Novel tear film supplements: a potential application for synthetic protein-phospholipid complexes

Purpose: Surfactant proteins A, B, C and D complex with (phospho)lipids to produce surfactants which provide low interfacial tensions. It is likely that similar complexation occurs in the tear film and contributes to its low surface tension. Synthetic protein-phospholipid complexes, with styrene maleic anhydrides (SMAs) as the protein analogue, have been shown to have similarly
low surface tensions. This study investigates the potential of modified SMAs and/or SMA-phospholipid complexes, which form under physiological conditions, to supplement natural tear film surfactants.
Method: SMAs were modified to provide structural variants which can form complexes under varying conditions. Infrared spectroscopy and Nuclear Magnetic Resonance were used to confirm SMA structure. Interfacial behaviour of the SMA and SMA-phospholipid complexes was studied using Langmuir trough, du Nûoy ring and pulsating bubblemethods. Factors which
affect SMA-phospholipid complex formation, such as temperature and pH, were also investigated.
Results: Structural manipulation of SMAs allows control over complex formation, including under physiological conditions (e.g. partial SMAesterfication allowed complexation with dimyristoylphosphatidylcholine, at pH7). The low surface tensions of the SMAs (42mN/m for static (du Nûoy ring) and 34mN/m for dynamic (Langmuir) techniques) demonstrate their
surface activity at the air-aqueous interface. SMA-phospholipid complexes provide even lower surface tensions (~2 mN/m), approaching that of lung surfactant, as measured by the pulsating bubblemethod.
Conclusions: Design of the molecular architecture of SMAs allows control over their surfactant properties. These SMAs could be used as novel tear films supplements, either alone to complex with native tear film phospholipids or delivered as synthetic protein-phospholipid complexes.