Impact of a large dam on reproduction of a non-migratory teleost species, Acestrorhynchus lacustris (Characiformes: Acestrorhynchidae)

The release of water from the reservoir hypolimnion, lower concentration of oxygen and the anthropogenic regulation of the river flow, could affect the reproduction of fish, especially migratory species. However, little is known about the effects of these changes in water on non-migratory species. In this sense, the reproduction of Acestrohynchus lacustris was evaluated in two sections of São Francisco River, Minas Gerais, Brazil. Section 1, located immediately downstream from Três Marias Dam (18°09'31.65"S and 45°13'36.00"W) and section 2, located at the confluence of the São Francisco and the Abaeté Rivers (18°02'47.78"S and 45°10'57.95"W). For this, we obtained the physico-chemical parameters of water of each study section. Additionally, biometric data and biological indices of all specimens were measured. Fecundity and follicles diameters were measured in females. Temperature, dissolved oxygen and flow showed lower values in section 1. Fish captured in this section, had lower values of GSI in both sexes, and females presented decreased values of fecundity and follicles diameter. This species showed reproductive activity in the two sections analyzed, however, in section 1 where the temperature and dissolved oxygen presented significant lower values, the reproductive capacity of A. lacustris, was negatively affected.

Stimulatory effects of the multi-kinase inhibitor sorafenib on human bladder cancer cells

BACKGROUND AND PURPOSE

Sorafenib is an inhibitor of several intracellular signalling kinases with anti-proliferative, anti-angiogenic and pro-apoptotic effects in tumour cells. Sorafenib is used in the therapy of advanced renal cell carcinoma, and several phase II clinical trials are being carried out in patients with urothelial carcinomas.

EXPERIMENTAL APPROACH

Using a panel of human bladder cancer cell lines (RT4, T24, J82), we characterized systematically the effects of sorafenib on intracellular signalling, migration, proliferation and apoptosis.

KEY RESULTS

We demonstrated that at low concentrations (<1 microM), sorafenib is capable of significantly stimulating migration and proliferation of the bladder cancer cells. We hypothesize that these stimulatory effects on tumour cell functions might be explained by an activation of the Ras/ERK-1/2 signal transduction pathway. In addition, the comparison of different bladder cancer cell lines not only revealed a different biology (e.g. cell migration), but also a differential susceptibility to the anti-apoptotic effects of sorafenib. Finally, we confirmed in different bladder cancer cell lines the known inhibitory actions of sorafenib in pharmacological concentrations (> or =3 microM) on ERK-1/2 phosphorylation, migration and proliferation, as well as the pro-apoptotic effects of the compound.

CONCLUSIONS AND IMPLICATIONS

Taken together, these findings suggest that although sorafenib has the potential to be used in the treatment of urothelial carcinoma, this compound might also activate bladder cancer cells at low concentrations. This should be relevant for dosing regiments to optimize the treatment with this promising anti-tumour drug.

Epac inhibits migration and proliferation of human prostate carcinoma cells

Background:

It was recently found that cAMP mediates protein kinase A-independent effects through Epac proteins. The aim of this study was to investigate the role of Epac in migration and proliferation of prostate carcinoma cells.

Methods:

The effect of Epac activation was determined by [³H]thymidine incorporation and scratch assays in PC-3 and DU 145 cells. Furthermore, cytoskeletal integrity was analysed by phalloidin staining. The participation of intracellular Epac effectors such as mitogen-activated protein (MAP) kinases, Rap1- and Rho-GTPases was determined by immunoblotting and pull-down assay.

Results:

The specific Epac activator 8-pCPT-2′-O-Me-cAMP (8-pCPT) interfered with cytoskeletal integrity, reduced DNA synthesis, and migration. Although 8-pCPT activated Rap1, it inhibited MAP kinase signalling and RhoA activation. These findings were translated into functional effects such as inhibition of mitogenesis, cytoskeletal integrity, and migration.

Conclusion:

In human prostate carcinoma cells, Epac inhibits proliferative and migratory responses likely because of inhibition of MAP kinase and RhoA signalling pathways. Therefore, Epac might represent an attractive therapeutic target in the treatment of prostate cancer.

cAMP is an important messenger for ADP-induced platelet aggregation

In rat platelets, basal cAMP levels were not changed upon stimulation with ADP and it was concluded that cAMP is not an important messenger for ADP-induced aggregation (Savi et al., Blood Coagul Fibrinolysis, 1996; 7: 249-52). In the present study, the effects of prostaglandin E(1) (PGE(1)) and ADP on human platelet aggregation, cAMP generation and VASP phosphorylation were studied. Phosphorylation of the protein kinase A (PKA) substrate VASP and inhibition of platelet aggregation by PGE(1) occurred without measurable changes in cellular cAMP levels. In addition, a marked inhibition of basal VASP phosphorylation by ADP was observed. It is concluded that cAMP determinations do not necessarily detect a possible activation or inhibition of the cAMPPKA pathway in platelets. Thus, cAMP might well be an important second messenger for ADP-induced platelet aggregation.

Epac inhibits apoptosis of human leukocytes

cAMP is known to participate in the regulation of apoptosis in leukocytes. Depending on the cell type, pro- and antiapoptotic effects of cAMP have been described. Thus far, most of the cAMP-dependent effects have been attributed to the activation of PKA. However, Epac proteins (direct cAMP targets and guanine nucleotide exchange factors for Ras-like GTPases) have been shown recently to contribute to cAMP-dependent regulation of apoptosis. Therefore, we investigated the effects of the selective Epac activators 8-pCPT and Sp on apoptosis in human leukocytic cells (U937, HL-60, primary human mononuclear cells). We report here that Epac activation inhibits leukocyte apoptosis significantly.

Synthesis of hyaluronan in oesophageal cancer cells is uncoupled from the prostaglandin-cAMP pathway

BACKGROUND AND PURPOSE

Cyclooxygenase-2 (COX2) and hyaluronic acid (HA) are common in tumours and both independently promote tumour progression. Furthermore, COX2-dependent synthesis of prostaglandins (PGs) stimulates HA synthase-1 (HAS1) and HAS2 mRNA expression, together with HA synthesis via the cAMP/protein kinase A pathway in vascular smooth muscle cells. Therefore, the aim of the present study was to elucidate whether COX2-mediated PGs induce transcription of HAS isoforms in cancer cells as well.

