Translocation of Ultrafine Particles

Referencing: Ultrafine Particles Cross Cellular Membranes by Nonphagocytic Mechanisms in Lungs and in Cultured Cells

We read with great interest the article by Geiser et al. (2005) on the mechanism of translocation of ultrafine particles (UFPs) across cellular membranes in vivo in rats following inhalation and in vitro using porcine pulmonary macrophages and human red blood cells.

We are delighted to see this study that vindicates our hypothesis that translocation of UFPs is a possible pathway for the cardiovascular effects of particulate air pollution. A few years ago we reported extrapulmonary translocation of UFPs after intratracheal instillation in hamsters (Nemmar et al. 2001) and after inhalation in healthy human volunteers (Nemmar et al. 2002a), suggesting an alternative and/or a complementary explanation for the extrapulmonary effects of particles.

In their study, Geiser et al. (2005) very elegantly provided novel morphologic data showing the occurrence of translocation of UFPs, and they also reported--for the first time--that this translocation did not occur by endocytic processes but rather by diffusion or adhesive interactions. However, we noted with some surprise that the authors cited Brown et al. (2002) when referring to previous studies on the occurrence of UFP translocation. Indeed, Brown et al. (2002) studied the deposition and clearance of an ultrafine (60 nm) technetium-99m-labeled aerosol in human volunteers after 2 hr, and found no significant radioactivity in the liver (1.3 ± 1.2%). This activity was attributed to scatter from the lung and/or overlap of lung parenchyma in the liver. Consequently, Brown et al. (2002) excluded the occurrence of translocation and, although they did not measure radioactivity in blood, they challenged our conclusion that UFPs (5-10 nm) could pass from the lungs into blood and extrapulmonary organs (Nemmar et al. 2002a). Therefore, for the sake of accuracy, Geiser et al. (2005) should have referred to our study (Nemmar et al. 2002a) rather than that of Brown et al. (2002).

Geiser et al. (2005) provided micrographs of fluorescent polystyrene particles taken up by macrophages (Figure 3) or red blood cells (Figure 4). It is not clear whether these polystyrene particles contained surface charges, for example, carboxylate-modified (negatively charged) or amine-modified (positively charged), although Geiser et al. (2005) briefly discussed the possible effect of surface charge. This aspect is important; we (Nemmar et al. 2002b) and others (Silva et al. 2005) have reported that hemostasis may be affected by the intravenous or intratracheal administration of UFPs and also established that this phenomenon is dependent on the surface properties of the particles. Thus, only positively charged amine-modified particles led to a marked increase in prothrombotic tendency, which we showed to result, at least in part, from platelet activation

In conclusion, although the article by Geiser et al. (2005) adds a significant amount of information to the literature related to the extrapulmonary effect of inhaled particles, this issue needs to be clarified in more detail. Therefore, we look forward to this group and others providing more detailed quantification of the proportion of inhaled UFPs that can be found in extrapulmonary organs.

The authors declare they have no competing financial interests.

Abderrahim Nemmar
Peter H.M. Hoet
Benoit Nemery
Laboratory of Pneumology
Unit of Lung Toxicology
Katholieke Universiteit Leuven
Leuven, Belgium
E-mail: abderrahim.nemmar@med.kuleuven.ac.be

References

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Ultrafine Particles: Geiser et al. Respond

Figure 1. (A) Gamma camera image after the inhalation of Tc-99m radiolabeled ultrafine carbon particles not controlled for leaching. Reproduced from Nemmar et al. (2002) with permission from Lippincott Williams & Wilkins. (B) Gamma camera image after the inhalation of soluble Tc-99m pertechnetate. Reproduced from Kreyling et al. (in press) with permission from The Journal of Aerosol Medicine. (C) Gamma camera images after the inhalation of nonleaching Tc-99m radiolabeled ultrafine carbon particles.

