# Patent

## Title
Method for identifying a malodor inhibitor

## Abstract

Provided is a method for identifying a malodor inhibitor based on a response of an olfactory receptor. The present invention provides a method for identifying a malodor inhibitor including: adding a test substance and a malodor-causing substance to at least one olfactory receptor selected from the group consisting of OR5P3, OR5K1, OR2W1, OR8H1, and a polypeptide which has 80% or more identity in amino acid sequence to any one of the aforementioned polypeptides; measuring the response of the olfactory receptor to the malodor-causing substance; identifying the test substance which can suppress the response of the olfactory receptor based on the measured response; and selecting, as a malodor inhibitor, the test substance which can suppress the response of the olfactory receptor.

## Background
REFERENCE TO SEQUENCE LISTING SUBMITTED ELECTRONICALLY
The content of the electronically submitted substitute sequence listing, file name 2537—094001_SequenceListing_ST25.txt, size 21,771 bytes; and date of creation Mar. 5, 2014, filed herewith, is incorporated herein by reference in its entirety.
FIELD OF THE INVENTION
The present invention relates to a method for identifying a malodor inhibitor.
BACKGROUND OF THE INVENTION
In our living environment, there are a large number of malodorous molecules having different polarization characteristics and molecular weights. Hitherto, a variety of methods have been developed for reducing various malodorous molecules. Generally, the methods for reducing malodors are broadly classified into a biological method, a chemical method, a physical method, or a sensory method. Among malodorous molecules, short-chain fatty acids and amines, having high polarity, can be reduced through a chemical method; i.e., neutralization. Sulfur-containing compounds such as thiol can be reduced through a physical method; i.e., adsorption. However, there still remain many malodorous molecules, such as medium-chain and long-chain fatty acids and skatole, which cannot be reduced through known malodor reducing techniques.
In our everyday lives, among other malodors, fecal odor and foul breath are a particularly unpleasant odor. One of the main causal ingredients of such malodors is skatole. Known means for reducing a skatole odor or a fecal odor include the following: a composition containing a porous substance, an aminopolycarboxylic acid, and a metal (Patent Document 1); a silk burned product supporting a catalyst such as platinum (Patent Document 2); a deodorant containing, as an active ingredient, allyl heptanoate, ethyl vanillin, methyl dihydrojasmonate, raspberry ketone, or eugenol (Patent Document 3); and use of an aromatic component such as amylcinnamaldehyde, ethyl cinnamate, 2-cyclohexylpropanal (Pollenal II), geranyl acetone, cis-3-hexenyl heptanoate, cis-3-hexenyl hexanoate, 3-methyl-3-butenyl 2,2-dimethylpropionate (Lomilat), methylheptenone, valencene, dimethyltetrahydrobenzaldehyde (Triplal or Ligustral), cis-jasmon, acetylcedrene, benzyl acetate, geraniol, orange recovery flavor, or a plant extract of Dipterocarpaceae (Patent Documents 3 and 4).
According to the aforementioned means, a malodor is reduced by decreasing the amount of target malodorous substance through adsorption/decomposition or by means of an aromatic. However, the combination of adsorption and decomposition of a malodorous substance is not immediately effective, since the decrease of the amount thereof requires a long period of time. Use of an aromatic also has drawbacks in that the odor of the aromatic itself sometimes causes an unpleasant sensation to users, and the aromatic tends to mask odor of substances other than the target malodorous substance.
In mammals including humans, the mechanism for odorant recognition includes binding odorant molecules to olfactory receptors present on olfactory sensory neurons included in the olfactory epithelium, which is present in an upper portion of the nasal cavity, and transmitting the response of the receptors to the central nervous system. It has been reported that, 387 different olfactory receptors are present in human, and the genes encoding these olfactory receptors account for about 3% of the human genome.
Generally, a plurality of olfactory receptors respond to a plurality of odorant molecules. Specifically, one single olfactory receptor responds to a plurality of structurally similar odorant molecules at different affinities, while one single odorant molecule is detected by a plurality of olfactory receptors. It is also reported that a certain odorant molecule which can activate one olfactory receptor serves as an antagonist which inhibits activation of another olfactory receptor. Such combined response of these olfactory receptors leads to recognition of each odor.
Thus, when a first odorant molecule is co-present with a second odorant molecule, in some cases, the response of an olfactory receptor to the first odorant molecule is inhibited by the second odorant molecule. Through the inhibition, the odor of the first odorant molecule recognized by olfactory receptors may vary considerably. This mechanism is called “olfactory receptor antagonism.” Odor modulation by olfactory receptor antagonism, which differs in mechanism from a malodor reducing method by adding a perfume, an aromatic, or a like substance to the target odorant, can inhibits recognition specific to a malodor. In addition, the odor of an aromatic causing an unpleasant sensation to users can be prevented. Therefore, odor modulation based on olfactory receptor antagonism is a preferred means for reducing malodor.
In order to attain olfactory receptor antagonism, an olfactory receptor which responds to a target malodorous substance must be determined, and a substance which exhibits an antagonistic effect on an olfactory receptor of the malodorous substance must be identified. However, such identification is not easy. Hitherto, odor evaluation has been carried out through a sensory test by experts. However, the sensory test has problems. These problems include for example, odor-evaluators must be trained, and the throughput of the test is low.
PRIOR ART DOCUMENTS
Patent Documents


