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K. Ozasa, M. Nakao, Y. Watanabe, K. Hayashi, T. Miki, K. Mikami, M. Mori, F. Sakauchi, M. Washio, Y. Ito, K. Suzuki, K. Wakai, A. Tamakoshi and JACC Study Group, “Serum Phytoestrogens and Prostate Cancer Risk in a Nested Case-Control Study among Japanese Men,” Cancer Science, Vol. 95, No. 1, 2004, pp. 65-71. doi:10.1111/j.1349-7006.2004.tb03172.x

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• TITLE: The Development of S-Equol Diastereoisomer Specific ELISA

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

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

  JOURNAL NAME: American Journal of Analytical Chemistry, Vol.3 No.6, June 21, 2012

  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.