Antimitogenic effects of trapidil in coronary artery smooth muscle cells by direct activation of protein kinase A

Endothelin-1 induces lysyl oxidase expression in pulmonary artery smooth muscle cells

The increase in thickening of the arterial wall of pulmonary arterial hypertension (PAH) includes cellular proliferation as well as matrix deposition and interrupted internal elastic lamina (IEL) consisting of a thick homogeneous sheet of elastin. Little is, although, known about the detail of IEL formation in PAH. Endothelin-1 is overexpressed in pulmonary arterioles of PAH. We aimed to examine the expression of genes contributing to IEL formation in pulmonary artery smooth muscle cells (PASMCs) especially focused on lysyl oxidase (LOx), an exreacellular matrix enzyme that catalyzes the cross-linking of collagens or elastin. We quantified mRNA expressions of genes contributing to IEL formation including LOx in PASMCs using real-time quantitative polymerase chain reaction. We stimulated human PASMCs with endothelin-1 with prostacyclin or trapidil. Endothelin-1 significantly increased LOx expression. Prostacyclin and trapidil restored endothelin-1-induced LOx expression to the basal level. Endothelin-1 increased LOx expression strongly in PASMCs from PAH patients compared to those from controls. Trapidil reduced LOx expression only in PASMCs from PAH patients. Overexpressed endothelin-1 in PAH patients can increase expression of LOx and agitate cross-linking of elastin and collagen, resulting in ectopic deposition of these in the vascular media.

Protective effect of trapidil and l-arginine against renal and hepatic toxicity induced by cyclosporine in rats

RATIONALE

Cyclosporine A (CsA) leads to renal and liver injury, production of free radicals and nitric oxide (NO) deficiency. This study investigates the possible protective effects of trapidil and L-arginine against CsA-induced tissue injury.

OBJECTIVES

Forty adult male Wistar rats (180 +/- 20 g) were divided into five groups, eight animals in each. The first group served as control, second group served as CsA group, third group served as CsA + trapidil group, fourth group served as CsA + L-arginine group, and fifth group served as CsA + trapidil + L-arginine group. Kidney and liver functions, inflammatory mediators, cytokines, oxidant and antioxidant parameters as well as histopathological studies of renal and liver tissue were assessed in all groups.

MAIN FINDINGS

CsA induced renal and hepatic dysfunction, which was confirmed by laboratory and histopathological examination. Administration of trapidil diminished the renal and liver injury and significantly attenuated the levels of serum creatinine, urea, aspartate aminotransferase (AST), alanine aminotransferase (ALT), interleukin-1beta (IL-1beta), tumor necrosis factor alpha (TNF-alpha), monocyte chemoattractant protein-1 (MCP-1), and oxidative stress, while it significantly elevated the level of serum nitric oxide and the activity of antioxidative stress. L-Arginine gave the same trend as trapidil, but trapidil effect was more pronounced. Coadministration of trapidil + L-arginine significantly ameliorated the toxic effect of CsA, but did not differ significantly from the effect of trapidil alone.

CONCLUSIONS

Treatment with trapidil or L-arginine diminished the renal and hepatic CsA-induced toxicity. However, the effect of trapidil was more pronounced. Therefore, treatment with trapidil alone may be the most economic and effective as a potential therapeutic agent in CsA injury.

Osteitis fibrosa is mediated by Platelet-Derived Growth Factor-A via a phosphoinositide 3-kinase-dependent signaling pathway in a rat model for chronic hyperparathyroidism

Abnormal secretion of PTH by the parathyroid glands contributes to a variety of common skeletal disorders. Prior studies implicate platelet-derived growth factor-A (PDGF-A) as an important mediator of selective PTH actions on bone. The present studies used targeted gene profiling and small-molecule antagonists directed against candidate gene products to elucidate the roles of specific PTH-regulated genes and signaling pathways. A group of 29 genes in rats continuously infused with PTH and cotreated with the PDGF receptor antagonist trapidil were differentially expressed compared with PTH treatment alone. Several of the identified genes were functionally clustered as regulators of fibroblast differentiation and extracellular matrix modeling, including the matrix cross-linking enzyme lysyl oxidase (LOX). Treatment with beta-aminopropionitrile, an irreversible inhibitor of LOX activity, dramatically reduced diffuse mineralization but had no effect on PTH-induced fibrosis. In contrast, the receptor tyrosine kinase inhibitor Gleevec and the phosphoinositide 3-kinase inhibitor wortmannin each reduced bone marrow fibrosis. In summary, the present studies support the hypotheses that PTH-induced bone marrow fibrosis is mediated by PDGF-A via a phosphoinositide 3-kinase-dependent signaling pathway and that increased LOX gene expression plays a key role in abnormal mineralization, a hallmark of chronic hyperparathyroidism.

