Inhibitors of cyclic nucleotide phosphodiesterase isozymes type-III and type-IV suppress mitogenesis of rat mesangial cells

Phosphodiesterase-4 enzyme as a therapeutic target in neurological disorders

Phosphodiesterases (PDE) are a diverse family of enzymes (11 isoforms so far identified) responsible for the degradation of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) which are involved in several cellular and biochemical functions. Phosphodiesterase 4 (PDE4) is the major isoform within this group and is highly expressed in the mammalian brain. An inverse association between PDE4 and cAMP levels is the key mechanism in various pathophysiological conditions like airway inflammatory diseases-chronic obstruction pulmonary disease (COPD), asthma, psoriasis, rheumatoid arthritis, and neurological disorders etc. In 2011, roflumilast, a PDE4 inhibitor (PDE4I) was approved for the treatment of COPD. Subsequently, other PDE4 inhibitors (PDE4Is) like apremilast and crisaborole were approved by the Food and Drug Administration (FDA) for psoriasis, atopic dermatitis etc. Due to the adverse effects like unbearable nausea and vomiting, dose intolerance and diarrhoea, PDE4 inhibitors have very less clinical compliance. Efforts are being made to develop allosteric modulation with high specificity to PDE4 isoforms having better efficacy and lesser adverse effects. Interestingly, repositioning PDE4Is towards neurological disorders including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS) and sleep disorders, is gaining attention. This review is an attempt to summarize the data on the effects of PDE4 overexpression in neurological disorders and the use of PDE4Is and newer allosteric modulators as therapeutic options. We have also compiled a list of on-going clinical trials on PDE4 inhibitors in neurological disorders.

Emerging therapeutic strategies for minimal change disease and focal and segmental glomerulosclerosis

INTRODUCTION

Minimal change disease (MCD) and Focal and segmental glomerulosclerosis (FSGS) are two of the major causes of nephrotic syndrome (NS) in children and adults. According to KDIGO (Kidney Disease: Improving Global Outcomes) guidelines, the treatment of adult primary MCD and FSGS should be based on immunosuppressants and antiproteinuric drugs. Recently, Rituximab, a humanized monoclonal antibody (mAb) has emerged as a potential treatment for steroid or calcineurin inhibitor-dependent patients; it has however demonstrated lower efficacy in those with nephrotic syndrome that is resistant to the above indicated drugs.

AREAS COVERED

Analysis of ongoing and already completed clinical trials, retrieved from clinicaltrials.gov, clinicaltrialsregister.eu and PubMed involving new therapies for nephrotic syndrome secondary to MCD and FSGS.

EXPERT OPINION

The most promising drugs under investigation for MCD and FSGS are mAbs. We are hopeful that new therapeutic options to treat multi-drug resistant MCD and FSGS will emerge from currently ongoing studies. What appears certain is the difficulty in enrolling patients affected by orphan renal diseases and the selection of valid endpoints in clinical trials, such as kidney failure.

Therapeutic efficacy of pentoxifylline on proteinuria and renal progression: an update

Blood pressure control with renin-angiotensin system (RAS) blockade has remained the gold standard for treating patients with proteinuric chronic kidney disease (CKD) up to date. Nevertheless, RAS blockade slows but does not halt the progression of kidney disease, thus highlighting the need to search for additional therapeutic approaches. The nonselective phosphodiesterase (PDE) inhibitor pentoxifylline (PTX) is an old drug that exhibits prominent anti-inflammatory, anti-proliferative and anti-fibrotic activities both in vitro and in vivo. Studies in human subjects have shown that PTX monotherapy decreases urinary protein excretion, and add-on therapy of PTX to background RAS blockade additively reduces proteinuria in patients with CKD of various etiology. More recent studies find that PTX combined with RAS blockade delays the decline of glomerular filtration rate in diabetic patients with mild to moderate CKD, and reduces the risk of end-stage renal disease in diabetic and non-diabetic patients in late stage of CKD with high proteinuria levels. In this review, we update the clinical trial results of PTX as monotherapy, or in conjunction or in comparison with RAS blockade on patients with proteinuria and CKD, and propose a mechanistic scheme explaining the renoprotective activities of this drug.

A biphasic and brain-region selective down-regulation of cyclic adenosine monophosphate concentrations supports object recognition in the rat

BACKGROUND

We aimed to further understand the relationship between cAMP concentration and mnesic performance.

METHODS AND FINDINGS

Rats were injected with milrinone (PDE3 inhibitor, 0.3 mg/kg, i.p.), rolipram (PDE4 inhibitor, 0.3 mg/kg, i.p.) and/or the selective 5-HT4R agonist RS 67333 (1 mg/kg, i.p.) before testing in the object recognition paradigm. Cyclic AMP concentrations were measured in brain structures linked to episodic-like memory (i.e. hippocampus, prefrontal and perirhinal cortices) before or after either the sample or the testing phase. Except in the hippocampus of rolipram treated-rats, all treatment increased cAMP levels in each brain sub-region studied before the sample phase. After the sample phase, cAMP levels were significantly increased in hippocampus (1.8 fold), prefrontal (1.3 fold) and perirhinal (1.3 fold) cortices from controls rat while decreased in prefrontal cortex (∼0.83 to 0.62 fold) from drug-treated rats (except for milrinone+RS 67333 treatment). After the testing phase, cAMP concentrations were still increased in both the hippocampus (2.76 fold) and the perirhinal cortex (2.1 fold) from controls animals. Minor increase were reported in hippocampus and perirhinal cortex from both rolipram (respectively, 1.44 fold and 1.70 fold) and milrinone (respectively 1.46 fold and 1.56 fold)-treated rat. Following the paradigm, cAMP levels were significantly lower in the hippocampus, prefrontal and perirhinal cortices from drug-treated rat when compared to controls animals, however, only drug-treated rats spent longer time exploring the novel object during the testing phase (inter-phase interval of 4 h).

CONCLUSIONS

Our results strongly suggest that a "pre-sample" early increase in cAMP levels followed by a specific lowering of cAMP concentrations in each brain sub-region linked to the object recognition paradigm support learning efficacy after a middle-term delay.

Phosphodiesterase 3A (PDE3A) deletion suppresses proliferation of cultured murine vascular smooth muscle cells (VSMCs) via inhibition of mitogen-activated protein kinase (MAPK) signaling and alterations in critical cell cycle regulatory proteins

Cyclic nucleotide phosphodiesterase 3 (PDE3) is an important regulator of cyclic adenosine monophosphate (cAMP) signaling within the cardiovascular system. In this study, we examined the role of PDE3A and PDE3B isoforms in regulation of growth of cultured vascular smooth muscle cells (VSMCs) and the mechanisms by which they may affect signaling pathways that mediate mitogen-induced VSMC proliferation. Serum- and PDGF-induced DNA synthesis in VSMCs grown from aortas of PDE3A-deficient (3A-KO) mice was markedly less than that in VSMCs from PDE3A wild type (3A-WT) and PDE3B-deficient (3B-KO) mice. The reduced growth response was accompanied by significantly less phosphorylation of extracellular signal-regulated kinase (ERK) in 3A-KO VSMCs, most likely due to a combination of greater site-specific inhibitory phosphorylation of Raf-1(Ser-²⁵⁹) by protein kinase A (PKA) and enhanced dephosphorylation of ERKs due to elevated mitogen-activated protein kinase phosphatase 1 (MKP-1). Furthermore, 3A-KO VSMCs, compared with 3A-WT, exhibited higher basal PKA activity and cAMP response element-binding protein (CREB) phosphorylation, higher levels of p53 and p53 phosphorylation, and elevated p21 protein together with lower levels of Cyclin-D1 and retinoblastoma (Rb) protein and Rb phosphorylation. Adenoviral overexpression of inactive CREB partially restored growth effects of serum in 3A-KO VSMCs. In contrast, exposure of 3A-WT VSMCs to VP16 CREB (active CREB) was associated with inhibition of serum-induced DNA synthesis similar to that in untreated 3A-KO VSMCs. Transfection of 3A-KO VSMCs with p53 siRNA reduced p21 and MKP-1 levels and completely restored growth without affecting amounts of Cyclin-D1 and Rb phosphorylation. We conclude that PDE3A regulates VSMC growth via two complementary pathways, i.e. PKA-catalyzed inhibitory phosphorylation of Raf-1 with resulting inhibition of MAPK signaling and PKA/CREB-mediated induction of p21, leading to G₀/G₁ cell cycle arrest, as well as by increased accumulation of p53, which induces MKP-1, p21, and WIP1, leading to inhibition of G₁ to S cell cycle progression.

n-3 Fatty acids block TNF-α-stimulated MCP-1 expression in rat mesangial cells

Monocyte chemoattractant protein 1 (MCP-1) is a CC cytokine that fundamentally contributes to the pathogenesis of inflammatory renal disease. MCP-1 is highly expressed in cytokine-stimulated mesangial cells in vitro and following glomerular injury in vivo. Interventions to limit MCP-1 expression are commonly effective in assorted experimental models. Fish oil, an abundant source of n-3 fatty acids, has anti-inflammatory properties, the basis of which remains incompletely defined. We examined potential mechanisms whereby fish oil reduces MCP-1 expression and thereby suppresses inflammatory responses to tissue injury. Cultured mesangial cells were treated with TNF-α in the presence of the n-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA); equimolar concentrations of the n-6 fatty acids LA and OA served as controls. MCP-1 mRNA expression was assessed by Northern blotting, and transcriptional activity of the MCP-1 promoter was assessed by transient transfection. The involvement of the ERK and NF-κB pathways was evaluated through transfection analysis and the use of the MEK inhibitor U0126. DHA and EPA decreased TNF-α-stimulated MCP-1 mRNA expression by decreasing transcription of the MCP-1 gene. DHA and EPA decreased p-ERK expression and nuclear translocation of NF-κB, both of which are necessary for TNF-α-stimulated MCP-1 expression. Both NF-κB and AP-1 sites were involved in transcriptional regulation of the MCP-1 gene by DHA and EPA. We conclude that DHA and EPA inhibit TNF-α-stimulated transcription of the MCP-1 gene through interaction of signaling pathways involving ERK and NF-κB. We speculate that such effects may contribute to the salutary effect of fish oil in renal and vascular disease.

