title: The mechanism of uptake of biodegradable microparticles in Caco-2 cells is size dependent.
abstract: OBJECTIVE
  To study the uptake of biodegradable microparticles in Caco-2 cells.
  
  
  METHODS
  Biodegradable microparticles of polylactic polyglycolic acid co-polymer (PLGA 50:50) of mean diameters 0.1 micron, 1 micron, and 10 microns containing bovine serum albumin as a model protein and 6-coumarin as a fluorescent marker were formulated by a multiple emulsion technique. The Caco-2 cell monolayers were incubated with each diameter microparticles (100 micrograms/ml) for two hours. The microparticle uptake in Caco-2 cells was studied by confocal microscopy and also by quantitating the 6-coumarin content of the microparticles taken up by the cells. The effects of microparticle concentration, and incubation time and temperature on microparticle cell uptake were also studied.
  
  
  RESULTS
  The study demonstrated that the Caco-2 cell microparticle uptake significantly depends upon the microparticle diameter. The 0.1 micron diameter microparticles had 2.5 fold greater uptake on the weight basis than the 1 micron and 6 fold greater than the 10 microns diameter microparticles. Similarly in terms of number the uptake of 0.1 micron diameter microparticles was 2.7 x 10(3) fold greater than the 1 micron and 6.7 x 10(6) greater than the 10 microns diameter microparticles. The efficiency of uptake of 0.1 micron diameter microparticles at 100 micrograms/ml concentration was 41% compared to 15% and 6% for the 1 micron and the 10 microns diameter microparticles, respectively. The Caco-2 cell microparticle (0.1 micron) uptake increased with concentration in the range of 100 micrograms/ml to 500 micrograms/ml which then reached a plateau at higher concentration. The uptake of microparticles increased with incubation time, reaching a steady state at two hours. The uptake was greater at an incubation temperature of 37 degrees C compared to at 4 degrees C.
  
  
  CONCLUSIONS
  The Caco-2 cell microparticle uptake was microparticle diameter, concentration, and incubation time and temperature dependent. The small diameter microparticles (0.1 micron) had significantly greater uptake compared to larger diameter microparticles. The results thus suggest that the mechanism of uptake of microparticles in Caco-2 cell is particle diameter dependent. Caco-2 cells are used as an in vitro model for gastrointestinal uptake, and therefore the results obtained in these studies could be of significant importance in optimizing the microparticle-based oral drug delivery systems.
authors.affiliation: College of Pharmacy, University of Michigan, Ann Arbor 48109, USA.
authors.forename: M P
authors.initials: MP
authors.lastname: Desai
authors.forename: V
authors.initials: V
authors.lastname: Labhasetwar
authors.forename: E
authors.initials: E
authors.lastname: Walter
authors.forename: R J
authors.initials: RJ
authors.lastname: Levy
authors.forename: G L
authors.initials: GL
authors.lastname: Amidon
mesh_terms: D000818:Animals; D018938:Caco-2 Cells / Q000378:metabolism*; D002417:Cattle; D002463:Cell Membrane Permeability; D006801:Humans; D007408:Intestinal Absorption; D019344:Lactic Acid / Q000737:chemistry* / Q000493:pharmacokinetics*; D018613:Microscopy, Confocal; D008863:Microspheres; D008954:Models, Biological; D010316:Particle Size; D011100:Polyglycolic Acid / Q000737:chemistry* / Q000493:pharmacokinetics*; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011108:Polymers / Q000737:chemistry* / Q000493:pharmacokinetics*; D012710:Serum Albumin, Bovine / Q000378:metabolism
chemical_list: D011108:Polymers; D000077182:Polylactic Acid-Polyglycolic Acid Copolymer; D011100:Polyglycolic Acid; D012710:Serum Albumin, Bovine; D019344:Lactic Acid