Effects Of Engineered Latex Nanoparticles On Platelet Function: Role Of Physicochemistry

E Smyth, A Solomon, AJ Thorley, TD Tetley, M Emerson. Imperial College London, National Heart and Lung Institute, London, UK

Particulate matter present in air pollution has been shown, by both epidemiological and clinical studies, to increase the risk of cardiovascular events such as myocardial infarction. Particulate matter < 100 nm (defined as nanoparticles) is of particular interest due to its ability to penetrate the alveolar region of the lung and there is evidence to suggest that it is capable of translocating into the systemic circulation. Additionally, engineered nanoparticles are increasingly utilised for both commercial and therapeutic purposes, leading to further human exposure. The physicochemical properties of nanoparticles have been demonstrated to determine their biological and toxicological effects in various cell types. Activation and aggregation of platelets underlies many of the cardiovascular events associated with ambient particulate matter exposure, therefore the aim of this study was to investigate how the physicochemical properties of nanoparticles can influence their effects on platelet function.

Isolated human platelets were exposed to 50nm or 100nm, carboxy-modified (CM), amine-modified (AM) or unmodified (UM) latex nanoparticles (8, 15, 30, 60 μg ml-1) and aggregation responses were measured using optical aggregometry. Isolated human platelets were stimulated with an approximate EC50 concentration of thrombin (0.06 U ml-1) in the presence of subthreshold concentrations of nanoparticles (2 μg ml-1). The effects of AM and UM 50nm nanoparticles (1.2 μg mouse-1 administered i.v) were measured on subsequent collagen (50 μg kg-1 i.v) and thrombin (32 U kg-1 i.v) induced platelet aggregation in vivo in W.T C57 B/6 male mice (20-25g) by measuring radiolabelled platelet aggregation in real-time via external scintillation probes connected to a spectrometer (Tymvios et al., 2008). All animals were aneasthetised using urethane (10 ml kg-1 of 25% (w/v) i.p) and procedures were non-recovery. Groups were compared using a kruskal-Wallis test, Wilcoxin signed rank test or Mann Whitney U test and all data is presented as mean ± SEM.

All 50nm nanoparticles (EC50 concentrations: AM 31±7, CM 26±2, UM 38±3 μg ml-1, n=5) and 100nm nanoparticles (EC50 concentrations: AM 29±13, CM 33±7, UM 12±9 μg ml-1, n=5) induced platelet aggregation in vitro. AM 50nm nanoparticles potentiated aggregation induced by an EC50 concentration of thrombin (24±7 treated versus 10±3 control % aggregation, p<0.05, n = 6) whereas nanoparticles with different physicochemical properties had no significant effect. In vivo, AM 50nm nanoparticles enhanced collagen (16±2 control versus 24±1 treated, maximum change in % counts, p<0.05, n = 5) and thrombin (154±6 control versus 252±48 treated, area under the curve, p<0.05, n=4) induced platelet aggregation.

Latex nanoparticles have the ability to induce platelet aggregation with differential potencies, depending on their physicochemical properties. Cationic 50nm particles possess specific characteristics which makes them capable of potentiating agonist induced platelet aggregation when present at subthreshold concentrations both in vitro and in vivo. Our data provides a potential mechanism to explain the detrimental effects of particulate matter on the cardiovascular system should they translocate the pulmonary epithelial barrier. Future work with pharmacological tools will determine the mechanisms by which nanoparticles induce and enhance platelet aggregation.

Tymvios C et al. (2008) Thromb Haemost, 99(2), 435-440.