Carbon Nanoparticles Activate Platelets

Researchers have found that carbon nanoparticles, regardless of whether precisely manufactured in a laboratory or as a random collection present in polluted air, activate human platelets, thereby promoting blood clotting and the potential for thrombosis.

Investigators at the University of Texas Health Center (Houston, USA; www.uth.edu) prepared a series of precisely engineered carbon nanoparticles: multiple wall (MWNT) and single wall (SWNT) nanotubes, C60 fullerenes (C60CS), and mixed carbon nanoparticles (MCN). These were compared to nanoparticles comprising standard urban particulate matter (SRM1648).

In vitro experiments with human platelets and in vivo studies on rat carotid arteries were performed. Platelet function was studied using lumi-aggregometry, phase-contrast, immunofluorescence, and transmission electron microscopy, flow cytometry, zymography, and pharmacologic inhibitors of platelet aggregation. Vascular thrombosis was induced by ferric chloride, and the rate of thrombosis was measured, in the presence of carbon particles, with an ultrasonic flow probe.

Results published in the September 12, 2005, online edition of the British Journal of Pharmacology revealed that all forms of nanoparticles except for the C60 fullerenes (bucky balls) stimulated platelet aggregation and accelerated the rate of vascular thrombosis in rat carotid arteries. The order of efficacy was MCN > SWNT > MWNT > SRM1648. At the molecular level it was found that for each type of nanoparticle a different biochemical pathway carried out platelet stimulation.

The investigators suggested that drug developers working with nanoparticles might wish to use the bucky ball form to avoid contributing to the risk of atherosclerosis and heart attack. "This research is not a case against nanotechnology,” said senior author Dr. Marek Radomski, professor of integrative biology and pharmacology at the University of Texas Health Center. "It is difficult to overestimate the importance of this amazing technology's ability to transform medicine. But it is good to assess the risk of a new technology in advance. This is a case for moving ahead in a cautious and informed way.”