Phosphodiesterases in the central nervous system: implications in mood and cognitive disorders

Cyclic nucleotide phosphodiesterases (PDEs) are a superfamily of enzymes that are involved in the regulation of the intracellular second messengers cyclic AMP (cAMP) and cyclic GMP (cGMP) by controlling their rates of hydrolysis. There are 11 different PDE families and each family typically has multiple isoforms and splice variants. The PDEs differ in their structures, distribution, modes of regulation, and sensitivity to inhibitors. Since PDEs have been shown to play distinct roles in processes of emotion and related learning and memory processes, selective PDE inhibitors, by preventing the breakdown of cAMP and/or cGMP, modulate mood and related cognitive activity. This review discusses the current state and future development in the burgeoning field of PDEs in the central nervous system. It is becoming increasingly clear that PDE inhibitors have therapeutic potential for the treatment of neuropsychiatric disorders involving disturbances of mood, emotion, and cognition.

Study design and rationale of 'Influence of Cilostazol-based triple anti-platelet therapy on ischemic complication after drug-eluting stent implantation (CILON-T)' study: A multicenter randomized trial evaluating the efficacy of Cilostazol on ischemic vascular complications after drug-eluting stent implantation for coronary heart disease

Background

Current guidelines recommend dual anti-platelet therapy, aspirin and clopidogrel, for patients treated with drug-eluting stent for coronary heart disease. In a few small trials, addition of cilostazol on dual anti-platelet therapy (triple anti-platelet therapy) showed better late luminal loss. In the real-world unselected patients with coronary heart disease, however, the effect of cilostazol on platelet reactivity and ischemic vascular events after drug-eluting stent implantation has not been tested. It is also controversial whether there is a significant interaction between lipophilic statin and clopidogrel.

Methods/Design

CILON-T trial was a prospective, randomized, open-label, multi-center, near-all-comer trial to demonstrate the superiority of triple anti-platelet therapy to dual anti-platelet therapy in reducing 6 months' major adverse cardiovascular/cerebrovascular events, composite of cardiac death, nonfatal myocardial infarction, target lesion revascularization and ischemic stroke. It also tested whether triple anti-platelet therapy is superior to dual anti-platelet therapy in inhibiting platelet reactivity in patients receiving percutaneous coronary intervention with drug-eluting stent. Total 960 patients were randomized to receive either dual anti-platelet therapy or triple anti-platelet therapy for 6 months and also, randomly stratified to either lipophilic statin (atorvastatin) or non-lipophilic statin (rosuvastatin) indefinitely. Secondary endpoints included all components of major adverse cardiovascular/cerebrovascular events, platelet reactivity as assessed by VerifyNow P2Y12 assay, effect of statin on major adverse cardiovascular/cerebrovascular events, bleeding complications, and albumin-to-creatinine ratio to test the nephroprotective effect of cilostazol. Major adverse cardiovascular/cerebrovascular events will also be checked at 1, 2, and 3 years to test the 'legacy' effect of triple anti-platelet therapy that was prescribed for only 6 months after percutaneous coronary intervention.

Discussion

CILON-T trial will give powerful insight into whether triple anti-platelet therapy is superior to dual anti-platelet therapy in reducing ischemic events and platelet reactivity in the real-world unselected patients treated with drug-eluting stent for coronary heart disease. Also, it will verify the laboratory and clinical significance of drug interaction between lipophilic statin and clopidogrel.

Trial Registration

National Institutes of Health Clinical Trials Registry (ClinicalTrials.gov identifier# NCT00776828).

Cilostazol reduces proliferation through c-Myc down-regulation in MDCK cells

Cilostazol, a drug commonly used in the treatment of intermittent claudication is a selective phosphodiesterase III inhibitor. It affects cell proliferation, increases cAMP levels, activates the cyclic AMP-dependent protein kinase and inhibits E2F in vascular cells. Polycystic kidney disease, a common genetic disorder, is characterized by increased cell proliferation, basement membrane abnormalities and fluid secretion. An established in vitro model of this disease is the canine Madin-Darby cell line (MDCK). In this communication, we investigated the effects of cilostazol exposure in MDCK cells. A reduced cell proliferation rate with an arrest in the G1 phase of the cell cycle was detected. Accordingly, several transcription factors associated with cell cycle control were affected by cilostazol, particularly c-myc. c-Myc DNA binding as well as its transcriptional activity was severely impaired in cilostazol-treated cells. Pharmacological tools demonstrated that besides the involvement of the cyclic AMP-dependent protein kinase, the extracellular signal-regulated kinases I/II participate in the response. These results suggest that cilostazol inhibits cell proliferation through c-myc transcriptional control, also pave the way to our better understanding of molecular transactions triggered by this drug and strengthen its potential use in other malignancies.

Intervention with cilostazol attenuates renal inflammation in streptozotocin-induced diabetic rats

AIMS

An inflammatory reaction is commonly found in the pathogenesis of diabetic nephropathy (DN). Cilostazol, a type 3 phosphodiesterase (PDE) inhibitor, has been previously reported to be anti-inflammatory, independent of an anti-platelet property. In the present study, we evaluated the hypothesis that cilostazol has protective effects on diabetic nephropathy by modulating the inflammatory process.

MAIN METHODS

Cilostazol was administered (27 or 9 mg kg(-1)d(-1)) to streptozotocin (STZ)-induced diabetic rats for eight weeks. We studied the kidney expression of vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1 by immunofluorescence, western blotting and real-time PCR. The renal monocyte chemoattractant protein (MCP)-1 and vascular endothelial growth factor (VEGF) levels were examined by ELISA. The nuclear factor (NF)-kappaB-DNA binding activity was assessed by electrophoresis mobility shift assay (EMSA).

KEY FINDINGS

Our results showed cilostazol inhibited diabetes-induced hypertrophy of the glomeruli and infiltration of inflammatory cells, as well as the increase in the VCAM-1 and ICAM-1 mRNA and protein expression, and MCP-1 and VEGF contents in the kidneys. Consistent with these findings, cilostazol attenuated the enhanced activation of NF-kappaB in diabetic rats.

SIGNIFICANCE

These results demonstrate that the renoprotective effects of cilostazol may be mediated by its anti-inflammatory actions, including inhibition of NF-kappaB activation and the subsequent decrease in proinflammatory factors, such as VCAM-1, ICAM-1, MCP-1 and VEGF expression in kidneys of diabetic rats.

PDE-5 inhibition impedes TSP-1 expression, TGF-beta activation and matrix accumulation in experimental glomerulonephritis

BACKGROUND

Matrix expansion and mesangial proliferation are hallmarks of mesangial proliferative glomerulonephritis. Specific inhibition of PDE-5, an enzyme catalyzing the intracellular degradation of cyclic GMP, can be achieved by the inhibitor vardenafil. In this study, we investigated the effects of PDE-5 inhibition in the anti-Thy1 model in the rat in vivo.

METHODS

After disease induction, rats received 10 mg/kg bw vardenafil twice a day via gavage. On Days 2 and 6, renal biopsies, as well as glomerular isolates, urine and blood samples were taken to compare vardenafil- and placebo-treated groups during the course of disease.

RESULTS

Small amounts of PDE-5 were detected in healthy kidneys, but induced in a typical mesangial pattern during disease (by IHC and WB). Specific PDE-5 inhibition resulted in increased glomerular levels of cGMP. Treated animals demonstrated inhibition of MC proliferation and matrix accumulation while renal function and influx of inflammatory cells were not affected. Due to PDE-5 inhibition, the endogenous TGF-beta-activating protein TSP-1 and the TGF-beta-signalling protein p-smad-2/3 were decreased suggesting this as an antifibrotic mechanism of action of vardenafil in this model.

CONCLUSION

Considering the availability and safety profile of vardenafil, the beneficial antiproliferative and antifibrotic effect in experimental glomerulonephritis may potentially be applicable to the treatment of mesangial proliferative glomerulonephritis in man.

Cilostazol attenuates MCP-1 and MMP-9 expression in vivo in LPS-administrated balloon-injured rabbit aorta and in vitro in LPS-treated monocytic THP-1 cells

Monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-9 (MMP-9) are involved in vascular inflammation. We tested the hypothesis, and explored the underlining mechanisms that cilostazol, a phosphodiesterase 3 inhibitor with antiplatelet and antithrombotic properties, inhibits lipopolysaccharide (LPS)-induced MCP-1 and MMP-9 expression. In a rabbit aorta balloon-injury model, administration of LPS increased macrophage infiltration and MCP-1 and MMP-9 expression; cilostazol supplementation prevented this phenomenon and reduced intimal hyperplasia. In contrast, the reverse zymography showed that cilostazol did not affect TIMP-1 expression in serum. In monocytic THP-1 cells, cilostazol and N6,O2'-dibutyryl-cAMP (dioctanoyl-cAMP, a cAMP analog) dose-dependently inhibited LPS-induced MCP-1 protein expression and MMP-9 activation, but did not affect the tissue inhibitor of metalloproteinase-1. Quantitative real-time polymerase chain reaction (PCR) showed that cilostazol inhibited MCP-1 and MMP-9 mRNA expression. Cilostazol significantly inhibited LPS-induced activation of p38, JNK, and nuclear factor-kappaB, and the respective inhibitors of p38 and JNK greatly reduced the level of LPS-induced MCP-1 and MMP-9, suggesting the involvement of the p38 and JNK pathways. In conclusion, cilostazol administered with LPS in vivo reduced neointimal hyperplasia and macrophage infiltration in the balloon-injured rabbit aorta; in vitro, cilostazol inhibits LPS-induced MCP-1 and MMP-9 expression. These data suggest that cilostazol may play an important role in preventing endotoxin- and injured-mediated vascular inflammation.

Management of peripheral arterial disease in the elderly: focus on cilostazol

Symptomatic and asymptomatic peripheral arterial disease (PAD) is a common problem in the elderly. The management of PAD includes the prevention of cardiovascular events and relief of symptoms--most commonly intermittent claudication (IC). Both require treatment of the causes and consequences of atherothrombosis, but some strategies are more effective for prevention of cardiovascular events and others are more effective for the relief of symptoms. Priorities for the prevention of cardiovascular events include smoking cessation, exercise, antiplatelet therapy, and the treatment of dyslipidemia, hypertension, and diabetes. Walking time and ability are improved by exercise. The benefit of numerous drugs in the treatment of IC has been assessed. The results have generally been disappointing, but there is some evidence that statins and cilostazol (an inhibitor of phosphodiesterase 3) are of benefit. Meta-analyses suggest that cilostazol increases maximum walking distance by 40%-50% and improves other objective measures of walking. The safety profile of cilostazol in patients with PAD appears to be acceptable although the mechanism for its effect on IC is unclear. In addition to risk factor management, treatment with cilostazol should be considered in patients with disabling IC.

