(86a) Investigation of the Interactions of Drug Delivery Vehicles with Pulmonary Mucus Layer

Pulmonary route is considered to be advantageous in drug delivery owing to very large surface area and absorption characteristics of lungs. However, the airways are covered with the mucus layer, which serves as a barrier to exogenous matters and provides a natural defense to immune system with its self-cleaning mechanism. Therefore, it is difficult to achieve a successfully working drug delivery system through the lungs. Moreover, during the course of several lung diseases such as Chronic Obstructive Pulmonary Disease (COPD) or cystic fibrosis (CF), the thickness and the viscosity of the mucus layer increases and this change at the physicochemical parameters of the barrier turns out to be a real challenge towards the diffusion and the delivery of the therapeutics[1]. In this case, traditional aerosolized drugs can be ineffective and a more efficient way to provide a better treatment should be considered. It is known that the diffusion of drugs, particles or nanocarriers is considerably hindered by the mucus via several interactions between the particles and mucus layer. Most of them are removed from the airways via the mucus clearance mechanism before they reach to underlying epithelium. In the literature, different approaches have been developed in order to protect the drug carriers from both the macrophages and clearance mechanism and to enhance the penetration of drugs. These include the encapsulation of the drugs in synthetic or natural degradable polymeric particles/capsules, stealth design of the particles, usage of liposomal delivery systems, etc. Mostly, the surface of the particles within the size range of 100-500 nm modified with non-ionic surfactants, carboxyl or amine groups, which provided the opportunity to study with different surface charges[2]. However, the penetration behavior of the drug delivery systems through the mucus layer is still needs to be enhanced. In order to achieve better diffusion of drug carriers, primarily interactions between the drug carriers and mucus should be understood well.

In this study, solid lipid nanoparticles (SLN) with different size and surface properties are used as the model drug delivery vehicle and their interactions with mucin, which is the key glycoprotein of mucus, are investigated in detail. SLNs are biocompatible structures and their lipid contents makes them advantageous in drug delivery. In addition, their stability is considerably high and they can be used as nanocarriers by encapsulating drugs. These and many other properties makes SLNs as preferred carriers to be used in a lot of areas especially in biomedical[3]. Interactions of SLNs with mucin are firstly determined by using Dynamic Light Scattering and Zeta Potential before and after incubating the SLNs to mucin solution. This method provided us to detect a possible evidence for interactions between particles and mucin by investigating the changes at the surface charge and size of the particles. Within the study, in order to determine the effect of zeta potential and size of the particles, three different SLNs are used. Investigations are studied further with Langmuir Through at the air/PBS interface by introducing the particles beneath the mucin layer that is previously formed and compressed to a chosen surface pressure. This lead us to study with mucin layer at different thicknesses and helped us to understand if the particles can adsorb, integrate and penetrate through mucin membrane. Moreover, the interfaces obtained at different surface pressures are transferred to substrates and analyzed by using Atomic Force Microscopy (AFM).

In the literature, it is reported that the penetration behavior of the particles enhance when their charge is close to zero due to their less interactions with mucus[4]. In this study, zeta potential values of the SLNs in 1 mM NaCl solution are obtained as -9.49 ±1.41 mV, -22.14 ±2.08 mV and -25.17 ±3.18 mV, respectively. It is obtained that, after incubation in mucin solution, the potential values of the particles have not changed significantly even when the mucin concentration was increased. This proves the fact that mucin does not stick on the particles and particles have no interaction with adhesive mucin. This result has been also supported by the DLS and AFM measurements: size of the particles has not increased significantly. In order to mimic the mucus membrane, mucin solution is spread on air/NaCl solution interface and to understand if the particles can adsorb or create a change at the membrane, interfacial behaviors of both the mucin membrane and SLNs have also been obtained by measuring the surface pressure with time. Cyclic compression-expansion behavior of the interfaces formed by mucin and SLNs are also obtained. From the surface pressure-time isotherms, for all surface pressures, it is determined that SLNs have adsorbed to the mucin layer, diffused through the membrane and reached to the interface even at high surface pressures and increased mucin thickness. The results of this study are promising in terms of obtaining a mucus penetrating drug delivery vehicle and understanding its interactions with mucin.

REFERENCES

[1] S.K. Lai, YY. Wang, J. Hanes, Advanced Drug Delivery Reviews, 61 (2009) 158â??171.

[2] J.S. Suk, S.K. Lai, YY. Wang, L.M. Ensign, P.L. Zeitlin, M.P. Boyle, J. Hanes, Biomaterials, 30 (2009) 2591â??2597.

[3] L. Battaglia, M. Gallarate, E. Peira, D. Chirio, E. Muntoni, E. Biasibetti, M.T. Capucchio, A. Valazza, P.P. Panciani, M. Lanotte, D. Schiffer, L. Annovazzi, V. Caldera, M. Mellai, C. Riganti, Journal of Pharmaceutical Sciences, 103 (2014) 2157â??2165.

[4] Y. Cu, W.M. Saltzman , Molecular Pharmaceutics, 6 (2008) 173-181.