Glucocorticoid influence on growth of vascular wall cells in culture

Effects of Exogenous Glucocorticoid Infusion on Appetitic Center Development in Postnatal Dairy Bull Calves

The objective of this study was to determine the effects of exogenous glucocorticoid administration on leptin concentrations and brain development markers, such as protein and hypothalamic gene expression, in dairy bull calves. Within 4 h of parturition, Holstein bulls were intravenously infused with either a low cortisol dose (LC; n = 9, 3.5 µg/kg of body weight (BW)), high cortisol dose (HC; n = 9, 7.0 µg/kg BW), or control (CON; n = 9, saline) dose, with a 2nd infusion 24 h postpartum. Jugular blood was collected prior to infusion and daily until the calves were euthanized (day 5). Cerebrospinal fluid (CSF) from the third ventricle and adipose (omental, perirenal, and mesenteric) and hypothalamic tissue were collected. The blood and CSF samples were analyzed for leptin concentrations. The data were analyzed using SAS. Serum (p = 0.013) and CSF (p = 0.005) leptin concentrations in HC- and LC-treated calves were decreased compared with CON-treated calves. Leptin protein expression was decreased (p < 0.044) in perirenal and omental adipose tissue of LC-treated calves compared with CON-treated calves. Gene abundance of brain-derived neurotrophic factor and fibroblast growth factors 1 and 2 were decreased (p < 0.006) in HC- and LC-treated calves compared with CON-treated calves. In summary, cortisol administered to dairy bull calves reduced leptin concentrations, decreased leptin protein expression in perirenal and omental adipose tissue, and altered gene expression in hypothalamic tissue.

Effect of intravitreal dexamethasone implant versus ranibizumab on vessel density in branch retinal vein occlusion

PURPOSE

This study aimed to compare the effect of intravitreal dexamethasone implant with that of ranibizumab on vessel density (VD) in eyes with branch retinal vein occlusion (BRVO).

METHODS

Sixty-three eyes of 63 patients with superotemporal BRVO treated either with intravitreal dexamethasone implant (DEX group, n = 31) or ranibizumab (RNB group, n = 32) were prospectively enrolled. Swept-source optical coherence tomography angiography 6 × 6 mm scans of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) in all eyes were analyzed.

RESULTS

The mean baseline VD of the SCP and the DCP was similar between groups in all quadrants (p > 0.05 for all). At 12 months, the VD of the SCP in the parafoveal superior and temporal quadrants was significantly higher in the RNB group than in the DEX group (p = 0.002 and p = 0.001, respectively). The VD of the DCP in the parafoveal temporal, nasal, and superior quadrants was significantly higher in the RNB group than in the DEX group (p < 0.05 for all). Further, there was a statistically significant positive correlation between the improvement of visual acuity and increased VD of the SCP and the DCP in the parafoveal temporal quadrant in both groups (R = 0.589, p = 0.001 and R = 0.455, p = 0 .017, respectively).

CONCLUSION

Our findings support that ranibizumab does not inhibit collateral vessel formation in eyes with superotemporal BRVO compared to dexamethasone implant. VD and vessel formation can positively affect the vision prognosis in long-term follow-up.

Species-specific regulation of angiogenesis by glucocorticoids reveals contrasting effects on inflammatory and angiogenic pathways

Glucocorticoids are potent inhibitors of angiogenesis in the rodent in vivo and in vitro but the mechanism by which this occurs has not been determined. Administration of glucocorticoids is used to treat a number of conditions in horses but the angiogenic response of equine vessels to glucocorticoids and, therefore, the potential role of glucocorticoids in pathogenesis and treatment of equine disease, is unknown. This study addressed the hypothesis that glucocorticoids would be angiostatic both in equine and murine blood vessels.The mouse aortic ring model of angiogenesis was adapted to assess the effects of cortisol in equine vessels. Vessel rings were cultured under basal conditions or exposed to: foetal bovine serum (FBS; 3%); cortisol (600 nM), cortisol (600nM) plus FBS (3%), cortisol (600nM) plus either the glucocorticoid receptor antagonist RU486 or the mineralocorticoid receptor antagonist spironolactone. In murine aortae cortisol inhibited and FBS stimulated new vessel growth. In contrast, in equine blood vessels FBS alone had no effect but cortisol alone, or in combination with FBS, dramatically increased new vessel growth compared with controls. This effect was blocked by glucocorticoid receptor antagonism but not by mineralocorticoid antagonism. The transcriptomes of murine and equine angiogenesis demonstrated cortisol-induced down-regulation of inflammatory pathways in both species but up-regulation of pro-angiogenic pathways selectively in the horse. Genes up-regulated in the horse and down-regulated in mice were associated with the extracellular matrix. These data call into question our understanding of glucocorticoids as angiostatic in every species and may be of clinical relevance in the horse.

Hypothalamic-Pituitary-Adrenal Axis Modulation of Glucocorticoids in the Cardiovascular System

The collective of endocrine organs acting in homeostatic regulation—known as the hypothalamic-pituitary-adrenal (HPA) axis—comprises an integration of the central nervous system as well as peripheral tissues. These organs respond to imminent or perceived threats that elicit a stress response, primarily culminating in the release of glucocorticoids into the systemic circulation by the adrenal glands. Although the secretion of glucocorticoids serves to protect and maintain homeostasis in the typical operation at baseline levels, inadequate regulation can lead to physiologic and psychologic pathologies. The cardiovascular system is especially susceptible to prolonged dysregulation of the HPA axis and glucocorticoid production. There is debate about whether cardiovascular health risks arise from the direct detrimental effects of stress axis activation or whether pathologies develop secondary to the accompanying metabolic strain of excess glucocorticoids. In this review, we will explore the emerging research that indicates stress does have direct effects on the cardiovascular system via the HPA axis activation, with emphasis on the latest research on the impact of glucocorticoids signaling in the vasculature and the heart.

Safety and feasibility of adjunctive dexamethasone infusion into the adventitia of the femoropopliteal artery following endovascular revascularization

OBJECTIVE

Restenosis following endovascular treatment of the femoropopliteal segment is associated with the inflammatory response produced in the artery wall at the time of the procedure. Although local drug delivery to the superficial femoral and popliteal arteries promises improved patency, data are currently limited. We hypothesized that improved percutaneous delivery of an anti-inflammatory compound into the adventitia of the femoropopliteal at the time of endovascular treatment would be safe, feasible, and decrease the inflammatory response.

METHODS

This was a prospective, investigator-initiated, phase I, first-in-man study testing the safety and feasibility of percutaneous adventitial delivery of dexamethasone. Following successful intervention, an adventitial microinfusion catheter was advanced over a 0.014-inch wire to the treated segment. Its microneedle (0.9 mm long × 140-μm diameter) was deployed into the adventitia to deliver dexamethasone (4 mg/mL) mixed with contrast agent (80:20 ratio), providing fluoroscopic visualization. The primary safety outcome measure was freedom from vessel dissection, thrombosis, or extravasation while the primary efficacy outcome was duplex-determined binary restenosis defined as a peak systolic velocity ratio >2.5.