Trapidil is as effective as isosorbidedinitrate for treating stable angina pectoris—

OBJECTIVE

Nitrates have long been used in the treatment of stable angina pectoris. We set out to show that trapidil, a triazolo-pyrimidine with a mode of action different from that of nitrates, is not inferior to isosorbide-dinitrate (ISDN) in the treatment of this clinical syndrome.

PATIENTS AND METHODS

We studied the efficacy of 200 mg trapidil (t.i.d.) vs. ISDN (20 mg b.i.d.) in patients with chronic stable angina treated for 12 weeks. The therapeutic effect was measured in terms of responder rate as change in total exercise time (TET) by at least 60 seconds using the bicycle ergometer test.

RESULTS

A total of 648 patients were included in the study. Responder rates in the Per- Protocol (PP) population (n = 529) were 50.4% (n = 133) in the trapidil group and 52.5% (n = 139) in the ISDN group (p = 0.233). As the lower non-inferiority limit (-15%) was clearly excluded from the 95% CI (pp: -10.6%, +6.4%; ITT -9.7%, 5.7%), non-inferiority of trapidil compared to ISDN can be concluded. Trapidil 200 mg t.i.d. combined with short-acting NTG prn as rescue medication over 12 weeks in subjects with chronic stable angina pectoris proved to have similar effects on TET and on other clinical endpoints as ISDN 20 mg b.i.d. The secondary efficacy analyses did not reveal any clinically relevant differences between treatment groups, and were not in conflict with the non-inferiority claim. Patients in the ISDN group had significantly more headache (34.1%; n = 110) compared to those taking trapidil (19.3%, n = 62; p <0.0001).

CONCLUSIONS

Overall results of this study show that both drugs are equally effective and safe for the short-term treatment of patients with chronic stable angina pectoris and that trapidil can be considered as therapeutically equivalent to ISDN.

Trapidil inhibits platelet-derived growth factor-induced migration via protein kinase A and RhoA/Rho-associated kinase in rat vascular smooth muscle cells

Trapidil suppresses platelet-derived growth factor (PDGF)-induced vascular smooth muscle cell (VSMC) proliferation by inhibiting Raf-1/extracellular signal-regulated kinase (ERK) via cAMP/protein kinase A (PKA). We examined whether trapidil inhibits PDGF-induced VSMC migration and investigated its mechanisms of action. VSMC migration was inhibited to a similar extent by trapidil and forskolin. A PKA inhibitor N-(2-[p-bromocinnamylamino]ethyl)-5-isoquinolinesulfonamide (H89) blocked the inhibition by forskolin to a greater degree than that by trapidil. Trapidil but not forskolin suppressed PDGF-stimulated RhoA activation. In the presence of both H89 and (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl)cyclohexanecarboxamide dihydrochloride monohydrate, an inhibitor of Rho-associated kinase (ROCK), trapidil and forskolin inhibited migration to a similar extent. Thus, in addition to cAMP/PKA activation, trapidil inhibits RhoA/ROCK activation, which may be important in trapidil's inhibitory effect on migration.

Pharmacological treatment for prevention of restenosis

Coronary artery disease (CAD) is the leading cause of mortality and morbidity among adults in the Western world. Coronary artery bypass grafting and percutaneous coronary interventions (PCI) have gained widespread acceptance for the treatment of symptomatic CAD. There has been an explosive growth worldwide in the utilisation of PCI, such as balloon angioplasty and stenting, which now accounts for over 50% of coronary revascularisation. Despite the popularity of PCI, the problem of recurrent narrowing of the dilated artery (restenosis) continues to vex investigators. In recent years, significant advances have occurred in the understanding of restenosis. Two processes seem to contribute to restenosis: remodelling (vessel size changes) and intimal hyperplasia (vascular smooth muscle cell [VSMC] proliferation and extracellular matrix [ECM] deposition). Despite considerable efforts, pharmacological approaches to decrease restenosis have been largely unsuccessful and the only currently applied modality to reduce the restenosis rate is stenting. However, stenting only prevents remodelling and does not inhibit intimal hyperplasia. Several potential targets for inhibiting restenosis are currently under investigation including platelet activation, the coagulation cascade, VSMC proliferation and migration, and ECM synthesis. In addition, new approaches for local drug therapy, such as drug eluting stents, are currently being evaluated in preclinical and clinical studies. In this article, we critically review the current status of drugs that are being evaluated for restenosis at various stages of development (in vitro, preclinical animal models and human trials).

