Effect of sirolimus on the cholesterol content of aortic arch in ApoE knockout mice

Glucosamine increases macrophage lipid accumulation by regulating the mammalian target of rapamycin signaling pathway

Elevated blood glucose is associated with an increased risk of atherosclerosis. Data from the current study showed that glucosamine (GlcN), a normal glucose metabolite of the hexosamine biosynthetic pathway (HBP), promoted lipid accumulation in RAW264.7 macrophage cells. Oleic acid- and lipopolysaccharide (LPS)-induced lipid accumulation was further enhanced by GlcN in RAW264.7 cells, although there was no a significant change in the rate of fatty acid uptake. GlcN increased acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), scavenger receptor class A, liver X receptor, and sterol regulatory elementbinding protein-1c (SREBP-1c) mRNA expression, and; conversely, suppressed ATP-binding cassette transporter A1 (ABCA-1) and ABCG-1 expression. Additionally, GlcN promoted O-GlcNAcylation of nuclear SREBP-1 but did not affect its DNA binding activity. GlcN stimulated phosphorylation of mammalian target of rapamycin (mTOR) and S6 kinase. Rapamycin, a mTOR-specific inhibitor, suppressed GlcN-induced lipid accumulation in RAW264.7 cells. The GlcN-mediated increase in ACC and FAS mRNA was suppressed, while the decrease in ABCA-1 and ABCG-1 by GlcN was not significantly altered by rapamycin. Together, our results highlight the importance of the mTOR signaling pathway in GlcN-induced macrophage lipid accumulation and further support a potential link between mTOR and HBP signaling in lipogenesis. [BMB Reports 2024; 57(2): 92-97].

Cholesterol trafficking, lysosomal function, and atherosclerosis

Despite years of study and major research advances over the past 50 years, atherosclerotic diseases continue to rank as the leading global cause of death. Accumulation of cholesterol within the vascular wall remains the main problem and represents one of the early steps in the development of atherosclerotic lesions. There is a complex relationship between vesicular cholesterol transport and atherosclerosis, and abnormalities in cholesterol trafficking can contribute to the development and progression of the lesions. The dysregulation of vesicular cholesterol transport and lysosomal function fosters the buildup of cholesterol within various intracytoplasmic compartments, including lysosomes and lipid droplets. This, in turn, promotes the hallmark formation of foam cells, a defining feature of early atherosclerosis. Multiple cellular processes, encompassing endocytosis, exocytosis, intracellular trafficking, and autophagy, play crucial roles in influencing foam cell formation and atherosclerotic plaque stability. In this review, we highlight recent advances in the understanding of the intricate mechanisms of vesicular cholesterol transport and its relationship with atherosclerosis and discuss the importance of understanding these mechanisms in developing strategies to prevent or treat this prevalent cardiovascular disease.

Rapamycin: A Bacteria-Derived Immunosuppressant That Has Anti-atherosclerotic Effects and Its Clinical Application

Atherosclerosis (AS) is the leading cause of stroke and death worldwide. Although many lipid-lowering or antiplatelet medicines have been used to prevent the devastating outcomes caused by AS, the serious side effects of these medicines cannot be ignored. Moreover, these medicines are aimed at preventing end-point events rather than addressing the formation and progression of the lesion. Rapamycin (sirolimus), a fermentation product derived from soil samples, has immunosuppressive and anti-proliferation effects. It is an inhibitor of mammalian targets of rapamycin, thereby stimulating autophagy pathways. Several lines of evidence have demonstrated that rapamycin possess multiple protective effects against AS through various molecular mechanisms. Moreover, it has been used successfully as an anti-proliferation agent to prevent in-stent restenosis or vascular graft stenosis in patients with coronary artery disease. A thorough understanding of the biomedical regulatory mechanism of rapamycin in AS might reveal pathways for retarding AS. This review summarizes the current knowledge of biomedical mechanisms by which rapamycin retards AS through action on various cells (endothelial cells, macrophages, vascular smooth muscle cells, and T-cells) in early and advanced AS and describes clinical and potential clinical applications of the agent.

Effect of sirolimus on carotid atherosclerosis in kidney transplant recipients: data derived from a prospective randomized controlled trial

Background

In animal models, the mammalian target of rapamycin inhibitors (mTORIs) may prevent atherogenesis by the regulation of homeostasis of cholesterol and by a reduced inflammatory response. The aim of this study is to compare the carotid intima–media thickness (cIMT) between de novo tacrolimus/mycophenolate and tacrolimus/sirolimus at low doses. The cIMT is considered a surrogate marker of atherosclerosis.

