title: Influence of molecular shape, conformability, net surface charge, and tissue interaction on transscleral macromolecular diffusion.
abstract: The purpose of this study was to investigate the influence of molecular shape, conformability, net surface charge and tissue interaction on transscleral diffusion. Unfixed, porcine sclera was clamped in an Ussing chamber. Fluorophore-labelled neutral albumin, neutral dextran, or neutral ficoll were placed in one hemi-chamber and the rate of transscleral diffusion was measured over 24 h using a spectrophotometer. Experiments were repeated using dextrans and ficoll with positive or negative net surface charges. Fluorescence recovery after photobleaching (FRAP) was undertaken to compare transscleral diffusion with diffusion through a solution. All molecules were 70 kDa. With FRAP, the diffusion coefficient (D) of neutral molecules was highest for albumin, followed by ficoll, then dextran (p < 0.0001). Positive dextrans diffused fastest, followed by negative, then neutral dextrans (p = 0.0004). Neutral ficoll diffused the fastest, followed by positive then negative ficoll (p = 0.5865). For the neutral molecules, transscleral D was highest for albumin, followed by dextran, then ficoll (p < 0.0001). D was highest for negative ficoll, followed by neutral, then positive ficoll (p < 0.0001). By contrast, D was highest for positive dextran, followed by neutral, then negative dextran (p = 0.0021). In conclusion, diffusion in free solution does not predict transscleral diffusion and the molecular-tissue interaction is important. Molecular size, shape, and charge may all markedly influence transscleral diffusion, as may conformability to a lesser degree, but their effects may be diametrically opposed in different molecules, and their influence on diffusion is more complex than previously thought. Each variable cannot be considered in isolation, and the interplay of all these variables needs to be tested, when selecting or designing drugs for transscleral delivery.
authors: Department of Physics, King's College London, United Kingdom; School of Medicine, King's College London, London, United Kingdom.
authors: Nishanthan
authors: N
authors: Srikantha
authors: Fatma
authors: F
authors: Mourad
authors: Klaus
authors: K
authors: Suhling
authors: Naba
authors: N
authors: Elsaid
authors: James
authors: J
authors: Levitt
authors: Pei Hua
authors: PH
authors: Chung
authors: Satyanarayana
authors: S
authors: Somavarapu
authors: Timothy L
authors: TL
authors: Jackson
mesh_terms: D000818:Animals; D003911:Dextrans / Q000737:chemistry / Q000493:pharmacokinetics*; D004058:Diffusion; D015194:Diffusion Chambers, Culture; D005362:Ficoll / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000737:chemistry / Q000493:pharmacokinetics; D017078:Laser-Doppler Flowmetry; D008027:Light; D008970:Molecular Weight; D046912:Multiprotein Complexes / Q000737:chemistry / Q000493:pharmacokinetics*; D010539:Permeability; D011487:Protein Conformation; D012542:Scattering, Radiation; D012590:Sclera / Q000378:metabolism*; D012709:Serum Albumin / Q000737:chemistry / Q000493:pharmacokinetics*; D013050:Spectrometry, Fluorescence; D013552:Swine
chemical_list: D003911:Dextrans; C518288:FITC-albumin; D046912:Multiprotein Complexes; D012709:Serum Albumin; C045540:fluorescein 5-isothiocyanate-Ficoll; C015219:fluorescein isothiocyanate dextran; D005362:Ficoll; D016650:Fluorescein-5-isothiocyanate