Irsogladine maleate potentiates the effects of nitric oxide on activation of cAMP signalling pathways and suppression of mesangial cell mitogenesis

BACKGROUND AND PURPOSE

Deficiency in nitric oxide (NO) is a major factor leading to deterioration and progression of certain glomerular diseases. Agents enhancing NO availability and potentiality are renoprotective. Irsogladine maleate (IM), an anti-ulcer drug, is reported to improve gastric blood flow via NO-dependent mechanisms. We, therefore, asked whether and how IM interacted with NO on glomerular mesangial cells.

EXPERIMENTAL APPROACH

Mesangial cells were exposed to IM and NO donors. Activation of cAMP signalling pathways was assessed by intracellular cAMP, phosphorylation of VASP, activation of the cAMP response element (CRE) and expression of CRE-regulated proteins.

KEY RESULTS

IM alone did not affect cell proliferation. However, it greatly enhanced the growth-inhibitory effect of NO donor S-nitroso-N-acetylpenicillamine (SNAP). IM acted synergistically with NO on suppression of mitogen-activated protein kinase activation, induction of gap junction protein connexin43, increase of intracellular cAMP, and phosphorylation of VASP. With the use of the CRE-SEAP-based reporting system, IM and SNAP cooperatively activated cAMP response elements (CRE). A similar activation of cAMP was induced by IM with two different NO donors, the sGC activator Bay 41-2272 and the cGMP analogue 8-bromo-cGMP. The effects of SNAP and IM on cAMP activation were mimicked by phosphodiesterase 3 (PDE3) and PDE4 inhibitors. In addition, IM markedly augmented cytokine-induced expression of iNOS, production of NO and activation of CRE.

CONCLUSION AND IMPLICATIONS

The effects of NO were greatly potentiated by IM through synergistic activation of cAMP pathway. Combined therapy with IM and NO may be developed for certain renal diseases.

Profiling of functional phosphodiesterase in mesangial cells using a CRE-SEAP-based reporting system

1. Phosphodiesterases (PDEs) are critically implicated in the regulation of mesangial cell function, but profile of functional PDEs in mesangial cells is still unclear. In this study, we investigated roles of individual PDEs in the regulation of mesangial cell behavior by the cAMP pathway. 2. Reporter mesangial cells that express secreted alkaline phosphatase (SEAP) under the control of the cAMP response element (CRE) were exposed to selective PDE inhibitors in the presence or absence of cAMP, and activity of CRE, expression of CRE-regulated protein, mitogenesis and cell survival were examined. 3. Exposure of reporter cells to cAMP-elevating agents resulted in time- and concentration-dependent activation of CRE. Treatment of the cells with any PDE inhibitors alone did not induce CRE activation. Under stimulation with 8-bromo-cAMP or 8-bromo-cGMP, however, inhibitors of PDE2, PDE3, PDE4 and PDE5 enhanced activation of CRE. Inhibition of PDE1 or PDE6 did not affect the CRE activation. 4. Among different combinations tested, only inhibitors of PDE3 and PDE4 cooperatively increased the level of intracellular cAMP, activity of protein kinase A, activation of CRE, and CRE-regulated protein, connexin43. 5. Concomitant inhibition of PDE3 and PDE4 attenuated mitogen-induced activation of extracellular signal-regulated kinases and cell proliferation. Under serum deprivation, combinational inhibition of PDE3 and PDE4 exclusively caused activation of caspase-3 and apoptosis. 6. The present data elucidated that PDE3 and PDE4 play critical roles in the regulation of mesangial cell function. PDE3 and PDE4 were identified as the novel, antiapoptotic machinery that supports survival of mesangial cells.

Lixazinone stimulates mitogenesis of Madin-Darby canine kidney cells

Polycystic kidney diseases (PKD) are characterized by excessive proliferation of renal tubular epithelial cells, development of fluid-filled cysts, and progressive renal insufficiency. cAMP inhibits proliferation of normal renal tubular epithelial cells but stimulates proliferation of renal tubular epithelial cells derived from patients with PKD. Madin-Darby canine kidney (MDCK) epithelial cells, which are widely used as an in vitro model of cystogenesis, also proliferate in response to cAMP. Intracellular cAMP levels are tightly regulated by phosphodiesterases (PDE). Isoform-specific PDE inhibitors have been developed as therapeutic agents to regulate signaling pathways directed by cAMP. In other renal cell types, we have previously demonstrated that cAMP is hydrolyzed by PDE3 and PDE4, but only PDE3 inhibitors suppress proliferation by inhibiting Raf-1 activity (Cheng J, Thompson MA, Walker HJ, Gray CE, Diaz Encarnacion MM, Warner GM, Grande JP. Am J Physiol Renal Physiol 287:F940-F953, 2004.) A potential role for PDE isoform(s) in cAMP-mediated proliferation of MDCK cells has not previously been established. Similar to what we have previously found in several other renal cell types, cAMP hydrolysis in MDCK cells is directed primarily by PDE4 (85% of total activity) and PDE3 (15% of total activity). PDE4 inhibitors are more effective than PDE3 inhibitors in increasing intracellular cAMP levels in MDCK cells. However, only PDE3 inhibitors, and not PDE4 inhibitors, stimulate mitogenesis of MDCK cells. PDE3 but not PDE4 inhibitors activate B-Raf but not Raf-1, as assessed by an in vitro kinase assay. PDE3 but not PDE4 inhibitors activate the ERK pathway and activate cyclins D and E, as assessed by histone H1 kinase assay. We conclude that mitogenesis of MDCK cells is regulated by a functionally compartmentalized intracellular cAMP pool directed by PDE3. Pharmacologic agents that stimulate PDE3 activity may provide the basis for new therapies directed toward reducing cystogenesis in patients with PKD.

TGF-beta1 stimulates monocyte chemoattractant protein-1 expression in mesangial cells through a phosphodiesterase isoenzyme 4-dependent process

Monocyte chemoattractant protein-1 (MCP-1) and transforming growth factor (TGF)-beta1 are critical mediators of renal injury by promoting excessive inflammation and extracellular matrix deposition, thereby contributing to progressive renal disease. In renal disease models, MCP-1 stimulates the production of TGF-beta1. However, a potential role for TGF-beta1 in the regulation of MCP-1 production by mesangial cells (MCs) has not previously been evaluated. The objectives of this study were to define the role of TGF-beta1 in regulation of MCP-1 expression in cultured MCs and to define mechanisms through which rolipram (Rp), a phosphodiesterase isoenzyme 4 (PDE4) inhibitor with anti-inflammatory properties, alters MCP-1 expression. TGF-beta1 induced MCP-1 in a time- and dose-dependent manner without increasing transcription of the MCP-1 gene. TGF-beta1-mediated induction of MCP-1 occurred without activation of the NF-kappaB pathway. Rp blocked TGF-beta1-stimulated MCP-1 expression via a protein kinase A-dependent process, at least in part, by decreasing MCP-1 message stability. Rp exerted no effect on activation of the Smad pathway by TGF-beta1. TGF-beta1-mediated induction of MCP-1 required activation of ERK and p38, both of which were suppressed by a PDE4 inhibitor. TGF-beta1-stimulated reactive oxygen species (ROS) generation by MCs, and Rp inhibited ROS generation in TGF-beta1-stimulated MCs; in addition, both Rp and ROS scavengers blocked TGF-beta1-stimulated MCP-1 expression. We conclude that TGF-beta1 stimulates MCP-1 expression through pathways involving activation of ERK, p38, and ROS generation. Positive cross-talk between TGF-beta1 and MCP-1 signaling in MCs may underlie the development of progressive renal disease. Rp, by preventing TGF-beta1-stimulated MCP-1 production, may offer a therapeutic approach in retarding the progression of renal disease.

Role of cyclins in cAMP inhibition of glomerular mesangial cell proliferation

MC (mesangial cell) proliferation is closely linked to the progression of glomerular disease. It has been reported that cAMP effectors suppress MC proliferation, inhibiting activation of MAPK (mitogen-activated protein kinase). In fibroblasts, activation of MAPK induces the expression of type D cyclin, whereas, in MCs, this induction has not been shown. In the present study, we explored the effects of cAMP on MAPK and expression of cell-cycle-regulated proteins. PDGF (platelet-derived growth factor) stimulated MAPK activity, up-regulated protein levels of cyclin D1, CDK2 (cyclin-dependent kinase 2) and PCNA (proliferating cell nuclear antigen), decreased the protein level of p27 and increased DNA synthesis. Fsk (forskolin) or PD98059 suppressed PDGF-induced DNA synthesis. Both agents inhibited PDGF-stimulated mRNA and protein expression of cyclin D1 and CDK2. Fsk or PD98059 also inhibited protein expression of PCNA and blocked a decrease in p27 protein. Fsk induced the phosphorylation of Raf-1 at Ser259, which was inhibited by KT5720. These data suggest that cAMP inhibits MC proliferation through inhibition of MAPK activity, and this mechanism partly involves alteration in the levels of cell-cycle-regulated proteins.

Differential regulation of mesangial cell mitogenesis by cAMP phosphodiesterase isozymes 3 and 4

Mesangial cell (MC) mitogenesis is regulated through "negative cross talk" between cAMP-PKA and ERK signaling. Although it is widely accepted that cAMP inhibits mitogenesis through PKA-mediated phosphorylation of Raf-1, recent studies have indicated that cAMP-mediated inhibition of mitogenesis may occur independently of Raf-1 phosphorylation or without inhibiting ERK activity. We previously showed that MCs possess functionally compartmentalized intracellular pools of cAMP that are differentially regulated by cAMP phosphodiesterases (PDE); an intracellular pool directed by PDE3 but not by PDE4 suppresses mitogenesis. We therefore sought to determine whether there was a differential effect of PDE3 vs. PDE4 inhibitors on the Ras-Raf-MEK-ERK pathway in cultured MC. Although PDE3 and PDE4 inhibitors activated PKA and modestly elevated cAMP levels to a similar extent, only PDE3 inhibitors suppressed MC mitogenesis (-57%) and suppressed Raf-1 kinase and ERK activity (-33 and -68%, respectively). Both PDE3 and PDE4 inhibitors suppressed B-Raf kinase activity. PDE3 inhibitors increased phosphorylation of Raf-1 on serine 43 and serine 259 and decreased phosphorylation on serine 338; PDE4 inhibitors were without effect. Overexpression of a constitutively active MEK-1 construct reversed the antiproliferative effect of PDE3 inhibitors. PDE3 inhibitors also reduced cyclin A levels (-27%), cyclin D and cyclin E kinase activity (-30 and -50%, respectively), and induced expression of the cell cycle inhibitor p21 (+90%). We conclude that the antiproliferative effects of PDE3 inhibitors are mechanistically related to inhibition of the Ras-Raf-MEK-ERK pathway. Additional cell cycle targets of PDE3 inhibitors include cyclin A, cyclin D, cyclin E, and p21.