Methods

We evaluated cIMT at baseline and at 6 and 12 months after kidney transplantation in a database derived from a previously published trial. That trial had prospectively randomly assigned kidney transplant recipients older than 60 years of age to one of two groups: tacrolimus/sirolimus (n = 21) or tacrolimus/mycophenolate (n = 23). The cIMT was evaluated by using ultrasound in the common carotid artery wall on both sides.

Results

The total and high-density lipoprotein cholesterol levels were higher in the sirolimus group at 6 and 12 months. The cIMT decreased over time at 6 and 12 months in the sirolimus group (P = 0.012); this decrease continued to be significant in a model adjusted for age, sex, presence of diabetes, statin use and smoking.

Conclusions

The use of sirolimus plus tacrolimus de novo in kidney transplantation is associated with a reduction in cIMT after 12 months, a decrease more significant than seen with the combination of mycophenolate plus tacrolimus. This suggests a class effect of mTORI in the prevention of atherosclerosis.

Effects of Rapamycin on Clinical Manifestations and Blood Lipid Parameters in Different Preeclampsia-like Mouse Models

Background:

The pathogenesis of some types of preeclampsia is related to fatty acid oxidation disorders. Rapamycin can regulate fatty acid metabolism. This study aimed to investigate the effects of rapamycin on the clinical manifestations and blood lipid parameters in different preeclampsia-like mouse models.

Methods:

Two preeclampsia-like mouse models and a control group were established: L-NA (injected with Nω-nitro-L-arginine methyl ester), LPS (injected with lipopolysaccharide), and the control group with normal saline (NS). The mouse models were established at preimplantation (PI), early- and late-pregnancy (EP, LP) according to the time of pregnancy. The administration of rapamycin (RA; L-NA+RA, LPS+RA, and NS+RA) or vehicle as controls (C; L-NA+C, LPS+C, NS+C) were followed on the 2^nd day after the mouse models’ establishment. Each subgroup consisted of eight pregnant mice. The mean arterial pressure (MAP), 24-h urinary protein, blood lipid, fetus, and placental weight were measured. The histopathological changes and lipid deposition of the liver and placenta were observed. Student's t-test was used for comparing two groups. Repeated measures analysis of variance was used for blood pressure analysis. Qualitative data were compared by Chi-square test.

Results:

The MAP and 24-h urinary protein in the PI, EP, and LP subgroups of the L-NA+C and LPS+C groups were significantly higher compared with the respective variables in the NS+C group (P < 0.05). The preeclampsia-like mouse models were established successfully. There was no significant difference in the MAP between the PI, EP, and LP subgroups of the L-NA+RA and L-NA+C groups and the LPS+RA and LPS+C groups. The 24-h urine protein levels in the PI and EP subgroups of the L-NA+RA group were significantly lower compared with the respective levels in the L-NA+C groups (1037 ± 63 vs. 2127 ± 593 μg; 976 ± 42 vs. 1238 ± 72 μg; both P < 0.05), also this effect appeared similar in the PI and EP subgroups of the LPS+RA and LPS+C groups (1022 ± 246 vs. 2141 ± 432 μg; 951 ± 41 vs. 1308 ± 30 μg; both P < 0.05). The levels of serum-free fatty acid (FFA) in the PI and EP subgroups of the L-NA+RA groups were significantly lower compared with the respective levels in the L-NA+C group (2.49 ± 0.44 vs. 3.30 ± 0.18 mEq/L; 2.23 ± 0.29 vs. 2.84 ± 0.14 mEq/L; both P < 0.05). The levels of triglycerides (TG) and total cholesterol in the PI subgroup of the L-NA+RA group were significantly lower compared with the respective levels in the L-NA+C (1.51 ± 0.16 vs. 2.41 ± 0.37 mmol/L; 2.11 ± 0.17 vs. 2.47 ± 0.26 mmol/L; both P < 0.05), whereas high-density lipoprotein serum concentration was significantly higher (1.22 ± 0.19 vs. 0.87 ± 0.15 mmol/L; P < 0.05) and low-density lipoprotein serum concentration did not exhibit a significant difference. There were no significant differences in the FFA of the PI, EP, and LP subgroups between the LPS+RA and the LPS+C groups. The levels of TG in the PI subgroup of the LPS+RA group were significantly lower compared with the respective levels in the LPS+C group (0.97 ± 0.05 vs. 1.22 ± 0.08 mmol/L; P < 0.05).

