Spectrometric Studies On The Interaction Between Four Anti-Malarial Drugs Of The Artemisinins And Human Serum Albumin

Objective: This paper was taken human serum albumin （HSA） as model protein,studied on the the interaction between artemisinins drugs （artemisinin,dihydroartemisinin, artemether, artesunate） and HSA under simulative physiologicalconditions （pH=7.40）. The binding mode of artemisinins drugs with HSA wereinvestigated by using different spectrum experiments.Methods: The mechanism of interaction between artemisinins drugs and HSA wereinvestigated with fluorescence spectrum （synchronous fluorescence andthree–dimensional fluorescence spectrum）, UV–vis absorption spectrum, circulardichroism and molecular modeling, etc. The binding position between artemisininsdrugs and HSA were obtained by using molecular docking method. The interactionparameters were obtained by using fluorescence quenching method, includingquenching rate constants, quenching constants, binding constants, number of bindingsites, interaction force types, and the influence of metal ions such as Al³⁺, Fe³⁺, Cu²⁺,Ca²⁺, Ni²⁺, Zn²⁺, Hg²⁺, Pb²⁺, Na⁺, K⁺, Li+on the interaction. The synchronousfluorescence and three–dimensional fluorescence spectra were used to investigate theconformation change of HSA molecules after adding drugs. Furthermore, thesecondary structure variations of HSA were quantitatively analyzed by circulardichroism （CD）. Through analysising parameters and comparing different drugs’structures, the reason that interaction between drugs and HSA has different junctionswas obtained.Results and Conclusion: Four antimalarial drugs （artemisinin, dihydroartemisinin,artemether and artesunate） have strong binding ability to HSA and quench theintrinsic fluorescence. This phenomenon belongs to static quenching process ofdegreasing quenching constant and increasing temperature. Molecular modelingresults indicated that drugs and HSA have bound in Site I. Circular dichroism resultsshowed that the relative content of secondary structure had changed after theirinteractions, while fluorescence intensity from synchronous fluorescence and three–dimensional declined in different degrees, and tryptophan characteristicemission peak has shifted to short wavelength. All these indicating that the proteinsecondary structure has been changed （α–helix structure turned into β–sheet andβ–turn structure）. Metal ions affected the interaction. The non–radiation energytransfer was occurred between drugs and HSA, and the major acting force werehydrophobic ineraction and hydrogen bond force. Meanwhile, they have only onebinding site. The order of binding strength is as follows: artesunate> artemether>dihydroartemisinin> artemisinin. According to the interaction degree of drugs andprotein molecules, we can provide a valid theoretical basis and guidance for choosingthe dose of clinical drug.