Rolipram, a phosphodiesterase 4 inhibitor, stimulates inducible cAMP early repressor expression in osteoblasts

Oral dosing of pentoxifylline, a pan-phosphodiesterase inhibitor restores bone mass and quality in osteopenic rabbits by an osteogenic mechanism: A comparative study with human parathyroid hormone

The non-selective phosphodiesterase inhibitor pentoxifylline (PTX) is used for the treatment of intermittent claudication due to artery occlusion. Previous studies in rodents have reported salutary effects of the intraperitoneal administration of PTX in segmental bone defect and fracture healing, as well as stimulation of bone formation. We determined the effect of orally dosed PTX in skeletally mature ovariectomized (OVX) rabbits with osteopenia. The half-maximal effective concentration (EC₅₀) of PTX in rabbit bone marrow stromal cells was 3.07 ± 1.37 nM. The plasma PTX level was 2.05 ± 0.522 nM after a single oral dose of 12.5mg/kg, which was one-sixth of the adult human dose of PTX. Four months of daily oral dosing of PTX at 12.5 mg/kg to osteopenic rabbits completely restored bone mineral density, bone mineral content (BMC), microarchitecture and bone strength to the level of the sham-operated (ovary intact) group. The bone strength to BMC relationship between PTX and sham was similar. The bone restorative effect of PTX was observed in both axial and appendicular bones. In osteopenic rabbits, PTX increased serum amino-terminal propeptide, mineralized nodule formation by stromal cells and osteogenic gene expression in bone. PTX reversed decreased calcium weight percentage and poor crystal packing found in osteopenic rabbits. Furthermore, similar to parathyroid hormone (PTH), PTX had no effect on bone resorption. Taken together, our data show that PTX completely restored bone mass, bone strength and bone mineral properties by an anabolic mechanism. PTX has the potential to become an oral osteogenic drug for the treatment of post-menopausal osteoporosis.

Selective inhibitors of phosphodiesterases: therapeutic promise for neurodegenerative disorders

PDE inhibitors: significant contributors to the treatment of neurodegenerative diseases.

NCS 613 exhibits anti-inflammatory effects on PBMCs from lupus patients by inhibiting p38 MAPK and NF-κB signalling pathways while reducing proinflammatory cytokine production

Systemic lupus erythematosus (SLE) is a polymorphic and multigenic autoimmune disease that evolves into progressive and chronic inflammation of multiple joints and organs. Phosphorylation and activation of p38 MAPK, along with the resulting overproduction of interleukin (IL)-1β, IL-6, and tumour necrosis factor (TNF)-α is a hallmark of inflammatory disorders. Here, we investigated the anti-inflammatory pathway modulated by NCS 613, a specific PDE4 inhibitor, on human peripheral blood mononuclear cells (PBMCs) from 5 healthy donors and 12 SLE patients. PDE4 subtypes, p38 MAPK, and IκBα protein levels were analyzed by Western blot, while NF-κB and PDE4B immunostaining was assessed in control and lipopolysaccharide (LPS) -pretreated PBMCs. Proinflammatory cytokines were quantified by ELISA, while IL-1β mRNA was resolved by RT-qPCR. NCS 613 treatment decreased PDE4B and upregulated PDE4C in human PBMCs from healthy donors and SLE patients. LPS stimulation increased p38 MAPK phosphorylation and NF-κB translocation to the nucleus, which was abolished by NCS 613 treatment. Concomitantly, NCS 613 restored IκBα detection levels in human PBMCs from both healthy donors and SLE patients. This compound also abolished LPS-induced inflammation in PBMCs by reducing IL-6, IL-8, and TNF-α cytokines. NCS 613 is a small molecule displaying anti-inflammatory properties that may provide an alternative or complementary strategy for SLE management.

Cyclic nucleotide phosphodiesterase (PDE) isozymes as targets of the intracellular signalling network: benefits of PDE inhibitors in various diseases and perspectives for future therapeutic developments

Cyclic nucleotide phosphodiesterases (PDEs) that specifically inactivate the intracellular messengers cAMP and cGMP in a compartmentalized manner represent an important enzyme class constituted by 11 gene-related families of isozymes (PDE1 to PDE11). Downstream receptors, PDEs play a major role in controlling the signalosome at various levels of phosphorylations and protein/protein interactions. Due to the multiplicity of isozymes, their various intracellular regulations and their different cellular and subcellular distributions, PDEs represent interesting targets in intracellular pathways. Therefore, the investigation of PDE isozyme alterations related to various pathologies and the design of specific PDE inhibitors might lead to the development of new specific therapeutic strategies in numerous pathologies. This manuscript (i) overviews the different PDEs including their endogenous regulations and their specific inhibitors; (ii) analyses the intracellular implications of PDEs in regulating signalling cascades in pathogenesis, exemplified by two diseases affecting cell cycle and proliferation; and (iii) discusses perspectives for future therapeutic developments.

NCS 613, a potent and specific PDE4 inhibitor, displays anti-inflammatory effects on human lung tissues