Conclusion:

Rapamycin can improve clinical manifestations and blood lipid profile in part of the preeclampsia-like mouse models.

Multiple pathway assessment to predict anti-atherogenic efficacy of drugs targeting macrophages in atherosclerotic plaques

BACKGROUND

Macrophages play a central role in atherosclerosis development and progression, hence, targeting macrophage activity is considered an attractive therapeutic. Recently, we documented nanomedicinal delivery of the anti-inflammatory compound prednisolone to atherosclerotic plaque macrophages in patients, which did however not translate into therapeutic efficacy. This unanticipated finding calls for in-depth screening of drugs intended for targeting plaque macrophages.

METHODS AND RESULTS

We evaluated the effect of several candidate drugs on macrophage activity, rating overall performance with respect to changes in cytokine release, oxidative stress, lipid handling, endoplasmic reticulum (ER) stress, and proliferation of macrophages. Using this in vitro approach, we observed that the anti-inflammatory effect of prednisolone was counterbalanced by multiple adverse effects on other key pathways. Conversely, pterostilbene, T0901317 and simvastatin had an overall anti-atherogenic effect on multiple pathways, suggesting their potential for liposomal delivery.

CONCLUSION

This dedicated assay setup provides a framework for high-throughput assessment. Further in vivo studies are warranted to determine the predictive value of this macrophage-based screening approach and its potential value in nanomedicinal drug development for cardiovascular patients.

Autophagy: an emerging therapeutic target in vascular diseases

Autophagy is a cellular catabolic process responsible for the destruction of long-lived proteins and organelles via lysosome-dependent pathway. This process is of great importance in maintaining cellular homeostasis, and deregulated autophagy has been implicated in the pathogenesis of a wide range of diseases. A growing body of evidence suggests that autophagy can be activated in vascular disorders such as atherosclerosis. Autophagy occurs under basal conditions and mediates homeostatic functions in cells but in the setting of pathological states up-regulated autophagy can exert both protective and detrimental functions. Therefore, the precise role of autophagy and its relationship with the progression of the disease need to be clarified. This review highlights recent findings regarding autophagy activity in vascular cells and its potential contribution to vascular disorders with a focus on atherogenesis. Finally, whether the manipulation of autophagy represents a new therapeutic approach to treat or prevent vascular diseases is also discussed.

Activation of mTORC1 disrupted LDL receptor pathway: a potential new mechanism for the progression of non-alcoholic fatty liver disease

Our previous studies demonstrated that inflammation exacerbates the progression of non-alcoholic fatty liver disease (NAFLD) by disrupting cholesterol homeostasis. This study aimed to investigate the role of mammalian target of rapamycin complex 1 (mTORC1) in NAFLD under conditions of inflammation. Chronic inflammation was induced by using subcutaneous injections of 10% casein in apolipoprotein E knockout (ApoE KO) mice in vivo and interleukin-1β stimulation of the HepG2 hepatoblastoma cell line in vitro. Results demonstrated that inflammation increased lipid accumulation in HepG2 cells and in livers of apolipoprotein E knockout mice. These effects were correlated with an increase in low density lipoprotein receptor (LDLR) gene transcription, which was mediated through the up-regulation of sterol regulatory element-binding protein (SREBP) cleavage-activating protein (SCAP), SREBP-2, and through enhanced translocation of the SCAP/SREBP-2 complex from endoplasmic reticulum (ER) to Golgi. In addition, our data indicated that inflammation down-regulated the expression of proprotein convertase subtilisin kexin 9 (PCSK9) and prevented the degradation of LDLR protein via posttranscriptional mechanisms. Further analysis showed that inflammation increased the protein phosphorylation of mTOR, eukaryotic initiation factor 4E-binding protein 1, and p70 S6 kinase. Interestingly, blocking mTORC1 activity inhibited the translocation of SCAP/SREBP-2 complex from the ER to the Golgi and decreased the expression of LDLR, SCAP, and SREBP-2. These effects were accompanied by an increase in the expression of PCSK9 and accelerated LDLR degradation. Our findings demonstrated that increased mTORC1 activity exacerbated the progression of NAFLD by disrupting LDLR expression via transcriptional and posttranscriptional mechanisms.

