Lysozyme Transport to the Brain by Liposomes

Abstract

Delivery of drugs into the brain is limited due to poor penetrability of many drugs via the blood-brain barrier. Previous studies have shown that the brain is kept under close surveillance by the immune system, implying that circulating phagocytic cells, such as neutrophils and monocytes, are crossing the blood-brain barrier. We hypothesized that charged liposomes could be transported to the brain following their phagocytosis by circulating monocytes. In this work, we investigated the capacity of circulating monocytes to be exploited as a drug delivery system following IV administration of nano-sized, positively fluorescently labeled liposomes containing the protein lysozyme. Negatively charged fluorescently labeled liposomes were used for comparison. By using a modified thin-film hydration technique, the desired properties of the liposomal formulations were achieved including size, polydispersity index, high drug concentration, and stability. In vitro results showed a significant time-dependent uptake of positively charged liposomes by RAW264.7 cells. In vivo results revealed that circulating white blood cells (mainly monocytes) contained high levels of fluorescently labeled liposomes. Screening of brain sections using confocal microscopy uncovered that a substantial amount of fluorescently labeled liposomes, in contrast to the fluorescent markers in solution, was transported into the brain. In addition, anti-CD68 immunofluorescent staining of brain sections demonstrated co-localization of positively charged liposomes and macrophages in different brain sections. Furthermore, significantly higher levels of lysozyme were detected in brain lysates from rats treated with positively charged liposomes compared to rats treated with lysozyme solution. Taken together this confirms our hypothesis that the designed liposomes were transported to the brain following their phagocytosis by circulating monocytes. [READ ARTICLE](https://precisionnanomedicine.com/article/6490)