Dexamethasone conjugated polyethylenimine as an efficient gene carrier with anti-inflammatory effect for gene therapy of LPS-induced acute lung injury

Abstract

Acute respiratory distress syndrome(ARDS)/acute lung injury (ALI) is caused by disruption of the lung alveolar-capillary membrane barrier. ARDS/ALI is characterized by a severe acute inflammatory response in the lung and neurtrophilic alveolitis. In this study, dexamethasone conjugated low molecular polyethylenimine (2 kDa, PEI-Dexa) was synthesized as a water-soluble glucocorticoid steroid and a gene carrier for gene therapy of ALI. To confirm the anti-inflammatory effect of PEI-Dexa, PEI-Dexa/p -Luc complexes were transfected into LPS stimulated macrophage cell line (RAW 264.7). After 24hrs, ELISA was performed to measure the levels of TNF- , IL-1 , and IL-6. The results showed that PEI-Dexa transfected RAW 264.7 cells secreted less amount of inflammatory cytokines compared to LPS induced control cells. However, PEI 2K/p -Luc and PEI 25K/p -Luc complexes transfected cells did not show this effect. This result indicated that PEI-Dexa had anti-inflammatory effect. Then, PEI-Dexa was characterized as a gene carrier. In vitro transfection and MTT assays showed that PEI-Dexa showed lower toxicity to L2 lung epithelial cells than high molecular weight polyethylenimine (PEI 25K). In addition, PEI-Dexa had transfection efficiency comparable to PEI 25K, suggesting that PEI-Dexa is useful for gene delivery to lung epithelial cells. For in vivo study, PEI-Dexa, PEI 2K and PEI 25K/pCMV-Luc complexes were administrated into the mice lungs by intratracheal injection. Saline was used as a control. Gene delivery efficiency of carriers was measured by luciferase assay. The results showed PEI-Dexa had higher delivery efficiency to the mouse lung than PEI 2K or PEI 25K. Finally, in vivo anti-inflammatory effect of PEI-Dexa was evaluated. ALI was induced by intratracheal administration of LPS (0.5mg/kg) in male BALB/c mice. PEI-Dexa/p -Luc complexes were administered to ALI mouse model. After 24hrs, the level of TNF- was determined in BALF and lung tissues. The results indicated that PEI-Dexa reduced the inflammation in the LPS induced ALI. Therefore, PEI-Dexa is a gene carrier with dual-functions of anti-inflammation and gene delivery, and may be useful for gene therapy of ALI.