Platelet adhesion onto immobilized fibrinogen under arterial and venous in-vitro flow conditions does not significantly differ between men and women

Physicochemical Targeting of Lipid Nanoparticles to the Lungs Induces Clotting: Mechanisms and Solutions

Lipid nanoparticles (LNPs) have become the dominant drug delivery technology in industry, holding the promise to deliver RNA to up or down-regulate any protein of interest. LNPs have mostly been targeted to specific cell types or organs by physicochemical targeting in which LNP's lipid compositions are adjusted to find mixtures with the desired tropism. Here lung-tropic LNPs are examined, whose organ tropism derives from containing either a cationic or ionizable lipid conferring a positive zeta potential. Surprisingly, these LNPs are found to induce massive thrombosis. Such thrombosis is shown in the lungs and other organs, and it is shown that it is greatly exacerbated by pre-existing inflammation. This clotting is induced by a variety of formulations with cationic lipids, including LNPs and non-LNP nanoparticles, and even by lung-tropic ionizable lipids that do not have a permanent cationic charge. The mechanism depends on the LNPs binding to and then changing the conformation of fibrinogen, which then activates platelets and thrombin. Based on these mechanisms, multiple solutions are engineered that enable positively charged LNPs to target the lungs while ameliorating thrombosis. The findings illustrate how physicochemical targeting approaches must be investigated early for risks and re-engineered with a careful understanding of biological mechanisms.

Physicochemical Targeting of Lipid Nanoparticles to the Lungs Induces Clotting: Mechanisms and Solutions

Lipid nanoparticles (LNPs) have become the dominant drug delivery technology in industry, holding the promise to deliver RNA to up- or down-regulate any protein of interest. LNPs have been targeted to specific cell types or organs by physicochemical targeting, in which LNP's lipid compositions are adjusted to find mixtures with the desired tropism. In a popular approach, physicochemical targeting is accomplished by formulating with charged lipids. Negatively charged lipids localize LNPs to the spleen, and positively charged lipids to the lungs. Here we found that lung-tropic LNPs employing cationic lipids induce massive thrombosis. We demonstrate that thrombosis is induced in the lungs and other organs, and greatly exacerbated by pre-existing inflammation. This clotting is induced by a variety of formulations with cationic lipids, including LNPs and non-LNP nanoparticles. The mechanism depends on the LNPs binding to fibrinogen and inducing platelet and thrombin activation. Based on these mechanisms, we engineered multiple solutions which enable positively charged LNPs to target the lungs while not inducing thrombosis. Our findings implicate thrombosis as a major barrier that blood erects against LNPs with cationic components and illustrate how physicochemical targeting approaches must be investigated early for risks and re-engineered with a careful understanding of biological mechanisms.

Extracting Mural and Volumetric Growth Patterns of Platelet Aggregates on Engineered Surfaces by Use of an Entity Tracking Algorithm

Thrombosis is a major complication that can occur in both blood-contacting devices and regions and in regions of vascular damage. Microfluidic devices are popular templates to model various thrombogenic settings and to assess conditions that lead to bulk channel occlusion. However, area-averaged measurements miss the opportunity to extract real-time information on thrombus evolution and early dynamics of thrombus formation and propagation, which result in late-stage bulk channel occlusion. To clarify these dynamics, we have developed a standalone tracking algorithm that uses consecutive image connectivity and minimal centroid distance mappings to uniquely index all appearing thrombi in fluorescence time-lapse videos http://links.lww.com/ASAIO/A887 , and http://links.lww.com/ASAIO/A888 . This leads to measurements of all individual aggregates that can in turn be studied as ensembles. We applied tracking to fluorescence time-lapse videos http://links.lww.com/ASAIO/A887 , and http://links.lww.com/ASAIO/A888 of thrombosis across both collagen-functionalized substrate and across the surface of a roughened titanium alloy (Ti6Al4V) at a shear rate of 4000 s -1 . When comparing ensemble-averaged measurements to area-averaged metrics, we unveil immediate, steady thrombus growth at early phases on collagen surfaces and unstable thrombus attachment to roughened Ti6Al4V surfaces on Ti6Al4V surfaces. Additionally, we introduce tracked thrombus eccentricity and fluorescence intensity as additional volumetric measures of thrombus growth that relate back to the primary thrombosis mechanism at play. This work advocates for the complementation of surface macrostate metrics with characteristic thrombus microstate growth patterns to accurately predict critical thrombosis events.

