Dexamethasone suppresses vascular smooth muscle cell proliferation

Beta arrestin-related signalling axes are influenced by dexamethasone and metformin in vascular smooth muscle cells cultured in high glucose condition

BACKGROUND

Metformin (Met) and dexamethasone (Dexa) are known to reduce blood sugar levels and anti-inflammatory effects, respectively. Based on the acceleration of atherosclerosis process in diabetes, the β-arrestin 2 (BARR2) gene and protein expression levels were evaluated in vascular smooth muscle cells (VSMCs) treated with Met and Dexa in high glucose conditions in this study.

METHODS AND MATERIALS

Human VSMCs were cultured in Dulbecco's Modified Eagle Medium/Nutrient Mixture F-12 (DMEM-F12) medium and, were treated with different values of Met (1 mM, 5 mM and 7 mM) and Dexa (10-7  M, 10-6  M and 10-5  M) in 24- and 48-h periods. The BARR2 gene and protein expression levels were identified with RT-qPCR and western blotting techniques, respectively. The signalling axes were predicted from gene network made using Cytoscape software and, were annotated with Gene Ontology.

RESULTS

The BARR2 gene and protein expression levels reduced in VSMCs treated with Dexa and Met after 24- and 48-h periods. These results were more changed after 48 h. Furthermore, many BARR2-related signalling axes were found from the network genes.

CONCLUSION

Met and Dexa suppressed the BARR2 protein and gene expression levels in the VSMCs. Moreover, the gene network suggested some the cellular signalling axes related to BARR2 that may be affected by Met and Dexa.

Dexamethasone suppresses the proliferation and migration of VSMCs by FAK in high glucose conditions

Background

High glucose conditions cause some changes in the vessels of diabetes through the signal transduction pathways. Dexamethasone and other corticosteroids have a wide range of biological effects in immunological events. In the present study, the effects of dexamethasone were investigated on the VSMC (vascular smooth muscle cell) proliferation, and migration based on the FAK gene and protein changes in high glucose conditions.

Methods and materials

The vascular smooth muscle cells were cultured in DMEM and were treated with dexamethasone (10^–7 M, 10^–6 M, and 10^–5 M) for 24, and 48 h in high glucose conditions. The cell viability was estimated by MTT method. The FAK gene expression levels and pFAK protein values were determined by RT-qPCR and western blotting techniques, respectively. A scratch assay was used to evaluate cellular migration.

Results

The FAK gene expression levels decreased significantly dependent on dexamethasone doses at 24 and 48 h. The pFAK protein values decreased significantly with a time lag at 24- and 48-h periods as compared with gene expression levels.

Conclusion

The results showed that the inhibition of VSMC proliferation and migration by dexamethasone in the high glucose conditions may be related to the changes of FAK.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40360-022-00604-3.

Glucocorticoids: Fuelling the Fire of Atherosclerosis or Therapeutic Extinguishers?

Glucocorticoids are steroid hormones with key roles in the regulation of many physiological systems including energy homeostasis and immunity. However, chronic glucocorticoid excess, highlighted in Cushing's syndrome, is established as being associated with increased cardiovascular disease (CVD) risk. Atherosclerosis is the major cause of CVD, leading to complications including coronary artery disease, myocardial infarction and heart failure. While the associations between glucocorticoid excess and increased prevalence of these complications are well established, the mechanisms underlying the role of glucocorticoids in development of atheroma are unclear. This review aims to better understand the importance of glucocorticoids in atherosclerosis and to dissect their cell-specific effects on key processes (e.g., contractility, remodelling and lesion development). Clinical and pre-clinical studies have shown both athero-protective and pro-atherogenic responses to glucocorticoids, effects dependent upon their multifactorial actions. Evidence indicates regulation of glucocorticoid bioavailability at the vasculature is complex, with local delivery, pre-receptor metabolism, and receptor expression contributing to responses linked to vascular remodelling and inflammation. Further investigations are required to clarify the mechanisms through which endogenous, local glucocorticoid action and systemic glucocorticoid treatment promote/inhibit atherosclerosis. This will provide greater insights into the potential benefit of glucocorticoid targeted approaches in the treatment of cardiovascular disease.