Counteractive effects of HGF on PDGF-induced mesangial cell proliferation in a rat model of glomerulonephritis

Activation and proliferation of glomerular mesangial cells play an important role in the development of mesangioproliferative glomerulonephritis. We investigated the role of hepatocyte growth factor (HGF) in regulating activated mesangial cell proliferation. In glomeruli of normal rats, mesangial cells barely expressed the c-Met/HGF receptor. However, when mesangioproliferative glomerulonephritis was induced in rats by the administration of an anti-Thy 1.1 antibody, glomerular HGF expression transiently decreased along with mesangiolysis, and activation of mesangial cells was associated with upregulation of the c-Met receptor. Activated mesangial cells in culture also expressed the c-Met/HGF receptor. Although addition of HGF to cultured mesangial cells did not increase DNA synthesis, HGF did diminish PDGF-induced DNA synthesis. PDGF induced activation of ERK, which continued for at least 48 h. When PDGF and HGF were simultaneously added, HGF inhibited the prolonged activation of ERK, which suggests that early inactivation of PDGF-induced ERK may be involved in the inhibitory effect of HGF on mesangial cell proliferation. Furthermore, administration of HGF to rats with anti-Thy 1.1 nephritis resulted in a selective suppression of activated mesangial cell proliferation, and this suppressive effect was associated with attenuation of phosphorylated glomerular ERK. These results indicate that HGF counteracts PDGF-induced mesangial cell proliferation and functions as a negative regulator of activated mesangial cell proliferation.

Differential effects of low-dose docosahexaenoic acid and eicosapentaenoic acid on the regulation of mitogenic signaling pathways in mesangial cells

Although dietary fish oil supplementation has been used to prevent the progression of kidney disease in patients with IgA nephropathy, relatively few studies provide a mechanistic rationale for its use. Using an antithymocyte (ATS) model of mesangial proliferative glomerulonephritis, we recently demonstrated that fish oil inhibits mesangial cell (MC) activation and proliferation, reduces proteinuria, and decreases histologic evidence of glomerular damage. We therefore sought to define potential mechanisms underlying the antiproliferative effect of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), the predominant omega-3 polyunsaturated fatty acids found in fish oil, in cultured MC. DHA and EPA were administered to MC as bovine serum albumin fatty-acid complexes. Low-dose (10-50 micromol/L) DHA, but not EPA, inhibited basal and epidermal growth factor (EGF)-stimulated [(3)H]-thymidine incorporation in MCs. At higher doses (100 micromol/L), EPA and DHA were equally effective in suppressing basal and EGF-stimulated MC mitogenesis. Low-dose DHA, but not EPA, decreased ERK activation by 30% (P <.01), as assessed with Western-blot analysis using phosphospecific antibodies. JNK activity was increased by low-dose DHA but not by EPA. p38 activity was not significantly altered by DHA or EPA. Cyclin E activity, as assessed with a histone H1 kinase assay, was inhibited by low-dose DHA but not by EPA. DHA increased expression of the cell cycle inhibitor p21 but not p27; EPA had no effect on p21 or p27. We propose that the differential effect of low-dose DHA vs EPA in suppressing MC mitogenesis is related to down-regulation of ERK and cyclin E activity and to induction of p21.

Tumor necrosis factor-alpha stimulates fractalkine production by mesangial cells and regulates monocyte transmigration: down-regulation by cAMP

BACKGROUND

Fractalkine is a CX3C chemokine for mononuclear cells that has been implicated in the recruitment and accumulation of monocytes seen in glomerular diseases. We investigated the mechanisms by which tumor necrosis factor (TNF)-alpha stimulates mesangial cell (MC) fractalkine expression, and the effects of MC-derived fractalkine on monocyte transmigration.

METHODS

Cultured rat MCs were incubated with TNF-alpha, with or without pretreatment with pharmacologic inhibitors of protein kinases or transcriptional factors downstream to TNF-alpha. Fractalkine mRNA and protein were analyzed by Northern and Western blotting. Translocation of nuclear factor (NF)-kappaB was evaluated by immunocytochemical staining. Monocyte transmigration was determined by in vitro chemotaxis assay.

RESULTS

TNF-alpha stimulated MC fractalkine mRNA as well as cell-bound and soluble protein expression in a dose- and time-dependent manner. The soluble fractalkine was shed from the cell-bound form via metalloproteinase-dependent cleavage, and mediated in part TNF-alpha-induced monocyte transmigration in vitro. The incubation of MCs with calphostin C [a selective inhibitor of protein kinase C (PKC)] or PD98059 [a selective inhibitor of p42/44 mitogen-activated protein kinase (MAPK) kinase] attenuated TNF-alpha-stimulated fractalkine mRNA and protein expression. Coincubation of MCs with calphostin C and PD98059 resulted in a synergistic inhibition of TNF-alpha-stimulated fractalkine mRNA and protein expression. Incubation of MCs with phorbol myristate acetate (PMA) for four hours resulted in an increase in fractalkine mRNA expression that could be suppressed by calphostin C or depletion of PKC by pretreatment with PMA for 24 hours. Further, activation of PKC-depleted MCs with TNF-alpha stimulated fractalkine mRNA expression that could be blocked by calphostin C. PD 98059, but not calphostin C, inhibited TNF-alpha-activated phospho-p42/44 MAPK and phospho-c-Jun levels, whereas only calphostin C inhibited TNF-alpha-activated phosphorylation of PKCzeta/iota. The incubation of MCs with MG132, a NF-kappaB inhibitor, abolished TNF-alpha-induced degradation of inhibitory protein of NF-kappaB (I-kappaB)alpha, nuclear translocation of NF-kappaB, and fractalkine expression, without affecting phospho-c-Jun levels. In contrast, curcumin, an activating protein (AP)-1 inhibitor, attenuated TNF-alpha-stimulated phospho-c-Jun levels and fractalkine expression without discernible effects on TNF-alpha-induced degradation of I-kappaBalpha or NF-kappaB nuclear translocation. Neither PD 98059 nor calphostin C affected TNF-alpha-induced degradation of I-kappaBalpha or NF-kappaB nuclear translocation. Additional experiments examining the role of cAMP on MC fractalkine expression showed that the incubation of MCs with TNF-alpha and either db-cAMP or forskolin attenuated TNF-alpha-stimulated fractalkine mRNA and protein expression, preceded by attenuation of TNF-alpha-activated phosphorylation of p42/44 MAPK, and c-Jun, but not phosphorylation of PKCzeta/iota or nuclear translocation of NF-kappaB.

CONCLUSION

The present data indicate that TNF-alpha activation of PKCzeta/iota, p42/44 MAPK, c-Jun/AP-1, and p65/NF-kappaB are involved in TNF-alpha-stimulated MC fractalkine expression, with the soluble fractalkine mediating in part the TNF-alpha-induced monocyte transmigration in vitro. Uncoupling of p42/44 MAPK or c-Jun/AP-1 signals may contribute to cAMP inhibition of MC fractalkine expression activated by TNF-alpha.

Effects of cilostazol on resting ankle pressures and exercise-induced ischemia in patients with intermittent claudication

During exercise, patients with intermittent claudication (IC) have decreased limb arterial blood pressure that recovers during rest. A novel method for assessing dynamic recovery of function is measurement of the hemodynamic response after exercise. Cilostazol (Pletal), a new agent for the treatment of IC, increases walking distance and may decrease ischemic burden. The objective of this study was to assess the effect of cilostazol versus placebo on hemodynamic measurements after exercise-induced ischemia in patients with IC. Two double-blind, placebo-controlled studies with similar inclusion/exclusion criteria and duration (24 weeks) were pooled. Patients walked on a treadmill at 2.0 miles/h (3.2 km/h) on a 12.5% grade until the claudication-limited maximal walking distance (MWD) was reached. Anterior and posterior tibial pressures were measured with Doppler ultrasound at baseline and at 1, 5, and 9 min during recovery. Area under the curve (AUC), a measure of the time course of recovery of systolic pressure after exercise-induced ischemia, and ankle-brachial index (ABI) were calculated and compared using analysis of variance (ANOVA). All three treatment groups (308 patients randomized to cilostazol 100 mg bid, 303 to cilostazol 50 mg bid, and 299 to placebo) had similar baseline characteristics. Mean post-exercise AUC for cilostazol 100 mg and 50 mg bid versus placebo increased by 0.31 (p = 0.001) and 0.26 (p = 0.004), respectively. Mean resting ABI increased by 0.03 (p = 0.0039) and 0.04 (p = 0.0001) in the cilostazol 100 mg and 50 mg bid groups, respectively. In conclusion, following 24 weeks of treatment, cilostazol increased the ABI at rest and improved the recovery time of ankle pressures post-exercise.

Selection of a WEHI-3B leukemia cell subclone resistant to inhibition by cholera toxin

The studies on the inhibitory effect exerted by Cholera Toxin (CT) on cell growth and proliferation indicate a remarkable heterogeneity of cell response suggesting that the inhibition represents the final event of many different ways or mechanisms. After CT binding, cAMP accumulation may not occur (as in L1210 leukemia cells) or, when occurring (as in SR-4987 stromal cells), may not be coupled with the antiproliferative effect of CT. In WEHI-3B cells CT binds a Gal-GalNac-GM1b receptor and the anticlonogenic effect of CT seems correlated with cAMP accumulation. To demonstrate the central role of cAMP in WEHI-3B cells, starting from the sensitive cell strain we selected and established a clone of WEHI-3B resistant to CT. This revertant clone (WEHI-3B/CT/REV) is currently cultured in the absence of CT and in the proliferation assay shows a dramatic resistance (>46,000 than the parental cells). Stimulation ofWEHI-3B/CT/REV cells by cholera toxin failed to enhance cAMP and the ganglioside-CT binding studied on Thin Layer Chromatography (TLC) blots showed that the resistant cells lost the spot correspondent to the migration of Gal-GalNac-GM1b ganglioside. Both the lines respond at the same level to the adenylate cyclase stimulation by forskolin and the incorporation of GM1a did not decrease the resistance of WEHl-3B/CT/REV. These data confirm that Gal-GalNac-GM1b is the most important functional receptor for CT in WEHI-3B cells able to transduce the signal by enhancing cAMP which in turn inhibits cell proliferation (probably by cAMP dependent protein kinase activation). Our study describes the first cell line resistant to CT originated from a susceptible parental strain and provides a new interesting cell model for studying the cAMP dependent mechanisms involved in cell growth regulation.

