Comparison of the rate of phagocytosis of orthorhombic cyclosporine A (CsA) and latex particles by alveolar macrophages from hamsters

Abstract.

The aim of this study was to develop an in vitro model to estimate the clearance of pulmonary administered cyclosporine A (CsA). To do this we estimated the volume of CsA particles phagocytosed by alveolar macrophages (AM) lavaged from hamsters. AM were cultured with CsA particles at two doses of particles (0.1 mg or 0.5 mg) and at three incubation times (1 h, 6 h or 24 h). The AM were also incubated with or without latex particles. After incubation, AM were processed for light and electron microscopy and the mean volume of phagocytosed particles was esti mated stereologically from micrographs of the cells. Here, however, the CsA particles were dissolved during the embedding process and only their negative images (vacuoles) could be detected. An indirect method was therefore developed. The volume of cytoplasmic vacuoles (called 'background' vacuoles) was estimated in control macrophages (without particles or with latex particles and subtracted from the total volume of vac uoles in macrophages incubated with CsA, which gave the volume of phagocytosed CsA. The volume of the 'background' vacuoles remained constant in all study conditions. At a dose of 0.1 mg CsA the volume phagocytosed per macrophage was 13.83 μm³ at 1 h, 8.43 μm³ at 6 h and 4.50 μm³ at 24 h. At a dose of 0.5 mg CsA, the volume phagocytosed varied from 26.59 μm³ at 1 h, to 4.13 μm³ at 6 h and 49.10 μm³ at 24 h. These results show no statistically significant dependence on time for either dose, and a statistically significant dose effect only at 24 h. With latex particles, the phagocytosed volume increased significantly with time and dose and was significantly higher than for CsA particles. This study showed that CsA particles are phagocytosed by AM from hamsters but to a lesser extent than latex particles. This difference could be correlated with physical properties, i.e. a difference between particle size and shape and/or chemical properties, latex particles being inert and CsA particles being peptidic. Moreover, different surface receptors on AM could be involved in the process of phagocytosis of CsA and latex particles.