Starc II, a multicenter randomized placebo-controlled double-blind clinical trial of trapidil for 1-year clinical events and angiographic restenosis reduction after coronary angioplasty and stenting

The objective of this study was to investigate the effect of trapidil 200 mg t.i.d. in preventing the occurrence of death, of myocardial infarction and the need for repeat revascularization at 12 months after balloon PTCA with or without stenting. Coronary restenosis after stenting is still a major drawback of percutaneous coronary interventions (PCI) for 30-40% of patients. Trapidil has been shown to prevent restenosis after PTCA. Eligible patients were randomized to placebo or oral trapidil 200 mg t.i.d. at least 48 hr before PCI and continuing 6 months after a successful balloon angioplasty or stent implantation. Aspirin was given to all patients, and ticlopidine 250 mg b.i.d. to those who received a stent for 4 weeks. In a randomized subgroup of 216 patients, quantitative coronary angiography was performed also at 6-month follow-up. Out of the 933 patients enrolled, primary endpoint incidence was 20.3% in trapidil and 18.0% in placebo (P = 0.37). When recurrence or deterioration of angina was added to the combined endpoint, incidence was 27.4% in trapidil and 23.0% in placebo (P = 0.12). Restenosis rate in patients with 6-month angiography was 25.0% in trapidil arm vs. 30.1% in placebo (P = 0.43). Stent restenosis rate was similar in patients randomized to trapidil or placebo (30.2% vs. 23.8%, respectively; P = 0.44), while in patients treated with balloon angioplasty, it was lower in trapidil (17.1%) than in placebo (40.0%; P = 0.03). Oral trapidil 200 mg t.i.d. for 6 months in addition to aspirin did not influence the occurrence of major cardiac events after coronary angioplasty with or without stenting. In a prespecified subgroup of 191 patients treated with balloon angioplasty only, trapidil reduced angiographic restenosis.

Src tyrosine kinase regulates CYP17 expression and androstenedione secretion in theca-enriched mouse ovarian cells

Src tyrosine kinase belongs to a non-receptor tyrosine kinase family and has been shown to be involved in G protein-coupled receptor desensitization and internalization. Stimulation of ovarian thecal cells with lutein-izing hormone (LH) activates adenylyl cyclase via a G protein-coupled LH receptor leading to an increase in cAMP. Subsequently, cAMP activates protein kinase A (PKA) that increases steroidogenesis. In order to evaluate the role of Src in thecal cell steroidogenesis, a pharmacological approach was utilized by treating a population of mouse ovarian theca-enriched cells (TEC) in vitro with two Src inhibitors, geldanamycin (GA) and herbimycin A (HA). Treatment of TEC with either GA or HA increased basal androstenedione secretion without alteration of cAMP. In the presence of forskolin, GA and HA treatment further increased androstenedione secretion. RT-PCR analysis of RNA from cells treated with GA for 8, 24, and 48 h revealed that GA increased cytochrome P450 17alpha-hydroxylase/lyase (CYP17) mRNA at 48 h. CYP17 promoter activity also increased after treatment of cells with GA and after co-transfection with a Src dominant negative plasmid. Inhibition of PKA using H89 blocked the effect GA and HA on androstenedione secretion. These results indicate that the pharmacological inhibitors of Src, GA and HA, tested in vitro increased thecal CYP17 promoter activity, CYP17 mRNA, and androstenedione secretion. In addition, GA and HA induced thecal androstenedione secretion may be cAMP independent but possibly requires PKA.

Trapidil inhibits monocyte CD40 expression by preventing IFN-γ-induced STAT1 S727 phosphorylation

Trapidil is a triazolopyrimidine that has been found to prevent restenosis after vascular injury. Although its precise mode of action is still unclear, several biological effects have been described including inhibition of IFN-gamma-induced CD40 expression on monocytes. Herein, we investigated the molecular mechanisms by which Trapidil exerts this inhibitory action. First, we observed that the inhibition of CD40 expression is associated with the suppression of CD40 gene transcription, as demonstrated by a clear decrease of CD40 nuclear RNA (nRNA) levels and unchanged CD40 mRNA half-life. IFN-gamma-induced CD40 transcription has been shown to be mediated by STAT1alpha dimers (p91/p84) which, after nuclear translocation, bind to GAS elements present in the promoter of IFN-gamma responsive genes. Electrophoresis mobility shift assay (EMSA) with both STAT1 consensus and CD40 mGAS probes showed that Trapidil did not affect the DNA binding ability of STAT1 dimers. STAT1 dimerization and activation are conferred by upstream phosphorylation of two amino acid residues of the STAT1 protein. The subsequent studies on these two potential STAT1 phosphorylation sites (Tyr701, Ser727) revealed that Trapidil attenuated IFN-gamma-induced Ser727 but not Tyr701 phosphorylation. The inhibition of CD40 transcription by Trapidil could at least partially owing to the impaired Ser727 phosphorylation of STAT1, since IFN-gamma failed to trigger CD40 expression in U3A S727A cells, a cell line displaying a point mutation at the Ser727 site. Collectively, our results indicate that phosphorylation of STAT1 at the Ser727 site enhances CD40 transcription and that Trapidil might be used as a selective inhibitor that could differentially modulate STAT1 target genes.

