Inhibition of bacterial growth and intramniotic infection in a guinea pig model of chorioamnionitis using PAMAM dendrimers

Dendrimers have emerged as topical microbicides to treat vaginal infections. This study explores the in vitro, in vivo antimicrobial activity of PAMAM dendrimers, and the associated mechanism. Interestingly, topical cervical application of 500μg of generation-4 neutral dendrimer (G₄-PAMAM-OH) showed potential to treat the Escherichia coli induced ascending uterine infection in guinea pig model of chorioamnionitis. Amniotic fluid collected from different gestational sacs of infected guinea pigs posttreatment showed absence of E. coli growth in the cultures plated with it. The cytokine level [tumor necrosis factor (TNFα) and interleukin (IL-6 and IL-1β)] in placenta of the G₄-PAMAM-OH treated animals were comparable to those in healthy animals while these were notably high in infected animals. Since, antibacterial activity of amine-terminated PAMAM dendrimers is known, the activity of hydroxyl and carboxylic acid terminated PAMAM dendrimers was compared with it. Though the G₄-PAMAM-NH₂ shows superior antibacterial activity, it was found to be cytotoxic to human cervical epithelial cell line above 10μg/mL, while the G₄-PAMAM-OH was non-cytotoxic up to 1mg/mL concentration. Cell integrity, outer (OM) and inner (IM) membrane permeabilization assays showed that G₄-PAMAM-OH dendrimer efficiently changed the OM permeability, while G₄-PAMAM-NH₂ and G_3.5-PAMAM-COOH damaged both OM and IM causing the bacterial lysis. The possible antibacterial mechanism are G₄-PAMAM-NH₂ acts as polycation binding to the polyanionic lipopolysaccharide in E. coli, the G₄-PAMAM-OH forms hydrogen bonds with the hydrophilic O-antigens in E. coli membrane and the G_3.5-PAMAM-COOH acts as a polyanion, chelating the divalent ions in outer cell membrane of E. coli. This is the first study which shows that G₄-PAMAM-OH dendrimer acts as an antibacterial agent.