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

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.

Colon cancer-derived myofibroblasts increase endothelial cell migration by glucocorticoid-sensitive secretion of a pro-migratory factor

Angiogenesis is important in cancer progression and can be influenced by tumor-associated myofibroblasts. We addressed the hypothesis that glucocorticoids indirectly affect angiogenesis by altering the release of pro-angiogenic factors from colon cancer-derived myofibroblasts. Our study shows that glucocorticoids reduced prostanoids, urokinase-type plasminogen activator (uPA) and angiopoietin-like protein-2 (ANGPTL2) levels, but increased angiogenin (ANG) in supernatant from human CT5.3hTERT colon cancer-derived myofibroblasts. Conditioned medium from solvent- (CMS) and dexamethasone (Dex)-treated (CMD) myofibroblasts increased human umbilical vein endothelial cell (HUVEC) proliferation, but did not affect expression of pro-angiogenic factors or tube-like structure formation (by HUVECs or human aortic ECs). In a HUVEC scratch assay CMS-induced acceleration of wound healing was blunted by CMD treatment. Moreover, CMS-induced neovessel growth in mouse aortic rings ex vivo was also blunted using CMD. The latter effect could be ascribed to both Dex-driven reduction of secreted factors and potential residual Dex present in CMD (indicated using a dexamethasone-spiked CMS control). A similar control in the scratch assay, however, revealed that altered levels of factors in the CMD, and not potential residual Dex, were responsible for decreased wound closure. In conclusion, our results suggest that glucocorticoids indirectly alter endothelial cell function during tumor development in vivo.

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.

Antioxidant treatment alters peripheral vascular dysfunction induced by postnatal glucocorticoid therapy in rats

BACKGROUND

Postnatal glucocorticoid therapy in premature infants diminishes chronic lung disease, but it also increases the risk of hypertension in adulthood. Since glucocorticoid excess leads to overproduction of free radicals and endothelial dysfunction, this study tested the hypothesis that adverse effects on cardiovascular function of postnatal glucocorticoids are secondary to oxidative stress. Therefore, combined postnatal treatment of glucocorticoids with antioxidants may diminish unwanted effects.

METHODOLOGY/PRINCIPAL FINDINGS

Male rat pups received a course of dexamethasone (Dex), or Dex with vitamins C and E (DexCE), on postnatal days 1-6 (P1-6). Controls received vehicle (Ctrl) or vehicle with vitamins (CtrlCE). At P21, femoral vascular reactivity was determined via wire myography. Dex, but not DexCE or CtrlCE, increased mortality relative to Ctrl (81.3 versus 96.9 versus 90.6 versus 100% survival, respectively; P<0.05). Constrictor responses to phenylephrine (PE) and thromboxane were enhanced in Dex relative to Ctrl (84.7+/-4.8 versus 67.5+/-5.7 and 132.7+/-4.9 versus 107.0+/-4.9% Kmax, respectively; P<0.05); effects that were diminished in DexCE (58.3+/-7.5 and 121.1+/-4.3% Kmax, respectively; P<0.05). Endothelium-dependent dilatation was depressed in Dex relative to Ctrl (115.3+/-11.9 versus 216.9+/-18.9, AUC; P<0.05); however, this effect was not restored in DexCE (68.3+/-8.3, AUC). Relative to Ctrl, CtrlCE alone diminished PE-induced constriction (43.4+/-3.7% Kmax) and the endothelium-dependent dilatation (74.7+/-8.7 AUC; P<0.05).

CONCLUSIONS/SIGNIFICANCE

Treatment of newborn rats with dexamethasone has detrimental effects on survival and peripheral vasoconstrictor function. Coadministration of dexamethasone with antioxidant vitamins improves survival and partially restores vascular dysfunction. Antioxidant vitamins alone affect peripheral vascular function.

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.

The favorable clinical and angiographic outcomes of a high-dose dexamethasone-eluting stent: randomized controlled prospective study

BACKGROUND

Previous studies with dexamethasone-eluting stents could not elucidate the role of dexamethasone in the prevention of neointimal hyperplasia because they did not compare their results with a control group. We prospectively evaluated the clinical and angiographic outcomes of dexamethasone-eluting stents, comparing them with unloaded stents of an identical design.

