Erythropoietin suppresses the formation of macrophage foam cells: role of liver X receptor alpha

Role of Erythropoiesis-Stimulating Agents in Cardiovascular Protection in CKD Patients: Reappraisal of Their Impact and Mechanisms

Erythropoiesis-stimulating agents (ESAs) have markedly reduced the need for blood transfusion for renal anemia and are included in standard therapies for patients with chronic kidney disease (CKD). Various protective effects of ESAs on the cardiovascular system have been discovered through basic research, and the effects have received much attention because the rates of cardiovascular events and mortality are high in CKD patients. However, randomized clinical trials did not provide strong evidence that ESAs exert cardioprotection in humans, including CKD patients. It is difficult to assess the cardioprotective effects of ESAs in CKD patients through the clinical data that has been reported to date because the relationship between hemoglobin level rather than ESA dose and cardiovascular event rates was examined in most studies. Interestingly, recent studies using a rat model of CKD showed that the infarct size-limiting effect of an ESA was lost when its dose was increased to a level that normalized blood hemoglobin levels, suggesting that the optimal dose of an ESA for myocardial protection is less than the dose required to normalize hemoglobin levels. Furthermore, animal models of traditional coronary risk factors or comorbidities were resistant to the cardioprotective effects of ESAs because of interruptions in signal-mediated mechanisms downstream of erythropoietin receptors. In this review, we briefly discuss basic and clinical data on the impact of anemia on coronary and systemic circulation, the effects of CKD on the cardiovascular system, and the multiple pharmacological actions of ESAs to examine whether the ESAs that are prescribed for renal anemia exert any cardioprotection in patients with CKD.

Investigation of the effective components inhibited macrophage foam cell formation in Ophiopogonis Radix

ETHNOPHARMACOLOGICAL RELEVANCE

Ophiopogonis Radix, the commonly used traditional Chinese medicine in clinic for treating cardiovascular diseases, is returned to the stomach, lung and heart meridian. It is reported to nourish yin, moisten lung and is used to treat heart yin deficiency syndromes and asthenia of heart and lung, which indicated that Ophiopogonis Radix may have a protective effect on heart disorders. Atherosclerosisis is an important process in the development of cardiovascular diseases and abnormal lipid deposition induced macrophage foam cells is its crucial foundation. Our previous study showed the extract of Ophiopogonis Radix (EOR) ameliorates atherosclerosis in vitro. However, it may protect against cardiovascular diseases through inhibiting macrophage foam cell formation and its potential effective components and mechanisms are still unclear.

AIM OF THE STUDY

Our study aimed to investigate the effect of Ophiopogonis Radix on macrophage foam cell formation and its potential active constituents and mechanisms.

MATERIALS AND METHODS

Ox-LDL induced macrophage cells were employed to evaluate the effect of Ophiopogonis Radix on macrophage foam cell formation. Then the potential active constituents inhibited formation of macrophage foam cells were screened by biospecific cell extraction and its underlying mechanisms were also explored by Western blot.

RESULTS

The extract of Ophiopogonis Radix was found to significantly inhibit macrophage foam cell formation, evidenced by the decrease of TG and TC and Oil Red O staining analysis in macrophage cells, which indicated that EOR reduced the formation of macrophage foam cells. At the same time, EOR was showed to increase antioxidant capacity in macrophage cells. After treatment with EOR, two potential active components interacted with macrophage foam cells specifically were identified to inhibit macrophage foam cell formation including methylophiopogonanone A and methylophiopogonanone B. Methylophiopogonanone A was then proved to decrease the expression of CD36, Lox-1 and SREBP2, increase the expression of ABCA1 obviously, while the expression of ABCG1 and SREBP1 had no changes.

CONCLUSIONS

In our study, Ophiopogonis Radix was found to protect against atherosclerosis through suppressing ox-LDL induced macrophage foam cell formation and two potential compounds were identified by biospecific cell extraction including methylophiopogonanone A and methylophiopogonanone B. Moreover, methylophiopogonanone A was proved to inhibit foam cells through reducing uptake, synthesis and increasing efflux, which may provide guidance and reference for application of Ophiopogonis Radix and investigation of the effective components of TCMs.

STUDY OF THE PHARMACOLOGICAL ACTIVITY OF NOVEL EPOR/CD131 HETERORECEPTOR AGONISTS IN MICE WITH ENDOTHELIAL-SPECIFIC EXPRESSION OF MUTANT POLG GENE

The aim of the research was to study antiatherosclerotic and endothelial kinds of a protective activity of peptides mimicking an erythropoietin a-helix B tertiary structure with laboratory codes EP-11-1 (UEHLERALNSS), EP-11-2. (UEQLERALNCS), EP-11-3 (UEQLERALNTS).

Materials and methods. The study was conducted on 96 C57Bl/6J male double transgenic Polgmut/mut/Cdh5-CRE mice. Atherosclerosis was induced by a balloon injury accompanied by Western diet. Then, for 27 days, the drugs under study were administered once per 3 days at the dose of 20 μg/kg. On the 28th day, the animals were euthanized and the area of atherosclerotic plaques was collected for an assessment. The expression of genes associated with the processes of inflammation, apoptosis, and angiogenesis was determined in the tissues of the aorta. In addition, the endothelial protective effect of peptides in isolated segments of the thoracic aorta of wild and transgenic ransgenic Polgmut/mut mice was studied.

Results. The assessment of the plaque size in the animals with the Polgmut/mut/Cdh5-CRE genotype against the background of the peptides under study did not reveal statistically significant differences in comparison to control. However, a quantitative PCR showed a statistically significant decreased expression of pro-apoptotic factors p-53 and Bax, and also increase the expression of anti-apoptotic factor Bcl-2 against the background of the peptides EP-11-1 and EP-11-2 administration. The administration of EP-11-1 and the original peptide pHBSP resulted in a statistically significant decrease in the Bax/Bcl-2 ratio. Compounds EP-11-1, EP-11-2, and EP-11-3 were more effective than the original peptide pHBSP, in reducing the increased expression of genes for inflammatory markers iNos, intercellular adhesion molecules Icam-1, Vcam-1 and E-selectin. The use of EP-11-1 led to a more efficient, in comparison with pHBSP, restoration of endothelial-dependent vasodilation of the aortic segments in mice with endothelial-specific overexpression of the mutant Polg gene.

Conclusion. The study carried out on a murine model of the endothelial-specific expression of mutant gamma polymerase has shown that derivatives of the pHBSP peptide with laboratory codes EP-11-1, EP-11-2, EP-11-3, obtained by BLAST-searching for groups of pHBSP related peptides, have atheroprotective and endothelial protective kinds of a protective activity, which is more pronounced in comparison with the original peptide pHBSP.

CTRP9 alleviates foam cells apoptosis by enhancing cholesterol efflux

The apoptosis of foam cells leads to instability of atherosclerotic plaques. This study was designed to explore the protective role of CTRP9 in foam cell apoptosis. In our experiment, CTRP9 alleviated foam cell apoptosis. Meanwhile, CTRP9 upregulated the expression of proteins important for cholesterol efflux, such as LXRα, CYP27A1, ABCG1 and ABCA1, and improved cholesterol efflux in foam cells. Moreover, CTRP9 inhibited Wnt3a and β-catenin expression and β-catenin nuclear translocation in foam cells. In addition, adenovirus overexpression of Wnt3a abolished the effect of CTRP9 on macrophage apoptosis. Mechanistically, the AMPK inhibitor abolished the effect of CTRP9 on foam cell apoptosis, and downregulation of AdipoR1 by siRNA abrogated the activation of AMPK and the effect of CTRP9 on foam cell apoptosis. We concluded that CTRP9 achieved these protective effects on foam cells through the AdipoR1/AMPK pathway.

