Targeting inhaled therapy beyond the lungs

Pulmonary disease has been the primary target of inhaled therapeutics for over 50 years. During that period, increasing interest has arisen in the use of this route of administration to gain access to the systemic circulation for the treatment of a number of diseases beyond the airways. In order to effectively employ this route, the barriers to transport from the lungs following deposition of aerosols must be considered, including the nature of the disease (whether proximal, as in pulmonary hypertension, or distal, as in diabetes). Delivery to the systemic circulation begins with the efficiency of aerosol generation and subsequent deposition in the airways and proceeds to the influence of mechanisms of clearance, including absorption, metabolism, and mucociliary and cell-mediated transport, on the residence time of the drugs in the lungs. The nature of the drug (small or large molecules/low or high molecular weight), susceptibility to degradation and general physicochemical properties play a role in the chemistry of its formulation, physics of aerosol delivery and biology of disposition.

Aerosol delivery of muramyl dipeptide to rodent lungs

Tuberculosis is the single most serious infectious disease worldwide. The respiratory tract is the primary site of infection by Mycobacterium tuberculosis(MTB). A number of immunogenic components of the cell wall of MTB, if delivered to the lungs as aerosols, can be used to study the local immune response. The site of deposition of these aerosols can be employed to control their residence time in the lungs. Muramyl dipeptide (MDP) aerosols were delivered to alveolar macrophages in the lungs of rodents. Guinea pig macrophages harvested by bronchoalveolar lavage were examined by differential interference contrast microscopy for morphological changes indicative of activation. Bronchoalveolar lavage fluid was analyzed for the presence of alkaline phosphatase, lactate dehydrogenase, N-acetyl-glucosaminidase (NAG), and total protein content. Rat alveolar macrophages were studied for the production of nitric oxide, by induction of nitric oxide synthase. Twenty-four hours following exposure to an aerosol of MDP, alveolar macrophages exhibited morphological characteristics (spreading and pseudopodia), enzyme activity (NAG 50% above control), and production of the reactive intermediate nitric oxide. Rat macrophages subjected to aerosol exposure to MDP when challenged with a second dose of MDP or lipopolysaccharide exhibited a linear dose response as measured by nitric oxide production. These studies indicate that the topical delivery of an MTB bacterial cell wall component, muramyl dipeptide, results in activation of alveolar macrophages. This approach may be useful in elucidating elements of the immune response to MTB.