PDE5抑制剂与cGMP信号通路相关疾病的研究进展

磷酸二酯酶5(phosphodiesterase 5,PDE5)抑制剂通过阻断环磷酸鸟苷(cyclic guanosine monophos?phate,cGMP)的分解,使包括一氧化氮(nitric oxide, NO)在内的血管舒张介质作用延长,从而导致阴茎和肺的血管舒张.PDE5主要在阴茎海绵体和肺血管中发现,所...     

Evidence to suggest that the phosphodiesterase 4 isoenzyme is present and involved in the proliferation of umbilical cord blood mononuclear cells

BACKGROUND: The type 4 phosphodiesterase (PDE) isoenzyme is the main isoenzyme of PDE involved in the control of adult mononuclear cell proliferation. OBJECTIVE: To establish whether PDE isoenzymes are present in umbilical cord blood mononuclear cells by the use of selective PDE inhibitors, and to identify which PDE isoenzymes are involved in controlling the proliferation of cord blood mononuclear cells. METHODS: Cord blood was obtained from normal deliveries and mononuclear cells isolated as described previously [1] with some modifications. Mononuclear cells were then stimulated to proliferate with phytohaemagglutinin (PHA) (2 microg/mL) in the presence of selective PDE inhibitors. Proliferation was measured by [3H]-thymidine incorporation. RESULTS: The type 4 PDE inhibitors (CDP840, rolipram and RO 20-1724), and the mixed PDE3/4 inhibitor, zardaverine, produced a concentration-related inhibition of PHA-stimulated cord blood mononuclear cell proliferation (P < 0.05, ANOVA). The non-selective PDE inhibitor, theophylline, also produced a concentration-related inhibition of proliferation (P < 0.05, ANOVA). In contrast, the PDE1 inhibitor, vinpocetine, the PDE3 inhibitor, siguazodan, and the PDE5 inhibitor, zaprinast, were unable to inhibit cord blood mononuclear cell proliferation. CONCLUSION: PDE4 is present in umbilical cord mononuclear cells and is involved in the control of cord blood mononuclear cell proliferation.     

Selective type IV phosphodiesterase inhibitors prevent IL-4-induced IgE production by human peripheral blood mononuclear cells

Background Selective type IV phosphodiesterase (PDE) inhibitors elicit anti-inflammatory and bronchodilatory activities in vitro and in vivo which suggest that these drugs could provide a new therapeutic approach for asthma treatment. Objective Regarding the role of IgE production in allergic and inflammatory reactions of the airways, we investigated the effect of selective PDE inhibitors on IL-4-driven IgE production by peripheral blood mononuclear cells (PBMC) or by purified B lymphocytes. Methods PBMC or purified B lymphocytes from non-allergic donors were stimulated for 13 days with IL-4 (100U/mL) in the presence or in the absence of selective PDE inhibitors. IgE production is evaluated by an ELISA technique. Results The selective PDE IV inhibitors, rolipram and Ro 20–1724 (10μM), inhibit lL-4-induced IgE production by PBMC. but not by purified B lymphocytes. No modification of the IgE production was noted with the selective PDE III inhibitors, milrinone and SK&F94-836, or the selective PDE V inhibitor, SK&F 96–231 (10 μM). Flow cytometry experiments showed that the effect of Rolipram could not be explained by the inhibition of the cell surface expression of the IL-4 receptor. Similarly, no significant effect of PDE IV inhibitors was observed on PHA-induced cell proliferation. The incubation of monocytes only with rolipram was sufficient to achieve a significant reduction of IgE production induced by IL-4. Conclusion Taken together, these results indicate that PDE IV inhibitors reduce lL-4-induced IgE production by PBMC and suggest that the inhibition of IgE production could be explained by a failure of monocytes to provide the necessary costimulatory signals.     