Autophagy and cardiometabolic risk factors

Autophagy is an essential cellular pathway by which protein aggregates, long-lived proteins, or defective organelles are sequestered in double membrane vesicles and then degraded upon fusion of those vesicles with lysosomes. Although autophagy plays a critical role in maintaining intracellular homeostasis and keeping the cell in a healthy state, this key pathway can become dysregulated in various cardiometabolic disorders, such as; obesity, dyslipidemia, inflammation, and insulin resistance. In these conditions, autophagy may actually worsen the pathological state instead of protecting the cell or organism. In this review, we discuss how dysregulated autophagy may be linked to increases in cardiovascular risk factors, and how manipulation of the autophagic machinery might reduce those risks.

mTOR inhibition: a promising strategy for stabilization of atherosclerotic plaques

Statins are currently able to stabilize atherosclerotic plaques by lowering plasma cholesterol and pleiotropic effects, but a residual risk for atherosclerotic disease remains. Therefore, effective prevention of atherosclerosis and treatment of its complications is still a major clinical challenge. A large body of evidence indicates that mammalian target of rapamycin (mTOR) inhibitors such as rapamycin or everolimus have pleiotropic anti-atherosclerotic effects so that these drugs can be used as add-on therapy to prevent or delay the pathogenesis of atherosclerosis. Moreover, bioresorbable scaffolds eluting everolimus trigger a healing process in the vessel wall, both in pigs and humans, that results in late lumen enlargement and plaque regression. At present, this phenomenon of atheroregression is poorly understood. However, given that mTOR inhibitors suppress cell proliferation and trigger autophagy, a cellular survival pathway and a process linked to cholesterol efflux, we hypothesize that these compounds can inhibit (or reverse) the basic mechanisms that control plaque growth and destabilization. Unfortunately, adverse effects associated with mTOR inhibitors such as dyslipidemia and hyperglycemia have recently been identified. Dyslipidemia is manageable via statin treatment, while the anti-diabetic drug metformin would prevent hyperglycemia. Because metformin has beneficial macrovascular effects, this drug in combination with an mTOR inhibitor might have significant promise to treat patients with unstable plaques. Moreover, both statins and metformin are known to inhibit mTOR via AMPK activation so that they would fully exploit the beneficial effects of mTOR inhibition in atherosclerosis.

Autophagy in obesity and atherosclerosis: Interrelationships between cholesterol homeostasis, lipoprotein metabolism and autophagy in macrophages and other systems

The incidence of diseases characterized by a dysregulation of lipid metabolism such as obesity, diabetes and atherosclerosis is rising at alarming rates, driving research to uncover new therapies to manage dyslipidemias and resolve the metabolic syndrome conundrum. Autophagy and lipid homeostasis - both ancient cellular pathways - have seemingly co-evolved to share common regulatory elements, and autophagy has emerged as a prominent mechanism involved in the regulation of lipid metabolism. This review highlights recent findings on the role of autophagy in the regulation of cellular cholesterol homeostasis and lipoprotein metabolism, with special emphasis on macrophages. From modulation of inflammation to regulation of cellular cholesterol levels, a protective role for autophagy in atherosclerosis is emerging. The manipulation of autophagic activity represents a new possible therapeutic approach for the treatment complex metabolic disorders such as obesity and the metabolic syndrome.

Drug-induced macrophage autophagy in atherosclerosis: for better or worse?

Autophagy is a reparative, life-sustaining process by which cytoplasmic components are sequestered in double membrane vesicles and degraded upon fusion with lysosomal compartments. Mice with a macrophage-specific deletion of the essential autophagy gene Atg5 develop plaques with increased apoptosis and oxidative stress as well as enhanced plaque necrosis. This finding indicates that basal autophagy in macrophages is anti-apoptotic and present in atherosclerotic plaques to protect macrophages against various atherogenic stressors. However, autophagy is impaired in advanced stages of atherosclerosis and its deficiency promotes atherosclerosis in part through activation of the inflammasome. Because basal autophagy can be intensified selectively in macrophages by specific drugs such as mammalian target of rapamycin (mTOR) inhibitors or Toll-like receptor 7 (TLR7) ligands, these drugs were recently tested as potential plaque stabilizing compounds. Stent-based delivery of the mTOR inhibitor everolimus promotes a stable plaque phenotype, whereas local administration of the TLR7 ligand imiquimod stimulates inflammation and plaque progression. Therefore, more drugs capable of inducing autophagy should be tested in plaque macrophages to evaluate the feasibility of this approach. Given that drug-induced macrophage autophagy is associated with pro-inflammatory responses due to cytokine release, induction of postautophagic necrosis or activation of phagocytes after clearance of the autophagic corpse, cotreatment with anti-inflammatory compounds may be required. Overall, this review highlights the pros and cons of macrophage autophagy as a drug target for plaque stabilization.

