1-(5-oxohexyl)-3,7-Dimethylxanthine, a phosphodiesterase inhibitor, activates MAPK cascades and promotes osteoblast differentiation by a mechanism independent of PKA activation (pentoxifylline promotes osteoblast differentiation)

Therapeutic potential of phosphodiesterase inhibitors in the treatment of osteoporosis: Scopes for therapeutic repurposing and discovery of new oral osteoanabolic drugs

Cyclic nucleotide phosphodiesterases (PDEs) are ubiquitously expressed enzymes that hydrolyze phosphodiester bond in the second messenger molecules including cAMP and cGMP. A wide range of drugs blocks one or more PDEs thereby preventing the inactivation of cAMP/cGMP. PDEs are differentially expressed in bone cells including osteoblasts, osteoclasts and chondrocytes. Intracellular increases in cAMP/cGMP levels in osteoblasts result in osteogenic response. Acting via the type 1 PTH receptor, teriparatide and abaloparatide increase intracellular cAMP and induce osteoanabolic effect, and many PDE inhibitors mimic this effect in preclinical studies. Since all osteoanabolic drugs are injectable and that oral drugs are considered to improve the treatment adherence and persistence, osteogenic PDE inhibitors could be a promising alternative to the currently available osteogenic therapies and directly assessed clinically in drug repurposing mode. Similar to teriparatide/abaloparatide, PDE inhibitors while stimulating osteoblast function also promote osteoclast function through stimulation of receptor activator of nuclear factor kappa-B ligand production from osteoblasts. In this review, we critically discussed the effects of PDE inhibitors in bone cells from cellular signalling to a variety of preclinical models that evaluated the bone formation mechanisms. We identified pentoxifylline (a non-selective PDE inhibitor) and rolipram (a PDE4 selective inhibitor) being the most studied inhibitors with osteogenic effect in preclinical models of bone loss at ≤ human equivalent doses, which suggest their potential for post-menopausal osteoporosis treatment through therapeutic repurposing. Subsequently, we treated pentoxifylline and rolipram as prototypical osteogenic PDEs to predict new chemotypes via the computer-aided design strategies for new drugs, based on the structural biology of PDEs.

Fabrication of Pentoxifylline-Loaded Hydroxyapatite/Alginate Scaffold for Bone Tissue Engineering

Background: Hydroxyapatite (HAP), as a common biomaterial in bone tissue engineering, can be fabricated in combination with other osteogenic agents. Pentoxifylline (PTX) is demonstrated to have positive roles in bone defect healing. Since local administration can diminish the systemic side effects of the drug, the objectives of the current in vitro study were to find the effects of PTX on the osteoblast functions for tissue engineering applications. Methods: a HAP scaffold was fabricated by casting the HAP slurry within polyurethane foam. The scaffold was enriched with 5 mg/mL PTX. Alginate (Alg) was used as drug carrier to regulate the PTX releasing rate. MG-63 osteosarcoma cells were cultured on 3D scaffolds and 2D Alg films in the presence or absence of PTX. Results: PTX did not affect the cell viability, attachment and phenotype. Also, the ultrastructure of the scaffolds was not modified by PTX enrichment. Alizarin red S staining showed that PTX has no effect on calcium deposition. Besides, Raman confocal microscopy demonstrated an increase in the organic matrix formation including proline, valine and phenylalanine deposition (represented collagen). Although PTX increased the total protein secretion, it led to a decrease in the alkaline phosphatase activity and vascular endothelial growth factor (VEGF) content. PTX reduced the hydration and degradation rates and it was released mainly at the first 24 hours of incubation. Conclusion: Based on our in vitro study, application of engineered PTX-loaded HAP scaffold in bone regeneration can act on behalf of organic matrix production, but not angiogenesis and mineralization.

The effects of pentoxifylline adminstration on fracture healing in a postmenopausal osteoporotic rat model

