**1. Introduction**

O ffensive or strong body odors can be a source of social embarrassment. Axillary osmidrosis (AO) is a chronic skin condition characterized by such body odors and excessive sweating from the armpits [1]. In Asian countries such as Japan and China where fewer people have strong body odor, AO is perceived even more negatively [2]. However, except for surgical treatments, no causal therapy has been established for AO.

The inhibition of human ATP-binding cassette transporter C11 (ABCC11, also known as MRP8)—a risk factor of AO—may induce physiological changes related to body odors [1,3–5]. ABCC11 is one of

the ABC proteins that transport various molecules across cellular membranes in an ATP-dependent manner [6,7]. A non-synonymous single nucleotide polymorphism c.538G>A (p.Gly180Arg) in the *ABCC11* gene, which codes a functionally null variant with a high allele frequency in East Asians [8], has been found to be a determinant of AO risk [1,3–5]. Considering the facts that (1) genetically *ABCC11*-deficient subjects carry little AO risk and (2) the ABCC11 wild-type (WT) is expressed in human axillary apocrine glands that produce a variety of odor precursors [9], the inhibition of ABCC11 may lead to ways to prevent and treat AO. However, no medication is currently approved for AO treatment by ABCC11 inhibition. Hence, the exploration and identification of biologically safe ABCC11 inhibitors is an important issue.

In this study, we examined the ABCC11-inhibitory activities of 34 dietary plant products using an in vitro transport assay system. By screening the plant extracts and a subsequent fractional approach, genistein, a well-recognized soy isoflavone, was identified as a novel ABCC11 inhibitor with a half-maximal inhibitory concentration (IC50) of 61.5 μM. Moreover, since little is known about food ingredients with the potential to inhibit ABCC11, we further investigated the effects of other dietary flavonoids on the ABCC11 function.

#### **2. Materials and Methods**
