Alternative Methods for the Detection of Superoxide Anion Generation in Platelets

Summary

The generation of superoxide anion is essential for the stimulation of platelets and, if dysregulated, critical for thrombotic diseases. Here, we present three protocols for the selective detection of superoxide anions and the study of redox-dependent platelet regulation.

Abstract

Reactive oxygen species (ROS) are highly unstable oxygen-containing molecules. Their chemical instability makes them extremely reactive and gives them the ability to react with important biological molecules such as proteins, nucleic acids, and lipids. Superoxide anions are important ROS generated by the reduction of molecular oxygen reduction (i.e., acquisition of one electron). Despite their initial implication exclusively in aging, degenerative, and pathogenic processes, their participation in important physiological responses has recently become apparent. In the vascular system, superoxide anions have been shown to modulate the differentiation and function of vascular smooth muscle cells, the proliferation and migration of vascular endothelial cells in angiogenesis, the immune response, and the activation of platelets in hemostasis. The role of superoxide anions is particularly important in the dysregulation of platelets and the cardiovascular complications associated with a plethora of conditions, including cancer, infection, inflammation, diabetes, and obesity. It has, therefore, become extremely relevant in cardiovascular research to be able to effectively measure the generation of superoxide anions by human platelets, understand the redox-dependent mechanisms regulating the balance between hemostasis and thrombosis and, eventually, identify novel pharmacological tools for the modulation of platelet responses leading to thrombosis and cardiovascular complications. This study presents three experimental protocols successfully adopted for the detection of superoxide anions in platelets and the study of the redox-dependent mechanisms regulating hemostasis and thrombosis: 1) dihydroethidium (DHE)-based superoxide anion detection by flow cytometry; 2) DHE-based superoxide anion visualization and analysis by single platelet imaging; and 3) spin probe-based quantification of superoxide anion output in platelets by electron paramagnetic resonance (EPR).

Introduction

The superoxide anion (O₂^•-) is the most functionally relevant ROS generated in platelets¹. O₂^•- is the product of the reduction of molecular oxygen and the precursor of many different ROS ². The dismutation of O₂^•- leads to the generation of hydrogen peroxide (H₂O₂) via spontaneous reactions in aqueous solution or reactions catalyzed by superoxide dismutases (SODs³). Although different enzymatic sources have been suggested (e.g., xanthine oxidase⁴, lipoxygenase

Protocol

The collection of peripheral blood from consenting volunteers is approved by the local Ethics Committee and the National Health Service Health Research Authority (REC reference: 21/SC/0215; IRAS ID: 283854).

1. Method 1: Superoxide anion detection using DHE by flow cytometry

1. Pre-warm (37 °C) sodium citrate solution (4% w/v) and use it as an anti-coagulant by adding it directly to the blood at the time of venepuncture at a ratio of 1:7 (0.5% w/v final).
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Discussion

In this manuscript, we present three different techniques with the potential to advance the capability to investigate the redox-dependent regulation of platelet function via the selective detection of O₂^•-. The first two methods are an improvement on existing techniques because of the redox probe utilized (DHE instead of the more common but less reliable DCFDA). These techniques are, therefore, easily accessible, and most laboratories can adopt them effectively without particular eq.......

Materials

Name	Company	Catalog Number	Comments
1-hydroxy-3-methoxycarbonyl-2,2,5,5-tetramethylpyrrolidine (CMH)	Noxygen Science trasfer and Diagnostics GmbH	NOX-02.1-50mg	Reagent for EPR (spin probe)
BD FACSAria III	BD Biosciences	NA	Flow cytometer
Bovine Serum Albumin	Merck/Sigma	A7030	For μ-slide coating
Bruker E-scan M (Noxyscan)	Noxygen Science trasfer and Diagnostics GmbH	NOX-E.11-BES	EPR spectrometer
Catalase–polyethylene glycol (PEG-Cat.)	Merck/Sigma	C4963	Hydrogen peroxide scavenger (specificity control)
ChronoLog Model 490+4	Labmedics/Chronolog	NA	Aggregometer
CM radical	Noxygen Science trasfer and Diagnostics GmbH	NOX-20.1-100mg	Reagent for EPR (calibration control)
deferoxamine	Noxygen Science trasfer and Diagnostics GmbH	NOX-09.1-100mg	Reagent for EPR
diethyldithiocarbamate (DETC)	Noxygen Science trasfer and Diagnostics GmbH	NOX-10.1-1g	Reagent for EPR
Dihydroethidium	Thermo Fisher Scientifics	D11347	Superoxide anion probe
Dimethyl sulfoxide	Merck/Sigma	34869	For stock solution preparation
EPR sealing wax plates	Noxygen Science trasfer and Diagnostics GmbH	NOX-A.3-VPM	Consumable for EPR
EPR-grade water	Noxygen Science trasfer and Diagnostics GmbH	NOX-07.7.1-0.5L	Reagent for EPR
Fibrinogen from human plasma	Merck/Sigma	F4883	For μ-slide coating
FITC anti-human CD41 Antibody	BioLegend	303704	Platelet-specific staining for flow cytometry
Glass cuvettes	Labmedics/Chronolog	P/N 312	Consumable for incubation in aggregometer
Horm Collagen	Labmedics/Chronolog	P/N 385	For platelet stimulation
ImageJ	National Institutes of Health (NIH)	NA	ImageJ 1.53t (Wayne Rasband)
Indomethacin	Merck/Sigma	I7378	For platelet isolation
Micropipettes DURAN 50µl	Noxygen Science trasfer and Diagnostics GmbH	NOX-G.6.1-50µL	Consumable for EPR
Poly-L-lysine hydrochloride	Merck/Sigma	P2658	For μ-slide coating
Prostaglandin E1 (PGE1)	Merck/Sigma	P5515	For platelet isolation
Sodium citrate (4% w/v solution)	Merck/Sigma	S5770	For platelet isolation
Stirring bars (Teflon-coated)	Labmedics/Chronolog	P/N 313	Consumable for incubation in aggregometer
Superoxide dismutase–polyethylene glycol (PEG-SOD)	Merck/Sigma	S9549	Superoxide anion scavenger (specificity control)
Thrombin from human plasma	Merck/Sigma	T6884	For platelet stimulation and μ-slide coating
VAS2870	Enzo Life Science	BML-EI395	NOX inhibitor
Zeiss 510 LSM confocal microscope	Zeiss	NA	Confocal microscope