Potential role of phosphodiesterase 7 in human T cell function: comparative effects of two phosphodiesterase inhibitors

Even though the existence of phosphodiesterase (PDE) 7 in T cells has been proved, the lack of a selective PDE7 inhibitor has confounded an accurate assessment of PDE7 function in such cells. In order to elucidate the role of PDE7 in human T cell function, the effects of two PDE inhibitors on PDE7A activity, cytokine synthesis, proliferation and CD25 expression of human peripheral blood mononuclear cells (PBMC) were determined. Recombinant human PDE7A was obtained and subjected to cyclic AMP-hydrolysis assay. PBMC of Dermatophagoides farinae mite extract (Df)-sensitive donors were stimulated with the relevant antigen or an anti-CD3 monoclonal antibody (MoAb). PBMC produced IL-5 and proliferated in response to stimulation with Df, while stimulation with anti-CD3 MoAb induced CD25 expression and messenger RNA (mRNA) synthesis of IL-2, IL-4 and IL-5 in peripheral T cells. A PDE inhibitor, T-2585, which suppressed PDE4 isoenzyme with high potency (IC50 = 0.00013 microM) and PDE7A with low potency (IC50 = 1.7 microM) inhibited cytokine synthesis, proliferation and CD25 expression in the dose range at which the drug suppressed PDE7A activity. A potent selective inhibitor of PDE4 (IC50 = 0.00031 microM), RP 73401, which did not effectively suppress PDE7A (IC50 > 10 microM), inhibited the Df- and anti-CD3 MoAb-stimulated responses only weakly, even at 10 microM. PDE7 may play a critical role in the regulation of human T cell function, and thereby selective PDE7 inhibitors have the potential to be used to treat immunological and inflammatory disorders.     

Phosphodiesterase Type 4 Inhibitors

Phosphodiesterases (PDEs) are involved in the regulation of intracellular levels of the second messengers cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). These enzymes hydrolyse the cyclic nucleotides to the corresponding nucleoside 5'-monophosphates. Nine PDE subtypes have been identified; these differ in their substrate specificity and mode of activation. The type 4 PDE (PDE(4)) hydrolyses cAMP, is activated by elevated levels of cAMP, and is inhibited by rolipram. Inhibition of enzyme activity has been shown to modulate the activity of cells of the immune system. The production of tumour necrosis factor (TNF)(alpha) by activated monocytes and macrophages is inhibited, and cytokine secretion and proliferation of type 1 T helper cells are suppressed. Both immune cell activation and their concomitant induction of cytokine secretion are implicated in multiple sclerosis (MS), which is the major demyelinating disease of the central nervous system. Studies with the selective PDE(4) inhibitor rolipram in experimental autoimmune encephalomyelitis (an animal model of MS) in mice, rats and nonhuman primates have demonstrated the efficacy of the compound in this disease model, suggesting that PDE(4) inhibitors could ameliorate the clinical course of MS. Unfortunately, clinical trials with PDE(4) inhibitors revealed the major adverse effects of these drugs, namely nausea and vomiting. However, novel PDE(4) inhibitors, which target only a subpopulation of PDE(4) enzymes, may provoke fewer adverse effects. The efficacy of a PDE(4) inhibitor in MS still needs to be demonstrated in a well designed clinical trial.     

Selective phosphodiesterase inhibitors for the treatment of bronchial asthma and chronic obstructive pulmonary disease

Theophylline is commonly used in the treatment of obstructive airway diseases. The identification and functional characterization of different phosphodiesterase (PDE) isoenzymes has led to the development of various isoenzyme-selective inhibitors as potential anti-asthma drugs. Considering the distribution of isoenzymes in target tissues, with high activity of PDE3 and PDE4 in airway smooth muscle and inflammatory cells, selective inhibitors of these isoenzymes may add to the therapy of chronic airflow obstruction. However, initial data from clinical trials with selective PDE3 and PDE4 inhibitors have been somewhat disappointing and have tempered the expectations considerably since these drugs had limited efficacy and their use was clinically limited through side effects. The improved understanding of the molecular biology of PDEs enabled the synthesis of novel drugs with an improved risk/benefit ratio. These 'second generation' selective drugs have produced more promising clinical results not only for the treatment of bronchial asthma but also for the treatment of chronic obstructive pulmonary disease.     

