Solid Lipid Nanoparticles Modified With Amphipathic Chitosan Derivatives

Solid lipid nanoparticles(SLN)is widely used as the vehicle for oral drug delivery.However,there are two limitations connecting with SLN:on the one side,because of the poor stability performance,it’s necessary to improve the physical stability of SLN during storage.Expulsion of encapsulated drug of SLN may take place during storage due to crystalline polymorphism transformation towards to lower-energy state,and formation of a more perfect crystalline lattice.On the other side,the potential of SLN to enhance oral drug absorption need to be improved further.Objective to tackle these hurdles,N-fatty acyl-N,N,N-trimethyl chitosans(FTMCs,comb-shaped polymeric surfactants)were synthesized and used as emulsifiers for preparation of solid lipid nanoparticles(FTMC-SLNs)with bioadhesive properties in present study.SLN prepared by traditional surfactant Tween-80(Tween-SLN)was used as a control.Physical stability of SLNs and oral bioavailability of their encapsulated drug were investigated.N-stearyl-N,N,N-trimethyl chitosan(STMC)and N-linoleoyl-N,N,N-trimethyl chitosan(LTMC)were synthesized using chitosan as a raw material by two steps.And their structures were confirmed by infrared spectroscopy(IR)and proton nuclear magnetic resonance spectroscopy(~1H-NMR).The results of elemental analysis showed that the substitution degrees of trimethyl groups were 42.74%and the substitution degrees of stearyl and linoleoyl were 23.63%and 28.28%,respectively.SLNs were prepared by a high speed stirring-ultrasonication method with Compritol 888 ATO used as the solid lipid,STMC and LTMC as emulsifiers,and Cy A as model drug.SLN prepared using Tween-80 as emulsifier was used as a control,and SLNs respectively prepared by STMC and LTMC were compared with each other to study the effect of unsaturation degree of fatty acyl chain on physical stability of SLN.Several variables of formulation and manufacture process were optimized.The mean particle sizes(PS)of optimal STMC-Cy A-SLN,LTMC-Cy A-SLN and Tween-Cy A-SLN were 219.8,173.6,and 97.9 nm,respectively.Their zeta-potentials(ZP)were+51.7,+44.6,and-23.9 m V,respectively.Entrapment efficiencies(EE)were 92.27%,85.75%,and 80.14%,respectively.The results of in vitro release showed that the cumulative release percentage of Cy A released from STMC-Cy A-SLN,LTMC-Cy A-SLN and Tween-Cy A-SLN were 36.1%,47.1%and47.5%in the medium of 0.2%lecithin solution during 72 h,respectively.FTMC showed better bioadhesive property than Tween-80 from the results of interaction between SLNs and mucin measured by turbidimetry.The results of DSC and XRD analyses indicated that Cy A was dispersed in SLN at an amorphous or molecular status.Compared with Tween-80,FTMC could remarkably increase the lattice defects and reduce crystallinity of lipid,besides,the effect of STMC was higher than that of LTMC.The stability tests showed that after storage for 6 months at 4℃and 25℃under dark condition,the stability of blank Tween-SLN was poor,its particle size increased,and absolute value of ZP decreased.The polymorphism of lipid crystalline had been mainly transformed from metastableα-modification to more stableβ′-modification,then theβ′-modification gradually transformed to intermediateβ_i-modification and stableβ-modification.The transition at 25℃was more obvious than at 4℃.However,after storage for 6 months under the same condition,PS and ZP of blank FTMC-SLNs all changed slightly and there were no significant transitions of crystal forms.After storage at 4℃and 25℃for 3 months and 6 months respectively,PS of drug-loaded SLNs tended to increase,and their EE had a tendency toward decrease.The sequences of transition rates of them from fast to slow were both Tween-Cy A-SLN,LTMC-Cy A-SLN,STMC-Cy A-SLN.And the absolute values of ZP of Tween-Cy A-SLN decreased more significantly than that of LTMC-Cy A-SLN and STMC-Cy A-SLN.The crystalline polymorphism of FTMC-SLNs transformed from metastable modification to stable modification to some extent.But there were still a large part ofα-modification of lipid with more imperfect lattices in them.After storage at 25℃for 6 months,the crystallization peak intensity ofβ_i-orβ-modification in XRD pattern of Tween-Cy A-SLN was the strongest among all the Cy A-SLNs,the next was LTMC-Cy A-SLN,and the weakest was STMC-Cy A-SLN,indicating the proportion ofβ_i-orβ-modification in STMC-Cy A-SLN was the lest among all the Cy A-SLNs,under the same storage conditions.The sequence of transition rate of lipid polymorphism among all the Cy A-SLNs from slow to fast was Tween-Cy A-SLN,LTMC-Cy A-SLN,and STMC-Cy A-SLN.All above results revealed the blank and drug-loaded SLNs prepared using FTMC as emulsifiers were more stable than that prepared by Tween-80,and the STMC-SLN showed the stability,which suggested that the potential of FTMC to suppress the transitions of lipid polymorphism was better than Tween 80,and STMC was better than LTMC between the two FTMCs.The preliminary toxicity assessment by Caco-2 cell suggested a good biosecurity of FTMC-SLN as well as Tween-SLN,with cell viability all more than 85%.The pharmacokinetic study performed in rats demonstrated the relatively bioavailabilities of STMC-Cy A-SLN and LTMC-Cy A-SLN were 292.17%and 128.45%compared to Tween-Cy A-SLN.Hence,this study suggests the amphiphilic chitosan derivatives are promising surfactants to enhance the physical stability of SLN,and further improve the oral bioavailability using SLN prepared with the derivatives as a carrier in oral delivery of lipophilic drugs.