EXPERIMENTAL APPROACH

Human oesophageal squamous cell (OSC) carcinoma specimens were characterized with respect to HA, COX2 and CD44 expression by immunohistochemistry. OSC cell lines (OSC1, OSC2) and HeLa cell lines (D98, H21) were exposed to exogenous PG analoques (100 nmol.L(-1)), etoricoxib (10 micromol.L(-1)) and forskolin (10 micromol.L(-1)). Subsequently, cAMP levels, HA secretion and HAS isoform expression were determined by elisa and real-time RT-PCR (reverse transcriptase polymerase chain reaction) respectively.

KEY RESULTS

COX2, HA and CD44 were detected immunohistochemically in >90% of human oesophageal tumour samples. Under basal conditions, OSC1 and OSC2 cells express HAS2 and HAS3, COX2 and Galpha(s)-coupled EP(2) and EP(4) PG receptors. Neither stimulation with the PGI(2) analogue, iloprost, addition of exogenous PGE(2) nor forskolin induced HAS1 or HAS2 mRNA expression in OSC1 and OSC2 cells. Furthermore, in HeLa cells after induction of COX2 by tumour necrosis factor alpha and subsequent PGE(2) release, inhibition of COX2 by etoricoxib did not affect HAS expression or HA secretion.

CONCLUSIONS AND IMPLICATIONS

We conclude that in oesophageal and HeLa cancer cells, HAS1/2 expression was not responsive to the PG/cAMP pathway.

Effects of fibroblast extracellular matrix calcification on platelet adhesion in vitro

Calcified atherosclerotic lesions are more prone to rupture during angioplasty than non-calcified lesions and are associated with an increased risk of thrombotic complications following angioplasty. This study investigates the possible role of extracellular matrix (ECM) calcification for platelet adhesion. Human cultured fibroblasts (CRL-1635) were subjected to beta-glycerophosphate (10 mM) for 10 to 16 days. Calcification was visualized by von Kossa staining and quantified by the O-cresolphthalein complexone method. Adhesion of calcein-labelled platelets was measured by fluorescence microscopy at static conditions and in a parallel-flow chamber at a shear rate of 1000 s(-1). beta-glycerophosphate treatment resulted in a marked calcification of the ECM. In parallel, a small, albeit significant increase in platelet adhesion under static conditions was observed. In contrast, at flow conditions, the area covered by thrombi was significantly lower when calcified ECM was used. The number of thrombi was not significantly different which is compatible with a smaller thrombus size. Taken together, it appears unlikely that calcification of atherosclerotic lesions contributes to thrombotic complications by an increased platelet adhesion.

[Methods to evaluate aspirin and clopidogrel resistance]

Based on the concept that the so-called resistance to anti-platelet drugs is meant to describe a phenomenon where the drug does not hit its direct pharmacodynamic target, assays, used to evaluated the effects of anti-platelet drugs, should as closely as possible measure the direct pharmacodynamic effect of a particular drug. Thus, for the detection of aspirin effects, thromboxane concentrations or arachidonic acid-induced responses (light aggregometry, whole-blood aggregometry) should be measured. For the detection of clopidogrel actions, VASP phosphorylation (flow cytometry) or ADP-induced responses (light aggregometry, whole blood aggregometry) should be analysed.

Pyrazolinone analgesics prevent the antiplatelet effect of aspirin and preserve human platelet thromboxane synthesis

BACKGROUND

Anti-inflammatory analgesics, including ibuprofen and naproxen, are known to interfere with the antiplatelet effect of aspirin, presumably as a result of a drug-drug interaction at the level of platelet cyclooxygenase-1 (COX-1).

OBJECTIVE

We studied whether dipyrone, which has recently been reported to inhibit COX isoforms by a mechanism different from conventional non-steroidal anti-inflammatory drugs (NSAIDs), also interferes with the antiplatelet effect of aspirin.

METHODS

Arachidonic acid- and collagen-induced aggregation, as well as thromboxane formation, were measured in human platelet-rich plasma. Platelet P-selectin expression was determined by flow cytometry and cell-free COX enzyme activity was quantified by luminol-enhanced luminescence of human platelet microsomes. In addition, computerized docking was performed based on the crystal structure of COX-1.

RESULTS

4-Methylaminoantipyrine (MAA), the active metabolite of dipyrone, largely attenuated or even completely abolished the inhibition of arachidonic acid-induced platelet aggregation, thromboxane formation and P-selectin expression by aspirin. Similar results were obtained for other pyrazolinones, as well as for the conventional NSAIDs ibuprofen and naproxen. Moreover, MAA attenuated the effect of aspirin on COX activity of platelet microsomes, suggesting a competition with aspirin at the COX-1 enzyme. This was confirmed by docking studies, which revealed that MAA forms a strong hydrogen bond with serine 530 within the COX-1, thereby preventing enzyme acetylation by aspirin.

CONCLUSION

This study demonstrates for the first time that dipyrone and other pyrazolinones have a high potential to attenuate or prevent the antiplatelet effect of aspirin. This should be considered if pyrazolinone analgesics are administered to patients with cardiovascular disease requiring antiplatelet aspirin therapy.

The significance of platelet-derived growth factors for proliferation of vascular smooth muscle cells

Platelets are important in acute thrombotic occlusion of injured vessels, e.g., subsequent to angioplasty. In contrast to these acute events of thrombus formation, much less is known about the significance of platelets for the control of smooth muscle cell (SMC) proliferation. A body of experimental and clinical evidence indicates an involvement of platelets in the pathology of atherosclerosis and restenosis. However, the precise role of platelet-derived growth factors for SMC proliferation in atherosclerotic and restenotic vessels is not clear and many questions remain unresolved. Platelet-dependent SMC mitogenesis is determined by a coordinate action of several classes of mitogenic factors which are either released from storage pools or generated upon platelet activation. Although platelet-derived growth factor (PDGF) is considered to be the most important platelet mitogen it is very likely that yet unknown factors and mechanisms are involved. Differential (stimulatory or inhibitory) effects on SMC growth and differentiation have been reported for different platelet-derived growth factors. Thus, for the overall response, complex interactions between multiple factors need to be considered. In addition, multicellular interactions, e.g., between platelets and endothelial cells may modulate the effects of platelet-derived factors on SMC mitogenesis. Taken together, the mechanisms of platelet-dependent SMC proliferation need to be reevaluated. The assessment of the precise role of platelet mitogens in the complex proliferative repair mechanisms of an injured vessel wall clearly requires further studies.

Aspirin resistance – does it clinically matter?