RESULTS

Twenty patients with Rutherford clinical category 2-5 enrolled in this study. The mean age was 66, and 55% had diabetes mellitus. Treated lesion length was 8.9 ± 5.3 cm, and 50% were chronic total occlusions. Eighty percent of treated lesions were in the distal superficial femoral or popliteal arteries. All lesions were treated by balloon angioplasty with provisional stenting (n = 6) for suboptimal result. Three patients were treated with atherectomy as well. A mean of 1.6 ± 1.1 mg (0.5 ± 0.3 mL) of dexamethasone sodium phosphate was injected per centimeter of lesion length. In total, a mean of 12.1 ± 6.1 mg of dexamethasone was injected per patient. The mean number of injections required per lesion was 3.0 ± 1.3 cm, minimum one and maximum six injections. There was 100% technical success of drug delivery and no procedural or drug-related adverse events. The mean Rutherford score decreased from 3.1 ± .7 (median, 3.0) preoperatively to .5 ± .7 at 6 months (median, 0.0; P < .00001). Over this same time interval, the index leg ankle-brachial index increased from .68 ± .15 to .89 ± .19 (P = .0003). The preoperative C-reactive protein in this study was 6.9 ± 8.5 indicating severe baseline inflammation, which increased to 14.0 ± 23.1 mg/L (103% increase) at 24 hours following the procedure. However, this increase did not reach statistical significance of P = .14. Two patients met the primary efficacy end point of loss of primary patency by reoccluding their treated segment of the index lesion during the follow-up period.

CONCLUSIONS

Adventitial drug delivery via a microinfusion catheter is a safe and feasible alternative to intimal-based methods for adjunctive treatment in the femoropopliteal segment. The 6-month preliminary results suggest perivascular dexamethasone treatment may improve outcomes following angioplasty to the femoral and popliteal arteries, and support further clinical investigation of this approach.

Glucocorticoid-mediated inhibition of angiogenic changes in human endothelial cells is not caused by reductions in cell proliferation or migration

Background

Glucocorticoid-mediated inhibition of angiogenesis is important in physiology, pathophysiology and therapy. However, the mechanisms through which glucocorticoids inhibit growth of new blood vessels have not been established. This study addresses the hypothesis that physiological levels of glucocorticoids inhibit angiogenesis by directly preventing tube formation by endothelial cells.

Methodology/Principal Findings

Cultured human umbilical vein (HUVEC) and aortic (HAoEC) endothelial cells were used to determine the influence of glucocorticoids on tube-like structure (TLS) formation, and on cellular proliferation (5-bromo-2′-deoxyuridine (BrdU) incorporation), viability (ATP production) and migration (Boyden chambers). Dexamethasone or cortisol (at physiological concentrations) inhibited both basal and prostaglandin F_2α (PGF_2α)-induced and vascular endothelial growth factor (VEGF) stimulated TLS formation in endothelial cells (ECs) cultured on Matrigel, effects which were blocked with the glucocorticoid receptor antagonist RU38486. Glucocorticoids had no effect on EC viability, migration or proliferation. Time-lapse imaging showed that cortisol blocked VEGF-stimulated cytoskeletal reorganisation and initialisation of tube formation. Real time PCR suggested that increased expression of thrombospodin-1 contributed to glucocorticoid-mediated inhibition of TLS formation.

Conclusions/Significance

We conclude that glucocorticoids interact directly with glucocorticoid receptors on vascular ECs to inhibit TLS formation. This action, which was conserved in ECs from two distinct vascular territories, was due to alterations in cell morphology rather than inhibition of EC viability, migration or proliferation and may be mediated in part by induction of thrombospodin-1. These findings provide important insights into the anti-angiogenic action of endogenous glucocorticoids in health and disease.

Reciprocal regulation of 11β-hydroxysteroid dehydrogenase 1 and glucocorticoid receptor expression by dexamethasone inhibits human coronary artery smooth muscle cell proliferation in vitro

The actions of glucocorticoids are mediated, in part, by 11β-hydroxysteroid dehydrogenase 1 (11β-HSD1), which amplifies their effects at the pre-receptor level by converting cortisone to cortisol. Glucocorticoids, such as dexamethasone, inhibit vascular smooth muscle cell proliferation; however, the role of 11β-HSD1 in this response remains unknown. Accordingly, we treated human coronary artery smooth muscle cells (HCSMC) with dexamethasone (10(-9)-10(-6) mol/l) and found that after 72 h dexamethasone increased 11β-HSD1 expression (14.16 ± 1.6-fold, P < 0.001) and activity (6.21 ± 1.2-fold, P < 0.001) in a dose- and time-dependent manner, which was dependent upon glucocorticoid receptor (GR) activation and C/EBPβ and C/EBPδ signaling. As glucocorticoids are known to negatively regulate GR expression, we examined the effect of decreasing 11β-HSD1 expression on GR expression. In HCSMC transfected with 11β-HSD1 siRNA, GR expression was increased; this effect was associated with protein kinase A activation and CREB phosphorylation. To examine the role of 11β-HSD1 in HCSMC proliferation, we decreased 11β-HSD1 expression and stimulated cells with platelet-derived growth factor (PDGF) (10 ng/ml). Decreased 11β-HSD1 expression was associated with increased cell proliferation in the absence of PDGF compared to scrambled control-transfected cells (236.10 ± 13.11%, n = 4, P < 0.001) and this effect was augmented by PDGF. Furthermore, the inhibitory effect of dexamethasone on cellular proliferation was abrogated in 11β-HSD1 siRNA-transfected HCSMC. Downregulation of 11β-HSD1 was associated with decreased p27(kip1) expression and increased phosphorylated retinoblastoma protein, consistent with a proliferative response. These findings suggest that 11β-HSD1 plays a role in the effects of glucocorticoids on vascular smooth muscle cell phenotype.

Therapeutic manipulation of glucocorticoid metabolism in cardiovascular disease

The therapeutic potential for manipulation of glucocorticoid metabolism in cardiovascular disease was revolutionized by the recognition that access of glucocorticoids to their receptors is regulated in a tissue-specific manner by the isozymes of 11beta-hydroxysteroid dehydrogenase. Selective inhibitors of 11beta-hydroxysteroid dehydrogenase type 1 have been shown recently to ameliorate cardiovascular risk factors and inhibit the development of atherosclerosis. This article addresses the possibility that inhibition of 11beta-hydroxsteroid dehydrogenase type 1 activity in cells of the cardiovascular system contributes to this beneficial action. The link between glucocorticoids and cardiovascular disease is complex as glucocorticoid excess is linked with increased cardiovascular events but glucocorticoid administration can reduce atherogenesis and restenosis in animal models. There is considerable evidence that glucocorticoids can interact directly with cells of the cardiovascular system to alter their function and structure and the inflammatory response to injury. These actions may be regulated by glucocorticoid and/or mineralocorticoid receptors but are also dependent on the 11beta-hydroxysteroid dehydrogenases which may be expressed in cardiac, vascular (endothelial, smooth muscle) and inflammatory (macrophages, neutrophils) cells. The activity of 11beta-hydroxysteroid dehydrogenases in these cells is dependent upon differentiation state, the action of pro-inflammaotory cytokines and the influence of endogenous inhibitors (oxysterols, bile acids). Further investigations are required to clarify the link between glucocorticoid excess and cardiovascular events and to determine the mechanism through which glucocorticoid treatment inhibits atherosclerosis/restenosis. This will provide greater insights into the potential benefit of selective 11beta-hydroxysteroid dehydrogenase inhibitors in treatment of cardiovascular disease.