Anti-atherogenic properties of Kgengwe (Citrullus lanatus) seed powder in low-density lipoprotein receptor knockout mice are mediated through beneficial alterations in inflammatory pathways

Kgengwe fruits are commonly consumed in sub-Saharan countries. Recent reports indicated low coronary artery disease rates in those regions. To investigate anti-atherogenic properties and potential mechanisms of action of Kgengwe seed powder (KSP), male low-density lipoprotein receptor knockout (LDL-r-KO) mice were fed with an atherogenic diet supplemented with (treated, n = 10) or without (controls, n = 10) 10% (w/w) KSP for 20 weeks. Proximate analysis revealed that KSP contained 38% fibre and 15% lipids. KSP supplementation was not associated with significant changes in body weight gain rate, food intake, and plasma lipid levels. However, the average atherosclerotic lesion size in the aortic roots in the KSP-treated group was 58% smaller than that in the control group (0.26 vs 0.11 mm2, p < 0.05). This strong anti-atherogenic effect was associated with significant increases in the average plasma levels of certain cytokines such as IL-10 (6 vs 13 pg/mL, p < 0.05), GM-CSF (0.1 vs 0.2 pg/mL, p < 0.05), and EPO (7 vs 16 pg/mL, p < 0.05) along with reductions in the average levels of plasma MCP-1 (19 vs 14 pg/mL, p < 0.05) and MIP-2 (28 vs 13 pg/mL, p < 0.05). Except for relatively high levels of saturated fatty acids, KSP possesses balanced nutrient compositions with strong anti-atherogenic properties, which may be mediated through alterations in inflammatory pathways. Additional studies warrant confirmation and mechanism(s) of action of such effects. Novelty: Kgengwe seeds prevent atherogenesis in LDL-r-KO mice. Kgengwe seeds increase circulating levels of IL-10 and EPO. No reduction in plasma total cholesterol levels.

Erythropoietin regulates metabolic response in mice via receptor expression in adipose tissue, brain, and bone

Erythropoietin (EPO) acts by binding to erythroid progenitor cells to regulate red blood cell production. While EPO receptor (Epor) expression is highest on erythroid tissue, animal models exhibit EPO activity in nonhematopoietic tissues, mediated, in part, by tissue-specific Epor expression. This review describes the metabolic response in mice to endogenous EPO and EPO treatment associated with glucose metabolism, fat mass accumulation, and inflammation in white adipose tissue and brain during diet-induced obesity and with bone marrow fat and bone remodeling. During high-fat diet-induced obesity, EPO treatment improves glucose tolerance, decreases fat mass accumulation, and shifts white adipose tissue from a pro-inflammatory to an anti-inflammatory state. Fat mass regulation by EPO is sex dimorphic, apparent in males and abrogated by estrogen in females. Cerebral EPO also regulates fat mass and hypothalamus inflammation associated with diet-induced obesity in males and ovariectomized female mice. In bone, EPO contributes to the balance between adipogenesis and osteogenesis in both male and female mice. EPO treatment promotes bone loss mediated via Epor in osteoblasts and reduces bone marrow adipocytes before and independent of change in white adipose tissue fat mass. EPO regulation of bone loss and fat mass is independent of EPO-stimulated erythropoiesis. EPO nonhematopoietic tissue response may relate to the long-term consequences of EPO treatment of anemia in chronic kidney disease and to the alternative treatment of oral hypoxia-inducible factor prolyl hydroxylase inhibitors that increase endogenous EPO production.

Biomimetic 3D Models for Investigating the Role of Monocytes and Macrophages in Atherosclerosis

Atherosclerosis, the inflammation of artery walls due to the accumulation of lipids, is the most common underlying cause for cardiovascular diseases. Monocytes and macrophages are major cells that contribute to the initiation and progression of atherosclerotic plaques. During this process, an accumulation of LDL-laden macrophages (foam cells) and an alteration in the extracellular matrix (ECM) organization leads to a local vessel stiffening. Current in vitro models are carried out onto two-dimensional tissue culture plastic and cannot replicate the relevant microenvironments. To bridge the gap between in vitro and in vivo conditions, we utilized three-dimensional (3D) collagen matrices that allowed us to mimic the ECM stiffening during atherosclerosis by increasing collagen density. First, human monocytic THP-1 cells were embedded into 3D collagen matrices reconstituted at low and high density. Cells were subsequently differentiated into uncommitted macrophages (M0) and further activated into pro- (M1) and anti-inflammatory (M2) phenotypes. In order to mimic atherosclerotic conditions, cells were cultured in the presence of oxidized LDL (oxLDL) and analyzed in terms of oxLDL uptake capability and relevant receptors along with their cytokine secretomes. Although oxLDL uptake and larger lipid size could be observed in macrophages in a matrix dependent manner, monocytes showed higher numbers of oxLDL uptake cells. By analyzing major oxLDL uptake receptors, both monocytes and macrophages expressed lectin-like oxidized low-density lipoprotein receptor-1 (LOX1), while enhanced expression of scavenger receptor CD36 could be observed only in M2. Notably, by analyzing the secretome of macrophages exposed to oxLDL, we demonstrated that the cells could, in fact, secrete adipokines and growth factors in distinct patterns. Besides, oxLDL appeared to up-regulate MHCII expression in all cells, while an up-regulation of CD68, a pan-macrophage marker, was found only in monocytes, suggesting a possible differentiation of monocytes into a pro-inflammatory macrophage. Overall, our work demonstrated that collagen density in the plaque could be one of the major factors driving atherosclerotic progression via modulation of monocyte and macrophages behaviors.

Anti-Atherosclerotic Properties of Wild Rice in Low-Density Lipoprotein Receptor Knockout Mice: The Gut Microbiome, Cytokines, and Metabolomics Study

Background and aim: We previously reported the anti-atherogenic properties of wild rice in low-density lipoprotein receptor knockout (LDL-r-KO) mice. The present study aimed to discover the mechanism of action for such effects. Materials: Fecal and plasma samples from the wild rice treated and control mice were used. Fecal bacterial population was estimated while using 16S rDNA technology. The plasma samples were used to estimate the levels of 35 inflammatory markers and metabolomics, while using Meso Scale multiplex assay and liquid chromatography-mass spectrometry (LC-MS/MS) techniques. Results: Many bacteria, particularly Anaeroplasma sp., Acetatifactor sp., and Prophyromonadaceae sp., were found in higher quantities in the feces of wild rice fed mice as compared to the controls. Cytokine profiles were significantly different between the plasma of treated and control mice. Among them, an increase in the level of IL-10 and erythropoietin (EPO) could explain the anti-atherogenic properties of wild rice. Among many metabolites tested in plasma of these animals, surprisingly, we found an approximately 60% increase in the levels of glucose in the wild rice fed mice as compared to that in the control mice. Conclusion: Additional studies warrant further investigation of the interplay among gut microbiome, inflammatory status, and macronutrient metabolism.

The detrimental effect of asymmetric dimethylarginine on cholesterol efflux of macrophage foam cells: Role of the NOX/ROS signaling

BACKGROUND

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide synthase inhibitor and has been proposed to be an independent risk factor for cardiovascular diseases. However, little is known about its role in the regulation of lipid metabolism. In this study, we investigated the effect of ADMA on cholesterol metabolism and its underlying molecular mechanism.

METHODS

Oxidized low-density lipoprotein (oxLDL)-induced macrophage foam cells were used as an in vitro model. Apolipoprotein E-deficient (apoE^-/-) hyperlipidemic mice were used as an in vivo model. Western blot analysis was used to evaluate protein expression. Luciferase reporter assays were used to assess the activity of promoters and transcription factors. Conventional assay kits were used to measure the levels of ADMA, cholesterol, triglycerides, and cytokines.

RESULTS

Treatment with oxLDL decreased the protein expression of dimethylarginine dimethylaminohydrolase-2 (DDAH-2) but not DDAH-1. Incubation with ADMA markedly increased oxLDL-induced lipid accumulation in macrophages. ADMA impaired cholesterol efflux following oxLDL challenge and downregulated the expression of ATP-binding cassette transporter A1 (ABCA1) and ABCG1 by interfering with liver X receptor α (LXRα) expression and activity. Additionally, this inhibitory effect of ADMA on cholesterol metabolism was mediated through the activation of the NADPH oxidase/reactive oxygen species pathway. In vivo experiments revealed that chronic administration of ADMA for 4 weeks exacerbated systemic inflammation, decreased the aortic protein levels of ABCA1 and ABCG1, and impaired the capacity of reverse cholesterol transport, ultimately, leading to the progression of atherosclerosis in apoE^-/- mice.

CONCLUSION

Our findings suggest that the ADMA/DDAH-2 axis plays a crucial role in regulating cholesterol metabolism in macrophage foam cells and atherosclerotic progression.