    [Patent Document 1] JP2002-153545 A
    [Patent Document 2] WO 2005/007287
    [Patent Document 3] JP2005-296169 A
    [Patent Document 4] JP2008-136841 A


SUMMARY OF THE INVENTION
The present invention provides a method for identifying a malodor inhibitor comprising:
adding a test substance and a malodor-causing substance to at least one olfactory receptor selected from the group consisting of OR5P3, OR2W1, OR5K1, OR8H1, and a polypeptide which has 80% or more identity in amino acid sequence to any one of the aforementioned polypeptides;
measuring the response of the olfactory receptor to the malodor-causing substance;
identifying, based on the measured response, the test substance which can suppress the response of the olfactory receptor; and
selecting, as a malodor inhibitor, the test substance which can suppress the response of the olfactory receptor.



BRIEF DESCRIPTION OF THE DRAWINGS
[FIG. 1] A chart showing the responses of olfactory receptors to skatole (X-axis: type of olfactory receptor, Y-axis: response intensity),
[FIG. 2] Graphs each showing the response of an olfactory receptor to skatole at different concentration (error bar: ±SE),
[FIG. 3] Graphs each showing the response of an olfactory receptor to skatole and indole. (filled circle: response to indole, open circle: response to skatole)
[FIG. 4] A graph showing suppression effects on skatole odor by test substances (n=4, error bar: ±SE).
[FIG. 5] A graph showing suppression effects on skatole and Hexanoic acid odor by test substances (n=3, error bar: ±SE),



