP and cGMP) play a central role in signal transduction and regulation of physiologic responses. Their intracellular levels are controlled by the complex superfamily of cyclic nucleotide phosphodiesterase (PDE) enzymes. Continuing advances in our understanding of the molecular pharmacology of these enzymes has led to the development of selective inhibitors as therapeutic agents for disease states ranging from cancer and heart failure to depression and sexual dysfunction. Several PDE types have been identified as therapeutic targets for immune/inflammatory diseases. This article briefly reviews the available in vitro, preclinical, and clinical data supporting the potential for selective PDE inhibitors as immunomodulatory agents.

Phosphodiesterase 4 (PDE4) inhibitors in asthma and chronic obstructive pulmonary disease (COPD)

Phosphodiesterases (PDE) are a family of enzymes responsible for the metabolism of the intracellular second messengers cyclic AMP and cyclic GMP. PDE4 is a cyclic AMP specific PDE that is the major if not sole cyclic AMP metabolizing enzymes found in inflammatory and immune cells, and contributes significantly to cyclic AMP metabolism in smooth muscles. Based on its cellular and tissue distribution and the demonstration that selective inhibitors of this isozyme reduce bronchoconstriction in animals and suppress the activation of inflammatory cells, PDE4 has become an important molecular target for the development of novel therapies for asthma and COPD. This chapter will review the evidence demonstrating the ability of PDE4 inhibitors to modify airway obstruction, airway inflammation and airway remodelling and hyperreactivity, will present some preliminary findings obtained with theses compounds in clinical trials and and will discuss experimental approaches designed to identify novel compounds that maintain the beneficial activity of the initial selective PDE4 inhibitors but with a reduced tendency of elicit the gastrointestinal side effects observed with this class of compounds.

Cyclic nucleotide phosphodiesterase (PDE) inhibitors and immunomodulation

Intracellular levels of cyclic nucleotide second messengers are regulated predominantly by the complex superfamily of cyclic nucleotide phosphodiesterase (PDE) enzymes. Recent advances in our understanding of the molecular pharmacology of these enzymes has led to their identification as biologic regulators of certain disease states and the development of isozyme-selective inhibitors as potential therapeutic agents. A large body of in vitro and preclinical data suggests the therapeutic utility of PDE4 inhibitors as potent anti-inflammatory agents. Early clinical trials with selective PDE inhibitors substantiate this approach while highlighting pharmacodynamic and toxicologic pitfalls inherent to the inhibition of specific PDE isozymes. This commentary will review our current understanding of PDE inhibitors as immunomodulatory agents.

Characterization of phosphodiesterase 4 in guinea-pig macrophages: multiple activities, association states and sensitivity to selective inhibitors