A variable responsiveness to acetylsalicylic acid(ASA) is a clinical reality that does not principally differ from variable responses to other kinds of drug treatment in other therapeutic fields. Two questions arise: (i) is any resulting "treatment failure"due to a pharmacological failure of the drug to act and (ii) is any reduced antiplatelet activity to ASA related to the clinical outcome oft he patient?Two major laboratory techniques are available to quantify platelet variability to ASA ex vivo: Measurement of platelet function and measurement of thromboxane formation. Both methods have limitations and did not yet result in a generally accepted definition of a pharmacological ASA "resistance".A "true" pharmacological resistance to ASA exists in selected groups of patients. However, unless more information is available,results from in vitro assays of platelet function should not be over-interpreted. More data from prospective trials are required,predominantly by measuring serum thromboxane formation which is a platelet-specific, ASA sensitive reaction. At this time,there is no reason to change there commended daily maintenance dose of about 100 mg ASA without particular requirements in patients who need coronary protection.

Differential Effects of Vasodilatory Prostaglandins on Focal Adhesions, Cytoskeletal Architecture, and Migration in Human Aortic Smooth Muscle Cells

OBJECTIVE

Cyclooxygenases 1 and 2 are expressed in atherosclerotic arteries, and local generation of prostacyclin and prostaglandin E2 (PGE2) occurs. However, the role of cyclooxygenases and individual prostaglandins during plaque progression is currently uncertain. The present study characterizes the effect of vasodilatory prostaglandins on morphology, focal adhesion (FA) function, and migration in human aortic smooth muscle cells (SMCs).

METHODS AND RESULTS

The stable prostacyclin analog iloprost transiently induced: (1) disassembly of FA and stress fibers, (2) partial retraction and rounding of SMCs, (3) hypophosphorylation of FA kinase (FAK) and paxillin, and (4) inhibition of platelet-derived growth factor-BB-induced migration. Inhibition of FAK phosphorylation and morphological changes were mimicked by forskolin, inhibited by H89, and prevented by the protein tyrosine phosphatase inhibitor vanadate and by calpeptin. PGE2 was by far less efficient with respect to all parameters investigated. This difference correlated with the respective cAMP induction in response to iloprost and PGE2.

CONCLUSIONS

Inhibition of FAK phosphorylation and FA function is a new target of vasodilatory prostaglandins, which might be causally involved in the antimigratory effects of prostaglandins. Importantly, prostacyclin analogs and PGE2 differ dramatically with respect to dephosphorylation of FAK and inhibition of migration, which might be of relevance for their respective functions in atherosclerosis.

Functional and biochemical evaluation of platelet aspirin resistance after coronary artery bypass surgery

BACKGROUND

Aspirin inhibits platelet activation and reduces atherothrombotic complications in patients at risk of myocardial infarction and stroke. However, a sufficient inhibition of platelet function by aspirin is not always achieved. The causes of this aspirin resistance are unknown.

METHODS AND RESULTS

Patients undergoing coronary artery bypass grafting (CABG) have a high incidence of aspirin resistance. To evaluate functional and biochemical responses to aspirin, platelet-rich plasma was obtained before and at days 1, 5, and 10 after CABG. Thromboxane formation, aggregation, and alpha-granule secretion were effectively inhibited by 30 or 100 micromol/L aspirin in vitro before CABG, but this inhibition was prevented or attenuated after CABG. Whereas the inhibition of thromboxane formation and aggregation by aspirin in vitro partly recovered at day 10 after CABG, oral aspirin (100 mg/d) remained ineffective. The inducible isoform of cyclooxygenase in platelets, COX-2, has been suggested to confer aspirin resistance. In fact, immunoreactive COX-2 was increased 16-fold in platelets at day 5 after CABG, but the COX-2 selective inhibitor celecoxib did not alter aspirin-resistant thromboxane formation. By contrast, the combined inhibitor of thromboxane synthase and thromboxane receptor antagonist terbogrel equally prevented thromboxane formation of platelets obtained before (control) and after CABG.

CONCLUSIONS

Platelet aspirin resistance involves an impairment of both in vivo and in vitro inhibition of platelet functions and is probably due to a disturbed inhibition of platelet COX-1 by aspirin.

[Combination therapy with anticoagulants and platelet-active drugs]

Platelets and the coagulation system cannot be regarded as completely separate systems. Both systems become activated upon vessel injury and multiple functional interactions exist. Thus with a combination therapy with anticoagulants and platelet-active drugs, drug interactions relevant for hemostasis must be expected. This includes a synergistic inhibition of the hemostatic system but also possible synergistic effects on bleeding complications. This concise review discusses the clinical efficacy of a combination therapy with anticoagulants and platelet-active drugs in patients with acute coronary syndromes (unstable angina, myocardial infarction).

Troglitazone and rosiglitazone inhibit the low density lipoprotein-induced vascular smooth muscle cell growth

Troglitazone (TRO) and rosiglitazone (RSG) belong to the thiazolidinedione class (insulin-sensitizing agents) and exert many of their metabolic effects as peroxisome proliferator-activated receptor gamma (PPARgamma) ligands. In the present study we examined the effects of TRO and RSG on LDL-induced VSMC growth. Pretreatment of VSMC with 1 microM TRO or 0.1 microM RSG completely blocked the LDL-induced cell proliferation as measured by [3H]thymidine incorporation into DNA and by determination of the cell number. We then examined with Western blotting whether these growth suppressing effects are mediated through the mitogen-activated protein kinase (MAPK) pathway, a common signaling pathway activated by growth factors. TRO and RSG had no effect on the LDL-induced stimulation of the MAP kinases ERK1/2, p38 and SAP/JNK. We conclude that thiazolidinediones are potent inhibitors of LDL-induced VSMC growth acting downstream of the cytoplasmic activation of MAPK.

Differential inhibition of adenosine diphosphate- versus thrombin receptor-activating peptide-stimulated platelet fibrinogen binding by abciximab due to different glycoprotein IIb/IIIa activation kinetics

The exposure of internal glycoprotein (GP) IIb/IIIa receptors has been proposed to explain the incomplete inhibition of aggregation of thrombin receptor-activating peptide (TRAP)-stimulated platelets by abciximab. However, a marked and rapid externalization of GPIIb/IIIa was also observed upon stimulation with 30 microM adenosine diphosphate (ADP). ADP-induced fibrinogen binding was completely inhibited by 10 microg/mL abciximab, 30 nM tirofiban, or 3 microg/mL eptifibatide, while fibrinogen binding induced by 100 microM TRAP was inhibited only by 50%. Interestingly, striking differences in fibrinogen binding kinetics in ADP- versus TRAP-stimulated platelets were observed. ADP-induced fibrinogen binding was much slower than that of abciximab. These differences in the fibrinogen binding rate were due to differential GPIIb/IIIa activation kinetics because the actual fibrinogen binding rate (measured by adding fibrinogen after platelet activation) was similar in ADP- and TRAP-stimulated platelets. Thus, the TRAP-induced GPIIb/IIIa activation rate would allow significant amounts of fibrinogen to occupy externalized GPIIb/IIIa receptors even in the presence of the inhibitor.