A novel method for the collection of nanoscopic vesicles from an organotypic culture model

Nanovesicles, exosomes and other membrane bound particles excreted by cells are currently gaining research attention since they have been shown to play a significant role in many biologically related processes. Vesicles are now thought to mediate cellular communication, transmission of some diseases and pathologically mediated calcification. Matrix vesicles have long been proposed to be central to the controlled mineralisation of bone. They remain relatively poorly studied, however, since they are challenging to extract from biological media. One difficulty is the presence of a mineral content in comparison to pure lipid vesicles, meaning that standard separation process such as ultracentrifugation are unable to precisely separate on the basis of size or weight. In this paper we report the separation of matrix vesicles from an organotypic bone culture system using a process of immunoprecipitation. Matrix vesicles were extracted using polymeric beads that were modified with an antibody for tissue non-specific alkaline phosphatase (TNALP), a surface marker abundant in bone-derived vesicles. The vesicles isolated were positive for adenosine triphosphate (ATP), the substrate for TNALP and were demonstrated to have a high-binding affinity to type I collagen, the principal collagen type found in bone. This protocol enables more detailed study of the process and regulation of mineralisation.

Cellular nanovesicles have been shown to play a significant role in many biological processes. Organotypic bone culture systems are a source of physiologically-relevant mineralisation vesicles, which can be immuno-selected for investigation.

Standardization and reference ranges for whole blood platelet function measurements using a flow cytometric platelet activation test

Introduction

Platelet function testing with flow cytometry has additional value to existing platelet function testing for diagnosing bleeding disorders, monitoring anti-platelet therapy, transfusion medicine and prediction of thrombosis. The major challenge is to use this technique as a diagnostic test. The aim of this study is to standardize preparation, optimization and validation of the test kit and to determine reference values in a population of 129 healthy individuals.

Methods

Platelet function tests with 3 agonists and antibodies against P-selectin, activated αIIbβ3 and glycoprotein Ib (GPIb), were prepared and stored at -20°C until used. Diluted whole blood was added and platelet activation was quantified by the density of activation markers, using flow cytometry. Anti-mouse Ig κ particles were included to validate stability of the test and to standardize results. Reference intervals were determined.

Results

Blood stored at room temperature (RT) for up to 4h after blood donation and preheated/tested at 37°C resulted in stable results (%CV<10%), in contrast to measuring at RT. The intra-assay %CV was <5%. Incubation of anti-mouse Ig κ particles with antibodies stored for up to 12 months proved to give a stable fluorescence. The inter-individual variation measured in the 129 individuals varied between 23% and 37% for P-selectin expression and αIIbβ3 activation, respectively.

Conclusions

The current study contributes to the translation of flow cytometry based platelet function testing from a scientific tool to a diagnostic test. Platelet function measurements, using prepared and stored platelet activation kits, are reproducible if executed at 37°C. The reference ranges can be validated in clinical laboratories and ongoing studies are investigating if reduced platelet reactivity in patients with bleeding complications can be detected.

A novel culture device for the evaluation of three-dimensional extracellular matrix materials

Cell-matrix interactions in a three-dimensional (3D) extracellular matrix (ECM) are of fundamental importance in living tissue, and their in vitro reconstruction in bioartificial structures represents a core target of contemporary tissue engineering concepts. For a detailed analysis of cell-matrix interaction under highly controlled conditions, we developed a novel ECM evaluation culture device (EECD) that allows for a precisely defined surface-seeding of 3D ECM scaffolds, irrespective of their natural geometry. The effectiveness of EECD was evaluated in the context of heart valve tissue engineering. Detergent decellularized pulmonary cusps were mounted in EECD and seeded with endothelial cells (ECs) to study EC adhesion, morphology and function on a 3D ECM after 3, 24, 48 and 96 h. Standard EC monolayers served as controls. Exclusive top-surface-seeding of 3D ECM by viable ECs was demonstrated by laser scanning microscopy (LSM), resulting in a confluent re-endothelialization of the ECM after 96 h. Cell viability and protein expression, as demonstrated by MTS assay and western blot analysis (endothelial nitric oxide synthase, von Willebrand factor), were preserved at maintained levels over time. In conclusion, EECD proves as a highly effective system for a controlled repopulation and in vitro analysis of cell-ECM interactions in 3D ECM.