Perspectives of Targeting mTORC1-S6K1 in Cardiovascular Aging

The global population aging is accelerating and age-associated diseases including cardiovascular diseases become more challenging. The underlying mechanisms of aging and age-associated cardiovascular dysfunction remain elusive. There are substantial evidences demonstrating a pivotal role of the mammalian target of rapamycin complex 1 (mTORC1) and its down-stream effector S6K1 signaling in mammalian lifespan regulation and age-related diseases such as type II diabetes mellitus and cancer. The role of mTORC1–S6K1 in age-related cardiovascular diseases is, however, largely unknown and the available experimental results are controversial. This review article primarily summarizes the most recent advances toward understanding the role of mTORC1–S6K1 in cardiovascular aging and discusses the future perspectives of targeting mTORC1–S6K1 signaling as a healthy lifespan extension modality in anti-aging and anti-cardiovascular aging.

Toll-like receptor 4 is up-regulated by mTOR activation during THP-1 macrophage foam cells formation

Macrophage foam cells formation is the most important process in atherosclerotic plaque formation and development. Toll-like receptor 4 (TLR4) is one of the important innate immune sensors of endogenous damage signals and crucial for regulating inflammation. Growing evidence indicates that TLR4 plays a very important role in macrophage foam cells formation. However, the underlying mechanisms regulating TLR4 expression in macrophage are not fully understood. In this study, we induced THP-1 macrophage foam cells formation with oxidative modified low-density lipoprotein (ox-LDL). We observed that TLR4 mRNA and protein expression were markedly up-regulated, and the phosphorylation of mammalian target of rapamycin (mTOR) and its downstream target p70S6K were promoted during foam cells formation. The mTOR inhibitor rapamycin blocked mTOR phosphorylation and inhibited TLR4 expression induced by ox-LDL. Silencing mTOR, rictor or raptor protein expression by small interfering RNA, also inhibited the up-regulation of TLR4 expression, respectively. Inhibition of mTOR with rapamycin reversed the down-regulation of cellular lipid efflux mediator ABCA1, which resulted from the activation of TLR4 by ligands. These data suggested that TRL4 expression was up-regulated by a mechanism dependent on mTOR signal pathway activation during THP-1 macrophage foam cells formation. Inhibition of ox-LDL induced mTOR activation reduced TLR4 expression, and improved the impaired lipid efflux.

Autophagy regulates cholesterol efflux from macrophage foam cells via lysosomal acid lipase

The lipid droplet (LD) is the major site of cholesterol storage in macrophage foam cells and is a potential therapeutic target for the treatment of atherosclerosis. Cholesterol, stored as cholesteryl esters (CEs), is liberated from this organelle and delivered to cholesterol acceptors. The current paradigm attributes all cytoplasmic CE hydrolysis to the action of neutral CE hydrolases. Here, we demonstrate an important role for lysosomes in LD CE hydrolysis in cholesterol-loaded macrophages, in addition to that mediated by neutral hydrolases. Furthermore, we demonstrate that LDs are delivered to lysosomes via autophagy, where lysosomal acid lipase (LAL) acts to hydrolyze LD CE to generate free cholesterol mainly for ABCA1-dependent efflux; this process is specifically induced upon macrophage cholesterol loading. We conclude that, in macrophage foam cells, lysosomal hydrolysis contributes to the mobilization of LD-associated cholesterol for reverse cholesterol transport.