The present invention provides a method for identifying a malodor inhibitor based on the response of an olfactory receptor as an index.
The present inventors have successfully determined olfactory receptors which respond to malodor-causing substances such as skatole. The present inventors have found that a substance which can suppress the response of any of the olfactory receptors can be employed as a malodor inhibitor which can suppress a malodor by masking through olfactory receptor antagonism. The present invention has been accomplished on the basis of this finding.
According to the present invention, a malodor inhibitor which can specifically reduce a malodor can be effectively identified, without causing problems which have previously arisen in a conventional malodor reducing method employing a deodorant or an aromatic; e.g., a long time until effectiveness and unpleasant sensation from the odor of the aromatic.
As used herein, the term “masking” in the odor-related field generally refers to means for inhibiting or weakening recognition of a target odor. The term “masking” may encompass chemical means, physical means, biological means, and sensory means. Examples of the masking means include any means for removing a odorant molecule responsible for a target odor from the environment (e.g., adsorption and chemical decomposition of the odorant); means for preventing release of a target odor to the environment (e.g., sealing); and a method in which recognition of a target odor is inhibited by adding another odorant such as a perfume or an aromatic.
As used herein, the term “masking through olfactory receptor antagonism” refers to one embodiment of the aforementioned broadly defined “masking” and is means for inhibiting the response of an olfactory receptor to a target odorant molecule by an additional odorant molecule, to thereby modulate the smell of the target odorant molecule recognized by a subject. Although masking through olfactory receptor antagonism employs an additional odorant molecule, the masking differs from means for canceling out a target odor by use of a strong odorant such as a perfume. In one embodiment of masking through olfactory receptor antagonism, a substance which can inhibit the response of an olfactory receptor such as an antagonist is used. When a response-inhibiting substance which can specifically inhibit the response of a receptor related to recognition of a certain odor is employed, the response of the receptor is suppressed, whereby the odor recognized by a subject can be modulated.
Accordingly, the present invention provides a method for identifying a malodor inhibitor. The method includes: adding a test substance and a malodor-causing substance to at least one olfactory receptor selected from the group consisting of OR5P3, OR2W1, OR5K1, OR8H1, and a polypeptide which has 80% or more identity in amino acid sequence to any one of the aforementioned polypeptides; measuring the response of the olfactory receptor to the malodor-causing substance; identifying, based on the measured response, the test substance which can suppress the response of the olfactory receptor; and selecting, as a malodor inhibitor, the test substance which can suppress the response of the olfactory receptor.
In the method of the present invention, a test substance and a target malodor-causing substance are added to an olfactory receptor which responds to the malodor. The olfactory receptor employed in the method of the present invention may be at least one selected from the group consisting of OR2W1, OR5K1, OR5P3, and OR8H1. OR2W1, OR5K1, OR5P3, and OR8H1 are olfactory receptors each being expressed in human olfactory sensory neurons and are registered in GenBank as GI: 169234788, GI: 115270955, GI: 23592230, and GI: 52353290, respectively.
OR2W1 is a protein encoded by a gene having a nucleotide sequence represented by SEQ ID NO: 1 and consisting of an amino acid sequence represented by SEQ ID NO: 2.
OR5K1 is a protein encoded by a gene having a nucleotide sequence represented by SEQ ID NO: 3 and consisting of an amino acid sequence represented by SEQ ID NO: 4.
OR5P3 is a protein encoded by a gene having a nucleotide sequence represented by SEQ ID NO: 5 and consisting of an amino acid sequence represented by SEQ ID NO: 6.
OR8H1 is a protein encoded by a gene having a nucleotide sequence represented by SEQ ID NO: 7 and consisting of an amino acid sequence represented by SEQ ID NO: 8.
The olfactory receptor employed in the present invention includes a polypeptide which has 80% or more, preferably 85% or more, more preferably 90% or more, still more preferably 95% or more, yet more preferably 98% or more identity in amino acid sequence to any one of the aforementioned OR2W1, OR5K1, OR5P3, and OR8H1. The polypeptide has responsiveness to a malodor-causing substance such as a skatole odor, an indole odor, a fecal odor, or foul breath (e.g., skatole or indole). According to the method of the present invention, the aforementioned olfactory receptors may be used singly or in combination of two or more species. However, the olfactory receptor selected from the group consisting of OR5K1, OR5P3, and OR8H1 is preferably used, and OR5P3 is more preferably used.