Glucocorticoids and cardiovascular disease

Chronic excessive activation of glucocorticoid receptors induces obesity, insulin resistance, glucose intolerance, dyslipidaemia and hypertension. Subtle abnormalities of the hypothalamic-pituitary-adrenal axis and/or of tissue sensitivity to glucocorticoids are also associated with these cardiovascular risk factors in patients with the metabolic syndrome. Furthermore, glucocorticoids have direct effects on the heart and blood vessels, mediated by both glucocorticoid and mineralocorticoid receptors and modified by local metabolism of glucocorticoids by the 11beta-hydroxysteroid dehydrogenase enzymes. These effects influence vascular function, atherogenesis and vascular remodelling following intra-vascular injury or ischaemia. This article reviews the systemic and cardiovascular effects of glucocorticoids, and the evidence that glucocorticoids not only promote the incidence and progression of atherogenesis but also modify the recovery from occlusive vascular events and intravascular injury. The conclusion is that manipulation of glucocorticoid action within metabolic and cardiovascular tissues may provide novel therapeutic avenues to combat cardiovascular disease.

Dexamethasone inhibits interleukin-1beta-induced corneal neovascularization: role of nuclear factor-kappaB-activated stromal cells in inflammatory angiogenesis

Dexamethasone, a synthetic corticosteroid, is widely used as a potent anti-inflammatory drug in various diseases including corneal angiogenesis. However, dexamethasone's impact on interleukin (IL)-1beta-dependent inflammatory angiogenesis is unknown. Here, we show that dexamethasone inhibits IL-1beta-induced neovascularization and the expression of the angiogenesis-related factors, vascular endothelial growth factor-A, KC, and prostaglandin E(2) in the mouse cornea 2 days after IL-1beta implantation. IL-1beta caused IkappaB-alpha phosphorylation in corneal stromal cells but not in infiltrated CD11b(+) cells 2 days after IL-1beta implantation. In contrast, both cell types were positive for phosphorylated IkappaB-alpha 4 days after IL-1beta implantation. Dexamethasone significantly inhibited IkappaB-alpha phosphorylation 2 and 4 days after IL-1beta implantation. Furthermore, dexamethasone inhibited IL-1beta-induced expression of vascular endothelial growth factor-A, KC, and prostaglandin E(2), and signaling of nuclear factor (NF)-kappaB in corneal fibroblasts in vitro. A selective NF-kappaB inhibitor attenuated IL-1beta-induced corneal angiogenesis. These findings suggest that NF-kappaB activation in the corneal stromal cells is an important early event during IL-1beta-induced corneal angiogenesis and that dexamethasone inhibits IL-1beta-induced angiogenesis partially via blocking NF-kappaB signaling.

Isoform-specific modulation of coronary artery PKC by glucocorticoids

Glucocorticoids (GC) exert diverse cellular effects in response to both acute and chronic stress, the functional consequences of which have been implicated in the development of cardiovascular pathology such as hypertension and atherosclerosis. However, the mechanisms by which GCs activate divergent signaling pathways are poorly understood. The present study examined the direct effects of natural (cortisol) and synthetic (dexamethasone) GCs on protein kinase C (PKC) isoform expression in coronary arteries. Porcine right coronary arteries were treated in vitro for 18 h in the presence and absence of either dexamethasone (10, 100, or 500 nM) or cortisol (50, 125, 250, or 500 nM). PKC isoform levels and subcellular distribution were determined by immmunoblotting of whole cell homogenates and immunocytofluorescence using PKC-alpha, -betaII, -epsilon, -delta, and -zeta specific antibodies. Dexamethasone caused a approximately 4-fold increase in PKC-alpha, a approximately 2.5-fold increase in PKC-betaII, and a 2-fold increase in PKC-epsilon (p<0.05). In contrast, dexamethasone had no effect on PKC-delta or PKC- zeta levels. Dexamethasone also caused an increase in the activity of PKC-alpha (285%), -betaII (170%), and -epsilon (210%). Cortisol produced similar effects on PKC isoform expression. Confocal microscopy revealed that while dexamethasone altered localization patterns for PKC-alpha, -betaII and -epsilon, no such effect was observed for PKC-delta or PKC-zeta. The stimulatory effects of dexamethasone and cortisol on coronary PKC levels and translocation were prevented by the GC receptor (GR) blocker, RU486. These results demonstrate, for the first time, that GCs modulate coronary PKC expression and subcellular distribution in an isoform-specific manner through a GR-dependent mechanism.

Inhaled corticosteroids decrease vascularity of the bronchial mucosa in patients with asthma

BACKGROUND

Increased vascularity in airway mucosa is a distinctive feature of airway remodelling in asthma. While corticosteroids have proved most effective in modifying airway inflammation, the effect of inhaled corticosteroids on increased airway mucosal vascularity in asthmatics has been little studied.

OBJECTIVE

We examined the effect of inhaled corticosteroid on airway vascularity in bronchial biopsy specimens taken from asthmatic patients.

SUBJECTS AND METHODS

We studied bronchial biopsies from 28 asthmatic patients before and after treatment with inhaled beclomethasone dipropionate (BDP) 800 microg/daily, or placebo, for 6 months in a double-blind manner. Biopsy specimens were evaluated for number of vessels and percentage of area occupied by vessels, using computerized image analysis after staining for type IV collagen in vessel walls. Specimens were also examined for extent of collagen III in the subepithelial basement membrane. In addition, we compared asthmatic specimens with biopsy specimens taken from non-asthmatic control subjects.

RESULTS

There was a significant increase in number of vessels (P < 0.01) and percent vascularity (P < 0.001) in the submucosa of asthmatic patients compared with control subjects. After 6 months of treatment, we observed significant improvements in forced expiratory volume in 1 s (FEV1), FEV1% and airway responsiveness (P < 0.05, each) in the BDP treatment group compared with the placebo group. This was accompanied by significant decreases in both vessel number and percent vascularity in the airways of BDP-treated patients (P < 0.05, each). We also observed a significant correlation between change in percent vascularity and change in collagen III thickness in the BDP-treated patients (rs = 0.90, P < 0.001). Furthermore, the change in percent vascularity was inversely correlated with both FEV1 (rs = -0.49, P < 0.05) and airway responsiveness (rs = -0.36, P < 0.05).

CONCLUSION

These findings suggest that inhaled corticosteroid treatment of asthma reduced airway wall vascularity during airway remodelling.

Using CCM and DHPLC to detect mutations in the glucocorticoid receptor in atherosclerosis: a comparison

Growing evidence suggests that restenosis may be caused by a failure in growth inhibitory and apoptotic systems that would normally mediate lesion regression. One such inhibitory system is the glucocorticoid receptor. This paper develops, assesses and compares chemical cleavage of mismatch (CCM) and denaturing high-performance liquid chromatography (DHPLC) for their utility in detecting mutations in this system. The results of the two methods correlated in 74% of cases in a cohort of endarterectomy patients studied by these two methods.

