Aspirin regulates expression and function of scavenger receptor‐BI in macrophages: studies in primary human macrophages and in mice

Current and future therapies for addressing the effects of inflammation on HDL cholesterol metabolism

Cardiovascular disease (CVD) is a major cause of morbidity and mortality worldwide. Inflammatory processes arising from metabolic abnormalities are known to precipitate the development of CVD. Several metabolic and inflammatory markers have been proposed for predicting the progression of CVD, including high density lipoprotein cholesterol (HDL-C). For ~50 years, HDL-C has been considered as the atheroprotective 'good' cholesterol because of its strong inverse association with the progression of CVD. Thus, interventions to increase the concentration of HDL-C have been successfully tested in animals; however, clinical trials were unable to confirm the cardiovascular benefits of pharmaceutical interventions aimed at increasing HDL-C levels. Based on these data, the significance of HDL-C in the prevention of CVD has been called into question. Fundamental in vitro and animal studies suggest that HDL-C functionality, rather than HDL-C concentration, is important for the CVD-preventive qualities of HDL-C. Our current review of the literature positively demonstrates the negative impact of systemic and tissue (i.e. adipose tissue) inflammation in the healthy metabolism and function of HDL-C. Our survey indicates that HDL-C may be a good marker of adipose tissue health, independently of its atheroprotective associations. We summarize the current findings on the use of anti-inflammatory drugs to either prevent HDL-C clearance or improve the function and production of HDL-C particles. It is evident that the therapeutic agents currently available may not provide the optimal strategy for altering HDL-C metabolism and function, and thus, further research is required to supplement this mechanistic approach for preventing the progression of CVD.

LINKED ARTICLES

This article is part of a themed section on Targeting Inflammation to Reduce Cardiovascular Disease Risk. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.22/issuetoc and http://onlinelibrary.wiley.com/doi/10.1111/bcp.v82.4/issuetoc.

Paradoxical Increase in Mortality and Rupture of Intracranial Aneurysms in Microsomal Prostaglandin E2 Synthase Type 1-Deficient Mice: Attenuation by Aspirin

BACKGROUND

Inflammation plays an important role in formation and rupture of intracranial aneurysms. Expression of microsomal prostaglandin E2 (PGE2) synthase type 1 (mPGES-1) is increased in the wall of intracranial aneurysms in humans. PGE2, a by-product of mPGES-1, is associated with inflammation and cerebrovascular dysfunction.

OBJECTIVE

To test the hypothesis that deletion of mPGES-1 decreases the formation and rupture of intracranial aneurysms in a murine model.

METHODS

Intracranial aneurysms were induced in wild-type and mPGES-1 knockout (mPGES-1 KO) mice by using a combination of deoxycorticosterone acetate-salt-induced hypertension and intracranial injection of elastase in the basal cistern. Prevalence of aneurysms, subarachnoid hemorrhage, and mortality were assessed. We also tested the effects of administration of aspirin (6 mg/kg/d) by gavage and PGE2 (1 mg/kg/d) by subcutaneous infusion.

RESULTS

Systolic blood pressure and prevalence of aneurysm were similar in wild-type and mPGES-1 KO mice. However, mortality and the prevalence of subarachnoid hemorrhage were markedly increased in mPGES-1 KO mice (P < .05). Bone marrow reconstitution studies suggest that mPGES-1 derived from leukocytes does not appear to increase rupture of intracranial aneurysms. Aspirin, but not PGE2, attenuated the increased mortality in mPGES-1 KO mice (P < .05).

CONCLUSION

Vascular mPGES-1 plays a protective role in blood vessels and attenuates rupture of cerebral aneurysms. In contrast to effects on abdominal aneurysms, mPGES-1 deficiency is associated with an increase in rupture of cerebral aneurysms and mortality, which are attenuated by low-dose aspirin.

