This study focused on the separation, characterization, content determination, and antiviral efficacy research on colloidal particles with different sizes in Maxing Shigan Decoction(MXSG). The mixed colloidal phase of MXSG was initially separated into small colloidal particle segment(S), medium colloidal particle segment(M), and big colloidal particle segment(B) using ultrafiltration. Further fine separation was performed using size-exclusion chromatography. Dynamic light scattering(DLS) and transmission electron microscopy(TEM) were employed to characterize the size and morphology of the separated colloidal particles. UPLC-MS/MS was used to determine the content of ephedrine, amygdalin, glycyrrhizic acid, and the EDTA complexometric titration was used to measure the calcium(Ca~(2+)) content in different colloidal phases. Finally, a respiratory syncytial virus(RSV) infection mouse model was established using intranasal administration. The experimental groups included a blank group, a model group, a ribavirin group, an MXSG group, an S group, an M group, and a B group. Oral administration was given for treatment, and pathological changes in mouse lung tissue and organ indices were evaluated. The results of the study showed that the distribution of ephedrine, amygdalin, glycyrrhizic acid, and Ca~(2+) content was not uniform among different colloidal segments. Among them, the B segment had the highest proportions of the three components, except for Ca~(2+), accounting for 46.35%, 53.72%, and 92.36%, respectively. Size-exclusion chromatography separated colloidal particles with uniform morphology in the size range of 100-500 nm. Compared to the S and M segments, the B segment showed an increased lung index inhibition rate(38.31%), spleen index, and thymus index in RSV-infected mice, and it improved the infiltration of inflammatory cells and lung injury in the lung tissue of mice. The complex components in MXSG form colloidal particles of various sizes and morphologies through heating, and small-molecule active components such as ephedrine, amygdalin, glycyrrhizic acid, and Ca~(2+) participate in the assembly to varying degrees. The main material basis for the antiviral effect of MXSG is the colloidal particles with certain particle sizes formed by the assembly of active components during the heating process.
Keywords: Maxing Shigan Decoction; antiviral; colloidal particles; self-assembly.