Recovery of platelet function after discontinuation of clopidogrel treatment in healthy volunteers

AIMS

To study the recovery of platelet function after discontinuation of clopidogrel treatment in healthy volunteers.

METHODS

Ten healthy volunteers were treated with clopidogrel (75 mg day(-1)) for 7 days. CD62P expression and PAC-1 binding were measured by flow cytometry.

RESULTS

Adenosine diphosphate (ADP, 30 microM)-induced platelet responses were almost completely inhibited by clopidogrel. After discontinuation of the drug, platelet function gradually increased and complete recovery was seen 7 days after the last clopidogrel dose. The mean difference (95% CI) for ADP-induced PAC-1 binding (fluorescence intensity) between baseline and 7 days after the last dose was 0.01 (0.61, -0.59). Single cell analysis provides direct evidence for an irreversible mode of action of clopidogrel.

CONCLUSIONS

This is the first report to directly demonstrate irreversibility of clopidogrel action in humans.

A prospective study of a caries prevention program in pregnant women and their children five and six years of age

A preventive dental program (PDP) instituted in pregnant women and comprising an educational and a preventive part was evaluated when their children were five and six years of age. Dental caries was examined in sixty-seven mother-child pairs belonging to the program and in sixty-nine control mother-child pairs. In the five-year-old children 87 percent of the PDP group were caries free compared with the 50 percent in the control group. Comparable figures for six-year-old children were 89 percent and 62 percent in the PDP and control group, respectively. The mean dft of the PDP children five and six years of age was 0.4 and 0.2, respectively, versus 1.3 and 1.4 for the control children. The differences in caries-free status and caries prevalence were statistically significant. In conclusion, the preventive dental program which started in pregnant women and continued in the mothers and their children were highly effective for a long-term reduction of dental caries.

Platelet CD40 ligand (CD40L)--subcellular localization, regulation of expression, and inhibition by clopidogrel

This study compares the subcellular localization and the regulation of expression of the platelet activation markers CD62P and CD63 with CD40 ligand (CD40L) on the surface of washed human platelets. CD40L was expressed upon stimulation with a wide range of platelet activators. However, quantitative flow cytometry demonstrated that, as compared with CD62P and CD63, CD40L expression was low. Upon stimulation with thrombin receptor-activating peptide (TRAP-6), all activation markers were expressed. In contrast, upon stimulation with low concentrations of collagen (1-3 microg/ml), CD40L, but not the granule proteins (CD62P, CD63), were expressed. Using immunofluorescence microscopy, a cytoplasmic staining was observed for CD40L, and cytoplasmic localization of CD40L was verified by Western blotting of subcellular platelet fractions. The staining of CD40L was different from that of filamentous actin and only little association of CD40L with platelet cytoskeleton was found. Surface expression of CD40L was dependent on internal Ca2+ stores and protein kinase C, while the mitogen-activated protein kinases (ERK, p38) or tyrosine kinases were not involved. ADP (30 microM)-induced CD40L expression was not inhibited by aspirin. In contrast, clopidogrel treatment completely abolished ADP-induced expression of CD40L. Finally, the expression level of CD40L was shown to be upregulated by phorbol myristate acetate (PMA) in the promegakaryocytic cell line MEG-01.

Effectiveness of a caries preventive program in pregnant women and new mothers on their offspring

OBJECTIVE

The medical centre at Almirante Nef Naval Hospital, Vina del Mar, Chile, operates a mother and child preventive dental program (PDP) which includes women from their fourth month of pregnancy and mothers with their offspring. The aim was to evaluate the effectiveness of this prenatal and postnatal prevention program after the first four years.

METHODS

The prevalence of early childhood caries of 180 1- to 3.5-year-old children enrolled in the PDP was compared with 180 non-participating children. The control group was randomly selected from the rolls of the healthy child system of of the Valparaiso-San Antonio Health Service and was comparable by age, socio-economic status and level of fluoride in the drinking water (1.0 p.p.m. F) with the PDP group. Clinical caries examinations were conducted by two calibrated examiners using the WHO visual criteria.

RESULTS

In the PDP group, 97% of the children were caries free compared with the 77% in the control group. The dft (mean +/- SD) of the PDP children was 0.11 +/- 0.78 versus 0.66 +/- 1.55 for the control children, a difference of 83.3%. The differences between the groups in caries-free status and caries prevalence were both statistically significant (P < 0.05).

CONCLUSIONS

The preventive dental program was effective in inhibiting caries in pre-school children, even in a population already receiving the benefits of community water fluoridation.

Troglitazone and rosiglitazone induce apoptosis of vascular smooth muscle cells through an extracellular signal-regulated kinase-independent pathway

Recent evidence suggests that apoptosis may be involved in the control of vascular smooth muscle cell (VSMC) number in atherosclerotic lesions. The peroxisome proliferator-activated receptor gamma (PPARgamma) ligands thiazolidinediones have been reported to induce apoptosis in macrophages and in a variety of tumor cell lines. To evaluate whether these agents also induce apoptosis in VSMC, cultured rat VSMC were treated with increasing doses of the thiazolidinedione analogues troglitazone (TRO) and rosiglitazone (RSG). Both ligands induced cell death in a concentration-dependent manner (EC50 12.1+/-3.3 microM and 1.43+/-0.39 microM, respectively), causing almost complete cell death at the highest concentrations (100 microM and 10 microM for TRO and RSG, respectively), along with an expected parallel decrease in [3H]thymidine uptake into cell DNA (EC50 6.7+/-2.4 microM and 0.75+/-0.19 microM, respectively). The cell count was determined by the coulter counter principle. Furthermore two apoptotic markers were measured, the caspase 3 activity and the cytoplasmic histone-associated DNA fragments, both of which were significantly increased when the aforementioned high concentrations were used. This indicates that apoptosis is involved in the TRO- and RSG-induced VSMC growth suppression. The same concentrations of TRO and RSG caused an unexpected stimulation of the extracellular signal-regulated response kinases 1 and 2 (ERK1/2) and stimulated the p38 mitogenic-activated protein (MAP) kinase as determined by Western blotting. In order to establish whether the proapoptotic effects of TRO and RSG are mediated through ERK1/2 activation, we used the selective MAP kinase kinase (MEK) inhibitor PD98059 (20 microM), which suppressed the TRO- and RSG-induced ERK1/2 activation but did not abolish their proapoptotic effects. We conclude that the thiazolidinedione analogues TRO and RSG induce cell death due to apoptosis in VSMC through an ERK1/2-independent pathway.