METHODS

A total of 92 patients (98 lesions) were randomly assigned to the dexamethasone group (67 patients, 71 lesions) or control group (25 patients, 27 lesions). The inclusion criteria for a stent implantation were a de novo lesion with a diameter of 2.60 to 4.0 mm. BiodivYsio Drug Delivery phosphorylcholine-coated stents (Biocompatibles Ltd, Galway, Ireland) were immersed in a 20-mg/mL dexamethasone solution, yielding a total dexamethasone dose of 0.5 microg/mm2 per stent.

RESULTS

The total major adverse cardiac events rate at 12 months was significantly lower in the dexamethasone group, as compared with the control group (10.4% [7/67] vs 28.0% [7/25], P = .037). The binary restenosis rate at 6 months was 11.9% (7/59) in the dexamethasone group and 42.9% (9/21) in the control group (P = .002). The use of dexamethasone-eluting stents was the only independent predictor for the major adverse cardiac event at 12 months (relative risk 0.20, 95% CI 0.06-0.68, P = .009) and binary restenosis at 6 months (relative risk 0.17, 95% CI 0.05-0.60, P = .006) by multivariate analysis.

CONCLUSIONS

Dexamethasone-eluting stents exhibited an improvement in the clinical and angiographic outcomes, as compared with the control stents. These results suggest that dexamethasone may play an important role in the inhibition of the polymer-induced inflammation in the era of drug-eluting stents.

Intravascular ultrasonic comparative analysis of degree of intimal hyperplasia produced by four different stents in the coronary arteries

Intravascular ultrasound studies were performed at angiographic follow-up on 121 native coronary lesions treated with 1 bare metal stent (n = 50), high-dose dexamethasone-eluting stents (n = 18), non-polymer-based paclitaxel-eluting stents (n = 18), or sirolimus-eluting stents (n = 35). Paclitaxel- and sirolimus-eluting stents reduced mean intimal hyperplasia thickness compared with bare metal stents by 49% and 90% (p = 0.048 and p <0.001), respectively, whereas mean intimal hyperplasia thickness treated with dexamethasone-eluting stents was similar to those lesions treated with bare metal stents.

Evaluation of a high-dose dexamethasone-eluting stent

This study evaluated the safety and efficacy of a dexamethasone-eluting stent with a special high dexamethasone-loading dose for treatment of de novo coronary lesions in 30 patients. Eight patients had in-stent restenosis (restenosis rate 31%) at 6-month follow-up, and the in-stent late lumen loss was 0.96 +/- 0.63 mm due to an average intimal hyperplasia area obstruction of 32 +/- 21%, indicating that high-dose dexamethasone-loaded stents do not significantly reduce neointimal proliferation.

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.

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.

p38 Kinase is a negative regulator of angiotensin II signal transduction in vascular smooth muscle cells: effects on Na+/H+ exchange and ERK1/2

Activation of the Na+/H+ exchanger isoform-1 (NHE-1) by angiotensin II is an early signal transduction event that may regulate vascular smooth muscle cell (VSMC) growth and migration. Many signal transduction events stimulated by angiotensin II are mediated by the mitogen-activated protein (MAP) kinases. To define their roles in angiotensin II-mediated NHE-1 activity, VSMCs were treated with angiotensin II and the activities of p38, c-Jun N-terminal kinase (JNK), and extracellular signal-regulated kinases 1 and 2 (ERK1/2) were measured. Angiotensin II rapidly (peak, 5 minutes) activated p38 and ERK1/2, whereas JNK was activated more slowly (peak, 30 minutes). Because angiotensin II stimulated Na+/H+ exchange within 5 minutes, the effects of p38 and ERK1/2 antagonists on Na+/H+ exchange were studied. The MEK-1 inhibitor PD98059 decreased ERK1/2 activity and Na+/H+ exchange stimulated by angiotensin II. In contrast, the specific p38 antagonist SKF-86002 increased Na+/H+ exchange. Two mechanisms were identified that may mediate the effects of p38 and SKF-86002 on angiotensin II-stimulated Na+/H+ exchange. First, angiotensin II activation of ERK1/2 was increased 1. 5- to 2.5-fold (depending on assay technique) in the presence of SKF-86002, demonstrating that p38 negatively regulates ERK1/2. Second, the ability of angiotensin II-stimulated MAP kinases to phosphorylate a glutathione S-transferase fusion protein containing amino acids 625 to 747 of NHE-1 in vitro was analyzed. The relative activities of endogenous immunoprecipitated p38, ERK1/2, and JNK were 1.0, 2.0, and 0.05 versus control, respectively suggesting that p38 and ERK1/2, but not JNK, may phosphorylate NHE-1 in VSMC. These data indicate important roles for p38 and ERK1/2 in angiotensin II-mediated regulation of the Na+/H+ exchanger in VSMC.