Effects of trapidil on the healing of colonic anastomoses in an experimental rat model

BACKGROUND

Trapidil has various properties including vasodilatation, inhibition of lipid peroxidation and platelet aggregation as well as, and reduction of, the inflammatory response to injury. The aim of the present study was to investigate the effects of trapidil on dexamethasone-impaired colonic anastomotic healing in an experimental rat model.

METHODS

Twenty-four Wistar rats underwent colonic transsection and primary anastomosis. Rats were divided into four groups of six: group 1 (G1), control; group 2 (G2) trapidil, 8 mg/kg per day intravenously; group 3 (G3) dexamethasone, 0.1 mg/kg per day intramuscularly; and group 4 (G4) dexamethasone 0.1 mg/kg intramuscularly and trapidil 8 mg/kg intravenously per day, for 1 week. Anastomotic bursting pressure, hydroxyproline level, histopathological grading, malondialdehyde and nitrite/nitrate levels were determined.

RESULTS

Dexamethasone-impaired anastomotic healing was found to be improved by trapidil administration in terms of anastomotic bursting pressure and hydroxyproline content (P = 0.026, and P = 0.017). In addition, histopathological examination revealed an increase in fibroblast proliferation and collagen deposition (P = 0.004, and P = 0.015) and a decrease in leucocyte infiltration (P = 0.004). Moreover, serum nitrite/nitrate and malondialdehyde levels decreased when G3 was compared to G4 (P < 0.001, P = 0.38).

CONCLUSIONS

Trapidil may improve the dexamethasone-impaired anastomotic healing due to its preventive effects on inflammatory response and lipid peroxidation in rats.

Triazolopyrimidine (trapidil), a platelet-derived growth factor antagonist, inhibits parathyroid bone disease in an animal model for chronic hyperparathyroidism

Parathyroid bone disease in humans is caused by chronic hyperparathyroidism (HPT). Continuous infusion of PTH into rats results in histological changes similar to parathyroid bone disease, including increased bone formation, focal bone resorption, and severe peritrabecular fibrosis, whereas pulsatile PTH increases bone formation without skeletal abnormalities. Using a cDNA microarray with over 5000 genes, we identified an association between increased platelet-derived growth factor-A (PDGF-A) signaling and PTH-induced bone disease in rats. Verification of PDGF-A overexpression was accomplished with a ribonuclease protection assay. Using immunohistochemistry, PDGF-A peptide was localized to mast cells in PTH-treated rats. We also report a novel strategy for prevention of parathyroid bone disease using triazolopyrimidine (trapidil). Trapidil, an inhibitor of PDGF signaling, did not have any effect on indexes of bone turnover in normal rats. However, dramatic reductions in marrow fibrosis and bone resorption, but not bone formation, were observed in PTH-treated rats given trapidil. Also, trapidil antagonized the PTH-induced increases in mRNA levels for PDGF-A. These results suggest that PDGF signaling is important for the detrimental skeletal effects of HPT, and drugs that target the cytokine or its receptor might be useful in reducing or preventing parathyroid bone disease.

Vascular tissue fragility assessed by a new double stain method

Although matrix metalloproteinases (MMPs) are known to be involved in the development of atherosclerosis and the instability of atheromatous plaques, much remains to be learned about their roles at the tissue level. To help clarify this area, we established a new double staining method using film in situ zymography and immunohistochemistry. Using this technique, a comprehensive analysis of the gelatinolytic activity in human vessel tissue demonstrated that gelatinolytic activity is enhanced in the shoulder region and fibrous cap at superficial areas of the atheromatous plaque in the presence of thrombolysis. Enzyme assay clarified high activity in the superficial area (7.50 +/- 5.04 U/mg weight; P < 0.001). Gelatin zymography also indicated that addition of the antiplatelet agent, trapidil, alters the amount of secretion of MMP-2 and MMP-9 and their activation ratio. This novel approach to detect the activity of gelatinases in resected tissues may aid in the selection of optimal treatment of individual patients.

