Dexamethasone and enalapril suppress intimal hyperplasia individually but have no synergistic effect

Biodegradable nanoparticles mimicking platelet binding as a targeted and controlled drug delivery system

This research aims to develop targeted nanoparticles as drug carriers to the injured arterial wall under fluid shear stress by mimicking the natural binding ability of platelets via interactions of glycoprotein Ib-alpha (GPIbα) of platelets with P-selectin of damaged endothelial cells (ECs) and/or with von Willebrand factor (vWF) of the subendothelium. Drug-loaded poly(d,l-lactic-co-glycolic acid) (PLGA) nanoparticles were formulated using a standard emulsion method and conjugated with glycocalicin, the external fraction of platelet GPIbα, via carbodiimide chemistry. Surface-coated and cellular uptake studies in ECs showed that conjugation of PLGA nanoparticles, with GPIb, significantly increased nanoparticle adhesion to P-selectin- and vWF-coated surfaces as well as nanoparticle uptake by activated ECs under fluid shear stresses. In addition, effects of nanoparticle size and shear stress on adhesion efficiency were characterized through parallel flow chamber studies. The observed decrease in bound nanoparticle density with increased particle sizes and shear stresses is also explained through a computational model. Our results demonstrate that the GPIb-conjugated PLGA nanoparticles can be used as a targeted and controlled drug delivery system under flow conditions at the site of vascular injury.

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.

Short-term dexamethasone treatment inhibits vein graft thickening in hypercholesterolemic ApoE3Leiden transgenic mice

OBJECTIVE

The aim of this study was to assess whether the anti-inflammatory agent dexamethasone can inhibit vein graft thickening without the occurrence of serious side effects.

METHODS

Venous interposition grafting was performed in the common carotid artery of hypercholesterolemic ApoE3Leiden transgenic mice. Mice were treated with dexamethasone (0.15 mg.kg(-1).d(-1) orally), and after 28 days, vein graft thickening was quantified.

RESULTS

Treatment with dexamethasone resulted in a significant 43% reduction in lesion area without changes in lesion composition when compared with nontreated controls. However, dexamethasone, when administered for a prolonged period of time, is known for its potentially serious side effects. To overcome these potential side effects of prolonged dexamethasone treatment, the effect of a short-term 7-day dexamethasone treatment was studied. This short dexamethasone treatment resulted in a 49% decrease of vein graft thickening at 28 days. Furthermore, it was demonstrated that dexamethasone treatment led to reduced local expression of several proinflammatory cytokines and factors in the vein grafts 24 hours after surgery. Finally, observations in mice were verified in human saphenous organ cultures. Exposure to dexamethasone for either 7 or 28 days significantly reduced intimal hyperplasia formation on cultured saphenous vein segments.

CONCLUSIONS

Short-term anti-inflammatory treatment with dexamethasone leads to a significant reduction in vein graft thickening over an extended period, possibly by the reduction of early expression of proinflammatory cytokines. This 7-day treatment minimizes the risk of unwanted side effects of long-term dexamethasone treatment and may be a new approach to prevent graft failure.

In vivo quantitative assessment of catheter patency in rats

Formation of fibrin sleeves around catheter tips is a central factor in catheter failure during chronic implantation, and such tissue growth can occur despite administration of anticoagulants. We developed a novel method for monitoring catheter patency. This method recognizes the progressive nature of catheter occlusion, and tracks this process over time through measurement of changes in catheter resistance to a standardized 1 mL bolus infusion from a pressurized reservoir. Two indirect measures of catheter patency were used: (a) reservoir residual pressure and (b) reservoir discharge time. This method was applied to the study of catheter patency in rats comparing the effect of catheter material (silastic, polyurethane, Microrenathanetrade mark), lock solution (heparin, heparin/dexamethasone) and two different cannulation sites (superior vena cava via the external jugular vein, inferior vena cava via the femoral vein). Our findings reveal that application of flexible smaller-size silastic catheters and a dexamethasone lock solution resulted in prolonged catheter patency. Patency could be maintained over nine weeks with the femoral vein catheters, compared with five weeks with the external jugular vein catheters. The current method for measuring catheter patency provides a useful index for the assessment of tissue growth around the catheter tip. The method also provides an objective and quantitative way of comparing changes in catheter patency for different surgical methods and catheter types. Our method improves on the conventional method of assessing catheter occlusion by judging the ability to aspirate from the catheter.