Cyclic nucleotides differentially regulate the synthesis of tumour necrosis factor-alpha and interleukin-1 beta by human mononuclear cells.

Recent reports have shown that phosphodiesterase (PDE) inhibitors suppress production of tumour necrosis factor-alpha (TNF-alpha) in mouse macrophages. In the present study we show that theophylline, pentoxifylline and 3-isobutyl-1-methylxanthine markedly suppress the lipopolysaccharide (LPS)-induced synthesis of TNF-alpha (also) in human mononuclear cells. This effect is selective for TNF-alpha since up to several-fold higher concentrations of these PDE inhibitors do not affect production of interleukin-1 beta (IL-1 beta) in the same system. The observed effect of PDE inhibitors appears to be mediated by accumulation of cAMP since (i) addition of PDE inhibitors increases cAMP while cGMP levels are only marginally elevated; (ii) raising cAMP by another mechanism (enhanced formation induced by prostaglandin E2; PGE2) leads to a similar suppression of TNF-alpha production; and (iii) raising cGMP by activating the soluble guanylate cyclase by 3-morpholinosydnonimine (SIN 1) does not inhibit TNF-alpha synthesis. However, SIN 1 suppressed the synthesis of IL-1 beta. Selective suppression of TNF-alpha synthesis by PDE inhibitors may contribute to their beneficial effects in animal models of septic shock or lung injury and may thus have clinical implications.     

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.     

Milrinone, a phosphodiesterase III inhibitor, antagonizes the neuromuscular blocking effect of a non-depolarizing muscle relaxant in vitro

Phosphodiesterase (PDE) inhibitors are occasionally used in patients receiving non-depolarizing muscle relaxants during anesthesia and intensive care. However, little is known about the influence of PDE III inhibitors on the effects of non-depolarizing muscle relaxants. The aim of this study was to elucidate the effects of milrinone, a PDE III inhibitor, on d-tubocurarine (dTc)-induced muscle relaxation in vitro and then to compare its effects with those of other activators of the adenylate cyclase (AC) system (aminophylline, a non-selective PDE inhibitor; forskolin, a direct AC activator; and isoproterenol, a beta-adrenoceptor agonist). Isometric twitch tensions of rat nerve-hemidiaphragm preparations elicited by indirect or direct stimulation (0.1 Hz) were measured. Indirectly elicited twitch tension partially depressed by dTc (1 microM) was antagonized by milrinone, aminophylline, and forskolin but was attenuated by isoproterenol. Directly elicited twitch tension was increased by aminophylline, forskolin, and isoproterenol but was not altered by milrinone. The results indicate that milrinone antagonizes dTc-induced muscle relaxation by recovering the neuromuscular transmission. It is noteworthy that PDE inhibitors and a beta-adrenergic agonist affect non-depolarizing muscle relaxation in opposite direction.     

The role of phosphodiesterase isoforms 2, 5, and 9 in the regulation of NO-dependent and NO-independent cGMP production in the rat cervical spinal cord

NO-responsive, cGMP-producing structures are abundantly present in the cervical spinal cord. NO-mediated cGMP synthesis has been implicated in nociceptive signaling and it has been demonstrated that cGMP has a role establishing synaptic connections in the spinal cord during development. As cGMP levels are controlled by the activity of soluble guanylyl cyclase (synthesis) and the phosphodiesterase (PDE) activity (breakdown), we studied the influence of PDE activity on NO-stimulated cGMP levels in the rat cervical spinal cord.

