Molecular imaging of experimental atherosclerosis using anti-malondialdehyde-modified low-density lipoprotein humanised antibody fragment targeted nanoparticles

Introduction

Oxidative modification of low-density lipoprotein (LDL), for example by malondialdehyde (MDA) adduction with subsequent uptake by macrophages to form foam cells and later the plaque necrotic core, is a key initiating event in atherogenesis. Accordingly, a larger lipid necrotic core is a key plaque vulnerability factor, predisposing plaques to rupture and subsequent thrombosis and development of an acute coronary syndrome. Thus, MDA-LDL is an attractive focus for the molecular targeting of atherosclerotic plaques.

Purpose

To develop antibody fragment-targeted nanoparticles that can be utilised for both the molecular imaging and therapeutics of vulnerable atherosclerotic plaques.

Methods

LO1 is an IgG3k natural monoclonal murine antibody that reacts with MDA-LDL. Humanised LO1Fab fragments have been engineered to reduce immunogenicity and improve lesion penetration. These humanised LO1Fab fragments were used to functionalise fluorescent poly(lactic-co-glycolic acid) (PLGA) - polyethylene glycol (PEG) nanoparticles. Nanoparticle in vitro function was assessed, prior to fluorescence molecular tomography (FMT) co-registered with micro-CT, four-hours after iv injection in atherosclerotic LDL-receptor−/− mice fed a high-fat diet for 40-weeks.

Results

Humanised LO1Fab fragment conjugated fluorescent PLGA-PEG nanoparticles were formulated with 210nm size and polydispersity index (variability of nanoparticle size around the average) of <0.2. Antibody conjugation efficiency was 30%. In vitro function was confirmed on ELISA versus the blank untargeted nanoparticles with MDA-LDL on solid phase, detecting nanoparticle presence via the conjugated LO1Fab, PEG corona or fluorescence. Fluorescence microscopy on stained aortic root cryosections from atherosclerotic mice confirmed binding to fatty lesions. Construct in vivo in half-life was 90-minutes for both the targeted and untargeted nanoparticles in a two-phase model in LDL-receptor−/− mice, based on fluorescence analysis of serial tail vein blood samples. There was greater uptake in the region-of-interest (heart and aortic arch vessels) in mice injected with LO1Fab-conjugated nanoparticles versus untargeted nanoparticles (mean ± standard deviation) (64.7±22.9 versus 25.2±26.5pmol of Cy5; n=7; p=0.02). Ex vivo analysis fluorescence reflectance imaging and quantitative FMT of the extracted aortae confirmed these findings (1.0±0.3 versus 0.5±0.2pmol of Cy5; n=7; p=0.002; Figure 1).

Conclusions

Humanised antibody Fab fragment fluorescent nanoparticles have been developed that successfully target MDA-LDL and localise to atherosclerotic plaques in murine experimental atherosclerosis. These targeted nanoparticles have the potential to amplify fluorescent signal for imaging and carry a therapeutic cargo for targeted drug delivery direct to atherosclerotic plaques.

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Wellcome Trust Clinical Research Fellowship

The transcription factor ERG regulates a low shear stress-induced anti-thrombotic pathway in the microvasculature

Endothelial cells actively maintain an anti-thrombotic environment; loss of this protective function may lead to thrombosis and systemic coagulopathy. The transcription factor ERG is essential to maintain endothelial homeostasis. Here, we show that inducible endothelial ERG deletion (ErgiEC-KO) in mice is associated with spontaneous thrombosis, hemorrhages and systemic coagulopathy. We find that ERG drives transcription of the anticoagulant thrombomodulin (TM), as shown by reporter assays and chromatin immunoprecipitation. TM expression is regulated by shear stress (SS) via Krüppel-like factor 2 (KLF2). In vitro, ERG regulates TM expression under low SS conditions, by facilitating KLF2 binding to the TM promoter. However, ERG is dispensable for TM expression in high SS conditions. In ErgiEC-KO mice, TM expression is decreased in liver and lung microvasculature exposed to low SS but not in blood vessels exposed to high SS. Our study identifies an endogenous, vascular bed-specific anticoagulant pathway in microvasculature exposed to low SS.

Domain I of β2GPI is capable of blocking serum IgA antiphospholipid antibodies binding in vitro: an effect enhanced by PEGylation

Objectives

This study aims to inhibit antiphospholipid syndrome (APS) serum derived IgA anti-beta-2-glycoprotein I (aβ2GPI) binding using Domain I (DI).