Pseudovasculitis and corticosteroid therapy

Pseudovasculitis, vasculitis-like syndromes, vasculitis look-alikes, or mimics of vasculitis represent a heterogeneous collection of disorders that are capable of simulating vasculitis. Inappropriate diagnosis leads to delay or absence of proper management and exposure to potentially deleterious treatment modalities such as corticosteroids and cytotoxic agents. We report the case of fibromuscular dysplasia suspected to be a polyarteritis nodosa. The progression of the lesions visualized by the ultrasonographic study and computed tomography (CT) scan after 10 days of treatment led to an emergency laparotomy. The possible deleterious role of steroids given to treat the suspected vasculitis is discussed.

Rat and human aortic smooth muscle cells display differing migration and matrix metalloproteinase activities in response to dexamethasone

OBJECTIVE

The steroid dexamethasone inhibits neointimal hyperplasia development in rats but not in humans. This study investigates the differential effects of dexamethasone on rat and human smooth muscle cell migration and matrix metalloproteinase (MMP) activity.

METHODS

Rat aortic smooth muscle cells were harvested from Sprague-Dawley rats. Human aortic smooth muscle cells were obtained from Clonetics. Boyden chamber migration assays were performed with chemoattractant (platelet-derived growth factor) and varying concentrations of dexamethasone (10(-9) to 10(-5) mol/L). Zymography of culture media was used to assess MMP activity, and Western blot analysis was used for quantification of MMP-2 and tissue inhibitor of MMP-2 (TIMP-2) secretion.

RESULTS

Dexamethasone inhibits rat aortic smooth muscle cell migration in a dose-dependent fashion. An increase in concentrations of dexamethasone does not effect human aortic smooth muscle cell migration. Rat aortic smooth muscle cell MMP-2 activity is inhibited with dexamethasone in a dose-dependent fashion, and human aortic smooth muscle cell MMP-2 activity is unchanged with dexamethasone. MMP-2 secretion is inhibited with dexamethasone in rat aortic smooth muscle cells but remains unaltered in human aortic smooth muscle cells. Dexamethasone increases rat aortic smooth muscle cell TIMP-2 secretion, and human aortic smooth muscle cell TIMP-2 secretion remains constant.

CONCLUSION

Dexamethasone inhibits rat aortic smooth muscle cell migration, MMP-2 activity, and MMP-2 secretion and increases TIMP-2 secretion. These effects are not observed in human aortic smooth muscle cells. These findings may explain why dexamethasone inhibits neointimal hyperplasia in animal models but is ineffective in humans. Inhibition of human smooth muscle cell migration in vitro may be useful in predicting the effectiveness of future therapeutic agents for treatment of neointimal hyperplasia in humans.

Dexamethasone inhibits vascular smooth muscle cell migration via modulation of matrix metalloproteinase activity

BACKGROUND

Dexamethasone (DEX) has been shown to inhibit development of neointimal hyperplasia in rats. We hypothesize that DEX inhibits neointimal hyperplasia by altering matrix metalloproteinase (MMP) activity, resulting in inhibition of smooth muscle cell migration.

METHODS

Rat aortic smooth muscle cells (RASMC) were harvested and cultured for two to four passages. A migration assay was performed in a Boyden chamber with chemoattractant (platelet-derived growth factor) and varying concentrations of DEX (10(-9) to 10(-5) M). The number of migrated cells was counted under light microscopy. Zymography was performed on culture media to assess MMP activity, and Western blotting was performed to assay MMP and levels of tissue inhibitors of MMPs (TIMPs).