IL-4 and IL-13 upregulate arginase I expression by cAMP and JAK/STAT6 pathways in vascular smooth muscle cells

The objectives of this study were to determine whether rat aortic smooth muscle cells (RASMC) express arginase and to elucidate the possible mechanisms involved in the regulation of arginase expression. The results show that RASMC contain basal arginase I (AI) activity, which is significantly enhanced by stimulating the cells with either interleukin (IL)-4 or IL-13, but arginase II (AII) expression was not detected under any condition studied here. We further investigated the signal transduction pathways responsible for AI induction. AI mRNA and protein levels were enhanced by addition of forskolin (1 microM) and inhibited by H-89 (30 microM), suggesting positive regulation of AI by a protein kinase A pathway. Genistein (10 microgramg/ml) and sodium orthovanadate (Na(3)VO(4); 10 microM) were used to investigate the role of tyrosine phosphorylation in the control of AI expression. Genistein inhibited, whereas Na(3)VO(4) enhanced the induction of AI by IL-4 or IL-13. Along with immunoprecipitation and immunoblot analyses, these data implicate the JAK/STAT6 pathway in AI regulation. Dexamethasone (Dex) and interferon (IFN)-gamma were investigated for their effects on AI induction. Dex (1 microM) and IFN-gamma (100 U/ml) alone had no effect on basal AI expression in RASMC, but both reduced AI induction by IL-4 and IL-13. In combination, Dex and IFN-gamma abolished AI induction by IL-4 and IL-13. Finally, both IL-4 and IL-13 significantly increased RASMC DNA synthesis as monitored by [(3)H]thymidine incorporation, demonstrating that upregulation of AI is correlated with an increase in cell proliferation. Blockade of AI induction by IFN-gamma, H-89, or genistein also blocked the increase in cell proliferation. These observations are consistent with the possibility that upregulation of AI might play an important role in the pathophysiology of vascular disorders characterized by excessive smooth muscle growth.

Glucocorticoid modulates Na+/H+ exchange activity in vascular smooth muscle cells by nongenomic and genomic mechanisms

BACKGROUND

In vascular smooth muscle cells (VSMCs), Na+/H+ exchange (NHE) plays an important role in intracellular pH (pHi) regulation. The genomic effect of glucocorticoid (GC) on NHE activity has been suggested in VSMCs. However, the nongenomic and genomic effects of GC on NHE activity and the underlying intracellular signaling mechanisms have not yet been demonstrated in VSMCs. Also, it is not known whether there are specific surface-binding sites of GC to the plasma membrane of VSMCs.

METHODS

The effects of short (3 h)- and long (24 h)-term exposure to corticosterone (CORTI) on NHE activity were studied in cultured rat aortic VSMCs by using pHi measurement with the pH-sensitive fluorescent dye 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. The NHE activity was calculated from the initial rate of Na+-dependent pHi recovery after the acid load.

RESULTS

Short-term exposure of VSMCs to CORTI (10-6 mol/L) increased NHE activity, whereas long-term exposure to CORTI decreased it. The inhibitors of gene transcription (actinomycin D) and of protein synthesis (cycloheximide) did not affect the short-term effect of CORTI on NHE activity, but inhibited the long-term effect of CORTI on NHE activity. The cytosolic GC receptor (GR) antagonist (RU38486) inhibited both the short- and long-term effects of CORTI on NHE activity, but the cytosolic mineralocorticoid receptor antagonist (spironolactone) did not influence either the short- or long-term CORTI effects. Two protein kinase C (PKC) inhibitors (staurosporine A and calphostin C) and PKC down-regulation [24-h pre-exposure to phorbol 12-myristate 13-acetate (PMA)] inhibited both short- and long-term CORTI effects. Exposure to PMA for three hours mimicked the short-term CORTI effect. The short-term CORTI effect was inhibited by the disruptor of microtubule (colchicine), but not by the disruptor of filamentous-actin (cytochalasin B). The long-term exposure to CORTI decreased NHE (NHE-1) mRNA levels to 0.65 times the control level, whereas the short-term exposure to CORTI caused no effect. Scatchard analysis of [3H]CORTI surface binding to VSMCs showed a single class of CORTI binding sites with a Bmax of 876.2 fmol per mg of cell protein and a Kd of 12.2 nmol/L. RU38486 also inhibited [3H]CORTI surface binding to VSMCs.

CONCLUSIONS

In VSMCs, NHE activity is stimulated by short-term exposure to CORTI, but is inhibited by long-term exposure to CORTI. The short-term stimulatory effect of CORTI on NHE activity is independent of gene transcription and protein synthesis, is mediated through the CORTI surface receptor, and occurs through a microtubule-dependent process. The long-term inhibitory effect of CORTI on NHE activity requires gene transcription and protein synthesis and occurs only through the cytosolic GR. The short- and long-term effects of CORTI on NHE activity occur via PKC activation. Therefore, CORTI differentially modulates NHE activity in VSMCs by nongenomic and genomic mechanisms.

Glucocorticoid resistance caused by reduced expression of the glucocorticoid receptor in cells from human vascular lesions

Mechanisms that control the balance between cell proliferation and death are important in the development of vascular lesions. Rat primary smooth muscle cells were 80% inhibited by low microgram doses of hydrocortisone (HC) and 50% inhibited by nanogram concentrations of transforming growth factor-beta1 (TGF-beta1), although some lines acquired resistance in late passage. However, comparable doses of HC, or TGF-beta1, failed to inhibit most human lesion-derived cell (LDC) lines. In sensitive LDC, HC (10 microg/mL) inhibited proliferation by up to 50%, with obvious apoptosis in some lines, and TGF-beta1 inhibited proliferation by more than 90%. Collagen production, as measured by [3H]proline incorporation or RIA for type III pro-collagen, was either unaffected or increased in the LDCs by HC. These divergent responses between LDC lines were partially explained by the absence of the glucocorticoid receptor (GR) and heat shock protein 90 mRNA in 10 of 12 LDC lines, but the presence of the mineralocorticoid receptor and 11beta-hydroxysteroid dehydrogenase type II. Western blot analysis confirmed the absence of the GR protein in cells lacking GR mRNA. Immunohistochemistry of human carotid lesions showed high levels of GR in the tunica media, but large areas lacking GR in the fibrous lesion. Considering the absence of the GR in most lines, the effects of HC may be elicited through the mineralocorticoid receptor. Functional resistance to the antiproliferative and antifibrotic effects of HC may contribute to excessive wound repair in atherosclerosis and restenosis.

Effect on intimal hyperplasia of dexamethasone released from coated metal stents compared with non-coated stents in canine femoral arteries

PURPOSE

Polymer-coated, dexamethasone (DXM)-releasing stents were tested in order to assess the efficacy of DXM released locally for the prevention of stent restenosis due to intimal hyperplasia.

METHODS

Strecker stents coated with a biodegradable membrane containing DXM were implanted percutaneously into the femoral artery in 14 dogs. The contralateral artery received a conventional non-coated stent serving as control. The drugs are eluted by degradation of the carrier membrane. Follow-up intraarterial digital subtraction angiography (DSA) was obtained at 3, 6, 9, 12, and 24 weeks with subsequent autopsy. Specimens for gross and microscopic pathology were obtained and histomorphometry was performed.

RESULTS

Four of 14 DXM-coated stents showed thrombotic occlusion within the first 3 weeks; ten DXM-coated stents remained patent. At follow-up DSA, DXM-coated stents showed a significantly wider lumen than the non-coated stents. At morphometry there was less intimal hyperplasia over DXM-coated stents than over non-coated stents (p < 0.05).

