Preparation of Washed Human Platelets for Quantitative Metabolic Flux Studies

Summary

Platelet metabolism is of interest, particularly as it relates to the role of platelet hyper- and hypoactivity in bleeding and thrombotic disorders. Isolating platelets from plasma is necessary for some metabolic assays; presented here is a method for isolating of intracellular metabolites from washed platelets.

Abstract

Platelets are blood cells that play an integral role in hemostasis and the innate immune response. Platelet hyper- and hypoactivity have been implicated in metabolic disorders, increasing risk for both thrombosis and bleeding. Platelet activation and metabolism are tightly linked, with the numerous methods to measure the former but relatively few for the latter. To study platelet metabolism without the interference of other blood cells and plasma components, platelets must be isolated, a process that is not trivial because of platelets shear sensitivity and ability to irreversibly activate. Presented here is a protocol for platelet isolation (washing) that produces quiescent platelets that are sensitive to stimulation by platelet agonists. Successive centrifugation steps are used with the addition of platelet inhibitors to isolate platelets from whole blood and resuspend them in a controlled, isosmotic buffer. This method reproducibly produces 30%–40% recovery of platelets from whole blood with low activation as measured by markers of granule secretion and integrin activity. Platelet count and fuel concentration can be precisely controlled to allow the user to probe a variety of metabolic situations.

Introduction

Platelets are small (2–4 µm diameter), anucleate cells that play an important role in hemostasis, the tightly regulated process of clot formation¹. While vital for vascular integrity, platelets are also implicated in adverse health events. Platelets are involved in deep vein thrombosis (DVT) and arterial thrombosis (AT), which are clots that occlude blood vessels, leading to diminished blood supply locally, or, if pieces of the clot break off (embolize), they can block blood supply to the lungs, heart, or brain^2,3,4,

Protocol

The study received Institutional Review Board approval from the University of Colorado Anschutz Medical Campus. Written consent was obtained from all study participants. Participants reported they did not consume alcohol for the previous 48 h or non-steroidal anti-inflammatory drugs (NSAIDs) for the previous ten days. This project is supported by the National Heart, Lung, and Blood Institute of the National Institutes of Health under award number R61HL141794.

1. Blood collection

1. Set up for blood draw. It is recommended blood collection is carried out by a trained phlebotomist.
2. Perform venipuncture on t....

Results

Representative results in Figure 2 represent 6 different blood donors, including 3 males and 3 females. The platelet yield relative to whole blood is shown in Figure 2A. Final platelet recovery was an average of 52% ± 3% (standard deviation, n=6). Final platelet count compared to white blood cell contamination was measured using an automated hematology analyzer. White blood cell counts were less than 0.1% of total cells (Figure 2B)........

Discussion

Platelets are very sensitive to their environment, including shear stress and presence of agonists^38,39. This makes platelets challenging to handle and isolate, making the use of inhibitors and wide bore pipettes crucial⁴⁰. Proper storage and preparation of PGI₂ is vital, as failing to prepare PGI₂ in basic PBS will result in rapid degradation of PGI₂⁴¹. To minimize the risk of shear.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
0.22 µM filter Spin-X tubes	Millapore-Sigma	CLS8160	Reagent prep
19 G x 3/4" needle	McKesson Corporation	448406	Phlebotomy
21 G 1.5 inch needle with luer lock	Amazon	B0C39PJD23	Reagent prep
96 well plate, half area	Greiner Bio-One	675101	Flow cytometry
ACD-A vaccutainers	Fisher Scientific	364606	Phlebotomy
Adapter	McKesson Corporation	609	Phlebotomy
Alcohol swab	VWR	15648-916	Phlebotomy
Apyrase from potatoes	Sigma	A6410-100UN	Reagent prep
CD42a Monoclonal Antibody	Thermo Fisher Scientific	48-0428-42	Flow cytometry
Chilled microcentrifuge	ThermoFisher Scientific	75002441	Quenching
D-Glucose	Sigma	G7021	Reagent prep
FITC Anti-Fibrinogen antibody	Abcam	4217	Flow cytometry
Flow cytometer	Beckman Coulter	82922828	Flow cytometry
Gauze	VWR	76049-110	Phlebotomy
Glycerol	Sigma Aldrich	G5516	Reagent prep
HEPES	Sigma Aldrich	H4034	Reagent prep
Human alpha-thrombin	Prolytix	HCT-0020	Flow cytometry
KCl	Sigma Aldrich	P9333	Reagent prep
KH2PO4	Sigma Aldrich	P5655	Reagent prep
MgCl2	Sigma	M8266	Reagent prep
Microcentrifuge tubes	VWR	87003-292	General
Na2HPO4	Sigma	S3264	Reagent prep
NaCl	Sigma Aldrich	S7653	Reagent prep
NaHCO3	Sigma Aldrich	S5761	Reagent prep
Narrow bore transfer pipette	VWR	16001-176	Platelet washing
Paraformaldehyde solution, 4% in PBS	Santa Cruz Biotechnology	sc-281692	Flow cytometry
PECy5 Mouse Anti-Human CD62P	BD Pharmingen	551142	Flow cytometry
Plate cover	Thermo Fisher Scientific	AB0626	Flow cytometry
Polypropylene 15 mL conical tubes	VWR	89039-658	Reagent prep
Polypropylene 50 mL conical tubes	VWR	352070	Platelet washing
Prostaglandin I2 (sodium salt)	Cayman Chemical	18220	Reagent prep
SKC Inc. C-Chip Disposable Hemocytometers	Fisher Scientific	22-600-100	Cell counting
Syringe	BD Pharmingen	14-823-41	Reagent prep
Tourniquet	VWR	76235-371	Phlebotomy
Vacutainer needle holder	BD	364815	Phlebotomy
Vortexer	VWR	102091-234	Reagent prep
Water bath	Thermo Fisher Scientific	TSGP02	Platelet washing
Wide bore transfer pipette	VWR	76285-362	Platelet washing