The phosphatase activity of soluble epoxide hydrolase regulates ATP-binding cassette transporter-A1-dependent cholesterol efflux

The contribution of soluble epoxide hydrolase (sEH) to atherosclerosis has been well defined. However, less is understood about the role of sEH and its underlying mechanism in the cholesterol metabolism of macrophages. The expression of sEH protein was increased in atherosclerotic aortas of apolipoprotein E‐deficient mice, primarily in macrophage foam cells. Oxidized low‐density lipoprotein (oxLDL) increased sEH expression in macrophages. Genetic deletion of sEH (sEH^−/−) in macrophages markedly exacerbated oxLDL‐induced lipid accumulation and decreased the expression of ATP‐binding cassette transporters‐A1 (ABCA1) and apolipoprotein AI‐dependent cholesterol efflux following oxLDL treatment. The down‐regulation of ABCA1 in sEH^−/− macrophages was due to an increase in the turnover rate of ABCA1 protein but not in mRNA transcription. Inhibition of phosphatase activity, but not hydrolase activity, of sEH decreased ABCA1 expression and cholesterol efflux following oxLDL challenge, which resulted in increased cholesterol accumulation. Additionally, oxLDL increased the phosphatase activity, promoted the sEH‐ABCA1 complex formation and decreased the phosphorylated level of ABCA1 at threonine residues. Overexpression of phosphatase domain of sEH abrogated the oxLDL‐induced ABCA1 phosphorylation and further increased ABCA1 expression and cholesterol efflux, leading to the attenuation of oxLDL‐induced cholesterol accumulation. Our findings suggest that the phosphatase domain of sEH plays a crucial role in the cholesterol metabolism of macrophages.

Metformin ameliorates Ox-LDL-induced foam cell formation in raw264.7 cells by promoting ABCG-1 mediated cholesterol efflux

AIMS

The accumulation of lipids in macrophages contributes to the development of atherosclerosis. Cholesterol efflux of lipid-loaded macrophages mediated by ATP binding cassette (ABC) cholesterol transporters, on the other hand, has been shown to attenuate atherosclerosis progression in patients with unknown mechanism. We therefore sought to test the effect of metformin that reduced cardiovascular risk in diabetic patients independent of its hypoglycemia effect on cholesterol transport in murine raw264.7 macrophages.

MATERIALS AND METHODS

Mouse raw264.7 macrophages were loaded with Ox-LDL (50 μg/ml) for 24 h before incubated with metformin (15 μM) for 24 h. Foam cell formation was assessed by Oil red staining and BIODIPY fluorescent staining as well as cholesterol-ester quantification by commercial kit. Cholesterol uptake and expression of scavenger receptors were detected by flow-cytometry. Cholesterol efflux capacity was measured by fluorescent plate-reader and ABC transporters were detected by Western Blots. Cytokines were detected by ELISA in supernatants and normalized by cellular lysates.

KEY FINDINGS

Our results showed that metformin decreased oxidized low-density lipoprotein (Ox-LDL)-induced cholesterol accumulation and foam cell formation by increasing cholesterol efflux to HDL, which was associated with an upregulation of ABC transporter ABCG-1. Moreover, metformin increased Ox-LDL-impaired IL-10 secretion, an important anti-foam cell cytokine in atherosclerosis.

SIGNIFICANCE

Our data highlighted the therapeutic potential of targeting macrophage cholesterol efflux with new or existing drugs for the possible reduction of foam cell formation in the prevention and treatment of diabetes-accelerated atherosclerosis.

Silencing LAIR-1 in human THP-1 macrophage increases foam cell formation by modulating PPARγ and M2 polarization

Formation of macrophage-derived foam cells may mark the initial stages of atherosclerosis. We investigated the association between the expression of the leukocyte-associated immunoglobulin-like receptor 1 (LAIR-1) in macrophages and foam cell formation. A foam cell model was established by incubating THP-1-derived macrophages and bone marrow macrophages (BMMs) with oxidized low-density lipoprotein (ox-LDL). The role of LAIR-1 in foam cell formation was evaluated via Oil Red O staining and Dil-ox-LDL fluorescence intensities. Peroxisome proliferator-activated receptor gamma (PPARγ), cholesterol metabolism-related genes, and the role of LAIR-1 in activating classically activated (M1) and alternatively activated (M2) macrophages were evaluated by qPCR. Additionally, activation of protein-tyrosine phosphatase-1 (SHP-1) and cAMP-response element binding protein (CREB) were detected by western blotting. Results indicated that silencing LAIR-1 in macrophages modulated the SHP-1/CREB/PPARγ pathway, thereby promoting M2 macrophage polarization and increasing foam cell formation. Therefore, Inhibition of LAIR-1 in macrophages may promote foam cell formation and atherosclerosis.

Curcumin increases cholesterol efflux via heme oxygenase‑1‑mediated ABCA1 and SR‑BI expression in macrophages

Curcumin, which is an extract from a traditional Chinese medicine, has previously been demonstrated to exhibit an anti‑atherosclerotic effect, which is closely associated with an increase in cholesterol efflux. However, it is unclear as to whether the increased effect is mediated by heme oxygenase (HO)‑1. Macrophages were treated with different concentrations of curcumin, HO‑1 inhibitor and small interfering (si)RNA in different experiments. Analysis of protein expression was conducted via western blotting. mRNA expression levels were measured using reverse transcription‑polymerase chain reaction. Antioxidant response element (ARE)‑driven promoter activity was measured by a dual‑luciferase reporter assay. The cholesterol efflux analysis was performed by fluorescence‑labelled cholesterol (NBD) using a multi‑label counter. In the present study, the results indicated that curcumin increased the cholesterol efflux from macrophages. Additionally, curcumin significantly upregulated HO‑1 expression. The HO‑1 inhibitor (zinc protoporphyrin) partly blocked this effect. Curcumin also promoted scavenger receptor class B type I (SR‑BI) and ATP‑binding cassette transporter A1 (ABCA1) expression. HO‑1 small interfering (si)RNA partly abolished the increased SR‑BI and ABCA1 expression induced by curcumin. Furthermore, the nuclear factor, erythroid 2 like 2 (Nrf2) expression in the nucleus was dose‑dependently increased by curcumin. Nrf2 siRNA successfully inhibited the curcumin‑induced HO‑1 expression. Curcumin significantly increased Nrf2‑driven luciferase activity. Overall, these data indicated that curcumin activates the Nrf2‑ARE signaling pathway and upregulates HO‑1 expression, which mediates SR‑BI and ABCA1 expression and thereby increases cholesterol efflux.

Andrographolide Inhibits Oxidized LDL-Induced Cholesterol Accumulation and Foam Cell Formation in Macrophages

oxLDL is involved in the pathogenesis of atherosclerotic lesions through cholesterol accumulation in macrophage foam cells. Andrographolide, the bioactive component of Andrographis paniculata, possesses several biological activities such as anti-inflammatory, anti-oxidant, and anticancer functions. Scavenger receptors (SRs), including class A SR (SR-A) and CD36, are responsible for the internalization of oxLDL. In contrast, receptors for reverse cholesterol transport, including ABCA1 and ABCG1, mediate the efflux of cholesterol from macrophage foam cells. Transcription factor liver X receptor [Formula: see text] (LXR[Formula: see text] plays a key role in lipid metabolism and inflammation as well as in the regulation of ABCA1 and ABCG1 expression. Because of the contribution of inflammation to macrophage foam cell formation and the potent anti-inflammatory activity of andrographolide, we hypothesized that andrographolide might inhibit oxLDL-induced macrophage foam cell formation. The results showed that andrographolide reduced oxLDL-induced lipid accumulation in macrophage foam cells. Andrographolide decreased the mRNA and protein expression of CD36 by inducing the degradation of CD36 mRNA; however, andrographolide had no effect on SR-A expression. In contrast, andrographolide increased the mRNA and protein expression of ABCA1 and ABCG1, which were dependent on LXR[Formula: see text]. Andrographolide enhanced LXR[Formula: see text] nuclear translocation and DNA binding activity. Treatment with the LXR[Formula: see text] antagonist GGPP and transfection with LXR[Formula: see text] siRNA reversed the ability of andrographolide to stimulate ABCA1 and ABCG1 protein expression. In conclusion, inhibition of CD36-mediated oxLDL uptake and induction of ABCA1- and ABCG1-dependent cholesterol efflux are two working mechanisms by which andrographolide inhibits macrophage foam cell formation, which suggests that andrographolide could be a potential candidate to prevent atherosclerosis.

Erythropoietin mediates brain-vascular-kidney crosstalk and may be a treatment target for pulmonary and resistant essential hypertension

Organ crosstalk pathways represent the next frontier for target-mining in molecular medicine for existing syndromes. Pulmonary hypertension and resistant essential hypertension are syndromes that have been proven elusive in etiology, and frequently refractory to first-line management. Underlying crosstalk mechanisms, not yet considered in these treatments, may hinder outcomes or unlock novel treatments. This review focuses systematically on erythropoietin, a synthesizable molecule, as a mediator of brain-kidney crosstalk. Insights gained from this review will be applied to cardiovascular diseases in a clinician-directed fashion.

