Lysozyme Transport to the Brain by Liposomes

One of the major limiting factors in the development of new drugs for brain diseases is the blood–brain barrier (BBB). Developing an efficient and non-invasive drug delivery system for brain therapy, without affecting the BBB tissue, is of high merit. Both circulating monocytes and neutrophils phagocyte foreign particles in the blood. Since the brain is under immunological surveillance, allowing monocytes and neutrophils to cross the BBB, those cells can be exploited to deliver particulate drugs into the brain. The propensity of monocytes for rapid recognition of particulate matter, the major clearance mechanism of IV administered particulate delivery systems, provides a rational approach to formulate specific ‘non-stealth’ liposomes for increased uptake by circulating monocytes. In this work, we investigated circulating monocytes capacity to be exploited as a drug delivery system following IV administration of positively fluorescently labeled liposomes containing the protein lysozyme. Negatively charged fluorescently labeled liposomes were used for comparison. In vivo results disclosed that circulating WBC (mainly monocytes) contained high levels of fluorescently-labeled liposomes. Screening of brain sections using confocal microscopy revealed that a substantial amount of fluorescently-labeled liposomes, compared to free fluorophore, was transported into the brain. In addition, anti-CD68 immunofluorescent staining of brain sections, demonstrated co-localization of positively charged liposomes and monocytes in different sections of the brain. Furthermore, significant higher levels of lysozyme were detected in brain lysates from rats treated with positively charged liposomes containing lysozyme compared to rats treated with lysozyme solution. It can be concluded that blood circulating monocytes, phagocytize the IV injected lysozyme laden liposomes and migrate to the brain with their cargo. Since enhanced monocyte migration to the brain is associated with various brain pathologies (Alzheimer’s, Parkinson’s, and brain tumors), this delivery system could be found useful in delivering drugs to the brain.