1. The cyclic AMP phosphodiesterases (PDE) in guinea-pig peritoneal macrophages were isolated, partially characterized and their role in regulating the cyclic AMP content in intact cells evaluated. 2. Differential centrifugation of macrophage lysates revealed that approximately 90% of the PDE activity was membrane-bound and exclusively hydrolyzed cyclic AMP. This activity was not removed by KCl (200 mM) but was readily solubilized by the non-ionic detergent, Triton X-100 (1% v/v). Greater than 80% of the hydrolytic activity was suppressed by the PDE4 inhibitors, R-rolipram and nitraquazone with IC50s of 240 and 540 nM, respectively. 3. Anion-exchange chromatography of the total protein extracted from macrophages resolved two major peaks of cyclic AMP PDE activity that were insensitive to cyclic GMP (10 microM), calmodulin (50 units plus 2 mM CaCl2) and a PDE3 inhibitor, SK&F 95654 (10 microM), but were markedly suppressed by RS-rolipram (10 microM). The two peaks of PDE activity were arbitrarily designated CPPDE4alpha and CPPDE4beta with respect to the order from which they were eluted from the column where the prefix, CP, refers to the species, Cavia porcellus. 4. The hydrolysis of cyclic AMP catalyzed by CPPDE4alpha and CPPDE4beta conformed to Michaelis-Menten kinetic behaviour with similar K(m)s (13.4 and 6.4 microM, respectively). 5. Thermal denaturation of membrane-bound PDE4 at 50 degrees C followed bi-exponential kinetics with t1/2 values of 1.5 and 54.7 min for the first and second components, respectively. In contrast, CPPDE4alpha and CPPDE4beta each decayed mono-exponentially with significantly different thermostabilities (t1/2 = 2.77 and 1.15 min, respectively). 6. Gel filtration of CPPDE4beta separated two peaks of rolipram-sensitive PDE activity. The main peak eluted at a volume indicative of a approximately 180 kDa protein but was preceded by a much larger form of the enzyme that had an estimated weight of 750 kDa. Size exclusion chromatography of CPPDE4alpha resolved a broad peak of activity with molecular weights spanning 50 to 200 kDa. 7. Of ten PDE inhibitors examined, none distinguished CPPDE4alpha from CPPDE4beta with respect to their IC50 values or their rank order of potency. RS-rolipram acted as a purely competitive inhibitor of cyclic AMP hydrolysis with K(i)s of 2 microM and 1.5 microM for CPPDE4alpha and CPPDE4beta, respectively. In contrast to the membrane-associated enzyme(s), R-rolipram and nitraquazone were 4 to 19 fold less potent as inhibitors of CPPDE4alpha and CPPDE4beta. 8. In intact macrophages, Ro 20-1724 and RS-rolipram potentiated isoprenaline-induced cyclic AMP accumulation under conditions where a PDE3 inhibitor, SK&F 94120, was essentially inactive. 9. These data demonstrate that the predominant cyclic AMP hydrolyzing activity in guinea-pig macrophages is a PDE4. Moreover, thermostability studies and size exclusion chromatography indicates the possible expression of two intrinsic, membrane-associated isoenzymes which can regulate the cyclic AMP content in intact cells. The finding that soluble and particulate forms of the same enzyme exhibit different sensitivities to rolipram and nitraquazone implies that PDE4 can change conformation. Finally, the identification of multiple molecular weight species of CPPDE4 suggests that this enzyme(s) might form multimeric complexes of variable association states.

Immunocytochemical expression of human muscle cell p75 neurotrophin receptor is down-regulated by cyclic adenosine 3',5'-monophosphate

To investigate whether the immunocytochemical expression of low affinity neurotrophin receptor (p75) in human muscle is modulated by increased levels of intracellular cyclic adenosine 3',5'-monophosphate (cAMP), human cultured myogenic cells were treated with cAMP analogues dibutyryl cAMP (dbcAMP 0.5-1 mM) and 8-bromo cAMP (1 mM) or the adenylate cyclase activator forskolin (10-100 microM). Cultures were processed for indirect immunofluorescence microscopy using an anti-human p75 mAb. The treatment of cultured muscle cells with cAMP analogues or forskolin for two days induced a decrease of immunoreactivity for p75 and a reduction of both myotube formation and morphological cell differentiation. Removal of cAMP derivatives from the medium resulted in a return of immunoreactive cells to the levels of untreated controls. These data indicate that adenylate cyclase is involved in the regulation of human muscle p75.

The effect of selective phosphodiesterase 3 and 4 isoenzyme inhibitors and established anti-asthma drugs on inflammatory cell activation