Nucleolin protects macrophages from oxLDL-induced foam cell formation through up-regulating ABCA1 expression

Our recent studies have indicated that nucleolin, as a multifunctional RNA-binding protein, exerts protective effects in the myocardial cells and endothelial cells under the condition of oxidative stress. However, the function of nucleolin and its potential mechanism in macrophage-derived foam cell formation remain largely unexplored. ApoE-/- mice were fed with a high-fat diet (HFD) for 10-24 weeks. Protein expression was measured by western blotting or immunofluorescence, and gene expression at the mRNA level was detected by qRT-PCR. The level of lipid in macrophages was examined by Oil Red O staining, high-performance liquid chromatography (HPLC) and NBD-cholesterol. Actinomycin D (Act D) was used to determine the stability of ABCA1 mRNA in macrophages. The interaction of nucleolin with ABCA1 mRNA was assessed using co-immunoprecipitation (co-IP). The aortas advanced plaques demonstrated significantly lower levels of nucleolin protein compared with early plaques in ApoE-/- mice, in which the macrophage foam cells occupied main body. Nucleolin expression at the mRNA and protein levels in RAW264.7 macrophages was significantly reduced by oxidized low-density lipoprotein (oxLDL) in a dose- and time-dependent manner. Furthermore, nucleolin overexpression markedly attenuated lipid accumulation in oxLDL-challenged macrophages through increasing cholesterol efflux. In addition, nucleolin overexpression significantly increased the expression of ATP-binding cassette transporter A1 (ABCA1) at the mRNA and protein levels without affecting expressions of scavenger receptors (SR)-A, SR-B1, CD36 and ATP-binding cassette transporter G1 (ABCG1) at the mRNA level. Moreover, nucleolin overexpression increased the stability of ABCA1 mRNA in macrophages, whereas nucleolin ablation abrogated the oxLDL-induced up-regulation of ABCA1. The up-regulation of ABCA1 by nucleolin resulted from its protein-RNA interaction. Our data suggested that nucleolin inhibited foam cell formation through enhancing stability of ABCA1 mRNA and subsequently increasing cholesterol efflux.

Possible Inhibitory Effect of Erythropoiesis-Stimulating Agents at the Predialysis Stage on Early-Phase Coronary Events after Hemodialysis Initiation

BACKGROUND

We examined whether the use of erythropoiesis-stimulating agents (ESAs) to correct anemia at the predialysis stage could inhibit early-phase coronary events after hemodialysis initiation.

METHODS

We enrolled 242 patients with chronic kidney disease who had received continued medical treatments and initiated maintenance hemodialysis from 1 September 2000 to 31 December 2014 at Toujinkai Hospital. Patients with a previous history of blood transfusion or any cardiovascular events or interventions were excluded. The coronary events were followed for 1 year after initiation of hemodialysis.

RESULTS

Coronary events occurred in 51 of 242 patients: 10 patients had acute coronary syndrome [9 with percutaneous coronary intervention (PCI), 1 without intervention], and 41 had elective coronary revascularization (38 PCI and 3 coronary artery bypass graft). ESA was administered in 118 of 242 patients (48.8%). In stepwise logistic analysis, coronary events were positively associated with nonuse of ESA at the predialysis stage (odds ratio 2.66, p = 0.005) and diabetes mellitus (odds ratio 5.33, p < 0.001). When dividing the patients into 4 subgroups by blood hemoglobin (Hb) level (8.5 g/dl) and the use/nonuse of ESA, coronary event-free survival rates were higher (p = 0.005) in those with Hb ≥8.5 g/dl, ESA+ (86.6%, n = 82) and tended to be higher (p = 0.055) in those with Hb <8.5 g/dl, ESA+ (86.1%, n = 36) than in patients with Hb <8.5 g/dl, ESA- (68.6%, n = 86) in a Kaplan-Meier analysis.

CONCLUSIONS

The use of ESA to correct anemia at the predialysis stage may inhibit early-phase coronary events after hemodialysis initiation.

Fermentation induced changes in bioactive properties of wine from Phyllanthus with respect to atherosclerosis

Wine was prepared from three varieties of Phyllanthus viz., P. emblica (wild and cultivated) and P. acidus. Among the wines prepared, cultivated Emblica wine had the highest total phenolic (11.02 μg gallic acid equivalent/ml) and flavonoid (59.46 μg quercetin equivalent/ml) content. Further gallic acid, syringic acid, protocatechuic acid and caffeic acid were present in higher amounts in wine from the cultivated variety compared to other wines. HPLC analysis showed that in juice of the cultivated variety, gallic acid and coumaric acid were found in higher amounts than that in the corresponding wine. Antioxidant assays, LDL oxidation prevention, foam cell prevention and nitrite scavenging activities (cell lines) were found to be highest in cultivated Emblica juice and wine with an activity of 15 μg/ml and 14 μg/ml (nitrite assay) and 108.649 μg ascorbic acid equivalent/mg and 321.622 μg ascorbic acid equivalent /mg (total antioxidant capacity) respectively. CD36 expression was reduced and ABCA1 expression was increased to the highest extent by the cultivated Emblica wine and juice. Further, antioxidant activity was seen to increase during the course of fermentation. Sensory analysis showed that cultivated Emblica wine was sweeter compared to the other wines.

Transient Receptor Potential Ankyrin 1 Channel Involved in Atherosclerosis and Macrophage-Foam Cell Formation

Transient receptor potential ankyrin 1 channel (TRPA1) plays an important role in the pathogenesis of inflammatory diseases, yet its role and the underlying mechanism in atherosclerosis remain unclear. We aimed to investigate the role of TRPA1 in atherosclerosis and foam-cell formation in vivo in mice and in vitro in mouse macrophages. Histopathology was examined by hematoxylin and eosin staining, levels of cytokines and lipid profile were evaluated by assay kits, and protein expression was determined by western blot analysis. TRPA1 expression was increased in macrophage foam cells in atherosclerotic aortas of apolipoprotein E-deficient (apoE^-/-) mice. Atherosclerotic lesions, hyperlipidemia and systemic inflammation were worsened with chronic administration of the TRPA1 channel antagonist HC030031 or genetic ablation of TRPA1 (TRPA1^-/-) in apoE^-/- mice. Treatment with allyl isothiocyanate (AITC, a TRPA1 agonist) retarded the progression of atherosclerosis in apoE^-/- mice but not apoE^-/-TRPA1^-/- mice. Mouse macrophages showed oxidized low-density lipoprotein (oxLDL) activated TRPA1 channels. OxLDL-induced lipid accumulation of macrophages was exacerbated by HC030031 or loss of function of TRPA1. Inhibition of TRPA1 activity did not alter oxLDL internalization but impaired cholesterol efflux by downregulating the ATP-binding cassette transporters. Furthermore, tumor necrosis factor-α-induced inflammatory response was attenuated in AITC-activated macrophages. TRPA1 may be a pivotal regulator in the pathogenesis of atherosclerosis and cholesterol metabolism of macrophage foam cells.

Low ambient oxygen prevents atherosclerosis

Large population studies have shown that living at higher altitudes, which lowers ambient oxygen exposure, is associated with reduced cardiovascular disease mortality. However, hypoxia has also been reported to promote atherosclerosis by worsening lipid metabolism and inflammation. We sought to address these disparate reports by reducing the ambient oxygen exposure of ApoE-/- mice. We observed that long-term adaptation to 10% O2 (equivalent to oxygen content at ∼5000 m), compared to 21% O2 (room air at sea level), resulted in a marked decrease in aortic atherosclerosis in ApoE-/- mice. This effect was associated with increased expression of the anti-inflammatory cytokine interleukin-10 (IL-10), known to be anti-atherogenic and regulated by hypoxia-inducible transcription factor-1α (HIF-1α). Supporting these observations, ApoE-/- mice that were deficient in IL-10 (IL10-/- ApoE-/- double knockout) failed to show reduced atherosclerosis in 10% oxygen. Our study reveals a specific mechanism that can help explain the decreased prevalence of ischemic heart disease in populations living at high altitudes and identifies ambient oxygen exposure as a potential factor that could be modulated to alter pathogenesis. Key messages: Chronic low ambient oxygen exposure decreases atherosclerosis in mice. Anti-inflammatory cytokine IL-10 levels are increased by low ambient O2. This is consistent with the established role of HIF-1α in IL10 transactivation. Absence of IL-10 results in the loss of the anti-atherosclerosis effect of low O2. This mechanism may contribute to decreased atherosclerosis at high altitudes.