Adhesion and proliferation of cultured human aortic smooth muscle cells on polystyrene implanted with N+, F+ and Ar+ ions: correlation with polymer surface polarity and carbonization

Physicochemical surface properties and biocompatibility were studied in polystyrene (PS) implanted with 150 keV N+, F+ and Ar+ at doses ranging from 1 x 10(12) to 1 x 10(15) cm-2. Adhesion and proliferation of cultured human aortic smooth muscle cells (SMCs) on ion implanted PS were thoroughly examined for dependence on implanted dose and ion species and in close relation to polymer surface oxidation, surface polarity, concentration of conjugated double bonds and sheet resistivity. The surface polarity of PS was a smooth, increasing function of the implanted dose. However, the dependence of SMC population density on the implanted dose was found to be more complicated. After 18 h cultivation time (i.e. when only cell attachment and spreading took place), the number of adhered SMCs and their degree of spreading first increased with increasing ion dose, and after reaching a maximum at the dose of 5 x 10(12) cm-2, they decreased to original values. For doses above 5 x 10(14) cm-2, an increase in SMC population density and spreading was again observed. The first maximum in cell adhesion can be explained by slight increases in the surface polarity and wettability, optimal for cell adhesion, and the second maximum by progressive carbonization of the PS surface. After 96 h cultivation time (i.e. when the cells proliferated intensively), the dramatic dependence of the SMC population density on implanted dose is mostly smeared out. This observed dependence of SMC attachment, spreading and subsequent proliferation on the implanted dose was similar in all three ion species, but highest cell densities were achieved on PS implanted with F+ ions.

Activity and expression of the Na+/H+ exchanger in human endothelial cells cultured in high glucose

Establishing whether high ambient glucose affects the plasma membrane Na+/H+ exchanger is relevant to understanding the adverse effects of high glucose on cell replication and the mechanisms of the increased exchanger activity encountered in diabetic patients with nephropathy. In 8 primary and 15 first-passage isolates of human endothelial cells cultured in 30 mmol/l glucose for 8.7 +/- 2.3 and 15.8 +/- 2.3 days, respectively, we determined Na+/H+ exchanger activity and mRNA levels. Activity was determined by measuring 22Na+ influx in the presence or absence of dimethylamiloride (DMA) after intracellular acidification. We also measured fibronectin mRNA because fibronectin provides signals for cell replication through the Na+/H+ antiporter. Control cells grown in 5 mmol/l glucose showed at morphologic confluency a total Na+ influx (in nmol.mg protein-1.min-1) of 10.1 +/- 3.2 in primary and 11.7 +/- 2.2 in first subculture, which was reduced to 5.3 +/- 0.3 in the presence of DMA. Paired cultures exposed to 30 mmol/l glucose and exhibiting pHi and cell densities identical to controls showed in both primary and first subculture a reduction in total Na+ influx (delta = -0.98 +/- 0.93 nmol.mg protein-1.min-1 p < 0.005) whereas DMA-resistant Na+ influx was identical to that of control. Neither chronic hypertonicity nor acute exposure to high glucose mimicked the effects of chronic high glucose. The level of the Na+/H+ exchanger isoform 1 (NHE-1) mRNA was unchanged by high glucose whereas fibronectin mRNA levels were increased 1.5-fold.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucocorticoids but not mineralocorticoids modulate endothelin-1 and angiotensin II binding in SHR vascular smooth muscle cells