Previous studies report positive effects of pentoxifylline (PTX) alone or in combination with other drugs on some pathologic bone diseases as well as an ability to accelerate osteogensis and fracture healing in both animal models and human patients. The aim of this present study was to evaluate the effects of PTX administration on Hounsfield unit and bone strength at catabolic response (bone resorbing) of a fracture in an experimental rat model of ovariectomy induced osteoporosis (OVX-D). Thirty adult female rats were divided into groups as follows: 1 (OVX, control, no treatment); 2 (OVX, sham: daily distilled water); 3 (OVX, daily alendronate: 3 mg/kg); 4 (OVX, twice daily 100 mg/kg PTX) and 5 (OVX, PTX+alenderonate). OVX was induced by bilateral ovariectomy in all rats. A complete standardized osteotomy of the right femur was made after 3.5 months. PTX and alendronate treatments were performed for eight weeks. Then, rats were euthanized and had its right femur subjected to computerized tomography scanning for measuring Hounsfield unit; eventually, the samples were sent for a three point bending test for evaluation of the bone strength. Administration of PTX with 200 mg/kg and alendronate alone and in combination showed no significant alteration in Hounsfield unit and biomechanical properties of repairing callus of the complete osteotomy compared with the control group. Results showed increased bending stiffness and stress high load mean values of repairing complete osteotomy in PTX-treated rats compared to the control OVX-D.

Effect of Pentoxifylline on Spinal Fusion: An Experimental Study in Rabbits

STUDY DESIGN

Randomized, double-blinded, animal model.

OBJECTIVE

The objective of this study is to evaluate the effect of pentoxifylline (PTX) on spinal fusion in a rabbit model.

SUMMARY OF BACKGROUND DATA

Previous studies assert that PTX increases new bone formation. Because PTX seems to have these profound effects on bone metabolism, it may be hypothesized that it may enhance spinal fusion.

METHODS

Twenty-four New Zealand white rabbits were randomized and each received single-level posterolateral, inter-transverse process fusion with autologous iliac crest. In group 1, 12 male New Zealand white rabbits were treated with intravenous PTX treatment in 100-mg/kg/day dose after the surgical procedure. In group 2, 12 received no PTX medication and were accepted as the control group. Nine weeks after surgery, the animals were killed. The spines were tested via a manual palpation test, biomechanical testing, plain radiography, computed tomographic scans, and histomorphometric analysis.

RESULTS

The fusion rates of manual palpation were 40% in the control group and 80% in the PTX group (P = 0.17). Using a 5-grade radiographical system, the mean fusion grade was 2.4 in the control group and 3.1 in PTX group (P = 0.012). Total displacement of the fused level for the control group under flexion and extension was 0.2515 mm and was lower for the PTX-treated group: 0.1266 mm (P = 0.012). In the control group, the mean bone volume of the fusion mass determined from computed tomographic analysis was 4.0678 cm, whereas in the PTX group it was 4.7802 cm (P = 0.009). The mean trabecular bone area was 14% and 19% for the control and PTX groups, respectively (P = 0.002).

CONCLUSION

The differences between groups was statistically significant in terms of radiological fusion grading, biomechanical testing, volume of the fusion mass, and percentage of trabecular bone area. These results suggest that PTX may have a beneficial effect on spinal fusion.

LEVEL OF EVIDENCE

2.

Cyclic nucleotide phosphodiesterase activity in stem cells of human periodontal ligament (PDL-MSCs) before and after osteogenic induction

OBJECTIVE

The aim of this work was to evaluate both the level of endogenous cyclic nucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cAMP) and phosphodiesterase activity in mesenchymal stem cells (MSCs) before and during the osteogenic induction.

STUDY DESIGN

Samples were organized into control (nondifferentiated) and test groups which were analyzed at 3 different time points: 1, 2, and 4 weeks. Periodontal ligament MSCs were isolated and then expanded in an MSCM medium while cyclic nucleotide levels and phosphodiesterase activity were assessed.

RESULTS

cAMP and cGMP levels were markedly higher in the first week than in the following stages. Similarly, PDE activity increased during the first week and reached the peak in the second week.

CONCLUSIONS

This work validates that cAMP, cGMP, and PDE activities are important factors in the first phase of the osteogenic induction of a human stem cell.

Effect of pentoxifylline on histopathological changes in steroid-induced osteonecrosis of femoral head: experimental study in chicken

PURPOSE

Pentoxifylline (PTX) is a derivative of methylxanthine and is used in peripheral vascular and cerebrovascular diseases for its effect on the regulation of blood circulation. We investigated whether PTX could be beneficial for femoral head osteonecrosis associated with steroid through these effects.

METHODS

Sixty mature Leghorn type chickens were chosen and divided into three groups. The 25 chickens in group A were given a weekly dose of 3 mg/kg/week methylprednisolone acetate intramuscularly. Four chickens in group B died after the first drug injection and were excluded from the study. Therefore, the remaining 21 chickens in group B were additionally given 25 mg/kg/day pentoxifylline intramuscularly, along with the steroid medication as given in group A. The ten chickens in group C were not given any injections, as they were accepted as the control group. After the sacrifice of the animals at week 14, both femoral heads were taken from each animal. The animals which died along the course of the study also underwent pathological examination but were not a part of the statistical analysis.

