Transport of poly(amidoamine) dendrimers across Caco-2 cell monolayers: Influence of size, charge and fluorescent labeling

Purpose. To investigate the transport of poly(amidoamine) (PAMAM) dendrimers with positive, neutral and negatively charged surface groups across Caco-2 cell monolayers. Methods. Cationic PAMAM-NH2 (G2 and G4), neutral PAMAM-OH (G2), and anionic PAMAM-COOH (G1.5-G3.5) dendrimers were conjugated to fluorescein isothiocyanate (FITC). The permeability of fluorescently labeled PAMAM dendrimers was measured in the apical-to-basolateral direction. C-14-Mannitol permeability was measured in the presence of unlabeled and FITC labeled PAMAM dendrimers. Caco-2 cells were incubated with the dendrimers followed by mouse anti-occludin or rhodamine phalloidin, and visualized using confocal laser scanning microscopy to examine tight junction integrity. Results. The overall rank order of PAMAM permeability was G3.5COOH > G2NH(2) > G2.5COOH > G1.5COOH > G2OH. C-14-Mannitol permeability significantly increased in the presence of cationic and anionic PAMAM dendrimers with significantly greater permeability in the presence of labeled dendrimers compared to unlabeled. PAMAM dendrimers had a significant influence on tight junction proteins occludin and actin, which was microscopically evidenced by disruption in the occludin and rhodamine phalloidin staining patterns. Conclusions. These studies demonstrate that enhanced PAMAM permeability is in part due to opening of tight junctions, and that by appropriate engineering of PAMAM surface chemistry it is possible to increase polymer transepithelial transport for oral drug delivery applications.