Anti-inflammatory and anti-oxidant activity of anionic dendrimer–N-acetyl cysteine conjugates in activated microglial cells

Abstract

Dendrimers are emerging as potential intracellular drug delivery vehicles. Understanding and improving the cellular efficacy of dendrimer–drug conjugates, can lead to significant in vivo benefits. This study explores efficacy of anionic polyamidoamine (PAMAM–COOH) dendrimer–N-acetyl cysteine (NAC) conjugates for applications in neuroinflammation. The anti-oxidative and anti-inflammatory effects of PAMAM–(COOH) 46–(NAC) 18 conjugate is evaluated on microglial cells in vitro. Cell entry and localization of PAMAM–(COOH) 62–(FITC) 2 conjugate in BV-2 microglial cells were assessed using flow cytometry and confocal microscopy. ELISA assays were used to evaluate markers of oxidative stress (ROS, NO) and inflammation (TNF-α) after stimulation of microglial cells with lipopolysaccharides (LPS), following treatment with increasing doses of free N-acetyl- l-cysteine (NAC) or PAMAM–(COOH) 46–(NAC) 18 conjugate containing an equivalent molar concentration of NAC. Flow cytometry and confocal microscopy demonstrated the PAMAM–(COOH) 62–(FITC) 2 conjugate entered BV-2 cells rapidly with significant increase in fluorescence within 15 min and localized mostly in the cytoplasm. PAMAM–(COOH) 46–(NAC) 18 conjugate was non-toxic, and significantly reduced ROS, NO and TNF-α release by activated microglial cells after 24 h and 72 h stimulation of LPS following 3 h pre-treatment when compared to the same concentration of free NAC ( P < 0.05 or P < 0.01). Anionic PAMAM dendrimer–NAC conjugate was synthesized with a glutathione sensitive linker for intracellular release. The non-toxic conjugate is a more effective anti-oxidant and anti-inflammatory agent when compared to free NAC in vitro. The conjugate showed significant efficacy even at the lowest dose (0.5 mM NAC), where the activity was comparable or better than that of free drug at 8 mM (16× higher dosage). The improved efficacy of the conjugate, when combined with the intrinsic neuroinflammation-targeting ability of the PAMAM dendrimers, may provide new opportunities for in vivo applications.