Drug delivery to atherosclerotic plaques using superparamagnetic iron oxide nanoparticles

INTRODUCTION

Magnetic drug targeting utilizes superparamagnetic iron oxide nanoparticles (SPIONs) to accumulate drugs in specified vasculature regions.

METHODS

We produced SPIONs conjugated with dexamethasone phosphate (SPION-DEXA). The efficacy of magnetic drug targeting was investigated in a rabbit model of atherosclerosis induced by balloon injury and high cholesterol diet.

RESULTS

In vitro, SPION-DEXA were well-tolerated by endothelial cells. SPION-DEXA were internalized by human peripheral blood mononuclear cells and induced CD163 expression comparable with the free drug. In vivo, magnetic targeting of SPIONs to abdominal aorta was confirmed by histology. Upon vascular injury followed by high-cholesterol diet, early administration of SPION-DEXA enhanced the inflammatory burden in the plaques. Increased macrophage content and larger intima- media thickness were observed in animals treated with SPION-DEXA compared with controls. In advanced atherosclerosis, no beneficial effect of local glucocorticoid therapy was detectable.

CONCLUSION

Magnetic drug targeting represents an efficient platform to deliver drugs to diseased arteries in vivo. However, targeting of vascular injury in the lipid-rich environment using dexamethasone-conjugated SPIONs may cause accelerated inflammatory response.

Liposomal prednisolone inhibits vascular inflammation and enhances venous outward remodeling in a murine arteriovenous fistula model

Arteriovenous fistulas (AVF) for hemodialysis access have a 1-year primary patency rate of only 60%, mainly as a result of maturation failure that is caused by insufficient outward remodeling and intimal hyperplasia. The exact pathophysiology remains unknown, but the inflammatory vascular response is thought to play an important role. In the present study we demonstrate that targeted liposomal delivery of prednisolone increases outward remodeling of the AVF in a murine model. Liposomes accumulate in the post-anastomotic area of the venous outflow tract in which the vascular pathology is most prominent in failed AVFs. On a histological level, we observed a reduction of lymphocytes and granulocytes in the vascular wall. In addition, a strong anti-inflammatory effect of liposomal prednisolone on macrophages was demonstrated in vitro. Therefore, treatment with liposomal prednisolone might be a valuable strategy to improve AVF maturation.

Prednisolone- and sirolimus-eluting stent: Anti-inflammatory approach for inhibiting in-stent restenosis

Glucocorticoids are powerful anti-inflammatory, immunosuppressive, and anti-proliferative agents. The aim of this study was to evaluate the effectiveness of a prednisolone- (PDScs) and sirolimus-coated stent (SRLcs) in preventing artery vessel neointimal hyperplasia and inflammatory reactions in vitro and in vivo. PDS, a synthetic glucocorticoid, is a derivative of cortisol, which is used to treat a variety of inflammatory and autoimmune conditions. The stents were fabricated with PDS, SRL, or both agents using a layer-by-layer coating system (designated as PDScs, SRLcs, and PDSRLcs, respectively). The surface morphology of the PDScs showed an evenly dispersed and roughened shape, which was smoothened by the SRL coating. Half of the total drug amounts were released within seven days, followed by an additional release, which continued for up to 28 days. The proliferation of smooth muscle cells was inhibited in the SRLcs group (31.5 ± 4.08%), and this effect was enhanced by PDS addition (PDSRLcs, 46.8 ± 8.11%). Consistently, in the animal study, the restenosis rate was inhibited by the SRLcs and PDSRLcs (18.5 ± 6.23% and 14.5 ± 3.55%, respectively). Especially, fibrin expression and inflammation were suppressed in the PDS-containing group (PDScs, 0.6 ± 0.12 and 1.4 ± 0.33; PDSRLcs, 0.7 ± 0.48 and 1.7 ± 0.12, respectively) compared to PDS non-containing groups (BMS, 1.1 ± 0.12, and 1.8 ± 0.55; SRLcs, 1.6 ± 0.32 and 2.0 ± 0.62, respectively). Moreover, re-endothelialization was enhanced in the PDScs group as determined using immunohistochemistry with a cluster of differentiation (CD)-31 antibodies. These results suggest that the inhibitory effect of SRLcs on anti-restenosis can be accelerated by additional coating with PDS, which has promising properties as a bioactive compound with useful anti-inflammatory effects.