Macrophage SR-BI mediates efferocytosis via Src/PI3K/Rac1 signaling and reduces atherosclerotic lesion necrosis

Macrophage apoptosis and efferocytosis are key determinants of atherosclerotic plaque inflammation and necrosis. Bone marrow transplantation studies in ApoE- and LDLR-deficient mice revealed that hematopoietic scavenger receptor class B type I (SR-BI) deficiency results in severely defective efferocytosis in mouse atherosclerotic lesions, resulting in a 17-fold higher ratio of free to macrophage-associated dead cells in lesions containing SR-BI^−/− cells, 5-fold more necrosis, 65.2% less lesional collagen content, nearly 7-fold higher dead cell accumulation, and 2-fold larger lesion area. Hematopoietic SR-BI deletion elicited a maladaptive inflammatory response [higher interleukin (IL)-1β, IL-6, and TNF-α lower IL-10 and transforming growth factor β]. Efferocytosis of apoptotic thymocytes was reduced by 64% in SR-BI^−/− versus WT macrophages, both in vitro and in vivo. In response to apoptotic cells, macrophage SR-BI bound with phosphatidylserine and induced Src phosphorylation and cell membrane recruitment, which led to downstream activation of phosphoinositide 3-kinase (PI3K) and Ras-related C3 botulinum toxin substrate 1 (Rac1) for engulfment and clearance of apoptotic cells, as inhibition of Src decreased PI3K, Rac1-GTP, and efferocytosis in WT cells. Pharmacological inhibition of Rac1 reduced macrophage efferocytosis in a SR-BI-dependent fashion, and activation of Rac1 corrected the defective efferocytosis in SR-BI^−/− macrophages. Thus, deficiency of macrophage SR-BI promotes defective efferocytosis signaling via the Src/PI3K/Rac1 pathway, resulting in increased plaque size, necrosis, and inflammation.

The arachidonic acid metabolome serves as a conserved regulator of cholesterol metabolism

Cholesterol metabolism is closely interrelated with cardiovascular disease in humans. Dietary supplementation with omega-6 polyunsaturated fatty acids including arachidonic acid (AA) was shown to favorably affect plasma LDL-C and HDL-C. However, the underlying mechanisms are poorly understood. By combining data from a GWAS screening in >100,000 individuals of European ancestry, mediator lipidomics, and functional validation studies in mice, we identify the AA metabolome as an important regulator of cholesterol homeostasis. Pharmacological modulation of AA metabolism by aspirin induced hepatic generation of leukotrienes (LTs) and lipoxins (LXs), thereby increasing hepatic expression of the bile salt export pump Abcb11. Induction of Abcb11 translated in enhanced reverse cholesterol transport, one key function of HDL. Further characterization of the bioactive AA-derivatives identified LX mimetics to lower plasma LDL-C. Our results define the AA metabolomeasconserved regulator of cholesterol metabolism, and identify AA derivatives as promising therapeutics to treat cardiovascular disease in humans.

Influence of annexin A7 on insulin sensitivity of cellular glucose uptake

Insulin sensitivity is decreased by prostaglandin E2 (PGE2), a major product of cyclooxygenase (COX). As shown in erythrocytes, PGE2 formation is inhibited by annexin A7. The present study defined the role of annexin A7 in glucose metabolism. Gene-targeted mice lacking annexin A7 (annexin7 (-/-)) were compared to wild-type mice (annexin7 (+/+)). The serum 6-Keto-prostaglandin-F1α (6-Keto-PGF1α) concentration was measured by ELISA and hepatic COX activity determined by an enzyme assay. Expression of COX-1, COX-2, prostaglandin E synthase, GLUT-4, and insulin receptor was determined by Western blotting. Glucose and insulin serum concentrations were analyzed following an intraperitoneal glucose load and glucose serum levels after intraperitoneal injection of insulin. Experiments were done without and with pretreatment of the mice with COX-inhibitor aspirin. The serum 6-Keto-PGF1α level and hepatic COX activity were significantly higher in annexin7 (-/-) than in annexin7 (+/+) mice. Hepatic COX-1 expression was higher in annexin7 (-/-) mice. Glucose tolerance was decreased in annexin7 (-/-) mice. Intraperitoneal insulin injection decreased the serum glucose level in both genotypes, an effect significantly less pronounced in annexin7 (-/-) mice. Glucose-induced insulin secretion was higher in annexin7 (-/-) mice. GLUT-4 expression in skeletal muscle from annexin7 (-/-) mice was reduced. Aspirin pretreatment lowered the increase in insulin concentration following glucose injection in both genotypes and virtually abrogated the differences in serum insulin between the genotypes. Aspirin pretreatment improved glucose tolerance in annexin7 (-/-) mice. In conclusion, annexin A7 influences insulin sensitivity of cellular glucose uptake and thus glucose tolerance. These effects depend on COX activity.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