1. This study aimed to evaluate the effects of phosphodiesterase (PDE) inhibitors and currently prescribed anti-asthma drugs for their ability to inhibit inflammatory cell activation in vitro. 2. Alveolar macrophages and eosinophils were isolated from the bronchoalveolar lavage (BAL) fluid of ovalbumin (Ovalb)-sensitized guinea-pigs. Opsonized zymosan (OZ) and PAF stimulated leukotriene B4 (LTB4) release from eosinophils was measured by radioimmunoassay. Ovalb-induced superoxide generation was measured by reduction of cytochrome C. 3. Monocytes were separated from human peripheral venous blood and mast cells were dispersed from human lung fragments. Lipopolysaccharide (LPS)-induced tumour necrosis factor-alpha (TNF-alpha) release from monocytes was measured by ELISA and anti-IgE stimulated histamine release from mast cells was measured by a radioenzymatic method. 4. The beta 2 agonist, salbutamol inhibited TNF-alpha release from monocytes and histamine release from mast cells whilst having no effect on eosinophil-derived LTB4 release or macrophage superoxide generation. 5. The PDE 3 inhibitor, milrinone produced a concentration-related inhibition of TNF-alpha release from monocytes which achieved statistical significance at 10(-5) M but inhibited LTB4 release from eosinophils and superoxide generation from macrophages only at the highest concentration (10(-3) M) examined. Milrinone had no effect on histamine release from mast cells. 6. The selective PDE 4 inhibitors, denbufylline and rolipram and the corticosteroid, beclomethasone produced a concentration-related inhibition of LTB4 release from eosinophils, TNF-alpha release from monocytes and superoxide generation from alveolar macrophages whilst having no effect on histamine release from mast cells. 7. The mixed PDE 3/4 inhibitor, benzafentrine produced a concentration-related inhibition of LTB4 release from eosinophils, TNF-alpha release from monocytes, superoxide generation from alveolar macrophages and histamine release from mast cells. 8. In conclusion these data clearly show that both established anti-asthma medication as well as PDE inhibitors have the potential to inhibit inflammatory cell activation in vitro but that the anti-secretory actions of beta 2 agonists, corticosteroids and PDE inhibitors are distinct.

Association of the anti-inflammatory activity of phosphodiesterase 4 (PDE4) inhibitors with either inhibition of PDE4 catalytic activity or competition for [3H]rolipram binding

Phosphodiesterase 4 (PDE4) inhibitors are novel anti-inflammatory compounds. Unfortunately, the archetypal PDE4 inhibitor rolipram produces central nervous system and gastrointestinal side-effects. To exploit these agents, we need to identify PDE4 inhibitors that retain the anti-inflammatory activity with a reduced potential to elicit unwanted side-effects. PDE4 possesses both cyclic AMP catalytic activity that is inhibitable by rolipram and a high affinity binding site for rolipram. The function of this high affinity rolipram binding site is unclear; however, certain pharmacological effects of PDE4 inhibitors are associated with competition for this site. Since PDE4 inhibitors suppress both monocyte and neutrophil activation, the present experiments were carried out to establish a correlation between suppression of monocyte activation [tumor necrosis factor alpha (TNF alpha) formation] or suppression of neutrophil activation (degranulation) with inhibition of either PDE4 catalytic activity or [3H] rolipram binding. Suppression of TNF alpha formation demonstrated a strong correlation with inhibition of PDE4 catalytic activity (r=0.87; P<0.01; Spearman's Rho = 0.79, P<0.05), whereas there was no correlation with inhibition of [3H]rolipram binding(r=0.21, P>0.5; Spearman's Rho=0.16, P>0.5). Suppression of neutrophil degranulation was not associated with inhibition of PDE4 catalytic activity (r=0.25, P>0.4; Spearman's Rho=0.33, P>0.2), but was associated with inhibition of [3H]rolipram binding (r=0.68, P<0.05; Spearman's Rho=0.6, P=0.06). These results indicate that anti-inflammatory effects of PDE4 inhibitors can be associated with either inhibition of PDE4 catalytic activity or high affinity rolipram binding.

Cyclic nucleotide phosphodiesterase isoenzyme activities in human alveolar macrophages

BACKGROUND

Alveolar macrophages and their precursors, the monocytes are involved in airway inflammation in asthma. An increase in intracellular cAMP by PDE inhibitors is known to suppress macrophage and monocyte functions. A comparison of the PDE-isoenzyme profiles of human alveolar macrophages from normal and atopic donors and of human peripheral blood monocytes might form a basis to differentially affect functions of these cells by PDE inhibitors.