As shown in FIGS. 1 to 3, the aforementioned olfactory receptors respond to malodorous substances such as skatole and indole. Therefore, a substance which can suppress the response of such an olfactory receptor can modulate malodor recognition via the central nervous system based on masking through olfactory receptor antagonism, whereby a malodor originating from skatole, indole, or a similar substance can be suppressed. Meanwhile, skatole and indole are generally known odorant molecules causing a malodor such as a fecal odor or foul breath. Thus, the malodor-causing substance employed in the present invention is preferably a fecal odor or foul breath, more preferably skatole or indole. Examples of the malodor suppressed by the malodor inhibitor identified by the method of the present invention include a fecal odor, foul breath, a skatole odor, and an indole odor.
No particular limitation is imposed on the test substance tested in the method of the present invention, so long as the test substance is thought to be used as a malodor inhibitor. The test substance may be a naturally occurring substance or a chemically or biologically synthesized artificial substance. The test substance may be a compound, a composition, or a mixture.
According to the method of the present invention, the test substance and the malodor may be added simultaneously or sequentially in any order.
So long as the function of the olfactory receptor is not impaired, the olfactory receptor may be used in any form in the method of the present invention. For example, the olfactory receptor may be use in the following embodiments: tissues or cells which intrinsically express an olfactory receptor such as olfactory sensory neurons isolated from living bodies and cultured products thereof; olfactory cell membrane bearing the olfactory receptor; recombinant cells genetically modified so as to express the olfactory receptor and cultured products thereof; membrane of the recombinant cells; and artificial lipid bilayer membrane having the olfactory receptor. All of these embodiments are included within the scope of the olfactory receptor used in the present invention.
One preferred embodiment of the present invention employs cells which intrinsically express an olfactory receptor such as olfactory sensory neurons, recombinant cells genetically modified so as to express the olfactory receptor, or a cultured product of any of these. The recombinant cells may be produced through transformation by use of a vector to which a gene encoding the olfactory receptor has been incorporated.
Preferably, in order to promote expression of olfactory receptors in the cell membrane, RTP1S and a target receptor are genetically transfected to cells. An example of RTP1S used in the production of the recombinant cells is human RTP1S. Human RTP1S is registered in GenBank as GI: 50234917, Human RTP1S is encoded by a gene having a nucleotide sequence represented by SEQ ID NO: 9 and is a protein consisting of an amino acid sequence represented by SEQ ID NO: 10, instead of human RTP1S, a polypeptide consisting of an amino acid sequence having 80% or more, preferably 85% or more, more preferably 90% or more, still more preferably 95% or more, yet more preferably 98% or more identity in amino acid sequence to human RTP1S (SEQ ID NO: 10) and which promotes expression of an olfactory receptor in the membrane like human RTP1S may be employed in the present invention. For example, an RTP1S mutant employed in the examples of the specification consisting of an amino acid sequence represented by SEQ ID NO: 11 has 78.9% amino acid sequence identity to the amino acid sequence represented by SEQ ID NO: 10 and can promote expression of an olfactory receptor in the membrane. Thus, the RTP1S mutant is a protein which can be used in production of the aforementioned recombinant cells. Also, mouse RTP1S (Saito H., Chi Q., Zhuang H., Matsunami H., Mainland J. D. Sci, Signal, 2009, 2: ra9) has 89% amino acid sequence identity to the amino acid sequence represented by SEQ ID NO: 10 and can promote expression of an olfactory receptor in the membrane. Thus, mouse RTP1S is a protein which can be used in production of the aforementioned recombinant cells.
In the present invention, the sequence identity (nucleotide sequence and amino acid sequence) is calculated through the Lipman-Pearson method (Science, 227, 1435, (1985)). More specifically, the identity is calculated by a homology analysis program (Search homology) of the genetic information processing software Genetyx-Win (Ver. 5.1.1; Software Development) at a unit size to compare (ktup) of 2
According to the method of the present invention, a test substance and a malodor-causing substance are added to an olfactory receptor, and then the response of the olfactory receptor to the malodor-causing substance is measured. The measurement may be performed through any method known in the art as a response measurement method of olfactory receptors; e.g., the calcium imaging method. When activated by an odorant molecule, an olfactory receptor activates adenylyl cyclase with the aid of Gαs present in cells, to thereby elevate the intracellular cAMP level (Mombaerts P., Nat. Neurosci., 5, 263-278). Therefore, the response of an olfactory receptor can be measured by employing, as an index, the intracellular cAMP level determined after addition of the odorant. The method for determining the cAMP level employed in the present invention includes ELISA, reporter gene assay, and the like.
