title: Development of bioluminescent enzyme immunoassay for s-equol using firefly luciferase and its application to the assessment of equol-producer status.
abstract: In this study, we developed a specific bioluminescent enzyme immunoassay (BLEIA) for S-equol, employing firefly luciferase as a labeling enzyme, as an alternative to HPLC methods. Satisfactory correlation (r=0.992) was shown when this S-equol BLEIA was compared with HPLC. The cross-reactivity with R-equol as its diastereoisomer is <5%, and that with daidzein, which is the substrate of equol, is 0.02%. Frequencies of Japanese equol producers determined using two distinct approaches were compared: a threshold value for urinary S-equol concentration of 232 ng/ml gave frequencies of 32% of men and 19% of women. These values correspond to the results for log(10)-transformed urinary S-equol to daidzein ratio threshold of -1.75, namely, 34% of men and 19% of women. When the changes in concentration of urinary equol and daidzein were measured after ingestion of isoflavone, the maximum concentration (C(max)) of urinary equol appeared after 9.6 h of isoflavone consumption; this C(max) was 2 h later than that for daidzein. The S-equol BLEIA documented in this study is expected to be an important tool for the assessment of equol producer status and demonstration of the bioavailability of isoflavone.
authors.affiliation: Biochemical Research Laboratory, Eiken Chemical Co., Ltd., Shimotsuga-gun, Tochigi, Japan. Takayuki_Minekawa@eiken.co.jp
authors.forename: Takayuki
authors.initials: T
authors.lastname: Minekawa
authors.forename: Akira
authors.initials: A
authors.lastname: Kambegawa
authors.forename: Kumiko
authors.initials: K
authors.lastname: Shindome
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ohkuma
authors.forename: Katsushi
authors.initials: K
authors.lastname: Abe
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Maekawa
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Arakawa
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods; D060754:Equol; D005260:Female; D006801:Humans; D007124:Immunoenzyme Techniques / Q000379:methods*; D007529:Isoflavones / Q000737:chemistry / Q000378:metabolism / Q000652:urine*; D049409:Luciferases, Firefly / Q000737:chemistry*; D049408:Luminescent Agents / Q000737:chemistry*; D008297:Male; D013237:Stereoisomerism; D013997:Time Factors
chemical_list: C007610:4',7-dihydroxy-3,4-dihydroisoflavone; D007529:Isoflavones; D049408:Luminescent Agents; D060754:Equol; C004742:daidzein; D049409:Luciferases, Firefly