Dual encapsulation of hydrophobic and hydrophilic drugs in PLGA nanoparticles by a single-step method: drug delivery and cytotoxicity assays

Dual drug encapsulation in biodegradable nanoparticles is always challenging and often requires strenuous optimization of the synthesis–encapsulation processes.

Ribosome profiling reveals an important role for translational control in circadian gene expression

Physiological and behavioral circadian rhythms are driven by a conserved transcriptional/translational negative feedback loop in mammals. Although most core clock factors are transcription factors, post-transcriptional control introduces delays that are critical for circadian oscillations. Little work has been done on circadian regulation of translation, so to address this deficit we conducted ribosome profiling experiments in a human cell model for an autonomous clock. We found that most rhythmic gene expression occurs with little delay between transcription and translation, suggesting that the lag in the accumulation of some clock proteins relative to their mRNAs does not arise from regulated translation. Nevertheless, we found that translation occurs in a circadian fashion for many genes, sometimes imposing an additional level of control on rhythmically expressed mRNAs and, in other cases, conferring rhythms on noncycling mRNAs. Most cyclically transcribed RNAs are translated at one of two major times in a 24-h day, while rhythmic translation of most noncyclic RNAs is phased to a single time of day. Unexpectedly, we found that the clock also regulates the formation of cytoplasmic processing (P) bodies, which control the fate of mRNAs, suggesting circadian coordination of mRNA metabolism and translation.

Maximal Dexamethasone Inhibition of Luminal Epithelial Proliferation Involves Progesterone Receptor (PR)- and Non-PR-Mediated Mechanisms in Neonatal Mouse Uterus

Progesterone (P4) and the synthetic glucocorticoid dexamethasone (Dex) inhibit luminal epithelial (LE) proliferation in neonatal mouse uteri. This study determined the roles of progesterone receptor and estrogen receptor 1 (PR and ESR1, respectively) in P4- and Dex-induced inhibition of LE proliferation using PR knockout (PRKO) and Esr1 knockout (Esr1KO) mice. Wild-type (WT), heterozygous, and homozygous PRKO female pups were injected with vehicle, P4 (40 μg/g body weight), or Dex (4 or 40 μg/g body weight) on Postnatal Day 5, then 24 h later immunostained for markers of cell proliferation. In WT and heterozygous mice, P4 sharply reduced LE proliferation, and Dex produced dose-responsive decreases equaling those of P4 at the higher dose. Critically, although both doses of Dex similarly decreased proliferation compared to vehicle-treated PRKOs, treatment of PRKO pups with the high Dex dose (40 μg/g) did not inhibit LE as much as treatments of WT mice with this Dex dose or with P4. Stromal proliferation was stimulated by P4 in WT but not PRKO mice, and Dex did not alter stromal proliferation. Uteri of all genotypes strongly expressed glucocorticoid receptor (GR), demonstrating that impaired Dex effects in PRKOs did not reflect GR deficiency. Furthermore, inhibition of LE proliferation by Dex (40 μg/g body weight) in Esr1KO mice was normal, so this process does not involve ESR1. In summary, inhibitory Dex effects on LE proliferation occur partially through non-PR-mediated mechanisms, presumably GR, as indicated by Dex inhibition of LE proliferation in PRKOs. However, maximal inhibitory Dex effects on uterine LE proliferation are not seen in PRKO mice with even high Dex, indicating that maximal Dex effects in WT mice also involve PR.