Subsequently, the suppression effect of the test substance on the response of the olfactory receptor is evaluated on the basis of the measured response of the olfactory receptor, to thereby identify the test substance which can suppress the response. The evaluation of suppression effect can be conducted, for example, by comparing the response of the receptor to the malodor-causing substance measured at different test substance concentrations. As a more specific example, the response to the malodor-causing substance of a higher test substance concentration group and that of a lower test substance concentration group; the response of a test substance addition group and that of a test substance non-addition group; or the response of a group after addition of the test substance and that of the same group before addition of the test substance are compared. In the case where the response of the olfactory receptor is suppressed through addition of the test substance or addition of the test substance at higher concentration, the test substance can be identified as a substance which can suppress the response of the olfactory receptor.
For example, when the olfactory response of a test substance addition group has been suppressed to 80% or less, preferably 50% or less than that of the control group, the test substance may be selected as a malodor inhibitor. In the case where a plurality of olfactory receptors are employed in the method of the present invention, the response of any one of the receptors may be suppressed, but it is preferred that the responses of a plurality of said receptors are suppressed.
The thus-identified test substance is a substance which suppresses the response of the olfactory receptor to the malodor employed in the above procedure, to thereby modulate the malodor recognition at the central nervous system through masking based on olfactory receptor antagonism, causing a subject to disable recognition of the malodor. Thus, the test substance identified in the above procedure is selected as a malodor inhibitor to the malodor employed in the above procedure.
The malodor inhibitor selected in the method of the present invention may be used for suppressing a malodor through olfactory masking based on inhibition of the olfactory receptor of the malodor. Alternatively, the malodor inhibitor may be used for producing a compound or composition for suppressing the malodor. The compound or composition for suppressing the malodor may appropriately contain, in addition to the malodor inhibitor, an additional deodorization ingredient or any ingredient used in a deodorant or a deodorizer, in accordance with the purpose of use. Examples of such ingredients include perfume, powder ingredients, liquid fat and oil, solid fat and oil, wax, hydrocarbon, plant extract, herbal medicines, higher alcohol, lower alcohol, ester, long-chain fatty acid, surfactants (nonionic, anionic, cationic, amphoteric, etc.), sterol, polyol, humectants, water-soluble polymers, thickeners, coating agents, sterilizers, antiseptics, UV-absorbers, fixing agents, cold-sensation agents, hot-sensation agents, stimulators, metal-ion-sequestering agents, sugar, amino acid, organic amine, synthetic resin emulsion, pH-adjusters, anti-oxidants, anti-oxidant aids, oil ingredients, powder, capsules, chelating agents, inorganic salts, organic salt dyes, thickeners, sterilizers, antiseptics, anti-mold agents, colorants, defoaming agents, extenders, modifiers, organic acid, polymer, polymer dispersants, enzymes, and enzyme-stabilizers.
The additional ingredient which can be incorporated into the compound or composition for suppressing the malodor may be any known deodorant having a chemical or physical deodorization effect. Examples of the deodorant include deodorization effective agents extracted from plant leaves, petioles, fruits, stems, roots, and bark (e.g., green tea extract); organic acids such as lactic acid, gluconic acid, succinic acid, glutaric acid, adipic acid, malic acid, tartaric acid, maleic acid, fumaric acid, itaconic acid, citric acid, benzoic acid, and salicylic acid, amino acids, salts thereof, glyoxal, oxidizing agents, flavonoid, catechin, and polyphenol; porous substances such as activated carbon and zeolite; clathrating agents such as cyclodextrin; photocatalysts; and masking agents.
EXAMPLES
The present invention will next be described in more detail by way of examples.
Example 1
Identification of Olfactory Receptors to Malodors
(1) Cloning of Human Olfactory Receptor Genes
Cloning of human olfactory receptors was performed based on the sequence information registered in GenBank, through PCR with human genomic DNA female (G1521: Promega) as a template. Each of the genes amplified through PCR was inserted into a pENTR vector (Invitrogen) according to an instruction manual. Then, the gene-inserted vector was digested with NotI and AscI, and the obtained fragments were inserted into NotI and AscI sites located downstream of the Flag-Rho tag sequence in the pME18S vector.
(2) Production of pME18S-RTP1S Vector
Cloning of human RTP1S was performed through PCR with a human RTP1 gene (MHS1010-9205862: Open Biosystems) as a template. EcoRI site was added to the forward primer employed in PCR, and XhoI site was added to the reverse primer. A hRTP1S gene (SEQ ID NO: 9) was amplified through PCR and inserted into EcoRI and XhoI site of the pME18S vector.
In a similar manner, instead of the hRTP1S gene (SEQ ID NO: 9), a gene encoding an RTP1S mutant (SEQ ID NO: 11) was inserted into EcoRI and XhoI site of the pME18S vector.
(3) Production of Olfactory Receptor-Expressed Cells
Each of the 369 types of human olfactory receptors was expressed in HEK293 cells. A reaction solution having a composition shown in Table 1 was prepared on a clean bench, and left to stand for 15 minutes. The solution was dispensed to each well of a 96-well plate (BD). Subsequently, HEK293 cells (100 μL, 3×105 cells/cm2) were seeded in each well and cultured for 24 hours in an incubator at 37° C. and under 5% CO2 conditions.