OBJECTIVE

The study compares the PDE isoenzyme activity profiles of human alveolar macrophages from normal and atopic asthmatic donors and human peripheral blood monocytes. In addition, the effect of in vitro maturation of monocytes on their PDE isoenzyme profile is studied.

METHODS

Macrophages were purified (95-97%) by adherence to plastic, and blood monocytes were purified (88%) by counter-current elutriation. PDE isoenzyme activity profiles were investigated using isoenzyme selective inhibitors and activators.

RESULTS

In macrophages substantial PDE I activity, which was significantly higher than PDE III-V activity was detected and PDE II was absent. PDE III was membrane-bound whereas PDE I, IV and V were soluble. No difference was found between alveolar macrophages of normal donors and atopic asthmatics. Monocytes exclusively contained PDE IV but their in vitro maturation led to a PDE isoenzyme profile similar to that of alveolar macrophages.

CONCLUSION

These results indicate that human monocytes and alveolar macrophages are distinct targets for the effects of selective PDE inhibitors while alveolar macrophages from normal and atopic individuals appear to be equally sensitive.

The cDNA of a human lymphocyte cyclic-AMP phosphodiesterase (PDE IV) reveals a multigene family

Five protein families are needed to encompass the diversity of cyclic-AMP (cAMP) phosphodiesterases (PDE). Family IV PDEs (PDE IV) specifically hydrolyze cAMP with a low Km, and are selectively inhibited by rolipram (Rp) and related drugs. Cloned cDNAs from rat (r) suggest that the PDE IV family comprises four distinct members, designated A, B, C and D. Using RN from a human lymphocytic B-cell line (43D-Cl2), we have isolated a 3.8-kb cDNA by low-stringency screening using a rat PDE IV member B (r-PDE IVB) probe. Expression of the human (h) cDNA in Escherichia coli results in cAMP-specific PDE activity that is Rp sensitive. A single large open reading frame (ORF) predicts a 564-amino-acid protein with 92.9% identity to r-PDE IVB; at the nucleotide level the identity is 86.3%. This h-PDE IVB clone, HPB106, differs from a related cDNA clone isolated by others from h-monocytes [Livi et al., Mol. Cell. Biol. 10 (1990) 2678-2686]. Our analysis identifies the monocyte clone with r-PDE IVA. Southern blots using a 1.2-kb h-PDE IVB probe at low stringency suggest the presence of additional uncloned human PDE IV family members. Analysis of genomic Southern blots using short specific probes from the h-PDE IVA and h-PDE IVB cDNAs indicates that distinct genes encode these two PDE IV family members. RNA from fractionated normal human leukocytes shows major specific messages of 3.0 and 4.6 kb for h-PDE IVA and 3.7 kb for h-PDE IVB.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of cyclic AMP and cyclic GMP phosphodiesterase inhibitors on the superoxide burst of guinea-pig peritoneal macrophages

