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Morphological aspects of interactions between microparticles and mammalian cells: intestinal uptake and onward movement |
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| Authors: | Carr Katharine E Smyth Sharon H McCullough Melissa T Morris John F Moyes Siobhan M |
| Affiliation: | a Department of Physiology, Anatomy and Genetics, University of Oxford b The Queen's University of Belfast c Department of Physiology, Anatomy and Genetics, University of Oxford, current address Centre for Nephrology, University College London |
| Abstract: | Uptake of ingested microparticles into small intestinal tissues and on to secondary organs has moved from being an anecdotal phenomenon to a recognised and quantifiable process, which is relevant to risk assessment of accidental exposure, treatment of multi-organ dysfunction syndrome and therapeutic uses of encapsulated drug or vaccine delivery. This review puts in context with the literature the findings of a morphological study of microparticle uptake, using two approaches.The first is a rat in vivo in situ model, appropriate to a study rooted in the exposure of human populations to microparticles. Latex microspheres 2 μm in diameter are the principal particle type used, although others are also investigated. Most data are based on microscopy, but analysis of macerated bulk tissue is also useful. Uptake occurs at early time points after a single dose and is shown to take place almost entirely at villous rather than Peyer's patch sites: however, multiple feeding and therefore a longer time-span produces a higher proportion of particles associated with Peyer's patches, albeit for very small total uptake at those later time points. Uptake is less affected by species, fasting and immunological competence than by age and reproductive status.The second approach uses in vitro methods to confirm the role of intercellular junctions in particle uptake. Particle-associated tight junction opening, in a Caco-2 monolayer, is reflected in changes in transepithelial resistance and particle uptake across the epithelial monolayer: Tight junction opening and particle uptake are both increased further by external irradiation, ethanol and sub-epithelial macrophages, but reduced by exposure to ice. An M cell model has looser tight junctions than Caco-2 cells, but a similar level of particle uptake. These results, along with the changes seen in junctional proteins after particle addition, confirm the role of tight junctions in uptake but suggest that adhering junctions are also important. |
| Keywords: | AUC, area under curve Baseline model (in vitro), 21-day Caco-2 cell monolayer grown on polyester inserts with 3 μm pores Baseline model (in vivo), young adult (7-week-old) non-fasted male rats BEI, backscattered electron image or imaging Compartmentalised culture, exposure of the Caco-2 monolayer to cells of the lymphoreticular system in the lower well, but indirectly, through the shared medium CLSM, confocal laser scanning microscope or microscopy Delta, TER change, calculated by subtraction of later from earlier reading EM, electron microscopy LM, light microscopy Morphological project, term used for microscopic analysis of in vivo in situ particle uptake, followed by the use of a similar analytical approach to an in vitro model SEM, Scanning electron microscopy S.E.M., Standard error of the mean Standard dose (in vitro), 5.9 × 109 non-ionic yellow/green fluorescent latex microspheres 2 μm in diameter Standard dose (in vivo), administered dose in 0.25 ml of 2 μm yellow/green fluorescent latex microparticles (1.9 × 109) stock suspension in distilled water as provided by the supplier TEM, Transmission electron microscopy TER, Transepithelial resistance TJ/TJs, Tight junction(s) Z-stacks, series of images or &lsquo optical slices&rsquo , taken with a CLSM, of a feature in a sample, each image recorded at a different height, the whole series allowing interpretation of structural relationships in the Z axis |
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