Maternal food restriction modulates cerebrovascular structure and contractility in adult rat offspring: effects of metyrapone

Although the effects of prenatal undernutrition on adult cardiovascular health have been well studied, its effects on the cerebrovascular structure and function remain unknown. We used a pair-fed rat model of 50% caloric restriction from day 11 of gestation to term, with ad libitum feeding after birth. We validated that maternal food restriction (MFR) stress is mediated by glucocorticoids by administering metyrapone, a corticosterone synthesis inhibitor, to MFR mothers at day 11 of gestation. At age 8 mo, offspring from Control, MFR, and MFR + Metyrapone groups were killed, and middle cerebral artery (MCA) segments were studied using vessel-bath myography and confocal microscopy. Colocalization of smooth muscle α-actin (SMαA) with nonmuscle (NM), SM1 and SM2 myosin heavy-chain (MHC) isoforms was used to assess smooth muscle phenotype. Our results indicate that artery stiffness and wall thickness were increased, pressure-evoked myogenic reactivity was depressed, and myofilament Ca(2+) sensitivity was decreased in offspring of MFR compared with Control rats. MCA from MFR offspring exhibited a significantly greater SMαA/NM colocalization, suggesting that the smooth muscle cells had been altered toward a noncontractile phenotype. MET significantly reversed the effects of MFR on stiffness but not myogenic reactivity, lowered SMαA/NM colocalization, and increased SMαA/SM2 colocalization. Together, our data suggest that MFR alters cerebrovascular contractility via both glucocorticoid-dependent and glucocorticoid-independent mechanisms.

Dexamethasone dipropionate loaded nanoparticles of α-elastin-g-PLGA for potential treatment of restenosis

A graft copolymer of α-elastin with poly(lactic-co-glycolic) acid (PLGA) has been synthesized and successfully employed to produce nanoparticles. Exploiting the known biological activity of α-elastin to promote the maintenance of smooth muscle cells (SMCs) contractile phenotype and the antiproliferative effect of glucocorticoids, the aim of this research was to produce drug-loaded nanoparticles suitable for potential treatment of restenosis. In particular, nanoparticles of α-elastin-g-PLGA with a mean size of 200 nm have been produced and loaded with dexamethasone dipropionate (10% w/w), chosen as a model drug that inhibits proliferation of vascular SMCs. These nanoparticles are able to prolong the drug release and show a pronounced sensibility to elastase. Drug unloaded nanoparticles stimulate the differentiation of human umbilical artery smooth muscle cells (HUASMCs) toward the contractile phenotype as demonstrated by immunofluorescence, flow cytofluorimetric, and western blotting analyses. Finally, drug-loaded nanoparticles efficiently reduce viability of HUASMCs as evidenced by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2- (4-sulfophenyl)-2H-tetrazolium, inner salt (MTS) assay.

Dexamethasone-eluting vascular stents

Percutaneous transluminal angioplasty (PTA) with stenting is widely used in the treatment of vascular disorders, but restenosis remains a significant problem. Drug-eluting stents (DES) have been developed as an attempt to reduce the intimal response leading to restenosis. Drugs used in DES include mainly immunosuppressive and anti-proliferative compounds. Glucocorticoids are also an interesting possibility for those purposes because they have anti-proliferative effects in vascular smooth muscle cells and down-regulate the production of cytokines and growth factors driving inflammation and fibrosis. In this MiniReview, feasibility and safety of drug-eluting metal and biodegradable vascular stents are discussed with special emphasis on dexamethasone-eluting stents.

Cardiac and vascular atrogin-1 mRNA expression is not associated with dexamethasone efficacy in the monocrotaline model of pulmonary hypertension