Fibroblast growth factor-2 gene transfer can stimulate hepatocyte growth factor expression irrespective of hypoxia-mediated downregulation in ischemic limbs

Hepatocyte growth factor (HGF) is a potent angiogenic polypeptide that stimulates angiogenesis. Transcriptional regulation of HGF, however, has not been fully defined, with the exception of the hypoxia-mediated downregulation in cultured cells. In the present study, we report that angiogenic growth factors, including HGF, were upregulated in a murine model of critical limb ischemia in vivo, a finding that was in conflict with previous in vitro data. Mice deficient in basic fibroblast growth factor-2 (FGF-2) showed reduced induction of HGF protein in ischemic muscles, and overexpression of FGF-2 via gene transfer stimulated endogenous HGF, irrespective of the presence of ischemia. In culture, FGF-2 rapidly stimulated HGF mRNA, and a sustained expression was evident in the time course in vascular smooth muscle cells and fibroblasts. FGF-2-mediated induction of HGF was fully dependent on the mitogen-activated protein kinase pathway yet was not affected by either hypoxia or a protein kinase A inhibitor. In the early expression, FGF-2 directly stimulated HGF mRNA without the requirement of new protein synthesis, whereas sustained induction of HGF in the later phase was partly mediated by platelet-derived growth factor-AA. Furthermore, in vivo overexpression of FGF-2 significantly improved the blood perfusion, and the effect was abolished by systemic blockade of HGF in ischemic limbs. This is the first demonstration of a regulational mechanism of HGF expression via FGF-2 that was independent of the presence of hypoxia. The harmonized therapeutic effects of FGF-2, accompanied with the activity of endogenous HGF, may provide a beneficial effect for the treatment of limb ischemia.

CD40 ligand (CD40L) does not stimulate proliferation of vascular smooth muscle cells

The present study investigates the effects of CD40 ligand (CD40L) on mitogenic signalling, proliferation, and migration of cultured bovine coronary artery smooth muscle cells (SMC). A time- and concentration-dependent phosphorylation of the extracellular signal-regulated kinases-1/2 (ERK-1/2) and the mitogen-activated protein kinase p38 (p38-MAPK) was observed upon stimulation with soluble CD40L (sCD40L). This phosphorylation was inhibited by neutralizing antibodies against the CD40 and CD40L, respectively. Activation of the phosphatidylinositol-3-phosphate (PI-3) kinase pathway by sCD40L, as determined by the measurement of Akt phosphorylation, was not detected. However, there was evidence for direct activation of the NFkappaB system (degradation of IkappaBalpha and nuclear translocation of the p65 NFkappaB subunit) by sCD40L. Accordingly, sCD40L caused a small but significant increase in DNA synthesis. However, sCD40L-induced DNA synthesis was not followed by proliferation (increase in cell number). Furthermore, sCD40L did not potentiate SMC mitogenesis induced by known mitogens such as platelet-derived growth factor-BB, thrombin or serum. The lack of cell proliferation was not caused by a concomitant induction of SMC apoptosis by sCD40L. The possible role of membrane-bound CD40L in SMC mitogenesis was also studied using different membrane preparations (platelets, lymphocytes). However, no mitogenic effects of membrane-bound CD40L were detected. Finally, sCD40L did not induce SMC migration. From these data it is concluded that CD40L activates mitogenic signalling and DNA synthesis but does not contribute to proliferation or migration of vascular SMC.

Effect of trapidil on effector functions of monocytes related to atherosclerotic plaque

The infiltration and activation of inflammatory cells play an important role in the formation and stability of coronary atherosclerotic plaque in patients with acute coronary syndrome. In this study, we evaluated the effect of trapidil, an anti-platelet agent, on atheroma-related functions of human T cells and monocytes. Trapidil and anti-CD154 (CD40 ligand) antibody inhibited the increase of procoagulant activity in the mixed lymphocyte reaction; trapidil also suppressed the induction of tissue factor, monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-9 in the mixed lymphocyte reaction. Trapidil did not alter CD154 expression on isolated T cells, but it diminished CD40 expression on isolated monocytes and human monocytic leukemia THP-1 cells stimulated with interferon-gamma. Moreover, trapidil reduced MCP-1 production of isolated monocytes and THP-1 cells stimulated with interferon-gamma plus CD154-transfected cells. This effect was not seen with other tested anti-platelet agents and coronary vasodilators. In conclusion, trapidil directly acts on monocytes/macrophages to lower their susceptibility to CD154 on T cells.