Chronic inflammation is a hallmark of pulmonary diseases, which leads to lung parenchyma destruction (emphysema) and obstructive bronchiolitis occurring in both chronic obstructive pulmonary disease and asthma. Inflammation is strongly correlated with low intracellular cAMP levels and increase in specific cAMP hydrolyzing activity. The aim of the present study was to investigate the role of the cyclic phosphodiesterase type 4 (PDE4) in human lung and to determine the effects of NCS 613, a new PDE4 inhibitor, on lung inflammation and bronchial hyperresponsiveness. High cAMP-PDE activities were found in the cytosoluble fractions from human lung parenchyma and distal bronchi. PDE4 (rolipram sensitive) represented 40% and 56% of total cAMP-PDE activities in the above-corresponding tissues. Moreover, PDE4A, PDE4B, PDE4C, and PDE4D isoforms were detected in all three subcellular fractions (cytosolic, microsomal, and nuclear) with differential distributions according to specific variants. Pharmacological treatments with NCS 613 significantly decreased PDE4 activity and reduced IκBα degradation in cultured parenchyma, both of which are usually correlated with a lower inflammation status. Moreover, NCS 613 pretreatment potentiated isoproterenol-induced relaxations in human distal bronchi, while reducing TNF-α-induced hyperresponsiveness in cultured bronchi, as assessed in the presence of methacholine, U-46619, or histamine. This reducing effect of NCS 613 on human bronchi hyperresponsiveness triggered by TNF-α was related to a lower expression level of PDE4B and PDE4C, as well as a downregulation of the phosphorylated forms of p38-MAPK, CPI-17, and MYPT-1, which are known to control tone. In conclusion, specific PDE4 inhibitors, such as NCS 613, may represent an alternative and isoform-specific approach toward reducing human lung inflammation and airway overreactivity.

Synthesis and biological evaluation of novel phthalazinone derivatives as topically active phosphodiesterase 4 inhibitors

Inhibitors of phosphodiesterase 4 (PDE4) are an important class of anti-inflammatory drug that act by inhibiting the production of proinflammatory cytokines, including tumor necrosis factor-alpha (TNF-alpha). We have synthesized and evaluated a series of 2-substituted phthalazinone derivatives as PDE4 inhibitors. Structure-activity relationship studies led to the identification of benzylamine-substituted phthalazinones as potent PDE4 inhibitors that also suppressed TNF-alpha production by whole rat blood cells. The most potent of these, when topically administered, were effective in a mouse model of dermatitis.

In cardiac myocytes, cAMP elevation triggers the down-regulation of transcripts and promoter activity for cyclic AMP phosphodiesterase-4A10 (PDE4A10)

Transcripts for the PDE4A10 cyclic AMP phosphodiesterase isoform are present in a wide variety of rat tissues including the heart. Sequence comparisons between the putative human and mouse promoters revealed a number of conserved regions including both an Sp1 and a CREB-binding site. The putative mouse PDE4A10 promoter was amplified from genomic DNA and sub-cloned into a luciferase reporter vector for investigation of activity in neonatal cardiac myocytes. Transfection with this construct identified a high level of luciferase expression in neonatal cardiac myocytes. Surprisingly, this activity was down-regulated by elevation of intracellular cAMP through a process involving PKA, but not EPAC, signalling. Such inhibition of the rodent PDE4A10 promoter activity in response to elevated cAMP levels is in contrast to the PDE4 promoters so far described. Site-directed mutagenesis revealed that the Sp1 binding site at promoter position -348 to -336 is responsible for the basal constitutive expression of murine PDE4A10. The conserved CREB-binding motif at position -370 to -363 also contributes to basal promoter activity but does not in itself confer cAMP inhibition upon the PDE4A10 promoter. EMSA analysis confirmed the authenticity of CREB and Sp1 binding sites. The transcriptional start site was identified to be an adenine residue at position -55 in the mouse PDE4A10 promoter. We present evidence that this novel down-regulation of PDE4A10 is mediated by the transcription factor ICER in a PKA dependent manner. The pool of cAMP in cardiac myocytes that down-regulates PDE4A10 is regulated by beta-adrenoceptor coupled adenylyl cyclase activity and via hydrolysis determined predominantly by the action of PDE4 (cAMP phosphodiesterase-4) and not PDE3 (cAMP phosphodiesterase-3). We suggest that increased cAMP may remodel cAMP-mediated signalling events by not only increasing the expression of specific PDE4 cAMP phosphodiesterases but also by down-regulating specific isoforms, such as is shown here for PDE4A10 in cardiac myocytes.

Beneficial effects of rolipram in a quinolinic acid model of striatal excitotoxicity

Activity of c-AMP responsive element-binding protein (CREB) is decreased in Huntington's disease (HD). Such decrease was also described by our group in the quinolinic acid lesion model of striatal excitotoxicity. The phosphodiesterase type IV inhibitor rolipram increases CREB phosphorylation. Such drug has a protective effect in global ischaemia and embolism in rats. In this study, we sought to determine whether rolipram displays a neuroprotective effect in our rat model of HD. Animals were surgically administered QA and subsequently treated with rolipram daily up to 2 and 8 weeks respectively. After these time points, rats were sacrificed and immunohistochemical studies were performed in the striata. In the rolipram-treated animals, striatal lesion size was about 62% smaller that in the vehicle-treated ones at 2 weeks time point. Moreover, the surviving cell number was several times higher in the rolipram-treated animals than in the vehicle group at both time points. Rolipram also showed to be effective in increasing significantly the levels of activated CREB in the striatal spiny neurons, which accounts mostly for its beneficial effect in our rodent model of excitotoxicity. Our findings show that rolipram could be considered as a valid therapeutic approach for HD.

Cyclic nucleotide phosphodiesterases as targets for treatment of haematological malignancies

The cAMP signalling pathway has emerged as a key regulator of haematopoietic cell proliferation, differentiation and apoptosis. In parallel, general understanding of the biology of cyclic nucleotide PDEs (phosphodiesterases) has advanced considerably, revealing the remarkable complexity of this enzyme system that regulates the amplitude, kinetics and location of intracellular cAMP-mediated signalling. The development of therapeutic inhibitors of specific PDE gene families has resulted in a growing appreciation of the potential therapeutic application of PDE inhibitors to the treatment of immune-mediated illnesses and haematopoietic malignancies. This review summarizes the expression and function of PDEs in normal haematopoietic cells and the evidence that family-specific inhibitors will be therapeutically useful in myeloid and lymphoid malignancies.