Patients with elevated levels of lipoprotein(a) Lp(a) are hallmarked by increased metabolic activity in the arterial wall on positron emission tomography/computed tomography, indicative of a ...proinflammatory state.
We hypothesized that Lp(a) induces endothelial cell inflammation by rewiring endothelial metabolism.
We evaluated the impact of Lp(a) on the endothelium and describe that Lp(a), through its oxidized phospholipid content, activates arterial endothelial cells, facilitating increased transendothelial migration of monocytes. Transcriptome analysis of Lp(a)-stimulated human arterial endothelial cells revealed upregulation of inflammatory pathways comprising monocyte adhesion and migration, coinciding with increased 6-phophofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB)-3-mediated glycolysis. ICAM (intercellular adhesion molecule)-1 and PFKFB3 were also found to be upregulated in carotid plaques of patients with elevated levels of Lp(a). Inhibition of PFKFB3 abolished the inflammatory signature with concomitant attenuation of transendothelial migration.
Collectively, our findings show that Lp(a) activates the endothelium by enhancing PFKFB3-mediated glycolysis, leading to a proadhesive state, which can be reversed by inhibition of glycolysis. These findings pave the way for therapeutic agents targeting metabolism aimed at reducing inflammation in patients with cardiovascular disease.
Mendelian randomization studies revealed a causal role for remnant cholesterol in cardiovascular disease. Remnant particles accumulate in the arterial wall, potentially propagating local and systemic ...inflammation. We evaluated the impact of remnant cholesterol on arterial wall inflammation, circulating monocytes, and bone marrow in patients with familial dysbetalipoproteinemia (FD).
Arterial wall inflammation and bone marrow activity were measured using
F-FDG PET/CT. Monocyte phenotype was assessed with flow cytometry. The correlation between remnant levels and hematopoietic activity was validated in the CGPS (Copenhagen General Population Study). We found a 1.2-fold increase of
F-FDG uptake in the arterial wall in patients with FD (n=17, age 60±8 years, remnant cholesterol: 3.26 2.07-5.71) compared with controls (n=17, age 61±8 years, remnant cholesterol 0.29 0.27-0.40;
<0.001). Monocytes from patients with FD showed increased lipid accumulation (lipid-positive monocytes: Patients with FD 92% 86-95, controls 76% 66-81,
=0.001, with an increase in lipid droplets per monocyte), and a higher expression of surface integrins (CD11b, CD11c, and CD18). Patients with FD also exhibited monocytosis and leukocytosis, accompanied by a 1.2-fold increase of
F-FDG uptake in bone marrow. In addition, we found a strong correlation between remnant levels and leukocyte counts in the CGPS (n=103 953,
for trend 5×10-276). In vitro experiments substantiated that remnant cholesterol accumulates in human hematopoietic stem and progenitor cells coinciding with myeloid skewing.
Patients with FD have increased arterial wall and cellular inflammation. These findings imply an important inflammatory component to the atherogenicity of remnant cholesterol, contributing to the increased cardiovascular disease risk in patients with FD.
Abstract
Aims
Elevated lipoprotein(a) Lp(a) is strongly associated with an increased cardiovascular disease (CVD) risk. We previously reported that pro-inflammatory activation of circulating ...monocytes is a potential mechanism by which Lp(a) mediates CVD. Since potent Lp(a)-lowering therapies are emerging, it is of interest whether patients with elevated Lp(a) experience beneficial anti-inflammatory effects following large reductions in Lp(a).
Methods and results
Using transcriptome analysis, we show that circulating monocytes of healthy individuals with elevated Lp(a), as well as CVD patients with increased Lp(a) levels, both have a pro-inflammatory gene expression profile. The effect of Lp(a)-lowering on gene expression and function of monocytes was addressed in two local sub-studies, including 14 CVD patients with elevated Lp(a) who received apolipoprotein(a) apo(a) antisense (AKCEA-APO(a)-LRx) (NCT03070782), as well as 18 patients with elevated Lp(a) who received proprotein convertase subtilisin/kexin type 9 antibody (PCSK9ab) treatment (NCT02729025). AKCEA-APO(a)-LRx lowered Lp(a) by 47% and reduced the pro-inflammatory gene expression in monocytes of CVD patients with elevated Lp(a), which coincided with a functional reduction in transendothelial migration capacity of monocytes ex vivo (−17%, P < 0.001). In contrast, PCSK9ab treatment lowered Lp(a) by 16% and did not alter transcriptome nor functional properties of monocytes, despite an additional reduction of 65% in low-density lipoprotein cholesterol (LDL-C).
Conclusion
Potent Lp(a)-lowering following AKCEA-APO(a)-LRx, but not modest Lp(a)-lowering combined with LDL-C reduction following PCSK9ab treatment, reduced the pro-inflammatory state of circulating monocytes in patients with elevated Lp(a). These ex vivo data support a beneficial effect of large Lp(a) reductions in patients with elevated Lp(a).
