Hepatitis B virus (HBV) infection continues to be a global public health concern. Efficient diagnosis of HBV surface antigen (HBsAg) is useful for identification of infection, treatment and prevention of transfusion-transmitted viral infections. Seronegative window reduction afforded by a highly sensitive measurement methodology is necessary as a small quantity of virus with infection risk exists for the period characterized by undetectable HBsAg following HBV infection. In this study, a bioluminescent enzyme immunoassay (BLEIA) for HBsAg was developed employing firefly luciferase as a labeling enzyme and a two-step sandwich immunoassay method. The cut-off value (10 mIU/mL) was 50-fold more sensitive relative to conventional chemiluminescent enzyme immunoassay based on luminol luminescence involving peroxidase as the labeling enzyme and the identical antibodies. Preliminary clinical data for this BLEIA revealed that the HBV seroconversion panel derived sequentially from HBV-infected human blood was detected 11 days following window closure from the first bleed, whereas detection occurred 14-25 days following window closure with the three conventional commercial kits.

Equol [7-hydroxy-3-(4Ј-hydroxyphenyl)-chroman] is a metabolite produced in vivo from the soy isoflavone daidzein by the action of enterobacteria. It is known to be estrogenic, so exposure to equol could have significant biological effects on humans. Epidemiological studies suggest that it might be beneficial in the prevention of many diseases, including breast cancer, 1) prostate cancer, 2,3) and osteoporosis.4) The production of equol in humans varies: only 30-50% of any population group can produce equol after ingestion of soy foods, and they are called equol producers.4) It is thought that certain bacteria in the intestinal microflora are greatly involved in equol bioconversion. Recently, bacteria that convert daidzein to equol were isolated from human feces (ex. Lactocossus garvieae).5-7) A clinical trial intended to identify soy health benefits is taking place, using S-equol. Ishiwata et al. reported that S-equol supplement improved moodrelated symptoms in premenopausal/postmenopausal equol non-producers. 8) Jackson et al. reported using pure synthetic S-equol for the clinical indications of vasomotor symptoms (VMS, hot flashes) in women and benign prostatic hyperplasia (BPH, enlarged prostate) in men, as well as osteoporosis. 9)The major methods used today for the determination of equol are high-performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS). 10)These methods are useful for basic study that measures multiple molecules, such as equol, daidzein and genistein, and they show excellent specificity. However, these methods require sample extraction and have relatively low throughput, but the measurement of a large number of samples is necessary for epidemiological study to examine the evidence that the clinical efficacy of isoflavones in humans depends on the production of an enterobacterial metabolite, equol. As an alternative method, enzyme immunoassay is the most useful. Brouwers et al. reported a time-resolved fluoroimmunoassay (TR-FIA) method that uses rabbit polyclonal antibodies. 11)Talbot et al. reported successful development of monoclonal antibodies and applied them to a TR-FIA method.12) As a result, a large number of samples have become measurable.Equol, unlike the soy isoflavones daidzein and genistein, has a chiral center, and therefore it can occur as two distinct diastereoisomers, R-equol and S-equol. When equol is chemically synthesized, it is the (Ϯ) equol that is usually obtained. S-Equol has a high affinity for estrogen receptor b (K i ϭ 0.73Ϯ0.2 nmol/l), whereas R-equol is relatively inactive (K i ϭ15.4Ϯ1.3 nmol/l). The exclusive product of human enterobacterial synthesis from soy isoflavones is S-equol. 13)Therefore, a measurement system that can specifically measure S-equol is anticipated in clinical research. However, conventional methods have drawbacks with regard to their specificity for S-equol.The measurement of urine samples is known to be influenced by the matrix effect. The extraction of equol from urine reduces this influence, but it re...