Sirolimus inhibits endogenous cholesterol synthesis induced by inflammatory stress in human vascular smooth muscle cells

Inflammatory stress accelerates the progression of atherosclerosis. Sirolimus, a new immunosuppressive agent, has been shown to have pleiotropic antiatherosclerotic effects. In this study we hypothesized that sirolimus inhibits 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR)-mediated cholesterol synthesis in human vascular smooth muscle cells (VSMCs) under inflammatory stress. Using radioactive assay, we demonstrated that sirolimus inhibited the increase of interleukin-1beta (IL-1beta)-induced cholesterol synthesis in VSMCs. Further studies showed that sirolimus inhibited both the HMGR gene and protein expression in VSMCs treated with or without IL-1beta. These effects were mediated by inhibiting the gene expression of sterol regulatory element-binding protein-2 (SREBP-2) and SREBP-2 cleavage-activating protein (SCAP) as checked by real-time PCR, Western blot analysis, and confocal microscopy for the observation of decreased protein translocation of the SCAP/SREBP-2 complex from the endoplasmic reticulum (ER) to the Golgi. Insulin-induced gene-1 (Insig-1) is a key ER protein controlling the feedback regulation of HMGR at transcriptional and posttranscriptional levels. We demonstrated that sirolimus increased Insig-1 expression which may bind to the SCAP, preventing the exit of SCAP-SREBP complexes from the ER. The increased Insig-1 also accelerated HMGR protein degradation in VSMCs as shown by pulse-chase analysis. In conclusion, sirolimus inhibits cholesterol synthesis induced by inflammatory stress through the downregulation of HMGR expression and the acceleration of HMGR protein degradation. These findings may improve our understanding of the molecular mechanisms of the antiatherosclerosis properties of sirolimus.

Validation of anti-aging drugs by treating age-related diseases

Humans die from age-related diseases, which are deadly manifestations of the aging process. In order to extend life span, an anti-aging drug must delay age-related diseases. All together age-related diseases are the best biomarker of aging. Once a drug is used for treatment of any one chronic disease, its effect against other diseases (atherosclerosis, cancer, prostate enlargement, osteoporosis, insulin resistance, Alzheimer's and Parkinson's diseases, age-related macular degeneration) may be evaluated in the same group of patients. If the group is large, then the anti-aging effect could be validated in a couple of years. Startlingly, retrospective analysis of clinical and preclinical data reveals four potential anti-aging modalities.

Prevention of atherosclerosis by the mTOR inhibitor everolimus in LDLR-/- mice despite severe hypercholesterolemia

Everolimus inhibits the mammalian target of rapamycin (mTOR) in proliferating cells. It is widely used in transplant patients and has also been exploited by drug-eluting stents for the treatment of cardiovascular disease. However, there is only limited data on the pathophysiological effects of mTOR-inhibitors on the vascular wall. We aimed to unravel the effects of everolimus on cholesterol-induced atherosclerosis and on circulating cell mediators in LDL-receptor-deficient (LDLR(-/-)) mice. Male hypercholesterolemic LDLR(-/-) mice received either solvent (group A; n=28) or everolimus at 0.05 mg/kg (group B, n=22) and 1.5 mg/kg (group C, n=29) per body weight per day by subcutaneously implanted osmotic minipumps for the study period of 12 weeks. Group B showed 44% reduction of atherosclerotic lesions at the brachiocephalic artery (BCA). In group C atherosclerotic lesions were reduced by 85% in the BCA and by 60% at the aortic root. This was associated with a significantly lower complexity of lesions in both treated groups (p<0.001) and despite a 40% increase of plasma cholesterol. Everolimus caused a significant reduction of circulating cell mediators such as interleukin-1alpha, interleukin-5, GM-CSF and interleukin-12p40. Everolimus increased the plasma levels of KC but had no effect on eighteen other circulating cell mediators studied. Everolimus strongly inhibits atherosclerosis development in LDL-receptor(-/-) mice despite severe hypercholesterolemia. Everolimus application had only small effects on circulating cell mediators. The significant reduction of atherosclerotic lesions was associated with a delayed transition from early macrophages enriched lesions to advanced atherosclerotic plaques.