RESULTS

In this study, steroid induced femoral head osteonecrosis has been experimentally observed in chickens after high doses of corticosteroid therapy. The chickens were given pentoxifylline in order to prevent the effects of steroid on bones and bone marrow. The results showed that chickens are suitable osteonecrosis models, and that steroid causes adipogenesis and necrosis in the bone marrow and the death of the subchondral bone.

CONCLUSIONS

The results of this study hint at the assumption that PTX may have a positive benefit on ONFH. PTX seems to minimise the effects of the steroid and reduce the incidence of ONFH.

Cilomilast enhances osteoblast differentiation of mesenchymal stem cells and bone formation induced by bone morphogenetic protein 2

A rapid and efficient method to stimulate bone regeneration would be useful in orthopaedic stem cell therapies. Rolipram is an inhibitor of phosphodiesterase 4 (PDE4), which mediates cyclic adenosine monophosphate (cAMP) degradation. Systemic injection of rolipram enhances osteogenesis induced by bone morphogenetic protein 2 (BMP-2) in mice. However, there is little data on the precise mechanism, by which the PDE4 inhibitor regulates osteoblast gene expression. In this study, we investigated the combined ability of BMP-2 and cilomilast, a second-generation PDE4 inhibitor, to enhance the osteoblastic differentiation of mesenchymal stem cells (MSCs). The alkaline phosphatase (ALP) activity of MSCs treated with PDE4 inhibitor (cilomilast or rolipram), BMP-2, and/or H89 was compared with the ALP activity of MSCs differentiated only by osteogenic medium (OM). Moreover, expression of Runx2, osterix, and osteocalcin was quantified using real-time polymerase chain reaction (RT-PCR). It was found that cilomilast enhances the osteoblastic differentiation of MSCs equally well as rolipram in primary cultured MSCs. Moreover, according to the H89 inhibition experiments, Smad pathway was found to be an important signal transduction pathway in mediating the osteogenic effect of BMP-2, and this effect is intensified by an increase in cAMP levels induced by PDE4 inhibitor.

Estrogen cross-talk with the melatonin signaling pathway in human osteoblasts derived from adolescent idiopathic scoliosis patients

Adolescent idiopathic scoliosis (AIS) represents the most frequently occurring form of scoliosis that occurs and progresses in puberty. This critical period coincides with many biological changes related to estrogens. The aim of this study was to determine the effect of 17-beta-estradiol on the responsiveness of AIS osteoblasts to melatonin and the cross-talk between estrogen and melatonin at the levels of the G(S)alpha and G(i)alpha proteins. Human osteoblasts derived from AIS (n = 40) and control patients (n = 10) were first screened for their functional response to the melatonin and 17-beta-estradiol. In response to the 17-beta-estradiol in a specific group of scoliotic patients, the level of 3',5'-cyclic adenosine monophosphate (cAMP) was significantly decreased when compared with the level observed in the presence of increasing concentrations of melatonin alone. Ours results provide strong evidence of the cross-talk between 17-beta-estradiol and melatonin signaling in human AIS osteoblasts. These results indicate a novel role for 17-beta-estradiol and melatonin in AIS, controlling the coupling of G(S)alpha protein and MT2 receptor on human osteoblasts. We found that the increased cAMP levels induced by melatonin can be corrected by the treatment of the cells with 17-beta-estradiol. Thus, estrogens or estrogen receptor agonists become important compounds to consider in AIS osteoblast cell functioning. Consequently, our results add a new facet to the understanding the role and function of melatonin in AIS.

Effects of phosphodiesterase 7 inhibition by RNA interference on the gene expression and differentiation of human mesenchymal stem cell-derived osteoblasts

