Synthesis and characterization of a cysteine xyloglucan conjugate as mucoadhesive polymer

Mangesh Bhalekar,Shamkant Shimpi,Savita Sonawane

doi:10.1590/s1984-82502013000200010

Mangesh Bhalekar, Shamkant Shimpi + Show 1 more

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https://doi.org/10.1590/s1984-82502013000200010

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Abstract

The aim of this study was to improve the mucoadhesive potential of xyloglucan polymer by the covalent attachment of cysteine as thiol moiety. The parent polymer xyloglucan was chemically modified by introducing sulphydryl bearing compound L-cysteine HCl. Different batches of xyloglucan-cysteine conjugates were prepared at varying reaction pH (2-6) and evaluated for optimum thiol incorporation, disulphide group content, swelling behavior, rheological properties and mucoadhesive properties. The obtained conjugates characterized in vitro by quantification of immobilized thiol groups; showed maximum thiol incorporation on xyloglucan (7.67 ± 0.14 %) at pH 5. The disulphide group content was found maximum (2.83 ± 0.12) at pH 6. The water uptake at end of 4 h was 5.0 for xyloglucan and was found to decrease in thiolated derivatives with increase in thiolation. Mucoadhesion studies revealed that mucoadhesion of xyloglucan-cysteine conjugate increased more than twice compared to the unmodified polymer. The viscosity of thiomer was more than that of xyloglucan because of formation of disulphide bonds.

Highlights

The concept of mucoadhesion was pioneered in the 1980s which led to formulation of mucoadhesive delivery systems to reduce the frequency of dosing by enhancing gastric residence and improving patient-compliance
Numerous attempts to improve the adhesive properties of polymers; led to synthesis of ‘thiolated’ polymers or so-called thiomers have proven to be a promising new class of polymeric excipients in mucoadhesive drug delivery system
The covalent attachment of cysteine to xyloglucan was achieved by the formation of ester bonds between the hydroxyl group of the xyloglucan and a carboxylic acid group of the cysteine (Leitner et al, 2003; Bilicic et al, 2005)

Summary

Introduction

The concept of mucoadhesion was pioneered in the 1980s which led to formulation of mucoadhesive delivery systems to reduce the frequency of dosing by enhancing gastric residence and improving patient-compliance. It is observed that the traditionally used mucoadhesive polymers provide mucoadhesion by noncovalent bonds to the mucus (such as hydrogen bonds and ionic interaction) which are relatively weak Numerous attempts to improve the adhesive properties of polymers; led to synthesis of ‘thiolated’ polymers or so-called thiomers have proven to be a promising new class of polymeric excipients in mucoadhesive drug delivery system. Thiomers are capable of forming covalent bonds leading to improved mucoadhesive properties (Bernkop-Schnürch, 1999). The thiomers process improved adhesion because of formation of disulfide bonds between thiol bearing side chains of the polymer and cysteine-rich subdomains of mucus glycoproteins (Gum Jr. et al, 1992)

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