Study On Chitosan And Its Derivatives As Low Molecular Weight Heparin Oral Absorption Vector

In the present study,the feasibility of polyelectrolyte complexes（PEC）formation between low molecular weight heparin（enoxaparin）and various chitosan derivatives（trimethyl chitosan,PEGylated trimethyl chitosan,chitosan-cysteine conjugate）by self-assembly was evaluated,parameters influencing complex formation were characterized and oral absorption of enoxaparin based on the PEC was studied in vivo.Chitosan has been extensively used as an absorption enhancer for macromolecules and as a gene delivery vehicle.Both properties are molecular weight（Mw）dependent.In this work, factors affecting the oxidative depolymerization of chitosan were investigated.The molecular weight decreased with the increase of NaNO₂/chitosan ratio.Recently,the interest in bioadhesion has been inspired by the development of novel bioadhesive polymers for mucosal delivery and a promising new approach was the generation of thiolated polymers.In this work,chitosan-cysteine conjugate was synthesized mediated by carbodiimide and N-hydroxysuccinimide and the factors influencing the reaction were evaluated.The optimal coupling conditions were chitosan/cysteine ratio 1:3,pH 4.5,and reaction time 6 h.More than 10-fold increase in the adhesion time of thiolated chitosan was found compared to unmodified chitosan,which also demonstrated that there is a correlation between the degree of thiolation and the adhesion time.The Azure A colorimetric method for the ex vivo determination of enoxaparin was established.PEC formed from enoxaparin and chitosan derivatives were prepared and parameters influencing complex formation were characterized.Dynamic light scattering（DLS）and laser doppler anemometry（LDA）were used to study the complexation process.Surface morphology of the PECs was observed with atomic force microscopy（AFM）.The PEC formation process was influenced by a variety of parameters,including the system pH, polymer/enoxaparin mass ratio,polymer molecular weight,concentration and structure. Soluble complexes in the size range of 200-500 nm with spherical morphology could be obtained at optimized polymer/enoxaparin ratios in the pH range of 3.0-6.5,with positive charge and drug encapsulation efficiency of approximately 90%.An increase in ionic strength of the medium accelerated the dissociation of chitosan/enoxaparin complexes. Physicochemical properties of the PECs,including particle size,charge density and morphology,could be modified by using different chitosan derivatives.On the basis of our results,we suggest that interactions involved in PEC formation were partly electrostatic in nature,involving the positively charged chitosan derivatives and the negatively charged enoxaparin at pH in the vicinity of the pKa interval of the two polymers.Mucoadhesion of PECs was ex vivo evaluated by the change of the system Kcps values,under static conditions by applying nanocomplexes suspensions on rat intestinal mucosal surfaces.Both the molecular weight of chitosan and the polymer structure influenced the mucoadhesion of PEC. All PECs were quite stable in pH 1.2,6.8 or with the presence of pepsin and trypsin.All complexes could be lyophilized with 3%sucrose,without influencing the properties of PECs.After oral administration of chitosan/enoxaparin complexes in rats（1070IU/kg）,increases in activated partial thromboplastin time（APTT）were studied.Moreover,the APTT was lasted for a longer period than when a heparin solution was administered intravenously and influenced by both the molecular weight of chitosan and the polymer structure.