The second messenger molecule cyclic adenosine monophosphate (cAMP) plays an important role in the hormonal regulation of bone metabolism. cAMP is inactivated by the cyclic nucleotide phosphodiesterases (PDEs), a superfamily of enzymes divided into 11 known families designated PDE 1-11. The aim of this study was to investigate the effect of PDE7 and PDE8 inhibition on the gene expression and differentiation of human osteoblasts. Osteoblasts differentiated from human mesenchymal stem cells (hMSC) were cultured and treated with short interfering RNAs (siRNAs) generated from PDE7 and PDE8 PCR products. Total RNA was isolated from the cells, and gene expression was assayed with cDNA microarray and quantitative real-time PCR. bALP measurements were assayed during differentiation, and mineralization was determined by quantitative Alizarin red S staining. PDE7 and PDE8 inhibition by RNA interference decreased the gene expression of PDE7A by 60-70%, PDE7B by 40-50%, and PDE8A by 30%. PDE7 silencing increased the expression of beta-catenin, osteocalcin, caspase-8, and cAMP-responsive element-binding protein 5 (CREB-5) genes and decreased the expression of the 1, 25-dihydroxyvitamin D3 receptor gene. PDE8A silencing increased the expression of anti-apoptotic genes, but decreased the expression of osteoglycin (osteoinductive factor) and bone morphogenetic protein 1 (BMP-1). PDE7 silencing increased bALP and mineralization up to three-fold compared to controls. Treatment with the PDE7-selective PDE inhibitor BRL-50481 had similar effects on mineralization as the gene silencing. The PDE7 silencing also increased forskolin stimulated cAMP response, but had no effect on the proliferation rate. Furthermore, osteocalcin expression was increased by PDE7 silencing by a mechanism dependent on protein kinase A. Our results show that specific gene silencing with the RNAi method is a useful tool for inhibiting the gene expression of specific PDEs and that PDE7 silencing upregulates several osteogenic genes and increases mineralization. PDE7 may play an important role in the regulation of osteoblastic differentiation.

Pentoxifylline attenuates nociceptive sensitization and cytokine expression in a tibia fracture rat model of complex regional pain syndrome

BACKGROUND

Tibia fracture in rats evokes chronic hindpaw warmth, edema, allodynia, and regional osteopenia, a syndrome resembling complex regional pain syndrome (CRPS). Previous studies suggest that the pathogenesis of some of these changes involves an exaggerated regional inflammatory response to injury and we postulated that inflammatory cytokines contribute to the development of CRPS-like changes after fracture.

METHODS

The distal tibia was fractured and the hindlimb casted for 4 weeks. The rats were given drinking water with or without the cytokine inhibitor pentoxifylline (PTX) starting the day before fracture and continuing for 4 weeks, after which time the cast was removed and multiple assays were performed in the hindpaw. PCR and immunoassays were used to evaluate changes in cytokine expression. Bilateral hindpaw thickness, temperature, and nociceptive thresholds were determined, and bone microarchitecture was measured by microcomputed tomography (microCT).

RESULTS

Tibia fracture chronically up-regulated TNFalpha, IL-1beta and IL-6 mRNA and protein levels in hindpaw skin and PTX treatment significantly reduced the mRNA expression and cytokine protein levels for all these cytokines. PTX inhibited the nociceptive sensitization and some vascular changes, but had insignificant effects on most of the bone-related parameters measured in these studies. Immunostaining of hindpaw skin was negative for immunocyte infiltration at 4 weeks post-fracture.

CONCLUSIONS

These results suggest that pro-inflammatory cytokines contribute to the nociceptive and vascular sequelae of fracture and that PTX treatment can reverse these CRPS-like changes.

Expression profiles of phosphodiesterase 4D splicing variants in osteoblastic cells

The promotion of osteoblastic differentiation by bone morphogenetic proteins (BMPs) is accelerated by chemical compounds that increase the intracellular concentration of cyclic 3',5'-adenosine monophosphate (cAMP). cAMP is synthesized from adenosine triphosphate (ATP) by adenyl cyclase and degraded by phosphodiesterase (PDE) family enzymes. Inhibition of PDEs leads to prolonged accumulation of cAMP within cells and Camp-mediated reactions. Rolipram, a specific inhibitor of PDE4, is a compound effective in inducing osteoblastic differentiation. Four PDE4 family members are transcribed from four distinct genes (4A, 4B, 4C, and 4D). Expression of PDE4A and PDE4D has been observed in osteoblastic cells. We identified PDE4D splicing variants that expressed in ST2 or primary calvarial osteoblasts by rapid amplification of the 5'-ends of cDNA when they were cultured with BMP. PDE4D9 mRNA was identified from ST2, and PDE4D1 and -4D2 mRNAs were identified from primary calvarial osteoblasts. Expression of these three variants of PDE4D mRNA was found in ST2, MC3T3-E1, C3H10T1/2, C2C12, and primary calvarial osteoblasts by RT-PCR, but not PDE4D1 or -4D2 in ST2 or PDE4D2 in MC3T3-E1. Expression of these three variants was detectable in brain, heart, lung, liver, kidney, placenta, and femur, and was thus ubiquitous. Purified recombinant PDE4D9 protein exhibited phosphodiesterase activity, which degraded cAMP to AMP, and this activity was inhibited by rolipram. These findings suggest that PDE4D1, -2, and -9 play some roles in bone formation.