Polydatin Inhibits Formation of Macrophage-Derived Foam Cells

Rhizoma Polygoni Cuspidati, a Chinese herbal medicine, has been widely used in traditional Chinese medicine for a long time. Polydatin, one of the major active ingredients in Rhizoma Polygoni Cuspidati, has been recently shown to possess extensive cardiovascular pharmacological activities. In present study, we examined the effects of Polydatin on the formation of peritoneal macrophage-derived foam cells in Apolipoprotein E gene knockout mice (ApoE^−/−) and explored the potential underlying mechanisms. Peritoneal macrophages were collected from ApoE^−/− mice and cultured in vitro. These cells sequentially were divided into four groups: Control group, Model group, Lovastatin group, and Polydatin group. Our results demonstrated that Polydatin significantly inhibits the formation of foam cells derived from peritoneal macrophages. Further studies indicated that Polydatin regulates the metabolism of intracellular lipid and possesses anti-inflammatory effects, which may be regulated through the PPAR-γ signaling pathways.

Retinoic acid induces macrophage cholesterol efflux and inhibits atherosclerotic plaque formation in apoE-deficient mice

It has been suggested that retinoic acid (RA) has a potential role in the prevention of atherosclerotic CVD. In the present study, we used J774A.1 cell lines and primary peritoneal macrophages to investigate the protective effects of RA on foam cell formation and atherogenesis in apoE-deficient (apoE- / -) mice. A total of twenty male apoE- / - mice (n 10 animals per group), aged 8 weeks, were fed on a high-fat diet (HFD) and treated with vehicle or 9-cis-RA for 8 weeks. The atherosclerotic plaque area in the aortic sinus of mice in the 9-cis-RA group was 40·7 % less than that of mice in the control group (P< 0·01). Mouse peritoneal macrophages from the 9-cis-RA group had higher protein expression levels of ATP-binding cassette transporter A1 (ABCA1) and G1 (ABCG1) than those from the control group. Serum total and LDL-cholesterol concentrations were lower in the 9-cis-RA group than in the control group (P< 0·05). In vitro studies showed that incubation of cholesterol-loaded J774A.1 macrophages with 9-cis-RA (0·1, 1 and 10 μmol/l) induced cholesterol efflux in a dose-dependent manner. The 9-cis-RA treatment markedly attenuated lipid accumulation in macrophages exposed to oxidised LDL. Moreover, treatment with 9-cis-RA significantly increased the protein expression levels of ABCA1 and ABCG1 in J774A.1 macrophages in a dose-dependent manner. Furthermore, 9-cis-RA dose-dependently enhanced the protein expression level of liver X receptor-α (LXRα), the upstream regulator of ABCA1 and ABCG1. Taken together, the present results show that 9-cis-RA suppresses foam cell formation and prevents HFD-induced atherogenesis via the LXRα-dependent up-regulation of ABCA1 and ABCG1.

UFM1 Protects Macrophages from oxLDL-Induced Foam Cell Formation Through a Liver X Receptor α Dependent Pathway

AIM

Macrophage foam cell formation is the most prominent characteristic of the early stages of atherosclerosis. Ubiquitin Fold Modifier 1 (UFM1) is a new member of the ubiquitin-like protein family, and its underlying mechanism of action in macrophage foam cell formation is poorly understood. Our current study focuses on UFM1 and investigates its role in macrophage foam cell formation.

METHODS

Using real-time quantitative PCR (qRT-PCR) and western blot analysis, we first analyzed the UFM1 expression in mouse peritoneal macrophages (MPMs) from ApoE－/－ mice in vivo and in human macrophages treated with oxLDL in vitro. Subsequently, the effects of UFM1 on macrophages foam cell formation were determined by Nile Red staining and direct lipid analysis. We then examined whether UFM1 affects the process of lipid metabolism in macrophages. Lastly, with the method of small interfering RNA (siRNA), we delineated the mechanism of UFM1 to attenuate lipid accumulation in THP-1 macrophages.

RESULTS

UFM1 is dramatically upregulated under atherosclerosis conditions both in vivo and in vitro. Moreover, UFM1 markedly decreased macrophage foam cell formation. Mechanistic studies revealed that UFM1 increased the macrophage cholesterol efflux, which was due to the increased expression of ATP-binding cassette transporters A1 (ABCA1) and G1 (ABCG1). Furthermore, the upregulation of ABCA1 and ABCG1 by UFM1 resulted from liver X receptor α (LXRα) activation, which was confirmed by the observation that LXRα siRNA prevented the expression of ABCA1 and ABCG1. Consistent with this, the UFM1-mediated attenuation of lipid accumulation was abolished by such inhibition.

CONCLUSIONS

Taken together, our results showed that UFM1 could suppress foam cell formation via the LXRα-dependent pathway.

β Common Receptor Mediates Erythropoietin-Conferred Protection on OxLDL-Induced Lipid Accumulation and Inflammation in Macrophages

Erythropoietin (EPO), the key factor for erythropoiesis, also protects macrophage foam cells from lipid accumulation, yet the definitive mechanisms are not fully understood. β common receptor (βCR) plays a crucial role in the nonhematopoietic effects of EPO. In the current study, we investigated the role of βCR in EPO-mediated protection in macrophages against oxidized low-density lipoprotein- (oxLDL-) induced deregulation of lipid metabolism and inflammation. Here, we show that βCR expression was mainly in foamy macrophages of atherosclerotic aortas from apolipoprotein E-deficient mice. Results of confocal microscopy and immunoprecipitation analyses revealed that βCR was colocalized and interacted with EPO receptor (EPOR) in macrophages. Inhibition of βCR activation by neutralizing antibody or small interfering RNA (siRNA) abolished the EPO-conferred protection in oxLDL-induced lipid accumulation. Furthermore, EPO-promoted cholesterol efflux and upregulation of ATP-binding cassette (ABC) transporters ABCA1 and ABCG1 were prevented by pretreatment with βCR neutralizing antibody or βCR siRNA. Additionally, blockage of βCR abrogated the EPO-conferred anti-inflammatory action on oxLDL-induced production of macrophage inflammatory protein-2. Collectively, our findings suggest that βCR may play an important role in the beneficial effects of EPO against oxLDL-elicited dysfunction of macrophage foam cells.

Erythropoietin and obesity-induced white adipose tissue inflammation: redefining the boundaries of the immunometabolism territory

The adipose tissue represents a critical and predominant site for the interaction between metabolic and inflammatory responses during health and disease. In the white adipose tissue microenvironment, macrophages/adipocytes cross-talk have been shown to influence the metabolic and inflammatory states of both cell types, and contribute to the development of systemic insulin resistance during obesity. Indeed, the existence of paracrine loops between mature adipocytes and macrophages, especially during obesity-induced stress, involving the release of, and response to, an array of cytokines and regulatory factors, have been extensively studied using several in vitro and in vivo model systems. Published evidence together with recent observations, brought to light the unexpected role of erythropoietin and its receptor in the regulation of white adipose tissue mass, energy homeostasis, and inflammation as demonstrated by erythropoietin effects on adipocyte development and metabolic profile, and macrophage infiltration, cytokine responses, and activation state during diet-induced obesity. In this commentary, we discuss the newly added elements and perspectives to our understanding of the erythropoietin/erythropoietin-receptor axis as a regulator of obesity-induced white adipose tissue inflammation, providing insight into its effects on cytokine responses of macrophages and adipocytes, and possible links to glucose metabolism and insulin resistance.

Effect of erythropoietin on hepatic cytochrome P450 expression and function in an adenine-fed rat model of chronic kidney disease

BACKGROUND AND PURPOSE

Erythropoietin (EPO) is used to treat anaemia associated with chronic kidney disease (CKD). Hypoxia is associated with anaemia and is known to cause a decrease in cytochrome P450 (P450) expression. As EPO production is regulated by hypoxia, we investigated the role of EPO on P450 expression and function.

EXPERIMENTAL APPROACH

Male Wistar rats were subjected to a 0.7% adenine diet for 4 weeks to induce CKD. The diet continued for an additional 2 weeks while rats received EPO by i.p. injection every other day. Following euthanasia, hepatic P450 mRNA and protein expression were determined. Hepatic enzyme activity of selected P450s was determined and chromatin immunoprecipitation was used to characterize binding of nuclear receptors involved in the transcriptional regulation of CYP2C and CYP3A.