Validated electrospray liquid chromatographic-mass spectrometric assay for the determination of the mushroom toxins alpha- and beta-amanitin in urine after immunoaffinity extraction

Specific detection of amanitins in body fluids is necessary for an early diagnosis of an intoxication with amanita mushrooms. In this paper, a liquid chromatographic-mass spectrometric assay after immunoaffinity extraction (IAE-LC-MS) is described for the determination of alpha- and beta-amanitin in urine. The method has been validated according to the criteria established by the Journal of Chromatography B. The assay was found to be selective. The calibration curves for alpha- and beta-amanitin were linear from 5 to 75 ng/ml. Intra- and inter-day accuracy and precision were inside the required limits. Amatoxins in frozen urine samples or immunoaffinity extracts were stable for more than 6 months, and the IAE columns could be used more than fifty times without remarkable loss in performance. LOD for alpha- and beta-amanitin was 2.5 ng/ml and LOQ for both was 5.0 ng/ml. The absolute recoveries of alpha- and beta-amanitin were 63% and 58% for the low quality control and 61% and 57% for the high quality control. The absolute recovery for the internal standard gamma-amanitin methyl ether at 25 ng/ml was 60%. The analysis of 5 authentic urine samples from patients intoxicated by amanita mushrooms showed a good correlation between the results measured by radioimmunoassay and the IAE-LC-MS assay. A partial validation showed that the assay was also suitable for plasma analysis.

Habitual smoking causes an abnormality in platelet thromboxane A2 metabolism and results in an altered susceptibility to aspirin effects

The present study investigates the effects of aspirin (100 mg every second day for 14 days) on platelet function in nine healthy non-smokers and in nine healthy habitual smokers. There was a significantly (P < 0.05) stronger inhibition of collagen (0.6 microgram/ml)- and ADP (2 microM)-induced platelet aggregation by aspirin in smokers as compared to non-smokers. This difference occurred in the presence of an almost complete (> 95%) inhibition of thromboxane A2 (TXA2) synthesis in both groups. The platelet capacity to generate TXA2 in vitro was significantly reduced in smokers, urinary excretion of TXA2, however, was significantly increased. Thus, the better susceptibility of smokers to anti-aggregatory effects of aspirin is very likely to be related to a chronic smoking-induced alteration of platelet TXA2 system. Cessation of smoking should, therefore, be encouraged.

Studies on the metabolism and toxicological detection of the amphetamine-like anorectic fenproporex in human urine by gas chromatography-mass spectrometry and fluorescence polarization immunoassay

Studies on the metabolism and the toxicological analysis of fenproporex (R,S-3-[(1-phenyl-2-propyl)-amino]-propionitrile, FP) using GC-MS and fluorescence polarization immunoassay are described. The metabolites were identified in urine samples of volunteers by GC-MS after cleavage of conjugates, extraction and acetylation. Besides unchanged FP, fourteen metabolites, including amphetamine, could be identified. Two partially overlapping metabolic pathways could be postulated: ring degradation by one- and two-fold aromatic hydroxylation followed by methylation and side chain degradation by N-dealkylation to amphetamine (AM). A minor pathway leads via beta-hydroxylation of AM to norephedrine. For GC-MS detection, the systematic toxicological analysis procedure including acid hydrolysis, extraction at pH 8-9 and acetylation was suitable (detection limits 50 ng/ml for FP and 100 ng/ml for AM). Excretion studies showed, that only AM but neither FP nor its specific metabolites were detectable 30-60 h after ingestion of 20 mg of FP. Therefore, misinterpretation can occur. The Abbott TDx FPIA amphetamine/methamphetamine II gave positive results up to 58 h. All the positive immunoassay results could be confirmed by the described GC-MS procedure.

Platelet surface membranes are highly mitogenic for coronary artery smooth muscle cells--A novel mechanism for sustained proliferation after vessel injury?

The effects of isolated platelet surface membranes on DNA synthesis and proliferation of bovine coronary artery smooth muscle cells (SMC) were studied. Platelet membranes were very potent mitogens for SMC. The potency was about 10-fold higher than the maximum effects of platelet-derived growth factor-BB (PDGF). Platelet membrane-induced mitogenesis was inhibited by rapamycin, wortmannin or heating for 15 min at 70 degrees C but not by the PDGF receptor antagonist SCH 13.929 or by neutralizing PDGF antibodies. Only a partial (30%) inhibition was seen with PD 98059. In contrast, PDGF-induced SMC mitogenesis was heat-stable but sensitive to SCH 13. 929, PDGF antibodies, and PD 98059. These findings provide evidence for a novel mechanism for platelet-induced SMC proliferation that is independent of PDGF secretion. Platelet membranes, attached to or incorporated into the vessel wall, could maintain sustained SMC proliferation following injury.

Antimitogenic effects of vasodilatory prostaglandins in coronary artery smooth muscle cells

Vasodilatory prostaglandins (PGI2, PGE2, PGE1) are known inhibitors of proliferation of vascular smooth muscle cells (SMC) after stimulation with mitogenic factors. However, endogenous prostaglandins do not prevent SMC proliferation subsequent to vessel injury in vivo. Since vascular cells produce large amounts of antiproliferative prostaglandins, especially subsequent to COX-2 expression, insufficient vascular PGI2 formation is not likely to explain the failure of endogenous prostaglandins to prevent excessive SMC growth. In this paper we demonstrate a rapid development of tolerance to PGI2 in SMC, resulting in diminished antiproliferative activity. These findings may not only be relevant for the control of SMC growth by endogenously synthesized prostaglandins but also for clinical use of PGI2 mimetics.