CONCLUSION

DXM-coated stents reduce neointimal hyperplasia in dogs when compared with non-coated stents.

Effects of brief glucocorticoid exposure on growth of vascular smooth muscle cells in culture

While prolonged exposure of vascular smooth muscle cells (VSMC) to glucocorticoid has been shown to inhibit cell proliferation, the effect of a brief pulse exposure is not known. We studied the short-term effects of pulse exposure to dexamethasone (DEX) on DNA synthesis in cultured VSMC. VSMC were pulsed with DEx for varying time intervals and [3H]thymidine incorporation into cells after 24 h was measured. Exposure to DEX for 24 h decreased [3H]thymidine incorporation, while pulse treatments with DEX from 2 min to 6 h significantly increased [3H]thymidine incorporation. Maximal proliferative effect was observed with a 20-min exposure. The effect of a 20-min pulse was dose-dependent, with the half-maximal dose of DEX being approximately 10(-7) M. A selective glucocorticoid receptor antagonist, RU486, inhibited the proliferative effect of DEx. Concentrated conditioned medium from cells exposed to 10(-6) M DEX increased [3H]thymidine incorporation by other VSMC in a dose-dependent manner. These results suggest that short-term pulse DEX exposure is capable of producing one or more autocrine growth factors in VSMC via a glucocorticoid receptor action. This effect of glucocorticoid pulses may contribute to the pathogenesis of arteriosclerosis and hypertension.

Corticosterone metabolism and effects on angiotensin II receptors in vascular smooth muscle

It has been postulated that mineralocorticoids can bind to corticosteroid receptors in the kidney, because glucocorticoids are metabolized to inactive compounds. The present study was performed to delineate glucocorticoid metabolism by rat vascular tissue and to determine the activity of these metabolites. Vascular segments converted 25% to 30% of corticosterone (compound B), the major glucocorticoid in the rat, to 11-dehydrocorticosterone (compound A) but not to aldosterone or 6 beta-hydroxycorticosterone. In cultured vascular smooth muscle cells, 10% of compound B was converted to compound A, whereas > 60% of compound A was converted to compound B. The 11 beta-hydroxysteroid dehydrogenase inhibitor carbenoxolone (1 mumol/L) completely blocked conversion in both directions. Whereas 6 beta-hydroxycorticosterone did not upregulate angiotensin II receptor binding (a marker for corticosteroid action in vascular smooth muscle), compound A caused concentration-dependent upregulation. Compound A was almost (75%) as effective and as potent as compound B in upregulating angiotensin II binding. Upregulation elicited by exposure to compound A persisted in the presence of 1 mumol/L carbenoxolone, which completely prevented the conversion of compound A to compound B. Compound A, even in the presence of carbenoxolone, effected other glucocorticoid actions by inhibiting cell growth and potentiating angiotensin II-stimulated inositol phosphate formation. In summary, compound B and compound A are interconverted in vascular tissue, and the latter displays significant glucocorticoid action. The concentration excess of compound B in the circulation and the activity of its metabolite compound A will make it difficult for mineralocorticoids to gain access to corticosteroid receptors in the vasculature.

Effects of glucocorticoids and beta-adrenoceptor agonists on the proliferation of airway smooth muscle

An increase in airway smooth muscle is a characteristic feature of asthma. Because beta-adrenoceptor agonists and corticosteroids are commonly used in the treatment of asthma we have studied the effects of these medicines on the growth of airway smooth muscle. These agents were incubated with bovine airway smooth muscle cells for 40 h for measurement of thymidine incorporation and 64 h for measurement of cell counts. Salbutamol inhibited thymidine incorporation (IC50 = 60 nM) and led to a reduction in cell number (IC50 = 10 nM). At 10 microM there was a 14.6 +/- 2.6% reduction in cell number. Salmeterol also inhibited the growth of the airway smooth muscle cells but the effect did not plateau at 10 microM. At this concentration there was an 89.5 +/- 3.6% reduction in thymidine incorporation and a 44.1 +/- 5.2% reduction in cell number. Cortisol and beclomethasone dipropionate were more potent than salbutamol in inhibiting thymidine incorporation with IC50 values of 5 nM and 0.2 nM respectively. Cortisol 100 nM led to a 16.6 +/- 6.5% reduction and beclomethasone dipropionate 3 nM led to a 17.8 +/- 5.8% reduction in cell number. If similar effects occur in man and in vivo, these medicines could act directly on airway smooth muscle to inhibit the development of hyperplasia.

Impact of risk factors on limb salvage after angioplasty in chronic critical lower limb ischemia. A prospective trial

The impact of various general risk factors on long-term results of percutaneous transluminal angioplasty (PTA) in chronic critical lower limb ischemia is poorly known. In a prospective trial 209 PTAs were performed in 103 consecutive patients with 117 limbs with chronic critical ischemia. The general risk factors that might affect the long-term results of PTA in this patient population were reviewed. Among the factors that showed no statistical significance were all associated diseases, smoking history, and medication used. Of the various clinical chemical parameters, only serum high density lipoprotein (S-HDL) cholesterol and plasma fibrinogen had a statistically significant influence on limb salvage rate in Kaplan-Meier analysis. These parameters proved to be significant determinants also in Cox multiple regression analysis when PTA target-vessel-related parameters (peripheral runoff and number of diseased vessels) were also included in the model. Cox model predicts up to 86% one-year limb salvage for the "good" group (one to five diseased lower limb vessels/limb, S-HDL cholesterol > 0.78 mmol/L, plasma fibrinogen < 4.9 g/L).

Local delivery of dexamethasone for prevention of neointimal proliferation in a rat model of balloon angioplasty

A periadventitial polymer system is an alternative local drug delivery technique to obtain and maintain high tissue levels of the drug at the site of vascular injury. To determine if local periadventitial delivery of dexamethasone decreases neointimal proliferation after balloon vascular injury, in three groups of Sprague-Dawley rats, 5% dexamethasone, 0.5% dexamethasone, and placebo silicone polymers were implanted around the left common carotid artery after balloon injury. In a fourth group, placebo polymers were implanted without balloon injury. Dexamethasone serum and tissue levels after polymer implantation were significantly higher in the 5% dexamethasone group compared with the 0.5% dexamethasone group. There was no neointima formation in any of the arterial segments covered with placebo polymers for 3 wk, but without balloon injury. In the arterial segments covered by the 5 and 0.5% dexamethasone polymers, there was a 76 and 75% reduction in intima/media ratios, respectively, compared with the placebo group (5% dexamethasone, 0.26 +/- 0.04; 0.5% dexamethasone, 0.27 +/- 0.03; placebo, 1.09 +/- 0.16, respectively; P < 0.0001). These results suggest that: (a) silicone polymers wrapped around the common carotid arteries for 3 wk did not, without balloon injury, stimulate neointimal proliferation in the rat model; (b) the activity of the drug-eluting polymer for suppressing intimal proliferation was chiefly, but not exclusively, site specific; and (c) transadventitial local delivery of dexamethasone at two different doses markedly inhibits neointimal proliferation after balloon vascular injury.

