2006 Progress Report: Cellular Uptake and Toxicity of Dendritic Nanomaterials: An Integrated Physicochemical and Toxicogenomics StudyEPA Grant Number: R832525
Title: Cellular Uptake and Toxicity of Dendritic Nanomaterials: An Integrated Physicochemical and Toxicogenomics Study
Investigators: Diallo, Mamadou S. , Goddard, William A. , Riechmann, Jose Luis
Institution: California Institute of Technology , Howard University
EPA Project Officer: Carleton, James N
Project Period: November 1, 2005 through November 30, 2008
Project Period Covered by this Report: November 1, 2005 through November 30, 2006
Project Amount: $375,000
RFA: Exploratory Research: Nanotechnology Research Grants Investigating Environmental and Human Health Effects of Manufactured Nanomaterials: A Joint Research Solicitation - EPA, NSF, NIOSH (2005) RFA Text | Recipients Lists
Research Category: Health Effects , Nanotechnology , Health , Safer Chemicals
Dendrimers are relatively monodisperse and highly branched nanoparticles that can be designed to: (i) chelate metal ions; (ii) encapsulate metal clusters; (iii) bind organic solutes or bioactive compounds; and (iv) become soluble in appropriate media or bind onto appropriate surfaces (Giri, et al., 2007a). Because of these unique properties, dendrimers are providing unprecedented opportunities to develop functional nanomaterials for a variety of applications, including chemical separations and catalysis, chemical sensing, medical imaging, DNA/drug delivery and water purification (Giri, et al., 2007a). As the U.S. Environmental Protection Agency (EPA) begins its assessment of the impact of nanotechnology on human health and the environment (Giri, et al., 2007b), there is a critical need of data and quantitative tools for assessing the environmental fate and toxicity of engineered nanomaterials such as dendrimers. The overall objective of this project is to advance our fundamental understanding of the relationships between the affinity of poly(amidoamine) (PAMAM) dendrimers (Figure 1) to cell membranes and their vascular and ingestion toxicity using: (i) n-octanol and solid-supported phosphatidylcholine lipid bilayers as model cell membranes; and (ii) endothelial cells as model human cells.
During the first phase of this project, we completed the measurements of: (i) the octanol-water partition coefficient (log Kow); and (ii) the liposomes-water partition coefficient (log Klipsw) of PAMAM dendrimers using phosphatidylcholine (PC) as a model lipid. Log Kow and log Klipsw are among the most widely used measures of the bioaccumulation of an organic compound in cell membranes. We found that all the log Klipsw values of the PAMAM dendrimers are positive, thereby suggesting these nanomaterials preferentially partition to the model PC liposomes. Conversely, the negative values of the log Kow of the dendrimers suggest they prefer to remain in the water phase. These results strongly suggest that the octanol-water partition is not a good predictor of the bioaccumulation tendency of a PAMAM dendrimer. The environmental implications of these findings will be discussed elsewhere (Giri, et al., 2007a; Giri, et al., 2007b).
Figure 1. Structures of the PAMAM Dendrimers Evaluated in this Study
A.G4-NH2 PAMAM dendrimer with ethylene diamine core
B. Dendrimer terminal group chemistry
C. Dendrimer core chemistry
We have also completed measurements of the binding of PAMAM dendrimers to human serum albumin (HAS). In the next 3 months, we will initiate nuclear magnetic resonance (NMR) spectroscopic investigations of dendrimer binding to HAS. In parallel, we will also continue our cytoxicity (IC50) assays using Caoco-2 cell lines. We already have carried out measurements of the IC50 of G4 PAMAM dendrimers with terminal NH2, ethanolamine, and Tris groups. Once the cytoxicity experiments are completed, we will initiate the toxicogenomic studies to gain insight into the molecular biology of dendrimer toxicity.
Giri J, Diallo MS, Dalleska N, Fang X, Goddard WA III. Bioaccumulation and toxicity of nanomaterials: octanol-water partition coefficients (log Kow) of poly(amidoamine) dendrimers. Environmental Science and Technology (to be submitted, 2007a).
Giri J, Diallo MS, Goddard WA III. Bioaccumulation and toxicity of nanomaterials: liposomes-water partition coefficients (log Klipsw) of poly(amidoamine) dendrimers. Environmental Science and Technology (to be submitted, 2007b).