Both glucocorticoids and mineralocorticoids are involved in circulatory homoeostasis and blood pressure control. In recent years direct effects of both steroid classes on vascular smooth muscle cells (VSMC) have been reported. We have thus examined the effects of RU 28362, a pure glucocorticoid agonist, and aldosterone, the physiologic mineralocorticoid, on the binding to VSMC from spontaneously hypertensive rats (SHR) of two key vasoactive peptides, endothelin-1 and angiotensin II. Binding of angiotensin II rose, and that of endothelin-1 declined, in a time- and dose-dependent fashion with maximal effects observed at 24 h and half-maximal effects for each at 2-3 nM RU 28362. Scatchard analysis showed that for both endothelin-1 and angiotensin II, RU 28362 alters receptor number but not affinity; competition studies with receptor-selective ligands (BQ123, S6C, DuP753 and PD123319) show that glucocorticoids specifically elevate (X2) AT-1 receptors and specifically lower (to approximately 30%) levels of ETA receptors. Treatment of VSMC with the antiglucocorticoid RU 38486 reversed the effect of glucocorticoids on endothelin-1 and angiotensin II binding, confirming the Type II (glucocorticoid) receptor mediated effect of the glucocorticoids. Aldosterone (100 nM) also lowers endothelin-1 binding and increases angiotensin II binding in VSMC; that this effect reflects aldosterone occupancy of classical glucocorticoid receptors is shown by the blockade of the aldosterone effect by an equal concentration (100 nM) of RU 38486--i.e. there is no evidence for an action of aldosterone via mineralocorticoid receptors. We interpret our results as evidence for a complex modulation of receptors for vasoactive peptides in VSMC by glucocorticoid but not mineralocorticoid hormones.

Glucocorticoids induce angiotensin-converting enzyme expression in vascular smooth muscle

Angiotensin-converting enzyme (ACE) activity plays a central role in vessel growth and remodeling as shown by the fact that ACE inhibitors reduce neointimal proliferation after rat carotid injury. To investigate the mechanisms that regulate smooth muscle cell ACE expression, we studied the effects of steroids on ACE activity and mRNA in cultured rat aortic smooth muscle cells. ACE activity was present at low levels independent of growth state. In response to the glucocorticoid dexamethasone (100 nmol/L for 72 hours), ACE activity (hydrolysis of [3H]benzoyl-Phe-Ala-Pro) increased 10.1 +/- 3.1-fold. The increase in activity occurred within 12 hours and peaked after 72 hours of treatment. The increase in ACE activity was specific for glucocorticoids and paralleled their potency (dexamethasone > hydrocortisone = prednisolone). Dexamethasone increased the steady-state level of ACE mRNA in a concentration-dependent manner (21.4 +/- 0.4-fold at 100 nmol/L for 72 hours). Dexamethasone stimulation of ACE expression appeared to be due to both increased transcription and stabilization of ACE enzyme mRNA. This was suggested by the finding that dexamethasone stimulated nuclear run-on expression of ACE mRNA by only threefold, in contrast to the 21-fold increase in steady-state mRNA. These findings establish that ACE is a dynamically regulated enzyme in rat aortic smooth muscle cells. In addition, the present findings suggest an important role for stress steroids in the vascular response to injury in vivo.

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.

Rapid effects of aldosterone on sodium transport in vascular smooth muscle cells

Increasing evidence has accumulated for rapid nongenomic steroid actions in various cell systems and, more recently, for rapid aldosterone effects on the Na(+)-H+ antiport in human mononuclear leukocytes. The aim of the present study was to demonstrate a rapid, nongenomic aldosterone action in rat vascular smooth muscle cells as a key effector cell in cardiovascular regulation. Basal 22Na+ influx in quiescent vascular smooth muscle cells was 22.1 +/- 1.9 nmol/mg protein per minute (mean +/- SEM, n = 9). Aldosterone (1 nmol/L) stimulated influx to 28.6 +/- 1.5 nmol/mg protein per minute after 4 minutes (n = 9, P < .05), with a half-maximal effect between 0.1 and 0.5 nmol/L; the effects were inhibited by ethylisopropylamiloride, the specific inhibitor of the Na(+)-H+ exchanger, demonstrating the involvement of this transport system in rapid effects of aldosterone. Hydrocortisone (1 mumol/L) was ineffective, and fludrocortisone and deoxycorticosterone increased influx with half-maximal effects at approximately 0.5 nmol/L. Canrenone, a classic antagonist of aldosterone action, did not inhibit stimulation by aldosterone at a 1000-fold excess concentration. Aldosterone significantly stimulated intracellular inositol 1,4,5-trisphosphate levels (P < .05) after 30 seconds; the inhibitors of phospholipase C, neomycin and U-73122, inhibited aldosterone-stimulated Na+ influx and increase of intracellular inositol 1,4,5-trisphosphate. The rapid stimulation of sodium transport in vascular smooth muscle cells and the pharmacological characteristics of this effect are clearly incompatible with the classic, genomic pathway of steroid action and represent further evidence for nongenomic effects of aldosterone.