cGMP-immunoreactivity (cGMP-IR) was localized in sections prepared from slices incubated in vitro. A number of reported PDE isoform-selective PDE inhibitors was studied in combination with diethylamineNONOate (DEANO) as a NO-donor including isobutyl-methylxanthine (IBMX) as a non-selective PDE inhibitor. We studied 8-methoxy-IBMX as a selective PDE1 inhibitor, erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) and BAY 60-7550 as selective PDE2 inhibitors, sildenafil as a selective PDE5 inhibitor, dipyridamole as a mixed type PDE5 and PDE10 inhibitor, rolipram as a PDE4 inhibitor, and SCH 81566 as a selective PDE9 inhibitor. cGMP-IR structures (nerve fibers, axons, and terminals) were characterized using the following neurochemical markers: vesicular transporter molecules for acetylcholine, GABA, and glutamate (type 1 and type 2), parvalbumin, glutamate transporter molecule EAAT3, synaptophysin, substance P, calcitonin gene-related peptide, and isolectin B4. Most intense cGMP-IR was observed in the dorsal lamina. Ventral motor neurons were devoid of cGMP-IR. cGMP-IR was observed in GABAergic, and glutamatergic terminals in all gray matter laminae. cGMP-IR was abundantly colocalized with anti-vesicular glutamate transporter 2 (vGLUT2), however not with the anti-vesicular glutamate transporter 1 (vGLUT1), suggesting a functional difference between structures expressing vGLUT1 or vGLUT2. cGMP-IR did not colocalize with substance P- or calcitonin-gene related peptide-IR structures, however did partially colocalize with isolectin B4 in the dorsal horn. cGMP-IR in cholinergic structures was observed in dorsal root fibers entering the spinal cord, occasionally in laminae 1–3, in laminae 8 and 9 in isolated boutons and in the C-type terminals, and in small cells and varicosities in lamina 10. This latter observation suggests that the proprioceptive interneurons arising in lamina 10 are also NO-responsive.

No region-specific nor a constant co-expression of cGMP-IR with various neuronal markers was observed after incubation of the slices with one of the selected PDE inhibitors. Expression of the mRNA of PDE2, 5, and 9 was observed in all lamina. The ventral motor neurons and the ependymal cells lining the central canal expressed all three PDE isoforms.

Incubation of the slices in the presence of IBMX, DEANO in combination with BAY 41-2272, a NO-independent activator of soluble guanylyl cyclase, provided evidence for endogenous NO synthesis in the slice preparations and enhanced cGMP-IR in all lamina. Under these conditions cGMP-IR colocalized with substance P in a subpopulation of substance P-IR fibers.

It is concluded that NO functions as a retrograde neurotransmitter in the spinal cord but that also postsynaptic structures are NO-responsive by producing cGMP. cGMP-IR in a subpopulation of isolectin B4 positive fibers and boutons is indicative for a role of NO-cGMP signaling in nociceptive processing. cGMP levels in the spinal cord are controlled by the concerted action of a number of PDE isoforms, which can be present in the same cell.     

Effects of cyclooxygenase inhibition on bone, tendon, and ligament healing

Cyclooxygenases (COX-1 and COX-2) catalyze the conversion of arachidonic acid to prostaglandins (PGs). PGs play a significant role in bone metabolism in health and disease. Conventional non-selective, non-steroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 inhibitors (COXIBs) are widely used in patients with musculoskeletal conditions and as a post-surgical analgesics. Due to their effects on PG synthesis, these drugs have been hypothesized to affect the healing process of bone fractures and orthopedic surgical sites. A variety of experimental models of bone, ligament, and tendon repair have assessed the effects of these selective and non-selective COX inhibitors in animals, but with variable outcomes. At this time, large-scale, robust clinical study data do not exist, limiting the relevant assessment of experimental animal data to humans. Here, we provide a critical review of available data on the role of PGs and the effect of COX inhibitors on bone, tendon, and ligament repair. Collectively, this assessment suggests potential involvement of PGs in the healing process of these tissues via modulation by non-selective NSAIDs and selective COX-2 inhibitors. Received 25 April 2005; returned for revision 9 June 2005; accepted by G. Geisslinger 10 June 2005     

Effects of selective phosphodiesterase inhibitors on the polymorphonuclear leukocyte respiratory burst

