Assessment of mucoadhesion by a resonant mirror biosensor
Introduction
The concept of mucosal adhesives, or mucoadhesives, was introduced into the controlled drug delivery area in the early 1980s (Ahuja et al., 1997) and has gained much attention in the last two decades. Mucoadhesive polymers are able to interact with mucus which is secreted by the underlying tissue (Mathiowitz et al., 1999). More specifically, it is predicted that such polymers interact with mucus glycoprotein, called mucins, which are responsible for gel-type characteristics of the mucus. Mucoadhesive polymers can increase the contact time with the mucosal tissue and moreover also increase directly drug permeability across epithelial barriers (Robinson and Mlynek, 1995). Mucoadhesive polymers are applied in the field of local drug delivery, i.e. nasal, ocular, vaginal and intra-oral, and can increase the bioavailability dramatically.
Duchene et al. (1988) proposed the following three stages in mucoadhesion. Initially, an intimate contact (wetting) between the mucus gel and the swelling mucoadhesive polymer is required. This is followed by the penetration of the mucoadhesive polymer into the mucus gel network and entanglement of polymer and mucin chains. Third stage is the formation of weak chemical bonds between entangled chains. However, despite many studies in recent years, the phenomenon of mucoadhesion is not fully understood. Adhesion of certain polymers to mucus is a complex event and depends on the properties of the polymer, the biological substrate and the surrounding environment (Tamburic and Craig, 1997). Visualization studies of the mucoadhesive interface have questioned the second step in the mucoadhesion process (Lehr et al., 1992c). In this study, no evidence for intermixing between mucus and mucoadhesive hydrogel was found to occur in the μm-range. Interpenetration of free polymer chain ends, however, may still be possible in the nm-range.
Many papers have been published presenting slightly different theories and mechanisms of mucoadhesion. The reason for this disagreement is maybe not so surprising because there have been so many different in vivo and in vitro methods utilized to measure mucoadhesive properties of polymers, resulting in inconsistent results (Peppas and Buri, 1985, Saettone et al., 1989, Junginger, 1991, Lehr et al., 1992b, Mortazavi and Smart, 1994, Mortazavi and Smart, 1995, Tamburic and Craig, 1997, Madsen et al., 1998a, Madsen et al., 1998b, Sigurdsson et al., 2002, Keely et al., 2005). Some viscosity enhancing polymers have also been considered as mucoadhesive. Although formulations containing these viscosity enhancing polymers may eventually also lead to a reduced clearance from the site of application (e.g. after ocular or nasal instillation), such effects must not be confused with “wet-on-wet” mucoadhesion, which should be only used to address the rather remarkable adhesion of a polymeric hydrogel to another one in the presence of excess liquid. Moreover, besides such “wet-on-wet” adhesion, there may also be some remarkable sticking of dry hydrophilic polymers when brought in contact to a wet or humid surface. Although this kind of “sticking” has been referred to as mucoadhesion by some authors as well (Mortazavi and Smart, 1995, Accili et al., 2004, Smart, 2005), binding forces typically decrease dramatically in the presence of excess amounts of water (“over hydration”) (Henriksen et al., 1996). Such “dry-on-wet” adhesion probably involves quite different mechanisms (including, e.g. capillary attraction) and should therefore be strictly separated from the “wet-on-wet” adhesion of swollen mucoadhesive polymers to mucous surfaces, to which we are referring in this article.
In this situation, mucoadhesive polymers must demonstrate significant interaction with the mucus glycoprotein even in fully hydrated state and in the presence of excess amount of water. The initial phase stage of mucoadhesive contact, penetration and subsequent binding, appears to be mainly governed by surface energy effects and spreading phenomena, as it was found that measuring surface energy and spreading coefficients can predict mucoadhesive performance (Lehr et al., 1992a, Lehr et al., 1993). However, for optimal design of mucoadhesive drug delivery system, a better understanding of the molecular interactions between the glycoprotein and the polymer is needed, which most likely govern the later stages of mucoadhesive bonding after the surface energy initial contact and spreading.
In the last decade, the optical biosensor technique based on evanescent waves has become an established method of measuring molecular interactions (Rich and Myszka, 2000, Ward and Winzor, 2000). This technique allows monitoring any interaction between two molecules in real time without any label or tag as long as one of the molecules can be immobilized, with covalent or non-covalent bonds, on the surface of such system and the other stays in solution above the surface. Binding of molecules in solution to surface-immobilized molecules alters the refractive index of the medium near the surface and by utilizing a red laser which sweeps a range of incident angles, this tiny change in refractive index gives rise to a measurable signal. Great care must be taken to monitor all non-specific binding to the system surface. Common applications include ligand fishing, assay development and target identification (Cooper, 2002). To our knowledge, the resonant mirror biosensor has not been used before to quantify interactions between glycoprotein and polymers.
The aim of this study was to use an optical biosensor technique based on the resonant mirror principle to measure the interaction between several different polymers and mucus glycoprotein (step 3 in the mucoadhesion process defined by Duchene). This study should answer the following questions:
- 1.
Which polymers are can form weak chemical bond to proteins and when?
- 2.
What structural features of polymers are necessary for the formation of these bonds?
Bovine submaxillary mucin was chosen as a substrate, representing the major glycosylated protein in mucus. For comparison, non-glycosylated bovine serum albumin was also used as a substrate.