1. The cyclic nucleotide phosphodiesterase (PDE) activity of guinea-pig peritoneal macrophages was partially characterized and the effects of selective and non-selective inhibitors of adenosine 3':5'-cyclic monophosphate (cyclic AMP PDE) and guanosine 3':5'-cyclic monophosphate (cyclic GMP PDE) phosphodiesterases on superoxide generation were investigated using peritoneal macrophages from horse-serum pretreated guinea-pigs. 2. The non-selective PDE inhibitor, 3-isobutyl-1-methylxanthine (IBMX) and the PDE I/V selective inhibitor, zaprinast, inhibited spontaneous superoxide generation with IC50s of 30.7 +/- 11.3 microM and 145 +/- 17 microM respectively (n = 6 and 5). The concentration-response curves for the PDE IV selective inhibitors rolipram and Ro20-1724 were biphasic; mean maximum inhibitions were 56.9 +/- 5.9% and 66.8 +/- 10.5% respectively at 300 microM, but in 2 out of 6 (rolipram) and 2 out of 5 (Ro20-1724) experiments inhibition was < 50%. The PDE III inhibitor SK&F 94120 was without effect. Spontaneous superoxide generation was reduced 57 +/- 10% by 1 microM prostaglandin E2 (PGE2) and 62.6 +/- 3.76% by 1 microM salbutamol. 3. The increase in superoxide generation elicited by FMLP (10(-9)-10(-5)M) was unaffected by any of the PDE inhibitors studied. Inhibition of FMLP-stimulated superoxide generation by PGE2 was enhanced in the presence of 10 microM IBMX. 4. Macrophages were found to contain a predominantly membrane bound cyclic AMP PDE (90% of total activity) which was unaffected by cyclic GMP or calcium/calmodulin. The cyclic AMP PDE activity in the cytosolic fraction was enhanced in the presence of calcium/calmodulin. Selective inhibitors of PDE IV inhibited the particulate cyclic AMP PDE activity (IC50s rolipram 1.5 +/- 0.3 microM, Ro 20-17244.1 +/- 0.6 microm) as did the non-selective inhibitor IBMX (IC50 22 +/- 8 microM). The macrophage particulate PDE activity was resistant to inhibition by the PDE III inhibitor SK&F 94836 and the PDE I/V inhibitor, zaprinast. The cytosolic calcium/calmodulin stimulated cyclic AMP hydrolytic activity was inhibited by zaprinast (IC50 - calcium/calmodulin 123 +/- 39 microM; + calcium/calmodulin IC50 17.7 +/- 6.3 microM).5. The results indicate that guinea-pig peritoneal macrophages contain a type IV cyclic AMP PDE which is predominantly membrane associated and a predominantly cytosolic calcium/calmodulin stimulated cyclic AMP PDE. Functional studies suggest that both of these PDE activities contribute to cyclic AMP hydrolysis and regulation of superoxide generation in these cells. Inhibition of spontaneous superoxide generation, but not that stimulated by FMLP, suggests that the activity of PDE inhibitors is subject to functional antagonism but that this can be overcome by enhancing cyclic AMP formation.

Inhibition of eosinophil cyclic nucleotide PDE activity and opsonised zymosan-stimulated respiratory burst by 'type IV'-selective PDE inhibitors

1. The cyclic nucleotide phosphodiesterase (PDE) of guinea-pig eosinophils was partially characterized and the effects of selective inhibitors of PDE isoenzymes upon opsonized zymosan (OZ)-stimulated respiratory burst were studied. 2. PDE activity in eosinophil lysates appeared to be membrane-associated, displayed substrate specificity for adenosine 3':5' cyclic monophosphate (cyclic AMP) versus guanosine 3':5' cyclic monophosphate (cyclic GMP) and was insensitive to cyclic GMP or Ca2+ and calmodulin. 3. The non-selective PDE inhibitor, 3-isobutyl-1-methylxanthine caused a concentration-dependent inhibition of both OZ-stimulated hydrogen peroxide (H2O2) generation and cyclic AMP hydrolysis. The type IV-selective PDE inhibitors, rolipram and denbufylline, also inhibited H2O2 generation and cyclic AMP hydrolysis in a concentration-dependent manner whilst SK&F 94120 and Org 9935 (type III-selective) and zaprinast (type Ia or V-selective) were ineffective. 4. Dibutyryl cyclic AMP, a cell-permeable, non-hydrolysable analogue of cyclic AMP, caused a concentration-dependent inhibition of H2O2 generation stimulated by OZ. Dibutyryl cyclic GMP was ineffective. 5. It is concluded that eosinophil respiratory burst activity induced by OZ can be regulated by intracellular cyclic AMP and that the levels of cyclic AMP are controlled exclusively by a rolipram- and denbufylline-sensitive PDE isoenzyme that resembles a type IV species.