Modulation of the human polymorphonuclear leukocyte (PMN) respiratory burst by selective cyclic 3',5' adenosine monophosphate (cAMP) phosphodiesterase (PDE) inhibitors was studied with respect to PDE isozyme characteristics. Zaprinast, an inhibitor of a cyclic guanosine monophosphate (cGMP)-specific PDE (PDE I), at concentrations up to 100 mumol/L, had no significant effect on the respiratory burst. Milrinone and imazodan, inhibitors of cAMP-metabolizing, cGMP-sensitive PDE (PDE III), reduced the respiratory burst to 60% of control magnitude but only had significant effects when they were introduced at high (100 mumol/L) concentrations. In contrast, rolipram and RO 20-1724, inhibitors of a cAMP-metabolizing, cGMP-insensitive PDE (PDE IV), had significant effects at low concentrations (0.1 mumol/L) and caused marked reduction of the respiratory burst at higher concentrations (25% of control at 10 mumol/L). The selective PDE IV inhibitors significantly potentiated PMN inhibition by isoproterenol. Diethylaminoethyl (DEAE)-Sepharose chromatography demonstrated a predominant PDE isozyme with high affinity and selectivity for cAMP that was insensitive to cGMP and was completely inhibited by rolipram, a PDE IV inhibitor. These results are consistent with the conclusion that the PMN respiratory burst is inhibited by an elevation of cAMP induced by PDE IV inhibition.     

PDE4 inhibitors attenuate fibroblast chemotaxis and contraction of native collagen gels

Therapies that mitigate the fibrotic process may be able to slow progressive loss of function in many lung diseases. Because cyclic adenosine monophosphate is known to regulate fibroblasts, the current study was designed to evaluate the activity of selective phosphodiesterase (PDE) inhibitors on two in vitro fibroblast responses: chemotaxis and contraction of three-dimensional collagen gels. Selective PDE4 inhibitors, rolipram and cilomilast, each inhibited the chemotaxis of human fetal lung fibroblasts (HFL-1) toward fibronectin in the blindwell assay system (control: 100% versus cilomilast [10 microM]: 40.5 +/- 7.3% versus rolipram: [10 microM] 32.1 +/- 2.7% cells/5 high-power fields; P < 0.05, both comparisons). These PDE4 inhibitors also inhibited contraction of three-dimensional collagen gels (control: 100% versus cilomilast: 167.7 +/- 6.9% versus rolipram: 129.9 +/- 1.9% of initial size; P < 0.05, both comparisons). Amrinone, a PDE3 inhibitor, and zaprinast, a PDE5 inhibitor, had no effect in either system. Prostaglandin E(2) (PGE(2)) inhibited both chemotaxis and gel contraction, and the PDE4 inhibitors shifted the PGE(2) concentration-dependence curve to the left in both systems. The inhibition of endogenous PGE(2) production by indomethacin diminished the effects of the PDE4 inhibitors in both chemotaxis and gel contraction, consistent with the concept that the PDE4 inhibitory effects on fibroblasts are related to the presence of cyclic adenosine monophosphate in the cells. In summary, these in vitro results suggest that PDE4 inhibitors may be able to suppress fibroblast activity and, thus, have the potential to block the development of progressive fibrosis.     

Effects of the 3′,5′-phosphodiesterase inhibitors isobutylmethylxanthine and zaprinast on NO-mediated cGMP accumulation in the hippocampus slice preparation: an immunocytochemical study

The effect of inhibition of 3′,5′-phosphodiesterase (PDE) activity on the cGMP accumulation was studied in control and nitric oxide (NO) stimulated hippocampal slices incubated in vitro using immunohistochemical visualisation of cGMP. Isobutylmethylxanthine (IBMX) was used as a non-selective PDE inhibitor and zaprinast was used as a selective inhibitor of CGMP-specific PDE activity. In the absence of PDE inhibitors cGMP-immunoreactivity (cGMP-IR) was found in blood vessel walls only. After incubation with the NO-donor sodium nitroprusside (SNP) cGMP-IR was found in a few isolated varicose fibres which were distributed throughout the slice. Incubation in the presence of either 1 mM IBMX or 10 μM zaprinast resulted in cGMP-IR in small numbers of varicose fibres distributed throughout the hippocampal slice. SNP in combination with IBMX resulted in cGMP-IR in a multitude of varicose fibres throughout the slice; occasionally cell somata were observed. After incubation with SNP and zaprinast cGMP-IR was found in varicose fibres, although with a more restricted distribution and less numerous than in the presence of IBMX. In the latter combination, varicose fibres were observed predominantly in the CA2/CA3 region and in the stratum lacunosum moleculare of the hippocampus, and cell somata were occasionally observed throughout the hippocampus. The differential distribution of cGMP-IR in the presence of different PDE inhibitors is consistent with the notion that there are regional differences in the localization of cGMP hydrolyzing enzymes in the hippocampus.     

