Microsphere-Based Drug Delivery to Alveolar Macrophages - a Review

Abstract

The lungs have a large surface area and high permeability, hence pulmonary delivery systems provide both local and systemic therapeutic effects. Pulmonary delivery system has been selected by many researchers because the route of administration is not invasive, has low metabolic activity, controlled environment for systemic absorption and avoids first pass metabolism. Alveolar macrophages are the first defense in the lung tissue to fight airborne pollutant, other foreign particle and pathogen by phagocytosis mechanism. Alveolar macrophages play an important role in the process of activation of the adaptive immunity including in inflammation and cancer diseases. Drug targeting to alveolar macrophages can achieve improvement in efficacy of therapeutic treatment for medical conditions including tumor, cancer, inflammation and infection. Respiratory infection-causing bacteria such as tuberculosis and pneumonia are able to survive in alveolar macrophages and they turn macrophages become a reservoir. This presents the challenge of making macrophages as targets in pulmonary delivery system because most of drugs do not reach the macrophages level effectively. To achieve this goal, the use of carrier particles in either micro-sized or nano-sized technology is the right choice. This review focuses on the influences of various physicochemical properties of microspheres carrier include particle size, aerosolisation property, morphology surface charge, surface properties and hydrophilicity on their uptake by alveolar macrophages either enhance macrophages uptake or decrease macrophages uptake. Making macrophage a target of treatment especially for infectious diseases is a promising strategy to improve the efficacy of treatment although in its development there are still many challenges.