TABLE 1









OPTI-MEM (GIBCO)
50
μL



Human olfactory receptor gene
0.075
μg



(incorporated into pME18S vector in which



Flag-Rho tag is added to the N-terminal)



pGL4.29 (fluc2P-CRE-hygro, Promega)
0.03
μg



pGL4.75 (hRluc-CMV, Promega)
0.03
μg



pME18S-hRTP1S vector or pME18S-RTP1S
0.03
μg



mutant vector produced in (2)



Lipofectamine 2000 (Invitrogen)
0.4
μL










(4) Luciferase Assay

The olfactory receptor expressed in HEK293 cells activates adenylate cyclase with the aid of Gαs present in cells, to thereby increase intracellular cAMP level. In this study, odorant response was measured by a luciferase reporter gene assay which monitored the intracellular cAMP level as the luminescence value derived from a firefly luciferase gene (fluc2P-CRE-hygro). Also, a Renilla luciferase gene fused downstream of a CMV promoter (hRluc-CMV) was also transfected to HEK293 cells as an internal standard to correct errors in gene transfer efficiency and number of cells.
The culture medium was removed from the culture plate produced in (3) above, and a solution (75 μL) containing an odorant substance (1 mM skatole) in CD293 medium (Invitrogen) was added to each well. Cell culturing was performed for four hours in a CO2-incubator, whereby the luciferase gene sufficiently expressed in the cells. Luciferase activity was measured by means of a Dual-GloTM luciferase assay system (promega) according to an instruction manual thereof. The luminescence value derived from firefly luciferase induced by odorant stimulation was divided by the luminescence value of cells which were not stimulated with odorants. The thus-obtained—called “fold increase”—was employed as an index for response intensity.
(5) Results
Four olfactory receptors: OR2W1, OR5K1, OR5P3, and OR8H1 exhibited response to skatole (FIG. 1). These are novel skatole receptors whose response to skatole has never been reported.
In Example 1, effective olfactory receptor expression was observed in cells transfected with a RTP1S mutant gene (SEQ ID NO: 11). Such olfactory receptor expression was also observed in cells transfected with an hRTP1S gene (SEQ ID NO: 9). Therefore, the RTP1S transformant (SEQ ID NO: 12) can be employed as a polypeptide which promotes olfactory receptor expression in the cell membrane, instead of hRTP1S (SEQ ID NO: 10).
Example 2
Dose-dependent Response of Skatole Receptor
In a manner similar to that employed in Example 1, each of olfactory receptor OR2W1 (SEQ ID NO: 2), OR5K1 (SEQ ID NO: 4), OR5P3 (SEQ ID NO: 6), and OR8H1 (SEQ ID NO: 8) was expressed with RTP1S mutant (SEQ ID NO: 12) in HEK293 cells. The response of each receptor to skatole (0, 3, 10, 30, 100, 300, and 1000 μM) was determined. As a result, all of the four olfactory receptors exhibited a dose-dependent response to skatole (FIG. 2).
Example 3
Response of Receptor to Skatole and Indole
In a manner similar to that employed in Example 2, the response of each olfactory receptor to skatole and indole (each 0, 3, 10, 30, 100, 300, and 1000 μM) was determined. As a result, these olfactory receptors exhibited a response not only to skatole but also to indole (FIG. 3).
Example 4
Determination of Malodor Receptor Antagonists
Antagonists of the skatole receptors found in Example 1 were identified.
To identify antagonists which can suppress the response of olfactory receptors of skatole, each of 121 test substances (100 μM) was mixed with 300 μM skatole and was applied to HEK293 cells expressing each of OR2W1, OR5K1, OR5P3 and OR8H1.
The response inhibition rate of a test substance was calculated as follows. Firstly, luminescence value derived from firefly luciferase induced by stimulation with skatole (X), and luminescence value in cells which expressed the same receptor but were not stimulated with skatole (Y) were determined. By subtracting Y from X, the receptor activity by stimulation with skatole alone (X−Y) was determined. Similarly, the luminescence value induced by stimulation with a mixture of skatole and a test substance (Z) was determined. Through subtracting Y (the luminescence value in cells which expressed the same receptor but were not stimulated with skatole) from Z, the receptor activity (Z−Y) by stimulation with a mixture of skatole and the test substance was obtained. From the thus-obtained receptor activity by stimulation with skatole alone (X−Y) and the receptor activity in the presence of a test material (Z−Y), the response inhibition rate of the test substance was calculated by the following equation:

Inhibition rate (%)={1−(Z−Y)/(X−Y)}×100.

In each case, multiple independent experiments were performed in duplicate, and the average of each experiment was used.
As shown in Table 2, we found 43 antagonists of OR8H1, 38 antagonists of OR5K1, 42 antagonists of OR5P3, and 42 antagonists of OR2W1.











TABLE 2





Test substances
2W1
5K1
5P3
8H1







1-(2,3,4,7,8,8a-Hexahydro-3,6,8,8-tetramethyl-1H-3a,7-
A
A
A
A


methanoazulen-5-yl)-ethanone


[acetylcedrene]


Ethyl 2-tert-butyl cyclohexyl carbonate
A
B
A
A


[Flormat]


3-Methyl-5-(2,2,3-trimethyl-3-cyclopenten-1-yl)-4-
B
A
A
B


penten-2-ol [Ebanol]


1-(5,5-Dimethyl-cyclohexen-1-yl)-4-penten-1-one
A
B
B
A


[Dinascone]


1-(2-tert-Butylcyclohexyloxy)-2-butanol [Ambercore]
A
B
B
A


Oxacyclohexadecan-2-one [pentalide]
B
B
B
A


(Z)-Cycloheptadeca-9-en-1-one [civetone]
A
B
B
B


Dodecahydro-3a,6,6,9a-tetramethyl-naphtho[2.1-
A
C
B
A


b]furan [Ambroxane]


4-(1,1-Dimethylethyl)-cyclohexanol
—
A
A
A


[p-tert-butlcyclohexanol]


1,3,4,6,7,8-Hexahydro-4,6,6,7,8,8-
B
A
C
A


hexamethylcyclopenta-γ-2-benzopyran [Galaxolide]


5-Heptyl dihydro-2(3H)-furanone
B
B
B
B


[γ-undecalactone]


β-Methyl-3-(1-methylethyl)benzenepropanal
B
B
B
B


[Florhydral]


3,7-Dimethyl-1-octanol [tetrahydrogenol]
C
B
B
A


5-Methyl-2-(1-methylethyl)-phenol [thymol]
C
A
A
C


1-(2,2-Dimethyl-6-methylen cyclohexyl)-1-penten-3-one
B
B
C
B


[γ-methylionone]


3-(1-Ethoxy)-3,7-dimethyl-1,6-octadiene
B
B
C
B


[acetaldehyde ethyl linalyl acetal]