Angiotensin II-induced vascular smooth muscle cell hypertrophy: PDGF A-chain mediates the increase in cell size

We report here that angiotensin II-mediated hypertrophy of vascular smooth muscle cells (VSMC) exhibits PDGF A-chain-dependent and -independent pathways. Secretion of PDGF A-chain is required for the increase in cell size, but not for the increase in protein synthesis. Angiotensin II stimulates a hypertrophic growth response in VSMC characterized by increases in cell size and protein synthesis, but not cell number. Because angiotensin II-stimulated VSMC hypertrophy has been associated with increased PDGF A-chain expression, we studied its role in the hypertrophic response by inhibiting PDGF A-chain expression with hydrocortisone or anti-PDGF antibody. Hydrocortisone (1 microM for 48 h) inhibited basal protein synthesis by 47%, but angiotensin II-stimulated protein synthesis was enhanced (111% increase after hydrocortisone treatment vs. 25% increase in control). In contrast, hypertrophy, as measured by cell size, was completely inhibited. Although hydrocortisone had no effect on early growth signals stimulated by angiotensin II (e.g., activation of protein kinase C, stimulation of Na+/H+ exchange, and c-fos and c-myc expression), it significantly decreased angiotensin II-stimulated secretion of PDGF-like material into the medium from 0.4 to 0.1 ng/ml/24 h (p < 0.01). However, the time course for PDGF secretion (maximal at 16-24 h) was significantly slower than the time course for angiotensin II-stimulated protein synthesis (maximal at 4-12 h). To block the action of PDGF A-chain selectively, VSMC were treated with anti-PDGF A-chain antibody. The antibody completely inhibited the angiotensin II-stimulated increase in cell size, but it had no significant effect on protein synthesis at early times (< 8 h). These findings demonstrate two pathways involved in angiotensin II-stimulated VSMC hypertrophy: an increase in cell size dependent on PDGF A-chain and an increase in protein synthesis independent of PDGF A-chain.

Pituitary factors in blood plasma are necessary for smooth muscle cell proliferation in response to injury in vivo

Intimal thickening in response to vascular injury is inhibited in animals previously subjected to hypophysectomy. We have investigated the nature and cell kinetics of this effect in a balloon catheter model of injury to the rat carotid artery. The ability of injury to stimulate [3H]thymidine labeling 48 hours after injury was almost completely eliminated in hypophysectomized (hypox) compared with control animals (0.1% versus 32.1%). Total DNA content of the developing neointima 14 days after injury was only 30% of the values found in ballooned carotid arteries of normal rats. If hypox rats were treated with recombinant human growth hormone, the proliferative response was not restored. There are two possible general explanations for the reduction of proliferative response in hypox animals: 1) that smooth muscle cells in the hypox animals have lost the ability to respond to the stimulus of injury or 2) that the ability of the smooth muscle cells to respond has not been reduced by prior hypophysectomy, but that the response itself requires the presence of pituitary-dependent factors. Transplantation experiments were performed in vivo to distinguish between these possibilities. Carotid arteries in inbred Lewis rats were excised 1 hour after balloon injury to give platelets the opportunity to adhere. These vessels were then transplanted from hypox into control animals and vice versa. At 48 hours, proliferation of smooth muscle cells in "control-to-hypox" transplants was 0.3% compared with 14.3% in "control-to-control" transplants, whereas vessels from hypox rats increased their indices to 4.8% if transplanted into control animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacology of smooth muscle cell replication

The suggestion that smooth muscle cell proliferation contributes to hypertension, atherosclerosis, and restenosis after angioplasty has led to a growing interest in the use of drugs to inhibit this process. This review summarizes pharmacological studies of smooth muscle cell proliferation in vitro and in vivo and identifies specific mediators of proliferation that are implicated by drugs binding with high affinity to enzymes or receptors.

Pharmacologic roles of heparin and glucocorticoids to prevent restenosis after coronary angioplasty

Restenosis after successful percutaneous transluminal coronary angioplasty is the major clinical problem limiting the long-term efficacy of this treatment for coronary atherosclerosis. Recent advances in the understanding of the biology of restenosis indicate that intimal hyperplasia of smooth muscle cells is the predominant cause for restenosis. Therefore, therapeutic agents that inhibit vascular smooth muscle cell proliferation should be candidate drugs to prevent restenosis. Heparin has documented antiproliferative effects on smooth muscle cells, and the availability of low molecular weight heparins that lack anticoagulant properties makes them ideal agents. Glucocorticoids have wide effects on inflammatory and wound healing events and inhibit smooth muscle cell growth in culture and in animal models of arterial injury. Recent laboratory data suggest that combination therapy with both low molecular weight heparin and hydrocortisone may be a powerful treatment regimen to limit restenosis.

Effects of glucocorticoids on Na+/H+ exchange and growth in cultured vascular smooth muscle cells

We have examined the effects of hydrocortisone on growth and Na+/H+ exchange in cultured rat aortic vascular smooth muscle cells (VSMC). Hydrocortisone (2 microM) treatment of growth-arrested VSMC significantly decreased VSMC growth in response to 10% calf serum assayed by 3H-thymidine incorporation and cell number at confluence. This effect was associated with the appearance of an altered cell phenotype characterized by large, flat VSMC that did not form typical "hillocks." Na+/H+ exchange was also altered in hydrocortisone-treated cells assayed by dimethylamiloride-sensitive 22Na+ influx into acid-loaded cells or by intracellular pH (pHi) change using the fluorescent dye BCECF. Resting pHi was 7.25 +/- 0.04 and 7.15 +/- 0.05 in control and hydrocortisone-treated cells, respectively (0.1 less than P less than 0.05). Following intracellular acidification in the absence of external Na+, pHi recovery upon addition of Na+ was increased 89% in hydrocortisone-treated cells relative to control. This was due to an increase in the Vmax for the Na+/H+ exchanger from 17.5 +/- 2.4 to 25.9 +/- 2.0 nmol Na+/mg protein x min (P less than 0.01) without a significant change in Km. Treatment of VSMC with actinomycin D (1 microgram/ml) or cycloheximide (10 microM) completely inhibited the hydrocortisone-mediated increase in Na+/H+ exchange, indicating a requirement for both RNA and protein synthesis. Because hydrocortisone altered the Vmax for Na+/H+ exchange, in contrast to agonists such as serum or angiotensin II which alter the Km for intracellular H+ or extracellular Na+, respectively, we studied the effect of hydrocortisone on activation of Na+/H+ exchange by these agonists. In cells maintained at physiological pHi (7.2), the initial rate (2 min) of angiotensin II-stimulated alkalinization was increased 66 +/- 39% in hydrocortisone-treated compared with control cells. Hydrocortisone caused no change in angiotensin II-stimulated phospholipase C activity assayed by measurement of changes in intracellular Ca2+ or diacylglycerol formation. However, angiotensin II and serum stimulated only small increases in Na+/H+ exchange in acid-loaded (pHi = 6.8) hydrocortisone-treated cells. These findings suggest that hydrocortisone-mediated increases in VSMC Na+/H+ exchange occur in association with a nonproliferating phenotype that has altered regulation of Na+/H+ exchange activation. We propose that hydrocortisone-mediated growth inhibition may be a useful model for studying the role of Na+/H+ exchange in cell growth responsiveness.