Atrophic signaling elements of the ubiquitin-proteasome system (UPS) are involved in skeletal muscle wasting as well as pressure overload models of heart failure. In our prior experiments, we demonstrated a transcriptional downregulation of atrophy-inducing vascular E3 ubiquitin ligases in a toxic model of pulmonary hypertension where pulmonary artery and right ventricle (RV) hypertrophy are evident. Given the numerous reports of glucocorticoid activation of the UPS and the negative regulator of muscle mass, myostatin, we investigated the efficacy of dexamethasone to reverse monocrotaline (MCT)-induced pulmonary hypertension and augment atrogin-1 expression in both pulmonary arteries and myocardium. Dexamethasone caused significant reductions in body weight in combination with MCT. As predicted, MCT-induced pulmonary hypertension was evident by increases in RV systolic pressure, right ventricle to left ventricle plus septal weight ratios (RV/LVS) and arterial remodeling. MCT treatment significantly reduced both RV and PA atrogin-1 expression. Dexamethasone treatment reversed the MCT-induced pathological indices and restored RV atrogin-1 expression, but did not impact atrogin-1 expression in pulmonary arteries. Myostatin was poorly expressed in pulmonary arteries compared to the RV, and dexamethasone treatment increase RV myostatin in controls but not MCT-treated rats. These findings suggest that mechanisms independent of myostatin/atrogin-1 are responsible for glucocorticoid efficacy in this model of pulmonary hypertension.

The inhibitory effect of dexamethasone on platelet-derived growth factor-induced vascular smooth muscle cell migration through up-regulating PGC-1α expression

Dexamethasone has been shown to inhibit vascular smooth muscle cell (VSMC) migration, which is required for preventing restenosis. However, the mechanism underlying effect of dexamethasone remains unknown. We have previously demonstrated that peroxisome proliferator-activated receptor gamma (PPARγ) coactivator-1 alpha (PGC-1α) can inhibit VSMC migration and proliferation. Here, we investigated the role of PGC-1α in dexamethasone-reduced VSMC migration and explored the possible mechanism. We first examined PGC-1α expression in cultured rat aortic VSMCs. The results revealed that incubation of VSMCs with dexamethasone could significantly elevate PGC-1α mRNA expression. In contrast, platelet-derived growth factor (PDGF) decreased PGC-1α expression while stimulating VSMC migration. Mechanistic study showed that suppression of PGC-1α by small interfering RNA strongly abrogated the inhibitory effect of dexamethasone on VSMC migration, whereas overexpression of PGC-1α had the opposite effect. Furthermore, an analysis of MAPK signal pathways showed that dexamethasone inhibited ERK and p38 MAPK phosphorylation in VSMCs. Overexpression of PGC-1α decreased both basal and PDGF-induced p38 MAPK phosphorylation, but it had no effect on ERK phosphorylation. Finally, inhibition of PPARγ activation by a PPARγ antagonist GW9662 abolished the suppressive effects of PGC-1α on p38 MAPK phosphorylation and VSMC migration. These effects of PGC-1α were enhanced by a PPARγ agonist troglitazone. Collectively, our data indicated for the first time that one of the anti-migrated mechanisms of dexamethasone is due to the induction of PGC-1α expression. PGC-1α suppresses PDGF-induced VSMC migration through PPARγ coactivation and, consequently, p38 MAPK inhibition.

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.

IL-4 and IL-13 upregulate ornithine decarboxylase expression by PI3K and MAP kinase pathways in vascular smooth muscle cells

Ornithine decarboxylase (ODC) is the first and rate-controlling enzyme in the synthesis of polyamines, which are essential for normal cell growth. We have previously demonstrated that IL-4 and IL-13 can stimulate rat aortic smooth muscle cell (RASMC) proliferation. The objective of this study was to determine whether IL-4 and IL-13 induce cell proliferation by upregulating ODC expression in RASMC. The results revealed that incubation of RASMC with IL-4 and IL-13 for 24 h caused four- to fivefold induction of ODC catalytic activity. The increased ODC catalytic activity was attributed to the increased expression of ODC mRNA. Moreover, these observations were paralleled by increased production of polyamines. We further investigated the signal transduction pathways responsible for ODC induction by IL-4 and IL-13. The data illustrated that PD-98059, a MEK (MAPK kinase) inhibitor, LY-294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor, and H-89, a protein kinase A (PKA) inhibitor, substantially decreased the induction of ODC catalytic activity and ODC mRNA expression induced by IL-4 and IL-13, suggesting positive regulation of the ODC gene by ERK, PI3K, and PKA pathways. Interestingly, dexamethasone, a known inhibitor of cell proliferation, completely abrogated the response of RASMC to IL-4 and IL-13. Furthermore, the inhibition of ODC by these inhibitors led to the reduced production of polyamines and decreased DNA synthesis as monitored by [(3)H]thymidine incorporation. Our data indicate that upregulation of ODC by IL-4 and IL-13 might play an important role in the pathophysiology of vascular disorders characterized by excessive smooth muscle growth.