Glucocorticoid uncoupling of antiogensin II-dependent phospholipase C activation in rat vascular smooth muscle cells

Vascular tone is maintained by both angiotensin II (Ang II) and glucocorticoids, but the effect of glucocorticoids on Ang II function in vascular smooth muscle cells (VSMC) is unclear. To determine the direct influence of glucocorticoids on VSMC Ang II receptor function, the effects of dexamethasone on Ang II receptor binding, Ang II-induced phospholipase C (PLC) activation, and Ang II-dependent cell growth were studied in cultured rat VSMC. Dexamethasone caused concentration- and time-dependent increases in Ang II binding which were prevented by glucocorticoid receptor inhibition with RU 38486. Dexamethasone-induced enhancement of Ang II binding resulted from increased AT1 receptors, as indicated by Northern blot analysis and competitive binding assays. Despite causing increased Ang II receptor number, dexamethasone preincubation prevented Ang II-induced PLC activation, as indicated by phosphatidylinositol 4,5-bisphosphate degradation and inositol trisphosphate formation. When PLC activity was directly measured in VSMC soluble and membrane fractions, Ang II receptor activation caused decreased soluble and increased membrane PLC activity, consistent with the interpretation that Ang II caused cytosol-to-membrane PLC translocation. The effect of Ang II on PLC translocation was prevented by dexamethasone preincubation. Finally, prolonged incubation with dexamethasone and Ang II had additive effects on VSMC hypertrophy. In conclusion, glucocorticoids directly altered Ang II function in VSMC by causing increased Ang II receptor number, Ang II receptor/PLC uncoupling, and enhanced Ang II-dependent hypertrophy.

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).

Vascular smooth muscle cell proliferation in SHR and WKY rats: evidence for specific differences in growth inhibitory regulatory mechanisms

1. This study examined and compared the actions of transforming growth factor-beta 1 (TGF-beta 1), heparin, dexamethasone and interferon-gamma on platelet-derived growth factor-BB (PDGF-BB)-stimulated proliferation of vascular smooth muscle cells (VSMC) from normotensive, Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR). 2. Heparin, dexamethasone and interferon-gamma all inhibited VSMC proliferation stimulated by PDGF-BB in both SHR and WKY rats. There was no difference (P > 0.05) in their inhibitory effects, which varied between 40 and 85% for the different agents. 3. Similarly, TGF-beta 1 inhibited PDGF-BB-stimulated VSMC proliferation in WKY rats by approximately 50%. In contrast, TGF-beta 1 potentiated growth factor action on cell proliferation in the SHR by approximately 40%. 4. Specific TGF-beta 1-stimulated regulatory mechanisms involved in the inhibition of proliferation are absent in SHR and this defect may contribute to the vascular hypertrophy which is apparent in genetic hypertension.

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)

5-HT2 receptor mRNA is overexpressed in cultured rat aortic smooth muscle cells relative to normal aorta

