title: Interaction of poly(amidoamine) dendrimers with supported lipid bilayers and cells: hole formation and the relation to transport.
abstract: We have investigated poly(amidoamine) (PAMAM) dendrimer interactions with supported 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) lipid bilayers and KB and Rat2 cell membranes using atomic force microscopy (AFM), enzyme assays, flow cell cytometry, and fluorescence microscopy. Amine-terminated generation 7 (G7) PAMAM dendrimers (10-100 nM) were observed to form holes of 15-40 nm in diameter in aqueous, supported lipid bilayers. G5 amine-terminated dendrimers did not initiate hole formation but expanded holes at existing defects. Acetamide-terminated G5 PAMAM dendrimers did not cause hole formation in this concentration range. The interactions between PAMAM dendrimers and cell membranes were studied in vitro using KB and Rat 2 cell lines. Neither G5 amine- nor acetamide-terminated PAMAM dendrimers were cytotoxic up to a 500 nM concentration. However, the dose dependent release of the cytoplasmic proteins lactate dehydrogenase (LDH) and luciferase (Luc) indicated that the presence of the amine-terminated G5 PAMAM dendrimer decreased the integrity of the cell membrane. In contrast, the presence of acetamide-terminated G5 PAMAM dendrimer had little effect on membrane integrity up to a 500 nM concentration. The induction of permeability caused by the amine-terminated dendrimers was not permanent, and leaking of cytosolic enzymes returned to normal levels upon removal of the dendrimers. The mechanism of how PAMAM dendrimers altered cells was investigated using fluorescence microscopy, LDH and Luc assays, and flow cytometry. This study revealed that (1) a hole formation mechanism is consistent with the observations of dendrimer internalization, (2) cytosolic proteins can diffuse out of the cell via these holes, and (3) dye molecules can be detected diffusing into the cell or out of the cell through the same membrane holes. Diffusion of dendrimers through holes is sufficient to explain the uptake of G5 amine-terminated PAMAM dendrimers into cells and is consistent with the lack of uptake of G5 acetamide-terminated PAMAM dendrimers.
authors.affiliation: Program in Applied Physics, Department of Internal Medicine, University of Michigan, Ann Arbor 48109, USA.
authors.forename: Seungpyo
authors.initials: S
authors.lastname: Hong
authors.forename: Anna U
authors.initials: AU
authors.lastname: Bielinska
authors.forename: Almut
authors.initials: A
authors.lastname: Mecke
authors.forename: Balazs
authors.initials: B
authors.lastname: Keszler
authors.forename: James L
authors.initials: JL
authors.lastname: Beals
authors.forename: Xiangyang
authors.initials: X
authors.lastname: Shi
authors.forename: Lajos
authors.initials: L
authors.lastname: Balogh
authors.forename: Bradford G
authors.initials: BG
authors.lastname: Orr
authors.forename: James R
authors.initials: JR
authors.lastname: Baker
authors.forename: Mark M
authors.initials: MM
authors.lastname: Banaszak Holl
mesh_terms: D000081:Acetamides / Q000737:chemistry / Q000378:metabolism; D000577:Amides / Q000737:chemistry* / Q000378:metabolism*; D000588:Amines / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D002463:Cell Membrane Permeability; D004396:Coloring Agents / Q000737:chemistry / Q000378:metabolism; D004058:Diffusion; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry / Q000378:metabolism; D016503:Drug Delivery Systems; D005434:Flow Cytometry; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism*; D008156:Luciferases / Q000378:metabolism; D018625:Microscopy, Atomic Force; D015394:Molecular Structure; D011073:Polyamines / Q000737:chemistry* / Q000378:metabolism*; D011108:Polymers / Q000737:chemistry* / Q000378:metabolism*; D051381:Rats
chemical_list: D000081:Acetamides; D000577:Amides; D000588:Amines; D004396:Coloring Agents; D008051:Lipid Bilayers; D011073:Polyamines; D011108:Polymers; C030686:acetamide; D008156:Luciferases; D004134:Dimyristoylphosphatidylcholine