Methods

Serum from 13 APS patients was tested for IgA aβ2GPI and Anti-Domain I. Whole IgA was purified by peptide M affinity chromatography from positive serum samples. Serum was tested for IgA aβ2GPI binding in the presence and absence of either DI or of two biochemically modified variants containing either 20 kDa of poly(ethylene glycol) (PEG) or 40 kDa of PEG.

Results

Significant inhibition with DI was possible with average inhibition of 23% (N = 13). Further inhibitions using 20 kDa PEG-DI and 40 kDa PEG-DI variants showed significant inhibition (p = 0.0001) with both the 40 kDa PEG-DI and 20 kDa PEG-DI variants showing increased inhibition compared with DI alone (p = 0.0001 and p = 0.001, n = 10).

Conclusions

Inhibition of IgA aβ2GPI by DI is possible and can be enhanced by biochemical modification in a subset of patients.

Domain I: the hidden face of antiphospholipid syndrome

IgG antiphospholipid antibodies (aPL) against β2-glycoprotein I (β2GPI) can target any of its five domains; however, aPL against the N-terminal domain (anti-DI, aDI) are considered the most clinically relevant in the antiphospholipid syndrome (APS). Circulating levels of aDI are elevated in patients with APS compared with disease and healthy controls, and crucially aDI are prothrombotic in in vivo and in vitro models. In addition, human recombinant DI has been shown to abrogate aPL-induced thrombosis in vivo. Therefore, although the potential of utilizing DI for management of APS is not yet fully defined, there is promise that DI could prove valuable both as a diagnostic and therapeutic tool.

Are endothelial microparticles potential markers of vascular dysfunction in the antiphospholipid syndrome?

Vascular dysfunction is key to the development of thrombosis in the antiphospholipid syndrome. This has been largely demonstrated by the upregulation of various cell surface and intracellular signalling molecules, as well as proinflammatory cytokine release from activated endothelial cells. Endothelial microparticles (EMP) are a further marker of endothelial activation but have been less extensively studied. We summarise evidence suggesting that these microparticles may be critical effectors of thrombosis in the antiphospholipid syndrome. There is evidence that levels of EMP are raised in patients with circulating antiphospholipid antibodies and that these EMP may be prothrombotic. The balance between markers of endothelial dysfunction (including EMP and circulating endothelial cells) and markers of repair such as circulating endothelial progenitor cells may be abnormal in patients with APS but this has not been proved and requires further study.

In vivo inhibition of antiphospholipid antibody-induced pathogenicity utilizing the antigenic target peptide domain I of beta2-glycoprotein I: proof of concept

SUMMARY OBJECTIVES

In the antiphospholipid syndrome (APS), the immunodominant epitope for the majority of circulating pathogenic antiphospholipid antibodies (aPLs) is the N-terminal domain I (DI) of beta(2)-glycoprotein I. We have previously shown that recombinant DI inhibits the binding of aPLs in fluid phase to immobilized native antigen, and that this inhibition is greater with the DI(D8S/D9G) mutant and absent with the DI(R39S) mutant. Hence, we hypothesized that DI and DI(D8S/D9G) would inhibit aPL-induced pathogenicity in vivo.

METHODS

C57BL/6 mice (n = 5, each group) were injected with purified IgG derived from APS patients (IgG-APS, 500 microg) or IgG from normal healthy serum (IgG-NHS) and either recombinant DI, DI(R39S), DI(D8S/D9G), or an irrelevant control peptide (at 10-40 microg). Outcome variables measured were femoral vein thrombus dynamics in treated and control groups following standardized vessel injury, expression of vascular cell adhesion molecule-1 (VCAM-1) on the aortic endothelial surface, and tissue factor (TF) activity in murine macrophages.

RESULTS

IgG-APS significantly increased thrombus size as compared with IgG-NHS. The IgG-APS thrombus enhancement effect was abolished in mice pretreated with recombinant DI (P

CONCLUSION

Our findings in this proof-of-concept study support the development of recombinant DI or the novel variant DI(D8S/D9G) as a potential future therapeutic agent for APS.

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MESH Headings

• Animals
• Antibodies, Antiphospholipid/immunology
• Antibodies, Antiphospholipid/physiology
• Enzyme-Linked Immunosorbent Assay
• Macrophages, Peritoneal/metabolism
• Mice
• Mice, Inbred C57BL
• Thromboplastin/metabolism
• beta 2-Glycoprotein I/chemistry
• beta 2-Glycoprotein I/metabolism

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Grants

• R01 AR056745 NIAMS NIH HHS
• Arthritis Research UK

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