Radiation-induced reduction of osteoblast differentiation in C2C12 cells

Therapeutic radiation causes bone damage and may increase fracture risks in treatment for head-and-neck cancer and in pelvic irradiation. These properties can also be used for prevention of heterotopic ossification in hip arthroplasty. To evaluate the effects of ionizing radiation on osteoblast differentiation, C2C12 cells were directed into an osteogenic lineage by treatment with a combination of bone morphogenic protein 2 (BMP-2) (100 ng/ml) and heparin (30 mug/ml) 6 h after irradiation (2 and 4 Gy). Osteoblast differentiation was evaluated based on alkali phosphatase (ALP) activity and expression of mRNA encoding ALP and collagen type I. Ionizing radiation suppressed the growth of C2C12 cells and decreased expression of ALP and collagen type I mRNAs with concomitant reduction of the ALP activity. Although further studies are needed to elucidate the molecular mechanism, our findings suggest that ionizing radiation at therapeutic doses interferes with bone formation by reducing ALP activity and expression of mRNA encoding ALP and collagen type I.

Melatonin enhances alkaline phosphatase activity in differentiating human adult mesenchymal stem cells grown in osteogenic medium via MT2 melatonin receptors and the MEK/ERK (1/2) signaling cascade

The goals of this study were to determine (a) if melatonin enhances human adult mesenchymal stem cell (hAMSC) differentiation into osteoblasts as assessed by measuring alkaline phosphatase (ALP) enzyme activity, and (b) identify potential signal transduction pathways that mediate this process. ALP activity significantly increased in hAMSCs following a 10-day incubation in osteogenic medium, relative to hAMSCs incubated in basal growth medium alone. Melatonin (50 nm), added in combination with the osteogenic medium, significantly increased ALP activity relative to osteogenic medium alone. Co-exposure of hAMSCs to osteogenic medium supplemented with melatonin and either pertussis toxin or the melatonin receptor antagonists, luzindole or 4P-PDOT (MT2 receptor selective), inhibited the melatonin-induced increase in ALP activity, indicating the involvement of melatonin receptors, in particular, MT2 receptors. Assessment of melatonin receptor function following exposure to osteogenic medium containing either vehicle or melatonin produced dichotomous results. That is, if the differentiation of hAMSCs into an osteoblast was induced by osteogenic medium alone, then 2-[125I]-iodomelatonin binding and melatonin receptor function increased. However, examination of melatonin receptor function following chronic melatonin exposure, an exposure that resulted in a 50% enhancement in ALP activity, revealed that these receptors were desensitized. This was reflected by a complete loss in specific 2-[125I]-iodomelatonin binding as well as melatonin efficacy to inhibit forskolin-induced cAMP accumulation. Further characterization of the mechanisms underlying melatonin's effects on these differentiation processes revealed that MEK (1/2) and ERK (1/2), epidermal growth factor receptors, metalloproteinase and clathrin-mediated endocytosis were essential while PKA was not. Our results are consistent with a role for melatonin in osteoblast differentiation. If so, then, the decrease in plasma melatonin levels observed in humans during late adulthood may further enhance susceptibility to osteoporosis.

Bone morphogenetic protein activities are enhanced by 3',5'-cyclic adenosine monophosphate through suppression of Smad6 expression in osteoprogenitor cells