Anti-atherosclerotic effects of sirolimus on human vascular smooth muscle cells

Sirolimus is a potent immunosuppressive agent and has an anti-atherosclerotic effect through its anti-proliferative property. The present study was undertaken to investigate the effect of sirolimus on intracellular cholesterol homeostasis in human vascular smooth muscle cells (VSMCs) in the presence of inflammatory cytokine IL-1β. We explored the effect of sirolimus on the lipid accumulation of VSMCs in the presence of IL-1β, using Oil Red O staining and quantitative measurement of intracellular cholesterol. The effect of sirolimus on the gene and protein expression of lipoprotein receptors and ATP binding cassettes (ABCA1 and ABCG1) was examined by real-time PCR and Western blotting, respectively. Furthermore, the effect of sirolimus on cholesterol efflux from VSMCs in the presence or absence of IL-1β was also investigated using [3H] cholesterol efflux. Finally, we examined the effect of sirolimus on the production of inflammatory cytokines in VSMCs using ELISA. Sirolimus reduced intracellular lipid accumulation in VSMCs mediated by IL-1β possibly due to the reduction of expression of low-density lipoprotein (LDL) and very low-density lipoprotein (VLDL) receptors. Sirolimus increased cholesterol efflux from VSMCs and overrode the suppression of cholesterol efflux induced by IL-1β. Sirolimus also increased ABCA1 and ABCG1 genes expression, even in the presence of IL-1β. We further confirmed that sirolimus inhibited mRNA and protein expression of inflammatory cytokines IL-6, tumor necrosis factor-α, IL-8, and monocyte chemoattractant protein-1. Inhibition of lipid uptake together with increasing cholesterol efflux and the inhibition of inflammatory cytokines are all important aspects of the anti-atherosclerotic effects of sirolimus on VSMCs.

Drug-induced immunomodulation to affect the development and progression of atherosclerosis: a new opportunity?

Inflammation and cytokine pathways are crucial for the development and progression of atherosclerotic lesions. In this review, the hypothesis that immunomodulatory drugs provide a possible therapeutic modality for cardiovascular disease is evaluated. Therefore, after a short overview of the specific inflammatory pathways involved in atherosclerosis, literature on the effect of several immunomodulatory drugs, such as nonsteroidal anti-inflammatory drugs, specific cyclooxygenase inhibitors and immunosuppressive drugs, used currently in the prevention of rejection after organ transplant, on the development and progression of atherosclerosis is reviewed. In addition, the pleiotropic immunomodulatory effect of two established cardiovascular drugs (angiotensin-converting enzyme inhibitors and statins) is discussed.

Rapamycin Attenuates Atherosclerotic Plaque Progression in Apolipoprotein E Knockout Mice

Rapamycin has been shown to reduce neointimal thickening in the setting of balloon angioplasty and chronic graft vessel disease. This study was designed to test the effect of oral rapamycin on atherosclerotic plaque progression and the possible mechanism involved. Apolipoprotein E (apoE) knockout mice were fed either a diet supplemented with cholesterol or with cholesterol and rapamycin. At 4 and 8 weeks, quantitative analyses of plaque area and macrophage numbers were determined. Plasma cholesterol, triglyceride, and whole-blood rapamycin levels were measured. Rapamycin could be detected in the blood of mice (117+/-7 pg/mL). In mice fed with rapamycin, atherosclerotic lesions covered 22% of the aortic arch as compared with 41% in cholesterol-fed mice. The macrophage count was significantly lower in the rapamycin-fed mice as compared with cholesterol-fed mice. Rapamycin, in a dose-dependent manner, inhibited monocyte chemotaxis elicited by stromal cell-derived factor-1. Lesions in the cholesterol-fed mice had complex atherosclerotic plaque with acellular core, cholesterol clefts, and an abundant collection of monocytes/macrophages. Lesions in the rapamycin-fed mice were mainly composed of monocytes/macrophages. Oral rapamycin is effective in slowing the progression of atherosclerosis. Along with its multitude actions, attenuation of monocyte chemotaxis may be one more way by which rapamycin attenuates plaque progression.

Preclinical restenosis models and drug-eluting stents: still important, still much to learn

Percutaneous coronary intervention continues to revolutionize the treatment of coronary atherosclerosis. Restenosis remains a significant problem but may at last be yielding to technologic advances. The examination of neointimal hyperplasia in injured animal artery models has helped in our understanding of angioplasty and stenting mechanisms, and as drug-eluting stent (DES) technologies have arrived, they too have been advanced through the study of animal models. These models are useful for predicting adverse clinical outcomes in patients with DESs because suboptimal animal model studies typically lead to problematic human trials. Similarly, stent thrombosis in animal models suggests stent thrombogenicity in human patients. Equivocal animal model results at six or nine months occasionally have been mirrored by excellent clinical outcomes in patients. The causes of such disparities are unclear but may result from differing methods, including less injury severity than originally described in the models. Ongoing research into animal models will reconcile apparent differences with clinical trials and advance our understanding of how to apply animal models to clinical stenting in the era of DESs.