Cyclooxygenase-2 expression in human esophageal carcinoma

On the basis of epidemiological observations that nonsteroidal antiinflammatory drugs reduce the risk of esophageal carcinoma, we studied the expression of cyclooxygenase-2 (COX-2) in esophageal squamous cell carcinomas (SCCs; n = 172) and in esophageal adenocarcinomas (ADCs; n = 27). Using immunohistochemistry, we observed COX-2 expression in 91% of the SCCs and in 78% of the ADCs. Western blot analysis showed enhanced expression of the COX-2 protein in some tumors as compared with normal esophageal squamous epithelium, whereas similar amounts of the COX-1 protein were found in normal and cancerous tissues. COX expression was also studied in two esophageal cancer cell lines (OSC-1 and OSC-2) to evaluate the functional relevance of COX-2-derived prostaglandins (PGs). OSC-2 cells expressed COX-2 but not COX-1, whereas OSC-1 cells expressed high levels of COX-1 but showed only a very weak COX-2 expression. Accordingly, PGE2 synthesis was 600 times higher in the OSC-2 cells as compared with the OSC-1 cells. Treatment of OSC-2 cells with the selective COX-2 inhibitors flosulide and NS-398 concentration dependently suppressed PGE2 synthesis and proliferation and also induced apoptosis. In contrast, no effect of the COX-2 inhibitors was seen in OSC-1 cells. Our data demonstrate that COX-2 is expressed in the majority of esophageal SCCs and ADCs and that COX-2-derived PGs play an important role in the regulation of proliferation and apoptosis of esophageal tumor cells. It is concluded that inhibition of COX-2 may be useful in the therapy of esophageal cancer.

Constitutive cyclooxygenase-2 expression in healthy human and rabbit gastric mucosa

Selective cyclooxygenase (COX)-2 inhibitors are expected to cause fewer gastric side effects because of sparing of COX-1-dependent prostaglandin (PG) synthesis in the gastric mucosa. However, the possible contribution of COX-2 to overall gastric PG biosynthesis is not known. This study demonstrates constitutive expression of COX-2 mRNA and protein in apparently healthy human and rabbit gastric mucosa. This basal expression of COX-2 protein in human gastric mucosa was increased by lipopolysaccharide and phorbol ester, indicating its up-regulation in response to appropriate stimuli. The functional significance of COX-2-dependent PG formation was studied in terms of PGE2 generation in the rabbit mucosa and its inhibition by the COX-2-selective inhibitor flosulide. There was concentration-dependent (IC50 = 107 +/- 55 nM) and ultimately complete inhibition of PGE2 generation by flosulide. In addition, gastric mucosa generated 15-hydroxyeicosatetraenoic acid upon treatment with acetylsalicylic acid. The data suggest an important role for COX-2-dependent PG production in apparently healthy gastric mucosa and raise the issue of whether selective COX-2 inhibitors might also interfere with physiological PG formation and actions in the stomach.

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

The triazolopyrimidine trapidil has been found in controlled clinical trials to prevent restenosis after vascular injury. Although trapidil is widely regarded as a platelet-derived growth factor receptor (PDGF) antagonist, its precise mode of action is still unknown. This study was designed to investigate the inhibition of mitogenesis by trapidil in cultured bovine coronary artery smooth muscle cells (SMC) and to identify major signal transduction pathways involved. Trapidil inhibited PDGF-BB-induced mitogenesis in SMC in a concentration-dependent manner. Comparable inhibitory effects were obtained after stimulation of smooth muscle cells by phorbol ester, which suggests that the action of trapidil was not restricted to PDGF receptor-mediated mechanisms. Trapidil also inhibited PDGF- and phorbol ester-induced mitogen-activated protein kinase as well as Raf-1 kinase activity. As a possible target of trapidil, stimulation of cellular protein kinase A (PKA) activity was detected. Trapidil also induced the phosphorylation of vasodilator-stimulated phosphoprotein in SMC. Antimitogenic effects of trapidil were completely abolished by PKA inhibitors. Neither a direct stimulation of cAMP formation nor a phosphodiesterase inhibition was observed at antimitogenic concentrations of trapidil. However, trapidil directly activated purified PKA holoenzyme in a cAMP-independent manner. In conclusion, trapidil exerts its antimitogenic effects on SMC by direct activation of PKA. Thus, PKA-mediated inhibition of the Raf-1/MAP kinase pathway may be involved in the antimitogenic actions of the compound.

Thromboxane A2 potentiates thrombin-induced proliferation of coronary artery smooth muscle cells

The activation of thrombin is the key event in clot formation after vascular injury. Thrombin itself, but also other clot-derived factors, such as thromboxane A2 (TXA2), are mitogenic for vascular smooth muscle cells. We have studied the possible interactions between thrombin and TXA2 in stimulation of coronary artery smooth muscle cell (SMC) proliferation. Thrombin (1 U/ml) caused a significant proliferatory response in SMC. U 46619, a stable TXA2 mimetic, had only a minor stimulating effect by its own but markedly potentiated the thrombin-induced mitogenesis. A possible mechanism for these potentiating effects is provided by the demonstration of a marked (6 fold) but transient (maximum after 20 min) increase in the expression of TXA2 receptor (TP receptor) mRNA in SMC by thrombin. Since a significant clot-related TXA2 generation was detected for at least 2 hours, the up-regulation of TP receptors by thrombin may represent a mechanism that is relevant for the in vivo situation of SMC proliferation after vessel injury.

Tolerance development to antimitogenic actions of prostacyclin but not of prostaglandin E1 in coronary artery smooth muscle cells

This study compares the antimitogenic effects of iloprost and prostaglandin E1 on platelet-derived growth factor-BB stimulated DNA synthesis ([3H]thymidine incorporation) in bovine coronary artery smooth muscle cells. When added 20-24 h after stimulation with platelet-derived growth factor-BB (20 ng/ml), both iloprost and prostaglandin E1, concentration-dependently (IC50 3-5 nM) inhibited DNA synthesis. However, when added together with the growth factor (0-24 h), the inhibition of DNA synthesis by iloprost was markedly attenuated, indicating tolerance development. In contrast, no tolerance to antimitogenic effects of prostaglandin E1 or forskolin were observed. When added to iloprost-tolerant cells, both prostaglandin E1 and forskolin, still inhibited DNA synthesis. There was no evidence for transcriptional down-regulation of prostacyclin receptor gene by iloprost. The data demonstrate a tolerance development to antimitogenic actions of prostacyclin but not of prostaglandin E1 and suggest that the receptors, mediating the antiproliferative actions of these prostaglandins, may be different.

