Study On The Intestinal Permeability And Bioavailability Of Acyclovir Based On Amphiphilic Chitosan

Acyclovir(ACV)is the second-generation broad-spectrum antiviral drug.However,the clinical efficacy of ACV was affected by low permeability and low bioavailability.Due to the unique physical and chemical properties and biological functions of chitosan(CS),chitosan-based nanosystems can be used as delivery systems for many drugs.Thus,the new type of amphiphilic chitosans have been constructed,which could provide a kind of possible choice for improving the permeability and bioavailability of ACVIn this paper,N,N,N-trimethyl-O-alkyl amphiphilic chitosan(TMACs)with three different alkyl chains were prepared by modifying the chitosan.Then,structural characterization,the analysis of particle size and zeta potential and biosafety evaluation of the synthesized three TMACs were carried out.Especially,N,N,N-trimethyl-O-octadecyl amphiphilic chitosan(TMSC)was more meaningful for further study.To obtain the best process parameters of ACV NP,single factor experiment and response surface experiment were then carried out.The structure and morphology of the optimized ACV NP were then characterized.Besides,the interaction mechanism between ACV and TMSC and the release mechanism of ACV NP in water were also investigated.Finally,the optimized ACV NP was evaluated for its permeability and bioavailability by in vitro intestinal permeation and pharmacokinetic experiments.The main experimental contents and conclusions are as follows:(1)Three different alkyl chains which acted as a hydrophobic group were introduced to the hydroxyl group at the 6-position of CS,Respectively.The amino group,at the 2-position of CS,conversed to quaternary ammonium saltation to increase the hydrophilicity of the CS,then three TMACs were obtained.The hydrophobic group was successfully grafted onto the CS,and a part of the amino groups have been converted into quaternary ammonium salts,which determined by FT-IR and ~1H NMR.It was found that the particle size and zeta potential which were detected by laser particle size analyzer were related to the concentration of TMACs.The safety of the three TMACs was found to be good in biocompatibility.(2)The ACV NP was prepared by ultrasonic method.The optimal process for the preparation of ACV NP was determined by single factor experiment and response surface experiment:when the ultrasonic time was 15×3 min,the temperature was39.76°C,the concentration was 0.87 mg/mL,and the mass ratio of ACV and TMSC was 1.2:1.The encapsulation ratio of the fit was 43.77%.The ACV NP prepared by the optimum process had a particle size of about 135.1 nm and a zeta potential of 31.10 mV.The structure characterizations of ACV NP were investigated by FT-IR,~1H NMR,DSC,XRD.It was found that the crystal structure of ACV has changed in the nanoparticles and a new hydrogen bond was generated.The binding mechanism of ACV to TMSC was further explored by molecular simulation,which was mainly bound by hydrophobic interaction.The release mechanism of ACV NP included ACV diffusion,TMSC skeleton swelling and dissolution.(3)In vitro intestinal permeation experiments showed that the main absorption site of ACV was in the upper end of the small intestine(duodenum,jejunum),and the drug absorption was concentration-dependent.The results of intestinal permeability studies by drugs in different intestinal segments and different concentrations of drugs in a same segment showed that the intestinal permeation of ACV NP was higher than that of ACV under same conditions,indicating that ACV NP promoted the absorption.The LDH experiment showed that the isolated intestine had some damage during the study,but the damage was much lower than that caused by Triton X-100(3%w/v).(4)In vivo pharmacokinetic experiments indicated that the half-time of ACV NP was 1.6 times higher than that of ACV,and the relative bioavailability of ACV NP was4.5 times higher than that of ACV,which suggesting that ACV NP could significantly improve the bioavailability of ACV.