KEY RESULTS

EPO administration decreased hepatic mRNA and protein expression of CYP3A2 (P < 0.05), but not CYP2C11. Similarly, EPO administration decreased CYP3A2 protein expression by 81% (P < 0.001). A 32% decrease (P < 0.05) in hepatic CYP3A enzymatic activity (Vmax ) was observed for the formation of 6βOH-testosterone in the EPO-treated group. Decreases in RNA pol II recruitment (P < 0.01), hepatocyte nuclear factor 4α binding (P < 0.05) and pregnane X receptor binding (P < 0.01) to the promoter region of CYP3A were also observed in EPO-treated rats.

CONCLUSIONS AND IMPLICATIONS

Our data show that EPO decreases the expression and function of CYP3A, but not CYP2C in rat liver.

Saphenous Vein Graft Disease Is Associated with a Low Serum Erythropoietin Level

OBJECTIVE

To measure the serum erythropoietin (EPO) level in patients with saphenous vein grafts (SVGs) and to compare the EPO level in those with and without SVG disease.

SUBJECTS AND METHODS

The study included 85 consecutive patients with a history of coronary artery bypass graft surgery that underwent elective coronary angiography. Patients with >30% stenosis (diseased grafts) in at least one saphenous graft were included in group 1 (diseased group: n = 40), and group 2 (nondiseased group: n = 45) consisted of patients without diseased SVGs. The EPO level was measured using enzyme-linked immunosorbent assay (ELISA) using a commercially available ELISA kit; x03C7;2 test and independent samples t test were used where appropriate. Logistic regression was used for multivariate analysis.

RESULTS

There were not any significant differences in age, gender, or cardiovascular risk factors between the two groups except for increased triglyceride and low high-density lipoprotein levels in group 2. The EPO level was significantly higher in the nondiseased SVG group than in the diseased SVG group (25.5 ± 9.6 vs. 17.8 ± 6.8 mU ml-1, p = 0.002). Multivariate logistic regression analysis showed that the serum EPO level was an independent predictor of SVG disease (OR 1.14, 95% CI 1.06-1.24, p = 0.001).

CONCLUSION

In this study, SVG disease was associated with a low serum EPO level, suggesting that a low EPO level could be predictive of and contributes to the pathophysiology of SVG disease.

Erythropoietin, a novel versatile player regulating energy metabolism beyond the erythroid system

Erythropoietin (EPO), the required cytokine for promoting the proliferation and differentiation of erythroid cells to stimulate erythropoiesis, has been reported to act as a pleiotropic cytokine beyond hematopoietic system. The various activities of EPO are determined by the widespread distribution of its cell surface EPO receptor (EpoR) in multiple tissues including endothelial, neural, myoblasts, adipocytes and other cell types. EPO activity has been linked to angiogenesis, neuroprotection, cardioprotection, stress protection, anti-inflammation and especially the energy metabolism regulation that is recently revealed. The investigations of EPO activity in animals and the expression analysis of EpoR provide more insights on the potential of EPO in regulating energy metabolism and homeostasis. The findings of crosstalk between EPO and some important energy sensors and the regulation of EPO in the cellular respiration and mitochondrial function further provide molecular mechanisms for EPO activity in metabolic activity regulation. In this review, we will summarize the roles of EPO in energy metabolism regulation and the activity of EPO in tissues that are tightly associated with energy metabolism. We will also discuss the effects of EPO in regulating oxidative metabolism and mitochondrial function, the interactions between EPO and important energy regulation factors, and the protective role of EPO from stresses that are related to metabolism, providing a brief overview of previously less appreciated EPO biological function in energy metabolism and homeostasis.

Erythropoietin action in stress response, tissue maintenance and metabolism

Erythropoietin (EPO) regulation of red blood cell production and its induction at reduced oxygen tension provides for the important erythropoietic response to ischemic stress. The cloning and production of recombinant human EPO has led to its clinical use in patients with anemia for two and half decades and has facilitated studies of EPO action. Reports of animal and cell models of ischemic stress in vitro and injury suggest potential EPO benefit beyond red blood cell production including vascular endothelial response to increase nitric oxide production, which facilitates oxygen delivery to brain, heart and other non-hematopoietic tissues. This review discusses these and other reports of EPO action beyond red blood cell production, including EPO response affecting metabolism and obesity in animal models. Observations of EPO activity in cell and animal model systems, including mice with tissue specific deletion of EPO receptor (EpoR), suggest the potential for EPO response in metabolism and disease.

Rutaecarpine suppresses atherosclerosis in ApoE-/- mice through upregulating ABCA1 and SR-BI within RCT

ABCA1 and scavenger receptor class B type I (SR-BI)/CD36 and lysosomal integral membrane protein II analogous 1 (CLA-1) are the key transporter and receptor in reverse cholesterol transport (RCT). Increasing the expression level of ABCA1 and SR-BI/CLA-1 is antiatherogenic. The aim of the study was to find novel antiatherosclerotic agents upregulating expression of ABCA1 and SR-BI/CLA-1 from natural compounds. Using the ABCA1p-LUC and CLA-1p-LUC HepG2 cell lines, we found that rutaecarpine (RUT) triggered promoters of ABCA1 and CLA-1 genes. RUT increased ABCA1 and SR-BI/CLA-1 expression in vitro related to liver X receptor alpha and liver X receptor beta. RUT induced cholesterol efflux in RAW264.7 cells. ApoE-deficient (ApoE(-/-)) mice treated with RUT for 8 weeks showed ∼68.43, 70.23, and 85.56% less en face lesions for RUT (L), RUT (M), and RUT (H) groups, respectively, compared with the model group. Mouse macrophage-specific antibody and filipin staining indicated that RUT attenuated macrophages and cholesterol accumulations in atherosclerotic lesions, respectively. Additionally, ABCA1 and SR-BI expression was highly induced by RUT in livers of ApoE(-/-) mice. Meanwhile, RUT treatment significantly increased the fecal (3)H-cholesterol excretion, which demonstrated that RUT could promote RCT in vivo. RUT was identified to be a candidate that protected ApoE(-/-) mice from developing atherosclerosis through preferentially promoting activities of ABCA1 and SR-BI within RCT.

Novel effect of paeonol on the formation of foam cells: promotion of LXRα-ABCA1-dependent cholesterol efflux in macrophages

Paeonol, a phenolic component purified from Paeonia suffruticosa (Cortex Moutan), is used in traditional Chinese medicine to treat inflammatory diseases. However, little is known about the effect of paeonol on cholesterol metabolism. We investigated the efficacy of paeonol on cholesterol metabolism and the underlying mechanism in macrophages and apolipoprotein E deficient (apoE(-/-)) mice. Treatment with paeonol markedly attenuated cholesterol accumulation induced by oxidized LDL in macrophages, which was due to increased cholesterol efflux. Additionally, paeonol enhanced the mRNA and protein expression of ATP-binding membrane cassette transport protein A1 (ABCA1) but did not alter the protein level of ABCG1 or other scavenger receptors. Inhibition of ABCA1 activity with a pharmacological inhibitor, neutralizing antibody or small interfering RNA (siRNA), negated the effects of paeonol on cholesterol efflux and cholesterol accumulation. Furthermore, paeonol induced the nuclear translocation of liver X receptor α (LXRα) by increasing its activity. siRNA knockdown of LXRα abolished the paeonol-induced upregulation of ABCA1, promotion of cholesterol efflux and suppression of cholesterol accumulation. Moreover, atherosclerotic lesions, hyperlipidemia and systemic inflammation were reduced and the protein expression of ABCA1 was increased in aortas of paeonol-treated apoE(-/-) mice. Paeonol may alleviate the formation of foam cells by enhancing LXRα-ABCA1-dependent cholesterol efflux.

Activation of soluble guanylyl cyclase prevents foam cell formation and atherosclerosis

AIMS

Soluble guanylyl cyclase (sGC) is a key modulator in the regulation of vascular tone. However, its role and involving mechanism in cholesterol metabolism of macrophages and atherosclerosis remain unclear.

METHODS

Oil red O staining, Dil-oxidized low-density lipoprotein (oxLDL)-binding assay and cholesterol efflux assay were performed in biology of foam cells. Levels of cytokines or intracellular lipid were evaluated by ELISA or colorimetric kits. Expression of gene or protein was determined by quantitative real-time PCR or Western blotting. Histopathology was examined by haematoxylin and eosin staining.