Thromboxane and vascular smooth muscle cell growth in genetically hypertensive rats

The vascular wall has the capacity to produce thromboxane A2. However, the role of vascular thromboxane A2 is still uncertain. In this study, we examined the relationship between vascular thromboxane A2 generation and vascular smooth muscle cell growth in spontaneously hypertensive rats (SHR). Vascular thromboxane A2 generation was significantly enhanced by 49% in 5-week-old and by 117% in 15-week-old SHR as compared with age-matched Wistar-Kyoto rats (WKY). Thromboxane A2 generation was also significantly enhanced by 59% in the cultured vascular smooth muscle cells of SHR when compared with production in WKY. Vascular smooth muscle cells of SHR exhibited a significantly shortened doubling time (by 32%) and greater [3H]thymidine uptake (by 56%), as compared with those of WKY. OKY 046 (10(-5) M), a thromboxane synthase inhibitor, significantly tempered the rapid vascular smooth muscle cell growth in SHR by 9% for doubling time and by 10% for [3H]thymidine uptake. OKY 046 did not influence the doubling time of WKY. Conversely, a stable analogue of thromboxane A2 dose-dependently stimulated the [3H]thymidine uptake by vascular smooth muscle cells of WKY, and, at a concentration of 10(-5) M, shortened the doubling time of vascular smooth muscle cells of WKY by 11%, whereas it showed slight effects on SHR. These data indicate that vascular thromboxane A2 is involved in the regulatory mechanism of vascular smooth muscle cell growth and that enhanced vascular thromboxane A2 generation is partly responsible for the rapid proliferation of vascular smooth muscle cells of SHR. The alterations of vascular thromboxane production may be a key trait for genetic hypertension.

1,25-Dihydroxyvitamin D3 binds specifically to rat vascular smooth muscle cells and stimulates their proliferation in vitro

Cultured vascular smooth muscle cells (VSMC) derived from rat aorta were found to contain a specific receptor for 1,25-dihydroxyvitamin D3 [1,25-(OH)2D3]. Its Kd (5.0 x 10(-11) M) and capacity (22.9 fmol/mg of cytosol protein) for 1,25-(OH)2D3, its sedimentation coefficient on a sucrose density gradient (3.2 S), its relative affinities for various vitamin D3 metabolites [1,25-(OH)2D3 greater than 25-hydroxyvitamin D3 greater than 24,25-dihydroxyvitamin D3 greater than vitamin D3] and its affinity for DNA-cellulose were similar to those reported for the 1,25-(OH)2D3 receptor in other tissues. 1,25-(OH)2D3 at concentrations of more than 10(-10) M caused dose-dependent enhancement of the proliferation of VSMC in DMEM with 10% FCS. 25-Hydroxyvitamin D3 stimulated the proliferation of VSMC only at its highest concentration tested (10(-6) M). These data show that 1,25-(OH)2D3 stimulates the proliferation of VSMC after its binding to a cytoplasmic receptor of the cells in vitro, and support the possibility that VSMC are target cells of the hormone.

Inhibition of DNA synthesis by phorbol esters through protein kinase C in cultured rabbit aortic smooth muscle cells

In cultured rabbit aortic smooth muscle cells (SMC), 12-O-tetradecanoylphorbol-13-acetate (TPA) induced DNA synthesis in the presence of plasma-derived serum to a small extent, but inhibited markedly the rabbit whole blood serum (WBS)-, platelet-derived growth factor (PDGF)- and epidermal growth factor-induced DNA synthesis. Phorbol-12,13-dibutyrate (PDBu) mimicked this antiproliferative action of TPA, but 4 alpha-phorbol-12,13-didecanoate was inactive in this capacity. Prolonged treatment of the cells with PDBu caused the partial down-regulation of protein kinase C. In these protein kinase C-reduced cells, WBS still induced DNA synthesis, but TPA did not inhibit the WBS-induced DNA synthesis. We have previously shown that protein kinase C is involved at least partially in the PDGF-induced DNA synthesis in rabbit aortic SMC. The present results together with this earlier observation suggest that protein kinase C has not only a proliferative but also an antiproliferative action in rabbit aortic SMC.

Purification and subunit composition of atrial natriuretic peptide receptor

A receptor for atrial natriuretic peptide (ANP) was purified 2700-fold, to apparent homogeneity, from cultured bovine aortic smooth muscle cells by affinity chromatography. The native ANP receptor has a molecular weight of 125,000 as determined by both metrizamide gradient centrifugation and nonreducing NaDodSO4/polyacrylamide gel electrophoresis. With 125I-labeled ANP as ligand, the purified receptor bound a maximum of 5.70 nmol of ligand per mg of protein and the dissociation constant was 4.0 X 10(-10)M. Upon treatment with 10 mM dithiothreitol, the purified receptor migrated as a single band at Mr 60,500 in NaDodSO4/polyacrylamide gel electrophoresis. These findings show that the holoreceptor for ANP in vascular tissue is composed of two subunits of identical apparent molecular weight, presumably linked by a disulfide bridge(s).

Forskolin, phosphodiesterase inhibitors, and cyclic AMP analogs inhibit proliferation of cultured bovine aortic endothelial cells

The role of cyclic AMP on endothelial cell proliferation was investigated, since these cells can be exposed to high concentrations of physiological and pharmacological agents that alter cyclic AMP metabolism. Cloned bovine aortic endothelial cells were plated at 25,000 cells/35mm dish and grown for 5 days in the presence of phosphodiesterase (PDE) inhibitors, forskolin, or cyclic AMP analogs. The PDE inhibitors dipyridamole, ZK 62 711, isobutylmethylxanthine (IBMX) and theophylline inhibited cell growth in a concentration-dependent manner. Dipyridamole produced a 30% and a 50% inhibition at 5 microM and 12.5 microM, while higher concentrations were cytotoxic. At its therapeutic plasma concentration range (50-100 microM) theophylline inhibited cell proliferation by 15-25%, while IBMX and the highly specific cyclic AMP phosphodiesterase inhibitor, ZK 62 711 inhibited growth by 60-80% and 40-50%, respectively. Forskolin (5 microM) increased cyclic AMP levels and cyclic AMP-kinase activity ratios by 2.5-fold and 2-fold. In the absence of PDE inhibitors forskolin produced a 20% growth inhibition at 0.5 microM and a 60% inhibition at 10 microM. The forskolin dose-response curve was not altered by theophylline, but was shifted to the left by approximately 10-fold with dipyridamole and ZK 62 711 and 5-fold with IBMX. Forskolin (5 microM), by itself produced a 1.8-fold increase in cyclic AMP. In the presence of 5 microM theophylline, dipyridamole, IBMX, and ZK 62 711, cyclic AMP was increased by forskolin 2.0, 2.6, 3.5, and 6.6-fold, respectively. 8-Bromo cyclic AMP and dibutyryl cyclic AMP produced a 55% and 60% growth inhibition at 100 microM. The cyclic GMP analogs were less effective inhibitors of growth (15-30%). Our results demonstrate that cyclic AMP analogs and pharmacological agents that elevate intracellular cyclic AMP levels inhibit cell growth and suggest that cyclic AMP may be an important endogenous regulator of endothelial cell proliferation.