Inhibition of glycosphingolipid synthesis by threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) and the modulation of IL-1beta-stimulated expression of inducible nitric oxide synthase in rat aortic smooth muscle cells

1. The composition of glycosphingolipids is altered in atherosclerotic tissue. In order to study the possible modulation of interleukin-1beta (IL-1beta)-induced expression of inducible nitric oxide synthase (iNOS) by endogenously synthesized glycosphingolipids, we investigated rat aortic vascular smooth muscle cells (VSMC) grown in the presence of the inhibitor of glycosphingolipid synthesis, threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP). 2. Depletion of glycosphingolipids by PDMP (20-30 microM) was demonstrated by thin-layer chromatography of D-[1-(14)C]-galactose- or L-[-U14C]-serine-labelled glycosphingolipids. Nitrite generation was measured by the diaminonaphthalene assay, nitric oxide was determined by the oxyhaemoglobin technique and iNOS protein was detected by immunocytochemistry. 3. In VSMC grown in the presence of PDMP, the glycosphingolipid content was reduced by 30-50%. In PDMP-treated VSMC, IL-1beta (3 micro ml[-1])-stimulated release of nitrite (135 +/- 4 nmol mg(-1) protein 48 h[-1]) was significantly increased as compared to IL-1beta-stimulated control cells (40 +/- 3 nmol mg(-1) protein 48 h(-1); n = 6, P < 0.001). Similarly, IL-1beta (3 micro ml(-1), 36 h)-stimulated release of nitric oxide was higher in PDMP-treated VSMC (6.1 +/- 0.5 nmol mg(-1) protein h[-1]) as compared to untreated cells (2.0 +/- 0.6 nmol mg(-1) protein h(-1); n = 3, P < 0.01). These findings were confirmed by the demonstration of increased expression of iNOS protein (14.9 +/- 1.2% vs 6.4 +/- 0.2%; n = 4, P < 0.001), as shown by immunocytochemistry. 4. Evidence is presented that endogenous glycosphingolipids are important modulators of cytokine-induced iNOS expression. In view of an altered glycosphingolipid profile in atherosclerotic arteries, these mechanisms might be of relevance for the pathogenesis of atherosclerosis and restenosis subsequent to vessel injury.

Effects of terbogrel on platelet function and prostaglandin endoperoxide transfer

The present study describes the platelet-inhibitory effects of terbogrel (5-hexenoic acid, 6-[3-[[(cyanoamino)[(1,1-dimethylethyl)amino]methylene]amino]pheny l]-6-(3-pyridinyl)-, (epsilon)-), a novel combined thromboxane A2 synthase inhibitor and thromboxane A2 receptor antagonist. Terbogrel concentration-dependently inhibited collagen (0.6 microg/ml)- and U46619 (11alpha,9alpha-epoxymethano-15(S)-hydroxy-prosta-5Z,+ ++13E-dienoic acid) (1 microM)-induced aggregation and thromboxane synthesis of washed human platelets. In this system, terbogrel exhibited an equipotent (IC50 of about 10 nM) activity as thromboxane A2 synthase inhibitor and thromboxane A2 receptor antagonist. In addition, the compound favoured prostacyclin synthesis in cultured vascular smooth muscle cells by increasing the transfer of platelet-derived prostaglandin endoperoxides. Terbogrel appears to be a compound with an equipotent molar potency as thromboxane A2 synthase inhibitor and receptor antagonist.

Thrombin-induced mitogenesis in coronary artery smooth muscle cells is potentiated by thromboxane A2 and involves upregulation of thromboxane receptor mRNA

BACKGROUND

Previous studies have shown that thrombin is a potent though slow-acting mitogen for vascular smooth muscle cells (SMC). Because thrombin generation in vivo is accompanied by platelet activation, it has been suggested that platelet-derived factors might enhance thrombin-induced SMC proliferation. No information is available so far on the possible role of thromboxane A2.

METHODS AND RESULTS

Thrombin (1 U/mL) caused a threefold to fourfold increase of DNA synthesis in cultured bovine coronary artery SMC as assessed from [3H]thymidine incorporation. U 46619, a stable thromboxane A2 mimetic, had only a minor stimulating effect on its own but potentiated the thrombin effect sixfold to sevenfold above control (P<.05). These findings were paralleled by a 52+/-5% (P<.05) increase in cell number at 48 hours after addition of both mitogens as compared with 24+/-5% with thrombin alone and no change with U 46619 alone. Thromboxane A2 receptor mRNA was found to be upregulated sixfold 20 minutes after thrombin stimulation. Pretreatment of SMC with thrombin for 4 hours markedly increased U 46619-induced mitogen-activated protein kinase activity, indicating thrombin-induced upregulation of functional thromboxane receptors in SMC.

CONCLUSIONS

Thrombin-induced proliferation of SMC is markedly enhanced by thromboxane A2. This might result in an enhancement of SMC proliferation by platelet-derived thromboxane A2 in vivo.

The bovine thromboxane A2 receptor: molecular cloning, expression, and functional characterization

This study describes the molecular cloning and functional characterization of the bovine thromboxane A2 (TP) receptor. Two partial nucleotide sequences coding for the bovine TP receptor were isolated from a bovine genomic and a bovine heart cDNA library. The deduced amino acid sequence suggests a heptahelical protein of 343 amino acids. The receptor protein is homologous with that of human placenta and endothelium at 84.0% and 81.4%, respectively. COS-7 cells were transfected with the bovine TP receptor cDNA, and binding affinities were assessed by radioligand binding studies. Specific displacement of [3H]SQ 29548 was demonstrated in COS-7 cell membranes with the unlabeled TP receptor antagonist SQ 29548 (Kd = 12.6+/-1.1 nM) and the TP receptor agonist U46619 (Kd = 192.1+/-58.9 nM), but not with other prostaglandins (PGD2, PGE1, PGF2alpha), or the PGI2 mimetic cicaprost. Agonist-induced stimulation of adenylyl cyclase in transfected COS-7 cells indicates a linkage to the cAMP signal transduction pathway via coupling to a stimulatory G-protein. Since bovine cells, e.g. vascular smooth muscle cells, are an established model to study the role of eicosanoids in cell signaling, this report on the molecular structure of the bovine TP receptor will allow further studies on receptor regulation.

