Macrophages as Nanocarriers for Drug Delivery: Novel Therapeutics for Central Nervous System Diseases

Many central nervous system (CNS) diseases were thought to be untreatable due to the presence of the blood-brain barrier (BBB). The chemokine gradients secreted from CNS parenchyma can induce macrophage migration to the brain, induce firm adherence to the endothelium of BBB, and eventually to enter the brain parenchyma. Macrophages migrating into CNS can promote neuron regeneration, induce inflammation and angiogenesis. These properties can potentially allow macrophages to act as carriers for drug/nano formulations across the BBB, and reach the potential target sites. Many nanomaterials cannot be used for the management of CNS diseases because of their low carrying efficiency. Macrophage which transports nanomaterials to pathological sites is rendered as an attractive tool for the transportation of drugs to previously inaccessible regions within the brain parenchyma. Nanomaterials engulfed by macrophages can be released at target sites, and be used for therapeutic or diagnostic purposes. In this review, we focus on macrophages as the cell-carrier to deliver nano-drugs into CNS, describe the biological behavior of macrophages during pathological conditions and discuss the application of cell drug delivery system in recent years.