Cell cycle-dependent inhibition of human vascular smooth muscle cell proliferation by prostaglandin E1

We examined the influence of prostaglandins on the initiation of proliferation of growth-arrested human adult aortic and fetal smooth muscle cells. Prostaglandins of the E series (25 nM) exerted a significant (p less than or equal to 0.05) inhibitory effect on DNA synthesis. Inhibition was observed when PGE1 was added in the G1 phase of the cell cycle. PGE1 had no effect when added once DNA synthesis had started. Thus prostaglandins of the E series may inhibit the responsiveness of smooth muscle cells to the mitogenic action of critical growth factors, such as PGDF. This inhibitory response is cell-cycle dependent. Once smooth muscle cells have entered S phase, PGE1 is no longer effective. Our data also suggest that cAMP is involved in the PGE1-induced growth inhibition, since concomitant with PGE1 addition, cAMP levels rose rapidly; addition of the cAMP analogue db-cAMP resulted in a cell-cycle-dependent inhibition pattern comparable to that observed with PGE1.

Distinct atrial natriuretic factor receptor sites on cultured bovine aortic smooth muscle and endothelial cells

Cultured bovine aortic smooth muscle and endothelial cells each display distinct specific binding sites for radiolabeled atrial natriuretic peptide (ANF). 125I-pro-rANF (103-126)I binding to both cell types is rapid, reversible and competitive. Scatchard plots of the binding data show Bmax values of 5.5 and 0.1 - 2.1 X 10(5) sites/cell and Kd values of 2.1 and 0.3 nM for smooth muscle and endothelial cells, respectively. In addition, ANF elevates levels of cGMP substantially in both cell types at concentrations of ANF close to its Kd and Ki for binding. Sodium nitroprusside, however, has essentially no effect on cGMP levels in either cell type. These results show that distinct functionally active receptor sites for ANF exist on both vascular smooth muscle and endothelial cells.

Glucocorticoids stimulate collagen and noncollagen protein synthesis in cultured vascular smooth muscle cells

The effect of glucocorticoids on collagen synthesis was examined in cultured bovine aortic smooth muscle (BASM) cells. BASM cells treated with 0.1 microM dexamethasone during their proliferative phase (11 d) were labeled with [3H]proline for 24 h, and the acid-precipitable material was incubated with bacterial collagenase. Dexamethasone produced an approximate twofold increase in the incorporation of proline into collagenase-digestible protein (CDP) and noncollagen protein (NCP) in the cell layer and medium. The stimulation was present in both primary mass cultures and cloned BASM. An increase in CDP and NCP was detected at 0.1 nM, while maximal stimulation occurred at 0.1 microM. Only cells exposed to dexamethasone during their log phase of growth (1-6 d after plating) showed the increase in CDP and NCP when labeled 11 d after plating. The stimulatory effect was observed in BASM cells treated with the natural bovine glucocorticoid, cortisol, dexamethasone, and testosterone, but was absent in cells treated with aldosterone, corticosterone, cholesterol, 17 beta-estradiol, and progesterone. The increase in CDP and NCP was absent in cells treated with the inactive glucocorticoid, epicortisol, and totally abolished by the antagonist, 17 alpha-hydroxyprogesterone, suggesting that the response was mediated by specific cytoplasmic glucocorticoid receptors. Dexamethasone-treated BASM cells showed a 4.5-fold increase in the specific activity of intracellular proline, which was the result of a twofold increase in the uptake of proline and depletion of the total proline pool. After normalizing for specific activity, dexamethasone produced a 2.4- and 2.8-fold increase in the rate of collagen and NCP synthesis, respectively. Cells treated with dexamethasone secreted 1.7-fold more collagen protein in 24 h compared to control cultures. The BASM cells secreted 70% Type I and 30% Type III collagen into the media as assessed by two-dimensional gel electrophoresis. The ratio of these two types was not altered by dexamethasone. The results of the present study demonstrate that glucocorticoids can act directly on vascular smooth muscle cells to increase the synthesis and secretion of collagen and NCP.

Glucocorticoid inhibition of vascular smooth muscle cell proliferation: influence of homologous extracellular matrix and serum mitogens

We examined the influence of glucocorticoid hormones on the proliferation of cultured adult bovine aortic smooth muscle cells (BASM) using both primary mass cultures and a cloned strain. Cloned BASM cells maintained on plastic culture dishes were inhibited by approximately 40% by dexamethasone treatment but showed no inhibition when grown of homologous extracellular matrix (ECM) coated dishes. Dexamethasone inhibited growth of primary cultures by 73% on plastic and by 45% on ECM. The inhibitory effect was specific for the glucocorticoids, dexamethasone, corticosterone, and cortisol and was not observed with progesterone, aldosterone, estradiol or 17-alpha OH progesterone. In cloned cells, the abolition of glucocorticoid inhibition by ECM was independent of seeding density and serum concentration. The inhibition on plastic was dependent on serum concentrations greater than 1% and resulted in both a slow rate of proliferation and a lower saturation density. A specific subset of peptides detected on two-dimensional gels was induced by glucocorticoids under growth inhibitory conditions but was not induced when the cells were grown on ECM. Primary cultures grown on ECM and exposed to Dulbecco's modified Eagle's Medium (DME) containing high density lipoprotein and transferrin grew at 40% of the rate observed for cultures exposed to DME with 10% serum. Both conditions showed growth inhibition of 70% in the presence of dexamethasone. The addition of epidermal and platelet-derived growth factors in DME containing high density lipoprotein and transferrin to cells grown on ECM resulted in growth rates comparable to that observed with cultures exposed to 10% serum and were inhibited 45% by dexamethasone. These results suggest that glucocorticoids inhibit smooth muscle proliferation by decreasing the sensitivity of the cells to mitogenic stimulation by high density lipoprotein when the cells are maintained on a homologous substrate.

Proliferative variability of endothelial clones derived from adult bovine aorta: influence of fibroblast growth factor and smooth muscle cell extracellular matrix

Four endothelial cell clones derived from adult bovine aorta were examined with respect to their proliferative characteristics in vitro. Three of these clones, derived in the absence of fibroblast growth factor (FGF), displayed variable basal proliferative rates. One of these non-FGF derived clones grew at a maximal rate which could not be further enhanced with FGF. The other two clones grew at a suboptimal rate which was stimulated by low doses of FGF (10-50 ng/ml) and inhibited by higher doses (100-250 ng/ml). The fourth clone, derived in the presence of FGF, was stimulated by FGF in a dose-dependent manner (10-250 ng/ml) and was not growth inhibited at high FGF concentrations (250-1,000 ng/ml). Growth of all four clones on extracellular matrix (ECM) derived from bovine aortic smooth muscle (BASM) cells was optimal in the absence of FGF. ECM-coated dishes also significantly increased the sensitivity of all clones by at least fivefold to mitogenic stimulation by serum. The proliferative lifespans of the clones ranged between 60 and 120 generations with the most actively proliferating clones attaining the greatest lifespan. Continuous subculture of two of the endothelial clones in the presence of FGF or on ECM-coated dishes did not induce a dependence of the cells on either factor for subsequent growth in its absence. The results indicate that aortic endothelial cells display considerable clonal variability in ther basal proliferative rate and in their response to FGF. This clonal variability is not observed when the cells are maintained on ECM-coated dishes derived from vascular smooth muscle cells.