Nemmar et al. were surprised that we did not cite their study in our article (Geiser et al. 2005) when we referenced state-of-the-art experiments about the translocation of ultrafine particles into secondary organs. We did not cite their human study (Nemmar et al. 2002) because in Figure 2 of their article, they presented clear evidence that a major fraction of the radiolabeled technetium-99 (Tc-99m) came off the Technegas particles. Thus, for methodologic reasons, the fraction of translocated particles could not be determined adequately and was certainly overestimated by Nemmar et al. (2002). This was recently discussed by Kreyling et al. (2004). To briefly illustrate this, we have included Figure 1. Figure 1A shows the original whole-body scintigram published by Nemmar et al. (2002) in which the salivary glands, the thyroid gland, and the urinary bladder are clearly visible, demonstrating that they contain large fractions of the Tc-99m radiolabel. This and the Tc-99m activity in the soft tissue, which shows the contour of the whole body, are clear indications of nonparticulate Tc-99m in the form of pertechnetate. Pertechnetate typically accumulates in these organs, as can be inferred from the Figure 1B, where the same pattern of radiolabel was detected after inhalation of soluble Tc-99m pertechnetate.

In the case of inhalation of nonleaching Tc-99m radiolabeled ultrafine carbon particles (Figure 1C), no activity is detectable in these organs or in the soft tissue. Figure 1C shows three images taken from the head (little larynx retention), the thorax (main carbon particle retention in lungs), and the lower abdomen, with a rather faint image of the urinary bladder. A similar pattern has been reported by Brown et al. (2002).

In addition, Nemmar et al. are interested in the surface charges of the particles we used for the in vitro studies, because surface charges are likely to be important determinants for the translocation of ultrafine particles as well as for their biologic effects. The polystyrene particles we used for the studies with the macrophages and erythrocytes were either uncharged, amino-modified, or carboxylate-modified (Rothen-Rutishauser B, Gehr P, Schürch S, unpublished data). The surface charges of the gold and titanium particles are not known. We found nonphagocytic uptake of ultrafine particles of all the different materials and surface charges by macrophages and erythrocytes. However, because the aim of our study was not to investigate the effects of surface charges on cellular uptake, we did not measure the actual surface charges of the particles or estimate the total number of particles within cells to quantify particle uptake. We certainly agree with Nemmar et al. on the importance of surface charges for particle-cell interaction, and we hope that we will soon find more literature published on this aspect.

The authors declare they have no competing financial interests.

Marianne Geiser
Barbara Rothen-Rutishauser
Nadine Kapp
Peter Gehr
Institute for Anatomy
University of Bern
Bern, Switzerland
E-mail: geiser@ana.unibe.ch

Samuel Schürch
Department of Physiology and Biophysics
Faculty of Medicine
The University of Calgary
Calgary, Canada

Wolfgang Kreyling
Holger Schulz
Manuela Semmler
Joachim Heyder
GSF - National Research Center for Environment and Health
Institute for Inhalation Biology
Neuherberg/Munich, Germany

Vinzenz Im Hof
Institute of Pathophysiology
University of Bern
Bern, Switzerland

Brown JS, Zeman KL, Bennett WD. 2002. Ultrafine particle deposition and clearance in the healthy and obstructed lung. Am J Respir Crit Care Med 166:1240-1247.

Geiser M, Rothen-Rutishauser B, Kapp N, Schürch S, Kreyling W, Schulz H, et al. 2005. Ultrafine particles cross cellular membranes by non-phagocytic mechanisms in lungs and in cultured cells. Environ Health Perspect 113:1555-1560. [CrossRef].

Kreyling WG, Semmler M, Moller W. 2004. Dosimetry and toxicology of ultrafine particles. J Aerosol Med 17:140-152.

Kreyling WG, Semmler M, Möller W. In press. Ultrafine particle-lung interactions: does size matter? J Aerosol Med.

Nemmar A, Hoet PH, Vanquickenborne B, Dinsdale D, Thomeer M, Hoylaerts MF, et al. 2002. Passage of inhaled particles into the blood circulation in humans. Circulation 105:411-414.

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Last Updated: April 20, 2006