Differential effects of PDE4 inhibitors on cortical neurons and T-lymphocytes

Comparison of the Pharmacological Profiles of Selective PDE4B and PDE4D Inhibitors in the Central Nervous System

Inhibition of cyclic AMP (cAMP)-specific phosphodiesterase 4 (PDE4) has been proposed as a potential treatment for a series of neuropsychological conditions such as depression, anxiety and memory loss. However, the specific involvement of each of the PDE4 subtypes (PDE4A, 4B and 4C) in different categories of behavior has yet to be elucidated. In the present study, we compared the possible pharmacological effects of PDE4B and PDE4D selective inhibitors, A-33 and D159687, in mediating neurological function in mice. Both compounds were equally potent in stimulating cAMP signaling in the mouse hippocampal cell line HT-22 leading to an increase in CREB phosphorylation. In contrast, A-33 and D159687 displayed distinct neuropharmacological effects in mouse behavioral tests. A-33 has an antidepressant-like profile as indicated by reduced immobility time in the forced swim and tail suspension tasks, as well as reduced latency to feed in the novelty suppressed feeding test. D159687, on the other hand, had a procognitive profile as it improved memory in the novel object recognition test but had no antidepressant or anxiolytic benefit. The present data suggests that inhibitors targeting specific subtypes of PDE4 may exhibit differential pharmacological effects and aid a more efficient pharmacotherapy towards neuropsychological conditions.

Characterization of the cellular activity of PDE 4 inhibitors using two novel PDE 4 reporter cell lines

We report here the generation and pharmacological characterization of two novel PDE 4B1 and PDE 4D3 reporter cell lines. Intracellular cAMP levels are monitored in these cells by a cAMP-sensitive biosensor. We used the recombinant PDE 4B1 and PDE 4D3 reporter cell lines to characterize the cellular effects of various competitive and allosteric PDE 4 inhibitors. In addition, we compared the cellular activity of these PDE 4 inhibitors with the in vitro inhibition of full-length PDE 4D3 and a truncated enzyme comprising the PDE 4D3 catalytic domain. Two different groups of PDE 4 inhibitors could be identified. The first group, including competitive inhibitors like roflumilast, cilomilast and piclamilast, shows similar in vitro activity on full-length and truncated PDE 4D3 and comparably low cellular activity. The second group, including the allosteric inhibitors PMNPQ, D159153, and D159404, shows much better inhibition of full-length versus truncated PDE 4D3. In addition, these compounds show high cellular activity. Our data obtained with the prototype PDE 4 inhibitor rolipram show that rolipram has properties intermediate between the two groups. The results imply that these novel PDE 4 reporter cell lines are well-suited for the characterization of the cellular activity of PDE 4 inhibitors and may also support a better understanding of the complex PDE 4 pharmacology.

Role of yessotoxin in calcium and cAMP-crosstalks in primary and K-562 human lymphocytes: the effect is mediated by anchor kinase A mitochondrial proteins

Yessotoxin (YTX) is a marine polyether toxin previously described as a phosphodiesterase (PDE) activator in fresh human lymphocytes. This toxin induces a decrease of adenosine 3',5'-cyclic monophosphate (cAMP) levels in fresh human lymphocytes in a medium with calcium (Ca(2+) ), whereas the contrary effect has been observed in a Ca(2+) -free medium. In the present article, the effect of YTX in K-562 lymphocytes cell line has been analysed. Surprisingly, results obtained in K-562 cell line are completely opposite than in fresh human lymphocytes, since in K-562 cells YTX induces an increase of cAMP levels. YTX cytotoxicity was also studied in both K-562 cell line and fresh human lymphocytes. Results demonstrate that YTX does not modify fresh human lymphocytes viability, whereas in K-562 cells, YTX has a highly cytotoxic effect. It has been described in a previous study that YTX induces a small cytosolic Ca(2+) increase in fresh human lymphocytes but no effect was observed on Ca(2+) pools depletion in these cells. However, our results show that, in K-562 cells, YTX has no effect on cytosolic Ca(2+) levels in a medium with Ca(2+) and induces an increase on Ca(2+) pools depletion followed by a Ca(2+) influx. As far as Ca(2+) modulation is concerned these results demonstrate that YTX has a clear opposite effect in tumoural and fresh human lymphocytes. In addition, intracellular Ca(2+) reservoirs affected by YTX are different than thapsigargin-sensible pools. Furthermore, YTX-dependent Ca(2+) pools depletion was abolished by cAMP analogue (dibutyryl cAMP), phosphodiesterase-4 (PDE4) inhibitor (rolipram), protein kinase A inhibitor (H89) and oxidative phosphorylation uncoupler carbonyl cyanide p-(trifluoromethoxy) (FCCP) treatments. This evidences the crosstalks between Ca(2+) , YTX and cAMP pathways. Also, results obtain demonstrate that YTX-dependent Ca(2+) influx was only abolished by FCCP pre-treatment, which indicates a link between YTX and mitochondria in K-562 cell line. Cytosolic expression of A-kinase anchor proteins (AKAPs), the proteins which integrates phosphodiesterases (PDEs) and PKA to the mitochondria, was determined in both cell models. On the one hand, in human fresh lymphocytes, YTX increases AKAP149 cytosolic expression. This fact is accompanied with a decrease in cAMP levels, and therefore PDEs activation, which finally leads to cell survival. On the other hand, in tumoural lymphocytes, YTX has an opposite effect since decreases AKAP149 cytosolic expression and increase cAMP levels which leads to cell death. This is the first time that YTX and mitochondrial AKAPs proteins relationship is characterised.