Antimitogenic actions of organic nitrates are potentiated by sildenafil and mediated via activation of protein kinase A

Migration and proliferation of vascular smooth muscle cells (SMC) in response to platelet-derived growth factor (PDGF) and other mitogens play an important role in restenosis after coronary angioplasty. Elevation of both cAMP and cGMP has been shown to inhibit SMC mitogenesis. The aim of this study was to examine the antimitogenic actions of organic nitrates and sildenafil and to clarify the role of cyclic nucleotide-dependent protein kinases (PKA, PKG) in this action. Organic nitrates [glycerol trinitrate (GTN), isosorbide 5'-mononitrate (ISMN), pentaerythrityl-tetranitrate (PETN)] and the PDE5 inhibitor sildenafil reduced PDGF-induced DNA synthesis, measured by ((3)H]thymidine incorporation. GTN, ISMN, and PETN acted synergistically with sildenafil (1 microM) on inhibition of PDGF-induced DNA synthesis, increase of intracellular cyclic nucleotides, and vasodilator-stimulated phosphoprotein phosphorylation. The highly selective PKA inhibitor PKI abolished these actions of sildenafil and organic nitrates, whereas the PKG inhibitors KT5823 and (Rp)-8-pCPT-cGMPS had no effect. In addition, selective activation of PKG without inhibition of PDE3 by the cGMP analog 8-pCPT-cGMP (100 microM) had no antimitogenic effect. The data suggest that 1) organic nitrates and sildenafil exert antimitogenic actions by activation of PKA via inhibition of PDE3, but not by activation of PKG and 2) that antimitogenic effects of organic nitrates are potentiated by sildenafil at therapeutic plasma levels.

Coupling of the insulin-like growth factor-I receptor tyrosine kinase to Gi2 in human intestinal smooth muscle: Gbetagamma -dependent mitogen-activated protein kinase activation and growth

Endogenous insulin-like growth factor-1 (IGF-I) stimulates growth of cultured human intestinal smooth muscle by activating distinct mitogen-activated protein (MAP) kinase-dependent and phosphatidylinositol 3-kinase-dependent signaling pathways. In Rat1 and Balb/c3T3 fibroblasts and in neurons the IGF-I receptor is coupled to an inhibitory G protein, G(i), which mediates G(beta)gamma-dependent MAP kinase activation. The present study determined whether in normal human intestinal smooth muscle cells the IGF-I receptor activates a heterotrimeric G protein and the role of G protein activation in mediating IGF-I-induced growth. IGF-I elicited IGF-I receptor tyrosine phosphorylation, resulting in the specific activation of G(i2). G(beta)gamma subunits selectively mediated IGF-I-dependent MAP kinase activation; G(alpha)i2 subunits selectively mediated IGF-I-dependent inhibition of adenylyl cyclase activity. IGF-I-stimulated MAP kinase activation and growth were inhibited by pertussis toxin, an inhibitor of G(i)/G(o) activation. Cyclic AMP inhibits growth of human intestinal muscle cells. IGF-I inhibited both basal and forskolin-stimulated cAMP levels. This inhibition was attenuated in the presence of pertussis toxin. IGF-I stimulated phosphatidylinositol 3-kinase activation, in contrast to MAP kinase activation, occurred independently of G(i2) activation. These data suggest that IGF-I specifically activates G(i2), resulting in concurrent G(beta)gamma-dependent stimulation of MAP kinase activity and growth, and G(alpha)i2-dependent inhibition of cAMP levels resulting in disinhibition of cAMP-mediated growth suppression.

Inhibition of platelet-derived growth factor-induced mitogenesis by phosphodiesterase 3 inhibitors: role of protein kinase A in vascular smooth muscle cell mitogenesis

Proliferation of vascular smooth muscle cells (SMC) in response to platelet-derived growth factor (PDGF) and other mitogens plays an important role in restenosis following coronary angioplasty. Elevation of adenosine 3',5'-cyclic monophosphate (cAMP) concentration in SMC has been shown to inhibit SMC mitogenesis and could be obtained either directly by stimulation of adenylyl cyclase-coupled receptors or indirectly by inhibition of cAMP-specific phosphodiesterase (PDE4) or the cyclic guanosine 3', 5'-monophosphate-inhibitable phosphodiesterase (PDE3). This study compared the effects of the selective PDE3 inhibitors trequinsin and quazinone with the selective PDE4 inhibitors Ro 20-1724 and rolipram on PDGF-induced DNA synthesis, mitogen-activated protein (MAP) kinase activation, cAMP levels, and protein kinase A (PKA) activation in SMC. Both PDE3 and PDE4 inhibitors stimulated intracellular PKA activation as seen from phosphorylation of vasodilator-stimulated phosphoprotein (VASP). However, only PDE3 inhibitors, and not inhibitors of PDE4, reduced PDGF-induced DNA synthesis and inhibited p42/p44 MAP kinase phosphorylation. At antimitogenic concentrations, the PDE3 inhibitors had only minor effects on cAMP levels. In contrast, PDE4 inhibitors increased the forskolin-induced cellular cAMP concentration 13- to 17-fold above control. These data demonstrate that inhibitors of PDE3 are potent antimitogenic agents and that a general increase in cellular cAMP levels and PKA activation per se are not sufficient to inhibit PDGF-induced SMC mitogenesis.