Effect of maternal administration of betamethasone on peripheral arterial development in fetal rabbit lungs

OBJECTIVES

Glucocorticoids promote lung maturation and reduce the incidence of respiratory distress syndrome in premature newborns. We hypothesized that betamethasone (BM), which is known to induce thinning of the alveolar walls, would also thin the arterial media and adventitia of intra-parenchymatic vessels in developing rabbit lungs.

STUDY DESIGN

112 fetuses from 21 time-mated, pregnant, giant white rabbits received maternal injections of BM at either 0.05 or 0.1 mg/kg/day on days 25-26 of gestational age. Controls received either saline (10 does, 56 fetuses) or no injection (10 does, 59 fetuses). Fetuses were harvested from day 27 onwards until term (day 31). 44 additional fetuses (8 does) were harvested between days 23 and 26. Endpoints were wet lung-to-body weight ratio, vascular morphometric indices and immunohistochemistry staining for alpha-smooth muscle actin, Flk-1, vascular endothelial growth factor (VEGF) and endothelial nitric oxide synthase (eNOS). ANOVA (Tukey's test) and independent t test (p < 0.05) were used for comparison between BM and saline groups.

RESULTS

Maternal BM injected on days 25-26 to pregnant rabbits induced a significant decrease in fetal body and lung weight and the lung-to-body weight ratio in the preterm pups shortly after injection. BM led to a dose-dependent thinning of the arterial media and adventitia (pulmonary arteries with an external diameter (ED) of <100 microm), to an increase in the percentage of non-muscularized peripheral vessels (ED <60 microm), in eNOS and VEGF immunoreactivity of the endothelial and smooth muscle cells in the pulmonary vessels and to an increase in Flk-1-positive pulmonary epithelial cell density.

CONCLUSIONS

Maternal administration of BM caused thinning of the arterial wall of pulmonary vessels (ED <100 microm) and a decrease in muscularization in peripheral vessels (ED <60 microm). This coincided with increased expression of Flk-1 in the endothelium and smooth muscle cells of the pulmonary arteries. All the effects studied were dose-dependent.

Dexamethasone nano-aggregates composed of PEG–PLA–PEG triblock copolymers for anti-proliferation of smooth muscle cells

Dexamethasone nano-aggregate was prepared for the treatment of intimal hyperplasia caused by abnormal proliferation of smooth muscle cells. Triblock copolymers composed of poly(ethylene glycol) [PEG] and poly(D,L-lactic acid) [PLA] were synthesized with different chain lengths of PEG. Triblock copolymers in organic phase were mixed with dexamethasone and dexamethasone nano-aggregates was prepared by dispersing the organic phase into water. The average diameter of the nano-aggregates ranged from 200 to 300 nm. Dexamethasone was released out from the nano-aggregates and the release profile was dependent on PEG chain lengths. The dexamethasone nano-aggregates showed superior anti-proliferation effects on smooth muscle cells compared to dexamethasone. Flow cytometry showed that smooth muscle cells treated with dexamethasone nano-aggregates was arrested at a dormant phase in a dose-dependent manner. The dexamethasone nano-aggregates are expected to be a potent candidate for anti-proliferating smooth muscle tissues after a balloon-catheter treatment.

Drug-eluting stents studies in mice: Do we need atherosclerosis to study restenosis?