Section snippets
Materials
Carboxymethylcellulose sodium salt (Tylopur C300P) (CMC) (Hoechst, Frankfurt, Germany), hydroxypropyl methylcellulose (Pharmacoat 606) (HPMC) (Shin-Etsu Chemical, Mühlheim, Germany), Carbopol® 934 (BF Goodrich, Chicago, USA), chitosan (Seacure 210+) (Pronova A/S, Drammen, Norge), chitosan (Protasan UP G) (Novamatrix, Oslo, Norway), Sodium alginate (Pronova UP) (Novamatrix, Oslo, Norway), and sodium hyaluronate pharma grade (Novamatrix, Oslo, Norway).
Bovine submaxillary mucin type I-S (BSM) and
Results
Examples of chitosan binding curves to BSM at various concentrations are shown in Fig. 1. Maximum binding capacity of the immobilized protein can be calculated from this data. At least six different concentrations of polymers were tested to calculate the maximum binding capacity (for method A).
Fig. 2, Fig. 3 show relative binding (w/w) of the polymers tested to BSM and BSA utilizing method A and method B, respectively. Both methods gave similar results. HPMC and hyaluronate did not interact
About the methods
Method A has two drawbacks when studying glycoprotein–polymer interaction. The glycoprotein is very large molecule and therefore is unlikely to completely cover the surface of the cuvette when immobilized (because of spatial hindrance). This opens up the possibility for the polymer to bind non-specifically to the bare surface of the cuvette, even though all the unreacted sites have been blocked with ethanolamine.
Mucoadhesive polymers bind very strongly to the glycoprotein. Some acid or base is
Conclusion
The use of an optical biosensor technique based on a resonant mirror has not been used before to quantify the interaction between mucin and candidate mucoadhesive polymers. The ranking of mucoadhesive binding strength obtained by resonant mirror technique corroborates with the outcome of earlier studies by other techniques except those performed under “dry-on-wet” conditions. Candidate mucoadhesive polymers must feature ionizable functional groups to be able to from weak chemical bonds with
Acknowledgement
This study was supported by the Marie-Curie Fellowship (MEST-CT-2004-504992).
References (34)
- et al.
Mucoadhesion dependence of pharmaceutical polymers on mucosa characteristics
Eur. J. Pharm. Sci.
(2004) - et al.
Molecular parameters of submaxillary mucins
Arch. Biochem. Biophys.
(1965) - et al.
Light-scattering studies of bovine submaxillary mucin
Biochim. Biophys. Acta
(1962) - et al.
Principle and investigation of the bioadhesion mechanism of solid dosage forms
Biomaterials
(1992) - et al.
Mucoadhesive buccal disks for novel nalbuphine prodrug controlled delivery: effect of formulation variables on drug release and mucoadhesive performance
Int. J. Pharm.
(1999) - et al.
Bioadhesion of hydrated chitosans: An in vitro and in vivo study
Int. J. Pharm.
(1996) - et al.
A surface-energy analysis of mucoadhesion. 2. Prediction of mucoadhesive performance by spreading coefficients
Eur. J. Pharm. Sci.
(1993) - et al.
Invitro evaluation of mucoadhesive properties of chitosan and some other natural polymers
Int. J. Pharm.
(1992) - et al.
Visualization studies of the mucoadhesive interface
J. Contr. Release
(1992) - et al.
A rheological assessment of the nature of interactions between mucoadhesive polymers and a homogenised mucus gel
Biomaterials
(1998)
A rheological examination of the mucoadhesive/mucus interaction: the effect of mucoadhesive type and concentration
J. Contr. Release
An investigation of some factors influencing the in-vitro assessment of mucoadhesion
Int. J. Pharm.
Surface, interfacial and molecular aspects of polymer bioadhesion on soft tissues
J. Contr. Release
Nanoscale technology of mucoadhesive interactions
Adv. Drug Deliver. Rev.
Advances in surface plasmon resonance biosensor analysis
Curr. Opin. Biotechnol.
Bioadhesive and phase-change polymers for ocular drug-delivery
Adv. Drug Deliver. Rev.
Evaluation of muco-adhesive properties and invivo activity of ophthalmic vehicles based on hyaluronic-acid
Int. J. Pharm.
Cited by (48)
An optical sensor combining surface plasmon resonance, light extinction, and near-critical angle reflection, for thin liquid film biochemical sensing
2022, Optics and Lasers in EngineeringCitation Excerpt :They offer significant advantages over other well-developed technologies such as electrochemical [11], piezoelectric [12] or magnetic sensors [13], including lower noise and immunity to electromagnetic interference [10]. Refractometric sensing devices [14,15] belong to the optical sensors that include integrated optical Mach-Zehnder interferometers [16], resonant mirrors [17], grating coupler sensors [18], and surface plasmon resonance (SPR) sensors [19–21]. The latter sensors are thin film refractometers that measure changes in the refractive index (RI) occurring at the surface of a metal film supporting a surface plasmon.
Mucoadhesive Polymers: Gateway to Innovative Drug Delivery
2021, Modeling and Control of Drug Delivery SystemsMucoadhesion as a strategy to enhance the direct nose-to-brain drug delivery
2021, Direct Nose-to-Brain Drug Delivery: Mechanism, Technological Advances, Applications, and Regulatory UpdatesApplications of Polymers in Buccal Drug Delivery
2020, Applications of Polymers in Drug DeliveryFunctionalized materials for multistage platforms in the oral delivery of biopharmaceuticals
2017, Progress in Materials Science