Role of cAMP-dependent pathway in eosinophil apoptosis and survival

The survival and apoptosis of eosinophils is of pivotal importance for controlling allergic diseases such as asthma and rhinitis. In this study we have investigated the role for cAMP in regulating eosinophil survival and apoptosis in the absence of eosinophil-active cytokines. The treatment with dibutyryl cyclic AMP (dbcAMP) increased eosinophil survival with a concomitant decrease of apoptosis in a dose-dependent manner. The pretreatment with a protein kinase A (PKA) inhibitor blocked the effects of dbcAMP on survival and apoptosis of eosinophils. The catalytic subunit of PKA was translocated to nucleus in parallel with a robust increase of intracellular cAMP levels upon exposure to dbcAMP but not IL-5, suggesting the separation of PKA activation from the IL-5-induced suppression of eosinophil apoptosis. When eosinophils were treated with pharmacological inhibitors of protein kinases prior to exposure to dbcAMP or IL-5, only the mitogen-activating protein kinase (MAPK) inhibitor, PD098059, was partly able to block dbcAMP-induced augmentation of eosinophil viability, whereas both Janus kinase 2 and MAPK inhibitors effectively interrupted the IL-5-induced prolongation of eosinophil survival. The effects of dbcAMP and these protein kinase inhibitors on eosinophil apoptosis were confirmed by morphologic analysis. We propose that a cAMP-dependent pathway may constitute an important component for regulating eosinophil survival/apoptosisand that cAMP may inhibit eosinophil apoptosis through the activation of PKA and of subsequent MAPK in part.

Platelet-derived microparticles stimulate coronary artery smooth muscle cell mitogenesis by a PDGF-independent mechanism

This study investigates the role of platelet-derived microparticles for vascular smooth muscle cell (SMC) proliferation. Microparticles concentration dependently stimulated p42/p44 MAP kinase phosphorylation, c-fos induction, DNA synthesis, and proliferation of cultured bovine coronary artery SMC. The maximum mitogenic effects of microparticles were significantly higher than those of platelet-derived growth factor (PDGF)-BB. Microparticle-induced SMC mitogenesis was heat sensitive, whereas the effects of PDGF were not. In addition, neutralizing anti-PDGF antibodies prevented PDGF-induced DNA synthesis but did not inhibit the effects of microparticles. In contrast to PDGF, which potently stimulated SMC migration, microparticles had only minor migratory activity. These results demonstrate a novel mechanism of SMC mitogenesis by platelet-derived microparticles that is probably independent of PDGF.

Complex actions of protein kinase A inhibitors on mitogenesis of bovine coronary artery smooth muscle cells

This study investigates the possible modulation of platelet-derived growth factor-(PDGF, 20 ng/ml)-induced DNA synthesis in bovine coronary artery smooth muscle cells by the protein kinase A inhibitors Rp-adenosine-3',5'-cyclic phosphorothioate (Rp-cAMPS, 0. 03-10 microM) and ¿N-[2-((p-bromocinnamyl)amino)ethyl]-5-isoquinolinesulfonamide, HCl¿ (H-89, 0.01-1 microM). Rp-cAMPS concentration dependently enhanced PDGF-induced DNA synthesis. In contrast, no potentiation of PDGF-induced DNA synthesis was seen with H-89. However, H-89 but not Rp-cAMPS, inhibited p42/p44 mitogen-activated protein kinase phosphorylation. Thus, Rp-cAMPS, but not H-89, unmasks inhibitory actions of protein kinase A on PDGF-induced mitogenesis of vascular smooth muscle cells. Low specificity may limit the use of H-89 as protein kinase A inhibitor.

