Construction And Application Of Lipid Carrier Based On Conjugated Linoleic Acid

Lipid carriers include liposomes,micelles,emulsions and nanostructured lipid carriers(NLCs).Liposomes are two-layer or multilayer closed vesicles composed of amphiphilic lipids,which are widely used in drug delivery systems.Fatty acids are the simplest lipids,good biocompatibility,fatty acid vesicles formed by self-assembly can be used as potential excellent carriers.However,the self-assembly behavior of fatty acids in aqueous solution strongly depends on the ionization state,concentration,temperature and counterions,which makes pure fatty acid vesicles highly sensitive to environmental changes.On the other hand,the stability of the embedded active substance and its bioactivity,as well as the bioaccessibility of the embedded active substance not only respond to the stimulation of the application environment,but also are affected by the coexistence of fatty acid vesicles.These problems make the application of fatty acid vesicles in the encapsulation and delivery of bioactive substances very uncertain.Therefore,it is of great significance to study different fatty acid delivery systems represented by fatty acid vesicles.In this paper,the unsaturated fatty acid conjugated linoleic acid(CLA)was taken as the main research object,and the formation mechanism of CLA as a drug carrier and its encapsulation performance for bioactive substances were thoroughly analyzed.Firstly,the self-assembly process and vesicles formed by CLA coexisting with other fatty acids,food-drug grade surfactants and polysaccharides were studied.Then,oligo-CLA and chitosan were used to construct a hydrogel system containing vesicles.Finally,fatty acid nano-lipids carrier with CLA as liquid lipids and stearic acid as solid lipids were constructed in the non-vesicular domain of fatty acids.Through the above studies,the prerequisite for the size of fatty acid hybrid vesicles to transition from nanometer to micron and the self-assembly mechanism were elucidated,and the reason for the stable existence of drug-loaded fatty acid vesicles in hydrogels was revealed.The injectable drug-loaded fatty acid vesicles composite hydrogels were obtained.At the same time,various kinds of fatty acid vesicles and lipid carriers constructed above were embedded with antioxidant unstable water-soluble vitamin C(VC),oil-soluble ginsenoside Rg3,curcumin and steviol,respectively.The synergistic effects of different fatty acid lipid carriers on the encapsulation,sustained release,bioaccessibility and antioxidant properties of embedded bioactive substances were studied.The main research contents and results are as follows:1.Mixed fatty acid vesicles were prepared by adding a certain amount of saturated fatty acid(SFA)and anionic surfactant sodium dodecyl sulfate(SDS)with CLA as the main vesicle material.The addition of SDS caused the vesiculation p H window to migrate from p H 8.0-9.0 to p H 3.8-9.0,and the degree of migration depended on the ratio of SDS to fatty acids.However,the addition of saturated fatty acids shifted the p H window to the alkaline direction within 0.3,and the longer the carbon chain length of saturated fatty acids,the more alkaline the p H window.At the same time,the addition of saturated fatty acids increased the particle size and wall thickness of vesicles,thus improving the encapsulation efficiency and sustained release of VC.At p H5.5,the VC entrapment rate of CLA-SA-SDS vesicles was 58.6%,which was higher than that of CLA vesicles 47.5%.The cumulative release rates of VC in CLA-VC,CLA-SDS-VC and CLA-SA-SDS-VC systems were90.5%,48.4% and 35.9% within 160 min in simulated gastric fluid,respectively.At the same time,the encapsulation of fatty acid vesicles significantly improved the antioxidant stability of VC,and the obtained mixed fatty acid-SDS-VC system had excellent physical stability after 14 days of storage at 25℃.2.The prerequisite and self-assembly mechanism of CLA-saturated fatty acid-SDS hybrid vesicles transitioning from nano to micron