Aqueous Solubility And Stability Enhancement Of Astilbin From Smilax Glabra Roxb. Through Complexation With Cyclodextrins

Astilbin has many notable bioactivities, such as strong antioxidant activity,hypoglycemic effect, regulate lipid metabolism, selective immunosuppression,etc. It hashigh value to exploit for the drug. However, poor aqueous solubility and instability limitsits application. Obviously, it is very necessary to improve aqueous solubility and stability.Astilbin is the main constitute of flavanoids in Smilax glabra Roxb. The S. glabra wasmaterial on this experiment. Study on the optimum conditions for separating and purifingflavonoids from S. glabra by macroporous adsorption resin. Investigated not only theinclusion between cyclodextrins and astilbin, but aslo the enhancement of solubility andstability through inclusion. Cogrinding and Freeze-drying was the method used to producethe complexes of cyclodextrins(CD) and astilbin. The characterizations of complexes werecompared. Main achievements are as follow.(1) The static adsorption tests of D101, NKA-9, AB-8, H103and X-5macroporousresins showed that D101has the strongest capacity (18.32mg/g resins) to adsorpt the totalflavanoids from S. glabra among five macroporous resins and its adsorption process couldbe equilibriumed after2.5hours later. Adsorption isotherm studies indicated that theadsorption process of those resins was multilayer adsorption, which is in accord withFreundlich adsorption model. The dynamic adsorption and elution tests showed theoptimum conditions to separate astilbin from total flavonoids.2times bed volume ofdistilled water was firstly used to wash the water soluble impurities, such as sugar, protein,etc. Then,2times bed volume of20%ethanol was used to clean resin column so that otherconstitutes of flavanoids could be removed. Finally, astilbin could be totally eluted when3.5times bed volume of50%ethanol was used as eluent.The content of astilbin reached90.54%by HPLC detection.(2) Inclusion reactions of astilbin with α-CD, β-CD and γ-CD were studied by PhaseSolubility Studies and uV Vis Spectral Titration. Phase solubility diagrams in5kinds ofdiffrent temperatures were all in conformity with the AL, which indicated that astilbin canform complex with cyclodextrin at a molar ratio of1:1. The Ka values decreased with therise of temperature, indicating that the affinity between CDs and astilbin decreased.Negative ΔH and ΔS values implied that the inclusion process was exothermic andentropically unfavorable. As the complex formed, the solubility of astilbin was improved.With5mmol/L β-CD and γ-CD, the solubility of astilbin was increased7.58±0.35and6.71±0.39times, respectively. Stability in alkaline solution was obviously enhanced,andβ-CD showed the best protection effect.(3) Inclusion complexes prepared by freeze-drying and cogrinding method wereshowing better solubility and fast dissolution in37℃. Most notably, its solubility in β-CD complexes compared to astilbin alone was122.5times increased by freeze-drying and97.8times increased by cogrinding. During the cogrinding process, inclusion rate increasedwith the increasing molar ratio of cyclodextrin and astilbin; It aslo increased with theimprovement of moisture content.