Cyclooxygenase-independent inhibition of smooth muscle cell mitogenesis by ibuprofen

The aryl-propionic acid derivative, ketoprofen, has been shown to inhibit fibroblast growth by a cylooxygenase-dependent mechanism [Sánchez, T., Moreno, J.J., 1999. S(+) enantiomer inhibits prostaglandin production and cell growth in 3T6 fibroblast cultures. Eur. J. Pharmacol. 370, 63-67]. The present study demonstrates that ibuprofen, another aryl-propionic acid derivative, inhibited platelet-derived growth factor-BB (20 ng/ml)-induced mitogenesis of cultured bovine coronary artery smooth muscle cells in a stereo-independent manner. In addition, pretreatment of the cells with indomethacin (3 microM) did not affect the inhibitory effects of ibuprofen enantiomers on smooth muscle cell mitogenesis. Thus, aryl-propionic acid-type cyclooxygenase inhibitors can inhibit cell proliferation by both, cyclooxygenase-dependent and -independent ways.

Effects of local delivery of trapidil on neointima formation in a rabbit angioplasty model

1. Smooth muscle cell (SMC) proliferation can result in luminal reduction of a vessel following balloon angioplasty. This study was designed (i) to determine if local administration of trapidil (triazolopyrimidine) into a vessel wall reduces neointima formation, and (ii) to explore the mechanism involved in the subsequent reduction in cell proliferation. 2. Following balloon angioplasty in 40 anaesthetized New Zealand White rabbits, trapidil (50-200 mg) or its vehicle (saline) was injected into the dilated vessel wall of the right femoral artery. Experimental groups and time of investigation: (I) vehicle (2 weeks, n = 3), (II) trapidil-100 mg (2 weeks, n = 3), (III) vehicle (3 weeks, n = 8), (IV) trapidil-50 mg (3 weeks, n = 5); (V) trapidil-100 mg (3 weeks, n = 9) or (V) trapidil-200 mg (3 weeks, n = 7). 3. After 2 weeks, there was a significant reduction of intimal hyperplasia (expressed as intima to media area ratio) in the trapidil group compared with vehicle (0.44 +/- 0.04 vs 0.93 +/- 0.04, *P < 0.05) and also a significant reduction in cell proliferation (% ratio of BrdU-positive cells to total cell number: vehicle 14 +/- 2% vs trapidil 6 +/- 1%, *P < 0.05). 4. After 3 weeks, there was a dose-dependent reduction of intimal hyperplasia in the trapidil groups compared with vehicle (trapidil 50 mg 1.14 +/- 0.04; trapidil 100 mg 0.91 +/- 0.09*; trapidil 200 mg 0.77 +/- 0.09* vs vehicle 1.67 +/- 0.23, *P < 0.05). 5. Thus, the local administration of trapidil to the rabbit femoral artery reduces the neointima formation, which occurs 2 or 3 weeks after balloon angioplasty via a mechanism, which is dependent on inhibition of cell proliferation.

Inhibition of the CD40 pathway of monocyte activation by triazolopyrimidine

Blockade of the CD40/CD40L pathway of monocyte/macrophage activation represents a promising strategy for the treatment of several inflammatory disorders. So far, most pharmacological agents developed for that purpose target CD40L (CD154) expressed on activated T cells. Herein, we provide evidence that triazolopyrimidine, a chemical compound primarily developed for the prevention of arterial thrombosis, strongly inhibits the response of human monocytes to CD40 ligation. First, we found that triazolopyrimidine inhibits the production of IL-12, TNF-alpha, and IL-6 by monocytes activated by coculture with fibroblasts transfected with the CD40L gene as well as the induction of procoagulant activity at their membrane. This was related to a decreased expression of CD40 on monocytes exposed to triazolopyrimidine, an effect that was already apparent at the mRNA level. Furthermore, the addition of triazolopyrimidine to monocytes cultured with IL-4 and GM-CSF prevented their differentiation into fully competent dendritic cells (DC) as DC differentiated in the presence of triazolopyrimidine expressed less CD40 at their surface and were profoundly deficient in the production of IL-12 upon exposure to CD40L transfectants. We conclude that triazolopyrimidine strongly inhibits the CD40 pathway of monocyte activation at least in part by downregulating the gene expression of CD40.

[Pathophysiologic significance of growth factors and new therapeutic concepts in cardiovascular disease]

Peptide growth factors such as PDGF, FGF, VEGF, and TGF-beta play a critical role in the pathogenesis of cardiovascular diseases. In addition to their pathophysiological role in atherosclerosis and myocardial remodeling, growth factors also promote beneficial effects such as stimulation of angiogenesis and formation of collateral vessels in ischemic tissue. This review focuses on the mechanisms of action and signal relay cascades of peptide growth factors, and summarizes novel therapeutic approaches in cardiovascular medicine. These approaches include both inhibition of growth factors in order to suppress pathogenic processes, and stimulation of growth factors to promote their beneficial effects.