SNX3-dependent regulation of epidermal growth factor receptor (EGFR) trafficking and degradation by aspirin in epidermoid carcinoma (A-431) cells

Since being introduced globally as aspirin in 1899, acetylsalicylic acid has been widely used as an analgesic, anti-inflammation, anti-pyretic, and anti-thrombotic drug for years. Aspirin had been reported to down-regulate surface expression of CD40, CD80, CD86, and MHCII in myeloid dendritic cells (DC), which played essential roles in regulating the immune system. We hypothesized that the down-regulation of these surface membrane proteins is partly due to the ability of aspirin in regulating trafficking/sorting of endocytosed surface membrane proteins. By using an established epidermoid carcinoma cell line (A-431), which overexpresses the epidermal growth factor receptor (EGFR) and transferrin receptor (TfnR), we show that aspirin (1) reduces cell surface expression of EGFR and (2) accumulates endocytosed-EGFR and -TfnR in the early/sorting endosome (ESE). Further elucidation of the mechanism suggests that aspirin enhances recruitment of SNX3 and SNX5 to membranes and consistently, both SNX3 and SNX5 play essential roles in the aspirin-mediated accumulation of endocytosed-TfnR at the ESE. This study sheds light on how aspirin may down-regulate surface expression of EGFR by inhibiting/delaying the exit of endocytosed-EGFR from the ESE and recycling of endocytosed-EGFR back to the cell surface.

13-hydroxy linoleic acid increases expression of the cholesterol transporters ABCA1, ABCG1 and SR-BI and stimulates apoA-I-dependent cholesterol efflux in RAW264.7 macrophages

BACKGROUND

Synthetic activators of peroxisome proliferator-activated receptors (PPARs) stimulate cholesterol removal from macrophages through PPAR-dependent up-regulation of liver × receptor α (LXRα) and subsequent induction of cholesterol exporters such as ATP-binding cassette transporter A1 (ABCA1) and scavenger receptor class B type 1 (SR-BI). The present study aimed to test the hypothesis that the hydroxylated derivative of linoleic acid (LA), 13-HODE, which is a natural PPAR agonist, has similar effects in RAW264.7 macrophages.

METHODS

RAW264.7 macrophages were treated without (control) or with LA or 13-HODE in the presence and absence of PPARα or PPARγ antagonists and determined protein levels of LXRα, ABCA1, ABCG1, SR-BI, PPARα and PPARγ and apolipoprotein A-I mediated lipid efflux.

RESULTS

Treatment of RAW264.7 cells with 13-HODE increased PPAR-transactivation activity and protein concentrations of LXRα, ABCA1, ABCG1 and SR-BI when compared to control treatment (P < 0.05). In addition, 13-HODE enhanced cholesterol concentration in the medium but decreased cellular cholesterol concentration during incubation of cells with the extracellular lipid acceptor apolipoprotein A-I (P < 0.05). Pre-treatment of cells with a selective PPARα or PPARγ antagonist completely abolished the effects of 13-HODE on cholesterol efflux and protein levels of genes investigated. In contrast to 13-HODE, LA had no effect on either of these parameters compared to control cells.

CONCLUSION

13-HODE induces cholesterol efflux from macrophages via the PPAR-LXRα-ABCA1/SR-BI-pathway.

A time course study on prothrombotic parameters and their modulation by anti-platelet drugs in hyperlipidemic hamsters

