Study On The Interaction Between Amphiphilic Chinese Medicine Molecules And Liposomes

Objective:To study the interaction of the amphiphilic drug molecules with liposomes.Then to clarify the position of paeonol,baicalin and emodin in liposomes and the effect of drug molecules on the phase state of liposomes,which provided a theoretical basis for the preparation of drug liposomes.Using liposome as the model membrane,the possible mechanism of antioxidation effect of three drugs was discussed based on the point of the effect of drugs on cell membrane.Method:The liposomes of paeonol,baicalin and emodin were prepared by film dispersion method using dipalmitylphosphatidylcholine(DPPC)as the membrane material.Differential scanning calorimetry(DSC)was used to study the effect of drugs on the pre-and main-thermal phase transition of liposome membrane.Synchrotron small and wide angle X-ray diffractions were employed to investigate the influences of drugs on the double layer structure and tail chain arrangement of liposomes.The sub-molecular information was obtained by Fourier transform infrared spectroscopy(FTIR)to study the effect of drugs on liposomes.Combined with these three techniques,the position of the drugs in liposomes and the effect of drugs on the phase state of liposome membrane were revealed from macroscopic,structural and microcosmic.Result:The location of the paeonol molecules in liposomes is concentration dependent.When the concentration of peaonol is not more than 5 mol%,paeonol molecules incorporate into the hydrophobic region of DPPC liposomes.When the concentration of the paeonol is between 5 and 15 mol%,additional paeonol molecules will incorporate into the hydrophilic region of the DPPC molecules and interact with its polar groups.When the concentration of the paeonol is more than 15 mol%,the additional paeonol molecules locate at the region of hydrocarbon chains of DPPC again.Paeonol molecules can induce the phase transition of liposomes.Both pure DPPC liposomes and low concentration paeonol liposomes exist as lamellar gel phase(Lβ’)at room temperature.When the concentration of peaonol is more than 20 mol%,paeonol liposomes exist as rippled gel phase(Pβ’)at room temperature.The results of FTIR indicate that the addition of paeonol molecules have no effect on both conformational order and the paking of tail chains,the all-trans conformation predominate in liposomes of differerent concentration paeonol and the arrangement of methylene chain is hexagonal.However,the hydration degree of C=O will be promoted when the paeonol molecules locate at the hydrophilic head region.The location of the baicalein molecules in liposomes is also concentration dependent.When the concentration of the baicalein(x)is not more than 5 mol%,the baicalein molecules locate at the hydrophilic head region of DPPC liposomes.When 5<x≤10 mol%,the additional baicalein molecules incorporate into the hydrophobic tail chains of DPPC liposomes.When 10<x ≤ 20 mol%,the additional baicalein molecules were introducted into polar head region again.The introduction of baicalein has an important influence on the phase state of liposomes.At room temperature,when x≤5 mol%,the baicalein liposomes exist as lamellar gel phase,while the tail chains of liposomes is no longer tilted when x=5 mol%and the liposomes exist as un-tilted lamellar gel phase(Lβ).When 5<x≤ 10 mol%,the liposomes undergo a trasition from un-tilted lamellar gel phase(Lβ)to rippled gel phase(Pβ’).When 10<x≤20 mol%,the repeat distance of lipid bilayer increases significantly and the hydrophobic tail chains are un-tilted.So the liposomes in this concentration range exist as un-tilted rippled gel phase(Pβ).The incorporation of baicalin has no effect on the all-trans conformation and hexagonal arrangement of the tail chain of phospholipid.When the baicalein molecules act on the hydrophilic head of the liposome,it mainly promotes the hydration state of C=O,changes the orientation of the head groups,and affects the inclination of the tail chain.Emodin molecules mainly incorporate into the hydrophobic tail chains of DPPC liposomes.When x≥15 mol%,phase separation occurrs due to the introduction of emodin molecules.One phase formed by emodin-rich domain coexists with another phase formed by emodin-poor domain in this concentration range.The addition of emodin molecules could induce the change of phase states of liposome.When x≤2.5mol%,emodin liposomes are in the lamellar gel phase(Lβ’)at the room temperature.When x ≥ 5 mol%,the incorporation of emodin promoted the formation of the rippled gel phase(Pβ’)of liposomes.When x≥10 mol%,the hydrophobic tail chains of liposome are no longer tilted under the influence of emodin molecules,and therefore the liposomes are in un-tilted rippled gel phase(Pβ).It is the proper fluidity of cell membrane that ensures the performance of cell function.Lipid peroxidation could increase the order and decrease the fluidity of cell membrane.According to this study,paeonol,baicalin and emodin could result in the decrease of phase transition temperature and/or phase change enthalpy of liposome membrane,the increase of repeat distance between layers,and the formation of rippled gel phase of liposomes.And these three drugs have fluidization effect on liposome membrane.Therefore,the enhancement of membrane fluidity may be one of the mechanisms of anti-oxidation of paeonol,baicalin and emodin.Conclusion:Paeonol and baicalin could be incorporated into either the hydrophobic tail chain or the hydrophilic head of liposome,and the location of them in liposomes is concentration dependent.Emodin molecules mainly locate at the hydrophobic tail chain of DPPC liposomes.The location of amphiphilic drugs in liposomes is not noly relate to the oil-water partition coefficient,but also may be relate to the spatial configuration and functional groups of drugs.The introduction of these three drugs has an important effect on the phase state of liposomes,which could promote the formation of rippled gel phase of liposomes at room temperature,but the required concentrations were different:paeonol>baicalin>emodin.In the range of drug concentration studied in this paper,paeonol and baicalein liposomes are relatively stable without phase separation.However,high concentration of emodin could induce the phase separation of liposomes,which will affect the stability of emodin liposomes.These three drugs could improve the fluidity of the membrane,which may be one of the mechanisms of their antioxidant effects.