The analysis of nonsteroidal antiinflammatory drug selectivity in prostaglandin G/H synthase (PGHS)-null cells

OBJECTIVES: Nonsteroidal antiinflammatory drugs (NSAIDs) that are more selective for PGHS-2 maintain their antiinflammatory properties but exhibit fewer unfavorable gastrointestinal side effects. To evaluate the usefulness of the murine PGHS-null cell system in analyzing PGHS-2 selective inhibitors, we tested PGHS-2 non-selective NSAIDs and two PGHS-2 specific compounds using either endogenous or exogenous sources of substrate, arachidonic acid. MATERIALS AND METHODS: A whole-cell assay system for testing the efficacy of PGHS isozyme-specific inhibitors using murine PGHS-1 or PGHS-2-null fibroblast cell lines derived from lung tissues of PGHS-2(-/-) and PGHS-(-/-) mice, respectively, was employed. PGHS-1 and PGHS-2 null cell lines were exposed to three widely used NSAIDs, ibuprofen, indomethacin and aspirin, and two PGHS-2 specific inhibitors, MK-966 (rofecoxib) and NS-398. Excess arachidonic acid (AA) was provided externally and internally via calcium ionophore A23187. PGHS-1 and PGHS-2 activity were determined by measuring the prostaglandin E2 production by radioimmunoassay. IC50 and IC80 values of each compound were determined from the reduction of PGE2 levels as a measure of inhibition of existing PGHS isozyme in the PGHS-null cells. RESULTS: In our murine PGHS-null cell systems, both PGHS-1 and PGHS-2 null cells can use both externally provided AA and endogenous, A23187-derived AA. Both NS-398 and MK-966 were potent inhibitors and demonstrated strong selectivity for PGHS-2. Among the non-selective NSAIDs, based on the PGHS-2 IC50/PGHS-1 IC50 ratio ranking, ibuprofen is more selective for PGHS-2 than indomethacin while aspirin is the least selective inhibitor regardless of the arachidonic acid source. Indomethacin and MK-966 IC50 values for PGHS-2 were in the range of 10(-9)-10(-8) M while the IC50 values for aspirin were in the range of 10(-5) M. There were differences in the ranking of indomethacin and ibuprofen when the IC80 ratios were used. CONCLUSION: Here, we report on a whole cell assay system for testing the efficacy of PGHS isozyme-specific inhibitors using murine PGHS-1 or PGHS-2-null cell lines. This system, using cells that express either PGHS-1 or PGHS-2, offers a convenient and reliable method to determine IC50 and IC80 values of the two PGHS isoforms, entirely independent of each other, in the same cell type. The results of our evaluation using a panel of NSAIDs, both PGHS-2 selective and non-selective inhibitors, correlate well with previously published clinical and laboratory data, demonstrating the usefulness of the whole-cell assay system described here.     

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 intraceliular cAMP by PDE inhibitors is known to suppress macrophage and monocyte functions. A comparison of the PDE-isoenzyine 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 IIF-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.     