4-(2,6,6-Trimethyi-1-cyclohexen-1-yl)-3-buten-2-one
C
B
—
A


[β-ionone]


Methyl 2-penthyl-3-oxocyclopent-1-yl acetate
B
—
B
B


[methyl dihydrojasmonate]


2-Methyl-4-phenylpentanol
—
C
A
B


[Pumple fleur]


3,7,11-Trimethyl-1,6,10-dodecatrien-3-ol [nerolidol]
A
—
A
—


7-Methoxy-3,7-dimethyl-octanal
C
B
C
C


[methoxycitronellal]


3(Z)-Hexenyl 2-hydroxy benzoate
B
C
B
—


[cis-3-hexynlyl salicylate]


1,2,3,4,5,6,7,8-octahydro-8,8-dimethyl-2-
B
C
C
C


naphthaldehyde [Cyclemone A]


2-trans-3,7-Dimethyl-2,6-octadien-1-ol
—
C
B
B


[geraniol]


3-(4-tert-butylphenyl)propionaldehyde
A
B
—
—


[bourgeonal]


p-tert-Butyl-α-methyl hydrocinnamic aldehyde
C
C
C
C


[lilial]


1-(2,6,6-Trimethyl-3-cyclohexenyl)-2-buten-1-one
C
C
C
C


[δ-damascones]


7-Hydroxy-3,7-dimethyl-octanal
C
—
B
C


[hydroxycitronellal]


Ethyl-2,3-epoxy-3-methyl-3-phenyl propionate
—
C
C
B


8-Cyclohexadecen-1-one [globanone]
A
—
C
—


4-(4-Methyl-3-penten-1-yl)-3-cyclohexene-1-
A
—
—
C


carboxaldehyde [myrac aldehyde]


(Z)-2-(2-Pentenyl)-3-methyl-2-cyclopenten-1-one
B
—
C
C


[cis-jasmone]


α,α-Dimethyl phenylethyl acetate
—
C
C
B


[dimethylbenzylcarbinyl acetate]


Hexahydro-4,7-methanoinden-5(6)-yl acetate
—
C
C
B


[tricyclodecenyl acetate]


3,7-Dimethyl-6-octen-1-yl acetate
C
C
—
C


[citronellyl acetate]


3-Methyl-5-phenyl-1-pentanol
—
—
A
—


[phenylhexanol]


3,7-Dimethyl-6-octenal [citronellal]
C
C
C
—


4(3)-(4-Methyl-3-pentenyl)-3-cyclohexenylmethyl
C
—
C
C


acetate [myraldyl acetate]


Allyl cyclohexylpropionate
C
C
—
C


2,6-Dimethyl-2-octanol/3,7-Dimethyl-3-octanol
—
C
C
C


[tetrahydromugol]


α-Methyl-4-(2-methylpropyl)-benzenepropanal [suzaral]
C
—
—
B


(5E)-3-methylcyclopentadec-5-en-1-one
C
—
C
C


[Muscenone delta]


Dimethyl-3-cyclohexene-1-carboxaldehyde
C
—
C
C


[Triplal]


1,3,3-trimethyl-bicyclo[2.2.1]heptan-2-ol [fenchyl alcohol]
C
—
C
C


2,4,4,7-Tetramethyl-6,8-nonadiene-3-one oxime
B
—
—
C


[Labienoxime]


2-Cyclohexylpropanal [Pollenal II]
C
C
C
—


n-Hexyl-o-hydroxy benzoate
B
—
C
—


[hexyl salicylate]


4-(1-Methylethenyl)-1-cyclohexene-1-carboxyaldehyde
—
C
—
B


[perillaldehyde]