Bone morphogenetic proteins (BMPs) belong to the transforming growth factor (TGF)-beta superfamily, and some display potent osteogenic activity both in vivo and in vitro. The BMP signaling cascade involving BMP receptors at the cell membrane and intracellular messengers (Smads) has been elucidated, but the regulatory mechanisms of BMP signaling have not been clarified. We previously found that pentoxifyline (PeTx), a nonspecific inhibitor of phosphodiesterase (PDE), and rolipram, a PDE-4-specific inhibitor, enhance BMP-4-induced osteogenic differentiation of mesenchymal cells, probably through the elevation of intracellular cyclic adenosine monophosphate (cAMP) accumulation and modulation of BMP signaling pathways as enhanced BMP-4 action was reproduced by addition of dibutylyl-cAMP (dbcAMP). However, the precise mechanisms underlying the enhancing effects of those agents on BMP signaling were not completely revealed. As already reported, BMPs utilize a specific intracellular signaling cascade to target genes via R-Smads (Smad1,5,8), Co-Smad (Smad4) and I-Smads (Smad6,7). One possibility for cAMP-mediated effects on BMP signaling might be suppression of I-Smads expression since these proteins form a negative feedback loop in BMP signaling. To examine this possibility, changes in I-Smad (Smad6) expression on addition of dbcAMP or PeTx were examined in a bone-marrow-derived osteogenic cell line (ST2). Alkaline phosphatase activity in ST2 cells was consistently induced by BMP-4 treatment (300 ng/ml), and Smad6 mRNA expression was also induced by BMP-4 treatment. Although concurrent treatment of ST2 cells with BMP-4 and dbcAMP elicited further activation of alkaline phosphatase, addition of dbcAMP reduced BMP-4-induced Smad6 expression in a dose-dependent manner. Furthermore, detection of phosphorylated Smad1/5/8 on Western blotting analysis was prolonged, suggesting prolonged kinase activity of BMP receptors through suppressed expression of Smad6. Elevated intracellular cAMP might thus enhance BMP signaling by suppressing Smad6 induction and prolonging intracellular BMP signaling.

Phosphodiesterase inhibitors stimulate osteoclast formation via TRANCE/RANKL expression in osteoblasts: possible involvement of ERK and p38 MAPK pathways

Phosphodiesterases (PDEs) are enzymes that degrade intracellular cAMP. In the present study, 3-isobutyl-1-methylxanthine (IBMX) and pentoxifylline, PDE inhibitors, induced osteoclast formation in cocultures of mouse bone marrow cells and calvarial osteoblasts. These inhibitors induced the expression of the osteoclast differentiation factor, TNF-related activation induced cytokine (TRANCE, identical to RANKL, ODF, and OPGL), in calvarial osteoblasts. IBMX induced phosphorylation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (MAPK) in osteoblasts. Induction of TRANCE expression by IBMX was partially suppressed by the inhibitors of protein kinase A (PKA), ERK, and p38 MAPK, suggesting that activation of ERK and p38 MAPK, as well as PKA, is involved in TRANCE expression by IBMX. Osteoblasts expressed PDE4, a PDE subtype, and rolipram, a selective inhibitor of PDE4, induced TRANCE expression. These results suggest that PDE4 is a key regulator of TRANCE expression in osteoblasts, which in turn controls osteoclast formation.

Dexamethasone down-regulates cAMP-phosphodiesterase in human osteosarcoma cells

Cyclic adenosine monophosphate (cAMP) is an important second messenger in the hormonal regulation of bone metabolism. cAMP is inactivated by the cyclic nucleotide phosphodiesterases (PDEs), a superfamily of enzymes divided into 11 known families, designated PDE1-11. Interference with the cAMP signaling pathway has been suggested as one mechanism causing glucocorticoid induced osteoporosis. We speculated that glucocorticoids could affect the cAMP pathway by a down-regulation of PDE-mediated cAMP hydrolysis. The main cAMP hydrolysing enzyme families of human MG-63 and SaOS-2 osteosarcoma cells were identified as PDE1 and PDE4 by assaying the PDE activity of Q-sepharose fractions and cell homogenates with selective inhibitors. Treatment with the glucocorticoid dexamethasone (Dex) decreased cAMP-PDE activity by up to 50%, without affecting cGMP-PDE activity. Dex treatment reduced the sensitivity of the total cAMP-PDE activity towards the PDE4 selective PDE inhibitor rolipram. Forskolin stimulated cAMP accumulation was increased 30-60-fold in the presence of rolipram. Treatment with Dex did not affect the basal or forskolin stimulated cAMP accumulation, but treatment resulted in a reduced effect of rolipram on cAMP accumulation. Expression of the following cAMP-PDE subtypes were detected by reverse transcriptase PCR (RT-PCR): PDE1A, PDE1C, PDE2A, PDE3A, PDE4A, PDE4B, PDE4C, PDE4D, PDE7A, PDE7B, PDE8A, PDE10A and PDE11A. Using semi-quantitative RT-PCR, we detected a 50-70% decrease in the mRNA of PDE4A and PDE4B subtypes following Dex treatment. Further analysis revealed that Dex reduced the PDE4A4 and PDE4B1 isoforms. PDE4A1 PDE4A, PDE4A7, PDE4A10, PDE4B2 were also expressed, but Dex did not affect the transcription of these isoforms. We conclude that Dex treatment could affect the cAMP signaling pathway of human osteosarcoma cells by reducing type 4 cAMP-phosphodiesterase (PDE4).