Proliferation of smooth muscle cells in arteries is associated with contractile hypersensitivity to serotonin (5-HT). A possible explanation is that smooth muscle cells express increased numbers of phospholipase C (PLC)-coupled 5-HT receptors (5-HTR), which could mediate contractile and mitogenic signals via phosphatidylinositol turnover. To test this hypothesis, we performed a molecular characterization of 5-HTR subtypes in normal aorta and passaged rat aortic smooth muscle cells (RASM) in culture. Northern blot analysis revealed that growth-arrested cultured cells expressed 5-HT2R mRNA at 50-fold greater levels than aorta. 5-HT1CR mRNA was not detected in either case. 5-HT stimulated intracellular Ca2+ mobilization (fivefold peak increase) and c-fos mRNA induction (10-fold peak increase); both responses were strongly inhibited by selective 5-HT2R antagonists. Specific agonists for the 5-HT1AR, 5-HT1BR, and 5-HT1DR failed to induce c-fos mRNA. Although 5-HT (10 microM) increased [3H]thymidine incorporation (28% relative to 10% calf serum), it was a weak mitogen for cultured RASM based on cell counts. Thus there is high level expression of 5-HT2R mRNA by cultured RASM relative to aorta, and the 5-HT2R appears to be the only 5-HTR subtype mediating early growth signals in these cells. These data suggest that, following arterial injury in vivo, smooth muscle cells may overexpress the 5-HT2R, resulting in 5-HT contractile hypersensitivity and increased responsiveness to other growth factors.

Coronary aneurysms after stent placement: a suggestion of altered vessel wall healing in the presence of anti-inflammatory agents

Coronary aneurysms are rare after conventional angioplasty and have not been reported after coronary stenting. Coronary artery stent sites were examined by follow-up angiography at a median of 4 months in 29 patients who received the Cook stent (Gianturco-Roubin) for acute coronary closure. Nineteen patients were treated with glucocorticoids administered intravenously or orally, or both, with or without colchicine and results were compared with those in 10 patients who were treated with neither agent. Standard therapy for all patients included routine administration of aspirin and heparin before and warfarin sodium (Coumadin) and aspirin after stent placement. Most patients also received dipyridamole and lovastatin during the follow-up period. Compliance with medications was confirmed by telephone conversation with each patient. Six (32%) of the 19 stented arteries showed evidence of coronary artery aneurysm, defined as expansion of the lumen outside the margins of the stent. None of the patients in the control group (who did not receive steroids or colchicine) developed aneurysm. This pattern of altered vascular healing in stented coronary segments appears to be due to the addition of multiple anti-inflammatory drugs rather than to stent presence alone. This observation demonstrates the possibility of medical impairment of normal vascular remodeling after acute injury and stent placement, which may be of benefit in designing future trials on restenosis.

Glucocorticoids increase Ca2+ uptake and [3H]dihydropyridine binding in A7r5 vascular smooth muscle cells

Increased levels of corticosteroids result in the development of hypertension in vivo. To investigate whether corticosteroids modulate calcium handling in vascular smooth muscle cells, we studied 45Ca2+ uptake and binding of [methyl-3H]PN 200-110, a potent dihydropyridine Ca2+ antagonist, in A7r5 vascular smooth muscle cells. Forty-eight-hour treatment with 100 nM dexamethasone increased the unidirectional 45Ca2+ uptake during a 2-min period, and the 30-min 45Ca2+ uptake of dexamethasone-treated cells was 95% greater than that of nontreated cells. The lag time for the dexamethasone effect on Ca2+ uptake was approximately 8 h. The effect of dexamethasone was blocked by the glucocorticoid antagonist RU 38486, whereas it was not affected by the mineralocorticoid antagonist RU 26752. After cessation of the dexamethasone treatment, 45Ca2+ uptake returned to the control level by 24 h. The effect of dexamethasone was completely blocked by nifedipine in a dose-dependent manner. Scatchard plots of [methyl-3H]PN 200-110 binding revealed two binding sites (Kd; 0.02 and 1 nM), and dexamethasone increased the number of the higher affinity binding sites. These results indicate that glucocorticoids increase Ca2+ uptake possibly mediated by an increase in the number of dihydropyridine-sensitive Ca2+ channels.

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.

Long-term regulation of Na(+)-H+ exchange in vascular smooth muscle cells: role of protein kinase C