Migration of monocytes into the arterial wall contributes to arterial inflammation and atherosclerosis progression. Since elevated low-density lipoprotein cholesterol (LDL-C) levels have been ...associated with activation of plasma monocytes, intensive LDL-C lowering may reverse these pro-inflammatory changes. Using proprotein convertase subtilisin/kexin type 9 (PCSK9) monoclonal antibodies (mAbs) which selectively reduce LDL-C, we studied the impact of LDL-C lowering on monocyte phenotype and function in patients with familial hypercholesterolaemia (FH) not using statins due to statin-associated muscle symptoms.
We assessed monocyte phenotype and function using flow cytometry and a trans-endothelial migration assay in FH patients (n = 22: LDL 6.8 ± 1.9 mmol/L) and healthy controls (n = 18, LDL 2.9 ± 0.8 mmol/L). Monocyte chemokine receptor (CCR) 2 expression was approximaterly three-fold higher in FH patients compared with controls. C-C chemokine receptor type 2 (CCR2) expression correlated significantly with plasma LDL-C levels (r = 0.709) and was positively associated with intracellular lipid accumulation. Monocytes from FH patients also displayed enhanced migratory capacity ex vivo. After 24 weeks of PCSK9 mAb treatment (n = 17), plasma LDL-C was reduced by 49%, which coincided with reduced intracellular lipid accumulation and reduced CCR2 expression. Functional relevance was substantiated by the reversal of enhanced migratory capacity of monocytes following PCSK9 mAb therapy.
Monocytes of FH patients have a pro-inflammatory phenotype, which is dampened by LDL-C lowering by PCSK9 mAb therapy. LDL-C lowering was paralleled by reduced intracellular lipid accumulation, suggesting that LDL-C lowering itself is associated with anti-inflammatory effects on circulating monocytes.
Lipoproteins are important regulators of hematopoietic stem and progenitor cell (HSPC) biology, predominantly affecting myelopoiesis. Since myeloid cells, including monocytes and macrophages, promote ...the inflammatory response that propagates atherosclerosis, it is of interest whether the atherogenic low-density lipoprotein (LDL)-like particle lipoprotein(a) Lp(a) contributes to atherogenesis via stimulating myelopoiesis.
To assess the effects of Lp(a)-priming on long-term HSPC behavior we transplanted BM of Lp(a) transgenic mice, that had been exposed to elevated levels of Lp(a), into lethally-irradiated C57Bl6 mice and hematopoietic reconstitution was analyzed. No differences in HSPC populations or circulating myeloid cells were detected ten weeks after transplantation. Likewise, in vitro stimulation of C57Bl6 BM cells for 24 h with Lp(a) did not affect colony formation, total cell numbers or myeloid populations 7 days later.
To assess the effects of elevated levels of Lp(a) on myelopoiesis, C57Bl6 bone marrow (BM) cells were stimulated with lp(a) for 24 h, and a marked increase in granulocyte-monocyte progenitors, pro-inflammatory Ly6high monocytes and macrophages was observed. Seven days of continuous exposure to Lp(a) increased colony formation and enhanced the formation of pro-inflammatory monocytes and macrophages. Antibody-mediated neutralization of oxidized phospholipids abolished the Lp(a)-induced effects on myelopoiesis.
Lp(a) enhances the production of inflammatory monocytes at the bone marrow level but does not induce cell-intrinsic long-term priming of HSPCs. Given the short-term and direct nature of this effect, we postulate that Lp(a)-lowering treatment has the capacity to rapidly revert this multi-level inflammatory response.
•Lp(a) does not induce intrinsic priming of hematopoietic stem and progenitor cells.•Lp(a) enhances the production of inflammatory monocytes at the bone marrow level.•Lp(a)-lowering treatment may rapidly revert this multi-level inflammatory response.
The inflammatory profile of circulating monocytes is an important biomarker for atherosclerotic plaque vulnerability. Recent research revealed that peripheral lipid uptake by monocytes alters their ...phenotype toward an inflammatory state and this coincides with an increased lipid droplet (LD) content. Determination of lipid content of circulating monocytes is, however, not very well established. Based on Nile Red (NR) neutral LD imaging, using confocal microscopy and computational analysis, we developed NR Quantifier (NRQ), a novel quantification method to assess LD content in monocytes. Circulating monocytes were isolated from blood and used for the NR staining procedure. In monocytes stained with NR, we clearly distinguished, based on 3D imaging, phospholipids and exclusively intracellular neutral lipids. Next, we developed and validated NRQ, a semi-automated quantification program that detects alterations in lipid accumulation. NRQ was able to detect LD alterations after ex vivo exposure of isolated monocytes to freshly isolated LDL in a time- and dose-dependent fashion. Finally, we validated NRQ in patients with familial hypercholesterolemia and obese subjects in pre- and postprandial state. In conclusion, NRQ is a suitable tool to detect even small differences in neutral LD content in circulating monocytes using NR staining.
