Sedimentation analysis of potential interactions between mucins and a putative bioadhesive polymer

Abstract

Abstract.A potentially fruitful but hitherto relatively unexplored application of the analytical ultracentrifuge is the investigation of interactions in pharmaceutical polymer drug carrier systems. In this study we investigate the interactions of the cationic material chitosan with gastric mucin: 1) The physicochemical properties of gastric mucin and chitosan (highly deacetylated chitosan "Sea Cure + 210") in solution are summarised; 2) We described how the gastric mucin (from pig) can be purified by a combination of preparative isopycnic density gradient ultracentrifugation and gel chromatography, and how its purity and structural integrity can be checked by analytical isopycnic density gradient ultracentrifugation (on a MSE Centriscan 75 Analytical Ultracentrifuge) and on line GPC/MALLS (gel permeation chromatography coupled on-line to a multi-angle laser light scattering photometer); 3) Using co-sedimentation experiments with the appropriate controls in an XL-A Ultracentrifnge (absorption optics) and an MSE Mk II Analytical Ultracentrifuge (Schlieren optics) a definite interaction between chitosan and pig gastric mucin was demonstrated, with complexes sedimenting faster than 1000 S, depending on the amount of the mucin used.

Atomic force microscopy of gastric mucin and chitosan mucoadhesive systems

“…150 nm (visualized in the same way as those structures at 0.1 M). Noticeably there is a greater number of these ' mucoadhesive complexes ' at 0.1 M ionic strength, suggesting a reduction in interaction between the mucin and chitosan as the ionic strength increases beyond physiologically relevant conditions, and consistent with what was observed earlier by molecular hydrodynamics [7,29]. Charge suppression clearly reduces the amount of electrostatic interaction.…”

“…As has been previously indicated [7,19,20,29] a significant interaction has been shown between the purified PGM and this form of chitosan on the basis of molecular hydrodynamics, electron microscopy and scanning tunnelling microscopy, consistent with macroscopic tensiometry studies [9]. Figure 4 illustrates the complex formed between the chitosan and mucin structures when mixed together in solution and then immobilized to the APTES-coated substrate.…”

“…Earlier hydrodynamic studies [13,29] have shown a clear effect on mucin-chitosan complexes by increasing the ionic strength. Figure 5 shows the characteristic mucin (Figures 5a and 5c) and complex (Figures 5b and 5d) structures at 0.2 M and 0.3 M ionic strength, respectively.…”

Advances in Mucoadhesion and Mucoadhesive Polymers

“…[61] When hydroxypropylmethylcellulose (HPMC) was added to mucin dispersion instead of chitosans and Carbopols, the zeta-potential of particles remained unchanged, indicating poor mucoadhesive affinity of this non-ionic polysaccharide. [61] In a series of publications Harding and coworkers [69][70][71][72] have reported the use of analytical centrifugation to probe mucoadhesive interactions between freshly isolated mucins and various polymers in solution mixtures. They demonstrated that interactions between mucins and mucoadhesive polymers result in the changes of the sedimentation velocity and molecular weights due to the formation of large complex aggregates.…”

Drug Targeting in IBD Treatment – Existing and New Approaches

“…Anionic polymers (polyacrylates and cellulose derivatives) and cationic polymers (chitosan) interact with mucus layer through non-covalent interactions (hydrophobic interactions, hydrogen binding, van der Waals interactions, electrostatic interactions) modulated by pH and ionic strength of the environment. Alginate (anionic polymer) is also citied among polymers with mucoadhesive properties involving hydrogen bonding of alginate carboxylic groups with mucus layer as a mechanism of mucoadhesive interaction (Chickering, 1995;Deacon et al, 2000;Fiebrig, 1994;Gombotz & Wee, 1998;Hejazi & Amiji, 2003;Wittaya-Areekul et al, 2006). Thiolated polymers of polyacrylates and cellulose derivatives as well as chitosan thiolated polymers exibit cationic covalent bonding building strong covalent disulfide bonds with the cysteine domains of mucins (Bernkop-Schnurch et al, 1999).…”