Inhibition rate: A >80%, B >50%, C >20%






Example 5
Sensory Evaluation of Ability of Antagonists for Suppressing Malodor
The abilities of each of the antagonists identified in Example 4 for reducing odor of skatole were investigated through a sensory test.
A cotton ball was put into a glass bottle (Hakuyo. Glass No. 11, capacity: 110 mL), and skatole diluted by 0.001% with propylene glycol (20 μL) and a test substance also diluted by 0.001% (20 μL) were added to the cotton ball. The glass bottle was left to stand for one night at room temperature, to thereby sufficiently evaporate the odorant molecule. The sensory test was performed by four panelists. In the case where skatole alone was added to a glass bottle, the odor intensity was rated to 5. Then, the malodor intensity in the case where skatole and a test substance were added was evaluated with a rating of 0 to 10 (by 0.5) (i.e., 20 ratings)
The following test substances were employed:
1-(2,3,4,7,8,8a-hexahydro-3,6,8,8-tetramethyl-1H-3a,7-methanoazulen-5-yl)-ethanone (acetylcedrene);
ethyl 2-tert-butylcyclohexylcarbonate (Floramat (registered trademark));
oxacyclohexadecan-2-one (pentalide);
(Z)-cycloheptadeca-9-en-1-one (civetone);
dodecahydro-3a,6,6,9a-tetramethyl-naphtho[2.1-b]furan (Ambroxane (registered trademark));
1-(5,5-dimethyl-cyclohexen-1-yl)-4-penten-1-one (Dinascone (registered trademark));
p-tert-butylcyclohexanol;
γ-undecalactone;
β-methyl-3-(1-methylethyl)benzenepropanal (Florhydral (registered trademark));
3,7-dimethyl-1-octanol (tetrahydrogeraniol);
1-(2,2-dimethyl-6-methylenecyclohexyl)-1-penten-3-one (γ-methylionone);
3,7,11-trimethyl-1,6,10-dodecatrien-3-ol (nerolidol);
3,7-dimethyl-6-octen-1-yl acetate (citronellyl acetate);
8-cyclohexadecan-1-one (globanone); and
tricyclodecanyl acetate.
FIG. 4 shows the results. As is clear from FIG. 4, skatole odor was found to be suppressed in the presence of an antagonist to OR2W1, OR5K1, OR5P3, or OR8H1.
Example 6
Specificity of Malodor Suppression Effect
In order to investigate specificity of malodor suppressing effect of a test substance identified in Example 4, the sensory test was also performed with hexanoic acid, a malodorous compound but structurally differs from skatole. In the experiment, hexanoic acid diluted by 1% with propylene glycol was used as a malodorous compound, and methyl dihydrojasmonate diluted by 1% with propylene glycol was used as a test substance.
As a result, it was found that methyl dihydrojasmonate suppressed skatole odor, did not suppress hexanoic acid odor (FIG. 5). Thus, the malodor suppressing effect by an antagonist was found to be odor-specific.

## Claims

1. A method for identifying a malodor inhibitor comprising:
adding a test substance and a malodor-causing substance to at least one olfactory receptor polypeptide selected from the group consisting of OR5P3, OR2W1, OR5K1, OR8H1, and a polypeptide that has 95% or more identity in amino acid sequence to any one of the aforementioned polypeptides;
measuring the response of the olfactory receptor polypeptide to the malodor-causing substance;
identifying, based on the measured response, a test substance that can suppress the response of the olfactory receptor; and
selecting, as a malodor inhibitor, the test substance that suppresses the response of the olfactory receptor, wherein the malodor is a skatole odor, an indole odor, a fecal odor, or foul breath due to a skatole or indole odor.

2. The method according to claim 1, wherein the malodor is a skatole odor or an indole odor.

3. The method according to claim 1, wherein the at least one olfactory receptor polypeptide is selected from the group consisting of OR5P3, OR5K1, and OR8H1.

4. The method according to claim 1, wherein the olfactory receptor polypeptide is expressed on a cell that can intrinsically express the olfactory receptor polypeptide or on a recombinant cell that is genetically modified so as to express the olfactory receptor polypeptide.

5. The method according to claim 1, which further includes measuring the response of the olfactory receptor polypeptide to which no test substance has been added.

6. The method according to claim 5, wherein, when the response of the olfactory receptor polypeptide to which the test substance has been added is suppressed to 80% or less than the response of the olfactory receptor polypeptide to which no test substance has been added, the test substance is selected as a malodor inhibitor.

7. The method according claim 1, wherein measuring the response of the olfactory receptor polypeptide is performed through a reporter gene assay.

8. The method according to claim 1, wherein the malodor is fecal odor or foul breath due to a skatole or indole odor.

9. The method according to claim 1, wherein at least one of olfactory receptor polypeptide is selected from the group consisting of OR5P3, OR2W1, OR5K1, OR8H1 and a polypeptide that has 98% or more identity in amino acid sequence to any one of the aforementioned polypeptides.

10. The method according to claim 2, wherein the malodor is a skatole odor.

11. The method according to claim 2, wherein the malodor is an indole odor.

12. The method according to claim 8, wherein the malodor is fecal odor.

13. The method according to claim 8, wherein the malodor is foul breath due to a skatole or indole odor.

14. The method according to claim 1, wherein the at least one olfactory receptor polypeptide is OR5P3.

15. The method according to claim 1, wherein the at least one olfactory receptor polypeptide is OR2W1.

16. The method according to claim 1, wherein the at least one olfactory receptor polypeptide is OR5K1.

17. The method according to claim 1, wherein the at least one olfactory receptor polypeptide is OR8H1.