size were studied,and the drug-loaded and in vitro release behaviors of nano and micron vesicles were comparatively analyzed.It was found that the change of vesicle size between nano/micron could be regulated by changing the concentration of PBS and p H.CLA vesicles of 2-10 μm size could be formed when the concentration of PBS was10-200 mmol/L.However,at higher salt concentrations,CLA vesicles accumulate and collapse,and the vesicle structure is destroyed.This salt concentration dependence is consistent with the variation of Zeta potential of CLAVs suspensions at different salt concentrations.The p H dependence of CLA-fatty acid-SDS hybrid vesicles is as follows: the CLA-fatty acid-SDS system is micellar system when p H>10.0;At p H7.0-10.0,protonated CLA and CLA-Na co-assemble into 2-15 μm micron scale vesicles.However,at p H<7.0,the CLA-fatty acid-SDS system showed blue opaline,which was a typical mixture of emulsion and vesicle.The maximum encapsulation efficiency(EE)of Rg3 by nano and micron vesicle system was 86.3% and 93.2%,respectively.The drug loading(LC)of nano and micron vesicle systems were 10.9% and 18.6%,respectively.It was also found that the micron CLA-SDS hybrid vesicles(CLAVs)were more rigid than the nano ones,and the average particle size of nano and micron CLAVs increased by 325% and 140%,respectively,after over-encapsulation of Rg3.In addition,drug-loaded micron vesicles have better continuous release and good stability.3.An injectable and temperature-sensitive Cur/Rh6G-OCLAVS-CS fatty acid vesicles composite hydrogel was constructed.The vesicles(OCLAVs)were prepared with oligomeric CLA with a crosslinking degree of 28.6%.The vesicles coated with curcumin(Cur)and rhodamine 6G(Rh6G)were added to the aqueous solution of chitosan(CS),and gel to obtain drug-loaded fatty acid vesicles composite hydrogels.The rheological behavior and swelling rate of Cur-OCLAVS-CS hydrogels were studied.It was found that CS,OCLAVS-CS and Cur-OCLAVS-CS formed stable gels at 37°C.The presence of OCLAVs and OCLAVS-Cur does not prevent the gelation process of chitosan solution.TEM results showed that Cur-OCLAVs existed stably in the hydrogel system,and the vesicle size was lower than that before the gel,which may be caused by the electrostatic interaction between CS and OCLAVs.This is attributed to the porous structure inside the CS hydrogel.At the same time,the drug-loaded fatty acid vesicles composite hydrogel can significantly improve the release of hydrophobic drug Cur and hydrophilic dye Rh6 G in vitro.After 96 h,the cumulative release rate of Cur(400μm)-OCLAVS-CS gel system was 51.23%,while the cumulative release rate of Cur(400μm)-CS gel system was 93.37%.The results of antioxidant activity experiment showed that Cur-OCLAVS-CS system had good synergistic antioxidant activity.The construction of fatty acid vesicles composite hydrogels provided theoretical support for overcoming the “burst effect” of polysaccharide drug loading system.4.The nanostructured lipid carrier CLA-NLC was constructed with CLA as liquid lipid and stearic acid(SA)as solid lipid.The effects of Tween 80 concentration,solid-liquid lipid mass ratio and lipid concentration on CLA-NLC particle size and particle size dispersion index(PDI)were studied.The optimum conditions of Tween 80 concentration of 3%(w/v),ratio of solid to liquid lipid of 2:1 and total lipid concentration of 4%(w/v)were determined.FT-IR,XRD and DSC analysis showed that curcumin was well encapsulated in the nanostructured lipid support.As the liquid lipid in NLC,CLA enhanced the antioxidant activity of the system,which was attributed to the synergistic antioxidant effect of CLA and Cur.In vitro simulated digestion showed that the bioacceptability of curcumin in Cur-CLA-NLC(85.7%)was much higher than that of Cur-PBS(11.7%)and Cur-SA-CLA mixture(9.3%).The NLC system improved the stability of CLA,reduced its peroxide value,and showed good biocompatibility.At the same time,CLA-NLC system reduced the peroxidation value of CLA and improved the stability of CLA.