Nonlinear estimation reveals a working mechanism of Xie-Xin decoction, a traditional Chinese combinatorial formula

Abstract

Xie-Xin decoction (XXD) is a commonly used traditional Chinese combinatorial formula containing Rhei rhizome (rhizomes of Rheum officinale Baill; RR), Scutellariae radix (roots of Scutellaria baicalensis Georgi; SR) and Coptidis rhizoma (rhizomes of Coptis chinensis Franch; CR). In the present study, a central composite design (CCD) and the nonlinear estimation were adopted to reveal the changed regularity of anthraquinones and the working mechanism in Xie-Xin decoction. On the CCD experimental matrix, dosages of RR were fixed at 1 g, independent variables of CR and SR were set at the range of 0.01–0.99 g and pH values were set at 0.1–9.9. The dissolving-out quantity of the summed anthraquinones was selected as the dependent variable and measured by HPLC. The experimental data were fitted by using quadratic and cubic polynomial models, and surface plots were generated for further analyses. It showed that the cubic polynomial model with the R² value of 0.9933 is more appropriate than the quadratic polynomial model (R² = 0.8806) in explaining the relationship between factors and the response, in which CR and pH values contributed most to the changes of anthraquinones. Surface plots showed the interactive effects of CR and pH values: the responses were increased with the increase of CR when on the low pH values (namely acidic solution), while the responses were decreased with the increase of CR on the high pH values (namely alkaline solution). It is suggested that obtaining a high dissolving-out quantity of anthraquinones needs a stable pH condition during the process of decoction, which could be achieved when the combinatorial herbs of RR, CR and SR in XXD are used at an appropriate dosage ratio. The complete working mechanism remains to be further investigated by multidisciplinary cooperation from different perspectives.