Aortic valve stenosis (AVS) is the most prevalent valvular heart disease in the Western World with exponentially increased incidence with age. If left untreated, the yearly mortality rates increase ...up to 25%. Currently, no effective pharmacological interventions have been established to treat or prevent AVS. The only treatment modality so far is surgical or transcatheter aortic valve replacement (AVR). Lipoprotein(a) Lp(a) has been implicated as a pivotal player in the pathophysiology of calcification of the valves. Patients with elevated levels of Lp(a) have a higher risk of hospitalization or mortality due to the presence of AVS. Multiple studies indicated Lp(a) as a likely causal and independent risk factor for AVS. This review discusses the most important findings and mechanisms related to Lp(a) and AVS in detail. During the progression of AVS, Lp(a) enters the aortic valve tissue at damaged sites of the valves. Subsequently, autotaxin converts lysophosphatidylcholine in lysophosphatidic acid (LysoPA) which in turn acts as a ligand for the LysoPA receptor. This triggers a nuclear factor-κB cascade leading to increased transcripts of interleukin 6, bone morphogenetic protein 2, and runt-related transcription factor 2. This progresses to the actual calcification of the valves through production of alkaline phosphatase and calcium depositions. Furthermore, this review briefly mentions potentially interesting therapies that may play a role in the treatment or prevention of AVS in the near future.
The endothelium is crucial for maintaining vascular homeostasis and functions as a barrier between blood components and tissue. In atherosclerosis, this barrier function is impaired, which is ...characterized by secretion of chemoattractants and cytokines, upregulation of adhesion molecules and increased vascular permeability. This facilitates enhanced leukocyte migration through the vessel wall. Fortunately, we can utilize these features to our advantage by using nanomedicine to deliver drugs and imaging tracers into the interstitial space. This provides us with targeted, local delivery of therapeutic agents, which enhances the specificity and efficacy of these agents and thus, could be used to inhibit disease progression. Additionally, delivery of imaging tracers in the interstitial space will give us insight into the vulnerability of atherosclerotic plaques by targeting resident macrophages and activated endothelial cells, providing pivotal information that is currently lacking in the clinic. In this review, we discuss how the endothelial barrier is affected during atherosclerosis and how to surmount this barrier for successful delivery of nanomedicine carrying drugs and imaging tracers to both the endothelium and macrophages.
Display omitted
•The endothelium serves as a refined barrier, crucial in guarding vascular homeostasis.•Impaired endothelial barrier function offers opportunities for targeted delivery of therapeutic agents/imaging tracers.•Nanosized technology provides the ability to distinguish between stable and rupture-prone atherosclerotic plaques.•The ‘Trojan Horse Strategy’ fools the endothelium and immune system in order to specifically deliver drugs at target sites.
6-phosphofructo-2-kinase/fructose-2,6-biphosphatase (PFKFB)3-mediated glycolysis is pivotal in driving macrophage- and endothelial cell activation and thereby inflammation. Once activated, these ...cells play a crucial role in the progression of atherosclerosis. Here, we analyzed the expression of PFKFB3 in human atherosclerotic lesions and investigated the therapeutic potential of pharmacological inhibition of PFKFB3 in experimental atherosclerosis by using the glycolytic inhibitor PFK158.
PFKFB3 expression was higher in vulnerable human atheromatous carotid plaques when compared to stable fibrous plaques and predominantly expressed in plaque macrophages and endothelial cells. Analysis of advanced plaques of human coronary arteries revealed a positive correlation of PFKFB3 expression with necrotic core area. To further investigate the role of PFKFB3 in atherosclerotic disease progression, we treated 6-8 weeks old male
mice. These mice were fed a high cholesterol diet for 13 weeks, of which they were treated for 5 weeks with the glycolytic inhibitor PFK158 to block PFKFB3 activity. The incidence of fibrous cap atheroma (advanced plaques) was reduced in PFK158-treated mice. Plaque phenotype altered markedly as both necrotic core area and intraplaque apoptosis decreased. This coincided with thickening of the fibrous cap and increased plaque stability after PFK158 treatment. Concomitantly, we observed a decrease in glycolysis in peripheral blood mononuclear cells compared to the untreated group, which alludes that changes in the intracellular metabolism of monocyte and macrophages is advantageous for plaque stabilization.
High PFKFB3 expression is associated with vulnerable atheromatous human carotid and coronary plaques. In mice, high PFKFB3 expression is also associated with a vulnerable plaque phenotype, whereas inhibition of PFKFB3 activity leads to plaque stabilization. This data implies that inhibition of inducible glycolysis may reduce inflammation, which has the ability to subsequently attenuate atherogenesis.
PDF