The present study was undertaken to assess the chronology of major pathological events associated with high cholesterol (HC) diet and their modulation by anti-platelet drugs. Male Golden Syrian hamsters were fed HC diet up to 90 days. Plasma lipid, glucose and coagulation parameters (commercial kits), platelet activation (whole blood aggregation and static adhesion), endothelial dysfunction (aortic ring vasoreactivity), splenocyte TNF-α, IFN-γ and iNOS mRNA transcripts (RT-PCR), and ferric chloride (time to occlusion) induced thrombosis were monitored at 15, 30, 60, and 90 days after HC feeding and compared with normolipidemic hamsters. A significant increase in plasma lipid levels was observed at 15 days of HC feeding, but other parameters remain unaltered. Enhanced ADP, collagen, and thrombin-induced platelet aggregation, splenocyte TNF-α expression along with endothelial dysfunction were observed from 30 to 90 days of HC feeding. Platelet adhesion on collagen-/fibrinogen-coated surface and IFN-γ expression were augmented only after 60 days, while enhanced iNOS expression, reduction in thrombin time, and potentiation of ferric chloride-induced thrombosis was observed only at 90 days of HC feeding. Thus, pathological changes induced by HC diet depend on the duration and extent of hyperlipidemia. Moreover, hamsters treated with anti-platelet drugs aspirin (5 mg/kg) or clopidogrel (10 mg/kg) along with HC feeding exhibited reduction in platelet activation as well as subsequent changes observed in the abovementioned parameters following HC feeding. Since reduction in TNF-α was associated with reversion in endothelial dysfunction and prothrombotic state, the role of platelets is implicated in the pathological changes associated with HC feeding.

Influence of aspirin on SR-BI expression in human carotid plaques

BACKGROUND

We recently showed that aspirin promotes scavenger receptor class-B type I (SR-BI) protein expression in vitro in primary human macrophages and in vivo in resident peritoneal macrophages of mice.

METHODS

We compared SR-BI and CD68 expression in carotid atherosclerotic specimens from endarterectomized patients with (n=38) or without (n=19) low-dose aspirin medication (100 mg/day) prior to endarterectomy.

RESULTS

We found no differences concerning expression of CD68, indicating that aspirin did not influence macrophage content within atherosclerotic plaques. However, aspirin increased the expression of SR-BI protein in the analyzed specimens. In human THP-1-derived macrophages, induction of SR-BI protein by aspirin was abrogated by concomitant pharmacological inhibition of nuclear factor-kappa B (NF-kappaB). In in vitro experiments employing cultured primary macrophages from NF-kappaB/p50 KO mice, aspirin was not able to influence SR-BI expression. Additionally, no considerable effects on SR-BI expression were observed in vivo in resident macrophages of NF-kappaB/p50 KO mice orally treated with low or high doses of aspirin, respectively.

CONCLUSIONS

We suggest that aspirin treatment might lead to enhanced expression of SR-BI in human plaque macrophages and that this effect is dependent on the presence of NF-kappaB.

The thyromimetic T-0681 protects from atherosclerosis

This report describes studies in hyperlipidemic New Zealand White (NZW) rabbits investigating the impact of the liver-selective thyromimetic T-0681 on lipoprotein metabolism and the development of atherosclerosis. Prolonged treatment with T-0681 increased the hepatic expression of both LDL receptor and scavenger receptor class B, type I without affecting cholesteryl ester transfer protein activity. Upregulation of hepatic lipoprotein receptors was accompanied by a marked decrease of apolipoprotein B-containing lipoproteins, reflected by a 60% reduction of plasma cholesterol and a >70% reduction of plasma triglyceride levels. Most importantly, T-0681 reduced the development of atherosclerosis by 80% in NZW rabbits on high-cholesterol chow. Our data suggest that liver-selective thyromimetics, such as T-0681, may prove to be useful therapeutic agents against the development of atherosclerosis in humans.

The significantly enhanced frequency of functional CD4+CD25+Foxp3+ T regulatory cells in therapeutic dose aspirin-treated mice

CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells, produced in the thymus or periphery as a functionally mature T cell subpopulation, play pivotal roles in maintenance of self-tolerance and negative regulation of immune responses. Aspirin (ASA) is widely used to reduce pain, the risk of cardiovascular diseases and allo-graft rejection. However, the effect of ASA on CD4(+)CD25(+)Foxp3(+) Treg cells has yet to be determined. The frequency, phenotype and immunosuppressive function of CD4(+)CD25(+)Foxp3(+) Treg cells were detected in BALB/c mice treated with low or high doses of ASA for 4 weeks. ASA significantly decreased the percentage and number of CD4(+) T cells in the periphery, while ASA remarkably increased the percentage of CD4(+)CD25(+)Foxp3(+) Treg cells in CD4(+)T cells. The total cell numbers of thymocytes were significantly decreased in ASA-treated mice, but the number of CD4(+) CD25(+)Fxop3(+) cells and its ratio in CD4(+)CD8(-) thymocytes were markedly enhanced in the thymi of ASA-treated mice. The phenotype of CD4(+)CD25(+) Treg cells, including the expressions of CD44, CD45RB, CD62L, CD69, GITR and CTLA-4, did not show detectable changes in ASA-treated mice. CD4(+)CD25(+) Treg cells in ASA-treated mice exhibited unimpaired immunosuppressive function on CD4(+)CD25(-) T effector cells. ASA significantly enhanced the frequency of functional CD4(+)CD25(+)Foxp3(+) Treg cells in mice in a therapeutic dose range. The different effects of ASA on CD4(+)CD25(+)Foxp3(+) Treg cells and CD4(+)CD25(-) T cells may potentially make hosts susceptible to tolerance induction which would be beneficial for tolerance induction in patients with autoimmune diseases or allo-grafts. This study may have potential impacts in the clinical application of ASA.

Suppression of inflammatory signaling in monocytes from patients with coronary artery disease

Monocytes and T-cells play an important role in the development of atherosclerotic coronary artery disease (CAD). Transcriptome analysis of circulating mononuclear cells from carefully matched atherosclerotic and control patients will potentially provide insights into the pathophysiology of atherosclerosis and supply biomarkers for diagnostic purposes. From patients undergoing coronary angiography because of anginal symptoms, we carefully matched 18 patients with severe triple-vessel CAD to 13 control patients without angiographic signs of CAD. All patients were on statin and aspirin treatment. Elevated soluble-ICAM levels demonstrated increased vascular inflammation in atherosclerotic patients. RNA from circulating CD4+ T-cells, CD14+ monocytes, lipopolysaccharide-stimulated monocytes, and macrophages was subjected to genome-wide expression analysis. In CD14+ monocytes, few inflammatory genes were overexpressed in control patients, while atherosclerotic patients showed overexpression of a group of Krüppel-associated box - containing transcription factors involved in negative regulation of gene expression. These differences disappeared upon LPS-stimulation or differentiation towards macrophages. No consistent changes in T cell transcriptomes were detected. Large inter-individual variability prevented the use of single differentially expressed genes as biomarkers, while monocyte gene expression signature predicted patient status with an accuracy of 84%. In this comprehensive analysis of circulating cell transcriptomes in atherosclerotic CAD, cautious patient matching revealed only small differences in transcriptional activity in different mononuclear cell types. Only an indication of a negative feedback to inflammatory gene expression was detected in atherosclerotic patients. Transcriptome differences of circulating cells possibly play less of a role than hitherto thought in the individual patient's susceptibility to atherosclerotic CAD, when appropriately matched for clinical symptoms and medication taken.

Neurokinin-1 receptor blockade and murine lung tumorigenesis

RATIONALE

Analogous to the adenoma-carcinoma sequence in the colon, it has been proposed that adenocarcinoma (AC) in the lung arises from adenomatous hyperplasia that progresses through atypical adenomatous hyperplasia to AC. However, the data supporting this sequence are largely circumstantial and the almost impossible task of identifying these lesions before resection rules out any longitudinal study in humans.

OBJECTIVES, METHODS, AND RESULTS

We show in mice that the loss of function of the neurokinin-1 receptor (NK-1R)-due to either a pharmacologic or genetic manipulation-results in a sequence of morphologic changes in response to bleomycin treatment that precede the development of AC. We also demonstrate that a series of alterations in gene expression of proliferation markers (i.e., PCNA and Ki-67) and cell cycle regulators (i.e., FHIT, p53, and p21) characterizes the sequence of the precursor lesions. The loss of function of the NK-1R results in changes of the apoptotic rate and in a delay of DNA break recovery of alveolar epithelial cells following bleomycin treatment. The NK-1R blockade interferes with a caspase-independent pathway of apoptosis by affecting both the translocation of Nur77 into the cytoplasm and the expression of some important Bcl2 family members such as Bcl2 and Bak.

CONCLUSIONS

To our knowledge, this is the first model to demonstrate a role for NK-1R in lung epithelial cell death and tumorigenesis. This animal model may provide new information on the biology of AC and will facilitate designing and testing of new therapeutic interventions.