The Development of S-Equol Diastereoisomer Specific ELISA

Takayuki Minekawa, Akira Kambegawa, Kumiko Shindome, Shizuka Takehara, Hidetoshi Arakawa

Biochemical Research Laboratory, Eiken Chemical Co., Ltd., Tochigi, Japan.
Kambegawa Laboratory, Tokyo, Japan.
School of Pharmaceutical Science, Showa University, Tokyo, Japan.

DOI: 10.4236/ajac.2012.36059                

Abstract

Equol is a metabolite of soybean isoflavone, daidzein, and many health benefits are expected. Endogenous equol in urine is S-equol and mostly exists as glucuronate or sulfate conjugate. In this study we preliminary established the simple enzyme-linked immunosorbent assay (ELISA) without deconjugation, then developed the S-equol specific ELISA involves deconjugation showing high stereospecificity to S-equol without using stereospecific antibody. For the simple ELISA, we used a polyclonal antibody that targets the regions not influenced by inhibition by conjugation of glucuronate and sulfate and achieved the correlation coefficient; r = 0.975, but the value was 30 % lower than high performance liquid chromatography (HPLC). Developing upon this we invented the specific ELISA established from S-equol homogeneous combination for the standard and enzyme-labeled antigen to enhance stereospecificity. The correlation with HPLC was favorable: r = 0.986, y = 0.996x – 6. Compared to the previous method using (R,S)-equol combination, cross-reactivity with R-equol was reduced from 65 to 13 %, and that with daidzein from 0.31% to 0.08%, markedly increased in the specificity. This study is expected to be applied for both simple clinical researches, and stereospecific immunoassays in which specific antibody preparation is difficult.

Keywords

S-Equol; Diastereoisomer; Immunoassay; ELISA; Isoflavone; Deconjugation

Conflicts of Interest

The authors declare no conflicts of interest.

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