Cyclic AMP specific phosphodiesterase activity and colon cancer cell motility

To investigate mechanisms for regulation of intracellular cAMP involved in cancer cell invasion, phosphodiesterase (PDE) activity in a colon cancer cell line, DLD-1, was studied. Activities of PDE 2, 4, and 5 were detected in DLD-1 cells by pharmacological approach. Specific and cell permeable inhibitors for those PDEs were used to determine which PDE is responsible for cAMP turnover involved in cancer cell motility. Treatment of DLD-1 cells with rolipram and Ro-20-1724 inhibitors for PDE 4, elevated intracellular cAMP contents three to five times of control. EHNA, an inhibitor for PDE 2, and zaprinast. an inhibitor for PDE 5, did not affect cAMP levels. To assess cellular motility, we utilized chemotaxis assay. EHNA and zaprinast did not suppress serum-induced chemotaxis. In contrast, rolipram and Ro-20-1724, suppressed chemotaxis in a dose dependent fashion. These suggest that PDE 4 plays a critical role in regulating intracellular cAMP levels of colon cancer cells and is involved in cancer invasion. PDE 4 can be a novel target of anti-invasion drug.

cADP-ribose/ryanodine channel/Ca2+-release signal transduction pathway in mesangial cells

Signaling via release of Ca2+ from intracellular stores is mediated by several systems, including the inositol 1,4,5-trisphosphate (IP3) and cADP-ribose (cADPR) pathway. We recently discovered a high capacity for cADPR synthesis in rat glomeruli and cultured mesangial cells (MC). We sought to determine whether 1) cADPR synthesis in MC is regulated by cytokines and hormones, 2) ryanodine receptors (RyRs) are expressed in MC, and 3) Ca2+ is released through RyRs in response to cADPR. We found that ADP-ribosyl cyclase, a CD38-like enzyme that catalyzes cADPR synthesis, is upregulated in MC by tumor necrosis factor-alpha, interleukin-1beta, and all-trans retinoic acid (atRA). [3H]ryanodine binds to microsomal fractions from MC with high affinity in a Ca2+-dependent manner; binding is enhanced by specific RyR agonists and blocked by ruthenium red and cADPR. Western blot analysis confirmed the presence of RyR in MC. Release of 45Ca2+ from MC microsomes was stimulated by cADPR; release was blocked by ruthenium red and 8-bromo-cADPR. ADPR (non-cyclic) was without effect. In MC, TNF-alpha and atRA amplified the increment of cytoplasmic Ca2+ elicited by vasopressin. We conclude that MC possess elements of a novel ADP-ribosyl cyclase-->cADPR-->RyR-->Ca2+-release signaling pathway subject to regulation by proinflammatory cytokines and steroid superfamily hormones.

Expression of phosphodiesterase 3 in rat submandibular gland cell lines

A recent preliminary (unpublished) study showed that phosphodiesterase (PDE) 3A and 3B are expressed in rat submandibular glands. Here, PDE3 activity was detected in homogenates of rat submandibular gland acinar epithelial (SMIE) cells, but not rat A5 (epithelial duct) cells. Most of the PDE3 activity in SMIE cells was recovered in the particulate fraction. Only PDE3B mRNA was detected by reverse transcription-polymerase chain reaction in RNA from SMIE cells. The nucleotide sequence of the fragment was identical to the sequence of rat PDE3B. The PDE3 specific inhibitor, OPC3689 (10 and 50 microM), inhibited the growth of SMIE cells (19 and 63%), but not A5 cells. As the submandibular gland contains many types of cells, these results indicate that PDE3B may regulate a cAMP pool that is important in submandibular gland acinar epithelial cell function.

Nephron distribution of total low Km cyclic AMP phosphodiesterase in mouse, rat and rabbit kidney

The activity of cAMP degradation enzyme, cAMP phosphodiesterase (cAMP PDE), in renal tubules is a critically important factor in determining cellular cAMP levels, particularly in response to hormones. In this study we examine the nephron distribution of cAMP PDE activity in the mouse, rat and rabbit kidney and important cellular regulators of cAMP PDE, namely calmodulin and adenosine triphosphate (ATP). We assayed total low Km cAMP PDE in microdissected tubule segments, using 10(-6) M (3H) cAMP as a substrate. Activities were expressed in fentomol cAMP hydrolyzed per minute per mm tubular length or per one glomerulus. The content of ATP was measured in outer medullary collecting duct and medullary thick ascending limb of Henle's loop with microbioluminescence assay using firefly luciferase. In mouse kidney, cAMP PDE was significantly higher in all tubular segments compared to glomerulus. Proximal convoluted tubule, proximal straight tubule, medullary thick ascending limb of Henle's loop (mTAL), and outer medullary collecting duct (OMCD) had intermediated activity. Greater cAMP PDE activity was detected in cortical ascending limb of Henle's loop (cTAL), cortical collecting duct and in distal convoluted tubule (DCT). The highest activity was found in connecting tubules. In rat, nephron distribution of cAMP PDE activities was similar to mouse, except that activity in glomeruli was higher than in mouse glomeruli. In rabbit, nephron distribution of cAMP PDE activities was different from those of mouse and rat. There was no single prominent segment with high cAMP PDE activity. DCT and cTAL showed low enzyme activity. Overall, the highest cAMP PDE activities were measured in the mouse and the lowest were measured in the rabbit nephrons, with those of rat nephron showing an intermediate activity. The maximum effective dose of the calmodulin antagonist, trifluoperazine (200 microM), inhibited cAMP PDE in all nephron segments from the rat kidney. However, there is no statistical significance of its inhibition among nephron segments. In OMCD and mTAL of the rat kidney, cAMP PDE activity was inhibited by ATP (5 mM to approximately 10 mM) which is far beyond the physiological concentartion of ATP in normal epithelial cell. Actual determinations of ATP in mTAL and OMCD were 0.1 mM and 0.17 mM, respectively. These observations show that distal segments of tubules have more active catabolism of cAMP than proximal segments. cAMP PDE in each nephron segment appear to be almost equally dependent on trifluoperazine-sensitive pathway that may reflect the Ca2+-calmodulin system. Cellular concentration of ATP might not be involved in the regulation of the total low Km cAMP PDE activity in rat mTAL and OMCD.

Nicotinic acid-adenine dinucleotide phosphate (NAADP) elicits specific microsomal Ca2+ release from mammalian cells

Nicotinic acid-adenine dinucleotide phosphate (NAADP), a molecule derived from beta-NADP, has been shown to promote intracellular calcium release in sea urchin eggs. However, there is little information regarding the role of NAADP in the regulation of intracellular calcium fluxes in mammalian cells. We found recently that several mammalian tissues have a high capacity for NAADP synthesis, as assessed by sea urchin egg bioassay. To determine the functional significance of NAADP production by mammalian tissues, we sought to determine whether NAADP is capable of inducing calcium release from microsomes prepared from cultured cells. We found that NAADP, but not beta-NADP, activates a specific microsomal calcium release system in mesangial cells isolated from rat kidney; NAADP was without effect in renal tubular epithelial cells. NAADP-induced calcium release is not affected by inhibitors of the inositol 1,4,5-trisphosphate or ryanodine channels. However, NAADP-elicited calcium release was inhibited by L-type calcium channel blockers and by alkaline phosphatase treatment of NAADP. NAADP also promotes specific microsomal calcium release in rat vascular smooth muscle cells, cardiac myocytes, fibroblasts and a human leukaemia cell line, indicating that the capacity for NAADP-induced calcium release is widespread in mammalian cells. We propose that NAADP may be an important regulator of intracellular calcium in many mammalian tissues.

Cilostazol: treatment of intermittent claudication

OBJECTIVE

To review the pharmacology and clinical utility of cilostazol, an antiplatelet and vasodilator agent approved for the management of intermittent claudication.

DATA SOURCES

Primary literature on cilostazol was identified from a comprehensive MEDLINE literature search (1980-February 2000). Selected meeting abstracts and manufacturer literature were also used as source material. Indexing terms included cilostazol, intermittent claudication, platelet inhibitors, and restenosis.

STUDY SELECTION

Human clinical, pharmacokinetic and randomized comparative trials performed in the US and Asia were reviewed. Selected in vitro, ex vivo, and animal studies were evaluated when human data were not available.

DATA SYNTHESIS

Intermittent claudication, defined as reproducible discomfort of a muscle group induced by exercise and relieved by rest, is the most common clinical manifestation of peripheral arterial disease (PAD). Cilostazol, a specific inhibitor of cyclic adenosine monophosphate phosphodiesterase in platelets and vascular smooth-muscle cells, is a potent antiplatelet agent and vasodilator that reduces vascular proliferation and has lipid-lowering effects in vivo. Recent multicenter, randomized, placebo-controlled trials have led to approval of cilostazol by the Food and Drug Administration for relief of intermittent claudication in patients with stable PAD. Cilostazol doubled walking distances and improved quality of life compared with placebo in these studies. One trial found that cilostazol was more effective than pentoxifylline, the only alternative pharmacologic therapy for claudication. Although frequent (approximately 50%) minor adverse effects, including headache, diarrhea, and palpitations, may occur in clinical practice, cilostazol has not been associated with major adverse events or increased mortality. Small, nonblind studies suggest that cilostazol may prove useful in preventing thrombosis and restenosis following percutaneous coronary interventions, although these remain unlabeled uses.

CONCLUSIONS

The unique combination of antiplatelet, vasodilatory, and antiproliferative effects of cilostazol appear to make it an attractive agent for use in patients with PAD. Clinical trials demonstrating a significant improvement in walking distances with cilostazol therapy suggest that it will be an important tool in improving symptoms and quality of life in patients with intermittent claudication.