RESULTS

DEX progressively inhibited RASMC migration in a dose-dependent fashion. This effect was statistically significant for concentrations of 10(-7) to 10(-5) M (P < 0.0005). Zymography showed that DEX inhibits MMP-2 activity in a dose-dependent manner. Western blots indicated that total MMP-2 secretion was inhibited and that TIMP-2 secretion was increased by DEX.

CONCLUSIONS

DEX inhibits platelet-derived growth factor-induced migration of RASMCs and MMP-2 activity in vitro. Our data suggest that DEX suppresses MMP activity and secretion, resulting in the inhibition of smooth muscle cell migration. This may explain the mechanism by which DEX inhibits neointimal hyperplasia.

Dexamethasone inhibits the phosphorylation of retinoblastoma protein in the suppression of human vascular smooth muscle cell proliferation

We have previously demonstrated that dexamethasone (DEX) suppresses neointimal hyperplasia and proliferation of rat aortic smooth muscle cells (SMC) by inducing a late G1 phase cell cycle arrest. Phosphorylation of retinoblastoma protein (Rb) regulates cell proliferation by controlling progression from G1 to S phase of the cell cycle. We hypothesized that DEX inhibits human vascular SMC proliferation and causes cell cycle arrest through inhibition of Rb phosphorylation. Human aortic SMC were cultured and treated with incremental doses of DEX. Cell counts and [(3)H]thymidine uptake were determined after 72 h. To examine the effects of DEX on the cell cycle, cells were synchronized by serum deprivation, restimulated to enter G1 phase, and treated with 10(-5) M DEX, and protein was extracted at sequential time points. Flow cytometry was performed to track cell cycle progression. Western blots were performed to examine Rb phosphorylation. DEX inhibited smooth muscle cell proliferation and DNA synthesis in a concentration-dependent fashion. Flow cytometry indicated that DEX induces a G1 phase cell cycle arrest. DEX inhibited the phosphorylation of Rb protein compared to control. DEX inhibits the proliferation of human vascular SMC by inducing G1 phase cell cycle arrest. DEX inhibited the phosphorylation of Rb, a key step in the progression of the cell from G1 to S phase. Elucidation of the mechanism of DEX may be helpful in treatment strategies for preventing neointimal hyperplasia as well as other disorders of cell proliferation.

Dexamethasone suppresses vascular smooth muscle cell proliferation

BACKGROUND

Experimental studies in vivo have demonstrated that dexamethasone inhibits neointimal hyperplasia following arterial injury. The mechanisms of this inhibition have not been clearly defined. Our objective was to test the hypothesis that dexamethasone directly suppresses smooth muscle cell (SMC) proliferation by inhibiting cell cycle progression and the expression of key cell cycle-dependent genes.

METHODS

Cultured rat aortic SMC were treated with incremental concentrations of dexamethasone and cell number was determined after 72 h. To determine if dexamethasone inhibited cell cycle progression, cells were synchronized, then restimulated to enter the cell cycle, and treated with or without dexamethasone. DNA synthesis was determined 24 h after restimulation by measuring [3H]thymidine incorporation. To define the point of action of dexamethasone in the cell cycle, synchronized SMC were treated with dexamethasone (10(-7) M) at various time points after entry into the cell cycle. Flow cytometry and Northern blots were performed to examine cell cycle progression and the expression of smooth muscle cell cycle-dependent genes c-fos, c-myc, and thymidine kinase (TK).

RESULTS

Dexamethasone treatment induced a concentration-dependent inhibition of SMC proliferation and DNA synthesis. The cell cycle progression of synchronized SMC from G1 into S phase was inhibited by dexamethasone, even when added as late as 16 h after restimulation. The expression of TK was suppressed by dexamethasone, while c-fos and c-myc were not affected.

CONCLUSIONS

Dexamethasone inhibits the proliferation of SMC in a concentration-dependent fashion. This inhibition is associated with a block in cell cycle progression late in G1 phase of the cell cycle. Consistent with this finding, dexamethasone does not alter the expression of the early cell cycle-dependent genes c-fos and c-myc, but significantly inhibits the expression of TK, a marker of late G1 phase.

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.