Activation of NFkappaB is essential but not sufficient to stimulate mitogenesis of vascular smooth muscle cells

This study investigates the role of the transcription factor NFkappaB in thrombin- and thrombin receptor activating peptide (TRAP, SFLLRNPNDKYEPYF)-induced mitogenesis of cultured bovine coronary artery smooth muscle cells (SMC). Stimulation of resting cells by thrombin (10 nM) or TRAP (10-100 microM) resulted in a comparable time-dependent activation of NFkappaB as detected by Western blotting and electrophoretic mobility shift assay (EMSA) of nuclear extracts. The NFkappaB activation was antagonized by N-acetyl-L-cysteine (20 mM) and pentoxifylline (0.5 mM). Thrombin caused a 3-4-fold increase in [3H]thymidine incorporation within 24 h which was prevented by inhibitors of NFkappaB activation. In contrast, TRAP did not cause any mitogenic response. These results demonstrate that activation of NFkappaB is an essential but not a sufficient signal for SMC mitogenesis.

Gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS) in toxicological analysis. Studies on the detection of clobenzorex and its metabolites within a systematic toxicological analysis procedure by GC-MS and by immunoassay and studies on the detection of alpha- and beta-amanitin in urine by atmospheric pressure ionization electrospray LC-MS

GC-MS is the method of choice for toxicological analysis of toxicants volatile in GC while non-volatile and/or thermally labile toxicants need LC-MS for their determination. Studies are presented on the toxicological detection of the amphetamine-like anorectic clobenzorex in urine by GC-MS after acid hydrolysis, extraction and acetylation and by fluorescence polarization immunoassay (FPIA, TDx (meth)amphetamine II). After ingestion of 60 mg of clobenzorex, the parent compound and/or its metabolites could be detected by GC-MS for up to 84 h or by FPIA for up to 60 h. Since clobenzorex shows no cross-reactivity with the used immunoassay, the N-dealkylated metabolite amphetamine is responsible for the positive TDx results. The intake of clobenzorex instead of amphetamine can be differentiated by GC-MS detection of hydroxyclobenzorex which is detectable for at least as long as amphetamine. In addition, the described GC-MS procedure allows the simultaneous detection of most of the toxicologically relevant drugs. Furthermore, studies are described on the atmospheric pressure ionization electrospray LC-MS detection of alpha- and beta-amanitin, toxic peptides of amanita mushrooms, in urine after solid-phase extraction on RP-18 columns. Using the single ion monitoring mode with the ions m/z 919 and 920 the amanitins could be detected down to 10 ng/ml of urine which allows us to diagnose intoxications with amanita mushrooms.

Thromboxane A2 induces cell signaling but requires platelet-derived growth factor to act as a mitogen

This study investigates thromboxane A2-induced cell signaling and mitogenesis of bovine coronary artery smooth muscle cells. The thromboxane mimetic U 46619 [(15S)-hydroxy-11,9-(epoxymethano) prosta-5Z,13E-dienoic acid] (10 microM) stimulated [Ca2+]i signals, phosphorylation of MAP kinase (mitogen-activated protein kinase), and expression of c-fos mRNA in smooth muscle cells. In contrast, no stimulation of DNA synthesis or cell proliferation by U 46619 was observed. However, platelet-derived growth factor-BB (20 ng/ml)-induced mitogenesis was potentiated by U 46619. Similar results were obtained with I-BOP [1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R*), 4 alpha)]-7-[3-(3-hydroxy-4-(4'-iodophenoxy)-1-butenyl)-7-oxabicyclo [2.2.1] heptan-2-yl]-5-heptenoic acid]. These potentiating effects were abrogated by a specific thromboxane receptor antagonist, suggesting that the potentiation of platelet-derived growth factor-BB-induced smooth muscle cell mitogenesis by U 46619 and I-BOP was mediated by thromboxane receptors. It is concluded that thromboxane A2 generated by blood platelets at the site of vessel injury induces cell signaling in smooth muscle cells but acts as a mitogen only in the presence of growth factor(s).

Roles of vasodilatory prostaglandins in mitogenesis of vascular smooth muscle cells

Vasodilatory prostaglandins (PGI2, PGE1) and synthetic prostacyclin mimetics inhibit smooth muscle cell proliferation in vitro after stimulation by growth factors. Similar results are obtained in vivo after endothelial injury, suggesting that vasodilatory prostaglandins might also control smooth muscle cell proliferation in vivo. However, available data from clinical trials are conflicting and currently do not support the concept that these compounds might be successfully used to suppress excessive smooth muscle cell growth in response to tissue injury, specifically restenosis after PTCA. One possible explanation for these different results is an agonist-induced down-regulation of prostacyclin receptors in vascular smooth muscle cells. It is possible that enhanced endogenous prostacyclin biosynthesis, subsequent to induction of COX-2 and/or in relation to the formation of a neointima from media smooth muscle cells, might have a similar effect. There is still uncertainty regarding the cellular signal transduction pathways and their possibly complex interaction, although cAMP-dependent reactions are probably involved. In addition, vasodilatory prostaglandins might also interfere with the generation and action of other growth modulating factors, including PDGF, hepatocyte growth factor and nitric oxide. In conclusion, vasodilatory prostaglandins might be considered as growth modulating endogenous mediators in vascular smooth muscle cells.

Cholesterol enhances platelet-derived growth factor-BB-induced [Ca2+]i and DNA synthesis in rat aortic smooth muscle cells

In the present study, we describe possible mechanisms by which hypercholesterolemia may contribute to the development of cardiovascular diseases. Treatment of rat aortic smooth muscle cells for 20 hours with cholesterol-rich liposomes (500 micrograms/mL cholesterol, 100 micrograms/mL low-density lipoprotein) resulted in a 76 +/- 12% increase in total cholesterol content. The effects of cholesterol enrichment were examined by determination of changes in cell membrane fluidity. Fluidity of the cholesterol-enriched cell membranes was decreased at all temperatures between 15 degrees C and 40 degrees C. Changes in membrane fluidity in whole cell membranes represented changes in fluidity of microsomal membranes isolated by Percoll gradient ultracentrifugation. The basal [Ca2+]i and the maximal platelet-derived growth factor (PDGF)-BB-induced [Ca2+]i was elevated by 30% and 90% in cholesterol-enriched cells, respectively. In contrast, the resting pH, and the PDGF-BB-induced stimulation of the Na+/H+ exchange were not affected in cholesterol-enriched cells. The effect of PDGF-BB on [3H]thymidine incorporation in cholesterol-enriched cells was elevated by 40% in comparison with untreated cells. Our findings show that cellular cholesterol may be involved in the development of vascular diseases via modulation of the PDGF-induced increase in [Ca2+]i and DNA synthesis in vascular smooth muscle cells.