Nicotinic acid adenine dinucleotide phosphate: a new Ca2+ releasing agent in kidney

Nicotinic acid adenine dinucleotide phosphate (NAADP), a molecule derived from beta-NADP, has been shown to trigger Ca2+ release from intracellular stores of invertebrate eggs and mammalian cell microsomes. NAADP-induced Ca2+ release occurs through a mechanism distinct from that of inositol-1,4,5-trisphosphate- or cyclic ADP-ribose-elicited Ca2+ release. This study investigated whether NAADP can be synthesized in rat kidney. Extracts from glomeruli, mesangial cells, and papilla have high NAADP synthetic capacities. Conversely, synthesis of NAADP in kidney cortex was almost undetectable. Furthermore, 9-cis-retinoic acid significantly up-regulated NAADP synthesis in mesangial cells. Authenticity of NAADP biosynthesis in glomeruli was affirmed by HPLC analysis. NAADP stimulated Ca2+ release from mesangial cell microsomes through a pathway distinct from that of inositol-1,4,5-trisphosphate or cyclic ADP-ribose. NAADP-triggered Ca2+ release may play an important role in regulation of renal function.

Cell type-specific regulation of B-Raf kinase by cAMP and 14-3-3 proteins

Cyclic AMP can either activate or inhibit the mitogen-activated protein kinase (MAPK) pathway in different cell types; MAPK activation has been observed in B-Raf-expressing cells and has been attributed to Rap1 activation with subsequent B-Raf activation, whereas MAPK inhibition has been observed in cells lacking B-Raf and has been attributed to cAMP-dependent protein kinase (protein kinase A)-mediated phosphorylation and inhibition of Raf-1 kinase. We found that cAMP stimulated MAPK activity in CHO-K1 and PC12 cells but inhibited MAPK activity in C6 and NB2A cells. In all four cell types, cAMP activated Rap1, and the 95- and 68-kDa isoforms of B-Raf were expressed. cAMP activation or inhibition of MAPK correlated with activation or inhibition of endogenous and transfected B-Raf kinase. Although all cell types expressed similar amounts of 14-3-3 proteins, approximately 5-fold less 14-3-3 was associated with B-Raf in cells in which cAMP was inhibitory than in cells in which cAMP was stimulatory. We found that the cell type-specific inhibition of B-Raf could be completely prevented by overexpression of 14-3-3 isoforms, whereas expression of a dominant negative 14-3-3 mutant resulted in partial loss of B-Raf activity. Our data suggest that 14-3-3 bound to B-Raf protects the enzyme from protein kinase A-mediated inhibition; the amount of 14-3-3 associated with B-Raf may explain the tissue-specific effects of cAMP on B-Raf kinase activity.

MAPK signaling and the kidney

Following an overview of the biochemistry of mitogen-activated protein kinase (MAPK) pathways, the relevance of these signaling events to specific models of renal cell function and pathophysiology, both in vitro and in vivo, will be emphasized. In in vitro model systems, events activating the principal MAPK families [extracellular signal-regulated and c-Jun NH(2)-terminal kinase and p38] have been best characterized in mesangial and tubular epithelial cell culture systems and include peptide mitogens, cytokines, lipid mediators, and physical stressors. Several in vivo models of proliferative or toxic renal injury are also associated with aberrant MAPK regulation. It is anticipated that elucidation of downstream effector signaling mechanisms and a clearer understanding of the immediate and remote upstream activating pathways, when applied to these highly clinically relevant model systems, will ultimately provide much greater insight into the basis for specificity now seemingly absent from these signaling events.

ADP-Ribosyl cyclase in rat vascular smooth muscle cells: properties and regulation

We investigated whether ADP-ribosyl cyclase (ADPR-cyclase) in rat vascular smooth muscle cells (VSMCs) has enzymatic properties that differ from the well-characterized CD38-antigen ADPR-cyclase, expressed in HL-60 cells. ADPR-cyclase from VSMCs, but not CD38 ADPR-cyclase from HL-60 cells, was inhibited by gangliosides (10 micromol/L) GT(1B), GD(1), and GM(3). Preincubation of membranes from CD38 HL-60 cells, but not from VSMCs, with anti-CD38 antibodies increased ADPR-cyclase activity; CD38 antigen was detected both in VSMCs and in HL-60 cells. ADPR-cyclase in VSMC membranes was more sensitive than CD38 HL-60 ADPR-cyclase to inactivation by N-endoglycosidase F and to thermal inactivation at 45 degrees C. The specific activity of ADPR-cyclase in membranes from VSMCs was >20-fold higher than in membranes from CD38 HL-60 cells. Most importantly, VSMC ADPR-cyclase was inhibited by Zn(2+) and Cu(2+) ions; the inhibition by Zn(2+) was dose dependent, noncompetitive, and reversible by EDTA. In contrast, Zn(2+) stimulated the activity of CD38 HL-60 ADPR-cyclase and other known types of ADPR-cyclases. Retinoids act either via the nuclear receptor retinoic acid receptor or retinoid X receptor, including all-trans retinoic acid (atRA), and panagonist 9-cis-retinoic acid-upregulated VSMC ADPR-cyclase; the stimulatory effect of atRA was blocked by actinomycin D and cycloheximide. 1,25(OH)(2)-Vitamin D(3) (calciferol) stimulated VSMC ADPR-cyclase dose dependently at subnanomolar concentrations (ED(50) congruent with 56 pmol/L). Oral administration of atRA to rats resulted in an increase of ADPR-cyclase activity in aorta ( congruent with+60%) and, to a lesser degree, in myocardium of left ventricle (+18%), but atRA had no effect on ADPR-cyclases in lungs, spleen, intestinal smooth muscle, skeletal muscle, liver, or testis. Administration of 3,5,3'-triiodothyronine (T(3)) to rats resulted in an increase of ADPR-cyclase activity in aorta ( congruent with+89%), but not in liver or brain. We conclude the following: (1) ADPR-cyclase in VSMCs has enzymatic properties distinct from "classic" CD38 ADPR-cyclase, especially sensitivity to inhibition by Zn(2+) and Cu(2+); (2) ADPR-cyclase in VSMCs is upregulated by various retinoids, calcitriol, and T(3) in vitro; and (3) administration of atRA and T(3) increases ADPR-cyclase in aorta in vivo. We suggest that the cADPR signaling system plays an important role in the regulation of VSMC functions in response to steroid superfamily hormones.

Suppression of arterial intimal hyperplasia by cilostamide, a cyclic nucleotide phosphodiesterase 3 inhibitor, in a rat balloon double-injury model

The effects of cilostamide, a cyclic nucleotide phosphodiesterase 3 (PDE3) selective inhibitor, on vascular intimal hyperplasia were evaluated using a single-balloon injury model and a double-injury model in which the rat common carotid artery was subjected to a second injury at a site injured 14 days previously. In the double-injury model, the second balloon injury caused more severe intimal hyperplasia (intima/media (IM) ratio, 1.88+/-0.10) than in the single-injury model (1.09+/-0.08). Histopathological study revealed that vascular smooth muscle cells (VSMC) were the predominant cell-type in the affected neointimal area. Oral administration of cilostamide for 2 weeks after the second injury suppressed intimal hyperplasia in the double-injury model (30 mg kg(-1) bid, 83% inhibition in terms of the IM ratio, P<0.05; 100 mg kg(-1) bid, 69% inhibition, P<0.05). Similar effects were also observed in the single-injury model with oral administration of cilostamide for 2 weeks (100 mg kg(-1) bid, 36% inhibition, P<0.01). Cilostamide inhibited DNA synthesis of cultured VSMC stimulated by foetal calf serum or different kinds of growth factors, but did not affect their migration stimulated by platelet-derived growth factor (PDGF)-BB. Cilostamide significantly increased the cyclic AMP concentration of VSMC dose-dependently. These results indicate that cilostamide suppresses intimal hyperplasia both in the single- and double-injury models of rat, presumably by inhibiting proliferation rather than migration of VSMC. It is suggested that PDE3 inhibitors might find application in preventing intimal hyperplasia following angioplasty such as percutaneous transluminal coronary angioplasty (PTCA) or stent.

Phosphodiesterase type III inhibitor, cilostazol, inhibits colon cancer cell motility

Metastasis of cancer cells is initiated by the cellular migration into extracellular matrix and surrounding vessels. We previously showed that elevation of cAMP levels in cancer cells suppressed trans-cellular migration in vitro. Drugs that can elevate cAMP levels in cancer cells effectively may be applied to prevent metastasis in cancer patients. Cilostazol, an oral anti-platelet drug, is a specific cAMP phosphodiesterase type III inhibitor and has been clinically used to treat thrombosis patients. In chemotaxis assay, cellular migration of human colon cancer cells, DLD- 1, was induced by 10 microg/ml of soluble fibronectin or 10% of fetal bovine serum (FBS). Treatment with cilostazol (50 microM) suppressed 92.3% or 84.6% of the migration in control cells, respectively. When DLD-1 cells were stimulated by soluble fibronectin in phagokinetic assay, migration assessed by the area of gold particle phagocytosis track was induced and cilostazol also decreased 67.3% of the cellular migration in control cells. Furthermore, in the trans-cellular migration assay, cilostazol suppressed cancer cell invasion induced by FBS. Thus, cilostazol can suppress colon cancer cell motility and might be effective as an anti-metastasis drug for cancer patients.

cAMP stimulates the in vitro proliferation of renal cyst epithelial cells by activating the extracellular signal-regulated kinase pathway

BACKGROUND

: Cellular proliferation is a key factor in the enlargement of renal cysts in autosomal dominant polycystic kidney disease (ADPKD). We determined the extent to which adenosine 3':5'-cyclic monophosphate (cAMP) may regulate the in vitro proliferation of cyst epithelial cells derived from human ADPKD cysts.

METHODS

: Epithelial cells from cysts of individuals with ADPKD and from normal human kidney cortex (HKC) of individuals without ADPKD were cultured. The effects of agonists and inhibitors on the rate of cellular proliferation and the activation of extracellular signal-regulated kinase (ERK1/2) were determined.

RESULTS

: 8-Br-cAMP (100 micromol/L) stimulated the proliferation of cells from eight different ADPKD subjects to 99.0% above baseline; proliferation was inhibited by protein kinase A (PKA) antagonists H-89 (97%) and Rp-cAMP (90%). Forskolin (10 micromol/L), which activates adenylyl cyclase, increased proliferation 124%, and receptor-mediated agonists arginine vasopressin, desmopressin, secretin, vasoactive intestinal polypeptide, and prostaglandin E2 stimulated proliferation 54.2, 56.3, 46.7, 37.1, and 48.3%, respectively. The mitogen extracellular kinase (MEK) inhibitor PD98059 completely inhibited ADPKD cell proliferation in response to cAMP agonists, but genistein, a receptor tyrosine kinase inhibitor, did not block cAMP-dependent proliferation. cAMP agonists increased the activity of ERK above control levels within five minutes. In contrast to ADPKD, proliferation and ERK activity of cells derived from normal HKC were not stimulated by cAMP agonists, although electrogenic Cl- secretion was increased by these agonists in both ADPKD and HKC cell monolayers.