PDE4: a novel target in the treatment of chronic obstructive pulmonary disease

Phosphodiesterases (PDEs) are important modulators of inflammation and wound healing. In this capacity, specific targeting of PDEs for the treatment of many diseases, including chronic obstructive pulmonary disease (COPD), has been investigated. Currently, treatment of COPD is suboptimal. PDE4 modulates the inflammatory response of the lung, and inhibition of PDE4 may be a novel, COPD-specific approach toward more effective treatment strategies. This review describes the state of PDE4-inhibitor therapy for use in COPD treatment.

GSK256066, an exceptionally high-affinity and selective inhibitor of phosphodiesterase 4 suitable for administration by inhalation: in vitro, kinetic, and in vivo characterization

Oral phosphodiesterase (PDE) 4 inhibitors such as roflumilast have established the potential of PDE4 inhibition for the treatment of respiratory diseases. However, PDE4 inhibitor efficacy is limited by mechanism-related side effects such as emesis and nausea. Delivering the inhibitor by the inhaled route may improve therapeutic index, and we describe 6-({3-[(dimethylamino)carbonyl]phenyl}sulfonyl)-8-methyl-4-{[3-methyloxy) phenyl]amino}-3-quinolinecarboxamide (GSK256066), an exceptionally high-affinity inhibitor of PDE4 designed for inhaled administration. GSK256066 is a slow and tight binding inhibitor of PDE4B (apparent IC(50) 3.2 pM; steady-state IC(50) <0.5 pM), which is more potent than any previously documented compound, for example, roflumilast (IC(50) 390 pM), tofimilast (IC(50) 1.6 nM), and cilomilast (IC(50) 74 nM). Consistent with this, GSK256066 inhibited tumor necrosis factor α production by lipopolysaccharide (LPS)-stimulated human peripheral blood monocytes with 0.01 nM IC(50) (compared with IC(50) values of 5, 22, and 389 nM for roflumilast, tofimilast, and cilomilast, respectively) and by LPS-stimulated whole blood with 126 pM IC(50). GSK256066 was highly selective for PDE4 (>380,000-fold versus PDE1, PDE2, PDE3, PDE5, and PDE6 and >2500-fold against PDE7), inhibited PDE4 isoforms A-D with equal affinity, and had a substantial high-affinity rolipram binding site ratio (>17). When administered intratracheally to rats, GSK256066 inhibited LPS-induced pulmonary neutrophilia with ED(50) values of 1.1 μg/kg (aqueous suspension) and 2.9 μg/kg (dry powder formulation) and was more potent than an aqueous suspension of the corticosteroid fluticasone propionate (ED(50) 9.3 μg/kg). Thus, GSK256066 has been demonstrated to have exceptional potency in vitro and in vivo and is being clinically investigated as a treatment for chronic obstructive pulmonary disease.

Cyclic adenosine monophosphate (cAMP)-specific phosphodiesterase is functional in bovine mammary gland

Previous studies have shown that using nonspecific phosphodiesterase (PDE) inhibitors such as caffeine improved milk production, supporting the premise that modulation of intracellular concentration of cyclic nucleotides (cyclic AMP, cyclic guanosine 3'-5'-monophosphate) is involved. Intracellular cyclic nucleotides are degraded by the PDE enzyme family. The contribution of type IV PDE (PDE4) in the secretion of casein has been reported in rat mammary gland. The objective of this study was to demonstrate the functional presence of the PDE4 family in the bovine mammary gland. To understand the enzymatic expression pattern in the mammary gland, tissue samples were taken randomly from udders obtained from a local slaughterhouse. Reverse transcription PCR revealed that the PDE4D transcript was amplified, and the expected size fragment was obtained in a 1% agarose gel. Sequence analysis of the amplicon resulted in 99% homology to PDE4D. Moreover, Western blotting using a specific PDE4D antibody has confirmed that the protein of the isoenzyme PDE4D1 is present. A clear immunoreactive signal was also observed within the acini where epithelial cells are located. Assaying cyclic AMP PDE activity reported a total activity of 38.71 +/- 3.22 fmol/min per microg of total protein. Rolipram, a specific PDE4 inhibitor, showed a sensitive activity of 8.48 +/- 1.28 fmol/min per microg of total protein, indicating that PDE4 is responsible for one-fifth of the total enzymatic activity of PDE in the mammary gland. To further validate the presence of PDE4D in the bovine mammary epithelial cells, protein extracts from bovine mammary epithelial cells were separated on SDS-PAGE gels, and PDE4D protein was detected. The PDE assays reported a total activity of 30.16 +/- 4.82 fmol/min per microg of total protein. Rolipram showed a sensible activity of 11.91 +/- 5.93 fmol/min per microg of total protein. In conclusion, these results not only demonstrate the presence of PDE4D transcript and protein, but also show an active enzyme, suggesting a functional role of PDE4D in bovine mammary gland.