In 2001, the first human study with drug-eluting stents (DES) was published showing a nearly complete abolition of restenosis by using a sirolimus-eluting stent. This success was very encouraging to test new compounds in combination with the DES platform. Nevertheless, several other anti-restenotic compounds have been used in human clinical trials with disappointing outcomes. Little is known concerning potential adverse effects on vessel wall integrity and (re)healing, atherosclerotic lesion formation, progression, and plaque stability of these DES. Although efficacy and safety need to be determined clinically, preclinical testing of candidate drugs in well-defined animal models is extremely helpful to gain insight into the basic biological responses to candidate compounds. Here, we discuss and report an animal model which enables rapid screening of candidate drugs for DES on an atherosclerotic background. The results from drug testing using this novel model could help to quickly and cost-effectively establish the dose range of candidate drugs with reasonable potential for DES.

Dexamethasone-releasing biodegradable polymer scaffolds fabricated by a gas-foaming/salt-leaching method

Dexamethasone, a steroidal anti-inflammatory drug, was incorporated into porous biodegradable polymer scaffolds for sustained release. The slowly released dexamethasone from the degrading scaffolds was hypothesized to locally modulate the proliferation and differentiation of various cells. Dexamethasone containing porous poly(D,L-lactic-co-glycolic acid) (PLGA) scaffolds were fabricated by a gas-foaming/salt-leaching method. Dexamethasone was loaded within the polymer phase of the PLGA scaffold in a molecularly dissolved state. The loading efficiency of dexamethasone varied from 57% to 65% depending on the initial loading amount. Dexamethasone was slowly released out in a controlled manner for over 30 days without showing an initial burst release. Release amount and duration could be adjusted by controlling the initial loading amount within the scaffolds. Released dexamethasone from the scaffolds drastically suppressed the proliferations of lymphocytes and smooth muscle cells in vitro. This study suggests that dexamethasone-releasing PLGA scaffolds could be potentially used either as an anti-inflammatory porous prosthetic device or as a temporal biodegradable stent for reducing intimal hyperplasia in restenosis.

Biodegradable nanoparticles for drug and gene delivery to cells and tissue

Biodegradable nanoparticles formulated from poly (D,L-lactide-co-glycolide) (PLGA) have been extensively investigated for sustained and targeted/localized delivery of different agents including plasmid DNA, proteins and peptides and low molecular weight compounds. Research about the mechanism of intracellular uptake of nanoparticles, their trafficking and sorting into different intracellular compartments, and the mechanism of enhanced therapeutic efficacy of nanoparticle-encapsulated agent at cellular level is more recent and is the primary focus of the review. Recent studies in our laboratory demonstrated rapid escape of PLGA nanoparticles from the endo-lysosomal compartment into cytosol following their uptake. Based on the above mechanism, various potential applications of nanoparticles for delivery of therapeutic agents to the cells and tissue are 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.

Identification of a novel dexamethasone-sensitive RNA-destabilizing region on rat monocyte chemoattractant protein 1 mRNA

Glucocorticoids are potent anti-inflammatory agents widely used in the treatment of human disease. We have previously shown that the inflammatory cytokine monocyte chemoattractant protein 1 (MCP-1) is regulated posttranscriptionally by glucocorticoids in arterial smooth muscle cells (SMC). To elucidate the mechanism mediating this effect, in vitro-transcribed radiolabeled MCP-1 mRNA was incubated with cytoplasmic extracts from SMC and analyzed by gel electrophoresis. Extracts from SMC treated with platelet-derived growth factor (PDGF) did not degrade the transcripts for up to 3 h. In contrast, extracts from cells treated with 1 microM dexamethasone (Dex) alone or in combination with PDGF degraded the probe with a half-life of approximately 15 min. Dex had maximal effect at concentrations above 0.01 microM and was effective on both rat and human MCP-1 transcripts. By deletion analysis, the Dex-sensitive region of the MCP-1 mRNA was localized to the initial 224 nucleotides (nt) at the 5' end and did not involve an AU-rich sequence in the 3' untranslated end. The 224-nt region conferred Dex sensitivity to heterologous mRNA. These studies provide new insights into the molecular mechanisms underlying the effect of glucocorticoids on gene expression.