Extrapulmonary Surfactant Therapy: Review of Available Data and Research/Development Issues

Surfactant proteins and innate immunity of otitis media

Otitis media (OM) is the most common disease among young children and one of the most frequent reasons to visit the pediatrician. Development of OM requires nasopharyngeal colonization by a pathogen which must gain access to the tympanic cavity through the eustachian tube (ET) along with being able to overcome the defense mechanisms of the immune system and middle ear mucosa. OM can be caused by viral or bacterial infection. The three main bacterial pathogens are Streptococcus pneumoniae, nontypeable Haemophilus influenzae (NTHi), and Moraxella catarrhalis. Innate immunity is important in OM resolution as the disease occurs in very young children before the development of specific immunity. Elements of innate immunity include natural barriers and pattern recognition receptors such as Toll like receptors (TLRs), and Nod like receptors (NLRs). Surfactant proteins A (SP-A) and D (SP-D) act as pattern recognition receptors and are found in the lung and many other tissues including the ET and the middle ear where they probably function in host defense. Surfactant has a potential for use in the treatment of OM due to surface tension lowering function in the ET, and the possible immune functions of SP-D and SP-A in the middle ear and ET.

Pulmonary surfactant: a unique biomaterial with life-saving therapeutic applications

Pulmonary surfactant is a complex lipoprotein mixture secreted into the alveolar lumen by type 2 pneumocytes, which is composed by tens of different lipids (approximately 90% of its entire mass) and surfactant proteins (approximately 10% of the mass). It is crucially involved in maintaining lung homeostasis by reducing the values of alveolar liquid surface tension close to zero at end-expiration, thereby avoiding the alveolar collapse, and assembling a chemical and physical barrier against inhaled pathogens. A deficient amount of surfactant or its functional inactivation is directly linked to a wide range of lung pathologies, including the neonatal respiratory distress syndrome. This paper reviews the main biophysical concepts of surfactant activity and its inactivation mechanisms, and describes the past, present and future roles of surfactant replacement therapy, focusing on the exogenous surfactant preparations marketed worldwide and new formulations under development. The closing section describes the pulmonary surfactant in the context of drug delivery. Thanks to its peculiar composition, biocompatibility, and alveolar spreading capability, the surfactant may work not only as a shuttle to the branched anatomy of the lung for other drugs but also as a modulator for their release, opening to innovative therapeutic avenues for the treatment of several respiratory diseases.