Abstract
Purpose::
Poly(amidoamine) (PAMAM) dendrimers have been investigated as drug delivery agents in eukaryotic cells, but their effects on prokaryotic cells have been largely unexplored. Here we show that 5th generation PAMAM is toxic to common ocular flora, but when passivated with oligo (ethylene glycol) (OEG) is non-toxic to human corneal epithelial cells (HCECs).
Methods::
The toxicity of unmodified and OEG-passivated PAMAM (2 hr, 37° C)was measured against P. aeruginosa (PA) (ATCC 19660 and a clinical isolate 2219) and S. aureus (SA) (ATCC 29213). Colony count assays were used to determine the concentration where 50% of the bacteria were killed (EC50). MTT cytotoxicity assays were used to measure the toxicity of PAMAM to SV40-transformed HCECs (24 hr, 37° C).
Results::
PAMAM with and without OEG was toxic to PA 19660. The EC50 values were 1.5 ± 0.1 and 0.9 ± 0.1 µg/ml (n = 4) for unmodified and OEG-modified PAMAM, respectively. PA 2219 showed a slightly increased resistance to OEG-modified PAMAM (EC50 1.4 ± 0.2 µg/ml, n = 4) as compared to the lab strain (p < 0.05). Only unmodified PAMAM showed measurable toxicity to SA (EC50 = 20.8 ± 3.4 µg/ml, n = 4). At low concentrations (0.001-1 µg/ml) PAMAM did not show significant toxicity to HCECs. At the highest concentration tested (10 µg/ml), exposure to unmodified PAMAM resulted in only 25% survival of HCECs, but OEG-modified PAMAM was not toxic.
Conclusions::
PAMAM was significantly toxic to PA, a Gram negative organism, but not SA a Gram positive organism. This result may be due to significant differences between the structures of the cell walls of these organisms. OEG-passivation reduced PAMAM toxicity to HCECs, but its toxicity to PA was retained. Again, the differences between bacterial and eukaryotic membranes may be the reason for these results. Our findings indicate that in addition to being potential agents for drug delivery to the ocular surface, PAMAM dendrimers may have further attractive antimicrobial properties.
Keywords: antibiotics/antifungals/antiparasitics • cornea: epithelium • drug toxicity/drug effects