RESULTS

Soluble guanylyl cyclase was expressed in macrophages of mouse atherosclerotic lesions. Treatment with 1H-[1, 2, 4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, sGC inhibitor) exacerbated oxLDL-induced cholesterol accumulation in macrophages. In contrast, 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1, sGC activator) attenuated the oxLDL-induced cholesterol accumulation because of increased cholesterol efflux. Additionally, YC-1 dose dependently increased the protein expression of ATP-binding cassette transporter A1 (ABCA1) but did not alter that of scavenger receptor class A (SR-A), CD36, SR-BI or ABCG1. Moreover, YC-1-upregulated ABCA1 level depended on liver X receptor α (LXRα). Inhibition of the LXRα-ABCA1 pathway by LXRα small interfering RNA (siRNA), ABCA1 neutralizing antibody or ABCA1 siRNA abolished the effect of YC-1 on cholesterol accumulation and cholesterol efflux. In vivo, YC-1 retarded the development of atherosclerosis, accompanied by reduced serum levels of cholesterol and pro-inflammatory cytokines, in apolipoprotein E-deficient mice.

CONCLUSION

Activation of sGC by YC-1 leads to LXRα-dependent upregulation of ABCA1 in macrophages and may confer protection against atherosclerosis.

Darbepoetin alpha reduces oxidative stress and chronic inflammation in atherosclerotic lesions of apo E deficient mice in experimental renal failure

Background

Cardiovascular morbidity and mortality is very important in patients with chronic renal failure. This occurs even in mild impairment of renal function and may be related to oxidative stress and chronic inflammation. The nephrectomized apo E knockout mouse is an accepted model for evaluating atherosclerosis in renal dysfunction. Erythropoietin derivates showed anti-oxidative and anti-inflammatory effects. Therefore, this study evaluates the effects of Darbepoetin on markers of oxidative stress and chronic inflammation in atherosclerotic lesions in apo E knockout mice with renal dysfunction.

Methods

Apo E knockout mice underwent unilateral (Unx, n = 20) or subtotal (Snx, n = 26) nephrectomy or sham operation (Sham, n = 16). Mice of each group were either treated with Darbepoetin or saline solution, a part of Snx mice received a tenfold higher dose of Darbepoetin. The aortic plaques were measured and morphologically characterized. Additional immunhistochemical analyses were performed on tissue samples taken from the heart and the aorta.

Results

Both Unx and Snx mice showed increased expression of markers of oxidative stress and chronic inflammation. While aortic plaque size was not different, Snx mice showed advanced plaque stages when compared to Unx mice. Darbepoetin treatment elevated hematocrit and lowered Nitrotyrosin as one marker of oxidative stress, inflammation in heart and aorta, plaque stage and in the high dose even plaque cholesterol content. In contrast, there was no influence of Darbepoetin on aortic plaque size; high dose Darbepoetin treatment resulted in elevated renal serum parameters.

Conclusion

Darbepoetin showed some protective cardiovascular effects irrespective of renal function, i.e. it improved plaque structure and reduced some signs of oxidative stress and chronic inflammation without affecting plaque size. Nevertheless, the dose dependent adverse effects must be considered as high Darbepoetin treatment elevated serum urea. Elevation of hematocrit might be a favorable effect in anemic Snx animals but a thrombogenic risk in Sham animals.

mTOR enhances foam cell formation by suppressing the autophagy pathway

Recently, autophagy has drawn more attention in cardiovascular disease as it has important roles in lipid metabolism. Mammalian target of rapamycin (mTOR) is a key regulator of autophagy; however, its effect on atherosclerosis and the underlying mechanism remains undefined. In this study, an obvious upregulation of mTOR and p-mTOR protein was observed in macrophage-derived foam cells. Blocking mTOR expression with specific small interference RNA (siRNA) dramatically suppressed foam cell formation, accompanied by a decrease of lipid deposition. Further mechanistic analysis indicated that suppressing mTOR expression significantly upregulated autophagic marker LC3 expression and downregulated autophagy substrate p62 levels, indicating that mTOR silencing triggered autophagosome formation. Moreover, blocking mTOR expression obviously accelerated neutral lipid delivery to lysosome and cholesterol efflux from foam cells, implying that mTOR could induce macrophage foam cell formation by suppressing autophagic pathway. Further, mTOR silencing significantly upregulated ULK1 expression, which was accounted for mTOR-induced foam cell formation via autophagic pathway as treatment with ULK1 siRNA dampened LC3-II levels and increased p62 expression, concomitant with lipid accumulation and decreased cholesterol efflux from foam cells. Together, our data provide an insight into how mTOR accelerates the pathological process of atherosclerosis. Accordingly, blocking mTOR levels may be a promising therapeutic agent against atherosclerotic complications.

Intermedin inhibits macrophage foam-cell formation via tristetraprolin-mediated decay of CD36 mRNA

AIMS

CD36-mediated uptake of oxidized low-density lipoprotein (oxLDL) plays a pivotal role in macrophage foam-cell formation and atherogenesis. Previously we reported on intermedin (IMD), a novel member of the calcitonin gene-related peptide family, in atherosclerotic plaque reducing atherogenesis in apolipoprotein E-deficient (apoE(-/-)) mice. Here, we studied the role of IMD in CD36-mediated macrophage foam-cell formation.

METHODS AND RESULTS

In apoE(-/-) mice, 6-week IMD infusion reduced oxLDL uptake, intracellular cholesterol content, and foam-cell formation in peritoneal macrophages and reduced protein and mRNA levels of CD36. These in vivo results agreed with in vitro observations in primary peritoneal macrophages. Reduced CD36 protein and mRNA levels were due to an IMD-accelerated decay of CD36 mRNA. Tristetraprolin (TTP), which binds to AU-rich elements in the 3' untranslated regions (UTRs) of mRNA and promotes its degradation, mediated CD36 mRNA destabilization. TTP knockdown by short-hairpin RNA increased and TTP overexpression reduced CD36 expression, and TTP knockdown rescued IMD-reduced CD36 expression. Moreover, IMD repressed TTP phosphorylation, thereby activating TTP, for increased TTP binding to the 3'-UTR of CD36 mRNA.

CONCLUSION

Thus, IMD attenuates macrophage foam-cell formation via TTP-mediated degradation of CD36 mRNA. Our findings reveal a new mechanism of the anti-atherogenic role of IMD and a novel pattern for regulation of CD36 expression in macrophages.

Suppression of coronary atherosclerosis by helix B surface Peptide, a nonerythropoietic, tissue-protective compound derived from erythropoietin

Erythropoietin (EPO), a type I cytokine originally identified for its critical role in hematopoiesis, has been shown to have nonhematopoietic, tissue-protective effects, including suppression of atherosclerosis. However, prothrombotic effects of EPO hinder its potential clinical use in nonanemic patients. In the present study, we investigated the antiatherosclerotic effects of helix B surface peptide (HBSP), a nonerythropoietic, tissue-protective compound derived from EPO, by using human umbilical vein endothelial cells (HUVECs) and human monocytic THP-1 cells in vitro and Watanabe heritable hyperlipidemic spontaneous myocardial infarction (WHHLMI) rabbits in vivo. In HUVECs, HBSP inhibited apoptosis (≈70%) induced by C-reactive protein (CRP), a direct mediator of atherosclerosis. By using a small interfering RNA approach, Akt was shown to be a key molecule in HBSP-mediated prevention of apoptosis. HBSP also attenuated CRP-induced production of tumor necrosis factor (TNF)-α and matrix metalloproteinase-9 in THP-1 cells. In the WHHLMI rabbit, HBSP significantly suppressed progression of coronary atherosclerotic lesions as assessed by mean cross-sectional stenosis (HBSP 21.3 ± 2.2% versus control peptide 38.0 ± 2.7%) and inhibited coronary artery endothelial cell apoptosis with increased activation of Akt. Furthermore, TNF-α expression and the number of M1 macrophages and M1/M2 macrophage ratio in coronary atherosclerotic lesions were markedly reduced in HBSP-treated animals. In conclusion, these data demonstrate that HBSP suppresses coronary atherosclerosis, in part by inhibiting endothelial cell apoptosis through activation of Akt and in association with decreased TNF-α production and modified macrophage polarization in coronary atherosclerotic lesions. Because HBSP does not have the prothrombotic effects of EPO, our study may provide a novel therapeutic strategy that prevents progression of coronary artery disease.