Evidence against a role of cyclic nucleotides in the regulation of anaphylactic histamine release in isolated rat mast cells

The effect of different phosphodiesterase (PDE) inhibitors on the antigen or 48/80 induced histamine release from isolated Hooded Lister rat mast cells was tested. The unselective PDE inhibitors theophylline (2.5 mM) and IBMX (0.2 mM) and the selective cyclic GMP PDE inhibitor M & B 22948 (0.1 mM) inhibited the antigen induced histamine release by 50% while 48/80 induced release was inhibited by about 25%. The cyclic AMP selective PDE inhibitors ICI 63197 (0.5 mM) or Ro 20-1724 (0.2 mM) had no effect on 48/80 induced histamine release but tended to enhance antigen induced release. There was no correlation between the measured levels of cyclic AMP and the effect on histamine release by the investigated PDE inhibitors. Cyclic AMP or cyclic GMP up to 10(-3) M did not affect the anaphylactic histamine release. Dibutyryl-cAMP and dibutyryl-cGMP (10(-4) M) both inhibited the release about 20% but this effect could be explained by the effect of butyric acid as sodium butyrate (2 X 10(-4) M) also inhibited the release by 20%. The presence results suggest that cyclic nucleotides are not important regulators of histamine release from isolated mast cells.     

Enhanced tumor necrosis factor suppression and cyclic adenosine monophosphate accumulation by combination of phosphodiesterase inhibitors and prostanoids

We investigated cooperative effects of phosphodiesterase (PDE) inhibitors and prostanoids on cyclic adenosine monophosphate (cAMP) accumulation and tumor necrosis factor (TNF)-α synthesis in human peripheral blood mononuclear cells (PBMC). PDE inhibitors alone induced only a small increase in cAMP levels in lipopolysaccharide (LPS)-stimulated PBMC. Cicaprost (a stable analogue of prostacyclin) and pentoxifylline added simultaneously to LPS-stimulated PBMC (2.0 × 10⁶/ml) induced a rapid increase of cAMP to a level of 100 nM that peaked within 10 min and remained at a plateau for up to 4 h. Thus combined prostanoids and PDE inhibitors enhanced cAMP accumulation. TNF-α suppression in the presence of pentoxifylline and prostanoids exceeded that of either drug alone. The potency of different PDE inhibitors (theophylline, pentoxifylline, penthy-droxifylline, albifylline, torbafylline, A 802715, amrinone and rolipram) to increase cAMP levels in combination with cicaprost was evaluated after 1 h of incubation. The dose-dependent increase of cAMP for all PDE inhibitors tested in this combined stimulation provided a useful tool for evaluating the potency of PDE inhibitors on cAMP accumulation. The effective concentration of PDE inhibitors, which raised cAMP levels to 300% of control, (EC³⁰⁰), correlated with the IC₅₀ for TNF-α suppression (r = 0.930, p = 0.007, with theophylline excluded from the analysis). Interestingly, by contrast, the specific type IV PDE inhibitor rolipram caused only a moderate rise of accumulated cAMP in the same cells. Our data support cAMP as an essential mediator for TNF-α suppression by PDE inhibitors. Furthermore, an enhanced inhibiting effect on TNF-α production may prove therapeutically advantageous. It may occur in inflammatory and infectious diseases in vivo, since high levels of endogenous prostaglandins are liberated in these conditions.     

Are phosphodiesterase 4 inhibitors just more theophylline?

Theophylline has been relegated to a second- or even third-line therapy in the treatment of asthma and chronic obstructive pulmonary disease (COPD), behind glucocorticosteroids and beta2-agonists, although recent findings have suggested that theophylline possesses anti-inflammatory and immunomodulatory effects in addition to its well-recognized effects as a bronchodilator. In part, theophylline has fallen out of favor because of its adverse side-effect profile, and this has led to the search for more effective and safer drugs based on the knowledge that theophylline is orally active and that it is a nonselective phosphodiesterase (PDE) inhibitor. This has led to the development of selective PDE4 inhibitors, originally designed for depression, for the treatment of both COPD and asthma. Such drugs have shown clinical efficacy in the treatment of respiratory disease while having a considerably safer side-effect profile in comparison with theophylline, particularly because there are no reported drug interactions with PDE4 inhibitors, a feature that complicates the use of theophylline. In addition, it is also becoming increasingly apparent that theophylline is not working solely through PDE inhibition, as formerly assumed, and that this drug has other relevant pharmacologic activities that are likely to contribute to its efficacy, such as adenosine receptor antagonism and induction of histone deacetylase. Thus, the introduction of PDE4 inhibitors represents an entirely new class of drugs for the treatment of respiratory disease.