CONCLUSIONS

: We conclude that cAMP agonists stimulate the proliferation of ADPKD but not HKC epithelial cells through PKA activation of the ERK pathway at a locus distal to receptor tyrosine kinase. We suggest that the adenylyl cyclase signaling pathway may have a unique role in determining the rate of cyst enlargement in ADPKD through its actions to stimulate cellular proliferation and transepithelial solute and fluid secretion.

Expression of profilin, an actin-binding protein, in rat experimental glomerulonephritis and its upregulation by basic fibroblast growth factor in cultured rat mesangial cells

Profilin binds to actin monomer to regulate actin polymerization, and to phosphatidylinositol 4,5-bisphosphate to inhibit hydrolysis by phospholipase Cgamma1. This study investigated the expression of profilin in rat anti-Thy-1.1 mesangial proliferative glomerulonephritis (GN) and examined the effect of growth factors on its expression in cultured rat mesangial cells. Profilin mRNA was constitutively expressed in isolated glomeruli of untreated rats. However, in glomeruli of anti-Thy-1.1 GN rats, its expression was upregulated beginning on day 1, reaching a peak level on day 4 (3.9-fold versus control glomeruli), and decreased on day 14, as determined by competitive reverse transcription-PCR. Increased expression of profilin protein was confirmed using immunoblotting and immunohistochemistry. Immunoelectron microscopy revealed the presence of profilin in plasma membrane and the rough endoplasmic reticulum of mesangial cells, indicating that profilin was produced in mesangial cells. In cultured rat mesangial cells, expression of profilin mRNA and protein was upregulated by basic fibroblast growth factor but not by platelet-derived growth factor or transforming growth factor-beta. Suppression of profilin expression using an antisense oligonucleotide against profilin inhibited [3H]thymidine uptake. These findings indicated the involvement of profilin in anti-Thy-1.1 GN and suggest that the upregulation of profilin might be involved in the progression of anti-Thy-1.1 GN possibly by affecting cell growth.

Suppressive effects of fish oil on mesangial cell proliferation in vitro and in vivo

BACKGROUND

Mesangial cell proliferation is a characteristic feature of IgA nephropathy and many other forms of glomerulonephritis. Recent clinical studies have shown that dietary fish oil supplementation retards renal disease progression in patients with IgA nephropathy. The mechanism by which this effect occurs is unknown.

METHODS

The anti-Thy 1.1 (ATS) model of mesangial proliferative glomerulonephritis was employed to test the hypothesis that dietary fish oil supplementation reduces mesangial cell proliferation following acute injury. Subcultured rat mesangial cells were used to determine the in vitro effects of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the primary components of fish oil, on proliferation.

RESULTS

Following antithymocyte serum (ATS) administration, proteinuria was significantly decreased in animals treated with fish oil compared with sesame oil-treated controls. In ATS rats given fish oil, there was less mesangial cell and matrix expansion, mesangiolysis, or basement membrane disruption (delta% = -40%). ATS rats receiving fish oil had less glomerular cell proliferation (PCNA-delta% = -50%) and a reduction of alpha-smooth muscle actin expression (delta% = -27%) by mesangial cells. In subcultured rat mesangial cells, DHA, but not EPA, significantly inhibited proliferation.

CONCLUSIONS

Fish oil inhibits mesangial cell activation and proliferation in ATS glomerulonephritis, reduces proteinuria, and decreases histologic evidence of glomerular damage. In vitro, the antiproliferative effects of fish oil are more likely related to the action of DHA. We suggest that orally administered fish oil, or purified DHA, may have a suppressive effect in acute phases or relapses of glomerulopathies by inhibiting activation and proliferation of mesangial cells.

Synthesis of NAADP and cADPR in mitochondria

Here we investigated whether cADPR and NAADP are synthesized in mitochondria. We found that ADPR-cyclase activity is present in mitochondria. In addition, we describe for the first time synthesis of NAADP in this intracellular organelle. ADPR-cyclase activities (V(MAX)) and NAADP synthesis in mitochondria were about 4-fold lower than that in plasma membranes. Otherwise, ADPR-cyclases in mitochondria and in plasma membranes have similar catalytic properties in terms of apparent K(m) for the substrate NGD and K(i) values for inhibition by dithiotreitol, beta-NAD, and nicotinamide. ADPR-cyclase in plasma membranes and to a lesser degree mitochondrial enzyme, was inhibited by Zn(2+) and Cu(2+); ADPR-cyclase from mitochondria was more stable upon thermal inactivation. CD38 antigen, determined by Western blot, was well-expressed in plasma membranes but was far less so (17-fold less) in mitochondria. The major difference between ADPR-cyclase activity in mitochondria and plasma membranes is that mitochondrial cyclase activity was increased by incubation with nonionic detergents. Conversely, the incubation with phosphatidylinositol-specific phosphodiesterase C (PI-PLC) released ADPR-cyclase activity from plasma membranes, but not from mitochondria. We conclude that ADPR-cyclase in mitochondria and in plasma membranes are both multifunctional enzymes with similar catalytic properties; however, the two ADPR-cyclases differ in the mode of anchoring to the membrane: by glycosylphosphoinositol anchor in plasma membranes and by hydrophobic interactions in mitochondria. In addition, synthesis of NAADP can also be found in intracellular organelles via mitochondria. We propose that independent mitochondrial cADPR and NAADP systems may have an intracrine signaling function that is not dependent on direct input by extracellular hormonal stimuli, but rather responds to changes of intermediary cellular metabolism.

Cyclic nucleotide phosphodiesterases (PDE) 3 and 4 in normal, malignant, and HTLV-I transformed human lymphocytes

Intracellular cyclic AMP, determined in part by cyclic nucleotide phosphodiesterases (PDEs), regulates proliferation and immune functions in lymphoid cells. Total PDE, PDE3, and PDE4 activities were measured in phytohemagglutinin (PHA)-activated peripheral blood mononuclear cells (PBMC-PHA), normal natural killer (NK) cells, Jurkat and Kit225-K6 leukemic T-cells, T-cell lines transformed with human T-lymphotropic virus (HTLV)-I (a retrovirus that causes adult T-cell leukemia/lymphoma) and HTLV-II (a nonpathogenic retrovirus), normal B-cells, and B-cells transformed with Epstein-Barr virus (EBV). All cells exhibited PDE3 and PDE4 activities but in different proportions. In EBV-transformed B cells, PDE4 was much higher than PDE3. HTLV-I+ T-cells differed significantly from other T-lymphocyte-derived cells in also having a higher proportion of PDE4 activities, which apparently were not related to selective induction of any one PDE4 mRNA (judged by reverse transcription-polymerase chain reaction) or expression of the HTLV-I regulatory protein Tax. In MJ cells (an HTLV-I+ T-cell line), Jurkat cells, and PBMC-PHA cells, the tyrosine kinase inhibitor herbimycin A strongly inhibited PDE activity. Growth of MJ cells was inhibited by herbimycin A and a protein kinase C (PKC) inhibitor, and was arrested in G1 by rolipram, a specific PDE4 inhibitor. Proliferation of several HTLV-I+ T-cell lines, PBMC-PHA, and Jurkat cells was inhibited differentially by forskolin (which activates adenylyl cyclase), the selective PDE inhibitors cilostamide and rolipram, and the nonselective PDE inhibitors pentoxifylline and isobutyl methylxanthine. These results suggest that PDE4 isoforms may be functionally up-regulated in HTLV-I+ T-cells and may contribute to the virus-induced proliferation, and that PDEs could be therapeutic targets in immune/inflammatory and neoplastic diseases.

Pentoxifylline attenuates experimental mesangial proliferative glomerulonephritis

BACKGROUND

Accumulation of glomerular macrophages, proliferation of mesangial cells (MCs), and deposition of extracellular matrix proteins are pathobiological hallmarks of glomerulonephritis. We previously reported that a clinically available nonselective inhibitor of cyclic 3',5'-nucleotide phosphodiesterase, pentoxifylline (PTX), inhibits proliferation of cultured rat MCs, as well as collagen production by these cells. In this study, we investigated the in vivo effects of PTX on rat anti-Thy1 disease, a model of mesangial proliferative nephritis.

METHODS

Anti-Thy1 nephritis was induced in Sprague-Dawley rats by injecting mouse anti-rat Thy1 antibodies intravenously. Nephritic rats were randomly assigned to receive PTX (0.1 g/kg/day) or vehicle (phosphate-buffered saline) and were sacrificed at various time points. Paraffin kidney sections were stained with hematoxylin and periodic acid-Schiff reagents for glomerular histology. Frozen kidney sections were stained by monoclonal antibodies against proliferating cell nuclear antigen, ED-1, and alpha-smooth muscle actin and were visualized by color development from a horseradish peroxidase reaction. Monocyte chemoattractant protein-1 (MCP-1), intercellular adhesion molecule-1 (ICAM-1), and various extracellular matrix mRNAs were analyzed by Northern blotting. Urine protein concentrations were determined by Lowry's method.

RESULTS

Nephritic rats treated with PTX excreted less urinary protein on day 5 of nephritis than vehicle-treated nephritic rats. In periodic acid-Schiff-stained kidneys from PTX-treated nephritic rats, there was attenuation of both glomerular cellularity and glomerular sclerosis compared with vehicle-treated nephritic rats. PTX decreased the augmented glomerular mRNA levels of MCP-1 and ICAM-1 at two hours and on day 1 of nephritis. Immunoreactive staining showed that PTX reduced the number of proliferating glomerular macrophages on days 1, 2, and 3, but not at two hours of nephritis, compared with vehicle-treated nephritic rats. On day 5, PTX decreased the number of activated proliferating MCs and attenuated the glomerular mRNA levels of type I (alpha1), type III (alpha1), and type IV (alpha1) collagen and fibronectin compared with vehicle-treated nephritic rats.

CONCLUSION

The administration of PTX to rats with anti-Thy1 disease reduces accumulation and proliferation of glomerular macrophages, attenuates proteinuria, suppresses activation and proliferation of MCs, and ameliorates glomerular sclerosis. These results suggest that PTX may have a suppressive effect in acute phases or relapses of mesangial proliferative glomerulonephritis.