Activation of TRPV1 prevents OxLDL-induced lipid accumulation and TNF-α-induced inflammation in macrophages: role of liver X receptor α

The transient receptor potential vanilloid type 1 (TRPV1) is crucial in the pathogenesis of atherosclerosis; yet its role and underlying mechanism in the formation of macrophage foam cells remain unclear. Here, we show increased TRPV1 expression in the area of foamy macrophages in atherosclerotic aortas of apolipoprotein E-deficient mice. Exposure of mouse bone-marrow-derived macrophages to oxidized low-density lipoprotein (oxLDL) upregulated the expression of TRPV1. In addition, oxLDL activated TRPV1 and elicited calcium (Ca²⁺) influx, which were abrogated by the pharmacological TRPV1 antagonist capsazepine. Furthermore, oxLDL-induced lipid accumulation in macrophages was ameliorated by TRPV1 agonists but exacerbated by TRPV1 antagonist. Treatment with TRPV1 agonists did not affect the internalization of oxLDL but promoted cholesterol efflux by upregulating the efflux ATP-binding cassette (ABC) transporters ABCA1 and ABCG1. Moreover, the upregulation of ABC transporters was mainly through liver X receptor α- (LXRα-) dependent regulation of transcription. Moreover, the TNF-α-induced inflammatory response was alleviated by TRPV1 agonists but aggravated by the TRPV1 antagonist and LXRα siRNA in macrophages. Our data suggest that LXRα plays a pivotal role in TRPV1-activation-conferred protection against oxLDL-induced lipid accumulation and TNF-α-induced inflammation in macrophages.

Kaempferol suppresses lipid accumulation in macrophages through the downregulation of cluster of differentiation 36 and the upregulation of scavenger receptor class B type I and ATP-binding cassette transporters A1 and G1

The accumulation of foam cells in atherosclerotic lesions is a hallmark of early-stage atherosclerosis. Kaempferol has been shown to inhibit oxidized low-density lipoprotein (oxLDL) uptake by macrophages; however, the underlying molecular mechanisms are not yet fully investigated. In this study, we shown that treatment with kaempferol markedly suppresses oxLDL-induced macrophage foam cell formation, which occurs due to a decrease in lipid accumulation and an increase in cholesterol efflux from THP-1-derived macrophages. Additionally, the kaempferol treatment of macrophages led to the downregulation of cluster of differentiation 36 (CD36) protein levels, the upregulation of ATP-binding cassette (ABC) transporter A1 (ABCA1), scavenger receptor class B type I (SR-BI) and ABCG1 protein levels, while no effects on scavenger receptor A (SR-A) expression were observed. Kaempferol had similar effects on the mRNA and protein expression of ABCA1, SR-BI, SR-A, CD36 and ABCG1. The reduced CD36 expression following kaempferol treatment involved the inhibition of c-Jun-activator protein-1 (AP-1) nuclear translocation. The inhibition of AP-1 using the inhibitor, SP600125, confirmed this involvement, as the AP-1 inhibition significantly augmented the kaempferol-induced reduction in CD36 expression. Accordingly, the kaempferol-mediated suppression of lipid accumulation in macrophages was also augmented by SP600125. The increased expression of ABCA1, SR-BI and ABCG1 following kaempferol treatment was accompanied by the enhanced protein expression of heme oxygenase-1 (HO-1). This increase was reversed following the knockdown of the HO-1 gene using small hairpin RNA (shRNA). Moreover, the kaempferol-mediated attenuation of lipid accumulation and the promotion of cholesterol efflux was also inhibited by HO-1 shRNA. In conclusion, the c-Jun-AP‑1-dependent downregulation of CD36 and the HO-1-dependent upregulation of ABCG1, SR-BI and ABCA1 may mediate the beneficial effects of kaempferol on foam cell formation.

Liver X receptors, atherosclerosis and inflammation

Liver X receptors (LXRs) belong to the nuclear receptor superfamily of ligand-dependent transcription factors. LXRs are activated by oxysterols, metabolites of cholesterol, and therefore act as intracellular sensors of this lipid. There are two LXR genes (α and β) that display distinct tissue/cell expression profiles. LXRs interact with regulatory sequences in target genes as heterodimers with retinoid X receptor. Such direct targets of LXR actions include important genes implicated in the control of lipid homeostasis, particularly reverse cholesterol transport. In addition, LXRs attenuate the transcription of genes associated with the inflammatory response indirectly by transrepression. In this review, we describe recent evidence that both highlights the key roles of LXRs in atherosclerosis and inflammation and provides novel insights into the mechanisms underlying their actions. In addition, we discuss the major limitations of LXRs as therapeutic targets for the treatment of atherosclerosis and how these are being addressed.

Genetics of cholesterol efflux

Plasma levels of high-density lipoprotein cholesterol (HDL-C) show an inverse association with coronary heart disease (CHD). As a biological trait, HDL-C is strongly genetically determined, with a heritability index ranging from 40 % to 60 %. HDL represents an appealing therapeutic target due to its beneficial pleiotropic effects in preventing CHD. This review focuses on the genetic basis of cellular cholesterol efflux, the rate-limiting step in HDL biogenesis. There are several monogenic disorders (e.g., Tangier disease, caused by mutations within ABCA1) affecting HDL biogenesis. Importantly, many disorders of cellular cholesterol homeostasis cause a reduced HDL-C. We integrate information from family studies and linkage analyses with that derived from genome-wide association studies (GWAS) and review the recent identification of micro-RNAs (miRNA) involved in cellular cholesterol metabolism. The identification of genomic pathways related to HDL may help pave the way for novel therapeutic approaches to promote cellular cholesterol efflux as a therapeutic modality to prevent atherosclerosis.

AMP-activated protein kinase mediates erythropoietin-induced activation of endothelial nitric oxide synthase

We investigated whether AMP-activated protein kinase (AMPK), a multi-functional regulator of energy homeostasis, participates in the regulation of erythropoietin (EPO)-mediated activation of endothelial nitric oxide synthase (eNOS) in endothelial cells (ECs) and mice. In ECs, treatment with EPO increased the phosphorylation of AMPK, acetyl-CoA carboxylase (ACC), and eNOS, as revealed by Western blot analysis. Inhibition of AMPK activation by compound C or dominant-negative AMPK mutant abrogated the EPO-induced increase in the phosphorylation of AMPK, ACC, and eNOS, as well as nitric oxide (NO) production. Additionally, suppression of AMPK activation abolished EPO-induced EC proliferation, migration and tube formation. Immunoprecipitation analysis demonstrated that AMPK mediated the EPO-induced increase in the phosphorylation of β common receptor (βCR) and the formation of a βCR-AMPK-eNOS complex. In mice, inhibition of AMPK activation by compound C markedly decreased EPO-elicited angiogenesis in Matrigel plugs. Furthermore, the phosphorylation of AMPK and eNOS was significantly higher in aortas from EPO transgenic mice than wild-type mice. Moreover, treatment with EPO neutralizing antibody greatly reduced the exercise training-induced increase in phosphorylation of AMPK and eNOS in aortas of wild-type mice. Taken together, EPO may trigger AMPK-dependent signaling, which leads to enhanced phosphorylation of βCR and eNOS, increased βCR-AMPK-eNOS complex formation, NO production, and, ultimately, angiogenesis.

α-Lipoic acid ameliorates foam cell formation via liver X receptor α-dependent upregulation of ATP-binding cassette transporters A1 and G1

α-Lipoic acid (α-LA), a key cofactor in cellular energy metabolism, has protective activities in atherosclerosis, yet the detailed mechanisms are not fully understood. In this study, we examined whether α-LA affects foam cell formation and its underlying molecular mechanisms in murine macrophages. Treatment with α-LA markedly attenuated oxidized low-density lipoprotein (oxLDL)-mediated cholesterol accumulation in macrophages, which was due to increased cholesterol efflux. Additionally, α-LA treatment dose-dependently increased protein levels of ATP-binding cassette transporter A1 (ABCA1) and ABCG1 but had no effect on the protein expression of SR-A, CD36, or SR-BI involved in cholesterol homeostasis. Furthermore, α-LA increased the mRNA expression of ABCA1 and ABCG1. The upregulation of ABCA1 and ABCG1 by α-LA depended on liver X receptor α (LXRα), as evidenced by an increase in the nuclear levels of LXRα and LXRE-mediated luciferase activity and its prevention of the expression of ABCA1 and ABCG1 after inhibition of LXRα activity by the pharmacological inhibitor geranylgeranyl pyrophosphate (GGPP) or knockdown of LXRα expression with small interfering RNA (siRNA). Consistently, α-LA-mediated suppression of oxLDL-induced lipid accumulation was abolished by GGPP or LXRα siRNA treatment. In conclusion, LXRα-dependent upregulation of ABCA1 and ABCG1 may mediate the beneficial effect of α-LA on foam cell formation.