Regulation of intracellular pH (pHi) plays an important role in vascular smooth muscle cell (VSMC) contractile tone and growth. We have shown that pHi in proliferating VSMC is more alkaline (7.25) than in growth-arrested cells (7.10). To study the Na(+)-H+ exchanger in the growth-dependent regulation of VSMC pHi, ethylisopropylamiloride (EIPA)-sensitive Na+ influx was measured. Exposure of growth-arrested VSMC to 10% serum initially increased Na+ influx (145% of baseline at 30 min), which then decreased (52% of baseline at 24 h). Serum-induced alterations in the kinetic properties of the Na(+)-H+ exchanger were studied by analysis of its external Na+ binding site properties. Exposure of growth-arrested VSMC to 10% serum for 24 h increased the Km for external Na+ from 54 to 380 mM, with a change in the Vmax from 155 to 199 nmol Na+.mg protein-1.min-1. The change in Km was due to activation of protein kinase C (PKC). Phorbol 12,13-dibutyrate caused a 48% decrease in EIPA-sensitive influx, the inactive 4 alpha-phorbol 12,13-didecanoate had no effect, and the PKC inhibitor sphingosine reversed the effect. Therefore, the Na(+)-H+ exchanger in VSMC is regulated in a growth-dependent manner via PKC.

Interleukin 1 regulates heparin-binding growth factor 2 gene expression in vascular smooth muscle cells

The angiogenic polypeptide heparin-binding growth factor 2 (HBGF-2), or basic fibroblast growth factor, is a mitogen for vascular smooth muscle cells in vitro and in vivo. Smooth muscle cells also synthesize HBGF-2; thus, it may stimulate their proliferation in vivo by both autocrine and paracrine mechanisms. We report here that HBGF-2 gene expression in human saphenous vein smooth muscle cells is induced by interleukin (IL)-1 alpha and IL-1 beta, inflammatory cytokines produced by many cell types in response to a variety of signals. Maximal HBGF-2 mRNA levels are detected 2-4 hr after IL-1 treatment; induction may require de novo protein synthesis and does not occur if transcription is inhibited. Immunoprecipitation analysis indicates that IL-1-stimulated cells also express an increased amount of HBGF-2 protein. Interferon gamma and glucocorticoids, inhibitors of smooth muscle cell proliferation in vitro and in vivo, suppress the induction of HBGF-2 expression by IL-1. These results imply that cytokines released at sites of vascular injury or inflammation may regulate HBGF-2 production by smooth muscle cells. Increased HBGF-2 levels within the vessel wall could play a role in both the smooth muscle cell proliferation and the neovascularization associated with the development of atherosclerotic lesions.

Characterization of the vascular thromboxane A2/prostaglandin endoperoxide receptor in rabbit aorta. Regulation by dexamethasone

Recently, we have shown that dexamethasone treatment of rabbits specifically reduces vascular smooth muscle responsiveness to agonists that interact with the vascular thromboxane A2/prostaglandin H2 (TXA2/PGH2) receptor. One potential site at which dexamethasone can influence prostanoid-mediated vasoconstriction may be at the level of the vascular TXA2/PGH2 receptor. Therefore, we characterized the vascular TXA2/PGH2 receptor in rabbit aortic membranes and examined the influence of dexamethasone treatment on vascular TXA2/PGH2 receptor affinity and number. The binding of [125I][1S-(1 alpha,2 beta(5Z),3 alpha(1E,3R)4 alpha)]-7-[3-(3- hydroxy-4-(p-iodophenoxy)-1-butenyl)-7-oxabicyclo[2.2.1] heptan-2-yl]-5-heptanoic acid ([125I]BOP), a potent TXA2/PGH2 receptor agonist, to rabbit aortic membranes was saturable, displaceable, and dependent on protein concentration. Scatchard analysis of equilibrium binding data disclosed one class of high affinity binding sites with a Kd of 0.44 +/- 0.13 nM and a Bmax of 114.4 +/- 5.2 fmol/mg protein (n = 7). Removal of the endothelium before membrane preparation did not significantly alter the affinity or number of binding sites for [125I]BOP. Kinetic analysis of the rates of [125I]BOP association/dissociation yielded a Kd of 0.62 nM. The ability of various agonists at the TXA2/PGH2 receptor to displace [125I]BOP from vascular membranes correlated well with their contractile potencies in rabbit aortic rings. Moreover, stereospecific displacement of [125I]BOP binding in aortic membranes and inhibition of U46619-mediated aortic contractions were obtained with the stereoisomers L657925(-) and L657926(+). Collectively, these data suggest that this binding site represents the functionally relevant vascular TXA2/PGH2 receptor. In functional experiments, [127I]BOP induced concentration-dependent contractions of the rabbit aorta, which were reduced by 52% in vessels from dexamethasone-treated rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)