Roles of prostaglandin E receptors in mesangial cells under high-glucose conditions

BACKGROUND

High glucose reportedly stimulates prostaglandin (PG) E2 production and DNA synthesis in mesangial cells (MCs). However, the pathophysiological significance of PGE2 in MCs has remained unclear.

METHODS

The effects of prostanoids on [3H]-thymidine uptake and cAMP production in rat MCs cultured with 5.6 mM glucose, 25 mM glucose, or 5.6 mM glucose supplemented with 19.4 mM mannitol were examined. The gene expression of PGE2 receptor (EP) subtypes in MCs was analyzed with Northern blotting techniques.

RESULTS

Northern blotting indicated EP1 and EP4 gene expression in MCs. EP1 agonists and PGE2 stimulated [3H]-thymidine uptake in MCs. EP1 antagonists dose dependently attenuated high-glucose-induced [3H]-thymidine uptake, which suggests EP1 involvement, by an increase in intracellular Ca2+, in DNA synthesis of MCs. On the other hand, forskolin, db-cAMP, and 11-deoxy-PGE1, an EP4/EP3/EP2 agonist, significantly decreased DNA synthesis in MCs. These inhibitory effects are thought to be mediated via EP4 as a result of an increase in cAMP synthesis. The effects via EP4 seem to be particularly important because PGE2-induced cAMP synthesis was significantly attenuated in the high-glucose group compared with the mannitol group, in which [3H]-thymidine uptake did not increase in spite of augmented PGE2 production.

CONCLUSION

The increase in DNA synthesis in MCs under high-glucose conditions can be explained, at least in part, by the high-glucose-induced inhibition of cAMP production via EP4, which augments EP1 function in conjunction with the overproduction of PGE2.

Transcriptional regulation of the interleukin-6 gene in mesangial cells

Cytokine secretion by mesangial cells (MC) plays a major role in the pathogenesis of glomerulonephritis. To define signaling events that occur during the activation of MC, the cell-specific transcriptional regulation of the interleukin-6 (IL-6) gene was studied. Stimulation with lipopolysaccharide and IL-1beta resulted in the full induction of IL-6 expression only if the cells were coincubated with cAMP agonists; this effect was attenuated by protein kinase A inhibitors. In reporter gene experiments, the IL-6 promoter showed a stimulation pattern comparable to that of the endogenous gene. Elimination of individual transcription factor binding sites provided evidence for functional roles for four cis-acting elements, i.e., activator protein-1, cAMP response element-binding protein (CREB), nuclear factor for IL-6 expression (NF-IL6), and nuclear factor-kappaB (NF-kappaB). Electrophoretic mobility shift assays using nuclear extracts from MC revealed that the DNA-binding activities of activator protein-1 and NF-KB were inducible, whereas no change could be observed for CREB and NF-IL6. The presence of several transcription factor proteins, including JunB, JunD, c-Fos, Fra-1, CREB-1, activating transcription factor-2, NF-KB p50, p52, and p65, and CAAT/enhancer-binding protein-delta, was demonstrated by supershift analysis. Of particular interest was the novel finding of the participation of NF-kappaB p65 in the NF-IL6 complex. In summary, a signal transduction pathway in MC that requires protein kinase A activation in addition to a second signal provided by lipopolysaccharide or IL-1beta was identified.

Modulation of human airway smooth muscle proliferation by type 3 phosphodiesterase inhibition

Elevation in cell cAMP content can inhibit mitogenic signaling in cultured human airway smooth muscle (HASM) cells. We studied the effects of the type 3-selective phosphodiesterase inhibitor siguazodan, the type 4-selective phosphodiesterase inhibitor rolipram, and the nonselective inhibitor 3-isobutyl-1-methylxanthine (IBMX) on proliferation of cultured HASM cells. At concentrations selective for the type 3 phosphodiesterase isoform, siguazodan inhibited both [3H]thymidine incorporation (IC50 2 microM) and the increase in cell number (10 microM; 64% reduction) induced by platelet-derived growth factor-BB (20 ng/ml). These effects were mimicked by IBMX. At concentrations selective for type 4 phosphodiesterase inhibition, rolipram was without effect. A 20-min exposure to siguazodan and rolipram did not increase whole cell cAMP levels. However, in HASM cells transfected with a cAMP-responsive luciferase reporter (p6CRE/Luc), increases in cAMP-driven luciferase expression were seen with siguazodan (3.9-fold) and IBMX (16.5-fold). These data suggest that inhibition of the type 3 phosphodiesterase isoform present in airway smooth muscle results in inhibition of mitogenic signaling, possibly through an increase in cAMP-driven gene expression.

Cyclic-3',5'-nucleotide phosphodiesterase isozymes in cell biology and pathophysiology of the kidney

Investigations of recent years revealed that isozymes of cyclic-3', 5'-nucleotide phosphodiesterase (PDE) are a critically important component of the cyclic-3',5'-adenosine monophosphate (cAMP) protein kinase A (PKA) signaling pathway. The superfamily of cyclic-3', 5'-phosphodiesterase (PDE) isozymes consists of at least nine gene families (types): PDE1 to PDE9. Some PDE families are very diverse and consist of several subtypes and numerous PDE isoform-splice variants. PDE isozymes differ in molecular structure, catalytic properties, intracellular regulation and location, and sensitivity to selective inhibitors, as well as differential expression in various cell types. A number of type-specific "second-generation" PDE inhibitors have been developed. Current evidence indicates that PDE isozymes play a role in several pathobiologic processes in kidney cells. In rat mesangial cells, PDE3 and PDE4 compartmentalize cAMP signaling to the PDE3-linked cAMP-PKA pathway that modulates mitogenesis and PDE4-linked cAMP-PKA pathway that modulates generation of reactive oxygen species. Administration of selective PDE isozyme inhibitors in vivo suppresses proteinuria and pathologic changes in experimental anti-Thy-1.1 mesangial proliferative glomerulonephritis in rats. Increased activity of PDE5 (and perhaps also PDE9) in glomeruli and in cells of collecting ducts in sodium-retaining states, such as nephrotic syndrome, accounts for renal resistance to atriopeptin; diminished ability to excrete sodium can be corrected by administration of the selective PDE5 inhibitor zaprinast. Anomalously high PDE4 activity in collecting ducts is a basis of unresponsiveness to vasopressin in mice with hereditary nephrogenic diabetes insipidus. Apparently, PDE isozymes apparently also play an important role in the pathogenesis of acute renal failure of different origins. Administration of PDE isozyme-selective inhibitors suppresses some components of immune responses to allograft transplant and improves preservation and survival of transplanted organ. PDE isozymes are a target for action of numerous novel selective PDE inhibitors, which are key components in the design of novel "signal transduction" pharmacotherapies of kidney diseases.

Signaling role of PDE isozymes in pathobiology of glomerular mesangial cells. Studies in vitro and in vivo

Mesangial cells (MC) of renal glomeruli respond to immune-inflammatory injury by accelerated proliferation and generation of reactive oxygen metabolites (ROM). We studied in vivo and in vitro roles of cAMP-protein kinase A (PKA) signaling in modulation of these pathobiologic processes with focus on PDE isozymes. Mitogenic synthesis of DNA in mesangial cells grown in primary culture was blocked by forskolin and dibutyryl cyAMP. Incubation of MC with PDE-3 inhibitors, cilostamide and lixazinone, inhibited (> 50%) mitogenesis, whereas inhibitors of PDE-4, rolipram and denbufylline, caused little or no inhibition. Conversely, inhibitors of PDE-4 suppressed generation of ROM in MC, whereas inhibitors of PDE-3 had no effect. Incubation of mesangial cells with cilostamide or with rolipram increased in situ activity of PKA, and effects of the two inhibitors were additive. PDE inhibitors also decreased activity of mitogen-activated protein kinase. The efficacy of PDE isozyme inhibitors (IC50) to suppress mitogenesis or ROM generation paralleled IC50 for inhibition of cAMP hydrolysis by extracts from mesangial cells. Administration of lixazinone or lixazinone in combination with rolipram to rats with mesangial proliferative glomerulonephritis induced by antithymic serum suppressed proliferation of mesangial cells and also reduced other histopathologic manifestations of the disease. Based on these observations, we propose that in MC, a cAMP pool that is hydrolyzed by PDE-3 inhibits by negative crosstalk via activation of PKA, mitogen-activated protein kinase (MAPK) pathway, and mitogenesis; whereas cAMP pool linked to PDE-4 inhibits, also via activation of PKA, ROM generation in mesangial cells. Results also suggest that PDE isozyme inhibitors, in particular inhibitors of PDE-3, should be investigated for potential use for "signal transduction pharmacotherapy" of glomerulonephritis.

Trapidil inhibits platelet-derived growth factor-stimulated mitogen-activated protein kinase cascade

Trapidil, an antiplatelet drug, has been shown to reduce restenosis after angioplasty. It exerts its action, at least in part, by inhibiting vascular smooth muscle cell proliferation, antagonizing platelet-derived growth factor (PDGF). We examined its site of action on PDGF cellular signaling. Exposure of cultured rat vascular smooth muscle cells to increasing concentrations of trapidil for 18 hours resulted in a dose-dependent reduction in PDGF-BB-stimulated [3H] thymidine incorporation. Trapidil (400 microg/mL) increased PDGF beta-receptor protein by 28+/-8%, whereas PDGF-induced tyrosine phosphorylation of PDGF beta-receptor remained unchanged. PDGF-induced tyrosine phosphorylation of phospholipase Cgamma, the p85 regulatory subunit of phosphatidyl-inositol 3 kinase, Ras GTPase-activating protein, and an adaptor molecule Shc were also not altered. On the other hand, trapidil inhibited PDGF-stimulated mitogen-activated protein kinase (MAP kinase) activity by 35+/-7% at 10 minutes and by 32+/-10% at 6 hours. Activation of Raf-1, an upstream activator of MAP kinase, by PDGF was also attenuated by trapidil. Moreover, protein content of MAP kinase phosphatase-1, which inactivates MAP kinase, was elevated in trapidil-treated cells. These actions of trapidil may be mediated by cAMP. Thus, there was a 1.9-fold increase in cellular cAMP generation in trapidil-treated cells. The present results demonstrate that trapidil antagonizes PDGF-induced mitogenesis and MAP kinase activation in vascular smooth muscle cells, probably through cAMP.